The host protein CALCOCO2 interacts with bovine viral diarrhoea virus Npro, inhibiting type I interferon production and thereby promoting viral replication

Bovine viral diarrhoea-mucosal disease caused by bovine viral diarrhoea virus (BVDV) is a major infectious disease that affects the cattle industry. The nonstructural protein Npro of BVDV antagonizes the type I interferon (IFN-I) pathway, thereby escaping the host immune response. The exact mechanism by which Npro uses host proteins to inhibit IFN-I production is unclear. The host protein CALCOCO2 was identified as a binding partner of Npro using a yeast two-hybrid screen. The interaction between Npro and CALCOCO2 was confirmed by yeast co-transformation, co-immunoprecipitation assays, and GST pull-down assays. The stable overexpression of CALCOCO2 markedly promoted BVDV propagation, while the knockdown of CALCOCO2 significantly inhibited BVDV replication in MDBK cells. Interestingly, CALCOCO2 inhibited IFN-I and IFN-stimulated gene production in BVDV-infected cells. Ectopic expression of CALCOCO2 effectively reduced IRF3 protein levels via the proteasome pathway. CALCOCO2 was found to promote Npro-mediated ubiquitination degradation of IRF3 by interacting with IRF3. Our results demonstrate the molecular mechanism by which Npro recruits the CALCOCO2 protein to regulate IRF3 degradation to inhibit IFN-I production.

BRD4 promotes LPS-induced endothelial cells senescence via activating and cooperating STING-IRF3 pathway

Endothelial cells (ECs) senescence is closely associated with the initiation and development of multiple age-related cardiovascular diseases. It is necessary to explore the underlying molecular mechanisms of ECs senescence, which is not only the basis to decipher cellular senescence, but also a novel therapeutic target for the endothelial senescence-related diseases. BRD4, a key epigenetic regulator, is universally related to gene expression regulation and has been reported to accelerate cell senescence. Besides, emerging evidence has suggested that the stimulator of interferon genes protein (STING) can regulate inflammatory and senescence-related diseases. However, whether STING pathway activation is regulated by BRD4 in the context of ECs senescence remains largely unclear. Here, we observed that elevated BRD4 and activated STING-IRF3 signaling pathway during ECs senescence and further confirmed that BRD4 could abolish STING activation. We demonstrated that BRD4 could inhibit E3 ubiquitin ligase HRD1-mediated ubiquitination degradation of STING via inhibiting HRD1 transcription. In addition to the direct regulatory effect of BRD4 on STING activation, we have confirmed that BRD4 cooperates with IRF3 and P65 to promote SASP gene expression, thereby accelerating ECs senescence. Here, we proposed a novel mechanism underlying BRD4' key dual role in activating the STING pathway during ECs senescence.

Deubiquitinase USP4 suppresses antitumor immunity by inhibiting IRF3 activation and tumor cell-intrinsic interferon response in colorectal cancer

Despite the approval of immune checkpoint blockade (ICB) therapy for various tumor types, its effectiveness is limited to only approximately 15% of patients with microsatellite instability-high (MSI-H) or mismatch repair deficiency (dMMR) colorectal cancer (CRC). Approximately 80%-85% of CRC patients have a microsatellite stability (MSS) phenotype, which features a rare T-cell infiltration. Thus, elucidating the mechanisms underlying resistance to ICB in patients with MSS CRC is imperative. In this study, we demonstrate that ubiquitin-specific peptidase 4 (USP4) is upregulated in MSS CRC tumors and negatively regulates the immune response against tumors in CRC. Additionally, USP4 represses the cellular interferon (IFN) response and antigen presentation and impairs PRR signaling-mediated cell death. Mechanistically, USP4 impedes the nuclear localization of interferon regulator Factor 3 (IRF3) by deubiquitinating the K63-polyubiquitin chain of TRAF6 and IRF3. Knockdown of USP4 enhances the infiltration of T cells in CRC tumors and overcomes ICB resistance in an MC38 syngeneic mouse model. Moreover, published datasets revealed that patients showing higher USP4 expression exhibited decreased responsiveness to anti-PD-L1 therapy. These findings highlight an essential role of USP4 in the suppression of antitumor immunity in CRC.

Mitochondrial (mt)DNA-cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signaling promotes pyroptosis of macrophages via interferon regulatory factor (IRF)7/IRF3 activation to aggravate lung injury during severe acute pancreatitis

BACKGROUND

Macrophage proinflammatory activation contributes to the pathology of severe acute pancreatitis (SAP) and, simultaneously, macrophage functional changes, and increased pyroptosis/necrosis can further exacerbate the cellular immune suppression during the process of SAP, where cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) plays an important role. However, the function and mechanism of cGAS-STING in SAP-induced lung injury (LI) remains unknown.

METHODS

Lipopolysaccharide (LPS) was combined with caerulein-induced SAP in wild type, cGAS -/- and sting -/- mice. Primary macrophages were extracted via bronchoalveolar lavage and peritoneal lavage. Ana-1 cells were pretreated with LPS and stimulated with nigericin sodium salt to induce pyroptosis in vitro.

RESULTS

SAP triggered NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasome activation-mediated pyroptosis of alveolar and peritoneal macrophages in mouse model. Knockout of cGAS/STING could ameliorate NLRP3 activation and macrophage pyroptosis. In addition, mitochondrial (mt)DNA released from damaged mitochondria further induced macrophage STING activation in a cGAS- and dose-dependent manner. Upregulated STING signal can promote NLRP3 inflammasome-mediated macrophage pyroptosis and increase serum interleukin (IL)-6, IL-1β, and tumor necrosis factor (TNF)-α levels and, thus, exacerbate SAP-associated LI (SAP-ALI). Downstream molecules of STING, IRF7, and IRF3 connect the mtDNA-cGAS-STING axis and the NLRP3-pyroptosis axis.

CONCLUSIONS

Negative regulation of any molecule in the mtDNA-cGAS-STING-IRF7/IRF3 pathway can affect the activation of NLRP3 inflammasomes, thereby reducing macrophage pyroptosis and improving SAP-ALI in mouse model.

Computational investigation of the inhibitory interaction of IRF3 and SARS-CoV-2 accessory protein ORF3b

ORF3b is one of the SARS-CoV-2 accessory proteins. Previous experimental study suggested that ORF3b prevents IRF3 translocating to nucleus. However, the biophysical mechanism of ORF3b-IRF3 interaction is elusive. Here, we explored the conformation ensemble of ORF3b using all-atom replica exchange molecular dynamics simulation. Disordered ORF3b has mixed α-helix, β-turn and loop conformers. The potential ORF3b-IRF3 binding modes were searched by docking representative ORF3b conformers with IRF3, and 50 ORF3b-IRF3 complex poses were screened using molecular dynamics simulations ranging from 500 to 1000 ns. We found that ORF3b binds IRF3 predominantly on its CBP binding and phosphorylated pLxIS motifs, with CBP binding site has the highest binding affinity. The ORF3b-IRF3 binding residues are highly conserved in SARS-CoV-2. Our results provided biophysics insights into ORF3b-IRF3 interaction and explained its interferon antagonism mechanism.

IL-6/STAT3 axis is hijacked by GCRV to facilitate viral replication via suppressing type Ⅰ IFN signaling

Grass carp reovirus (GCRV) infections and hemorrhagic disease (GCHD) outbreaks are typically seasonally periodic and temperature-dependent, yet the molecular mechanism remains unclear. Herein, we depicted that temperature-dependent IL-6/STAT3 axis was exploited by GCRV to facilitate viral replication via suppressing type Ⅰ IFN signaling. Combined multi-omics analysis and qPCR identified IL-6, STAT3, and IRF3 as potential effector molecules mediating GCRV infection. Deploying GCRV challenge at 18 °C and 28 °C as models of resistant and permissive infections and switched to the corresponding temperatures as temperature stress models, we illustrated that IL-6 and STAT3 expression, genome level of GCRV, and phosphorylation of STAT3 were temperature dependent and regulated by temperature stress. Further research revealed that activating IL-6/STAT3 axis enhanced GCRV replication and suppressed the expression of IFNs, whereas blocking the axis impaired viral replication. Mechanistically, grass carp STAT3 inhibited IRF3 nuclear translocation via interacting with it, thus down-regulating IFNs expression, restraining transcriptional activation of the IFN promoter, and facilitating GCRV replication. Overall, our work sheds light on an immune evasion mechanism whereby GCRV facilitates viral replication by hijacking IL-6/STAT3 axis to down-regulate IFNs expression, thus providing a valuable reference for targeted prevention and therapy of GCRV.

