The Bromodomain Protein 4 Contributes to the Regulation of Alternative Splicing

Abstract

SUMMARY The bromodomain protein 4 (BRD4) is an atypical kinase and histone acetyl transferase (HAT) that binds to acetylated histones and contributes to chromatin remodeling and early transcriptional elongation. During transcription, BRD4 travels with the elongation complex. Since most alternative splicing events take place co-transcriptionally, we asked if BRD4 plays a role in regulating alternative splicing. We report that distinct patterns of alternative splicing are associated with a conditional deletion of BRD4 during thymocyte differentiation in vivo. Similarly, the depletion of BRD4 in T cell acute lymphoblastic leukemia (T-ALL) cells alters patterns of splicing. Most alternatively spliced events affected by BRD4 are exon skipping. Importantly, BRD4 interacts with components of the splicing machinery, as assessed by both immunoprecipitation (IP) and proximity ligation assays (PLAs), and co-localizes on chromatin with the splicing regulator, FUS. We propose that BRD4 contributes to patterns of alternative splicing through its interaction with the splicing machinery during transcription elongation.

The Functions of BET Proteins in Gene Transcription of Biology and Diseases

“…In castrationresistant prostate cancer (CRPC), BET-BD inhibition affects the regulation of alternative splicing of androgen receptor (AR), leading to reduced AR-V7 expression and abrogating AR signaling and growth of CRPC patient-derived models (Welti et al, 2018). In T-cell acute lymphoblastic leukemia (T-ALL) cancer cells and during thymocyte differentiation in vivo, distinct patterns of alternative splicing are associated with BRD4 deletion (Uppal et al, 2019). Specifically, BRD4 directly interacts with splicing machinery (FUS, HnRNPM, HnRNPL, U1-70, and U1-A), suggesting interplay of BRD4 and splicing factors that modulates exon usage (Uppal et al, 2019).…”

Bromodomain proteins regulate human cytomegalovirus latency and reactivation allowing epigenetic therapeutic intervention

“…The UL44 -promoter is unique to HCMV in having three separate transcription start sites (TSSs) (two early and one late) ( 61 ), with RNAPII regulation as well as genomic sequence likely controlling TSS selection. BRD4 has been shown to be an important factor in the regulation of alternative RNA splicing ( 62 ), and, more recently, over 100 possible alternative splice sites have been described across the HCMV genome ( 63 , 64 ). Whereas redistribution of BRD4 described in a study of herpes simplex virus increased recruitment of P-TEFb to virus genomes ( 65 ), here inhibition of BRD4 interaction directly with the HCMV genome may have effects on transcription and translation.…”

RNA Epigenetics: Fine-Tuning Chromatin Plasticity and Transcriptional Regulation, and the Implications in Human Diseases

“…Recent studies show depletion of the pre-exon junction complex (EJC), a protein complex formed at the junction of two exons of a pre-messenger RNA during RNA splicing, led to a global decrease in RNAPII pausing and premature entry into elongation by CDK9/P-TEFb, suggesting that the pre-EJC serves as an early transcriptional checkpoint to prevent premature entry into elongation and proper exon definition [150]. RNA splicing factors to contribute to spliceosome formation and alternative splicing regulation at the co-and post-transcriptional levels [153][154][155][156][157], as shown in Figure 7.…”

“…The poly(A) tail is added to nascent RNA when the nascent Other trans-acting factors, such as MYC, BRD4 and many RNA-binding proteins (RBPs) regulate transcription elongation and alternative splicing in tissue-specific patterns and sizes [151,152]. MYC and BRD4 have been shown to physically interact with RNA splicing factors to contribute to spliceosome formation and alternative splicing regulation at the co-and post-transcriptional levels [153][154][155][156][157], as shown in Figure 7.…”