Identification of a varicella-zoster virus replication inhibitor that blocks capsid assembly by interacting with the floor domain of the major capsid protein

Varicella zoster virus-induced autophagy in human neuronal and hematopoietic cells exerts antiviral activity

Autophagy is a degradational pathway with pivotal roles in cellular homeostasis and survival, including protection of neurons in the central nervous system (CNS). The significance of autophagy as antiviral defense mechanism is recognized and some viruses hijack and modulate this process to their advantage in certain cell types. Here, we present data demonstrating that the human neurotropic herpesvirus varicella zoster virus (VZV) induces autophagy in human SH-SY5Y neuronal cells, in which the pathway exerts antiviral activity. Productively VZV-infected SH-SY5Y cells showed increased LC3-I-LC3-II conversion as well as co-localization of the viral glycoprotein E and the autophagy receptor p62. The activation of autophagy was dependent on a functional viral genome. Interestingly, inducers of autophagy reduced viral transcription, whereas inhibition of autophagy increased viral transcript expression. Finally, the genotype of patients with severe ocular and brain VZV infection were analyzed to identify potential autophagy-associated inborn errors of immunity. Two patients expressing genetic variants in the autophagy genes ULK1 and MAP1LC3B2, respectively, were identified. Notably, cells of both patients showed reduced autophagy, alongside enhanced viral replication and death of VZV-infected cells. In conclusion, these results demonstrate a neuro-protective role for autophagy in the context of VZV infection and suggest that failure to mount an autophagy response is a potential predisposing factor for development of severe VZV disease.

Kaempferol Interferes with Varicella-Zoster Virus Replication in Human Foreskin Fibroblasts

Kaempferol, a natural flavonoid abundantly found in plants, is known to have pharmacological properties, such as anti-inflammatory and anti-cancer effects. In this study, we investigated the antiviral effects of kaempferol against a varicella-zoster virus (VZV) clinical isolate in vitro. We found that kaempferol significantly inhibited VZV replication without exhibiting cytotoxicity. Kaempferol exerted its antiviral effect at a similar stage of the VZV life cycle as acyclovir, which inhibits VZV DNA replication. Taken together, our results suggest that kaempferol inhibits VZV infection by blocking the DNA replication stage in the viral life cycle.

Varicella pneumonia in an immunocompetent, unvaccinated man: A case report

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An immunocompetent 50-year-old man developed varicella after household exposure.

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He had no history of previous varicella or vaccination against varicella.

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He developed varicella pneumonia which responded to acyclovir.

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The incidence of primary varicella in immunocompetent adults has increased.

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There is a need to increase varicella vaccination coverage among adults.

Varicella is a common vaccine-preventable disease that typically affects children aged 2–8 years and usually has a benign outcome. However, varicella infection in adults may cause serious complications, including varicella pneumonia. We report a case of varicella pneumonia in an immunocompetent, unvaccinated man in Japan.

A 50-year-old Egyptian man who had been living in Japan for 20 years was brought to the hospital with a 3-day history of fever and a 2-day history of rash and dyspnea. Chest computed tomography revealed an 8-mm-long nodule with a halo in the right S3 segment and mild ground-glass opacities in both lungs. A final diagnosis was made based on identification of varicella-zoster virus via positive immunochromatographic test and polymerase chain reaction from a blister fluid. The patient's pneumonia had improved with acyclovir for 10 days.

In Japan routine varicella vaccination in childhood (at ages 12 and 18 months) was introduced in 2014. However, in Egypt, where the patient spent his childhood, varicella vaccine is still not designated as a routine vaccination. The introduction of universal varicella vaccination in more countries and an increase in vaccination coverage are essential to reduce the number of cases of varicella infection, including varicella pneumonia.

The Ins and Outs of Herpesviral Capsids: Divergent Structures and Assembly Mechanisms across the Three Subfamilies

Human herpesviruses, classified into three subfamilies, are double-stranded DNA viruses that establish lifelong latent infections within most of the world’s population and can cause severe disease, especially in immunocompromised people. There is no cure, and current preventative and therapeutic options are limited. Therefore, understanding the biology of these viruses is essential for finding new ways to stop them. Capsids play a central role in herpesvirus biology. They are sophisticated vehicles that shelter the pressurized double-stranded-DNA genomes while ensuring their delivery to defined cellular destinations on the way in and out of the host cell. Moreover, the importance of capsids for multiple key steps in the replication cycle makes their assembly an attractive therapeutic target. Recent cryo-electron microscopy reconstructions of capsids from all three subfamilies of human herpesviruses revealed not only conserved features but also remarkable structural differences. Furthermore, capsid assembly studies have suggested subfamily-specific roles of viral capsid protein homologs. In this review, we compare capsid structures, assembly mechanisms, and capsid protein functions across human herpesvirus subfamilies, highlighting the differences.

