Rewiring cellular networks by members of the Flaviviridae family

JEV infection leads to dysfunction of lysosome by downregulating the expression of LAMP1 and LAMP2

Japanese Encephalitis Virus (JEV), the predominant cause of viral encephalitis in many Asian countries, affects approximately 68,000 people annually. Lysosomes are dynamic structures that regulate cellular metabolism by mediating lysosomal biogenesis and autophagy. Here, we showed that lysosome-associated membrane protein 1 (LAMP1) and LAMP2 were downregulated in cells after JEV infection, resulting in a decrease in the quantity of acidified lysosomes and impaired lysosomal catabolism. What's more, JEV nonstructural protein 4B plays key roles in the reduction of LAMP1/2 via the autophagy-lysosome pathway. JEV NS4B also promoted abnormal aggregation of SLA-DR, an important component of the swine MHC-II molecule family involved in antigen presentation and CD4+ cell activation initiation. Mechanistically, NS4B localized to the ER during JEV infection and interacted with GRP78, leading to the activation of ER stress-mediated autophagy. The 131-204 amino acid (aa) region of NS4B is essential for autophagy induction and LAMP1/2 reduction. In summary, our findings reveal a novel pathway by which JEV induces autophagy and disrupts lysosomal function.

The Interactions between Cells and Viruses

Many infectious diseases are caused by life-threatening DNA and RNA viruses and have been reported worldwide, including those caused by emerging and re-emerging viruses [...].

Characterisation of ten NS2B-NS3 proteases: Paving the way for pan-flavivirus drugs

Flaviviruses can cause severe illness in humans. Effective and safe vaccines are available for some species; however, for many flaviviruses disease prevention or specific treatments remain unavailable. The viral replication cycle depends on the proteolytic activity of the NS2B-NS3 protease, which releases functional viral proteins from a non-functional polyprotein precursor, rendering the protease a promising drug target. In this study, we characterised recombinant NS2B-NS3 proteases from ten flaviviruses including three unreported proteases from the Usutu, Kyasanur forest disease and Powassan viruses. All protease constructs comprise a covalent Gly4-Ser-Gly4 linker connecting the NS3 serine protease domain with its cofactor NS2B. We conducted a comprehensive cleavage site analysis revealing areas of high conversion. While all proteases were active in enzymatic assays, we noted a 1000-fold difference in catalytic efficiency across proteases from different flaviviruses. Two bicyclic peptide inhibitors displayed anti-pan-flaviviral protease activity with inhibition constants ranging from 10 to 1000 nM.

Innovations in dengue virus detection: An overview of conventional and electrochemical biosensor approaches

Globally, people are in great threat due to the highly spreading of viral infectious diseases. Every year like 100-300 million cases of infections are found, and among them, above 80% are not recognized and irrelevant. Dengue virus (DENV) is an arbovirus infection that currently infects people most frequently. DENV encompasses four viral serotypes, and they each express comparable sign. From a mild febrile sickness to a potentially fatal dengue hemorrhagic fever, dengue can induce a variety of symptoms. Presently, the globe is being challenged by the untimely identification of dengue infection. Therefore, this review summarizes advances in the detection of dengue from conventional methods (nucleic acid-based, polymerase chain reaction-based, and serological approaches) to novel biosensors. This work illustrates an extensive study of the current designs and fabrication approaches involved in the formation of electrochemical biosensors for untimely identifications of dengue. Additionally, in electrochemical sensing of DENV, we skimmed through significances of biorecognition molecules like lectins, nucleic acid, and antibodies. The introduction of emerging techniques such as the CRISPR/Cas' system and their integration with biosensing platforms has also been summarized. Furthermore, the review revealed the importance of electrochemical approach compared with traditional diagnostic methods.

Host caveolin-1 facilitates Zika virus infection by promoting viral RNA replication

Zika virus (ZIKV) has gained notoriety in recent years because there are no targeted therapies or vaccines available so far. Caveolin-1 (Cav-1) in host cells plays crucial functions in the invasion of many viruses. However, its specific involvement in ZIKV infection has remained unclear. Here, we reveal that depleting Cav-1 leads to a substantial reduction in ZIKV RNA levels, protein expression and viral particle production, indicating that ZIKV exploits Cav-1 for its infection. By dissecting each stage of the viral life cycle, we unveil that, unlike its invasion role in many other viruses, Cav-1 depletion selectively impairs ZIKV replication, resulting in altered replication dynamics and reduced strand-specific RNA levels, but does not affect viral entry, maturation and release. These results reveal an unforeseen function of Cav-1 in facilitating ZIKV replication, which provides new insights into the intricate interaction between Cav-1 and ZIKV and underscores Cav-1 as a potential candidate for anti-ZIKV approaches.

Japanese encephalitis virus NS1 and NS1' proteins induce vimentin rearrangement via the CDK1-PLK1 axis to promote viral replication

The host cytoskeleton plays crucial roles in various stages of virus infection, including viral entry, transport, replication, and release. However, the specific mechanisms by which intermediate filaments are involved in orthoflavivirus infection have not been well understood. In this study, we demonstrate that the Japanese encephalitis virus (JEV) remodels the vimentin network, resulting in the formation of cage-like structures that support viral replication. Mechanistically, JEV NS1 and NS1' proteins induce the translocation of CDK1 from the nucleus to the cytoplasm and interact with it, leading to the phosphorylation of vimentin at Ser56. This phosphorylation event recruits PLK1, which further phosphorylates vimentin at Ser83. Consequently, these phosphorylation modifications convert the typically filamentous vimentin into non-filamentous "particles" or "squiggles." These vimentin "particles" or "squiggles" are then transported retrogradely along microtubules to the endoplasmic reticulum, where they form cage-like structures. Notably, NS1' is more effective than NS1 in triggering the CDK1-PLK1 cascade response. Overall, our study provides new insights into how JEV NS1 and NS1' proteins manipulate the vimentin network to facilitate efficient viral replication.

IMPORTANCE

Japanese encephalitis virus (JEV) is a mosquito-borne orthoflavivirus that causes severe encephalitis in humans, particularly in Asia. Despite the availability of a safe and effective vaccine, JEV infection remains a significant public health threat due to limited vaccination coverage. Understanding the interactions between JEV and host proteins is essential for developing more effective antiviral strategies. In this study, we investigated the role of vimentin, an intermediate filament protein, in JEV replication. Our findings reveal that JEV NS1 and NS1' proteins induce vimentin rearrangement, resulting in the formation of cage-like structures that envelop the viral replication factories (RFs), thus facilitating efficient viral replication. Our research highlights the importance of the interplay between the cytoskeleton and orthoflavivirus, suggesting that targeting vimentin could be a promising approach for the development of antiviral strategies to inhibit JEV propagation.

A Highly Sensitive Molecular Technique for RNA Virus Detection

Zika (ZIKV) and Chikungunya (CHIKV) viruses are mosquito-transmitted infections, or vector-borne pathogens, that emerged a few years ago. Reliable diagnostic tools for ZIKV and CHIKV-inexpensive, multiplexed, rapid, highly sensitive, and specific point-of-care (POC) systems-are vital for appropriate risk management and therapy. We recently studied a detection system with great success in Mexico (Villahermosa, state of Tabasco), working with human sera from patients infected with those viruses. The research conducted in Mexico validated the efficacy of a novel two-step rapid isothermal amplification technique (RAMP). This approach, which encompasses recombinase polymerase amplification (RPA) followed by loop-mediated isothermal amplification (LAMP), had been previously established in the lab using lab-derived Zika (ZIKV) and Chikungunya (CHIKV) viruses. Crucially, our findings confirmed that this technique is also effective when applied to human sera samples collected from locally infected individuals in Mexico.

