Antigenic variation of varicella zoster virus Fc receptor gE: loss of a major B cell epitope in the ectodomain

Personalized viral genomic investigation of herpes simplex virus 1 perinatal viremic transmission with dual fatality

Here we present a personalized viral genomics approach to investigating a rare case of perinatal herpes simplex virus 1 (HSV-1) transmission that ended in death of both mother and neonate. We sought to determine whether the virus involved in this rare case had any unusual features that may have contributed to the dire patient outcome. A pregnant woman with negative HerpeSelect antibody test underwent cesarean section at 30 wk gestation and died the same day. The premature newborn died 5 d later. Both individuals were found postmortem to have positive blood HSV-1 PCR tests. Using oligonucleotide enrichment and deep sequencing, we determined that viral transmission from mother to infant was nearly perfect at the consensus genome level. At the virus population level, 77% of minor variants (MVs) in the mother's blood also appeared on the neonate's skin, of which more than half were disseminated into the neonate's blood. We also detected nonmaternal MVs that arose de novo in the neonate's viral populations. Of note, one de novo MV in the neonate's skin virus induced a nonsynonymous mutation in the UL6 protein, which is a component of the portal that allows DNA entry into new progeny capsids. This case suggests that perinatal viremic HSV-1 transmission includes the majority of genetic diversity from the maternal virus population and that new, nonsynonymous mutations can occur after relatively few rounds of replication. This report expands our understanding of viral transmission in humans and may lead to improved diagnostic strategies for neonatal HSV-1 acquisition.

Escaping the immune system by DNA repair and recombination in African trypanosomes

African trypanosomes escape the mammalian immune response by antigenic variation-the periodic exchange of one surface coat protein, in Trypanosoma brucei the variant surface glycoprotein (VSG), for an immunologically distinct one. VSG transcription is monoallelic, with only one VSG being expressed at a time from a specialized locus, known as an expression site. VSG switching is a predominantly recombination-driven process that allows VSG sequences to be recombined into the active expression site either replacing the currently active VSG or generating a 'new' VSG by segmental gene conversion. In this review, we describe what is known about the factors that influence this process, focusing specifically on DNA repair and recombination.

Recombinant Glycoprotein E of Varicella Zoster Virus Contains Glycan-Peptide Motifs That Modulate B Cell Epitopes into Discrete Immunological Signatures

A recombinant subunit vaccine (Shingrix^®) was recently licensed for use against herpes zoster. This vaccine is based on glycoprotein E (gE) of varicella zoster virus (VZV), the most abundantly expressed protein of VZV, harboring sites for N- and O-linked glycosylation. The subunit vaccine elicits stronger virus-specific CD4+ T cell response as well as antibody B cell response to gE, compared to the currently used live attenuated vaccine (Zostavax^®). This situation is at variance with the current notion since a live vaccine, causing an active virus infection, should be far more efficient than a subunit vaccine based on only one single viral glycoprotein. We previously found gE to be heavily glycosylated, not least by numerous clustered O-linked glycans, when it was produced in human fibroblasts. However, in contrast to Zostavax^®, which is produced in fibroblasts, the recombinant gE of Shingrix^® is expressed in Chinese hamster ovary (CHO) cells. Hence, the glycan occupancy and glycan structures of gE may differ considerably between the two vaccine types. Here, we aimed at (i) defining the glycan structures and positions of recombinant gE and (ii) identifying possible features of the recombinant gE O-glycosylation pattern contributing to the vaccine efficacy of Shingrix^®. Firstly, recombinant gE produced in CHO cells (“Shingrix situation”) is more scarcely decorated by O-linked glycans than gE from human fibroblasts (“Zostavax situation”), with respect to glycan site occupancy. Secondly, screening of immunodominant B cell epitopes of gE, using a synthetic peptide library against serum samples from VZV-seropositive individuals, revealed that the O-linked glycan signature promoted binding of IgG antibodies via a decreased number of interfering O-linked glycans, but also via specific O-linked glycans enhancing antibody binding. These findings may, in part, explain the higher protective efficacy of Shingrix^®, and can also be of relevance for development of subunit vaccines to other enveloped viruses.

Identification of Herpes Zoster-Associated Temporal Arteritis Among Cases of Giant Cell Arteritis

PURPOSE

To examine whether herpes zoster antigen (also called varicellazoster virus antigen) was detectable in temporal artery biopsies taken from individuals with giant cell arteritis (GCA).

DESIGN

Retrospective comparative case series.

METHODS

Sections of formalin-fixed paraffin-embedded temporal arteries were examined first by hematoxylin-eosin (H&E) staining to establish the diagnosis of GCA. Adjacent sections of the same biopsy were then examined by immunohistochemistry, using 2 different monoclonal antibodies against a major antigen of varicella-zoster virus called gE. Pathologic specimens were obtained from patients cared for at the University of Iowa and Washington University in St. Louis ophthalmology clinics.

RESULTS

The study included biopsies from 25 patients with symptoms of GCA as well as positive H&E pathology and 25 patients with symptoms compatible with GCA but negative H&E pathology. Among the GCA-positive group, 3 patients had positive staining for herpes zoster antigen. Among the GCA-negative group, herpes zoster antigen was not detected in any biopsy. In both groups of patients, false-positive staining for herpes zoster antigen was detected in the presence of calcifications in the arteries. False-positive staining was also detected on some extra-arterial skeletal muscle and erythrocytes.

CONCLUSION

Herpes zoster antigen was detected in 3 of 25 temporal arteries from patients with biopsy-proven GCA. One of the 3 positive cases was noteworthy because the patient had had herpes zoster ophthalmicus diagnosed 3 weeks before the onset of GCA symptoms. False-positive staining for herpes zoster antigen was detected on several temporal artery biopsies.

Herpes Simplex Virus and Varicella-Zoster Virus

The most common specimens from immunocompromised patients that are analyzed for detection of herpes simplex virus (HSV) or varicella-zoster virus (VZV) are from skin lesions. Many types of assays are applicable to these samples, but some, such as virus isolation and direct fluorescent antibody testing, are useful only in the early phases of the lesions. In contrast, nucleic acid (NA) detection methods, which generally have superior sensitivity and specificity, can be applied to skin lesions at any stage of progression. NA methods are also the best choice, and sometimes the only choice, for detecting HSV or VZV in blood, cerebrospinal fluid, aqueous or vitreous humor, and from mucosal surfaces. NA methods provide the best performance when reliability and speed (within 24 hours) are considered together. They readily distinguish the type of HSV detected or the source of VZV detected (wild type or vaccine strain). Nucleic acid detection methods are constantly being improved with respect to speed and ease of performance. Broader applications are under study, such as the use of quantitative results of viral load for prognosis and to assess the efficacy of antiviral therapy.

