Cholesterol dependence of varicella-zoster virion entry into target cells

Validation of nuclear receptor RORγ isoform 1 as a novel host-directed antiviral target based on the modulation of cholesterol levels

Currently, the clinically approved repertoire of antiviral drugs predominantly comprises direct-acting antivirals (DAAs). However, the use of DAAs is frequently limited by adverse effects, restriction to individual virus species, or the induction of viral drug resistance. These issues will likely be resolved by the introduction of host-directed antivirals (HDAs) targeting cellular proteins crucial for viral replication. However, experiences with the development of antiviral HDAs and clinical applications are still in their infancy. With the present study, we explored the human nuclear receptor and transcription factor RORγ isoform 1 (RORγ1), a member of the retinoic acid receptor-related orphan receptor (ROR) family, as a putative target of antiviral HDAs. To this end, cell culture models were used to investigate major viral human pathogens, i.e. the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), human cytomegalovirus (HCMV), varicella zoster virus (VZV) and human immunodeficiency virus 1 (HIV-1). Our results demonstrated (i) an antiviral activity of the clinically relevant RORγ modulators cedirogant and others, (ii) that isoform RORγ1 acts as the responsible determinant and drug target in the analyzed cell culture-based models, (iii) a selectivity of the antiviral effect for RORγ1 over related receptors RORα and RORβ, (iv) a late-phase inhibition exerted by cedirogant in HCMV replication and (v) a mechanistic link to the cellular cholesterol biosynthesis. Combined, the data highlight this novel RORγ-specific antiviral targeting concept and the developmental potential of RORγ-directed small molecules.

Oxysterols in Infectious Diseases

Oxysterols have emerged as important bioactive lipids in the immune response to infectious diseases. This chapter discusses our current knowledge of oxysterols and their receptors in bacterial and viral infections of the respiratory and gastrointestinal tracts. Oxysterols are produced in response to infections and have multiple roles including chemotaxis of immune cells to the site of infection and regulation of inflammation. Some oxysterols have been shown to possess antiviral or antibacterial activity.Lastly, we delve into the emerging mechanisms of action of oxysterols. Oxysterols can enhance host cell resistance via reduction of membrane accessible cholesterol, modulate membrane immune signalling, and impact inflammasome activation and efferocytosis.

Aminotransferasas y perfil lipídico en pacientes ecuatorianos con infección activa por virus dengue

El dengue es la arbovirosis con mayor incidencia a nivel mundial. Aproximadamente 100 millones de casos de dengue con signos de alarma y entre 250.000 y 500.000 casos de dengue grave, se registran anualmente. En Ecuador, en los últimos cuatro años se han registrado 83.472 casos de dengue. Estudios previos evidencian un incremento de los casos que cursan con disfunción hepática. El objetivo de este estudio fue analizar la asociación entre los niveles séricos de las enzimas aspartato aminotransferasa y alanino aminotransferasa y el perfil lipídico en pacientes con infección confirmada de Dengue. Se estudiaron 110 pacientes seleccionados sin distingo de edad, género o procedencia, cuyo diagnóstico fue confirmado virológica y serológicamente. Se incluyó un grupo control seronegativo al virus. En el perfil lipídico se evidenciaron diferencias significativas (p<0,003) en los valores de colesterol total y en infecciones secundarias; mientras que la frecuencia de elevación de ambas aminotransferasas fue alta en pacientes con dengue, no obstante, al comparar cuantitativamente los valores séricos no arrojaron cambios significativos, ni asociación. Se confirma la endemicidad del dengue, los cambios en el perfil lipídico, sin embargo, es evidente la necesidad de estudios poblacionales tomando en cuenta la genética de las poblaciones

Cellular Lipids-Hijacked Victims of Viruses

Over the millions of years-long co-evolution with their hosts, viruses have evolved plenty of mechanisms through which they are able to escape cellular anti-viral defenses and utilize cellular pathways and organelles for replication and production of infectious virions. In recent years, it has become clear that lipids play an important role during viral replication. Viruses use cellular lipids in a variety of ways throughout their life cycle. They not only physically interact with cellular membranes but also alter cellular lipid metabolic pathways and lipid composition to create an optimal replication environment. This review focuses on examples of how different viruses exploit cellular lipids in different cellular compartments during their life cycles.

The Cholesterol Transport Inhibitor U18666A Interferes with Pseudorabies Virus Infection

Many viruses require the maintenance of lysosomal cholesterol homeostasis for a successful infection; however, the role of lysosomal cholesterol homeostasis in the alphaherpesvirus life cycle is not clear. Here we show that the lysosomal cholesterol transport inhibitor U18666A interferes with the replication of pseudorabies virus (PRV), a member of the alphaherpesvirus subfamily. The treatment with U18666A caused a significant reduction in the production of infectious virus particles. The U18666A treatment was shown to suppress the release of PRV particles. Pretreating PRV virions with U18666A did not affect virus production, whereas pretreating target cells with U18666A led to a substantial reduction in virus yield. Our previous study showed that two cyclodextrin derivatives, 2-hydroxypropyl-β-cyclodextrin (HPβCD) and 2-hydroxypropyl-γ-cyclodextrin (HPγCD), can rescue the cholesterol accumulation defect in primary fibroblasts derived from a Niemann–Pick disease type C (NPC) patient. Here, we demonstrate that treatment with HPβCD or HPγCD not only rescues the U18666A-induced cholesterol accumulation but also rescues the U18666A-induced inhibition of PRV production. Collectively, our data suggest that U18666A interferes with PRV infection via altering cellular functions that are critical for the viral life cycle and may include lysosomal cholesterol homeostasis.

The constellation of cholesterol-dependent processes associated with SARS-CoV-2 infection

The role of cholesterol in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and other coronavirus-host cell interactions is currently being discussed in the context of two main scenarios: i) the presence of the neutral lipid in cholesterol-rich lipid domains involved in different steps of the viral infection and ii) the alteration of metabolic pathways by the virus over the course of infection. Cholesterol-enriched lipid domains have been reported to occur in the lipid envelope membrane of the virus, in the host-cell plasma membrane, as well as in endosomal and other intracellular membrane cellular compartments. These membrane subdomains, whose chemical and physical properties distinguish them from the bulk lipid bilayer, have been purported to participate in diverse phenomena, from virus-host cell fusion to intracellular trafficking and exit of the virions from the infected cell. SARS-CoV-2 recruits many key proteins that participate under physiological conditions in cholesterol and lipid metabolism in general. This review analyses the status of cholesterol and lipidome proteins in SARS-CoV-2 infection and the new horizons they open for therapeutic intervention.

