Characterization of regulatory functions of the varicella-zoster virus gene 63-encoded protein

Comparative Analysis of the Simian Varicella Virus and Varicella Zoster Virus Genomes

Varicella zoster virus (VZV) and simian varicella virus (SVV) cause varicella (chickenpox) in children and nonhuman primates, respectively. After resolution of acute disease, the viruses establish latent infection in neural ganglia, after which they may reactivate to cause a secondary disease, such as herpes zoster. SVV infection of nonhuman primates provides a model to investigate VZV pathogenesis and antiviral strategies. The VZV and SVV genomes are similar in size and structure and share 70–75% DNA homology. SVV and VZV DNAs are co-linear in gene arrangement with the exception of the left end of the viral genomes. Viral gene expression is regulated into immediate early, early, and late transcription during in vitro and in vivo infection. During viral latency, VZV and SVV gene expression is limited to transcription of a viral latency-associated transcript (VLT). VZV and SVV are closely related alphaherpesviruses that likely arose from an ancestral varicella virus that evolved through cospeciation into species-specific viruses.

ICP22/IE63 Mediated Transcriptional Regulation and Immune Evasion: Two Important Survival Strategies for Alphaherpesviruses

In the process of infecting the host, alphaherpesviruses have derived a series of adaptation and survival strategies, such as latent infection, autophagy and immune evasion, to survive in the host environment. Infected cell protein 22 (ICP22) or its homologue immediate early protein 63 (IE63) is a posttranslationally modified multifunctional viral regulatory protein encoded by all alphaherpesviruses. In addition to playing an important role in the efficient use of host cell RNA polymerase II, it also plays an important role in the defense process of the virus overcoming the host immune system. These two effects of ICP22/IE63 are important survival strategies for alphaherpesviruses. In this review, we summarize the complex mechanism by which the ICP22 protein regulates the transcription of alphaherpesviruses and their host genes and the mechanism by which ICP22/IE63 participates in immune escape. Reviewing these mechanisms will also help us understand the pathogenesis of alphaherpesvirus infections and provide new strategies to combat these viral infections.

Varicella-zoster virus VLT-ORF63 fusion transcript induces broad viral gene expression during reactivation from neuronal latency

Varicella-zoster virus (VZV) establishes lifelong neuronal latency in most humans world-wide, reactivating in one-third to cause herpes zoster and occasionally chronic pain. How VZV establishes, maintains and reactivates from latency is largely unknown. VZV transcription during latency is restricted to the latency-associated transcript (VLT) and RNA 63 (encoding ORF63) in naturally VZV-infected human trigeminal ganglia (TG). While significantly more abundant, VLT levels positively correlated with RNA 63 suggesting co-regulated transcription during latency. Here, we identify VLT-ORF63 fusion transcripts and confirm VLT-ORF63, but not RNA 63, expression in human TG neurons. During in vitro latency, VLT is transcribed, whereas VLT-ORF63 expression is induced by reactivation stimuli. One isoform of VLT-ORF63, encoding a fusion protein combining VLT and ORF63 proteins, induces broad viral gene transcription. Collectively, our findings show that VZV expresses a unique set of VLT-ORF63 transcripts, potentially involved in the transition from latency to lytic VZV infection.

GaHV-2 ICP22 protein is expressed from a bicistronic transcript regulated by three GaHV-2 microRNAs

Herpesviruses have a lifecycle consisting of successive lytic, latent and reactivation phases. Only three infected cell proteins (ICPs) have been described for the oncogenic Marek's disease virus (or Gallid herpes virus 2, GaHV-2): ICP4, ICP22 and ICP27. We focus here on ICP22, confirming its cytoplasmic location and showing that ICP22 is expressed during productive phases of the lifecycle, via a bicistronic transcript encompassing the US10 gene. We also identified the unique promoter controlling ICP22 expression, and its core promoter, containing functional responsive elements including E-box, ETS-1 and GATA elements involved in ICP22 transactivation. ICP22 gene expression was weakly regulated by DNA methylation and activated by ICP4 or ICP27 proteins. We also investigated the function of GaHV-2 ICP22. We found that this protein repressed transcription from its own promoter and from those of IE ICP4 and ICP27, and the late gK promoter. Finally, we investigated posttranscriptional ICP22 regulation by GaHV-2 microRNAs. We found that mdv1-miR-M5-3p and -M1-5p downregulated ICP22 mRNA expression during latency, whereas, unexpectedly, mdv1-miR-M4-5p upregulated the expression of the protein ICP22, indicating a tight regulation of ICP22 expression by microRNAs.

Molecular Aspects of Varicella-Zoster Virus Latency

Primary varicella-zoster virus (VZV) infection causes varicella (chickenpox) and the establishment of a lifelong latent infection in ganglionic neurons. VZV reactivates in about one-third of infected individuals to cause herpes zoster, often accompanied by neurological complications. The restricted host range of VZV and, until recently, a lack of suitable in vitro models have seriously hampered molecular studies of VZV latency. Nevertheless, recent technological advances facilitated a series of exciting studies that resulted in the discovery of a VZV latency-associated transcript (VLT) and provide novel insights into our understanding of VZV latency and factors that may initiate reactivation. Deducing the function(s) of VLT and the molecular mechanisms involved should now be considered a priority to improve our understanding of factors that govern VZV latency and reactivation. In this review, we summarize the implications of recent discoveries in the VZV latency field from both a virus and host perspective and provide a roadmap for future studies.

Varicella zoster virus infection of human fetal lung cells alters mitochondrial morphology

Varicella zoster virus (VZV) is a ubiquitous alphaherpesvirus that establishes latency in ganglionic neurons throughout the neuraxis after primary infection. Here, we show that VZV infection induces a time-dependent significant change in mitochondrial morphology, an important indicator of cellular health, since mitochondria are involved in essential cellular functions. VZV immediate-early protein 63 (IE63) was detected in mitochondria-rich cellular fractions extracted from infected human fetal lung fibroblasts (HFL) by Western blotting. IE63 interacted with cytochrome c oxidase in bacterial 2-hybrid analyses. Confocal microscopy of VZV-infected HFL cells at multiple times after infection revealed the presence of IE63 in the nucleus, mitochondria, and cytoplasm. Our data provide the first evidence that VZV infection induces alterations in mitochondrial morphology, including fragmentation, which may be involved in cellular damage and/or death during virus infection.

Varicella Viruses Inhibit Interferon-Stimulated JAK-STAT Signaling through Multiple Mechanisms

Varicella zoster virus (VZV) causes chickenpox in humans and, subsequently, establishes latency in the sensory ganglia from where it reactivates to cause herpes zoster. Infection of rhesus macaques with simian varicella virus (SVV) recapitulates VZV pathogenesis in humans thus representing a suitable animal model for VZV infection. While the type I interferon (IFN) response has been shown to affect VZV replication, the virus employs counter mechanisms to prevent the induction of anti-viral IFN stimulated genes (ISG). Here, we demonstrate that SVV inhibits type I IFN-activated signal transduction via the JAK-STAT pathway. SVV-infected rhesus fibroblasts were refractory to IFN stimulation displaying reduced protein levels of IRF9 and lacking STAT2 phosphorylation. Since previous work implicated involvement of the VZV immediate early gene product ORF63 in preventing ISG-induction we studied the role of SVV ORF63 in generating resistance to IFN treatment. Interestingly, SVV ORF63 did not affect STAT2 phosphorylation but caused IRF9 degradation in a proteasome-dependent manner, suggesting that SVV employs multiple mechanisms to counteract the effect of IFN. Control of SVV ORF63 protein levels via fusion to a dihydrofolate reductase (DHFR)-degradation domain additionally confirmed its requirement for viral replication. Our results also show a prominent reduction of IRF9 and inhibition of STAT2 phosphorylation in VZV-infected cells. In addition, cells expressing VZV ORF63 blocked IFN-stimulation and displayed reduced levels of the IRF9 protein. Taken together, our data suggest that varicella ORF63 prevents ISG-induction both directly via IRF9 degradation and indirectly via transcriptional control of viral proteins that interfere with STAT2 phosphorylation. SVV and VZV thus encode multiple viral gene products that tightly control IFN-induced anti-viral responses.

