Blood group antigen synthesis and degradation in normal and cancerous colonic tissues.

ABH antigens are expressed by colonic epithelial cells throughout the colon during fetal life but only in proximal segments during adulthood. Malignant and premalignant colonic tumors frequently exhibit ABH reappearance (distal lesions) or ABH deletion (proximal lesions) and occasionally express incompatible A or B substances. Mechanisms governing these developmental and cancer-associated alterations are unknown. Therefore, experiments were performed to assess the activities of biosynthetic (glycosyltransferase) and degradative (glycosidase) enzymes in normal and cancerous tissues of the proximal and distal colon. In normal colonic mucosa, A, B, and H transferase activities were similar in proximal and distal segments. Analysis of enzyme substrate affinities and product characterization confirmed that the ABH transferases in colonic tissues were similar to the gene-specified transferases in human serum. Glycosidase enzyme activities were also comparable in proximal and distal normal colon. Cancers had lower A and B transferase but similar H transferase activities compared with paired normal mucosa. Thus, the absence of ABH antigen expression in normal distal colon is not caused by insufficient glycosyltransferase activity or excessive glycosidase activity.