Interaction of glycoprotein gIII with a cellular heparinlike substance mediates adsorption of pseudorabies virus

Single amino acid mutation of nectin-1 provides remarkable resistance against lethal pseudorabies virus infection in mice

An approach to genetically engineered resistance to pseudorabies virus (PRV) infection was examined by using a mouse model with defined point mutation in primary receptor for alphaherpesviruses, nectin-1, by the CRISPR/Cas9 system. It has become clear that phenylalanine at position 129 of nectin-1 is important for binding to viral glycoprotein D (gD), and mutation of phenylalanine 129 to alanine (F129A) prevents nectin-1 binding to gD and virus entry in vitro. Here, to assess the antiviral potential of the single amino acid mutation of nectin-1, F129A, in vivo, we generated genome-edited mutant mouse lines; F129A and 135 knockout (KO). The latter, 135 KO used as a nectin-1 knockout line for comparison, expresses a carboxy-terminal deleted polypeptide consisting of 135 amino acids without phenylalanine 129. In the challenge with 10 LD50 PRV via intranasal route, perfect protection of disease onset was induced by expression of the mutation of nectin-1, F129A (survival rate: 100% in F129A and 135 KO versus 0% in wild type mice). Neither viral DNA/antigens nor pathological changes were detected in F129A, suggesting that viral entry was prevented at the primary site in natural infection. In the challenge with 50 LD50 PRV, lower but still strong protective effect against disease onset was observed (survival rate: 57% in F129A and 75% in 135 KO versus 0% in wild type mice). The present results indicate that single amino acid mutation of nectin-1 F129A provides significant resistance against lethal pseudorabies.

Pseudorabies virus upregulates low-density lipoprotein receptors to facilitate viral entry

Pseudorabies virus (PRV) is the causative agent of Aujeszky's disease in pigs. The low-density lipoprotein receptor (LDLR) is a transcriptional target of the sterol-regulatory element-binding proteins (SREBPs) and participates in the uptake of LDL-derived cholesterol. However, the involvement of LDLR in PRV infection has not been well characterized. We observed an increased expression level of LDLR mRNA in PRV-infected 3D4/21, PK-15, HeLa, RAW264.7, and L929 cells. The LDLR protein level was also upregulated by PRV infection in PK-15 cells and in murine lung and brain. The treatment of cells with the SREBP inhibitor, fatostatin, or with SREBP2-specific small interfering RNA prevented the PRV-induced upregulation of LDLR expression as well as viral protein expression and progeny virus production. This suggested that PRV activated SREBPs to induce LDLR expression. Furthermore, interference in LDLR expression affected PRV proliferation, while LDLR overexpression promoted it. This indicated that LDLR was involved in PRV infection. The study also demonstrated that LDLR participated in PRV invasions. The overexpression of LDLR or inhibition of proprotein convertase subtilisin/kexin type 9 (PCSK9), which binds to LDLR and targets it for lysosomal degradation, significantly enhanced PRV attachment and entry. Mechanistically, LDLR interacted with PRV on the plasma membrane, and pretreatment of cells with LDLR antibodies was able to neutralize viral entry. An in vivo study indicated that the treatment of mice with the PCSK9 inhibitor SBC-115076 promoted PRV proliferation. The data from the study indicate that PRV hijacks LDLR for viral entry through the activation of SREBPs.IMPORTANCEPseudorabies virus (PRV) is a herpesvirus that primarily manifests as fever, pruritus, and encephalomyelitis in various domestic and wild animals. Owing to its lifelong latent infection characteristics, PRV outbreaks have led to significant financial setbacks in the global pig industry. There is evidence that PRV variant strains can infect humans, thereby crossing the species barrier. Therefore, gaining deeper insights into PRV pathogenesis and developing updated strategies to contain its spread are critical. This study posits that the low-density lipoprotein receptor (LDLR) could be a co-receptor for PRV infection. Hence, strategies targeting LDLR may provide a promising avenue for the development of effective PRV vaccines and therapeutic interventions.

Membrane fusion, potential threats, and natural antiviral drugs of pseudorabies virus

Pseudorabies virus (PrV) can infect several animals and causes severe economic losses in the swine industry. Recently, human encephalitis or endophthalmitis caused by PrV infection has been frequently reported in China. Thus, PrV can infect animals and is becoming a potential threat to human health. Although vaccines and drugs are the main strategies to prevent and treat PrV outbreaks, there is no specific drug, and the emergence of new PrV variants has reduced the effectiveness of classical vaccines. Therefore, it is challenging to eradicate PrV. In the present review, the membrane fusion process of PrV entering target cells, which is conducive to revealing new therapeutic and vaccine strategies for PrV, is presented and discussed. The current and potential PrV pathways of infection in humans are analyzed, and it is hypothesized that PrV may become a zoonotic agent. The efficacy of chemically synthesized drugs for treating PrV infections in animals and humans is unsatisfactory. In contrast, multiple extracts of traditional Chinese medicine (TCM) have shown anti-PRV activity, exerting its effects in different phases of the PrV life-cycle and suggesting that TCM compounds may have great potential against PrV. Overall, this review provides insights into developing effective anti-PrV drugs and emphasizes that human PrV infection should receive more attention.

Gallocatechin Gallate Inhibits the Replication of Pseudorabies Virus via Suppressing the Entry and Release Stages in Its Replication Cycle

The pseudorabies virus is a widespread swine pathogen that has caused significant economic losses to the global pig industry. Due to the emergence of PRV variant strains in recent years, vaccines cannot provide complete protection against the infection of PRV. Therefore, the research on antiviral compounds is of great importance for PRV treatment. In this study, an EGFP-labeled PRV was used to screen anti-PRV compounds from 86 natural product extracts. Gallocatechin gallate was found to efficiently inhibit the replication of PRV with a half-maximal inhibitory concentration (IC50) of 0.41 μM. In addition, it was found that gallocatechin gallate was unable to directly inactivate PRV and had no effect on the attachment stage of PRV. However, it was found that gallocatechin gallate significantly suppressed the viral entry stage. Furthermore, it was found that the release stage of PRV was also significantly suppressed by gallocatechin gallate. Together, this study found that gallocatechin gallate could efficiently inhibit the replication of PRV by suppressing the entry and release stages of PRV, which will contribute to the development of a new therapeutic strategy against PRV infection.

