Studies on the paramyxovirus accessory genes by reverse genetics in the Sendai virus-mouse system

Sendai virus C protein affects macrophage function, which plays a critical role in modulating disease severity during Sendai virus infection in mice

Sendai virus (SeV) accessory protein C limits the generation of double-stranded RNAs, defective interfering RNAs, or both, during viral transcription and replication, thereby limiting interferon-β production. Our recent in vitro analyses on murine macrophage cell lines demonstrated that this protein also contributes to restricting macrophage function, including the production of nitric oxide (NO) and inflammatory cytokines in addition to interferon-β, in infected macrophages. This study showed that depletion of airway macrophages by clodronate-loaded liposomes led to the development of severe viral pneumonia in recombinant C gene-knockout SeV (SeV∆C)-infected mice, but did not modulate disease severity in wild-type SeV-infected mice. Furthermore, the severe disease observed in macrophage-depleted, SeV∆C-infected mice was associated with exacerbated virus replication in the lungs, leading to severe airway inflammation and pulmonary edema, indicating lung injury. These results suggested that the antimacrophage activity of SeV C protein might play a critical role in modulating lung injury and associated diseases caused by SeV.

Pathogenicity and transmissibility of a novel respirovirus isolated from a Malayan pangolin

The identification of SARS-CoV-2-like viruses in Malayan pangolins (Manis javanica) has focused attention on these endangered animals and the viruses they carry. We successfully isolated a novel respirovirus from the lungs of a dead Malayan pangolin. Similar to murine respirovirus, the full-length genome of this novel virus was 15 384 nucleotides comprising six genes in the order 3'-(leader)-NP-P-M-F-HN-l-(trailer)-5'. Phylogenetic analysis revealed that this virus belongs to the genus Respirovirus and is most closely related to murine respirovirus. Notably, animal infection experiments indicated that the pangolin virus is highly pathogenic and transmissible in mice, with inoculated mice having variable clinical symptoms and a fatality rate of 70.37 %. The virus was found to replicate in most tissues with the exception of muscle and heart. Contact transmission of the virus was 100 % efficient, although the mice in the contact group displayed milder symptoms, with the virus mainly being detected in the trachea and lungs. The isolation of a novel respirovirus from the Malayan pangolin provides new insight into the evolution and distribution of this important group of viruses and again demonstrates the potential infectious disease threats faced by endangered pangolins.

RNase L Amplifies Interferon Signaling by Inducing Protein Kinase R-Mediated Antiviral Stress Granules

Double-stranded RNAs produced during viral infections serve as pathogen-associated molecular patterns (PAMPs) and bind pattern recognition receptors to stimulate IFN production. RNase L is an IFN-regulated endoribonuclease that is activated in virus-infected cells and cleaves single-stranded viral and cellular RNAs. The RNase L-cleaved dsRNAs signal to Rig-like helicases to amplify IFN production. This study identifies a novel role of antiviral stress granules induced by RNase L as an antiviral signaling hub to coordinate the RNA ligands with cognate receptors to mount an effective host response during viral infections.

Virus infection leads to activation of the interferon (IFN)-induced endoribonuclease RNase L, which results in degradation of viral and cellular RNAs. Both cellular and viral RNA cleavage products of RNase L bind pattern recognition receptors (PRRs), like retinoic acid-inducible I (Rig-I) and melanoma differentiation-associated protein 5 (MDA5), to further amplify IFN production and antiviral response. Although much is known about the mechanics of ligand binding and PRR activation, how cells coordinate RNA sensing with signaling response and interferon production remains unclear. We show that RNA cleavage products of RNase L activity induce the formation of antiviral stress granules (avSGs) by regulating activation of double-stranded RNA (dsRNA)-dependent protein kinase R (PKR) and recruit the antiviral proteins Rig-I, PKR, OAS, and RNase L to avSGs. Biochemical analysis of purified avSGs showed interaction of a key stress granule protein, G3BP1, with only PKR and Rig-I and not with OAS or RNase L. AvSG assembly during RNase L activation is required for IRF3-mediated IFN production, but not IFN signaling or proinflammatory cytokine induction. Consequently, cells lacking avSG formation or RNase L signaling produced less IFN and showed higher susceptibility during Sendai virus infection, demonstrating the importance of avSGs in RNase L-mediated host defense. We propose a role during viral infection for RNase L-cleaved RNAs in inducing avSGs containing antiviral proteins to provide a platform for efficient interaction of RNA ligands with pattern recognition receptors to enhance IFN production to mount an effective antiviral response.

IMPORTANCE Double-stranded RNAs produced during viral infections serve as pathogen-associated molecular patterns (PAMPs) and bind pattern recognition receptors to stimulate IFN production. RNase L is an IFN-regulated endoribonuclease that is activated in virus-infected cells and cleaves single-stranded viral and cellular RNAs. The RNase L-cleaved dsRNAs signal to Rig-like helicases to amplify IFN production. This study identifies a novel role of antiviral stress granules induced by RNase L as an antiviral signaling hub to coordinate the RNA ligands with cognate receptors to mount an effective host response during viral infections.

