STING mediates neuronal innate immune response following Japanese encephalitis virus infection

Dual inhibitors of DNMT and HDAC remodels the immune microenvironment of colorectal cancer and enhances the efficacy of anti-PD-L1 therapy

Colorectal cancer is the second most prevalent and deadly cancer worldwide. The emergence of immune checkpoint therapy has provided a revolutionary strategy for the treatment of solid tumors. However, less than 5 % of colorectal cancer patients respond to immune checkpoint therapy. Thus, it is of great scientific significance to develop "potentiators" for immune checkpoint therapy. In this study, we found that knocking down different DNMT and HDAC isoforms could increase the expression of IFNs in colorectal cancer cells, which can enhance the effectiveness of immune checkpoint therapy. Therefore, the combined inhibition of DNMT and HDAC cloud synergistically enhance the effect of immunotherapy. We found that dual DNMT and HDAC inhibitors C02S could inhibit tumor growth in immunocompetent mice but not in immunocompromised nude mice, which indicates that C02S exerts its antitumor effects through the immune system. Mechanistically, C02S could increase the expression of ERVs, which generated the intracellular levels of dsRNA in tumor cells, and then promotes the expression of IFNs through the RIG-I/MDA5-MAVS signaling pathway. Moreover, C02S increased the immune infiltration of DCs and T cells in microenvironment, and enhanced the efficacy of anti-PD-L1 therapy in MC38 and CT26 mice model. These results confirmed that C02S can activate IFNs through the RIG-I/MDA5-MAVS signaling pathway, remodel the tumor immune microenvironment and enhance the efficacy of immune checkpoint therapy, which provides new evidence and solutions for the development of "potentiator" for colorectal cancer immunotherapy.

Molluscum contagiosum virus protein MC089 inhibits interferon regulatory factor 3 activation

Molluscum contagiosum virus (MCV) is a human-specific poxvirus that causes a highly common but mild infection characterized by distinctive and persistent papular skin lesions. These lesions can persist for long periods without an effective clearance response from the host. MCV, like all poxviruses, encodes multiple known immunosuppressive proteins which target innate immune signalling pathways involved in viral nucleic acid sensing, interferon production and inflammation which should trigger antiviral immunity leading to clearance. Two major families of transcription factors responsible for driving the immune response to viruses are the NF-κB and the interferon regulatory factor (IRF) families. While NF-κB broadly drives pro-inflammatory gene expression and IRFs chiefly drive interferon induction, both collaborate in transactivating many of the same genes in a concerted immune response to viral infection. Here, we report that the MCV protein MC089 specifically inhibits IRF activation from both DNA- and RNA-sensing pathways, making it the first characterized MCV inhibitor to selectively target IRF activation to date. MC089 interacts with proteins required for IRF activation, namely IKKε, TBKBP1 and NAP1. Additionally, MC089 targets RNA sensing by associating with the RNA-sensing adaptor protein mitochondrial antiviral-signalling protein on mitochondria. MC089 displays specificity in its inhibition of IRF3 activation by suppressing immunostimulatory nucleic acid-induced serine 396 phosphorylation without affecting the phosphorylation of serine 386. The selective interaction of MC089 with IRF-regulatory proteins and site-specific inhibition of IRF3 phosphorylation may offer a tool to provide novel insights into the biology of IRF3 regulation.

The cytosolic DNA-sensing cGAS-STING pathway in neurodegenerative diseases

BACKGROUND

With the widespread prevalence of neurodegenerative diseases (NDs) and high rates of mortality and disability, it is imminent to find accurate targets for intervention. There is growing evidence that neuroimmunity is pivotal in the pathology of NDs and that interventions targeting neuroimmunity hold great promise. Exogenous or dislocated nucleic acids activate the cytosolic DNA sensor cyclic GMP-AMP synthase (cGAS), activating the stimulator of interferon genes (STING). The activated STING triggers innate immune responses and then the cGAS-STING signaling pathway links abnormal nucleic acid sensing to the immune response. Recently, numerous studies have shown that neuroinflammation regulated by cGAS-STING signaling plays an essential role in NDs.

AIMS

In this review, we summarized the mechanism of cGAS-STING signaling in NDs and focused on inhibitors targeting cGAS-STING.

CONCLUSION

The cGAS-STING signaling plays an important role in the pathogenesis of NDs. Inhibiting the cGAS-STING signaling may provide new measures in the treatment of NDs.

Nuclear localization of STING1 competes with canonical signaling to activate AHR for commensal and intestinal homeostasis

Extensive studies demonstrate the importance of the STING1 (also known as STING) protein as a signaling hub that coordinates immune and autophagic responses to ectopic DNA in the cytoplasm. Here, we report a nuclear function of STING1 in driving the activation of the transcription factor aryl hydrocarbon receptor (AHR) to control gut microbiota composition and homeostasis. This function was independent of DNA sensing and autophagy and showed competitive inhibition with cytoplasmic cyclic guanosine monophosphate (GMP)-AMP synthase (CGAS)-STING1 signaling. Structurally, the cyclic dinucleotide binding domain of STING1 interacted with the AHR N-terminal domain. Proteomic analyses revealed that STING1-mediated transcriptional activation of AHR required additional nuclear partners, including positive and negative regulatory proteins. Although AHR ligands could rescue colitis pathology and dysbiosis in wild-type mice, this protection was abrogated by mutational inactivation of STING1. These findings establish a key framework for understanding the nuclear molecular crosstalk between the microbiota and the immune system.

Regulation of microglia-mediated inflammation by host lncRNA Gm20559 upon flaviviral infection

BACKGROUND

Japanese Encephalitis Virus (JEV) and West Nile Viruses (WNV) are neurotropic flaviviruses which cause neuronal death and exaggerated glial activation in the central nervous system. Role of host long non coding RNAs in shaping microglial inflammation upon flavivirus infections has been unexplored. This study attempted to decipher the role of lncRNA Gm20559 in regulating microglial inflammatory response in context of flaviviruses.

METHODS

Antisense oligonucleotide LNA Gapmers designed against lncRNA Gm20559 and non-specific site (negative control) were used for Gm20559 knockdown in JEV and WNV-infected N9 microglial cells. Upon establishing successful Gm20559 knockdown, expression of various proinflammatory cytokines, chemokines, interferon-stimulated genes (ISGs) and RIG-I were checked by qRT-PCR and cytometric bead array. Western Blotting was done to analyse the phosphorylation level of various inflammatory markers and viral non-structural protein expression. Plaque Assays were employed to quantify viral titres in microglial supernatant upon knocking down Gm20559. Effect of microglial supernatant on HT22 neuronal cells was assessed by checking expression of apoptotic protein and viral non-structural protein by Western Blotting.

RESULTS

Upregulation in Gm20559 expression was observed in BALB/c pup brains, primary microglia as well as N9 microglia cell line upon both JEV and WNV infection. Knockdown of Gm20559 in JEV and WNV-infected N9 cell led to the reduction of major proinflammatory cytokines - IL-1β, IL-6, IP-10 and IFN-β. Inhibition of Gm20559 upon JEV infection in N9 microglia also led to downregulation of RIG-I and OAS-2, which was not the case in WNV-infected N9 microglia. Phosphorylation level of P38 MAPK was reduced in case of JEV-infected N9 microglia and not WNV-infected N9 microglia. Whereas phosphorylation of NF-κB pathway was unchanged upon Gm20559 knockdown in both JEV and WNV-infected N9 microglia. However, treating HT22 cells with JEV and WNV-infected microglial supernatant with and without Gm20559 could not trigger cell death or influence viral replication.