G-quadruplexes formed by Varicella-Zoster virus reiteration sequences suppress expression of glycoprotein C and regulate viral cell-to-cell spread

G-quadruplex (G4) formed by repetitive guanosine-rich sequences plays important roles in diverse cellular processes; however, its roles in viral infection are not fully understood. In this study, we investigated the genome-wide distribution of G4-forming sequences (G4 motifs) in Varicella-Zoster virus (VZV) and found that G4 motifs are enriched in the internal repeat short and the terminal repeat short regions flanking the unique short region and also in some reiteration (R) sequence regions. A high density of G4 motifs in the R2 region was found on the template strand of ORF14, which encodes glycoprotein C (gC), a virulent factor for viral growth in skin. Analyses such as circular dichroism spectroscopy, thermal difference spectra, and native polyacrylamide gel electrophoresis with oligodeoxynucleotides demonstrated that several G4 motifs in ORF14 form stable G4 structures. In transfection assays, gC expression from the G4-disrupted ORF14 gene was increased at the transcriptional level and became more resistant to suppression by G4-ligand treatment. The recombinant virus containing the G4-disrupted ORF14 gene expressed a higher level of gC mRNA, while it showed a slightly reduced growth. This G4-disrupted ORF14 virus produced smaller plaques than the wild-type virus. Our results demonstrate that G4 formation via reiteration sequences suppresses gC expression during VZV infection and regulates viral cell-to-cell spread.

Replication and Spread of Oncolytic Herpes Simplex Virus in Solid Tumors

Oncolytic herpes simplex virus (oHSV) is a highly promising treatment for solid tumors. Intense research and development efforts have led to first-in-class approval for an oHSV for melanoma, but barriers to this promising therapy still exist that limit efficacy. The process of infection, replication and transmission of oHSV in solid tumors is key to obtaining a good lytic destruction of infected cancer cells to kill tumor cells and release tumor antigens that can prime anti-tumor efficacy. Intracellular tumor cell signaling and tumor stromal cells present multiple barriers that resist oHSV activity. Here, we provide a review focused on oncolytic HSV and the essential viral genes that allow for virus replication and spread in order to gain insight into how manipulation of these pathways can be exploited to potentiate oHSV infection and replication among tumor cells.

A Genome-Wide CRISPR/Cas9 Screen Reveals the Requirement of Host Sphingomyelin Synthase 1 for Infection with Pseudorabies Virus Mutant gD-Pass

Herpesviruses are large DNA viruses, which encode up to 300 different proteins including enzymes enabling efficient replication. Nevertheless, they depend on a multitude of host cell proteins for successful propagation. To uncover cellular host factors important for replication of pseudorabies virus (PrV), an alphaherpesvirus of swine, we performed an unbiased genome-wide CRISPR/Cas9 forward screen. To this end, a porcine CRISPR-knockout sgRNA library (SsCRISPRko.v1) targeting 20,598 genes was generated and used to transduce porcine kidney cells. Cells were then infected with either wildtype PrV (PrV-Ka) or a PrV mutant (PrV-gD^-Pass) lacking the receptor-binding protein gD, which regained infectivity after serial passaging in cell culture. While no cells survived infection with PrV-Ka, resistant cell colonies were observed after infection with PrV-gD^-Pass. In these cells, sphingomyelin synthase 1 (SMS1) was identified as the top hit candidate. Infection efficiency was reduced by up to 90% for PrV-gD^-Pass in rabbit RK13-sgms1_KO cells compared to wildtype cells accompanied by lower viral progeny titers. Exogenous expression of SMS1 partly reverted the entry defect of PrV-gD^-Pass. In contrast, infectivity of PrV-Ka was reduced by 50% on the knockout cells, which could not be restored by exogenous expression of SMS1. These data suggest that SMS1 plays a pivotal role for PrV infection, when the gD-mediated entry pathway is blocked.

Proteomic analysis of host cellular proteins co-immunoprecipitated with duck enteritis virus gC

Duck enteritis virus (DEV), the causative agent of duck viral enteritis, causes a contagious, lethal viral disease in Anseriformes (waterfowls). In virus infection, host-virus interaction plays a crucial role in virus replication and pathogenesis. In our previous study, mRFP was fused with the C-terminus of DEV glycoprotein C (gC) to construct a fluorescent-tag DEV virus rgCRFP. In the current study, fluorescent fusion protein (gC-mRFP) was used as the proteomic probe. Co-immunoprecipitation and mass spectrometric analysis of proteins from rgCRFP-infected chicken embryo fibroblasts using commercial anti-RFP antibody led to the identification of a total of 21 gC interacting host proteins. Out of these 21 proteins, the interaction of seven host proteins (GNG2, AR1H1, PPP2CA, UBE2I, MCM5, NUBP1, HN1) with DEV gC protein was validated using membrane-bound split-ubiquitin yeast two-hybrid system (MbYTH) and bimolecular fluorescence complementation (BiFC) analyses. It indicated direct interaction between these proteins with DEV gC protein. This study has furthered the current understanding of DEV virus infection and pathogenesis. SIGNIFICANCE: gC is an crucial glycoprotein of duck enteritis virus that plays an important role in the viral life cycle. Uncovering the interaction between virus-host is very important to elucidate the pathogenic mechanism of the virus. In this study, host factors interacting with DEV gC have been discerned. And seven host proteins (GNG2, AR1H1, PPP2CA, UBE2I, MCM5, NUBP1, HN1) have been further validated to interact with DEV gC using MbYTH and BiFC analyses. These outcomes could shed light on how DEV manipulates the cellular machinery, which could further our understanding of DEV pathogenesis.

Symmetrical arrangement of positively charged residues around the 5-fold axes of SAT type foot-and-mouth disease virus enhances cell culture of field viruses

Field isolates of foot-and-mouth disease viruses (FMDVs) utilize integrin-mediated cell entry but many, including Southern African Territories (SAT) viruses, are difficult to adapt to BHK-21 cells, thus hampering large-scale propagation of vaccine antigen. However, FMDVs acquire the ability to bind to cell surface heparan sulphate proteoglycans, following serial cytolytic infections in cell culture, likely by the selection of rapidly replicating FMDV variants. In this study, fourteen SAT1 and SAT2 viruses, serially passaged in BHK-21 cells, were virulent in CHO-K1 cells and displayed enhanced affinity for heparan, as opposed to their low-passage counterparts. Comparative sequence analysis revealed the fixation of positively charged residues clustered close to the icosahedral 5-fold axes of the virus, at amino acid positions 83-85 in the βD-βE loop and 110-112 in the βF-βG loop of VP1 upon adaptation to cultured cells. Molecular docking simulations confirmed enhanced binding of heparan sulphate to a model of the adapted SAT1 virus, with the region around VP1 arginine 112 contributing the most to binding. Using this information, eight chimeric field strain mutant viruses were constructed with additional positive charges in repeated clusters on the virion surface. Five of these bound heparan sulphate with expanded cell tropism, which should facilitate large-scale propagation. However, only positively charged residues at position 110-112 of VP1 enhanced infectivity of BHK-21 cells. The symmetrical arrangement of even a single amino acid residue in the FMD virion is a powerful strategy enabling the virus to generate novel receptor binding and alternative host-cell interactions.

