Urokinase induces receptor mediated brain tumor cell migration and invasion

The plasminogen activation (PA) system plays an important role in tumor inv asion by initiating pericellular proteolysis of the extracellular matrix (E CM) and inducing cell migration. Malignant brain tumors overexpress PA memb ers and characteristically invade by migrating on ECM-producing white matte r tracts and blood vessel walls. To determine whether urokinase-type plasmi nogen activator (uPA) and its receptor (uPAR) directly modulate the migrati on of brain tumor cells, we examined six human brain tumor cell lines, 2 as trocytomas (SW1088, SW1783), 2 medullobastomas (Daoy, D341Med), and 2 gliob lastomas (U87MG, U118MG), for their surface uPAR expression, endogenous PA activity, and functional proteolytic activity by an ECM-degradation assay. Migration on Transwell membranes and invasion of Matrigel was then tested b y pre-incubating the cells with increasing concentrations of either uPA, th e proteolytically inactive amino-terminal fragment (ATF) of uPA, or the uPA R cleaving enzyme, phosphatidylinositol-specific phospholipase C (PI-PLC). All of the cell lines, except D341Med, express surface uPAR protein and uPA activity. High levels of uPAR and uPA activity correlated with cellular de gradation of ECM, cell migration, and Matrigel invasion. Cell migration and invasion were enhanced by uPA or ATF in a dose dependent manner, while PI- PLC treatment abolished the uPA effect and inhibited migration and invasion . We conclude that ligation of uPAR by uPA directly induces brain tumor cel l migration, independent of uPA-mediated proteolysis; and in concert with E CM degradation, markedly enhances invasion. Conversely, removing membrane b ound uPAR from the surface of the cells studied inhibited their ability to migrate and invade even in the presence of proteolytically active uPA.