TNF receptor-associated factor 1 is a positive regulator of the NF-kappaB alternative pathway

What frog gill resorption brings: loss of function, cell death, and metabolic reorganization

BACKGROUND

Anuran metamorphosis, which is driven by thyroid hormone (TH)-mediated processes, orchestrates intricate morphological and functional transformations for the transition from aquatic tadpoles to terrestrial life, providing a valuable model for studying organ functionalization, remodeling, and regression. Larva-specific organ regression is one of the most striking phenomena observed during the anuran metamorphic climax. While previous studies extensively analyzed the regression mechanisms of the tail, the molecular processes governing gill resorption remain elusive.

RESULTS

We employed Microhyla fissipes as a model, and utilized a comprehensive approach involving histological analysis, transmission electron microscopy, and transcriptomics to unravel gill development and resorption. The pro-metamorphic stages revealed highly developed gill structures, emphasizing their crucial role as the primary respiratory organ for tadpoles. The transcriptomic analysis highlighted the upregulation of genes associated with enhanced respiratory efficiency, such as hemoglobin and mucins. However, as metamorphosis progressed, gill filaments underwent shrinkage, decreases in blood vessel density, and structural changes that signified a decline in respiratory function. The molecular mechanisms driving gill resorption involved the TH pathway-in particular, the upregulation of thyroid hormone receptor (TR) β, genes associated with the tumor necrosis factor pathway and matrix metalloproteinases. Two distinct pathways orchestrate gill resorption, involving apoptosis directly induced by TH and cell death through the degradation of the extracellular matrix. In addition, metabolic reorganization during metamorphosis is a complex process, with tadpoles adapting their feeding behavior and mobilizing energy storage organs. The gills, which were previously overlooked, have been unveiled as potential energy storage organs that undergo metabolic reorganization. The transcriptomic analysis revealed dynamic changes in metabolism-related genes, indicating decreased protein synthesis and energy production and enhanced substrate transport and metabolism during metamorphic climax.

CONCLUSION

This study sheds light on the structural, molecular, and metabolic dynamics during gill development and resorption in M. fissipes. The findings deepen our understanding of the intricate mechanisms governing organ regression and underscore the pivotal role of the gills in facilitating the transition from aquatic to terrestrial habitats.

The Role of Tumor Necrosis Factor Associated Factors (TRAFs) in Vascular Inflammation and Atherosclerosis

TNF receptor associated factors (TRAFs) represent a family of cytoplasmic signaling adaptor proteins that regulate, bundle, and transduce inflammatory signals downstream of TNF- (TNF-Rs), interleukin (IL)-1-, Toll-like- (TLRs), and IL-17 receptors. TRAFs play a pivotal role in regulating cell survival and immune cell function and are fundamental regulators of acute and chronic inflammation. Lately, the inhibition of inflammation by anti-cytokine therapy has emerged as novel treatment strategy in patients with atherosclerosis. Likewise, growing evidence from preclinical experiments proposes TRAFs as potent modulators of inflammation in atherosclerosis and vascular inflammation. Yet, TRAFs show a highly complex interplay between different TRAF-family members with partially opposing and overlapping functions that are determined by the level of cellular expression, concomitant signaling events, and the context of the disease. Therefore, inhibition of specific TRAFs may be beneficial in one condition and harmful in others. Here, we carefully discuss the cellular expression and signaling events of TRAFs and evaluate their role in vascular inflammation and atherosclerosis. We also highlight metabolic effects of TRAFs and discuss the development of TRAF-based therapeutics in the future.

