Molecular and functional characterization of pigeon (Columba livia) tumor necrosis factor receptor-associated factor 3

Grouper TRAF3 inhibits nodavirus infection by regulating the STING-mediated antiviral signaling pathway

Tumor necrosis factor (TNF) receptor-associated factors (TRAFs) are major signal transducers for the TNF and interleukin-1/Toll-like receptor superfamilies that transduce signals from various immune receptors. To investigate the interaction of TRAF3 and other proteins in signaling pathways and to identify its antiviral function in teleosts, we cloned and characterized a TRAF3 homolog from orange-spotted grouper (Epinephelus coioides) (EcTRAF3). The open reading frame of EcTRAF3 consists of 1767 base pairs encoding a 588 amino acid protein, and the predicted molecular mass is 66.71 kDa EcTRAF3 shares 99.83% identity with TRAF3 of Epinephelus lanceolatus. Expression analysis revealed that EcTRAF3 was broadly distributed in examined tissues and was up-regulated under polyinosinic-polycytidylic acid and red-spotted grouper nervous necrosis virus (RGNNV) stimulation in vivo. EcTRAF3 was identified as a cytosolic protein based on fluorescence microscopy analysis. Overexpression of EcTRAF3 inhibited RGNNV replication in grouper spleen cells, and it interacted with the coat protein of RGNNV. Overexpression of EcTRAF3 also induced the activation of interferon β (IFN-β), IFN-stimulated response element (ISRE), and nuclear factor-κB (NF-κB). EcTRAF3 co-transfected with Stimulator of Interferon Genes (STING) of grouper (EcSTING) induced a significantly higher level of IFN-β promoter activity. Moreover, EcTRAF3 interacted with EcSTING, implying that EcTRAF3 may function as an enhancer in EcSTING-mediated signaling. Taken together, our results suggest that EcTRAF3 negatively regulates the RGNNV-induced cellular antiviral response and plays an important role in the immune response system of fish.

Functional differences in the products of two TRAF3 genes in antiviral responses in the Chinese giant salamander, Andrias davidianus

Tumour necrosis factor receptor associated factor 3 (TRAF3) is a crucial transducing protein for linking upstream receptor signals and downstream antiviral signalling pathways. Previous studies mostly clarified the functions of TRAF3 in mammals, birds and fish, but little is known about the characterization and function of TRAF3 in amphibians. In this study, the molecular and functional identification of two TRAF3 genes, AdTRAF3A and AdTRAF3B, were investigated in the Chinese giant salamander Andrias davidianus. The complete open reading frames (ORFs) of AdTRAF3A and AdTRAF3B were 1698 bp and 1743 bp in length, encoding 565 and 580 amino acids, respectively. Both AdTRAF3A and AdTRAF3B deduced proteins contained a RING finger, two TRAF-type zinc fingers, a coiled-coil and a MATH domain. Phylogenetic analysis showed that the AdTRAF3 protein clustered together with other known TRAF3 proteins. Gene expression analysis showed that AdTRAF3s were broadly distributed in all examined tissues with similar distribution patterns. AdTRAF3s in the blood or spleen positively responded to Giant salamander iridovirus (GSIV) and poly (I:C) induction but exhibited distinct response patterns. Silencing AdTRAF3A/B remarkably suppressed the expression of IFN signalling pathway-related genes when leukocytes were treated with DNA virus and the viral RNA analogue. Moreover, overexpression of AdTRAF3A may induce the activation of the IFN-β promoter, and the zinc finger, coiled coil and MATH domains of AdTRAF3A were essential for IFN-β promoter activation. However, the overexpression of AdTRAF3B significantly suppressed IFN-β promoter activity, and its inhibitory effect was enhanced when the RING finger or MATH domain was deleted. Furthermore, AdTRAF3A rather than AdTRAF3B significantly induced NF-κB activation, implying that AdTRAF3A may function as an enhancer in both the IFN and NF-κB signalling pathways. Taken together, our results suggest that the two TRAF3 genes play different crucial regulatory roles in innate antiviral immunity in Chinese giant salamanders.