Key roles for phosphorylation and the Coiled-coil domain in TRIM56-mediated positive regulation of TLR3-TRIF-dependent innate immunity

Tripartite-motif protein-56 (TRIM56) positively regulates the induction of type I interferon response via the TLR3 pathway by enhancing IRF3 activation and depends on its C-terminal residues 621-750 for interacting with the adaptor TRIF. However, the precise underlying mechanism and detailed TRIM56 determinants remain unclear. Herein, we show ectopic expression of murine TRIM56 also enhances TLR3-dependent interferon-β promoter activation, suggesting functional conservation. We found that endogenous TRIM56 and TRIF formed a complex early (0.5-2 h) after poly-I:C stimulation and that TRIM56 overexpression also promoted activation of NF-κB by poly-I:C but not that by TNF-α or IL-1β, consistent with a specific effect on TRIF prior to the bifurcation of NF-κB and IRF3. Using transient transfection and Tet-regulated cell lines expressing various TRIM56 mutants, we demonstrated the Coiled-coil domain and a segment spanning residues ∼434-610, but not the B-box or residues 355-433, were required for TRIM56 augmentation of TLR3 signaling. Moreover, alanine substitution at each putative phosphorylation site, Ser471, Ser475, and Ser710, abrogated TRIM56 function. Concordantly, mutants bearing Ser471Ala, Ser475Ala, or Ser710Ala, or lacking the Coiled-coil domain, all lost the capacity to enhance poly-I:C-induced establishment of an antiviral state. Furthermore, the Ser710Ala mutation disrupted the TRIM56-TRIF association. Using phospho-specific antibodies, we detected biphasic phosphorylation of TRIM56 at Ser471 and Ser475 following TLR3 stimulation, with the early phase occurring at ∼0.5 to 1 h, prior to IRF3 phosphorylation. Together, these data reveal novel molecular details critical for the TRIM56 augmentation of TLR3-dependent antiviral response and highlight important roles for TRIM56 scaffolding and phosphorylation.

HDAC5 enhances IRF3 activation and is targeted for degradation by protein C6 from orthopoxviruses including Monkeypox virus and Variola virus

Histone deacetylases (HDACs) regulate gene expression and innate immunity. Previously, we showed that HDAC5 is degraded during Vaccinia virus (VACV) infection and is a restriction factor for VACV and herpes simplex virus type 1. Here, we report that HDAC5 promotes interferon regulatory factor 3 (IRF3) activation downstream of Toll-IL-1 receptor (TIR) domain-containing adaptor molecule-1 or Sendai virus-mediated stimulation without requiring HDAC activity. Loss of HDAC5-mediated IRF3 activation is restored by re-introduction of HDAC5 but not HDAC1 or HDAC4. The antiviral activity of HDAC5 is antagonized by VACV protein C6 and orthologs from the orthopoxviruses cowpox, rabbitpox, camelpox, monkeypox, and variola. Infection by many of these viruses induces proteasomal degradation of HDAC5, and expression of C6 alone can induce HDAC5 degradation. Mechanistically, C6 binds to the dimerization domain of HDAC5 and prevents homodimerization and heterodimerization with HDAC4. Overall, this study describes HDAC5 as a positive regulator of IRF3 activation and provides mechanistic insight into how the poxviral protein C6 binds to HDAC5 to antagonize its function.

Foot-and-mouth disease virus VP1 degrades YTHDF2 through autophagy to regulate IRF3 activity for viral replication

Many viruses, including foot-and-mouth disease virus (FMDV), can promote the degradation of host proteins through macroautophagy/autophagy, thereby promoting viral replication. However, the regulatory mechanism between autophagy and innate immune responses is not fully understood during FMDV infection. Here, we found that the host GTPBP4/NOG1 (GTP binding protein 4) is a negative regulator of innate immune responses. GTPBP4 deficiency promotes the antiviral innate immune response, resulting in the ability of GTPBP4 to promote FMDV replication. Meanwhile, GTPBP4-deficient mice are more resistant to FMDV infection. To antagonize the host's antiviral immunity, FMDV structural protein VP1 promotes the expression of GTPBP4, and the 209th site of VP1 is responsible for this effect. Mechanically, FMDV VP1 promotes autophagy during virus infection and interacts with and degrades YTHDF2 (YTH N6-methyladenosine RNA binding protein F2) in an AKT-MTOR-dependent autophagy pathway, resulting in an increase in GTPBP4 mRNA and protein levels. Increased GTPBP4 inhibits IRF3 binding to the Ifnb/Ifn-β promoter, suppressing FMDV-induced type I interferon production. In conclusion, our study revealed an underlying mechanism of how VP1 negatively regulates innate immunity through the autophagy pathway, which would contribute to understanding the negative regulation of host innate immune responses and the function of GTPBP4 and YTHDF2 during FMDV infection.Abbreviation: 3-MA:3-methyladenine; ACTB: actin beta; ATG: autophagy related; ChIP:chromatin immunoprecipitation; CQ: chloroquine; DAPI:4',6-diamidino-2-phenylindole; dpi: days post-infection; EV71:enterovirus 71; FMDV: foot-and-mouth disease virus; GTPBP4/NOG1: GTPbinding protein 4; HIF1A: hypoxia inducible factor 1 subunit alpha;hpt:hours post-transfection; IFNB/IFN-β:interferon beta; IRF3: interferon regulatory factor 3; MAP1LC3/LC3:microtubule associated protein 1 light chain 3; MAVS: mitochondriaantiviral signaling protein; MOI: multiplicity of infection; MTOR:mechanistic target of rapamycin kinase; m6A: N(6)-methyladenosine;qPCR:quantitativePCR; SIRT3:sirtuin 3; SQSTM1/p62: sequestosome 1; STING1: stimulator ofinterferon response cGAMP interactor 1; siRNA: small interfering RNA;TBK1: TANK binding kinase 1; TCID50:50% tissue culture infectious doses; ULK1: unc-51 like autophagyactivating kinase 1; UTR: untranslated region; WT: wild type; YTHDF2:YTH N6-methyladenosine RNA binding protein F2.

The transcription factor NF-κB orchestrates nucleosome remodeling during the primary response to Toll-like receptor 4 signaling

Inducible nucleosome remodeling at hundreds of latent enhancers and several promoters shapes the transcriptional response to Toll-like receptor 4 (TLR4) signaling in macrophages. We aimed to define the identities of the transcription factors that promote TLR-induced remodeling. An analysis strategy based on ATAC-seq and single-cell ATAC-seq that enriched for genomic regions most likely to undergo remodeling revealed that the transcription factor nuclear factor κB (NF-κB) bound to all high-confidence peaks marking remodeling during the primary response to the TLR4 ligand, lipid A. Deletion of NF-κB subunits RelA and c-Rel resulted in the loss of remodeling at high-confidence ATAC-seq peaks, and CRISPR-Cas9 mutagenesis of NF-κB-binding motifs impaired remodeling. Remodeling selectivity at defined regions was conferred by collaboration with other inducible factors, including IRF3- and MAP-kinase-induced factors. Thus, NF-κB is unique among TLR4-activated transcription factors in its broad contribution to inducible nucleosome remodeling, alongside its ability to activate poised enhancers and promoters assembled into open chromatin.

IRF3 regulates neuroinflammatory responses and the expression of genes associated with Alzheimer's disease

The pathological role of interferon signaling is emerging in neuroinflammatory disorders, yet, the specific role of Interferon Regulatory Factor 3 (IRF3) in neuroinflammation remains poorly understood. Here, we show that global IRF3 deficiency delays TLR4-mediated signaling in microglia and attenuates the hallmark features of LPS-induced inflammation such as cytokine release, microglial reactivity, astrocyte activation, myeloid cell infiltration, and inflammasome activation. Moreover, expression of a constitutively active IRF3 (S388D/S390D:IRF3-2D) in microglia induces a transcriptional program reminiscent of the Activated Response Microglia and the expression of genes associated with Alzheimer's Disease, notably apolipoprotein-e. Lastly, using bulk-RNAseq of IRF3-2D brain myeloid cells, we identified Z-DNA binding protein-1 as a target of IRF3 that is relevant across various neuroinflammatory disorders. Together, our results identify IRF3 as an important regulator of LPS-mediated neuroinflammatory responses and highlight IRF3 as a central regulator of disease-specific gene activation in different neuroinflammatory diseases.

NDV inhibited IFN-β secretion through impeding CHCHD10-mediated mitochondrial fusion to promote viral proliferation

Newcastle disease virus (NDV) is an RNA virus that can promote its own replication through the inhibition of cellular mitochondrial fusion. The proteins involved in mitochondrial fusion, namely mitofusin 1 (Mfn1) and optic atrophy 1 (OPA1) are associated with interferon-beta (IFN-β) secretion during NDV infection. However, the precise mechanism by which NDV modulates the Mfn1-mediated or OPA1-mediated fusion of mitochondria, thereby impacting IFN-β, remains elusive. This study revealed that the downregulation of the mitochondrial protein known as coiled-coil-helix-coiled-coil-helix domain containing 10 (CHCHD10) exerts a negative regulatory effect on OPA1 and Mfn1 in human lung adenocarcinoma (A549) cells during the late stage of NDV infection. This reduction in CHCHD10 expression impeded cellular mitochondrial fusion, subsequently leading to a decline in the activation of interferon regulatory factor 3 (IRF3) and nuclear factor kappa B (NF-κB), ultimately resulting in diminished secretion of IFN-β. In contrast, the overexpression of CHCHD10 alleviated infection-induced detrimental effect in mitochondrial fusion, thereby impeding viral proliferation. In summary, NDV enhances its replication by inhibiting the CHCHD10 protein, which impedes mitochondrial fusion and suppresses IFN-β production through the activation of IRF3 and NF-κB.

