Roles of coactivator proteins in dioxin induction of CYP1A1 and CYP1B1 in human breast cancer cells.
Cytochrome P450 (CYP) 1A1 and CYP1B1 are inducible by 2,3,7,8-tetrachlorodibenzo-p-dioxin (dioxin) in the human breast cancer cell line, MCF-7. Since CYP1A1 was inducible to a much greater degree than CYP1B1, we hypothesized that there may be differences in coactivator recruitment to the promoter and/or enhancer regions of these genes. Dioxin treatment leads to recruitment of the aryl hydrocarbon receptor to the enhancer regions but not to the proximal promoter regions of both the CYP1A1 and CYP1B1 genes. On the other hand, dioxin treatment facilitated recruitment of RNA polymerase II to the promoters but not the enhancer regions. Dioxin treatment also elicited recruitment of the transcriptional coactivators, steroid receptor coactivator 1 (SRC-1) and steroid receptor coactivator 2 (SRC-2) and p300, which possess intrinsic histone acetyltranferase activities, to both genes, whereas Brahma (BRM)/Switch 2-related gene 1 (BRG-1), a subunit of nucleosomal remodeling factors, was recruited more robustly to CYP1A1 relative to CYP1B1. Small inhibitory RNA-mediated knockdown of p300 and SRC-2 adversely affected dioxin induction of both genes, whereas knockdown of BRM/BRG-1 reduced CYP1A1 induction but had little, if any, effect on CYP1B1 induction. These results suggest that nucleosomal remodeling is less significant for dioxin-mediated induction of CYP1B1 than that of CYP1A1 and may be related to the more modest inducibility of the former. Interestingly, simultaneous knockdown of SRC-2 and BRM/BRG-1 had no greater effect on CYP1A1 induction than knockdown of each coactivator individually, while simultaneous knockdown of p300 and BRM/BRG-1 had a much greater effect than knockdown of each individual gene, suggesting that the recruitment of SRC-2 to CYP1A1 depends upon BRM/BRG-1, while the recruitments of p300 and BRM/BRG-1 are independent of each other. These observations provide novel insights into the functional roles of the endogenous coactivators in dioxin induction of the human CYP1A1 and CYP1B1 genes in their natural chromosomal configurations.
Molecular Toxicology Program, Department of Pathology and Laboratory Medicine, University of California, Los Angeles, California 90095, USA.
Robert T
RT
Taylor
Feng
F
Wang
Erin L
EL
Hsu
Oliver
O
Hankinson
D001189:Aryl Hydrocarbon Hydroxylases; D001943:Breast Neoplasms / Q000378:metabolism; D045744:Cell Line, Tumor; D019363:Cytochrome P-450 CYP1A1 / Q000235:genetics / Q000378:metabolism*; D065633:Cytochrome P-450 CYP1B1; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism*; D004265:DNA Helicases / Q000378:metabolism; D004742:Enhancer Elements, Genetic / Q000187:drug effects; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D055785:Gene Knockdown Techniques; D051548:Histone Acetyltransferases / Q000378:metabolism; D006801:Humans; D009687:Nuclear Proteins / Q000378:metabolism; D056920:Nuclear Receptor Coactivator 1; D051958:Nuclear Receptor Coactivator 2 / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D000072317:Polychlorinated Dibenzodioxins / Q000494:pharmacology*; D011401:Promoter Regions, Genetic / Q000187:drug effects; D034741:RNA, Small Interfering / Q000378:metabolism; D018336:Receptors, Aryl Hydrocarbon / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism; D050880:p300-CBP Transcription Factors / Q000378:metabolism
D009687:Nuclear Proteins; D051958:Nuclear Receptor Coactivator 2; D000072317:Polychlorinated Dibenzodioxins; D034741:RNA, Small Interfering; D018336:Receptors, Aryl Hydrocarbon; C084011:SMARCA2 protein, human; D014157:Transcription Factors; D003577:Cytochrome P-450 Enzyme System; D001189:Aryl Hydrocarbon Hydroxylases; C585496:CYP1B1 protein, human; D019363:Cytochrome P-450 CYP1A1; D065633:Cytochrome P-450 CYP1B1; D051548:Histone Acetyltransferases; C538859:NCOA1 protein, human; D056920:Nuclear Receptor Coactivator 1; D050880:p300-CBP Transcription Factors; C084108:SMARCA4 protein, human; D004265:DNA Helicases