Redox Homeostasis in Poultry: Regulatory Roles of NF-κB

Redox biology is a very quickly developing area of modern biological sciences, and roles of redox homeostasis in health and disease have recently received tremendous attention. There are a range of redox pairs in the cells/tissues responsible for redox homeostasis maintenance/regulation. In general, all redox elements are interconnected and regulated by various means, including antioxidant and vitagene networks. The redox status is responsible for maintenance of cell signaling and cell stress adaptation. Physiological roles of redox homeostasis maintenance in avian species, including poultry, have received limited attention and are poorly characterized. However, for the last 5 years, this topic attracted much attention, and a range of publications covered some related aspects. In fact, transcription factor Nrf2 was shown to be a master regulator of antioxidant defenses via activation of various vitagenes and other protective molecules to maintain redox homeostasis in cells/tissues. It was shown that Nrf2 is closely related to another transcription factor, namely, NF-κB, responsible for control of inflammation; however, its roles in poultry have not yet been characterized. Therefore, the aim of this review is to describe a current view on NF-κB functioning in poultry with a specific emphasis to its nutritional modulation under various stress conditions. In particular, on the one hand, it has been shown that, in many stress conditions in poultry, NF-κB activation can lead to increased synthesis of proinflammatory cytokines leading to systemic inflammation. On the other hand, there are a range of nutrients/supplements that can downregulate NF-κB and decrease the negative consequences of stress-related disturbances in redox homeostasis. In general, vitagene-NF-κB interactions in relation to redox balance homeostasis, immunity, and gut health in poultry production await further research.

Comprehensive Evolutionary Analysis of Lamprey TNFR-Associated Factors (TRAFs) and Receptor-Interacting Protein Kinase (RIPKs) and Insights Into the Functional Characterization of TRAF3/6 and RIPK1

TNFR-associated factors (TRAFs) and receptor-interacting protein kinases (RIPKs) are important immunological linker molecules in mammals and play important roles in the TNFα, TLR and IFN signaling pathways. However, the evolutionary origins of these genes in vertebrates have not previously been described in lampreys. In this study, we searched the genomes of Lampetra japonicum, Lethenteron reissneri, and Petromyzon marinus for genes encoding trafs and ripks and performed homologous sequence alignment, phylogenetic tree, functional domain, conserved motif, gene structure, and synteny analyses to determine their evolutionary relationships. The distribution of the lamprey traf and ripk families and the immune response of the gene families in lampreys stimulated by different pathogens were also demonstrated, suggesting a role of structural changes in expression and functional diversification. Additionally, the dual luciferase reporter gene assay showed that the addition of exogenous immunomodulator (TNFα or IFN) to the overexpression of LjLRIPK1a or LjTRAF3/6 significantly downregulated NF-κB or ISRE activation. LjRIPK1a can significantly enhance caspase-8 activity, and overexpression of LjRIPK1a or LjTRAF3a/6 in HEK293T cells results in cell apoptosis. In summary, this study makes an important contribution to the understanding of the traf and ripk gene families in different vertebrates. Our results also provide new evidence for the evolution of vertebrate TRAFs and RIPKs and their impacts on immune regulation.

Molecular cloning and functional analysis of TRAF6 from Yangzhou great white goose Anser anser

TNF receptor-associated factor 6 (TRAF6) is an adaptor protein and an E3 ubiquitin ligase mediating multiple cell signaling pathway activation in a context-dependent manner. TRAF6 plays critical roles in innate immune response and regulates function of antigen-presenting cells. Here, we cloned the goose TRAF6 (goTRAF6) gene from a healthy Yangzhou great white goose (Anser anser), which had a typical TRAF structure and shared a high-sequence identity with TRAF6 of other birds. Quantitative real-time PCR revealed that goTRAF6 mRNA was broadly expressed in all the studied tissues, with highest expression in the heart and pectoral muscle. Overexpression of goTRAF6 caused NF-κB activation in a dose-dependent manner and substantially upregulated IFN-β expression in HEK293T cells. Following Toll-like receptor (TLR) ligand stimulation of goose peripheral blood mononuclear cells, goTRAF6 and downstream inflammatory cytokine mRNA levels considerably up-regulated, especially at early stages. Salmonella Enteritidis challenge caused overexpression of goTRAF6 and cytokine mRNA in all the examined organs. These findings demonstrated that goTRAF6 played a substantial role in TLR-TRAF6 signaling cascade, and further contributed to the antibacterial-responses in host.