Conjunctivitis as a Sentinel of SARS-CoV-2 Infection: a Need of Revision for Mild Symptoms

COVID-19 has been declared a pandemic by the World Health Organization on March 11, and since then, more than 3 million cases and a quarter million deaths have occurred due to it. Lately, there is a growing evidence for an ophthalmologic symptom (conjunctivitis) to be connected with the disease. This seems to happen in early stages of the infection by SARS-CoV-2, and thus, it is of major importance to understand the mechanism through which the virus can facilitate such a symptom. Here, we are proposing a molecular mechanism through which the novel coronavirus could act in order to affect the eye and use it as another, secondary but alternative, point of entry to the host organism.

Common characteristics and unique features: A comparison of the fusion machinery of the alphaherpesviruses Pseudorabies virus and Herpes simplex virus

Membrane fusion is a fundamental biological process that allows different cellular compartments delimited by a lipid membrane to release or exchange their respective contents. Similarly, enveloped viruses such as alphaherpesviruses exploit membrane fusion to enter and infect their host cells. For infectious entry the prototypic human Herpes simplex viruses 1 and 2 (HSV-1 and -2, collectively termed HSVs) and the porcine Pseudorabies virus (PrV) utilize four different essential envelope glycoproteins (g): the bona fide fusion protein gB and the regulatory heterodimeric gH/gL complex that constitute the "core fusion machinery" conserved in all members of the Herpesviridae; and the subfamily specific receptor binding protein gD. These four components mediate attachment and fusion of the virion envelope with the host cell plasma membrane through a tightly regulated sequential activation process. Although PrV and the HSVs are closely related and employ the same set of glycoproteins for entry, they show remarkable differences in the requirements for fusion. Whereas the HSVs strictly require all four components for membrane fusion, PrV can mediate cell-cell fusion without gD. Moreover, in contrast to the HSVs, PrV provides a unique opportunity for reversion analyses of gL-negative mutants by serial cell culture passaging, due to a limited cell-cell spread capacity of gL-negative PrV not observed in the HSVs. This allows a more direct analysis of the function of gH/gL during membrane fusion. Unraveling the molecular mechanism of herpesvirus fusion has been a goal of fundamental research for years, and yet important mechanistic details remain to be uncovered. Nevertheless, the elucidation of the crystal structures of all key players involved in PrV and HSV membrane fusion, coupled with a wealth of functional data, has shed some light on this complex puzzle. In this review, we summarize and discuss the contemporary knowledge on the molecular mechanism of entry and membrane fusion utilized by the alphaherpesvirus PrV, and highlight similarities but also remarkable differences in the requirements for fusion between PrV and the HSVs.

Multivalent Flexible Nanogels Exhibit Broad-Spectrum Antiviral Activity by Blocking Virus Entry

The entry process of viruses into host cells is complex and involves stable but transient multivalent interactions with different cell surface receptors. The initial contact of several viruses begins with attachment to heparan sulfate (HS) proteoglycans on the cell surface, which results in a cascade of events that end up with virus entry. The development of antiviral agents based on multivalent interactions to shield virus particles and block initial interactions with cellular receptors has attracted attention in antiviral research. Here, we designed nanogels with different degrees of flexibility based on dendritic polyglycerol sulfate to mimic cellular HS. The designed nanogels are nontoxic and broad-spectrum, can multivalently interact with viral glycoproteins, shield virus surfaces, and efficiently block infection. We also visualized virus-nanogel interactions as well as the uptake of nanogels by the cells through clathrin-mediated endocytosis using confocal microscopy. As many human viruses attach to the cells through HS moieties, we introduce our flexible nanogels as robust inhibitors for these viruses.

Initial Contact: The First Steps in Herpesvirus Entry

The entry process of herpesviruses into host cells is complex and highly variable. It involves a sequence of well-orchestrated events that begin with virus attachment to glycan-containing proteinaceous structures on the cell surface. This initial contact tethers virus particles to the cell surface and results in a cascade of molecular interactions, including the tight interaction of viral envelope glycoproteins to specific cell receptors. These interactions trigger intracellular signaling and finally virus penetration after fusion of the viral envelope with cellular membranes. Based on the engaged cellular receptors and co-receptors, and the subsequent signaling cascades, the entry pathway will be decided on the spot. A number of viral glycoproteins and many cellular receptors and molecules have been identified as players in one or several of these events during virus entry. This chapter will review viral glycoproteins, cellular receptors and signaling cascades associated with the very first interactions of herpesviruses with their target cells.

Polyvalent 2D Entry Inhibitors for Pseudorabies and African Swine Fever Virus

African swine fever virus (ASFV) is one of the most dangerous viruses for pigs and is endemic in Africa but recently also spread into the Russian Federation and the Eastern border of the EU. So far there is no vaccine or antiviral drug available to curtail the infection. Thus, control strategies based on novel inhibitors are urgently needed. Another highly relevant virus infection in pigs is Aujeszky's disease caused by the alphaherpesvirus pseudorabies virus (PrV). This article reports the synthesis and biological evaluation of novel extracellular matrix-inspired entry inhibitors based on polyglycerol sulfate-functionalized graphene sheets. The developed 2D architectures bind enveloped viruses during the adhesion process and thereby exhibit strong inhibitory effects, which are equal or better than the common standards enrofloxacin and heparin as demonstrated for ASFV and PrV. Overall, the developed polyvalent 2D entry inhibitors are nontoxic and efficient nanoarchitectures, which interact with various types of enveloped viruses. Therefore they prevent viral adhesion to the host cell and especially target viruses that rely on a heparan sulfate-dependent cell entry mechanism.

A high-temperature passaging attenuated Pseudorabies vaccine protects piglets completely against emerging PRV variant

Emerging variant of pseudorabies virus (PRV) have evaded the antiviral immunity of commercially available PRV vaccine and have led to PRV outbreaks in Chinese pig farms. Here, we attenuated a PRV variant strain by serial passages in vitro and evaluate the protective efficacy of the attenuated strain as a vaccine candidate. The virulent PRV variant strain JS-2012 was continuously passaged in Vero cells at 40°C and attenuated rapidly. After 90 passages in Vero cells, the passaged virus lost its ability to cause death in 2-week-old piglets. The 120th passage virus was avirulent in the sucking piglets. An attenuated strain, JS-2012-F120 derived from the 120th passage virus by three rounds of plaque cloning grew better than its parent strain JS-2012 in Vero cells and showed notably different cytopathic effects and plaque morphology from JS-2012. PCR combined with sequence analysis showed that JS-2012-F120 contained a 2307-bp deletion covering nucleotide 487 of gE gene to 531 of US2 gene. After inoculation with JS-2012-F120, young piglets were completely protected from challenge with the classical and emerging virulent PRVs. Moreover, the piglets did not develop specific gE antibodies. Thus, JS-2012-F120 appears to be a promising marker vaccine to control PRV variant circulating in Chinese pig farms, and the high-temperature passaging in vitro was an efficient method to attenuated alphaherpesvirus.