Entry of the Varicellovirus Canid herpesvirus 1 into Madin-Darby canine kidney epithelial cells is pH-independent and occurs via a macropinocytosis-like mechanism but without increase in fluid uptake

Canid herpesvirus 1 (CHV-1) is a Varicellovirus that causes self-limiting infections in adult dogs but morbidity and mortality in puppies. Using a multipronged approach, we discovered the CHV-1 entry pathway into Madin-Darby canine kidney (MDCK) epithelial cells. We found that CHV-1 triggered extensive host cell membrane lamellipodial ruffling and rapid internalisation of virions in large, uncoated vacuoles, suggestive of macropinocytosis. Treatment with inhibitors targeting key macropinocytosis factors, including inhibitors of Na⁺ /H⁺ exchangers, F-actin, myosin light-chain kinase, protein kinase C, p21-activated kinase, phosphatidylinositol-3-kinase and focal adhesion kinase, significantly reduced viral replication. Moreover, the effect was restricted to exposure to the inhibitors early in infection, confirming a role for the macropinocytic machinery during entry. The profile of inhibitors also suggested a role for signalling via integrins and receptor tyrosine kinases in viral entry. In contrast, inhibitors of clathrin, caveolin, microtubules and endosomal acidification did not affect CHV-1 entry into MDCK cells. We found that the virus colocalised with the fluid-phase uptake marker dextran; however, surprisingly, CHV-1 infection did not enhance the uptake of dextran. Thus, our results indicate that CHV-1 uses a macropinocytosis-like, pH-independent entry pathway into MDCK cells, which nevertheless is not based on stimulation of fluid uptake. TAKE AWAYS: CHV-1 enters epithelial cells via a macropinocytosis-like mechanism. CHV-1 induces extensive lamellipodial ruffling. CHV-1 entry into MDCK cells is pH-independent.

Cyclodextrin Monomers and Polymers for Drug Activity Enhancement

Cyclodextrins (CDs) and cyclodextrin (CD)-based polymers are well-known complexing agents. One of their distinctive features is to increase the quantity of a drug in a solution or improve its delivery. However, in certain instances, the activity of the solutions is increased not only due to the increase of the drug dose but also due to the drug complexation. Based on numerous studies reviewed, the drug appeared more active in a complex form. This review aims to summarize the performance of CDs and CD-based polymers as activity enhancers. Accordingly, the review is divided into two parts, i.e., the effect of CDs as active drugs and as enhancers in antimicrobials, antivirals, cardiovascular diseases, cancer, neuroprotective agents, and antioxidants.

Structural Domains of the Herpes Simplex Type 1 gD Protein that Restrict HIV-1 Particle Infectivity

Previously, we showed that the presence of the herpes simplex virus type 1 (HSV-1) gD glycoprotein but not gB potently restricted HIV-1 particle infectivity. This restriction was characterized by incorporation of HSV-1 gD and the exclusion of the HIV-1 gp120/gp41 from budding virus particles. To determine the structural domains involved in gD restriction of HIV-1, a series of deletion mutants and chimeric proteins between gD and the non-restrictive gB were generated. Our results show that deletion of the cytoplasmic tail domain (CTD) of gD or that replacement of the transmembrane domain (TMD) with the TMD from gB slightly reduced restriction activity. However, replacement of the gD CTD with that of gB resulted in lower cell surface expression, significantly less incorporation into HIV-1 particles, and inefficient restriction of the release of infectious HIV-1. Analysis of gB/gD chimeric proteins revealed that removal of the gB CTD or replacement with gD CTD resulted in enhanced surface expression and an increase in restriction activity. Finally, we show that expression of gD without other HSV-1 proteins resulted in gD fractionation into detergent resistant membranes (DRM) and that gD co-localized with the raft marker GM1, which may partially explain its incorporation into budding virus particles. Taken together, our results suggest that expression of gD at the cell surface is likely a major factor but that other intrinsic properties are also involved in the gD-mediated restriction of HIV-1 particle infectivity.IMPORTANCE Previously, we showed that unlike the HSV-1, the presence of the gD glycoprotein in virus producer cells but not gB potently restricted HIV-1 particle infectivity. To better understand the relationship between cell surface expression, virus incorporation and restriction of HIV-1, we analyzed a series of deletion mutants and chimeric proteins in which domains of gD and gB were swapped. Our results indicate that: a) gD/gB chimeras having the cytoplasmic domain (CTD) of gB significantly reduced cell surface expression, release from cells, incorporation into virus, and reduced HIV-1 restriction; b) removal of the gB CTD or replacement with the gD CTD resulted in better surface expression, incorporation into HIV-1, and enhanced restriction; and c) the transmembrane domain of gB can influence transport and ultimately effect incorporation of gB into HIV-1. Overall, these data support a role for gD surface expression as crucial to restriction of infectious HIV-1 release.

Roles of Cholesterol in Early and Late Steps of the Nipah Virus Membrane Fusion Cascade

Cholesterol has been implicated in various viral life cycle steps for different enveloped viruses, including viral entry into host cells, cell-cell fusion, and viral budding from infected cells. Enveloped viruses acquire their membranes from their host cells. Although cholesterol has been associated with the binding and entry of various enveloped viruses into cells, cholesterol's exact function in the viral-cell membrane fusion process remains largely elusive, particularly for the paramyxoviruses. Furthermore, paramyxoviral fusion occurs at the host cell membrane and is essential for both virus entry (virus-cell fusion) and syncytium formation (cell-cell fusion), central to viral pathogenicity. Nipah virus (NiV) is a deadly member of the Paramyxoviridae family, which also includes Hendra, measles, mumps, human parainfluenza, and various veterinary viruses. The zoonotic NiV causes severe encephalitis, vasculopathy, and respiratory symptoms, leading to a high mortality rate in humans. We used NiV as a model to study the role of membrane cholesterol in paramyxoviral membrane fusion. We used a combination of methyl-beta cyclodextrin (MβCD), lovastatin, and cholesterol to deplete or enrich cell membrane cholesterol outside cytotoxic concentrations. We found that the levels of cellular membrane cholesterol directly correlated with the levels of cell-cell fusion induced. These phenotypes were paralleled using NiV/vesicular stomatitis virus (VSV)-pseudotyped viral infection assays. Remarkably, our mechanistic studies revealed that cholesterol reduces an early F-triggering step but enhances a late fusion pore formation step in the NiV membrane fusion cascade. Thus, our results expand our mechanistic understanding of the paramyxoviral/henipaviral entry and cell-cell fusion processes.IMPORTANCE Cholesterol has been implicated in various steps of the viral life cycle for different enveloped viruses. Nipah virus (NiV) is a highly pathogenic enveloped virus in the Henipavirus genus within the Paramyxoviridae family, capable of causing a high mortality rate in humans and high morbidity in domestic and agriculturally important animals. The role of cholesterol for NiV or the henipaviruses is unknown. Here, we show that the levels of cholesterol influence the levels of NiV-induced cell-cell membrane fusion during syncytium formation and virus-cell membrane fusion during viral entry. Furthermore, the specific role of cholesterol in membrane fusion is not well defined for the paramyxoviruses. We show that the levels of cholesterol affect an early F-triggering step and a late fusion pore formation step during the membrane fusion cascade. Thus, our results expand our mechanistic understanding of the viral entry and cell-cell fusion processes, which may aid the development of antivirals.

Membrane Rafts: Portals for Viral Entry

Membrane rafts are dynamic, small (10-200 nm) domains enriched with cholesterol and sphingolipids that compartmentalize cellular processes. Rafts participate in roles essential to the lifecycle of different viral families including virus entry, assembly and/or budding events. Rafts seem to participate in virus attachment and recruitment to the cell surface, as well as the endocytic and non-endocytic mechanisms some viruses use to enter host cells. In this review, we will introduce the specific role of rafts in viral entry and define cellular factors implied in the choice of one entry pathway over the others. Finally, we will summarize the most relevant information about raft participation in the entry process of enveloped and non-enveloped viruses.

