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Men S, Wang H. Phenobarbital in Nuclear Receptor Activation: An Update. Drug Metab Dispos 2023; 51:210-218. [PMID: 36351837 PMCID: PMC9900862 DOI: 10.1124/dmd.122.000859] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2022] [Revised: 09/26/2022] [Accepted: 09/27/2022] [Indexed: 11/11/2022] Open
Abstract
Phenobarbital (PB) is a commonly prescribed anti-epileptic drug that can also benefit newborns from hyperbilirubinemia. Being the first drug demonstrating hepatic induction of cytochrome P450 (CYP), PB has since been broadly used as a model compound to study xenobiotic-induced drug metabolism and clearance. Mechanistically, PB-mediated CYP induction is linked to a number of nuclear receptors, such as the constitutive androstane receptor (CAR), pregnane X receptor (PXR), and estrogen receptor α, with CAR being the predominant regulator. Unlike prototypical agonistic ligands, PB-mediated activation of CAR does not involve direct binding with the receptor. Instead, dephosphorylation of threonine 38 in the DNA-binding domain of CAR was delineated as a key signaling event underlying PB-mediated indirect activation of CAR. Further studies revealed that such phosphorylation sites appear to be highly conserved among most human nuclear receptors. Interestingly, while PB is a pan-CAR activator in both animals and humans, PB activates human but not mouse PXR. The species-specific role of PB in gene regulation is a key determinant of its implication in xenobiotic metabolism, drug-drug interactions, energy homeostasis, and cell proliferation. In this review, we summarize the recent progress in our understanding of PB-provoked transactivation of nuclear receptors with a focus on CAR and PXR. SIGNIFICANCE STATEMENT: Extensive studies using PB as a research tool have significantly advanced our understanding of the molecular basis underlying nuclear receptor-mediated drug metabolism, drug-drug interactions, energy homeostasis, and cell proliferation. In particular, CAR has been established as a cell signaling-regulated nuclear receptor in addition to ligand-dependent functionality. This mini-review highlights the mechanisms by which PB transactivates CAR and PXR.
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Affiliation(s)
- Shuaiqian Men
- Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, Baltimore, Maryland (S.M., H.W.)
| | - Hongbing Wang
- Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, Baltimore, Maryland (S.M., H.W.)
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2
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Noncanonical Constitutive Androstane Receptor Signaling in Gene Regulation. Int J Mol Sci 2020; 21:ijms21186735. [PMID: 32937916 PMCID: PMC7555422 DOI: 10.3390/ijms21186735] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2020] [Revised: 09/04/2020] [Accepted: 09/10/2020] [Indexed: 11/17/2022] Open
Abstract
The constitutive androstane receptor (CAR, NR1I3) is extremely important for the regulation of many physiological processes, especially xenobiotic (drug) metabolism and transporters. CAR differs from steroid hormone receptors in that it can be activated using structurally unrelated chemicals, both through direct ligand-binding and ligand-independent (indirect) mechanisms. By binding to specific responsive elements on DNA, CAR increases the expression of its target genes encoding drug-metabolizing enzymes and transporters. Therefore, CAR is mainly characterized as a ligand-dependent or ligand-independent transcription factor, and the induction of gene expression is considered the canonical mode of CAR action. Consistent with its central role in xenobiotic metabolism, CAR signaling includes a collection of mechanisms that are employed alongside the core transcriptional machinery of the receptor. These so-called noncanonical CAR pathways allow the receptor to coordinate the regulation of many aspects of cell biology. In this mini-review, we review noncanonical CAR signaling, paying special attention to the role of CAR in energy homeostasis and cell proliferation.
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Chai SC, Lin W, Li Y, Chen T. Drug discovery technologies to identify and characterize modulators of the pregnane X receptor and the constitutive androstane receptor. Drug Discov Today 2019; 24:906-915. [PMID: 30731240 PMCID: PMC6421094 DOI: 10.1016/j.drudis.2019.01.021] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2018] [Revised: 12/27/2018] [Accepted: 01/30/2019] [Indexed: 11/24/2022]
Abstract
The pregnane X receptor (PXR) and the constitutive androstane receptor (CAR) are ligand-activated nuclear receptors (NRs) that are notorious for their role in drug metabolism, causing unintended drug-drug interactions and decreasing drug efficacy. They control the xenobiotic detoxification system by regulating the expression of an array of drug-metabolizing enzymes and transporters that excrete exogenous chemicals and maintain homeostasis of endogenous metabolites. Much effort has been invested in recognizing potential drugs for clinical use that can activate PXR and CAR to enhance the expression of their target genes, and in identifying PXR and CAR inhibitors that can be used as co-therapeutics to prevent adverse effects. Here, we present current technologies and assays used in the quest to characterize PXR and CAR modulators, which range from biochemical to cell-based and animal models.
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Affiliation(s)
- Sergio C Chai
- Department of Chemical Biology & Therapeutics, St. Jude Children's Research Hospital, 262 Danny Thomas Place, Memphis, TN 38105, USA
| | - Wenwei Lin
- Department of Chemical Biology & Therapeutics, St. Jude Children's Research Hospital, 262 Danny Thomas Place, Memphis, TN 38105, USA
| | - Yongtao Li
- Department of Chemical Biology & Therapeutics, St. Jude Children's Research Hospital, 262 Danny Thomas Place, Memphis, TN 38105, USA
| | - Taosheng Chen
- Department of Chemical Biology & Therapeutics, St. Jude Children's Research Hospital, 262 Danny Thomas Place, Memphis, TN 38105, USA.
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Mackowiak B, Hodge J, Stern S, Wang H. The Roles of Xenobiotic Receptors: Beyond Chemical Disposition. Drug Metab Dispos 2018; 46:1361-1371. [PMID: 29759961 DOI: 10.1124/dmd.118.081042] [Citation(s) in RCA: 74] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2018] [Accepted: 05/07/2018] [Indexed: 02/06/2023] Open
Abstract
Over the past 20 years, the ability of the xenobiotic receptors to coordinate an array of drug-metabolizing enzymes and transporters in response to endogenous and exogenous stimuli has been extensively characterized and well documented. The constitutive androstane receptor (CAR) and the pregnane X receptor (PXR) are the xenobiotic receptors that have received the most attention since they regulate the expression of numerous proteins important to drug metabolism and clearance and formulate a central defensive mechanism to protect the body against xenobiotic challenges. However, accumulating evidence has shown that these xenobiotic sensors also control many cellular processes outside of their traditional realms of xenobiotic metabolism and disposition, including physiologic and/or pathophysiologic responses in energy homeostasis, cell proliferation, inflammation, tissue injury and repair, immune response, and cancer development. This review will highlight recent advances in studying the noncanonical functions of xenobiotic receptors with a particular focus placed on the roles of CAR and PXR in energy homeostasis and cancer development.
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Affiliation(s)
- Bryan Mackowiak
- Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, Baltimore, Maryland
| | - Jessica Hodge
- Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, Baltimore, Maryland
| | - Sydney Stern
- Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, Baltimore, Maryland
| | - Hongbing Wang
- Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, Baltimore, Maryland
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5
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Negishi M. Phenobarbital Meets Phosphorylation of Nuclear Receptors. Drug Metab Dispos 2017; 45:532-539. [PMID: 28356313 DOI: 10.1124/dmd.116.074872] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2016] [Accepted: 03/13/2017] [Indexed: 02/01/2023] Open
Abstract
Phenobarbital was the first therapeutic drug to be characterized for its induction of hepatic drug metabolism. Essentially at the same time, cytochrome P450, an enzyme that metabolizes drugs, was discovered. After nearly 50 years of investigation, the molecular target of phenobarbital induction has now been delineated to phosphorylation at threonine 38 of the constitutive androstane receptor (NR1I3), a member of the nuclear receptor superfamily. Determining this mechanism has provided us with the molecular basis to understand drug induction of drug metabolism and disposition. Threonine 38 is conserved as a phosphorylation motif in the majority of both mouse and human nuclear receptors, providing us with an opportunity to integrate diverse functions of nuclear receptors. Here, I review the works and accomplishments of my laboratory at the National Institutes of Health National Institute of Environmental Health Sciences and the future research directions of where our study of the constitutive androstane receptor might take us.
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Affiliation(s)
- Masahiko Negishi
- Pharmacogenetics, Reproductive and Developmental Biology, National Institutes of Health National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina
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A brief history of the discovery of PXR and CAR as xenobiotic receptors. Acta Pharm Sin B 2016; 6:450-452. [PMID: 27709013 PMCID: PMC5045536 DOI: 10.1016/j.apsb.2016.06.011] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2016] [Revised: 04/21/2016] [Accepted: 04/28/2016] [Indexed: 02/01/2023] Open
Abstract
The nuclear receptors pregnane X receptor (PXR) and constitutive androstane receptor (CAR) were cloned and/or established as xenobiotic receptors in 1998. Due to their activities in the transcriptional regulation of phase I and phase II enzymes as well as drug transporters, PXR and CAR have been defined as the master regulators of xenobiotic responses. The discovery of PXR and CAR provides the essential molecular basis by which drugs and other xenobiotic compounds regulate the expression of xenobiotic enzymes and transporters. This article is intended to provide a historical overview on the discovery of PXR and CAR as xenobiotic receptors.
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Hedrich WD, Hassan HE, Wang H. Insights into CYP2B6-mediated drug-drug interactions. Acta Pharm Sin B 2016; 6:413-425. [PMID: 27709010 PMCID: PMC5045548 DOI: 10.1016/j.apsb.2016.07.016] [Citation(s) in RCA: 86] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2016] [Revised: 05/18/2016] [Accepted: 05/27/2016] [Indexed: 01/11/2023] Open
Abstract
Mounting evidence demonstrates that CYP2B6 plays a much larger role in human drug metabolism than was previously believed. The discovery of multiple important substrates of CYP2B6 as well as polymorphic differences has sparked increasing interest in the genetic and xenobiotic factors contributing to the expression and function of the enzyme. The expression of CYP2B6 is regulated primarily by the xenobiotic receptors constitutive androstane receptor (CAR) and pregnane X receptor (PXR) in the liver. In addition to CYP2B6, these receptors also mediate the inductive expression of CYP3A4, and a number of important phase II enzymes and drug transporters. CYP2B6 has been demonstrated to play a role in the metabolism of 2%–10% of clinically used drugs including widely used antineoplastic agents cyclophosphamide and ifosfamide, anesthetics propofol and ketamine, synthetic opioids pethidine and methadone, and the antiretrovirals nevirapine and efavirenz, among others. Significant inter-individual variability in the expression and function of the human CYP2B6 gene exists and can result in altered clinical outcomes in patients receiving treatment with CYP2B6-substrate drugs. These variances arise from a number of sources including genetic polymorphism, and xenobiotic intervention. In this review, we will provide an overview of the key players in CYP2B6 expression and function and highlight recent advances made in assessing clinical ramifications of important CYP2B6-mediated drug–drug interactions.
