Gq-mediated Akt translocation to the membrane: a novel PIP3-independent mechanism in platelets

Blood. 2015 Jan 1;125(1):175-84. doi: 10.1182/blood-2014-05-576306. Epub 2014 Oct 20.

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.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Biological Transport
  • Blood Platelets / cytology
  • Blood Platelets / metabolism*
  • Cell Membrane / metabolism
  • GTP-Binding Protein alpha Subunits, Gq-G11 / metabolism*
  • Humans
  • Mice
  • Phosphatidylinositol Phosphates / metabolism*
  • Phosphorylation
  • Platelet Aggregation*
  • Protein Transport
  • Proto-Oncogene Proteins c-akt / metabolism*
  • Signal Transduction
  • Thrombin / metabolism

Substances

  • Phosphatidylinositol Phosphates
  • phosphatidylinositol 3-phosphate
  • Akt1 protein, mouse
  • Proto-Oncogene Proteins c-akt
  • Thrombin
  • GTP-Binding Protein alpha Subunits, Gq-G11