Nuclear Receptor CAR Requires Early Growth Response 1 to Activate the Human Cytochrome P450 2B6 Gene

Inoue, Kaoru; Negishi, Masahiko

doi:10.1074/jbc.m800729200

Cited by 34 publications

(35 citation statements)

References 30 publications

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“…The mechanism of nuclear translocation of CAR uses various cell-signaling molecules, such as protein phosphatase 2A and extracellular signal-regulated kinase 1/2 (Yoshinari et al, 2003;Koike et al, 2007). In addition to what is observed in the cytoplasm, early growth response 1 promotes CAR to transactivate the CYP2B6 gene in HepG2 cells as effectively as that in primary hepatocytes and livers (Swales et al, 2005;Inoue and Negishi, 2008). Thus, CAR-mediated transactivation of its target genes appears to be coregulated by CAR activators and cell-signaling molecules.…”

Section: Introductionmentioning

confidence: 99%

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p38 Mitogen–Activated Protein Kinase Regulates Nuclear Receptor CAR that Activates the CYP2B6 Gene

2013

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The constitutive active/androstane receptor (CAR) regulates hepatic drug metabolism by activating genes, such as cytochrome P450, and certain transferases. p38 Mitogen-activated protein kinase (MAPK) is highly activated in human primary hepatocytes but barely in human hepatoma cell lines including HepG2 cells. Liganded-CAR induced CYP2B6 mRNA in human primary hepatocytes far more effectively than in HepG2 cells ectopically expressing CAR. In the present study, we found that activation of p38 MAPK by anisomycin potentiated induction of CYP2B6 mRNA by CAR ligand in HepG2 cells to levels observed in ligandtreated human primary hepatocytes. siRNA knockdown of p38 MAPK abrogated the ability of anisomycin to synergistically induce CYP2B6 mRNA. In addition to CYP2B6, anisomycin cotreatment potentiated an increase in CYP2A7 and CYP2C9 mRNAs but not CYP3A4 or UDP-glucuronosyltransferase 1A1 mRNAs. Thus, activated p38 MAPK is required for liganded-CAR to selectively activate a set of genes that encode drug-metabolizing enzymes. Our present results suggest that CAR-mediated induction of these enzymes cannot be understood by ligand binding alone because the specificity and magnitude of induction are codetermined by a given cell signaling, such as p38 MAPK; both physiologic and pathophysiological states of cell signaling may have a strong impact in hepatic drug-metabolizing capability during treatments.

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Section: Introductionmentioning

confidence: 99%

“…Hepatocyte and cell extracts were prepared by lysis of cells with 1 Â LDS buffer (Life Technologies) with 1% beta-mercaptoethanol. Protein separation and detection were performed as described previously (Inoue and Negishi, 2008).…”

Section: Introductionmentioning

confidence: 99%

p38 Mitogen–Activated Protein Kinase Regulates Nuclear Receptor CAR that Activates the CYP2B6 Gene

2013

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“…15 Finally, this would be in line with the finding that cotreatment with the CAR agonist TCPOBOP and PMA had an additive effect on activation of the human CYP2B6 gene in vitro. 50 The presence of putative PKC phosphorylation sites on the Rfc1 protein 11 suggested that downregulation of Rfc1-dependent MTX uptake may be due to carrier phosphorylation associated with a modified substrate affinity. However, our results indicate Resistance to MTX chemotherapy by antiepileptic drugs S Halwachs et al that cPKC activation by PB-dependent induction of the CAR signaling pathway does not result in elevated Rfc1 phosphorylation levels.…”

Section: Discussionmentioning

confidence: 99%

Antiepileptic drugs reduce efficacy of methotrexate chemotherapy by downregulation of Reduced folate carrier transport activity

et al. 2009

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Concurrent treatment with methotrexate (MTX) and antiepileptic drugs, such as phenobarbital (PB), reduces the efficacy of MTX chemotherapy in childhood acute lymphoblastic leukemia (ALL). This can result from defective Reduced folate carrier (Rfc1)-dependent cellular uptake of MTX. Indeed, we have shown that functional Rfc1 activity is significantly reduced by clinically relevant concentrations of the anticonvulsant drugs PB or carbamazepine in an adequate in vitro model. As PB is known to regulate carrier-associated transport by the nuclear receptor constitutive androstane receptor (CAR), we investigated the involvement of the CAR signaling cascade and the mode of PB-induced downregulation of Rfc1 activity. CAR activation by PB or the CAR agonist 1,4-bis[2-(3,5-dichloropyridyloxy)]-benzene resulted in translocation of Ca 2 þ -dependent protein kinase Ca (cPKCa) to the plasma membrane related to significantly elevated PKC activities. In contrast, subcellular localization of Ca 2 þ -independent PKCd was only marginally altered. Studies on intracellular distribution of the Rfc1 protein indicated that PB-induced activation of cPKCa was associated with carrier internalization from the plasma membrane into the cytosol independent of the Rfc1 phosphorylation status. In conclusion, we identified for the first time the molecular mechanism of this clinically relevant drug resistance in patients with ALL concurrently receiving MTX chemotherapy and antiepileptic drugs.

