Cellular nucleic acid-binding protein is essential for type I interferon-mediated immunity to RNA virus infection

Host Innate Antiviral Response to Influenza A Virus Infection: From Viral Sensing to Antagonism and Escape

Influenza virus possesses an RNA genome of single-stranded, negative-sensed, and segmented configuration. Influenza virus causes an acute respiratory disease, commonly known as the "flu" in humans. In some individuals, flu can lead to pneumonia and acute respiratory distress syndrome. Influenza A virus (IAV) is the most significant because it causes recurring seasonal epidemics, occasional pandemics, and zoonotic outbreaks in human populations, globally. The host innate immune response to IAV infection plays a critical role in sensing, preventing, and clearing the infection as well as in flu disease pathology. Host cells sense IAV infection through multiple receptors and mechanisms, which culminate in the induction of a concerted innate antiviral response and the creation of an antiviral state, which inhibits and clears the infection from host cells. However, IAV antagonizes and escapes many steps of the innate antiviral response by different mechanisms. Herein, we review those host and viral mechanisms. This review covers most aspects of the host innate immune response, i.e., (1) the sensing of incoming virus particles, (2) the activation of downstream innate antiviral signaling pathways, (3) the expression of interferon-stimulated genes, (4) and viral antagonism and escape.

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.

Roles and functions of IAV proteins in host immune evasion

Influenza A viruses (IAVs) evade the immune system of the host by several regulatory mechanisms. Their genomes consist of eight single-stranded segments, including nonstructural proteins (NS), basic polymerase 1 (PB1), basic polymerase 2 (PB2), hemagglutinin (HA), acidic polymerase (PA), matrix (M), neuraminidase (NA), and nucleoprotein (NP). Some of these proteins are known to suppress host immune responses. In this review, we discuss the roles, functions and underlying strategies adopted by IAV proteins to escape the host immune system by targeting different proteins in the interferon (IFN) signaling pathway, such as tripartite motif containing 25 (TRIM25), inhibitor of nuclear factor κB kinase (IKK), mitochondrial antiviral signaling protein (MAVS), Janus kinase 1 (JAK1), type I interferon receptor (IFNAR1), interferon regulatory factor 3 (IRF3), IRF7, and nuclear factor-κB (NF-κB). To date, the IAV proteins NS1, NS2, PB1, PB1-F2, PB2, HA, and PA have been well studied in terms of their roles in evading the host immune system. However, the detailed mechanisms of NS3, PB1-N40, PA-N155, PA-N182, PA-X, M42, NA, and NP have not been well studied with respect to their roles in immune evasion. Moreover, we also highlight the future perspectives of research on IAV proteins.

Cellular nucleic acid-binding protein restricts SARS-CoV-2 by regulating interferon and disrupting RNA-protein condensates

A detailed understanding of the innate immune mechanisms involved in restricting SARS-CoV-2 infection and how the virus disrupts these processes could reveal new strategies to boost antiviral mechanisms and develop therapeutics for COVID-19. Here, we identify cellular nucleic acid-binding protein (CNBP) as a key host factor controlling SARS-CoV-2 infection. In response to RNA-sensing pathways, CNBP is phosphorylated and translocates from the cytosol to the nucleus where it binds to the interferon-β enhancer to initiate transcription. Because SARS-CoV-2 evades immune detection by the host's RNA-sensing pathways, CNBP is largely retained in the cytosol where it restricts SARS-CoV-2 directly, leading to a battle between the host and SARS-CoV-2 that extends beyond antiviral immune signaling pathways. We further demonstrated that CNBP binds SARS-CoV-2 viral RNA directly and competes with the viral nucleocapsid protein to prevent viral RNA and nucleocapsid protein from forming liquid-liquid phase separation (LLPS) condensates critical for viral replication. Consequently, cells and animals lacking CNBP have higher viral loads, and CNBP-deficient mice succumb rapidly to infection. Altogether, these findings identify CNBP as a key antiviral factor for SARS-CoV-2, functioning both as a regulator of antiviral IFN gene expression and a cell-intrinsic restriction factor that disrupts LLPS to limit viral replication and spread. In addition, our studies also highlight viral condensates as important targets and strategies for the development of drugs to combat COVID-19.

