Mapping of the varicella zoster virus deoxypyrimidine kinase gene and preliminary identification of its transcript

Bench-to-bedside review: rare and common viral infections in the intensive care unit--linking pathophysiology to clinical presentation

Viral infections are common causes of respiratory tract disease in the outpatient setting but much less common in the intensive care unit. However, a finite number of viral agents cause respiratory tract disease in the intensive care unit. Some viruses, such as influenza, respiratory syncytial virus (RSV), cytomegalovirus (CMV), and varicella-zoster virus (VZV), are relatively common. Others, such as adenovirus, severe acute respiratory syndrome (SARS)-coronavirus, Hantavirus, and the viral hemorrhagic fevers (VHFs), are rare but have an immense public health impact. Recognizing these viral etiologies becomes paramount in treatment, infection control, and public health measures. Therefore, a basic understanding of the pathogenesis of viral entry, replication, and host response is important for clinical diagnosis and initiating therapeutic options. This review discusses the basic pathophysiology leading to clinical presentations in a few common and rare, but important, viruses found in the intensive care unit: influenza, RSV, SARS, VZV, adenovirus, CMV, VHF, and Hantavirus.

Analyses of the transcriptional pattern of glycoproteins E and I of Varicella-zoster virus and evidence for a monocistronic transcription

Glycoproteins I and E of the Varicella-zoster virus, encoded by the neighbouring open reading frames 67 and 68, are transcribed into several transcript species that differ in size. From gI, three transcripts of 1.65, 2.7, and 3.6 kb are known, and from gE, two transcripts of 2.15 and 3.6 kb in size are known. Here, we demonstrate that these various transcript species appear in different amounts at different times post infection. At 12 hr post infection, the transcripts of 1.65 (gI) and 2.15 (gE) were clearly detectable, whereas the other transcripts appeared later on. RT-PCR studies using a set of different primers provided clear evidence that gI and gE are transcribed both, mono- and bicistronically, with predominance on the respective monocistronic transcript. Additional evidence for monocistronic transcription was found in the fact that both glycoproteins contain their own transcriptional start sites. Both promoter regions have their own basal transcription activity and include active TATA-boxes that were recognized by the TATA-box binding protein.

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.

Retroviral-mediated gene therapy for the treatment of hepatocellular carcinoma: an innovative approach for cancer therapy

An approach involving retroviral-mediated gene therapy for the treatment of neoplastic disease is described. This therapeutic approach is called "virus-directed enzyme/prodrug therapy" (VDEPT). The VDEPT approach exploits the transcriptional differences between normal and neoplastic cells to achieve selective killing of neoplastic cells. We now describe development of the VDEPT approach for the treatment of hepatocellular carcinoma. Replication-defective, amphotrophic retroviruses were constructed containing a chimeric varicella-zoster virus thymidine kinase (VZV TK) gene that is transcriptionally regulated by either the hepatoma-associated alpha-fetoprotein or liver-associated albumin transcriptional regulatory sequences. Subsequent to retroviral infection, expression of VZV TK was limited to either alpha-fetoprotein- or albumin-positive cells, respectively. VZV TK metabolically activated the nontoxic prodrug 6-methoxypurine arabinonucleoside (araM), ultimately leading to the formation of the cytotoxic anabolite adenine arabinonucleoside triphosphate (araATP). Cells that selectively expressed VZV TK became selectively sensitive to araM due to the VZV TK-dependent anabolism of araM to araATP. Hence, these retroviral-delivered chimeric genes generated tissue-specific expression of VZV TK, tissue-specific anabolism of araM to araATP, and tissue-specific cytotoxicity due to araM exposure. By utilizing such retroviral vectors, araM was anabolized to araATP in hepatoma cells, producing a selective cytotoxic effect.

Comparison of biotinylated DNA and RNA probes for rapid detection of varicella-zoster virus genome by in situ hybridization

We describe a general method for the production of nonisotopic DNA and RNA probes for the detection of the varicella-zoster virus (VZV) genome by in situ hybridization. VZV DNA was extracted from purified viral nucleocapsids, cleaved with restriction enzyme (RE) BamHI, and cloned into plasmid pBR322 by the standard vector insert procedure. We cloned over 85% of the VZV genome and obtained 18 recombinants. Plasmids containing the B, F, G, H, and J fragments of VZV DNA were labeled by the nick translation method with biotin-11-dUTP as the dTTP analog. Additionally, the B fragment was cleaved with RE AvaI, subcloned into the plasmid pGEM-4 transcription vector, and subsequently linearized with REs PstI and EcoRI. RNA was transcribed with T7 or SP6 polymerase, with a substitution of allylamine-UTP as the UTP analog, and labeled with epsilon-caproylamidobiotin-N-hydroxysuccinimide ester. The DNA and RNA probes were used under full-stringency conditions for in situ hybridization with alkaline phosphatase as the detector and 5-bromo-4-chloro-3-indolyl phosphate-Nitro Blue Tetrazolium as the substrate. When tested under comparable conditions, the RNA probe was slightly more sensitive than was the DNA probe: both probes showed homology only with VZV-infected cells and clinical tissues and not with the other herpesviruses. Probes prepared from variable regions of the genome (fragments F and J) performed as well as did those from conserved regions (fragments B. G. and H). Biotinylated probes have distinct advantages over isotopic probes and retain their full potency for more than 2 years when stored properly.

