Molecular chaperone Hsp90 is a therapeutic target for noroviruses

Hsp90, a team player in protein quality control and the stress response in bacteria

SUMMARYHeat shock protein 90 (Hsp90) participates in proteostasis by facilitating protein folding, activation, disaggregation, prevention of aggregation, degradation, and protection against degradation of various cellular proteins. It is highly conserved from bacteria to humans. In bacteria, protein remodeling by Hsp90 involves collaboration with the Hsp70 molecular chaperone and Hsp70 cochaperones. In eukaryotes, protein folding by Hsp90 is more complex and involves collaboration with many Hsp90 cochaperones as well as Hsp70 and Hsp70 cochaperones. This review focuses primarily on bacterial Hsp90 and highlights similarities and differences between bacterial and eukaryotic Hsp90. Seminal research findings that elucidate the structure and the mechanisms of protein folding, disaggregation, and reactivation promoted by Hsp90 are discussed. Understanding the mechanisms of bacterial Hsp90 will provide fundamental insight into the more complex eukaryotic chaperone systems.

The Picornaviridae Family: Knowledge Gaps, Animal Models, Countermeasures, and Prototype Pathogens

Picornaviruses are nonenveloped particles with a single-stranded RNA genome of positive polarity. This virus family includes poliovirus, hepatitis A virus, rhinoviruses, and Coxsackieviruses. Picornaviruses are common human pathogens, and infection can result in a spectrum of serious illnesses, including acute flaccid myelitis, severe respiratory complications, and hand-foot-mouth disease. Despite research on poliovirus establishing many fundamental principles of RNA virus biology and the first transgenic animal model of disease for infection by a human virus, picornaviruses are understudied. Existing knowledge gaps include, identification of molecules required for virus entry, understanding cellular and humoral immune responses elicited during virus infection, and establishment of immune-competent animal models of virus pathogenesis. Such knowledge is necessary for development of pan-picornavirus countermeasures. Defining enterovirus A71 and D68, human rhinovirus C, and echoviruses 29 as prototype pathogens of this virus family may provide insight into picornavirus biology needed to establish public health strategies necessary for pandemic preparedness.

ASFV transcription reporter screening system identifies ailanthone as a broad antiviral compound

African swine fever (ASF) is an acute, highly contagious and deadly viral disease in swine that jeopardizes the worldwide pig industry. Unfortunately, there are no authoritative vaccine and antiviral drug available for ASF control. African swine fever virus (ASFV) is the etiological agent of ASF. Among the ASFV proteins, p72 is the most abundant component in the virions and thus a potential target for anti-ASFV drug design. Here, we constructed a luciferase reporter system driven by the promoter of p72, which is transcribed by the co-transfected ASFV RNA polymerase complex. Using this system, we screened over 3200 natural product compounds and obtained three potent candidates against ASFV. We further evaluated the anti-ASFV effects and proved that among the three candidates, ailanthone (AIL) inhibits the replication of ASFV at the nanomolar concentration (IC50 ​= ​15 ​nmol/L). Our in vitro experiments indicated that the antiviral effect of AIL is associated with its inhibition of the HSP90-p23 cochaperone. Finally, we showed the antiviral activity of AIL on Zika virus and hepatitis B virus (HBV), which supports that AIL is a potential broad-spectrum antiviral agent.

Hsp90 Regulates GCRV-II Proliferation by Interacting with VP35 as Its Receptor and Chaperone

The frequent outbreak of grass carp hemorrhagic disease caused by grass carp reovirus (GCRV), especially the mainly prevalent type II GCRV (GCRV-II), has seriously affected the grass carp culture in China. However, its pathogenic mechanism is still far from clear. In this study, the GCRV-II outer capsid protein VP35 was used as bait to capture interacting partners from Ctenopharyngon idellus kidney (CIK) cells, and heat shock protein 90 (Hsp90) was selected and confirmed interacting with VP35 through the C-terminal domain of Hsp90. Knockdown of Hsp90 or inhibition of Hsp90 activity suppressed GCRV-II proliferation, demonstrating that Hsp90 is an essential factor for GCRV-II proliferation. The confocal microscopy and flow cytometry showed that Hsp90 localized at both membrane and cytoplasm of CIK cells. The entry of GCRV-II into CIK cells was efficiently blocked by incubating the cells with Hsp90 antibody or by pretreating the virus with recombinant Hsp90 protein. Whereas overexpression of Hsp90 in CIK cells, grass carp ovary (GCO) cells, or 293T cells promoted GCRV-II entry, indicating that the membrane Hsp90 functions as a receptor of GCRV-II. Furthermore, Hsp90 interacted with clathrin and mediated GCRV-II entry into CIK cells through clathrin endocytosis pathway. In addition, we found that the cytoplasmic Hsp90 acted as a chaperone of VP35 because inhibition of Hsp90 activity enhanced VP35 polyubiquitination and degraded VP35 through the proteasome pathway. Collectively, our data suggest that Hsp90 functions both as a receptor for GCRV-II entry and a chaperone for the maturation of GCRV-II VP35, thus ensuring efficient proliferation of GCRV-II. IMPORTANCE Identification of viral receptors has always been the research hot spot in virus research field as receptor functions at the first stage of viral infection, which can be designed as efficient antiviral drug targets. GCRV-II, the causative agent of the grass carp epidemic hemorrhagic disease, has caused tremendous losses in grass carp culture in China. To date, the receptor of GCRV-II remains unknown. This study focused on identifying cellular receptor interacting with the GCRV-II outer capsid protein VP35, studying the effects of their interaction on GCRV-II proliferation, and revealing the underlying mechanisms. We demonstrated that Hsp90 acts both as a receptor of GCRV-II by interacting with VP35 and as a chaperone for the maturation of VP35, thus ensuring efficient proliferation of GCRV-II. Our data provide important insights into the role of Hsp90 in GCRV-II life cycle, which will help understand the mechanism of reovirus infection.

