Involvement of CRAF1, a relative of TRAF, in CD40 signaling

TRAF6 and TRAF2/3 Binding Motifs in CD40 Differentially Regulate B Cell Function in T-Dependent Antibody Responses and Dendritic Cell Function in Experimental Autoimmune Encephalomyelitis

Expression of the costimulatory molecule CD40 on both B cells and dendritic cells (DCs) is required for induction of experimental autoimmune encephalomyelitis (EAE), and cell-autonomous CD40 expression on B cells is required for primary T-dependent (TD) Ab responses. We now ask whether the function of CD40 expressed by different cell types in these responses is mediated by the same or different cytoplasmic domains. CD40 has been reported to possess multiple cytoplasmic domains, including distinct TRAF6 and TRAF2/3 binding motifs. To elucidate the in vivo function of these motifs in B cells and DCs involved in EAE and TD germinal center responses, we have generated knock-in mice containing distinct CD40 cytoplasmic domain TRAF-binding site mutations and have used these animals, together with bone marrow chimeric mice, to assess the roles that these motifs play in CD40 function. We found that both TRAF2/3 and TRAF6 motifs of CD40 are critically involved in EAE induction and demonstrated that this is mediated by a role of both motifs for priming of pathogenic T cells by DCs. In contrast, the TRAF2/3 binding motif, but not the TRAF6 binding motif, is required for B cell CD40 function in TD high-affinity Ab responses. These data demonstrate that the requirements for expression of specific TRAF-binding CD40 motifs differ for B cells or DCs that function in specific immune responses and thus identify targets for intervention to modulate these responses.

Targeted RNAseq Improves Clinical Diagnosis of Very Early-Onset Pediatric Immune Dysregulation

Despite increased use of whole exome sequencing (WES) for the clinical analysis of rare disease, overall diagnostic yield for most disorders hovers around 30%. Previous studies of mRNA have succeeded in increasing diagnoses for clearly defined disorders of monogenic inheritance. We asked if targeted RNA sequencing could provide similar benefits for primary immunodeficiencies (PIDs) and very early-onset inflammatory bowel disease (VEOIBD), both of which are difficult to diagnose due to high heterogeneity and variable severity. We performed targeted RNA sequencing of a panel of 260 immune-related genes for a cohort of 13 patients (seven suspected PID cases and six VEOIBD) and analyzed variants, splicing, and exon usage. Exonic variants were identified in seven cases, some of which had been previously prioritized by exome sequencing. For four cases, allele specific expression or lack thereof provided additional insights into possible disease mechanisms. In addition, we identified five instances of aberrant splicing associated with four variants. Three of these variants had been previously classified as benign in ClinVar based on population frequency. Digenic or oligogenic inheritance is suggested for at least two patients. In addition to validating the use of targeted RNA sequencing, our results show that rare disease research will benefit from incorporating contributing genetic factors into the diagnostic approach.

L-Plastin Phosphorylation: Possible Regulation by a TNFR1 Signaling Cascade in Osteoclasts

Tumor necrosis factor-alpha (TNF-α) signaling regulates phosphorylation of L-plastin, which is involved in forming the nascent sealing zone, a precursor zone for the matured sealing ring. This study aimed to illustrate the molecular mechanisms of L-plastin phosphorylation and the subsequent formation of the nascent sealing zone in osteoclasts treated with TNF-α. Here, we report that anti-TNF-receptor 1, inhibitors of signaling proteins (Src, PI3-K, Rho, and Rho-kinase), and siRNA of TRAF-6 attenuated the phosphorylation of LPL and filamentous actin content significantly in the presence of TNF-α. An inhibitor of integrin αvβ3, PKC, or PKA did not inhibit TNF-α-induced L-plastin phosphorylation. Inhibitors of Src and PI3-K and not Rho or Rho-kinase reduced tyrosine phosphorylation of TRAF-6, suggesting that Src and PI3-K regulate TRAF-6 phosphorylation, and Rho and Rho-kinase are downstream of TRAF-6 regulation. Osteoclasts expressing constitutively active or kinase-defective Src proteins were used to determine the role of Src on L-plastin phosphorylation; similarly, the effect of Rho was confirmed by transducing TAT-fused constitutively active (V14) or dominant-negative (N19) Rho proteins into osteoclasts. Pull-down analysis with glutathione S-transferase-fused SH2 and SH3 domains of Src and PI3-K demonstrated coprecipitation of L-plastin and TRAF-6 with the SH3 and SH2 domains of the PI3-K and Src proteins. However, the actual order of the interaction of proteins requires further elucidation; a comprehensive screening should corroborate the initial findings of protein interactions via the SH2/SH3 domains. Ultimately, inhibition of the interaction of proteins with SH2/SH3 could reduce L-plastin phosphorylation and affect NSZ formation and bone resorption in conditions that display osteoclast activation and bone loss.

The immunological significance of tumor necrosis factor receptor-associated factors (TRAFs)

The tumor necrosis factor receptor (TNFR)-associated factor (TRAF) family of molecules are intracellular signaling adaptors and control diverse signaling pathways mediated not only by the TNFR superfamily and the Toll-like receptor/interleukin-1 receptor superfamily but also by unconventional cytokine receptors such as IL-6 and IL-17 receptors. There are seven family members, TRAF1 to TRAF7, in mammals. Exaggerated immune responses induced through TRAF signaling downstream of these receptors often lead to inflammatory and autoimmune diseases including rheumatoid arthritis, inflammatory bowel disease, psoriasis and autoinflammatory syndromes, and thus those signals are major targets for therapeutic intervention. For this reason, it has been very important to understand signaling mechanisms regulated by TRAFs that greatly impact on life/death decisions and the activation, differentiation and survival of cells of the innate and adaptive immune systems. Accumulating evidence suggests that dysregulated cellular expression and/or signaling of TRAFs causes overproduction of proinflammatory cytokines, which facilitates aberrant activation of immune cells. In this review, I will explain the structural and functional aspects that are responsible for the cellular activity and disease outcomes of TRAFs, and summarize the findings of recent studies on TRAFs in terms of how individual TRAF family molecules regulates biological and disease processes in the body in both positive and negative ways. This review also discusses how TRAF mutations contribute to human disease.

Brief Research Report Regional Difference in TRAF2 and TRAF3 Gene Mutations in Colon Cancers

TRAF2 and TRAF3 genes of tumor necrosis factor receptor (TNF-R)-associated factor (TRAF) family are involved in diverse cell signaling, and function as both tumor suppressor gene and oncogene. Alterations of TRAF2 and TRAF3 in colon cancer (CC) along with their regional difference and microsatellite instability (MSI) are largely unknown. In the present study, we analyzed TRAF2 and TRAF3 frameshift mutations in 168 sporadic CCs (100 high MSI (MSI-H) and 68 microsatellite-stable (MSS) CCs). We identified TRAF2 and TRAF3 frameshift mutations in 4 (4%) and 3 CCs (3%) with MSI-H, respectively, but none in 68 cases of MSS CCs. Of the 168 CCs, we analyzed the mutations in multi-regions for 39 CCs (16 MSI-H and 23 MSS CCs), and discovered that 12.5% (2/16) and 6.3% (1/16) of MSI-H CCs exhibited regional difference in TRAF2 and TRAF3 mutations, respectively. In the multi-region samples of 23 MSS CCs, neither TRAF2 nor TRAF3 frameshift mutation was found. In 40% of CCs, both TRAF2 and TRAF3 expressions were increased compared to normal colon cells. Our data indicate that TRAF2 and TRAF3 frameshift mutations and their regional difference as well as altered expressions are present in MSI-H CCs, which could contribute to MSI-H cancer development.

