Alice P. W. Poon

Herpes Simplex Virus 1 Gene Expression Is Accelerated by Inhibitors of Histone Deacetylases in Rabbit Skin Cells Infected with a Mutant Carrying a cDNA Copy of the Infected-Cell Protein No. 0

ABSTRACT An earlier report showed that the expression of viral genes by a herpes simplex virus 1 mutant [HSV-1(vCPc0)] in which the wild-type, spliced gene encoding infected-cell protein no. 0 (ICP0) was replaced by a cDNA copy is dependent on both the cell type and multiplicity of infection. At low multiplicities of infection, viral gene expression in rabbit skin cells was delayed by many hours, although ultimately virus yield was comparable to that of the wild-type virus. This defect was rescued by replacement of the cDNA copy with the wild-type gene. To test the hypothesis that the delay reflected a dysfunction of ICP0 in altering the structure of host protein-viral DNA complexes, we examined the state of histone deacetylases (HDACs) (HDAC1, HDAC2, and HDAC3). We report the following. (i) HDAC1 and HDAC2, but not HDAC3, were modified in infected cells. The modification was mediated by the viral protein kinase US3 and occurred between 3 and 6 h after infection with wild-type virus but was delayed in rabbit skin cells infected with HSV-1(vCPc0) mutant, concordant with a delay in the expression of viral genes. (ii) Pretreatment of rabbit skin cells with inhibitors of HDAC activity (e.g., sodium butyrate, Helminthosporium carbonum toxin, or trichostatin A) accelerated the expression of HSV-1(vCPc0) but not that of wild-type virus. We conclude the following. (i) In the interval in which HSV-1(vCPc0) DNA is silent, its DNA is in chromatin-like structures amenable to modification by inhibitors of histone deacetylases. (ii) Expression of wild-type virus genes in these cells precluded the formation of DNA-protein structures that would be affected by either the HDACs or their inhibitors. (iii) Since the defect in HSV-1(vCPc0) maps to ICP0, the results suggest that this protein initiates the process of divestiture of viral DNA from tight chromatin structures but could be replaced by other viral proteins in cells infected with a large number of virions.

Of the three tegument proteins that package mRNA in herpes simplex virions, one (VP22) transports the mRNA to uninfected cells for expression prior to viral infection

An earlier report has shown that herpes simplex virus 1 virions package RNA. Experiments designed to reveal the identity of the virion proteins capable of binding the RNA and to show whether the mRNA carried in the newly infected cells was expressed showed the following: (i) 32P-labeled riboprobe generated by in vitro transcription of the US8.5 ORF bound three proteins identified as the products of US11, UL47, and UL49 (VP22) genes. (ii) Viral RNA was bound to UL47 or US11 proteins immune precipitated from cells transduced with baculoviruses expressing UL47 or US11 and then superinfected with HSV-1 under conditions that blocked DNA synthesis and assembly of virions. (iii) Virions were purified from cells transduced with a baculovirus encoding a US8.5 protein fused to green fluorescent protein and superinfected with an HSV-1 mutant lacking the US8–12 genes. HEp-2 cells infected with these virions expressed the chimeric protein in ≈1% of infected cells. (iv) In mixed cultures, untreated Vero cells acquired the mRNA encoding the green fluorescent–US8.5 chimeric protein from HEp-2 cells doubly transduced with the genes encoding VP22 and the chimeric protein. The transfer was RNase sensitive and VP22 dependent, indicating that the RNA encoded by the chimeric gene was transferred to Vero cells as mRNA. We conclude that (i) three virion proteins are capable of binding RNA; (ii) the packaged RNA can be expressed in newly infected cells; and (iii) the UL47 protein was earlier reported to shuttle from nucleus to the cytoplasm and may transport RNA. VP22 thus appears to be a member of a new class of viral proteins whose major function is to bind and transport infected cell mRNA to uninfected cells to create the environment for effective initiation of infection.

