Histone deacetylases 1 and 2 are phosphorylated at novel sites during varicella-zoster virus infection

Varicella Zoster Virus Impairs Expression of the Nonclassical Major Histocompatibility Complex Class I-Related Gene Protein (MR1)

The antigen presentation molecule MR1 (major histocompatibility complex, class I-related) presents ligands derived from the riboflavin (vitamin B) synthesis pathway, which is not present in mammalian species or viruses, to mucosal-associated invariant T (MAIT) cells. In this study, we demonstrate that varicella zoster virus (VZV) profoundly suppresses MR1 expression. We show that VZV targets the intracellular reservoir of immature MR1 for degradation, while preexisting, ligand-bound cell surface MR1 is protected from such targeting, thereby highlighting an intricate temporal relationship between infection and ligand availability. We also identify VZV open reading frame (ORF) 66 as functioning to suppress MR1 expression when this viral protein is expressed during transient transfection, but this is not apparent during infection with a VZV mutant virus lacking ORF66 expression. This indicates that VZV is likely to encode multiple viral genes that target MR1. Overall, we identify an immunomodulatory function of VZV whereby infection suppresses the MR1 biosynthesis pathway.

Computational approach to decipher cellular interactors and drug targets during co-infection of SARS-CoV-2, Dengue, and Chikungunya virus

The world is reeling under severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic, and it will be frightening if compounded by other co-existing infections. The co-occurrence of the Dengue virus (DENV) and Chikungunya virus (CHIKV) has been into existence, but recently the co-infection of DENV and SARS-CoV-2 has been reported. Thus, the possibility of DENV, CHIKV, and SARS-CoV-2 co-infection could be predicted in the future with enhanced vulnerability. It is essential to elucidate the host interactors and the connected pathways to understand the biological insights. The in silico approach using Cytoscape was exploited to elucidate the common human proteins interacting with DENV, CHIKV, and SARS-CoV-2 during their probable co-infection. In total, 17 interacting host proteins were identified showing association with envelope, structural, non-structural, and accessory proteins. Investigating the functional and biological behaviour using PANTHER, UniProtKB, and KEGG databases uncovered their association with several cellular pathways including, signaling pathways, RNA processing and transport, cell cycle, ubiquitination, and protein trafficking. Withal, exploring the DrugBank and Therapeutic Target Database, total seven druggable host proteins were predicted. Among all integrin beta-1, histone deacetylase-2 (HDAC2) and microtubule affinity-regulating kinase-3 were targeted by FDA approved molecules/ drugs. Furthermore, HDAC2 was predicted to be the most significant target, and some approved drugs are available against it. The predicted druggable targets and approved drugs could be investigated to obliterate the identified interactions that could assist in inhibiting viral infection.

Host Innate Immune Response and Viral Immune Evasion During Alphaherpesvirus Infection

Both the development of the mammalian innate immune system and the antagonistic strategies acquired by alphaherpesviruses to dismantle it have been shaped by co-evolving virus-host interactions over millions of years. Here, we review mechanisms employed by mammalian cells to detect pathogen molecules, such as viral glycoproteins and nucleic acids, and induce innate immune signaling upon infection with alphaherpesviruses. We further explore strategies acquired by these viruses to bypass immune detection and activation, thereby supporting virus replication and spread. Finally, we discuss the contributions of advanced 'omics' and microscopy methods to these discoveries in immune signaling and highlight emerging technologies that can help to further our understanding of the dynamic interplay between host innate immune responses and virus immune evasion.