Pharmacological inhibition of NF-κB-inducing kinase (NIK) with small molecules for the treatment of human diseases

NIK is a key kinase required for the activation of alternative NF-κB signaling pathways. Overactivation of NIK in patients has been observed and is implicated in the pathogenesis of inflammatory diseases, B-cell malignances, and solid tumors. Over the past decade, inhibition of NIK overactivation with small molecules has been pursued as an attractive strategy for drug discovery, where numerous potent and selective NIK inhibitors with novel pharmacophores have been identified. This review summarizes the structural features and key efficacy studies of the NIK inhibitors reported, which justify the mechanism of action of such inhibitors in animal models driven by NIK overactivation. Given the strong pathological associations between overactivation of NIK and human diseases, human clinical trials of NIK inhibitors as drug candidates are eagerly awaited. Information showcased in this review article might be helpful for the discovery and clinical development of the next generation of NIK inhibitors in the near future.

TNF receptor-associated factor 6 (TRAF6) plays crucial roles in multiple biological systems through polyubiquitination-mediated NF-κB activation

NF-κB was first identified in 1986 as a B cell-specific transcription factor inducing immunoglobulin κ light chain expression. Subsequent studies revealed that NF-κB plays important roles in development, organogenesis, immunity, inflammation, and neurological functions by spatiotemporally regulating cell proliferation, differentiation, and apoptosis in several cell types. Furthermore, studies on the signal pathways that activate NF-κB led to the discovery of TRAF family proteins with E3 ubiquitin ligase activity, which function downstream of the receptor. This discovery led to the proposal of an entirely new signaling mechanism concept, wherein K63-ubiquitin chains act as a scaffold for the signaling complex to activate downstream kinases. This concept has revolutionized ubiquitin studies by revealing the importance of the nonproteolytic functions of ubiquitin not only in NF-κB signaling but also in a variety of other biological systems. TRAF6 is the most diverged among the TRAF family proteins, and our studies uncovered its notable physiological and pathological functions.

miR-339-3p regulated acute pancreatitis induced by caerulein through targeting TNF receptor-associated factor 3 in AR42J cells

Acute pancreatitis (AP) is an inflammatory disease with high morbidity and mortality. The regulation mechanism of miRNA is involved in the production and development of various diseases, but the regulation mechanism of miRNA in AP is still not fully elucidated. The expression of miR-339-3p was detected using quantitative real-time PCR. The levels of TNF-α, IL-1β, and IL-6 were detected using enzyme-linked immunosorbent assay. Cell apoptosis was measured using flow cytometry. The protein expressions of TNF receptor-associated factor 3 (TRAF3), Bcl-2, C-caspase 3, Bax, p-p38, and p38 were measured using western blot. Luciferase reporter assay and RNA immunoprecipitation assay were applied to ensure that miR-399-3p targeted TRAF3. Caerulein promoted the expression of TNF-α, IL-1β, and IL-6, enhanced the expression of C-caspase 3 and Bax while inhibited Bcl-2 protein expression. Meanwhile, caerulein also reduced the expression of miR-339-3p and induced the expression of TRAF3 in rat pancreatic acinar cells. miR-399-3p transfection inhibited the levels of TNF-α, IL-1β, and IL-6 and C-caspase 3 and Bax protein expression as well as suppressed cell apoptosis, while increased Bcl-2 protein expression in caerulein-induced AP. TRAF3 has been verified as a target of miR-339-3p. Interestingly, the reduction of miR-399-3p inhibited the p38 pathway, which was impaired by the upregulation of TRAF3. In addition, the suppression effects of miR-339-3p on cell inflammation and apoptosis in caerulein-induced AP were reversed by enhancing TRAF3 expression. In this study, in vitro model of AP was characterized by strong inflammation and cell apoptosis. We have first demonstrated the regulatory network of miR-339-3p and TRAF3. Overexpression of miR-339-3p inhibited cell inflammation and cell apoptosis in caerulein-induced AP through modulating TRAF3 expression via the p38 pathway, providing a new therapeutic target in the treatment of AP.

Methionine selenium antagonizes LPS-induced necroptosis in the chicken liver via the miR-155/TRAF3/MAPK axis

Organic selenium has antioxidation and disease treatment effects. To explore the mechanisms of how methionine selenium alleviates necroptosis in the liver and whether this process is related to microRNA (miRNA) and the mitogen-activated protein kinase (MAPK) pathway, an animal model of methionine selenium and the lipopolysaccharide (LPS) interaction was established. The morphology, inflammatory factor (tumor necrosis factor-α [TNF-α]), necroptosis-related genes (RIP1, RIP3, MLKL, and caspase 8), MAPK pathway-related genes (JNK, ERK, and p38, p-JNK, p-ERK, and p-p38), gga-miR-155, TRAF3 (predicted target of gga-miR-155), and oxidative stress-related indicators (SOD, MDA, CAT, GSH, and GSH-Px) were analyzed from the perspective of the miR-155/TRAF3/MAPK axis to elucidate the mechanism of methionine selenium on the LPS-induced necroptosis mechanism in the chicken liver. The current results suggested that methionine selenium antagonizes oxidative stress, inflammation, and the MAPK pathway, thereby antagonizing the occurrence of necroptosis through multiple mechanisms. At the same time, methionine selenium affects miR-155/TRAF3/MAPK signaling, reduces miR-155 expression, and upregulates TRAF3 expression to inhibit necroptosis. This information provided new ideas and a theoretical basis for the practical application of methionine selenium, and it also enriched the study of miRNAs in birds and provided a reference for comparative medicine.

The roles of grouper TANK in innate immune defense against iridovirus and nodavirus infections

The TRAF family member-associated nuclear factor (NF)-κB activator (TANK) was first identified as a TRAF-binding protein with both stimulatory and inhibitory properties in host innate immune activation. To elucidate the roles of TANK in teleosts, we cloned and characterized the TANK homologue of orange-spotted grouper (Epinephelus coioides). The open reading frame (ORF) of EcTANK consists of 1026 nucleotides encoding a 342 amino acid protein with a predicted molecular mass of 38.24 kDa. EcTANK shares 89.47% and 88.89% identity with Larimichthys crocea TANK and Lates calcarifer TANK, respectively. EcTANK was distributed in all 11 examined tissues. The expression of EcTANK in the spleen increased after infection with Singapore grouper iridovirus (SGIV) and red-spotted grouper nervous necrosis virus (RGNNV). EcTANK was mainly located in the cytoplasm of grouper spleen cells. EcTANK enhanced SGIV and RGNNV replication during viral infection in vitro. Overexpression EcTANK decreased the expression levels of interferon-associated cytokines and pro-inflammatory factors, and enhanced activation of NF-κB. Taken together, these results suggest that EcTANK may play an important role in antiviral innate immune activation in grouper.

