U.S. patent application number 13/276918 was filed with the patent office on 2012-04-12 for cripto antagonism of activin and tgf-b signaling.
This patent application is currently assigned to RESEARCH DEVELOPMENT FOUNDATION. Invention is credited to Peter C. Gray, Craig A. Harrison, Wylie Vale.
Application Number | 20120088287 13/276918 |
Document ID | / |
Family ID | 34375305 |
Filed Date | 2012-04-12 |
United States Patent
Application |
20120088287 |
Kind Code |
A1 |
Vale; Wylie ; et
al. |
April 12, 2012 |
CRIPTO ANTAGONISM OF ACTIVIN AND TGF-B SIGNALING
Abstract
Cripto, a developmental oncoprotein, antagonizes activin and
TGF-b signaling by forming a complex with activin and TGF-b and
their type II receptors. This complex precludes the formation of a
functional activin/TGF-b.cndot.type II.cndot.type I complex,
thereby blocking the signaling of activin and TGF-b. Cripto may be
generally capable of blocking antiproliferative Smad2/3 signals and
provides a novel mechanism of oncogenic action with multiple
therapeutic implications. Inhibiting the formation of Cripto and
activin/TGF-b complex may enhance antiproliferative effects of
activin and TGF-b.
Inventors: |
Vale; Wylie; (La Jolla,
CA) ; Harrison; Craig A.; (Nunswading, AU) ;
Gray; Peter C.; (San Diego, CA) |
Assignee: |
RESEARCH DEVELOPMENT
FOUNDATION
Carson City
NV
|
Family ID: |
34375305 |
Appl. No.: |
13/276918 |
Filed: |
October 19, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12887272 |
Sep 21, 2010 |
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13276918 |
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10940431 |
Sep 14, 2004 |
7820620 |
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12887272 |
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60503046 |
Sep 15, 2003 |
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Current U.S.
Class: |
435/194 ;
435/375 |
Current CPC
Class: |
C07K 14/475 20130101;
A61P 15/16 20180101; C07K 14/82 20130101; A61P 17/02 20180101; A61P
43/00 20180101; C07K 14/71 20130101; A61P 35/00 20180101; C07K
14/47 20130101; A61P 5/00 20180101; A61P 37/02 20180101; C07K 16/22
20130101 |
Class at
Publication: |
435/194 ;
435/375 |
International
Class: |
C12N 5/09 20100101
C12N005/09; C12N 5/071 20100101 C12N005/071; C12N 9/12 20060101
C12N009/12 |
Claims
1.-27. (canceled)
28. A soluble extracellular domain (ECD) of Activin receptor-Like
Kinase 4 (ALK4).
29. The soluble ALK4-ECD of claim 28, wherein the ALK-4 ECD is
human ALK4-ECD.
30. The soluble ALK4-ECD of claim 28, wherein the ALK4-ECD
comprises a mutation at one or more positions selected from the
group consisting of amino acid position 70, 75 and 77.
31. The soluble ALK4-ECD of claim 30, wherein the ALK4-ECD
comprises an alanine at one or more positions selected from the
group consisting of amino acid position 70, 75 and 77.
32. The soluble ALK4-ECD of claim 30, wherein the ALK4-ECD
comprises a mutation at amino acid position 75.
33. The soluble ALK4-ECD of claim 32, wherein the mutation
comprises an alanine at amino acid position 75.
34. The soluble ALK4-ECD of claim 30, wherein the ALK4-ECD
comprises mutations at amino acid positions 70, 75, and 77.
35. A method of decreasing cell proliferation comprising contacting
the cell with an effective amount of a soluble ALK4-ECD of claim
28, wherein proliferation of the cell is decreased.
36. The method of claim 35, wherein the cell is derived from an
organ selected from the group consisting of breast, colon, stomach,
pancreas, lung, ovary, endometrial, testis, bladder and
prostate.
37. The method of claim 36, wherein the cell is a tumor cell or a
cancer cell.
38. The method of claim 37, wherein the tumor cell or cancer cell
is a breast tumor cell or breast cancer cell.
39. The method of claim 38, wherein the breast tumor cell or breast
cancer cell is contacted with a soluble ALK4-ECD comprising an
alanine at amino acid position 75.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This non-provisional patent application claims benefit of
provisional patent application U.S. Ser. No. 60/503,046, filed Sep.
15, 2003, now abandoned.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to signaling of
TGF-b superfamily. More specifically, the present invention relates
to antagonism of signaling of TGF-b superfamily ligands.
[0004] 2. Description of the Related Art
[0005] The transforming growth factor b (TGF-b) superfamily
comprise over 30 secreted ligands in human that control cell
growth, homeostasis, differentiation, tissue development, immune
responses, angiogenesis, wound repair, endocrine function and many
other physiologic processes. Members of this superfamily include
TGF-b, activins, bone morphogenetic protein (BMP), Growth and
Differentiation Factor (GDF) and nodal-related families. Disruption
or dysregulation of activin and TGF-b signaling is associated with
multiple pathological states including carcinogenesis.
[0006] TGF-b superfamily members share a distinct structural
framework known as the cystine knot scaffold. Activin and TGF-b are
each disulfide-linked dimmers. Activin consists of two b chains.
Although there are several activin b subunit genes and an extensive
array of possible b-b dimers, only bA-bA (activin-A), bA-bB
(activin-AB) and bB-bB (activin-B) have been isolated as dimeric
proteins and shown to be biologically active. Three TGF-b genes
exist in mammals giving rise to the TGF-b.sub.1, TGF-b.sub.2 and
TGF-b.sub.3 isoforms.
Activin And TGF-b Signaling Via Receptor Serine Kinases
[0007] TGF-bs, activins and other members of the TGF-b superfamily
exert their biological effects by interacting with two types of
transmembrane receptors (type I and type II) with intrinsic
serine/threonine kinase activities, called receptor serine kinases
(RSKs). Type I receptor serine kinases are referred to as ALK1 to
7, for Activin receptor-Like Kinases. The receptor activation
mechanism was first established for TGF-b which was shown to bind
its type II receptor (TbRII) leading to the recruitment,
phosphorylation and activation of its type I receptor (ALK5). A
similar mechanism of ligand-mediated receptor assembly and type I
receptor phosphorylation has been demonstrated for activin
receptors involving initial binding of activin to ActRII or ActRIIB
followed by recruitment, phosphorylation and activation of the type
I receptor ALK4.
[0008] The ligand binding properties of the receptor extracellular
domains (ECDs) have been extensively examined. The crystal
structure of the ActRII-ECD provided detailed information regarding
sites predicted to be involved in receptor:ligand interactions. The
crystal structure of the ActRII-ECD bound to BMP-7 has recently
been solved and it was shown that the amino acids on ActRII
required for activin-A binding make up interfacial contacts between
ActRII and BMP-7 and are required for BMP-7 binding. An allosteric
conformational change was observed in BMP-7 in its predicted type I
receptor binding site following binding to ActRII. This suggested a
general model for cooperative type I/type II receptor assembly
induced by BMPs (or activin) to form a hexameric complex containing
the dimeric ligand, two type II receptors and two type I
receptors.
[0009] The structure of activin-A bound to the ActRIIB-ECD was also
solved recently and was generally consistent with previous findings
regarding the activin-A binding site on the ActRIIA receptor. Using
the crystal structure of BMP2 bound to the BMP type I receptor
(ALK3-ECD) as a guide, an activin-A binding surface on the type I
receptor ALK4-ECD was recently identified.
[0010] The structure of TGF-b.sub.3 bound to the TbRII-ECD has also
been solved and indicated unexpectedly that the TGF-b binding
interface with its type II receptor is very different from the
corresponding interface of activin and BMP7 with ActRII. This
suggests that although activin and TGF-b have a similar mechanism
of receptor activation, they apparently have unrelated ligand-type
II receptor interfaces.
[0011] Regardless of the precise mechanism of receptor assembly by
TGF-b superfamily ligands, it has been generally established that
following receptor assembly, type II receptors phosphorylate type I
receptors within a juxtamembrane cytoplasmic glycine- and
serine-rich region called the GS domain and this phosphorylation
event activates the type I receptor kinase to initiate downstream
signaling.
Regulation of Activin And TGF-b Receptor Access
[0012] Activins are secreted in their processed, biologically
active form. However, the ability of activins to access and
assemble signaling receptors can be inhibited in several distinct
ways. Inhibins (a-b) share a b subunit with activins and are TGF-b
superfamily members that act in conjunction with the membrane
proteoglycan betaglycan to form high affinity complexes with
activin type II receptors, thereby preventing these receptors from
binding activin and initiating signaling. The soluble,
extracellular activin binding follistatins bind activins with
high-affinity and also block the ability of activin to bind its
cell-surface receptors and initiate signaling. In addition, the
pseudo (decoy) type I receptor BAMBI (BMP and Activin
Membrane-Bound Inhibitor) can bind BMP or activin in non-functional
complexes with activin and BMP receptors to block signaling.
[0013] Unlike activin, TGF-b isoforms are not secreted in an active
form but rather are secreted as inactive "latent" complexes. These
complexes comprise the inactive TGF-b dimer in non-covalent
complexes with two prosegments to which one of several "latent
TGF-b binding proteins" is often linked. Latent TGF-b complexes and
their binding proteins associate with the extracellular matrix and
await one of several possible activating stimuli to provide a
rapidly available pool of releasable TGF-b that can respond to
highly localized signals.
Smad Signaling
[0014] Based upon genetic studies in Drosophila and Caenorhabditis
elegans, a group of proteins now called Smads have been found to
transduce signals from receptor serine kinases and mediate
regulation of target gene transcription by activin, TGF-b and other
TGF-b superfamily members. Structural and functional considerations
allow subdivision of Smads into three subfamilies:
pathway-specific, common mediator, and inhibitory Smads.
[0015] Ligand/receptor assembly and activin receptor-like kinase
(ALK) phosphorylation triggers a transient ALK/pathway-specific
Smad association during which the ALK phosphorylates the Smad on
its last two serine residues in the C terminal SSXS motif. Activin
and TGF-b signals are mediated by the pathway-specific Smads, Smad2
and Smad3 and these Smads are sequestered near their signaling
receptors by Smad Anchor for Receptor Activation (SARA), a
cytoplasmic membrane-associated protein that has been shown to
facilitate Smad2/3 signaling.
[0016] Once activated, Smad2 and Smad3 form hetero-oligomeric
complexes with the common mediator Smad, Smad4, that was first
discovered in humans as the pancreatic tumor suppressor gene, DPC4.
Smad2/3/4 complexes translocate to the nucleus and interact
directly with DNA and/or with cell-type specific co-activator or
co-repressor proteins leading to the activation or repression of
target genes.
[0017] Two vertebrate inhibitory Smads have been identified, Smad6
and 7, which lack the C-terminal SSXS motif found in the pathway
specific Smads. Smad6 and 7 are inhibitors of Smad signaling and
bind to activin receptor-like kinases (ALKs) to prevent
phosphorylation and activation of the pathway-specific Smads. In
transfected cells, Smad7 inhibits transcriptional responses induced
by activin or TFG-b or by a constitutively active ALK4. Smad7 may
therefore provide an intracellular feedback signal to restrain the
effects of activin and TFG-b.
Smad2/3 Signaling and Growth Control
[0018] TGF-b and activin are both well known for their ability to
inhibit proliferation of multiple cell types including most
epithelial cells, and gene expression profiling has indicated
essential similarity of transcriptional responses to constitutively
active activin or TGF-b type I receptors in cancer cells.
Activation of the Smad2/3 signaling pathway leads to inhibition of
cell cycle progression during G1 and in some cases terminal
differentiation, or apoptosis. The growth inhibitory response to
Smad2/3 signals has been divided into two major classes: gene
responses that lead to inhibition of cyclin-dependent kinases
(cdks) and down regulation of c-myc.
[0019] The retinoblastoma tumor suppressor protein (pRb) and its
family members p107 and p130 control cell cycle progression and
have activity that is regulated by cdk phosphorylation. TGF-b
signals have been shown to induce cdk inhibitors including
p15.sup.INK4B (p15) and p21.sup.CIP1/WAF1 (p21) and to down
regulate the tyrosine phosphatase cdc25A. p15 binds and inactivates
cdk4 and cdk6 causing displacement of p27 from cyclin D-cdk4/6,
allowing it to bind and inhibit cyclin E-cdk2. p21 also binds and
inhibits cyclin E-cdk2. cdc25A is an activator of cyclin D-cdk4 and
its down regulation therefore reduces the activity of this cdk.
