TRIM59 interacts with ECSIT and negatively regulates NF-κB and IRF-3/7-mediated signal pathways

The TRIMendous Role of TRIMs in Virus-Host Interactions

The innate antiviral response is integral in protecting the host against virus infection. Many proteins regulate these signaling pathways including ubiquitin enzymes. The ubiquitin-activating (E1), -conjugating (E2), and -ligating (E3) enzymes work together to link ubiquitin, a small protein, onto other ubiquitin molecules or target proteins to mediate various effector functions. The tripartite motif (TRIM) protein family is a group of E3 ligases implicated in the regulation of a variety of cellular functions including cell cycle progression, autophagy, and innate immunity. Many antiviral signaling pathways, including type-I interferon and NF-κB, are TRIM-regulated, thus influencing the course of infection. Additionally, several TRIMs directly restrict viral replication either through proteasome-mediated degradation of viral proteins or by interfering with different steps of the viral replication cycle. In addition, new studies suggest that TRIMs can exert their effector functions via the synthesis of unconventional polyubiquitin chains, including unanchored (non-covalently attached) polyubiquitin chains. TRIM-conferred viral inhibition has selected for viruses that encode direct and indirect TRIM antagonists. Furthermore, new evidence suggests that the same antagonists encoded by viruses may hijack TRIM proteins to directly promote virus replication. Here, we describe numerous virus–TRIM interactions and novel roles of TRIMs during virus infections.

Knockdown of tripartite motif-59 inhibits the malignant processes in human colorectal cancer cells

The aim of the present study was to clarify the clinical implication and functional role of tripartite motif-59 (TRIM59) in colorectal carcinoma (CRC) and explore the underlying mechanism of aberrant high expression of TRIM59 in cancer. We validated that TRIM59 was upregulated in CRC samples, and also demonstrated that its upregulation was associated with advanced tumor stage of CRC patients; and its high expression indicated shorter overall survival and faster recurrence. Knockdown of TRIM59 significantly inhibited cell proliferation, migration and invasion. Cell cycle analysis showed that TRIM59-depleted cells accumulated in S-phase. In addition, the cell cycle regulators CDC25C, cyclin B1 and cyclin D1 were decreased by TRIM59 siRNA mediated knockdown. Furthermore, the depletion of TRIM59 promoted apoptosis in cell culture as indicated by the cleavage of caspase-3 and PARP when TRIM59 was depleted. These results suggested that TRIM59 is upregulated in human colorectal tumors compared with non-tumor tissues. The level of TRIM59 is correlated with malignant features of CRC and may serve as potential therapeutic and preventive strategies for CRC.

Tripartite motif-containing 28 bridges endothelial inflammation and angiogenic activity by retaining expression of TNFR-1 and -2 and VEGFR2 in endothelial cells

Angiogenesis and inflammation are regarded as important factors in the pathogenesis of chronic inflammation, cancer, and wound healing. Recent studies have supported prior evidence that common signaling pathways are involved in angiogenesis and inflammatory responses; however, key factors controlling both processes remain unclear. Although tripartite motif-containing (TRIM)-28 is known to have an immunosuppressive role in immune cells, its expression level and role in endothelial cells (ECs) are still unclear. In this study, we investigated the role of TRIM28 in inflammatory responses and angiogenic activity of ECs for the first time. We showed that TRIM28 is the most abundant TRIM family member and is localized in nuclei of ECs. Small interfering RNA-mediated knockdown of TRIM28 strikingly suppressed expression of TNF receptor (TNFR)-1 and -2, decreased TNF-α-induced phosphorylation of IKKα/β and IκBα and degradation of IκBα and nuclear translocation of p65, and suppressed basal level and TNF-α-induced expression of chemokines and adhesion molecules, including VCAM-1, IL-6, ICAM-1, E-selectin, and monocyte chemoattractant protein (MCP)-1. Unexpectedly, IL-8 was potentiated by TRIM28 knockdown in ECs in an NF-κB-inducing kinase-dependent manner. Meanwhile, knockdown of TRIM28 inhibited expression of VEGF receptor 2 and suppressed VEGF-induced proliferation and tube formation by ECs. Finally, knockdown of TRIM28 suppressed recruitment of ECs in vivo in a murine synthetic basement membrane model. In summary, we found that TRIM28 acts as a central factor in controlling endothelial inflammatory responses and angiogenic activities by retaining expression of TNFR-1 and -2 and VEGF receptor 2 in ECs.-Wang, Y., Li, J., Huang Y., Dai, X., Liu, Y., Liu, Z., Wang, Y., Wang, N., Zhang, P. Tripartite motif-containing 28 bridges endothelial inflammation and angiogenic activity by retaining expression of TNFR1 and -2 and VEGFR2 in endothelial cells.

