title: GPVI potentiation of platelet activation by thrombin and adhesion molecules independent of Src kinases and Syk.
abstract: OBJECTIVE
  The present study investigates the role of Src and Syk tyrosine kinases in signaling by G-protein coupled and platelet adhesion receptors.
  
  
  RESULTS
  Using Syk-/- platelets or the Src kinase inhibitor PP2, we demonstrate a critical role for Src and Syk kinases in mediating lamellipodia formation on VWF, collagen, CRP, fibrinogen, and fibronectin. In all cases, the spreading defect was overcome by addition of thrombin. Conversely, platelet aggregation and alphaIIb beta3 activation induced by thrombin was similar to controls, arguing against a functional role for Src and Syk in alphaIIb beta3 activation. Unexpectedly, CRP potentiated integrin alphaIIb beta3 activation and platelet aggregation induced by subthreshold concentrations of thrombin in Syk-/- platelets or in the presence of the Src kinase inhibitor PP2. Potentiation in the presence of PP2 was lost in the absence of FcRgamma-chain or GPVI confirming that it was mediated through the immunoglobulin receptor. Further delineation of this PP2-resistant synergy revealed that PAR4 could trigger the enhanced response in combination with CRP.
  
  
  CONCLUSIONS
  We show that Syk is critical for lamellipodia formation on a range of immobilized proteins but that this can be overcome by addition of thrombin. Further, we reveal a novel role for GPVI in supporting thrombin-induced activation, independent of Syk and Src kinases.
authors.affiliation: Centre for Cardiovascular Sciences, Institute of Biomedical Research, University of Birmingham, UK. Sascha.hughan@med.monash.edu.au
authors.forename: Sascha C
authors.initials: SC
authors.lastname: Hughan
authors.forename: Craig E
authors.initials: CE
authors.lastname: Hughes
authors.forename: Owen J T
authors.initials: OJ
authors.lastname: McCarty
authors.forename: Edina
authors.initials: E
authors.lastname: Schweighoffer
authors.forename: Izoumroud
authors.initials: I
authors.lastname: Soultanova
authors.forename: Jerry
authors.initials: J
authors.lastname: Ware
authors.forename: Victor L J
authors.initials: VL
authors.lastname: Tybulewicz
authors.forename: Steve P
authors.initials: SP
authors.lastname: Watson
mesh_terms: D000818:Animals; D002097:C-Reactive Protein / Q000494:pharmacology; D015815:Cell Adhesion Molecules / Q000494:pharmacology* / Q000502:physiology; D002462:Cell Membrane / Q000502:physiology; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D010766:Phosphorylation; D015539:Platelet Activation / Q000502:physiology*; D010974:Platelet Aggregation / Q000187:drug effects / Q000502:physiology; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000502:physiology; D010980:Platelet Membrane Glycoproteins / Q000502:physiology*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011554:Pseudopodia / Q000502:physiology; D011743:Pyrimidines / Q000494:pharmacology; D043562:Receptors, G-Protein-Coupled / Q000502:physiology; D044462:Receptors, Proteinase-Activated / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology; D000072377:Syk Kinase; D013917:Thrombin / Q000502:physiology*; D014443:Tyrosine / Q000378:metabolism; D019061:src-Family Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: C412373:AG 1879; D015815:Cell Adhesion Molecules; D047908:Intracellular Signaling Peptides and Proteins; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D010980:Platelet Membrane Glycoproteins; D011743:Pyrimidines; D043562:Receptors, G-Protein-Coupled; D044462:Receptors, Proteinase-Activated; C098341:platelet membrane glycoprotein VI; D014443:Tyrosine; D002097:C-Reactive Protein; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; C000606897:Syk protein, mouse; D019061:src-Family Kinases; D013917:Thrombin