Calcitriol attenuates poly(I:C)-induced lung injury in obese mice via modulating toll-like receptor 3- and renin-angiotensin system-associated signal pathways

This study investigated the effects of calcitriol on polyinosinic-polycytidylic acid (poly(I:C))-induced acute lung injury (ALI) and its association with Toll-like receptor 3 (TLR3) and renin-angiotensin system (RAS) signal pathways in obese mice. Normal mice were fed a high-fat diet to induce obesity. Obese mice were divided into four groups: SS group, intratracheally instilled with saline and intravenous (IV) saline injection via tail vein; SD group, instilled with saline and IV calcitriol injection; PS group, instilled with poly(I:C) and IV saline injection; and PD group, instilled with poly(I:C) and IV calcitriol injection. All mice were sacrificed 12 or 24 h after poly(I:C) stimulation. The results showed that poly(I:C) instillation led to increased production of systemic inflammatory cytokines. In the lungs, the population of macrophages decreased, while more neutrophils were recruited. TLR3-associated genes including IRF3, nuclear factor-κB, interferon-β and phosphorylated IRF3 expression levels, were upregulated. The RAS-associated AT1R and ACE2 protein levels increased, whereas AT2R, Ang(1-7), and MasR levels decreased. Also, reduced tight junction (TJ) proteins and elevated lipid peroxide levels were observed 24 h after poly(I:C) stimulation. Compared to the PS group, the PD group exhibited reduced systemic and lung inflammatory cytokine levels, increased macrophage while decreased neutrophil percentages, downregulated TLR3-associated genes and phosphorylated IRF3, and polarized toward the RAS-AT2R/Ang(1-7)/MasR pathway in the lungs. Higher lung TJ levels and lower injury scores were also noted. These findings suggest that calcitriol treatment after poly(I:C) instillation alleviated ALI in obese mice possibly by downregulating TLR3 expression and tending toward the RAS-associated anti-inflammatory pathway.

The African Swine Fever Virus Virulence Determinant DP96R Suppresses Type I IFN Production Targeting IRF3

DP96R of African swine fever virus (ASFV), also known as uridine kinase (UK), encodes a virulence-associated protein. Previous studies have examined DP96R along with other genes in an effort to create live attenuated vaccines. While experiments in pigs have explored the impact of DP96R on the pathogenicity of ASFV, the precise molecular mechanism underlying this phenomenon remains unknown. Here, we describe a novel molecular mechanism by which DP96R suppresses interferon regulator factor-3 (IRF3)-mediated antiviral immune responses. DP96R interacts with a crucial karyopherin (KPNA) binding site within IRF3, disrupting the KPNA-IRF3 interaction and consequently impeding the translocation of IRF3 to the nucleus. Under this mechanistic basis, the ectopic expression of DP96R enhances the replication of DNA and RNA viruses by inhibiting the production of IFNs, whereas DP96R knock-down resulted in higher IFNs and IFN-stimulated gene (ISG) transcription during ASFV infection. Collectively, these findings underscore the pivotal role of DP96R in inhibiting IFN responses and increase our understanding of the relationship between DP96R and the virulence of ASFV.

Singapore grouper iridovirus VP20 interacts with grouper TBK1 and IRF3 to attenuate the interferon immune response

Singapore grouper iridovirus (SGIV), belonging to genus Ranavirus, family Iridoviridae, is a highly pathogenic agent and causes heavy economic losses in the global grouper aquaculture. Recent studies demonstrated that SGIV infection attenuated antiviral immune and inflammatory response induced by poly (I:C) in vitro. However, little was known about the potential functions of the immune regulatory proteins encoded by SGIV. Here, we identified the detailed roles of VP20 and clarified the potential mechanism underlying its immune regulatory function during SGIV infection. Our results showed that VP20 was an IE gene, and partially co-localized with Golgi apparatus and lysosomes in grouper cells. Overexpression of VP20 enhanced SGIV replication, demonstrated by the increase in the transcription levels of viral core genes and the protein synthesis of MCP. Reporter gene assays showed that SGIV VP20 overexpression significantly reduced the IFN promoter activity induced by poly (I:C), grouper stimulator of interferon genes (EcSTING) and TANK-binding kinase 1 (EcTBK1). Consistently, the transcription levels of IFN related genes were significantly decreased in VP20 overexpressing cells compared to those in control cells. Co-IP assay and confocal microscopy observations indicated that VP20 co-localized and interacted with EcTBK1 and EcIRF3, but not EcSTING. In addition, VP20 was able to degrade EcIRF3 and attenuate the antiviral action of EcIRF3, while had no effect on EcTBK1. Together, SGIV VP20 was speculated to promote viral replication through attenuating the IFN response mediated by TBK1-IRF3 in vitro. Our findings provided new insights into the immune regulatory function of SGIV encoded unknown proteins.

Functional characterization of RIP2 in large yellow croaker (Larimichthys crocea), a protein involved in the host antiviral responses via NF-κΒ, IRF3/7 related signaling

As an adaptor protein functions essentially in the activation of NF-κΒ and MAPK signaling pathways mediated by NOD1 and NOD2, RIP2 plays important roles in the host innate immune responses. In the present study, the RIP2 ortholog termed Lc-RIP2 was identified and characterized in large yellow croaker (Larimichthys crocea). It was revealed that Lc-RIP2 is consisted of an open reading frame (ORF) of 1695 bp, encoding a protein of 564 aa, with an N-terminal kinase domain and a C-terminal caspase activation and recruitment domain (CARD). Subcellular localization assays demonstrated that Lc-RIP2 was a cytosolic protein, which was broadly distributed in the examined tissues/organs, and could be induced in response to poly I:C, LPS, PGN, and Pseudomonas plecoglossicida stimulations in vivo according to qRT-PCR analysis. Notably, Lc-RIP2 overexpression in vitro was sufficient to abolish SVCV proliferation in EPC cells, and could significantly induce the activation of NF-κB, IRF3, IRF7, and IFN1 promoters. In addition, luciferase assays found that Lc-RIP2 could cooperate with Lc-MAVS, Lc-TRAF3, Lc-TRAF6, Lc-IRF3, and Lc-IRF7 in NF-κB activation, associate with Lc-TRIF, Lc-MAVS, Lc-TRAF3, Lc-IRF3, and Lc-IRF7 in IRF3 activation, enhance Lc-TRIF, Lc-MAVS, Lc-TRAF3, and Lc-TRAF6 mediated IRF7 activation, and Lc-IRF3 mediated IFN1 activation, whereas suppress NF-κB activation when co-expressed with Lc-TRIF. Co-immunoprecipitation (Co-IP) assays also demonstrated that Lc-RIP2 interacts separately with Lc-TRIF, Lc-MAVS, Lc-TRAF3, Lc-TRAF6, Lc-IRF3, and Lc-IRF7. It is thus collectively indicated that Lc-RIP2 function dominantly in the regulation of the host innate immune signaling.

Interferon-Gamma-Inducible Protein 16 Inhibits Hepatocellular Carcinoma via Interferon Regulatory Factor 3 on Chemosensitivity

BACKGROUND AND AIM

Previous reports have suggested IFI16 as a tumor suppressor in hepatocellular carcinoma (HC). Nonetheless, the biological significance of IFI16 and its mechanism concerning resistance to cisplatin (DDP) in HC requires further exploration.

METHODS

Samples of tumor and corresponding para-carcinoma tissues were acquired from patients with HC. Furthermore, DDP-resistant cell lines of HC, specifically HCC, Huh7 and Hepatoblastoma, HepG3, were generated by gradually increasing the concentration of DDP. Cell apoptosis and DNA damage were evaluated by utilizing flow cytometry assay and TUNEL staining. The interaction between IFI16 and interferon regulatory factor 3 (IRF3) proteins were analyzed using Co-Immunoprecipitation (Co-IP) assay. In vivo assays were conducted by establishing HC subcutaneous xenograft tumor models.

RESULTS

The study found a reduction in IFI16 expression in both HC tissues and DDP-resistant HC cell lines. The binding of IFI16 to IRF3 regulated DNA damage-associated markers in vitro. Overexpression of IFI16 heightened the susceptibility of DDP-induced apoptosis and DNA damage, which was counteracted by IRF3 knockdown, while strengthened by IRF3 overexpression. Moreover, overexpression of IFI16 diminished in vivo DDP-resistant HC tumorigenicity.

CONCLUSION

In summary, our findings suggest that IFI16 serves as a tumor suppressor in HC by promoting DNA damage via its interaction with IRF3, thereby reversing DDP resistance.

