Biochemical characterization and tissue distribution of the Cora antigen, a cell surface glycoprotein differentially expressed on malignant and benign gastrointestinal epithelia.

A monoclonal antibody designated Cora was isolated which discriminates between malignant and benign colon epithelium. It identifies a novel, variably glycosylated membrane glycoprotein. Expression of the Cora antigen was shown to be characteristic for gastrointestinal carcinomas (100% of tested colorectal carcinomas, 70% of tested gastric carcinomas) but could not be detected on normal gastrointestinal tissues using histochemical methods on frozen tissue sections. An extensive survey of normal tissues revealed that the Cora antigen has a very restricted distribution pattern, being detected only on alveoli of the lung, granulocytes, and bone marrow. Polyacrylamide gel electrophoresis of immunoprecipitates prepared from [35S]methionine, 125I, or [3H]glucosamine labeled colon carcinoma cell lines showed that the Cora antigen consists of a group of glycoproteins ranging in apparent molecular weight from 75,000 to 95,000. Following treatment with neuraminidase, the apparent molecular weights were reduced (65,000 to 85,000) but the size heterogeneity remained. Culturing the cells in the presence of tunicamycin, which inhibits N-linked glycosylation, removed this heterogeneity and under these conditions monoclonal antibody Cora precipitated a major band with an apparent molecular weight of 33,000. Because this monoclonal antibody can distinguish between normal and malignant gastrointestinal epithelia, expression of the Cora antigen may be associated with the process of malignant transformation in this tissue.