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“…Other studies have also demonstrated that the cross-talk of HNF4␣ with CAR or PXR is critical for the appropriate drug-mediated induction of major human CYP genes, such as CYP3A4 or CYP2C9 (49 -52). More recently, the important role of the proximal HNF4␣ response element in the cooperation between EGR1 and CAR for CYP2B6 induction has also been demonstrated (25). All of A, total RNA from six liver donors showing high (n ϭ 3) and low (n ϭ 3) CYP2B6 expression was purified, and the mRNA levels of CYP2B6, C/EBP␣, HNF4␣, and CAR were determined by real-time quantitative RT-PCR analysis.…”

Section: Discussionmentioning

confidence: 99%

“…Deletion assays delineate the OA-responsive activity to a proximal 50 bp (Ϫ217 to Ϫ268 bp) sequence in the CYP2B6 promoter (24,25). In this OA-responsive module, EGR1 (early growth response 1) and HNF4␣ (hepatocyte nuclear factor 4␣) bind and determine the CAR-mediated induction of the human CYP2B6 gene.…”

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CCAAT/Enhancer-binding Protein α (C/EBPα) and Hepatocyte Nuclear Factor 4α (HNF4α) Synergistically Cooperate with Constitutive Androstane Receptor to Transactivate the Human Cytochrome P450 2B6 (CYP2B6) Gene

Benet

Lahoz

Guzmán

et al. 2010

Journal of Biological Chemistry

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The transcription of tissue-specific and inducible genes is usually subject to the dynamic control of multiple activators. Dedifferentiated hepatic cell lines lose the expression of tissue-specific activators and many characteristic hepatic genes, such as drug-metabolizing cytochrome P450. Here we demonstrate that by combining adenoviral vectors for CCAAT/ enhancer-binding protein ␣ (C/EBP␣), hepatocyte nuclear factor 4␣ (HNF4␣), and constitutive androstane receptor, the CYP2B6 expression and inducibility by CITCO are restored in human hepatoma HepG2 cells at levels similar to those in cultured human hepatocytes. Moreover, several other phase I and II genes are simultaneously activated, which suggests that this is an effective approach to endow dedifferentiated human hepatoma cells with a particular metabolic competence and response to inducers. In order to gain insight into the molecular mechanism, we examined the cooperation of these three transcription factors on the CYP2B6 5-flanking region. We show new CYP2B6-responsive sequences for C/EBP␣ and HNF4␣ and a novel synergistic regulatory mechanism whereby C/EBP␣, HNF4␣, and constitutive androstane receptor bind and cooperate through proximal and distal response elements to confer a maximal level of expression. The results obtained from human liver also suggest that important differences in the expression and binding of C/EBP␣ and HNF4␣ could account for the large interindividual variability of the hepatic CYP2B6 enzyme, which metabolizes commonly used drugs.Cytochromes P450 (CYPs) 3 are involved in the oxidative metabolism of drugs, carcinogens, and environmental pollutants to more polar metabolites, thereby facilitating their excretion and preventing these potentially harmful compounds from accumulating. In addition, many CYPs participate in the metabolism and conversion of a diverse range of endogenous compounds, including steroid hormones, bile acids, fatty acids, and prostaglandins (1, 2).CYP2B6 accounts for 2-10% of the total CYP content in the human liver, where it plays an important role in the metabolism of an increasing number of clinically important drugs (3). These include anti-neoplastics like cyclophosphamide, ifosfamide, and tamoxifen (4, 5); the anti-malarial artemisinin (6); the antiretrovirals nevirapine (7) and efavirenz (8); anesthetics like propofol (9) and ketamine (10); the anti-Parkinsonian selegiline (11); the anti-epileptic mephobarbital (12); and the anti-depressant bupropion, which is now the most commonly used probe drug for CYP2B6 (13). Moreover, CYP2B6 plays a key role in the metabolism of many environmental pollutants, which can serve as substrates, inhibitors, and/or inducers of CYP2B6 and can cause metabolic interactions between environmental chemicals and clinical drugs (14).A 20 -250-fold interindividual variation in CYP2B6 expression has been demonstrated, which is presumably due to polymorphisms and the induction of transcription by xenobiotics. These interindividual differences may result in variable systemic exposure to...

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Nuclear Receptor CAR Requires Early Growth Response 1 to Activate the Human Cytochrome P450 2B6 Gene

Cited by 34 publications

References 30 publications

p38 Mitogen–Activated Protein Kinase Regulates Nuclear Receptor CAR that Activates the CYP2B6 Gene

p38 Mitogen–Activated Protein Kinase Regulates Nuclear Receptor CAR that Activates the CYP2B6 Gene

Antiepileptic drugs reduce efficacy of methotrexate chemotherapy by downregulation of Reduced folate carrier transport activity

CCAAT/Enhancer-binding Protein α (C/EBPα) and Hepatocyte Nuclear Factor 4α (HNF4α) Synergistically Cooperate with Constitutive Androstane Receptor to Transactivate the Human Cytochrome P450 2B6 (CYP2B6) Gene

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