A trypsin-like platelet protease propagates protease-activated receptor-1 cleavage and platelet activation

Protease-activated receptor-1 (PAR-1) is a G-protein-linked receptor on pla telets and perivascular cells activated by alpha-thrombin and the PAR-1-act ivating peptide, SFLLRN. alpha-Thrombin activates PAR-1 by cleaving it at R -41-S-42 to release the 41-residue peptide TR(1-41). Unexpectedly, platelet activation with SFLLRN was also associated with PAR-1 cleavage and the rel ease of TR(1-41). Both PAR-1 cleavage and platelet activation resulting fro m SFLLRN addition to platelets were markedly inhibited by the serine protea se inhibitor 4,2-(aminoethyl)benzene sulphonylfluoride . HCl (pefabloc SC) and soybean trypsin inhibitor, but not by inhibitors of calpain, cysteine p roteases or metalloproteases. Thus, a trypsin-like platelet protease propag ates SFLLRN-dependent PAR-1 cleavage and platelet activation.