Blocking caspase-3-mediated proteolysis of IKKβ suppresses TNF-α-induced apoptosis

The transcription factor NF-kappaB is essential for survival of many cell types. However, cells can undergo apoptosis despite the concurrent NF-kappaB activation. It is unknown how the protection conveyed by NF-kappaB is overridden during apoptosis. We report here that I kappaB kinase (IKK) beta was specifically proteolyzed by Caspase-3-related caspases at aspartic acid residues 78, 242, 373, and 546 during tumor necrosis factor (TNF)alpha -induced apoptosis. Proteolysis of IKK beta eliminated its enzymatic activity, interfered with IKK activation, and promoted TNF-alpha killing. Point mutations that abrogate IKK beta proteolysis generated a caspase-resistant IKK beta mutant, which suppressed TNF-alpha -induced apoptosis. Thus, our study demonstrates that TNF-alpha -induced apoptosis requires caspase-mediated proteolysis of IKK beta.