The E3 ubiquitin ligase RNF182 regulates the induction of innate immune response against GCRV by mediating the ubiquitination of RIG-I in grass carp (Ctenopharyngodon idella) and rare minnow (Gobiocypris rarus)

Innate immunity is the first line of antiviral or antimicrobial defence for the host. A cytoplasmic viral RNA sensor, which is known as retinoic acid-inducible gene 1 (RIG-I), makes a vital impact on the production of type I interferons (IFN) and eliminating RNA virus. This study indicated that E3 ubiquitin ligase RING finger protein 182 (RNF182) inhibited the antiviral activity of type I IFN in grass carp reovirus (GCRV)-infected cells by directly interplaying with RIG-I. The CiE3RNF182 cDNA encode a polypeptide of 158 amino acids. Cellular distribution analysis results suggested that cytoplasm was the main site of CiE3RNF182 location. Real-time quantitative PCR showed universal expression of CiE3RNF182 in all investigated tissues, with extremely high expression in liver. During virus infection, the CiE3RNF182 associates with the CiRIG-I and then induces the Lys-33-linked ubiquitin to the Lys33 residues of CiRIG-I to trigger its degradation, causing the inhibition of CiRIG-I downstream signalling. Furthermore, we obtained CRISPR/Cas9-mediated generation of E3RNF182-null rare minnows, finding that E3RNF182 deletion facilitates the survival ratio of GCRV-infected rare minnows. Additionally, the E3RNF182-/- rare minnows exhibited significantly lower relative copy number of GCRV compared to the wild-type group. In summary, our findings demonstrate the function of E3 ligase in controlling the anti-GCRV innate immunity through RIG-I in fish.

Tanshinone IIA alleviates myocarditis in Trex1-D18N lupus-like mice by inhibiting the interaction between STING and SEC24C

The cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) signaling pathway serves as a crucial component of the innate immune defense, playing a vital role in combating pathogen invasion. However, its dysregulation or abnormal activation can trigger the development of autoimmune diseases. This study demonstrated that Tanshinone IIA, a major lipid-soluble component of Salvia miltiorrhiza Bunge, can effectively inhibit the activation of the cGAS-STING signaling pathway. Mechanistically, Tanshinone IIA inhibits the transport of STING from the ER to the Golgi apparatus by weakening the interaction between STING and SEC24C, thereby preventing the activation of the cGAS-STING signaling pathway. Furthermore, Tanshinone IIA significantly ameliorated myocardial inflammation in WT and Trex1D18N/D18N mice. Our research indicates that Tanshinone IIA shows potential therapeutic value in alleviating autoimmune diseases by effectively inhibiting the abnormal activation of the cGAS-STING pathway.

STING-∆C, a novel splice isoform of STING, inhibits DNA virus-induced innate immunity and autophagy

Stimulator of interferon genes (STING) plays a critical role in the innate immune response to cytosolic DNA, primarily activating type I interferons (IFNs). Although alternative splicing is known to modulate immune pathways, the influence of STING splice isoforms requires further exploration. Here, we identified STING-∆C, a novel splice isoform of STING generated by retention of intron 6, resulting in a truncated C-terminus. While STING-∆C shares its N-terminal domain with full-length STING, it contains a unique C-terminal sequence. STING-∆C acts as a dominant negative regulator of cGAS-STING signaling pathway by suppressing cGAS-, 2'3'-cGAMP-, and STING-mediated activation of the IFN response. Gain- and loss-of-function experiments showed that STING-∆C inhibited IFN production in response to double-stranded DNA and DNA virus, including HSV-1 and HPV. Furthermore, STING-∆C promoted HSV-1 replication and reduces STING-induced autophagy. Mechanistically, STING-∆C interacts with full-length STING, preventing its oligomerization and assembly with TBK1, a vital component of the STING-TBK1-IRF3 signalsome. This interaction blocks IRF3 phosphorylation and nuclear translocation, thereby halting IFN production. STING-∆C thus represents a newly identified splice isoform that negatively regulates cGAS-STING signaling. These findings broaden our understanding of STING's regulatory mechanisms and may guide therapeutic strategies for autoimmune diseases and viral infections linked to excessive STING activation.

Metabolic remodelling produces fumarate via the aspartate-argininosuccinate shunt in macrophages as an antiviral defence

Metabolic remodelling underpins macrophage effector functions in response to various stimuli, but the mechanisms involved are unclear. Here we report that viral-infection-induced inflammatory stimulation causes a rewiring of the urea cycle and the tricarboxylic acid cycle metabolism in macrophages to form a cyclic pathway called the aspartate-argininosuccinate (AAS) shunt. Using RNA sequencing, unbiased metabolomics and stable isotope tracing, we found that fumarate generated from the AAS shunt is driven by argininosuccinate synthase (ASS1) in the cytosol and potentiates inflammatory effects. Genetic ablation of ASS1 reduces intracellular fumarate levels and interferon-β production, and mitochondrial respiration is also suppressed. Notably, viral challenge or fumarate esters enhance interferon-β production via direct succination of the mitochondrial antiviral signalling protein and activation of the retinoic acid-inducible gene-I-like receptor signalling. In addition to the vesicular stomatitis virus, the Sendai virus and influenza A virus can also exert these effects. In addition, patients with Ebola virus disease have increased ASS1 expression and ASS1-deficient mice show suppressed macrophage interferon responses to vesicular stomatitis virus infection. These findings reveal that fumarate can be produced from the viral inflammation-induced AAS shunt and is essential for antiviral innate immunity.

Nuclear scaffold attachment factor A functions as a potential viral recognition receptor involved in the antiviral immunity of grass carp (Ctenopharyngodon idella)

As one of the most primitive vertebrates, fish have evolved a distinct repertoire of viral recognition receptors. However, the existence of nuclear viral recognition receptors in fish remains uncertain. In this study, we identified a scaffold attachment factor A (SAFA), CiSAFA, as a potential nuclear recognition receptor for grass carp reovirus (GCRV) in grass carp (Ctenopharyngodon idella). CiSAFA shares high amino acid sequence similarity (70.3-99.6 %) and identity (56.1-98.6 %) with its counterparts from other vertebrates and contains three conserved domains, namely, SAP, SPRY, and AAA_33. On the basis of the subcellular location analysis, CiSAFA was found to localize to the nucleus. In vitro, CiSAFA can bind to poly(I:C) and induce interferon (IFN) expression. The expression data revealed that CiSAFA exhibited ubiquitous mRNA expression across all the tissues of grass carp. After GCRV infection, CiSAFA showed significantly upregulated mRNA expression levels and exhibited an expression pattern similar to that of IFN1 in the spleen and head kidney. The results of RNA immunoprecipitation indicated that CiSAFA might interact with dsRNA segment 6 of GCRV. The overexpression of CiSAFA significantly increased the expression levels of several representative antiviral genes, including interferon regulatory factor 3 (IRF3), IRF7, IFN1, and virus-induced gene 1 (GIG1), and inhibited GCRV replication. To our knowledge, this study represents the first discovery of a potential nuclear recognition receptor, CiSAFA, for GCRV in grass carp and reveals its antiviral immune mechanism against GCRV infection, which may provide new insight into host immune recognition system-virus interactions in fish.

Streptococcus mutans-derived extracellular vesicles promote skin wound healing via tRNA cargo

BACKGROUND

The human oral cavity harbors a diverse microbiota, including Streptococcus species. Oral mucosal wounds heal rapidly, although the exact cause remains unclear. This study investigates the impact of Streptococcus mutans-derived extracellular vesicles (Sm EVs) on wound healing in both oral mucosal organoids and mouse skin. To explore whether microbial EV RNA cargo influences wound healing, RNA sequences from Sm EVs were identified, and the most abundant sequences were synthesized into oligomers and encapsulated in E. coli EVs (Ec EVs) for further in vivo testing. We assessed the role of Toll-like receptor 3 (TLR3) in the wound healing mechanism in TLR3 knockout (KO) mice.