Host cell stress response as a predictor of COVID-19 infectivity and disease progression

The coronavirus disease (COVID-19) caused by a coronavirus identified in December 2019 has caused a global pandemic. COVID-19 was declared a pandemic in March 2020 and has led to more than 6.3 million deaths. The pandemic has disrupted world travel, economies, and lifestyles worldwide. Although vaccination has been an effective tool to reduce the severity and spread of the disease there is a need for more concerted approaches to fighting the disease. COVID-19 is characterised as a severe acute respiratory syndrome . The severity of the disease is associated with a battery of comorbidities such as cardiovascular diseases, cancer, chronic lung disease, and renal disease. These underlying diseases are associated with general cellular stress. Thus, COVID-19 exacerbates outcomes of the underlying conditions. Consequently, coronavirus infection and the various underlying conditions converge to present a combined strain on the cellular response. While the host response to the stress is primarily intended to be of benefit, the outcomes are occasionally unpredictable because the cellular stress response is a function of complex factors. This review discusses the role of the host stress response as a convergent point for COVID-19 and several non-communicable diseases. We further discuss the merits of targeting the host stress response to manage the clinical outcomes of COVID-19.

Human Norovirus-Induced Gene Expression Biomarkers in Zebrafish

ABSTRACT

The challenges associated with development of an animal model system to replicate human norovirus (HuNoV) has hampered the study of the pathogenesis and therapeutic interventions for this virus. In this study, we replicated HuNoV GII.4 and evaluated virus gene expression in infected zebrafish. Three doses of inoculation resulted in successful virus replication. Genes for transmembrane transporters (tfa, cftr, slc26a3, and slc26a6), a heat shock chaperone (hspa8), and immune response cytokines (ifng1 and il1b) were highly expressed in HuNoV-infected zebrafish; however, expression levels of genes were reduced in zebrafish infected with thermally inactivated HuNoV. These results confirm HuNoV replication in juvenile zebrafish and will facilitate the investigation of biomarker gene expression during HuNoV infection.

HIGHLIGHTS

Vinyl-Stilbene Inhibits Human Norovirus RNA Replication by Activating Heat-Shock Factor-1

Norovirus (NV) is the most common cause of viral gastroenteritis, with the potential to develop into a fatal disease in those who are immuno-compromised, and effective vaccines and treatments are still non-existent. In this study, we aimed to elucidate the molecular mechanism of the previously identified NV replication inhibitor utilizing a vinyl-stilbene backbone, AC-1858. First, we confirmed the inhibition of the NV RNA replication by a structural analog of AC-1858, AC-2288 with its exclusive cytoplasmic subcellular localization. We further validated the induction of one specific host factor, the phosphorylated form of heat shock factor (HSF)-1, and its increased nuclear localization by AC-1858 treatment. Finally, we verified the positive and negative impact of the siRNA-mediated downregulation and lentivirus-mediated overexpression of HSF-1 on NV RNA replication. In conclusion, these data suggest the restrictive role of the host factor HSF-1 in overall viral RNA genome replication during the NV life cycle.

Current and Future Antiviral Strategies to Tackle Gastrointestinal Viral Infections

Acute gastroenteritis caused by virus has a major impact on public health worldwide in terms of morbidity, mortality, and economic burden. The main culprits are rotaviruses, noroviruses, sapoviruses, astroviruses, and enteric adenoviruses. Currently, there are no antiviral drugs available for the prevention or treatment of viral gastroenteritis. Here, we describe the antivirals that were identified as having in vitro and/or in vivo activity against these viruses, originating from in silico design or library screening, natural sources or being repurposed drugs. We also highlight recent advances in model systems available for this (hard to cultivate) group of viruses, such as organoid technologies, and that will facilitate antiviral studies as well as fill some of current knowledge gaps that hamper the development of highly efficient therapies against gastroenteric viruses.

Hsp90 Is Required for Snakehead Vesiculovirus Replication via Stabilization of the Viral L Protein

Snakehead vesiculovirus (SHVV), a kind of fish rhabdovirus isolated from diseased hybrid snakehead fish, has caused great economic losses in snakehead fish culture in China. The large (L) protein, together with its cofactor phosphoprotein (P), forms a P/L polymerase complex and catalyzes the transcription and replication of viral genomic RNA. In this study, the cellular heat shock protein 90 (Hsp90) was identified as an interacting partner of SHVV L protein. Hsp90 activity was required for the stability of SHVV L because Hsp90 dysfunction caused by using its inhibitor destabilized SHVV L and thereby suppressed SHVV replication via reducing viral RNA synthesis. SHVV L expressed alone was detected mainly in the insoluble fraction, and the insoluble L was degraded by Hsp90 dysfunction through the proteasomal pathway, while the presence of SHVV P promoted the solubility of SHVV L and the soluble L was degraded by Hsp90 dysfunction through the autophagy pathway. Collectively, our data suggest that Hsp90 contributes to the maturation of SHVV L and ensures the effective replication of SHVV, which exhibits an important anti-SHVV target. This study will help us to understand the role of Hsp90 in stabilizing the L protein and regulating the replication of negative-stranded RNA viruses. IMPORTANCE It has long been proposed that cellular proteins are involved in viral RNA synthesis via interacting with the viral polymerase protein. This study focused on identifying cellular proteins interacting with the SHVV L protein, studying the effects of their interactions on SHVV replication, and revealing the underlying mechanisms. We identified Hsp90 as an interacting partner of SHVV L and found that Hsp90 activity was required for SHVV replication. Hsp90 functioned in maintaining the stability of SHVV L. Inhibition of Hsp90 activity with its inhibitor degraded SHVV L through different pathways based on the solubility of SHVV L due to the presence or absence of SHVV P. Our data provide important insights into the role of Hsp90 in SHVV polymerase maturation, which will help us to understand the polymerase function of negative-stranded RNA viruses.

