Arthropod-borne flaviviruses and RNA interference: seeking new approaches for antiviral therapy

NSP4 promotes replication of porcine reproductive and respiratory syndrome virus-2

Porcine reproductive and respiratory syndrome (PRRS) is one of the most detrimental contagious swine ailments worldwide. Currently, no effective drugs are available for its treatment. Targeting the structural and non-structural proteins (NSP) of the type 2 PRRS virus (PRRSV-2) with small interfering RNA (siRNA) is an effective approach to inhibit PRRSV replication. NSP4, which is highly conserved and possesses 3 C-like serine protease activity (3CLSP), can cleave PRRSV self-proteins, thereby contributing to viral replication. To investigate the mechanism by which NSP4 regulates PRRSV-2 replication and screen for effective siRNA inhibitors of PRRSV-2 replication, the recombinant plasmid pEGFP-C1-NSP4 was constructed, and a control siRNA pair and two siRNA pairs targeting the PRRSV-2 NSP4 gene (shRNA-ctr, shRNA-150, and shRNA-536) were synthesized and cloned into the pSilencer4.1-CMV vector. After 24 h of incubation, Marc-145 cells were transfected with recombinant plasmids, and subsequently infected with different PRRSV-2 (XH-GD, ZQ-GD, GDr180, and JXA1-R). Subsequently, the effects of NSP4 overexpression, shRNA on PRRSV-2 replication were evaluated by assessing cytopathic effects (CPE), TCID50, quantitative real-time PCR (qPCR), immunofluorescence assays (IFA), and Western blotting. The data from these CPE, TCID50, qPCR, and IFA experiments revealed that NSP4 overexpression significantly enhanced PRRSV-2 replication and shRNA targeting NSP4 can inhibit PRRSV-2 replication in Marc-145 cells, indicating that shRNA could serve as candidate molecules for fundamental research on PRRSV-2.

The Continuous Adaptive Challenge Played by Arboviruses: An In Silico Approach to Identify a Possible Interplay between Conserved Viral RNA Sequences and Host RNA Binding Proteins (RBPs)

Climate change and globalization have raised the risk of vector-borne disease (VBD) introduction and spread in various European nations in recent years. In Italy, viruses carried by tropical vectors have been shown to cause viral encephalitis, one of the symptoms of arboviruses, a spectrum of viral disorders spread by arthropods such as mosquitoes and ticks. Arboviruses are currently causing alarm and attention, and the World Health Organization (WHO) has released recommendations to adopt essential measures, particularly during the hot season, to restrict the spreading of the infectious agents among breeding stocks. In this scenario, rapid analysis systems are required, because they can quickly provide information on potential virus-host interactions, the evolution of the infection, and the onset of disabling clinical symptoms, or serious illnesses. Such systems include bioinformatics approaches integrated with molecular evaluation. Viruses have co-evolved different strategies to transcribe their own genetic material, by changing the host's transcriptional machinery, even in short periods of time. The introduction of genetic alterations, particularly in RNA viruses, results in a continuous adaptive fight against the host's immune system. We propose an in silico pipeline method for performing a comprehensive motif analysis (including motif discovery) on entire genome sequences to uncover viral sequences that may interact with host RNA binding proteins (RBPs) by interrogating the database of known RNA binding proteins, which play important roles in RNA metabolism and biological processes. Indeed, viral RNA sequences, able to bind host RBPs, may compete with cellular RNAs, altering important metabolic processes. Our findings suggest that the proposed in silico approach could be a useful and promising tool to investigate the complex and multiform clinical manifestations of viral encephalitis, and possibly identify altered metabolic pathways as targets of pharmacological treatments and innovative therapeutic protocols.

Magnitude of Antibody Cross-Reactivity in Medically Important Mosquito-Borne Flaviviruses: A Systematic Review

Introduction

Flaviviruses are a genus of enveloped single-stranded RNA viruses that include dengue virus (DENV), yellow fever virus, West Nile virus (WNV), Japanese encephalitis virus, and Zika virus. Nowadays, diverse serological assays are available to diagnose flaviviruses. However, infection with flaviviruses induces cross-reactive antibodies, which are a challenge for serological diagnosis.

Objective

This systematic review aimed to assess the magnitude of medically important mosquito-borne flavivirus–induced antibody cross-reactivity and its influence on serological test outcomes.