In this manuscript we demonstrate that the immediate early protein ORF63 encoded by varicella zoster virus (VZV) and simian varicella virus (SVV) interferes with interferon type I-mediated activation of JAK-STAT signaling and thereby inhibits the expression of interferon stimulated genes. ORF63 blocks this pathway by degrading IRF9, which plays a central role in JAK-STAT signaling. In addition, both viruses code for immune evasion mechanisms affecting the JAK-STAT pathway upstream of IRF9, which results in the inhibition of STAT2 phosphorylation. By fusing a degradation domain derived from dihydrofolate reductase (DHFR) to ORF63 we further demonstrate that this protein is essential for SVV growth and gene expression, indicating that ORF63 also affects IFN-signaling indirectly by regulating the expression of other immune evasion genes.

A sequence within the varicella-zoster virus (VZV) OriS is a negative regulator of DNA replication and is bound by a protein complex containing the VZV ORF29 protein

The architecture of the varicella-zoster virus (VZV) origin of DNA replication (OriS) differs significantly from that of the herpes simplex virus (HSV) DNA replication origin. Novel aspects of the VZV OriS include a GA-rich region, three binding sites for the VZV origin-binding protein (OBP) all on the same strand and oriented in the same direction, and a partial OBP binding site of unknown function. We have designated this partial binding site Box D and have investigated the role it plays in DNA replication and flanking gene expression. This has been done with a model system using a replication-competent plasmid containing OriS and a replication- and transcription-competent dual-luciferase reporter plasmid containing both the OriS and the intergenic region between VZV open reading frames (ORFs) 62 and 63. We have found that (i) Box D is a negative regulator of DNA replication independent of flanking gene expression, (ii) the mutation of Box D results in a decrease in flanking gene expression, thus a sequence within the VZV OriS affects transcription, which is in contrast to results reported for HSV-1, (iii) there is a specific Box D complex formed with infected cell extracts in electrophoretic mobility shift assay experiments, (iv) supershift assays show that this complex contains the VZV ORF29 single-strand DNA-binding protein, and (v) the formation of this complex is dependent on the presence of CGC motifs in Box D and its downstream flanking region. These findings show that the VZV ORF29 protein, while required for DNA replication, also plays a novel role in the suppression of that process.

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.

Identification of phosphorylated residues on varicella-zoster virus immediate-early protein ORF63

Efficient replication of varicella-zoster virus (VZV) in cell culture requires expression of protein encoded by VZV open reading frame 63 (ORF63p). Two-dimensional gel analysis demonstrates that ORF63p is extensively modified. Mass spectroscopy analysis of ORF63p isolated from transiently transfected HEK 293 and stably transfected MeWo cells identified 10 phosphorylated residues. In VZV-infected MeWo cells, only six phosphorylated residues were detected. This report identifies phosphorylation of two previously uncharacterized residues (Ser5 and Ser31) in ORF63p extracted from cells infected with VZV or transfected with an ORF63p expression plasmid. Computational analysis of ORF63p for known kinase substrates did not identify Ser5 or Ser31 as candidate phosphorylation sites, suggesting that either atypical recognition sequences or novel cellular kinases are involved in ORF63p post-translational modification.

Regulation of the ORF61 promoter and ORF61 functions in varicella-zoster virus replication and pathogenesis

Varicella-zoster virus (VZV) open reading frame 61 (ORF61) encodes a protein that transactivates viral and cellular promoters in transient-transfection assays and is the ortholog of herpes simplex virus ICP0. In this report, we mapped the ORF61 promoter and investigated its regulation by viral and cellular proteins in transient-expression experiments and by mutagenesis of the VZV genome (parent Oka strain). The 5' boundary of the minimal ORF61 promoter required for IE62 transactivation was mapped to position -95 relative to the mRNA start site, and three noncanonical GT-rich Sp1-binding sites were documented to occur within the region comprising positions -95 to -45. Contributions of the three Sp1-binding-site motifs, designated Sp1a, Sp1b, and Sp1c, to ORF61 expression and viral replication were varied despite their similar sequences. Two sites, Sp1a and Sp1c, functioned synergistically. When both sites were mutated in the pOka genome to produce pOka-61proDeltaSp1ac, the mutant virus expressed significantly less ORF61 protein. Using this mutant to investigate ORF61 functions resulted in reductions in the expression levels of IE proteins, viral kinases ORF47 and ORF66, and the major glycoprotein gE, with the most impact on gE. Virion morphogenesis appeared to be intact despite minimal ORF61 expression. Pretreating melanoma cells with sodium butyrate enhanced titers of pOka-61proDeltaSp1ac but not pOka, suggesting that ORF61 has a role in histone deacetylase inhibition. Growth of pOka-61proDeltaSp1ac was impaired in SCIDhu skin xenografts, indicating that the regulation of the ORF61 promoter by Sp1 family proteins is important for ORF61 expression in vivo and that ORF61 contributes to VZV virulence at skin sites of replication.

The IR4 auxiliary regulatory protein expands the in vitro host range of equine herpesvirus 1 and is essential for pathogenesis in the murine model

IR4, an early regulatory protein of equine herpesvirus 1 (EHV-1), is not a DNA-binding protein, but interacts with the sole immediate-early protein (IEP) to increase both IEP site-specific DNA-binding and IEP-mediated trans-activation of EHV-1 promoters. To investigate the biological properties of IR4 and ascertain whether this regulatory protein is essential for virus growth, bacterial artificial chromosome methods were employed to generate an IR4-null EHV-1. The IR4 gene was dispensable for EHV-1 growth in non-immortalized equine NBL-6 cells, but virus replication was delayed and was reduced by greater than 10-fold. In addition, replication of the IR4 mutant was abrogated in all other cell types tested, including equine ETCC tumor cells and cells of mouse, rabbit, monkey, and human origin. Further, in contrast to the highly pathogenic parent virus, the IR4 deletion mutant failed to cause disease in the CBA mouse as judged by assessing body weight and clinical signs and was unable to replicate in the murine lung. To define the nature of the block in the replication of the IR4-null virus, molecular analyses were carried out in RK-13 rabbits' cells infected with the IR4-deleted virus and revealed that: 1) the synthesis of the sole IEP was not inhibited; 2) the synthesis of early viral proteins examined was either not affected or was delayed to late times; 3) viral DNA replication was inhibited by more than 99.9%; and 4) synthesis of essential late proteins such as glycoprotein D and glycoprotein K was prevented. These findings indicate that the IR4 protein is required for EHV-1 DNA replication in non-permissive cells, and, like its homologues in other alphaherpesviruses, contributes a function required for virus replication in a variety of cell types.

Construction of recombinant mouse IgG1 antibody directed against varicella zoster virus immediate early protein 63

Five varicella zoster virus (VZV) genes are known to be transcribed in latently infected human ganglia. Transcripts from VZV gene 63, which encodes an immediate early (IE) protein, are the most prevalent and abundant. To obtain a reagent that might facilitate studies of the role of the IE63 protein in latency and reactivation, we selected an IE63-specific Fab fragment from a phage library and used it to prepare a recombinant mouse IgG1 antibody that detects IE63 and functions in Western blot, immunoprecipitation, enzyme-linked immunosorbent assay (ELISA), and immunofluorescence assays.

