1
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Würger LTD, Alarcan J, Braeuning A. Effects of marine biotoxins on drug-metabolizing cytochrome P450 enzymes and their regulation in mammalian cells. Arch Toxicol 2024; 98:1311-1322. [PMID: 38416141 PMCID: PMC10965580 DOI: 10.1007/s00204-024-03694-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2023] [Accepted: 01/23/2024] [Indexed: 02/29/2024]
Abstract
Marine biotoxins are a heterogenous group of natural toxins, which are able to trigger different types of toxicological responses in animals and humans. Health effects arising from exposure to marine biotoxins are ranging, for example, from gastrointestinal symptoms to neurological effects, depending on the individual toxin(s) ingested. Recent research has shown that the marine biotoxin okadaic acid (OA) can strongly diminish the expression of drug-metabolizing cytochrome P450 (CYP) enzymes in human liver cells by a mechanism involving proinflammatory signaling. By doing so, OA may interfere with the metabolic barrier function of liver and intestine, and thus alter the toxico- or pharmacokinetic properties of other compounds. Such effects of marine biotoxins on drug and xenobiotic metabolism have, however, not been much in the focus of research yet. In this review, we present the current knowledge on the effects of marine biotoxins on CYP enzymes in mammalian cells. In addition, the role of CYP-regulating nuclear receptors as well as inflammatory signaling in the regulation of CYPs by marine biotoxins is discussed. Strong evidence is available for effects of OA on CYP enzymes, along with information about possible molecular mechanisms. For other marine biotoxins, knowledge on effects on drug metabolism, however, is scarce.
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Affiliation(s)
- Leonie T D Würger
- Department Food Safety, German Federal Institute for Risk Assessment, Max-Dohrn-Str. 8-10, 10589, Berlin, Germany
| | - Jimmy Alarcan
- Department Food Safety, German Federal Institute for Risk Assessment, Max-Dohrn-Str. 8-10, 10589, Berlin, Germany
| | - Albert Braeuning
- Department Food Safety, German Federal Institute for Risk Assessment, Max-Dohrn-Str. 8-10, 10589, Berlin, Germany.
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2
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Sato T, Shizu R, Miura Y, Hosaka T, Kanno Y, Sasaki T, Yoshinari K. Development of a strategy to identify and evaluate direct and indirect activators of constitutive androstane receptor in rats. Food Chem Toxicol 2022; 170:113510. [DOI: 10.1016/j.fct.2022.113510] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2022] [Revised: 10/25/2022] [Accepted: 11/03/2022] [Indexed: 11/09/2022]
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3
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Liang D, Li L, Lynch C, Diethelm-Varela B, Xia M, Xue F, Wang H. DL5050, a Selective Agonist for the Human Constitutive Androstane Receptor. ACS Med Chem Lett 2019; 10:1039-1044. [PMID: 31312405 DOI: 10.1021/acsmedchemlett.9b00079] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2019] [Accepted: 06/12/2019] [Indexed: 11/30/2022] Open
Abstract
The constitutive androstane receptor (CAR) is a xenobiotic sensor governing the transcription of genes involved in drug disposition, energy homeostasis, and cell proliferation. However, currently available human CAR (hCAR) agonists are nonselective, which commonly activate hCAR along with other nuclear receptors, especially the closely related human pregnane X receptor (hPXR). Using a well-known hCAR agonist CITCO as a template, we report our efforts in the discovery of a potent and highly selective hCAR agonist. Two of the new compounds of the series, 18 and 19 (DL5050), demonstrated excellent potency and selectivity for hCAR over hPXR. DL5050 preferentially induced the expression of CYP2B6 (target of hCAR) over CYP3A4 (target of hPXR) on both the mRNA and protein levels. The selective hCAR agonist DL5050 represents a valuable tool molecule to further define the biological functions of hCAR, and may also be used as a new lead in the discovery of hCAR agonists for various therapeutic applications.
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Affiliation(s)
- Dongdong Liang
- Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, Baltimore, Maryland 21201, United States
| | - Linhao Li
- Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, Baltimore, Maryland 21201, United States
| | - Caitlin Lynch
- National Center for Advancing Translational Sciences, National Institutes of Health, Bethesda, Maryland 20892-3375, United States
| | - Benjamin Diethelm-Varela
- Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, Baltimore, Maryland 21201, United States
| | - Menghang Xia
- National Center for Advancing Translational Sciences, National Institutes of Health, Bethesda, Maryland 20892-3375, United States
| | - Fengtian Xue
- Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, Baltimore, Maryland 21201, United States
| | - Hongbing Wang
- Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, Baltimore, Maryland 21201, United States
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4
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McMahon M, Ding S, Jimenez LA, Terranova R, Gerard MA, Vitobello A, Moggs J, Henderson CJ, Wolf CR. Constitutive androstane receptor 1 is constitutively bound to chromatin and 'primed' for transactivation in hepatocytes. Mol Pharmacol 2019; 95:97-105. [PMID: 30361333 PMCID: PMC6277922 DOI: 10.1124/mol.118.113555] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2018] [Accepted: 10/19/2018] [Indexed: 12/15/2022] Open
Abstract
The constitutive androstane receptor (CAR) is a xenobiotic sensor expressed in hepatocytes that activates genes involved in drug metabolism, lipid homeostasis, and cell proliferation. Much progress has been made in understanding the mechanism of activation of human CAR by drugs and xenobiotics. However, many aspects of the activation pathway remain to be elucidated. In this report, we have used viral constructs to express human CAR, its splice variants, and mutant CAR forms in hepatocytes from Car-/- mice in vitro and in vivo. We demonstrate CAR expression rescued the ability of Car-/- hepatocytes to respond to a wide range of CAR activators including phenobarbital. Additionally, two major splice isoforms of human CAR, CAR2 and CAR3, were inactive with almost all the agents tested. In contrast to the current model of CAR activation, ectopic CAR1 is constitutively localized in the nucleus and is loaded onto Cyp2b10 gene in the absence of an inducing agent. In studies to elucidate the role of threonine T38 in CAR regulation, we found that the T38D mutant was inactive even in the presence of CAR activators. However, the T38A mutant was activated by CAR inducers, showing that T38 is not essential for CAR activation. Also, using the inhibitor erlotinib, we could not confirm a role for the epidermal growth factor receptor in CAR regulation. Our data suggest that CAR is constitutively bound to gene regulatory regions and is regulated by exogenous agents through a mechanism which involves protein phosphorylation in the nucleus.
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Affiliation(s)
- Michael McMahon
- School of Medicine, Jacqui Wood Cancer Centre, Ninewells Hospital and Medical School, University of Dundee, Dundee, United Kingdom (M.M., S.D., L.A.J., C.J.H., C.R.W.) and Preclinical Safety, Translational Medicine, Novartis Institutes for BioMedical Research, Basel, Switzerland (R.T., M.-A.G., A.V., J.M.)
| | - Shaohong Ding
- School of Medicine, Jacqui Wood Cancer Centre, Ninewells Hospital and Medical School, University of Dundee, Dundee, United Kingdom (M.M., S.D., L.A.J., C.J.H., C.R.W.) and Preclinical Safety, Translational Medicine, Novartis Institutes for BioMedical Research, Basel, Switzerland (R.T., M.-A.G., A.V., J.M.)
| | - Lourdes Acosta Jimenez
- School of Medicine, Jacqui Wood Cancer Centre, Ninewells Hospital and Medical School, University of Dundee, Dundee, United Kingdom (M.M., S.D., L.A.J., C.J.H., C.R.W.) and Preclinical Safety, Translational Medicine, Novartis Institutes for BioMedical Research, Basel, Switzerland (R.T., M.-A.G., A.V., J.M.)
| | - Remi Terranova
- School of Medicine, Jacqui Wood Cancer Centre, Ninewells Hospital and Medical School, University of Dundee, Dundee, United Kingdom (M.M., S.D., L.A.J., C.J.H., C.R.W.) and Preclinical Safety, Translational Medicine, Novartis Institutes for BioMedical Research, Basel, Switzerland (R.T., M.-A.G., A.V., J.M.)
| | - Marie-Apolline Gerard
- School of Medicine, Jacqui Wood Cancer Centre, Ninewells Hospital and Medical School, University of Dundee, Dundee, United Kingdom (M.M., S.D., L.A.J., C.J.H., C.R.W.) and Preclinical Safety, Translational Medicine, Novartis Institutes for BioMedical Research, Basel, Switzerland (R.T., M.-A.G., A.V., J.M.)
| | - Antonio Vitobello
- School of Medicine, Jacqui Wood Cancer Centre, Ninewells Hospital and Medical School, University of Dundee, Dundee, United Kingdom (M.M., S.D., L.A.J., C.J.H., C.R.W.) and Preclinical Safety, Translational Medicine, Novartis Institutes for BioMedical Research, Basel, Switzerland (R.T., M.-A.G., A.V., J.M.)
| | - Jonathan Moggs
- School of Medicine, Jacqui Wood Cancer Centre, Ninewells Hospital and Medical School, University of Dundee, Dundee, United Kingdom (M.M., S.D., L.A.J., C.J.H., C.R.W.) and Preclinical Safety, Translational Medicine, Novartis Institutes for BioMedical Research, Basel, Switzerland (R.T., M.-A.G., A.V., J.M.)
| | - Colin J Henderson
- School of Medicine, Jacqui Wood Cancer Centre, Ninewells Hospital and Medical School, University of Dundee, Dundee, United Kingdom (M.M., S.D., L.A.J., C.J.H., C.R.W.) and Preclinical Safety, Translational Medicine, Novartis Institutes for BioMedical Research, Basel, Switzerland (R.T., M.-A.G., A.V., J.M.)
| | - C Roland Wolf
- School of Medicine, Jacqui Wood Cancer Centre, Ninewells Hospital and Medical School, University of Dundee, Dundee, United Kingdom (M.M., S.D., L.A.J., C.J.H., C.R.W.) and Preclinical Safety, Translational Medicine, Novartis Institutes for BioMedical Research, Basel, Switzerland (R.T., M.-A.G., A.V., J.M.)