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Key Words
- 4-OH-CPA, 4-hydroxycyclophosphamide
- C/EBP, CCAAT/enhancer-binding protein
- CAR
- CAR, constitutive androstane receptor
- CHOP, cyclophosphamide–doxorubicin–vincristine–prednisone
- CITCO, (6-(4-chlorophenyl)imidazo[2,1-b][1,3]thiazole-5-carbaldehyde-O-(3,4-dichlorobenzyl)oxime)
- COUP-TF, chicken ovalbumin upstream promoter-transcription factor
- CPA, cyclophosphamide
- CYP, cytochrome P450
- CYP2B6
- Cyclophosphamide
- DDI, drug–drug interaction
- DEX, dexamethasone
- Drug–drug interaction
- E2, estradiol
- EFV, efavirenz
- ERE, estrogen responsive element
- Efavirenz
- GR, glucocorticoid receptor
- GRE, glucocorticoid responsive element
- HAART, highly active antiretroviral therapy
- HNF, hepatocyte nuclear factor
- IFA, Ifosfamide
- MAOI, monoamine oxidase inhibitor
- NNRTI, non-nucleotide reverse-transcriptase inhibitor
- NR1/2, nuclear receptor binding site 1/2
- NVP, nevirapine
- PB, phenobarbital
- PBREM, phenobarbital-responsive enhancer module
- PCN, pregnenolone 16 alpha-carbonitrile
- PXR
- PXR, pregnane X receptor
- Polymorphism
- RIF, rifampin
- SNP, single nucleotide polymorphism
- TCPOBOP, 1,4-bis[3,5-dichloropyridyloxy]benzene
- UGT, UDP-glucuronosyl transferase
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Affiliation(s)
| | | | - Hongbing Wang
- Corresponding author at: Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, 20 Penn Street, Baltimore, MD 21201, USA. Tel.: +1 410 706 1280; fax: +1 410 706 5017.
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Ibrahim ZS, Ahmed MM, El-Shazly SA, Ishizuka M, Fujita S. Clofibric acid induces hepatic CYP 2B1/2 via constitutive androstane receptor not via peroxisome proliferator activated receptor alpha in rat. Biosci Biotechnol Biochem 2014; 78:1550-9. [PMID: 25052003 DOI: 10.1080/09168451.2014.923302] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Peroxisome proliferator activated receptor α (PPARα) ligands, fibrates used to control hyperlipidemia. We demonstrated CYP2B induction by clofibric acid (CFA) however, the mechanism was not clear. In this study, HepG2 cells transfected with expression plasmid of mouse constitutive androstane receptor (CAR) or PPARα were treated with CFA, phenobarbital (PB) or TCPOBOP. Luciferase assays showed that CFA increased CYP2B1 transcription to the same level as PB, or TCPOBOP in HepG2 transfected with mouse CAR But failed to induce it in PPARα transfected cells. CYP2B expressions were increased with PB or CFA in Wistar female rats (having normal levels of CAR) but not in Wistar Kyoto female rats (having low levels of CAR). The induction of CYP2B by PB or CFA was comparable to nuclear CAR levels. CAR nuclear translocation was induced by CFA in both rat strains. This indicates that fibrates can activate CAR and that fibrates-insulin sensitization effect may occur through CAR, while hypolipidemic effect may operate through PPARα.
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Affiliation(s)
- Zein Shaban Ibrahim
- a Faculty of Veterinary Medicine, Department of Physiology , Kafrelsheikh University , Kafrelsheikh , Egypt
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Timsit YE, Negishi M. Coordinated regulation of nuclear receptor CAR by CCRP/DNAJC7, HSP70 and the ubiquitin-proteasome system. PLoS One 2014; 9:e96092. [PMID: 24789201 PMCID: PMC4008524 DOI: 10.1371/journal.pone.0096092] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2013] [Accepted: 04/03/2014] [Indexed: 01/14/2023] Open
Abstract
The constitutive active/androstane receptor (CAR) plays an important role as a coordinate transcription factor in the regulation of various hepatic metabolic pathways for chemicals such as drugs, glucose, fatty acids, bilirubin, and bile acids. Currently, it is known that in its inactive state, CAR is retained in the cytoplasm in a protein complex with HSP90 and the tetratricopeptide repeat protein cytosoplasmic CAR retention protein (CCRP). Upon activation by phenobarbital (PB) or the PB-like inducer 1,4-bis[2-(3,5-dichloropyridyloxy)]-benzene (TCPOBOP), CAR translocates into the nucleus. We have identified two new components to the cytoplasmic regulation of CAR: ubiquitin-dependent degradation of CCRP and protein-protein interaction with HSP70. Treatment with the proteasome inhibitor MG132 (5 µM) causes CAR to accumulate in the cytoplasm of transfected HepG2 cells. In the presence of MG132, TCPOBOP increases CCRP ubiquitination in HepG2 cells co-expressing CAR, while CAR ubiquitination was not detected. MG132 treatment of HepG2 also attenuated of TCPOBOP-induced CAR transcriptional activation on reporter constructs which contain CAR-binding DNA elements derived from the human CYP2B6 gene. The elevation of cytoplasmic CAR protein with MG132 correlated with an increase of HSP70, and to a lesser extent HSP60. Both CCRP and CAR were found to interact with endogenous HSP70 in HepG2 cells by immunoprecipitation analysis. Induction of HSP70 levels by heat shock also increased cytoplasmic CAR levels, similar to the effect of MG132. Lastly, heat shock attenuated TCPOBOP-induced CAR transcriptional activation, also similar to the effect of MG132. Collectively, these data suggest that ubiquitin-proteasomal regulation of CCRP and HSP70 are important contributors to the regulation of cytoplasmic CAR levels, and hence the ability of CAR to respond to PB or PB-like inducers.
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Affiliation(s)
- Yoav E. Timsit
- The Pharmacogenetics Section, Laboratory of Reproductive and Developmental Toxicology, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina, United States of America
| | - Masahiko Negishi
- The Pharmacogenetics Section, Laboratory of Reproductive and Developmental Toxicology, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina, United States of America
- * E-mail:
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Elcombe CR, Peffer RC, Wolf DC, Bailey J, Bars R, Bell D, Cattley RC, Ferguson SS, Geter D, Goetz A, Goodman JI, Hester S, Jacobs A, Omiecinski CJ, Schoeny R, Xie W, Lake BG. Mode of action and human relevance analysis for nuclear receptor-mediated liver toxicity: A case study with phenobarbital as a model constitutive androstane receptor (CAR) activator. Crit Rev Toxicol 2013; 44:64-82. [PMID: 24180433 DOI: 10.3109/10408444.2013.835786] [Citation(s) in RCA: 198] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The constitutive androstane receptor (CAR) and pregnane X receptor (PXR) are important nuclear receptors involved in the regulation of cellular responses from exposure to many xenobiotics and various physiological processes. Phenobarbital (PB) is a non-genotoxic indirect CAR activator, which induces cytochrome P450 (CYP) and other xenobiotic metabolizing enzymes and is known to produce liver foci/tumors in mice and rats. From literature data, a mode of action (MOA) for PB-induced rodent liver tumor formation was developed. A MOA for PXR activators was not established owing to a lack of suitable data. The key events in the PB-induced liver tumor MOA comprise activation of CAR followed by altered gene expression specific to CAR activation, increased cell proliferation, formation of altered hepatic foci and ultimately the development of liver tumors. Associative events in the MOA include altered epigenetic changes, induction of hepatic CYP2B enzymes, liver hypertrophy and decreased apoptosis; with inhibition of gap junctional intercellular communication being an associative event or modulating factor. The MOA was evaluated using the modified Bradford Hill criteria for causality and other possible MOAs were excluded. While PB produces liver tumors in rodents, important species differences were identified including a lack of cell proliferation in cultured human hepatocytes. The MOA for PB-induced rodent liver tumor formation was considered to be qualitatively not plausible for humans. This conclusion is supported by data from a number of epidemiological studies conducted in human populations chronically exposed to PB in which there is no clear evidence for increased liver tumor risk.
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Chatuphonprasert W, Rermraksakul P, Udomsuk L, Lao-ong T, Jarukamjorn K. Different profiles of hepatic alkoxyresorufinO-dealkylase activities in small rodents. J Appl Toxicol 2012; 32:1002-7. [DOI: 10.1002/jat.2756] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2012] [Revised: 02/25/2012] [Accepted: 02/27/2012] [Indexed: 01/12/2023]
Affiliation(s)
- Waranya Chatuphonprasert
- Research Group for Pharmaceutical Activities of Natural Products using Pharmaceutical Biotechnology (PANPB), Faculty of Pharmaceutical Sciences; National Research University-Khon Kaen University; Khon Kaen; 40002; Thailand
| | - Papimon Rermraksakul
- Research Group for Pharmaceutical Activities of Natural Products using Pharmaceutical Biotechnology (PANPB), Faculty of Pharmaceutical Sciences; National Research University-Khon Kaen University; Khon Kaen; 40002; Thailand
| | - Latiporn Udomsuk
- Research Group for Pharmaceutical Activities of Natural Products using Pharmaceutical Biotechnology (PANPB), Faculty of Pharmaceutical Sciences; National Research University-Khon Kaen University; Khon Kaen; 40002; Thailand
| | - Thinnakorn Lao-ong
- Research Group for Pharmaceutical Activities of Natural Products using Pharmaceutical Biotechnology (PANPB), Faculty of Pharmaceutical Sciences; National Research University-Khon Kaen University; Khon Kaen; 40002; Thailand
| | - Kanokwan Jarukamjorn
- Research Group for Pharmaceutical Activities of Natural Products using Pharmaceutical Biotechnology (PANPB), Faculty of Pharmaceutical Sciences; National Research University-Khon Kaen University; Khon Kaen; 40002; Thailand
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Chung H, Boey A, Lumb C, Willoughby L, Batterham P, Daborn PJ. Induction of a detoxification gene in Drosophila melanogaster requires an interaction between tissue specific enhancers and a novel cis-regulatory element. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2011; 41:863-871. [PMID: 21807095 DOI: 10.1016/j.ibmb.2011.07.002] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2011] [Accepted: 07/19/2011] [Indexed: 05/31/2023]
Abstract
Organisms induce the expression of detoxification enzymes such as cytochrome P450s to deal with xenobiotics encountered in the environment. Research using cell culture systems has identified some of the cis-regulatory elements (CREs) and transcription factors involved in the induction of P450 genes in response to xenobiotic challenges. It was recently found that the CREs required for the basal expression of some P450s are distinct from the CREs involved in their induction. How these CREs mediate induction to xenobiotics in a tissue specific manner is not known. In this paper we show that, in Drosophila melanogaster, the induction response of the P450 gene Cyp6g1 to the xenobiotic Phenobarbital (PB) requires the presence of both tissue specific enhancers and a distinct CRE. The CRE does not drive gene expression but is required for the induction response. Site-directed mutagenesis of sequences within the CRE, sequences similar to mouse PB induction sequences, reduces the level of induction by PB, suggesting some degree of mechanistic conservation between flies and mice. This CRE may represent a unique class of CREs that has no inherent role in the basal transcriptional activity of genes, but is required for induction responses. Variations within this class of CREs may explain the variability of gene induction responses.
