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.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Aryl Hydrocarbon Hydroxylases / antagonists & inhibitors
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Aryl Hydrocarbon Hydroxylases / biosynthesis
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Aryl Hydrocarbon Hydroxylases / genetics
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Aryl Hydrocarbon Hydroxylases / metabolism
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Aryl Hydrocarbon Receptor Nuclear Translocator / metabolism
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Benzoflavones / pharmacology
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Carcinoma, Hepatocellular
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Cell Line, Tumor
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Cytochrome P-450 CYP1A1 / antagonists & inhibitors
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Cytochrome P-450 CYP1A1 / biosynthesis
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Cytochrome P-450 CYP1A1 / deficiency*
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Cytochrome P-450 CYP1A1 / genetics
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Cytochrome P-450 CYP1B1
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Dioxins / metabolism
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Dioxins / toxicity*
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Ellipticines / pharmacology
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Enzyme Inhibitors / pharmacology
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Gene Expression / drug effects
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Humans
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Liver / drug effects*
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Liver / enzymology*
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Liver / metabolism
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Plasmids
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RNA, Messenger / biosynthesis
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RNA, Messenger / genetics
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Receptors, Aryl Hydrocarbon / agonists
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Receptors, Aryl Hydrocarbon / antagonists & inhibitors
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Receptors, Aryl Hydrocarbon / genetics
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Receptors, Aryl Hydrocarbon / metabolism
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Reverse Transcriptase Polymerase Chain Reaction
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Transfection
Substances
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Benzoflavones
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Dioxins
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Ellipticines
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Enzyme Inhibitors
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RNA, Messenger
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Receptors, Aryl Hydrocarbon
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ellipticine
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Aryl Hydrocarbon Receptor Nuclear Translocator
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alpha-naphthoflavone
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Aryl Hydrocarbon Hydroxylases
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CYP1B1 protein, human
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Cytochrome P-450 CYP1A1
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Cytochrome P-450 CYP1B1