title: AH receptor antagonist inhibits constitutive CYP1A1 and CYP1B1 expression in rat BP8 cells.
abstract: The BP8 variant of the 5L rat hepatoma cell line is completely devoid of aryl hydrocarbon receptor (AHR) and is a useful model to examine AHR function. Previous studies showed that BP8 cells, when transfected with mouse AHR, exhibit induction of a plasmid-based reporter even in the absence of exogenous ligands. We transfected BP8 cells with full-length human AHR and found that presence of the AHR alone was sufficient to induce substantial CYP1A1 and CYP1B1 mRNA without any exogenous AHR ligand. An AHR antagonist, 3,4-dimethoxyflavone, inhibited CYP1A1 and CYP1B1 expression in a dose-dependent manner. When we transfected BP8 cells with a mutated human AHR that is defective in ligand binding, expression of CYP1A1 and CYP1B1 was diminished but not abolished. Inhibition by the AHR antagonist along with the diminished response to the mutated AHR indicates that BP8 cells contain some agent that acts as an agonist ligand for the AHR.
authors.affiliation: Developmental Biology Program, The Hospital for Sick Children, Toronto, Ont, Canada.
authors.forename: Steven
authors.initials: S
authors.lastname: Roblin
authors.forename: Allan B
authors.initials: AB
authors.lastname: Okey
authors.forename: Patricia A
authors.initials: PA
authors.lastname: Harper
mesh_terms: D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases / Q000037:antagonists & inhibitors* / Q000096:biosynthesis; D045744:Cell Line, Tumor; D019363:Cytochrome P-450 CYP1A1 / Q000037:antagonists & inhibitors* / Q000096:biosynthesis; D065633:Cytochrome P-450 CYP1B1; D004305:Dose-Response Relationship, Drug; D004790:Enzyme Induction / Q000187:drug effects; D005419:Flavonoids / Q000737:chemistry / Q000494:pharmacology; D006801:Humans; D008114:Liver Neoplasms, Experimental / Q000201:enzymology; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D018336:Receptors, Aryl Hydrocarbon / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D014162:Transfection
chemical_list: D005419:Flavonoids; D012333:RNA, Messenger; D018336:Receptors, Aryl Hydrocarbon; D011994:Recombinant Proteins; D001189:Aryl Hydrocarbon Hydroxylases; C585496:CYP1B1 protein, human; C585498:Cyp1b1 protein, mouse; C585499:Cyp1b1 protein, rat; D019363:Cytochrome P-450 CYP1A1; D065633:Cytochrome P-450 CYP1B1