Suppression of viral RNA polymerase activity is necessary for persistent infection during the transformation of measles virus into SSPE virus.

Subacute sclerosing panencephalitis (SSPE) is a fatal neurodegenerative disease caused by measles virus (MV), which typically develops 7 to 10 years after acute measles. During the incubation period, MV establishes a persistent infection in the brain and accumulates mutations that generate neuropathogenic SSPE virus. The neuropathogenicity is closely associated with enhanced propagation mediated by cell-to-cell fusion in the brain, which is principally regulated by hyperfusogenic mutations of the viral F protein.

Middle East respiratory syndrome coronavirus ORF4b protein inhibits TLR7- and TLR9-dependent alpha interferon induction.

The Toll-like receptor (TLR)7- and TLR9-dependent signalling cascade is responsible for production of a large amount of alpha interferon by plasmacytoid dendritic cells upon viral infection. Here, we show that Middle East respiratory syndrome coronavirus (MERS-CoV) accessory protein ORF4b has the most potential among the MERS-CoV accessory proteins to inhibit the TLR7/9-signaling-dependent alpha interferon production. ORF4b protein, which has a bipartite nuclear localization signal, was found to bind to IKKα, a kinase responsible for phosphorylation of interferon regulatory factor (IRF)7.

Human metapneumovirus M2-2 protein inhibits RIG-I signaling by preventing TRIM25-mediated RIG-I ubiquitination.

Retinoic acid-inducible gene I (RIG-I) is a receptor that senses viral RNA and interacts with mitochondrial antiviral signaling (MAVS) protein, leading to the production of type I interferons and inflammatory cytokines to establish an antiviral state. This signaling axis is initiated by the K63-linked RIG-I ubiquitination, mediated by E3 ubiquitin ligases such as TRIM25. However, many viruses, including several members of the family and human respiratory syncytial virus (HRSV), a member of the family , escape the immune system by targeting RIG-I/TRIM25 signaling.

Upregulation of viral RNA polymerase activity promotes adaptation of SSPE virus to neuronal cells.

Subacute sclerosing panencephalitis (SSPE) is a rare progressive neurodegenerative disease caused by measles virus variants (SSPE viruses) that results in eventual death. Amino acid substitution(s) in the viral fusion (F) protein are key for viral propagation in the brain in a cell-to-cell manner, a specific trait of SSPE viruses, leading to neuropathogenicity. In this study, we passaged an SSPE virus in cultured human neuronal cells and isolated an adapted virus that propagated more efficiently in neuronal cells and exhibited increased cell-to-cell fusion.

M protein of subacute sclerosing panencephalitis virus, synergistically with the F protein, plays a crucial role in viral neuropathogenicity.

Subacute sclerosing panencephalitis (SSPE) is a rare fatal neurodegenerative disease caused by a measles virus (MV) variant, SSPE virus, that accumulates mutations during long-term persistent infection of the central nervous system (CNS). Clusters of mutations identified around the matrix (M) protein in many SSPE viruses suppress productive infectious particle release and accelerate cell-cell fusion, which are features of SSPE viruses. It was reported, however, that these defects of M protein function might not be correlated directly with promotion of neurovirulence, although they might enable establishment of persistent infection.

Neutralizing antibody-dependent and -independent immune responses against SARS-CoV-2 in cynomolgus macaques.

We examined the pathogenicity of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) in cynomolgus macaques for 28 days to establish an animal model of COVID-19 for the development of vaccines and antiviral drugs. Cynomolgus macaques infected with SARS-CoV-2 showed body temperature rises and X-ray radiographic pneumonia without life-threatening clinical signs of disease. A neutralizing antibody against SARS-CoV-2 and T-lymphocytes producing interferon (IFN)-γ specifically for SARS-CoV-2 N-protein were detected on day 14 in one of three macaques with viral pneumonia.

Respirovirus C protein inhibits activation of type I interferon receptor-associated kinases to block JAK-STAT signaling.

Respirovirus C protein blocks the type I interferon (IFN)-stimulated activation of the JAK-STAT pathway. It has been reported that C protein inhibits IFN-α-stimulated tyrosine phosphorylation of STATs, but the underlying mechanism is poorly understood. Here, we show that the C protein of Sendai virus (SeV), a member of the Respirovirus genus, binds to the IFN receptor subunit IFN-α/β receptor subunit (IFNAR)2 and inhibits IFN-α-stimulated tyrosine phosphorylation of the upstream receptor-associated kinases, JAK1 and TYK2.

Sendai virus C protein limits NO production in infected RAW264.7 macrophages.