A conserved methyltransferase active site residue of Zika virus NS5 is required for the restriction of STING activation and interferon expression

Zika virus (ZIKV) is a re-emerging RNA virus and causes major public health events due to its link to severe neurological complications in foetuses and neonates. The cGAS-STING signalling pathway regulates innate immunity and plays an important role in the invasion of DNA and RNA viruses. This study reveals a distinct mechanism by which ZIKV restricts the cGAS-STING signalling to repress IFN-β expression. ZIKV attenuates IFN-β expression induced by DNA viruses (herpes simplex virus type 1, HSV-1) or two double-stranded DNAs (dsDNA90 and HSV120) in mouse embryonic fibroblasts (MEFs). Notably, ZIKV NS5, the viral RNA-dependent RNA polymerase, was responsible for the repression of IFN-β. NS5 interacts with STING in the cytoplasm, suppresses IRF3 phosphorylation and nucleus localization and promotes the cleavage of STING K48-linked polyubiquitination. Furthermore, the NS5 methyltransferase (MTase) domain interacts with STING to restrict STING-induced IFN-β expression. Interestingly, point mutation analyses of conserved methyltransferase active site residue D146 indicate that it is critical for repressing IFN-β expression induced by STING stimulation in cGAS-STING signalling.

Histone H1.2 Inhibited EMCV Replication through Enhancing MDA5-Mediated IFN-β Signaling Pathway

Histone H1.2 is a member of the linker histone family, which plays extensive and crucial roles not only in the regulation of chromatin dynamics, cell cycle, and cell apoptosis, but also in viral diseases and innate immunity response. Recently, it was discovered that H1.2 regulates interferon-β and inhibits influenza virus replication, whereas its role in other viral infections is poorly reported. Here, we first found the up-regulation of H1.2 during Encephalomyocarditis virus (EMCV) infection, implying that H1.2 was involved in EMCV infection. Overexpression of H1.2 inhibited EMCV proliferation, whereas knockdown of H1.2 showed a significant promotion of virus infection in HEK293T cells. Moreover, we demonstrated that overexpression of H1.2 remarkably enhanced the production of EMCV-induced type I interferon, which may be the crucial factor for H1.2 proliferation-inhibitory effects. We further found that H1.2 up-regulated the expression of the proteins of the MDA5 signaling pathway and interacted with MDA5 and IRF3 in EMCV infection. Further, we demonstrated that H1.2 facilitated EMCV-induced phosphorylation and nuclear translocation of IRF3. Briefly, our research uncovers the mechanism of H1.2 negatively regulating EMCV replication and provides new insight into antiviral targets for EMCV.

Retinoic Acid-Mediated Inhibition of Mouse Coronavirus Replication Is Dependent on IRF3 and CaMKK

The ongoing COVID-19 pandemic has revealed the shortfalls in our understanding of how to treat coronavirus infections. With almost 7 million case fatalities of COVID-19 globally, the catalog of FDA-approved antiviral therapeutics is limited compared to other medications, such as antibiotics. All-trans retinoic acid (RA), or activated vitamin A, has been studied as a potential therapeutic against coronavirus infection because of its antiviral properties. Due to its impact on different signaling pathways, RA's mechanism of action during coronavirus infection has not been thoroughly described. To determine RA's mechanism of action, we examined its effect against a mouse coronavirus, mouse hepatitis virus strain A59 (MHV). We demonstrated that RA significantly decreased viral titers in infected mouse L929 fibroblasts and RAW 264.7 macrophages. The reduced viral titers were associated with a corresponding decrease in MHV nucleocapsid protein expression. Using interferon regulatory factor 3 (IRF3) knockout RAW 264.7 cells, we demonstrated that RA-induced suppression of MHV required IRF3 activity. RNA-seq analysis of wildtype and IRF3 knockout RAW cells showed that RA upregulated calcium/calmodulin (CaM) signaling proteins, such as CaM kinase kinase 1 (CaMKK1). When treated with a CaMKK inhibitor, RA was unable to upregulate IRF activation during MHV infection. In conclusion, our results demonstrate that RA-induced protection against coronavirus infection depends on IRF3 and CaMKK.

Hepatocyte GPCR signaling regulates IRF3 to control hepatic stellate cell transdifferentiation

BACKGROUND

Interferon Regulatory Factor 3 (IRF3) is a transcription factor that plays a crucial role in the innate immune response by recognizing and responding to foreign antigens. Recently, its roles in sterile conditions are being studied, as in metabolic and fibrotic diseases. However, the search on the upstream regulator for efficient pharmacological targeting is yet to be fully explored. Here, we show that G protein-coupled receptors (GPCRs) can regulate IRF3 phosphorylation through of GPCR-Gα protein interaction.

RESULTS

IRF3 and target genes were strongly associated with fibrosis markers in liver fibrosis patients and models. Conditioned media from MIHA hepatocytes overexpressing IRF3 induced fibrogenic activation of LX-2 hepatic stellate cells (HSCs). In an overexpression library screening using active mutant Gα subunits and Phos-tag immunoblotting, Gαs was found out to strongly phosphorylate IRF3. Stimulation of Gαs by glucagon or epinephrine or by Gαs-specific designed GPCR phosphorylated IRF3. Protein kinase A (PKA) signaling was primarily responsible for IRF3 phosphorylation and Interleukin 33 (IL-33) expression downstream of Gαs. PKA phosphorylated IRF3 on a previously unrecognized residue and did not require reported upstream kinases such as TANK-binding kinase 1 (TBK1). Activation of Gαs signaling by glucagon induced IL-33 production in hepatocytes. Conditioned media from the hepatocytes activated HSCs, as indicated by α-SMA and COL1A1 expression, and this was reversed by pre-treatment of the media with IL-33 neutralizing antibody.

CONCLUSIONS

Gαs-coupled GPCR signaling increases IRF3 phosphorylation through cAMP-mediated activation of PKA. This leads to an increase of IL-33 expression, which further contributes to HSC activation. Our findings that hepatocyte GPCR signaling regulates IRF3 to control hepatic stellate cell transdifferentiation provides an insight for understanding the complex intercellular communication during liver fibrosis progression and suggests therapeutic opportunities for the disease. Video Abstract.

RNF5: inhibiting antiviral immunity and shaping virus life cycle

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.

Knockout of IRF3 and IRF7 genes by CRISPR/Cas9 technology enhances porcine virus replication in the swine testicular (ST) cell line

Antiviral vaccines for pig diseases are essential to prevent epidemic outbreaks. However, their production is often hindered by inefficient manufacturing processes that yield lower quantities of the vaccine. To accelerate the progress of various areas of bioproduction, we have considered the necessity of enhancing viral replication efficiency by optimizing ST (swine testicular) cell lines that are commonly utilized in virus manufacturing. CRISPR/Cas9 gene-editing technology were utilized to create IRF3 or IRF7 knockout cell lines that facilitate high-titer viral stock production. Compared to the parental cell lines, the ST IRF3/7 KO cell line displayed a compromised antiviral response to a panel of viruses (Porcine epidemic diarrhea virus, Senecavirus A, Parainfluenza virus 5, and Getah virus), as evidenced by decreased expression of interferon and certain antiviral factors. The inhibition of these responses led to heightened viral replication and increased cytopathic effects, ultimately promoting apoptosis. As a result, the development of these cell lines offers a more efficient approach for biopharmaceutical companies to boost their virus production and reduce associated costs.

Adenovirus E1A binding to DCAF10 targets proteasomal degradation of RUVBL1/2 AAA+ ATPases required for quaternary assembly of multiprotein machines, innate immunity, and responses to metabolic stress

IMPORTANCE

Inactivation of EP300/CREBB paralogous cellular lysine acetyltransferases (KATs) during the early phase of infection is a consistent feature of DNA viruses. The cell responds by stabilizing transcription factor IRF3 which activates transcription of scores of interferon-stimulated genes (ISGs), inhibiting viral replication. Human respiratory adenoviruses counter this by assembling a CUL4-based ubiquitin ligase complex that polyubiquitinylates RUVBL1 and 2 inducing their proteasomal degradation. This inhibits accumulation of active IRF3 and the expression of anti-viral ISGs, allowing replication of the respiratory HAdVs in the face of inhibition of EP300/CBEBBP KAT activity by the N-terminal region of E1A.

Glabridin improves autoimmune disease in Trex1-deficient mice by reducing type I interferon production

BACKGROUND

The cGAS-STING signaling pathway is an essential section of the natural immune system. In recent years, an increasing number of studies have shown a strong link between abnormal activation of the cGAS-STING signaling pathway, a natural immune pathway mediated by the nucleic acid receptor cGAS, and the development and progression of autoimmune diseases. Therefore, it is important to identify an effective compound to specifically downregulate this pathway for disease.

METHODS

The effect of Glabridin (Glab) was investigated in BMDMs and Peripheral blood mononuclear cell (PBMC) by establishing an in vitro model of cGAS-STING signaling pathway activation. An activation model stimulated by DMXAA was also established in mice to study the effect of Glab. On the other hand, we investigated the possible mechanism of action of Glab and the effect of Glab on Trex1-deficient mice.