Marek's disease virus US3 protein kinase phosphorylates chicken HDAC 1 and 2 and regulates viral replication and pathogenesis

Marek’s disease virus (MDV) is a potent oncogenic alphaherpesvirus that elicits a rapid onset of malignant T-cell lymphomas in chickens. Three MDV types, including GaHV-2 (MDV-1), GaHV-3 (MDV-2) and MeHV-1 (HVT), have been identified and all encode a U_S3 protein kinase. MDV-1 U_S3 is important for efficient virus growth in vitro. To study the role of U_S3 in MDV replication and pathogenicity, we generated an MDV-1 U_S3-null virus and chimeric viruses by replacing MDV-1 U_S3 with MDV-2 or HVT U_S3. Using MD as a natural virus-host model, we showed that both MDV-2 and HVT U_S3 partially rescued the growth deficiency of MDV-1 U_S3-null virus. In addition, deletion of MDV-1 U_S3 attenuated the virus resulting in higher survival rate and lower MDV specific tumor incidence, which could be partially compensated by MDV-2 and HVT U_S3. We also identified chicken histone deacetylase 1 (chHDAC1) as a common U_S3 substrate for all three MDV types while only U_S3 of MDV-1 and MDV-2 phosphorylate chHDAC2. We further determined that U_S3 of MDV-1 and HVT phosphorylate chHDAC1 at serine 406 (S406), while MDV-2 U_S3 phosphorylates S406, S410, and S415. In addition, MDV-1 U_S3 phosphorylates chHDAC2 at S407, while MDV-2 U_S3 targets S407 and S411. Furthermore, biochemical studies show that MDV U_S3 mediated phosphorylation of chHDAC1 and 2 affect their stability, transcriptional regulation activity, and interaction network. Using a class I HDAC specific inhibitor, we showed that MDV U_S3 mediated phosphorylation of chHDAC1 and 2 is involved in regulation of virus replication. Overall, we identified novel substrates for MDV U_S3 and characterized the role of MDV U_S3 in MDV pathogenesis.

Marek’s disease virus (MDV) is a highly contagious and oncogenic avian alphaherpesvirus that causes T-cell lymphomas in chickens. Alphaherpesviruses encoded U_S3 is a multifunctional protein kinase involved in viral replication, apoptosis resistance, and cell-to-cell spread. In this study, we evaluated the importance of MDV U_S3 in regulating MDV replication and pathogenesis in chickens. Our results provide first evidence that MDV U_S3 protein kinase is involved in the replication and pathogenicity of MDV in its natural host. We also identified chicken histone deacetylase 1 and 2 (chHDAC1 and 2) as novel substrates of U_S3 for MDV and characterized the potential impacts of MDV U_S3 induced phosphorylation in their protein stability, transcriptional regulation and protein interactions; to our knowledge, this is the first comparative study of the functions of U_S3 from all three MDV types. This is an important finding towards a better understanding of the functions of alphaherpesviruses encoded U_S3 protein kinase.

Marek's disease virus Meq oncoprotein interacts with chicken HDAC 1 and 2 and mediates their degradation via proteasome dependent pathway

Marek's disease virus (MDV) encodes a basic-leucine zipper (BZIP) protein, Meq, which is considered the major MDV oncoprotein. It has been reported that the oncogenicity of Meq is associated with its interaction with C-terminal binding protein 1 (CtBP), which is also an interaction partner of Epstein-Barr virus encoded EBNA3A and EBNA3C oncoproteins. Since both EBNA3C and CtBP interact with histone deacetylase 1 (HDAC1) and HDAC2, we examined whether Meq shares this interaction with chicken HDAC1 (chHDAC1) and chHDAC2. Using confocal microscopy analysis, we show that Meq co-localizes with chHDAC1 and chHDAC2 in the nuclei of MDV lymphoblastoid tumor cells. In addition, immunoprecipitation assays demonstrate that Meq interacts with chHDAC1 and chHDAC2 in transfected cells and MDV lymphoblastoid tumor cells. Using deletion mutants, interaction domains were mapped to the N-terminal dimerization domain of chHDAC1 and chHDAC2, and the BZIP domain of Meq. Our results further demonstrate that this interaction mediates the degradation of chHDAC1 and chHDAC2 via the proteasome dependent pathway. In addition, our results show that Meq also induces the reduction of global ubiquitinated proteins through a proteasome dependent pathway. In conclusion, our results provide evidence that Meq interacts with chHDAC1 and chHDAC2, and induces their proteasome dependent degradation.

