Tyrosine phosphorylation and activation of mitogen-activated protein kinases by thrombin in human platelets: possible involvement in late arachidonic acid release.

Thrombin induced tyrosine phosphorylation of 41-kDa and 43-kDa mitogen-activated protein (MAP) kinases in human platelets which was detectable at 1 min and peaked at 2 min after thrombin stimulation as assessed by immunoprecipitation and immunoblotting. The kinase activity, measured by phosphorylation of myelin basic protein, increased concurrently with tyrosine phosphorylation. The present results indicate that thrombin activates MAP kinases which may not be involved in aggregation and secretory responses but may play a role in the late arachidonic acid release via activation of cytosolic phospholipase A2 in human platelets.