Magnolol and honokiol from Magnolia officinalis enhanced antiviral immune responses against grass carp reovirus in Ctenopharyngodon idella kidney cells

Medicinal plants have been widely used for a long history. Exploration of pharmacologically active compounds from medicinal plants present a broad prevalent of application. By examining viral mRNA expression in GCRV-infected Ctenopharyngodon idella kidney (CIK) cells treated with thirty kinds of plant extracts, we identified Magnolia officinalis Rehd et Wils. was able to preferably suppress viral replication. Further studies demonstrated that the main ingredients of magnolia bark, namely, magnolol and honokiol presented protective pharmacological function when treated GCRV-infected CIK cells with a concentration of 2.00 μg/ml and 1.25 μg/ml, respectively. Furthermore, reverse transcript quantitative polymerase chain reaction (RT-qPCR) and western blot showed that both magnolol and honokiol were efficient to restrain the replication of GCRV in CIK cells at non-toxic concentration (2.51 ± 0.51 μg/ml for magnolol, and 3.18 ± 0.61 μg/ml for honokiol). Moreover, it was found that magnolol and honokiol promoted the expression of immune-related genes. Magnolol obviously significantly increased the expression of interferon (IFN) regulatory factor (IRF)7 rather than that of IRF3 in the GCRV-infected cells, leading to the activation of type I IFN (IFN-I). Simultaneously, magnolol drastically facilitated the expression of interleukin (IL)-1β, but failed to induce the molecules in nuclear factor (NF)-κB pathways. Differently, honokiol strikingly motivated not only the expression of IL-1β, but also those of tumor necrosis factor α (TNFα) and NF-κB. Interestingly, though honokiol motivated the expression of IFN-β promoter stimulator 1 (IPS-1), IRF3 and IRF7, it failed to up-regulate the expression of IFN-I, indicating that honokiol enhanced the host innate antiviral response to GCRV infection via NF-κB pathways. Collectively, the present study revealed that magnolol and honokiol facilitated the expression of innate immune-related genes to strengthen the innate immune signaling responses to resist GCRV infection, which contributed to understanding the mechanisms by which small-molecule drugs possessed antiviral activities. In addition, these results lay a foundation for the development of broad-spectrum antiviral compounds in aquaculture industry.

Expression profiling of TRIM protein family in THP1-derived macrophages following TLR stimulation

Activated macrophages play an important role in many inflammatory diseases including septic shock and atherosclerosis. However, the molecular mechanisms limiting macrophage activation are not completely understood. Members of the tripartite motif (TRIM) family have recently emerged as important players in innate immunity and antivirus. Here, we systematically analyzed mRNA expressions of representative TRIM molecules in human THP1-derived macrophages activated by different toll-like receptor (TLR) ligands. Twenty-nine TRIM members were highly induced (>3 fold) by one or more TLR ligands, among which 19 of them belong to TRIM C-IV subgroup. Besides TRIM21, TRIM22 and TRIM38 were shown to be upregulated by TLR3 and TLR4 ligands as previous reported, we identified a novel group of TRIM genes (TRIM14, 15, 31, 34, 43, 48, 49, 51 and 61) that were significantly up-regulated by TLR3 and TLR4 ligands. In contrast, the expression of TRIM59 was down-regulated by TLR3 and TLR4 ligands in both human and mouse macrophages. The alternations of the TRIM proteins were confirmed by Western blot. Finally, overexpression of TRIM59 significantly suppressed LPS-induced macrophage activation, whereas siRNA-mediated knockdown of TRIM59 enhanced LPS-induced macrophage activation. Taken together, the study provided an insight into the TLR ligands-induced expressions of TRIM family in macrophages.

