THROMBIN ACTIVATES MAPKAP2 KINASE IN VASCULAR SMOOTH-MUSCLE

Purpose: Thrombin mediates hemostasis by promoting thrombus developmen t and vasospasm, which reduces the size of the arterial injury. Thromb in stimulation of vascular smooth muscle is associated with activation of mitogen-associated protein kinase. The purpose of this investigati on was to determine the subsequent cellular signaling events in thromb in-stimulated vascular smooth muscle contraction. Methods: Contractile responses of bovine carotid artery smooth muscle were determined in a muscle bath and compared with phosphorylation events with two-dimensi onal gel electrophoresis. The activity of a novel kinase, mitogen-acti vated protein kinase-activated protein-2 kinase (MAPKAP2 kinase), was determined by immunoprecipitation and a phosphotransferase assay. A sm all heat shock protein, HSP27, was identified with immunoblotting. Res ults: Thrombin induces contraction of vascular smooth muscle and is as sociated with increased activity of MAPKAP2 kinase and increased phosp horylation of HSP27. Multiple isoforms of HSP27 are the predominant ph osphoproteins in vascular smooth muscle, and peptide mapping suggests that the isoforms of HSP27 are structurally related and phosphorylated within similar peptide sequences. Conclusions: Activation of the MAPK AP2 kinase pathway and phosphorylation of HSP27 are associated with th rombin-induced contraction of vascular smooth muscle.