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Infectious Salmon Anaemia Virus (ISAV) RNA Binding Protein Encoded by Segment 8 ORF2 and Its Interaction with ISAV and Intracellular Proteins.

ABSTRACT: Infectious salmon anaemia virus (ISAV) is an orthomyxovirus infecting salmonid fish. The virus is adapted to low temperature and has a replication optimum between 10-15 °C. In this study the subcellular localization and protein interactions for the protein encoded by the largest open reading frame of gene segment 8 (s8ORF2) were investigated. In ISAV infected cells the s8ORF2 protein was found mainly in the cytosol but a minor fraction of cells expressed the protein in the nucleus as well. Green fluorescent protein-tagged s8ORF2 did not leak out of the cell when the plasma membrane was permeabilized, suggesting interactions with intracellular structural components. The s8ORF2 protein exists both as monomer and homodimer, and co-immunoprecipitation experiments strongly suggests it binds to the ISAV fusion-, nucleo- and matrix proteins. Two versions of s8ORF2 were detected with apparent molecular weights of 24-26 and 35 kDa in lysates of infected cells. The 35 kDa type is an early viral protein while the smaller version appears during the later phases of infection. The 24-26 kDa type was also the predominant form in viral particles. The s8ORF2 protein has previously been shown to bind RNA and interfere with interferon induction and signaling. Here we found that a fraction of the s8ORF2 protein pool in infected cells is likely to be conjugated to the interferon stimulated gene 15 (ISG15) and ubiquitin. Furthermore, several endogenous proteins pulled down by the s8ORF2 protein were identified by liquid chromatography mass spectrometry (LC-MS).

SUBMITTER: Olsen CM

PROVIDER: S-EPMC4776207 | biostudies-literature | 2016 Feb

REPOSITORIES: biostudies-literature

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Infectious Salmon Anaemia Virus (ISAV) RNA Binding Protein Encoded by Segment 8 ORF2 and Its Interaction with ISAV and Intracellular Proteins.

Olsen Christel M CM Markussen Turhan T Thiede Bernd B Rimstad Espen E

Viruses 20160218 2

Infectious salmon anaemia virus (ISAV) is an orthomyxovirus infecting salmonid fish. The virus is adapted to low temperature and has a replication optimum between 10-15 °C. In this study the subcellular localization and protein interactions for the protein encoded by the largest open reading frame of gene segment 8 (s8ORF2) were investigated. In ISAV infected cells the s8ORF2 protein was found mainly in the cytosol but a minor fraction of cells expressed the protein in the nucleus as well. Green ...[more]

PMID: 26901217

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Project description:ABSTACT: Infectious salmon anaemia (ISA) is a serious disease of marine-farmed Atlantic salmon (Salmo salar) caused by ISA virus (ISAV), which belongs to the genus Isavirus, family Orthomyxoviridae. ISA is caused by virulent ISAV strains with deletions in a highly polymorphic region (HPR) of the hemagglutinin-esterase (HE) protein (designated virulent ISAV-HPR?). This study shows the historic dynamics of ISAV-HPR? and ISAV-HPR0 in Chile, the genetic relationship among ISAV-HPR0 reported worldwide and between ISAV-HPR0 and ISAV-HPR? in Chile, and reports the 2013 ISA outbreak in Chile. The first ISA outbreak in Chile occurred from mid-June 2007 to 2010 and involved the virulent ISAV-HPR7b, which was then replaced by a low pathogenic ISAV-HPR0 variant. We analyzed this variant in 66 laboratory-confirmed ISAV-HPR0 cases in Chile in comparison to virulent ISAV-HPR? that caused two new ISA outbreaks in April 2013. Multiple alignment and phylogenetic analysis of HE sequences from all ISAV-HPR0 viruses allowed us to identify three genomic clusters, which correlated with three residue patterns of ISAV-HPR0 (360PST362, 360PAN362 and 360PAT362) in HPR. The virus responsible for the 2013 ISAV-HPR? cases in Chile belonged to ISAV-HPR3 and ISAV-HPR14, and in phylogenetic analyses, both clustered with the ISAV-HPR0 found in Chile. The ISAV-HPR14 had the ISAV-HPR0 residue pattern 360PAT362, which is the only type of ISAV-HPR0 variant found in Chile. This suggested to us that the 2013 ISAV-HPR? re-emerged from ISAV-HPR0 that is enzootic in Chilean salmon aquaculture and were not new introductions of virulent ISAV-HPR? to Chile. The clinical presentations and diagnostic evidence of the 2013 ISA cases indicated a mixed infection of ISAV with the ectoparasite Caligus rogercresseyi and the bacterium Piscirickettsia salmonis, which underscores the need for active ISAV surveillance in areas where ISAV-HPR0 is enzootic, to ensure early detection and control of new ISA outbreaks, as it is considered a risk factor. This is the first report of ISA linked directly to the presence of ISAV-HPR0, and provides strong evidence supporting the contention that ISAV-HPR0 shows a strong relationship to virulent ISAV-HPR? viruses and the possibility that it could mutate to virulent ISAV-HPR?.

