Mapping ERβ genomic binding sites reveals unique genomic features and identifies EBF1 as an ERβ interactor

Considerable effort by numerous laboratories has resulted in an improved understanding of estrogen and SERM action mediated by the two estrogen receptors, ERα and ERβ. However, many of the targets for ERβ in cell physiology remain elusive. Here, the C4-12/Flag.ERβ cell line which stably expressed Flag.ERβ is used to study ERβ genomic functions without ERα interference. Mapping ERβ binding sites in these cells reveals ERβ unique distribution and motif enrichment patterns. Accompanying our mapping results, nascent RNA profiling is performed on cells at the same treatment time. The combined results allow the identification of ERβ target genes. Gene ontology analysis reveals that ERβ targets are enriched in differentiation, development and apoptosis. Concurrently, E2 treatment suppresses proliferation in these cells. Within ERβ binding sites, while the most prevalent binding motif is the canonical ERE, motifs of known ER interactors are also enriched in ERβ binding sites. Moreover, among enriched binding motifs are those of GFI, REST and EBF1, which are unique to ERβ binding sites in these cells. Further characterization confirms the association between EBF1 and the estrogen receptors, which favors the N-terminal region of the receptor. Furthermore, EBF1 negatively regulates ERs at the protein level. In summary, by studying ERβ genomic functions in our cell model, we confirm the anti-proliferative role of ERβ and discover the novel cross talk of ERβ with EBF1 which has various implications in normal physiology.