Modulation of endogenous smad expression in normal skin fibroblasts by transforming growth factor-β
Modulation of endogenous smad expression in normal skin fibroblasts by transforming growth factor-β
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DOI：
10.1006/excr.2000.4930
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发表时间：
2000-08-01
影响因子：
3.7
通讯作者：
Varga, J
中科院分区：
文献类型：
--
作者：
Mori, Y;Chen, SJ;Varga, J
转化生长因子-β(转化生长因子-β)刺激胶原合成在生理性组织修复和病理性纤维化中起着基础性作用，细胞内蛋白SMAD家族成员被转化生长因子-β受体磷酸化，并将信号传递给特定的转化生长因子-β诱导基因。配体结合通过SMAD途径启动信号传递，但目前尚不清楚信号是如何终止的。Smads的表达和调控主要是通过瞬时表达系统在转化细胞中进行的。在本研究中，我们研究了转化生长因子-β对体外未转化的正常皮肤成纤维细胞内源性Smads的生理调节作用。经转化生长因子-β处理后，Smad3和SRAD4呈时间和剂量依赖性地从胞浆移位到胞核。Smad3和Smads基因转录产物的稳定性不受转化生长因子-β1或转化生长因子-β3的影响，而拮抗型Smad7的表达可被快速、短暂地诱导。放线菌酮可阻断Smad3的抑制作用，但不能阻断Smad7mRNA的表达，表明Smad7是成纤维细胞中转化生长因子β的即时早期基因靶点。在Smad4缺失的乳腺癌细胞中，转化生长因子-β未能调节Smad的表达，这表明Smads通过调节自身对配体的反应而发挥调节作用。这些结果表明，转化生长因子-β不仅能激活原代皮肤成纤维细胞中SMAD信号通路的功能，而且对内源性SMAD的表达和细胞内转运也有很强的作用。结合最近的报道，泛素化在SMAD周转中的作用，这些发现表明，在调节成纤维细胞中SMAD介导的转化生长因子-β信号方面存在多个水平的控制。(C)2000年学术出版社。
Transforming growth factor-beta (TGF-beta) stimulation of collagen synthesis plays a fundamental role in physiological tissue repair as well as pathological fibrosis, Members of the SMAD family of intracellular proteins are phosphorylated by TGF-beta receptors and convey signals to specific TGF-beta-inducible genes. Ligand binding initiates signaling through the SMAD pathway, but it is unknown how signaling is terminated. The expression and regulation of Smads have been characterized mostly in transformed cells using transient expression systems. In this study, we investigated the physiological regulation of endogenous Smads by TGF-beta in nontransformed normal skin fibroblasts in vitro. Treatment with TGF-beta resulted in time- and dose-dependent translocation of SMAD3 and SRAD4 from the cytoplasm to the nucleus. The levels of SMAD3 and Smads mRNA were profoundly down-regulated by TGF-beta 1 or TGF-beta 3 in a time-dependent manner, whereas expression of antagonistic Smad7 was rapidly and transiently induced, The stability of Smad3 mRNA transcripts was unaffected by TGF-beta. Cycloheximide prevented the inhibition of Smad3, but not the induction of Smad7, mRNA expression by TGF-beta 1, identifying Smad7 as an immediate-early gene target of TGF-beta in fibroblasts. In Smad4-deficient breast cancer cells, TGF-beta failed to modulate Smad expression, suggesting that SMADs mediate their own regulation in response to ligand. These results demonstrate that TGF-beta not only triggers functional activation of the SMAD signaling cascade in primary skin fibroblasts, but also simultaneously exerts potent effects on endogenous SMAD expression and intracellular trafficking. Taken together with recent reports implicating ubiquitination in SMAD turnover, these findings indicate the existence of multiple levels of control for modulating SMAD-mediated TGF-beta signaling in fibroblasts. (C) 2000 Academic Press.