Methods

This study was designed based on the PRISMA guidelines. It includes original research articles published between 1994 and 2019 that reported serological cross-reactions between medically important mosquito-borne flaviviruses. Articles were searched on PubMed using controlled vocabulary. Eligibility was assessed by title, abstract, and finally by reading the full paper. The articles included are compared, evaluated, and summarized narratively.

Results

A total of 2,911 articles were identified, and finally 14 were included. About 15.4%–84% of antibodies produced against non-DENV flaviviruses were cross-reactive with DENV on different assays. Up to 30% IgM and up to 60% IgG antibodies produced against non-WNV flaviviruses were cross-reactive with WNV on EIA assays. The magnitude of antibodies produced against flaviviruses that are cross-reactive with chikungunya virus (Alphavirus) was minimal (only about 7%). The highest antibody cross-reactivity of flaviviruses was reported in IgG-based assays compared to IgM-based assays and assays based on E-specific immunoglobulin compared to NS1-specific immunoglobulin. It was found that preexisting immunity due to vaccination or prior flavivirus exposure to antigenetically related species enhanced the cross-reactive antibody titer.

Conclusion

This review found the highest cross-reaction between DENV and non-DENV flaviviruses, especially yellow fever virus, and the least between chikungunya virus and DENV. Moreover, cross-reaction was higher on IgG assays than IgM ones and assays based on Eprotein compared to NS1protein. This implies that the reliability of serological test results in areas where more than one flavivirus exists is questionable. Therefore, interpretation of the existing serological assays should be undertaken with a great caution. Furthermore, research on novel diagnostic signatures for differential diagnosis of flaviviruses is needed.

Tick-virus interactions: Current understanding and future perspectives

Ticks are the primary vector of arboviruses in temperate climates worldwide. They are both the vector of these pathogens to humans and an integral component of the viral sylvatic cycle. Understanding the tick-pathogen interaction provides information about the natural maintenance of these pathogens and informs the development of countermeasures against human infection. In this review, we discuss currently available information on tick-viral interactions within the broader scope of general tick immunology. While the tick immune response to several pathogens has been studied extensively, minimal work centres on responses to viral infection. This is largely due to the high pathogenicity of tick-borne viruses; this necessitates high-containment laboratories or low-pathogenicity substitute viruses. This has biased most research towards tick-borne flaviviruses. More work is required to fully understand the role of tick-virus interaction in sylvatic cycling and transmission of diverse tick-borne viruses.

Suppression of the pelo protein by Wolbachia and its effect on dengue virus in Aedes aegypti

The endosymbiont Wolbachia is known to block replication of several important arboviruses, including dengue virus (DENV), in the mosquito vector Aedes aegypti. So far, the exact mechanism of this viral inhibition is not fully understood. A recent study in Drosophila melanogaster has demonstrated an interaction between the pelo gene and Drosophila C virus. In this study, we explored the possible involvement of the pelo protein, that is involved in protein translation, in Wolbachia-mediated antiviral response and mosquito-DENV interaction. We found that pelo is upregulated during DENV replication and its silencing leads to reduced DENV virion production suggesting that it facilities DENV replication. However, in the presence of Wolbachia, specifically in female mosquitoes, the pelo protein is downregulated and its subcellular localization is altered, which could contribute to reduction in DENV replication in Ae. aegypti. In addition, we show that the microRNA aae-miR-2940-5p, whose abundance is highly enriched in Wolbachia-infected mosquitoes, might mediate regulation of pelo. Our data reveals identification of pelo as a host factor that is positively involved in DENV replication, and its suppression in the presence of Wolbachia may contribute to virus blocking exhibited by the endosymbiont.

Downregulation of Aedes aegypti chromodomain helicase DNA binding protein 7/Kismet by Wolbachia and its effect on dengue virus replication

Dengue virus (DENV) is a mosquito-transmitted virus imposing a significant burden on human health around the world. Since current control strategies are not sufficient, there is an urgent need to find alternative methods to control DENV transmission. It has been demonstrated that introduction of Wolbachia pipientis in Aedes aegypti mosquitoes can impede DENV transmission with the mechanism(s) not fully understood. Recently, a number of studies have found the involvement of chromodomain DNA binding helicases in case of Human Immunodeficiency virus (HIV) and Influenza A virus infection. In this study, we have identified three chromodomain helicase DNA binding protein (CHD) genes in Ae. aegypti and looked at their response in the case of Wolbachia and DENV infections. Foremost amongst them we have found that AeCHD7/Kismet is significantly downregulated in the presence of Wolbachia infection only in female mosquitoes. Furthermore, AeCHD7 levels showed significant increase during DENV infection, and AeCHD7 depletion led to severe reduction in the replication of DENV. Our data have identified AeCHD7 as a novel Ae. aegypti host factor that is important for DENV replication, and Wolbachia downregulates it, which may contribute towards the mechanism(s) of limiting DENV replication.