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Affiliation(s)
- Henry Chung
- Department of Genetics, Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Victoria 3010, Australia
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Higgins LG, Hayes JD. Mechanisms of induction of cytosolic and microsomal glutathione transferase (GST) genes by xenobiotics and pro-inflammatory agents. Drug Metab Rev 2011; 43:92-137. [PMID: 21495793 DOI: 10.3109/03602532.2011.567391] [Citation(s) in RCA: 138] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Glutathione transferase (GST) isoezymes are encoded by three separate families of genes (designated cytosolic, microsomal and mitochondrial transferases), with distinct evolutionary origins, that provide mammalian species with protection against electrophiles and oxidative stressors in the environment. Members of the cytosolic class Alpha, Mu, Pi and Theta GST, and also certain microsomal transferases (MGST2 and MGST3), are up-regulated by a diverse spectrum of foreign compounds typified by phenobarbital, 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene, pregnenolone-16α-carbonitrile, 3-methylcholanthrene, 2,3,7,8-tetrachloro-dibenzo-p-dioxin, β-naphthoflavone, butylated hydroxyanisole, ethoxyquin, oltipraz, fumaric acid, sulforaphane, coumarin, 1-[2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oyl]imidazole, 12-O-tetradecanoylphorbol-13-acetate, dexamethasone and thiazolidinediones. Collectively, these compounds induce gene expression through the constitutive androstane receptor (CAR), the pregnane X receptor (PXR), the aryl hydrocarbon receptor (AhR), NF-E2-related factor 2 (Nrf2), peroxisome proliferator-activated receptor-γ (PPARγ) and CAATT/enhancer binding protein (C/EBP) β. The microsomal T family includes 5-lipoxygenase activating protein (FLAP), leukotriene C(4) synthase (LTC4S) and prostaglandin E(2) synthase (PGES-1), and these are up-regulated by tumour necrosis factor-α, lipopolysaccharide and transforming growth factor-β. Induction of genes encoding FLAP, LTC4S and PGES-1 is mediated by the transcription factors C/EBPα, C/EBPδ, C/EBPϵ, nuclear factor-κB and early growth response-1. In this article we have reviewed the literature describing the mechanisms by which cytosolic and microsomal GST are up-regulated by xenobiotics, drugs, cytokines and endotoxin. We discuss cross-talk between the different induction mechanisms, and have employed bioinformatics to identify cis-elements in the upstream regions of GST genes to which the various transcription factors mentioned above may be recruited.
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Affiliation(s)
- Larry G Higgins
- Biomedical Research Institute, Ninewells Hospital and Medical School, University of Dundee, Dundee DD1 9SY, Scotland, United Kingdom
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14
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Min G. Estrogen modulates transactivations of SXR-mediated liver X receptor response element and CAR-mediated phenobarbital response element in HepG2 cells. Exp Mol Med 2011; 42:731-8. [PMID: 20871212 DOI: 10.3858/emm.2010.42.11.074] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022] Open
Abstract
The nuclear receptors, steroid and xenobiotic receptor (SXR) and constitutive androstane receptor (CAR) play important functions in mediating lipid and drug metabolism in the liver. The present study demonstrates modulatory actions of estrogen in transactivations of SXR-mediated liver X receptor response element (LXRE) and CAR-mediated phenobarbital response element (PBRU). When human estrogen receptor (hERα) and SXR were exogenously expressed, treatment with either rifampicin or corticosterone promoted significantly the SXR-mediated transactivation of LXRE reporter gene in HepG2. However, combined treatment with estrogen plus either rifampicin or corticosterone resulted in less than 50% of the mean values of the transactivation by rifampicin or corticosterone alone. Thus, it is suggested that estrogen may repress the SXR-mediated transactivation of LXRE via functional cross-talk between ER and SXR. The CAR-mediated transactivation of PBRU was stimulated by hERa in the absence of estrogen. However, the potentiation by CAR agonist, TCPOBOP, was significantly repressed by moxestrol in the presence of ER. Thus, ER may play both stimulatory and inhibitory roles in modulating CAR-mediated transactivation of PBRU depending on the presence of their ligands. In summary, this study demonstrates that estrogen modulates transcriptional activity of SXR and CAR in mediating transactivation of LXRE and PBRU, respectively, of the nuclear receptor target genes through functional cross-talk between ER and the corresponding nuclear receptors.
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Affiliation(s)
- Gyesik Min
- Department of Pharmaceutical Engineering, Jinju National University, Jinju 660-758, Korea.
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15
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Omiecinski CJ, Vanden Heuvel JP, Perdew GH, Peters JM. Xenobiotic metabolism, disposition, and regulation by receptors: from biochemical phenomenon to predictors of major toxicities. Toxicol Sci 2011; 120 Suppl 1:S49-75. [PMID: 21059794 PMCID: PMC3145385 DOI: 10.1093/toxsci/kfq338] [Citation(s) in RCA: 242] [Impact Index Per Article: 18.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2010] [Accepted: 11/01/2010] [Indexed: 02/07/2023] Open
Abstract
To commemorate the 50th anniversary of the Society of Toxicology, this special edition article reviews the history and current scope of xenobiotic metabolism and transport, with special emphasis on the discoveries and impact of selected "xenobiotic receptors." This overall research realm has witnessed dynamic development in the past 50 years, and several of the key milestone events that mark the impressive progress in these areas of toxicological sciences are highlighted. From the initial observations regarding aspects of drug metabolism dating from the mid- to late 1800's, the area of biotransformation research witnessed seminal discoveries in the mid-1900's and onward that are remarkable in retrospect, including the discovery and characterization of the phase I monooxygenases, the cytochrome P450s. Further research uncovered many aspects of the biochemistry of xenobiotic metabolism, expanding to phase II conjugation and phase III xenobiotic transport. This led to hallmark developments involving integration of genomic technologies to elucidate the basis for interindividual differences in response to xenobiotic exposures and discovery of nuclear and soluble receptor families that selectively "sense" the chemical milieu of the mammalian cell and orchestrate compensatory changes in gene expression programming to accommodate complex xenobiotic exposures. This review will briefly summarize these developments and investigate the expanding roles of xenobiotic receptor biology in the underlying basis of toxicological response to chemical agents.
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Affiliation(s)
- Curtis J Omiecinski
- Department of Veterinary and Biomedical Sciences, Center for Molecular Toxicology and Carcinogenesis, Penn State University, University Park, Pennsylvania 16802, USA.
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Correia MA, Sinclair PR, De Matteis F. Cytochrome P450 regulation: the interplay between its heme and apoprotein moieties in synthesis, assembly, repair, and disposal. Drug Metab Rev 2010; 43:1-26. [PMID: 20860521 DOI: 10.3109/03602532.2010.515222] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Heme is vital to our aerobic universe. Heme cellular content is finely tuned through an exquisite control of synthesis and degradation. Heme deficiency is deleterious to cells, whereas excess heme is toxic. Most of the cellular heme serves as the prosthetic moiety of functionally diverse hemoproteins, including cytochromes P450 (P450s). In the liver, P450s are its major consumers, with >50% of hepatic heme committed to their synthesis. Prosthetic heme is the sine qua non of P450 catalytic biotransformation of both endo- and xenobiotics. This well-recognized functional role notwithstanding, heme also regulates P450 protein synthesis, assembly, repair, and disposal. These less well-appreciated aspects are reviewed herein.
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Affiliation(s)
- Maria Almira Correia
- Department of Cellular and Molecular Pharmacology, The Liver Center, University of California, San Francisco, 94158, USA.
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Interplay between cholesterol and drug metabolism. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2010; 1814:146-60. [PMID: 20570756 DOI: 10.1016/j.bbapap.2010.05.014] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/30/2010] [Revised: 05/17/2010] [Accepted: 05/24/2010] [Indexed: 12/14/2022]
Abstract
Cholesterol biosynthetic and metabolic pathways contain several branching points towards physiologically active molecules, such as coenzyme Q, vitamin D, glucocorticoid and steroid hormones, oxysterols, or bile acids. Sophisticated regulatory mechanisms are involved in maintenance of the homeostasis of not only cholesterol but also other cholesterogenic molecules. In addition to endogenous cues, cholesterol homeostasis needs to accommodate also to exogenous cues that are imported into the body, such as chemicals and medications. Steroid and nuclear receptors together with sterol regulatory element-binding protein (SREBP) mediate the fine tuning of biosynthetic and metabolic routes as well as transports of cholesterol and its derivatives. Similarly, drug/xenobiotic metabolism is the subject to the feedback regulation of cytochrome P450 enzymes and transporters. The regulatory mechanisms that maintain the homeostasis of cholesterogenic molecules and are involved in drug metabolism share similarities. Cholesterol and cholesterogenic compounds (bile acids, glucocorticoids, vitamin D, etc.) regulate the xenosensor signaling in drug-mediated induction of the major drug-metabolizing cytochrome P450 enzymes. The key cellular receptors, pregnane X receptor (PXR), constitutive androstane receptor (CAR), vitamin D receptor (VDR), and glucocorticoid receptor (GR) provide a functional cross-talk between the pathways maintaining cholesterol homeostasis and controlling the expression of drug-metabolizing enzymes. These receptors serve as metabolic sensors, resulting in a coordinate regulation of cholesterogenic compounds metabolism and of the defense against xenobiotic and endobiotic toxicity. Herein we present a comprehensive review of functional interactions between cholesterol homeostasis and drug metabolism involving the main nuclear and steroid receptors.
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Audet-Walsh E, Auclair-Vincent S, Anderson A. Glucocorticoids and phenobarbital induce murine CYP2B genes by independent mechanisms. Expert Opin Drug Metab Toxicol 2010; 5:1501-11. [PMID: 19732027 DOI: 10.1517/17425250903234709] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
BACKGROUND Genes for CYP of the 2B subfamily (CYP2B genes) have long been known to be inducible in murine liver by phenobarbital and phenobarbital-like inducers. More recently, it has become clear that glucocorticoids can also induce these genes by a mechanism independent of that of phenobarbital-like inducers. OBJECTIVE To summarize the evidence for the existence of two distinct molecular mechanisms for induction of murine CYP2B genes and to analyze the wider implications of this situation for inducible xenobiotic metabolism. METHODS The mechanism of action of phenobarbital-like inducers of murine CYP2B genes is first briefly summarized. The role of glucocorticoids in the induction of various proteins, particularly rat phosphoenolpyruvate carboxykinase, where transcriptional activation is achieved via a glucocorticoid response unit, is also discussed. Finally, recent results are presented on glucocorticoid induction of murine CYP2B genes, including evidence for the presence of a functional glucocorticoid response unit in the rat CYP2B2 gene and for the role of constitutive androstane receptor as an accessory factor in this response. RESULTS/CONCLUSION Murine CYP2B genes are seen to respond to two distinct regulatory mechanisms, but much remains to be learned concerning the interactions between these two regulatory loops, as well as the details of glucocorticoid induction.