Overall, decreased cdk activity in response to Smad2/3 signaling
reduces pRb phosphorylation by these cdks, allowing pRb to prevent
E2F function and block cell cycle progression.
[0020] Unlike cdk inhibition, which exhibits cell type dependent
diversity, down regulation of c-Myc, a member of the basic
helix-loop-helix leucine zipper (bHLH-LZ) family of transcription
factors, is observed in most cell types that are growth inhibited
by Smad2/3 signals. In addition, down regulation of c-Myc by Smad
signals is required for the inactivation of cdks, and evidence also
implicates c-Myc as a positive regulator of cdc25A expression. It
was recently shown that E2F4/5 proteins and the Rb protein p107
form a pre-formed complex with Smad3 in the cytoplasm that awaits
TGF-b receptor activation, Smad3 phosphorylation and Smad4 assembly
leading to translocation of the complex to the nucleus to bind the
c-myc promoter and repression of the c-myc gene.
[0021] The Id family of transcriptional regulators inhibit terminal
differentiation, promote cell proliferation and have been
implicated in cancer. Myc and Id proteins can form complexes that
cooperate to override the tumor suppressor function of pRb.
Interestingly, it was recently shown that TGF-b causes repression
of Id gene expression via preassembled, cytoplasmic Smad3-ATF3
complexes that translocate to the nucleus with Smad4 and target Id
promoters following TGF-b receptor activation. It was also recently
demonstrated that key cellular responses to TGF-b signals,
including induction of the cdk inhibitor p21, rely on direct
interactions between Smad2 and the tumor suppressor and
transcriptional regulator p53. In summary, these results indicate
that Smad2 and Smad3 likely play essential but distinct roles in
regulating cell proliferation.
Smad2/3 Pathway And Cancer
[0022] It is not surprising that disruptions or alterations in the
activin and TGF-b signaling pathways have been observed in several
types of human cancer. Inactivating mutations in TbRII have been
observed in colorectal and gastric carcinomas and inactivation of
ActRII was recently observed in gastrointestinal cancers. An
inactivating mutation in TbRI (ALK5) occurs in one third of ovarian
cancers observed and ALK4 mutations have been described in
pancreatic cancer leading to the designation of ALK4 as a tumor
suppressor gene.
[0023] The activin/TGF-b signaling pathway is also disrupted by
mutations in Smad4 and Smad2. As mentioned above, Smad4 was
originally identified as DPC4 (deleted in pancreatic carcinoma
locus 4) and this gene is functionally absent in half of all
pancreatic cancers and one third of colon carcinomas. Smad2 is also
inactivated in a small proportion of colorectal cancers and lung
cancers. Although Smad3 mutations have not yet been observed in
human cancers, Smad3.sup.-/- mice developed colorectal cancer.
[0024] Interestingly, despite its antiproliferative effects,
Smad2/3 signaling can also exacerbate the cancer phenotype under
conditions in which cells have become refractory to Smad2/3-induced
growth inhibition. For example, increased production of TGF-b or
activin by tumor cells that are no longer growth inhibited by
Smad2/3 signals may lead to increased angiogenesis, decreased
immune surveillance and/or an increase in the epithelial to
mesenchymal transition (EMT) of tumor cells. Collectively, these
effects can lead to increased tumor growth and metastasis.
Epidermal Growth Factor-Cripto, FRL-1, Cryptic (EGF-CFC) Protein
Family
[0025] Similar to activin, members of the nodal family and
GDF-1/Vg1 have been shown to signal via the activin receptors
ActRII/IIB and ALK4. Unlike activin, however, these TGF-b
superfamily members require additional co-receptors from the
Epidermal Growth Factor-Cripto, FRL-1, Cryptic (EGF-CFC) protein
family to assemble type II and type I receptors and generate
signals.
[0026] The EGF-CFC family consists of small, glycosylated,
extracellular signaling proteins including human and mouse Cripto
and Cryptic, Xenopus FRL-1 and zebrafish one-eyed pinhead (oep).
EGF-CFC proteins are known to act as anchored cell surface
co-receptors but they also have activity when expressed as soluble
proteins or when they are secreted from the cell surface following
enzymatic cleavage of their GPI anchor. Genetic studies in
zebrafish and mice have shown that EGF-CFC proteins are required
for mesoderm and endoderm formation, cardiogenesis, and the
establishment of left/right asymmetry during embryonic development.
Cripto knockout mouse embryos lack a primitive streak and fail to
form embryonic mesoderm. This phenotype is very similar to that
observed in ActRIIA.sup.-/-; ActRIIB.sup.-/- mice, ALK4.sup.-/-
mice and Nodal.sup.-/- mice, consistent with a requirement for
nodal signaling via activin receptors and a role for Cripto to
initiate primitive streak elongation and mesoderm formation.
[0027] It has been shown that Cripto independently binds nodal via
its EGF-like domain and ALK4 via its CFC domain. Furthermore,
selected point mutations in Cripto that block nodal binding or ALK4
binding disrupt nodal signaling. Substantial biochemical evidence
indicates that nodal and Vg1/GDF1 form a complex with activin
receptors only in the presence of EGF-CFC proteins.
Cripto Is A Tumor Growth Factor
[0028] Cripto is an EGF-CFC protein that was first isolated as a
putative oncogene from a human teratocarcinoma cell line and it was
subsequently shown to be able to confer anchorage independent
growth to NOG-8 mouse mammary epithelial cells. Cripto is expressed
at high levels in human breast, colon, stomach, pancreas, lung,
ovary, endometrial, testis, bladder and prostate tumors while being
absent or expressed at low levels in their normal counterparts. The
elucidation of the signals and transcriptional events underlying
the high level of Cripto expression in these tumors remains an
important area of future research.
[0029] With regard to Cripto's mechanism(s) of mitogenic action, it
has been shown that recombinant, soluble Cripto and a synthetic 47
amino acid Cripto fragment spanning the EGF-like domain can
activate both the mitogen activated protein kinase (MAPK) pathway
and the phosphatidylinositol-3-kinase (PI3K) pathway. Treatment of
HC-11 mammary epithelial cells with soluble Cripto or the 47-mer
peptide resulted in tyrosine phosphorylation of the SH2-adaptor
protein Shc, association of Shc with Grb2 and activation of the
p42/44 Erk/MAPK pathway. It was also shown that soluble Cripto
caused phosphorylation of the p85 regulatory subunit of PI3K
leading to phosphorylation and activation of AKT in SiHa cervical
carcinoma cells. Cripto does not bind to members of the EGF
receptor family, although [.sup.125I]-Cripto specifically labeled
breast cancer cell lines and formed crosslinked complexes with 60
kDa and 130 kDa membrane proteins. Although these proteins were not
identified, the 60 kDa protein may have been ALK4.
[0030] It was recently shown that the cytoplasmic tyrosine kinase
c-Src can be activated by soluble Cripto and that its activity is
required for activation of the MAPK/PI3K pathways by Cripto. The
GPI-anchored proteoglycan glypican was also reported to be
important in facilitating these Cripto signals and glypican was
also shown to bind Cripto in a manner dependent on glycanation of
glypican. The ability of Cripto to activate the MAPK and PI3K
pathways, which are frequently growth-stimulatory in nature, has
generally been proposed to explain Cripto's oncogenic effects.
Smad Signaling, Cripto And Cancer
[0031] The first demonstration of a physiologic role for TGF-b was
its potent and reversible inhibition of developing mouse mammary
gland in situ. TGF-b is now well established as an important
inhibitor of mammary ductal growth and branching in vivo and over
90% of mammary carcinomas are ductal in nature. Loss of TbRII has
been associated with increased risk of invasive breast cancer in
women. Consistent with a role in regulating mammary ductal growth,
TGF-b.sub.1 heterozygous null mice display accelerated mammary
epithelial proliferation and ductal outgrowth. Furthermore,
transgenic expression of a dominant negative TbRII construct in
mammary gland diminishes responsiveness to TGF-b and caused
increased incidence of tumors in response to carcinogen relative to
control mice. Conversely, transgenic overexpression of TGF-b.sub.1
in mammary gland protects against chemical-induced tumors. These
results provide direct evidence that TGF-b signaling can actively
prevent tumorigenesis in mouse mammary gland. There is also
evidence that activin inhibits proliferation of both primary and
transformed mammary epithelial cells. Together, these results
indicate the importance of the Smad2/3 pathway in inhibiting
mammary epithelial cell proliferation and tumorigenesis.
[0032] Cripto is overexpressed in many types of human tumors,
including .about.80% of breast carcinomas, while its expression is
low or absent in their normal counterparts. In contrast to TGF-b,
Cripto promotes growth in mammary cells and Cripto overexpression
transforms mouse NOG-8 and CID-9 mammary epithelial cells. Cripto
overexpression in these cell lines enabled them to grow in soft
agar and each displayed an enhanced proliferation rate in monolayer
culture. These cells were, however, unable to form tumors in nude
mice.
[0033] It was also shown that targeted disruption of endogenous
Cripto in CID-9 cells via a retroviral antisense construct led to a
decreased rate of cellular proliferation. Both the soluble Cripto
protein and the 47 amino acid EGF-like domain Cripto peptide have
also been shown to facilitate ductal branching and cause mammary
ductal hyperplasia. As discussed above, these effects have been
explained as the result of the ability of Cripto to activate
mitogenic signaling pathways including the MAPK and PI3K pathways.
However, many of the growth-related effects of Cripto are also
generally consistent with antagonism of the Smad2/3 pathway.
[0034] The prior art is lacking in evidence on whether Cripto can
play a dual role as an oncogene, not only acts by activating
mitogenic MAPK/PI3K pathways, but also antagonizes the
antiproliferative Smad2/3 pathway. The present invention thus
studies the oncogenic mechanism of Cripto protein in order to gain
insight into its effects on activin/TGF-b signaling.
SUMMARY OF THE INVENTION
[0035] TGF-b and activin regulate tissue homeostasis by activating
the Smad2/3 intracellular signaling pathway leading to potent
inhibition of proliferation of multiple cell types including
epithelial cells. Disruption of this signaling pathway is
associated with oncogenesis and tumorigenesis. Cripto is a
developmental oncoprotein that is highly expressed in human tumors
but not their normal tissue counterparts. Overexpression of Cripto
transforms mammary epithelial cells in vitro. The present invention
shows that Cripto can antagonize activin and TGF-b signaling. These
results suggest that Cripto may be generally capable of blocking
antiproliferative Smad2/3 signals and provides a novel mechanism of
oncogenic action with multiple therapeutic implications.
[0036] Based on the data presented below, a model for the mechanism
of Cripto regulation of activin and TGF-b signaling is proposed
(FIG. 13). In the absence of Cripto, activin and TGF-b signal by
binding their respective type II receptors and then recruiting
their type I receptors (ALK4 and ALK5). Activin and TGF-b type II
receptors phosphorylate the GS domain of ALK4 and ALK5, thereby
activating the type I kinase and initiating downstream signaling.
Cripto antagonizes activin and TGF-b signaling by forming a complex
with activin and TGF-b and their type II receptors. This complex
precludes the formation of a functional activin/TGF-b.cndot.type
II.cndot.type I complex and therefore blocks signaling.
[0037] In one embodiment of the present invention, there is
provided a method of augmenting signaling of a ligand of receptor
serine kinase in a cell. The method involves inhibiting the
formation of complexes between Cripto and a ligand of receptor
serine kinase on the surface of a cell.
[0038] In another embodiment, there is provided a method of using a
mutant of a ligand of receptor serine kinase to augment Smad2/3
signaling in a cell.
[0039] The present invention also provides a method of using a
Cripto mutant that lacks the EGF domain to selectively antagonize
activin-B signaling.
[0040] In another embodiment, there is provided a method of
inhibiting signaling of a ligand of receptor serine kinase in a
cell. The method involves enhancing the formation of complexes
between Cripto and a ligand of receptor serine kinase on the
surface of a cell.
