Chemotactic effect of urokinase plasminogen activator: a major role for mechanisms independent of its proteolytic or growth factor domains.

Urokinase type plasminogen activator (uPA) converts plasminogen to plasmin and is highly chemotactic for many cell types. We examined, using recombinant wild type and mutated forms of uPA, the extent to which its proteolytic properties, its growth-like domain (GFD) and/or interactions with the specific receptor (uPAR) contribute to the chemotactic activity towards vascular smooth muscle cells (SMC). Recombinant wild type uPA (r-uPA) stimulated cell migration nearly 5.8-fold, inactive r-uPA, with a mutation in the catalitic domain (r-uPA(H/Q)), 3-fold, uPA without growth factor like domain (r-uPA(GFD )), 2.6-fold, and a form containing both mutations (r-uPA(H/Q, GFD ), 3.3-fold. All recombinant forms of uPA, wild type and those with mutations were equally and highly effective (IC50 approximately 20 nM) in displacing 125I-r-uPA bound to SMC. These results indicate that additional mechanisms, not dependent on uPA's proteolytic activity or the binding ability of its GFD to uPAR, are the major contributors to its chemotactic action on SMC.