Plasmin-induced platelet aggregation is accompanied by cleavage of aggregin and indirectly mediated by calpain.
We recently reported that thrombin-induced platelet aggregation 1) is accompanied by cleavage of aggregin, a 100-kDa membrane protein and a putative ADP receptor, 2) is indirectly mediated by intracellularly activated calpain, and 3) requires the occupancy of high-affinity thrombin receptors. Because of the similarities between responses after platelet activation induced by thrombin and plasmin (greater than or equal to 1.0 casein unit/ml), we investigated whether or not plasmin-induced platelet aggregation proceeds by the same mechanism that underlies thrombin-induced platelet aggregation. We found that the rate of plasmin-induced aggregation of washed intact platelets and that of platelets modified by 5'-p-fluorosulfonylbenzoyladenosine (FSBA, an affinity analogue of ADP, which covalently modifies aggregin) were similar, indicating that the aggregation is independent of the ADP effect. Plasmin completely cleaved [3H]FSBA-labeled aggregin in intact platelets. A mixture of metabolic inhibitors (2-deoxy-D-glucose, gluconolactone, and antimycin A) completely inhibited plasmin-induced platelet aggregation and plasmin-induced cleavage of aggregin, demonstrating that an energy-requiring step is involved in the reaction. The synthetic hexapeptide affinity reagent Phe-Gln-Val-Val-Cys(NpyS)-Gly-NH2 (NpyS = 3-nitro-2-thiopyridine), a potent and specific inhibitor of thrombin-induced platelet aggregation and platelet calpain, completely inhibited plasmin-induced platelet aggregation and plasmin-induced cleavage of aggregin. These results suggest that, like thrombin, plasmin-induced platelet aggregation is accompanied by the cleavage of aggregin and these responses are indirectly mediated by the intracellularly activated calpain.(ABSTRACT TRUNCATED AT 250 WORDS)
Puri
R N
RN
Thrombosis Research Center, Temple University Health Sciences Center, Philadelphia, Pennsylvania 19104.
Zhou
F X
FX
Colman
R F
RF
Colman
R W
RW
D000595:Amino Acid Sequence; D001792:Blood Platelets / Q000187:drug effects / Q000502:physiology*; D002154:Calpain / Q000097:blood*; D005341:Fibrinolysin / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000494:pharmacology; D010974:Platelet Aggregation; D010980:Platelet Membrane Glycoproteins / Q000502:physiology*
D009842:Oligopeptides; D010980:Platelet Membrane Glycoproteins; C055422:aggregin; D005341:Fibrinolysin; D002154:Calpain