Molecular mechanism of inhibition of cell motility

鞘氨醇-1-磷酸(S1P)是一种生物活性的溶血磷脂，在不同类型的细胞中诱导多种生物反应。其中许多反应是由S1P受体、S1P_1/EDG1、S1P_3/EDG3和S1P_2/EDG5介导的。我们先前的研究表明，S1P_2/EDG5通过G_(12)和G_(13)蛋白介导抑制胰岛素样生长因子-I(IGF-I)诱导的RAC激活和细胞迁移，而S1P_1/EDG1和S1P_3/EDG3各自单独通过G_1蛋白介导RAC激活和刺激细胞迁移。然而，在S1P_2/EDG5信号通路中，G_(12)和G_(13)蛋白是如何介导抑制RAC和细胞迁移的，目前尚不清楚。我们发现，C3毒素可使Rho失活，而优势负性Rho A的表达可阻止S1P_2/EDG5对Rac和细胞迁移的抑制。另一方面，结构性活性Rho的表达抑制了IGF-I诱导的Rac激活和细胞迁移。然而，Rho激酶抑制剂不影响S1P_2/EDG5介导的抑制RAC或细胞迁移的作用。这些结果表明，在S1P_2/EDG5刺激下，Rho而不是Rho激酶介导了Rac活性和细胞迁移率的抑制。

Sphingosine-1-phosphate (S1P) is a bioactive lysophospholipid that induces a variety of biological responses in diverse cell types. Many of these responses are mediated by S1P receptors, S1P_1/EDG1, S1P_3/EDG3, and S1P_2/EDG5. We previously showed that S1P_2/EDG5, via G_<12> and G_<13> proteins, mediated inhibiton of insulin-like growth factor-I (IGF-I)-induced Rac activation and cell migration, whereas S1P_1/EDG1 and S1P_3/EDG3 each alone, via G_1 protein, mediated Rac activation and stimulation of cell migration. However, it is not known how G_<12> and G_<13> proteins mediate inhibition of Rac and cell migration in S1P_2/EDG5 signaling. We found that the pretreatment with C3 toxin, which inactivates Rho, and the expresson of dominat negative Rho A prevented S1P_2/EDG5-mediated inhibition of Rac and cell migration. On other hand, the expression of constitutively active Rho inhibited IGF-I induced Rac activation and cell migration. However, Rho kinase inhibitors did not affect S1P_2/EDG5-mediated inhibition of Rac or cell migration. These results indicate that Rho, but not Rho kinase, mediates inhibition of Rac activity and cell mobility on stimulation of S1P_2/EDG5.