Nonredundant and complementary functions of TRAF2 and TRAF3 in a ubiquitination cascade that activates NIK-dependent alternative NF-κB signaling

Abstract

The adaptor and signaling proteins TRAF2, TRAF3 and cIAP1 and cIAP2 were suggested to inhibit alternative nuclear factor kappa B (NF-κB) signaling in resting cells by targeting NF-κB inducing kinase (NIK) to ubiquitin-dependent degradation, thus preventing processing of the NF-κB2 precursor protein p100 to release p52. However, the respective functions of TRAF2 and TRAF3 in NIK degradation and activation of alternative NF-κB signaling has remained elusive. We now show that CD40 or BAFF receptor activation resulted in TRAF3 degradation in a cIAP1-cIAP2-and TRAF2-dependent way due to enhanced cIAP1, cIAP2 TRAF3-directed ubiquitin ligase activity. Receptor-induced activation of cIAP1 and cIAP2 correlated with their K63-linked ubiquitination by TRAF2. Degradation of TRAF3 prevented association of NIK with the cIAP1-cIAP2-TRAF2 ubiquitin ligase complex, which resulted in NIK stabilization and NF-κB2-p100 processing. Constitutive activation of this pathway causes perinatal lethality and lymphoid defects.

Dichotomy in NF-κB signaling and chemoresistance in immunoglobulin variable heavy-chain-mutated versus unmutated CLL cells upon CD40/TLR9 triggering

“…Furthermore, alternative NF-kB signaling in many cell types relies on NF-kB-inducing kinase (NIK), which is controlled in a complex manner through interaction with TRAF and IAP family members. Important in the context of our studies, regulation of NIK can be under the control of CD40 or BAFF signaling (Vallabhapurapu et al, 2008;Zarnegar et al, 2008). If and how CpG/TLR9 signaling interferes with these signaling pathways to affect NF-kB activity, in partcular in the context of CLL, is currently unresolved.…”

NIK promotes tissue destruction independently of the alternative NF-κB pathway through TNFR1/RIP1-induced apoptosis

“…11,[26][27][28] Apart from these chemicals, a set of biological ligand of the TNF family, such as lymphotoxin LTα 1 β 2 , CD40L or Tweak, also appeared to target c-IAP1/2 toward the proteasomal and/ or lysosomal degradative pathways. [29][30][31][32][33][34] c-IAP1/2 depletion leads to NIK (NF-κB-inducing kinase) stabilization and the phosphorylation of both IKKα and NF-κB2/p100 prior to the processing of p100 into p52, a pathway defined as the alternative, or non-canonical, NF-κB pathway. [35][36][37] Genetic mouse models revealed that NIK is required for the proper development and/or maintenance of secondary lymphoid organs, for osteoclastogenesis, for T-cell activation as well for B-cell survival.…”

Transcriptional repression by the HDAC4–RelB–p52 complex regulates multiple myeloma survival and growth

“…1b). Although NIK stabilization is required for receptor-induced processing of p100 and activation of RelBp52 (refs 25,26), some basal processing of p100 and nuclear translocation of RelB-p52 does occur under resting conditions in the absence of visible NIK levels as well as in the absence of functional NIK 25,28 . Moreover, basal cytoplasmic-nuclear shuttling of NF-kB family members has been reported to contribute to the basal transcriptional regulation of target genes by NF-kB 52 .…”

“…Cells were cultured for 48 h after transfection and the lentiviral particles were collected from the supernatants and were used to transduce different MM cell lines as described 25 . Thirty-six hours post infection, gene silencing efficiency was analysed by immunoblotting for the respective proteins.…”

“…Among these, mutations in the genes encoding TRAF3, TRAF2 and combined loss of cIAP1 and cIAP2 leading to the stabilization and activation of NIK, were frequently found in MM 24 . Stabilization of NIK leads to constitutive processing of p100 to p52 and activation of the alternative RelB-p52 pathway 25,26 . While NIK was found to be dispensable for the activation of IKKb-dependent classical pathway 27,28 , in MM, NIK stabilization was shown to activate the classical pathway presumably due to direct interaction between NIK and IKKb 23 .…”