Molecular characterization and functional analysis of tumor necrosis factor receptor-associated factor 2/7 and tumor necrosis factor receptor 1-associated death domain protein from Larimichthys crocea

In the present study, we characterized tumor necrosis factor receptor-associated factor 2/7 (lcTRAF2/7) and TNFR1-associated death domain protein (lcTRADD) in Larimichthys crocea (L. crocea) and examined their expression profiles in tissues of Vibrio-challenged and unchallenged fish. The coding sequences of lcTRAF2, lcTRAF7, and lcTRADD were 1488, 2454, and 744 nucleotides, and they encoded proteins of 495, 344, and 248 amino acids, respectively. The results of phylogenetic analysis revealed that lcTRAF2, lcTRAF7, and lcTRADD were closest to Oplegnathus fasciatus (85%), Xiphophorus maculatus (97%), and Acanthochromis polyacanthus (65%), respectively. Multiple sequence alignment showed that lcTRAF2 and lcTRAF7 were highly conserved with other vertebrate TRAFs in their functional domains; however, lcTRADD was poorly conserved. The results of quantitative real-time polymerase chain reaction analysis indicated that lcTRAF2, lcTRAF7, and lcTRADD were constitutively expressed in the spleen, liver, kidney, heart, brain, gill, bladder, skin, fin, eye, and muscle. After challenging fish with Vibrio parahaemolyticus, the mRNA expression levels of lcTRAF2, lcTRAF7, and lcTRADD were upregulated in liver, spleen, and kidney. Immunofluorescence staining revealed that lcTRAF2 and lcTRADD were cytoplasmic in localization, whereas lcTRAF7 targeted both the cytoplasm and nucleus. In addition, the NF-κB protein level was upregulated after lipopolysaccharide stimulation in lcTRAF2, lcTRAF7, or lcTRADD overexpressing cells. Taken collectively, these results have improved our understanding of the functions of TRAF2, TRAF7, and TRADD in pathogenic infections in teleosts.

TRAF3 can interact with GMEB1 and modulate its anti-apoptotic function

Background

Members of Tumor Necrosis Factor (TNF) Receptor-Associated Factors (TRAFs) family interact with the cytoplasmic tails of TNF receptor family members to mediate signal transduction processes. TRAF3 has a major immunomodulatory function and TRAF3 deficiency has been linked to malignancies, such as multiple myeloma and lymphoid defects. In order to characterize the molecular mechanisms of TRAF3 signaling, the yeast two-hybrid system was used to identify proteins that interact with TRAF3.

Results

The yeast two-hybrid screen of a human B cell cDNA library with TRAF3 as bait, identified Glucocorticoid Modulatory Element-Binding Protein 1 (GMEB1) as a TRAF3-interacting protein. Previous studies indicated that GMEB1 functions as a potent inhibitor of caspase activation and apoptosis. The interaction of TRAF3 and GMEB1 proteins was confirmed in mammalian cells lines, using immunoprecipitation assays. The RING and TRAF-C domains of TRAF3 were not essential for this interaction. The overexpression of TRAF3 protein enhanced the anti-apoptotic function of GMEB1 in HeLa cells. On the other hand, downregulation of TRAF3 by RNA interference decreased significantly the ability of GMEB1 to inhibit apoptosis. In addition, LMP1(1–231), a truncated form of the EBV oncoprotein LMP1, that can interact and oligomerize with TRAF3, was also able to cooperate with GMEB1, in order to inhibit apoptosis.

Conclusions

Our protein-interaction experiments demonstrated that TRAF3 can interact with GMEB1, which is an inhibitor of apoptosis. In addition, cell viability assays showed that overexpression of TRAF3 enhanced the anti-apoptotic activity of GMEB1, supporting a regulatory role of TRAF3 in GMEB1-mediated inhibition of apoptosis. Better understanding of the molecular mechanism of TRAF3 function will improve diagnostics and targeted therapeutic approaches for TRAF3-associated disorders.

TRAF3 enhances TRIF-mediated signaling via NF-κB and IRF3 activation in large yellow croaker Larimichthys crocea

As a member of tumor necrosis factor receptor (TNFR)-associated factor (TRAF) family, TRAF3 is an important regulator of NF-κB and type I interferon (IFN) activation, especially in Toll-like receptors (TLRs)- and retinoic acid inducible gene I (RIG-I)-like receptors (RLRs)-mediated signaling pathway. In the present study, a TRAF3 homologue named Lc-TRAF3 was characterized in large yellow croaker (Larimichthys crocea). The open reading frame (ORF) of Lc-TRAF3 contains 1788 bp encoding a protein of 595 amino acids (aa). Sequence analysis indicated that Lc-TRAF3 is conserved in vertebrates, constituted with a N-terminal RING finger, two TRAF-type zinc fingers, and a C-terminal TRAF-MATH domain. The genome organization of Lc-TRAF3 is conserved in fish, with 13 exons and 12 introns, but different from that in birds or mammals, which contains 10 exons and 9 introns. Lc-TRAF3 was identified as cytosolic protein base on fluorescence microscopy analysis. Expression analysis revealed that Lc-TRAF3 was broadly distributed in examined organs/tissues, with the highest expression level in gill and weakest in brain, and could be up-regulated under poly I:C, LPS, PGN, and Pseudomonas plecoglossicida stimulation in vivo. Interestingly, overexpression Lc-TRAF3 could induce the activation of NF-κB, and Lc-TRAF3 co-transfected with Lc-TRIF induced a significantly higher level of NF-κB and IRF3 promoter activity, implying that Lc-TRAF3 may function as an enhancer in Lc-TRIF-mediated signaling pathway.

Identification and characterisation of tumour necrosis factor receptor (TNFR) associated factor 3 from Nile tilapia, Oreochromis niloticus

In this study, we cloned the complementary (c)DNA sequences of tumour necrosis factor receptor (TNFR)-associated factor 3 (traf3) in Nile tilapia, Oreochromis niloticus. The expression patterns of the traf3 gene were investigated and preliminary functional analyses were performed. In healthy fish, traf3 transcript was broadly expressed in all examined tissues, with the highest expression level in the blood and the lowest in the liver. The traf3 gene reached its highest expression at 8 days post-fertilisation (dpf) during embryonic development. Moreover, we found that expression of traf3 was clearly altered following stimulation with Streptococcus agalactiae in vivo and that traf3 could be induced by lipopolysaccharides (LPS), Poly I: C and S. agalactiae WC1535 in Nile tilapia macrophages. Overexpression in 293T cells showed that Traf3 protein was mainly distributed in the cytoplasm and could significantly increase nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) activation. Taken together, these results implied that traf3 could play important roles in the immune response to pathogen invasion.

Molecular characterization and expression analysis of tumor necrosis factor receptor-associated factors 3 and 6 in large yellow croaker (Larimichthys crocea)

The large yellow croaker (Larimichthys crocea) has a well-developed innate immune system. To gain a better understanding of the defense mechanisms involved in this system, we studied tumor necrosis factor receptor-associated factors (TRAFs), which play important roles in the Toll-like receptor (TLR) pathway. We characterized the full-length open reading frames and protein structures of TRAF3 and TRAF6 to determine their identities, and conducted phylogenetic analysis to determine their evolutionary relationships. To assess the roles of TRAFs in innate immune responses in the large yellow croaker, we performed quantitative reverse-transcription PCR (qRT-PCR) to characterize expression profiles in a range of tissues at different stages after challenge with polyinosinic polycytidylic acid (poly I:C) and Vibrio anguillarum. Following poly I:C challenge, the expression levels of TRAF3 and TRAF6 were highest in the kidneys and lowest in the spleen, whereas after infection with V. anguillarum, TRAF6 expression was the highest in the kidneys and lowest in the liver.