Differential HDAC1/2 network analysis reveals a role for prefoldin/CCT in HDAC1/2 complex assembly

HDAC1 and HDAC2 are components of several corepressor complexes (NuRD, Sin3, CoREST and MiDAC) that regulate transcription by deacetylating histones resulting in a more compact chromatin environment. This limits access of transcriptional machinery to genes and silences transcription. While using an AP-MS approach to map HDAC1/2 protein interaction networks, we noticed that N-terminally tagged versions of HDAC1 and HDAC2 did not assemble into HDAC corepressor complexes as expected, but instead appeared to be stalled with components of the prefoldin-CCT chaperonin pathway. These N-terminally tagged HDACs were also catalytically inactive. In contrast to the N-terminally tagged HDACs, C-terminally tagged HDAC1 and HDAC2 captured complete histone deacetylase complexes and the purified proteins had deacetylation activity that could be inhibited by SAHA (Vorinostat), a Class I/II HDAC inhibitor. This tag-mediated reprogramming of the HDAC1/2 protein interaction network suggests a mechanism whereby HDAC1 is first loaded into the CCT complex by prefoldin to complete folding, and then assembled into active, functional HDAC complexes. Imaging revealed that the prefoldin subunit VBP1 colocalises with nuclear HDAC1, suggesting that delivery of HDAC1 to the CCT complex happens in the nucleus.

HISTONE DEACETYLASE6 Acts in Concert with Histone Methyltransferases SUVH4, SUVH5, and SUVH6 to Regulate Transposon Silencing

Histone deacetylases (HDACs) play important roles in regulating gene expression. In yeast and animals, HDACs act as components of multiprotein complexes that modulate transcription during various biological processes. However, little is known about the interacting proteins of plant HDACs. To identify the plant HDAC complexes and interacting proteins, we developed an optimized workflow using immunopurification coupled to mass spectrometry-based proteomics in Arabidopsis thaliana We found that the histone deacetylase HDA6 can interact with the histone methyltransferases SUVH4, SUVH5, and SUVH6 (SUVH4/5/6). Domain analysis revealed that the C-terminal regions of HDA6 and SUVH5 are important for their interaction. Furthermore, HDA6 interacts with SUVH4/5/6 and coregulates a subset of transposons through histone H3K9 methylation and H3 deacetylation. In addition, two phosphorylated serine residues, S427 and S429, were unambiguously identified in the C-terminal region of HDA6. Phosphomimetics (amino acid substitutions that mimic a phosphorylated protein) of HDA6 resulted in increased enzymatic activity, whereas the mutation of S427 to alanine in HDA6 abolished its interaction with SUVH5 and SUVH6, suggesting that the phosphorylation of HDA6 is important for its activity and function.

Diverse mechanisms evolved by DNA viruses to inhibit early host defenses

In mammalian cells, early defenses against infection by pathogens are mounted through a complex network of signaling pathways shepherded by immune-modulatory pattern-recognition receptors. As obligate parasites, the survival of viruses is dependent on the evolutionary acquisition of mechanisms that tactfully dismantle and subvert the cellular intrinsic and innate immune responses. Here, we review the diverse mechanisms by which viruses that accommodate DNA genomes are able to circumvent activation of cellular immunity. We start by discussing viral manipulation of host defense protein levels by either transcriptional regulation or protein degradation. We next review viral strategies used to repurpose or inhibit these cellular immune factors by molecular hijacking or by regulating their post-translational modification status. Additionally, we explore the infection-induced temporal modulation of apoptosis to facilitate viral replication and spread. Lastly, the co-evolution of viruses with their hosts is highlighted by the acquisition of elegant mechanisms for suppressing host defenses via viral mimicry of host factors. In closing, we present a perspective on how characterizing these viral evasion tactics both broadens the understanding of virus-host interactions and reveals essential functions of the immune system at the molecular level. This knowledge is critical in understanding the sources of viral pathogenesis, as well as for the design of antiviral therapeutics and autoimmunity treatments.