RESULTS

Sm EVs significantly enhanced cell proliferation and migration in oral mucosa, with enhanced focal adhesion complex formation. Sm EVs improved wound healing in mouse dorsal skin compared to PBS controls. RNA sequencing revealed that bacterial tRNAs, particularly the tRNA-Met variant (Oligo 1), were the most abundant RNAs in Sm EVs. Ec EVs carrying Oligo 1 produced similar wound healing effects to Sm EVs in mucosal organoids and mouse dorsal skin. However, in TLR3 knockout mice, Oligo 1 did not improve wound healing.

CONCLUSIONS

This study highlights the role of Sm EVs, particularly their tRNA variants, in promoting skin wound healing through a TLR3-dependent mechanism. These findings suggest that EVs from oral commensal bacteria may offer therapeutic potential for chronic, non-healing skin wounds.

Mitochondrial DNA signals driving immune responses: Why, How, Where?

There has been a recent expansion in our understanding of DNA-sensing mechanisms. Mitochondrial dysfunction, oxidative and proteostatic stresses, instability and impaired disposal of nucleoids cause the release of mitochondrial DNA (mtDNA) from the mitochondria in several human diseases, as well as in cell culture and animal models. Mitochondrial DNA mislocalized to the cytosol and/or the extracellular compartments can trigger innate immune and inflammation responses by binding DNA-sensing receptors (DSRs). Here, we define the features that make mtDNA highly immunogenic and the mechanisms of its release from the mitochondria into the cytosol and the extracellular compartments. We describe the major DSRs that bind mtDNA such as cyclic guanosine-monophosphate-adenosine-monophosphate synthase (cGAS), Z-DNA-binding protein 1 (ZBP1), NOD-, LRR-, and PYD- domain-containing protein 3 receptor (NLRP3), absent in melanoma 2 (AIM2) and toll-like receptor 9 (TLR9), and their downstream signaling cascades. We summarize the key findings, novelties, and gaps of mislocalized mtDNA as a driving signal of immune responses in vascular, metabolic, kidney, lung, and neurodegenerative diseases, as well as viral and bacterial infections. Finally, we define common strategies to induce or inhibit mtDNA release and propose challenges to advance the field.

The mRNA export pathway licenses viral mimicry response and antitumor immunity by actively exporting nuclear retroelement transcripts

Nuclear retroelement transcripts (RTs), which can be elicited both transcriptionally and posttranscriptionally, form double-stranded RNA (dsRNA) in cytosol to trigger the viral mimicry response (VMR) and antitumor immunity. However, the strength of the induced VMR varies tremendously across tumor types, and the underlying mechanisms remain poorly understood. Here, we demonstrate that the mRNA export pathway modulates the VMR through actively exporting nuclear RTs for cytosolic dsRNA formation after their induction. Tumor cells hijack this process for immune evasion through aberrant coactivator-associated arginine methyltransferase 1 (CARM1) expression. Mechanistically, we show that the cytoplasmic transportation of RTs by the mRNA export pathway is counteracted by the RNA exosome, which cleaves multiple transcripts within this pathway, including those encoding the essential DExD-box helicase 39A (DDX39A) and the adaptor protein ALYREF. CARM1 enhances the RNA exosome activity to attenuate the nuclear export of RTs by the mRNA export pathway through two synergistic mechanisms: (i) transcriptionally activating several RNA exosome components and (ii) posttranslationally methylating arginine 6 of the RNA exosome subunit EXOSC1, which protects it from proteasome-mediated degradation. Collectively, our study highlights the critical active regulatory role of the mRNA export pathway in transporting nuclear RTs into the cytosol for triggering the VMR and tumor immunity. Furthermore, we propose that enhancing the mRNA export pathway activity, either through CARM1 inhibition or RNA exosome modulation, could reinforce the therapeutic agent-induced VMR, thus holding the promise for overcoming tumor immune evasion and immunotherapy resistance.

Bidirectional Communication Between the Innate and Adaptive Immune Systems

Effective bidirectional communication between the innate and adaptive immune systems is crucial for tissue homeostasis and protective immunity against infections. The innate immune system is responsible for the early sensing of and initial response to threats, including microbial ligands, toxins, and tissue damage. Pathogen-related information, detected primarily by the innate immune system via dendritic cells, is relayed to adaptive immune cells, leading to the priming and differentiation of naive T cells into effector and memory lineages. Memory T cells that persist long after pathogen clearance are integral for durable protective immunity. In addition to rapidly responding to reinfections, memory T cells also directly instruct the interacting myeloid cells to induce innate inflammation, which resembles microbial inflammation. As such, memory T cells act as newly emerging activators of the innate immune system and function independently of direct microbial recognition. While T cell-mediated activation of the innate immune system likely evolved as a protective mechanism to combat reinfections by virulent pathogens, the detrimental outcomes of this mechanism manifest in the forms of autoimmunity and other T cell-driven pathologies. Here, we review the complexities and layers of regulation at the interface between the innate and adaptive immune systems to highlight the implications of adaptive instruction of innate immunity in health and disease.

The USP43/RNF2 axis negatively regulates antiviral innate immunity by promoting TBK1 ubiquitination and degradation

The E3 ubiquitin ligase usually regulates the substrate proteins ubiquitination and degradation, but the study of itself post-translational modification and stability is still elusive. Here, we reveal that E3 ubiquitin ligase ring finger protein 2 (RNF2) is deubiquitinated and stabilized by ubiquitin specific peptidase 43 (USP43) through interactome and quantitative ubiquitinome mass spectrometry analysis. This study demonstrated that USP43, as a deubiquitinating enzyme, negatively regulates the expression of type I interferon (IFN) and the Usp43 deficient enhances antiviral innate immune response against VSV infection both in vitro and in vivo. Mechanistically, USP43 negatively regulates antiviral immunity by promoting RNF2-mediated TBK1 ubiquitination and degradation. USP43 stabilizes RNF2 by removing K48-linked ubiquitination of RNF2 at Lys239 and Lys249, while RNF2 promotes TBK1 degradation by increasing K48-linked ubiquitination of TBK1 at Lys670. These findings uncover the E3 ubiquitin ligase RNF2 post-translational ubiquitination modification and stability regulation, and reveals a novel mechanism that the USP43/RNF2 axis in regulating antiviral innate immunity.

Melatonin-mediated cGAS-STING signal in senescent macrophages promote TNBC chemotherapy resistance and drive the SASP

The build-up of senescent cells in tissues is a key indicator of aging, associated with negative prognosis and therapy resistance. Despite immune dysfunction related to aging, also known as immunosenescence, is recognized as a factor in this process, the exact mechanisms are still unclear. In this study, we reported that melatonin deficiency accelerated macrophage senescence in triple-negative breast cancer, whereas melatonin could defend macrophages against senescence through the Nfatc1-Trim26-cgas-Sting pathway. Mechanistically, melatonin enhanced the nuclear translocation of Nfatc1 and elevated Trim26 transcription levels. Trim26, functioning as an E3 ligase, ubiquitinates cgas, thereby inhibiting the activation of the cgas-Sing pathway and consequently preventing cell senescence. Conversely, melatonin deficiency induced cgas-Sting pathway activation to promote macrophage aging. Our results show that melatonin inhibited macrophage senescence and improved chemotherapy responsiveness, with further enhancement when combined with the cgas inhibitor (G150). Overall, our findings indicated that melatonin protects macrophages from immunosenescence, suggesting its therapeutic potential for enhancing chemotherapy response.