Hsp90 is involved in pseudorabies virus virion assembly via stabilizing major capsid protein VP5

Many viruses utilize molecular chaperone heat shock protein 90 (Hsp90) for protein folding and stabilization, however, the role of Hsp90 in herpesvirus lifecycle is obscure. Here, we provide evidence that Hsp90 participates in pseudorabies virus (PRV) replication. Viral growth kinetics assays show that Hsp90 inhibitor geldanamycin (GA) abrogates PRV replication at the post-penetration step. Transmission electron microscopy demonstrates that dysfunction of Hsp90 diminishes the quantity of PRV nucleocapsids. Overexpression and knockdown of Hsp90 suggest that de novo Hsp90 is involved in PRV replication. Mechanismly, dysfunction of Hsp90 inhibits PRV major capsid protein VP5 expression. Co-immunoprecipitation and indirect immunofluorescence assays indicate that Hsp90 interacts with VP5. Interestingly, Hsp70, a collaborator of Hsp90, also interacts with VP5, but doesn't affect PRV growth. Finally, inhibition of Hsp90 results in PRV VP5 degradation in a proteasome-dependent manner. Collectively, our data suggest that Hsp90 contributes to PRV virion assembly and replication via stabilization of VP5.

Are Hsp90 inhibitors good candidates against Covid-19?

Drug reposition, or repurposing, has become a promising strategy in therapeutics due to its advantages in several aspects of drug therapy. General drug development is expensive and can take more than 10 years to go through the designing, development, and necessary approval steps. However, established drugs have already overcome these steps and thus a potential candidate may be already available decreasing the risks and costs involved. Viruses invade cells, usually provoking biochemical changes, leading to tissue damage, alteration of normal physiological condition in organisms and can even result in death. Inside the cell, the virus finds the machinery necessary for its multiplication, as for instance the protein quality control system, which involves chaperones and Hsps (heat shock proteins) that, in addition to physiological functions, help in the stabilization of viral proteins. Recently, many inhibitors of Hsp90 have been developed as therapeutic strategies against diseases such as the Hsp90 inhibitors used in anticancer therapy. Several shreds of evidence indicate that these inhibitors can also be used as therapeutic strategies against viruses. Therefore, since a drug treatment for COVID-19 is urgently needed, this review aims to discuss the potential use of Hsp90 inhibitors in the treatment of this globally threatening disease.

Stress proteins: the biological functions in virus infection, present and challenges for target-based antiviral drug development

Stress proteins (SPs) including heat-shock proteins (HSPs), RNA chaperones, and ER associated stress proteins are molecular chaperones essential for cellular homeostasis. The major functions of HSPs include chaperoning misfolded or unfolded polypeptides, protecting cells from toxic stress, and presenting immune and inflammatory cytokines. Regarded as a double-edged sword, HSPs also cooperate with numerous viruses and cancer cells to promote their survival. RNA chaperones are a group of heterogeneous nuclear ribonucleoproteins (hnRNPs), which are essential factors for manipulating both the functions and metabolisms of pre-mRNAs/hnRNAs transcribed by RNA polymerase II. hnRNPs involve in a large number of cellular processes, including chromatin remodelling, transcription regulation, RNP assembly and stabilization, RNA export, virus replication, histone-like nucleoid structuring, and even intracellular immunity. Dysregulation of stress proteins is associated with many human diseases including human cancer, cardiovascular diseases, neurodegenerative diseases (e.g., Parkinson’s diseases, Alzheimer disease), stroke and infectious diseases. In this review, we summarized the biologic function of stress proteins, and current progress on their mechanisms related to virus reproduction and diseases caused by virus infections. As SPs also attract a great interest as potential antiviral targets (e.g., COVID-19), we also discuss the present progress and challenges in this area of HSP-based drug development, as well as with compounds already under clinical evaluation.

Inhibition of heat shock protein 90 suppresses Bombyx mori nucleopolyhedrovirus replication in B. mori

Heat shock protein 90 (Hsp90) plays a very important role in facilitating the replication of many viruses. Until now, little has been known about the role of Hsp90 in Bombyx mori virus infection. In this study, we explored the role of BmHsp90 in B. mori nucleopolyhedrovirus (BmNPV) replication. We found that BmHsp90 inhibition by geldanamycin (GA) significantly reduced the BmNPV titre, the protein expression level of BmNPV nucleocapsid protein 39 (VP39) and the transcript level of BmNPV genes. Silencing the hsp90 gene in BmN cells by small interfering RNA suppressed BmNPV replication whereas overexpression of hsp90 promoted the replication of BmNPV. After inhibition of Hsp90, the expression of three key genes [signal transducing activator of transcription (stat), suppressor of cytokine signalling protein 2 (socs2), socs6] involved in the Janus kinase/STAT pathway significantly changed, with up-regulation of stat and down-regulation of socs2 and socs6. In addition, the expression of two antiapoptosis genes, BmNPV inhibitor of apoptosis protein1 (BmNPV-iap1) and Bmiap2, was greatly decreased in GA-treated cells, whereas their expression was significantly increased in hsp90-overexpressed silkworm larvae. Our results indicated that inhibition of Hsp90 can suppress BmNPV proliferation in B. mori. Our findings may provide new clues to elucidate the molecular mechanisms of silkworm-virus interactions.