Dynamic phosphorylation of Histone Deacetylase 1 by Aurora kinases during mitosis regulates zebrafish embryos development

Histone deacetylases (HDACs) catalyze the removal of acetyl molecules from histone and non-histone substrates playing important roles in chromatin remodeling and control of gene expression. Class I HDAC1 is a critical regulator of cell cycle progression, cellular proliferation and differentiation during development; it is also regulated by many post-translational modifications (PTMs). Herein we characterize a new mitosis-specific phosphorylation of HDAC1 driven by Aurora kinases A and B. We show that this phosphorylation affects HDAC1 enzymatic activity and it is critical for the maintenance of a proper proliferative and developmental plan in a complex organism. Notably, we find that Aurora-dependent phosphorylation of HDAC1 regulates histone acetylation by modulating the expression of genes directly involved in the developing zebrafish central nervous system. Our data represent a step towards the comprehension of HDAC1 regulation by its PTM code, with important implications in unravelling its roles both in physiology and pathology.

Primary macrophages rely on histone deacetylase 1 and 2 expression to induce type I interferon in response to gammaherpesvirus infection

Type I interferon is induced shortly following viral infection and represents a first line of host defense against a majority of viral pathogens. Not surprisingly, both replication and latency of gammaherpesviruses, ubiquitous cancer-associated pathogens, are attenuated by type I interferon, although the mechanism of attenuation remains poorly characterized. Gammaherpesviruses also target histone deacetylases (HDACs), a family of pleiotropic enzymes that modify gene expression and several cell signaling pathways. Specifically, we have previously shown that a conserved gammaherpesvirus protein kinase interacts with HDAC1 and -2 to promote gammaherpesvirus replication in primary macrophages. In the current study, we have used genetic approaches to show that expression of HDAC1 and -2 is critical for induction of a type I interferon response following gammaherpesvirus infection of primary macrophages. Specifically, expression of HDAC1 and -2 was required for phosphorylation of interferon regulatory factor 3 (IRF3) and accumulation of IRF3 at the beta interferon promoter in gammaherpesvirus-infected primary macrophages. To our knowledge, this is the first demonstration of a specific role for HDAC1 and -2 in the induction of type I interferon responses in primary immune cells following virus infection. Furthermore, because HDAC1 and -2 are overexpressed in several types of cancer, our findings illuminate potential side effects of HDAC1- and -2-specific inhibitors that are currently under development as cancer therapy agents. IMPORTANCE Gammaherpesviruses establish chronic infection in a majority of the adult population and are associated with several malignancies. Infected cells counteract gammaherpesvirus infection via innate immune signaling mediated primarily through type I interferon. The induction of type I interferon expression proceeds through several stages using molecular mechanisms that are still incompletely characterized. In this study, we show that expression of HDAC1 and -2 by macrophages is required to mount a type I interferon response to incoming gammaherpesvirus. The involvement of HDAC1 and -2 in the type I interferon response highlights the pleiotropic roles of these enzymes in cellular signaling. Interestingly, HDAC1 and -2 are deregulated in cancer and are attractive targets of new cancer therapies. Due to the ubiquitous and chronic nature of gammaherpesvirus infection, the role of HDAC1 and -2 in the induction of type I interferon responses should be considered during the clinical development of HDAC1- and -2-specific inhibitors.