CONCLUSION

Knockdown studies on lncRNA Gm20559 suggests its pivotal role in maintaining the inflammatory milieu of microglia in flaviviral infection by modulating the expression of various pro-inflammatory cytokines. However, Gm20559-induced increased microglial proinflammatory response upon flavivirus infection fails to trigger neuronal death.

Seneca Valley Virus Degrades STING via PERK and ATF6-Mediated Reticulophagy

Seneca Valley Virus (SVV), a member of the Picornaviridae family, is an emerging porcine virus that can cause vesicular disease in pigs. However, the immune evasion mechanism of SVV remains unclear, as does its interaction with other pathways. STING (Stimulator of interferon genes) is typically recognized as a critical factor in innate immune responses to DNA virus infection, but its role during SVV infection remains poorly understood. In the present study, we observed that STING was degraded in SVV-infected PK-15 cells, and SVV replication in the cells was affected when STING was knockdown or overexpressed. The STING degradation observed was blocked when the SVV-induced autophagy was inhibited by using autophagy inhibitors (Chloroquine, Bafilomycin A1) or knockdown of autophagy related gene 5 (ATG5), suggesting that SVV-induced autophagy is responsible for STING degradation. Furthermore, the STING degradation was inhibited when reticulophagy regulator 1 (FAM134B), a reticulophagy related receptor, was knocked down, indicating that SVV infection induces STING degradation via reticulophagy. Further study showed that in eukaryotic translation initiation factor 2 alpha kinase 3 (PERK)/activating transcription factor 6 (ATF6) deficient cells, SVV infection failed to induce reticulophagy-medaited STING degradation, indicating that SVV infection caused STING degradation via PERK/ATF6-mediated reticulophagy. Notably, blocking reticulophagy effectively hindered SVV replication. Overall, our study suggested that SVV infection resulted in STING degradation via PERK and ATF6-mediated reticulophagy, which may be an immune escape strategy of SVV. This finding improves the understanding of the intricate interplay between viruses and their hosts and provides a novel strategy for the development of novel antiviral drugs.

Bat STING drives IFN-beta production in anti-RNA virus innate immune response

The ability of stimulator of interferon genes (STING) to activate interferon (IFN) responses during RNA virus infection has been demonstrated in different mammalian cells. Despite being the host of numerous RNA viruses, the role of STING in bats during RNA virus infection has not been elucidated. In this study, we identified and cloned the STING gene of the Brazilian free-tailed bat Tadarida brasiliensis (T. brasiliensis) and tested its ability to induce IFN-β by overexpressing and knocking down bat STING (BatSTING) in T. brasiliensis 1 lung (TB1 Lu) cells. In addition, we used green fluorescent protein (GFP)-labeled vesicular stomatitis virus (VSV) VSV-GFP as a model to detect the antiviral activity of BatSTING. The results showed that overexpression of STING in TB1 Lu cells stimulated by cGAS significantly inhibited RNA virus replication, and the antiviral activities were associated with its ability to regulate basal expression of IFN-β and some IFN stimulated genes (ISGs). We also found that BatSTING was able to be activated after stimulation by diverse RNA viruses. The results of TB1 Lu cells with STING deficiency showed that knockdown of BatSTING severely hindered the IFN-β response triggered by VSV-GFP. Based on this, we confirm that BatSTING is required to induce IFN-β expression during RNA virus infection. In conclusion, our experimental data clearly show that STING in bat hosts plays an irreplaceable role in mediating IFN-β responses and anti-RNA virus infection.

Reducing lipid peroxidation attenuates stress-induced susceptibility to herpes simplex virus type 1

Psychological stress increases the susceptibility to herpes simplex virus type 1 (HSV-1) infection. There is no effective intervention due to the unknown pathogenesis mechanisms. In this study we explored the molecular mechanisms underlying stress-induced HSV-1 susceptibility and the antiviral effect of a natural compound rosmarinic acid (RA) in vivo and in vitro. Mice were administered RA (11.7, 23.4 mg·kg-1·d-1, i.g.) or acyclovir (ACV, 206 mg·kg-1·d-1, i.g.) for 23 days. The mice were subjected to restraint stress for 7 days followed by intranasal infection with HSV-1 on D7. At the end of RA or ACV treatment, mouse plasma samples and brain tissues were collected for analysis. We showed that both RA and ACV treatment significantly decreased stress-augmented mortality and alleviated eye swelling and neurological symptoms in HSV-1-infected mice. In SH-SY5Y cells and PC12 cells exposed to the stress hormone corticosterone (CORT) plus HSV-1, RA (100 μM) significantly increased the cell viability, and inhibited CORT-induced elevation in the expression of viral proteins and genes. We demonstrated that CORT (50 μM) triggered lipoxygenase 15 (ALOX15)-mediated redox imbalance in the neuronal cells, increasing the level of 4-HNE-conjugated STING, which impaired STING translocation from the endoplasmic reticulum to Golgi; the abnormality of STING-mediated innate immunity led to HSV-1 susceptibility. We revealed that RA was an inhibitor of lipid peroxidation by directly targeting ALOX15, thus RA could rescue stress-weakened neuronal innate immune response, thereby reducing HSV-1 susceptibility in vivo and in vitro. This study illustrates the critical role of lipid peroxidation in stress-induced HSV-1 susceptibility and reveals the potential for developing RA as an effective intervention in anti-HSV-1 therapy.

STING strengthens host anti-hantaviral immunity through an interferon-independent pathway

Hantaan virus (HTNV), the prototype virus of hantavirus, could escape innate immunity by restraining type I interferon (IFN) responses. It is largely unknown whether there existed other efficient anti-hantaviral tactics in host cells. Here, we demonstrate that the stimulator of interferon genes (STING) strengthens the host IFN-independent anti-hantaviral immunity. HTNV infection activates RIG-I through IRE1-XBP 1-mediated ER stress, which further facilitates the subcellular translocation and activation of STING. During this process, STING triggers cellular autophagy by interacting with Rab7A, thus restricting viral replication. To note, the anti-hantaviral effects of STING are independent of canonical IFN signaling. Additionally, neither application of the pharmacological antagonist nor the agonist targeting STING could improve the outcomes of nude mice post HTNV challenge in vivo. However, the administration of plasmids exogenously expressing the mutant C-terminal tail (ΔCTT) STING, which would not trigger the type I IFN responses, protected the nude mice from lethal HTNV infection. In summary, our research revealed a novel antiviral pathway through the RIG-I-STING-autophagy pathway, which offered novel therapeutic strategies against hantavirus infection.

The Many Ways to Deal with STING

The stimulator of interferon genes (STING) is an adaptor protein involved in the activation of IFN-β and many other genes associated with the immune response activation in vertebrates. STING induction has gained attention from different angles such as the potential to trigger an early immune response against different signs of infection and cell damage, or to be used as an adjuvant in cancer immune treatments. Pharmacological control of aberrant STING activation can be used to mitigate the pathology of some autoimmune diseases. The STING structure has a well-defined ligand binding site that can harbor natural ligands such as specific purine cyclic di-nucleotides (CDN). In addition to a canonical stimulation by CDNs, other non-canonical stimuli have also been described, whose exact mechanism has not been well defined. Understanding the molecular insights underlying the activation of STING is important to realize the different angles that need to be considered when designing new STING-binding molecules as therapeutic drugs since STING acts as a versatile platform for immune modulators. This review analyzes the different determinants of STING regulation from the structural, molecular, and cell biology points of view.