Development of a New Highly Selective Monoclonal Antibody against Preferentially Expressed Antigen in Melanoma (PRAME) and Identification of the Target Epitope by Bio-Layer Interferometry

Background: Monoclonal antibodies (mAbs) against cancer biomarkers are key reagents in diagnosis and therapy. One such relevant biomarker is a preferentially expressed antigen in melanoma (PRAME) that is selectively expressed in many tumors. Knowing mAb’s epitope is of utmost importance for understanding the potential activity and therapeutic prospective of the reagents. Methods: We generated a mAb against PRAME immunizing mice with PRAME fragment 161–415; the affinity of the antibody for the protein was evaluated by ELISA and SPR, and its ability to detect the protein in cells was probed by cytofluorimetry and Western blotting experiments. The antibody epitope was identified immobilizing the mAb on bio-layer interferometry (BLI) sensor chip, capturing protein fragments obtained following trypsin digestion and performing mass spectrometry analyses. Results: A mAb against PRAME with an affinity of 35 pM was obtained and characterized. Its epitope on PRAME was localized on residues 202–212, taking advantage of the low volumes and lack of fluidics underlying the BLI settings. Conclusions: The new anti-PRAME mAb recognizes the folded protein on the surface of cell membranes suggesting that the antibody’s epitope is well exposed. BLI sensor chips can be used to identify antibody epitopes.

The Contact Allergen NiSO4 Triggers a Distinct Molecular Response in Primary Human Dendritic Cells Compared to Bacterial LPS

Dendritic cells (DC) play a central role in the pathogenesis of allergic contact dermatitis (ACD), the most prevalent form of immunotoxicity in humans. However, knowledge on allergy-induced DC maturation is still limited and proteomic studies, allowing to unravel molecular effects of allergens, remain scarce. Therefore, we conducted a global proteomic analysis of human monocyte-derived dendritic cells (MoDC) treated with NiSO4, the most prominent cause of ACD and compared proteomic alterations induced by NiSO4 to the bacterial trigger lipopolysaccharide (LPS). Both substances possess a similar toll-like receptor (TLR) 4 binding capacity, allowing to identify allergy-specific effects compared to bacterial activation. MoDCs treated for 24 h with 2.5 μg/ml LPS displayed a robust immunological response, characterized by upregulation of DC activation markers, secretion of pro-inflammatory cytokines and stimulation of T cell proliferation. Similar immunological reactions were observed after treatment with 400 μM NiSO4 but less pronounced. Both substances triggered TLR4 and triggering receptor expressed on myeloid cells (TREM) 1 signaling. However, NiSO4 also activated hypoxic and apoptotic pathways, which might have overshadowed initial signaling. Moreover, our proteomic data support the importance of nuclear factor erythroid 2-related factor 2 (Nrf2) as a key player in sensitization since many Nrf2 targets genes were strongly upregulated on protein and gene level selectively after treatment with NiSO4. Strikingly, NiSO4 stimulation induced cellular cholesterol depletion which was counteracted by the induction of genes and proteins relevant for cholesterol biosynthesis. Our proteomic study allowed for the first time to better characterize some of the fundamental differences between NiSO4 and LPS-triggered activation of MoDCs, providing an essential contribution to the molecular understanding of contact allergy.

Temporal Splicing Switches in Elements of the TNF-Pathway Identified by Computational Analysis of Transcriptome Data for Human Cell Lines

Alternative splicing plays an important role in numerous cellular processes and aberrant splice decisions are associated with cancer. Although some studies point to a regulation of alternative splicing and its effector mechanisms in a time-dependent manner, the extent and consequences of such a regulation remains poorly understood. In the present work, we investigated the time-dependent production of isoforms in two Hodgkin lymphoma cell lines of different progression stages (HD-MY-Z, stage IIIb and L-1236, stage IV) compared to a B lymphoblastoid cell line (LCL-HO) with a focus on tumour necrosis factor (TNF) pathway-related elements. For this, we used newly generated time-course RNA-sequencing data from the mentioned cell lines and applied a computational pipeline to identify genes with isoform-switching behaviour in time. We analysed the temporal profiles of the identified events and evaluated in detail the potential functional implications of alterations in isoform expression for the selected top-switching genes. Our data indicate that elements within the TNF pathway undergo a time-dependent variation in isoform production with a putative impact on cell migration, proliferation and apoptosis. These include the genes TRAF1, TNFRSF12A and NFKB2. Our results point to a role of temporal alternative splicing in isoform production, which may alter the outcome of the TNF pathway and impact on tumorigenesis.

TRAF1 Signaling in Human Health and Disease

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.

