Effects of cathepsin G pretreatment of platelets on their subsequent responses to aggregating agents.
Cathepsin G, a proteolytic enzyme from activated leukocytes, can interact with platelets during inflammation and thrombosis. Platelets that have been exposed to cathepsin G in thrombi may recirculate if they are freed during fibrinolysis. To determine whether some of the subsequent functions of such platelets would be impaired, we investigated the responses of cathepsin G-pretreated platelets to agonists that they would encounter in the circulation. Suspensions of washed human platelets were labeled with [14C]serotonin and resuspended in Tyrode-albumin solution (with 2 mM Ca2+ and apyrase). After 15 minute incubation with 400 nM cathepsin G at 37 degrees C, 52+/-3% of [14C]serotonin had been released, and glycoprotein Ib was degraded. The platelets were washed and resuspended in fresh medium to remove cathepsin G and released materials. Ristocetin-induced agglutination was abolished, indicating that the binding site for von Willebrand Factor on glycoprotein Ib had been removed. Aggregation and release of residual [14C]serotonin in response to 0.1-1.0 U/mL thrombin was blocked or greatly reduced by the cathepsin G pretreatment. This inhibition is probably largely due to cleavage by cathepsin G of some of the protease-activated receptors at the C-terminal side of Ser42 so that the tethered ligand is lost. Pretreatment with cathepsin G did not affect responses to ADP or a low concentration of platelet-activating factor in the presence of fibrinogen, indicating that receptors for these agonists were unaffected and that the function of the fibrinogen receptor, GPIIb/IIIa was unchanged. Responses to cathepsin G, the thrombin receptor-activating peptide SFLLRN, collagen, or the thromboxane A2 mimetic U46619 were partially inhibited, even in the presence of added fibrinogen. Platelet adhesion to a collagen-coated surface was 51+/-7% inhibited, which may indicate cleavage of a collagen receptor or receptors; this may partly account for strong inhibition of collagen-induced aggregation and release of granule contents; additionally, as shown by inhibition of responses to U46619, the function of the thromboxane A2 receptor may be compromised. Thus, although cathepsin G activates platelets, if they recirculate after interaction with it, their subsequent adhesion to damaged vessel walls, aggregation, and release of granule contents induced by thrombin and collagen will be diminished.
Kinlough-Rathbone
R L
RL
Department of Pathology and Molecular Medicine, McMaster University, Hamilton, Ontario, Canada.
Perry
D W
DW
Rand
M L
ML
Packham
M A
MA
D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid / Q000494:pharmacology; D000244:Adenosine Diphosphate / Q000494:pharmacology; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001792:Blood Platelets / Q000378:metabolism / Q000473:pathology; D056649:Cathepsin G; D002403:Cathepsins / Q000494:pharmacology*; D004347:Drug Interactions; D006490:Hemostatics / Q000494:pharmacology; D006801:Humans; D010972:Platelet Activating Factor / Q000494:pharmacology; D010974:Platelet Aggregation / Q000187:drug effects*; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000378:metabolism; D012310:Ristocetin / Q000494:pharmacology*; D012697:Serine Endopeptidases; D012701:Serotonin / Q000378:metabolism; D013917:Thrombin / Q000494:pharmacology; D014662:Vasoconstrictor Agents / Q000494:pharmacology
D000900:Anti-Bacterial Agents; D006490:Hemostatics; D010972:Platelet Activating Factor; D019038:Platelet Glycoprotein GPIb-IX Complex; D014662:Vasoconstrictor Agents; D012310:Ristocetin; D012701:Serotonin; D000244:Adenosine Diphosphate; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D002403:Cathepsins; D012697:Serine Endopeptidases; C534094:CTSG protein, human; D056649:Cathepsin G; D013917:Thrombin