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TAX1BP1 is a selective macroautophagy/autophagy receptor that inhibits NFKB and RIGI-like receptor (RLR) signaling to prevent excessive inflammation and maintain homeostasis. Selective autophagy receptors such as SQSTM1/p62 and OPTN are phosphorylated by the kinase TBK1 to stimulate their selective autophagy function. However, it is unknown if TAX1BP1 is regulated by TBK1 or other kinases under basal conditions or during RNA virus infection. Here, we found that TBK1 and IKBKE/IKKi function redundantly to phosphorylate TAX1BP1 and regulate its autophagic turnover through canonical macroautophagy. TAX1BP1 phosphorylation promotes its localization to lysosomes, resulting in its degradation. Additionally, we found that during vesicular stomatitis virus infection, TAX1BP1 is targeted to lysosomes in an ATG8-family protein-independent manner. Furthermore, TAX1BP1 plays a critical role in the clearance of MAVS aggregates, and phosphorylation of TAX1BP1 controls its MAVS aggrephagy function. Together, our data support a model whereby TBK1 and IKBKE license TAX1BP1-selective autophagy function to inhibit MAVS and RLR signaling.Abbreviations: ATG: autophagy related; BafA1: bafilomycin A1; CALCOCO2: calcium binding and coiled-coil domain 2; GFP: green fluorescent protein; IFA: indirect immunofluorescence assay; IFN: interferon; IκB: inhibitor of nuclear factor kappa B; IKK: IκB kinase; IRF: interferon regulatory factor; KO: knockout; LAMP1: lysosomal associated membrane protein 1; LIR: LC3-interacting region; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MAVS: mitochondrial antiviral signaling protein; MEF: mouse embryonic fibroblast; MOI: multiplicity of infection; IKBKG/NEMO: inhibitor of nuclear factor kappa B kinase regulatory subunit gamma; NFKB: nuclear factor kappa B; OPTN: optineurin; Poly(I:C): polyinosinic-polycytidylic acid; RB1CC1/FIP200: RB1 inducible coiled-coil 1; RIGI: RNA sensor RIG-I; RLR: RIGI-like receptor; SDD-AGE: semi-denaturing detergent-agarose gel electrophoresis; SeV: Sendai virus; SLR: SQSTM1-like receptor; SQSTM1: sequestosome 1; TAX1BP1: Tax1 binding protein 1; TBK1: TANK binding kinase 1; TNF: tumor necrosis factor; TRAF: TNF receptor associated factor; VSV: vesicular stomatitis virus; ZnF: zinc finger. [ABSTRACT FROM AUTHOR]

Severe fever with thrombocytopenia syndrome is an emerging viral hemorrhagic fever caused by a tick-borne bunyavirus, severe fever with thrombocytopenia syndrome virus (SFTSV), with a high case fatality. We previously found that SFTSV nucleoprotein (NP) induces macroautophagy/autophagy to facilitate virus replication. However, the role of NP in antagonizing host innate immunity remains unclear. Mitophagy, a selected form of autophagy, eliminates damaged mitochondria to maintain mitochondrial homeostasis. Here, we demonstrate that SFTSV NP triggers mitophagy to degrade MAVS (mitochondrial antiviral signaling protein), thereby blocking MAVS-mediated antiviral signaling to escape the host immune response. Mechanistically, SFTSV NP translocates to mitochondria by interacting with TUFM (Tu translation elongation factor, mitochondrial), and mediates mitochondrial sequestration into phagophores through interacting with LC3, thus inducing mitophagy. Notably, the N-terminal LC3-interacting region (LIR) motif of NP is essential for mitophagy induction. Collectively, our results demonstrated that SFTSV NP serves as a novel virulence factor, inducing TUFM-mediated mitophagy to degrade MAVS and evade the host immune response.Abbreviation: 3-MA: 3-methyladenine; ACTB: actin beta; co-IP: co-immunoprecipitation; CQ: chloroquine; DAPI: 4ʹ,6-diamidino-2-phenylindole, dihydrochloride; DMSO: dimethyl sulfoxide; FCCP: carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone; GFP: green fluorescent protein; HTNV: Hantan virus; IAV: influenza A virus; IFN: interferon; LAMP1: lysosomal associated membraneprotein 1; LIR: LC3-interacting region; MAP1LC3B/LC3B: microtubule associatedprotein 1 light chain 3 beta; MAVS: mitochondrial antiviral signaling protein; Mdivi-1: mitochondrial division inhibitor 1; MOI: multiplicity of infection; MT-CO2/COXII: mitochondrially encoded cytochrome C oxidase II; NP: nucleoprotein; NSs: nonstructural proteins; poly(I:C): polyinosinic:polycytidylic acid; RIGI: RNA sensor RIG-I; RLR: RIGI-like receptor; SFTSV: severe fever withthrombocytopenia syndrome virus; TCID50: 50% tissue culture infectiousdose; TIMM23: translocase of inner mitochondrial membrane 23; TOMM20:translocase of outer mitochondrial membrane 20; TUFM: Tu translation elongationfactor, mitochondrial. [ABSTRACT FROM AUTHOR]

Cysteine palmitoylation or S-palmitoylation catalyzed by the ZDHHC family of acyltransferases regulates the biological function of numerous mammalian proteins as well as viral proteins. However, understanding of the role of S-palmitoylation in antiviral immunity against RNA viruses remains very limited. The adaptor protein MAVS forms functionally essential prion-like aggregates upon activation by viral RNA-sensing RIG-I-like receptors. Here, we identify that MAVS, a C-terminal tail-anchored mitochondrial outer membrane protein, is S-palmitoylated by ZDHHC7 at Cys508, a residue adjacent to the tail-anchor transmembrane helix. Using superresolution microscopy and other biochemical techniques, we found that the mitochondrial localization of MAVS at resting state mainly depends on its transmembrane tail-anchor, without regulation by Cys508 S-palmitoylation. However, upon viral infection, MAVS S-palmitoylation stabilizes its aggregation on the mitochondrial outer membrane and thus promotes subsequent propagation of antiviral signaling. We further show that inhibition of MAVS S-palmitoylation increases the host susceptibility to RNA virus infection, highlighting the importance of S-palmitoylation in the antiviral innate immunity. Also, our results indicate ZDHHC7 as a potential therapeutic target for MAVS-related autoimmune diseases. [ABSTRACT FROM AUTHOR]

Safe Micro Aerial Vehicle (MAV) navigation requires detecting and avoiding obstacles. For safe MAV navigation, expansion‐based algorithms are effective for detecting obstacles. However, accurate and real‐time obstacle detection is a fundamental challenge. Some traditional methods focus on extracting geometric features from images and applying geometric constraints to identify potential obstacles. Others may leverage machine learning algorithms for object detection and classification, using features such as texture, shape, and context to distinguish obstacles from background clutter. The choice of approach depends on factors such as the specific requirements of the application, the complexity of the scene, and the available computational resources. Since obstacles, in reality, take the form of objects (e.g., persons, walls, pillars, trees, automobiles, and other structures), it is preferable to represent them according to human comprehension and as objects. Therefore, the objective of this study is to reflect on the previous research and address the issues mentioned above by extracting objects from the fisheye image using a panoptic deep‐learning network. The extracted object regions are, then, used to identify obstacles with a novel area‐based expansion rate we developed in a previous study. We compared the accuracy of obstacle detection in our proposed method to the existing method when moving forward and to the right; thus, we improved it between 10% and 18%, respectively. In addition, compared with the existing method, and due to replacing a single object with multiple regions, obstacle‐detection runtime for forward and right direction is 15.71 and 25.5 times faster, respectively, and the required match points have decreased by 49% and 55%. [ABSTRACT FROM AUTHOR]

