Nucleocytoplasmic shuttling of BEFV M protein-modulated by lamin A/C and chromosome maintenance region 1 through a transcription-, carrier- and energy-dependent pathway

This study demonstrates for the first time that the matrix (M) protein of BEFV is a nuclear targeting protein that shuttles between the nucleus and the cytoplasm in a transcription-, carrier-, and energy-dependent manner. Experiments performed in both intact cells and digitonin-permeabilized cells revealed that M protein targets the nucleolus and requires carrier, cytosolic factors or energy input. By employing sequence and mutagenesis analyses, we have determined both nuclear localization signal (NLS) 6KKGKSK11 and nuclear export signal (NES) 98LIITSYL TI106 of M protein that are important for the nucleocytoplasmic shuttling of M protein. Furthermore, we found that both lamin A/C and chromosome maintenance region 1 (CRM-1) proteins could be coimmunoprecipitated and colocalized with the BEFV M protein. Knockdown of lamin A/C by shRNA and inhibition of CRM-1 by leptomycin B significantly reduced virus yield. Collectively, this study provides novel insights into nucleocytoplasmic shuttling of the BEFV M protein modulated by lamin A/C and CRM-1 and by a transcription- and carrier- and energy-dependent pathway.

Stretching the wings further- susceptibility of Culex pipiens Linnaeus to bovine ephemeral fever virus infection under experimental conditions

Bovine ephemeral fever (BEF) is a significant viral disease of cattle in the tropical, subtropical, and temperate climatic zones. This disease is also known as three-day sickness due to the spontaneous recovery of the cattle within a short period (usually 3-5 days). Despite its short duration, the disease may have a considerable impact. It can cause heavy economic losses, primarily due to decreased milk production, lowered fertility in bulls, and even fatality in severe cases. The virus is suspected to be transmitted by haematophagous insects (mainly mosquitoes and Culicoides biting midges); however, the identity of a competent vector for BEFV remains a mystery. Here, we investigated whether BEFV may replicate for a short duration in Culex pipiens Linnaeus, 1758, the most prevalent mosquito species in Israel and a potential vector of this virus to Israeli cattle. We applied nested- qPCR to test BEFV abundance in Cx. pipiens every 24 h for 14 consecutive days post-infection. Additionally, we collected eggs laid by BEFV-infected females and investigated BEFV abundance in the different developmental stages of F1 mosquitos. Our results suggest that Cx. pipiens mosquitoes have the potential to act as a vector of BEFV and also indicate that BEFV may be vertically transmitted from Cx. pipiens female parent to her female offspring.

Development and validation of a DIVA ELISA for differentiating BEFV infected from vaccinated animals

Inactivated vaccine is considered safe and used for prevention of bovine ephemeral fever in several endemic countries. To differentiate between BEFV-infected and vaccinated animals, we developed an ELISA capable of detecting infection-related antibodies against BEFV. Recombinant proteins, including N, P, M, L, G_NS, α2, β and γ, were expressed in E. coli and screened by Western blotting and ELISA. The results showed G_NS, α2 and β specifically reacted with sera from BEFV infected cattle but not sera from vaccinated cattle. A DIVA ELISA based on a C-terminal truncated form of G_NS was developed, with 100% sensitivity and 98.0% specificity at a sample to positive-control optical density ratio (S/P) threshold of 0.18. Specificity analysis showed that the assay has no cross-reactivity with antisera of other common bovine viruses. Anti-G_NS antibody appears at 3-4 days post infection (dpi) and persists up to 240-300 dpi in the experimentally infected cattle. Sero-epidemiological survey using sera collected from vaccinated cattle in an endemic area in Jiangsu Province revealed sero-positive rate of 2.36% (6/254), indicating that the DIVA ELISA could be used as a reliable diagnostic tool for differentiating BEFV infected from vaccinated animals.

Molecular characterization and phylogenetic analysis of bovine ephemeral fever viruses in Khuzestan province of Iran in 2018 and 2020

BACKGROUND

Bovine ephemeral fever (BEF) is an arthropod-borne viral disease caused by the BEF virus (BEFV). This single-stranded RNA virus that affects cattle and water buffalo is endemic in tropical and subtropical regions including Iran. While BEF is a major disease of cattle in Iran, information regarding its agent, molecular characterization, and circulating viruses are highly limited. The current study aimed to, firstly, determine the genetic and antigenic characteristics of BEFV strains in Khuzestan province in Southwest of Iran in 2018 and 2020 and, secondly, to compare them with strains obtained from other areas.