A conserved gammaherpesvirus protein kinase targets histone deacetylases 1 and 2 to facilitate viral replication in primary macrophages

Gammaherpesviruses are ubiquitious pathogens that establish lifelong infection and are associated with several malignancies. All gammaherpesviruses encode a conserved protein kinase that facilitates viral replication and chronic infection and thus represents an attractive therapeutic target. In this study, we identify a novel function of gammaherpesvirus protein kinase as a regulator of class I histone deacetylases (HDAC). Mouse gammaherpesvirus 68 (MHV68)-encoded protein kinase orf36 interacted with HDAC1 and 2 and prevented association of these HDACs with the viral promoter driving expression of RTA, a critical immediate early transcriptional activator. Furthermore, the ability to interact with HDAC1 and 2 was not limited to the MHV68 orf36, as BGLF4, a related viral protein kinase encoded by Epstein-Barr virus, interacted with HDAC1 in vitro. Importantly, targeting of HDAC1 and 2 by orf36 was independent of the kinase's enzymatic activity. Additionally, orf36 expression, but not its enzymatic activity, induced changes in the global deacetylase activity observed in infected primary macrophages. Combined deficiency of HDAC1 and 2 rescued attenuated replication and viral DNA synthesis of the orf36 null MHV68 mutant, indicating that the regulation of HDAC1 and 2 by orf36 was relevant for viral replication. Understanding the mechanism by which orf36 facilitates viral replication, including through HDAC targeting, will facilitate the development of improved therapeutics against gammaherpesvirus kinases.

Human cytomegalovirus pUL97 regulates the viral major immediate early promoter by phosphorylation-mediated disruption of histone deacetylase 1 binding

Human cytomegalovirus (HCMV) is a common agent of congenital infection and causes severe disease in immunocompromised patients. Current approved therapies focus on inhibiting viral DNA replication. The HCMV kinase pUL97 contributes to multiple stages of viral infection including DNA replication, controlling the cell cycle, and virion maturation. Our studies demonstrate that pUL97 also functions by influencing immediate early (IE) gene expression during the initial stages of infection. Inhibition of kinase activity using the antiviral compound maribavir or deletion of the UL97 gene resulted in decreased expression of viral immediate early genes during infection. Expression of pUL97 was sufficient to transactivate IE1 gene expression from the viral genome, which was dependent on viral kinase activity. We observed that pUL97 associates with histone deacetylase 1 (HDAC1). HDAC1 is a transcriptional corepressor that acts to silence expression of viral genes. We observed that inhibition or deletion of pUL97 kinase resulted in increased HDAC1 and decreased histone H3 lysine 9 acetylation associating with the viral major immediate early (MIE) promoter. IE expression during pUL97 inhibition or deletion was rescued following inhibition of deacetylase activity. HDAC1 associates with chromatin by protein-protein interactions. Expression of active but not inactive pUL97 kinase decreased HDAC1 interaction with the transcriptional repressor protein DAXX. Finally, using mass spectrometry, we found that HDAC1 is uniquely phosphorylated upon expression of pUL97. Our results support the conclusion that HCMV pUL97 kinase regulates viral immediate early gene expression by phosphorylation-mediated disruption of HDAC1 binding to the MIE promoter.

Potential of protein kinase inhibitors for treating herpesvirus-associated disease

Herpesviruses are ubiquitous human pathogens that establish lifelong persistent infections. Clinical manifestations range from mild self-limiting outbreaks such as childhood rashes and cold sores to the more severe and life-threatening outcomes of disseminated infection, encephalitis, and cancer. Nucleoside analog drugs that target viral DNA replication provide the primary means of treatment. However, extended use of these drugs can result in selection for drug-resistant strains, particularly in immunocompromised patients. In this review we will present recent observations about the participation of cellular protein kinases in herpesvirus biology and discuss the potential for targeting these protein kinases as well as the herpesvirus-encoded protein kinases as an anti-herpesvirus therapeutic strategy.

