gms | German Medical Science

Vascular smooth muscle cells (VSMC) play a fundamental role in hypertension-associated vascular remodelling due to increased cell growth, cell migration, extracellular matrix deposition and inflammation. Urokinase-type plasminogen activator (uPA) and its receptor (uPAR) not only serve to localize proteolysis on cell surface, but also induce cellular responses towards cell migration, adhesion and proliferation in a non-proteolytic fashion. We demonstrated recently that the uPAR-Tyk2-PI3-K-RhoA-Rho kinase pathway mediates uPA-induced VSMC migration, whereas uPA-dependent changes of VSMC proliferation are mediated by STAT1. However, since uPAR is a GPI-anchored protein and lacks any transmembrane domain, it remained unknown how these two cascades are linked to uPAR. Here we provide evidence that in VSMC platelet-derived growth factor receptor (PDGFRß) serves as a transmembrane adaptor for uPAR.

We demonstrate that PDGFR tyrosine kinase activity is required for uPA to promote both, promigratory and profilerative effects. Thus, inhibition of PDGFR tyrosine kinase activity with either specific inhibitor AG 1295 or by overexpression of tyrosine kinase inactive PDGFR mutant prevented uPA-induced VSMC migration and proliferation. Further, we demonstrate by co-immunoprecipitation approach that uPAR and PDGFR in VSMC are associated in a uPA-dependent manner. Furthermore, we observed increased uPAR- and time-dependent PDGFR autophosphorylation in response to uPA stimulation in VSMC in the absence of PDGF. Tyrosine kinase activity of PDGFR is also required for the uPA-induced RhoA activation, and STAT1 tyrosine phosphorylation, since its inhibition by either pharmacological inhibitor or by overexpression of tyrosine kinase inactive PDGFR mutant abolished uPA-induced responses.

Taken together, these findings suggest that PDGFR is involved in regulation of uPA-induced signaling and functional behaviour of human VSMC and can serve as a transmembrane adaptor of uPAR.