Current Understanding of the Role of Cholesterol in the Life Cycle of Alphaviruses

Enveloped viruses rely on different lipid classes present in cell membranes to accomplish several steps of their life cycle in the host. Particularly for alphaviruses, a medically important group of arboviruses, which are part of the Togaviridae family, cholesterol seems to be a critical lipid exploited during infection, although its relevance may vary depending on which stage of the virus life cycle is under consideration and whether infection takes place in vertebrate or invertebrate hosts. In this review, the role of cholesterol in both early and late events of alphavirus infection and how viral replication may affect cholesterol metabolism are summarized, taking into account studies on Old World and New World alphaviruses in different cell lines. Moreover, the importance of cholesterol for the structural stability of alphavirus particles is also discussed, shedding light on the role played by this lipid when they leave the host cell.

Cyclic Oligosaccharides as Active Drugs, an Updated Review

There have been many reviews of the cyclic oligosaccharide cyclodextrin (CD) and CD-based materials used for drug delivery, but the capacity of CDs to complex different agents and their own intrinsic properties suggest they might also be considered for use as active drugs, not only as carriers. The aim of this review is to summarize the direct use of CDs as drugs, without using its complexing potential with other substances. The direct application of another oligosaccharide called cyclic nigerosyl-1,6-nigerose (CNN) is also described. The review is divided into lipid-related diseases, aggregation diseases, antiviral and antiparasitic activities, anti-anesthetic agent, function in diet, removal of organic toxins, CDs and collagen, cell differentiation, and finally, their use in contact lenses in which no drug other than CDs are involved. In the case of CNN, its application as a dietary supplement and immunological modulator is explained. Finally, a critical structure-activity explanation is provided.

The Lord of the NanoRings: Cyclodextrins and the battle against SARS-CoV-2

A handful of singular structures and laws can be observed in nature. They are not always evident but, once discovered, it seems obvious how to take advantage of them. In chemistry, the discovery of reproducible patterns stimulates the imagination to develop new functional materials and technological or medical applications. Two clear examples are helical structures at different levels in biological polymers as well as ring and spherical structures of different size and composition. Rings are intuitively observed as holes able to thread elongated structures. A large number of real and fictional stories have rings as inanimate protagonists. The design, development or just discovering of a special ring has often been taken as a symbol of power or success. Several examples are the Piscatory Ring wore by the Pope of the Catholic Church, the NBA Championship ring and the One Ring created by the Dark Lord Sauron in the epic story The Lord of the Rings. In this work, we reveal the power of another extremely powerful kind of rings to fight against the pandemic which is currently affecting the whole world. These rings are as small as ~1 nm of diameter and so versatile that they are able to participate in the attack of viruses, and specifically SARS-CoV-2, in a large range of different ways. This includes the encapsulation and transport of specific drugs, as adjuvants to stabilize proteins, vaccines or other molecules involved in the infection, as cholesterol trappers to destabilize the virus envelope, as carriers for RNA therapies, as direct antiviral drugs and even to rescue blood coagulation upon heparin treatment.

“One ring to rule them all. One ring to find them. One ring to bring them all and in the darkness bind them.” J. R. R. Tolkien.

Cyclodextrins: Emerging Medicines of the New Millennium

Cyclodextrins, since their discovery in the late 19th century, were mainly regarded as excipients. Nevertheless, developments in cyclodextrin research have shown that some of these hosts can capture and include biomolecules, highlighting fatty acids and cholesterol, which implies that they are not inert and that their action may be used in specific medicinal purposes. The present review, centered on literature reports from the year 2000 until the present day, presents a comprehensive description of the known biological activities of cyclodextrins and their implications for medicinal applications. The paper is divided into two main sections, one devoted to the properties and applications of cyclodextrins as active pharmaceutical ingredients in a variety of pathologies, from infectious ailments to cardiovascular dysfunctions and metabolic diseases. The second section is dedicated to the use of cyclodextrins in a range of biomedical technologies.

Role of Sphingomyelin in Alphaherpesvirus Entry

Bovine herpesvirus 1 (BoHV-1) is an alphaherpesvirus that causes disease in cattle populations worldwide. Sphingomyelin (SM) is the most abundant sphingolipid in the mammalian cell membrane, where it preferentially associates with cholesterol to form lipid raft domains. SM is a substrate for the lysosome-resident enzyme acid sphingomyelinase, which plays a role in cell membrane repair following injury. Treatment of cells with noncytotoxic concentrations of Staphylococcus aureus-derived sphingomyelinase successfully reduced cell surface-exposed sphingomyelin but did not significantly inhibit BoHV-1 entry and infection, as measured by the beta-galactosidase reporter assay. Interestingly, entry of the porcine alphaherpesvirus pseudorabies virus (PRV) was inhibited by sphingomyelin-depletion of cells. Treatment of BoHV-1 particles with sphingomyelinase inhibited viral entry activity, suggesting that viral SM plays a role in BoHV-1 entry, while cellular SM does not. Treatment of cells with noncytotoxic concentrations of the functional inhibitors of host acid sphingomyelinase, imipramine and amitriptyline, which induce degradation of the cellular enzyme, did not significantly inhibit BoHV-1 entry. In contrast, inhibition of cellular acid sphingomyelinase inhibited PRV entry. Entry of the human alphaherpesvirus herpes simplex virus 1 (HSV-1) was independent of both host SM and acid sphingomyelinase, in a manner similar to BoHV-1. Together, the results suggest that among the alphaherpesviruses, there is variability in entry requirements for cellular sphingomyelin and acid sphingomyelinase activity.IMPORTANCE Bovine herpesvirus 1 (BoHV-1) is an ubiquitous pathogen affecting cattle populations worldwide. Infection can result in complicated, polymicrobial infections due to the immunosuppressive properties of the virus. Available vaccines limit disease severity and spread but do not prevent infection. The financial and animal welfare ramifications of BoHV-1 are significant. In order to develop more effective prevention and treatment regimens, a more complete understanding of the initial steps in viral infection is necessary. We recently identified a low pH endocytosis pathway for BoHV-1. Here, we examine the role of cellular factors responsible for membrane integrity and repair in alphaherpesviral entry. This study allows comparisons of the BoHV-1 entry pathway with those of other alphaherpesviruses (pseudorabies virus [PRV] and herpes simplex virus 1 [HSV-1]). Lastly, this is the first report of sphingomyelin and lysosomal sphingomyelinase playing a role in the entry of a herpesvirus. The results may lead to the development of more effective prevention and treatment regimens.