Nuclear receptor mRNA expression by HBV in human hepatoblastoma cell lines

Recent studies have implicated nuclear receptors (NRs) in the development of hepatocarcinogenesis. We assumed that hepatitis B virus (HBV) alters the expression of NRs and coregulators, and compared the gene expression profiling for 84 NRs and related genes between HpeG2.2.15, which secretes complete HBV virion, and HepG2 by real-time RT-PCR with SyBr green. Forty (47.6%) genes were upregulated 2-fold or greater, and only 5 (5.9%) were downregulated 2-fold or more, in HepG2.2.15 compared to HepG2. These results suggest that HBV affects NRs and their related signal transduction, and that they play important roles in viral replication and HBV-related hepatocarcinogenesis.

Nucleocytoplasmic shuttling of the HSV-2 serine/threonine kinase Us3

The alphaherpesvirus serine/threonine kinase Us3 plays diverse roles in virus multiplication and modifies both nuclear and cytoplasmic substrates. We recently reported that treatment of HSV-2 Us3-transfected and HSV-2-infected cells with leptomycin B, an inhibitor of nuclear export mediated by interaction of chromosomal regional maintenance protein (CRM1) with leucine rich nuclear export signals (NESs), resulted in nuclear trapping of Us3. Here, we utilized fluorescence loss in photobleaching to monitor nuclear export of HSV-2 Us3 and confirm that this process proceeds solely via a CRM1-mediated mechanism. Analysis of deletion derivatives of HSV-2 Us3 fused to a nuclear export reporter protein implicated the involvement of NES-like sequences in nuclear export. However, nuclear trapping of HSV-2 Us3 proteins carrying mutations in these potential NESs was not observed, indicating that these sequences are not functional in the context of full-length protein. Our analyses also revealed previously unidentified regions of HSV-2 Us3 that contribute to its kinase activity.

Epigenetic modulation of host: new insights into immune evasion by viruses

Viruses have evolved with their hosts, which include all living species. This has been partly responsible for the development of highly advanced immune systems in the hosts. However, viruses too have evolved ways to regulate and evade the host's immune defence. In addition to mutational mechanisms that viruses employ to mimic the host genome and undergo latency to evade the host's recognition of the pathogen, they have also developed epigenetic mechanisms by which they can render the host's immune responses inactive to their antigens. The epigenetic regulation of gene expression is intrinsically active inside the host and is involved in regulating gene expression and cellular differentiation. Viral immune evasion strategies are an area of major concern in modern biomedical research. Immune evasion strategies may involve interference with the host antigen presentation machinery or host immune gene expression capabilities, and viruses, in these manners, introduce and propagate infection. The aim of this review is to elucidate the various epigenetic changes that viruses are capable of bringing about in their host in order to enhance their own survivability and pathogenesis.

The alphaherpesvirus serine/threonine kinase us3 disrupts promyelocytic leukemia protein nuclear bodies

Us3, a serine/threonine kinase encoded by all alphaherpesviruses, plays diverse roles during virus infection, including preventing virus-induced apoptosis, facilitating nuclear egress of capsids, stimulating mRNA translation and promoting cell-to-cell spread of virus infection. Given this diversity, the full spectrum of Us3 function may not yet be recognized. We noted, in transiently transfected cells, that herpes simplex virus type 2 (HSV-2) Us3 disrupted promyelocytic leukemia protein nuclear bodies (PML-NBs). However, PML-NB disruption was not observed in cells expressing catalytically inactive HSV-2 Us3. Analysis of PML-NBs in Vero cells transfected with pseudorabies virus (PRV) Us3 and those in Vero cells infected with Us3-null or -repaired PRV strains indicated that PRV Us3 expression also leads to the disruption of PML-NBs. While loss of PML-NBs in response to Us3 expression was prevented by the proteasome inhibitor MG132, Us3-mediated degradation of PML was not observed in infected cells or in transfected cells expressing enhanced green fluorescent protein (EGFP)-tagged PML isoform IV. These findings demonstrate that Us3 orthologues derived from distantly related alphaherpesviruses cause a disruption of PML-NBs in a kinase- and proteasome-dependent manner but, unlike the alphaherpesvirus ICP0 orthologues, do not target PML for degradation.

