Bromodomain Protein, BRD4, Contributes to the Regulation of Alternative Splicing
Bromodomain protein 4 (BRD4) is an atypical kinase and a histone acetyl transferase (HAT) which plays an important role in chromatin remodeling and early transcriptional elongation. During transcription elongation, BRD4 travels with the elongation complex. Since most of the alternative splicing events take place co-transcriptionally, we asked if BRD4 plays a role in regulation of alternative splicing. We find that distinct patterns of alternative splicing are associated with conditional deletion of BRD4 during thymocyte differentiation in vivo. Similarly, depletion of BRD4 in T-ALL cells alters patterns of splicing. Most of the alternatively spliced events affected by BRD4 are usage of exon skipping. In an established insulin receptor minigene model of splicing, BRD4 over expression modulates alternative splicing. Importantly, as assessed by both immunoprecipitation (IP) and proximity ligation (PLA) assays, BRD4 interacts with components of the splicing machinery. BRD4 also co-localizes on chromatin with one of the splicing regulators. We propose that BRD4 contributes to patterns of alternative splicing through its interaction with the splicing machinery during transcription elongation.\n\nSignificance StatementThe bromodomain protein, BRD4, is a transcriptional and epigenetic regulator that plays a critical role in both cancer and inflammation. It has pleiotropic activities, including chromatin organization, transcriptional pause release and initiation. We now report that it also contributes to the regulation of alternative splicing. Taken together, these findings indicate that BRD4 functions to coordinate the various steps in gene expression.