Identification of Orbivirus Non-Structural Protein 5 (NS5), Its Role and Interaction with RNA/DNA in Infected Cells.

Bioinformatic analyses have predicted that orbiviruses encode an additional, small non-structural protein (NS5) from a secondary open reading frame on genome segment 10. However, this protein has not previously been detected in infected mammalian or insect cells. NS5-specific antibodies were generated in mice and were used to identify NS5 synthesised in orbivirus-infected BSR cells or cells transfected with NS5 expression plasmids. Confocal microscopy shows that although NS5 accumulates in the nucleus, particularly in the nucleolus, which becomes disrupted, it also appears in the cell cytoplasm, co-localising with mitochondria. NS5 helps to prevent the degradation of ribosomal RNAs during infection and reduces host-cell protein synthesis However, it helps to extend cell viability by supporting viral protein synthesis and virus replication. Pulldown studies showed that NS5 binds to ssRNAs and supercoiled DNAs and demonstrates interactions with ZBP1, suggesting that it modulates host-cell responses.

Modeling Abundance of Culicoides stellifer, a Candidate Orbivirus Vector, Indicates Nonrandom Hemorrhagic Disease Risk for White-Tailed Deer (Odocoileus virginianus).

(1) Background: Hemorrhagic diseases in white-tailed deer (Odocoileus virginianus) are caused by orbiviruses and have significant economic impact on the deer ranching industry in the United States. Culicoides stellifer is a suspected vector of epizootic hemorrhagic disease virus (EHDV), with recent field evidence from Florida, but its natural history is poorly understood. Studying the distribution and abundance of C. stellifer across the landscape can inform our knowledge of how virus transmission can occur locally. We may then target vector management strategies in areas where viral transmission can occur. (2) Methods: Here, we used an occupancy modeling approach to estimate abundance of adult C. stellifer females at various physiological states to determine habitat preferences. We then mapped midge abundance during the orbiviral disease transmission period (May-October) in Florida. (3) Results: We found that overall, midge abundance was positively associated with sites in closer proximity to large-animal feeders. Additionally, midges generally preferred mixed bottomland hardwood and agricultural/sand/water habitats. Female C. stellifer with different physiological states preferred different habitats. (4) Conclusions: The differences in habitat preferences between midges across states indicate that disease risk for deer is heterogeneous across this landscape. This can inform how effective vector management strategies should be implemented.

Partial glycosylation of the Ibaraki virus NS3 protein is sufficient to support virus propagation.

Ibaraki virus (IBAV) causes Ibaraki disease. We have previously shown that IBAV NS3 protein is highly glycosylated and that tunicamycin, an inhibitor of N-linked glycosylation, suppressed NS3 glycosylation and viral propagation. Since tunicamycin is known to cause endoplasmic reticulum (ER) stress, we explored the effects of ER stress and NS3 glycosylation on IBAV infection using tunicamycin and thapsigargin. These reagents both induced ER stress and NS3 glycosylation inhibition in a concentration-dependent manner, and as in our previous report, high concentrations of tunicamycin and thapsigargin suppressed IBAV propagation. However, lower concentrations of these reagents produced limited differences in IBAV propagation, despite their ability to suppress NS3 glycosylation and induce ER stress. These findings suggest that a considerable degree of NS3 glycosylation inhibition and ER stress induction does not suppress IBAV propagation. Conversely, lower concentrations of thapsigargin enhanced IBAV propagation, suggesting that moderate ER stress could benefit IBAV.

Experimental infection of small ruminants with bluetongue virus expressing Toggenburg Orbivirus proteins.