TRIM52: A nuclear TRIM protein that positively regulates the nuclear factor-kappa B signaling pathway

Emerging evidence suggests that TRIM family proteins play a crucial role in regulating the NF-κB signaling pathway. TRIM52 is a novel noncanonical antiviral TRIM gene with a unique expanded RING domain. Information on the biological function of TRIM52 is limited. Herein, we demonstrated TRIM52 involvement in NF-κB activation. We found that TRIM52 overexpression specifically activated the NF-κB signal. TRIM52 overexpression can significantly induce TNFα and IL-6 expression. We also found that the RING domain of TRIM52 was essential for its activation of the NF-κB signal. Further study showed that TRIM52 overexpression did not affect the protein level of IκBα and phosphorylated p65 protein. We found that the pro-inflammatory cytokines TNFα and IL-6 could induce TRIM52 expression. Overall, these data suggested that TRIM52 was a positive regulator of the NF-κB pathway.

TRIM59 is upregulated and promotes cell proliferation and migration in human osteosarcoma

Osteosarcoma is a prevalent type of cancer and has a high metastatic ability, particularly for metastasis to the lungs. Effective treatment strategies have improved, however, the detailed molecular mechanism underlying the onset of this malignancy remains to be fully elucidated. The current study investigated the role of the tripartite motif (TRIM) family protein TRIM59 in osteosarcoma growth and metastasis. It was identified that TRIM59 was overexpressed in clinical osteosarcoma tissues and cultured osteosarcoma cell lines. In addition, the MTT assay demonstrated that in U2OS and MG63 cells, knockdown of TRIM59 by specific siRNA inhibited proliferation, whereas overexpression of TRIM59 promoted cell proliferation. Furthermore, overexpression of TRIM59 significantly increased the U2OS cell migrative and invasive abilities in a Transwell chamber assay. In addition, TRIM59 was able to negatively regulate the protein levels of P53 without significantly affecting the mRNA levels in U2OS and MG63 cells. These data suggest the oncogenic abilities of TRIM59 in osteosarcoma, which promote osteosarcoma cell proliferation, migration and invasion.

TRIM39 negatively regulates the NFκB-mediated signaling pathway through stabilization of Cactin

NFκB is one of the central regulators of cell survival, immunity, inflammation, carcinogenesis and organogenesis. The activation of NFκB is strictly regulated by several posttranslational modifications including phosphorylation, neddylation and ubiquitination. Several types of ubiquitination play important roles in multi-step regulations of the NFκB pathway. Some of the tripartite motif-containing (TRIM) proteins functioning as E3 ubiquitin ligases are known to regulate various biological processes such as inflammatory signaling pathways. One of the TRIM family proteins, TRIM39, for which the gene has single nucleotide polymorphisms, has been identified as one of the genetic factors in Behcet's disease. However, the role of TRIM39 in inflammatory signaling had not been fully elucidated. In this study, to elucidate the function of TRIM39 in inflammatory signaling, we performed yeast two-hybrid screening using TRIM39 as a bait and identified Cactin, which has been reported to inhibit NFκB- and TLR-mediated transcriptions. We show that TRIM39 stabilizes Cactin protein and that Cactin is upregulated after TNFα stimulation. TRIM39 knockdown also causes activation of the NFκB signal. These findings suggest that TRIM39 negatively regulates the NFκB signal in collaboration with Cactin induced by inflammatory stimulants such as TNFα.

