Cell surface glycosylation and characterization of a differentially expressed glycoprotein in metastatic and non metastatic cell lines of the rat BSp73 tumor

Abstract

The highly (ASML) and non metastatic (AS) variants of the rat tumor BSp73 were compared with respect to cell surface carbohydrate proteins. Fluorescence labelling with lectins (ConA, MPA, PNA, SBA, UEA-I, WGA) revealed a differentiated carbohydrate pattern at the cell surface of these cell lines. The highly metastatic variant was significantly more glycosylated with respect to galactosyl, mannosyl and N-acetylgalactosylamine residues; fucosyl residues were exclusively expressed in the metastatic variant. Examination of isolated plasma membrane fractions showed quantitative differences with respect to glycosylated proteins separated on polyacrylamide gels. A 30 kDa glycoprotein (GP30-ASML) dominant in the metastatic variant was further characterized. Various detergents (CHAPS, Nonidet, SDS, Triton X-100) and urea extracted it exclusively from the highly metastatic variant. GP30-ASML is a predominantly O-glycosylated single polypeptide chain with terminal N-acetylgalactosamine and galactosyl residues; its molecular weight determined by SDS-PAGE is 30 kDa and its isoelectric point is 7.8. Immunofluorescence localization experiments with monoclonal antibodies specific for GP30-ASML and polyclonal antibodies raised against GP30-ASML showed this protein at the cell surface and in the lysosomal compartment of both cell lines; exclusively in the non metastatic variant it was also found in the nuclear membrane. The function of this protein is still unknown.