Functional Role of p38 Mitogen Activated Protein Kinase in Platelet Activation induced by a Thromboxane A2 Analogue and by 8-iso-prostaglandin F2 α

Abstract

We investigated similarities in the signaling pathways elicited by the F2 isoprostane 8-iso-PGF2alpha and by low doses of U46619 to induce platelet activation. Both 0.01-0.1 micromol/L U46619 and 0.01-1 micromol/L 8-iso-PGF2alpha triggered shape change and filopodia extension, as well as adhesion to immobilized fibrinogen of washed platelets. At these doses the two platelet agonists failed to trigger secretion and aggregation, which were however induced by higher doses of U46619 (0.1-1 micromol/L). SB203580 (1-10 micromol/L), a specific inhibitor of the p38 mitogen activated protein (MAP) kinase blunted platelet shape change and adhesion induced by 0.05-1 micromol/L 8-iso-PGF2alpha and by 0.01 micromol/L U46619. These platelet responses were also inhibited by 20 micromol/L cytochalasin D, an inhibitor of actin polymerization, and 50 micromol/L piceatannol, an inhibitor of the Syk tyrosine kinases. Both 8-iso-PGF2alpha and U46619-induced p38 MAP kinase phosphorylation in suspended platelets and this was inhibited by piceatannol, indicating that Syk activation occurs upstream of p38 MAP kinase phosphorylation. These findings suggest that the signaling pathway triggered by both 8-iso-PGFalpha and low concentrations of U46619 to induce platelet adhesion and shape change implicates Syk, the p38 MAP kinase, and actin polymerization.