Inactivated Sendai virus particle upregulates cancer cell expression of intercellular adhesion molecule-1 and enhances natural killer cell sensitivity on cancer cells

We have already reported that the inactivated Sendai virus (hemagglutinating virus of Japan; HVJ) envelope (HVJ‐E) has multiple anticancer effects, including induction of cancer‐selective cell death and activation of anticancer immunity. The HVJ‐E stimulates dendritic cells to produce cytokines and chemokines such as β‐interferon, interleukin‐6, chemokine (C‐C motif) ligand 5, and chemokine (C‐X‐C motif) ligand 10, which activate both CD8⁺ T cells and natural killer (NK) cells and recruit them to the tumor microenvironment. However, the effect of HVJ‐E on modulating the sensitivity of cancer cells to immune cell attack has yet to be investigated. In this study, we found that HVJ‐E induced the production of intercellular adhesion molecule‐1 (ICAM‐1, CD54), a ligand of lymphocyte function‐associated antigen 1, in several cancer cell lines through the activation of nuclear factor‐κB downstream of retinoic acid‐inducible gene I and the mitochondrial antiviral signaling pathway. The upregulation of ICAM‐1 on the surface of cancer cells increased the sensitivity of cancer cells to NK cells. Knocking out expression of ICAM‐1 in MDA‐MB‐231 cells using the CRISPR/Cas9 method significantly reduced the killing effect of NK cells on ICAM‐1‐depleted MDA‐MB‐231 cells. In addition, HVJ‐E suppressed tumor growth in MDA‐MB‐231 tumor‐bearing SCID mice, and the HVJ‐E antitumor effect was impaired when NK cells were depleted by treatment with the anti‐asialo GM1 antibody. Our findings suggest that HVJ‐E enhances NK cell sensitivity against cancer cells by increasing ICAM‐1 expression on the cancer cell surface.

Oncolytic Sendai virus-based virotherapy for cancer: recent advances

Many drugs have been developed and optimized for the treatment of cancer; however, it is difficult to completely cure cancer with anticancer drugs alone. Therefore, the development of new therapeutic technologies, in addition to new anticancer drugs, is necessary for more effective oncotherapy. Oncolytic viruses are one potential new anticancer strategy. Various oncolytic viruses have been developed for safe and effective oncotherapy. Recently, Sendai virus-based oncotherapy has been reported by several groups, and attention has been drawn to its unique anticancer mechanisms, which are different from those of the conventional oncolytic viruses that kill cancer cells by cancer cell-selective replication. Here, we introduce Sendai virus-based virotherapy and its anticancer mechanisms.

Reverse Genetics of Mononegavirales: The Rabies Virus Paradigm

The neurotropic rabies virus (RABV) is a prototype member of the Mononegavirales order of viruses and is the most significant human pathogen of the Rhabdoviridae family. A reverse genetics system for RABV was established almost 20 years ago, providing a paradigm for other Mononegavirales members as well. The availability of engineered recombinant viruses opened a new era to study common aspects of Mononegavirales biology and specific aspects of the unique lifestyle and pathogenesis of individual members. Above all, the knowledge gained has allowed engineering of beneficial biomedical tools such as viral vectors, vaccines, and tracers. In this chapter, the development of the classical rabies virus reverse genetics approach is described, and some of the most exciting biomedical applications for recombinant RABV and other Mononegavirales are briefly addressed.

Inhibition of interferon regulatory factor 3 activation by paramyxovirus V protein

The V protein of Sendai virus (SeV) suppresses innate immunity, resulting in enhancement of viral growth in mouse lungs and viral pathogenicity. The innate immunity restricted by the V protein is induced through activation of interferon regulatory factor 3 (IRF3). The V protein has been shown to interact with melanoma differentiation-associated gene 5 (MDA5) and to inhibit beta interferon production. In the present study, we infected MDA5-knockout mice with V-deficient SeV and found that MDA5 was largely unrelated to the innate immunity that the V protein suppresses in vivo. We therefore investigated the target of the SeV V protein. We previously reported interaction of the V protein with IRF3. Here we extended the observation and showed that the V protein appeared to inhibit translocation of IRF3 into the nucleus. We also found that the V protein inhibited IRF3 activation when induced by a constitutive active form of IRF3. The V proteins of measles virus and Newcastle disease virus inhibited IRF3 transcriptional activation, as did the V protein of SeV, while the V proteins of mumps virus and Nipah virus did not, and inhibition by these proteins correlated with interaction of each V protein with IRF3. These results indicate that IRF3 is important as an alternative target of paramyxovirus V proteins.

Analysis of interaction of Sendai virus V protein and melanoma differentiation-associated gene 5

Sendai virus (SeV), a pneumotropic virus of rodents, has an accessory protein, V, and the V protein has been shown to interact with MDA5, inhibiting IRF3 activation and interferon-β production. In the present study, interaction of the V protein with various IRF3-activating proteins including MDA5 was investigated in a co-immunoprecipitation assay. We also investigated interaction of mutant V proteins from SeVs of low pathogenicity with MDA5. The V protein interacted with at least retinoic acid inducible gene I, inhibitor of κB kinase epsilon and IRF3 other than MDA5. However, only MDA5 interacted with the V protein dependently on the C-terminal V unique (Vu) region, inhibiting IRF3 reporter activation. The Vu region has been shown to be important for viral pathogenicity. We thus focused on interaction of the V protein with MDA5. Point mutations in the Vu region destabilized the V protein or abolished the interaction with MDA5 when the V protein was stable. The V-R₃₂₀G protein was highly stable and interacted with MDA5, but did not inhibit activation of IRF3 induced by MDA5. Viral pathogenicity of SeV is related to the inhibitory effect of the V protein on MDA5, but is not always related to the binding of V protein with MDA5.