Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0406810 (NAME)
 13,345 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The xenobiotic receptors CAR and PXR constitute two important members of the NR1I nuclear receptor family. They function as sensors of toxic byproducts derived from the endogenous metabolism and of exogenous chemicals, in order to enhance their elimination. They regulate numerous genes which are involved in drug and xenobiotic metabolism, including Phase I (cytochrome P450), Phase II (conjugation catalyzed by sulfotransferases, glucuronosyltransferases and glutathione S-transferases), and transporters (multidrug resistance proteins, multidrug resistance-associated proteins, and organic anion-transporting polypeptides). Although CAR and PXR were initially characterized as xenosensors, it is now evident that CAR and PXR also trigger pleiotropic effects on physiological or pathological functions. Recent studies have shown that the activation of CAR and PXR alters lipid metabolism, glucose homeostasis, and inflammation. Therefore, in addition to regulating drug elimination pathways, they also play important roles in regulating metabolic pathways. As a result, these receptors may be closely associated with the pathogenesis of many diseases. However, the pathophysiological roles of CAR and PXR are not fully understood. The purpose of this review is to discuss the physiological and pathological roles of CAR and PXR in liver diseases.
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PMID:New insights on the xenobiotic-sensing nuclear receptors in liver diseases--CAR and PXR--. 1878 13

The constitutive androstane receptor (CAR; NR1I3) is a nuclear receptor responsible for the recognition of potentially toxic endo- and exogenous compounds whose elimination from the body is accelerated by the CAR-mediated inducible expression of metabolizing enzymes and transporters. Despite the importance of CAR, few human agonists are known so far. Following a sequential virtual screening procedure using a 3D pharmacophore and molecular docking approach, we identified 17 novel agonists that could activate human CAR in vitro and enhance its association with the nuclear receptor co-activator SRC1. Selected agonists also increased the expression of the human CAR target CYP2B6 mRNA in primary hepatocytes. Composed of substituted sulfonamides and thiazolidin-4-one derivatives, these agonists represent two novel chemotypes capable of human CAR activation, thus broadening the agonist spectrum of CAR.
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PMID:Discovery of substituted sulfonamides and thiazolidin-4-one derivatives as agonists of human constitutive androstane receptor. 1878 10

Expression of hepatic drug metabolizing enzymes (DMEs) is altered in infection and inflammation. However, the role of Gram+ve bacterial components and their receptor, Toll-like receptor (TLR) 2 in regulation of hepatic DMEs is unknown. Gene expression of DMEs is regulated by members of the nuclear receptor superfamily (PXR, CAR and RXRalpha). The TLR2 ligand, lipoteichoic acid (LTA) reduced RNA levels of CAR and its target genes, Cyp2b10, Cyp2a4 and Sultn in mouse liver ( approximately 60-80% reduction). Hepatic genes regulated by PXR and CAR, Cyp3a11 and Mrp2 were moderately reduced by LTA, along with approximately 50% reduction of PXR RNA and nuclear protein levels of RXRalpha. The effects of LTA were significantly attenuated by pre-treatment with the Kupffer cell inhibitor, gadolinium chloride, indicating that Kupffer cells contribute to LTA-mediated down-regulation of hepatic genes. These results indicate that treatment with Gram+ve bacterial components preferentially down-regulate CAR and its target genes in the liver.
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PMID:Regulation of gene expression of hepatic drug metabolizing enzymes and transporters by the Toll-like receptor 2 ligand, lipoteichoic acid. 1894 Jan 78

Constitutive androstane receptor (CAR, NR1I3) belongs to the nuclear receptor family of transcription factors and acts as a chemical sensor of drugs and endogenous compounds. The ligand-binding preferences of CAR are diverse, and more importantly, there are significant species differences in ligand specificity. Here, we show that while certain residues are critical for the basal activity of mouse CAR (mCAR) and/or affect the binding of all tested ligands, mutation of some ligand-binding pocket (LBP) residues (e.g., F171 and Y336) paradoxically decreased the activity of a specific ligand while increasing that of others. Comparisons to previously reported human CAR (hCAR) residues indicated that the function of key CAR residues (e.g., N175, L253) is dramatically different between species. The docking results provide some mechanistic rationale for the ability of 17alpha-ethinyl-3,17beta-estradiol (EE2) to both activate mCAR and repress hCAR.
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PMID:Ligand specificity of constitutive androstane receptor as probed by induced-fit docking and mutagenesis. 1897 26