Orchestration of Mitochondrial Function and Remodeling by Post-Translational Modifications Provide Insight into Mechanisms of Viral Infection

The regulation of mitochondria structure and function is at the core of numerous viral infections. Acting in support of the host or of virus replication, mitochondria regulation facilitates control of energy metabolism, apoptosis, and immune signaling. Accumulating studies have pointed to post-translational modification (PTM) of mitochondrial proteins as a critical component of such regulatory mechanisms. Mitochondrial PTMs have been implicated in the pathology of several diseases and emerging evidence is starting to highlight essential roles in the context of viral infections. Here, we provide an overview of the growing arsenal of PTMs decorating mitochondrial proteins and their possible contribution to the infection-induced modulation of bioenergetics, apoptosis, and immune responses. We further consider links between PTM changes and mitochondrial structure remodeling, as well as the enzymatic and non-enzymatic mechanisms underlying mitochondrial PTM regulation. Finally, we highlight some of the methods, including mass spectrometry-based analyses, available for the identification, prioritization, and mechanistic interrogation of PTMs.

Role of cGAS-Sting Signaling in Alzheimer's Disease

There is mounting evidence that the development of Alzheimer's disease (AD) interacts extensively with immunological processes in the brain and extends beyond the neuronal compartment. Accumulation of misfolded proteins can activate an innate immune response that releases inflammatory mediators and increases the severity and course of the disease. It is widely known that type-I interferon-driven neuroinflammation in the central nervous system (CNS) accelerates the development of numerous acute and chronic CNS diseases. It is becoming better understood how the cyclic GMP-AMP synthase (cGAS) and its adaptor protein Stimulator of Interferon Genes (STING) triggers type-I IFN-mediated neuroinflammation. We discuss the principal elements of the cGAS-STING signaling pathway and the mechanisms underlying the association between cGAS-STING activity and various AD pathologies. The current understanding of beneficial and harmful cGAS-STING activity in AD and the current treatment pathways being explored will be discussed in this review. The cGAS-STING regulation offers a novel therapeutic opportunity to modulate inflammation in the CNS because it is an upstream regulator of type-I IFNs.

The role of STING signaling in central nervous system infection and neuroinflammatory disease

The cyclic guanosine monophosphate-adenosine monophosphate (GMP-AMP) synthase-Stimulator of Interferon Genes (cGAS-STING) pathway is a critical innate immune mechanism for detecting the presence of double-stranded DNA (dsDNA) and prompting a robust immune response. Canonical cGAS-STING activation occurs when cGAS, a predominantly cytosolic pattern recognition receptor, binds microbial DNA to promote STING activation. Upon STING activation, transcription factors enter the nucleus to cause the production of Type I interferons, inflammatory cytokines whose primary function is to prime the host for viral infection by producing a number of antiviral interferon-stimulated genes. While the pathway was originally described in viral infection, more recent studies have implicated cGAS-STING signaling in a number of different contexts, including autoimmune disease, cancer, injury, and neuroinflammatory disease. This review focuses on how our understanding of the cGAS-STING pathway has evolved over time with an emphasis on the role of STING-mediated neuroinflammation and infection in the nervous system. We discuss recent findings on how STING signaling contributes to the pathology of pain, traumatic brain injury, and stroke, as well as how mitochondrial DNA may promote STING activation in common neurodegenerative diseases. We conclude by commenting on the current knowledge gaps that should be filled before STING can be an effective therapeutic target in neuroinflammatory disease. This article is categorized under: Neurological Diseases > Molecular and Cellular Physiology Infectious Diseases > Molecular and Cellular Physiology Immune System Diseases > Molecular and Cellular Physiology.

Innate immune pathway modulator screen identifies STING pathway activation as a strategy to inhibit multiple families of arbo and respiratory viruses

RNA viruses continue to remain a threat for potential pandemics due to their rapid evolution. Potentiating host antiviral pathways to prevent or limit viral infections is a promising strategy. Thus, by testing a library of innate immune agonists targeting pathogen recognition receptors, we observe that Toll-like receptor 3 (TLR3), stimulator of interferon genes (STING), TLR8, and Dectin-1 ligands inhibit arboviruses, Chikungunya virus (CHIKV), West Nile virus, and Zika virus to varying degrees. STING agonists (cAIMP, diABZI, and 2',3'-cGAMP) and Dectin-1 agonist scleroglucan demonstrate the most potent, broad-spectrum antiviral function. Furthermore, STING agonists inhibit severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and enterovirus-D68 (EV-D68) infection in cardiomyocytes. Transcriptome analysis reveals that cAIMP treatment rescue cells from CHIKV-induced dysregulation of cell repair, immune, and metabolic pathways. In addition, cAIMP provides protection against CHIKV in a chronic CHIKV-arthritis mouse model. Our study describes innate immune signaling circuits crucial for RNA virus replication and identifies broad-spectrum antivirals effective against multiple families of pandemic potential RNA viruses.

Interplay between RNA viruses and cGAS/STING axis in innate immunity

While the function of cGAS/STING signalling axis in the innate immune response to DNA viruses is well deciphered, increasing evidence demonstrates its significant contribution in the control of RNA virus infections. After the first evidence of cGAS/STING antagonism by flaviviruses, STING activation has been detected following infection by various enveloped RNA viruses. It has been discovered that numerous viral families have implemented advanced strategies to antagonize STING pathway through their evolutionary path. This review summarizes the characterized cGAS/STING escape strategies to date, together with the proposed mechanisms of STING signalling activation perpetrated by RNA viruses and discusses possible therapeutic approaches. Further studies regarding the interaction between RNA viruses and cGAS/STING-mediated immunity could lead to major discoveries important for the understanding of immunopathogenesis and for the treatment of RNA viral infections.

Potential Therapeutic Value of the STING Inhibitors

The stimulator of interferon genes (STING) is a critical protein in the activation of the immune system in response to DNA. It can participate the inflammatory response process by modulating the inflammation-preferred translation program through the STING-PKR-like endoplasmic reticulum kinase (PERK)-eIF2α pathway or by inducing the secretion of type I interferons (IFNs) and a variety of proinflammatory factors through the recruitment of TANK-binding kinase 1 (TBK1) and interferon regulatory factor 3 (IRF3) or the regulation of the nuclear factor kappa-B (NF-κB) pathway. Based on the structure, location, function, genotype, and regulatory mechanism of STING, this review summarizes the potential value of STING inhibitors in the prevention and treatment of infectious diseases, psoriasis, systemic lupus erythematosus, non-alcoholic fatty liver disease, and other inflammatory and autoimmune diseases.

Leaked genomic and mitochondrial DNA contribute to the host response to noroviruses in a STING-dependent manner

The cGAS-STING pathway is central to the interferon response against DNA viruses. However, recent studies are increasingly demonstrating its role in the restriction of some RNA viruses. Here, we show that the cGAS-STING pathway also contributes to the interferon response against noroviruses, currently the commonest causes of infectious gastroenteritis worldwide. We show a significant reduction in interferon-β induction and a corresponding increase in viral replication in norovirus-infected cells after deletion of STING, cGAS, or IFI16. Further, we find that immunostimulatory host genome-derived DNA and mitochondrial DNA accumulate in the cytosol of norovirus-infected cells. Lastly, overexpression of the viral NS4 protein is sufficient to drive the accumulation of cytosolic DNA. Together, our data find a role for cGAS, IFI16, and STING in the restriction of noroviruses and show the utility of host genomic DNA as a damage-associated molecular pattern in cells infected with an RNA virus.