Japanese encephalitis virus hijacks ER-associated degradation regulators for its replication

Flaviviruses target their replication on membranous structures derived from the ER, where both viral and host proteins play crucial structural and functional roles. Here, we have characterized the involvement of the ER-associated degradation (ERAD) pathway core E3 ligase complex (SEL1L-HRD1) regulator proteins in the replication of Japanese encephalitis virus (JEV). Through high-resolution immunofluorescence imaging of JEV-infected HeLa cells, we observe that the virus replication complexes marked by NS1 strongly colocalize with the ERAD adapter SEL1L, lectin OS9, ER-membrane shuttle factor HERPUD1, E3 ubiquitin ligase HRD1 and rhomboid superfamily member DERLIN1. NS5 positive structures also show strong overlap with SEL1L. While these effectors show significant transcriptional upregulation, their protein levels remain largely stable in infected cells. siRNA mediated depletion of OS9, SEL1L, HERPUD1 and HRD1 significantly inhibit viral RNA replication and titres, with SEL1L depletion showing the maximum attenuation of replication. By performing protein translation arrest experiments, we show that SEL1L, and OS9 are stabilised upon JEV infection. Overall results from this study suggest that these ERAD effector proteins are crucial host-factors for JEV replication.

The Inhibition of NS2B/NS3 Protease: A New Therapeutic Opportunity to Treat Dengue and Zika Virus Infection

In the global pandemic scenario, dengue and zika viruses (DENV and ZIKV, respectively), both mosquito-borne members of the flaviviridae family, represent a serious health problem, and considering the absence of specific antiviral drugs and available vaccines, there is a dire need to identify new targets to treat these types of viral infections. Within this drug discovery process, the protease NS2B/NS3 is considered the primary target for the development of novel anti-flavivirus drugs. The NS2B/NS3 is a serine protease that has a dual function both in the viral replication process and in the elusion of the innate immunity. To date, two main classes of NS2B/NS3 of DENV and ZIKV protease inhibitors have been discovered: those that bind to the orthosteric site and those that act at the allosteric site. Therefore, this perspective article aims to discuss the main features of the use of the most potent NS2B/NS3 inhibitors and their impact at the social level.

An evolutionarily conserved ubiquitin ligase drives infection and transmission of flaviviruses

Mosquito-borne flaviviruses such as dengue (DENV) and Zika (ZIKV) cause hundreds of millions of infections annually. The single-stranded RNA genome of flaviviruses is translated into a polyprotein, which is cleaved equally into individual functional proteins. While structural proteins are packaged into progeny virions and released, most of the nonstructural proteins remain intracellular and could become cytotoxic if accumulated over time. However, the mechanism by which nonstructural proteins are maintained at the levels optimal for cellular fitness and viral replication remains unknown. Here, we identified that the ubiquitin E3 ligase HRD1 is essential for flaviviruses infections in both mammalian hosts and mosquitoes. HRD1 directly interacts with flavivirus NS4A and ubiquitylates a conserved lysine residue for ER-associated degradation. This mechanism avoids excessive accumulation of NS4A, which otherwise interrupts the expression of processed flavivirus proteins in the ER. Furthermore, a small-molecule inhibitor of HRD1 named LS-102 effectively interrupts DENV2 infection in both mice and Aedes aegypti mosquitoes, and significantly disturbs DENV transmission from the infected hosts to mosquitoes owing to reduced viremia. Taken together, this study demonstrates that flaviviruses have evolved a sophisticated mechanism to exploit the ubiquitination system to balance the homeostasis of viral proteins for their own advantage and provides a potential therapeutic target to interrupt flavivirus infection and transmission.

Electron microscopy: The key to resolve RNA viruses replication organelles

Positive-sense single-stranded RNA viruses significantly reshape intracellular membranes to generate viral replication organelles that form a controlled niche in which nucleic acids, enzymes, and cofactors accumulate to assure an efficient replication of the viral genome. In recent years, advancements in electron microscopy (EM) techniques have enabled imaging of these viral factories in a near-native state providing significantly higher molecular details that have led to progress in our general understanding of virus biology. In this review, we describe the contribution of the cutting-edge EM approaches to the current knowledge of replication organelles biogenesis, structure, and functions.

The Zika virus infection remodels the expression of the synaptotagmin-9 secretory protein

The exact mechanisms involved in flaviviruses virions' release and the specific secretion of viral proteins, such as the Non Structural protein-1 (NS1), are still unclear. While these processes might involve vesicular transport to the cell membrane, NS1 from some flaviviruses was shown to participate in viral assembly and release. Here, we assessed the effect of the Zika virus (ZIKV) NS1 expression on the cellular proteome to identify trafficking-related targets that may be altered in the presence of the viral protein. We detected an increase in the synaptotagmin-9 (SYT9) secretory protein, which participates in the intracellular transport of protein-laden vesicles. We confirmed the effect of NS1 on SYT9 levels by transfection models while also detecting a significant subcellular redistribution of SYT9. We found that ZIKV prM-Env proteins, required for the viral particle release, also increased SYT9 levels and changed its localization. Finally, we demonstrated that ZIKV cellular infection raises SYT9 levels and promotes changes in its subcellular localization, together with a co-distribution with both Env and NS1. Altogether, the data suggest SYT9's implication in the vesicular transport of viral proteins or virions during ZIKV infection, showing for the first time the association of synaptotagmins with the flavivirus' life cycle.

Co-opted cytosolic proteins form condensate substructures within membranous replication organelles of a positive-strand RNA virus

Positive-strand RNA viruses co-opt organellar membranes for biogenesis of viral replication organelles (VROs). Tombusviruses also co-opt pro-viral cytosolic proteins to VROs. It is currently not known what type of molecular organization keeps co-opted proteins sequestered within membranous VROs. In this study, we employed tomato bushy stunt virus (TBSV) and carnation Italian ringspot virus (CIRV) - Nicotiana benthamiana pathosystems to identify biomolecular condensate formation in VROs. We show that TBSV p33 and the CIRV p36 replication proteins sequester glycolytic and fermentation enzymes in unique condensate substructures associated with membranous VROs. We find that p33 and p36 form droplets in vitro driven by intrinsically disordered region. The replication protein organizes partitioning of co-opted host proteins into droplets. VRO-associated condensates are critical for local adenosine triphosphate production to support energy for virus replication. We find that co-opted endoplasmic reticulum membranes and actin filaments form meshworks within and around VRO condensates, contributing to unique composition and structure. We propose that p33/p36 organize liquid-liquid phase separation of co-opted concentrated host proteins in condensate substructures within membranous VROs. Overall, we demonstrate that subverted membranes and condensate substructures co-exist and are critical for VRO functions. The replication proteins induce and connect the two substructures within VROs.

Targeting ABCG1 and SREBP-2 mediated cholesterol homeostasis ameliorates Zika virus-induced ocular pathology

Zika virus (ZIKV) infection during pregnancy causes severe neurological and ocular abnormalities in infants, yet no vaccine or antivirals are available. Our transcriptomic analysis of ZIKV-infected retinal pigment epithelial (RPE) cells revealed alterations in the cholesterol pathway. Thus, we investigated the functional roles of ATP binding cassette transporter G1 (ABCG1) and sterol response element binding protein 2 (SREPB-2), two key players in cholesterol metabolism, during ocular ZIKV infection. Our in vitro data showed that increased ABCG1 activity via liver X receptors (LXRs), reduced ZIKV replication, while ABCG1 knockdown increased replication with elevated intracellular cholesterol. Conversely, inhibiting SREBP-2 or its knockdown reduced ZIKV replication by lowering cholesterol levels. In vivo, LXR agonist or SREBP-2 inhibitor treatment mitigated ZIKV-induced chorioretinal lesions in mice, concomitant with decreased expression of inflammatory mediators and increased activation of antiviral response genes. In summary, our study identifies ABCG1's antiviral role and SREBP-2's proviral effects in ocular ZIKV infection, offering cholesterol metabolism as a potential target to develop antiviral therapies.

Packaging Quantum Dots in Viral Particles via a Strep-tag II/Streptavidin System for Single-Virus Tracking

Single-virus tracking provides a powerful tool for studying virus infection with high spatiotemporal resolution. Quantum dots (QDs) are used to label and track viral particles due to their brightness and photostability. However, labeling viral particles with QDs is not easy. We developed a new method for labeling viral particles with QDs by using the Strep-tag II/streptavidin system. In this method, QDs were site-specifically ligated to viral proteins in live cells and then packaged into viral-like particles (VLPs) of tick-borne encephalitis virus (TBEV) and Ebola virus during viral assembly. With TBEV VLP-QDs, we tracked the clathrin-mediated endocytic entry of TBEV and studied its intracellular dynamics at the single-particle level. Our Strep-tag II/streptavidin labeling procedure eliminates the need for BirA protein expression or biotin addition, providing a simple and general method for site-specifically labeling viral particles with QDs for single-virus tracking.

