Inhibition of the NF-κB survival pathway via caspase-dependent cleavage of the IKK complex scaffold protein and NF-κB essential modulator NEMO

Apoptosis is mediated by cysteine-dependent, aspartate-directed proteases of the caspase family that proteolyse strategic intracellular substrates to induce cell suicide. We describe here that engagement of apoptotic processes by Fas triggering or by staurosporine stimulation leads to the caspase-dependent inactivation of the nuclear factor kappa B (NF-kappa B) pathway after cleavage of IKK1 (I kappa B kinase 1) and NEMO (NF-kappa B essential modulator), which are needed to transduce NF-kappa B activation signals. In this study, we have analyzed in more detail, the role of NEMO cleavage, as NEMO, but not IKK1, is important for the prosurvival actions of NF-kappa B. We demonstrate that NEMO is cleaved after Asp355 to remove the last 64 C-terminal amino acids. This short form was unable to rescue NF-kappa B activation by tumor necrosis factor-alpha (TNF-alpha) when transfected in NEMO-deficient cells. Consequently, inactivation of NEMO resulted in an inhibition of the expression of antiapoptotic NF-kappa B-target genes coding for caspase inhibitors (cIAP-1, cIAP-2) or adaptors of the TNF receptor family. NEMO-deficient Jurkat cells transiently expressing a non-cleavable mutant of NEMO were less sensitive to TNF-alpha-induced apoptosis. Therefore, downmodulation of NF-kappa B activation via the proteolytic cleavage of NEMO could represent an amplification loop for apoptosis.