Protein Kinase C Isoform ε Negatively Regulates ADP-Induced Thromboxane Generation by Regulating cPLA₂ Activation and Calcium Mobilization In Platelets

Abstract 2020

Positive regulatory role of Protein Kinase C (PKC) isoforms in platelets have been extensively studied. However, negative regulatory roles of PKCs in platelets are poorly understood. In this study we investigated the mechanism by which PKCs negatively regulate ADP-induced thromboxane generation and identified PKC isoforms involved in this process. Pan PKC inhibition with GF109203X potentiated ADP-induced cPLA₂ phosphorylation suggesting that PKCs negatively regulate thromboxane generation by regulating cPLA₂ activation. Inhibition of PKCs potentiated ADP-induced ERK activation and intracellular calcium mobilization, two upstream signaling molecules of cPLA₂.These data suggest that PKCs negatively regulate thromboxane by regulating ERK activation and calcium mobilization, which inturn regulate cPLA₂ activation. Pan-PKC inhibition potentiated ADP-induced, P2Y1 receptor-mediated calcium mobilization in platelets independent of P2Y12-receptor. Pretreatment of platelets with GF109203X, a Pan PKC inhibitor, but not Go-6976, a classical PKC isoform inhibitor, potentiated ADP-induced thromboxane generation. Thus, we investigated the role of various novel class of PKC isoforms (nPKCs) in platelets. We have previously demonstrated that nPKC η, θ, δ positively regulates agonist-induced thromboxane generation in platelets. Thus, we investigated if the role of nPKC ε in ADP-induced thromboxane generation using PKC ε knockout mice (PKCε KO). ADP-induced thromboxane generation in PKC ε KO murine platelets was ten-fold higher than that of wild type platelets. Furthermore, PKC ε KO mice exhibited shorter times to occlusion in FeCl₃-induced arterial injury model and shorter bleeding times in Tail bleeding experiments. We conclude that PKCε negatively regulates ADP-induced thromboxane generation in platelets and thereby offers protection against thrombosis.