Regulating the regulators: the post-translational code of class I HDAC1 and HDAC2

Class I histone deacetylases (HDACs) are cellular enzymes expressed in many tissues and play crucial roles in differentiation, proliferation, and cancer. HDAC1 and HDAC2 in particular are highly homologous proteins that show redundant or specific roles in different cell types or in response to different stimuli and signaling pathways. The molecular details of this dual regulation are largely unknown. HDAC1 and HDAC2 are not only protein modifiers, but are in turn regulated by post-translational modifications (PTMs): phosphorylation, acetylation, ubiquitination, SUMOylation, nitrosylation, and carbonylation. Some of these PTMs occur and crosstalk specifically on HDAC1 or HDAC2, creating a rational "code" for a differential, context-related regulation. The global comprehension of this PTM code is central for dissecting the role of single HDAC1 and HDAC2 in physiology and pathology.

Viral serine/threonine protein kinases

Phosphorylation represents one the most abundant and important posttranslational modifications of proteins, including viral proteins. Virus-encoded serine/threonine protein kinases appear to be a feature that is unique to large DNA viruses. Although the importance of these kinases for virus replication in cell culture is variable, they invariably play important roles in virus virulence. The current review provides an overview of the different viral serine/threonine protein kinases of several large DNA viruses and discusses their function, importance, and potential as antiviral drug targets.

Regulation of the expression of the varicella-zoster virus open reading frame 66 gene

The varicella-zoster virus (VZV) open reading frame (ORF) 66 encodes a serine/threonine kinase that phosphorylates the major viral transactivator protein, immediate-early (IE) 62, preventing its nuclear importation. Cytoplasmic sequestration of IE62 may alter viral gene transcription and could serve as a mechanism for maintaining VZV latency. We examined the regulation of expression of the ORF66 gene by mapping the promoter region, which was localized to within 150 bases of the start codon. The ORF66 promoter was activated by two viral regulatory proteins, IE62 and IE63. We evaluated the binding of viral regulatory proteins and cellular transcription factors based on recognized cellular transcription factor binding sites identified within the ORF66 promoter. These included Sp1 and TBP binding sites, several of which were essential for optimal promoter activity. Site-directed mutations in Sp1 and TBP binding sites led to varying degrees of impairment of ORF66 gene expression in the context of VZV infection. We also examined the effect of Sp1 and TBP mutations on IE62, Sp1, and TBP binding. These studies reveal that host cell-derived and viral factors contribute to and cooperate in the expression of this important viral kinase gene.

The alphaherpesvirus US3/ORF66 protein kinases direct phosphorylation of the nuclear matrix protein matrin 3

The protein kinase found in the short region of alphaherpesviruses, termed US3 in herpes simplex virus type 1 (HSV-1) and pseudorabies virus (PRV) and ORF66 in varicella-zoster virus (VZV), affects several viral and host cell processes, and its specific targets remain an area of active investigation. Reports suggesting that HSV-1 US3 substrates overlap with those of cellular protein kinase A (PKA) prompted the use of an antibody specific for phosphorylated PKA substrates to identify US3/ORF66 targets. HSV-1, VZV, and PRV induced very different substrate profiles that were US3/ORF66 kinase dependent. The predominant VZV-phosphorylated 125-kDa species was identified as matrin 3, one of the major nuclear matrix proteins. Matrin 3 was also phosphorylated by HSV-1 and PRV in a US3 kinase-dependent manner and by VZV ORF66 kinase at a novel residue (KRRRT150EE). Since VZV-directed T150 phosphorylation was not blocked by PKA inhibitors and was not induced by PKA activation, and since PKA predominantly targeted matrin 3 S188, it was concluded that phosphorylation by VZV was PKA independent. However, purified VZV ORF66 kinase did not phosphorylate matrin 3 in vitro, suggesting that additional cellular factors were required. In VZV-infected cells in the absence of the ORF66 kinase, matrin 3 displayed intranuclear changes, while matrin 3 showed a pronounced cytoplasmic distribution in late-stage cells infected with US3-negative HSV-1 or PRV. This work identifies phosphorylation of the nuclear matrix protein matrin 3 as a new conserved target of this kinase group.

