U.S. patent application number 13/098923 was filed with the patent office on 2011-10-13 for methods and compositions for detecting the activation state of multiple proteins in single cells.
Invention is credited to Garry P. Nolan, Omar D. Perez.
Application Number | 20110250614 13/098923 |
Document ID | / |
Family ID | 27737231 |
Filed Date | 2011-10-13 |
United States Patent
Application |
20110250614 |
Kind Code |
A1 |
Perez; Omar D. ; et
al. |
October 13, 2011 |
METHODS AND COMPOSITIONS FOR DETECTING THE ACTIVATION STATE OF
MULTIPLE PROTEINS IN SINGLE CELLS
Abstract
The invention provides methods and compositions for
simultaneously detecting the activation state of a plurality of
proteins in single cells using flow cytometry. The invention
further provides methods and compositions of screening for
bioactive agents capable of coordinately modulating the activity of
a plurality of proteins in single cells. The methods and
compositions can be used to determine the protein activation
profile of a cell for predicting or diagnosing a disease state, and
for monitoring treatment of a disease state.
Inventors: |
Perez; Omar D.; (San
Francisco, CA) ; Nolan; Garry P.; (San Francisco,
CA) |
Family ID: |
27737231 |
Appl. No.: |
13/098923 |
Filed: |
May 2, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12372670 |
Feb 17, 2009 |
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13098923 |
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10193462 |
Jul 10, 2002 |
7563584 |
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12372670 |
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60304434 |
Jul 10, 2001 |
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60310141 |
Aug 2, 2001 |
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Current U.S.
Class: |
435/7.1 ;
435/29 |
Current CPC
Class: |
G01N 2333/96466
20130101; G01N 33/5008 20130101; G01N 33/573 20130101; G01N 33/5091
20130101; G01N 33/582 20130101; G01N 21/6428 20130101; G01N
2333/91205 20130101; G01N 33/6845 20130101; Y10T 436/101666
20150115; Y10T 436/25 20150115; Y10S 435/973 20130101; C12Q 1/485
20130101; G01N 2405/00 20130101; G01N 2021/6441 20130101; G01N
2440/14 20130101; G01N 33/5302 20130101; G01N 33/5041 20130101;
G01N 33/54313 20130101; G01N 33/5094 20130101 |
Class at
Publication: |
435/7.1 ;
435/29 |
International
Class: |
C12Q 1/02 20060101
C12Q001/02; G01N 33/569 20060101 G01N033/569 |
Goverment Interests
[0002] The invention was made with United States Government support
under Grant Numbers P01-AI39646, AR44565, AI35304, NO01-AR-6-2227,
and A1/GF41520-01 awarded by the National Institutes of Health. The
United States Government has certain rights in the invention.
Claims
1-9. (canceled)
10. A method of detecting the activation state of at least a first
activatable protein in single cells, said method comprising the
steps of: a) providing a population of cells comprising at least
said first activatable protein; b) contacting said population of
cells with a plurality of substrates; wherein said plurality of
substrates comprise at least a first substrate that is capable of
being modified by a corresponding isoform of said first activatable
protein in said population of cells; and c) using flow cytometry to
detect the modification of said first substrate in single cells of
said population of cells, wherein said modification is indicative
of a specific activation state of said first activatable
protein.
11. The method according to claim 10, wherein said population of
cells further comprises a second activatable protein, wherein said
plurality of substrates further comprise a second substrate that is
capable of being modified by a corresponding isoform of said second
activable protein in said population of cells and, wherein step c)
further comprises using said flow cytometry to detect the
modification of said second substrate in single cells of said
population of cells, wherein said modification of said second
substrate is indicative of a specific activation state of said
second activatable protein.
12. A method of detecting a protein activation state profile of
single cells based on the activation state of at least a first
activatable protein in said cells, said method comprising the steps
of: a) providing a population of cells comprising at least said
first activatable protein; b) contacting said population of cells
with a plurality of substrates; wherein said plurality of
substrates comprise at least a first substrate that is capable of
being modified by a corresponding isoform of said first activatable
protein in said population of cells; c) contacting said population
of cells with a plurality of activation state-specific antibodies,
wherein said activation state-specific antibodies comprise at least
one first activation state-specific antibody that is capable of
binding to a corresponding isoform of said first activatable
protein in said population of cells; and d) using flow cytometry to
simultaneously detect: i) said binding of said first activation
state-specific antibody in single cells of said population of
cells, wherein said binding of said first activation state-specific
antibody is indicative of a specific activation, state of said
first activatable protein; and ii) the modification of said first
substrate said single cells, wherein said modification is
indicative of said specific activation state of said first
activatable protein.
13-32. (canceled)
Description
[0001] This application [is a continuing application and] claims
the benefit of U.S. provisional applications Ser. No. 60/304,434,
filed Jul. 10, 2001, and Ser. No. 60/310,141, filed Aug. 2,
2001.
FIELD OF THE INVENTION
[0003] The invention relates generally to the field of protein
detection using flow cytometry. More specifically, the invention
relates to simultaneously detecting the activation states of
multiple proteins in single cells using flow cytometry and, more
particularly, using polychromatic flow cytometry.
BACKGROUND OF THE INVENTION
[0004] Proteins are the major components of cells. The
spatiotemporal expression pattern and the subcellular localization
of proteins determines the shape, structure, and function of cells.
Proteins are assembled from 20 different amino acids, each with a
distinct side chain and chemical property. This provides for
enormous variety in the chemical properties of proteins and the
activities they exhibit.
[0005] In addition, many proteins are dynamically regulated such
that their activity is altered in response to certain intrinsic or
extrinsic cues. One form of regulation involves covalent
modification of the regulated protein. An example of such a
covalent modification is the substitution of a phosphate group for
a hydroxyl group in the side chain of an amino acid
(phosphorylation). Such modification is often associated with an
alteration in the activity of a protein. Protein kinases can
recognize specific protein substrates and catalyze the
phosphorylation of serine, threonine, or tyrosine residues on their
protein substrates. Such substrate proteins capable of being
phosphorylated are referred to as phosphoproteins. Once
phosphorylated, a substrate protein may have its phosphorylated
residue converted back to a hydroxylated one by the action of a
protein phosphatase which specifically recognizes the substrate
protein. Protein phosphatases catalyze the replacement of phosphate
groups by hydroxyl groups on serine, threonine, or tyrosine
residues. Through the action of kinases and phosphatases a protein
may be reversibly phosphorylated on a multiplicity of residues and
its activity may be regulated thereby.
[0006] Many kinases and phosphatases are known and play important
roles in signal transduction. Many kinases and phosphatases are
phosphoproteins, the kinase and phosphatase activities of which are
regulated by phosphorylation. The phosphorylation of kinases and
phosphatases is often regulated by other or same type kinases and
phosphatases. In this way, the regulators of signal transduction
are themselves regulated as part of a signaling cascade.
[0007] Many intracellular kinases and phosphatases transduce
signals in response to extracellular signals that stimulate
receptors at the cell surface. As a result, extracellular signals
induce changes in the phosphorylation and activation states of many
proteins in receptive cells. For example, many mitogens induce JNK
and MAPK signaling activity which causes cell to proliferate. As
another example, neurotrophic factors have been shown to induce AKT
signaling activity which supports neuronal survival. In addition,
many diseases, such as cancer, are associated with an alteration in
the activation state of many signaling proteins. In many instances,
the signaling activity observed in cancer cells is reminiscent of
growth factor stimulated signaling activity in non-cancer
cells.
[0008] Some lipids of the cell membrane are also substrates for
kinases. For example, phosphatidylinositol 3-kinase (PI3K)
specifically recognizes phosphatidylinositol 4,5-diphosphate (PIP2)
and catalyzes its phosphorylation at the 3' position of the
inositol moiety. PIP2 is generated by the activity of another
kinase, phosphatidylinositol 4-kinase which catalyzes
phosphorylation of phosphatidylinositol at the 4' and 5' positions
of the inositol moiety. PI3K regulates a variety of cellular
functions and is activated by growth factors such as nerve growth
factor (NGF), platelet derived growth factor (PDGF), insulin
receptor substrate 1 (IRS-1) and CD28. Many of the proteins that
activate PI3K also activate GTPases, predominantly the ras family,
which in turn activate PI3K by binding to its p110 subunit. The
direct pathway from tyrosine phosphorylated receptors to PI3K and
activation of PI3K by GTPase proteins function synergistically.
PI3K is a heterodimeric enzyme composed of a catalytic subunit
(p110) and a regulatory subunit. Several genes encoding regulatory
subunits of PI3K have been identified, including p85.alpha. and
p85.beta.. In addition, a number of splice variants of p85.alpha.
are known (including p55.alpha. and p50.alpha.).
[0009] It is understood that kinase signaling cascades play an
important role in nearly every critical decision process in cells
(for review see Hunter, Cell 100:113-127, 2000). Determining the
role of specific signal transduction pathways in a given system has
been aided by the advent of pharmacological inhibitors for specific
kinases. However, monitoring activities for such kinases, for
example, protein kinase B/AKT, cJun-N-terminal kinase (JNK), p38
mitogen activated protein kinase (p38), p44/42 ERK1/2 (ERK), PKA,
PKC or TYK2 or others, is usually dependent upon in vitro kinase
assays or more recently by immunoblotting to determine the
phosphorylation state of these proteins using phospho-specific
antibodies. To date it has not been possible to correlate rare
subpopulations of cells with the activation state of kinases in
important signaling pathways.
[0010] Another form of protein regulation involves proteolytic
cleavage of a peptide bond. While random or misdirected proteolytic
cleavage may be detrimental to the activity of a protein, many
proteins are activated by the action of proteases that recognize
and cleave specific peptide bonds. Many proteins derive from
precursor proteins, or pro-proteins, which give rise to a mature
isoform of the protein following proteolytic cleavage of specific
peptide bonds. Many growth factors are synthesized and processed in
this manner, with a mature isoform of the protein typically
possessing a biological activity not exhibited by the precursor
form. Many enzymes are also synthesized and processed in this
manner, with a mature isoform of the protein typically being
enzymatically active, and the precursor form of the protein being
enzymatically inactive. This type of regulation is apparently not
reversible. Thus, to inhibit the activity of a proteolytically
activated protein, mechanisms other than de-cleavage must be used.
It is the case that many proteolytically activated proteins are
relatively short lived proteins.
[0011] Among the enzymes that are proteolytically activated are the
caspases. The caspases are an important class of proteases that
mediate programmed cell death (referred to in the art as
"apoptosis"). Caspases are constitutively present in most cells,
residing in the cytosol as a single chain proenzyme. These are
activated to fully functional proteases by a first proteolytic
cleavage to divide the chain into large and small caspase subunits
and a second cleavage to remove the N-terminal domain. The subunits
assemble into a tetramer with two active sites (Green, Cell
94:695-698, 1998).
[0012] Antibodies are particularly useful for the study of
proteins. Antibodies are a large family of glycoproteins that
specifically bind antigens, and do so with a high affinity.
Antibodies comprise a constant domain and a variable domain. The
variable domain of an antibody binds to antigen. Polyclonal
antibodies comprise a multiplicity of variable region types.
Monoclonal antibodies comprise a single type of variable region,
and are thus more likely to specifically bind to fewer proteins.
Monoclonal and polyclonal antibodies are routinely generated by
means known in the art, and have been raised against many known
proteins for use in both research and therapy. Antibodies may be
used to determine the presence of antigens or proteins to which
they specifically bind. Well known immunochemical methods that
employ this approach include Western blotting, immunoprecipitation,
and enzyme linked immunoassay (ELISA).
[0013] In particular, antibodies may be used to determine the
presence of a specific isoform of a protein, especially, when the
isoform possesses an antigen not present in other isoforms of the
protein, or when the isoform lacks an antigen not present in other
isoforms of the protein. Thus, the isoform can be antigenically
distinct from other isoforms of the same protein. The antigenically
distinct isoform may uniquely possess or lack a covalently attached
moiety, or may be in a conformation distinct from other isoforms
and thereby present the same amino acid sequence in an
antigenically distinguishable way.
[0014] For example, the determination of PI3K activity has
typically involved immunoprecipitation of PI3K and an in vitro
enzymatic assay using phospholipids and labeled ATP. Recently,
antibodies that specifically bind to phosphatidylinositol
4,5-diphosphate and phosphatidylinositol 3,4,5-triphosphate have
been developed (Molecular Probes, A-21327 anti-phosphatidylinositol
4,5-diphosphate, mouse IgM monoclonal 2C11; A-21328
anti-phosphatidylinositol 3,4,5-triphosphate, mouse IgM monoclonal
RC6F8). These antibodies serve as useful tools for the detection of
PI3K substrate (PIP2) and product (PIP3), and can be used to
determine the activity of PI3K.
[0015] Biochemical investigations of protein expression and
function have traditionally focused on one or a few proteins at a
time. This has largely been due to limitations imposed by the
available investigative techniques. It is well understood that a
cell's normal and abnormal physiology is the product of a large
number of proteins participating in a large number of molecular
interactions. For the purposes of designing treatments and cures,
an understanding of the mechanisms underlying disease is desired.
Such an understanding requires consideration of multiple proteins
and their molecular interactions over time. In this regard, one
important experimental hurdle is how to analyze large numbers of
proteins in a single experiment, for example to determine a protein
expression profile and, more specifically, active protein profiling
for a single protein sample, or even for a single cell.
[0016] In addition to qualitative measurements of protein
expression in cells, quantitative measures of protein expression
are desirable. It is well known that many proteins can function
differently at different expression levels, and such differences in
protein function can lead to differences in cell physiology.
[0017] It is highly desirable to determine expression levels of
particular isoforms of proteins in a sample, given that different
isoforms of a protein can have different activities. For example,
proteins involved in signal transduction can often exist in two or
more forms, and it is usually a particular form of the signaling
protein that transmits a signal that mediates the effects of a
signaling pathway. Conversion from one form to another is often
used to turn a signal on or off through a change in protein
activity.
[0018] In addition, in order to study protein expression and
function, it is often necessary to immobilize proteins on a solid
support. In Western blot analysis, proteins of interest are first
separated by electrophoresis and then transferred and immobilized
onto a nitrocellulose or a polyvinylidene difluoride (PVDF)
membrane. In the phage display screening of a protein expression
library, several hundred thousand proteins expressed by phages are
immobilized on membranes. In both Western blotting and phage
display screening, proteins are immobilized non-covalently. The
protein of interest is then selected by its unique property, i.e.,
interaction with an antibody. In some other applications such as
immunoprecipitation and affinity purification, agents (e.g.,
antibodies, ligands) are covalently conjugated onto solid supports
(e.g., agarose beads) through their primary amines, sulfhydryls or
other reactive groups. In general, proteins retain their abilities
of interacting with other proteins or ligands after immobilization.
However, even with the immobilization of a multiplicity of proteins
from a sample, the problems of simultaneous detection of protein
expression, protein form, and protein level for a multiplicity of
proteins remains.
[0019] Thus, an object of the present invention is to overcome the
problems described above. Accordingly, the present invention
provides an approach for the simultaneous determination of the
activation states of a plurality of proteins in single cells. This
approach permits the rapid detection of heterogeneity in a complex
cell population based on protein activation states, and the
identification of cellular subsets that exhibit correlated changes
in protein activation within the cell population. Moreover, this
approach allows the correlation of cellular activities or
properties, such as surface molecule expression or cell
granularity, with protein activation at the single cell level.
SUMMARY OF THE INVENTION
[0020] In accordance with the above objects, the present invention
provides methods and compositions for simultaneously detecting the
activation state of a plurality of activatable proteins in single
cells using flow cytometry. The invention further provides methods
and compositions of screening for bioactive agents capable of
coordinately modulating the activity or activation state of a
plurality of activatable proteins in single cells. The methods and
compositions can be used to determine the protein activation
profile of a cell for predicting or diagnosing a disease state, and
for monitoring treatment of a disease state. Further, the methods
and compositions of the present invention can be used optionally to
sequentially detect the activation state of a plurality of
activatable proteins in single cells. In addition, the methods and
compositions of the present invention can be used optionally detect
the activation state of a single protein or modulate the activity
or activation state of a single protein.
[0021] The invention provides populations of cells, single cells,
cell lysates, proteins, and samples comprising populations of
cells, single cells, cell lysates, proteins useful in the methods
of the present invention. In particular, the invention provides
activatable proteins and activation state-specific antibodies that
bind to a specific isoform of an activatable protein. In one
aspect, the activation state-specific antibodies are conjugated to
a label, preferably a fluorescent label, and more preferably a FRET
label.
[0022] In one aspect, the invention provides methods of detecting
the activation state of at least a first and a second activatable
protein in single cells, the method comprising the steps of: a)
providing a population of cells comprising the first and the second
activatable proteins; b) contacting the population of cells with a
plurality of activation state-specific antibodies, wherein the
plurality of activation state-specific antibodies comprise: i) at
least one first activation state-specific antibody that is capable
of binding to a corresponding isoform of the first activable
protein in the population of cells; and ii) at least one second
activation state-specific antibody that is capable of binding to a
corresponding isoform of the second activatable protein in the
population of cells; and c) using flow cytometry to detect the
binding of the first and second activation state-specific
antibodies in single cells of the population of cells, wherein the
binding of the first activation state-specific antibody is
indicative of a specific activation state of the first activatable
protein, and the binding of the second activation state-specific
antibody is indicative of a specific activation state of the second
activatable protein.
[0023] In a further aspect, the first activatable protein is a
kinase. Also in a further aspect, the first activatable protein is
a caspase.
[0024] In a further aspect, the first activatable protein is a
first kinase and the second activatable protein is a second kinase.
Also in a further aspect, the isoform of the first kinase is a
first phosphorylated kinase, and the isoform of the second kinase
is a second phosphorylated kinase. In another aspect, the first
activation site-specific antibody binds to the first phosphorylated
kinase, and the second activation site-specific antibody binds the
second phorphorylated kinase.
[0025] In a further aspect, the first activatable protein is a
first caspase and the second activatable protein is a second
caspase. Also in a further aspect, the isoform of the first caspase
is a cleaved product of a first pro-caspase, and the isoform of the
second caspase is a cleaved product of a second pro-caspase. In
another aspect, the plurality of activation site-specific
antibodies comprise a first activation site-specific antibody that
binds to the isoform of the first caspase, and a second activation
site-specific antibody that binds to the isoform of the second
caspase.
[0026] In another aspect, the invention provides methods of
detecting the activation state of at least a first activatable
protein in single cells, the method comprising the steps of: a)
providing a population of cells comprising at least the first
activatable protein; b) contacting the population of cells with a
plurality of substrates; wherein the plurality of substrates
comprise at least a first substrate that is capable of being
modified by a corresponding isoform of the first activatable
protein in the population of cells; and c) using flow cytometry to
detect the modification of the first substrate in single cells of
the population of cells, wherein the modification is indicative of
a specific activation state of the first activatable protein.
[0027] In a further aspect, the population of cells further
comprises a second activatable protein; the plurality of substrates
further comprise a second substrate that is capable of being
modified by a corresponding isoform of the second activable protein
in the population of cells; and step c) further comprises using the
flow cytometry to detect the modification of the second substrate
in single cells of the population of cells, wherein the
modification of the second substrate is indicative of a specific
activation state of the second activatable protein.
[0028] In another aspect, the invention provides methods of
detecting a protein activation state profile of single cells based
on the activation state of at least a first activatable protein in
the cells, the method comprising the steps of: a) providing a
population of cells comprising at least the first activatable
protein; b) contacting the population of cells with a plurality of
substrates; wherein the plurality of substrates comprise at least a
first substrate that is capable of being modified by a
corresponding isoform of the first activatable protein in the
population of cells; c) contacting the population of cells with a
plurality of activation state-specific antibodies, wherein the
activation state-specific antibodies comprise at least one first
activation state-specific antibody that is capable of binding to a
corresponding isoform of the first activatable protein in the
population of cells; and d) using flow cytometry to simultaneously
detect: i) the binding of the first activation state-specific
antibody in single cells of the population of cells, wherein the
binding of the first activation state-specific antibody is
indicative of a specific activation, state of the first activatable
protein; and ii) the modification of the first substrate the single
cells, wherein the modification is indicative of the specific
activation state of the first activatable protein.
[0029] In a further aspect, the population of cells further
comprises a second activatable protein; the plurality of substrates
further comprises a second substrate that is capable of being
modified by a corresponding isoform of the second activatable
protein in the population of cells; and step d) further comprises
using the flow cytometry to detect the modification of the second
substrate in the single cells, wherein the modification is
indicative of a specific activation state of the second activatable
protein.
[0030] In a further aspect, the plurality of activation
state-specific antibodies further comprises a second activation
state-specific antibody that is capable of binding to a
corresponding isoform of the second activatable protein in the
population of cells, and step c) further comprises using the flow
cytometry to detect the binding of the second activation
state-specific antibody the single cells of the population of
cells, wherein the binding of the second activation state-specific
antibody is indicative of the specific activation state of the
second activatable protein.
[0031] In another aspect, the invention provides methods of
screening for a bioactive agent capable of modulating the activity
of at least a first activatable protein in cells, the method
comprising: a) providing a population of cells, each of the cells
comprising at least the a first activable protein, a second
activatable protein, and a third activatable protein, wherein the
first activable protein can activate the second activatable protein
thereby forming a specific isoform of the second activable protein
(isoform-2), and wherein the second activable protein can activate
the third activatable protein thereby forming a specific isoform of
the third activatable protein (isoform-3); b) contacting the cells
with a second activation state-specific antibody, a third
activation state-specific antibody, and a candidate bioactive
agent, wherein the second activation state-specific antibody is
capable of binding to the isoform-2, and wherein the third
activation state-specific antibody is capable of binding to the
isoform-3; c) using fluorescent activated cell sorting (FACS) to
sort single cells of the population of cells based on the presence
of the isoform-2 and the isoform-3; and d) determining the ratio of
the isoform-2 to the isoform-3 in the single cells in the presence
and absence of the candidate bioactive agent, wherein a difference
in the ratio of the isoform-2 to the isoform-3 in the presence and
absence of the candidate bioactive agent is indicative of the
ability of the candidate bioactive agent to modify the activity of
the first activable protein.
[0032] In a further aspect, the first activatable protein is
activated by an activating agent.
[0033] In a further aspect, the first activatable protein is a
caspase. In another aspect, the first activatable protein is a
kinase; in an additional aspect, the kinase is PI3K; and in a
further aspect the PI3K is activated by a growth factor or by
activation of a cell surface receptor.
[0034] In a further aspect, the kinase is PI3K; the second
activatable protein is PIP2; the third activatable protein is PIP3;
the isoform-2 is PIP 4,5 bisphosphate; and the isoform-3 is PIP
3,4,5.
[0035] In a further aspect, the first activatable protein is
ICAM-2; the activity is apoptosis; the second activatable lipid is
PIP2; the third activatable protein is PIP3; the isoform-2 is PIP
4,5 bisphosphate; and the isoform-3 is PIP 3,4,5. In a further
aspect step a) further comprises clustering the ICAM-2, ICAM-3, or
ICAM-1.
[0036] In a further aspect, the plurality of activation
state-specific antibodies comprise at least one antibody selected
from a group of antibodies consisting of: anti-AKT-phospho-Ser473,
anti-AKT phospho-Thr308, anti-p44/42 MAPK phospho-Thr202/Tyr204,
anti-TYK2 phospho-Tyr1054/1055, anti-p38 MAPK
phospho-Thr180/Tyr182, anti-JNK/SAPK phospho-Thr183/Tyr185,
anti-phospho-tyrosine, anti-phospho-threonine, anti-PIP2, and
anti-PIP3.
[0037] In a further aspect, of the step a) further comprises
contacting the population of cells with an agent that induces the
activation of at least the first activatable protein.
[0038] In a further aspect, step a) further comprises contacting
the population of cells with an agent that induces the activation
of at least one of the first and the second activatable
proteins.
[0039] The method according to any of claims 15-22, wherein step a)
further comprises contacting the population of cells with an agent
that induces the activation of at least one of the first, the
second, and the third activatable proteins.
[0040] In a further aspect, the methods further comprises sorting
the single cells based on the activation state of the first
activatable protein, and the activation state of the second
activatable protein.
[0041] In a further aspect, the first activation state-specific
antibody comprises a first label, wherein the second activation
state-specific antibody comprises a second fluorescent label and,
wherein the sorting is by fluorescent activated cell sorting
(FACS).
[0042] In a further aspect, the first activation state-specific
antibody comprises a first FRET label; the second activation
state-specific antibody comprises a second FRET label and the
sorting is by fluorescent activated cell sorting (FAGS).
[0043] In a further aspect, the first activation state-specific
antibody comprises a FRET label; the second activation
state-specific antibody comprises a label; and the sorting is by
fluorescent activated cell sorting (FACS).
[0044] In a further aspect, step a) further comprises fixing the
cells.
[0045] In a further aspect, the cells are mammalian cells.
BRIEF DESCRIPTION OF THE DRAWINGS
[0046] FIG. 1 depicts the results of experiments demonstrating that
phospho-specific antibodies correlate with kinase activity. A)
Phospho specific antibodies for i) p44/42, ii) p38, iii) JNK/SAPK,
iv) AKTser473/AKTthr308, v) TYK2, vi) PKA-substrate, and vii)
PKC-PAN substrate were tested for phospho-specificity by specific
kinase inducing and inhibitory conditions. The inducing conditions
for kinase are shown as well as specific inhibitor(s) of the
pathway. The ability of the kinase to have activity upon a known
substrate is shown beneath each phospho-western set. Non-phospho
specific antibodies for AKT, p38, SAPK/JNK, p44/42, MAPK, and TYK2
reflect total kinase present. Kinase activity was determined under
conditions found to elicit phosphorylation of respective kinase and
correlated with the phosphorylated state of the kinase as detected
by phospho-specific antibodies. Given the nature of the phospho-PKA
substrate and phospho-PKC-PAN substrate antibodies, direct kinase
activities could not be measured. Conditions used determined a
general activation of PKC and PKA, since both antibodies recognize
multiple PKC and PKA target proteins in the phosphorylated form of
their respective kinase substrate recognition motif.
Immunoblots/kinase assays for AKT, p44/42, p38, and JNK kinases
were performed in NIH3T3 and data for TYK2, PKC, and PKA were
performed in Jurkat cells (see Material and Methods for elaboration
on treatment conditions).
[0047] B) Jurkat cells were treated with a kinase inducing agent
(induced), or kinase inhibitor (inhibited) before induction
conditions as diagramed in Table 2. Cells were prepared for
intracellular FACS staining and analyzed for kinase activities
noted in the figures by log fluorescence of phospho-specific
antibody-fluorophore conjugate. Plot overlays illustrate shifts
respective of either increased or decreased kinase activity. The
bottom right panel represents a dose response curve of EGF
treatment as measured by phospho-ERK activity (0.001, 0.01, 0.1,
1.0, 10 .mu.g/ml). The inhibitors and activators used were the
following: p44/42 (ERK1/2), was activated with epidermal growth
factor (EGF) and inhibited with MEK1/2 inhibitor U0126.sup.21-23*;
AKT activation was achieved by addition of growth media and
platelet derived growth factor and inhibited by incubation with
PI3K kinase inhibitor LY294002.sup.20*; JNK was activated by
anisomycin.sup.29* and inhibited by staurosporine; p38 MAPK was
activated by anisomycin.sup.29* and inhibited with compound
SB203580.sup.24,29*; PKA was activated by phorbal 12 myristalated
13-acetate (PMA) and phospho detection was made possible by
incubation with protein phosphatase inhibitor calyculin A.sup.25*;
PKC was activated by ionomycin (IO) and inhibited using
bisindolymaleimide II.sup.26,27*; TYK2 activity was induced by
interferon .gamma. (IFN.gamma.) and inhibited using the general
tyrosine kinase inhibitor genistein.sup.26,3*. *See the
corresponding reference number and cite in Example 1 under
"References."
[0048] C) TYK2, PKA and PKC substrate probes are phospho specific.
Treatment of stimulated samples (stated above) with lambda
phosphatase prior to intracellular staining decreased detection by
phospho-TYK2 and phospho-PKA substrate probes. Treatment of cells
with calf intestinal phosphatase in addition to lambda phosphatase
was required for decreased detection of phosphorylated PKC
substrates.
[0049] D) Phosphorylation of p44/42 correlates with mean
fluorescent intensity as measured by flow cytometry.
Semiquantitative analysis of p44/42 phosphorylation as measured by
both phospho specific detection and mean fluorescence intensity
(MFI) by phospho-p44/42 kinase probe. Jurkat cells were subjected
to a dose response curve of EGF at the indicated concentrations for
30 minutes, and assessed for p44/42 phosphorylation by both
immunoblotting with phospho-specific antibodies and flow cytometry
with developed p44/42 kinase probe. Y error bars are standard
deviation for MFI values. X error bars are standard deviation for
percent phosphorylated relative to unstimulated control. Values
displayed are representative of 3 independent experiments. Error
bars not visible are concealed by data point.
[0050] FIG. 2 depicts the results of experiments demonstrating that
multi-dimensional analysis provides insights into signaling
networks as induced by differing stimuli.
[0051] A) Differential kinase activity within CD4+ and CD19+
lymphocyte subsets. PBMC were treated with the indicated stimulus
for 1 hour and prepared for intracellular kinase phosphorylation
status determination by flow cytometry. Both hyper and hypo
responses can be observed with respect to p44/42 activity in CD4+
upon different stimuli.
[0052] B) T cell activation measured by CD69 presents differential
p44/42 kinase activity to CD3/CD28 and PMA/ionomycin stimulation.
The stimulation conditions are shown in the Figure.
[0053] C) Multiple kinase activities measured in artificial T cell
stimulation. Jurkat cells in growth media and PMA/ionomycin (IO)
treated were prepared for intracellular kinase phosphorylation
status determination by flow cytometry. CD69 expression serves to
indicate T cell activation. X-axis corresponds to log fluorescence
values, Y-axis corresponds relative cell number.
[0054] D) Phosphorylation of p38 as a function of cell granularity.
Simultaneous measurement of phosphorylated and non-phosphorylated
p38 exemplifies a shift from non-phosphorylated to phosphorylated
p38 as cell granularity increases (indicated by the open bar in the
side scatter parameter).
[0055] E) 3-parameter analysis of p44/42 and p38 kinase activity as
a function of JNK activity illustrate potential mapping of
signaling crosstalk. PBMC were treated with IL-1.alpha.. JNK,
p44/42, and p38 activity was simultaneously measured by flow
cytometry. Open bar in phospho-JNK/SAPK plot indicates intensity of
JNK activation.
[0056] F) 5-parameter analysis of AKT, p38, PKA, and p44/42
activity as a function of TYK2 activity in IL-1.beta. treated PBMC.
At initiation of TYK2 activity, all 4 kinase activities are not
detectable. Synchronous activation of p38, p44/42, and AKT activity
is observed at a greater level of TYK2 activity. PKA activity is
observed at a greater level of p38 and p44/42 activity.
[0057] FIG. 3 shows a flow diagram of resting T cell isolation,
preparation, and analysis by polychromatic flow cytometry
(11-color, 13 parameter).
[0058] Isolation of lymphocytes was achieved by a Ficoll-plaque
gradient and depleted for adherent cells. Flow cytometry plots
illustrate typical lymphocyte gate and presence of CD3-populations.
Magnetically activated cell sorting eliminated activated T cells,
NK cells, remaining macrophages, and B cells, enriching for resting
T cells. The enriched population was assessed prior to stimulation
to ensure presence of CD4+ and CD8+ cells. Stimulation to IL-1a,
IL-10, or IL-2 was performed and cells were prepared for flow
cytometry using stains depicted in Table 1. Occasionally,
downregulation of some surface markers was observed to certain
stimuli and is presented by receptor downregulation of key
molecules, namely CD3, CD4, CD8, (apparent when comparing flow
cytometry plots of these markers prior to stimulus treatment). An
example of memory and naive gating by 5 differentiation markers is
depicted for both CD4+ and CD8+ T cells. Appropriate placement of
CD45RA gate was done according to De Rosa et al and was carried out
separately for CD4+ and CD8+ populations. After identification of
naive and memory cells by multiple-gating according to
differentiation markers, intracellular kinase activity was
determined. Kinase profiles are plotted against CD11a markers,
although they are gated for all naive and memory markers.
Assessment of multiple kinase activities was made possible by
combining two 11-color experiments.
[0059] FIG. 4 depicts the results of experiments demonstrating that
signaling profiles are readily discernible in particular lymphocyte
subsets using polychromatic flow cytometry.
[0060] Naive and memory T cell kinase profiles are overlayed for
direct comparison. Mechanisms involving threshold dependent kinase
activation can be observed when kinase phosphorylation approaches
but does not exceed Log 10 fluorescence intensity (value defined
from inhibitor/inducer experiments FIG. 2) in CD8+ naive cells.
Hyporesponses can be seen for IL-1.alpha. CD4+ naive cells.
[0061] FIG. 5 depicts the results of experiments monitoring
intensities of both active and non-active kinases by flow
cytometry
[0062] A) Phospho and non-phospho-specific probes for p44/42, p38,
AKT, TYK2, and JNK detect respective kinase in its native state.
Jurkat cells were treated to the following: AKT activity stimulated
with PDGF, MAPK activity stimulated with EGF, p38 and JNK activity
stimulated with anisomycin--for 10 minutes to induce initial
activation of respective kinase with inducers as per the
concentrations stated in Table 2. Phospho-p44/42, phospho-p38,
phospho-AKTser473, and phosphoAKTthr308, and phospho-JNK/SAPK
detected distinct populations upon a given stimulus in respect to
their non-phospho specific counterparts. AKT positive cells were
gated and plotted against AKTser473- and AKTthr308 phosphorylation
plot as denoted in panel. Unstimulated cells for all non-phospho
specific kinases are appropriately displayed for comparison.
[0063] FIG. 6 depicts the results of experiments demonstrating that
LFA-1 stimulus induces JAB1 and Cytohesin-1 release and
phosphorylation in human naive CD4+ T cells. A) Phospho-cJun
immunoblot of nuclear extracts from cells stimulated with CD3, CD28
and sICAM-2 (5 .mu.g/ml, 30 min). B) Single cell analysis of
phospho-cJun(S63) in .alpha.-JAB1, IgG transfected and
untransfected cells. The median fluorescence intensity is
plotted.+-.SD. C) Confocal of JAB1 and cytohesin-1 in unstimulated
(panel A-C), LFA-1 stimulated (sICAM-2 5 .mu.g/ml) (panel D-F), and
.alpha.-JAB1 transfected cells (G-I). Panels G-I were not stained
with .alpha.-JAB1 antibody. D) Immunoprecipitates of JAB1 and
Cytohesin-1 from unstimulated, sICAM-2 and CD3 (5 .mu.g/ml, 30 min)
stimulated cells were immunostained for phospho-serine and
phospho-threonine and subsequently stripped and stained for
.alpha.-JAB1 and .alpha.-cytohesin-1 respectively. E) Flow
cytometric detection of phospho-p44/42(T202/Y204) in IgG, a-JAB1,
.alpha.-cytohesin-1 N-terminal, .alpha.-cytohesin-1 C-terminal, and
C-terminal cytohesin-1 peptide transfected cells stimulated with
sICAM-2 (5 .mu.g/ml, 30 min).
[0064] F) depicts the results of experiments demonstrating: A)
Kinetic analyses of CD3, CD28, and LFA-1 stimulus of
phospho-p38(T1801Y182), phospho-AKT(S473), phospho-Lck(S158),
phospho-mek1/2(S2171221), phospho-elk(S38) by flow cytometry. We
observed phospho-AKT, phospho-p38, and phospho-mek1/2 to be induced
by CD28 stimulation to a greater extent than CD3 or LFA-1 stimulus.
These reports are consistent with recent findings suggesting the
activation of these pathways by CD28 stimulation (Kane et al.,
2001; Li et al., 2001). We noted that phospho-Ick was induced over
time in the LFA-1 stimulus differentially with respect to CD3 and
CD28 stimulation. Phosphorylation of elk-1 was imparted by CD3 and
CD28 stimulation, and to a lesser degree by LFA-1 stimulus.
[0065] FIG. 7 depicts the results of experiments demonstratin
CD3/CD28/LFA-1 signaling in human naive T cells by phospho-protein
antibody array. A) Differential phospho-protein profile of
CD3/CD28/LFA-1 vs. C3/CD28 stimulated naive CD4+ T cells. Ratios of
the fluorescent phospho-protein array were calculated from the
following equation where MFI equals mean fluorescent intensity:
Log, (see Materials and Methods). Fold-phosphorylation is depicted
by the fluorescence intensity scale where green corresponds to high
and red corresponds to low. B) Cell cycle analysis of CD4+ T cells
stimulated with CD3, CD28, and sICAM-2. Cells in G0, G1, S+G2/M
phases of the cell cycle were determined using double staining for
expression of Ki-67 and DNA content. Low Ki-67-signals were
considered cells in G0, Ki-67+ signals with 2n DNA were considered
cells in G1 and Ki-67+ signals with 2n DNA were considered to be in
S or G2/M.
[0066] FIG. 8 A) and B) shows a flow diagram depicting
multidimensional analysis of naive CD4+ T cells. Magnetic cell
sorting, 13-parameter flow cytometry, transcription factor
profiling, and cytokine bead arrays were multiplexed to determine
stimulations effect on immunophenotyed naive human CD4+ T cells
(CD3.sup.+CD4.sup.+CD8.sup.-CD45RA.sup.+CD62L.sup.+CD11a.sup.dimCD27.sup.-
+CD28.sup.+). Intracellular levels of cytokines and
phospho-proteins were correlated with surface phenotypes/activation
markers as indicated in figure. C) demonstrates that the cells are
naive gated CD4+ T cells (as indicated by 5 differentiation
markers) for individual stimulations of sICAM-2 and CD28, as well
as the CD3/sICAM-2 combination. B) CD25 expression post 24 and 48
hr stimulus (as indicated, 10 .mu.g/ml).
[0067] FIG. 9 depicts the results of experiments demonstratin T
cell activation as monitored by intracellular IL-2, and surface
CD25 and CD69 markers. A) Intracellular detection of IL-2 of
titration of CD3/CD28 vs. LFA-1 stimulus or CD3 vs. CD28 stimulus
for 6 hours. Median Fluorescent intensity is plotted as a visual
array. B) Bivariate analysis of CD69 and CD25 expression in
unstimulated, CD3/CD28/LFA-1 (0.001 .mu.g/ml, 1:1:1) stimulated,
and CD3/CD28 (10 .mu.g/ml) stimulated CD4 T cells. C) Bivariate
plot of CD69 expression and intracellular detection of IL-2 post 12
hour stimulation of unstimulated, CD3/CD28, and CD3/CD28/LFA-1
stimulation.
[0068] FIG. 10 depicts the results of experiments demonstrating the
profiling of transcription factor nuclear localization and
activity. A) Reporter gene assays of NFAT-luciferase,
NF-.kappa.K-luciferase, and AP-1-luciferase transfected Jurkat
cells. CD3, CD3/CD28, and CD3/CD28/LFA-1 stimulus was performed (6
hr, 10 .mu.g/ml) and fold luciferase activity is plotted. B)
Nuclear profile of transcription factors (as indicated in figure)
to CD3, CD28, and LFA-1 stimulus (10 .mu.g/ml, 12 hr). Nuclear
extracts (5 .mu.g/ml) were hybridized to transcription factor
specific consensus sequence DNA coated plates, and detected by
ELISA. Values were normalized to negative control and displayed as
absorbance units of 655 nm. Nuclear profile of CD3/CD28 and
CD3/CD28/sICAM-2 stimulated cells (as described above). C)
NFAT-luciferase reporter activity on CD3/CD28 and CD3/CD28/LFA-1
titrations (as indicated) as described above. D-E) depict the
results of experiments demonstrating the transcription factor
profiling and cytometric bead array of CD3, CD28, and LFA-1
stimulation. A) Nuclear extracts of stimulated cells were prepared
and hybridized to 96 well plates coated with consensus sequences to
p65, p50, cFos, creb, atf2, and cRel. Bound protein was detected
using standard ELISA techniques. CD3 stimulation presented low
levels of the NF-.kappa.B subunits p65 and p50 and no detectable
levels of cFos, cRel, CREB, effects of which were similar to LFA-1
stimulation. However, CD3 stimulation alone presented higher levels
of aft2 than CD28 and LFA-1 stimulus. CD28 stimulation alone
presented low levels of the NF-.kappa.B p65 and p50 subunits, with
elevated levels of CREB. LFA-1 stimulation presented slightly
higher levels of NE-KB p65 subunit and cRel. B) Cytometric bead
array (CBA) for secreted IFN.gamma., IL-10, IL-2, IL-4, IL-5, IL-2,
and TNF.alpha. to CD3/CD28 and CD3/CD28/LFA-1 stimulus (10
.mu.g/ml, 16 hr). Values were computed to standard curve using
recombinant cytokines and were simultaneously measured from the
supernatant of treated cells. Measurement of cytokine secretion
after CD3 and LFA-1 stimulus alone did not report significant
cytokine secretion CD28 stimulation gave elevated levels of IL-4
and IL-5, with low levels of IFN.gamma..
[0069] FIG. 11 depicts the results of experiments demonstrating the
intracellular production of IL-4 and IFN.gamma. in human naive CD4
T cells. Intracellular levels of IFN.gamma. and IL-4 post 6 hr
stimulus of titrations of CD3 vs. CD28 and CD3/CD28 vs. LFA-1
stimulus. Median fluorescence values were normalized to
unstimulated cells, and log ratios of IL-4/IFN.gamma. were computed
and plotted as intensity contour plots. Intensity levels are
depicted in range indicator (right).
[0070] FIG. 12 depicts the results of experiments demonstrating
cytometric bead arrays and Cytometric bead array (CBA) for secreted
IFN.gamma., IL-10, IL-2, IL-4, IL-5, IL-5, and TNF.alpha. to
CD3/CD28 and CD3/CD28/LFA-1 stimulus (10 .mu.g/ml, 16 hr). Values
were computed to a standard curve using recombinant cytokines and
were simultaneously measured from the supernatant of treated cells
using CBA arrays from PharMingen.
[0071] FIG. 13 depicts the results of experiments demonstrating
clustering of ectopic ICAM-2 in NIH3T3 activated the p44/42 MAPK
cascade. A) ICAM-2 and ICAM2-.DELTA.C retroviral expression vectors
target to the cell surface. Plasma membrane targeting of ICAM-2 and
ICAM2-.DELTA.C transduced NIH3T3 was verified by flow cytometry
using specific anti-human antibodies to respective termini. B)
Western-blot verified ICAM-2 and ICAM2-.DELTA.C expression to
compare with endogenous ICAM-2 from Jurkat cells. C) p44/42 MAPK
cascade is initiated upon surface ICAM-2 clustering. Serum starved
ICAM-2 cells were ICAM-2 crosslinked (10 .mu.g/ml) for the
indicated time by an anti-human ICAM-2 monoclonal antibody. Cell
lysates were harvested and subjected to standard electrophoretic
and immunoblotting protocols. Phospho specific antibodies for RAF,
MEK, p44/42 MAPK (ERK1/2), Elk-1, and Rsk1 were used to detect
phosphorylated proteins. Blots were then stripped and reprobed
using a normalizing antibody (non-phospho specific antibody) to the
each respective kinase. D) ICAM-2 clustering induces p44/42 MAPK
activity as determine by p44/42 MAPK kinase activity assay. Serum
starved cells were crosslinked for ICAM-2 (10 .mu.g/ml) for 30
minutes and assessed for p44/42 MAPK activity. Positive and
negative denoted lanes indicate internal MAPK kinases controls and
a control IgG served as a negative control for induction
condition.
[0072] FIG. 14 depicts the results of experiments demonstrating
that p44/42 MAPK activity mediates enhanced growth kinetics. A)
Cell cycle re-entry in initiated upon ICAM-2 clustering. Cells were
serum starved for 72 hours to synchronize cells in the absence of
chemical agents and subsequently ICAM-2 crosslinked (10 .mu.g/ml,
18 hrrs) and subjected to cell cycle analysis by flow cytometry.
Errors bars denote standard deviation of triplicate experiments.
Gating for specific cell cycle stages is presented (left). B)
Contact inhibition induced cell cycle arrest as measured by the MTT
cell viability assay. Indicated cell types were seeded in a 96 well
plate at increasing cell density as indicated and cellular
respiration was measured by incubating the cells with the MTT
reagent. Detection of product was done by reading absorbance at 580
nm 4 hrs post an initial 2-hour settling period. Error bars denote
standard deviation of triplicate experiments. C) Growth kinetics
monitored by cell density over time. Indicated cell types were
seeded at 10.sup.4 cells and cell density was monitored by standard
clonogenic assay over the indicated time period. Error bars denote
standard deviation of triplicate experiments.
[0073] FIG. 15 depicts the results of experiments demonstrating
that ICAM-2 binds surface .beta. 1, .beta. 2, and .beta. 3
integrins. A) Affinity chromatography detects several ICAM-2
interacting surface proteins. An ICAM-2FITC probe was generated by
immuno-depletion of ICAM-2 from transduced NIH3T3, chemically
conjugated to FITC (1st and 2nd panels), and tested by anti-ICAM-2
immunoblot and fluorescent labeling. A farwestern approach
utilizing ICAM-2-FITC as a labeled probe detects a 96 and 16 kdA
interacting protein bands in ICAM-2 lysates (3rd panel). Surface
proteins of ICAM-2 and vector control cells were biotinylated and
subjected to affinity chromatography dual column system utilizing a
constructed ICAM-2 coupled solid support and a streptavidin-agarose
support. Several protein bands were identified that are both ICAM-2
interacting and surface expressed (biotinylation detected by
streptavidinFITC) (4.sup.th panel). B) ICAM-2 soluble protein binds
to the surface of cells. The ICAM-2-FITC probe was used to label
NIH3T3, Jurkat, and BaF3 cells and was detected by flow cytometry.
Prior treatment of cells with trypsin attenuated the ICAM-2-FITC
binding (right panel). C) ICAM-2 interacts with .beta. 1, .beta. 2,
and .beta. 3 integrins. Final elusions from the ICAM-2 solid
support and subsequent streptavidin-agarose column passage were
immunoblotted for .beta.-integrins using monoclonal antibodies.
Detection of .beta. 1, .beta. 2, and .beta. 3 refined and verified
the mass spectrometry reading of the MALDLMS analysis. D) ICAM-2
interaction with .beta. 2 integrin induces p44/42 MAPK kinase
activity. Beta-1, .beta. 2, and .beta. 3 integrin were blocked with
monoclonal antibodies in serum starved cells prior to ICAM-2
crosslinking in ICAM-2, ICAM2-.DELTA.C, and vector control cells.
E) Integrin profile assessment by quantitative flow cytometry.
Alpha-5, .alpha.L, .beta. 1, .beta. 2, .beta. 3, .beta. 4
monoclonal antibodies were conjugated to phycoerythrin (PE) and
quantitated using QuantiBRiTE PE beads by flow cytometry (see
materials and methods for elaboration). Linear regression analysis
of fluorescent signal as a function of a standard antigen
concentration curve allows quanititation of the number of surface
molecules per cell. Error bars denote standard deviation of
triplicate experiments. F) Soluble ICAM-2 induced p44/42 MAPK
phosphorylation and activity is blocked by antibodies to .alpha.L
integrin. ICAM-2 soluble protein was incubated for 30 minutes in
serum starved Jurkat cells at the indicated concentrations in the
presence or absence of monoclonal antibody pre-treatment to
.alpha.L (similar to mAb blocking experiments). Immunoblot for
phospho-p44/42 MAPK (left) and p44/42 MAPK activity assay
(right).
[0074] FIG. 16 depicts the results of experiments demonstrating
that ICAM-2/LFA-1 interaction is transmitted to Raf by PYK2 and
SYK. Inhibitor screens using various pharmacological inhibitors to
Src related kineses identify PYK2 and SYK to be necessary in
relaying the ICAM-2 induced signal to Raf and p44/42 MAPK kinase.
Serum starved cells were treated with 10 .mu.M of indicated
compound 30 minutes prior to being ICAM-2 crosslinked for 30
minutes (10 .mu.g/ml) and assessed for phosphorylated Raf and
p44/42 MAPK using phospho specific antibodies in standard
immunoblot procedures. Control IgG dissolved in 0.1% DMSO served as
negative control. Blots are representative of triplicate
experiments. B) SYK and PYK interaction with LFA-1 subunits is
intensified upon ICAM-2 interaction. Co-immunoprecipitation
experiments were performed immunoprecipitating .alpha.L and .beta.2
integrin and immunoblotting for the presence of SYK and PYK as a
function of a stimulus for 30 minutes as indicated (antibodies used
at 10 .mu.g/ml, compounds used at 1 .mu.M and control 19 served as
negative control). Reciprocal co-immunoprecipitations confirm PYK
and SYK associations with 132 integrin (bottom panel). C) PYK2 is
phosphorylated in the presence of ICAM-2 or additional stimuli as
determined by an anti-phosphotyrosine immunoprecipitation and
subsequent immunoblot for PYK2.
[0075] FIG. 17 depicts result from experiments demonstrating that
confocal microscopy reveals cellular the redistribution of PYK2 and
SYK to the surface membrane in Jurkat cells after ICAM-2
interaction with LFA-1 and subsequent phosphorylation of PYK2.
Jurkat cells were treated with soluble ICAM-2 protein (10 .mu.g/ml)
or bovine serum albumin (Unstimulated, 10 .mu.g/ml) for 10 minutes
and prepared for confocal microscopy (see material and methods).
Cells were stained for PYK2, SYK2, and phosphorylated PYK2 at
tyrosine 402 (denoted as PYK2 pTyr402). Panels A-F represent
unstimulated cells and panels G-L represent ICAM-2 treated cells.
Arrows serve to highlight marked differences in cellular
distribution of PYK2 and SYK. Scale bar is denoted in lower left
corner of panels (in micrometers). Panels G-L are at a higher
magnification to see distribution differences clearly.
[0076] FIG. 18 depicts result from experiments demonstrating that
cell-to-cell contact initiates p44/42 MAPK activity in LFA-1
expressing and AKT activity in ICAM-2 expressing cells as
determined by flow cytometry based kineses assays. A) Jurkat cells
and retrovirally transduced ICAM-2 cells were mixed for 30 minutes
and subjected for flow cytometry by surface staining for CD3 and
CD4 surface markers, and stained intracellularly for phospho-p44/42
MAPK and phospho-AKT using fluorescently conjugated
phospho-specific monoclonal antibodies (see materials and methods
for elaboration). Gating on high and low phosphorylated AKT and
p44/42 MAPK populations, as determined for fluorescence log
intensity, were analyzed according to the CD3 and CD4 surface
markers. Plots depict CD3 vs. phospho-AKTser473 or phospho-p44/42
but are similar for CD4. B) Model of signaling pathways initiated
upon intercellular ICAM-2/LFA-1 interaction. LFA-1, upon engagement
of ICAM-2 activates the RAF/MEK/MAPK cascade, mediated through PYK2
and SYK. ICAM-2 expressing cells activate the AKT survival pathway
as ICAM-2 is clustered on the cell surface.
[0077] FIG. 19 depicts the results of experiments demonstrating
that a retroviral library screen for anti-apoptotic molecules to
staurosporine induced apoptosis identifies ICAM-2. A) cDNA library
screening scheme. 10.sup.7 NIH3T3 cells were infected with a Jurkat
T cell retroviral cDNA library and treated with staurosporine (1
.mu.M) for 24 hours to induce apoptosis (Stolzenberg et al., 2000).
Surviving clones were grown out for one week and subjected to a
repeat selection three times. To determine which viral integrants
encoded an antiapoptotic function, a phenotypic transfer assay was
performed. An aliquot of the surviving cell population was infected
with native Moloney murine leukemia virus (MMLV). This rescued the
replication-defective viral vector proviruses, generating
infectious particles. NIH3T3 cells were infected with the rescued
viral vectors and treated with staurosporine to confirm the
anti-apoptotic phenotype. B) Complexity of populations surviving
staurosporine induced apoptotic screen. RT-PCR was performed to
assess the complexity of the surviving populations. Surviving
population (1.degree.) exhibited several discrete bands and the
post-transfer population)(2.degree. exhibited a single band.
M-molecular weight marker. A negative control vector (LacZ),
initially spiked into the library at 10% was undetectable, while an
independent infection of a Bcl-2-expressing vector was readily
detected. C) Retroviral vector encoding ICAM-2 western blot
analysis in infected NIH3T3. D) Retroviral vector encoding ICAM-2
ectopically expresses surface ICAM-2. Right Panel: BaF3 pro-B-cells
infected with a retroviral vector construct encoding ICAM-2 or
vector control and assayed for either endogenous and expressed
ICAM-2 surface expression levels by flow cytometry. Left Panel:
HUVEC cells stained for endogenous ICAM-2 expression by flow
cytometry. E) Dose response curves of ICAM-2 transduced NIH3T3 and
Jurkat T-cells to treatment of staurosporine or anti-Fas antibody
for 24 hours. Open squares: ICAM-2 expressing cells. Closed
squares: control cells expressing vector alone. The proportion of
apoptotic cells in each culture without staurosporine or anti-Fas
mAb was less then 3%. The percentage of apoptotic cells is
expressed as the mean (bar).+-.SD of triplicate cultures.
[0078] FIG. 20 depicts the results of experiments demonstrating
that the overexpression of ICAM-2 results in a broadly acting
anti-apoptotic phenotype. A) Effect of ICAM-2 on staurosporine
induced apoptosis was assessed by annexin-V binding assay. ICAM-2
expressing NIH3T3 and vector control NIH3T3 were subjected to an
annexin-V binding assay in the presence or absence of staurosporine
(1 .mu.M,24 hrs). DMSO vehicle served as the negative control. The
proportion of apoptotic cells in each culture without staurosporine
was 5%+/-1.2. B) Effects of ICAM-2 overexpression in Jurkat,
NIH3T3, 70Z/3, and BaF3 cells in the context of different apoptotic
inducers. Infected cells were treated with either staurosporine (1
.mu.1 M), anti-Fas antibody (5 .mu.g/ml), or deprived of IL-3 for
24 hours as indicated and evaluated for apoptosis as described
(Jacobson and Raff, 1995). Cells were infected with retroviral
constructs encoding ICAM-2, ICAM2-AN, vector control, or Bcl-2 and
subjected to apoptose as indicated (24 hrs, 70Z/3 cells: 0.2 .mu.M
STP, 4 hrs). The percentage of apoptotic cells is expressed as the
mean (bar)+/-SD of triplicate cultures. C) The .alpha.-actinin
binding site is required for survival. ICAM-2, wild-type sequence
(red line); ICAM2.DELTA.C, cytoplasmic domain deletion (solid, thin
line); ICAM-2 C-scrambled, full length with scrambled
[a].alpha.-actinin binding site (hatched line) were FACS sorted by
an anti-ICAM-2-FITC monoclonal antibody (IC2/2), and incubated with
etoposide (100 .mu.M, 24 hrs). Viable cells were scored after a 24
hr recovery period following etoposide treatment. The percentage of
surviving cells is expressed as the mean (bar)+/-SD of triplicate
cultures.
[0079] FIG. 21 depicts the results of experiments demonstrating
that PI3-kinase is necessary for ICAM-2's anti-apoptotic effect. A)
Pharmacological inhibitors of PI3K abrogate ICAM-2's
anti-apoptotic. ICAM-2 or vector transduced BaF3 cells were treated
with staurosporine (1 .mu.M) with (unfilled) or without (filled)
the addition of 100 nM wortmannin for 24 hours (left bar graph).
Apoptosis was determined by nuclear staining and fluorescence
microscopy (left bar graph) and by annexin-V binding assay (right
bar graph). The proportion of apoptotic cells in each culture
without staurosporine was 8%+/-2. The percentage of apoptotic cells
is expressed as the mean (bar)+SD of triplicate cultures.
ICAM-2,1CAM2-AC, or vector transduced NIH3T3 were treated with
staurosporine (1 .mu.1 M) in the presence or absence of 10 .mu.M
LY294002 for 24 hours (right bar graph). DMSO vehicle served as
negative control. The percentage of apoptotic cells is expressed as
the mean (bar)+/-SD of triplicate cultures. B) Confocal images of
PI3K and AKT localization in ICAM-2 (top) or vector control cells
(bottom). C) Confocal images of ezrin and the p85 subunit of PI3K
(green) localization in ICAM-2 (top) or vector control cells
(bottom).
[0080] FIG. 22 depicts the results of experiments demonstrating
that ICAM-2 signal results in phosphatidylinositol 3,4,5
triphosphate production, PDK-1 and AKT activation, and subsequent
phosphorylation of AKT downstream effectors. A) ICAM-2 interacts
with .alpha.-actinin and ezrin. ICAM-2, ICAM2-.DELTA.C or control
cells were immunoprecipiated for ICAM-2 and immunoblotted for
either a-actinin or ezrin. Control lysates were not subjected to
immunoprecipitation and reflect positive controls for detected
interacting protein. B) ICAM-2 cells exhibit high levels of
phosphatidylinositol 3,4,5 triphosphate. ICAM-2 and control cells
were serum starved (48 hrs), treated with LY294002 (10 .mu.M, 24
hrs), or cultured in growth media, and prepared for intracellular
detection of phosphatidyinositol 3,4,5 triphosphate detection by
flow cytometry. C) PDK-1 I kinase levels are elevated in ICAM-2
cells and are partially inhibited by Y-27632. PDK-1 kinase was
immunoprecipitated from cells incubated with the indicated
compounds (10 .mu.M, 1 hr) and subjected to an immuno-kinase
reaction with inactive SGK enzyme and peptide substrate.
