Fievet Bruno T, Gautreau Alexis, Roy Christian, Del Maestro Laurence, Mangeat Paul, Louvard Daniel, Arpin Monique
Laboratoire de Morphogenèse et Signalisation Cellulaires, UMR144 CNRS, 26 Rue d'Ulm, Institut Curie, Paris, Cedex 05, 75248 France.
J Cell Biol. 2004 Mar 1;164(5):653-9. doi: 10.1083/jcb.200307032.
Ezrin, a membrane-actin cytoskeleton linker, which participates in epithelial cell morphogenesis, is held inactive in the cytoplasm through an intramolecular interaction. Phosphatidylinositol 4,5-bisphosphate (PIP2) binding and the phosphorylation of threonine 567 (T567) are involved in the activation process that unmasks both membrane and actin binding sites. Here, we demonstrate that ezrin binding to PIP2, through its NH2-terminal domain, is required for T567 phosphorylation and thus for the conformational activation of ezrin in vivo. Furthermore, we found that the T567D mutation mimicking T567 phosphorylation bypasses the need for PIP2 binding for unmasking both membrane and actin binding sites. However, PIP2 binding and T567 phosphorylation are both necessary for the correct apical localization of ezrin and for its role in epithelial cell morphogenesis. These results establish that PIP2 binding and T567 phosphorylation act sequentially to allow ezrin to exert its cellular functions.
埃兹蛋白是一种膜 - 肌动蛋白细胞骨架连接蛋白，参与上皮细胞形态发生，通过分子内相互作用在细胞质中保持无活性状态。磷脂酰肌醇4,5 - 二磷酸（PIP2）结合以及苏氨酸567（T567）的磷酸化参与激活过程，该过程会暴露膜结合位点和肌动蛋白结合位点。在此，我们证明埃兹蛋白通过其NH2末端结构域与PIP2结合是T567磷酸化所必需的，因此也是埃兹蛋白在体内构象激活所必需的。此外，我们发现模拟T567磷酸化的T567D突变绕过了PIP2结合对于暴露膜结合位点和肌动蛋白结合位点的需求。然而，PIP2结合和T567磷酸化对于埃兹蛋白正确的顶端定位及其在上皮细胞形态发生中的作用都是必需的。这些结果表明，PIP2结合和T567磷酸化依次发挥作用，以使埃兹蛋白发挥其细胞功能。
