IGF-I stimulates chemotaxis of human neuroblasts. Involvement of type 1 IGF receptor, IGF binding proteins, phosphatidylinositol-3 kinase pathway andplasmin system

SH-SY5Y human neuroblastoma cells express IGF receptors, IGFs and IGF bindi ng proteins (IGFBPs), and provide a model for studying the role of the IGF system in human neuronal development. We investigated the effect of IGF-I a nd des(1-3)IGF-I on the motility of SH-SY5Y cells by a cell migration assay based on the assessment of the number of cells which migrated across 8 mu m pore size membranes and around an agarose drop. IGF-I and des(1-3)IGF-I s timulated neuroblast chemotaxis in a dose-dependent manner. Treatment of ce lls with these agents for 24 h resulted in a significant increase (IGF-I by 70% and des(1-3)IGF-I by 90%; P < 0.0001) in cell motility relative to con trol conditions. Addition of monoclonal antibody against type 1 IGF recepto r (alpha-IR3), significantly (P < 0.05) reduced the cell motility induced b y IGF-I (by 30%) and des(1-3)LGF-I (by 70%). Wortmannin, a specific inhibit or of phosphatidylinositol (PI)-3 kinase intracellular signalling, also red uced the IGF-stimulated cell migration (by over 40%, P < 0.01), indicating a key role of the PI-3 kinase pathway in mediating the IGF effect on neurob last migration. Finally, cell treatment with plasminogen (PLG) markedly enh anced neuroblast migration (by over 200%, P < 0.01), whereas incubation wit h the PLG inhibitor 4-(2-aminoethyl)-benzenesulphonyl fluoride reduced cell motility (by 80%, P < 0.01), thus suggesting an involvement of PLG-depende nt IGFBP proteolysis in the regulation of neuroblast motility. In conclusio n, IGF-I is a potent stimulator of neuroblast migration through the activat ion of type 1 IGF receptor and the PI-3 kinase intracellular pathway. IGFBP s and the plasmin system seem to play a role in cell motility, although the nature and the extent of their involvement has yet to be elucidated.