Nucleophosmin 1a translocated from nucleus to cytoplasm and facilitate GCRV replication

To decipher the functional characterization of Nucleophosmin 1a (NPM1a) from grass carp (Ctenopharyngodon idellus) (CiNPM1a), its cDNA was cloned and bioinformatic analysis were conducted. The full-length cDNA sequence of CiNPM1a is 1732 bp, which encodes 307 amino acids. CiNPM1a contains conserved domains of Nucleoplasmin domain, NPM1-C terminal domain, as well as nuclear localization signals, nuclear export signal (NES) and acid patches. There are 52 and 20 consensus amino acids exist in the Nucleoplasmin domain and the NPM1-C terminal domain of all blasted species. In addition, the immune function of CiNPM1a were analyzed. The Ciirf7, Ciifn1 and Ciifn2 transcription was inhibited, whereas the vp2 and vp7 expressions were enhanced in CiNPM1a overexpressing cells after GCRV infection (P < 0.05). Moreover, the Ciirf7, Ciifn1 and Ciifn2 mRNA levels were significantly up-regulated, but the vp2 and vp7 expressions were significantly down-regulated in CiNPM1a knockdown cells after infection. This indicated that CiNPM1a played negative roles in the induction of Type I IFN reaction and thus the GCRV replication. Finally, the NES domain that affect the nucleous-cytoplasm shuttle and the replication of GCRV were investigated. The deletion of NES1 and NES(1 + 2+3) absolutely limited the transloacation of CiNPM1a△NES1 protein and CiNPM1a △NES(1 + 2+3) protein to cytoplasm after infection, and the deletion of NES2 resulted in partially limitation of protein shuttle. In general, Ciirf3, Ciirf7, Ciifn1 and Ciifn2 expressions were enhanced in the CiNPM1a△NES1, CiNPM1a△NES2 and CiNPM1a△NES3 overexpression groups, and the deletion of functional domains in CiNPM1a led to significantly reduction of the vp2 and vp7 replication. The results indicated that CiNPM1a may be a target molecular for GCRV infection curation, and a candidate molecular for resistance strain breeding of grass carp.

Molecular mechanisms and cellular functions of liquid-liquid phase separation during antiviral immune responses

Spatiotemporal separation of cellular components is vital to ensure biochemical processes. Membrane-bound organelles such as mitochondria and nuclei play a major role in isolating intracellular components, while membraneless organelles (MLOs) are accumulatively uncovered via liquid-liquid phase separation (LLPS) to mediate cellular spatiotemporal organization. MLOs orchestrate various key cellular processes, including protein localization, supramolecular assembly, gene expression, and signal transduction. During viral infection, LLPS not only participates in viral replication but also contributes to host antiviral immune responses. Therefore, a more comprehensive understanding of the roles of LLPS in virus infection may open up new avenues for treating viral infectious diseases. In this review, we focus on the antiviral defense mechanisms of LLPS in innate immunity and discuss the involvement of LLPS during viral replication and immune evasion escape, as well as the strategy of targeting LLPS to treat viral infectious diseases.

Role of the OTUB1/IRF7/NOX4 axis in oxidative stress injury and inflammatory responses in mice with Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is one of the most devastating neurodegenerative disorders and is associated with oxidative stress injury (OSI) and inflammatory responses. This study sought to investigate the mechanism of ovarian tumour domain-containing ubiquitin aldehyde binding 1 (OTUB1) in OSI and inflammatory responses in PD, providing a theoretical foundation for PD treatment.

METHODS

The PD mouse model was established by an intraperitoneal injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, followed by behavioural tests, observation of brain pathological changes, and quantification of inflammatory (TNF-α, IL-1β, and IL-10) and OS (ROS, SOD, and MDA) factors. Next, the expression levels of OTUB1, interferon regulatory factor 7 (IRF7), and NADPH oxidase 4 (NOX4) levels were determined by real-time quantitative polymerase chain reaction and western blot assay, the binding of OTUB1 to IRF7 was analysed by co-immunoprecipitation, and the ubiquitination level of IRF7 and the enrichment and binding of IRF7 and the NOX4 promoter were measured by chromatin immunoprecipitation and dual-luciferase assays. Afterwards, rescue experiments were performed with IRF7 or NOX4 overexpression in OTUB1 knockout PD mice.