Inhibition of MicroRNA-23b Attenuates Immunosuppression During Late Sepsis Through NIK, TRAF1, and XIAP

Background

microRNA-23b (miR-23b) is a multiple functional miRNA. We hypothesize that miR-23b plays a role in the pathogenesis of sepsis. Our study investigated the effect of miR-23b on sepsis-induced immunosuppression.

Methods

Mice were treated with miR-23b inhibitors by tail vein injection 2 days after cecal ligation puncture (CLP)-induced sepsis. Apoptosis in spleens and apoptotic signals were investigated, and survival was monitored. T-cell immunoreactivities were examined during late sepsis. Nuclear factor κB (NF-κB)-inducing kinase (NIK), tumor necrosis factor (TNF)-receptor associated factor 1 (TRAF1), and X-linked inhibitor of apoptosis protein (XIAP), the putative targets of miR-23b, were identified by a dual-luciferase reporter assay.

Results

miR-23b expression is upregulated and sustained during sepsis. The activation of the TLR4/TLR9/p38 MAPK/STAT3 signal pathway contributes to the production of miR-23b in CLP-induced sepsis. miR-23b inhibitor decreased the number of spleen cells positive by terminal deoxynucleotidyl transferase dUTP nick-end labeling and improved survival. miR-23b inhibitor restored the immunoreactivity by alleviating the development of T-cell exhaustion and producing smaller amounts of immunosuppressive interleukin 10 and interleukin 4 during late sepsis. We demonstrated that miR-23b mediated immunosuppression during late sepsis by inhibiting the noncanonical NF-κB signal and promoting the proapoptotic signal pathway by targeting NIK, TRAF1, and XIAP.

Conclusions

Inhibition of miR-23b reduces late-sepsis-induced immunosuppression and improves survival. miR-23b might be a target for immunosuppression.

Roles of TRAFs in NF-κB signaling pathways mediated by BAFF

B cell activating factor (BAFF) is an important cytokine for the maintenance of B cell development, survival and homeostasis. BAFF/BAFF-R could directly activate nuclear factor kappa B (NF-κB) pathway. Tumour necrosis factor receptor-associated factors (TRAFs) are key regulatory proteins in NF-κB signaling pathways. TRAF1 enhances the activation of tumor necrosis factor receptor 2 (TNF-R2) induced by NF-κB. TRAF2 and TRAF3 signal adapters act cooperatively to control the maturation and survival signals mediated by BAFF receptor. TRAF5 is most homologous to TRAF3, as well as most functionally similar to TRAF2. TRAF6 is also required for the BAFF-mediated activation of NF-κB signal pathway. TRAF7 is involved in signal transduction pathways that lead either to activation or repression of NF-κB transcription factor. In this article, we reviewed the roles of TRAFs in NF-κB signaling pathway mediated by BAFF.

Tumour necrosis factor receptor-associated factor-1 (TRAF-1) expression is increased in renal cell carcinoma patient serum but decreased in cancer tissue compared with normal: potential biomarker significance

Renal cell carcinoma (RCC) generally has a poor prognosis because of late diagnosis and metastasis. We have previously described decreased tumour necrosis factor receptor-associated factor-1 (TRAF-1) in RCC compared with paired normal kidney in a patient cohort in Australia. In the present study, TRAF-1 expression in clear cell RCC (ccRCC) and normal kidney was again compared, but in a cohort from University Malaya Medical Centre. Serum TRAF-1 was also evaluated in RCC and normal samples.Immunohistochemistry with automated batch staining and Aperio ImageScope morphometry was used to compare TRAF-1 in 61 ccRCC with paired normal kidney tissue. Serum from 15 newly diagnosed and untreated ccRCC and 15 healthy people was tested for TRAF-1 using ELISA.In this cohort, TRAF-1 was highly expressed in proximal tubular epithelium of normal kidney, and significantly decreased in ccRCC tissue (p < 0.001). Conversely, TRAF-1 in serum from ccRCC patients was significantly increased over control serum (132 ± 30 versus 54 ± 14 pg/mL, respectively; p = 0.013).Decreased TRAF-1 in RCC tissue, reported previously, was confirmed. This, along with significantly increased serum TRAF-1 may indicate the protein is actively secreted during development and progression of ccRCC. Therefore, the increased serum TRAF-1 may be a useful non-invasive indicator of RCC development.

