BRD2 bridging TFIID and histone acetylation in transcriptional initiation [ChIP-Seq]

Members of the bromodomain and extraterminal domain (BET) transcription factor family play a central role in the regulation of gene expression. BET domain factors have also been proposed as major targets for multiple diseases, with inhibitors designed to block the binding of BET bromodomains to acetylated histones. However, recent studies demonstrated that the BETdomain of BRD4 is not involved in its transcriptional function and the specific mechanisms by which other individual BET-domain containing proteins distinctly regulate transcription remain poorly understood. Here, we demonstrate that BRD2 promotes transcriptional initiation by RNA Polymerase II (Pol II) at gene promoters and enhancers, predominantly in a bromodomaindependent manner. Our biochemical studies demonstrated that histone H4K16 acetylated histone-bound BET domain of BRD2 facilitates the recruitment of the transcription preinitiation complex TBP/TFIID to chromatin. Loss or inhibition of BRD2 bromodomains prompts the formation of BRD2-specific nuclear foci that sequester TFIID away from chromatin, leading to a genome-wide defect in transcriptional initiation. Our molecular studies demonstrated that the BET domains of BRD2 and BRD4 are not functionally exchangeable, highlighting distinct but cooperative roles for BET-domain family members in transcriptional initiation and elongation control to promote proper regulation of gene expression