The bovine herpesvirus 1 immediate-early protein (bICP0) associates with histone deacetylase 1 to activate transcription

Histone Deacetylase (HDAC)-1, -2, -4, and -6 in Uveal Melanomas: Associations with Clinicopathological Parameters and Patients' Survival

Simple Summary

Histone Deacetylases (HDACs) have been reportedly associated with tumor development and progression in several types of human malignancy, being currently investigated as potential targets of anti-cancer therapy. The aim of this study is to assess the clinical significance and prognostic role of the of HDAC-1, -2, -4, and -6 immunohistochemical expression, in 75 uveal melanoma (UM) cases. HDACs are differentially expressed in UMs, HDAC-2 being the most frequently expressed isoform, whereas cytoplasmic expression of class I HDAC isoforms is also observed. Additionally, HDAC-1 was associated with increased tumor size, HDAC-6 with mitotic index, and HDAC-2 with epithelioid cell morphology and presence of tumor-infiltrating lymphocytes, both parameters of adverse prognosis. Moreover, our data support a significant association of HDAC-2 with patients’ improved OS. These findings suggest that HDACs, and especially HDAC-2, may be implicated in the formation and progression of UM.

Abstract

Background: Uveal melanoma (UM) represents the most common primary intraocular malignancy in adults, exerting high metastatic potential and poor prognosis. Histone deacetylases (HDACs) play a key role in carcinogenesis, and HDAC inhibitors (HDACIs) are currently being explored as anti-cancer agents in clinical settings. The aim of this study was to evaluate the clinical significance of HDAC-1, -2, -4, and -6 expression in UM. Methods: HDAC-1, -2, -4, and -6 expression was examined immunohistochemically in 75 UM tissue specimens and was correlated with tumors’ clinicopathological characteristics, the presence of tumor-infiltrating lymphocytes (TILS), as well as with our patients’ overall survival (OS). Results: HDAC-2 was the most frequently expressed isoform (66%), whereas we confirmed in addition to the expected nuclear expression the presence of cytoplasmic expression of class I HDAC isoforms, namely HDAC-1 (33%) and HDAC-2 (9.5%). HDAC-4 and -6 expression was cytoplasmic. HDAC-1 nuclear expression was associated with increased tumor size (p = 0.03), HDAC-6 with higher mitotic index (p = 0.03), and nuclear HDAC-2 with epithelioid cell morphology (p = 0.03) and presence of tumor-infiltrating lymphocytes (p = 0.04). The association with the remaining parameters including Monosomy 3 was not significant. Moreover, the presence as well as the nuclear expression pattern of HDAC-2 were correlated with patients’ improved OS and remained significant in multivariate survival analysis. Conclusions: These findings provide evidence for a potential role of HDACs and especially HDAC-2 in the biological mechanisms governing UM evolution and progression.

Regulation of neurotropic herpesvirus productive infection and latency-reactivation cycle by glucocorticoid receptor and stress-induced transcription factors

Neurotropic α-herpesvirinae subfamily members, herpes simplex virus type 1 (HSV-1) and bovine herpesvirus 1 (BoHV-1), are important viral pathogens in their respective hosts. Following acute infection on mucosal surfaces, these viruses establish life-long latency in neurons within trigeminal ganglia (TG) and central nervous system. Chronic or acute stress (physiological or psychological) increases the frequency of reactivation from latency, which leads to virus shedding, virus transmission, and recurrent disease. While stress impairs immune responses and inflammatory signaling cascades, we predict stressful stimuli directly stimulate viral gene expression and productive infection during early stages of reactivation from latency. For example, BoHV-1 and HSV-1 productive infection is impaired by glucocorticoid receptor (GR) antagonists but is stimulated by the synthetic corticosteroid dexamethasone. Promoters that drive expression of key viral transcriptional regulatory proteins are cooperatively stimulated by GR and specific Krüppel like transcription factors (KLF) induced during stress induced reactivation from latency. The BoHV-1 immediate early transcription unit 1 promoter and contains two GR response elements (GRE) that are essential for cooperative transactivation by GR and KLF15. Conversely, the HSV-1 infected cell protein 0 (ICP0) and ICP4 promoter as well as the BoHV-1 ICP0 early promoter lack consensus GREs: however, these promoters are cooperatively transactivated by GR and KLF4 or KLF15. Hence, growing evidence suggests GR and stress-induced transcription factors directly stimulate viral gene expression and productive infection during early stages of reactivation from latency. We predict the immune inhibitory effects of stress enhance virus spread at late stages during reactivation from latency.

Regulation of Krüppel-Like Factor 15 Expression by Herpes Simplex Virus Type 1 or Bovine Herpesvirus 1 Productive Infection

Expression of Krüppel-like factor 15 (KLF15), a stress-induced transcription factor, is induced during bovine herpesvirus 1 (BoHV-1) reactivation from latency, and KLF15 stimulates BoHV-1 replication. Transient transfection studies revealed that KLF15 and glucocorticoid receptor (GR) cooperatively transactivate the BoHV-1-immediate-early transcription unit 1 (IEtu1), herpes simplex virus type 1 (HSV-1) infected cell protein 0 (ICP0), and ICP4 promoters. The IEtu1 promoter drives expression of bICP0 and bICP4, two key BoHV-1 transcriptional regulatory proteins. Based on these studies, we hypothesized infection is a stressful stimulus that increases KLF15 expression and enhances productive infection. New studies demonstrated that silencing KLF15 impaired HSV-1 productive infection, and KLF15 steady-state protein levels were increased at late stages of productive infection. KLF15 was primarily localized to the nucleus following infection of cultured cells with HSV-1, but not BoHV-1. When cells were transfected with a KLF15 promoter construct and then infected with HSV-1, promoter activity was significantly increased. The ICP0 gene, and to a lesser extent, bICP0 transactivated the KLF15 promoter in the absence of other viral proteins. In contrast, BoHV-1 or HSV-1 encoded VP16 had no effect on KLF15 promoter activity. Collectively, these studies revealed that HSV-1 and BoHV-1 productive infection increased KLF15 steady-state protein levels, which correlated with increased virus production.

Short Chain Fatty Acids (SCFA) Reprogram Gene Expression in Human Malignant Epithelial and Lymphoid Cells

The effect of short chain fatty acids (SCFAs) on gene expression in human, malignant cell lines was investigated, with a focus on signaling pathways. The commensal microbial flora produce high levels of SCFAs with established physiologic effects in humans. The most abundant SCFA metabolite in the human microflora is n-butyric acid. It is well known to activate endogenous latent Epstein-Barr virus (EBV), that was used as a reference read out system and extended to EBV+ epithelial cancer cell lines. N-butyric acid and its salt induced inflammatory and apoptotic responses in tumor cells of epithelial and lymphoid origin. Epithelial cell migration was inhibited. The n-butyric gene activation was reduced by knock-down of the cell membrane transporters MCT-1 and -4 by siRNA. N-butyric acid show biologically significant effects on several important cellular functions, also with relevance for tumor cell phenotype.

Histone deacetylases in herpesvirus replication and virus-stimulated host defense

Emerging evidence highlights a critical role for protein acetylation during herpesvirus infection. As prominent modulators of protein acetylation, histone deacetylases (HDACs) are essential transcriptional and epigenetic regulators. Not surprisingly, viruses have evolved a wide array of mechanisms to subvert HDAC functions. Here, we review the mechanisms underlying HDAC regulation during herpesvirus infection. We next discuss the roles of acetylation in host defense against herpesvirus infection. Finally, we provide a perspective on the contribution of current mass spectrometry-based “omic” technologies to infectious disease research, offering a systems biology view of infection.

