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 abnormalities in this system have been shown to result in a number of human pathological conditions. A secreted member of the tumor necrosis factor receptor superfamily, DcR3, was recently reported to be amplified in human lung and colon cancers as a negative regulator of Fas-mediated apoptosis. We identified this gene, which we call M68. M68 genomic DNA, mRNA, and protein levels 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 examined by Northern blot revealed M68 mRNA highly elevated in a similar fraction of primary tumors from the same gastrointestinal tract regions, as well as in the colon adenocarcinoma cell lines SW480 and SW1116. Further, we found M68 protein to be overexpressed in a substantial number of tumors in which gene amplification could not be detected by fluorescence in situ hybridization or quantitative genomic PCR, suggesting that overexpression of M68 may 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 stathmin family, amplification or overexpression of which may also contribute to cell growth and tumor progression.