A Review on The Pathogenesis of Cardiovascular Disease of Flaviviridea Viruses Infection

Members of the Flaviviridae family, encompassing the Flavivirus and Hepacivirus genera, are implicated in a spectrum of severe human pathologies. These diseases span a diverse spectrum, including hepatitis, vascular shock syndrome, encephalitis, acute flaccid paralysis, and adverse fetal outcomes, such as congenital heart defects and increased mortality rates. Notably, infections by Flaviviridae viruses have been associated with substantial cardiovascular compromise, yet the exploration into the attendant cardiovascular sequelae and underlying mechanisms remains relatively underexplored. This review aims to explore the epidemiology of Flaviviridae virus infections and synthesize their cardiovascular morbidities. Leveraging current research trajectories and our investigative contributions, we aspire to construct a cogent theoretical framework elucidating the pathogenesis of Flaviviridae-induced cardiovascular injury and illuminate prospective therapeutic avenues.

Zika virus: Antiviral immune response, inflammation, and cardiotonic steroids as antiviral agents

Zika virus (ZIKV) is a mosquito-borne virus first reported from humans in Nigeria in 1954. The first outbreak occurred in Micronesia followed by an outbreak in French Polynesia and another in Brazil when the virus was associated with numerous cases of severe neurological manifestations such as Guillain-Barre syndrome in adults and congenital zika syndrome in fetuses, particularly congenital microcephaly. Innate immunity is the first line of defense against ZIKV through triggering an antiviral immune response. Along with innate immune responses, a sufficient balance between anti- and pro-inflammatory cytokines and the amount of these cytokines are triggered to enhance the antiviral responses. Here, we reviewed the complex interplay between the mediators and signal pathways that coordinate antiviral immune response and inflammation as a key to understanding the development of the underlying diseases triggered by ZIKV. In addition, we summarize current and new therapeutic strategies for ZIKV infection, highlighting cardiotonic steroids as antiviral drugs for the development of this agent.

Aminopyrimidine Derivatives as Multiflavivirus Antiviral Compounds Identified from a Consensus Virtual Screening Approach

Around three billion people are at risk of infection by the dengue virus (DENV) and potentially other flaviviruses. Worldwide outbreaks of DENV, Zika virus (ZIKV), and yellow fever virus (YFV), the lack of antiviral drugs, and limitations on vaccine usage emphasize the need for novel antiviral research. Here, we propose a consensus virtual screening approach to discover potential protease inhibitors (NS3pro) against different flavivirus. We employed an in silico combination of a hologram quantitative structure-activity relationship (HQSAR) model and molecular docking on characterized binding sites followed by molecular dynamics (MD) simulations, which filtered a data set of 7.6 million compounds to 2,775 hits. Lastly, docking and MD simulations selected six final potential NS3pro inhibitors with stable interactions along the simulations. Five compounds had their antiviral activity confirmed against ZIKV, YFV, DENV-2, and DENV-3 (ranging from 4.21 ± 0.14 to 37.51 ± 0.8 μM), displaying aggregator characteristics for enzymatic inhibition against ZIKV NS3pro (ranging from 28 ± 7 to 70 ± 7 μM). Taken together, the compounds identified in this approach may contribute to the design of promising candidates to treat different flavivirus infections.

Nuclear membrane protein SUN2 promotes replication of flaviviruses through modulating cytoskeleton reorganization mediated by NS1

Cytoskeleton is extensively recruited by flaviviruses for their infection. In this study, we uncovered an essential role of a nuclear membrane protein, SAD1/UNC84 domain protein 2 (SUN2) linking cytoskeleton and nucleoskeleton in the flavivirus replication. CRISPR/Cas9-mediated knockout of SUN2, but not SUN1, significantly reduces the replication of Zika virus (ZIKV), dengue virus (DENV), and Japanese encephalitis virus (JEV). In contrast, SUN2 does not affect the infection of non-flaviviridae RNA viruses. All three regions of SUN2 are required for its proviral effect. Mechanistically, SUN2 facilitates rearrangement of cytoskeleton and formation of replication organelles induced by viral infection, and hence promotes viral RNA synthesis. SUN2 is required for the interaction between cytoskeleton actin and ZIKV nonstructural protein 1 (NS1). Expression of dominant negative Nesprin-1 and Nesprin-2, which connect SUN2 to cytoskeleton proteins, alleviates the interaction between actin and NS1 and reduces viral replication levels. In a neonatal mouse infection model, SUN2 knockout dramatically alleviates the in vivo ZIKV replication and development of neuropathology. This work elucidates that recruitment of cytoskeleton proteins by flavivirus is coordinated by nuclear membrane proteins SUN2 and Nesprins, providing evidence for a link between nuclear membrane proteins and flavivirus infection.

Identification of a critical role for ZIKV capsid α3 in virus assembly and its genetic interaction with M protein

Flaviviruses such as Zika and dengue viruses are persistent health concerns in endemic regions worldwide. Efforts to combat the spread of flaviviruses have been challenging, as no antivirals or optimal vaccines are available. Prevention and treatment of flavivirus-induced diseases require a comprehensive understanding of their life cycle. However, several aspects of flavivirus biogenesis, including genome packaging and virion assembly, are not well characterized. In this study, we focused on flavivirus capsid protein (C) using Zika virus (ZIKV) as a model to investigate the role of the externally oriented α3 helix (C α3) without a known or predicted function. Alanine scanning mutagenesis of surface-exposed amino acids on C α3 revealed a critical CN67 residue essential for ZIKV virion production. The CN67A mutation did not affect dimerization or RNA binding of purified C protein in vitro. The virus assembly is severely affected in cells transfected with an infectious cDNA clone of ZIKV with CN67A mutation, resulting in a highly attenuated phenotype. We isolated a revertant virus with a partially restored phenotype by continuous passage of the CN67A mutant virus in Vero E6 cells. Sequence analysis of the revertant revealed a second site mutation in the viral membrane (M) protein MF37L, indicating a genetic interaction between the C and M proteins of ZIKV. Introducing the MF37L mutation on the mutant ZIKV CN67A generated a double-mutant virus phenotypically consistent with the isolated genetic revertant. Similar results were obtained with analogous mutations on C and M proteins of dengue virus, suggesting the critical nature of C α3 and possible C and M residues contributing to virus assembly in other Aedes-transmitted flaviviruses. This study provides the first experimental evidence of a genetic interaction between the C protein and the viral envelope protein M, providing a mechanistic understanding of the molecular interactions involved in the assembly and budding of Aedes-transmitted flaviviruses.

The high-density lipoprotein binding protein HDLBP is an unusual RNA-binding protein with multiple roles in cancer and disease

The high-density lipoprotein binding protein (HDLBP) is the human member of an evolutionarily conserved family of RNA-binding proteins, the vigilin protein family. These proteins are characterized by 14 or 15 RNA-interacting KH (heterologous nuclear ribonucleoprotein K homology) domains. While mainly present at the cytoplasmic face of the endoplasmic reticulum, HDLBP and its homologs are also found in the cytosol and nucleus. HDLBP is involved in various processes, including translation, chromosome segregation, cholesterol transport and carcinogenesis. Especially, its association with the latter two has attracted specific interest in the HDLBP's molecular role. In this review, we give an overview of some of the functions of the protein as well as introduce its impact on different kinds of cancer, its connection to lipid metabolism and its role in viral infection. We also aim at addressing the possible use of HDLBP as a drug target or biomarker and discuss its future implications.

Meta-transcriptomics for the diversity of tick-borne virus in Nujiang, Yunnan Province

Ticks, an arthropod known for transmitting various pathogens such as viruses, bacteria, and fungi, pose a perpetual public health concern. A total of 2,570 ticks collected from Nujiang Prefecture in Yunnan Province between 2017 and 2022 were included in the study. Through the meta-transcriptomic sequencing of four locally distributed tick species, we identified 13 RNA viruses belonging to eight viral families, namely, Phenuiviridae, Nairoviridae, Peribunyaviridae, Flaviviridae, Chuviridae, Rhabdoviridae, Orthomyxoviridae, and Totiviridae. The most prevalent viruses were members of the order Bunyavirales, including three of Phenuiviridae, two were classified as Peribunyaviridae, and one was associated with Nairoviridae. However, whether they pose a threat to human health still remains unclear. Indeed, this study revealed the genetic diversity of tick species and tick-borne viruses in Nujiang Prefecture based on COI gene and tick-borne virus research. These data clarified the genetic evolution of some RNA viruses and furthered our understanding of the distribution pattern of tick-borne pathogens, highlighting the importance and necessity of monitoring tick-borne pathogens.

