The bromodomain protein BRD4 regulates the KEAP1/NRF2-dependent oxidative stress response

Abstract

The epigenetic sensor BRD4 (bromodomain protein 4) is a potent target for anti-cancer therapies. To study the transcriptional impact of BRD4 in cancer, we generated an expression signature of BRD4 knockdown cells and found oxidative stress response genes significantly enriched. We integrated the RNA-Seq results with DNA-binding sites of BRD4 generated by chromatin immunoprecipitations, correlated these with gene expressions from human prostate cancers and identified 21 top BRD4 candidate genes among which the oxidative stress pathway genes KEAP1, SESN3 and HDAC6 are represented. Knock down of BRD4 or treatment with the BRD4 inhibitor JQ1 resulted in decreased reactive oxygen species (ROS) production and increased cell viability under H2O2 exposure. Consistently, a deregulation of BRD4 diminished the KEAP1/NRF2 axis and led to a disturbed regulation of the inducible heme oxygenase 1 (HMOX1). Without exogenous stress induction, we also found BRD4 directly targeting the HMOX1 promoter over the SP1-binding sites. Our findings provide insight into the transcriptional regulatory network of BRD4 and highlight BRD4 as signal transducer of the cellular response to oxidative stress.

Targeting BET Bromodomains for Cancer Treatment

“…A function of BRD4 in the oxidative stress response has recently been described [54]. The KEAP1/NRF2 pathway is deregulated following JQ1 treatment, and binding of BRD4 to regulatory regions of the stress-related HMOX1 gene was observed.…”

The Bromodomain and Extra-Terminal Domain (BET) Family: Functional Anatomy of BET Paralogous Proteins

“…The features of the heat shock response are the production of heat shock proteins and a partial inhibition of pre-mRNA splicing [81]. BRD4 has been identified as a regulator of the IFN-stimulated and oxidative stress-induced responses [77,82]. Alternative splicing analysis from RNA splicing data of heat shock-treated cells and heat shock-treated cells with BRD4 knockdown shows a significant increase in splicing inhibition, in particular intron retentions, in BRD4-depleted cells after heat shock, indicating that BRD4 prevents cells from heat stress-induced splicing inhibition [83].…”

Utility of Checklist to Describe Experimental Methods for Investigating Molecular Biomarkers

“…In the 55.5% (10/18) of NRF2 and 42.8% (6/14) of Keap1 articles, primers were specific for the target mRNA, although, in the remaining articles, primers were not specific as they annealed to genomic DNA [15,18,28,30,39,40] (Figure 1A & Supplementary Tables 1 & 2). Citation of the gene accession number was found in approximately the 29% of publications ( Figure 1A & Supplementary Tables 1 & 2), whereas details on PCR conditions (time, temperature and number of cycles) were reported only in the 33.3% (7/21) of NRF2 and 50% (7/14) of Keap1 research articles ( Figure 1A & Supplementary Tables 1 & 2) [14][15][16][17][18][19]21,22].…”