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Hoffmann, R. A wiki for the life sciences where authorship matters. Nature Genetics (2008)

Rapid Ca2+-mediated activation of Rap1 in human platelets.

Rap1 is a small, Ras-like GTPase whose function and regulation are still largely unknown. We have developed a novel assay to monitor the active, GTP-bound form of Rap1 based on the differential affinity of Rap1GTP and Rap1GDP for the Rap binding domain of RalGDS (RBD). Stimulation of blood platelets with alpha-thrombin or other platelet activators caused a rapid and strong induction of Rap1 that associated with RBD in vitro. Binding to RBD increased from undetectable levels in resting platelets to >50% of total Rap1 within 30 s after stimulation. An increase in the intracellular Ca2+ concentration is both necessary and sufficient for Rap1 activation since it was induced by agents that increase intracellular Ca2+ and inhibited by a Ca2+-chelating agent. Neither inhibition of translocation of Rap1 to the cytoskeleton nor inhibition of platelet aggregation affected thrombin- induced activation of Rap1. In contrast, prostaglandin I2 (PGI2), a strong negative regulator of platelet function, inhibited agonist-induced as well as Ca2+-induced activation of Rap1. From our results, we conclude that Rap1 activation in platelets is an important common event in early agonist-induced signalling, and that this activation is mediated by an increased intracellular Ca2+ concentration.[1]


  1. Rapid Ca2+-mediated activation of Rap1 in human platelets. Franke, B., Akkerman, J.W., Bos, J.L. EMBO J. (1997) [Pubmed]
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