Advances and Perspectives in the Management of Varicella-Zoster Virus Infections

Varicella-zoster virus (VZV), a common and ubiquitous human-restricted pathogen, causes a primary infection (varicella or chickenpox) followed by establishment of latency in sensory ganglia. The virus can reactivate, causing herpes zoster (HZ, shingles) and leading to significant morbidity but rarely mortality, although in immunocompromised hosts, VZV can cause severe disseminated and occasionally fatal disease. We discuss VZV diseases and the decrease in their incidence due to the introduction of live-attenuated vaccines to prevent varicella or HZ. We also focus on acyclovir, valacyclovir, and famciclovir (FDA approved drugs to treat VZV infections), brivudine (used in some European countries) and amenamevir (a helicase-primase inhibitor, approved in Japan) that augur the beginning of a new era of anti-VZV therapy. Valnivudine hydrochloride (FV-100) and valomaciclovir stearate (in advanced stage of development) and several new molecules potentially good as anti-VZV candidates described during the last year are examined. We reflect on the role of antiviral agents in the treatment of VZV-associated diseases, as a large percentage of the at-risk population is not immunized, and on the limitations of currently FDA-approved anti-VZV drugs. Their low efficacy in controlling HZ pain and post-herpetic neuralgia development, and the need of multiple dosing regimens requiring daily dose adaptation for patients with renal failure urges the development of novel anti-VZV drugs.

Cryo-EM structure of the varicella-zoster virus A-capsid

Varicella-zoster virus (VZV), a member of the Alphaherpesvirinae subfamily, causes severe diseases in humans of all ages. The viral capsids play critical roles in herpesvirus infection, making them potential antiviral targets. Here, we present the 3.7-Å-resolution structure of the VZV A-capsid and define the molecular determinants underpinning the assembly of this complicated viral machinery. Overall, the VZV capsid has a similar architecture to that of other known herpesviruses. The major capsid protein (MCP) assembles into pentons and hexons, forming extensive intra- and inter-capsomer interaction networks that are further secured by the small capsid protein (SCP) and the heterotriplex. The structure reveals a pocket beneath the floor of MCP that could potentially be targeted by antiviral inhibitors. In addition, we identified two alphaherpesvirus-specific structural features in SCP and Tri1 proteins. These observations highlight the divergence of different herpesviruses and provide an important basis for developing antiviral drugs.

Varicella-zoster virus (VZV) is the causative agent of chickenpox and herpes zoster (shingles). Cryo-EM structure of VZV capsid provides insights into the capsid assembly and reveals a pocket that could potentially be targeted by antiviral drugs.

DNA Encapsidation and Capsid Assembly Are Underexploited Antiviral Targets for the Treatment of Herpesviruses

Although there are effective nucleoside analogs to treat HSV, VZV, and HCMV disease, herpesvirus infections continue to contribute to significant morbidity and mortality. Acyclovir is the drug of choice for HSV encephalopathy, yet there is an estimated 6-19% mortality rate with half of the survivors experiencing moderate to severe chronic neurological deficits. For VZV, current treatments are inadequate to prevent acute and persistent pain due to zoster. Treatment of HCMV with GCV requires close monitoring particularly in patients with impaired renal function and there are no approved treatments for congenital HCMV infections. New therapeutic options to control cytomegalovirus reactivation in bone marrow and stem cell transplant patients are needed to improve patient outcome. No successful chemotherapeutic options are available for EBV, HHV-6, 7, and 8. Drug resistance is a concern for HCMV, HSV, and VZV since approved drugs share common mechanisms of action. Targeting DNA encapsidation or capsid assembly provide additional options for the development of non-nucleoside, small molecule anti-herpesviral drugs.