Regulation of alphaherpesvirus infections by the ICP0 family of proteins

Immediate-early protein ICP0 of herpes simplex virus type 1 (HSV-1) is important for the regulation of lytic and latent viral infection. Like the related proteins expressed by other alphaherpesviruses, ICP0 has a zinc-stabilized RING finger domain that confers E3 ubiquitin ligase activity. This domain is essential for the core functions of ICP0 and its activity leads to the degradation of a number of cellular proteins, some of which are involved in cellular defences that restrict viral infection. The article reviews recent advances in ICP0-related research, with an emphasis on the mechanisms by which ICP0 and related proteins counteract antiviral restriction and the roles in this process of cellular nuclear substructures known as ND10 or PML nuclear bodies. We also summarize recent advances in the understanding of the biochemical aspects of ICP0 activity. These studies highlight the importance of the SUMO conjugation pathway in both intrinsic resistance to HSV-1 infection and in substrate targeting by ICP0. The topics discussed in this review are relevant not only to HSV-1 infection, but also to cellular intrinsic resistance against herpesviruses more generally and the mechanisms by which viruses can evade this restriction.

A pre-immediate-early role for tegument ICP0 in the proteasome-dependent entry of herpes simplex virus

Herpes simplex virus (HSV) entry requires host cell 26S proteasomal degradation activity at a postpenetration step. When expressed in the infected cell, the HSV immediate-early protein ICP0 has E3 ubiquitin ligase activity and interacts with the proteasome. The cell is first exposed to ICP0 during viral entry, since ICP0 is a component of the inner tegument layer of the virion. The function of tegument ICP0 is unknown. Deletion of ICP0 or mutations in the N-terminal RING finger domain of ICP0 results in the absence of ICP0 from the tegument. We show here that these mutations negatively influenced the targeting of incoming capsids to the nucleus. Inhibitors of the chymotrypsin-like activity of the proteasome the blocked entry of virions containing tegument ICP0, including ICP0 mutants that are defective in USP7 binding. However, ICP0-deficient virions were not blocked by proteasomal inhibitors and entered cells via a proteasome-independent mechanism. ICP0 appeared to play a postpenetration role in cells that supported either endocytosis or nonendosomal entry pathways for HSV. The results suggest that ICP0 mutant virions are defective upstream of viral gene expression at a pre-immediate-early step in infection. We propose that proteasome-mediated degradation of a virion or host protein is regulated by ICP0 to allow efficient delivery of entering HSV capsids to the nuclear periphery.

Infection of cultured bovine cells with bovine herpesvirus 1 (BHV-1) or Sendai virus induces different beta interferon subtypes

In contrast to mice or humans, cattle contain three beta interferon (IFN-β) genes with distinct transcriptional promoters suggesting IFN-β gene expression is not stimulated the same by different viruses. To test this hypothesis, we compared expression of the three IFN-β subtypes after infection with a RNA virus, Sendai, versus a large DNA virus, bovine herpesvirus 1 (BHV-1). Infection of low passage bovine kidney (BK) or established bovine kidney cells (CRIB) with Sendai virus has consistently led to high levels of IFN-β1 RNA. Conversely, infection of CRIB cells, but not BK cells, with BHV-1 increased IFN-β3 RNA levels and to a lesser extent the other two IFN-β subtypes. Inhibition of de novo protein synthesis with cycloheximide resulted in higher levels of IFN-β1 and IFN-β2 RNA levels after BHV-1 infection. Further studies demonstrated that BHV-1 immediate early and/or early genes were primarily responsible for inhibiting the IFN response in BK cells. The three bovine IFN-β promoters were cloned upstream of a reporter gene construct, and their properties analyzed in transient transfection assays. Only the IFN-β3 promoter was trans-activated by IRF3 (interferon responsive factor 3). IRF7 and double stranded RNA (polyI:C) stimulated IFN-β1 and IFN-β3 promoter activity, but not IFN-β2. Relative to the human IFN-β promoter, the IFN-β3 promoter contained fewer nucleotide differences in the positive regulatory domain III (PRD III), PRD IV, and PRD I compared to the IFN-β1 and IFN-β2 promoter. Collectively, these studies provide evidence that virus infection differentially stimulates expression of the three bovine IFN-β genes.

Bovine herpesvirus type 1 (BHV-1) is an important cofactor in the bovine respiratory disease complex

BHV-1 is an important pathogen of cattle. Because of its ability to induce immune suppression, BHV-1 is an important agent in the multifactorial disorder, bovine respiratory disease complex (BRDC). BHV-1 encodes several proteins that inhibit various arms of the immune system suggesting that these proteins are important in the development of BRDC.

Human cytomegalovirus UL29/28 protein interacts with components of the NuRD complex which promote accumulation of immediate-early RNA

Histone deacetylation plays a pivotal role in regulating human cytomegalovirus gene expression. In this report, we have identified candidate HDAC1-interacting proteins in the context of infection by using a method for rapid immunoisolation of an epitope-tagged protein coupled with mass spectrometry. Putative interactors included multiple human cytomegalovirus-coded proteins. In particular, the interaction of pUL38 and pUL29/28 with HDAC1 was confirmed by reciprocal immunoprecipitations. HDAC1 is present in numerous protein complexes, including the HDAC1-containing nucleosome remodeling and deacetylase protein complex, NuRD. pUL38 and pUL29/28 associated with the MTA2 component of NuRD, and shRNA-mediated knockdown of the RBBP4 and CHD4 constituents of NuRD inhibited HCMV immediate-early RNA and viral DNA accumulation; together this argues that multiple components of the NuRD complex are needed for efficient HCMV replication. Consistent with a positive acting role for the NuRD elements during viral replication, the growth of pUL29/28- or pUL38-deficient viruses could not be rescued by treating infected cells with the deacetylase inhibitor, trichostatin A. Transient expression of pUL29/28 enhanced activity of the HCMV major immediate-early promoter in a reporter assay, regardless of pUL38 expression. Importantly, induction of the major immediate-early reporter activity by pUL29/28 required functional NuRD components, consistent with the inhibition of immediate-early RNA accumulation within infected cells after knockdown of RBBP4 and CHD4. We propose that pUL29/28 modifies the NuRD complex to stimulate the accumulation of immediate-early RNAs.

A key event in regulating gene expression involves changes in the acetylation status of core histones. Regulation is accomplished by a balance between the addition of acetyl groups by histone acetyltransferase enzymes and removal of the moieties by deacetylases. These changes are essential in regulating cellular differentiation and proliferation and, likewise, disruption results in a variety of pathologies, including cancer. In addition, these key regulators are targeted by herpesviruses to ensure persistent infection during the life of the host. In the case of the herpesvirus human cytomegalovirus (HCMV), changes in histone acetylation have been implicated in the choice between latent and acute phases of infection. We have used a focused proteomics approach to identify proteins that are interacting with and regulating the histone deacetylase 1 (HDAC1) protein during acute cytomegalovirus infection. Our studies identified numerous cellular and viral proteins including HCMV pUL29/28. This protein bound to components of the nucleosome remodeling and deacetylase complex, NuRD, and functional NuRD components were necessary for HCMV gene expression and infection. Our study demonstrates a new tool for studying host-pathogen interactions as well as provides new insights into the complex regulation of HDAC1 during HCMV replication.

