The Viral Oncoprotein LMP1 Exploits TRADD for Signaling by Masking Its Apoptotic Activity

Abstract

The tumor necrosis factor (TNF)-receptor 1–associated death domain protein (TRADD) mediates induction of apoptosis as well as activation of NF-κB by cellular TNF-receptor 1 (TNFR1). TRADD is also recruited by the latent membrane protein 1 (LMP1) oncoprotein of Epstein-Barr virus, but its role in LMP1 signaling has remained enigmatic. In human B lymphocytes, we have generated, to our knowledge, the first genetic knockout of TRADD to investigate TRADD's role in LMP1 signal transduction. Our data from TRADD-deficient cells demonstrate that TRADD is a critical signaling mediator of LMP1 that is required for LMP1 to recruit and activate I-κB kinase β (IKKβ). However, in contrast to TNFR1, LMP1-induced TRADD signaling does not induce apoptosis. Searching for the molecular basis for this observation, we characterized the 16 C-terminal amino acids of LMP1 as an autonomous and unique virus-derived TRADD-binding domain. Replacing the death domain of TNFR1 by LMP1′s TRADD-binding domain converts TNFR1 into a nonapoptotic receptor that activates NF-κB through a TRAF6-dependent pathway, like LMP1 but unlike wild-type TNFR1. Thus, the unique interaction of LMP1 with TRADD encodes the transforming phenotype of viral TRADD signaling and masks TRADD's pro-apoptotic function.

Inhibition of Latent Membrane Protein 1 Impairs the Growth and Tumorigenesis of Latency II Epstein-Barr Virus-Transformed T Cells

“…A recent study has shown that when the death domain of TNFR1 was replaced with LMP1 CTAR2, cells previously responsive to TNF-induced cell death became resistant. The authors concluded that recruitment of TRADD by CTAR2 masks the apoptotic properties of TRADD (37). In contrast to our model, their proteins are localized to the membrane, and NF-B is activated.…”

The Latent Membrane Protein 1 (LMP1)

“…Lipid rafts are membrane subdomains enriched in sphingolipids and cholesterol that are actively involved in signal transduction processes. LMP1 specifically recruits cellular signaling molecules such as TRAF2 and 3, the TNF receptor-associated death domain protein (TRADD), or PI3-K into lipid rafts, suggesting a role for these membrane domains in LMP1 signaling (Ardila-Osorio et al 1999;Brown et al 2001;Schneider et al 2008;Meckes et al 2013).…”

“…CTAR2 activity depends on the presence of a minor TRAF-binding motif P 379 VQLSYY in order to induce signaling, although direct binding of TRAF proteins to this site has never been demonstrated (Floettmann and Rowe 1997;Kieser et al 1999;Schneider et al 2008). Instead, it was the death domain protein TRADD that was first described to interact directly with CTAR2, the motif Y 384 Y of CTAR2 being essential for TRADD recruitment (Izumi and Kieff 1997).…”

“…Instead, it was the death domain protein TRADD that was first described to interact directly with CTAR2, the motif Y 384 Y of CTAR2 being essential for TRADD recruitment (Izumi and Kieff 1997). This interaction, however, is unique and differs from cellular TRADD-interacting receptors, as it (i) does not require the death domain of TRADD and (ii) dictates an LMP1-specific, transferable, and non-apoptotic type of TRADD signaling (Kieser et al 1999;Schneider et al 2008). LMP1 is thus another impressive example of a viral protein that reprograms and thereby exploits cellular proteins and functions for its own purposes, in this case the subversion of cellular pathways regulating cell survival.…”

Canonical NF-κB Activation Is Essential for Epstein-Barr Virus Latent Membrane Protein 1 TES2/CTAR2 Gene Regulation

“…p52 homodimers, or heterodimers with RelA, RelB, c-Rel (REL), p50 (NF-B1), or BCL3, translocate to the nucleus to regulate transcription (42). LMP1 TES2 (residues 351 to 386) engages the death domain-containing proteins TRADD and RIP (RIPK1), as well as IRF7 (27,50,58). TES2 requires the E3 ubiquitin ligase TRAF6 to activate the MAPKs, IRF7, and canonical NF-B pathways (7,41,51,68).…”