Activation of NF-κB by FADD, Casper, and caspase-8

Fas-associated death domain protein (FADD), caspase-8-related protein (Casper), and caspase-8 are components of the tumor necrosis factor receptor type 1 (TNF-R1) and Fas signaling complexes that are involved in TNF-R1- and Fas-induced apoptosis. Here we show that overexpression of FADD and Gasper potently activates NF-kappa B, In the presence of caspase inhibitors, overexpression of caspase-8 also activates NF-kappa B. A caspase-inactive point mutant, caspase-8(C360S), activates NF-kappa B as potently as wild-type caspase-8, suggesting that caspase-8-induced apoptosis and NF-kappa B activation are uncoupled. NF-kappa B activation by FADD and Gasper is inhibited by the caspase-specific inhibitors crmA and BD-fmk, suggesting that FADD- and Gasper-induced NF-kappa B activation is mediated by caspase-8, FADD, Gasper, and caspase-8-induced NF-kappa B activation are inhibited by dominant negative mutants of TRAF2, NIK, I kappa B kinase alpha, and I kappa B kinase beta. A dominant negative mutant of RIP inhibits FADD- and caspase-8-induced but not Gasper-induced NF-kappa B activation. A mutant of Gasper and the caspase-specific inhibitors crmA and BD-fmk partially inhibit TNF-R1-, TRADD, and TNF-induced NF-kappa B activation, suggesting that FADD, Gasper, and caspase-8 function downstream of TRADD and contribute to TNF-R1-induced NF-kappa B activation. Moreover, activation of caspase-8 results in proteolytic processing of NIK, which is inhibited by crmA. When overexpressed, the processed fragments of NIK do not activate NF-kappa B, and the processed G-terminal fragment inhibits TNF-R1-induced NF-kappa B activation. These data indicate that FADD, Gasper, and pro-caspase-8 are parts of the TNF-R1-induced NF-kappa B activation pathways, whereas activated caspase-8 can negatively regulate TNF-R1-induced NF-kappa B activation by proteolytically inactivating NIK.