Chromatinisation of herpesvirus genomes

The double-stranded DNA genomes of herpesviruses exist in at least three alternative global chromatin states characterised by distinct nucleosome content. When encapsidated in virus particles, the viral DNA is devoid of any nucleosomes. In contrast, within latently infected nuclei herpesvirus genomes are believed to form regular nucleosomal structures resembling cellular chromatin. Finally, during productive infection nuclear viral DNA appears to adopt a state of intermediate chromatin formation with irregularly spaced nucleosomes. Nucleosome occupancy coupled with posttranslational histone modifications and other epigenetic marks may contribute significantly to the extent and timing of transcription from the viral genome and, consequently, to the outcome of infection. Recent research has provided first insights into the viral and cellular mechanisms that either maintain individual herpesvirus chromatin states or mediate transition between them. Here, we summarise and discuss both early work and new developments pointing towards common principles pertinent to the dynamic structure and epigenetic regulation of herpesvirus chromatin. Special emphasis is given to the emerging similarities in nucleosome assembly and disassembly processes on herpes simplex virus type 1 and human cytomegalovirus genomes over the course of the viral productive replication cycle and during the switch between latent and lytic infectious stages.

HDAC1 nuclear export induced by pathological conditions is essential for the onset of axonal damage

Histone deacetylase 1 (HDAC1) is a nuclear enzyme involved in transcriptional repression. We detected cytosolic HDAC1 in damaged axons in brains of humans with multiple sclerosis and of mice with cuprizone-induced demyelination, in ex vivo models of demyelination and in cultured neurons exposed to glutamate and tumor necrosis factor-alpha. Nuclear export of HDAC1 was mediated by the interaction with the nuclear receptor CRM-1 and led to impaired mitochondrial transport. The formation of complexes between exported HDAC1 and members of the kinesin family of motor proteins hindered the interaction with cargo molecules, thereby inhibiting mitochondrial movement and inducing localized beading. This effect was prevented by inhibiting HDAC1 nuclear export with leptomycin B, treating neurons with pharmacological inhibitors of HDAC activity or silencing HDAC1 but not other HDAC isoforms. Together these data identify nuclear export of HDAC1 as a critical event for impaired mitochondrial transport in damaged neurons.

Regulation of Innate Immune Responses by Bovine Herpesvirus 1 and Infected Cell Protein 0 (bICP0)

Bovine herpesvirus 1 (BoHV-1) infected cell protein 0 (bICP0) is an important transcriptional regulatory protein that stimulates productive infection. In transient transfection assays, bICP0 also inhibits interferon dependent transcription. bICP0 can induce degradation of interferon stimulatory factor 3 (IRF3), a cellular transcription factor that is crucial for activating beta interferon (IFN-β) promoter activity. Recent studies also concluded that interactions between bICP0 and IRF7 inhibit trans-activation of IFN-β promoter activity. The C3HC4 zinc RING (really important new gene) finger located near the amino terminus of bICP0 is important for all known functions of bICP0. A recombinant virus that contains a single amino acid change in a well conserved cysteine residue of the C3HC4 zinc RING finger of bICP0 grows poorly in cultured cells, and does not reactivate from latency in cattle confirming that the C3HC4 zinc RING finger is crucial for viral growth and pathogenesis. A bICP0 deletion mutant does not induce plaques in permissive cells, but induces autophagy in a cell type dependent manner. In summary, the ability of bICP0 to stimulate productive infection, and repress IFN dependent transcription plays a crucial role in the BoHV-1 infection cycle.

Epigenetic modulation of gene expression from quiescent herpes simplex virus genomes

The ability of herpes simplex virus to persist in cells depends on the extent of viral-gene expression, which may be controlled by epigenetic mechanisms. We used quiescent infection with the viral mutants d109 and d106 to explore the effects of cell type and the presence of the viral protein ICP0 on the expression and chromatin structure of the human cytomegalovirus (HCMV) tk and gC promoters on the viral genome. Expression from the HCMV promoter on the d109 genome decreased with time and was considerably less in HEL cells than in Vero cells. Expression from the HCMV promoter in d106 was considerably more abundant than in d109, and this increased with time in both cell types. The same pattern of expression was seen on the tk and gC genes on the viral genomes, although the levels of tk and gC RNA were approximately 10(2)- and 10(5)-fold lower than those of wild-type virus in d106 and d109, respectively. In micrococcal-nuclease digestion experiments, nucleosomes were evident on the d109 genome, and the amount of total H3 as determined by chromatin immunoprecipitation was considerably greater on d109 than d106 genomes. The acetylation of histone H3 on the d106 genomes was evident at early and late times postinfection in Vero cells, but only at late times in HEL cells. The same pattern was observed for H3 acetylated on lysine 9. Trimethylation of H3K9 on d109 genomes was evident only at late times postinfection in Vero cells, while it was observed both early and late in HEL cells. Heterochromatin protein 1gamma (HP1gamma) was generally present only on d109 genomes at late times postinfection of HEL cells. The observations of chromatin structure correlate with the expression patterns of the three analyzed genes on the quiescent genomes. Therefore, several mechanisms generally affect the expression and contribute to the silencing of persisting genomes. These are the abundance of nucleosomes, the acetylation state of the histones, and heterochromatin. The extents to which these different mechanisms contribute to repression vary in different cell types and are counteracted by the presence of ICP0.

A review of the biology of bovine herpesvirus type 1 (BHV-1), its role as a cofactor in the bovine respiratory disease complex and development of improved vaccines

Infection of cattle by bovine herpesvirus type 1 (BHV-1) can lead to upper respiratory tract disorders, conjunctivitis, genital disorders and immune suppression. BHV-1-induced immune suppression initiates bovine respiratory disease complex (BRDC), which costs the US cattle industry approximately 3 billion dollars annually. BHV-1 encodes at least three proteins that can inhibit specific arms of the immune system: (i) bICP0 inhibits interferon-dependent transcription, (ii) the UL41.5 protein inhibits CD8+ T-cell recognition of infected cells by preventing trafficking of viral peptides to the surface of the cells and (iii) glycoprotein G is a chemokine-binding protein that prevents homing of lymphocytes to sights of infection. Following acute infection of calves, BHV-1 can also infect and induce high levels of apoptosis of CD4+ T-cells. Consequently, the ability of BHV-1 to impair the immune response can lead to BRDC. Following acute infection, BHV-1 establishes latency in sensory neurons of trigeminal ganglia (TG) and germinal centers of pharyngeal tonsil. Periodically BHV-1 reactivates from latency, virus is shed, and consequently virus transmission occurs. Two viral genes, the latency related gene and ORF-E are abundantly expressed during latency, suggesting that they regulate the latency-reactivation cycle. The ability of BHV-1 to enter permissive cells, infect sensory neurons and promote virus spread from sensory neurons to mucosal surfaces following reactivation from latency is also regulated by several viral glycoproteins. The focus of this review is to summarize the biology of BHV-1 and how this relates to BRDC.

Chk2 is required for HSV-1 ICP0-mediated G2/M arrest and enhancement of virus growth

ICP0 is a multi-functional herpes simplex virus type 1 (HSV-1) immediate-early (IE) gene product that contributes to efficient virus growth and reactivation from latency. Here we show that HSV-1-induced cell-cycle arrest at the G2/M border requires ICP0 and Chk2 kinase and that ICP0 expression by transfection or infection induces ATM-dependent phosphorylation of Chk2 and Cdc25C. Infection of cells with a replication-defective mutant virus deleted for all the regulatory IE genes except ICP0 (TOZ22R) induced G2/M arrest whereas a mutant virus deleted in addition for ICP0 (QOZ22R) failed to do so. Chk2-deficient cells and cells expressing a kinase-deficient Chk2 did not undergo cell-cycle arrest in response to TOZ22R infection. Chk2 deficiency diminished the growth of wild-type HSV-1, but not the growth of an ICP0-deleted recombinant virus. Together, these results are consistent with the interpretation that ICP0 activates a DNA damage response pathway to arrest cells in G2/M phase and promote virus growth.