Exocytosis of Varicella-Zoster Virus Virions Involves a Convergence of Endosomal and Autophagy Pathways

Varicella-zoster virus (VZV) is an extremely cell-associated herpesvirus with limited egress of viral particles. The induction of autophagy in VZV-infected monolayers is easily detectable; inhibition of autophagy leads to decreased VZV glycoprotein biosynthesis and diminished viral titers. To explain how autophagic flux could exert a proviral effect on the VZV infectious cycle, we postulated that the VZV exocytosis pathway following secondary envelopment may converge with the autophagy pathway. This hypothesis depended on known similarities between VZV gE and autophagy-related (Atg) Atg9/Atg16L1 trafficking pathways. Investigations were carried out with highly purified fractions of VZV virions. When the virion fraction was tested for the presence of autophagy and endosomal proteins, microtubule-associated protein 1 light chain (MAP1LC3B) and Ras-like GTPase 11 (Rab11) were detected. By two-dimensional (2D) and 3D imaging after immunolabeling, both proteins also colocalized with VZV gE in a proportion of cytoplasmic vesicles. When purified VZV virions were enumerated after immunoelectron microscopy, gold beads were detected on viruses following incubation with antibodies to VZV gE (∼100%), Rab11 (50%), and LC3B (30%). Examination of numerous electron micrographs demonstrated that enveloped virions were housed in single-membraned vesicles; viral particles were not observed in autophagosomes. Taken together, our data suggested that some viral particles after secondary envelopment accumulated in a heterogeneous population of single-membraned vesicular compartments, which were decorated with components from both the endocytic pathway (Rab11) and the autophagy pathway (LC3B). The latter cytoplasmic viral vesicles resembled an amphisome.

IMPORTANCE

VZV infection leads to increased autophagic flux, while inhibition of autophagy leads to a marked reduction in virus spread. In this investigation of the proviral role of autophagy, we found evidence for an intersection of viral exocytosis and autophagy pathways. Specifically, both LC3-II and Rab11 proteins copurified with some infectious VZV particles. The results suggested that a subpopulation of VZV particles were carried to the cell surface in single-walled vesicles with attributes of an amphisome, an organelle formed from the fusion of an endosome and an autophagosome. Our results also addressed the interpretation of autophagy/xenophagy results with mutated herpes simplex virus lacking its ICP34.5 neurovirulence gene (HSVΔ34.5). The VZV genome lacks an ICP34.5 ortholog, yet we found no evidence of VZV particles housed in a double-membraned autophagosome. In other words, xenophagy, a degradative process documented after infection with HSVΔ34.5, was not observed in VZV-infected cells.

A highly conserved epitope-vaccine candidate against varicella-zoster virus induces neutralizing antibodies in mice

Varicella-zoster virus (VZV) is a highly infectious agent of varicella and herpes zoster (HZ). Vaccination is by far the most effective way to prevent these diseases. More safe, stable and efficient vaccines, such as epitope-based vaccines, now have been increasingly investigated by many researchers. However, only a few VZV neutralizing epitopes have been identified to date. We have previously identified a linear epitope between amino acid residues 121 and 135 of gE. In this study, we validated that this epitope is highly conserved amongst different VZV strains that covered five existing phylogenetic clades with an identity of 100%. We evaluated the immunogenicity of the recombinant hepatitis B virus core (HBc) virus-like particles (VLPs) which included amino acids (121-135). VZV-gE-specific antibodies were detected in immunized mouse serum using ELISA. The anti-peptide antiserum positively detected VZV via Western blot and immunofluorescent staining assays. More importantly, these peptides could neutralize VZV, indicating that these peptides represented neutralizing epitopes. These findings have important implications for the development of epitope-based protective VZV vaccines.

Post-mortem diagnosis, of cytomegalovirus and varicella zoster virus co-infection by combined histology and tissue molecular biology, in a sudden unexplained infant death

BACKGROUND

An autopsy case of a two-month-old male infant who suddenly and unexpectedly died during his sleep, eight days after the onset of benign varicella.

OBJECTIVES

To describe post-mortem combined histological and tissue molecular biological techniques for the diagnosis of cytomegalovirus and varicella zoster virus co-infection as a cause of death.

STUDY DESIGN

Real-time quantitative PCR and RT-PCR assays for Herpesviruses, respiratory viruses, Adenovirus, Enterovirus and Parvovirus B19 were performed on multi-organ frozen samples and paraffin-embedded tissues in combination with histology.

RESULTS

Cytomegalovirus and varicella zoster virus were detected by molecular biology with highest viral loads detected in the lungs (4.6×10(7) and 1.9×10(5) genome copies per million of cells, respectively). Pulmonary extensive necrotizing inflammation and immunohistochemistry correlated to virological data. Virological molecular biology was negative on paraffin-embedded tissues.

CONCLUSIONS

This case shows that thorough quantitative virological investigations on frozen tissues must be performed in combination with histology and immunohistochemistry for the determination of the cause of a sudden unexplained infant death.

Genetic analysis of clinical VZV isolates collected in China reveals a more homologous profile

Forty-four varicella-zoster virus (VZV) isolates from China were genotyped by using a scattered single nucleotide polymorphism (SNP) method, including open reading frames (ORFs) 1, 22, 31, 37, 60, 62, 67, and 68. Based on the analysis of the polymorphic markers in the 8 ORFs, all of the 44 isolates can be placed in genotype J defined by the SNP profiles in ORF22 or clade B defined by the SNP profiles in ORFs 31, 37, 60, 62, 67, and 68. The three consecutive nucleotide (CGG) in-frame insertions in ORF 1 were found in 8 (18.2%) isolates, which has not been described in VZV strains from any other part of the world. A novel synonymous A>G substitution in ORF60 was revealed in 4 (9.1%) of the isolates. In addition, a previously described three consecutive nucleotide (ATC) insertion in ORF 60 was found in all the Chinese isolates but not in the US isolate MLS. The results showed all the 44 strains that belong to genotype J/clade B with significantly high homogeneity, and phylogenetic analysis suggested that the 44 Chinese isolates consist of 4 clusters, but interstrain variations also exist. Overall, VZV isolates obtained in China showed significantly higher genetic homogeneity than isolates reported from other countries.

Bioinformatics of varicella-zoster virus: single nucleotide polymorphisms define clades and attenuated vaccine genotypes

Varicella zoster virus (VZV) is one of the human herpesviruses. To date, over 40 complete VZV genomes have been sequenced and analyzed. The VZV genome contains around 125,000 base pairs including 70 open reading frames (ORFs). Enumeration of single nucleotide polymorphisms (SNPs) has determined that the following ORFs are the most variable (in descending order): 62, 22, 29, 28, 37, 21, 54, 31, 1 and 55. ORF 62 is the major immediate early regulatory VZV gene. Further SNP analysis across the entire genome has led to the observation that VZV strains can be broadly grouped into clades within a phylogenetic tree. VZV strains collected in Singapore provided important sequence data for construction of the phylogenetic tree. Currently five VZV clades are recognized; they have been designated clades 1 through 5. Clades 1 and 3 include European/North American strains; clade 2 includes Asian strains, especially from Japan; and clade 5 includes strains from India. Clade 4 includes some strains from Europe, but its geographic origins need further documentation. Within clade 1, five variant viruses have been isolated with a missense mutation in the gE (ORF 68) glycoprotein; these strains have an altered increased cell spread phenotype. Bioinformatics analyses of the attenuated vaccine strains have also been performed, with a subsequent discovery of a stop-codon SNP in ORFO as a likely attenuation determinant. Taken together, these VZV bioinformatics analyses have provided enormous insights into VZV phylogenetics as well as VZV SNPs associated with attenuation.

