TRIM35 negatively regulates TLR7- and TLR9-mediated type I interferon production by targeting IRF7

TRIM35 triggers cardiac remodeling by regulating SLC7A5-mediated amino acid transport and mTORC1 activation in fibroblasts

BACKGROUND

Cardiac maladaptive remodeling is one of the leading causes of heart failure with highly complicated pathogeneses. The E3 ligase tripartite motif containing 35 (TRIM35) has been identified as a crucial regulator governing cellular growth, immune responses, and metabolism. Nonetheless, the role of TRIM35 in fibroblasts in cardiac remodeling remains elusive.

METHODS

Heart tissues from human donors were used to verify tissue-specific expression of TRIM35. Fibroblast-specific Trim35 gene knockout mice (Trim35cKO) were used to investigate the function of TRIM35 in fibroblasts. Cardiac function, morphology, and molecular changes in the heart tissues were analyzed after transverse aortic constriction (TAC) surgery. The mechanisms by which TRIM35 regulates fibroblast phenotypes were elucidated using liquid chromatography-tandem mass spectrometry (LC-MS/MS) and RNA sequencing (RNA-Seq). These findings were further validated through the use of adenoviral and adeno-associated viral transfection systems, as well as the mTORC1 inhibitor Rapamycin.

RESULTS

TRIM35 expression is primarily up-regulated in cardiac fibroblasts in both murine and human fibrotic hearts, and responds to TGF-β1 stimulation. Specific deletion of TRIM35 in cardiac fibroblasts significantly improves cardiac fibrosis and hypertrophy. Consistently, the overexpression of TRIM35 promotes fibroblast proliferation, migration, and differentiation. Through paracrine signaling, it induces hypertrophic growth of cardiomyocytes. Mechanistically, we found that TRIM35 interacts with, ubiquitinates, and up-regulates the amino acid transporter SLC7A5, which enhances amino acid transport and activates the mTORC1 signaling pathway. Furthermore, overexpression of SLC7A5 significantly reverses the reduced cardiac fibrosis and hypertrophy caused by conditional knockout of TRIM35.

CONCLUSION

Our findings demonstrate a novel role of fibroblast-TRIM35 in cardiac remodeling and uncover the mechanism underlying SLC7A5-mediated amino acid transport and mTORC1 activation. These results provide a potential novel therapeutic target for treating cardiac remodeling.

Emerging roles of tripartite motif family proteins (TRIMs) in breast cancer

Breast cancer (BC) is the most common malignant tumor worldwide. Despite enormous progress made in the past decades, the underlying mechanisms of BC remain further illustrated. Recently, TRIM family proteins proved to be engaged in BC progression through regulating various aspects. Here we reviewed the structures and basic functions of TRIM family members and first classified them into three groups according to canonical polyubiquitination forms that they could mediate: K48- only, K63- only, and both K48- and K63-linked ubiquitination. Afterwards, we focused on the specific biological functions and mechanisms of TRIMs in BCs, including tumorigenesis and invasiveness, drug sensitivity, tumor immune microenvironment (TIME), cell cycle, and metabolic reprogramming. We also explored the potential of TRIMs as novel biomarkers for predicting prognosis and future therapeutic targets in BC.

Genetic Association and Differential RNA Expression of Histone (De)Acetylation-Related Genes in Pemphigus Foliaceus-A Possible Epigenetic Effect in the Autoimmune Response

Pemphigus foliaceus (PF) is an autoimmune skin blistering disease characterized by antidesmoglein-1 IgG production, with an endemic form (EPF) in Brazil. Genetic and epigenetic factors have been associated with EPF, but its etiology is still not fully understood. To evaluate the genetic association of histone (de)acetylation-related genes with EPF susceptibility, we evaluated 785 polymorphisms from 144 genes, for 227 EPF patients and 194 controls. Carriers of HDAC4_rs4852054*A were more susceptible (OR = 1.79, p = 0.0038), whereas those with GSE1_rs13339618*A (OR = 0.57, p = 0.0011) and homozygotes for PHF21A_rs4756055*A (OR = 0.39, p = 0.0006) were less susceptible to EPF. These variants were not associated with sporadic PF (SPF) in German samples of 75 SPF patients and 150 controls, possibly reflecting differences in SPF and EPF pathophysiology. We further evaluated the expression of histone (de)acetylation-related genes in CD4+ T lymphocytes, using RNAseq. In these cells, we found a higher expression of KAT2B, PHF20, and ZEB2 and lower expression of KAT14 and JAD1 in patients with active EPF without treatment compared to controls from endemic regions. The encoded proteins cause epigenetic modifications related to immune cell differentiation and cell death, possibly affecting the immune response in patients with PF.