Wolbachia interferes with Zika virus replication by hijacking cholesterol metabolism in mosquito cells

IMPORTANCE

Arthropod-borne viruses are emerging pathogens that are spread widely by mosquitos. Zika virus is an arbovirus that can infect humans and be transmitted from an infected mother to the fetus, potentially leading to microcephaly in infants. One promising strategy to prevent disease caused by arboviruses is to target the insect vector population. Recent field studies have shown that mosquito populations infected with Wolbachia bacteria suppress arbovirus replication and transmission. Here, we describe how intracellular bacteria redirect resources within their host cells and suppress Zika virus replication at the cellular level. Understanding the mechanism behind Wolbachia-induced interference of arbovirus replication could help advance strategies to control arbovirus pathogens in insect vectors and human populations.

Zika virus remodelled ER membranes contain proviral factors involved in redox and methylation pathways

Zika virus (ZIKV) has emerged as a global health issue, yet neither antiviral therapy nor a vaccine are available. ZIKV is an enveloped RNA virus, replicating in the cytoplasm in close association with ER membranes. Here, we isolate ER membranes from ZIKV-infected cells and determine their proteome. Forty-six host cell factors are enriched in ZIKV remodeled membranes, several of these having a role in redox and methylation pathways. Four proteins are characterized in detail: thioredoxin reductase 1 (TXNRD1) contributing to folding of disulfide bond containing proteins and modulating ZIKV secretion; aldo-keto reductase family 1 member C3 (AKR1C3), regulating capsid protein abundance and thus, ZIKV assembly; biliverdin reductase B (BLVRB) involved in ZIKV induced lipid peroxidation and increasing stability of viral transmembrane proteins; adenosylhomocysteinase (AHCY) indirectly promoting m6A methylation of ZIKV RNA by decreasing the level of S- adenosyl homocysteine and thus, immune evasion. These results highlight the involvement of redox and methylation enzymes in the ZIKV life cycle and their accumulation at virally remodeled ER membranes.

Development of flavivirus subviral particles with low cross-reactivity by mutations of a distinct antigenic domain

The most conserved fusion loop (FL) domain present in the flavivirus envelope protein has been reported as a dominant epitope for cross-reactive antibodies to mosquito-borne flaviviruses (MBFVs). As a result, establishing accurate serodiagnosis for MBFV infections has been difficult as anti-FL antibodies are induced by both natural infection and following vaccination. In this study, we modified the most conserved FL domain to overcome this cross-reactivity. We showed that the FL domain of lineage I insect-specific flavivirus (ISFV) has differences in antigenicity from those of MBFVs and lineage II ISFV and determined the key amino acid residues (G106, L107, or F108), which contribute to the antigenic difference. These mutations were subsequently introduced into subviral particles (SVPs) of dengue virus type 2 (DENV2), Zika virus (ZIKV), Japanese encephalitis virus (JEV), and West Nile virus (WNV). In indirect enzyme-linked immunosorbent assays (ELISAs), these SVP mutants when used as antigens reduced the binding of cross-reactive IgG and total Ig induced by infection of ZIKV, JEV, and WNV in mice and enabled the sensitive detection of virus-specific antibodies. Furthermore, immunization of ZIKV or JEV SVP mutants provoked the production of antibodies with lower cross-reactivity to heterologous MBFV antigens compared to immunization with the wild-type SVPs in mice. This study highlights the effectiveness of introducing mutations in the FL domain in MBFV SVPs with lineage I ISFV-derived amino acids to produce SVP antigens with low cross-reactivity and demonstrates an improvement in the accuracy of indirect ELISA-based serodiagnosis for MBFV infections. KEY POINTS: • The FL domain of Lineage I ISFV has a different antigenicity from that of MBFVs. • Mutated SVPs reduce the binding of cross-reactive antibodies in indirect ELISAs. • Inoculation of mutated SVPs induces antibodies with low cross-reactivity.

Dengue virus NS1 secretion is regulated via importin-subunit β1 controlling expression of the chaperone GRp78 and targeted by the clinical drug ivermectin

IMPORTANCE

Dengue virus (DENV) is a major human pathogen that can cause hemorrhagic fever and shock syndrome. One important factor of DENV pathogenicity is non-structural protein 1 (NS1), a glycoprotein that is secreted from infected cells. Here we study the mode of action of the widely used drug ivermectin, used to treat parasitic infections and recently shown to lower NS1 blood levels in DENV-infected patients. We found that ivermectin blocks the nuclear transport of transcription factors required for the expression of chaperones that support the folding and secretion of glycoproteins, including NS1. Impairing nuclear transport of these transcription factors by ivermectin or depleting them from infected cells dampens NS1 folding and thus its secretion. These results reveal a novel mode of action of ivermectin that might apply to other flaviviruses as well.

Tick-Borne Encephalitis (TBE): From Tick to Pathology

Tick-borne encephalitis (TBE) is a viral arthropod infection, endemic to large parts of Europe and Asia, and is characterised by neurological involvement, which can range from mild to severe, and in 33-60% of cases, it leads to a post-encephalitis syndrome and long-term morbidity. While TBE virus, now identified as Orthoflavivirus encephalitidis, was originally isolated in 1937, the pathogenesis of TBE is not fully appreciated with the mode of transmission (blood, tick, alimentary), viral strain, host immune response, and age, likely helping to shape the disease phenotype that we explore in this review. Importantly, the incidence of TBE is increasing, and due to global warming, its epidemiology is evolving, with new foci of transmission reported across Europe and in the UK. As such, a better understanding of the symptomatology, diagnostics, treatment, and prevention of TBE is required to inform healthcare professionals going forward, which this review addresses in detail. To this end, the need for robust national surveillance data and randomised control trial data regarding the use of various antivirals (e.g., Galidesivir and 7-deaza-2'-CMA), monoclonal antibodies, and glucocorticoids is required to improve the management and outcomes of TBE.

Expression of dengue virus and Zika virus NS2B-NS3pro constructs alter cellular fatty acids, but co-expression with a Zika virus virus-like particle is detrimental to virus-like particle expression

OBJECTIVE

Studies have shown that Flavivirus infection remodels the host cell to favour viral replication. In particular, the host cell lipid profile is altered, and it has been proposed that this process alters membrane fluidity to allow wrapping of the outer structural proteins around the viral nucleocapsid. We investigated whether expression of the Zika virus (ZIKV) and dengue virus (DENV) protease induced alterations in the cellular lipid profile, and subsequently whether co-expression of these proteases with VLP constructs was able to improve VLP yield.

RESULTS

Our results showed that both ZIKV and DENV proteases induced alterations in the lipid profile, but that both active and inactive proteases induced many of the same changes. Neither co-transfection of protease and VLP constructs nor bicistronic vectors allowing expression of both protease and VLP separated by a cell cleavable linker improved VLP yield, and indeed many of the constructs showed significantly reduced VLP production. Further work in developing improved VLP expression platforms is required.

Calpain-2 protein influences chikungunya virus replication and regulates vimentin rearrangement caused by chikungunya virus infection

Chikungunya fever (CHIF), a vector-borne disease transmitted mainly by Aedes albopictus and Aedes aegypti, is caused by Chikungunya virus (CHIKV) infection. To date, it is estimated that 39% of the world's population is at risk of infection for living in countries and regions where CHIKV is endemic. However, at present, the cellular receptors of CHIKV remains not clear, and there are no specific drugs and vaccines for CHIF. Here, the cytotoxicity of calpain-2 protein activity inhibitor III and specific siRNA was detected by MTT assays. The replication of CHIKV was detected by qPCR amplification and plaque assay. Western blot was used to determine the level of the calpain-2 protein and vimentin protein. Immunofluorescence was also operated for detecting the rearrangement of vimentin protein. Our results indicated that calpain-2 protein activity inhibitor III and specific siRNA might suppress CHIKV replication. Furthermore, CHIKV infection led to vimentin remodeling and formation of cage-like structures, which could be inhibited by the inhibitor III. In summary, we confirmed that calpain-2 protein influenced chikungunya virus replication and regulated vimentin rearrangement caused by chikungunya virus infection, which could be important for understanding the biological significance of CHIKV replication and the future development of antiviral strategies.