Project description:BackgroundInfectious salmon anaemia (ISA) virus (ISAV) belongs to the genus Isavirus, family Orthomyxoviridae. ISAV occurs in two basic genotypes, North American and European. The European genotype is more widespread and shows greater genetic variation and greater virulence variation than the North American genotype. To date, all of the ISAV isolates from the clinical disease, ISA, have had deletions in the highly polymorphic region (HPR) on ISAV segment 6 (ISAV-HPRΔ) relative to ISAV-HPR0, named numerically from ISAV-HPR1 to over ISAV-HPR30. ISA outbreaks have only been reported in farmed Atlantic salmon, although ISAV has been detected by RT-PCR in wild fish. It is recognized that asymptomatically ISAV-infected fish exist. There is no universally accepted ISAV RT-qPCR TaqMan® assay. Most diagnostic laboratories use the primer-probe set targeting a 104 bp-fragment on ISAV segment 8. Some laboratories and researchers have found a primer-probe set targeting ISAV segment 7 to be more sensitive. Other researchers have published different ISAV segment 8 primer-probe sets that are highly sensitive.MethodsIn this study, we tested 1,106 fish tissue samples collected from (i) market-bought farmed salmonids and (ii) wild salmon from throughout British Columbia (BC), Canada, for ISAV using real time RT-qPCR targeting segment 8 and/or conventional RT-PCR with segment 8 primers and segment 6 HPR primers, and by virus isolation attempts using Salmon head kidney (SHK-1 and ASK-2) cell line monolayers. The sequences from the conventional PCR products were compared by multiple alignment and phylogenetic analyses.ResultsSeventy-nine samples were "non-negative" with at least one of these tests in one or more replicates. The ISAV segment 6 HPR sequences from the PCR products matched ISAV variants, HPR5 on 29 samples, one sample had both HPR5 and HPR7b and one matched HPR0. All sequences were of European genotype. In addition, alignment of sequences of the conventional PCR product segment 8 showed they had a single nucleotide mutation in the region of the probe sequence and a 9-nucleotide overlap with the reverse primer sequence of the real time RT-qPCR assay. None of the classical ISAV segment 8 sequences in the GenBank have this mutation in the probe-binding site of the assay, suggesting the presence of a novel ISAV variant in BC. A phylogenetic tree of these sequences showed that some ISAV sequences diverted early from the classical European genotype sequences, while others have evolved separately. All virus isolation attempts on the samples were negative, and thus the samples were considered "negative" in terms of the threshold trigger set for Canadian federal regulatory action; i.e., successful virus isolation in cell culture.ConclusionsThis is the first published report of the detection of ISAV sequences in fish from British Columbia, Canada. The sequences detected, both of ISAV-HPRΔ and ISAV-HPR0 are of European genotype. These sequences are different from the classical ISAV segment 8 sequences, and this difference suggests the presence of a new ISAV variant of European genotype in BC. Our results further suggest that ISAV-HPRΔ strains can be present without clinical disease in farmed fish and without being detected by virus isolation using fish cell lines.