Effect of Agaricus bisporus Polysaccharides (ABPs) on anti-CCV immune response of channel catfish

Herein, the effects of Agaricus bisporus Polysaccharides (ABPs) on anti-channel catfish virus (CCV) infections to promote their application in channel catfish culture were explored. Transcriptome and metabolome analyses were conducted on the spleen of a CCV-infected channel catfish model fed with or without ABPs. CCV infections upregulated many immune and apoptosis-related genes, such as IL-6, IFN-α3, IFN-γ1, IL-26, Casp3, Casp8, and IL-10, and activated specific immunity mediated by B cells. However, after adding ABPs, the expression of inflammation-related genes decreased in CCV-infected channel catfish, and the inflammatory inhibitors NLRC3 were upregulated. Meanwhile, the expression of apoptosis-related genes was reduced, indicating that ABPs can more rapidly and strongly enhance the immunity of channel catfish to resist viral infection. Moreover, the metabonomic analysis showed that channel catfish had a high energy requirement during CCV infection, and ABPs could enhance the immune function of channel catfish. In conclusion, ABPs can enhance the antiviral ability of channel catfish by enhancing immune response and regulating inflammation. Thus, these findings provided new insights into the antiviral response effects of ABPs, which might support their application in aquaculture.

Mechanisms of Immune-Related Long Non-Coding RNAs in Spleens of Mice Vaccinated with 23-Valent Pneumococcal Polysaccharide Vaccine (PPV23)

The 23-valent pneumococcal vaccine (PPV23) is a classical common vaccine used to prevent pneumococcal disease. In past decades, it was thought that vaccination with this vaccine induces humoral immunity, thereby reducing the disease associated with infection with 23 common serotypes of Streptococcus pneumoniae (Sp). However, for this polysaccharide vaccine, the mechanism of immune response at the transcriptional level has not been fully studied. To identify the lncRNAs (long noncoding RNAs) and mRNAs in spleens related to immunity after PPV23 vaccination in mice, high-throughput RNA sequencing of spleens between a PPV23 treatment group and a control group were performed and evaluated in this study. The RNA-seq results identified a total of 41,321 mRNAs and 34,375 lncRNAs, including 55 significantly differentially expressed (DE) mRNAs and 389 DE lncRNAs (p < 0.05) between the two groups. GO and KEGG annotation analysis indicated that the target genes of DE lncRNAs and DE mRNAs were related to T-cell costimulation, positive regulation of alpha–beta T-cell differentiation, the CD86 biosynthetic process, and the PI3K-Akt signaling pathway, indicating that the polysaccharide component antigens of PPV23 might activate a cellular immune response during the PPV23 immunization process. Moreover, we found that Trim35 (tripartite motif containing 35), a target gene of lncRNA MSTRG.9127, was involved in regulating immunity. Our study provides a catalog of lncRNAs and mRNAs associated with immune cells’ proliferation and differentiation, and they deserve further study to deepen the understanding of the biological processes in the regulation of PPV23 during humoral immunity and cellular immunity.

Population pharmacokinetic/pharmacodynamic models of JNJ-64794964, a toll-like receptor 7 agonist, in healthy adult participants

BACKGROUND

JNJ-4964 is a TLR7 agonist, which, via a type I interferon (IFN)-dependent mechanism, may enhance host immunity suppressed by persistent exposure to hepatitis B antigens in chronic hepatitis B.

METHODS

PK and PD data were pooled from 2 studies involving 90 participants (n = 74 JNJ-4964, dose range 0.2-1.8 mg; n = 16 placebo) in a fasted state. Food effects on PK were studied in 24 participants (1.2 or 1.25 mg). A population PK model and PK/PD models were developed to characterize the effect of JNJ-4964 plasma levels on the time course of IFN-α, IFN-γ-inducible protein 10 (IP-10 or CXCL10), IFN-stimulated gene 15 (ISG15), neopterin and lymphocytes following single and weekly dosing in healthy adults. Covariate effects, circadian rhythms and negative feedback were incorporated in the models.

RESULTS

A 3-compartment linear PK model with transit absorption adequately described JNJ-4964 PK. Bioavailability was 44.2% in fed state relative to fasted conditions. Indirect response models with maximum effect (Emax) stimulation on production rate constant (kin) described IFN-α, IP-10, ISG15 and neopterin, while a precursor-dependent indirect response model with inhibitory effect described the transient lymphocyte reduction. Emax, EC50 and γ (steepness) estimates varied according to PD markers, with EC50 displaying substantial between-subject variability. Female and Asian race exhibited lower EC50, suggesting higher responsiveness.

CONCLUSIONS

PK/PD models well characterized the time course of immune system markers in healthy adults. Our results supported sex and race as covariates on JNJ-4964 responsiveness, as well as circadian rhythms and negative feedback as homeostatic mechanisms that are relevant in TLR7-induced type I IFN responses.