In-vitro synthesis of functional varicella zoster and herpes simplex viral thymidine kinase

The varicella zoster virus (VZV) and herpes simplex virus type 1 (HSV-1) thymidine kinase (TK) genes were cloned into the transcription vector pGEM4. In-vitro translation (ivt) of RNA transcribed from these genes showed prominent expression of functional TK proteins with the expected molecular weights of 36 kD for VZV and 43, 39, and 38 kD for HSV-1. The TK proteins were recognized by rabbit anti-VZV and anti-HSV-1 antibodies, respectively. Analysis of the ivt products by thin-layer chromatography revealed the conversion of thymidine to its phosphorylated forms (TMP, TDP, and TTP) by both the VZV and HSV-1 TK genes. The estimated specific activities of the in-vitro translated VZV and HSV-1 TKs were comparable. VZV TK templates were linearized at internal restriction sites and RNAs transcribed from these templates directed the synthesis of polypeptides with sizes consistent with the colinearity of the VZV TK gene. Deletion of 107 amino acids at the carboxy terminus of the VZV TK gene abolished the in-vitro TK activity. In addition, immunoprecipitation of truncated proteins synthesized in vitro suggested the possible involvement of the region between amino acid residues 101 and 168 from the amino terminus of the VZV TK molecule in the formation of structures necessary for antigenicity.

Mapping of two varicella-zoster virus-encoded genes that activate the expression of viral early and late genes

A transient assay system was used to identify varicella-zoster virus (VZV)-encoded genes whose products are able to activate the expression of an early gene promoter, the thymidine kinase (tk) promoter, and a late gene promoter, and the glycoprotein I (gpI) promoter. Vero cells were cotransfected with individual cloned DNA fragments spanning the entire VZV genome and with the recombinant construct p1tkCAT which contained the chloramphenicol acetyl transferase (CAT) gene under the control of putative regulatory sequences. Five- to 20-fold increases in the expression p1tkCAT was observed in cotransfections with plasmids containing VZV open reading frame (ORF)4 (map location 0.02-0.03) or ORF62 (0.82-0.86). Expression of p68CAT (contains -682 to +222 bp relative to the AUG of gpI) was also enhanced by the products of ORF4 and ORF62. Synergy between ORF4 and ORF62 products was observed in the activation of p68CAT, resulting in a 22-fold increase in CAT activity. RNA analysis indicated that activation of these promoters was at the transcriptional level. A VZV-encoded "repressor" sequence, containing ORF60 and ORF61, was also identified which repressed expression of p1tkCAT and modulated its activation by ORF4 and ORF62.

Differential regulation by varicella-zoster virus (VZV) and herpes simplex virus type-1 trans-activating genes

Transient expression assays were performed in Vero cells in order to compare varicella-zoster virus (VZV)-encoded trans-activating proteins [defined by the products of open reading frames (ORF) 4 and 62] with herpes simplex virus type-1 (HSV-1) trans-activating proteins, ICP4 and ICP0, with respect to activation of gene expression. We demonstrate that the product of VZV ORF4 and ORF62 (which are the HSV-1 analogs of ICP27 and ICP4, respectively) stimulate a variety of viral and cellular gene promoters, including the HSV-1 thymidine kinase (tk) promoter. On the other hand, expression of a recombinant vector containing the VZV tk promoter could not be stimulated, by HSV-1 infection or by the HSV-1 ICP4 or ICP0 proteins expressed during cotransfection experiments. These data suggest different mechanisms of activation of the VZV and the HSV-1 tk gene promoters by "trans-activating" factors.

