title: Lack of CYP1A1 expression is involved in unresponsiveness of the human hepatoma cell line SK-HEP-1 to dioxin.
abstract: The aryl hydrocarbon receptor (AhR) mediates a wide variety of toxic effects due to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The human hepatoma cell line SK-HEP-1 expresses AhR and ARNT. However, TCDD failed to induce CYP1A1 and XRE-dependent reporter genes in these cells. Although CYP1A1 was not induced by TCDD exposure, both CYP1B1 and AhR repressor (AhRR) were constitutively expressed. The AhR antagonist alpha-naphthoflavone altered the basal level of XRE-dependent reporter gene expression dose-dependently. As our results suggested the activation of AhR signals by putative endogenous ligands, we established SK-HEP-1-derived cell lines that stably expressed CYP1A1. The inducibility of XRE-dependent reporter genes and CYP1B1 by TCDD was restored in these cells. Our findings demonstrated the presence of endogenous ligands in SK-HEP-1 cells due to the absence of the metabolizing enzyme CYP1A1, but not CYP1B1, which allowed the constitutive expression of AhR target genes.
authors.affiliation: Environmental Health Sciences Division, National Institute for Environmental Studies, Tsukuba 305-8506, Japan.
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Shiizaki
authors.forename: Seiichiroh
authors.initials: S
authors.lastname: Ohsako
authors.forename: Toshie
authors.initials: T
authors.lastname: Koyama
authors.forename: Ryoichi
authors.initials: R
authors.lastname: Nagata
authors.forename: Junzo
authors.initials: J
authors.lastname: Yonemoto
authors.forename: Chiharu
authors.initials: C
authors.lastname: Tohyama
mesh_terms: D001189:Aryl Hydrocarbon Hydroxylases / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D051784:Aryl Hydrocarbon Receptor Nuclear Translocator / Q000378:metabolism; D001571:Benzoflavones / Q000494:pharmacology; D006528:Carcinoma, Hepatocellular; D045744:Cell Line, Tumor; D019363:Cytochrome P-450 CYP1A1 / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000172:deficiency* / Q000235:genetics; D065633:Cytochrome P-450 CYP1B1; D004147:Dioxins / Q000378:metabolism / Q000633:toxicity*; D004611:Ellipticines / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D008099:Liver / Q000187:drug effects* / Q000201:enzymology* / Q000378:metabolism; D010957:Plasmids; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D018336:Receptors, Aryl Hydrocarbon / Q000819:agonists / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014162:Transfection
chemical_list: D001571:Benzoflavones; D004147:Dioxins; D004611:Ellipticines; D004791:Enzyme Inhibitors; D012333:RNA, Messenger; D018336:Receptors, Aryl Hydrocarbon; C034192:ellipticine; D051784:Aryl Hydrocarbon Receptor Nuclear Translocator; C011512:alpha-naphthoflavone; D001189:Aryl Hydrocarbon Hydroxylases; C585496:CYP1B1 protein, human; D019363:Cytochrome P-450 CYP1A1; D065633:Cytochrome P-450 CYP1B1