The mucin carbohydrate epitope sialyl-Lex, detected with the monoclonal antibody AM-3, is strongly overexpressed in >90% of human colon carcinomas. We show here that in colon carcinoma one of the mucin cores bearing the sialyl-Lex group is MUC-1, whereas sialy-Lex 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 tissue are 60–180% of those in normal tissue. Two other carbohydrate epitopes located on MUC-1 in mucins from normal and tumor tissue have also been characterized. In contrast to sialyl-Lex, their expression on MUC-1 is variable and does not correlate with the malignant transformation of colonic mucosa. The transfer of the sialyl-Lex group onto the MUC-1 core contributes to the colon carcinoma-associated overexpression of the sialyl-Lex epitope.
This work was supported by the Deutsche Forschungsgemeinschaft Projects Ha 152/3-1 and Ha 152/5-1 and the Deutsche Krebshilfe Project No. W 17/92/Ri2.