Complex interaction between dengue virus replication and expression of miRNA-133a

Background

Dengue virus (DENV) is the most common vector-borne viral infection worldwide with approximately 390 million cases and 25,000 reported deaths each year. MicroRNAs (miRNAs) are small non-coding RNA molecules responsible for the regulation of gene expression by repressing mRNA translation or inducing mRNA degradation. Although miRNAs possess antiviral activity against many mammalian-infecting viruses, their involvement in DENV replication is poorly understood.

Methods

Here, we explored the relationship between DENV and cellular microRNAs using bioinformatics tools. We overexpressed miRNA-133a in Vero cells to test its role in DENV replication and analyzed its expression using RT-qPCR. Furthermore, the expression of polypyrimidine tract binding protein (PTB), a protein involved in DENV replication, was analyzed by western blot. In addition, we profiled miRNA-133a expression in Vero cells challenged with DENV-2, using Taqman miRNA.

Results

Bioinformatic analysis revealed that the 3' untranslated region (3'UTR) of the DENV genome of all four DENV serotypes is targeted by several cellular miRNAs, including miRNA-133a. We found that overexpression of synthetic miRNA-133a suppressed DENV replication. Additionally, we observed that PTB transcription , a miRNA-133a target, is down-regulated during DENV infection. Based in our results we propose that 3'UTR of DENV down-regulates endogenous expression of miRNA-133a in Vero cells during the first hours of infection.

Conclusions

miRNA-133a regulates DENV replication possibly through the modulation of a host factor such as PTB. Further investigations are needed to verify whether miRNA-133a has an anti-DENV effect in vivo.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-016-1364-y) contains supplementary material, which is available to authorized users.

Limonoids from Melia azedarach Fruits as Inhibitors of Flaviviruses and Mycobacterium tubercolosis

The biological diversity of nature is the source of a wide range of bioactive molecules. The natural products, either as pure compounds or as standardized plant extracts, have been a successful source of inspiration for the development of new drugs. The present work was carried out to investigate the cytotoxicity, antiviral and antimycobacterial activity of the methanol extract and of four identified limonoids from the fruits of Melia azedarach (Meliaceae). The extract and purified limonoids were tested in cell-based assays for antiviral activity against representatives of ssRNA, dsRNA and dsDNA viruses and against Mycobacterium tuberculosis. Very interestingly, 3-α-tigloyl-melianol and melianone showed a potent antiviral activity (EC₅₀ in the range of 3–11μM) against three important human pathogens, belonging to Flaviviridae family, West Nile virus, Dengue virus and Yellow Fever virus. Mode of action studies demonstrated that title compounds were inhibitors of West Nile virus only when added during the infection, acting as inhibitors of the entry or of a very early event of life cycle. Furthermore, 3-α-tigloyl-melianol and methyl kulonate showed interesting antimycobacterial activity (with MIC values of 29 and 70 μM respectively). The limonoids are typically lipophilic compounds present in the fruits of Melia azeradach. They are known as cytotoxic compounds against different cancer cell lines, while their potential as antiviral and antibacterial was poorly investigated. Our studies show that they may serve as a good starting point for the development of novel drugs for the treatment of infections by Flaviviruses and Mycobacterium tuberculosis, for which there is a continued need.

Inhibition of porcine reproductive and respiratory syndrome virus by specific siRNA targeting Nsp9 gene

To screen siRNAs for effectively inhibiting the replication of porcine reproductive and respiratory syndrome virus (PRRSV). Four pairs of siRNA targeting Nsp9 gene of PRRSV and one non-efficient pair used as control were designed, synthesized and cloned into pSilencer4.1-CMV neo, designated as pSi-294, pSi-367, pSi-409, pSi-1488, pSi-Ctr. The recombinant plasmids were transfected into Marc-145 cells and infected with PRRSV 24h post transfection. Subsequently, IFA, real-time PCR, TCID50 and western blot were used for evaluating the inhibitory effect of the siRNA. IFA and western-blot results showed that pSi-294, pSi-1488 can effectively inhibit the expression of Nsp9 and M protein of PRRSV, real-time PCR result showed that the expression of Nsp9 gene were decreased from 86.56% to 93.66% compared to the negative control. siRNAs can be used as candidates for basic research of PRRSV.