The gamma 1(34.5) gene of herpes simplex virus 1 precludes neuroblastoma cells from triggering total shutoff of protein synthesis characteristic of programed cell death in neuronal cells

An investigation of herpes simplex virus type 1 latency in a novel mouse dorsal root ganglion model suggests a role for ICP34.5 in reactivation

After a primary lytic infection at the epithelia, herpes simplex virus type 1 (HSV-1) enters the innervating sensory neurons and translocates to the nucleus, where it establishes a quiescent latent infection. Periodically, the virus can reactivate and the progeny viruses spread back to the epithelium. Here, we introduce an embryonic mouse dorsal root ganglion (DRG) culture system, which can be used to study the mechanisms that control the establishment, maintenance and reactivation from latency. Use of acyclovir is not necessary in our model. We examined different phases of the HSV-1 life cycle in DRG neurons, and showed that WT HSV-1 could establish both lytic and latent form of infection in the cells. After reactivating stimulus, the WT viruses showed all markers of true reactivation. In addition, we showed that deletion of the γ(1)34.5 gene rendered the virus incapable of reactivation, even though the virus was clearly able to replicate and persist in a quiescent form in the DRG neurons.

Characterization of herpes simplex virus 2 primary microRNA Transcript regulation

In order to understand factors that may influence latency-associated transcription and latency-associated transcript (LAT) phenotypes, we studied the expression of the herpes simplex virus 2 (HSV-2) LAT-associated microRNAs (miRNAs). We mapped the transcription initiation sites of all three primary miRNA transcripts and identified the ICP4-binding sequences at the transcription initiation sites of both HSV-2 LAT (pri-miRNA for miR-I and miR-II, which target ICP34.5, and miR-III, which targets ICP0) and L/ST (a pri-miRNA for miR-I and miR-II) but not at that of the primary miR-H6 (for which the target is unknown). We confirmed activity of the putative HSV-2 L/ST promoter and found that ICP4 trans-activates the L/ST promoter when the ICP4-binding site at its transcription initiation site is mutated, suggesting that ICP4 may play a dual role in regulating transcription of L/ST and, consequently, of miR-I and miR-II. LAT exon 1 (containing LAT enhancer sequences), together with the LAT promoter region, comprises a bidirectional promoter required for the expression of both LAT-encoded miRNAs and miR-H6 in latently infected mouse ganglia. The ability of ICP4 to suppress ICP34.5-targeting miRNAs and to activate lytic viral genes suggests that ICP4 could play a key role in the switch between latency and reactivation.

IMPORTANCE

The HSV-2 LAT and viral miRNAs expressed in the LAT region are the most abundant viral transcripts during HSV latency. The balance between the expression of LAT and LAT-associated miRNAs and the expression of lytic viral transcripts from the opposite strand appears to influence whether individual HSV-infected neurons will be latently or productively infected. The outcome of neuronal infection may thus depend on regulation of gene expression of the corresponding primary miRNAs. In the present study, we characterize promoter sequences responsible for miRNA expression, including identification of the primary miRNA 5' ends and evaluation of ICP4 response. These findings provide further insight into the virus' strategy to tightly control expression of lytic cycle genes (especially the neurovirulence factor, ICP34.5) and suggest a mechanism (via ICP4) for the transition from latency to reactivated productive infection.

Intrinsic innate immunity fails to control herpes simplex virus and vesicular stomatitis virus replication in sensory neurons and fibroblasts

Herpes simplex virus 1 (HSV-1) establishes lifelong latent infections in the sensory neurons of the trigeminal ganglia (TG), wherein it retains the capacity to reactivate. The interferon (IFN)-driven antiviral response is critical for the control of HSV-1 acute replication. We therefore sought to further investigate this response in TG neurons cultured from adult mice deficient in a variety of IFN signaling components. Parallel experiments were also performed in fibroblasts isolated concurrently. We showed that HSV-1 replication was comparable in wild-type (WT) and IFN signaling-deficient neurons and fibroblasts. Unexpectedly, a similar pattern was observed for the IFN-sensitive vesicular stomatitis virus (VSV). Despite these findings, TG neurons responded to IFN-β pretreatment with STAT1 nuclear localization and restricted replication of both VSV and an HSV-1 strain deficient in γ34.5, while wild-type HSV-1 replication was unaffected. This was in contrast to fibroblasts in which all viruses were restricted by the addition of IFN-β. Taken together, these data show that adult TG neurons can mount an effective antiviral response only if provided with an exogenous source of IFN-β, and HSV-1 combats this response through γ34.5. These results further our understanding of the antiviral response of neurons and highlight the importance of paracrine IFN-β signaling in establishing an antiviral state.

IMPORTANCE

Herpes simplex virus 1 (HSV-1) is a ubiquitous virus that establishes a lifelong latent infection in neurons. Reactivation from latency can cause cold sores, blindness, and death from encephalitis. Humans with deficiencies in innate immunity have significant problems controlling HSV infections. In this study, we therefore sought to elucidate the role of neuronal innate immunity in the control of viral infection. Using neurons isolated from mice, we found that the intrinsic capacity of neurons to restrict virus replication was unaffected by the presence or absence of innate immunity. In contrast, neurons were able to mount a robust antiviral response when provided with beta interferon, a molecule that strongly stimulates innate immunity, and that HSV-1 can combat this response through the γ34.5 viral gene. Our results have important implications for understanding how the nervous system defends itself against virus infections.

Oncolytic Immunotherapy: Dying the Right Way is a Key to Eliciting Potent Antitumor Immunity

Oncolytic viruses (OVs) are novel immunotherapeutic agents whose anticancer effects come from both oncolysis and elicited antitumor immunity. OVs induce mostly immunogenic cancer cell death (ICD), including immunogenic apoptosis, necrosis/necroptosis, pyroptosis, and autophagic cell death, leading to exposure of calreticulin and heat-shock proteins to the cell surface, and/or released ATP, high-mobility group box 1, uric acid, and other damage-associated molecular patterns as well as pathogen-associated molecular patterns as danger signals, along with tumor-associated antigens, to activate dendritic cells and elicit adaptive antitumor immunity. Dying the right way may greatly potentiate adaptive antitumor immunity. The mode of cancer cell death may be modulated by individual OVs and cancer cells as they often encode and express genes that inhibit/promote apoptosis, necroptosis, or autophagic cell death. We can genetically engineer OVs with death-pathway-modulating genes and thus skew the infected cancer cells toward certain death pathways for the enhanced immunogenicity. Strategies combining with some standard therapeutic regimens may also change the immunological consequence of cancer cell death. In this review, we discuss recent advances in our understanding of danger signals, modes of cancer cell death induced by OVs, the induced danger signals and functions in eliciting subsequent antitumor immunity. We also discuss potential combination strategies to target cells into specific modes of ICD and enhance cancer immunogenicity, including blockade of immune checkpoints, in order to break immune tolerance, improve antitumor immunity, and thus the overall therapeutic efficacy.

Herpes simplex virus type 1 virion-derived US11 inhibits type 1 interferon-induced protein kinase R phosphorylation

The herpes simplex virus type 1 (HSV-1) VRTK(-) strain that was previously isolated in our laboratory as an acyclovir-resistant thymidine kinase (TK)-deficient mutant, is more sensitive to type 1 interferon than is the parent strain VR3. The properties of this mutant were investigated to clarify the mechanism for its hyper-sensitivity to interferon (IFN). It was found that: (i) IFN-pretreated cells, but not those treated with IFN after adsorption, are hyper-sensitive to IFN; (ii) the mutant cannot inhibit protein kinase R phosphorylation efficiently during the early stage of replication (2 hrs post-infection); (iii) expression of US11 in infected cells and its incorporation into the virion is reduced in the mutant compared to the wild type, despite the fact that a similar degree of DNA synthesis occurs during replication of both strains and; (iv) over-expression of wild-type viral TK has no effect on the phenotype of the VRTK(-) strain, indicating that the phenotype is induced by a mutation(s) that does not involve the TK gene. These results suggested that the presence of US11 in the virion, but not that expressed after infection, plays an important role in the escape function of HSV-1 from the antiviral activity of type 1 IFN.

