title: Arsenic transport by the human multidrug resistance protein 1 (MRP1/ABCC1). Evidence that a tri-glutathione conjugate is required.
abstract: Inorganic arsenic is an established human carcinogen, but its metabolism is incompletely defined. The ATP binding cassette protein, multidrug resistance protein (MRP1/ABCC1), transports conjugated organic anions (e.g. leukotriene C(4)) and also co-transports certain unmodified xenobiotics (e.g. vincristine) with glutathione (GSH). MRP1 also confers resistance to arsenic in association with GSH; however, the mechanism and the species of arsenic transported are unknown. Using membrane vesicles prepared from the MRP1-overexpressing lung cancer cell line, H69AR, we found that MRP1 transports arsenite (As(III)) only in the presence of GSH but does not transport arsenate (As(V)) (with or without GSH). The non-reducing GSH analogs L-gamma-glutamyl-L-alpha-aminobutyryl glycine and S-methyl GSH did not support As(III) transport, indicating that the free thiol group of GSH is required. GSH-dependent transport of As(III) was 2-fold higher at pH 6.5-7 than at a more basic pH, consistent with the formation and transport of the acid-stable arsenic triglutathione (As(GS)(3)). Immunoblot analysis of H69AR vesicles revealed the unexpected membrane association of GSH S-transferase P1-1 (GSTP1-1). Membrane vesicles from an MRP1-transfected HeLa cell line lacking membrane-associated GSTP1-1 did not transport As(III) even in the presence of GSH but did transport synthetic As(GS)(3). The addition of exogenous GSTP1-1 to HeLa-MRP1 vesicles resulted in GSH-dependent As(III) transport. The apparent K(m) of As(GS)(3) for MRP1 was 0.32 microM, suggesting a remarkably high relative affinity. As(GS)(3) transport by MRP1 was osmotically sensitive and was inhibited by several conjugated organic anions (MRP1 substrates) as well as the metalloid antimonite (K(i) 2.8 microM). As(GS)(3) transport experiments using MRP1 mutants with substrate specificities differing from wild-type MRP1 suggested a commonality in the substrate binding pockets of As(GS)(3) and leukotriene C(4). Finally, human MRP2 also transported As(GS)(3). In conclusion, MRP1 transports inorganic arsenic as a tri-GSH conjugate, and GSTP1-1 may have a synergistic role in this process.
authors.affiliation: Inorganic Carcinogenesis Section, Laboratory of Comparative Carcinogenesis, National Cancer Institute at National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina 27709, USA.
authors.forename: Elaine M
authors.initials: EM
authors.lastname: Leslie
authors.forename: Anass
authors.initials: A
authors.lastname: Haimeur
authors.forename: Michael P
authors.initials: MP
authors.lastname: Waalkes
mesh_terms: D000818:Animals; D000838:Anions; D000911:Antibodies, Monoclonal / Q000737:chemistry / Q000378:metabolism; D001151:Arsenic / Q000378:metabolism / Q000493:pharmacokinetics*; D001224:Aspartic Acid / Q000737:chemistry; D001692:Biological Transport; D019256:Cadmium Chloride / Q000494:pharmacology; D002273:Carcinogens; D002460:Cell Line; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004351:Drug Resistance; D005822:Genetic Vectors; D005978:Glutathione / Q000378:metabolism*; D005982:Glutathione Transferase / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D006863:Hydrogen-Ion Concentration; D015151:Immunoblotting; D007700:Kinetics; D007930:Leucine / Q000737:chemistry; D008239:Lysine / Q000737:chemistry; D051379:Mice; D018613:Microscopy, Confocal; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000378:metabolism*; D009154:Mutation; D009842:Oligopeptides / Q000494:pharmacology; D009995:Osmosis; D020033:Protein Isoforms; D013379:Substrate Specificity; D013438:Sulfhydryl Compounds; D013997:Time Factors; D014162:Transfection
chemical_list: D000838:Anions; D000911:Antibodies, Monoclonal; D001151:Arsenic; D001224:Aspartic Acid; D019256:Cadmium Chloride; D002273:Carcinogens; D005978:Glutathione; D005982:Glutathione Transferase; D007930:Leucine; D008239:Lysine; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D009842:Oligopeptides; D020033:Protein Isoforms; D013438:Sulfhydryl Compounds; C000715087:ABCC2 protein, human; C016632:ophthalmic acid; C421109:multidrug resistance-associated protein 1