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Affiliation(s)
- Etienne Audet-Walsh
- Centre de recherche en cancérologie de l'Université Laval, L'Hôtel-Dieu de Québec, CHUQ, 11, côte du Palais, Québec, Canada
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Lachaud AA, Auclair-Vincent S, Massip L, Audet-Walsh E, Lebel M, Anderson A. Werner's syndrome helicase participates in transcription of phenobarbital-inducible CYP2B genes in rat and mouse liver. Biochem Pharmacol 2009; 79:463-70. [PMID: 19737542 DOI: 10.1016/j.bcp.2009.09.002] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2009] [Revised: 09/01/2009] [Accepted: 09/01/2009] [Indexed: 10/20/2022]
Abstract
Werner's syndrome (WS) is a rare human autosomal recessive segmental progeroid syndrome clinically characterized by atherosclerosis, cancer, osteoporosis, type 2 diabetes mellitus and ocular cataracts. The WRN gene codes for a RecQ helicase which is present in many tissues. Although the exact functions of the WRN protein remain unclear, accumulating evidence suggests that it participates in DNA repair, replication, recombination and telomere maintenance. It has also been proposed that WRN participates in RNA polymerase II-dependent transcription. However no promoter directly targeted by WRN has yet been identified. In this work, we report mammalian genes that are WRN targets. The rat CYP2B2 gene and its closely related mouse homolog, Cyp2b10, are both strongly induced in liver by phenobarbital. We found that there is phenobarbital-dependent recruitment of WRN to the promoter of the CYP2B2 gene as demonstrated by chromatin immunoprecipitation analysis. Mice homozygous for a Wrn mutation deleting part of the helicase domain showed a decrease in basal and phenobarbital-induced CYP2B10 mRNA levels compared to wild type animals. The phenobarbital-induced level of CYP2B10 protein was also reduced in the mutant mice. Electrophoretic mobility shift assays showed that WRN can participate in the formation of a complex with a specific sequence within the CYP2B2 basal promoter. Hence, there is a WRN binding site in a region of DNA sequence to which WRN is recruited in vivo. Taken together, these results suggest that WRN participates in transcription of CYP2B genes in liver and identifies the first physical interaction between a specific promoter sequence and WRN.
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Affiliation(s)
- Antoine Amaury Lachaud
- Centre de recherche en cancérologie de l'Université Laval, L'Hôtel-Dieu de Québec, CHUQ, Québec, Canada
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He J, Xie W. Chapter 3 Nuclear Xenobiotic Receptors. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2009; 87:87-116. [DOI: 10.1016/s1877-1173(09)87003-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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Audet-Walsh E, Anderson A. Dexamethasone induction of murine CYP2B genes requires the glucocorticoid receptor. Drug Metab Dispos 2008; 37:580-8. [PMID: 19047470 DOI: 10.1124/dmd.108.022772] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Hepatic cytochrome P450 (P450) enzymes metabolize exogenous and endogenous compounds, and many are inducible by xenobiotics. Their synthesis is tightly regulated, particularly through nuclear receptors. Expression of murine CYP2B genes is strongly activated by treatment with phenobarbital or phenobarbital-like inducers, and a detectable response requires the presence of the constitutive androstane receptor (CAR). However, other compounds can also induce murine CYP2B proteins. For example, dexamethasone is known to induce rat CYP2B1 and CYP2B2 and mouse CYP2B10. Using human HepG2 and rat H4IIEC3 hepatoma cell lines, we found that dexamethasone induction of CYP2B2 and Cyp2b10 luciferase reporters required the glucocorticoid receptor. Given the well known observation that CYP2B genes are not phenobarbital-responsive in cultured cell lines, the dexamethasone responsiveness of CYP2B reporter constructs in cell lines demonstrates in itself that the mechanism of dexamethasone induction is distinct from that of phenobarbital. We also analyzed the relative importance of the phenobarbital response unit (PBRU) and of a known glucocorticoid response element in this response. Both sites contributed to the response, but other sites were required for maximal induction. CAR was also found to act as an accessory factor to stimulate the response to dexamethasone by the glucocorticoid receptor. Furthermore, in H4IIEC3 cells, CAR activated the PBRU in the natural sequence context of the CYP2B2 and Cyp2b10 5' flanks. In summary, there are at least two independent mechanisms of CYP2B induction: one involving phenobarbital and phenobarbital-like inducers and another involving glucocorticoids that induce via the glucocorticoid receptor with CAR acting as an accessory factor.
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Affiliation(s)
- Etienne Audet-Walsh
- Centre de Recherche en Cancérologie de l'Université Laval, L'Hôtel-Dieu de Québec, Centre Hospitalier Universitaire de Québec, Québec, Québec, Canada
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Wang H, Tompkins LM. CYP2B6: new insights into a historically overlooked cytochrome P450 isozyme. Curr Drug Metab 2008; 9:598-610. [PMID: 18781911 DOI: 10.2174/138920008785821710] [Citation(s) in RCA: 229] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Human CYP2B6 has been thought to account for a minor portion (<1%) of total hepatic cytochrome P450 (CYP) content and to have a minor function in human drug metabolism. Recent studies, however, indicate that the average relative contribution of CYP2B6 to total hepatic CYP content ranges from 2% to 10%. An increased interest in CYP2B6 research has been stimulated by the identification of an ever-increasing substrate list for this enzyme, polymorphic and ethnic variations in expression levels, and evidence for cross-regulation with CYP3A4, UGT1A1 and several hepatic drug transporters by the nuclear receptors pregnane X receptor and constitutive androstane receptor. Moreover, 20- to 250-fold interindividual variation in CYP2B6 expression has been demonstrated, presumably due to transcriptional regulation and polymorphisms. These individual differences may result in variable systemic exposure to drugs metabolized by CYP2B6, including the antineoplastics cyclophosphamide and ifosfamide, the antiretrovirals nevirapine and efavirenz, the anesthetics propofol and ketamine, the synthetic opioid methadone, and the anti-Parkinsonian selegiline. The potential clinical significance of CYP2B6 further enforces the need for a comprehensive review of this xenobiotic metabolizing enzyme. This communication summarizes recent advances in our understanding of this traditionally neglected enzyme and provides an overall picture of CYP2B6 with respect to expression, localization, substrate-specificity, inhibition, regulation, polymorphisms and clinical significance. Emphasis is given to nuclear receptor mediated transcriptional regulation, genetic polymorphisms, and their clinical significance.
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Affiliation(s)
- Hongbing Wang
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland at Baltimore, 20 Penn Street, Baltimore, MD 21201, USA.
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The CYP2B2 5′ flank contains a complex glucocorticoid response unit. Biochem Pharmacol 2008; 76:1298-306. [DOI: 10.1016/j.bcp.2008.08.015] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2008] [Revised: 08/08/2008] [Accepted: 08/13/2008] [Indexed: 11/24/2022]
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Kodama S, Negishi M. Phenobarbital Confers its Diverse Effects by Activating the Orphan Nuclear Receptor Car. Drug Metab Rev 2008; 38:75-87. [PMID: 16684649 DOI: 10.1080/03602530600569851] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
In the early 1960s, phenobarbital (PB) was shown to induce hepatic drug metabolism and the induction was implicated in the molecular mechanism of drug tolerance development. Since then, it has become evident that PB not only induces drug metabolism, but also triggers pleiotropic effects on liver function, such as cell growth and communication, proliferation of the endoplasmic reticulum, tumor promotion, glucose metabolism, steroid/thyroid hormone metabolism, and bile acid synthesis. Upon activation by PB and numerous PB-type inducers, the nuclear receptor CAR mediates those pleiotropic actions by regulating various hepatic genes, utilizing multiple regulatory mechanisms.
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Affiliation(s)
- Susumu Kodama
- Pharmacogenetics Section, Laboratory of Reproductive and Developmental Toxicology, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA
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Pascussi JM, Gerbal-Chaloin S, Drocourt L, Assénat E, Larrey D, Pichard-Garcia L, Vilarem MJ, Maurel P. Cross-talk between xenobiotic detoxication and other signalling pathways: clinical and toxicological consequences. Xenobiotica 2008; 34:633-64. [PMID: 15672753 DOI: 10.1080/00498250412331285454] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
1. Recent investigations on nuclear receptors and other transcription factors involved in the regulation of genes encoding xenobiotic metabolizing and transport systems reveal that xenobiotic-dependent signalling pathways are embedded in, and establish functional interactions with, a tangle of regulatory networks involving the glucocorticoid and oestrogen receptors, the hypoxia-inducible factor, the vitamin D receptor and other transcription factors/nuclear receptors controlling cholesterol/bile salt homeostasis and liver differentiation. 2. Such functional interferences provide new insight, first for understanding how xenobiotics might exert adverse effects, and second how physiopathological stimuli affect xenobiotic metabolism.
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Affiliation(s)
- J M Pascussi
- INSERM U632, Hepatic Physiopathology, Montpellier F-34293, France
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Pustylnyak VO, Gulyaeva LF, Lyakhovich VV. Induction of cytochrome P4502B: Role of regulatory elements and nuclear receptors. BIOCHEMISTRY (MOSCOW) 2007; 72:608-17. [PMID: 17630905 DOI: 10.1134/s000629790706003x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Cytochrome P450 of the 2B subfamily is easily induced by many xenobiotics. In spite of intensive investigations, the molecular mechanisms of regulation of the CYP2B genes are not clear. The nuclear receptor CAR is shown to play a crucial role in the activation of CYP2B genes by xenobiotics, but many problems of CAR activation in different animal species and humans remain unsolved. This review focuses on signaling pathways involved in the control of CYP2B gene expression in mammals.
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Affiliation(s)
- V O Pustylnyak
- Institute of Molecular Biology and Biophysics, Siberian Division of the Russian Academy of Medical Sciences, Novosibirsk 630117, Russia.
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Min G. Effects of TK promotor and hepatocyte nuclear factor-4 in CAR-mediated transcriptional activity of phenobarbital responsive unit of CYP2B gene in monkey kidney epithelial-derived cell line COS-7. Ann N Y Acad Sci 2007; 1091:258-69. [PMID: 17341620 DOI: 10.1196/annals.1378.072] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Previous studies reported that constitutive androstane receptor (CAR) does not transactivate phenobarbital responsive unit (PBRU)2C1luciferase reporter gene in COS cells in which endogenous CYP2B1 gene is not induced with PB. In order to understand molecular mechanism(s) whereby PBRU is transactivated, this article determined if the use of strong thymidine kinase (TK) promotor rather than the minimal CYP2C1 promotor, and hepatocyte nuclear factor-4 (HNF-4) can affect CAR-mediated transactivation of PBRU in the monkey kidney epithelial-derived COS-7 cells. To examine CAR-mediated transactivation, cultured COS-7 cells were transfected with CAR expression plasmid, pEGFP-mCAR1, and confirmed for high level of the protein expression. In COS-7 cells, TK promotor induced CAR-mediated PBRU transactivation in a dose-dependent manner. Whereas expression of HNF-4 slightly promoted PBRU transactivation with low amount of CAR transfected, it repressed PBRU transactivation in a dose-dependent manner with high amount of CAR. Consistent with the previous reports in Hep G2 cells, CAR transactivated PBRU2C1luciferase in a dose-dependent manner and this CAR-mediated transactivation required functional NR-1 and NF-1 sites. However, HNF-4 did not affect CAR-mediated PBRU transactivation in Hep G2 cells. These results suggest that proximal promotor and a trans-acting factor, HNF-4, can affect CAR-mediated transactivation of PBRU in COS-7 cells.
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Affiliation(s)
- Gyesik Min
- Department of Microbiological Engineering, Jinju National University, Jinju, Gyeongsangnam-Do, 660-758 Korea.
