Gautreau A, Louvard D, Arpin M
Laboratoire de Morphogénèse et Signalisation Cellulaires, UMR 144 CNRS/Institut Curie, 75248 Paris Cedex 05, France.
J Cell Biol. 2000 Jul 10;150(1):193-203. doi: 10.1083/jcb.150.1.193.
ERM (ezrin, radixin, moesin) proteins act as linkers between the plasma membrane and the actin cytoskeleton. An interaction between their NH(2)- and COOH-terminal domains occurs intramolecularly in closed monomers and intermolecularly in head-to-tail oligomers. In vitro, phosphorylation of a conserved threonine residue (T567 in ezrin) in the COOH-terminal domain of ERM proteins disrupts this interaction. Here, we have analyzed the role of this phosphorylation event in vivo, by deriving stable clones producing wild-type, T567A, and T567D ezrin from LLC-PK1 epithelial cells. We found that T567A ezrin was poorly associated with the cytoskeleton, but was able to form oligomers. In contrast, T567D ezrin was associated with the cytoskeleton, but its distribution was shifted from oligomers to monomers at the membrane. Moreover, production of T567D ezrin induced the formation of lamellipodia, membrane ruffles, and tufts of microvilli. Both T567A and T567D ezrin affected the development of multicellular epithelial structures. Collectively, these results suggest that phosphorylation of ERM proteins on this conserved threonine regulates the transition from membrane-bound oligomers to active monomers, which induce and are part of actin-rich membrane projections.
ERM（埃兹蛋白、根蛋白、膜突蛋白）家族蛋白作为质膜与肌动蛋白细胞骨架之间的连接蛋白。在封闭的单体中，它们的氨基末端和羧基末端结构域之间会发生分子内相互作用；在头对头的寡聚体中，则会发生分子间相互作用。在体外，ERM蛋白羧基末端结构域中一个保守的苏氨酸残基（埃兹蛋白中的T567）发生磷酸化会破坏这种相互作用。在此，我们通过从LLC-PK1上皮细胞中获得产生野生型、T567A和T567D埃兹蛋白的稳定克隆，分析了这种磷酸化事件在体内的作用。我们发现，T567A埃兹蛋白与细胞骨架的结合较差，但能够形成寡聚体。相比之下，T567D埃兹蛋白与细胞骨架相关，但其在膜上的分布从寡聚体转变为单体。此外，T567D埃兹蛋白的产生诱导了片状伪足、膜皱褶和微绒毛簇的形成。T567A和T567D埃兹蛋白均影响多细胞上皮结构的发育。总的来说，这些结果表明，ERM蛋白在这个保守苏氨酸上的磷酸化调节了从膜结合寡聚体到活性单体的转变，而活性单体诱导并构成富含肌动蛋白的膜突起。