[0041] Other and further aspects, features, and advantages of the
present invention will be apparent from the following description
of the presently preferred embodiments of the invention. These
embodiments are given for the purpose of disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0042] FIG. 1 shows a model indicating the proposed dual oncogenic
mechanisms of Cripto. Cripto activates mitogenic MAPK and PI3K
pathways by binding an as-yet uncharacterized transmembrane
receptor leading to activation of c-Src. It is proposed that Cripto
also blocks Smad2/3 signaling by competitively antagonizing
functional recruitment of type I activin and TGF-b receptors to
ligand.cndot.type II receptor complexes.
[0043] FIG. 2 shows Cripto binds activin in the presence of ActRII
and competes with ALK4 for activin.cndot.ActRII binding. 293T cells
were transfected with the indicated constructs and subjected to
crosslinking with [.sup.125I]-activin-A as previously described
(Gray et al., 2003). The cells were solubilized and crosslinked
complexes were isolated by immunoprecipitation using the indicated
antibodies. Immunoprecipitated proteins were resolved by SDS-PAGE
and visualized by autoradiography as previously described (Gray et
al., 2003).
[0044] FIG. 3 shows Cripto binds TGF-b.sub.1 in the presence of
TbRII and competes with ALK5 for TGF-b.sub.1.cndot.TbRII binding.
293T cells were transfected with the indicated constructs and
subjected to crosslinking with [.sup.1251]-TGF-b.sub.1 as
previously described (Gray et al., 2003). The cells were
solubilized and crosslinked complexes were isolated by
immunoprecipitation using the indicated antibodies.
Immunoprecipitated proteins were resolved by SDS-PAGE and
visualized by autoradiography as previously described (Gray et al.,
2003).
[0045] FIG. 4 shows Cripto blocks activin-A and TGF-b.sub.1
signaling in HepG2 cells. HepG2 cells were transfected with either
empty vector or Cripto as previously described (Gray et al., 2003)
and then treated with the indicated doses of either activin-A (FIG.
4A) or TGF-b.sub.1 (FIG. 4B). Luciferase activities were normalized
relative to b-galactosidase activities and data were presented as
fold increases in luciferase activity relative to untreated
cells.
[0046] FIGS. 5A-B show expression of Cripto mutants at the cell
surface of 293T cells. FIG. 5A is a diagram of mouse Cripto
indicating the positions of the signal peptide, N-terminal FLAG
epitope, EGF-like domain, CFC domain and the C-terminal site of
GPI-anchor attachment. In addition, the site of fucosylation
(threonine 72) and the positions of the tryptophan residues that
are substituted with glycine residues in the mCFC mutant (W104G,
W107G) are indicated. (B) Empty vector or the indicated Cripto
constructs were transfected in triplicate into 293T cells and the
resulting cell surface expression of these constructs in intact
cells was measured using anti-FLAG antibody in an ELISA-based assay
(FIG. 5B).
[0047] FIG. 6 shows the EGF-like domain of Cripto mediates
antagonism of TGF-b signaling. 293T cells were transfected in
triplicate with vector or the indicated Cripto constructs and
A3-luciferase/FAST-2/CMV-b-galactosidase. Cells were treated with
vehicle or with 100 pM TGF-b.sub.1 and resulting luciferase
activities were normalized relative to b-gal activities. Data were
presented as fold increase in luciferase activities in TGF-b.sub.1
treated cells relative to vehicle treated cells.
[0048] FIG. 7 shows the EGF-like domain of Cripto is required for
antagonism of activin-A and TGF-b.sub.1 signaling in 293T cells.
293T cells were transfected with the indicated constructs and then
treated with vehicle or 1 nM activin-A or 0.3 nM TGF-b.sub.1.
Luciferase activities were normalized to b-galactosidase activities
and data were presented as fold increase in luciferase activities
relative to untreated cells
[0049] FIGS. 8A-B show the CFC domain of Cripto is not required for
binding to TGF-b. 293T cells were transfected with the indicated
constructs and subjected to crosslinking with
[.sup.125I]-TGF-b.sub.1. Solubilized, crosslinked complexes were
isolated by immunoprecipitation using anti-His antibody targeting
TbRII (FIG. 8A) or anti-FLAG antibody targeting Cripto (FIG. 8B).
Immunoprecipitated proteins were resolved by SDS-PAGE and
visualized by autoradiography.
[0050] FIGS. 9A-C show Cripto T72A mutation disrupted the ability
to block TGF-b and activin signaling. 293T cells were transfected
in triplicate with vector, Cripto or Cripto mutant (T72A) and
A3-luciferase/FAST-2/CMV-b-galactosidase. Cells were treated with
vehicle or with 100 pM TGF-b.sub.1 (FIG. 9A), 300 pM activin-A
(FIG. 9B) or 300 pM activin-B (FIG. 9C) and resulting luciferase
activities were normalized and presented as fold increase relative
to b-galactosidase activities in vehicle-treated cells.
[0051] FIG. 10 shows the EGF-like and CFC domains of Cripto can
independently mediate antagonism of activin-B signaling 293T cells
were transfected in triplicate with vector, Cripto DEGF or Cripto
DCFC in addition to A3-luciferase/FAST-2/CMV-b-galactosidase. Cells
were treated with vehicle or with either 300 pM activin-A or 300 pM
activin-B as indicated, and resulting luciferase activities were
normalized and presented as the fold-increase relative to
b-galactosidase activities in vehicle-treated cells.
[0052] FIGS. 11A-B show Cripto DCFC mutant binds activin-A. 293T
cells were transfected with the indicated constructs and subjected
to crosslinking with [125I]-activin-A. Solubilized, crosslinked
complexes were isolated by immunoprecipitation using anti-myc
antibody targeting ActRII (FIG. 11A) or anti-FLAG antibody
targeting Cripto (FIG. 11B). Immunoprecipitated proteins were
resolved by SDS-PAGE and visualized by autoradiography.
[0053] FIG. 12 shows Cripto antagonizes activin/TGF-b but
facilitates nodal signaling in 293T cells. 293T cells were
transfected with either empty vector or nodal and the indicated
amount of Cripto DNA as previously described (Gray et al., 2003)
and then treated as indicated with 1 nM activin-A or 0.3 nM
TGF-b.sub.1. Luciferase values were normalized to b-galactosidase
activities and data were presented as fold increase in luciferase
activities relative to untreated cells.
[0054] FIGS. 13A-B depict proposed mechanisms of Cripto regulation
of TGF-b ligand signaling. The model illustrates the ability of
Cripto to either facilitate (FIG. 13A) or inhibit (FIG. 13B)
signaling of TGF-b superfamily members. Cripto and related
Epidermal Growth Factor-Cripto, FRL-1, Cryptic (EGF-CFC) protein
family proteins bind directly to nodal or Vg1/GDF1, allowing these
ligands to assemble type II and type I signaling receptors and
initiating responses including mesoderm induction (FIG. 13A).
Conversely, by binding TGF-b and activin while these ligands are in
complex with their respective type II receptors, Cripto disrupts
functional recruitment of type I receptors and inhibits signaling
responses such as growth inhibition (FIG. 13B).
[0055] FIG. 14 depict diagrams of Cripto and Cripto mutant
constructs. The domain structure of wild type mouse Cripto is
indicated showing attachment to membrane via C-terminal GPI
anchorage. Position of incorporated epitope tags and sites of
deletions and selected mutations are indicated.
[0056] FIG. 15 shows alignment of Epidermal Growth Factor-Cripto,
FRL-1, Cryptic (EGF-CFC) proteins. Mouse Cripto was aligned with
other members of the EGF-CFC family including human Cripto, mouse
Cryptic, human Cryptic, Xenopus FRL-1 and zebrafish one-eyed
pinhead (oep) using the CLUSTAL algorithm of the MEGALIGN program
(DNASTAR). The EGF-like domain is boxed and shaded red, the CFC
domain is boxed and shaded blue, and conserved cysteines within
these domains are shaded yellow. Disulfide arrangement of the
EGF-like domain is indicated. The signal peptide of mouse Cripto is
indicated with red lettering, the hydrophobic C-terminal domain is
indicated with purple lettering and the fucosylated threonine is
shaded white. Conserved residues targeted for mutagenesis are
indicated by asterisks and the EGF1, EGF2 and mCFC mutations are
indicated by red asterisks.
DETAILED DESCRIPTION OF THE INVENTION
[0057] The present invention provides methods of augmenting
signaling induced by a ligand of receptor serine kinase in a cell
by inhibiting the formation of complexes between Cripto and the
receptor serine kinase ligand on the surface of the cell. Ligands
of receptor serine kinase include, but are not limited to, activin
and TGF-b, whereas examples of receptor serine kinase include type
I activin receptor-like kinases-4 (ALK-4) or activin receptor-like
kinases-5 (ALK-5). In general, the cells are derived from breast,
colon, stomach, pancreas, lung, ovary, endometrial, testis, bladder
or prostate. Augmentation of signaling mediated by receptor serine
kinase would increase phosphorylation and activation of Smad2 and
Smad3, resulting in decreased cellular proliferation.
[0058] In one embodiment, formation of complexes between Cripto and
ligand of receptor serine kinase is inhibited by an anti-Cripto
antibody directed against an epitope of Cripto. For example, the
anti-Cripto antibody is directed against an epitope in the EGF-like
domain of Cripto. Alternatively, formation of complexes between
Cripto and receptor serine kinase ligand can be inhibited by a
soluble receptor serine kinase extracellular domain that binds
Cripto but not ligand of receptor serine kinase. In one embodiment,
the soluble extracellular domain is an activin receptor-like
kinases-4 (ALK-4) extracellular domain. Preferably, the ALK-4
extracellular domain comprises a mutation at one or more positions
such as amino acid position 70, 75 and/or 77. For example, the
ALK-4 extracellular domain comprises an alanine at amino acid
position 70, 75 and/or 77.
[0059] In another embodiment, formation of complexes between Cripto
and ligand of receptor serine kinase is inhibited by inhibiting the
expression of Cripto in the cell. Cripto expression can be
inhibited by antisense transcript of Cripto, small inhibitory RNA
(siRNA) directed against Cripto or by mutating at least one allele
of Cripto by homologous recombination.
[0060] In yet another embodiment, there is provided a method of
using a mutant of a ligand of receptor serine kinase to augment
Smad2/3 signaling in a cell. The mutant ligand retains signaling
activity but is unable to bind to Cripto, thereby bypassing
antagonism by Cripto. In general, ligands of receptor serine kinase
include, but are not limited to, activin and TGF-b.
[0061] The present invention also provides a method of using a
Cripto mutant that lacks the EGF domain to selectively antagonize
activin-B signaling. In general, the Cripto mutant can be soluble
or cell surface-bound. Results disclosed herein show that the
EGF-like domain of Cripto is required to antagonize activin-A,
activin-B and TGF-b while the CFC domain is sufficient to block
activin-B but not activin-A or TGF-b. Therefore Cripto mutant that
lacks the EGF domain will be a useful research tool to distinguish
the relative importance of activin-A as opposed to activin-B
signaling in various biological contexts. For example, it has also
been previously demonstrated that release of FSH from rat anterior
pituitary gonadotropes is mediated by activin-B. Therefore, a
Cripto mutant such as DEGF is predicted to block FSH release
without affecting activin-A or TGF-b signaling. By blocking FSH
release, spermatogenesis will be disrupted potentially causing
reversible infertility. Therefore, cell attached or soluble Cripto
constructs in which the EGF-like domain has been deleted may have
utility as male contraceptives.
[0062] The present invention further provides a method of
inhibiting signaling induced by a ligand of receptor serine kinase
in a cell by enhancing the formation of complexes between Cripto
and the receptor serine kinase ligand on the surface of the cell.
Ligands of receptor serine kinase include, but are not limited to,
activin and TGF-b, whereas examples of receptor serine kinase
include type I activin receptor-like kinases-4 (ALK-4) or activin
receptor-like kinases-5 (ALK-5). In general, the cells are derived
from breast, colon, stomach, pancreas, lung, ovary, endometrial,
testis, bladder or prostate. In one embodiment, formation of
complexes between Cripto and ligand of receptor serine kinase is
enhanced by increasing the expression of Cripto in the cell. For
example, Cripto expression can be increased by administering to the
cell viral or plasmid vectors that encodes Cripto protein.
Alternatively, formation of complexes between Cripto and receptor
serine kinase ligand can be enhanced by administering soluble
Cripto or cell surface-bound Cripto to the cell.