Transcriptomic Characterization of Innate and Acquired Immune Responses in Red-Legged Partridges (Alectoris rufa): A Resource for Immunoecology and Robustness Selection

Present and future challenges for wild partridge populations include the resistance against possible disease transmission after restocking with captive-reared individuals, and the need to cope with the stress prompted by new dynamic and challenging scenarios. Selection of individuals with the best immune ability may be a good strategy to improve general immunity, and hence adaptation to stress. In this study, non-infectious challenges with phytohemagglutinin (PHA) and sheep red blood cells allowed the classification of red-legged partridges (Alectoris rufa) according to their overall immune responses (IR). Skin from the area of injection of PHA and spleen, both from animals showing extreme high and low IR, were selected to investigate the transcriptional profiles underlying the different ability to cope with pathogens and external aggressions. RNA-seq yielded 97 million raw reads from eight sequencing libraries and approximately 84% of the processed reads were mapped to the reference chicken genome. Differential expression analysis identified 1488 up- and 107 down-regulated loci in individuals with high IR versus low IR. Partridges displaying higher innate IR show an enhanced activation of host defence gene pathways complemented with a tightly controlled desensitization that facilitates the return to cellular homeostasis. These findings indicate that the immune system ability to respond to aggressions (either diseases or stress produced by environmental changes) involves extensive transcriptional and post-transcriptional regulations, and expand our understanding on the molecular mechanisms of the avian immune system, opening the possibility of improving disease resistance or robustness using genome assisted selection (GAS) approaches for increased IR in partridges by using genes such as AVN or BF2 as markers. This study provides the first transcriptome sequencing data of the Alectoris genus, a resource for molecular ecology that enables integration of genomic tools in further studies.

Control of FoxO4 Activity and Cell Survival by TRIM22 Directs TLR3-Stimulated Cells Toward IFN Type I Gene Induction or Apoptosis

Activation of innate immune response, induced after the recognition of double-stranded RNA (dsRNA), formed during replication of most viruses, results in intracellular signaling cascades ultimately culminating in the expression of type I interferon (IFN). In this study, we provide the first evidence that FoxO4 triggers the activation of the innate immune signaling pathway in coupling stimulation of TLR3 and RIG-like receptors by the synthetic dsRNA analog, poly(I:C), to IFN-β and IFN-induced gene induction, whereas knockdown of FoxO4 had opposite effects. Similar effects of FoxO4 were observed during paramyxovirus-mediated IFN-β transcriptional induction. We further found that knockdown of FoxO4 did not affect IRF3 and NF-κB activation by poly(I:C), suggesting that FoxO4 would act downstream in the signaling pathway. In addition, we show that the IFN-induced TRIM22 ubiquitin ligase targets FoxO4 and antagonizes its activity through an unrelated ubiquitin/autophagosomic-lysosomal pathway. Unexpectedly, TRIM22 knockdown strongly sensitizes cells to dsRNA-induced caspase-dependent apoptosis, as early as 2 h after poly(I:C) stimulation, concomitantly to the inhibition of the expression of the antiapoptotic protein, Bcl-2, indicating that TRIM22 might be a key factor for controlling the cell survival after TLR3 stimulation. Taken together, our data demonstrate that the regulation of FoxO4 protein expression and cell survival by TRIM22 controls TLR3-mediated IFN type I gene induction, preventing excessive antiviral response through dsRNA-induced apoptosis.

