Phospholipase A(2) enzymes regulate alpha(IIb)beta(3)-mediated, but not Fcgamma RII receptor-mediated, pp125FAK phosphorylation in platelets

The alpha(IIb)beta(3) integrin and Fc gamma RII receptors mediate, respecti vely, platelet adhesion and spreading on fibrinogen and immunoglobulin (IgG ) coated surfaces. Platelet adhesion to fibrinogen resulted in a partial co nversion of the faster to the slower migrating (phosphorylated) form of Ca2-sensitive cytosolic phospholipase A(2) (cPLA(2)) but failed to trigger ar achidonic acid (AA) release. Full mobility shift of cPLA(2) and a massive r elease of AA release were stimulated by platelet adhesion to IgG or additio n of thrombin to the fibrinogen adherent platelets. IgG and thrombin induce d AA production were blocked by methyl arachidonyl fluorophosphonate (MAFP) , an irreversible inhibitor of cPLA(2) and the Ca+2-independent phospholipa se A(2) (iPLA(2)). In contrast, bromoenol lactone (BEL), a specific inhibit or of iPLA(2) had no effect on the release of AA. MAFP and EEL prevented pp 125FAK phosphorylation and platelet spreading on fibrinogen having no effec t on pp125FAK phosphorylation or platelet spreading on immobilized IgG. We conclude that alpha(IIb)beta(3)-mediated pp125FAK phosphorylation and plate let spreading on fibrinogen are regulated by PLA(2) enzymes.