Nucleic-acid-induced ZCCHC3 condensation promotes broad innate immune responses

Retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs) and cyclic GMP-AMP synthase (cGAS) recognize aberrant nucleic acids and initiate antiviral responses. Host factor zinc finger CCHC domain-containing protein 3 (ZCCHC3) positively regulates both RLRs- and cGAS-mediated signaling through unknown mechanisms. Here, we show that ZCCHC3 employs a broad and unified strategy to promote these pathways in human cell lines. Rather than developing strong protein-protein interactions, ZCCHC3 harbors multiple nucleic-acid-binding modules and undergoes robust liquid phase condensation with nucleic acids. RNA-induced ZCCHC3 condensates enrich and activate RLRs, which then facilitate the interaction of RLRs with the downstream adaptor mitochondrial antiviral-signaling (MAVS). Direct and high-resolution structure determination of liquid condensates confirms the assembly of active-form MAVS filaments. Furthermore, ZCCHC3 efficiently promotes the condensation and enrichment of DNA, cGAS, ATP, and GTP, thereby enhancing cGAS signaling. ZCCHC3 mutants defective in RNA/DNA-induced condensation lost their regulatory efficiency in both pathways. These results highlight unexpectedly broad connections between biomolecular condensation and innate immunity.

Endogenous metabolite N-chlorotaurine attenuates antiviral responses by facilitating IRF3 oxidation

Cellular microenvironments critically control the activation of innate immune responses. N-chlorotaurine (Tau-Cl) is an endogenous metabolite that is markedly produced and secreted during pathogenic invasion. However, its effect on the antiviral innate immune responses remains unclear. Here, we demonstrate that viral infection upregulates cellular Tau-Cl level. Tau-Cl attenuates viral infection-induced expression of type I IFNs and facilitates viral replication both in vitro and in vivo. Mechanistically, Tau-Cl facilitates the oxidation of IRF3 at Cys222 and Cys371, a key transcription factor that governs the transcription of type I IFNs. Tau-Cl inhibits phosphorylation and nuclear translocation of IRF3, and blocks IRF3 binding to the IFN-β promoter region. Therefore, we identify Tau-Cl as an endogenous suppressor of IRF3-driven antiviral innate responses and uncover an immune escape mechanism of viruses by affecting host microenvironments.

RNF167 mediates atypical ubiquitylation and degradation of RLRs via two distinct proteolytic pathways

The precise regulation of the RIG-I-like receptors (RLRs)-mediated type I interferon (IFN-I) activation is crucial in antiviral immunity and maintaining host immune homeostasis in the meantime. Here, we identify an E3 ubiquitin ligase, namely RNF167, as a negative regulator of RLR-triggered IFN signaling. Mechanistically, RNF167 facilitates both atypical K6- and K11-linked polyubiquitination of RIG-I/MDA5 within CARD and CTD domains, respectively, which leads to degradation of the viral RNA sensors through dual proteolytic pathways. RIG-I/MDA5 conjugated with K6-linked ubiquitin chains in CARD domains is recognized by the autophagy cargo adaptor p62, that delivers the substrates to autolysosomes for selective autophagic degradation. In contrast, K11-linked polyubiquitination in CTD domains leads to proteasome-dependent degradation of RLRs. Thus, our study clarifies a function of atypical K6- and K11-linked polyubiquitination in the regulation of RLR signaling. We also unveil an elaborate synergistic effect of dual proteolysis systems to control amplitude and duration of IFN-I activation, hereby providing insights into physiological roles of the cross-talk between these two protein quality control pathways.

Innate Sensing of Viral Nucleic Acids and Their Use in Antiviral Vaccine Development

Viruses pose a significant threat to humans by causing numerous infectious and potentially fatal diseases. Understanding how the host's innate immune system recognizes viruses is essential to understanding pathogenesis and ways to control viral infection. Innate immunity also plays a critical role in shaping adaptive immune responses induced by vaccines. Recently developed adjuvants often include nucleic acids that stimulate pattern recognition receptors which are essential components of innate immunity necessary for activating antigen-presentation cells and thereby bridging innate and adaptive immunity. Therefore, understanding viral nucleic acid sensing by cytosolic sensors is essential, as it provides the potential means for developing new vaccine strategies, including effective adjuvants.

RNA-binding proteins hnRNPM and ELAVL1 promote type-I interferon induction downstream of the nucleic acid sensors cGAS and RIG-I

The cytosolic nucleic acid sensors RIG-I and cGAS induce type-I interferon (IFN)-mediated immune responses to RNA and DNA viruses, respectively. So far no connection between the two cytosolic pathways upstream of IKK-like kinase activation has been investigated. Here, we identify heterogeneous nuclear ribonucleoprotein M (hnRNPM) as a positive regulator of IRF3 phosphorylation and type-I IFN induction downstream of both cGAS and RIG-I. Combining interactome analysis with genome editing, we further uncover the RNA-binding protein ELAV-like protein 1 (ELAVL1; also known as human antigen R, HuR) as an hnRNPM interactor. Depletion of hnRNPM or ELAVL1 impairs type-I IFN induction by herpes simplex virus 1 or Sendai virus. In addition, we show that hnRNPM and ELAVL1 interact with TANK-binding kinase 1, IκB kinase ε, IκB kinase β, and NF-κB p65. Our confocal microscopy experiments demonstrate cytosolic and perinuclear interactions between hnRNPM, ELAVL1, and TBK1. Furthermore, pharmacological inhibition of ELAVL1 strongly reduces cytokine release from type-I interferonopathy patient fibroblasts. The RNA-binding proteins hnRNPM and ELAVL1 are the first non-redundant regulators to bridge the cGAS/STING and RIG-I/MAVS pathways. Overall, our study characterizes the hnRNPM-ELAVL1 complex as a novel system promoting antiviral defense, pointing to a potential therapeutic target to reduce auto-inflammation in patients with type-I interferonopathies.

Ku suppresses RNA-mediated innate immune responses in human cells to accommodate primate-specific Alu expansion

Ku70 and Ku80 form Ku, a ring-shaped protein that initiates the non-homologous end-joining (NHEJ) DNA repair pathway. 1 Specifically, Ku binds to double-stranded DNA (dsDNA) ends and recruits other NHEJ factors ( e.g. , DNA-PKcs and LIG4). While Ku binds to double-stranded RNA (dsRNA) 2 and traps mutated-DNA-PKcs on ribosomal RNA in vivo, 3,4 the physiological significance of Ku-dsRNA interactions in otherwise wild-type cells remains elusive. Intriguingly, while dispensable for murine development, 5,6 Ku is essential in human cells. 7 Despite similar genome sizes, human cells express ∼100-fold more Ku than mouse cells, implying functions beyond NHEJ, possibly through a dose-sensitive interaction with dsRNA, which is ∼100 times weaker than with dsDNA. 2,8 While investigating the essentiality of Ku in human cells, we found that depletion of Ku - unlike LIG4 - induces profound interferon (IFN) and NF-kB responses reliant on the dsRNA-sensor MDA5/RIG-I and adaptor MAVS. Prolonged Ku-degradation also activates other dsRNA-sensors, e.g. PKR that suppresses protein translation, and OAS/RNaseL that cleaves rRNAs and eventually induces growth arrest and cell death. MAVS, RIG-I, or MDA5 knockouts suppressed IFN signaling and, together with PKR knockouts, partially rescued Ku-depleted human cells. Ku-irCLIP analyses revealed that Ku binds to diverse dsRNA, predominantly stem-loops in primate-specific Alu elements 9 at anti-sense orientation in introns and 3'-UTRs. Ku expression rose sharply in higher primates tightly correlating with Alu-expansion (r = 0.94/0.95). Together, our study identified a vital role of Ku in accommodating Alu-expansion in primates by mitigating a dsRNA-induced innate immune response, explaining the rise of Ku levels and its essentiality in human cells.

