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 recombina nt wild type and mutated forms of uPA, the extent to which its proteolytic properties, its growth-like domain (GFD) and/or interactions with the speci fic receptor (uPAR) contribute to the chemotactic activity towards vascular smooth muscle cells (SMC). Recombinant wild type uPA (r-uPA) stimulated ce ll migration nearly 5.8-fold, inactive r-uPA, with a mutation in the catali tic domain (r-uPA(H/Q)), 3-fold, uPA without growth factor like domain (r-u PA(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 muta tions were equally and highly effective (IC(50)similar to 20 nM) in displac ing I-125-r-uPA bound to SMC. These results indicate that additional mechan isms, 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 S MC.