Division of Cardiology, Department of Medicine, Emory University, Atlanta, GA 30322, USA.
Free Radic Biol Med. 2011 Jan 15;50(2):354-62. doi: 10.1016/j.freeradbiomed.2010.11.007. Epub 2010 Nov 11.
In contrast to other cell types, vascular smooth muscle cells modify their phenotype in response to external signals. NADPH oxidase 4 (Nox4) is critical for maintenance of smooth muscle gene expression; however, the underlying mechanisms are incompletely characterized. Using smooth muscle α-actin (SMA) as a prototypical smooth muscle gene and transforming growth factor-β (TGF-β) as a differentiating agent, we examined Nox4-dependent signaling. TGF-β increases Nox4 expression and activity in human aortic smooth muscle cells (HASMC). Transfection of HASMC with siRNA against Nox4 (siNox4) abolishes TGF-β-induced SMA expression and stress fiber formation. siNox4 also significantly inhibits TGF-β-stimulated p38MAPK phosphorylation, as well as that of its substrate, mitogen-activated protein kinase-activated protein kinase-2. Moreover, the p38MAPK inhibitor SB-203580 nearly completely blocks the SMA increase induced by TGF-β. Inhibition of either p38MAPK or NADPH oxidase-derived reactive oxygen species impairs the TGF-β-induced phosphorylation of Ser103 on serum response factor (SRF) and reduces its transcriptional activity. Binding of SRF to myocardin-related transcription factor (MRTF) is also necessary, because downregulation of MRTF by siRNA abolishes TGF-β-induced SMA expression. Taken together, these data suggest that Nox4 regulates SMA expression via activation of a p38MAPK/SRF/MRTF pathway in response to TGF-β.
与其他细胞类型相比，血管平滑肌细胞会对外界信号做出表型改变。NADPH 氧化酶 4（Nox4）对于维持平滑肌基因表达至关重要；然而，其潜在机制尚未完全阐明。本研究以平滑肌α-肌动蛋白（SMA）作为典型的平滑肌基因，以转化生长因子-β（TGF-β）作为分化剂，检测了 Nox4 依赖性信号通路。TGF-β可增加人主动脉平滑肌细胞（HASMC）中的 Nox4 表达和活性。用 Nox4 特异性 siRNA（siNox4）转染 HASMC 可消除 TGF-β诱导的 SMA 表达和应激纤维形成。siNox4 还显著抑制 TGF-β刺激的 p38MAPK 磷酸化及其底物丝裂原激活蛋白激酶激活的蛋白激酶-2（MAPKAPK-2）磷酸化。此外，p38MAPK 抑制剂 SB-203580 几乎完全阻断了 TGF-β诱导的 SMA 增加。抑制 p38MAPK 或 NADPH 氧化酶衍生的活性氧均可损害 TGF-β诱导的血清反应因子（SRF）Ser103 磷酸化，并降低其转录活性。SRF 与肌球蛋白相关转录因子（MRTF）的结合也是必需的，因为 siRNA 下调 MRTF 可消除 TGF-β诱导的 SMA 表达。综上，这些数据表明，Nox4 通过 TGF-β 激活 p38MAPK/SRF/MRTF 通路调节 SMA 表达。
