title: Impaired activation of platelets lacking protein kinase C-theta isoform.
abstract: Protein kinase C (PKC) isoforms have been implicated in several platelet functional responses, but the contribution of individual isoforms has not been thoroughly evaluated. Novel PKC isoform PKC-theta is activated by glycoprotein VI (GPVI) and protease-activated receptor (PAR) agonists, but not by adenosine diphosphate. In human platelets, PKC-theta-selective antagonistic (RACK; receptor for activated C kinase) peptide significantly inhibited GPVI and PAR-induced aggregation, dense and alpha-granule secretion at low agonist concentrations. Consistently, in murine platelets lacking PKC-theta, platelet aggregation and secretion were also impaired. PKC-mediated phosphorylation of tSNARE protein syntaxin-4 was strongly reduced in human platelets pretreated with PKC-theta RACK peptide, which may contribute to the lower levels of granule secretion when PKC-theta function is lost. Furthermore, the level of JON/A binding to activated alpha(IIb)beta(3) receptor was also significantly decreased in PKC-theta(-/-) mice compared with wild-type littermates. PKC-theta(-/-) murine platelets showed significantly lower agonist-induced thromboxane A(2) (TXA(2)) release through reduced extracellular signal-regulated kinase phosphorylation. Finally, PKC-theta(-/-) mice displayed unstable thrombus formation and prolonged arterial occlusion in the FeCl(3) in vivo thrombosis model compared with wild-type mice. In conclusion, PKC-theta isoform plays a significant role in platelet functional responses downstream of PAR and GPVI receptors.
authors.affiliation: Department of Physiology, Temple University School of Medicine, Philadelphia, PA 19140, USA.
authors.forename: Bela
authors.initials: B
authors.lastname: Nagy
authors.forename: Kamala
authors.initials: K
authors.lastname: Bhavaraju
authors.forename: Todd
authors.initials: T
authors.lastname: Getz
authors.forename: Yamini S
authors.initials: YS
authors.lastname: Bynagari
authors.forename: Soochong
authors.initials: S
authors.lastname: Kim
authors.forename: Satya P
authors.initials: SP
authors.lastname: Kunapuli
mesh_terms: D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D002352:Carrier Proteins / Q000494:pharmacology; D003435:Crotalid Venoms / Q000494:pharmacology; D006801:Humans; D007527:Isoenzymes / Q000235:genetics* / Q000276:immunology / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D009842:Oligopeptides / Q000494:pharmacology; D010446:Peptide Fragments / Q000494:pharmacology; D010455:Peptides / Q000494:pharmacology; D010456:Peptides, Cyclic / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D015539:Platelet Activation / Q000235:genetics*; D010980:Platelet Membrane Glycoproteins / Q000819:agonists / Q000378:metabolism / Q000502:physiology; D011493:Protein Kinase C / Q000235:genetics* / Q000276:immunology / Q000378:metabolism; D000074121:Protein Kinase C-theta; D050765:Qa-SNARE Proteins / Q000378:metabolism; D044462:Receptors, Proteinase-Activated / Q000819:agonists / Q000378:metabolism / Q000502:physiology; D013912:Threonine / Q000378:metabolism
chemical_list: D000906:Antibodies; D002352:Carrier Proteins; D003435:Crotalid Venoms; D007527:Isoenzymes; D009842:Oligopeptides; D010446:Peptide Fragments; D010455:Peptides; D010456:Peptides, Cyclic; D010980:Platelet Membrane Glycoproteins; D050765:Qa-SNARE Proteins; D044462:Receptors, Proteinase-Activated; C475455:YM-254890; C455901:alanyl-tyrosyl-prolyl-glycyl-lysyl-phenylalanine; C112003:alboaggregin A; C435908:collagen-related peptide; C098341:platelet membrane glycoprotein VI; C082835:thrombin receptor peptide (42-47); D013912:Threonine; C489593:Prkcq protein, mouse; D011493:Protein Kinase C; D000074121:Protein Kinase C-theta