Phenotypic analysis of human CD4+ T cells specific for immediate-early 63 protein of varicella-zoster virus

Open reading frame 63 of varicella-zoster Virus (VZV) encodes an immediate early (IE) phosphoprotein (IE63) that is believed to be important for viral infectivity and establishing latency. Evidence suggests that VZV-specific T cells are crucial in the control of viral replication; however, data addressing the existence of IE63 protein-specific CD4+ T cells are limited. Using IFN-gamma immunosorbent assays, we identified high frequencies of responses to overlapping peptides spanning the IE63 protein both ex vivo and after in vitro restimulation in healthy VZV-seropositive individuals. We identified a commonly recognised epitope, restricted by HLA-DRB1*1501, which was naturally processed and presented by keratinocytes. We proceeded to investigate the frequency and phenotype of the epitope-specific CD4+ T cells using HLA class II tetrameric complexes. Epitope-specific CD4+ T cells were detectable ex vivo and showed a mixed central and effector-memory differentiation phenotype, with a significant proportion showing evidence of recent activation and rapid effector function. In summary these data implicate persistent low-level or recurrent VZV antigen exposure in healthy immune donors and are compatible with a role for IE63-specific CD4+ T cells in the control of viral reactivation.

Expression of a human cytomegalovirus latency-associated homolog of interleukin-10 during the productive phase of infection

The human cytomegalovirus UL111A region is active during both productive and latent phases of infection. During productive infection, the virus expresses ORF79, a protein with oncogenic properties, and cmvIL-10, a functional homolog of human IL-10. During latent infection of myeloid progenitor cells, an alternately spliced variant of cmvIL-10, termed latency-associated (LA) cmvIL-10 has previously been identified. To determine whether LAcmvIL-10 transcription occurs during productive infection, we performed 5' and 3' RACE to map UL111A-region transcripts in productively infected human foreskin fibroblasts (HFFs). This analysis revealed the presence of a singly spliced UL111A-region transcript predicted to encode LAcmvIL-10. This transcript was expressed in HFFs with early (beta) kinetics, a temporal class that differs from that of ORF79 (alpha kinetics) and cmvIL-10 (gamma kinetics). These data identify and map a transcript encoding a latency-associated homolog of IL-10 which is expressed by the virus during the productive phase of infection.

Downregulation of varicella-zoster virus (VZV) immediate-early ORF62 transcription by VZV ORF63 correlates with virus replication in vitro and with latency

Varicella-zoster virus (VZV) open reading frame 63 (ORF63) protein is expressed during latency in human sensory ganglia. Deletion of ORF63 impairs virus replication in cell culture and establishment of latency in cotton rats. We found that cells infected with a VZV ORF63 deletion mutant yielded low titers of cell-free virus and produced very few enveloped virions detectable by electron microscopy compared with those infected with parental virus. Microarray analysis of cells infected with a recombinant adenovirus expressing ORF63 showed that transcription of few human genes was affected by ORF63; a heat shock 70-kDa protein gene was downregulated, and several histone genes were upregulated. In experiments using VZV transcription arrays, deletion of ORF63 from VZV resulted in a fourfold increase in expression of ORF62, the major viral transcriptional activator. A threefold increase in ORF62 protein was observed in cells infected with the ORF63 deletion mutant compared with those infected with parental virus. Cells infected with ORF63 mutants impaired for replication and latency (J. I. Cohen, T. Krogmann, S. Bontems, C. Sadzot-Delvaux, and L. Pesnicak, J. Virol. 79:5069-5077, 2005) showed an increase in ORF62 transcription compared with those infected with parental virus. In contrast, cells infected with an ORF63 mutant that is not impaired for replication or latency showed ORF62 RNA levels equivalent to those in cells infected with parental virus. The ability of ORF63 to downregulate ORF62 transcription may play an important role in virus replication and latency.

Mutational analysis of the varicella-zoster virus ORF62/63 intergenic region

The varicella-zoster virus (VZV) ORF62/63 intergenic region was cloned between the Renilla and firefly luciferase genes, which acted as reporters of ORF62 and ORF63 transcription, and recombinant viruses were generated that carried these reporter cassettes along with the intact native sequences in the repeat regions of the VZV genome. In order to investigate the potential contributions of cellular transregulatory proteins to ORF62 and ORF63 transcription, recombinant reporter viruses with mutations of consensus binding sites for six proteins within the intergenic region were also created. The reporter viruses were used to evaluate ORF62 and ORF63 transcription during VZV replication in cultured fibroblasts and in skin xenografts in SCIDhu mice in vivo. Mutations in putative binding sites for heat shock factor 1 (HSF-1), nuclear factor 1 (NF-1), and one of two cyclic AMP-responsive elements (CRE) reduced ORF62 reporter transcription in fibroblasts, while mutations in binding sites for HSF-1, NF-1, and octamer binding proteins (Oct-1) increased ORF62 reporter transcription in skin. Mutations in one CRE and the NF-1 site altered ORF63 transcription in fibroblasts, while mutation of the Oct-1 binding site increased ORF63 reporter transcription in skin. The effect of each of these mutations implies that the intact binding site sequence regulates native ORF62 and ORF63 transcription. Mutation of the only NF-kappaB/Rel binding site had no effect on ORF62 or ORF63 transcription in vitro or in vivo. The segment of the ORF62/63 intergenic region proximal to ORF63 was most important for ORF63 transcription, but mutagenesis also altered ORF62 transcription, indicating that this region functions as a bidirectional promoter. This first analysis of the ORF62/63 intergenic region in the context of VZV replication indicates that it is a dual promoter and that cellular transregulatory factors affect the transcription of these key VZV regulatory genes.

Transactivation of the simian varicella virus (SVV) open reading frame (ORF) 21 promoter by SVV ORF 62 is upregulated in neuronal cells but downregulated in non-neuronal cells by SVV ORF 63 protein

Simian varicella virus (SVV) infection in primates closely resembles varicella-zoster virus (VZV) infection in humans. SVV ORF 63 has 51.6% homology at the amino acid level to VZV ORF 63. We cloned SVV ORFs 63 and 62, transcribed and translated in vitro, and immunoprecipitated the expected proteins with rabbit polyclonal antibodies. Immunoprecipitation analysis revealed that SVV ORF 63 is expressed as a 43-kDa phosphorylated protein in virus-infected cells. In both neuronal and non-neuronal cells, SVV ORF 62 protein alone upregulated the SVV 21 promoter, while SVV ORF 63 protein alone did not have any effect. SVV ORF 62-mediated transactivation of the SVV ORF 21 promoter was upregulated in neuronal cells, but downregulated in non-neuronal cells, by SVV ORF 63 protein. This is the first study in which a varicella protein (ORF 63) expressed during latency has been shown to have a differential effect on a promoter that is also active during latency, in neuronal as compared to non-neuronal cells.

Varicella-zoster virus IE63 protein represses the basal transcription machinery by disorganizing the pre-initiation complex

Using transient transfection assays, regulation properties of varicella-zoster virus (VZV)-encoded IE63 protein were analyzed on several VZV immediate early (ORF4), early (ORF28) and late (ORF67) promoters. IE63 was shown to repress the basal activity of most of the promoters tested in epithelial (Vero) and neuronal (ND7) cells to various extents. Trans-repressing activities were also observed on heterologous viral and cellular promoters. Since a construct carrying only a TATA box sequence and a series of wild-type or mutated interleukin (IL)-8 promoters was also repressed by IE63, the role of upstream regulatory elements was ruled out. Importantly, the basal activity of a TATA-less promoter was not affected by IE63. Using a series of IE63 deletion constructs, amino acids 151-213 were shown to be essential to the trans-repressing activity in Vero cells, while in ND7 cells the essential region extended to a much larger carboxy-terminal part of the protein. We also demonstrate that IE63 is capable of disrupting the transcriptional pre-initiation complex and of interacting with several general transcription factors. The central and carboxy-terminal domains of IE63 are important for these effects. Altogether, these results demonstrate that IE63 protein is a transcriptional repressor whose activity is directed towards general transcription factors.