A herpes simplex virus-derived replicative vector expressing LIF limits experimental demyelinating disease and modulates autoimmunity

Herpes simplex virus type 1 (HSV-1) has properties that can be exploited for the development of gene therapy vectors. The neurotropism of HSV enables delivery of therapeutic genes to the nervous system. Using a bacterial artificial chromosome (BAC), we constructed an HSV-1(17⁺)-based replicative vector deleted of the neurovirulence gene γ₁34.5, and expressing leukemia inhibitory factor (LIF) as a transgene for treatment of experimental autoimmune encephalomyelitis (EAE). EAE is an inducible T-cell mediated autoimmune disease of the central nervous system (CNS) and is used as an animal model for multiple sclerosis. Demyelination and inflammation are hallmarks of both diseases. LIF is a cytokine that has the potential to limit demyelination and oligodendrocyte loss in CNS autoimmune diseases and to affect the T-cell mediated autoimmune response. In this study SJL/J mice, induced for EAE, were treated with a HSV-LIF vector intracranially and the subsequent changes in disease parameters and immune responses during the acute disease were investigated. Replicating HSV-LIF and its DNA were detected in the CNS during the acute infection, and the vector spread to the spinal cord but was non-virulent. The HSV-LIF significantly ameliorated the EAE and contributed to a higher number of oligodendrocytes in the brains when compared to untreated mice. The HSV-LIF therapy also induced favorable changes in the expression of immunoregulatory cytokines and T-cell population markers in the CNS during the acute disease. These data suggest that BAC-derived HSV vectors are suitable for gene therapy of CNS disease and can be used to test the therapeutic potential of immunomodulatory factors for treatment of EAE.

Herpes simplex virus 2 expresses a novel form of ICP34.5, a major viral neurovirulence factor, through regulated alternative splicing

Herpes simplex virus 1 (HSV-1) and HSV-2, two closely related neurotropic human herpesviruses, achieve neurotropism through ICP34.5, a major viral neurovirulence factor. In this report, in addition to the full-length 38-kDa protein (ICP34.5α), we identified a 28-kDa novel form of ICP34.5 (ICP34.5β) in HSV-2-infected cells. ICP34.5β is translated from unspliced ICP34.5 mRNA, with the retained intron introducing a premature stop codon. Thus, ICP34.5β lacks the C-terminal conserved GADD34 domain but includes 19 additional amino acids encoded by the intron. Although a fraction of both HSV-2 ICP34.5 proteins are detected in the nucleolus, ICP34.5α is predominantly located in cytoplasm, and ICP34.5β is mainly detected more diffusely in the nucleus. ICP34.5β is unable to counteract PKR-mediated eIF2 phosphorylation but does not interfere with ICP34.5α's function in this process. Efficient expression of ICP34.5β in cell culture assays is dependent on viral infection or expression of ICP27, a multifunctional immediate-early gene. The effect of ICP27 on the ICP34.5β protein level is attributed to its selective inhibition of ICP34.5 splicing, which results in increased expression of ICP34.5β but a reduced level of ICP34.5α. The C- terminal KH3 domain but not the RNA binding domain of ICP27 is required for its specific inhibition of ICP34.5 splicing and promotion of ICP34.5β expression. Our results suggest that the expression of ICP34.5α and ICP34.5β is tightly regulated in HSV-2 and likely contributes to viral pathogenesis.

A proautophagic antiviral role for the cellular prion protein identified by infection with a herpes simplex virus 1 ICP34.5 mutant

The cellular prion protein (PrP) often plays a cytoprotective role by regulating autophagy in response to cell stress. The stress of infection with intracellular pathogens can stimulate autophagy, and autophagic degradation of pathogens can reduce their replication and thus help protect the infected cells. PrP also restricts replication of several viruses, but whether this activity is related to an effect on autophagy is not known. Herpes simplex virus 1 (HSV-1) effectively counteracts autophagy through binding of its ICP34.5 protein to the cellular proautophagy protein beclin-1. Autophagy can reduce replication of an HSV-1 mutant, Δ68H, which is incapable of binding beclin-1. We found that deletion of PrP in mice complements the attenuation of Δ68H, restoring its capacity to replicate in the central nervous system (CNS) to wild-type virus levels after intracranial or corneal infection. Cultured primary astrocytes but not neurons derived from PrP(-/-) mice also complemented the attenuation of Δ68H, enabling Δ68H to replicate at levels equivalent to wild-type virus. Ultrastructural analysis showed that normal astrocytes exhibited an increase in the number of autophagosomes after infection with Δ68H compared with wild-type virus, but PrP(-/-) astrocytes failed to induce autophagy in response to Δ68H infection. Redistribution of EGFP-LC3 into punctae occurred more frequently in normal astrocytes infected with Δ68H than with wild-type virus, but not in PrP(-/-) astrocytes, corroborating the ultrastructural analysis results. Our results demonstrate that PrP is critical for inducing autophagy in astrocytes in response to HSV-1 infection and suggest that PrP positively regulates autophagy in the mouse CNS.

Modulating vascular intimal hyperplasia using HSV-1 mutant requires activated MEK

Outcomes of cardiovascular procedures, such as angioplasty and stent or bypass grafting are limited by failure, predominantly caused by pathological smooth muscle cell (SMC) proliferation, known as intimal hyperplasia. Local delivery of a genetically engineered herpes simplex virus (HSV) is known to block vascular SMC proliferation while allowing for re-endothelialization. However, the mechanism this mutant virus uses to prevent SMC hyperplasia is unknown. The Ras signaling cascade is activated in SMCs undergoing hyperplasia leading to phosphorylation of the mitogen-activated protein kinase (MAPK). In this study we tested the hypothesis that MAPK kinase (MEK) activity is the molecular basis by which SMCs are susceptible to mutant HSV. We show that genetically engineered herpes simplex-1 viruses (HSV-1) can target proliferating SMCs. We demonstrate that the molecular basis of this HSV-1 anti-proliferative effect is MEK activation in SMCs. We demonstrate efficacy and practicality of the MEK-dependent HSV-1 for the treatment of intimal hyperplasia in a clinically relevant in vivo model. Important to this strategy is the ability to modulate the effects by controlling viral dose. These results propel genetically engineered HSV-1 therapy towards clinical evaluation in treatment of intimal hyperplasia.

A neuron-specific role for autophagy in antiviral defense against herpes simplex virus

Type I interferons (IFNs) are considered to be the universal mechanism by which viral infections are controlled. However, many IFN-stimulated genes (ISGs) rely on antiviral pathways that are toxic to host cells, which may be detrimental in nonrenewable cell types, such as neurons. We show that dorsal root ganglionic (DRG) neurons produced little type I IFNs in response to infection with a neurotropic virus, herpes simplex type 1 (HSV-1). Further, type I IFN treatment failed to completely block HSV-1 replication or to induce IFN-primed cell death in neurons. We found that DRG neurons required autophagy to limit HSV-1 replication both in vivo and in vitro. In contrast, mucosal epithelial cells and other mitotic cells responded robustly to type I IFNs and did not require autophagy to control viral replication. These findings reveal a fundamental difference in the innate antiviral strategies employed by neurons and mitotic cells to control HSV-1 infection.

