Lysis of plasma clots by urokinase-soluble urokinase receptor complexes.
Single-chain urokinase plasminogen activator (scuPA), the unique form secreted by cells, expresses little intrinsic plasminogen activator activity. scuPA can be activated by proteolytic cleavage to form a two-chain enzyme (tcuPA), which is susceptible to inhibition by plasminogen activator inhibitor type I (PAI-1). scuPA is also activated when it binds to its cellular receptor (uPAR), in which case the protein remains as a single chain molecule with less susceptibility to PAIs. Fibrin clots are invested with PAI-1 derived from plasma and from activated platelets. Therefore, we compared the fibrinolytic activity of complexes between scuPA and recombinant soluble uPAR (suPAR) to that of scuPA, tcuPA, and tcuPA/suPAR complexes. scuPA/suPAR complexes mediated the lysis of plasma-derived fibrin clots 14-fold more extensively than did equimolar concentrations of scuPA and threefold more extensively than did tcuPA or tcuPA/suPAR, respectively. The enhanced catalytic activity of scuPA/suPAR required that all three domains of the receptor be present, correlated with its PAI-1 resistance, was not dependent on fibrin alone, and required a plasma cofactor that was identified as IgG. Human IgG bound specifically to suPAR and scuPA/suPAR as determined by using affinity chromatography and immunoprecipitation. Plasma depleted of IgG lost most of its capacity to promote the fibrinolytic activity of scuPA/suPAR, and the activity of the complex was restored by adding plasma concentrations of purified IgG. These studies indicate that scuPA/suPAR can function as a plasminogen activator in a physiological milieu.
Higazi
A A
AA
Department of Clinical Biochemistry, Hadassah University Hospital and Hebrew University-Hadassah Medical School, Jerusalem, Israel. abd@md2.huji.ac.il
Bdeir
K
K
Hiss
E
E
Arad
S
S
Kuo
A
A
Barghouti
I
I
Cines
D B
DB
D000595:Amino Acid Sequence; D001777:Blood Coagulation / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D005342:Fibrinolysis / Q000187:drug effects / Q000235:genetics; D006801:Humans; D007074:Immunoglobulin G / Q000302:isolation & purification / Q000502:physiology; D007143:Immunoglobulin Heavy Chains / Q000302:isolation & purification; D007135:Immunoglobulin Variable Region / Q000302:isolation & purification / Q000502:physiology; D008969:Molecular Sequence Data; D011956:Receptors, Cell Surface / Q000235:genetics / Q000502:physiology*; D055293:Receptors, Urokinase Plasminogen Activator; D011994:Recombinant Proteins / Q000494:pharmacology; D012995:Solubility; D014568:Urokinase-Type Plasminogen Activator / Q000235:genetics / Q000502:physiology*
D007074:Immunoglobulin G; D007143:Immunoglobulin Heavy Chains; D007135:Immunoglobulin Variable Region; C524898:PLAUR protein, human; D011956:Receptors, Cell Surface; D055293:Receptors, Urokinase Plasminogen Activator; D011994:Recombinant Proteins; D014568:Urokinase-Type Plasminogen Activator