Early endosomal regulation of Smad-dependent signaling in endothelial cells
Early endosomal regulation of Smad-dependent signaling in endothelial cells
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DOI：
10.1074/jbc.m107983200
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发表时间：
2002-05-17
影响因子：
4.8
通讯作者：
Fotsis, T
中科院分区：
文献类型：
--
作者：
Panopoulou, E;Gillooly, DJ;Fotsis, T
转化生长因子β（TGF β）受体需要SARA用于下游转导Smad蛋白的磷酸化。SARA是一种FYVE指蛋白，与膜脂质结合，表明激活的受体可能在离散的内吞位置与下游信号分子相互作用。在本研究中，我们揭示了一个关键的作用，早期内吞隔室在调节Smad依赖的信号。SARA不仅定位于早期内体，而且其最小FYVE指序列足以用于早期内体靶向。缺乏FYVE指的SARA突变蛋白的表达抑制内皮细胞中的下游激活素A信号传导。此外，Rab 5（早期内体动力学的关键蛋白）的显性负突变体引起Smads的磷酸化和核转位，导致内皮细胞中Smad依赖性启动子的组成性（即配体非依赖性）转录激活。由于使用发动蛋白和RN-tre的K44 A阴性突变体抑制内吞作用并不导致Smad依赖性转录的激活，显性阴性Rab 5的作用可能是在早期内体水平上组成性形成的TGF β/激活素I/II型受体复合物的膜运输改变的结果。结果表明，早期内体动力学和TGF β/激活素信号转导通路之间的重要互连。
Transforming growth factor beta (TGFbeta) receptors require SARA for phosphorylation of the downstream transducing Smad proteins. SARA, a FYVE finger protein, binds to membrane lipids suggesting that activated receptors may interact with downstream signaling molecules at discrete endocytic locations. In the present study, we reveal a critical role for the early endocytic compartment in regulating Smad-dependent signaling. Not only is SARA localized on early endosomes, but also its minimal FYVE finger sequence is sufficient for early endosomal targeting. Expression of a SARA mutant protein lacking the FYVE finger inhibits downstream activin A signaling in endothelial cells. Moreover, a dominant-negative mutant of Rab5, a crucial protein for early endosome dynamics, causes phosphorylation and nuclear translocation of Smads leading to constitutive (i.e. ligand independent) transcriptional activation of a Smad-dependent promoter in endothelial cells. As inhibition of endocytosis using the K44A negative mutant of dynamin and RN-tre did not lead to activation of Smad-dependent transcription, the effects of the dominant-negative Rab5 are likely to be a consequence of altered membrane trafficking of constitutively formed TGFbeta/activin type I/II receptor complexes at the level of early endosomes. The results suggest an important interconnection between early endosomal dynamics and TGFbeta/activin signal transduction pathways.