RESULTS

By phylogenetic analysis based on the Glycoprotein gene, BEFV strains were divided into four clusters of Middle East, East Asia, South Africa, and Australia; in which the 2018 and 2020 Iranian BEFV strains were grouped in the Middle East cluster with the Turkish, Indian, and Israeli strains. Depending on the chronology and geographical area, the outbreaks of Turkey (2020), Iran (2018 and 2020), and India (2018 and 2019) are proposed to be related. These BEFVs had the highest identity matrix and the lowest evolutionary distance among the studied strains. Multiple sequence alignment of G1, G2, and G3 antigenic sites showed that these neutralizing epitopes are highly conserved among the strains of the Middle East cluster; however, the strains previously identified in Iran differed in three amino acids placed in G1 and G2 epitopes.

CONCLUSION

The findings revealed that BEFVs circulating in the Middle East are closely related phylogenetically and geographically. They also have similar antigenic structures; therefore, developing a vaccine based on these strains can be effective for controlling BEF in the Middle East.

Annexin A2 gene interacting with viral matrix protein to promote bovine ephemeral fever virus release

Bovine ephemeral fever virus (BEFV) causes bovine ephemeral fever, which can produce considerable economic damage to the cattle industry. However, there is limited experimental evidence regarding the underlying mechanisms of BEFV. Annexin A2 (AnxA2) is a calcium and lipid-conjugated protein that binds phospholipids and the cytoskeleton in a Ca²⁺-dependent manner, and it participates in various cellular functions, including vesicular trafficking, organization of membrane domains, and virus proliferation. The role of the AnxA2 gene during virus infection has not yet been reported. In this study, we observed that AnxA2 gene expression was up-regulated in BHK-21 cells infected with the virus. Additionally, overexpression of the AnxA2 gene promoted the release of mature virus particles, whereas BEFV replication was remarkably inhibited after reducing AnxA2 gene expression by using the small interfering RNA (siRNA). For viral proteins, overexpression of the Matrix (M) gene promotes the release of mature virus particles. Moreover, the AnxA2 protein interaction with the M protein of BEFV was confirmed by GST pull-down and co-immunoprecipitation assays. Experimental results indicate that the C-terminal domain (268-334 aa) of AxnA2 contributes to this interaction. An additional mechanistic study showed that AnxA2 protein interacts with M protein and mediates the localization of the M protein at the plasma membrane. Furthermore, the absence of the AnxA2-V domain could attenuate the effect of AnxA2 on BEFV replication. These findings can contribute to elucidating the regulation of BEFV replication and may have implications for antiviral strategy development.

Data on production of mammalian stable cells expressing secretory BEFV transmembrane deleted G protein

Generation of stable cell lines is a widely used technique for continuous recombinant protein production. Advantages of the constitutive stable over the transient protein expression are uniformity of the expression across cell populations as well as high quantity and consistency of the protein yields. This data describe step-by-step procedure for the production of glycoprotein without a transmembrane domain (GΔTM) of bovine ephemeral fever virus (BEFV) by mammalian stable cells. LentiX-293T cells were transfected with four plasmid constructs to generate a recombinant lentivirus. Subsequently, 293T cells were transduced by the recombinant virus and the polyclonal stable cell pools were then selected by puromycin. Next, limiting dilution was performed from each cell pool to isolate the monoclonal stable cells expressing GΔTM protein. Western blot analysis showed that all monoclonal cell clones could stably express GΔTM protein. The data confirms that the stable 293T cell line expressing the secretory GΔTM protein is an attractive platform for antigen production.

Development of a quick dot blot assay for the titering of bovine ephemeral fever virus

Background

Bovine ephemeral fever virus (BEFV) causes fever and muscle stiffness in cattle, resulting in negative economic impact for cattle and dairy farms. During the manufacturing process of inactivated vaccine for virus control, it is important to determine the virus titer, but traditional methods such as plaque assay and TCID₅₀ assay require days of waiting time. We sought to develop a quick dot blot assay for BEFV titering.

