Toggling of BRD4 functions is triggered through its phosphorylation by JNK [RNAseq-JQ1]

BRD4 is a key regulatory factor in multiple cancers and cellular stress responses with pleotropic functions. It regulates chromatin remodeling and transcription through its histone acetyltransferase (HAT) and kinase activities, respectively. The mechanism responsible for switching BRD4 from a chromatin to transcriptional regulator is currently unknown. Here, we report that in response to a broad range of stimuli, this switch is mediated by the JNK kinase which directly interacts with BRD4. JNK specifically phosphorylates human BRD4 at Thr1186 and Thr1212, triggering transient BRD4 release from chromatin. JNK phosphorylation of BRD4 halts its HAT-mediated chromatin regulation and activates its transcription-enhancing kinase function. BRD4 release from chromatin is necessary to toggle between its enzymatic activities: chromatin-bound BRD4 is kinase inactive and RNA Pol II-bound BRD4 does not acetylate chromatin. BRD4 release from chromatin augments its interaction with and phosphorylation of key transcriptional regulators RNA Pol II, PTEFb and c-MYC. The PP4 phosphatase dephosphorylates JNK phosphorylated BRD4 in the nucleoplasm, which promotes its interaction with RNA Pol II at transcriptionally active sites. Accordingly, JNK-mediated release of BRD4 from chromatin leads to significantly elevated transcription of BRD4-regulated immune and inflammatory response genes through enhanced BRD4-Pol II interaction at the promoters of these genes. JNK phosphorylation of BRD4 occurs during T-cell activation and is required for epithelial to mesenchymal transition (EMT) in prostate cancer cells. These findings thus characterize a novel mechanism that triggers the transition of BRD4 from a chromatin regulator to transcriptional activator during stress/immune/inflammatory responses and EMT.