UBIQUITIN-RIBOSOMAL PROTEIN-S27A GENE OVEREXPRESSED IN HUMAN COLORECTAL-CARCINOMA IS AN EARLY GROWTH-RESPONSE GENE

One of the extension proteins on the carboxy terminus of ubiquitin was reported as the ribosomal protein S27a. We have cloned a gene which e ncodes this ubiquitin hybrid protein from a complementary DNA library of a human colon carcinoma cell line. Northern blot analysis of surgic al specimens from colon cancer patients showed that these messenger RN A levels were higher in tumor tissue than in adjacent normal mucosa. F urthermore, to investigate the role of this novel ubiquitin hybrid gen e in cellular growth control, the responsiveness of this gene to serum growth factors was examined. Within 30 min after serum or 12-O-tetrad ecanoylphorbol-13-acetate stimulation, its messenger RNA expression in rat fibroblast cells (Rat 1) was increased. Nuclear runoff transcript ion studies showed that the kinetics of induction of this gene is almo st identical to that of protooncogene c-jun or c-fos, the known early growth response genes. Thus, this ubiquitin hybrid gene appears to be a novel early growth response gene overexpressed in human colon cancer and warrants further studies in the pathogenesis of colorectal carcin oma.