ALTERED GLYCOSYLATION OF THE MUC-1 PROTEIN CORE CONTRIBUTES TO THE COLON CARCINOMA-ASSOCIATED INCREASE OF MUCIN-BOUND SIALYL-LEWIS(X) EXPRESSION

The mucin carbohydrate epitope sialyl-Le(x), detected with the monoclo nal antibody AM-3, is strongly overexpressed in >90% of human colon ca rcinomas. We show here that in colon carcinoma one of the mucin cores bearing the sialyl-Le(x) group is MUC-1, whereas sialyl-Le(x) present in normal colon is not detectable on MUC-1. The amounts of MUC-1 core detectable with the monoclonal antibody BC3 in extracts of tumor tissu e are 60-180% of those in normal tissue. Two other carbohydrate epitop es located on MUC-1 in mucins from normal and tumor tissue have also b een characterized. In contrast to sialyl-Le(x), their expression on MU C-1 is variable and does not correlate with the malignant transformati on of colonic mucosa. The transfer of the sialyl-Le(x) group onto the MUC-1 core contributes to the colon carcinoma-associated overexpressio n of the sialyl-Le(x) epitope.