Innate sensing of picornavirus infection involves cGAS-STING-mediated antiviral responses triggered by mitochondrial DNA release

Cyclic GMP-AMP synthase (cGAS) plays a key role in the innate immune responses to both DNA and RNA virus infection. Here, we found that enterovirus 71 (EV-A71), Seneca Valley virus (SVV), and foot-and-mouth disease virus (FMDV) infection triggered mitochondria damage and mitochondrial DNA (mtDNA) release in vitro and vivo. These responses were mediated by picornavirus 2B proteins which induced mtDNA release during viral replication. SVV infection caused the opening of mitochondrial permeability transition pore (mPTP) and led to voltage-dependent anion channel 1 (VDAC1)- and BCL2 antagonist/killer 1 (Bak) and Bak/BCL2-associated X (Bax)-dependent mtDNA leakage into the cytoplasm, while EV-A71 and FMDV infection induced mPTP opening and resulted in VDAC1-dependent mtDNA release. The released mtDNA bound to cGAS and activated cGAS-mediated antiviral immune response. cGAS was essential for inhibiting EV-A71, SVV, and FMDV replication by regulation of IFN-β production. cGAS deficiency contributed to higher mortality of EV-A71- or FMDV-infected mice. In addition, we found that SVV 2C protein was responsible for decreasing cGAS expression through the autophagy pathway. The 9th and 153rd amino acid sites in 2C were critical for induction of cGAS degradation. Furthermore, we also show that EV-A71, CA16, and EMCV 2C antagonize the cGAS-stimulator of interferon genes (STING) pathway through interaction with STING, and highly conserved amino acids Y155 and S156 were critical for this inhibitory effect. In conclusion, these data reveal novel mechanisms of picornaviruses to block the antiviral effect mediated by the cGAS-STING signaling pathway, which will provide insights for developing antiviral strategies against picornaviruses.

Radix Isatidis polysaccharide (RIP) resists the infection of QX-type infectious bronchitis virus via the MDA5/TLR3/IRF7 signaling pathway

Although vaccines play a major role in the prevention of infectious bronchitis (IB), Anti-IB drugs still have great potential in poultry production. Radix Isatidis polysaccharide (RIP) is a crude extract of Banlangen with antioxidant, antibacterial, antiviral, and multiple immunomodulatory functions. The aim of this study was to explore the innate immune mechanisms responsible for RIP-mediated alleviation of infectious bronchitis virus (IBV)-induced kidney lesions in chickens. Specific-pathogen-free (SPF) chicken and chicken embryo kidney (CEK) cells cultures were pretreated with RIP and then infected with the QX-type IBV strain, Sczy3. Morbidity, mortality, and tissue mean lesion scores were calculated for IBV-infected chickens, and the viral loads, inflammatory factor gene mRNA expression levels, and innate immune pathway gene mRNA expression levels in infected chickens and CEK cell cultures were determined. The results show that RIP could alleviate IBV-induced kidney damage, decrease CEK cells susceptibility to IBV infection, and reduce viral loads. Additionally, RIP reduced the mRNA expression levels of the inflammatory factors IL-6, IL-8, and IL-1β by decreasing the mRNA expression level of NF-κB. Conversely, the expression levels of MDA5, TLR3, STING, Myd88, IRF7, and IFN-β were increased, indicating that RIP conferred resistance to QX-type IBV infection via the MDA5, TLR3, IRF7 signaling pathway. These results provide a reference for both further research into the antiviral mechanisms of RIP and the development of preventative and therapeutic drugs for IB.

Broad-spectrum antiviral inhibitors targeting pandemic potential RNA viruses

RNA viruses continue to remain a clear and present threat for potential pandemics due to their rapid evolution. To mitigate their impact, we urgently require antiviral agents that can inhibit multiple families of disease-causing viruses, such as arthropod-borne and respiratory pathogens. Potentiating host antiviral pathways can prevent or limit viral infections before escalating into a major outbreak. Therefore, it is critical to identify broad-spectrum antiviral agents. We have tested a small library of innate immune agonists targeting pathogen recognition receptors, including TLRs, STING, NOD, Dectin and cytosolic DNA or RNA sensors. We observed that TLR3, STING, TLR8 and Dectin-1 ligands inhibited arboviruses, Chikungunya virus (CHIKV), West Nile virus (WNV) and Zika virus, to varying degrees. Cyclic dinucleotide (CDN) STING agonists, such as cAIMP, diABZI, and 2',3'-cGAMP, and Dectin-1 agonist scleroglucan, demonstrated the most potent, broad-spectrum antiviral function. Comparative transcriptome analysis revealed that CHIKV-infected cells had larger number of differentially expressed genes than of WNV and ZIKV. Furthermore, gene expression analysis showed that cAIMP treatment rescued cells from CHIKV-induced dysregulation of cell repair, immune, and metabolic pathways. In addition, cAIMP provided protection against CHIKV in a CHIKV-arthritis mouse model. Cardioprotective effects of synthetic STING ligands against CHIKV, WNV, SARS-CoV-2 and enterovirus D68 (EV-D68) infections were demonstrated using human cardiomyocytes. Interestingly, the direct-acting antiviral drug remdesivir, a nucleoside analogue, was not effective against CHIKV and WNV, but exhibited potent antiviral effects against SARS-CoV-2, RSV (respiratory syncytial virus), and EV-D68. Our study identifies broad-spectrum antivirals effective against multiple families of pandemic potential RNA viruses, which can be rapidly deployed to prevent or mitigate future pandemics.

Host immune responses in the central nervous system during fungal infections

Fungal infections in the central nervous system (CNS) cause high morbidity and mortality. The frequency of CNS mycosis has increased over the last two decades as more individuals go through immunocompromised conditions for various reasons. Nevertheless, options for clinical interventions for CNS mycoses are still limited. Thus, there is an urgent need to understand the host-pathogen interaction mechanisms in CNS mycoses for developing novel treatments. Although the CNS has been regarded as an immune-privileged site, recent studies demonstrate the critical involvement of immune responses elicited by CNS-resident and CNS-infiltrated cells during fungal infections. In this review, we discuss mechanisms of fungal invasion in the CNS, fungal pathogen detection by CNS-resident cells (microglia, astrocytes, oligodendrocytes, neurons), roles of CNS-infiltrated leukocytes, and host immune responses. We consider that understanding host immune responses in the CNS is crucial for endeavors to develop treatments for CNS mycosis.

Flaviviridae Nonstructural Proteins: The Role in Molecular Mechanisms of Triggering Inflammation

Members of the Flaviviridae family are posing a significant threat to human health worldwide. Many flaviviruses are capable of inducing severe inflammation in humans. Flaviviridae nonstructural proteins, apart from their canonical roles in viral replication, have noncanonical functions strongly affecting antiviral innate immunity. Among these functions, antagonism of type I IFN is the most investigated; meanwhile, more data are accumulated on their role in the other pathways of innate response. This review systematizes the last known data on the role of Flaviviridae nonstructural proteins in molecular mechanisms of triggering inflammation, with an emphasis on their interactions with TLRs and RLRs, interference with NF-κB and cGAS-STING signaling, and activation of inflammasomes.

