FUNCTIONAL-HETEROGENEITY OF COLONIC ADENOCARCINOMA MUCINS FOR INHIBITION OF ENTAMOEBA-HISTOLYTICA ADHERENCE TO TARGET-CELLS

Mucins secreted from the gastrointestinal epithelium form the basis of the adherent mucus layer which is the host's first line of defense ag ainst invasion by Entamoeba histolytica. Galactose and N-acelyl-D-gala ctosamine residues of mucins specifically inhibit binding of the amebi c 170 kDa heavy subunit Gal-lectin to target cells, an absolute prereq uisite for pathogenesis. Herein we characterized the secretory mucins isolated from the human colon and from three human colonic adenocarcin oma cell lines: two with goblet cell-like (LS174T and T84) and one wit h absorptive cell-like morphology (Caco-2). By Northern blot analysis the intestinal mucin genes MUC2 and MUC3 were constitutively expressed by confluent LS174T and Caco-2, cells, whereas T84 cells only transcr ibed MUC2 and not MUC3 mRNA. H-3-glucosamine and H-3-threonine metabol ically labeled proteins separated as high M-r mucins in the void (V-o > 10(6) Da) of Sepharose-4B column chromatography and remained in the stacking gel of SDS-PAGE as depicted by fluorography. All mucin prepar ations contained high amounts of N-acetyl-glucosamine, galactose, N-ac etyl-galactosamine, fucose and sialic acid, saccharides typical of the O-linked carbohydrate side chains, Mucin samples from the human colon and from LS171T and Caco-2 cells inhibited E. histolytica adherence t o chinese hamster ovary cells, whereas mucins from T84 cells did not. These results suggest that genetic heterogeneity and/or posttranslatio nal modification in glycosylation of colonic mucins can affect specifi c epithelial barrier function against intestinal pathogens.