Infection-induced trained immunity: a twist in paradigm of innate host defense and generation of immunological memory

In contrast to adaptive immunity, which relies on memory T and B cells for long-term pathogen-specific responses, trained immunity involves the enhancement of innate immune responses through cellular reprogramming. Experimental evidence from animal models and human studies supports the concept of trained immunity and its potential therapeutic applications in the development of personalized medicine. However, there remains a huge gap in understanding the mechanisms, identifying specific microbial triggers responsible for the induction of trained immunity. This underscores the importance of investigating the potential role of trained immunity in redefining host defense and highlights future research directions. This minireview will provide a comprehensive summary of the new paradigm of trained immunity or innate memory pathways. It will shed light on infection-induced pathways through non-specific stimulation within macrophages and natural killer cells, which will be further elaborated in multiple disease perspectives caused by infectious agents such as bacteria, fungi, and viruses. The article further elaborates on the biochemical and cellular basis of trained immunity and its impact on disease status during recurrent exposures. The review concludes with a perspective segment discussing potential therapeutic benefits, limitations, and future challenges in this area of study. The review also sheds light upon potential risks involved in the induction of trained immunity.

The SP140-RESIST pathway regulates interferon mRNA stability and antiviral immunity

Type I interferons (IFN-Is) are essential for antiviral immunity but must be tightly regulated1-3. The conserved transcriptional repressor SP140 inhibits interferon beta (Ifnb1) expression via an unknown mechanism4,5. Here we report that SP140 does not directly repress Ifnb1 transcription. Instead, SP140 negatively regulates Ifnb1 mRNA stability by directly repressing the expression of a previously uncharacterized regulator we call RESIST (REgulated Stimulator of Interferon via Stabilization of Transcript, previously annotated as Annexin-2 Receptor). RESIST promotes Ifnb1 mRNA stability by counteracting Ifnb1 mRNA destabilization mediated by the Tristetraprolin (TTP) family of RNA-binding proteins and the CCR4-NOT deadenylase complex. SP140 localizes within nuclear bodies, punctate structures that play important roles in silencing DNA virus gene expression in the nucleus4. Consistent with this observation, we found that SP140 inhibits replication of the gammaherpesvirus MHV68. The antiviral activity of SP140 was independent of its ability to regulate Ifnb1. Our results establish dual antiviral and interferon regulatory functions for SP140. We propose that SP140 and RESIST participate in antiviral effector-triggered immunity6,7.

The TLR7/9 adaptors TASL and TASL2 mediate IRF5-dependent antiviral responses and autoimmunity in mouse

Endosomal nucleic acid sensing by Toll-like receptors (TLRs) is central to antimicrobial immunity and several autoimmune conditions such as systemic lupus erythematosus (SLE). The innate immune adaptor TASL mediates, via the interaction with SLC15A4, the activation of IRF5 downstream of human TLR7, TLR8 and TLR9, but the pathophysiological functions of this axis remain unexplored. Here we show that SLC15A4 deficiency results in a selective block of TLR7/9-induced IRF5 activation, while loss of TASL leads to a strong but incomplete impairment, which depends on the cell type and TLR engaged. This residual IRF5 activity is ascribed to a previously uncharacterized paralogue, Gm6377, named here TASL2. Double knockout of TASL and TASL2 (TASLDKO) phenocopies SLC15A4-deficient feeble mice showing comparable impairment of innate and humoral responses. Consequently, TASLDKO mice fail to control chronic LCMV infection, while being protected in a pristane-induced SLE disease model. Our study thus demonstrates the critical pathophysiological role of SLC15A4 and TASL/TASL2 for TLR7/9-driven inflammatory responses, further supporting the therapeutic potential of targeting this complex in SLE and related diseases.

Direct lysine dimethylation of IRF3 by the methyltransferase SMYD3 attenuates antiviral innate immunity

Interferon regulatory factor 3 (IRF3) is the key transcription factor in the type I IFN signaling pathway, whose activation is regulated by multiple posttranslational modifications. Here, we identify SMYD3, a lysine methyltransferase, as a negative regulator of IRF3. SMYD3 interacts with IRF3 and catalyzes the dimethylation of IRF3 at lysine 39. This modification reduces IRF3 phosphorylation, dimerization, and subsequent nuclear translocation, leading to the inhibition of downstream type I interferon production. In addition, Smyd3-deficient mice are more resistant to RNA and DNA viral infections. Zebrafish lacking smyd3 or treated with the inhibitor BCI121 are also more resistant to viral infection. Our findings reveal a role for SMYD3 in the regulation of antiviral innate immunity and provide insight into a specific modulation of IRF3 that affects its activation.

Genetic evidence for the suppressive role of zebrafish vhl targeting mavs in antiviral innate immunity during RNA virus infection

The von Hippel-Lindau (VHL) tumor suppressor gene VHL is a classic tumor suppressor that has been identified in family members with clear cell renal cell carcinomas, central nervous system and retinal hemangioblastomas, phaeochromocytomas, and pancreatic neuroendocrine tumors. The well-defined function of VHL is to mediate proteasomal degradation of hydroxylated hypoxia-inducible factor α proteins, resulting in the downregulation of hypoxia-responsive gene expression. Previously, we reported that VHL inhibits antiviral signaling by targeting mitochondrial antiviral signaling protein (MAVS) for proteasomal degradation. However, due to the lack of a viable animal model, the physiological role and underlying mechanism of VHL in antiviral immunity remains to be elucidated. In this study, we found that heterozygous vhl-deficient zebrafish have normal neutrophils and no gross phenotypic alterations. However, upon spring viremia of carp virus or grass carp reovirus infection, antiviral gene expression is induced in vhl+/- zebrafish compared with wild-type zebrafish. In addition, spring viremia of carp virus replication is suppressed in vhl+/- zebrafish, owing to the enhancement of antiviral ability. Furthermore, by crossing with mavs-/- zebrafish line, we observed that disruption of mavs in vhl+/- zebrafish abrogates the viral resistance exhibited in vhl+/- zebrafish. Thus, we reveal that heterozygous vhl deficiency enhances the antiviral ability of zebrafish against RNA virus infection, and we provide genetic evidence to support that zebrafish mavs serves as a mediator for the suppressive role of vhl in antiviral innate immunity.

Oxymatrine, a novel TLR2 agonist, promotes megakaryopoiesis and thrombopoiesis through the STING/NF-κB pathway

Radiation-induced thrombocytopenia (RIT) faces a perplexing challenge in the clinical treatment of cancer patients, and current therapeutic approaches are inadequate in the clinical settings. In this research, oxymatrine, a new molecule capable of healing RIT was screened out, and the underlying regulatory mechanism associated with magakaryocyte (MK) differentiation and thrombopoiesis was demonstrated. The capacity of oxymatrine to induce MK differentiation was verified in K-562 and Meg-01 cells in vitro. The ability to induce thrombopoiesis was subsequently demonstrated in Tg (cd41:enhanced green fluorescent protein (eGFP)) zebrafish and RIT model mice. In addition, we carried out network pharmacological prediction, drug affinity responsive target stability assay (DARTS) and cellular thermal shift assay (CETSA) analyses to explore the potential targets of oxymatrine. Moreover, the pathway underlying the effects of oxymatrine was determined by Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses, Western blot (WB), and immunofluorescence. Oxymatrine markedly promoted MK differentiation and maturation in vitro. Moreover, oxymatrine induced thrombopoiesis in Tg (cd41:eGFP) zebrafish and accelerated thrombopoiesis and platelet function recovery in RIT model mice. Mechanistically, oxymatrine directly binds to toll-like receptor 2 (TLR2) and further regulates the downstream pathway stimulator of interferon genes (STING)/nuclear factor-kappaB (NF-κB), which can be blocked by C29 and C-176, which are specific inhibitors of TLR2 and STING, respectively. Taken together, we demonstrated that oxymatrine, a novel TLR2 agonist, plays a critical role in accelerating MK differentiation and thrombopoiesis via the STING/NF-κB axis, suggesting that oxymatrine is a promising candidate for RIT therapy.

