title: Okadaic acid potentiates 3-methylcholanthrene-induced CYP2A8 gene expression in primary cultures of Syrian hamster hepatocytes: possible involvement of activator protein-1.
abstract: In Syrian hamster liver, treatment with 3-methylcholanthrene (3-MC) markedly induces an isozyme of cytochrome P450 (CYP), CYP2A8. To elucidate the mechanism of this induction, we studied the effect of okadaic acid (OA), an inhibitor of serine threonine protein phosphatases 1 and 2A, on 3-MC-induced CYP2A8 expression in primary cultures of Syrian hamster hepatocytes. The addition of OA to the cultured hepatocytes at a concentration of 1 nM potentiated 3-MC- (0.1 and 1 microM) induced expression of mRNA and protein of CYP2A8 and its associated coumarin 7-hydroxylase activity. In addition, OA not only induced c-fos and jun-D mRNA, components of transcription factor activator protein-1 (AP-1), with an increase in AP-1 binding activity in the nucleus, but also activated AP-1-dependent gene transcription in the hepatocytes. The dose-dependent effect of OA on 3-MC-induced CYP2A8 expression corresponded to that of OA on c-fos and jun-D mRNA induction and on the activation of AP-1-dependent gene transcription. The expression of c-fos and jun-D mRNA induced by OA preceded the expression of CYP2A8 mRNA potentiated by co-treatment with 3-MC and OA. Treatment with anisomycin and cycloheximide also potentiated 0.1 microM 3-MC-induced coumarin 7-hydroxylase activity, induced c-fos and jun-D mRNA expression, and activated AP-1-dependent gene transcription in the hepatocytes. Furthermore, 3-MC-induced CYP2A8 expression was potentiated in the hepatocytes transfected with c-Jun expression plasmid. These results suggest that AP-1, inducible by serine threonine protein kinase, may be one of the components of the signal transduction system from 3-MC to CYP2A8 gene expression.
authors.affiliation: Department of Pharmaceutical Sciences, National Institute of Public Health, Tokyo, Japan. mtohkin@iph.go.jp
authors.forename: M
authors.initials: M
authors.lastname: Tohkin
authors.forename: K
authors.initials: K
authors.lastname: Kurose
authors.forename: M
authors.initials: M
authors.lastname: Fukuhara
mesh_terms: D000818:Animals; D000841:Anisomycin / Q000494:pharmacology; D001189:Aryl Hydrocarbon Hydroxylases; D001483:Base Sequence; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D016384:Consensus Sequence; D006224:Cricetinae; D003513:Cycloheximide / Q000494:pharmacology; D065637:Cytochrome P-450 CYP2A6; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis*; D000072467:Cytochrome P450 Family 2; D003907:Dexamethasone / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004790:Enzyme Induction / Q000187:drug effects*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005260:Female; D016762:Genes, fos; D016758:Genes, jun; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008647:Mesocricetus; D008748:Methylcholanthrene / Q000494:pharmacology*; D006899:Mixed Function Oxygenases / Q000096:biosynthesis*; D008969:Molecular Sequence Data; D019319:Okadaic Acid / Q000494:pharmacology*; D009838:Oligodeoxyribonucleotides; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors; D016760:Proto-Oncogene Proteins c-fos / Q000096:biosynthesis; D016755:Proto-Oncogene Proteins c-jun / Q000096:biosynthesis; D012333:RNA, Messenger / Q000096:biosynthesis; D018808:Transcription Factor AP-1 / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects
chemical_list: D004791:Enzyme Inhibitors; D009838:Oligodeoxyribonucleotides; D016760:Proto-Oncogene Proteins c-fos; D016755:Proto-Oncogene Proteins c-jun; D012333:RNA, Messenger; D018808:Transcription Factor AP-1; D005576:Colforsin; D019319:Okadaic Acid; D008748:Methylcholanthrene; D000841:Anisomycin; D003907:Dexamethasone; D003577:Cytochrome P-450 Enzyme System; D003513:Cycloheximide; D006899:Mixed Function Oxygenases; D001189:Aryl Hydrocarbon Hydroxylases; C101150:CYP2A8 protein, Mesocricetus auratus; D065637:Cytochrome P-450 CYP2A6; D000072467:Cytochrome P450 Family 2; D010749:Phosphoprotein Phosphatases