The Carboxyl-Terminal Domain of RNA Polymerase II Is Phosphorylated by a Complex Containing cdk9 and Infected-Cell Protein 22 of Herpes Simplex Virus 1

ABSTRACT The infected-cell protein 22 (ICP22), a regulatory protein encoded by the α22 gene of herpes simplex virus 1, is required for the optimal expression of a set of late viral proteins that includes the products of the US11, UL38, and UL41 genes. ICP22 has two activities. Thus, ICP22 and the UL13 protein kinase mediate the activation of cdc2 and degradation of its partners, cyclins A and B. cdc2 and its new partner, the DNA polymerase accessory factor (UL42), bind topoisomerase IIα in an ICP22-dependent manner. In addition, ICP22 and UL13 mediate an intermediate phosphorylation of the carboxyl terminus of RNA polymerase II (RNA POL II). Here we report another function of ICP22. Thus, ICP22 physically interacts with cdk9, a constitutively active cyclin-dependent kinase involved in transcriptional regulation. A protein complex containing ICP22 and cdk9 phosphorylates in vitro the carboxyl-terminal domain of RNA POL II in a viral US3 protein kinase-dependent fashion. Finally, the carboxyl-terminal domain of RNA POL II fused to glutathione S-transferase is phosphorylated in reaction mixtures containing complexes pulled down with ICP22 or cdk9 immune precipitated from lysates of wild-type parent virus or ΔUL13 but not ΔUS3 mutant-infected cells. The experiments described here place ICP22 and cdk9 in a complex with the carboxyl-terminal domain of RNA POL II. At the same time we confirm the requirement of ICP22 and the UL13 protein kinase in the posttranslational modification of RNA POL II that alters its electrophoretic mobility, although US3 kinase appears to play a role in a cell-type-dependent fashion.

US3 Protein Kinase of Herpes Simplex Virus 1 Blocks Caspase 3 Activation Induced by the Products of US1.5 and UL13 Genes and Modulates Expression of Transduced US1.5 Open Reading Frame in a Cell Type-Specific Manner

ABSTRACT The coding domain of the herpes simplex virus type 1 (HSV-1) α22 gene encodes two proteins, the 420-amino-acid infected-cell protein 22 (ICP22) and US1.5, a protein colinear with the carboxyl-terminal domain of ICP22. In HSV-1-infected cells, ICP22 and US1.5 are extensively modified by the UL13 and US3 viral protein kinases. In this report, we show that in contrast to other viral proteins defined by their properties as α proteins, US1.5 becomes detectable and accumulated only at late times after infection. Moreover, significantly more US1.5 protein accumulated in cells infected with a mutant lacking the UL13 gene than in cells infected with wild-type virus. To define the role of viral protein kinases on the accumulation of US1.5 protein, rabbit skin cells or Vero cells were exposed to recombinant baculoviruses that expressed US1.5, UL13, or US3 proteins under a human cytomegalovirus immediate-early promoter. The results were as follows. (i) Accumulation of the US1.5 protein was reduced by concurrent expression of the UL13 protein kinase and augmented by concurrent expression of the US3 protein kinase. The magnitude of the reduction or increase in the accumulation of the US1.5 protein was cell type dependent. The effect of UL13 kinase appears to be specific inasmuch as it did not affect the accumulation of glycoprotein D in cells doubly infected by recombinant baculoviruses expressing these genes. (ii) The reduction in accumulation of the US1.5 protein was partially due to proteasome-dependent degradation. (iii) Both US1.5 and UL13 proteins activated caspase 3, indicative of programmed cell death. (iv) Concurrent expression of the US3 protein kinase blocked activation of caspase 3. The results are concordant with those published elsewhere (J. Munger and B. Roizman, Proc. Natl. Acad. Sci. USA 98:10410–10415, 2001) that the US3 protein kinase can block apoptosis by degradation or posttranslational modification of BAD.

US3 and US3.5 Protein Kinases of Herpes Simplex Virus 1 Differ with Respect to Their Functions in Blocking Apoptosis and in Virion Maturation and Egress

ABSTRACT Previously, we reported that the US3 protein kinase blocks apoptosis, that it activates protein kinase A (PKA), that activation of PKA blocks apoptosis in cells infected with a US3 deletion mutant, and that an overlapping transcriptional unit encodes a truncated kinase designated US3.5. Here, we report the properties of the kinases based on comparisons of herpes simplex virus and baculoviruses expressing US3 or US3.5 kinase. Specifically, we report the following. (i) Both kinases mediate the phosphorylation of HDAC1, HDAC2, and the PKA regulatory IIα subunit in the absence of other viral proteins. (ii) Both enzymes mediate the phosphorylation of largely identical sets of proteins carrying the phosphorylation consensus site of PKA, but only US3 blocks apoptosis, suggesting that it is US3 and not PKA that is responsible for the phosphorylation of the proteins bearing the shared consensus phosphorylation site and the antiapoptotic activity. (iii) Both kinases cofractionate with mitochondria. Immune depletion of the US3 and US3.5 kinases from the cytoplasm removed the kinases from the supernatant fraction, but not from the mitochondrial fraction, and therefore, if the antiapoptotic activity of the US3 kinase is expressed in mitochondria, the localization signal and the antiapoptotic functions are located on different parts of the protein. (iv) The US3 protein kinase is required for the translocation of virus particles from the nucleus. Although the UL31 protein is phosphorylated in cells infected with the mutant expressing US3.5 kinase, the release of virus particles from nuclei was impeded in some cells, suggesting that the US3 kinase affects the modification of the nuclear membrane more efficiently than the US3.5 kinase.

