Role of phosphoinositide 3-kinase beta in glycoprotein VI-mediated Akt activation in platelets.
Glycoprotein (GP) VI is a critical platelet collagen receptor. Phosphoinositide 3-kinase (PI3K) plays an important role in GPVI-mediated platelet activation, yet the major PI3K isoforms involved in this process have not been identified. In addition, stimulation of GPVI results in the activation of Akt, a downstream effector of PI3K. Thus, we investigated the contribution of PI3K isoforms to GPVI-mediated platelet activation and Akt activation. A protein kinase C inhibitor GF 109203X or a P2Y(12) receptor antagonist AR-C69931MX partly reduced GPVI-induced Akt phosphorylation. Platelets from mice dosed with clopidogrel also showed partial Akt phosphorylation, indicating that GPVI-mediated Akt phosphorylation is regulated by both secretion-dependent and -independent pathways. In addition, GPVI-induced Akt phosphorylation in the presence of ADP antagonists was completely inhibited by PI3K inhibitor LY294002 and PI3Kbeta inhibitor TGX-221 indicating an essential role of PI3Kbeta in Akt activation directly downstream of GPVI. Moreover, GPVI-mediated platelet aggregation, secretion, and intracellular Ca(2+) mobilization were significantly inhibited by TGX-221, and less strongly inhibited by PI3Kalpha inhibitor PIK75, but were not affected by PI3Kgamma inhibitor AS252424 and PI3Kdelta inhibitor IC87114. Consistently, GPVI-induced integrin alpha(IIb)beta(3) activation of PI3Kgamma(-/-) and PI3Kdelta(-/-) platelets also showed no significant difference compared with wild-type platelets. These results demonstrate that GPVI-induced Akt activation in platelets is dependent in part on G(i) stimulation through P2Y(12) receptor activation by secreted ADP. In addition, a significant portion of GPVI-dependent, ADP-independent Akt activation also exists, and PI3Kbeta plays an essential role in GPVI-mediated platelet aggregation and Akt activation.
Kim
Soochong
S
Department of Physiology, Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA.
Mangin
Pierre
P
Dangelmaier
Carol
C
Lillian
Rivka
R
Jackson
Shaun P
SP
Daniel
James L
JL
Kunapuli
Satya P
SP
D000818:Animals; D001792:Blood Platelets / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005434:Flow Cytometry / Q000379:methods; D006801:Humans; D051379:Mice; D008822:Mice, Transgenic; D008954:Models, Biological; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism* / Q000502:physiology*; D010766:Phosphorylation; D010974:Platelet Aggregation; D010980:Platelet Membrane Glycoproteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*
D004791:Enzyme Inhibitors; D010980:Platelet Membrane Glycoproteins; C098341:platelet membrane glycoprotein VI; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt
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