Bovine herpesvirus type 1 induces cell death by a cell-type-dependent fashion

Bovine herpesvirus 1 (BHV-1), a member of the alpha-herpesvirinae sub-family, causes significant losses to the cattle industry. BHV-1 establishes latency in trigeminal ganglionic sensory neurons, but periodically reactivates from latency. Previous studies suggested that infection with BHV-1-induced novel morphological changes in rabbit skin (RS) cells versus bovine kidney cells (MDBK). Consequently, we hypothesized that viral infection led to a novel form of cell death in RS cells compared to MDBK cells. To test this hypothesis, we examined the levels of apoptosis in these cell types following infection with BHV-1. Infection of RS, but not MDBK, cells leads to high levels of apoptosis compared to mock-infected cells. Previous studies indicated that a BHV-1 recombinant virus that does not express the bICP0 protein grows poorly in permissive cells and induces a persistent-like infection. This suggested that bICP0 played an important role in regulating cell death following infection. To test this hypothesis, we compared the levels of apoptosis in cells infected with the bICP0 null mutant versus viral strains that expressed bICP0. The bICP0 null mutant induces low levels of apoptosis in RS or MDBK cells. When MDBK cells are treated with UV light prior to infection, bICP0 expressing viral strains, but not the bICP0 null mutant, inhibited UV-induced apoptosis. Infection of MDBK cells with the bICP0 null mutant, leads to an accumulation of autophagosomes that are not detected following infection with bICP0 expressing viruses. These studies suggest that the bICP0 null mutant induces autophagy in MDBK cells, and bICP0 protein expression mediates cell-type specific cytotoxicity.

The varicella-zoster virus immediate-early 63 protein affects chromatin-controlled gene transcription in a cell-type dependent manner

Background

Varicella Zoster Virus Immediate Early 63 protein (IE63) has been shown to be essential for VZV replication, and critical for latency establishment. The activity of the protein as a transcriptional regulator is not fully clear yet. Using transient transfection assays, IE63 has been shown to repress viral and cellular promoters containing typical TATA boxes by interacting with general transcription factors.

Results

In this paper, IE63 regulation properties on endogenous gene expression were evaluated using an oligonucleotide-based micro-array approach. We found that IE63 modulates the transcription of only a few genes in HeLa cells including genes implicated in transcription or immunity. Furthermore, we showed that this effect is mediated by a modification of RNA POL II binding on the promoters tested and that IE63 phosphorylation was essential for these effects. In MeWo cells, the number of genes whose transcription was modified by IE63 was somewhat higher, including genes implicated in signal transduction, transcription, immunity, and heat-shock signalling. While IE63 did not modify the basal expression of several NF-κB dependent genes such as IL-8, ICAM-1, and IκBα, it modulates transcription of these genes upon TNFα induction. This effect was obviously correlated with the amount of p65 binding to the promoter of these genes and with histone H3 acetylation and HDAC-3 removal.

Conclusion

While IE63 only affected transcription of a small number of cellular genes, it interfered with the TNF-inducibility of several NF-κB dependent genes by the accelerated resynthesis of the inhibitor IκBα.

A protein encoded by the bovine herpesvirus 1 open reading frame E gene induces neurite-like morphological changes in mouse neuroblastoma cells and is expressed in trigeminal ganglionic neurons

Bovine herpes virus 1 (BHV-1), like other alpha-herpesvirinae subfamily members, establishes latency in sensory neurons. Periodically BHV-1 reactivates from latency, resulting in virus shedding and spread to uninfected cattle. Although reactivation from latency does not usually lead to recurrent disease, the latency-reactivation cycle is crucial for virus transmission. The latency-related (LR) RNA is abundantly expressed during latency, and expression of a LR encoded protein is necessary for dexamethasone-induced reactivation from latency in cattle. Within LR promoter sequences, a small open reading frame (ORF) was identified (ORF-E) that is antisense to the LR-RNA, and downstream of the bICP0 gene. ORF-E transcription is consistently detected in trigeminal ganglia (TG) of latently infected calves, suggesting ORF-E expression plays a role in the latency-reactivation cycle. Polyclonal antiserum directed against an ORF-E peptide or the entire ORF-E protein specifically recognizes the nucleus of sensory neurons in TG of latently infected calves. The ORF-E peptide-specific antiserum also recognizes a protein when mouse neuroblastoma cells (neuro-2A) are transfected with an ORF-E expression construct. In contrast to the growth inhibiting properties of the LR gene, stably transfected ORF-E-expressing cells were obtained. Neuro-2A cells stably transfected with a plasmid expressing ORF-E induced morphological changes that resembled neurite-like projections. In contrast, neurite-like projections were not observed following transfection of neuro-2A cells with an empty vector. These studies suggest that a protein encoded by ORF-E has the potential to alter the physiology or metabolism of neuronal cell types, which may be important for long-term latency.

The infected cell protein 0 encoded by bovine herpesvirus 1 (bICP0) induces degradation of interferon response factor 3 and, consequently, inhibits beta interferon promoter activity

The ICP0 protein (bICP0) encoded by bovine herpesvirus 1 is the major viral regulatory protein because it stimulates all viral promoters and, consequently, productive infection. Like other ICP0 analogues encoded by Alphaherpesvirinae subfamily members, bICP0 contains a zinc RING finger near its amino terminus that is necessary for activating transcription, regulating subcellular localization, and inhibiting interferon-dependent transcription. In this study, we discovered that sequences near the C terminus, and the zinc RING finger, are necessary for inhibiting the human beta interferon (IFN-beta) promoter. In contrast to herpes simplex virus type 1-encoded ICP0, bICP0 reduces interferon response factor 3 (IRF3), but not IRF7, protein levels in transiently transfected cells. The zinc RING finger and sequences near the C terminus are necessary for bICP0-induced degradation of IRF3. A proteasome inhibitor, lactacystin, interfered with bICP0-induced degradation of IRF3, suggesting that bICP0, directly or indirectly, targets IRF3 for proteasome-dependent degradation. IRF3, but not IRF7, is not readily detectable in the nuclei of productively infected bovine cells during the late stages of infection. In the context of productive infection, IRF3 and IRF7 are detected in the nucleus at early times after infection. At late times after infection, IRF7, but not IRF3, is still detectable in the nuclei of infected cells. Collectively, these studies suggest that the ability of bICP0 to reduce IRF3 protein levels is important with respect to disarming the IFN response during productive infection.

RING finger proteins of infectious spleen and kidney necrosis virus (ISKNV) function as ubiquitin ligase enzymes

Infectious spleen and kidney necrosis virus (ISKNV) is the etiological agent that causes a pandemic and severe disease in fish characteristic of enlarged and damaged spleen and kidney. To identify viral proteins involved in infection and pathogenesis, we characterized five open reading frames (ORFs) of the ISKNV genome, ORF12, ORF65, ORF66, ORF99 and ORF111, which encode RING finger proteins (RFPs). We assessed the ubiquitin ligase (E3) activity of these recombinant RFPs fused to maltose-binding protein (MBP) using an in vitro ubiquitination assay and demonstrated that ORF12, ORF65, ORF66 and ORF111 possess the E3 activity in the presence of ubiquitin activating enzyme (E1), ubiquitin conjugating enzyme (E2), ubiquitin and zinc ion. E3 activity of ISKNV RFPs strictly depends on the UbcH5 E2 subfamily (ORF12 and ORF65 depend on UbcH5a/c, ORF66 and ORF111 depend on UbcH5a/b/c). Furthermore, point mutation in the RING domain completely abrogated ORF66 E3 activity, indicating the RING motif was essential for RFP of ISKNV. In addition, zinc ion was required as an enhancer for ISKNV RFP to exert its E3 function. Investigation of RFPs of ISKNV helps to understand their functions in the infection process and in the virus-host interaction.

