Mechanisms of Non-segmented Negative Sense RNA Viral Antagonism of Host RIG-I-Like Receptors

Research progress on the nonstructural protein 1 (NS1) of influenza a virus

Influenza A virus (IAV) is the leading cause of highly contagious respiratory infections, which poses a serious threat to public health. The non-structural protein 1 (NS1) is encoded by segment 8 of IAV genome and is expressed in high levels in host cells upon IAV infection. It is the determinant of virulence and has multiple functions by targeting type Ι interferon (IFN-I) and type III interferon (IFN-III) production, disrupting cell apoptosis and autophagy in IAV-infected cells, and regulating the host fitness of influenza viruses. This review will summarize the current research on the NS1 including the structure and related biological functions of the NS1 as well as the interaction between the NS1 and host cells. It is hoped that this will provide some scientific basis for the prevention and control of the influenza virus.

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

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

Pathogenicity and virulence of human respiratory syncytial virus: Multifunctional nonstructural proteins NS1 and NS2

Human respiratory syncytial virus (hRSV) is a major cause of acute lower respiratory tract infections in children under the age of two as well as in the elderly and immunocompromised worldwide. Despite its discovery over 60 years ago and the global impact on human health, limited specific and effective prophylactic or therapeutic options have been available for hRSV infections. Part of the lack of treatment options is attributed to the legacy of vaccine failure in the 1960s using a formalin-inactivated RSV (FI-RSV), which led to enhancement of disease post exposure to hRSV infection and hampered subsequent development of vaccine candidates. Recent FDA approval of a vaccine for older adults and impending approval for a maternal vaccine are major advancements but leaves children between 6 months and 5 years of age unprotected. Part of this limitation can be attributed to a lack of complete understanding of the factors that contribute to hRSV pathogenesis. The nonstructural proteins NS1 and NS2 are multifunctional virulence factors that are unique to hRSV and that play critical roles during hRSV infection, including antagonizing interferon (IFN) signalling to modulate host responses to hRSV infection. However, the molecular mechanisms by which the nonstructural proteins mediate their IFN inhibitory functions have not been completely defined. Current progress on the characterization of NS1 and NS2 during infection provides deeper insight into their roles. Furthermore, reverse genetics systems for hRSV provide a viable strategy to generate attenuated viruses by introduction of select mutations while maintaining immunogenicity required to elicit a long-term protective response. Here we will review the current state of knowledge of the nonstructural proteins, their contributions to RSV pathogenesis, and their potential as targets for therapeutic development.

Bat MAVS involved in antiviral innate immunity via regulating IFN-beta production

Mitochondrial antiviral signaling protein (MAVS) is an essential articulatory protein in immune responses against most RNA viruses. Whether bats, the natural hosts of numerous zoonotic RNA viruses, utilize conserved signaling pathways involving MAVS-mediated interferon (IFN) responses remains elusive. In this study, we performed the cloning and functional analysis of bat MAVS (BatMAVS). Amino acid sequence analysis revealed that BatMAVS was poorly conserved among species and evolutionarily closer to other mammals. Overexpression of BatMAVS significantly inhibited the replication of green fluorescent protein (GFP)-tagged VSV (VSV-GFP) and GFP-tagged Newcastle disease virus (NDV) (NDV-GFP) by activating the type I IFN pathway, and its expression at the transcriptional level was upregulated at the late stage of VSV-GFP infection. We further demonstrated that the CARD_2 and TM domains occupy a large proportion in the ability of BatMAVS to activate IFN-β. These results suggest that BatMAVS acts as an important regulatory molecule in IFN-induction and anti-RNA viruses in bats.

Role of circRNAs in viral infection and their significance for diagnosis and treatment (Review)

Circular RNAs (circRNAs) are a class of non-coding RNAs with a circular, covalent structure that lack both 5' ends and 3' poly(A) tails, which are stable and specific molecules that exist in eukaryotic cells and are highly conserved. The role of circRNAs in viral infections is being increasingly acknowledged, since circRNAs have been discovered to be involved in several viral infections (such as hepatitis B virus infection and human papilloma virus infection) through a range of circRNA/microRNA/mRNA regulatory axes. These findings have prompted investigations into the potential of circRNAs as targets for the diagnosis and treatment of viral infection-related diseases. The aim of the present review was to systematically examine and discuss the role of circRNAs in several common viral infections, as well as their potential as diagnostic markers and therapeutic targets.