Concurrent chemotherapy inhibits herpes simplex virus-1 replication and oncolysis

Herpes simplex virus-1 (HSV-1) replication in cancer cells leads to their destruction (viral oncolysis) and has been under investigation as an experimental cancer therapy in clinical trials as single agents, and as combinations with chemotherapy. Cellular responses to chemotherapy modulate viral replication, but these interactions are poorly understood. To investigate the effect of chemotherapy on HSV-1 oncolysis, viral replication in cells exposed to 5-fluorouracil (5-FU), irinotecan (CPT-11), methotrexate (MTX) or a cytokine (tumor necrosis factor-α (TNF-α)) was examined. Exposure of colon and pancreatic cancer cells to 5-FU, CPT-11 or MTX in vitro significantly antagonizes both HSV-1 replication and lytic oncolysis. Nuclear factor-κB (NF-κB) activation is required for efficient viral replication, and experimental inhibition of this response with an IκBα dominant-negative repressor significantly antagonizes HSV-1 replication. Nonetheless, cells exposed to 5-FU, CPT-11, TNF-α or HSV-1 activate NF-κB. Cells exposed to MTX do not activate NF-κB, suggesting a possible role for NF-κB inhibition in the decreased viral replication observed following exposure to MTX. The role of eukaryotic initiation factor 2α (eIF-2α) dephosphorylation was examined; HSV-1-mediated eIF-2α dephosphorylation proceeds normally in HT29 cells exposed to 5-FU, CPT-11 or MTX. This report demonstrates that cellular responses to chemotherapeutic agents provide an unfavorable environment for HSV-1-mediated oncolysis, and these observations are relevant to the design of both preclinical and clinical studies of HSV-1 oncolysis.

Herpes simplex virus γ34.5 interferes with autophagosome maturation and antigen presentation in dendritic cells

The cellular autophagy response induced by herpes simplex virus 1 (HSV-1) is countered by the viral γ34.5 protein. γ34.5 modulates autophagy by binding to the host autophagy protein Beclin-1 and through this binding inhibits the formation of autophagosomes in fibroblasts and neurons. In contrast, in this study dendritic cells (DCs) infected with HSV-1 showed an accumulation of autophagosomes and of the long-lived protein p62. No such accumulations were observed in DCs infected with a γ34.5-null virus or a virus lacking the Beclin-binding domain (BBD) of γ34.5. To explore this further, we established stably transduced DC lines to show that γ34.5 expression alone induced autophagosome accumulation yet prevented p62 degradation. In contrast, DCs expressing a BBD-deleted mutant of γ34.5 were unable to modulate autophagy. DCs expressing γ34.5 were less capable of stimulating T-cell activation and proliferation in response to intracellular antigens, demonstrating an immunological consequence of inhibiting autophagy. Taken together, these data show that in DCs, γ34.5 antagonizes the maturation of autophagosomes and T cell activation in a BBD-dependent manner, illustrating a unique interface between HSV and autophagy in antigen-presenting cells.

Herpes simplex virus 1 (HSV-1) is a highly prevalent pathogen causing widespread morbidity and some mortality. HSV infections are lifelong, and there are no vaccines or antivirals to cure HSV infections. The ability of HSV to modulate host immunity is critical for its virulence. HSV inhibits host autophagy, a pathway with importance in many areas of health and disease. Autophagy is triggered by many microbes, some of which harness autophagy for replication; others evade autophagy or prevent it from occurring. Autophagy is critical for host defense, either by directly degrading the invading pathogen (“xenophagy”) or by facilitating antigen presentation to T cells. In this study, we show that HSV manipulates autophagy through an unsuspected mechanism with a functional consequence of reducing T cell stimulation. These data further our understanding of how HSV evades host immunity to persist for the lifetime of its host, facilitating its spread in the human population.

Oncolytic viruses & their specific targeting to tumour cells

Cancer is one of the major causes of death worldwide. In spite of achieving significant successes in medical sciences in the past few decades, the number of deaths due to cancer remains unchecked. The conventional chemotherapy and radiotherapy have limited therapeutic index and a plethora of treatment related side effects. This situation has provided an impetus for search of novel therapeutic strategies that can selectively destroy the tumour cells, leaving the normal cells unharmed. Viral oncotherapy is such a promising treatment modality that offers unique opportunity for tumour targeting. Numerous viruses with inherent anti-cancer activity have been identified and are in different phases of clinical trials. In the era of modern biotechnology and with better understanding of cancer biology and virology, it has become feasible to engineer the oncolytic viruses (OVs) to increase their tumour selectivity and enhance their oncolytic activity. In this review, the mechanisms by which oncolytic viruses kill the tumour cells have been discussed as also the development made in virotherapy for cancer treatment with emphasis on their tumour specific targeting.

Induction of apoptosis accelerates reactivation of latent HSV-1 in ganglionic organ cultures and replication in cell cultures

Herpes simplex viruses replicate at the portal of entry into the body and are transported retrograde to sensory neurons in which they can establish a silent, latent infection characterized by the expression of a noncoding latency-associated transcript and a set of microRNAs. At the portal of entry into the body and in cell culture a viral protein, VP16, recruits cellular proteins that initiate a sequential derepression of several kinetic classes of viral genes. Earlier studies have shown that upon reactivation of latent virus in ganglionic organ cultures all genes are derepressed at once, thus obviating the need for VP16 to initiate sequential derepression of viral genes. One hypothesis that could explain the data is that the massive reactivation of all classes of viral genes is the consequence of activation of an apoptotic pathway. Here we show that two proapoptotic drugs, dexamethasone and 2[[3-(2,3-dichlorophenoxy)propyl]amino]-ethanol, each accelerates viral gene expression in ganglionic organ cultures. We also show that in cultured cells apoptosis induced by dexamethasone accelerates viral gene expression and accumulation of infectious virus. The results are surprising in light of the relatively large number of viral proteins that independently block apoptosis induced by viral gene products or exogenous agents. The results suggest that the virus may rely on apoptosis to exit from latency but that apoptosis may be detrimental for virus replication or spread at the portal of entry into the body.

Dysregulation of autophagy in murine fibroblasts resistant to HSV-1 infection

The mouse L cell mutant, gro29, was selected for its ability to survive infection by herpes simplex virus type 1 (HSV-1). gro29 cells are fully susceptible to HSV-1 infection, however, they produce 2000-fold less infectious virus than parental L cells despite their capacity to synthesize late viral gene products and assemble virions. Because productive HSV-1 infection is presumed to result in the death of the host cell, we questioned how gro29 cells might survive infection. Using time-lapse video microscopy, we demonstrated that a fraction of infected gro29 cells survived infection and divided. Electron microscopy of infected gro29 cells, revealed large membranous vesicles that contained virions as well as cytoplasmic constituents. These structures were reminiscent of autophagosomes. Autophagy is an ancient cellular process that, under nutrient deprivation conditions, results in the degradation and catabolism of cytoplasmic components and organelles. We hypothesized that enhanced autophagy, and resultant degradation of virions, might explain the ability of gro29 to survive HSV-1 infection. Here we demonstrate that gro29 cells have enhanced basal autophagy as compared to parental L cells. Moreover, treatment of gro29 cells with 3-methyladenine, an inhibitor of autophagy, failed to prevent the formation of autophagosome-like organelles in gro29 cells indicating that autophagy was dysregulated in these cells. Additionally, we observed robust co-localization of the virion structural component, VP26, with the autophagosomal marker, GFP-LC3, in infected gro29 cells that was not seen in infected parental L cells. Collectively, these data support a model whereby gro29 cells prevent the release of infectious virus by directing intracellular virions to an autophagosome-like compartment. Importantly, induction of autophagy in parental L cells did not prevent HSV-1 production, indicating that the relationship between autophagy, virus replication, and survival of HSV-1 infection by gro29 cells is complex.

Making the case: married versus separate models of alphaherpes virus anterograde transport in axons

Alphaherpesvirus virions infect neurons and are transported in axons for long distance spread within the host nervous system. The assembly state of newly made herpesvirus particles during anterograde transport in axons is an essential question in alphaherpesvirus biology. The structure of the particle has remained both elusive and controversial for the past two decades, with conflicting evidence from EM, immunofluorescence, and live cell imaging studies. Two opposing models have been proposed-the Married and Separate Models. Under the Married Model, infectious virions are assembled in the neuronal cell body before sorting into axons and then traffic inside a transport vesicle. Conversely, the Separate Model postulates that vesicles containing viral membrane proteins are sorted into axons independent of capsids, with final assembly of mature virions occurring at a distant egress site. Recently, a complementary series of studies employing high-resolution EM and live cell fluorescence microscopy have provided evidence consistent with the Married Model, whereas other studies offer evidence supporting the Separate Model. In this review, we compare and discuss the published data and attempt to reconcile divergent findings and interpretations as they relate to these models.