Bluetongue virus (BTV) is the prototype orbivirus (Reoviridae family, genus Orbivirus) consisting of more than 24 recognized serotypes or neutralization groups. Recently, new BTV serotypes in goats have been found; serotype 25 (Toggenburg Orbivirusor TOV), serotype 26 (KUW2010/02), and serotype 27 from Corsica, France. KUW2010/02 has been isolated in mammalian cells but is not replicating in Culicoides cells. TOVhas been detected in goats but could not been cultured, although TOV has been successfully passed to naïve animals by experimental infection using viremic blood. Genome segments Seg-2[VP2], Seg-6[VP5], Seg-7[VP7], and Seg-10[NS3/NS3a] expressing the respective TOV proteins were incorporated in BTV using reverse genetics, demonstrating that these TOV proteins are functional in BTV replication. Depending on the incorporated TOV proteins, in vitro replication is, however, decreased compared to the ancestor BTV, in particular by TOV-VP5. Sheep and goats were experimentally infected with BTV expressing both outer capsid proteins VP2 and VP5 of TOV, so-named 'TOV-serotyped BTV'. Viremia was not detected in sheep, and hardly detected in goats after infection with TOV-serotyped BTV. Seroconversion by cELISA, however, was detected, suggesting that TOV-serotyped BTV replicates in small ruminants. One goat was coincidentally pregnant, and the fetus was strong PCR-positive in blood samples and several organs, which conclusively demonstrates that TOV-serotyped BTV replicates in vivo.

Detection of a fourth orbivirus non-structural protein.

The genus Orbivirus includes both insect and tick-borne viruses. The orbivirus genome, composed of 10 segments of dsRNA, encodes 7 structural proteins (VP1-VP7) and 3 non-structural proteins (NS1-NS3). An open reading frame (ORF) that spans almost the entire length of genome segment-9 (Seg-9) encodes VP6 (the viral helicase). However, bioinformatic analysis recently identified an overlapping ORF (ORFX) in Seg-9. We show that ORFX encodes a new non-structural protein, identified here as NS4. Western blotting and confocal fluorescence microscopy, using antibodies raised against recombinant NS4 from Bluetongue virus (BTV, which is insect-borne), or Great Island virus (GIV, which is tick-borne), demonstrate that these proteins are synthesised in BTV or GIV infected mammalian cells, respectively. BTV NS4 is also expressed in Culicoides insect cells. NS4 forms aggregates throughout the cytoplasm as well as in the nucleus, consistent with identification of nuclear localisation signals within the NS4 sequence. Bioinformatic analyses indicate that NS4 contains coiled-coils, is related to proteins that bind nucleic acids, or are associated with membranes and shows similarities to nucleolar protein UTP20 (a processome subunit). Recombinant NS4 of GIV protects dsRNA from degradation by endoribonucleases of the RNAse III family, indicating that it interacts with dsRNA. However, BTV NS4, which is only half the putative size of the GIV NS4, did not protect dsRNA from RNAse III cleavage. NS4 of both GIV and BTV protect DNA from degradation by DNAse. NS4 was found to associate with lipid droplets in cells infected with BTV or GIV or transfected with a plasmid expressing NS4.

Effects of domain-switching and site-directed mutagenesis on the properties and functions of the VP7 proteins of two orbiviruses.

Based on the crystal structure of the VP7 major core protein of bluetongue virus serotype 10 (BTV-10) and that of the top domain of the VP7 protein of African horsesickness virus serotype 4 (AHSV-4), chimeras and site-directed mutants of the proteins were constructed and the products analyzed with respect to their properties and functions. Chimeras with the central upper domain of BTV-10 VP7 replaced by that of AHSV-4 VP7 (construct BAB) formed trimers, as did the converse construct (ABA). Further, both proteins exhibited the expected conformational epitopes of the constituent sequences. Using BAB VP7 it was demonstrated that residues of the upper domain of AHSV-4 VP7 contribute to the observed insolubility of the protein. By contrast, ABA VP7 protein was as soluble as wild-type BTV-10 VP7. Replacement of selected amino acid residues in the top domain (e.g., A167 by R; F209 by T) improved the solubility of BAB VP7. Since the trimeric BAB and ABA VP7 proteins did not form core-like particles (CLPs) when coexpressed with BTV VP3, it was concluded that trimerization of chimeric VP7 is not sufficient for CLP formation. When the N-terminal region of the ABA protein (aa 1-120) was replaced by the respective sequences of BTV VP7 (construct BBA), the protein aggregated and did not form CLPs with coexpressed BTV VP3, most likely due to disruption of the required contacts between the N- and C-terminal regions of the bottom domain, leading to incorrect folding of the chimera.

Salt- and pH-dependent hemagglutination with Kasba virus, a member of the Palyam serogroup of the genus Orbivirus.