CRISPR systems: Novel approaches for detection and combating COVID-19

Type V and VI CRISPR enzymes are RNA-guided, DNA and RNA-targeting effectors that allow specific gene knockdown. Cas12 and Cas13 are CRISPR proteins that are efficient agents for diagnosis and combating single-stranded RNA (ssRNA) viruses. The programmability of these proteins paves the way for the detection and degradation of RNA viruses by targeting RNAs complementary to its CRISPR RNA (crRNA). Approximately two-thirds of viruses causing diseases contain ssRNA genomes. The Severe Acute Respiratory Syndrome coronavirus 2 (SARS-CoV-2) has caused the outbreak of the coronavirus disease 2019 (COVID-19), which has infected more than 88 million people worldwide with near 2 million deaths since December 2019. Thus, accurate and rapid diagnostic and therapeutic tools are essential for early detection and treatment of this widespread infectious disease. For us, the CRISPR based platforms seem to be a plausible new approach for an accurate detection and treatment of SARS-CoV-2. In this review, we talk about Cas12 and Cas13 CRISPR systems and their applications in diagnosis and treatment of RNA virus mediated diseases. In continue, the SARS-CoV-2 pathogenicity, and its conventional diagnostics and antivirals will be discussed. Moreover, we highlight novel CRISPR based diagnostic platforms and therapies for COVID-19. We also discuss the challenges of diagnostic CRISPR based platforms as well as clarifying the proposed solution for high efficient selective in vivo delivery of CRISPR components into SARS-CoV-2-infected cells.

Immunoglobulin A Targeting on the N-Terminal Moiety of Viral Phosphoprotein Prevents Measles Virus from Evading Interferon-β Signaling

Immunoglobulin A (IgA) can inhibit intracellular viral replication during its transport across the epithelial cells. We find a monoclonal IgA antibody 7F1-IgA against the N-terminal moiety of the phosphoprotein (PNT) of measles virus (MV), which inhibits the intracellular replication of MV in Caco-2 cells but not in interferon-deficient Vero-pIgR cells. Transcytosis of 7F1-IgA across the MV-infected Caco-2 cells enhances the production of interferon-β (IFN-β) and the expression of IFN-stimulated genes, rendering Caco-2 cells with higher antiviral immunity. 7F1-IgA specifically interacts with MV phosphoprotein inside the MV-infected Caco-2 cell and prevents MV phosphoprotein from inhibiting the phosphorylation of JAK1 and STAT1. The intraepithelial interaction between 7F1-IgA and the viral phosphoprotein results in an earlier and stronger phosphorylation of JAK1 and STAT1 and, consequently, a more efficient nuclear translocation of STAT1 for the activation of the type I interferon pathway. Thus, IgA against phosphoprotein prevents a virus from evading type I IFN signaling and confers host epithelial cells efficient innate antiviral immunity, which potentiates a new antiviral target and an antiviral strategy.

RNA-Seq Revealed a Circular RNA-microRNA-mRNA Regulatory Network in Hantaan Virus Infection

Hantaan virus (HTNV), a Hantavirus serotype that is prevalent in Asia, causes hemorrhagic fever with renal syndrome (HFRS) with high mortality in human race. However, the pathogenesis of HTNV infection remains elusive. Circular RNAs (circRNAs), a new type of non-coding RNAs, play a crucial role in various pathogenic processes. Nevertheless, circRNA expression profiles and their effects on pathogenesis of HTNV infection are still completely unknown. In the present study, RNA sequencing was performed to analyze the circRNA, microRNA (miRNA), and mRNA expression profiles in HTNV-infected and mock-infected human umbilical vein endothelial cells (HUVECs). A total of 70 circRNAs, 66 miRNAs, and 788 mRNAs were differently expressed. Several differentially expressed RNAs were validated by RT-qPCR. Moreover, we verified that some differentially expressed RNAs, such as circ_0000479, miR-149-5p, miR-330-5p, miR-411-3p, RIG-I, CMPK2, PARP10, and GBP1, promoted or inhibited HTNV replication. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis demonstrated that the host genes of differentially expressed circRNAs were principally involved in the innate immune response, the type I interferon (IFN) signaling pathway, and the cytokine-mediated signaling pathway. Additionally, the circRNA-miRNA-mRNA regulatory network was integrally analyzed. The data showed that there were many circRNA-miRNA-mRNA interactions in HTNV infection. By dual-luciferase reporter assay, we confirmed that circ_0000479 indirectly regulated RIG-I expression by sponging miR-149-5p, hampering viral replication. This study for the first time presents a comprehensive overview of circRNAs induced by HTNV and reveals that a network of enriched circRNAs and circRNA-associated competitive endogenous RNAs (ceRNAs) is involved in the regulation of HTNV infection, thus offering new insight into the mechanisms underlying HTNV-host interaction.