Tissue Determinants of Antiviral Immunity in the Liver

The liver is an organ bearing important metabolic and immune functions. Hepatocytes are the main metabolically active cells of the liver and are the target of infection by hepatotropic viruses. Virus-specific CD8 T cells are essential for the control of hepatocyte infection with hepatotropic viruses but may be subject to local regulation of their effector function. Here, we review our current knowledge of the tissue determinants of antiviral immunity in the liver. Liver Sinusoidal Endothelial Cells (LSECs) not only allow through their fenestrations the access of circulating virus-specific CD8 T cells to engage in direct contact with infected hepatocytes without the need for extravasation but also cross-present viral antigens released from infected hepatocytes to these CD8 T cells. Two important features of LSECs and hepatocytes contribute to antiviral immune surveillance and liver failure. First, CD8 T cell immunity targeting LSECs leads to widespread endothelial cell death and results in sinusoidal microcirculation failure, causing fulminant viral hepatitis, whereas immune-mediated loss of hepatocytes is rapidly compensated by the regenerative capacity of the liver. Second, virus-infected hepatocytes support clearance of infection by responding to TNF, which is released from virus-specific CD8 T cells, with the selective induction of apoptosis. This increased sensitivity for TNF-induced death is caused by reduced mitochondrial resilience in virus-infected hepatocytes and may assist antiviral immunity in preferential targeting of virus-infected hepatocytes. Thus, hepatocytes and LSECs actively contribute to the outcome of antiviral CD8 T cell immunity in the liver. The knowledge of the mechanisms determining CD8 T cell control of hepatotropic viral infection will help to improve strategies to increase antiviral immune surveillance.

Corilagin inhibits human cytomegalovirus infection and replication via activating the cGAS-STING signaling pathway in vitro and in vivo

AIM

The existence of human cytomegalovirus (HCMV) is extremely widespread, causing serious diseases in patients with low immune function. The purpose of this study is to explore the efficacy and mechanism of Corilagin in the control of CMV infection, in order to provide scientific basis for the control of CMV infection.

METHODS

Our study employed an animal model in Balb/c mice, infected with MCMV, alongside cellular models in HFF cells and THP-1 cells, stimulated with HCMV. The expression of cGAS-STING signaling pathway molecules was detected in liver tissue, lung tissue, serum, cells and cell supernatant. The liver function and histopathological changes of mice were evaluated.

RESULTS

In vivo and in vitro experiments showed that Corilagin significantly inhibits CMV levels and attenuates pathological damage in liver and lung tissues in vivo, and similarly inhibits viral load in cells in vitro. Corilagin promotes the expression levels of STING and its downstream molecules in vivo and in vitro. Inhibition/down-regulation of STING significantly promotes CMV replication, on the contrary, activation/up-regulation of STING inhibits CMV replication, and Corilagin also promotes the expression levels of molecules related to the cGAS-STING signaling pathway in the above cases.

CONCLUSION

Corilagin could effectively inhibit the infection and replication of CMV in vitro and in vivo, which may be through the activation of cGAS-STING signaling pathway.

Butyrate attenuates intestinal inflammation in Crohn's disease by suppressing pyroptosis of intestinal epithelial cells via the cGSA-STING-NLRP3 axis

Butyrate can strengthen the intestinal epithelial barrier. However, the mechanisms by which butyrate affects intestinal epithelial cells (IECs) pyroptosis in Crohn's disease (CD) remain unclear. In this study, we collected colonic biopsy samples from CD patients and healthy controls to assess pyroptosis levels. Our findings indicated elevated expression of pyroptosis markers in CD patients, alongside distinct morphological evidence of pyroptosis in IECs. We further investigated the effects of tributyrin on pyroptosis and the cGAS-STING pathway in a trinitrobenzene sulfonic acid-induced colitis rat model. Tributyrin significantly mitigated intestinal inflammation, reduced pathological progression, and inhibited pyroptosis and cGAS-STING pathway activation in the colitis rat model. Similarly, in an in vitro model of IECs pyroptosis, sodium butyrate inhibited pyroptosis and cGAS-STING pathway activation in HT-29 cells. Co-treatment with a cGAS-STING pathway activator and butyrate demonstrated that the activator reversed the inhibitory effects of butyrate on pyroptosis and cGAS-STING pathway activation in both the colitis rat model and HT-29 cells. Mechanistically, the cGAS-STING pathway was found to interact with NLRP3. Taken together, butyrate may mitigate intestinal inflammation in CD by suppressing cGAS-STING-NLRP3 axis-mediated IECs pyroptosis. These findings offer new insights into potential therapeutic strategies for managing CD.

Antigen-presenting cell activation requires intrinsic and extrinsic STING signaling after the phagocytosis of DNA-damaged cells

Antigen-presenting cells (APCs) are readily activated after phagocytosing infected or DNA-damaged cells but not normal apoptotic cells for reasons that are not well understood. Here, we demonstrate that after DNA damage events, cytosolic dsDNA species trigger intrinsic STING signaling and the production of key immunogenic proteins, including CCL5, which renders such cells capable of APC activation upon phagocytosis. These events involve the generation of immunogenic STING-inducible endosomal vesicles (SIEVEs) additionally comprising critical autophagy-associated proteins associated with cytosolic DNA species. After phagocytosis, extrinsic cGAS-STING signaling is triggered via engulfed, immunogenic transactivating DNA vesicles resulting in APC stimulation. These results help explain how APCs are predominantly activated by DNA-damaged or infected cells in contrast with normal apoptotic cells and suggest that reconstitution of STING signaling or key inducible genes in cGAS-STING-defective malignancies could substantially augment cancer immunotherapies.

Duck plague virus UL24 protein initiates K48/K63-linked IRF7 polyubiquitination to antagonize the innate immune response

Duck plague virus (DPV), which is the causative agent of duck viral enteritis, is highly infectious and can cause severe disease and death in ducks, geese and other waterfowl. Several tegument proteins of DPV have been shown to affect the cyclic GMP-AMP synthase (cGAS)-STING signaling pathway to modulate host innate immune responses. DPV UL24, an important DPV tegument protein, can inhibit the activity of the IFN-β promoter. However, the mechanism by which the DPV UL24 protein regulates the host innate immune response remains unclear. In this study, we found that the UL24 protein can significantly inhibit the activity of the interferon-β promoter induced by poly(I:C) and reduce the production of IFN-β, interferon-stimulated genes (OASL, Mx), and the cellular inflammatory factor IL-6. 2) The UL24 protein can widely inhibit the mRNA level of immune signaling molecules. The UL24 protein can also downregulate the protein expression of RIG-I, MDA5, MAVS, cGAS, STING, TBK1 and IRF7 in DEFs. RT-qPCR results revealed that UL24 significantly inhibited the mRNA accumulation for the immune signaling molecules cGAS, STING, TBK1 and IRF7. 3) The UL24 protein induced the degradation of IRF7 via ubiquitination. After the DEFs were treated with the ubiquitin proteasome inhibitor MG132, the degradation of IRF7 by the UL24 protein was alleviated. Coimmunoprecipitation results revealed that DPV UL24 induced the K48/K63-linked ubiquitination of IRF7, which promoted its degradation and thus antagonized the host innate immune response.

The roles of DNA damage repair and innate immune surveillance pathways in HPV pathogenesis

Human papillomaviruses (HPV) infect epithelial tissues and induce a variety of proliferative lesions. A subset of HPV types are also the causative agents of many anogenital as well as oropharyngeal cancers. Following infection of basal epithelial cells, HPVs establish their genomes as episomes in undifferentiated cells and require differentiation for their productive life cycles. During HPV infections, viral oncoproteins alter cellular pathways such as those for DNA damage repair and innate immune surveillances to regulate their productive life cycles. These pathways provide potential targets for therapeutic intervention.