Ionizing Radiation Activates Late Herpes Simplex Virus 1 Promoters via the p38 Pathway in Tumors Treated with Oncolytic Viruses

Ionizing radiation potentiates the oncolytic activity of attenuated herpes simplex viruses in tumors exposed to irradiation at specific time intervals by inducing higher virus yields. Cell culture studies have shown that an attenuated virus lacking the viral gamma(1)34.5 genes underproduces late proteins whose synthesis depends on sustained synthesis of viral DNA. Here we report that ionizing radiation enhances gene expression from late viral promoters in transduced cells in the absence of other viral gene products. Consistent with this result, we show that in tumors infected with the attenuated virus, ionizing radiation increases 13.6-fold above baseline the gene expression from a late viral promoter as early as 2 hours after virus infection, an interval too short to account for viral DNA synthesis. The radiation-dependent up-regulation of late viral genes is mediated by the p38 pathway, inasmuch as the enhancement is abolished by p38 inhibitors or a p38 dominant-negative construct. The p38 pathway is not essential for wild-type virus gene expression. The results suggest that ionizing radiation up-regulates late promoters active in the course of viral DNA synthesis and provide a rationale for use of radiation to up-regulate cytotoxic genes introduced into tumor cells by viral vectors for cytoreductive therapy.

Herpes Simplex Virus 1 ICP22 Regulates the Accumulation of a Shorter mRNA and of a Truncated US3 Protein Kinase That Exhibits Altered Functions

ABSTRACT The US3 open reading frame of herpes simplex virus 1 (HSV-1) was reported to encode two mRNAs each directing the synthesis of the same protein. We report that the US3 gene encodes two proteins. The predominant US3 protein is made in wild-type HSV-1-infected cells. The truncated mRNA and a truncated protein designated US3.5 and initiating from methionine 77 were preeminent in cells infected with a mutant lacking the gene encoding ICP22. Both the wild-type and truncated proteins also accumulated in cells transduced with a baculovirus carrying the entire US3 open reading frame. The US3.5 protein accumulating in cells infected with the mutant lacking the gene encoding ICP22 mediated the phosphorylation of histone deacetylase 1, a function of US3 protein, but failed to block apoptosis of the infected cells. The US3.5 and US3 proteins differ with respect to the range of functions they exhibit.

Posttranslational processing of infected cell protein 22 mediated by viral protein kinases is sensitive to amino acid substitutions at distant sites and can be cell-type specific.

ABSTRACT Infected cell protein 22 (ICP22) is posttranslationally phosphorylated by the viral kinases encoded by US3 and UL13 and nucleotidylylated by casein kinase II. In rabbit and rodent cells and in primary human fibroblasts infected with mutants from which the α22 gene encoding ICP22 had been deleted, a subset of late (γ2) gene products exemplified by UL38 and US11 proteins are expressed at a reduced level, as measured by the accumulation of both mRNA and protein. The same phenotype was observed in cells infected with mutants lacking the UL13 gene. The focus of this report is on three serine- and threonine-rich domains of ICP22. Two of these domains are homologs located between residues 38 to 66 and 300 to 328. The third domain is near the carboxyl terminus and contains the sequence T374SS. The results were as follows. (i) Alanine substitutions in the amino-terminal homolog precluded the posttranslational processing of ICP22 in rabbit skin cells and in Vero cells but had no effect on the accumulation of either US11 or UL38 protein. (ii) Alanine substitutions in the carboxyl-terminal homolog had no effect on posttranslational processing of ICP22 accumulating in Vero cells but precluded full processing of ICP22 accumulating in rabbit skin cells. The effect on accumulation of UL38 and US11 proteins was insignificant in Vero cells and minimal in rabbit skin cells. (iii) Substitutions of alanine for the threonine and serines in the third domain precluded full processing of ICP22 and caused a reduction of accumulation of US11 and UL38 proteins. These results indicate the following. (i) The posttranslational processing of ICP22 is sensitive to mutations within the domains of ICP22 tested and is cell-type dependent. (ii) Posttranslational processing of ICP22 is not required for accumulation of UL38 and US11 proteins to the same level as that seen in cells infected with the wild-type virus. (iii) The T374SS sequence shared by ICP22 and the US1.5 proteins is essential for the accumulation of a subset of γ2 proteins exemplified by US11 and UL38 and is the first step in mapping of the sequences necessary for optimal accumulation of US11 and UL38 proteins.

