Department of Cell Biology, National Cerebral and Cardiovascular Center Research Institute, Suita, Osaka 565-8565, Japan.
J Cell Biol. 2013 Sep 16;202(6):901-16. doi: 10.1083/jcb.201301115. Epub 2013 Sep 9.
Reorganization of the actin cytoskeleton is responsible for dynamic regulation of endothelial cell (EC) barrier function. Circumferential actin bundles (CAB) promote formation of linear adherens junctions (AJs) and tightening of EC junctions, whereas formation of radial stress fibers (RSF) connected to punctate AJs occurs during junction remodeling. The small GTPase Rap1 induces CAB formation to potentiate EC junctions; however, the mechanism underlying Rap1-induced CAB formation remains unknown. Here, we show that myotonic dystrophy kinase-related CDC42-binding kinase (MRCK)-mediated activation of non-muscle myosin II (NM-II) at cell-cell contacts is essential for Rap1-induced CAB formation. Our data suggest that Rap1 induces FGD5-dependent Cdc42 activation at cell-cell junctions to locally activate the NM-II through MRCK, thereby inducing CAB formation. We further reveal that Rap1 suppresses the NM-II activity stimulated by the Rho-ROCK pathway, leading to dissolution of RSF. These findings imply that Rap1 potentiates EC junctions by spatially controlling NM-II activity through activation of the Cdc42-MRCK pathway and suppression of the Rho-ROCK pathway.
细胞骨架的重排负责调节内皮细胞（EC）屏障功能的动态变化。环形肌动蛋白束（CAB）促进线性黏附连接（AJ）的形成和 EC 连接的收紧，而与点状 AJ 相连的放射状应力纤维（RSF）的形成则发生在连接重塑过程中。小分子 GTP 酶 Rap1 诱导 CAB 的形成以增强 EC 连接；然而，Rap1 诱导的 CAB 形成的机制仍不清楚。在这里，我们表明肌萎缩性侧索硬化症相关 CDC42 结合激酶（MRCK）在细胞-细胞连接处对非肌肉肌球蛋白 II（NM-II）的激活对于 Rap1 诱导的 CAB 形成是必需的。我们的数据表明，Rap1 诱导 FGD5 依赖性 Cdc42 在细胞连接处激活，通过 MRCK 局部激活 NM-II，从而诱导 CAB 的形成。我们进一步揭示 Rap1 抑制 Rho-ROCK 通路刺激的 NM-II 活性，导致 RSF 的溶解。这些发现表明，Rap1 通过激活 Cdc42-MRCK 通路和抑制 Rho-ROCK 通路来空间控制 NM-II 活性，从而增强 EC 连接。
