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 unijuga lectin (VUA)-binding (Vgu) glycoproteins, which are human malignant tumor-associated antigens, in cultured human tumor and non-tumor cells by pulse-labeling experiments with [35S]-methionine, followed by immunoprecipitation using immobilized VUA, 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 glycoproteins synthesized by non-tumor cells were secreted from the cells while more than 80% of the antigen synthesized by tumor cells was not secreted, and that Vgu glycoproteins consisted of multiple molecular species with the same epitope. To estimate the epitope structure of Vgu glycoproteins, in preliminary experiments we prepared sialoglycoproteins and/or sialoglycopeptides 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 Newcastle disease virus (NDV) to remove alpha2-3 linked sialic acid residues, and by Edman's degradation to eliminate N-terminal amino acid of GP-As. Partial or complete desialylation reactions resulted in disappearance of the reactivity of GP-A(M) and GP-A(N) with corresponding antisera and in appearance of reactivities with VUA and VGA. Elimination of N-terminal amino acid of GP-As also resulted in appearance of reactivities with VUA. These results show that sialoglycoproteins with similar serological properties of Vgu glycoprotein 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.