N-linked glycosylation of flavivirus E protein contributes to viral particle formation

In the case of the Japanese encephalitis virus (JEV), the envelope protein (E), a major component of viral particles, contains a highly conserved N-linked glycosylation site (E: N154). Glycosylation of the E protein is thought to play an important role in the ability of the virus to attach to target cells during transmission; however, its role in viral particle formation and release remains poorly understood. In this study, we investigated the role of N-glycosylation of flaviviral structural proteins in viral particle formation and secretion by introducing mutations in viral structural proteins or cellular factors involved in glycoprotein transport and processing. The number of secreted subviral particles (SVPs) was significantly reduced in N154A, a glycosylation-null mutant, but increased in D67N, a mutant containing additional glycosylation sites, indicating that the amount of E glycosylation regulates the release of SVPs. SVP secretion was reduced in cells deficient in galactose, sialic acid, and N-acetylglucosamine modifications in the Golgi apparatus; however, these reductions were not significant, suggesting that glycosylation mainly plays a role in pre-Golgi transport. Fluorescent labeling of SVPs using a split green fluorescent protein (GFP) system and time-lapse imaging by retention using selective hooks (RUSH) system revealed that the glycosylation-deficient mutant was arrested before endoplasmic reticulum (ER)- Golgi transport. However, the absence of ERGIC-53 and ERGIC-L, ER-Golgi transport cargo receptors that recognize sugar chains on cargo proteins, does not impair SVP secretion. In contrast, the solubility of the N154A mutant of E or the N15A/T17A mutant of prM in cells was markedly lower than that of the wild type, and proteasome-mediated rapid degradation of these mutants was observed, indicating the significance of glycosylation of both prM and E in proper protein folding and assembly of viral particles in the ER.

Evaluating Known Zika Virus NS2B-NS3 Protease Inhibitor Scaffolds via In Silico Screening and Biochemical Assays

The NS2B-NS3 protease (NS2B-NS3pro) is regarded as an interesting molecular target for drug design, discovery, and development because of its essential role in the Zika virus (ZIKV) cycle. Although no NS2B-NS3pro inhibitors have reached clinical trials, the employment of drug-like scaffolds can facilitate the screening process for new compounds. In this study, we performed a combination of ligand-based and structure-based in silico methods targeting two known non-peptide small-molecule scaffolds with micromolar inhibitory activity against ZIKV NS2B-NS3pro by a virtual screening (VS) of promising compounds. Based on these two scaffolds, we selected 13 compounds from an initial library of 509 compounds from ZINC15's similarity search. These compounds exhibited structural modifications that are distinct from previously known compounds yet keep pertinent features for binding. Despite promising outcomes from molecular docking and initial enzymatic assays against NS2B-NS3pro, confirmatory assays with a counter-screening enzyme revealed an artifactual inhibition of the assessed compounds. However, we report two compounds, 9 and 11, that exhibited antiviral properties at a concentration of 50 μM in cellular-based assays. Overall, this study provides valuable insights into the ongoing research on anti-ZIKV compounds to facilitate and improve the development of new inhibitors.

Alpha-mangostin, piperine and beta-sitosterol as hepatitis C antivirus (HCV): In silico and in vitro studies

Hepatitis C is still a serious liver case of health. Up to now the development of anti-Hepatitis C Virus (HCV) drugs is challenging, especially the development of natural material compounds as anti-HCV. In the present study, we evaluated the probability of α-mangostin, piperine, and β-sitosterol as anti-HCV with the in silico and in vitro approaches. Molecular docking was performed between nonstructural protein 5B (NS5B, PDB ID 3FQL) with α-mangostin, piperine, and β-sitosterol by Autodock Tools® and BIOVIA Discovery Studio®. Subsequently, molecular dynamics simulations were conducted for 200 ns, evaluating the dynamic interaction between the ligands and the viral protein NS5B. Furthermore, compound characterization at the hepatocarcinoma cell line was employed. α-Mangostin with NS5B complex demonstrated the most negative binding free energy value based on MM-PBSA calculation with a value of -9.13 kcal/mol. In vitro test showed that IC50 of α -mangostin was 2.70 ± 0.92 μM, IC50 of piperine was 52.18 ± 3.21 μM, IC50 of β-sitosterol was >100 μM. α-Mangostin can serve as a valuable lead compound for further development of the anti-HCV.

Establishment of a CPER reverse genetics system for Powassan virus defines attenuating NS1 glycosylation sites and an infectious NS1-GFP11 reporter virus

Powassan virus (POWV) is an emerging tick-borne Flavivirus that causes lethal encephalitis and long-term neurologic damage. Currently, there are no POWV therapeutics, licensed vaccines, or reverse genetics systems for producing infectious POWVs from recombinant DNA. Using a circular polymerase extension reaction (CPER), we generated recombinant LI9 (recLI9) POWVs with attenuating NS1 protein mutations and a recLI9-split-eGFP reporter virus. NS1 proteins are highly conserved glycoproteins that regulate replication, spread, and neurovirulence. POWV NS1 contains three putative N-linked glycosylation sites that we modified individually in infectious recLI9 mutants (N85Q, N208Q, and N224Q). NS1 glycosylation site mutations reduced replication kinetics and were attenuated, with 1-2 log decreases in titer. Severely attenuated recLI9-N224Q exhibited a 2- to 3-day delay in focal cell-to-cell spread and reduced NS1 secretion but was lethal when intracranially inoculated into suckling mice. However, footpad inoculation of recLI9-N224Q resulted in the survival of 80% of mice and demonstrated that NS1-N224Q mutations reduce POWV neuroinvasion in vivo. To monitor NS1 trafficking, we CPER fused a split GFP11-tag to the NS1 C-terminus and generated an infectious reporter virus, recLI9-NS1-GFP11. Cells infected with recLI9-NS1-GFP11 revealed NS1 trafficking in live cells and the novel formation of large NS1-lined intracellular vesicles. An infectious recLI9-NS1-GFP11 reporter virus permits real-time analysis of NS1 functions in POWV replication, assembly, and secretion and provides a platform for evaluating antiviral compounds. Collectively, our robust POWV reverse genetics system permits analysis of viral spread and neurovirulence determinants in vitro and in vivo and enables the rational genetic design of live attenuated POWV vaccines. IMPORTANCE Our findings newly establish a mechanism for genetically modifying Powassan viruses (POWVs), systematically defining pathogenic determinants and rationally designing live attenuated POWV vaccines. This initial study demonstrates that mutating POWV NS1 glycosylation sites attenuates POWV spread and neurovirulence in vitro and in vivo. Our findings validate a robust circular polymerase extension reaction approach as a mechanism for developing, and evaluating, attenuated genetically modified POWVs. We further designed an infectious GFP-tagged reporter POWV that permits us to monitor secretory trafficking of POWV in live cells, which can be applied to screen potential POWV replication inhibitors. This robust system for modifying POWVs provides the ability to define attenuating POWV mutations and create genetically attenuated recPOWV vaccines.

Acetylation of the NS3 helicase by KAT5γ is essential for flavivirus replication

Direct targeting of essential viral enzymes such as proteases, polymerases, and helicases has long been the major focus of antiviral drug design. Although successful for some viral enzymes, targeting viral helicases is notoriously difficult to achieve, demanding alternative strategies. Here, we show that the NS3 helicase of Zika virus (ZIKV) undergoes acetylation in its RNA-binding tunnel. Regulation of the acetylated state of K389 in ZIKV NS3 modulates RNA binding and unwinding and is required for efficient viral replication. NS3 acetylation is mediated by a specific isoform of the host acetyltransferase KAT5 (KAT5γ), which translocates from the nucleus to viral replication complexes upon infection. NS3 acetylation by KAT5γ and its proviral role are also conserved in West Nile virus (WNV), dengue virus (DENV), and yellow fever virus (YFV). Our study provides molecular insight into how a cellular acetyltransferase regulates viral helicase functions, unveiling a previously unknown target for antiviral drug development.

