ERK5 activation of MEF2-mediated gene expression plays a critical role in BDNF-promoted survival of developing but not mature cortical neurons

Extracellular signal-regulated kinase 5 (ERK5) is a member of the mitogen-activated protein kinase family whose biological function in the CNS has not been defined. In contrast to ERK1 and ERK2, which are activated by neurotrophins (NTs), cAMP, and neuronal activity in cortical neurons, ERK5 is activated only by NTs. Here, we report that ERK5 expression is high in the brain during early embryonic development but declines as the brain matures to almost undetectable levels by postnatal day (P) 49. Interestingly, expression of a dominant-negative ERK5 blocked brain-derived neurotrophic factor protection against trophic withdrawal in primary cortical neurons cultured from embryonic day (E) 17 but not PO. Furthermore, expression of a dominant-negative ERK5 induced apoptosis in E17 but not PO cortical neurons maintained in the presence of serum. We also present evidence that ERK5 protection of E17 cortical neurons may be mediated through myocyte enhancer factor 2-induced gene expression. These data suggest that ERK5 activation of myocyte enhancer factor 2-induced gene expression may play an important and novel role in the development of the CNS by mediating NT-promoted survival of embryonic neurons.