Dietary nucleic acids promote oral tolerance through innate sensing pathways in mice

Oral tolerance is essential for intestinal homeostasis and systemic immune function. However, our understanding of how oral tolerance is maintained is inadequate. Here we report that food-derived nucleic acids promote oral tolerance through innate sensing pathways. We find that dietary nucleic acids, but not microbiota, expand the natural intraepithelial lymphocyte (IEL) pool, specifically in the small intestine. TGF-β1, produced by natural IELs, then promotes activation of gut CD103+ dendritic cells to support the induction of antigen-specific Treg cells in a mouse model of OVA-induced oral tolerance. Mechanistically, MAVS and STING are redundantly required for sensing dietary RNAs and DNAs to activate downstream TBK1 signalling to induce IL-15 production, which results in the accumulation of natural IELs. Thus, our study demonstrates a key role of food-triggered innate sensing pathways in the maintenance of natural IELs and oral tolerance.

Recognition of phylogenetically diverse pathogens through enzymatically amplified recruitment of RNF213

Innate immunity senses microbial ligands known as pathogen-associated molecular patterns (PAMPs). Except for nucleic acids, PAMPs are exceedingly taxa-specific, thus enabling pattern recognition receptors to detect cognate pathogens while ignoring others. How the E3 ubiquitin ligase RNF213 can respond to phylogenetically distant pathogens, including Gram-negative Salmonella, Gram-positive Listeria, and eukaryotic Toxoplasma, remains unknown. Here we report that the evolutionary history of RNF213 is indicative of repeated adaptation to diverse pathogen target structures, especially in and around its newly identified CBM20 carbohydrate-binding domain, which we have resolved by cryo-EM. We find that RNF213 forms coats on phylogenetically distant pathogens. ATP hydrolysis by RNF213's dynein-like domain is essential for coat formation on all three pathogens studied as is RZ finger-mediated E3 ligase activity for bacteria. Coat formation is not diffusion-limited but instead relies on rate-limiting initiation events and subsequent cooperative incorporation of further RNF213 molecules. We conclude that RNF213 responds to evolutionarily distant pathogens through enzymatically amplified cooperative recruitment.

The role of post-translational modifications of cGAS in γδ T cells

Cyclic GMP-AMP (cGAMP) synthase (cGAS) senses DNA in a sequence-independent manner, triggering cGAMP synthesis, which activates stimulator of interferon genes (STING) and the subsequent expression of type I interferons, tumour necrosis factor alpha (TNF-α) and other proinflammatory factors in two downstream pathways. However, the function of the cGASSTING pathway in γδ T cells remains unclear. The γδ T-cell population differs from the innate-like lymphocyte population, particularly with respect to tissue distribution, indicating the unique potential of γδ T cells in treating infections and cancers. On the basis of accumulating evidence, cGAS activity is modulated by protein posttranslational modifications (PTMs), including phosphorylation, O-GlcNAcylation, acetylation, ubiquitylation and methylation, which affect multiple cGAS functions. Thus, here, we summarize recent research on PTMs of the cGAS protein that modulate γδ T-cell function. An understanding of cGAS features and modulation mechanisms may facilitate the design of therapies for γδ T-cell-related immune diseases and cancer.

Loss of Nrf2 aggravates ionizing radiation-induced intestinal injury by activating the cGAS/STING pathway via Pirin

Ionizing radiation (IR)-induced intestinal injury remains a major limiting factor in abdominal radiation therapy, and its pathogenesis remains unclear. In this study, mouse models of IR-induced intestinal injury were established, and the effect of IR on nuclear factor erythroid 2-related factor 2 (Nrf2) was determined. More severe IR-induced intestinal damage was observed in Nrf2 knockout (KO) mice than in wild-type mice. Then, the negative regulation of cyclic GMP-AMP synthase/stimulator of interferon genes (cGAS/STING) signaling by Nrf2 was examined both in vivo and in vitro after IR. This was accompanied by alterations in the intestinal neutrophil and macrophage populations in mice. Subsequently, the effect of the cGAS/STING pathway on the intestinal toxicity of IR was also investigated. Moreover, the downregulation of cGAS/STING by Nrf2 via its target gene, Pirin, was confirmed using transfection assays. A rescue experiment with Pirin was also conducted using adeno-associated virus in Nrf2 KO mice. Finally, the protective effect of calcitriol against IR-induced intestinal injury, along with increased Nrf2 and Pirin levels and decreased cGAS, pSTING, and interferon-beta levels, were observed. Taken together, our results suggest that Nrf2 alleviates IR-induced intestinal injury through Pirin-mediated inhibition of the innate immunity-related cGAS/STING pathway.

A TBK1-independent primordial function of STING in lysosomal biogenesis

Stimulator of interferon genes (STING) is activated in many pathophysiological conditions, leading to TBK1-dependent interferon production in higher organisms. However, primordial functions of STING independent of TBK1 are poorly understood. Here, through proteomics and bioinformatics approaches, we identify lysosomal biogenesis as an unexpected function of STING. Transcription factor EB (TFEB), an evolutionarily conserved regulator of lysosomal biogenesis and host defense, is activated by STING from multiple species, including humans, mice, and frogs. STING-mediated TFEB activation is independent of TBK1, but it requires STING trafficking and its conserved proton channel. GABARAP lipidation, stimulated by the channel of STING, is key for STING-dependent TFEB activation. STING stimulates global upregulation of TFEB-target genes, mediating lysosomal biogenesis and autophagy. TFEB supports cell survival during chronic sterile STING activation, a common condition in aging and age-related diseases. These results reveal a primordial function of STING in the biogenesis of lysosomes, essential organelles in immunity and cellular stress resistance.

Poxin-deficient poxviruses are sensed by cGAS prior to genome replication

Poxviruses are dsDNA viruses infecting a wide range of cell types, where they need to contend with multiple host antiviral pathways, including DNA and RNA sensing. Accordingly, poxviruses encode a variety of immune antagonists, most of which are expressed early during infection from within virus cores before uncoating and genome release take place. Amongst these antagonists, the poxvirus immune nuclease (poxin) counteracts the cyclic 2'3'-GMP-AMP (2'3'-cGAMP) synthase (cGAS)/stimulator of interferon genes DNA sensing pathway by degrading the immunomodulatory cyclic dinucleotide 2'3'-cGAMP, the product of activated cGAS. Here, we use poxviruses engineered to lack poxin to investigate how virus infection triggers the activation of STING and its downstream transcription factor interferon-responsive factor 3 (IRF3). Our results demonstrate that poxin-deficient vaccinia virus (VACV) and ectromelia virus (ECTV) induce IRF3 activation in primary fibroblasts and differentiated macrophages, although to a lower extent in VACV compared to ECTV. In fibroblasts, IRF3 activation was detectable at 10 h post-infection (hpi) and was abolished by the DNA replication inhibitor cytosine arabinoside (AraC), indicating that the sensing was mediated by replicated genomes. In macrophages, IRF3 activation was detectable at 4 hpi, and this was not affected by AraC, suggesting that the sensing in this cell type was induced by genomes released from incoming virions. In agreement with this, macrophages expressing short hairpin RNA (shRNA) against the virus uncoating factor D5 showed reduced IRF3 activation upon infection. Collectively, our data show that the viral genome is sensed by cGAS prior to and during genome replication, but immune activation downstream of it is effectively suppressed by poxin. Our data also support the model where virus uncoating acts as an immune evasion strategy to simultaneously cloak the viral genome and allow the expression of early immune antagonists.

Nucleic acid sensing in the central nervous system: Implications for neural circuit development, function, and degeneration

Nucleic acids are a critical trigger for the innate immune response to infection, wherein pathogen-derived RNA and DNA are sensed by nucleic acid sensing receptors. This subsequently drives the production of type I interferon and other inflammatory cytokines to combat infection. While the system is designed such that these receptors should specifically recognize pathogen-derived nucleic acids, it is now clear that self-derived RNA and DNA can also stimulate these receptors to cause aberrant inflammation and autoimmune disease. Intriguingly, similar pathways are now emerging in the central nervous system in neurons and glial cells. As in the periphery, these signaling pathways are active in neurons and glia to present the spread of pathogens in the CNS. They further appear to be active even under steady conditions to regulate neuronal development and function, and they can become activated aberrantly during disease to propagate neuroinflammation and neurodegeneration. Here, we review the emerging new roles for nucleic acid sensing mechanisms in the CNS and raise open questions that we are poised to explore in the future.

