title: ADP-stimulated activation of Akt during integrin outside-in signaling promotes platelet spreading by inhibiting glycogen synthase kinase-3β.
abstract: OBJECTIVE
  Integrins mediate platelet adhesion and transmit outside-in signals leading to platelet spreading. Phosphoinositide 3-kinases (PI3Ks) play a critical role in outside-in signaling and platelet spreading; however, the mechanisms of PI3K activation and function in outside-in signaling are unclear. We sought to determine the role of the Akt family of serine/threonine kinases and activation mechanisms of the PI3K/Akt pathway in outside-in signaling.
  
  
  RESULTS
  Akt inhibitors and Akt3 knockout inhibited platelet spreading on fibrinogen, indicating that Akt is important in integrin outside-in signaling. Akt inhibitors and Akt3 knockout also diminished integrin-dependent phosphorylation of glycogen synthase kinase-3β. Inhibition of glycogen synthase kinase-3β reversed the inhibitory effects of Akt3 knockout and inhibitors of Akt or PI3K on platelet spreading, indicating that glycogen synthase kinase-3β is a downstream target of Akt in outside-in signaling. Integrin-dependent activation of the PI3K-Akt pathway requires Src family kinase. Akt phosphorylation is also significantly inhibited in ADP receptor P2Y12 knockout platelets and further inhibited in P2Y12 knockout platelets treated with a P2Y1 antagonist. Consistently, P2Y12 knockout and P2Y1 inhibition together reduced platelet spreading.
  
  
  CONCLUSIONS
  These results demonstrate that integrin outside-in signaling and platelet spreading requires Src family kinase-dependent and ADP receptor-amplified activation of the PI3K-Akt-GSK-3β pathway.
authors: Department of Pharmacology, University of Illinois College of Medicine, 835 S. Wolcott Avenue, Chicago, IL 60612, USA.
authors: Kelly A
authors: KA
authors: O'Brien
authors: T Kent
authors: TK
authors: Gartner
authors: Nissim
authors: N
authors: Hay
authors: Xiaoping
authors: X
authors: Du
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism*; D000818:Animals; D001792:Blood Platelets / Q000187:drug effects / Q000201:enzymology*; D048430:Cell Shape / Q000187:drug effects; D004789:Enzyme Activation; D038362:Glycogen Synthase Kinase 3 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D016023:Integrins / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D015539:Platelet Activation / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D058921:Purinergic P2Y Receptor Antagonists / Q000494:pharmacology; D058472:Receptors, Purinergic P2Y1 / Q000187:drug effects / Q000378:metabolism; D058925:Receptors, Purinergic P2Y12 / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013997:Time Factors; D019061:src-Family Kinases / Q000378:metabolism
chemical_list: D016023:Integrins; C548576:P2RY12 protein, human; C548577:P2ry12 protein, mouse; D047428:Protein Kinase Inhibitors; D058921:Purinergic P2Y Receptor Antagonists; D058472:Receptors, Purinergic P2Y1; D058925:Receptors, Purinergic P2Y12; D000244:Adenosine Diphosphate; D019869:Phosphatidylinositol 3-Kinases; D019061:src-Family Kinases; C514862:Akt1 protein, mouse; C494922:Akt2 protein, mouse; C491753:Akt3 protein, mouse; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; C000605507:Gsk3b protein, mouse; D051057:Proto-Oncogene Proteins c-akt; D038362:Glycogen Synthase Kinase 3