TRAF3 as a Multifaceted Regulator of B Lymphocyte Survival and Activation

The adaptor protein TNF receptor-associated factor 3 (TRAF3) serves as a powerful negative regulator in multiple aspects of B cell biology. Early in vitro studies in transformed cell lines suggested the potential of TRAF3 to inhibit signaling by its first identified binding receptor, CD40. However, because the canonical TRAF3 binding site on many receptors also mediates binding of other TRAFs, and whole-mouse TRAF3 deficiency is neonatally lethal, an accurate understanding of TRAF3's specific functions was delayed until conditional TRAF3-deficient mice were produced. Studies of B cell-specific TRAF3-deficient mice, complemented by investigations in normal and malignant mouse and human B cells, reveal that TRAF3 has powerful regulatory roles that are unique to this TRAF, as well as functions context-specific to the B cell. This review summarizes the current state of knowledge of these roles and functions. These include inhibition of signaling by plasma membrane receptors, negative regulation of intracellular receptors, and restraint of cytoplasmic NF- κB pathways. TRAF3 is also now known to function as a resident nuclear protein, and to impact B cell metabolism. Through these and additional mechanisms TRAF3 exerts powerful restraint upon B cell survival and activation. It is thus perhaps not surprising that TRAF3 has been revealed as an important tumor suppressor in B cells. The many and varied functions of TRAF3 in B cells, and new directions to pursue in future studies, are summarized and discussed here.

TRAF3 regulation of inhibitory signaling pathways in B and T lymphocytes by kinase and phosphatase localization

This brief review presents current understanding of how the signaling adapter protein TRAF3 can both induce and block inhibitory signaling pathways in B and T lymphocytes, via association with kinases and phosphatases, and subsequent regulation of their localization within the cell. In B lymphocytes, signaling through the interleukin 6 receptor (IL-6R) induces association of TRAF3 with IL-6R-associated JAK1, to which TRAF3 recruits the phosphatase PTPN22 (protein tyrosine phosphatase number 22) to dephosphorylate JAK1 and STAT3, inhibiting IL-6R signaling. An important biological consequence of this inhibition is restraining the size of the plasma cell compartment, as their differentiation is IL-6 dependent. Similarly, in T lymphocytes, interleukin 2 receptor (IL-2R) signaling recruits TRAF3, which in turn recruits the phosphatase TCPTP (T cell protein tyrosine phosphatase) to dephosphorylate JAK3. The resulting inhibition of IL-2R signaling limits the IL-2-dependent size of the T regulatory cell (Treg) compartment. TRAF3 also inhibits type 1 IFN receptor (IFNαR) signaling to T cells by this mechanism, restraining expression of IFN-stimulated gene expression. In contrast, TRAF3 association with two inhibitors of TCR signaling, C-terminal Src kinase (Csk) and PTPN22, promotes their localization to the cytoplasm, away from the membrane TCR complex. TRAF3 thus enhances TCR signaling and downstream T cell activation. Implications are discussed for these regulatory roles of TRAF3 in lymphocytes, as well as potential future directions.

Fifty years later: Emerging functions of IgE antibodies in host defense, immune regulation, and allergic diseases

Fifty years ago, after a long search, IgE emerged as the circulating factor responsible for triggering allergic reactions. Its extremely low concentration in plasma created significant hurdles for scientists working to reveal its identity. We now know that IgE levels are invariably increased in patients affected by atopic conditions and that IgE provides the critical link between the antigen recognition role of the adaptive immune system and the effector functions of mast cells and basophils at mucosal and cutaneous sites of environmental exposure. This review discusses the established mechanisms of action of IgE in pathologic immediate hypersensitivity, as well as its multifaceted roles in protective immunity, control of mast cell homeostasis, and its more recently revealed immunomodulatory functions.

MicroRNA-3178 ameliorates inflammation and gastric carcinogenesis promoted by Helicobacter pylori new toxin, Tip-α, by targeting TRAF3

BACKGROUND

Helicobacter pylori infection is the main cause of chronic gastritis, peptic ulcer, and gastric cancer. Tip-α is a newly identified carcinogenic factor present in H. pylori. TRAF3 can activate NF-κB by both canonical and noncanonical signaling pathways. In this study, we found that the expression of TRAF3 and NF-κB was upregulated, while microRNA-3178 (miR-3178) was decreased in H. pylori-positive gastric tissues but not in H. pylori-negative tissues.

MATERIALS AND METHODS

GES-1 cells were incubated with 12.5 μg/mL recombinant Tip-α (rTip-α) in RPMI1640 for 2 hours. After another 24 hours, the supernatant medium was designed as inflammatory-conditioned medium (ICM) and that from the untreated control cells was designed as untreated control medium. The release of proinflammatory cytokines from GES-1 cells and proliferation of gastric cancer cells was determined by ELISA and CCK-8 kits. Cells were transfected with the mimic, inhibitor, negative control of miR-3178, or TRAF3 siRNA control siRNA. The medium was then replaced with RPMI1640, 12.5 μg/mL rTip-α, and collected, and the total cellular RNA and protein were extracted for the following detection.

RESULTS

MiR-3178 mimic prevented the increasement of TRAF3 and hence decreased activation of NF-κB signals, whereas miR-3178 inhibitor could not, in GES-1 cells with Tip-α treatment. The condition medium from miR-3178 mimic transfected GES-1 cells could inhibit proliferation and induce apoptosis of inflammation-related gastric cancer cells SGC7901 and MGC803 by decreasing the production of inflammatory cytokines TNF-α and IL-6, which were secreted by GES-1 cells.

CONCLUSIONS

Taken all together, Tip-α might activate NF-κB to promote inflammation and carcinogenesis by inhibiting miR-3178 expression, which directly targeting TRAF3, during H. pylori infection in gastric mucosal epithelial cells.

Comparison of the peptide binding preferences of three closely related TRAF paralogs: TRAF2, TRAF3, and TRAF5

Tumor necrosis factor receptor-associated factors (TRAFs) constitute a family of adapter proteins that act in numerous signaling pathways important in human biology and disease. The MATH domain of TRAF proteins binds peptides found in the cytoplasmic domains of signaling receptors, thereby connecting extracellular signals to downstream effectors. Beyond several very general motifs, the peptide binding preferences of TRAFs have not been extensively characterized, and differences between the binding preferences of TRAF paralogs are poorly understood. Here we report a screening system that we established to explore TRAF peptide-binding specificity using deep mutational scanning of TRAF-peptide ligands. We displayed single- and double-mutant peptide libraries based on the TRAF-binding sites of CD40 or TANK on the surface of Escherichia coli and screened them for binding to TRAF2, TRAF3, and TRAF5. Enrichment analysis of the library sequencing results showed differences in the permitted substitution patterns in the TANK versus CD40 backgrounds. The three TRAF proteins also demonstrated different preferences for binding to members of the CD40 library, and three peptides from that library that were analyzed individually showed striking differences in affinity for the three TRAFs. These results illustrate a previously unappreciated level of binding specificity between these close paralogs and demonstrate that established motifs are overly simplistic. The results from this work begin to outline differences between TRAF family members, and the experimental approach established herein will enable future efforts to investigate and redesign TRAF peptide-binding specificity.

CD40-Dependent Activation of Phosphatidylinositol 3-Kinase/Akt Pathway Inhibits Apoptosis of Human Cultured Mesangial Cells Induced by Oxidized LDL

Deposition of atherogenic lipoproteins is associated with various glomerular diseases. In particular, oxidized LDL (oxLDL) may affect mesangial cells and favour the development of glomerulosclerosis. The aim of the present study was to investigate on cultured human mesangial cells (HMC) whether oxLDL induces apoptosis by a mechanism dependent on the inhibition of Akt survival pathway, and whether the engagement of mesangial CD40 by its ligand CD154 inhibits the apoptotic effect of oxLDL. Tunel assays demonstrated that incubation of HMC for 24h with oxLDL, but not with unmodified LDL, induced a dose-dependent increase in apoptosis of HMC associated with a decrease in Akt phosphorylation. Enzymatic kinase assay showed that also the Akt activity was reduced in a dose-dependent manner by treatment with oxLDL. Stimulation of mesangial CD40 with sCD154 rescued HMC from oxLDL-dependent apoptosis, while two unrelated pharmacological inhibitors of PI3K LY294002 and wortmannin abrogated this anti-apoptotic effect, suggesting an involvement of the PI3K/Akt pathway. Moreover CD40 stimulation maintained an elevated phosphorylation of Akt and preserved its enzymatic activity in the presence of oxLDL. Indeed, CD154 induced a rapid enhancement in Akt enzymatic activity, that was temporarily correlated with the association of CD40 with TRAF3, TRAF6, c-Cbl and the p85 subunit of PI3K. In conclusion, these results suggest that CD40 stimulation protects HMC from toxic effects of oxLDL by promoting PI3K/Akt-dependent cell survival.

