A phosphoinositide 3-kinase-AKT-nitric oxide-cGMP signaling pathway in stimulating platelet secretion and aggregation.
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.
Stojanovic
Aleksandra
A
Department of Pharmacology, University of Illinois College of Medicine, 835 South Wolcott Avenue, Chicago, IL 60612, USA.
Marjanovic
Jasna A
JA
Brovkovych
Viktor M
VM
Peng
Xiaoding
X
Hay
Nissim
N
Skidgel
Randal A
RA
Du
Xiaoping
X
D001792:Blood Platelets / Q000378:metabolism*; D006152:Cyclic GMP / Q000031:analogs & derivatives / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D008954:Models, Biological; D009569:Nitric Oxide / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D015539:Platelet Activation; D010974:Platelet Aggregation; D015398:Signal Transduction; D013917:Thrombin / Q000378:metabolism; D013997:Time Factors
D004791:Enzyme Inhibitors; C016276:8-bromocyclic GMP; D009569:Nitric Oxide; D019869:Phosphatidylinositol 3-Kinases; D013917:Thrombin; D006152:Cyclic GMP