MUCINS (MUC1 AND MUC3) OF GASTROINTESTINAL AND BREAST EPITHELIA REVEAL DIFFERENT AND HETEROGENEOUS TUMOR-ASSOCIATED ABERRATIONS IN GLYCOSYLATION

In a comprehensive study, we examined the expression of the membrane a nd secretory mucins MUC1 and MUC3, respectively, in normal and neoplas tic gastrointestinal and breast epithelia before and after specific al terations of their glycan structures by neuraminidase, a-fucosidase, o r carbohydrate-specific periodate oxidation. MUC1 mRNA was also identi fied in normal colorectal tissues by in situ hybridization. The data r evealed that normal colorectal epithelia express both MUC1 mKNA and pr otein, which were detectable after periodate oxidation with all tested MUC1-specific antibodies. During tumorigenesis in the colon, MUC1 bec ame recognizable without periodate treatment concomitantly with highly dysplastic lesions and the malignant state. In the breast, in which M UC1 is detectable with most antibodies in normal epithelium as well as in carcinomas, staining could be enhanced by pretreatment with period ate and casually by enzyme treatments. MUC3 was detectable in normal a nd neoplastic colorectal tissues and was more intensely stained after periodate oxidation. It was absent in normal breast even after pretrea tment but was expressed in seven of 20 breast carcinomas. Therefore, i ncomplete glycosylation, abnormal distribution, and ectopic expression of mucins are characteristics of malignancy. Periodate oxidation may be widely applicable to immunohistochemistry for examining changes in glycosylation and for detecting antigens masked by glycans.