To suppress virus multiplication, infected macrophages produce NO. However, it remains unclear how infecting viruses then overcome NO challenge. In the present study, we report the effects of accessory protein C from Sendai virus (SeV), a prototypical paramyxovirus, on NO output.

Sendai Virus V Protein Inhibits the Secretion of Interleukin-1β by Preventing NLRP3 Inflammasome Assembly.

Inflammasomes play a key role in host innate immune responses to viral infection by caspase-1 (Casp-1) activation to facilitate interleukin-1β (IL-1β) secretion, which contributes to the host antiviral defense. The NLRP3 inflammasome consists of the cytoplasmic sensor molecule NLRP3, adaptor protein ASC, and effector protein pro-caspase-1 (pro-Casp-1). NLRP3 and ASC promote pro-Casp-1 cleavage, leading to IL-1β maturation and secretion.

Nonstructural protein of severe fever with thrombocytopenia syndrome phlebovirus targets STAT2 and not STAT1 to inhibit type I interferon-stimulated JAK-STAT signaling.

The nonstructural protein NSs of severe fever with thrombocytopenia syndrome phlebovirus blocks type I interferon (IFN)-stimulated JAK-STAT signaling. However, there is continuing controversy as to whether NSs targets STAT1 or STAT2 or both for this blockade. The present study was designed to gain a further understanding of the blockade mechanism.

Human Metapneumovirus M2-2 Protein Acts as a Negative Regulator of Alpha Interferon Production by Plasmacytoid Dendritic Cells.

Human metapneumovirus (HMPV) has the ability to inhibit Toll-like receptor 7 (TLR7)- and TLR9-dependent alpha interferon (IFN-α) production by plasmacytoid dendritic cells (pDCs). However, the inhibition mechanism remains largely unknown. To identify viral proteins responsible for this inhibition, we performed a screening of HMPV open reading frames (ORFs) for the ability to block TLR7/9-dependent signaling reconstituted in HEK293T cells by transfection with myeloid differentiation factor 88 (MyD88), tumor necrosis factor receptor-associated factor 6 (TRAF6), IKKα, and IFN regulatory factor 7 (IRF7).

Induction of necroptotic cell death by viral activation of the RIG-I or STING pathway.

Necroptosis is a form of necrotic cell death that requires the activity of the death domain-containing kinase RIP1 and its family member RIP3. Necroptosis occurs when RIP1 is deubiquitinated to form a complex with RIP3 in cells deficient in the death receptor adapter molecule FADD or caspase-8. Necroptosis may play a role in host defense during viral infection as viruses like vaccinia can induce necroptosis while murine cytomegalovirus encodes a viral inhibitor of necroptosis.

A residue located at the junction of the head and stalk regions of measles virus fusion protein regulates membrane fusion by controlling conformational stability.

The fusion (F) protein of measles virus performs refolding from the thermodynamically metastable prefusion form to the highly stable postfusion form via an activated unstable intermediate stage, to induce membrane fusion. Some amino acids involved in the fusion regulation cluster in the heptad repeat B (HR-B) domain of the stalk region, among which substitution of residue 465 by various amino acids revealed that fusion activity correlates well with its side chain length from the Cα (P<0.01) and van der Waals volume (P<0.

Intramolecular complementation of measles virus fusion protein stability confers cell-cell fusion activity at 37 °C.

The fusion (F) protein of measles virus mediates membrane fusion. In this study, we investigated the molecular basis of the cell-cell fusion activity of the F protein. The N465H substitution in the heptad repeat B domain of the stalk region of the F protein eliminates this activity, but an additional mutation in the DIII domain of the head region - N183D, F217L, P219S, I225T or G240R - restores cell-cell fusion.

An anti-interferon activity shared by paramyxovirus C proteins: inhibition of Toll-like receptor 7/9-dependent alpha interferon induction.

Paramyxovirus C protein targets the host interferon (IFN) system for virus immune evasion. To identify its unknown anti-IFN activity, we examined the effect of Sendai virus C protein on activation of the IFN-α promoter via various signaling pathways. This study uncovers a novel ability of C protein to block Toll-like receptor (TLR) 7- and TLR9-dependent IFN-α induction, which is specific to plasmacytoid dendritic cells.

Human parainfluenza virus type 2 V protein inhibits TRAF6-mediated ubiquitination of IRF7 to prevent TLR7- and TLR9-dependent interferon induction.

Paramyxovirus V proteins block Toll-like receptor 7 (TLR7)- and TLR9-dependent signaling leading to alpha interferon production. Our recent study has provided evidence that interaction of the V proteins with IRF7 is important for the blockade. However, the detailed mechanisms still remain unclear.