Cell lines containing varicella-zoster virus open reading frame 62 and expressing the "IE" 175 protein complement ICP4 mutants of herpes simplex virus type 1

Vero cells were cotransfected with pSV2neo and a recombinant plasmid containing the varicella-zoster virus (VZV) open reading frame 62 (ORF62). Three neomycin-resistant cell lines were isolated and shown to complement two different ICP4 mutants (tsB21 and d120) of herpes simplex virus (HSV) type 1 (HSV-1). VZV-specific RNA could not be detected in these cell lines, but following infection with tsB21, a 4.3-kilobase VZV transcript was detected. This RNA increased in quantity when cells were infected in the presence of cycloheximide. A VZV-specific protein of 175 kilodaltons was detected in extracts of all three cell lines following infection with wild-type HSV-1 but not in uninfected cells. That VZV RNA and protein were detected only in HSV-1 infected cells suggests that a component of the HSV virion activates the expression of VZV ORF62. The increase in RNA expression seen in the presence of cycloheximide indicates that the protein encoded by VZV ORF62, "IE"175, may be autoregulatory. These data provide further evidence that VZV "IE"175 is the functional analog of the HSV ICP4.

Directionality and further mapping of varicella zoster virus transcripts

Our laboratory previously identified and preliminarily mapped 58 viral RNA transcripts in varicella zoster virus (VZV) infected cells (Ostrove et al., 1985). This study was initiated to more precisely map these transcripts, to identify additional transcripts, and to determine transcript directionality. To accomplish this, 32 overlapping BamHI, EcoRI, and SmaI fragments representing 99.7% of the genome were cloned into pGEM-2, a plasmid which contains a multiple cloning site flanked by SP6 and T7 RNA polymerase promoters. Each of these clones was used to produce 32P-labeled double-stranded DNA probes to detect transcripts homologous to either strand of the VZV insert, and single-stranded [32P]RNA probes in order to detect RNAs of either polarity. These probes were hybridized to Northern blots of VZV-infected cell RNA. In all, 77 RNAs were detected with both DNA and RNA probes. The direction of transcription and localization of 57 of the 58 previously identified RNAs and of 20 newly recognised abundant transcripts were determined. Thirty-three additional low-abundance transcripts were detected only by the relatively more sensitive RNA probes. A map indicating the directionality and approximate locations of the abundant VZV transcripts was constructed.

Map location of the thymidine kinase gene of bovine herpesvirus 1

Bovine herpesvirus 1 has been reported to contain a thymidine kinase (tk) gene which is nonessential for virus replication. We have isolated a thymidine kinase-negative mutant of the virus and localized the mutation by marker rescue experiments to a 1.1-kilobase BglII-SalI fragment which maps at 0.47 to 0.48 on the bovine herpesvirus 1 genomic map. A thymidine kinase-negative bovine cell line isolated in our laboratory was used in these studies.

Isomerization of the UL region of varicella-zoster virus DNA

Varicella-zoster virus (VZV) DNA exists principally as two isomers. Despite the presence of inverted repeats bounding the long sequence region, the unique long sequence, UL, is found in one (prototype) orientation in 95-98% of VZV DNA molecules and in the inverted orientation in only 2-5% of the molecules. In searching for an explanation for this disparity, we superinfected VZV-infected cells with herpes simplex virus type 1 or pseudorabies virus. Neither superinfecting virus produced a measurable change in the frequency of isomerization of the VZV DNA long sequence region.

Varicella-zoster virus as a live vector for the expression of foreign genes

The previous demonstration of the efficacy and tolerability of the Oka strain of varicella-zoster virus (VZV) in clinical trials involving vaccination of both normal and immunocompromised individuals has laid the foundation for its use in preventing chickenpox. In this context, VZV could be useful as a vector for vaccinating against other infectious agents as well. As an initial application, a live recombinant VZV expressing Epstein-Barr virus (EBV) membrane glycoproteins (gp350/220) was generated by inserting a gene fusion of the VZV gpI promoter and hydrophobic leader-encoding sequence with the gp350/220 coding sequence into the thymidine kinase (TK) gene of VZV (Oka). Insertion of the foreign DNA into the thymidine kinase gene was demonstrated by Southern blot analysis and the ability of the recombinant virus to replicate in the presence of bromodeoxyuridine. RNA splicing, glycosylation, and plasma membrane presentation of gp350/220 in cells infected with the recombinant virus were similar to those seen in EBV-infected cells. In addition, the expression of VZV-specific glycoproteins was unaltered by the concomitant expression of this large foreign glycoprotein. Thus, VZV can be used as a live viral vector for active immunization against EBV and other pathogens.

Varicella-zoster virus complements herpes simplex virus type 1 temperature-sensitive mutants

Varicella-zoster virus (VZV) can complement temperature-sensitive mutants of herpes simplex virus. Of seven mutants tested, two, carrying mutations in the immediate-early ICP4 and ICP27 proteins, were complemented. This complementation was not seen in coinfections with adenovirus type 5 or cytomegalovirus. Following transfection into CV-1 cells, a DNA fragment containing the VZV short repeat sequence complemented the ICP4 mutant. These data demonstrate a functional relationship between VZV and herpes simplex virus and have allowed localization of a putative VZV immediate-early gene.