title: Gq-mediated Akt translocation to the membrane: a novel PIP3-independent mechanism in platelets.
abstract: Akt is an important signaling molecule regulating platelet aggregation. Akt is phosphorylated after translocation to the membrane through Gi signaling pathways by a phosphatidylinositol-3,4,5-trisphosphate (PIP3)-dependent mechanism. However, Akt is more robustly phosphorylated by thrombin compared with adenosine 5'-diphosphate in platelets. This study investigated the mechanisms of Akt translocation as a possible explanation for this difference. Stimulation of washed human platelets with protease-activated receptor agonists caused translocation of Akt to the membrane rapidly, whereas phosphorylation occurred later. The translocation of Akt was abolished in the presence of a Gq-selective inhibitor or in Gq-deficient murine platelets, indicating that Akt translocation is regulated downstream of Gq pathways. Interestingly, phosphatidylinositol 3-kinase (PI3K) inhibitors or P2Y12 antagonist abolished Akt phosphorylation without affecting Akt translocation to the membrane, suggesting that Akt translocation occurs through a PI3K/PIP3/Gi-independent mechanism. An Akt scaffolding protein, p21-activated kinase (PAK), translocates to the membrane after stimulation with protease-activated receptor agonists in a Gq-dependent manner, with the kinetics of translocation similar to that of Akt. Coimmunoprecipitation studies showed constitutive association of PAK and Akt, suggesting a possible role of PAK in Akt translocation. These results show, for the first time, an important role of the Gq pathway in mediating Akt translocation to the membrane in a novel Gi/PI3K/PIP3-independent mechanism.
authors.affiliation: Department of Physiology, Sol Sherry Thrombosis Research Center, Temple University School of Medicine, Philadelphia, PA; and.
authors.forename: Rachit
authors.initials: R
authors.lastname: Badolia
authors.affiliation: Department of Physiology, Sol Sherry Thrombosis Research Center, Temple University School of Medicine, Philadelphia, PA; and.
authors.forename: Bhanu Kanth
authors.initials: BK
authors.lastname: Manne
authors.affiliation: Department of Physiology, Sol Sherry Thrombosis Research Center, Temple University School of Medicine, Philadelphia, PA; and.
authors.forename: Carol
authors.initials: C
authors.lastname: Dangelmaier
authors.affiliation: Fox Chase Cancer Center, Temple Health, Philadelphia, PA.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Chernoff
authors.affiliation: Department of Physiology, Sol Sherry Thrombosis Research Center, Temple University School of Medicine, Philadelphia, PA; and.
authors.forename: Satya P
authors.initials: SP
authors.lastname: Kunapuli
mesh_terms: D000818:Animals; D001692:Biological Transport; D001792:Blood Platelets / Q000166:cytology / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000378:metabolism*; D006801:Humans; D051379:Mice; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism*; D010766:Phosphorylation; D010974:Platelet Aggregation; D021381:Protein Transport; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D015398:Signal Transduction; D013917:Thrombin / Q000378:metabolism
chemical_list: D018129:Phosphatidylinositol Phosphates; C055525:phosphatidylinositol 3-phosphate; C514862:Akt1 protein, mouse; D051057:Proto-Oncogene Proteins c-akt; D013917:Thrombin; D043802:GTP-Binding Protein alpha Subunits, Gq-G11