A novel long non-coding RNA in the rheumatoid arthritis risk locus TRAF1-C5 influences C5 mRNA levels

Long non-coding RNAs (lncRNAs) can regulate the transcript levels of genes in the same genomic region. These locally acting lncRNAs have been found deregulated in human disease and some have been shown to harbour quantitative trait loci (eQTLs) in autoimmune diseases. However, lncRNAs linked to the transcription of candidate risk genes in loci associated to rheumatoid arthritis (RA) have not yet been identified. The TRAF1 and C5 risk locus shows evidence of multiple eQTLs and transcription of intergenic non-coding sequences. Here, we identified a non-coding transcript (C5T1lncRNA) starting in the 3' untranslated region (UTR) of C5. RA-relevant cell types express C5T1lncRNA and RNA levels are further enhanced by specific immune stimuli. C5T1lncRNA is expressed predominantly in the nucleus and its expression correlates positively with C5 mRNA in various tissues (P=0.001) and in peripheral blood mononuclear cells (P=0.02) indicating transcriptional co-regulation. Knockdown results in a concurrent decrease in C5 mRNA levels but not of other neighbouring genes. Overall, our data show the identification of a novel lncRNA C5T1lncRNA that is fully located in the associated region and influences transcript levels of C5, a gene previously linked to RA pathogenesis.

Targeting signaling factors for degradation, an emerging mechanism for TRAF functions

Tumor necrosis factor receptor (TNFR)-associated factors (TRAFs) form a family of proteins that are best known as signaling adapters of TNFRs. However, emerging evidence suggests that TRAF proteins, particularly TRAF2 and TRAF3, also regulate signal transduction by controlling the fate of intracellular signaling factors. A well-recognized function of TRAF2 and TRAF3 in this aspect is to mediate ubiquitin-dependent degradation of nuclear factor-κB (NF-κB)-inducing kinase (NIK), an action required for the control of NIK-regulated non-canonical NF-κB signaling pathway. TRAF2 and TRAF3 form a complex with the E3 ubiquitin ligase cIAP (cIAP1 or cIAP2), in which TRAF3 serves as the NIK-binding adapter. Recent evidence suggests that the cIAP-TRAF2-TRAF3 E3 complex also targets additional signaling factors for ubiquitin-dependent degradation, thereby regulating important aspects of immune and inflammatory responses. This review provides both historical aspects and new insights into the signaling functions of this ubiquitination system.

Protecting intestinal epithelial cell number 6 against fission neutron irradiation through NF-κB signaling pathway

The purpose of this paper is to explore the change of NF-κB signaling pathway in intestinal epithelial cell induced by fission neutron irradiation and the influence of the PI3K/Akt pathway inhibitor LY294002. Three groups of IEC-6 cell lines were given: control group, neutron irradiation of 4Gy group, and neutron irradiation of 4Gy with LY294002 treatment group. Except the control group, the other groups were irradiated by neutron of 4Gy. LY294002 was given before 24 hours of neutron irradiation. At 6 h and 24 h after neutron irradiation, the morphologic changes, proliferation ability, apoptosis, and necrosis rates of the IEC-6 cell lines were assayed and the changes of NF-κB and PI3K/Akt pathway were detected. At 6 h and 24 h after neutron irradiation of 4Gy, the proliferation ability of the IEC-6 cells decreased and lots of apoptotic and necrotic cells were found. The injuries in LY294002 treatment and neutron irradiation group were more serious than those in control and neutron irradiation groups. The results suggest that IEC-6 cells were obviously damaged and induced serious apoptosis and necrosis by neutron irradiation of 4Gy; the NF-κB signaling pathway in IEC-6 was activated by neutron irradiation which could protect IEC-6 against injury by neutron irradiation; LY294002 could inhibit the activity of IEC-6 cells.

