title: Akt and mitogen-activated protein kinase enhance C-type lectin-like receptor 2-mediated platelet activation by inhibition of glycogen synthase kinase 3α/β.
abstract: BACKGROUND
  The C-type lectin-like receptor 2 (CLEC-2) and the collagen receptor glycoprotein (GP)VI activate platelets through Src and Syk tyrosine kinases, and phospholipase Cγ2. The initial events in the two signaling cascades, however, are distinct, and there are quantitative differences in the roles of proteins downstream of Syk activation. The activation of Akt and mitogen-activated protein kinases (MAPKs) has been shown to enhance platelet activation by GPVI, but their role in CLEC-2 signaling is not known.
  
  
  OBJECTIVE
  We sought to investigate the role of the Akt and MAPK pathways in platelet activation by CLEC-2.
  
  
  RESULTS
  The CLEC-2 agonist rhodocytin stimulated phosphorylation of Akt and p38 and extracellular signal-related kinase (ERK) MAPKs, but with a delay relative to Syk. Phosphorylation of these proteins was markedly inhibited in the combined presence of apyrase and indomethacin, consistent with the reported feedback action of ADP and thromboxane A2 in CLEC-2 signaling. Phosphorylation of Akt and phosphorylation of ERK were blocked by the phosphoinositide 3-kinase (PI3K) inhibitor wortmannin and the protein kinase C (PKC) inhibitor Ro31-8220, respectively, whereas Syk phosphorylation was not altered. On the other hand, both inhibitors reduced phosphorylation of the Akt substrate glycogen synthase kinase 3α/β (GSK3α/β). Phosphorylation of GSK3α/β was also blocked by the Akt inhibitor MK2206, and reduced at late, but not early, times by the MEK inhibitor PD0325901. MK2206 and PD0325901 inhibited aggregation and secretion in response to a low concentration of rhodocytin, which was restored by GSK3α/β inhibitors.
  
  
  CONCLUSIONS
  These results demonstrate that CLEC-2 regulates Akt and MAPK downstream of PI3K and PKC, leading to phosphorylation and inhibition of GSK3α/β, and enhanced platelet aggregation and secretion.
authors: Centre for Cardiovascular Science, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK.
authors: A J
authors: AJ
authors: Moroi
authors: Centre for Cardiovascular Science, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK.
authors: S P
authors: SP
authors: Watson
mesh_terms: D001792:Blood Platelets / Q000187:drug effects* / Q000201:enzymology; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism*; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D037181:Lectins, C-Type / Q000819:agonists* / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000819:agonists* / Q000378:metabolism; D010766:Phosphorylation; D010974:Platelet Aggregation / Q000187:drug effects*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D000072377:Syk Kinase; D013997:Time Factors; D014757:Viper Venoms / Q000494:pharmacology*
chemical_list: C104778:CLEC2B protein, human; D047908:Intracellular Signaling Peptides and Proteins; D037181:Lectins, C-Type; D008562:Membrane Glycoproteins; D047428:Protein Kinase Inhibitors; D014757:Viper Venoms; C112292:rhodocytin protein, Calloselasma rhodostoma; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; D000071679:Glycogen Synthase Kinase 3 beta; D051057:Proto-Oncogene Proteins c-akt; D011493:Protein Kinase C; D048049:Extracellular Signal-Regulated MAP Kinases; D038362:Glycogen Synthase Kinase 3
keywords: C-type lectin; glycogen synthase kinase 3; mitogen-activated protein kinases; phosphatidylinositol 3-kinases; protein kinase B