Study of Cancer-Associated Colonic Mucin

Boland, Clement

Abstract

The mucins present in colon cancer appear to be abnormally glycosylated compared to those found in the normal colon. Cancer-associated mucins have been defined immunologically and histochemically, however relatively little is known regarding the biochemical structures of cancer-associated mucins or the mechanisms leading to their synthesis. Cancer-associated mucins have been found in premalignant colonic lesions in the human and animal models of cancer; additional diversity in mucin structure appears in metastatic colorectal cancer. The plan of this proposal is to isolate mucins from specimens of normal human colon and from a mucin-producing human colon cancer cell line. The carbohydrate portion of the mucins (oligosaccharides) will be cleaved from the mucins and separated into monospecific peaks. The oligosaccharides will be characterized using nuclear magnetic resonance and other techniques to determine the differences in expression of oligosaccharide structures between the normal and cancerous colon. The enzymes responsible for generating the diversity of carbohydrate structure in colonic mucins are membrane-bound glycosyltransferase. Using newly available substrates for the precise measurement of glycosyltransferase activity, the ability to synthesize a variety of """"""""core oligosaccharide structures"""""""" will be investigated in membrane preparations from normal and malignant colons. It will be determined whether the abnormal glycosylation of cancer-associated mucins is due to the deletion of certain oligosaccharide chain-elongating enzymes, or to the synthesis of abnormal core structures that do not serve as appropriate acceptors for additional glycosylation. After using the cultured cell line for in-depth structural analysis of carbohydrate structures, the relative expression of cancer- associated oligosaccharides will be sought in individual specimens of colorectal cancer, and related to such variable biological behaviors as tumor cell differentiation, invasiveness, and ability to metastasize. These human studies will be supplemented by animal models of colon cancer with differing biological behavior, such as increasing metastatic potential, and the ability to give rise to peritoneal carcinomatosis. The long term objectives of this research are to understand the process of abnormal glycosylation that occurs in tumor cells, and to relate the diversity of abnormal glycosylation to the different behaviors observed among individual tumors.