Thrombin rapidly induces protein kinase D phosphorylation, and protein kinase C δ mediates the activation

Thrombin plays a critical role in hemostasis, thrombosis, and inflammation. However, the responsible intracellular signaling pathways triggered by thrombin are still not well defined. We report here that thrombin rapidly and transiently induces activation of protein kinase D (PYD) in aortic smooth muscle cells. Our data demonstrate that protein kinase C (PKC) inhibitors completely block thrombin-induced PKD activation, suggesting that thrombin induces PKD activation via a PKC-dependent pathway. Furthermore, our results show that thrombin rapidly induces PKCdelta phosphorylation and that the PKCS-specific inhibitor rottlerin blocks thrombin-induced PKD activation, suggesting that PKCS mediates the thrombin-induced PKD activation. Using dominant negative approaches, we demonstrated that expression of a dominant negative PKCdelta inhibits the phosphorylation and activation of PKD induced by thrombin, whereas neither PKCEepsilon nor PKCzeta affects thrombin-induced PKD activation. In addition, our results of co-immunoprecipitation assays showed that PKD forms a complex with PKCdelta in smooth muscle cells. Taken together, the findings of the present study demonstrate that thrombin induces activation of PKD and reveal a novel role of PKCdelta in mediating thrombin-induced PKD activation in vascular smooth muscle cells.