Phosphotransfer of ATP to peptide substrate was detected by
scintillation counting and presented as counts per minute CPM. D)
Immunoblot for AKT in membrane/cytosol fractions of ICAM-2 and
controls cells and AKT kinase activity. E) AKT kinase level and
dual phosphorylation at serine 473 and threonine 308 are sustained
in ICAM-2 cells in the presence of staurosporine. F) The AKT kinase
substrates BAD and GSK3 remain phosphorylated in ICAM-2-expressing
cells following staurosporine treatment. Extracts from ICAM-2,
ICAM-2.DELTA.C and control vector cells treated with DMSO-vehicle
(-) or 1 .mu.M staurosporine (+) were assayed for BAD and GSK3
phosphorylation by immunoblotting as indicated.
[0081] FIG. 23 depicts the results of experiments demonstrating
that ligation of endogenous ICAM-2 induces tyrosine phosphorylation
of ezrin and recruits PI3K to the membrane, resulting in PDK-1 and
AKT kinase activation. A) Expression levels of ICAM-2 vary across
cell lines of different origins. Quantitative flow cytometry
analysis was performed to assess the number of ICAM-2 surface
molecules across transformed and untransformed fibroblasts,
lymphocytes of T-cell and different B-cell differentiation states
and myeloid lineages (see Material and Methods for elaboration).
The number of surface molecules/cell is expressed as the mean
(bar)+/-SD of triplicate experiments. B) Crosslinking of endogenous
ICAM-2 induces ezrin tyrosine phosphorylation and enhanced ICAM-2
interaction. Jurkat cells were crosslinked for ICAM-2 using
monoclonal antibody for the indicated times and subjected to
immunoprecipitation/immunoblotting as indicated. C) Inhibition of
ezrin phosphotyrosine by chemical inhibitors of src and
Rho-dependent kinases. D) Ezrin phosphorylation and enhanced
interaction with the p85 subunit of PI3K as a function of ICAM-2.
Determined as described above. E) PDK-1 activity as a function of
ICAM-2 ligation, as described above). F) PI3K and AKT localize to
the membrane as a function of ICAM-2 ligation. Membrane/cytosolic
fractionation was performed on ICAM-2 ligated Jurkat cells as a
function of time and subjected to immunoblotting for PI3K and
AKT.
[0082] FIG. 24 depicts the results of experiments demonstrating
that ligation of endogenous ICAM-2 induced AKT activation in
lymphoid cells conferring cell survival. A) ICAM-2 crosslinking
induced AKT activity in Jurkat T cells and subsequent
phosphorylation of GSK3, FKHR, and AFX as a function of time. Serum
starved Jurkat T cells were incubated with either isotype control
or anti-human ICAM-2 (10 .mu.g/ml) for the indicated times. AKT
kinase activity was determined as described. Immunoblot analysis
verified AKT dual phosphorylation, FKHR and GSK3 phosphorylation,
and BAD phosphorylation as a function of ICAM-2 crosslinking. B)
ICAM-2 crosslinking induces AKT activity in BaF3 pre-B cells. C)
ICAM-2 clustering on Jurkat T cells treated with staurosporine (1
.mu.m for 6 hours) shows a decrease in apoptosis as measured by
flow cytometry annexin-V binding assay. ICAM-2 was crosslinked on
106 Jurkat T cells using an ICAM-2 mAb (10 .mu.g/ml) 30 minutes
prior to treatment with staurosporine (+) or DMSO vehicle (-).
Apoptosis was determined by flow cytometry using annexin-V binding
assay. D) ICAM-2 survival signal is abrogated in the presence of
GTP.gamma.S, Psi-tectorigenin, Y-27632 and herbimycin A. Jurkat
cells were incubated with indicated inhibitor (10 .mu.M, 1 hour)
prior to being crosslinked for ICAM-2 (10 .mu.g/ml, one hour) and
treated with anti-Fas (50 ng/ml, 8 hours). Cells were assessed for
apoptosis by annexin-V binding assay. E) ICAM-2 crosslinking
induces ezrin association with PI3K. ICAM-2, vector control, Jurkat
and Jurkat cells crosslinked for ICAM-2 (10 .mu.g/ml, 15 minutes)
were subjected to immunoprecipitation and subsequent immunoblotting
as indicated.
[0083] FIG. 25 depicts the results of experiments demonstrating
that ligation of ICAM-2 induces AKT activity and protects primary B
cells from apoptosis. A) Human peripheral blood monocytes were
crosslinked for ICAM-2 (10 .mu.g/ml 45 minutes) prior to being
subjected to apoptosis by treatment with TNF.alpha. 200 ng/ml plus
1 .mu.g/ml cycloheximide) and anti-Fas antibody (10 ng/ml CH11) for
12 hours. Multi-parameter FACS analysis illustrates ICAM-2 induced
AKT activity in CD4+ and CD19+ populations protects from apoptosis.
(1.times.10.sup.6 events collected to enumerate a minimum of 80,000
CD19+ cells). B) PBMC were crosslinked for ICAM-1, -2, -3, CD43, or
CD44 (10 .mu.g/ml 45 minutes) and subjected to phosphatidylinositol
detection of phosphatidylinositol 3,4,5 triphosphate,
phosphatidylinositol 4,5 bisphosphate, or phospho-AKTser473
detection by flow cytometry. Cell subsets are gated and displayed
as indicated. C) PBMC were crosslinked for ICAM-1, -2, -3, CD43, or
CD44 (10 .mu.g/ml 45 minutes) prior to being induced to apoptose as
described above. Apoptosis was measured by annexin-V binding
detected by flow cytometry, and gated for CD19+ cells. D) PBMC was
crosslinked for ICAM-2 prior to being induced to apoptose as
described above in the presence or absence of inhibitory compounds
Psi-tectorigenin and Y-27632 (10 .mu.M, 30 minutes). Apoptosis was
measured by annexin-V binding assay. E) LFA-1 overlay assay. LFA-1+
Jurkat cells were overlayed on either vector control or ICAM-2
expressing cells after being treated with LY294002 (2 .mu.M, one
hour). Some Jurkat samples were treated with monoclonal antibodies
to LFA-1 or Mac-1 (5 .mu.g/ml, 30 minutes) prior to being overlayed
on ICAM-2 or vector control. Cells were mixed for 30 minutes at
37.degree. C., and then subjected for flow cytometry. Jurkat cells
were gated and removed from displayed analysis of phospho-AktSer473
ICAM-2 cells F) Model for ICAM-2 mediated cell survival signal.
ICAM-2 oligomerization recruits and phosphorylates ezrin through a
Src/Rho dependent mechanism. This results in recruitment of PI3K to
the membrane through ezrin's interaction with the p85 regulatory
subunit of PI3K. Membrane translocation of PI3K generates
phosphatidylinositol 3,4,5 triphosphates that activate PDK-1 and
recruit AKT to the plasma membrane by binding to its PH domain.
Translocation of cytosolic AKT to the membrane allows PDK1/2 to
phosphorylate AKT at ser473 and thr308, activating AKT. AKT
subsequently phosphorylates downstream effectors GSK3, BAD, FKHR
(and potentially others depending on the cell type).
Phosphorylation of these effectors can block apoptosis alone or
synergistically to generate a survival signal.
[0084] FIG. 26 depicts the results of experiments demonstrating the
retroviral library screen for anti-apoptotic molecules to
staurosporine induced apoptosis. A) cDNA library screening scheme.
10.sup.7 NIH3T3 cells were infected with a Jurkat T cell retroviral
cDNA library and treated with staurosporine (1 .mu.M) for 24 hours
to induce apoptosis (Stolzenberg et al., 2000). Surviving clones
were grown out for one week and subjected to a repeat selection
three times. To determine which viral integrants encoded an
anti-apoptotic function, a phenotypic transfer assay was performed.
An aliquot of the surviving cell population was infected with
native Moloney murine leukemia virus (MMLV). This rescued the
replication-defective viral vector proviruses, generating
infectious particles. NIH3T3 cells were infected with the rescued
viral vectors and treated with staurosporine to confirm the
anti-apoptotic phenotype. B) Complexity of populations surviving
staurosporine induced apoptotic screen. RT-PCR was performed to
assess the complexity of the surviving populations. Surviving
population (1.degree.) exhibited several discrete bands and the
post-transfer population)(2.degree.) exhibited a single band.
M-molecular weight marker. A negative control vector (LacZ,
initially spiked into the library at 10% was undetectable, while an
independent infection of a BcL2-expressing vector was readily
detected.
[0085] FIG. 27 depicts the results of experiments demonstrating
that overexpression of ICAM-2 inhibits staurosporine induced
apoptosis. A) Retroviral vector encoding ICAM-2 western blot
analysis in infected NIH3T3. B) Retroviral vector encoding ICAM-2
ectopically expresses surface ICAM-2. Right Panel: BaF3 pro-B-cells
infected with a retroviral vector construct encoding ICAM-2 or
vector control and assayed for either endogenous and expressed
ICAM-2 surface expression levels by flow cytometry. Left Panel:
HUVEC cells stained for endogenous ICAM-2 expression by flow
cytometry. C) Dose response curves of ICAM-2 transduced NIH3T3 and
Jurkat T-cells to treatment of staurosporine or anti-Fas antibody
for 24 hours. Open squares: ICAM-2 expressing cells. Closed
squares: control cells expressing vector alone. The proportion of
apoptotic cells in each culture without staurosporine or anti-Fas
mAb was less then 3%. The percentage of apoptotic cells is
expressed as the mean (bar).+-.SD of triplicate cultures. D)
Pyknotic nuclei of negative control NIH3T3 vector control (-STP),
positive control NIH3T3 vector control (+STP), and ICAM-2
expressing NIH3T3, Nuclei were stained with Hoescht (5 .mu.g/ml)
and acridine orange (25 .mu.M) and ethidium bromide (25 .mu.M).
Inserts indicate degree of cell death or cell viability. E) Effect
of ICAM-2 on staurosporine induced apoptosis was assessed by
annexin-V binding assay ICAM-2 expressing NIH3T3 and vector control
NIH3T3 were subjected to an annexn-V binding assay in the presence
or absence of staurosporine (1 .mu.M, 24 hr). DMSO vehicle served
as the negative control. The proportion of apoptotic cells in each
culture without staurosporine was 5%.+-.1.2.
[0086] FIG. 28 depicts the results of experiments demonstrating
that ICAM-2 mediates an anti-apoptotic effect. A) Effects of ICAM-2
overexpression in Jurkat, NIH3T3, 70Z/3, and BaF3 cells in the
context of different apoptotic inducers. Infected cells were
treated with either staurosporine (1 .mu.M), anti-Fas antibody (5
.mu.g/ml), or deprived of IL-3 for 24 hours as indicated and
evaluated for apoptosis as described (Jacobson and Raff, 1995).
Jurkat T cells were infected with retroviral constructs encoding
ICAM-2 or vector control. Mouse pre-B 70Z/3 cells were infected
with a retroviral vector construct encoding ICAM-2 or vector
control and treated with staurosporine (0.2 .mu.M) for 4 hours and
evaluated for apoptosis. IL-3-dependent BaF3 cells were infected
with retroviral vector constructs encoding ICAM-2, ICAM2-.DELTA.N,
or Bcl2. To induce apoptosis, cells were maintained in
IL-3-deficient medium for 24 hours. BaF3-cells expressing
retroviral vector encoded ICAM-2 or an in-frame deletion of the
extracellular domain were treated with anti-mouse Fas for 24 hours
and evaluated for cell death. The percentage of apoptotic cells is
expressed as the mean (bar).+-.SD of triplicate cultures. B) The
.alpha.-actinin binding site is required for survival. NIH3T3 cells
were transduced with ICAM-2 encoding retroviral constructs: ICAM-2,
wild-type sequence(hatched line); ICAM-2.DELTA.C, cytoplasmic
domain deletion (solid, thin line); ICAM-2 C-scrambled, full length
with scrambled .alpha.-actinin binding site (hatched line).
Transduced cells were labeled with a fluorescently conjugated
anti-ICAM-2 monoclonal antibody that recognized only the native
protein (IC2/2). Cells were then purified by FACS (MoFlo,
Cytomation, Ft. Collins, Co.). Sorted cells were cultured and then
cells were challenged with 100 .mu.M etoposide for 24 hours. The
surviving cells were allowed to recover for 24 hours following
removal of the drug and the number of viable cells was scored. The
percentage of surviving cells is expressed as the mean (bar).+-.SD
of triplicate cultures. C) .alpha.-actinin and ezrin both
co-immunoprecipitate with ICAM-2 and interact with the C-terminus
of ICAM-2. ICAM-2 was immunoprecipitated from ICAM-2,
ICAM2-.DELTA.C, and vector control transduced NIH3T3.
Immunoprecipitates were resolved by SDS-PAGE and subjected to
immoblotting for .alpha.-actinin, ezrin, and ICAM-2
[0087] FIG. 29 depicts the results of experiments demonstrating
that pharmacological inhibitors of PI3K abrogate ICAM-2's
anti-apoptotic effect. A) The anti-apoptotic effect of ICAM-2 is
both wortmannin and LY294002 sensitive. ICAM-2 or vector transduced
BaF3 cells were treated with staurosporine (1 .mu.M) with
(unfilled) or without (filled) the addition of 100 nM wortmannin
for 24 hours. Apoptosis was determined by nuclear staining and
fluorescence microscopy (left bar graph) and by annexin-V binding
assay (right bar graph). The proportion of apoptotic cells in each
culture without staurosporine was 8%.+-.2. The percentage of
apoptotic cells is expressed as the mean (bar).+-.SD of triplicate
cultures. ICAM-2, ICAM2-.DELTA.C, or vector transduced NIH3T3 were
treated with staurosporine (1 .mu.M) in the presence or absence of
10 .mu.M LY294002 for 24 hours. DMSO vehicle served as negative
control. The percentage of apoptotic cells is expressed as the mean
(bar).+-.SD of triplicate cultures. B) ICAM-2 expressing NIH3T3
cells are sensitive to apoptosis in the presence of PI3K inhibitor
LY294002. BrdU TUNEL assay was performed in staurosporine (1 .mu.M)
or LY294002 (10 .mu.M) treated ICAM-2, ICAM2-.DELTA.C, and control
vector transduced NIH3T3 cells. The percentage of apoptotic cells
is expressed as the mean (bar).+-.SD of triplicate cultures.
[0088] FIG. 30 depicts the results of experiments demonstrating
that ICAM-2 induces AKT kinase activity and phosphorylation of BAD
and GSK. A) AKT kinase levels and dual phosphorylation at serine
473 and threonine 308 are elevated in ICAM-2 expressing cells and
sustained in the presence of staurosporine. AKT kinase was
immunoprecipitated from ICAM-2, ICAM-2.DELTA.C and control vector
(pBMN-Z-IN-GFP) expressing NIH3T3 fibroblasts in the presence or
absence of staurosporine (with 1 .mu.M staurosporine (+) or
DMSO-vehicle (-) and incubated with a GSK protein substrate.
Phosphorylated GSK was identified by anti-phospho-GSK specific
immunoblotting. B) The AKT kinase substrates BAD, FKHR, and GSK3
remain phosphorylated in ICAM-2-expressing cells following
staurosporine treatment Extracts from ICAM-2, ICAM-2.DELTA.C and
control vector expressing NIH3T3 fibroblasts treated with
DMSO-vehicle (-) or 1 .mu.M staurosporine (+) were assayed for BAD
and GSK3 phosphorylation and by immunoprecipitating BAD or GSK3 and
immunoblotting with phospho-BAD, or phospho-GSK3 specific
antibodies. C) ICAM-2's anti-apoptotic effect is independent of
Bcl-2 or Bcl-X.sub.L/S as determined by immunoblotting. ICAM-2 or
ICAM2-.DELTA.C transduced NIH3T3 were treated with DMSO vehicle (-)
or 1 .mu.M staurosporine (+) for 24 hours and assayed for Bcl2 and
Bcl-X.sub.L/S expression by immunoblotting. D) Expression levels of
ICAM-2 vary across cell lines of different origins. Quantitative
flow cytometry analysis was performed to assess the number of
ICAM-2 surface molecules across transformed and untransformed
fibroblasts, lymphocytes of T-cell and different B-cell
differentiation states, and myeloid lineages. Geometric mean
fluorescence values were calibrated to standard curve derived from
geometric mean fluorescence values of beads labeled with known
amounts of phycoeyrthrin molecules (see experimental procedures for
elaboration). The number of surface molecules/cell is expressed as
the mean (bar).+-.SD of triplicate experiments.
[0089] FIG. 31 depicts the results of experiments demonstrating
that cross-linking of endogenous ICAM-2 induces AKT activation in
BaF3 B-cells and protects Jurkat T cells from apoptosis. A)
Cross-linking ICAM-2 with monoclonal anti-ICAM2 antibody induced
AKT activity. Serum starved BaF3 preB cells were incubated with
either normal rat IgG2 (isotype control) or anti-mouse ICAM-2 at 10
.mu.g/ml for the indicated times. AKT kinase activity was
determined as described. immunoblot analysis was performed to
verify AKT dual phosphorylation, FKHR phosphorylation, and BAD
phosphorylation as a function of ICAM-2 crosslinking. Isotype
control did not induce AKT phosphorylation or phosphorylation of
FKHR or BAD (data not shown). B) ICAM-2 clustering on Jurkat T
cells treated with staurosporine (1 .mu.m for 6 hours) shows a
decrease in apoptosis as measured by flow cytometry annexin-V
binding assay. ICAM-2 was crosslinked on 10.sup.6 Jurkat T-cells
using a monoclonal anti-ICAM-2 antibody (10 .mu.g/ml) 30 minutes
prior to treatment with staurosporine (+) or DMSO vehicle (-).
Apoptosis was determined by flow cytometry using annexin-V binding
assay. (100,000 events collected). C) ICAM-2 crosslinking on Jurkat
T cells decreases percentage of death in staurosporine treatment.
The percentage of dead cells is expressed as the mean (bar).+-.SD
of triplicate experiments. D) ICAM-2 cross-linking induces AKT
activity in Jurkat T cells and subsequent phosphorylation of GSK3,
FKHR, AFX as a function of time. E) ICAM-2 crosslinking can
overcome staurosporine induce apoptosis. 10.sup.6 Jurkat T-cells
were treated with staurosporine (1 .mu.M) for one hour as indicated
by (+) to induce apoptosis. After one hour of staurosporine induced
apoptosis, ICAM-2 was crosslinked using a monoclonal anti-ICAM2
antibody (10 .mu.g/ml) for the indicated times. Attenuation of
cleaved caspases was not observed in isotype control (10 .mu.g/ml)
(data not shown). F) ICAM-2 cross-linking induces AKT activity,
subsequent phosphorylation of BAD, and is sufficient to override
apoptotic induction by staurosporine. Jurkat cells were treated as
mentioned above. AKT activity was determined by AKT kinase assay
and detection of dually phosphorylation AKT by immunoblotting with
phospho-specific antibodies against ser473 and thr308. BAD
phosphorylation was detected by immunoprecipitation for BAD,
followed by immunoblotting with phospho-specific antibodies ser112
and ser136. Isotype control (10 .mu.g/ml) did not generate AKT
activation (data not shown).
[0090] FIG. 32 depicts the results of experiments demonstrating
that resistance to TNF.alpha. and Fas induced apoptosis in primary
human CD4+ and CD19+ cells is mediated by active AKT following
ICAM-2 crosslinking. A) Human periperal blood monocytes were
assayed for AKT activity following ICAM-2 clustering using
monoclonal antibodies (middle panel) or antiIICAM-2 labeled
antibodies (bottom panel) and subsequently gated for CD4 or CD19
markers (50,000 events collected). B) Human peripheral blood
monocytes were crosslinked for ICAM-2 (10 .mu.g/ml 45 minutes)
prior to being subjected to apoptosis by treatment with TNF.alpha.
200 ng/ml plus 1 .mu.g/ml cycloheximide) and anti-Fas antibody (10
ng/ml CH11) for 12 hours. Multi-parameter FACS analysis illustrates
ICAM-2 induced AKT activity in CD4+ and CD19+ populations protects
from apoptosis. (1.times.10.sup.6 events collected to enumerate a
minimum of 80,000 CD19+ cells). C) Model for ICAM-2 mediated
anti-apoptotic signaling. ICAM-2 binds intracellular linker
proteins .alpha.-actinin and ezrin, which recruit PI3K to the
plasma membrane. PI3K generates inositol phosphates that recruit
AKT to the plasma membrane by binding to its PH domain.
Translocation of cytosolic AKT to the membrane allows PDK1/2 to
phosphorylate AKT at ser473 and thr308, activating AKT. AKT
subsequently phosphorylates downstream effectors GSK3, BAD, FKHR
(and potentially others depending on the cell type).
Phosphorylation of these effectors can block apoptosis alone or
synergistically to generate a survival signal.
[0091] FIG. 33 depicts results demonstrating that soluble ICAM-2
binding induces LFA-1 clustering and cytoskeletal polarization. A)
Purified human ICAM-2 from retrovirally transduced NIH3T3 (see
materials and methods) was tested for purity, size, and aggregate
formation by native gel electrophoresis and gel filtration.
Analysis of purified ICAM-2 from two different preps and ICAM2-FC
from NSO cells. Molecular weight was calculated using relative
distance migration from a molecular weight standard. Concentration
was determined using serial dilutions of BSA as a standard.
Molecular weight and concentration are displayed in the figure. B)
ICAM-2 ligand binding to cell surface as a function of time.
5.times.10.sup.6 unstimulated and PMA stimulated (1 .mu.g/ml, 30
min) Jurkat T cells were incubated with ICAM-2-FITC or LFA-1-FITC
antibody (1 .mu.g/ml) and subjected to time dependent flow
cytometry. Mean fluorescence intensity was plotted per time of a
gated homogenous cell population. Flow rate was maintained at
200-300 cells/second, with fluorescence intensity values acquired
at 10 millisecond intervals for 1200 seconds. C) Flow cytometric
analysis of ICAM-2-FITC and .alpha.-LFA-1-FITC surface binding on
cytochalisin D treated (10 .mu.M, 30 min) Jurkat cells at
37.degree. C. and 4.degree. C. D) Curve fit analysis of ICAM-2-FITC
binding per 10.sup.4 cells. Jurkat cells were incubated with
ICAM-2-FITC at 37.degree. C. for 30 min at indicated concentrations
in 50 .mu.L volume. Cells were washed 1.times., and analyzed for
mean fluorescent intensity (MFI) of 10.sup.4 cells. Percent
ICAM-2-FITC bound was calculated from the following equation:
100.times.[(MFI.sub.[x]-MFI.sub.unstained)/(MFI.sub.[saturated]-MFI.sub.u-
nstained)] were [x]=ICAM-2-FITC concentration and
[saturated]=concentration that saturated binding. Values were fit
to the equation Y=m1*M0/(m2+M0) (see materials and methods).
[0092] Supplementary FIG. 33 depicts soluble ICAM-2 and ICAM-2-FITC
generation. A) Native gel electrophoresis of purified ICAM-2. Gel
was coomasie stained and purified ICAM-2 did not display aggregates
(after gel filtration, we found that the added glycerol in the
purification step eliminated higher molecular weight species
formation). B) Purity analysis of ICAM-2 by native PAGE. Quantity
was determined from densitometry measurements of entire lane.
Percent purity was determined from calculating density of band
relative to total density of the lane. ICAM-2 from prep one (left)
and from prep 2 (right). Purity was greater than 98%. C). ICAM-2
was conjugated to FITC and purified conjugate (by spin
chromatography) was immunoblotted with anti-ICAM-2 antibody (left
panel) and subsequently verified for fluorescent conjugation in gel
(right panel). D) Treatment of cells with cytochalisin D at low
concentrations at 40 C led to enhanced ICAM-2 binding in a subset
of cells and saturated at 370 C. Titration of ICAM-2-FITC surface
binding at 370 C and 40 C in cytochalisin D treated (10 mM, 30 min)
and untreated Jurkat cells by flow cytometry. Median Fluorescence
Intensity (MFI) is plotted as a function of ICAM-2-FITC
concentration.
[0093] FIG. 34 depicts the results of experiments demonstrating the
simultaneous detection of ICAM-2 induced LFA-1 clustering,
activation, and actin/microtubule reorganization. A) Confocal
microscopy of actin and microtubule architecture upon ICAM-2
stimulus (10 .mu.g/ml, 30 min) in Jurkat cells. Actin was stained
by phalloidin-alexa633 and tubulin by taxol-alexa546. Inserts
display enlarged cell image of representative treatment B) Flow
cytometric staining for actin and microtubules as described above.
C) Left: Fluorescence topography analysis of ICAM-2-FITC (1
.mu.g/ml, time as indicated) surface distribution. Intensity color
gradient depicts high and low fluorescent intensity values. Right:
Confocal microscopy of ICAM-2-FITC surface binding (10 .mu.g/ml,30
min) and anti-.beta.2-alexa568 (clone CTB104). D) Staining for
ICAM-2-FITC surface binding (fluorescence intensity) and surface
distribution (fluorescence pulse) in cytochalisin D treated Jurkat
cells at 37.degree. C. and 4.degree. C. by flow cytometry. E)
Values for ICAM-2-FITC fluorescence intensity per time-of-flight
per cell as described in text. F) Flow cytometric staining for
LFA-1 activation by mAb24-alexa633. Stimuli as indicated (10 .mu.M,
30 min), PMA (1 .mu.g/ml) prior to ICAM-2 stimulation (10 .mu.g/ml,
30 min). Staining was performed at 37.degree. C. G) Mean
fluorescence intensity (MFI) values of mAb24-633 and ICAM-2 cluster
values, computed as described above, as a function of time.
[0094] H-I) depict ICAM-2 induced p44/42 MAPK phosphorylation, and
inhibition by LFA-1 mAb and comparison with other stimuli. H)
Phospho-p44/42 MAPK immunoblot of total lysates from Jurkat cells
stimulated with ICAM-2 (concentrations indicated in figure, 30 min)
and subsequently blocked with increasing concentrations of LFA-1
mAb. I) Comparison of phospho-p44/2 MAPK induction to stimuli using
FACS based detection of phospho-p44/42 MAPK. Stimuli were either 1
mg/ml (PHA, PMA, ionomycin), 10 mg/ml (LFA-1 mAb and ICAM-2), or 10
mM for PD98059 and U0126. Chemical inhibition was done 30 min prior
to stimulation. Data is presented as percent phospho-p44/24 MAPK
positive cells relative to unstimulated cells. Note the difference
between LFA-1 mAb crosslinking and ICAM-2 stimulation.
[0095] FIG. 35 depicts the results of experiments demonstrating
ICAM-2 induced p44/42 MAPK activation via LFA-1 interaction. A)
Mean fluorescent intensity values (MFI) of ICAM-2-FITC (adhesion)
and mAb24-Alexa633 (LFA-1 activation) in treated Jurkat cells (as
above). Control unstimulated and/or compound pretreated values were
subtracted. B) Top panel: Intracellular phospho-p44/42 MAPK
detection as a function of ICAM-2 dose in Jurkat cells by flow
cytometry (see Material and Methods). Mean fluorescent intensity
values (MFI) were plotted.+-.standard deviation (SD). Bottom panel:
ICAM-2 treated Jurkat cells were stained for intracellular
phospho-p44/42 MAPK as described above. mAbs to .beta.2 and
.alpha..sub.L integrins (10 .mu.g/ml, 10 minutes) were titrated
prior to ICAM-2 treatment as indicated and plotted for MFI.+-.SD.
C) ICAM-2 induced p44/42 MAPK activity is blocked by .beta.2 and
.alpha..sub.L integrin antibodies as determined by a p44/42 MAPK
kinase assay. Conditions for induction and inhibition are as
described above. Recombinant active p44/42 MAPK served as an
internal positive control (denoted by "+"). D) Inhibition and
activation profile for intracellular phospho-p44/42 by flow
cytometry in the presences of chemical agents (10 .mu.M), EDTA (1
mM), or PMA, ionomycin and ICAM-2 stimulus (as indicated above).
MFI values.+-.SD are plotted.
[0096] E) depicts that sICAM-2 induces Pyk2 and Syk membrane
localization. Confocal Microscopy of Jurkat cells treated with
ICAM-2 protein (10 mg/ml) or bovine serum albumin (Unstimulated, 10
mg/ml) for 10 minutes and prepared for confocal microscopy (see
material and methods). Cells were stained for Pyk2 and Syk. Panels
A-C represents unstimulated cells and panels D-F represent ICAM-2
treated cells. Scale bar is denoted in lower left corner of panels
(in micrometers).
[0097] FIG. 36 depicts the results of experiments demonstrating
ICAM-2 induced phosphorylation of Pyk2 and Syk, and .beta.2
integrin association. A) Phospho-raf and phospho-p44/42 immunoblot
inhibition profile by tyrosine kinase inhibitors. 1.times.10.sup.6
cells were treated with indicated compound (10 .mu.M, 30 min) and
then stimulated with ICAM-2 (10 .mu.g/ml, 30 min). Cell lysates
were immunoblotted for phospho-raf and phospho-p44/42. Compound
alone did not induce detectable phosphorylation. B) Pyk2 and Syk
are phosphorylated and co-immunoprecipitate with 132 integrin upon
ICAM-2 stimulus. Phospho-specificity was determined by
phospho-PykpY402 and phospho-syk(Tyr525/526) antibodies. C) Kinetic
analyses of the phosphorylation state of PKC.alpha./.beta., Pyk2,
and Syk as a function of ICAM-2 stimulus per time. Cells were
treated and processed as above. Phospho-specific
PKC.alpha./.beta..sub.II(Thr638) and the following antibodies were
used; Pyk2 and Syk were first immunoprecipated, probed with
anti-phosphotyrosine antibody (PY20), stripped and subsequently
probed with indicated non-phospho specific antibody. Immunoblots
are representative of triplicate experiments.
[0098] E) depicts that LFA-1 induced phosphorylation of Pyk2 and
Syk is dependent on PKC. We screened for the inhibition of sICAM-2
induced Pyk2 and Syk phosphorylation by chemical inhibitors to
tyrosine kinases using a phospho-tyrosine based ELISA. Pyk2
phosphorylation was abrogated in the presence of PKC inhibitors
bisindolymaleimide II (BIM II) and staurosporine (STP), in addition
to tyrphostin A9, a specific Pyk2 inhibitor. Pyk2 phosphorylation
was also affected by inhibitors of phospholipase Cg (neomycin),
inhibitors of Syk (piceatannol), and PKC inhibitor BIM I
(Supplementary FIG. 4A). Syk phosphorylation was completely
abolished by inhibition of Pyk2, PLCg1, and strongly affected by
PKC inhibitors. Thus, both Pyk2 and Syk phosphorylations were
dependent on PKC activity, while Syk phosphorylation was
additionally dependent on PLCg1 and Pyk2 activity. It was not
possible to assess specific PKC isozymes by this method.
[0099] A chemical genetic approach was undertaken to determine the
hierarchy of PKC, Pyk2, PLCg1, and Syk activities in response to
sICAM-2 stimulus by verifying phosphorylation status of each kinase
in the presence of respective chemical inhibitors. Inhibition of
PKC with BIM II abrogated phosphorylation of Pyk2, PLCg1, and Syk.
Inhibition of PLCg1 by neomycin abrogated phosphorylation of Syk,
with no inhibition observed for Pyk2. Inhibition of Syk by
piceatannol did not block phosphorylation of Pyk2 or PLCg1. These
observations suggest that PKC activation is upstream of PYK2, PLCg,
and SYK activities, and also that SYK activity is consequential to
PYK2 and PLCg1 activity. Thus, the upstream signaling events from
LFA-1 to Raf-1 appear to involve PKC/Pyk2/PLCg1/Syk. However, we
acknowledge that phospho-protein immunoprecipitation techniques do
not exclude the possibility of these molecules existing in
complexes. We are currently pursuing these complexes in a separate
study.
[0100] FIG. 37 depicts the results of experiments demonstrating
that ICAM-2 induces cytotoxic lymphocyte activity in IL-2 activated
human PBMC. A) PBMC were either treated with ICAM-2 (10 .mu.g/ml)
in the presence of IL-2 for 12 hr and then incubated with CFSE
labeled target HL60 cells at a 50:1 E:T ratio for 4 hrs. Remaining
HL60 cells were quantified by flow cytometry. B) PBMC were treated
with IL-2 (100 U/ml, 12 hrs) and treated with ICAM-1,-2, or 3 FC
proteins (10 .mu.g/ml) and used in a cytotoxicity assay as
described above. Results are representative of 4 independent
experiments.
[0101] FIG. 38 depicts the results of experiments demonstrating
ICAM-2 exhibits differences to ICAM-1 and ICAM-3 in mediating
perforin and granzyme release from CD56.sup.+CD8.sup.+ cytotoxic
lymphocytes subsets. IL-2 activated PBMC were mock-treated (IgG),
ICAM-1, ICAM-2, or ICAM-3 treated (10 .mu.g/ml of FC fusion
protein) for 12 hrs prior to incubation with target HL60 cells at a
50:1 E:T ratio for 4 hrs. Cells were then prepared for flow
cytometry with CD8-CY5PE, CD56-PE surface stains, and perforin-CY5
and granzyme-A-FITC intracellular stains. Cells were gated for
CD56.sup.+CD8.sup.low, CD56.sup.+CD8.sup.med,
CD56.sup.+CD8.sup.high, CD56.sup.-CD8.sup.-, CD56.sup.-CD8.sup.high
populations as shown in panel I and population frequencies within
appropriate gate. Panels II-V are subset gated populations
displayed for perforin and granzyme-A log fluorescent intensities.
Results are representative of 3 independent experiments and were
similar at 25:1 and 12.5:1 E:T ratios (data not shown). Manual
calibration was performed. B) CD56CD8 population subsets were gated
(as indicated) and displayed for intracellular perforin for ICAM-1,
-2, -3 stimulated cells. Perforin percentage was calculated from
the following equation where MFI equals mean fluorescent intensity:
100.times.[(MFI.sub.experimental-MFI.sub.isotype
mAb)/(MFI.sub.control-MFI.sub.isotype mAb)]. Unstimulated cells
were used as control. C) Intracellular granzyme-A values were
calculated and displayed as described above.
[0102] FIG. 39 depicts the results of experiments demonstrating
that ICAM-2 induced LFA-1 mediated p44/42 MAPK correlates with
LFA-1 activation in human CD56.sup.+CD8+ cells. A) Conjugate
formation of CFSE labeled HL60 cells and CD56.sup.+CD8.sup.+ cells.
Conjugate flow cytometric based assay was performed on PBMC treated
with indicated chemicals (10 .mu.M, 30 min) prior to treatment with
ICAM-2 (10 .mu.g/ml, 30 min). CFSE labeled HL60 cells were
incubated at 25:1 E:T ratio for 5 min, and fixed with 1%
paraformaldehyde. Cells were then immunolabeled with CD8 and CD56
antibodies, gated for CD8.sup.+CD56.sup.+ cell populations and
percent HL60 fluorescence was made relative to total HL60 cells. B)
IL-2 activated PBMC were either treated with ICAM-2 (10 .mu.g/ml,
30 min) or mock-treated (IgG) and stained for active-LFA-1
(mAb24-Alexa633), phospho-p44/42-Ax488, CD8-CY5PE, and CD56-PE.
CD56.sup.+CD8.sup.+ cell populations are gated and displayed for
active LFA-1 vs. phospho-p44/42. The mean fluorescent intensities
(MFI) of mAb24-Ax633 and phospho-44/42-Ax488 were computed and
displayed over time as described above.
DETAILED DESCRIPTION OF THE INVENTION
[0103] Intracelluar assays of signaling systems have been limited
by an inability to correlate functional subsets of cells in complex
populations based on the activity of signaling agents, for example,
the activity of kinases. Such correlations are important for
distinguishing changes in signaling status that arise in rare cell
subsets during signaling or in disease manifestations. The present
invention solves these problems by providing methods and
compositions for simultaneously detecting the activation state of a
plurality of activatable proteins in single cells using flow
cytometry. The invention further provides methods and compositions
of screening for bioactive agents capable of coordinately
modulating the activity or activation state of a plurality of
activatable proteins in single cells. The methods and compositions
can be used to determine the protein activation profile of a cell
for predicting or diagnosing a disease state, and for monitoring
treatment of a disease state. Further, the methods and compositions
of the present invention can be used optionally to sequentially
detect the activation state of a plurality of activatable proteins
in single cells. In addition, the methods and compositions of the
present invention can be used optionally to detect the activation
state of a single protein or modulate the activity or activation
state of a single protein in single cells.
[0104] The methods and compositions of the present invention may be
used to detect any particular protein isoform in a sample that is
antigenically detectable and antigenically distinguishable from
other isoforms of the protein which are present in the sample. For
example, as demonstrated (see, e.g., the Examples) and described
herein, the activation state-specific antibodies of the present
invention can be used in the present methods to identify distinct
signaling cascades of a subset or subpopulation of complex cell
populations; and the ordering of protein activation (e.g., kinase
activation) in potential signaling hierarchies. Further, in the
methods of the present invention, the use of flow cytometry,
particularly polychromatic flow cytometry, permits the
multi-dimensional analysis and functional assessment of the
signaling pathway in single cells.
[0105] As used herein, the term "activation state-specific
antibody" or "activation state antibody" or grammatical equivalents
thereof, refer to an antibody that specifically binds to a
corresponding and specific antigen. Preferably, the corresponding
and specific antigen is a specific isoform of an activable protein.
Also preferably, the binding of the activation state-specific
antibody is indicative of a specific activation state of a specific
activatable protein. Thus, in preferred embodiments, the binding of
an activation state-specific antibody to a corresponding isoform of
an activable protein is indicative of the identity of the
activatable protein and of the activation state of the activatable
protein.
[0106] In a preferred embodiment, the activation state-specific
antibody is a peptide comprising a recognition structure that binds
to a target structure on an activatable protein. A variety of
recognition structures are well known in the art and can be made
using methods known in the art, including by phage display
libraries (see e.g., Gururaja et al. Chem. Biol. (2000) 7:515-27;
Houimel et al., Eur. J. Immunol. (2001) 31:3535-45; Cochran et al.
J. Am. Chem. Soc. (2001) 123:625-32; Houimel et al. Int. J. Cancer
(2001) 92:748-55, each incorporated herein by reference). In a
preferred embodiment, the activation state-specific antibody
comprises the following recognition structure: SKVILFE--random
peptide loop--SKVILFE. Antibodies having such recognition
structures can bind with high affinity to specific target
structures. Further, fluorophores can be attached to such
antibodies for use in the methods of the present invention.
[0107] A variety of recognitions structures are known in the art
(e.g., Cochran et al., J. Am. Chem. Soc. (2001) 123:625-32; Boer et
al., Blood (2002) 100:467-73, each expressly incorporated herein by
reference)) and can be produced using methods known in the art (see
e.g., Boer et al., Blood (2002) 100:467-73; Gualillo et al., Mol.
Cell. Endocrinol. (2002) 190:83-9, each expressly incorporated
herein by reference)), including for example combi chem methods for
producing recognition structures such as polymers with affinity for
a target structure on an activable protein (see e.g., Barn et al.,
J. Comb. Chem. (2001) 3:534-41; Ju et al., Biotechnol. (1999)
64:232-9, each expressly incorporated herein by reference). In
another preferred embodiment, the activation state-specific
antibody is a protein that only binds to an isoform of a specific
activatable protein that is phosphorylated and does not bind to the
isoform of this activable protein when it is not phosphorylated or
nonphosphorylated. In another preferred embodiment the activation
state-specific antibody is a protein that only binds to an isoform
of an activatable protein that is intracellular and not
extracellular, or vice versa.
[0108] In a preferred embodiment, the recognition structure is an
anti-laminin single-chain antibody fragment (scFv) (see e.g., Sanz
et al., Gene Therapy (2002) 9:1049-53; Tse et al., J. Mol. Biol.
(2002) 317:85-94, each expressly incorporated herein by
reference).
[0109] As used herein, the terms "polypeptide" and "protein" may be
used interchangeably and mean at least two covalently attached
amino acids, which includes proteins, polypeptides, oligopeptides
and peptides. The protein may be made up of naturally occurring
amino acids and peptide bonds, or synthetic peptidomimetic
structures. Thus "amino acid", or "peptide residue", as used herein
means both naturally occurring and synthetic amino acids. For
example, homo-phenylalanine, citrulline and noreleucine are
considered amino acids for the purposes of the invention. "Amino
acid" also includes imino acid residues such as proline and
hydroxyproline. The side chains may be in either the (R) or the (S)
configuration. In the preferred embodiment, the amino acids are in
the (S) or L-configuration. If non-naturally occurring side chains
are used, non-amino acid substituents may be used, for example to
prevent or retard in vivo degradation.
[0110] As used herein, an "activatable protein" or "substrate" or
"substrate protein" or "protein substrate" grammatical equivalents
thereof, refers to a protein that has at least one isoform (and in
some cases two or more isoforms) that corresponds to a specific
form of the protein having a particular biological, biochemical, or
physical property, e.g., an enzymatic activity, a modification
(e.g., post-translational modification), or a conformation. The
activable protein can be activated or nonactivated with respect to
a particular biological activity, modification, or conformation.
Specifically, the "activated" or "active" form of the activatable
protein has the particular biological activity, modification, or
conformation, whereas the "non-activated" or "non-active" form of
the activatable protein does not have (or has a lesser or
diminished level of) the particular biological activity,
modification, or conformation, respectively. In some embodiments,
there may be more than one isoform associated with activity or
activation state; for example, there may be an isoform associated
with an "open" conformation available for substrate binding, a
second "transition state" isoform, and an isoform devoid of
activity (e.g., where the activity is inhibited). Examples of
activatable proteins include, but are not limited to,
phospho-proteins and phospho-lipids. Further examples of
activatable proteins include, but are not limited to, kinases,
phosphatases, PIP2, PIP3, and proteases such as cysteine and serine
proteases, including, but not limited to caspases, cathepsins and a
variety of well known serine proteases.
[0111] In a preferred embodiment, the biological, biochemical, or
physical property (e.g. enzymatic activity, modification, or
conformation) of the activatable protein is inducible or
"activatable" by an activating agent or by cell signaling events.
Examples of activating agents include, but are not limited to,
kinases, phosphatases, proteases (e.g., caspases), and hormones.
Examples of cell signaling events include, but are not limited to,
receptor clustering or binding of a cognate molecule or ligand.
[0112] As used herein, an "isoform" or grammatical equivalents
thereof, refers to a form of an activatable protein having a
specific, and preferably detectable, biological activity,
modification, or conformation. The isoform can be an activated (or
active) form, or non-activated (or not active) form of an
activatable protein. As mentioned, in preferred embodiments, the
binding of an activation state-specific antibody to a corresponding
isoform of an activable protein is indicative of the identity of
the activatable protein and of the activation state of the
activatable protein. In a preferred embodiment, the invention
provides methods for determining a protein isoform profile which
comprise determining the presence of an isoform of an activatable
protein that is activated (or activated isoform).
[0113] In a preferred embodiment, the activated isoform or
activated state of an activable protein is a form of the activable
protein having a particular or specific biological, biochemical, or
physical property that is not possessed by at least one other
isoform of activatable protein. Examples of such properties
include, but are not limited to, enzymatic activity (e.g., kinase
activity and protease activity), and protein binding activity.
Thus, such particular or specific properties or activities are
associated with an activated isoform of an activatable protein.
Such properties or activities are sometimes referred to herein as
activation state activities.
[0114] An example of activation state activity is kinase activity
for an activated protein kinase. As used herein, a protein kinase
may refer to a protein that when activated is capable of catalyzing
the phosphorylation of amino acids, or derivatives thereof, which
possess an hydroxyl group. Preferred kinases are those which are
capable of catalyzing the phosphorylation of serine, threonine, and
tyrosine residues. Kinase activity may be determined by supplying a
substrate for phosphorylation by kinase, a source of phosphate
usable by kinase, and determining the phosphorylation of substrate
in the presence of kinase.
[0115] Another example of activation state activity is protease
activity for an activated protease. As used herein, a protease may
refer to a protein that when activated is capable of hydrolyzing a
peptide bond within a polypeptide comprising an amino acid
sequence. Preferred proteases are the family of cysteine proteases
known as caspases. Caspase activity may be determined by providing
a substrate of a caspase and determining the cleavage of substrate
in the presence of caspase. Other cysteine proteases having
activations states that may be monitored using the methods of the
invention include, but are not limited to, cathespins. Similarly,
an additional class of proteases that may be monitored using the
methods of the invention include serine proteases, of which a wide
variety of suitable classes are known.
[0116] The antigenicity of an activated isoform of an activatable
protein is distinguishable from the antigenicity of non-activated
isoform of an activatable protein or from the antigenicity of an
isoform of a different activation state. In a preferred embodiment,
an activated isoform of a protein possesses an epitope that is
absent in a non-activated isoform of a protein, or vice versa. In
another preferred embodiment, this difference is due to covalent
addition of moieties to a protein, such as phosphate moieties, or
due to a structural change in a protein, as through protein
cleavage, or due to an otherwise induced conformational change in a
protein which causes the protein to present the same sequence in an
antigenically distinguishable way. In another preferred embodiment,
such a conformational change causes an activated isoform of a
protein to present at least one epitope that is not present in a
non-activated isoform, or to not present at least one epitope that
is presented by a non-activated isoform of the protein. In some
embodiments, the epitopes for the distinguishing antibodies are
centered around the active site of the enzyme, although as is known
in the art, conformational changes in one area of a protein may
cause alterations in different areas of the protein as well.
[0117] Among proteins that are capable of existing in a
non-activated isoform and an activated isoform, which isoforms are
antigenically distinguishable, are kinases. Kinases are enzymes
that catalyze protein phosphorylation on serine, threonine, or
tyrosine residues. The majority of kinases are phosphoproteins that
are reversibly phosphorylated as a form of activity regulation. In
the phosphorylated form (phosphorylated isoform), protein kinases
are typically enzymatically active kinases. In the
un-phosphorylated form, protein kinases are typically enzymatically
inactive.
[0118] Many antibodies, many of which are commercially available
(for example, see Cell Signaling Technology, www.cellsignal.com,
the contents which are incorporated herein by reference). have been
produced which specifically bind to the phosphorylated isoform of a
protein but do not specifically bind to a non-phosphorylated
isoform of a protein. Many such antibodies have been produced for
the study of signal transducing proteins which are reversibly
phosphorylated. Particularly, many such antibodies have been
produced which specifically bind to phosphorylated, activated
isoforms of protein kinases and are sometimes referred to herein as
kinase activation state antibodies or grammatical equivalents
thereof. Particularly preferred antibodies for use in the present
invention include: phospho-AKT Ser473 monoclonal anti-4E2,
phospho-p44/42 MAP kinase (Thr202/Tyr204) monoclonal antibody,
phospho-TYK2 (Tyr1054/1055) antibody, phospho-p38 MAP kinase
(Thr180/Tyr182) monoclonal antibody 28B10, phospho-PKC-PAN
substrate antibody, phospho-PKA-substrate, phospho-SAPK/JNK
(Thr183/Tyr185) G9 monoclonal antibody, phospho-tyrosine monoclonal
antibody (P-tyr-100), p44/42 MAPK, p38 MAPK, JNK/SAPK, and
phospho-AKT-Thr308.
[0119] The present invention provides methods for the determination
of a kinase activation state profile for a sample which comprise
simultaneously determining the presence of activated isoforms of a
multiplicity of kinases using a multiplicity of antibodies that
specifically bind to active, phosphorylated isoforms of the
multiplicity of kinases.
[0120] Another example of proteins that are capable of existing in
a non-activated isoform and an activated isoform, which isoforms
are antigenically distinguishable, are caspases. Caspases are
proteases that catalyze the hydrolysis of peptide bonds within
proteins. Caspases are synthesized as pro-caspases which are
proteolytically inactive precursors of caspases. A pro-caspase is
specifically cleaved by protease to yield an active caspase. As is
known in the art, this is known to be true for a variety of other
proteases, including both cysteine and serine proteases such as
cathepsins, tissue plasminogen activators, etc., that are known to
exist as pro-proteases, as is well known in the art.
[0121] The present invention provides methods for the determination
of a caspase activation state profile for a sample which comprise
simultaneously determining the presence of activated isoforms of a
multiplicity of caspases using a multiplicity of antibodies that
specifically bind to a multiplicity of caspases but not to the
correlating pro-caspases from which they may be derived. For
example, antibodies which specifically bind to caspases but do not
specifically bind to pro-caspases from which caspases are derived
are useful in the methods of the invention. Many such antibodies
are commercially available (for example, see Cell Signaling
Technology, www.cellsignal.com, the contents of which are
incorporated herein by reference).
[0122] Additional means for determining kinase activation are
provided by the present invention. Substrates that are specifically
recognized by protein kinases and phosphorylated thereby are known.
Antibodies that specifically bind to such phosphorylated substrates
but do not bind to such non-phosphorylated substrates
(phospho-substrate antibodies) may be used to determine the
presence of activated kinase in a sample.
[0123] In a preferred embodiment, the present invention provides
methods for determining a kinase activation state profile for a
sample, comprising providing a population of cells comprising a
plurality of activatable proteins and contacting the cells with at
least one non-phosphorylated protein kinase substrate under
conditions which provide for phosphorylation of the substrate by
activated kinase if present, and determining the presence of
phosphorylated protein kinase substrate using a phospho-substrate
antibody that binds specifically to the phosphorylated substrate.
In a preferred embodiment, the present invention provides methods
for determining a kinase activation state profile for a sample
which comprises the use of a multiplicity of protein kinase
substrates, a multiplicity of phospho-substrate antibodies, and a
multiplicity of activation state antibodies to simultaneously
determine the activation state of a multiplicity of kinases.
[0124] In another embodiment, the present invention provides
methods for determining the activation state of one or more protein
kinases and one or more caspases in a sample by combining the
methods described for determining the activation state profile of
each provided herein. Preferably, the sample comprises a population
of cells, a cell, cell lysate, or proteins.
[0125] Similarly, the invention provides methods utilizing any and
all other combinations of kinases and proteases (e.g., kinases and
caspases, kinases and cathepsins, kinases and serine proteases,
caspases and cathepsins, etc.).
[0126] In a further embodiment, a protein activation state profile
is determined using a multiplicity of activation state antibodies
that are immobilized. Antibodies may be non-diffusibly bound to an
insoluble support having isolated sample receiving areas (e.g. a
microtiter plate, an array, etc.). The insoluble supports may be
made of any composition to which the compositions can be bound, is
readily separated from soluble material, and is otherwise
compatible with the overall method of screening. The surface of
such supports may be solid or porous and of any convenient shape.
Examples of suitable insoluble supports include microtiter plates,
arrays, membranes, and beads. These are typically made of glass,
plastic (e.g., polystyrene), polysaccharides, nylon or
nitrocellulose, teflon.TM., etc. Microtiter plates and arrays are
especially convenient because a large number of assays can be
carried out simultaneously, using small amounts of reagents and
samples. In some cases magnetic beads and the like are
included.
[0127] The particular manner of binding of the composition is not
crucial so long as it is compatible with the reagents and overall
methods of the invention, maintains the activity of the composition
and is nondiffusable. Preferred methods of binding include the use
of antibodies (which do not sterically block either the ligand
binding site or activation sequence when the protein is bound to
the support), direct binding to "sticky" or ionic supports,
chemical crosslinking, the synthesis of the antibody on the
surface, etc. Following binding of the antibody, excess unbound
material is removed by washing. The sample receiving areas may then
be blocked through incubation with bovine serum albumin (BSA),
casein or other innocuous protein or other moiety.
[0128] In a preferred embodiment, an epitope-recognizing fragment
of an activation state antibody rather than the whole antibody is
used. In another preferred embodiment, the epitope-recognizing
fragment is immobilized. In another preferred embodiment, the
antibody light chain which recognizes an epitope is used. A
recombinant nucleic acid encoding a light chain gene product which
recognizes an epitope may be used to produce such an antibody
fragment by recombinant means well known in the art.
[0129] A chip analogous to a DNA chip can be used in the methods of
the present invention. Arrayers and methods for spotting nucleic
acid to a chip in a prefigured array are known. In addition,
protein chips and methods for synthesis are known. These methods
and materials may be adapted for the purpose of affixing activation
state antibodies to a chip in a prefigured array.
[0130] In a preferred embodiment, such a chip comprises a
multiplicity of kinase activation state antibodies, and is used to
determine a kinase activation state profile for a sample. In a
preferred embodiment, such a sample is a cell extract. In such a
method, detection of activated kinase is by "sandwich assay" as
known in the art. Briefly, a sample, preferably a cell extract, is
passed over a the chip under conditions which allow the
multiplicity of immobilized kinase activation state antibodies to
simultaneously bind to a multiplicity of activated kinases if
present in the sample. The immobilized antibody-kinase complex is
optionally washed and contacted with a second plurality of
antibodies comprising non-activation state antibodies that are
capable of specifically binding to activated kinases while the
kinases are specifically bound to kinase activation state specific
antibodies. Such non-activation state specific antibodies
specifically bind to activated kinases via an epitope that is not
recognized by the kinase activation state specific antibody.
Binding of the non-activation state specific antibodies to the
activation state antibody-activated kinase complex is determined
and reveals the presence of activated kinase in sample. As will be
appreciated, the determination of binding of second antibody in the
sandwich assay can be accomplished in many different ways.
Preferably, the multiplicity of non-activation state specific
antibodies are uniquely labeled to facilitate detection.
[0131] In an alternative embodiment, a chip comprises a
multiplicity of non-activation state specific antibodies. Such a
chip is contacted with sample, preferably cell extract, and a
second multiplicity of antibodies comprising kinase activation
state specific antibodies is used in the sandwich assay to
simultaneously determine the presence of a multiplicity of
activated kinases in sample. Preferably, the multiplicity of
activation state specific antibodies are uniquely labeled to
facilitate detection.
[0132] In a preferred embodiment, one or more components of the
methods of the present invention comprise a tag. By "tag" is meant
an attached molecule or molecules useful for the identification or
isolation of the attached molecule(s), which are preferably
substrate molecules. For example, a tag can be an attachment tag or
a label tag. Components having a tag are referred to as "tag-X",
wherein X is the component. Preferably, the tag is covalently bound
to the attached component. When more than one component of a
combination has a tag, the tags will be numbered for
identification, for example, "tag1-antibody", "tag1-protein", and
"tag1-substrate". Components may comprise more than one tag, in
which case each tag will be numbered, for example "tag
1,2-antibody", "tag1,2-protein", and tag1,2-substrate. Preferred
tags include, but are not limited to, a label, a partner of a
binding pair, and a surface substrate binding molecule (or
attachment tag). As will be evident to the skilled artisan, many
molecules may find use as more than one type of tag, depending upon
how the tag is used.
[0133] By "label" is meant a molecule that can be directly (i.e., a
primary label) or indirectly (i.e., a secondary label) detected;
for example a label can be visualized and/or measured or otherwise
identified so that its presence or absence can be known. A compound
can be directly or indirectly conjugated to a label which provides
a detectable signal, e.g. radioisotope, fluorescers, enzyme,
antibodies, particles such as magnetic particles, chemiluminescers,
or specific binding molecules, etc. Specific binding molecules
include pairs, such as biotin and streptavidin, digoxin and
antidigoxin etc. Preferred labels include, but are not limited to,
fluorescent labels, label enzymes and radioisotopes.
[0134] By "fluorescent label" is meant any molecule that may be
detected via its inherent fluorescent properties. Suitable
fluorescent labels include, but are not limited to, fluorescein,
rhodamine, tetramethylrhodamine, eosin, erythrosin, coumarin,
methyl-coumarins, pyrene, Malacite green, stilbene, Lucifer Yellow,
Cascade Blue.TM., Texas Red, IAEDANS, EDANS, BODIPY FL, LC Red 640,
Cy 5, Cy 5.5, LC Red 705 and Oregon green. Suitable optical dyes
are described in the 1996 Molecular Probes Handbook by Richard P.
Haugland, hereby expressly incorporated by reference. Suitable
fluorescent labels also include, but are not limited to, green
fluorescent protein (GFP; Chalfie, et al., Science
263(5148):802-805 (Feb. 11, 1994); and EGFP; Clontech--Genbank
Accession Number U55762), blue fluorescent protein (BFP; 1. Quantum
Biotechnologies, Inc. 1801 de Maisonneuve Blvd. West, 8th Floor,
Montreal (Quebec) Canada H3H 1J9; 2. Stauber, R. H. Biotechniques
24(3):462-471 (1998); 3. Heim, R. and Tsien, R. Y. Curr. Biol.
6:178-182 (1996)), enhanced yellow fluorescent protein (EYFP; 1.
Clontech Laboratories, Inc., 1020 East Meadow Circle, Palo Alto,
Calif. 94303), luciferase (Ichiki, et al., J. Immunol.
150(12):5408-5417 (1993)), .beta.-galactosidase (Nolan, et al.,
Proc Natl Acad Sci USA 85(8):2603-2607 (April 1988)) and Renilla WO
92/15673; WO 95/07463; WO 98/14605; WO 98/26277; WO 99/49019; U.S.
Pat. No. 5,292,658; U.S. Pat. No. 5,418,155; U.S. Pat. No.
5,683,888; U.S. Pat. No. 5,741,668; U.S. Pat. No. 5,777,079; U.S.
Pat. No. 5,804,387; U.S. Pat. No. 5,874,304; U.S. Pat. No.
5,876,995; and U.S. Pat. No. 5,925,558). All of the above-cited
references are expressly incorporated herein by reference.
[0135] Particularly preferred labels for use in the present
invention include: Alexa-Fluor dyes (Alexa Fluor 350, Alexa Fluor
430, Alexa Fluor 488, Alexa Fluor 546, Alexa Fluor 568, Alexa Fluor
594, Alexa Fluor 633, Alexa Fluor 660, Alexa Fluor 680), Cascade
Blue, Cascade Yellow and R-phycoerythrin (PE) (Molecular Probes)
(Eugene, Oreg.), FITC, Rhodamine, and Texas Red (Pierce, Rockford,
Ill.), Cy5, Cy5.5, Cy7 (Amersham Life Science, Pittsburgh, Pa.).