TNF superfamily protein-protein interactions: feasibility of small- molecule modulation

The tumor necrosis factor (TNF) superfamily (TNFSF) contains about thirty structurally related receptors (TNFSFRs) and about twenty protein ligands that bind to one or more of these receptors. Almost all of these cell surface protein-protein interactions (PPIs) represent high-value therapeutic targets for inflammatory or immune modulation in autoimmune diseases, transplant recipients, or cancers, and there are several biologics including antibodies and fusion proteins targeting them that are in various phases of clinical development. Small-molecule inhibitors or activators could represent possible alternatives if the difficulties related to the targeting of protein-protein interactions by small molecules can be addressed. Compounds proving the feasibility of such approaches have been identified through different drug discovery approaches for a number of these TNFSFR-TNFSF type PPIs including CD40-CD40L, BAFFR-BAFF, TRAIL-DR5, and OX40-OX40L. Corresponding structural, signaling, and medicinal chemistry aspects are briefly reviewed here. While none of these small-molecule modulators identified so far seems promising enough to be pursued for clinical development, they provide proof-of-principle evidence that these interactions are susceptible to small-molecule modulation and can serve as starting points toward the identification of more potent and selective candidates.

Patient samples of renal cell carcinoma show reduced expression of TRAF1 compared with normal kidney and functional studies in vitro indicate TRAF1 promotes apoptosis: potential for targeted therapy

AIMS

The tumour necrosis factor (TNF) receptor-associated factor (TRAF) family of proteins links the TNF receptor superfamily to cell signalling cascades. TRAF1 is involved in regulation of apoptosis, proliferation, differentiation and stress responses. It has a role in development of several malignancies, but no information for renal cell carcinoma (RCC) is available.

METHODS

Expression profiles for TRAF1 were investigated in 121 samples of human RCC of various subtypes plus paired normal kidney prepared in tissue microarrays, in comparison with apoptosis (morphology, ApopTag) and mitosis (morphology, proliferating cell nuclear antigen/PCNA). TRAF1 function was tested in vitro in RCC ACHN cells. TRAF1 short interfering RNA (siRNA) was used to inhibit expression of TRAF1 in ACHN cells untreated or treated with cancer therapies known to induce apoptosis (20 Gy X-irradiation and/or 500 IU/mL interferon-alpha).

RESULTS

In patient samples, TRAF1 localised to proximal tubular epithelium in normal kidney and was significantly decreased in clear cell RCC as one group (p < 0.01) and all other RCC subclassifications grouped together (p < 0.05). There was little apoptosis identified in any RCC samples. In vitro, TRAF1 siRNA caused significant reduction in TRAF1 expression and a concurrent decrease in apoptosis and increase in proliferative activity (both p < 0.05) in the ACHN RCC cells treated with radiation and interferon-alpha.

CONCLUSION

TRAF1 may have a pro-apoptotic, anti-mitotic role in RCC. The low TRAF1 expression in untreated RCC patient samples compared with normal kidney, and the localisation of TRAF1 to the proximal tubular epithelium from which many RCC originate, may indicate a potential for targeted therapy in RCC.

Non-Canonical NF-κB Signaling Initiated by BAFF Influences B Cell Biology at Multiple Junctures

It has been more than a decade since it was recognized that the nuclear factor of kappa light polypeptide gene enhancer in B cells (NF-κB) transcription factor family was activated by two distinct pathways: the canonical pathway involving NF-κB1 and the non-canonical pathway involving NF-κB2. During this time a great deal of evidence has been amassed on the ligands and receptors that activate these pathways, the cytoplasmic adapter molecules involved in transducing the signals from receptors to nucleus, and the resulting physiological outcomes within body tissues. In contrast to NF-κB1 signaling, which can be activated by a wide variety of receptors, the NF-κB2 pathway is typically only activated by a subset of receptor and ligand pairs belonging to the tumor necrosis factor (TNF) family. Amongst these is B cell activating factor of the TNF family (BAFF) and its receptor BAFFR. Whilst BAFF is produced by many cell types throughout the body, BAFFR expression appears to be restricted to the hematopoietic lineage and B cells in particular. For this reason, the main physiological outcomes of BAFF mediated NF-κB2 activation are confined to B cells. Indeed BAFF mediated NF-κB2 signaling contributes to peripheral B cell survival and maturation as well as playing a role in antibody responses and long term maintenance plasma cells. Thus the importance BAFF and NF-κB2 permeates the entire B cell lifespan and impacts on this important component of the immune system in a variety of ways.

