Lepley Denise, Paik Ji-Hye, Hla Timothy, Ferrer Fernando
Department of Urology and Surgery, Connecticut Children's Medical Center, Hartford, Connecticut, USA.
Cancer Res. 2005 May 1;65(9):3788-95. doi: 10.1158/0008-5472.CAN-04-2311.
Sphingosine 1-phosphate (S1P) is a lysophospholipid that exerts a variety of responses in cells such as proliferation, migration, and survival. These effects are mediated by G protein-coupled receptors on the cell surface (S1P1-5), which activate downstream signaling intermediates such as Rac and Rho GTPases. Mechanisms of S1P action in human glioblastoma cells are not well defined. S1P receptors (1-5) and S1P-metabolizing enzymes were expressed in three human glioblastoma cell lines. S1P had a profound and differential effect on glioblastoma cell migration. U87 cells treated with S1P showed a significant increase in migration, whereas U118 and U138 cell lines were strongly inhibited. S1P-mediated inhibition correlated with S1P2 receptor expression. FTY720-P, an S1P analogue that binds all S1P receptors except S1P2, did not inhibit glioblastoma cell migration. Overexpression of S1P2 further suppressed migration, and blockage of S1P2 mRNA expression by small interfering RNA reversed the inhibitory effect. Contrary to previous reports showing bimodal regulation of Rac activity and migration by S1P2 receptor stimulation, both Rac1 and RhoA GTPases were activated by S1P treatment in native cells and cells overexpressing S1P2. Treatment of U118 cells with the Rho-associated protein kinase (ROCK) inhibitor Y-27632 restored migration suggesting that ROCK-dependent mechanisms are important. Actin staining of S1P stimulated U118 cells overexpressing beta-galactosidase resulted in pronounced stress fiber formation that was exacerbated by S1P2 overexpression, partially blocked by S1P1, or totally abolished by pretreatment with Y-27632. These data provide evidence of a novel mechanism of S1P inhibition of tumor cell migration via Rho kinase-dependent pathway.
鞘氨醇-1-磷酸（S1P）是一种溶血磷脂，可在细胞中引发多种反应，如增殖、迁移和存活。这些效应由细胞表面的G蛋白偶联受体（S1P1-5）介导，它们激活下游信号中间体，如Rac和Rho GTP酶。S1P在人胶质母细胞瘤细胞中的作用机制尚不明确。S1P受体（1-5）和S1P代谢酶在三种人胶质母细胞瘤细胞系中表达。S1P对胶质母细胞瘤细胞迁移有深远且不同的影响。用S1P处理的U87细胞迁移显著增加，而U118和U138细胞系则受到强烈抑制。S1P介导的抑制与S1P2受体表达相关。FTY720-P是一种S1P类似物，可结合除S1P2之外的所有S1P受体，它不会抑制胶质母细胞瘤细胞迁移。S1P2的过表达进一步抑制迁移，小干扰RNA阻断S1P2 mRNA表达可逆转这种抑制作用。与先前报道的S1P2受体刺激对Rac活性和迁移的双峰调节相反，在天然细胞和过表达S1P2的细胞中，S1P处理均可激活Rac1和RhoA GTP酶。用Rho相关蛋白激酶（ROCK）抑制剂Y-27632处理U118细胞可恢复迁移，表明ROCK依赖性机制很重要。对过表达β-半乳糖苷酶的S1P刺激的U118细胞进行肌动蛋白染色，导致明显的应力纤维形成，S1P2过表达会加剧这种形成，S1P1可部分阻断，或用Y-27632预处理可完全消除。这些数据提供了S1P通过Rho激酶依赖性途径抑制肿瘤细胞迁移的新机制的证据。