Pseudorabies virus (PRV) has evolved multiple strategies to evade host antiviral responses to benefit virus replication and establish persistent infection. Recently, tripartite motif 26 (TRIM26), a TRIM family protein, has been shown to be involved in a broad range of biological processes involved in innate immunity, especially in regulating viral infection. Herein, we found that the expression of TRIM26 was significantly induced after PRV infection. Surprisingly, the overexpression of TRIM26 promoted PRV production, while the depletion of this protein inhibited virus replication, suggesting that TRIM26 could positively regulate PRV infection. Further analysis revealed that TRIM26 negatively regulates the innate immune response by targeting the RIG-I-triggered type I interferon signalling pathway. TRIM26 was physically associated with MAVS independent of viral infection and reduced MAVS expression. Mechanistically, we found that NDP52 interacted with both TRIM26 and MAVS and that TRIM26-induced MAVS degradation was almost entirely blocked in NDP52-knockdown cells, demonstrating that TRIM26 degrades MAVS through NDP52-mediated selective autophagy. Our results reveal a novel mechanism by which PRV escapes host antiviral innate immunity and provide insights into the crosstalk among virus infection, autophagy, and the innate immune response. [ABSTRACT FROM AUTHOR]

Mitochondria are key orchestrators of antiviral responses that serve as platforms for the assembly and activation of innate immune-signaling complexes. In response to viral infection, mitochondria can be triggered to release immune-stimulatory molecules that can boost interferon production. These same molecules can be released by damaged mitochondria to induce pathogenic, antiviral-like immune responses in the absence of infection. This review explores how members of the tripartite motif-containing (TRIM) protein family, which are recognized for their roles in antiviral defense, regulate mitochondria-based innate immune activation. In antiviral defense, TRIMs are essential components of immune signal transduction pathways and function as directly acting viral restriction factors. TRIMs carry out conceptually similar activities when controlling immune activation related to mitochondria. First, they modulate immune-signaling pathways that can be activated by mitochondrial molecules. Second, they co-ordinate the direct removal of mitochondria and associated immune-activating factors through mitophagy. These insights broaden the scope of TRIM actions in innate immunity and may implicate TRIMs in diseases associated with mitochondria-derived inflammation. [ABSTRACT FROM AUTHOR]

Apoptosis is an important cellular response to viral infection. In this study, we identified activating molecule in Beclin1-regulated autophagy protein 1 (AMBRA1) as a positive regulator of apoptosis triggered by double-stranded (ds)RNA. Depletion of AMBRA1 by gene editing significantly reduced dsRNA-induced apoptosis, which was largely restored by trans-complementation of AMBRA1. Mechanistically, AMBRA1 interacts with mitochondrial antiviralsignaling protein (MAVS), a key mitochondrial adaptor in the apoptosis pathway induced by dsRNA and viral infection. Further co-immunoprecipitation analysis demonstrated that the mitochondrial localization of MAVS was essential for their interaction. The impact of AMBRA1 on dsRNA-induced apoptosis relied on the presence of MAVS and caspase-8. AMBRA1 was involved in the stabilization of MAVS through preventing its dsRNA-induced proteasomal degradation. Consistently, AMBRA1 upregulated the apoptosis induced by Semliki Forest virus infection. Taken together, our work illustrated a role for AMBRA1 in virus-induced apoptosis through interacting with and stabilizing MAVS. [ABSTRACT FROM AUTHOR]

African swine fever virus (ASFV) is notoriously known for evolving strategies to modulate IFN signaling. Despite lots of efforts, the underlying mechanisms have remained incompletely understood. This study concerns the regulatory role of viral inner membrane protein p17. We found that the ASFV p17 shows a preferential interaction with cGAS-STING-IRF3 pathway, but not the RIG-IMAVS-NF-κB signaling, and can inhibit both poly(I:C)- and poly(A:T)-induced activation of IRF3, leading to attenuation of IFN-β induction. Mechanistically, p17 interacts with STING and IRF3 and recruits host scaffold protein PR65A, a subunit of cellular phosphatase PP2A, to down-regulate the level of p-IRF3. Also, p17 targets STING for partial degradation via induction of cellular apoptosis that consequently inhibits activation of both p-TBK1 and p-IRF3. Thus, our findings reveal novel regulatory mechanisms for p17 modulation of IFN signaling and shed light on the intricate interplay between ASFV proteins and host immunity. [ABSTRACT FROM AUTHOR]

Abstract Pseudorabies virus (PRV) has evolved multiple strategies to evade host antiviral responses to benefit virus replication and establish persistent infection. Recently, tripartite motif 26 (TRIM26), a TRIM family protein, has been shown to be involved in a broad range of biological processes involved in innate immunity, especially in regulating viral infection. Herein, we found that the expression of TRIM26 was significantly induced after PRV infection. Surprisingly, the overexpression of TRIM26 promoted PRV production, while the depletion of this protein inhibited virus replication, suggesting that TRIM26 could positively regulate PRV infection. Further analysis revealed that TRIM26 negatively regulates the innate immune response by targeting the RIG-I-triggered type I interferon signalling pathway. TRIM26 was physically associated with MAVS independent of viral infection and reduced MAVS expression. Mechanistically, we found that NDP52 interacted with both TRIM26 and MAVS and that TRIM26-induced MAVS degradation was almost entirely blocked in NDP52-knockdown cells, demonstrating that TRIM26 degrades MAVS through NDP52-mediated selective autophagy. Our results reveal a novel mechanism by which PRV escapes host antiviral innate immunity and provide insights into the crosstalk among virus infection, autophagy, and the innate immune response.

The mitochondrial anti-viral signaling (MAVS) protein is an intermediary adaptor protein of retinoic acid-inducible gene-1 (RIG-I) like receptor (RLR) signaling, which activates the transcription factor interferon (IFN) regulatory factor 3 (IRF3) and NF-kB to produce type I IFNs. MAVS expression has been reported in different fish species, but few studies have shown its functional role in anti-viral responses to fish viruses. In this study, we used the transcription activator-like effector nuclease (TALEN) as a gene editing tool to disrupt the function of MAVS in Chinook salmon (Oncorhynchus tshawytscha) embryonic cells (CHSE) to understand its role in induction of interferon I responses to infections with the (+) RNA virus salmonid alphavirus subtype 3 (SAV-3), and the dsRNA virus infectious pancreatic necrosis virus (IPNV) infection. A MAVS-disrupted CHSE clone with a 7-aa polypeptide (GVFVSRV) deletion mutation at the N-terminal of the CARD domain infected with SAV-3 resulted in significantly lower expression of IRF3, IFNa, and ISGs and increased viral titer (1.5 log10) compared to wild-type. In contrast, the IPNV titer in MAVS-disrupted cells was not different from the wild-type. Furthermore, overexpression of salmon MAVS in MAVS-disrupted CHSE cells rescued the impaired type I IFN-mediated anti-viral effect against SAV-3. [ABSTRACT FROM AUTHOR]

Coronavirus disease 2019 (COVID-19) is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and characterized by dysregulated immune response. Studies have shown that the SARS-CoV-2 accessory protein ORF7b induces host cell apoptosis through the tumor necrosis factor alpha (TNF-α) pathway and blocks the production of interferon beta (IFN-β). The underlying mechanism remains to be investigated. In this study, we found that ORF7b facilitated viral infection and production, and inhibited the RIG-I-like receptor (RLR) signaling pathway through selectively interacting with mitochondrial antiviral-signaling protein (MAVS). MAVS439-466 region and MAVS Lys461 were essential for the physical association between MAVS and ORF7b, and the inhibition of the RLR signaling pathway by ORF7b. MAVSK461/K63 ubiquitination was essential for the RLR signaling regulated by the MAVS--ORF7b complex. ORF7b interfered with the recruitment of tumor necrosis factor receptor-related factor 6 (TRAF6) and the activation of the RLR signaling pathway by MAVS. Furthermore, interfering peptides targeting the ORF7b complex reversed the ORF7b-suppressed MAVS-RLR signaling pathway. The most potent interfering peptide V disrupts the formation of ORF7b tetramers, reverses the levels of the ORF7b-inhibited physical association between MAVS and TRAF6, leading to the suppression of viral growth and infection. Overall, this study provides a mechanism for the suppression of innate immunity by SARS-CoV-2 infection and the mechanism-based approach via interfering peptides to potentially prevent SARS-CoV-2 infection. [ABSTRACT FROM AUTHOR]

