MUC1 glycoforms in breast cancer - Cell line T47D as a model for carcinoma-associated alterations of O-glycosylation

A highly immunogenic peptide motif within the tandem repeat domain of MUC1 mucin is assumed to be exposed during development of breast cancer due to altered O-glycosylation. To elucidate the structural aspects of these changes, we have isolated and analysed the integrated or secretory MUC1 glycoforms from carcinoma cell lines or solid tumors and from human milk. The buoyant densities measured in CsCl gradients for MUC1 glycoforms from cancer cells revealed heterogeneity of the physicochemical species and a significant reduction of their carbohydrate contents compared to MUC1 from skim milk. Immunoreactivity patterns of MUC1 glycoforms from tumor or T47D cells exhibited a lack of fucosylated Lewis blood-group-related antigens and the appearance of core-type antigen sialyl-(NeuGl)-TF, Gal beta 1-3(NeuGl alpha 2-6)GalNAc Structural chemistry of MUC1 oligosaccharides demonstrated that the cancer-associated glycoforms carry mainly sialylated trisaccharides NeuAc alpha 2-3Gal beta 1-3GalNAc or NeuAc alpha 2-6(Gal beta 1-3)GalNAc, exhibit a concomitant decrease in the ratio of GlcNAc/GalNAc, a reduction or disappearance of L-fucose, and a partial substitution of N-acetylneuraminic acid by the N-glycolylated variant. On comparison to the secretory MUC1 in human milk, the glycoforms on human milk fat globule membranes showed apparently identical patterns of O-linked oligosaccharides with a preponderance of neutral polylactosamino-glycans. During serum-free cultivation of T47D cells over 4 weeks, the expression of secretory MUC1 glycoforms was inconsistent based on the decreasing contents of sialic acid and on the concomitant increase of immunodetectable TF antigen.