High-frequency epigenetic repression and silencing of retroviruses can be antagonized by histone deacetylase inhibitors and transcriptional activators, but uniform reactivation in cell clones is restricted by additional mechanisms

Integrated retroviral DNA is subject to epigenetic gene silencing, but the viral and host cell properties that influence initiation, maintenance, and reactivation are not fully understood. Here we describe rapid and high-frequency epigenetic repression and silencing of integrated avian sarcoma virus (ASV)-based vector DNAs in human HeLa cells. Initial studies utilized a vector carrying the strong human cytomegalovirus (hCMV) immediate-early (IE) promoter to drive expression of a green fluorescent protein (GFP) reporter gene, and cells were sorted into two populations based on GFP expression [GFP(+) and GFP(-)]. Two potent epigenetic effects were observed: (i) a very broad distribution of GFP intensities among cells in the GFP(+) population as well as individual GFP(+) clones and (ii) high-frequency GFP reporter gene silencing in GFP(-) cells. We previously showed that histone deacetylases (HDACs) can associate with ASV DNA soon after infection and may act to repress viral transcription at the level of chromatin. Consistent with this finding, we report here that treatment with the histone deacetylase inhibitor trichostatin A (TSA) induces GFP activation in GFP(-) cells and can also increase GFP expression in GFP(+) cells. In the case of the GFP(-) populations, we found that after removal of TSA, GFP silencing was reestablished in a subset of cells. We used that finding to enrich for stable GFP(-) cell populations in which viral GFP reporter expression could be reactivated by TSA; furthermore, we found that the ability to isolate such populations was independent of the promoter driving the GFP gene. In such enriched cultures, hCMV IE-driven, but not the viral long terminal repeat-driven, silent GFP reporter expression could be reactivated by the transcriptional activator prostratin. Microscopy-based studies using synchronized cells revealed variegated reactivation in cell clones, indicating that secondary epigenetic effects can restrict reactivation from silencing. Furthermore we found that entry into S phase was not required for reactivation. We conclude that HDACs can act rapidly to initiate and maintain promoter-independent retroviral epigenetic repression and silencing but that reactivation can be restricted by additional mechanisms.

Evidence that the herpes simplex virus type 1 ICP0 protein does not initiate reactivation from latency in vivo

The stress-induced host cell factors initiating the expression of the herpes simplex virus lytic cycle from the latent viral genome are not known. Previous studies have focused on the effect of specific viral proteins on reactivation, i.e., the production of detectable infectious virus. However, identification of the viral protein(s) through which host cell factors transduce entry into the lytic cycle and analysis of the promoter(s) of this (these) first protein(s) will provide clues to the identity of the stress-induced host cell factors important for reactivation. In this report, we present the first strategy developed for this type of analysis and use this strategy to test the established hypothesis that the herpes simplex virus ICP0 protein initiates reactivation from the latent state. To this end, ICP0 null and promoter mutants were analyzed for the abilities (i) to exit latency and produce lytic-phase viral proteins (initiate reactivation) and (ii) to produce infectious viral progeny (reactivate) in explant and in vivo. Infection conditions were manipulated so that approximately equal numbers of latent infections were established by the parental strains, the mutants, and their genomically restored counterparts, eliminating disparate latent pool sizes as a complicating factor. Following hyperthermic stress (HS), which induces reactivation in vivo, equivalent numbers of neurons exited latency (as evidenced by the expression of lytic-phase viral proteins) in ganglia latently infected with either the ICP0 null mutant dl1403 or the parental strain. In contrast, infectious virus was detected in the ganglia of mice latently infected with the parental strain but not with ICP0 null mutant dl1403 or FXE. These data demonstrate that the role of ICP0 in the process of reactivation is not as a component of the switch from latency to lytic-phase gene expression; rather, ICP0 is required after entry into the lytic cycle has occurred. Similar analyses were carried out with the DeltaTfi mutant, which contains a 350-bp deletion in the ICP0 promoter, and the genomically restored isolate, DeltaTfiR. The numbers of latently infected neurons exiting latency were not different for DeltaTfi and DeltaTfiR. However, DeltaTfi did not reactivate in vivo, whereas DeltaTfiR reactivated in approximately 38% of the mice. In addition, ICP0 was detected in DeltaTfiR-infected neurons exiting latency but was not detected in those neurons exiting latency infected with DeltaTfi. We conclude that while ICP0 is important and perhaps essential for infectious virus production during reactivation in vivo, this protein is not required and appears to play no major role in the initiation of reactivation in vivo.

Trichostatin-A enhances adaptive immune responses to DNA vaccination

BACKGROUND

The efficacy of DNA vaccines to date has overall been disappointing, especially in large animal models and in humans, which might be partially explained by the chromatinization of the administered foreign DNA. Trichostatin-A (TSA) is a specific inhibitor for histone deacetylase (HDAC) and a gene expression enhancer in in vitro DNA viral infection, including herpes simplex type 1 (HSV-1) and cytomegalovirus (CMV).

OBJECTIVES

We sought to determine if increasing antigen expression of DNA vaccines through inhibition of HDAC-induced chromatin silencing using TSA would enhance DNA vaccine efficacy in vivo.

STUDY DESIGN

A luciferase assay was used to detect effects of TSA on different promoters in vitro. The effects of TSA on DNA vaccination of mice were determined by neutralization assays for antibody production and interleukin staining for detection of specific T cell responses.

RESULTS

Mice receiving TSA in combination with a DNA vaccine exhibited higher antibody responses to the vaccine than mice not given TSA. Co-administration of TSA also enhanced specific CD8 T cells response.

CONCLUSION

Drugs such as TSA that reduce initial gene silencing by preventing histone deacetylation can increase immune responses to DNA vaccination.

Bovine herpesvirus 1 immediate-early protein (bICP0) interacts with the histone acetyltransferase p300, which stimulates productive infection and gC promoter activity

The immediate-early protein, bICP0, ofBovine herpesvirus 1(BHV-1) transactivates viral promoters and stimulates productive infection. bICP0 is expressed constitutively during productive infection, as its gene contains an immediate-early and an early promoter. Like other ICP0 homologues encoded by members of the subfamilyAlphaherpesvirinae, bICP0 contains a zinc RING finger located near its N terminus. Mutations that disrupt the bICP0 zinc RING finger impair its ability to activate transcription, stimulate productive infection, inhibit interferon-dependent transcription in certain cell types and regulate subnuclear localization. bICP0 also interacts with a cellular chromatin-remodelling enzyme, histone deacetylase 1 (HDAC1), and can relieve HDAC1-mediated transcriptional repression, suggesting that bICP0 inhibits silencing of the viral genome. In this study, it was shown that bICP0 interacted with the histone acetyltransferase p300 during productive infection and in transiently transfected cells. In addition, p300 enhanced BHV-1 productive infection and transactivated a late viral promoter (gC). In contrast, a CH3-domain deletion mutant of p300, which is a dominant-negative mutant, did not activate the gC promoter. bICP0 and p300 cooperated to activate the gC promoter, suggesting that there is a synergistic effect on promoter activation. As p300 can activate certain antiviral signalling pathways (for example, interferon), it was hypothesized that interactions between p300 and bICP0 may dampen the antiviral response following infection.