Effect of heat shock on murine norovirus replication in RAW264.7 cells

Murine norovirus (MNV), is a prevalent pathogen of laboratory mice closely related to human norovirus (HuNoV), a contagious pathogen known to cause gastroenteritis worldwide; however, the mechanism of norovirus replication remains poorly understood. Both heat shock protein 90 (Hsp90) and heat shock protein 70 (Hsp70) play an important role in viral genome replication and viral gene expression. In this study, we first found that heat stress exerted a positive effect on the replication of MNV in the murine macrophage RAW264.7 cell line. Inhibition of Hsp70 and Hsp90 by the specific inhibitors, KNK437 and 17-AGG, respectively showed that Hsp70 and Hsp90 enhanced MNV genome replication and virion production. In addition, we found that KNK437 and 17-AGG could decrease the level of IL-1β, IL-10, and TNF-α mRNA expression in MNV-infected cells. These data suggested that heat stress can positively regulate MNV replication, which advances our understanding of the molecular mechanism of MNV infection.

Medicinal chemistry strategies toward host targeting antiviral agents

Direct‐acting antiviral agents (DAAs) represent a class of drugs targeting viral proteins and have been demonstrated to be very successful in combating viral infections in clinic. However, DAAs suffer from several inherent limitations, including narrow‐spectrum antiviral profiles and liability to drug resistance, and hence there are still unmet needs in the treatment of viral infections. In comparison, host targeting antivirals (HTAs) target host factors for antiviral treatment. Since host proteins are probably broadly required for various viral infections, HTAs are not only perceived, but also demonstrated to exhibit broad‐spectrum antiviral activities. In addition, host proteins are not under the genetic control of viral genome, and hence HTAs possess much higher genetic barrier to drug resistance as compared with DAAs. In recent years, much progress has been made to the development of HTAs with the approval of chemokine receptor type 5 antagonist maraviroc for human immunodeficiency virus treatment and more in the pipeline for other viral infections. In this review, we summarize various host proteins as antiviral targets from a medicinal chemistry prospective. Challenges and issues associated with HTAs are also discussed.

iTRAQ-based high-throughput proteomics analysis reveals alterations of plasma proteins in patients infected with human bocavirus

Human bocavirus (HBoV) is a member of the genus Bocavirus, family Parvoviridae, and subfamily Parvovirus and was first identified in nasopharyngeal aspirates of Swedish children with acute respiratory tract infection (ARTI) in 2005. It is the causative agent of nasopharyngeal aspirate disease and death in children. The HboV genomic structure is a linear single-stranded DNA (ssDNA). Its clinical pathogenic characteristics have been extensively studied, however, at present the molecular mechanism underlying the pathogenesis of HBoV infection is not completely clear. In this study, a total of 293 differentially expressed proteins (DEPs) between ARTI cases and healthy plasma samples were characterized using isobaric tags for relative and absolute quantitation (iTRAQ)-coupled bioinformatics analysis, among which 148 were up-regulated and 135 were down-regulated. Gene Ontology (GO) and Cluster of Orthologous Groups of proteins (COG) annotated an enrichment of DEPs in complement activation and biological processes like immunity, inflammation, signal transduction, substance synthesis, and metabolism. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis enriched DEPs mainly in the Wnt signaling pathway (ko04310), PPAR signaling pathway (ko03320), intestinal immune network for IgA production (ko04672), complement and coagulation cascades (ko04610), Toll-like receptor signaling pathway (ko04620) and B cell receptor signaling pathway (ko04662). Further, expression levels of three candidate proteins (upregulated PPP2R1A and CUL1, and downregulated CETP) were validated using western blotting. Our investigation is the first analysis of the proteomic profile of HBoV-infected ARTI cases using the iTRAQ approach, providing a foundation for a better molecular understanding of the pathogenesis of ARTI in children.

Quantitative proteomics analysis provides insight into the biological role of Hsp90 in BmNPV infection in Bombyx mori

Heat shock protein 90, an essential chaperone responsible for the correct maturation of key proteins, has been confirmed to facilitate Bombyx mori nucleopolyhedrovirus (BmNPV) proliferation but the mechanism is not clear. In this study, we use quantitative proteomics analysis to investigate the mechanism of Hsp90 in BmNPV replication. In total, 195 differentially expressed proteins (DEPs) were identified with 136 up-regulated proteins and 59 down-regulated proteins. The protein expression level of small heat shock proteins, immune-related proteins, cellular DNA repair-related proteins and zinc finger proteins is significantly enhanced while that of protein kinases is declined. KEGG pathway analysis reveals that DEPs are involved in longevity regulating pathway, mTOR signaling pathway, FoxO signaling pathway and Toll and Imd signaling pathway. Based on the DEPs results, we speculate that inhibition of Hsp90 suppresses the BmNPV infection may because it could not only stimulate the host innate immune, induce small heat shock proteins expression to maintain the cellular proteostasis but activate host transcription factors to bind to virus DNA or protein and subsequently hinder virus replication. The results will help understand the roles of Hsp90 in BmNPV infection and shed light on new clue to illustrate the molecular mechanism of silkworm-virus interaction. SIGNIFICANCE: This is the first report on Hsp90 roles in BmNPV infection based on proteomic analysis. Our findings may provide new clue and research orientation to illustrate the molecular mechanism of silkworm-virus interaction and a set of BmHsp90 candidate clients, which may involve in BmNPV infection in BmN cells.

Norovirus antivirals: Where are we now?

Human noroviruses inflict a significant health burden on society and are responsible for approximately 699 million infections and over 200 000 estimated deaths worldwide each year. Yet despite significant research efforts, approved vaccines or antivirals to combat this pathogen are still lacking. Safe and effective antivirals are not available, particularly for chronically infected immunocompromised individuals, and for prophylactic applications to protect high‐risk and vulnerable populations in outbreak settings. Since the discovery of human norovirus in 1972, the lack of a cell culture system has hindered biological research and antiviral studies for many years. Recent breakthroughs in culturing human norovirus have been encouraging, however, further development and optimization of these novel methodologies are required to facilitate more robust replication levels, that will enable reliable serological and replication studies, as well as advances in antiviral development. In the last few years, considerable progress has been made toward the development of norovirus antivirals, inviting an updated review. This review focuses on potential therapeutics that have been reported since 2010, which were examined across at least two model systems used for studying human norovirus or its enzymes. In addition, we have placed emphasis on antiviral compounds with a defined chemical structure. We include a comprehensive outline of direct‐acting antivirals and offer a discussion of host‐modulating compounds, a rapidly expanding and promising area of antiviral research.