Viral and cellular gene transcription in fibroblasts infected with small plaque mutants of varicella-zoster virus

Varicella-zoster virus (VZV) is an alphaherpesvirus that causes varicella and herpes zoster. In these experiments, cDNA corresponding to 69 VZV open reading frames was added to 42K human cDNA microarrays and used to examine viral as well as cellular gene transcription concurrently in fibroblasts infected with two genetically distinct small plaque VZV mutants, rOka/ORF63rev[T171] and rOkaDeltagI. rOka/ORF63rev[T171] has a point mutation in ORF63, which encodes the immediate early regulatory protein, IE63, and rOkaDeltagI has a deletion of ORF67, encoding glycoprotein I (gI). rOka/ORF63rev[T171] was deficient in the transcription of several viral genes compared to the recombinant rOka control virus. Deletion of ORF67 had minimal effects on viral gene transcription. Effects of rOka/ORF63rev[T171] and rOkaDeltagI on host cell gene transcription were similar to the rOka control, but a few host cell genes were regulated differently in rOkaDeltagI-infected cells. Infection of fibroblasts with intact or small plaque VZV mutants was associated with down-regulation of NF-kappaB and interferon responsive genes, down-regulation of TGF-beta responsive genes accompanied by reduced amounts of fibrotic/wound healing response genes (e.g. collagens, follistatin) and activation of cellular proliferation genes, and alteration of neuronal growth markers, as well as cellular genes encoding proteins important in protein and vesicle trafficking. These observations suggest that replication of VZV small plaque mutant viruses and intact VZV have similar consequences for host cell gene transcription in infected cells, and that the small plaque phenotype in these mutants reflects deficiencies in viral gene expression.

The varicella-zoster virus-mediated delayed host shutoff: open reading frame 17 has no major function, whereas immediate-early 63 protein represses heterologous gene expression

We reported that varicella-zoster virus (VZV) causes a delayed host shutoff during its replicative cycle. VZV open reading frame 17 (ORF17) is the homologue of the herpes simplex virus (HSV) UL41 gene encoding the virion host shutoff (vhs) protein which is responsible for the shutoff effect observed in HSV-infected cells. In the present study, we demonstrated that ORF17 is expressed as a late protein during the VZV replicative cycle in different infected permissive cell lines which showed a delayed shutoff of cellular RNA. A cell line with stable expression of VZV ORF17 was infected with VZV. In these cells, VZV replication and delayed host shutoff remained unchanged when compared to normal infected cells. ORF17 was not capable of repressing the expression of the beta-gal reporter gene under the control of the human cytomegalovirus immediate-early gene promoter or to inhibit the expression of a CAT reporter gene under the control of the human GAPDH promoter, indicating that ORF17 has no major function in the VZV-mediated delayed host shutoff. To determine whether other viral factors are involved in the host shutoff, a series of cotransfection assays was performed. We found that the immediate-early 63 protein (IE63) was able to downregulate the expression of reporter genes under the control of the two heterologous promoters, indicating that this viral factor can be involved in the VZV-mediated delayed host shutoff. Other factors can be also implicated to modulate the repressing action of IE63 to achieve a precise balance between the viral and cellular gene expression.

Varicella-zoster virus IE63 protein phosphorylation by roscovitine-sensitive cyclin-dependent kinases modulates its cellular localization and activity

During the first stage of Varicella-Zoster virus (VZV) infection, IE63 (immediate early 63 protein) is mostly expressed in the nucleus and also slightly in the cytoplasm, and during latency, IE63 localizes in the cytoplasm quite exclusively. Because phosphorylation is known to regulate various cellular mechanisms, we investigated the impact of phosphorylation by roscovitine-sensitive cyclin-dependent kinase (RSC) on the localization and functional properties of IE63. We demonstrated first that IE63 was phosphorylated on Ser-224 in vitro by CDK1 and CDK5 but not by CDK2, CDK7, or CDK9. Furthermore, by using roscovitine and CDK1 inhibitor III (CiIII), we showed that CDK1 phosphorylated IE63 on Ser-224 in vivo. By mutagenesis and the use of inhibitors, we demonstrated that phosphorylation on Ser-224 was important for the correct localization of the protein. Indeed, the substitution of these residues by alanine led to an exclusive nuclear localization of the protein, whereas mutations into glutamic acid did not modify its subcellular distribution. When transfected or VZV-infected cells were treated with roscovitine or CiIII, an exclusive nuclear localization of IE63 was also observed. By using a transfection assay, we also showed that phosphorylation on Ser-224 and Thr-222 was essential for the down-regulation of the basal activity of the VZV DNA polymerase gene promoter. Similarly, roscovitine and CiIII impaired these properties of the wild-type form of IE63. These observations clearly demonstrated the importance of CDK1-mediated IE63 phosphorylation for a correct distribution of IE63 between both cellular compartments and for its repressive activity toward the promoter tested.

Varicella-zoster virus infection of human dorsal root ganglia in vivo

Varicella-zoster virus (VZV) causes varicella and establishes latency in sensory ganglia. VZV reactivation results in herpes zoster. We developed a model using human dorsal root ganglion (DRG) xenografts in severe combined immunodeficient (SCID) mice to investigate VZV infection of differentiated neurons and satellite cells in vivo. DRG engrafted under the kidney capsule and contained neurons and satellite cells within a typical DRG architecture. VZV clinical isolates infected the neurons within DRG. At 14 days postinfection, VZ virions were detected by electron microscopy in neuronal cell nuclei and cytoplasm but not in satellite cells. The VZV genome copy number was 7.1 x 10(7) to 8.0 x 10(8) copies per 10(5) cells, and infectious virus was recovered. This initial phase of viral replication was followed within 4-8 weeks by a transition to VZV latency, characterized by the absence of infectious virus release, the cessation of virion assembly, and a reduction in VZV genome copies to 3.7 x 10(5) to 4.7 x 10(6) per 10(5) cells. VZV persistence in DRG was achieved without any requirement for VZV-specific adaptive immunity and was associated with continued transcription of the ORF63 regulatory gene. The live attenuated varicella vaccine virus exhibited the same pattern of short-term replication, persistence of viral DNA, and prominent ORF63 transcription as the clinical isolates. VZV-infected T cells transferred virus from the circulation into DRG, suggesting that VZV lymphotropism facilitates its neurotropism. DRG xenografts may be useful for investigating neuropathogenic mechanisms of other human viruses.

The varicella-zoster virus open reading frame 63 latency-associated protein is critical for establishment of latency

Varicella-zoster virus (VZV) expresses at least six viral transcripts during latency. One of these transcripts, derived from open reading frame 63 (ORF63), is one of the most abundant viral RNAs expressed during latency. The VZV ORF63 protein has been detected in human and experimentally infected rodent ganglia by several laboratories. We have deleted >90% of both copies of the ORF63 gene from the VZV genome. Animals inoculated with the ORF63 mutant virus had lower mean copy numbers of latent VZV genomes in the dorsal root ganglia 5 to 6 weeks after infection than animals inoculated with parental or rescued virus, and the frequency of latently infected animals was significantly lower in animals infected with the ORF63 mutant virus than in animals inoculated with parental or rescued virus. In contrast, the frequency of animals latently infected with viral mutants in other genes that are equally or more impaired for replication in vitro, compared with the ORF63 mutant, is similar to that of animals latently infected with parental VZV. Examination of dorsal root ganglia 3 days after infection showed high levels of VZV DNA in animals infected with either ORF63 mutant or parental virus; however, by days 6 and 10 after infection, the level of viral DNA in animals infected with the ORF63 mutant was significantly lower than that in animals infected with parental virus. Thus, ORF63 is not required for VZV to enter ganglia but is the first VZV gene shown to be critical for establishment of latency. Since the present vaccine can reactivate and cause shingles, a VZV vaccine based on the ORF63 mutant virus might be safer.

