Activation of p21ras by nerve growth factor in neuroblastoma cells.

Nerve growth factor (NGF) is essential for the differentiation and survival of sympathetic and sensory neurones and is thought to play a role in the differentiation of neuroblastoma. In this study we have shown NGF decreased the mRNA level of the two GTPase activating proteins neurofibromin (containing the NF1-GRD) and type 1 GAP120 in two neuroblastoma cell lines, IMR-32 and SK-N-SH. This effect was seen within 15 min exposure to NGF and was maintained up to 2 h after the addition of NGF. Treatment with NGF increased the amount of GTP bound p21ras 3-fold, within 20 min exposure. Western blot analysis showed SK-N-SH and IMR-32 cells to contain equal amounts of p21ras protein and these levels were unchanged by NGF treatment. However, NGF induced an increase in the level of neurofilament L protein, which was accompanied by an increase in neurite extension. These effects of NGF occurred in the absence of growth inhibition. In conclusion, our results demonstrate a decrease in GTPase activating proteins and activation of p21ras by NGF in IMR-32 and SK-N-SH cells, thus implicating p21ras in NGF signal transduction in neuroblastoma.