Inhibition of TANK binding kinase 1 by herpes simplex virus 1 facilitates productive infection

The γ(1)34.5 protein of herpes simplex viruses (HSV) is essential for viral pathogenesis, where it precludes translational arrest mediated by double-stranded-RNA-dependent protein kinase (PKR). Paradoxically, inhibition of PKR alone is not sufficient for HSV to exhibit viral virulence. Here we report that γ(1)34.5 inhibits TANK binding kinase 1 (TBK1) through its amino-terminal sequences, which facilitates viral replication and neuroinvasion. Compared to wild-type virus, the γ(1)34.5 mutant lacking the amino terminus induces stronger antiviral immunity. This parallels a defect of γ(1)34.5 for interacting with TBK1 and reducing phosphorylation of interferon (IFN) regulatory factor 3. This activity is independent of PKR. Although resistant to IFN treatment, the γ(1)34.5 amino-terminal deletion mutant replicates at an intermediate level between replication of wild-type virus and that of the γ(1)34.5 null mutant in TBK1(+/+) cells. However, such impaired viral growth is not observed in TBK1(-/-) cells, indicating that the interaction of γ(1)34.5 with TBK1 dictates HSV infection. Upon corneal infection, this mutant replicates transiently but barely invades the trigeminal ganglia or brain, which is a difference from wild-type virus and the γ(1)34.5 null mutant. Therefore, in addition to PKR, γ(1)34.5 negatively regulates TBK1, which contributes viral replication and spread in vivo.

The evolution of infectious agents in relation to sex in animals and humans: brief discussions of some individual organisms

The following series of concise summaries addresses the evolution of infectious agents in relation to sex in animals and humans from the perspective of three specific questions: (1) what have we learned about the likely origin and phylogeny, up to the establishment of the infectious agent in the genital econiche, including the relative frequency of its sexual transmission; (2) what further research is needed to provide additional knowledge on some of these evolutionary aspects; and (3) what evolutionary considerations might aid in providing novel approaches to the more practical clinical and public health issues facing us currently and in the future?

Δγ₁134.5 herpes simplex viruses encoding human cytomegalovirus IRS1 or TRS1 induce interferon regulatory factor 3 phosphorylation and an interferon-stimulated gene response

The chimeric herpes simplex viruses (HSV) are Δγ₁34.5 vectors encoding the human cytomegalovirus (HCMV) IRS1 or TRS1 genes. They are capable of late viral protein synthesis and are superior to Δγ₁34.5 HSVs in oncolytic activity. The interferon (IFN) response limits efficient HSV gene expression and replication. HCMV TRS1 and IRS1 restore one γ₁34.5 gene function: evasion of IFN-inducible protein kinase R, allowing late viral protein synthesis. Here we show that, unlike wild-type HSV, the chimeric HSV do not restore another γ₁34.5 function, the suppression of early IFN signaling mediated by IFN regulatory factor 3 (IRF3).

Activation of NF-κB in CD8+ dendritic cells Ex Vivo by the γ134.5 null mutant correlates with immunity against herpes simplex virus 1

The γ(1)34.5 protein of herpes simplex viruses (HSV) is essential for virulence. Accordingly, an HSV mutant lacking γ(1)34.5 is attenuated in vivo. Despite its vaccine potential, the mechanism by which the γ(1)34.5 null mutant triggers protective immunity is unknown. In this report we show that vaccination with the γ(1)34.5 null mutant protects against lethal challenge from wild-type virus via IκB kinase in dendritic cells (DCs), which sense virus-associated molecular patterns. Unlike mock-treated DCs, DCs primed with the γ(1)34.5 null mutant ex vivo mediate resistance to wild-type HSV after adoptive transfer into naïve mice. Furthermore, the γ(1)34.5 null mutant activates IκB kinase, which facilitates p65/RelA phosphorylation and nuclear translocation, resulting in DC maturation. While unable to produce infectious virus in DCs, this mutant virus expresses early and late genes. In its abortive infection, the γ(1)34.5 null mutant induces protective immunity more effectively in CD8(+) DCs than in CD8(-) DCs. This is mirrored by a higher level of interleukin-6 (IL-6) and IL-12 secretion by CD8(+) DCs than CD8(-) DCs. Remarkably, inhibition of p65/RelA phosphorylation or nuclear translocation in CD8(+) DCs disrupts protective immunity. These results suggest that engagement of the γ(1)34.5 null mutant with CD8(+) DCs elicits innate immunity to activate NF-κB, which translates into protective immunity.

RNA binding properties of the US11 protein from four primate simplexviruses

Background

The protein encoded by the Us11 gene of herpes simplex viruses is a dsRNA binding protein which inhibits protein kinase R activity, thereby preventing the interferon-induced shut down of protein synthesis following viral infection. Us11 protein is not essential for infectivity in vitro and in mice in herpes simplex virus type 1 (HSV1), however this virus has a second, and apparently more important, inhibitor of PKR activity, the γ₁34.5 protein. Recently sequenced simian simplexviruses SA8, HVP2 and B virus do not have an ORF corresponding to the γ₁34.5 protein, yet they have similar, or greater, infectivity as HSV1 and HSV2.

Methods

We have expressed the US11 proteins of the simplexviruses HSV1, HSV2, HVP2 and B virus and measured their abilities to bind dsRNA, in order to investigate possible differences that could complement the absence of the γ₁34.5 protein. We employed a filter binding technique that allows binding of the Us11 protein under condition of excess dsRNA substrate and therefore a measurement of the true Kd value of Us11-dsRNA binding.

Results and Conclusions

The results show a Kd of binding in the range of 0.89 nM to 1.82 nM, with no significant difference among the four Us11 proteins.

Activation of autophagy by α-herpesviruses in myeloid cells is mediated by cytoplasmic viral DNA through a mechanism dependent on stimulator of IFN genes

Autophagy has been established as a player in host defense against viruses. The mechanisms by which the host induces autophagy during infection are diverse. In the case of HSV type 1 (HSV-1), dsRNA-dependent protein kinase is essential for induction of autophagy in fibroblasts through phosphorylation of eukaryotic initiation factor 2α (eIF2α). HSV-1 counteracts autophagy via ICP34.5, which dephosphorylates eIF2α and inhibits Beclin 1. Investigation of autophagy during HSV-1 infection has largely been conducted in permissive cells, but recent work suggests the existence of a eIF2α-independent autophagy-inducing pathway in nonpermissive cells. To clarify and further characterize the existence of a novel autophagy-inducing pathway in nonpermissive cells, we examined different HSV and cellular components in murine myeloid cells for their role in autophagy. We demonstrate that HSV-1-induced autophagy does not correlate with phosphorylation of eIF2α, is independent of functional dsRNA-dependent protein kinase, and is not antagonized by ICP34.5. Autophagy was activated independent of viral gene expression, but required viral entry. Importantly, we found that the presence of genomic DNA in the virion was essential for induction of autophagy and, conversely, that transfection of HSV-derived DNA induced microtubule-associated protein 1 L chain II formation, a marker of autophagy. This occurred through a mechanism dependent on stimulator of IFN genes, an essential component for the IFN response to intracellular DNA. Finally, we observed that HSV-1 DNA was present in the cytosol devoid of capsid material following HSV-1 infection of dendritic cells. Thus, our data suggest that HSV-1 genomic DNA induces autophagy in nonpermissive cells in a stimulator of IFN gene-dependent manner.

