A simple technique for cell surface radioactive labeling of human and animal neoplastic cells: reductive methylation with formaldehyde and tritiated borohydride.

Avian sarcoma virus-, or 3,4-benzopyrene-transformed cultured rat cells and human leukemia or lymphoblastoid cell lines were radiolabeled by reductive methylation with formaldehyde and tritiated sodium borohydride--an application of a known technique for radiolabeling of soluble proteins. Optimal conditions for tritium incorporation into cell proteins with the aid of this technique were ascertained. Analysis of cell proteins tritium radiolabeled with the aid of this technique by acrylamide electrophoresis or by two-dimensional electrophoretic analysis allowed to disclose typical transformation-associated alterations in oncovirus-, or chemical carcinogen-transformed cells, as well as cell type-associated protein patterns in examined lymphoid cell lines. An individual protein (class II MHC antigen) radiolabeled by this technique has been identified as bimolecular complex p30,35 by immunoprecipitation with a monoclonal antibody recognizing this antigen; electrophoretic properties of immunoprecipitated antigen were identical to those observed after immunoprecipitation of the same antigen radiolabeled by sodium periodate/tritiated borohydride glycoprotein radiolabeling.