Abstract: Nerve growth factor (NGF) activates the transcription factors nuclear factor κB (NF-κB) and activator protein-1 (AP-1) in sympathetic neurons. Whereas NGF-inducible NF-κB is required for the survival of neurons, c-Jun has the ability to promote neuronal death. In this report, we have examined the effect of NGF withdrawal on c-Jun and NF-κB transcription factors in PC12 cells differentiated to a neuronal phenotype. We show that the withdrawal of NGF from these cultures results in de novo synthesis of c-Jun, increase in AP-1 activity, and down-regulation of NF-κB activity. To investigate how the signal transduction pathways activating c-Jun and NF-κB are differentially regulated by NGF, we performed transcriptional analyses. Expression of RelA (NF-κB) suppressed the c-Jun-dependent transcription of c-jun, and this effect was reversed by overexpression of the coactivator p300. RelA’s effects on c-Jun transcription were mediated by competitive binding of the carboxy-terminal region of RelA to the CH1 domain of p300, which also binds to c-Jun; deletion of this region abrogated the ability of RelA to inhibit c-Jun activity. Furthermore, the inhibition of endogenous NF-κB in NGF-maintained neuronal PC12 cells led to the induction of c-Jun synthesis and a marked increase in cell death. Together, these studies demonstrate a functional interaction between NF-κB and c-Jun and suggest a novel mechanism of NF-κB-mediated neuroprotection.