[0063] The following examples are given for the purpose of
illustrating various embodiments of the invention and are not meant
to limit the present invention in any fashion. The present
examples, along with the methods, procedures, treatments,
molecules, and specific compounds described herein are presently
representative of preferred embodiments. One skilled in the art
will appreciate readily that the present invention is well adapted
to carry out the objects and obtain the ends and advantages
mentioned, as well as those objects, ends and advantages inherent
herein. Changes therein and other uses which are encompassed within
the spirit of the invention as defined by the scope of the claims
will occur to those skilled in the art.
EXAMPLE 1
[0064] Cripto Binds Activin in the Presence of ActRII and Competes
with ALK4 for Activin.cndot.ActRII Binding
[0065] The ability of [.sup.125I]-activin-A to form crosslinked
complexes with Cripto was tested in the presence or absence of
activin receptors. FIG. 2 shows that when 293T cells were
transfected with ActRII (FIG. 2A, lane 2) and then subjected to
labeling and crosslinking with [.sup.125I]-activin-A followed by
immunoprecipitation with an antibody directed against ActRII, an
activin-ActRII crosslinked complex of .about.80 kDa was evident
consistent with previous crosslinking results. The appearance of
two ActRII.cndot.activin bands is routinely observed and is likely
the result of differential glycosylation of ActRII.
[0066] Co-transfection of ActRII with ALK4 (FIG. 2A, lane 5)
results in crosslinking of [.sup.125I]-activin-A to both receptor
types as indicated by the appearance of the activin.cndot.ALK4
crosslinked complex at .about.60 kDa. No binding of
[.sup.125I]-activin-A to Cripto was detected in the absence of
activin type II receptors (FIG. 2C, lane 2). However, when ActRII
was co-transfected with Cripto, activin-crosslinked complexes of
.about.32, 45 and 52 kDa were observed (FIG. 2A, lane 6). These
complexes were not present in samples in which Cripto was not
transfected (lanes 1-3,5; the .about.28 kDa band represents
crosslinked [.sup.125I]-activin-A dimer). The Cripto species of
.about.18, 31 and 38 kDa (the activin bA monomer is .about.14 kDa
and the gels were run under reducing conditions) likely have
differential glycosylation and/or other modifications.
[0067] The presence of [.sup.125I]-activing-A.cndot.Cripto bands
indicates the formation of stable activin.cndot.ActRII.cndot.Cripto
complexes since an antibody directed against ActRII was used in the
immunoprecipitation. Activin.cndot.ActRII and activin.cndot.Cripto
crosslinked bands were also evident when 293T cells were
co-transfected with ActRII and Cripto and then subjected to
immunoprecipitation using an antibody directed against Cripto (FIG.
2C, lanes 3 and 5).
[0068] The effects of co-transfecting 293T cells with Cripto,
ActRII and ALK4 were further tested. When Cripto was transfected
with ActRII and ALK4 (FIG. 2A, lane 8), [.sup.125I]-activin-A
formed a crosslinked complex with ActRII and Cripto, while
crosslinking to ALK4 was greatly decreased relative to crosslinking
in the absence of Cripto (FIG. 2A, compare lane 5 and lane 8).
Co-transfection with Cripto did not decrease expression of ALK4 as
shown by Western blot (data not shown).
[0069] The effects of Cripto on activin.cndot.ActRII.cndot.ALK4
complex formation as assessed following immunoprecipitation with an
antibody directed against ALK4. FIG. 2B shows that when 293T cells
were transfected with vector (FIG. 2B, lane 1), ActRII (FIG. 2B,
lane 2), ALK4 (FIG. 2B, lane 3), Cripto (FIG. 2B, lane 4) or
co-transfected with ActRII and Cripto (FIG. 2B, lane 6) or ALK4 and
Cripto (FIG. 2B, lane 7) and then subjected to crosslinking with
[.sup.125I]-activin-A, an ALK4 antibody failed to isolate labeled
complexes. This is consistent with the inability of either Cripto
or ALK4 to bind [.sup.125I]-activin-A in the absence of type II
receptors. When ActRII and ALK4 were co-expressed, the anti-ALK4
antibody precipitated a complex in which both ActRII and ALK4 were
labeled (FIG. 2B, lane 5).
[0070] Co-transfection of Cripto with ActRII and ALK4 substantially
blocked the appearance of these bands (FIG. 2B, lane 8), consistent
with its ability to block crosslinking of activin to ALK4 and the
association of ALK4 with ActRII. However, when ActRII, ALK4 and
Cripto were co-transfected and cells were labeled with
[.sup.125I]-activin-A, the ALK4 antibody could precipitate labeled
[.sup.125I]-activin-A.cndot.Cripto complexes (FIG. 2B, lane 8).
[0071] Cripto blocks labeling and crosslinking of
[.sup.125I]-activin-A to ALK4 in a dose dependent manner. FIG. 2D
shows that as the amount of transfected Cripto DNA is increased,
the ability of [.sup.125I]-activin-A to crosslink to ALK4
decreases. These results provide a mechanism for competitive
antagonism of activin signaling by Cripto.
EXAMPLE 2
[0072] Cripto Binds TGF-b.sub.1 in the Presence of TbRII and
Competes with ALK5 for TGF-b.sub.1.cndot.TbRII Binding
[0073] Similar to activin-A, TGF-b1 binds Cripto in the presence of
its type II receptor TbRII. FIG. 3A shows crosslinking of
[.sup.125I]-TGF-b.sub.1 to 293T cells transfected with TbRII and
the indicated amounts of Cripto DNA. A prominent
[.sup.125I]-TGF-b.sub.1.cndot.Cripto crosslinked band of .about.32
kDa appeared and increased in intensity as the amount of Cripto DNA
transfected was increased. Fainter species of .about.40 kDa were
also visible (FIG. 3A).
[0074] The effects of Cripto on the ability of
[.sup.125I]-TGF-b.sub.1 to crosslink to its type I receptor ALK5
were examined. FIG. 3B shows that [.sup.125I]-TGF-b.sub.1 forms a
crosslinked complex with its type II receptor of .about.85 kDa
(FIG. 3B, lane 2) and that co-transfection of Cripto with TbRII
results in the [.sup.125I]TGF-b.sub.1.cndot.TbRII complex as well
as the [.sup.125I]-TGF-b.sub.1.cndot.Cripto complex. When TbRII and
ALK5 were co-transfected, [125I]-TGF-b.sub.1 labeled both receptors
to yield complexes of .about.85 kDa and 60 kDa respectively (FIG.
3B, lane4). When TbRII, ALK5 and Cripto were co-transfected, all
three bands were evident (FIG. 3B, lane 5). However, the intensity
of the ALK5 band was reduced, 2 5 indicating Cripto may compete
with ALK5 for available TGF-b.cndot.TbRII binding sites.
EXAMPLE 3
Cripto Blocks Activin-A and TGF-b.sub.1 Signaling in HepG2
Cells
[0075] HepG2 cells do not express Cripto and require transfected
Cripto to respond to nodal signals. Therefore, the effects of
transfected Cripto on activin-A and TGF-b.sub.1 signaling were
tested in this cell line. Cripto and the activin/TGF-b responsive
luciferase reporter construct 3TP-lux were transfected into HepG2
cells and the effect of Cripto on activin-A and TGF-b.sub.1-induced
luciferase expression was measured. As shown in FIG. 4, activin-A
and TGF-b.sub.1 caused dose-dependent increases in luciferase
expression that were inhibited by Cripto. At maximal doses of these
ligands there was an approximately four-fold reduction in signaling
(FIG. 4A, B). As a control, the effect of Cripto on the ability of
the activin-A paralog BMP7 to induce luciferase expression using
the BMP-selective reporter BRE-luc has previously been tested.
Although BMP7 induced luciferase expression in HepG2 cells in a
dose-dependent manner, Cripto did not affect this induction,
indicating that Cripto's effects may be selective for activin,
TGF-b and the Smad2/3 pathway (Gray et al., 2003).
[0076] EXAMPLE 4
Expression of Cripto Mutants at the Cell Surface of 293T Cells
[0077] The domain structure of mouse Cripto is illustrated in FIG.
5A. This diagram indicates the locations of the signal peptide, the
EGF-like domain, the CFC domain and the C-terminal hydrophobic
region required for GPI-anchor attachment. In addition, the
positions of the FLAG epitope, the fucosylated threonine residue
(Thr 72), and the mCFC mutations (H104G, W107G) (Yeo and Whitman,
2001) are shown.
[0078] Five Cripto constructs were evaluated in this study: wild
type Cripto; Cripto (T72A), which is unable to be fucosylated and
does not facilitate nodal signaling; Cripto DEGF, in which the
EGF-like domain has been deleted; Cripto mCFC, which does not
facilitate nodal signaling and has two mutations in the CFC domain
that block ALK4 binding (H104G, W107G); and Cripto DCFC, in which
the CFC domain has been deleted.
[0079] Cell surface expression levels of wild type Cripto and these
four Cripto mutants are shown in FIG. 5B. 293T cells were
transfected with the indicated Cripto constructs and cell surface
expression was subsequently measured using anti-FLAG antibody in an
intact cell ELISA-based assay that we have previously used to
measure expression levels of cell surface proteins (Harrison et
al., 2003). Briefly, 293T cells were plated on 24 well
polylysine-coated plates at a density of 100,000 cells per well;
transfected 24 h later with 0.5 mg vector or Cripto DNA per well
and then assayed for cell surface expression 48 h after
transfection. Cells were rinsed in Hepes Dissociation Buffer (HDB)
(12.5 mM Hepes (pH 7.4), 140 mM NaCl and 5 mM Kcl), fixed in 4%
paraformaldehyde for 30 min at 4.degree. C., rinsed with HDB and
then incubated in HDB with 3% bovine serum albumin (BSA) for 30 min
at room temperature (RT). Cells were then incubated for 2 h with 2
.mu.g/ml anti-Myc antibody in HDB with 3% BSA, rinsed with HDB, and
incubated with peroxidase-conjugated anti-mouse IgG in HDB with 3%
BSA for 1 h at room temperature. Wells were rinsed with HDB and
then 100 .mu.l of TMB peroxidase substrate was added to each well.
Plates were incubated at RT until the solutions turned visibly
blue. Peroxidase activity was stopped by adding 100 .mu.l of 0.18 M
H.sub.2SO.sub.4 to each well and peroxidase activity was quantified
by measuring the absorbance of the resulting yellow solutions at
450 nm.
[0080] As shown in FIG. 5B, these Cripto constructs were expressed
at cell surface at similar levels.
EXAMPLE 5
The EGF-Like Domain of Cripto is Required for Antagonism of
Activin-A and TGF-b Signaling
[0081] Like other Epidermal Growth Factor-Cripto, FRL-1, Cryptic
(EGF-CFC) protein family members, Cripto has two conserved
cysteine-rich domains, an N-terminal EGF-like domain and a
C-terminal CFC domain. Each of these modular domains can have
activity in the absence of the other and both have been implicated
in specific protein-protein interactions and signaling functions.
To determine the roles of the Cripto EGF-like and CFC domains in
blocking TGF-b signaling, we compared the ability of wild type
Cripto to inhibit TGF-b with that of Cripto mutants in which either
the EGF-like or CFC domain was mutated or deleted.
[0082] Luciferase assays were carried out essentially as previously
described (Gray et al., 2003). HepG2 cells were plated at 150,000
cells per well in 24-well plates and transfected in triplicate
approximately 24 h later with 1 mg DNA per well with a ratio of 800
ng Cripto/100 ng 3TP-lux/100 ng cytomegalovirus
(CMV)-b-galactosidase (CMV-b-galactosidase). Cells were treated
with TGF-b.sub.1 approximately 30 h after transfection and
harvested 16 h following treatment. Cells were incubated in
solubilization buffer (1% Triton X-100, 25 mM glycylglycine (pH
7.8), 15 mM MgSO.sub.4, 4 mM EGTA and 1 mM DTT) for 30 min on ice
and luciferase reporter activity was measured and normalized
relative to CMV-b-gal activities. 293T cells were plated on 24-well
plates treated with polylysine at 100,000 cells per well and
transfected in triplicate approximately 24 h later with 0.5 mg DNA
per well using 400 ng Cripto/50 ng FAST2 (FoxH1)/25 ng A3-lux/25 ng
CMV-b-galactosidase per well. Cells were treated approximately 24 h
following transfection and then harvested approximately 16 h
following treatment. Luciferase assays were performed as described
for HepG2 cells described above.
