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How IL-17 signaling is regulated remains poorly understood. Dong and colleagues identify the ubiquitin-specific protease USP25 as a negative regulator of IL-17-mediated signaling and inflammation. Interleukin 17 (IL-17) is important in infection and autoimmunity; how it signals remains poorly understood. In this study, we identified the ubiquitin-specific protease USP25 as a negative regulator of IL-17-mediated signaling and inflammation. Overexpression of USP25 inhibited IL-17-triggered signaling, whereas USP25 deficiency resulted in more phosphorylation of the inhibitor IκBα and kinase Jnk and higher expression of chemokines and cytokines, as well as a prolonged half-life for chemokine CXCL1–encoding mRNA after treatment with IL-17. Consistent with that, Usp25 −/− mice showed greater sensitivity to IL-17-dependent inflammation and autoimmunity in vivo . Mechanistically, stimulation with IL-17 induced the association of USP25 with the adaptors TRAF5 and TRAF6, and USP25 induced removal of Lys63-linked ubiquitination in TRAF5 and TRAF6 mediated by the adaptor Act1. Thus, our results demonstrate that USP25 is a deubiquitinating enzyme (DUB) that negatively regulates IL-17-triggered signaling.

TNF receptor-associated factors (TRAFs) function as intracellular adaptor proteins utilized by members of the TNF receptor superfamily, such as CD40. Among the TRAF family proteins, TRAF5 has been identified as a potential regulator of CD40. However, it remains unclear whether TRAF5 regulates the generation of germinal center (GC) B cells and antigen-specific antibody production in the T-dependent (TD) immune response. TRAF5-deficient (Traf5−/−) and TRAF5-sufficient (Traf5+/+) mice were immunized in the footpad with 2,4,6-trinitrophenol-conjugated keyhole limpet hemocyanin (TNP-KLH) and complete Freund’s adjuvant (CFA). We found that GC B cell generation and antigen-specific IgM and IgG1 production were significantly impaired in Traf5−/− mice compared to Traf5+/+ mice. The expression levels of CD40-target genes Fas and Lta, which are involved in GC formation, were significantly decreased in B220+ cells isolated from immunized Traf5−/− mice. Traf5−/− B cells showed decreased antibody production, proliferation, and induction of CD40-target genes Tnfaip3, Tnfsf4, and Cd80 in response to agonistic Fc-CD40L protein in vitro. Furthermore, administration of TNP-KLH and Fc-CD40L to Traf5−/− mice resulted in a severe loss of GC B cell development. These results highlight the crucial role of TRAF5 in driving CD40-mediated TD immune response in vivo.

Interleukin 17 promotes antibacterial and antifungal immune defenses. Hamilton and colleagues show that it induces complexes of the adaptors Act1 and TRAF2 or TRAF5 that inhibit the mRNA-destabilizing action of the splicing factor SF2 (ASF), thereby prolonging the half-life of chemokine and cytokine mRNAs. Interleukin 17 (IL-17) promotes the expression of chemokines and cytokines via the induction of gene transcription and post-transcriptional stabilization of mRNA. We show here that IL-17 enhanced the stability of chemokine CXCL1 mRNA and other mRNAs through a pathway that involved the adaptor Act1, the adaptors TRAF2 or TRAF5 and the splicing factor SF2 (also known as alternative splicing factor (ASF)). TRAF2 and TRAF5 were necessary for IL-17 to signal the stabilization of CXCL1 mRNA. Furthermore, IL-17 promoted the formation of complexes of TRAF5-TRAF2, Act1 and SF2 (ASF). Overexpression of SF2 (ASF) shortened the half-life of CXCL1 mRNA, whereas depletion of SF2 (ASF) prolonged it. SF2 (ASF) bound chemokine mRNA in unstimulated cells, whereas the SF2 (ASF)-mRNA interaction was much lower after stimulation with IL-17. Our findings define an IL-17-induced signaling pathway that links to the stabilization of selected mRNA species through Act1, TRAF2-TRAF5 and the RNA-binding protein SF2 (ASF).

The adaptor Act1 links the interleukin 17 receptor to downstream signaling pathways. Li and colleagues show that phosphorylation of Act1 by the kinase IKKi is necessary for recruitment of the adaptors TRAF2 and TRAF5 and activation of the pathway of mitogen-activated protein kinases. Interleukin 17 (IL-17) is critical in the pathogenesis of inflammatory and autoimmune diseases. Here we report that Act1, the key adaptor for the IL-17 receptor (IL-7R), formed a complex with the inducible kinase IKKi after stimulation with IL-17. Through the use of IKKi-deficient mice, we found that IKKi was required for IL-17-induced expression of genes encoding inflammatory molecules in primary airway epithelial cells, neutrophilia and pulmonary inflammation. IKKi deficiency abolished IL-17-induced formation of the complex of Act1 and the adaptors TRAF2 and TRAF5, activation of mitogen-activated protein kinases (MAPKs) and mRNA stability, whereas the Act1–TRAF6–transcription factor NF-κB axis was retained. IKKi was required for IL-17-induced phosphorylation of Act1 on Ser311, adjacent to a putative TRAF-binding motif. Substitution of the serine at position 311 with alanine impaired the IL-17-mediated Act1-TRAF2-TRAF5 interaction and gene expression. Thus, IKKi is a kinase newly identified as modulating IL-17 signaling through its effect on Act1 phosphorylation and consequent function.

