Department of Biomedical Engineering, Division of Hematology and Medical Oncology, Oregon Health & Science University, Portland, OR 97239, USA.
Arterioscler Thromb Vasc Biol. 2013 Jul;33(7):1544-51. doi: 10.1161/ATVBAHA.112.301165. Epub 2013 May 2.
Rho GTPase proteins play a central role in regulating the dynamics of the platelet actin cytoskeleton. Yet, little is known regarding how Rho GTPase activation coordinates platelet activation and function. In this study, we aimed to characterize the role of the Rho GTPase effector, p21 activated kinase (PAK), in platelet activation, lamellipodia formation, and aggregate formation under shear.
Stimulation of platelets with the glycoprotein receptor VI agonist, collagen-related peptide, rapidly activated PAK in a time course preceding phosphorylation of PAK substrates, LIM domain kinase LIMK1 and the MAPK/ERK kinase MEK, and the subsequent activation of MAPKs and Akt. Pharmacological inhibitors of PAK blocked signaling events downstream of PAK and prevented platelet secretion as well as platelet aggregation in response to collagen-related peptide. PAK inhibitors also prevented PAK activation and platelet spreading on collagen surfaces. PAK was also required for the formation of platelet aggregates and to maintain aggregate stability under physiological shear flow conditions.
These results suggest that PAK serves as an orchestrator of platelet functional responses after activation downstream of the platelet collagen receptor, glycoprotein receptor VI.
Rho GTPase 蛋白在调节血小板肌动球蛋白细胞骨架动力学方面起着核心作用。然而，对于 Rho GTPase 激活如何协调血小板激活和功能，人们知之甚少。在这项研究中，我们旨在研究 Rho GTPase 效应物 p21 激活激酶（PAK）在血小板激活、片状伪足形成和剪切下聚集中的作用。
用糖蛋白受体 VI 激动剂胶原蛋白相关肽刺激血小板，PAK 在磷酸化 PAK 底物、LIM 结构域激酶 LIMK1 和丝裂原活化蛋白激酶/细胞外信号调节激酶激酶 MEK 以及随后的 MAPK 和 Akt 激活之前，迅速激活 PAK 的时间过程。PAK 的药理学抑制剂阻断了 PAK 下游的信号事件，并防止了胶原蛋白相关肽引起的血小板分泌和聚集。PAK 抑制剂还阻止了 PAK 的激活和血小板在胶原表面的扩散。PAK 还需要在血小板胶原受体激活后形成血小板聚集，并在生理剪切流条件下维持聚集稳定性。
这些结果表明，PAK 作为血小板胶原受体激活后血小板功能反应的协调者。