Annexin A2 associates to feline calicivirus RNA in the replication complexes from infected cells and participates in an efficient viral replication

Cellular proteins have been identified to participate in calicivirus replication in association with viral proteins and/or viral RNAs. By mass spectrometry from pull-down assays, we identified several cellular proteins bound to the feline calicivirus (FCV) genomic RNA; among them the lipid raft-associated scaffold protein Annexin (Anx) A2. AnxA2 colocalizes with FCV NS6/7 protein and with the dsRNA in infected cells; moreover, it was found associated with the viral RNA in the membrane fraction corresponding to the replication complexes (RCs), suggesting its role during FCV replication. AnxA2-knockdown from CrFK cells prior to infection with FCV caused a delay in the cytopathic effect, a strong reduction of viral non-structural proteins and dsRNA production, and a decrease of FCV yield in both cell-associated and supernatant fractions. Taken together, these results indicate that AnxA2 associates to the genomic RNA of FCV and is required for an efficient FCV replication.

Chaperones, Membrane Trafficking and Signal Transduction Proteins Regulate Zaire Ebola Virus trVLPs and Interact With trVLP Elements

Ebolavirus (EBOV) life cycle involves interactions with numerous host factors, but it remains poorly understood, as does pathogenesis. Herein, we synthesized 65 siRNAs targeting host genes mostly connected with aspects of the negative-sense RNA virus life cycle (including viral entry, uncoating, fusion, replication, assembly, and budding). We produced EBOV transcription- and replication-competent virus-like particles (trVLPs) to mimic the EBOV life cycle. After screening host factors associated with the trVLP life cycle, we assessed interactions of host proteins with trVLP glycoprotein (GP), VP40, and RNA by co-immunoprecipitation (Co-IP) and chromatin immunoprecipitation (ChIP). The results demonstrate that RNAi silencing with 11 siRNAs (ANXA5, ARFGAP1, FLT4, GRP78, HSPA1A, HSP90AB1, HSPA8, MAPK11, MEK2, NTRK1, and YWHAZ) decreased the replication efficiency of trVLPs. Co-IP revealed nine candidate host proteins (FLT4, GRP78, HSPA1A, HSP90AB1, HSPA8, MAPK11, MEK2, NTRK1, and YWHAZ) potentially interacting with trVLP GP, and four (ANXA5, GRP78, HSPA1A, and HSP90AB1) potentially interacting with trVLP VP40. Ch-IP identified nine candidate host proteins (ANXA5, ARFGAP1, FLT4, GRP78, HSPA1A, HSP90AB1, MAPK11, MEK2, and NTRK1) interacting with trVLP RNA. This study was based on trVLP and could not replace live ebolavirus entirely; in particular, the interaction between trVLP RNA and host proteins cannot be assumed to be identical in live virus. However, the results provide valuable information for further studies and deepen our understanding of essential host factors involved in the EBOV life cycle.

Therapeutics and Immunoprophylaxis Against Noroviruses and Rotaviruses: The Past, Present, and Future

Background:

Noroviruses and rotaviruses are important viral etiologies of severe gastroenteritis. Noroviruses are the primary cause of nonbacterial diarrheal outbreaks in humans, whilst rotaviruses are a major cause of childhood diarrhea. Although both enteric pathogens substantially impact human health and economies, there are no approved drugs against noroviruses and rotaviruses so far. On the other hand, whilst the currently licensed rotavirus vaccines have been successfully implemented in over 100 countries, the most advanced norovirus vaccine has recently completed phase-I and II trials.

Methods:

We performed a structured search of bibliographic databases for peer-reviewed research litera-ture on advances in the fields of norovirus and rotavirus therapeutics and immunoprophylaxis.

Results:

Technological advances coupled with a proper understanding of viral morphology and replication over the past decade has facilitated pioneering research on therapeutics and immunoprophylaxis against noroviruses and rotaviruses, with promising outcomes in human clinical trials of some of the drugs and vaccines. This review focuses on the various developments in the fields of norovirus and rotavirus thera-peutics and immunoprophylaxis, such as potential antiviral drug molecules, passive immunotherapies (oral human immunoglobulins, egg yolk and bovine colostral antibodies, llama-derived nanobodies, and anti-bodies expressed in probiotics, plants, rice grains and insect larvae), immune system modulators, probiot-ics, phytochemicals and other biological substances such as bovine milk proteins, therapeutic nanoparti-cles, hydrogels and viscogens, conventional viral vaccines (live and inactivated whole virus vaccines), and genetically engineered viral vaccines (reassortant viral particles, virus-like particles (VLPs) and other sub-unit recombinant vaccines including multi-valent viral vaccines, edible plant vaccines, and encapsulated viral particles).

Conclusions:

This review provides important insights into the various approaches to therapeutics and im-munoprophylaxis against noroviruses and rotaviruses..

