Journal
BIOCHEMICAL JOURNAL
Volume 393, Issue -, Pages 555-564Publisher
PORTLAND PRESS LTD
DOI: 10.1042/BJ20050796
Keywords
bisindolylmaleimide I (BIM I); platelet; protein kinase C (PKC); Rho kinase; thrombin; vasodilator-stimulated phosphoprotein (VASP)
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Funding
- Wellcome Trust Funding Source: Medline
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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 Ser(137) by PKC (protein kinase C). In the present paper, we show that, in human platelets, VASP is phosphorylated by PKC on Ser(157), but not Ser(239), 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 Ser(157)', 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 Ser(157) VASP phosphorylation, and its effects were additive with BIM I. This implicates Rho kinase and PKC as the major kinases that phosphorylate VASP Ser(157) in response to thrombin in platelets.
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