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Kang S, Huang J, Lee BK, Jung YS, Im E, Koh JM, Im DS. Omega-3 polyunsaturated fatty acids protect human hepatoma cells from developing steatosis through FFA4 (GPR120). Biochim Biophys Acta Mol Cell Biol Lipids 2017; 1863:105-116. [PMID: 29126901 DOI: 10.1016/j.bbalip.2017.11.002] [Citation(s) in RCA: 39] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2017] [Revised: 11/03/2017] [Accepted: 11/04/2017] [Indexed: 10/18/2022]
Abstract
Protective effect of omega-3 polyunsaturated fatty acids (n-3 PUFA) on non-alcoholic fatty liver disease has been demonstrated. FFA4 (also known as GPR120; a G protein-coupled receptor) has been suggested to be a target of n-3 PUFA. FFA4 expression in hepatocytes has also been reported from liver biopsies in child fatty liver patients. In order to assess the functional role of FFA4 in hepatic steatosis, we used an in vitro model of liver X receptor (LXR)-mediated hepatocellular steatosis. FFA4 expression was confirmed in Hep3B and HepG2 human hepatoma cells. T0901317 (a specific LXR activator) induced lipid accumulation and docosahexaenoic acid (DHA; a representative n-3 PUFA) inhibited lipid accumulation. This DHA-induced inhibition was blunted by treatment of AH7614 (a FFA4 antagonist) and by transfection of FFA4 siRNA. SREBP-1c (a key transcription factor of lipogenesis) was induced by treatment with T0901317, and SREBP-1c induction was also inhibited by DHA at mRNA and protein levels. DHA-induced suppression of SREBP-1c expression was also blunted by FFA4-knockdown. Furthermore, DHA inhibited T0901317-induced lipid accumulation in primary hepatocytes from wild type mice, but not in those from FFA4 deficient mice. In addition, DHA-induced activations of Gq/11 proteins, CaMKK, and AMPK were found to be signaling components of the steatosis protective pathway. The results of this study suggest that n-3 PUFA protect hepatic steatosis by activating FFA4 in hepatocytes, and its signaling cascade sequentially involves FFA4, Gq/11 proteins, CaMKK, AMPK, and SREBP-1c suppression.
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Affiliation(s)
- Saeromi Kang
- Molecular Inflammation Research Center for Aging Intervention (MRCA) and College of Pharmacy, Pusan National University, Busan 469241, Republic of Korea
| | - Jin Huang
- Molecular Inflammation Research Center for Aging Intervention (MRCA) and College of Pharmacy, Pusan National University, Busan 469241, Republic of Korea
| | - Bo-Kyung Lee
- Molecular Inflammation Research Center for Aging Intervention (MRCA) and College of Pharmacy, Pusan National University, Busan 469241, Republic of Korea
| | - Young-Suk Jung
- Molecular Inflammation Research Center for Aging Intervention (MRCA) and College of Pharmacy, Pusan National University, Busan 469241, Republic of Korea
| | - Eunok Im
- Molecular Inflammation Research Center for Aging Intervention (MRCA) and College of Pharmacy, Pusan National University, Busan 469241, Republic of Korea
| | - Jung-Min Koh
- Division of Endocrinology and Metabolism, Asan Medical Center, University of Ulsan College of Medicine, Seoul 05505, Republic of Korea
| | - Dong-Soon Im
- Molecular Inflammation Research Center for Aging Intervention (MRCA) and College of Pharmacy, Pusan National University, Busan 469241, Republic of Korea.
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6
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Yamasaki Y, Kobayashi K, Inaba A, Uehara D, Tojima H, Kakizaki S, Chiba K. Indirect activation of pregnane X receptor in the induction of hepatic CYP3A11 by high-dose rifampicin in mice. Xenobiotica 2017; 48:1098-1105. [PMID: 29095659 DOI: 10.1080/00498254.2017.1400128] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Rifampicin (RIF), a typical ligand of human pregnane X receptor (PXR), powerfully induces the expression of cytochrome P450 3A4 (CYP3A4) in humans. Although it is thought that RIF is not a ligand of rodent PXR, treatment with high-dose RIF (e.g. more than 20 mg/kg) increases the expression of CYP3A in the mouse liver. In this study, we investigated whether the induction of CYP3A by high-dose RIF in the mouse liver is mediated via indirect activation of mouse PXR (mPXR). The results showed that high-dose RIF increased the expression of CYP3A11 and other PXR-target genes in the liver of wild-type mice but not PXR-knockout mice. However, the results of reporter gene and ligand-dependent assembly assays showed that RIF does not activate mPXR in a ligand-dependent manner. In addition, high-dose RIF stimulated nuclear accumulation of mPXR in the mouse liver, and geldanamycin and okadaic acid attenuated the induction of Cyp3a11 and other PXR-target genes in primary hepatocytes, suggesting that high-dose RIF triggers nuclear translocation of mPXR. In conclusion, the present study suggests that high-dose RIF stimulates nuclear translocation of mPXR in the liver of mice by indirect activation, resulting in the transactivation of Cyp3a11 and other PXR-target genes.
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Affiliation(s)
- Yuki Yamasaki
- a Laboratory of Pharmacology and Toxicology, Graduate School of Pharmaceutical Sciences, Chiba University , Chiba , Japan and
| | - Kaoru Kobayashi
- a Laboratory of Pharmacology and Toxicology, Graduate School of Pharmaceutical Sciences, Chiba University , Chiba , Japan and
| | - Asumi Inaba
- a Laboratory of Pharmacology and Toxicology, Graduate School of Pharmaceutical Sciences, Chiba University , Chiba , Japan and
| | - Daisuke Uehara
- b Division of Gastroenterology and Hepatology, Department of Internal Medicine, Graduate School of Medicine, Gunma University , Maebashi , Japan
| | - Hiroki Tojima
- b Division of Gastroenterology and Hepatology, Department of Internal Medicine, Graduate School of Medicine, Gunma University , Maebashi , Japan
| | - Satoru Kakizaki
- b Division of Gastroenterology and Hepatology, Department of Internal Medicine, Graduate School of Medicine, Gunma University , Maebashi , Japan
| | - Kan Chiba
- a Laboratory of Pharmacology and Toxicology, Graduate School of Pharmaceutical Sciences, Chiba University , Chiba , Japan and
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7
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Cheng SL, Bammler TK, Cui JY. RNA Sequencing Reveals Age and Species Differences of Constitutive Androstane Receptor-Targeted Drug-Processing Genes in the Liver. Drug Metab Dispos 2017; 45:867-882. [PMID: 28232382 DOI: 10.1124/dmd.117.075135] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2017] [Accepted: 02/17/2017] [Indexed: 12/26/2022] Open
Abstract
The constitutive androstane receptor (CAR/Nr1i3) is an important xenobiotic-sensing nuclear receptor that is highly expressed in the liver and is well known to have species differences. During development, age-specific activation of CAR may lead to modified pharmacokinetics and toxicokinetics of drugs and environmental chemicals, leading to higher risks for adverse drug reactions in newborns and children. The goal of this study was to systematically investigate the age- and species-specific regulation of various drug-processing genes (DPGs) after neonatal or adult CAR activation in the livers of wild-type, CAR-null, and humanized CAR transgenic mice. At either 5 or 60 days of age, the three genotypes of mice were administered a species-appropriate CAR ligand or vehicle once daily for 4 days (i.p.). The majority of DPGs were differentially regulated by age and/or CAR activation. Thirty-six DPGs were commonly upregulated by CAR activation regardless of age or species of CAR. Although the cumulative mRNAs of uptake transporters were not readily altered by CAR, the cumulative phase I and phase II enzymes as well as efflux transporters were all increased after CAR activation in both species. In general, mouse CAR activation produced comparable or even greater fold increases of many DPGs in newborns than in adults; conversely, humanized CAR activation produced weaker induction in newborns than in adults. Western blotting and enzyme activity assays confirmed the age and species specificities of selected CAR-targeted DPGs. In conclusion, this study systematically compared the effect of age and species of CAR proteins on the regulation of DPGs in the liver and demonstrated that the regulation of xenobiotic biotransformation by CAR is profoundly modified by age and species.
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Affiliation(s)
- Sunny Lihua Cheng
- Department of Environmental and Occupational Health Sciences, University of Washington, Seattle, Washington
| | - Theo K Bammler
- Department of Environmental and Occupational Health Sciences, University of Washington, Seattle, Washington
| | - Julia Yue Cui
- Department of Environmental and Occupational Health Sciences, University of Washington, Seattle, Washington
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8
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Abe T, Takahashi M, Kano M, Amaike Y, Ishii C, Maeda K, Kudoh Y, Morishita T, Hosaka T, Sasaki T, Kodama S, Matsuzawa A, Kojima H, Yoshinari K. Activation of nuclear receptor CAR by an environmental pollutant perfluorooctanoic acid. Arch Toxicol 2016; 91:2365-2374. [DOI: 10.1007/s00204-016-1888-3] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2016] [Accepted: 11/02/2016] [Indexed: 01/12/2023]
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Basu D, Huq A, Iqbal J, Hussain MM, Jiang XC, Jin W. Hepatic S1P deficiency lowers plasma cholesterol levels in apoB-containing lipoproteins when LDLR function is compromised. Nutr Metab (Lond) 2015; 12:35. [PMID: 26495026 PMCID: PMC4613744 DOI: 10.1186/s12986-015-0031-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2015] [Accepted: 09/28/2015] [Indexed: 01/03/2023] Open
Abstract
Background Site-1 protease (S1P) is the key enzyme required for activation of the sterol regulatory element binding proteins (SREBPs) that govern lipid synthesis. While S1P has been speculated to influence plasma apoB-containing lipoprotein (Blp) metabolism, there has been little investigative work. LDL receptor (LDLR) is the major receptor for clearing plasma LDL cholesterol (LDL-c). Proprotein convertase subtilisin kexin type 9 (PCSK9) modulates LDL-c through post-translational degradation of the LDLR. Methods A hepatic-specific knockdown (KD) of S1P was achieved using floxed S1P mouse models (S1Pf/f and LDLR-/-S1Pf/f) and hepatic expression of Cre recombinase. Lipids were measured in total plasma and size fractionated plasma using colorimetric assays. Realtime polymerase chain reaction, western blotting and ELISA were used to determine hepatic expression of key genes/protein. Plasmid mediated overexpression and siRNA mediated knockdown of genes were performed in mouse primary hepatocytes to determine the mechanistic basis of PCSK9 gene regulation. Results A hepatic-specific KD of S1P resulted in a 45 % and 38 % reduction in plasma total cholesterol and triglyceride levels, respectively. Hepatic S1P KD had a minimal effect on plasma Blp cholesterol (Blp-c) in S1Pf/f mice, despite significantly reducing VLDL secretion. Notably, hepatic S1P KD decreased the LDL receptor (LDLR) mRNA expression by 50 %. However, the reduction in LDLR protein levels was less than that of mRNA expression, especially under fed conditions. Further assessment of hepatic S1P deficiency revealed that it increased LDLR protein stability in vivo. Mechanistically, hepatic S1P KD was shown to decrease the liver and plasma levels of the protein proprotein convertase subtilisin/kexin type 9 (PCSK9), which degrades LDLR protein. This effect was more prominent in the fed condition and sufficient to account for the discordance in LDLR mRNA and protein levels. Furthermore, hepatic S1P was shown to regulate PCSK9 expression through activation of the SREBPs. In the LDLR-/- background, hepatic S1P KD significantly reduced Blp-c levels. Conclusion Hepatic S1P is a physiological modulator of plasma Blp metabolism through its regulation of LDLR and PCSK9. Hepatic S1P is a valid target for lowering plasma Blp-c levels in the situation where LDLR function is compromised.
