CLP36 is a Negative Regulator of GPVI Signaling in Platelets
Rationale: At sites of vascular injury exposed subendothelial collagens trigger sudden platelet adhesion and aggregation thereby initiating normal hemostasis but can also lead to acute ischemic diseases such as myocardial infarction or stroke. The glycoprotein (GP)VI/Fc receptor γ(FcRγ)-chain complex is a central regulator of these processes as it mediates platelet activation on collagens through a series of tyrosine phosphorylation events downstream of the FcRγ-chain-associated immunoreceptor tyrosine-based activation motif (ITAM). 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 (PDLIM) family member CLP36 in platelet physiology in vitro and in vivo.
Methods and Results: We report that CLP36 acts as a major inhibitor of GPVI-ITAM signaling in platelets. Platelets from mice either expressing a low amount of a truncated form of CLP36 lacking the LIM-domain (Clp36ΔLIM) 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 Ca2+ mobilization, granule secretion and integrin activation downstream of GPVI. The lack of functional CLP36 translated into accelerated thrombus formation and enhanced pro-coagulant activity assembling a pro-thrombotic phenotype in vivo.
Conclusions: These data reveal an inhibitory function of CLP36 in GPVI-ITAM signaling and establish it as a key regulator of arterial thrombosis.
- Received January 11, 2012.
- Accepted September 5, 2012.
- Copyright © 2012, American Heart Association