Tandem conjugate protocols for Cy5PE, Cy5.5PE, Cy7PE, Cy5.5APC,
Cy7APC can be found at www.drmr.com/abcon. Quantitation of
fluorescent probe conjugation may be assessed to determine degree
of labeling and protocols including dye spectral properties can be
found at www.metazoa.com/UPL3419.
[0136] In another preferred embodiment, the fluorescent label is a
GFP and, more preferably, a renilla, ptilosarcus, or aequorea
species of GFP.
[0137] In preferred embodiments, multiple fluorescent labels are
employed in the methods and compositions of the present invention.
In a preferred embodiment, at least two fluorescent labels are used
which are members of a fluorescence resonance energy transfer
(FRET) pair.
[0138] FRET is phenomenon known in the art wherein excitation of
one fluorescent dye is transferred to another without emission of a
photon. A FRET pair consists of a donor fluorophore and an acceptor
fluorophore. The fluorescence emission spectrum of the donor and
the fluorescence absorption spectrum of the acceptor must overlap,
and the two molecules must be in close proximity. The distance
between donor and acceptor at which 50% of donors are deactivated
(transfer energy to the acceptor) is defined by the Forster radius
(R.sub.0), which is typically 10-100 .ANG.. Changes in the
fluorescence emission spectrum comprising FRET pairs can be
detected, indicating changes in the number of that are in close
proximity (i.e., within 100 .ANG. of each other). This will
typically result from the binding or dissociation of two molecules,
one of which is labeled with a FRET donor and the other of which is
labeled with a FRET acceptor, wherein such binding brings the FRET
pair in close proximity. Binding of such molecules will result in
an increased fluorescence emission of the acceptor and/or quenching
of the fluorescence emission of the donor.
[0139] FRET pairs (donor/acceptor) useful in the invention include,
but are not limited to, EDANS/fluorescien, IAEDANS/fluorescein,
fluorescein/tetramethylrhodamine, fluorescein/LC Red 640,
fluorescein/Cy 5, fluorescein/Cy 5.5 and fluorescein/LC Red
705.
[0140] In another aspect of FRET, a fluorescent donor molecule and
a nonfluorescent acceptor molecule ("quencher") may be employed. In
this application, fluorescent emission of the donor will increase
when quencher is displaced from close proximity to the donor and
fluorescent emission will decrease when the quencher is brought
into close proximity to the donor. Useful quenchers include, but
are not limited to, TAMRA, DABCYL, QSY 7 and QSY 33. Useful
fluorescent donor/quencher pairs include, but are not limited to
EDANS/DABCYL, Texas Red/DABCYL, BODIPY/DABCYL, Lucifer
yellow/DABCYL, coumarin/DABCYL and fluorescein/QSY 7 dye.
[0141] The skilled artisan will appreciate that FRET and
fluorescence quenching allow for monitoring of binding of labeled
molecules over time, providing continuous information regarding the
time course of binding reactions.
[0142] By "label enzyme" is meant an enzyme which may be reacted in
the presence of a label enzyme substrate which produces a
detectable product. Suitable label enzymes for use in the present
invention include but are not limited to, horseradish peroxidase,
alkaline phosphatase and glucose oxidase. Methods for the use of
such substrates are well known in the art. The presence of the
label enzyme is generally revealed through the enzyme's catalysis
of a reaction with a label enzyme substrate, producing an
identifiable product. Such products may be opaque, such as the
reaction of horseradish peroxidase with tetramethyl benzedine, and
may have a variety of colors. Other label enzyme substrates, such
as Luminol (available from Pierce Chemical Co.), have been
developed that produce fluorescent reaction products. Methods for
identifying label enzymes with label enzyme substrates are well
known in the art and many commercial kits are available. Examples
and methods for the use of various label enzymes are described in
Savage et al., Previews 247:6-9 (1998), Young, J. Virol. Methods
24:227-236 (1989), which are each hereby incorporated by reference
in their entirety.
[0143] By "radioisotope" is meant any radioactive molecule.
Suitable radioisotopes for use in the invention include, but are
not limited to .sup.14C, .sup.3H, .sup.32P, .sup.33P, .sup.35S,
.sup.125I, and .sup.131I. The use of radioisotopes as labels is
well known in the art.
[0144] As mentioned, labels may be indirectly detected, that is,
the tag is a partner of a binding pair. By "partner of a binding
pair" is meant one of a first and a second moiety, wherein the
first and the second moiety have a specific binding affinity for
each other. Suitable binding pairs for use in the invention
include, but are not limited to, antigens/antibodies (for example,
digoxigenin/anti-digoxigenin, dinitrophenyl (DNP)/anti-DNP,
dansyl-X-anti-dansyl, Fluorescein/anti-fluorescein, lucifer
yellow/anti-lucifer yellow, and rhodamine anti-rhodamine),
biotin/avid (or biotin/streptavidin) and calmodulin binding protein
(CBP)/calmodulin. Other suitable binding pairs include polypeptides
such as the FLAG-peptide [Hopp et al., BioTechnoloqy, 6:1204-1210
(1988)]; the KT3 epitope peptide [Martin et al., Science,
255:192-194 (1992)]; tubulin epitope peptide [Skinner of al., J.
Biol. Chem., 266:15163-15166 (1991)]; and the T7 gene 10 protein
peptide tag [Lutz-Freyermuth et al., Proc. Natl. Acad. Sci. USA,
87:6393-6397 (1990)] and the antibodies each thereto. As will be
appreciated by those in the art, binding pair partners may be used
in applications other than for labeling, as is described
herein.
[0145] As will be appreciated by those in the art, a partner of one
binding pair may also be a partner of another binding pair. For
example, an antigen (first moiety) may bind to a first antibody
(second moiety) which may, in turn, be an antigen for a second
antibody (third moiety). It will be further appreciated that such a
circumstance allows indirect binding of a first moiety and a third
moiety via an intermediary second moiety that is a binding pair
partner to each.
[0146] As will be appreciated by those in the art, a partner of a
binding pair may comprise a label, as described above. It will
further be appreciated that this allows for a tag to be indirectly
labeled upon the binding of a binding partner comprising a label.
Attaching a label to a tag which is a partner of a binding pair, as
just described, is referred to herein as "indirect labeling".
[0147] By "surface substrate binding molecule" or "attachment tag"
and grammatical equivalents thereof is meant a molecule have
binding affinity for a specific surface substrate, which substrate
is generally a member of a binding pair applied, incorporated or
otherwise attached to a surface. Suitable surface substrate binding
molecules and their surface substrates include, but are not limited
to poly-histidine (poly-his) or poly-histidine-glycine
(poly-his-gly) tags and Nickel substrate; the Glutathione-S
Transferase tag and its antibody substrate (available from Pierce
Chemical); the flu HA tag polypeptide and its antibody 12CA5
substrate [Field et al., Mol. Cell. Biol., 8:2159-2165 (1988)]; the
c-myc tag and the 8F9, 3C7, 6E10, G4, B7 and 9E10 antibody
substrates thereto [Evan et al., Molecular and Cellular Biology,
5:3610-3616 (1985)]; and the Herpes Simplex virus glycoprotein D
(gD) tag and its antibody substrate [Paborsky et al., Protein
Engineering, 3(6):547-553 (1990)]. In general, surface binding
substrate molecules useful in the present invention include, but
are not limited to, polyhistidine structures (His-tags) that bind
nickel substrates, antigens that bind to surface substrates
comprising antibody, haptens that bind to avidin substrate (e.g.,
biotin) and CBP that binds to surface substrate comprising
calmodulin. Production of antibody-embedded substrates is well
known; see Slinkin et al., Bioconi. Chem. 2:342-348 (1991);
Torchilin et al., supra; Trubetskoy et al. Bioconi. Chem. 3:323-327
(1992); King et al., Cancer Res. 54:6176-6185 (1994); and Wilbur et
al., Bioconjugate Chem. 5:220-235 (1994) (all of which are hereby
expressly incorporated by reference), and attachment of or
production of proteins with antigens is described above.
Calmodulin-embedded substrates are commercially available, and
production of proteins with CBP is described in Simcox et al.,
Strategies 8:40-43 (1995), which is hereby incorporated by
reference in its entirety.
[0148] As will be appreciated by those in the art, tag-components
of the invention can be made in various ways, depending largely
upon the form of the tag. Components of the invention and tags are
preferably attached by a covalent bond.
[0149] The production of tag-polypeptides by recombinant means when
the tag is also a polypeptide is described below. Production of
tag-labeled proteins is well known in the art and kits for such
production are commercially available (for example, from Kodak and
Sigma). Examples of tag labeled proteins include, but are not
limited to, a Flag-polypeptide and His-polypeptide. Methods for the
production and use of tag-labeled proteins are found, for example,
in Winston et al., Genes and Devel. 13:270-283 (1999), incorporated
herein in its entirety, as well as product handbooks provided with
the above-mentioned kits.
[0150] Biotinylation of target molecules and substrates is well
known, for example, a large number of biotinylation agents are
known, including amine-reactive and thiol-reactive agents, for the
biotinylation of proteins, nucleic acids, carbohydrates, carboxylic
acids; see chapter 4, Molecular Probes Catalog, Haugland, 6th Ed.
1996, hereby incorporated by reference. A biotinylated substrate
can be attached to a biotinylated component via avidin or
streptavidin. Similarly, a large number of haptenylation reagents
are also known (Id.).
[0151] Methods for labeling of proteins with radioisotopes are
known in the art. For example, such methods are found in Ohta et
al., Molec. Cell 3:535-541 (1999), which is hereby incorporated by
reference in its entirety.
[0152] Production of proteins having tags by recombinant means is
well known, and kits for producing such proteins are commercially
available. For example, such a kit and its use is described in the
QIAexpress Handbook from Qiagen by Joanne Crowe et al., hereby
expressly incorporated by reference.
[0153] The functionalization of labels with chemically reactive
groups such as thiols, amines, carboxyls, etc. is generally known
in the art. In a preferred embodiment, the tag is functionalized to
facilitate covalent attachment. The covalent attachment of the tag
may be either direct or via a linker. In one embodiment, the linker
is a relatively short coupling moiety, that is used to attach the
molecules. A coupling moiety may be synthesized directly onto a
component of the invention and contains at least one functional
group to facilitate attachment of the tag. Alternatively, the
coupling moiety may have at least two functional groups, which are
used to attach a functionalized component to a functionalized tag,
for example. In an additional embodiment, the linker is a polymer.
In this embodiment, covalent attachment is accomplished either
directly, or through the use of coupling moieties from the
component or tag to the polymer. In a preferred embodiment, the
covalent attachment is direct, that is, no linker is used. In this
embodiment, the component preferably contains a functional group
such as a carboxylic acid which is used for direct attachment to
the functionalized tag. It should be understood that the component
and tag may be attached in a variety of ways, including those
listed above. In a preferred embodiment, the tag is attached to the
amino or carboxl terminus of the polypeptide. As will be
appreciated by those in the art, the above description of the
covalent attachment of a label applies to the attachment of
virtually any two molecules of the present disclosure.
[0154] In a preferred embodiment, the tag is functionalized to
facilitate covalent attachment, as is generally outlined above.
Thus, a wide variety of tags are commercially available which
contain functional groups, including, but not limited to,
isothiocyanate groups, amino groups, haloacetyl groups, maleimides,
succinimidyl esters, and sulfonyl halides, all of which may be used
to covalently attach the tag to a second molecule, as is described
herein. The choice of the functional group of the tag will depend
on the site of attachment to either a linker, as outlined above or
a component of the invention. Thus, for example, for direct linkage
to a carboxylic acid group of a protein, amino modified or
hydrazine modified tags will be used for coupling via carbodiimide
chemistry, for example using
1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDAC) as is known
in the art (see Set 9 and Set 11 of the Molecular Probes Catalog,
supra; see also the Pierce 1994 Catalog and Handbook, pages T-155
to T-200, both of which are hereby incorporated by reference). In
one embodiment, the carbodiimide is first attached to the tag, such
as is commercially available for many of the tags described
herein.
[0155] Antibody conjugation may be performed using standard
procedures (http://drmr.com.abcon) or by using
protein-protein/protein-dye crosslinking kits from Molecular Probes
(Eugene, Oreg.).
[0156] Using the example of two activation state specific
antibodies, by "uniquely labeled" is meant that a first activation
state antibody recognizing a first activated kinase comprises a
first label, and second activation state antibody recognizing a
second activated kinase comprises a second label, wherein the first
and second label are detectable and distinguishable, making the
first antibody and the second antibody uniquely labeled.
[0157] Non-activation state antibodies may also be used in the
present invention. In a preferred embodiment, non-activation state
antibodies bind to epitopes in both activated and non-activated
forms of a protein. Such antibodies may be used to determine the
amount of non-activated plus activated protein in a sample. In
another preferred embodiment, non-activation state antibodies bind
to epitopes present in non-activated forms of a protein but absent
in activated forms of a protein. Such antibodies may be used to
determine the amount of non-activated protein in a sample. Both
types of non-activation state antibodies may be used to determine
if a change in the amount of activation state protein, for example
from samples before and after treatment with a candidate bioactive
agent as described herein, coincide with changes in the amount of
non-activation state protein. For example, such antibodies can be
used to determine whether an increase in activated protein is due
to activation of non-activation state protein, or due to increased
expression of protein, or both.
[0158] In another preferred embodiment, antibodies are immobilized
using beads analogous to those known and used for standardization
in flow cytometry. Attachment of a multiplicity of activation state
specific antibodies to beads may be done by methods known in the
art and/or described herein. Such conjugated beads may be contacted
with sample, preferably cell extract, under conditions which allow
for a multiplicity of activated kinases, if present, to bind to the
multiplicity of immobilized antibodies. A second multiplicity of
antibodies comprising non-activation state antibodies which are
uniquely labeled may be added to the immobilized activation state
specific antibody-activated kinase complex and the beads may be
sorted by FACS on the basis of the presence of each label, wherein
the presence of label indicates binding of corresponding second
antibody and the presence of corresponding activated kinase.
[0159] In a preferred embodiment, the present invention provides
methods for determining a protein activation state profile for a
single cell. The methods comprise sorting cells by FACS on the
basis of the activation state of at least two proteins. Activation
state-specific antibodies are used to sort cells on the basis of
protein activation state.
[0160] When using fluorescent labeled components in the methods and
compositions of the present invention, it will recognized that
different types of fluorescent monitoring systems, e.g., FACS
systems, can be used to practice the invention. Preferably, FACS
systems are used or systems dedicated to high throughput screening,
e.g. 96 well or greater microtiter plates. Methods of performing
assays on fluorescent materials are well known in the art and are
described in, e.g., Lakowicz, J. R., Principles of Fluorescence
Spectroscopy, New York: Plenum Press (1983); Herman, B., Resonance
energy transfer microscopy, in: Fluorescence Microscopy of Living
Cells in Culture, Part B, Methods in Cell Biology, vol. 30, ed.
Taylor, D. L. & Wang, Y.-L., San Diego: Academic Press (1989),
pp. 219-243; Turro, N.J., Modern Molecular Photochemistry, Menlo
Park: Benjamin/Cummings Publishing Col, Inc. (1978), pp.
296-361.
[0161] Fluorescence in a sample can be measured using a
fluorimeter. In general, excitation radiation, from an excitation
source having a first wavelength, passes through excitation optics.
The excitation optics cause the excitation radiation to excite the
sample. In response, fluorescent proteins in the sample emit
radiation which has a wavelength that is different from the
excitation wavelength. Collection optics then collect the emission
from the sample. The device can include a temperature controller to
maintain the sample at a specific temperature while it is being
scanned. According to one embodiment, a multi-axis translation
stage moves a microtiter plate holding a plurality of samples in
order to position different wells to be exposed. The multi-axis
translation stage, temperature controller, auto-focusing feature,
and electronics associated with imaging and data collection can be
managed by an appropriately programmed digital computer. The
computer also can transform the data collected during the assay
into another format for presentation.
[0162] In a preferred embodiment, flow cytometry is used to detect
fluorescence. Other methods of detecting fluorescence may also be
used, e.g., Quantum dot methods (see, e.g., Goldman et al., J. Am.
Chem. Soc. (2002) 124:6378-82; Pathak et al. J. Am. Chem. Soc.
(2001) 123:4103-4; and Remade et al., Proc. Natl. Sci. USA (2000)
18:553-8, each expressly incorporated herein by reference).
[0163] In a preferred embodiment, FRET is used as a way of
monitoring the activation state of proteins inside a cell. The
degree of FRET can be determined by any spectral or fluorescence
lifetime characteristic of the excited construct, for example, by
determining the intensity of the fluorescent signal from the donor,
the intensity of fluorescent signal from the acceptor, the ratio of
the fluorescence amplitudes near the acceptor's emission maxima to
the fluorescence amplitudes near the donor's emission maximum, or
the excited state lifetime of the donor. For example, cleavage of
the linker can increase the intensity of fluorescence from the
donor, decreases the intensity of fluorescence from the acceptor,
decreases the ratio of fluorescence amplitudes from the acceptor to
that from the donor, and increases the excited state lifetime of
the donor.
[0164] Preferably, changes in the degree of FRET are determined as
a function of the change in the ratio of the amount of fluorescence
from the donor and acceptor moieties, a process referred to as
"ratioing." Changes in the absolute amount of substrate, excitation
intensity, and turbidity or other background absorbances in the
sample at the excitation wavelength affect the intensities of
fluorescence from both the donor and acceptor approximately in
parallel. Therefore the ratio of the two emission intensities is a
more robust and preferred measure of cleavage than either intensity
alone.
[0165] The ratio-metric fluorescent reporter system described
herein has significant advantages over existing reporters for
protein integration analysis, as it allows sensitive detection and
isolation of both expressing and non-expressing single living
cells. In a preferred embodiment, the assay system uses a
non-toxic, non-polar fluorescent substrate which is easily loaded
and then trapped intracellularly. Modification of the fluorescent
substrate by a cognate protein yields a fluorescent emission shift
as substrate is converted to product. Because the reporter readout
is ratiometric it is unique among reporter protein assays in that
it controls for variables such as the amount of substrate loaded
into individual cells. The stable, easily detected, intracellular
readout eliminates the need for establishing clonal cell lines
prior to expression analysis. This system and other analogous flow
sorting systems can be used to isolate cells having a particular
protein activation profile from pools of millions of viable
cells.
[0166] The detecting, sorting, or isolating step of the methods of
the present invention can entail fluorescence-activated cell
sorting (FACS) techniques, where FACS is used to select cells from
the population containing a particular surface marker, or the
selection step can entail the use of magnetically responsive
particles as retrievable supports for target cell capture and/or
background removal. A variety FACS systems are known in the art and
can be used in the methods of the invention (see e.g., WO99/54494,
filed Apr. 16, 1999; U.S.A.N. 20010006787, filed Jul. 5, 2001, each
expressly incorporated herein by reference).
[0167] In a preferred embodiment, a FACS cell sorter (e.g. a
FACSVantage.TM. Cell Sorter, Becton Dickinson Immunocytometry
Systems, San Jose, Calif.) is used to sort and collect cells based
on their protein activation profile (positive cells). The cells are
first contacted with fluorescent-labeled activation state-specific
antibodies directed against specific isoforms of specific
activatable proteins. In one embodiment, the amount of bound
antibody on each cell can be measured by passing droplets
containing the cells through the cell sorter. By imparting an
electromagnetic charge to droplets containing the positive cells,
the cells can be separated from other cells. The positively
selected cells can then be harvested in sterile collection vessels.
These cell sorting procedures are described in detail, for example,
in the FACSVantage.TM. Training Manual, with particular reference
to sections 3-11 to 3-28 and 10-1 to 10-17.
[0168] In another embodiment, positive cells can be sorted using
magnetic separation of cells based on the presence of an isoform of
an activatable protein. In such separation techniques, cells to be
positively selected are first contacted with specific binding agent
(e.g., an antibody or reagent that binds an isoform of an
activatable protein). The cells are then contacted with retrievable
particles (e.g., magnetically responsive particles) which are
coupled with a reagent that binds the specific binding agent (that
has bound to the positive cells). The cell-binding agent-particle
complex can then be physically separated from non-positive or
non-labeled cells, for example, using a magnetic field. When using
magnetically responsive particles, the positive or labeled cells
can be retained in a container using a magnetic filed while the
negative cells are removed. These and similar separation procedures
are described, for example, in the Baxter Immunotherapy Isolex
training manual.
[0169] In a preferred embodiment, methods for the determination of
a kinase activation state profile for a single cell are provided.
The methods comprise providing a population of cells and sorting
the population of cells by FACS. Preferably, cells are separated on
the basis of the activation state of at least two kinases. In a
preferred embodiment, a multiplicity of kinase activation state
antibodies (sometimes referred to herein as kinase activation state
specific antibodies) are used to simultaneously determine the
activation state of a multiplicity of kinases. Particularly
preferred is the use of at least two, preferably more than two,
preferably all of the following kinase activation state antibodies:
anti-AKT-phospho-Ser473, anti-AKT phospho-Thr308, anti-p44/42 MAPK
phospho-Thr202/Tyr204, anti-TYK2 phospho-Tyr1054/1055, anti-p38
MAPK phospho-Thr180/Tyr182, anti-JNK/SAPK phospho-Thr183/Tyr185,
anti-phospho-tyrosine, anti-phospho-threonine.
[0170] In addition to the direct detection of phosphorylated
kinases in single cells, the methods provide for the detection of
activated kinases in single cells using specific substrates for
kinases and phospho-substrate antibodies as described herein. In a
preferred embodiment, cells are contacted with at least two such
substrates, contacted with phospho-substrate antibodies, and then
sorted on the basis of kinase activation using a FACS machine.
Particularly preferred are phospho-substrate antibodies that
specifically bind to PKC substrate PAN phospho-substrate (which is
a substrate for .alpha., .beta.I, .beta.II, and .delta. isoforms of
PKC only when phosphorylated at a carboxy terminal residue
homologous to Ser660 of PKC.beta.II), and phospho-substrate
antibodies that specifically bind to PKA phospho-substrate
(consensus phosphorylation site of PKA phosphorylation of threonine
with arginine at -3 position).
[0171] In another preferred embodiment, a combination of kinase
activation state antibodies that specifically bind to
phosphorylated kinases, specific substrates for kinases, and
phospho-substrate antibodies are used to determine a kinase
activation state profile for a single cell. The methods comprise
sorting cells on the basis of the activation state of at least two
kinases using a FACS machine. Activation of at least two kinases is
determined using at least one kinase activation state antibody and
at least one specific substrate for a kinase and at least one
phospho-substrate antibody for the measurement of the at least one
phosphorylated substrate. Preferably, a kinase activation state
antibody is selected from the group consisting of
anti-AKT-phospho-Ser473, anti-AKT phospho-Thr308, anti-p44/42 MAPK
phospho-Thr202/Tyr204, anti-TYK2 phospho-Tyr1054/1055, anti-p38
MAPK phospho-Thr180/Tyr182, anti-JNK/SAPK phospho-Thr183/Tyr185,
anti-phospho-tyrosine, anti-phospho-threonine. Preferably, a
phospho-substrate antibody is selected from an antibody that
specifically binds to PKC substrate PAN phospho-substrate (which is
a substrate for .alpha., .beta.I, .beta.II, and .delta. isoforms of
PKC only when phosphorylated at a carboxy terminal residue
homologous to Ser660 of PKC.beta.II), and an antibody that
specifically binds to PKA phospho-substrate (consensus
phosphorylation site of PKA phosphorylation of threonine with
arginine at -3 position).
[0172] In a preferred embodiment, cell sorting by FACS on the basis
of the activation state of at least two proteins, preferably
kinases and/or caspases, is combined with a determination of other
FACS readable outputs, such as the presence of surface markers,
granularity and cell size to provide a correlation between the
activation state of a multiplicity of proteins and other cell
qualities measurable by FACS for single cells.
[0173] As will be appreciated, the present invention also provides
for the ordering of protein activation events in signal
transduction. Particularly, the present invention allows the
artisan to construct a kinase activation hierarchy based on the
correlation of levels of activation of a multiplicity of kinases
within single cells.
[0174] The present invention may also be used to determine the
presence of cellular subsets, based on correlated protein
activation, preferably kinase activation, within complex cellular
mixtures such as peripheral blood mononuclear cells. These subsets
may represent different differentiation or activation states or
different cell lineages or sublineages.
[0175] It will also be recognized that a homogeneous cell
population is desirable for studying signal transduction in order
that variances in signaling between cells not qualitatively and
quantitatively mask signal transduction events. The ultimate
homogeneous system is the single cell. The present invention
provides methods for the analysis of signal transduction in single
cells, where the activated state of the signal transducing proteins
involved is antigenically distinguishable from a non-activated
state.
[0176] As will be appreciated, these methods provide for the
identification of distinct signaling cascades for both artificial
and stimulatory conditions in complex cell populations, such a
peripheral blood mononuclear cells, or naive and memory
lymphocytes.
[0177] The methods provided herein may also involve the use of
specific inhibitors of particular kinases. The methods provided
herein may also involve the use of specific inhibitors of caspases.
The methods provided herein may also involve the use of other
pharmacological inhibitors of signaling pathways. These inhibitors
may be used as controls to ensure that antibodies specifically bind
to activated isoforms of proteins. For example, an inhibitor of a
kinase known to phosphorylate and activate a second kinase may be
used to inhibit phosphorylation of the second kinase and examine
whether an antibody specifically recognizes a phosphorylated
isoform of the second kinase. Alternatively, the inhibitors may be
used to further probe signaling pathways and correlations in
protein activity, particularly in single cells.
[0178] In a preferred embodiment, methods for the determination of
a caspase activation state profile for a single cell are provided.
The methods comprise providing a population of cells and sorting
the population of cells by FACS. Preferably, cells are separated on
the basis of the activation state of at least one caspase. In a
preferred embodiment, caspase cleavage product antibodies as
described herein are used to determine the activation state of at
least one caspase.
[0179] In a preferred embodiment, a method for screening for a
bioactive agent capable of modulating kinase activity is provided
which comprises contacting a cell with a candidate bioactive agent
and determining kinase activation in said cell by cell sorting said
cell by FAGS.
[0180] In a preferred embodiment, the method comprises contacting a
plurality of cells with a plurality of candidate bioactive agents
and sorting the cells by FACS on the basis of the activation of at
least one kinase.
[0181] In a preferred embodiment, a method for screening for a
bioactive agent capable of modulating caspase activity is provided
which comprises contacting a cell with a candidate bioactive agent
and determining caspase activation in said cell by cell sorting
said cell by FACS.
[0182] In a preferred embodiment, the method comprises contacting a
plurality of cells with a plurality of candidate bioactive agents
and sorting the cells by FACS on the basis of the activation of at
least one caspase.
[0183] By "candidate bioactive agent", "candidate agent",
"candidate modulator", "candidate modulating agent", or "exogeneous
compound" or grammatical equivalents herein is meant any molecule,
e.g., protein, small organic molecule, carbohydrates (including
polysaccharides), polynucleotide, lipids, etc. Generally a
plurality of assay mixtures can be run in parallel with different
agent concentrations to obtain a differential response to the
various concentrations. Typically, one of these concentrations can
serve as a negative control, i.e., at zero concentration or below
the level of detection. In addition, positive controls can be
used.
[0184] Candidate agents encompass numerous chemical classes. In a
preferred embodiment, the candidate agents are small molecules. In
another preferred embodiment, the candidate agents are organic
molecules, particularly small organic molecules, comprising
functional groups necessary for structural interaction with
proteins, particularly hydrogen bonding, and typically include at
least an amine, carbonyl, hydroxyl or carboxyl group, preferably at
least two of the functional chemical groups. The candidate agents
often comprise cyclical carbon or heterocyclic structures and/or
aromatic or polyaromatic structures substituted with one or more
chemical functional groups.
[0185] Candidate agents are obtained from a wide variety of
sources, as will be appreciated by those in the art, including
libraries of synthetic or natural compounds. As will be appreciated
by those in the art, the present invention provides a rapid and
easy method for screening any library of candidate modulators,
including the wide variety of known combinatorial chemistry-type
libraries.
[0186] In a preferred embodiment, candidate agents are synthetic
compounds. Any number of techniques are available for the random
and directed synthesis of a wide variety of organic compounds and
biomolecules, including expression of randomized oligonucleotides.
See for example WO 94/24314, hereby expressly incorporated by
reference, which discusses methods for generating new compounds,
including random chemistry methods as well as enzymatic methods. As
described in WO 94/24314, one of the advantages of the present
method is that it is not necessary to characterize the candidate
agent prior to the assay. Using the methods of the present
invention, any candidate agents can be screened for the ability to
modulate (e.g., increase or decease) the activity of an activatable
protein. In addition, as is known in the art, coding tags using
split synthesis reactions may be used to essentially identify the
chemical moieties tested.
[0187] Alternatively, a preferred embodiment utilizes libraries of
natural compounds, as candidate agents, in the form of bacterial,
fungal, plant and animal extracts that are available or readily
produced.
[0188] Additionally, natural or synthetically produced libraries
and compounds are readily modified through conventional chemical,
physical and biochemical means. Known pharmacological agents may be
subjected to directed or random chemical modifications, including
enzymatic modifications, to produce structural analogs.
[0189] In a preferred embodiment, candidate agents include
proteins, nucleic acids, and chemical moieties.
[0190] In a preferred embodiment, the candidate agents are
proteins, as defined above. In a preferred embodiment, the
candidate agents are naturally occurring proteins or fragments of
naturally occurring proteins. Thus, for example, cellular extracts
containing proteins, or random or directed digests of proteinaceous
cellular extracts, may be tested, as is more fully described below.
In this way libraries of prokaryotic and eukaryotic proteins may be
made for screening against any number of candidate agents.
Particularly preferred in this embodiment are libraries of
bacterial, fungal, viral, and mammalian proteins, with the latter
being preferred, and human proteins being especially preferred.
[0191] In a preferred embodiment, the candidate agents are peptides
of from about 2 to about 50 amino acids, with from about 5 to about
30 amino acids being preferred, and from about 8 to about 20 being
particularly preferred. The peptides may be digests of naturally
occurring proteins as is outlined above, random peptides, or
"biased" random peptides. By "randomized" or grammatical
equivalents herein is meant that each nucleic acid and peptide
consists of essentially random nucleotides and amino acids,
respectively. Since generally these random peptides (or nucleic
acids, discussed below) are chemically synthesized, they may
incorporate any nucleotide or amino acid at any position. The
synthetic process can be designed to generate randomized proteins
or nucleic acids, to allow the formation of all or most of the
possible combinations over the length of the sequence, thus forming
a library of randomized candidate bioactive proteinaceous
agents.
[0192] The library should provide a sufficiently structurally
diverse population of randomized agents to effect a
probabilistically sufficient range of diversity to allow
interaction with a particular activatable protein. Accordingly, an
interaction library must be large enough so that at least one of
its members will have a structure that interacts with an
activatable protein or other specific components of the signal
transduction pathway involving the activable protein. Although it
is difficult to gauge the required absolute size of an interaction
library, nature provides a hint with the immune response: a
diversity of 10.sup.7-10.sup.6 different antibodies provides at
least one combination with sufficient affinity to interact with
most potential antigens faced by an organism. Published in vitro
selection techniques have also shown that a library size of
10.sup.7 to 10.sup.8 is sufficient to find structures with affinity
for a target. A library of all combinations of a peptide 7 to 20
amino acids in length, such as generally proposed herein, has the
potential to code for 20.sup.7 (10.sup.9) to 20.sup.20. Thus, with
libraries of 10.sup.7 to 10.sup.8 different molecules the present
methods allow a "working" subset of a theoretically complete
interaction library for 7 amino acids, and a subset of shapes for
the 20.sup.20 library. Thus, in a preferred embodiment, at least
10.sup.6, preferably at least 10.sup.7, more preferably at least
10.sup.8 and most preferably at least 10.sup.9 different sequences
are simultaneously analyzed in the subject methods. Preferred
methods maximize library size and diversity.
[0193] In one embodiment, the library is fully randomized, with no
sequence preferences or constants at any position. In a preferred
embodiment, the library is biased. That is, some positions within
the sequence are either held constant, or are selected from a
limited number of possibilities. For example, in a preferred
embodiment, the nucleotides or amino acid residues are randomized
within a defined class, for example, of hydrophobic amino acids,
hydrophilic residues, sterically biased (either small or large)
residues, towards the creation of cysteines, for cross-linking,
prolines for SH-3 domains, serines, threonines, tyrosines or
histidines for phosphorylation sites, etc., or to purines, etc.
[0194] In a preferred embodiment, the bias is towards peptides or
nucleic acids that interact with known classes of molecules. For
example, when the candidate agent is a peptide, it is known that
much of intracellular signaling is carried out via short regions of
polypeptides interacting with other polypeptides through small
peptide domains. For instance, a short region from the HIV-1
envelope cytoplasmic domain has been previously shown to block the
action of cellular calmodulin. Regions of the Fas cytoplasmic
domain, which shows homology to the mastoparan toxin from Wasps,
can be limited to a short peptide region with death-inducing
apoptotic or G protein inducing functions. Magainin, a natural
peptide derived from Xenopus, can have potent anti-tumor and
anti-microbial activity. Short peptide fragments of a protein
kinase C isozyme (.beta.PKC), have been shown to block nuclear
translocation of .beta.PKC in Xenopus oocytes following
stimulation. And, short SH-3 target peptides have been used as
psuedosubstrates for specific binding to SH-3 proteins. This is of
course a short list of available peptides with biological activity,
as the literature is dense in this area. Thus, there is much
precedent for the potential of small peptides to have activity on
intracellular signaling cascades. In addition, agonists and
antagonists of any number of molecules may be used as the basis of
biased randomization of candidate modulators as well.
[0195] Thus, a number of molecules or protein domains are suitable
as starting points for the generation of biased randomized
candidate modulators. A large number of small molecule domains are
known, that confer a common function, structure or affinity. In
addition, as is appreciated in the art, areas of weak amino acid
homology may have strong structural homology. A number of these
molecules, domains, and/or corresponding consensus sequences, are
known, including, but are not limited to, SH-2 domains, SH-3
domains, Pleckstrin, death domains, protease cleavage/recognition
sites, enzyme inhibitors, enzyme substrates, and Traf.
[0196] In a preferred embodiment, the candidate modulating agent is
a polypeptide. In another preferred embodiment, the polypeptide is
a cyclic peptide having at least 4 to 20 amino acids. Also in
another preferred embodiment, the polypeptide is a catalytically
inactive polypeptide. Examples of catalytically inactive
polypeptides include, but are not limited to, catalytically
inactive activable proteins and, more specifically a catalytically
inactive kinases (e.g., PI3K) or caspases. In a further aspect, the
candidate modulating agent is peptide fragment of an activatable
protein, wherein the peptide fragment comprises an amino acid
sequence that is a subsequence of the full-length amino acid
sequence of the activable protein.
[0197] In a preferred embodiment, the candidate agents are nucleic
acids. With reference to candidate agents, by "nucleic acid" or
"oligonucleotide" or grammatical equivalents herein means at least
two nucleotides covalently linked together. A nucleic acid of the
present invention will generally contain phosphodiester bonds,
although in some cases, as outlined below, nucleic acid analogs are
included that may have alternate backbones, comprising, for
example, phosphoramide (Beaucage et al., Tetrahedron 49(10):1925
(1993) and references therein; Letsinger, J. Org. Chem. 35:3800
(1970); Sprinzl et al., Eur. J. Biochem. 81:579 (1977); Letsinger
et al., Nucl. Acids Res. 14:3487 (1986); Sawai et al, Chem. Lett.
805 (1984), Letsinger et al., J. Am. Chem. Soc. 110:4470 (1988);
and Pauwels et al., Chemica Scripta 26:141 91986)),
phosphorothioate (Mag et al., Nucleic Acids Res. 19:1437 (1991);
and U.S. Pat. No. 5,644,048), phosphorodithioate (Briu et al., J.
Am. Chem. Soc. 111:2321 (1989), O-methylphosphoroamidite linkages
(see Eckstein, Oligonucleotides and Analogues: A Practical
Approach, Oxford University Press), and peptide nucleic acid
backbones and linkages (see Egholm, J. Am. Chem. Soc. 114:1895
(1992); Meier et al., Chem. Int. Ed. Engl. 31:1008 (1992); Nielsen,
Nature, 365:566 (1993); Carlsson et al., Nature 380:207 (1996), all
of which are incorporated by reference). Other analog nucleic acids
include those with positive backbones (Denpcy et al., Proc. Natl.
Acad. Sci. USA 92:6097 (1995); non-ionic backbones (U.S. Pat. Nos.
5,386,023, 5,637,684, 5,602,240, 5,216,141 and 4,469,863;
Kiedrowshi et al., Angew. Chem. Intl. Ed. English 30:423 (1991);
Letsinger et at, J. Am. Chem. Soc. 110:4470 (1988); Letsinger et
al., Nucleoside & Nucleotide 13:1597 (1994); Chapters 2 and 3,
ASC Symposium Series 580, "Carbohydrate Modifications in Antisense
Research", Ed. Y. S. Sanghui and P. Dan Cook; Mesmaeker et al.,
Bioorganic & Medicinal Chem. Lett. 4:395 (1994); Jeffs et al.,
J. Biomolecular NMR 34:17 (1994); Tetrahedron Lett. 37:743 (1996))
and non-ribose backbones, including those described in U.S. Pat.
Nos. 5,235,033 and 5,034,506, and Chapters 6 and 7, ASC Symposium
Series 580, "Carbohydrate Modifications in Antisense Research", Ed.
Y. S. Sanghui and P. Dan Cook. Nucleic acids containing one or more
carbocyclic sugars are also included within the definition of
nucleic acids (see Jenkins et al., Chem. Soc. Rev. (1995) pp
169-176). Several nucleic acid analogs are described in Rawls, C
& E News Jun. 2, 1997 page 35. All of these references are
hereby expressly incorporated by reference. These modifications of
the ribose-phosphate backbone may be done to facilitate the
addition of additional moieties such as labels, or to increase the
stability and half-life of such molecules in physiological
environments.
[0198] As will be appreciated by those in the art, all of these
nucleic acid analogs may find use in the present invention. In
addition, mixtures of naturally occurring nucleic acids and analogs
can be made. Alternatively, mixtures of different nucleic acid
analogs, and mixtures of naturally occurring nucleic acids and
analogs may be made. Particularly preferred are peptide nucleic
acids (PNA) which includes peptide nucleic acid analogs. These
backbones are substantially non-ionic under neutral conditions, in
contrast to the highly charged phosphodiester backbone of naturally
occurring nucleic acids.
[0199] The nucleic acids may be single stranded or double stranded,
as specified, or contain portions of both double stranded or single
stranded sequence. The nucleic acid may be DNA, both genomic and
cDNA, RNA or a hybrid, where the nucleic acid contains any
combination of deoxyribo- and ribo-nucleotides, and any combination
of bases, including uracil, adenine, thymine, cytosine, guanine,
inosine, xathanine hypoxathanine, isocytosine, isoguanine, etc. As
used herein, the term "nucleoside" includes nucleotides and
nucleoside and nucleotide analogs, and modified nucleosides such as
amino modified nucleosides. In addition, "nucleoside" includes
non-naturally occurring analog structures. Thus for example the
individual units of a peptide nucleic acid, each containing a base,
are referred to herein as a nucleoside.
[0200] As described above generally for proteins, nucleic acid
candidate agent may be naturally occurring nucleic acids, random
nucleic acids, or "biased" random nucleic acids. For example,
digests of prokaryotic or eukaryotic genomes may be used as is
outlined above for proteins. Where the ultimate expression product
is a nucleic acid, at least 10, preferably at least 12, more
preferably at least 15, most preferably at least 21 nucleotide
positions need to be randomized, with more preferable if the
randomization is less than perfect. Similarly, at least 5,
preferably at least 6, more preferably at least 7 amino acid
positions need to be randomized; again, more are preferable if the
randomization is less than perfect.
[0201] In a preferred embodiment, the candidate modulating agent is
a mutant cDNA encoding a catalytically inactive polypeptide.
Examples of such catalytically inactive polypeptides include, but
are not limited to, catalytically inactive activatable proteins
and, more specifically, catalytically inactive kinases (e.g., PI3K)
or caspases.
[0202] In a preferred embodiment, the candidate modulating agent is
an RNA, for example an antisense RNA or siRNA (small inhibitory
RNA). In another preferred embodiment, the siRNA cleaves RNA
encoding an activatable protein. The siRNAs can be prepared using
the methods described herein and known in the art.
[0203] In a preferred embodiment, the candidate agents are organic
moieties. In this embodiment, as is generally described in WO
94/24314, candidate agents are synthesized from a series of
substrates that can be chemically modified. "Chemically modified"
herein includes traditional chemical reactions as well as enzymatic
reactions. These substrates generally include, but are not limited
to, alkyl groups (including alkanes, alkenes, alkynes and
heteroalkyl), aryl groups (including arenes and heteroaryl),
alcohols, ethers, amines, aldehydes, ketones, acids, esters,
amides, cyclic compounds, heterocyclic compounds (including
purines, pyrimidines, benzodiazepins, beta-lactams, tetracylines,
cephalosporins, and carbohydrates), steroids (including estrogens,
androgens, cortisone, ecodysone, etc.), alkaloids (including
ergots, vinca, curare, pyrollizdine, and mitomycines),
organometallic compounds, hetero-atom bearing compounds, amino
acids, and nucleosides. Chemical (including enzymatic) reactions
may be done on the moieties to form new substrates or candidate
agents which can then be tested using the present invention.
[0204] As will be appreciated by those in the art, it is possible
to screen more than one type of candidate agent at a time, e.g., by
combining the candidate agents in the methods of the present
invention. Thus, the library of candidate agents used may include
only one type of agent (i.e. peptides), or multiple types (peptides
and organic agents).
[0205] By "combining" is meant the combining of the various
components in a reaction mixture in vitro or in a cell in vivo
under conditions which promote an activity that is detectable using
known methods or using the methods of the present invention (e.g.,
the binding of an antibody to a corresponding antigen or isoform of
an activatable protein, or activation state of an activatable
protein).
[0206] It is understood by the skilled artisan that the steps of
the assays provided herein can vary in order. It is also
understood, however, that while various options (of compounds,
properties selected or order of steps) are provided herein, the
options are also each provided individually, and can each be
individually segregated from the other options provided herein.
Moreover, steps which are obvious and known in the art that will
increase the sensitivity of the assay are intended to be within the
scope of this invention. For example, there may be additionally
washing steps, blocking steps, etc.
[0207] In a preferred embodiment, the reaction mixture or cells are
contained in a well of a 96 well plate or other commercially
available multiwell plate. In an alternate preferred embodiment,
the reaction mixture or cells are in a FACS machine. Other
multiwell plates useful in the present invention include, but are
not limited to 384 well plates and 1536 well plates. Still other
vessels for containing the reaction mixture or cells and useful in
the present invention will be apparent to the skilled artisan.
[0208] The addition of the components of the assay for detecting
the activation state or activity of an activatable protein, or
modulation of such activation state or activity, may be sequential
or in a predetermined order or grouping under conditions
appropriate for the activity that is assayed for. Such conditions
are described here and known in the art. Moreover, further guidance
is provided below (see, e.g., in the Examples).
[0209] In a preferred embodiment, the methods of the invention
include the use of liquid handling components. The liquid handling
systems can include robotic systems comprising any number of
components. In addition, any or all of the steps outlined herein
may be automated; thus, for example, the systems may be completely
or partially automated.
[0210] As will be appreciated by those in the art, there are a wide
variety of components which can be used, including, but not limited
to, one or more robotic arms; plate handlers for the positioning of
microplates; automated lid or cap handlers to remove and replace
lids for wells on non-cross contamination plates; tip assemblies
for sample distribution with disposable tips; washable tip
assemblies for sample distribution; 96 well loading blocks; cooled
reagent racks; microtitler plate pipette positions (optionally
cooled); stacking towers for plates and tips; and computer
systems.
[0211] Fully robotic or microfluidic systems include automated
liquid-, particle-, cell- and organism-handling including high
throughput pipetting to perform all steps of screening
applications. This includes liquid, particle, cell, and organism
manipulations such as aspiration, dispensing, mixing, diluting,
washing, accurate volumetric transfers; retrieving, and discarding
of pipet tips; and repetitive pipetting of identical volumes for
multiple deliveries from a single sample aspiration. These
manipulations are cross-contamination-free liquid, particle, cell,
and organism transfers. This instrument performs automated
replication of microplate samples to filters, membranes, and/or
daughter plates, high-density transfers, full-plate serial
dilutions, and high capacity operation.
[0212] In a preferred embodiment, chemically derivatized particles,
plates, cartridges, tubes, magnetic particles, or other solid phase
matrix with specificity to the assay components are used. The
binding surfaces of microplates, tubes or any solid phase matrices
include non-polar surfaces, highly polar surfaces, modified dextran
coating to promote covalent binding, antibody coating, affinity
media to bind fusion proteins or peptides, surface-fixed proteins
such as recombinant protein A or G, nucleotide resins or coatings,
and other affinity matrix are useful in this invention.
[0213] In a preferred embodiment, platforms for multi-well plates,
multi-tubes, holders, cartridges, minitubes, deep-well plates,
microfuge tubes, cryovials, square well plates, filters, chips,
optic fibers, beads, and other solid-phase matrices or platform
with various volumes are accommodated on an upgradable modular
platform for additional capacity. This modular platform includes a
variable speed orbital shaker, and multi-position work decks for
source samples, sample and reagent dilution, assay plates, sample
and reagent reservoirs, pipette tips, and an active wash
station.
[0214] In a preferred embodiment, thermocycler and thermoregulating
systems are used for stabilizing the temperature of heat exchangers
such as controlled blocks or platforms to provide accurate
temperature control of incubating samples from 0.degree. C. to
100.degree. C.
[0215] In a preferred embodiment, interchangeable pipet heads
(single or multi-channel) with single or multiple magnetic probes,
affinity probes, or pipetters robotically manipulate the liquid,
particles, cells, and organisms. Multi-well or multi-tube magnetic
separators or platforms manipulate liquid, particles, cells, and
organisms in single or multiple sample formats.
[0216] In some embodiments, the instrumentation will include a
detector, which can be a wide variety of different detectors,
depending on the labels and assay. In a preferred embodiment,
useful detectors include a microscope(s) with multiple channels of
fluorescence; plate readers to provide fluorescent, ultraviolet and
visible spectrophotometric detection with single and dual
wavelength endpoint and kinetics capability, fluoroescence
resonance energy transfer (FRET), luminescence, quenching,
two-photon excitation, and intensity redistribution; CCD cameras to
capture and transform data and images into quantifiable formats;
and a computer workstation.
[0217] In a preferred embodiment, the detecting is by FACS. In
another aspect, the detecting is by high pressure liquid
chromatography (HPLC), for example, reverse phase HPLC, and in a
further aspect, the detecting is by mass spectromety.
[0218] These instruments can fit in a sterile laminar flow or fume
hood, or are enclosed, self-contained systems, for cell culture
growth and transformation in multi-well plates or tubes and for
hazardous operations. The living cells may be grown under
controlled growth conditions, with controls for temperature,
humidity, and gas for time series of the live cell assays.
Automated transformation of cells and automated colony pickers may
facilitate rapid screening of desired cells.
[0219] Flow cytometry or capillary electrophoresis formats can be
used for individual capture of magnetic and other beads, particles,
cells, and organisms.
[0220] The flexible hardware and software allow instrument
adaptability for multiple applications. The software program
modules allow creation, modification, and running of methods. The
system diagnostic modules allow instrument alignment, correct
connections, and motor operations. The customized tools, labware,
and liquid, particle, cell and organism transfer patterns allow
different applications to be performed. The database allows method
and parameter storage. Robotic and computer interfaces allow
communication between instruments.
[0221] In a preferred embodiment, the robotic apparatus includes a
central processing unit which communicates with a memory and a set
of input/output devices (e.g., keyboard, mouse, monitor, printer,
etc.) through a bus. Again, as outlined below, this may be in
addition to or in place of the CPU for the multiplexing devices of
the invention. The general interaction between a central processing
unit, a memory, input/output devices, and a bus is known in the
art. Thus, a variety of different procedures, depending on the
experiments to be run, are stored in the CPU memory.
[0222] These robotic fluid handling systems can utilize any number
of different reagents, including buffers, reagents, samples,
washes, assay components such as label probes, etc.
[0223] The following examples serve to more fully describe the
manner of using the above-described invention, as well as to set
forth the best modes contemplated for carrying out various aspects
of the invention. It is understood that these examples in no way
serve to limit the true scope of this invention, but rather are
presented for illustrative purposes. All references cited herein
are expressly incorporated by reference in their entirety.
EXAMPLES
Example 1
Functional Signaling Analysis in Single Cells: Simultaneous
Measurement of Multiple Kinase Activities Using Polychromatic Flow
Cytometry
[0224] Intracellular assays of signaling systems has been limited
by an inability to correlate functional subsets of cells in complex
populations based on kinase activity. Such correlations could be
important to distinguish changes in signaling status that arise in
rare cell subsets during signaling or in disease manifestation. In
this Example, using the methods and compositions of the present
invention, the present inventors (also referred to herein as "we")
demonstrate the ability to simultaneously detect the kinase
activities of members of the mitogen activated protein kineses
family (p38 MAPK, p44142 MAPK, JNKISAPK), members of cell survival
pathways (PKA, AKT/PKB), and members of T-cell activation pathways
(TYK2, PKC) in subpopulations of complex cell populations by
multi-parameter flow cytometric analysis. Further, in this Example
the present inventors demonstrate the utility of these probes in
identifying distinct signaling cascades for: 1) both artificial and
physiological stimulatory conditions of peripheral blood
mononuclear cells (PBMC); 2) cytokine stimulation in human memory
and naive lymphocyte subsets as identified by 5 differentiation
markers; and 3) ordering of kinase activation in potential
signaling hierarchies. Polychromatic flow cytometric kinase
activity measurements (PFC-KA) demonstrate that multi-dimensional
analysis of signaling pathway interplay can provide functional
signaling pathway assessment on a single cell level.
Introduction
[0225] The study of multiple activated signaling pathways in
complex populations of cells, such as peripheral blood, at the
single cell level has not been previously possible. Multiparameter
flow cytometric analysis allows for small
subpopulations--representing different cellular subsets,
differentiation or activation states--to be discerned using cell
surface markers Downstream activation of signaling pathways can be
read out by reporter systems that include intracellular detection
of enzyme activity for .beta.-galactoside.sup.1,2, and
.beta.-glucuronidase.sup.3 to study transcription from defined
promoter(s) and green fluorescent proteins (GFP). Interactions
between proteins can be determined by both Fluorescence Resononance
Energy Transfer and Bioluminescence Resonance Energy
Transfer.sup.4,5,6,7. In either of these latter cases, the
activation of the signaling system is determined through
overexpression of reporter proteins-as such the endogenous kinase
activation states are not accessible.
[0226] It is understood that kinase signaling cascades play an
important role in nearly every critical decision process in cells'.
Determining the role of specific signal transduction pathways in a
given system has been aided by the advent of pharmacological
inhibitors for specific kinases. However, monitoring activities for
such kinases as Protein Kinase B/AKT, c-Jun-N-terminal Kinase
(JNK), p38 mitogen activated protein kinase (p38), p44/42 ERK1/2
(ERK) activity, PKA activity, PKC activity, or TYK2 activity is
usually dependent upon in vitro kinase assays or, more recently, by
immunoblotting to determine their phosphorylation state using
phospho-specific antibodies. To date it has not been possible to
correlate rare subpopulations with the activation state of kinases
in important signaling paths. With the recent advent of 11-color
flow cytometry.sup.9 we sought to dissect biologically relevant
subsets of cells based on defined kinase activation states.
[0227] Phospho-specific monoclonal, phospho-substrate specific
polyclonal, and cognate (nonphospho-specific) kinase antibodies
were conjugated to fluorophores (see Table 1 herein; and Table 1
legends below) as probes for specific kinase activities. Each
antibody was tested for phospho-specificity prior to conjugation by
treating cells with appropriate kinase inducing agents or specific
kinase inhibitors (see Table 2 herein; and Table 2 legends below)
and subjected to traditional western blot analysis and kinase
activity assays (FIG. 1A). Antibodies exhibiting specificity for
the phosphorylated state of the kinase were: AKT phospho-Ser473,
AKT phospho-Thr308, p44/42 MAPK phosphoThr202 Tyr204, TYK2
phospho-Tyr1054/1055, p38 MAPK phosho-Thr1BO Tyr182, PKC-PAN
phospho-substrate (detects PKC.alpha., .beta. I, .beta.11, and
.delta. isoforms only when phosphorylated at a carboxy terminal
residue homologous to ser660 of PKC.beta.11), PKA phospho-substrate
(consensus phosphorylation site of PKA phosphorylation of threonine
with arginine at -3 position), JNK/SAPK phospho-Thr183/Tyr185,
phosphotyrosine (p-tyr-100) and phosho-threonine. All kinase
activation states were verified using specific inhibitors for the
upstream kinase known to phosphorylate the cognate kinase (FIG.
1A). The inhibitors applied are listed in Table 2.
[0228] FACS based detection of kinase activity, after 24-hour
serum-starvation, was tested as a function of a given stimulus
specific to kinase activation and inhibition by kinase selective
inhibitors. Table 1 provides staining combinations for the flow
cytometry experiments used in this report. Kinase selective
activators and inhibitors used are listed in Table 2 and FACS based
kinase activity plots are illustrated in FIG. 1B. Kinase probes for
p44/42, AKT, JNK, TYK2, p38, and phospho-tyrosine containing
proteins exhibited the strongest resolution of peaks between
uninduced and induced conditions (FIG. 1B). Kinase probes for PKC
and PKA exhibited the lowest apparent induction from basal
fluorescence levels as determined by FACS; this could have been
dependent on the conditions we had established for induction and
staining or the substrate motif recognition might not be optimal
for these probes. We therefore determined that the fluorescence
observed was due to a phosphorylation of a target protein by
treating the sample prior to staining with one or more phosphatases
to support the phospho-PKC-PAN, phospho-PKA substrate, and
phospho-TYK2's probe phospho-specificity (FIG. 1 C). FIG. 1C
highlights the phospho-PKC-PAN, phospho I PKA-substrate and
phospho-TYK2 probes are dependent on their respective
phosphorylated substrate for recognition as phosphatase treatment
diminishes their ability to recognize the stimulus induced
phosphorylation product(s).
[0229] To exemplify that these probes can differentiate amongst
varying levels of kinase activity a FACS dose response curve
demonstrates there is excellent p44/42 activity to fluorescence
correlation (FIG. 1B, bottom right panel). Furthermore, the mean
fluorescence intensity values of the phospho-p44/42 probe had a
correlation coefficient of 0.96 with the densitometry values of
phosphorylated p44/42 in a dose response curve, validating the
kinase probes as being able to measure small differences in kinase
activity (FIG. 1 D).
[0230] To demonstrate the ability of these probes to represent
biologically relevant signaling events we activated peripheral
blood mononuclear cells (PBMC), a population of cells that is
likely to be heterogeneous in terms of potential kinase activities,
to see if subsets of cells demonstrated differing kinase activation
kinetics. Total PBMC in mixed culture were stimulated with CD3 and
CD28 monoclonal antibodies to mimic physiological T cell activation
of surface receptors. As another form of stimulus we activated
these cells with the artificial T cell activation agents phorbal
myristyl acetate (PMA) and ionomycin. Cell subsets were gated for
CD4+ (a T cell subset marker) or CD19+ (a B cell marker). The T
cell and B cell subsets were compared to discern differential
kinase activity profiles between these two cell types upon a given
stimulus. FIG. 2A illustrates that primary B and T cells have
inherent differences with respect to kinase activity of p38 MAPK
and p44/42 MAPK in an unstimulated state, and respond differently
to the various stimulatory conditions applied. Dramatic differences
for T cells in both p38 and p44/42 activity can be seen when
comparing PMA/ionomycin and CD3/CD28 stimulation, suggesting that
CD3/CD28 does not engage full activation of CD4+ T cells along the
p38 or p44/42 pathway. Some activation of the CD19+ B cells is
observed using combinations of CD3 and CD28 that we presume is due
to T cell activation and their production of stimulatory cytokines:
for B cells. Alternatively other T cell helper interactions with B
cells could lead to the B cell activations observed with CD3 and
CD28.
[0231] We also determined in a cell line differential responses to
cytokines. Using CD69, an early T cell activator marker..sup.10,11
as a surface antigen to distinguish between activated and
non-activated Jurkat cells, CD69 expression was plotted as a
function of p44/42 activity to a variety of T cell stimulatory
agents (FIG. 2B). The differences observed in kinase activity and
CD69 expression when comparing CD3/CD28 stimulation to that of
PMA/ionomycin (artificial) would suggest that other co-stimulatory
molecules exist and are necessary for optimal T cell activation
with respect to p44/42 MAPK. In addition, experiments involving
PMA/ionomycin stimulated Jurkat cells demonstrated decreased
activation of TYK2 activity in CD69+ cells (data not shown) This
would suggest that T cell activation could induce intrinsic
regulatory mechanisms that cause cells to become hyporesponsive to
further stimuli and point out that the kinase profiling probes can
potentially be used to study anergic responses.