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Affiliation(s)
- Debapriya Basu
- Department of Cell Biology, State University of New York, Downstate Medical Center, Brooklyn, NY 11203 USA
| | - Afroza Huq
- Department of Cell Biology, State University of New York, Downstate Medical Center, Brooklyn, NY 11203 USA
| | - Jahangir Iqbal
- Department of Cell Biology, State University of New York, Downstate Medical Center, Brooklyn, NY 11203 USA ; Department of Pediatrics, State University of New York, Downstate Medical Center, Brooklyn, NY 11203 USA
| | - M Mahmood Hussain
- Department of Cell Biology, State University of New York, Downstate Medical Center, Brooklyn, NY 11203 USA ; Department of Pediatrics, State University of New York, Downstate Medical Center, Brooklyn, NY 11203 USA
| | - Xian-Cheng Jiang
- Department of Cell Biology, State University of New York, Downstate Medical Center, Brooklyn, NY 11203 USA
| | - Weijun Jin
- Department of Cell Biology, State University of New York, Downstate Medical Center, Brooklyn, NY 11203 USA
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Kobayashi K, Hashimoto M, Honkakoski P, Negishi M. Regulation of gene expression by CAR: an update. Arch Toxicol 2015; 89:1045-55. [PMID: 25975989 DOI: 10.1007/s00204-015-1522-9] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2015] [Accepted: 04/27/2015] [Indexed: 11/30/2022]
Abstract
The constitutive androstane receptor (CAR), a member of the nuclear receptor superfamily, is a well-known xenosensor that regulates hepatic drug metabolism and detoxification. CAR activation can be elicited by a large variety of xenobiotics, including phenobarbital (PB) which is not a directly binding CAR ligand. The mechanism of CAR activation is complex and involves translocation from the cytoplasm into the nucleus, followed by further activation steps in the nucleus. Recently, epidermal growth factor receptor (EGFR) has been identified as a PB-responsive receptor, and PB activates CAR by inhibiting the EGFR signaling. In addition to regulation of drug metabolism, activation of CAR has multiple biological end points such as modulation of xenobiotic-elicited liver injury, and the role of CAR in endobiotic functions such as glucose metabolism and cholesterol homeostasis is increasingly recognized. Thus, investigations on the molecular mechanism of CAR activation are critical for the real understanding of CAR-mediated processes. Here, we summarize the current understanding of mechanisms by which CAR activators regulate gene expression through cellular signaling pathways and the roles of CAR on xenobiotic-elicited hepatocellular carcinoma, liver injury, glucose metabolism and cholesterol homeostasis.
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Affiliation(s)
- Kaoru Kobayashi
- Laboratory of Pharmacology and Toxicology, Graduate School of Pharmaceutical Sciences, Chiba University, Chiba, Japan,
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11
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Manchekar M, Liu Y, Sun Z, Richardson PE, Dashti N. Phospholipid transfer protein plays a major role in the initiation of apolipoprotein B-containing lipoprotein assembly in mouse primary hepatocytes. J Biol Chem 2015; 290:8196-205. [PMID: 25638820 DOI: 10.1074/jbc.m114.602748] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
In this study, we tested the hypothesis that phospholipid transfer protein (PLTP) is a plausible mediator of phospholipid (PL) transfer to the N-terminal 1000 residues of apoB (apoB:1000) leading to the initiation of apoB-containing lipoprotein assembly. To this end, primary hepatocytes from wild type (WT) and PLTP knock-out (KO) mice were transduced with adenovirus-apoB:1000 with or without co-transduction with adenovirus-PLTP, and the assembly and secretion of apoB:1000-containing lipoproteins were assessed. PLTP deficiency resulted in a 65 and 72% reduction in the protein and lipid content, respectively, of secreted apoB:1000-containing lipoproteins. Particles secreted by WT hepatocytes contained 69% PL, 9% diacylglycerol (DAG), and 23% triacylglycerol (TAG) with a stoichiometry of 46 PL, 6 DAG, and 15 TAG molecules per apoB:1000. PLTP absence drastically altered the lipid composition of apoB:1000 lipoproteins; these particles contained 46% PL, 13% DAG, and 41% TAG with a stoichiometry of 27 PL, 10 DAG, and 23 TAG molecules per apoB:1000. Reintroduction of Pltp gene into PLTP-KO hepatocytes stimulated the lipidation and secretion of apoB:1000-containing lipoproteins by ∼3-fold; the lipid composition and stoichiometry of these particles were identical to those secreted by WT hepatocytes. In contrast to the WT, apoB:1000 in PLTP-KO hepatocytes was susceptible to intracellular degradation predominantly in the post-endoplasmic reticulum, presecretory compartment. Reintroduction of Pltp gene into PLTP-KO hepatocytes restored the stability of apoB:1000. These results provide compelling evidence that in hepatocytes initial recruitment of PL by apoB:1000 leading to the formation of the PL-rich apoB-containing initiation complex is mediated to a large extent by PLTP.
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Affiliation(s)
- Medha Manchekar
- From the Department of Medicine, Division of Gerontology, Geriatrics, and Palliative Care, Basic Sciences Section, University of Alabama, Birmingham, Alabama 35294 and
| | - Yanwen Liu
- From the Department of Medicine, Division of Gerontology, Geriatrics, and Palliative Care, Basic Sciences Section, University of Alabama, Birmingham, Alabama 35294 and
| | - Zhihuan Sun
- From the Department of Medicine, Division of Gerontology, Geriatrics, and Palliative Care, Basic Sciences Section, University of Alabama, Birmingham, Alabama 35294 and
| | - Paul E Richardson
- the Department of Chemistry and Physics, Coastal Carolina University, Conway, South Carolina 29528
| | - Nassrin Dashti
- From the Department of Medicine, Division of Gerontology, Geriatrics, and Palliative Care, Basic Sciences Section, University of Alabama, Birmingham, Alabama 35294 and
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12
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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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13
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Jung EJ, Kwon SW, Jung BH, Oh SH, Lee BH. Role of the AMPK/SREBP-1 pathway in the development of orotic acid-induced fatty liver. J Lipid Res 2011; 52:1617-25. [PMID: 21757781 DOI: 10.1194/jlr.m015263] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Orotic acid (OA), an intermediate in pyrimidine metabolism, has been used for a variety of purposes, such as dietary supplements. Although it is well documented that OA induces fatty liver in a species-specific manner, the precise molecular mechanisms remain unclear. The present study investigated the role of the adenosine monophosphate-activated protein kinase (AMPK)-sterol regulatory element-binding protein-1 (SREBP-1) pathway in the OA-induced fatty liver. Treatment with OA suppressed the phosphorylation of AMPK via proteasomal degradation of upstream kinase LKB1 and induced activation of SREBP-1 in both human hepatoma cell lines and primary rat hepatocytes. OA-induced SREBP-1 transcriptional activity was suppressed by cotreatment with aminoimidazole carboxamide ribonucleotide (AICAR) or metformin, or by overexpression of constitutively active AMPK (CA-AMPK) in the human hepatoma cell line. Importantly, in vivo data corroborated these results. Feeding 1% OA with diet decreased the phosphorylation of AMPK and increased the maturation of SREBP-1 and the expression of SREBP-responsive genes in the rat liver. OA-induced lipid accumulation was also completely inhibited by rapamycin. Mouse hepatocytes and mice were resistant to OA-induced lipogenesis because of little if any response in AMPK and downstream effectors. In conclusion, OA induces hepatic lipogenesis, mediated predominantly by the AMPK/SREBP-1 pathway in rat hepatocytes and human hepatoma cell lines.
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Affiliation(s)
- Eun-Jeong Jung
- College of Pharmacy and Research Institute of Pharmaceutical Sciences, Seoul National University
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14
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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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15
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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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16
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Cytochrome-P450 2B1 gene silencing attenuates puromycin aminonucleoside-induced cytotoxicity in glomerular epithelial cells. Kidney Int 2010; 78:182-90. [PMID: 20407477 DOI: 10.1038/ki.2010.100] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Previously, we demonstrated that cytochrome P450 2B1 (CYP2B1) can generate reactive oxygen species in puromycin aminonucleoside (PAN)-induced nephrotic syndrome, an animal model of minimal-change disease in humans. In this study we found that overexpression of CYP2B1 in rat glomerular epithelial cells in vitro significantly increased PAN-induced reactive oxygen species generation, cytotoxicity, cell death, and collapse of the actin cytoskeleton. All of these pathological changes were markedly attenuated by siRNA-induced CYP2B1 silencing. The cellular CYP2B1 protein content was significantly decreased whereas its mRNA level was markedly increased, suggesting regulation by protein degradation rather than transcriptional inhibition in the PAN-treated glomerular epithelial cells. This degradation of CYP2B1 was accompanied by the induction of heme oxygenase-1, an important indicator of heme-induced oxidative stress. In PAN-treated CYP2B1-silenced glomerular epithelial cells the induction of heme oxygenase-1 and caspase-3 activity were significantly decreased. Further, cleavage of the stress-induced pro-apoptotic endoplasmic reticulum-specific pro-caspase-12 was prevented in the silenced cells. Our results support a pivotal role of CYP2B1 for reactive oxygen species production in the endoplasmic reticulum in PAN-induced cytotoxicity.
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17
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Masuyama H, Nakatsukasa H, Hiramatsu Y. Effect of oncostatin M on uridine diphosphate-5'-glucuronosyltransferase 1A1 through cross talk with constitutive androstane receptor. Mol Endocrinol 2010; 24:745-53. [PMID: 20197307 DOI: 10.1210/me.2009-0478] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Hyperbilirubinemia remains a common condition in neonates. The constitutive androstane receptor (CAR) is an orphan nuclear receptor that has been shown to participate in the activation of the uridine diphosphate-5'-glucuronosyltransferase 1A1 (UGT1A1) gene, which plays an important role in bilirubin clearance. Oncostatin M (OSM), a member of the IL-6 family, is involved in the maturation of fetal hepatocytes. We have demonstrated that low OSM levels are a potential indicator of neonatal jaundice and the need for phototherapy. In this study we examined the effects of OSM on CAR-mediated signaling to investigate its potential role in neonatal jaundice via the CAR-UGT1A1 pathway. We observed that OSM positively augmented the CAR and UGT1A1 expressions and CAR-mediated signaling in vivo and in vitro, through cross talk between the nuclear CAR receptor and the plasma membrane OSM receptor, via the MAPK cascade. These data suggest that OSM might play a role in bilirubin metabolism via the CAR-UGT1A1 pathway.
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Affiliation(s)
- Hisashi Masuyama
- Department of Obstetrics and Gynecology, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama, Japan.