Enhancement of guinea pig cytomegalovirus infection by two endogenously expressed components of the pentameric glycoprotein complex in epithelial cells

A better understanding of the mechanisms underlying cell tropisms and the efficiency of viral infection is critical for the development of vaccines and antiviral drugs for viral diseases. In this study, we worked on the entry mechanisms of guinea pig cytomegalovirus and found that endogenous expression of a combination of two components (GP131 and GP133) of the pentameric glycoprotein complex, which is required for non-fibroblast cell tropisms, enhanced viral infection more than 10-fold. In addition, D138A alteration in GP131 increased this enhancement by an additional 10-fold. Although differences in the efficiency of viral infection among various cell types are usually explained by differences in viral entry or traffic processes, our experimental evidences dismissed such possibilities. Instead, our findings that i) endogenous expression of GP131 and GP133 after nuclear delivery of viral DNA still enhanced infection and ii) an HDAC inhibitor overcame the need of the endogenous expression led us to hypothesize a novel mechanism that controls the efficiency of viral infection through the activation of gene expression from viral DNA delivered to the nuclei. Further studies of this unexpected phenomena warrant to understand novel but also general mechanisms for cell tropisms of viral infection and determinants that control infection efficiency.

Honeysuckle-derived microRNA2911 directly inhibits varicella-zoster virus replication by targeting IE62 gene

Varicella-zoster virus (VZV) leads to chicken pox on primary infection and herpes zoster on reactivation. Recent studies suggest that microRNA2911 (MIR2911), honeysuckle (HS)-encoded atypical microRNA, has potential as a therapeutic agent against influenza and EV71 virus infections. Here, we report that MIR2911 directly inhibits VZV replication by targeting the IE62 gene. The luciferase reporter assay and bioinformatics prediction revealed that MIR2911 could target the IE62 gene of VZV. The VZV-encoded IE62 protein expression was inhibited significantly by synthetic MIR2911, while the expression of the mutants, whose MIR2911-binding sites were modified, was not inhibited. The RNA extracted from HS decoction and synthetic MIR2911 considerably suppressed VZV infection. However, it did not influence viral replication of a mutant virus with alterations in the nucleotide sequences of IE62. At the same time, the RNA extracted from HS decoction treated with the anti-MIR2911 antagomir could not inhibit the VZV replication, demonstrating that VZV replication was specifically and sufficiently inhibited by MIR2911. These results indicated that, by targeting the IE62 gene, MIR2911 may effectively inhibit VZV replication. Our results also suggest a potential novel strategy for the treatment and prevention of diseases caused by VZV infection.

The Apical Region of the Herpes Simplex Virus Major Capsid Protein Promotes Capsid Maturation

The herpesvirus capsid assembles in the nucleus as an immature procapsid precursor built around viral scaffold proteins. The event that initiates procapsid maturation is unknown, but it is dependent upon activation of the VP24 internal protease. Scaffold cleavage triggers angularization of the shell and its decoration with the VP26 and pUL25 capsid-surface proteins. In both the procapsid and mature angularized capsid, the apical region of the major capsid protein (VP5) is surface exposed. We investigated whether the VP5 apical region contributes to intracellular transport dynamics following entry into primary sensory neurons and also tested the hypothesis that conserved negatively charged amino acids in the apical region contribute to VP26 acquisition. To our surprise, neither hypothesis proved true. Instead, mutation of glutamic acid residues in the apical region delayed viral propagation and induced focal capsid accumulations in nuclei. Examination of capsid morphogenesis based on epitope unmasking, capsid composition, and ultrastructural analysis indicated that these clusters consisted of procapsids. The results demonstrate that, in addition to established events that occur inside the capsid, the exterior capsid shell promotes capsid morphogenesis and maturation.IMPORTANCE Herpesviruses assemble capsids and encapsidate their genomes by a process that is unlike those of other mammalian viruses but is similar to those of some bacteriophage. Many important aspects of herpesvirus morphogenesis remain enigmatic, including how the capsid shell matures into a stable angularized configuration. Capsid maturation is triggered by activation of a protease that cleaves an internal protein scaffold. We report on the fortuitous discovery that a region of the major capsid protein that is exposed on the outer surface of the capsid also contributes to capsid maturation, demonstrating that the morphogenesis of the capsid shell from its procapsid precursor to the mature angularized form is dependent upon internal and external components of the megastructure.