Mammalian alphaherpesvirus miRNAs

Mammalian alphaherpesviruses are major causes of human and veterinary disease. During productive infection, these viruses exhibit complex and robust patterns of gene expression. These viruses also form latent infections in neurons of sensory ganglia in which productive cycle gene expression is highly repressed. Both modes of infection provide advantageous opportunities for regulation by microRNAs. Thus far, published data regarding microRNAs are available for six mammalian alphaherpesviruses. No microRNAs have yet been detected from varicella zoster virus. The five other viruses-herpes simplex viruses-1 and -2, herpes B virus, bovine herpesvirus-1, and pseudorabies virus-representing both genera of mammalian alphaherpesviruses have been shown to express microRNAs. In this article, we discuss these microRNAs in terms of where they are encoded in the viral genome relative to other viral transcripts; whether they are expressed during productive or latent infection; their potential targets; what little is known about their actual targets and functions during viral infection; and what little is known about the interactions of these viruses with the host microRNA machinery. This article is part of a Special Issue entitled: "MicroRNAs in viral gene regulation".

Oncolytic herpes simplex virus 1 encoding 15-prostaglandin dehydrogenase mitigates immune suppression and reduces ectopic primary and metastatic breast cancer in mice

Oncolytic herpes simplex virus 1 (HSV-1) viruses armed with immunomodulatory transgenes have shown potential for enhanced antitumor therapy by overcoming tumor-based immune suppression and promoting antitumor effector cell development. Previously, we reported that the new oncolytic HSV-1 virus, OncSyn (OS), engineered to fuse tumor cells, prevented tumor growth and metastasis to distal organs in the 4T1/BALB/c immunocompetent breast cancer mouse model, suggesting the elicitation of antitumor immune responses (Israyelyan et al., Hum. Gen. Ther. 18:5, 2007, and Israyelyan et al., Virol. J. 5:68, 2008). The OSV virus was constructed by deleting the OS viral host shutoff gene (vhs; UL41) to further attenuate the virus and permit dendritic cell activation and antigen presentation. Subsequently, the OSVP virus was constructed by inserting into the OSV viral genome a murine 15-prostaglandin dehydrogenase (15-PGDH) expression cassette, designed to constitutively express 15-PGDH upon infection. 15-PGDH is a tumor suppressor protein and the primary enzyme responsible for the degradation of prostaglandin E2 (PGE2), which is known to promote tumor development. OSVP, OSV, and OS treatment of 4T1 tumors in BALB/c mice effectively reduced primary tumor growth and inhibited metastatic development of secondary tumors. OSVP was able to significantly inhibit the development and accumulation of 4T1 metastatic tumor cells in the lungs of treated mice. Ex vivo analysis of immune cells following treatment showed increased inflammatory cytokine production and the presence of mature dendritic cells for the OSVP, OSV, and OS viruses. A statistically significant decrease in splenic myeloid-derived suppressor cells (MDSC) was observed only for OSVP-treated mice. These results show that intratumoral oncolytic herpes is highly immunogenic and suggest that 15-PGDH expression by OSVP enhanced the antitumor immune response initiated by viral infection of primary tumor cells, leading to reduced development of pulmonary metastases. The availability of the OSVP genome as a bacterial artificial chromosome allows for the rapid insertion of additional immunomodulatory genes that could further assist in the induction of potent antitumor immune responses against primary and metastatic tumors.

Clinical development directions in oncolytic viral therapy

Oncolytic virotherapy is an emerging experimental treatment platform for cancer therapy. Oncolytic viruses are replicative-competent viruses that are engineered to replicate selectively in cancer cells with specified oncogenic phenotypes. Multiple DNA and RNA viruses have been clinically tested in a variety of tumors. This review will provide a brief description of these novel anticancer biologics and will summarize the results of clinical investigation. To date oncolytic virotherapy has shown to be safe, and has generated clinical responses in tumors that are resistant to chemotherapy or radiotherapy. The major challenge for researchers is to maximize the efficacy of these viral therapeutics, and to establish stable systemic delivery mechanisms.

A herpesvirus virulence factor inhibits dendritic cell maturation through protein phosphatase 1 and Ikappa B kinase

Dendritic cells are sentinels in innate and adaptive immunity. Upon virus infection, a complex program is in operation, which activates IκB kinase (IKK), a key regulator of inflammatory cytokines and costimulatory molecules. Here we show that the γ(1)34.5 protein, a virulence factor of herpes simplex viruses, blocks Toll-like receptor-mediated dendritic cell maturation. While the wild-type virus inhibits the induction of major histocompatibility complex (MHC) class II, CD86, interleukin-6 (IL-6), and IL-12, the γ(1)34.5-null mutant does not. Notably, γ(1)34.5 works in the absence of any other viral proteins. When expressed in mammalian cells, including dendritic cells, γ(1)34.5 associates with IKKα/β and inhibits NF-κB activation. This is mirrored by the inhibition of IKKα/β phosphorylation, p65/RelA phosphorylation, and nuclear translocation in response to lipopolysaccharide or poly(I:C) stimulation. Importantly, γ(1)34.5 recruits both IKKα/β and protein phosphatase 1, forming a complex that dephosphorylates two serine residues within the catalytic domains of IκB kinase. The amino-terminal domain of γ(1)34.5 interacts with IKKα/β, whereas the carboxyl-terminal domain binds to protein phosphatase 1. Deletions or mutations in either domain abolish the activity of γ(1)34.5. These results suggest that the control of IκB kinase dephosphorylation by γ(1)34.5 represents a critical viral mechanism to disrupt dendritic cell functions.

Drosophila melanogaster as a model for studying the function of animal viral proteins

Studies in which Drosophila melanogaster individuals carrying transgenes of animal viruses were used to analyze the action of animal viral proteins on the cell are reviewed. The data presented suggest that host specificity of viruses is determined by their proteins responsible for the penetration of the virus into the cell, while viral proteins responsible for interactions with the host cell are much less host-specific. Due to this, the model of Drosophila with its developed system of searching for genetic interactions can be used to find intracellular targets for the action of viral proteins of the second group.

Cross-talking between autophagy and viral infection in mammalian cells

Autophagy is a cellular process in degradation of long-lived proteins and organelles in the cytosol for maintaining cellular homeostasis, which has been linked to a wide range of human health and disease states, including viral infection. The viral infected cells exhibit a complicated cross-talking between autophagy and virus. It has been shown that autophagy interacts with both adaptive and innate immunity. For adaptive immunity, viral antigens can be processed in autophagosomes by acidic proteases before major histocompatibility complex (MHC) class II presentation. For innate immunity, autophagy may assist in the delivery of viral nucleic acids to endosomal TLRs and also functions as a part of the TLR-or-PKR-downstream responses. Autophagy was also reported to suppress the magnitude of host innate antiviral immunity in certain cases. On the other hand, viruses has evolved many strategies to combat or utilize the host autophagy for their own benefit. In this review we discussed recent advances toward clarifying the cross-talking between autophagy and viral infection in mammalian cells.

OPTIM trial: a Phase III trial of an oncolytic herpes virus encoding GM-CSF for unresectable stage III or IV melanoma

There are few effective treatment options available for patients with advanced melanoma. An oncolytic herpes simplex virus type 1 encoding granulocyte macrophage colony-stimulating factor (GM-CSF; Oncovex(GM-CSF)) for direct injection into accessible melanoma lesions resulted in a 28% objective response rate in a Phase II clinical trial. Responding patients demonstrated regression of both injected and noninjected lesions highlighting the dual mechanism of action of Oncovex(GM-CSF) that includes both a direct oncolytic effect in injected tumors and a secondary immune-mediated anti-tumor effect on noninjected tumors. Based on these preliminary results a prospective, randomized Phase III clinical trial in patients with unresectable Stage IIIb or c and Stage IV melanoma has been initiated. The rationale, study design, end points and future development of the Oncovex(GM-CSF) Pivotal Trial in Melanoma (OPTIM) trial are discussed in this article.

