Abstract
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. [Arg^54^,Arg^55^]IGF‐II and [Leu^27^]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 ^125^I‐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. J. Cell. Physiol. 197: 131–138, 2003© 2003 Wiley‐Liss, Inc.