[0232] As an example of the type of information yielded by
kinase-activity gating analysis, both traditional histogram
analysis and kinase-activity gating analysis was undertaken and is
presented as follows. Jurkat cells in either growth media or
stimulated with PMA/ionomycin were assessed for multiple
intracellular kinase activity and CD69 expression (FIG. 2C). Basal
activity of PKC, p38 and p44/42 is observed, however, kinase
activity for JNK, p38, p44/42, PKC, and PKA is dramatically altered
for PMA/ionomycin stimulated cells (FIG. 2C). This is congruent
with the observations for the CD69+ PBMC data (FIG. 2B). Thus,
monitoring phosphorylation events in intact cells makes it possible
to correlate activity with other parameters such as surface
molecule expression, cell size, or cell granularity approaches not
possible with conventional lysate analysis of kinase
phosphorylation states.
[0233] To further explore subset analysis of cells we
anisomycin-treated Jurkat cells and probed them for total p38 MAPK
(using an antibody against a presumed nonphosphorylated region of
p38) and with phospho-p38 MAPK probe. This would allow us to follow
not only the changes to p38 phosphorylation but also to
simultaneously measure steady state levels. Since FACS based kinase
assays allow alternative analytical correlations to be made with
cellular size (forward scatter) and shape of the cell (side
scatter), we determined the status of the phosphorylation as a
function of the side scatter parameter (a measurement of
granularity). Cell granularity is a function of surface molecule
distribution, cell structure and conformation, and can be
influenced by internal cellular signals that result in outward cell
surface modulation (events that are common for instance in the
field of integrin "inside-out" signaling.sup.12,13,14,15). Contour
plots depict a shift from non-phosphorylated to phosphorylated p38
as the granularity of the cell increases (FIG. 2D). Similarly, a
direct correlation between elevated p44/42 kinase activity and
increased cell size (forward scatter parameter) was observed when
kinase activity was monitored as a function of cell size (data not
shown). We note that the phospho-p38 fluorescence staining occurs
at the expense of the apparent p38 nonphospho staining. We believe
this might be due to occlusion of binding of the
nonphospho-specific probe in the activated state by a cellular
protein (see below).
[0234] We illustrate a three-kinase gating analysis by correlating
the phosphorylated states of p38 and p44/42 to phospho-JNK for
total PBMC stimulated with IL-1a (FIG. 2E). Excerpts from regions
representing the lower end of phospho-JNK levels, up to higher
levels, demonstrate an initial phosphorylation of p44/42 is
followed by a phosphorylation in p38 as the intensity of JNK
phosphorylation increases. Thus in the cell, higher levels of JNK
activation correlate to an apparent passing of signals from p44/42
to p38. Although the phosphorylation events are not normalized
according to time, the phosphorylation shifts observed in p38 and
p44 as a function of JNK phosphorylation suggest pathway interplay,
and could represent the result of one signaling cascade activating
another (further experiments are underway to determine the cell
subsets responsible for these shifts). Simultaneous monitoring of
AKT, PKA, p44/42, and p38 kinase activity as a function of TYK2
activity in IL-1p stimulated PBMC exemplifies that kinase cascades
can be ordered with respect to their activation status when
analyzed in a multi-parameter fashion (FIG. 2F). In regards to
IL-1.beta. stimulation, concomitant activation of p38 and p44/42 is
observed when activation of TYK2 begins to be detected. However, a
distinct profile is observed with respect to AKT and PKA
activation, as the shift in detected phosphorylated AKT is
correlated to lower levels of phospho-TYK2 and PKA phosphorylation
of PKA substrates. The utility of these probes to spatially resolve
as many as five simultaneous kinase activations allows global
assessment of signaling pathways. In addition, population subsets
can be distinguished based upon intracellular kinase activity and
be correlated for phenotype by using multiple surface
markers--(alternative data analysis not presented here). To
demonstrate the ability of these kinase probes to screen for
activation of individual signaling pathways to other specific
stimuli, we treated human peripheral blood monocytes (PBMC) with
several different cytokines. We used the phospho-kinase probes to
correlate phospho-kinase profiles in the responding cells using
polychromatic flow cytometry (11-color, 13 parameters).
[0235] In initial experiments functional characterization of T
cells occasionally varied from donor to donor. Apparent donor
variability was reduced when magnetically activated cell sorting
(MACS) was used to isolate resting T cells by negative isolation
prior to stimulation and analysis. This is most likely due to the
depletion of pre-existing activated T cells and other cell types
that might be producing cytokines. FIG. 3 illustrates a flow
diagram of the protocol used to isolate, characterize, and analyze
truly naive
(CD3+CD4.sup.+CD8.sup.-CD62L.sup.+CD45RA.sup.+CD11a.sup.dimCD28.sup.+CD27-
.sup.+) and memory
(CD3.sup.+CD4.sup.+CD8.sup.-CD62L.sup.+CD45RA.sup.+CD11a.sup.brCD28.sup.--
CD27.sup.-) T cell intracellular kinase activities. We observed
clear constitutive activation, for instance, of AKT in the CD4, and
to a lesser degree CD8, positive subsets of naive T cells, as
opposed to memory T cells, even in non-activated cell types (FIG.
3, bottom panels). Other differences were apparent as well in the
non-stimulated cells, including differences in p38 phosphorylation.
FIG. 4 demonstrates the power of polychromatic flow cytometry based
kinase assays to identify functional differences in naive and
memory T cells in their response to IL-1.alpha., IL-1.beta., and
IL-2 as measured by the phospho-kinase profiles. Interestingly,
stimulation with any of these cytokines led to a drop in p44/42
phosphorylation in CD4+ naive cells relative to CD8+ cells. A less
dramatic drop also occurs in JNK activity in these same cell
subsets. Other kinase profiles are not effected.
[0236] Differences in kinase expression as consequences of stimuli
are typically controlled for in standard western blot/kinase
analysis by protein content normalization or by running a
comparative blot with a normalizing antibody that recognizes the
kinase irrespective of phosphorylation. We determined whether we
could simultaneously assess kinases in their active and inactive
state using cognate non-phospho specific fluorescent probes for
AKT, p44/42 MAPK, p38 MAPK, and JNK/SAPK (normalizing antibodies).
In unstimulated cells, we observed strong staining using the
normalization antibody to p44/42. After EGF stimulation, all cells
showed phosphorylated p44/42, but the normalization antibody
revealed a negative population. This result could be due to
EGF-induced binding by an unknown protein to the site recognized by
the p44/42 antibody probe, or a change in the structure of the
p44/42 molecule that occludes the antibody binding site. For p38 we
observed a strong increase after anisomycin stimulation in the
levels of apparent p38 (or loss of a bound protein that occludes
the normalization antibody recognition site) as well as a subset of
cells that show increased phosphorylation of p38. For JNK, three
distinct populations were observed before stimulation and four
distinct populations could be visualized after stimulation.
[0237] One possibility is that the plots could depict two
phosphorylation events of the p46 and p54 isoforms of JNK/SAPK,
phosphorylation of JNK coupled by a rapid onset of JNK or p54
isoform expression, or if phosphorylation alters the capacity for
interacting proteins to occlude/expose the antibody recognition
site(s). For AKT, two distinct cellular populations that differed
from the unstimulated state appeared after PDGF stimulation of
Jurkat cells. The population of cells that had a higher AKT
fluorescence intensity existed in both a mono and bi-phosphorylated
state (FIG. 5A lower panel). The apparent AKT negative population
of PDGF stimulated cells presented minimal phosphorylation as
detected by the phospho-thr308 and the phospho-ser473 probes. It is
unlikely that total AKT levels rapidly decrease within the 10
minutes of PDGF stimulation since this was not observed in standard
western and kinase assays (see FIG. 1A) and thus we infer a new
protein binds there or a signal induced change in structure prevent
binding of the antibody.
[0238] These latter results lead us to believe that the changes in
subpopulations observed represent changes in the binding of
cellular proteins to the kinases. Thus, there are potential
pitfalls in the simultaneous use of antibodies to normalize
intracellular staining on the basis of a normalizing antibody--this
warrants caution in the interpretation of such data. However, the
results suggest that a series of antibodies, that recognize
different epitopes on the same protein, could both infer the
existence of cellular binding partners, map where they interact on
the target protein structure, and derive specific functional
correlations associated with such binding. We know of no other
technique that allows protein interactions to be mapped on
endogenous proteins in a cell-by cell analysis of subsets of cells
in complex populations.
SUMMARY
[0239] Utilizing multi-parameter flow cytometry, we demonstrate
that lymphocyte subsets can be distinguished based upon levels of
as many as five intracellular kinase activities. The power of the
approach can be appreciated not only in dissection of intracellular
signaling pathways, but presents for the first time the ability to
perform multiple kinase activity measurements in a single cell by
flow cytometry. Functional signaling dissection on a single cell
level could be applicable to rare cell subpopulations such as stem
cells or stem cell progenitors and can be extended to many systems
where the rarity of certain cellular subsets preclude isolation of
cells for in vitro functional characterization. The application of
these kinase specific probes is the following: (1) To obtain a
unique signaling profile for a stimulus to understand the biology
of various cellular processes (2) To monitor signaling mechanisms
in rare cell populations in the development, differentiation, or
maintenance of cellular fates, (3) The potential to utilize these
kinase probes (and others) in high-throughput FACS based screens
for pharmacological inhibitors of specific kinase activity within
mammalian cells, (4) the potential to temporally and spatially
resolve kinase activation cascades on a global scale, and (5) the
possibility that binding partners might be inferred before and
after stimulation with appropriate antibody sets. Development of
other intracellular kinase probes can contribute to the elucidation
of signaling networks and in combination with polychromatic flow
cytometry (11-color, 13 parameter) technology.sup.9 could aid an
understanding of the complexity of intracellular signals in the
immune system. Furthermore, the utility of these probes might be
extended to clinical settings to determine intracellular knase
activities for cells derived from diseased patients as a diagnostic
indicator of disease progression.
Experimental Procedures
[0240] Cell Culture and Primary cell Isolation Jurkat T cells were
maintained in RPML1640, 10% FCS 1% PSQ (10% fetal calf serum, 1%
penicillin-streptomycin (1000 units/ml and 2 mM L-glutamine PSQ).
NIH3T3 cells were maintained in DMEM (Dulbecco modified eagle
medium), 10% donar calf serum, 1% PSQ. For preparation of primary
cells, mononuclear cells were isolated from blood of healthy donors
(Stanford Blood Bank, Stanford, Calif.). Human peripheral blood
monocytes were obtained by Ficoll-plaque density centrifugation
(Amersham Pharmacia, Uppsala, Sweden) of whole blood and depletion
of adherent cells by adherence to plastic culture dishes. Isolated
cells were maintained in complete media. Magnetically activated
cell sorting (MACS, Miltenyl Biotech, Baraisch-Gladbach, Germany)
was used in some experiments as noted to enrich for CD3+ T cells by
negative isolation using combinations of CD16, CD14, CD44, HLA-DR,
or CD19 biotinylated antibodies (Dynal, Oslo, Norway) and
streptavidin-magnetic beads (Dynal, Oslo, Norway). Chemical and
biological agents used were either obtained form Sigma (St. Louis,
Mo.), Cell Signaling Technologies (Beverly, Mass.), Roche
Biochemicals (Indianapolis, Ind.), or Peprotech (Rocky Hill, N.J.):
ionomycin (1-.mu.M, Sigma), phorbal myristyl acetate (1 .mu.M,
Sigma), anisomycin (10 .mu.M, Sigma), PDGF 10 pg/ml or as indicated
(Roche Biochemicals), SB203580 (10 .mu.M, Cell Signaling
Technology), LY294002 (10 .mu.M, Cell Signaling Technology), U0126
(10 .mu.M, Cell Signaling Technobgy), Bisindolymaleimeide II (10
.mu.M, Sigma), Calyculin A (10 .mu.M, Sigma), staurosporine (1
.mu.M, Sigma), genistein (10 .mu.M, Sigma), IL-2 (10 pg/ml,
Peprotech), IL-3 (10 pg/ml, Peprotech), IL-1.alpha. (Roche
Biochemicals (10 pg/ml), epidermal growth factor (EGF, Roche
Biochemicals), lambda phosphatase and calf intestinal phosphatase
(CIP) (New England Biolabs, Beverly, Mass.), CD40L was a gift from
Dr. Strobl (Department of Molecular Pharmacology, Stanford
University). CD3 (OKT3) and CD28 endotoxin/azide free monoclonal
antibodies where from PharMingen (La Jolla, Calif.).
[0241] For serum starvation, Jurkat cells were deprived of serum
for 24 hours and were considered uninduced with respect to kinase
activity. Kinase activity inhibition was done with the appropriate
kinase inhibitor added 30 minutes prior to being stimulated by the
kinase activating agent. Stimulation by either kinase activating
agent or exogenous stimuli was performed for 30 minutes before
cells were prepared for flow cytometry. Stimulation of Jurkat cells
with PMA/Ionomycin was for 2 hours at 1 .mu.M. Stimulation of PBMC
was performed for 12 hours prior to 11-color analysis at 10 ng/ml
of indicated cytokine. Chemical agents were dissolved in DMSO
(Sigma), and uninduced cells received 0.1% DMSO carrier as control
treatment. UV treatment for samples in FIG. 1A was performed by
incubation under a UV light in a typical tissue culture hood for
the indicated time. Lambda phosphatase treatment (1000 units at
37.degree. C. for 15 min) and calf intestinal phosphatase treatment
(CIP, 50 U at 37.degree. C. for 15 min) was performed after FACS
permeabilization prior to intracellular staining.
Immunoblotting
[0242] Cell extracts were prepared by washing 2.times.10.sup.6
cells in ice cold PBS and harvesting in lysis buffer (20 mM Tris pH
7.5, 150 mM NaCl 1 mM EDTA 1 mM EGTA, 1% Triton X100, 2.5 mM
Na.sub.2PO.sub.4, 1 mM .beta.-glycerolphosphate, 1 mM Na3VO4, 1
ug/ml Leupeptin, 1 mM PMSF, protease inhibitor cocktail tablet
(Boehringer Mannheim, Basel, Switzerland). Extracts were
centrifuged 14,000 RPM for 5 min at 4c and cell lysates (20 g as
determine by BCA protein assay (Pierce, Rockford, Ill.) were
fractionated on 12% or 15% SDS-polyacrylamide gel electrophoresis
and transferred to PVDF membranes using standard procedures.
Antibodies used are indicated adJacent to blots and were purchased
from Cell Signaling Technologies) (Beverly, Mass.). Cell treatments
are indicated where appropriate.
Kinase Assays
[0243] Kinase activity assay protocol was similar for AKT, p38,
p44/42, JNK and substituted reagents used for respective kinase
assay is noted. All reagents used for kinase activity assays were
obtained from Cell Signaling Technologies (Beverly, Mass.). Kinase
activity was detected by immunoprecipitation of kinase AKT, p38,
p44/42, or JNK using immobilized AKT1G1 monoclonal antibody,
immobilized phospho-p38 MAPK monoclonal antibody, immobilized
phospho-p44/42 monoclonal antibody, or c-Jun fusion protein beads
respectively, from cells. Immobilized kinase was used in a kinase
assay with GSK3 fusion protein, ATF-2 fusion protein, Elk-1 fusion
protein, or c-Jun fusion protein beads respectively.
2.times.10.sup.6 NIH3T3 or 2.times.10.sup.6Jurkat cell were washed
twice in PBS and lists were incubated with immobilized kinase
antibody or beads (1:200) at 4.degree. C. with gentle rocking
motion for 2 hrs. Immunocomplexes were washed 4.times. with cell
lysis buffer and resuspended in 40 .mu.l kinase buffer (25 mM Tris
pH 7.5, 5 mM .beta.-glycerolphosphate, 2 mM DTT, 0.1 mM
Na.sub.3VO.sub.4, 10 mM MgCl.sub.2) supplemented with 200 .mu.M ATP
and 1 .mu.g of fusion protein (except for JNK activity assay, in
which ATP was sufficient to induce activation) for 30 min at
30.degree. C. Kinase reaction was terminated with SDS sample buffer
boiled for 5 min, and phosphorylation state of GSK3, ATF, EIK-1, or
cJun was detected by immunoblotting with phospho specific
antibodies phospho-GSK3.alpha..beta. (ser21/9), phospho-Elk-1
(ser383), phospho-ATF2 (thr71) or phospho-cJun (ser63) respectively
and visualized using ECL detection (Amersham). Immunoblots are
representative of 3 independent experiments.
Kinase Probe Generation
[0244] Antibody conjugation was done using standard procedures
(http://drmr.com.abcon) or by using protein-protein/protein-dye
crosslinking kits from Molecular Probes (Eugene, Oreg.).
Phospho-specific and non-phospho specific antibodies were from Cell
Signaling Technologies (Beverly, Mass.) or as indicated. Antibodies
conjugated were the following: phospho-AKT Ser473 monoclonal
anti-4E2, phospho p44/42 MAP Kinase (Thr202/Tyr204) monoclonal
antibody, phospho-TYK2 (Tyr1054/1055) antibody, phosho-p38 MAP
Kinase (Thr180/Tyr182) monoclonal antibody 28B10, phospho-PKC-PAN
substrate antibody, phospho-PKA-substrate, phospho-SAPK JNK (Thr183
Tyr 185) G9 monoclonal antibody, phospho-tyrosine monoclonal
antibody (P-tyr-100), p44/42 MAPK, p38 MAPK, JNK/SAPK, and
phosphoAKTthr308. Anti-TYK2 was obtained from Santa Cruz
Biotechnologies (Santa Cruz, Calif.). Phospho-PYK2 (pY402) antibody
and phospho-FAK (pY397) were obtained from Biosource (Carillo,
Calif.). Alexa-Fluor dyes (Alexa Fluor 350, Alexa Fluor 430, Alexa
Fluor 488, Alexa Fluor 546, Alexa Fluor 568, Alexa Fluor 594, Alexa
Fluor 633, Alexa Fluor 660 Alexa Fluor 680), Cascade Blue, Cascade
Yellow and Rphycoerythrin (PE) were purchased from Molecular Probes
(Eugene, Oreg.). FITC, Rhodamine, and Texas Red were purchased from
Pierce (Rockford, Ill.). Cy5, Cy5.5, Cy7 were obtained from
Amersham Life Science (Pittsburgh, Pa.). Tandem conjugate protocols
for Cy5PE, Cy5.5PE, Cy7PE, Cy5.5APC, Cy7APC can be found at
www.drmr.com/abcon. Quantitation of fluorescent probe conjugation
was assessed to determine degree of labeling and protocols
including dye spectral properties can be found at
www.metazoa.com/UPL3419. In general, probes used had [29] 2-9 moles
of fluorescent dye per mole of protein.
Flow Cytometry and FACS Analysis
[0245] Intracellular and [extracell.about.lar] extracellular
staining was initially performed as described
(www.metezoa.com\UPL3287) but modified. Approximately
1-10.times.10.sup.7 peripheral blood mononuclear cells were
obtained by magnetically activated cell sorting, treated with a
stimulatory condition for 12 hours, and prepared for flow
cytometry. Surface stained for 20 minutes, and divided into
aliquots for intracellular stain reagents (see below for details).
Intracellular staining was achieved by permeabilizing with
CytoFix/CytoPerm buffer (PharMingen, La Jolla, Calif.),
intracellular stained for 30 minutes on ice, and final resuspension
in 1% paraformaldehyde. Isotype control match antibodies were used
for stain controls. Purified antibodies to cell surface markers
listed in Table 1 in addition to the following where either
obtained from PharMingen (La Jolla, Calif.) or conjugated to the
indicated fluorophore in the Herzenberg laboratory (Department of
Genetics, Stanford University): CD69-APC, CD69-PE, CD4-FITC,
CD4-APC, CD4-PE, CD3-APC, CD3-PE, CD3-PERCP, CD19-FITC,
CD19-APC.
[0246] For each blood sample, PBMC were stained with all the
reagents in stain combination 4, 5, 6 (Table 1) except for FITC,
PE, Alexa 594, and APC. The stained cells were divided into
aliquots and then individually stained with different intracellular
cocktail combinations as depicted in combinations 4, 5, 6 (Table
1). Intracellular FACS staining requires mild cell fixation and
subsequent permeabilization. Though it has been possible to perform
intracellular stains by using a two-step antibody staining protocol
(primary plus conjugated secondary), optimal results were achieved
with a primary conjugated antibody. Furthermore, conjugates
comprised of phycobiliproteins such as phycoerythrin (PE) and
allophycocyanin (APC), required significant optimization of
permeabilization conditions perhaps because phycobiliproteins are
large and might contribute to background binding to intracellular
surfaces. For these reasons, the phospho-specific probes generated
using the Alexa-Fluor dye series were used in multi-label
experiments. In addition, several phospho-specific probes developed
for other kinase activities (phospho-PYK2, phospho-FAK, among
others) that recognize the phosphorylated form of these antibodies
in standard western blots lost their ability to recognize the
phosphoepitopes by FACS. This could be either due to the fixation
process altering the epitope recognized by the antibody, or the
epitope being occluded from antibody recognition in the protein's
native form. After extensive testing we determined that in general,
directly conjugated phospho-specific monoclonal antibodies
exhibited the greatest signal to noise ratio.
[0247] Single and four color flow cytometry data acquisition was
collected on a FACSCalibur machine (Beckton Dickinson, San Jose
Calif.) using CELLQuest software, analyzed and presented using
FlowJo software (Tree Star, San Carlos, Calif.). Data for four or
less colors are representative of 3 independent experiments of
10.sup.6 cells/sample and 50,000 events were collected and
calibrated using Calibrite beads (Becton Dickinson, San Jose
Calif.). 11-color data acquisition was collected on a modified
FACStarPlus (Becton Dickinson, San Jose, Calif.) connected to MoFlo
electronics (Cytomation, Fort Collins, Colo.). Data were collected
by FACSDesk software and compensated, analyzed, and presented using
FlowJo software. Data for 11-color flow cytometry collected a
minimum of 200,000 events.
Table 1
[0248] Top table shows single, 3, and 4 color combinations were
used for FIGS. 1 and 2A-D. The antibody-dye sets for these can be
found in rows 1, 2, and 3 above. The antibody-dye combinations are
grouped according to their excitation wavelength as determined by
the laser line applied during the experiment. 11-color staining
combinations (rows 4, 5, 6) were used to generate the data in FIGS.
2E-F, 3, 4, and 5. Regions left blank indicate no reagent used.
Conditions used ethidium monoazide bromide (EMA) to identify dead
cells by intercalating into DNA and forming a covalent adduct prior
to permeabilization of the cells. Serum underlays, as well as
forward and side scatter gating were used to physically remove and
identify dead cells, respectively (FIG. 4).
[0249] Bottom table illustrates Alexa fluorescent dye labeled
probes used in these experiments. The various kinases were
conjugated with one or more of 7 different Phospho-specific
antibodies labeled with Alexa dyes are referred in the above tables
as p-probe to indicate phospho specific probe was used in that
color. They were applied in the various stains in the top section
of Table 1 to allow for complementary dye combinations for
multiparameter analysis.
[0250] Table 2 shows agents used to induce and inhibit specific
kinase activity in serum starved Jurkat cells are
denote.sup.3,20-32. 24 hour serum starvation reduced background
phosphorylation significantly. Concentrations used other than those
depicted is stated where appropriate. See Methods for treatment
protocols.
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Rolli-Derkinderen, M. & Gaestel, M. p38/SAPK2-dependent gene
expression in Jurkat T cells. Biol Chem 381, 193-8. (2000). [0280]
30. Chini, C. C., Boos, M. D., Dick, C. J., Schoon, R. A. &
Leibson, P. J. Regulation of p38 mitogen-activated protein kinase
during NK cell activation. Eur J Immunol 30, 2791-8. (2000). [0281]
31. Sotsios, Y., Blair, P. J., Westwick, J. & Ward, S. G.
Disparate effects of phorbol esters, CD3 and the costimulatory
receptors CD2 and CD28 on RANTES secretion by human T lymphocytes.
Immunology 101, 30-7. (2000). [0282] 32. Vlahos, C. J., Matter, W.
F., Hui, K. Y. & Brown, R. F. A specific inhibitor of
phosphatidylinositol 3-kinase,
2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4 one (LY294002). J Biol
Chem 269, 5241-8. (1994).
Example 2
LFA-1 Functionally Contributes to T-Cell Activation and Polarized
Effector Cell Cytokine Production to a TH1 Profile
[0283] In this Example, using the methods and compositions of the
present invention, the present inventors (also referred to herein
as "we") demonstrate that LFA-1 stimulation by ICAM-2 functionally
contributes in activating human naive T-cells
(CD3.sup.+CD4.sup.4CD8.sup.-CD62L.sup.+CD45RA.sup.+CD28.sup.+CD27.sup.+CD-
11a.sup.dim) in the presence of CD3/CD28 co-stimulation as
determined by simultaneous multidimensional (33 parameters)
assessment of immunophenotype, phospho-protein signaling, cytokine
production, and transcriptional activity. Soluble ICAM-2 (sICAM-2),
upon interacting with LFA-1, initiated phosphorylation and release
of LFA-1 binding proteins cytohesin-1 and JAB1, which induced
activation of the p44/42 MAPK pathway and cJun respectively.
sICAM-2 enforced rapid kinetics of multiple active kinases (p44/42,
p38, JNK MAPKs, Ick, AKT, PLC.gamma.) when combined with CD3/CD28
stimulation, lowering the CD3/CD28 stimulus threshold by 10,000
fold as determined by activation markers CD25 and CD69.
CD3/CD28/LFA-1 signal integration resulted in enhanced nuclear
localization of NF-kB, Creb, Atf2, c-Fos, and c-Rel. These
conditions optimized T-cell activation as measured by IL-2
expression, NFAT, NF-kB, and AP-1 activity, and cell cycle
progression. Furthermore, the CD3/CD28/LFA-1 trio-stimulation
polarized naive human T cells towards a TH1 phenotype, with
CD3/CD28 stimulus favoring a TH2 phenotype. These results
demonstrate that ICAM-2 interaction with LFA-1 can functionally
contribute in T cell activation and differentiation.
[0284] In particular, this Example demonstrates that polychromatic
flow cytometry based on the methods and compositions of the present
invention allow for the rapid identification of specific lymphocyte
subsets with simultaneous measurement of multiple intracellular
kinase activities. This approach provides functional signaling
information on unique cellular processes, for example, T cell
activation, at the single cell level.
Introduction
[0285] T-cell activation is a multi-step process involving
integration of antigen receptor (TCR-CD3) signals with
co-stimulatory signals such as B7/CD28 (Croft and Dubey, 1997).
Engagement of the antigen-specific TCR-CD3 complex with a
recognized peptide-MHC complex on antigen-presenting cells (APC) is
necessary for in vivo T-cell activation. T-cell co-stimulatory
surface molecules CD28, CD2 (LFA-2), and their APC counter
receptors B7 (CD80-86), CD58 (LFA-3), initiate T cell activation
(Bjorndahl et al., 1989; Cefai et al., 1996; Cerdan et al., 1992;
Chambers and Allison, 1999; Lenschow et al., 1996). Adhesion
between T-cells and APCs is necessary for the formation of the
immunological synapse and is mediated by T-cell surface molecules
LFA-1 (CD11a/CD18) (de Fougerolles et al., 1991; Dustin et al.,
1989; Koopman et al., 1992) and the intercellular adhesion molecule
ligands (ICAMs).
[0286] In contrast to the extensive data available concerning
signals involved in TCR-CD3 and CD28 ligation, much less is known
about specific signals generated by adhesion mediated events
involved in T cell contact with APCs. However, there is evidence
that optimal proliferation of T-cells and enhancement of IL-2
production requires stimulation other than TCR-CD3 and CD28 that
results from adhesive interactions between costimulatory receptors
on T-cells and their counter ligands on APCs (Fine and Kruisbeek,
1991; Salomon and Bluestone, 1998; Simmons, 1995; Starling et al.,
1995; Zhang et al., 1997). Insect and fibroblast model systems
utilized to study T cell activation have demonstrated that
increasing antigen density by more than 10,000-fold fail to
initiate naive CD4+T cell proliferation or cytokine synthesis in
the absence of an ICAM/LFA-1 interaction (Abraham et al., 1999;
Ragazzo et al., 2001). In addition, it has also been observed that
the ICAM-1/LFA-1 interaction can promote the appearance of the
hyper-phosphorylated p23 form of the TCR .zeta. chain (Ragazzo et
al., 2001). Despite these and other observations that in
co-ligation with TCR-CD3, LFA-1/ICAM interaction can lead to
sustained intracellular calcium response, and increased inositol
phospholipid hydrolysis (van Seventer 1992; Wulfing 1998; Rovere
1996), the specific functional consequences for an LFA-1 mediated
"co-stimulatory" signal are not fully understood. Furthermore,
these latter studies downplay a suggestion by some that LFA-1/ICAM
interactions simply allow for longer TCR engagement and rather
suggested to us that the LFA-1/ICAM interaction is capable by
itself of initiating important intracellular signaling events.
[0287] Development of methodologies for intracellular
phospho-protein staining has allowed us to simultaneously monitor
multiple active kinases in up to 13 dimensions in single cells
(Perez and Nolan, 2002). Utilizing this in conjunction with surface
immunophenotyping, transcription factor nuclear profiling and
cytokine bead arrays, we observed that human naive T cells
(CD3+CD4+CD8-CD62L+CD45RA+CD11a.sup.dimCD27+CD28+) are optimally
activated upon CD3/CD28/LFA-1 stimulation. Co-stimulation with LFA
resulted in an over 10,000 fold higher sensitivity to CD3/CD28
co-stimulation. In characterizing the mechanism of this
observation, we demonstrate that cytohesin-1, an LFA-1 interacting
protein, is released and phosphorylated upon LFA-1 stimulation, and
mediates activation of the p44/42 MAPK pathway, correlated to
activation of several downstream transcriptional regulators. In
conjunction, JAB1, another interacting LFA-1 protein, is similarly
released and phosphorylated upon LFA-1 stimulation, leading to
c-Jun phosphorylation in the absence of JNK activity. The
integration of signaling pathways from CD3, CD28, and LFA-1
converge to mediate activation of multiple pathways (MAPKs, PKC,
Src kinases, and focal adhesion kinases) which enhanced NFAT,
NF-.kappa.B, and AP-1 activities, cell cycle entry, and expression
of IL-2, CD25, and CD69. Furthermore, the CD3/CD28/LFA-1 stimulus
polarized T cell differentiation towards a TH1 phenotype as
compared to the TH2 phenotype observed for a CD3/CD28 stimulus.
Thus, the additional LFA-1 signal contributes functionally to both
T cell activation and effector cell differentiation.
Results
[0288] ICAM-21LFA-1 Interaction Induces Release and Phosphorylation
of JAB1 and cytohesin-1
[0289] In a series of kinase profiling experiments we had observed
that a solubilized version of membrane-ICAM-2 (sICAM-2, see
Materials and Methods) induced activation of the p44/42 MAPK
through LFA-1 activation (Perez and Nolan, manuscript submitted)
that kinetically differed from CD3 or CD28 stimulation (data not
shown). It was also observed that LFA-1 stimulation induced c-Jun
phosphorylation in the absence of JNK activity (data not shown). We
therefore decided to investigate the functional differences of the
ICAM-2-induced signaling in human naive CD4+ T cells.
[0290] LFA-1 stimulation induced phosphorylation and nuclear
translocation of c-Jun, an effect that was additive with CD3/CD28
stimulation (FIG. 6A). Inhibition of JNK with the specific chemical
inhibitor SP600125 (Bennett et al., 2001) did not abrogate the
sICAM-2 induced cJun phosphorylation as determined by single cell
analysis (FIG. 6B, top panel). Recently, JAB1 has been identified
as an LFA-1 binding protein that mediated cJun phosphorylation in
the absence of JNK activity (Bianchi et al., 2000). Intracellular
delivery of .alpha.-JAB1 antibodies (see Materials and Methods),
abrogated LFA-1 induced c-Jun phosphorylation (FIG. 6B, bottom
panel). Visualizing both cytohesin-1 and JAB1 in T cells revealed
membrane delocalization upon LFA-1 stimulation (FIG. 6C). Cells
artificially loaded with anti-JAB1 exhibited membrane delocalized
JAB1, in the absence of stimulus, and exhibited no change in
cytohesin-1 localization (FIG. 6C). Thus, antibody disruption of
JAB1 from LFA-1 blocked the LFA-1 induced c-Jun phosphorylation,
indicating that the receptor-ligand interaction was necessary for
receptor signaling to c-Jun through JAB1.
[0291] We assessed if modifications to cytohesin-1 and/or JAB1
occurred upon LFA-1 stimulus. It was observed that LFA-1
stimulation induced threonine phosphorylation of cytohesin-1 and
serine phosphorylation of JAB1, an effect that was not observed
after CD3 stimulation (FIG. 6D). We investigated if JAB1 or
cytohesin-1 was responsible for LFA-1 induced p44/42 MAPK activity
as previously observed (Reviewers please see attached manuscript)
by using intracellular delivery of antibodies and/or peptides to
functionally modulate respective protein's signaling. Intracellular
delivery of an .alpha.-cytohesin-1 antibody to the C-terminal
blocked the LFA-1 induced p44/42 MAPK activity, a property shared
by intracellular delivery of a peptide corresponding to the
cytohesin-1 C-terminal (FIG. 6E). Neither intracellular delivery of
.alpha.-JAB1 or an IgG control affected the LFA-1 induced p44/42
MAPK activation (FIG. 6E). In contrast, intracellular delivery of
antibodies directed at the cytohesin-1 N-terminal induced p44/42
MAPK activation (FIG. 6E). These results are supported by the
observation that the N-terminal of Cytohesin-1 contains the domain
that directly interacts with LFA-1 (Geiger et al., 2000; Kolanus et
al., 1996). Therefore, the dissociation of cytohesin-1 from LFA-1,
here induced by antibodies to the N-terminal, led to dissociation
of the LFA-1/cytohesin interaction in vivo and consequently
activated the p44/42 MAPK. The intracellular delivery of antibodies
against JAB1 were capable of interfering with JAB1 binding and cJun
phosphorylation whereas intracellular delivery of a corresponding
C-terminal sequence of cytohesin-1 blocked LFA-1 induced p44/42
MAPK activity. Thus, intracellular delivery of antibodies can
functionally modulate protein function and suggest that distinct
signaling pathways are coupled to cytohesin-1 and JAB1, two LFA-1
interacting proteins that were mobilized upon stimulus.
Integration of CD3, CD28, and LFA-1 Signaling Supercede Signaling
Induced by CD3/CD28 Co-Stimulation
[0292] We had performed kinetic analyses of multiple active kinases
by flow cytometry to CD3, CD28 and LFA-1 stimulation (FIG. 6F).
Since activation rates varied for individual stimuli tested (data
not shown), we decided to study the combinations of CD3/CD28 versus
CD3/CD28/LFA-1 in phospho-protein based analyses. We developed a
phospho-protein array by spotting a combination of 96 phospho and
non-phospho specific antibodies for differential analysis of
signaling proteins induced by CD31CD28 versus CD3/CD28/LFA-1
stimulation in purified human naive CD4 T cells. (FIG. 7A).
Enrichment of primary na ve T cells was performed by magnetically
activated cell sorting using markers CD8, CD19, CD16, CD14, HLA-DR,
and CD44 to remove cytotoxic T cells, B cells, NK cells,
macrophages, and activated T cells from human PBMC respectively.
After lysis of cells, equivalent protein lysates were labeled with
Alexa532 or Alexa680, and the samples were co-hybridized to the
array. The fluorescent intensities for both dyes were read by a
fluorescent plate reader, and the log ratios were computed to
obtain a differential signal between the stimulations tested. The
fluorescent intensities for both channels is plotted on an XY
coordinate grid (FIG. 7A). The fold induction in phosphorylation,
as determined by the log ratios and is displayed on the plotted
fluorescence intensity coordinates yielded for CD3/CD28 and
CD3/CD28/LFA-1 stimulation (FIG. 7A). Analysis identified a 2-5
fold phospho-induction of MAPK kinases (p44/p42, p38, JNK, raf,
mek1/2, mek3/6, rsk, raf), src related kinases (src, pyk2), and
integrin signaling kinases (FAK), among others (FIG. 7A). Internal
reference controls of non-phospho proteins (p44/42 MAPK, p38 MAPK,
JNK, mek1/2, mek3/6, rsk, raf, src, pyk, fak) for these kinases
showed induction in the range of 0.8-1.5 fold and were not expected
to change significantly at the endpoint tested (data not shown).
Antibodies against structural proteins (actinin, actin, tubulin)
were used to verify equivalent protein quantities (data not shown).
These results indicated that the triple CD3/CD28/LFA-1 stimulation
induced overall phosphorylation of multiple proteins (kinases and
transcription factors) to a greater extent than CD3/CD28
stimulation.
[0293] T cell activation requires cell cycle entry and subsequent
cell proliferation, which is an important downstream outcome of
cellular activity induced by signal transduction pathways. Cellular
proliferation and concomitant cell cycle initiation was measured by
flow cytometry staining for DNA content and Ki-67 proliferation
antigen. FIG. 7C demonstrates cell cycle entry after 12 hours in
CD3/CD28/LFA-1 stimulus as noted by >2n DNA content and
expression of nuclear antigen Ki-67. Proliferation associated
antigen Ki-67 and total DNA content quantify the cells residing
within different cell cycle phases (Endl et al., 2001). As shown in
FIG. 7C, CD3/CD28/LFA-1 stimulation invokes far greater percentages
of cells in the S and G2/M phase than CD3/CD28 stimulation. Thus, a
more profound cell cycle entry is observed in CD3/CD28/LFA-1 vs.
CD3/CD28 stimulated cells.
Simultaneous Assessment of Immunophenotype, Intracellular
Signaling, and Cellular Function in Single Cells
[0294] We were interested in determining the contribution LFA-1
signaling possessed for naive T cell activation in conjunction with
CD3/CD28 co-stimulation. As evidenced below, we multiplexed
magnetically activated cell sorting, 13-dimensional multiparameter
flow cytometry (surface immunophenotyping, intracellular production
of active kinases and cytokines) with profiling of secreted
cytokines (cytometric bead arrays) and nuclear localized
transcription factor profiling to obtain a multidimensional
assessment of T cell activation and effector cell function. FIG. 8
represents a flow diagram of the various techniques multiplexed for
functional analysis and these data sets were cross-referenced for
correlatives of cell surface receptor activation, intracellular
signaling, and functional outcomes.
[0295] Enrichment of primary naive T cells was performed by
magnetically activated cell sorting (MACS negative depletion) using
markers CD8, CD19, CD16, CD14, HLA-DR, and CD44 to remove cytotoxic
T cells, B cells, NK cells, macrophages, and activated T cells from
PBMC respectively (FIG. 8). We utilized 8 markers to identify naive
human T cells
(CD3.sup.+CD4.sup.+CD8.sup.-CD45RA.sup.+CD62L.sup.+CD11a.sup.dimCD27.sup.-
+CD28.sup.+). CD3, CD28, and LFA-1 single and combined stimulation
was performed on enriched non-activated T cells. Mature naive T
cells, as determined by 8 immunophenotypical markers, were analyzed
for CD69, CD25, and IL-2 expression, simultaneously by
13-dimensional flow cytometry as expression of these markers
defines an activated T cell (Yu et al., 2000; Zola, 2000). Flow
cytometric kinetic experiments identified signaling pathways as
tested for individual stimulation to peak and subside within 0.5-4
hours post stimulation and were unique to each phospho-kinase
tested (data not shown). We analyzed samples at 8, 12, and 24 hours
post stimulation to observe the phospho-levels of stimulated cells.
Post 8 hour stimulations, CD3 stimulation alone resulted in minor
CD69 activation and low levels of phospho-p44/42 (FIG. 8, panel I).
CD3/CD28 co-stimulation induced more CD69 activation, but the
levels of phospho-p44/42 MAPK returned back to a basal level (FIG.
8, panel II). However, optimal activation of naive T cells
(CD3.sup.+CD4.sup.+CD8.sup.-CD45RA.sup.+CD62L.sup.+CD11a.sup.dimCD27.sup.-
+CD28.sup.+) was observed in the presence of LFA-1 plus CD3/CD28
stimulation at 8 hours (FIG. 8, panel III). sICAM-2 gave rise to
some phospho-p44/42 induction and intermediate CD69 induction
whereas CD28 stimulation alone was incapable of inducing either
marker to express (FIG. 8B-C). At this timepoint, CD25 and IL-2
expression was observed for the CD3/CD28 stimulation, but the
levels were greater in the CD3/CD28/LFA-1 stimulated cells (FIG. 8,
panel III). Thus, these results suggested a signaling threshold was
a consequence of 3 surface mediated signal integration for CD3,
CD28, and LFA-1.
[0296] We performed titration and kinetic analyses for stimulus
induced T cell activation as measured by IL-2 intracellular
production and CD25 and CD69 surface expression by flow cytometry.
The mean fluorescent intensities (MFI) of the intracellular IL-2
detection were computed, and the log ratio of the
MFI.sub.stimulated to the MFI.sub.unstimulated was calculated and
plotted as a function of the concentrations of the titrations for
the stimulants used (both for single and the various ratios for the
combined stimulants (FIG. 9)). A fluorescence intensity gradient
was applied to the range of values to visually plot the differences
(FIG. 9). At 6 hour stimulation, titration of LFA-1 and CD3/CD28
stimulation increased production of intracellular IL-2, depicting a
threshold for IL-2 production at 0.1 .mu.g/ml of a 1:1:1 ratio of
CD3/CD28/LFA-1 stimulation (FIG. 9A, right panel).
[0297] Similar levels of CD3 and CD28 titrations showed lower
levels of detected intracellular IL-2 (FIG. 9A, left panel). Higher
levels than 0.1 .mu.g/ml of CD3/CD28/LFA-1 demonstrated a linear
response in concentration of stimulus to that of IL-2 production
(FIG. 9A). Levels of inducer as high as 10 .mu.g/ml of CD3/CD28 did
not produce the same intracellular levels of IL-2 after 6 hr
CD3/CD28/LFA-1 stimulation (FIG. 9A). Varying the ratio of either
CD3 or CD28 up to 10,000 fold higher in the CD3/CD28/LFA-1
combination did not result in increased levels of intracellular
IL-2 (data not shown). Therefore, ratiometric titration analyses
indicates that the LFA-1 signal contribution cannot be compensated
by increased CD3 or CD28 stimulation.
[0298] At 6 hr stimulation, 10,000 fold less CD3/CD28/LFA-1
stimulus was necessary than in CD3/CD28 costimulation for similar
expression of CD69 and CD25 (FIG. 9B). After 6 hrs of
CD3/CD28/LFA-1 stimulation we observed detectable secreted IL-2,
contrasting the 12 hrs necessary for first detection of CD3/CD28
mediated IL-2 secretion (data not shown). At 12 hrs post
stimulation, extracellular IL-2 after CD3/CD28/LFA-1 stimulation
was reflected by significant production of intracellular IL-2 and
correlated with enhanced CD69 expression (FIG. 9C). Furthermore,
CD25 expression is maintained in the CD3/CD28/LFA-1 stimulated T
cells at 48 hours, contrasting to a decrease observed in the
CD3/CD28 stimulated cell population (FIG. 8B). Thus, the LFA-1
stimulus positively contributes to overcome the threshold of IL-2
production, allowing T cells to become activated more proficiently
and with considerably enhanced longevity.
Stimulus Through LFA-1 Contributes to Transcription Factor Nuclear
Translocation and Activity
[0299] Transcription factor nuclear localization and activation
profiling was performed in single CD3, CD28 and LFA-1 stimulations,
as well as CD3/CD28 vs. CD3/CD28/LFA-1 stimulation. Luciferase
reporter constructs were used to verify NFAT, NF-.kappa.B, and AP-1
activities. CD3/CD28/LFA-1 stimulus presented higher fold
inductions of NFAT, NE-.kappa.B, and AP-1 transcriptional activity
than CD3 or CD3/CD28 stimulation (FIG. 10A). Nuclear extracts of
stimulated naive CD4 T cells were bound to 96-well plates spotted
with consensus sequences to the transcription factors NF-.kappa.B
p65, NF-.kappa.B p50, cFos, CREB, aft2, and cRel. Detection of
bound transcription factors was performed by standard ELISA
techniques. Stimulation to CD3, CD28, and LFA-1 induced distinct
profiles of nuclear localized transcription factors (FIGS. 10D-E).
CD3/CD28 stimulus induced nuclear localization of all transcription
factors tested here, with somewhat higher levels detected for the
CD3/CD28/LFA-1 stimulus (FIG. 10B). The presence of the LFA-1
stimulus was slightly additive with CD3/CD28 in enhancing the
levels of nuclear localized transcription factors. Titration
experiments of NFAT activity verified that the LFA-1 signaling
cannot be compensated for by increased concentrations of CD3/CD28
(FIG. 10C), results consistent with the expression of IL-2 (see
FIG. 9A). Thus, the addition of the LFA-1 signaling integrates with
that of CD3 and CD28 co-stimulation to enhance gene expression of
at least the T cell transcription activities tested here.
LFA-1 Stimulation in the Presence of CD31CD28 Polarizes T Cell
Differentiation Towards a TH1 Phenotype
[0300] We performed titration experiments of both CD3 vs. CD28 and
CD3/CD28 vs. LFA-1 stimulation and monitored intracellular
production of IL-4 and INF.gamma., Activated T cells, differentiate
to either TH1 or TH2 effector T cells and can be preferentially
directed towards one pathway by cytokines or additional stimuli
(Asnagli and Murphy, 2001; Moser and Murphy, 2000). Effector cells
can be identified by their cytokine secretion profile. TH1 cells
are characterized by high IFN.gamma. and low IL-4, whereas TH2
cells are characterized by high IL-4 and low IFN.gamma. (Murphy et
al., 2000). Computing the ratio of the median fluorescence of
IL-4/IFN.gamma. demonstrates that the LFA-1 stimulus, at all
concentrations tested, favors a low IL-4/IFN.gamma. ratio (FIG.
11). This is consistent with the TH1 phenotype. In the absence of
the LFA-1 stimulus, CD3 and CD28 titrations favored a TH2
phenotype.
[0301] We used cytometric bead arrays to assess the secretion of
IFN.gamma., IL-10, IL-2, IL-4, IL-5, and TNF.alpha., in naive T
cells after 24 hours stimulation. The combination of CD3/CD28
presented high levels of IL-4, and low levels of IL-5, and IL-10.
This contrasted CD3/CD28/LFA-1 stimulation which displayed similar
levels of IFN.gamma., but significantly lower levels of IL-4 (FIG.
12). The triple stimulation reported elevated levels of IL-5 and
IL-10, with similar levels of IL-2 at 24 hours (FIG. 12). Neither
stimulation reported elevated levels of TNF.alpha. (FIG. 12) and
this effects were not observed in single stimulated cells (FIG.
10E). Thus, the stimulation by LFA-1 polarizes T cell
differentiation toward a TH1 phenotype in the presence of CD31CD28
stimulation.
Discussion
[0302] The work presented demonstrates that the ICAM-2/LFA-1
interaction contributes a distinct signal to CD3/CD28
co-stimulation and leads to rapid and optimal naive T cell
activation. Furthermore, it demonstrates that this accessory
stimulation can, together with CD3 and CD28 and in the absence of
additional signals, polarize T cell differentiation towards an
apparent TH1 phenotype. Although it is expected that T cell
signaling integrates numerous additional signals in the native
environment, this finding suggests strongly that ICAM-2 induced
LFA-1 signaling can be an important determinant of phenotypic
outcomes in naive T cell maturation.
[0303] Initiation of T cell activation requires cell-to-cell
contact, an adhesion process primarily mediated by Leukocyte
Function-Antigen 1 (LEA-1). Adhesive events involved in T cell
contact have largely been unrecognized as transducing signals that
may enhance T cell functions. However, there is increasing evidence
for the importance of adhesion mediated events in optimal T cell
activation (Neeson et al., 2000; Somersalo et al., 1995; Wulfing et
al., 1998). Model systems of T cell stimulation using insect or
fibroblast transfected cells report ICAM/LFA-1 interactions to be
necessary for T proliferation (Damle et al., 1992a; Damle et al.,
1993; Damle et al., 1992b; Damle et al., 1992c; Deeths and Mescher,
1999). We utilized a solubilized form of a normally surface-bound
ligand of LFA-1, ICAM-2, to study the contribution of LFA-1
signaling to naive T cell activation as ICAM-2 was able to mediate
the active form of LFA-1 and induce a calcium influx (characterized
in Perez and Nolan manuscript submitted[, reviewers please see
manuscript in Appendix]). We report here that two LFA-1 binding
proteins, JAB1 and cytohesin-1, are released, and subsequently
phosphorylated upon ICAM-2 binding. Utilizing intracellular
delivery of specific antibodies/peptides towards JAB1 and
cytohesin-1, these LFA-1 interacting proteins mapped to distinct
signaling pathways upon stimulation.
[0304] Cyohesin-1 is a guanine exchange factor that has recently
been identified to be phosphorylated by PKC.delta. in vitro (Dierks
et al., 2001) and enhances LEA-1 mediated leukocyte adhesion in T
cell lines (Weber et al., 2001). Recently, a study identified the
human herpesvirus 8 protein kaposin A as capable of mediating
signaling by recruitment of cytohesin-1 and that a cytohesin-1
mutant (defective in guanine nucleotide exchange) was defective in
p44/42 MAPK activation (Kliche et al., 2001). Interestingly,
antibodies and a peptide directed to cytohesin-1's C-terminal (SEC7
domain), which contain the PKC consensus sites to threonine,
blocked cytohesin-1 signaling to p44/42 MAPK. JAB1 another LFA-1
integrin binding protein, contains PKC serine consensus sites by
sequence analysis, and has been identified as a mediator of cJun
phosphorylation and AP-1 activity in cell culture models (Bianchi
et al., 2000). Therefore these studies corroborate the direct
observation that JAB1 and cytohesin-1 are involved in signaling
upon LFA-1 stimulation in naive CD4 T cells.
[0305] Multidimensional analysis of LFA-1 signaling events, in
conjunction with CD3/CD28 stimulation, indicated that T cell
activation was optimal upon triple stimulation. Differential
phospho-protein analysis suggested that LFA-1 signaling induced
phosphorylation of many signaling events. The integration of these
signaling events mediated by LFA-1 in addition to CD3/CD28
costimulation is exemplified by the enhanced NFAT, NF-.kappa.B, and
AP-1 activities. The presence of LFA-1 signaling lowered the
threshold for IL-2, CD25, and CD69 expression (see FIG. 9) and
initiated cell cycle progressions. Furthermore, the levels of
nuclear translocated transcription factors as tested were greater
in the CD3/CD28/LFA-1 stimulus vs. CD3/CD28, demonstrating the
result of multiple kinase cascades. However the global analysis of
transcriptional activity is expected to yield insights into the
consequences of signal integration for factors not tested here as
phosphorylation of other transcription factors, namely dun, Creb,
Rsk, JNK, p44/42, and elk were also observed (see FIG. 7A).
[0306] Consequences of the LFA-1 integrin signaling included
kinetically enhanced naive T cell activation, lowering of the
stimulus threshold for T cell activation, and apparent polarization
of T cells to favor a TH1 phenotype, as determined by low IL-4 and
high IFN.gamma. levels. Of significance, T cell lines expressing a
constitutively active LFA-1 respond to sub-threshold stimuli
(Kaplan et al., 2000 (Damle et al., 1993) and blocking LFA-1/ICAM
interactions has been demonstrated to favor TH2 cytokine production
(Salomon and Bluestone, 1998). Therefore these results reconcile
with the evidence provided here that LFA-1 plays an active role in
T cell activation in addition to its adhesive properties. Based on
these observations, it is predicted that LFA-1 knockout mice, will
not only have impaired immune responses, but will be deficient in
the ability to surmount an inflammatory response or recover from
infections necessitating a TH1 response for clearance. Studies
utilizing CD18 knockout mice, the .beta. 2 integrin of LFA-1, do
indeed show impaired responses in a delayed-type hypersensitivity
(DTH) inflammation model (Grabbe et al., 2002), as well as a defect
in the induction of peripheral immune responses
(Scharffetter-Kochanek et al., 1998). Thus, LFA-1 is important for
in vivo TH1 responses.
[0307] In conclusion, LFA-1 contributes significantly to naive T
cell functionality as demonstrated by multiple independent assays.
Most importantly, it greatly potentiates CD3/CD28 costimulation
allowing for T cell maturation (as measured by CD69/CD25
expression, IL-2 secretion and progression to the S+G2/M phases of
the cell cycle. Under the defined circumstances it also appears to
contribute to commitment decisions as measured by the enhanced
expression of TH1 cytokines. Underlying these outcomes we
correlated these results with stimulation of multiple transcription
factors and kinases, such as p44/p42, known to play roles in
expression of these genes. Inhibition of LFA-1 by small molecules
has also shown efficacy in various inflammation murine models
although the molecular mechanisms for these observations remain
unknown. The small molecule LFA-1 antagonist BIX 642, inhibited the
DTH response in a trans-vivo DTH model (Winquist et al., 2001).
Recently, an oral LFA-1 inhibitor LFA703 suppressed the
inflammatory response in a murine model of peritonitis
(Weitz-Schmidt et al., 2001). Furthermore, Leukocyte Adhesion
Deficient (LAD) patients, a disease in which CD18 is either mutated
or missing, display severe and recurrent bacterial infections (Hogg
et al., 1999; Lipnick et al., 1996), in addition to LAD afflicted
children having increased risk for infection of pseudomonoas
aerguinos (Pollard et al., 2001), an infection typically cleared by
a TH1 response (Fruh et al., 1995; Moser et al., 2002). Therefore,
the clinical manifestations reported in both LAD patients and LFA-1
knockout mice can validate the physiological significance of
LFA-1's signaling role demonstrated here in T cell activation and
effector cell differentiation. We expect, given our current
studies, that LFA-1 signaling will be further implicated in
important immune cell regulatory events.
Materials and Methods
Immunological and Chemical Reagents
[0308] The following phospho-antibodies (p-Ab) were obtained from
Cell Signaling Technologies (CST): p-Raf1 (Ser259), p-MEK1/2
(Ser217/221), p-p44/42 MAP kinase (Thr202/Tyr204), p-p44/42 MAPK
(Thr202/Tyr204) mAb, p-Elk-1 (Ser383), p-p38 MAP kinase
(Thr180/Tyr182), p-cJun (S63), non-phospho specific antibodies to
the above proteins were also obtained from CST. Anti-Ki-67 mAb
(Transduction Laboratories). All surface antibodies, cytokine
antibodies, and isotype controls were obtained from PharMingen:
CD3, CD4, CD8, CD69, CD25, IL-2, IL-4, IFN.gamma. on
FITC/PEIPerCp/APC. Alexa-Fluor dyes (350, 430, 488, 532, 546, 568,
594, 633, 660, 680), Cascade Blue, Cascade Yellow and
R-phycoerythrin (PE) were purchased from Molecular Probes (Eugene,
Oreg.). FITC and Texas Red were purchased from Pierce (Rockford,
Ill.). Cy5, Cy5.5, Cy7 were obtained from Amersham Life Science
(Pittsburgh, Pa.). Tandem conjugate protocols for Cy5PE, Cy5.5PE,
Cy7PE, Cy5.5APC, Cy7APC can be found at www.drmr.com/abcon.
Antibodies to CD62L, CD28, CD27, CD45RA, CD11a, CD3, CD4, CD8,
IL-2, IL-4, IFN.gamma. (PharMingen) were conjugated to FITC, PE,
Cy5PE, Cy5.5PE, Cy7PE, Cy5.5APC, Cy7APC, cascade blue, cascade
yellow, or alexa fluor dyes as needed. Quantitation of fluorescent
probe conjugation was assessed to determine degree of labeling and
protocols including dye spectral properties can be found at
www.metazoa.com/UPL3419. In general, alexa conjugates used had 2-12
moles of fluorescent dye per mole of protein. The following
antibodies were obtained from varying vendors: CD102-FITC (Research
Diagnostics), anti-rabbit IgG HRP (CST), anti-mouse/rabbit Alexa
488/568/633 (Molecular Probes). Anti-JAB1, anti-cytohesin-1
C-terminal cytohesin-1 peptide, and anti-mouse IgG HRP (Santa Cruz
Biotechnologies). Protein and chemical reagents used: DMSO, phorbol
myristelated acetate (PMA) ionomycin, phytohemmagluttin A (PHA),
propidium iodide (PI) RNASE (Sigma). U0126, PD98059, SB600125
(Calbiochem). Anti-CD3 (OKT3, NA/EN) and anti-CD28 mAb (NA/NE,
PharMingen). ICAM-2-FC was purchased from Genzyme.
Cell Culture and Primary Cell Isolation
[0309] Jurkat T-cells were maintained in RPMI-1640, 10% FCS, 1%
PSQ. Cells were maintained at 5% CO.sub.2/37.degree. C. humidified
incubator and serum starved 12 hours for phospho analysis. For
preparation of primary cells, mononuclear cells were isolated from
blood of healthy donors (Stanford Blood Bank, Stanford, Calif.).
Human peripheral blood monocytes were obtained by Ficoll-plaque
density centrifugation (Amersham Pharmacia, Uppsala, Sweden) of
whole blood and depletion of adherent cells by adherence to plastic
culture dishes. Isolated cells were maintained in complete media.
Magnetically activated cell sorting was to enrich for naive CD4 T
cells by negative isolation using combinations of CD16, CD14, CD44,
HLA-DR, CD8 or CD19 biotinylated antibodies (Dynal, Oslo, Norway)
and streptavidin-magnetic beads (Dynal, Oslo, Norway).
