E6-AP facilitates efficient transcription at estrogen responsive promoters through recruitment of chromatin modifiers

E6-AP is a known coactivator of the estrogen receptor alpha (ERα), however the coactivation mechanism of E6-AP is not clear. This work was undertaken to elucidate the coactivation mechanism of E6-AP. In order to examine the role of E6-AP in ERα signaling, we knocked-down the expression of E6-AP and examined the transactivation functions of ERα. Knockdown of E6-AP showed reduced mRNA production of the ERα target genes pS2 and GREB1 suggesting that E6-AP is required for their proper transcription facilitated by ERα. In order to study the mechanism(s) by which E6-AP regulates the transcriptional functions of ERα, we performed chromatin immunoprecipitation (ChIP) assays under E6-AP knockdown conditions. Our ChIP data suggest that knockdown of E6-AP leads to decreased recruitment of the histone acetylase p300 to the ERα target gene pS2 promoter as well as reduced histone modifications at the promoter. Although there was reduced p300 recruitment to the pS2 promoter, loss of p300 did not account fully for the loss of histone acetylation. Taken together our data suggest that E6-AP regulates the transactivation functions of ERα in part by complexing with p300 and other chromatin modifying enzymes at target gene promoters to create a transcriptionally active promoter environment.