Abstract
Cripto is a developmental oncoprotein that signals via mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK), phosphatidylinositol 3-kinase (PI3K)/Akt and Smad2/3 pathways. However, the molecular basis for Cripto coupling to these pathways during embryogenesis and tumorigenesis is not fully understood. In this regard, we recently demonstrated that Cripto forms a cell surface complex with the HSP70 family member glucose-regulated protein-78 (GRP78). Here, we provide novel functional evidence demonstrating that cell surface GRP78 is a necessary mediator of Cripto signaling in human tumor, mammary epithelial and embryonic stem cells. We show that targeted disruption of the cell surface Cripto/GRP78 complex using shRNAs or GRP78 immunoneutralization precludes Cripto activation of MAPK/PI3K pathways and modulation of activin-A, activin-B, Nodal and transforming growth factor-beta1 signaling. We further demonstrate that blockade of Cripto binding to cell surface GRP78 prevents Cripto from increasing cellular proliferation, downregulating E-Cadherin, decreasing cell adhesion and promoting pro-proliferative responses to activin-A and Nodal. Thus, disrupting the Cripto/GRP78 binding interface blocks oncogenic Cripto signaling and may have important therapeutic value in the treatment of cancer.
Publication types
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Research Support, N.I.H., Extramural
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Research Support, Non-U.S. Gov't
MeSH terms
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Activins / pharmacology
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Antibodies / pharmacology
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Blotting, Western
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Cadherins / metabolism
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Cell Adhesion / drug effects
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Cell Line
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Cell Line, Tumor
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Cell Proliferation / drug effects
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Endoplasmic Reticulum Chaperone BiP
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Epidermal Growth Factor / genetics
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Epidermal Growth Factor / metabolism*
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GPI-Linked Proteins
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Heat-Shock Proteins / genetics
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Heat-Shock Proteins / immunology
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Heat-Shock Proteins / metabolism*
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Humans
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Immunoprecipitation
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Intercellular Signaling Peptides and Proteins
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Luciferases / genetics
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Luciferases / metabolism
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Membrane Glycoproteins / genetics
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Membrane Glycoproteins / metabolism*
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Microscopy, Confocal
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Mitogen-Activated Protein Kinases / metabolism*
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Models, Biological
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Neoplasm Proteins / genetics
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Neoplasm Proteins / metabolism*
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Phosphatidylinositol 3-Kinases / metabolism*
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Protein Binding / drug effects
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RNA, Small Interfering / genetics
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Radioligand Assay
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Signal Transduction / drug effects
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Signal Transduction / physiology*
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Smad Proteins / metabolism*
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Smad2 Protein / metabolism
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Smad3 Protein / metabolism
Substances
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Antibodies
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Cadherins
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Endoplasmic Reticulum Chaperone BiP
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GPI-Linked Proteins
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HSPA5 protein, human
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Heat-Shock Proteins
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Intercellular Signaling Peptides and Proteins
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Membrane Glycoproteins
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Neoplasm Proteins
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RNA, Small Interfering
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SMAD2 protein, human
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SMAD3 protein, human
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Smad Proteins
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Smad2 Protein
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Smad3 Protein
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TDGF1 protein, human
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activin A
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Activins
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Epidermal Growth Factor
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Luciferases
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Mitogen-Activated Protein Kinases