Duck TRIM29 negatively regulates type I IFN production by targeting MAVS

The innate immune response is a host defense mechanism that induces type I interferon and proinflammatory cytokines. Tripartite motif (TRIM) family proteins have recently emerged as pivotal regulators of type I interferon production in mammals. Here, we first identified duck TRIM29, which encodes 571 amino acids and shows high sequence homology with other bird TRIM29 proteins. DuTRIM29 inhibited IFN-β and IRF7 promoter activation in a dose-dependent manner and downregulated the mRNA expression of IFN-β, IRF7, Mx and IL-6 mediated by duRIG-I. Moreover, duTRIM29 interacted and colocalized with duMAVS in the cytoplasm. DuTRIM29 interacted with duMAVS via its C-terminal domains. In addition, duTRIM29 inhibited IFN-β and IRF7 promoter activation and significantly downregulated IFN-β and immune-related gene expression mediated by duMAVS in ducks. Furthermore, duTRIM29 induced K29-linked polyubiquitination and degradation of duMAVS to suppress the expression of IFN-β. Overall, our results demonstrate that duTRIM29 negatively regulates type I IFN production by targeting duMAVS in ducks. This study will contribute to a better understanding of the molecular mechanism regulating the innate immune response by TRIM proteins in ducks.

Duck Tembusu Virus Inhibits Type I Interferon Production through the JOSD1-SOCS1-IRF7 Negative-Feedback Regulation Pathway

Duck Tembusu virus (DTMUV) is an emerging pathogenic flavivirus that mainly causes a decrease in egg production in infected waterfowl. Similar to other members of the Flaviviridae family, it can proliferate in most mammalian cells and may also pose a potential threat to nonavian animals. In previous studies, we found that DTMUV infection can upregulate suppressor of cytokine signaling 1 (SOCS1) to inhibit type I interferon (IFN) production and promote virus replication, but the specific mechanism is unclear. Furthermore, little is known about the regulatory role of ubiquitination during flavivirus infection. In this study, we found that activation of Toll-like receptor 3 (TLR3) signaling rather than type I IFN stimulation led to the upregulation of SOCS1 during DTMUV infection. Further studies revealed that JOSD1 stabilized SOCS1 expression by binding to the SH2 domain of SOCS1 and mediating its deubiquitination. In addition, JOSD1 also inhibited type I IFN production through SOCS1. Finally, SOCS1 acts as an E3 ubiquitin ligase that binds to IFN regulatory factor 7 (IRF7) through its SH2 domain and mediates K48-linked ubiquitination and proteasomal degradation of IRF7, ultimately inhibiting type I IFN production mediated by IRF7 and promoting viral proliferation. These results will enrich and deepen our understanding of the mechanism by which DTMUV antagonizes the host interferon system. IMPORTANCE DTMUV is a newly discovered flavivirus that seriously harms the poultry industry. In recent years, there have been numerous studies on the involvement of ubiquitination in the regulation of innate immunity. However, little is known about the involvement of ubiquitination in the regulation of flavivirus-induced type I IFN signaling. In this study, we found that SOCS1 was induced by TLR3 signaling during DTMUV infection. Furthermore, we found for the first time that duck SOCS1 protein was also modified by K48-linked polyubiquitination, whereas our previous study found that SOCS1 was upregulated during DTMUV infection. Further studies showed that JOSD1 stabilized SOCS1 expression by mediating the deubiquitination of SOCS1. While SOCS1 acts as a negative regulator of cytokines, we found that DTMUV utilized SOCS1 to mediate the ubiquitination and proteasomal degradation of IRF7 and ultimately inhibit type I IFN production, thereby promoting its proliferation.

Nile tilapia TRIM39 recruits I3K413 and I3KL45 as adaptors and is involved in the NF-κB pathway

Tripartite motif (TRIM) proteins play a regulatory function in cancer, cell apoptosis and innate immunity. To understand the role of TRIM39 in Nile tilapia (Oreochromis niloticus), TRIM39 cDNA was isolated. The total length of TRIM39 cDNA was 5025 bp. The deduced OnTRIM39 protein contains 549 amino acids and has conserved domains of the TRIM family, which are the RING, B-box, coiled-coil and PRY-SPRY domains. OnTRIM39 mRNA was widely expressed in various tissues. After challenge with Streptococcus agalactiae and stimulation with polyinosinic polycytidylic acid [poly (I:C)] and lipopolysaccharides (LPS), the amount of OnTRIM39 transcript was changed in various tested tissues. OnTRIM39 overexpression increased NF-κB activity. OnTRIM39 was present in the cytoplasm. Mass spectrometry of proteins pulled down with recombinant OnTRIM39 showed that 250 proteins potentially interact with OnTRIM39. The authors selected I3K4I3 from the 250 candidate proteins to verify its interaction with TRIM39. They also selected I3KL45, a member of the same 14-3-3 protein family, to verify its interaction with TRIM39. The results of pull-down assays showed that OnTRIM39 interacted with both I3K413 and I3KL45. These results contribute to further study of the innate immune mechanism of tilapia.