Pangaea and the Out-of-Africa Model of Varicella-Zoster Virus Evolution and Phylogeography

The goal of this minireview is to provide an overview of varicella-zoster virus (VZV) phylogenetics and phylogeography when placed in the broad context of geologic time. Planet Earth was formed over 4 billion years ago, and the supercontinent Pangaea coalesced around 400 million years ago (mya). Based on detailed tree-building models, the base of the phylogenetic tree of the Herpesviridae family has been estimated at 400 mya. Subsequently, Pangaea split into Laurasia and Gondwanaland; in turn, Africa rifted from Gondwanaland. Based on available data, the hypothesis of this minireview is that the ancestral alphaherpesvirus VZV coevolved in simians, apes, and hominins in Africa. When anatomically modern humans first crossed over the Red Sea 60,000 years ago, VZV was carried along in their dorsal root ganglia. Currently, there are five VZV clades, distinguishable by single nucleotide polymorphisms. These clades likely represent continued VZV coevolution, as humans with latent VZV infection left Arabia and dispersed into Asia (clades 2 and 5) and Europe (clades 1, 3, and 4). The prototype VZV sequence contains nearly 125,000 bp, divided into 70 open reading frames. Generally, isolates within a clade display >99.9% identity to one another, while members of one clade compared to a second clade show 99.8% identity to one another. Recently, four different VZV genotypes that do not segregate into the previously defined five clades have been identified, a result indicating a wider than anticipated diversity among newly collected VZV strains around the world.

Sequence analysis of the glycoprotein E gene of varicella-zoster virus strains of clades 1, 3 and 5

Eighty-six varicella-zoster virus (VZV) strains of clades 1, 3 and 5, isolated from varicella and zoster patients in Germany, were analyzed by sequencing the glycoprotein E gene. Four novel non-synonymous and 10 novel synonymous mutations were detected. Of these, two synonymous (C513T, C885T) and two non-synonymous mutations (T485G, C524T) were located within the coding regions of e1 and c1. The profile of single-nucleotide polymorphisms was found to be significantly associated with the VZV clades 1, 3 and 5.

Regulation of the expression of the varicella-zoster virus open reading frame 66 gene

The varicella-zoster virus (VZV) open reading frame (ORF) 66 encodes a serine/threonine kinase that phosphorylates the major viral transactivator protein, immediate-early (IE) 62, preventing its nuclear importation. Cytoplasmic sequestration of IE62 may alter viral gene transcription and could serve as a mechanism for maintaining VZV latency. We examined the regulation of expression of the ORF66 gene by mapping the promoter region, which was localized to within 150 bases of the start codon. The ORF66 promoter was activated by two viral regulatory proteins, IE62 and IE63. We evaluated the binding of viral regulatory proteins and cellular transcription factors based on recognized cellular transcription factor binding sites identified within the ORF66 promoter. These included Sp1 and TBP binding sites, several of which were essential for optimal promoter activity. Site-directed mutations in Sp1 and TBP binding sites led to varying degrees of impairment of ORF66 gene expression in the context of VZV infection. We also examined the effect of Sp1 and TBP mutations on IE62, Sp1, and TBP binding. These studies reveal that host cell-derived and viral factors contribute to and cooperate in the expression of this important viral kinase gene.

VZV molecular epidemiology

The molecular epidemiology of varicella zoster virus (VZV) has led to an understanding of virus evolution, spread, and pathogenesis. The availability of over 20 full length genomes has confirmed the existence of at least five virus clades and generated estimates of VZV evolution, with evidence of recombination both past and ongoing. Genotyping by restriction enzyme analysis (REA) and single nucleotide polymorphisms (SNP) has proven that the virus causing varicella is identical to that which later reactivates as zoster in an individual. Moreover, these methods have shown that reinfection, which is mostly asymptomatic, may also occur and the second virus may establish latency and reactivate. VZV is the only human herpesvirus that is spread by the respiratory route. Genotyping methods, together with epidemiological data and modeling, have provided insights into global differences in the transmission patterns of this ubiquitous virus.

VZV ORF47 serine protein kinase and its viral substrates

ORF47, a serine protein kinase of varicella-zoster virus (VZV) and homolog of herpes simplex virus UL13, is an interesting modulator of VZV pathogenesis. This chapter summarizes research showing that ORF47 protein kinase activity, by virtue of phosphorylation of or binding to various viral substrates, regulates VZV proteins during all phases of viral infection and has a pronounced effect on the trafficking of gE, the predominant VZV glycoprotein, which in turn is critical for cell-to-cell spread of the virus. Casein kinase II, an ubiquitous cellular protein kinase, recognizes a similar but less stringent phosphorylation consensus sequence and can partially compensate for lack of ORF47 activity in VZV-infected cells. Differences between the phosphorylation consensus sites of the viral and cellular kinases are outlined in detail.

Insulin-degrading enzyme binds to the nonglycosylated precursor of varicella-zoster virus gE protein found in the endoplasmic reticulum

Insulin degradation enzyme (IDE) is a 110-kDa zinc metalloprotease found in the cytosol of all cells. IDE degrades insulin and a variety of small proteins including amyloid-beta. Recently, IDE has been proposed as the receptor for varicella-zoster virus (VZV) attachment. During our reassessment, some of the original studies were repeated and expanded in scope. We first confirmed that IDE antibody reduced VZV spread. For additional controls, we repeated the same experiments with herpes simplex virus (HSV)-infected cells as well as uninfected cells. There was a visible reduction in HSV spread but less than seen in the VZV system. Of greater importance, IDE antibody also inhibited the growth of uninfected cells. Second, we repeated the coprecipitation assays. We confirmed that antibodies to VZV gE (open reading frame 68) coprecipitated IDE and that anti-IDE antibody coprecipitated gE. However, the detected gE protein was not the mature 98-kDa form; rather, it was a precursor 73-kDa gE form found in the endoplasmic reticulum. Additional control experiments included VZV-infected cell cultures treated with tunicamycin to block gE glycosylation in the endoplasmic reticulum; again, the anti-IDE antibody coprecipitated a 73-kDa gE product. Finally, Orbitrap mass spectrometry analysis of a chromatographically purified gE sample revealed four cellular proteins associated with the unfolded protein response: BiP (HSPA5), HSPA8, HSPD1, and PPIA (peptidyl-propyl cis-trans isomerase). We conclude that IDE protease binds to the 73-kDa gE precursor and that this event occurs in the cytosol but not as a receptor/ligand interaction.

Egress of light particles among filopodia on the surface of Varicella-Zoster virus-infected cells

Varicella-zoster virus (VZV) is renowned for its very low titer when grown in cultured cells. There remains no single explanation for the low infectivity. In this study, viral particles on the surfaces of infected cells were examined by several imaging technologies. Few surface particles were detected at 48 h postinfection (hpi), but numerous particles were observed at 72 and 96 hpi. At 72 hpi, 75% of the particles resembled light (L) particles, i.e., envelopes without capsids. By 96 hpi, 85% of all particles resembled L particles. Subsequently, the envelopes of complete virions and L particles were investigated to determine their glycoprotein constituents. Glycoproteins gE, gI, and gB were detected in the envelopes of both types of particles in similar numbers; i.e., there appeared to be no difference in the glycoprotein content of the L particles. The viral particles emerged onto the cell surface amid actin-based filopodia, which were present in abundance within viral highways. Viral particles were easily detected at the base of and along the exterior surfaces of the filopodia. VZV particles were not detected within filopodia. In short, these results demonstrate that VZV infection of cultured cells produces a larger proportion of aberrant coreless particles than has been seen with any other previously examined alphaherpesvirus. Further, these results suggested a major disassociation between capsid formation and envelopment as an explanation for the invariably low VZV titer in cultured cells.

Novel varicella-zoster virus glycoprotein E gene mutations associated with genotypes A and D

Here, we describe the association of certain varicella-zoster virus (VZV) genotypes with unique glycoprotein E (gE) gene mutations. Within 45 analyzed VZV wild-type strains of genotypes A and D, five novel gE mutations were discovered. A statistically significant (P < 0.0001) association of certain gE mutations with VZV genotype D was found.

