Activation of p44 and p42 MAP Kinases is not Essential for the Survival of Rat Sympathetic Neurons

We have examined whether activation of MAP kinases or extracellular signal-regulated kinases (ERKs)] is required for the survival of rat sympathetic neurons by comparing the actions of three survival factors whose survival-promoting actions can be blocked by neutralizing Fab fragments to p21 ras (Nobes and Tolkovsky, 1995, Eur. J. Neurosci. , 7, 344–350), nerve growth factor (NGF), the cytokines ciliary neurotrophic factor (CNTF) and leukaemia inhibitory factor (LIF), and the cyclic AMP analogue 4-(8-chlorophenylthio)cAMP (CPTcAMP). NGF-induced survival was accompanied by an intense (15- to 30-fold) and steady (>24 h) activation of p44 and p42 ERKs which waned rapidly ( t _1/2∼30 min) upon NGF withdrawal. However, concentrations of NGF that induced a weak (4- to 5-fold) stimulation of the ERKs were not sufficient to maintain long-term survival. Moreover, prolonged and intense stimulation of the ERKs by NGF for up to 15.5 h was unable to confer long-term survival, since withdrawal of NGF after this time resulted in neuronal death that was kinetically indistinguishable from the death of neurons that had not been exposed to NGF. By contrast, CNTF and LIF continued to support survival for up to 3 days after eliciting only transient (<30 min and 1 h respectively) activation of p44 and p42 ERKs, while CPTcAMP induced survival for several days without any measurable activation of the ERKs. Taken together, these data suggest that ERK activation perse is neither necessary nor sufficient for survival and that alternative pathways exist for effecting long-term survival of rat sympathetic neurons.