Sex-dependent host-microbiome dynamics in zebrafish: Implications for toxicology and gastrointestinal physiology

The physiology of males and females can be vastly different, complicating interpretation of toxicological and physiological data. The objectives of this study were to elucidate the sex differences in the microbiome-gastrointestinal (GI) transcriptome of adult zebrafish. We compared microbial composition and diversity in both males and females fed the same diet and housed in the same environment. There were no sex-specific differences in weight gain nor gastrointestinal morphology based on histopathology. There was no difference in gut microbial diversity, richness (Shannon and Chao1 index) nor predicted functional composition of the microbiome between males and females. Prior to post-hoc correction, male zebrafish showed higher abundance for the bacterial families Erythrobacteraceae and Lamiaceae, both belonging to the phyla Actinobacteria and Proteobacteria. At the genus level, Lamia and Altererythrobacter were more dominant in males and an unidentified genus in Bacteroidetes was more abundant in females. There were 16 unique differentially expressed transcripts in the gastrointestinal tissue between male and female zebrafish (FDR corrected, p < 0.05). Relative to males, the mRNA expression for trim35-9, slc25a48, chchd3b, csad, and hsd17b3 were lower in female GI while cyp2k6, adra2c, and bckdk were higher in the female GI. Immune and lipid-related gene network expression differed between the sexes (i.e., cholesterol export and metabolism) as well as networks related to gastric motility, gastrointestinal system absorption and digestion. Such data provide clues as to putative differences in gastrointestinal physiology between male and female zebrafish. This study identifies host-transcriptome differences that can be considered when interpreting the microgenderome of zebrafish in studies investigating GI physiology and toxicology of fishes.

Porcine TRIM35 positively regulate TRAF3-mediated IFN-β production and inhibit Japanese encephalitis virus replication

Tripartite motif 35 (TRIM35) protein is a ubiquitin E3 ligase that mediates interferon-beta (IFN-β) production via regulating ubiquitination of multiple adaptor proteins in innate immune signaling pathways. Here, we cloned the porcine TRIM35 (porTRIM35) gene and analyzed its involvement in IFN-β expression as well as the antiviral response against Japanese encephalitis virus (JEV). The full-length porTRIM35 gene encoded a 493-amino acid protein and exhibited 79.6%-89.5% sequence similarity with its orthologues in humans, mice, monkeys and rabbits. porTRIM35 possessed typical structural features of TRIMs, including a RING domain, a B-box domain, a coiled-coil domain and a PRY/SPYR domain. Exogenous overexpression of porTRIM35 significantly up-regulated the mRNA expression level of IFN-β in swine testicular (ST) cell in response to poly(I:C) stimulation, whereas knockdown endogenous expression of porTRIM35 lead to a decrease in the expression level of IFN-β. Mechanically, porTRIM35 directly interacted with porcine TNF-receptor associated factor 3 (TRAF3) and catalyzed its Lys63-linked polyubiquitination, thereby leading to the up-regulation of IFN-β production. Meanwhile, we demonstrated that the RING and PRY/SPRY domains were essential for the E3 ligase activity of porTRIM35. In response to JEV infection, the endogenous expression of porTRIM35 was markedly inhibited at the mRNA level, while exogenous expression of porTRIM35 significantly elevated the expression of IFN-β induced by JEV infection and reduced viral titers in ST cells, suggesting that porTRIM35 is a negative regulator for JEV replication. These data demonstrate the importance of porTRIM35 in IFN-β expression as well as the antiviral response against JEV replication.

Stress hematopoiesis induces a proliferative advantage in TET2 deficiency

TET2 loss-of-function mutations are recurrent events in a wide range of hematological malignancies and a physiologic occurrence in blood cells of healthy older adults. It is currently unknown what determines if a person harboring a somatic TET2 mutation will progress to myelodysplastic syndrome or acute myeloid leukemia. Here we develop a zebrafish tet2 mutant through which we show that tet2 loss leads to restricted hematopoietic differentiation combined with a modest upregulation of p53, which is also characteristic of many inherited bone marrow failure syndromes. Uniquely in the context of emergency hematopoiesis by external stimuli, such as infection or cytokine stimulation, lack of tet2 leads hematopoietic stem cells to undergo excessive proliferation, resulting in an accumulation of immature cells, which are poised to become leukemogenic following additional genetic/epigenetic perturbations. This same phenomenon observed in zebrafish extends to human hematopoietic stem cells, identifying TET2 as a critical relay switch in the context of stress hematopoiesis.

TRIMs: selective recruitment at different steps of the NF-κB pathway-determinant of activation or resolution of inflammation

TNF-α-induced NF-κB pathway is an essential component of innate and adaptive immune pathway, and it is tightly regulated by various post-translational modifications including ubiquitination. Oscillations in NF-κB activation and temporal gene expression are emerging as critical determinants of inflammatory response, however, the regulators of unique outcomes in different patho-physiological conditions are not well understood. Tripartite Motif-containing proteins (TRIMs) are RING domain-containing E3 ligases involved in the regulation of cellular homeostasis, metabolism, cell death, inflammation, and host defence. Emerging reports suggest that TRIMs are recruited at different steps of TNF-α-induced NF-κB pathway and modulate via their E3 ligase activity. TRIMs show synergy and antagonism in the regulation of the NF-κB pathway and also regulate it in a feedback manner. TRIMs also regulate pattern recognition receptors (PRRs) mediated inflammatory pathways and may have evolved to directly regulate a specific arm of immune signalling. The review emphasizes TRIM-mediated ubiquitination and modulation of TNF-α-regulated temporal and NF-κB signaling and its possible impact on unique transcriptional and functional outcomes.