Surgical Strikes on Host Defenses: Role of the Viral Protease Activity in Innate Immune Antagonism

As a frontline defense mechanism against viral infections, the innate immune system is the primary target of viral antagonism. A number of virulence factors encoded by viruses play roles in circumventing host defenses and augmenting viral replication. Among these factors are viral proteases, which are primarily responsible for maturation of viral proteins, but in addition cause proteolytic cleavage of cellular proteins involved in innate immune signaling. The study of these viral protease-mediated host cleavages has illuminated the intricacies of innate immune networks and yielded valuable insights into viral pathogenesis. In this review, we will provide a brief summary of how proteases of positive-strand RNA viruses, mainly from the Picornaviridae, Flaviviridae and Coronaviridae families, proteolytically process innate immune components and blunt their functions.

Duck plague virus UL41 protein inhibits RIG-I/MDA5-mediated duck IFN-β production via mRNA degradation activity

Retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs) are cytosolic pattern recognition receptors that initiate innate antiviral immunity. Recent reports found that duck RLRs significantly restrict duck plague virus (DPV) infection. However, the molecular mechanism by which DPV evades immune responses is unknown. In this study, we first found that the DPV UL41 protein inhibited duck interferon-β (IFN-β) production mediated by RIG-I and melanoma differentiation-associated gene 5 (MDA5) by broadly downregulating the mRNA levels of important adaptor molecules, such as RIG-I, MDA5, mitochondrial antiviral signalling protein (MAVS), stimulator of interferon gene (STING), TANK-binding kinase 1 (TBK1), and interferon regulatory factor (IRF) 7. The conserved sites of the UL41 protein, E229, D231, and D232, were responsible for this activity. Furthermore, the DPV CHv-BAC-ΔUL41 mutant virus induced more duck IFN-β and IFN-stimulated genes (Mx, OASL) production in duck embryo fibroblasts (DEFs) than DPV CHv-BAC parent virus. Our findings provide insights into the molecular mechanism underlying DPV immune evasion.

STING1 in Different Organelles: Location Dictates Function

Stimulator of interferon response cGAMP interactor 1 (STING1), also known as TMEM173, is an immune adaptor protein that governs signal crosstalk that is implicated in many physiological and pathological processes. Although it has been established that STING1 traffics from the endoplasmic reticulum (ER) to Golgi apparatus (Golgi) upon DNA-triggered activation, emerging evidence reveals that STING1 can be transported to different organelles, which dictate its immune-dependent (e.g., the production of type I interferons and pro-inflammatory cytokines) and -independent (e.g., the activation of autophagy and cell death) functions. In this brief review, we outline the roles of STING1 in different organelles (including the ER, ER-Golgi intermediate compartment, Golgi, mitochondria, endosomes, lysosomes, and nucleus) and discuss the potential relevance of these roles to diseases and pharmacological interventions.

Type I Interferon Response Is Mediated by NLRX1-cGAS-STING Signaling in Brain Injury

Background

Inflammation is a significant contributor to neuronal death and dysfunction following traumatic brain injury (TBI). Recent evidence suggests that interferons may be a key regulator of this response. Our studies evaluated the role of the Cyclic GMP-AMP Synthase-Stimulator of Interferon Genes (cGAS-STING) signaling pathway in a murine model of TBI.

Methods

Male, 8-week old wildtype, STING knockout (^−/−), cGAS^−/−, and NLRX1^−/− mice were subjected to controlled cortical impact (CCI) or sham injury. Histopathological evaluation of tissue damage was assessed using non-biased stereology, which was complemented by analysis at the mRNA and protein level using qPCR and western blot analysis, respectively.

Results

We found that STING and Type I interferon-stimulated genes were upregulated after CCI injury in a bi-phasic manner and that loss of cGAS or STING conferred neuroprotection concomitant with a blunted inflammatory response at 24 h post-injury. cGAS^−/− animals showed reduced motor deficits 4 days after injury (dpi), and amelioration of tissue damage was seen in both groups of mice up to 14 dpi. Given that cGAS requires a cytosolic damage- or pathogen-associated molecular pattern (DAMP/PAMP) to prompt downstream STING signaling, we further demonstrate that mitochondrial DNA is present in the cytosol after TBI as one possible trigger for this pathway. Recent reports suggest that the immune modulator NLR containing X1 (NLRX1) may sequester STING during viral infection. Our findings show that NLRX1 may be an additional regulator that functions upstream to regulate the cGAS-STING pathway in the brain.

Conclusions

These findings suggest that the canonical cGAS-STING-mediated Type I interferon signaling axis is a critical component of neural tissue damage following TBI and that mtDNA may be a possible trigger in this response.

Flaviviruses: Innate Immunity, Inflammasome Activation, Inflammatory Cell Death, and Cytokines

The innate immune system is the host’s first line of defense against the invasion of pathogens including flavivirus. The programmed cell death controlled by genes plays an irreplaceable role in resisting pathogen invasion and preventing pathogen infection. However, the inflammatory cell death, which can trigger the overflow of a large number of pro-inflammatory cytokines and cell contents, will initiate a severe inflammatory response. In this review, we summarized the current understanding of the innate immune response, inflammatory cell death pathway and cytokine secretion regulation during Dengue virus, West Nile virus, Zika virus, Japanese encephalitis virus and other flavivirus infections. We also discussed the impact of these flavivirus and viral proteins on these biological processes. This not only provides a scientific basis for elucidating the pathogenesis of flavivirus, but also lays the foundation for the development of effective antiviral therapies.

Modulation of SF3B1 in the pre-mRNA spliceosome induces a RIG-I-dependent type I IFN response

Nucleic acid-sensing pathways play critical roles in innate immune activation through the production of type I interferon (IFN-I) and proinflammatory cytokines. These factors are required for effective antitumor immune responses. Pharmacological modulators of the pre-mRNA spliceosome splicing factor 3b subunit 1 (SF3B1) are under clinical investigation as cancer cytotoxic agents. However, potential roles of these agents in aberrant RNA generation and subsequent RNA-sensing pathway activation have not been studied. In this study, we observed that SF3B1 pharmacological modulation using pladienolide B (Plad B) induces production of aberrant RNA species and robust IFN-I responses via engagement of the dsRNA sensor retinoic acid-inducible gene I (RIG-I) and downstream interferon regulatory factor 3. We found that Plad B synergized with canonical RIG-I agonism to induce the IFN-I response. In addition, Plad B induced NF-κB responses and secretion of proinflammatory cytokines and chemokines. Finally, we showed that cancer cells bearing the hotspot SF3B1K700E mutation, which leads to global aberrant splicing, had enhanced IFN-I response to canonical RIG-I agonism. Together, these results demonstrate that pharmacological modulation of SF3B1 in cancer cells can induce an enhanced IFN-I response dependent on RIG-I expression. The study suggests that spliceosome modulation may not only induce direct cancer cell cytotoxicity but also initiate an innate immune response via activation of RNA-sensing pathways.

