The focal adhesion kinase Pyk2 links Ca2{+} signaling to Src family kinase activation and protein tyrosine phosphorylation in thrombin-stimulated platelets

In blood platelets, stimulation of G protein-coupled receptors by thrombin triggers the activation of Src family kinases (SFKs), resulting in the tyrosine-phosphorylation of multiple substrates, but the mechanism underlying this process is still poorly understood. Here we show that the time-dependent protein-tyrosine phosphorylation triggered by thrombin in human or murine platelets was totally suppressed only upon concomitant chelation of intracellular Ca2+ and inhibition of SFKs. Thrombin-induced activation of SFKs was regulated by intracellular Ca2+, and accordingly, the Ca2+ ionophore A23187 was sufficient to stimulate SFKs. A23187 also triggered the phosphorylation and activation of the Ca2+-dependent focal adhesion kinase Pyk2, and Pyk2 activation by thrombin was Ca2+-dependent. Stimulation of SFKs by thrombin or A23187 was strongly reduced in platelets from Pyk2 knockout mice, as it was the overall pattern of protein-tyrosine phosphorylation. By immunoprecipitation experiments, we demonstrate that Lyn and Fyn, but not Src, were activated by Pyk2. Inhibition of SFKs by PP2 also reduced the phosphorylation of Pyk2 in thrombin- or A23187-stimulated platelets. Analysis of knockout mice demonstrated that Fyn, but not Lyn, was required for complete Pyk2 phosphorylation by thrombin. Finally, PP2 reduced aggregation of murine platelets to a level comparable to that of Pyk2-deficient platelets, but did not have further effects in the absence o...

Source: BJ Signal - May 13, 2015 Category: Biochemistry Authors: I Canobbio, L Cipolla, G Francesco Guidetti, D Manganaro, C Visconte, S Kim, M Okigaki, M Falasca, S P Kunapuli, M Torti Tags: BJ Signal Source Type: research