Dioxin increases the interaction between aryl hydrocarbon receptor and estrogen receptor alpha at human promoters

Abstract

Recent studies have shown that activated aryl hydrocarbon receptor (AHR) induced the recruitment of estrogen receptor-α (ERα) to AHR-regulated genes and that AHR is recruited to ERα-regulated genes. However, these findings were limited to a small number of well-characterized AHR- or ERα-responsive genes with little knowledge of what was occurring at other genomic regions. In this study, we showed using chromatin immunoprecipitation followed by hybridization to promoter focused microarrays (ChIP-chip) that 2,3,7,8-tetrachlorodibenzo-p-dioxin treatment significantly increased the overlap of genomic regions bound by both AHR and ERα. Conventional and sequential ChIPs confirmed the recruitment of AHR and ERα to many of the identified regions. Transcription factor binding site analysis revealed an overrepresentation of aryl hydrocarbon receptor response elements in regions bound by both AHR and ERα, suggesting that AHR was the important factor determining the recruitment of ERα to these regions. RNA interference-mediated knockdown of AHR confirmed its requirement for the recruitment of ERα to some, but not all, of the shared regions. Our findings demonstrate not only that dioxin induces the recruitment of ERα to AHR target genes but also that AHR is recruited to estrogen-responsive regions in a gene-specific manner, suggesting that AHR utilizes both of these mechanisms to modulate estrogen-dependent signaling. © The Author 2009. Published by Oxford University Press on behalf of the Society of Toxicology. All rights reserved.