Abstract
The epigenetic reader BRD4 binds acetylated histones and plays a central role in controlling cellular gene transcription and proliferation. Dysregulation of BRD4′s activity has been implicated in the pathogenesis of a wide variety of cancers. While blocking BRD4 interaction with acetylated histones using BET inhibitors (BETis) has been tested in clinical trials, many cancers have acquired BETi resistance. However, the underlying mechanisms are poorly understood and BETi resistance remains a pressing clinical problem. We previously showed that BRD4 phosphorylation supports stronger chromatin binding and target oncogene expression. In this study, we discovered that BRD4 is hyperphosphorylated by CDK1 during mitosis and determined the major CDK1 phosphorylation sites in BRD4. Using CRISPR/Cas9 gene editing, we replaced endogenous BRD4 with a non-phosphorylatable mutant and demonstrated that CDK1-mediated BRD4 phosphorylation contributes to BETi resistance. CDK1 over-activation frequently observed in cancers has the potential to cause aberrant BRD4 hyperphosphorylation persisting outside of mitosis to strengthen its target gene binding and confer BETi resistance. We found that dual CDK1 and BET inhibition generates a synergistic effect in killing BETi-resistant cancer cells. Our study therefore suggests that CDK1 inhibition can be employed to overcome tumor BETi resistance and improve treatments for BRD4-associated cancers.
Highlights
Bromodomain-containing protein 4 (BRD4) belongs to the bromodomain and extraterminal (BET)family of proteins
Combined treatment with RO-3306 and (+)-JQ1 achieved a strong synergistic effect (CI value of
Combination treatment of MDA-MB-231 cells with (+)-JQ1 and RO-3306 resulted in a much stronger synergistic effect on cell viability compared to those observed in DLD-1 cells (Figure 5D)
Summary
It binds acetylated histones on chromatin through its bromodomains [1], and actively recruits P-TEFb (positive transcription elongation factor b) to facilitate transcriptional activation of RNA polymerase II (RNAPII) [2,3,4]. BRD4 binds M/G1 growth-associated genes during mitosis and functions as a mitotic bookmarker, preserving the epigenetic memory of these genes throughout mitosis to ensure their rapid postmitotic transcriptional re-activation [5,6,7,8]. BRD4 functions as an epigenetic reader and plays a central role in transcriptional regulation and cellular growth control [2,5,6,7,8,10,11,12,13]. Aberrant BRD4 function has been implicated in the pathogenesis of a wide range of cancers [4,14,15,16,17,18,19,20,21,22,23,24,25,26,27]
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call