Induction of cell death by myristylated death domain of p55 tnf receptor is not abolished by ipr-tike point mutation

We transiently expressed the intracellular domains of p55 TXF receptor(TNFRl) as either a cytosolic- or a membrane-associated form and examined their effects on the endogenous receptor-mediated gene expression as well as on ceil viability. The gene expression as measured by luciferase activity under NF-kB-controlling elements was blocked by all forms of the intracellu lar domains of TNFR.1. The blockade of reporter gene expression was due to the ceil death induced by the intracellular domain of TNFR1 per se. The killing mechanism of the intracellular domain peptides appears to be apoptotic. Interestingly, myristylated form of the intracellular domain, consist ing of mainly death domain, showed the most potent cell-killing activity.This myristylated death domain could still induce cell death even if Ipr-Iike point mutation(Leu351 to Aîa), which had been reported to abrogate TNF-induced cytotoxicity, was introduced. This suggests that the myristylated death domain activates an additional death signaling pathway which is not involved in TNF-induced cell death.