Activation of p21ras by nerve growth factor in embryonic sensory neurons and PC12 cells.

p21ras is believed to be involved in the neuronal differentiation of cells responsive to nerve growth factor (NGF). We show that NGF stimulates the activation of p21ras in embryonic sensory neurons and in PC12 cells. In the initial 5 min of exposure to NGF, the activation is concentration-dependent. In the sensory neurons and PC12 cells, the apparent maximal activation was reached at 50 and 10 ng/ml, respectively, with half-maximal activation at approximately 5 and 2-3 ng/ml, respectively. Kinetic analysis at low concentrations of NGF showed that p21ras activation slowly increases with time in both types of cells, while high concentrations result in rapid activation within 5 min. These results indicate that NGF regulates the activation state of p21ras in these cells and provides evidence suggesting that activation of p21ras is involved in NGF signal transduction. Treatment of PC12 cells with brain-derived neurotrophic factor or neurotrophin-3 (NT-3) failed to activate p21ras, suggesting that binding alone to p75LNGFR is insufficient for ras activation. Treatment with the kinase inhibitor, K252a, which inhibits the NGF tyrosine kinase receptor p140trk, abolished ras activation, suggesting that p140trk is the major mediator of p21ras activation by NGF.