Epstein–Barr virus latent membrane protein 1 activation of NF-κB through IRAK1 and TRAF6

Abstract

Epstein–Barr virus latent membrane protein 1 (LMP1) activation of NF-κB is critical for Epstein–Barr virus-infected B lymphocyte survival. LMP1 activates the IκB kinase complex and NF-κB through two cytoplasmic signaling domains that engage tumor necrosis factor receptor-associated factor (TRAF)1/2/3/5 or TRADD and RIP. We now use cells lacking expression of TRAF2, TRAF5, TRAF6, IKKα, IKKβ, IKKγ, TAB2, IL-1 receptor-associated kinase (IRAK)1, or IRAK4 to assess their roles in LMP1-mediated NF-κB activation. LMP1-induced RelA nuclear translocation was similar in IKKα knockout (KO) and WT murine embryo fibroblasts (MEFs) but substantially deficient in IKKβ KO MEFs. NF-κB-dependent promoter responses were also substantially deficient in IKKβ KO MEFs but were hyperactive in IKKα KO MEFs. More surprisingly, NF-κB responses were near normal in TRAF2 and TRAF5 double-KO MEFs, IKKγ KO MEFs, TAB2 KO MEFs, and IRAK4 KO MEFs but were highly deficient in TRAF6 KO MEFs and IRAK1 KO HEK293 cells. Consistent with the importance of TRAF6, LMP1-induced NF-κB activation in HEK293 cells was inhibited by expression of dominant-negative TAB2 and Ubc13 alleles. These data extend a role for IKKα in IKKβ regulation, identify an unusual IKKβ-dependent and IKKγ-independent NF-κB activation, and indicate that IRAK1 and TRAF6 are essential for LMP1-induced NF-κB activation.

Roles of TNF Receptor-Associated Factor 3 in Signaling to B Lymphocytes by Carboxyl-Terminal Activating Regions 1 and 2 of the EBV-Encoded Oncoprotein Latent Membrane Protein 1

“…Fourth, LMP1-stimulated JNK activation is unaffected in TRAF2 Ϫ/Ϫ mouse embryonic fibroblasts (MEFs) (41). Finally, LMP1-induced NF-B activation is nearly normal in TRAF2 and TRAF5 double-knockout MEFs (48). Thus, the preponderance of accumulating evidence indicates that TRAF2 does not play essential, nonredundant roles in key LMP1-mediated activation events in B cells and fibroblasts.…”

“…However, the functional roles of TRAF5 in LMP1-mediated signaling remain to be determined. Although it has been previously shown that overexpression of dominant-negative TRAF5 abrogates CTAR1-mediated NF-B activation (5), it was recently found that LMP1-induced NF-B activation is nearly normal in TRAF2 and TRAF5 double-knockout MEFs (48). Interestingly, recent studies reported that both JNK activation and NF-B activation mediated by LMP1 signaling are severely impaired in TRAF6 Ϫ/Ϫ MEFs, suggesting an indispensable role for TRAF6 in LMP1 signaling in fibroblasts (41,48).…”

“…Although it has been previously shown that overexpression of dominant-negative TRAF5 abrogates CTAR1-mediated NF-B activation (5), it was recently found that LMP1-induced NF-B activation is nearly normal in TRAF2 and TRAF5 double-knockout MEFs (48). Interestingly, recent studies reported that both JNK activation and NF-B activation mediated by LMP1 signaling are severely impaired in TRAF6 Ϫ/Ϫ MEFs, suggesting an indispensable role for TRAF6 in LMP1 signaling in fibroblasts (41,48). It has been shown previously that endogenous TRAF6 is translocated to membrane microdomains by LMP1 signaling in HeLa cells as visualized by immunostaining and can be coimmunoprecipitated with transfected LMP1 in HEK 293T cells (40,41).…”

TRAF interactions with raft‐like buoyant complexes, better than TRAF rates of degradation, differentiate signaling by CD40 and EBV latent membrane protein 1

“…A series of recent publications suggest that TRAF2 has a key role in CD40 activation of the JNK and NF-KB pathways, whereas it seems to have only a marginal role in the activation of the same pathways by LMP1. 7,44,45,46 This would suggest that TRAF2 association with buoyant complexes is linked in some way with its contribution to JNK and NF-KB cascades. On the other hand, a binding of TRAF2 to LMP1 in vivo is well documented in several types of cell contexts.…”

Current insights into the regulation of programmed cell death by NF-κB

“…Among them, activation of NF-kB by the latent membrane protein 1 (LMP1) of the human Herpesvirus Epstein-Barr virus (EBV), implicated in Burkitt's lymphoma, is critical for transformation of human B cells (Cahir-McFarland et al, 2000;Feuillard et al, 2000;He et al, 2000;reviewed in Hiscott et al, 2006). Recent work implicates interleukin-1b receptorassociated kinase 1 (IRAK1) and TRAF6 in NF-kB activation via latent membrane protein 1 (LMP1) and in phosphorylation of the RelA transactivation domain (Luftig et al, 2003;Song et al, 2006;Wu et al, 2006). A second study has reported that activation of the noncanonical NF-kB pathway, leading to accumulation of nuclear p52/RelB complexes, is required for LMP-1-mediated transformation of human B cells (Luftig et al, 2004).…”