Immunoprecipitations and Immunoblotting
[0310] Cell extracts were prepared by washing 2.times.10.sup.6
cells (treated as indicated) in ice cold PBS and harvesting in
lysis buffer (20 mM Tris pH 7.5, 150 mM NaCl 1 mM EDTA 1 mM EGTA,
1% Triton X-100, 2.5 mM Na.sub.2PO.sub.4, 1 mM
.beta.-glycerolphosphate, 1 mM Na.sub.3V0.sub.4, 1 .mu.g/ml
Leupeptin, 1 mM PMSF, protease inhibitor cocktail tablet
(Boehringer Mannheim). Extracts were centrifuged 14,000 RPM (5 min,
4.degree. C.) and 10 .mu.g (BCA protein assay (Pierce)) were
immunoblotted using standard procedures. Immunoprecipitations (IP)
were pre-cleared with protein A/G plus-agarose beads, incubated
with primary ab (1 h), protein A/G plus-agarose beads (1 h) and
washed 4.times. with lysis buffer. Blots were incubated with the
indicated antibodies and developed using ECL (Amersham).
Flow Cytometry and FACS Analysis
[0311] Intracellular and extracellular staining was performed as
described for phospho-staining (Perez and Nolan, 2002).
Approximately 1-10.times.10.sup.7 peripheral blood mononuclear
cells (unactivated CD4+ T cells) were obtained by magnetically
activated cell sorting (negative isolation), treated with a
stimulatory condition for indicated time, and prepared for flow
cytometry. Brefaldin A (10 .mu.M) was added for intracellular
cytokine detection for 6 hours (or as indicated). Isotype control
match antibodies were used for stain controls. Kinetic analyses was
done on synchronized 96-wells and directly fixed as described
(Perez and Nolan, Submitted). Four or less color flow cytometry
data acquisition was collected on a FACSCalibur machine (Beckton
Dickinson, San Jose Calif.) using CELLQuest software, analyzed and
presented using FlowJo software (Tree Star, San Carlos, Calif.).
Data for four or less colors are representative of 3 independent
experiments of 10.sup.6 cells/sample and 50,000 events were
collected and manually calibrated. 11-color data acquisition was
collected on a modified FACStarPlus (Becton Dickinson, San Jose,
Calif.) connected to MoFlo electronics (Cytomation, Fort Collins,
Colo.). Data were collected by FACS-Desk software and compensated,
analyzed, and presented using FlowJo software. Data for 11-color
flow cytometry collected a minimum of 200,000 events. Cytometric
bead arrays (CBA) were from PharMingen. Ratios of intracellular
flow cytometric measurements were calculated from the following
equation where MFI equals mean fluorescent intensity: Log
[(MFI.sub.experimental-MFI.sub.isotype
mAb)/(MFI.sub.control-MFI.sub.isotype mAb)]. Values were then
designated a color intensity of two chosen colors to depict high
and low, and displayed where appropriate.
Phospho-Protein Arrays
[0312] Protein A coated 96 well plates were coated with phospho and
non-phospho specific antibodies (1 .mu.g/ml) for 1 hr. Plates were
washed twice with PBS, and antibodies were covalently coupled with
dissuccimidyl succinate as suggested by manufacturer (Pierce).
Plates were washed three times (PBS) and blocked with 4% BSA (in
PBS, 30 min). Protein samples from stimulated CD4+ naive T cells
were quantified and equivalent amounts conjugated to either
succimydyl ester reactive Alexa 532 and 680 dyes in 0.1 M pH8.0
sodium bicarbonate. After 1 hr the reactions were quenched (100
.mu.M Tris pH 8.0) and washed in centricon YM-10 spin columns.
Labeled protein samples were resuspended in PBST (plus 1% BSA).
Plates were hybridized with 30 .mu.g of Alexa532 and Alexa680
conjugated protein samples for 1 hr, 25.degree. C. Plates were
washed three times in PBST (PBS, 0.1% Tween-20) and three times in
PBS. Fluorescent intensities were detected using a Molecular
Devices Gemini Xs machine and fold induction was computed as the
log ratio of the mean fluorescent intensities (MFI) of
CD3/CD28/LFA-1 to CD3/CD28 stimulation, calculated from the
following equation: Log.
Nuclear Transcription Factor profiling
[0313] Mercury TransFactor kits (Clontech) spotted for consensus
sequences for NF-.kappa.B p50, NF-.kappa.B p65, c-Rel, c-Fos, CREB,
and ATF2 were used to hybridize transcription factors from nuclear
extracts of 1.times.10.sup.7 stimulated CD4+ naive T cells
(prepared as suggested by manufacturer). Detection of bound protein
to DNA complex was made by standard ELISA methods.
Laser Scanning Confocal Microscopy
[0314] Cells were treated as indicated and adhered to poly-L-lysine
(Sigma) coated sterilized coverslips (10 mg/ml, 30 minutes) by mild
centrifugation (1000 RPM, 10 minutes), washed twice in phosphate
buffered saline pH 7.4 (PBS) and fixed in 2.7% paraformaldehyde (in
PBS). Cells were stained as described for flow cytometry: (primary
at 0.1 mg/ml, secondary at 1:1000 dilution, in 4% FCS, with several
washing steps in between). Stained coverslips were mounted onto
glass slides with Prolong Antifade reagent (Molecular Probes) and
visualized using a Zeiss laser scanning confocal microscope 510.
Images were acquired using Zeiss LSM510 software and compiled using
Adobe Photoshop 6.0.
Intracellular Delivery of Antibodies/Peptides
[0315] Antibodies were buffer exchanged into PBS by spin dialysis
(centricon YM-100 spin columns) and mixed in 1:20 ratio of Fugene
(Roche) for 30 min. Liposome/antibody complex was mixed with
1.times.10.sup.5 cells in 50 .mu.L, serum free media for 1 hr.
Cells were washed twice (RPMI/4% FCS) and used for cellular assays
within 2-4 hrs. Transfection efficiencies using FACS analysis of
IgG-FITC was 30-40%.
Reporter Gene Assays
[0316] Jurkat cells were transfected with 5 .mu.g of NF-.kappa.B
driven luciferase reporter gene (gift of S. Kinoshita, Stanford
University) or AP-1 driven luciferase reporter gene (gift of J. F.
Fortin, Stanford University) using Fugene 6 reagent (Boehringer
Mannheim). NFAT-luciferase transfected cells were a gift of J. F.
Fortin. Twenty-four hours after transfection, cells were stimulated
as indicated for 6 hr at 37.degree. C. Luciferase activity was
analyzed in cell lysates of 1.times.10.sup.4 cells (Promega).
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Example 3
ICAM-2/LFA-1 Activates p44/42 MAPK Through PYK2 and SYK
[0362] In this Example, using the methods and compositions of the
present invention, the present inventors (also referred to herein
as "we") demonstrate that Leukocyte Function Antigen-1-(LFA-1) was
found to activate the RAS/RAF/MEK/MAPK cascade upon engagement with
ICAM-2. Dissection of the signaling pathway in revealed the
ICAM-2/LFA-1 interaction depended on both PYK2 and SYK tyrosine
kineses. Both PYK2 and SYK were found to associate with LFA-1 only
after interaction with ICAM-2 and were rapidly re-distributed to
the plasma membrane with concomitant phosphorylation of PYK2 and
SYK as revealed by biochemical analysis and confocal microscopy.
Chemical genetic approaches identify an LFA-1 mediated signal to
phosphorylate PYK2, with subsequent signal relay to SYK to be
contingent on PKC and PLC.gamma. activities. Furthermore,
cell-to-cell contact of ICAM-2+ cells with LFA-1+ initiated the
transactivation of the p44/42 MAPK pathway in LFA-1 expressing
cells and simultaneously activated the AKT cell survival pathway
ICAM-2 presenting cells, as determined by single cell kinase
profiling by multiparameter flow cytometry. These results highlight
that specific trans-signaling events occur upon cellular adhesion
events mediated by the interaction of ICAM-2 and LFA-1, implicating
the importance of ICAM interactions in consequential processes such
as cellular adhesion and T cell activation.
Introduction
[0363] Leukocyte mediated functions are largely governed by their
ability to localize to appropriate tissue compartments via adhesion
molecule recognition of ligands on target tissues. Targeting of:
leukocytes to distinct cellular environments is of pivotal
importance in cellular processes such as blood clot formation
(Bowes et al., 1995; Nagaoka et al., 2000; Schleef et al., 2001),
immune surveillance (Patarroyo and Makgoba, 1989; Plate et al.,
2000), inflammatory responses (Chihara et al., 2000; Cid et al.,
2000; Krull et al., 1999; Zhang et al., 1999), angiogenesis
(Griffoen et al., 1998; Melder et al., 1996; Patey et al., 1996;
Radisavljevic et al., 2000; Verkarre et al., 1999), and cellular
migration (All et al., 2000; Sans et al., 2001). Leukocyte
targeting and adhesion is primarily mediated by the a and .about.
integrin subunits and their intercellular adhesion molecule
(ICAMs)-1, -2, -3, -4, -5 ligands (Douglas et al., 2000; Kruger et
al., 2001; Sixt et al., 2001; Tian et al., 2000; van den Berg et
al., 2001; Wang and Springer, 1998). The .alpha. and .beta.
integrin subunits form heterodimeric ICAM receptors such as
leukocyte function antigen-1 (LFA-1, CD11a/CD18, or
.alpha..sub.L.beta.B2), MAC-1 (macrophage receptor 1, CD11
.beta./CD18, or .alpha..sub.M.beta.B2), CD11c/CD18
(.alpha..sub.x.beta.B2 or p150,95) and recently identified
CD11d/CD18 (.alpha..sub.D.beta.B2) (Binnerts and van Kooyk, 1999;
de Fougerolles et al., 1995; Gahmberg et al., 1998; Hayflick et
al., 1998; Hermand et al., 2000). The ICAMs are members of the
immunoglobin superfamily, a subclass of the adhesion molecules that
include cadherins, integrins, and selecting. ICAMs show differences
in their cell type distribution-which is believed to reflect their
varying functions. In addition, they can be differentially induced
by various inflammatory cytokines (Hayflick et al., 1998; Simmons,
1995; Somersalo, 1996). ICAM molecules are expressed on lymphoid
lineages that include B cells, T-cells, red blood cells,
macrophages (Hayflick et al., 1998), and also expressed on a subset
of vascular endothelial cells (Griffioen et al., 1996) and neurons
(Tian et al., 2000).
[0364] Deficiencies or augmentation of cellular adhesion properties
are both detrimental and life-threatening, as exemplified in a
variety of immunopathologies such as leukocyte adhesion deficiency
type I (LAD I, allergic encephalomyelitis, tumor vasculature,
vascular permeability diseases, hypertension, severe sepsis
syndrome/septic shock, tumor metastasis, and osteoporosis among
others (Allende et al., 2000; Angelopoulou et al., 1999; Collins et
al., 2000; Etzioni and Tonetti, 2000; Ghaisas et al., 2000; Kiarash
et al., 2001; Lalancette et al., 2000; Schnitzler et al., 1999;
Tanaka et al., 2000; Weigand et al., 1999). Although extensive work
has been conducted on leukocyte cell surface molecules to correlate
mutations in, or absence of, the integrin receptors to the
aforementioned immunopathologies it is not clear to what extent the
ICAMs contribute to the progression of these diseases (Craig et
al., 2000; Daniel et al., 2000; Koga et al., 2000; Mori et al.,
2000; Muanza et al., 1999; Oishi et al., 2000). There is increasing
evidence that elucidation of mechanisms involved in ICAM mediated
cell-to-cell contact (Gottlieb et al., 2000) and in mechanisms that
underscore the irregular production of soluble ICAM molecules may
be of therapeutic interest (De Vita et al., 1998; Guo et al., 2000;
Salmaggi et al., 1999). Blockade of LFA-1/ICAM interaction by
peptides and monoclonal antibodies is proving to be effective in
inhibiting processes such as T cell activation (Tibbetts et al.,
2000), attenuation of organ transplant rejection and various
adhesion related diseases (Gottlieb et al., 2000; Storck et al.,
1994; Sun et al., 2000). Thus, ICAM molecules and their ligands are
being recognized as important immunomodulators.
[0365] We have demonstrated that ICAM-2 can illicit a pro-survival
signal upon surface clustering on human B cells rendering
protection against FAS and TNF.alpha. induced apoptosis. Similarly,
ICAM-1 has been shown to transmit an intracellular signal upon
interaction with the extracellular matrix (Pluskota and D'Souza,
2000) and mice deficient in ICAM receptors or ICAM molecules have
irregularities in a functional immune system (Ding et al., 1999;
Gerwin et al., 1999; Igietseme et al., 1999; Schneeberger et al.,
200p; van Den Engel et al., 2000). Crystallographic, molecular, and
mutational analysis of ICAMs (1-4) and LFA-1 suggest that
overlapping but not identical binding regions exist (Casasnovas et
al., 1998; Casasnovas et al., 1999; Casasnovas et al., 1997;
Edwards et al., 1998; Kotovuori et al., 1999 Hermand et al., 2000).
In addition, dimerization requirements for ICAM-1 but not ICAM-2 or
-3 binding to LFA-1 are indicative of differences in molecular
interactions involving ICAM and LFA-1 and may allow differential
cellular responses to distinct ICAM molecules (Casasnovas et al.,
1998; Miller et al., 1995; Reilly et al., 1995). Finally, the
repertoire of ICAM-binding integrin heterodimeric receptors and
their subsequent signaling has not been investigated in depth.
[0366] Utilizing both retrovirally transduced NIH3T3 to express
human ICAM-2 and a biochemically purified soluble ICAM-2, we
demonstrate that in T cells, LFA-1 interaction with ICAM-2 induces
activation of the RAS/RAF/MEK/ERK pathway (p44/42 Mitogen Activated
Protein Kinase, MAPK). Monoclonal antibodies against LEA-1a (CD11a)
or .beta.2 integrin (CD18) blocked p44/42 MAPK activation. The
signal was independent of ZAP-70, Src, FAK, and Lck as
phosphorylation was not observed as a function of ICAM-21LFA-1
interaction. ICAM-2/LFA-1 induced p44/42 MAPK activity was
dependent on proline-rich tyrosine kinase 2 (PYK2) and spleen
tyrosine kinase (SYK), members of the Src family non-receptor
tyrosine kineses, and p44/42 activity was abrogated with specific
pharmacological inhibitors piceatannol and tyrphostin A9
respectively. Confocal microscopy reveals that there is a
re-distribution of both PYK2 and SYK to the cellular membrane upon
LFA-1 engagement with ICAM-2 and that this interaction yields
phosphorylation of PYK2. Furthermore, PYK2 and SYK co
immunoprecipated with LFA-1 only after engagement of ICAM-2,
indicating a ligand induced conformational change was responsible
for the interaction.
[0367] Development of a phospho-tyrosine protein elisa to screen
for potential kineses involved in the LFA-1 to PYK2/SYK activation
identify LFA-1 ligation to induce PYK2 phosphorylation, with
subsequent SYK phosphorylation dependent on PCK and PLCy.
Biochemical purification of ICAM-2 binding proteins not only
identified .beta.2 integrin, but also .beta.1 and .beta.3 integrins
as being capable of interacting with ICAM-2, emphasizing that
additional heterodimeric receptors involving .beta.1 or .beta.3
integrin subunits may exist for the 1CAMs and that differential
cellular responses can be regulated at the level of receptor
subunit expression at the level of receptor aviditly. Recently,
other integrin heterodimeric receptors have been shown to influence
the activity of .beta.2 integrin receptors, illustrating that
concerted cell adhesion might represent an additional level of
intracellular signaling or regulation (May et al., 2000).
Simultaneous measurement of intracellular kinase activities in
mixed population experiments demonstrated that when ICAM-2
overexpressing fibroblasts engage LFA-1 expressing T-cells,
activation of the AKT pathway is exclusively seen in the ICAM-2
expressing cells while activation of the p44/42 MAPK (ERK1/2)
pathway is exclusively seen on the LFA-1 expressing T-cells. This
trans-stimulatory effect of the ICAM-2/LFA-1 interaction is not
dependent on additional co-stimulatory molecules, as ICAM2-/-
fibroblasts did not result in either AKT or p44/42 MAPK activation.
These results elucidate a previously unrecognized signaling
mechanism for LFA-1 and have implications for its role in cellular
adhesion and T cell activation.
Results
ICAM-2 Clustering Activates the RAFIMEK/ERK Pathway
[0368] Previous work utilizing retrovirally transduced NIH3T3 to
overexpress human ICAM-2 allowed for the dissection of an ICAM-2
induced signaling pathway that was dependent on PKB/AKT and
mediated through the intracellular C-terminal. In this work,
clustering of surface expressed ICAM-2 molecules by monoclonal
antibodies revealed a distinct and separate activation of the
RAF/MEK/ERK mitogen activated protein kinase pathway (p44/42 MAPK)
that was not abrogated in the presence of PI3K inhibitors (data not
shown). The extracellular portion of ICAM-2 was sufficient to
induce MAPK activity as both an ICAM-2 C-terminal truncated
molecule (ICAM2-.DELTA.C) and full length ICAM-2 induced activation
of p44/p42 MAPK when clustered on the cell surface. The ICAM2-DC
molecule was not capable of transducing the PI3K/AKT intracellular
signal characterized to ICAM-2 in a separate study. Expression of
human ICAM-2 and ICAM2-.DELTA.C was verified to target to the
cellular membrane by flow cytometry (FIG. 13A) and was confirmed by
western blot analysis to present a similar electrophoretic mobility
as the endogenous ICAM-2 protein in Jurkat cells (FIG. 13B). NIH3T3
fibroblasts do not express levels of murine ICAM-3 but do express
low levels of murine ICAM-1 and ICAM-2, however, retrovirally
enforced ectopic expression of human ICAM-2 was found to be 5
magnitudes higher than endogenous levels as determined by
quantitative flow cytometry.
[0369] ICAM-2 clustering initiated activation of the RAF/MEK/ERK
cascade (p44/42 MAPK pathway) in NIH3T3 cells as a function of time
as observed by immunoblotting for each respective kinase's active
phosphorylated state. (FIG. 13C). ERK kinase activity led, as
expected, to phosphorylation of Elk-1. Phosphorylation of Elk-1 has
been demonstrated to be sufficient for its activation and nuclear
translocation (Wang and Prywes, 2000). Incidentally, other p44/42
MAPK activated proteins capable of transcription activity, namely
Rsk-1 (FIG. 13C) and CREB (data not shown), were also
phosphorylated as a function ICAM-2 clustering. The ICAM-2 induced
phosphorylation of p44/42 MAPK was verified by kinase activity
assays and was present in both ICAM-2 and ICAM2-.DELTA.C transduced
fibroblasts, and by endogenous ICAM-2 in Jurkat T cells when
crosslinked (FIG. 13D). Furthermore, activation of JNK, p38 MAPK or
activities of MEK3/6, or MEK 4/7 were not observed following ICAM-2
crosslinking (data not shown). Verification of the truncated
ICAM2-.DELTA.C expression by intracellular flow cytometry (see FIG.
13A) and its apparent inability to induce an intracellular signal
led us to believe that the p44/42 MAPK activity observed was due by
a surface-bound ICAM-2 interacting protein (discussed below).
ICAM-2 Induced p44/42 MAPK Activity Attenuates Growth Kinetics and
Augments Cellular Contact Inhibition
[0370] The p44/42 MAPK family is important in a variety of cellular
process that govern growth, survival, and differentiation of cells
(Chang and Karin, 2001). Several assays were used to assess p44/42
MAPK mediated events. Cell cycle analysis was performed to
determine if the ICAM-2 induced p44/42 MAPK activity was able to
initiate cell cycle re-entry. ICAM-2, ICAM2-.DELTA.C, vector
control, and varying cell types were serum starved for 72 hours to
synchronize cells in the absence of chemical agents. Cells were
then crosslinked for ICAM-2 using a monoclonal antibody and
analyzed 18 hours later. The percentage of cells in S-phase
increased following ICAM-2 crosslinking (FIG. 14A). Cell cycle
re-entry was dramatically apparent in ICAM2-.DELTA.C (versus vector
control and ICAM-2 cells). Continual stimulation of cell cycle
re-entry is sufficient to override growth inhibition signals, often
the case in cells that have lost the ability to arrest growth by
contacting inhibition and exemplified in the metastatic spread of
cancerous cells. Since ICAM-2 and ICAM2-AC presented p44/42 MAPK
activity upon ICAM-2 clustering, we postulated that constitutive
activation of the p44/42 MAPK pathway could potentially enhance
growth kinetics, consequential to the cell cycle re-entry observed
and may be sufficient to circumvent contact inhibitory mechanisms.
We tested this by monitoring cellular respiration as a function of
cell density to determine the extent of growth arrest induced, if
any, by contact inhibition. We expected contact inhibition to
induce a growth arrest in adherent cells, and therefore a decrease
in cellular respiration as the cell density increased. Vector
control cells (negative control) showed reduced cellular
respiration at high cell densities in contrast to both Jurkat cells
(suspension cells not capable of contact inhibition) and 293T cells
(transformed fibroblast that fail to contact inhibit) (FIG. 14B).
Both ICAM-2 and 1CAM2-.DELTA.C expressing cells exhibited enhanced
cellular respiration at high cell densities over vector control
(FIG. 14B). Despite these observations, ICAM-2 and ICAM2-.DELTA.C
expressing cells were not found to be transformant, a property of
cells that have lost contact inhibition, using a top agar
transformation assay and did not form tumors when subcutaneously
implanted in nude mice (data not shown). Irrespective of this, both
ICAM-2 and ICAM2-.DELTA.C expressing cells displayed enhanced
growth kinetics over vector control cells (FIG. 14C). Since the
ICAM2-.DELTA.C construct elicited p44/42 MAPK activity and was able
to initiate a robust cell cycle re-entry in comparison to vector
controls, this suggested that an ICAM-2 surface interacting protein
was responsible for the activation of p44/42 MAPK. The observation
that the p44/42 MAPK induction effect was intensified when ICAM-2
was relieved of C-terminal cytoskeleton interactions (FIG. 14A)
illustrates a potential role for cytoskeleton-mediated regulation
of ICAM surface protein signal transduction (Heiska et al., 1998;
Heiska et al., 1996; van Kooyk et al., 1999).
ICAM-2 Interacts with .beta. Integrins 1, 2, and 3
[0371] A soluble form of ICAM-2 was used to verify the ability of
ICAM-2 to bind to the cell surface. Full length ICAM-2 was
immuno-depleted from ICAM-2 transduced cell lysates and conjugated
to FITC (FIG. 15A). The ICAM-2-FITC probe was used to stain the
surface of NIH3T3 fibroblast cells, Jurkat T cells, and BaF3 proB
cells (FIG. 14B) on the presumption that ICAM-2 will bind, at least
to its normal ligand partner .beta.2 integrin on these cells.
Pre-treatment of cells with the protease trypsin drastically
decreased ICAM-2-FITC binding, suggesting that ICAM-2 was binding
to a surface bound protein. The ICAM-2-FITC probe was found to be
partially competed by antibodies to .beta.2-integrin on NIH3T3
fibroblasts, a cell line that lacks LFA-1a expression (data not
shown). ICAM-2-FITC binding was confirmed by epifluorescence
microscopy and was titrateable and inhibited with an unlabeled
control in a competition assay (data not shown). Since ICAM2-FITC
binding was not completely inhibited by anti-132 integrin
antibodies in NIH3T3, in addition to these cells lacking expression
of LFA-1.alpha., it suggested that an additional molecule(s)
capable of binding ICAM-2 existed on the surface of these
cells.
[0372] A two-column affinity chromatography approach was utilized
to determine surface bound target molecules capable of binding
ICAM-2. ICAM-2, ICAM2-.DELTA.C, and vector control cell surface
proteins were biotinylated and subjected to affinity chromatography
on an ICAM-2 coupled solid support, and subsequently passed through
a streptavdin agarose support. A two-column system was preferred in
order to identify proteins that were both surface expressed
(biotinylated) and ICAM-2 binding. Final protein elusions were
tested for both biotinylation by immunoblotting techniques and
-ICAM-2 interaction by the use of the ICAM-2FITC probe in a
farwestern approach (FIG. 15A). Protein bands of 112, 95, 67
kilodaltons (kDa) were gel eluted and sequenced by MALDI-MS. The
biotinylation of the surface proteins interfered with a direct
analysis of the proteins eluted, and fragments of peptide sequences
generated suggested that the molecules contained RGD domains, with
homologies to several surface bound receptors, although no apparent
single protein could be identified from the peptide fragments
generated. Therefore, we decided to test for integrin binding
partners, given that ICAM-2 has been shown to bind .beta. 2
integrin. Immunoblotting the final two-column elusions confirmed
.beta. 1, .beta. 2, and .beta. 3 integrins to be both surface
expressed (biotinylated) and ICAM-2 interacting (FIG. 15C). .beta.
4, .beta. 5, and .beta. 6 integrins were not identified in
immunoblotting final two-column elusions (data not shown).
Performing reciprocal column systems (i.e. streptavidin-agarose
support followed by ICAM-2 affinity column) in addition to, ICAM-2
immunoblots.
[0373] Monoclonal antibody (mAb) blocking experiments were used to
distinguish the contribution of the integrin binding partners to
the ICAM-2 induced p44/42 MAPK activation. Pretreatment of ICAM-2,
ICAM2-.DELTA.C, and vector control cells with mAbs for .beta.1,
.beta.2, and .beta.3 integrin prior to ICAM-2 clustering
demonstrated occlusion of .beta.2 integrin to selectively inhibit
ICAM-2 induced p44/42 MAPK activity (FIG. 15C). Unexpected results
were observed by using mAbs to .beta.1 and .beta.3, in that both
partial inhibition and induction of p44/42 MAPK activity was
observed (elaborated in the discussion). Therefore, differences
observed in the antibody blocking experiments for .beta.1 and
.beta.3 integrins cannot be differentiated between ICAM-2/integrin
block or integrin-induced signaling given the nature of the
experiment and were not explored any further. However, the
experiments do illustrate that antibody blockade of .beta.2
integrin is sufficient to abrogate ICAM-2's induced p44/42 MAPK
activity. Since ICAM-2 clustering via the extracellular domain
induced p44/42 MAPK activity in the ICAM2-.DELTA.C transduced cell
population and was blocked by .beta.2 integrin monoclonal antibody,
it suggested that the ICAM2-.DELTA.C molecule was capable of
interacting with .beta.2 integrin on the same cell. Thus, the
surface interaction of these two molecules mediated p44/42 MAPK
activity through the .beta.2 integrin. Interestingly, ICAM-2's
natural receptor Leukocyte Function-Antigen-1 (LFA-1) is an
.alpha..beta. heterodimeric receptor composed of both .beta.2 and
.alpha..sub.L integrins (CD11a) (Kaplan et al., 2000). Therefore,
we decided to test the ICAM-2 induced p44/42 MAPK activation in
Jurkat T-cells, which endogenously express the low levels of the
LFA-1 receptor subunits, with a biochemically purified soluble
ICAM-2 protein. Treatment of Jurkat cells with soluble ICAM-2
induced p44/42 MAPK phosphorylation and activity and was blocked by
monoclonal antibodies to both p2 and a.sub.L integrins (FIG. 15F)
indicating that the ICAM-2/LFA-1 interaction can mediate activation
of p44/42 MAPK in LFA-1 expressing cells.
ICAM-21LFA-1 Engagement Induces p44/42 MAPK Activity Through PYK2
and SYK
[0374] To identify upstream kineses that would be responsible for
signal transmission from LFA-1 to Raf (and subsequently to p44/42
MAPK), a series of kinase inhibitor screens were conducted.
Tyrphostin A9 and piceatannol, specific inhibitors of
proline-tyrosine kinase 2 (PYK2) and Spleen-tyrosine kinase (SYK)
respectively (Avdi et al., 2001; Fuortes et al., 1999) were found
to abrogate the ICAM-2 induced activation of Raf and subsequently
p44/42 MAPK (FIG. 16A). Other protein kineses that include p38
MAPK, and two members of the src related tyrosine kineses p56Lck
and Src were not found to be involved by the inability of specific
pharmacological inhibitors of these kineses to block ICAM-2 induced
p44/42 MAPK activity. Furthermore, immunoblotting for
phosphotyrosine residues of immunoprecipitated tyrosine kineses
involved in T-cell activation, namely LAT and ZAP-70, and tyrosine
kineses involved in integrin signaling, FAK and Src, did not
implicate these kineses in the ICAM-2/LFA-1 mediated signal (data
not shown). However the ICAM-2/LFA-1 activation of p44/42 MAPK was
dependent on guanosine triphosphate, implying the involvement of
Ras (data not shown).
[0375] It was apparent that p44/42 MAPK activation was a function
of an ICAM2/LFA-1 interaction that was initiated when ICAM-2
engaged LFA-1. It has been reported that adhesion molecule
receptors require an activation step in order for intracellular
signaling to occur that usually results in changes in it's the
receptor's avidity and/or affinity for its respective ligand or in
its formation if composed of a heterodimeric association (van Kooyk
et al., 1999). This prompted us to test whether contact of ICAM-2
with LFA-1 induced an "activation state" that allowed for the
subsequent binding of PYK2 or SYK to transmit the signal through an
SH2/GRB/Ras dependent pathway to p44/42 MAPK. Typical exogenous
treatments with phorbal esters to activate LFA-1 could not be used,
since we noted eventual activation of the p44/42 MAPK pathway
following treatment (data not shown). Therefore, the interaction of
PYK2 and SYK with both subunits of LFA-1, .beta.2 and .alpha.L
integrins was tested by co-immunoprecipitation as a function of
soluble ICAM-2 and various T cell activating stimulants. Tyrosine
phosphorylation of neither .beta.2 nor .alpha..sub.L integrin was
observed as a function of any stimulus tested (data not shown). An
association between .beta.2 and .alpha..sub.L integrin was only
observed after treatment with soluble ICANrr2 and was absent in
unstimulated cells (FIG. 16B). This suggested that the formation of
the LFA-1 receptor can be initiated by a ligand induced event
mediated by ligand induced recruitment of the ap subunits. LFA-1
receptor integrity was found to be stabilized by treatment with
various T cell stimulants in addition to soluble ICAM-2 resulting
in an enhanced interaction between .beta.2 and .alpha..sub.L
integrin.
[0376] SYKs interaction with .alpha..sub.L integrin was present
under unstimulated conditions and was attenuated by stimulatory
conditions with a concomitant association with .beta.2 integrin.
This suggested that the interaction of .beta.2 and .alpha..sub.L
integrins induced by ICAM-2 resulted in an activation of SYK--a
process that can result from a conformational change proceeding
LFA-1 formation as suggested by studies reporting avidity changes
in ligand binding of LFA-1. PYK2 presented a weak association with
.beta.2 integrin, an interaction that was enhanced upon ICAM-2
stimulus, and only interacted with .alpha.L integrin after the
ICAM-2 stimulus was provided (FIG. 16B). Although the exact
molecular details of the temporal kinetics of PYK2 and SYK
association with LFA-1 as a function of stimulus were not
investigated, the data would suggest that ICAM-2 could induce
formation of its LFA-1 receptor by recruiting .beta.2 and
.alpha..sub.L integrin. We speculate that "activated" LFA-1 induces
a conformational change that is transmitted to PYK2 and SYK, either
through direct physical contact, or exposure of binding sites that
would in turn allow binding of PYK2 or SYK.
[0377] Ligand induced conformational changes of LFA-1 have been
reported (Kotovuori et al., 1999; van Kooyk and Figdor, 2000), but
lack linkage of LFA-1 to specific intracellular signaling
mechanism. Furthermore, reciprocal coimmunoprecipitations of PYK2
and SYK association with .beta.2 integrin was observed to be
maximal in the presence of one or more stimuli (FIG. 16B). Both
PYK2 and SYK2 were found to by phosphorylated in response to ICAM-2
as a function of time in LFA-1 expressing cells. Phosphorylation of
PYK2 tyrosine residues tyr402 (autophosphorylation site) and tyr881
(SH2 binding site) was induced by ICAM-2 binding LFA-1 as
determined by immunoblotting for respective phosphorylated
residues. This confirmed that phosphorylation of PYK2 is mediated
by an ICAM-2 induced LFA1 activation (FIG. 16C).
[0378] Confocal laser scanning microscopy was used to assess the
cellular distribution of PYK2 and SYK, and their respective
localization and/or phosphorylation after treatment of Jurkat cells
with soluble ICAM-2. A cellular redistribution of both PYK2 and SYK
upon ICAM-2/LFA-1 interaction was observed as diffused cytoplasmic
PYK2 and SYK localized to the plasma membrane (FIG. 17, panel C and
L). Phosphorylation of PYK2 was observed at the plasma membrane
only after the ICAM-2 stimulus was provided as detected by a
phospho-specific antibody to PYK2 at tyrosine 402 (FIG. 17, panel F
and I). Recruitment of PYK2 to the plasma membrane by ICAM-2s
interaction with LFA-1 resulted in PYK2 phosphorylation as PYK2
phosphorylation was not observed in the absence of the ICAM-2
stimulus. It is not clear which specific events mediate PYK2 or SYK
recruitment to LFA-1 upon ligand interaction, at present, we
hypothesize that a ligand induced conformational change to LFA-1
exposes protein binding sites for PYK2 and SYK interaction.
ICAM-2/LFA-1 Interaction Transmits Distinct Signals to Both
Contacting Cells
[0379] LFA-1 and ICAM-have been implicated in cellular adhesion of
leukocytes, in essential processes that include lymphocyte
trafficking (Etienne-Manneville et al., 2000; Sato et al., 2000;
Sigal et al., 2000), stabilizing T-cell:antigen-presenting cell
contact (Hwang et al., 2000; Neeson et al., 2000), metastatic
spread (Dosquet et al., 1997; Griffoen et al., 1996; Griffoen et
al., 1996; Regidor et al., 1998; Tang and Honn, 1994), and organ
transplant rejection (Rentsch et al., 2000). Considering the
severity of diseases associated with the absence of ICAM/LFA-1
interactions, we sought to understand the signaling mechanisms
initiated upon [celLto-cell] cell-to-cell contact that utilize
ICAM-2 and LFA-1. To do this, we developed specific kinase probes
for AKT and p44/42 MAPK, among others, to simultaneously monitor
kinase activity within individual cells. These probes detect
phosphorylated AKTser473 and phosphorylated p44/42 MAPK
(Thr202/Tyr204) by flow cytometry and phosphorylation at these
residues was found to correlate with respective kinase activity by
immunoblotting and kinase activity assays. These probes, in
conjunction with specific cell type markers, allowed us to test for
the activation of signaling pathways in heterogeneous cell mixing
experiments by flow cytometry.
[0380] NIH3T3 cells were engineered by retroviral transduction to
overexpress human ICAM-2 and were used as a presenting cell to
Jurkat T cells. NIH3T3 lack expression of costimulatory molecules
CD86 and CD80, and express low levels of murine ICAM1,-3 as
determined by flow cytometry (data not shown). The engineered
ICAM-2 overexpressing cells present [106] 10.sup.6 fold surface
human ICAM-2 protein compared to vector control as determined by
quantitative flow cytometry. ICAM-2 cells and vector control cells
were mixed with Jurkat T cells and prepared for flow cytometry by
surface staining for T cell markers CD3 and CD4, and intracellular
detection of phosphorylated p44/42 and AKT. FIG. 18 displays a FACS
plot of both ICAM-2 (CD3 CD4-) and Jurkat cells (CD3+CD4+) as
distinguished by CD4 and CD3 markers. Forward and scatter voltages
were experimentally determined to allow visualization of both
cellular populations denoting the autofluorescence of fibroblast
cells. Intracellular kinase activities for both AKT and p44/42
present two distinguishable peaks that can be attributed to
distinct cell populations-only single peaks were observed in
homogenous control populations (data not shown). AKT.sup.high
activity is observed primarily in CD3/CD4 double negative cells
while ERK.sup.high activity is observed primarily in CD3/CD4 double
positive cells. Therefore, ICAM-2/LFA-1 interaction between a
presenting cell and a leukocyte activates AKT and p44/42 within
each cell respectively.
Discussion
[0381] The results presented demonstrate (1) ICAM-2/LFA-1
interaction activates the p44/p42 MAPK cascade in LFA-1 expressing
cells and can be blocked by antibodies to both .alpha.L and .beta.
2 integrins, (2) LFA-1 transmits a signal to PYK2 and SYK upon
ligand binding, (3) ICAM-2/LFA-1 engagement activates AKT in ICAM2
expressing cells and p44/42 in LFA-1 expressing cells, a concerted
transtimulation to contacting cells upon celLto-cell contact
respectively.
[0382] We have previously shown that ICAM-2 can intracellularly
activate the PKB/AKT pathway protecting fibroblasts, T and B cells
from apoptosis. Recently, it was shown that ICAM-1 interactions
with fibrinogen can activate ERK1/2 and regulate endothelial cell
survival (Pluskota and D'Souza, 2000). Therefore it is likely that
ICAMs can transduce specific signals to their host cell upon
engagement of LFA-1. Since the ICAMs are members of immunoglobulin
superfamily, extensive work has been focused around their adhesive
properties in cell-to-cell contact and lymphocyte recirculation
(EtienneManneville et al., 2000; Geijtenbeek et al., 2000; Gerwin
et al., 1999). This in part is due to the cell specific expression
patterns exhibited by the ICAMs and their attenuation upon the
presence of inflammatory cytokine (McLaughlin et al., 1999; Wolf et
al., 2001). For example, ICAM-1 is expressed at low levels and is
upregulated by inflammatory cytokines on leukocytes, endothelial
cells, fibroblasts, and dendritic cells in contrast to ICAM-2 which
is constitutively expressed on leukocytes, endothelial cells, and
platelets (Staunton et al., 1989; Xu et al., 1996) and
overexpressed in many lymphoprolferative diseases (Eichelmann et
al., 1992; Molica et al., 1996).
[0383] Adhesion properties attributed to the ICAMs include cell
migration (Ding et al., 1999; Nagaoka et al., 2000; Somersalo,
1996), lymphocyte trafficking (Devine et al., 1996; Geljtenbeek et
al., 2000; Jutila, 1992), enhancing the avidity of the interaction
between a T cell and antigen-presenting cell (APC) (Kotovuori et
al., 1999; van Kooyk and Figdor, 2000; VanCompernolle et al., 2001;
Wulfing et al., 1998) and contribute to the pathogenecity of viral
infections (Belle and Rossmann, 1999; Hioe et al., 2001; Nagaoka et
al., 2000; Shigeta, 1998). These adhesion roles partially overlap
with the roles ascribed to the integrins, a distinct superfamily of
.alpha..beta. heterodimeric transmembrane proteins that are
essential in adhesion/migration and proliferation/differentiation
cellular processes (Geginat et al., 1999). It is now becoming clear
that integrins themselves can function as signal transducers in
integrin-mediated T cell co-stimulation (Gaglia et al., 2000;
Goldstein et al., 2000), in interactions involving the
extracellular matrix (ECM), in addition to migratory properties
(Epler et al., 2000; Holly et al., 2000; Tarone et al., 2000).
Signal transduction for the Ig superfamily has largely gone
unrecognized, with the majority of attention focused on other
cellular adhesion molecules that include the integrin, selectin,
and cadherin family of proteins (Braga, 1999; Elangbam et al.,
1997; Gonzalez-Amaro and Sanchez-Madrid, 1999). Furthermore, a
subset of integrins more commonly known by their CD number as
leukocyte antigens-.beta.1 (CD29), .beta.2 (CD18), .beta.3 (CD61)
.beta.4 (CD 104) .alpha.1-6 (CD49a-f respectively), in addition to
the ICAMs ICAM-1 (CD54), ICAM-2 (CD102), ICAM-3 (CD50) indirectly
suggest that these molecules may possess specific signaling roles
with functional consequences in lymphocyte populations.
[0384] Dissection of the downstream signaling pathways involving
the LFA1/ICAM-2 interaction was found to be dependent on both PYK2
and SYK. PYK2 (also known as CAK-B or RAFTK) is a second member of
the focal adhesion kinase family and activated by many types of
cell surface receptors that include integrins, cytokines, immune
receptors, stress stimuli, and PKC activation (Avraham et al.,
2000; Hauck et al., 2000). Recently, phosphorylation of PYK2 has
been associated with homotypic adhesion mediated by an LFA-1/ICAM-1
interaction in B cells (McDonald et al., 2000), and has also been
implicated to be positively regulated by .beta.1 and .beta.3
integrin in myeloid cells (Litvak et al., 2000; Miura et al., 2000;
van Seventer et al., 1998). Positive regulation of PYK2 by 132
integrins has been reported in regards to cell spreading and
migration in macrophages (Duong and Rodan, 2000) and to induce
apoptosis in neutrophils (Avdi et al., 2001). In addition,
activation of PYK2 has been stated to be downstream of SYK in
Fc.epsilon.RI signaling in basophils (Okazaki et al., 1997).
Therefore PYK2 is recently being regarded as a key signaling
molecule in transmiting adhesion mediated events
intracellularly.
[0385] SYK is a spleen non-receptor tyrosine kinase that is
essential in signal transmission of .alpha.III.beta.3 inside out
signaling (SacI et al., 2000), has roles in Fc.epsilon.RI signaling
(Jabril-Cuenod et al., 1996), and phosphorylated by integrin
mediated signaling (Miller et al., 1999; Moores et al., 2000).
Given the numerous reports depicting both PYK2 and SYK
phosphorylation events, these events can be categorized by
stimulatory conditions and present differential outcomes among
different cell types: (1) signaling events involving .beta.
integrins with regards to B cell signaling (Babe et al., 2001; Li
et al., 2001); (2) events involving .beta.2 integrins with regards
to cellular migration and invasion (Holly et al., 2000); (3)
activation induced by immune receptors CD2 and CD28 (Fukai et al.,
2000; Tsuchida et al., 1999). Here we report that PYK2 and SYK2
associate with LFA-1 components .alpha.L and .beta.2 upon LFA-1s
interaction with ICAM-2 in Jurkat T cells as determined by both
co-immunoprecipitation experiments and confocal microscopy to
demonstrate that the ICAM-2/LFA-1 interaction mediates
phosphorylation of PYK2 at the plasma membrane. Furthermore, we are
the first group to report that both PYK2 and SYK2 are necessary in
transmitting the ICAM-2/LFA-1 induced signal to Raf, the upstream
kinase in the RAF/MEK/ERK cascade, as determined by usage of
specific pharmacological inhibitors piceatannol and tryphostin A9
in Jurkat T cells. PYK2 and SYK interactions have been reported in
G protein coupled MAPK activity in PC12 cells (Dikic et al., 1996)
and activation of HL40 cells (Miura et al., 2000), supporting the
notion of PYK2 and SYK interactions in cellular processes.
[0386] Activation of the RAF/MEK/ERK cascade was monitored as a
function of time per induction of ICAM-2 clustering. Blockade of
p44/42 MAPK activity with monoclonal antibodies to .beta.2 and
.alpha..sub.L integrins indicated the ICAM-2 induced activity was
mediated in part by interaction of these integrins on the cellular
surface. Since monoclonal antibody treatment to other
.beta.-integrins, namely .beta.1 and .beta.3 induced p44/42 MAPK
activity in vector control cells, it could suggest a general role
for p44/42. MAPK activation by these specific integrins in the
fibroblast cell line used, since this was not observed in Jurkat
cells. The results of .beta.1 and .beta.3 mAb treatment can be
accounted for by at least three possible interpretations on the
ICAM-2 and ICAM2-.DELTA.C expressing NIH3T3: (1) partial
ICAM-2/partner inhibition; (2) partial integrin activation by
antibody clustering; (3) combination of 1 and 2. Beta-integrins 1
and 3 have been reported to interact with Ras via G-proteins, and
been implicated in the cellular adhesion/ECM signal transduction
pathways resulting in p44/42 MAPK activity in adherent cell lines
(Yokosaki et al., 1996; Zhu et al., 1999). Interestingly, .beta.1
integrin was recently implicated in p44/42 MAPK activity and
subsequent cell cycle reentry (Qiang et al., 2000). Furthermore,
integrin clustering initiated by extracellular matrix attachment
can initiate specific signals as observed by antibody clustering
(Chen et al., 1996; Hotchin and Hall, 1995).
[0387] Studies involving dominant negative Ras implicated .beta.2
integrin with the p44/42 MAPK in response to T cell receptor
triggered ICAM-1 dependent adhesion (O'Rourke et al., 1998). Here
we observed that p44/42 MAPK activity is due to ICAM-2 interacting
with LFA-1, although both observations are not mutually exclusive
and could suggest a mechanism in which low affinity ICAM/LFA-1
interactions are strengthened by a co-stimulatory condition such as
that obtained through the T cell receptor in cell-to-cell contact
processes. The ICAM-2 induced LFA-1 activation of p44/42 MAPK
activity was confirmed by a soluble ICAM-2 molecule in Jurkat T
cells and subsequently blocked by antibodies to the LFA-1 receptor
subunits. Thus, LFA-1 is capable of initiating a signal to p44/42
MAPK after binding to its ligand ICAM-2. Although ICAM-1 and ICAM-3
also bind LFA-1, further studies are warranted to generalize the
LFA-1 induced signal to binding of all its cognate ligands, in
addition to elucidating signaling pathways for other ICAM-2
receptors such as DC-SIGN.
[0388] Development of intracellular kinase probes to monitor kinase
activity in distinct cell populations allowed us to determine the
activation of p44/42 MAPK and AKT in cell-to-cell contact in LFA-1
and ICAM-2 expressing cells respectively. These trans signaling
events initiated upon cellular contact were not only distinct to
each participating cell type but illustrate that adhesion mediated
events may transmit specific signaling events that have largely
gone unrecognized. Detection of p44/42 MAPK and AKT activities in
LFA-1/ICAM-2 engagement exemplify the significant impact that could
result from deregulation of adhesion molecules, largely in part
because p44/42 MAPK and AKT are two pivotal kineses involved in
growth, proliferation, and survival pathways (Chang and Karin,
2001; Datta et al., 1999). The work presented herein brings to
question the canonical segregation of integrins and leukocyte
antigens as strictly playing adhesive/targeting roles and
exemplifies that distinct signaling mechanisms are initiated upon
ICAM-2 encountering LFA-1 to both interacting cells. Elucidating
the roles of (I)CAM mediated adhesion in vivo could provide
fundamental knowledge of their roles in functionally relevant
cellular processes such as T cell activation, angiogenesis, and
metastatic spread.
Materials and Methods
Immunological and Chemical Reagents
[0389] The following antibodies were obtained from Cell Signaling
Technologies (CST): phospho-Raf1 (Ser259) polyclonal,
phospho-MEK1/2 (Ser217/221) polyclonal, phospho-p44/42 MAP kinase
(Thr202/Tyr204), phospho-p44/42 MAPK (Thr202/Tyr204) monoclonal,
phospho-p90RSK (Ser381) polyclonal, phosphoElk-1 (Ser383)
polyclonal, phospho-p38 MAP kinase (Thr180/Tyr182), polyclonal,
immobilized phospho-p44/42 (Thr202/Tyr204) monoclonal,
phospho-SAPK/JNK (Thr183/Tyr185) polyclonal, phospho-CREB (Ser133)
polyclonal, phosphoSEK1/MKK4 (Thr261) polyclonal, phospho-Jun (Ser
63) polyclonal, phosphoMKK3/MKK6 (Sell 89/207) polyclonal,
phosho-AKTSer473 monoclonal, nonphospho specific antibodies to the
above proteins were also obtained from Cell Signal Technologies.
The following antibodies were obtained from Transduction
Laboratories: anti-.beta.1 monoclonal, anti-.beta.2 monoclonal,
anti-.beta.3 monoclonal, anti-.alpha..sub.L monoclonal,
anti-.alpha.4 monoclonal, anti-.alpha.5 monoclonal, anti-.alpha.6
monoclonal, anti-LFA-1 monoclonal, anti-.alpha.5 monoclonal,
anti-.alpha.1 monoclonal, anti-.alpha.4 monoclonal, anti-PYK2,
anti-SYK, anti-CD3.
[0390] The following antibodies were obtained from varying vendors:
ICAM-2 monoclonal (IC2/2 Research Diagnostics), ICAM-2 Cterminal
polyclonal (Santa Cruz Biotechnologies; SCBT), anti-PYK2p402
(Biosource), anti-phosphotyrosine-FITC (CST), CD3-APC (PharMingen),
CD4 PerCP (PharMingen), CD8O-PE (PharMingen), CD86-FITC
(PharMingen), CD54PE (PharMingen), CD50 (PharMingen), CD102-FITC
(Research Diagnostics), anti-rabbit IgG HRP conjugated (CST),
anti-mouse IgG HRP conjugated (SCBT), anti-mouse IgG FITC
conjugated (PharMingen), anti-rabbit-PE conjugated (PharMingen),
anti-goat rhodamine conjugated (SCBT), anti-mouse Alexa Fluor 488
conjugated (Molecular Probes), anti-rabbit Alexa Fluor 488
conjugated (Molecular Probes) anti-rabbit Alexa Fluor 568
conjugated (Molecular Probes), anti-rabbit Alexa Fluor 568
conjugated (Molecular Probes), anti-rat IgG (PharMingen). Protein
and chemical reagents used: streptavidin-FITC (SCBT), fluorescein
isothiocyanate (FITC) (Pierce), R-phycoerythrin (Molecular Probes),
Alexa488 (Molecular Probes), Alexa Fluor 546 (Molecular Probes),
Elk-1 fusion protein (CST), p42 MAP kinase (Erk2) (CST), Tyrphostin
A9 (Calbiochem), tyrphostin 18 (Calbiochem), SB203580 (CST),
herbimycin A (Sigma), emodin (Sigma), piceatannol (Calbiochem),
genistein (Sigma), DMSO (Sigma), phorbal myristelated acetate (PMA)
(Sigma), ionomycin (Sigma), propidium iodide (PI) (Sigma), RNASE
(Sigma), MTT (Sigma), steptavidin-agarose (SCBT).
Cell Culture and cDNA Isolation and Retroviral Transduction
[0391] Full length ICAM2 cDNA was obtained from a retroviral cDNA
library produced from Jurkat cDNA and cloned into retroviral vector
PBM-Z-IN backbone (Kinoshita et al., 1998) at BamHI/Sal1 site.
ICAM2-.DELTA.C was generated by PCR and cloned into the BamHI/Sal1
site. Retroviral constructs containing ICAM-2 or ICAM2-.DELTA.C
were used to transduce NIH3T3 murine fibroblast. NIH3T3 cells were
maintained in DMEM, 10% DCS, 1% PSQ (Duelbecco Modified Eagle
Media, 10% Donor calf serum, 1% penicillinstreptomycin (1000
units/ml and 2 mM L-glutamine PSQ). Jurkat T-cells were maintained
in RPMI-1640, 10% FCS, 1% PSQ. BaF3 pro-B-cells were maintained in
RPML1640, 10% FCS, 1% PSQ, 400 U/ml IL-3 (Peprotech). HL60 myeloid
leukemia cells were maintained in Opti-Mem 1, 10% FCS, 1% PSQ. 293T
human fibroblast cells were maintained in DMEM, 10% FCS, 1% PSQ.
Cells were maintained at 5% CO.sub.2/37.degree. C. humidified
incubator. Transduced cells were maintained in 500 1 .mu.g/ml G418
(Sigma) and proper expression of construct was verified by western
blots and FACS analysis of full length ICAM-2 and IC.DELTA.M2-AC as
indicated. Vector controls consisted of pBMN-Z-IN (empty vector)
transduction as indicated. The infection frequency of pBMN-Z-IN was
48%+/-10 for three independent viral transductions. Continual
neomycin selection yielded homogenous ICAM-2, ICAM2-.DELTA.C, or
control vector populations as routinely monitored by flow cytometry
for protein expression.
Cross-Linking
[0392] Antibody cross-linking experiments were performed using a
mouse monoclonal anti-ICAM-2 that recognizes the N-terminal region
(extracellular domain) (IC2/2 Research Diagnostics) at 10 .mu.g/ml.
Spin dialysis (Biorad) was used for buffer exchange of azide
containing antibodies (0.01%) to phosphate buffered saline buffer
pH 7.4. Anti-mouse IgG (Sigma) was used as a control antibody in
crosslinking experiments. 10.sup.5 cells as indicated were serum
starved for 3 hours or 4 hours respectively. Cells were incubated
with either ICAM-2 (10 .mu.g/ml) or mouse IgG (10 .mu.g/ml) at
37.degree. C. for the indicated time. Time points began post serum
starvation to attenuate most of the signaling pathways or as
indicated. Cells extracts were taken and subjected to either
immunoprecipitation or immunoblotting.
Cell Growth Assays
[0393] Cell cycle analysis was performed as described
(http://www.metazoa.com/upl2072) and analyzed by flow cytometry.
Cellular respiration was determined by the metabolic indicator dye
3-(4,5-cimethylthiazot 2-yl)-2,5-diphenyl tetrazolium bromide)
(MTT) (http://www.metazoa.com/upl2102) (Sigma).
Affinity Chromatography, ICAM-2-FITC Probe Generation, and Surface
Protein Biotinylation
[0394] Surface proteins of ICAM-2, ICAM2-.DELTA.C, and vector
control were biotinylated using sulfo-NHS-LC-Biotin (Pierce) as
suggested by manufacturer and verified by flow cytometry and
western blot techniques (data not shown). An ICAM-2 solid support
was synthesized by coupling an anti-ICAM2 C-terminal antibody to an
Affi-Prep 10 solid support (Biorad) as stated by manufacturer's
instruction. The anti-ICAM-2 support was used to isolate ICAM-2
from retrovirally transduced ICAM-2 expressing NIH3T3 cells,
thoroughly washed, and antibody/protein complex stabilized by
chemical crosslinking with bis(sulfosuccinimidyl)suberate (Pierce)
as suggested by manufacturer. Alternating washes with low/high pH
solutions removed contaminating proteins and or chemicals. Solid
support was tested for human ICAM-2 coupling by immunoblot
techniques (data not shown). The ICAM-2 solid support was designed
to orientate the anchored ICAM-2 molecule by the C-terminal (via an
antibody), allowing the extracellular N-terminal to freely interact
with passaged material (see Materials and Methods for
elaboration).
[0395] Cell lysates were then passaged over the column and were
initially subjected to a step gradient elusion using increments of
100, 250, 500 and 1 mM NaCl (in Tris pH 6.8) to elute binding
proteins. Dual column system utilized the ICAM-2 solid support,
binding proteins eluted with 500 mM NaCl (in Tris pH 6.8),
concentrated (Centricon 3 kDa cutoff), dialyzed using dialysis
membrane (3 kDa cutoff) in PBS pH 7.4 overnight, and depleted for
biotinylated proteins by streptavidin-agarose. Further procedure
was similar to immunoprecipitation protocol described below.
Interacting proteins that survived the procedure were reduced in
SDS-PAGE buffer, boiled for 5 minutes, and subjected to SDS-PAGE
analysis. Bands appearing were gel eluted and subjected to protein
sequencing by MALDI-MS. Verification of the identity of the
interacting proteins was done using monoclonal antibodies as
indicated in immunoblots. ICAM-2-FITC generation was achieved by
immunodepleting ICAM-2, antibody complex stripped by using 4.5 M
NaCl (in Tris pH 6.8), concentrated, dialyzed, and chemically
conjugated to NHS-Fluorescein (Pierce) as suggested by
manufacturer. ICAM-2-FITC probe was stored in PBS containing 0.1%
azide.
Flow Cytometry
Intracellular and Extracellular Staining was Performed as
Described
[0396] (http://www.metazoa.com/UPL3287). Intracellular probes for
AKT and p44/42 MAPK activity was made by conjugating monoclonal
anti-AKTser473 antibody or monoclonal anti-p44/42 phospho
(Thr202/Tyr204) (Cell Signaling Technology) to Alexa-568 dye or
Alexa Fluor 488 (Molecular Probes), using Alexa Fluor protein
conjugation kit (Molecular Probes) respectively. Phospho
specificity was tested by western blotting and FACS analysis to a
variety of PI3K activators (platelet derived growth factor) and
inhibitors (LY294002) for AKT activity, and to epidermal growth
factor and MEK1/2 inhibitors U0126 (CST) for p44/42 MAPK activity
(data not shown). Intracellular staining by
phospho-AKTser473Alexa568 and phospho-p44/42-Alexa488 reflected AKT
kinase and p44/42 MAPK activity in Jurkat cells when stimulated and
inhibited prior to stimulation. Quantitative FACS analysis was
performed as described (Davis et al., 1998; Iyer et al., 1998;
Lenkei et al., 1998).
[0397] In brief, R-phycoerythrin (PE) (Molecular Probes) was
conjugated to indicated antibody as suggested by manufacturer of
protein cross-linking kit (Molecular Probes), tested for proper
stochiometry (data not shown) and quantitated using QuantiBRITE-PE
beads (BD systems). A quantitative calibration curve was generated
using QuantiBRITE-PE beads that contain a known amount of PE
molecule/bead. A linear regression analysis is performed using the
following equation: log.sub.10(PE fluorescence)=slope*log.sub.10(PE
molecules/bead)+intercept. PE fluorescence is determined by taking
the geometric mean of the PE channel. Quantitation is valid only
for antibodies directly conjugated to PE. Using saturating amounts
of antibody and thorough washing ensures all surface antigens are
bound. Preparation of samples on ice reduces antibody
internalization. Surface antigens of cells for an unknown cell
population are determined by computing the PE geometric mean using
the calibration curve. Quantitative FACS analysis provides
approximate estimates for surface antigen expression. Numbers
plotted represent relative surface molecules and not absolute
numbers since antibody valency was not investigated for the
monoclonal antibodies used. Flow cytometry analysis was performed
on a BD FACSCalibur machine and analyzed using FlowJo software
(Tree Star). CellQuest was used for quantitative flow cytometry and
linear regression analysis of QuantiBRITE-PE beads. Flow cytometry
data are representative of 3 independent experiments of 10.sup.6
cells/sample analyzed. 50,000 events were collected or otherwise
noted and calibrated using Calibrite beads (BD systems). Data
plotted in bar graph format is expressed as the mean (bar)+/-SD of
triplicate experiments.