RESULTS

In this research, we report that Glab, a major component of licorice, specifically inhibits the cGAS-STING signaling pathway by inhibiting the level of type I interferon and inflammatory cytokines (IL-6 and TNF-α). In addition, Glab has a therapeutic effect on innate immune diseases caused by abnormal cytoplasmic DNA in Trex1-deficient mice. Mechanistically, Glab can specifically inhibit the interaction of STING with IRF3.

CONCLUSION

Glab is a specific inhibitor of the cGAS-STING signaling pathway and may be used in the clinical therapy of cGAS-STING pathway-mediated autoimmune diseases.

Epigenetic switch reshapes epithelial progenitor cell signatures and drives inflammatory pathogenesis in hidradenitis suppurativa

Hidradenitis suppurativa (HS) is a complex inflammatory skin disease with undefined mechanistic underpinnings. Here, we investigated HS epithelial cells and demonstrated that HS basal progenitors modulate their lineage restriction and give rise to pathogenic keratinocyte clones, resulting in epidermal hyperproliferation and dysregulated inflammation in HS. When comparing to healthy epithelial stem/progenitor cells, in HS, we identified changes in gene signatures that revolve around the mitotic cell cycle, DNA damage response and repair, as well as cell-cell adhesion and chromatin remodeling. By reconstructing cell differentiation trajectory and CellChat modeling, we identified a keratinocyte population specific to HS. This population is marked by S100A7/8/9 and KRT6 family members, triggering IL1, IL10, and complement inflammatory cascades. These signals, along with HS-specific proinflammatory cytokines and chemokines, contribute to the recruitment of certain immune cells during the disease progression. Furthermore, we revealed a previously uncharacterized role of S100A8 in regulating the local chromatin environment of target loci in HS keratinocytes. Through the integration of genomic and epigenomic datasets, we identified genome-wide chromatin rewiring alongside the switch of transcription factors (TFs), which mediated HS transcriptional profiles. Importantly, we identified numerous clinically relevant inflammatory enhancers and their coordinated TFs in HS basal CD49fhigh cells. The disruption of the S100A enhancer using the CRISPR/Cas9-mediated approach or the pharmacological inhibition of the interferon regulatory transcription factor 3 (IRF3) efficiently reduced the production of HS-associated inflammatory regulators. Our study not only uncovers the plasticity of epidermal progenitor cells in HS but also elucidates the epigenetic mechanisms underlying HS pathogenesis.

ZBP1 mediates the progression of Alzheimer's disease via pyroptosis by regulating IRF3

Alzheimer's disease (AD) is one of the leading causes of death throughout the world. Z-DNA binding protein 1 (ZBP1), a DNA-related gene, is associated with inflammation, and its expression is altered in AD brain. We aimed to elucidate the exact role of ZBP1 in AD development and its potential regulatory mechanism. First, we constructed both in vivo and in vitro models of AD and investigated the ZBP1 expression profile. A loss-of-function assay was performed by transfecting lentivirus carrying ZBP1 short hairpin RNA (shRNA). By evaluating cell death, oxidative stress, inflammation response and pyroptosis, the function of ZBP1 was validated. Finally, the correlation between ZBP1 and interferon regulatory factor 3 (IRF3) was verified. We also performed rescue experiments to validate the crucial role of IRF3 in ZBP1-mediated AD progression. According to our results, ZBP1 was upregulated in AD rat tissue and AD neurons. Silencing ZBP1 dramatically decreased cell injury, oxidative stress and inflammation in AD neurons and improved the cognitive function of AD rats. Additionally, IRF3 expression and phosphorylation were significantly elevated during AD development and positively correlated with ZBP1. Taken together, silencing ZBP1 suppressed cell injury and pyroptosis of AD neurons and improved cognitive function of AD rats via inhibiting IRF3. These findings might provide a novel insight for AD target diagnosis and therapy.

Bovine herpesvirus-1 gE protein inhibits IFN-β production to enhance replication by promoting MAVS ubiquitination and interfering with the interaction between IRF3 and CBP/p300

Bovine herpesvirus-1 (BoHV-1) can infect all breeds of cattle and cause respiratory and genital tract diseases. In the process of viral infection, viruses can use their own proteins to suppress the innate immunity of the host and promote its replication; however, the mechanism by which BoHV-1 evades the innate immune response is not fully understood. In this study, we found that rabbits inoculated with the live gene deletion vaccine BoHV-1-△gI/gE/TK generated higher interferon-β (IFN-β) production in the serum, liver, lung and kidney than rabbits inoculated with wt BoHV-1, which led to milder lesions in the lung and kidney. We performed gene deletion and ectopic expression experiments on viral proteins and found that gE was the major protein that inhibited IFN-β expression. Further studies showed that MAVS and IRF3 were the targets of gE, and the specific mechanism was that gE inhibited IFN-β production by promoting MAVS ubiquitination and interfering with the interaction between IRF3 and CBP/p300. These results suggest a new way of BoHV-1 inhibition of IFN-β production to evade the host innate immunity.

Interferon induction by STING requires its translocation to the late endosomes

To combat microbial infections, mammalian cells use a variety of innate immune response pathways to induce synthesis of anti-microbial proteins. The cGAS/STING pathway recognizes cytoplasmic viral or cellular DNA to elicit signals that lead to type I interferon and other cytokine synthesis. cGAMP, synthesized by DNA-activated cGAS, activates the ER-associated protein, STING, which oligomerizes and translocates to other intracellular membrane compartments to trigger different branches of signaling. We have reported that, in the ER, EGFR-mediated phosphorylation of Tyr245 of STING is required for its transit to the late endosomes, where it recruits and activates the transcription factor IRF3 required for IFN induction. In the current study, we inquired whether STING Tyr245 phosphorylation per se or STING's location in the late endosomes was critical for its ability to recruit IRF3 and induce IFN. Using pharmacological inhibitors or genetic ablation of proteins that are essential for specific steps of STING trafficking, we demonstrated that the presence of STING in the late endosomal membranes, even without Tyr245 phosphorylation, was sufficient for IRF3-mediated IFN induction.

African swine fever virus S273R protein antagonizes type I interferon production by interfering with TBK1 and IRF3 interaction

African swine fever (ASF) is originally reported in East Africa as an acute hemorrhagic fever. African swine fever virus (ASFV) is a giant and complex DNA virus with icosahedral structure and encodes a variety of virulence factors to resist host innate immune response. S273R protein (pS273R), as a SUMO-1 specific cysteine protease, can affect viral packaging by cutting polymeric proteins. In this study, we found that pS273R was an important antagonistic viral factor that suppressed cGAS-STING-mediated type I interferon (IFN-I) production. A detailed analysis showed that pS273R inhibited IFN-I production by interacting with interferon regulatory factor 3 (IRF3). Subsequently, we showed that pS273R disrupted the association between TBK1 and IRF3, leading to the repressed IRF3 phosphorylation and dimerization. Deletion and point mutation analysis verified that pS273R impaired IFN-I production independent of its cysteine protease activity. These findings will help us further understand ASFV pathogenesis.

Molecular and functional characterization of golden pompano (Trachinotus blochii) TBK1 on IFN regulation

The golden pompano (Trachinotus blochii), a pivotal commercial marine species in China, has gained significant popularity worldwide. However, accompanied with rapid growth and high density aquaculture, golden pompano has been seriously threatened by Nervous necrosis virus (NNV), while its molecular biology research regarding the innate immune system remains unexplored, which is crucial for understanding the activation of interferon (IFN) production and antiviral responses. In this study, we aimed to identify the characterization and function of golden pompano TANK-binding kinase 1 (gpTBK1), thereby providing evidence of the conservation of this classical factor in the RLR pathway among marine fish. Initially, we found the expression of gpTBK1 upregulation in diseased golden pompano with NNV infection and we successfully cloned the full-length open reading frame (ORF) of gpTBK1, consisting of 2172 nucleotides encoding 723 amino acids, from the head kidney. Subsequent analysis of the amino acid sequence revealed homology between gpTBK1 and other fish TBK1 proteins, with conserved N-terminal Serine/Threonine protein kinases catalytic domain (S_TKc) and C-terminal coiled coil domain (CCD). Moreover, the expression pattern showed that gpTBK1 exhibited ubiquitous expression across all evaluated tissues. Furthermore, functional identification experiments indicated that gpTBK1 activated interferon promoters' activity in golden pompano and induced the expression of downstream IFN-stimulated genes (ISGs). Notably, gpTBK1 was found to co-localize and interact with gpIRF3 in the cytoplasm. Collectively, these data provide a comprehensive analysis of the characterization and functional role of gpTBK1 in promoting interferon production. This research may facilitate the further study of the innate antiviral response, particularly the anti-NNV mechanisms, in golden pompano.