Chewing the Fat: The Conserved Ability of DNA Viruses to Hijack Cellular Lipid Metabolism

Viruses manipulate numerous host factors and cellular pathways to facilitate the replication of viral genomes and the production of infectious progeny. One way in which viruses interact with cells is through the utilization and exploitation of the host lipid metabolism. While it is likely that most-if not all-viruses require lipids or intermediates of lipid synthesis to replicate, many viruses also actively induce lipid metabolic pathways to sustain a favorable replication environment. From the formation of membranous replication compartments, to the generation of ATP or protein modifications, viruses exhibit differing requirements for host lipids. Thus, while the exploitation of lipid metabolism is a common replication strategy, diverse viruses employ a plethora of mechanisms to co-opt these critical cellular pathways. Here, we review recent literature regarding the exploitation of host lipids and lipid metabolism specifically by DNA viruses. Importantly, furthering the understanding of the viral requirements for host lipids may offer new targets for antiviral therapeutics and provide opportunities to repurpose the numerous FDA-approved compounds targeting lipid metabolic pathways as antiviral agents.

Cellular Cholesterol Facilitates the Postentry Replication Cycle of Herpes Simplex Virus 1

Cholesterol is an essential component of cell membranes and is required for herpes simplex virus 1 (HSV-1) entry (1-3). Treatment of HSV-1-infected Vero cells with methyl beta-cyclodextrin from 2 to 9 h postentry reduced plaque numbers. Transport of incoming viral capsids to the nuclear periphery was unaffected by the cholesterol reduction, suggesting that cell cholesterol is important for the HSV-1 replicative cycle at a stage(s) beyond entry, after the arrival of capsids at the nucleus. The synthesis and release of infectious HSV-1 and cell-to-cell spread of infection were all impaired in cholesterol-reduced cells. Propagation of HSV-1 on DHCR24-/- fibroblasts, which lack the desmosterol-to-cholesterol conversion enzyme, resulted in the generation of infectious extracellular virions (HSVdes) that lack cholesterol and likely contain desmosterol. The specific infectivities (PFU per viral genome) of HSVchol and HSVdes were similar, suggesting cholesterol and desmosterol in the HSV envelope support similar levels of infectivity. However, infected DHCR24-/- fibroblasts released ∼1 log less infectious HSVdes and ∼1.5 log fewer particles than release of cholesterol-containing particles (HSVchol) from parental fibroblasts, suggesting that the hydrocarbon tail of cholesterol facilitates viral synthesis. Together, the results suggest multiple roles for cholesterol in the HSV-1 replicative cycle.IMPORTANCE HSV-1 infections are associated with a wide range of clinical manifestations that are of public health importance. Cholesterol is a key player in the complex interaction between viral and cellular factors that allows HSV-1 to enter host cells and establish infection. Previous reports have demonstrated a role for cellular cholesterol in the entry of HSV-1 into target cells. Here, we employed both chemical treatment and cells that were genetically defined to synthesize only desmosterol to demonstrate that cholesterol is important at stages following the initial entry and transport of viral capsids to the nucleus. Viral protein expression, encapsidation of the viral genome, and the release of mature virions were impacted by the reduction of cellular cholesterol. Cholesterol was also critical for cell-to-cell spread of infection. These findings provide new insights into the cholesterol dependence of HSV-1 replication.

Interactions between cyclodextrins and cellular components: Towards greener medical applications?

In the field of host-guest chemistry, some of the most widely used hosts are probably cyclodextrins (CDs). As CDs are able to increase the water solubility of numerous drugs by inclusion into their hydrophobic cavity, they have been widespread used to develop numerous pharmaceutical formulations. Nevertheless, CDs are also able to interact with endogenous substances that originate from an organism, tissue or cell. These interactions can be useful for a vast array of topics including cholesterol manipulation, treatment of Alzheimer's disease, control of pathogens, etc. In addition, the use of natural CDs offers the great advantage of avoiding or reducing the use of common petroleum-sourced drugs. In this paper, the general features and applications of CDs have been reviewed as well as their interactions with isolated biomolecules leading to the formation of inclusion or exclusion complexes. Finally, some potential medical applications are highlighted throughout several examples.

Cholesterol conjugation potentiates the antiviral activity of an HIV immunoadhesin

Immunoadhesins are engineered proteins combining the constant domain (Fc) of an antibody with a ligand-binding (adhesion) domain. They have significant potential as therapeutic agents, because they maintain the favourable pharmacokinetics of antibodies with an expanded repertoire of ligand-binding domains: proteins, peptides, or small molecules. We have recently reported that the addition of a cholesterol group to two HIV antibodies can dramatically improve their antiviral potency. Cholesterol, which can be conjugated at various positions in the antibody, including the constant (Fc) domain, endows the conjugate with affinity for the membrane lipid rafts, thus increasing its concentration at the site where viral entry occurs. Here, we extend this strategy to an HIV immunoadhesin, combining a cholesterol-conjugated Fc domain with the peptide fusion inhibitor C41. The immunoadhesin C41-Fc-chol displayed high affinity for Human Embryonic Kidney (HEK) 293 cells, and when tested on a panel of HIV-1 strains, it was considerably more potent than the unconjugated C41-Fc construct. Potentiation of antiviral activity was comparable to what was previously observed for the cholesterol-conjugated HIV antibodies. Given the key role of cholesterol in lipid raft formation and viral fusion, we expect that the same strategy should be broadly applicable to enveloped viruses, for many of which it is already known the sequence of a peptide fusion inhibitor similar to C41. Moreover, the sequence of heptad repeat-derived fusion inhibitors can often be predicted from genomic information alone, opening a path to immunoadhesins against emerging viruses.

Critical role of the lipid rafts in caprine herpesvirus type 1 infection in vitro

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A dose-dependent fall of CpHV.1 yeld was observed after MβCD treatment of MDBK cells.

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Cholesterol is mainly required during virus entry rather than during post-entry stage.

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Alteration of the lipid composition of the viral envelope affected virus entry.

The fusion machinery for herpesvirus entry in the host cells involves the interactions of viral glycoproteins with cellular receptors, although additional viral and cellular domains are required. Extensive areas of the plasma membrane surface consist of lipid rafts organized into cholesterol-rich microdomains involved in signal transduction, protein sorting, membrane transport and in many processes of viruses infection. Because of the extraction of cholesterol leads to disorganization of lipid microdomains and to dissociation of proteins bound to the lipid rafts, we investigated the effect of cholesterol depletion by methyl-β-cyclodextrin (MβCD) on caprine herpesvirus 1 (CpHV.1) in three important phases of virus infection such as binding, entry and post-entry. MβCD treatment did not prejudice virus binding to cells, while a dose-dependent reduction of the virus yield was observed at the virus entry stage, and 30 mM MβCD reduced infectivity evidently. Treatment of MDBK after virus entry revealed a moderate inhibitory effect suggesting that cholesterol is mainly required during virus entry rather than during the post-entry stage. Alteration of the envelope lipid composition affected virus entry and a noticeable reduction in virus infectivity was detected in the presence of 15 mM MβCD. Considering that the recognition of a host cell receptor is a crucial step in the start-up phase of infection, these data are essential for the study of CpHV.1 pathogenesis. To date virus receptors for CpHV.1 have not yet been identified and further investigations are required to state that MβCD treatment affects the expression of the viral receptors.

