Mrp3(Abcc3) is markedly induced following bile duct ligation (BDL) in the rat and in some human cholestatic liver diseases and is believed to ameliorate liver injury in this setting. Recently, the orphan nuclear receptor fetoprotein transcription factor/cholesterol-7␣-hydroxylase promoter factor (CPF/FTF/Lrh-1) has been shown to activate Mrp3 expression. However, whether inflammatory cytokines or elevated bile acid levels increased Lrh-1/Mrp3 expression in obstructive cholestasis was not known. We hypothesized that induction of Mrp3 would be associated with Lrh-1 up-regulation and would require intact cytokine signaling. Male tumor necrosis factor (Tnf) receptor I (Tnfr؊/؊) mice and C57BLJ wild type (WT) controls were subjected to sham surgery or bile duct ligation. HepG2 cells were treated with bile acids or cytokines. Immunoblot assay and real time reverse transcriptase-PCR were used to determine expression of MRP3/Mrp3, CPF/Lrh-1, Mrp2, and Bsep. CPF/ Lrh-1 DNA binding to the MRP3/Mrp3 promoter was assessed using electrophoretic mobility shift assay, and promoter activity was determined by luciferase assay. Total bile acids and lactate dehydrogenase were measured using colorimetric assays, and cytokine abundance was determined by enzyme-linked immunosorbent assay. Lrh-1 and Mrp3 were significantly induced after BDL in WT but not Tnfr؊/؊ mice. This was associated with more severe hepatocellular necrosis in Tnfr؊/؊ mice. Lrh-1 binding to the Mrp3 promoter increased after BDL in WT but not in Tnfr؊/؊ mice. Tnf␣ treatment of HepG2 cells also up-regulated CPF and MRP3, increased CPF binding to the MRP3 promoter, and upregulated MRP3 promoter activity. These results indicate that induction of Mrp3 after BDL is due to Tnf␣-dependent up-regulation of Lrh-1. They provide strong evidence that induction of Mrp3 plays a significant role in hepatocyte protection during obstructive cholestasis.

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Hepatocellular and canalicular transport proteins are major determinants of the hepatic uptake and biliary excretion of xenobiotics and their metabolites. Recent advances in molecular cloning have resulted in the characterization of many of these transport systems. These advances have enabled the identification of a number of drugs that are substrates for the transporters, and it has facilitated studies of mechanisms of drug-induced cholestasis. This review summarizes the normal function of hepatobiliary transporters and their alteration by drugs or other foreign compounds. Although most of these investigations have been performed in animal models of drug-induced cholestasis, the application to human forms of drug-induced cholestasis is also discussed when possible. One important finding is that genetic polymorphisms can result in changes in drug transporter expression and function that could increase susceptibility to cholestatic drug reactions.

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