Mutant p53R211* ameliorates inflammatory arthritis in AIA rats via inhibition of TBK1-IRF3 innate immune response

BACKGROUND

Rheumatoid arthritis (RA) is an autoimmune inflammation disease characterized by imbalance of immune homeostasis. p53 mutants are commonly described as the guardian of cancer cells by conferring them drug-resistance and immune evasion. Importantly, p53 mutations have also been identified in RA patients, and this prompts the investigation of its role in RA pathogenesis.

METHODS

The cytotoxicity of disease-modifying anti-rheumatic drugs (DMARDs) against p53 wild-type (WT)/mutant-transfected RA fibroblast-like synoviocytes (RAFLSs) was evaluated by MTT assay. Adeno-associated virus (AAV) was employed to establish p53 WT/R211* adjuvant-induced arthritis (AIA) rat model. The arthritic condition of rats was assessed by various parameters such as micro-CT analysis. Knee joint samples were isolated for total RNA sequencing analysis. The expressions of cytokines and immune-related genes were examined by qPCR, ELISA assay and immunofluorescence. The mechanistic pathway was determined by immunoprecipitation and Western blotting in vitro and in vivo.

RESULTS

Among p53 mutants, p53R213* exhibited remarkable DMARD-resistance in RAFLSs. However, AAV-induced p53R211* overexpression ameliorated inflammatory arthritis in AIA rats without Methotrexate (MTX)-resistance, and our results discovered the immunomodulatory effect of p53R211* via suppression of T-cell activation and T helper 17 cell (Th17) infiltration in rat joint, and finally downregulated expressions of pro-inflammatory cytokines. Total RNA sequencing analysis identified the correlation of p53R211* with immune-related pathways. Further mechanistic studies revealed that p53R213*/R211* instead of wild-type p53 interacted with TANK-binding kinase 1 (TBK1) and suppressed the innate immune TBK1-Interferon regulatory factor 3 (IRF3)-Stimulator of interferon genes (STING) cascade.

CONCLUSIONS

This study unravels the role of p53R213* mutant in RA pathogenesis, and identifies TBK1 as a potential anti-inflammatory target.

Alternative splicing of IRF3 plays an important role in the development of hepatocarcinoma

Alternative splicing is a process causing mRNA translation to produce different proteins, and it is crucial for the development of tumours. In this study, we constructed a prognostic model related to alternative splicing events in hepatocarcinoma using bioinformatics analysis, including the alternative splicing of CSAD, AFMID, ZDHHC16, and IRF3. The model is an independent prognostic factor and can accurately predict a patient's prognosis. IRF3 is a transcription factor related to the immune response. Its alternative splicing can affect the expression of various genes related to prognosis and plays an essential role in the tumour microenvironment. We also verified the expression of IRF3 exon skipping isoform in hepatocarcinoma at the mRNA level. In conclusion, we discovered that the alternative splicing of IRF3 is essential for the development of hepatocarcinoma. This study provides new insight into the development of treatments for hepatocarcinoma.

Smyd3 negatively regulates the anti-viral pathway by promoting TAK1 degradation in teleost fish

IMPORTANCE

In this study, we have found that the existence of Smyd3 promoted the replication of SCRV. Additionally, we report that Smyd3 negatively regulates the NF-κB and IRF3 signaling pathway by facilitating the degradation of TAK1 in fish. Our findings suggest that Smyd3 interacts with TAK1. Further investigations have revealed that Smyd3 specifically mediates K48-linked ubiquitination of TAK1 and enhances TAK1 degradation, resulting in a significant inhibition of the NF-κB and IRF3 signaling pathway. These results not only contribute to the advancement of fish anti-viral immunity but also provide new evidence for understanding the mechanism of TAK1 in mammals.

Porcine promyelocytic leukemia protein isoforms suppress Japanese encephalitis virus replication in PK15 cells

BACKGROUND

Promyelocytic leukemia protein (PML) is a primary component of PML nuclear bodies (PML-NBs). PML and PML-NBs play critical roles in processes like the cell cycle, DNA damage repair, apoptosis, and the antiviral immune response. Previously, we identified five porcine PML alternative splicing variants and observed an increase in the expression of these PML isoforms following Japanese encephalitis virus (JEV) infection. In this study, we examined the functional roles of these PML isoforms in JEV infection.

METHODS

PML isoforms were either knocked down or overexpressed in PK15 cells, after which they were infected with JEV. Subsequently, we analyzed the gene expression of PML isoforms, JEV, and the interferon (IFN)-β signaling pathway using quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and Western blot. Viral titers were determined through 50% tissue culture infectious dose (TCID50) assays.

RESULTS

Our results demonstrated that the knockdown of endogenous PML promoted JEV replication, while the overexpression of PML isoforms 1, 3, 4, and 5 (PML1, PML3, PML4, and PML5) inhibited JEV replication. Further investigation revealed that PML1, PML3, PML4, and PML5 negatively regulated the expression of genes involved in the interferon (IFN)-β signaling pathway by inhibiting IFN regulatory factor 3 (IRF3) post-JEV infection.

CONCLUSIONS

These findings demonstrate that porcine PML isoforms PML1, PML3, PML4, and PML5 negatively regulate IFN-β and suppress viral replication during JEV infection. The results of this study provide insight into the functional roles of porcine PML isoforms in JEV infection and the regulation of the innate immune response.

Early enterovirus translation deficits extend viral RNA replication and elicit sustained MDA5-directed innate signaling

IMPORTANCE

Multiple pattern recognition receptors sense vRNAs and initiate downstream innate signaling: endosomal Toll-like receptors (TLRs) 3, 7, and 8 and cytoplasmic RIG-I-like receptors (RLRs) RIG-I, and MDA5. They engage distinct signaling scaffolds: mitochondrial antiviral signaling protein (RLR), MyD88, and TLR-adaptor interacting with SLC15A4 on the lysosome (TLR7 and TLR8) and toll/IL-1R domain-containing adaptor inducing IFN (TLR3). By virtue of their unusual vRNA structure and direct host cell entry path, the innate response to EVs uniquely is orchestrated by MDA5. We reported that PVSRIPO's profound attenuation and loss of cytopathogenicity triggers MDA5-directed polar TBK1-IRF3 signaling that generates priming of polyfunctional antitumor CD8+ T-cell responses and durable antitumor surveillance in vivo. Here we unraveled EV-host relations that control suppression of host type-I IFN responses and show that PVSRIPO's deficient immediate host eIF4G cleavage generates unopposed MDA5-directed downstream signaling cascades resulting in sustained type-I IFN release.

RNF138 Downregulates Antiviral Innate Immunity by Inhibiting IRF3 Activation

A viral infection activates the transcription factors IRF3 and NF-κB, which synergistically induces type I interferons (IFNs). Here, we identify the E3 ubiquitin ligase RNF138 as an important negative regulator of virus-triggered IRF3 activation and IFN-β induction. The overexpression of RNF138 inhibited the virus-induced activation of IRF3 and the transcription of the IFNB1 gene, whereas the knockout of RNF138 promoted the virus-induced activation of IRF3 and transcription of the IFNB1 gene. We further found that RNF138 promotes the ubiquitination of PTEN and subsequently inhibits PTEN interactions with IRF3, which is essential for the PTEN-mediated nuclear translocation of IRF3, thereby inhibiting IRF3 import into the nucleus. Our findings suggest that RNF138 negatively regulates virus-triggered signaling by inhibiting the interaction of PTEN with IRF3, and these data provide new insights into the molecular mechanisms of cellular antiviral responses.

Prohibitin1 facilitates viral replication by impairing the RIG-I-like receptor signaling pathway

IMPORTANCE

Type I interferon (IFN-I), produced by the innate immune system, plays an essential role in host antiviral responses. Proper regulation of IFN-I production is required for the host to balance immune responses and prevent superfluous inflammation. IFN regulatory factor 3 (IRF3) and subsequent sensors are activated by RNA virus infection to induce IFN-I production. Therefore, proper regulation of IRF3 serves as an important way to control innate immunity and viral replication. Here, we first identified Prohibitin1 (PHB1) as a negative regulator of host IFN-I innate immune responses. Mechanistically, PHB1 inhibited the nucleus import of IRF3 by impairing its binding with importin subunit alpha-1 and importin subunit alpha-5. Our study demonstrates the mechanism by which PHB1 facilitates the replication of multiple RNA viruses and provides insights into the negative regulation of host immune responses.

Liuwei Dihuang Prevents Human Umbilical Vein Endothelial Cells Senescence via the JPX-STING-IRF3 Pathway

BACKGROUND

Cellular senescence plays a crucial role in age-related diseases. Endothelial senescence is closely associated with age-related vascular disorders. This study aimed to reveal the role of traditional Chinese medicine Liuwei Dihuang (LWDH) in anti-endothelial cell senescence.