The recognition of nucleic acids by the innate immune system during viral infection results in the production of type I interferons and the activation of antiviral immune responses. The RNA helicases RIG-I and MDA-5 recognize distinct types of cytosolic RNA species and signal through the mitochondrial protein MAVS to stimulate the phosphorylation and activation of the transcription factors IRF3 and IRF7, thereby inducing type I interferon expression. Alternatively, the activation of NF-kappaB leads to proinflammatory cytokine production. The function of MAVS is dependent on both its C-terminal transmembrane (TM) domain and N-terminal caspase recruitment domain (CARD). The TM domain mediates MAVS dimerization in response to viral RNA, allowing the CARD to bind to and activate the downstream effector TRAF3. Notably, dimerization of the MAVS CARD alone is sufficient to activate IRF3, IRF7, and NF-kappaB. However, TRAF3-deficient cells display only a partial reduction in interferon production in response to RNA virus infection and are not defective in NF-kappaB activation. Here we find that the related ubiquitin ligase TRAF5 is a downstream target of MAVS that mediates both IRF3 and NF-kappaB activation. The TM domain of MAVS allows it to dimerize and thereby associate with TRAF5 and induce its ubiquitination in a CARD-dependent manner. Also, NEMO is recruited to the dimerized MAVS CARD domain in a TRAF3 and TRAF5-dependent manner. Thus, our findings reveal a possible function for TRAF5 in mediating the activation of IRF3 and NF-kappaB downstream of MAVS through the recruitment of NEMO. TRAF5 may be a key molecule in the innate response against viral infection.

The cytoplasmic signaling protein TNF receptor-associated factor 5 (TRAF5) has been implicated in several biological roles in Tlymphocyte responses. However, a clear connection between in vivo TRAF5 immune cell functions and specific signaling pathways has not been made. This study shows that TRAF5 associated strongly with the viral oncogenic CD40 mimic latent membrane protein 1 (LMP1), in contrast to weaker association with CD40, for which it has been shown to play a modest role. LMP1 uses specific TRAFs differently than CD40, resulting in amplified and dysregulated CD40-like activation of B lymphocytes. When the cytoplasmic domain of LMP1 is expressed as a transgenic replacement for CD40 in mouse B cells, the resulting mouse exhibits measures of B-cell hyperactivity such as splenomegaly, lymphadenopathy, elevated serum IL-6, elevated serum autoantibodies, and abnormal splenic architecture. Thus, in contrast to CD40, TRAF5 may have an important nonredundant role as a positive mediator of LMP1 signaling and functions in B cells. To test this hypothesis, mice were created that express mCD40LMP1 in place of CD40, and are either sufficient or deficient in TRAF5. Results revealed that TRAF5 plays a critical role in LMP1-mediated c-Jun kinase signaling and is required for much of the abnormal phenotype observed in mCD40LMP1 transgenic mice. This is the first report showing a major requirement for TRAF5 in signaling by a specific receptor both in vitro and in vivo, as well as playing an important role in biological function in B lymphocytes.

Background Gastrointestinal nematode (GIN) infections are the predominant cause of economic losses in sheep. Infections are controlled almost exclusively by the use of anthelmintics which has lead to the selection of drug resistant nematode strains. An alternative control approach would be the induction of protective immunity to these parasites. This study exploits an ovine microarray biased towards immune genes, an artificially induced immunity model and the use of pseudo-afferent lymphatic cannulation to sample immune cells draining from the intestine, to investigate possible mechanisms involved in the development of immunity. Results During the development of immunity to, and a subsequent challenge infection with Trichostrongylus colubriformis , the transcript levels of 2603 genes of cells trafficking in afferent intestinal lymph were significantly modulated (P < 0.05). Of these, 188 genes were modulated more than 1.3-fold and involved in immune function. Overall, there was a clear trend for down-regulation of many genes involved in immune functions including antigen presentation, caveolar-mediated endocytosis and protein ubiquitination. The transcript levels of TNF receptor associated factor 5 (TRAF5), hemopexin (HPX), cysteine dioxygenase (CDO1), the major histocompatability complex Class II protein (HLA-DMA), interleukin-18 binding protein (IL-18BP), ephrin A1 (EFNA1) and selenoprotein S (SELS) were modulated to the greatest degree. Conclusions This report describes gene expression profiles of afferent lymph cells in sheep developing immunity to nematode infection. Results presented show a global down-regulation of the expression of immune genes which may be reflective of the natural temporal response to nematode infections in livestock.

