The cleaved peptide of PAR1 results in a redistribution of the platelet surface GPIb-IX-V complex to the surface-connected canalicular system.
The only known function of the 41 amino acid cleaved peptide (TR1-41) of the seven transmembrane domain thrombin receptor (PARI) is to activate platelets (as determined by aggregation, surface P-selectin, and fibrinogen binding to activated GPIIb-IIIa). We now demonstrate that TR1-41 results in a concentration-dependent decrease in the platelet surface expression of each component of the GPIb-IX-V complex, as determined by flow cytometry with a panel of monoclonal antibodies (including 6D1, directed against the von Willebrand factor binding site on GPIbalpha, and TM60, directed against the thrombin binding site on GPIbalpha). TR1-41 also decreased ristocetin-induced platelet agglutination. Immunoblotting after incubation of platelets with TR1-41 revealed neither a loss of platelet GPIb nor increase in supernatant GPIb fragments. As demonstrated by immunoelectron microscopy, TR1-41 resulted in a redistribution of GPIb, GPIX, and GPV from the platelet surface to the surface-connected canalicular system (SCCS). In summary, the cleaved peptide (TR1-41) of PAR1 results in a redistribution of the platelet surface GPIb-IX-V complex to the SCCS, thereby negatively regulating the GPIbalpha binding sites for von Willebrand factor and thrombin.
Furman
M I
MI
Center for Platelet Function Studies, Department of Medicine, UMass Memorial Health Care, University of Massachusetts Medical School, Worcester 01655, USA.
Nurden
P
P
Berndt
M C
MC
Nurden
A T
AT
Benoit
S E
SE
Barnard
M R
MR
Ofosu
F A
FA
Michelson
A D
AD
D000818:Animals; D001792:Blood Platelets / Q000378:metabolism*; D006801:Humans; D051379:Mice; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000378:metabolism*; D010980:Platelet Membrane Glycoproteins; D018179:Receptors, Thrombin / Q000378:metabolism*; D015398:Signal Transduction; D013917:Thrombin / Q000378:metabolism*; D014841:von Willebrand Factor / Q000378:metabolism
D019038:Platelet Glycoprotein GPIb-IX Complex; D010980:Platelet Membrane Glycoproteins; D018179:Receptors, Thrombin; C032193:glycoprotein receptor GPIb-IX; D014841:von Willebrand Factor; D013917:Thrombin