The function of nuclear factor (NF)-kappaB within the developing and mature CNS is controversial. We have generated transgenic mice to reveal NF-kappaB transcriptional activity in vivo. As expected, constitutive NF-kappaB activity was observed within immune organs, and tumor necrosis factor-inducible NF-kappaB activity was present in mesenchymal cells. Intriguingly, NF-kappaB activity was also prominent in the CNS throughout development, especially within neocortex, olfactory bulbs, amygdala, and hippocampus. NF-kappaB in the CNS was restricted to neurons and blocked by overexpression of dominant-negative NF-kappaB-inducible kinase or the IkappaBalphaM super repressor. Blocking endogenous neuronal NF-kappaB activity in cortical neurons using recombinant adenovirus induced neuronal death, whereas induction of NF-kappaB activity increased levels of anti-apoptotic proteins and was strongly neuroprotective. Together, these data demonstrate a physiological role for NF-kappaB in maintaining survival of central neurons.

The mechanisms employed by the p75 neurotrophin receptor (p75NTR) to mediate neurotrophin-dependent apoptosis are poorly defined. Two-hybrid analyses were used to identify proteins involved in p75NTR apoptotic signaling, and a p75NTR binding partner termed NRAGE (for neurotrophin receptor-interacting MAGE homolog) was identified. NRAGE binds p75NTR in vitro and in vivo, and NRAGE associates with the plasma membrane when NGF is bound to p75NTR. NRAGE blocks the physical association of p75NTR with TrkA, and, conversely, TrkA overexpression eliminates NRAGE-mediated NGF-dependent death, indicating that interactions of NRAGE or TrkA with p75NTR are functionally and physically exclusive. NRAGE overexpression facilitates cell cycle arrest and permits NGF-dependent apoptosis within sympathetic neuron precursors cells. Our results show that NRAGE contributes to p75NTR-dependent cell death and suggest novel functions for MAGE family proteins.