Role of the lipid rafts in the life cycle of canine coronavirus

Coronaviruses are enveloped RNA viruses that have evolved complex relationships with their host cells, and modulate their lipid composition, lipid synthesis and signalling. Lipid rafts, enriched in sphingolipids, cholesterol and associated proteins, are special plasma membrane microdomains involved in several processes in viral infections. The extraction of cholesterol leads to disorganization of lipid microdomains and to dissociation of proteins bound to lipid rafts. Because cholesterol-rich microdomains appear to be a general feature of the entry mechanism of non-eneveloped viruses and of several coronaviruses, the purpose of this study was to analyse the contribution of lipids to the infectivity of canine coronavirus (CCoV). The CCoV life cycle is closely connected to plasma membrane cholesterol, from cell entry to viral particle production. The methyl-β-cyclodextrin (MβCD) was employed to remove cholesterol and to disrupt the lipid rafts. Cholesterol depletion from the cell membrane resulted in a dose-dependent reduction, but not abolishment, of virus infectivity, and at a concentration of 15 mM, the reduction in the infection rate was about 68 %. MβCD treatment was used to verify if cholesterol in the envelope was required for CCoV infection. This resulted in a dose-dependent inhibitory effect, and at a concentration of 9 mM MβCD, infectivity was reduced by about 73 %. Since viral entry would constitute a target for antiviral strategies, inhibitory molecules interacting with viral and/or cell membranes, or interfering with lipid metabolism, may have strong antiviral potential. It will be interesting in the future to analyse the membrane microdomains in the CCoV envelope.

Encapsulation of biocides by cyclodextrins: toward synergistic effects against pathogens

Host-guest chemistry is useful for the construction of nanosized objects. Some of the widely used hosts are probably the cyclodextrins (CDs). CDs can form water-soluble complexes with numerous hydrophobic compounds. They have been widespread used in medicine, drug delivery and are of interest for the biocides encapsulation. Indeed, this enables the development of more or less complex systems that release antimicrobial agents with time. In this paper, the general features of CDs and their applications in the field of biocides have been reviewed. As the key point is the formation of biocide-CD inclusion complexes, this review deals with this in depth and the advantages of biocide encapsulation are highlighted throughout several examples from the literature. Finally, some future directions of investigation have been proposed. We hope that scientists studying biocide applications receive inspiration from this review to exploit the opportunities offered by CDs in their respective research areas.

Cholesterol-conjugated peptide antivirals: a path to a rapid response to emerging viral diseases

While it is now possible to identify and genetically fingerprint the causative agents of emerging viral diseases, often with extraordinary speed, suitable therapies cannot be developed with equivalent speed, because drug discovery requires information that goes beyond knowledge of the viral genome. Peptides, however, may represent a special opportunity.

For all enveloped viruses, fusion between the viral and the target cell membrane is an obligatory step of the life cycle. Class I fusion proteins harbor regions with a repeating pattern of amino acids, the heptad repeats (HRs), that play a key role in fusion, and HR‐derived peptides such as enfuvirtide, in clinical use for HIV, can block the process. Because of their characteristic sequence pattern, HRs are easily identified in the genome by means of computer programs, providing the sequence of candidate peptide inhibitors directly from genomic information.

Moreover, a simple chemical modification, the attachment of a cholesterol group, can dramatically increase the antiviral potency of HR‐derived inhibitors and simultaneously improve their pharmacokinetics. Further enhancement can be provided by dimerization of the cholesterol‐conjugated peptide. The examples reported so far include inhibitors of retroviruses, paramyxoviruses, orthomyxoviruses, henipaviruses, coronaviruses, and filoviruses. For some of these viruses, in vivo efficacy has been demonstrated in suitable animal models.

The combination of bioinformatic lead identification and potency/pharmacokinetics improvement provided by cholesterol conjugation may form the basis for a rapid response strategy, where development of an emergency cholesterol‐conjugated therapeutic would immediately follow the availability of the genetic information of a new enveloped virus. Copyright © 2014 European Peptide Society and John Wiley & Sons, Ltd.

Entry of Bombyx mori nucleopolyhedrovirus into BmN cells by cholesterol-dependent macropinocytic endocytosis

Bombyx mori nucleopolyhedrovirus (BmNPV) is a serious viral pathogen of silkworm, and no drug or specific protection against BmNPV infection is available at present time. Although functions of most BmNPV genes were depicted in recent years, knowledge on the mechanism of BmNPV entry into insect cells is still limited. Here BmNPV cell entry mechanism is investigated by different endocytic inhibitor application and subcellular analysis. Results indicated that BmNPV enters BmN cells by clathrin-independent macropinocytic endocytosis, which is mediated by cholesterol in a dose-dependent manner, and cholesterol replenishment rescued the BmNPV infection partially.

Molecular requirement for sterols in herpes simplex virus entry and infectivity

Herpes simplex virus 1 (HSV-1) required cholesterol or desmosterol for virion-induced membrane fusion. HSV successfully entered DHCR24(-/-) cells, which lack a desmosterol-to-cholesterol conversion enzyme, indicating that entry can occur independently of cholesterol. Depletion of desmosterol from these cells resulted in diminished HSV-1 entry, suggesting a general sterol requirement for HSV-1 entry and that desmosterol can operate in virus entry. Cholesterol functioned more effectively than desmosterol, suggesting that the hydrocarbon tail of cholesterol influences viral entry.

Multiphasic effects of cholesterol on influenza fusion kinetics reflect multiple mechanistic roles

The envelope lipid composition of influenza virus differs from that of the cellular plasma membrane from which it buds. Viruses also appear to fuse preferentially to specific membrane compartments, suggesting that the lipid environment may influence permissiveness for fusion. Here, we investigated the influence of the membrane environment on fusion, focusing on cholesterol composition. Strikingly, manipulating cholesterol levels in the viral membrane had different effects on fusion kinetics compared with analogous changes to the target membrane. Increasing cholesterol content in target vesicles increased lipid- and contents-mixing rates. Moderate cholesterol depletion from the viral membrane sped fusion rates, whereas severe depletion slowed the process. The pleiotropic effects of cholesterol include alterations in both membrane-bending moduli and lateral organization. Because influenza virions have demonstrated cholesterol-dependent lateral organization, to separate these effects, we deliberately selected a target vesicle composition that does not support lateral heterogeneity. We therefore postulate that the monotonic response of fusion kinetics to target membrane cholesterol reflects bending and curvature effects, whereas the multiphasic response to viral cholesterol levels reflects the combined effects of lateral organization and material properties.

Molecular Signaling and Cellular Pathways for Virus Entry

The cell signaling plays a pivotal role in regulating cellular processes and is often manipulated by viruses as they rely on the functions offered by cells for their propagation. The first stage of their host life is to pass the genetic materials into the cell. Although some viruses can directly penetrate into cytosol, in fact, most virus entry into their host cells is through endocytosis. This machinery initiates with cell type specific cellular signaling pathways, and the signaling compounds can be proteins, lipids, and carbohydrates. The activation can be triggered in a very short time after virus binds on target cells, such as receptors. The signaling pathways involved in regulation of viral entry are wide diversity that often cross-talk between different endocytosis results. Furthermore, some viruses have the ability to use the multiple internalization pathways which leads to the regulation being even more complex. In this paper, we discuss some recent advances in our understanding of cellular pathways for virus entry, molecular signaling during virus entry, formation of endocytic vesicles, and the traffic.