Inducible tumor necrosis factor (TNF) receptor-associated factor-1 expression couples the canonical to the non-canonical NF-κB pathway in TNF stimulation

The NF-κB transcription factor mediates the inflammatory response through distinct (canonical and non-canonical) signaling pathways. The mechanisms controlling utilization of either of these pathways are largely unknown. Here we observe that TNF stimulation induces delayed NF-κB2/p100 processing and investigate the coupling mechanism. TNF stimulation induces TNF-associated factor-1 (TRAF-1) that directly binds NF-κB-inducing kinase (NIK) and stabilizes it from degradation by disrupting its interaction with TRAF2·cIAP2 ubiquitin ligase complex. We show that TRAF1 depletion prevents TNF-induced NIK stabilization and reduces p52 production. To further examine the interactions of TRAF1 and NIK with NF-κB2/p100 processing, we mathematically modeled TRAF1·NIK as a coupling signaling complex and validated computational inference by siRNA knockdown to show non-canonical pathway activation is dependent not only on TRAF1 induction but also NIK stabilization by forming TRAF1·NIK complex. Thus, these integrated computational-experimental studies of TNF-induced TRAF1 expression identified TRAF1·NIK as a central complex linking canonical and non-canonical pathways by disrupting the TRAF2-cIAP2 ubiquitin ligase complex. This feed-forward kinase pathway is essential for the activation of non-canonical pathway.

Tumor necrosis factor receptor-associated factor 1 influences KRN/I-Ag7 mouse arthritis autoantibody production

PURPOSE

Recently, genomewide association analysis has revealed that the Tumor Necrosis Factor Receptor-associated factor 1-Complement 5 (TRAF1-C5) containing locus on chromosome 9 was associated with an increased risk for RA. Studies in model systems suggested that either gain- or loss-of-function TRAF1 mutations have immune effects that could plausibly lead to or exacerbate the arthritis phenotype. KRN/I-A(g7) (KxB/N) is a genetic mouse model of inflammatory arthritis. We aimed to assess the impact of TRAF1 deficiency on KRN/I-A(g7) mice.

METHODS

We have bred KRN/I-A(g7) mice onto a TRAF1-deficient background and followed cohorts for the spontaneous appearance of arthritis. We have also transferred KxB/N serum to B6.I-A(g7) TRAF1KO recipients. In addition, systemic autoimmunity was induced through cGVH by injecting bm12 splenocytes into TRAF1KO recipient mice.

RESULTS

TRAF1-deficient KRN/I-A(g7) mice spontaneously developed severe, progressive arthritis, comparable to that seen in TRAF1-intact KRN/I-A(g7) mice. However, the anti-GPI antibody titer was significantly lower in the former group. Interestingly, the TRAF1KO mice that had background levels of anti-GPI antibodies still showed severe arthritis, although with a brief delay compared to TRAF1 sufficient mice. In addition, TRAF1KO mice were fully susceptible to passive, serum transfer experiments. In another model of autoimmunity, TRAF1KO had no effect on cGVH autoantibodies production; nor was the response to an exogenous antigen impaired.

CONCLUSION

The pathogenesis of spontaneous KRN/I-A(g7) arthritis can largely proceed by TRAF1-independent pathways. The production of anti-GPI autoantibody, but not other autoantibody or antibody responses, was markedly impaired by TRAF1 deficiency. The spontaneous arthritis model in KRN mice appears to be much less antibody dependent than previously believed.

