Multiple Forms of Intracellular and Secreted Mucins in a Pancreatic Cancer Cell Line

Mucins have been implicated in circumventing the defenses of the body against tumorigenesis. A better understanding of the structures of mucins may assist in the development of new therapeutic approaches. Monoclonal antibody Ea6, developed against mucins purified from xenografts of the pancreatic cancer cell line SW1990, was used to identify a new type of pancreatic cancer mucin. The following characteristics suggest that Ea6 antibody reacts with the core structure of O-linked oligosaccharides, the Tn antigen (N-acetylgalactosamine-serine/threonine): (a) increased reactivity with ovine and bovine submaxillary mucins after desialylation; (b) reactivity was inhibitable by N-acetylgalactosamine; and (c) no reactivity with blood group A oligosaccharides. Ea6 mucins from cultured SW1990 cells had lower buoyant densities (1.36 versus 1.44 g/ml) than mucins identified by another monoclonal antibody directed against SW1990 mucins, SPan-1, and were less acidic. High density and molecular mass (> or = 400 kD) secreted antigens were unaffected by sulfhydryl bond reduction. After partial deglycosylation secreted SPan-1 antigens reacted with MUC1 peptide specific antibodies, SM-3 and HMFG-2, as well as polyclonal antisera directed against deglycosylated xenograft mucins. However, Ea6 antigens did not. SW1990 cytosol also contained SPan-1 antigens with apparent molecular weights of 160,000 and 210,000 and low buoyant densities (< or = 1.22 g/ml). These reacted with monoclonal antibodies specific for the MUC1 apomucin with no prior treatment. No Ea6 reactivity was detected with this fraction. These results suggest that Ea6 antibody identifies a new population of mucins that is distinct from SPan-1 mucins.