Type Iα phosphatidylinositol-4-phosphate 5-kinase mediates Rac-dependent actin assembly
Type Iα phosphatidylinositol-4-phosphate 5-kinase mediates Rac-dependent actin assembly
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DOI：
10.1016/s0960-9822(00)00315-8
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发表时间：
2000-02-10
期刊：
影响因子：
9.2
通讯作者：
Carpenter, CL
中科院分区：
文献类型：
--
作者：
Tolias, KF;Hartwig, JH;Carpenter, CL
肌动蛋白聚合在多种细胞过程中是必不可少的，包括运动、细胞分裂和形状改变。肌动蛋白聚合的诱导需要产生游离的肌动蛋白细丝带刺末端，这是由Arp2/3复合体[3-7]启动的先前存在的肌动蛋白细丝[1，2]或从头成核的结果。尽管对调节肌动蛋白组装的信号通路知之甚少，但Rho家族的小GTP酶似乎是必要的[8-11]。在凝血酶刺激的血小板中，Rho家族GTP酶Rad通过刺激肌动蛋白细丝带刺末端的脱帽而诱导肌动蛋白聚合[2]。然而，Pac监管放开上限的机制尚不清楚。我们以前证明了Pac以一种不依赖于GTP的方式与I型磷脂酰肌醇-4-磷酸B-激酶(PIP-5-Kinase)相互作用[12，13]，因为PIP-B-激酶合成了磷脂酰肌醇-4，5-二磷酸(PI(4，5)P-2)，这是一种将覆盖蛋白从肌动蛋白细丝的倒钩末端解离出来的脂类[14-16]，它们是介导Pac对肌动蛋白组装影响的很好的候选者。在这里，我们已经确定RAC相关的PIP 5-激酶是PIP B-激酶的α和β亚型，当加入到通透性的血小板中时，PIP B-Kα诱导肌动蛋白细丝的解帽和组装。相反，一个非激活的PIP5激酶α突变体不能诱导肌动蛋白组装，也不能阻断凝血酶或Pac刺激的组装。此外，凝血酶或Pac诱导的肌动蛋白聚合被Pac羧基末端的点突变所抑制，该点突变破坏了PIP-L-激酶结合，这些结果表明PIP B-激酶α是凝血酶和Rac依赖的肌动蛋白组装的关键介质。
Actin polymerization is essential for a variety of cellular processes including movement, cell division and shape change. The induction of actin polymerization requires the generation of free actin filament barbed ends, which results from the severing or uncapping of pre-existing actin filaments [1,2], or de novo nucleation, initiated by the Arp2/3 complex [3-7]. Although little is known about the signaling pathways that regulate actin assembly, small GTPases of the Rho family appear to be necessary [8-11]. In thrombin-stimulated platelets, the Rho family GTPase Rad induces actin polymerization by stimulating the uncapping of actin filament barbed ends [2]. The mechanism by which Pac regulates uncapping is unclear, however. We previously demonstrated that Pac interacts with a type I phosphatidylinositol-4-phosphate B-kinase (PIP 5-kinase) in a GTP-independent manner [12,13], Because PIP B-kinases synthesize phosphatidylinositol-4,5-bisphosphate (PI(4,5)P-2), a lipid that dissociates capping proteins from the barbed ends of actin filaments [14-16], they are good candidates for mediating the effects of Pac on actin assembly. Here, we have identified the Rac-associated PIP 5-kinase as the PIP B-kinase isoforms alpha and beta When added to permeabilized platelets, PIP B-kinase alpha induced actin filament uncapping and assembly. In contrast, a kinase-inactive PIP 5 kinase alpha mutant failed to induce actin assembly and blocked assembly stimulated by thrombin or Pac. Furthermore, thrombin- or Pac-induced actin polymerization was inhibited by a point mutation in the carboxyl terminus of Pac that disrupts PIP L-kinase binding, These results demonstrate that PIP B-kinase alpha is a critical mediator of thrombin- and Rac dependent actin assembly.