JunkRNA Laboratory, Division of Infection, Inflammation and Immunity, University of Southampton School of Medicine, Southampton General Hospital, Southampton SO16 6YD, United Kingdom.
J Biol Chem. 2010 Dec 31;285(53):41328-36. doi: 10.1074/jbc.M110.146852. Epub 2010 Oct 29.
Transforming growth factor-beta (TGF-β) is a pleiotropic cytokine with important effects on processes such as fibrosis, angiogenesis, and immunosupression. Using bioinformatics, we identified SMAD2, one of the mediators of TGF-β signaling, as a predicted target for a microRNA, microRNA-155 (miR-155). MicroRNAs are a class of small non-coding RNAs that have emerged as an important class of gene expression regulators. miR-155 has been found to be involved in the regulation of the immune response in myeloid cells. Here, we provide direct evidence of binding of miR-155 to a predicted binding site and the ability of miR-155 to repress SMAD2 protein expression. We employed a lentivirally transduced monocyte cell line (THP1-155) containing an inducible miR-155 transgene to show that endogenous levels of SMAD2 protein were decreased after sustained overexpression of miR-155. This decrease in SMAD2 led to a reduction in both TGF-β-induced SMAD-2 phosphorylation and SMAD-2-dependent activation of the expression of the CAGA(12)LUC reporter plasmid. Overexpression of miR-155 altered the cellular responses to TGF-β by changing the expression of a set of genes that is involved in inflammation, fibrosis, and angiogenesis. Our study provides firm evidence of a role for miR-155 in directly repressing SMAD2 expression, and our results demonstrate the relevance of one of the two predicted target sites in SMAD2 3'-UTR. Altogether, our data uncover an important role for miR-155 in modulating the cellular response to TGF-β with possible implications in several human diseases where homeostasis of TGF-β might be altered.
转化生长因子-β（TGF-β）是一种具有重要作用的多功能细胞因子，可影响纤维化、血管生成和免疫抑制等过程。我们利用生物信息学方法，发现 SMAD2 是 TGF-β信号转导的一种介质，也是 microRNA-155（miR-155）的一个预测靶点。miRNA 是一类小的非编码 RNA，作为一种重要的基因表达调控因子而出现。miR-155 已被发现参与调节髓样细胞中的免疫反应。在这里，我们提供了 miR-155 与预测结合位点结合的直接证据，以及 miR-155 抑制 SMAD2 蛋白表达的能力。我们采用含有诱导型 miR-155 转基因的慢病毒转导单核细胞系（THP1-155），表明在持续过表达 miR-155 后，内源性 SMAD2 蛋白水平降低。SMAD2 的减少导致 TGF-β诱导的 SMAD-2 磷酸化和 SMAD-2 依赖性 CAGA(12)LUC 报告质粒表达的激活减少。miR-155 的过表达通过改变一组参与炎症、纤维化和血管生成的基因的表达，改变了细胞对 TGF-β的反应。我们的研究为 miR-155 在直接抑制 SMAD2 表达中的作用提供了确凿的证据，我们的结果证明了 SMAD2 3'-UTR 中两个预测靶点之一的相关性。总之，我们的数据揭示了 miR-155 在调节细胞对 TGF-β反应中的重要作用，这可能对 TGF-β 稳态发生改变的几种人类疾病具有重要意义。