TRAF3, ubiquitination, and B-lymphocyte regulation

The signaling adapter protein tumor necrosis factor receptor (TNFR)-associated factor 3 (TRAF3) is both modified by and contributes to several types of ubiquitination events. TRAF3 plays a variety of context-dependent regulatory roles in all types of immune cells. In B lymphocytes, TRAF3 contributes to regulation of signaling by members of both the TNFR superfamily and innate immune receptors. TRAF3 also plays a unique cell type-specific and critical role in the restraint of B-cell homeostatic survival, a role with important implications for both B-cell differentiation and the pathogenesis of B-cell malignancies. This review focuses upon the relationship between ubiquitin and TRAF3, and how this contributes to multiple functions of TRAF3 in the regulation of signal transduction, transcriptional activation, and effector functions of B lymphocytes.

TRAF3 as a powerful and multitalented regulator of lymphocyte functions

This review summarizes the current state of knowledge regarding the roles of the signaling adapter protein tumor necrosis factor receptor (TNFR)-associated factor 3 in regulating the functions of B and T lymphocytes. In B lymphocytes, TNFR-associated factor 3 inhibits signaling by TNFR superfamily receptors, Toll-like receptors, and interleukin-6R. In contrast, signaling to B cells by the virally encoded oncogenic protein latent membrane protein 1 is promoted by TNFR-associated factor 3. An important B cell-specific role for TNFR-associated factor 3 is the inhibition of homeostatic survival, directly relevant to the common occurrence of TNFR-associated factor 3 mutations in human B cell malignancies. TNFR-associated factor 3 was recently found to be a resident nuclear protein in B cells, where it interacts with and inhibits gene expression mediated by the cAMP response element-binding protein transcription complex, including expression of the prosurvival protein myeloid leukemia cell differentiation protein 1. In T lymphocytes, TNFR-associated factor 3 is required for normal signaling by the T cell antigen receptor, while inhibiting signaling by the interleukin-2 receptor. Cytoplasmic TNFR -associated factor 3 restrains nuclear factor-κB2 activation in both T and B cells. Clinical implications and future directions for the study of this context-dependent signaling regulator are discussed.

Intracellular osteopontin stabilizes TRAF3 to positively regulate innate antiviral response

Osteopontin (OPN) is a multifunctional protein involved in both innate immunity and adaptive immunity. However, the function of OPN, especially the intracellular form OPN (iOPN) on innate antiviral immune response remains elusive. Here, we demonstrated that iOPN is an essential positive regulator to protect the host from virus infection. OPN deficiency or knockdown significantly attenuated virus-induced IRF3 activation, IFN-β production and antiviral response. Consistently, OPN-deficient mice were more susceptible to VSV infection than WT mice. Mechanistically, iOPN was found to interact with tumor necrosis factor receptor (TNFR)-associated factor 3 (TRAF3) and inhibit Triad3A-mediated K48-linked polyubiquitination and degradation of TRAF3 through the C-terminal fragment of iOPN. Therefore, our findings delineated a new function for iOPN to act as a positive regulator in innate antiviral immunity through stabilization of TRAF3.

Tumor Necrosis Factor Receptor Associated Factors (TRAFs) 2 and 3 Form a Transcriptional Complex with Phosho-RNA Polymerase II and p65 in CD40 Ligand Activated Neuro2a Cells

The tumor necrosis factor receptor-associated factors (TRAFs) have been classically described as adaptor proteins that function as solely cytosolic signaling intermediates for the TNF receptor superfamily, Toll-like receptors (TLRs), NOD, like receptors (NLRs), cytokine receptors, and others. In this study, we show for the first time that TRAFs are present within the cytoplasm and nucleus of Neuro2a cells and primary cortical neurons, and that TRAF2 and TRAF3 translocate into the nucleus within minutes of CD40L stimulation. Analysis of the transcriptional regulatory potential of TRAFs by luciferase assay revealed that each of the TRAFs differentially functions as a transcriptional activator or repressor in a cell-specific manner. Interestingly, ChIP-qPCR data demonstrate that TRAFs 2/3, p65, and pRNAPol II form part of a transcriptional complex on the Icam-1 gene promoter upon CD40L stimulation. We further determined that TRAF2 recruitment to the nucleus is critical for the ubiquitination of H2b, a transcription permissive epigenetic modification. Our findings demonstrate for the first time that TRAFs 2/3 participate in the formation of a CD40L-induced transcriptional complex in neuronal cells.

Roles of TRAF3 in T cells: many surprises

Tumor necrosis factor receptor (TNFR)-associated factor 3 (TRAF3) is broadly involved in different receptor-mediated signaling pathways. Considerable progress was made recently in understanding the role of TRAF3 in T cell biology. Here we review these new findings about how TRAF3 participates in T cell development and function. The different roles of TRAF3 in distinct immune cells are also compared. That TRAF3 is required for T cell effector functions, and invariant Natural Killer T cell function and development, was unexpected. Another surprising finding is that TRAF3 normally restrains regulatory T cell development. It is now clear that TRAF3 regulates signaling to T cells not only through costimulatory members of the TNFR superfamily, but also through the T cell receptor complex, and cytokine receptors. The diverse roles it plays support the multifaceted nature of this molecule. How TRAF3 mediates integration of different signaling cascades is an important topic for future study.

Identification and characterization of tumor necrosis factor receptor (TNFR)-associated factor 3 from humphead snapper, Lutjanus sanguineus

Tumor necrosis factor receptor (TNFR)-associated factor 3(TRAF3) is a key regulator in TNFR and Toll-like receptor (TLRs)/RIG-I-like receptors (RLRs) signal pathway. Here, a TRAF3 gene (Ls-TRAF3, GenBank Accession No: KJ789921) is cloned from humphead snapper (Lutjanus sanguineus). The Ls-TRAF3 cDNA contains an open reading frame of 1788 bp, which encodes a polypeptide of 595 amino acids. The deduced amino acid of Ls-TRAF3 possesses a RING finger, two TRAF-type zinc fingers, a coiled-coil and a MATH domain. Ls-TRAF3 protein shares high identities with other known TRAF3 proteins. In healthy fish, Ls-TRAF3 transcripts were broadly expressed in all examined tissues with highest expression levels in spleen, liver and head kidney. Quantitative real-time PCR (qRT-PCR) analysis revealed that Ls-TRAF3 could be induced by bacteria or viral PAMP poly I:C stimulation in vivo. Here, we also showed Ls-TRAF3 that, positively regulated IRF3 and Mx upon poly I:C stimuli, whereas prevented production of proinflammatory cytokine IL-6 after LPS injection. Moreover, over-expression of wide type (WT) Ls-TRAF3 and truncated forms, including ΔZinc finger 1, ΔZinc finger 2 and Δcoiled-coil suppressed NF-κB activity significantly, whereas the inhibitory effect of NF-κB was partially impaired when the RING finger or MATH domain deletion, suggesting the latter was more important for downstream signal transduction. Taken together, these results implicated that Ls-TRAF3 might play regulatory roles in immune response to pathogen invasion.