Prophylactic efficacy of orally administered Bacillus poly-γ-glutamic acid, a non-LPS TLR4 ligand, against norovirus infection in mice

Poly-gamma-glutamic acid (γ-PGA), an extracellular biopolymer produced by Bacillus sp., is a non-canonical toll-like receptor 4 (TLR4) agonist. Here we show its antiviral efficacy against noroviruses. γ-PGA with a molecular mass of 2,000-kDa limited murine norovirus (MNV) replication in the macrophage cell line RAW264.7 by inducing interferon (IFN)-β and conferred resistance to viral infection-induced cell death. Additionally, γ-PGA interfered with viral entry into cells. The potent antiviral state mounted by γ-PGA was not attributed to the upregulation of TLR4 or TLR3, a sensor known to recognize norovirus RNA. γ-PGA sensing by TLR4 required the two TLR4-associated accessory factors MD2 and CD14. In ex vivo cultures of mouse ileum, γ-PGA selectively increased the expression of IFN-β in villi. In contrast, IFN-β induction was negligible in the ileal Peyer’s patches (PPs) where its expression was primarily induced by the replication of MNV. Oral administration of γ-PGA, which increased serum IFN-β levels without inducing proinflammatory cytokines, reduced MNV loads in the ileum with PPs and mesenteric lymph nodes in mice. Our results disclose a γ-PGA-mediated non-conventional TLR4 signaling in the ileum, highlighting the potential use of γ-PGA as a prophylactic antiviral agent against noroviruses.

TLR7 Agonists Display Potent Antiviral Effects against Norovirus Infection via Innate Stimulation

Norovirus infections are a significant health and economic burden globally, accounting for hundreds of millions of cases of acute gastroenteritis every year. In the absence of an approved norovirus vaccine, there is an urgent need to develop antivirals to treat chronic infections and provide prophylactic therapy to limit viral spread during epidemics and pandemics. Toll-like receptor (TLR) agonists have been explored widely for their antiviral potential, and several are progressing through clinical trials for the treatment of human immunodeficiency virus (HIV) and hepatitis B virus (HBV) and as adjuvants for norovirus viruslike particle (VLP) vaccines. However, norovirus therapies in development are largely direct-acting antivirals (DAAs) with fewer compounds that target the host. Our aim was to assess the antiviral potential of TLR7 agonist immunomodulators on norovirus infection using the murine norovirus (MNV) and human Norwalk replicon models. TLR7 agonists R-848, Gardiquimod, GS-9620, R-837, and loxoribine were screened using a plaque reduction assay, and each displayed inhibition of MNV replication (50% effective concentrations [EC₅₀s], 23.5 nM, 134.4 nM, 0.59 μM, 1.5 μM, and 79.4 μM, respectively). RNA sequencing of TLR7-stimulated cells revealed a predominant upregulation of innate immune response genes and interferon (IFN)-stimulated genes (ISGs) that are known to drive an antiviral state. Furthermore, the combination of R-848 and the nucleoside analogue (NA) 2'C-methylcytidine elicited a synergistic antiviral effect against MNV, demonstrating that combinational therapy of host modulators and DAAs might be used to reduce drug cytotoxicity. In summary, we have identified that TLR7 agonists display potent inhibition of norovirus replication and are a therapeutic option to combat norovirus infections.

Vibrio vulnificus quorum-sensing molecule cyclo(Phe-Pro) inhibits RIG-I-mediated antiviral innate immunity

The recognition of pathogen-derived ligands by pattern recognition receptors activates the innate immune response, but the potential interaction of quorum-sensing (QS) signaling molecules with host anti-viral defenses remains largely unknown. Here we show that the Vibrio vulnificus QS molecule cyclo(Phe-Pro) (cFP) inhibits interferon (IFN)-β production by interfering with retinoic-acid-inducible gene-I (RIG-I) activation. Binding of cFP to the RIG-I 2CARD domain induces a conformational change in RIG-I, preventing the TRIM25-mediated ubiquitination to abrogate IFN production. cFP enhances susceptibility to hepatitis C virus (HCV), as well as Sendai and influenza viruses, each known to be sensed by RIG-I but did not affect the melanoma-differentiation-associated gene 5 (MDA5)-recognition of norovirus. Our results reveal an inter-kingdom network between bacteria, viruses and host that dysregulates host innate responses via a microbial quorum-sensing molecule modulating the response to viral infection.

The Cellular Chaperone Heat Shock Protein 90 Is Required for Foot-and-Mouth Disease Virus Capsid Precursor Processing and Assembly of Capsid Pentamers

Productive picornavirus infection requires the hijacking of host cell pathways to aid with the different stages of virus entry, synthesis of the viral polyprotein, and viral genome replication. Many picornaviruses, including foot-and-mouth disease virus (FMDV), assemble capsids via the multimerization of several copies of a single capsid precursor protein into a pentameric subunit which further encapsidates the RNA. Pentamer formation is preceded by co- and posttranslational modification of the capsid precursor (P1-2A) by viral and cellular enzymes and the subsequent rearrangement of P1-2A into a structure amenable to pentamer formation. We have developed a cell-free system to study FMDV pentamer assembly using recombinantly expressed FMDV capsid precursor and 3C protease. Using this assay, we have shown that two structurally different inhibitors of the cellular chaperone heat shock protein 90 (hsp90) impeded FMDV capsid precursor processing and subsequent pentamer formation. Treatment of FMDV permissive cells with the hsp90 inhibitor prior to infection reduced the endpoint titer by more than 10-fold while not affecting the activity of a subgenomic replicon, indicating that translation and replication of viral RNA were unaffected by the drug.IMPORTANCE FMDV of the Picornaviridae family is a pathogen of huge economic importance to the livestock industry due to its effect on the restriction of livestock movement and necessary control measures required following an outbreak. The study of FMDV capsid assembly, and picornavirus capsid assembly more generally, has tended to be focused upon the formation of capsids from pentameric intermediates or the immediate cotranslational modification of the capsid precursor protein. Here, we describe a system to analyze the early stages of FMDV pentameric capsid intermediate assembly and demonstrate a novel requirement for the cellular chaperone hsp90 in the formation of these pentameric intermediates. We show the added complexity involved for this process to occur, which could be the basis for a novel antiviral control mechanism for FMDV.

Could targeting the heat shock protein 90 revolutionize antiviral therapy?

