Richard E. Randall

Interferons: cell signalling, immune modulation, antiviral response and virus countermeasures.

IP: 54.70.40.11 On: Sat, 15 Dec 2018 21:37:32 Journal of General Virology (2000), 81, 2341–2364. Printed in Great Britain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Inhibition of Interferon Signaling by the New York 99 Strain and Kunjin Subtype of West Nile Virus Involves Blockage of STAT1 and STAT2 Activation by Nonstructural Proteins

ABSTRACT The interferon (IFN) response is the first line of defense against viral infections, and the majority of viruses have developed different strategies to counteract IFN responses in order to ensure their survival in an infected host. In this study, the abilities to inhibit IFN signaling of two closely related West Nile viruses, the New York 99 strain (NY99) and Kunjin virus (KUN), strain MRM61C, were analyzed using reporter plasmid assays, as well as immunofluorescence and Western blot analyses. We have demonstrated that infections with both NY99 and KUN, as well as transient or stable transfections with their replicon RNAs, inhibited the signaling of both alpha/beta IFN (IFN-α/β) and gamma IFN (IFN-γ) by blocking the phosphorylation of STAT1 and its translocation to the nucleus. In addition, the phosphorylation of STAT2 and its translocation to the nucleus were also blocked by KUN, NY99, and their replicons in response to treatment with IFN-α. IFN-α signaling and STAT2 translocation to the nucleus was inhibited when the KUN nonstructural proteins NS2A, NS2B, NS3, NS4A, and NS4B, but not NS1 and NS5, were expressed individually from the pcDNA3 vector. The results clearly demonstrate that both NY99 and KUN inhibit IFN signaling by preventing STAT1 and STAT2 phosphorylation and identify nonstructural proteins responsible for this inhibition.

VECTORS FOR THE EXPRESSION OF TAGGED PROTEINS IN SCHIZOSACCHAROMYCES POMBE

A series of vectors is described which enables the episomal expression of proteins fused to different tag sequences in Schizosaccharomyces pombe. Proteins can be expressed with their amino termini fused to GFP/EGFP, three copies of the HA or Pk epitopes or a combined tag which contains two copies of the myc epitope and six histidine residues (MH). Fusion of the carboxyl terminus of a protein to a tag is possible with GFP/EGFP or Pk. Expression of the fusion proteins is controlled by the medium strength mutant version of the regulatable nmt1 promoter.

Influenza A virus NS1 protein binds p85β and activates phosphatidylinositol-3-kinase signaling

Influenza A virus NS1 is a multifunctional protein, and in virus-infected cells NS1 modulates a number of host-cell processes by interacting with cellular factors. Here, we report that NS1 binds directly to p85β, a regulatory subunit of phosphatidylinositol-3-kinase (PI3K), but not to the related p85α subunit. Activation of PI3K in influenza virus-infected cells depended on genome replication, and showed kinetics that correlated with NS1 expression. Additionally, it was found that expression of NS1 alone was sufficient to constitutively activate PI3K, causing the phosphorylation of a downstream mediator of PI3K signal transduction, Akt. Mutational analysis of a potential SH2-binding motif within NS1 indicated that the highly conserved tyrosine at residue 89 is important for both the interaction with p85β, and the activation of PI3K. A mutant influenza virus (A/Udorn/72) expressing NS1 with the Y89F amino acid substitution exhibited a small-plaque phenotype, and grew more slowly in tissue culture than WT virus. These data suggest that activation of PI3K signaling in influenza A virus-infected cells is important for efficient virus replication.

Taxonomy of the order Mononegavirales: update 2016

In 2016, the order Mononegavirales was emended through the addition of two new families (Mymonaviridae and Sunviridae), the elevation of the paramyxoviral subfamily Pneumovirinae to family status (Pneumoviridae), the addition of five free-floating genera (Anphevirus, Arlivirus, Chengtivirus, Crustavirus, and Wastrivirus), and several other changes at the genus and species levels. This article presents the updated taxonomy of the order Mononegavirales as now accepted by the International Committee on Taxonomy of Viruses (ICTV).

The NPro Product of Bovine Viral Diarrhea Virus Inhibits DNA Binding by Interferon Regulatory Factor 3 and Targets It for Proteasomal Degradation

ABSTRACT Bovine viral diarrhea virus (BVDV) is a pestivirus that can establish a persistent infection in the developing fetus and has the ability to disable the production of type I interferon. In this report, we extend our previous observations that BVDV encodes a protein able to specifically block the activity of interferon regulatory factor 3 (IRF-3), a transcription factor essential for interferon promoter activation, by demonstrating that this is a property of the N-terminal protease fragment (NPro) of the BVDV polyprotein. Although BVDV infections cause relocalization of cellular IRF-3 from the cytoplasm to the nucleus early in infection, NPro blocks IRF-3 from binding to DNA. NPro has the additional property of targeting IRF-3 for polyubiquitination and subsequent destruction by cellular multicatalytic proteasomes. The autoprotease activity of NPro is not required for the inhibition of type I interferon induction or the targeting of IRF-3 for degradation.