To effectively protect the host from viral infection while avoiding excessive immunopathology, the innate immune response must be tightly controlled. However, the precise regulation of antiviral innate immunity and the underlying mechanisms remain unclear. Here, we find that sirtuin3 (SIRT3) interacts with mitochondrial antiviral signaling protein (MAVS) to catalyze MAVS deacetylation at lysine residue 7 (K7), which promotes MAVS aggregation, as well as TANK-binding kinase I and IRF3 phosphorylation, resulting in increased MAVS activation and enhanced type I interferon signaling. Consistent with these findings, loss of Sirt3 in mice and zebrafish renders them more susceptible to viral infection compared to their wild-type (WT) siblings. However, Sirt3 and Sirt5 double-deficient mice exhibit the same viral susceptibility as their WT littermates, suggesting that loss of Sirt5 in Sirt3-deficient mice may counteract the increased viral susceptibility displayed in Sirt3-deficient mice. Thus, we not only demonstrate that SIRT3 positively regulates antiviral immunity in vitro and in vivo, likely via MAVS, but also uncover a previously unrecognized mechanism by which SIRT3 acts as an accelerator and SIRT5 as a brake to orchestrate antiviral innate immunity. [ABSTRACT FROM AUTHOR]

Porcine reproductive and respiratory syndrome (PRRS) is an epidemic animal infectious disease worldwide, causing huge economic losses to the global swine industry. Fas-associated death domain (FADD) was previously reported to be an adaptor protein that functions in transferring the apoptotic signals regulated by the death receptors. In the current study, we unravel its unidentified role in promoting type I interferon (IFN) production during PRRS virus (PRRSV) infection. We identified that FADD inhibited PRRSV infection via promotion of type I IFN transcription. Overexpression of FADD suppressed the replication of PRRSV, while knockout of FADD increased viral titer and nucleocapsid protein expression. Mechanistically, FADD promoted mitochondrial antiviral signaling protein (MAVS)-mediated production of IFN-β and some IFN-stimulated genes (ISGs). Furthermore, FADD exerted anti-PRRSV effects in a MAVS-dependent manner and increased the type I IFN signaling during PRRSV infection. This study highlights the importance of FADD in PRRSV replication, which may have implications for the future control of PRRS. [ABSTRACT FROM AUTHOR]

RIG-I-like receptors (RLRs) are crucial for pathogen detection and triggering immune responses and have immense physiological importance. In this review, we first summarize the interferon system and innate immunity, which constitute primary and secondary responses. Next, the molecular structure of RLRs and the mechanism of sensing non-self RNA are described. Usually, self RNA is refractory to the RLR; however, there are underlying host mechanisms that prevent immune reactions. Studies have revealed that the regulatory mechanisms of RLRs involve covalent molecular modifications, association with regulatory factors, and subcellular localization. Viruses have evolved to acquire antagonistic RLR functions to escape the host immune reactions. Finally, the pathologies caused by the malfunction of RLR signaling are described. RIG-I-like receptors (RLRs) are crucial for viral non-self RNA detection and triggering innate immune responses. Fujita et al. review the molecular basis of RNA recognition, regulatory mechanisms, viral antagonistic strategies, and pathologies caused by the malfunction of RLRs. [ABSTRACT FROM AUTHOR]

In pathogen recognition, the nucleotide-binding domain (NBD) and leucine rich repeat receptors (NLRs) have noteworthy functions in the activation of the innate immune response. These receptors respond to several viral infections, among them NOD2, a very dynamic NLR, whose role in dengue virus (DENV) infection remains unclear. This research aimed to determine the role of human NOD2 in THP-1 macrophage-like cells during DENV-2 infection. NOD2 levels in DENV-2 infected THP-1 macrophage-like cells was evaluated by RT-PCR and Western blot, and an increase was observed at both mRNA and protein levels. We observed using confocal microscopy and co-immunoprecipitation assays that NOD2 interacts with the effector protein MAVS (mitochondrial antiviral signaling protein), an adaptor protein promoting antiviral activity, this occurring mainly at 12 h into the infection. After silencing NOD2, we detected increased viral loads of DENV-2 and lower levels of IFN-α in supernatants from THP-1 macrophage-like cells with NOD2 knock-down and further infected with DENV-2, compared with mock-control or cells transfected with Scramble-siRNA. Thus, NOD2 is activated in response to DENV-2 in THP-1 macrophage-like cells and participates in IFN-α production, in addition to limiting virus replication at the examined time points. [ABSTRACT FROM AUTHOR]

The role that human papillomavirus (HPV) oncogenes play in suppressing responses to immunotherapy in cancer deserves further investigation. In particular, the effects of HPV E5 remain poorly understood relative to E6 and E7. Here, we demonstrate that HPV E5 is a negative regulator of anti-viral interferon (IFN) response pathways, antigen processing, and antigen presentation. Using head and neck cancer as a model, we identify that E5 decreases expression and function of the immunoproteasome and that the immunoproteasome, but not the constitutive proteasome, is associated with improved overall survival in patients. Moreover, immunopeptidome analysis reveals that HPV E5 restricts the repertoire of antigens presented on the cell surface, likely contributing to immune escape. Mechanistically, we discover a direct interaction between E5 and stimulator of interferon genes (STING), which suppresses downstream IFN signaling. Taken together, these findings identify a powerful molecular mechanism by which HPV E5 limits immune detection and mediates resistance to immunotherapy.

Ubiquitination is a key mechanism for post-translational protein modification, affecting protein localization, metabolism, degradation and various cellular physiological processes. Dysregulation of ubiquitination is associated with the pathogenesis of various diseases, such as tumors and cardiovascular diseases, making it a primary area of interest in biochemical research and drug development endeavors. E3 ubiquitin ligases play a pivotal role in modulating the ubiquitination of substrate proteins through their unique recognition functions. TRIM31, a member of the TRIM family of E3 ubiquitin ligases, is aberrantly expressed in different pathophysiological conditions. The biological function of TRIM31 is associated with the occurrence and development of diverse diseases. TRIM31 has been demonstrated to inhibit inflammation by promoting ubiquitin-proteasome-mediated degradation of the sensing protein NLRP3 in the inflammasome. TRIM31 mediates ubiquitination of MAVS, inducing the formation of prion-like aggregates, and triggering innate antiviral immune responses. TRIM31 is also implicated in tumor pathophysiology through its ability to promote ubiquitination of the tumor suppressor protein p53. These findings indicate that TRIM31 is a potential therapeutic target, and subsequent in-depth research of TRIM31 is anticipated to provide information on its clinical application in therapy.

The discovery of MPTP, an industrial chemical and contaminant of illicit narcotics, which causes parkinsonism in humans, non-human primates and rodents, has led to environmental pollutants exposure being convicted as key candidate in Parkinson’s disease (PD) pathogenesis. Though MPTP-induced mitochondrial dysfunction and neuroinflammation are mainly responsible for the causative issue of MPTP neurotoxicity, the underlying mechanism involved remains unclear. Here, we reveal a novel signaling mechanism of CDK5-USP30-MAVS regulating MPTP/MPP+ induced PD. MPP+ (the toxic metabolite of MPTP) treatment not only led to the increased protein levels of USP30 but also to mitophagy inhibition, mitochondrial dysfunction, and MAVS-mediated inflammation in BV2 microglial cells. Both mitophagy stimulation (Urolithin A administration) and USP30 knockdown relieved MAVS-mediated inflammation via restoring mitophagy and mitochondrial function in MPP+-induced cell model. Notably, MPTP/MPP+-induced CDK5 activation regulated USP30 phosphorylation at serine 216 to stabilize USP30. Moreover, CDK5-USP30 pathway promoted MAVS-mediated inflammation in MPTP/MPP+-induced PD model. Inhibition of CDK5 not only had a protective effect on MPP+-induced cell model of PD via suppressing the upregulation of USP30 and the activation of MAVS inflammation pathway in vitro, but also prevented neurodegeneration in vivo and alleviated movement impairment in MPTP mouse model of PD. Overall, our study reveal that CDK5 blocks mitophagy through phosphorylating USP30 and activates MAVS inflammation pathway in MPTP/MPP+-induced PD model, which suggests that CDK5-USP30-MAVS signaling pathway represents a valuable treatment strategy for PD induced by environmental neurotoxic pollutants in relation to MPTP.

