Biosynthesis of Vicia graminea lectin- and Vicia unijuga lectin-binding glycoproteins in human tumor and nontumor cells and an estimation of its epitope structure

We investigated biosynthesis of Vicia graminea lectin (VGA)- and Vicia unij uga lectin (VUA)-binding (Vgu) glycoproteins, which are human malignant tum or-associated antigens, in cultured human tumor and non-tumor cells by puls e-labeling experiments with [S-35]-methionine, followed by immunoprecipitat ion using immobilized WA, SDS-PAGE and autofluorography. It was shown that Vgu glycoproteins synthesized by tumor cells were 15-30 times greater than those of non-tumor cells. it was also shown that about 40-70% of Vgu glycop roteins synthesized by non-tumor cells were secreted from the cells while m ore than 80% of the antigen synthesized by tumor cells was not secreted, an d that Vgu glycoproteins consisted of multiple molecular species with the s ame epitope. To estimate the epitope structure of Vgu glycoproteins, in pre liminary experiments we prepared sialoglycoproteins and/or sialoglycopeptid es from purified human glycophorin A. Human glycophorins A(M) and A(N) (GPs -A(M) and A(N)) were treated with Clostridium perfringens neuraminidase to remove all sialic acid residues linked to carbohydrate chains, with Newcast le disease virus (NDV) to remove alpha 2-3 linked sialic acid residues, and by Edman's degradation to eliminate N-terminal amino acid of GP-As. Partia l or complete desialylation reactions resulted in disappearance of the reac tivity of GP-A(M) and GP-A(N) with corresponding antisera and in appearance of reactivities with WA and VGA. Elimination of N-terminal amino acid of G P-As also resulted in appearance of reactivities with WA. These results sho w that sialoglycoproteins with similar serological properties of Vgu glycop rotein could be prepared from GP-As, and suggest that the epitope structure of Vgu glycoprotein may be related to the MN blood type-epitope structure and its sialic acid residues at N-terminal moiety of GP-As.