Varicella-Zoster Virus Glycoproteins: Entry, Replication, and Pathogenesis

Varicella-zoster virus (VZV), an alphaherpesvirus that causes chicken pox (varicella) and shingles (herpes zoster), is a medically important pathogen that causes considerable morbidity and, on occasion, mortality in immunocompromised patients. Herpes zoster can afflict the elderly with a debilitating condition, postherpetic neuralgia, triggering severe, untreatable pain for months or years. The lipid envelope of VZV, similar to all herpesviruses, contains numerous glycoproteins required for replication and pathogenesis.

PURPOSE OF REVIEW

To summarize the current knowledge about VZV glycoproteins and their roles in cell entry, replication and pathogenesis.

RECENT FINDINGS

The functions for some VZV glycoproteins are known, such as gB, gH and gL in membrane fusion, cell-cell fusion regulation, and receptor binding properties. However, the molecular mechanisms that trigger or mediate VZV glycoproteins remains poorly understood.

SUMMARY

VZV glycoproteins are central to successful replication but their modus operandi during replication and pathogenesis remain elusive requiring further mechanistic based studies.

Functional Characterization of Glycoprotein H Chimeras Composed of Conserved Domains of the Pseudorabies Virus and Herpes Simplex Virus 1 Homologs

Membrane fusion is indispensable for entry of enveloped viruses into host cells. The conserved core fusion machinery of the Herpesviridae consists of glycoprotein B (gB) and the gH/gL complex. Recently, crystal structures of gH/gL of herpes simplex virus 2 (HSV-2) and Epstein-Barr virus and of a core fragment of pseudorabies virus (PrV) gH identified four structurally conserved gH domains. To investigate functional conservation, chimeric genes encoding combinations of individual domains of PrV and herpes simplex virus 1 (HSV-1) gH were expressed in rabbit kidney cells, and their processing and transport to the cell surface, as well as activity in fusion assays including gB, gD, and gL of PrV or HSV-1, were analyzed. Chimeric gH containing domain I of HSV-1 and domains II to IV of PrV exhibited limited fusion activity in the presence of PrV gB and gD and HSV-1 gL, but not of PrV gL. More strikingly, chimeric gH consisting of PrV domains I to III and HSV-1 domain IV exhibited considerable fusion activity together with PrV gB, gD, and gL. Replacing PrV gB with the HSV-1 protein significantly enhanced this activity. A cell line stably expressing this chimeric gH supported replication of gH-deleted PrV. Our results confirm the specificity of domain I for gL binding, demonstrate functional conservation of domain IV in two alphaherpesviruses from different genera, and indicate species-specific interactions of this domain with gB. They also suggest that gH domains II and III might form a structural and functional unit which does not tolerate major substitutions.

IMPORTANCE

Envelope glycoprotein H (gH) is essential for herpesvirus-induced membrane fusion, which is required for host cell entry and viral spread. Although gH is structurally conserved within the Herpesviridae, its precise role and its interactions with other components of the viral fusion machinery are not fully understood. Chimeric proteins containing domains of gH proteins from different herpesviruses can serve as tools to elucidate the molecular basis of gH function. The present study shows that the C-terminal part of human herpesvirus 1 (herpes simplex virus 1) gH can functionally substitute for the corresponding part of suid herpesvirus 1 (pseudorabies virus) gH, whereas other tested combinations proved to be nonfunctional. Interestingly, the exchangeable fragment included the membrane-proximal end of the gH ectodomain (domain IV), which is most conserved in sequence and structure and might be capable of transient membrane interaction during fusion.

A 2,5-Dihydroxybenzoic Acid-Gelatin Conjugate: The Synthesis, Antiviral Activity and Mechanism of Antiviral Action Against Two Alphaherpesviruses

Various natural and synthetic polyanionic polymers with different chemical structures are known to exhibit potent antiviral activity in vitro toward a variety of enveloped viruses and may be considered as promising therapeutic agents. A water-soluble conjugate of 2,5-dihydroxybezoic acid (2,5-DHBA) with gelatin was synthesized by laccase-catalyzed oxidation of 2,5-DHBA in the presence of gelatin, and its antiviral activity against pseudorabies virus (PRV) and bovine herpesvirus type 1 (BoHV-1), two members of the Alphaherpesvirinae subfamily, was studied. The conjugate produced no direct cytotoxic effect on cells, and did not inhibit cell growth at concentrations up to 1000 µg/mL. It exhibited potent antiviral activity against PRV (IC50, 1.5-15 µg/mL for different virus strains) and BoHV-1 (IC50, 0.5-0.7 µg/mL). When present during virus adsorption, the conjugate strongly inhibited the attachment of PRV and BoHV-1 to cells. The 2,5-DHBA-gelatin conjugate had no direct virucidal effect on the viruses and did not influence their penetration into cells, cell-to-cell spread, production of infectious virus particles in cells, and expression of PRV glycoproteins E and B. The results indicated that the 2,5-DHBA-gelatin conjugate strongly inhibits the adsorption of alphaherpesviruses to cells and can be a promising synthetic polymer for the development of antiviral formulations against alphaherpesvirus infections.

DSTP-27 prevents entry of human cytomegalovirus

Human cytomegalovirus (HCMV) can cause life-threatening diseases in neonates and immunocompromised patients. Due to multiple problems caused by the current available drugs, development of new antiviral compounds is urgently needed. In this study, we characterize the anti-HCMV spectrum and mechanism of action of the N-N'-(bis-5 nitropyrimidyl)dispirotripiperazine derivate 27 (DSTP-27). DSTP-27 exhibited strong antiviral activity against two laboratory HCMV strains with different cell tropism as well as ganciclovir (GCV)-sensitive and GCV-resistant clinical isolates in plaque reduction assays and viral growth kinetics experiments. Interestingly, neither infectious nor noninfectious viral particles were observed by electron microscopy. Pretreatment of cell-free virus with DSTP-27 prevented virus infection. The results from time of addition assays, in which DTSP-27 was added to cells (i) before infection, (ii) during virus adsorption, or (iii) after adsorption, demonstrated an inhibitory effect on early steps of the HCMV replication cycle. This observation was confirmed by immunofluorescence as well as Western blot analysis, whereby reduced levels of the immediate early protein IE1, the processivity factor pUL44, and the tegument protein pp28 were detected. Results from attachment and penetration analyses of prechilled human embryonic lung fibroblasts revealed that virus attachment is not blocked. In addition, DSTP-27 inactivated HCMV by stable binding. Taken together, these results demonstrate that DSTP-27 (i) blocks viral penetration by interacting with the host cell and (ii) inactivates HCMV by interacting with the virus.