Kasba virus grown in BHK21-WI2 cells was tested for hemagglutination (HA) with erythrocytes of a variety of species at 4 degrees C, 25 degrees C and 37 degrees C. HA was observed at all temperatures with cattle, sheep and goat but not with swine, chicken, and goose erythrocytes. The HA was dependent on not only the NaCl concentration but also the pH of the diluent. The HA titer significantly improved by increasing the NaCl molarity to 0.6 M and standardizing pH to 7.5. The HA titer was 16- or 32-fold higher in 0.4 M or 0.6 M solution than in 0.2 M solution of not only NaCl but also several other salts. The HA reaction was inhibited by specific antibody.

Comparison of the expression and phosphorylation of the non-structural protein NS2 of three different orbiviruses: evidence for the involvement of an ubiquitous cellular kinase.

The non-structural protein NS2 of epizootic haemorrhagic disease (EHD), bluetongue (BT) and African horsesickness (AHS) viruses has each been expressed to high levels using a baculovirus vector gene expression system. It was found that the recombinant baculovirus-expressed EHDV NS2 protein was resolved as a doublet following PAGE. Peptide mapping of these protein bands indicated that they were identical. The difference in the sizes of the NS2 protein bands could not be attributed to the phosphorylation of NS2 or other posttranslational modification such as N-glycosylation and remains obscure. The EHDV, BTV and AHSV baculovirus-expressed NS2 proteins were all phosphorylated in vitro without the addition of an exogenous kinase. An unphosphorylated form of EHDV NS2, obtained by expressing the NS2 gene as a fusion protein in Escherichia coli cells, could be phosphorylated in vitro by a protein kinase associated with the cytoplasm of insect cells. The phosphorylated version of this protein was found to be significantly less efficient in binding ssRNA, compared to the unphosphorylated version.

Subcore- and core-like particles of Broadhaven virus (BRDV), a tick-borne orbivirus, synthesized from baculovirus expressed VP2 and VP7, the major core proteins of BRDV.

The genes encoding the two major core proteins (VP2 and VP7) of Broadhaven (BRD) virus, a tick-borne orbivirus, were inserted into the genome of Autographa californica nuclear polyhedrosis virus (AcNPV) under the control of copies of the AcNPV polyhedrin promoter to produce two recombinant baculoviruses. Infection of Spodoptera frugiperda (Sf) cells with a recombinant AcNPV that synthesized BRDV VP2 produced large numbers of BRDV subcore-like particles. Co-infection of cells with the two recombinants that made either BRDV VP2 or VP7 produced core-like particles similar in appearance to authentic BRDV cores. No evidence was obtained for the formation of core-like particles between the major core proteins of BRDV and those of bluetongue virus (BTV) following the co-expression of BRDV VP2 and BTV VP7, or BRDV VP7 and BTV VP3, indicating that in this respect the proteins of these two orbiviruses are incompatible, unlike the situation previously described for epizootic haemorrhagic disease virus and BTV core proteins.

Polypeptides induced in chick embryo cells by Kemerovo virus.

Fifteen polypeptides induced by Kemerovo virus were detected in chick embryo cells (Mr 140, 98, 89, 72, 65, 62, 57, 54, 50, 47, 43, 41, 39, 31 kD, and 30 kD). Nine of them, namely the 140, 98, 65, 62, 57, 54, 50, 47 kD, and 41 kD polypeptides were also found in the partially purified virus. However, the latter contained also considerable amount of host cell proteins, predominantly the 205 kD, 45 kD, and 37 kD polypeptides. In the electron microscope the spherical viral particles exhibited a poorly defined surface structure of a diameter of 70-75 nm.

Proteins expressed by Mill Door/79 virus, a Kemerovo serogroup orbivirus transmitted by the ticks Ixodes uriae.

Mill Door/79 virus, an orbivirus of the Kemerovo serogroup, Great Island Complex, was shown to induce in infected cells 10 segments of double-stranded RNA with a total molecular weight of 11.46 X 10(6) daltons. Using methyl mercuric hydroxide as a denaturing agent the double-stranded RNA was translated in a cell-free system producing 11 polypeptides, 10 of which co-migrated with those produced in Mill Door/79 virus infected Vero cells. The segments were separated and individually translated in a cell-free system allowing their coding assignments to be made. These assignments were confirmed by partial proteolysis.