METHODS

Human umbilical vein endothelial cells (HUVECs) were exposed to LPS treatment to induce senescence. Senescence-associated β-galactosidase (SA-β-gal) positive staining, p53 and p16 expression, BrdU staining, and relative telomere length (RTL) experiments were conducted to estimate LPS-induced cellular senescence of HUVECs. Real-time qPCR analysis was performed to identify differentially expressed lncRNAs in LPS-induced senescent HUVECs before and after treatment with LWDH. Bioinformatics analysis and ChIP assay were conducted to explore the mechanism of JPX in the anti-endothelial cell aging effect of LWDH.

RESULTS

We first discovered that lncRNA JPX and STING-IRF3 pathways are involved in the process of anti-endothelial senescence of LWDH. Mechanistically, LWDH could reverse abnormally elevated JPX induced by LPS and inhibit the activation of STING, as well as the interaction between JPX and STING.

CONCLUSION

Overall, our study explores the potential therapeutic value of LWDH and provides key insights into the potential avenues for preventing and treating HUVECs senescence.

Targeting the mechanism of IRF3 in sepsis-associated acute kidney injury via the Hippo pathway

Sepsis-induced inflammatory damage and adaptive repair are critical in the pathophysiological mechanisms of acute kidney injury (AKI). Here, we investigated the role of interferon regulatory factor three (IRF3) and subsequent activation of the Hippo pathway in inflammatory damage and repair using an in vitro cell model of LPS-induced AKI. LPS caused the phosphorylation and activation of IRF3 in the early stages of sepsis, and activated IRF3 enhanced the production of type I interferon (IFN), resulting in an excessive inflammatory response. Furthermore, LPS generated considerably more inflammatory injury than intended cell death, and IRF3 activation triggered the Hippo pathway, causing a reduction in YAP, which eventually impaired proliferation and repair in surviving renal tubular epithelial cells and exacerbated the development of AKI. In conclusion, IRF3 promoted the development of sepsis-associated AKI (SAKI) by modulating the Hippo pathway.

SADS-CoV nsp1 inhibits the IFN-β production by preventing TBK1 phosphorylation and inducing CBP degradation

Swine acute diarrhea syndrome (SADS) is first reported in January 2017 in Southern China. It subsequently causes widespread outbreaks in multiple pig farms, leading to economic losses. Therefore, it is an urgent to understand the molecular mechanisms underlying the pathogenesis and immune evasion of Swine acute diarrhea syndrome coronavirus (SADS-CoV). Our research discovered that SADS-CoV inhibited the production of interferon-β (IFN-β) during viral infection. The nonstructural protein 1 (nsp1) prevented the phosphorylation of TBK1 by obstructing the interaction between TBK1 and Ub protein. Moreover, nsp1 induced the degradation of CREB-binding protein (CBP) through the proteasome-dependent pathway, thereby disrupting the IFN-β enhancer and inhibiting IFN transcription. Finally, we identified nsp1-Phe39 as the critical amino acid that downregulated IFN production. In conclusion, our findings described two mechanisms in nsp1 that inhibited IFN production and provided new insights into the evasion strategy adopted by SADS-CoV to evade host antiviral immunity.

SHIP1 modulates antimalarial immunity by bridging the crosstalk between type I IFN signaling and autophagy

Stringent control of the type I interferon (IFN-I) signaling is critical for host immune defense against infectious diseases, yet the molecular mechanisms that regulate this pathway remain elusive. Here, we show that Src homology 2 containing inositol phosphatase 1 (SHIP1) suppresses IFN-I signaling by promoting IRF3 degradation during malaria infection. Genetic ablation of Ship1 in mice leads to high levels of IFN-I and confers resistance to Plasmodium yoelii nigeriensis (P.y.) N67 infection. Mechanistically, SHIP1 promotes the selective autophagic degradation of IRF3 by enhancing K63-linked ubiquitination of IRF3 at lysine 313, which serves as a recognition signal for NDP52-mediated selective autophagic degradation. In addition, SHIP1 is downregulated by IFN-I-induced miR-155-5p upon P.y. N67 infection and severs as a feedback loop of the signaling crosstalk. This study reveals a regulatory mechanism between IFN-I signaling and autophagy, and verifies SHIP1 can be a potential target for therapeutic intervention against malaria and other infectious diseases. IMPORTANCE Malaria remains a serious disease affecting millions of people worldwide. Malaria parasite infection triggers tightly controlled type I interferon (IFN-I) signaling that plays a critical role in host innate immunity; however, the molecular mechanisms underlying the immune responses are still elusive. Here, we discover a host gene [Src homology 2-containing inositol phosphatase 1 (SHIP1)] that can regulate IFN-I signaling by modulating NDP52-mediated selective autophagic degradation of IRF3 and significantly affect parasitemia and resistance of Plasmodium-infected mice. This study identifies SHIP1 as a potential target for immunotherapies in malaria and highlights the crosstalk between IFN-I signaling and autophagy in preventing related infectious diseases. SHIP1 functions as a negative regulator during malaria infection by targeting IRF3 for autophagic degradation.

Downregulation of miR-92a in Decidual Stromal Cells Suppresses Migration Ability of Trophoblasts by Promoting Macrophage Polarization

Preeclampsia (PE) is a severe pregnancy complication that accounts for about 14% of maternal deaths. Its clinical manifestations commonly include hypertension and proteinuria. However, it is largely limited in understanding its pathogenetic mechanism. In this study, we used bioinformatics to compare differential gene expressions in decidual stromal cells from PE patients and healthy donors. The result indicated that higher levels of CCL5 and CXCL2 were expressed in decidual stromal cells of PE patients compared with healthy pregnancy. The bioinformatics analysis confirmed that decidual stromal cells derived from PE patients expressed significantly lower miR-92a compared with those derived from healthy donors. Transfection of miR-92a inhibitors upregulated IL-6, CXCL2, CXCL3, CCL5, and CXCL8 expressions in decidual stromal cells. Luciferase activity assay confirmed that miR-92a directly targeted the mRNA of IRF3 whose overexpression could promote the secretion of cytokines. The flow cytometric analysis demonstrated that M1 macrophage infiltration was higher in the placentas of PE patients than in those of healthy donors. We also observed that after transfection of miR-92a inhibitor, condition medium (CM) derived from decidual stromal cells significantly promoted M1 polarization of macrophages. In addition, the transwell migration assay and flow cytometric analysis together showed that decidual stromal cell-derived CM induced macrophages to suppress the trophoblast migration and proliferation. Taken together, our result indicates that downregulation of miR-92a in decidual stromal cells promotes the macrophage polarization and suppresses the trophoblast migration and proliferation.

Inflammatory Control of Viral Infection

Inflammatory responses during virus infection differentially impact the host. Managing inflammatory responses is essential in controlling viral infection and related diseases. Recently, we identified a cellular anti-inflammatory mechanism, RIKA (Repression of IRF3-mediated inhibition of NF-κB activity), which controls viral inflammation and pathogenesis. The RIKA function of IRF3 may be explored further in other inflammatory diseases beyond viral infection.

The Cytomegalovirus M35 Protein Directly Binds to the Interferon-β Enhancer and Modulates Transcription of Ifnb1 and Other IRF3-Driven Genes

Induction of type I interferon (IFN) gene expression is among the first lines of cellular defense a virus encounters during primary infection. We previously identified the tegument protein M35 of murine cytomegalovirus (MCMV) as an essential antagonist of this antiviral system, showing that M35 interferes with type I IFN induction downstream of pattern-recognition receptor (PRR) activation. Here, we report structural and mechanistic details of M35's function. Determination of M35's crystal structure combined with reverse genetics revealed that homodimerization is a key feature for M35's immunomodulatory activity. In electrophoretic mobility shift assays (EMSAs), purified M35 protein specifically bound to the regulatory DNA element that governs transcription of the first type I IFN gene induced in nonimmune cells, Ifnb1. DNA-binding sites of M35 overlapped with the recognition elements of interferon regulatory factor 3 (IRF3), a key transcription factor activated by PRR signaling. Chromatin immunoprecipitation (ChIP) showed reduced binding of IRF3 to the host Ifnb1 promoter in the presence of M35. We furthermore defined the IRF3-dependent and the type I IFN signaling-responsive genes in murine fibroblasts by RNA sequencing of metabolically labeled transcripts (SLAM-seq) and assessed M35's global effect on gene expression. Stable expression of M35 broadly influenced the transcriptome in untreated cells and specifically downregulated basal expression of IRF3-dependent genes. During MCMV infection, M35 impaired expression of IRF3-responsive genes aside of Ifnb1. Our results suggest that M35-DNA binding directly antagonizes gene induction mediated by IRF3 and impairs the antiviral response more broadly than formerly recognized. IMPORTANCE Replication of the ubiquitous human cytomegalovirus (HCMV) in healthy individuals mostly goes unnoticed but can impair fetal development or cause life-threatening symptoms in immunosuppressed or -deficient patients. Like other herpesviruses, CMV extensively manipulates its hosts and establishes lifelong latent infections. Murine CMV (MCMV) presents an important model system as it allows the study of CMV infection in the host organism. We previously showed that during entry into host cells, MCMV virions release the evolutionary conserved protein M35 protein to immediately dampen the antiviral type I interferon (IFN) response induced by pathogen detection. Here, we show that M35 dimers bind to regulatory DNA elements and interfere with recruitment of interferon regulatory factor 3 (IRF3), a key cellular factor for antiviral gene expression. Thereby, M35 interferes with expression of type I IFNs and other IRF3-dependent genes, reflecting the importance for herpesviruses to avoid IRF3-mediated gene induction.

