Plasma membrane-associated antigens on tumor cells derived from transitional-cell carcinoma of the human urinary bladder. II. Identification at the molecular level of plasma membrane-associated antigens.

The surface proteins of seven human cell lines (three bladder carcinomas (TCC), two normal urothelial lines, one colon carcinoma, and one malignant melanoma) were labelled with 125I by the glucose oxidase-lactoperoxidase technique. Plasma membranes of the cells were isolated and analysed by sodium dodecyl sulphate electrophoresis (SDS-PAGE). When analysed under reducing conditions by staining with protein stain, approximately 45 distinct membrane polypeptides were detected in all membrane preparations. Although the banding patterns for all cell lines were very similar, a 23 K and a 110 K band were only seen in the five unrothelial lines. When the same gels were analysed by autoradiography, between 13 and 17 bands were detected for each of the cell lines. However, in this case, analysis revealed individual and stable banding profiles for each. One 180 K band and one 100 K band were only seen in the autoradiographs of the two normal lines but not in those of the tumor membranes. Analysis under non-reducing conditions gave similar results. The antigenicity of these surface components was analysed by incubating detergent extracts of surface-iodinated cells with IgG from a rabbit anti-TCC serum, absorbed with fetal bovine serum and bound to protein A (from Staphylococcus aureus) on a matrix of Sepharose 4B. Analysis of the eluates by autoradiography after SDS-PAGE under reducing conditions showed that many of the labelled polypeptides were antigenic and shared by all seven cell lines. Analysis of eluates from IgG preparations, exhaustively absorbed with human spleen, revealed the presence of at least one antigenic 110 K polypeptide confined to the membrane of the urothelial cells. Preparation of a rabbit antiserum to this 110 K component, isolated from one of the TCC-lines and tested by ADCC, indicated that this polypeptide constitutes an important surface antigen, present on urothelial cells of both TCC- and normal origin but absent from the colon carcinoma and malignant melanoma used for control.