Stojanovic Aleksandra, Marjanovic Jasna A, Brovkovych Viktor M, Peng Xiaoding, Hay Nissim, Skidgel Randal A, Du Xiaoping
Department of Pharmacology, University of Illinois College of Medicine, 835 South Wolcott Avenue, Chicago, IL 60612, USA.
J Biol Chem. 2006 Jun 16;281(24):16333-9. doi: 10.1074/jbc.M512378200. Epub 2006 Apr 13.
Phosphoinositide 3-kinase (PI3K) and Akt play important roles in platelet activation. However, the downstream mechanisms mediating their functions are unclear. We have recently shown that nitric-oxide (NO) synthase 3 and cGMP-dependent protein kinase stimulate platelet secretion and aggregation. Here we show that PI3K-mediated Akt activation plays an important role in agonist-stimulated platelet NO synthesis and cGMP elevation. Agonist-induced elevation of NO and cGMP was inhibited by Akt inhibitors and reduced in Akt-1 knock-out platelets. Akt-1 knock-out or Akt inhibitor-treated platelets showed reduced platelet secretion and aggregation in response to low concentrations of agonists, which can be reversed by low concentrations of 8-bromo-cGMP or sodium nitroprusside (an NO donor). Similarly, PI3K inhibitors diminished elevation of cGMP and inhibited platelet secretion and the second wave platelet aggregation, which was also partially reversed by 8-bromo-cGMP. These results indicate that the NO-cGMP pathway is an important downstream mechanism mediating PI3K and Akt signals leading to platelet secretion and aggregation. Conversely, the PI3K-Akt pathway is the major upstream mechanism responsible for activating the NO-cGMP pathway in platelets. Thus, this study delineates a novel platelet activation pathway involving sequential activation of PI3K, Akt, nitric-oxide synthase 3, sGC, and cGMP-dependent protein kinase.
磷酸肌醇-3激酶（PI3K）和Akt在血小板活化过程中发挥重要作用。然而，介导其功能的下游机制尚不清楚。我们最近发现一氧化氮（NO）合酶3和环磷酸鸟苷（cGMP）依赖性蛋白激酶可刺激血小板分泌和聚集。在此我们表明，PI3K介导的Akt活化在激动剂刺激的血小板NO合成和cGMP升高过程中发挥重要作用。Akt抑制剂可抑制激动剂诱导的NO和cGMP升高，且在Akt-1基因敲除的血小板中这一升高现象有所降低。Akt-1基因敲除或经Akt抑制剂处理的血小板对低浓度激动剂的反应中，血小板分泌和聚集减少，而低浓度的8-溴-cGMP或硝普钠（一种NO供体）可使其逆转。同样，PI3K抑制剂可减少cGMP升高，并抑制血小板分泌和第二波血小板聚集，8-溴-cGMP也可部分逆转这一现象。这些结果表明，NO-cGMP途径是介导PI3K和Akt信号导致血小板分泌和聚集的重要下游机制。相反，PI3K-Akt途径是负责激活血小板中NO-cGMP途径的主要上游机制。因此，本研究描绘了一条涉及PI3K、Akt、一氧化氮合酶3、可溶性鸟苷酸环化酶（sGC）和cGMP依赖性蛋白激酶顺序激活的新型血小板活化途径。
