PROTEIN-KINASE C-DELTA ACTIVATION AND TYROSINE PHOSPHORYLATION IN PLATELETS

Several protein kinase C (PKC) isoforms are expressed in human platele ts. We report that PKC-delta is tyrosine phosphorylated within 30 s of platelet activation by thrombin. This correlated with a 2-3-fold incr ease in the kinase activity of PKC-delta relative to unstimulated plat elets. The tyrosine phosphorylated PKC-delta isoform was associated wi th the platelet particulate (100000 x g insoluble) fraction. alpha(IIb )beta(3) integrin mediated platelet adhesion to fibrinogen did not sig nificantly affect PKC-delta activity, Tyrosine phosphorylation of PKC- delta was similarly not detected in fibrinogen adherent platelet lysat es. Treatment of the platelets with mAb 7E3 prior to the addition of t hrombin blocked aggregation having no effect on the thrombin induced P KC-delta activation, We conclude that PKC-delta is activated in platel ets by an alpha(IIb)beta(3) independent pathway. (C) 1998 Federation o f European Biochemical Societies.