Varicella-zoster virus (VZV)-specific polypeptides detected in cells treated with metabolic inhibitors

The transcriptional regulatory proteins encoded by varicella-zoster virus open reading frames (ORFs) 4 and 63, but not ORF 61, are associated with purified virus particles

Of the five varicella-zoster virus (VZV) open reading frames (ORFs) known to encode proteins which influence viral transcriptional events, two (ORFs 10 and 62) encode proteins associated with the tegument of virus particles, where they may function during the immediate-early events of infection. In this study, antibodies which recognize the products of the three additional VZV ORFs, ORFs 4, 61, and 63, were made and used to characterize their association with virus particles. ORF 4 encoded a 52-kDa polypeptide, and antibodies to ORF 63 reacted with polypeptides of 47 and 28 kDa. Antibodies to ORF 61 recognized heterogeneous polypeptides of 62 to 66 kDa in cells infected with a vaccinia virus recombinant expressing ORF 61 and in VZV-infected melanoma cells but reacted very weakly with polypeptides of VZV-infected human foreskin fibroblasts, suggesting that cell-specific factors were involved in ORF 61 protein accumulation. Analysis of virus particles purified from melanoma cells indicated that a 52-kDa polypeptide from ORF 4 and the 47-kDa polypeptide from ORF 63, but not any from ORF 61, were associated with virus particles. The virion proteins were likely components of the tegument, as they were not solubilized by treatment of virus with mild detergents and were completely resistant to trypsin digestion unless prior envelope solubilization was performed. The products of ORFs 4 and 63 were not found in purified VZV nucleocapsids. These results suggest that forms of the ORF 4- and ORF 63-encoded transcriptional regulatory proteins are also structural and may also have roles in the immediate-early events of infection.

Varicella-zoster virus gene 63 encodes an immediate-early protein that is abundantly expressed during latency

Varicella-zoster virus (VZV) gene 63 encodes a protein with a predicted molecular mass of 30.5 kDa which has amino acid similarities with the immediate-early (IE) protein 22 (ICP-22) of herpes simplex virus type 1. In order to study the expression of this protein during lytic and latent infection, gene 63 was cloned in frame and downstream from the glutathione-S-transferase gene, expressed as a fusion protein, and purified. In VZV-infected Vero cells, antibodies directed against this protein detect two polypeptides of 45 and 38 kDa which are localized both in the cytoplasm and in the nucleus. Using a sequential combination of transcription and protein synthesis inhibitors (actinomycin D and cycloheximide, respectively), we demonstrated the immediate-early nature of this protein, which can thus be named IE63. Using a rat model of VZV latency, we showed that IE63 is heavily expressed, essentially in neurons, during latency. IE63 can also be detected in the skin of patients showing early herpes zoster symptoms.

Transcriptional mapping of the varicella-zoster virus regulatory genes encoding open reading frames 4 and 63

Four of the 68 varicella-zoster virus (VZV) unique open reading frames (ORFs), i.e., ORFs 4, 61, 62, and 63, encode proteins that influence viral transcription and are considered to be positional homologs of herpes simplex virus type 1 (HSV-1) immediate-early (IE) proteins. In order to identify the elements that regulate transcription of VZV ORFs 4 and 63, the encoded mRNAs were mapped in detail. For ORF 4, a major 1.8-kb and a minor 3.0-kb polyadenylated [poly(A)+] RNA were identified, whereas ORF 63-specific probes recognized 1.3- and 1.9-kb poly(A)+ RNAs. Probes specific for sequences adjacent to the ORFs and mapping of the RNA 3' ends indicated that the ORF 4 RNAs were 3' coterminal, whereas the RNAs for ORF 63 represented two different termination sites. S1 nuclease mapping and primer extension analyses indicated a single transcription initiation site for ORF 4 at 38 bp upstream of the ORF start codon. For ORF 63, multiple transcriptional start sites at 87 to 95, 151 to 153, and (tentatively) 238 to 243 bp upstream of the ORF start codon were identified. TATA box motifs at good positional locations were found upstream of all mapped transcription initiation sites. However, no sequences resembling the TAATGARAT motif, which confers IE regulation upon HSV-1 IE genes, were found. The finding of the absence of this motif was supported through analyses of the regulatory sequences of ORFs 4 and 63 in transient transfection assays alongside those of ORFs 61 and 62. Sequences representing the promoters for ORFs 4, 61, and 63 were all stimulated by VZV infection but failed to be stimulated by coexpression with the HSV-1 transactivator Vmw65. In contrast, the promoter for ORF 62, which contains TAATGARAT motifs, was activated by VZV infection and coexpression with Vmw65. These results extend the transcriptional knowledge for VZV and suggest that ORFs 4 and 63 contain regulatory signals different from those of the ORF 62 and HSV-1 IE genes.

Regulation of thymidine kinase activity in mouse L cells biochemically transformed by varicella-zoster virus

Regulation of thymidine kinase (TK) activity was examined in L(O)c133 and L(H3) cells carrying varicella-zoster virus-TK gene. TK activity of L(O)c133 cells was similarly high in either medium but that of L(H3) cells was high in HAT medium and low in non-HAT medium. Cell growth was well correlated with TK activities of L(O)c133 and L(H3) cells in medium conditions. Regulation of the TK gene in L cells carrying the VZV-TK gene is discussed.

The immediate early proteins of varicella-zoster virus

Stable, relatively high-titer varicella-zoster virus (VZV) stocks as well as a high-titer anti-VZV serum prepared in inbred guinea pigs have allowed the identification of VZV immediate early proteins using the classic inhibitor approach. VZV infection was initiated in the presence of cycloheximide. Following the removal of cycloheximide, actinomycin D and radiolabel were added. After the labeling period, extracts were immunoprecipitated with anti-VZV guinea pig serum and subjected to polyacrylamide gel electrophoresis and fluorography or autoradiography. Four immediate early proteins of mol wts 185,000, 69,000, 43,000, and 34,000 were identified. The largest three were phosphoproteins.

Varicella-zoster virus infection of human sensory neurons

Primary varicella-zoster virus (VZV) infection of humans may result in latent infection of sensory neurons in the peripheral nervous system. To examine the interaction of VZV with the sensory neuron we infected immunochemically defined human neurons with cell-associated VZV. Utilizing double-label immunofluorescence technology, a VZV-specific glycoprotein and a nonglycosylated phosphoprotein were detected in human fetus dorsal root ganglion (DRG) neurons, as defined by the presence of the neuron-specific enolase isoenzyme and the A2B5 ganglioside antigen, respectively. In addition to VZV antigen expression, progressive virus-induced cytopathic damage (neuronal enlargement and nuclear granulation of a fraction of the neuron population) was evident. As determined by transmission electron microscopy, VZV-infected human fetus DRG neurons contained empty and complete nucleocapsids with numerous pleomorphic virus particles in the cytoplasm, often in association with vacuoles. Although virus-specific antigen expression, particle synthesis, and cytopathic effects were observed in the human neuron population, neurons were less susceptible to VZV-induced cytopathic damage than supporting nonneuronal cells, suggesting neuronal modulation of VZV infection in vitro. This system provides the first model to examine the neuron- and virus-specific gene(s) and gene product(s) pertinent to the interaction of VZV with the human neuron.