Respiratory Research Group, Faculty of Pharmacy, University of Sydney, NSW 2006, Australia.
Cell Signal. 2012 Apr;24(4):907-13. doi: 10.1016/j.cellsig.2011.12.013. Epub 2011 Dec 19.
Airway smooth muscle (ASM) plays an important immunomodulatory role in airway inflammation in asthma. In our previous in vitro studies in ASM cells delineating the pro-inflammatory mitogen-activated protein kinase (MAPK) signaling pathways activated by tumor necrosis factor α (TNFα), we observed that TNFα concomitantly induces the rapid, but transient, upregulation of the anti-inflammatory protein-mitogen-activated protein kinase phosphatase 1 (MKP-1). As this was suggestive of a negative feedback loop, the aim of this study was to investigate the molecular mechanisms of MKP-1 upregulation by TNFα and to determine whether MKP-1 is a negative feedback effector that represses MAPK-mediated pro-inflammatory signaling pathways and cytokine secretion in ASM cells. Herein, we show that TNFα increases MKP-1 mRNA expression and protein upregulation in a p38 MAPK-dependent manner. TNFα does not increase MKP-1 transcription (measured by MKP-1 promoter activity); rather, we found that TNFα-induced MKP-1 mRNA stability is regulated by the p38 MAPK pathway. Inhibiting MKP-1 upregulation (with triptolide) demonstrated the precise temporal control exerted on MAPK signaling by MKP-1. In the absence of MKP-1, downstream phosphoprotein targets of MAPKs (such as MSK-1 and histone H3) are not turned off at the right time, allowing pro-inflammatory pathways to continue in an unrestrained manner. This is confirmed by knocking-down MKP-1 by siRNA where enhanced secretion of the neutrophil chemoattractant cytokine-interleukin 8 was detected in the absence of MKP-1. Thus, by activating p38 MAP kinase, TNFα concomitantly upregulates the MAPK deactivator MKP-1 to serve as an important negative feedback effector, limiting the extent and duration of pro-inflammatory MAPK signaling and cytokine secretion in ASM cells.
气道平滑肌（ASM）在哮喘气道炎症中发挥着重要的免疫调节作用。在我们之前的体外研究中，我们在 ASM 细胞中研究了肿瘤坏死因子 α（TNFα）激活的促炎丝裂原活化蛋白激酶（MAPK）信号通路，观察到 TNFα 同时诱导抗炎蛋白-丝裂原活化蛋白激酶磷酸酶 1（MKP-1）的快速但短暂的上调。由于这表明存在负反馈回路，本研究旨在研究 TNFα 上调 MKP-1 的分子机制，并确定 MKP-1 是否是一种负反馈效应物，可抑制 ASM 细胞中 MAPK 介导的促炎信号通路和细胞因子分泌。在此，我们表明 TNFα 以 p38 MAPK 依赖性方式增加 MKP-1 mRNA 表达和蛋白上调。TNFα 不会增加 MKP-1 的转录（通过 MKP-1 启动子活性测量）；相反，我们发现 TNFα 诱导的 MKP-1 mRNA 稳定性受到 p38 MAPK 途径的调节。抑制 MKP-1 的上调（用雷公藤甲素）证明了 MKP-1 对 MAPK 信号的精确时间控制。在没有 MKP-1 的情况下，MAPKs 的下游磷酸化蛋白靶标（如 MSK-1 和组蛋白 H3）不会在正确的时间关闭，从而允许促炎途径以不受限制的方式继续进行。这通过 siRNA 敲低 MKP-1 得到证实，其中在没有 MKP-1 的情况下，检测到中性粒细胞趋化因子白细胞介素 8 的分泌增强。因此，通过激活 p38 MAP 激酶，TNFα 同时上调 MAPK 失活酶 MKP-1 作为重要的负反馈效应物，限制 ASM 细胞中促炎 MAPK 信号和细胞因子分泌的程度和持续时间。