Results

Three different kinds of BEFV antigens were prepared to raise primary antibodies for BEFV detection in dot blot assays: 1) purified BEFV particles, 2) Escherichia coli (E. coli)-expressed BEFV G1 region, and 3) E. coli-expressed BEFV N protein. Results showed that antibodies raised against purified BEFV particles can detect BEFV particles, but it also showed a high background level from the proteins of BHK-21 cells. Antibodies raised against E.coli-expressed BEFV G1 region could not detect BEFV particles in dot blot assays. Finally, antibodies raised against E.coli-expressed BEFV N protein detected BEFV particles with a high signal-to-noise ratio in dot blot assays.

Conclusions

E.coli-expressed N protein is a suitable antigen for the production of antiserum that can detect BEFV particles with a high signal-to-noise ratio. A dot blot assay kit using this antiserum can be developed as a quick and economical way for BEFV titering.

Electronic supplementary material

The online version of this article (10.1186/s12917-019-2059-6) contains supplementary material, which is available to authorized users.

The immunogenicity of the secretory GΔTM protein of bovine ephemeral fever virus stably expressed by mammalian cells

Bovine ephemeral fever virus (BEFV) causes an acute febrile disease in cattle and water buffalo. The disease has an impact on dairy and beef production in tropical and subtropical countries. Vaccination is used for disease prevention and control. In this study, we developed a recombinant lentivirus to produce mammalian stable cells expressing histidine-tagged BEFV G protein with a deleted transmembrane domain (GΔTM) as a secretory protein. In addition, guinea pigs were immunised with the purified GΔTM protein and booster immunised at a 3-week interval. The mammalian stable cells were able to continuously produce GΔTM protein for a minimum of 25 passages. All of the mammalian stable cells expressing GΔTM protein could react specifically with a BEFV convalescent bovine serum. Serum samples from the immunised guinea pigs could react strongly and specifically with the purified GΔTM protein. Moreover, post-immunised guinea pig sera contained antibodies that could neutralise BEFV. These results indicate that the G protein without a transmembrane domain can be used as a subunit vaccine for the prevention and control of BEFV. The availability of the mammalian stable cells, which constitutively express GΔTM protein, could facilitate the potential use of the secretory protein for BEFV diagnosis and vaccine development.

Biopanning of polypeptides binding to bovine ephemeral fever virus G1 protein from phage display peptide library

Background

The bovine ephemeral fever virus (BEFV) glycoprotein neutralization site 1 (also referred as G₁ protein), is a critical protein responsible for virus infectivity and eliciting immune-protection, however, binding peptides of BEFV G₁ protein are still unclear. Thus, the aim of the present study was to screen specific polypeptides, which bind BEFV G₁ protein with high-affinity and inhibit BEFV replication.

Methods

The purified BEFV G₁ was coated and then reacted with the M13-based Ph.D.-7 phage random display library. The peptides for target binding were automated sequenced after four rounds of enrichment biopanning. The amino acid sequences of polypeptide displayed on positive clones were deduced and the affinity of positive polypeptides with BEFV G₁ was assayed by ELISA. Then the roles of specific G₁-binding peptides in the context of BEFV infection were analyzed.

Results

The results showed that 27 specific peptide ligands displaying 11 different amino acid sequences were obtained, and the T18 and T25 clone had a higher affinity to G₁ protein than the other clones. Then their antiviral roles of two phage clones (T25 and T18) showed that both phage polypeptide T25 and T18 exerted inhibition on BEFV replication compared to control group. Moreover, synthetic peptide based on T18 (HSIRYDF) and T25 (YSLRSDY) alone or combined use on BEFV replication showed that the synthetic peptides could effectively inhibit the formation of cytopathic plaque and significantly inhibit BEFV RNA replication in a dose-dependent manner.

Conclusion

Two antiviral peptide ligands binding to bovine ephemeral fever virus G₁ protein from phage display peptide library were identified, which may provide a potential research tool for diagnostic reagents and novel antiviral agents.

Electronic supplementary material

The online version of this article (10.1186/s12917-017-1315-x) contains supplementary material, which is available to authorized users.

