Relative contribution of G-protein-coupled pathways to protease-activated receptor-mediated Akt phosphorylation in platelets.
Protease-activated receptors (PARs) activate Gq and G(12/13) pathways, as well as Akt (protein kinase B [PKB/Akt]) in platelets. However, the relative contribution of different G-protein pathways to Akt phosphorylation has not been elucidated. We investigated the contribution of Gq and G(12/13) to Gi/Gz-mediated Akt phosphorylation downstream of PAR activation. Selective G(12/13) activation failed to cause Akt phosphorylation in human and Galpha q-deficient mouse platelets. However, supplementing Gi/Gz signaling to G(12/13) caused significant increase in Akt phosphorylation, confirming that G(12/13) potentiates Akt phosphorylation. Inhibition of PAR-mediated Akt phosphorylation in the presence of the Gq-selective inhibitor YM-254890 was restored to the normal extent achieved by PAR agonists if supplemented with Gi signaling, indicating that Gq does not have any direct effect on Akt phosphorylation. Selective G(12/13) activation resulted in Src kinase activation, and Akt phosphorylation induced by costimulation of G(12/13) and Gi/Gz was inhibited by a Src kinase inhibitor but not by a Rho kinase inhibitor. These data demonstrate that G(12/13), but not Gq, is essential for thrombin-induced Akt phosphorylation in platelets, whereas Gq indirectly contributes to Akt phosphorylation through Gi stimulation by secreted ADP. G(12/13) activation might mediate its potentiating effect through Src activation, and Src kinases play an important role in thrombin-mediated Akt phosphorylation.
Kim
Soochong
S
Department of Physiology, Temple University School of Medicine, Philadelphia, PA 19140, USA.
Jin
Jianguo
J
Kunapuli
Satya P
SP
D000244:Adenosine Diphosphate / Q000378:metabolism; D000818:Animals; D001792:Blood Platelets / Q000166:cytology / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D044365:GTP-Binding Protein alpha Subunits, G12-G13 / Q000172:deficiency / Q000378:metabolism*; D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D010456:Peptides, Cyclic / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D011499:Protein Processing, Post-Translational / Q000187:drug effects / Q000502:physiology; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D044462:Receptors, Proteinase-Activated / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D013917:Thrombin / Q000378:metabolism; D019061:src-Family Kinases / Q000378:metabolism
D004791:Enzyme Inhibitors; D010456:Peptides, Cyclic; D044462:Receptors, Proteinase-Activated; C475455:YM-254890; D000244:Adenosine Diphosphate; D019061:src-Family Kinases; D051057:Proto-Oncogene Proteins c-akt; D013917:Thrombin; D044365:GTP-Binding Protein alpha Subunits, G12-G13; D043802:GTP-Binding Protein alpha Subunits, Gq-G11