Division of Nephrology, University of Michigan Medical School, Ann Arbor, Michigan, United States of America.
PLoS One. 2011;6(12):e28710. doi: 10.1371/journal.pone.0028710. Epub 2011 Dec 14.
Actin dynamics has emerged at the forefront of podocyte biology. Slit diaphragm junctional adhesion protein Nephrin is necessary for development of the podocyte morphology and transduces phosphorylation-dependent signals that regulate cytoskeletal dynamics. The present study extends our understanding of Nephrin function by showing in cultured podocytes that Nephrin activation induced actin dynamics is necessary for lamellipodia formation. Upon activation Nephrin recruits and regulates a protein complex that includes Ship2 (SH2 domain containing 5' inositol phosphatase), Filamin and Lamellipodin, proteins important in regulation of actin and focal adhesion dynamics, as well as lamellipodia formation. Using the previously described CD16-Nephrin clustering system, Nephrin ligation or activation resulted in phosphorylation of the actin crosslinking protein Filamin in a p21 activated kinase dependent manner. Nephrin activation in cell culture results in formation of lamellipodia, a process that requires specialized actin dynamics at the leading edge of the cell along with focal adhesion turnover. In the CD16-Nephrin clustering model, Nephrin ligation resulted in abnormal morphology of actin tails in human podocytes when Ship2, Filamin or Lamellipodin were individually knocked down. We also observed decreased lamellipodia formation and cell migration in these knock down cells. These data provide evidence that Nephrin not only initiates actin polymerization but also assembles a protein complex that is necessary to regulate the architecture of the generated actin filament network and focal adhesion dynamics.
肌动蛋白动力学已成为足细胞生物学的前沿领域。裂孔隔膜连接黏附蛋白 Nephrin 是足细胞形态发生所必需的，它转导磷酸化依赖性信号，调节细胞骨架动力学。本研究通过显示在培养的足细胞中，Nephrin 激活诱导的肌动蛋白动力学对于形成片状伪足是必需的，从而扩展了我们对 Nephrin 功能的理解。在激活后，Nephrin 募集并调节一个包含 Ship2（含有 5'肌醇磷酸酶的 SH2 结构域）、Filamin 和 Lamellipodin 的蛋白质复合物，这些蛋白质在调节肌动蛋白和焦点附着动力学以及片状伪足形成中很重要。使用先前描述的 CD16-Nephrin 聚类系统，Nephrin 的连接或激活导致肌动蛋白交联蛋白 Filamin 的磷酸化，这是一种依赖于 p21 激活激酶的方式。在细胞培养中，Nephrin 的激活导致片状伪足的形成，这一过程需要细胞前缘的特殊肌动蛋白动力学以及焦点附着的转换。在 CD16-Nephrin 聚类模型中，当 Ship2、Filamin 或 Lamellipodin 被单独敲低时，Nephrin 的连接导致人足细胞中肌动蛋白尾部的异常形态。我们还观察到这些敲低细胞中片状伪足的形成和细胞迁移减少。这些数据提供了证据表明，Nephrin 不仅启动肌动蛋白聚合，而且组装一个蛋白质复合物，这对于调节生成的肌动蛋白丝网络的结构和焦点附着动力学是必需的。
