Src-dependence and pertussis-toxin sensitivity of urokinase receptor-dependent chemotaxis and cytoskeleton reorganization in rat smooth muscle cells

The catalytically inactive precursor of urokinase-type plasminogen activator (pro-u-PA) induced a chemotactic response in rat smooth muscle cells (RSMC) through binding to the membrane receptor of urokinase (u-PA receptor [u-PAR]). A soluble form of u-PAR activated by chymotrypsin cleavage as well as a peptide located between domain 1 and 2 of u-PAR reproduced the effect of pro-u-PA on cell migration. The chemotactic pro-u-PA effect correlates with a dramatic reorganization of actin cytoskeleton, of adhesion plaques, and with major cell shape changes in RSMC. Pro-u-PA induced a decrease in stress fiber content, membrane ruffling, actin ring formation, and disruption leading to the characteristic elongated cell shape of motile cells with an actin semi-ring located close to the leading edge of cells. u-PAR effects on both chemotaxis and cytoskeleton were sensitive to pertussis toxin and, hence, possibly require G proteins. u-PAR effects are accompanied by a relocation of u-PAR, vitronectin receptor (VNR) alphavbeta3, beta1 integrin subunit, and Src tyrosine kinase to the leading membrane of migrating cells. In conclusion, our data show that pro-u-PA, via binding to u-PAR, controls a signaling pathway, regulated by tyrosine kinases and possibly G proteins, leading to cell cytoskeleton reorganization and cell migration.