Ring Finger Protein 34 Facilitates Nervous Necrosis Virus Evasion of Antiviral Innate Immunity by Targeting TBK1 and IRF3 for Ubiquitination and Degradation in Teleost Fish

Ubiquitination, as one of the most prevalent posttranslational modifications of proteins, enables a tight control of host immune responses. Many viruses hijack the host ubiquitin system to regulate host antiviral responses for their survival. Here, we found that the fish pathogen nervous necrosis virus (NNV) recruited Lateolabrax japonicus E3 ubiquitin ligase ring finger protein 34 (LjRNF34) to inhibit the RIG-I-like receptor (RLR)-mediated interferon (IFN) response via ubiquitinating Lateolabrax japonicus TANK-binding kinase 1 (LjTBK1) and interferon regulatory factor 3 (LjIRF3). Ectopic expression of LjRNF34 greatly enhanced NNV replication and prevented IFN production, while deficiency of LjRNF34 led to the opposite effect. Furthermore, LjRNF34 targeted LjTBK1 and LjIRF3 via its RING domain. Of note, the interactions between LjRNF34 and LjTBK1 or LjIRF3 were conserved in different cellular models derived from fish. Mechanically, LjRNF34 promoted K27- and K48-linked ubiquitination and degradation of LjTBK1 and LjIRF3, which in turn diminished LjTBK1-induced translocation of LjIRF3 from the cytoplasm to the nucleus. Ultimately, NNV capsid protein (CP) was found to bind with LjRNF34, CP induced LjTBK1 and LjIRF3 degradation, and IFN suppression depended on LjRNF34. Our finding demonstrates a novel mechanism by which NNV CP evaded host innate immunity via LjRNF34 and provides a potential drug target for the control of NNV infection. IMPORTANCE Ubiquitination plays an essential role in the regulation of innate immune responses to pathogens. NNV, a type of RNA virus, is the causal agent of a highly destructive disease in a variety of marine and freshwater fish. A previous study reported NNV could hijack the ubiquitin system to manipulate the host's immune responses; however, how NNV utilizes ubiquitination to facilitate its own replication is not well understood. Here, we identified a novel distinct role of E3 ubiquitin ligase LjRNF34 as an IFN antagonist to promote NNV infection. NNV capsid protein utilized LjRNF34 to target LjTBK1 and LjIRF3 for K27- and K48-linked ubiquitination and degradation. Importantly, the interactions between LjRNF34 and CP, LjTBK1, or LjIRF3 are conserved in different cellular models derived from fish, suggesting it is a general immune evasion strategy exploited by NNV to target the IFN response via RNF34.

A Golgi-resident GPR108 cooperates with E3 ubiquitin ligase Smurf1 to suppress antiviral innate immunity

The regulation of antiviral immunity is crucial in maintaining host immune homeostasis, a process that involves dynamic modulations of host organelles. The Golgi apparatus is increasingly perceived as a host organelle functioning as a critical platform for innate immunity, but the detailed mechanism by which it regulates antiviral immunity remains elusive. Here, we identify the Golgi-localized G protein-coupled receptor 108 (GPR108) as a regulator of type Ι interferon responses by targeting interferon regulatory factor 3 (IRF3). Mechanistically, GPR108 enhances the ubiquitin ligase Smad ubiquitylation regulatory factor 1 (Smurf1)-mediated K63-linked polyubiquitination of phosphorylated IRF3 for nuclear dot 10 protein 52 (NDP52)-dependent autophagic degradation, leading to suppression of antiviral immune responses against DNA or RNA viruses. Taken together, our study provides insight into the crosstalk between the Golgi apparatus and antiviral immunity via a dynamic and spatiotemporal regulation of GPR108-Smurf1 axis, thereby indicating a potential target for treating viral infection.

Strongylocentrotus nudus egg polysaccharide (SEP) suppresses HBV replication via activation of TLR4-induced immune pathway

Chronic hepatitis B virus (HBV) infection is a worldwide public health problem that causes significant liver-related morbidity and mortality. In our previous study, Strongylocentrotus nudus eggs polysaccharide (SEP), extracted from sea urchins, had immunomodulatory and antitumor effects. Whether SEP has anti-HBV activity is still obscure. This study demonstrated that SEP decreased the secretion of hepatitis B surface antigen (HBsAg) and e antigen (HBeAg), as well as the replication and transcription of HBV both in vitro and in vivo. Immunofluorescence and immunohistochemistry results showed that the level of HBV core antigen (HBcAg) was clearly reduced by SEP treatment. Mechanistically, RT-qPCR, western blot, and confocal microscopy analysis showed that SEP significantly increased the expression of toll-like receptor 4 (TLR4) and co-localization with TLR4. The downstream molecules of TLR4, including NF-κb and IRF3, were activated and the expression of IFN-β, TNF-α, IL-6, OAS, and MxA were also increased, which could suppress HBV replication. Moreover, SEP inhibited other genotypes of HBV and hepatitis C virus (HCV) replication in vitro. In summary, SEP could be investigated as a potential anti-HBV drug capable of modulating the innate immune.

Multi-functional regulation of cGAS by the nuclear localization signal2 (NLS2) motif: Nuclear localization, enzyme activity and protein degradation

Cyclic GMP-AMP synthase (cGAS), which recognizes double-stranded DNA (dsDNA) and activates the innate immune system, is mainly localized in the cytosol, but also shows nuclear localization. Here, we sought to determine the role of nuclear cGAS by mutating known nuclear localization signal (NLS) motifs in cGAS and assessing its functionality by monitoring phosphorylation of the downstream target, interferon regulatory factor-3 (IRF3). Interestingly, NLS2-mutated cGAS failed to promote phosphorylation of IRF3, reflecting the loss of its ability to produce cyclic GMP-AMP (cGAMP). We further found that insertion of an NLS from SV40 large T antigen could not restore this loss of activity, indicating that this loss was attributable to the mutation of NLS2 itself, but not dependent on the inability of cGAS to enter the nucleus. NLS2-mutant cGAS protein also showed decreased stability dependent on polyubiquitination, an effect that was independent of both its loss of catalytic function and its inability to enter into the nucleus. Collectively, these findings indicate that the NLS2 motif of cGAS is not only involved in regulating the subcellular localization of cGAS protein but also influences its stability and enzymatic activity through independent mechanisms, highlighting the novel roles of NLS2 in regulating the intracellular functions of cGAS.

Helicobacter pylori promotes gastric intestinal metaplasia through activation of IRF3-mediated kynurenine pathway

BACKGROUND

Metabolic reprogramming is a critical event for cell fate and function, making it an attractive target for clinical therapy. The function of metabolic reprogramming in Helicobacter pylori (H. pylori)-infected gastric intestinal metaplasia remained to be identified.

METHODS

Xanthurenic acid (XA) was measured in gastric cancer cells treated with H. pylori or H. pylori virulence factor, respectively, and qPCR and WB were performed to detect CDX2 and key metabolic enzymes expression. A subcellular fractionation approach, luciferase and ChIP combined with immunofluorescence were applied to reveal the mechanism underlying H. pylori mediated kynurenine pathway in intestinal metaplasia in vivo and in vitro.

RESULTS

Herein, we, for the first time, demonstrated that H. pylori contributed to gastric intestinal metaplasia characterized by enhanced Caudal-related homeobox transcription factor-2 (CDX2) and mucin2 (MUC2) expression, which was attributed to activation of kynurenine pathway. H. pylori promoted kynurenine aminotransferase II (KAT2)-mediated kynurenine pathway of tryptophan metabolism, leading to XA production, which further induced CDX2 expression in gastric epithelial cells. Mechanically, H. pylori activated cyclic guanylate adenylate synthase (cGAS)-interferon regulatory factor 3 (IRF3) pathway in gastric epithelial cells, leading to enhance IRF3 nuclear translocation and the binding of IRF3 to KAT2 promoter. Inhibition of KAT2 could significantly reverse the effect of H. pylori on CDX2 expression. Also, the rescue phenomenon was observed in gastric epithelial cells treated with H. pylori after IRF3 inhibition in vitro and in vivo. Most importantly, phospho-IRF3 was confirmed to be a clinical positive relationship with CDX2.

CONCLUSION

These finding suggested H. pylori contributed to gastric intestinal metaplasia through KAT2-mediated kynurenine pathway of tryptophan metabolism via cGAS-IRF3 signaling, targeting the kynurenine pathway could be a promising strategy to prevent gastric intestinal metaplasia caused by H. pylori infection. Video Abstract.