ACTIVATION OF P21(RAS) BY NERVE GROWTH-FACTOR IN NEUROBLASTOMA-CELLS

Nerve growth factor (NGF) is essential for the differentiation and sur vival of sympathetic and sensory neurones and is thought to play a rol e in the differentiation of neuroblastoma. In this study we have shown NGF decreased the mRNA level of the two GTPase activating proteins ne urofibromin (containing the NF1-GRD) and type 1 GAP(120) in two neurob lastoma 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 o f NGF. Treatment with NGF increased the amount of GTP bound p21(ras) 3 -fold, within 20 min exposure. Western blot analysis showed SK-N-SH an d IMR-32 cells to contain equal amounts of p21(ras) protein and these levels were unchanged by NGF treatment. However, NGF induced an increa se in the level of neurofilament L protein, which was accompanied by a n 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 p21(ras) by NGF in IMR-32 and SK-N-SH cells, thus implicating p21(ras) in NGF sign al transduction in neuroblastoma.