Negative Regulation of the Innate Immune Response through Proteasomal Degradation and Deubiquitination

The rapid and dynamic activation of the innate immune system is achieved through complex signaling networks regulated by post-translational modifications modulating the subcellular localization, activity, and abundance of signaling molecules. Many constitutively expressed signaling molecules are present in the cell in inactive forms, and become functionally activated once they are modified with ubiquitin, and, in turn, inactivated by removal of the same post-translational mark. Moreover, upon infection resolution a rapid remodeling of the proteome needs to occur, ensuring the removal of induced response proteins to prevent hyperactivation. This review discusses the current knowledge on the negative regulation of innate immune signaling pathways by deubiquitinating enzymes, and through degradative ubiquitination. It focusses on spatiotemporal regulation of deubiquitinase and E3 ligase activities, mechanisms for re-establishing proteostasis, and degradation through immune-specific feedback mechanisms vs. general protein quality control pathways.

TRIMming Type I Interferon-Mediated Innate Immune Response in Antiviral and Antitumor Defense

The tripartite motif (TRIM) family comprises at least 80 members in humans, with most having ubiquitin or SUMO E3 ligase activity conferred by their N-terminal RING domain. TRIMs regulate a wide range of processes in ubiquitination- or sumoylation-dependent manners in most cases, and fewer as adaptors. Their roles in the regulation of viral infections, autophagy, cell cycle progression, DNA damage and other stress responses, and carcinogenesis are being increasingly appreciated, and their E3 ligase activities are attractive targets for developing specific immunotherapeutic strategies for immune diseases and cancers. Given their importance in antiviral immune response, viruses have evolved sophisticated immune escape strategies to subvert TRIM-mediated mechanisms. In this review, we focus on their regulation of IFN-I-mediated innate immune response, which plays key roles in antiviral and antitumor defense.

Tripartite motif-containing 35 (TRIM35) is up-regulated in UUO-induced renal fibrosis animal model

Renal fibrosis has been recognized as a serious health threat in the world because of the high cost of treatment and poor prognosis. However, the molecular mechanism of renal fibrosis is still largely unknown. In this study, we aimed at illustrating the role of TRIM35 in the renal fibrosis process. A UUO mouse model and a TGF-β1-induced tubulointerstitial fibrosis model were constructed for the research of renal fibrosis at animal and cell level, respectively. Hematoxylin-eosin and Masson staining were used for visualizing the pathological change. qRT-PCR, Western blot analysis and immunohistochemical staining were used to detect the expression of fibrosis-associated proteins and TRIM35. The results showed that, after the modeling, the expressions of α-SMA, Collagen I, Collagen III, Fibronectin and Snail1 were up-regulated, while the expression of E-cadherin was down-regulated, indicating the successful construction of animal and cell models. More importantly, TRIM35 was proved to be up-regulated in both animal and cell models. Therefore, this study demonstrates the potential promotional effect of TRIM35 in the renal fibrosis process, which may prove to be a new biomarker for the diagnosis and development of new treatments of renal fibrosis.

MicroRNA-30e-5p has an Integrated Role in the Regulation of the Innate Immune Response during Virus Infection and Systemic Lupus Erythematosus

Precise regulation of innate immunity is crucial for development of appropriate host immunity against microbial infections and maintenance of immune homeostasis. MicroRNAs are small non-coding RNAs, post-transcriptional regulator of multiple genes, and act as a rheostat for protein expression. Here, we identified microRNA-30e-5p induced by hepatitis B virus and other viruses that act as a master regulator for innate immunity. Moreover, pegylated interferons treatment of patients with HBV for viral reduction also reduces miRNA. Additionally, we have also shown the immuno-pathological effects of miR-30e in patients with systemic lupus erythematosus (SLE) and mouse model. Mechanistically, miR-30e targets multiple negative regulators of innate immune signaling and enhances immune responses. Furthermore, sequestering of miR-30e in patients with SLE and mouse model significantly reduces type-I interferon and pro-inflammatory cytokines. Collectively, our study demonstrates the novel role of miR-30e in innate immunity and its prognostic and therapeutic potential in infectious and autoimmune diseases.

Tripartite-motif family protein 35-28 regulates microglia development by preventing necrotic death of microglial precursors in zebrafish

Microglia are tissue-resident macrophages in the central nervous system (CNS) that play essential roles in the regulation of CNS development and homeostasis. Yet, the genetic networks governing microglia development remain incompletely defined. Here, we report the identification and characterization of a microglia-defective zebrafish mutant wulong^hkz12 (wul^hkz12 ) isolated from an ethylnitrosourea (ENU)-based genetic screen. We show that wul^hkz12 mutants harbors a missense point mutation in the gene region encoding the PRY/SPRY domain of the tripartite-motif family protein 35-28 (trim35-28) gene. Time-lapse imaging revealed that the loss of Trim35-28 function causes lytic necrosis of microglial precursors/peripheral macrophages, as indicated by cytoplasmic swelling and membrane rupture of these precursors and accompanied by neutrophil infiltration and systemic inflammation. Intriguingly, the lytic necrosis of microglial precursors in trim35-28-deficient mutants appeared to depend neither on the canonical pyroptotic nor necroptotic pathways, as inhibition of the key component in each pathway could not rescue the microglia phenotype in trim35-28-deficient mutants. Finally, results from tissue-specific rescue experiments suggested that Trim35-28 acts cell-autonomously in the survival of microglial precursors. Taken together, the findings of our study reveal Trim35-28 as a regulatory protein essential for microglia development.