Mitochondria: a target for bacteria

Eukaryotic cells developed strategies to detect and eradicate infections. The innate immune system, which is the first line of defence against invading pathogens, relies on the recognition of molecular patterns conserved among pathogens. Pathogen associated molecular pattern binding to pattern recognition receptor triggers the activation of several signalling pathways leading to the establishment of a pro-inflammatory state required to control the infection. In addition, pathogens evolved to subvert those responses (with passive and active strategies) allowing their entry and persistence in the host cells and tissues. Indeed, several bacteria actively manipulate immune system or interfere with the cell fate for their own benefit. One can imagine that bacterial effectors can potentially manipulate every single organelle in the cell. However, the multiple functions fulfilled by mitochondria especially their involvement in the regulation of innate immune response, make mitochondria a target of choice for bacterial pathogens as they are not only a key component of the central metabolism through ATP production and synthesis of various biomolecules but they also take part to cell signalling through ROS production and control of calcium homeostasis as well as the control of cell survival/programmed cell death. Furthermore, considering that mitochondria derived from an ancestral bacterial endosymbiosis, it is not surprising that a special connection does exist between this organelle and bacteria. In this review, we will discuss different mitochondrial functions that are affected during bacterial infection as well as different strategies developed by bacterial pathogens to subvert functions related to calcium homeostasis, maintenance of redox status and mitochondrial morphology.

Insights into the antiviral immunity against grass carp (Ctenopharyngodon idella) reovirus (GCRV) in grass carp

Global fish production from aquaculture has rapidly grown over the past decades, and grass carp shares the largest portion. However, hemorrhagic disease caused by grass carp reovirus (GCRV) results in tremendous loss of grass carp (Ctenopharyngodon idella) industry. During the past years, development of molecular biology and cellular biology technologies has promoted significant advances in the understanding of the pathogen and the immune system. Immunoprophylaxis based on stimulation of the immune system of fish has also got some achievements. In this review, authors summarize the recent progresses in basic researches on GCRV; viral nucleic acid sensors, high-mobility group box proteins (HMGBs); pattern recognition receptors (PRRs), Toll-like receptors (TLRs) and retinoic acid inducible gene I- (RIG-I-) like receptors (RLRs); antiviral immune responses induced by PRRs-mediated signaling cascades of type I interferon (IFN-I) and IFN-stimulated genes (ISGs) activation. The present review also notices the potential applications of molecule genetic markers. Additionally, authors discuss the current preventive and therapeutic strategies (vaccines, RNAi, and prevention medicine) and highlight the importance of innate immunity in long term control for grass carp hemorrhagic disease.

Role of evolutionarily conserved signaling intermediate in Toll pathways (ECSIT) in the antibacterial immunity of Marsupenaeus japonicus

The Toll/Toll-like receptor (TLR) signaling pathway has an important role in the innate immunity of animals. Evolutionarily conserved signaling intermediate in Toll pathways (ECSIT) is a protein that functions as an adaptor protein for the Toll/TLR and bone morphogenetic protein signaling pathways. ECSIT is also a key component in the macrophage bactericidal activity of mammals. However, the function of ECSIT in crustaceans remains unclear. In this study, we cloned and identified a functional ECSIT homologue, MjECSIT 1, from kuruma shrimp Marsupenaeus japonicus. The complementary DNA of MjEcsit 1 is 1442 base pairs long, with an open reading frame of 1221 base pairs that encodes a 407-residue polypeptide. Transcripts of MjEcsit 1 are detected in hemocytes, gills, hepatopancreas, stomach, heart, intestines, testes, and ovaries. Such transcripts are upregulated by Gram-positive bacteria (Staphylococcus aureus) and Gram-negative bacteria (Vibrio anguillarum) injections. The knockdown of MjEcsit 1 by double-stranded RNA injection increases the sensitivity of M. japonicus to S. aureus challenge and weakens the bacterial clearance ability of M. japonicus in vivo. In addition, suppressing MjEcsit 1 restrains the upregulation of two anti-lipopolysaccharide factors by S. aureus injection. The results indicate that MjECSIT 1 is important in the antibacterial immunity of M. japonicus.

ECSIT bridges RIG-I-like receptors to VISA in signaling events of innate antiviral responses

Upon binding to RNA structures from invading viruses, RIG-I and MDA5 are recruited to mitochondria to interact with VISA and initiate antiviral type I interferon (IFN) responses. How this process is mediated is less understood. In this report, we demonstrate that ECSIT is an essential scaffolding protein that mediates the association of VISA and RIG-I or MDA5. Overexpression of ECSIT potentiated virus-triggered activation of IFN-regulatory factor 3 (IRF3) and expression of IFNB1, whereas knockdown of ECSIT impaired viral infection-induced activation of IRF3 and expression of IFNB1 as well as cellular antiviral responses. Mechanistically, ECSIT was associated with VISA on mitochondria and important for bridging RIG-I and MDA5 to VISA. Our findings suggest that ECSIT mediates virus-triggered type I IFN induction by bridging RIG-I and MDA5 to the VISA complex, and provide new insights into the molecular events of innate antiviral immune responses.

