PAI‐1 inhibits urokinase‐induced chemotaxis by internalizing the urokinase receptor

PAI‐1 (plasminogen activator inhibitor‐1) binds the urokinase‐type plasminogen activator (uPA) and causes its degradation via its receptor uPAR and low‐density lipoprotein receptor‐related protein (LRP). While both uPA and PAI‐1 are chemoattractants, we find that a preformed uPA–PAI‐1 complex has no chemotactic activity and that PAI‐1 inhibits uPA‐induced chemotaxis. The inhibitory effect of PAI‐1 on uPA‐dependent chemotaxis is reversed when uPAR internalization is inhibited by the 39 kDa receptor‐associated protein or by anti‐LRP antibodies. Under the same conditions, the uPA–PAI‐1 complex is turned into a chemoattractant causing cytoskeleton reorganization and extracellular‐regulated kinase/mitogen‐activated protein kinases activation. Thus, uPAR internalization by PAI‐1 regulates cell migration.