Inflammatory response is essential to host defense and repair, and requires tight regulation as excessive and constant inflammatory response is deleterious. We recently identified that one of the general but key mechanisms for inflammatory gene transcription regulation is controlled by the formation of super enhancers mediated by NF-κB, and bromodomain and extraterminal (BET) proteins. Given that microRNA transcription shares a similar mechanism to mRNA, we assume that the inflammatory microRNAs transcription could be NF-κB and BET bromodomain dependent. In the present study, we confirmed that inflammatory stimuli changed human umbilical vein endothelial cells (HUVEC) microRNA profile. Among these microRNAs, miR-146a and miR-155, two well-established inflammatory microRNAs, are both downregulated at transcriptional level by NF-κB and BET bromodomain inhibition. To pursue this mechanism, we analyzed the ChIP-seq data and found that NF-κB, BRD4 and RNA POL II were rapidly distributed at the upstream regions of miR-146a and miR-155, and more importantly mediated the formation of the super enhancers that drive miR-146a and miR-155 transcription. These microRNAs transcription driven by super enhancers in turn downregulate both in vitro and in vivo canonical inflammatory genes expression through targeting inflammatory mediators. This novel finding demonstrated how the host self-regulates inflammatory genes expression at both transcriptional and post-transcriptional level to ensure the appropriate level of the host inflammatory response.

Transcriptional coactivator with PDZ-binding motif (TAZ) is a key transcriptional mediator of Hippo signaling that has been recently reported to mediate Wnt-activated transcription and serve as a component to suppress canonical Wnt/β-catenin activity. The Bromodomain and Extra-terminal domain (BET) family of proteins can recognize the acetylated lysine chain on histones and plays a critical role in transcriptional regulation. However, the mechanisms underlying transcriptional repression by the BET bromodomain are poorly understood. Here, we found that BET bromodomain inhibition upregulated TAZ protein and its transcriptional output, independent of its well-established role as a mediator of Hippo and Wnt signaling. Additionally, JQ1, a synthetic BET inhibitor, suppressed Wnt/β-catenin activity by upregulating TAZ. Although JQ1 upregulated TAZ, which is known to promote cell proliferation, it drastically suppressed the growth of colon cancer cells by inducing cell cycle arrest. Collectively, our study identified an unexpected transcriptional repression function of the BET bromodomain and a novel mechanism for TAZ upregulation.