ICP0 and the US3 protein kinase of herpes simplex virus 1 independently block histone deacetylation to enable gene expression

SK-N-SH cells exposed to low ratios of ICP0-null (DeltaICP0) mutants of herpes simplex virus per cell express the viral alpha proteins, but the progression to beta and gamma gene expression does not ensue. In these restrictive cells, post-alpha gene expression can be induced after exposure of the infected cells to sodium butyrate, an indication that VP16 brought into cells by the virus and the alpha gene products made after infection cannot block the silencing of viral post-alpha genes by histone deacetylases (HDACs). This observation is consistent with evidence reported earlier that ICP0 dissociates HDAC1/2 from the CoREST/REST complex. In permissive U2OS cells, replication is independent of the ratio of DeltaICP0 mutant per cell. To determine whether other viral genes are involved in blocking HDACs, we used a surrogate system consisting of baculoviruses carrying viral or cellular genes driven by CMV immediate-early promoter. Expression of these genes requires blocking of histone deacetylation. We report that (i) cotransduced U(S)3 or U(S)3.5 protein kinase substitutes for sodium butyrate in enabling the expression of a reporter gene in restrictive cells and enhancing it in permissive cells; (ii) HDAC1 is phosphorylated concomitant with the expression of reporter genes; and (iii) the amounts and appearance of HDAC1 are altered in transduced cells expressing U(S)3 protein kinase in the absence of other viral proteins. We conclude that the U(S)3 protein kinase blocks histone deacetylation by a mechanism distinct from that of ICP0 and that debilitated histone deacetylation contributes to the permissiveness of U2OS cells for DeltaICP0 mutants.

Chromatin regulation of virus infection

Cellular chromatin forms a dynamic structure that maintains the stability and accessibility of the host DNA genome. Viruses that enter and persist in the nucleus must, therefore, contend with the forces that drive chromatin formation and regulate chromatin structure. In some cases, cellular chromatin inhibits viral gene expression and replication by suppressing DNA accessibility. In other cases, cellular chromatin provides essential structure and organization to the viral genome and is necessary for successful completion of the viral life cycle. Consequently, viruses have acquired numerous mechanisms to manipulate cellular chromatin to ensure viral genome survival and propagation.

Host cell targets of immediate-early protein BICP22 of bovine herpesvirus 1

The immediate-early (IE) protein BICP22 of bovine herpesvirus 1 (BHV-1) acts as transrepressor protein on viral promoters of different kinetic classes. In the present work, we looked for host cell targets of BICP22 using a yeast two-hybrid system and identified seven candidates: (1) JIK, a serine/threonine kinase of the sterile 20 protein (STE20) family that inhibits stress-related pathways; (2) cAMP response element binding protein-like 2 (CREBL2), which in its bZip domain shares homology with CREB, modulating transcription of cAMP responsive genes; (3) DNA-dependent ATPase and helicase (ATRX), a protein of the SNF2 family altering nucleosome structure; (4) scaffold attachment factor B (SAF-B), which helps to organize chromatin into topologically separated loops; (5) peptidylglycine alpha-amidating monooxygenase COOH-terminal interactor protein 1 (PAMCIP1), involved in regulation of the secretory pathway in the perinuclear area; (6) zinc finger protein (ZNF38) found in proliferating cells and possibly associated with meiosis in male and female gametogenesis; (7) FLJ22709, hypothetical protein conserved among various species, containing an occludin/ELL domain. To confirm some of the interactions by confocal fluorescence microscopy, BICP22 was tagged with red fluorescent protein in an amplicon, and selected target sequences were tagged with green fluorescent protein in plasmid expression vectors. Upon amplicon transduction of Vero cells and plasmid transfection, CREBL2 and ZNF38 both colocalized with BICP22 in distinct nuclear domains.

Functional analysis of bovine herpesvirus 1 (BHV-1) genes expressed during latency

Bovine herpes virus 1 (BHV-1) establishes latency in sensory neurons of trigeminal ganglia (TG), and germinal centers of pharyngeal tonsil. Periodically BHV-1 reactivates from latency, virus is shed, and consequently virus transmission occurs. Two transcripts, the latency related (LR) RNA and ORF-E, are abundantly expressed in TG of latently infected cattle. A LR mutant strain of BHV-1 was constructed that contains stop codons near the beginning of the LR-RNA. The LR mutant virus does not express two proteins encoded by the LR gene, or reactivate from latency suggesting that LR protein expression regulates the latency-reactivation cycle. Higher levels of apoptosis occur in TG of calves infected with the LR mutant versus wild type BHV-1 indicating that the anti-apoptotic properties of the LR gene regulate the latency-reactivation cycle. The LR gene also inhibits bICP0 expression and mammalian cell growth, but these functions do not require LR protein expression. In contrast, the ability of the LR gene to inhibit apoptosis appears to require LR protein expression. A small open reading frame (ORF-E) that is located within the LR promoter is expressed in the nucleus of neuroblastoma cells. We predict that the LR gene and ORF-E regulate the BHV-1 latency-reactivation cycle.

The bovine herpesvirus 1 gene encoding infected cell protein 0 (bICP0) can inhibit interferon-dependent transcription in the absence of other viral genes

The infected cell protein 0 (bICP0) encoded byBovine herpesvirus 1(BHV-1) stimulates viral gene expression and productive infection. As bICP0 is expressed constitutively during productive infection, it is considered to be the major viral regulatory protein. Like other alphaherpesvirus ICP0 homologues, bICP0 contains a zinc RING finger near its N terminus that activates transcription and regulates subcellular localization. In this study, evidence is provided that bICP0 represses the human beta interferon (IFN-β) promoter and a simple promoter with consensus IFN-stimulated response elements following stimulation with double-stranded RNA (polyinosinic–polycytidylic acid), IFN regulatory factor 3 (IRF3) or IRF7. bICP0 also inhibits the ability of two protein kinases (TBK1 and IKKε) to activate IFN-βpromoter activity. The zinc RING finger is necessary for inhibiting IFN-dependent transcription in certain cell types. Collectively, these studies suggest that bICP0 activates productive infection by stimulating viral gene expression and inhibiting IFN-dependent transcription.

Analysis of a bovine herpesvirus 1 recombinant virus that does not express the bICP0 protein

Bovine herpesvirus 1 (BHV-1) infected-cell protein 0 (bICP0) stimulates productive infection by activating viral gene expression. In this study, an attempt was made to construct a recombinant virus with point mutations in the C3HC4zinc RING finger of bICP0, as this domain is necessary for activating viral transcription and productive infection. A virus was identified in bovine cells that induced small clusters of infected cells resembling a small plaque. Instead of the expected mutations within the zinc RING finger, this virus contained a point mutation within the initiating ATG of bICP0, a point mutation two bases downstream from the ATG mutation and deletion of flanking plasmid sequences used for homologous recombination. The bICP0 mutant was rescued with wild-type (wt) bICP0 sequences and the bICP0-rescued virus produced wt plaques. The bICP0-rescued virus and wt BHV-1, but not the mutant, expressed the bICP0 protein during productive infection of bovine cells, suggesting that the mutant virus was a null mutant. Consequently, the mutant was designated the bICP0 null mutant. Infection of bovine cells with the bICP0 null mutant resulted in at least 100-fold lower virus titres, indicating that bICP0 protein expression is important, but not required, for virus production. When bovine cells infected with the bICP0 null mutant virus were subcultured, the cells continued to divide, but viral DNA could be detected after more than 35 passages, suggesting that the bICP0 null mutant induced a persistent-like infection in bovine cells and that it may be useful for generating additional bICP0 mutants.

