Emerging data suggest that urokinase-type plasminogen activator (UPA),beyond its role in pericellular proteolysis, may also act as a mitogen. We investigated the function of endogenous UPA in mediating the mitogenic effects of platelet-derived growth factor (PDGF) and basic fibroblast growth factor(bFGF) on human vascular smooth muscle cells (SMC). Growth-arrested SMC constitutively expressed UPA, but UPA expression and secretion increased several times upon stimulation with either PDGF or bFGF. Inhibition of endogenous UPA with a polyclonal antibody significantly reduced DNA synthesis and proliferation of PDGF or bFGF stimulated SMC, this effect already being evident when the cells entered S-phase. The proliferative activity of endogenous UPA was dependent on a functional catalytic domain as demonstrated by inhibition experiments with a specific monoclonal antibody (394OA) and p-aminobenzamidine, respectively. In contrast, neither plasmin generation nor binding of UPA to its receptor (CD87) were required for UPA-mediated mitogenic effects. The results demonstrate that endogenous UPA is not only overexpressed in SMC upon stimulation with PDGF/bFGF, but also mediates the mitogenic activity of the growth factors in a catalytic-domain-dependent manner. Specific inhibition of this UPA domain may represent an attractive target for pharmacological interventions in atherogenesis and restenosis after angioplasty.

You do not currently have access to this content.