Temperature-Sensitive Mutations in the Putative Herpes Simplex Virus Type 1 Terminase Subunits pUL15 and pUL33 Preclude Viral DNA Cleavage/Packaging and Interaction with pUL28 at the Nonpermissive Temperature

ABSTRACT Terminases comprise essential components of molecular motors required to package viral DNA into capsids in a variety of DNA virus systems. Previous studies indicated that the herpes simplex virus type 1 UL15 protein (pUL15) interacts with the pUL28 moiety of a pUL28-pUL33 complex to form the likely viral terminase. In the current study, a novel temperature-sensitive mutant virus was shown to contain a mutation in UL33 codon 61 predicted to change threonine to proline. At the nonpermissive temperature, this virus, designated ts8-22, replicated viral DNA and produced capsids that became enveloped at the inner nuclear membrane but failed to form plaques or to cleave or package viral DNA. Incubation at the nonpermissive temperature also precluded coimmunoprecipitation of UL33 protein with its normal interaction partners encoded by UL28 and UL15 in ts8-22-infected cells and with pUL28 in transient-expression assays. Moreover, a temperature-sensitive mutation in UL15 precluded coimmunoprecipitation of pUL15 with the UL28 and UL33 proteins at the nonpermissive temperature. We conclude that interactions between putative terminase components are tightly linked to successful viral DNA cleavage and packaging.

An Early Regulatory Function Required in a Cell Type-Dependent Manner Is Expressed by the Genomic but Not the cDNA Copy of the Herpes Simplex Virus 1 Gene Encoding Infected Cell Protein 0

ABSTRACT The α0 genes of herpes simplex virus 1 (HSV-1) contain three exons. Earlier studies have shown that the substitution of genomic sequences with a cDNA copy does not alter the capacity of the virus to replicate or establish latent infection. Other studies have demonstrated that HSV-1 may express alternatively spliced forms of α0 transcripts. The studies reported here centered on a mutant HSV-1(vCPc0) strain in which the genomic copies of the α0 gene were replaced with cDNA copies. From our research, we report the following observations. (i) In contrast to events transpiring in cells infected with wild-type virus, the expression of HSV-1(vCPc0) genes was delayed or restricted to α genes for many hours in rabbit skin cells and to a lesser extent in HEp-2 cells but not in Vero cells. This delay in the expression of HSV-1(vCPc0) β or γ genes was also multiplicity of infection dependent. (ii) Exposure to MG132, a proteasomal inhibitor, before infection with wild-type virus had no significant effect on the accumulation of viral proteins in Vero cells and caused an only slight delay in viral gene expression in rabbit skin cells in a multiplicity of infection-dependent fashion. The drug had no effect when it was added to the medium 3 h after infection. (iii) Rabbit skin or HEp-2 cells exposed to MG132 3 h after infection with the HSV-1(vCPc0) mutant accumulated only α proteins. This restriction was cell type dependent but not multiplicity of infection dependent. (iv) Both the delay in the expression of β and γ genes and the effect of MG132 added to the medium 3 h after infection were rescued by restoration of the intron 1 sequences in the HSV-1(vCPc0) mutant. However, cells transduced by baculoviruses expressing intron 1 RNA did not complement the HSV-1(vCPc0) mutant, suggesting that the function of intron 1 is in cis rather than in trans. We came to the following conclusions as a result. (i) Post-α gene expression requires the involvement of the proteasomal pathway in a cell type-dependent manner. Consistent with this requirement, the proapoptotic functions of MG132 are blocked in cells infected before exposure to the drug but not after exposure. (ii) A function encoded by the α0 gene that is absent from the cDNA copy is required for viral gene expression in a cell type- and multiplicity of infection-dependent fashion. The absence of this master function delays but does not ultimately block viral gene expression in the cell lines tested here.