Directional spread of alphaherpesviruses in the nervous system

Alphaherpesviruses are pathogens that invade the nervous systems of their mammalian hosts. Directional spread of infection in the nervous system is a key component of the viral lifecycle and is critical for the onset of alphaherpesvirus-related diseases. Many alphaherpesvirus infections originate at peripheral sites, such as epithelial tissues, and then enter neurons of the peripheral nervous system (PNS), where lifelong latency is established. Following reactivation from latency and assembly of new viral particles, the infection typically spreads back out towards the periphery. These spread events result in the characteristic lesions (cold sores) commonly associated with herpes simplex virus (HSV) and herpes zoster (shingles) associated with varicella zoster virus (VZV). Occasionally, the infection spreads transsynaptically from the PNS into higher order neurons of the central nervous system (CNS). Spread of infection into the CNS, while rarer in natural hosts, often results in severe consequences, including death. In this review, we discuss the viral and cellular mechanisms that govern directional spread of infection in the nervous system. We focus on the molecular events that mediate long distance directional transport of viral particles in neurons during entry and egress.

Felid herpesvirus type 1 infection in cats: a natural host model for alphaherpesvirus pathogenesis

Feline herpesvirus 1 (FeHV-1) is an alphaherpesvirus that causes feline viral rhinotracheitis, an important viral disease of cats on a worldwide basis. Acute FeHV-1 infection is associated with both upper respiratory and ocular signs. Following the acute phase of the disease lifelong latency is established, primarily in sensory neuronal cells. As is the case with human herpes simplex viruses, latency reactivation can result in recrudescence, which can manifest itself in the form of serious ocular lesions. FeHV-1 infection in cats is a natural host model that is useful for the identification of viral virulence genes that play a role in replication at the mucosal portals of entry or are mediators of the establishment, maintenance, or reactivation of latency. It is also a model system for defining innate and adaptive immunity mechanisms and for immunization strategies that can lead to better protection against this and other alphaherpesvirus infections.

Proteomic characterization of pseudorabies virus extracellular virions

Pseudorabies virus (PRV), a member of the Alphaherpesvirinae, has a complex multilayered extracellular virion that is structurally conserved among other herpesviruses. PRV virions contain a double-stranded DNA genome within a proteinaceous capsid surrounded by the tegument, a layer of viral and cellular proteins. The envelope layer, which encloses the capsid and tegument, contains viral transmembrane proteins anchored in a phospholipid bilayer. The viral and host proteins contained within virions execute important functions during viral spread and pathogenesis, but a detailed understanding of the composition of PRV virions has been lacking. In this report, we present the first comprehensive proteomic characterization of purified PRV virions by mass spectrometry using two complementary approaches. To exclude proteins present in the extracellular medium that may nonspecifically associate with virions, we also analyzed virions treated with proteinase K and samples prepared from mock-infected cells. Overall, we identified 47 viral proteins associated with PRV virions, 40 of which were previously localized to the capsid, tegument, and envelope layers using traditional biochemical approaches. Additionally, we identified seven viral proteins that were previously undetected in virions, including pUL8, pUL20, pUL32, pUL40 (RR2), pUL42, pUL50 (dUTPase), and Rsp40/ICP22. Furthermore, although we did not enrich for posttranslational modifications, we detected phosphorylation of four virion proteins: pUL26, pUL36, pUL46, and pUL48. Finally, we identified 48 host proteins associated with PRV virions, many of which have known functions in important cellular pathways such as intracellular signaling, mRNA translation and processing, cytoskeletal dynamics, and membrane organization. This analysis extends previous work aimed at determining the composition of herpesvirus virions and provides novel insights critical for understanding the mechanisms underlying PRV entry, assembly, egress, spread, and pathogenesis.

Equine herpesvirus 4: recent advances using BAC technology

The equine herpesviruses are major infectious pathogens that threaten equine health. Equine herpesvirus 4 (EHV-4) is an important equine pathogen that causes respiratory tract disease, known as rhinopneumonitis, among horses worldwide. EHV-4 genome manipulation with subsequent understanding of the viral gene functions has always been difficult due to the limited number of susceptible cell lines and the absence of small-animal models of the infection. Efficient generation of mutants of EHV-4 would significantly contribute to the rapid and accurate characterization of the viral genes. This problem has been solved recently by the cloning of the genome of EHV-4 as a stable and infectious bacterial artificial chromosome (BAC) without any deletions of the viral genes. Very low copy BAC vectors are the mainstay of present genomic research because of the high stability of inserted clones and the possibility of mutating any gene target in a relatively short time. Manipulation of EHV-4 genome is now feasible using the power of BAC technology, and should aid greatly in assessing the role of viral genes in the virus-host interaction.

Fusion protein consisting of the first immunoglobulin-like domain of porcine nectin-1 and Fc portion of human IgG1 provides a marked resistance against pseudorabies virus infection to transgenic mice

Nectin-1 is a Ca2+-independent Ig-like cell-cell adhesion molecule and an alphaherpesvirus receptor that binds to virion glycoprotein D by the first Ig-like domain. We have investigated the antiviral potentials of soluble forms of porcine nectin-1 to PRV infection by generating transgenic mice expressing different types of fusion protein. Previously, we reported that mice transgenic for a chimera that carried the entire ectodomain of porcine nectin-1 fused to the Fc portion of porcine IgG1 were more resistant than those transgenic for a chimera that carried the first Ig-like domain fused to the Fc portion. Recently, we generated transgenic mice expressing a fusion protein made of the first Ig-like domain fused to the Fc portion of human IgG1, and reported that they showed a microphthalmia. Here, two transgenic mouse lines expressing the fusion protein were challenged with PRV for comparing their resistances with those of transgenic mice expressing different types of fusion protein. Surprisingly, both transgenic mouse lines showed a high resistance to the viral infection, especially via the i.n. route. Significant resistance of the embryonic fibroblasts was also observed. Altogether, these findings indicated that the fusion protein consisting of the first Ig-like domain fused to the human Fc portion provided a marked resistance against PRV infection to the transgenic mice.

Spinal cord injury reduces the efficacy of pseudorabies virus labeling of sympathetic preganglionic neurons

The retrograde transsynaptic tracer pseudorabies virus (PRV) is used as a marker for synaptic connectivity in the spinal cord. Using PRV, we sought to document putative synaptic plasticity below a high thoracic (T) spinal cord transection. This lesion has been linked to the development of a number of debilitating conditions, including autonomic dysreflexia. Two weeks after injury, complete T4-transected and/or T4-hemisected and sham rats were injected with PRV-expressing enhanced green fluorescent protein (EGFP) or monomeric red fluorescent protein (mRFP1) into the kidneys. We expected greater PRV labeling after injury because of the plasticity of spinal circuitry, but 96 hours post-PRV-EGFP inoculation, we found fewer EGFP+ cells in the thoracolumbar gray matter of T4-transected compared with sham rats (p < 0.01); Western blot analysis corroborated decreased EGFP protein levels (p < 0.01). Moreover, viral glycoproteins that are critical for cell adsorption and entry were also reduced in the thoracolumbar spinal cord of injured versus sham rats (p < 0.01). Pseudorabies virus labeling of sympathetic postganglionic neurons in the celiac ganglia innervating the kidneys was also significantly reduced in injured versus sham rats (p < 0.01). By contrast, the numbers and distribution of Fluoro-Gold-labeled (intraperitoneal injection) sympathetic preganglionic neurons throughout the sampled regions appeared similar in injured and sham rats. These results question whether spinal cord injury exclusively retards PRV expression and/or transport or whether this injury broadly affects host cell-viral interactions.