The crosstalk between viral RNA- and DNA-sensing mechanisms

Viral infections pose a severe threat to humans by causing many infectious, even fatal, diseases, such as the current pandemic disease (COVID-19) since 2019, and understanding how the host innate immune system recognizes viruses has become more important. Endosomal and cytosolic sensors can detect viral nucleic acids to induce type I interferon and proinflammatory cytokines, subsequently inducing interferon-stimulated genes for restricting viral infection. Although viral RNA and DNA sensing generally rely on diverse receptors and adaptors, the crosstalk between DNA and RNA sensing is gradually appreciated. This minireview highlights the overlap between the RNA- and DNA-sensing mechanisms in antiviral innate immunity, which significantly amplifies the antiviral innate responses to restrict viral infection and might be a potential novel target for preventing and treating viral diseases.

Emerging roles of peroxisomes in viral infections

Peroxisomes, essential subcellular organelles that fulfill important functions in lipid and reactive oxygen species metabolism, have recently emerged as key players during viral infections. Their importance for the establishment of the cellular antiviral response has been highlighted by numerous reports of specific evasion of peroxisome-dependent signaling by different viruses. Recent data demonstrate that peroxisomes also assume important proviral functions. Here, we review and discuss the recent advances in the study of the diverse roles of peroxisomes during viral infections, from animal to plant viruses, and from basic to translational perspectives. We further discuss the future development of this emerging area and propose that peroxisome-related mechanisms represent a promising target for the development of novel antiviral strategies.

cGAS- Stimulator of Interferon Genes Signaling in Central Nervous System Disorders

Cytosolic nucleic acid sensors contribute to the initiation of innate immune responses by playing a critical role in the detection of pathogens and endogenous nucleic acids. The cytosolic DNA sensor cyclic-GMP-AMP synthase (cGAS) and its downstream effector, stimulator of interferon genes (STING), mediate innate immune signaling by promoting the release of type I interferons (IFNs) and other inflammatory cytokines. These biomolecules are suggested to play critical roles in host defense, senescence, and tumor immunity. Recent studies have demonstrated that cGAS-STING signaling is strongly implicated in the pathogenesis of central nervous system (CNS) diseases which are underscored by neuroinflammatory-driven disease progression. Understanding and regulating the interactions between cGAS-STING signaling and the nervous system may thus provide an effective approach to prevent or delay late-onset CNS disorders. Here, we present a review of recent advances in the literature on cGAS-STING signaling and provide a comprehensive overview of the modulatory patterns of the cGAS-STING pathway in CNS disorders.

STING Signaling and Sterile Inflammation

Innate immunity is regulated by a broad set of evolutionary conserved receptors to finely probe the local environment and maintain host integrity. Besides pathogen recognition through conserved motifs, several of these receptors also sense aberrant or misplaced self-molecules as a sign of perturbed homeostasis. Among them, self-nucleic acid sensing by the cyclic GMP-AMP synthase (cGAS)/stimulator of interferon genes (STING) pathway alerts on the presence of both exogenous and endogenous DNA in the cytoplasm. We review recent literature demonstrating that self-nucleic acid detection through the STING pathway is central to numerous processes, from cell physiology to sterile injury, auto-immunity and cancer. We address the role of STING in autoimmune diseases linked to dysfunctional DNAse or related to mutations in DNA sensing pathways. We expose the role of the cGAS/STING pathway in inflammatory diseases, neurodegenerative conditions and cancer. Connections between STING in various cell processes including autophagy and cell death are developed. Finally, we review proposed mechanisms to explain the sources of cytoplasmic DNA.

STING nuclear partners contribute to innate immune signaling responses

STimulator of INterferon Genes (STING) is an adaptor for cytoplasmic DNA sensing by cGAMP/cGAS that helps trigger innate immune responses (IIRs). Although STING is mostly localized in the ER, we find a separate inner nuclear membrane pool of STING that increases mobility and redistributes to the outer nuclear membrane upon IIR stimulation by transfected dsDNA or dsRNA mimic poly(I:C). Immunoprecipitation of STING from isolated nuclear envelopes coupled with mass spectrometry revealed a distinct nuclear envelope-STING proteome consisting of known nuclear membrane proteins and enriched in DNA- and RNA-binding proteins. Seventeen of these nuclear envelope STING partners are known to bind direct interactors of IRF3/7 transcription factors, and testing a subset of these revealed STING partners SYNCRIP, MEN1, DDX5, snRNP70, RPS27a, and AATF as novel modulators of dsDNA-triggered IIRs. Moreover, we find that SYNCRIP is a novel antagonist of the RNA virus, influenza A, potentially shedding light on reports of STING inhibition of RNA viruses.

STING1 is essential for an RNA-virus triggered autophagy

While the functions of STING1 (stimulator of interferon response cGAMP interactor 1) during DNA virus infection had been well documented, the roles STING1 plays during RNA viruses infection is obscure. Infection with foot-and-mouth disease virus (FMDV), a well-known picornavirus, induces endoplasmic reticulum (ER) stress response and autophagy. Here, we found that the FMDV-induced integrated stress response originates from the cellular pattern recognition receptor DDX58/RIG-I (DExD/H-box helicase 58). DDX58 transmits signals to the ER-anchored adaptor protein STING1, which specifically activates the EIF2AK3/PERK (eukaryotic translation initiation factor 2A)-dependent integrated stress response and finally leads to reticulophagy and degradation of STING1 itself. Knockdown/knockout of STING1 or EIF2AK3 suppresses FMDV genome replication and viral protein expression. Reticulophagy induction by STING1 does not require its translocation to the Golgi or IFN response activation. However, STING1 polymerization is necessary for the FMDV-induced integrated stress response and reticulophagy. Our work illustrated the signaling cascades that mediate the cellular stress response to FMDV infection and indicated that induction of autophagy in response to both DNA and RNA virus infection may be an evolutionarily conserved function of STING1. Abbreviations: ATF6: activating transcription factor 6; CGAS: cyclic GMP-AMP synthase; DDX58/RIG-I: DExD/H-box helicase 58; EIF2A/eIF2α: eukaryotic translation initiation factor 2A; EIF2AK3/PERK: eukaryotic translation initiation factor 2 alpha kinase 2; ER: endoplasmic reticulum; ERN1/IRE1: endoplasmic reticulum to nucleus signaling 1; FMD: foot-and-mouth disease; FMDV: foot-and-mouth disease virus; IFIH1/MDA5: interferon induced with helicase C domain 1; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; MAVS: mitochondrial antiviral signaling protein; MOI: multiplicity of infection; RETREG1/FAM134B: reticulophagy regulator 1; STING1: stimulator of interferon response cGAMP interactor 1; TCID50: 50% tissue culture infectious dose; XBP1: X-box binding protein 1.

Making Sense of Intracellular Nucleic Acid Sensing in Type I Interferon Activation in Sjögren's Syndrome

Primary Sjögren's syndrome (pSS) is a systemic autoimmune rheumatic disease characterized by dryness of the eyes and mucous membranes, which can be accompanied by various extraglandular autoimmune manifestations. The majority of patients exhibit persistent systemic activation of the type I interferon (IFN) system, a feature that is shared with other systemic autoimmune diseases. Type I IFNs are integral to anti-viral immunity and are produced in response to stimulation of pattern recognition receptors, among which nucleic acid (NA) receptors. Dysregulated detection of endogenous NAs has been widely implicated in the pathogenesis of systemic autoimmune diseases. Stimulation of endosomal Toll-like receptors by NA-containing immune complexes are considered to contribute to the systemic type I IFN activation. Accumulating evidence suggest additional roles for cytosolic NA-sensing pathways in the pathogenesis of systemic autoimmune rheumatic diseases. In this review, we will provide an overview of the functions and signaling of intracellular RNA- and DNA-sensing receptors and summarize the evidence for a potential role of these receptors in the pathogenesis of pSS and the sustained systemic type I IFN activation.