TRIM13 is a negative regulator of MDA5-mediated type I interferon production

Retinoic acid-inducible gene I (RIG-I) and melanoma differentiation-associated gene 5 (MDA5) are essential intracellular detectors of viral RNA. They contribute to the type I interferon (IFN) response that is crucial for host defense against viral infections. Given the potent antiviral and proinflammatory activities elicited by the type I IFNs, induction of the type I IFN response is tightly regulated. Members of the tripartite motif (TRIM) family of proteins have recently emerged as key regulators of antiviral immunity. We show that TRIM13, an E3 ubiquitin ligase, is expressed in immune cells and is upregulated in bone marrow-derived macrophages upon stimulation with inducers of type I IFN. TRIM13 interacts with MDA5 and negatively regulates MDA5-mediated type I IFN production in vitro, acting upstream of IFN regulatory factor 3. We generated Trim13(-/-) mice and show that upon lethal challenge with encephalomyocarditis virus (EMCV), which is sensed by MDA5, Trim13(-/-) mice produce increased amounts of type I IFNs and survive longer than wild-type mice. Trim13(-/-) murine embryonic fibroblasts (MEFs) challenged with EMCV or poly(I · C) also show a significant increase in beta IFN (IFN-β) levels, but, in contrast, IFN-β responses to the RIG-I-detected Sendai virus were diminished, suggesting that TRIM13 may play a role in positively regulating RIG-I function. Together, these results demonstrate that TRIM13 regulates the type I IFN response through inhibition of MDA5 activity and that it functions nonredundantly to modulate MDA5 during EMCV infection.

IMPORTANCE

The type I interferon (IFN) response is crucial for host defense against viral infections, and proper regulation of this pathway contributes to maintaining immune homeostasis. Retinoic acid-inducible gene I (RIG-I) and melanoma differentiation-associated gene 5 (MDA5) are intracellular detectors of viral RNA that induce the type I IFN response. In this study, we show that expression of the gene tripartite motif 13 (Trim13) is upregulated in response to inducers of type I IFN and that TRIM13 interacts with both MDA5 and RIG-I in vitro. Through the use of multiple in vitro and in vivo model systems, we show that TRIM13 is a negative regulator of MDA5-mediated type I IFN production and may also impact RIG-I-mediated type I IFN production by enhancing RIG-I activity. This places TRIM13 at a key junction within the viral response pathway and identifies it as one of the few known modulators of MDA5 activity.

TRIM68 negatively regulates IFN-β production by degrading TRK fused gene, a novel driver of IFN-β downstream of anti-viral detection systems

In recent years members of the tripartite motif-containing (TRIM) family of E3 ubiquitin ligases have been shown to both positively and negatively regulate viral defence and as such are emerging as compelling targets for modulating the anti-viral immune response. In this study we identify TRIM68, a close homologue of TRIM21, as a novel regulator of Toll-like receptor (TLR)- and RIG-I-like receptor (RLR)-driven type I IFN production. Proteomic analysis of TRIM68-containing complexes identified TRK-fused gene (TFG) as a potential TRIM68 target. Overexpression of TRIM68 and TFG confirmed their ability to associate, with TLR3 stimulation appearing to enhance the interaction. TFG is a known activator of NF-κB via its ability to interact with inhibitor of NF-κB kinase subunit gamma (IKK-γ) and TRAF family member-associated NF-κB activator (TANK). Our data identifies a novel role for TFG as a positive regulator of type I IFN production and suggests that TRIM68 targets TFG for lysosomal degradation, thus turning off TFG-mediated IFN-β production. Knockdown of TRIM68 in primary human monocytes resulted in enhanced levels of type I IFN and TFG following poly(I:C) treatment. Thus TRIM68 targets TFG, a novel regulator of IFN production, and in doing so turns off and limits type I IFN production in response to anti-viral detection systems.