Abstract Bovine viral diarrhea virus (BVDV) belongs to the genus Pestivirus within the family Flaviviridae. Mitophagy plays important roles in virus-host interactions. Here, we provide evidence that non-cytopathic (NCP) BVDV shifts the balance of mitochondrial dynamics toward fission and induces mitophagy to inhibit innate immune responses. Mechanistically, NCP BVDV triggers the translocation of dynamin-related protein (Drp1) to mitochondria and stimulates its phosphorylation at Ser616, leading to mitochondrial fission. In parallel, NCP BVDV-induced complete mitophagy via Parkin-dependent pathway contributes to eliminating damaged mitochondria to inhibit MAVS- and mtDNA-cGAS-mediated innate immunity responses, mtROS-mediated inflammatory responses and apoptosis initiation. Importantly, we demonstrate that the LIR motif of ERNS is essential for mitophagy induction. In conclusion, this study is the first to show that NCP BVDV-induced mitophagy plays a central role in promoting cell survival and inhibiting innate immune responses in vitro.

Objective To investigate the effect and mechanism of HBV 一 stimulated HTR8 一 S/Vneo mitochondrial antiviral signaling protein (MAVS) signaling pathway on the immune response of peripheral blood mononuclear cell (PBMC) to hepatitis B vaccine. Methods The HTR8 - S/Vneo were co 一 incubated with serum of HBV - DNA positive patients. MAVS siRNA transfection was hereby applied for silencing of MAVS and MAVS plasmid transfection was applied for overexpression of MAVS in HTR8 一 S/Vneo. We then cocultured them with human immune cells assembly PBMC and subsequently stimulated with hepatitis B vaccine. The mRNA and protein expression levels of MAVS, NF - kB, pNF - kB, IRF3 and pIRF3 in HTR8 一 S/Vneo were detected by reverse transcription 一 quantitative real 一 time PCR (RT 一 qPCR) and flow cytometry (FCM). The levels of IL - 2, IL - 6, IFN 一 p and IL 一 17 were detected by enzyme - linked immunosorbent assay (ELISA), and the proportion of CD4+ T cell were detected by flow cytometry. The data were analyzed for t test. Results HBV down 一 regulated the mRNA expression levels of MAVS, NF - kB, IRF3 (£ 二 6. 66, P 二 0. 003; £ 二 14. 18, P < 0. 001; £ 二 3. 70, P 二 0. 021) and the protein expression levels of MAVS, NF - kB, pNF - kB(£ 二 3. 42, P = 0. 042; £ 二 4. 23, P = 0. 013; £ 二 4. 86, P - 0. 008), and inhibited the production of IFN - p(£ 二 9. 83, P = 0. 010). Silencing MAVS down 一 regulated the mRNA and protein expression of MAVS(£ 二 31. 20, P < 0. 001; £ 二 6. 53, P = 0. 023), inhibited the expression of IFN - p(£ 二 5. 46, P =0. 032), and reduced the proportion of CD4+ T cells in PBMC(£ 二 9. 07, P = 0. 001). Overexpression of MAVS induced IFN 一 B production(£ 二一 34. 26, P < 0. 001; t - -5. 11, P = 0, 036), but the proportion of CD4 * T cells did not show significant effect (/二 一 0. 73, P 二 0. 506). Conclusion HBV can inhibit the MAVS signaling pathway in HTR8 一 S/Vneo. Overexpression of MAVS could promote the immune response to hepatitis B vaccine in PBMC. [ABSTRACT FROM AUTHOR]

Bovine viral diarrhea virus (BVDV) belongs to the genus Pestivirus within the family Flaviviridae. Mitophagy plays important roles in virus-host interactions. Here, we provide evidence that non-cytopathic (NCP) BVDV shifts the balance of mitochondrial dynamics toward fission and induces mitophagy to inhibit innate immune responses. Mechanistically, NCP BVDV triggers the translocation of dynamin-related protein (Drp1) to mitochondria and stimulates its phosphorylation at Ser616, leading to mitochondrial fission. In parallel, NCP BVDV-induced complete mitophagy via Parkin-dependent pathway contributes to eliminating damaged mitochondria to inhibit MAVS- and mtDNA-cGAS-mediated innate immunity responses, mtROS-mediated inflammatory responses and apoptosis initiation. Importantly, we demonstrate that the LIR motif of ERNS is essential for mitophagy induction. In conclusion, this study is the first to show that NCP BVDV-induced mitophagy plays a central role in promoting cell survival and inhibiting innate immune responses in vitro. [ABSTRACT FROM AUTHOR]

Many viruses, including mammarenaviruses, have evolved mechanisms to counteract different components of the host cell innate immunity, which is required to facilitate robust virus multiplication. The double-stranded RNA (dsRNA) sensor protein kinase receptor (PKR) pathway plays a critical role in the cell anti-viral response. Whether PKR can restrict the multiplication of the Old World mammarenavirus lymphocytic choriomeningitis virus (LCMV) and the mechanisms by which LCMV may counteract the anti-viral functions of PKR have not yet been investigated. Here we present evidence that LCMV infection results in very limited levels of PKR activation, but LCMV multiplication is enhanced in the absence of PKR. In contrast, infection with a recombinant LCMV with a mutation affecting the 3'-5' exonuclease (ExoN) activity of the viral nucleoprotein resulted in robust PKR activation in the absence of detectable levels of dsRNA, which was associated with severely restricted virus multiplication that was alleviated in the absence of PKR. However, pharmacological inhibition of PKR activation resulted in reduced levels of LCMV multiplication. These findings uncovered a complex role of the PKR pathway in LCMV-infected cells involving both pro- and anti-viral activities. [ABSTRACT FROM AUTHOR]

Tight control of the type I interferon (IFN) signaling pathway is critical for maintaining host innate immune responses, and the ubiquitination and deubiquitination of signaling molecules are essential for signal transduction. Deubiquitinase ubiquitin‐specific protein 19 (USP19) is known to be involved in deubiquitinating Beclin1, TRAF3, and TRIF for downregulation of the type I IFN signaling. Here, we show that SIAH1, a cellular E3 ubiquitin ligase that is involved in multicellular pathway, is a potent positive regulator of virus‐mediated type I IFN signaling that maintains homeostasis within the antiviral immune response by targeting USP19. In the early stages of virus infection, stabilized SIAH1 directly interacts with the USP19 and simultaneously mediates K27‐linked ubiquitination of 489, 490, and 610 residues of USP19 for proteasomal degradation. Additionally, we found that USP19 specifically interacts with MAVS and deubiquitinates K63‐linked ubiquitinated MAVS for negative regulation of type I IFN signaling. Ultimately, we identified that SIAH1‐mediated degradation of USP19 reversed USP19‐mediated deubiquitination of MAVS, Beclin1, TRAF3, and TRIF, resulting in the activation of antiviral immune responses. Taken together, these findings provide new insights into the molecular mechanism of USP19 and SIAH1, and suggest a critical role of SIAH1 in antiviral immune response and homeostasis. [ABSTRACT FROM AUTHOR]

Pigeons can be infected with various RNA viruses, and their innate immune system responds to viral infection to establish an antiviral response. Mitochondrial antiviral signaling protein (MAVS), an important adaptor protein in signal transduction, plays a pivotal role in amplifying the innate immune response. In this study, we successfully cloned pigeon MAVS (piMAVS) and performed a bioinformatics analysis. The results showed that the caspase recruitment domain (CARD) and transmembrane (TM) domain are highly conserved in poultry and mammals but poorly conserved in other species. Furthermore, we observed that MAVS expression is upregulated both in pigeons and pigeon embryonic fibroblasts (PEFs) upon RNA virus infection. Overexpression of MAVS resulted in increased levels of β-interferon (IFN-β), IFN-stimulated genes (ISGs), and interleukin (ILs) mRNA and inhibited Newcastle disease virus (NDV) replication. We also found that piMAVS and human MAVS (huMAVS) induced stronger expression of IFN-β and ISGs when compared to chicken MAVS (chMAVS), and this phenomenon was also reflected in the degree of inhibition of NDV replication. Our findings demonstrate that piMAVS plays an important role in repressing viral replication by regulating the activation of the IFN signal pathway in pigeons. This study not only sheds light on the function of piMAVS in innate immunity but also contributes to a more comprehensive understanding of the innate immunity system in poultry. Our data also provide unique insights into the differences in innate immunity between poultry and mammal. [ABSTRACT FROM AUTHOR]