Mitochondria Associated Membranes (MAMs): Architecture and physiopathological role

In the last decades, the communication between the Endoplasmic reticulum (ER) and mitochondria has obtained great attention: mitochondria-associated membranes (MAMs), which represent the contact sites between the two organelles, have indeed emerged as central hub involved in different fundamental cell processes, such as calcium signalling, apoptosis, autophagy and lipid biosynthesis. Consistently, dysregulation of ER-mitochondria crosstalk has been associated with different pathological conditions, ranging from diabetes to cancer and neurodegenerative diseases. In this review, we will try to summarize the current knowledge on MAMs' structure and functions in health and their relevance for human diseases.

A Critical Role for STING Signaling in Limiting Pathogenesis of Chikungunya Virus

The stimulator of interferon gene (STING) pathway controls both DNA and RNA virus infection. STING is essential for induction of innate immune responses during DNA virus infection, while its mechanism against RNA virus remains largely elusive. We show that STING signaling is crucial for restricting chikungunya virus infection and arthritis pathogenesis. Sting-deficient mice (Stinggt/gt) had elevated viremia throughout the viremic stage and viral burden in feet transiently, with a normal type I IFN response. Stinggt/gt mice presented much greater foot swelling, joint damage, and immune cell infiltration than wild-type mice. Intriguingly, expression of interferon-γ and Cxcl10 was continuously upregulated by approximately 7 to 10-fold and further elevated in Stinggt/gt mice synchronously with arthritis progression. However, expression of chemoattractants for and activators of neutrophils, Cxcl5, Cxcl7, and Cxcr2 was suppressed in Stinggt/gt joints. These results demonstrate that STING deficiency leads to an aberrant chemokine response that promotes pathogenesis of CHIKV arthritis.

Chikungunya virus antagonizes cGAS-STING mediated type-I interferon responses by degrading cGAS

Chikungunya virus (CHIKV) is a mosquito-borne alphavirus known to cause epidemics resulting in predominantly symptomatic infections, which in rare cases cause long term debilitating arthritis and arthralgia. Significant progress has been made in understanding the roles of canonical RNA sensing pathways in the host recognition of CHIKV; however, less is known regarding antagonism of CHIKV by cytosolic DNA sensing pathways like that of cyclic GMP-AMP synthase (cGAS) and Stimulator of Interferon Genes (STING). With the use of cGAS or STING null cells we demonstrate that the pathway restricts CHIKV replication in fibroblasts and immune cells. We show that DNA accumulates in the cytoplasm of infected cells and that CHIKV blocks DNA dependent IFN-β transcription. This antagonism of DNA sensing is via an early autophagy-mediated degradation of cGAS and expression of the CHIKV capsid protein is sufficient to induce cGAS degradation. Furthermore, we identify an interaction of CHIKV nsP1 with STING and map the interaction to 23 residues in the cytosolic loop of the adaptor protein. This interaction stabilizes the viral protein and increases the level of palmitoylated nsP1 in cells. Together, this work supports previous publications highlighting the relevance of the cGAS-STING pathway in the early detection of (+)ssRNA viruses and provides direct evidence that CHIKV interacts with and antagonizes cGAS-STING signaling.

Innate Immune DNA Sensing of Flaviviruses

Flaviviruses are arthropod-borne RNA viruses that have been used extensively to study host antiviral responses. Often selected just to represent standard single-stranded positive-sense RNA viruses in early studies, the Flavivirus genus over time has taught us how truly unique it is in its remarkable ability to target not just the RNA sensory pathways but also the cytosolic DNA sensing system for its successful replication inside the host cell. This review summarizes the main developments on the unexpected antagonistic strategies utilized by different flaviviruses, with RNA genomes, against the host cyclic GAMP synthase (cGAS)/stimulator of interferon genes (STING) cytosolic DNA sensing pathway in mammalian systems. On the basis of the recent advancements on this topic, we hypothesize that the mechanisms of viral sensing and innate immunity are much more fluid than what we had anticipated, and both viral and host factors will continue to be found as important factors contributing to the host innate immune system in the future.

Neurocognitive impacts of arbovirus infections

Arthropod-borne viruses or arbovirus, are most commonly associated with acute infections, resulting on various symptoms ranging from mild fever to more severe disorders such as hemorrhagic fever. Moreover, some arboviral infections can be associated with important neuroinflammation that can trigger neurological disorders including encephalitis, paralysis, ophthalmological impairments, or developmental defects, which in some cases, can lead to long-term defects of the central nervous system (CNS). This is well illustrated in Zika virus-associated congenital brain malformations but also in West Nile virus-induced synaptic dysfunctions that can last well beyond infection and lead to cognitive deficits. Here, we summarize clinical and mechanistic data reporting on cognitive disturbances triggered by arboviral infections, which may highlight growing public health issues spanning the five continents.

The interactions between cGAS-STING pathway and pathogens

Cytosolic DNA is an indicator of pathogen invasion or DNA damage. The cytosolic DNA sensor cyclic guanosine monophosphate-adenosine monophosphate (cGAMP) synthase (cGAS) detects DNA and then mediates downstream immune responses through the molecule stimulator of interferon genes (STING, also known as MITA, MPYS, ERIS and TMEM173). Recent studies focusing on the roles of the cGAS-STING pathway in evolutionary distant species have partly sketched how the mammalian cGAS-STING pathways are shaped and have revealed its evolutionarily conserved mechanism in combating pathogens. Both this pathway and pathogens have developed sophisticated strategies to counteract each other for their survival. Here, we summarise current knowledge on the interactions between the cGAS-STING pathway and pathogens from both evolutionary and mechanistic perspectives. Deeper insight into these interactions might enable us to clarify the pathogenesis of certain infectious diseases and better harness the cGAS-STING pathway for antimicrobial methods.

The roles of mandarin fish STING in innate immune defense against Infectious spleen and kidney necrosis virus infections

The mandarin fish Siniperca chuatsi is a cultured freshwater fish species that is popular in China because of its high market value. With the development of high-density cultural mode in mandarin fish, viral diseases such as Infectious spleen and kidney necrosis virus (ISKNV) are becoming increasingly serious. Stimulator of interferon genes (STING) is a central component in the innate immune response to cytosolic DNA and RNA derived from different pathogens. However, the roles of STING in innate immune response of mandarin fish remain unknown. In the present study, S. chuatsi STING (scSTING)-mediated host immune response against ISKNV infection was investigated. ScSTING transcription level increased remarkably in response to ISKNV infection, LPS, PMA, or poly (I:C) stimulation in mandarin fish fry (MFF-1) cells. Immunofluorescence results showed that scSTING localized majorly in the endoplasmic reticulum. scSTING overexpression remarkably increased the expression levels of scIFN-h, scMx, scISG15, scPKR, scViperin, scIL-1β, scIL-18, and scTNF-α genes. IFN-β-luciferase report assay results showed that the relative expressions of luciferin were remarkably increased in MFF-1 cells. Site mutation of serine (S) on C-terminus of scSTING showed that both S388 and S396 were important for mediated signaling. Furthermore, scSTING overexpression inhibited ISKNV infection, and knockdown of scSTING promoted ISKNV infection, indicating that scSTING could suppress ISKNV infection in MFF-1 cells. These observations suggested that the scSTING played an important role in innate immune against ISKNV infection. Our work would help elucidate the roles of teleost fish STING in innate immunity.

