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Abstract
Cripto is a developmental oncoprotein and a member of the epidermal growth factor-Cripto, FRL-1, Cryptic family of extracellular signaling molecules. In addition to having essential functions during embryogenesis, Cripto is highly expressed in tumors and promotes tumorigenesis. During development, Cripto acts as an obligate coreceptor for transforming growth factor β (TGF-β) ligands, including nodals, growth and differentiation factor 1 (GDF1), and GDF3. As an oncogene, Cripto is thought to promote tumor growth via mechanisms including activation of mitogenic signaling pathways and antagonism of activin signaling. Here, we provide evidence supporting a novel mechanism in which Cripto inhibits the tumor suppressor function of TGF-β. Cripto bound TGF-β and reduced the association of TGF-β with its type I receptor, TβRI. Consistent with its ability to block receptor assembly, Cripto suppressed TGF-β signaling in multiple cell types and diminished the cytostatic effects of TGF-β in mammary epithelial cells. Furthermore, targeted disruption of Cripto expression by use of small inhibitory RNA enhanced TGF-β signaling, indicating that endogenous Cripto plays a role in restraining TGF-β responses.
We thank Craig Harrison for important contributions to the early phases of this work. We also thank Sandra Guerra and Dave Dalton for providing assistance in preparing the manuscript.
This work was supported by the Foundation for Medical Research, Inc., the Robert J., Jr., and Helen C. Kleberg Foundation, NIH grant CA107420-01, and the International Human Frontier Science Program Organization.
W. Vale is a senior investigator of the Foundation for Medical Research, Inc.