title: Downregulation of aryl hydrocarbon receptor function and cytochrome P450 1A1 induction by expression of Ha-ras oncogenes.
abstract: The immortalized human epithelial cell line MCF10A has the phenotypic characteristics of normal breast cells. Exposure of MCF10A cultures to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) stimulated the transcriptional activation of cytochrome P450 1A1 (CYP1A1), and CYP1B1, and NAD(P)H:quinone oxidoreductase. Northern blot hybridization and nuclear run-on assays demonstrated that transcriptional activation of these genes was suppressed in stably transfected cultures expressing an Ha-ras oncogene (the MCF10A-NeoT line). Similar suppression did not occur in stably transfected lines carrying the expression vector or a normal c-Ha-ras protooncogene. Western blot analyses and immunofluorescence microscopy demonstrated that the lack of inducibility in MDF10A-NeoT cells reflected neither reductions in aryl hydrocarbon receptor (AHR) and aryl hydrocarbon nuclear translocator protein nor prevention of TCDD-induced AHR translocation to the nucleus. Suppression did correlate with reductions in DNA-AHR complex formation, as analyzed by gel retardation assays of soluble cell extracts treated in vitro with TCDD. The induction of Cyp1a-1 by TCDD was also analyzed in transgenic mice that expressed a v-Ha-ras oncogene exclusively in their keratinocytes. Relative to littermates lacking the transgene, the induction of Cyp1a-1 by TCDD was partially suppressed (about 50%) in the epidermises of v-Ha-ras-positive transgenic mice. However, normal levels of Cyp1a-1 induction occurred in the livers of the same mice. induction of Cyp1a-1 by TCDD was also suppressed (more than 98%) in chemically induced skin papillomas having Ha-ras mutations, relative to uninvolved surrounding skin. These studies suggest that the p21-ras protein controls signal transduction pathways capable of modulating AHR function.
authors.affiliation: Institute of Chemical Toxicology, Wayne State University, Detroit, Michigan 48201, USA.
authors.forename: J J
authors.initials: JJ
authors.lastname: Reiners
authors.forename: C L
authors.initials: CL
authors.lastname: Jones
authors.forename: N
authors.initials: N
authors.lastname: Hong
authors.forename: R E
authors.initials: RE
authors.lastname: Clift
authors.forename: C
authors.initials: C
authors.lastname: Elferink
mesh_terms: D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D015153:Blotting, Western; D001940:Breast / Q000378:metabolism; D002460:Cell Line; D019363:Cytochrome P-450 CYP1A1 / Q000378:metabolism*; D065633:Cytochrome P-450 CYP1B1; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D015536:Down-Regulation; D011905:Genes, ras; D006801:Humans; D015603:Keratinocytes / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D000072317:Polychlorinated Dibenzodioxins / Q000494:pharmacology; D011808:Quinone Reductases / Q000378:metabolism; D018336:Receptors, Aryl Hydrocarbon / Q000378:metabolism*; D012878:Skin Neoplasms / Q000201:enzymology; D014162:Transfection
chemical_list: D000072317:Polychlorinated Dibenzodioxins; D018336:Receptors, Aryl Hydrocarbon; D003577:Cytochrome P-450 Enzyme System; D001189:Aryl Hydrocarbon Hydroxylases; C585496:CYP1B1 protein, human; C585498:Cyp1b1 protein, mouse; D019363:Cytochrome P-450 CYP1A1; D065633:Cytochrome P-450 CYP1B1; C041831:NADH dehydrogenase (quinone); D011808:Quinone Reductases