Deciphering the pathways to antiviral innate immunity and inflammation

The antiviral innate immune and inflammatory responses are critical for host defense against viral infection. How these antiviral responses are initiated and regulated has been intensively investigated. Viral nucleic acids are sensed by pattern-recognition receptors (PRRs), which trigger various signaling pathways by utilizing distinct adaptor proteins, kinases and regulatory proteins. These pathways lead to activation of the transcriptional factors NF-κB and IRF3 and ultimate induction of antiviral effector proteins including type I interferons (IFNs), TNF and IL-1β, which are critical mediators of antiviral innate immune and inflammatory responses. For the past 20 years, our groups at Peking University and Wuhan University have made restless efforts in deciphering the molecular mechanisms of antiviral innate immune and inflammatory responses. Here, we summarize the major discoveries from our groups, including the identifications of the critical adaptors VISA/MAVS and MITA/STING, regulatory mechanisms of these adapter-mediated signaling, and regulation of TNF- and IL1β-triggered inflammatory responses.

The role of mitochondria-associated membranes in cellular homeostasis and diseases

Mitochondria and endoplasmic reticulum (ER) are fundamental in the control of cell physiology regulating several signal transduction pathways. They continuously communicate exchanging messages in their contact sites called MAMs (mitochondria-associated membranes). MAMs are specific microdomains acting as a platform for the sorting of vital and dangerous signals. In recent years increasing evidence reported that multiple scaffold proteins and regulatory factors localize to this subcellular fraction suggesting MAMs as hotspot signaling domains. In this review we describe the current knowledge about MAMs' dynamics and processes, which provided new correlations between MAMs' dysfunctions and human diseases. In fact, MAMs machinery is strictly connected with several pathologies, like neurodegeneration, diabetes and mainly cancer. These pathological events are characterized by alterations in the normal communication between ER and mitochondria, leading to deep metabolic defects that contribute to the progression of the diseases.

Yellow Fever: Integrating Current Knowledge with Technological Innovations to Identify Strategies for Controlling a Re-Emerging Virus

Yellow fever virus (YFV) represents a re-emerging zoonotic pathogen, transmitted by mosquito vectors to humans from primate reservoirs. Sporadic outbreaks of YFV occur in endemic tropical regions, causing a viral hemorrhagic fever (VHF) associated with high mortality rates. Despite a highly effective vaccine, no antiviral treatments currently exist. Therefore, YFV represents a neglected tropical disease and is chronically understudied, with many aspects of YFV biology incompletely defined including host range, host–virus interactions and correlates of host immunity and pathogenicity. In this article, we review the current state of YFV research, focusing on the viral lifecycle, host responses to infection, species tropism and the success and associated limitations of the YFV-17D vaccine. In addition, we highlight the current lack of available treatments and use publicly available sequence and structural data to assess global patterns of YFV sequence diversity and identify potential drug targets. Finally, we discuss how technological advances, including real-time epidemiological monitoring of outbreaks using next-generation sequencing and CRISPR/Cas9 modification of vector species, could be utilized in future battles against this re-emerging pathogen which continues to cause devastating disease.

The Interplay between Dengue Virus and the Human Innate Immune System: A Game of Hide and Seek

With 40% of the world population at risk, infections with dengue virus (DENV) constitute a serious threat to public health. While there is no antiviral therapy available against this potentially lethal disease, the efficacy of the only approved vaccine is not optimal and its safety has been recently questioned. In order to develop better vaccines based on attenuated and/or chimeric viruses, one must consider how the human immune system is engaged during DENV infection. The activation of the innate immunity through the detection of viruses by cellular sensors is the first line of defence against those pathogens. This triggers a cascade of events which establishes an antiviral state at the cell level and leads to a global immunological response. However, DENV has evolved to interfere with the innate immune signalling at multiple levels, hence dampening antiviral responses and favouring viral replication and dissemination. This review elaborates on the interplay between DENV and the innate immune system. A special focus is given on the viral countermeasure mechanisms reported over the last decade which should be taken into consideration during vaccine development.

Functional Characterization of Duck STING in IFN-β Induction and Anti-H9N2 Avian Influenza Viruses Infections

The stimulator of interferon genes (STING) protein has been shown to play a pivotal role in response to both cytosolic RNA and dsDNA to elicit interferon (IFN) production in mammals. However, the role of duck STING (DuSTING) in antiviral innate immunity, especially in anti-RNA virus infection, has yet to be elucidated. In this study, the function of DuSTING in IFN induction and its role in anti-RNA virus infections were studied. DuSTING was amplified via reverse transcription-polymerase chain reaction (RT-PCR) from Pekin duck, showing that its cDNA sequence contains an open reading frame (ORF) of 1,149 bp and encodes 382 amino acids (aa). Sequence alignment showed that DuSTING protein shares 71.1, 43.4, and 33.3% identity with chickens, humans, and zebra fish, respectively. Overexpression of DuSTING in duck embryo fibroblasts (DEFs) strongly activated IFN-β promotor activity. Deletion mutant analysis revealed that the first 42 aa containing the first transmembrane (TM) domains and the last 32 aa containing a part of the C-terminal tail (CTT) are essential for its IFN-β activation. In vitro experiments showed that the mRNA levels of DuSTING and IFNs were all upregulated when the DEFs were infected with H9N2 avian influenza virus (AIV) SH010, while overexpression of DuSTING inhibited the replication of this virus. In vivo studies showed that DuSTING mRNA was widely expressed in different tissues, and was up-regulated in the spleen and lung of ducks challenged with SH010. In conclusion, our results indicate that DuSTING is an essential IFN mediator and plays a role in anti-RNA virus innate immunity.

STING is required for host defense against neuropathological West Nile virus infection

West Nile Virus (WNV), an emerging and re-emerging RNA virus, is the leading source of arboviral encephalitic morbidity and mortality in the United States. WNV infections are acutely controlled by innate immunity in peripheral tissues outside of the central nervous system (CNS) but WNV can evade the actions of interferon (IFN) to facilitate CNS invasion, causing encephalitis, encephalomyelitis, and death. Recent studies indicate that STimulator of INterferon Gene (STING), canonically known for initiating a type I IFN production and innate immune response to cytosolic DNA, is required for host defense against neurotropic RNA viruses. We evaluated the role of STING in host defense to control WNV infection and pathology in a murine model of infection. When challenged with WNV, STING knock out (-/-) mice displayed increased morbidity and mortality compared to wild type (WT) mice. Virologic analysis and assessment of STING activation revealed that STING signaling was not required for control of WNV in the spleen nor was WNV sufficient to mediate canonical STING activation in vitro. However, STING-/- mice exhibited a clear trend of increased viral load and virus dissemination in the CNS. We found that STING-/- mice exhibited increased and prolonged neurological signs compared to WT mice. Pathological examination revealed increased lesions, mononuclear cellular infiltration and neuronal death in the CNS of STING-/- mice, with sustained pathology after viral clearance. We found that STING was required in bone marrow derived macrophages for early control of WNV replication and innate immune activation. In vivo, STING-/- mice developed an aberrant T cell response in both the spleen and brain during WNV infection that linked with increased and sustained CNS pathology compared to WT mice. Our findings demonstrate that STING plays a critical role in immune programming for the control of neurotropic WNV infection and CNS disease.