Titration of cell-associated varicella-zoster virus with the MV9G reporter cell line for antiviral studies

Titration of the cell-associated virus (CAV) of varicella-zoster virus (VZV) is essential for antiviral studies. A VZV reporter cell line, MV9G, generated in our previous study expresses firefly luciferase upon CAV infection in a dose-dependent manner, suggesting that use of the cell line for titration is feasible. In this study, MeWo cells infected with VZV vaccine Oka (vOka) strain or with clinical isolates obtained from patients with varicella or zoster were used as CAV. A co-culture of MV9G cells with the virus-infected MeWo cells were set up and optimized for titration of CAV. Luciferase activities of MV9G cells measured as relative light units (RLUs) of chemiluminescence correlated well (r > 0.9, p < 0.05) both with quantities of viral DNAs measured by TaqMan PCR and with numbers of viral foci detected by immunostaining with a monoclonal antibody against VZV IE62. In addition, the usefulness of MV9G for antiviral studies was exemplified by treatment of the VZV-infected cells with various concentrations of acyclovir. Thus, the reporter cell-based titration of CAV by measuring the induced RLUs may be a reliable way to estimate viral foci and viral DNAs.

Characterization of an anti-varicella-zoster virus compound that targets the portal protein encoded by ORF54

An anti-varicella-zoster virus compound, a 5-chlorobenzo[b]thiophen derivative (45B5), was characterized. Its 50% effective concentration against the cell-free vaccine Oka strain and 50% cytotoxic concentration in human fibroblasts were 16.9 µM and more than 100 µM, respectively. Treatment with 45B5 decreased viral DNA synthesis and IE62 expression weakly but significantly. All 45B5-resistant viral clones isolated were found to have at least one mutation in ORF54 that encodes the portal protein. There were no effects on interaction between the portal and scaffold proteins. Thus, 45B5 may inhibit nuclear delivery of viral DNA.

Characterization of a thienylcarboxamide derivative that inhibits the transactivation functions of cytomegalovirus IE2 and varicella zoster virus IE62

Previously we established reporter cell lines for human cytomegalovirus (HCMV) and varicella zoster virus (VZV) and identified several antiviral compounds against these viruses using the reporter cells. In this study, we found that one of the identified anti-HCMV compounds, a thienylcarboxamide derivative (coded as 133G4), was effective against not only HCMV but also VZV. The following findings indicate that 133G4 inhibits the activation of early gene promoters by HCMV IE2 and VZV IE62: i) 133G4 decreased the expression of HCMV early and late genes but not that of HCMV IE1/IE2 in HCMV-infected cells, ii) 133G4 inhibited the activation of several HCMV early gene promoters of transiently-transfected plasmids in HCMV-infected cells, and iii) in transient transfection assays, 133G4 decreased the activation of HCMV (or VZV) early gene promoters by HCMV IE2 (or VZV IE62) in the absence of other viral protein expression. The inhibition of early gene activation was observed in the human and African green monkey cell lines but not in the rodent cell lines, and the compound was not effective against murine CMV. In addition, VZV IE62 activated HCMV early promoters, and 133G4 still inhibited such promoter activation. Therefore, we hypothesized that 133G4 targets a cellular factor used commonly in activation of human herpesvirus promoters and examined whether 133G4 affects the functions of cellular proteins USF1, TBP, Med25 and EAP, the involvement of which in VZV IE62-dependent viral gene activation has been well characterized. Our experimental results using one-hybrid and bimolecular fluorescence complementation assays demonstrated that 133G4 did not inhibit the recruitment of USF1 or TBP to their binding sites, nor inhibited the direct interactions of VZV IE62 with Med25 and EAP. Thus, 133G4 is a unique anti-VZV and -HCMV compound, which warrants further studies to find out its inhibitory mechanism.

