Transforming growth factor-β receptor type I-dependent fibrogenic gene program is mediated via activation of Smad1 and ERK1/2 pathways
Transforming growth factor-β receptor type I-dependent fibrogenic gene program is mediated via activation of Smad1 and ERK1/2 pathways
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DOI：
10.1074/jbc.m611742200
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发表时间：
2007-04-06
影响因子：
4.8
通讯作者：
Trojanowska, Maria
中科院分区：
文献类型：
--
作者：
Pannu, Jaspreet;Nakerakanti, Sashidhar;Trojanowska, Maria
转化生长因子（TGF）-β/Smad 3信号通路被认为是病理性器官纤维化的中心介质;然而，Smad 2/3非依赖性TGF-β信号通路的贡献尚未被充分探索。本研究利用先前描述的基于TGF-β RI（ALK 5）的强制表达的硬皮病（SSc）纤维化模型（Pannu，J.，加德纳，H.，Shearstone，J.R.，史密斯，E.，和Trojanowska，M.（2006年）风湿关节炎。54，3011 - 3021）。本研究旨在确定该模型中促纤维化程序的分子机制。我们证明，胶原和CCN 2（CTGF）的TGF-β RI依赖性上调不涉及Smad 2/3激活，但由ALK 1/Smad 1和ERK 1/2途径介导。以下调查结果支持这一结论：（i）Smad 2和Smad 3在对TGF-β RI的反应中不被磷酸化，（ii）Smad 2/3活化缺陷的TGF-β RI突变体ALK 5（3A），有效地刺激胶原蛋白的产生，（iii）TGF-β RI的升高触发ALK 5与ALK 1的持续结合和高水平的Smad 1磷酸化，（iv）通过小干扰RNA阻断Smad 1可消除该模型中胶原和CCN 2的上调，（v）升高的TGF-β RI导致ERK 1/2活化延长，（vi）ERK 1/2的药理学抑制剂抑制Smad 1磷酸化并消除升高的TGF-β RI的促纤维化作用。另外的实验表明，在该模型中，位于CCN 2启动子中-6至-16（转录起始位点上游）的富含GC的响应元件介导Smad 1依赖性的启动子活性增加。该元件先前显示介导SSc成纤维细胞中CCN 2启动子的上调。总之，这项研究定义了一种新的ALK 1/Smad 1-和ERK 1/2-依赖性，Smad 3-独立的TGF-β信号传导模式，可能在SSc纤维化的慢性阶段起作用。
The transforming growth factor (TGF)- beta/Smad3 signaling pathway is considered a central mediator of pathological organ fibrosis; however, contribution of Smad2/3-independent TGF-beta signaling has not been fully explored. The present study utilized previously a described model of scleroderma (SSc) fibrosis based on forced expression of the TGF-beta RI ( ALK5) ( Pannu, J., Gardner, H., Shearstone, J. R., Smith, E., and Trojanowska, M. ( 2006) Arthritis Rheum. 54, 3011 - 3021). This study was aimed at determining the molecular mechanisms underlying the profibrotic program in this model. We demonstrate that the TGF-beta RI-dependent up-regulation of collagen and CCN2 ( CTGF) does not involve Smad2/3 activation but is mediated by ALK1/Smad1 and ERK1/2 pathways. The following findings support this conclusion: (i) Smad2 and - 3 were not phosphorylated in response to TGF-beta RI, ( ii) a TGF- beta RI mutant defective in Smad2/3 activation, ALK5( 3A), potently stimulated collagen production, (iii) elevation of TGF-beta RI triggered sustained association of ALK5 with ALK1 and high levels of Smad1 phosphorylation, (iv) blockade of Smad1 via small interfering RNA abrogated collagen and CCN2 up-regulation in this model, ( v) elevated TGF-beta RI led to a prolonged activation of ERK1/2, ( vi) the pharmacologic inhibitor of ERK1/2 inhibited Smad1 phosphorylation and abrogated profibrotic effects of elevated TGF beta-RI. Additional experiments demonstrated that a GC- rich response element located -6 to -16 ( upstream of the transcription start site) in the CCN2 promoter mediated Smad1- dependent increased promoter activity in this model. This element was shown previously to mediate up- regulation of the CCN2 promoter in SSc fibroblasts. In conclusion, this study defines a novel ALK1/Smad1- and ERK1/2-dependent, Smad3-independent mode of TGF-beta signaling that may operate during chronic stages of fibrosis in SSc.