Tumor necrosis factor receptor-associated factors (TRAFs) are a family of adaptor proteins that transmit signals from immunoregulatory receptors—such as TNF receptors, Toll-like receptors, and interleukin receptors—to coordinate immune and inflammatory responses. Among them, TRAF5 is highly expressed in lymphocytes and implicated in obesity-associated inflammation, but its role in secondary lymphoid organs during chronic low-grade inflammation remains unclear. We examined splenic B and T cell phenotypes in wild-type (WT) and Traf5-deficient (KO) mice fed a high-fat diet (HFD). Although lymphocyte composition was broadly comparable, KO mice showed reduced spontaneous immunoglobulin G2c (IgG2c) production ex vivo—about 1.5-fold lower than WT. Notably, despite elevated TNF-α and CD40 ligand (CD40L) expression in HFD-fed KO splenocytes, IgG2c production remained diminished—about 1.9-fold lower than WT—upon soluble CD40L stimulation, indicating impaired CD40-mediated class-switch recombination (CSR). Consistently, B cells from KO mice on a normal diet exhibited reduced activation-induced cytidine deaminase (AID) expression—about 4.4-fold lower than WT—after CD40L stimulation, and decreased IgG2c secretion—about 6.6-fold lower—upon CD40L and IFN-γ co-stimulation in vitro. Collectively, these findings suggest that TRAF5 is involved in CD40-dependent CSR in B cells under inflammatory conditions and may contribute to sustaining adaptive immune responses during obesity-associated chronic inflammation.

Tumor necrosis factor receptor (TNFR) associated factor 1 (TRAF1) is a signaling adaptor first identified as part of the TNFR2 signaling complex. TRAF1 plays a key role in pro-survival signaling downstream of TNFR superfamily members such as TNFR2, LMP1, 4-1BB, and CD40. Recent studies have uncovered another role for TRAF1, independent of its role in TNFR superfamily signaling, in negatively regulating Toll-like receptor and Nod-like receptor signaling, through sequestering the linear ubiquitin assembly complex, LUBAC. TRAF1 has diverse roles in human disease. TRAF1 is overexpressed in many B cell related cancers and single nucleotide polymorphisms (SNPs) in TRAF1 have been linked to non-Hodgkin's lymphoma. Genome wide association studies have identified an association between SNPs in the 5' untranslated region of the TRAF1 gene with increased incidence and severity of rheumatoid arthritis and other rheumatic diseases. The loss of TRAF1 from chronically stimulated CD8 T cells results in desensitization of the 4-1BB signaling pathway, thereby contributing to T cell exhaustion during chronic infection. These apparently opposing roles of TRAF1 as both a positive and negative regulator of immune signaling have led to some confusion in the literature. Here we review the role of TRAF1 as a positive and negative regulator in different signaling pathways. Then we discuss the role of TRAF1 in human disease, attempting to reconcile seemingly contradictory roles based on current knowledge of TRAF1 signaling and biology. We also discuss avenues for future research to further clarify the impact of TRAF1 in human disease.

Type II innate lymphoid cells (ILC2) play a very important role in the pathogenesis of allergic asthma. This study aims to investigate whether miR-146a inhibition of asthma is related with interleukin (IL)-33 signaling path way in ILC2 and the underlying mechanisms. Asthma mice model was induced by ovalbumin. miRNA146a mimics was administrated to asthma mice or transfected to activated ILC2 purified from asthma mice lung. RT-PCR was used to detect miRNA146a level in lung tissue and ILC2. IL-5 and IL-13 levels in culture supernatant were detected by flow cytometry. Interleukin-1 receptor-associated kinase 1 (IRAK1), TNF receptor-associated factor 6 (TRAF6), signal transducer and activator of transcription 1 (STAT1) protein expression levels were detected by western blot. miR-146a directly inhibited ILC2 function and suppressed ILC2 proliferation both in vivo and in vitro. During stimulation of ILC2, miR-146a expression gradually increased with a decrease of cell proliferation. Modulation of ILC2 function by miR-146a may depend on IL-33/interleukin 1 receptor-like 1 (IL1RL1 or ST2) signaling through inhibiting IRAK1 and TRAF6.miR-146a can inhibit IRAK1 and TRAF6, downstream molecules of ST2 signal pathway, thereby negatively regulate IL-33/ST2-activated ILC2 to inhibit asthma. Targeting miR-146 maybe a novel strategy for the treatment of allergic asthma.