BRD4 Regulates EZH2 Transcription through Upregulation of C-MYC and Represents a Novel Therapeutic Target in Bladder Cancer

Abstract

People who develop bladder cancer frequently succumb to the intractable disease. Current treatment strategies are limited presumably due to the underlying molecular complexity and insufficient comprehension. Therefore, exploration of new therapeutic targets in bladder cancer remains necessary. Here, we identify that bromodomain-4 protein (BRD4), an important epigenome reader of bromodomain and extraterminal domain (BET) family member, is a key upstream regulator of enhancer of zeste homologue 2 (EZH2), and represents a novel therapeutic target in bladder cancer. We found that BRD4 was significantly overexpressed in bladder cancer cells and tissues. Inhibition of BRD4 decreased bladder cancer cell proliferation concomitantly with the accumulation of cell apoptosis in vitro and suppressed tumor growth in vivo. We further found that suppression of BRD4 decreased the mRNA and protein levels of EZH2, which was reversed by ectopic expression of C-MYC. In particular, individual silencing of BRD4 using shRNA or the BET inhibitor JQ1 strikingly diminished the recruitment of C-MYC to EZH2 promoter in bladder cancer. Briefly, our research reveals that BRD4 positively regulates EZH2 transcription through upregulation of C-MYC, and is a novel promising target for pharmacologic treatment in transcriptional program intervention against this intractable disease.

Comprehensive Molecular Characterization of Muscle-Invasive Bladder Cancer

“…Recent studies have identified BRD4 - EZH2 chromatin modification as an important growth pathway in bladder cancer, especially in tumors with loss of KDM6A , and shown in preclinical models that the BET inhibitor JQ1 and inhibition of EZH2 have therapeutic benefit (Ler et al, 2017; Wu et al, 2016). Recently, a Phase 2 study of Mocetinostat, a histone deacetylase inhibitor, in patients with locally advanced or metastatic urothelial carcinoma has completed accrual and results are awaited (NCT02236195).…”

E2F4 functions as a tumour suppressor in acute myeloid leukaemia via inhibition of the MAPK signalling pathway by binding to EZH2

“…A-C, Tumour images and weights at experimental end-points in NC and shE2F4 NB4 xenografts (n = 5 for each group). 47 E2Fs have also been reported to manipulate EZH2 transcription in several malignancies including BC. E, Western blot analysis of cyclin D1, cyclin A2, P-Rb and CDK4 in tumour tissues of NC and shE2F4 groups.…”

CXCL6‐EGFR‐induced Kupffer cells secrete TGF‐β1 promoting hepatic stellate cell activation via the SMAD2/BRD4/C‐MYC/EZH2 pathway in liver fibrosis

“…A ChIP assay was performed using an EZ‐ChIP kit (Upstate Biotechnology, Lake Placid, NY, USA), as previously described 20. Briefly, chromatin DNA was immunoprecipitated with the corresponding antibody or normal IgG.…”

“…There is evidence from various cancer cell types that BRD4 can interact with the C‐MYC promoter and directly regulate its transcriptional expression 16, 17, 18. Furthermore, recent studies by one research group into the role of BRD4 in bladder cancer reported that BRD4 positively regulates enhancer of zeste homologue 2 ( EZH2 ) transcription through the upregulation of the C‐MYC promoter 19, 20…”