Urokinase-type plasminogen activator (uPA) binds to its receptor, uPAR, on the surface of cancer cells, leading to the formation of plasmin. Rhabdomyosarcoma (RMS) cell lines secrete high levels of insulin-like growth factor II (IGF-II), suggesting autocrine IGFs play a major role in the unregulated growth and metastasis of RMS. In vitro, IGF-II and IGF-I increased migration of RD cells to 124+/-9% (P<0.01) and 131+/-8% (P<0.05) of control, respectively. IGF-II-induced migration was abolished by insulin-like growth factor binding protein-6 (IGFBP-6) (P<0.01), a relatively specific inhibitor of IGF-II, and by plasminogen activator inhibitor type 1 (PAI-1) (P<0.05). Aprotinin, a plasmin inhibitor, and mannosamine, which inhibits the synthesis of glycosylphosphatidylinositol (GPI), thereby preventing anchorage of GPI-linked proteins such as uPAR to the cell membrane, also decreased IGF-II- (P<0.05 for both) but not IGF-I-induced migration. [Arg54,Arg55]IGF-II and [Leu27]IGF-II, which preferentially bind to the IGF-I and IGF-II/mannose-6-phosphate receptors (IGF-II/M6PR), respectively, both induced RD cell migration to 146+/-8% (P<0.01) and 120+/-7% (P<0.05) of control, respectively. An anti-uPAR anti-serum reduced IGF-II- and IGF-I-induced migration (P<0.05 for both). An anti-low density lipoprotein-related protein (LRP) anti-serum reduced IGF-I-induced migration (P<0.05). IGF-I and -II both increased specific 125I-single chain uPA (scuPA) binding to RD cells in a dose-dependent manner (P<0.01). These results suggest involvement of the PA/plasmin system in IGF-induced migration and indicate important roles these systems may have in RMS metastasis.
Copyright 2003 Wiley-Liss, Inc.