Genome-wide mapping of estrogen receptor-beta-binding regions reveals extensive cross-talk with transcription factor activator protein-1.

Estrogen signaling can occur through a nonclassical pathway involving the interaction of estrogen receptors (ER) with other transcription factors such as activator protein-1 (AP-1) and SP-1. However, there is little mechanistic understanding about this pathway, with conflicting results from in vitro investigations. In this study, we applied the ChIP-on-chip approach to identify ERbeta-binding sites on a genome-wide scale, identifying 1,457 high-confidence binding sites in ERbeta-overexpressing MCF7 breast cancer cells. Genes containing ERbeta-binding sites can be regulated by E2. Notably, approximately 60% of the genomic regions bound by ERbeta contained AP-1-like binding regions and estrogen response element-like sites, suggesting a functional association between AP-1 and ERbeta signaling. Chromatin immunoprecipitation (ChIP) analysis confirmed the association of AP-1, which is composed of the oncogenic transcription factors c-Fos and c-Jun, to ERbeta-bound DNA regions. Using a re-ChIP assay, we showed co-occupancy of ERbeta and AP-1 on chromatin. Short interfering RNA-mediated knockdown of c-Fos or c-Jun expression decreased ERbeta recruitment to chromatin, consistent with the role of AP-1 in mediating estrogen signaling in breast cancer cells. Additionally, ERalpha and ERbeta recruitment to AP-1/ERbeta target regions exhibited gene-dependent differences in response to antiestrogens. Together, our results broaden insights into ERbeta DNA-binding at the genomic level by revealing crosstalk with the AP-1 transcription factor.