The Cleaved Peptide of PAR1 Results in a Redistribution of the Platelet Surface GPIb-IX-V Complex to the Surface-Connected Canalicular System
Mark I. Furman (1) , Paquita Nurden (2) , Michael C. Berndt (3) , Alan T. Nurden (2) , Stephen E. Benoit (1), (4) , Marc R. Barnard (4) , Frederick A. Ofosu (5) , Alan D. Michelson (4)
From the (1) Center for Platelet Function Studies, Division of Cardiovascular Medicine, Department of Medicine, UMass Memorial Health Care, University of Massachusetts Medical School, Worcester, Massachusetts, USA; (2) UMR 5533 CNRS, Hopital Cardiologiq
Summary The only known function of the 41 amino acid cleaved peptide (TR 1-41 )of the seven transmembrane domain thrombin receptor (PAR1) is toactivate platelets (as determined by aggregation, surface P-selectin,and fibrinogen binding to activated GPIIb-IIIa). We now demonstratethat TR 1-41 results in a concentration-dependent decrease in the plateletsurface expression of each component of the GPIb-IX-V complex, asdetermined by flow cytometry with a panel of monoclonal antibodies(including 6D1, directed against the von Willebrand factor binding siteon GPIb, and TM60, directed against the thrombin binding site onGPIb). TR 1-41 also decreased ristocetin-induced platelet agglutination.Immunoblotting after incubation of platelets with TR1-41 revealedneither a loss of platelet GPIb nor increase in supernatant GPIb fragments.As demonstrated by immunoelectron microscopy, TR 1-41 resultedin a redistribution of GPIb, GPIX, and GPV from the platelet surfaceto the surface-connected canalicular system (SCCS). In summary,the cleaved peptide (TR 1-41 ) of PAR1 results in a redistribution of theplatelet surface GPIb-IX-V complex to the SCCS, thereby negativelyregulating the GPIbbinding sites for von Willebrand factor andthrombin.