How host ER membrane chaperones and morphogenic proteins support virus infection

The multi-functional endoplasmic reticulum (ER) is exploited by viruses to cause infection. Morphologically, this organelle is a highly interconnected membranous network consisting of sheets and tubules whose levels are dynamic, changing in response to cellular conditions. Functionally, the ER is responsible for protein synthesis, folding, secretion and degradation, as well as Ca2+ homeostasis and lipid biosynthesis, with each event catalyzed by defined ER factors. Strikingly, these ER host factors are hijacked by viruses to support different infection steps, including entry, translation, replication, assembly and egress. Although the full repertoire of these ER factors that are hijacked is unknown, recent studies have uncovered several ER membrane machineries that are exploited by viruses - ranging from polyomavirus to flavivirus and coronavirus - to facilitate different steps of their life cycle. These discoveries should provide better understanding of virus infection mechanisms, potentially leading to the development of more effective anti-viral therapies.

Hepatitis C Virus Disrupts Annexin 5-Mediated Occludin Integrity through Downregulation of Protein Kinase Cα (PKCα) and PKCη Expression, Thereby Promoting Viral Propagation

Annexins (ANXs) comprise a family of calcium- and phospholipid-binding proteins and are implicated in the hepatitis C virus (HCV) life cycle. Here, we demonstrate a novel role of ANX5 in the HCV life cycle. Comparative analysis by quantitative PCR in human hepatoma cells revealed that ANX2, ANX4, and ANX5 were highly expressed among the ANX family proteins. Knockdown of ANX5 mRNA resulted in marked enhancement of HCV RNA replication but had no effect on either HCV translation or assembly. Using the HCV pseudoparticle (HCVpp) system, we observed enhancement of HCVpp infectivity in ANX5 knockdown Huh-7OK1 cells, suggesting that ANX5 is involved in suppression of HCV entry. Additionally, we observed that subcellular localizations of tight-junction proteins, such as claudin 1 (CLDN1) and occludin (OCLN), were disrupted in the ANX5 knockdown cells. It was reported that HCV infection was facilitated by disruption of OCLN distribution and that proper distribution of OCLN was regulated by its phosphorylation. Knockdown of ANX5 resulted in a decrease of OCLN phosphorylation, thereby disrupting OCLN distribution and HCV infection. Further analysis revealed that protein kinase C (PKC) isoforms, including PKCα and PKCη, play important roles in the regulation of ANX5-mediated phosphorylation and distribution of OCLN and in the restriction of HCV infection. HCV infection reduced OCLN phosphorylation through the downregulation of PKCα and PKCη expression. Taken together, these results suggest that ANX5, PKCα, and PKCη contribute to restriction of HCV infection by regulating OCLN integrity. We propose a model that HCV disrupts ANX5-mediated OCLN integrity through downregulation of PKCα and PKCη expression, thereby promoting HCV propagation. IMPORTANCE Host cells have evolved host defense machinery to restrict viral infection. However, viruses have evolved counteracting strategies to achieve their infection. In the present study, we obtained results suggesting that ANX5 and PKC isoforms, including PKCα and PKCη, contribute to suppression of HCV infection by regulating the integrity of OCLN. The disruption of OCLN integrity increased HCV infection. We also found that HCV disrupts ANX5-mediated OCLN integrity through downregulation of PKCα and PKCη expression, thereby promoting viral infection. We propose that HCV disrupts ANX5-mediated OCLN integrity to establish a persistent infection. The disruption of tight-junction assembly may play important roles in the progression of HCV-related liver diseases.

Tick-Borne Encephalitis Virus: A Comprehensive Review of Transmission, Pathogenesis, Epidemiology, Clinical Manifestations, Diagnosis, and Prevention

Tick-borne encephalitis virus (TBEV), a member of the Flaviviridae family, can cause serious infection of the central nervous system in humans, resulting in potential neurological complications and fatal outcomes. TBEV is primarily transmitted to humans through infected tick bites, and the viral agent circulates between ticks and animals, such as deer and small mammals. The occurrence of the infection aligns with the seasonal activity of ticks. As no specific antiviral therapy exists for TBEV infection, treatment approaches primarily focus on symptomatic relief and support. Active immunization is highly effective, especially for individuals in endemic areas. The burden of TBEV infections is increasing, posing a growing health concern. Reported incidence rates rose from 0.4 to 0.9 cases per 100,000 people between 2015 and 2020. The Baltic and Central European countries have the highest incidence, but TBE is endemic across a wide geographic area. Various factors, including social and environmental aspects, improved medical awareness, and advanced diagnostics, have contributed to the observed increase. Diagnosing TBEV infection can be challenging due to the non-specific nature of the initial symptoms and potential co-infections. Accurate diagnosis is crucial for appropriate management, prevention of complications, and effective control measures. In this comprehensive review, we summarize the molecular structure of TBEV, its transmission and circulation in natural environments, the pathogenesis of TBEV infection, the epidemiology and global distribution of the virus, associated risk factors, clinical manifestations, and diagnostic approaches. By improving understanding of these aspects, we aim to enhance knowledge and promote strategies for timely and accurate diagnosis, appropriate management, and the implementation of effective control measures against TBEV infections.

Antiviral Evaluation of New Synthetic Bioconjugates Based on GA-Hecate: A New Class of Antivirals Targeting Different Steps of Zika Virus Replication

Re-emerging arboviruses represent a serious health problem due to their rapid vector-mediated spread, mainly in urban tropical areas. The 2013-2015 Zika virus (ZIKV) outbreak in South and Central America has been associated with cases of microcephaly in newborns and Guillain-Barret syndrome. We previously showed that the conjugate gallic acid-Hecate (GA-FALALKALKKALKKLKKALKKAL-CONH2)-is an efficient inhibitor of the hepatitis C virus. Here, we show that the Hecate peptide is degraded in human blood serum into three major metabolites. These metabolites conjugated with gallic acid were synthesized and their effect on ZIKV replication in cultured cells was evaluated. The GA-metabolite 5 (GA-FALALKALKKALKKL-COOH) was the most efficient in inhibiting two ZIKV strains of African and Asian lineage at the stage of both virus entry (virucidal and protective) and replication (post-entry). We also demonstrate that GA-metabolite 5 does not affect cell growth after 7 days of continuous treatment. Thus, this study identifies a new synthetic antiviral compound targeting different steps of ZIKV replication in vitro and with the potential for broad reactivity against other flaviviruses. Our work highlights a promising strategy for the development of new antivirals based on peptide metabolism and bioconjugation.

Morphogenesis and functional organization of viral inclusion bodies

Eukaryotic viruses are obligate intracellular parasites that rely on the host cell machinery to carry out their replication cycle. This complex process involves a series of steps, starting with virus entry, followed by genome replication, and ending with virion assembly and release. Negative strand RNA and some DNA viruses have evolved to alter the organization of the host cell interior to create a specialized environment for genome replication, known as IBs, which are precisely orchestrated to ensure efficient viral replication. The biogenesis of IBs requires the cooperation of both viral and host factors. These structures serve multiple functions during infection, including sequestering viral nucleic acids and proteins from innate immune responses, increasing the local concentration of viral and host factors, and spatially coordinating consecutive replication cycle steps. While ultrastructural and functional studies have improved our understanding of IBs, much remains to be learned about the precise mechanisms of IB formation and function. This review aims to summarize the current understanding of how IBs are formed, describe the morphology of these structures, and highlight the mechanism of their functions. Given that the formation of IBs involves complex interactions between the virus and the host cell, the role of both viral and cellular organelles in this process is also discussed.