Confocal Microscopy
[0398] Jurkat cells were treated as indicated and adhered to
poly-L-lysine (Sigma) coated sterilized coverslips (10 mg/ml, 30
minutes) by mild centrifugation (1000 RPM, 10 minutes), washed
twice in phosphate buffered saline pH 7.4 (PBS) and fixed in 2.7%
paraformaldehyde (in PBS). Cells were permeabilized for 5 minutes
with 0.1% saponin (in PBS), washed twice in PBS, blocked in 4%
bovine serum albumin (BSA, in PBS), and subjected to antibody
incubation: (primary at 0.1 mg/ml, secondary at 1:1000 dilution in
1% BSA, with several washing steps in between). Primary antibodies
used: anti-PYK2 monoclonal, anti-SYK polyclonal, anti-PYK ptyr402
monoclonal, anti-SYK polyclonal, phospho-tyrosine-FITC. Secondaries
used: anti-mouse-Alexa 488, anti-rabbit-Alexa 488,
anti-rabbitAlexa-568, anti-rabbit-Alexa-568. Stained coverslips
were mounted onto glass slides with Prolong Antifade reagent
(Molecular Probes) and visualized using a Molecular Dynamics
Multiprobe 2010 confocal laser scanning microscope. Images were
compiled using Adobe Photoshop 6.0.
MAPK Kinase Assays
[0399] MAPK activity was detected by immunoprecipitation of active
phosphorylated p44/42 from cells and used in a kinase assay with
Elk-1 fusion protein (Cell Signaling Technologies; CST).
2.times.10.sup.6 NIH3T3 or Jurkat cells were incubated with
immobilized phospho-p44/42 monoclonal antibody (mAb) (1:200, CST)
at 4.degree. C. with gentle rocking motion for 2 hrs.
Immunocomplexes were washed 4.times. with cell lysis buffer and
resuspended in 40 .mu.l kinase buffer (25 mM Tris pH 7.5, 5 mM,
.beta.-glycerolphosphate, 2 mM DTT, 0.1 mM Na.sub.3VO.sub.4, 10 mM
MgCl.sub.2) supplemented with 200 .mu.M ATP and 1 .mu.g of Elk-1
fusion protein (CST) for 30 min at 30.degree. C. Kinase reaction
was terminated with SDS sample buffer boiled for 5 min, and
phosphorylation state of Elk-1 was detected by immunoblotting and
visualized using ECL detection (Amersham). Immunoblots are
representative of 3 independent virally transduced cell populations
each repeated 3 times (n=9). MAPK activity was verified by MAPK
phosphorylation by immunoblotting with phospho-specific
antibodies
Immunoprecipitations and Immunoblotting
[0400] Cell extracts were prepared by washing 2.times.10.sup.6
cells (treated as indicated) in ice cold PBS and harvesting in
lysis buffer (20 mM Tris pH 7.5, 150 mM NaCl 1 mM EDTA 1 mM EGTA,
1% Triton X-100, 2.5 mM Na.sub.2PO.sub.4, 1 mM,
.beta.-glycerolphosphate, 1 mM Na.sub.3VO.sub.4, 1 .mu.g/ml
Leupeptin, 1 mM PMSF, protease inhibitor cocktail tablet
(Boehringer Mannheim)). Extracts were centrifuged 14,000 RPM for 5
min at 4.degree. C. and cell lysates (20 .mu.g as determine by BCA
protein assay (Pierce)) were fractionated on 15% SDS-polyacrylamide
gel electrophoresis and transferred to PVDF membranes using
standard procedures. Immunoprecipitations (IP) were pre-cleared
with protein A/G plus-agarose beads (Santa Cruz Biotechnologies;
SCBT). IP was incubated for 1 hr with primary antibody, 1 hr with
protein A/G plus-agarose beads and washed 4.times. with lysis
buffer. Blots were incubated with the indicated antibodies and
developed using ECL (Amersham). Fluorescent blots were visualized
on a Kodak Digital Image station 440 C station. Immunoblots
stripped and reprobed (as indicated) were done by incubating with
stripping buffer (62.5 mM Tris, pH 6.8, 10% SDS, 1%
3-mercaptoethanol) for 30 minutes at 55.degree. C. and subjected to
a repeat of the entire immunoblot protocol.
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Example 4
Immune Cell Survival: Activation of the PKB/AKT Pathway
Intracellular Adhesion Molecule-2 (ICAM-2)
[0538] In this Example, using the methods and compositions of the
present invention, the present inventors (also referred to herein
as "we") using a retroviral cDNA library in a functional genetic
screen, identified intracellular adhesion molecule-2 (ICAM-2), a
member of the immunoglobin-family of adhesion molecules, as a
potent inhibitor of several activators of apoptosis in varying cell
types and induction settings. The anti-apoptotic effect was mapped
to the activation of the PI3K/AKT pathway. ICAM-2 induced tyrosine
phosphorylation of ezrin recruited PI3 kinase to the membrane and
resulted in phosphatidylinositol 3,4,5 production, PDK-1 activity,
AKT membrane translocation and activation and subsequent
phosphorylation of AKT targets BAD, GSK3, FKHR and AFX. The ICAM-2
mediated survival function was abrogated by pharmacological
inhibitors of Src (herbimycin A), Rho-dependent kineses (Y-27632),
phosphoinositide turnover (Psi-tectorigenin), and of PI3 kinase
(wortmannin and LY294002), indicating activation of AKT and its
downstream effectors were dependent on PI3K recruitment to the
plasma membrane by an ICAM-2 induced ezrin activation. Primary
CD19+ cells were protected from TNFa and Fas mediated apoptosis
following ICAM-2 clustering and presented elevated AKT activity and
phosphatidylinositol 3, 4, 5 (PIP3) as detected by direct single
cell flow cytometric measurements of intracellular AKT kinase
activity and phosphatidylinositol levels. ICAM-2s engagement with
its natural receptor, LFA-1, induced AKT activity similar to that
of antibody crosslinking. This cell survival signal was shared only
by ICAM-3 in primary B cells, and not by ICAM-1, CD43, and CD44,
indicating that the binding of ezrin or interaction with LFA-1 is
not sufficient for initiation of the cell survival signal as
observed for ICAM-2. These results attribute a novel survival
signaling function to ICAM-2 that might provide an explanation for
both the role of ICAM-2 overexpression in B-cell lymphomas and
mechanisms by which ICAM-2 might signal intracellular communication
in cell-to-cell contact at various immunological synapses.
Introduction
[0539] A cell's commitment to cellular proliferation or programmed
cell death is a balance of the survival and death signals
communicated from both the immediate environs, such as
extracellular matrix (ECM) interactions, cell-cell contact, or more
distant sites through endocrine and paracrine factors (Ruoslahti
and Reed, 1994). Survival pathways are proposed to function during
early development where apoptosis plays a key role in shaping
organogenesis (Raft, 1992) and are eminent in the maturation of the
immune system. Clonal selection of antibody forming cells and
maintenance of memory B cells are essential processes that require
activation of cell survival pathways. Similarly, the lack of
survival signals is exemplified in the phenomenon of anoikis, where
epithelial cells undergo apoptosis when ECM-attachment is blocked
(Frisch and Ruoslahti, 1997). ECM survival signals are presumably
mediated by activation of cell-surface receptors via integrin
clustering, contributes to the specificity of cell cell/cell-matrix
interactions, and deregulation of ECM-integrin signaling leads to
anchorage-independent growth (Hulleman and Boonstra, 2001).
Identification of analogous molecules in lymphoid cells as those
that can antagonize cell death or override growth inhibition
programs would be pivotal in understanding intrinsic cell survival
programs that can go awry in lymphatic disorders and possibly
contribute to metastatic spread.
[0540] Functional characterization of molecules involved in
cellular adhesion has been focused on signal transduction pathways
attributed to integrins and cadherins, which can contribute to
ECM-survival signals (de Fougerolles et al., 2000; Schneller, 2001;
Shinohara et al., 2001). Adhesion molecules of the immunoglobin
(Ig) superfamily have been largely overlooked as potential
signaling molecules. ICAM-2 (CD102) is a member of the
Ig-superfamily of cell surface proteins and mediates leukocyte
binding to LFA-1 (CD11a/CD18) and MAC-1 (CD11b/CD18) (van Kooyk and
Figdor, 2000). As a cell surface adhesion member involved in
leukocyte recruitment in tissues, ICAM-2 is expressed in low levels
on most leukocytes including T and B lymphocytes, monocytes,
platelets and early CD34.sup.+ hematopoetic progenitor cells (de
Fougerolles et al., 1991; Diacovo et al., 1994; Nortamo et al.,
1991). In addition, ICAM-2 constitutive expression has been
observed on all vascular endothelium (de Fougerolles et al., 1991).
Based on the expression pattern of ICAM-2, it has been postulated
to be involved in lymphocyte recirculation, trafficking, and
extravasation. ICAM-2 deficient mice support this by demonstrating
that eosinophil trafficking is augmented in inflammatory responses
(Gerwin et al., 1999). Surprisingly, this phenotype is relatively
mild considering the range of cell types upon which ICAM-2 is
expressed. It suggests that the roles ICAM-2 plays are subtle or
are redundant with other pathways. Thus, the ICAM-2 deficient mice
do not sufficiently detail the roles of ICAM-2, warranting further
characterizations of the mechanisms by which ICAM-2 acts are
needed.
[0541] In contrast to ICAM-2's putative role as an adhesion
molecule, it is surprising to find ICAM-2 highly expressed on both
endothelial cells in lymphomas and CD5.sup.+ B cells from B-cell
chronic lymphatic leukemia (B-CLL) patients (Molica et al., 1996;
Renkonen et al., 1992). Lymphoproliferative diseases inevitably
inhibit adhesion dependency-loss of adhesion is one of the primary
means by which metastatic spread occurs. However, recent gene
expression profiling of large B-cell lymphomas from patients
indicated an elevated expression of ICAM-2 (Alizadeh et al., 2000).
Interestingly, ICAM-2 is the only ICAM (1-5) that maps to
chromosome 1 7q23-25 (Sansom et al., 1991), a segment associated
with genomic instability and recently identified as a segment of
high aberration in various cancers (Dion et al., 2000; Dobo et al.,
1995; Russell et al., 2000; Sugai et al., 2000). Despite these
observations, ICAM-2's role and molecular characterization in the
progression of lymphatic disease states has not been addressed.
[0542] We devised a genetic screen to identify genes that are
involved in regulation of apoptosis and augmented in malignant
phenotypes. Cells transduced with a human lymphoid cell line
(Jurkat) retroviral vector cDNA library were screened for an
anti-apoptotic phenotype. One cDNA demonstrated reproducible
antiapoptotic activity in a phenotypic transfer assay. This cDNA
encoded full-length intracellular adhesion molecule-2 (ICAM-2).
Here we show functional characterization of the ICAM-2 signal as
being capable of mediating a cell survival signal upon its ligation
and interaction with its endogenous receptor leukocyte
function-antigen-1 (LFA-1). ICAM-2 mediates a survival signal
sufficient to block apoptosis by activation of the PI3K/AKT
pathway, being contingent on ezrin activation by Src tyrosine
phosphorylation and Rho-kinase dependent threonine phosphorylation.
Ezrin activation recruited PI3K to the cell membrane in lymphoid
cells, thereby initiating activation of the PI3K/AKT pathway.
Furthermore, development of [prob] probes to measure intracellular
AKT and PI3K activity by flow cytometry allowed for the
simultaneous measurement of kinase activity as a function of ICAM-2
clustering on human peripheral blood monocytes (PBMC).
Multi-parameter FACS analysis confirmed ICAM-2 clustering led to
phosphatidylinositol 3,4,5 production and AKT activity in CD19+
primary human cells and subsequent protection from Fas and [TNFa]
TNF.alpha. mediated apoptosis. Interestingly, activation of the
PI3K/AKT pathway was shared by ICAM-3 and not by [ICA.about.1]
ICAM-1, CD43, CD44 indicating that molecular differences exist
amongst the 19 adhesion molecules that are capable of binding ezrin
(Serrador et al., 1997; Yonemura and Tsukita, 1999). Ligation of
ICAM-2 by its endogenous receptor LFA-1 was observed to induce AKT
activity, illustrating that the ICAM-2/LFA-1 interaction is capable
of activating the PI3K/AKT pathway. These observations identify a
bimodal functional role for [ICA.about.2] ICAM-2 in mediating cell
survival. Overexpression of ICAM-2 conferred an anti-apoptotic
phenotype, suggesting that inappropriate expression of ICAM-2 could
contribute significantly to the antiapoptotic phenotypes in the
cumulative process that leads to tumor progression and metastatic
spread. The findings also underscore a novel positive role for
ICAM-2 in signaling pathways involving
Src/Rho-Kinase/Ezrin/PI3K/PDK-1/AKT and downstream effectors upon
LFA-1 engagement in cell-to-cell contact with implications for
other ICAM-2 interactions such as ICAM-2/DC-SIGN and
ICAM2/Mac-1.
Results
[0543] Screening a retroviral cDNA library in an anti-apoptotic
functional assay
[0544] We devised a retroviral library approach to screen for cDNAs
that alter apoptotic signaling and encode for anti-apoptotic
molecules (FIG. 19A). cDNAs from a malignant cell type (Jurkat T
cell leukemia) were screened for anti-apoptotic function in a
recipient non-malignant (fibroblast) cell. Apoptosis was induced
with staurosporine (STP), a kinase-inhibiting plant-derived
alkaloid, and a potent inducer of caspase-dependent cell death in
most cell types. Induction conditions were determined that limited
the level of spontaneous background while maximizing the extent of
apoptotic death (minimal background of one surviving cell in a
STP-treated mock library control in .about.10.sup.4 starting
cells). 10.sup.7 NIH3T3 fibroblasts were infected with a retroviral
cDNA library derived from Jurkat cells at an infection frequency of
40% to limit the number of integrations to a single event per cell.
Control retroviruses were prepared expressing LacZ- or Bcl2, and
infected into a similar number of NIH3T3 cells. Apoptosis was
induced in the transduced cell culture by staurosporine treatment
and the cells were then allowed to recover (FIG. 19A). Surviving
cell clones were expanded, replated and retreated with
staurosporine. The complexity of the expressed cDNAs in the
surviving population was assessed with RT-PCR. A few major bands
were observed following three rounds of selection (FIG. 19B).
[0545] Replication-competent Moloney murine leukemia virus (MMLV)
was applied to the enriched cell populations. Upon integration and
expression of the MMLV proteins, resident retroviral constructs
from the library were co-packaged into infectious virions and
transferred to naive target NIH3T3 cells. The staurosporine
selection process was then reapplied. In this manner true
phenotype-inducing clones enrich at a rate of 1/background (see
materials and methods for elaboration). Three of the pooled
libraries showed enrichment for specific bands after PCR (see FIG.
19B lanes 1 and 2). Several bands were rescued by PCR cloning and
one of these bands was sequenced and demonstrated to encode
full-length ICAM-2 cDNA (Staunton et al., 1989), an immunoglobulin
superfamily member that regulates leukocyte adhesion through
interaction with its integrin counter-receptor, LFA-1 (de
Fougerolles et al., 1991; Simmons, 1995).
ICAM-2 Mediates a Survival Signal
[0546] The ICAM-2 cDNA was cloned into a retroviral vector
(pBMN-Z-IN) that carries an internal ribosome entry site (IRES)
upstream of the neomycin resistance gene. NIH3T3 fibroblasts were
infected with retroviruses capable of expressing the ICAM-2 gene,
along with appropriate control vectors pBMN-Z-IN (vector control)
and pBMN-Z-IN-GFP (GFP vector control). Expression of the 60 kD
ICAM-2 glycoprotein in neomycin-selected NIH3T3 fibroblasts
infected with the pBMN-Z-IN-ICAM-2 construct (referred to as ICAM-2
cells) was verified by immunoblotting (FIG. 19C), flow cytometry
(FIG. 19D), and immunoprecipitation (FIG. 22A). The expressed
ICAM-2 protein co-migrated with the native protein from Jurkat T
cells (data not shown).
[0547] Staurosporine treatment is thought to mimic
factor-withdrawal in cells (Raff, 1992), and induces apoptosis by
inhibiting PKC, PKA, and PKG at nanomolar concentrations among
other kineses (Meggio et al., 1995). ICAM-2 expression. in NIH3T3
cells limited the extent of apoptosis induced by staurosporine
treatment as determined by an annexin-V binding assay (FIG. 20A),
pyknotic nuclei count (FIG. 20B) and the BrdU TUNEL assay (data not
shown confirming the clone's selection by phenotype in the screen.
Interestingly, not all forms of apoptosis were inhibited by
overexpression. ICAM-2 overexpressing Jurkat T cells did not
inhibit apoptosis across a range of concentrations of a monoclonal
antibody to the Fas receptor, contrasting inhibition of
staurosporine induced apoptosis (FIG. 19E, panel 2-3, elaborated
below).
[0548] A report correlating ICAM-2 expression with a
lymphoproliferative disorder, B-cell chronic lymphatic leukemia
(B-CLL) (Molica et al., 1996), prompted us to test the
anti-apoptotic activity of ICAM-2 in the mouse pre-B-cell line,
70Z/3. ICAM-2 expression inhibited staurosporine-induced apoptosis
in 70Z/3 cells (FIG. 20B). Given the indication that staurosporine
mimics factor withdrawal, we assessed the ability of ICAM-2
expression to protect factor-dependent cells from factor
withdrawal. ICAM-2 expression in the IL-3-dependent pro-B cell line
BaF3 resulted in a delayed onset of apoptosis following IL-3
deprivation (FIG. 20B). Furthermore, we tested the ability of
ICAM-2 to rescue BaF3 cells from apoptosis induced by treatment
with anti-Fas antibodies. ICAM-2 demonstrated a potent inhibition
of apoptosis through the Fas-pathway in these cells (FIG. 20B).
These results are as good as or better than transduction controls
with Bcl2 and therefore the apparent effects cannot be attributed
to modest effects on apoptosis or retroviral transduction (FIG.
20B, data not shown). There is, however, cell specificity to the
anti-apoptotic effect by virtue of ICAM-2 ectopic expression as
ICAM-2 overexpressing Jurkat T cells were not protected from
Fas-induced apoptosis but were protected from staurosporine induced
apoptosis (FIG. 20B). High throughput proteome analysis recently
identified that in Jurkat T cells, Fas induced apoptosis results in
a rapid destruction of 12 cytoskeletal proteins, alters
phosphorylation states of various chaperone proteins and
cytoskeletal structural proteins, and presents a more "aggressive"
form of cell death than staurosporine induced apoptosis (Gerner et
al., 2000). Therefore different cell death inducers have specific
physiological characteristics in Jurkat T cells supporting the
differences observed (Johnson et al., 2000). However, we later
provide evidence for a bimodal function of ICAM-2, in which
ligation of endogenous ICAM-2 on Jurkat cells is sufficient to
block Fas induced apoptosissuggesting that overexpression is
insufficient to initiate cell survival in this cell type (described
below).
[0549] The initial screening was performed in fibroblasts, and it
is therefore unlikely that ICAM-2's anti-apoptotic effect was
mediated through its lymphocyte-specific integrin ligand, LFA-1
(CD11a/CD18), since NIH3T3 do not express LFA-1 (data not shown).
To address this possibility in lymphoid cells, we prepared an
extracellular domain-deleted AN version of ICAM-2 and tested it in
BaF3 cells. Expression of the cytoplasmic domain was sufficient to
impart full anti-apoptotic activity (FIG. 20B). This indicates that
the cytoplasmic domain of ICAM-2 provides a survival signal when
overexpressed ectopically, and likely exerts its effect by
mimicking receptor crosslinking. Since signaling through
ICAM-family cytoplasmic domains is poorly understood, we sought to
identify the signaling pathway by which it conferred resistance to
apoptosis. The ICAM-2 survival function maps to a
membrane-cytoskeleton linker protein binding motif ICAM-2 is
regarded as an adhesion molecule and has been shown to be
interconnected with the actin cytoskeleton by linker proteins
.alpha.-actinin and ezrin, both of which bind the ICAM-2
cytoplasmic domain. (Heiska et al., 1996; Helander et al., 1996).
To assess the potential role of .alpha.-actinin in mediating the
ICAM-2 anti-apoptotic signal, the .alpha.-actinin recognition
sequence was changed to a scrambled sequence unable to bind
.alpha.-actinin in vitro (Heiska et al., 1996). Retroviral
constructs encoding ICAM-2, a C-terminal deletion mutant
(ICAM2-.DELTA.C) and a full-length ICAM-2 protein with the mutated
.alpha.-actinin binding motif (ICAM2C scrambled) were used to
transduce NIH3T3 cells (FIG. 20C). The infected cells were sorted
by FACS using an ICAM-2 monoclonal antibody (IC2/2) recognizing
only native N-terminal ICAM-2 (de Fougerolles et al., 1991). This
verified that ICAM-2, ICAM2-.DELTA.C, or ICAM2-C-scrambled proteins
were properly folded and targeted to the outer face of the plasma
membrane. The NIH3T3 cells expressing the ICAM-2 mutants were
assayed for survival following both etoposide treatment (another
potent inducer of apoptosis in NIH3T3 cells) and staurosporine
treatment. ICAM-2 imparted potent long-term survival on NIH3T3
cells and the survival signal was lost when the terminal deletion
of ICAM-2 (ICAM2-.DELTA.C) was expressed in cells (FIG. 20C).
Mutation of the a-actinin binding site in the ICAM-2 cytoplasmic
tail also did not provide any protection against etoposide or
staurosporine treatments. Although the motif within ICAM-2's
C-terminal is identified as an .alpha.-actinin binding site, recent
studies have shown that the positively charged amino acid cluster
the cytoplasmic domain can also interact with ezrin, a member of
the ezrin/radixin/moesin (ERM) cytoplasmic linker protein family
(Yonemura et al., 1998). Whereas both .alpha.-actinin and ezrin
co-immunoprecipated with only full length ICAM-2, a significant
difference in the quantity of ezrin binding protein was observed
relative to .alpha.-actinin (FIG. 22A), supporting the postulate
that these cytoskeleton linker proteins were necessary but may
differentially relay an anti-apoptotic signal. Experiments designed
to block activation steps of each of these cytoplasmic linker
proteins elucidated differences between fibroblastoid and lymphoid
cell types and their requirements for .alpha.-actinin and/or ezrin
to relay the anti-apoptotic signal (elaborated below).
ICAM-2 Signals Through PI3K/AKT Kinase
[0550] As survival signaling through many adhesion molecules
involves PI3 kinase (Frisch and Ruoslahti, 1997; Khwaja et al.,
1997), we analyzed the role of this pathway in the ICAM-2
anti-apoptotic signal. Pretreatment of ICAM-2 expressing BaF3 cells
with the PI3 kinase inhibitor wortmannin blocked the ICAM-2
mediated anti-apoptotic effect (FIG. 21A, left panel), implicating
PI3 kinase in the ICAM-2 survival signaling cascade. Under these
conditions vehicle-treated ICAM-2 expressing BaF3 cells were
resistant to staurosporine induced apoptosis. Similarly, treating
ICAM-2 transduced NIH3T3 with LY294002 abrogated ICAM-2's
anti-apoptotic effect as measured by both annexin-V binding and
BrdU TUNEL assay using flow cytometry (FIG. 21A, data not shown[,
reviewers see Supplementary FIG. 19]). Anti-apoptotic effect was
not abrogated with inhibitors to p44/42 MAPK (U0126 and PD98059),
p38 MAPK (SB 203580), PKC isozymes (bisindolymaleimide I and 11),
or PKA (H-89), excluding the involvement of these kinases in the
signal transduction pathway (data not shown).
[0551] We utilized confocal microscopy to visualize the cellular
distribution of PI3K, AKT, the p85 regulatory subunit of PI3K, and
ezrin. We observe both PI3K and AKT to be concentrated at the outer
periphery of ICAM-2 cells (FIG. 21B). Ezrin and the p85 subunit was
visualized to co-localize more extensively in ICAM-2 cells versus
vector control (FIG. 21C). ICAM-2 overexpression had augmented the
distribution of PI3K and AKT to favor a membrane localization which
is required for their respective activation. Alpha-actinin and
ezrin both co-immunoprecipated with ICAM-2 (FIG. 22A) and
subsequently tested for PI3K interaction since direct PI3K
interaction with ICAM-2 was not observed in the absence of either
.alpha.-actinin or ezrin (data not shown).
[0552] Development of single cell based phosphatidylinositol 3,4,5
triphosphate (PIP3) and phosphatidylinositol 4,5 bisphosphate
(PIP2) detection made it possible to assess PIP3/PIP2 levels within
intact cells and reflect PI3K and PI4K/PLCy1 kinase activities
(Perez and Nolan, manuscript in preparation). ICAM-2 cells
presented uniformly high levels of PIP3 versus the asynchronous
production of PIP3 in vector controls and were inhibited by serum
starvation and incubation with LY294002 (FIG. 22B). Production of
PIP3 serves as a secondary messenger to recruit pleckstrin domain
containing proteins, such as AKT, to the plasma membrane, and also
serves to activate others, namely phosphatidylinositoLdependent
kineses (PDK-1 and PDK-2) (Blume-Jensen and Hunter, 2001). The
production of PIP3 in ICAM-2 cells paralleled the AKT localization
pattern observed as expected for active PI3K.
[0553] PI3 kinase is known to regulate apoptosis through its
downstream effector AKT (PKB) kinase (Downward, 1998). AKT kinase
has a potent anti-apoptotic effect downstream of diverse apoptotic
stimuli, including staurosporine (Marte and Downward, 1997)(data
not shown). We assessed PDK-1 kinase activity in ICAM2 cells and
found elevated PDK-1 activity in comparison with vector control
(FIG. 22C). This effect reflected the increased levels of PIP3
detected in ICAM-2 cells as it was inhibited by incubation with
LY294002, and to a lesser extent, Y-27632, a specific
pharmacological inhibitor of Rho-associated protein kineses.
Cytosolic/membrane fractionation of ICAM-2 cells confirmed
localization of AKT to the membrane versus cytoplasmic localization
in vector controls (FIG. 22D), congruent with confocal microscopy
of AKT localization. ICAM-2 expressing fibroblast demonstrated an
elevated level of AKT activation that was absent in ICAM2-AC or
mock transduced cells (FIG. 22D). We further verified that this
ICAM-2-dependent elevated AKT kinase activity is maintained
following STP treatment using both kinase assays and by verifying
phosphorylation of both ser473 and thr308 (FIG. 22E). A target of
AKT kinase is the pro-apoptotic Bcl2 family member, BAD which is
normally held in an inactive state by phosphorylation of serines
112 and 136, and is bound to 14-3-3. Upon induction of apoptosis,
BAD is dephosphorylated at both ser112 and ser136, and dimerizes
with Bcl2. As a result, the equilibrium of Bck2/Bcl-XL is shifted
to favor release of BC.about.XL to mediate Cytochrome C release and
apoptosis (Datta et al., 2000). BAD is dephosphorylated following
staurosporine-treatment of ICAM2-.DELTA.C and mock-transduced
NIH3T3 cells, concomitant with the induction of apoptosis (FIG.
22F); however, ICAM-2 expression results in the maintenance of BAD
phosphorylation consistent (FIG. 22F) with sustained AKT kinase
activity (FIG. 22E).
[0554] BAD itself can integrate a number of signal transduction
pathways with a similar outcome, possessing 3 phosphorylation sites
that can be phosphorylated independent of one another: ser112
mediated by active p90Rsk1, ser136 mediated by active AKT, and
ser155 mediated by both active PKA and active p90Rsk1. ICAM-2 and
its role in connection to BAD ser112 phosphorylation is to be
described elsewhere (Perez and Nolan, manuscript in preparation).
Phosphorylation of BAD ser155 was not observed (data not shown).
The anti-apoptotic signal had little apparent effects on the
anti-apoptotic proteins Bcl-2 and Bcl-x.sub.L/S (FIG. 22E) and was
found to be independent of caspase inhibitory proteins, cell cycle
regulators, anti-apoptotic pathways using Bcl2 or additional cell
survival programs (data not shown). This indicated that typical
anti-apoptotic pathways did not mediate the survival signal (data
not shown). Another target of AKT kinase involved in anti-apoptotic
signaling, GSK3, was found to be phosphorylated in ICAM-2
expressing NIH3T3 and probably contributes to the anti-apoptotic
effect (FIG. 22F, bottom panel). Additional AKT substrates, namely
p70S6K and FKHR were also found to be phosphorylated in addition to
a decreased detection of cleaved caspase products in ICAM-2 cells
induced to apoptose (data not shown).
ICAM-2 Crosslinking Confirms a Role for Endogenous ICAM-2 in
Providing an Anti-Apoptotic Signal
[0555] The ICAM-2-dependent elevation of activated AKT levels in
fibroblasts is independent of ligand interactions as determined by
the fact that ICAM-2 .DELTA.N can protect cells from apoptosis and
ICAM2-.DELTA.C cannot activate AKT. This is indicative of the
signaling mechanism driven by oligomerization of surface ICAM-2
molecules, a common modus operandi for adhesion molecules. The
surface oligomers may create interaction sites within their
cytoplasmic domains, recruiting signaling molecules to participate
in membrane proximal interactions. Quantitative FACS analysis
revealed that the density of ICAM-2 molecules on the cell surface
vary widely between cell types (FIG. 23A see Experimental
Procedures for elaboration) and correlated with varied expression
patterns as previously described (de Fougerolles et al., 1991).
Basal expression levels of ICAM-2 on lymphocytes was 2-4 orders of
magnitude less than the enforced expression from the retroviral
vector as determined by the number of ICAM-2 surface molecules. We
postulated that antibody cross-linking could emulate ICAM-2s
interaction with its receptor, and therefore decided to test
whether endogenous ICAM-2, when cross-linked, could confer the
phenotypes observed as in the overexpression systems.
[0556] We cross-linked (clustered) endogenous Jurkat T cell ICAM-2
surface molecules with monoclonal antibodies and assayed activation
of the PI3K/AKT pathway. Ezrin was found to associate and become
tyrosine phosphorylated as a function of ICAM-2 cross-linking as
detected by co-immunoprecipitation with ICAM-2 (FIG. 23B). This
suggests that ezrin translocates to membrane in order to interact
with the C-terminal of ICAM-2. Subsequently, ezrin becomes tyrosine
phosphorylated upon interacting with ICAM-2 as a time delay is
detected upon co-immunoprecipitation, indicating that
phosphorylation is mediated by a membrane proximal protein tyrosine
kinase, since ICAM-2 lacks tyrosine kinase activity (data not
shown). Ezrin tyrosine phosphorylation and concomitant association
with p85 was observed as a function of ICAM-2 cross-linking, with a
notable enhancement of ezrin threonine phosphorylation (FIG. 23D)
effects of which were not shared by .alpha.-actinin (data not
shown).
[0557] In order to identify upstream kineses capable of tyrosine
phosphorylating ezrin as a function of ICAM-2 ligation, we
developed a phosphotyrosine-protein based elisa to screen for the
inhibition of ezrin tyrosine phosphorylation in vivo by various
known inhibitors of protein kineses (Perez and Nolan, manuscript in
preparation). Of the inhibitors screened, herbimycin A, a potent
inhibitor of src tyrosine kinase family members src and p62.sup.yes
(Haas et al., 2000; Schieven et al., 1992) was found to inhibit
tyrosine phosphorylation of ezrin, comparable to genistein, which
served as a control for general tyrosine kinase inhibition (FIG.
23C). Surprisingly, we also found inhibitors of ROCK, a
Rho-dependent serine/threonine kinase (Y-27632), inhibitors of
GTPases, and inhibitors of phosphoinositide turnover
(Psi-Tectorigenin) to inhibit the tyrosine phosphorylation of
ezrin, with minor affects by PKC isozyme inhibitors
bisindolymaleimide I and II. Given the design of the screen to
detect tyrosine residue phosphorylation, we speculate that
activation of Rho-dependent processes may be a prerequisite for
ezrin to be tyrosine phosphorylated by src (elaborated below).
[0558] Ligation of ICAM-2 on the surface of Jurkat T cells induced
PDK-1 activity (FIG. 23E) and incidentally membrane localization of
PI3K and AKT (FIG. 23F). Pursuant AKT activation, dual
phosphorylation of AKTser473 and AKTthr308, and phosphorylation of
AKT substrates BAD, GSK3, FKHR, and AFX followed ICAM-2
crosslinking in Jurkat T cells as a function of time (FIG. 24A).
Crosslinking of ICAM-2 on a different cell type, pro-B cells, which
also express low endogenous levels of ICAM-2 (see FIG. 23C) and
displayed an antiapoptotic phenotype upon ICAM-2 transduction (FIG.
20B) similarly activated AKT and phosphorylation of AKT substrates
BAD and FKHR in a time dependent manner (FIG. 24B). ICAM-2
crosslinking was found to protect Jurkat T cells from staurosporine
induced apoptosis verifying the resultant outcome of the PI3K/AKT
pathway activation (FIG. 24C). Incubation with LY294002 abrogated
the antiapoptotic effects initiated by cross-linking ICAM-2 in
Jurkat T cells and BaF3 cells (data not shown).
[0559] We had observed that overexpression of ICAM-2 was not
sufficient to block Fas induced apoptosis in Jurkat T cells (FIG.
19E, 20C). Contrary but not necessarily contradictory, we observed
crosslinking of endogenous ICAM-2 on Jurkat T cells to efficiently
protect against Fas induced apoptosis and be abrogated in the
presence of GTP.gamma.S, Psi-tectorigenin, Y-27632, and herbimycin
A (FIG. 24D), inhibitors identified to block ezrin tyrosine
phosphorylation (see FIG. 23C). These observations suggest that
ICAM-2 clustering by virtue of antibody crosslinking is necessary
for imparting the cell survival signal and that ICAM-2
overexpression in this cell type is not sufficient to block Fas
induced apoptosis. Furthermore, the abated ICAM-2 induced cell
survival signal by compounds GTP.gamma.S, Psi-tectorigenin,
Y-27632, and herbimycin A in lymphoid cells contrasts the mild
effects observed in ICAM-2 overexpressing NIH3T3 cell types (data
not shown). This suggests that ezrin is the predominant linker
between ICAM-2 and PI3K in lymphoid cells, since these compounds
affect the activation of ezrin and not .alpha.-actinin (Freeman et
al., 2000; Izaguirre et al., 1999; Morishige et al., 2001; Nakamura
et al., 2000). This was verified by ezrin, and to a lesser extent
.alpha.-actinin, predominantly coimmunoprecipitating with PI3K
proceeding Jurkat ICAM-2 crosslinking (FIG. 24E), although PI3K
co-immunoprecipitated with both ezrin and .alpha.-actinin in
reciprocal co-immunoprecipitations in fibroblastoid cells (see FIG.
22C). In addition, we have observed ICAM-2 overexpressing
fibroblastoid cells to dampen the dynamics of the cytoskeleton
architecture and require this augmentation for maintenance of its
survival signal, contrasting the requirements of a dynamic
cytoskeleton architecture in lymphoid cells. Therefore, ICAM-2
ligation and ICAM-2 overexpression present molecular differences in
their mode of activating the PI3K/AKT pathway in cells of different
origins.
ICAM-2 Protects Primary CD19+ B Cells from TNF.alpha. and Fas
Induced Apoptosis Via PI3K/AKT Activation and is Distinct from
ICAM-1, ICAM-3, CD43, and CD44
[0560] Although the results for AKT activity were reproducible, we
were unsatisfied with the western blot analysis/kinase activity
assays for whole blood derived cells and so developed a new
procedure for single cell analysis of AKT activity by flow
cytometry described below (Perez and Nolan). We also developed FACS
based methodologies for phosphatidylinositol 3,4,5 triphosphate,
and phosphatidylinositol 4,5 bisphosphate detection, reflective of
phospholipid turnover, PI3K and PI4K/PLCy activity respectively
within single cells (Perez and Nolan, manuscript in preparation).
We utilized FACS based AKT kinase assays and FACS based PIP3 and
PIP2 measurements to attribute a physiological relevance for ICAM-2
in vivo. Human PBMC were crosslinked for ICAM-2 prior to treatment
with TNF.alpha. and anti-Fas monoclonal antibody. Treated PBMC were
subjected to flow cytometry, gated by immunophenotype for CD4 (T
cell marker) and CD19 (B cell marker) and subsequently assayed for
AKT activity and apoptosis by multi-parameter FAGS. Intracellular
AKT kinase activity measurements were achieved by development of a
phospho-specific fluorescent probe for AKT-phospho ser473
phosphorylation site on AKT detectable by FAGS (Perez and Nolan,
submitted). Both CD4+ T cells and CD19+ B cells exhibited AKT
activity when ICAM-2 was clustered and induced AKT activity
preferentially protected B cells from apoptosis to Fas and
TNF.alpha. induced apoptosis (FIG. 25A). There was little apparent
antiapoptotic effect on CD4+ T cells perhaps due to the fact that
these T cells were not strongly induced by Fas or TNF.alpha. to
undergo apoptosis with our conditions and require prior stimulation
with IL-2 or PMA/ionomycin (data not shown). Protection from
apoptosis in primary B cells correlated perfectly with AKT
phosphorylation at serine 473, confirming prior roles for this
target serine in the protective effect of AKT against Fas and
TNF.alpha. induced apoptosis. FACS based kinase activity
measurements for AKT allow unique activation profiles in distinct
lymphocyte populations to be assessed and circumvent the functional
augmentation often observed in pre-sorting for such cell
populations (data not shown). Differences were observed when ICAM-2
was compared to other ezrin binding surface molecules, namely
ICAM-1, -3, CD43, and CD44. PIP3 and PIP2 FACS based measurements
identify ICAM-2 as increasing the ratio of PIP3/PIP2, congruent
with PI3K activity (FIG. 25B). ICAM-3 was found to increase both
PIP3 and PIP2, with no effect on phosphoinositide levels by ICAM-1
(FIG. 25B). Although, ICAM-2, -3, CD44, and CD43 were found to
activate AKT in primary CD4+ and CD19+ cells to varying extents
(FIG. 25B, lower panel), only ICAM-2 and ICAM-3 effectively blocked
TNF.alpha. induced apoptosis (FIG. 25C) and Fas induced apoptosis
(data not shown) in CD19+ B cells, indicative of functionally
distinct properties possessed by ICAM-3, CD44, and CD43. The ICAM-2
anti-apoptotic effect was abrogated by incubation with
Psitectorigenin and Y-27632 in CD19+ human B cells (FIG. 25E),
verifying the Rho kinase and phosphoinositide dependency in primary
human cells. Incubation with GTP.gamma.S loading conditions and
herbimycin A induced apoptosis in primary cells for unknown reasons
(data not shown). Thus, ICAM-2 oligomerization leads to the
apparent membrane recruitment of PI3-kinase, results in PIP3
production, and subsequent activation of AKT kinase, initiating a
potent inhibition of apoptosis in Jurkat T cells, BaF3 pro-B cells,
and human primary lymphoid cells.
ICAM-2 Interactions with its Natural Receptor LFA-1 Activates
AKT
[0561] We decided to test whether ICAM-2 oligomerization by virtue
of interacting with its natural receptor, LFA-1 was sufficient to
activate the PI3K/AKT pathway as elucidated by antibody
crosslinking experiments. We developed an overlay assay, using the
ICAM-2 retrovirally transduced NIH3T3 cells as ICAM-2 presenting
cells to LFA-1+Jurkat cells, to see if mixing of these two cell
populations would induce AKT activation in the ICAM-2 expressing
cells. Pre-incubation of the ICAM-2 cells with LY294002 abolished
the intrinsic AKT activity due to the consequences of ICAM-2
overexpression in these cells. Provided that PI3K inhibition for
prolonged periods of time might present an irreversible inhibition,
the overlay assay was designed to identify AKT activity in the
ICAM-2 cells after one hour blockade of PI3K at a concentration (2
.mu.M) close to the IC.sub.50 of the compound. This time period and
concentration was found to block AKT activity in control
experiments and be inducible upon ICAM-2 crossinking (data not
shown). The overlay assay takes advantage of our recently developed
FACS based AKT assay, in conjunction with immunophenotypic markers
to identify which specific cells in a heterogeneous mixture present
AKT kinase activity. Jurkat cells express low levels of LFA-1 and
no detectable levels of Mac-1, two endogenous receptors for ICAM-2
(data not shown). ICAM-2 cells express full length human ICAM-2,
and these NIH3T3 derived cells express low levels of mouse ICAM-1,
-2 and no detectable levels of mouse ICAM-3 (data not shown),
interactions of which are thought to be insignificant with human
LFA-1, given the species and stoichiometric ratios of human ICAM-2
to murine ICAM-1, -2 (see FIG. 23C, data not shown). We mixed
Jurkat cells with vector control and ICAM2 cells with conditions
that included prior blocking of Jurkat surface LFA-1 and Mac-1
proteins by incubation with monoclonal antibodies (mAb). We
identified the ICAM-2 cells by size differences and absence of the
CD4 T cell marker. We observed that incubation of LFA-1 positive
Jurkat cells activates AKT in ICAM-2 expressing cells and is
inhibited by prior treatment of Jurkat cells with LFA-1 monoclonal
antibodies when compared to Jurkat mixing with vector control cells
(FIG. 25E, Reviewers see attached manuscript similar experiment in
heterogenous lymphoid populations). Prior treatment of Jurkat cells
with Mac-1 mAb also inhibited AKT activation of ICAM-2 expressing
cells, indicating the common .beta. 2-integrin subunit between
LFA-1 and Mac-1 is necessary in ICAM-2 oligomerization by these
heterodimeric receptors. Because the ICAM-2 induced signal had to
overcome the transient PI3K inhibition in our conditions, we did
not expect to see a robust activation of AKT, but rather relied on
the cell-by-cell analysis to see if activation of AKT was inducible
in the presence of LFA-1+ Jurkat cells and inhibited by LFA-1
monoclonal antibodies. Although additional studies are necessary to
verify the activation state of LFA-1 and Mac-1, in addition to the
extent of ICAM-2 oligomerization, the data suggests that a receptor
induced ICAM-2 oligomerization is sufficient to activate ICAM-2s
intracellular PI3K/AKT signal and attributes a physiological role
for ICAM-2 as a signaling molecule in cell-to-cell contact. Wulfing
et al have visualized ICAM-1 surface clustering upon cell-to-cell
contact, supporting that LFA can induce ICAM surface
oligomerization required for intracellular signaling by ICAM-2
(Wulfing and Davis, 1998; Wulfing et al., 1998). In a separate
study, we have adopted the T cell/B cell mixing conditions of
Wulfing et al, and find dual activation of the ICAM-2 AKT signal
and a novel LFA-1 mediated p44/42 MAPK activation measured
simultaneously in leukocyte mixing reactions by FACS based kineses
assays (Perez and Nolan, submitted), further supporting an in vivo
signaling role upon ICAM-2/LFA-1 contact.
Discussion
[0562] A model for ICAM-2 Mediating a Cell Survival Signal
[0563] Our results demonstrate that ICAM-2 ectopic expression in a
wide variety of cell types, and ligation of endogenous ICAM-2 in
lymphoid cells including primary CD19+ B cells can initiate a
survival signal. ICAM-2 induced AKT activation is a survival signal
that can render a cell resistant to chemical (staurosporine and
etoposide), and physiological TNF.alpha. and Fas ligand) apoptotic
inducers and is contingent on ezrin activation, a tyrosine
phosphorylation event requiring both src tyrosine kinase and
Rho-dependent serine/threonine kinase. This results in PI3K
recruitment to the plasma membrane, PIP3 production and subsequent
activation of AKT, which is capable of initiating a variety of cell
survival signals through phosphorylation of downstream targets.
[0564] Although interactions with critical membrane-cytoskeletal
linker proteins .alpha.-actinin and ezrin was demonstrated through
co-immunoprecipitation studies, we note apparent differences
between the dependency of these linker proteins to relay the ICAM-2
survival signal in fibroblastoid and lymphoid cell types. ICAM-2's
antiapoptotic effect was dependent on the 21 amino acid cytoplasmic
domain known to bind .alpha.-actinin. Notably, .alpha.-actinin has
been shown to interact directly with PI3 kinase through the p85
SH3-domain (Shibasaki et al., 1994) and was found to
co-immunoprecipitate with PI3K in ICAM-2 overexpressing transduced
NIH3T3 and associate with PI3K in ICAM-2 crosslinked Jurkat cells
(FIG. 24E). We did not observe phosphorylation of .alpha.-actinin
(data not shown), but did observe ezrin phosphorylation as a
function of CAM-2 crosslinking (FIG. 23B), suggestive of an ICAM-2
induced ezrin activation mechanism.
[0565] The ICAM-2 cytoplasmic domain has been found to bind ezrin,
a member of the ezrin/radixin/moesin (ERM) family of
membrane-cytoskeleton linker proteins (Helander et al., 1996) and
notably bound ICAM-2 in contrast to .alpha.-actinin in our
experiments (FIG. 22A). ERM-proteins regulate cell morphology,
adhesion and growth by promoting membrane-cytoplasmic linkages
(Tsukita and Yonemura, 1997) and include the tumor suppressor,
merlin/schwannomin, implicated in neurofibroblastomatosis type II.
In addition, ezrin and other ERM proteins have been implicated in
different diseases for their modulation of adhesion molecule
distribution (Ichikawa et al., 1998; Stokowski and Cox, 2000;
Turunen et al., 1998; Vinores et al., 1995). Interestingly, exrin
overexpression has been shown to induce ICAM-2 clusterring
(Helander et al., 1996) suggesting that inappropriate surface
protein clustering and subsequent signaling can be strongly
influenced by ERM proteins. Additional studies are needed to
address if the deregulation of the ICAM-2/ezrin protein
stoichiometry by mutually exclusive pathways can impart similar
cell survival capabilities.
[0566] Ezrin has recently been reported to mediate adhesion
dependent survival in epithelial cells through a direct interaction
with PI3-kinase and pursuant AKT activation (Gautreau et al.,
1999). Here we report that ICAM-2 clustering induced ezrin tyrosine
phosphorylation and enhanced threonine phosphorylation, concomitant
with p85 and PI3K association in Jurkat T cells (FIGS. 23D and
24E). This was sufficient to translocate PI3K to the plasma
membrane (FIG. 23F) and initiate production of PIP3 as measured
directly by single cell analysis within primary cells (FIG. 25B)
and indirectly through a PDK-1 activity assay (FIG. 23E). Although
PI3KIAKT membrane localization, PIP3 production, ezrin
phosphorylation, and PDK-1 activity was also observed in ICAM-2
overexpressing transduced NIH3T3 cells, the profound effects of
ezrin tyrosine phosphorylation as induced by ICAM-2 clustering and
inhibition of the ICAM-2 anti-apoptotic effect with Y-27632 and
herbimycin A (FIG. 23D, 24D) preferentially in Jurkat cells lead us
to propose that ICAM-2 mediates a cell survival signal through a
Rho-dependent ezrin activation.
[0567] This then would initiate PI3K recruitment to the membrane
and resultant PIP3 induced PDK-1 and AKT activity. We postulate
that the increased binding of ezrin to the positively charged amino
acid cluster in ICAM-2s C-terminal is probably enhanced by the
oligomerization of ICAM-2 as induced by antibody clustering and
LFA-1 interaction, since we did not detect ICAM-2 to be tyrosine
phosphorylated. This could provide a mechanistic explanation as to
why ezrin is strongly associated with ICAM-2 in overexpression
models, but is only observed to associate with ICAM-2 upon ICAM-2
clustering of endogenous levels.
[0568] Current research focusing on the activating mechanisms of
ezrin, report a variety of differences among different cell types.
A two-step activation process has been proposed for ezrin
(Bretscher et al., 2000). ERM proteins are believed to reside in a
dormant closed conformation mediated by a C-to-N terminal
interactions (Bretscher et al., 1997; Gary and Bretscher, 1995).
Upon phosphorylation at threonine and possibly serine residues
(Bretscher, 1989; Simons et al., 1998), a conformational change
unmasks the F-actin binding sites in the C-terminal and the surface
protein interacting sites in the N-terminal (Bretscher et al.,
2000). RhoGDI (Rho-GDP-dissociation inhibitor) has been observed to
bind only activated ERM proteins (Takahashi et al., 1998),
suggesting that dissociation of Rho/RhoGDI is a prerequisite for
Rho kinase activation (Straw et al., 1998; Yasui et al., 1998).
Dissociation of RhoGDI is a prerequisite for activation of
Rhodependent pathways, including ROCK, and is dependent for GTP to
GDP conversion.
[0569] Evidence exists for ezrin functioning as both an upstream
regulator and as a downstream regulator of small GTP binding
proteins, making elucidation of molecular requirements and ordering
of activation systems across cell types difficult (Kosako et al.,
2000; Kotani et al., 1997; Mackay et al., 1997; Matsui et al.,
1998; Shaw et al., 1998). In the systems utilized here, we observed
the ICAM-2 anti-apoptotic effect to be abrogated by Y-27632 and
GTP.gamma.S, suggesting the Rho-dependent kineses and GTP are
necessary in relaying the ICAM-2 signal to PI3K. In addition,
inhibitors of src/p62.sup.yes similarly antagonized the ICAM-2
induced tyrosine phosphorylation. We did not find a dependency on
PCK isozymes, as PKC isozyme inhibitors bisindolymaleimide I,
bisindolymaleimide II, and staurosporine did not abrogate the
ICAM-2 induced survival signal and suggest that the PKC.alpha. and
PCK.THETA. dependent threonine phosphorylation of ezrin for its
activation as reported by others contributes minimally in this
system (Ng et al., 2001; Pietromonaco et al., 1998). We do note an
increase of threonine phosphorylation of ezrin as a function of
ICAM-2 crosslinking (FIG. 23D) but its presence at the zero time
point and difference observed in the fold induction of tyrosine
phosphorylation of ezrin lead us to believe that although the
threonine phosphorylation state may be contributory zrin tyrosine
phosphorylation is responsible for relaying the ICAM-2 survival
signal. Furthermore, site-directed mutagenesis of ezrin tyrosine
residue Y353 to phenylalanine (Y353F) has been shown to abrogate
PI3K binding in epithelial cells (Gautreau et al., 1999),
suggesting that kineses involved in phosphorylating Y353 may be key
regulators in ezrins capability to activate the PI3K/AKT pathway.
Additional tyrosine residues (Y154 and Y353) have been observed to
be phosphorylated by several membrane proteins possessing tyrosine
kinase activity, namely platelet derived growth factor receptor
(PDGF-R), epidermal growth factor receptor (EGFR) and hepatocyte
growth factor (HGF); however, mutants lacking both tyrosine
residues are still observed to be tyrosine phosphorylated, with
various augmentation in signaling properties (Bretscher et al.,
2000; Crepaldi et al., 1997; Jiang et al., 1995). This indirectly
suggests that ezrin's multiple tyrosine phosphorylation sites may
possess distinct and unique signaling properties within different
cells, suggestive of a potential explanation on how ezrin can
integrate and respond differently to a variety of signals, either
through direct interactions with key signaling molecules or
indirectly via adapter proteins. The identification of protein
kineses responsible for specific tyrosine residue phosphorylation
remains controversial, although preliminary studies for tyrosine
phosphorylation at Y353 have pointed to src and p62.sup.yes in
vitro (Dumenil et al., 2000; Moller et al., 1994). We see ablation
of ezrin tyrosine phosphorylation in the presence of herbimycin A
in vivo, an inhibitor of both src and p62.sup.yes, and further
studies are needed to differentiate between these two src family
protein tyrosine kineses and specific phosphorylation at Y353 or
potentially other sites.
[0570] Our data suggest that ROCK is involved in the activation of
ezrin that leads to its phosphorylation by src/p62.sup.yes since
incubation with Y-27362, a specific ROCK inhibitor, abolished
tyrosine phosphorylation of ezrin. We had noted hat ezrin threonine
phosphorylation, though initially present, was intensified upon
ICAM-2 ligation contrasting the induction of ezrin tyrosine
phosphorylation (see FIG. 23D), and its ablation in the presence of
inhibitors of Rho-dependent processes (see FIG. 23C). Although this
suggests that src/p62.sup.yes tyrosine phosphorylation of ezrin is
upstream of a Rho-dependent threonine phosphorylation, further
studies are needed to conclusively delineate the temporal kinetics
of ezrin activation as induced by ICAM-2 oligomerization. The
ICAM-2 PI3K/AKT survival signal requirements for Rho-dependent
kineses and phosphoinositides is apparent in Jurkat cells and in
primary B cells (FIG. 24D, 26C), however these requirements are
less constraining in ICAM-2 overexpressing cells (data not shown,
[Reviewers see Supplementary FIG. 20B]) illustrating differences
between the ICAM-2 overexpression and ICAM-2 clustering induced
activation of the PI3K/AKT pathway.
[0571] The PI3K/AKT signaling system is a general mediator of
extracellular stimuli, including growth factors, cytokines, as well
as adhesion to extracellular matrices (Downward, 1998). The
activation of AKT is dependent on phosphorylation at two sites,
threonine-308 by PDK-1 and serine-473 by an unidentified PDK-2
(Downward, 1998). The amino terminus of AKT contains a pleckstrin
homology (PH) domain that is thought to bind directly to
phospholipid products of PI3K. This binding recruits AKT to the
membrane, which has been proposed to induce a conformational change
allowing phosphorylation at threonine-308 and serine-473 by PDKI
and PDKII respectively (Alessi et al., 1996). Dually phosphorylated
AKT is then active and can phosphorylate a number of downstream
effectors contribute to cell survival that include, apart from
those investigated here, human caspase 9, and eNOS (endothelial
cells) which promotes angiogenesis of vascular endothelium (Cardone
et al., 1998; Kureishi et al., 2000) AKT hyperactivity has been
observed in a number of disorders (Haas-Kogan et al., 1998) (Kulik
et al., 1997; Shan et al., 2000; Wick et al., 1999) and therefore,
elucidating mechanism that initiate the activation of AKT may be of
therapeutic interest. Here, we demonstrate that ICAM-2 induced
activation of AKT kinase results in the activation of several
downstream effectors as detected by phosphorylation of BAD, GSK3,
FKHR and AFX, all of which can contribute to favor cell survival
(Brunet et al., 1999; Graff et al., 2000; Pap and Cooper, 1998; Zha
et al., 1996). These observations support that ICAM-2 activation
would be expected to lead to an extremely powerful anti-apoptotic
signal in a variety of cells. It is apparent that a major
regulation of the PI3K/AKT survival pathway is conditional on the
upstream activating events, since general PI3K activation is a
commonly observed in a variety of cancers and tumor models
(Blume-Jensen and Hunter, 2001; Roymans and Slegers, 2001). A
graphical illustration of ICAM-2 activating the PI3K/AKT pathway is
depicted in FIG. 25F, although differences in molecular mechanisms
may exist at the ICAM-2/ezrin and ICAM2/.alpha.-actinin interface
as alluded to above.
[0572] The data presented here illustrates that molecular
differences exist between the induction of a cell survival signal
in an ICAM-2 overexpression and ICAM-2 clustering model and further
suggest that these processes may be cell type dependent. The
anti-apoptotic effects mediated by ICAM-2 overexpression and by
ICAM-2 clustering illustrate that inappropriate ICAM-2 expression
may confer resistance to apoptotic stimuli but more importantly,
ICAM-2 oligomerization can initiate a cell survival signal upon
contact with LFA-1 bearing cells. This activation of the PI3K/AKT
pathway by ICAM-2 can be viewed as both anti-apoptotic, if a cell
where in an environment that predisposed it to apoptose, or as a
cell survival signal that is mediated by cell-to-cell contact. As
an adhesion molecule, ICAM-2 has been attributed a role in
lymphocyte recirculation and a role in enhancing and stabilizing
T-cell:B-cell contact via interactions with its receptor LFA-1
(Damle et al., 1992; Douglas et al., 2000). Here, we suggest that
in addition to possessing adhesion molecule properties, ICAM-2 is
capable of transmitting an intracellular signal when LFA-1
engagement clusters it on the cell surface. The significance of
ICAM-2 clustering is twofold (1) by virtue of its overexpression it
could lead to apoptotic resistance of cells otherwise destined to
die by apoptosis; (2) receptor-mediated engagement of ICAM-2 can
mediate cell survival selectively to cells that engage LFA-1
bearing cells, a process that occurs at the immunological synapse
(Perez and Nolan, manuscript in preparation). We speculate that
ICAM-2 clustering, as induced by antibody crosslinking or by
engagement of its natural receptor LFA-1 presents a regulateable
cell survival signal that is only initiated when an ICAM-2 cell
comes in contact with an LFA-1 expressing cells. Such cell-to-cell
contact is of functional necessity in T cell activation (Perez and
Nolan, manuscript submitted) and may be important in other
ICAM-2/receptor interactions such as those recently reported
between ICAM-2/DC-SIGN interactions in lymphocyte extravasation and
ICAM/LFA-1 enhanced HIV infection/transmission (Barbeau et al.,
1998; Butini et al., 1994; Geijtenbeek et al., 2000; Hioe et al.,
2001). Thus, differential physiological roles for CAM-2 may exist.
ICAM-2 overexpression could lead to tumor drug resistance and
cytoproliferative disorders such as B-cell chronic lymphatic
leukemia (B-CLL) since it has been reported that ICAM-2 is highly
expressed on CD5' B cells from B-CLL patients (Molica et al., 1996)
and on large B-cell lymphomas derived from patients (Alizadeh et
al., 2000). These observations, in conjunction with the work
described, here proposes that ICAM-2 or other adhesion molecules
may have a role in certain classes of leukemias. In normal
fibroblastoid cells, ICAM-2 mediated PI3K activation may likely
regulate the endothelial transmigration of eosinophils (Gerwin et
al., 1999) and potentially dendritic cells (via DC-SIGN)
(Geijtenbeek et al., 2000), in addition to lymphocyte
extravasation, two pivotal cell-contact dependent processes.
