Blood, Vol. 95 No. 4 (February 15), 2000:
pp. 1301-1308
Streptokinase-induced platelet activation involves
antistreptokinase antibodies and cleavage of protease-activated
receptor-1
James P. McRedmond,
Patrick Harriott,
Brian Walker, and
Desmond J. Fitzgerald
Centre for Cardiovascular Science, Department of Clinical
Pharmacology, The Royal College of Surgeons in Ireland, Dublin,
Ireland; Centre for Peptide and Protein Engineering, School of Biology
and Biochemistry, Queen's University of Belfast, Northern Ireland.
Streptokinase activates platelets, limiting its effectiveness as a
thrombolytic agent. The role of antistreptokinase antibodies and
proteases in streptokinase-induced platelet activation was investigated. Streptokinase induced localization of human IgG to the
platelet surface, platelet aggregation, and thromboxane A2
production. These effects were inhibited by a monoclonal antibody to
the platelet Fc receptor, IV.3. The platelet response to streptokinase was also blocked by an antibody directed against the cleavage site of
the platelet thrombin receptor, protease-activated receptor-1 (PAR-1),
but not by hirudin or an active site thrombin inhibitor, Ro46-6240. In
plasma depleted of plasminogen, exogenous wild-type plasminogen, but
not an inactive mutant protein, S741A plasminogen,
supported platelet aggregation, suggesting that the protease cleaving
PAR-1 was streptokinase-plasminogen. Streptokinase-plasminogen cleaved
a synthetic peptide corresponding to PAR-1, resulting in generation of
PAR-1 tethered ligand sequence and selectively reduced binding of a
cleavage-sensitive PAR-1 antibody in intact cells. A combination of
streptokinase, plasminogen, and antistreptokinase antibodies activated
human erythroleukemic cells and was inhibited by pretreatment with IV.3
or pretreating the cells with the PAR-1 agonist SFLLRN, suggesting Fc
receptor and PAR-1 interactions are necessary for cell activation in
this system also. Streptokinase-induced platelet activation is
dependent on both antistreptokinase-Fc receptor interactions and
cleavage of PAR-1.