Bunyamwera Bunyavirus Nonstructural Protein NSs Counteracts the Induction of Alpha/Beta Interferon

ABSTRACT Production of alpha/beta interferons (IFN-α/β) in response to viral infection is one of the main defense mechanisms of the innate immune system. Many viruses therefore encode factors that subvert the IFN system to enhance their virulence. Bunyamwera virus (BUN) is the prototype of the Bunyaviridae family. By using reverse genetics, we previously produced a recombinant virus lacking the nonstructural protein NSs (BUNdelNSs) and showed that NSs is a nonessential gene product that contributes to viral pathogenesis. Here we demonstrate that BUNdelNSs is a strong inducer of IFN-α/β, whereas in cells infected with the wild-type counterpart expressing NSs (wild-type BUN), neither IFN nor IFN mRNA could be detected. IFN induction by BUNdelNSs correlated with activation of NF-κB and was dependent on virally produced double-stranded RNA and on the IFN transcription factor IRF-3. Furthermore, both in cultured cells and in mice lacking a functional IFN-α/β system, BUNdelNSs replicated to wild-type BUN levels, whereas in IFN-competent systems, wild-type BUN grew more efficiently. These results suggest that BUN NSs is an IFN induction antagonist that blocks the transcriptional activation of IFN-α/β in order to increase the virulence of Bunyamwera virus.

Identification of an epitope on the P and V proteins of simian virus 5 that distinguishes between two isolates with different biological characteristics

Two canine isolates of simian virus 5 (SV5), termed CPI+ and CPI-, were examined for their ability to react with a bank of monoclonal antibodies (MAbs) that had been previously raised against a human isolate of SV5. CPI- virus was originally isolated from the brain of a gnotobiotic dog infected with CPI+ virus and establishes persistent infections more readily than CPI+ in vitro. Of more than 50 MAbs tested, only one (P-k) reacted with CPI+ but not CPI-, enabling distinction between the two canine isolates. It had been shown previously that MAb P-k reacts with an epitope common to both the P and V proteins. In order to characterize further the epitope binding site of this MAb the P/V genes of CPI+ and CPI- were sequenced. There were four nucleotide differences between CPI+ and CPI-, three of which resulted in predicted amino acid substitutions. Synthetic peptides corresponding to regions encompassing these changes were made and radioimmune competition assays were used to identify the epitope binding site of MAb P-k. Sequence comparison of the P/V gene of CPI+ with the published sequence of a monkey isolate of SV5 (W3) revealed 14 nucleotide differences with five amino acid substitutions. The only amino acid substitution observed between CPI+, CPI- and W3 which altered the predicted secondary structures of the P and V proteins was a leucine to proline change that induced a predicted beta-turn and resulted in the loss of binding of MAb P-k.

Innate sensing of HIV-infected cells.

Cell-free HIV-1 virions are poor stimulators of type I interferon (IFN) production. We examined here how HIV-infected cells are recognized by plasmacytoid dendritic cells (pDCs) and by other cells. We show that infected lymphocytes are more potent inducers of IFN than virions. There are target cell-type differences in the recognition of infected lymphocytes. In primary pDCs and pDC-like cells, recognition occurs in large part through TLR7, as demonstrated by the use of inhibitors and by TLR7 silencing. Donor cells expressing replication-defective viruses, carrying mutated reverse transcriptase, integrase or nucleocapsid proteins induced IFN production by target cells as potently as wild-type virus. In contrast, Env-deleted or fusion defective HIV-1 mutants were less efficient, suggesting that in addition to TLR7, cytoplasmic cellular sensors may also mediate sensing of infected cells. Furthermore, in a model of TLR7-negative cells, we demonstrate that the IRF3 pathway, through a process requiring access of incoming viral material to the cytoplasm, allows sensing of HIV-infected lymphocytes. Therefore, detection of HIV-infected lymphocytes occurs through both endosomal and cytoplasmic pathways. Characterization of the mechanisms of innate recognition of HIV-infected cells allows a better understanding of the pathogenic and exacerbated immunologic events associated with HIV infection.

Isolation and characterization of monoclonal antibodies to simian virus 5 and their use in revealing antigenic differences between human, canine and simian isolates.

Hybridomas secreting monoclonal antibodies to simian virus 5 (SV5) were obtained following immunization of mice with purified preparations of a human isolate (LN) of SV5. Immune precipitation studies showed that these monoclonal antibodies had specificities for the haemagglutinin-neuraminidase (HN), fusion (F), nucleo-, matrix and phospho- (P) proteins of SV5. By use of a radioimmune competition assay the monoclonal antibodies to the HN protein were assigned to four groups, members of which recognized different antigenic sites on the protein. All the anti-HN antibodies and the anti-F antibody neutralized virus infectivity. The 54 monoclonal antibodies obtained were used to determine whether there were antigenic differences between five human, two canine and one simian isolate of SV5. Although most of the monoclonal antibodies reacted with all isolates, a few did reveal antigenic differences in the HN, F and P proteins. Furthermore, analysis by SDS-PAGE showed that while the electrophoretic mobilities of most of the virus polypeptides of these isolates were similar some differences could be detected. In particular the P protein showed the most marked mobility differences between the human, canine and simian isolates. Slight differences in the mobility of the F1 glycoprotein could also be visualized.