Overexpression of M68/DcR3 in human gastrointestinal tract tumors independent of gene amplification and its location in a four-gene cluster

Fas-mediated apoptosis is an important regulator of cell survival, and abno rmalities in this system have been shown to result in a number of human pat hological conditions. A secreted member of the tumor necrosis factor recept or superfamily, DcR3, was recently reported to be amplified in human lung a nd colon cancers as a negative regulator of Fas-mediated apoptosis. We iden tified this gene, which we call M68. M68 genomic DNA, mRNA, and protein lev els were examined in a series of human gastrointestinal tract tumors. Using M68 immunohistochemistry and a scoring system similar to that used for HER -2/neu, we found that M68 protein was overexpressed in 30 of 68 (44%) human adenocarcinomas of the esophagus, stomach, colon, and rectum. Tumors exami ned by Northern blot revealed M68 mRNA highly elevated in a similar fractio n of primary tumors from the same gastrointestinal tract regions, as well a s in the colon adenocarcinoma cell lines SW480 and SW1116. Further, we foun d M68 protein to be overexpressed in a substantial number of tumors in whic h gene amplification could not be detected by fluorescence in situ hybridiz ation or quantitative genomic PCR, suggesting that overexpression of M68 ma y precede amplification in tumors. Finally, we find that M68 lies within a four-gene cluster that includes a novel helicase-like gene (NHL) related to RAD3/ERCC2, a plasma membrane Ras-related GTPase and a member of the stath min family, amplification or overexpression of which may also contribute to cell growth and tumor progression.