F-actin modulates measles virus cell-cell fusion and assembly by altering the interaction between the matrix protein and the cytoplasmic tail of hemagglutinin.

Actin filament (F-actin) is believed to be involved in measles virus (MV) assembly as a cellular factor, but the precise roles remain unknown. Here we show that Phe at position 50 of the MV matrix (M) protein is important for its association with F-actin, through which the function of the M protein is regulated. In plasmid-expressed or MV-infected cells, a coimmunoprecipitation study revealed that the wild-type M (M-WT) protein associated strongly with F-actin but only weakly with the cytoplasmic tail of the hemagglutinin (H) protein.

Expeditious neutralization assay for human metapneumovirus based on a recombinant virus expressing Renilla luciferase.

Background: Human metapneumovirus (HMPV) is a common cause of respiratory diseases in persons of all ages. Because of its slow replication and weak cytopathic effect in cultured cells, conventional neutralization assays for HMPV require around one week for completion.

Objectives: The purpose of this study is to establish a rapid neutralization assay based on a recombinant virus expressing Renilla luciferase (Rluc).

A tryptophan-rich motif in the human parainfluenza virus type 2 V protein is critical for the blockade of toll-like receptor 7 (TLR7)- and TLR9-dependent signaling.

Plasmacytoid dendritic cells (pDCs) do not produce alpha interferon (IFN-α) unless viruses cause a systemic infection or overcome the first-line defense provided by conventional DCs and macrophages. We show here that even paramyxoviruses, whose infections are restricted to the respiratory tract, have a V protein able to prevent Toll-like receptor 7 (TLR7)- and TLR9-dependent IFN-α induction specific to pDCs. Mutational analysis of human parainfluenza virus type 2 demonstrates that the second Trp residue of the Trp-rich motif (Trp-X(3)-Trp-X(9)-Trp) in the C-terminal domain unique to V, a determinant for IRF7 binding, is critical for the blockade of TLR7/9-dependent signaling.

Human metapneumovirus M2-2 protein inhibits viral transcription and replication.

M2-2 protein of human metapneumovirus (HMPV) is encoded by one of two overlapping open reading frames within M2 mRNA. The precise function of HMPV M2-2 protein remains unknown. We here examined effect of M2-2 protein on HMPV transcription and replication using a minigenome construct and monitoring luciferase reporter gene expression.

Sendai virus C protein plays a role in restricting PKR activation by limiting the generation of intracellular double-stranded RNA.

Sendai virus (SeV) C protein is a multifunctional protein that plays important roles in regulating viral genome replication and transcription, antagonizing the host interferon system, suppressing virus-induced apoptosis, and facilitating virus assembly and budding. We here report a novel role of SeV C protein, the limitation of double-stranded RNA (dsRNA) generation for maintaining the rate of protein synthesis in infected cells. It was found that the intracellular protein synthesis rate was maintained even after wild-type (wt) SeV infection, but markedly suppressed following C-knockout SeV infection.

Bovine parainfluenza virus type 3 accessory proteins that suppress beta interferon production.

The paramyxovirus P gene encodes accessory proteins antagonistic to interferon (IFN). Viral proteins responsible for the IFN antagonism, however, are distinct among paramyxoviruses. Here we determine bovine parainfluenza virus type 3 (bPIV3) IFN antagonists that suppress IFN-beta production, and investigate the underlying molecular mechanism.

Suppression of interferon-related promoter activation by hepatitis C virus proteins expressed in cultured cells.

Interferon is important for anti-viral defense of the host. The E2, NS3/4A, and NS5A proteins of hepatitis C virus (HCV) have recently been reported to confront anti-viral action induced by interferon. However, roles of the individual HCV proteins in anti-interferon action are still not well understood.

C and V proteins of Sendai virus target signaling pathways leading to IRF-3 activation for the negative regulation of interferon-beta production.

We here report a molecular basis for downregulation of interferon (IFN)-beta production by V and C proteins of Sendai virus (SeV). The infection of HeLa cells with SeV poorly induced IFN-beta even if the expression of C/C' was disrupted. In contrast, when the expression of C/C'/Y1/Y2 or V/W was disrupted, SeV infection strongly induced IFN-beta production and significantly activated the interferon regulatory factor (IRF)-3 pathway.

Inhibition of the gamma interferon response by a Sendai virus C protein mutant with no STAT1-binding ability.

Sendai virus C protein interacts with the signal transducer and activator of transcription (STAT) 1. This interaction is believed to be essential for the Sendai virus inhibition of the interferon (IFN) response. We here analyzed C(F170S) (a C protein mutant with the F170S mutation) with no STAT1-binding ability.