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18
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Mutoh S, Osabe M, Inoue K, Moore R, Pedersen L, Perera L, Rebolloso Y, Sueyoshi T, Negishi M. Dephosphorylation of threonine 38 is required for nuclear translocation and activation of human xenobiotic receptor CAR (NR1I3). J Biol Chem 2009; 284:34785-92. [PMID: 19858220 DOI: 10.1074/jbc.m109.048108] [Citation(s) in RCA: 107] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Upon activation by therapeutics, the nuclear xenobiotic/ constitutive active/androstane receptor (CAR) regulates various liver functions ranging from drug metabolism and excretion to energy metabolism. CAR can also be a risk factor for developing liver diseases such as hepatocellular carcinoma. Here we have characterized the conserved threonine 38 of human CAR as the primary residue that regulates nuclear translocation and activation of CAR. Protein kinase C phosphorylates threonine 38 located on the alpha-helix spanning from residues 29-42 that constitutes a part of the first zinc finger and continues into the region between the zinc fingers. Molecular dynamics study has revealed that this phosphorylation may destabilize this helix, thereby inactivating CAR binding to DNA as well as sequestering it in the cytoplasm. We have found, in fact, that helix-stabilizing mutations reversed the effects of phosphorylation. Immunohistochemical study using an anti-phospho-threonine 38 peptide antibody has, in fact, demonstrated that the classic CAR activator phenobarbital dephosphorylates the corresponding threonine 48 of mouse CAR in the cytoplasm of mouse liver and translocates CAR into the nucleus. These results define CAR as a cell signal-regulated constitutive active nuclear receptor. These results also provide phosphorylation/dephosphorylation of the threonine as the primary drug target for CAR activation.
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Affiliation(s)
- Shingo Mutoh
- Laboratories of Reproductive and Developmental Toxicology, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina 27709, USA
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19
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di Masi A, De Marinis E, Ascenzi P, Marino M. Nuclear receptors CAR and PXR: Molecular, functional, and biomedical aspects. Mol Aspects Med 2009; 30:297-343. [PMID: 19427329 DOI: 10.1016/j.mam.2009.04.002] [Citation(s) in RCA: 213] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2009] [Accepted: 04/28/2009] [Indexed: 12/31/2022]
Abstract
Nuclear receptors (NRs) are ligand-activated transcription factors sharing a common evolutionary history and having similar sequence features at the protein level. Selective ligand(s) for some NRs is not known, therefore these NRs have been named "orphan receptors". Whenever ligands have been recognized for any of the orphan receptor, it has been categorized and grouped as "adopted" orphan receptor. This group includes the constitutive androstane receptor (CAR) and the pregnane X receptor (PXR). They function as sensors of toxic byproducts derived from endogenous metabolites and of exogenous chemicals, in order to enhance their elimination. This unique function of CAR and PXR sets them apart from the steroid hormone receptors. The broad response profile has established that CAR and PXR are xenobiotic sensors that coordinately regulate xenobiotic clearance in the liver and intestine via induction of genes involved in drug and xenobiotic metabolism. In the past few years, research has revealed new and mostly unsuspected roles for CAR and PXR in modulating hormone, lipid, and energy homeostasis as well as cancer and liver steatosis. The purpose of this review is to highlight the structural and molecular bases of CAR and PXR impact on human health, providing information on mechanisms through which diet, chemical exposure, and environment ultimately impact health and disease.
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Affiliation(s)
- Alessandra di Masi
- Department of Biology, University Roma Tre, Viale Guglielmo Marconi 446, I-00146 Roma, Italy
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20
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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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21
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Li L, Chen T, Stanton JD, Sueyoshi T, Negishi M, Wang H. The peripheral benzodiazepine receptor ligand 1-(2-chlorophenyl-methylpropyl)-3-isoquinoline-carboxamide is a novel antagonist of human constitutive androstane receptor. Mol Pharmacol 2008; 74:443-53. [PMID: 18492798 DOI: 10.1124/mol.108.046656] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
As a promiscuous xenobiotic sensor, the constitutive androstane receptor (CAR; NR1I3) regulates the expression of multiple drug-metabolizing enzymes and transporters in liver. The constitutively activated nature of CAR in the cell-based transfection assays has hindered its use as a predictor of metabolism-based drug-drug interactions. Here, we have identified 1-(2-chlorophenylmethylpropyl)-3-isoquinoline-carboxamide (PK11195), a typical peripheral benzodiazepine receptor (PBR) ligand, as a selective and potent inhibitor of human (h) CAR. In cell-based transfection assays, PK11195 inhibited the constitutive activity of hCAR more than 80% at the concentration of 10 microM, and the PK11195-inhibited activity was efficiently reactivated by the direct CAR activator, 6-(4-chlorophenyl)imidazo[2,1-b][1,3]thiazole-5-carbaldehyde-O-(3,4-dichlorobenzyl) oxime, but not by the indirect hCAR activator, phenobarbital. Mammalian two-hybrid and GST pull-down assays showed that PK11195 repressed the interactions of hCAR with the coactivators steroid receptor coactivator-1 and glucocorticoid receptor-interacting protein 1 to inhibit hCAR activity. The inhibition by PK11195 specifically occurred to the hCAR: PK1195 strongly activated human pregnane X receptor (PXR), whereas it did not alter the activity of the mouse CAR and mouse PXR. In addition, PBR played no role in the PK11195 inhibition of hCAR because the inhibition fully occurred in the HeLa cells in which the PBR was knocked down by small interfering RNA. In the Car(-/-) mouse liver, PK11195 translocated enhanced yellow fluorescent protein-hCAR into the nucleus. These results are consistent with the conclusion that PK11195 is a novel hCAR-specific antagonist that represses the CAR-coactivator interactions to inhibit the receptor activity inside the nucleus. Thus, PK11195 can be used as a chemical tool for studying the molecular basis of CAR function.
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Affiliation(s)
- Linhao Li
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland at Baltimore, 20 Penn Street, Baltimore, MD 21201, USA
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22
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Timsit YE, Negishi M. CAR and PXR: the xenobiotic-sensing receptors. Steroids 2007; 72:231-46. [PMID: 17284330 PMCID: PMC1950246 DOI: 10.1016/j.steroids.2006.12.006] [Citation(s) in RCA: 321] [Impact Index Per Article: 18.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/05/2006] [Revised: 12/07/2006] [Accepted: 12/11/2006] [Indexed: 01/13/2023]
Abstract
The xenobiotic receptors CAR and PXR constitute two important members of the NR1I nuclear receptor family. They function as sensors of toxic byproducts derived from endogenous metabolism and of exogenous chemicals, in order to enhance their elimination. This unique function of CAR and PXR sets them apart from the steroid hormone receptors. In contrast, the steroid receptors, exemplified by the estrogen receptor (ER) and glucocorticoid receptor (GR), are the sensors that tightly monitor and respond to changes in circulating steroid hormone levels to maintain body homeostasis. This divergence of the chemical- and steroid-sensing functions has evolved to ensure the fidelity of the steroid hormone endocrine regulation while allowing development of metabolic elimination pathways for xenobiotics. The development of the xenobiotic receptors CAR and PXR also reflect the increasing complexity of metabolism in higher organisms, which necessitate novel mechanisms for handling and eliminating metabolic by-products and foreign compounds from the body. The purpose of this review is to discuss similarities and differences between the xenobiotic receptors CAR and PXR with the prototypical steroid hormone receptors ER and GR. Interesting differences in structure explain in part the divergence in function and activation mechanisms of CAR/PXR from ER/GR. In addition, the physiological roles of CAR and PXR will be reviewed, with discussion of interactions of CAR and PXR with endocrine signaling pathways.
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Affiliation(s)
| | - Masahiko Negishi
- *CORRESPONDING AUTHOR ADDRESS: Dr, Masahiko Negishi, Ph.D., Head, Pharmacogenetics Section, Laboratory of Reproductive and Developmental Toxicology, National Institute of Environmental Health Sciences, 111 T.W. Alexander Drive, Research Triangle Park, NC, 27709, Tel: (919) 541-2942, Fax (919) 541-0696,
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23
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Dvorák Z, Maurel P, Vilarem MJ, Ulrichová J, Modrianský M. Expression and transcriptional activities of nuclear receptors involved in regulation of drug-metabolizing enzymes are not altered by colchicine: focus on PXR, CAR, and GR in primary human hepatocytes. Cell Biol Toxicol 2006; 23:63-73. [PMID: 16964586 DOI: 10.1007/s10565-006-0127-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2006] [Accepted: 07/18/2006] [Indexed: 10/24/2022]
Abstract
Recent findings show that colchicine (COL) in submicromolar concentrations downregulates the expression of major drug-metabolizing P450 enzymes in human hepatocytes. Concomitantly, the expression of pregnane X receptor (PXR) and constitutive androstane receptor (CAR) was diminished by COL, whereas expression of glucocorticoid receptor (GR) remained unaltered. A tentative mechanism is perturbation of the GR-PXR/CAR-CYP2/3 signaling cascade, resulting in restricted transcriptional activity of GR receptor by colchicine. In this work we focused on 10-demethylcolchicine (colchiceine; EIN), a structural analogue and a putative metabolite of COL that lacks tubulin-binding activity. We investigated the effects of EIN on the expression of PXR, CAR, and GR receptors in primary cultures of human hepatocytes. In contrast with the effects of COL, EIN does not alter the expression of PXR, CAR, and/or GR receptors mRNAs. In addition, EIN had no effects on transcriptional activities of PXR, CAR, and GR receptors in reporter gene assays using transfected cell lines. Considering that COL and EIN are structurally very close and differ only in their tubulin-binding activity, the data presented imply that the deleterious effects of COL on the GR-PXR/CAR-CYP2/3 cascade are primarily due to perturbation of the microtubule network. Our data support the idea of replacing COL by EIN, which is less toxic and does not interact with xenoreceptors.
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MESH Headings
- Cells, Cultured
- Colchicine/analogs & derivatives
- Colchicine/toxicity
- Constitutive Androstane Receptor
- Gene Expression/drug effects
- Genes, Reporter
- Hepatocytes/drug effects
- Hepatocytes/metabolism
- Humans
- Pharmaceutical Preparations/metabolism
- Pregnane X Receptor
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- Receptors, Cytoplasmic and Nuclear/drug effects
- Receptors, Cytoplasmic and Nuclear/genetics
- Receptors, Cytoplasmic and Nuclear/metabolism
- Receptors, Glucocorticoid/genetics
- Receptors, Steroid/genetics
- Transcription Factors/genetics
- Transcription, Genetic/drug effects
- Transfection
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Affiliation(s)
- Z Dvorák
- Institute of Medical Chemistry and Biochemistry, Medical Faculty, Palacký University Olomouc, Hnevotínská 3, 77515 Olomouc, Czech Republic.