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Akgül B, Tu CPD. Regulation of mRNA stability through a pentobarbital-responsive element. Arch Biochem Biophys 2006; 459:143-50. [PMID: 17234150 PMCID: PMC2694843 DOI: 10.1016/j.abb.2006.10.026] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2006] [Revised: 10/22/2006] [Accepted: 10/24/2006] [Indexed: 11/23/2022]
Abstract
Pentobarbital, a general anesthetic and non-genotoxic carcinogen, can induce gene expression by activating transcription. In the Drosophila glutathione S-transferase D21 (gstD21) gene, pentobarbital's regulatory influence extends to the level of mRNA turnover. Transcribed from an intronless gene, gstD21 mRNA is intrinsically very labile. But exposure to pentobarbital renders it stabilized beyond what can be attributed to transcriptional activation. We aim here to identify cis-acting element(s) of gstD21 mRNA as contributors to the molecule's pentobarbital-mediated stabilization. In the context of hsp70 5'UTR and the 3'UTR of act5C, gstD21 mRNA, minus its native UTRs, is stable. Maintaining the same context of heterologous UTRs, we can reconstitute using the full-length gstD21 sequence the inherent instability of gstD21 mRNA and its stabilization by pentobarbital. Transgenic flies that express these chimeric gstD21 mRNA exhibit decay intermediates lacking 3'UTR, which are not stabilized by PB treatment. The 3'UTR sequence, when inserted downstream from a reporter transcript, stabilizes it 1.6-fold under PB treatment. The analysis of the decay intermediates suggests a polysome-associated decay pattern. We propose a regulatory model that features a 59-nucleotide pentobarbital-responsive element (PBRE) in the 3'UTR of gstD21 mRNA.
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Affiliation(s)
- Bünyamin Akgül
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802 U.S.A
- Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan 11529, Republic of China
- Department of Biology, Izmir Institute of Technology, Urla, Izmir, 35430, Turkey
| | - Chen-Pei D. Tu
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802 U.S.A
- Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan 11529, Republic of China
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Zhang Q, Bae Y, Kemper JK, Kemper B. Analysis of multiple nuclear receptor binding sites for CAR/RXR in the phenobarbital responsive unit of CYP2B2. Arch Biochem Biophys 2006; 451:119-27. [PMID: 16725103 DOI: 10.1016/j.abb.2006.04.016] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2006] [Revised: 04/19/2006] [Accepted: 04/20/2006] [Indexed: 10/24/2022]
Abstract
The phenobarbital (PB) responsive enhancers in CYP2B genes contain a core of two direct repeat-4 nuclear receptor binding sites, NR-1 and NR-2, which flank an NF-1 site and appear to be most important for PB responsiveness. Additional sequences outside the core are required for maximal PB responsiveness, including a third direct repeat-4 site, NR-3. The PB response is mediated by constitutive androstane receptor (CAR) which binds as a CAR/RXR heterodimer to the NR sites. To determine the relative importance of the third NR site, each of the NR sites was mutated individually and in all combinations in the rat PB responsive unit (PBRU). Mutation of NR-3 resulted in similar effects on transactivation of the PBRU by CAR in HepG2 cells as did mutations of NR-1 and NR-2. The recruitment of GRIP1/SRC-2 by CAR/RXR to the PBRU assessed by gel shift assays was cooperatively enhanced if more than one NR site in the PBRU was occupied by CAR/RXR. NR-3 in combination with NR-1 or NR-2 was equal to NR-1 and NR-2 in mediating this cooperative recruitment. Recruitment of SRC-1 and GRIP1/SRC-2 was similar for all NR sites, while some selectivity of NR-1 for SRC-3 was observed. SRC-3 also exhibited CAR-independent activation of the PBRU in HepG2 cells. Micrococcal nuclease mapping of nucleosomes revealed that the NR-1/NR-2 core of the PBRU is present in a nucleosome while NR-3 is present in the linker adjacent to the nucleosome. In the linear sequence NR-3 is further from NR-1 than NR-2 is, but in a nucleosomal structure, NR-3 is well positioned for cooperative recruitment of GRIP1/SRC-2 by CAR/RXR that is bound to NR-3 and either NR-1 or NR-2, while NR-1 and NR-2 are on opposite sides of the nucleosome separated by the histone core. These results demonstrate that NR-3 is functionally similar to NR-1 and NR-2 in CAR transactivation of the PBRU in vitro and suggest that NR-3 may have a greater role in a chromatin context in vivo than is apparent from transient transfection studies.
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MESH Headings
- Animals
- Base Sequence
- Binding Sites
- Carcinoma, Hepatocellular/enzymology
- Carcinoma, Hepatocellular/metabolism
- Carcinoma, Hepatocellular/pathology
- Cell Culture Techniques
- Cell Line, Tumor
- Constitutive Androstane Receptor
- Cytochrome P-450 CYP2B1/chemistry
- Cytochrome P-450 CYP2B1/metabolism
- Dimerization
- Hepatocytes/enzymology
- Hepatocytes/metabolism
- Humans
- Liver Neoplasms/enzymology
- Liver Neoplasms/metabolism
- Liver Neoplasms/pathology
- Mice
- Models, Molecular
- Molecular Sequence Data
- Mutagenesis, Site-Directed
- Mutation
- Nucleosomes/chemistry
- Phenobarbital/pharmacology
- Receptors, Cytoplasmic and Nuclear/chemistry
- Receptors, Cytoplasmic and Nuclear/genetics
- Receptors, Cytoplasmic and Nuclear/metabolism
- Retinoid X Receptors/chemistry
- Retinoid X Receptors/genetics
- Retinoid X Receptors/metabolism
- Sequence Analysis, DNA
- Transcription Factors/chemistry
- Transcription Factors/genetics
- Transcription Factors/metabolism
- Transcriptional Activation
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Affiliation(s)
- Quanyuan Zhang
- Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
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Lin JH. CYP Induction-Mediated Drug Interactions: in Vitro Assessment and Clinical Implications. Pharm Res 2006; 23:1089-116. [PMID: 16718615 DOI: 10.1007/s11095-006-0277-7] [Citation(s) in RCA: 170] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2005] [Accepted: 02/27/2006] [Indexed: 01/31/2023]
Abstract
Cytochrome P450 (CYP) induction-mediated interaction is one of the major concerns in clinical practice and for the pharmaceutical industry. There are two major issues associated with CYP induction: a reduction in therapeutic efficacy of comedications and an induction in reactive metabolite-induced toxicity. Because CYP induction is a metabolic liability in drug therapy, it is highly desirable to develop new drug candidates that are not potent CYP inducer to avoid the potential of CYP induction-mediated drug interactions. For this reason, today, many drug companies routinely include the assessment of CYP induction at the stage of drug discovery as part of the selection processes of new drug candidates for further clinical development. The purpose of this article is to review the molecular mechanisms of CYP induction and the clinical implications, including pharmacokinetic and pharmacodynamic consequences. In addition, factors that affect the degree of CYP induction and extrapolation of in vitro CYP induction data to in vivo situations will also be discussed. Finally, assessment of the potential of CYP induction at the drug discovery and development stage will be discussed.
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Affiliation(s)
- Jiunn H Lin
- Department of Preclinical Drug Metabolism, Merck Research Laboratories, West Point, Pennsylvania, USA.
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Joannard F, Rissel M, Gilot D, Anderson A, Orfila-Lefeuvre L, Guillouzo A, Atfi A, Lagadic-Gossmann D. Role for mitogen-activated protein kinases in phenobarbital-induced expression of cytochrome P450 2B in primary cultures of rat hepatocytes. Toxicol Lett 2006; 161:61-72. [PMID: 16154717 DOI: 10.1016/j.toxlet.2005.08.006] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2005] [Revised: 08/03/2005] [Accepted: 08/05/2005] [Indexed: 10/25/2022]
Abstract
Phenobarbital (PB) alters expression of numerous hepatic genes, including genes of cytochrome P450 2B1 and 2B2 (CYP2B). However, the intracellular mechanisms remain to be fully elucidated. The present study investigated the involvement of mitogen-activated protein kinases (MAPKs) in rat hepatocytes in primary culture. We showed that PB induced an early, dose-dependent activation of ERK (extracellular signal-regulated kinase), JNK (c-Jun N-terminal kinase) and p38 MAPKs. Regarding the PB (1mM) induction of CYP2B mRNA expression, while chemically inhibiting JNK had no effect, specific inhibitors of the ERK (U0-126) and p38 (SB-203580) pathways up- and down-regulated this expression, respectively. However, although such a regulation was confirmed when testing the effect of a dominant negative mutant of the ERK pathway on the CYP2B2 enhancer-promoter activity, no such transcriptional role was found with the p38 pathway. Moreover, upon arrest of transcription, the stability of CYP2B mRNA remained unaffected by SB-203580. In conclusion, we show that the ERK pathway negatively regulates CYP2B2 enhancer-promoter activity and that, despite p38 activation upon PB exposure, the sensitivity of CYP2B mRNA expression to SB-203580 appears to be unrelated to this kinase.
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Affiliation(s)
- Florence Joannard
- INSERM UMR 620, Faculté de Pharmacie, Université Rennes 1, 2 av Prof Léon Bernard, 35043 Rennes Cedex, France
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Beaudet MJ, Desrochers M, Lachaud A, Anderson A. The CYP2B2 phenobarbital response unit contains binding sites for hepatocyte nuclear factor 4, PBX-PREP1, the thyroid hormone receptor beta and the liver X receptor. Biochem J 2005; 388:407-18. [PMID: 15656786 PMCID: PMC1138947 DOI: 10.1042/bj20041556] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
A 163 bp enhancer in the CYP2B2 5' flank confers PB (phenobarbital) inducibility and constitutes a PBRU (PB response unit). The PBRU contains several transcription factor binding sites, including NR1, NR2 and NR3, which are direct repeats separated by 4 bp of the nuclear receptor consensus half-site AGGTCA, as well as an ER (everted repeat) separated by 7 bp (ER-7). Constitutive androstane receptor (CAR)-RXR (retinoic X receptor) heterodimers are known to bind to NR1, NR2 and NR3. Electrophoretic mobility-shift analysis using nuclear extracts from livers of untreated or PB-treated rats revealed binding of several other proteins to different PBRU elements. Using supershift analysis and in vitro coupled transcription and translation, the proteins present in four retarded complexes were identified as TRbeta (thyroid hormone receptor beta), LXR (liver X receptor), HNF-4 (hepatocyte nuclear factor 4) and heterodimers of PBX-PREP1 (pre-B cell homoeobox-Pbx regulatory protein 1). LXR-RXR heterodimers bound to NR3 and TRbeta bound to NR3, NR1 and ER-7, whereas the PBX-PREP1 site is contained within NR2. The HNF-4 site overlaps with NR1. A mutation described previously, GRE1m1, which decreases PB responsiveness, increased the affinity of this site for HNF-4. The PBRU also contains a site for nuclear factor 1. The PBRU thus contains a plethora of transcription factor binding sites. The profiles of transcription factor binding to NR1 and NR3 were quite similar, although strikingly different from, and more complex than, that of NR2. This parallels the functional differences in conferring PB responsiveness between NR1 and NR3 on the one hand, and NR2 on the other.