The varicella-zoster virus (VZV) ORF9 protein interacts with the IE62 major VZV transactivator

The varicella-zoster virus (VZV) ORF9 protein is a member of the herpesvirus UL49 gene family but shares limited identity and similarity with the UL49 prototype, herpes simplex virus type 1 VP22. ORF9 mRNA is the most abundantly expressed message during VZV infection; however, little is known concerning the functions of the ORF9 protein. We have found that the VZV major transactivator IE62 and the ORF9 protein can be coprecipitated from infected cells. Yeast two-hybrid analysis localized the region of the ORF9 protein required for interaction with IE62 to the middle third of the protein encompassing amino acids 117 to 186. Protein pull-down assays with GST-IE62 fusion proteins containing N-terminal IE62 sequences showed that amino acids 1 to 43 of the acidic transcriptional activation domain of IE62 can bind recombinant ORF9 protein. Confocal microscopy of transiently transfected cells showed that in the absence of other viral proteins, the ORF9 protein was localized in the cytoplasm while IE62 was localized in the nucleus. In VZV-infected cells, the ORF9 protein was localized to the cytoplasm whereas IE62 exhibited both nuclear and cytoplasmic localization. Cotransfection of plasmids expressing ORF9, IE62, and the viral ORF66 kinase resulted in significant colocalization of ORF9 and IE62 in the cytoplasm. Coimmunoprecipitation experiments with antitubulin antibodies indicate the presence of ORF9-IE62-tubulin complexes in infected cells. Colocalization of ORF9 and tubulin in transfected cells was visualized by confocal microscopy. These data suggest a model for ORF9 protein function involving complex formation with IE62 and possibly other tegument proteins in the cytoplasm at late times in infection.

Genomic cartography of varicella-zoster virus: a complete genome-based analysis of strain variability with implications for attenuation and phenotypic differences

In order to gain a better perspective on the true variability of varicella-zoster virus (VZV) and to catalogue the location and number of differences, 11 new complete genome sequences were compared with those previously in the public domain (18 complete genomes in total). Three of the newly sequenced genomes were derived from a single strain in order to assess variations that can occur during serial passage in cell culture. The analysis revealed that while VZV is relatively stable genetically it does posses a certain degree of variability. The reiteration regions, origins of replication and intergenic homopolymer regions were all found to be variable between strains as well as within a given strain. In addition, the terminal viral sequences were found to vary within and between strains specifically at the 3' end of the genome. Analysis of single nucleotide polymorphisms (SNPs) identified a total of 557 variable sites, 451 of which were found in coding regions and resulted in 187 different in amino acid substitutions. A comparison of the SNPs present in the two gE mutant strains, VZV-MSP and VZV-BC, suggested that the missense mutation in gE was primarily responsible for the accelerated cell spread phenotype. Some of the variations noted with high passage in cell culture are consistent with variations seen in the IE62 gene of the vaccine strains (S628G, R958G and I1260V) that may help in pinpointing variations essential for attenuation. Although VZV has been considered to be one of the most genetically stable human herpesviruses, this initial assessment of genomic VZV cartography provides insight into ORFs with previously unreported variations.

Delayed biosynthesis of varicella-zoster virus glycoprotein C: upregulation by hexamethylene bisacetamide and retinoic acid treatment of infected cells

In the course of examining the trafficking pathways of varicella-zoster virus (VZV) glycoproteins gE, gI, gH, and gB, we discovered that all four are synthesized within 4 to 6 h postinfection (hpi) in cultured cells. Thereafter, they travel via the trans-Golgi network to the outer cell membrane. When we carried out a similar analysis on VZV gC, we observed little gC biosynthesis in the first 72 hpi. Further examination disclosed that gC was present in the inocula of infected cells, but no new gC biosynthesis occurred during the first 24 to 48 h thereafter, during which time new synthesis of gE, gH, and major capsid protein was easily detectable. Similarly, delayed gC biosynthesis was confirmed with three different VZV strains and two different cell lines. Bioinformatics analyses disclosed the presence of PBX/HOX consensus binding domains in the promoter/enhancer regions of the genes for VZV gC and ORF4 protein (whose orthologs transactivate gC in other herpesviruses). Bioinformatics analysis also identified two HOXA9 activation regions on ORF4 protein. Treatment of infected cultures with chemicals known to induce the production of PBX/HOX transcription proteins, namely, hexamethylene bisacetamide (HMBA) and retinoic acid, led to more rapid gC biosynthesis. Immunoblotting demonstrated a fivefold increase in the HOXA9 protein after HMBA treatment. In summary, these results documented that gC was not produced during early VZV replication cycles, presumably related to a deficiency in the PBX/HOX transcription factors. Furthermore, these results explain the apparent spontaneous loss of VZV gC in some passaged viruses, as well as other anomalous gC results.

A novel mutation of varicella-zoster virus associated to fatal hepatitis

BACKGROUND

Lethal varicella in immunocompetent hosts is rare and its pathogenesis is largely unknown. The discovery of glycoprotein E (gE) mutants showing attributes consistent with increased virulence in vitro and in animal models, provided a possible molecular mechanism underlying a more aggressive virus infection. However, these mutants have never been associated with unusually severe clinical cases.

OBJECTIVES

To varicella-zoster virus (VZV) mutations that correlate with increased virulence.

RESULTS

We report a case of fatal hepatitis caused by a VZV bearing a novel mutation on the 3B3 monoclonal antibody epitope of gE in an immunocompetent host.

CONCLUSIONS

This report describes a mutant VZV responsible for an aggressive clinical course in an immunocompetent host. Linking these severe clinical presentations of VZV infection to virus mutations might provide insights into the underlying pathogenic mechanisms.

Molecular studies of Varicella zoster virus

VZV is a highly cell-associated member of the Herpesviridae family and one of the eight herpesviruses to infect humans. The virus is ubiquitous in most populations worldwide, primary infection with which causes varicella, more commonly known as chickenpox. Characteristic of members of the alphaherpesvirus sub-family, VZV is neurotropic and establishes latency in sensory neurones. Reactivation from latency, usually during periods of impaired cellular immunity, causes herpes zoster (shingles). Despite being one of the most genetically stable human herpesviruses, nucleotide alterations in the virus genome have been used to classify VZV strains from different geographical regions into distinct clades. Such studies have also provided evidence that, despite pre-existing immunity to VZV, subclinical reinfection and reactivation of reinfecting strains to cause zoster is also occurring. During both primary infection and reactivation, VZV infects several PBMC and skin cell lineages. Difficulties in studying the pathogenesis of VZV because of its high cell association and narrow host range have been overcome through the development of the VZV severe combined immunodeficient mouse model carrying human tissue implants. This model has provided a valuable tool for studying the importance of individual viral proteins during both the complex intracellular replication and assembly of new virions and for understanding the underlying mechanism of attenuation of the live varicella vaccine. In addition, a rat model has been developed and successfully used to uncover which viral proteins are important for both the establishment and maintenance of latent VZV infection.

A novel varicella-zoster virus gE mutation discovered in two Swedish isolates

BACKGROUND

Two VZV glycoprotein E (gE D150N) mutant strains were collected in North America in 1995 and in 1999. We now report a novel VZV gE mutant virus discovered in Europe in two VZV strains collected in Stockholm, Sweden, in 1990 and 1999.

OBJECTIVES

To characterize the two isolates identified among a total of 634 VZV isolates collected over a 15-year period at the Karolinska University Hospital.

STUDY DESIGN

VZV genes were amplified by polymerase chain reaction and their sequences were compared to the genomic sequence of VZV-Dumas prototype strain.