[0573] Our results illustrate that ICAM-2 overexpression and
clustering can provide an anti-apoptotic signal in cell lines and
primary human B cells rendering them resistant to physiological
death programs induced by TNF.alpha. and Fas ligand. Although
ICAM-3, CD43, and CD44 induced AKT activity in primary cells as
determined by single cell analysis, only ICAM-2 and ICAM-3 were
able to block apoptosis to FAS and TNF.alpha., with CD44 and CD43
actually perpetuating cell death. ICAM-3 crosslinking intensified
PIP2 production in addition to a temporal delay in AKT activation
(data not shown), which differed from ICAM-2 crosslinking and
suggests that ICAM-3 is affecting other signaling pathways.
Surprisingly, ICAM-1 was completely dissimilar to ICAM-2 in the
experiments conducted. These observations illustrate that molecular
differences exist in intracellular signaling pathways for adhesion
molecules capable of binding the same ERM proteins and interacting
with at least one shared receptor. Interestingly, it has been
reported that inflammatory cytokines can modulate ICAM-2 expression
on antigen presenting cells (APC) and that dendritic cell
maturation upregulates expression of ICAM-3 (Maki et al., 1998;
McLaughlin et al., 1998; McLaughlin et al., 1999; Ohh and Takei,
1996), suggesting that the similarities of ICAM-2 and ICAM-3
observed may have functionally similar roles in vivo. The work
presented herein attributes a previously unrecognized function for
ICAM-2. The finding that ICAM-2 can exert cell survival signaling,
ectopically and endogenously, as well as elicit an anti-apoptotic
phenotype in a variety of cell lines and human primary cells
suggests that deregulation or induced clustering is likely to
contribute significantly to the anti-apoptotic phenotype that leads
to tumor progression and/or cell survival.
[0574] Development of anti-metastatic approaches targeted to block
cancer cell adhesion by general blockade of adhesion molecules
warrants caution as the development of such agents may have
detrimental effects in normal physiological process that are
dependent on cell-to-cell contact interaction such as those
mediated by ICAM/LFA-1. Thus, pathways involved in the regulation
of ICAM-2 or other adhesion molecule expression, distribution, and
activation could be alternative targets to the development of
anti-tumor therapies and potentially as immunosuppresants.
Experimental Procedures
Antibodies and Chemicals
[0575] The following antibodies were purchased from Cell Signaling
Technologies (Beverly, Mass.): anti-phospho-AKT-ser473 mAb,
anti-phospho-AKT-thr308, anti-AKT, anti-phospho FKHR, anti-FKHR,
anti-phospho-Gsk3 alp21, anti-cleaved PARP, anti-cleaved caspase 9,
anti-cleaved caspase 3, anti-cleaved caspase 7, anti-caspase 9,
anti-caspase 7, anti-pAFX, anti-PARP, anti-BAD, anti-BADser112,
anti-BADser136, anti-phospho-BADser155, anti-rabbit-HRP.
Anti-ICAM-2 IC2/2 mAb, anti-ICAM-2-FITC mAb (IC2/2) were purchased
from Research Diagnostics (Flanders, N.J.) Anti-ICAM-2 N-terminal,
anti-ICAM-2 Cterminal, anti-a-actinin, anti-Bcl2, anti-Bclx/s,
anti-p27, anti-p21, anti-cFLIP, antiMYC, anti-p53, anti-NF.kappa.B,
anti-Ikk.alpha., anti-Ikk.beta. anti-phospho-tyrosine,
antiphospho-threonine, anti-mouse IgG-HRP, anti-goat-HRP,
annexin-V-biotin, were purchased from Santa Cruz Biotechnologies
(Santa Cruz, Calif.). Anti-ezrin mAb, anti-PI3K, were purchased
from Transduction Laboratories (San Diego, Calif.).
Anti-PDK-phospho-serine, anti-PDK-phospho-threonine, Y-27362,
00126, bisindolymaleimide I and II, psi-tectorigenin, etoposide,
PD98059, LY294002, TNF.alpha., IL-2 were purchased from Calbiochem
(San Diego, Calif.). Staurosporine, wortmannin, acridine orange,
ethidium bromide, propidium iodide, GTP.gamma.S were purchased from
Sigma (St. Louis, Mo.). Anti-mouse-alexa fluor 568, anti-rabbit
alexa flour 488, anti-mouse alexa fluor 488, anti-rabbit alexa
fluor 568, Prolong antifade, annexin-633, annexin-488, streptavidin
alexa fluor 488, streptavidin alexa fluor 633,
anti-phosphoinositide 3,4,5 triphosphate, anti-phosphoinositide 4,5
bisphosphate, were purchased from Molecular Probes (Eugene, Oreg.).
An nexin-V-FITC, anti-rabbit PE, anti-mouse-FITC, anti-goat FITC,
anti-goat texas red, Streptavidin-PE, were from BD Biosciences (San
Jose, Calif.). CD4-APC, CD19-PerCP, anti-ICAM-1, anti-CAM-3,
anti-CD43, anti-CD44, ANTI-LFA-1, anti-Mac1, were purchased from
PharMingen (San Diego, Calif.). Additional reagents are described
where appropriate.
Retroviral cDNA Screening
[0576] Production and infection of retroviruses was carried out as
described (Kitamura et al., 1995; Onishi et al., 1996; Rayner and
Gonda, 1994). A cDNA library was prepared from Jurkat T cells in
the pBabe-S vector (Hitoshi et al., 1998). The library
(2.times.10.sup.6 primary transformants) was used to transfect
.about.10.sup.7 PHOENIX-E packaging cells. The pBMN-LacZ control
vector was spiked into the library at 1:10 to monitor the
transfection/infection efficiency. Viral supernatants were
harvested and used to infect .about.10.sup.7 exponentially growing
NIH3T3 cells; 48 hours post infection the cells were split and
analyzed for .beta.-galactosidase activity. The library-transduced
NIH3T3 cells were plated at .about.25% confluency; 24 hours later
the medium was replaced with DMEM containing 1 .mu.M staurosporine
(STP). After 24 hours treatment the STP-containing medium was
replaced with complete DMEM/10% donor bovine serum. Surviving cells
were allowed to reach .about.80% confluency (7 days). Survivor
cells were retreated as described two additional rounds.
Phenotypic Transfer Assay
[0577] An aliquot of the surviving library-infected cells were
super-infected with Moloney Murine Leukemia Virus (gift of
T.Kinsella, Stanford). Super-infected cells were passaged for
two-weeks to allow efficient spread of the helper virus. Naive
NIH3T3 cells were infected with viral supernatants and allowed to
express for 48 hours. Re-infected cells were then treated with
staurosporine as described above. Surviving cells were cultured for
7 days and analyzed for transfer by RT-PCR.
RT-PCR Cloning of Proviral-cDNA Inserts and Construct
Generation
[0578] RNA was prepared by the acid-guanidium-phenol-chloroform
method as described (Chomczynski and Sacchi, 1987). cDNA was
prepared from 4 .mu.g heat-denatured total RNA in a 50 .mu.l
reaction volume (Promega, Madison, Wis.) and incubated at
42.degree. C. and 55.degree. C. for 45 minutes. The cDNA reaction
products (5 .mu.l) were amplified (primers: 5'-GATCCTCCCTTTATCCAG;
5'-GAATGAAAGACCCCACCTGT) in a 50 .mu.l PCR reaction mix
(Perkin-Elmer, Foster City, Calif.) at 95.degree. C./30 sec;
55.degree. C./60 sec; 72.degree. C./2 min for 25 cycles. Full
length ICAM2 cDNA was cloned into retroviral vector PBM-Z-IN
backbone (Kinoshita et al., 1998) at BamHI/Sal1 site.
ICAM2-.DELTA.C, ICAM2-.DELTA.N and ICAM2-C-terminal scrambled were
generated by PCR and cloned into the BamHI/Sal1 site.
Cell Culture and Preparation of Primary Cells
[0579] NIH3T3 murine fibroblast were maintained in DMEM, 10% DCS,
1% PSQ (Duelbecco Modified Eagle Media, 10% Donar calf serum, 1%
penicillin-streptomycin (1000 units/ml and 2 mM L-glutamine PSQ).
Jurkat T-cells and CH27 transformed B-cells were maintained in
RPMI-1640, 10% FCS, 1% PSQ. BaF3 pro-B-cells were maintained in
RPMI-1640, 10% FCS, 1% PSQ, 400 U/ml IL-3 (Peprotech). 70Z/3
pre-B-cells were maintained in RPMI-1640, 10% FCS, 1% PSQ, 50 .mu.m
.beta.-mercaptoethanol. HL60 myeloid leukemia cells were maintained
in Opti-Mem I, 10% FCS, 1% PSQ. 293T human fibroblast cells were
maintained in DMEM, 10% FCS, 1% PSQ. Cells were maintained at 5%
CO.sub.2/37.degree. C. humidified incubator. Transduced cells were
maintained in 500 .mu.g/ml G418 (Sigma) and proper expression of
construct was verified by western blots and FACS analysis of full
length ICAM-2, ICAM-2.DELTA.C, ICAM-.DELTA.N as indicated.
Staurosporine treatment was for 24 hrs at 1 .mu.M (unless otherwise
indicated). LY294002 treatment was at 10 .mu.m 30 minutes before
any subsequent treatment. Wortmannin treatment was for 24 hrs at
100 nM. Chemicals were dissolved in DMSO (final being 1:1000 for
solvent dilution) and vector controls were incubated with 1% DMSO
as negative control. Vector controls consisted of pBMN-Z-IN (empty
vector) transduction or pBMN-Z-IN-GFP as indicated. The infection
frequency of pBMN-Z-IN-GFP was 48%.+-.10 for three independent
viral transductions. Continual neomycin selection yielded
homogenous ICAM-2, ICAM2-.DELTA.C, ICAM2-.DELTA.N, or control
vector populations as routinely monitored by flow cytometry for
protein expression. For preparation of primary cells, mononuclear
cells were isolated from human peripheral blood by Ficoll-plaque
density centrifugation and depletion of adherent cells on adherent
plastic culture dishes. Isolated cells were maintained in complete
media and analyzed by FACS for CD4, CD3, CD19, and ICAM-2
expression.
Cross-Linking
[0580] Antibody cross-linking experiments were performed using mAbs
to anti-ICAM-1, anti-ICAM-2, anti-ICAM-3, anti-CD43, or anti-CD44
that recognizes the N-terminal region (extracellular domain) at 10
.mu.g/ml. Spin dialysis (Biorad) was used for buffer exchange of
azide containing antibodies (0.01%) to phosphate buffered saline
buffer pH 7.4. Anti-mouse IgG (Sigma) was used as a control
antibody in cross-linking experiments. 1.times.10.sup.6 Jurkat,
1.times.10.sup.6 BaF3, or 1.times.10.sup.7 PBMC cells were serum
starved for 4 hours respectively (except PBMC). Cells were
incubated with either mAb (10 .mu.g/ml) or mouse IgG (10 .mu.g/ml)
at 37.degree. C. for the indicated time. Time points began post
serum starvation to attenuate most of the signaling pathways or as
indicated. Serum starvation of 4 hrs lacked biochemical initiations
of apoptosis as tested by caspase 3 activity, cell cycle analysis,
annexin V/PI staining (data not shown). Cells extracts were taken
and subjected to either immunoprecipitation or immunoblotting were
appropriate. Primary cells were subjected to apoptotic treatment
followed by preparation for flow cytometry. GTP.gamma.S was made
cell permeant by pre-incubating compound with Fugene (Roche
Biochemicals) in a 1:4 molar ratio for 30 minutes at 25.degree. C.
prior to being applied to cells. Liposome mediated delivery of
radiolabeled/fluorescent triphosphates yields high cell
incorporation of highly charged molecular species (Perez, [O,D]
O.D. unpublished results).
Apoptosis Assays
[0581] Apoptosis was determined either by counting pyknotic nuclei,
annexin-V binding by flow cytometry, or TUNEL BrdU staining by flow
cytometry as indicated. Apoptosis was induced either by
staurosporine (1 .mu.m), treatment with anti-mouse Fas (5 [.mu./ml]
.mu.g/ml Santa Cruz Biotechnology (SCB), anti-human Fas (5 .mu.g/ml
Jo2 Biomed) or anti-human Fas (10 ng/ml CH11 Kamiya Biomedical) as
indicated in appropriate experiment, IL-3 withdrawal-(24 hrs) or as
indicated. For pyknolic nuclei count, NIH3T3 cells were grown on
glass coverslips and assayed for apoptosis. Suspension cells were
analyzed by nuclear staining with 25 .mu.M acridine orange/25 .mu.m
ethidium bromide or 5 .mu.g/ml Hoechst 33342 (Molecular Probes,
Eugene, Oreg.). Apoptosis was identified by the presence of
characteristic pyknotic nuclei as described (Jacobson and Raff,
1995). At least 5 individual fields were photographed and counted
using a Zeiss axioscope fluorescence microscope. For the survival
assay 10.sup.6 NIH3T3 cells were plated in 10 cm dishes and
incubated overnight at 37.degree. C. The cells were treated with 1
.mu.M staurosporine for 24 hours. The cells were washed and
cultured for 24 hours in complete medium. The cells were
trypsinized and viable cells counted following trypan blue
staining. Untreated cells were counted at the time of treatment. %
survival represents (number of viable cells post-treatment)/(number
of viable cells pretreatment). FACS based annexin-V-FITC/PI
staining was done as described (PharMingen). TUNEL assay was
performed as described by manufacturer of Apoptosis BrdU kit
(Promega). Flow cytometry data acquisition was performed 24 post
staurosporine treatment (1 .mu.M) for both BrdU (10,000 events
collected) and pyknotic nuclei count and 12 hr post-staurosporine
treatment for annexin V binding (100,000 events collected).
Annexin-V positive cells will have compromised membranes after 24
hr treatment. Flow cytometry analysis was performed on a BD
FACSCalibur machine with CELLQuest and analyzed using FlowJo
software (Tree Star).
Kinase Assays
[0582] PDK-1 activity was determined by a PDK-1 immunoprecipiation
kinase assay kit (Upstate Biotecnology, Lake Placid, N.Y.) as
recommended by manufacturer. In brief, PDK-1 was immunoprecipitated
from [1.times.10.sup.6]1.times.10.sup.6 treated cells, incubated
with inactivated SGK enzyme, and detection of (.gamma.-.sup.32P)
ATP incorporation to a SGK peptide substrate was measured by
scintillation counting. PI3K activity was detected by developed
PI3K FACS based assay (see below). AKT activity was detected by
immunoprecipitation of AKT1 from cells and used in a kinase assay
with GSK3 fusion protein (CST). [2.times.10.sup.6 NIH3T3,
2.times.10.sup.6 Jurkat, or 5.times.10.sup.5 BaF3]2.times.10.sup.6
NIH3T3, 2.times.10.sup.6 Jurkat, or 5.times.10.sup.5 BaF3 cells
were incubated with immobilized AKT 1G1 monoclonal antibody (mAb)
(1:200, CST) at 4.degree. C. with gentle rocking motion for 2 hrs.
Immunocomplexes were washed 4.times. with cell lysis buffer and
resuspended in [40 .mu.l] 40 .mu.l kinase buffer (25 mM Tris pH
7.5, 5 mM p-glycerolphosphate, 2 mM DTT, 0.1 mM Na.sub.3VO.sub.4,
10 mM MgCl.sub.2) supplemented with 200 .mu.M ATP and 1 .mu.g of
GSK-3 fusion protein (CST) for 30 min at 30.degree. C. Kinase
reaction was terminated with SDS sample buffer boiled for 5 min,
and phosphorylation state of GS3K was detected by immunoblotting
and visualized using ECL detection (Amersham). Immunoblots are
representative of 3 independent virally transduced cell populations
each repeated 3 times (n=9). AKT activity was verified by AKT
phosphorylation by immunoblotting with phospho-specific antibodies
to ser473 and thr308 (NEB). Kinase assays are representative of at
least three independent measurements and are represented as
standard deviations were appropriate.
Cell Fractionation, Immunoprecipitations and Immunoblotting
[0583] Triton-X-100 fractionation was carried out as described[(Ref
xxx)]. Cell extracts were prepared by washing 2.times.10.sup.6
cells in ice cold PBS and harvesting in lysis buffer (20 mM Tris pH
7.5, 150 mM NaCl 1 mM EDTA 1 mM EGTA, 1% Triton X100, [2.5 mM
Na.sub.2PO.sub.4,] 2.5 mM Na.sub.2PO.sub.4, 1 mM
.beta.-glycerolphosphate, 1 mM Na.sub.3VO.sub.4, 1 .mu.g/ml
Leupeptin, 1 mM PMSF, protease inhibitor cocktail tablet
(Boehringer Mannheim)). Extracts were centrifuged 14,000 RPM for 5
min at [4.sup.C] 4.degree. C. and cell lysates (20 .mu.g as
determine by BCA protein assay (Pierce)) were fractionated on 12%
or 15% SDS-polyacrylamide gel electrophoresis and transferred to
PVDF membranes using standard procedures. Immunoprecipitations were
pre-cleared with protein A/G plus-agarose beads (SBC). IP was
incubated for 1 hr or overnight with primary antibody, 1 hr with
protein A/G plus-agarose beads and washed 4.times. with lysis
buffer. Blots were incubated with the indicated antibodies.
Secondary antibodies used: anti-rabbit HRP (1:5000 NEB), anti-mouse
HRP or anti-goat HRP 1:5000, SBC) and visualized using ECL
detection (Amersham) or with a Kodak Digital Science 440 C station.
Blots are representative of at least 3 independent experiments.
Flow Cytometry and FACS Analysis
[0584] Intracellular and extracellular staining was performed as
described (www.metazoa.com\UPL3287) using indicated antibodies.
Intracellular probe for AKT activity was made by conjugating
monoclonal anti-AKTser473 antibody (Cell Signaling Technology) to
Alexa-568 dye (Molecular Probes), using Alexa-568 protein
conjugation kit (Molecular Probes). Phospho specificity was tested
by western blotting and FACS analysis to a yariety of PI3K
activators and inhibitors (data not shown, Perez and Nolan,
submitted). Intracellular staining by phosphoAKTser473-Alexa568
reflected AKT kinase activity when NIH3T3 cells were stimulated
with platelet derived growth factor (Sigma) and inhibited by
LY294002 prior to stimulation. Intracellular probe for
phosphatidylinositol 3,4,5 triphosphate, and phosphatidylinositol
4,5 bisphosphate was made by conjugating mAb to PIP3 or PIP2 to
alexa fluor 488 or alexa fluor 633 using alexa fluor protein
conjugation kits (Molecular Probes). PIP3 and PIP2 FACS based
measurements reflected PI3K and PI4K kinase activity (Perez and
Nolan, manuscript in preparation). Quantitative FACS analysis was
performed as described (Davis et al., 1998; Iyer et al., 1998;
Lenkei et al., 1998). In brief, Ilphycoerythrin (PE) (Molecular
Probes) was conjugated to a anti-ICAM2 N-terminal monoclonal
antibody (Research Diagnostics IC2/2) as suggested by manufacturer
of protein cross-linking kit (Molecular Probes), tested for proper
stoichiometry (data not shown) and quantitated using Quantibrite-PE
beads (BD systems). A quantitative calibration curve was generated
using Quantibrite-PE beads that contain a known amount of PE
molecule/bead. A linear regression analysis is performed using the
following equation: log.sub.10(PE fluorescence)=slope*log.sub.10(PE
molecules/bead)+intercept. PE fluorescence is determined by taking
the geometric mean of the PE channel. Quantitation is valid only
for antibodies directly conjugated to PK. Using saturating amounts
of antibody and thorough washing ensures all surface antigens are
bound. Preparation of samples on ice reduces antibody
internalization. Surface antigens of cells for an unknown cell
population are determined by computing the PE geometric mean using
the calibration curve. Quantitative FACS analysis provides
approximate estimates for surface antigen expression. Numbers
plotted represent relative surface molecules and not absolute
numbers since antibody valency was not investigated for the
monoclonal antibodies used. Flow cytometry analysis was performed
on a BD FACSCalibur machine and analyzed using FlowJo software
(Tree Star). CellQuest was used for quantitative flow cytometry and
linear regression analysis of Quantibrite-PE beads. Flow cytometry
data are representative of 3 independent experiments of 10.sup.6
cells/sample analyzed. 100,000 events were collected or otherwise
noted and calibrated using Calibrite beads (BD systems). Data
plotted in bar graph format is expressed as the mean (bar).+-.SD of
triplicate experiments.
Laser Scanning Confocal microscopy
[0585] Cells were grown in coverslips, washed twice in phosphate
buffered saline pH 7.4 (PBS) and fixed in 2.7% paraformaldehyde (in
PBS). Cells were permeabilized for 5 minutes with 0.1% Triton-X-100
washed twice in PBS, blocked in 4% bovine serum albumin (BSA, in
PBS), and subjected to antibody incubation: (primary at 0.1 mg/ml,
secondary at 1:1000 dilution in 1% BSA, with several washing steps
in between). Stained coverslips were mounted onto glass slides with
Prolong Antifade reagent (Molecular Probes) and visualized using a
Molecular Dynamics Multiprobe 2010 confocal laser scanning
microscope. Images were compiled using Adobe Photoshop 6.0.
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Example 5
Activation of PKB/AKT-Dependent Cell Survival by Intracellular
Adhesion Molecule-2 (ICAM-2)
[0660] In this Example, using the methods and compositions of the
present invention, the present inventors (also referred to herein
as "we") using a retroviral cDNA library in a functional genetic
screen identified intracellular adhesion molecule-2 (ICAM-2), a
member of the immunoglobin-family of adhesion molecules, as a
potent inhibitor of several activators of apoptosis. ICAM-2
expression blocked the onset of apoptosis in several cell types and
induction settings. ICAM-2's anti-apoptotic effect was mapped to
the activation of the PI3K/AKT pathway and resulted in subsequent
phosphorylation of BAD, GSK3, and FKHR. ICAM-2's cell survival
signal was found to be independent of caspase inhibitory proteins,
cell cycle regulators, or anti-apoptotic pathways using Bcl-2. The
survival function was dependent on the cytoplasmic tail of ICAM-2,
a region that bound membrane-cytoskeleton linker proteins
.alpha.-actinin and ezrin. The ICAM-2 mediated survival function
was abrogated by two pharmacological inhibitors of P13 kinase,
wortmannin and LY294002, indicating activation of AKT and its
downstream effectors were dependent on P13K recruitment to the
plasma membrane. Antibody clustering of endogenous ICAM-2 on BaF3
pro-B cells and Jurkat T-cells stimulated AKT kinase activity and
phosphorylation of downstream effectors BAD, GSK3, FKHR, and AFX,
congruent with the ectopic expression results. Primary CD4+ and
CD19+ cells were protected from TNF.alpha. and Fas mediated
apoptosis following ICAM-2 clustering and presented elevated AKT
activity as detected by direct single cell flow cytometric
measurement of intracellular AKT kinase activity. These results
attribute a novel survival signaling function to ICAM-2 that might
provide an explanation for both the role of ICAM-2 over-expression
in B-cell lymphomas and mechanisms by which ICAM-2 might signal
intracellular communication in a variety of important cell
types.
Introduction
[0661] Cellular homeostasis is achieved through a tightly regulated
balance of proliferation and apoptosis. Apoptosis is a distinct
form of cell death that is initiated by a number of events
including DNA damage, growth factor deprivation, receptor-mediated
death signaling, or by xenobiotic induction, among others.
Regulation of apoptotic signaling pathways is largely governed by a
cell's ability to sense its environment. Cellular apoptotic death
can occur by many paths with distinct apoptotic stimuli initiating
varied cell death mechanisms. For instance, chemically induced
apoptosis occurs with the release of cytochrome C and activation of
caspase 9 (Budihardjo et al., 1999). Receptor induced apoptosis
(Fas/TNF.alpha.) is mediated through activation of caspase 8
(Holmstrom and Eriksson, 2000; Kruidering and Evan, 2000; Rath and
Aggarwal, 1999; Schneider and Tschopp, 2000) and can operate
independent of the mitochondria (Gottlieb, 2000; Kroemer, 1999;
Kuida, 2000). Both caspase 8 and 9 converge on effector caspases 3
and 7 to mediate the characteristic hallmarks of apoptosis
(Earnshaw et al., 1999; Grater, 2000).
[0662] A cell's commitment to cellular proliferation or programmed
cell death is a balance of the survival and death signals
communicated from both the immediate environs, such as
extracellular matrix (ECM) interactions, cell-cell contact, or more
distant sites through endocrine and paracrine factors (Ruoslahti
and Reed, 1994). Survival pathways are proposed to function during
early development where apoptosis plays a key role in shaping
organogenesis (Raff, 1992). Similarly, the lack of survival signals
is exemplified in the phenomenon of anoikis, where epithelial cells
undergo apoptosis when ECM-attachment is blocked (Frisch and
Ruoslahti, 1997). ECM survival signals are presumably mediated by
activation of cell-surface receptors via integrin clustering,
contributes to the specificity of cell-cell/cell-matrix
interactions, and prevents unwarranted cell migration.
ECM-interactions are required for growth factor signaling in
adherent cells (Hulleman and Boonstra, 2001). Deregulation of
ECM-integrin signaling leads to anchorage-independent growth, which
correlates with malignancy. Hence it is clear that deregulation of
ECM signaling can desensitize a cell to apoptotic stimuli and
contribute to a malignant phenotype that allows cells to survive in
foreign milieus and under adverse conditions.
[0663] Functional characterization of molecules involved in
cellular adhesion has been focused on signal transduction pathways
attributed to integrins and cadherins (de Fougerolles et al., 2000;
Schneller, 2001; Shinohara et al., 2001). Adhesion molecules of the
immunoglobin (Ig) superfamily have been largely overlooked as
potential signaling molecules. ICAM-2 (CD102) is a member of the
Ig-superfamily of cell surface proteins and mediates leukocyte
binding to LFA-1 (CD11a/CD18) and MAC-1 (CD11b/CD18) whose
expression is restricted to leukocytes (van Kooyk and Figdor,
2000). As a cell surface adhesion member involved in leukocyte
recruitment in tissues, ICAM-2 is expressed in low levels on most
leukocytes including T and B lymphocytes, monocytes, platelets and
early CD34+ hematopoetic progenitor cells (de Fougerolles et al.,
1991; Diacovo et al., 1994; Nortamo et al., 1991). In addition,
ICAM-2 constitutive expression has been observed on all vascular
endothelium (de Fougerolles et al., 1991). Based on the expression
pattern of ICAM-2, it has been hypothesized to be involved in
leukocyte recirculation. ICAM-2 deficient mice support this by
demonstrating that eosinophil trafficking is augmented in
inflammatory responses (Gerwin et al., 1999). Surprisingly, this
phenotype is relatively mild considering the range of cell types
upon which ICAM-2 is expressed. It suggests that the roles ICAM-2
plays are subtle or are redundant with other pathways. Thus, the
ICAM-2 deficient mice do not sufficiently detail the roles of
ICAM-2, warranting further characterizations of the mechanisms by
which ICAM-2 acts are needed.
[0664] In contrast to ICAM-2's putative role as an adhesion
molecule, it is surprising to find ICAM-2 highly expressed on both
endothelial cells in lymphomas and CD5.sup.+B cells from B-cell
chronic lymphatic leukemia (B-CLL) patients (Molica et al., 1996;
Renkonen et al., 1992). Lymphoproliferative diseases inevitably
inhibit adhesion dependency-loss of adhesion is one of the primary
means by which metastatic spread occurs. However, recent gene
expression profiling of large B-cell lymphomas from patients
indicated an elevated expression of ICAM-2 (Alizadeh et al., 2000).
Interestingly, ICAM-2 is the only ICAM (1-5) that maps to
chromosome 17q23-25 (Sansom et al., 1991), a segment associated
with genomic instability and recently identified as a segment of
high aberration in various cancers (Dion et al., 2000; Dobo et al.,
1995; Russell et al., 2000; Sugai et al., 2000). Despite these
observations, ICAM-2's role and molecular characterization in the
progression of lymphatic disease states has not been addressed.
[0665] We devised a genetic screen to identify genes that are
involved in regulation of apoptosis and augmented in malignant
phenotypes. Cells transduced with a human transformed T cell
(Jurkat) retroviral vector cDNA library were screened for an
anti-apoptotic phenotype. One cDNA demonstrated reproducible
anti-apoptotic activity in a phenotypic transfer assay. This cDNA
encoded full-length intracellular adhesion molecule-2 (ICAM-2).
Here we show that ICAM-2 was identified as being capable of
transducing an anti-apoptotic effect. Functional characterization
of ICAM-2 reveals that it mediates a survival signal sufficient to
block apoptosis by activation of the PI3K/AKT pathway. Furthermore,
development of probes to measure intracellular AKT activity by flow
cytometry allowed for the simultaneous measurement of AKT activity
as a function of ICAM-2 clustering on human peripheral blood
monocytes (PBMC). Multi-parameter FACS analysis confirmed ICAM-2
clustering led to AKT activity in CD4+ and CD19+ primary human
cells and subsequent protection from Fas and TNF.alpha. mediated
apoptosis. These observations identify ICAM-2 as having a role in
mediating cell survival by activation of the PI3K/AKT cell survival
pathway. These finding suggest that inappropriate expression of
ICAM-2 could contribute significantly to the anti-apoptotic
phenotypes in the cumulative process that leads to tumor
progression and metastatic spread. The findings also underscore a
positive role for ICAM-2 in signaling pathways involving AKT and
downstream effectors.
Results
[0666] Screening a Retroviral cDNA Library in an Anti-Apoptotic
Functional Assay
[0667] To identify genes that alter signaling in apoptosis we
devised a retroviral library approach to screen for cDNAs that
encode anti-apoptotic molecules (FIG. 26A). cDNAs from a malignant
cell type (Jurkat T cell leukemia) were screened for anti-apoptotic
function in a recipient non-malignant (fibroblast) cell. Apoptosis
was induced with staurosporine (STP), a kinase-inhibiting
plant-derived alkaloid, activity, and a potent inducer of
caspase-dependent cell death in most cell types. Induction
conditions were determined that limited the level of spontaneous
background while maximizing the extent of apoptotic death (minimal
background of one surviving cell in a STP-treated mock library
control in .about.10.sup.4 starting cells). 10' NIH3T3 fibroblasts
were infected with a retroviral cDNA library derived from Jurkat
cells at an infection frequency of 40% to limit the number of
integrations to a single event per cell. Control retroviruses were
prepared, expressing LacZ- or Bcl-2, and infected into a similar
number of NIH3T3 cells. Apoptosis was induced in the transduced
cell culture by staurosporine treatment and the cells were then
allowed to recover (FIG. 26A). Surviving cell clones were expanded,
replated and retreated with staurosporine. The complexity of the
expressed cDNAs in the surviving population was assessed with
RT-PCR. A few major bands were observed following three rounds of
selection (FIG. 26 B).
[0668] Replication-competent Moloney murine leukemia virus (MMLV)
was applied to the enriched cell populations. Upon integration and
expression of the MMLV proteins resident retroviral constructs from
the library were co-packaged into infectious virions that can be
transferred to naive target NIH3T3 cells. The staurosporine
selection process was then reapplied. In this manner true
phenotype-inducing clones enrich at a rate of 1/background (see
materials and methods for elaboration). Three of the pooled
libraries showed enrichment for specific bands after PCR (see FIG.
26B lanes 1 and 2). Several bands were rescued by PCR cloning and
one of these bands was sequenced and demonstrated to encode
full-length ICAM-2 cDNA (Staunton et al., 1989), an immunoglobulin
superfamily member that regulates leukocyte adhesion through
interaction with its integrin counter-receptor, LFA-1 (de
Fougerolles et al., 1991; Simmons, 1995).
ICAM-2 Mediates a Survival Signal
[0669] The ICAM-2 cDNA was cloned into a retroviral vector
(pBMN-Z-IN) that carries an internal ribosome entry site (IRES)
upstream of the neomycin resistance gene. NIH3T3 fibroblasts were
infected with retroviruses capable of expressing the ICAM-2 gene,
along with appropriate control vectors pBMN-Z-IN (vector control)
and pBMN-Z-IN-GFP (GFP vector control). Expression of the 60 kD
ICAM-2 glycoprotein in neomycin-selected NIH3T3 fibroblasts
infected with the pBMN-Z-IN-ICAM-2 construct (referred to as
ICAM-2) was verified by immunoblotting (FIG. 27A), flow cytometry
(FIG. 27B, 28B), and immunoprecipitation (FIG. 28C). The expressed
ICAM-2 protein co-migrated with the native protein from Jurkat T
cells (data not shown).
[0670] Staurosporine treatment is thought to mimic
factor-withdrawal in cells (Raff, 1992), and induces apoptosis.
ICAM-2 expression in NIH3T3 cells limited the extent of apoptosis
induced by staurosporine treatment as determined by pyknotic nuclei
count (FIG. 27C, 27D) as well as an annexin-V binding assay (FIG.
27E) and the BrdU TUNEL assay (FIG. 29B) confirming the clone's
selection by phenotype in the screen. Interestingly, not all forms
of apoptosis were inhibited. Fas induced apoptosis in ICAM-2
expressing Jurkat T cells was not inhibited across a range of
concentrations of a monoclonal antibody to the Fas receptor (FIG.
27C, panel 3).
[0671] A report correlating ICAM-2 expression with a
lymphoproliferative disorder, B-cell chronic lymphatic leukemia
(B-CLL) (Molica et al., 1996), prompted us to test the
anti-apoptotic activity of ICAM-2 in the mouse pre-B-cell line,
70Z/3. ICAM-2 expression inhibited staurosporine-induced apoptosis
in 70Z/3 cells (FIG. 28A). Given the indication that staurosporine
mimics factor withdrawal, we assessed the ability of ICAM-2
expression to protect factor-dependent cells from factor
withdrawal. ICAM-2 expression in the IL-3-dependent pro-B cell line
BaF3 resulted in a delayed onset of apoptosis following IL-3
deprivation (FIG. 28A). Furthermore, we tested the ability of
ICAM-2 to rescue BaF3 cells from apoptosis induced by treatment
with anti-Fas antibodies. ICAM-2 demonstrated a potent inhibition
of apoptosis through the Fas pathway in these cells (FIG. 28A).
These results are as good as or better than transduction controls
with Bck2 and therefore the apparent effects cannot be attributed
to modest effects on apoptosis (data not shown). There is, however,
cell specificity to the anti-apoptotic effect as ICAM-2
over-expressing Jurkat T cells were not protected from Fas-induced
apoptosis (FIG. 27C) but were protected from staurosporine induced
apoptosis (FIG. 28A). High throughput proteome analysis recently
identified that in Jurkat T cells, Fas induced apoptosis results in
a rapid destruction of 12 cytoskeletal proteins, alters
phosphorylation states of various chaperone proteins and
cytoskeletal structural proteins, and presents a more "aggressive"
form of cell death than staurosporine induced apoptosis (Gerner et
al., 2000). Therefore different cell death inducers have specific
physiological characteristics in Jurkat T cells supporting the
differences observed. In addition, effector caspases have been
demonstrated to be dispensable in chemical induced apoptosis
(Johnson et al., 2000).
[0672] The initial screening was performed in fibroblasts, and it
is therefore unlikely that ICAM-2's anti-apoptotic effect was
mediated through its lymphocyte-specific integrin ligand, LFA-1
(CDT 1a/CD18). To address this possibility we prepared an
extracellular domain-deleted (AN) version of ICAM-2 and tested it
in the BaF3 cells. Expression of the cytoplasmic domain was
sufficient to impart full anti-apoptotic activity (FIG. 28A). This
indicates that the cytoplasmic domain of ICAM-2 provides a survival
signal when over-expressed ectopically, and likely exerts its
effect by mimicking receptor crosslinking. Since signaling through
ICAM-family cytoplasmic domains is poorly understood, we sought to
identify the signaling pathway by which it conferred resistance to
apoptosis.
The ICAM-2 Survival Function Maps to a Membrane-Cytoskeleton Linker
Protein Binding Motif.
[0673] ICAM-2 had been regarded as an adhesion molecule and has
been shown to be interconnected with the actin cytoskeleton by
linker proteins .alpha.-actinin and ezrin, which bind the ICAM-2
cytoplasmic domain. (Heiska et al., 1996; Helander et al., 1996).
To assess the potential role of .alpha.-actinin in mediating the
ICAM-2 antiapoptotic signal, the .alpha.-actinin recognition
sequence was changed to a scrambled sequence unable to bind
.alpha.-actinin in vitro (Heiska et al., 1996). Retroviral
constructs encoding ICAM-2, a C-terminal deletion mutant
(ICAM2-.DELTA.C) and a full-length ICAM-2 protein with the mutated
.alpha.-actinin binding motif (ICAM2-C scrambled) were used to
transduce NIH3T3 cells (FIG. 28B). The infected cells were sorted
by FACS using an ICAM-2 monoclonal antibody (IC2/2) recognizing
only native N-terminal ICAM-2 (de Fougerolles et al., 1991). This
verified that ICAM-2, ICAM2-.DELTA.C, or ICAM2-C-scrambled proteins
were properly folded and targeted to the outer face of the plasma
membrane. The NIH3T3 cells expressing the ICAM-2 mutants were
assayed for survival following both etoposide treatment (another
potent inducer of apoptosis in NIH3T3 cells) and staurosporine
treatment. ICAM-2 imparted potent long-term survival on NIH3T3
cells and the survival signal was lost when the C-terminal deletion
of ICAM-2 (ICAM2-.DELTA.C) was expressed in cells (FIG. 28B).
Mutation of the .alpha.-actinin binding site in the ICAM2
cytoplasmic tail also did not provide any protection against
etoposide or staurosporine treatments. Furthermore, both
.alpha.-actinin and ezrin co-immunoprecipated only with full length
ICAM-2 (FIG. 28C), supporting the postulate that these cytoskeleton
linker proteins were necessary to relay an anti-apoptotic
signal.
ICAM-2 Signals Through AKT Kinase
[0674] As survival signaling through many adhesion molecules
involves PI3 kinase (Frisch and Ruoslahti, 1997; Khwaja et al.,
1997), we analyzed the role of this pathway in the ICAM-2
anti-apoptotic signal. Pretreatment of ICAM-2 expressing BaF3 cells
with the PI3 kinase inhibitor wortmannin blocked the ICAM-2
mediated anti-apoptotic effect (FIG. 29A), implicating PI3 kinase
in the ICAM-2 survival signaling cascade. Under these conditions
vehicle-treated ICAM-2 expressing BaF3 cells were resistant to
staurosporine induced apoptosis. Similarly, treating ICAM-2
transduced NIH3T3 with LY294002 abrogated ICAM-2's anti-apoptotic
effect as measured by both annexin-V binding and BrdU TUNEL assay
using flow cytometry (FIG. 29A, 29B, and, reviewers see APPENDIX
for flow cytometry plots).
[0675] PI3 kinase is known to regulate apoptosis through its
downstream effector AKT (PKB) kinase (Downward, 1998). AKT kinase
has a potent anti-apoptotic effect downstream of diverse apoptotic
stimuli, including staurosporine (Made and Downward, 1997) (data
not shown). We assayed ICAM-2 expressing fibroblasts for AKT kinase
activity. NIH3T3 fibroblasts expressing ICAM-2 showed an elevated
level of activated AKT (FIG. 30A). This increase in AKT kinase
activity was not seen in ICAM2-AC or mock transduced cells. We
further verified that this ICAM-2-dependent increase in activated
AKT is maintained following STP-treatment using both kinase assays
and by verifying phosphorylation of both ser473 and thr308 (FIG.
30A). A target of AKT kinase is the pro-apoptotic BcL2 family
member, BAD. BAD is normally held in an inactive state by
phosphorylation of serines 112 and 136, and is bound to 14-3-3.
Upon induction of apoptosis, BAD is dephosphorylated at both ser112
and ser136, and dimerizes with Bc1-2. As a result, the equilibrium
of BcL-2/Bcl-X.sub.L is shifted to favor release of BCL-X.sub.L to
mediate Cytochrome C release and apoptosis (Datta et al., 2000).
BAD is dephosphorylpted following staurosporine-treatment of
ICAM2-.DELTA.C- and mock-transduced NIH3T3 cells, concomitant with
the induction of apoptosis (FIG. 30B). However, ICAM-2 expression
results in the maintenance of BAD-phosphorylation consistent (FIG.
30B) with sustained AKT kinase activity (FIG. 30A).
[0676] BAD has 3 phosphorylation sites, ser112 mediated by active
p90Rsk1, sen 36 mediated by active AKT, and ser155 mediated by both
active PKA and active p90Rsk1. ICAM-2 and its role in connection to
BAD ser112 phosphorylation is to be described elsewhere (Perez and
Nolan, manuscript in preparation). Phosphorylation of BAD ser155
was not observed (data not shown). Another target of AKT kinase
involved in anti-apoptotic signaling, GSK3, was found to be
phosphorylated in ICAM-2 expressing NIH3T3 and probably contribute
to the anti-apoptotic effect (FIG. 30B, bottom panel). The
anti-apoptotic signal had no apparent effects on the anti-apoptotic
proteins Bc1-2 and BCI-X.sub.L indicating that typical
anti-apoptotic pathways did not mediate the survival signal (FIG.
30C).
ICAM-2 Crosslinking Confirms a Role for Endogenous ICAM-2 in
Providing an Anti-Apoptotic Signal
[0677] This ICAM-2-dependent elevation of activated AKT levels in
fibroblasts is independent of ligand interactions as determined by
the fact that ICAM-2.DELTA.N can protect cells from apoptosis and
ICAM2-.DELTA.C cannot activate AKT. This is indicative of the
signaling mechanism driven by oligomerization of surface ICAM-2
molecules, a common modus operandi for adhesion molecules. The
surface oligomers create interaction sites within their cytoplasmic
domains, recruiting signaling molecules to participate in membrane
proximal interactions. Quantitative FACS analysis revealed that the
density of ICAM-2 molecules on the cell surface vary widely between
cell types (FIG. 30D, and, reviewers see APPENDIX for quantitative
methodology; see Experimental Procedures for elaboration) and
correlated with varied expression patterns as previously described
(de Fougerolles et al., 1991). Basal expression levels of ICAM-2 on
lymphocytes was 24 orders of magnitude less than the enforced
expression from the retroviral vector as determined by the number
of ICAM-2 surface molecules. We therefore decided to test whether
endogenous ICAM-2, when cross-linked, could confer the phenotypes
observed above.
[0678] To test this hypothesis in a physiological setting, we
cross-linked (clustered) endogenous pro-B cell ICAM-2 surface
molecules with monoclonal antibodies and assayed for activation of
AKT kinase activity using GSK3 as a target. We first chose BaF3
cells as these displayed low endogenous ICAM-2 levels (FIG. 30D)
and an anti-apoptotic phenotype upon ICAM-2 transduction (FIG.
28A). As shown in FIG. 31A, basal AKT activity is unaffected by
incubation with isotype control sera. In contrast, AKT kinase
activity increased 3.5-fold with fifteen minutes following addition
of anti-ICAM-2 and resulted in the subsequent phosphorylation of
BAD ser136, AKT ser473 thr308, and FKHR. This level of AKT kinase
activity is congruent with that measured in following
IGF-1-treatment of BaF3 cells (A. Bartels and J.B.L., unpublished
results). Though the results for AKT-activity were reproducible we
were unsatisfied with the western blot analysis and so developed a
new procedure for single cell analysis of AKT activity by flow
cytometry, described below (Perez and Nolan, submitted, reviewers
please see attached manuscript). Cross-linking ICAM-2 on a
different cell type, Jurkat T cells, also protected against
staurosporine-induced apoptosis as assessed by flow cytometry
analysis of annexin-V and propidium iodide staining (FIG. 31B-C).
AKT phosphorylation and activation was observed within 15 minutes.
Subsequently the AKT targets GSK3 and FKHR were phosphorylated by
cross-linking of ICAM-2 in a time dependent manner (FIG. 31D).
Incubation with LY294002 abrogated the anti-apoptotic effects
initiated by cross-linking ICAM-2 in Jurkat T cells and BaF3 cells
(data not shown).
[0679] It was of interest to understand if ICAM-2 antibody
clustering can initiate a cell survival signal able to overcome the
apoptotic machinery after induction of an apoptotic program. To
test this, Jurkat T cells were treated with staurosporine for one
hour to initiate an apoptotic program and then challenged to
survive by ICAM-2 antibody clustering. After 1 hour of
staurosporine treatment, hallmarks of apoptosis initiation were
evident as detected by cleavage of PARP, cleavage of caspase 9, and
cleavage of effector caspases 3 and 7 (FIG. 31E). Interestingly,
detection of these cleavage apoptotic indexes decreased as ICAM-2
clustering stimulated AKT activity as a function of time (FIG.
31E-F). This was not observed in cells that were treated with
staurosporine but ICAM-2 crosslinked (data not shown). ICAM-2
clustering initiated these hallmark cell survival signals in the
presence of the staurosporine induced death signal as detected by
increases in AKT phosphorylation and AKT activity. In addition, BAD
phosphorylation also followed ICAM-2 clustering in these challenged
T cells, demonstrating that activation of the PI3K/AKT pathway is
sufficient to override apoptotic paradigms.
[0680] To attribute a physiological relevance to ICAM-2 induced AKT
activity in vivo, human PBMC were crosslinked for ICAM-2 prior to
treatment with TNF.alpha. and anti-Fas monoclonal antibody. Treated
PBMC were gated by immunophenotype for CD4 and CD19 and
subsequently assayed for AKT activity and apoptosis by
muHi-parameter FACS. Intracellular AKT kinase activity measurements
were achieved by development of a phospho-specific fluorescent
probe for AKT-phospho ser473 phosphorylation site on AKT detectable
by FACS (Perez and Nolan, submitted). Both ICAM-2+/CD4+ T cells and
ICAM-2+/CD19+ B cells exhibited AKT activity when ICAM-2 was
clustered (FIG. 32A). ICAM-2 induced AKT activity protected B cells
from apoptosis to Fas and TNF-.alpha. induced apoptosis (FIG. 32B).
There was little apparent anti-apoptotic effect on CD4+ T cells
(FIG. 32B) perhaps due to the fact that these T cells were not
strongly induced by Fas or TNF-.alpha. to undergo apoptosis with
our conditions. Protection from apoptosis in primary B cells
correlated perfectly with AKT phosphorylation at serine 473,
confirming prior roles for this target serine in the protective
effect of AKT against Fas and TNF-.alpha. induced apoptosis. Thus,
ICAM-2 oligomerization leads to the apparent membrane recruitment
of PI3-kinase and subsequent activation of AKT kinase, resulting in
a potent inhibition of apoptosis in Jurkat T cells, BaF3 pro-B
cells, and human primary T and B cells.
Discussion
A Model for ICAM-2 Mediating a Cell Survival Signal
[0681] Our results demonstrate that ectopic expression, or
crosslinking of endogenous, ICAM-2 in a wide variety of cell types
as well as in and primary CD19+ B cells can initiate a survival
signal to cells. ICAM-2 induced AKT activation is a survival signal
that can render a cell resistant to chemical (staurosporine and
etoposide), and physiological (TNF.alpha. and Fas ligand) apoptotic
inducers.
[0682] ICAM-2 co-immunoprecipitated with both .alpha.-actinin and
ezrin, demonstrating interactions with critical
membrane-cytoskeletal linker proteins. ICAM-2's anti-apoptotic
effect was dependent on the 21 amino acid cytoplasmic domain known
to bind .alpha.-actinin. Notably, .alpha.-actinin was shown to
interact directly with PI3 kinase through the p85 SH3-domain
(Shibasaki et al., 1994). Furthermore, the ICAM-2 cytoplasmic
domain binds to members of the ezrin/radixin/moesin (ERM) family of
membrane-cytoskeleton linker proteins (Helander et al., 1996).
ERM-proteins regulate cell morphology, adhesion and growth by
promoting membrane cytoplasmic linkages (Tsukita and Yonemura,
1997) and include the tumor suppressor, merlin/schwannomin,
implicated in neurofibroblastomatosis type II. In addition, ezrin
and other ERM proteins have been implicated in different diseases
for their modulation of adhesion molecule distribution (Ichikawa et
al., 1998; Stokowski and Cox, 2000; Turunen et al., 1998; Vinores
et al., 1995). Adhesion dependent survival was recently reported to
be mediated by ezrin in epithelial cells through a direct
interaction with PI3-kinase and pursuant AKT activation (Gautreau
et al., 1999). Interestingly, ICAM-2 clustering was induced by
errin overexpression (Helander et al., 1996) suggesting that
inappropriate surface protein clustering and subsequent signaling
can be strongly influenced by ERM proteins. Hence, we propose that
the ICAM-2 cytoplasmic domain interacts with membrane-cytoskeletal
linker proteins such as .alpha.-actinin and/or ezrin, leading to
the recruitment and activation of PI3 kinase to the membrane and
the subsequent activation of AKT kinase-mediated survival
activity.
[0683] The PI3K/AKT signaling system is a general mediator of
extracellular stimuli, including growth factors, cytokines, as well
as adhesion to extracellular matrices (Downward, 1998). The
activation of AKT is dependent on phosphorylation at two sites,
threonine-308 and serine-473 (Downward, 1998). The amino terminus
of AKT contains a pleckstrin homology domain that is thought to
bind directly to phospholipid products of PI3K. This binding
recruits AKT to the membrane that has been proposed to induce a
conformational change allowing phosphorylation at threonine-308 and
serine-473 by PDKI and PDKII respectively (Alessi et al., 1996).
Dually phosphorylated AKT is then active and can phosphorylate a
number of downstream effectors. Another mode by which AKT is
thought to inhibit cell death is by preventing release of
cytochrome C from mitochondria (Kennedy et al., 1999). Activation
of AKT kinase induced by ICAM-2 clustering resulted in activation
of several downstream effectors as detected by phosphorylation of
BAD, GSK3, FKHR and AFX. Phosphorylation of BAD at ser-136 results
in binding to 14-3-3 instead of BCL-X.sub.L (Zha et al., 1996),
shifting the equilibrium of Bc1-2 family members to favor cell
survival. GSK3 activity has been shown to be necessary for
apoptosis resulting from PI3K inhibition (Pap and Cooper, 1998).
Phosphorylation of GSK3 inhibits its activity and therefore would
present an anti-apoptotic signal. Phosphorylation of FKHR inhibits
its ability to translocate to the nucleus and initiate
FKHR-dependent transcription. Within the nucleus, dephosphorylated
FKHR can induce target genes such as Fas ligand in certain cells
and trigger apoptosis (Brunet et al., 1999). Phosphorylation of AFX
inhibits transcriptional activation of p27, a cell cycle inhibitor
(Graff et al., 2000). In addition, AKT has the ability to
phosphorylate and inactivate caspase 9 (human caspase 9),
phosphorylate eNOS (endothelial cells) and promote angiogenesis of
vascular endothelium, and potentially other substrates (Cardone et
al., 1998; Kureishi et al., 2000). AKT hyperactivity has been
observed in a number of disorders (Haas-Kogan et al., 1998) (Kulik
et al., 1997; Shan et al., 2000; Wick et al., 1999). All these data
support the notion that ICAM-2 activation would be expected to lead
to an extremely powerful anti-apoptotic signal in cells. A model of
ICAM2's interaction with the PI3KIAKT pathway is depicted in FIG.
32C.
[0684] The anti-apoptotic effects mediated by ICAM-2 overexpression
and by ICAM-2 clustering suggest that inappropriate ICAM-2
expression contributes an anti-apoptotic phenotype. As an adhesion
molecule, ICAM-2 has been attributed a role in lymphocyte
recirculation and through interactions with its receptor LFA-1, a
role in enhancing and stabilizing T-cell:B-cell contact (Damle et
al., 1992; Douglas et al., 2000). Here, we suggest that in addition
to possessing adhesion molecule properties, ICAM-2 is capable of
transmitting an intracellular signal when it is clustered on the
cell surface. The significance of ICAM-2 clustering, by virtue of
its overexpression in a cancer or by receptor-mediated engagement,
could lead to survival in cells otherwise destined to die by
apoptosis. This could lead to tumor drug resistance and
cytoproliferative disorders such as B-cell chronic lymphatic
leukemia (B-CLL). For instance, it was reported that ICAM-2 is
highly expressed on CD5.sup.+ B cells from B-CLL patients (Molica
et al., 1996) and on large B-cell lymphomas derived from patients
(Alizadeh et al., 2000) indicating that ICAM-2 or other adhesion
molecules may have a role in certain classes of leukemias. In
normal cells, ICAM-2 mediated PI3K activation may likely regulate
the endothelial transmigration of eosinophils (Gerwin et al.,
1999), and potentially dendritic cells (via DC-SIGN) (Geijtenbeek
et al., 2000).
[0685] Our results illustrate that ICAM-2 overexpression and
clustering can provide an, anti-apoptotic signal in B cells
rendering them resistant to physiological death 2 programs induced
by TNF.alpha. and Fas ligand. Notably ICAM-2 expression is
upregulated in many tissue culture cell lines in comparison to
their normal counterparts, suggesting that cells in an ex vivo
context need to initiate cell survival programs (de Fougerolles et
al., 1991). The work presented herein attributes a previously
unrecognized function for ICAM-2. The finding that ICAM-2 can exert
cell survival signaling, ectopically and endogenously, as well as
elicit an anti-apoptotic phenotype in a variety of cell lines and
human primary cells suggests that deregulation or induced
clustering is likely to contribute significantly to the
anti-apoptotic phenotype that leads to tumor progression. Thus,
pathways involved in the regulation of ICAM-2 expression and
distribution or other adhesion molecules could be important in the
development of anti-tumor therapies.
Experimental Procedures
[0686] Retroviral cDNA Screening
[0687] Production and infection of retroviruses was carried out as
described (Kitamura et al., 1995; Onishi et al., 1996; Rayner and
Gonda, 1994). A cDNA library was prepared from Jurkat T cells in
the pBabe-S vector (Hitoshi et al., 1998). The library
(2.times.10.sup.6 primary transformants) was used to transfect
.about.10.sup.7 PHOENIX-E packaging cells. The pBMN-LacZ control
vector was spiked into the library at 1:10 to monitor the
transfection/infection efficiency. Viral supernatants were
harvested and used to infect .about.10.sup.7 exponentially growing
NIH3T3 cells; 48 hours post infection the cells were split and
analyzed for .beta.-galactosidase activity. The literary transduced
NIH3T3 cells were plated at .about.25% confluency; 24 hours later
the medium was replaced with DMEM containing 1 .mu.M staurosporine
(STP; Sigma, St. Louis Mo.). After 24 hours treatment the
STP-containing medium was replaced with complete DMEM/10% donor
bovine serum. Surviving cells were allowed to reach .about.80%
confluency (7 days). Survivor cells were retreated as described two
additional rounds.
Phenotypic Transfer Assay
[0688] An aliquot of the surviving library-infected cells were
super-infected with Moloney Murine Leukemia Virus (gift of T.
Kinsella, Stanford). Super-infected cells were passaged for
two-weeks to allow efficient spread of the helper virus. Naive
NIH3T3 cells were infected with viral supernatants and allowed to
express for 48 hours. Re-infected cells were then treated with
staurosporine as described above. Surviving cells were cultured for
7 days and analyzed for transfer by RT PCR.
RT-PCR Cloning of Provirap-cDNA Inserts and Construct
Generation
[0689] RNA was prepared by the acid-guanidium-phenol-chloroform
method as described (Chomczynski and Sacchi, 1987). cDNA was
prepared from 4 .mu.g heat-denatured total RNA in a 50 .mu.l
reaction volume (Promega, Madison, Wis.) and incubated at
42.degree. C. and 55.degree. C. for 45 minutes. The cDNA reaction
products (5 .mu.l) were amplified (primers: 5'-GATCCTCCCITTATCCAG;
5'GAATGAAAGACCCCACCTGT) in a 50 .mu.l PCR reaction mix
(Perkin-Elmer, Foster City, Calif.) at 95.degree. C./30 sec;
55.degree. C./60 sec; 72 C/2 min for 25 cycles. Full length ICAM2
cDNA was cloned into retroviral vector PBM-Z-IN backbone (Kinoshita
et al., 1998) at BamHI/Sal1 site. ICAM2-.DELTA.C, ICAM2-AN and
ICAM2-C-terminal scrambled were generated by PCR and cloned into
the BamHI/Sal1 site.
Cell Culture and Preparation of Primary Cells
[0690] NIH3T3 murine fibroblast were maintained in DMEM, 10% DCS,
1% PSQ (Duelbecco Modified Eagle Media, 10% Donar calf serum, 1%
penicilli nstreptomycin (1000 units/ml and 2 mM L-glutamine PSQ).
Jurkat T-cells and CH27 transformed B-cells were maintained in
RPMI-1640, 10% FCS, 1% PSQ. BaF3 pro-B-cells were maintained in
RPMk1640, 10% FCS, 1% PSQ, 400 U/ml IL-3 (Peprotech). 70Z/3
pre-B-cells were maintained in RPMI-1640, 10% FCS, 1% PSQ, 50 .mu.m
.beta.-mercaptoethanol. HL60 myeloid leukemia cells were maintained
in Opti-Mem 1,10% FCS, 1% PSQ. 293T human fibroblast cells were
maintained in DMEM, 10% FCS, 1% PSQ. Cells were maintained at 5%
CO.sub.2/37.degree. C. humidified incubator. Transduced cells were
maintained in 500 .mu.g/ml G418 (Sigma) and proper expression of
construct was verified by western blots and FACS analysis of full
length ICAM-2, ICAM-2AC, ICAM-.DELTA.N as indicated. Staurosporine
(Sigma) treatment was for 24 hrs at 1 .mu.M (unless otherwise
indicated). LY294002 (New England Biolabs) treatment was at 10
.mu.m 30 minutes before any subsequent treatment. Wortmannin
(Sigma) treatment was for 24 hrs at 100 nM. Chemicals were
dissolved in DMSO (final being 1:1000 for solvent dilution) and
vector controls were incubated with 1% DMSO as negative control.
