Martel V, Racaud-Sultan C, Dupe S, Marie C, Paulhe F, Galmiche A, Block M R, Albiges-Rizo C
LEDAC, UMR CNRS/UJF 5538, Institut Albert Bonniot, Faculté de Médecine de Grenoble, 38706 La Tronche Cedex, France.
J Biol Chem. 2001 Jun 15;276(24):21217-27. doi: 10.1074/jbc.M102373200. Epub 2001 Mar 28.
Talin is a structural component of focal adhesion sites and is thought to be engaged in multiple protein interactions at the cytoplasmic face of cell/matrix contacts. Talin is a major link between integrin and the actin cytoskeleton and was shown to play an important role in focal adhesion assembly. Consistent with the view that talin must be activated at these sites, we found that phosphatidylinositol 4-monophosphate and phosphatidylinositol 4,5-bisphosphate (PI4,5P(2)) bound to talin in cells in suspension or at early stages of adhesion, respectively. When phosphoinositides were associated with phospholipid bilayer, talin/phosphoinositide association was restricted to PI4,5P(2). This association led to a conformational change of the protein. Moreover, the interaction between integrin and talin was greatly enhanced by PI4,5P(2)-induced talin activation. Finally, sequestration of PI4,5P(2) by a specific pleckstrin homology domain confirms that PI4,5P(2) is necessary for proper membrane localization of talin and that this localization is essential for the maintenance of focal adhesions. Our results support a model in which PI4,5P(2) exposes the integrin-binding site on talin. We propose that PI4,5P(2)-dependent signaling modulates assembly of focal adhesions by regulating integrin-talin complexes. These results demonstrate that activation of the integrin-binding activity of talin requires not only integrin engagement to the extracellular matrix but also the binding of PI4,5P(2) to talin, suggesting a possible role of lipid metabolism in organizing the sequential assembly of focal adhesion components.
踝蛋白是粘着斑位点的一种结构成分，被认为在细胞/基质接触的细胞质面参与多种蛋白质相互作用。踝蛋白是整合素与肌动蛋白细胞骨架之间的主要连接物，并已证明在粘着斑组装中起重要作用。与踝蛋白必须在这些位点被激活的观点一致，我们发现单磷酸磷脂酰肌醇和磷脂酰肌醇4,5-二磷酸（PI4,5P₂）分别在悬浮细胞中或粘附早期与踝蛋白结合。当磷酸肌醇与磷脂双层相关联时，踝蛋白/磷酸肌醇的结合仅限于PI4,5P₂。这种结合导致了蛋白质的构象变化。此外，PI4,5P₂诱导的踝蛋白激活大大增强了整合素与踝蛋白之间的相互作用。最后，通过特定的普列克底物蛋白同源结构域隔离PI4,5P₂证实，PI4,5P₂对于踝蛋白正确的膜定位是必需的，并且这种定位对于粘着斑的维持至关重要。我们的结果支持一种模型，即PI4,5P₂暴露了踝蛋白上的整合素结合位点。我们提出，PI4,5P₂依赖性信号传导通过调节整合素-踝蛋白复合物来调节粘着斑的组装。这些结果表明，踝蛋白整合素结合活性的激活不仅需要整合素与细胞外基质的结合，还需要PI4,5P₂与踝蛋白的结合，这表明脂质代谢在组织粘着斑成分的顺序组装中可能发挥作用。