Mitochondrial antiviral signaling protein (MAVS) is a crucial signaling adaptor in the sensing of positive-sense RNA viruses and the subsequent induction of the innate immune response. Coronaviruses have evolved multiple mechanisms to evade this response, amongst others, through their main protease (Mpro), which is responsible for the proteolytic cleavage of the largest part of the viral replicase polyproteins pp1a and pp1ab. Additionally, it can cleave cellular substrates, such as innate immune signaling factors, to dampen the immune response. Here, we show that MAVS is cleaved in cells infected with Middle East respiratory syndrome coronavirus (MERS-CoV), but not in cells infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This cleavage was independent of cellular negative feedback mechanisms that regulate MAVS activation. Furthermore, MERS-CoV Mpro expression induced MAVS cleavage upon overexpression and suppressed the activation of the interferon-β (IFN-β) and nuclear factor-κB (NF-κB) response. We conclude that we have uncovered a novel mechanism by which MERS-CoV downregulates the innate immune response, which is not observed among other highly pathogenic coronaviruses. [ABSTRACT FROM AUTHOR]

RNF5 is an E3 ubiquitin ligase involved in various physiological processes such as protein localization and cancer progression. Recent studies have shown that RNF5 significantly inhibits antiviral innate immunity by promoting the ubiquitination and degradation of STING and MAVS, which are essential adaptor proteins, as well as their downstream signal IRF3. The abundance of RNF5 is delicately regulated by both host factors and viruses. Host factors have been found to restrict RNF5-mediated ubiquitination, maintaining the stability of STING or MAVS through distinct mechanisms. Meanwhile, viruses have developed ingenious strategies to hijack RNF5 to ubiquitinate and degrade immune proteins. Moreover, recent studies have revealed the multifaceted roles of RNF5 in the life cycle of various viruses, including SARS-CoV-2 and KSHV. Based on these emerging discoveries, RNF5 represents a novel means of modulating antiviral immunity. In this review, we summarize the latest research on the roles of RNF5 in antiviral immunity and virus life cycle. This comprehensive understanding could offer valuable insights into exploring potential therapeutic applications focused on targeting RNF5 during viral infections. [ABSTRACT FROM AUTHOR]

Severe COVID-19 patients exhibit impaired IFN-I response due to decreased IFN-β production, allowing persistent viral load and exacerbated inflammation. While the SARS-CoV-2 nucleocapsid (N) protein has been implicated in inhibiting innate immunity by interfering with IFN-β signaling, the specific underlying mechanism still needs further investigation for a comprehensive understanding. This study reveals that the SARS-CoV-2 N protein enhances interaction between the human SUMO-conjugating enzyme UBC9 and MAVS. Increased MAVS-UBC9 interaction leads to enhanced SUMOylation of MAVS, inhibiting its ubiquitination, resulting in the inhibition of phosphorylation events involving IKKα, TBK1, and IRF3, thus disrupting IFN-β signaling. This study highlights the role of the N protein of SARS-CoV-2 in modulating the innate immune response by affecting the MAVS SUMOylation and ubiquitination processes, leading to inhibition of the IFN-β signaling pathway. These findings shed light on the complex mechanisms utilized by SARS-CoV-2 to manipulate the host's antiviral defenses and provide potential insights for developing targeted therapeutic strategies against severe COVID-19. [ABSTRACT FROM AUTHOR]

The mechanism by which lipid metabolism regulates innate immunity is unknown. Here, we report that the key enzyme in cholesterol synthesis, 3ß-hydroxysteroid-Δ24 reductase (DHCR24), is inhibited by viral infection. DHCR24 deficiency significantly promotes interferon production and interferon-stimulated gene expression. Inhibition of DHCR24 enzyme activity or the addition of the precursor 24-dehydrocholesterol (24-DHC) can augment innate immunity. Mechanistically, DHCR24 interacts with MAVS or STING, and DHCR24 impairs K27-linked ubiquitination of MAVS mediated by TRIM21 and K27-linked ubiquitination of STING mediated by AMFR, blocking the activation of MAVS and STING, respectively. Collectively, DHCR24 plays a negative role in regulating innate immune responses that may be targeted to improve immunity. [ABSTRACT FROM AUTHOR]

The signaling adaptor MAVS is a vital adaptor protein in retinoic acid-inducible gene I-like receptors (RLRs) signaling; thus, its expression and responses must be tightly regulated to avoid uncontrolled production of type I IFN by various mechanisms, including ubiquitination. The protein-coding ability of circRNAs has recently been a hot topic, but the roles of protein-coding circRNAs in antiviral innate immunity of teleost have rarely been reported. In this study, we identify that a novel circRNA derived from vacuolar protein sorting-associated protein 13D (VPS13D) gene, named circVPS13D, was a suppressor of RLR signaling pathways during poly(I:C) stimulation or Siniperca chuatsi rhabdovirus (SCRV) infection. Mechanistically, circVPS13D contains a 513-nucleotide (nt) open reading frame (ORF) and a sequence that is -174 nt as an internal ribosome entry site (IRES), which is required for translation initiation in 5'-cap-independent coding RNAs. SCRV infection promoted the expression of circVPS13D and circVPS13D encodes a novel peptide, termed VPS13D-170 amino acid (aa), which directly interacted with MAVS and inhibited IFN-I production. VPS13D-170aa targeted the K172 residue of MAVS through K48-linked polyubiquitination, leading to proteasomal degradation of MAVS. [ABSTRACT FROM AUTHOR]

Mitochondrial antiviral signaling protein (MAVS) and stimulator of interferon (IFN) genes (STING) are crucial factors of IFN induction in RNA and DNA viral infections. However, unrestricted IFN was harmful to the host by causing cytokine storm. Here, we report that zebrafish transmembrane protein 47 (TMEM47), an IFN-negative regulator in fish, represses IFN expression stimulated by both spring viremia of carp virus (SVCV) and cyprinid herpesvirus 2, which represent RNA and DNA viruses, respectively. The mRNA level of tmem47 was rapidly upregulated during RNA and DNA virus infection. Overexpression of TMEM47 significantly blocked SVCV- and CyHV-2-mediated IFN induction, whereas knockdown of tmem47 promoted ifn transcription under these viral infections. Furthermore, TMEM47 interacted with MAVS and STING, which are considered as key factors for IFN induction during RNA and DNA viral infection. Mechanistically, both MAVS and STING were degraded by TMEM47 in an autophagy-lysosome-dependent manner, and the autophagy factor autophagy-related gene 5 (ATG5) was essential for this process. Finally, at the cellular level, MAVS- and STING-mediated antiviral capacities were significantly suppressed by TMEM47. Taken together, our results demonstrate that zebrafish TMEM47 acts as a brake to inhibit IFN production in both RNA and DNA viral infections. [ABSTRACT FROM AUTHOR]

Mitochondrial antiviral signaling protein (MAVS) is a key innate immune adaptor on the outer mitochondrial membrane that acts as a switch in the immune signal transduction response to viral infections. Some studies have reported that MAVS mediates NF-κB and type I interferon signaling during viral infection and is also required for optimal NLRP3 inflammasome activity. Recent studies have reported that MAVS is involved in various cancers, systemic lupus erythematosus, kidney diseases, and cardiovascular diseases. Herein, we summarize the structure, activation, pathophysiological roles, and MAVS-based therapies for renal diseases. This review provides novel insights into MAVS's role and therapeutic potential in the pathogenesis of renal diseases. [ABSTRACT FROM AUTHOR]