Effectiveness of a BHV-1/BEFV bivalent vaccine against bovine herpesvirus type 1 infection in cattle

Bovine herpesvirus type 1 (BHV-1) causes acute febrile respiratory diseases (infectious bovine rhinotracheitis, IBR), decreased milk production, weight loss and abortion. Bovine ephemeral fever virus (BEFV) causes acute febrile respiratory disease, with pulmonary emphysema and pulmonary edema as the main signs. These viruses infect domesticated herds and lead to significant economic losses. In our previous study, an inactivated BHV-1 and BEFV bivalent vaccine was formulated with water-in-oil-in-water adjuvant, and vaccine efficacy was evaluated in guinea pigs. In this study, we evaluated the efficacy of the bivalent vaccine in cattle. Results showed that immunized cattle had a significantly higher level of total anti-BHV-1 antibody response (S/P ratio of 12.7) than the control group (S/P ratio of 0.07) 32weeks post-vaccination. The immunized group also showed higher neutralizing antibody levels against BHV-1 (SN=2^3.8) and BEFV (SN=2^4.6) than the control group (SN<2) 4 to 32weeks post-vaccination (p<0.05). In a BHV-1 challenge experiment, immunized cattle showed low virus shedding (10^1.2TCID₅₀/mL) and a significant reduction in pathological lesion scores (p<0.01). In conclusion, the BHV-1+BEFV+w/o/w vaccine not only improved long-term antibody immune response but also significantly reduced clinical signs in a BHV-1 challenge experiment. Our approach may be feasible for developing an effective vaccine against bovine herpesvirus type 1 and bovine ephemeral fever virus.

Experimental infection with bovine ephemeral fever virus and analysis of its antibody response cattle

Bovine ephemeral fever (BEF) is an arthropod-borne viral disease that occurs throughout mainland China. LS11 obtained in the 2011 BEF epidemic was a wild strain, and its virulence and antibody response have never been studied in China. Therefore, the issues were investigated in this work. Experimental cattle were intravenously infected with different doses of BEF virus, and some non-infected cattle were simultaneously monitored. Blood and serum samples were collected from all animals over the course of our study. Infected cattle were challenged for a second time with BEF virus to determine protective period of the antibodies. BEF virus was detected in blood samples from infected cattle, but not in monitored cattle. The neutralizing antibodies (nAbs) against BEFV were easier to be detected and persisted for longer periods in cattle infected with higher doses of BEFV than in those infected with lower doses. When the titer of nAbs was equal to 5 or 6, re-infected cattle still could mount a challenge against BEFV. However, after 3 or 6months, when nAbs were no longer apparent, re-infected cattle displayed typical symptoms of BEF. Our findings indicated that vaccination should be performed once the titer of nAb decreased to 5 or 6.

New genetic mechanism, origin and population dynamic of bovine ephemeral fever virus

Bovine ephemeral fever virus (BEFV) is a typical species of the genusEphemerovirus in the family Rhabdoviridae. Today, prevailing BEFV can be divided into three phylogeographic lineages, East Asia, Mideast, and Australia. In this study, we provide evidence that the whole East Asia lineage originates from a homologous recombination (HR) between the Mideast and Australia lineages that probably occurred in the 1940s. To our knowledge, HR has not been proposed before as the genetic mechanism of BEFV. According to the HR event and Bayesian estimation, the three BEFV lineages might originate from Africa, and may have spread to Asia and Australia through the Mideast. In addition, the population of the virus may have augmented significantly in the 2000s, suggesting that the risk for outbreaks of BEFV may be high at present.

Relationships of bovine ephemeral fever epizootics to population immunity and virus variation

Bovine ephemeral fever is an arthropod-borne bovine viral disease caused by infection with bovine ephemeral fever virus which belongs to genus Ephemerovirus within the family Rhabdoviridae. In this study, serological data and virological information about the disease and the virus, spanning from 2001 to 2013, were employed to analyze the relationships of bovine ephemeral fever epizootics to population immunity and virus variation. National and regional surveillance data indicated that 2 of the 3 major epizootics and 87% regional outbreaks were associated with lower neutralizing antibody titers and immunity coverage, reflecting the importance of population immunity for the control of bovine ephemeral fever. Phylogenetic analysis and sequence comparison demonstrated that Taiwanese bovine ephemeral fever viruses were >96.0% and >97.6% similar to the East Asian isolates in nucleotide and amino acid sequences, respectively. These analyses supported that the Taiwanese viruses shared the same gene pool with the strains of the other East Asian countries, mainly Japan.