N-myc induction stimulated by insulin-like growth factor I through mitogen-activated protein kinase signaling pathway in human neuroblastoma cells

Insulin-like growth factor I (IGF-I) stimulates proliferation, survival, an d differentiation in many cell types, including pediatric neuroblastomas, T he effect is mediated via the type I IGF-I receptor (IGF-IR), which is esse ntial for growth in these cells. Several lines of evidence indicate that IG F-IR function may be particularly important in the pathogenesis of neurobla stoma, Amplification of the N-myc oncogene or overexpression of N-Myc oncop rotein has been reported to be associated with resistance to therapy and po or prognosis of neuroblastomas. It was therefore of interest to analyze whe ther IGF-I signaling regulated expression of N-myc in KP-N-RT human neurobl astoma cells as an experimental model that has amplified N-myc. We found th at IGF-I induces N-myc mRNA and protein in the KP-N-RT with maximums of fou r and six times more than the basal level at 2 and 3 h after stimulation, r espectively. These effects of IGF-I were blocked by a neutralizing antibody against IGF-IR (alpha-IR3), Exogenous IGF-I induced phosphorylation and ac tivation of extracellular signal-regulated kinases p44/42 (ERK1 and ERK2), with a maximal level 30 min after the stimulation. The MEK1 inhibitor PD980 59 reduced IGF-I-mediated p44/42 MAPKs phosphorylation and produced a paral lel reduction of IGF-I-stimulated N-Myc induction. Furthermore, both alpha- IR3 and PD98059 inhibited G(1)-S cell cycle progression stimulated by IGF-I , Our results demonstrate that IGF-I induces N-Myc in the KP-N-RT neuroblas toma cell line at the RNA level and establishes a clear correlation between N-Myc induction and activation of p44/42 MAPK signaling.