Comparison of the antiviral potentials among the pseudorabies-resistant transgenes encoding different soluble forms of porcine nectin-1 in transgenic mice

Nectin-1 is an alphaherpesvirus receptor that binds to virion glycoprotein D by the first immunoglobulin (Ig)-like domain. The possibility of making animals resistant to pseudorabies virus (PRV) infection has been investigated by generating transgenic mice expressing soluble forms of porcine nectin-1. Previously, transgenic mice were generated that expressed a fusion protein made of the entire ectodomain of nectin-1 fused to the Fc portion of human IgG, or the first Ig-like domain fused to the Fc portion of porcine IgG. Here, the contribution of the second and third Ig-like domains of nectin-1 was analysed by generating transgenic mice expressing the entire ectodomain of nectin-1 fused to the porcine Fc portion. Transgenic mice expressing each of three different fusion proteins were challenged with PRV for comparison of their resistance. Altogether, mice transgenic for a chimera that carried the entire ectodomain were more resistant than those transgenic for a chimera that carried the first Ig-like domain.

Cell biological and molecular characteristics of pseudorabies virus infections in cell cultures and in pigs with emphasis on the respiratory tract

In the present review, several cell biological and molecular aspects of virus-cell and virus-host (pig) interactions are reviewed for pseudorabies (Aujeszky's disease) virus. Concerning the virus-cell interactions, the complex cascade of events in the virus replication cycle is given together with the different mechanisms of cell-to-cell spread. The pathogenesis of pseudorabies virus infections in pigs is concentrated on the sequence of events in the respiratory tract. Finally, a short overview is given on the control of the disease and eradication of the virus by the combination of marker vaccines and discriminating ELISA.

Expression of nectin-1 in normal and herpes simplex virus type 1-infected murine brain

Nectin-1 is an adherens junction protein that serves as an entry receptor for neurotropic herpes simplex virus (HSV). The expression of nectin-1 in the central nervous system (CNS) has not been well defined. Furthermore, it is not known whether HSV infection has an effect on nectin-1 expression in the brain. To better understand nectin-1 expression in normal and HSV-infected brain, the authors used immunohistochemistry to characterize the expression of nectin-1 in brain tissue of uninfected adult mice and mice infected with HSV-1. In the CNS of untreated and mock-infected mice, virtually all neurons, ependymal cells, choroid plexus epithelial cells, meningothelial cells, and vascular endothelial cells expressed nectin-1. Many oligodendrocytes, astrocytes, and vascular smooth muscle cells also demonstrated nectin-1 expression, but a minority of these cells did not stain for nectin-1. Brain tissue derived from mice euthanized 5 to 8 days after intracerebral inoculation of HSV-1 showed inflammation and widespread expression of HSV-1 proteins in neurons. In HSV-1-infected brains, many inflammatory cells showed nectin-1 expression and neuronal nectin-1 staining showed a wider variation in signal strength than that detected in uninfected tissues. Many neurons showing nuclear fragmentation consistent with the morphologic appearance of apoptosis showed little or no evidence of nectin-1 expression, whereas occasional neurons stained more intensely positive for nectin-1 than those in uninfected brain tissue. These findings confirm and extend previous observations of nectin-1 expression in the nervous system and suggest that HSV-1 infection leads to changes in nectin-1 expression in the CNS, which may contribute to HSV-induced pathology and dissemination.

Comparison of protection levels against pseudorabies virus infection of transgenic mice expressing a soluble form of porcine nectin-1/HveC and vaccinated mice

We recently generated transgenic mice expressing a soluble form of porcine nectin-1 (PHveCIg) showing remarkable resistance to pseudorabies virus (PRV) infection. Nectin-1, also known as herpesvirus entry mediator C (HveC), is an alphaherpesvirus receptor that binds to virion glycoprotein D (gD). In order to evaluate the level of resistance to PRV infection induced by the expression of PHveCIg in the transgenic mice, the protective effects of vaccinated and transgenic mice were directly compared. Mice were immunized with a live vaccine, through intraperitoneal injection of PRV strain Begonia (an attenuated vaccine strain deleted for gE and thymidine kinase genes) at 4 weeks before challenge. The vaccinated and transgenic mice were challenged with 10LD(50), 20LD(50) or 50LD(50) of PRV strainYS-81 via intranasal route. In the vaccinated mice, no protection was observed in the challenges with 20LD(50) and 50LD(50). Only two out of six vaccinated mice survived in the challenge with 10LD(50). In contrast, four transgenic mouse lines showed significant resistance to PRV infection, although the survival rates varied in the challenge with each viral dose. These results demonstrate clearly the high potential of transgenic strategy in control of pseudorabies.

Porcine circovirus 2 uses heparan sulfate and chondroitin sulfate B glycosaminoglycans as receptors for its attachment to host cells

Monocyte/macrophage lineage cells are target cells in vivo for porcine circovirus 2 (PCV2) replication. The porcine monocytic cell line 3D4/31 supports PCV2 replication in vitro, and attachment and internalization kinetics of PCV2 have been established in these cells. However, PCV2 receptors remain unknown. Glycosaminoglycans (GAG) are used by several viruses as receptors. The present study examined the role of GAG in attachment and infection of PCV2. Heparin, heparan sulfate (HS), chondroitin sulfate B (CS-B), but not CS-A, and keratan sulfate reduced PCV2 infection when these GAG were incubated with PCV2 prior to and during inoculation of 3D4/31 cells. Enzymatic removal of HS and CS-B prior to PCV2 inoculation of 3D4/31 cells significantly reduced PCV2 infection. Similarly, when PCV2 virus-like particles (VLP) were allowed to bind onto 3D4/31 cells in the presence of heparin and CS-B, attachment was strongly reduced. Titration of field isolates and low- and high-passage laboratory strains of PCV2 in the presence of heparin significantly reduced PCV2 titers, showing that the capacity of PCV2 to bind GAG was not acquired during in vitro cultivation but is an intrinsic feature of wild-type virus. When Chinese hamster ovary (CHO) cells were inoculated with PCV2, relative percentages of PCV2-infected cells were 27% +/- 8% for HS-deficient and 12% +/- 10% for GAG-deficient cells compared to wild-type cells (100%). Furthermore, it was shown using heparin-Sepharose chromatography that both PCV2 and PCV2 VLP directly interacted with heparin. Together, these results show that HS and CS-B are attachment receptors for PCV2.