TRAF1 gene polymorphism correlates with the titre of Gp210 antibody in patients with primary biliary cirrhosis

Background. Polymorphisms of TRAF1 (Tumor necrosis factor receptor-associated factor 1) are associated with rheumatoid arthritis (RA). Whether TRAF1 polymorphisms confer increased risk for primary biliary cirrhosis (PBC), an autoimmune liver disease which can co-exist with RA, is unknown. Aim of the Study. To assess the frequency of the RA-conferring susceptibility TRAF1 polymorphisms rs3761847 and rs2900180 in a cohort of PBC patients. The association of TRAF1 polymorphisms with clinical features and autoantibody markers was also analyzed. Methods. We studied 179 PBC patients and 300 controls. Samples were genotyped for TRAF1 gene polymorphisms by real-time PCR. Autoantibodies were tested by ELISA. Results. The frequency of rs3761847 and rs2900180 polymorphisms did not differ between patients and controls. Laboratory or clinical features were not associated with specific polymorphisms. Gp210 autoantibody titres were conspicuously higher among GG homozygotes of rs3761847 as compared with AA homozygotes (P = 0.02). In contrast, antichromatin titers were higher in AA compared to GG rs3761847 homozygotes (P = 0.04). Rheumatoid factor IgG titres were significantly higher in rs2900180 TT homozygotes than CC homozygotes (P = 0.02). Conclusions. TRAF1 polymorphisms occur with the similar frequency in PBC patients and in the general population, but their presence is probably involved in the regulation of specific PBC-related autoantibodies.

Opposing roles for TRAF1 in the alternative versus classical NF-κB pathway in T cells

T cells lacking TRAF1 hyperproliferate in response to T cell receptor signaling but have impaired signaling downstream of specific TNFR family members such as 4-1BB. Here we resolve this paradox by showing that while TRAF1 is required for maximal activation of the classical NF-κB pathway downstream of 4-1BB in primary T cells, TRAF1 also restricts the constitutive activation of NIK in anti-CD3-activated T cells. Activation of the alternative NF-κB pathway is restricted in unstimulated cells by a cIAP1/2:TRAF2:TRAF3:NIK complex. Using knockdown of NIK by siRNA we show that in activated CD8 T cells TRAF1 is also involved in this process and that constitutive activation of the alternative NF-κB pathway is responsible for costimulation independent hyperproliferation and excess cytokine production in TRAF1-deficient CD8 T cells compared with WT CD8 T cells. The T cell costimulatory molecule 4-1BB critically regulates the survival of activated and memory CD8 T cells. We demonstrate that stimulation through 4-1BB induces cIAP1-dependent TRAF3 degradation and activation of the alternative NF-κB pathway. We also show that while both TRAF1 and cIAP1 have non-redundant roles in suppressing the alternative NF-κB pathway in T cells activated in the absence of costimulation, activation of the classical NF-κB pathway downstream of 4-1BB requires TRAF1, whereas cIAP1 plays a redundant role with cIAP2. Collectively these results demonstrate that TRAF1 plays a critical role in regulating T cell activation both through restricting the costimulation independent activation of NIK in activated T cells and by promoting the 4-1BB-induced classical NF-κB pathway.

The noncanonical NF-κB pathway

The noncanonical nuclear factor-κB (NF-κB) signaling pathway mediates activation of the p52/RelB NF-κB complex and, thereby, regulates specific immunological processes. This NF-κB pathway relies on the inducible processing of NF-κB2 precursor protein, p100, as opposed to the degradation of IκBα in the canonical NF-κB pathway. A central signaling component of the noncanonical NF-κB pathway is NF-κB-inducing kinase (NIK), which functions together with a downstream kinase, IKKα (inhibitor of NF-κB kinase α), to induce phosphorylation-dependent ubiquitination and processing of p100. Under normal conditions, NIK is targeted for continuous degradation by a tumor necrosis factor (TNF) receptor-associated factor-3 (TRAF3)-dependent E3 ubiquitin ligase. In response to signals mediated by a subset of TNF receptor superfamily members, NIK becomes stabilized as a result of TRAF3 degradation, leading to the activation of noncanonical NF-κB. This review discusses both the historical perspectives and the recent progress in the regulation and biological function of the noncanonical NF-κB pathway.