TRIM35 mediates protection against influenza infection by activating TRAF3 and degrading viral PB2

Tripartite motif (TRIM) family proteins are important effectors of innate immunity against viral infections. Here we identified TRIM35 as a regulator of TRAF3 activation. Deficiency in or inhibition of TRIM35 suppressed the production of type I interferon (IFN) in response to viral infection. Trim35-deficient mice were more susceptible to influenza A virus (IAV) infection than were wild-type mice. TRIM35 promoted the RIG-I-mediated signaling by catalyzing Lys63-linked polyubiquitination of TRAF3 and the subsequent formation of a signaling complex with VISA and TBK1. IAV PB2 polymerase countered the innate antiviral immune response by impeding the Lys63-linked polyubiquitination and activation of TRAF3. TRIM35 mediated Lys48-linked polyubiquitination and proteasomal degradation of IAV PB2, thereby antagonizing its suppression of TRAF3 activation. Our in vitro and in vivo findings thus reveal novel roles of TRIM35, through catalyzing Lys63- or Lys48-linked polyubiquitination, in RIG-I antiviral immunity and mechanism of defense against IAV infection.

TRIM34 attenuates colon inflammation and tumorigenesis by sustaining barrier integrity

Loss of the colonic inner mucus layer leads to spontaneously severe colitis and colorectal cancer. However, key host factors that may control the generation of the inner mucus layer are rarely reported. Here, we identify a novel function of TRIM34 in goblet cells (GCs) in controlling inner mucus layer generation. Upon DSS treatment, TRIM34 deficiency led to a reduction in Muc2 secretion by GCs and subsequent defects in the inner mucus layer. This outcome rendered TRIM34-deficient mice more susceptible to DSS-induced colitis and colitis-associated colorectal cancer. Mechanistic experiments demonstrated that TRIM34 controlled TLR signaling-induced Nox/Duox-dependent ROS synthesis, thereby promoting the compound exocytosis of Muc2 by colonic GCs that were exposed to bacterial TLR ligands. Clinical analysis revealed that TRIM34 levels in patient samples were correlated with the outcome of ulcerative colitis (UC) and the prognosis of rectal adenocarcinoma. This study indicates that TRIM34 expression in GCs plays an essential role in generating the inner mucus layer and preventing excessive colon inflammation and tumorigenesis.

Protective effect of Cordyceps sinensis extract on lipopolysaccharide-induced acute lung injury in mice

Background: To study the protective effect of Cordyceps sinensis extract (Dong Chong Xia Cao in Chinese [DCXC]) on experimental acute lung injury (ALI) mice.

Methods and results: ALI model was induced by intratracheal-instilled lipopolysaccharide (LPS, 2.4 mg/kg) in BALB/c male mice. The mice were administrated DCXC (ig, 10, 30, 60 mg/kg) in 4 and 8 h after receiving LPS. Histopathological section, wet/dry lung weight ratio and myeloperoxidase activity were detected. Bronchoalveolar lavage fluid (BALF) was collected for cell count, the levels of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interleukin-6 (IL-6) and nitric oxide (NO) in BALF was detected by ELISA, the protein and mRNA expression of nuclear factor-κB p65 (NF-κB p65), inducible NO synthase (iNOS) and cyclooxygenase-2 (COX-2) in lung tissue was detected by Western blot and RT-PCR. The result showed that DCXC could reduce the degree of histopathological injury, wet/dry weight ratio (W/D ratio) and myeloperoxidase activity (P<0.05) with a dose-dependent manner. The increased number of total cells, neutrophils and macrophages in BALF were significantly inhibited by DCXC treatment (P<0.05). The increased levels of TNF-α, IL-1β, IL-6 and NO in BALF after LPS administration was significantly reduced by DCXC (P<0.05). In addition, the increased protein and mRNA levels of iNOS, COX-2 and NF-κB p65 DNA binding ability in LPS group were dose-dependently reduced by DCXC treatment (P<0.05).

Conclusion: DCXC could play an anti-inflammatory and antioxidant effect on LPS-induced ALI through inhibiting NF-κB p65 phosphorylation, and the expression of COX-2 and iNOS in lung. The result showed that DCXC has a potential protective effect on the ALI.

Viruses Seen by Our Cells: The Role of Viral RNA Sensors

The role of the innate immune response in detecting RNA viruses is crucial for the establishment of proper inflammatory and antiviral responses. Different receptors, known as pattern recognition receptors (PRRs), are present in the cytoplasm, endosomes, and on the cellular surface. These receptors have the capacity to sense the presence of viral nucleic acids as pathogen-associated molecular patterns (PAMPs). This recognition leads to the induction of type 1 interferons (IFNs) as well as inflammatory cytokines and chemokines. In this review, we provide an overview of the significant involvement of cellular RNA helicases and Toll-like receptors (TLRs) 3, 7, and 8 in antiviral immune defenses.

