The PAK system links Rho GTPase signaling to thrombin-mediated platelet activation
The PAK system links Rho GTPase signaling to thrombin-mediated platelet activation
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DOI：
10.1152/ajpcell.00418.2012
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发表时间：
2013-09-01
影响因子：
5.5
通讯作者：
McCarty, Owen J. T.
中科院分区：
文献类型：
--
作者：
Aslan, Joseph E.;Baker, Sandra M.;McCarty, Owen J. T.
小 GTP 酶 Rho 家族对血小板肌动蛋白细胞骨架的调节对于正确维持止血至关重要。然而，人们对 Rho GTPase 家族成员（包括 Rac、Cdc42 和 Rho）的细胞内血小板激活如何转化为血小板肌动蛋白结构的变化知之甚少。为了更好地了解 Rho 家族 GTPase 如何协调血小板活化，我们鉴定了与 Rac1（Rho GTPase 家族成员）相关的血小板蛋白，以及血小板止血功能所必需的肌动蛋白调节蛋白。质谱分析显示，凝血酶激活血小板后，Rac1 与一组 p21 激活激酶 (PAK) 效应子结合，包括 GIT1、β PIX 和鸟嘌呤核苷酸交换因子 GEFH1。凝血酶激活血小板会触发 GIT1、GEFH1 和其他 PAK 效应子（包括 LIMK1 和 Merlin）的 PAK 依赖性磷酸化。 PAK 也是凝血酶介导的 MEK/ERK 通路激活、Akt、钙信号传导和磷脂酰丝氨酸 (PS) 暴露所必需的。抑制 PAK 信号传导可阻止凝血酶诱导的血小板聚集，并阻止响应凝血酶的血小板粘着斑和片状伪足形成。总之，这些结果表明，PAK 信号系统是血小板肌动蛋白动力学的关键协调器，将凝血酶刺激下游的 Rho GTPase 激活与 PAK 效应器功能、MAP 激酶激活、钙信号传导和血小板中的 PS 暴露联系起来。
Regulation of the platelet actin cytoskeleton by the Rho family of small GTPases is essential for the proper maintenance of hemostasis. However, little is known about how intracellular platelet activation from Rho GTPase family members, including Rac, Cdc42, and Rho, translate into changes in platelet actin structures. To better understand how Rho family GTPases coordinate platelet activation, we identified platelet proteins associated with Rac1, a Rho GTPase family member, and actin regulatory protein essential for platelet hemostatic function. Mass spectrometry analysis revealed that upon platelet activation with thrombin, Rac1 associates with a set of effectors of the p21-activated kinases (PAKs), including GIT1, beta PIX, and guanine nucleotide exchange factor GEFH1. Platelet activation by thrombin triggered the PAK-dependent phosphorylation of GIT1, GEFH1, and other PAK effectors, including LIMK1 and Merlin. PAK was also required for the thrombin-mediated activation of the MEK/ERK pathway, Akt, calcium signaling, and phosphatidylserine (PS) exposure. Inhibition of PAK signaling prevented thrombin-induced platelet aggregation and blocked platelet focal adhesion and lamellipodia formation in response to thrombin. Together, these results demonstrate that the PAK signaling system is a key orchestrator of platelet actin dynamics, linking Rho GTPase activation downstream of thrombin stimulation to PAK effector function, MAP kinase activation, calcium signaling, and PS exposure in platelets.