Xu Xiaofang, Mann Morgan, Qiao Dianhua, Li Yi, Zhou Jia, Brasier Allan R
Department of Medicine, University of Wisconsin-Madison School of Medicine and Public Health (SMPH), Madison, WI, United States.
Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston, TX, United States.
Front Mol Biosci. 2021 Oct 26;8:728661. doi: 10.3389/fmolb.2021.728661. eCollection 2021.
Bromodomain-containing protein 4 plays a central role in coordinating the complex epigenetic component of the innate immune response. Previous studies implicated BRD4 as a component of a chromatin-modifying complex that is dynamically recruited to a network of protective cytokines by binding activated transcription factors, polymerases, and histones to trigger their rapid expression via transcriptional elongation. Our previous study extended our understanding of the airway epithelial BRD4 interactome by identifying over 100 functionally important coactivators and transcription factors, whose association is induced by respiratory syncytial virus (RSV) infection. RSV is an etiological agent of recurrent respiratory tract infections associated with exacerbations of chronic obstructive pulmonary disease. Using a highly selective small-molecule BRD4 inhibitor (ZL0454) developed by us, we extend these findings to identify the gene regulatory network dependent on BRD4 bromodomain (BD) interactions. Human small airway epithelial cells were infected in the absence or presence of ZL0454, and gene expression profiling was performed. A highly reproducible dataset was obtained which indicated that BRD4 mediates both activation and repression of RSV-inducible gene regulatory networks controlling cytokine expression, interferon (IFN) production, and extracellular matrix remodeling. Index genes of functionally significant clusters were validated independently. We discover that BRD4 regulates the expression of its own gene during the innate immune response. Interestingly, BRD4 activates the expression of NFκB/RelA, a coactivator that binds to BRD4 in a BD-dependent manner. We extend this finding to show that BRD4 also regulates other components of its functional interactome, including the Mediator (Med) coactivator complex and the SWI/SNF-related, matrix-associated, actin-dependent regulator of chromatin (SMARC) subunits. To provide further insight into mechanisms for BRD4 in RSV expression, we mapped 7,845 RSV-inducible Tn5 transposase peaks onto the BRD4-dependent gene bodies. These were located in promoters and introns of cytostructural and extracellular matrix (ECM) formation genes. These data indicate that BRD4 mediates the dynamic response of airway epithelial cells to RNA infection by modulating the expression of its coactivators, controlling the expression of host defense mechanisms and remodeling genes through changes in promoter accessibility.
含溴结构域蛋白4在协调先天性免疫反应复杂的表观遗传成分中起核心作用。先前的研究表明，BRD4是一种染色质修饰复合物的组成部分，该复合物通过结合活化的转录因子、聚合酶和组蛋白，动态募集到保护性细胞因子网络，从而通过转录延伸触发它们的快速表达。我们之前的研究通过鉴定100多个功能重要的共激活因子和转录因子，扩展了我们对气道上皮BRD4相互作用组的理解，它们的结合是由呼吸道合胞病毒（RSV）感染诱导的。RSV是与慢性阻塞性肺疾病加重相关的反复呼吸道感染的病原体。使用我们开发的一种高度选择性的小分子BRD4抑制剂（ZL0454），我们扩展了这些发现，以确定依赖于BRD4溴结构域（BD）相互作用的基因调控网络。在有或没有ZL0454的情况下感染人小气道上皮细胞，并进行基因表达谱分析。获得了一个高度可重复的数据集，表明BRD4介导了控制细胞因子表达、干扰素（IFN）产生和细胞外基质重塑的RSV诱导基因调控网络的激活和抑制。对功能显著簇的索引基因进行了独立验证。我们发现BRD4在先天性免疫反应期间调节其自身基因的表达。有趣的是，BRD4激活NFκB/RelA的表达，NFκB/RelA是一种以BD依赖方式与BRD4结合的共激活因子。我们扩展了这一发现，表明BRD4还调节其功能相互作用组的其他成分，包括中介体（Med）共激活复合物和与SWI/SNF相关、与基质相关、肌动蛋白依赖性染色质调节因子（SMARC）亚基。为了进一步深入了解BRD4在RSV表达中的机制，我们将7845个RSV诱导的Tn5转座酶峰映射到BRD4依赖基因体上。这些峰位于细胞结构和细胞外基质（ECM）形成基因的启动子和内含子中。这些数据表明，BRD4通过调节其共激活因子的表达，通过改变启动子可及性来控制宿主防御机制和重塑基因的表达，从而介导气道上皮细胞对RNA感染的动态反应。