RESULTS

A mutation within the gE gene in an epitope recognized by the 3B3 monoclonal antibody was identified in both isolates. A different residue was changed (R152S) compared to the North American strains (D150N).

CONCLUSIONS

The occurrence of a VZV gE mutant virus is unusual, but probably a recurring event in Europe and North America. It is unknown whether widespread varicella vaccination programs will alter the rate at which these mutant viruses are isolated.

Case report: occupationally related recurrent varicella (chickenpox) in a hospital nurse

Commonly accepted outcomes of varicella-zoster virus (VZV) infections include chickenpox (primary) and shingles (recurrence or latency), as well lifetime immunity against chickenpox. We report the case of a registered nurse who worked in a neurologic surgery ward in a general hospital in Taipei, Taiwan. While working there for approximately 1 year, she developed recurrent chickenpox after caring for a paraparesis patient, who had herpes zoster during hospitalization in August 2002. The varicella incubation period was 10 days, which matched the range (10-21 days). Recently negative specific serum IgM and positive specific serum IgG indicated a past VZV infection. The nurse did not get herpes zoster from the second episode of varicella on 9 August 2002 to 4 April 2005 and is now convalescing. We conclude that occupational VZV hazards exist in the health care environment and suggest testing for VZV antibody and a VZV vaccination program for susceptible health care workers. Key words: chickenpox, indirect fluroscent antibody, occupational exposure, polymerase chain reaction, shingles, Taiwan, varicella-zoster virus.

A Chimeric Antibody to Varicella-Zoster Virus Glycoprotein E

Varicella-Zoster virus (VZV) immune globulin (VZIG) derived from pooled human serum is currently used in immunotherapy of VZV-associated complications of chickenpox and shingles. We developed a mouse-human chimeric antibody against a VZV glycoprotein E (gE) epitope as a safer replacement for VZIG. Variable (V) heavy- and V kappa light-chain exons, derived from an anti-VZV gE antibody secreting mouse hybridoma cell line, were cloned into expression vectors containing an immunoglobulin promoter and enhancer, and human IgG1 or kappa constant (C) region genes. The expression vectors were cotransfected into mouse myeloma cell line (NSO), generating transformants that secreted chimeric human-mouse IgGs. The chimeric and the parent mouse antibody were indistinguishable in their antigen binding specificity. VZV gE chimeric antibody may prove to be a prophylactic antibody that could provide significant advantages over VZIG in having defined specificity, lessened possibility of contamination with viral pathogens, and consistent availability.

Incorporation of three endocytosed varicella-zoster virus glycoproteins, gE, gH, and gB, into the virion envelope

The cytoplasmic tails of all three major varicella-zoster virus (VZV) glycoproteins, gE, gH, and gB, harbor functional tyrosine-based endocytosis motifs that mediate internalization. The aim of the present study was to examine whether endocytosis from the plasma membrane is a cellular route by which VZV glycoproteins are delivered to the final envelopment compartment. In this study, we demonstrated that internalization of the glycoproteins occurred in the first 24 h postinfection but was reduced later in infection. Using surface biotinylation of VZV-infected cells followed by a glutathione cleavage assay, we showed that endocytosis was independent of antibody binding to gE, gH, and gB. Subsequently, with this assay, we demonstrated that biotinylated gE, gH, and gB retrieved from the cell surface were incorporated into nascent virus particles isolated after density gradient sedimentation. To confirm and extend this finding, we repeated the above sedimentation step and specifically detected envelopes decorated with Streptavidin-conjugated gold beads on a majority of complete virions through examination by transmission electron microscopy. In addition, a gE-gI complex and a gE-gH complex were found on the virions. Therefore, the above studies established that VZV subsumed a postendocytosis trafficking pathway as one mechanism by which to deliver viral glycoproteins to the site of virion assembly in the cytoplasm. Furthermore, since a recombinant VZV genome lacking only endocytosis-competent gE cannot replicate, these results supported the conclusion that the endocytosis-envelopment pathway is an essential component of the VZV life cycle.

Complete DNA sequence analyses of the first two varicella-zoster virus glycoprotein E (D150N) mutant viruses found in North America: evolution of genotypes with an accelerated cell spread phenotype

Varicella-zoster virus (VZV) is considered to be one of the most genetically stable of all the herpesviruses. Yet two VZV strains with a D150N missense mutation within the gE glycoprotein were isolated in North America in 1998 and 2002. The mutant strains have an accelerated cell spread phenotype, which distinguishes them from all wild-type and laboratory viruses. Since the VZV genome contains 70 additional open reading frames (ORFs), the possibility existed that the phenotypic change was actually due to an as-yet-undiscovered mutation or deletion elsewhere in the genome. To exclude this hypothesis, the entire genomes of the two mutant viruses were sequenced and found to contain 124,883 (VZV-MSP) and 125,459 (VZV-BC) nucleotides. Coding single-nucleotide polymorphisms (SNPs) were identified in 14 ORFs. One missense mutation was discovered in gH, but none was found in gB, gI, gL, or gK. There were no coding SNPs in the major regulatory protein ORF 62. One polymorphism was discovered which could never have been anticipated based on current knowledge of herpesvirus genomics, namely, the origins of replication differed from those in the prototype strain but not in a manner expected to affect cell spread. When the two complete mutant VZV sequences were surveyed in their entirety, the most reasonable conclusion was that the increased cell spread phenotype was dependent substantially or solely on the single D150N polymorphism in glycoprotein gE. The genomic results also expanded the evolutionary database by identifying which VZV ORFs were more likely to mutate over time.

Wild-type Kaposi's sarcoma-associated herpesvirus isolated from the oropharynx of immune-competent individuals has tropism for cultured oral epithelial cells

Based on the observation that wild-type Kaposi's sarcoma-associated herpesvirus (KSHV) DNA can be detected in the oral cavity of healthy, immunocompetent individuals, we hypothesized that epithelial cells could be infected in vitro by wild-type (WT) KSHV isolated from immunocompetent individuals. Primary oral epithelial (P-EPI) cells and telomerase-immortalized oral epithelial cells were generated from human gingival tissue and were then infected in vitro with WT KSHV isolated from throat wash samples. Markers of lytic and latent KSHV infection were detected in cultures by 24 h postinfection by immunofluorescence confocal microscopic assays. The infectivity of the WT and BCBL virus was blocked by neutralizing antibodies against KSHV gB. The presence of KSHV DNA in these cells was confirmed by real-time PCR amplification of different regions of the viral genome. The significant in vitro viral replication that had occurred was inhibited by ganciclovir and by neutralizing antibodies against gB. When infected cultures were examined by scanning electron microscopy, thousands of KSHV particles were clearly visible across the surfaces of P-EPI cells. The detection of enveloped particles indicated that the infectious cycle had proceeded through assembly and egress. We thus demonstrated that oral WT KSHV isolated from immunocompetent individuals was able to infect and replicate in vitro in a relevant primary cell type. Furthermore, our results provide compelling evidence for KSHV transmission within infected oral epithelial cells derived from healthy, immunocompetent populations.

