ATP-dependent transport of aflatoxin B1 and its glutathione conjugates by the product of the multidrug resistance protein (MRP) gene.
Glutathione-S-transferase-catalyzed conjugation of glutathione (GSH) to aflatoxin B1-8,9-epoxide plays an important role in preventing binding of this ultimate carcinogen to target macromolecules. Once formed, the aflatoxin B1-epoxide-GSH conjugates are actively extruded from the cell by an unidentified ATP-dependent export pump or pumps. Two possible candidates for this GSH conjugate pump are the 190-kDa multidrug resistance protein (MRP) and the 170-kDa P-glycoprotein. Both proteins belong to the ATP-binding cassette superfamily of transmembrane transport proteins and confer resistance to a similar spectrum of natural-product drugs. Using membrane vesicles from MRP-transfected cells, we found that MRP transports GSH conjugates of both the endo-isomers and exo-isomers of aflatoxin B1-8,9-epoxide in an ATP-dependent, osmotically sensitive manner (V(max) = 180 pmol/mg/min, K(m) = 189 nM). Membrane vesicles from P-glycoprotein-overexpressing cells showed very low levels of transport. MRP-mediated transport was inhibited by an MRP-specific monoclonal antibody and by a variety of GSH derivatives and cholestatic steroid glucuronides. ATP-dependent transport of unmodified aflatoxin B1 by MRP-enriched membrane vesicles was low but markedly enhanced in the presence of 5 mM GSH, even though GSH conjugates of aflatoxin B1 were not formed by the vesicles. These data demonstrate that MRP is capable of energy-dependent transport of aflatoxin B1 and its GSH conjugates and suggest a potential protective role for MRP in mammalian chemical carcinogenesis.
Loe
D W
DW
Cancer Research Laboratories, Queen's University, Kingston, Ontario, Canada.
Stewart
R K
RK
Massey
T E
TE
Deeley
R G
RG
Cole
S P
SP
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000493:pharmacokinetics / Q000494:pharmacology*; D016604:Aflatoxin B1 / Q000378:metabolism* / Q000493:pharmacokinetics*; D001693:Biological Transport, Active / Q000187:drug effects; D002273:Carcinogens / Q000378:metabolism* / Q000493:pharmacokinetics*; D018288:Carcinoma, Small Cell / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D004347:Drug Interactions; D018432:Drug Resistance, Multiple; D005978:Glutathione / Q000378:metabolism* / Q000493:pharmacokinetics* / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D008175:Lung Neoplasms / Q000378:metabolism; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D009101:Multiple Myeloma / Q000378:metabolism; D013237:Stereoisomerism; D013379:Substrate Specificity; D014316:Tritium; D014407:Tumor Cells, Cultured
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D018528:ATP-Binding Cassette Transporters; D000255:Adenosine Triphosphate; D016604:Aflatoxin B1; D002273:Carcinogens; D005978:Glutathione; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D014316:Tritium