SOCS1 and SOCS3 Target IRF7 Degradation To Suppress TLR7-Mediated Type I IFN Production of Human Plasmacytoid Dendritic Cells

Type I IFN production of plasmacytoid dendritic cells (pDCs) triggered by TLR-signaling is an essential part of antiviral responses and autoimmune reactions. Although it was well-documented that members of the cytokine signaling (SOCS) family regulate TLR-signaling, the mechanism of how SOCS proteins regulate TLR7-mediated type I IFN production has not been elucidated yet. In this article, we show that TLR7 activation in human pDCs induced the expression of SOCS1 and SOCS3. SOCS1 and SOCS3 strongly suppressed TLR7-mediated type I IFN production. Furthermore, we demonstrated that SOCS1- and SOCS3-bound IFN regulatory factor 7, a pivotal transcription factor of the TLR7 pathway, through the SH2 domain to promote its proteasomal degradation by lysine 48-linked polyubiquitination. Together, our results demonstrate that SOCS1/3-mediated degradation of IFN regulatory factor 7 directly regulates TLR7 signaling and type I IFN production in pDCs. This mechanism might be targeted by therapeutic approaches to either enhance type I IFN production in antiviral treatment or decrease type I IFN production in the treatment of autoimmune diseases.

Intracellular Antiviral Immunity

Innate immunity is traditionally thought of as the first line of defense against pathogens that enter the body. It is typically characterized as a rather weak defense mechanism, designed to restrict pathogen replication until the adaptive immune response generates a tailored response and eliminates the infectious agent. However, intensive research in recent years has resulted in better understanding of innate immunity as well as the discovery of many effector proteins, revealing its numerous powerful mechanisms to defend the host. Furthermore, this research has demonstrated that it is simplistic to strictly separate adaptive and innate immune functions since these two systems often work synergistically rather than sequentially. Here, we provide a broad overview of innate pattern recognition receptors in antiviral defense, with a focus on the TRIM family, and discuss their signaling pathways and mechanisms of action with special emphasis on the intracellular antibody receptor TRIM21.

Cellular FLIP long isoform (cFLIPL)-IKKα interactions inhibit IRF7 activation, representing a new cellular strategy to inhibit IFNα expression

Interferon α (IFNα) is important for antiviral and anticancer defenses. However, overproduction is associated with autoimmune disorders. Thus, the cell must precisely up- and down-regulate IFNα to achieve immune system homeostasis. The cellular FLICE-like inhibitory protein (cFLIP) is reported to inhibit IFNα production. However, the mechanism for this antagonism remained unknown. The goal here was to identify this mechanism. Here we examined the signal transduction events that occur during TLR9-induced IRF7 activation. The cFLIP long isoform (cFLIPL) inhibited the expression of IRF7-controlled natural or synthetic genes in several cell lines, including those with abundant IRF7 protein levels (e.g. dendritic cells). cFLIPL inhibited IRF7 phosphorylation; however, cFLIPL-IRF7 interactions were not detectable, implying that cFLIPL acted upstream of IRF7 dimerization. Interestingly, cFLIPL co-immunoprecipitated with IKKα, and these interactions correlated with a loss of IKKα-IRF7 interactions. Thus, cFLIP appears to bind to IKKα to prevent IKKα from phosphorylating and activating IRF7. To the best of our knowledge, this is the first report of a cellular protein that uses this approach to inhibit IRF7 activation. Perhaps this cFLIP property could be engineered to minimize the deleterious effects of IFNα expression that occur during certain autoimmune disorders.

Fish TRIM35 negatively regulates the interferon signaling pathway in response to grouper nodavirus infection

Tripartite motif-containing protein 35 (TRIM35) has been demonstrated to exert critical roles in cancer, cell death and other multiple cell processes. However, the precisely roles of TRIM35 during virus infection still remained largely unknown. In the current study, we cloned a TRIM35 gene from orange spotted grouper (EcTRIM35) and uncovered its roles in response to nodavirus infection. EcTRIM35 encoded a 456-aa protein which showed 65% and 32% identity to large yellow croaker (Larimichthys crocea) and human (Homo sapiens), respectively. Structure prediction and amino acid alignment analysis indicated that EcTRIM35 contained three conserved domains, including RING domain, B-BOX and SPRY domain. In healthy grouper, the high expression level of EcTRIM35 could be detected in liver, spleen and intestine. After infection with red-spotted grouper nervous necrosis (RGNNV) and Singapore grouper iridovirus (SGIV) in GS cells, the transcript of EcTRIM35 was significantly up-regulated with the infection time increased. Under fluorescence microscopy, the bright fluorescence aggregates were observed in EcTRIM35 transfected cells, but the fluorescence distribution was obviously altered in the EcTRIM35-ΔRING transfected cells. After incubation with RGNNV, the overexpression of EcTRIM35 in vitro significantly enhanced the viral replication, evidenced by the enhancement of cytopathic effect (CPE) severity and the up-regulation of the viral gene transcription. Moreover, the ectopic expression of EcTRIM35 significantly decreased the expression of interferon signaling molecules or effectors. Further studies elucidated that EcTRIM35 overexpression significantly weakened the MAVS-, MITA- or TBK1-induced interferon immune response, but showed no effects on MDA5-induced immune response. Thus, our results will shed new lights on the roles of fish TRIM35 in innate immune response against grouper virus infection.