Recent discoveries highlighted intriguing molecular pathways that regulate synthesis, uptake, metabolism and excretion of bile acids and xenobiotics. The knowledge of factors that control these homeostatic processes is of clinical relevance to better understand the drug-drug interacting scenario as well as to control cholesterol detoxification, cholestasis and other conditions. Here we present evidences for the existence of a gut-liver safety network whereby activation of the nuclear receptor FXR, PXR, CAR trio provides protection against accumulation of exogenous and metabolic noxae.
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PMID:Master regulation of bile acid and xenobiotic metabolism via the FXR, PXR and CAR trio. 1927 85

ABCB1 (P-glycoprotein) is an efflux transporter that limits the cellular uptake levels of various drugs in intestine, brain, and other tissues. The expression of human ABCB1 has recently been reported to be under the control of nuclear receptor NR1I subfamily members, pregnane X receptor (PXR, NR1I2) and constitutive androstane receptor (CAR, NR1I3). Here, we have investigated the involvement of another NR1I member, vitamin D receptor (VDR, NR1I1), in ABCB1 expression. In the human colorectal adenocarcinoma cell line LS174T, which abundantly expresses VDR, both 1alpha,25-dihydroxyvitamin D(3) (1,25-VD3) and lithocholic acid (LCA) increased ABCB1 mRNA levels. Reporter gene assays in LS174T cells with constructs containing various lengths of the ABCB1 regulatory region revealed that the region containing multiple nuclear receptor binding motifs located at -7.8 kilobases [termed nuclear receptor-responsive module (NURREM)], to which PXR and CAR also bind, is essential for the VDR-mediated ABCB1 transactivation. Further reporter assays with constructs containing truncated NURREM and gel shift assays suggested simultaneous binding of multiple VDR/retinoid X receptor alpha heterodimers to NURREM. Furthermore, knockdown of VDR expression in LS174T cells blocked the LCA- and the 1,25-VD3-induced transcription of ABCB1 reporter genes. In human hepatoma HepG2 cells, in contrast with LS174T cells, 1,25-VD3 activated the ABCB1 transcription only in the presence of ectopically expressed VDR. These results suggest that the NR1I subfamily members regulate the ABCB1 expression sharing the binding sites within NURREM and that the physiologically produced LCA and 1,25-VD3 may modulate the ABCB1 expression in human intestines, possibly associated with interindividual variations of ABCB1 expression.
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PMID:Involvement of Vitamin D receptor in the intestinal induction of human ABCB1. 1946 Sep 46

Retinoids and carotenoids are frequently used as antioxidants to prevent cancer. In this study, a panel of retinoids and carotenoids was examined to determine their effects on activation of RXR/CAR-mediated pathway and regulation of CYP3A gene expression. Transient transfection assays of HepG2 cells revealed that five out of thirteen studied retinoids significantly induced RXRalpha/CAR-mediated activation of luciferase activity that is driven by the thymidine kinase promoter linked with a PXR binding site in the CYP3A4 gene [tk-(3A4)(3)-Luc reporter]. All-trans retinoic acid (RA) and 9-cis RA were more effective than CAR agonist TCBOPOP in induction of the tk-(3A4)(3)-Luc reporter. Addition of retinoid and TCBOPOP further enhanced the inducibility and the induction was preferentially mediated by RXRalpha/CAR and RXRgamma/CAR heterodimer. Chromatin immunoprecipitation assay showed that retinoids recruit RXRalpha and CAR to the proximal ER6 and distal XREM nuclear receptor response elements of the CYP3A4 gene promoter. The experimental data demonstrate that retinoids can effectively regulate CYP3A gene expression through the RXR/CAR-mediated pathway.
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PMID:Retinoids activate RXR/CAR-mediated pathway and induce CYP3A. 1968 1

