Proteolysis of thrombospondin during cathepsin-G-induced platelet aggregation: functional role of the 165-kDa carboxy-terminal fragment.
The serine-proteinase cathepsin G (CG) is a potent agonist of platelet aggregation inducing the release and surface expression of alpha-granule adhesive proteins such as fibrinogen (Fg) and thrombospondin-1 (TSP-1). Because Fg and TSP-1 are potential substrates for the enzymatic activity of CG, we investigated the fate of these proteins during CG-induced platelet aggregation using an immunoblot technique. Only a small proportion of secreted Fg was proteolyzed by CG and platelet aggregation was efficiently inhibited by anti-fibrinogen Fab fragments. In contrast, TSP-1 was extensively proteolyzed on aggregated platelets releasing in the milieu a fragment with Mr approximately 28 000, corresponding to the amino-terminal heparin-binding domain (HBD). Several antibodies, directed against the cell-associated carboxy-terminal TSP-1f fragment (Mr approximately 165000) impaired the formation of stable macroaggregates, indicating that this fragment may contribute to platelet aggregation in the absence of the HBD.
Rabhi-Sabile
S
S
INSERM Unité 353, Hôpital Saint-Louis, Paris, France.
Pidard
D
D
Lawler
J
J
Renesto
P
P
Chignard
M
M
Legrand
C
C
D000328:Adult; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D056649:Cathepsin G; D002403:Cathepsins / Q000378:metabolism / Q000494:pharmacology*; D005340:Fibrinogen / Q000187:drug effects / Q000276:immunology / Q000378:metabolism; D006493:Heparin / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D008562:Membrane Glycoproteins / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism; D010974:Platelet Aggregation; D012697:Serine Endopeptidases; D019699:Thrombospondins
D000911:Antibodies, Monoclonal; D008562:Membrane Glycoproteins; D010446:Peptide Fragments; D019699:Thrombospondins; D005340:Fibrinogen; D006493:Heparin; D002403:Cathepsins; D012697:Serine Endopeptidases; C534094:CTSG protein, human; D056649:Cathepsin G