Inhibition of nuclear factor-kappa B activation induces apoptosis in cerebellar granule cells

The nuclear factor (NF)-kappaB family of transcription factors plays import ant roles in the regulation of many activities of neuronal cells, such as s ynaptic transmission, inflammation, neuroprotection, and neurotoxicity. In resting cells, NF-kappaB activity is present both in the cytoplasm, as an i nducible-inactive complex, and in the nucleus, as a constitutive form. Regu lation of its inducible activity relies on processing Of I kappaB(s), which occurs through the proteasome. Here we show that in cerebellar granule cel ls (CGC) the induction of apoptosis, by potassium withdrawal (5 mM KCI), de creases the amount of nuclear NF-kappaB. To understand whether NF-kappaB wa s required for CGC survival, these cells, maintained under depolarizing con ditions (25 mM KCI and serum), were treated with proteasome inhibitors. The results show that these treatments reduce the nuclear amount of NF-kappaB and increase p65 cytoplasmic levels, a process partially regulated via I ka ppaB alpha. degradation. These events are also associated with an impairmen t in CGC survival, with changes in nuclear morphology, induction of DNA lad dering, and oligonucleosome formation, consistent with apoptosis. According to the K+ deprivation model, PSI-induced apoptosis is reversed by inhibito rs of transcription and translation as well as by specific caspase inhibito rs. Together our results show an important role for NF-kappaB in maintainin g CGC survival. Indeed, under conditions of mild depolarization (K25) neces sary for CGC survival, NF-kappaB is distributed between cytosol and nucleus , whereas, under apoptotic conditions (K5), it is depleted from the nucleus , such as after proteasome inhibitor treatment. Therefore, NF-kappaB nuclea r deprivation is involved in the induction of CGC apoptosis.(C) 2001 Wiley- Liss, Inc.