Boots for Achilles: progesterone's reduction of cholesterol is a second-order adaptation

Progesterone and cholesterol are both vital to pregnancy. Among other functions, progesterone downregulates inflammatory responses, allowing for maternal immune tolerance of the fetal allograft. Cholesterol a key component of cell membranes, is important in intracellular transport, cell signaling, nerve conduction, and metabolism Despite the importance of each substance in pregnancy, one exercises an antagonistic effect on the other, as periods of peak progesterone correspond with reductions in cholesterol availability, a consequence of progesterone's negative effects on cholesterol biosynthesis. This arrangement is understandable in light of the threat posed by pathogens early in pregnancy. Progesterone-induced immunomodulation entails increased vulnerability to infection, an acute problem in the first trimester, when fetal development is highly susceptible to insult. Many pathogens rely on cholesterol for cell entry, egress, and replication. Progesterone's antagonistic effects on cholesterol thus partially compensate for the costs entailed by progesterone-induced immunomodulation. Among pathogens to which the host's vulnerability is increased by progesterone's effects, approximately 90% utilize cholesterol, and this is notably true of pathogens that pose a risk during pregnancy. In addition to having a number of possible clinical applications, our approach highlights the potential importance of second-order adaptations, themselves a consequence of the lack of teleology in evolutionary processes.

Requirement of cholesterol in the viral envelope for dengue virus infection

The role of cholesterol in the virus envelope or in the cellular membranes for dengue virus (DENV) infection was examined by depletion with methyl-beta-cyclodextrin (MCD) or nystatin. Pretreatment of virions with MCD or nystatin significantly reduced virus infectivity in a dose-dependent manner. By contrast, pre-treatment of diverse human cell lines with MCD or nystatin did not affect DENV infection. The four DENV serotypes were similarly inactivated by cholesterol-extracting drugs and infectivity was partially rescued when virion suspensions were treated with MCD in the presence of bovine serum. The addition of serum or exogenous water-soluble cholesterol after MCD treatment did not produce a reversion of MCD inactivating effect. Furthermore, virion treatment with extra cholesterol exerted also a virucidal effect. Binding and uptake of cholesterol-deficient DENV into the host cell were not impaired, whereas the next step of fusion between virion envelope and endosome membrane leading to virion uncoating and release of nucleocapsids to the cytoplasm appeared to be prevented, as determined by the retention of capsid protein in cells infected with MCD inactivated-DENV virions. Thereafter, the infection was almost completely inhibited, given the failure of viral RNA synthesis and viral protein expression in cells infected with MCD-treated virions. These data suggest that envelope cholesterol is a critical factor in the fusion process for DENV entry.

Cyclodextrins - Fields of Application. Part II

This paper represents an analysis of potential and current applications of cyclodextrins as biologically active substances in medicine. The main applications described here include use of cyclodextrins as agents that form inclusion complexes with endogenous substances (membrane lipids, cellular cholesterol), agents that form inclusion complexes with exogenous substances with their man role as guest molecules (sugammadex, FBCx), agents that block endogenous and exogenous macromolecules (ion channels, anthrax toxin, α-hemolysin), and agents which activity is based on the chemical nature of them and of their derivatives (cyclodextrin polysulphate derivatives). The fi rst classifi cation for medically important biological activity of cyclodextrins has been proposed.

Scavenger receptor mediated endocytosis of silver nanoparticles into J774A.1 macrophages is heterogeneous

We investigated the scavenger receptor mediated uptake and subsequent intracellular spatial distribution and clustering of 57.7 ± 6.9 nm diameter silver nanoparticles (zeta-potential = -28.4 mV) in the murine macrophage cell line J774A.1 through colorimetric imaging. The NPs exhibited an overall red-shift of the plasmon resonance wavelength in the cell ensemble as function of time and concentration, indicative of intracellular NP agglomeration. A detailed analysis of the NP clustering in individual cells revealed a strong phenotypic variability in the intracellular NP organization on the single cell level. Throughout the observation time of 24h cells containing non- or low-agglomerated NPs with a characteristic blue color coexisted with cells containing NPs with varying degrees of agglomeration, as evinced by distinct spectral shifts of their resonance wavelengths. Pharmacological inhibition studies indicated that the observed differences in intracellular NP organization resulted from coexisting actin- and clathrin-dependent endocytosis mechanisms in the macrophage population. Correlation of intracellular NP clustering with macrophage maturity marker (F4/80, CD14) expression revealed that differentiated J774A.1 cells preferentially contained compact NP agglomerates, whereas monocyte-like macrophages contained non-agglomerated NPs.

Intracytoplasmic trapping of influenza virus by a lipophilic derivative of aglycoristocetin

We report on a new anti-influenza virus agent, SA-19, a lipophilic glycopeptide derivative consisting of aglycoristocetin coupled to a phenylbenzyl-substituted cyclobutenedione. In Madin-Darby canine kidney cells infected with influenza A/H1N1, A/H3N2, or B virus, SA-19 displayed a 50% antivirally effective concentration of 0.60 μM and a selectivity index (ratio of cytotoxic versus antiviral concentration) of 112. SA-19 was 11-fold more potent than unsubstituted aglycoristocetin and was active in human and nonhuman cell lines. Virus yield at 72 h p.i. was reduced by 3.6 logs at 0.8 μM SA-19. In contrast to amantadine and oseltamivir, SA-19 did not select for resistance upon prolonged virus exposure. SA-19 was shown to inhibit an early postbinding step in virus replication. The compound had no effect on hemagglutinin (HA)-mediated membrane fusion in an HA-polykaryon assay and did not inhibit the low-pH-induced refolding of the HA in a tryptic digestion assay. However, a marked inhibitory effect on the transduction exerted by retroviral pseudoparticles carrying an HA or vesicular stomatitis virus glycoprotein (VSV-G) fusion protein was noted, suggesting that SA-19 targets a cellular factor with a role in influenza virus and VSV entry. Using confocal microscopy with antinucleoprotein staining, SA-19 was proven to completely prevent the influenza virus nuclear entry. This virus arrest was characterized by the formation of cytoplasmic aggregates. SA-19 appeared to disturb the endocytic uptake and trap the influenza virus in vesicles distinct from early, late, or recycling endosomes. The aglycoristocetin derivative SA-19 represents a new class of potent and broad-acting influenza virus inhibitors with potential clinical relevance.

Cellular membrane cholesterol is required for porcine reproductive and respiratory syndrome virus entry and release in MARC-145 cells

Cholesterol represents one of the key constituents of small, dynamic, sterol- and sphingolipid-enriched domains on the plasma membrane. It has been reported that many viruses depend on plasma membrane cholesterol for efficient infection. In this study, the role of the plasma membrane cholesterol in porcine reproductive and respiratory syndrome virus (PRRSV) infection of MARC-145 cells was investigated. Pretreatment of MARC-145 cells with methyl-β-cyclodextrin (MβCD), a drug used to deplete cholesterol from cellular membrane, significantly reduced PRRSV infection in a dose-dependent manner. This inhibition was partially reversed by supplementing exogenous cholesterol following MβCD treatment, suggesting that the inhibition of PRRSV infection was specifically mediated by removal of cellular cholesterol. Further detailed studies showed that depletion of cellular membrane cholesterol significantly inhibited virus entry, especially virus attachment and release. These results indicate that the presence of cholesterol in the cellular membrane is a key component of PRRSV infection.