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Affiliation(s)
- Marie-Josée Beaudet
- Centre de recherche en cancérologie de l'Université Laval, L'Hôtel-Dieu de Québec, Centre hospitalier universitaire de Québec, Québec G1R 2J6, Canada, and Département de biologie, Université Laval, Québec G1K 7P4, Canada
| | - Marc Desrochers
- Centre de recherche en cancérologie de l'Université Laval, L'Hôtel-Dieu de Québec, Centre hospitalier universitaire de Québec, Québec G1R 2J6, Canada, and Département de biologie, Université Laval, Québec G1K 7P4, Canada
| | - Antoine Amaury Lachaud
- Centre de recherche en cancérologie de l'Université Laval, L'Hôtel-Dieu de Québec, Centre hospitalier universitaire de Québec, Québec G1R 2J6, Canada, and Département de biologie, Université Laval, Québec G1K 7P4, Canada
| | - Alan Anderson
- Centre de recherche en cancérologie de l'Université Laval, L'Hôtel-Dieu de Québec, Centre hospitalier universitaire de Québec, Québec G1R 2J6, Canada, and Département de biologie, Université Laval, Québec G1K 7P4, Canada
- To whom correspondence should be addressed (email )
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Kretschmer XC, Baldwin WS. CAR and PXR: xenosensors of endocrine disrupters? Chem Biol Interact 2005; 155:111-28. [PMID: 16054614 DOI: 10.1016/j.cbi.2005.06.003] [Citation(s) in RCA: 220] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2005] [Revised: 06/14/2005] [Accepted: 06/20/2005] [Indexed: 01/05/2023]
Abstract
The pregnane X-receptor (PXR) and the constitutive androstane receptor (CAR) are orphan nuclear receptors activated by a variety of ligands. Currently it remains uncertain whether these receptors have a high-affinity ligand or instead function as more generalized steroid/xenobiotic sensors. Both receptors are important regulators of several steroid and xenobiotic detoxification enzymes and transporters (phases I-III) in the liver and intestine and thus are important regulators of adaptation to chemical stress. The detoxification proteins induced are responsible for the metabolism, deactivation and transport of bile acids, thyroid and steroid hormones, numerous environmental chemicals, and several drugs. PXR and CAR received their names because of steroid ligands that activate and inhibit their transcriptional activity, respectively. Interestingly, some steroids and steroid mimics activate one or both receptors, including several endocrine disrupting chemicals. Environmental estrogens, such as the pesticides methoxychlor, endosulfan, dieldrin, DDT, and the plasticizer nonylphenol activate either PXR or both PXR and CAR. Because PXR and CAR are activated by numerous steroids and endocrine disrupters, it appears that these receptors protect the integrity of the endocrine system. They recognize an increase in steroid-like chemicals and, in turn, induce detoxification. Furthermore, PXR and CAR induce enzymes, such as the CYP2B and CYP3A family members, responsible for the metabolism of steroid and thyroid hormones and this may alter their normal physiological function. This review summarizes the available data on the activity of endocrine disrupters and endocrine active chemicals on PXR and CAR, examines the role of PXR and CAR in protection from these chemicals, and evaluates potential adverse physiological consequences of PXR and CAR activation.
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Affiliation(s)
- Xiomara C Kretschmer
- University of Texas at El Paso, Biological Sciences, 500 W. University Ave., El Paso, TX 79968, USA
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Eloranta JJ, Kullak-Ublick GA. Coordinate transcriptional regulation of bile acid homeostasis and drug metabolism. Arch Biochem Biophys 2005; 433:397-412. [PMID: 15581596 DOI: 10.1016/j.abb.2004.09.019] [Citation(s) in RCA: 193] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2004] [Revised: 09/13/2004] [Indexed: 02/08/2023]
Abstract
Drugs and bile acids are taken up into hepatocytes by specialized transport proteins localized at the basolateral membrane, e.g., organic anion transporting polypeptides . Following intracellular metabolism by cytochrome P450 (CYP) enzymes, drug metabolites are excreted into bile or urine via ATP-dependent multidrug resistance proteins (MDR1 and MRPs). Bile acids are excreted mainly via the bile salt export pump (BSEP, ABCB11). The genes coding for drug and bile acid transporters and CYP enzymes are regulated by a complex network of transcriptional cascades, notably by the ligand-activated nuclear receptors FXR, PXR, and CAR and by the ligand-independent nuclear receptor HNF-4alpha. The bile acid synthesizing enzymes CYP7A1, CYP8B1, and CYP27A1 are subject to negative feedback regulation by bile acids, which is partly mediated through the transcriptional repressor SHP. The role of transcriptional cofactors, such as SRC-1 and PGC-1, in mediating the gene-specific effects of individual nuclear receptors is becoming increasingly evident.
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Affiliation(s)
- Jyrki J Eloranta
- Laboratory of Molecular Gastroenterology and Hepatology, Department of Internal Medicine, University Hospital, CH-8091 Zurich, Switzerland
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Roberge C, Beaudet MJ, Anderson A. GABAA/central benzodiazepine receptor and peripheral benzodiazepine receptor ligands as inducers of phenobarbital-inducible CYP2B and CYP3A. Biochem Pharmacol 2004; 68:1383-9. [PMID: 15345328 DOI: 10.1016/j.bcp.2004.06.005] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2004] [Accepted: 06/07/2004] [Indexed: 10/26/2022]
Abstract
A sequence critical for phenobarbital (PB) induction, the PB response unit (PBRU), situated upstream of the rat CYP2B1 and CYP2B2 genes, includes two nuclear receptor binding sites, NR1 and NR2. When NR1 and NR2 are mutated PB responsiveness is abolished. While no nuclear receptor for which PB is an agonist ligand has yet been identified, PB is a ligand of GABA(A) receptors and it can displace [(3)H] 1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinolinecarboxamide (PK 11195) from its binding site on the peripheral benzodiazepine receptor (PBR). We assessed CYP2B levels in primary rat hepatocytes following treatment with 10 ligands of either or both of these receptors. All compounds tested were found to be CYP2B1/CYP2B2 inducers and most were CYP3A inducers. Five had not previously been described as CYP2B1/CYP2B2 inducers: bicuculline, flunitrazepam, 4'-chlorodiazepam (Ro5-4864), N,N-dihexyl-2-(4-fluorophenyl)indole-3-acetamide (FGIN 1-27) and 7-(dimethylcarbamoyloxy)-6-phenylpyrrolo-[2,1-d][1,5]benzothiazepine (DCPPBT). Reporter gene analysis demonstrated that CYP2B induction by these agents and other PBR or GABA(A) receptor ligands is mediated through the PBRU and the NR1/NR2 sites, suggesting a molecular mechanism similar to that for PB induction. The potencies for PBRU-dependent induction by 11 ligands of PBR or the GABA(A) receptor was evaluated. FGIN-127, DCPPBT and PK 11195 exhibited EC(50) values for PBRU-dependent transcription activation about three orders of magnitude higher than the reported affinities of the PBR for these agents, arguing against the involvement of the PBR in PB induction. However the EC(50) values found for the agents tested encourage further investigation on the possible involvement of the GABA(A) receptor in PB induction.
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Affiliation(s)
- Christian Roberge
- Centre de Recherche de l'Hôtel-Dieu de Québec, Québec, Canada G1R2J6
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Yamamoto M, Mise M, Matsumoto S, Ito S, Gohyama N, Ishida S, Sagara Y, Omiecinski CJ, Oguri K, Yamada H. Comparison of genomic and cDNA sequences of guinea pig CYP2B18 and rat CYP2B2: absence of a phenobarbital-responsive enhancer module in the upstream region of the CYP2B18 gene. J Biochem Mol Toxicol 2004; 18:124-30. [PMID: 15252867 DOI: 10.1002/jbt.20016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Potential mechanisms were investigated whereby CYP2B18, a cytochrome P450 gene exhibiting high constitutive expression but only low levels of phenobarbital-inducibility in the guinea pig liver, may be differentially regulated versus the highly inducible rat CYP2B2 gene. To comparatively assess potential regulatory sequences associated with CYP2B18, a guinea pig genomic library was screened enabling isolation of the CYP2B18 gene. The genomic screening process resulted in the identification of at least four closely-related CYP2B18 genes, designated here as CYP2B18A-D. Of these isolates, CYP2B18A exhibited sequence identical to that of the CYP2B18 cDNA. Further, the deduced amino acid sequence of the CYP2B18 cDNA was identical to that of N-terminal and internally-derived peptide sequences obtained in this investigation from CYP2B18 protein isolated from guinea pig liver. Genomic structural sequences were derived for CYP2B18A, together with the respective 5'-upstream and intronic regions of the gene. Comparison of the CYP2B18A and CYP2B2 gene sequences revealed the lack of repetitive LINE gene sequences in CYP2B18A, putative silencing elements that effect neighboring genes, although these sequences were present in both 5'-upstream and 3'-downstream regions of CYP2B2. We determined that the phenobarbital-responsive enhancer module was absent from the 5'-upstream region as well as the intronic regions of CYP2B18A gene. We hypothesize that the compromised phenobarbital inducibility of CYP2B18A stems from its lack of a functional phenobarbital responsive enhancer module.
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Affiliation(s)
- Midori Yamamoto
- Graduate School of Pharmaceutical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan
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Abstract
During the past several years, important advances have been made in our understanding of the mechanisms that regulate the expression of genes that determine drug clearance, including phase I and phase II drug-metabolising enzymes and drug transporters. Orphan nuclear receptors have been recognised as key mediators of drug-induced changes in both metabolism and efflux mechanisms. In this review, we summarise recent findings regarding the function of nuclear receptors in regulating drug-metabolising and transport systems, and the relevance of these receptors to clinical drug-drug interactions and the development of new drugs. Emphasis is given to two newly recognised 'orphan' receptors (the pregnane X receptor [PXR] and the constitutive androstane receptor [CAR]) and their regulation of cytochrome P450 enzymes, such as CYP3A4, CYP2Cs and CYP2B6; and transporters, such as P-glycoprotein (MDR1), multidrug resistance-associated proteins (MRPs) and organic anion transporter peptide 2 (OATP2). Although 'cross-talk' occurs between these two receptors and their target sequences, significant species differences exist between ligand-binding and activation profiles for both receptors, and PXR appears to be the predominant or 'master' regulator of hepatic drug disposition in humans. Several important physiological processes, such as cholesterol synthesis and bile acid metabolism, are also tightly controlled by certain ligand-activated orphan nuclear receptors (farnesoid X receptor [FXR] and liver X receptor [LXR]). In general, their ability to bind a broad range of ligands and regulate an extensive array of genes that are involved in drug clearance and disposition makes these orphan receptors attractive targets for drug development. Drugs have the capacity to alter nuclear receptor expression (modulators) and/or serve as ligands for the receptors (agonists or antagonists), and thus can have synergistic or antagonistic effects on the expression of drug-metabolising enzymes and transporters. Coadministration of drugs that are nuclear receptor agonists or antagonists can lead to severe toxicity, a loss of therapeutic efficacy or an imbalance in physiological substrates, providing a novel molecular mechanism for drug-drug interactions.