Herpesvirus vectors for therapy of brain tumors

Genetically modified, conditionally-replicating Herpes Simplex Virus Type 1 (HSV-1) vectors for the treatment of malignant glioma have provided encouraging results in the handful of Phase I and Phase II clinical trials conducted to date. In recent years, a number of new strategies have been developed to improve anti-tumor activity of these attenuated vectors, through either introduction of foreign gene inserts to enhance tumor killing through a variety of mechanisms, or through combination with existing treatment regimens, including radiation and/or chemotherapeutics. Another promising new approach has been the engineering of novel oncolytic HSV vectors that retain wildtype replication, but are targeted to tumor cells through a variety of mechanisms. This review summarizes the latest advances in herpesvirus-mediated oncolytic therapies from both preclinical results and clinical trials with oncolytic HSV vectors in patients, and their implication for design of future trials.

Mechanisms employed by herpes simplex virus 1 to inhibit the interferon response

The interferon (IFN) family of cytokines constitutes potent inducers of innate antiviral responses that also influence adaptive immune processes. Despite eliciting such formidable cellular defense responses, viruses have evolved ways to interfere with the IFN response. Herpes simplex virus 1 (HSV-1) is an enveloped, dsDNA virus and a member of the herpesvirus family. Like other herpesvirus family members, HSV-1 has become highly specialized for its host and establishes a lifelong infection by undergoing latency within neurons. A leading reason for the success of HSV-1 as a pathogen results from its ability to evade the IFN response. Specifically, HSV-1 encodes several proteins that function to inhibit both IFN production and subsequent signal transduction. This review will identify and summarize the current understanding of viral proteins encoded by HSV-1 involved in the evasion of the IFN response.

Spontaneous and Engineered Compensatory HSV Mutants that Counteract the Host Antiviral PKR Response

A virulent recombinant HSV lacking the diploid γ₁34.5 gene (Δγ₁34.5) have been investigated over the last two decades both for anti-tumor therapy and as vaccine vectors. The first generation vectors, while safe, are incapable of sustained replication in the majority of treated patients. An interferon inducible host antiviral kinase, protein kinase R (PKR), limits late viral protein synthesis and replication of Δγ₁34.5 viruses. This review describes the development of new Δγ₁34.5 vectors, through serial passage selection and direct viral genome engineering, which demonstrate selective PKR evasion in targeted cells and improved viral replication without restoring neurovirulence.

Dephosphorylation of eIF2alpha mediated by the gamma134.5 protein of herpes simplex virus 1 facilitates viral neuroinvasion

The gamma(1)34.5 protein, a virulence factor of herpes simplex viruses, redirects protein phosphatase 1 to dephosphorylate the alpha subunit of translation initiation factor 2 (eIF2alpha). Additionally, it inhibits the induction of antiviral genes by TANK-binding kinase 1. Nevertheless, its precise role in vivo remains to be established. Here we show that eIF2alpha dephosphorylation by gamma(1)34.5 is crucial for viral neuroinvasion. V(193)E and F(195)L substitutions in gamma(1)34.5 abrogate viral replication in the eye and spread to the trigeminal ganglia and brain. Intriguingly, inhibition of antiviral gene induction by gamma(1)34.5 is not sufficient to exhibit viral virulence.

A ROLE FOR APOPTOSIS INDUCED BY ACUTE HERPES SIMPLEX VIRUS INFECTION IN MICE

Acute herpes simplex virus (HSV) infection causes apoptosis in the adrenal cortex and myenteric plexus of the gut, ovary, pituitary gland, and liver of mice. Apoptosis of infected cells is increased in immunosuppressed regions of the adrenal cortex and liver of macrophage-depleted mice. HSV carries the US3 gene which interferes with host cell apoptosis. When the livers of macrophage-depleted mice are infected with a US3-null virus, apoptosis occurs in the narrow areas of inflammatory cell infiltration, restricting viral replication and spread. Thus, these data suggest that apoptosis may function as a primitive immune response to HSV infection in mice.

Viruses, gene therapy and stem cells for the treatment of human glioma

Cancer gene therapy is based on the transfer of genetic material to cancer cells to modify a normal or abnormal cellular function, or to induce cell death. Modified viruses or stem cells have been used as carriers to transfer the genetic material to cancer cells avoiding trafficking through normal cells. However, although the current vectors have been successful in delivering genes in vitro and in vivo, little has been achieved with human cerebral gliomas. Poor transduction efficiency of viruses in human glioma cells and limited spread and distribution to the tumor limits our current expectations for successful gene therapy of central nervous system cancer until and if effective transfer vehicles are available. Nevertheless, continuing research in better vector development may overcome these limitations and offer a therapeutic advantage over the standard therapies for glioma.

Increased eIF2alpha phosphorylation attenuates replication of herpes simplex virus 2 vhs mutants in mouse embryonic fibroblasts and correlates with reduced accumulation of the PKR antagonist ICP34.5

Herpes simplex virus 2 (HSV-2) strains containing mutations in the virion host shutoff (vhs) protein are attenuated for replication compared with wild-type virus in mouse embryonic fibroblasts (MEFs). However, HSV-2 vhs mutants replicate to near wild-type levels in the absence of the RNA-activated protein kinase (PKR). PKR is one of several kinases that phosphorylates the eukaryotic initiation factor 2alpha (eIF2alpha) to inhibit translation initiation, and we previously found that more of the phosphorylated form of eIF2alpha accumulates in MEFs infected with HSV-2 vhs mutants than with wild-type virus. Here, we show that this increase in phosphorylated eIF2alpha is primarily PKR dependent. Using MEFs expressing nonphosphorylatable eIF2alpha, we demonstrate that phosphorylated eIF2alpha is the primary cause of attenuated replication of HSV-2 vhs mutants and that attenuation correlates with decreased accumulation of viral proteins. Normally, HSV antagonizes eIF2alpha phosphorylation through the action of ICP34.5, which redirects protein phosphatase 1alpha (PP1alpha) to dephosphorylate eIF2alpha during infection. We show that ICP34.5 does not accumulate efficiently in MEFs infected with HSV-2 vhs mutant viruses, suggesting that the accumulation of phosphorylated eIF2alpha and the attenuated phenotype of HSV-2 vhs mutants in MEFs result from a deficiency in ICP34.5.

Oncolytic viral therapy of malignant glioma

Novel approaches to treatment of malignant glioma, the most frequently occurring primary brain tumor, have included the use of a wide range of oncolytic viral vectors. These vectors, either naturally tumor-selective, or engineered as such, have shown promise in the handful of phase I and phase II clinical trials conducted in recent years. The strategies developed for each of the different viruses currently being studied and the history of their development are summarized here. In addition, the results of clinical trials in patients and their implication for future trials are also discussed.

Relationship between 31P metabolites and oncolytic viral therapy sensitivity in human colorectal cancer xenografts

Background

Studies using phosphorus magnetic resonance spectroscopy (MRS) have pointed to the significance of phospholipid metabolite alterations as biochemical markers for tumour progression or therapy response.

Methods

Spectroscopic imaging was performed in colorectal flank tumours in nude mice. In vivo tumour doubling times for each cell line were measured. In vivo sensitivity of each tumour line to treatment with G207 and NV1020 oncolytic viruses was assessed. Correlations between viral sensitivity and tumour doubling time and phosphorus MRS were estimated.

Results

For G207 virus, in vitro cytotoxicity tests showed cell viability at multiplicities of infection (ratio of viral particles per tumour cell) of 0·1 on day 6 as follows: C85, less than 1 per cent; HCT8, 1 per cent; LS174T, 9 per cent; HT29, 18 per cent; and C18, 92 per cent. Respective values for NV1020 were 1, 18, 4, 18 and 86 per cent. The phosphoethanolamine to phosphocholine ratio was significantly lower in virus-sensitive than -insensitive cells, and was dependent on tumour doubling time.

Conclusion

Alterations in membrane phospholipid metabolites that relate to proliferation of cancer cells affect the efficacy of oncolytic viral therapy. MRS proved a highly sensitive non-invasive tool for predicting the efficacy of viruses.

