Single-Chain Urokinase-Type Plasminogen Activator Bound To Its Receptor Is Relatively Resistant To Plasminogen Activator Inhibitor Type 1

• Published in: Blood 1996-05, Vol.87 (9), p.3545-3549
• Main Authors: Higazi, Abd Al-Roof, Mazar, Andrew, Wang, Jieyi, Reilly, Regina, Henkin, Jack, Kniss, Douglas, Cines, Douglas
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Blood coagulation. Blood cells; Cell Line; Fundamental and applied biological sciences. Psychology; General aspects, investigation methods, hemostasis, fibrinolysis; Humans; Molecular and cellular biology; Peptide Fragments - chemical synthesis; Peptide Fragments - metabolism; Plasminogen Activator Inhibitor 1 - pharmacology; Protein Binding - drug effects; Receptors, Cell Surface - drug effects; Receptors, Cell Surface - metabolism; Receptors, Urokinase Plasminogen Activator; Urokinase-Type Plasminogen Activator - chemical synthesis; Urokinase-Type Plasminogen Activator - metabolism
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood.V87.9.3545.bloodjournal8793545

Urokinase-type plasminogen activator (uPA) is synthesized as single-chain protein (scuPA) with little intrinsic activity. scuPA is activated when it is converted to two-chain urokinase (tcuPA) by plasmin or when it binds as a single-chain molecule to its cellular receptor (uPAR). Previous data indicate that complexes between scuPA and its receptor have somewhat higher affinity for plasminogen than does tcuPA. The current study indicates that plasminogen activator activity of scuPA bound to recombinant, soluble uPAR (suPAR) is also fivefold less sensitive to inhibition by plasminogen activator type 1 (PAI-1) than is soluble or receptor-bound tcuPA. Binding of PAI-1 to suPAR/scuPA complexes is totally reversible and can be overcome by increasing the concentration of plasminogen, suggesting a competitive mechanism of inhibition (Ki = 18 nmol/L). Binding of scuPA to suPAR also retards its cleavage by plasmin. These results indicates that binding of single-chain urokinase to its receptor promotes its activity, retards its inhibition, and protects it from conversion to a two-chain form of the enzyme, a step that may precede its inactivation and clearance from cell surfaces. These results are consistent with a physiologic role for receptor-bound single-chain urokinase as a cellular plasminogen activator.