Hepatocyte nuclear factor 4-alpha (HNF4alpha, NR2A1) is a nuclear receptor (NR) required for liver development and for controlling the expression of many hepatic-specific genes associated with important metabolic pathways. Many studies have also identified HNF4alpha as a direct transactivator of numerous xenobiotic-metabolizing cytochrome P450 (CYP) genes, suggesting that this factor is a global regulator which supports CYP transcription in the liver. Moreover, HNF4alpha expression displays a significant variability in human liver which may account for a proportion of the inter-individual variability in the expression of drug-metabolism genes and the clearance rate of a wide variety of prescribed drugs. In the last few years, a number of complex interactions and cross-talks between HNF4alpha and other transcription factors and coregulators have also surfaced, and the impact on CYP gene expression has been demonstrated. Thus, it is now clear that HNF4alpha modulates CYP expression in the liver by interacting with the xenosensor receptors (PXR and CAR), the glucocorticoid receptor (GR), the feeding-fasting cycle target PGC-1alpha, the sexual-dimorphism factor Stat5b, and other liver-enriched factors, such as C/EBPs. In addition to regulating drug elimination pathways, HNF4alpha also triggers pleiotropic effects on cholesterol and fatty acid metabolism, glucose homeostasis and inflammation. As a whole, current evidence indicates that HNF4alpha is a central regulator in the network of NRs that integrates drug-metabolism not only with the liver intermediate metabolism, but also with a number of patho-physiological conditions where the CYP expression is altered. The purpose of this review is to summarize and discuss these studies and their conclusions, with particular emphasis on the role of HNF4alpha in the regulation of drug-metabolizing CYP genes in the human liver.
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PMID:Transcriptional regulation of cytochrome p450 genes by the nuclear receptor hepatocyte nuclear factor 4-alpha. 1968 47

The nuclear receptors CAR (constitutive androstane receptor) and PXR (pregnane X receptor) mediate the effects of phenobarbital on gene transcription. To investigate the relative contribution of these nuclear receptors to the expression of specific genes we studied the effect of phenobarbital in livers of wild type, CAR(-/-), PXR(-/-) and CAR/PXR(-/-) knockout mice. Spotted Steroltalk v1 cDNA arrays were applied containing probes for genes involved in drug metabolism, sterol biosynthesis, steroid synthesis/transport and heme synthesis. In the absence of CAR and PXR, phenobarbital unexpectedly induced mRNAs of several nuclear receptors, including PPARalpha and its target genes Cyp4a10 and Cyp4a14. Interestingly, in primary cultures of hepatocytes isolated from CAR/PXR(-/-) knockout mice, phenobarbital increased HNF-4alpha levels. In further experiments in these hepatocyte cultures we provide evidence that phenobarbital directly induces transcription of the PPARalpha gene via its HNF-4alpha response element, and indirectly by lack of inhibitory crosstalk of AMPK, CAR and PXR with HNF-4alpha. Our results provide further insight into CAR and PXR-independent effects of phenobarbital and the crosstalk between different nuclear receptor signaling pathways.
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PMID:Transcriptional activation of PPARalpha by phenobarbital in the absence of CAR and PXR. 1970 87

Cholestasis results in the intrahepatic retention of cytotoxic bile acid and it can thus lead to liver injury and/or liver fibrosis. Cholestatic liver damage is counteracted by a variety of intrinsic hepatoprotective mechanisms including a complex network of drug metabolizing enzymes and transporters. During the last decade, much progress has been made in dissecting the mechanisms which regulate the hepatic xeno- and endobiotic metabolism by nuclear receptors. The xenobiotic receptors CAR and PXR are two important members of the NR1I nuclear receptor family. They function as sensors of toxic byproducts derived from the endogenous metabolism and of exogenous chemicals, in order to enhance their elimination. Ligands for both receptors, including phenobarbital, have already been used to treat cholestatic liver diseases before the mechanisms of these receptors were revealed. Furthermore, Yin Zhi Huang, a traditional Chinese herbal medicine, which has been used to prevent and treat neonatal jaundice, was identified to be a CAR ligand which also accelerates bilirubin clearance. Therefore, CAR and PXR have a protective effect on cholestasis by activating both detoxification enzymes and transporters. As a result, novel compounds targeting CAR and PXR with specific effects and fewer side effects will therefore be useful for the treatment of cholestatic liver diseases. This article will review the current knowledge on xenobiotic-sensing nuclear receptors CAR and PXR, while also discussing their potential role in the treatment of cholestatic liver diseases.
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PMID:Xenobiotic-sensing nuclear receptors CAR and PXR as drug targets in cholestatic liver disease. 1992 51


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