Gα12 and Gα13 Are Phosphorylated during Platelet Activation

• Published in: The Journal of biological chemistry 1996-10, Vol.271 (42), p.26044
• Main Authors: Stefan Offermanns, Yi-Hui Hu, Melvin I. Simon
• Format: Article
• Language: English
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.271.42.26044

The ubiquitously expressed G-proteins G 12 and G 13 whose function is currently not clear have been shown to be activated in platelet membranes through receptors that stimulate platelet aggregation. We used intact human platelets to determine whether α subunits of both G-proteins can be phosphorylated under physiological conditions. Activation of human platelets by thrombin and the thromboxane A 2 receptor agonist U46619 lead to phosphorylation of Gα 12 and Gα 13 . Phosphorylation occurred rapidly after addition of thrombin and was not mediated by glycoprotein IIb/IIIa (integrin α IIb β 3 ) activation. Phosphorylation of Gα 12 and Gα 13 could be mimicked by phorbol 12-myristate 13-acetate, and thrombin-induced phosphorylation was inhibited by the protein kinase C inhibitor calphostin C indicating an involvement of protein kinase C in Gα 12/13 phosphorylation induced by thrombin in human platelets. The phosphorylation of both G protein α subunits was reconstituted in COS-7 cells cotransfected with Gα 12 or Gα 13 and different protein kinase C isoforms. Among the protein knase C isoforms tested, protein kinase C β, δ, and ϵ were most effective in promoting phosphorylation of Gα 12 and Gα 13 in a phorbol 12-myristate 13-acetate-dependent manner. These data demonstrate that Gα 12 and Gα 13 are phosphorylated under in vivo conditions and that this phosphorylation involves protein kinase C.