miR-4417 Targets Tripartite Motif-Containing 35 (TRIM35) and Regulates Pyruvate Kinase Muscle 2 (PKM2) Phosphorylation to Promote Proliferation and Suppress Apoptosis in Hepatocellular Carcinoma Cells

BACKGROUND MicroRNAs (miRNAs) are a class of small non-coding RNAs that are strongly involved in various types of carcinogenesis, including hepatocellular carcinoma (HCC). This study aimed to clarify whether miR-4417 promotes HCC growth by targeting TRIM35 and regulating PKM2 phosphorylation. MATERIAL AND METHODS Online software, including TargetScan and miRanda, was used to predict the potential target of miR-4417. Real-Time PCR (qRT-PCR) and Western blot assays were performed to detect the expression levels of mRNA and protein, respectively. Cell proliferation was measured by MTT assay and apoptosis in A549 cells was examined by flow cytometry. RESULTS Bioinformatics reveal that TRIM35 mRNA contains 1 conserved target site of miR-4417. High level of miR-4417 and low levels of TRIM35 mRNA and protein were observed in HCC cells compared with a normal liver cell line. Biological function analysis showed that miR-4417 inhibitor inhibits cell proliferation and promotes apoptosis in HCC cells. Furthermore, we verified that TRIM35 is a functional target of miR-4417 by use of luciferase reporter assay, and TRIM35 overexpressing showed an elevation of proliferation and a reduction of apoptosis in HCC cells. We subsequently investigated whether miR-4417 and TRIM35 regulate HCC cell proliferation and apoptosis through PKM2 Y105 phosphorylation, and the results supported our speculation that miR-4417 targets TRIM35 and regulates the Y105 phosphorylation of PKM2 to promote hepatocarcinogenesis. CONCLUSIONS Our findings indicate that miR-4417 may function as an oncogene in HCC and is a potential alternative therapeutic target for this deadly disease.

TLR8 Couples SOCS-1 and Restrains TLR7-Mediated Antiviral Immunity, Exacerbating West Nile Virus Infection in Mice

West Nile virus (WNV) is a neurotropic ssRNA flavivirus that can cause encephalitis, meningitis, and death in humans and mice. Human TLR7 and TLR8 and mouse TLR7 recognize viral ssRNA motifs and induce antiviral immunity. However, the role of mouse TLR8 in antiviral immunity is poorly understood. In this article, we report that TLR8-deficient (Tlr8^-/-) mice were resistant to WNV infection compared with wild-type controls. Efficient WNV clearance and moderate susceptibility to WNV-mediated neuronal death in Tlr8^-/- mice were attributed to overexpression of Tlr7 and IFN-stimulated gene-56 expression, whereas reduced expression of the proapoptotic gene coding Bcl2-associated X protein was observed. Interestingly, suppressor of cytokine signaling (SOCS)-1 directly associated with TLR8, but not with TLR7, indicating a novel role for TLR8 regulation of SOCS-1 function, whereas selective small interfering RNA knockdown of Socs-1 resulted in induced IFN-stimulated gene-56 and Tlr7 expression following WNV infection. Collectively, we report that TLR8 coupling with SOCS-1 inhibits TLR7-mediated antiviral immunity during WNV infection in mice.

TRIM14 inhibits hepatitis C virus infection by SPRY domain-dependent targeted degradation of the viral NS5A protein

Tripartite motif 14 (TRIM14) was reported to function as a mitochondrial signaling adaptor in mediating innate immune responses. However, the involvement of TRIM14 in host defense against viral infection and molecular mechanisms remain unclear. Here, we demonstrated that enforced expression of TRIM14 could potently inhibit the infection and replication of HCV in hepatocytes, whereas TRIM14 knockout cells became more susceptible to HCV infection. Interestingly, further experiments revealed that such anti-HCV activity was independent of activating the NF-κB or interferon pathways but required the C-terminal SPRY domain of no signaling capacity. In searching for mechanisms how TRIM14 exerts its antiviral function we found that TRIM14 interacted with HCV encoded non-structural protein NS5A and could strongly induce its degradation dependent on the NS5A1 subdomain. Interestingly extensive domain mapping analyses revealed that NS5A degradation was mediated by the highly conserved SPRY domain of TRIM14, which might involve the K48 ubiquitination pathway. Collectively, our work uncovered a new mechanism responsible for host defense against HCV infection, and could potentially aid the development of novel anti-HCV therapeutics.