DataSheet_1_The SWI/SNF-Related, Matrix Associated, Actin-Dependent Regulator of Chromatin A4 Core Complex Represses Respiratory Syncytial Virus-Induced Syncytia Formation and Subepithelial Myofibroblast Transition.pdf

Epigenetics plays an important role in the priming the dynamic response of airway epithelial cells to infectious and environmental stressors. Here, we examine the epigenetic role of the SWI/SNF Related, Matrix Associated, Actin Dependent Regulator of Chromatin A4 (SMARCA4) in the epithelial response to RSV infection. Depletion of SMARCA4 destabilized the abundance of the SMARCE1/ARID1A SWI/SNF subunits, disrupting the innate response and triggering a hybrid epithelial/mesenchymal (E/M) state. Assaying SMARCA4 complex-regulated open chromatin domains by transposase cleavage -next generation sequencing (ATAC-Seq), we observed that the majority of cleavage sites in uninfected cells have reduced chromatin accessibility. Paradoxically, SMARCA4 complex-depleted cells showed enhanced RSV-inducible chromatin opening and gene expression in the EMT pathway genes, MMP9, SNAI1/2, VIM, and CDH2. Focusing on the key MMP9, we observed that SMARCA4 complex depletion reduced basal BRD4 and RNA Polymerase II binding, but enhanced BRD4/Pol II binding in response to RSV infection. In addition, we observed that MMP9 secretion in SMARCA4 complex deficient cells contributes to mesenchymal transition, cellular fusion (syncytia) and subepithelial myofibroblast transition. We conclude the SMARCA4 complex is a transcriptional repressor of epithelial plasticity, whose depletion triggers a hybrid E/M state that affects the dynamic response of the small airway epithelial cell in mucosal remodeling via paracrine MMP9 activity.

表观遗传学（Epigenetics）在启动气道上皮细胞应对感染与环境应激的动态应答过程中发挥关键作用。本研究探讨了SWI/SNF相关、基质关联、肌动蛋白依赖的染色质调控因子A4（SWI/SNF Related, Matrix Associated, Actin Dependent Regulator of Chromatin A4, SMARCA4）在气道上皮细胞应对呼吸道合胞病毒（Respiratory Syncytial Virus, RSV）感染的表观遗传调控作用。SMARCA4耗竭会降低SMARCE1/ARID1A等SWI/SNF亚基的丰度稳定性，进而扰乱天然免疫应答，并诱发混合上皮-间质（epithelial/mesenchymal, E/M）表型。通过转座酶可及性测序（Assay for Transposase-Accessible Chromatin using sequencing, ATAC-Seq）分析SMARCA4复合物调控的开放染色质区域，我们发现未感染细胞中的绝大多数切割位点的染色质可及性均出现下降。与之相反，SMARCA4复合物耗竭的细胞中，RSV诱导的染色质开放程度以及上皮间质转化（epithelial-mesenchymal transition, EMT）通路基因（包括MMP9、SNAI1/2、VIM及CDH2）的表达均出现上调。以关键靶基因MMP9为研究对象，我们发现SMARCA4复合物耗竭会降低基础状态下溴结构域蛋白4（Bromodomain-containing protein 4, BRD4）与RNA聚合酶II（RNA Polymerase II）的结合水平，但在RSV感染后可增强BRD4/Pol II的结合能力。此外，我们发现SMARCA4复合物缺陷细胞分泌的MMP9可促进间质转化、细胞融合（合胞体形成）以及上皮下肌成纤维细胞转化。本研究最终得出结论：SMARCA4复合物是上皮可塑性的转录抑制因子，其耗竭会诱发混合E/M表型，并通过旁分泌MMP9活性影响小气道上皮细胞在黏膜重塑过程中的动态应答。