Regulation of varicella-zoster virus-induced cell-to-cell fusion by the endocytosis-competent glycoproteins gH and gE

The gH glycoprotein of varicella-zoster virus (VZV) is a major fusogen. The realigned short cytoplasmic tail of gH (18 amino acids) harbors a functional endocytosis motif (YNKI) that mediates internalization in both VZV-infected and transfected cells (T. J. Pasieka, L. Maresova, and C. Grose, J. Virol. 77: 4194-4202, 2003). During subsequent confocal microscopy studies of endocytosis-deficient gH mutants, we observed that cells transfected with the gH tail mutants exhibited marked fusion. Therefore, we postulated that VZV gH endocytosis served to regulate cell-to-cell fusion. Subsequent analyses of gH+gL transfection fusion assays by the Kolmogorov-Smirnov statistical test demonstrated that expression of the endocytosis-deficient gH mutants resulted in a statistically significant enhancement of cell-to-cell fusion (P < 0.0001) compared to wild-type gH. On the other hand, coexpression of VZV gE, another endocytosis-competent VZV glycoprotein, was able to temper the fusogenicity of the gH endocytosis mutants by facilitating internalization of the mutant gH protein from the cell surface. When the latter results were similarly analyzed, there was no longer any enhanced fusion by the endocytosis-deficient gH mutant protein. In summary, these studies support a role for gH endocytosis in regulating the cell surface expression of gH and thereby regulating gH-mediated fusion. The data also confirm and extend prior observations of a gE-gH interaction during viral glycoprotein trafficking in a VZV transfection system.

Genetic variation in clinical varicella-zoster virus isolates collected in Ireland between 2002 and 2003

Analysis of genetic variation in 16 varicella-zoster virus (VZV) isolates selected at random and circulating in the Irish population between March 2002 and February 2003 was carried out. A 919 bp fragment of the glycoprotein E gene (open reading frame 68) encompassing codon 150, at which a non-synonymous mutation defines the escape mutant VZV-MSP, and including two other epitope regions e1 and c1, was sequenced. No new single nucleotide polymorphisms (SNPs) were detected, indicating stability of these epitopes in clinical isolates of VZV. However, when four informative polymorphic markers consisting of defined regions from genes 1, 21, 50, and 54 were sequenced 14 variable nucleotide positions were identified. Phylogenetic analysis showed the presence of three highly supported clades A, B, and C circulating in the Irish population. Approximately one third (6/16; 37.5%) of the Irish VZV isolates in this study belonged to genotype C, 4/16 (25%) to genotype A, and 4/16 (25%) to genotype B. A smaller number 2/16 (12.5%) belonged to genotype J1. This indicates remarkable heterogeneity in the Irish population given the small sample size. No evidence was found to suggest any of the 16 isolates was a recombinant. These findings have implications for the model of geographic isolation of VZV clades to certain regions as the circulating Irish VZV population appears to comprise approximately equal numbers of each of the main genotypes. This data is inconsistent with a model of strict geographical separation of VZV genotypes and suggests that VZV diversity is more pronounced in certain areas than had been thought previously.

Are false negative direct immnufluorescence assays caused by varicella zoster virus gE mutant strains?

Strains of Varicella zoster virus (VZV) have been described recently in which a single base mutation in the gE epitope abrogates binding of the 3B3 monoclonal antibody, which is widely used for virus detection in diagnostic laboratories. These strains, named VZV-MSP, are associated with a distinct phenotype in both in vitro culture and in SCID-hu mice. We investigated the possibility that negative direct immunofluorescence results, using the 3B3 antibody, where the presence of virus was confirmed by polymerase chain reaction (PCR) or tissue culture are due in some cases to the MSP strain of VZV. A total of 249 vesicle fluid specimens from people with suspected shingles were examined using direct immunofluorescence, tissue culture and a nested multiplex PCR for VZV, herpes simplex virus type 1 (HSV-1) and 2 (HSV-2). VZV was detected in 218 of 249 (87.6%) cases. Forty-five confirmed VZV specimens, but with negative (30) or indeterminate (15) immunofluorescence results, were analysed further. PCR was used to amplify a fragment in ORF 68 that encodes the VZV gE ectodmain recognised by 3B3 antibody. The fragments were sequenced and analysed for the single base change G448A (D150N), which is present in VZV-MSP as compared with the reference Dumas strain. No VZV gE mutant (MSP/MSP-like) was detected. Overall, PCR was found to be the most sensitive method of confirming VZV infection. False negative VZV immunofluorescence results are unlikely to be due to virus variants.

Genomic analysis of varicella-zoster virus: primers for individual open reading frames

The genome of varicella-zoster virus (VZV) contains nearly 125,000 bp. Preliminary genomic analysis has revealed that VZV may be less immutable than once thought. Through the investigation of the VZV genome using specifically designed oligonucleotides, it has been learned that sequence variation within VZV open reading frame 62 can distinguish between vaccine and wild-type virus. Additionally, the presence of single nucleotide polymorphisms within the VZV genome has identified distinct VZV populations originating from circumscribed geographic locations. In order for future studies of VZV genetic diversity to be carried out, amplifying and sequencing primers for individual VZV genes have been catalogued. Additionally, this report will facilitate the selection of VZV primers by which to distinguish clinical VZV isolates from vaccinia virus isolates.

Membrane fusion mediated by herpesvirus glycoproteins: the paradigm of varicella-zoster virus

Varicella-zoster virus (VZV) is well known for its propensity to cause polykaryons (syncytia) in the vesicles within infected skin. Similarly in cultured cells, VZV induces extensive syncytial formation by virus-mediated cell-to-cell fusion. Statistical analyses of fusion parameters demonstrated three-way interactive effects among all three tested variables (incubation temperature, cell type and virus strain). For example, fusion was greatly enhanced at 33 degrees C vs 37 degrees C; also fusion was pronounced in epidermal cells but negligible in fibroblast cells. As with all herpesviruses, VZV gH was a major fusogen. VZV cell fusion was inhibited by antibody to gH, but surprisingly was enhanced by antibody to gE. Other evidence implicating a role for VZV gE in the fusion process was provided by two mutant viruses, in which gE cell surface expression was enhanced. Under transfection conditions, VZV fusion formation occurred after expression of the gH/gL complex; in contrast, pseudorabies virus requires expression of gH, gL and gB, while the herpes simplex virus (HSV) types 1 and 2 require the quartet of gH, gL, gB and gD. VZV has no gD gene and no apparent gD functional homologue. On the other hand, VZV gE exerts a greater effect than HSV gE on membrane fusion. Taken together, the data in this review suggest that VZV has evolved viral glycoprotein machinery more geared toward cell-to-cell fusion (fusion-from-within) than toward virus-to-cell fusion (entry/fusion-from-without), as a means for syncytium formation within the human epidermis.

Varicella-zoster virus infection facilitates VZV glycoprotein E trafficking to the membrane surface of melanoma cells

Varicella-zoster virus glycoprotein E (gE) is the most abundant VZV glycoprotein on the surface of virus-infected cells. VZV gE has targeting sequences for the trans-Golgi network (TGN) and is transported from the ER to the TGN in infected and gE-transfected cells. In this study, VZV gE expressing melanoma cell lines were generated. gE is expressed under the control of the reverse Tet repressor (Tet-On). gE induced by Tet-On is retained at the ER as well as in the cis Golgi by immunofluorescence confocal microscopy. To test whether other viral protein(s) may facilitate gE trafficking and surface localization, MSPgE-vOka virus that contains MSPgE in place of wt gE was made. MAb 3B3 anti-gE does not bind to MSPgE. This MAb was used to track the localization of gE in Met-gE cells post MSPgE-vOka infection. gE became detectable mostly at the TGN and on the cell surface after viral infection. These data indicate that viral proteins facilitate the trafficking and cell surface expression of gE.

