In vitro inhibition of Japanese encephalitis virus replication by capsid-targeted virus inactivation

Porcine Mx proteins inhibit pseudorabies virus replication through interfering with early gene synthesis

Pseudorabies virus (PRV) is an enveloped, linear double-stranded DNA herpesvirus that resulted in huge financial losses to the swine industry. In addition to vaccination, the development of antiviral molecules is also a beneficial supplement to the control of Pseudorabies (PR). Although our previous studies have shown that porcine Mx protein (poMx1/2) significantly inhibited the proliferation of RNA virus, it was unknown whether poMx1/2 could inhibit porcine DNA virus, such as PRV. In this study, it was investigated the inhibitory effect of porcine Mx1/2 protein on PRV multiplication. The results showed that both poMx1 and poMx2 had anti-PRV activities, which required GTPase ability and stable oligomerization. Interestingly, the two GTPase deficient mutants (G52Q and T148A) of poMx2 also had the antiviral ability against PRV, which was consistent with previous reports, indicating that these mutants recognized and blocked the viral targets. Mechanistically, the antiviral restriction of poMx1/2 came from their inhibition of the early gene synthesis of PRV. Our results for the first time shed light on the antiviral activities of two poMx proteins against DNA virus. The data from this study provide further insights to develop new strategies for preventing and controlling the diseases caused by PRV.

New Insights into the Biology of the Emerging Tembusu Virus

Reported for the first time in 1955 in Malaysia, Tembusu virus (TMUV) remained, for a long time, in the shadow of flaviviruses with human health importance such as dengue virus or Japanese encephalitis virus. However, since 2010 and the first large epidemic in duck farms in China, the threat of its emergence on a large scale in Asia or even its spillover into the human population is becoming more and more significant. This review aims to report current knowledge on TMUV from viral particle organization to the development of specific vaccines and therapeutics, with a particular focus on host-virus interactions.

Structure and function of capsid protein in flavivirus infection and its applications in the development of vaccines and therapeutics

Flaviviruses are enveloped single positive-stranded RNA viruses. The capsid (C), a structural protein of flavivirus, is dimeric and alpha-helical, with several special structural and functional features. The functions of the C protein go far beyond a structural role in virions. It is not only responsible for encapsidation to protect the viral RNA but also able to interact with various host proteins to promote virus proliferation. Therefore, the C protein plays an important role in infected host cells and the viral life cycle. Flaviviruses have been shown to affect the health of humans and animals. Thus, there is an urgent need to effectively control flavivirus infections. The structure of the flavivirus virion has been determined, but there is relatively little information about the function of the C protein. Hence, a greater understanding of the role of the C protein in viral infections will help to discover novel antiviral strategies and provide a promising starting point for the further development of flavivirus vaccines or therapeutics.

Therapeutic effects of duck Tembusu virus capsid protein fused with staphylococcal nuclease protein to target Tembusu infection in vitro

Tembusu virus (TMUV), a member of the genus flavivirus, primarily causes egg-drop syndrome in ducks and is associated with low disease mortality but high morbidity. The commercially available live vaccines for treating TMUV currently include the main WF100, HB, and FX2010-180P strains, and efficient treatment and/or preventative measures are still urgently needed. Capsid-targeted viral inactivation (CTVI) is a conceptually powerful new antiviral strategy that is based on two proteins from the capsid protein of a virus and a crucial effector molecule. The effector molecule can destroy the viral DNA/RNA or interfere with the proper folding of key viral proteins, while the capsid protein mainly plays a role in viral integration and assembly; the fusion proteins are incorporated into virions during packaging. This study aimed to explore the potential use of this strategy in duck TMUV. Our results revealed that these fusion proteins can be expressed in susceptible BHK21 cells without cytotoxicity and possess excellent Ca²⁺-dependent nuclease activity, and their expression is also detectable in DF-1 cells. Compared to those in the negative controls (BHK21 and BHK21/pcDNA3.1(+) cells), the numbers of viral RNA copies in TMUV-infected BHK21/Cap-SNase and BHK21/Cap-Linker-SNase cells were reduced by 48 h, and the effect of Cap-Linker-SNase was superior to that of Cap-SNase. As anticipated, these results suggest that these fusion proteins contribute to viral resistance to treatment. Thus, CTVI might be applicable for TMUV inhibition as a novel antiviral therapeutic candidate during viral infection.

Mx Is Not Responsible for the Antiviral Activity of Interferon-α against Japanese Encephalitis Virus

Mx proteins are interferon (IFN)-induced dynamin-like GTPases that are present in all vertebrates and inhibit the replication of myriad viruses. However, the role Mx proteins play in IFN-mediated suppression of Japanese encephalitis virus (JEV) infection is unknown. In this study, we set out to investigate the effects of Mx1 and Mx2 expression on the interferon-α (IFNα) restriction of JEV replication. To evaluate whether the inhibitory activity of IFNα on JEV is dependent on Mx1 or Mx2, we knocked down Mx1 or Mx2 with siRNA in IFNα-treated PK-15 cells and BHK-21 cells, then challenged them with JEV; the production of progeny virus was assessed by plaque assay, RT-qPCR, and Western blotting. Our results demonstrated that depletion of Mx1 or Mx2 did not affect JEV restriction imposed by IFNα, although these two proteins were knocked down 66% and 79%, respectively. Accordingly, expression of exogenous Mx1 or Mx2 did not change the inhibitory activity of IFNα to JEV. In addition, even though virus-induced membranes were damaged by Brefeldin A (BFA), overexpressing porcine Mx1 or Mx2 did not inhibit JEV proliferation. We found that BFA inhibited JEV replication, not maturation, suggesting that BFA could be developed into a novel antiviral reagent. Collectively, our findings demonstrate that IFNα inhibits JEV infection by Mx-independent pathways.