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24
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Webb SJ, Geoghegan TE, Prough RA, Michael Miller KK. The biological actions of dehydroepiandrosterone involves multiple receptors. Drug Metab Rev 2006; 38:89-116. [PMID: 16684650 PMCID: PMC2423429 DOI: 10.1080/03602530600569877] [Citation(s) in RCA: 160] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Dehydroepiandrosterone has been thought to have physiological functions other than as an androgen precursor. The previous studies performed have demonstrated a number of biological effects in rodents, such as amelioration of disease in diabetic, chemical carcinogenesis, and obesity models. To date, activation of the peroxisome proliferators activated receptor alpha, pregnane X receptor, and estrogen receptor by DHEA and its metabolites have been demonstrated. Several membrane-associated receptors have also been elucidated leading to additional mechanisms by which DHEA may exert its biological effects. This review will provide an overview of the receptor multiplicity involved in the biological activity of this sterol.
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Affiliation(s)
- Stephanie J Webb
- Department of Biochemistry & Molecular Biology, University of Louisville School of Medicine, KY 40292, USA
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25
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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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26
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Yoshinari K. Roles of Nuclear Receptors in the Gene Expression of Drug-metabolizing Enzymes under Various Physiological Conditions. YAKUGAKU ZASSHI 2006; 126:343-8. [PMID: 16679742 DOI: 10.1248/yakushi.126.343] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The nuclear receptor constitutive androstane receptor (CAR), a key transcription factor for the expression of cytochrome P450 (CYP) 2B genes, resides in the cytoplasm under untreated conditions and translocates into the nucleus upon xenobiotic exposure. CAR forms a multiprotein complex including heat shock protein 90 in the cytoplasm as the glucocorticoid receptor, and it is likely that protein phosphatase 2A plays a critical role in the first step of CAR nuclear translocation. In addition to the xenobiotic induction of CYP2Bs, our recent studies have indicated that CAR is important for sex and strain differences and obesity/diabetes-associated changes in the expression of CYP2B genes. These results have raised the hypothesis that the expression of nuclear receptors varies depending on the physiologic condition, leading to the dysregulation of CYP expression. In obese mice fed a high-fat diet, however, hepatic CYP3A levels are drastically decreased without any significant changes in the expression of nuclear receptors including the pregnane X receptor and hepatocyte nuclear factor-4, which are known to be key transcription factors in the expression of CYP3A genes. These results indicate that it is important to investigate the mechanism of the transcriptional regulation of nuclear receptor genes as well as the activation of nuclear receptors to understand the CYP expression system fully.
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Affiliation(s)
- Kouichi Yoshinari
- Department of Pharmaco-Biochemistry, School of Pharmaceutical Sciences, University of Shizuoka, Japan.
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27
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Pustylnyak VO, Gulyaeva LF, Lyakhovich VV. CAR expression and inducibility of CYP2B genes in liver of rats treated with PB-like inducers. Toxicology 2005; 216:147-53. [PMID: 16153763 DOI: 10.1016/j.tox.2005.08.002] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2005] [Revised: 08/02/2005] [Accepted: 08/02/2005] [Indexed: 11/20/2022]
Abstract
The expression of the CAR gene and inducibility of CYP2B protein in the liver of male Wistar rats treated with phenobarbital (PB) and triphenyldioxane (TPD) were investigated. To clarify the role of phosphorylation/dephosphorylation in these processes, rats were treated with inhibitors of Ca(2+)/calmodulin-dependent kinase II (W7) or protein phosphatases PP1 and PP2A (OA) before induction. Constitutive expression of the CAR gene in livers of untreated rats was detected by multiplex RT-PCR. Treatment with W7 resulted in a 2.8-fold induction of CAR gene expression, whereas OA led to a 2.4-fold decrease of the mRNA level. The same results were obtained for CYP2B genes expression, which were increased by W7 treatment (two-fold) and decreased by OA (2.3-fold). PB-induction did not lead to significant alteration in the level of CAR gene expression, although CYP2B genes expression was enhanced two-fold over control values. TPD caused a two-fold increase of both CAR and CYP2B mRNA levels. Both inducers reduced the effects of inhibitors on CAR gene expression. Results of EMSA showed that PB, TPD or W7 alone induced formation of complexes of NR1 with nuclear proteins. Appearance of the complexes correlated with an increase in CYP2B expression, and their intensities were modulated by the protein kinase inhibitors. Thus, our results demonstrate that constitutive expressions of CAR as well as CYP2B during induction are regulated by phosphorylation/dephosphorylation processes.
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Affiliation(s)
- Vladimir O Pustylnyak
- Institute of Molecular Biology and Biophysics, Timakova str. 2, Novosibirsk 630117, Russia.
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28
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Dirkx R, Vanhorebeek I, Martens K, Schad A, Grabenbauer M, Fahimi D, Declercq P, Van Veldhoven PP, Baes M. Absence of peroxisomes in mouse hepatocytes causes mitochondrial and ER abnormalities. Hepatology 2005; 41:868-78. [PMID: 15732085 DOI: 10.1002/hep.20628] [Citation(s) in RCA: 132] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/07/2022]
Abstract
Peroxisome deficiency in men causes severe pathology in several organs, particularly in the brain and liver, but it is still unknown how metabolic abnormalities trigger these defects. In the present study, a mouse model with hepatocyte-selective elimination of peroxisomes was generated by inbreeding Pex5-loxP and albumin-Cre mice to investigate the consequences of peroxisome deletion on the functioning of hepatocytes. Besides the absence of catalase-positive peroxisomes, multiple ultrastructural alterations were noticed, including hepatocyte hypertrophy and hyperplasia, smooth endoplasmic reticulum proliferation, and accumulation of lipid droplets and lysosomes. Most prominent was the abnormal structure of the inner mitochondrial membrane, which bore some similarities with changes observed in Zellweger patients. This was accompanied by severely reduced activities of complex I, III, and V and a collapse of the mitochondrial inner membrane potential. Surprisingly, these abnormalities provoked no significant disturbances of adenosine triphosphate (ATP) levels and redox state of the liver. However, a compensatory increase of glycolysis as an alternative source of ATP and mitochondrial proliferation were observed. No evidence of oxidative damage to proteins or lipids nor elevation of oxidative stress defence mechanisms were found. Altered expression of peroxisome proliferator-activated receptor alpha (PPAR-alpha) regulated genes indicated that PPAR-alpha is activated in the peroxisome-deficient cells. In conclusion, the absence of peroxisomes from mouse hepatocytes has an impact on several other subcellular compartments and metabolic pathways but is not detrimental to the function of the liver parenchyma. Supplementary material for this article can be found on the HEPATOLOGY website (http://interscience.wiley.com/jpages/0270-9139/suppmat/index.html).
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Affiliation(s)
- Ruud Dirkx
- Laboratory of Clinical Chemistry, K. U. Leuven, B 3000 Leuven, Belgium
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Rencurel F, Stenhouse A, Hawley SA, Friedberg T, Hardie DG, Sutherland C, Wolf CR. AMP-activated Protein Kinase Mediates Phenobarbital Induction of CYP2B Gene Expression in Hepatocytes and a Newly Derived Human Hepatoma Cell Line. J Biol Chem 2005; 280:4367-73. [PMID: 15572372 DOI: 10.1074/jbc.m412711200] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Phenobarbital (PB) administration is known to trigger pleiotropic responses, including liver hypertrophy, tumor promotion, and induction of genes encoding drug-metabolizing enzymes. The induction of human CYP2B6 and the rat (CYP2B1) and mouse (Cyp2b10) homologues by PB is mediated by the nuclear receptor constitutive androstane receptor (CAR). The study of CYP2B gene regulation and CAR activity by PB has been difficult due to the lack of a cellular model. In this study, we describe a novel differentiated human hepatoma cell line (WGA), derived from HepG2, which expresses CYP2B6 and CAR. WGA cells represent a powerful system to study the regulation of CYP2B6 gene expression by PB. There is evidence that CAR activity is regulated by phosphorylation and that regulation of some CYP genes depends on the nutritional status of cells. The AMP-activated protein kinase (AMPK) functions as an energy sensor and is activated when cells experience energy-depleting stresses. In this report, we show that addition of 5-amino-imidazole carboxamide riboside, an AMPK activator, to WGA and human hepatocytes induces CYP2B6 gene expression. Expression of a constitutively active form of AMPK mimics the PB induction of CYP2B6 and CYP2B1 gene expression. Conversely, the expression of a dominant negative form of AMPK inhibits the induction of these genes by PB. Finally, we demonstrate, for the first time, that AMPK activity increases in cells cultured with PB. Our data strongly support a role for AMPK in the PB induction of CYP2B gene expression and provide new insights into the regulation of gene expression by barbiturate drugs.
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MESH Headings
- AMP-Activated Protein Kinases
- Adenosine Triphosphate/chemistry
- Adenoviridae
- Aminoimidazole Carboxamide/analogs & derivatives
- Aminoimidazole Carboxamide/pharmacology
- Animals
- Aryl Hydrocarbon Hydroxylases/biosynthesis
- Aryl Hydrocarbon Hydroxylases/chemistry
- Barbiturates/pharmacology
- Blotting, Western
- Cell Line, Tumor
- Cells, Cultured
- Constitutive Androstane Receptor
- Culture Media
- Cytochrome P-450 CYP2B1/biosynthesis
- Cytochrome P-450 CYP2B6
- Gene Expression Regulation
- Gene Expression Regulation, Neoplastic
- Genes, Dominant
- Genes, Reporter
- Hepatocytes/metabolism
- Humans
- Male
- Mice
- Multienzyme Complexes/physiology
- Oxidoreductases, N-Demethylating/biosynthesis
- Oxidoreductases, N-Demethylating/chemistry
- Phenobarbital/metabolism
- Phenobarbital/pharmacology
- Phosphorylation
- Plasmids/metabolism
- Promoter Regions, Genetic
- Protein Serine-Threonine Kinases/physiology
- Protein Structure, Tertiary
- RNA/metabolism
- RNA, Messenger/metabolism
- Rats
- Rats, Sprague-Dawley
- Receptors, Cytoplasmic and Nuclear/metabolism
- Reverse Transcriptase Polymerase Chain Reaction
- Ribonucleosides/pharmacology
- Transcription Factors/metabolism
- Transcription, Genetic
- beta-Galactosidase/metabolism
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Affiliation(s)
- Franck Rencurel
- Biomedical Research Centre and Cancer Research UK Molecular Pharmacology Unit, Level 5, Ninewells Hospital and Medical School, University of Dundee, Dundee DD1 9SY, Scotland, United Kingdom
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Pustylnyak VO, Zakharova LY, Mikhailova ON, Rice RH, Gulyaeva LF, Lyakhovich VV. In vivo effects of protein kinase and phosphatase inhibitors on CYP2B induction in rat liver. Toxicology 2005; 207:315-22. [PMID: 15596261 DOI: 10.1016/j.tox.2004.10.003] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2004] [Revised: 10/13/2004] [Accepted: 10/13/2004] [Indexed: 10/26/2022]
Abstract
Effects of inhibiting protein kinases and phosphatases on induction of CYP2B by triphenyldioxane (TPD) and phenobarbital (PB) were investigated. Male Wistar rats were treated with test inhibitors before TPD or PB administration. Inhibitors of phosphatidylinositol-3-kinase (Wortmannin) and protein kinase C (bisindolylmaleimide I) did not have appreciable effects on TPD- or PB-induced pentoxyresorufin O-dealkylase (PROD) activity specific for CYP2B, although bisindolylmaleimide I did give substantial induction alone. W-7, an inhibitor of Ca2+/calmodulin-dependent kinase II, produced a 6-fold increase in the TPD-induced PROD activity and did not lead to a significant increase in basal PROD activity. Treatment of rats with okadaic acid (OA), an inhibitor of protein phosphatases PP1 and PP2A, caused considerable decreases in PROD activity during the induction by TPD and PB (8- and 2.5-fold, respectively). Results of multiplex RT-PCR showed that the increase in enzymatic activity from W7 and OA treatment reflected at least in part increased mRNA levels. CYP2B mRNA level in the liver of rats treated with W-7 and TPD was 1.5 times higher than in the liver of TPD-treated rats. This effect was not observed for PB-induction. OA treatment caused a decrease of the CYP2B mRNA levels of 44% and 33% respectively, for TPD- and PB-induction. Thus, our results are consistent with the hypothesis that phosphorylation/dephosphorylation signaling pathways are involved in regulation of CYP2B induction in rat liver.
