Insulin-like growth factor I is the key growth factor in serum that protects neuroblastoma cells from hyperosmotic-induced apoptosis

Abstract

Neuroblastoma is a childhood tumor of the peripheral nervous system that remains largely uncurable by conventional methods. Mannitol induces apoptosis in neuroblastoma cell types and insulin-like growth factor I (IGF-I) protects these cells from hyperosmotic-induced apoptosis by affecting apoptosis-regulatory proteins. In the current study, we investigate factors that enable SH-SY5Y neuroblastoma cells to survive in the presence of an apoptotic stimulus. When SH-SY5Y cells are exposed to high mannitol concentrations, more than 60% of the cells are apoptotic within 48 h. Normal CS prevents hyperosmotic-induced apoptosis in a dose-dependent manner, with 0.6% CS protecting 50% of the cells, and 3% CS rescuing more than 70% of the cells from apoptosis. Serum also delays the commitment point for SH-SY5Y cells from 9 h to 35 h. A survey of several growth factors, including epidermal growth factor (EGF), platelet-derived growth factor (PDGF), nerve growth factor (NGF), fibroblast growth factor (FGF), and IGF-I reveals that IGF-I is a component of serum necessary for protection of neuroblastoma cells from death. Mitochondrial membrane depolarization occurs in greater than 40% of the cells after mannitol exposure and caspase-3 activation is increased in high mannitol conditions after 9 h. IGF-I blocks both the mitochondrial membrane depolarization and caspase-3 activation normally induced by hyperosmotic treatment in neuroblastoma cells. Our results suggest that (1) IGF-I is a key factor in serum necessary for protection from death and (2) IGF-I acts upstream from the mitochondria and the caspases to prevent apoptosis in human neuroblastoma.