title: Protein kinase C isoform ε negatively regulates ADP-induced calcium mobilization and thromboxane generation in platelets.
abstract: OBJECTIVE
  Members of the protein kinase C (PKC) family are shown to positively and negatively regulate platelet activation. Although positive regulatory roles are extensively studied, negative regulatory roles of PKCs are poorly understood. We investigated the mechanism and specific isoforms involved in PKC-mediated negative regulation of ADP-induced functional responses.
  
  
  RESULTS
  A pan-PKC inhibitor, GF109203X, potentiated ADP-induced cPLA(2) phosphorylation and thromboxane generation as well as ERK activation and intracellular calcium (Ca(2+)(i)) mobilization, 2 signaling molecules, upstream of cPLA(2) activation. Thus, PKCs inhibit cPLA(2) activation by inhibiting ERK and Ca(2+)(i) mobilization. Because the inhibitor of classic PKC isoforms, GO-6976, did not affect ADP-mediated thromboxane generation, we investigated the role of novel class of PKC isoforms. ADP-induced thromboxane generation, calcium mobilization, and ERK phosphorylation were potentiated in PKCε null murine platelets compared with platelets from wild-type littermates. Interestingly, when thromboxane release is blocked, ADP-induced aggregation in PKCε knockout and wild-type was similar, suggesting that PKCε does not affect ADP-induced aggregation directly. PKCε knockout mice exhibited shorter times to occlusion in an FeCl(3)-induced arterial injury model and shorter bleeding times in tail-bleeding experiments.
  
  
  CONCLUSIONS
  We conclude that PKCε negatively regulates ADP-induced thromboxane generation in platelets and offers protection against thrombosis.
authors.affiliation: Temple University School of Medicine, Philadelphia, PA 19140, USA.
authors.forename: Yamini S
authors.initials: YS
authors.lastname: Bynagari-Settipalli
authors.forename: Parth
authors.initials: P
authors.lastname: Lakhani
authors.forename: Jianguo
authors.initials: J
authors.lastname: Jin
authors.forename: Kamala
authors.initials: K
authors.lastname: Bhavaraju
authors.forename: Mario C
authors.initials: MC
authors.lastname: Rico
authors.forename: Soochong
authors.initials: S
authors.lastname: Kim
authors.forename: Donna
authors.initials: D
authors.lastname: Woulfe
authors.forename: Satya P
authors.initials: SP
authors.lastname: Kunapuli
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology*; D000818:Animals; D001792:Blood Platelets / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D004195:Disease Models, Animal; D006801:Humans; D007424:Intracellular Fluid / Q000378:metabolism; D051379:Mice; D010974:Platelet Aggregation / Q000187:drug effects / Q000502:physiology*; D010976:Platelet Count; D051744:Protein Kinase C-epsilon / Q000378:metabolism*; D015398:Signal Transduction; D013927:Thrombosis / Q000378:metabolism / Q000473:pathology; D013931:Thromboxanes / Q000378:metabolism*
chemical_list: D013931:Thromboxanes; D000244:Adenosine Diphosphate; D051744:Protein Kinase C-epsilon; D002118:Calcium