Traditional antiviral strategies that target viral components are frequently associated with the generation of drug-resistant viruses. Thus, the development of novel antiviral drugs is critical. Hsp90 is a promising broad-spectrum antiviral drug target; however, whether targeting Hsp90 will revolutionize antiviral therapy remains ambiguous. Here, we summarize how Hsp90 functions in relation to its interactors, and listed the specific Hsp90 isoforms that participated in the virus life cycle. We also discuss the advantages and challenges of targeting Hsp90, taking into account antiviral activity, toxicity and the likelihood of emergence of drug-resistant viruses. Overall, we highlight that targeting Hsp90 might represent a novel and effective antiviral strategy. However, further studies are required before Hsp90 inhibitors can be used in antiviral therapy.

Proteomic interrogation of HSP90 and insights for medical research

INTRODUCTION

Heat shock protein 90 (HSP90) regulates protein homeostasis in eukaryotes. As a 'professional interactor', HSP90 binds to and chaperones many proteins and has both housekeeping and disease-related functions but its regulation remains in part elusive. HSP90 complexes are a target for therapy, notably against cancer, and several inhibitors are currently in clinical trials. Proteomic studies have revealed the vast interaction network of HSP90 and, in doing so, the extent of cellular processes the chaperone takes part in, especially in yeast and human cells. Furthermore, small-molecule inhibitors were used to probe the global impact of its inhibition on the proteome. Areas covered: We review here recent HSP90-related interactomics and total proteome studies and their relevance for research on cancer, neurodegenerative and pathogen diseases. Expert commentary: Proteomics experiments are our best chance to identify the context-dependent global proteome of HSP90 and thus uncover and understand its disease-specific biology. However, understanding the complexity of HSP90 will require multiple complementary, quantitative approaches and novel bioinformatics to translate interactions into ordered functional networks and pathways. Developing therapies will necessitate more knowledge on HSP90 complexes and networks with disease relevance and on total proteome changes induced by their perturbation. Most work has been done in cancer, thus a lot remains to be done in the context of other diseases.

HSP90: a promising broad-spectrum antiviral drug target

The emergence of antiviral drug-resistant mutants is the most important issue in current antiviral therapy. As obligate parasites, viruses require host factors for efficient replication. An ideal therapeutic target to prevent drug-resistance development is represented by host factors that are crucial for the viral life cycle. Recent studies have indicated that heat shock protein 90 (HSP90) is a crucial host factor that is required by many viruses for multiple phases of their life cycle including viral entry, nuclear import, transcription, and replication. In this review, we summarize the most recent advances regarding HSP90 function, mechanisms of action, and molecular pathways that are associated with viral infection, and provide a comprehensive understanding of the role of HSP90 in the immune response and exosome-mediated viral transmission. In addition, several HSP90 inhibitors have entered clinical trials for specific cancers that are associated with viral infection, which further implies a crucial role for HSP90 in the malignant transformation of virus-infected cells; as such, HSP90 inhibitors exhibit excellent therapeutic potential. Finally, we describe the challenge of developing HSP90 inhibitors as anti-viral drugs.

iTRAQ-based Proteomic Analysis of Porcine Kidney Epithelial PK15 cells Infected with Pseudorabies virus

Pseudorabies virus (PRV) is one of the most important pathogens of swine, resulting in severe economic losses to the pig industry. To improve our understanding of the host responses to PRV infection, we applied isobaric tags for relative and absolute quantification (iTRAQ) labeling coupled with liquid chromatography-tandem mass spectrometry to quantitatively identify the differentially expressed cellular proteins in PRV-infected PK15 cells. In total, relative quantitative data were identified for 4333 proteins in PRV and mock- infected PK15 cells, among which 466 cellular proteins were differentially expressed, including 234 upregulated proteins and 232 downregulated proteins. Bioinformatics analysis disclosed that most of these differentially expressed proteins were involved in metabolic processes, cellular growth and proliferation, endoplasmic reticulum (ER) stress response, cell adhesion and cytoskeleton. Moreover, expression levels of four representative proteins, beta-catenin, STAT1, GRB2 and PCNA, were further confirmed by western blot analysis. This is the first attempt to analyze the protein profile of PRV-infected PK15 cells using iTRAQ technology, and our findings may provide valuable information to help understand the host response to PRV infection.

Norovirus genetic diversity and evolution: implications for antiviral therapy

Human noroviruses are the leading cause of foodborne illness causing both acute and chronic gastroenteritis. In recent years, a number of vaccine candidates entered (pre-) clinical development and the first efforts to develop antiviral therapy have been made. We here discuss aspects of norovirus genetic evolution, persistence in immunocompromised patients as well as the risk and potential consequences of resistance development toward future antiviral drugs.

AR-12 Inhibits Multiple Chaperones Concomitant With Stimulating Autophagosome Formation Collectively Preventing Virus Replication

We have recently demonstrated that AR-12 (OSU-03012) reduces the function and ATPase activities of multiple HSP90 and HSP70 family chaperones. Combined knock down of chaperones or AR-12 treatment acted to reduce the expression of virus receptors and essential glucosidase proteins. Combined knock down of chaperones or AR-12 treatment inactivated mTOR and elevated ATG13 S318 phosphorylation concomitant with inducing an endoplasmic reticulum stress response that in an eIF2α-dependent fashion increased Beclin1 and LC3 expression and autophagosome formation. Over-expression of chaperones prevented the reduction in receptor/glucosidase expression, mTOR inactivation, the ER stress response, and autophagosome formation. AR-12 reduced the reproduction of viruses including Mumps, Influenza, Measles, Junín, Rubella, HIV (wild type and protease resistant), and Ebola, an effect replicated by knock down of multiple chaperone proteins. AR-12-stimulated the co-localization of Influenza, EBV and HIV virus proteins with LC3 in autophagosomes and reduced viral protein association with the chaperones HSP90, HSP70, and GRP78. Knock down of Beclin1 suppressed drug-induced autophagosome formation and reduced the anti-viral protection afforded by AR-12. In an animal model of hemorrhagic fever virus, a transient exposure of animals to low doses of AR-12 doubled animal survival from ∼30% to ∼60% and suppressed liver damage as measured by ATL, GGT and LDH release. Thus through inhibition of chaperone protein functions; reducing the production, stability and processing of viral proteins; and stimulating autophagosome formation/viral protein degradation, AR-12 acts as a broad-specificity anti-viral drug in vitro and in vivo. We argue future patient studies with AR-12 are warranted. J. Cell. Physiol. 231: 2286-2302, 2016. © 2016 Wiley Periodicals, Inc.

