ASSOCIATION OF SIALYL-LEWIS(A) AND SIALYL-LEWIS(X) WITH MUC-1 APOMUCIN IN A PANCREATIC-CANCER CELL-LINE

We have shown previously that the mucins of the human pancreatic cance r cell line, SW1990, have both sialyl-Lewis(a) and sialyl-Lewis(x) car bohydrate ligands that are implicated in tumor cell metastasis. In the present study, we undertook to identify the protein core of these muc ins. SW1990 mucins that carry sialyl-Lewis(a) and sialyl-Lewis(x) boun d to the MUC1 peptide-specific mAb 139H2. Removal of most of the siali c acids from SW1990 mucins by neuraminidase greatly enhanced binding o f two other MUC1 peptide specific antibodies, HMFG-2 and SM-3. After r emoval 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 sia lyl-Lewis(a) and sialyl-Lewis(x) in SW1990 cells is associated with th e MUC1 polypeptide. Moreover, sialic acids play an important role in d etermining the net negative charge of siaiyl-Lewis(a) and sialyl-Lewis (x) rich mucins and in obscuring MUC1 peptide regions.