UBIQUITIN FUSION PROTEINS ARE OVEREXPRESSED IN COLON-CANCER BUT NOT IN GASTRIC-CANCER

A cDNA clone (AF3) encoding the ubiquitin A gene 52 amino acid extensi on fusion protein (UbA52) was isolated from a subtracted cDNA library of human colorectal carcinoma minus adjacent normal mucosa. In Norther n hybridization the mRNA signal for UbA52 was greater in surgical samp les of colonic carcinoma (T) than in paired adjacent normal (N) tissue s in 24 of 29 cases (T/N = 3.4 +/- 0.5 P < 0.01). An oligonucleotide p robe specific for only the 52 amino acid extension confirmed the overe xpression of UbA52. In contrast, there was no overexpression of UbA52 mRNA in gastric cancer samples (n = 7, T/N = 1.0 +/- 0.3). The mRNA of several ribosomal proteins, and of another ubiquitin A gene fusion pr otein, UbA80, with an 80 amino acid extension of ribosomal protein S27 a, have been reported to be over-expressed in colon cancer, but not as yet at the protein level. Using rabbit antisera to the ribosomal prot ein component S27a we demonstrate over-expression of S27a at the prote in level in colonic (n = 5), but not gastric (n = 6) carcinomas. There fore it is likely that both UbA80 and UbA52 are overexpressed in colon cancer, but not in gastric cancer.