Clinical and molecular pathogenesis of varicella virus infection

Varicella zoster virus (VZV) is a neurotropic human herpesvirus that infects nearly all humans and causes chickenpox (varicella). After chickenpox, VZV becomes latent in cranial nerve, dorsal root, and autonomic nervous system ganglia along the entire neuraxis. Virus reactivation produces shingles (zoster), characterized by pain and rash usually restricted to 1-3 dermatomes. Zoster is often complicated by postherpetic neuralgia (PHN), pain that persists for months to years after rash resolves. Virus may also spread to the spinal cord and blood vessels of the brain, producing a unifocal or multifocal vasculopathy, particularly in immunocompromised individuals. The increased incidence of zoster in elderly and immunocompromised individuals appears to be due to a VZV-specific host immunodeficiency. PHN may reflect a chronic VZV ganglionitis, and VZV vasculopathy is due to productive virus infection in cerebral arteries. Strategies that might boost host cell-mediated immunity to VZV are discussed, as well as the physical state of viral nucleic acid during latency and the possible mechanisms by which herpesvirus latency is maintained and virus is reactivated. A current summary of varicella latency and pathogenesis produced by simian varicella virus (SVV), the counterpart of human VZV, points to the usefulness of a primate model of natural infection to study varicella latency, as well as the experimental model of intratracheal inoculation to study the effectiveness of antiviral agents in driving persistent varicella virus into a latent state.

Interaction between the varicella zoster virus IE62 major transactivator and cellular transcription factor Sp1

The varicella zoster virus (VZV) IE62 protein is involved in the activation of expression of all three kinetic classes of VZV proteins. Analysis of the viral promoter for VZV glycoprotein I has shown that the cellular factor Sp1 is involved in or required for the observed IE62 mediated activation. Co-immunoprecipitation experiments show that the two proteins are present in a complex in VZV-infected cells. Protein affinity pull-down assays using recombinant proteins showed that IE62 and Sp1 interact in the absence of any other viral and cellular proteins. Mapping studies using GST-fusion proteins containing truncations of IE62 and Sp1 have delimited the interacting regions to amino acids 612-778 in Sp1 and amino acids 226-299 in IE62. The region identified in Sp1 is involved in DNA-binding, synergistic Sp1 activation, and Sp1 interaction with cellular transcription factors. The interacting region identified in IE62 overlaps with or borders on sites involved in interactions with the VZV IE4 protein and the cellular factors TBP and TFIIB. Assays using wild-type and mutant promoter elements indicate that Sp1 is involved in recruitment of IE62 to the gI promoter and IE62 enhances Sp1 and TBP binding.

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.

Varicella-zoster virus latency in human ganglia

Varicella-zoster virus (VZV) is a human herpesvirus which causes varicella (chickenpox) as a primary infection, and, following a variable period during which it remains in latent form in trigeminal and dorsal root ganglia, reactivates in later life to cause herpes zoster (shingles). VZV is a significant cause of neurological disease including post-herpetic neuralgia which may be persistent and highly resistant to treatment, and small and large vessel encephalitis. VZV infections are more frequent with advancing age and in immunocompromised individuals. An understanding of the mechanisms of latency is crucial in developing effective therapies for VZV infections of the nervous system. Such studies have been hampered by the difficulties in working with the virus and also the lack of a good animal model of VZV latency. It is known that the ganglionic VZV burden during latency is low. Two of the key questions that have been addressed are the cellular site of latent VZV and the identity of the viral genes which are transcribed during latency. There is now a consensus that latent VZV resides predominantly in ganglionic neurons with less frequent infection of non-neuronal satellite cells. There is considerable evidence to show that at least five viral genes are transcribed during latency. Unlike herpes simplex virus-1 latency, viral protein expression has been demonstrated during VZV latency. A precise knowledge of which viral genes are expressed is crucial in devising novel antiviral therapy using expressed genes as therapeutic targets. Whether gene expression at both the transcriptional and translational levels is more extensive than currently reported will require much more work and probably new molecular technology.

Phosphorylation of varicella-zoster virus IE63 protein by casein kinases influences its cellular localization and gene regulation activity

During the early phase of varicella-zoster virus (VZV) infection, Immediate Early protein 63 (IE63) is expressed rapidly and abundantly in the nucleus, while during latency, this protein is confined mostly to the cytoplasm. Because phosphorylation is known to regulate many cellular events, we investigated the importance of this modification on the cellular localization of IE63 and on its regulatory properties. We demonstrate here that cellular casein kinases I and II are implicated in the in vitro and in vivo phosphorylation of IE63. A mutational approach also indicated that phosphorylation of the protein is important for its correct cellular localization in a cell type-dependent fashion. Using an activity test, we demonstrated that IE63 was able to repress the gene expression driven by two VZV promoters and that phosphorylation of the protein was required for its full repressive properties. Finally, we showed that IE63 was capable of exerting its repressive activity in the cytoplasm, as well as in the nucleus, suggesting a regulation at the transcriptional and/or post-transcriptional level.

Simian varicella virus DNA is present and transcribed months after experimental infection of adult African green monkeys

To study the pathogenesis of simian varicella virus (SVV) infection in its natural primate host, we inoculated adult SVV-seronegative African green monkeys intratracheally with 10(3)-10(4) PFU of SVV, sacrificed them 11 days, 2, 5, 10, and 12 months postinfection (p.i.), and examined lung, liver, and ganglia for SVV DNA and RNA. PCR analysis revealed SVV DNA in ganglia and viscera at 11 days and 2, 5, and 10 months p.i. Similarly, SVV transcripts corresponding to immediate early (IE), putative early (E), and late (L) SVV open-reading frames (ORFs) were found in liver, lung, and ganglia of most monkeys at multiple intervals for the 12-month study period. SVV-specific antigens were detected in ganglia and liver during acute varicella, but not in ganglia 12 months p.i. Analysis of control tissue (ganglia, lung, and liver) from uninfected SVV-seronegative adult African green monkeys did not reveal SVV DNA, SVV RNA, SVV-specific antigen, or varicella-specific pathological changes. Overall, intratracheal inoculation of SVV in African green monkeys resulted in the presence of viral DNA and transcription of multiple viral genes in many tissues for months after experimental infection.

Mutational analysis of the repeated open reading frames, ORFs 63 and 70 and ORFs 64 and 69, of varicella-zoster virus

Varicella-zoster virus (VZV) open reading frame 63 (ORF63), located between nucleotides 110581 and 111417 in the internal repeat region, encodes a nuclear phosphoprotein which is homologous to herpes simplex virus type 1 (HSV-1) ICP22 and is duplicated in the terminal repeat region as ORF70 (nucleotides 118480 to 119316). We evaluated the role of ORFs 63 and 70 in VZV replication, using recombinant VZV cosmids and PCR-based mutagenesis to make single and dual deletions of these ORFs. VZV was recovered within 8 to 10 days when cosmids with single deletions were transfected into melanoma cells along with the three intact VZV cosmids. In contrast, VZV was not detected in transfections carried out with a dual deletion cosmid. Infectious virus was recovered when ORF63 was cloned into a nonnative AvrII site in this cosmid, confirming that failure to generate virus was due to the dual ORF63/70 deletion and that replication required at least one gene copy. This requirement may be related to our observation that ORF63 interacts directly with ORF62, the major immediate-early transactivating protein of VZV. ORF64 is located within the inverted repeat region between nucleotides 111565 and 112107; it has some homology to the HSV-1 Us10 gene and is duplicated as ORF69 (nucleotides 117790 to 118332). ORF64 and ORF69 were deleted individually or simultaneously using the VZV cosmid system. Single deletions of ORF64 or ORF69 yielded viral plaques with the same kinetics and morphology as viruses generated with the parental cosmids. The dual deletion of ORF64 and ORF69 was associated with an abnormal plaque phenotype characterized by very large, multinucleated syncytia. Finally, all of the deletion mutants that yielded recombinants retained infectivity for human T cells in vitro and replicated efficiently in human skin in the SCIDhu mouse model of VZV pathogenesis.