The miR-322-TRAF3 circuit mediates the pro-apoptotic effect of high glucose on neural stem cells

Maternal diabetes increases the risk of neural tube defects (NTDs), and caspase-dependent apoptosis and gene dysregulation are implicated in this disease process. This study investigates the role of miR-322 and its putative target gene, TNF receptor-associated factor 3 (TRAF3), in high glucose-induced apoptosis. miR-322 and TRAF3 expression were assessed in embryos of nondiabetic and diabetic dams, and in neural stem cells under high glucose conditions. Maternal diabetes in vivo and high glucose in vitro significantly down-regulated miR-322 and up-regulated TRAF3 protein expression. Overexpression of the antioxidant enzyme, superoxide dismutase 1 (SOD1), or treatment with the SOD1 mimetic Tempol, abolished the effect of maternal diabetes or high glucose on miR-322 and TRAF3 expression, respectively. A miRNA target prediction algorithm reveals 2 miR-322 binding sites the 3'-untranslated region (UTR) of TRAF3 mRNA. A RNA pull-down assay using biotin-labeled miR-322 revealed that miR-322 interacted with the 3'-UTR of TRAF3 mRNA at one specific binding site. The miR-322 mimic or TRAF3 knockdown blocked high glucose-increased TRAF3 protein expression and apoptosis, whereas the miR-322 inhibitor mimicked the effect of high glucose leading to TRAF3 up-regulation and apoptosis. This study demonstrates that both maternal diabetes and high glucose negatively regulate miR-322 through oxidative stress. miR-322 interacts with the 3'-UTR of TRAF3 and represses its translation. The miR-322-TRAF3 pathway is implicated in high glucose-induced caspase activation and apoptosis.

Th17 differentiation and their pro-inflammation function

CD4(+) T helper cells are classical but constantly reinterpreted T-cell subset, playing critical roles in a diverse range of inflammatory responses or diseases. Depending on the cytokines they release and the immune responses they mediate, CD4(+) T cells are classically divided into two major cell populations: Th1 and Th2 cells. However, recent studies challenged this Th1/Th2 paradigm by discovering several T-helper cell subsets with specific differentiation program and functions, including Th17 cells, Treg cells, and Tfh cells. In this chapter, we summarize the current understanding and recent progresses on the Th17 lineage differentiation and its effector impacts on variety of inflammatory responses or disease pathogenesis.

Molecular characterization and functional analysis of TRAF6 in orange-spotted grouper (Epinephelus coioides)

Tumor necrosis factor receptor (TNFR)-associated factor 6 (TRAF6) is a crucial signal transducer in both the TNFR superfamily and Toll-like receptor/interleukin 1R family. Although significant progress has been made in clarifying the role of TRAF6 in mammals, the function of TRAF6 in fish is still poorly understood. In this study, we cloned the orange-spotted grouper (Epinephelus coioides) TRAF6 (EcTRAF6) cDNA, with an open reading frame of 1713bp encoding 570 amino acids. Sequence analysis indicated that EcTRAF6 contains the four characteristic domains conserved in the TRAF family, including an N-terminal RING finger, two zinc fingers, a coiled-coil domain, and a C-terminal MATH domain. Homology alignment and phylogenetic analysis demonstrated that EcTRAF6 shares high sequence identity with TRAF6 of other fish species. The EcTRAF6 gene contains seven exons and six introns, which is similar to the organization in ayu, but not in the common carp, human, or mouse (six exons and five introns). EcTRAF6 transcripts were broadly expressed in all tissues tested, and increased after infection with Cryptocaryon irritans. Intracellular localization showed EcTRAF6 was distributed mainly in the cytoplasm. Over-expression of wild type (WT) EcTRAF6, truncated forms of EcTRAF6, including ΔZinc finger 2 and ΔMATH, and a mutant of C78A activated NF-κB strongly in HEK293T cells; whereas truncations, including ΔRING, ΔZinc finger 1 and Δcoiled-coiled, and a mutant of K132R induced the activity of NF-κB slightly compared to WT EcTRAF6, implying the latter has a more crucial role in downstream signal transduction. Together, these results suggested EcTRAF6 functions like that of mammals to activate NF-κB, and it might have an important role in host defense against parasitic infections.

Roles for TNF-receptor associated factor 3 (TRAF3) in lymphocyte functions

TRAF3 is an adapter protein that serves and regulates the functions of several types of receptors, located both inside the cell and at the plasma membrane. These include members of the TNF receptor superfamily (TNFR-SF), toll-like receptors (TLR), and cytokine receptors. It has become increasingly evident that the roles and functions of TRAF3 are highly context-dependent. TRAF3 can serve distinct roles for different receptors in the same cell, and also has highly cell-type-dependent functions. This review focuses upon the current state of knowledge regarding how TRAF3 regulates the biology and effector functions of B and T lymphocytes, two major cell types of the adaptive immune response in which TRAF3 has markedly distinct roles.

Chloroquine reduces osteoclastogenesis in murine osteoporosis by preventing TRAF3 degradation

The cytokines RANKL and TNF activate NF-κB signaling in osteoclast precursors (OCPs) to induce osteoclast (OC) formation. Conversely, TNF can limit OC formation through NF-κB p100, which acts as an inhibitor, and TNF receptor-associated receptor 3 (TRAF3); however, a role for TRAF3 in RANKL-mediated OC formation is unknown. We found that TRAF3 limits RANKL-induced osteoclastogenesis by suppressing canonical and noncanonical NF-κB signaling. Conditional OC-specific Traf3-KO (cKO) mice had mild osteoporosis and increased OC formation. RANKL induced TRAF3 degradation via the lysosome/autophagy system. The autophagy/lysosome inhibitor chloroquine reduced RANKL-induced OC formation and function by increasing TRAF3 expression in OCPs in vitro and in vivo. Although chloroquine had no effect on basal bone resorption, it inhibited parathyroid hormone- and ovariectomy-induced OC activation in WT, but not cKO, mice. Deletion of the transcription factor gene Relb resulted in increased TRAF3 expression in OCPs, which was associated with decreased RANKL-induced TRAF3 degradation. RelB directly increased expression of BECN1, a key autophagy regulator, by binding to its promoter. These data indicate that autophagic/lysosomal degradation of TRAF3 is an important step in RANKL-induced NF-κB activation in OCPs. Furthermore, treatments that increase TRAF3 levels in OCPs, including pharmacological inhibition of its degradation with compounds such as chloroquine, may limit bone destruction in common bone diseases.

SUMOylation is required for optimal TRAF3 signaling capacity

TNF receptor-associated factors (TRAFs) are multifunctional adaptor proteins involved in temporal and spatial coordination of signals necessary for normal immune function. Here, we report that TRAF3, a TRAF family member with a key role in Toll-like and TNF family receptor signaling and suppressor of lymphomagenesis, is post-translationally modified by the small ubiquitin-related modifier (SUMO). Through yeast two-hybrid and co-immunoprecipitation assays we have identified Ubc9, the SUMO conjugating enzyme, as a novel TRAF3-interacting protein. We show that Ubc9-dependent SUMOylation of TRAF3 modulates optimal association with the CD40 receptor, thereby influencing TRAF3 degradation and non-canonical NF-κB activation upon CD40 triggering. Collectively, our findings describe a novel post-translational modification of a TRAF family member and reveal a link between SUMOylation and TRAF-mediated signal transduction.