Intracellular Vimentin Regulates the Formation of Classical Swine Fever Virus Replication Complex through Interaction with NS5A Protein

Vimentin (VIM), an indispensable protein, is responsible for the formation of intermediate filament structures within cells and plays a crucial role in viral infections. However, the precise role of VIM in classical swine fever virus (CSFV) infection remains unclear. Herein, we systematically investigated the function of VIM in CSFV replication. We demonstrated that both knockdown and overexpression of VIM affected CSFV replication. Furthermore, we observed by confocal microscopy the rearrangement of cellular VIM into a cage-like structure during CSFV infection. Three-dimensional (3D) imaging indicated that the cage-like structures were localized in the endoplasmic reticulum (ER) and ringed around the double-stranded RNA (dsRNA), thereby suggesting that VIM was associated with the formation of the viral replication complex (VRC). Mechanistically, phosphorylation of VIM at serine 72 (Ser72), regulated by the RhoA/ROCK signaling pathway, induced VIM rearrangement upon CSFV infection. Confocal microscopy and coimmunoprecipitation assays revealed that VIM colocalized and interacted with CSFV NS5A. Structurally, it was determined that amino acids 96 to 407 of VIM and amino acids 251 to 416 of NS5A were the respective important domains for this interaction. Importantly, both VIM knockdown and disruption of VIM rearrangement inhibited the localization of NS5A in the ER, implying that VIM rearrangement recruited NS5A to the ER for VRC formation. Collectively, our results suggest that VIM recruits NS5A to form a stable VRC that is protected by the cage-like structure formed by VIM rearrangement, ultimately leading to enhanced virus replication. These findings highlight the critical role of VIM in the formation and stabilization of VRC, which provides alternative strategies for the development of antiviral drugs. IMPORTANCE Classical swine fever (CSF), caused by classical swine fever virus (CSFV), is a highly infectious disease that poses a significant threat to the global pig industry. Therefore, gaining insights into the virus and its interaction with host cells is crucial for developing effective antiviral measures and controlling the spread of CSF. Previous studies have shown that CSFV infection induces rearrangement of the endoplasmic reticulum, leading to the formation of small vesicular organelles containing nonstructural protein and double-stranded RNA of CSFV, as well as some host factors. These organelles then assemble into viral replication complexes (VRCs). In this study, we have discovered that VIM recruited CSFV NS5A to form a stable VRC that was protected by a cage-like structure formed by rearranged VIM. This enhanced viral replication. Our findings not only shed light on the molecular mechanism of CSFV replication but also offer new insights into the development of antiviral strategies for controlling CSFV.

Chikungunya virus glycoproteins transform macrophages into productive viral dissemination vessels

Despite their role as innate sentinels, macrophages are cellular reservoirs for chikungunya virus (CHIKV), a highly pathogenic arthropod-borne alphavirus that has caused unprecedented epidemics worldwide. Here, we took interdisciplinary approaches to elucidate the CHIKV determinants that subvert macrophages into virion dissemination vessels. Through comparative infection using chimeric alphaviruses and evolutionary selection analyses, we discovered for the first time that CHIKV glycoproteins E2 and E1 coordinate efficient virion production in macrophages with the domains involved under positive selection. We performed proteomics on CHIKV-infected macrophages to identify cellular proteins interacting with the precursor and/or mature forms of viral glycoproteins. We uncovered two E1-binding proteins, signal peptidase complex subunit 3 (SPCS3) and eukaryotic translation initiation factor 3 (eIF3k), with novel inhibitory activities against CHIKV production. These results highlight how CHIKV E2 and E1 have been evolutionarily selected for viral dissemination likely through counteracting host restriction factors, making them attractive targets for therapeutic intervention.

Natural Products and Derivatives as Potential Zika virus Inhibitors: A Comprehensive Review

Zika virus (ZIKV) is an arbovirus whose infection in humans can lead to severe outcomes. This article reviews studies reporting the anti-ZIKV activity of natural products (NPs) and derivatives published from 1997 to 2022, which were carried out with NPs obtained from plants (82.4%) or semisynthetic/synthetic derivatives, fungi (3.1%), bacteria (7.6%), animals (1.2%) and marine organisms (1.9%) along with miscellaneous compounds (3.8%). Classes of NPs reported to present anti-ZIKV activity include polyphenols, triterpenes, alkaloids, and steroids, among others. The highest values of the selectivity index, the ratio between cytotoxicity and antiviral activity (SI = CC₅₀/EC₅₀), were reported for epigallocatechin gallate (SI ≥ 25,000) and anisomycin (SI ≥ 11,900) obtained from Streptomyces bacteria, dolastane (SI = 1246) isolated from the marine seaweed Canistrocarpus cervicorni, and the flavonol myricetin (SI ≥ 862). NPs mostly act at the stages of viral adsorption and internalization in addition to presenting virucidal effect. The data demonstrate the potential of NPs for developing new anti-ZIKV agents and highlight the lack of studies addressing their molecular mechanisms of action and pre-clinical studies of efficacy and safety in animal models. To the best of our knowledge, none of the active compounds has been submitted to clinical studies.

Viral subversion of selective autophagy is critical for biogenesis of virus replication organelles

Infection by many (+)RNA viruses is accompanied by ER-expansion and membrane remodelling to form viral replication organelles, followed by assembly and secretion of viral progenies. We previously identified that virus-triggered lipophagy was critical for flaviviral assembly, and is driven by the lipid droplet associated protein Ancient ubiquitin protein 1 (Aup1). A ubiquitin conjugating protein Ube2g2 that functions as a co-factor for Aup1 was identified as a host dependency factor in our study. Here we characterized its function: Ube2g2-deficient cells displayed a dramatic reduction in virus production, which could be rescued by reconstituting the wild-type but not the catalytically deficient (C89K) mutant of Ube2g2, suggesting that its enzymatic activity is necessary. Ube2g2 deficiency did not affect entry of virus particles but resulted in a profound loss in formation of replication organelles, and production of infectious progenies. This phenomenon resulted from its dual activity in (i) triggering lipophagy in conjunction with Aup1, and (ii) degradation of ER chaperones such as Herpud1, SEL1L, Hrd1, along with Sec62 to restrict ER-phagy upon Xbp1-IRE1 triggered ER expansion. Our results therefore underscore an exquisite fine-tuning of selective autophagy by flaviviruses that drive host membrane reorganization during infection to enable biogenesis of viral replication organelles.

Swine IFI6 confers antiviral effects against Japanese encephalitis virus in vitro and in vivo

Swine are considered to be an important intermediate host in the cycle of Japanese encephalitis virus (JEV) infection. Most existing antiviral studies of JEV mainly focus on the host factor of the dead-end hosts. However, little research has addressed this in swine. Here, we found that swine interferon alpha-inducible protein 6 (sIFI6) possessed antiviral activity against JEV. In vitro studies showed that overexpression of sIFI6 inhibited the infection of JEV, while sIFI6 knockdown enhanced the infection of JEV in PK-15 cells. In addition, we also found that the structural integrity of sIFI6 was required by anti-JEV activity and that sIFI6 interacted with JEV nonstructural protein 4A (NS4A), an integral membrane protein with a pivotal function in replication complex during JEV replication. The interaction domain was mapped to the fourth transmembrane domain (TMD), also known as the 2K peptide of NS4A. The antiviral activity of sIFI6 was regulated by endoplasmic reticulum (ER) stress-related protein, Bip. In vivo studies revealed that sIFI6 alleviated symptoms of JEV infection in C57BL/6 mice. In addition, the antiviral spectrum of sIFI6 showed that sIFI6 specifically inhibited JEV infection. In conclusion, this study identified sIFI6 as a host factor against JEV infection for the first time. Our findings provide a potential drug target against JEV infection.

Manipulation of the Cellular Membrane-Cytoskeleton Network for RNA Virus Replication and Movement in Plants

Viruses infect all cellular life forms and cause various diseases and significant economic losses worldwide. The majority of viruses are positive-sense RNA viruses. A common feature of infection by diverse RNA viruses is to induce the formation of altered membrane structures in infected host cells. Indeed, upon entry into host cells, plant-infecting RNA viruses target preferred organelles of the cellular endomembrane system and remodel organellar membranes to form organelle-like structures for virus genome replication, termed as the viral replication organelle (VRO) or the viral replication complex (VRC). Different viruses may recruit different host factors for membrane modifications. These membrane-enclosed virus-induced replication factories provide an optimum, protective microenvironment to concentrate viral and host components for robust viral replication. Although different viruses prefer specific organelles to build VROs, at least some of them have the ability to exploit alternative organellar membranes for replication. Besides being responsible for viral replication, VROs of some viruses can be mobile to reach plasmodesmata (PD) via the endomembrane system, as well as the cytoskeleton machinery. Viral movement protein (MP) and/or MP-associated viral movement complexes also exploit the endomembrane-cytoskeleton network for trafficking to PD where progeny viruses pass through the cell-wall barrier to enter neighboring cells.

