Differential effect of NGF and EGF on ERK in neuronally differentiated PC12 cells

The purpose of this study was to examine ERK enzymatic activity after neuronal differentiation and to determine if the intracellular enzyme continues to be responsive to changes in extracellular NGF. The results demonstrate that long-term NGF maintains ERK activity above normal resting levels, but that it is also greatly reduced from that achieved rapidly after NGF stimulation. Withdrawal of NGF reduces ERK activity further. Re-stimulation of the enzyme by readdition of NGF after NGF withdrawal results in a 10-fold increase in activity. Withdrawal and readdition of EGF is without such a marked effect. The ability of ERK to respond to changes in NGF after neuronal differentiation indicates that this enzyme may serve important functions in addition to the induction of the neuronal phenotype.