Phylogenetic Analysis of Brassica rapa MATH-Domain Proteins

The MATH (meprin and TRAF-C homology) domain is a fold of seven anti-parallel β-helices involved in protein-protein interaction. Here, we report the identification and characterization of 90 MATH-domain proteins from the Brassica rapa genome. By sequence analysis together with MATH-domain proteins from other species, the B. rapa MATH-domain proteins can be grouped into 6 classes. Class-I protein has one or several MATH domains without any other recognizable domain; Class-II protein contains a MATH domain together with a conserved BTB (Broad Complex, Tramtrack, and Bric-a-Brac ) domain; Class-III protein belongs to the MATH/Filament domain family; Class-IV protein contains a MATH domain frequently combined with some other domains; Class-V protein has a relative long sequence but contains only one MATH domain; Class-VI protein is characterized by the presence of Peptidase and UBQ (Ubiquitinylation) domains together with one MATH domain. As part of our study regarding seed development of B. rapa, six genes are screened by SSH (Suppression Subtractive Hybridization) and their expression levels are analyzed in combination with seed developmental stages, and expression patterns suggested that Bra001786, Bra03578 and Bra036572 may be seed development specific genes, while Bra001787, Bra020541 and Bra040904 may be involved in seed and flower organ development. This study provides the first characterization of the MATH domain proteins in B. rapa.

IL-17 family cytokines mediated signaling in the pathogenesis of inflammatory diseases

Inflammation is the immediate protective response of the body to pathogen invasions, allergen challenges, chemical exposures or physical injuries. Acute inflammation usually accompanies with transient infiltration of leukocytes, removal of danger signals and eventually tissue repair, while persistent and uncontrolled inflammation becomes a major stimulator in the progression of many chronic diseases in human, including autoimmune diseases, metabolic disorders and cancer. Interleukin (IL)-17 family is a recent classified subset of cytokines, playing critical roles in both acute and chronic inflammatory responses. In this review, we will summarize recent progresses on the signalings of this family cytokines and their impacts on the inflammatory responses or disorders.

The activation and regulation of IL-17 receptor mediated signaling

Interleukin-17 (IL-17), the signature cytokine produced by T helper 17 (Th17) cells, plays pivotal roles in host defense responses against microbial invasion, as well as in the pathogenesis of autoimmune diseases and allergic syndromes. IL-17 activates several downstream signaling pathways including NF-κB, MAPKs and C/EBPs to induce gene expression of antibacterial peptides, proinflammatory chemokines and cytokines and matrix metalloproteinases (MMPs). IL-17 can also stabilize mRNAs of genes induced by TNFα. Although the physiological and pathological functions of IL-17 have been studied for many years, the landscape of its signaling transduction has not been described until recently. The cytosolic adaptor molecule Act1 (also known as CIKS) is considered as the master mediator of IL-17 signaling. In this review, we will summarize recent progress on activation and regulation of IL-17 mediated signal transduction, especially on Act1 mediated regulation of the signaling.

Up-regulation and pre-activation of TRAF3 and TRAF5 in inflammatory bowel disease

OBJECTIVE

TRAF3 and TRAF5 share a common ancestral gene, and interact as essential components of signaling pathways in immunity. TRAF3 and TRAF5 are overexpressed in the colon of rat/mouse models with colitis. However, the expressions of TRAF3 and TRAF5 in patients with inflammatory bowel disease have not been elucidated. The aim of the present study is to explore the potential roles of TRAF3 and TRAF5 in patients with inflammatory bowel disease.

METHODS

Plasma levels of TRAF3 and TRAF5 proteins were detected by Enzyme-linked Immunosorbent Assay (ELISA). Colonic expression of TRAF3 and TRAF5 proteins was detected by western blot analysis. Quantitative Real-time PCR (qRT-PCR) was applied for gene expression. Inflamed intestinal mucosa and non-inflamed intestinal mucosa in patients with inflammatory bowel disease and normal mucosa was analyzed from healthy controls.

RESULTS

The plasma levels of TRAF3 and TRAF5 were significantly higher both in patients with Crohn's disease and ulcerative colitis than in healthy controls. Only soluble TRAF5 showed a weak correlation with endoscopic disease activity index (Baron score) in patients with ulcerative colitis (spearman's r=0.358, P=0.022). Gene expressions of TRAF3 and TRAF5 in peripheral blood mononuclear cells were significantly higher both in patients with Crohn's disease and ulcerative colitis than in healthy controls (all P<0.0001). Gene and protein expressions of TRAF3 and TRAF5 were significantly higher in inflamed colonic mucosa of patients with Crohn's disease and ulcerative colitis than in non-inflamed colonic mucosa and normal mucosa of healthy controls (all P<0.0001). Furthermore, gene and protein expressions of TRAF3 and TRAF5 were also significantly higher in non-inflamed colonic mucosa of patients with Crohn's disease and ulcerative colitis than in normal mucosa of healthy controls.

CONCLUSIONS

TRAF3 and TRAF5 are overexpressed in inflammatory bowel disease. Although the endoscopic appearance can be normal, TRAF3 and TRAF5 pre-activation can be detected in non-inflamed colonic segments.

Prohibitins and the cytoplasmic domain of CD86 cooperate to mediate CD86 signaling in B lymphocytes

CD86 engagement on a CD40L/IL-4-primed murine B cell activates signaling intermediates that promote NF-κB activation to increase Oct-2 and mature IgG1 mRNA and protein expression, as well as the rate of IgG1 transcription, without affecting class switch recombination. One of the most proximal signaling intermediates identified is phospholipase Cγ2, a protein reported to bind tyrosine residues, which are absent in the cytoplasmic domain of CD86. Using a proteomics-based identification approach, we show that the tyrosine-containing transmembrane adaptor proteins prohibitin (Phb)1 and Phb2 bind to CD86. The basal expression of Phb1/2 and association with CD86 was low in resting B cells, whereas the level of expression and association increased primarily after priming with CD40. The CD86-induced increase in Oct-2 and IgG1 was less when either Phb1/2 expression was reduced by short hairpin RNA or the cytoplasmic domain of CD86 was truncated or mutated at serine/threonine protein kinase C phosphorylation sites, which did not affect Phb1/2 binding to CD86. Using this approach, we also show that Phb1/2 and the CD86 cytoplasmic domain are required for the CD86-induced phosphorylation of IκBα, which we previously reported leads to NF-κB p50/p65 activation, whereas only Phb1/2 was required for the CD86-induced phosphorylation of phospholipase Cγ2 and protein kinase Cα/β(II), which we have previously reported leads to NF-κB (p65) phosphorylation and subsequent nuclear translocation. Taken together, these findings suggest that Phb1/2 and the CD86 cytoplasmic domain cooperate to mediate CD86 signaling in a B cell through differential phosphorylation of distal signaling intermediates required to increase IgG1.

Design of CD40 agonists and their use in growing B cells for cancer immunotherapy

CD40 stimulation has produced impressive results in early-stage clinical trials of patients with cancer. Further progress will be facilitated by a better understanding of how the CD40 receptor becomes activated and the subsequent functions of CD40-stimulated immune cells. This review focuses on two aspects of this subject. The first is the recent recognition that signaling by CD40 is initiated when the receptors are induced to cluster within the membrane of responding cells. This requirement for CD40 clustering explains the stimulatory effects of certain anti-CD40 antibodies and the activity of many-trimer, but not one-trimer, forms of CD40 ligand (CD40L, CD154). The second topic is the use of these CD40 activators to expand B cells ("CD40-B cells"). As antigen-presenting cells (APCs), CD40-B cells are as effective as dendritic cells, with the important difference that CD40 B cells can be induced to proliferate in vitro, whereas DCs proliferate poorly if at all. As a result, the use of CD40-B cells as antigen-presenting cells (APCs) promises to streamline the generation of anti-tumor CD8(+) T cells for the adoptive cell therapy (ACT) of cancer.