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Affiliation(s)
- Vladimir O Pustylnyak
- Institute of Molecular Biology and Biophysics, Timakova str. 2, Novosibirsk 630117, Russia.
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31
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Foulon V, Sniekers M, Huysmans E, Asselberghs S, Mahieu V, Mannaerts GP, Van Veldhoven PP, Casteels M. Breakdown of 2-hydroxylated straight chain fatty acids via peroxisomal 2-hydroxyphytanoyl-CoA lyase: a revised pathway for the alpha-oxidation of straight chain fatty acids. J Biol Chem 2005; 280:9802-12. [PMID: 15644336 DOI: 10.1074/jbc.m413362200] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
2-Hydroxyfatty acids, constituents of brain cerebrosides and sulfatides, were previously reported to be degraded by an alpha-oxidation system, generating fatty acids shortened by one carbon atom. In the current study we used labeled and unlabeled 2-hydroxyoctadecanoic acid to reinvestigate the degradation of this class of lipids. Both in intact and broken cell systems formate was identified as a main reaction product. Furthermore, the generation of an n-1 aldehyde was demonstrated. In permeabilized rat hepatocytes and liver homogenates, studies on cofactor requirements revealed a dependence on ATP, CoA, Mg(2+), thiamine pyrophosphate, and NAD(+). Together with subcellular fractionation data and studies on recombinant enzymes, this led to the following picture. In a first step, the 2-hydroxyfatty acid is activated to an acyl-CoA; subsequently, the 2-hydroxy fatty acyl-CoA is cleaved by 2-hydroxyphytanoyl-CoA lyase, to formyl-CoA and an n-1 aldehyde. The severe inhibition of formate generation by oxythiamin treatment of intact fibroblasts indicates that cleavage through the thiamine pyrophosphate-dependent 2-hydroxyphytanoyl-CoA lyase is the main pathway for the degradation of 2-hydroxyfatty acids. The latter protein was initially characterized as an essential enzyme in the peroxisomal alpha-oxidation of 3-methyl-branched fatty acids such as phytanic acid. Our findings point to a new role for peroxisomes in mammals, i.e. the breakdown of 2-hydroxyfatty acids, at least the long chain 2-hydroxyfatty acids. Most likely, the more abundant very long chain 2-hydroxyfatty acids are degraded in a similar manner.
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Affiliation(s)
- Veerle Foulon
- Afdeling Farmacologie, Departement Celbiologie, Katholieke Universiteit Leuven, Campus Gasthuisberg, 3000 Leuven, Belgium
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32
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Swales K, Kakizaki S, Yamamoto Y, Inoue K, Kobayashi K, Negishi M. Novel CAR-mediated mechanism for synergistic activation of two distinct elements within the human cytochrome P450 2B6 gene in HepG2 cells. J Biol Chem 2004; 280:3458-66. [PMID: 15563456 DOI: 10.1074/jbc.m411318200] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The constitutive active receptor (CAR) regulates the induction of the cytochrome P450 2B6 (CYP2B6) gene by phenobarbital-type inducers, such as 1,4 bis[2-(3,5-dichloropyridyloxy)]benzene (TCPOBOP) via the distal phenobarbital-responsive enhancer module (PBREM, at -1732/-1685 bp). Activation of the PBREM by TCPOBOP generated a 10-fold induction of CYP2B6 mRNA in HepG2 cells stably expressing mouse CAR (Ym17). Co-treatment with the protein phosphatase inhibitor okadaic acid (OA) synergistically increased this induction over 100-fold without directly activating CAR or the PBREM. Although OA synergy required the presence of PBREM, deletion assays delineated the OA-responsive activity to a proximal 24-bp (-256/-233) sequence (OARE) in the CYP2B6 promoter. CAR did not directly bind to the OARE in electrophoretic mobility shift assays. However, both DNA affinity and chromatin immunoprecipitation assays showed a significant increase in CAR association with the OARE after co-treatment with TCPOBOP and OA, indicating the indirect binding of CAR to the OARE. The two cis-acting elements, the distal PBREM and the proximal OARE, within the chromatin structure are both regulated by CAR in response to TCPOBOP and OA, respectively, to maximally induce the CYP2B6 promoter. This functional interaction between the two sites expands the current understanding of the mechanism of CAR-mediated inducible transcription.
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Affiliation(s)
- Karen Swales
- Pharmacogenetics Section, Laboratory of Reproductive and Developmental Toxicology, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina 27709, USA
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Handschin C, Blättler S, Roth A, Looser R, Oscarson M, Kaufmann MR, Podvinec M, Gnerre C, Meyer UA. The evolution of drug-activated nuclear receptors: one ancestral gene diverged into two xenosensor genes in mammals. NUCLEAR RECEPTOR 2004; 2:7. [PMID: 15479477 PMCID: PMC524364 DOI: 10.1186/1478-1336-2-7] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/08/2004] [Accepted: 10/12/2004] [Indexed: 01/22/2023]
Abstract
BACKGROUND: Drugs and other xenobiotics alter gene expression of cytochromes P450 (CYP) by activating the pregnane X receptor (PXR) and constitutive androstane receptor (CAR) in mammals. In non-mammalian species, only one xenosensor gene has been found. Using chicken as a model organism, the aim of our study was to elucidate whether non-mammalian species only have one or two xenosensors like mammals. RESULTS: To explore the evolutionary aspect of this divergence, we tried to identify additional xenobiotic sensing nuclear receptors in chicken using various experimental approaches. However, none of those revealed novel candidates. Ablation of chicken xenobiotic receptor (CXR) function by RNAi or dominant-negative alleles drastically reduced drug-induction in a chicken hepatoma cell line. Subsequently, we functionally and structurally characterized CXR and compared our results to PXR and CAR. Despite the high similarity in their amino acid sequence, PXR and CAR have very distinct modes of activation. Some aspects of CXR function, e.g. direct ligand activation and high promiscuity are very reminiscent of PXR. On the other hand, cellular localization studies revealed common characteristics of CXR and CAR in terms of cytoplasmic-nuclear distribution. Finally, CXR has unique properties regarding its regulation in comparison to PXR and CAR. CONCLUSION: Our finding thus strongly suggest that CXR constitutes an ancestral gene which has evolved into PXR and CAR in mammals. Future studies should elucidate the reason for this divergence in mammalian versus non-mammalian species.
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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
- (Present Address) Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA 02115, USA
| | - Sharon Blättler
- Division of Pharmacology/Neurobiology, Biozentrum of the University of Basel, Klingelbergstrasse 50-70, CH-4056 Basel, Switzerland
| | - Adrian Roth
- Division of Pharmacology/Neurobiology, Biozentrum of the University of Basel, Klingelbergstrasse 50-70, CH-4056 Basel, Switzerland
| | - Renate Looser
- Division of Pharmacology/Neurobiology, Biozentrum of the University of Basel, Klingelbergstrasse 50-70, CH-4056 Basel, Switzerland
| | - Mikael Oscarson
- Division of Pharmacology/Neurobiology, Biozentrum of the University of Basel, Klingelbergstrasse 50-70, CH-4056 Basel, Switzerland
| | - Michel R Kaufmann
- Division of Pharmacology/Neurobiology, Biozentrum of the University of Basel, Klingelbergstrasse 50-70, CH-4056 Basel, Switzerland
| | - Michael Podvinec
- Division of Pharmacology/Neurobiology, Biozentrum of the University of Basel, Klingelbergstrasse 50-70, CH-4056 Basel, Switzerland
| | - Carmela Gnerre
- Division of Pharmacology/Neurobiology, Biozentrum of the University of Basel, Klingelbergstrasse 50-70, CH-4056 Basel, Switzerland
- (Present Address) Actelion Pharmaceuticals Ltd., CH-4123 Allschwil, Switzerland
| | - Urs A Meyer
- Division of Pharmacology/Neurobiology, Biozentrum of the University of Basel, Klingelbergstrasse 50-70, CH-4056 Basel, Switzerland
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34
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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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35
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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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36
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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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Chen YC, Shen SC, Lin HY. Rutinoside at C7 attenuates the apoptosis-inducing activity of flavonoids. Biochem Pharmacol 2003; 66:1139-50. [PMID: 14505793 DOI: 10.1016/s0006-2952(03)00455-6] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Rutinoside (rhamnoglucoside; rhamnose+glucose) addition has been examined extensively in the metabolism of flavonoids, however the effect of rutinoside on apoptosis-inducing activity of flavonoids is still unknown. In the present study, the two pairs of flavonoids of hesperetin (HT) and hesperidin (HD; HT-7-rutinose), and naringenin (NE) and naringin (NE-7-rutinose), were used to study their apoptosis-inducing activities in HL-60 cells. Both HD and NI are flavonoids which contain a rutinoside at the C7 of HT and NE, respectively. Results of the MTT assay showed that HT and NE, but not HD and NI, exhibited significant cytotoxic effect in HL-60 cells, accompanied by the dose- and time-dependent appearance of characteristics of apoptosis including an increase in DNA ladder intensity, morphological changes, appearance of apoptotic bodies, and an increase in hypodiploid cells by flow cytometry analysis. HT and NE, but not HD and NI, caused rapid and transient induction of caspase-3/CPP32 activity, but not caspase-1 activity, according to the cleavage of caspase-3 substrates poly(ADP-ribose) polymerase and D4-GDI proteins, the appearance of cleaved caspase-3 fragments detected in HT- or NE-, but not in HD- or NI-treated HL-60 cells. A decrease in the anti-apoptotic protein, Mcl-1, was detected in HT- and NE-treated HL-60 cells, whereas other Bcl-2 family proteins including Bax, Bcl-2, Bcl-XL, and Bag remained unchanged. The caspase-3 inhibitor, Ac-DEVD-FMK, but not the caspase-1 inhibitor, Ac-YVAD-FMK, attenuated HT- and NE-induced cell death. Interestingly, neither HT nor NE induced apoptosis in the mature monocytic cell line THP-1 and primary human polymorphonuclear cells, as characterized by a lack of DNA ladders, caspase-3 activation, poly(ADP-ribose) polymerase cleavage, and Mcl-1 decrease, compared with those in HL-60 cells. In addition, the rutinoside group in HD and NI was removed by hesperidinase and naringinase, accompanied by the production of HT and NE, respectively, according to HPLC analysis. Accordingly, hesperidinase and naringinase digestion recovered the apoptosis-inducing activity of HD and NI in HL-60 cells. Our experiments provide the first evidence to suggest that rutinoside in flavonoids prevents the induction of apoptosis, and that activation of the traditional caspase-3 cascade participates in HT- and NE-induced apoptosis.