Conservation of antiviral systems across domains of life reveals immune genes in humans

Deciphering the immune organization of eukaryotes is important for human health and for understanding ecosystems. The recent discovery of antiphage systems revealed that various eukaryotic immune proteins originate from prokaryotic antiphage systems. However, whether bacterial antiphage proteins can illuminate immune organization in eukaryotes remains unexplored. Here, we use a phylogeny-driven approach to uncover eukaryotic immune proteins by searching for homologs of bacterial antiphage systems. We demonstrate that proteins displaying sequence similarity with recently discovered antiphage systems are widespread in eukaryotes and maintain a role in human immunity. Two eukaryotic proteins of the anti-transposon piRNA pathway are evolutionarily linked to the antiphage system Mokosh. Additionally, human GTPases of immunity-associated proteins (GIMAPs) as well as two genes encoded in microsynteny, FHAD1 and CTRC, are respectively related to the Eleos and Lamassu prokaryotic systems and exhibit antiviral activity. Our work illustrates how comparative genomics of immune mechanisms can uncover defense genes in eukaryotes.

Noncanonical microprotein regulation of immunity

The immune system is highly regulated but, when dysregulated, suboptimal protective or overly robust immune responses can lead to immune-mediated disorders. The genetic and molecular mechanisms of immune regulation are incompletely understood, impeding the development of more precise diagnostics and therapeutics for immune-mediated disorders. Recently, thousands of previously unrecognized noncanonical microprotein genes encoded by small open reading frames have been identified. Many of these microproteins perform critical functions, often in a cell- and context-specific manner. Several microproteins are now known to regulate immunity; however, the vast majority are uncharacterized. Therefore, illuminating what is often referred to as the "dark proteome," may present opportunities to tune immune responses more precisely. Here, we review noncanonical microprotein biology, highlight recently discovered examples regulating immunity, and discuss the potential and challenges of modulating dysregulated immune responses by targeting microproteins.

Microbe-material hybrids for therapeutic applications

As natural living substances, microorganisms have emerged as useful resources in medicine for creating microbe-material hybrids ranging from nano to macro dimensions. The engineering of microbe-involved nanomedicine capitalizes on the distinctive physiological attributes of microbes, particularly their intrinsic "living" properties such as hypoxia tendency and oxygen production capabilities. Exploiting these remarkable characteristics in combination with other functional materials or molecules enables synergistic enhancements that hold tremendous promise for improved drug delivery, site-specific therapy, and enhanced monitoring of treatment outcomes, presenting substantial opportunities for amplifying the efficacy of disease treatments. This comprehensive review outlines the microorganisms and microbial derivatives used in biomedicine and their specific advantages for therapeutic application. In addition, we delineate the fundamental strategies and mechanisms employed for constructing microbe-material hybrids. The diverse biomedical applications of the constructed microbe-material hybrids, encompassing bioimaging, anti-tumor, anti-bacteria, anti-inflammation and other diseases therapy are exhaustively illustrated. We also discuss the current challenges and prospects associated with the clinical translation of microbe-material hybrid platforms. Therefore, the unique versatility and potential exhibited by microbe-material hybrids position them as promising candidates for the development of next-generation nanomedicine and biomaterials with unique theranostic properties and functionalities.

The immune modules conserved across the tree of life: Towards a definition of ancestral immunity

Immune defence mechanisms exist across the tree of life in such diversity that prokaryotic antiviral responses have historically been considered unrelated to eukaryotic immunity. Mechanisms of defence in divergent eukaryotes were similarly believed to be largely clade specific. However, recent data indicate that a subset of modules (domains and proteins) from prokaryote defence systems are conserved in eukaryotes and populate many stages of innate immune pathways. In this Essay, we propose the notion of ancestral immunity, which corresponds to the set of immune modules conserved between prokaryotes and eukaryotes. After offering a typology of ancestral immunity, we speculate on the selective pressures that could have led to the differential conservation of specific immune modules across domains of life. The exploration of ancestral immunity is in its infancy and appears full of promises to illuminate immune evolution, and also to identify and decipher immune mechanisms of economic, ecological, and therapeutic importance.

Research progress of cGAS-STING signaling pathway in intestinal diseases

The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signal has drawn much consideration due to its sensitivity to DNA in innate immune mechanisms. Activation of the cGAS-STIN signaling pathway induces the production of interferon and inflammatory cytokines, resulting in immune responses, or inflammatory diseases. The intestinal tract is a vital organ for the body's nutrition absorption, recent studies have had various points of view on the job of cGAS-STING pathway in various intestinal sicknesses. Therefore, understanding its role and mechanism in the intestinal environment can help to develop new strategies for the treatment of intestinal diseases. This article examines the mechanism of the cGAS-STING pathway and its function in inflammatory bowel disease, intestinal cancer, and long-injury ischemia-reperfusion, lists the current medications that target it for the treatment of intestinal diseases, and discusses the impact of intestinal flora on this signaling pathway, to offer a theoretical and scientific foundation for upcoming targeted therapies for intestinal disorders via the cGAS-STING pathway.

Nucleic Acid Sensing by STING Induces an IFN-like Antiviral Response in a Marine Invertebrate

The cytosolic detection of pathogen-derived nucleic acids has evolved as an essential strategy for host innate immune defense in mammals. One crucial component in this process is the stimulator of IFN genes (STING), which acts as a vital signaling adaptor, connecting the cytosolic detection of DNA by cyclic GMP-AMP (cGAMP) synthase (cGAS) to the downstream type I IFN signaling pathway. However, this process remains elusive in invertebrates. In this study, we present evidence demonstrating that STING, an ortholog found in a marine invertebrate (shrimp) called Litopenaeus vannamei, can directly detect DNA and initiate an IFN-like antiviral response. Unlike its homologs in other eukaryotic organisms, which exclusively function as sensors for cyclic dinucleotides, shrimp STING has the ability to bind to both double-stranded DNA and cyclic dinucleotides, including 2'3'-cGAMP. In vivo, shrimp STING can directly sense DNA nucleic acids from an infected virus, accelerate IFN regulatory factor dimerization and nuclear translocation, induce the expression of an IFN functional analog protein (Vago4), and finally establish an antiviral state. Taken together, our findings unveil a novel double-stranded DNA-STING-IKKε-IRF-Vago antiviral axis in an arthropod, providing valuable insights into the functional origins of DNA-sensing pathways in evolution.

Viperin-like proteins interfere with RNA viruses in plants

Plant viruses cause substantial losses in crop yield and quality; therefore, devising new, robust strategies to counter viral infections has important implications for agriculture. Virus inhibitory protein endoplasmic reticulum-associated interferon-inducible (Viperin) proteins are conserved antiviral proteins. Here, we identified a set of Viperin and Viperin-like proteins from multiple species and tested whether they could interfere with RNA viruses in planta. Our data from transient and stable overexpression of these proteins in Nicotiana benthamiana reveal varying levels of interference against the RNA viruses tobacco mosaic virus (TMV), turnip mosaic virus (TuMV), and potato virus x (PVX). Harnessing the potential of these proteins represents a novel avenue in plant antiviral approaches, offering a broader and more effective spectrum for application in plant biotechnology and agriculture. Identifying these proteins opens new avenues for engineering a broad range of resistance to protect crop plants against viral pathogens.

