Daxx identified as a protein binds Fas has been reported to function as a transcriptional regulator. Recent studies have indicated that endogenous Daxx represses NF-κB transactivity in RNAi-treated cells. However, the mechanism by which Daxx regulates NF-κB activity remains unclear. This study demonstrated that Daxx inhibits NF-κB activation and represses the TNF induced transactivation of NF-κB in 293 cells. The ectopic expression of Daxx did not regulate stability of NF-κB. Down regulation of NF-κB activity by Daxx was not relieved by the treatment of HDAC inhibitor, TSA, however ASK1 that sequestered Daxx in the cytoplasm enhanced the repressive activity of Daxx in NF-κB activation, suggesting that NF-κB regulation by Daxx takes place in the cytoplasm of 293 cell. GST-pull down assay demonstrated that Daxx physically interacts with IkB. Daxx inhibited the phosphorylation of IkB in response to TNF. The reduced phosphorylation of IkB seems to result in the inhibition of NF-κB activation. Apoptotic cell death was increased by the overexpression of Daxx in TNF treated cells. Downregulated NF-κB activites by Daxx appeared to facilitate TNF induced apoptosis. In addition, the overexpression of NF-κB restored cells from cell death induced by Daxx/TNF. This proposes a mechanism by which Daxx induces apoptosis by inhibiting the NF-κB survival pathway.