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Affiliation(s)
- Yen-Chou Chen
- Graduate Institute of Pharmacognosy, Taipei Medical University, 250 Wu-Hsing Street, Taipei, Taiwan, ROC.
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Yoshinari K, Kobayashi K, Moore R, Kawamoto T, Negishi M. Identification of the nuclear receptor CAR:HSP90 complex in mouse liver and recruitment of protein phosphatase 2A in response to phenobarbital. FEBS Lett 2003; 548:17-20. [PMID: 12885400 DOI: 10.1016/s0014-5793(03)00720-8] [Citation(s) in RCA: 139] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The nuclear receptor CAR, a phenobarbital (PB)-responsive transcription factor, translocates into the nucleus of hepatocytes after PB induction. In non-induced mice, CAR forms a physical complex with heat shock protein 90 (HSP90) in the cytoplasm. In response to PB induction, protein phosphatase 2A is recruited to the CAR:HSP90 complex. This recruitment may lead CAR to translocate into the nucleus, consistent with the inhibitions of nuclear CAR accumulation in PB-induced mouse primary hepatocytes by okadaic acid as well as by geldanamycin.
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Affiliation(s)
- Kouichi Yoshinari
- 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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Dvorak Z, Modriansky M, Pichard-Garcia L, Balaguer P, Vilarem MJ, Ulrichová J, Maurel P, Pascussi JM. Colchicine down-regulates cytochrome P450 2B6, 2C8, 2C9, and 3A4 in human hepatocytes by affecting their glucocorticoid receptor-mediated regulation. Mol Pharmacol 2003; 64:160-9. [PMID: 12815172 DOI: 10.1124/mol.64.1.160] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The xenobiotic-mediated induction of three major human liver cytochrome P450 genes, CYP2B6, CYP2C9, and CYP3A4, is known to be regulated by the constitutive androstane receptor (CAR) and the pregnane X receptor (PXR). CAR and PXR are regulated, at least in part, by the glucocorticoid receptor (GR) and the hypothesis of a signal transduction cascade GR-[CAR/PXR]-P450 has been proposed. This study was aimed at testing this hypothesis in primary human hepatocytes by using the tubulin network disrupting agent colchicine. Colchicine (COL) decreased both basal and rifampicin- and phenobarbital-inducible expression of CYP2B6, CYP2C8/9, and CYP3A4. A parallel down-regulation of mRNA expression of CAR, PXR, and tyrosine aminotransferase, a prototypic gene directly regulated by GR, was observed. COL affected neither the level of GR mRNA nor ligand binding to GR. To evaluate the effect of colchicine on GR-mediated gene transactivation, HeLa cells stably or transiently transfected with a GR-responsive element-dependent luciferase reporter gene were used. COL decreased the dexamethasone-induced luciferase expression in stably transfected cell line by 50%, whereas GR transactivation in transiently transfected cells was not affected by COL. In contrast, ligand-dependent GR translocation in the human embryonic kidney 293 cell line transiently transfected with GFP-GR was inhibited by COL. We conclude that alteration of the signal transduction mediated through the GR-[CAR/PXR]-P450 cascade by colchicine is responsible for the down-regulation of CYP2C9 and CYP3A4, implicating cytoskeleton as necessary for correct functioning of this cascade under physiological conditions.
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Affiliation(s)
- Zdenek Dvorak
- Institute of Medical Chemistry and Biochemistry, Medical Faculty, Palacký University Olomouc, Olomouc, Czech Republic
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40
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Liu Y, Nakagawa Y, Wang Y, Li R, Li X, Ohzeki T, Friedman TC. Leptin activation of corticosterone production in hepatocytes may contribute to the reversal of obesity and hyperglycemia in leptin-deficient ob/ob mice. Diabetes 2003; 52:1409-16. [PMID: 12765951 DOI: 10.2337/diabetes.52.6.1409] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Glucocorticoids have been implicated as pathophysiological mediators of obesity and insulin resistance and are regulated by 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1). This enzyme regenerates active corticosterone from inactive 11-keto forms. To assess the role of 11beta-HSD1-mediated synthesis of active corticosterone in leptin-related obesity and diabetes, we examined the peripheral effect of leptin on 11beta-HSD1 activity and gene expression in vivo and in vitro in hepatocytes from ob/ob mice and in liver of streptozotocin (STZ)-treated ob/ob mice. We observed an inverse relationship between hepatic 11beta-HSD1 expression and body weight in ob/ob mice and lean littermates. Leptin treatment of ob/ob mice markedly increased hepatic 11beta-HSD1 activity and mRNA expression. This induction of 11beta-HSD1 expression corresponded to reduced levels of circulating corticosterone and weight loss in ob/ob mice treated with leptin, indicating that impaired hepatic 11beta-HSD1 expression may contribute to the pathogenesis of obesity in ob/ob mice. In addition, leptin treatment of STZ-treated ob/ob mice caused marked increases in hepatic 11beta-HSD1 levels associated with decreased body weight and a significant reduction in hyperglycemia due to pancreatic beta-cell damage. Addition of leptin to ob/ob mouse primary hepatocytes led to a dose-dependent increase in 11beta-HSD1 mRNA expression. In contrast, leptin did not influence 11beta-HSD1 expression in primary hepatocytes from db/db mice, indicating that leptin regulation of 11beta-HSD1 expression is probably mediated by the functional leptin receptor. Thus, leptin appears to be an important metabolic signal that directly activates intrahepatic corticosterone production. These findings suggest that the liver-specific interaction of leptin with 11beta-HSD1 is involved in the development of obesity and insulin resistance in ob/ob mice.
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Affiliation(s)
- Yanjun Liu
- Division of Endocrinology, Charles R. Drew University of Medicine & Sciences, UCLA School of Medicine, 1731 E. 120th Street, Los Angeles, CA 90059, USA.
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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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42
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Wang N, Chen W, Linsel-Nitschke P, Martinez LO, Agerholm-Larsen B, Silver DL, Tall AR. A PEST sequence in ABCA1 regulates degradation by calpain protease and stabilization of ABCA1 by apoA-I. J Clin Invest 2003. [DOI: 10.1172/jci200316808] [Citation(s) in RCA: 209] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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Wang N, Chen W, Linsel-Nitschke P, Martinez LO, Agerholm-Larsen B, Silver DL, Tall AR. A PEST sequence in ABCA1 regulates degradation by calpain protease and stabilization of ABCA1 by apoA-I. J Clin Invest 2003; 111:99-107. [PMID: 12511593 PMCID: PMC151839 DOI: 10.1172/jci16808] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Cholesterol-loaded macrophage foam cells are a central component of atherosclerotic lesions. ABCA1, the defective molecule in Tangier disease, mediates the efflux of phospholipids and cholesterol from cells to apoA-I, reversing foam cell formation. In ABCA1, we identified a sequence rich in proline, glutamic acid, serine, and threonine (PEST sequence) that enhances the degradation of ABCA1 by calpain protease and thereby controls the cell surface concentration and cholesterol efflux activity of ABCA1. In an apparent positive feedback loop, apoA-I binds ABCA1, promotes lipid efflux, inhibits calpain degradation, and leads to increased levels of ABCA1. ApoA-I infusion also increases ABCA1 in vivo. These studies reveal a novel mode of regulation of ABCA1 by PEST sequence-mediated calpain proteolysis that appears to be reversed by apolipoprotein-mediated phospholipid efflux. Inhibition of ABCA1 degradation by calpain could represent a novel therapeutic approach to increasing macrophage cholesterol efflux and decreasing atherosclerosis.
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Affiliation(s)
- Nan Wang
- Division of Molecular Medicine, Department of Medicine, Columbia University, New York, New York 10032, USA.
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Yamamoto Y, Kawamoto T, Negishi M. The role of the nuclear receptor CAR as a coordinate regulator of hepatic gene expression in defense against chemical toxicity. Arch Biochem Biophys 2003; 409:207-11. [PMID: 12464260 DOI: 10.1016/s0003-9861(02)00456-3] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The nuclear receptor CAR (constitutive active receptor) mediates the induction of transcription of cytochrome P450 (CYP) genes by phenobarbital (PB) and PB-type inducers. A recent study using CAR-null mice has shown that CAR regulates not only the CYP genes but also other genes encoding various drug/steroid-metabolizing enzymes. In addition to coordinating these enzymes, CAR plays other roles in hepatic gene expression: CAR represses various genes including carnitine palmitoyltransferase 1a and phosphoenolpyruvate carboxykinase 1 in response to PB, and the receptor regulates the constitutive expression of genes such as squalene epoxidase. On the other hand, induction of certain genes such as amino levulinate synthase 1 by PB is not regulated by CAR. Here we describe diverse roles of CAR in hepatic gene expression with a particular focus on endogenous substances such as cholesterol, bilirubin, and steroid hormones.