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Affiliation(s)
- Hongbing Wang
- Division of Drug Delivery and Disposition, School of Pharmacy, University of North Carolina at Chapel Hill, North Carolina 27599, USA
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Su T, Waxman DJ. Impact of dimethyl sulfoxide on expression of nuclear receptors and drug-inducible cytochromes P450 in primary rat hepatocytes. Arch Biochem Biophys 2004; 424:226-34. [PMID: 15047195 DOI: 10.1016/j.abb.2004.02.008] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2004] [Revised: 02/11/2004] [Indexed: 10/26/2022]
Abstract
Dimethyl sulfoxide (DMSO) is reported to induce hepatocyte redifferentiation. The impact of DMSO on liver transcription factors, cytochromes P450 (CYPs), and nuclear receptors regulating CYP expression was assayed in primary rat hepatocytes by QPCR. CYP 2B1, 3A1, and 4A1 mRNAs were reduced to 10-30% of initial liver levels without DMSO and restored at or above liver levels by DMSO treatment. In contrast, CYP1A1 mRNA increased approximately 5-fold during the course of culture, independent of DMSO. DMSO enhanced expression of the nuclear receptors CAR, PXR, and PPARalpha 2- to 5-fold, which may contribute to the increase in basal CYP expression. Without DMSO, liver transcription factors were decreased (HNF4, C/EBPalpha), largely unchanged (HNF1alpha, HNF3alpha, and C/EBPbeta) or elevated (HNF3beta, HNF6) compared to intact liver. DMSO largely restored hepatic levels of HNF4 and C/EBPalpha, partially suppressed the elevated levels of HNF6, increased HNF1alpha approximately 2-fold, and had little effect on HNF3alpha, HNF3beta, and C/EBPbeta. Overall, DMSO helped maintain normal hepatic transcription factor patterns and basal CYP and nuclear receptor profiles, suggesting that hepatocytes cultured with DMSO may be useful for CYP metabolic studies under conditions where the endogenous liver phenotype is preserved.
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Affiliation(s)
- Ting Su
- Department of Biology, Division of Cell and Molecular Biology, Boston University, 5 Cummington Street, Boston, MA 02215, USA
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Bae Y, Kemper JK, Kemper B. Repression of CAR-mediated transactivation of CYP2B genes by the orphan nuclear receptor, short heterodimer partner (SHP). DNA Cell Biol 2004; 23:81-91. [PMID: 15000748 DOI: 10.1089/104454904322759894] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The induction of CYP2B gene expression by phenobarbital (PB) is mediated by the translocation of the constitutive androstane receptor (CAR) from the cytoplasm to the nucleus. The CAR/RXR heterodimer binds to two DR-4 sites in a complex phenobarbital responsive unit (PBRU) in the CYP2B gene. The short heterodimer partner (SHP), an orphan nuclear receptor that lacks a conventional DNA binding domain, was initially identified by its interaction with CAR. We have examined the role of SHP in CAR-mediated transactivation of the CYP2B gene. Coexpression of SHP inhibited the transactivation of the CYP2B gene by CAR in cultured hepatoma cells and the p160 coactivator GRIP1 reversed the inhibition. The interaction of CAR with SHP was confirmed by GST pulldown experiments. SHP did not block the binding of either CAR/RXR to the PBRU or binding of GRIP1 to the CAR/RXR complex in gel mobility shift assays, but slightly increased CAR/RXR binding and slightly altered the mobility of the CAR/RXR/GRIP1 complex, suggesting an interaction of SHP with these complexes. The presence of SHP in the complexes, however, could not be detected in an antibody supershift assay. Recombinant corepressors mSin3A, SMRT, and HDAC1, but not NCoR1, interacted with GST-SHP but each of these corepressors in liver nuclear extracts bound to GST-SHP. SMRT and NCoR1 inhibited CAR-mediated activation independent of SHP, but mSin3A and HDAC1 had little effect alone, and were additive with SHP. These studies demonstrate that SHP does not inhibit CAR-mediated trans-activation by interfering with DNA binding or by competition with GRIP1. Instead, SHP may either inhibit recruitment of other coactivators by GRIP1 or actively recruit corepressors directly to the CAR/RXR/PBRU complex.
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Affiliation(s)
- Yangjin Bae
- Department of Molecular & Integrative Physiology, College of Medicine at Urbana-Champaign, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
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Bauer D, Wolfram N, Kahl GF, Hirsch-Ernst KI. Transcriptional regulation of CYP2B1 induction in primary rat hepatocyte cultures: repression by epidermal growth factor is mediated via a distal enhancer region. Mol Pharmacol 2004; 65:172-80. [PMID: 14722249 DOI: 10.1124/mol.65.1.172] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Phenobarbital (PB) alters expression of numerous hepatic genes, including genes involved in xenobiotic metabolism. Phenobarbital-dependent induction of cytochrome P-450 2B1 (CYP2B1) is subject to regulation by cytokines [e.g., by epidermal growth factor (EGF)], hormones [e.g., by growth hormone (GH)], or the cellular redox status. To investigate mechanisms involved in regulation of CYP2B1 transcription, we performed promoter activation studies using primary rat hepatocyte cultures transiently transfected with individual CYP2B1 promoter-luciferase reporter gene constructs. The 2679-bp native 5'-flanking region of the CYP2B1 gene conferred reporter gene activation by PB and the potent PB-like inducer permethrin (PM). Furthermore, this region mediated EGF- and GH-dependent repression of gene activation by PB-like inducers. A wide promoter mapping strategy with constructs bearing internal CYP2B1 promoter deletions led to identification of a distal responsive CYP2B1 enhancer region at -2230 to -2170, encompassing the section equivalent to the 51-bp PB-responsive enhancer module situated in the distal mouse Cyp2b10-5'-flanking region. The distal CYP2B1 enhancer region conferred gene activation by PM, repression of PM-dependent activation by EGF, and enhancement of activation by the antioxidant N-acetylcysteine (NAC). Mutational analyses of the region at -2230 to -2170 suggested that the mechanisms of PB-dependent induction of CYP2B1 and the modulating effects by EGF or NAC are closely related.
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Affiliation(s)
- Daniel Bauer
- Department of Toxicology, Institute of Pharmacology and Toxicology, University of Göttingen, Göttingen, Germany
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Sidhu JS, Liu F, Omiecinski CJ. Phenobarbital responsiveness as a uniquely sensitive indicator of hepatocyte differentiation status: requirement of dexamethasone and extracellular matrix in establishing the functional integrity of cultured primary rat hepatocytes. Exp Cell Res 2004; 292:252-64. [PMID: 14697333 DOI: 10.1016/j.yexcr.2003.09.001] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
We used a serum-free, highly defined primary hepatocyte culture model to investigate the mechanisms whereby dexamethasone (Dex) and extracellular matrix (ECM) coordinate cell differentiation and transcriptional responsiveness to the inducer, phenobarbital (PB). Low nanomolar levels of Dex and dilute concentrations of ECM overlay were essential in the maintenance of normal hepatocyte physiology, as assessed by cell morphology, LDH release, expression of the hepatic nuclear factors C/EBPalpha, -beta, -gamma, HNF-1alpha, -1beta, -4alpha, and RXRalpha, expression of prototypical hepatic marker genes, including albumin and transferrin, and ultimately, cellular capacity to respond to PB. The loss of hepatocyte integrity produced by deficiency of these components correlated with the activation of several stress signaling pathways including the MAPK, SAPK/JNK, and c-Jun signaling pathways, with resulting nuclear recruitment of the activated protein-1 (AP-1) complex. In Dex-deficient cultures, normal cellular function, including the PB induction response, was largely restored in a dose-dependent manner by reintroduction of nanomolar additions of the hormone, in the presence of ECM. Our results demonstrate critical and cooperative roles for Dex and ECM in establishing hepatocyte integrity and in the coordination of an array of liver-specific functions. These studies further establish the PB gene induction response as an exceptionally sensitive indicator of hepatocyte differentiation status.
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Affiliation(s)
- Jaspreet S Sidhu
- Department of Environmental Health, University of Washington, Seattle, WA 98105, USA
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Abstract
Induction of drug metabolism was described more than 40 years ago. Progress in understanding the molecular mechanism of induction of drug-metabolizing enzymes was made recently when the important roles of the pregnane X receptor (PXR) and the constitutive androstane receptor (CAR), two members of the nuclear receptor superfamily of transcription factors, were discovered to act as sensors for lipophilic xenobiotics, including drugs. CAR and PXR bind as heterodimeric complexes with the retinoid X receptor to response elements in the regulatory regions of the induced genes. PXR is directly activated by xenobiotic ligands, whereas CAR is involved in a more complex and less well understood mechanism of signal transduction triggered by drugs. Most recently, analysis of these xenobiotic-sensing nuclear receptors and their nonmammalian precursors such as the chicken xenobiotic receptor suggests an important role of PXR and CAR also in endogenous pathways, such as cholesterol and bile acid biosynthesis and metabolism. In this review, recent findings regarding xenosensors and their target genes are summarized and are put into an evolutionary perspective in regard to how a living organism has derived a system that is able to deal with potentially toxic compounds it has not encountered before.
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Affiliation(s)
- Christoph Handschin
- Division of Pharmacology/Neurobiology, Biozentrum of the University of Basel, Klingelbergstrasse 50-70, CH-4056 Basel, Switzerland
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Murray M, Fiala-Beer E, Sutton D. Upregulation of cytochromes P450 2B in rat liver by orphenadrine. Br J Pharmacol 2003; 139:787-96. [PMID: 12813002 PMCID: PMC1573901 DOI: 10.1038/sj.bjp.0705305] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2003] [Accepted: 03/27/2003] [Indexed: 11/08/2022] Open
Abstract
1 The alkylamine drug orphenadrine (ORPH) is an inducer and inhibitor of the microsomal cytochrome P450 (CYP) system in mammals. This study evaluated the selectivity of CYP induction by ORPH in rat liver. 2 Immunoblot analysis indicated that ORPH was a selective inducer of the phenobarbitone (PB)-inducible CYP2B in rat liver. CYP2B protein was increased to approximately 14-fold of levels in untreated rat liver. By comparison PB increased CYP2B expression 40-fold. Corresponding increases in the activity of CYP2B-dependent androstenedione 16beta-hydroxylation were measured in microsomes from ORPH and PB-induced rats. 3 Northern analysis indicated that CYP2B1/2 mRNA was increased in ORPH-induced rat liver. Consistent with this finding, ORPH was found to activate a PB-responsive enhancer module in constitutive androstane receptor (CAR)-transfected Hep G2 cells. 4 Other alkylamines like troleandomycin impair CYP turnover. We tested whether ORPH induction of CYP2B may include a post-translational component. In PB-pretreated animals ORPH administration delayed the loss of CYP2B after PB withdrawal, but no evidence for altered turnover was found. 5 These studies establish ORPH as a selective inducer of CYP2B in rat liver. Induction appears to be mediated pretranslationally by CAR activation of CYP2B gene transcription. Post-translational stabilisation by an ORPH metabolite does not elicit induction. Induction of CYP2B may influence pharmacokinetic interactions involving ORPH.
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Affiliation(s)
- Michael Murray
- Department of Physiology and Pharmacology, School of Medical Sciences, University of New South Wales, Sydney, NSW 2052, Australia.
