Oxidative and electrophilic stress induces multidrug resistance-associated protein transporters via the nuclear factor-E2-related factor-2 transcriptional pathway

Multidrug resistance-associated proteins (Mrps) are adenosine triphosphate- dependent transporters that efflux chemicals out of cells. In the liver, Mrp2 transports bilirubin-glucuronide, glutathione (GSH), and drug conjugates into bile, whereas Mrp3 and Mrp4 efflux these entities into blood. The purpose of this study was to determine whether oxidative conditions (that is, the disruption of hepatic GSH synthesis) or the administration of nuclear factor-E2-related factor-2 (Nrf2) activators (oltipraz and butylated hydroxyanisole) can induce hepatic Mrp, transporters and whether that induction is through the Nrf2 transcriptional pathway. Livers from hepatocyte-specific glutamate-cysteine ligase catalytic subunit-null mice had increased nuclear Nrf2 levels, marked gene and protein induction of the Nrf2 target gene NAD(P)H:quinone oxidoreductase 1, as well as Mrp2, Mrp3, and Mrp4 expression. The treatment of wild-type and Nrf2-null mice with oltipraz and butylated hydroxyanisole demonstrated that the induction of Mrp,2, Mrp3, and Mrp4 is Nrf2-dependent. In Hepa1c1c7 cells treated with the Nrf2 activator tert-butyl hydroquinone, chromatin immunoprecipitation with Nrf2 antibodies revealed the binding of Nrf2 to antioxidant response elements in the promoter regions of mouse Mrp2 [-185 base pairs (bp)], Mrp3 (-9919 bp), and Mrp4 (-3767 bp). Conclusion: The activation of the Nrf2 regulatory pathway stimulates the coordinated induction of hepatic Mrps.