A Luciferase Gene Driven by an Alphaherpesviral Promoter Also Responds to Immediate Early Antigens of the Betaherpesvirus HCMV, Allowing Comparative Analyses of Different Human Herpesviruses in One Reporter Cell Line

Widely used methods for quantification of human cytomegalovirus (HCMV) infection in cell culture such as immunoblotting or plaque reduction assays are generally restricted to low throughput and require time-consuming evaluation. Up to now, only few HCMV reporter cell lines have been generated to overcome these restrictions and they are afflicted with other limitations because permanently expandable cell lines are normally not fully permissive to HCMV. In this work, a previously existing epithelial cell line hosting a luciferase gene under control of a Varicella-zoster virus promoter was adopted to investigate HCMV infection. The cells were susceptible to different HCMV strains at infection efficiencies that corresponded to their respective degree of epithelial cell tropism. Expression of early and late viral antigens, formation of nuclear inclusions, release of infectious virus progeny, and focal growth indicated productive viral replication. However, viral release and spread occurred at lower levels than in primary cell lines which appears to be due to a malfunction of virion morphogenesis during the nuclear stage. Expression of the luciferase reporter gene was specifically induced in HCMV infected cultures as a function of the virus dose and dependent on viral immediate early gene expression. The level of reporter activity accurately reflected infection efficiencies as determined by viral antigen immunostaining, and hence could discriminate the cell tropism of the tested virus strains. As proof-of-principle, we demonstrate that this cell line is applicable to evaluate drug resistance of clinical HCMV isolates and the neutralization capacity of human sera, and that it allows comparative and simultaneous analysis of HCMV and human herpes simplex virus type 1. In summary, the permanent epithelial reporter cell line allows robust, rapid and objective quantitation of HCMV infection and it will be particularly useful in higher throughput analyses as well as in comparative analyses of different human herpesviruses.

Non-axial view of the varicella-zoster virus portal protein reveals conserved crown, wing and clip architecture

BACKGROUND

Herpesviridae encode a family of protein homologues that function as the 'port of entry' for insertion of the viral DNA into preformed capsids during encapsidation.

METHODS

Transmission electron microscopy (TEM) of recombinant varicella-zoster virus pORF54 was performed.

RESULTS

Results suggest that pORF54 forms higher-order structures with itself. Enriched fractions analyzed by TEM revealed non-axial oriented portals with defined central channels and distinguishable crown, wing and clip regions.

CONCLUSION

These morphological features are consistent with those previously reported for other herpesvirus and bacteriophage portal proteins.

Determination of HSV-1 infectivity by plaque assay and a luciferase reporter cell line

Quantification of infectious virus is crucial to many experimental approaches in virological research. A broadly used and facile technique is the so-called "plaque assay" which provides precise information on the absolute quantity of infectivity in a given volume. Due to advances in the understanding of viral gene expression, transactivator-promoter pairs have been identified which can be used in transgenic cell lines as reporters of viral infection. Even though such "cellular reporter assay" systems are mostly restricted to relative quantification, they are attractive tools which can complement or replace the conventional plaque assay. Cellular reporter assays become especially interesting in state-of-the-art high-throughput screening approaches, as for instance RNAi and compound library screens, since they are often compatible with small-scale and automated experimentation. In this chapter, a regular plaque assay as well as a cellular reporter assay employing a luciferase reporter gene are described. As an example, HSV-1 infectivity is assessed with both methods yielding complementary information. Advantages and disadvantages of the two techniques and possible applications are discussed.

Advances in the treatment of varicella-zoster virus infections

Varicella-zoster virus (VZV) causes two distinct diseases, varicella (chickenpox) and shingles (herpes zoster). Chickenpox occurs subsequent to primary infection, while herpes zoster (usually associated with aging and immunosuppression) appears as a consequence of reactivation of latent virus. The major complication of shingles is postherpetic neuralgia. Vaccination strategies to prevent varicella or shingles and the current status of antivirals against VZV will be discussed in this chapter. Varivax®, a live-attenuated vaccine, is available for pediatric varicella. Zostavax® is used to boost VZV-specific cell-mediated immunity in adults older than 50 years, which results in a decrease in the burden of herpes zoster and pain related to postherpetic neuralgia. Regardless of the availability of a vaccine, new antiviral agents are necessary for treatment of VZV infections. Current drugs approved for therapy of VZV infections include nucleoside analogues that target the viral DNA polymerase and depend on the viral thymidine kinase for their activation. Novel anti-VZV drugs have recently been evaluated in clinical trials, including the bicyclic nucleoside analogue FV-100, the helicase-primase inhibitor ASP2151, and valomaciclovir (prodrug of the acyclic guanosine derivative H2G). Different candidate VZV drugs have been described in recent years. New anti-VZV drugs should be as safe as and more effective than current gold standards for the treatment of VZV, that is, acyclovir and its prodrug valacyclovir.