[0083] FIG. 6 shows that when 293T cells were transfected with
empty vector or various Cripto constructs together with
FAST2/A3-luciferase and then treated with 100 pM TGF-b.sub.1,
luciferase induction was reduced .about.3-fold in cells transfected
with wild type Cripto (FIG. 6, lane 2) but was unaffected in cells
transfected with Cripto DEGF mutant (DEGF) (FIG. 6, lane 3)
relative to induction of luciferase in cells transfected with empty
vector (FIG. 6, lane 1). This result indicates that the EGF-like
domain of Cripto is required for antagonism of TGF-b.sub.1
signaling. In contrast, the mCFC mutant (H104G, W107G) blocked
TGF-b signaling as effectively as wild type Cripto (FIG. 6, lane 4)
while the Cripto DCFC mutant (DCFC) blocked TGF-b signaling even
more effectively than wild type Cripto (FIG. 6, lane 5). Therefore,
the CFC domain is not required for Cripto antagonism of TGF-b
signaling but rather it may partially interfere with Cripto's
ability to block TGF-b signaling as indicated by the fact that
Cripto DCFC had a greater blocking effect than wild type Cripto.
Together, these data indicate that the EGF-like domain of Cripto is
both necessary and sufficient for inhibition of TGF-b
signaling.
[0084] In another experiment, activin-A treatment caused a 30 to
40-fold and TGF-b.sub.1 treatment caused an .about.25 fold
induction of luciferase expression in 293T cells which were blocked
by wild type Cripto (FIG. 7). The ability of Cripto to block
activin-B signaling was similar to its ability to block activin-A
signaling in these cells (data not shown). Like wild type Cripto,
the Cripto mCFC mutant blocked activin-A and TGF-b.sub.1 signaling
in these cells (FIG. 7). In contrast, neither the Cripto DEGF
mutant with the EGF-like domain deleted nor the EGF1.cndot.2mCFC
mutant were able to block activin-A or TGF-b.sub.1 signaling in
293T cells (FIG. 7). These results indicate that the EGF-like
domain of Cripto is required for antagonism of activin-A and TGF-b
signaling.
EXAMPLE 6
The CFC Domain of Cripto is not Required for TGF-b Binding
[0085] Having demonstrated that the Cripto DCFC mutant can block
TGF-b.sub.1 signaling, we next tested whether this mutant can bind
and crosslink to TGF-b.sub.1. 293T cells were transfected with wild
type Cripto (FIG. 8, lane 1), Cripto DCFC (FIG. 8, lane 2), TbRII
alone (FIG. 8, lane 3), TbRII and Cripto (FIG. 8, lane 4) or TbRII
and Cripto DCFC (FIG. 8, lane 5). Cells were labeled with
[.sup.125I]-TGF-b.sub.1 and subjected to covalent crosslinking
followed by immunoprecipitation with an antibody directed against
TbRII (anti-His, FIG. 8A) or against Cripto (anti-FLAG, FIG.
8B).
[0086] For covalent crosslinking studies, 293T cells were plated on
six-well plates coated with polylysine at a density of 400,000
cells per well and then transfected approximately 24 h later. Cells
were transfected with 4 mg DNA per well with ratios of 0.5 mg
TbRII/0.5 mg ALK5/3 mg Cripto unless otherwise indicated for
[.sup.125I]TGF-b 1 crosslinking or 2 mg ActRII/1 mg Cripto/1 mg
vector for [.sup.125I]-activin-A crosslinking. As necessary, empty
vector was used to keep the amount of DNA transfected constant at 4
mg. Covalent crosslinking was performed approximately 48 h after
transfection by first washing cells in Hepes Dissociation Buffer
(HDB) and then incubating them with [125I]-TGF-b.sub.1 or
[.sup.125I]-activin-A in binding buffer (HDB containing 0.1% BSA,
5mM MgSO.sub.4 and 1.5 mM CaCl.sub.2) at room temperature for
approximately 4 h. Cells were then rinsed in
[0087] HDB, incubated in HDB containing 0.5 mM disuccinylsuberate
(DSS) for 30 min on ice, rinsed in HDB and then solubilized in
lysis buffer (TBS containing 1% NP-40, 0.5% deoxycholate and 2 mM
EDTA) for 1 h on ice. Solubilized, crosslinked complexes were
incubated for approximately 24 h at 4.degree. C. with 2 mg of
either anti-FLAG (M2), anti-His or anti-myc antibodies. Immune
complexes were precipitated using protein-G agarose and analyzed
using SDS-PAGE and autoradiography.
[0088] As expected, anti-His antibody targeting TbRII did not
precipitate labeled complexes from cells transfected with Cripto
alone (FIG. 8A, lane 1) or Cripto DCFC alone (FIG. 8A, lane 2), but
it did precipitate [.sup.125I]-TGF-b.sub.1-labeled TbRII from cells
in which TbRII was transfected either alone (FIG. 8A, lane 3), or
in which TbRII was co-transfected either with Cripto (FIG. 8A, lane
4) or Cripto DCFC (FIG. 8A, lane 5). In addition, a labeled Cripto
complex of .about.32 kDa was immunoprecipitated from cells
co-transfected with TbRII and Cripto (FIG. 8A, lane 4) while a
complex of .about.28 kDa was precipitated from cells co-transfected
with TbRII and Cripto DCFC. The latter complex was slightly larger
than [.sup.125I]-TGF-b.sub.1 dimer of .about.25 kDa (FIG. 8A, lane
5) and it was consistent with the predicted size of an
[.sup.125I]-TGF-b.sub.1.cndot.DCFC complex.
[0089] We also precipitated labeled complexes with anti-FLAG
antibody targeting Cripto and Cripto DCFC. When 293T cells were
transfected with Cripto alone (FIG. 8B, lane 1) or Cripto DCFC
alone (FIG. 8B, lane 2), crosslinked with [.sup.125I]-TGF-b.sub.1
and immunoprecipitated with an anti-FLAG antibody, no bands were
observed. This result is consistent with the inability of Cripto
and Cripto DCFC to bind TGF-b in the absence of TbRII. As
predicted, transfection of TbRII alone followed by cell labeling,
crosslinking and immunoprecipitation using anti-FLAG antibody did
not result in observation of crosslinked complexes (FIG. 8B, lane
3). However, co-transfection of 293T cells with TbRII and Cripto
(FIG. 8B, lane 4) or TbRII and Cripto DCFC (FIG. 8B, lane 5) led to
precipitation of complexes of .about.32 kDa and .about.28 kDa
representing the [.sup.125I]-TGF-b.sub.1.cndot.Cripto complex and
the [.sup.125I]-TGF-b.sub.1.cndot.DCFC complex, respectively. This
result provided further evidence that the CFC domain is not
required for Cripto binding to TGF-b. In addition, a .about.85 kDa
band representing [.sup.125I]-TGF-b.sub.1.cndot.TbRII was present
in each of these lanes (FIG. 8B, lanes 4, 5). Therefore, in the
context of [.sup.125I]-TGF-b.sub.1 crosslinking, either an
anti-TbRII antibody or an anti-Cripto antibody can precipitate
complexes containing both labeled TbRII and labeled Cripto. This is
similar to what is observed in crosslinking experiments with TbRII,
[.sup.125I]-TGF-b.sub.1 and ALK5 in which the ligand mediates
assembly of both Type II and Type I receptors into a stable
complex.
EXAMPLE 7
Mutation of Threonine 72 Blocks Cripto Antagonism of TGF-b and
Activin Signaling
[0090] It has previously been shown that Cripto is modified by
O-fucosylation on a conserved threonine residue (Thr 72 in mouse
Cripto, Thr 88 in human Cripto) within its EGF-like domain and that
mutation of this threonine to an alanine blocks the ability of
Cripto to bind nodal and facilitate nodal signaling. The EGF-like
domain of Cripto plays an important role in facilitating nodal
signaling, and results presented above indicate that it also plays
an important role in blocking both TGF-b.sub.1 and activin-A
signaling. Therefore, we tested whether mutation of Thr 72 to Ala,
which prevents fucosylation within this domain and blocks nodal
signaling, might similarly interfere with Cripto's ability to block
TGF-b and activin signaling.
[0091] FIG. 9 shows the relative effects of wild type Cripto and
the Thr 72.DELTA.Ala (T72A) Cripto fucosylation mutant on
TGF-b.sub.1 (FIG. 9A), activin-A (FIG. 9B) and activin-B (FIG. 9C)
signaling. 293T cells were transfected with empty vector, wild type
Cripto or the Cripto (T72A) mutant together with
FAST2/A3-luciferase. When 293T cells were treated with 100 pM
TGF-b.sub.1(Figure 9A), luciferase induction relative to
vector-transfected cells (FIG. 9A, lane 1) was reduced in cells
transfected with wild type Cripto (FIG. 9A, lane 2) but was
unaffected in cells transfected with the Cripto (T72A) mutant (FIG.
9A, lane 3).
[0092] Similarly, when cells were treated with 300 pM activin-A,
luciferase induction was blocked by wild type Cripto (FIG. 9B, lane
2) but not the Cripto (T72A) mutant (FIG. 9B, lane 3). Finally,
when cells were treated with 300 pM activin-B, Cripto blocked
luciferase induction consistent with our previous observations and
those of others. However, unlike what was observed with TGF-b and
activin-A, the Cripto (T72A) mutant could partially block activin-B
signaling (FIG. 9C, lane 3). This is consistent with a previous
report demonstrating that this mutant can bind activin-B and that
the CFC domain of Cripto is important for Cripto antagonism of
activin-B.
EXAMPLE 8
The EGF-Like and CFC Domains of Cripto Both Participate in Blocking
Activin-B Signaling
[0093] In an attempt to clarify the functional importance of the
EGF-like and CFC domains on Cripto antagonism of activin-A and
activin-B signaling, 293T cells were transfected with empty vector,
the Cripto DEGF mutant or the Cripto DCFC mutant together with
FAST2/A3-luciferase and luciferase induction was measured in
response to treatment with activin-A or activin-B. Consistent with
previous observations, Cripto DEGF mutant did not block activin-A
signaling (FIG. 10). In contrast, the Cripto DEGF mutant blocked
roughly half of the luciferase activity induced by activin-B (FIG.
10), indicating an independent role for the CFC domain in blocking
activin-B signaling. In contrast to the Cripto DEGF mutant, the
Cripto DCFC mutant strongly blocked luciferase induction by either
activin-A or activin-B (FIG. 10). Therefore, the EGF-like domain
appears to be necessary and sufficient for antagonism of activin-A
and TGF-b.sub.1 signaling by Cripto while either the EGF-like
domain or the CFC domain can apparently function independently to
block signaling by activin-B.
EXAMPLE 9
The CFC Domain of Cripto is not Required for Activin-A Binding
[0094] Having demonstrated that the CFC domain of Cripto is not
required for inhibition of activin-A signaling, we next tested
whether this domain is required for Cripto to bind activin-A and
activin-B. 293T cells were transfected with Cripto (FIG. 11, lane
1); Cripto DCFC (FIG. 11, lane 2); ActRII (FIG. 11, lane 3); ActRII
and Cripto (FIG. 11, lane 4); or ActRII and Cripto DCFC (FIG. 11,
lane 5), subjected to labeling and crosslinking with
[.sup.125I]-activin-A or [.sup.125I]-activin-B followed by
immunoprecipitation with either an anti-myc antibody targeting
ActRII (FIG. 11A) or an anti-FLAG antibody targeting Cripto and
Cripto DCFC (FIG. 11B).
[0095] As predicted, transfection of Cripto alone (FIG. 11A, lane
1) or Cripto DCFC alone (FIG. 11A, lane 1) followed by cell
labeling, crosslinking and immunoprecipitation using an antibody
targeting ActRII did not result in detection of crosslinked
complexes. However, transfection of 293T cells with ActRII alone
(FIG. 11A, lane 3) resulted in bands at .about.80 kDa representing
the [.sup.125I]-activin-A.cndot.ActRII complex and bands at
.about.28 kDa representing the [.sup.125I]-activing-A dimer.