Identification, characterization and immunological response analysis of stimulator of interferon gene (STING) from grass carp Ctenopharyngodon idella

Stimulator of interferon gene (STING), an important adapter responsible for RLR pathway, plays a pivotal role in both viral RNA- and DNA-triggered induction of IFNs in mammals. To understand the roles of STING in piscine immune system, STING gene (CiSTING) was identified from grass carp (Ctenopharyngodon idella). The genomic sequence of CiSTING was of 8548 base pairs (bp), including 899 bp 5' flank region, 7 exons and 6 introns. Promoter region was predicted and promoter activity was verified. The CiSTING cDNA was of 1358 bp with an open reading frame of 1185 bp, encoding a polypeptide of 394 amino acids with a signal peptide and three transmembrane motifs in the N-terminal region. mRNA expression of CiSTING was widespread in fifteen tissues investigated, and was up-regulated by GCRV in vivo and in vitro. Meanwhile, the transcription of CiSTING was inhibited at early stage, and then up-regulated at late phase upon poly(I:C) or PGN stimulation in vitro. Interestingly, CiSTING had little impact on LPS in vitro. In CiSTING over-expression cells, CiTBK1, CiIRF3 and CiIRF7 were significantly up-regulated post GCRV or viral/bacterial PAMPs stimulation. In addition, post GCRV or PGN stimulation, the transcription of CiIFN-I was remarkably inhibited while CiMx1 was up-regulated; as for poly(I:C) stimulation, mRNA expressions of CiIFN-I and CiMx1 were inhibited at early stage while enhanced at late phrase; after LPS stimulation, both CiIFN-I and CiMx1 were inhibited. Furthermore, antiviral activity of CiSTING was manifested by the inhibition of GCRV yield. Taken together, these results demonstrated that CiSTING may be involved in board innate immune responses via the TBK1-IRF3/IRF7 cascade, responding to not only dsRNA analogue in an IFN-dependent pathway, but also virus and bacterial PAMPs in an IFN-independent pathway. This study provided novel insights into the essential role of STING in innate immunity.

TRIMmunity: the roles of the TRIM E3-ubiquitin ligase family in innate antiviral immunity

Tripartite motif (TRIM) proteins have been implicated in multiple cellular functions, including antiviral activity. Research efforts so far indicate that the antiviral activity of TRIMs relies, for the most part, on their function as E3-ubiquitin ligases. A substantial number of the TRIM family members have been demonstrated to mediate innate immune cell signal transduction and subsequent cytokine induction. In addition, a subset of TRIMs has been shown to restrict viral replication by directly targeting viral proteins. Although the body of work on the cellular roles of TRIM E3-ubiquitin ligases has rapidly grown over the last years, many aspects of their molecular workings and multi-functionality remain unclear. The antiviral function of many TRIMs seems to be conferred by specific isoforms, by sub-cellular localization and in cell-type-specific contexts. Here we review recent findings on TRIM antiviral functions, current limitations and an outlook for future research.

IRF-7: an antiviral factor and beyond

This review will summarize main characteristics and functions of IRF-7. IRF-7 and the highly homologous IRF-3 are two members of the IRF family of transcription factors that have emerged as crucial regulators of type I interferon (IFN) in response to pathogenic infections downstream pathogen recognition receptors. IRF-7 is also part of a positive-feedback regulatory loop essential for sustained IFN responses. Thus, tight regulation of its expression and activity is necessary to balance IFN-mediated beneficial effects and unwanted pathological consequences of IFN overproduction. Its role as an antiviral factor independent of IFN expression, and its involvement in other cellular functions beyond antiviral functions, including regulation of oncogenesis and metabolism, underscore its important role in the regulation of cellular homeostasis.