Identification of the authentic varicella-zoster virus gB (gene 31) initiating methionine overlapping the 3' end of gene 30

The varicella-zoster virus (VZV) gB sequence was re-examined in light of recent knowledge about unusually long gB signal peptides in other herpesviral gB homologs. Through mutational analysis, the discovery was made that the authentic initiating methionine for VZV gB is a codon beginning at genome nucleotide 56,819. The total length for the VZV gB primary translation product was 931 amino acids (aa) with a 71-aa signal sequence. Considering the likely signal sequence cleavage site to be located between Ser 71 and Val 72, the length of the mature VZV gB polypeptide would then be 860 amino acids prior to further internal endoproteolytic cleavage between amino acids Arg 494 and Ser 495. In this report, we also produced a full-length gB and demonstrated its association with VZV gE, suggesting a possible gE-gB interaction during gB trafficking before its cleavage in the Golgi.

Comparison of varicella-zoster virus ORF47 protein kinase and casein kinase II and their substrates

ORF47, a serine/threonine protein kinase encoded by varicella-zoster virus (VZV), has often been compared to the ubiquitous cellular kinase, casein kinase II (CKII). However, no direct comparison of the two protein kinases has been carried out. Herein, we show that the ORF47 kinase was resistant to heparin, while CKII activity is profoundly inhibited by the acidic molecule in vitro. ORF47 required the presence of polyamines (aliphatic, positively-charged molecules) for in vitro activity. When polyamines were depleted from MeWo cells prior to VZV infection by pretreatment with D,L-alpha-difluoromethylornithine, VZV replication was reduced by 80%. Finally, the substrate specificity of the ORF47 kinase was defined using an in vitro assay. The ORF47 kinase phosphorylated maltose-binding protein, the mouse IgG2A heavy chain, the rabbit IgG heavy chain, casein, VZV ORF62, and VZV ORF63. The ORF47 kinase failed to phosphorylate an ORF62 truncation mutant, glutathione-S-transferase, or VZV gB. In contrast, CKII weakly phosphorylated VZV gB in vitro. By analyzing the sequences of these substrates, the minimal ORF47 consensus sequence was deduced to be the following motif: S/T-X-D/E-D/E, with a marked preference for additional acidic amino acids in the -1 and +1 position.

A functional YNKI motif in the short cytoplasmic tail of varicella-zoster virus glycoprotein gH mediates clathrin-dependent and antibody-independent endocytosis

The trafficking of varicella-zoster virus (VZV) gH was investigated under both infection and transfection conditions. In initial endocytosis assays performed in infected cells, the three glycoproteins gE, gI, and gB served as positive controls for internalization from the plasma membrane. Subsequently, we discovered that gH in VZV-infected cells was also internalized and followed a similar trafficking pattern. This observation was unexpected because all herpesvirus gH homologues have short endodomains not known to contain trafficking motifs. Further investigation demonstrated that VZV gH, when expressed alone with its chaperone gL, was capable of endocytosis in a clathrin-dependent manner, independent of gE, gI, or gB. Upon inspection of the short gH cytoplasmic tail, we discovered a putative tyrosine-based endocytosis motif (YNKI). When the tyrosine was replaced with an alanine, endocytosis of gH was blocked. Utilizing an endocytosis assay dependent on biotin labeling, we further documented that endocytosis of VZV gH was antibody independent. In control experiments, we showed that gE, gI, and gB also internalized in an antibody-independent manner. Alignment analysis of the VZV gH cytoplasmic tail to other herpesvirus gH homologues revealed two important findings: (i) herpes simplex virus type 1 and 2 homologues lacked an endocytosis motif, while all other alphaherpesvirus gH homologues contained a potential motif, and (ii) the VZV gH and simian varicella virus gH cytoplasmic tails were likely longer in length (18 amino acids) than predicted in the original sequence analyses (12 and 16 amino acids, respectively). The longer tails provided the proper context for a functional endocytosis motif.

The out of Africa model of varicella-zoster virus evolution: single nucleotide polymorphisms and private alleles distinguish Asian clades from European/North American clades

Until 1998, varicella-zoster virus (VZV) was generally considered sufficiently stable to allow the use of a single sequenced virus (VZV-Dumas) as a consensual representation of the world VZV genotype. But recent investigations have uncovered a gE mutant virus called VZV-MSP with a second genotype and a distinguishable accelerated cell spread phenotype. A subsequent study suggested that single nucleotide polymorphisms (SNPs) could be applied toward the genetic analysis of the VZV genome. To further assess the scope of genetic variation in the VZV genome on a worldwide basis, we carried out an extensive SNP analysis of structural glycoprotein genes gB, gE, gH, gI, gL, as well as the IE62 regulatory gene in viruses collected from Western Europe, North America and Asia, including the VZV vaccine strain. The SNP data showed segregation of viral isolates of Asian origin from those of Western ancestry into distinct phylogenetic clades. Unexpectedly, however, VZV from Thailand segregated with VZV from Iceland and the United States, i.e. it was more Western than Asian in nature. Further, SNP analysis disclosed strikingly unusual genotypes, e.g. gH genes with up to five missense mutations and gL genes with insertions of an in-frame methionine codon. In summary, these VZV genomic analyses have shown that individual VZV strains, like closely related human beings, have distinctive SNP profiles containing private alleles within just five VZV genes (gB, gH, gE, gL and IE62) that provide a fingerprint to localize ancestry of the viral strain.

The requirement of varicella zoster virus glycoprotein E (gE) for viral replication and effects of glycoprotein I on gE in melanoma cells

The glycoprotein E (gE) of varicella zoster virus (VZV), encoded by ORF68, is the most abundant viral glycoprotein. In the current experiments, we demonstrated that ORF68 deletion was incompatible with recovery of infectious virus from VZV cosmids. Replacing ORF68 at a nonnative AvrII site in the genome restored infectivity. Further, we found that VZV gE could be expressed under the control of the Tet-On promoter in stably transfected melanoma cell lines (Met-gE cells) without evidence of toxicity. In these Met-gE cells, gE colocalized with gamma-adaptin, a trans Golgi network marker, in perinuclear sites, but did not reach plasma membranes. In order to investigate how infection altered gE localization, we made a recombinant virus, vOka-MSPgE, with ORF68 from the VZV MSP strain. VZV MSP encodes a mutant gE protein (D150N) that lacks the mAb epitope, 3B3 (Santos et al., Virology 275, 306-317, 2000), whereas Met-gE protein binds mAb 3B3. Within 48 h after Met-gE cells were infected with vOka-MSPgE, the steady-state distribution of Met-gE protein extended beyond the perinuclear areas to other cytoplasmic sites and to plasma membranes. A second recombinant, vOka-MSPgE without gI (vOka-MSPgEdeltagI), was constructed to investigate Met-gE protein distribution in the absence of gI. The redistribution of Met-gE protein which was observed by 48 h after vOka-MSPgE infection did not occur until 5 days (140 h) within vOka-MSPgEdeltagI infected cells. After vOka-MSPgE infection of Met-gE cells, most Met-gE protein was in the final 94K mature form by 72 h. However, progression to predominance of mature gE was delayed in Met-gE cells infected with vOka-MSPgEdeltagI. These observations confirm our hypothesis that VZV gE is essential, based upon the demonstration of restored infectivity after replacing ORF68 in a nonnative site in the genome, and provide further evidence of the role of gI in facilitating the maturation and intracellular distribution of this critical VZV glycoprotein.

New variant of varicella-zoster virus

In 1998, a varicella-zoster virus glycoprotein E (gE) mutant virus (VZV-MSP) was isolated from a child with chickenpox. VZV-MSP, representing a second VZV serotype, was considered a rarity. We isolated another VZV-MSP-like virus from an elderly man with herpes zoster. These gE mutant viruses may have arisen through independent mutation or may represent a distinct VZV subpopulation that emerged more than 50 years ago.