Co-transfection of ActRII and Cripto (FIG. 11A, lane 4) or ActRII
and Cripto DCFC (FIG. 11A, lane 5) led to precipitation of
additional complexes of .about.34 kDa and .about.30 kDa likely
representing the [.sup.125I]-activin-A.cndot.Cripto complex and
[.sup.125I]-activin-A.cndot.DCFC complex, respectively. In parallel
experiments, we have been unable to detect crosslinked complexes
with [.sup.125I]-activin-B, apparently due to loss of binding
activity resulting from the iodination procedure.
[0096] We also precipitated [.sup.125I]-activin-A labeled complexes
with anti-FLAG antibody targeting Cripto and Cripto DCFC. When 293T
cells were transfected with Cripto alone or Cripto DCFC alone,
crosslinked with [.sup.125I]-activing-A and then subjected to
immunoprecipitation with anti-FLAG antibody, no bands were observed
(FIG. 11B). This result is similar to what was observed with TGF-b
crosslinking (FIG. 8), suggesting that when transfected alone
Cripto and Cripto DCFC are each unable to bind activin-A. As
predicted, transfection of ActRII alone followed by cell labeling,
crosslinking and immunoprecipitation using anti-FLAG antibody did
not result in observation of crosslinked complexes (FIG. 11B, lane
3). Co-transfection of 293T cells with ActRII and Cripto (FIG. 11B,
lane 4) or ActRII and Cripto DCFC (FIG. 11B, lane 5) led to
precipitation of complexes of .about.34 kDa and .about.30 kDa
representing the [.sup.125I]-activin-A.cndot.Cripto complex and the
[.sup.125I]-activin-A.cndot.DCFC complex, respectively, providing
evidence that the CFC domain is not required for binding of Cripto
to activin-A. Rather, consistent with functional data, the Cripto
DCFC mutant appears to bind and crosslink to [.sup.125I]-activing-A
more effectively than wild type Cripto as indicated by their
relative band intensities (FIG. 11B, lanes 4, 5). The .about.80 kDa
band representing [.sup.125I]-activin-A.cndot.ActRII was present in
each of these lanes (FIG. 11B, lanes 4, 5) indicating that in the
presence of activin-A, Cripto and Cripto DCFC each can form a
stable complex with ActRII.
EXAMPLE 10
Cripto Antagonizes Activin-A/TGF-b.sub.1 but Facilitates Nodal
Signaling in 293T Cells
[0097] The effects of Cripto on activin-A and TGF-b.sub.1 signaling
as opposed to nodal signaling were compared. It has previously been
shown that transfection of nodal and Cripto into 293T cells
resulted in secretion of processed nodal protein that generates
signals in the cells producing it. Thus 293T cells were transfected
with FAST2, the A3-luciferase reporter plasmid and various amounts
of Cripto DNA. The cells were then treated with activin-A or
TGF-b.sub.1 or co-transfected with a mouse nodal expression
vector.
[0098] FIG. 12 shows that in the absence of Cripto, activin-A
treatment induced luciferase expression .about.45 fold relative to
untreated cells and TGF-b.sub.1 treatment induced luciferase
expression .about.30 fold. Co-transfection with increasing amounts
of Cripto DNA caused a dose-dependent blockade of activin-A and
TGF-b.sub.1 signaling. Conversely, nodal did not generate a
detectable signal in the absence of Cripto but its signaling
increased as the amount of Cripto DNA transfected into the cells
was increased (FIG. 12). Therefore, Cripto can have opposing
effects on activin/TGF-b as opposed to nodal signaling despite the
fact that activin and nodal utilize the same signaling receptors
and each of these ligands signal via the Smad2/3 pathway.
EXAMPLE 11
Regulation of TGF-b Superfamily Signaling by Cripto
[0099] FIG. 13 illustrates proposed mechanisms by which Cripto
either facilitates nodal and Vg1/GDF1 signaling (FIG. 13A) or
inhibits TGF-b and activin signaling (FIG. 13B). Cripto binds nodal
or Vg1/GDF1 and ALK4 and allows these ligands to assemble type II
and type I receptors to elicit signaling responses such as
mesendoderm induction during vertebrate embryogenesis (FIG.
13A).
[0100] In contrast to its effects on nodal signaling, Cripto binds
activin-A in the presence of its type II receptors and antagonizes
activin signaling. Cripto also inhibits activin-B signaling,
although the mechanism of this antagonism appears to differ from
that of activin-A. Cripto also binds TGF-b.sub.1 in the presence of
TbRII and blocks TGF-b.sub.1 signaling, demonstrating a mechanism
of antagonism similar to that on activin-A signaling (FIG. 13B).
Type II receptor binding is required for activin-A and TGF-b.sub.1
to form complexes with either type I receptors or Cripto, and
crosslinking data presented herein indicate that Cripto may disrupt
the ability of activin-A and TGF-b.sub.1 to form functional
complexes with type I receptors (FIG. 13B). The ability of Cripto
to inhibit TGF-b.sub.1 and activins, which are tumor suppressors
and can potently inhibit cell growth, provides a mechanism by which
it could promote tumorigenesis.
EXAMPLE 12
Inhibition of Activin.cndot.Cripto or TGF-b.cndot.Cripto Complexes
Formation
[0101] It is hypothesized that antagonism of activin and TGF-b
signaling by Cripto can be disrupted using antibodies directed
against Cripto. Binding of these antibodies to Cripto is predicted
to disrupt the ability of Cripto to bind to activin or TGF-b,
thereby reversing the antagonism of activin and TGF-b signaling by
Cripto.
[0102] Cripto has two highly conserved domains, the EGF-like domain
and the CFC domain, that have been shown to be functionally
important and are involved in protein-protein interactions. The
EGF-like domain of Cripto binds directly to the TGF-b superfamily
member nodal and related ligands Vg1 and GDF1 to facilitate
signaling via activin receptors ActRII/IIB and ALK4. The EGF-like
domain of Cripto is required for antagonism of activin and TGF-b
signaling. Deletion of the EGF-like domain (DEGF) resulted in a
Cripto mutant with undetectable activin binding in crosslinking
assays and an inability to block activin or TGF-b signaling.
Therefore, it is proposed that, similar to nodal, activin and TGF-b
bind to the EGF-like domain of Cripto and this domain represents a
primary target for antibody blockade of Cripto antagonism of
activin and TGF-b.
[0103] It has also been shown that the CFC domain of Cripto binds
directly to ALK4 and, similar to the EGF-like domain, this domain
is required for nodal signaling. We have tested a Cripto mutant
with two point mutations in the CFC domain that was previously
shown to be defective in ALK4 binding and nodal signaling. This
mutant, called mCFC, bound activin in crosslinking assays when
co-expressed with activin type II receptors (ActRII/IIB) and
blocked activin signaling when transiently transfected into 293T
cells. This is consistent with activin binding to the EGF-like
domain of Cripto. Consequently, antibodies that can disrupt Cripto
binding to ALK4 may have effects on Cripto antagonism of activin
and TGF-b. Recently it was shown that monoclonal antibodies
targeting either the CFC domain (Adkins et al., 2003) or EGF-like
domain (Xing et al., 2004) of Cripto can inhibit tumor growth in
vivo.
[0104] Antibodies can be generated against recombinant soluble
Cripto protein (containing both the EGF-like and CFC domains)
purified from mammalian cells or a synthetic peptide spanning the
EGF-like domain of Cripto. Raising antibodies against the
full-length soluble Cripto protein will enable us to test the
effects of antibodies targeting both the EGF-like and CFC
domains.
[0105] Soluble Cripto with a C-terminal. FLAG epitope tag can be
expressed in mammalian cells (293T cells or CHO cells) following
transient transfection. Cells stably expressing soluble Cripto-FLAG
can be generated by selection in G418 for larger-scale production
of protein. Medium containing soluble Cripto-FLAG can be enriched
using FLAG-agarose immunoaffinity chromatography and purified by
reverse-phase HPLC. The Cripto EGF-like domain can also be
generated as a synthetic peptide to be used as an antigen to
generate anti-Cripto antibodies. Peptide spanning the human Cripto
EGF-like domain has previously been synthesized, refolded and shown
to have biological activity. A similar polypeptide spanning the
mouse Cripto EGF-like domain can be generated using mouse Cripto
sequence generally available in the art.
[0106] Initially, potential neutralizing anti-Cripto antibodies can
be tested at various doses for their ability to disrupt Cripto
antagonism of activin-A, activin-B and TGF-b.sub.1 signaling in
293T cells. The ability of activin-A, activin-B and TGF-b.sub.1 to
induce luciferase can be measured in cells transfected with Cripto,
FAST2 and A3-luciferase constructs. The effects of the anti-Cripto
antibodies can be compared to normal rabbit serum (NRS). If
antibodies directed against full-length Cripto or peptide
containing the EGF-like domain are found to block Cripto effects on
activin and TGF-b signaling in 293T cells, further testing can be
performed using other cells including breast epithelial and breast
cancer cell lines.
[0107] Alternatively, antagonistic activities of Cripto may be
inhibited by molecules that bind to Cripto, thereby disrupting the
ability of Cripto to bind to activin or TGF-b. For example, Lefty
and Tomoregulin have each been shown to bind directly to Cripto and
have been shown to block nodal signaling (nodal signaling requires
Cripto). The prediction is that by binding to Cripto they might
interfere with Cripto's ability to bind to TGF-b/activin thereby
blocking Cripto's effects on these ligands.
EXAMPLE 13
Inhibition of Activin.cndot.Cripto or TGF-b.cndot.Cripto Complexes
Formation by Soluble Mutated Activin Receptor-Like Kinases-4
(ALK-4)
[0108] The aim here is to generate a soluble version of the
ALK4-extracellular domains (ECD) that is capable of binding Cripto
but not a TGF-b superfamily ligand such as activin. It is
hypothesized that such a protein will not bind directly to a TGF-b
superfamily ligand and interfere with signaling, but rather will
have the ability to bind Cripto and disrupt the ability of Cripto
to block activin or TGF-b binding and signaling.
[0109] The functional binding site for activin on ALK4 has been
identified recently (Harrison et al., 2003). It was demonstrated
that 170A, L75A and P77A ALK4-ECD mutants were unable to bind
activin or mediate activate signaling. It was concluded that 170,
L75 and P77 are central to the activin binding site on the
ALK4-ECD. Although mutating one of these residues is sufficient to
disrupt activin.cndot.ALK4 binding, soluble versions of ALK4-ECD
incorporating these mutations individually, in pairs or
incorporating all three mutations can also be generated.
[0110] The soluble ALK4 ECD proteins incorporating the 170A, L75A
and/or P77A mutations and a C-terminal FLAG epitope tag can be
expressed in mammalian cells (293T cells or CHO cells) following
transient transfection. Cells stably expressing soluble
ALK4-ECD-FLAG proteins will be generated by selection in G418 for
larger-scale production of protein. Medium containing soluble
ALK4-ECD-FLAG proteins can be enriched using FLAG-agarose
immunoaffinity chromatography and purified by reverse-phase
HPLC.
[0111] Initially, soluble ALK4 ECD proteins incorporating the 170A,
L75A and/or P77A mutations can be tested at various doses for their
ability to disrupt Cripto antagonism of activin-A, activin-B and
TGF-b.sub.1 signaling in 293T cells. The ability of activin-A,
activin-B and TGF-b.sub.1 to induce luciferase will be measured in
cells transfected with Cripto, FAST2 and A3-luciferase constructs.
The mutant ALK4-ECD proteins will be compared to wild type soluble
ALK4-ECD. The effects of these ALK4-ECD proteins on activin
signaling in the absence of Cripto will also be tested to determine
if they interfere with activin signaling. In addition to 293T
cells, other cells including breast epithelial and breast cancer
cell lines can also be used.
EXAMPLE 14
Inhibition of Cripto Expression
[0112] Multiple strategies can be pursued to prevent Cripto
antagonism of activin and TGF-b signaling in a defined in vitro
system. Useful strategies include, but are not limited to,
disruption of Cripto expression by homologous recombination, the
previously validated Cripto antisense vector approach, and Cripto
RNA interference.