Vector controls consisted of pBMN-Z-IN (empty vector) transduction
or pBMN-Z-IN-GFP
(http://www.stanford.edu/group/nolan/plasmid_maps/pmaps.html) as
indicated. The infection frequency of pBMN-Z-IN-GFP was 48%.+-.10
for three independent viral transductions. Continual neomycin
selection yielded homogenous ICAM-2, ICAM2-.DELTA.C,
ICAM2-.DELTA.N, or control vector populations as routinely
monitored by flow cytometry for protein expression. For preparation
of primary cells, mononuclear cells were isolated from human
peripheral blood by Ficoll-plaque density centrifugation and
depletion of adherent cells on adherent plastic culture dishes.
Isolated cells were maintained in complete media and analyzed by
FACS for CD4, CD3, CD19, and ICAM-2 expression.
Cross-Linking
[0691] Antibody cross-linking experiments were performed using a
mouse monoclonal anti-ICAM-2 that recognizes the N-terminal region
(extracellular domain) at 10 .mu.g/ml. Spin dialysis (Biorad) was
used for buffer exchange of azide containing antibodies (0.01%) to
phosphate buffered saline buffer pH 7.4. Anti-mouse IgG (Sigma) was
used as a control antibody in cross-linking experiments. 10.sup.6
Jurkat or BaF3 cells were serum starved for 3 hours or 4 hours
respectively. Cells were incubated with either ICAM-2 (10 .mu.g/ml)
or mouse IgG (10 .mu.g/ml) at 37.degree. C. for the indicated time.
Time points began post serum starvation to attenuate most of the
signaling pathways or as indicated. Serum starvation of 3 or 4 hrs
lacked biochemical initiations of apoptosis as tested by caspase 3
activity, cell cycle analysis, annexin V/PI staining (data not
shown). Cells extracts were taken and subjected to either
immunoprecipitation or immunoblotting. ICAM-2 clustering of primary
human cells was performed using anti-human ICAM-2 (IC2/2 Research
Diagnostics) conjugated to FITC. The pursuant staining for ICAM-2
resulted in ICAM-2 clustering and signal transduction.
Apoptosis Assays
[0692] Apoptosis was determined either by counting pyknotic nuclei,
annexin-V binding by flow cytometry, or TUNEL BrdU staining by flow
cytometry as indicated. Apoptosis was induced either by
staurosporine (1 1 lm), treatment with anti-mouse Fas (5 .mu.g/ml
Santa Cruz Biotechnology (SCB), anti-human Fas (5 .mu.g/ml Jo2
Biomed) or anti-human Fas (10 ng/ml CH11 Kamiya Biomedical) as
indicated in appropriate experiment, IL-3 withdrawal (24 hrs) or as
indicated. For pyknotic nuclei count, NIH3T3 cells were grown on
glass coverslips and assayed for apoptosis. Suspension cells were
analyzed by nuclear staining with 25 .mu.M acridine orange/25 .mu.m
ethidium bromide or 5 .mu.g/ml Hoechst 33342 (Molecular Probes,
Eugene, Oreg.). Apoptosis was identified by the presence of
characteristic pyknotic nuclei as described (Jacobson and Raff,
1995). At least 5 individual fields were photographed and counted
using a Zeiss axioscope fluorescence microscope. For the survival
assay 10.sup.6 NIH3T3 cells were plated in 10 cm dishes and
incubated overnight at 37.degree. C. The cells were treated with 1
.mu.M staurosporine for 24 hours. The cells were washed and
cultured for 24 hours in complete medium. The cells were
trypsinized and viable cells counted following trypan blue
staining. Untreated cells were counted at the time of treatment. %
survival represents (number of viable cells post-treatment)/(number
of viable cells pretreatment). FACS based annexin-V-FITC(SCB)/PI
(Clontech) staining was done as described (PharMingen). TUNEL assay
was performed as described by manufacturer of Apoptosis BrdU kit
(Promega). Flow cytometry data acquisition was performed 24 post
staurosporine treatment (1 .mu.M) for both BrdU (10,000 events
collected) and pyknotic nuclei count and 12 hr post-staurosporine
treatment for annexin V binding (100,000 events collected).
Annexin-V positive cells will have compromised membranes after 24
hr treatment. Flow cytometry analysis was performed on a BD
FACSCalibur machine with CELLQuest and analyzed using FlowJo
software (Tree Star).
AKT Kinase Assays
[0693] AKT activity was detected by immunoprecipitation of AKT1
from cells and used in a kinase assay with GSK3 fusion protein
(NEB). 2.times.10.sup.6 NIH3T3, 2.times.10.sup.6 Jurkat, or
5.times.10.sup.5 BaF3 cells were incubated with immobilized AKT 1G1
monoclonal antibody (mAb) (1:200, NEB) at 4.degree. C. with gentle
rocking motion for 2 hrs. Immunocomplexes were washed 4.times. with
cell lysis buffer and resuspended in 40 .mu.l kinase buffer (25 mM
Tris pH 7.5, 5 mM .beta.-glycerolphosphate, 2 mM DTT, 0.1 mM
Na.sub.3VO.sub.4, 10 mM MgCl.sub.2) supplemented with 200 .mu.M ATP
and 1 .mu.g of GSK-3 fusion protein (NEB) for 30 min at 30.degree.
C. Kinase reaction was terminated with SDS sample buffer boiled for
5 min, and phosphorylation state of GS3K was detected by
immunoblotting and visualized using ECL detection (Amersham).
Immunoblots are representative of 3 independent virally transduced
cell populations each repeated 3 times (n=9). AKT activity was
verified by AKT phosphorylation by immunoblotting with
phospho-specific antibodies to ser473 and thr308 (NEB).
Immunoprecipitations and Immunoblotting
[0694] Cell extracts were prepared by washing 2.times.10.sup.6
cells in ice cold PBS and harvesting in lysis buffer (20 mM Tris pH
7.5, 150 mM NaCl 1 mM EDTA 1 mM EGTA, 1% Triton X-100, 2.5 mM
Na.sub.2PO.sub.4, 1 mM .beta.-glycerolphosphate, 1 mM
Na.sub.3VO.sub.4, 1 .mu.g/ml Leupeptin, 1 mM PMSF, protease
inhibitor cocktail tablet (Boehringer Mannheim)). Extracts were
centrifuged 14,000 RPM for 5 min at 4.sup.c and cell lysates (20
.mu.g as determine by BCA protein assay (Pierce)) were fractionated
on 12% or 15% SDS-polyacrylamide gel electrophoresis and
transferred to PVDF membranes using standard procedures.
Immunoprecipitations were pre-cleared with protein A/G plus-agarose
beads (SBC). IP was incubated for 1 hr or overnight with primary
antibody, 1 hr with protein A/G plus-agarose beads and washed
4.times. with lysis buffer. Blots were incubated with the following
antibodies: ICAM2 N-terminal (1:500 SBC), anti-ICAM2 C-terminal
(1:500 SBC), anti-ICAM2 IC2/2 mAb (1:500 BD Biosciences),
anti-.alpha.-actinin (1:500 SBC), anti-ezrin mAb (1:500
Transduction Laboratories), anti-Bcl2 (1:500 SBC), anti-p27 (1:1000
SBC), anti-p21 (1:500 SBC), anti-cFLIP (1:500 SBC),
anti-phospho-AKT-ser473 (1:1000 NEB), antiphospho-AKT-thr308
(1:1000 NEB), anti-AKT (1:1000 NEB), anti-phosphoBADser155 (1:1000
NEB), anti-FKHR (1:1000 wb, 1:200 IP NEB), anti-phospho FKHR
(1:1000 NEB), anti-phospho-Gsk3 .alpha./021 (1:500, NEB),
anti-cleaved PARP (1:1000 NEB), anti-cleaved caspase 9 (1:1000
NEB), anti-cleaved caspase 3 (1:1000 NEB), anti-cleaved caspase 7
(1:1000 NEB), anti-pAFX (1:1000 NEB), anti-caspase 9 (1:1000 NEB),
anti-caspase 7 (1:1000 NEB), anti-PARP (1:1000 NEB). BAD
phosphorylation was determined by immunoprecipitating total BAD
(1:200 NEB) and immunoblotting with anti-BADser112 (1:1000 NEB) and
antiBADser136 (1:1000 NEB) as recommended by manufacturer of BAD
phosphorylation detection kit (NEB). Secondary antibodies used:
anti-rabbit HRP (1:5000 NEB), anti-mouse HRP or anti-goat HRP
1:5000, SBC) and visualized using ECL detection (Amersham) or with
a Kodak Digital Science 440C station. Blots are representative of
at least 3 independent experiments.
Flow Cytometry and FACS Analysis
[0695] Intracellular and extracellular staining was performed as
described (www.metazoa.com\UPL3287). Antibodies used: anti-ICAM2
N-terminal (SBC), anti-ICAM2 N-terminal (SBC), anti-ICAM2-FITC mAb
(BD Biosciecnes/Fisher), annexin-V-FITC (BD Biosciences),
annexin-V-biotin (SBC), PI (Clonetech). Secondaries used:
anti-rabbit PE (BD Biosciences), anti-mouse-FITC (BD Biosciences),
anti-rabbit FITC (PharMingen), anti-goat FITC (BD Biosciences),
anti-goat texas red (BD Biosciences), Streptavidin-PE (BD
Biosciences), streptavidin-FITC (BD Biosciences), anti-human
CD4-APC (PharMingen), anti-human CD19-PerCP (PharMingen),
anti-human ICAM-2-FITC (Research Diagnostics IC2/2) Intracellular
probe for AKT activity was made by conjugating monoclonal
anti-AKTser473 antibody (Cell Signaling Technology) to Alexa-568
dye (Molecular Probes), using Alexa-568 protein conjugation kit
(Molecular Probes). Phospho specificity was tested by western
blotting and FACS analysis to a variety of PI3K activators and
inhibitors (data not shown). Intracellular staining by
phospho-AKTser473-Alexa568 reflected AKT kinase activity when
NIH3T3 cells were stimulated with platelet derived growth factor
(Sigma) and inhibited by LY294002 prior to stimulation.
Quantitative FACS analysis was performed as described (Davis et
al., 1998; Iyer et al., 1998; Lenkei et al., 1998). In brief,
R-phycoerythrin (PE) (Molecular Probes) was conjugated to a
anti-ICAM2 N-terminal monoclonal antibody (Research Diagnostics
IC2/2) as suggested by manufacturer of protein cross-linking kit
(Molecular Probes), tested for proper stochiometry (data not shown)
and quantitated using Quantibrite-PE beads (BD systems). A
quantitative calibration curve was generated using Quantibrite-PE
beads that contain a known amount of PE molecule/bead.
[0696] A linear regression analysis is performed using the
following equation: log.sub.10(PE fluorescence)=slope*log.sub.10(PE
molecules/bead)+intercept. PE fluorescence is determined by taking
the geometric mean of the PE channel. Quantitation is valid only
for antibodies directly conjugated to PK. Using saturating amounts
of antibody and thorough washing ensures all surface antigens are
bound. Preparation of samples on ice reduces antibody
internalization. Surface antigens of cells for an unknown cell
population are determined by computing the PE geometric mean using
the calibration curve. Quantitative FACS analysis provides
approximate estimates for surface antigen expression. Numbers
plotted represent relative surface molecules and not absolute
numbers since antibody valency was not investigated for the
monoclonal antibodies used. Flow cytometry analysis was performed
on a BD FACSCalibur machine and analyzed using FlowJo software
(Tree Star). CellQuest was used for quantitative flow cytometry and
linear regression analysis of Quantibrite-PE beads. Flow cytometry
data are representative of 3 independent experiments of 10.sup.6
cells/sample analyzed. 100,000 events were collected or otherwise
noted and calibrated using Calibrite beads (BD systems). Data
plotted in bar graph format is expressed as the mean (bar).+-.SD of
triplicate experiments.
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[0771] In this Example, using the methods and compositions of the
present invention, the present inventors (also referred to herein
as "we") show that Leukocyte Function Antigen-1 (LFA-1) is
essential in the formation of immune cell synapses and has a role
in the pathophysiology of various autoimmune diseases. In this
Example, using the methods and compositions of the present
invention, the present inventors demonstrate that ICAM-2 induced an
LFA-1 signal transduction pathway that is linked to receptor
clustering and activation by both the microtubule and actin
cytoskeleton. ICAM-2 exhibited a 21.7 pM/cell binding affinity as
determined by single cell analysis. ICAM-2/LFA-1 engagement induced
activation of PKC and a reorganization of both the actin and
microtubule cytoskeleton. These events resulted in a Syk dependent
activation of the p44/42 MAPK pathway upon cytotoxic T cell
effector-target cell binding via active LFA-1. ICAM-2 mediated
human CD56.sup.+CD8.sup.+ perforin release and resultant
cytotoxicity to target leukemia cells. In comparison to the other
ICAMs, ICAM-3 was found to be most similar to ICAM-2's effect and
dissimilar to ICAM-1. In IL-2 pre-activated human PBMC,
ICAM-2>ICAM-3>>ICAM-1 in mediating perforin release of a
CD56.sup.+CD8.sup.med population. All ICAMs contributed to perforin
and granzyme-A loss in CD56.sup.+CD8.sup.med populations. These
results identify a specific functional consequence for ICAM-2/LFA-1
in subset-specific cytotoxic T cell immunity.
Introduction
[0772] Leukocyte Function Antigen-1 (LFA-1) is an .alpha.,.beta.
heterodimer integrin involved in leukocyte adhesion (van Kooyk and
Figdor, 2000). At present, it is well understood that LFA-1
participates in lymphocyte adhesion, with prominent roles in the
formation of the immunological synapse (Dustin and Shaw, 1999), and
lymphocyte extravasation and recirculation (Volkov et al., 2001).
LFA-1 adhesion is governed by the intercellular adhesion molecule
(ICAMs)-1, -2, and -3 ligands (van Kooyk and Figdor, 2000).
Patients afflicted with Leukocyte Adhesion Deficiency disorder
(LAD), a syndrome in which the LFA-1 integrin is mutated or
missing, suffer sever recurrent bacterial infections and impaired
overall immunity (Bunting et al., 2002). Among these clinical
manifestations, the LEA-1 knockout mouse has suggested that LFA-1
may have a potential role in mediating tumor regression in adoptive
immunotherapy (Mukai et al., 1999; Nishimura et al., 1999).
Although these studies genetically link a lymphocyte adhesion
molecule with impaired immune function, the molecular details that
mediate these immunopathologies are less well understood.
[0773] Investigations of LFA-1 have primarily focused on the
integrin's adhesive role. It is unclear as to how the physical
processes of LFA-1 integrin activation and receptor clustering are
interconnected and translated into cellular signals upon ligand
binding. It is less understood how the absence of these events
leads to the devastating effects of LAD and the impaired immune
responses in LFA-1 knockout mice. We therefore sought to decipher
the molecular details of a model interaction of ICAM-LFA-1 to
understand LFA-1 signaling mechanisms initiated upon cell-to-cell
contact. Utilizing multiparameter single cell analysis to monitor
LFA-1 receptor dynamics upon treatment with a soluble ICAM-2, we
found that both the actin and the microtubule cytoskeleton couple
ICAM-2 adhesion to LFA-1 activation and clustering. The microtubule
cytoskeleton constrained the LFA-1 conformational change
(activation), an event that preceded LFA-1 clustering as measured
by multiparameter flow cytometry. The induced LFA-1 activation led
to the activation of the p44/42 Mitogen Activated Protein Kinase
pathway (MAPK; RAF/MEK/ERK), an event that was dependent on both
Pyk2 and Syk kinase activities.
[0774] The present inventors investigated these molecular details
of the ICAM-2 mediated LFA-1 activation in the adhesion between
cytotoxic T cells and a target leukemia cell, an event that
requires cell-to-cell contact. ICAM-2 stimulation of human
CD56.sup.+CD8.sup.+ T cells could induce perforin/granzyme-A
mediated cytotoxicity of leukemia cells. This directed killing was
shared by ICAM-3 and to a lesser extent by ICAM-1, two other LFA-1
ligands. These results distinguish a signaling mechanism for
ICAM-2/LFA-1 directed cytotoxic T lymphocyte immunity and suggest
possible mechanisms by which tumor secretion of ICAM-2 and possibly
ICAM-3 might allow for evasion of a directed cytotoxic T cell
immune response.
ResultsRecombinant ICAM-2 Promotes LFA-1 Mediated Adhesion
[0775] The present inventors chose a model Jurkat T cell line as a
system to initially dissect the LFA-1 signaling mechanism and then
verified the findings in human T cells. A biochemically purified
ICAM-2 protein was produced to study ICAM-2/LFA-1 interactions in
the absence of other ligands (FIG. 33E-H). We purified human ICAM-2
from retrovirally transduced NIH3T3 cells using immunoaffinity
chromatography and subsequent gel filtration. We compared it to an
ICAM-2-FC fusion protein produced in NSO murine myeloma cells.
These murine based mammalian expression systems were chosen on the
basis that they yielded a bioactive form of ICAM-2. Biochemical
analysis of ICAM-2FC protein was consistent with the expected
molecular weight of the fusion protein (76 kD, FIG. 33A) and
purified human ICAM-2 displayed a molecular weight of 72-74 kD
(FIG. 33A). This size was similar to the 75 kD ICAM-2 purified from
Jurkat T cells (data not shown).
[0776] The present inventors generated a FITC conjugated ICAM-2
(ICAM-2-FITC) to study LFA-1 receptor dynamics by flow cytometry
and laser scanning confocal microscopy (LSCM) (FIG. 33G). We tested
for ligand binding of the LFA-1 receptor by monitoring the binding
kinetics of ICAM2-FITC on single cells. Low binding was observed in
the first 150 seconds, whereupon there was a progressive increase
until 750 seconds, and leveled thereafter (FIG. 33B, middle panel).
In contrast, an .alpha.-LFA-1 antibody displayed an initial spike
in the first 50-100 seconds and equilibrated until 800 seconds
(FIG. 33B, bottom panel). Pre-activating LFA-1 by treatment with
PMA (McDowell et al., 1998) showed an immediate binding of ICAM-2
(FIG. 33C, top panel). The gradual ICAM-2 binding after 150 seconds
suggested an enhanced LFA-1 binding for its ICAM-2 ligand after
some binding-induced event--a property not observed using the
.alpha.-LFA-1 or upon PMA activated LFA-1 (FIG. 33B). Binding of
ICAM-2-FITC was not observed in trypsinized cells (data not shown)
and was blocked by antibodies to LFA-1 (described below).
Therefore, there appeared to be an increase in binding of the
ICAM-2 ligand as a function of time, suggesting the presence of an
induced binding site on the target cells.
[0777] Analysis of the ICAM-2 binding population by flow cytometry
showed a dependency on both the actin cytoskeleton and temperature.
ICAM-2 adhesion was enhanced at 37.degree. C. vs. 4.degree. C.
(FIG. 33C). Pre-treatment with the actin depolymerizing agent
cytochalisin D revealed two ICAM-2 binding populations at both
37.degree. C. and 4.degree. C., contrasting with the binding
phenomena observed for .alpha.-LEA-1 (FIG. 33C). Saturation of
ICAM-2-FITC was observed at 37.degree. C. more readily than at
4.degree. C. (data not shown, FIG. 33H). Single cell binding
affinity measurements for ICAM-2 were obtained by computing the
percent ICAM-2-FITC bound per cell (FIG. 33D). Curve fit analysis
indicated a dissociation constant of 0.21.+-.0.07 .mu.M/10.sup.4
cells (FIG. 33D). This value equates to 21.7 pM/cell, representing
the first ligand binding measurements reported for ICAM-2 within
the physiological context of cell surface LFA-1. Thus, quantitative
single cell analysis of ICAM-2 ligand binding suggests strong
binding at physiological temperatures.
Soluble ICAM-2 Induces LFA-1 Clustering and Cytoskeleton
Polarization
[0778] The present inventors investigated if LFA engagement altered
cytoskeletal structures and observed a reorganization of both the
actin and microtubule cytoskeleton upon ICAM-2 stimulus (FIG. 34A).
The present inventors monitored the cytoskeletal architecture by
flow cytometry and observed a simultaneous change in the actin and
microtubule organization upon ICAM-2 binding (FIG. 34B), an effect
consistent with depolymerization. ICAM-2 treatment induced a rapid
clustering of LFA-1 within one minute, with multiple clustering
events at five minutes (FIG. 34C, left panel). Using the
ICAM-2-FITC ligand to visualize the cell surface, indicated that
the ICAM-2 ligand induced clustering of the LFA-1 receptor (FIG.
34C, left panel). The clustering event showed some colocalization
using a non-blocking .beta.2 integrin antibody (clone CTB104) (FIG.
34C, right panel). Thus, we speculated that ICAM-2 binding to LFA-1
induced a signal that resulted in a reorganization of the
LFA-1/ICAM-2 complex. We therefore decided to investigate this in
relation to the observed changes in the actin/microtubule
cytoskeleton.
[0779] The present inventors assessed LFA-1 receptor dynamics by
multiparameter flow cytometry upon ICAM-2 binding to correlate
LFA-1 activation and clustering. We utilized the doublet
discriminator module on a FACSCalibur machine to distinguish
between distributed and focalized fluorescence pulses (FFP) upon
laser excitation of single cells. Incubation of ICAM-2 at
37.degree. C. vs. 4.degree. C. displayed a decrease in the FFP, an
effect that was greatly enhanced upon cytochalisin D treatment
(FIG. 34D). ICAM-2-FITC surface binding was monitored by the
fluorescence intensity and normalized against the time-of-flight
(TOF) of the fluorescence pulse (FP). We interpreted the value of
ICAM-2-FITC intensity per TOF as a quantitative assessment for
LFA-1 clustering, as the TOF is proportional to the laser-excited
cellular area. Computing this value as a function of time for an
ICAM-2 stimulus (FIG. 34E) is proportional to the increased
clustering events observed by LSCM (see FIG. 34C).
ICAM-2 Adhesion Induces a Conformational Change in LFA-1 that is
Regulated by the Microtubule Cytoskeleton.
[0780] Although the enhanced ICAM-2 adhesion and induced LFA-1
clustering is reflective of overall increased avidity for the
ICAM-2 ligand, it does not necessarily reflect an LFA-1 activation
state (high affinity state) (McDowall et al., 1998). Upon LFA-1
activation, a conformational change exposes an epitope that is
recognized by the mAb24 antibody (Neeson et al., 2000). A
mAb24-Alexa633 conjugate was used to assess the activation state of
LFA-1 upon ICAM-2 stimulus by flow cytometry. Unstimulated cells
did not display mAb24 binding, contrasting the induction observed
with PMA treatment (FIG. 34F). ICAM-2 stimulated cells displayed a
bimodal population in active LFA-1, an effect that was attenuated
by cytochalisin D (FIG. 34F). Treatment with microtubule disrupting
agents, nocodazole and taxol, resulted in full activation of LFA-1
upon ICAM-2 stimulus (FIG. 34F). In contrast, disrupting the actin
cytoskeleton via cytochalisin D diminished the ICAM-2 induced LFA-1
activation, although it enhanced LFA-1 receptor clustering and
subsequent ICAM-2 binding (see FIG. 34D). Therefore, the actin and
microtubule cytoskeletal network differentially impact LFA-1
activity and avidity.
[0781] The present inventors monitored LFA-1 activation and
clustering simultaneously as a function of ICAM-2 stimulus per time
by flow cytometry. Correlating the mean fluorescence of mAb24
antibody with the LFA-1 clustering value revealed LFA-1 activation
preceeded LFA-1 clustering (FIG. 34G) within 30 seconds there was a
significant increase in binding of the mAb24 antibody but only a
modest increase in clustering. However, after another 30 seconds up
to 30 minutes the relative binding of mAb24 increased somewhat but
there was a significant increase in the clustering value (FIG.
34G). Thus, these results suggest that the ICAM-2 ligand induced
activation of LFA-1 is followed by subsequent LFA-1 clustering.
[0782] The present inventors observed that treating cells with a
PKC inhibitor, bisindolymaleimide I (BIM I), inhibited ICAM-2
induced LFA-1 activation as measured by using mAb24 binding (FIG.
35A). ICAM-2 adhesion, as measured by the binding of ICAM-2-FITC,
was not affected (FIG. 35A). This suggested that the ligand induced
receptor conformational change was dependent on intracellular
kinases. Interestingly, ICAM-2 induced a calcium influx, a
component necessary in PKC activation (data not shown). Thus, these
observations suggest that the ICAM-2 ligand induced exposure of the
mAb24 neoepitope triggers a PKC dependent intracellular signaling
event. We decided to investigate the downstream signaling
consequences of ICAM-2 binding to LFA-1.
ICAM-2 Induces p44/42 MAPK Activity Through LFA-1
[0783] Flow cytometric based kinase profiling experiments were
performed to identify a signaling pathway downstream of PKC
activation upon ICAM-2 stimulus. Treatment with ICAM-2 induced both
p44/42 MAPK phosphorylation and activation (FIG. 35B-D). An ICAM-2
titration correlated with phosphorylation of p44/42 MAPK as
determined by single cell flow cytometric analysis (FIG. 35B, top
panel), results congruent with kinase activity analysis (see FIG.
35C). Titration of mAbs to .alpha..sub.L and .beta.2 integrins
competed with ICAM-2 binding, and thus diminished the induced
p44/42 MAPK phosphorylation (FIG. 35B, bottom panel). This
inhibition was not observed after pretreatment with mAbs to
.beta.1, .beta.3, .alpha..sub.M, or .alpha..sub.X integrins (FIG.
35C) indicating that the ICAM-2/LFA-1 interaction was mediating the
p44/42 MAPK activation.
Activation of PKC, PYK2, and SYK are Necessary for the ICAM-2/LFA-1
Induction of p44/42 MAPK Activity
[0784] The present inventors undertook flow cytometric based p44/42
MAPK kinase inhibition and activation profiling to identify
necessary components for LFA-1 signaling. PKC inhibitor BIM I,
cytoskeletal disrupting agents cytochalisin D, taxol, nocodozole,
and sequestering of divalent cations by EDTA diminished the ICAM-2
induced p44/42 MAPK signal (FIG. 35D), suggesting that the
ligand-induced events of LFA-1 are mechanically linked to signal
transduction by the actin-microtubule cytoskeleton. To identify
upstream kinases that were responsible for signal transmission from
LFA-1 to p44/42 MAPK, a series of kinase inhibitors were applied
and tested for their ability to abrogate the ICAM-2 induced p44/42
MAPK activity (FIG. 34H-I), whereas Herbimycin A and Emodin,
inhibitors of src and p56lck had no effect. Tyrphostin A9 and
piceatannol, specific inhibitors of proline-tyrosine kinase 2
(Pyk2) and Spleen-tyrosine kinase (Syk), respectively (Avdi et al.,
2001; Fuortes et al., 1999) abrogated the ICAM-2 induced activation
of p44/42 MAPK and its upstream activator Raf-1 (FIG. 36A).
[0785] The present inventors tested whether Pyk2 and Syk interacted
with the .beta. 2 integrin. Pyk2 and Syk were phosphorylated and
co-immunoprecipitated with .beta.2 integrin upon ICAM-2 treatment
(FIG. 36B), indicating Pyk2 and Syk translocated to the membrane
(FIG. 35E). This was coincident with phosphorylation of Pyk2 and
Syk upon ICAM-2 stimulus as a function of time (FIG. 36B-C).
Phosphorylation of PKC.alpha./.beta..sub.II, and Pyk2 were detected
at one minute, followed by Syk phosphorylation at 5 minutes (FIG.
36C). We confirmed that Pyk2 and Syk activities were dependent on
PKC activation (data not shown FIG. 36D-E). Taken together with the
above results, this suggested that the LFA-1 signaling mechanism
imparted by ICAM-2 is at least initiated by PKC and relayed to the
p44/42 MAPK pathway by Pyk2 and Syk.
LFA-1 is Involved in Effector-Target Cell Adhesion and Facilitates
Human Cytotoxic T Cell Activation
[0786] Since LFA-1 is involved in adhesion between lymphocytes, a
process that occurs at several immunological synapses, we were
interested in investigating the molecular events identified for the
ICAM-2/LFA-1 interaction in a physiological context. It has been
suggested that a clustered topographic presentation of ICAM-2,
independent of expression levels, is an effective target structure
by which natural killer cells initiated cytotoxicity (Helander et
al., 1996). We first applied a FACS based effector-target killing
assay to quantitatively monitor target cell lysis of HL60 leukemic
cells upon treatment with stimulated human PBMC at various
effector: target cell ratios. Flow cytometric detection of target
cell lysis has been reported to be more sensitive than the standard
chromium release assays (Lecoeur et al., 2001). We labeled HL60
cells with the fluorescent dye CFSE and monitored the cell quantity
by flow cytometry in standard effector-target cell based assays.
Soluble ICAM-2 could initiate target cell lysis in the presence of
IL-2 but not in the absence of IL-2 (FIG. 37A). In IL-2
pre-activated cells, ICAM-1 and ICAM-3 did not initiate as potent a
cytotoxic cell response in contrast to ICAM-2 (FIG. 37B).
[0787] Since natural killer cells (NK) comprise a heterogeneous
population, namely specific cytotoxic T lymphocytes (CTL, with
C8.sup.+ subsets therein), NK cells (CD16.sup.+ and subsets
therein), and CD4.sup.+ TH1 cells (Biron and Brossay, 2001), we
determined if ICAM-2 was unique to a particular human NK cell
subset. We utilized the multidimensional gating capability of flow
cytometry to identify distinct cellular populations that were
contributing to the cytolytic activity observed in human PBMC. We
also monitored intracellular levels of perforin and granzyme-A by
flow cytometry, two proteins that mediate target cell lysis by NK
cells in these populations. We identified 6 distinct populations by
CD8 and CD56 surface stains in human PBMC (FIG. 38 panel I) and
gated on these subsets for all subsequent intracellular functional
assays (FIG. 38A panels We performed effector-target cytotoxicity
assays in the presence of ICAM-1, ICAM-2, and ICAM-3 soluble ligand
and HL60 target cells. We did not observe significant changes in
population subset frequencies post stimulation (FIG. 38A, panel I).
The CD56.sup.+CD8.sup.low population displayed no significant
changes in intracellular perforin or granzyme-A upon stimulation
with ICAM-1, -2, or -3 (FIG. 38A, panel II). The
CD56.sup.+CD8.sup.med population displayed a slight increase (1.5-2
fold) in the frequency of the perforin negative population for
ICAM-2 and ICAM-3 (21.5% ICAM-2>19.8% ICAM-3>13.7% ICAM-1)
(FIG. 38A panel III). The CD56.sup.+CD8.sup.high population
displayed a loss in both granzyme-A and perforin for ICAM-1, -2, -3
stimulations compared to unstimulated with a significant loss in
the granzyme-A negative population for ICAM-2 (58.3%) compared to
ICAM-1 (4.12%) or ICAM-3 (3.07%) (FIG. 38A, panel IV). The
CD56.sup.-CD8.sup.high also displayed a loss of both granzyme-A and
perforin by all ICAM stimulations (FIG. 38A panel V). Since it was
not possible to positively identify the subsets within the
CD56.sup.-CD8.sup.- population, they were omitted from
analysis.
[0788] Quantifying the intracellular amounts of perforin and
granzyme-A in the CD56CD8 subsets relative to unstimulated cells
also identified similarities and differences for the ICAMs as
evidenced below. ICAM-2 and ICAM-3 mediated loss of granzyme-A and
perforin to a greater extent than ICAM-1 (FIGS. 38B-C).
Additionally, in IL-2 pre-activated cells, differences where seen
with the ICAM stimulations: ICAM-2>ICAM-3>>ICAM-1
displayed a loss of perforin, particularly in the
CD56.sup.+CD8.sup.med/high populations (FIG. 38B). ICAM-2 and
ICAM-3 also induced perforin loss in the CD56.sup.+CD8.sup.low,
however ICAM-2 required preactivation by IL-2 (FIG. 38B). There
were lower levels of granzyme-A detected for the CD8.sup.high
subsets (CD56.sup.+ or CD56.sup.-) for
ICAM-2>ICAM-3>ICAM-1>unstimulated (FIG. 38C). In the
presence of IL-2 pre-activation, all the ICAMs induced release of
granzyme-A in the CD56.sup.+CD8.sup.high/med populations, with a
particular decrease by ICAM-2 (FIG. 38C). No significant changes
were seen in the CD56.sup.+CD8.sup.low population for granzyme-A
(FIG. 38C). These differences were similar at various
effector-target cell ratios (50:1, 25:1, 12.5:1) (data not shown).
Thus, similarities and difference exist for ICAM-1, -2, and -3
stimulation of cytolytic activity in CD56CD8 subsets. All three
ICAMs mediated perforin release in the CD56.sup.-CD8.sup.high
populations. ICAM-2 and ICAM-3 were most similar in mediating
perforin/granzyme-A release in the CD56.sup.+CD8.sup.high and
CD56.sup.+CD8.sup.med populations.
[0789] We focused on the CD56.sup.+CD8.sup.- cells (both the
CD8.sup.med and CD8.sup.high subsets) and tested if inhibition of
Syk, p44/42 MAPK or disruption of the cytoskeleton detrimentally
affected effector-target (E:T) cell conjugation as measured by a
flow cytometric conjugate formation assay (Morgan et al., 2001).
Disruption of cytoskeletal actin and microtubules enhanced E:T
conjugate formation (FIG. 39A) congruent with prior results that
disruption by these agents enhanced LFA-1 activation. Inhibition of
Syk by piceatannol inhibited conjugate formation whereas inhibiting
p44/42 MAPK by PD98059 did not (FIG. 39A). These results suggest
that Syk activity is necessary for LFA-1 adhesion of
effector-target cells and is consistent with a report indicating
that Syk/ZAP-70 are necessary for LFA-1 to LFA-1 activation on the
same cell (Soede et al., 1999). p44/42 MAPK appeared to not be
necessary for E:T conjugate formation. Monitoring active LFA-1 and
intracellular activation of p44/42 depicted a time dependent
correlation between these two markers in CD56.sup.-CD8.sup.+ cells
as stimulated by ICAM-2 (FIG. 39B).
Discussion
[0790] In this report it was observed that (1) ICAM-2 can induce
LFA-1 clustering, activation, and cytoskeletal reorganization in
the absence of exogenous activators such as cytokines or TCR
signaling; (2) LFA-1 transmits a signal to the p44/42 MAPK pathway
involving PKC, Pyk2, and Syk upon ligand binding; and (3) LFA-1
receptor dynamics are mechanically coupled to signal transduction
by both the actin and microtubule cytoskeleton network. The
physiological outcome of these molecular events triggered perforin
and granzyme A mediated CD56.sup.+ CD8.sup.+ T cell cytotoxicity
that were mostly shared by ICAM-2 and ICAM-3 but not ICAM-1.
[0791] .beta.2 integrin signaling mechanisms vary depending on the
system of study and are centered on adhesive roles in cell
morphology and motility (Dib, 2000). .beta.2 integrin signaling has
been shown to involve cytoskeletal reorganization via tyrosine
phosphorylation of paxillin, vav, and GTPase activating proteins
among others (Fuortes et al., 1994; Zheng et al., 1996). Studies
focused on LFA-1 mediated leukocyte adhesion (CD11a/CD18) have
shown a regulatory role for PKC in LEA-1 avidity (Bleijs et al.,
2001; Hedman and Lundgren, 1992) and have demonstrated that TCR
signaling can activate LFA-1 (Peterson et al., 2001). It has also
been shown that chemokines, in the absence of TCR signaling, can
serve as activators of LFA-1 during lymphocyte/endothelial contact
(Constantin et al., 2000). It has not been clear how LFA-1 integrin
adhesion, clustering, and activation are coupled to intracellular
signaling events, in the absence of external (chemokine) or
internal (TCR or costimulatory molecule) stimulation.
[0792] A synthesized peptide of ICAM-2's first Ig domain (P1, amino
acids 21-42) can induce LFA-1 mediated adhesion at high
concentrations (62 .mu.M), which was comparable to a 48-fold lower
ICAM-2 soluble protein concentration (1.3 .mu.M) in a bulk cellular
adhesion assay (Kotovuori et al., 1999). However, P1 binding did
not induce the active conformation of LFA-1 and did not induce
calcium influx (Kotovuori et al., 1999), whereas full length ICAM-2
binding resulted in active LFA-1 (see FIG. 34D) and a calcium
influx event (data not shown). The calculated ICAM-2 affinity of
217.+-.66 nM (per 10.sup.4 cells) contrasts the 605.+-.55 nM
k.sub.D reported using BIAcore analysis of an engineered "active"
locked I domain of LFA-1 (Shimaoka et al., 2001). The reported
affinities for ICAM-2 binding here take advantage of single cell
resolution within a physiological context, something not possible
utilizing purified or genetically engineered LFA-1. The differences
observed for peptide vs. protein concentrations are likely
attributed to impurities in the peptide synthesis and/or presence
of carbohydrate moieties native to the endogenous ICAM-2, which
comprise greater than 30 kD of its approximate 66 kD molecular
weight and have been suggested to orient ICAM-2 binding to LFA-1
(Casasnovas et al., 1997; de Fougerolles et al., 1991).
[0793] We investigated the role of the actin and microtubule
cytoskeleton in LFA-1 receptor activation and clustering as induced
by the ICAM-2 ligand by multiparameter flow cytometry. Disruption
of the actin cytoskeleton enhanced LFA-1 clustering and ICAM-2
binding, corroborating previous studies that suggested the actin
cytoskeleton constrains LFA-1 mobility (Lub et al., 1997).
Interestingly, actin depolymerization abrogated the ICAM-2 induced
LFA-1 activation. In contrast, disruption of the microtubules by
both nocodazole and taxol enhanced LFA-1 activation as determined
by exposure of the neo-epitope recognized by the mAb24. Recently,
it has been reported that depolymerization of microtubules
increases the lateral mobility of .beta.2 integrins in macrophage
cell lines (Zhou et al., 2001); therefore its conceivable that the
microtubules regulate the conformational change upon ligand binding
necessary for exposure of the LFA-1 activation epitope. These
observations suggest the actin-microtubule cytoskeleton regulates
both the high-avidity and high affinity state of LFA-1 upon ligand
binding. We observed that LFA-1 signal transduction was abrogated
in the presence of all cytoskeletal disrupting agents tested
(cytochalisin D, nocodazole, and taxol) indicating that the LFA-1
receptor is linked to signal transduction machinery by the
cytoskeleton. Thus, the mechanistic uncoupling of the high avidity
and high affinity states of LFA-1 suggests that intracellular
events that regulate/mediate these two states exist at the LFA-1
integrin-cytoskeletal juncture and relay the LFA-1 receptor
dynamics to intracellular signaling proteins upon ligand
binding.
[0794] Several chemical inhibition screens were designed to
identify the proteins involved in the LFA-1 to p44/42 MAPK
signaling event. Both Pyk2 and Syk were identified to be necessary
for activation of the p44/42 MAPK pathway and were dependent on PKC
activity upon ICAM-2 binding. Phosphorylation of Pyk2 has been
associated with homotypic adhesion mediated by an LFA-1/ICAM-1
interaction in B cells (McDonald et al., 2000). In addition, Pyk2
activation has been shown to be necessary for p44/42 MAPK activity
in other model systems (Barsacchi et al., 1999; Lev et al., 1995).
Syk is a tyrosine kinase essential in .alpha.III.beta.3 signaling
(Saci et al., 2000), and links Fc.epsilon.RI signaling to the
ras/MAPK pathway (Jabril-Cuenod et al., 1996). Inhibition or
ablation of Syk, either by pharmacological means (via inhibition by
piceatannol), biochemical means (dominant negative Syk), or genetic
means (Syk mice) inhibits natural cytotoxicity (Brumbaugh et al.,
1997; Colucci et al., 1999). Thus LFA-1 activation signaling to
Syk, a kinase that has been shown to be important for NK cell
function, provides a biochemical link between surface integrin
activation and effector cell function.
[0795] The present inventors demonstrated that both Pyk2 and Syk
are necessary in ICAM-2 induced LFA-1 signaling to Raf-1, the
upstream kinase in the p44/42 MAPK (RAF/MEK/ERK) cascade.
Inhibition of p44/42 MAPK did not prevent the occurrence of
CD56.sup.+CD8.sup.+ cell conjugation. By immunofluorescence
analysis, it has been shown that treatment of the NK leukemic cell
line YT with the p44/42 MAPK inhibitor PD98059 inhibits perforin
redistribution to the site of effector-target cell contact (Wei et
al., 1998). In addition, the p44/42 MAPK pathway has been shown to
be important in the regulation of cytoxicity in natural killer
cells (Jiang et al., 2000). Thus, the p44/42 MAPK pathway, here
demonstrated to become active upon LFA-1/ICAM-2 binding, has been
shown to be connected to at least perforin granule exocytosis.
Thus, the LFA-1 signaling pathway as elicited by ICAM-2 contains
signaling junctures that map to both the effector-target cell
adhesion event and activation of cytolytic machinery in the human
CD56.sup.+CD8.sup.+ cytotoxic T cell population. These results
provide direct evidence for a functional consequence of LFA-1
integrin adhesion with cytolytic signaling mechanisms.
[0796] We also observed that ICAM-2 was similar to ICAM-3 in
mediating cytolytic activity as evidenced by release of perforin
and granzyme-A in effector-cell conjugation, effects of which
contrasted ICAM-1 (see FIG. 38). We have previously observed
similarities between ICAM-2 and ICAM-3 intracellular signaling
mechanism that also differed from that of ICAM-1 (Perez et al.,
2002). However, the results do not exclude the possibility of
ICAM-2 stimulating other yet to be identified cytotoxic capable
subsets, as high cytolytic activity was observed in bulk PBMC (see
FIG. 37).
[0797] Prior investigations into cytotoxic T cells have established
that blocking the LFA-1/ICAM interactions inhibits effector-target
cell adhesion and therefore concluded that it also blocks cytolytic
activity in NK cells (Donskov et al., 1996; Krensky et al., 1984;
Matsumoto et al., 2000). Functional studies of NK cells from
LFA-1'' mice have demonstrated that LFA-1 adhesion is necessary for
IL-2 activated NK killing (Matsumoto et al., 2000) and also that
LFA-1.sup.-/- CD8.sup.+ T cells are defective for T cell activation
and effector function (Shier et al., 1999). Interestingly, NK cell
cytotoxicity is defective in NK cells from LAD patients (Shibuya et
al., 1999). It has only recently been shown that the directed
killing of cytotoxic T lymphocytes involves polarization of the
microtubule-organizing center (MTOC) towards LFA-1 at the
CTL-target site (Kuhn and Poenie, 2002), an indication that LFA-1
may possess a functional role other than strictly adhesion.
[0798] In conclusion we find that ICAM-2, as an LFA-1 ligand, can
mediate activation and clustering of the LFA-1 receptor--an event
that in turn polarizes the microtubule and actin cytoskeleton and
activates the p44/42 MAPK pathway. These events were found to be
necessary for effector-target cell binding of CD56.sup.+CD8.sup.+ T
cells, and perforin/granzyme A mediated cytolytic activity. This
effect was shared by ICAM-3. The mechanisms governing LFA-1
receptor dynamics and intracellular signaling reported here suggest
LFA-1 signaling functionally contributes in
CD56.sup.+CD8.sup.+cytolytic activity in addition to possessing an
adhesive role upon which other molecular interactions occur.
Improper localization of the MTOC has been shown to inhibit
exocytosis of lytic granules in CD8.sup.+ tumor infiltrating T
cells, thereby ablating perforin mediated cytolytic activity
necessary for a CTL response in murine tumor models (Radoja et al.,
2001b). Ironically, defective CD8.sup.+ tumor infiltrating T cells
can effectively mediate cell killing in vitro (Radoja et al.,
2001a), suggesting tumor mediated inhibitory mechanisms exist
within the tumor microenvironment. The production of soluble ICAMs
(1 and 3) has been observed in sera from cancer and autoimmunity
patients, though analysis has not been extended to ICAM-2 (Bloom et
al., 2002). Only one report has indicated that elevated levels of
soluble ICAM-2 were present in leukemia patients and decreased upon
chemotherapy (Mustjoki et al., 2001). The etiology of these
observations is unknown. In the context of the work presented here,
it is plausible to speculate that either dysregulation of surface
ICAM-2 or secretion of soluble ICAM-2 can prematurely trigger or
block CD56.sup.+CD8.sup.+ cytolytic activity at the effector-target
site and permit tumor escape from T cell lysis. Other, specific
roles, of ICAM-2 in its interaction with other integrin ligands
could lead to a better understanding of events that promulgate from
the effector:target cell interface
Materials and Methods
[0799] Immunological and Chemical Reagents
[0800] mAbs to .beta.1, .beta.2, .beta.3, .beta.4, .beta.5,
.beta.6, .alpha.1, .alpha.4, .alpha.5, .alpha..sub.L, LFA-1, Pyk2,
SyK, Mac-1, ICAM-1, and ICAM-3 (PharMingen). CD3, CD4, CD8, CD19,
CD56, CD45 direct conjugates (FITC/PE/PERCP/APC/Biotin),
granzyme-A-FITC (PharMingen). Perforin-CY5 and CD8-CY5PE (gift from
the Herzenberg Laboratory, Stanford University). ICAM-2 mAb and
ICAM-2-FITC (IC2/2 Research Diagnostics). Anti-phospho PYK2(Y402),
anti-phospho-p44/42 (pT185Py187) (Biosource). Anti-phospho
PKC.alpha./.beta.(Thr638), anti-phospho-Syk(Tyr525/526),
anti-phosphoRaf1(Ser259) (Cell Signaling Technologies). Protein and
chemical reagents used: fluorescein isothiocyanate (FITC) (Pierce),
Alexa fluor dye series 488, 546, 568, 633, taxol-alexa546,
phalloidin-alexa633, and CFSE (Molecular Probes). Tyrphostin A9 and
18, SB203580, piceatannol, bisindolylmaleimide I and II, herbimycin
A (Calbiochem). Emodin, genistein, DMSO, PMA, PHA, staurosporine,
ionomycin, propidium iodide, cytochalisin D (Sigma). Protein A/G
agarose (SCBT). Recombinant human IL-2 (Roche), recombinant human
ICAM-1-FC, ICAM2-FC, ICAM3-FC (Genzyme). Secondary antibodies to
mouse and rabbit IgG (Santa Cruz). Mock treatments consisted of
mouse IgG (for antibodies), 1% BSA (for proteins), or 0.001% DMSO
vehicle (for chemicals).
Cell Culture
[0801] NIH3T3 cells were maintained in DMEM, 10% DCS, 1% PSQ
(Duelbecco Modified Eagle Media, 10% Donor calf serum, 1%
penicillin-streptomycin (1000 units/ml and 2 mM L-glutamine PSQ).
Jurkat T-cells were maintained in RPMI-1640, 10% FCS, 1% PSQ at
1.times.10.sup.5 cells/Frit and serum starved 12 hours for all
functional assays. Cells were maintained at 5% CO.sub.2/37.degree.
C. humidified incubator. Human peripheral blood monocytes were
obtained by Ficoll-plaque density centrifugation (Amersham
Pharmacia, Uppsala, Sweden) of whole blood from healthy donors
(Stanford Blood Bank) and depleted for adherent cells. Magnetically
activated cell sorting was used to negatively isolate naive
CD8.sup.+ T cells for studies as indicated (Dynal, Oslo,
Norway).
Soluble ICAM-2 Generation and Synthesis of ICAM-2-FITC and
ICAM2-Beads
[0802] Full length ICAM2 cDNA was obtained from Jurkat cells and
cloned into retroviral vector PBM-Z-IN at the BamHI/Sal1 site as
described (Perez et al., 2002). Human ICAM-2 was overexpressed in
NIH3T3 cells by retroviral infection and harvested by
immunoaffinity chromatography. ICAM-2 was affinity purified using a
two step lysing procedure and subsequent purification on an
anti-ICAM-2 solid support. Cells were lysed in buffer A (20 mM Tris
pH 7.5, 150 mM NaCl 1 mM EDTA 1 mM EGTA, 0.1% NP40, 2.5 mM
Na.sub.2PO.sub.4, 1 mM .beta.-glycerolphosphate, 1 mM
Na.sub.3V0.sub.4, 1 .mu.g/ml Leupeptin, 1 mM PMSF, protease
inhibitor cocktail tablet (Boehringer Mannheim) for 5 min 4.degree.
C., and subsequently permeabilized with 50% v/v with buffer B
(Buffer A plus 1% Triton-X-100) for 30 min 4.degree. C. Supernatant
was harvested by centrifugation (14,000 RPM, 5 min, 4.degree. C.).
An Anti-ICAM-2 pAb to the C-terminal (4 mgs, Santa Cruz) was
conjugated to an Affi-Gel Hz activated support (Biorad) as
suggested by manufacturer. This support couples Ig molecules via
the FC region, resulting in higher antigen binding capacity. Batch
lysate of harvested supernatant was performed (4.degree. C., for 2
hrs), and washed 4 times in buffer C (0.1% Tween-20, PBS pH 7.4).
ICAM-2 protein was eluted by 4.5 M NaCl (in Tris pH 6.8), dialyzed
overnight (in PBS pH 7.4, 0.001% azide, 0.01% glycerol, 4.degree.
C.), concentrated using size exclusion spin chromatography and
stabilized using 0.01% glycerol. Anti-ICAM-2 solid support was
re-equilibrated in buffer C, stored in 0.001% thimerosol and
re-used up to 3 times. Purity was >98% as assessed by coomasie
gel. Size exclusion chromatography removed higher molecular weight
aggregates and were not observed on purified ICAM-2 by native gel
electrophoresis. 20 mgs were purified by this method and used for
this study. ICAM-2-FITC synthesis was achieved by chemical
conjugation to NHS-Fluorescein (Pierce) and unreactive dye was
removed by gel filtration. ICAM-2-FITC probe did not integrate into
trypsinized Jurkat cells or bind when blocked by LFA-1 antibody
clones TS1/22 or TS1/18 (Developmental Hybridoma Studies Bank) or
unlabeled ICAM-2 protein as determined by flow cytometry.
ICAM-2-FITC binding was not blocked by .beta.2 integrin clone CT104
(Santa Cruz). Purified ICAM-2 was comparable to human recombinant
ICAM-2FC fusion protein purified from NSO murine myeloma cells
(Genzyme). ICAM-1FC and ICAM-3FC were also purified from NSO cells
(Genzyme). Proteins were spun at 14,000 RPM, 5 min prior to use. 1
mg of ICAM-2 protein was conjugated to 2.times.10.sup.8 epoxy
activated beads as suggested by manufacturer (Dynal).
4.times.10.sup.5 beads containing a total of 2 .mu.g ICAM-2 protein
were used as indicated. Gel imaging was performed on a VersaDoc
machine (Biorad) and analyzed using Quantity One quantitation
software (Biorad).
Flow Cytometry
[0803] Intracellular and extracellular staining was performed as
described (Perez and Nolan, 2002). Intracellular probes for active
kinases were made by conjugating phospho-specific antibodies to the
Alexa Fluor dye series as described and used in phospho-protein
optimized conditions (Perez and Nolan, 2002). Kinetic analyses was
performed by direct application of fixation buffer in time
synchronized 96-wells maintained at 37.degree. C. Intracellular
actin and microtubule staining was performed using
phalloidin-Alexa633 and taxol-Alexa546 dyes (Molecular Probes).
Adhesion and clustering assays were performed using ICAM-2-FITC as
described in text. LFA-1 activation was assessed by either
mAb24-Alexa633 or mAb24-Alexa546 conjugate, surface stained at
37.degree. C. Flow cytometry data are representative of 3
independent experiments of 10.sup.6 cells/sample. 10-50,000 events
were collected and manually calibrated on a FACSCalibur machine.
Data plotted in bar graph format is expressed as geometric mean
fluorescence intensity (MFI) and normalized for isotype controls.
Log ratios are defined as the MFI of stimulus to the MFI of
unstimulated cells. Data was analyzed using Flowjo software
(Treestar).
Single Cell ICAM-2 Binding Measurements
[0804] Percentage of ICAM-2-FITC binding was expressed as
100*(MFI.sub.exp-MFI.sub.ctl)/(MFI.sub.final-MFI.sub.ctl)), where
MFI.sub.exp equals the mean fluorescent intensity of experimental
concentration, MFI.sub.ctl equals mean fluorescent intensity of
unstained cells, MFI.sub.final equals mean fluorescent intensity of
final concentration that saturated binding. The samples were
incubated with final concentrations as indicted in Figure for 30
min at 37.degree. C. in 50 .mu.L staining media (def RPMI, 4% FCS),
washed 1.times. (500 .mu.L, PBS pH 7.4, containing 1 mM EDTA), and
resuspended in 100 .mu.L (1% paraformaldehyde). Dilution factor of
staining conditions and molecular weight of 72.1 kD was used in
determining molar concentrations. The staining buffer contained 2.4
mM calcium and 2 mM magnesium. The data were fit to the equation
V=V.sub.max[S]/(K.sub.m+[S]) where V is the percent bound, [S] is
the ICAM-2-FITC concentration, and k.sub.m is the Michaelis-Menten
binding constant using Kaleidagraph software.
[0805] Laser Scanning Confocal microscopy
[0806] Jurkat cells were treated as indicated and adhered to
poly-L-lysine (Sigma) coated sterilized coverslips (1 mg/ml, 30
min) by mild centrifugation (1000 RPM, 10 min), washed twice in
phosphate buffered saline pH 7.4 (PBS) and fixed in 2.7%
paraformaldehyde (in PBS). Cells were permeabilized (5 min, 0.1%
Triton-X-100 in PBS), washed twice in PBS, blocked in 4% FCS, and
subjected to antibody or intracellular staining as indicated.
Stained coverslips were mounted and visualized using a Zeiss laser
scanning confocal microscope 510.
Immunoprecipitations, Immunoblotting and Kinase Assays
[0807] Cell extracts were prepared by washing 2.times.10.sup.6
cells (treated as indicated) in ice cold PBS and harvesting in
lysis buffer (20 mM Tris pH 7.5, 150 mM NaCl 1 mM EDTA 1 mM EGTA,
1% Triton X-100, 2.5 mM Na.sub.2PO.sub.4, 1 mM
.beta.-glycerolphosphate, 1 mM Na.sub.3V0.sub.4, 1 .mu.g/ml
Leupeptin, 1 mM PMSF, protease inhibitor cocktail tablet
(Boehringer Mannheim). Extracts were centrifuged 14,000 RPM (5 min,
4.degree. C.) and 10-20 .mu.g (BCA protein assay (Pierce)) were
immunoblotted using standard procedures. Immunoprecipitations (IP)
were pre-cleared with protein AIG plus-agarose beads, incubated
with primary ab (1 h), protein A/G plus-agarose beads (1 h) and
washed 4.times. with lysis buffer. Blots were incubated with the
indicated antibodies and developed using ECL (Amersham).
Immunoblots stripped and reprobed (as indicated) were done by
incubating with stripping buffer (62.5 mM Tris, pH 6.8, 10% SDS, 1%
.beta.-mercaptoethanol) (30 min, 55.degree. C.). MAPK activity was
detected by a p44/42 MAPK kinase kit as suggested by manufacturer
(Cell Signaling Technologies).
Cytolytic Activity, Perforin Release Assays, and Conjugate
Formation Assays
[0808] Target cell lysis was measured by flow cytoemtric based
detection of CFSE labeled HL60 cells. HL60 cells were labeled with
1 .mu.g of CFSE (30 min, 37.degree. C.). Targets were washed twice
and mock treated, IL-2 activated (100 U/ml), CD3/CD28 activated (1
.mu.g/ml), or treated with ICAM2 beads or soluble ICAM-1, -2, or 3
(10 .mu.g/ml, 30 min, 37.degree. C.) before plating at 10.sup.4
target cells/well of a 96-well round bottom plate. CTLs were added
at 50:1, 25:1, and 12.5:1 E:T ratio, and incubated at 37.degree. C.
for 4 hrs. Cells were then processed for multiparameter flow
cytometry and intracellular perforin stain. Percent specific lysis
was calculated by the following equation: % specific
lysis=100-100.times.(experimental HL60 count/total control HL60
count). HL60 counts were detectable by the CFSE fluorescence.
Percent perforin was calculated by the following equation: %
perforin=100.times.[(experimental perforin MFI-isotype mAb
MFI)/(total perforin MFI-isotype mAb MFI)]. MFI refers to mean
fluorescent intensity of flow cytoemtric based intracellular
detection. Cell conjugates were determined by flow cytometry as
described (Morgan et al., 2001). Chemical inhibition was done at 10
.mu.M of indicated compound (30 min, 37.degree. C.) prior to
stimulation as indicated. All experiments were performed in
triplicate.
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Sequence CWU 1
1
517PRTArtificialSynthetic 1Ser Lys Val Ile Leu Phe Glu1
5218DNAArtificialSynthetic 2gatcctccct ttatccag
18320DNAArtificialSynthetic 3gaatgaaaga ccccacctgt
20426PRTArtificialSynthetic 4Gln His Leu Arg Gln Gln Arg Met Gly
Thr Tyr Gly Val Arg Ala Ala1 5 10 15Trp Arg Arg Leu Pro Gln Ala Phe
Arg Pro 20 25526PRTArtificialSynthetic 5Gln His Leu Arg Gln Gln Arg
Met Gly Thr Tyr Gly Arg Ala Val Arg1 5 10 15Ala Leu Trp Arg Pro Gln
Ala Phe Arg Pro 20 25
* * * * *
References