Phosphorylation by the varicella-zoster virus ORF47 protein serine kinase determines whether endocytosed viral gE traffics to the trans-Golgi network or recycles to the cell membrane

Like all alphaherpesviruses, varicella-zoster virus (VZV) infection proceeds by both cell-cell spread and virion production. Virions are enveloped within vacuoles located near the trans-Golgi network (TGN), while in cell-cell spread, surface glycoproteins fuse cells into syncytia. In this report, we delineate a potential role for serine/threonine phosphorylation of the cytoplasmic tail of the predominant VZV glycoprotein, gE, in these processes. The fact that VZV gE (formerly called gpI) is phosphorylated has been documented (E. A. Montalvo and C. Grose, Proc. Natl. Acad. Sci. USA 83:8967-8971, 1986), although respective roles of viral and cellular protein kinases have never been delineated. VZV ORF47 is a viral serine protein kinase that recognized a consensus sequence similar to that of casein kinase II (CKII). During open reading frame 47 (ORF47)-specific in vitro kinase assays, ORF47 phosphorylated four residues in the cytoplasmic tail of VZV gE (S593, S595, T596, and T598), thus modifying the known phosphofurin acidic cluster sorting protein 1 domain. CKII phosphorylated gE predominantly on the two threonine residues. In wild-type-virus-infected cells, where ORF47-mediated phosphorylation predominated, gE endocytosed and relocalized to the TGN. In cells infected with a VZV ORF47-null mutant, internalized VZV gE recycled to the plasma membrane and did not localize to the TGN. The mutant virus also formed larger syncytia than the wild-type virus, linking CKII-mediated gE phosphorylation with increased cell-cell spread. Thus, ORF47 and CKII behaved as "team players" in the phosphorylation of VZV gE. Taken together, the results showed that phosphorylation of VZV gE by ORF47 or CKII determined whether VZV infection proceeded toward a pathway likely involved with either virion production or cell-cell spread.

Physical and functional interaction between the varicella zoster virus IE63 and IE62 proteins

The varicella zoster virus (VZV) IE63 protein is required for growth of the virus in cell culture and is expressed during both lytic and latent phases of VZV infection. We have investigated the physical and functional interaction of this protein with the major VZV transactivating protein IE62. The region of the IE63 protein required for interaction with the IE62 protein has been identified and encompasses the N-terminal 142 amino acids. We have found that the interaction is stable at physiological ionic strength. We have also shown that a portion of the IE63 and IE62 proteins colocalize in VZV-infected cells at both 15 and 48 h postinfection. IE63 was found to have no transcriptional activating or repressing activity within the context of a minimal VZV glycoprotein promoter. The presence of the IE63, however, upmodulated the IE62 transactivation of this promoter. Finally, we show that the IE63 protein can be coimmunoprecipitated with the cellular RNA polymerase II from infected cell extracts, indicating that it is present in a complex with that enzyme.

Phylogenetic analysis of varicella-zoster virus: evidence of intercontinental spread of genotypes and recombination

A heteroduplex mobility assay was used to identify variants of varicella-zoster virus circulating in the United Kingdom and elsewhere. Within the United Kingdom, 58 segregating sites were found out of the 23,266 examined (0.25%), and nucleotide diversity was estimated to be 0.00063. These are an order of magnitude smaller than comparable estimates from herpes simplex virus type 1. Sixteen substitutions were nonsynonymous, the majority of which were clustered within surface-expressed proteins. Extensive genetic correlation between widely spaced sites indicated that recombination has been rare. Phylogenetic analysis of varicella-zoster viruses from four continents distinguished at least three major genetic clades. Most geographical regions contained only one of these three strains, apart from the United Kingdom and Brazil, where two or more strains were found. There was minimal genetic differentiation (one or fewer substitutions in 1,895 bases surveyed) between the samples collected from Africa (Guinea Bissau, Zambia) and the Indian subcontinent (Bangladesh, South India), suggesting recent rapid spread and/or low mutation rates. The geographic pattern of strain distribution would favor a major influence of the former. The genetic uniformity of most virus populations makes recombination difficult to detect. However, at least one probable recombinant between two of the major strains was found among the samples originating from Brazil, where mixtures of genotypes co-occur.

Varicella-zoster Virus gB and gE coexpression, but not gB or gE alone, leads to abundant fusion and syncytium formation equivalent to those from gH and gL coexpression

Varicella-zoster virus (VZV) is distinguished from herpes simplex virus type 1 (HSV-1) by the fact that cell-to-cell fusion and syncytium formation require only gH and gL within a transient-expression system. In the HSV system, four glycoproteins, namely, gH, gL, gB, and gD, are required to induce a similar fusogenic event. VZV lacks a gD homologous protein. In this report, the role of VZV gB as a fusogen was investigated and compared to the gH-gL complex. First of all, the VZV gH-gL experiment was repeated under a different set of conditions; namely, gH and gL were cloned into the same vaccinia virus (VV) genome. Surprisingly, the new expression system demonstrated that a recombinant VV-gH+gL construct was even more fusogenic than seen in the prior experiment with two individual expression plasmids containing gH and gL (K. M. Duus and C. Grose, J. Virol. 70:8961-8971, 1996). Recombinant VV expressing VZV gB by itself, however, effected the formation of only small syncytia. When VZV gE and gB genes were cloned into one recombinant VV genome and another fusion assay was performed, extensive syncytium formation was observed. The degree of fusion with VZV gE-gB coexpression was comparable to that observed with VZV gH-gL: in both cases, >80% of the cells in a monolayer were fused. Thus, these studies established that VZV gE-gB coexpression greatly enhanced the fusogenic properties of gB. Control experiments documented that the fusion assay required a balance between the fusogenic potential of the VZV glycoproteins and the fusion-inhibitory effect of the VV infection itself.

Varicella-zoster virus ORF47 protein serine kinase: characterization of a cloned, biologically active phosphotransferase and two viral substrates, ORF62 and ORF63

Varicella-zoster virus (VZV) codes for a protein serine kinase called ORF47; the herpes simplex virus (HSV) homolog is UL13. No recombinant alphaherpesvirus serine kinase has been biologically active in vitro. We discovered that preservation of the intrinsic kinase activity of recombinant VZV ORF47 required unusually stringent in vitro conditions, including physiological concentrations of polyamines. In this assay, ORF47 phosphorylated two VZV regulatory proteins: the ORF62 protein (homolog of HSV ICP4) and the ORF63 protein (homolog of HSV ICP22). Of interest, ORF47 kinase also coprecipitated ORF63 protein from the kinase assay supernatant.

Nucleotide sequence analysis of varicella-zoster virus glycoprotein E epitope coding regions

Varicella-zoster virus (VZV) glycoprotein E [gE] contains 623 amino acid residues. Fifty percent of the gE gene, codons 39 to 344 that encompasses two epitope coding regions e1 and c1, was sequenced and analyzed for variation among the 30 VZV isolates. A total of eleven isolates showed variance when compared with Dumas VZV strain sequence through base substitutions, with two isolates showing an amino acid change of tryptophan to arginine outside the coding regions of the epitopes e1 and c1 that are recognized by monoclonal antibodies 4F9 and c1, respectively. The results suggest that these epitopes were stable in the various VZV isolates. Thus, VZV glycoproteins with conserved epitopes are suitable candidates for both primary and booster vaccines.