Homologous Recombination
[0113] Disruption of Cripto expression by homologous recombination
in mouse embryonic stem cells has been previously described (Ding
et al., 1998). It was shown that mice lacking both alleles of
Cripto died very early during embryogenesis probably due to a loss
of nodal signaling which requires Cripto. However, the effects of
deleting one Cripto allele or of disrupting both alleles in the
adult in specific tissues (i.e. conditional knockout) remains to be
evaluated in terms of effects on cancer susceptibility.
Antisense Oligonucleotides
[0114] The use of antisense oligonucleotides to disrupt Cripto
expression has also been described (Niemeyer et al., 1998).
Retroviral vector was used to deliver Cripto antisense RNA to mouse
mammary CID-9 cells. Reduction of endogenous Cripto expression in
these cells via expression of an antisense Cripto vector construct
decreased cell proliferation while overexpression of Cripto led to
increased cell growth. Antisense inhibitors of Cripto also led to
loss of transformed phenotype in colon carcinoma cells (Ciardiello
et al., 1994).
[0115] Niemeyer et al. (1998) used the retroviral vector pGCEN
containing the antisense Cripto sequence to infect CID-9 cells and
generated cells stably expressing the antisense construct. Similar
approach can be performed with the retroviral pCLNC vector, which
was used previously to infect cells and generate stable lines (Gray
and Vale, unpublished data). One of ordinary skill in the art would
recognize that other vectors besides retroviral vectors can also be
used according to standard procedures in the art. In one example,
mouse Cripto sequence can be subcloned into the pCLNC vector in the
antisense or the sense orientation. These constructs or empty pCLNC
vector are used to generate virus, infect CID-9 cells and obtain
G418 resistant cells. The effectiveness of this approach in
increasing or decreasing Cripto can be measured directly by
examining Cripto expression in the resulting G418 resistant cells
by Western blot with anti-Cripto antibodies.
[0116] The effects of activin and TGF-b and their antagonists on
the proliferation of CID-9 cell (or other target cells well-known
in the art) can be measured using protocols generally available to
one of ordinary skill in the art. For example, the CyQUANT.RTM.
cell proliferation assay kit (Invitrogen) can be used according to
manufacturer's instructions. The sensitivity of a target cell line
to growth inhibition by activin and TGF-b and their antagonists can
be established by treating a range of cells with a range of doses
of each ligand, antagonist or vehicle and testing the effects on
proliferation over time. Once the effects of activin, TGF-b or
antagonist on the parental cells are established, these experiments
can be repeated on cells stably expressing the retroviral vector,
Cripto-sense or Cripto-antisense retroviral DNA and compare the
resulting effects of various doses of activin and TGF-b on cell
proliferation. It has been shown that Cripto overexpression
conferred anchorage independent growth capability on CID-9 cells.
Therefore, in addition to measuring the proliferation rate of
Cripto over- and under-expressing cells in monolayer culture, the
ability of these cells to grow in soft agar will also be measured.
Similar experiments can be performed on cells stably overexpressing
RNAi vectors (as described below).
RNA interference
[0117] The principle of RNA interference is the abrogation of
target gene expression initiated by small interfering RNA (siRNA)
homologous in sequence to the gene to be silenced (Elbashir et al.,
2001). Recently, it was shown that transfection of a synthetic
21-nucleotide siRNA duplexes could specifically suppress expression
of endogenous and heterologous genes in different mammalian cell
lines. Viral infection of target cells such as CID-9 cells to
express a 21-nucleotide siRNAs targeted against Cripto can be
performed using the U6 promoter system based on the pSilencer
vector (Ambion) and/or the polymerase III HI-RNA promoter (pSUPER)
(Brummelkamp et al., 2002). These RNAs require a 5' UU overhang to
bind their target genes. Therefore, target sequences for siRNAs
will be identified by scanning the Cripto gene for sequences
containing AA targets complementary to the siRNA UU overhang. The
AA and downstream 19 nucleotides will be compared to an appropriate
genome database to eliminate sequences with significant homology to
other genes. Sequences that are specific to the mouse Cripto gene
and are common between mouse, rat, and human Cripto will be initial
siRNA targets.
[0118] Retroviral and/or lentivirus vectors (provided by Dr. Inder
Verma, The Salk Institute) will be used for the infection and
stable expression of siRNAs in CID-9 cells. These vectors can be
designed to contain either a polymerase III HI-RNA promoter or a U6
small nuclear RNA promoter to continuously drive high levels of
siRNA expression in target cells. Cripto-specific inserts can be
designed such that the specified 19-nucleotide sequence of Cripto
is separated by a short spacer from the reverse complement of the
same 19-nucleotide sequence. The resulting transcript is predicted
to fold back on itself to form a 19 base pair hairpin-loop
structure necessary for siRNA function. Expression of Cripto siRNAs
using these two vector systems will allow for efficient Cripto
disruption.
[0119] In addition to validating this approach in cultured mouse
CID-9 cells, deliverance of siRNA or antisense RNA targeting Cripto
expression by retroviral or lentiviral vectors represents a
potential gene therapy approach to treat human cancer.
EXAMPLE 15
Augmenting Smad2/3 Signaling Using Mutant Activin
[0120] Another method of overcoming the antagonistic effects of
Cripto on activin and TGF-b signaling (i.e. Smad2/3 signaling) is
to design a mutant form of activin (or possibly TGF-b) that retains
signaling activity but is unable to bind Cripto. Such a mutant
ligand may have therapeutic value since it will be capable of
activating Smad2/3 signaling in tissues in which signaling by wild
type activin and TGF-b is otherwise suppressed by Cripto.
Cripto-Resistant Activin
[0121] In an effort to identify receptor-binding residues on
activin-A, a rapid functional screen for expressing and
characterizing activin-A and activin-A mutants has been established
using 293T cells. This system incorporates FAST2 and A3-luciferase
and is based on a system originally developed to characterize nodal
and Cripto signaling. Full-length activin bA cDNA has been
expressed in 293T cells and dimeric, processed activin-A was
secreted into the medium. When conditioned medium from these cells
was used to treat separate 293T cells transfected with
A3-luciferase and FAST2, luciferase reporter expression was
induced, indicating the secreted activin-A was fully active.
[0122] Using the above system, several activin-A mutants were
generated and quantitated from conditioned medium by Western blot
analysis. We have confirmed previous results indicating that
mutation of Lys 102 to Glu (K102E) disrupts activin-A activity.
However, most of the mutants we have generated appear to retain
full activity. We now propose to compare the ability of transfected
Cripto to antagonize wild type activin-A signaling in 293T cells
with its ability to antagonize these activin-A mutants. The goal is
to identify activin-A mutants that are resistant to Cripto
antagonism relative to wild type activin-A. Additional activin-A
alanine substitution point mutants can be generated with the aim of
identifying activin-A mutants with Cripto full signaling activity
and Cripto resistance.
EXAMPLE 16
Constructs and Uses of Soluble and Membrane-Bound Cripto
[0123] Cripto is expressed at high levels in tumors and has been
shown to promote tumorigenesis, whereas TGF-b and activin are tumor
suppressors and potently inhibit cell proliferation. Paradoxically,
TGF-b/activin can also promote tumorigenesis at later stages of
tumor progression when tumor cell proliferation is no longer
inhibited by TGF-b/activin signaling. At these later stages, TGF-b
and activin are produced at high levels by tumor cells and
signaling of these ligands causes angiogenesis, immunosuppression
and epithelial to mesenchymal transition which favor tumor growth
and spread. Threrefore, it may be of therapeutic value to either
facilitate TGF-b/activin signaling or to block TGF-b/activin
signaling depending on the context (i.e. stage of tumor
progression).
[0124] Blocking TGF-b/activin signaling may have therapeutic
benefit in several contexts including, but are not limited to,
cancer, wound healing and liver regeneration. As mentioned above,
during later stages of tumorigenesis tumor cells secrete TGF-b and
activin that cause effects favoring further tumor growth and
metastasis due to their effects on blood vessels, cells of the
immune system and organs which are targets for metastasis.
Directing Cripto expression or administering soluble forms of
Cripto to these sites may help to slow tumor progression.
[0125] TGF-b and activin accelerate wound healing but they also can
cause excessive extracellular matrix deposition and unwanted
scarring. Cripto may therefore have utility as a modulator of
TGF-b/activin in this context. With regard to liver regeneration,
TGF-b and activin are potent antiproliferative agents in liver and
therefore blocking their signaling with Cripto may prove useful in
facilitating liver regeneration.
Design of Cripto Mutants
[0126] Examples of Cripto constructs are indicated in FIG. 14.
Initially, all constructs can be generated in mammalian expression
vector such as pcDNA3 using standard PCR-based mutagenesis and
subcloning techniques.
[0127] Cell-attached Cripto constructs can incorporate Cripto
signal peptide with an in-frame epitope tag sequence (e.g. FLAG or
His) immediately downstream of the signal peptide followed by the
indicated Cripto sequences (FIG. 14), hydrophobic C-terminal domain
required for GPI attachment and a stop codon. The Epidermal Growth
Factor-Cripto, FRL-1, Cryptic (EGF-CFC) region of mouse Cripto (aa
60-134) has been shown to be sufficient to reconstitute one-eyed
pinhead (oep) signaling in zebrafish embryos. This region can be
expressed as a cell-attached protein and tested for its ability. to
bind activin and TGF-b and antagonize their signaling (FIG.
14).
[0128] The EGF-like domain of mouse Cripto spans residues 60-95
(FIGS. 14-15) and deleting this region abolishes the ability of
Cripto to bind activin-A as well as its ability to antagonize both
activin-A and TGF-b.sub.1 signaling. Cell-attached EGF-like domain
construct can be tested for its effects on activin-A and
TGF-b.sub.1 binding and signaling. The effects of the GPI-anchored
CFC domain (aa 99-134) on activin-A and TGF-b.sub.1 binding and
signaling can also be tested.
[0129] The functional role of individual amino acid in the Cripto
EGF-like and CFC domains for activin-A and TGF-b.sub.1 binding can
be determined as follows. Mutants such as Cripto mCFC (H104G,
W107G), which has two point mutations within the CFC domain and
does not bind ALK4, and Cripto DEGF, which has the entire EGF-like
domain deleted and is unable to bind the TGF-b/activin-related
ligand nodal, have been described above. Mutant Cripto
EGF1.cndot.2mCFC, which blocks Cripto binding to activin and
prevents Cripto antagonism of activin and TGF-b signaling,
incorporates mEGF1, mEGF2 and mCFC tandem point mutations (N69G,
T72A, R88G, E91G, H104G, W107G) (see FIGS. 14-15). The effects of
these mutations, individually or in combination, can be tested by
incorporating these or the corresponding alanine mutations into
cell-attached or soluble Cripto constructs. For example,
overlapping PCR mutagenesis can be used to generate these point
mutations in full-length, GPI-anchored Cripto background. Similar
mutations can also be generated in soluble EGF-like and CFC domain
constructs.
[0130] Furthermore, there are 14 highly conserved residues in the
EGF-like domain and 9 highly conserved residues in the CFC domain
(FIG. 15). Fifteen of these conserved residues have previously been
targeted for mutagenesis in the context of soluble mouse Cripto and
characterized with respect to their ability to reconstitute
one-eyed pinhead (oep) signaling in zebrafish embryos lacking both
maternal and zygotic expression of oep (MZoep). RNA encoding
soluble mouse Cripto or soluble EGF-CFC region could restore normal
embryonic development as could the soluble Pro52, Phe85, His92,
Arg95 and G1u97 Cripto Ala-substituted mutants (Minchiotti et al.,
2001). Injected RNA encoding the Gly71Asn or the Phe78Ala mutants
was unable to rescue the MZoep phenotype even at high doses while
the Asn63, Ser77, Arg88, Glu91, His104, Leu114, Leu114, Leu122 and
Arg116 Ala substituted mutants resulted in intermediate effects
(Minchiotti et al., 2001). Each mutant was expressed in 293T cells
and it was shown that with the exception of the Arg88Ala mutant,
each of the fifteen mutants was expressed at approximately wild
type levels (Minchiotti et al., 2001). To more fully characterize
the activin and TGF-b binding site(s) on Cripto, similar study can
be done with Ala substituted mutants in the context of full-length,
GPI-anchored Cripto constructs or soluble Cripto constructs. It is
expected that conserved residues within the EGF-like domain may
constitute the activin and TGF-b binding surfaces.
