OR12-04 Regulatory Sharing between Estrogen Receptor Alpha Bound Enhancers

Mammalian genomes encode an order of magnitude more gene expression enhancers than promoters, suggesting that most genes are regulated by combinations of enhancers. We previously found that neighboring estrogen-responsive enhancers exhibit cooperative/synergistic contributions to an estrogenic transcriptional response(1). However, when the same combinations of enhancers are targeted with synthetic activators in the absence of estrogens, then the regulatory regions exhibit independent effects on gene expression(2). Taken together, these findings indicate that estrogen receptor alpha (ER) bound enhancers cooperate with each other in cis but influence target gene promoters independently. To determine the molecular underpinnings of enhancer cooperativity, we generated genetic deletions of individual ER bound enhancers. We discovered “regulatory sharing” between enhancers in which loci containing full estrogen response elements (EREs) contribute ER binding to neighboring sites, while enhancers with pre-existing histone acetylation/accessibility contribute this permissible chromatin environment to the neighboring enhancers upon estrogen induction. Genome engineering revealed that a cluster of two half ERE enhancers could not compensate for a full ERE site loss within the cluster. However, two full ERE enhancers produced a transcriptional response greater than the wild-type locus, suggesting that combinations of enhancers are not necessarily configured for a maximal response. By swapping genomic sequences, we found that the genomic location in which a full ERE resides strongly influences enhancer activity. Our results lead to a model in which a full ERE is critical for ER recruitment, but the presence of pre-existing histone acetylation and accessibility within an enhancer cluster is also needed in order for estrogen-induced gene regulation to occur. References 1. Carleton JB, Berrett KC, Gertz J (2017). Multiplex Enhancer Interference Reveals Collaborative Control of Gene Regulation by Estrogen Receptor α-Bound Enhancers. Cell Syst, 5(4), 333-344.e5.2. 2. Ginley-Hidinger M, Carleton JB, Rodriguez AC, Berrett KC, Gertz J. Sufficiency analysis of estrogen responsive enhancers using synthetic activators. Life Sci Alliance, 2(5).