Epithelial tissue is at the forefront of innate immunity, playing a crucial role in the recognition and elimination of pathogens. Met is a receptor tyrosine kinase that is necessary for epithelial cell survival, proliferation, and regeneration. Here, we showed that Met is essential for the induction of cytokine production by cytosolic nonself double-stranded RNA through retinoic acid-inducible gene-I-like receptors (RLRs) in epithelial cells. Surprisingly, the tyrosine kinase activity of Met was dispensable for promoting cytokine production. Rather, the intracellular carboxy terminus of Met interacted with mitochondrial antiviral-signaling protein (MAVS) in RLR-mediated signaling to directly promote MAVS signalosome formation. These studies revealed a kinase activity-independent function of Met in the promotion of antiviral innate immune responses, defining dual roles of Met in both regeneration and immune responses in the epithelium. [ABSTRACT FROM AUTHOR]

Mitochondrial anti-viral signaling protein (MAVS) plays an important role in host defense against viral infection via coordinating the activation of NF-κB and interferon regulatory factors. The mitochondrial-bound form of MAVS is essential for its anti-viral innate immunity. Recently, tumor cells were proposed to mimic a viral infection by activating RNA-sensing pattern recognition receptors. Here, we demonstrate that MAVS is overexpressed in a panel of viral non-infected cancer cell lines and patient-derived tumors, including lung, liver, bladder, and cervical cancers, and we studied its role in cancer. Silencing MAVS expression reduced cell proliferation and the expression and nuclear translocation of proteins associated with transcriptional regulation, inflammation, and immunity. MAVS depletion reduced expression of the inflammasome components and inhibited its activation/assembly. Moreover, MAVS directly interacts with the mitochondrial protein VDAC1, decreasing its conductance, and we identified the VDAC1 binding site in MAVS. Our findings suggest that MAVS depletion, by reducing cancer cell proliferation and inflammation, represents a new target for cancer therapy.

In pathogen recognition, the nucleotide-binding domain (NBD) and leucine rich repeat receptors (NLRs) have noteworthy functions in the activation of the innate immune response. These receptors respond to several viral infections, among them NOD2, a very dynamic NLR, whose role in dengue virus (DENV) infection remains unclear. This research aimed to determine the role of human NOD2 in THP-1 macrophage-like cells during DENV-2 infection. NOD2 levels in DENV-2 infected THP-1 macrophage-like cells was evaluated by RT-PCR and Western blot, and an increase was observed at both mRNA and protein levels. We observed using confocal microscopy and co-immunoprecipitation assays that NOD2 interacts with the effector protein MAVS (mitochondrial antiviral signaling protein), an adaptor protein promoting antiviral activity, this occurring mainly at 12 h into the infection. After silencing NOD2, we detected increased viral loads of DENV-2 and lower levels of IFN-α in supernatants from THP-1 macrophage-like cells with NOD2 knock-down and further infected with DENV-2, compared with mock-control or cells transfected with Scramble-siRNA. Thus, NOD2 is activated in response to DENV-2 in THP-1 macrophage-like cells and participates in IFN-α production, in addition to limiting virus replication at the examined time points.

In this article, an attempt has been made to analyze the global development of technologies related to MAVs in the next decade by using the basics of technology forecasting (monitoring and experts' views) and by using the fuzzy Delphi method. The current research is applied in terms of purpose, in terms of combined strategy, and in terms of implementation in the form of descriptive-survey research. The statistical population is in two levels. The first level is made up of experts in the field of the MAVs industry, and the second level is made up of university professors in the field of technologies related to MAVs. According to the purpose of the research, the targeted sampling number was 9 people in the first level and 35 people elected in the second level. The data collection tool is a researcher-made questionnaire, whose validity was determined by content method and reliability by Cronbach's alpha method. Data analysis was also done through the fuzzy Delphi method using Spss and Excel software.The findings of this research show that the technologies related to MAVs can be counted in 29 indicators and out of these 9 indicators are in the field of artificial intelligence and electronics and telecommunication technologies are in priority and should be taken into consideration by the country's officials, decision-makers, and planners.

TRIM7 has been demonstrated to have significant roles in promoting host defense against viral infections and regulating immune signaling pathways. As an E3 ubiquitin ligase, it catalyzes the ubiquitination of various substrates, including adaptor proteins (MAVS and STING) and transcription factors (NF-kB and IRF3), thereby exerting positive or negative regulation on immune signal pathways. However, viruses have developed immune evasion mechanisms to counteract TRIM7. Some viruses can inhibit TRIM7 function by targeting it for degradation or sequestering it away from its targets. Moreover, TRIM7 may even facilitate viral infection by ubiquitinating viral proteins, including envelope proteins that are critical for tissue and species tropism. A comprehensive understanding of the interaction between TRIM7 and antiviral immunity is crucial for the development of innovative treatments for viral diseases. [ABSTRACT FROM AUTHOR]

Hepatitis A virus (HAV) infections are considered not to trigger innate immunity in vivo , in contrast to hepatitis C virus (HCV). This lack of induction has been imputed to strong interference by HAV proteases 3CD and 3ABC. We aimed to elucidate the mechanisms of immune activation and counteraction by HAV and HCV in vivo and in vitro. Albumin-urokinase-type plasminogen activator/severe combined immunodeficiency (Alb/uPA-SCID) mice with humanised livers were infected with HAV and HCV. Hepatic cell culture models were used to assess HAV and HCV sensing by Toll-like receptor 3 and retinoic acid-inducible gene I/melanoma differentiation-associated protein 5 (RIG-I/MDA5), respectively. Cleavage of the adaptor proteins TIR-domain-containing adapter-inducing interferon-β (TRIF) and mitochondrial antiviral-signalling protein (MAVS) was analysed by transient and stable expression of HAV and HCV proteases and virus infection. We detected similar levels of interferon-stimulated gene induction in hepatocytes of HAV- and HCV-infected mice with humanised liver. In cell culture, HAV induced interferon-stimulated genes exclusively upon MDA5 sensing and depended on LGP2 (laboratory of genetics and physiology 2). TRIF and MAVS were only partially cleaved by HAV 3ABC and 3CD, not sufficiently to abrogate signalling. In contrast, HCV NS3-4A efficiently degraded MAVS, as previously reported, whereas TRIF cleavage was not detected. HAV induces an innate immune response in hepatocytes via MDA5/LGP2, with limited control of both pathways by proteolytic cleavage. HCV activates Toll-like receptor 3 and lacks TRIF cleavage, suggesting that this pathway mainly contributes to HCV-induced antiviral responses in hepatocytes. Our results shed new light on the induction of innate immunity and counteraction by HAV and HCV. Understanding the mechanisms that determine the differential outcomes of HAV and HCV infections is crucial for the development of effective therapies. Our study provides insights into the interplay between these viruses and the host innate immune response in vitro and in vivo , shedding light on previously controversial or only partially investigated aspects. This knowledge could tailor the development of new strategies to combat HCV persistence, as well as improve our understanding of the factors underlying successful HAV clearance. [Display omitted] • Our data indicate that HAV induces an innate immune response in vitro and in vivo. • HAV 3C precursor proteases do not fully abolish the host response. • The HCV NS3-4A protease instead disrupts the RLR pathways, but cannot cleave TRIF and has no impact on TLR3 responses. • In systems devoid of adaptive immunity, HAV and HCV induce innate immune responses to similar degrees. [ABSTRACT FROM AUTHOR]

