A role for p38 MAP kinase in platelet activation by von Willebrand Factor
Ilaria Canobbio (1), Stefania Reineri (2), Fabiola Sinigaglia (2), Cesare Balduini (1), Mauro Torti (1)
(1) Center of Excellence on Applied Biology and Department of Biochemistry, University of Pavia, Italy (2) Department of Medical Sciences, University “A. Avogadro”, Novara, Italy
Summary Platelet activation induced by von Willebrand factor (VWF)binding to the membrane GPIb-IX-V receptor involves multiplesignal transduction pathways. Among these, recruitmentand activation of the FcγRIIA and stimulation of phospholipaseA2 represent independent events equally essential to support acomplete platelet response. Phospholipase A2 is activated bycalcium and by phosphorylation through MAP kinases. In thiswork, we found that VWF stimulated the rapid and sustainedphosphorylation of p38 MAP kinase (p38MAPK). In vitro kinaseassay revealed that VWF-stimulated phosphorylation ofp38MAPK was associated with increased kinase activity. Bindingof VWF to GPIb-IX-V, but not to integrin αIibβ3, was required tosupport phosphorylation of p38MAPK. Neither the blockade ofthe membrane FcγRIIA by a specific monoclonal antibody or the prevention of thromboxane A2 synthesis by cyclooxygenaseinhibitors affected VWF-induced p38MAPK activation. How-ever,phosphorylation of p38MAPK was prevented by the tyro-sinekinase Syk inhibitor piceatannol. Treatment of plateletswith the p38MAPK inhibitor SB203580 totally prevented VWF-stimulatedplatelet aggregation. Moreover, release of arachidonicacid induced by VWF was strongly impaired by inhibition ofp38MAPK.We also found that VWF induced phosphorylation ofcytosolic phospholipase A2, and that this process was preventedby the p38MAPK inhibitor SB203580.These results demonstratethat p38MAPK is a key element in the FcγRIIA-independentpathway for VWF-induced platelet activation, and is involvedin the stimulation of phospholipase A2 and arachidonic acidrelease.