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.

Comparison of DNA sequence and transactivation activity of open reading frame 62 of Oka varicella vaccine and its parental viruses

When nucleotide sequences of Oka vaccine and its parental viruses of varicella-zoster virus (VZV) were compared in 5 open reading frames (ORFs) including glycoprotein C (gC) and 4 immediate-early genes, mutations were detected only in gene 62 which is one of the immediate-early genes. Compared with its parental virus, the vaccine virus contained 15 nucleotide substitutions. With the differentiation method using the simplified restriction-enzyme fragment length polymorphism analysis by Nae I and Bss HII, which was established based on the sequence analysis data in this study, the Oka vaccine virus could be distinguished from its parental virus. Studies of the regulatory activities of the ORF62 gene product (IE62) in a transient assay indicate the IE62 of the parental virus had a stronger transactivational activity than that of the vaccine virus against immediate-early, early and late gene promoters. These data suggest that gene 62 might have an important role for attenuation of VZV. This is the first report in which many substitutions of nucleotides in gene 62 of Oka vaccine virus was found, compared with that of Oka parental virus.

Cis and trans elements regulating expression of the varicella zoster virus gI gene

We have identified cis- and trans-acting elements involved in the VZV IE62 protein-activated expression of the varicella zoster virus (VZV) gene which encodes the viral gI glycoprotein. The cis-acting elements include a non-canonical TATA box and a novel 19 base pair sequence located just upstream of the TATA element designated the "activating upstream sequence" or AUS. The AUS is a movable element and its presence results in IE62 activation of a chimeric promoter consisting of the VZV gC TATA box and the gI AUS. We have also determined that the VZV ORF 29 protein modulates the regulatory activity of the IE62 protein at the gI promoter. In combination with the IE62 transactivator, it yields a 10 to 15-fold increase in expression over the levels seen with the IE62 protein alone in T lymphocytes. The upmodulatory activity requires the presence of a 40 base pair sequence, designated the 29RE, which maps between positions -220 and -180 in the gI promoter. In this paper we review these and earlier findings from our laboratories concerning the regulation of the gI promoter.

Essential role played by the C-terminal domain of glycoprotein I in envelopment of varicella-zoster virus in the trans-Golgi network: interactions of glycoproteins with tegument

Varicella-zoster virus (VZV) is enveloped in the trans-Golgi network (TGN). Here we report that glycoprotein I (gI) is required within the TGN for VZV envelopment. Enveloping membranous TGN cisternae were microscopically identified in cells infected with intact VZV. These sacs curved around, and ultimately enclosed, nucleocapsids. Tegument coated the concave face of these sacs, which formed the viral envelope, but the convex surface was tegument-free. TGN cisternae of cells infected with VZV mutants lacking gI (gI(Delta)) or its C (gI(DeltaC))- or N-terminal (gI(DeltaN))-terminal domains were uniformly tegument coated and adhered to one another, forming bizarre membranous stacks. Viral envelopment was compromised, and no virions were delivered to post-Golgi structures. The TGN was not gI-immunoreactive in cells infected with the gI(Delta) or gI(DeltaN) mutants, but it was in cells infected with gI(DeltaC) (because the ectodomains of gI and gE interact). The presence in the TGN of gI lacking a C-terminal domain, therefore, was not sufficient to maintain enveloping cisternae. In cells infected with intact VZV or with gI(Delta), gI(DeltaN), or gI(DeltaC) mutants, ORF10p immunoreactivity was concentrated on the cytosolic face of TGN membranes, suggesting that it interacts with the cytosolic domains of glycoproteins. Because of the gE-gI interaction, cotransfected cells that expressed gE or gI were able to target truncated forms of the other to the TGN. Our data suggest that the C-terminal domain of gI is required to segregate viral and cellular proteins in enveloping TGN cisternae.

Varicella-zoster virus gene expression in latently infected and explanted human ganglia

A consistent feature of varicella-zoster virus (VZV) latency is the restricted pattern of viral gene expression in human ganglionic tissues. To understand further the significance of this gene restriction, we used in situ hybridization (ISH) to detect the frequency of RNA expression for nine VZV genes in trigeminal ganglia (TG) from 35 human subjects, including 18 who were human immunodeficiency virus (HIV) positive. RNA for VZV gene 21 was detected in 7 of 11 normal and 6 of 10 HIV-positive subjects, RNA for gene 29 was detected in 5 of 14 normal and 11 of 11 HIV-positive subjects, RNA for gene 62 was detected in 4 of 10 normal and 6 of 9 HIV-positive subjects, and RNA for gene 63 was detected in 8 of 17 normal and 12 of 15 HIV-positive subjects. RNA for VZV gene 4 was detected in 2 of 13 normal and 4 of 9 HIV-positive subjects, and RNA for gene 18 was detected in 4 of 15 normal and 5 of 15 HIV-positive subjects. By contrast, RNAs for VZV genes 28, 40, and 61 were rarely or never detected. In addition, immunocytochemical analysis detected the presence of VZV gene 63-encoded protein in five normal and four HIV-positive subjects. VZV RNA was also analyzed in explanted fresh human TG and dorsal root ganglia from five normal human subjects over a period of up to 11 days in culture. We found a very different pattern of gene expression in these explants, with transcripts for VZV genes 18, 28, 29, 40, and 63 all frequently detected, presumably as a result of viral reactivation. Taken together, these data provide further support for the notion of significant and restricted viral gene expression in VZV latency.

Nuclear accumulation of IE62, the varicella-zoster virus (VZV) major transcriptional regulatory protein, is inhibited by phosphorylation mediated by the VZV open reading frame 66 protein kinase

IE62, the major transcriptional activator protein encoded by varicella-zoster virus (VZV), locates to the nucleus when expressed in transfected cells. We show here that cytoplasmic forms of IE62 accumulate in transfected and VZV-infected cells as the result of the protein kinase activity associated with VZV open reading frame 66 (ORF66). Expression of the ORF66 protein kinase but not the VZV ORF47 protein kinase impaired the ability of coexpressed IE62 to transactivate promoter-reporter constructs. IE62 that was coexpressed with the ORF66 protein accumulated predominantly in the cytoplasm, whereas the normal nuclear localization of other proteins was not affected by the ORF66 protein. In cells infected with VZV, IE62 accumulated in the cytoplasm at late times of infection, whereas in cells infected with a VZV recombinant unable to express ORF66 protein (ROka66S), IE62 was completely nuclear. Point mutations introduced into the predicted serine/threonine catalytic domain and ATP binding domain of ORF66 abrogated its ability to influence IE62 nuclear localization, indicating that the protein kinase activity was required. The region of IE62 that was targeted by ORF66 was mapped to amino acids 602 to 733. IE62 peptides containing this region were specifically phosphorylated in cells coexpressing the ORF66 protein kinase and in cells infected with wild-type VZV but were not phosphorylated in cells infected with ROka66S. We conclude that the ORF66 protein kinase phosphorylates IE62 to induce its cytoplasmic accumulation, most likely by inhibiting IE62 nuclear import.

