Association of sialyl-Lewis(a) and sialyl-Lewis(x) with MUC-1 apomucin ina pancreatic cancer cell line.

We have shown previously that the mucins of the human pancreatic cancer cell line, SW1990, have both sialyl-Lewis(a) and sialyl-Lewis(x) carbohydrate ligands that are implicated in tumor cell metastasis. In the present study, we undertook to identify the protein core of these mucins. SW1990 mucins that carry sialyl-Lewis(a) and sialyl-Lewis(x) bound to the MUC1 peptide-specific mAb 139H2. Removal of most of the sialic acids from SW1990 mucins by neuraminidase greatly enhanced binding of two other MUC1 peptide specific antibodies, HMFG-2 and SM-3. After removal of sialic acids, most of the mucins rich in sialyl-Lewis(a) and sialyl-Lewis(x) oligosaccharides no longer bound to a DEAE-cellulose column at pH 8.0. These results indicate that at least part of the sialyl-Lewis(a) and sialyl-Lewis(x) in SW1990 cells is associated with the MUC1 polypeptide. Moreover, sialic acids play an important role in determining the net negative charge of sialyl-Lewis(a) and sialyl-Lewis(x) rich mucins and in obscuring MUC1 peptide regions.