UROKINASE MEDIATES BFGF-INDUCED VASCULAR SMOOTH-MUSCLE CELL-MIGRATIONUNDER THE CONTROL OF TGF-BETA

The present study was undertaken to evaluate in vitro, in a wound assa y, the relative importance of u-PA in the chemotactic potential of bas ic fibroblast growth factor (bFGF) for smooth muscle cells (SMC). Migr ation at the edge of confluent cultures of aortic SMC isolated from tr ansgenic mice showing single inactivations of the plasminogen activato r inhibitor-1 (PAI-I), t-PA, u-PA or urokinase receptor (u-PAR) genes was investigated. Compared to SMC isolated from wild-type or from t-PA or PAI-I-deficient mice, which responded normally, SMC isolated from u-PA- or u-PAR-deficient mice did not migrate in response to bFGF. The se data were confirmed on wild-type SMC by using neutralizing antibodi es against u-PA which blocked the chemotactic effect of bFGF. An antib ody directed against t-PA was without effect. Supplementation of u-PA- deficient cells with purified u-PA restored their migratory response t o bFGF, whereas on u-PAR-deficient cells, the addition of exogenous u- PA was without effect. The chemotactic activity of bFGF was not relate d to the generation of plasmin by u-PA and was not affected by direct u-PA inhibitors. In the presence of exogenous u-PA, the addition of la tent transforming growth factor beta (latent-TGF-beta) resulted in an inhibition of the chemotactic activity of bFGF. The dose-dependent inh ibitory effect of plasmin inhibitors showed that this enzyme was impor tant in the conversion of latent-TGF beta into TGF beta via u-PA. Thes e results therefore indicate that, at least in vitro, u-PA is a key fa ctor in the chemotactic effect of bFGF for SMC and show that u-PA regu lates the conversion of latent-TGF beta into TGF beta which in turn re gulates the activity of bFGF on these cells.