Proteomics and NF-κB: an update

The transcription factor NF-κB was discovered in 1986 and since then has been extensively studied in relation to cancer research and inflammatory or autoimmune diseases due to its important roles in the regulation of apoptosis and inflammation as well as innate and adaptive immunity. Although much is known about NF-κB signaling, novel NF-κB functions in different diseases are still being uncovered, together with its target proteins, interaction partners and regulators of its activation cascade. Proteomic approaches are particularly suited to the discovery of new proteins involved in distinct signal transduction cascades. This review provides an update on and extension of a recent review that summarized a number of proteomic approaches to NF-κB signaling. The studies discussed here utilized innovative techniques and offer several new hypotheses on the role of NF-κB in physiological and pathophysiological processes, which open new avenues for research on NF-κB in the future.

Identification, expression profiling of a grass carp TLR8 and its inhibition leading to the resistance to reovirus in CIK cells

TLR8 (toll-like receptor 8), a homolog of TLR3, TLR7 and TLR9 as prototypical intracellular members of TLR family, is generally associated with sensing single stranded RNA and plays a pivotal role in antiviral immune response. In this study, a TLR8 gene from grass carp Ctenopharyngodon idella (designated as CiTLR8) was obtained and characterized. The full-length cDNA of CiTLR8 was of 3766 bp. The open reading frame was of 3072 bp and encoded a polypeptide of 1023 amino acids, including seventeen LRR (leucine-rich repeat) motifs, one transmembrane domain and one TIR (toll/interleukin-1 receptor) domain. A single intron with the size of 839 bp was found on the neck of start codon (ATG). CiTLR8 mRNA was ubiquitously expressed in the 15 tested tissues and the expression level in gas bladder, spleen, brain, hindgut and trunk kidney tissues was high. Besides, the CiTLR8 expression in spleen and head kidney was significantly up-regulated and reached peak at 24 h post-injection of grass carp reovirus (GCRV). CiTLR8 transcription reached peak at 8 h and then declined below the normal level post-GCRV infection in the C. idella kidney (CIK) cell line; and it was rapidly and significantly down-regulated by the stimulation of the synthetic double-stranded RNA polyriboinosinic-polyribocytidylic acid sodium salt (poly I:C) in CIK cells in a dose and time-dependent manner. The inhibitor expression vectors were constructed and transfected into CIK cell line to obtain stably expressing shRNA targeting TLR8. In CiTLR8-knockdown cells, CiTLR7 transcript weakly increased, CiIFN-I mRNA was significantly down-regulated, and the expression of CiMyD88, CiIRF7 and CiMx1 scarcely changed. Post poly I:C stimulation, CiTLR8, CiTLR7 and CiMyD88 transcripts significantly increased, CiIRF7 was down-regulated after an initial phase of increase, and CiIFN-I and CiMx1 transcripts were up-regulated. After GCRV infection, the transcripts of CiTLR8, CiTLR7, CiMyD88 and CiIRF7 were up-regulated, but CiIFN-I and CiMx1 transcripts were inhibited. Nevertheless, cells transfected with pshTLR8 vectors had strong resistance against GCRV injection, suggesting CiTLR8 might play a negative role in antiviral immune response. These results collectively suggested that CiTLR8 was a novel member of TLR gene family, engaging in antiviral innate immune defense in C. idella, which laid a foundation for the further mechanism research of TLR8 in fishes.

Mitochondria: sensors and mediators of innate immune receptor signaling

By integrating stress signals with inputs from other cellular organelles, eukaryotic mitochondria are dynamic sensing systems that can confer substantial impact on innate immune signaling in both health and disease. This review highlights recently discovered elements of innate immune receptor signaling (TLR, RLR, NLR, and CLR) associated with mitochondrial function and discusses the role of mitochondria in the initiation and/or manifestation of inflammatory diseases and disorders. We also highlight the role of mitochondria as therapeutic targets for inflammatory disease.