Identification of functional domains within the bICP0 protein encoded by bovine herpesvirus 1

It is believed that the bICP0 protein encoded by bovine herpesvirus 1 (BoHV-1) stimulates productive infection by activating viral gene expression. Like the other ICP0-like proteins encoded byalphaherpesvirinaesubfamily members, bICP0 contains a zinc RING finger near its amino terminus. The zinc RING finger of bICP0 activates viral transcription, stimulates productive infection, and is toxic to certain cell types. Apart from the zinc RING finger, bICP0 possesses little similarity to the herpes simplex virus type 1 ICP0 protein making it difficult to predict what regions of bICP0 are important. To begin to identify bICP0 functional domains that are not part of the zinc RING finger, a panel of transposon insertion mutants that span bICP0 was developed. A large domain spanning aa 78–256, and a separate domain that is at or near aa 457 was necessary for efficient transactivation of a simple promoter. Transposon insertion at aa 91 impaired bICP0 protein stability in transfected cells. Insertion of transposons into the acidic domain of bICP0 had little or no effect on transactivation of a simple promoter or protein expression suggesting this region does not play a major role in activating gene expression. Sequences near the C terminus (aa 607–676) contain a functional nuclear localization signal. Collectively, these studies indicated that bICP0 contains several important functional domains: (i) the zinc RING finger, (ii) two separate domains that activate transcription, and (iii) a C-terminal nuclear localization signal that is also necessary for efficient transactivation.

Infected cell protein 0 encoded by bovine herpesvirus 1 can activate caspase 3 when overexpressed in transfected cells

Infection of cattle or bovine cells with bovine herpesvirus 1 (BHV-1) leads to increased apoptosis. Previous studies indicated that BHV-1 infected cell protein 0 (bICP0), the major transcriptional regulatory protein of BHV-1, is toxic in transiently transfected cells. Point mutations within the zinc RING finger of bICP0 reduced toxicity and eliminated the ability of bICP0 to activate viral gene expression. In mouse neuroblastoma cells (neuro-2A) and bovine turbinate cells, bICP0 activated caspase 3, a key regulatory protein in the apoptotic pathway. A pro-apoptotic gene (Bax), but not bICP0, induced caspase 3 cleavage and activation by 8 h after transfection of neuro-2A cells. Conversely, bICP0 or the N-terminal 356 aa of bICP0 did not induce caspase 3 cleavage in neuro-2A cells until 30 h after transfection, suggesting that bICP0 stimulates caspase 3 cleavage by an indirect mechanism. These studies indicate that the toxic functions of bICP0 correlate with caspase 3 cleavage and activation.

During lytic infection herpes simplex virus type 1 is associated with histones bearing modifications that correlate with active transcription

Herpes simplex virus type 1 (HSV-1) is a large (150-kb) double-stranded DNA virus that forms latent infections in neuronal cells of the human peripheral nervous system. Previous work determined that the HSV-1 genome is found in an ordered nucleosomal structure during latent infection. However, during lytic infection, it was unclear whether viral DNA was in a chromatin state. We examined HSV-1 during lytic infection using micrococcal nuclease digestion and chromatin immunoprecipitation. The HSV-1 genome is at least partially nucleosomal, although apparently not in a regular repeating structure. Analysis of histones associated with HSV-1, within both the promoter and the transcribed regions, revealed covalent amino tail modifications similar to those associated with active host mammalian genes. Certain of the modifications were detected in the temporal order expected of the immediate-early, early, and late gene classes. These data suggest that productive infection may be accompanied by acquisition of a permissive chromatin state.

Functional interaction between class II histone deacetylases and ICP0 of herpes simplex virus type 1

This study describes the physical and functional interactions between ICP0 of herpes simplex virus type 1 and class II histone deacetylases (HDACs) 4, 5, and 7. Class II HDACs are mainly known for their participation in the control of cell differentiation through the regulation of the activity of the transcription factor MEF2 (myocyte enhancer factor 2), implicated in muscle development and neuronal survival. Immunofluorescence experiments performed on transfected cells showed that ICP0 colocalizes with and reorganizes the nuclear distribution of ectopically expressed class I and II HDACs. In addition, endogenous HDAC4 and at least one of its binding partners, the corepressor protein SMRT (for silencing mediator of retinoid and thyroid receptor), undergo changes in their nuclear distribution in ICP0-transfected cells. As a result, during infection endogenous HDAC4 colocalizes with ICP0. Coimmunoprecipitation and glutathione S-transferase pull-down assays confirmed that class II but not class I HDACs specifically interacted with ICP0 through their amino-terminal regions. This region, which is not conserved in class I HDACs but homologous to the MITR (MEF2-interacting transcription repressor) protein, is responsible for the repression, in a deacetylase-independent manner, of MEF2 by sequestering it under an inactive form in the nucleus. Consequently, we show that ICP0 is able to overcome the HDAC5 amino-terminal- and MITR-induced MEF2A repression in gene reporter assays. This is the first report of a viral protein interacting with and controlling the repressor activity of class II HDACs. We discuss the putative consequences of such an interaction for the biology of the virus both during lytic infection and reactivation from latency.

Transactivator protein BICP0 of bovine herpesvirus 1 (BHV-1) is blocked by prostaglandin D2 (PGD2), which points to a mechanism for PGD2-mediated inhibition of BHV-1 replication

The immediate-early protein, BICP0, of bovine herpesvirus 1 (BHV-1) transactivates a variety of viral and cellular genes. In a yeast two-hybrid cDNA library screening, we found that lipocalin-type prostaglandin D synthase, which catalyzes the production of prostaglandin D(2) (PGD(2)), is a cellular target of BICP0. We observed that, during wild-type BHV-1 infection, PGD(2) levels were increased intracellularly and decreased in the medium. These effects were absent upon infection with recombinant BHV-1 expressing beta-galactosidase instead of BICP0 (A2G2). Transient-expression assays showed that BICP0 alone caused a significant increase in PGD(2) levels in the cell. PGD(2) repressed BHV-1 replication in cultured cells. Antiviral activities of prostaglandins have been documented long ago, but their mode of action remains to be clarified. Here we provide evidence that PGD(2) impairs the transactivation ability of BICP0 that is necessary for efficient virus replication.

A mutation in the latency-related gene of bovine herpesvirus 1 inhibits protein expression from open reading frame 2 and an adjacent reading frame during productive infection

The latency-related (LR) gene of bovine herpesvirus 1 (BHV-1) is abundantly expressed during latency. A mutant BHV-1 strain that contains three stop codons at the 5' terminus of the LR gene (LR mutant) does not reactivate from latency. This study demonstrates that the LR mutant does not express open reading frame 2 or an adjacent reading frame that lacks an initiating ATG (reading frame C). Since the LR mutant and wild-type BHV-1 express similar levels of LR RNA, we conclude that LR protein expression plays an important role in regulating the latency reactivation cycle in cattle.

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

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 U(S)3 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.

Generation and characterization of an EICP0 null mutant of equine herpesvirus 1

The EICP0 gene (gene 63) of equine herpesvirus 1 (EHV-1) encodes an early regulatory protein that is a promiscuous trans-activator of all classes of viral genes. Bacterial artificial chromosome (BAC) technology and RecE/T cloning were employed to delete the EICP0 gene from EHV-1 strain KyA. Polymerase chain reaction, Southern blot analysis, and DNA sequencing confirmed the deletion of the EICP0 gene and its replacement with a kanamycin resistance gene in mutant KyA. Transfection of rabbit kidney cells with the EICP0 mutant genome produced infectious virus, indicating that the EICP0 gene is not essential for KyA replication in cell culture. Experiments to assess the effect of the EICP0 deletion on EHV-1 gene programming revealed that mRNA expression of the immediate-early gene and representative early and late genes as well as the synthesis of these viral proteins were reduced as compared to the kinetics of viral mRNA and protein synthesis observed for the wild type virus. However, the transition from early to late viral gene expression was not prevented or delayed, suggesting that the absence of the EICP0 gene did not disrupt the temporal aspects of EHV-1 gene regulation. The extracellular virus titer and plaque areas of the EICP0 mutant virus KyADeltaEICP0, in which the gp2-encoding gene 71 gene that is absent in the KyA BAC was restored, were reduced by 10-fold and 19%, respectively, when compared to parental KyA virus; while the titer and plaque areas of mutant KyADeltaEICP0Deltagp2 that lacks both the EICP0 gene and gene 71 were reduced more than 50-fold and 67%, respectively. The above results show that the EICP0 gene is dispensable for EHV-1 replication in cell culture, and that the switch from early to late viral gene expression for the representative genes examined does not require the EICP0 protein, but that the EICP0 protein may be structurally required for virus egress and cell-to-cell spread.

