Abstract
Besides inducing apoptosis, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) activates NF-κB. 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-κB remains controversial. Here, we characterized the receptor–proximal mediators of NF-κB activation by TRAIL. Deletion of the DD of TRAIL receptors 1 and 2 revealed that it is essential in NF-κB 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-κB signaling by TRAIL. In contrast, TRAIL-induced activation of NF-κB 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-κB 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-κB activation. Accordingly, deficiency of caspase-8 inhibited TRAIL-induced activation of NF-κB, 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-κB 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-κB bifurcates downstream of caspase-8.
Highlights
Upon trimerization, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) can bind to five TRAIL receptors
We have shown that TRAIL activates the transcription factor nuclear factor ‘k-lightchain enhancer of B cells’ (NF-kB) in tumor cells[10] and induces survival/proliferation, which impedes the proapoptotic function of TRAIL.[11,12]
We have recently shown that TRAIL-R1/2 mediated TRAIL-induced proliferation and activation of NF-kB.[11,12]
Summary
Only TRAIL receptor 1 (TRAIL-R1, DR4) and TRAIL receptor 2 (TRAIL-R2, DR5) mediate apoptosis[1] as they contain a functional death domain (DD) required for apoptosis signaling. To signal TRAIL-induced apoptosis, the receptor DD binds the DD-containing adaptor molecule FADD (Fas-associated protein with DD), which, in turn, recruits the initiator caspase 8 to form the death-inducing signaling complex (DISC).[2]. In addition to cell death, TRAIL activates survival and/or proliferation, which results, for example, in endothelial growth.[9] Besides normal cells, we have shown that TRAIL activates the transcription factor NF-kB in tumor cells[10] and induces survival/proliferation, which impedes the proapoptotic function of TRAIL.[11,12] The molecular mechanisms of NF-kB activation by TRAIL remain elusive, several proteins were proposed as mediators, including TNFR-associated protein with DD (TRADD) and RIP1.13,14. Received 05.9.12; accepted 12.9.12; Edited by G Raschellausing mutated TRAIL receptor fusion proteins, knockdown strategies and rescue experiments in knockout cells
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have