Background: Interferon (IFN) responses are critical in the resolution of viral infections and are actively targeted by many viruses. They also play a role in inducing protective responses after vaccination and have been successfully tested as vaccine adjuvants. IFN responses are well conserved and function very similar in teleosts and mammals. Like in mammals, IFN responses in piscine cells are initiated by intracellular detection of the viral infection by different pattern recognition receptors. Upon the recognition of viral components, IFN responses are rapidly induced to combat the infection. However, many viruses may still replicate and be able to inhibit or circumvent the IFN response by different means. Methods: By employing CRISPR Cas9 technology, we have disrupted proteins that are central for IFN signaling in the salmonid cell line CHSE-214. We successfully generated KO clones for the mitochondrial antiviral signaling protein MAVS, the transcription factors IRF3 and IRF7-1, as well as a double KO for IRF7-1/3 using an optimized protocol for delivery of CRISPR-Cas ribonucleoproteins through nucleofection. Results: We found that MAVS and IRF3 KOs inhibited IFN and IFN-stimulated gene induction after intracellular poly I:C stimulation as determined through gene expression and promoter activation assays. In contrast, the IRF7-1 KO had no clear effect. This shows that MAVS and IRF3 are essential for initiation of intracellular RNA-induced IFN responses in CHSE-214 cells. To elucidate viral interference with IFN induction pathways, the KOs were infected with Salmon alphavirus 3 (SAV3) and infectious pancreatic necrosis virus (IPNV). SAV3 infection in control and IRF7-1 KO cells yielded similar titers and no cytopathic effect, while IRF3 and MAVS KOs presented with severe cytopathic effect and increased titers 6 days after SAV 3 infection. In contrast, IPNV yields were reduced in IRF3 and MAVS KOs, suggesting a dependency on interactions between viral proteins and pattern recognition receptor signaling components during viral replication. Conclusion: Aside from more insight in this signaling in salmonids, our results indicate a possible method to increase viral titers in salmonid cells. [ABSTRACT FROM AUTHOR]

ABSTRACT: Innate immunity, as an organism's first line of defense, plays a crucial role in rapidly responding to and protecting the body against invading pathogens. As a cytosolic RNA sensor for viral infections, including infections caused by influenza virus, the innate immune system in chickens has 2 major pathogen-recognition receptors (PRRs): Toll-like receptor 3 (TLR3) and melanoma differentiation-associated protein 5 (MDA5). The signaling pathways activated by PRRs are complex, systemic processes that underlie the response to foreign molecules. In this study, we investigated the interactions among MDA5, mitochondrial antiviral signaling protein (MAVS), and stimulator of interferon genes (STING) signaling in chicken cells. To exclude the effects of TLR3, we transfected the clustered regularly interspaced palindromic repeats/CRISPR-associated protein 9 (CRISPR-Cas9) expression vector and TLR3-targeted gRNA plasmid into chicken DF-1 cells. We selected TLR3-knockout (KO) cell line and sequentially, we established 2 double-KO cell lines: TLR3-MAVS KO and TLR3-STING KO. After treatment with polyinosinic:polycytidylic acid (poly(I:C)), type I interferon (IFN), IFN-stimulated gene, and antiviral gene (IFN regulatory factor 7, IFNβ, Mx1, and protein kinase R1) expression was not completely activated in TLR3-MAVS KO cells, whereas it was consistently upregulated in wild-type and TLR3-STING KO DF-1 cells. These results suggest that STING is not an intermediator between MDA5 and MAVS; moreover, it does not directly interact with MDA5 during innate immune activation in chicken DF-1 cells.

Corrosion has been concerned as a serious safety issue for metallic facilities. Visual inspection carried out by an engineer is expensive, subjective and time-consuming. Micro Aerial Vehicles (MAVs) equipped with detection algorithms have the potential to perform safer and much more efficient visual inspection tasks than engineers. Towards corrosion detection algorithms, convolution neural networks (CNNs) have enabled the power for high accuracy metallic corrosion detection. However, these detectors are restricted by MAVs on-board capabilities. In this study, based on You Only Look Once v3-tiny (Yolov3-tiny), an accurate deep learning-based metallic corrosion detector (AMCD) is proposed for MAVs on-board metallic corrosion detection. Specifically, a backbone with depthwise separable convolution (DSConv) layers is designed to realise efficient corrosion detection. The convolutional block attention module (CBAM), three-scale object detection and focal loss are incorporated to improve the detection accuracy. Moreover, the spatial pyramid pooling (SPP) module is improved to fuse local features for further improvement of detection accuracy. A field inspection image dataset labelled with four types of corrosions (the nubby corrosion, bar corrosion, exfoliation and fastener corrosion) is utilised for training and testing the AMCD. Test results show that the AMCD achieves 84.96% mean average precision (mAP), which outperforms other state-of-the-art detectors. Meanwhile, 20.18 frames per second (FPS) is achieved leveraging NVIDIA Jetson TX2, the most popular MAVs on-board computer, and the model size is only 6.1 MB. [ABSTRACT FROM AUTHOR]

Background/Aim: Cutaneous squamous cell carcinoma (cSCC) is a common non-melanoma skin cancer, and its incidence is increasing. Proteasome subunit alpha type-7 (PSMA7) has been found to be aberrantly expressed in several cancers. However, whether it functions as a tumor suppressor or oncogene in the pathogenesis of cancers, particularly cSCC, remains controversial. Here, we aimed to investigate the functions of PSMA7 in cSCC pathogenesis. Patients and Methods: Clinicopathological characteristics were evaluated in 131 patients with cSCC using tissue sections. The expression of PSMA7, nucleotide-binding oligomerization domain-containing protein 1 (NOD1), and mitochondrial antiviral signaling protein (MAVS) was determined in cSCC tissue sections using immunohistochemical staining. The effect of PSMA7 expression on the biological behavior of cSCC cells was investigated in vitro. Results: High immunoreactivity of PSMA7 (high-PSMA7) was detected in 53 (40.5%) patients with cSCC and was significantly associated with histologic grade (p=0.008) and favorable recurrence-free survival (p=0.018). The expression of PSMA7 and NOD1 (p=0.026) and MAVS (p=0.032) was negatively correlated in cSCC tissues. Contrary to the results of the cohort study, cell viability and invasiveness significantly decreased after PSMA7 down-regulation in cSCC cells in vitro. mRNA expression of tumor necrosis factor-alpha, interleukin-1 alpha (IL-1a), IL-6, and IL-8 were significantly increased after PSMA7 down-regulation in cSCC cells (all p=0.002). Conclusion: PSMA7-mediated degradation of NOD1 and MAVS as well as the subsequent reduction of the cancer-associated cytokine network may be a crucial mechanism of the antitumoral function of PSMA7 in patients with cSCC. [ABSTRACT FROM AUTHOR]

Mitophagy is a form of autophagy that plays a key role in maintaining the homeostasis of functional mitochondria in the cell. Viruses have evolved various strategies to manipulate mitophagy to escape host immune responses and promote virus replication. In this study, the nucleoprotein (NP) of H1N1 virus (PR8 strain) was identified as a regulator of mitophagy. We revealed that NP-mediated mitophagy leads to the degradation of the mitochondria-anchored protein MAVS, thereby blocking MAVS-mediated antiviral signaling and promoting virus replication. The NP-mediated mitophagy is dependent on the interaction of NP with MAVS and the cargo receptor TOLLIP. Moreover, Y313 of NP is a key residue for the MAVS-NP interaction and NP-mediated mitophagy. The NPY313F mutation significantly attenuates the virus-induced mitophagy and the virus replication in vitro and in vivo. Taken together, our findings uncover a novel mechanism by which the NP of influenza virus induces mitophagy to attenuate innate immunity. Abbreviations: ACTB: actin beta; ATG7: autophagy related 7; ATG12: autophagy related 12; CCCP: carbonyl cyanide 3-chlorophenyl hydrazone; co-IP: co-immunoprecipitation; COX4/COXIV: cytochrome c oxidase subunit 4; DAPI: 4ʹ,6-diamidino-2-phenylindole, dihydrochloride; EID50: 50% egg infective dose; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GFP: green fluorescent protein; HEK: human embryonic kidney; hpi: hours post-infection; IAV: influenza A virus; IFN: interferon; IP: immunoprecipitation; LAMP1: lysosomal associated membrane protein 1; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MAVS: mitochondrial antiviral signaling protein; Mdivi-1: mitochondrial division inhibitor 1; MLD50: 50% mouse lethal dose; MOI: multiplicity of infection; NBR1: NBR1 autophagy cargo receptor; NP: nucleoprotein; PB1: basic polymerase 1; RFP: red fluorescent protein; RIGI: RNA sensor RIG-I; RIGI-N: RIGI-CARD; SeV: Sendai virus; SQSTM1/p62: sequestosome 1; TIMM23: translocase of inner mitochondrial membrane 23; TOLLIP: toll interacting protein; TOMM20: translocase of outer mitochondrial membrane 20; TUBA: tubulin alpha; Vec: empty vector; vRNP: viral ribonucleoprotein. [ABSTRACT FROM AUTHOR]

