Vasodilator-stimulated phosphoprotein (VASP) is phosphorylated on Ser 157 by protein kinase C-dependent and -independent mechanisms in thrombin-stimulated human platelets

Department of Pharmacology, School of Medical Sciences, University Walk, Bristol BS8 1TD, UK.
Biochemical Journal (Impact Factor: 4.4). 02/2006; 393(Pt 2):555-64. DOI: 10.1042/BJ20050796
Source: PubMed


VASP (vasodilator-stimulated phosphoprotein) is an actin- and profilin-binding protein that is expressed in platelets at high levels and plays a major role in negatively regulating secretory and adhesive events in these cells. VASP is a major substrate for cAMP- and cGMP-regulated protein kinases and it has been shown to be directly phosphorylated on Ser157 by PKC (protein kinase C). In the present paper, we show that, in human platelets, VASP is phosphorylated by PKC on Ser157, but not Ser239, in response to phorbol ester stimulation, in a manner blocked by the PKC inhibitor BIM I (bisindolylmaleimide I). In response to thrombin, VASP was also phosphorylated on Ser157, but this response was only partially inhibited by BIM I, indicating PKC-dependent and -independent pathways to VASP phosphorylation by thrombin. Using inhibitors, we have ruled out the possibility that the PKC-independent pathway acts through guanylate cyclase generation of cGMP, or through a phosphoinositide 3-kinase-dependent kinase. Inhibition of Rho kinase, however, substantially reduced Ser157 VASP phosphorylation, and its effects were additive with BIM I. This implicates Rho kinase and PKC as the major kinases that phosphorylate VASP Ser157 in response to thrombin in platelets.

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    • "Mitogen activated protein kinases [MAPKs (ERK, P38, and JNK)] and phosphatidylinositide 3-kinase (PI-3K)/Akt signaling pathways have been identified in agonist induced platelet activation and aggregation [17]. In contrast, cyclic nucleotide monoamine phosphates such as cyclic adenosine monophosphate (cAMP) have shown broad spectrum antiplatelet activity through vasodilator-stimulated phosphoprotein (VASP) phosphorylation [33] and subsequent integrin αIIbβ3 inactivation [24]. Therefore, agents that enhance cAMP production with subsequent VASP phosphorylation, in one hand, and inhibit MAPK and Akt phosphorylation on the other are important to prevent intravascular platelet aggregation and thrombus formation. "
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