The first immunoglobulin-like domain of porcine nectin-1 is sufficient to confer resistance to pseudorabies virus infection in transgenic mice

Nectin-1 is an alphaherpesvirus receptor that binds to virion glycoprotein D (gD). Porcine nectin-1 mediates entry of pseudorabies virus (PRV), herpes simplex virus types 1 and 2 (HSV-1 and HSV-2), and bovine herpesvirus type 1 (BHV-1). The gD-binding domain of nectin-1 is the first or N-terminal immunoglobulin (Ig)-like domain of the entire ectodomain. Here, we generated three transgenic mouse lines expressing a fusion protein consisting of the first Ig-like domain of porcine nectin-1 and the Fc portion of porcine IgG1 to assess the antiviral potential of the first Ig-like domain of nectin-1 in vivo. All of the transgenic mouse lines showed significant resistance to PRV infection via intraperitoneal inoculation (survival rates of 67% to 100%). In the intranasal challenge, a lower but still significant protection was observed; 21% to 55% of the animals from the three transgenic mouse lines survived. The present results demonstrate that a soluble form of the first domain of porcine nectin-1 is able to exert a significant antiviral effect against pseudorabies virus infection.

Entry of pseudorabies virus: an immunogold-labeling study

Herpesviruses infect cells by fusion of the viral envelope with cellular membranes, primarily the plasma membrane. During this process structural components of the mature virion are lost from the invading nucleocapsid, which then travels along microtubules to the nuclear pore. We examined the penetration process by immunoelectron microscopy and analyzed which of the major tegument proteins remained associated with the incoming capsid. We show that the UL36, UL37, and US3 proteins were present at intracytoplasmic capsids after penetration, whereas the UL11, UL47, UL48, and UL49 tegument proteins were lost. Thus, the three capsid-associated tegument proteins are prime candidates for viral proteins that interact with cellular motor proteins for transport of nucleocapsids to the nucleus.

Transgenic mice expressing a soluble form of porcine nectin-1/herpesvirus entry mediator C as a model for pseudorabies-resistant livestock

An approach to genetically engineered resistance to pseudorabies virus (PRV) infection was examined by using a transgene encoding a soluble form of nectin-1, also known as herpesvirus entry mediator C. Nectin-1 is an alpha-herpesvirus receptor that binds to virion glycoprotein D. Nectin-1 mediates entry of PRV, herpes simplex virus types 1 and 2, and bovine herpesvirus type 1. To assess the antiviral potential of an ectopic expression of the nectin-1 ectodomain in vivo, six transgenic mouse lines expressing a soluble form of nectin-1, consisting of an extracellular domain of porcine nectin-1 and the Fc portion of human IgG1, were generated. All of the transgenic mouse lines showed nearly complete resistance to PRV infection by means of both i.p. and intranasal routes. These results suggest that the introduction into farm animals of a transgene encoding a soluble form of nectin-1 would offer a potent biological approach to generating alpha-herpesvirus-resistant livestock.

A novel strategy for defining critical amino acid residues involved in protein/glycosaminoglycan interactions

The binding of proteins to glycosaminoglycans (GAGs) is the prerequisite for a large number of cellular processes and regulatory events and is associated to many pathologies. However, progress in the understanding of these mechanisms has been hampered by the lack of simple and comprehensive analytical tools for the identification of the structural attributes involved in protein/saccharide interaction. Characterization of GAG binding motifs on proteins has so far relied on site-directed mutagenesis studies, protein sequence mapping using synthetic peptides, molecular modeling, or structural analysis. Here, we report the development of a novel approach for identifying protein residues involved in the binding to heparin, the archetypal member of the GAG family. This method, which uses native proteins, is based on the formation of cross-linked complexes of the protein of interest with heparin beads, the proteolytic digestion of these complexes, and the subsequent identification of the heparin binding containing peptides by N terminus sequencing. Analysis of the CC chemokine regulated on activation, normal T-cell expressed, and secreted (RANTES), the envelope glycoprotein gC from pseudorabies virus and the laminin-5 alpha 3LG4/5 domain validated the techniques and provided novel information on the heparin binding motifs present within these proteins. Our results highlighted this method as a fast and valuable alternative to existing approaches. Application of this technique should greatly contribute to facilitate the structural study of protein/GAG interactions and the understanding of their biological functions.

A synthetic peptide from a heptad repeat region of herpesvirus glycoprotein B inhibits virus replication

Glycoprotein B (gB) is the most conserved glycoprotein of herpesviruses and plays important roles in virus infectivity. Two intervening heptad repeat (HR) sequences were found in the C-terminal half of all herpesvirus gBs analysed. A synthetic peptide derived from the HR region (aa 477-510) of bovine herpesvirus type 1 (BoHV-1) gB was studied for its ability to inhibit virus replication. The peptide interfered with cell-to-cell spread and consistently inhibited replication of BoHV-1, with a 50 % effective concentration value (EC(50)) of 5 microM. Inhibition of replication was obtained not only with herpesviruses including pseudorabies virus and herpes simplex virus type 1 but also partly with Newcastle disease virus. Possible mechanisms of membrane fusion inhibition by the peptide are discussed.

Heparan sulphate mediates swine vesicular disease virus attachment to the host cell

Heparan sulphate (HS) has been found to serve as receptor for initial cell binding of numerous viruses. Different glycosaminoglycans (GAGs), including heparin and HS, were analysed for their ability to bind swine vesicular disease virus (SVDV), a picornavirus with close homology to human coxsackie B5 virus. Binding of SVDV was established by heparin-affinity chromatography. In addition, infection of IB-RS-2 epithelial porcine cells was inhibited by treating the virus with soluble HS, heparin, and chondroitin sulphate B (CS-B), as well as by enzymic digestion of cell surface GAGs. Analysis of the infection course showed that SVDV uses cellular HS for its binding to the cell surface and that this interaction occurs during attachment of the virus, prior to its internalization into the cell. Sequence analysis of SVDV variants selected for their lack of sensitivity to heparin inhibition in vitro led to the identification of two residues (A2135V and I1266K) potentially involved in heparin/HS interaction. The location of these residues in a three-dimensional model shows that they are clustered in a well-exposed region of the capsid, providing a physical mechanism that could account for the heparin-binding phenotype.