Capsid-Targeted Viral Inactivation: A Novel Tactic for Inhibiting Replication in Viral Infections

Capsid-targeted viral inactivation (CTVI), a conceptually powerful new antiviral strategy, is attracting increasing attention from researchers. Specifically, this strategy is based on fusion between the capsid protein of a virus and a crucial effector molecule, such as a nuclease (e.g., staphylococcal nuclease, Barrase, RNase HI), lipase, protease, or single-chain antibody (scAb). In general, capsid proteins have a major role in viral integration and assembly, and the effector molecule used in CTVI functions to degrade viral DNA/RNA or interfere with proper folding of viral key proteins, thereby affecting the infectivity of progeny viruses. Interestingly, such a capsid-enzyme fusion protein is incorporated into virions during packaging. CTVI is more efficient compared to other antiviral methods, and this approach is promising for antiviral prophylaxis and therapy. This review summarizes the mechanism and utility of CTVI and provides some successful applications of this strategy, with the ultimate goal of widely implementing CTVI in antiviral research.

Porcine Mx1 fused to HIV Tat protein transduction domain (PTD) inhibits classical swine fever virus infection in vitro and in vivo

Background

Classical swine fever (CSF) caused by CSF virus (CSFV) is highly contagious andcauses significant economic losses in the pig industry throughout the world. Previously we demonstrated that porcine Mx1 (poMx1), when fused to HIV Tat protein transduction domain (PTD), inhibits CSFV propagation in PK-15 cells, but it is unknown whether PTD-poMx1 exhibits antiviral activity in other porcine lines and it is efficacious for controlling CSFV infection in pigs in China.

Methods

Two porcine cell lines, ST and 3D4/21, were used to investigate in vitro antiviral activity of PTD-poMx1 against CSFV using confocal microscopy, western blot, flow cytometry, and real-time RT-PCR. Furthermore, in vivo antiviral activity of PTD-poMx1 was assessed by means of rectal temperature, clinical score, pathological lesion, white blood cell count, viral load, etc.

Results

PTD-poMx1 entered both cell lines within 3 h and maintained for 16 h, but did not affect CSFV binding and uptake. Viral titers and qRT-PCR data showed that PTD-poMx1 inhibited CSFV replication in both cell lines, showing significant antiviral activity after infection. Injection of PTD-poMx1 into CSFV-challenged pigs attenuated CSFV symptoms and viremia in dose-dependent manner but did not completely block virus replication within 14 days post challenge, suggesting that PTD-poMx1 confers partial protection against a lethal challenge.

Conclusion

We demonstrated the anti-CSFV activity of PTD-poMx1 in vitro and in vivo. The results have shown that treatment with PTD-poMx1 alleviated symptoms and viral load in infected pigs. The results support our previous in vitro studies and suggest that PTD-poMx1 could be promising in reducing the clinical signs caused by CSFV.

In vitro inhibition of the replication of classical swine fever virus by porcine Mx1 protein

Classical swine fever virus (CSFV) is the causative pathogen of classical swine fever (CSF), a highly contagious disease of swine. Mx proteins are interferon-induced dynamin-like GTPases present in all vertebrates with a wide range of antiviral activities. Although Zhao et al. (2011) have reported that human MxA can inhibit CSFV replication, whether porcine Mx1 (poMx1) has anti-CSFV activity remains unknown. In this study, we generated a cell line designated PK-15/EGFP-poMx1 which expressed porcine Mx1 protein constitutively, and we observed that the proliferation of progeny virus in this cell line was significantly inhibited as measured by virus titration, indirect immune fluorescence assay, Q-PCR and Western blot. Furthermore, when PTD-poMx1 fusion protein expressed in Escherichia coli (Zhang et al., 2013) was used to treat CSFV-infected PK-15 cells, the results showed that PTD-poMx1 inhibited CSFV replication in a dose-dependent manner. Additionally, the proliferation of progeny virus was inhibited as measured by virus titration and Q-PCR. Overall, the results demonstrated that poMx1 effectively inhibited CSFV replication, suggesting that poMx1 may be a valuable therapeutic agent against CSFV infection.

Fine mapping of a linear epitope on EDIII of Japanese encephalitis virus using a novel neutralizing monoclonal antibody

The domain III (EDIII) of the envelope protein of Japanese encephalitis virus (JEV) is proposed to play an essential role in JEV replication and infection; it is involved in binding to host receptors and contains specific epitopes that elicit neutralizing antibodies. However, most previous studies have not provided detailed molecular information about the functional epitopes on JEV EDIII protein. In this study, we described a monoclonal antibody (mAb 2B4) we produced and characterized by IFA, PRNT, ELISA and Western blot analyses. The results showed that mAb 2B4 was specific to JEV EDIII protein and possessed high neutralization activity against JEV in vitro. Furthermore, we found that the motif, (394)HHWH(397), was the minimal unit of the linear epitope recognized by mAb 2B4 through screening a phage-displayed random 12-mer peptide library. Using sequence alignment analysis it was found that this motif was highly conserved among JEV strains and was present in West Nile Virus (WNV). Indeed, ELISA data showed that this epitope could be recognized by both JEV-positive swine serum and WNV-positive swine serum. Notably, this linear epitope was highly hydrophilic and was located within the terminal end of a β-pleated sheet of EDIII. An analysis of the spatial conformation supported the possibility of inducing specific antibodies to this epitope. Taken together, we identified (394)HHWH(397) as an EDIII-specific linear epitope recognized by mAb 2B4, which would be beneficial for studying the pathogenic mechanism of JEV; and mAb 2B4 was also a potential diagnostic and therapeutic reagent.