[0131] It has been previously shown that Cripto can facilitate
nodal signaling and activate mitogenic MAPK and PI3K pathways when
present as a soluble protein, raising the possibility that Cripto
may act both cell autonomously and as a secreted, soluble factor.
Thus it is of interest to test the ability of several soluble
Cripto constructs to bind activin and TGF-b and antagonize their
signaling. Examples of soluble Cripto constructs are illustrated in
FIG. 14. It has been previously shown that the C-terminal
hydrophobic domain of Cripto is required for GPI-attachment and
deletion of this domain results in secretion of soluble Cripto
protein. Therefore, soluble Cripto constructs will incorporate this
C-terminal deletion in addition to an in-frame C-terminal FLAG
epitope tag followed by a stop codon (FIG. 14).
[0132] The following references are cited herein: [0133] Adkins et
al., Antibody blockade of the Cripto CFC domain suppresses tumor
cell growth in vivo. J. Clin. Invest. 112:575-87 (2003). [0134]
Brummelkamp et al., A system for stable expression of short
interfering RNAs in mammalian cells. Science 296:550-3 (2002).
[0135] Ciardiello et al., Inhibition of CRIPTO expression and
tumorigenicity in human colon cancer cells by antisense RNA and
oligodeoxynucleotides. Oncogene 9:291-8 (1994). [0136] Ding et al.,
Cripto is required for correct orientation of the
anterior-posterior axis in the mouse embryo. Nature 395:702-7
(1998). [0137] Elbashir et al., Duplexes of 21-nucleotide RNAs
mediate RNA interference in cultured mammalian cells. Nature
411:494-8 (2001). [0138] Gray et al., Cripto forms a complex with
activin and type II activin receptors and can block activin
signaling. Proc. Natl. Acad. Sci. USA. 100:5193-8 (2003). [0139]
Harrison et al., Identification of a functional binding site for
activin on the type I receptor ALK4. J. Biol. Chem. 278:21129-35
(2003). [0140] Minchiotti et al., Development 128:4501-10 (2001).
[0141] Niemeyer et al., Cripto: roles in mammary cell growth,
survival, differentiation and transformation. Cell Death Differ.
5:440-9 (1998). [0142] Xing et al., Cancer Res. 64:4018-23 (2004).
[0143] Yeo and Whitman, Mol. Cell 7:949-57 (2001).
[0144] Any patents or publications mentioned in this specification
are indicative of the levels of those skilled in the art to which
the invention pertains. Further, these patents and publications are
incorporated by reference herein to the same extent as if each
individual publication was specifically and individually indicated
to be incorporated by reference.
Sequence CWU 1
1
61171PRTMus musculus 1Met Gly Tyr Phe Ser Ser Ser Val Val Leu Leu
Val Ala Ile Ser Ser1 5 10 15Ala Phe Glu Phe Gly Pro Val Ala Gly Arg
Asp Leu Ala Ile Arg Asp 20 25 30Asn Ser Ile Trp Asp Gln Lys Glu Pro
Ala Val Arg Asp Arg Ser Phe 35 40 45Gln Phe Val Pro Ser Val Gly Ile
Gln Asn Ser Lys Ser Leu Asn Lys 50 55 60Thr Cys Cys Leu Asn Gly Gly
Thr Cys Leu Leu Gly Ser Phe Cys Ala65 70 75 80Cys Pro Pro Ser Glu
Tyr Gly Arg Asn Cys Glu His Asp Val Arg Lys 85 90 95Glu His Cys Gly
Ser Ile Leu His Gly Thr Trp Leu Pro Lys Lys Cys 100 105 110Ser Leu
Cys Arg Cys Trp His Gly Gln Leu His Cys Leu Pro Gln Thr 115 120
125Phe Leu Pro Gly Cys Asp Gly His Val Met Asp Gln Asp Leu Lys Ala
130 135 140Ser Arg Thr Pro Cys Gln Thr Pro Ser Val Thr Thr Thr Phe
Met Leu145 150 155 160Ala Gly Ala Cys Leu Phe Leu Asp Met Lys Val
165 1702188PRTHomo sapiens 2Met Asp Cys Arg Lys Met Ala Arg Phe Ser
Tyr Ser Val Ile Trp Ile1 5 10 15Met Ala Ile Ser Lys Val Phe Glu Leu
Gly Leu Val Ala Gly Leu Gly 20 25 30 His Gln Glu Phe Ala Arg Pro
Ser Arg Gly Tyr Leu Ala Phe Arg Asp 35 40 45Asp Ser Ile Trp Pro Gln
Glu Glu Pro Ala Ile Arg Pro Arg Ser Ser 50 55 60Gln Arg Val Pro Pro
Met Gly Ile Gln His Ser Lys Glu Leu Asn Arg65 70 75 80Thr Cys Cys
Leu Asn Gly Gly Thr Cys Met Leu Gly Ser Phe Cys Ala 85 90 95Cys Pro
Pro Ser Phe Tyr Gly Arg Asn Cys Glu His Asp Val Arg Lys 100 105
110Glu Asn Cys Gly Ser Val Pro His Asp Thr Trp Leu Pro Lys Lys Cys
115 120 125Ser Leu Cys Lys Cys Trp His Gly Gln Leu Arg Cys Phe Pro
Gln Ala 130 135 140Phe Leu Pro Gly Cys Asp Gly Leu Val Met Asp Glu
His Leu Val Ala145 150 155 160Ser Arg Thr Pro Glu Leu Pro Pro Ser
Ala Arg Thr Thr Thr Phe Met 165 170 175Leu Val Gly Ile Cys Leu Ser
Ile Gln Ser Tyr Tyr 180 1853202PRTMus musculus 3Met Arg Ala Asn Ser
Pro Thr Gln Gly Ile Ser Leu Lys Met His Gln1 5 10 15Ala Arg Pro Leu
Phe Leu Val Thr Val Ala Leu Gln Leu Ile Gly Leu 20 25 30Gly Tyr Ser
Tyr Gln Ser Glu Gly Asp Gly Ala Arg Glu Val Ser Asn 35 40 45Ile Leu
Ser Pro Val Ile Pro Gly Thr Thr Leu Asp Arg Thr Leu Ser 50 55 60Asn
Ser Ser Arg Lys Asn Asp Ile Pro Glu Gly Ala Arg Leu Trp Asp65 70 75
80Ser Leu Pro Asp Ser Ser Thr Leu Gly Glu Ser Ala Val Pro Val Ser
85 90 95Arg Cys Cys His Asn Gly Gly Thr Cys Val Leu Gly Ser Phe Cys
Val 100 105 110Cys Pro Ala Tyr Phe Thr Gly Arg Tyr Cys Glu His Asp
Gln Arg Arg 115 120 125Arg Asp Cys Gly Ala Leu Gly His Gly Ala Trp
Thr Leu His Ser Cys 130 135 140Arg Leu Cys Arg Cys Ile Phe Ser Ala
Leu Tyr Cys Leu Pro His Gln145 150 155 160Thr Phe Ser His Cys Asp
Leu Lys Ser Phe Leu Ser Ser Gly Ala Arg 165 170 175Gly Ser Arg Glu
Cys Ser Ile Pro Ser Leu Leu Leu Leu Val Leu Cys 180 185 190Leu Leu
Leu Gln Gly Val Ala Gly Lys Gly 195 2004223PRTHomo sapiens 4Met Thr
Trp Arg His His Val Arg Leu Leu Phe Thr Val Ser Leu Ala1 5 10 15Leu
Gln Ile Ile Asn Leu Gly Asn Ser Tyr Gln Arg Glu Lys His Asn 20 25
30Gly Gly Arg Glu Glu Val Thr Lys Val Ala Thr Gln Lys His Arg Gln
35 40 45Ser Pro Leu Asn Trp Thr Ser Ser His Phe Gly Glu Val Thr Gly
Ser 50 55 60Ala Glu Gly Trp Gly Pro Glu Glu Pro Leu Pro Tyr Ser Arg
Ala Phe65 70 75 80Gly Glu Gly Ala Ser Ala Arg Pro Arg Cys Cys Arg
Asn Gly Gly Thr 85 90 95Cys Val Leu Gly Ser Phe Cys Val Cys Pro Ala
His Phe Thr Gly Arg 100 105 110Tyr Cys Glu His Asp Gln Arg Arg Ser
Glu Cys Gly Ala Leu Glu His 115 120 125Gly Ala Trp Thr Leu Arg Ala
Cys His Leu Cys Arg Cys Ile Phe Gly 130 135 140Ala Leu His Cys Leu
Pro Leu Gln Thr Pro Asp Arg Cys Asp Pro Lys145 150 155 160Asp Phe
Leu Ala Ser His Ala His Gly Pro Ser Ala Gly Gly Ala Pro 165 170
175Ser Leu Leu Leu Leu Leu Pro Cys Ala Leu Leu His Arg Leu Leu Arg
180 185 190Pro Asp Ala Pro Ala His Pro Arg Ser Leu Val Pro Ser Val
Leu Gln 195 200 205Arg Glu Arg Arg Pro Cys Gly Arg Pro Gly Leu Gly
His Arg Leu 210 215 2205190PRTXenopus laevis 5Met Gln Phe Leu Arg
Phe Leu Ala Ile Leu Ile Phe Ser Ala Lys His1 5 10 15Phe Ile Lys His
Cys Lys Gly Glu Thr Cys Met Gly Leu Asn Cys Asn 20 25 30Asp Pro Gly
Leu Leu Glu Ala Ile Lys Ser Asn Thr Ile Asn Gln Leu 35 40 45Leu His
Asp Thr Ile Asn Ala Thr His Gly Lys Ser Pro Ala Lys Ser 50 55 60Thr
Lys Thr Leu Pro Phe Leu Gly Ile Thr Asp Ser Lys Lys Leu Asn65 70 75
80Arg Lys Cys Cys Gln Asn Gly Gly Thr Cys Phe Leu Gly Thr Phe Cys
85 90 95Ile Cys Pro Lys Gln Phe Thr Gly Arg His Cys Glu His Glu Arg
Arg 100 105 110Pro Ala Ser Cys Ser Gly Val Pro His Gly Asp Trp Ile
Thr Gln Gly 115 120 125Cys Leu Leu Cys Arg Cys Val Ser Gly Val Leu
His Cys Phe Lys Pro 130 135 140Glu Ser Glu Asp Cys Asp Val Val His
Glu Lys Asn Met Arg Ser Gly145 150 155 160Val Pro Arg Met Gln Leu
Ser Leu Ile Ile Tyr Cys Phe Leu Thr Ala 165 170 175Asn Leu Phe Tyr
His Ile Val Trp His Leu Asn Ile Gly Leu 180 185
1906190PRTBrachydanio rerio 6Met Thr Ser Gln Leu Phe Gly Phe Leu
Met Phe Ala Val Ile Ile Cys1 5 10 15Gln Ala Val Ser Leu Glu Ser Gly
Cys Glu Gly Ser Glu Cys Val Lys 20 25 30Val Gly Val Ser Gly Lys Pro
Lys Gln Tyr Ala Glu Phe Leu Asn Lys 35 40 45Phe Asn Glu Met Asn Thr
Gln Thr Pro Gln Arg Gln His Arg Asn Ala 50 55 60Glu Ala Ala Leu Pro
Phe Val Gly Leu Thr Gly Val Ala Lys Gln Ser65 70 75 80Arg Thr Cys
Cys Lys Asn Gly Gly Thr Cys Ile Leu Gly Ser Phe Cys 85 90 95Ala Cys
Pro Lys Tyr Phe Thr Gly Arg Ser Cys Glu Tyr Asp Glu Arg 100 105
110Leu Arg Asp Cys Gly Val Ile Pro His Gly Glu Trp Val Gln Lys Gly
115 120 125Cys Ser Tyr Cys Arg Cys Gly Tyr Gly Leu Leu His Cys Phe
Pro His 130 135 140Val Phe Ser Lys Asp Cys Asp Val Phe Ser Lys Asp
Cys Asp Asp Ser145 150 155 160Gln Glu Val Arg Trp His Arg Ser Gly
Ser Leu Arg Thr Leu Ser Ser 165 170 175Thr Ile Val Met Phe Ala Thr
Phe Ile Leu His Arg Leu Leu 180 185 190
* * * * *