Cell surface sialylation of glycoproteins and glycosphingolipids in cultured metastatic variant RNA-virus transformed non-producer BALB/c 3T3 cell lines

Abstract

The sialic acid composition and the display of cell surface sialyl components of several metastatic variant RNA-virus-transformed non-producer BALB/c 3T3 have been studied in culture. The following observations have been made concerning the sialyl components in these lines: (1) the compositions of whole-cell total, protein-bound and lipid-bound sialic acid were not appreciably different; (2) the surface sialic acid studied using the neuraminidase-galactose oxidase method and metabolic labelling followed by neuraminidase hydrolysis showed a positive correlation with the metastatic properties of these lines; (3) the degree of surface sialylation determined by galactose oxidase--sodium borotritide labelling of neuraminidase-treated and untreated cells revealed that 44--89% of exposed galactose and/or N-acetyl galactosamine residues of total cell-surface saccharides were sialylated in highly and intermediately metastatic lines as compared with 11-30% in the poorly and non-metastatic lines; (4) the cell surface glycoproteins and glycosphingolipids contributed equally well in their degree of sialylation and there was a positive correlation with the metastatic properties of the cells in vivo; (5) the cell surface proteins labelled by the lactoperoxidase-catalyzed iodination technique, followed by gel electrophoresis, showed some minor differences between metastatic variant lines. However, glycoproteins detected by the galactose oxidase labelling of neuraminidase-treated and untreated cells showed major differences in composition between the metastatic variant lines. The study of four highly metastatic lines has shown that the cells of these lines were enriched in several sialyl-glycoproteins, whereas three non tumorigenic lines and two poorly metastatic or non-metastatic lines contained unsialylated glycoproteins. The results indicate an enhancement of the degree of sialylation of surface glycoconjugates accompanying the metastatic process in RNA-virus-transformed mouse lines.