A urokinase‐sensitive region of the human urokinase receptor is responsible for its chemotactic activity

The role of urokinase‐type plasminogen activator (uPA) and its receptor (uPAR/CD87) in cell migration and invasion is well substantiated. Recently, uPA has been shown to be essential in cell migration, since uPA −/− mice are greatly impaired in inflammatory cell recruitment. We have shown previously that the uPA‐induced chemotaxis requires interaction with and modification of uPAR/CD87, which is the true chemoattracting molecule acting through an unidentified cell surface component which mediates this cell surface chemokine activity. By expressing and testing several uPAR/CD87 variants, we have located and functionally characterized a potent uPAR/CD87 epitope that mimics the effects of the uPA–uPAR interaction. The chemotactic activity lies in the region linking domains 1 and 2, the only protease‐sensitive region of uPAR/CD87, efficiently cleaved by uPA at physiological concentrations. Synthetic peptides carrying this epitope promote chemotaxis and activate p56/p59 hck tyrosine kinase. Both chemotaxis and kinase activation are pertussis toxin sensitive, involving a G i/o protein in the pathway.