Transcript mapping and transregulatory behavior of varicella-zoster virus gene 21, a latency-associated gene

Gene 21 is one of at least four genes transcribed during latent infection of varicella-zoster virus (VZV) in human ganglia. It may encode a nucleocapsid protein, but its function in lytic and latent infection is not clear. To characterize further the structure and the function of the gene 21 open reading frame (ORF 21), precise localization of its transcripts and their termini was determined by using Northern analysis, S1 nuclease or RNase protection, and primer extension assays. One abundant 3.5-kb transcript that spans ORF 21 was identified. A predominant transcription start site was defined at -78 nucleotide (nt) relative to the ORF 21 translation start codon ATG, and two potential TATA elements were identified at 26 and 83 nt upstream of the 5' end of gene 21 transcripts. Transcription was found to terminate 210 nt beyond the ORF 21 translation stop codon and immediately before the start codon of ORF 22. In transient expression assays, the ORF 21 showed no significant transregulatory activity on promoters of diverse kinetic classes. The ORF 21 promoter, however, was transactivated strongly by VZV infection or by ORF 62.

Aberrant intracellular localization of Varicella-Zoster virus regulatory proteins during latency

Varicella-Zoster virus (VZV) is a herpesvirus that becomes latent in sensory neurons after primary infection (chickenpox) and subsequently may reactivate to cause zoster. The mechanism by which this virus maintains latency, and the factors involved, are poorly understood. Here we demonstrate, by immunohistochemical analysis of ganglia obtained at autopsy from seropositive patients without clinical symptoms of VZV infection that viral regulatory proteins are present in latently infected neurons. These proteins, which localize to the nucleus of cells during lytic infection, predominantly are detected in the cytoplasm of latently infected neurons. The restriction of regulatory proteins from the nucleus of latently infected neurons might interrupt the cascade of virus gene expression that leads to a productive infection. Our findings raise the possibility that VZV has developed a novel mechanism for maintenance of latency that contrasts with the transcriptional repression that is associated with latency of herpes simplex virus, the prototypic alpha herpesvirus.

Varicella-zoster virus gene 21: transcriptional start site and promoter region

Varicella-zoster virus (VZV) causes chicken pox (varicella), becomes latent in dorsal root ganglia, and reactivates decades later to cause shingles (zoster). During latency, the entire VZV genome is present in a circular form, from which genes 21, 29, 62, and 63 are transcribed. Immediate-early (IE) VZV genes 62 and 63 encode regulators of virus gene transcription, and VZV gene 29 encodes a major DNA-binding protein. However, little is known about the function of VZV gene 21 or the control of its transcription. Using primer extensions, we mapped the start of VZV gene 21 transcription in VZV-infected cells to a single site located at -79 nucleotides (nt) with respect to the initiation codon. To identify the VZV gene 21 promoter, the 284-bp region of VZV DNA separating open reading frames (ORFs) 20 and 21 was cloned upstream from the chloramphenicol acetyltransferase gene. In transient-transfection assays, the VZV gene 21 promoter was transactivated in VZV-infected, but not uninfected, cells. Further, the protein encoded by ORF 62 (IE62), but not those encoded by VZV ORFs 4, 10, 61, and 63, transactivates the VZV gene 21 promoter. By use of transient-cotransfection assays in conjunction with 5' deletions of the VZV gene 21 promoter, a 40-bp segment was shown to be responsible for the transactivation of the VZV gene 21 promoter by IE62. This region was located at -96 to -56 nt with respect to the 5' start of gene 21 transcription.

Lessons to be learned from varicella-zoster virus

Varicella-zoster virus (VZV) is an alphaherpesvirus responsible for two human diseases: chicken pox and shingles. The virus has a respiratory port of entry. After two successive viremias, it reaches the skin where it causes typical lesions. There, it penetrates the peripheral nervous system and it remains latent in dorsal root ganglia. It is still debatable whether VZV persists in neurons or in satellite cells. During latency, VZV expresses a limited set of transcripts of its immediate early (IE) and early (E) genes but no protein has been detected. Mechanisms of reactivation from ganglia have not been identified. However, dysfunction of the cellular immune system appears to be involved in this process. The cell-associated nature of VZV has made it difficult to identify a temporal order of gene expression, but there appears to be a cascade mechanism as for HSV-1. The lack of high titre cell-free virions or recombination mutants has hindered so far the understanding of VZV gene functions. Five genes, ORFs 4, 10, 61, 62, and 63 that encode regulatory proteins could be involved in VZV latency. ORF4p activates gene promoters with basal activities. ORF10p seems to activate the ORF 62 promoter. ORF61p has trans-activating and trans-repressing activities. The major IE protein ORF62p, a virion component, has DNA-binding and regulatory functions, transactivates many VZV promoters and even regulates its own expression. ORF63p is a nuclear IE protein of yet unclear regulatory functions, abundantly expressed very early in infection. We have established an animal model of VZV latency in the rat nervous system, enabling us to study the expression of viral mRNA and protein expression during latency, and yielding results similar to those found in humans. This model is beginning to shed light on the molecular events in VZV persistent infection and on the regulatory mechanisms that maintain the virus in a latent stage in nerve cells.

Varicella-zoster virus. The virus

Varicella-zoster virus (VZV) causes chickenpox and herpes zoster. After acute infection the virus becomes latent in dorsal root and trigeminal ganglia for the lifetime of the individual. The viral genome encodes about 70 proteins, at least three of which are thought to be expressed during latency in humans. VZV grows in cell culture, but is very cell-associated; it is relatively difficult to obtain high titers of cell-free virus.

A simian varicella virus (SVV) homolog to varicella-zoster virus gene 21 is expressed in monkey ganglia latently infected with SVV

We have sequenced a simian varicella virus (SVV) open reading frame (ORF), 3,123 bp in length, whose product has 51% amino acid homology with the sequence encoded by the ORF of varicella-zoster virus gene 21. Several regions are highly conserved between the two ORFs, with homologies of approximately 80%. The SVV gene is transcribed in tissue culture cells productively infected with SVV and in monkey ganglia latently infected with SVV.

Varicella-zoster virus (VZV) transcription during latency in human ganglia: detection of transcripts mapping to genes 21, 29, 62, and 63 in a cDNA library enriched for VZV RNA

Information on the extent of virus DNA transcription and translation in infected tissue is crucial to an understanding of herpesvirus latency. To detect low-abundance latent varicella-zoster virus (VZV) transcripts, poly(A)+ RNA extracted from latently infected human trigeminal ganglia was enriched for VZV transcripts by hybridization to biotinylated VZV DNA. After hybridization, the RNA-DNA hybrid was isolated by binding to avidin-coated beads and extensively washed, and the RNA was released by heat denaturation. A lambda-based cDNA library was then constructed from the enriched RNA. PCR and DNA sequencing of DNA extracted from the cDNA library revealed the presence of VZV genes 21, 29, 62, and 63, but not VZV genes 4, 10, 40, 51, and 61, in the enriched cDNA library. These findings confirm the detection of VZV gene 29 and 62 transcripts on Northern (RNA) blots prepared from latently infected human ganglia (J.L. Meier, R.P. Holman, K.D. Croen, J.E. Smialek, and S.E. Straus, Virology 193:193-200, 1993) and the presence of VZV gene 21 transcripts in a cDNA library from mRNA of latently infected ganglia (R.J. Cohrs, K. Srock, M.B. Barbour, G. Owens, R. Mahalingam, M.E. Devlin, M. Wellish and D.H. Gilden, J. Virol. 68:7900-7908,1994) and also reveal, for the first time, the presence of VZV gene 63 RNA in latently infected human ganglia.

