D-Galactosyltransferase and its endogenous substrates in chick embryo fibroblasts transformed by rous sarcoma virus

Abstract

UDP= d-galactose: 2-acetamido-2-deoxy-β- d-glucopyranosyl 4=β- d-galactosyltransferase (GalTase) activity was purified, from primary chick embryo fibroblast (CEF) transformed by a temperature-sensitive, Rous sarcoma virus mutant (CEF-RSV), by chromatography on an affinity resin prepared with monoclonal antibodies to GalTase. Cellular glycopeptides from CEF, as well as CEF-RSV, maintained at permissive (37°) [CEF-RSV (37°)] and nonpermissive temperatures (41°) [CEF-RSV (41°)], were solubilized and galactosylated in vitro by incubation with purified GalTase substrates, composed of at least six discrete complex glycopeptides having bi- to tetra-antennary structures. The glycopeptides isolated from transformed cells, CEF-RSV (37°), included the six types observed in nontransformed cells, but demonstrated alterations in their relative amounts, including an increase in the content of a glycopeptide containing 3 mannose and 4 glucosamine residues. Furthermore, two additional complex-type glycopeptides were isolated from CEF- but demonstrated alterations in their relative amounts, including an increase in the content of a glycopeptide containing 3 mannose and 4 glucosamine residues. Furthermore, two additional complex type glycopeptides were isolated from CEF-RSV (37°). These malignant transformation-related glycopeptides were partially characterized and found to represent tri- and tetra-antennary complex glycopeptides. Endogenous galactosylation appeared to have occurred in a branched, nonspecific manner in these transformed cell-derived glycopeptides. These findings indicate that transformed cells may contain a greater preponderance of more highly branched, complex oligosaccharides which are randomly galactosylated at non-reducing termini by cellular GalTase.