Characterization of monoclonal antibodies recognizing a Mr 180,000 P-glycoprotein: differential expression of the Mr 180,000 and Mr 170,000 P-glycoproteins in multidrug-resistant human tumor cells.

P-glycoprotein is a plasma membrane protein believed to mediate resistance to natural product drugs such as vincristine, Adriamycin, and actinomycin D. To facilitate the study of human P-glycoprotein, monoclonal antibodies (designated HYB-612, HYB-241, and HYB-195) were raised against vincristine-resistant human neuroblastoma (SH-SY5Y/VCR) cells. The antibodies recognize a Mr 180,000 plasma membrane phosphoglycoprotein produced in increased amounts in SH-SY5Y/VCR as well as in vincristine-resistant human neuroepithelioma (MC-IXC/VCR), vinblastine-resistant human leukemia (CEM/VLB100), and actinomycin D- or vincristine-resistant Chinese hamster (DC-3F/AD X and DC-3F/VCRd-5L) cells, as compared to control cells. Radioimmunoprecipitation of proteins in cells metabolically labeled with [35S]methionine, 32Pi, or [3H]glucosamine and Western transfer procedures were used for these studies. Characterization of the HYB-612 or HYB-241 antigen by destructive degradation produced a pattern of results typical of a conformation-dependent protein epitope. HYB-612 recognizes complexes of the Mr 180,000 antigen with an iodinated photoaffinity analogue of vinblastine or with tritiated azidopine. Furthermore, pretreatment of MC-IXC and MC-IXC/VCR cells with HYB-612 or HYB-241 before measurement of tritium-labeled actinomycin D or vincristine uptake increases the amount of drug accumulation in resistant, but not in sensitive, cells. Of importance is the fact that the Mr 180,000 protein is expressed in cells which also contain a Mr 170,000 P-glycoprotein. The relative amounts of the Mr 180,000 and 170,000 species vary from one drug-resistant cell line to another. Evidence that the Mr 180,000 protein is a P-glycoprotein and that there is a conserved complex pattern of resistance-related surface proteins in multidrug-resistant cells is presented in this report.