The roles of MRP2, MRP3, OATP1B1, and OATP1B3 in conjugated hyperbilirubinemia.
Increased concentrations of bilirubin glucuronides in blood plasma indicate hepatocellular dysfunction. Elucidation of the transport processes of bilirubin conjugates across the basolateral (sinusoidal) and the canalicular plasma membrane domains of hepatocytes has decisively contributed to our current understanding of the molecular basis of conjugated hyperbilirubinemia in human liver diseases. Under normal conditions, unconjugated bilirubin is taken up into hepatocytes by transporters of the organic anion-transporting polypeptide (OATP) family, followed by conjugation with glucuronic acid, and ATP-dependent transport into bile. This efflux across the canalicular membrane is mediated by multidrug resistance protein 2 (MRP2 or ABCC2), which is a 190-kDa glycoprotein transporting with high affinity and efficiency monoglucuronosyl bilirubin and bisglucuronosyl bilirubin into bile. MRP2 is hereditarily deficient in human Dubin-Johnson syndrome. Under pathophysiological conditions such as cholestatic liver injury and MRP2 inhibition, the basolateral efflux pump multidrug resistance protein 3 (MRP3 or ABCC3) is responsible for the occurrence of conjugated hyperbilirubinemia. MRP3 is a glycoprotein with a similar molecular mass as MRP2, with 48% amino acid identity, and with overlapping substrate specificity. Human MRP3 is the only basolateral efflux pump shown to transport bilirubin glucuronides. In human and rat hepatocytes, MRP3/Mrp3 is strongly upregulated under conditions of cholestasis and MRP2 deficiency. This is in line with the concept that basolateral efflux pumps of the hepatocyte compensate for impaired canalicular efflux of compounds into bile and contribute to balance the rate of uptake or synthesis of compounds in hepatocytes with the capacity for efflux into bile.
German Cancer Research Center (DKFZ), Heidelberg, Germany.
Dietrich
D
Keppler
D000818:Animals; D001646:Bile / Q000378:metabolism; D001663:Bilirubin / Q000031:analogs & derivatives / Q000097:blood; D001692:Biological Transport; D022781:Hepatocytes / Q000378:metabolism; D006801:Humans; D006933:Hyperbilirubinemia, Hereditary / Q000097:blood / Q000378:metabolism*; D007566:Jaundice, Chronic Idiopathic / Q000097:blood / Q000378:metabolism; D027381:Liver-Specific Organic Anion Transporter 1; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000378:metabolism*; D027361:Organic Anion Transporters / Q000378:metabolism*; D029362:Organic Anion Transporters, Sodium-Independent / Q000378:metabolism*; D000074542:Solute Carrier Organic Anion Transporter Family Member 1B3
D001663:Bilirubin; D027381:Liver-Specific Organic Anion Transporter 1; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D027361:Organic Anion Transporters; D029362:Organic Anion Transporters, Sodium-Independent; D000074542:Solute Carrier Organic Anion Transporter Family Member 1B3; C000715087:ABCC2 protein, human; C503999:SLCO1B1 protein, human; C421209:SLCO1B3 protein, human; C114462:multidrug resistance-associated protein 3; C016266:bilirubin glucuronate