CAAT/enhancer-binding protein delta and cAMP-response element-binding protein mediate inducible expression of the nerve growth factor gene in the central nervous system

Nerve growth factor (NGF) synthesis in the rat cerebral cortex is induced by the β2-adrenergic receptor agonist clenbuterol (CLE). Because NGF is a crucial neurotrophic factor for basal forebrain cholinergic neurons, defining the mechanisms that regulate its transcription is important for developing therapeutic strategies to treat pathologies of these neurons. We previously showed that the transcription factor CCAAT/enhancer-binding protein δ (C/EBPδ) contributes to NGF gene regulation. Here we have further defined the function of C/EBPδ and identified a role for cAMP response element-binding protein (CREB) in NGF transcription. Inhibition of protein kinase A in C6-2B glioma cells suppressed CLE induction of an NGF promoter-reporter construct, whereas overexpression of protein kinase A increased NGF promoter activity, particularly in combination with C/EBPδ. A CRE-like site that binds CREB was identified in the proximal NGF promoter, and C/EBPδ and CREB were found to associate with the NGF promoter in vivo. Deletion of the CRE and/or C/EBP sites reduced CLE responsiveness of the promoter. In addition, ectopic expression of C/EBPδ in combination with CLE treatment increased endogenous NGF mRNA levels in C6-2B cells. C/EBPδ null mice showed complete loss of NGF induction in the cerebral cortex following CLE treatment, demonstrating a critical role for C/EBPδ in regulating β2-adrenergic receptor-mediated NGF expression in vivo. Thus, our findings demonstrate a critical role for C/EBPδ in regional expression of NGF in the brain and implicate CREB in CLE-induced NGF gene transcription.