Negative regulation of gene expression from the HTLV type II long terminal repeat by Rex: functional and structural dissociation from positive posttranscriptional regulation

Regulation of human T cell leukemia virus type II (HTLV-II) gene expression by Rex is mediated by cis-acting elements in the 5' viral long terminal repeat (LTR). Rex acts posttranscriptionally to enhance cytoplasmic accumulation of incompletely spliced viral mRNAs encoding structural proteins. We report a distinct negative regulatory function mediated by Rex affecting expression from the viral 5' LTR. Using both LTR-driven CAT reporters and a full-length HTLV-II proviral construct, we demonstrate that Rex decreases total cellular levels of LTR-containing mRNA in a dose-dependent manner. Negative regulation is an independent function as demonstrated by structural and functional dissociation from Rex positive posttranscriptional regulation. This negative regulatory action was dependent on nuclear localization sequences, but did not require the previously defined Rex-responsive element (RxRE). Negative regulation was observed in T cell lines but not in B cell lines, suggesting the involvement of cell type-specific factors distinct from those involved in posttranscriptional regulation. An internal deletion mutant of Rex removing aa 38-80 retained the ability to repress, but did not posttranscriptionally increase expression, while negative regulation requires a previously uncharacterized carboxy-terminal region (aa 154-170). These findings suggest that Rex may serve two simultaneous functions: to decrease overall levels of transcribed viral mRNA, and to facilitate nuclear to cytoplasmic export of mRNAs encoding structural proteins. The negative regulatory function of Rex may play a role in viral latency.

Enhancement of HSV-DNA infectivity, in Vero and RS cells, by a modified calcium-phosphate transfection technique

Infectivity of herpes simplex virus (HSV) DNA was assessed by employing the calcium-phosphate transfection technique described by Chen and Okayama, originally applied to increase the efficiency of plasmid transfection by N, N-bis (2-hydroxyethyl)-2-aminoethane sulfonic acid (BES). The experimental conditions and efficiency of this transfection procedure were evaluated comparing the viral progeny titers obtained by the Chen and Okayama transfection method using DNA from wild-type strains of HSV-1 and HSV-2, as well as from mutant strains, with the viral progeny obtained by the most widely used transfection technique introduced by Graham and van der Eb. Furthermore, recombinant virus production was evaluated in marker transfer and marker rescue experiments, comparing both transfection techniques, using DNA fragments cotransfected with whole viral DNA into African green monkey (Vero) or rabbit skin (RS) cells. The viral production obtained from HSV-DNA transfected cells was enhanced approximately 1000-fold when the Chen and Okayama procedure was applied.

Phosphorylation and nuclear localization of the varicella-zoster virus gene 63 protein

The protein encoded by varicella-zoster virus open reading frame 63 and carboxy-terminal deletions of the same were expressed either as fusion proteins at the carboxy terminus of the maltose-binding protein in Escherichia coli or independently in transfected mammalian cells. The truncations contained amino acids 1 to 142 (63 delta N) or 1 to 210 (63 delta K) of the complete 278-amino-acid primary sequence. Recombinant casein kinase II phosphorylated the 63F and 63 delta KF fusion proteins in vitro but did not phosphorylate the 63 delta NF fusion protein, implying that phosphorylation occurred between amino acids 142 and 210. Immunoprecipitation of 35S- or 32P-labelled extracts of cells transfected with plasmids expressing 63, 63 delta N, or 63 delta K also indicated that in situ phosphorylation most likely occurred between amino acids 142 and 210. These combined results suggest that casein kinase II plays a significant role in the phosphorylation of the varicella-zoster virus 63 protein. Indirect immunofluorescence of transfected cells indicated nuclear localization of the 63 protein and cytoplasmic localization of 63 delta K and 63 delta N, implying a requirement for sequences between amino acids 210 and 278 for efficient nuclear localization.

Immunohistochemical identification of varicella-zoster virus gene 63-encoded protein (IE63) and late (gE) protein on smears and cutaneous biopsies: implications for diagnostic use

Early and specific recognition of varicella zoster virus (VZV) infection is of vital concern in immunocompromised patients. The aim of this study was to compare the diagnostic accuracy of histochemical and immunohistochemical identification of the VZV ORF63 encoded protein (IE63) and of the VZV late protein gE on smears and formalin-fixed paraffin-embedded skin sections taken from lesions clinically diagnosed as varicella (n = 15) and herpes zoster (n = 51). Microscopic examinations of Tzanck smears and skin sections yielded a diagnostic accuracy of Herpesviridae infections in 66.7% (10/15) and 92.3% (12/13) of varicella, and 74.4% (29/39) and 87.8% (43/49) of herpes zoster, respectively. Immunohistochemistry applied to varicella provided a type-specific virus diagnostic accuracy of 86.7% (13/15; IE63) and 100% (15/15; gE) on smears, and of 92.3% for both VZV proteins on skin sections. In herpes zoster, the diagnostic accuracy of immunohistochemistry reached 92.3% (36/39; IE63) and 94.9% (37/39; gE) on smears, and 91.7% (44/48; IE63) and 91.8% (45/49; gE) on skin sections. These findings indicate that the immunohistochemical detection of IE63 and gE on both smears and skin sections yields a higher specificity and sensitivity than standard microscopic assessments.

The inverted repeat regions of the simian varicella virus and varicella-zoster virus genomes have a similar genetic organization

Simian varicella virus (SVV) causes a varicella-like disease in nonhuman primates. The DNA sequence and genetic organization of the inverted repeat region (RS) of the SVV genome was determined. The SVV RS is 7559 bp in size with 56% guanine+cytosine (G+C) content and includes 3 open reading frames (ORFs). The SVV RS1 ORF encodes a 1279 amino acid (aa) protein with 58 and 39% identity to the varicella-zoster virus (VZV) gene 62 and herpes simplex virus type 1 (HSV-1) ICP4 homologs, respectively. The predicted 261 aa SVV RS2 polypeptide possesses 52% identity with the VZV gene 63 homolog and 23% identity with the HSV-1 ICP22. The SVV RS3 encodes a 187 aa polypeptide with 56% and 28% identity to the VZV gene 64 and the HSV-1 US10 homologs, respectively, and includes an atypical zinc finger motif. A G+C-rich 16 base-pair (bp) sequence which is repeated 7 times and a putative SVV origin of replication were identified between the RS1 and RS2 ORFs. Comparison with the VZV RS indicates the SVV and VZV RS regions are similar in size and genetic organization.

Proteins and cis-acting elements associated with transactivation of the varicella-zoster virus (VZV) immediate-early gene 62 promoter by VZV open reading frame 10 protein

Varicella-zoster virus (VZV) open reading frame 10 (ORF10) protein, the homolog of herpes simplex virus type 1 (HSV-1) VP16, is a virion-associated transactivator of the VZV immediate-early (IE) gene 62 (IE62) promoter. VP16 forms a complex with cellular factors (Oct1 and host cell factor [HCF]) and TAATGARAT elements (found in all HSV-1 IE promoter/enhancer sequences) to mediate stimulation of IE transcription. The VZV IE62 promoter also contains three TAATGARAT-like elements. Mutagenesis studies of the VZV IE62 promoter indicated that TAATGARAT-like elements contribute to transactivation of the VZV IE62 promoter by ORF10 protein. Other cis-acting elements such as GA-rich and cyclic AMP-responsive elements were also needed for full transactivation by ORF10 protein. In mobility shift assays, ORF10 protein formed a complex with either of two TAATGARAT-like elements that lack an overlapping octamer-binding motif (octa-/TAATGARAT) but not with a TAATGARAT element with an overlapping octamer-binding motif (octa+/TAATGARAT). In contrast, VP16 formed a high-affinity ternary complex with an octa+/TAATGARAT element and a low-affinity complex with octa-/TAATGARAT elements. Addition of antibodies to ORF10 protein, Oct1, or HCF disrupted the complexes, demonstrating that ORF10 protein interacts with Oct1 and HCF. These results suggest that transactivation of the VZV IE62 gene by ORF10 protein and HSV IE genes by VP16 require similar cellular proteins but distinct cis-acting elements.