Nuclear Receptors CAR and PXR Cross Talk with FOXO1 To Regulate Genes That Encode Drug-Metabolizing and Gluconeogenic Enzymes

Pharmacogenetics Section, Laboratory of Reproductive and Developmental Toxicology, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA.
Molecular and Cellular Biology (Impact Factor: 4.78). 10/2004; 24(18):7931-40. DOI: 10.1128/MCB.24.18.7931-7940.2004
Source: PubMed


The nuclear receptors CAR and PXR activate hepatic genes in response to therapeutic drugs and xenobiotics, leading to the induction of drug-metabolizing enzymes, such as cytochrome P450. Insulin inhibits the ability of FOXO1 to express genes encoding gluconeogenic enzymes. Induction by drugs is known to be decreased by insulin, whereas gluconeogenic activity is often repressed by treatment with certain drugs, such as phenobarbital (PB). Performing cell-based transfection assays with drug-responsive and insulin-responsive enhancers, glutathione S-transferase pull down, RNA interference (RNAi), and mouse primary hepatocytes, we examined the molecular mechanism by which nuclear receptors and FOXO1 could coordinately regulate both enzyme pathways. FOXO1 was found to be a coactivator to CAR- and PXR-mediated transcription. In contrast, CAR and PXR, acting as corepressors, downregulated FOXO1-mediated transcription in the presence of their activators, such as 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene (TCPOBOP) and pregnenolone 16alpha-carbonitrile, respectively. A constitutively active mutant of the insulin-responsive protein kinase Akt, but not the kinase-negative mutant, effectively blocked FOXO1 activity in cell-based assays. Thus, insulin could repress the receptors by activating the Akt-FOXO1 signal, whereas drugs could interfere with FOXO1-mediated transcription by activating CAR and/or PXR. Treatment with TCPOBOP or PB decreased the levels of phosphoenolpyruvate carboxykinase 1 mRNA in mice but not in Car(-/-) mice. We conclude that FOXO1 and the nuclear receptors reciprocally coregulate their target genes, modulating both drug metabolism and gluconeogenesis.

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    • "In mammalian cells, FoxO binds to several nuclear hormone receptors (NHRs), such as constitutive androstane receptor (CAR) and pregnane X receptor (PXR), to regulate CYP450 expression (Kodama et al., 2004). The functional ecdysone receptor is composed of two NHRs, Ecdysone Receptor (EcR) and Ultraspiracle (Usp). "
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    ABSTRACT: Despite their fundamental importance for body size regulation, the mechanisms that stop growth are poorly understood. In Drosophila melanogaster, growth ceases in response to a peak of the molting hormone ecdysone that coincides with a nutrition-dependent checkpoint, critical weight. Previous studies indicate that insulin/insulin-like growth factor signaling (IIS)/Target of Rapamycin (TOR) signaling in the prothoracic glands (PGs) regulates ecdysone biosynthesis and critical weight. Here we elucidate a mechanism through which this occurs. We show that Forkhead Box class O (FoxO), a negative regulator of IIS/TOR, directly interacts with Ultraspiracle (Usp), part of the ecdysone receptor. While overexpressing FoxO in the PGs delays ecdysone biosynthesis and critical weight, disrupting FoxO-Usp binding reduces these delays. Further, feeding ecdysone to larvae eliminates the effects of critical weight. Thus, nutrition controls ecdysone biosynthesis partially via FoxO-Usp prior to critical weight, ensuring that growth only stops once larvae have achieved a target nutritional status.
    eLife Sciences 11/2014; 3. DOI:10.7554/eLife.03091 · 9.32 Impact Factor
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    • "Recently, CAR has received renewed attention as a molecular target for the treatment of metabolic diseases, because of its key role in energy homeostasis such as thyroid hormone metabolism (Maglich et al. 2004; Qatanani et al. 2005), glucogenesis (Ueda et al. 2002; Kodama et al. 2004; Miao et al. 2006), and lipogenesis (Roth et al. 2008a,b). Furthermore, in vivo studies using ob/ob mice and high-fat diet-fed mice have shown that CAR activation suppresses glucose production, stimulates glucose uptake, improves glucose tolerance and insulin sensitivity, and prevents obesity (Gao et al. 2009; Dong et al. 2009). "
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    ABSTRACT: The constitutive androstane receptor (CAR, NR1I3) is very important for drug development and for understanding pharmacokinetic drug–drug interactions. We screened by mammalian one hybrid assay among natural compounds to discover novel ligands of human constitutive androstane receptor (hCAR). hCAR transcriptional activity was measured by luciferase assay and mRNA levels of CYP2B6 and CYP3A4 in HepTR-hCAR cells and human primary hepatocytes were measured by real-time RT-PCR. Nigramide J (NJ) whose efficacy is comparable to those of hitherto known inverse agonists such as clotrimazole, PK11195, and ethinylestradiol. NJ is a naturally occurring cyclohexane-type amide alkaloid that was isolated from the roots of Piper nigrum. The suppressive effect of NJ on the CAR-dependent transcriptional activity was found to be species specific, in the descending order of hCAR, rat CAR, and mouse CAR. The unliganded hCAR-dependent transactivation of reporter and endogenous genes was suppressed by NJ at concentrations higher than 5 μmol/L. The ligand-binding cavity of hCAR was shared by NJ and CITCO, because they were competitive in the binding to hCAR. NJ interfered with the interaction of hCAR with coactivator SRC-1, but not with its interaction with the corepressor NCoR1. Furthermore, NJ is agonist of human pregnane X receptor (hPXR). NJ is a dual ligand of hCAR and hPXR, being an agonist of hPXR and an inverse agonist of hCAR.
    02/2014; 2(1). DOI:10.1002/prp2.18
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    • "cAMP and early growth response 1 synergize CAR-mediated transcription of CYP2B6 genes in HepG2 cells (Ding et al., 2006; Inoue and Negishi, 2008). AKT and NFkB signaling represses the CYP2B6 gene (Assenat et al., 2004; Kodama et al., 2004). However, those previous studies were limited only to the CYP2B gene. "
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    ABSTRACT: The constitutive active/androstane receptor (CAR) regulates hepatic drug metabolism by activating genes such as cytochrome P450 (CYP) and certain transferases. p38 mitogen activated protein kinase (MAPK) is highly activated in human primary hepatocytes but barely in human hepatoma cell-lines including HepG2 cells. Liganded-CAR induced CYP2B6 mRNA in human primary hepatocytes far more effectively than in HepG2 cells ectopically expressing CAR. Here, we have now found that activation of p38 MAPK by anisomycin potentiated induction of CYP2B6 mRNA by CAR ligand in HepG2 cells to levels observed in ligand-treated human primary hepatocytes. siRNA knockdown of p38 MAPK abrogated the ability of anisomycin to synergistically induce CYP2B6 mRNA. In addition to CYP2B6, anisomycin co-treatment potentiated an increase in CYP2A7 and CYP2C9 mRNAs but not CYP3A4 or UDP-glucuronosyltransferase 1A1 mRNAs. Thus, activated p38 MAPK is required for liganded-CAR to selectively activate a set of genes that encode drug metabolizing enzymes. Our present results suggest that CAR-mediated induction of these enzymes can not be understood by ligand binding alone because the specificity and magnitude of induction are co-determined by a given cell signaling such as p38 MAPK; both physiological and pathophysiological states of cell signaling may have a strong impact in hepatic drug metabolizing capability during therapeutic treatments.
    Drug metabolism and disposition: the biological fate of chemicals 03/2013; 41(6). DOI:10.1124/dmd.113.051623 · 3.25 Impact Factor
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