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MESH Headings
- 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine/analogs & derivatives
- 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine/pharmacology
- 5-Aminolevulinate Synthetase/metabolism
- Animals
- Blotting, Northern
- Calcium/metabolism
- Carnitine O-Palmitoyltransferase/metabolism
- Cells, Cultured
- Cholesterol/metabolism
- Constitutive Androstane Receptor
- Cytoplasm/metabolism
- Dose-Response Relationship, Drug
- Estrogens/pharmacology
- Gene Expression Regulation
- Liver/metabolism
- Male
- Mice
- Mice, Transgenic
- Models, Biological
- Oligonucleotide Array Sequence Analysis
- Oxygenases/metabolism
- Phosphoenolpyruvate Carboxykinase (ATP)/metabolism
- Protein Structure, Tertiary
- RNA, Messenger/metabolism
- Receptors, Cytoplasmic and Nuclear/metabolism
- Receptors, Cytoplasmic and Nuclear/physiology
- Squalene Monooxygenase
- Transcription Factors/metabolism
- Transcription Factors/physiology
- Transcription, Genetic
- Two-Hybrid System Techniques
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Affiliation(s)
- Yukio Yamamoto
- 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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Larsen AKR, Møller MTN, Blankson H, Samari HR, Holden L, Seglen PO. Naringin-sensitive phosphorylation of plectin, a cytoskeletal cross-linking protein, in isolated rat hepatocytes. J Biol Chem 2002; 277:34826-35. [PMID: 12095991 DOI: 10.1074/jbc.m205028200] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
To identify phosphoproteins that might play a role in naringin-sensitive hepatocellular cytoskeletal disruption and apoptosis induced by algal toxins, hepatocyte extracts were separated by gel electrophoresis and immunostained with a phosphothreonine-directed antibody. Use of dilute (5%) polyacrylamide gels containing 6 m urea allowed the resolution of one very large (approximately 500-kDa) okadaic acid- and naringin-sensitive phosphoprotein, identified by tryptic fingerprinting, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and immunostaining as the cytolinker protein, plectin. The naringin-sensitive phosphorylation induced by okadaic acid and microcystin-LR probably reflected inhibition of a type 2A protein phosphatase, whereas the naringin-resistant phosphorylation induced by calyculin A, tautomycin, and cantharidin probably involved a type 1 phosphatase. Okadaic acid caused a collapse of the plectin-immunostaining bile canalicular sheaths and the general cytoskeletal plectin network into numerous medium-sized plectin aggregates. Inhibitors of protein kinase C, cAMP-dependent protein kinase, or Ca(2+)/calmodulin-dependent kinase II had moderate or no protective effects on plectin network disruption, whereas naringin offered 86% protection. Okadaic acid induced a naringin-sensitive phosphorylation of AMP-activated protein kinase (AMPK), the stress-activated protein kinases SEK1 and JNK, and S6 kinase. The AMPK-activating kinase (AMPKK) is likely to be the target of inhibition by naringin, the other kinases serving as downstream components of an AMPKK-initiated signaling pathway.
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Affiliation(s)
- Ann-Kristin Ruud Larsen
- Proteomics and Mammalian Cell Biology Section, Department of Cell Biology, Institute for Cancer Research, The Norwegian Radium Hospital, Montebello, 0310 Oslo, Norway
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Xiao L, Cui X, Madison V, White RE, Cheng KC. Insights from a three-dimensional model into ligand binding to constitutive active receptor. Drug Metab Dispos 2002; 30:951-6. [PMID: 12167558 DOI: 10.1124/dmd.30.9.951] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Two orphan nuclear receptors, constitutive active (or androstane) receptor (CAR) and pregnane X receptor (PXR), are among the most important mediators of ligand-activated transcriptional induction of liver microsomal cytochrome P450 drug-metabolizing enzymes. CAR and PXR belong to the same NR1I receptor subfamily and show high sequence homology to each other. The vitamin D receptor (VDR) also belongs to the NR1I subfamily and has the second highest homology to CAR in the ligand binding domain. A 3D model of the ligand binding domain of human CAR (hCAR) was constructed based on the available X-ray structures of human PXR (hPXR) and VDR (hVDR). The model shows that the size of the ligand binding cavities of hCAR and hPXR are similar, but larger than that of hVDR. hPXR's capability of binding to extremely large ligands, such as rifampicin, implies that its binding cavity may be able to expand further through the flexibility of a surface loop. In contrast, hCAR does not have this loop so that its cavity cannot expand, suggesting that hCAR would not bind to the largest hPXR ligands. Docking calculations of selected ligands to hCAR, based on the structural model, are consistent with previously reported receptor binding data. The results from this study indicate that structural modeling will be a useful tool for understanding ligand binding to hCAR and for design of drugs free of hCAR-mediated enzyme induction.
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Affiliation(s)
- Li Xiao
- Department of Structural Chemistry, Schering-Plough Research Institute, 2015 Galloping Hill Road, Kenilworth, New Jersey 07033, USA.
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Goodwin B, Hodgson E, D'Costa DJ, Robertson GR, Liddle C. Transcriptional regulation of the human CYP3A4 gene by the constitutive androstane receptor. Mol Pharmacol 2002; 62:359-65. [PMID: 12130689 DOI: 10.1124/mol.62.2.359] [Citation(s) in RCA: 190] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Cytochrome P450 3A4 (CYP3A4), the predominant P450 expressed in adult human liver, is both constitutively expressed and transcriptionally activated by a variety of structurally diverse xenochemicals. In this study, we examined the role of the constitutive androstane receptor (CAR), a member of the steroid/retinoid/thyroid hormone receptor superfamily, in the transcriptional regulation of CYP3A4. Herein, we demonstrate that CAR is capable of trans-activating expression of the CYP3A4 gene, both in vitro and in vivo. Induction of CYP3A4 is dependent on cooperativity between elements within the promoter proximal region of the gene and the distal xenobiotic-responsive enhancer module. CAR responsiveness was shown to be primarily mediated by two high-affinity binding motifs located within the CYP3A4 gene 5'-flanking region, approximately 7720 and 150 bases upstream of the transcription initiation site. Importantly, the human CAR response elements also mediate trans-activation of CYP3A4 by the human pregnane X receptor, suggesting that interplay between these receptors is likely to be an important determinant of CYP3A4 expression.
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Affiliation(s)
- Bryan Goodwin
- Department of Clinical Pharmacology and Storr Liver Unit, University of Sydney, Westmead Millennium Institute, Westmead, New South Wales, Australia
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Mäkinen J, Frank C, Jyrkkärinne J, Gynther J, Carlberg C, Honkakoski P. Modulation of mouse and human phenobarbital-responsive enhancer module by nuclear receptors. Mol Pharmacol 2002; 62:366-78. [PMID: 12130690 DOI: 10.1124/mol.62.2.366] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The constitutive androstane receptor (CAR) regulates mouse and human CYP2B genes through binding to the direct repeat-4 (DR4) motifs present in the phenobarbital-responsive enhancer module (PBREM). The preference of PBREM elements for nuclear receptors and the extent of cross-talk between CAR and other nuclear receptors are currently unknown. Our transient transfection and DNA binding experiments indicate that binding to DR4 motifs does not correlate with the activation response and that mouse and human PBREM are efficiently 'insulated' from the effects of other nuclear receptors despite their substantial affinity for DR4 motifs. Certain nuclear receptors that do not bind to DR4 motifs, such as peroxisome proliferator-activated receptor-alpha and farnesoid X receptor, can suppress PBREM function via a coactivator-dependent process that may have relevance in vivo. In competition experiments, mouse PBREM is clearly more selective for CAR than human PBREM. Pregnane X, vitamin D, and thyroid hormone receptors can potentially compete with human CAR on human PBREM. In contrast to the selective nature of PBREM, CYP3A enhancers are highly and comparably responsive to CAR, pregnane X receptor, and vitamin D receptor. In addition, the ligand specificities of human and mouse CAR were defined by mammalian cotransfection and yeast two-hybrid techniques. Our results provide new mechanistic explanations to several previously unresolved aspects of CYP2B and CYP3A gene regulation.
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Affiliation(s)
- Janne Mäkinen
- Department of Pharmaceutics, University of Kuopio, Kuopio, Finland
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Kawano K, Qin S, Vieu C, Collet X, Jiang XC. Role of hepatic lipase and scavenger receptor BI in clearing phospholipid/free cholesterol-rich lipoproteins in PLTP-deficient mice. BIOCHIMICA ET BIOPHYSICA ACTA 2002; 1583:133-40. [PMID: 12117557 DOI: 10.1016/s1388-1981(02)00193-2] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Phospholipid transfer protein knock-out (PLTP0) mice have defective transfer of phospholipids (PL) from triglyceride-rich lipoproteins (TRL) into high-density lipoproteins (HDL). In this study, we examined the role of diet, hepatic lipase (HL) and scavenger receptor BI (SRBI) in determining the accumulation of excess PL and free cholesterol (FC, "surface remnants") in plasma of PLTP0 mice. PL and FC accumulated in the very low-density lipoprotein (VLDL)-LDL region of PLTP0 mice on a highly saturated, coconut oil-based diet, but not on chow or milk-fat based Western diets. Accumulation of PL and FC was dramatically increased in PLTP0/HL0 mice, compared to PLTP0 mice, but only on the coconut oil diet. Turnover studies indicated that the coconut oil diet was associated with delayed catabolism of PL of PL/FC-rich particles. Incubation of these particles with primary hepatocytes in the presence of SRBI neutralizing antibody indicated that SRBI was primarily responsible for removal of FC and PL on the Western diet. In hepatocytes of coconut oil-fed mice, removal of FC and PL from these particles by SRBI was markedly reduced, even though SRBI protein expression levels were unchanged. These studies indicate that HL and SRBI both have major role in the clearance of PL and FC of surface remnants in PLTP0 mice. SRBI appears to be dysfunctional in coconut oil diet-fed animals, possibly related to changes in hepatocyte membrane fatty acid composition.
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Affiliation(s)
- Koichi Kawano
- Department of Anatomy and Cell Biology, SUNY Downstate Medical Center, Brooklyn, NY 11203, USA
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50
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Cable EE, Kuhn BR, Isom HC. Effects of modulators of protein phosphorylation on heme metabolism in human hepatic cells: induction of delta-aminolevulinic synthase mRNA and protein by okadaic acid. DNA Cell Biol 2002; 21:323-32. [PMID: 12042071 DOI: 10.1089/104454902753759735] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Effects of modulators of protein phosphorylation on delta-aminolevulinic acid (ALA) synthase and heme oxygenase-1 mRNA were analyzed in the human hepatic cell lines Huh-7 and HepG2 using a quantitative RNase protection assay. Okadaic acid was found to induce ALA synthase mRNA in a concentration-dependent fashion in both Huh-7 and HepG2 cells. The EC(50) for induction of ALA synthase mRNA in Huh-7 cells was 13.5 nM, with maximum increases occurring at okadaic acid concentrations of 25-50 nM. The EC(50) for induction of ALA synthase mRNA in HepG2 cells was 35.5 nM, with maximum increases occurring at okadaic acid concentrations of 50 nM. Concentration-dependent induction of ALA synthase mRNA paralleled the increase in ALA synthase protein. Maximum induction of ALA synthase was observed between 5 and 10 h post-treatment in both cell lines. Induction of ALA synthase mRNA in Huh-7 cells, but not HepG2 cells, was associated with an increase in ALA synthase mRNA stability. Okadaic acid also induced heme oxygenase-1 mRNA in both cell lines, but the magnitude of induction was only twofold, and was rapid and transient. Okadaic acid and phorbol 12-myristate 13-acetate significantly decreased heme-mediated induction of heme oxygenase-1 mRNA in both Huh-7 and HepG2 cells. Wortmannin diminished the heme-mediated induction of heme oxygenase-1 mRNA in HepG2 cells, but not Huh-7 cells. These results report a novel property of okadaic acid to affect heme metabolism in human cell lines.
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Affiliation(s)
- Edward E Cable
- Department of Microbiology and Immunology, Penn State College of Medicine, Hershey, Pennsylvania 17033, USA
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