Abstract Background Vector-borne flaviviruses, including tick-borne encephalitis virus (TBEV), Zika virus (ZIKV), West Nile virus (WNV), yellow fever virus (YFV), dengue virus (DENV), and Japanese encephalitis virus (JEV), pose a growing threat to public health worldwide, and have evolved complex mechanisms to overcome host antiviral innate immunity. However, the underlying mechanisms of flavivirus structural proteins to evade host immune response remain elusive. Results We showed that TBEV structural protein, pre-membrane (prM) protein, could inhibit type I interferon (IFN-I) production. Mechanically, TBEV prM interacted with both MDA5 and MAVS and interfered with the formation of MDA5-MAVS complex, thereby impeding the nuclear translocation and dimerization of IRF3 to inhibit RLR antiviral signaling. ZIKV and WNV prM was also demonstrated to interact with both MDA5 and MAVS, while dengue virus serotype 2 (DENV2) and YFV prM associated only with MDA5 or MAVS to suppress IFN-I production. In contrast, JEV prM could not suppress IFN-I production. Overexpression of TBEV and ZIKV prM significantly promoted the replication of TBEV and Sendai virus. Conclusion Our findings reveal the immune evasion mechanisms of flavivirus prM, which may contribute to understanding flavivirus pathogenicity, therapeutic intervention and vaccine development.

The mitochondrial antiviral-signaling protein (MAVS), a core adaptor protein in the retinoic-acid-inducible gene-I-like receptors (RLRs)-MAVS pathway, has been demonstrated to play an important role in antiviral immune response and tumor immunology. Previous studies revealed that ubiquitylation is a key mechanism in the regulation of the RLRs-MAVS axis and immune response. Multiple E3 ubiquitin ligases and deubiquitinating enzymes control MAVS ubiquitylation and changes in MAVS function. In this review, we summarize the biological function of ubiquitylation in MAVS-related signaling and provide new insight into immunotherapy approaches that target MAVS.

Mitochondrial antiviral signaling protein (MAVS) is a crucial signaling adaptor in the sensing of positive-sense RNA viruses and the subsequent induction of the innate immune response. Coronaviruses have evolved multiple mechanisms to evade this response, amongst others, through their main protease (Mpro), which is responsible for the proteolytic cleavage of the largest part of the viral replicase polyproteins pp1a and pp1ab. Additionally, it can cleave cellular substrates, such as innate immune signaling factors, to dampen the immune response. Here, we show that MAVS is cleaved in cells infected with Middle East respiratory syndrome coronavirus (MERS-CoV), but not in cells infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This cleavage was independent of cellular negative feedback mechanisms that regulate MAVS activation. Furthermore, MERS-CoV Mpro expression induced MAVS cleavage upon overexpression and suppressed the activation of the interferon-β (IFN-β) and nuclear factor-κB (NF-κB) response. We conclude that we have uncovered a novel mechanism by which MERS-CoV downregulates the innate immune response, which is not observed among other highly pathogenic coronaviruses.

BackgroundInterferon (IFN) responses are critical in the resolution of viral infections and are actively targeted by many viruses. They also play a role in inducing protective responses after vaccination and have been successfully tested as vaccine adjuvants. IFN responses are well conserved and function very similar in teleosts and mammals. Like in mammals, IFN responses in piscine cells are initiated by intracellular detection of the viral infection by different pattern recognition receptors. Upon the recognition of viral components, IFN responses are rapidly induced to combat the infection. However, many viruses may still replicate and be able to inhibit or circumvent the IFN response by different means.MethodsBy employing CRISPR Cas9 technology, we have disrupted proteins that are central for IFN signaling in the salmonid cell line CHSE-214. We successfully generated KO clones for the mitochondrial antiviral signaling protein MAVS, the transcription factors IRF3 and IRF7-1, as well as a double KO for IRF7-1/3 using an optimized protocol for delivery of CRISPR-Cas ribonucleoproteins through nucleofection.ResultsWe found that MAVS and IRF3 KOs inhibited IFN and IFN-stimulated gene induction after intracellular poly I:C stimulation as determined through gene expression and promoter activation assays. In contrast, the IRF7-1 KO had no clear effect. This shows that MAVS and IRF3 are essential for initiation of intracellular RNA-induced IFN responses in CHSE-214 cells. To elucidate viral interference with IFN induction pathways, the KOs were infected with Salmon alphavirus 3 (SAV3) and infectious pancreatic necrosis virus (IPNV). SAV3 infection in control and IRF7-1 KO cells yielded similar titers and no cytopathic effect, while IRF3 and MAVS KOs presented with severe cytopathic effect and increased titers 6 days after SAV 3 infection. In contrast, IPNV yields were reduced in IRF3 and MAVS KOs, suggesting a dependency on interactions between viral proteins and pattern recognition receptor signaling components during viral replication.ConclusionAside from more insight in this signaling in salmonids, our results indicate a possible method to increase viral titers in salmonid cells.

Kaposi's sarcoma-associated herpesvirus (KSHV) and the Epstein–Barr virus (EBV) are double-stranded DNA oncogenic gammaherpesviruses. These two viruses are associated with multiple human malignancies, including both B and T cell lymphomas, as well as epithelial- and endothelial-derived cancers. KSHV and EBV establish a life-long latent infection in the human host with intermittent periods of lytic replication. Infection with these viruses induce the expression of both viral and host RNA transcripts and activates several RNA sensors including RIG-I-like receptors (RLRs), Toll-like receptors (TLRs), protein kinase R (PKR) and adenosine deaminases acting on RNA (ADAR1). Activation of these RNA sensors induces the innate immune response to antagonize the virus. To counteract this, KSHV and EBV utilize both viral and cellular proteins to block the innate immune pathways and facilitate their own infection. In this review, we summarize how gammaherpesviral infections activate RNA sensors and induce their downstream signaling cascade, as well as how these viruses evade the antiviral signaling pathways to successfully establish latent infection and undergo lytic reactivation. [ABSTRACT FROM AUTHOR]

Mitochondria are versatile organelles and essential components of numerous biological processes such as energy metabolism, signal transduction, and cell fate determination. In recent years, their critical roles in innate immunity have come to the forefront, highlighting impacts on pathogenic defense, tissue homeostasis, and degenerative diseases. This review offers an in-depth and comprehensive examination of the multifaceted mechanisms underlying the interactions between mitochondria and innate immune responses. We will delve into the roles of healthy mitochondria as platforms for signalosome assembly, the release of mitochondrial components as signaling messengers, and the regulation of signaling via mitophagy, particularly to cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) signaling and inflammasomes. Furthermore, the review will explore the impacts of mitochondrial proteins and metabolites on modulating innate immune responses, the polarization of innate immune cells, and their implications on infectious and inflammatory diseases. [ABSTRACT FROM AUTHOR]

The pattern recognition receptors (PRRs) sense exogenous molecular patterns most commonly derived from invading pathogens, to active the interferon (IFN) signalling. In the cytoplasm, the viral double‐stranded RNAs (dsRNAs) are sensed by retinoic acid‐inducible gene I (RIG‐I) or melanoma differentiation‐associated protein 5 (MDA5), depending on the length and chemical properties. Through the binding and oligomerizing onto the RNAs, they form filament to initiate the signalling cascade. Regulation of these receptors' activities are essential for manipulating the strength of IFN signalling. Here, through the virtual screening of chemical reagents using the published MDA5‐dsRNA complex structure (PDB: 4GL2), we identified an antibiotic, gramicidin A as a stimulator that enhanced MDA5‐mediated IFN signalling. Cytotoxic assay and IFN signalling assay suggested that disruption of lipid membrane, which is a well‐defined mechanism of gramicidin A to perform its action, was dispensable in this process. Sucrose gradient ultracentrifugation assay showed that the gramicidin A treatment enhanced MDA5 oligomerization status in the presence of dsRNA. Our work implicated a new role of gramicidin A in innate immunity and presented a new tool to manipulate MDA5 activity. [ABSTRACT FROM AUTHOR]