Source:http://linkedlifedata.com/resource/umls/id/C1516047
NCI: Activation of the protease-activated GPCRs in platelets contributes to platelet activation in clotting. The protease-activated receptors PAR1 and PAR4 are cleaved by the protease thrombin, releasing a tethered peptide ligand that activates the receptor and triggers intracellular calcium release. Platelets from mice lacking the PAR4 gene are not activated by thrombin and are impaired in clotting, supporting the importance of thrombin signaling through PAR4 in clotting. Human platelets express both PAR1 and PAR4, with PAR1 playing a more dominant role in clotting in humans. Calcium release induced by PARs activates PKC, modulating integrin alpha IIB beta 3 (glycoprotein IIb/IIIa) and opening integrin ligand binding sites to contribute to platelet aggregation. Intracellular calcium increases induced by thrombin activate phospholipase A2, liberating arachidonic acid, the first step in prostaglandin and thromboxane biosynthesis. Ras/Map kinase activation by the PAR receptors also activates phospholipase A2. T