CAAT/enhancer-binding protein δ 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 beta 2-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 delta(C/EBP delta) contributes to NGF gene regulation. Here we have further defined the function of C/EBP delta 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/EBP delta. A CRE-like site that binds CREB was identified in the proximal NGF promoter, and C/EBP delta 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/EBP delta in combination with CLE treatment increased endogenous NGF mRNA levels in C6-2B cells. C/EBP delta null mice showed complete loss of NGF induction in the cerebral cortex following CLE treatment, demonstrating a critical role for C/EBP delta in regulating beta 2-adrenergic receptor-mediated NGF expression in vivo. Thus, our findings demonstrate a critical role for C/EBP delta in regional expression of NGF in the brain and implicate CREB in CLE-induced NGF gene transcription.