Characterization of human constitutive photomorphogenesis protein 1, a RING finger ubiquitin ligase that interacts with Jun transcription factors and modulates their transcriptional activity

RING finger proteins have been implicated in many fundamental cellular processes, including the control of gene expression. A key regulator of light-dependent development in Arabidopsis thaliana is the constitutive photomorphogenesis protein 1 (atCOP1), a RING finger protein that plays an essential role in translating light/dark signals into specific changes in gene transcription. atCOP1 binds the basic leucine zipper factor HY5 and suppresses its transcriptional activity through a yet undefined mechanism that results in HY5 degradation in response to darkness. Furthermore, the pleiotropic phenotype of atCOP1 mutants indicates that atCOP1 may be a central regulator of several transcriptional pathways. Here we report the cloning and characterization of the human orthologue of atCOP1. Human COP1 (huCOP1) distributes both to the cytoplasm and the nucleus of cells and shows a striking degree of sequence conservation with atCOP1, suggesting the possibility of a functional conservation as well. In co-immunoprecipitation assays huCOP1 specifically binds basic leucine zipper factors of the Jun family. As a functional consequence of this interaction, expression of huCOP1 in mammalian cells down-regulates c-Jun-dependent transcription and the expression of the AP-1 target genes, urokinase and matrix metalloproteinase 1. The RING domain of huCOP1 displays ubiquitin ligase activity in an autoubiquitination assay in vitro; however, suppression of AP-1-dependent transcription by huCOP1 occurs in the absence of changes in c-Jun protein levels, suggesting that this inhibitory effect is independent of c-Jun degradation. Our findings indicate that huCOP1 is a novel regulator of AP-1-dependent transcription sharing the important properties of Arabidopsis COP1 in the control of gene expression.

Stimulation of bovine herpesvirus-1 productive infection by the adenovirus E1A gene and a cell cycle regulatory gene, E2F-4

Identifying cellular genes that promote bovine herpesvirus-1 (BHV-1) productive infection is important, as BHV-1 is a significant bovine pathogen. Previous studies demonstrated that BHV-1 DNA is not very infectious unless cotransfected with a plasmid expressing bICP0, a viral protein that stimulates expression of all classes of viral promoters. Based on these and other studies, we hypothesize that the ability of bICP0 to interact with and modify the function of cellular proteins stimulates virus transcription. If this prediction is correct, cellular proteins that activate virus transcription could, in part, substitute for bICP0 functions. The adenovirus E1A gene and bICP0 encode proteins that are potent activators of viral gene expression, they do not specifically bind DNA and both proteins interact with chromatin-remodelling enzymes. Because of these functional similarities, E1A was tested initially to see if it could stimulate BHV-1 productive infection. E1A consistently stimulates BHV-1 productive infection, but not as efficiently as bICP0. The ability of E1A to bind Rb family members plays a role in stimulating productive infection, suggesting that E2F family members activate productive infection. E2F-4, but not E2F-1, E2F-2 or E2F-5, activates productive infection with similar efficiency as E1A. Next, E2F family members were examined for their ability to activate the BHV-1 immediate-early (IE) transcription unit 1 (IEtu1) promoter, as it regulates IE expression of bICP0 and bICP4. E2F-1 and E2F-2 strongly activate the IEtu1 promoter, but not a BHV-1 IEtu2 promoter or a herpes simplex virus type 1 ICP0 promoter construct. These studies suggest that E2F family members can stimulate BHV-1 productive infection.

The viral control of cellular acetylation signaling

It is becoming clear that the post-translational modification of histone and non-histone proteins by acetylation is part of an important cellular signaling process controlling a wide variety of functions in both the nucleus and the cytoplasm. Recent investigations designate this signaling pathway as one of the primary targets of viral proteins after infection. Indeed, specific viral proteins have acquired the capacity to interact with cellular acetyltransferases (HATs) and deacetylases (HDACs) and consequently to disrupt normal acetylation signaling pathways, thereby affecting viral and cellular gene expression. Here we review the targeting of cellular HATs and HDACs by viral proteins and highlight different strategies adopted by viruses to control cellular acetylation signaling and to accomplish their life cycle.

The latency-related gene of bovine herpesvirus-1 can inhibit the ability of bICP0 to activate productive infection

Transfection of bovine cells with bovine herpesvirus-1 genomic DNA yields low levels of infectious virus. Cotransfection with the bICP0 gene enhances productive infection and virus yield because bICP0 can activate viral gene expression. Since the latency-related (LR) gene overlaps and is antisense to bICP0, the effects of LR gene products on productive infection were tested. The intact LR gene inhibited productive infection in a dose-dependent fashion but LR protein expression was not required. Further studies indicated that LR gene sequences near the 3' terminus of the LR RNA are necessary for inhibiting productive infection. When cotransfected with the bICP0 gene, the LR gene inhibited bICP0 RNA and protein expression in transiently transfected cells. Taken together, these results suggest that abundant LR RNA expression in sensory neurons is one factor that has the potential to inhibit productive infection and consequently promote the establishment and maintenance of latency.

The adenovirus protein Gam1 interferes with sumoylation of histone deacetylase 1

The adenovirus early gene product Gam1 is crucial for virus replication and induces certain cellular genes by inactivating histone deacetylase 1 (HDAC1). We demonstrate that Gam1 (i) destroys promyelocitic leukemia nuclear bodies, (ii) delocalizes SUMO-1 into the cytoplasm and (iii) influences the SUMO-1 pathway. In addition, we show that Gam1 counteracts HDAC1 sumoylation both in vivo and in vitro. Sumoylation of HDAC1 does not seem to be absolutely required for HDAC1 biological activity but is part of a complex regulatory circuit that also includes phosphorylation of the deacetylase. Our data demonstrate that Gam1 is a viral protein that can affect simultaneously two signaling pathways: sumoylation and acetylation.

Histone deacetylase 1 inactivation by an adenovirus early gene product

Gam1 is an early gene product of the avian adenovirus CELO and is essential for viral replication. Gam1 has no homology to any known proteins; however, its early expression and nuclear localization suggest that the protein functions to influence transcription in the infected cell. A determinant of eukaryotic gene expression is the acetylation state of chromosomal histones and other nuclear proteins. We find that Gam1 expression increases the level of transcription from a variety of eukaryotic promoters, similar to the effect of treating cells with the histone deacetylase (HDAC) inhibitor trichostatin A (TSA ). We show that Gam1 can effectively inhibit histone deacetylation by HDAC1 and that Gam1 binds to HDAC1 both in vitro and in vivo. A CELO virus lacking Gam1 (CELOdG) is replication defective, but the defect can be overcome by either expressing an interfering HDAC1 mutant or by treating infected cells with TSA. The identification of a viral early gene product having the specific function of binding and inactivating HDAC suggests that deacetylase complexes play an important role in limiting early gene expression from invading viruses.