Inactivation of R-Ras by Sema4D-Plexin-B1 GAP activity

Plexin-B1 functions as an R-Ras GTPase-activating protein (GAP) and directly and specifically down regulates R-Ras activity in response to Sema4D, inducing growth cone collapse. R-Ras inactivation promotes PI3K and Akt inactivation followed by GSK-3beta activation and CRMP inactivation. R-Ras inactivation also inhibits cell migration by regulating beta1 integrin activity. <br>

Plexin-B1 起作 R-Ras GTP 酶激活蛋白（GAP）的功能，并能直接且特异性地下调 R-Ras 活性，以响应 Sema4D 的作用，从而诱导生长锥的塌陷。R-Ras 的失活可促进 PI3K 和 Akt 的失活，继而导致 GSK-3β 的激活和 CRMP 的失活。此外，R-Ras 的失活亦通过调节 β1 整合素活性来抑制细胞迁移。