Activation of the IκB kinase complex is sufficient for neuronal differentiation of PC12 cells

We examined the role of the I kappa B kinase complex in nerve growth factor (NGF)-induced neuronal differentiation of PC12 cells. We showed that neurite outgrowth is accompanied by an activation of the IKK complex and a delayed elevation of NF-kappa B-dependent transcription. Ectopic expression of a constitutively active form of IKK2 but not of IKK1 promoted neurite outgrowth in the absence of NGF. In addition, increased expression of Bcl-2 and Bcl-xL and resistance to apoptosis upon serum withdrawal were found. The IKK2-driven neurite outgrowth was not blocked by MEK1/2 and PI3K inhibitors but was repressed by the SN50 peptide suggesting that NF-kappa B activation is critical for this differentiation process. Transdominant mutants of I kappa B alpha (32/36-SS/AA) and IKK1 only marginally reduced NGF-driven neuritogenesis. However, a dominant negative mutant of IKK2 or an I kappa B alpha protein lacking the complete N-terminus was able to repress neuritogenesis. We also detected tyrosine phosphorylation of I kappa B alpha during differentiation. Consequently, PC12 cells expressing mutant I kappa B alpha (Y42F) show an impaired neuritogenesis. Furthermore, PC12 cells ectopically expressing p65 show almost no signs of neurite outgrowth which is, however, found to some extent in c-Rel-expressing cells. Our data suggest that NGF-induced PC12 differentiation includes activation of IKK2 which may promote the release of c-Rel-containing dimers.