Tian Bing, Zhao Yingxin, Sun Hong, Zhang Yueqing, Yang Jun, Brasier Allan R
Department of Internal Medicine, University of Texas Medical Branch, Galveston, Texas;
Sealy Center for Molecular Medicine, University of Texas Medical Branch, Galveston, Texas.
Am J Physiol Lung Cell Mol Physiol. 2016 Dec 1;311(6):L1183-L1201. doi: 10.1152/ajplung.00224.2016. Epub 2016 Oct 28.
Chronic epithelial injury triggers a TGF-β-mediated cellular transition from normal epithelium into a mesenchymal-like state that produces subepithelial fibrosis and airway remodeling. Here we examined how TGF-β induces the mesenchymal cell state and determined its mechanism. We observed that TGF-β stimulation activates an inflammatory gene program controlled by the NF-κB/RelA signaling pathway. In the mesenchymal state, NF-κB-dependent immediate-early genes accumulate euchromatin marks and processive RNA polymerase. This program of immediate-early genes is activated by enhanced expression, nuclear translocation, and activating phosphorylation of the NF-κB/RelA transcription factor on Ser276, mediated by a paracrine signal. Phospho-Ser276 RelA binds to the BRD4/CDK9 transcriptional elongation complex, activating the paused RNA Pol II by phosphorylation on Ser2 in its carboxy-terminal domain. RelA-initiated transcriptional elongation is required for expression of the core epithelial-mesenchymal transition transcriptional regulators SNAI1, TWIST1, and ZEB1 and mesenchymal genes. Finally, we observed that pharmacological inhibition of BRD4 can attenuate experimental lung fibrosis induced by repetitive TGF-β challenge in a mouse model. These data provide a detailed mechanism for how activated NF-κB and BRD4 control epithelial-mesenchymal transition initiation and transcriptional elongation in model airway epithelial cells in vitro and in a murine pulmonary fibrosis model in vivo. Our data validate BRD4 as an in vivo target for the treatment of pulmonary fibrosis associated with inflammation-coupled remodeling in chronic lung diseases.
慢性上皮损伤引发转化生长因子-β（TGF-β）介导的细胞从正常上皮向间充质样状态转变，进而导致上皮下纤维化和气道重塑。在此，我们研究了TGF-β如何诱导间充质细胞状态并确定其机制。我们观察到TGF-β刺激激活了由核因子-κB（NF-κB）/RelA信号通路控制的炎症基因程序。在间充质状态下，NF-κB依赖的立即早期基因积累常染色质标记并募集进行性RNA聚合酶。这一立即早期基因程序通过旁分泌信号介导的NF-κB/RelA转录因子在Ser276位点的表达增强、核转位和激活磷酸化而被激活。磷酸化的Ser276 RelA与BRD4/细胞周期蛋白依赖性激酶9（CDK9）转录延伸复合物结合，通过其羧基末端结构域Ser2位点的磷酸化激活暂停的RNA聚合酶II（Pol II）。RelA启动的转录延伸是核心上皮-间充质转化转录调节因子SNAI1、TWIST1和ZEB1以及间充质基因表达所必需的。最后，我们观察到在小鼠模型中，对BRD4的药理学抑制可减轻重复TGF-β刺激诱导的实验性肺纤维化。这些数据提供了一个详细的机制，说明活化的NF-κB和BRD4如何在体外模型气道上皮细胞和体内小鼠肺纤维化模型中控制上皮-间充质转化的起始和转录延伸。我们的数据验证了BRD4作为治疗慢性肺病中与炎症偶联重塑相关的肺纤维化的体内靶点。
