Regulation of mRNA Expression of Xenobiotic Transporters by the Pregnane X Receptor in Mouse Liver, Kidney, and Intestine

Abstract

ABSTRACT:Multiple transporter systems are involved in the disposition of xenobiotics and endogenous compounds. The pregnane X receptor (PXR) is a major chemical sensor known to activate the expression of CYP3A/Cyp3a in humans and rodents. The purpose of this study is to systematically determine whether the major xenobiotic transporters in liver, kidney, duodenum, jejunum, and ileum are induced by pregnenolone-16␣-carbonitrile (PCN), and whether this increase is mediated by the nuclear receptor PXR. In liver, PCN induced the expression of Oatp1a4 and Mrp3 mRNA in wild-type (WT) mouse liver, but not in PXR-null mice. In kidney, PCN did not alter the expression of any drug transporter. In duodenum, PCN increased Abca1 and Mdr1a mRNA expression in WT mice, but not in PXR-null mice. In jejunum and ileum, PCN increased Mdr1a and Mrp2 mRNA, but decreased Cnt2 mRNA in WT mice, but none of these transporters was altered when PCN was administered to PXR-null mice. Therefore, PCN regulates the expression of some transporters, namely, Oatp1a4 and Mrp3 in liver, as well as Abca1, Cnt2, Mdr1a, and Mrp2 in small intestine via a PXR-mediated mechanism.The pregnane X receptor (PXR, NR1I2), also called steroid-xenobiotic receptor or pregnane-activated receptor, is an orphan nuclear receptor first identified by Kliewer and coworkers (Lehmann et al., 1998). PXRs have been characterized in rats, mice, humans, rabbits, and chickens. Mouse PXR shares 95% sequence similarity to rat and 77% to human PXR (Zhang et al., 1999;Moore et al., 2003).PXR is a master regulator of phase I and II metabolism of xenobiotics. Upon ligand binding, PXR forms a heterodimer with the retinoid X receptor ␣ and then transactivates target genes. PXR ligands generally induce Cyp3a/CYP3A genes in rats, mice, and humans (Goodwin et al., 2002;Guo et al., 2002b;Cheng et al., 2005b). One exception is CYP3A41, which is down-regulated by dexamethasone (DEX) in a PXR-dependent manner (Anakk et al., 2004). Pregnenolone-16␣-carbonitrile (PCN) also regulates phase II drug-metabolizing enzymes, such as glutathione S-transferase ␣1 and 1, rat UDP-glucuronosyltransferase 1a1 (Ugt1a1) (Chen et al., 2003), and sulfotransferase 1b1 (Dunn et al., 1999). In addition, PCN induces the expression of some transprters, such as rat Abca1 (Sporstol et al., 2005), human MRP2, and MRP3 (Kretschmer and Baldwin, 2005).The regulation of hepatic and small intestinal gene expression by two potent rat PXR agonists, L-742694 and DEX, has been examined after oral administration to female Sprague-Dawley rats using DNA microarray analysis (Hartley et al., 2004). Both L-742694 and DEX elicited robust increases in gene expression of Cyp3a1/23, Cyp3a18, Ugt1a1, Ugt2b1, and Oatp1a4 in rat liver. However, both L-742694 and DEX suppressed rat Cyp3a1/23, Cyp3a18, Ugt1a1, Ugt2b1, Oatp1a4, and Mrp3 expression in intestine (Hartley et al., 2004). There was a distinct lack of coordinated interorgan expression of genes common to both hepatic and intestinal tissues in rats (Hartley et al., 2004).Mice and rats...

Gestational and Pregnane X Receptor-Mediated Regulation of Placental ATP-Binding Cassette Drug Transporters in Mice

“…Activation of PXR has been shown to significantly induce the hepatic expression of Cyp3a11, Oatp2, and several of the ABC drug transporters including Mdr1, Mrp2, and Mrp3 in nonpregnant mice (Teng and Piquette-Miller, 2005;Anapolsky et al, 2006). Likewise, PCN-mediated induction of several PXR gene targets has been reported in the intestine and blood-brain barrier (Bauer et al, 2004;Cheng and Klaassen, 2006). Of interest, although a pronounced 30-fold elevation in the hepatic expression of Cyp3a11 was observed in the livers of pregnant PCN-treated mice, confirming PXR activation, we did not observe any significant changes in the expression of the ABC drug transporters in the placenta.…”

“…Likewise, PXR activation has been found to induce expression and activity of P-gp at the blood-brain barrier (Bauer et al, 2004(Bauer et al, , 2006. This regulation may be tissue-specific because PXR activation in mice has been reported to induce expression of target genes such as Cyp3a11 in the liver and intestine but not in kidney (Cheng and Klaassen, 2006). However, the involvement of PXR in the regulation of placental drug transporters has not been established.…”

“…Pregnane X receptor (PXR), a member of the superfamily nuclear receptor transcription factors, is believed to play a key role in the regulation of several major drug transporters and drug-metabolizing enzymes in response to environmental factors (Cheng and Klaassen, 2006). PXR is activated by numerous clinically important xenobiotics, herbal products, and endogenous steroids (Chang and Waxman, 2006).…”

Role of Pregnane X Receptor in Control of All-TransRetinoic Acid (ATRA) Metabolism and Its Potential Contribution to ATRA Resistance

“…PXR plays a crucial role in this regard, by regulating several superfamilies of genes involved in xenobiotic metabolism and elimination. Upon ligand binding, PXR forms a heterodimer with the RXR and then transactivates target genes, including oxidation enzymes, in particular, P450s and conjugation enzymes, together with transporters such as Pgp, MRPs, and OATPs (Bertilsson et al, 1998;Synold et al, 2001;Guo et al, 2002;Cheng and Klaassen, 2006). The most well known and important PXR target gene is CYP3A subfamily.…”

Coordinated Regulation of Hepatic Phase I and II Drug-Metabolizing Genes and Transporters using AhR-, CAR-, PXR-, PPARα-, and Nrf2-Null Mice

“…Likewise, phase II enzymes including sulfotransferases (Sults), UDP-glucuronosyltransferases (Ugts), and glutathione transferases (Gsts) are increased by chemical activators of all five transcription factors (Alnouti and Klaassen, 2008a;Knight et al, 2008;Buckley and Klaassen, 2009a;Yeager et al, 2009). Evidence also suggests that transport genes including isoforms of the ATP-binding cassette (Abc) and the solute carrier (Slc) families are up-or down-regulated by chemicals that activate AhR, CAR, PXR, PPAR␣, and Nrf2 Maher et al, 2005;Cheng and Klaassen, 2006;Moffit et al, 2006;Klaassen and Aleksunes, 2010). These studies have primarily been performed in male wild-type C57BL/6 mice and do not account for gender differences in responsiveness nor confirm the dependence of these mRNA changes on specific transcription factors.…”