Both Sp1 and Smad participate in mediating TGF-β1-induced HGF receptor expression in renal epithelial cells
Both Sp1 and Smad participate in mediating TGF-β1-induced HGF receptor expression in renal epithelial cells
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DOI：
10.1152/ajprenal.00318.2003
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发表时间：
2005-01-01
影响因子：
4.2
通讯作者：
Liu, YH
中科院分区：
文献类型：
--
作者：
Zhang, XH;Yang, JW;Liu, YH
肝细胞生长因子 (HGF) 受体是由 c-met 原癌基因编码的跨膜受体酪氨酸激酶。在这项研究中，我们证明小鼠阻塞性损伤后肾脏中的 c-met 表达上调。由于c-met诱导模式与体内转化生长因子-β1（TGF-β1）表达密切相关，因此我们进一步在体外研究了TGF-β1对肾小管上皮（HKC）细胞中c-met表达的调节。实时 RT-PCR 以及 Northern 和 Western blot 分析表明，TGF-β1 显着诱导 HKC 细胞中的 c-met 表达，这主要发生在基因转录水平。抑制性 Smad7 的过度表达完全消除了 c-met 诱导，表明其对 Smad 信号传导的依赖。有趣的是，TGF-β1 诱导的 c-met 表达也取决于功能性 Sp1，因为 Sp1 与光神霉素 A 结合的消除消除了 HKC 细胞中的 c-met 诱导。转染和序列分析鉴定了 c-met 启动子中的顺式作用 TGF-β1 响应区，其中存在推定的 Smad 结合元件 (SBE) 和相邻的 Sp1 位点。 TGF-β1不仅诱导Smad与c-met启动子中的SBE/Sp1位点结合，而且还增强Sp蛋白的结合。此外，Sp1 可以以 TGF-β1 依赖性方式与 Smads 形成复合物。这些结果表明肾上皮细胞中TGF-β1控制c-met表达的新调控机制，其中Smad和Sp蛋白参与并配合激活c-met基因转录。
Hepatocyte growth factor (HGF) receptor is a transmembrane receptor tyrosine kinase encoded by the c-met protooncogene. In this study, we demonstrated that c-met expression was upregulated in the kidney after obstructive injury in mice. Because the pattern of c-met induction was closely correlated with transforming growth factor-beta1 (TGF-beta1) expression in vivo, we further investigated the regulation of c-met expression in renal tubular epithelial (HKC) cells by TGF-beta1 in vitro. Real-time RT-PCR and Northern and Western blot analyses revealed that TGF-beta1 significantly induced c-met expression in HKC cells, which primarily took place at the gene transcriptional level. Overexpression of inhibitory Smad7 completely abolished c-met induction, indicating its dependence on Smad signaling. Interestingly, TGF-beta1-induced c-met expression was also contingent on a functional Sp1, as ablation of Sp1 binding with mithramycin A abrogated c-met induction in HKC cells. Transfection and sequence analysis identified a cis-acting TGF-beta1-responsive region in the c-met promoter, in which resided a putative Smad-binding element (SBE) and an adjacent Sp1 site. TGF-beta1 not only induced Smad binding to the SBE/Sp1 sites in the c-met promoter, but also enhanced the binding of Sp proteins. Furthermore, Sp1 could form a complex with Smads in a TGF-beta1-dependent fashion. These results suggest a novel regulatory mechanism controlling c-met expression by TGF-beta1 in renal epithelial cells, in which both Smad and Sp proteins participate and cooperate in activating c-met gene transcription.