Select membrane proteins modulate MNV-1 infection of macrophages and dendritic cells in a cell type-specific manner

Noroviruses cause gastroenteritis in humans and other animals, are shed in the feces, and spread through the fecal-oral route. Host cellular expression of attachment and entry receptors for noroviruses is thought to be a key determinant of cell tropism and the strict species-specificity. However, to date, only carbohydrates have been identified as attachment receptors for noroviruses. Thus, we investigated whether host cellular proteins play a role during the early steps of norovirus infection. We used murine norovirus (MNV) as a representative norovirus, since MNV grows well in tissue culture and is a frequently used model to study basic aspects of norovirus biology. Virus overlay protein binding assay followed by tandem mass spectrometry analysis was performed in two permissive cell lines, RAW264.7 (murine macrophages) and SRDC (murine dendritic cells) to identify four cellular membrane proteins as candidates. Loss-of-function studies revealed that CD36 and CD44 promoted MNV-1 binding to primary dendritic cells, while CD98 heavy chain (CD98) and transferrin receptor 1 (TfRc) facilitated MNV-1 binding to RAW 264.7 cells. Furthermore, the VP1 protruding domain of MNV-1 interacted directly with the extracellular domains of recombinant murine CD36, CD98 and TfRc by ELISA. Additionally, MNV-1 infection of RAW 264.7 cells was enhanced by soluble rCD98 extracellular domain. These studies demonstrate that multiple membrane proteins can promote efficient MNV-1 infection in a cell type-specific manner. Future studies are needed to determine the molecular mechanisms by which each of these proteins affect the MNV-1 infectious cycle.

Hsp90 protein interacts with phosphorothioate oligonucleotides containing hydrophobic 2'-modifications and enhances antisense activity

RNase H1-dependent antisense oligonucleotides (ASOs) are chemically modified to enhance pharmacological properties. Major modifications include phosphorothioate (PS) backbone and different 2′-modifications in 2–5 nucleotides at each end (wing) of an ASO. Chemical modifications can affect protein binding and understanding ASO-protein interactions is important for better drug design. Recently we identified many intracellular ASO-binding proteins and found that protein binding could affect ASO potency. Here, we analyzed the structure-activity-relationships of ASO-protein interactions and found 2′-modifications significantly affected protein binding, including La, P54nrb and NPM. PS-ASOs containing more hydrophobic 2′-modifications exhibit higher affinity for proteins in general, although certain proteins, e.g. Ku70/Ku80 and TCP1, are less affected by 2′-modifications. We found that Hsp90 protein binds PS-ASOs containing locked-nucleic-acid (LNA) or constrained-ethyl-bicyclic-nucleic-acid ((S)-cEt) modifications much more avidly than 2′-O-methoxyethyl (MOE). ASOs bind the mid-domain of Hsp90 protein. Hsp90 interacts with more hydrophobic 2′ modifications, e.g. (S)-cEt or LNA, in the 5′-wing of the ASO. Reduction of Hsp90 protein decreased activity of PS-ASOs with 5′-LNA or 5′-cEt wings, but not with 5′-MOE wing. Together, our results indicate Hsp90 protein enhances the activity of PS/LNA or PS/(S)-cEt ASOs, and imply that altering protein binding of ASOs using different chemical modifications can improve therapeutic performance of PS-ASOs.

Anti-norovirus therapeutics: a patent review (2010-2015)

INTRODUCTION

Human noroviruses are the primary causative agents of acute gastroenteritis and are a pressing public health burden worldwide. There are currently no vaccines or small molecule therapeutics available for the treatment or prophylaxis of norovirus infections. An improved understanding of norovirus biology, as well as the pathogenic mechanisms underlying the disease, has provided the impetus for a range of intense exploratory drug discovery efforts targeting viral and host factors.

AREAS COVERED

An overview of norovirus inhibitors disclosed in the patent literature (2010-present) and Clinicaltrials.gov is presented. The review is further enriched and supplemented by recent literature reports.

EXPERT OPINION

Seminal discoveries made in recent years, including a better understanding of the pathobiology and life cycle of norovirus, the identification and targeting of multiple viral and host factors, the advent of a replicon system and a small animal model for the preclinical evaluation of lead compounds, and the availability of high resolution X-ray crystal structures that can be utilized in structure-based drug design and lead optimization campaigns, collectively suggest that a small molecule therapeutic and prophylactic for norovirus infection is likely to emerge in the not too distant future.

Recent Advances in the Discovery of Norovirus Therapeutics

Noroviruses are members of the family Caliciviridae. Norovirus infections are a global health burden that impacts >20 million individuals annually in the U.S. alone. Noroviruses are associated with high morbidity among vulnerable populations, particularly immunocompromised patients. This perspective highlights recent developments related to the discovery and development of norovirus-specific small-molecule therapeutics as well as recent advances in our understanding of norovirus biology and pathogenesis. Most of the work in this area is at the early discovery stage and has been primarily focused on inhibitors of norovirus 3C-like protease and RNA dependent RNA polymerase. However, recent discoveries emanating from basic studies in norovirus research have resulted in the identification of new host-related drug targets that can be exploited. A repurposed compound has been advanced to human clinical studies.