Bromodomain protein BRD4 is required for estrogen receptor-dependent transcription and enhancer activation [RNA-Seq]

The estrogen receptor-a (ERa) is a transcription factor which plays a critical role in controlling cell proliferation and tumorigenesis by recruiting various cofactors to estrogen response elements (EREs) to induce or repress gene transcription. A deeper understanding of these transcriptional mechanisms may uncover novel therapeutic targets for ERa-dependent cancers. Here we show for the first time that BRD4 regulates ERa-induced gene expression by affecting elongation-associated phosphorylation of RNA Polymerase II (RNAPII P-Ser2) and histone H2B monoubiquitination (H2Bub1). Consistently, BRD4 activity is required for estrogen-induced proliferation of ER+ breast and endometrial cancer cells and uterine growth in mice. Genome-wide occupancy studies revealed an enrichment of BRD4 on transcriptional start sites as well as EREs enriched for H3K27ac and demonstrate a requirement for BRD4 for H2B monoubiquitination in the transcribed region of estrogen-responsive genes. Importantly, we further demonstrate that BRD4 occupancy correlates with active mRNA transcription and is required for the production of ERa-dependent enhancer RNAs (eRNAs). These results uncover BRD4 as a central regulator of ERa function and potential therapeutic target. Overall design: mRNA expression profiles of MCF7 cells treated with +/- estrogen treatment under negative control siRNA, BRD4 siRNA or JQ1 treatment, in duplicates.

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Nagarajan S, Hossan T, Alawi M, Najafova Z, Indenbirken D, Bedi U, Taipaleenmäki H, Ben-Batalla I, Scheller M, Loges S, Knapp S, Hesse E, Chiang CM, Grundhoff A, Johnsen SA