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Downregulation of aryl hydrocarbon receptor function and cytochrome P450 1A1 induction by expression of ha‐ ras oncogenes
Author(s) -
Reiners John J.,
Jones Carol L.,
Hong Nancy,
Clift Russell E.,
Elferink Cornelius
Publication year - 1997
Publication title -
molecular carcinogenesis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.254
H-Index - 97
eISSN - 1098-2744
pISSN - 0899-1987
DOI - 10.1002/(sici)1098-2744(199707)19:2<91::aid-mc4>3.0.co;2-o
Subject(s) - aryl hydrocarbon receptor , biology , microbiology and biotechnology , aryl hydrocarbon receptor nuclear translocator , oncogene , transfection , transgene , cell culture , western blot , northern blot , cytochrome p450 , gene expression , apoptosis , gene , cell cycle , biochemistry , transcription factor , enzyme , genetics
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 proto‐oncogene. 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 tansduction pathways capable of modulating AHR function. Mol. Carcinog. 19:91–100, 1997. © 1997 Wiley‐Liss, Inc.