Role of Protein Kinase C delta in regulating platelet functional responses

Abstract

Platelets upon activation change their shape, aggregate and secrete alpha and dense granule contents among which ADP acts as a feedback activator. Different Protein Kinase C (PKCδ) isoforms have specific non-redundant roles in mediating platelet responses including secretion and thrombus formation. Protein Kinase C delta (PKCδ), a novel class of PKC isoform requiring diacyl glycerol but not calcium for its activation, has been shown to play an important role in several pathological processes. The aims of our current study are 1) to identify possible PKCδ specific substrates in platelets, 2) evaluate a novel PKCδ selective inhibitor and 3) to investigate the role of PKCδ in ADP-induced platelet activation. We show that Protein kinase D2 (PKD2) is the major isoform of PKD that is expressed in human as well as murine platelets and is a specific substrate for PKCδ in platelets. CGX1037 was identified and characterized as a selective small molecule inhibitor of PKCδ in platelets. Furthermore, by using PKCδ knock out murine platelets, we showed that PKCδ plays a functional role in mediating ADP-induced thromboxane generation and classical PKC isoforms α/β regulate tyrosine phosphorylation on PKCδ and subsequent thromboxane generation through a tyrosine kinase, Lyn and a tyrosine phosphatase, Shp1 suggesting an important role of PKCδ to agonist-induced platelet activation.