Molecular cloning and functional characterisation of duck (Anas platyrhynchos) tumour necrosis factor receptor-associated factor 3

1. Tumour necrosis factor receptor-associated factor 3 (TRAF3) is a key regulator of innate immunity and acquired immunity, and has a salient anti-viral role. 2. In this experiment, the duck TRAF3 (DuTRAF3) gene was cloned according to the Anas platyrhynchos TRAF3 sequence to explore its function. The TRAF3 open reading frame contains 1704 bp that encode a protein of 567 amino acids, which contain a RING finger domain, two zinc finger motifs, a coiled-coil region, and a MATH domain. 3. Reverse transcription-polymerase chain reaction showed that DuTRAF3 was expressed in all the examined tissues, with a comparatively higher expression in the spleen and brain tissues. 4. In HEK293T cells, DuTRAF3 overexpression resulted in a significantly increased NF-κB activity and interferon (IFN)-β promoter activation. 5. Following resiquimod (R848) and poly(I:C) stimulation of duck peripheral blood mononuclear cells (PBMCs), the expressions of TRAF3 and IFN-β were significantly upregulated; in addition, following R848 stimulation, the mRNA levels of IL-6, IL-8 and IL-10 were also significantly upregulated. After infection with the Newcastle Disease Virus LaSota vaccine strain, the mRNA levels of IL-6 and IL-10 were significantly upregulated, while that of TRAF3 was downregulated. 6. These results suggest that DuTRAF3 has an important role to play in innate antiviral immune responses.

Negative Regulation of Interferon-β Production by Alternative Splicing of Tumor Necrosis Factor Receptor-Associated Factor 3 in Ducks

Tumor necrosis factor receptor-associated factor 3 (TRAF3), an intracellular signal transducer, is identified as an important component of Toll-like receptors and RIG-I-like receptors induced type I interferon (IFN) signaling pathways. Previous studies have clarified TRAF3 function in mammals, but little is known about the role of TRAF3 in ducks. Here, we cloned and characterized the full-length duck TRAF3 (duTRAF3) gene and an alternatively spliced isoform of duTRAF3 (duTRAF3-S) lacking the fragment encoding amino acids 217–319, from duck embryo fibroblasts (DEFs). We found that duTRAF3 and duTRAF3-S played different roles in regulating IFN-β production in DEFs. duTRAF3 through its TRAF domain interacted with duMAVS or duTRIF, leading to the production of IFN-β. However, duTRAF3-S, containing the TRAF domain, was unable to bind duMAVS or duTRIF due to the intramolecular binding between the N- and C-terminal of duTRAF3-S that blocked the function of its TRAF domain. Further analysis identified that duTRAF3-S competed with duTRAF3 itself for binding to duTRAF3, perturbing duTRAF3 self-association, which impaired the assembly of duTRAF3-duMAVS/duTRIF complex, ultimately resulted in a reduced production of IFN-β. These findings suggest that duTRAF3 is an important regulator of duck innate immune signaling and reveal a novel mechanism for the negative regulation of IFN-β production via changing the formation of the homo-oligomerization of wild molecules, implying a novel regulatory role of truncated proteins.

Tumor necrosis factor receptor-associated factor 3 from Anodonta woodiana is an important factor in bivalve immune response to pathogen infection

Tumor necrosis factor receptor-associated factor 3 (TRAF3) is a multifunctional adaptor protein in innate and acquired immune system that plays a key role in the regulation of the RIG-I-like receptor (RLR) and Toll-like receptor (TLR) signaling pathway in mammals. However, the immune function of TRAF3 homologs in freshwater mollusks is not well understood. In this study, we identified a bivalve TRAF3 gene (AwTRAF3) from Anodonta woodiana and investigated its potential roles during immune challenges. The present AwTRAF3 encoded a polypeptide of 562 amino acids with predicted molecular mass of 64.5 kDa and PI of 7.9. Similar to other reported TRAF3s, AwTRAF3 contained a RING finger domain, two TRAF domains with zinc finger domains, a coiled coli region and a conserved C-terminal meprin and TRAF homology (MATH) domain. Quantitative real-time PCR (qRT-PCR) analysis revealed that AwTRAF3 mRNA was broadly expressed in all of the examined tissues, with high expression in hepatopancreas, gill and heart. In addition, immune challenge experiments directly showed that transcript levels of AwTRAF3 in hepatopancreas were significantly regulated upon bacterial (Vibrio alginolyticus and Staphylococcus aureus) and viral (poly (I:C)) challenges, respectively. Moreover, GFP-tagged AwTRAF3 fusion protein was found to be located primarily in the cytoplasm in HEK293T cells. Altogether, these data provided the first experimental demonstration that freshwater mollusks possess a functional TRAF3 that was involved in the innate defense against bacterial and viral infection.