[Varicella-zoster virus (VZV)]

Varicella-zoster virus (VZV) causes varicella in primary infection and zoster after reactivation from latency. Both herpes simplex virus (HSV) and VZV are classified into the same alpha-herpesvirus subfamily. Although most VZV genes have their HSV homologs, VZV has many unique biological characteristics. In this review, we summarized recent studies on 1) animal models for VZV infection and outcomes from studies using the models, including 2) viral dissemination processes from respiratory mucosa, T cells, to skin, 3) cellular receptors for VZV entry, 4) functions of viral genes required uniquely for in vivo growth and for establishment of latency, 5) host immune responses and viral immune evasion mechanisms, and 6) varicella vaccine and anti-VZV drugs.

Cell entry of avian reovirus follows a caveolin-1-mediated and dynamin-2-dependent endocytic pathway that requires activation of p38 mitogen-activated protein kinase (MAPK) and Src signaling pathways as well as microtubules and small GTPase Rab5 protein

Very little is known about the mechanism of cell entry of avian reovirus (ARV). The aim of this study was to explore the mechanism of ARV entry and subsequent infection. Cholesterol mainly affected the early steps of the ARV life cycle, because the presence of cholesterol before and during viral adsorption greatly blocked ARV infectivity. Although we have demonstrated that ARV facilitating p38 MAPK is beneficial for virus replication, its mechanism remains unknown. Here, we show that ARV-induced phosphorylation of caveolin-1 (Tyr(14)), dynamin-2 expression, and Rac1 activation through activation of p38 MAPK and Src in the early stage of the virus life cycle is beneficial for virus entry and productive infection. The strong inhibition by dynasore, a specific inhibitor of dynamin-2, and depletion of endogenous caveolin-1 or dynamin-2 by siRNAs as well as the caveolin-1 colocalization study implicate caveolin-1-mediated and dynamin-2-dependent endocytosis as a significant avenue of ARV entry. By means of pharmacological inhibitors, dominant negative mutants, and siRNA of various cellular proteins and signaling molecules, phosphorylation of caveolin-1, dynamin-2 expression, and Rac1 activation were suppressed, suggesting that by orchestrating p38 MAPK, Src, and Rac1 signaling cascade in the target cells, ARV creates an appropriate intracellular environment facilitating virus entry and productive infection. Furthermore, disruption of microtubules, Rab5, or endosome acidification all inhibited ARV infection, suggesting that microtubules and small GTPase Rab5, which regulate transport to early endosome, are crucial for survival of ARV and that exposure of the virus to acidic pH is required for productive infection.

Structural requirements of virion-associated cholesterol for infectivity, buoyant density and apolipoprotein association of hepatitis C virus

Our earlier study has demonstrated that hepatitis C virus (HCV)-associated cholesterol plays a key role in virus infectivity. In this study, the structural requirement of sterols for infectivity, buoyant density and apolipoprotein association of HCV was investigated further. We removed cholesterol from virions with methyl β-cyclodextrin, followed by replenishment with 10 exogenous cholesterol analogues. Among the sterols tested, dihydrocholesterol and coprostanol maintained the buoyant density of HCV and its infectivity, and 7-dehydrocholesterol restored the physical appearance of HCV, but suppressed its infectivity. Other sterol variants with a 3β-hydroxyl group or with an aliphatic side chain did not restore density or infectivity. We also provide evidence that virion-associated cholesterol contributes to the interaction between HCV particles and apolipoprotein E. The molecular basis for the effects of different sterols on HCV infectivity is discussed.

Envelope lipid-packing as a critical factor for the biological activity and stability of alphavirus particles isolated from mammalian and mosquito cells

Alphaviruses are enveloped arboviruses. The viral envelope is derived from the host cell and is positioned between two icosahedral protein shells (T = 4). Because the viral envelope contains glycoproteins involved in cell recognition and entry, the integrity of the envelope is critical for the success of the early events of infection. Differing levels of cholesterol in different hosts leads to the production of alphaviruses with distinct levels of this sterol loaded in the envelope. Using Mayaro virus, a New World alphavirus, we investigated the role of cholesterol on the envelope of alphavirus particles assembled in either mammalian or mosquito cells. Our results show that although quite different in their cholesterol content, Mayaro virus particles obtained from both cells share a similar high level of lateral organization in their envelopes. This organization, as well as viral stability and infectivity, is severely compromised when cholesterol is depleted from the envelope of virus particles isolated from mammalian cells, but virus particles isolated from mosquito cells are relatively unaffected by cholesterol depletion. We suggest that it is not cholesterol itself, but rather the organization of the viral envelope, that is critical for the biological activity of alphaviruses.

Differential infectious entry of human influenza A/NWS/33 virus (H1N1) in mammalian kidney cells

In this report we focused our interest on the early events of the replication cycle of NWS/33 human influenza A (NWS) virus in MDCK (canine), LLC-MK2 (simian), and NSK (swine) kidney cells, with different susceptibility upon infection. We have previously demonstrated that actin organization induces restriction to viral replication during the early stages of NWS virus infection in simian kidney cells. To explore how cell endocytic mechanisms are hijacked by NWS virus and may modulate the outcome of viral infection, the effect of drugs affecting selectively the entry via clathrin-coated pits, caveolar/raft-dependent endocytosis and macropinocytosis was analyzed. Results point to critical differences in terms of internalization pathways exploited by NWS virus to enter the examined cell models. Moreover, we show that some ways of entry do not allow an effective virus internalization, depending on the cell type. Understanding how specific cell functions/components may regulate early phases of viral replication allows us to deepen our knowledge on influenza virus infection and provides new insights for anti-viral researches.

Cholesterol is important for a post-adsorption step in the entry process of transmissible gastroenteritis virus

Cholesterol is a major constituent of detergent-resistant membrane microdomains (DRMs). We localized transmissible gastroenteritis virus (TGEV) spike (S) protein in DRMs in the viral envelope. Though S protein was not solubilized by cold non-ionic detergents, this behavior was unchanged when cholesterol was depleted from viral membrane by methyl-β-cyclodextrin (MβCD) and the protein did not comigrate with cellular DRM marker proteins in flotation analyses. Therefore, the S protein is not anchored in the viral membrane DRMs as they are known to occur in the plasma membrane. Cholesterol depletion from viral membrane may not affect the adsorption process as neither the sialic acid binding activity nor the binding to aminopeptidase N was reduced post-MβCD treatment. Reduced infectivity of cholesterol-depleted TGEV was observed only when the adsorption process occurred at 37 °C but not when the virus was applied at 4 °C. Cholesterol is important for a post-adsorption step, allowing membrane rearrangements that facilitate virus entry.