Bioinformatics Analysis of Mutations Sheds Light on the Evolution of Dengue NS1 Protein With Implications in the Identification of Potential Functional and Druggable Sites

Non-structural protein (NS1) is a 350 amino acid long conserved protein in the dengue virus. Conservation of NS1 is expected due to its importance in dengue pathogenesis. The protein is known to exist in dimeric and hexameric states. The dimeric state is involved in its interaction with host proteins and viral replication, and the hexameric state is involved in viral invasion. In this work, we performed extensive structure and sequence analysis of NS1 protein, and uncovered the role of NS1 quaternary states in its evolution. A three-dimensional modeling of unresolved loop regions in NS1 structure is performed. "Conserved" and "Variable" regions within NS1 protein were identified from sequences obtained from patient samples and the role of compensatory mutations in selecting destabilizing mutations were identified. Molecular dynamics (MD) simulations were performed to extensively study the effect of a few mutations on NS1 structure stability and compensatory mutations. Virtual saturation mutagenesis, predicting the effect of every individual amino acid substitution on NS1 stability sequentially, revealed virtual-conserved and variable sites. The increase in number of observed and virtual-conserved regions across NS1 quaternary states suggest the role of higher order structure formation in its evolutionary conservation. Our sequence and structure analysis could enable in identifying possible protein-protein interfaces and druggable sites. Virtual screening of nearly 10,000 small molecules, including FDA-approved drugs, permitted us to recognize six drug-like molecules targeting the dimeric sites. These molecules could be promising due to their stable interactions with NS1 throughout the simulation.

Epidemiology, biology, pathogenesis, clinical manifestations, and diagnosis of dengue virus infection, and its trend in Ethiopia: a comprehensive literature review

Dengue fever is a dengue virus infection, emerging rapidly and posing public health threat worldwide, primarily in tropical and subtropical countries. Nearly half of the world's population is now at risk of contracting the dengue virus, including new countries with no previous history-like Ethiopia. However, little is known about the epidemiology and impact of the disease in different countries. This is especially true in countries, where cases have recently begun to be reported. This review aims to summarize epidemiology, biology, pathogenesis, clinical manifestations, and diagnosis of dengue virus infection and its trend in Ethiopia. It may help countries, where dengue fever is not yet on the public health list-like Ethiopia to alert healthcare workers to consider the disease for diagnosis and treatment. The review retrieved and incorporated 139 published and organizational reports showing approximately 390 million new infections. About 100 million of these infections develop the clinical features of dengue, and thousands of people die annually from severe dengue fever in 129 countries. It is caused by being bitten by a dengue virus-infected female mosquito, primarily Aedes aegypti and, lesser, Ae. albopictus. Dengue virus is a member of the Flavivirus genus of the Flaviviridae family and has four independent but antigen-related single-stranded positive-sense RNA virus serotypes. The infection is usually asymptomatic but causes illnesses ranging from mild febrile illness to fatal dengue hemorrhagic fever or shock syndrome. Diagnosis can be by detecting the virus genome using nucleic acids amplification tests or testing NS1 antigen and/or anti-dengue antibodies from serum, plasma, circulating blood cells, or other tissues. Dengue cases and outbreaks have increased in recent decades, with a significant public health impact. Ethiopia has had nearly annual outbreaks since 2013, devastating an already fragmented health system and economy. Standardization of medication, population-level screening for early diagnosis and prompt treatment, and minimization of mosquito bites reduce overall infection and mortality rates.

N-Phenylpyridine-3-Carboxamide and 6-Acetyl-1H-Indazole Inhibit the RNA Replication Step of the Dengue Virus Life Cycle

Dengue virus (DENV) is a Flavivirus that causes the most prevalent arthropod-borne viral disease. Clinical manifestation of DENV infection ranges from asymptomatic to severe symptoms that can lead to death. Unfortunately, no antiviral treatments against DENV are currently available. In order to identify novel DENV inhibitors, we screened a library of 1,604 chemically diversified fragment-based compounds using DENV reporter viruses that allowed quantification of viral replication in infected cells. Following a validation screening, the two best inhibitor candidates were N-phenylpyridine-3-carboxamide (NPP3C) and 6-acetyl-1H-indazole (6A1HI). The half maximal effective concentration of NPP3C and 6A1H1 against DENV were 7.1 μM and 6.5 μM, respectively. 6A1H1 decreased infectious DENV particle production up to 1,000-fold without any cytotoxicity at the used concentrations. While 6A1HI was DENV-specific, NPP3C also inhibited the replication of other flaviviruses such as West Nile virus and Zika virus. Structure-activity relationship (SAR) studies with 151 analogues revealed key structural elements of NPP3C and 6A1HI required for their antiviral activity. Time-of-drug-addition experiments identified a postentry step as a target of these compounds. Consistently, using a DENV subgenomic replicon, we demonstrated that these compounds specifically impede the viral RNA replication step and exhibit a high genetic barrier-to-resistance. In contrast, viral RNA translation and the de novo biogenesis of DENV replication organelles were not affected. Overall, our data unveil NPP3C and 6A1H1 as novel DENV inhibitors. The information revealed by our SAR studies will help chemically optimize NPP3C and 6A1H1 in order to improve their anti-flaviviral potency and to challenge them in in vivo models.

Dynamin2 functions as an accessory protein to reduce the rate of caveola internalization

Caveolae are small membrane invaginations that generally are stably attached to the plasma membrane. Their release is believed to depend on the GTPase dynamin 2 (Dyn2), in analogy with its role in fission of clathrin-coated vesicles. The mechanistic understanding of caveola fission is, however, sparse. Here, we used microscopy-based tracking of individual caveolae in living cells to determine the role of Dyn2 in caveola dynamics. We report that Dyn2 stably associated with the bulb of a subset of caveolae, but was not required for formation or fission of caveolae. Dyn2-positive caveolae displayed longer plasma membrane duration times, whereas depletion of Dyn2 resulted in shorter duration times and increased caveola fission. The stabilizing role of Dyn2 was independent of its GTPase activity and the caveola stabilizing protein EHD2. Thus, we propose that, in contrast to the current view, Dyn2 is not a core component of the caveolae machinery, but rather functions as an accessory protein that restrains caveola internalization.

Nucleo-Cytoplasmic Transport of ZIKV Non-Structural 3 Protein Is Mediated by Importin-α/β and Exportin CRM-1

Flaviviruses have a cytoplasmic replicative cycle, and crucial events, such as genome translation and replication, occur in the endoplasmic reticulum. However, some viral proteins, such as C, NS1, and NS5 from Zika virus (ZIKV) containing nuclear localization signals (NLSs) and nuclear export signals (NESs), are also located in the nucleus of Vero cells. The NS2A, NS3, and NS4A proteins from dengue virus (DENV) have also been reported to be in the nucleus of A549 cells, and our group recently reported that the NS3 protein is also located in the nucleus of Huh7 and C636 cells during DENV infection. However, the NS3 protease-helicase from ZIKV locates in the perinuclear region of infected cells and alters the morphology of the nuclear lamina, a component of the nuclear envelope. Furthermore, ZIKV NS3 has been reported to accumulate on the concave face of altered kidney-shaped nuclei and may be responsible for modifying other elements of the nuclear envelope. However, nuclear localization of NS3 from ZIKV has not been substantially investigated in human host cells. Our group has recently reported that DENV and ZIKV NS3 alter the nuclear pore complex (NPC) by cleaving some nucleoporins. Here, we demonstrate the presence of ZIKV NS3 in the nucleus of Huh7 cells early in infection and in the cytoplasm at later times postinfection. In addition, we found that ZIKV NS3 contains an NLS and a putative NES and uses the classic import (importin-α/β) and export pathway via CRM-1 to be transported between the cytoplasm and the nucleus. IMPORTANCE Flaviviruses have a cytoplasmic replication cycle, but recent evidence indicates that nuclear elements play a role in their viral replication. Viral proteins, such as NS5 and C, are imported into the nucleus, and blocking their import prevents replication. Because of the importance of the nucleus in viral replication and the role of NS3 in the modification of nuclear components, we investigated whether NS3 can be localized in the nucleus during ZIKV infection. We found that NS3 is imported into the nucleus via the importin pathway and exported to the cytoplasm via CRM-1. The significance of viral protein nuclear import and export and its relationship with infection establishment is highlighted, emphasizing the development of new host-directed antiviral therapeutic strategies.