Enhanced resistance to herpes simplex virus type 1 infection in transgenic mice expressing a soluble form of herpesvirus entry mediator

Herpesvirus entry mediator (HVEM) is a member of the tumor necrosis factor (TNF) receptor family used as a cellular receptor by virion glycoprotein D (gD) of herpes simplex virus (HSV). Both human and mouse forms of HVEM can mediate entry of HSV-1 but have no entry activity for pseudorabies virus (PRV). To assess the antiviral potential of HVEM in vivo, three transgenic mouse lines expressing a soluble form of HVEM (HVEMIg) consisting of an extracellular domain of murine HVEM and the Fc portion of human IgG1 were generated. All of the transgenic mouse lines showed marked resistance to HSV-1 infection when the mice were challenged intraperitoneally with HSV-1, but not to PRV infection. The present results demonstrate that HVEMIg is able to exert a significant antiviral effect against HSV-1 infection in vivo.

Evolution of cell recognition by viruses: a source of biological novelty with medical implications

The picture beginning to form from genome analyses of viruses, unicellular organisms, and multicellular organisms is that viruses have shared functional modules with cells. A process of coevolution has probably involved exchanges of genetic information between cells and viruses for long evolutionary periods. From this point of view present-day viruses show flexibility in receptor usage and a capacity to alter through mutation their receptor recognition specificity. It is possible that for the complex DNA viruses, due to a likely limited tolerance to generalized high mutation rates, modifications in receptor specificity will be less frequent than for RNA viruses, albeit with similar biological consequences once they occur. It is found that different receptors, or allelic forms of one receptor, may be used with different efficiency and receptor affinities are probably modified by mutation and selection. Receptor abundance and its affinity for a virus may modulate not only the efficiency of infection, but also the capacity of the virus to diffuse toward other sites of the organism. The chapter concludes that receptors may be shared by different, unrelated viruses and that one virus may use several receptors and may expand its receptor specificity in ways that, at present, are largely unpredictable.

Rise and survival of bovine herpesvirus 1 recombinants after primary infection and reactivation from latency

Recombination is thought to be an important source of genetic variation in herpesviruses. Several studies, performed in vitro or in vivo, detected recombinant viruses after the coinoculation of two distinguishable strains of the same herpesvirus species. However, none of these studies investigated the evolution of the relative proportions of parental versus recombinant progeny populations after coinoculation of the natural host, both during the excretion and the reexcretion period. In the present study, we address this by studying the infection of cattle with bovine herpesvirus 1 (BoHV-1). The recombination of two BoHV-1 mutants lacking either glycoprotein C (gC(-)/gE(+)) or E (gC(+)/gE(-)) was investigated after inoculation of cattle by the natural route of infection. The results demonstrated that (i) recombination is a frequent event in vivo since recombinants (gC(+)/gE(+) and gC(-)/gE(-)) were detected in all coinoculated calves, (ii) relative proportions of progeny populations evolved during the excretion period toward a situation where two populations (gC(+)/gE(+) and gC(-)/gE(+)) predominated without fully outcompeting the presence of the two other detected populations (gC(+)/gE(-) and gC(-)/gE(-)), and (iii) after reactivation from latency, no gC(+)/gE(-) and gC(-)/gE(-) progeny viruses were detected, although gC(+)/gE(-) mutants, when inoculated alone, were detected after reactivation treatment. In view of these data, the importance of gE in the biology of BoHV-1 infection and the role of recombination in herpesvirus evolution are discussed.

Antiviral activity of lactoferrin against canine herpesvirus

Lactoferrin (LF) is an iron-binding protein that is found in milk and other mammalian secretions. We found that bovine lactoferrin (bLF) inhibited both the in vitro infection and replication of canine herpesvirus (CHV) in Madin-Darby canine kidney (MDCK) cells. Incubation of CHV with bLF prevented subsequent infection of MDCK cells. Furthermore, proteins from CHV-infected MDCK cells were resolved by SDS-PAGE, and then bLF CHV-binding proteins were identified by far Western blotting. We demonstrated that the anti-CHV activity of bLF was due to its interaction with CHV as well as with MDCK cells. Both the apo- and holo-forms of bLF inhibited virus multiplication independently of their iron-withholding properties. We also demonstrated that human LF had anti-CHV activity. Our findings suggest that LF could be effective in dogs to provide protection against CHV infection.

Binding of a N,N'-bisheteryl derivative of dispirotripiperazine to heparan sulfate residues on the cell surface specifically prevents infection of viruses from different families

N,N'-bisheteryl derivatives of dispirotripiperazine (DSTP) are a novel class of antiviral compounds with some of their representatives very effectively inhibiting the replication of herpes simplex virus type 1 (HSV-1) in cell culture. Using one representative of these compounds, the N,N'-bis(1-oxido[1,2,5]oxadiazolo[3,4-d]pyrimidin-7-yl)-3,12-diaza-6,9-diazonia(5,2,5,2)dispirohexadecane dichloride (DSTP 27), we here further tried to elucidate the molecular mechanisms responsible for the antiviral activity. The results from plaque reduction assays under a variety of conditions suggest that inhibition of HSV-1 strain Kupka replication by DSTP 27 occurs at the level of viral attachment by blockade of heparan sulfate (HS) structures on the cell surface that are used as viral receptors. In contrast to heparin and pentosan polysulfate, pretreatment of cells with DSTP 27 resulted in efficient inhibition of viral adsorption and replication persisting several hours after removal of the inhibitor. Specific binding of DSTP 27 to heparin was demonstrated in vitro. Titrations of gC-positive and gC-negative pseudorabies virus (PrV) mutants on HS-positive and HS-negative cell lines confirmed that inhibitory action of DSTP 27 is strictly HS dependent. Aside from HSV-1 Kupka and PrV, DSTP 27 efficiently inhibits growth of several HSV-1 and HSV-2 strains, among them aciclovir/foscarnet-resistant strains, human cytomegalovirus, human respiratory syncytial virus, and human immunodeficiency viruses known to attach to the cell surface via HS.

A role for glycoprotein C in pseudorabies virus entry that is independent of virus attachment to heparan sulfate and which involves the actin cytoskeleton

Glycoprotein C (gC) of pseudorabies virus, a swine herpesvirus, initiates virus attachment by binding to heparan sulfate (HS) linked to proteoglycans (HSPGs) on the cell surface. This interaction facilitates a required step in virus entry, the binding to a non-HS coreceptor, likely by another viral glycoprotein, gD. We demonstrate that gC has an even more direct role in virus entry than simply promoting adhesion strengthening. A porcine cell line expressing gC trans-complemented the penetration, but not attachment, defect of gC null mutants. In addition, gC promoted the colocalization of cell surface HSPGs and the actin cytoskeleton, suggesting a role for filamentous actin in virus entry. This was supported by results showing that both the engagement of a non-HS coreceptor and entry events subsequent to coreceptor binding were impaired if cells were first treated with an actin depolymerizing agent, cytochalasin D. Our results suggest a model in which gC-HS interactions promote not only virus attachment but also virus entry by usurping the normal properties of HSPGs.