The adaptor protein FADD and the initiator caspase-8 mediate activation of NF-?B by TRAIL.

Besides inducing apoptosis, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) activates NF-?B. The apoptosis signaling pathway of TRAIL is well characterized involving TRAIL receptors, Fas-associated protein with death domain (FADD) and caspase-8. In contrast, the molecular mechanism of TRAIL signaling to NF-?B remains controversial. Here, we characterized the receptor-proximal mediators of NF-?B activation by TRAIL. Deletion of the DD of TRAIL receptors 1 and 2 revealed that it is essential in NF-?B signaling. Because FADD interacts with the TRAIL receptor DD, FADD was tested. RNAi-mediated knockdown of FADD or FADD deficiency in JURKAT T-cell leukemia cells decreased or disabled NF-?B signaling by TRAIL. In contrast, TRAIL-induced activation of NF-?B was maintained upon loss of receptor interacting protein 1 (RIP1) or knockdown of FLICE-like inhibitory protein (FLIP). Exogenous expression of FADD rescued TRAIL-induced NF-?B signaling. Loss-of-function mutations of FADD within the RHDLL motif of the death effector domain, which is required for TRAIL-induced apoptosis, abrogated FADD's ability to recruit caspase-8 and mediate NF-?B activation. Accordingly, deficiency of caspase-8 inhibited TRAIL-induced activation of NF-?B, which was rescued by wild-type caspase-8, but not by a catalytically inactive caspase-8 mutant. These data establish the mechanism of TRAIL-induced NF-?B activation involving the TRAIL receptor DD, FADD and caspase-8, but not RIP1 or FLIP. Our results show that signaling of TRAIL-induced apoptosis and NF-?B bifurcates downstream of caspase-8.     «

Besides inducing apoptosis, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) activates NF-?B. The apoptosis signaling pathway of TRAIL is well characterized involving TRAIL receptors, Fas-associated protein with death domain (FADD) and caspase-8. In contrast, the molecular mechanism of TRAIL signaling to NF-?B remains controversial. Here, we characterized the receptor-proximal mediators of NF-?B activation by TRAIL. Deletion of the DD of TRAIL receptors 1 and 2 revealed that it is...     »