Moreover, the 59-region of TMEFF2 gene is frequently hypermethylated in some cancers, suggesting a possible tumor suppressor role of TMEFF2 in these cancers. Platelet-derived growth factors not only play important roles in developmental and physiological processes, but also are directly Everolimus implicated in human cancer and other proliferative disorders. The human genome contains four PDGF ligands, PDGF-A, B, C and D, and two receptors, PDGFRa and PDGFRb All PDGFs can form functional disulfide-linked homodimers, while only PDGF-A and B have been shown to form functional heterodimers. PDGFRs also function as homo- and hetero-dimers that differ in their affinities to different PDGF dimers. The a subunit of PDGFR has been shown to bind the PDGF-A, B and C chains, whereas the b subunit is believed to bind only the B and D chains. The biological responses induced by the different PDGF ligands depend on the relative numbers of the receptor subunits on a given cell type and the specific PDGF dimers present. Follistatin module-containing proteins have been previously shown to be able to bind and modulate the function of a variety of growth factors including members of the transforming growth factor beta . To date, however, no binding partner has been reported for TMEFF2. In this report, we have identified PDGF-AA as a growth factor that interacts with TMEFF2. Moreover, we show that the extracellular domain of TMEFF2 interferes with PDGF-AA�Cstimulated fibroblast proliferation in a dose�Cdependent manner. Our data provide the first evidence that TMEFF2 can function to regulate PDGF signaling, and give new mechanistic insights into the seemingly conflicting roles of TMEFF2 in human cancers. In addition, we show for the first time that the expression of TMEFF2 is downregulated in glioma and several other cancers and that this downregulation correlates with DNA methylation. Together these data suggest an important role of TMEFF2 in the development and progression of human cancers. We next examined the effect of TMEFF2-ECD on PDGF stimulated proliferation. The murine fibroblast cell line NR6 expresses both PDGF receptors a and b, and exhibits dosedependent proliferation in response to PDGF-AA or PDGF-AB as measured by BrdU incorporation. When 10 ng/ml PDGF-AA was added in the presence of increasing concentrations of Fc-tagged TECD, BrdU incorporation was inhibited in a dosedependent INCB18424 abmole bioscience manner at concentrations between 0.6 and 2,000 ng/ ml of TECD-Fc. This effect was similar to that of sRa which also inhibited PDGF-AA�Cinduced BrdU incorporation at a similar concentration range, albeit with a slightly higher efficiency. PDGF-AB�Cinduced BrdU incorporation, on the other hand, was not affected by TECD-Fc under the same conditions.