Effect of TRAF6 on the biological behavior of human lung adenocarcinoma cell

Tumor necrosis factor receptor-associated factor 6 (TRAF6) is a unique adaptor protein of the tumor necrosis factor receptor-associated factor family that mediates both tumor necrosis factor receptor and interleukin-1 receptor/Toll-like receptor signaling. A recent study showed that TRAF6 played an important role in tumorigenesis and invasion through activation of nuclear factor kappa B (NF-κB). However, the biological role of TRAF6 remains unknown in lung cancer up to now. To address the expression of TRAF6 in lung cancer cells, four lung cancer cell lines (A549, HCC827, NCI-H292, and 95-D) and human bronchial epithelial cells were used to detect the expression of TRAF6 protein by western blotting. Results indicated that TRAF6 displayed an upregulation in human lung cancer cell lines. To investigate the effects of TRAF6 on the biological behavior of human lung adenocarcinoma cell, we generated human lung adenocarcinoma A549 cell line in which TRAF6 was depleted. The results showed that downregulation of TRAF6 could decrease cell viability, suppress cell proliferation and invasion, and promote cell apoptosis. At the same time, we explored the effects of TRAF6 on the expression of the following proteins: phosphor-NF-κB (p-p65), cyclin D1, caspase-3, and matrix metalloproteinase 9 (MMP9). Downregulation of TRAF6 could decrease the expression of p-p65, cyclin D1, and MMP9 and increase the expression of caspase-3. All these results suggested that TRAF6 might be involved in the potentiation of growth, proliferation, and invasion of A549 cell line, as well as the inhibition of A549 cell apoptosis by the activation of NF-κB. To make a long story short, the overexpression of TRAF6 might be related to the tumorigenesis and invasion of lung cancer.

Expression and secretion of TNF-α in mouse taste buds: a novel function of a specific subset of type II taste cells

Taste buds are chemosensory structures widely distributed on the surface of the oral cavity and larynx. Taste cells, exposed to the oral environment, face great challenges in defense against potential pathogens. While immune cells, such as T-cells and macrophages, are rarely found in taste buds, high levels of expression of some immune-response-associated molecules are observed in taste buds. Yet, the cellular origins of these immune molecules such as cytokines in taste buds remain to be determined. Here, we show that a specific subset of taste cells selectively expresses high levels of the inflammatory cytokine tumor necrosis factor-α (TNF-α). Based on immuno-colocalization experiments using taste-cell-type markers, the TNF-α-producing cells are predominantly type II taste cells expressing the taste receptor T1R3. These cells can rapidly increase TNF-α production and secretion upon inflammatory challenges, both in vivo and in vitro. The lipopolysaccharide (LPS)-induced TNF-α expression in taste cells was completely eliminated in TLR2^−/−/TLR4^−/− double-gene-knockout mice, which confirms that the induction of TNF-α in taste buds by LPS is mediated through TLR signaling pathways. The taste-cell-produced TNF-α may contribute to local immune surveillance, as well as regulate taste sensation under normal and pathological conditions.

Roles of tumor necrosis factor receptor associated factor 3 (TRAF3) and TRAF5 in immune cell functions

A large and diverse group of receptors utilizes the family of cytoplasmic signaling proteins known as tumor necrosis factor receptor (TNFR)-associated factors (TRAFs). In recent years, there has been a resurgence of interest and exploration of the roles played by TRAF3 and TRAF5 in cellular regulation, particularly in cells of the immune system, the cell types of focus in this review. This work has revealed that TRAF3 and TRAF5 can play diverse roles for different receptors even in the same cell type, as well as distinct roles in different cell types. Evidence indicates that TRAF3 and TRAF5 play important roles beyond the TNFR-superfamily (SF) and viral mimics of its members, mediating certain innate immune receptor and cytokine receptor signals, and most recently, signals delivered by the T-cell receptor (TCR) signaling complex. Additionally, much research has demonstrated the importance of TRAF3-mediated cellular regulation via its cytoplasmic interactions with additional signaling proteins. In particular, we discuss below evidence for the participation by TRAF3 in a number of the regulatory post-translational modifications involving ubiquitin that are important in various signaling pathways.

MIP-T3 is a negative regulator of innate type I IFN response

TNFR-associated factor (TRAF) 3 is an important adaptor that transmits upstream activation signals to protein kinases that phosphorylate transcription factors to induce the production of type I IFNs, the important effectors in innate antiviral immune response. MIP-T3 interacts specifically with TRAF3, but its function in innate IFN response remains unclear. In this study, we demonstrated a negative regulatory role of MIP-T3 in type I IFN production. Overexpression of MIP-T3 inhibited RIG-I-, MDA5-, VISA-, TBK1-, and IKKε-induced transcriptional activity mediated by IFN-stimulated response elements and IFN-β promoter. MIP-T3 interacted with TRAF3 and perturbed in a dose-dependent manner the formation of functional complexes of TRAF3 with VISA, TBK1, IKKε, and IFN regulatory factor 3. Consistent with this finding, retinoic acid-inducible gene I- and TBK1-induced phosphorylation of IFN regulatory factor 3 was significantly diminished when MIP-T3 was overexpressed. Depletion of MIP-T3 facilitated Sendai virus-induced activation of IFN production and attenuated the replication of vesicular stomatitis virus. In addition, MIP-T3 was found to be dissociated from TRAF3 during the course of Sendai virus infection. Our findings suggest that MIP-T3 functions as a negative regulator of innate IFN response by preventing TRAF3 from forming protein complexes with critical downstream transducers and effectors.

Glucocorticoid-induced immunoglobulin E synthesis by peripheral blood mononuclear cells from allergic and nonallergic subjects

BACKGROUND

Glucocorticoids (GCS) have been shown to induce IgE synthesis in human peripheral blood mononuclear cells (PBMCs) and purified B cells in vitro. However, the differences in immunoglobulin E (IgE) response to GCS between allergic and non-allergic individuals and the mechanism this interaction have not been elucidated.

OBJECTIVE

We aimed to compare the effect of GCS (budesonide) on interleukin (IL)-4-driven IgE production in vitro in allergic and non allergic subjects and assess the engagement of intracellular mechanisms.

METHODS

The study included 22 patients with allergic asthma and/or allergic rhinitis and 24 healthy volunteers. PBMCs were cultured for 11 days with IL-4 and budesonide and IgE concentrations in supernatants were assessed by immunoassays. T and B cell markers were assessed by flow cytometry.

RESULTS

Budesonide enhanced IgE synthesis to higher extent in healthy donors than in allergic patients (mean increase of 16.5 vs 6.3 kU/L, P< .05 respectively) acting through glucocorticoid receptor. Budesonide significantly increased lymhoplasmocytoid cells percentage in both media-controlled (2.5-fold increase) and IL-4-stimulated PBMCs (2-fold increase). Added to IL-4 budesonide decreased the percentage of both T cells and CD40L(+) T cells, but strongly increased the percentage of B cells. Protein tyrosine kinase (PTK) inhibitor decreased, but NF-κB and protein kinase A (PKA) inhibitors expressed modulatory effects on budesonide-induced IgE synthesis.

CONCLUSIONS

Budesonide-induced IgE generation in PBMCs differs in magnitude and seems to involve different mechanisms in atopic and non-atopic subjects.