Investigation of the mechanism by which herpes simplex virus type 1 LAT sequences modulate preferential establishment of latent infection in mouse trigeminal ganglia

We previously demonstrated that herpes simplex virus type 1 (HSV-1) preferentially establishes latent infection in monoclonal antibody (MAb) A5-positive ganglionic neurons and that a 2.8-kb portion of the HSV-1 genome, corresponding to the 5' end of the LAT (latency-associated transcript) coding region, is responsible for this phenotype (38, 65). In the current study we carried out further genetic mapping of this latency phenotype and investigated some of the mechanisms that might be responsible. Studies with the chimeric virus HSV-1 17syn+/LAT2, an HSV-1 virus engineered to express HSV-2 LAT, demonstrated that this virus exhibited an HSV-2 latency phenotype, preferentially establishing latency in MAb KH10-positive neurons. This result is complementary to that previously described for the chimeric virus HSV-2 333/LAT1 and indicate that the HSV-1 latency phenotype can be changed to that of HSV-2 by substitution of a 2.8-kb piece of complementary viral DNA. Sequential studies in which we evaluated the pattern of HSV-1 latent infection of the mouse trigeminal ganglion following ocular inoculation with viruses with deletions of functional thymidine kinase, glycoprotein E, ICP0, and US9 protein demonstrate that preferential establishment of HSV-1 latent infection in A5-positive neurons is not a consequence of (i) differential access of HSV-1 to A5-positive neurons,(ii) differential cell-to-cell spread of HSV-1 to A5-positive neurons, (iii) differential "round-trip" spread of HSV-1 to A5-positive neurons, or (iv) expression of ICP0. Additional mapping studies with the HSV-1 LAT deletion viruses dLAT371, 17DeltaSty, and 17Delta348 indicate that most of the LAT 5' exon is not required for HSV-1 to preferentially establish latent infection in A5-positive neurons.

The gamma 1 34.5 protein of herpes simplex virus 1 is required to interfere with dendritic cell maturation during productive infection

The gamma(1)34.5 protein of herpes simplex virus 1 is an essential factor for viral virulence. In infected cells, this viral protein prevents the translation arrest mediated by double-stranded RNA-dependent protein kinase R. Additionally, it associates with and inhibits TANK-binding kinase 1, an essential component of Toll-like receptor-dependent and -independent pathways that activate interferon regulatory factor 3 and cytokine expression. Here, we show that gamma(1)34.5 is required to block the maturation of conventional dendritic cells (DCs) that initiate adaptive immune responses. Unlike wild-type virus, the gamma(1)34.5 null mutant stimulates the expression of CD86, major histocompatibility complex class II (MHC-II), and cytokines such as alpha/beta interferon in immature DCs. Viral replication in DCs inversely correlates with interferon production. These phenotypes are also mirrored in a mouse ocular infection model. Further, DCs infected with the gamma(1)34.5 null mutant effectively activate naive T cells whereas DCs infected with wild-type virus fail to do so. Type I interferon-neutralizing antibodies partially reverse virus-induced upregulation of CD86 and MHC-II, suggesting that gamma(1)34.5 acts through interferon-dependent and -independent mechanisms. These data indicate that gamma(1)34.5 is involved in the impairment of innate immunity by inhibiting both type I interferon production and DC maturation, leading to defective T-cell activation.

HSV-2 ICP34.5 protein modulates herpes simplex virus glycoprotein processing

The ICP34.5 gene from HSV-2 strain 333 was cloned and, when expressed in Vero cells, enhanced the efficiency and extent of glycoprotein processing of glycoprotein C (gC1), a representative viral glycoprotein, during infection with HSV-1 SP7. The ICP34.5 from HSV-1 SP7 limits the extent and efficiency of viral glycoprotein processing. The ability of the HSV-2 ICP34.5 protein to enhance the efficiency and extent of HSV-1 SP7 glycoprotein processing indicates that modulation of viral glycoprotein processing is also a property of the HSV-2 ICP34.5 protein.

Novel less-abundant viral microRNAs encoded by herpes simplex virus 2 latency-associated transcript and their roles in regulating ICP34.5 and ICP0 mRNAs

We recently identified an acutely and latently expressed viral microRNA (miRNA), miR-I, encoded by herpes simplex virus 2 (HSV-2) latency-associated transcript (LAT) through small RNA cloning and two miRNAs encoded by HSV-1 LAT through prediction. We now report the use of high-throughput sequencing technology to identify two additional relatively less-abundant viral miRNAs, miR-II and miR-III, encoded by HSV-2 LAT exon 2. miR-II includes two miRNAs, miR-II-5p and miR-II-3p, which are processed from the same miRNA precursor. miR-II and miR-III map antisense to the 5' untranslated region of ICP34.5 and to the coding region of ICP0 exon 3, respectively. These novel miRNAs are conserved in different HSV-2 strains, and their presence in infected- and transfected-cell cultures was confirmed by Northern hybridization. All three HSV-2 LAT-encoded miRNAs map to genome locations similar to those of three out of four identified HSV-1 LAT-encoded miRNAs, but the sequences of these miRNAs are not conserved. The expression of LAT-encoded miRNAs is negatively regulated by ICP4, the major viral transactivator. We further show that, similar to miR-I, miR-II is able to efficiently silence the expression of ICP34.5, a key viral neurovirulence factor, and that miR-III is able to silence the expression of ICP0, a key viral transactivator. All these data suggest that LAT sequences likely contribute to HSV latency and reactivation through tight control of these LAT-encoded miRNAs and their viral targets.

Control of TANK-binding kinase 1-mediated signaling by the gamma(1)34.5 protein of herpes simplex virus 1

TANK-binding kinase 1 (TBK1) is a key component of Toll-like receptor-dependent and -independent signaling pathways. In response to microbial components, TBK1 activates interferon regulatory factor 3 (IRF3) and cytokine expression. Here we show that TBK1 is a novel target of the gamma(1)34.5 protein, a virulence factor whose expression is regulated in a temporal fashion. Remarkably, the gamma(1)34.5 protein is required to inhibit IRF3 phosphorylation, nuclear translocation, and the induction of antiviral genes in infected cells. When expressed in mammalian cells, the gamma(1)34.5 protein forms complexes with TBK1 and disrupts the interaction of TBK1 and IRF3, which prevents the induction of interferon and interferon-stimulated gene promoters. Down-regulation of TBK1 requires the amino-terminal domain. In addition, unlike wild type virus, a herpes simplex virus mutant lacking gamma(1)34.5 replicates efficiently in TBK1(-/-) cells but not in TBK1(+/+) cells. Addition of exogenous interferon restores the antiviral activity in both TBK1(-/-) and TBK(+/+) cells. Hence, control of TBK1-mediated cell signaling by the gamma(1)34.5 protein contributes to herpes simplex virus infection. These results reveal that TBK1 plays a pivotal role in limiting replication of a DNA virus.

ICP34.5-dependent and -independent activities of salubrinal in herpes simplex virus-1 infected cells

The small molecule salubrinal has antiviral activity against herpes simplex virus-1 (HSV-1) and inhibits dephosphorylation of eIF2 alpha mediated by the HSV-1 protein ICP34.5. We investigated whether salubrinal's activities in infected cells depend on ICP34.5. An ICP34.5 deletion mutant was as sensitive as wild type HSV-1 to salubrinal inhibition of plaque formation in Vero cells. However, salubrinal induced formation of syncytia in infected Vero cells, which was enhanced by ICP34.5 mutations. Expression of HSV-1 US11 with immediate early kinetics, which is known to suppress the effects of ICP34.5 mutations, resulted in slight resistance to salubrinal in murine embryonic fibroblasts, and substantial resistance in those cells when ICP34.5 was additionally mutated. ICP34.5 mutations, but not immediate early expression of US11, prevented salubrinal's ability to increase phosphorylation of eIF2 alpha during HSV-1 infection of Vero cells. Taken together, our data indicate that salubrinal has both ICP34.5-dependent and -independent activities in HSV-1 infected cells.