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45
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Pascussi JM, Gerbal-Chaloin S, Drocourt L, Maurel P, Vilarem MJ. The expression of CYP2B6, CYP2C9 and CYP3A4 genes: a tangle of networks of nuclear and steroid receptors. BIOCHIMICA ET BIOPHYSICA ACTA 2003; 1619:243-53. [PMID: 12573484 DOI: 10.1016/s0304-4165(02)00483-x] [Citation(s) in RCA: 238] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Numerous chemicals increase the metabolic capability of organisms by their ability to activate genes encoding various xenochemical-metabolizing enzymes, such as cytochromes P450 (CYPs), transferases and transporters. For example, natural and synthetic glucocorticoids (agonists and antagonists) as well as other clinically important drugs induce the hepatic CYP2B, CYP2C and CYP3A subfamilies in man, and these inductions might lead to clinically important drug-drug interactions. Only recently, the key cellular receptors that mediate such inductions have been identified. They include nuclear receptors, such as the constitutive androstane receptor (CAR, NR1I3), the retinoid X receptor (RXR, NR2B1), the pregnane X receptor (PXR, NR1I2), and the vitamin D receptor (VDR, NR1I1) and steroid receptors such as the glucocorticoid receptor (GR, NR3C1). There is a wide promiscuity of these receptors in the induction of CYPs in response to xenobiotics. Indeed, this adaptive system appears now as a tangle of networks, where receptors share partners, ligands, DNA response elements and target genes. Moreover, they influence mutually their relative expression. This review is focused on these different pathways controlling human CYP2B6, CYP2C9 and CYP3A4 gene expression, and the cross-talk between these pathways.
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Affiliation(s)
- J M Pascussi
- Institut National de la Santé et de la Recherche Médicale U128, IFR 24, Centre National de la Recherche Scientifique, 1919 route de Mende, 34293 05, Montpellier, France.
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Rivera-Rivera I, Kim J, Kemper B. Transcriptional analysis in vivo of the hepatic genes, Cyp2b9 and Cyp2b10, by intravenous administration of plasmid DNA in mice. BIOCHIMICA ET BIOPHYSICA ACTA 2003; 1619:254-62. [PMID: 12573485 DOI: 10.1016/s0304-4165(02)00484-1] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Phenobarbital (PB) responsiveness of CYP2B genes has been shown to be mediated by a PB responsive unit (PBRU). The core of the PBRU contains two nuclear receptor sites, NR-1 and NR-2, and a nuclear factor-1 (NF 1) binding site, which are required for PB responsiveness, but the importance of sequences flanking the core is not clear. We have used intravenous administration of plasmid DNA in the tail veins of mice to transfect hepatocytes in vivo and analyze sequence requirements for PB induction. In this assay PB treatment increased transactivation by the Cyp2b10 PBRU about 100-fold, which is similar to the increase in the expression of the endogenous gene while the Cyp2b9 PBRU was unresponsive. Analysis of chimeras of the two PBRUs and deletion mutants of the Cyp2b10 PBRU indicated that the core region containing the NR-1, NR-2 and NF-1 core sites is not sufficient for PB responsiveness. Additional sequence at the 3' side of the core sequence, which included a previously defined accessory factor-1 (AF-1) site, partially restored responsiveness. This region contained a binding site for NF-1 only in Cyp2b10 and not in Cyp2b9, but the intact site was not required for PB responsiveness. Purified constitutive androstane receptor (CAR)/retinoid X receptor (RXR) bound to the core NR-1 and NR-2 sites and to a third NR-3 site to the 5' side of the core in Cyp2b10. No binding of CAR/RXR to the Cyp2b9 PBRU was observed. These results indicate that changes in the NR sites which eliminate CAR/RXR binding are sufficient for the non-responsiveness to PB of Cyp2b9, but changes in sequences flanking the core independently eliminate PB responsiveness. The results demonstrate the advantages of transfection of mouse hepatocytes in vivo by tail vein injection of DNA as a method for transcriptional analysis of genes in vivo and show that sequences flanking the core region of the PBRU are required for PB induction in vivo.
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Affiliation(s)
- Ilia Rivera-Rivera
- Department of Molecular and Integrative Physiology and College of Medicine at Urbana-Champaign, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
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Kocarek TA, Mercer-Haines NA. Squalestatin 1-inducible expression of rat CYP2B: evidence that an endogenous isoprenoid is an activator of the constitutive androstane receptor. Mol Pharmacol 2002; 62:1177-86. [PMID: 12391282 DOI: 10.1124/mol.62.5.1177] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Because our previous studies indicated that squalestatin 1 treatment induces CYP2B expression in primary cultures of rat hepatocytes as a direct consequence of squalene synthase inhibition, we investigated possible underlying mechanisms. Cotransfection of cultured Sprague-Dawley male rat hepatocytes with each of the three sterol regulatory element binding protein (SREBP) transcription factors failed to induce luciferase expression from a squalestatin 1-responsive CYP2B1 reporter plasmid. Squalestatin 1 treatment of primary hepatocyte cultures from male Wistar-Kyoto rats produced a greater induction of CYP2B mRNA than occurred in cultures from female rats, consistent with the previously demonstrated response dimorphism that has been attributed to differences in constitutive androstane receptor (CAR) levels. Cotransfection of female Wistar-Kyoto rat hepatocyte cultures with plasmid expressing either mouse or rat CAR restored squalestatin 1-inducible CYP2B1-reporter expression. Cotransfection of Sprague-Dawley rat hepatocyte cultures with plasmid expressing rat CAR lacking the C-terminal AF-2 subdomain inhibited squalestatin 1-inducible CYP2B1-reporter expression. Squalestatin 1-mediated CYP2B mRNA induction in rat hepatocyte cultures was completely abolished by pretreatment with the 3-hydroxymethyl-3-glutaryl CoA reductase inhibitor pravastatin and was rescued by mevalonate supplementation, whereas phenobarbital-mediated induction was unaffected by these treatments. Finally, direct addition of trans,trans-farnesol to the culture medium caused the rapid induction of CYP2B mRNA. These results indicate that squalestatin 1 treatment induces CYP2B expression, not by inhibiting sterol synthesis and activating SREBPs, but by evoking the accumulation of an endogenous isoprenoid and activating CAR.
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Affiliation(s)
- Thomas A Kocarek
- Institute of Environmental Health Sciences, Wayne State University, Detroit, Michigan 48201, USA.
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Xiong H, Yoshinari K, Brouwer KLR, Negishi M. Role of constitutive androstane receptor in the in vivo induction of Mrp3 and CYP2B1/2 by phenobarbital. Drug Metab Dispos 2002; 30:918-23. [PMID: 12124310 DOI: 10.1124/dmd.30.8.918] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Phenobarbital (PB) induces the hepatic organic anion transporter, Mrp3. The present study tested the hypothesis that Mrp3 induction by PB is mediated by the constitutive androstane receptor (CAR). PB induction of Mrp3 and CYP2B was examined in lean and obese Zucker rats, male and female Wistar Kyoto (WKY) rats, HepG2 and mouse CAR-expressing HepG2 (g2car-3) cells; HepG2 and g2car-3 cells also were treated with 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene (TCPOBOP). In obese Zucker rat livers, total and nuclear CAR levels were markedly lower compared with lean rat livers, which correlated with the poor induction of CYP2B1/2 by PB in obese Zucker rats. Mrp3 induction by PB also was impaired in obese Zucker rat livers. Induction of Mrp3 by PB was similar in male and female WKY rat livers, despite the fact that CAR protein levels were significantly lower in female relative to male WKY rat livers. MRP3 levels in both HepG2 and g2car-3 cells were induced to a similar extent in the two cell lines by PB but not by TCPOBOP. In contrast, CYP2B6 levels were measurable and induced by TCPOBOP only in g2car-3 cells. In conclusion, data from WKY rats and HepG2 cells suggest that CAR does not play a key role in PB induction of Mrp3. Impaired induction of Mrp3 by PB in obese Zucker rats is not due solely to CAR deficiency. Interestingly, differences in the constitutive levels of Mrp3 were observed between obese and lean Zucker rats and between male and female WKY rats.
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Affiliation(s)
- Hao Xiong
- Division of Drug Delivery and Disposition, School of Pharmacy, University of North Carolina, Chapel Hill, North Carolina 27599-7360, USA
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Drocourt L, Ourlin JC, Pascussi JM, Maurel P, Vilarem MJ. Expression of CYP3A4, CYP2B6, and CYP2C9 is regulated by the vitamin D receptor pathway in primary human hepatocytes. J Biol Chem 2002; 277:25125-32. [PMID: 11991950 DOI: 10.1074/jbc.m201323200] [Citation(s) in RCA: 260] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The fully active dihydroxylated metabolite of vitamin D(3) induces the expression of CYP3A4 and, to a lesser extent, CYP2B6 and CYP2C9 genes in normal differentiated primary human hepatocytes. Electrophoretic mobility shift assays and cotransfection in HepG2 cells using wild-type and mutated oligonucleotides revealed that the vitamin D receptor (VDR) binds and transactivates those xenobiotic-responsive elements (ER6, DR3, and DR4) previously identified in CYP3A4, CYP2B6, and CYP2C9 promoters and shown to be targeted by the pregnane X receptor (PXR) and/or the constitutive androstane receptor (CAR). Full VDR response of various CYP3A4 heterologous/homologous promoter-reporter constructs requires both the proximal ER6 and the distal DR3 motifs, as observed previously with rifampicin-activated PXR. Cotransfection of a CYP3A4 homologous promoter-reporter construct (including distal and proximal PXR-binding motifs) and of PXR or CAR expression vectors in HepG2 cells revealed the ability of these receptors to compete with VDR for transcriptional regulation of CYP3A4. In conclusion, this work suggests that VDR, PXR, and CAR control the basal and inducible expression of several CYP genes through competitive interaction with the same battery of responsive elements.
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Affiliation(s)
- Lionel Drocourt
- INSERM U128, Institut Federatif de Recherche 24, CNRS, 1919 Route de Mende, 34293 Montpellier, Cedex 05, France
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de Longueville F, Surry D, Meneses-Lorente G, Bertholet V, Talbot V, Evrard S, Chandelier N, Pike A, Worboys P, Rasson JP, Le Bourdellès B, Remacle J. Gene expression profiling of drug metabolism and toxicology markers using a low-density DNA microarray. Biochem Pharmacol 2002; 64:137-49. [PMID: 12106614 DOI: 10.1016/s0006-2952(02)01055-9] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
DNA microarrays are useful tools to study changes of gene expression in response to a treatment with drugs. Here, we describe the optimization of conditions for the cDNA synthesis and hybridization protocols to be used for a low-density DNA microarray called 'Rat HepatoChips.' This DNA microarray with 59 carefully selected genes could be used to study changes in gene expression levels due to a treatment with xenobiotic. These 59 genes (including 8 housekeeping genes) have been selected among potential toxic markers involved in basic cellular processes and drug metabolism related genes. Using the optimized conditions, the results were shown to be reproducible, with 6% variation between the duplicated spots and 10% between arrays. Conditions were optimized to allow quantification with a dynamic range of four log units. In order to demonstrate the major advantage of these tool for studying gene expression, samples of control rat liver were compared with those of animals dosed with phenobarbital (PB) or pregnenolone-16 alpha-carbonitrile (PCN), two compounds well known to induce cytochrome P450 isoforms of 2B and 3A subfamilies, respectively. This microarray has shown that other genes apart from the corresponding CYP P450 genes have been changed due to PB and PCN treatment. Apoptosis-related genes have shown to be changed due to PB and PCN treatment, which confirms results from previous work.
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Affiliation(s)
- Françoise de Longueville
- Laboratory of Biochemistry and Cellular Biology, University of Namur, Rue de Bruxelles, Namur, Belgium.
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