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Blood, 1 October 2007, Vol. 110, No. 7, pp. 2449-2456. Prepublished online as a Blood First Edition Paper on June 19, 2007; DOI 10.1182/blood-2006-11-056069.
HEMOSTASIS, THROMBOSIS, AND VASCULAR BIOLOGY Hematopoietic lineage cell–specific protein 1 (HS1) is a functionally important signaling molecule in platelet activation1 Department of Physiology 2 Sol Sherry Thrombosis Research Center, and 3 Department of Pharmacology, Temple University School of Medicine, Philadelphia, PA; 4 Department of Medicine, University of Pennsylvania, Philadelphia; and 5 Research Institute for Biological Sciences, Tokyo University of Science, Noda, Japan Collagen activates platelets through an intracellular signaling cascade downstream of glycoprotein VI (GPVI). We have investigated the contribution of hematopoietic lineage cell–specific protein 1 (HS1) downstream of GPVI in platelet activation. Stimulation of GPVI leads to tyrosine phosphorylation of HS1, which is blocked by Src-family kinase inhibitors. Coimmunoprecipitation experiments revealed that HS1 associates with Syk and phosphatidylinositol 3-kinases. HS1-null mice displayed increased bleeding times and increased time to occlusion in the FeCl3 in vivo thrombosis model compared with their wild-type littermates. In addition, aggregation and secretion responses were diminished in HS1-null mouse platelets after stimulation of GPVI and protease-activated receptor 4 (PAR-4) agonists compared with wild-type littermate mouse platelets. Finally, Akt phosphorylation was diminished after GPVI or PAR-4 stimulation in platelets from HS1-null mice compared with their wild-type littermates. These results demonstrate that phosphorylation of the HS1 protein occurs downstream of GPVI stimulation and that HS1 plays a significant functional role in platelet activation downstream of GPVI and PARs.
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