Project description:BACKGROUND: Infectious salmon anaemia (ISA) virus (ISAV), an important pathogen of fish that causes disease accompanied by high mortality in marine-farmed Atlantic salmon, is the only species in the genus Isavirus, one of the five genera of the Orthomyxoviridae family. The Isavirus genome consists of eight single-stranded RNA species, and the virions have two surface glycoproteins; haemagglutinin-esterase (HE) protein encoded on segment 6 and fusion (F) protein encoded on segment 5. Based on the initial demonstration of two 5'-coterminal mRNA transcripts by RT-PCR, ISAV genomic segment 7 was suggested to share a similar coding strategy with segment 7 of influenza A virus, encoding two proteins. However, there appears to be confusion as to the protein sizes predicted from the two open reading frames (ORFs) of ISAV segment 7 which has in turn led to confusion of the predicted protein functions. The primary goal of the present work was to clone and express these two ORFs in order to assess whether the predicted protein sizes match those of the expressed proteins so as to clarify the coding assignments, and thereby identify any additional structural proteins of ISAV. RESULTS: In the present study we show that ISAV segment 7 encodes 3 proteins with estimated molecular masses of 32, 18, and 9.5 kDa. The 18-kDa and 9.5-kDa products are based on removal of an intron each from the primary transcript (7-ORF1) so that the translation continues in the +2 and +3 reading frames, respectively. The segment 7-ORF1/3 product is variably truncated in the sequence of ISAV isolates of the European genotype. All three proteins are recognized by rabbit antiserum against the 32-kDa product of the primary transcript, as they all share the N-terminal 22 amino acids. This antiserum detected a single 35-kDa protein in Western blots of purified virus, and immunoprecipitated a 32-kDa protein in ISAV-infected TO cells. Immunofluorescence staining of infected cells with the same antiserum revealed the protein(s) to be localized in the cytoplasm. Vaccination of farmed Atlantic salmon with the 32-kDa protein resulted in a higher survival rate than what was attainable with the HE protein, albeit a moderate protection against the low ISAV challenge. CONCLUSION: Collectively, our observations suggest that the product of ISAV segment 7 primary transcript (7-ORF1) is a structural protein. The 18-kDa (7-ORF1/2) protein is identified as the putative ISAV nuclear export protein based on the presence of nuclear export signals. The function of the 9.5-kDa (7-ORF1/3) protein is not presently known.

Project description:ISAV is a member of the Orthomyxoviridae family that affects salmonids with disastrous results. It was first detected in 1984 in Norway and from then on it has been reported in Canada, United States, Scotland and the Faroe Islands. Recently, an outbreak was recorded in Chile with negative consequences for the local fishing industry. However, few studies have examined available data to test hypotheses associated with the phylogeographic partitioning of the infecting viral population, the population dynamics, or the evolutionary rates and demographic history of ISAV. To explore these issues, we collected relevant sequences of genes coding for both surface proteins from Chile, Canada, and Norway. We addressed questions regarding their phylogenetic relationships, evolutionary rates, and demographic history using modern phylogenetic methods.A recombination breakpoint was consistently detected in the Hemagglutinin-Esterase (he) gene at either side of the Highly Polymorphic Region (HPR), whereas no recombination breakpoints were detected in Fusion protein (f) gene. Evolutionary relationships of ISAV revealed the 2007 Chilean outbreak group as a monophyletic clade for f that has a sister relationship to the Norwegian isolates. Their tMRCA is consistent with epidemiological data and demographic history was successfully recovered showing a profound bottleneck with further population expansion. Finally, selection analyses detected ongoing diversifying selection in f and he codons associated with protease processing and the HPR region, respectively.Our results are consistent with the Norwegian origin hypothesis for the Chilean outbreak clade. In particular, ISAV HPR0 genotype is not the ancestor of all ISAV strains, although SK779/06 (HPR0) shares a common ancestor with the Chilean outbreak clade. Our analyses suggest that ISAV shows hallmarks typical of RNA viruses that can be exploited in epidemiological and surveillance settings. In addition, we hypothesized that genetic diversity of the HPR region is governed by recombination, probably due to template switching and that novel fusion gene proteolytic sites confer a selective advantage for the isolates that carry them. Additionally, protein modeling allowed us to relate the results of phylogenetic studies with the predicted structures. This study demonstrates that phylogenetic methods are important tools to predict future outbreaks of ISAV and other salmon pathogens.

Dataset Information

Infectious Salmon Anaemia Virus (ISAV) RNA Binding Protein Encoded by Segment 8 ORF2 and Its Interaction with ISAV and Intracellular Proteins.

Publications

Infectious Salmon Anaemia Virus (ISAV) RNA Binding Protein Encoded by Segment 8 ORF2 and Its Interaction with ISAV and Intracellular Proteins.

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