Keep it in the subfamily: the conserved alphaherpesvirus US3 protein kinase

The US3 protein kinase is conserved over the alphaherpesvirus subfamily. Increasing evidence shows that, although the kinase is generally not required for virus replication in cell culture, it plays a pivotal and in some cases an essential role in virus virulence in vivo. The US3 protein is a multifunctional serine/threonine kinase that is involved in viral gene expression, virion morphogenesis, remodelling the actin cytoskeleton and the evasion of several antiviral host responses. In the current review, both the well conserved and virus-specific functions of alphaherpesvirus US3 protein kinase orthologues will be discussed.

Hyperphosphorylation of histone deacetylase 2 by alphaherpesvirus US3 kinases

A serine/threonine (S/T) kinase encoded by the US3 gene of herpes simplex virus type 1 (HSV-1) is conserved in varicella-zoster virus (VZV) and pseudorabies virus (PRV). Expression of US3 kinase in cells transformed with US3 expression plasmids or infected with each virus results in hyperphosphorylation of histone deacetylase 2 (HDAC2). Mapping studies revealed that each US3 kinase phosphorylates HDAC2 at the same unique conserved Ser residue in its C terminus. HDAC2 was also hyperphosphorylated in cells infected with PRV lacking US3 kinase, indicating that hyperphosphorylation of HDAC2 by PRV occurs in a US3-independent manner. Specific chemical inhibition of class I HDAC activity increases the plaquing efficiency of VZV and PRV lacking US3 or its enzymatic activity, whereas only minimal effects are observed with wild-type viruses, suggesting that VZV and PRV US3 kinase activities target HDACs to reduce viral genome silencing and allow efficient viral replication. However, no effect was observed for wild-type or US3 null HSV-1. Thus, we have demonstrated that while HDAC2 is a conserved target of alphaherpesvirus US3 kinases, the functional significance of these events is virus specific.

The RING finger domain of Varicella-Zoster virus ORF61p has E3 ubiquitin ligase activity that is essential for efficient autoubiquitination and dispersion of Sp100-containing nuclear bodies

Varicella zoster virus encodes an immediate-early (IE) protein termed ORF61p that is orthologous to the herpes simplex virus IE protein ICP0. Although these proteins share several functional properties, ORF61p does not fully substitute for ICP0. The greatest region of similarity between these proteins is a RING finger domain. We demonstrate that disruption of the ORF61p RING finger domain by amino acid substitution (Cys19Gly) alters ORF61p intranuclear distribution and abolishes ORF61p-mediated dispersion of Sp100-containing nuclear bodies. In addition, we demonstrate that an intact ORF61p RING finger domain is necessary for E3 ubiquitin ligase activity and is required for autoubiquitination and regulation of protein stability.

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.

Varicella-zoster virus open reading frame 66 protein kinase and its relationship to alphaherpesvirus US3 kinases

The varicella-zoster virus (VZV) open reading frame (ORF) 66 encodes a basophilic kinase orthologous to the US3 protein kinases found in all alphaherpesviruses. This review summarizes current information on the ORF66 kinase, and outlines apparent differences from other US3 kinases, as well as some of the conserved functions. One critical difference is the VZV ORF66 kinase targeting of the major regulatory VZV IE62 protein to control its nuclear import and assembly into the VZV virion, which is so far unprecedented in the alphaherpesviruses. However, ORF66 targets some cellular targets which are also targeted by US3 kinases of other herpesviruses, including the histone deacetylase-1 and 2 proteins, pathways that lead to changes in actin dynamics, and the targeting of substrates of protein kinase A, including the nuclear matrix protein matrin 3.