Activator protein-2? is a critical determinant of estrogen receptor interactome formation and gene transcription in breast cancer [expression]

Estrogen receptor α (ERα) is key player in the progression of breast cancer. ERα binds to DNA and mediates long-range chromatin interactions throughout the genome, but the underlying mechanism in this process is unclear. Here, we show that AP-2 motifs are highly enriched in the ERα binding sites (ERBS) identified from the recent ChIA-PET of ERα. More importantly, we demonstrate that AP-2γ (also known as TFAP2C), a member of the AP-2 family which has been implicated in breast cancer oncogenesis, is recruited to chromatin in a ligand-independent manner and co-localized with ERα binding events. Furthermore, pertubation of AP-2γ expression disrupts ERα DNA binding, long-range chromatin interactions, and gene transcription. Using ChIP-seq, we show that AP-2γ and ERα binding occurs in close proximity on a genome-wide scale. The majority of these shared genomic regions are also occupied by the pioneer factor, FoxA1. AP-2γ is required for efficient FoxA1 binding and vice versa. Finally, we show that most ERBS associated with long-range chromatin interactions are co-localized with both AP-2γ and FoxA1. Together, our results suggest AP-2γ is an essential factor in ERα-mediated transcription, primarily working together with FoxA1 to facilitate ERα binding and long-range chromatin interactions. Gene expression profiling of negative control (NC) and AP-2γ siRNA transfected MCF-7, with and without E2 (estradiol) stimulation using microarray.