Cholesterol dependence of pseudorabies herpesvirus entry

Lipid rafts are special microdomains in the plasma membrane. They are enriched in sphingolipids and cholesterol, playing critical roles in many biological processes. The purpose of this study is to analyze the requirement of cholesterol, a crucial component of lipid rafts for cell infection by pseudorabies virus (PrV). Cholesterol of plasma membrane or viral envelope was depleted with methyl-beta-cyclodextrin (MβCD), and the infectivity of three strains of PrV was determined with plaque assays. The effect of adding cholesterol to MβCD-treated cells and viruses on cell infection was analyzed. Furthermore, effect of post-adsorption cholesterol depletion on PrV infection was investigated. We show that cholesterol depletion of either the plasma membrane or the viral membrane by MβCD significantly impaired the infectivity of PrV strains Kaplan, Becker, and Bartha K-61. The virus was shown to have lower cholesterol content and to respond to lower MβCD concentrations. Exogenous cholesterol added to either MβCD-treated cells or virions partially restored the virus infectivity. Optimal PrV infection requires cholesterol in viral and plasma membranes.

Insulin degrading enzyme induces a conformational change in varicella-zoster virus gE, and enhances virus infectivity and stability

Varicella-zoster virus (VZV) glycoprotein E (gE) is essential for virus infectivity and binds to a cellular receptor, insulin-degrading enzyme (IDE), through its unique amino terminal extracellular domain. Previous work has shown IDE plays an important role in VZV infection and virus cell-to-cell spread, which is the sole route for VZV spread in vitro. Here we report that a recombinant soluble IDE (rIDE) enhances VZV infectivity at an early step of infection associated with an increase in virus internalization, and increases cell-to-cell spread. VZV mutants lacking the IDE binding domain of gE were impaired for syncytia formation and membrane fusion. Pre-treatment of cell-free VZV with rIDE markedly enhanced the stability of the virus over a range of conditions. rIDE interacted with gE to elicit a conformational change in gE and rendered it more susceptible to proteolysis. Co-incubation of rIDE with gE modified the size of gE. We propose that the conformational change in gE elicited by IDE enhances infectivity and stability of the virus and leads to increased fusogenicity during VZV infection. The ability of rIDE to enhance infectivity of cell-free VZV over a wide range of incubation times and temperatures suggests that rIDE may be useful for increasing the stability of varicella or zoster vaccines.

Caveolin-1-dependent occludin endocytosis is required for TNF-induced tight junction regulation in vivo

Although tight junction morphology is not obviously affected by TNF, this proinflammatory cytokine promotes internalization of occludin, resulting in disrupted barrier function within the intestine.

Epithelial paracellular barrier function, determined primarily by tight junction permeability, is frequently disrupted in disease. In the intestine, barrier loss can be mediated by tumor necrosis factor (α) (TNF) signaling and epithelial myosin light chain kinase (MLCK) activation. However, TNF induces only limited alteration of tight junction morphology, and the events that couple structural reorganization to barrier regulation have not been defined. We have used in vivo imaging and transgenic mice expressing fluorescent-tagged occludin and ZO-1 fusion proteins to link occludin endocytosis to TNF-induced tight junction regulation. This endocytosis requires caveolin-1 and is essential for structural and functional tight junction regulation. These data demonstrate that MLCK activation triggers caveolin-1–dependent endocytosis of occludin to effect structural and functional tight junction regulation.

Alphaherpesvirus use and misuse of cellular actin and cholesterol

Two major structural elements of a cell are the cytoskeleton and the lipid membranes. Actin and cholesterol are key components of the cytoskeleton and membranes, respectively, and are involved in a plethora of different cellular processes. This review summarizes and discusses the interaction of alphaherpesviruses with actin and cholesterol during different stages of the replication cycle: virus entry, replication and assembly in the nucleus, and virus egress. Elucidating these interactions not only yields novel insights into the biology of these important pathogens, but may also shed new light on cell biological aspects of actin and cholesterol, and lead to novel avenues in the design of antiviral strategies.

Critical role of cholesterol in bovine herpesvirus type 1 infection of MDBK cells

Cholesterol is involved in the life cycle of many viruses. Here, we examined the role of cholesterol for both viral envelope and target cell membrane for bovine herpesvirus type 1 (BoHV-1) infection. Cholesterol depletion by pretreatment of Madin-Darby bovine kidney (MDBK) cells with a cholesterol-sequestering drug methyl-beta-cyclodextrin (MbetaCD), inhibited the production of BoHV-1 in a dose-dependent manner. This inhibitory effect was partially reversed by cholesterol replenishment, indicating that the reduction was caused by cholesterol depletion. Cholesterol depletion at the post-entry stage only had a mild effect on the virus production. However, cell membrane cholesterol depletion did not reduce the virus attachment. In addition, treatment of BoHV-1 particles with MbetaCD also reduced the virus infectivity significantly and the effect was partially reversed by addition of exogenous cholesterol. Taken together, these data implicated that cell membrane cholesterol mainly contributed to BoHV-1 entry into MDBK cells and the viral envelope cholesterol was also essential for the virus infectivity.

VZV infection of keratinocytes: production of cell-free infectious virions in vivo

Varicella-zoster virus (VZV) is the cause of varicella (chickenpox) and zoster (shingles). Varicella is a primary infection that spreads rapidly in epidemics while zoster is a secondary infection that occurs sporadically as a result of the reactivation of previously acquired VZV. Reactivation is made possible by the establishment of latency during the initial episode of varicella. The signature lesions of both varicella and zoster are cutaneous vesicles, which are filled with a clear fluid that is rich in infectious viral particles. It has been postulated that the skin is the critical organ in which both host-to-host transmission of VZV and the infection of neurons to establish latency occur. This hypothesis is built on evidence that the large cation-independent mannose 6-phosphate receptor (MPR(ci)) interacts with VZV in virtually all infected cells, except those of the suprabasal epidermis, in a way that prevents the release of infectious viral particles. Specifically, the virus is diverted in an MPR(ci)-dependent manner from the secretory pathway to late endosomes where VZV is degraded. Because nonepidermal cells are thus prevented from releasing infectious VZV, a slow process, possibly involving fusion of infected cells with their neighbors, becomes the means by which VZV is disseminated. In the epidermis, however, the maturation of keratinocytes to give rise to corneocytes in the suprabasal epidermis is associated uniquely with a downregulation of the MPR(ci). As a result, the diversion of VZV to late endosomes does not occur in the suprabasal epidermis where vesicular lesions occur. The formation of the waterproof, chemically resistant barrier of the epidermis, however, requires that constitutive secretion outlast the downregulation of the endosomal pathway. Infectious VZV is therefore secreted by default, accounting for the presence of infectious virions in vesicular fluid. Sloughing of corneocytes, aided by scratching, then aerosolizes the virus, which can float with dust to be inhaled by susceptible hosts. Infectious virions also bathe the terminals of those sensory neurons that innervate the epidermis. These terminals become infected with VZV and provide a route, retrograde transport, which can conduct VZV to cranial nerve (CNG), dorsal root ganglia (DRG), and enteric ganglia (EG) to establish latency. Reactivation returns VZV to the skin, now via anterograde transport in axons, to cause the lesions of zoster. Evidence in support of these hypotheses includes observations of the VZV-infected human epidermis and studies of guinea pig neurons in an in vitro model system.