RESULTS

OTUB1 was upregulated in brain tissues of PD mice. Inhibition of OTUB1 alleviated PD progression, OSI, and inflammatory responses. OTUB1 stabilized IRF7 through deubiquitination, and IRF7 bound to the NOX4 promoter to promote NOX4 expression. IRF7 or NOX4 overexpression reversed the effects of silencing OTUB1 on OSI and inflammatory responses in PD mice.

CONCLUSION

OTUB1-mediated deubiquitination stabilized IRF7 and upregulated NOX4 expression, thereby promoting OSI and inflammatory responses in PD mice.

H1N1 Influenza A Virus Protein NS2 Inhibits Innate Immune Response by Targeting IRF7

Influenza A virus (IAV) is a globally distributed zoonotic pathogen and causes a highly infectious respiratory disease with high morbidity and mortality in humans and animals. IAV has evolved various strategies to counteract the innate immune response, using different viral proteins. However, the mechanisms are not fully elucidated. In this study, we demonstrated that the nonstructural protein 2 (NS2) of H1N1 IAV negatively regulate the induction of type-I interferon. Co-immunoprecipitation experiments revealed that NS2 specifically interacts with interferon regulatory factor 7 (IRF7). NS2 blocks the nuclear translocation of IRF7 by inhibiting the formation of IRF7 dimers, thereby prevents the activation of IRF7 and inhibits the production of interferon-beta. Taken together, these findings revealed a novel mechanism by which the NS2 of H1N1 IAV inhibits IRF7-mediated type-I interferon production.

CNBP restricts SARS-CoV2 by regulating IFN and disrupting RNA-protein condensates

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) evades antiviral immunity through the expression of viral proteins that block detection, signaling, interferon (IFN) induction, and IFN-stimulated gene (ISG) expression1, 2. Weak induction of type I IFNs is associated with a hyperinflammatory response in patients that develop severe COVID-193, 4, 5. Here we uncover a role for cellular nucleic acid-binding protein (CNBP) in restricting SARS-CoV-2. Typically, CNBP resides in the cytosol and, in response to RNA sensing pathways, undergoes phosphorylation, nuclear translocation, and IFNβ enhancer DNA binding to turn on IFNβ gene transcription. In SARS-CoV-2-infected cells CNBP coordinates IFNβ gene transcription. In addition, CNBP binds SARS-CoV-2 viral RNA directly. CNBP competes with the nucleocapsid (N) protein and prevents viral RNA and nucleocapsid protein from undergoing liquid-liquid phase separation (LLPS) forming condensates critical for viral replication. Consequently, cells and animals lacking CNBP have higher viral loads and CNBP-deficient mice succumb rapidly to infection. Altogether, these findings identify CNBP as a key antiviral factor for SARS-CoV-2, functioning both as a regulator of antiviral IFN gene expression and a cell intrinsic restriction factor that disrupts LLPS to limit viral replication and spread.

Old and New Biomarkers for Infection, Inflammation, and Autoimmunity in Treatment-Resistant Affective and Schizophrenic Spectrum Disorders

Affective (AF) and Schizophrenic (SZ) Spectrum disorders manifest with risk factors, involving inflammatory processes linked to infections and autoimmunity. This study searched for novel biomarkers in cerebrospinal fluid (CSF) and peripheral blood. A total of 29 AF and 39 SZ patients with treatment-resistant disease were included. In CSF, the chemokine IL-8 was significantly elevated in AF and SZ patients. IL-8 promotes chemotaxis by neutrophils and may originate from different tissues. S100B, a glia-derived brain damage marker, was higher in CSF from AF than SZ patients. Among the plasma-derived biomarkers, ferritin was elevated in AF and SZ. Soluble CD25, indicating Treg dysfunction, was higher in SZ than in AF patients. Interferon-γ, implying virus-specific immune activation, was positive in selective AF patients, only. Both groups showed elevated expression of immunosuppressive CD33 on monocytes, but higher amounts of CD123+ plasmacytoid dendritic cells were restricted to SZ. In conclusion, chemotactic IL-8 indicates neuronal stress and inflammation in the CSF of both groups. Novel plasma-derived biomarkers such as sCD25 and monocytic CD33 distinguish SZ from AF with an autoimmune phenotype.