Abstract
Using chromatin immunoprecipitation assays, we studied the 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-mediated recruitment of the aryl hydrocarbon receptor (AhR) and several co-regulators to the CYP1A1 promoter. AhR displayed a time-dependent recruitment, reaching a peak at 75 min and maintaining promoter occupancy for the remainder of the time course. Recruitment of AhR was followed by TIF2/SRC2, which preceded CBP, histone H3 acetylation, and RNA polymerase II (RNAPII). Simultaneous recruitment to the enhancer and the TATA box region suggests the formation of a large multiprotein complex bridging the two promoter regions. Interestingly, estrogen receptor alpha (ERalpha) displayed a TCDD- and time-dependent recruitment to the CYP1A1 promoter, which was increased by co-treatment with estradiol. Transfection in HuH7 human liver cells confirmed previously reported ERalpha enhancement of AhR activity. In contrast, TCDD did not induce the recruitment of ERalpha to the estrogen-responsive pS2 promoter, and after 120 min of co-treatment with estradiol, ERalpha is still present on the CYP1A1 promoter but no longer at pS2. RNA interference studies with T47D cells support a role for ERalpha in TCDD-dependent CYP1A1 expression. Our data suggest that ERalpha acts as a coregulator of AhR-mediated transcriptional activation and that the recruitment of ERalpha by AhR represents a novel mechanism AhR-ERalpha cross talk.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Acetylation
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Adaptor Proteins, Signal Transducing / genetics
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Adaptor Proteins, Signal Transducing / metabolism
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Breast Neoplasms / pathology
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Cell Line, Tumor
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Chromatin Immunoprecipitation
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Cyclic AMP Response Element-Binding Protein / genetics
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Cyclic AMP Response Element-Binding Protein / metabolism
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Cytochrome P-450 CYP1A1 / genetics
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Estradiol / pharmacology
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Estrogen Receptor alpha / drug effects
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Estrogen Receptor alpha / genetics
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Estrogen Receptor alpha / metabolism*
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Female
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Genes, Reporter
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Hepatocytes / metabolism
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Histones / metabolism
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Humans
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Kinetics
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Ligands
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Luciferases / metabolism
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Models, Biological
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Nuclear Receptor Coactivator 2
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Polychlorinated Dibenzodioxins / pharmacology*
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Promoter Regions, Genetic*
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Proto-Oncogene Proteins pp60(c-src) / genetics
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Proto-Oncogene Proteins pp60(c-src) / metabolism
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RNA Interference
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Receptor Cross-Talk / drug effects
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Receptors, Aryl Hydrocarbon / drug effects
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Receptors, Aryl Hydrocarbon / genetics
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Receptors, Aryl Hydrocarbon / metabolism*
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Transcription Factors / genetics
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Transcription Factors / metabolism
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Transcription, Genetic*
Substances
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Adaptor Proteins, Signal Transducing
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Cyclic AMP Response Element-Binding Protein
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Estrogen Receptor alpha
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Histones
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Ligands
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NCOA2 protein, human
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Nuclear Receptor Coactivator 2
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Polychlorinated Dibenzodioxins
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Receptors, Aryl Hydrocarbon
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SLA2 protein, human
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Transcription Factors
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Estradiol
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Luciferases
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Cytochrome P-450 CYP1A1
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Proto-Oncogene Proteins pp60(c-src)