ATP-dependent transport of bilirubin glucuronides by the multidrug resistance protein MRP1 and its hepatocyte canalicular isoform MRP2.
Bilirubin is secreted from the liver into bile mainly as monoglucuronosyl and bisglucuronosyl conjugates. We demonstrate for the first time that ATP-dependent transport of both bilirubin glucuronides is mediated by the multidrug resistance protein (MRP1) as well as by the distinct canalicular (apical) isoform MRP2, also termed cMRP or cMOAT (canalicular multispecific organic anion transporter). In membrane vesicles from MRP1-transfected HeLa cells mono[3H]glucuronosylbilirubin and bis[3H]glucuronosylbilirubin (each at 0.5 microM) were transported with rates of 5.3 and 3.1 pmol/min per mg of protein respectively. Rat hepatocyte canalicular membrane vesicles, which contain Mrp2 (the rat equivalent of MRP2), transported mono[3H]glucuronosylbilirubin and bis[3H]glucuronosylbilirubin at rates of 8.9 and 8.5 pmol/min per mg of protein, whereas membrane vesicles from mutant liver lacking Mrp2 showed no transport of the conjugates. In membrane vesicles from human hepatoma Hep G2 cells, which predominantly expressed MRP2, transport rates were 8.3 and 4.4 pmol/min per mg of protein for monoglucuronosylbilirubin and bisglucuronosylbilirubin respectively. ATP-dependent transport of the glutathione S-conjugate -3H-leukotriene C4, an established high-affinity substrate for MRP1 and MRP2, was inhibited by both bilirubin glucuronides with IC50 values between 0.10 and 0.75 microM. The ratios of leukotriene C4 transport and bilirubin glucuronide transport, determined in the same membrane vesicle preparation, indicated substrate specificity differences between MRP1 and MRP2 with a preference of MRP2 for the glucuronides.
Jedlitschky
G
G
Division of Tumor Biochemistry, Deutsches Krebsforschungszentrum, In Neuenheimer Feld 280, D-69120 Heidelberg, Federal Republic of Germany.
Leier
I
I
Buchholz
U
U
Hummel-Eisenbeiss
J
J
Burchell
B
B
Keppler
D
D
D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism*; D018528:ATP-Binding Cassette Transporters / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D001663:Bilirubin / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D017997:Leukotriene C4 / Q000031:analogs & derivatives / Q000378:metabolism; D008099:Liver / Q000737:chemistry / Q000378:metabolism*; D026901:Membrane Transport Proteins; D051381:Rats; D017208:Rats, Wistar; D013379:Substrate Specificity; D014162:Transfection / Q000235:genetics; D014407:Tumor Cells, Cultured
D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D018528:ATP-Binding Cassette Transporters; D002352:Carrier Proteins; D026901:Membrane Transport Proteins; C086860:glutathione transporter; C016266:bilirubin glucuronate; D017997:Leukotriene C4; D000255:Adenosine Triphosphate; C095122:multidrug resistance protein 3; D001663:Bilirubin