An acutely and latently expressed herpes simplex virus 2 viral microRNA inhibits expression of ICP34.5, a viral neurovirulence factor

Latency-associated transcript (LAT) sequences regulate herpes simplex virus (HSV) latency and reactivation from sensory neurons. We found a HSV-2 LAT-related microRNA (miRNA) designated miR-I in transfected and infected cells in vitro and in acutely and latently infected ganglia of guinea pigs in vivo. miR-I is also expressed in human sacral dorsal root ganglia latently infected with HSV-2. miR-I is expressed under the LAT promoter in vivo in infected sensory ganglia. We also predicted and identified a HSV-1 LAT exon-2 viral miRNA in a location similar to miR-I, implying a conserved mechanism in these closely related viruses. In transfected and infected cells, miR-I reduces expression of ICP34.5, a key viral neurovirulence factor. We hypothesize that miR-I may modulate the outcome of viral infection in the peripheral nervous system by functioning as a molecular switch for ICP34.5 expression.

Involvement of gD/HVEM interaction in NF-kB-dependent inhibition of apoptosis by HSV-1 gD

In the present paper, we aimed to verify whether the interaction of the glycoprotein D (gD) of herpes simplex 1 (HSV-1) with the HSV-1 receptor HVEM is involved in NF-kappaB-dependent protection against apoptosis by gD. To this purpose, first we utilized MAbs that interfere with gD/HVEM interaction and U937 cells that naturally express human HVEM on their surface. Pre-incubation with these MAbs, but not with a control antibody, partially reverted the protection of infectious HSV-1 towards anti-Fas induced apoptosis in U937 cells. Similarly, pre-incubation of UV-inactivated HSV-1 (UV-HSV-1) or recombinant gD with the same MAbs, significantly reduced the inhibition of Fas-mediated apoptosis by UV-HSV-1 or gD, respectively, in U937 cells. Moreover, coculture with stable transfectants expressing at surface level wild type gD protected U937 cells against Fas-induced apoptosis, while coculture with transfectants expressing a mutated form of gD, incapable to bind HVEM, did not protect. Finally, UV-HSV-1 protected against staurosporine-induced apoptosis in U937 cells as well as in the CHO transfectants expressing human HVEM on their surface, but not in the control CHO transfectants, which did not express HVEM. These results suggest that signaling triggered by binding of gD to HVEM could represent an additional mechanism of evasion from premature apoptotic death exerted by HSV-1-gD in HVEM-expressing cells, disclosing new opportunities of cell death manipulation by using gD preparations.

Herpes simplex virus type-1(HSV-1) oncolytic and highly fusogenic mutants carrying the NV1020 genomic deletion effectively inhibit primary and metastatic tumors in mice

Background

The NV1020 oncolytic herpes simplex virus type-1 has shown significant promise for the treatment of many different types of tumors in experimental animal models and human trials. Previously, we described the construction and use of the NV1020-like virus OncSyn to treat human breast tumors implanted in nude mice. The syncytial mutation gKsyn1 (Ala-to-Val at position 40) was introduced into the OncSyn viral genome cloned into a bacterial artificial chromosome using double-red mutagenesis in E. coli to produce the OncdSyn virus carrying syncytial mutations in both gB(syn3) and gK(syn1).

Results

The OncdSyn virus caused extensive virus-induced cell fusion in cell culture. The oncolytic potential of the OncSyn and OncdSyn viruses was tested in the highly metastatic syngeneic mouse model system, which utilizes 4T1 murine mammary cancer cells implanted within the interscapular region of Balb/c mice. Mice were given three consecutive intratumor injections of OncSyn, OncdSyn, or phosphate buffered saline four days apart. Both OncSyn and OncdSyn virus injections resulted in significant reduction of tumor sizes (p < 0.05) compared to control tumors. Virus treated mice but not controls showed a marked reduction of metastatic foci in lungs and internal organs. Mouse weights were not significantly impacted by any treatment during the course of the entire study (p = 0.296).

Conclusion

These results show that the attenuated, but highly fusogenic OncSyn and OncdSyn viruses can effectively reduce primary and metastatic breast tumors in immuncompetent mice. The available bac-cloned OncSyn and OncdSyn viral genomes can be rapidly modified to express a number of different anti-tumor and immunomodulatory genes that can further enhance their anti-tumor potency.

HSV-1 ICP34.5 confers neurovirulence by targeting the Beclin 1 autophagy protein

Autophagy is postulated to play a role in antiviral innate immunity. However, it is unknown whether viral evasion of autophagy is important in disease pathogenesis. Here we show that the herpes simplex virus type 1 (HSV-1)-encoded neurovirulence protein ICP34.5 binds to the mammalian autophagy protein Beclin 1 and inhibits its autophagy function. A mutant HSV-1 virus lacking the Beclin 1-binding domain of ICP34.5 fails to inhibit autophagy in neurons and demonstrates impaired ability to cause lethal encephalitis in mice. The neurovirulence of this Beclin 1-binding mutant virus is restored in pkr(-/-) mice. Thus, ICP34.5-mediated antagonism of the autophagy function of Beclin 1 is essential for viral neurovirulence, and the antiviral signaling molecule PKR lies genetically upstream of Beclin 1 in host defense against HSV-1. Our findings suggest that autophagy inhibition is a novel molecular mechanism by which viruses evade innate immunity and cause fatal disease.

Neurovirulent factor ICP34.5 uniquely expressed in the herpes simplex virus type 1 Delta gamma 1 34.5 mutant 1716

The herpes simplex virus type 1 (HSV-1) diploid gene gamma(1)34.5 encodes a neurovirulent factor, infected cell protein 34.5 (ICP34.5). The promoter to gamma(1)34.5 is located within the HSV-1 genome where there are repeated sequences. This region of the genome also contains important overlapping transcripts involved with the virus's ability to establish lytic and latent infections and reactivation. These transcripts include the latency-associated transcripts and regulator proteins ICP0 and ICP4. This study aimed to separate ICP34.5 from these overlapping transcripts and test if its expression from a single gene could restore wild-type HSV-1 strain 17+ virulence. To address these aims, different recombinant viruses were constructed using the Delta gamma(1)34.5 mutant 1716. Immunoblots probed with different ICP34.5 antisera demonstrated that one of the newly generated recombinant viruses, 1622, overexpresses ICP34.5 relative to a panel of wild-type viruses. Interestingly, the overexpression of ICP34.5 does not yield a more virulent virus. The onset of ICP34.5 expression from 1622-infected cells in vitro matched that of 17+, and its expression restored the function of maintaining protein synthesis in human neuroblastoma cells. Replication of 1622, however, was only partially restored to 17+ levels in vivo. Additionally, plaque morphology from 1622-infected cells indicates there is an additional defect. The authors report that the mutant virus 1622 can express ICP34.5 from a single gamma(1)34.5 gene and restore most (but not all) wild-type function. These findings are discussed with respect to the use of the gamma(1)34.5 deleted mutant, 1716, in oncolytic viral vector therapies and future studies for ICP34.5.

A conserved domain of herpes simplex virus ICP34.5 regulates protein phosphatase complex in mammalian cells

ICP34.5, encoded by herpes simplex virus 1, is a protein phosphatase 1 (PP1) regulatory subunit that mediates dephosphorylation of the alpha subunit of translation initiation factor 2 (eIF2alpha). However, the mechanism of its action remains poorly understood. Here, we show that amino acid substitutions in the arginine-rich motif have differential effects on ICP34.5 activity. The phenotypes parallel with viral protein synthesis and cytopathic effects in virus infected cells. Besides the consensus PP1 binding motif, the Arg-motif appears to enhance the interaction between ICP34.5 and PP1. These results suggest that concerted action between the PP1 binding domain and the effector domain of ICP34.5 is crucial for eIF2alpha dephosphorylation and viral protein synthesis.