Z-DNA binding protein 1 orchestrates innate immunity and inflammatory cell death

Innate immunity is not only the first line of host defense against microbial infections but is also crucial for the host responses against a variety of noxious stimuli. Z-DNA binding protein 1 (ZBP1) is a cytosolic nucleic acid sensor that can induce inflammatory cell death in both immune and nonimmune cells upon sensing of incursive virus-derived Z-form nucleic acids and self-nucleic acids via its Zα domain. Mechanistically, aberrantly expressed or activated ZBP1 induced by pathogens or noxious stimuli enables recruitment of TANK binding kinase 1 (TBK1), interferon regulatory factor 3 (IRF3), receptor-interacting serine/threonine-protein kinase 1 (RIPK1) and RIPK3 to drive type I interferon (IFN-I) responses and activation of nuclear factor kappa B (NF-κB) signaling. Meanwhile, ZBP1 promotes the assembly of ZBP1- and absent in melanoma 2 (AIM2)-PANoptosome, which ultimately triggers PANoptosis through caspase 3-mediated apoptosis, mixed lineage kinase domain like pseudokinase (MLKL)-mediated necroptosis, and gasdermin D (GSDMD)-mediated pyroptosis. In response to damaged mitochondrial DNA, ZBP1 can interact with cyclic GMP-AMP synthase to augment IFN-I responses but inhibits toll like receptor 9-mediated inflammatory responses. This review summarizes the structure and expression pattern of ZBP1, discusses its roles in human diseases through immune-dependent (e.g., the production of IFN-I and pro-inflammatory cytokines) and -independent (e.g., the activation of cell death) functions, and highlights the attractive prospect of manipulating ZBP1 as a promising therapeutic target in diseases.

An integrative epigenome-based strategy for unbiased functional profiling of clinical kinase inhibitors

More than 500 kinases are implicated in the control of most cellular process in mammals, and deregulation of their activity is linked to cancer and inflammatory disorders. 80 clinical kinase inhibitors (CKIs) have been approved for clinical use and hundreds are in various stages of development. However, CKIs inhibit other kinases in addition to the intended target(s), causing both enhanced clinical effects and undesired side effects that are only partially predictable based on in vitro selectivity profiling. Here, we report an integrative approach grounded on the use of chromatin modifications as unbiased, information-rich readouts of the functional effects of CKIs on macrophage activation. This approach exceeded the performance of transcriptome-based approaches and allowed us to identify similarities and differences among CKIs with identical intended targets, to recognize novel CKI specificities and to pinpoint CKIs that may be repurposed to control inflammation, thus supporting the utility of this strategy to improve selection and use of CKIs in clinical settings.

Early signaling pathways in virus-infected cells

Virus infection activates specific pattern recognition receptors and immune signal transduction, resulting in pro-inflammatory cytokine production and activation of innate immunity. We describe here the molecular organization of early signaling pathways downstream of viral recognition, including conformational changes, post-translational modifications, formation of oligomers, and generation of small-molecule second messengers. Such molecular organization allows tight regulation of immune signal transduction, characterized by swift but transient responses, nonlinearity, and signal amplification. Pathologies of early immune signaling caused by genomic mutations illustrate the fine regulation of the immune transduction cascade.

Ursonic acid from medicinal herbs inhibits PRRSV replication through activation of the innate immune response by targeting the phosphatase PTPN1

Porcine reproductive and respiratory syndrome (PRRS), caused by the PRRS virus (PRRSV), has caused substantial economic losses to the global swine industry due to the lack of effective commercial vaccines and drugs. There is an urgent need to develop alternative strategies for PRRS prevention and control, such as antiviral drugs. In this study, we identified ursonic acid (UNA), a natural pentacyclic triterpenoid from medicinal herbs, as a novel drug with anti-PRRSV activity in vitro. Mechanistically, a time-of-addition assay revealed that UNA inhibited PRRSV replication when it was added before, at the same time as, and after PRRSV infection was induced. Compound target prediction and molecular docking analysis suggested that UNA interacts with the active pocket of PTPN1, which was further confirmed by a target protein interference assay and phosphatase activity assay. Furthermore, UNA inhibited PRRSV replication by targeting PTPN1, which inhibited IFN-β production. In addition, UNA displayed antiviral activity against porcine epidemic diarrhoea virus (PEDV) and Seneca virus A (SVA) replication in vitro. These findings will be helpful for developing novel prophylactic and therapeutic agents against PRRS and other swine virus infections.

Virus versus host: influenza A virus circumvents the immune responses

Influenza A virus (IAV) is a highly contagious pathogen causing dreadful losses to humans and animals around the globe. As is known, immune escape is a strategy that benefits the proliferation of IAVs by antagonizing, blocking, and suppressing immune surveillance. The HA protein binds to the sialic acid (SA) receptor to enter the cytoplasm and initiate viral infection. The conserved components of the viral genome produced during replication, known as the pathogen-associated molecular patterns (PAMPs), are thought to be critical factors for the activation of effective innate immunity by triggering dependent signaling pathways after recognition by pattern recognition receptors (PRRs), followed by a cascade of adaptive immunity. Viral infection-induced immune responses establish an antiviral state in the host to effectively inhibit virus replication and enhance viral clearance. However, IAV has evolved multiple mechanisms that allow it to synthesize and transport viral components by "playing games" with the host. At its heart, this review will describe how host and viral factors interact to facilitate the viral evasion of host immune responses.

The tRNAVal half: A strong endogenous Toll-like receptor 7 ligand with a 5'-terminal universal sequence signature

Toll-like receptors (TLRs) are crucial components of the innate immune system. Endosomal TLR7 recognizes single-stranded RNAs, yet its endogenous ssRNA ligands are not fully understood. We previously showed that extracellular (ex-) 5'-half molecules of tRNAHisGUG (the 5'-tRNAHisGUG half) in extracellular vesicles (EVs) of human macrophages activate TLR7 when delivered into endosomes of recipient macrophages. Here, we fully explored immunostimulatory ex-5'-tRNA half molecules and identified the 5'-tRNAValCAC/AAC half, the most abundant tRNA-derived RNA in macrophage EVs, as another 5'-tRNA half molecule with strong TLR7 activation capacity. Levels of the ex-5'-tRNAValCAC/AAC half were highly up-regulated in macrophage EVs upon exposure to lipopolysaccharide and in the plasma of patients infected with Mycobacterium tuberculosis. The 5'-tRNAValCAC/AAC half-mediated activation of TLR7 effectively eradicated bacteria infected in macrophages. Mutation analyses of the 5'-tRNAValCAC/AAC half identified the terminal GUUU sequence as a determinant for TLR7 activation. We confirmed that GUUU is the optimal ratio of guanosine and uridine for TLR7 activation; microRNAs or other RNAs with the terminal GUUU motif can indeed stimulate TLR7, establishing the motif as a universal signature for TLR7 activation. These results advance our understanding of endogenous ssRNA ligands of TLR7 and offer insights into diverse TLR7-involved pathologies and their therapeutic strategies.

Oxygen enhances antiviral innate immunity through maintenance of EGLN1-catalyzed proline hydroxylation of IRF3

Oxygen is essential for aerobic organisms, but little is known about its role in antiviral immunity. Here, we report that during responses to viral infection, hypoxic conditions repress antiviral-responsive genes independently of HIF signaling. EGLN1 is identified as a key mediator of the oxygen enhancement of antiviral innate immune responses. Under sufficient oxygen conditions, EGLN1 retains its prolyl hydroxylase activity to catalyze the hydroxylation of IRF3 at proline 10. This modification enhances IRF3 phosphorylation, dimerization and nuclear translocation, leading to subsequent IRF3 activation. Furthermore, mice and zebrafish with Egln1 deletion, treatment with the EGLN inhibitor FG4592, or mice carrying an Irf3 P10A mutation are more susceptible to viral infections. These findings not only reveal a direct link between oxygen and antiviral responses, but also provide insight into the mechanisms by which oxygen regulates innate immunity.