title: CLP36 is a negative regulator of glycoprotein VI signaling in platelets.
abstract: BACKGROUND
  At sites of vascular injury, exposed subendothelial collagens not only trigger sudden platelet adhesion and aggregation, thereby initiating normal hemostasis, but also can lead to acute ischemic diseases, such as myocardial infarction or stroke. The glycoprotein (GP) VI/Fc receptor γ-chain complex is a central regulator of these processes because it mediates platelet activation on collagens through a series of tyrosine phosphorylation events downstream of the Fc receptor γ-chain-associated immunoreceptor tyrosine-based activation motif. GPVI signaling has to be tightly regulated to prevent uncontrolled intravascular platelet activation, but the underlying mechanisms are not fully understood.
  
  
  OBJECTIVE
  We studied the role of PDZ and LIM domain family member CLP36 in platelet physiology in vitro and in vivo.
  
  
  RESULTS
  We report that CLP36 acts as a major inhibitor of GPVI immunoreceptor tyrosine-based activation motif signaling in platelets. Platelets from mice either expressing a low amount of a truncated form of CLP36 lacking the LIM domain (Clp36(ΔLIM)) or lacking the whole protein (Clp36(-/-)) displayed profound hyperactivation in response to GPVI agonists, whereas other signaling pathways were unaffected. This was associated with hyperphosphorylation of signaling proteins and enhanced Ca(2+) mobilization, granule secretion, and integrin activation downstream of GPVI. The lack of functional CLP36 translated into accelerated thrombus formation and enhanced procoagulant activity, assembling a prothrombotic phenotype in vivo.
  
  
  CONCLUSIONS
  These data reveal an inhibitory function of CLP36 in GPVI immunoreceptor tyrosine-based activation motif signaling and establish it as a key regulator of arterial thrombosis.
authors.affiliation: Vascular Medicine, Rudolf Virchow Center, University of Würzburg, Josef-Schneider-St 2, D15, 97080 Würzburg, Germany.
authors.forename: Shuchi
authors.initials: S
authors.lastname: Gupta
authors.forename: Attila
authors.initials: A
authors.lastname: Braun
authors.forename: Martina
authors.initials: M
authors.lastname: Morowski
authors.forename: Thomas
authors.initials: T
authors.lastname: Premsler
authors.forename: Markus
authors.initials: M
authors.lastname: Bender
authors.forename: Zoltan
authors.initials: Z
authors.lastname: Nagy
authors.forename: Albert
authors.initials: A
authors.lastname: Sickmann
authors.forename: Heike M
authors.initials: HM
authors.lastname: Hermanns
authors.forename: Michael
authors.initials: M
authors.lastname: Bösl
authors.forename: Bernhard
authors.initials: B
authors.lastname: Nieswandt
mesh_terms: D000818:Animals; D001780:Blood Coagulation Tests; D001792:Blood Platelets / Q000378:metabolism* / Q000648:ultrastructure; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D003094:Collagen / Q000378:metabolism; D005260:Female; D015870:Gene Expression; D061625:Immunoreceptor Tyrosine-Based Activation Motif; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D060588:LIM Domain Proteins / Q000235:genetics / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D018613:Microscopy, Confocal; D046529:Microscopy, Electron, Transmission; D010766:Phosphorylation; D010974:Platelet Aggregation; D010980:Platelet Membrane Glycoproteins / Q000378:metabolism*; D011485:Protein Binding; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D013927:Thrombosis / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014443:Tyrosine / Q000378:metabolism
chemical_list: D060588:LIM Domain Proteins; C106649:Ldb2 protein, mouse; D010980:Platelet Membrane Glycoproteins; D014157:Transcription Factors; C098341:platelet membrane glycoprotein VI; D014443:Tyrosine; D015544:Inositol 1,4,5-Trisphosphate; D003094:Collagen; D002118:Calcium