title: Positively cooperative sites for drug transport by P-glycoprotein with distinct drug specificities.
abstract: In this paper, we show that P-glycoprotein contains two distinct sites for drug binding and transport, and that, unexpectedly, these sites interact in a positively cooperative manner. The kinetics of transport of rhodamine 123 and Hoechst 33342 in isolated P-glycoprotein-rich plasma membrane vesicles from Chinese hamster ovary CH(R)B30 cells were followed by continuous fluorescence monitoring. Each substrate stimulated P-glycoprotein-mediated transport of the other. Colchicine and quercetin stimulated rhodamine 123 transport and inhibited Hoechst 33342 transport. In contrast, anthracyclines such as daunorubicin and doxorubicin stimulated Hoechst 33342 transport and inhibited rhodamine 123 transport. Vinblastine, actinomycin D, and etoposide inhibited transport of both dyes. The results are consistent with a functional model of P-glycoprotein containing at least two positively cooperative sites (H site and R site) for drug binding and transport. This model is consistent with earlier observations of competitive and non-competitive effects of P-glycoprotein substrates and chemosensitizers. Such a two-site model may be fundamental to multidrug transport by P-glycoprotein, and it may be a feature common to other ATP-dependent transporters belonging to the ATP-binding cassette superfamily.
authors.affiliation: The British Columbia Cancer Research Centre, Vancouver, Canada.
authors.forename: A B
authors.initials: AB
authors.lastname: Shapiro
authors.forename: V
authors.initials: V
authors.lastname: Ling
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism*; D000818:Animals; D001562:Benzimidazoles / Q000378:metabolism*; D001665:Binding Sites; D001692:Biological Transport / Q000187:drug effects; D002460:Cell Line; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D003078:Colchicine / Q000494:pharmacology; D006224:Cricetinae; D003412:Cricetulus; D003609:Dactinomycin / Q000494:pharmacology; D003630:Daunorubicin / Q000494:pharmacology; D004317:Doxorubicin / Q000494:pharmacology; D005047:Etoposide / Q000494:pharmacology; D005453:Fluorescence; D005456:Fluorescent Dyes / Q000378:metabolism; D007700:Kinetics; D008081:Liposomes / Q000378:metabolism; D011485:Protein Binding; D011794:Quercetin / Q000494:pharmacology; D020112:Rhodamine 123; D012235:Rhodamines / Q000378:metabolism / Q000494:pharmacology; D014747:Vinblastine / Q000494:pharmacology
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D001562:Benzimidazoles; D005456:Fluorescent Dyes; D008081:Liposomes; D012235:Rhodamines; D003609:Dactinomycin; D020112:Rhodamine 123; D014747:Vinblastine; D005047:Etoposide; D004317:Doxorubicin; D011794:Quercetin; C017807:bisbenzimide ethoxide trihydrochloride; D003078:Colchicine; D003630:Daunorubicin