Differential effects of nerve growth factor and dexamethasone on herpes simplex virus type 1 oriL- and oriS-dependent DNA replication in PC12 cells

Impaired glucocorticoid receptor function attenuates herpes simplex virus 1 production during explant-induced reactivation from latency in female mice

IMPORTANCE

A correlation exists between stress and increased episodes of human alpha-herpes virus 1 reactivation from latency. Stress increases corticosteroid levels; consequently, the glucocorticoid receptor (GR) is activated. Recent studies concluded that a GR agonist, but not an antagonist, accelerates productive infection and reactivation from latency. Furthermore, GR and certain stress-induced transcription factors cooperatively transactivate promoters that drive the expression of infected cell protein 0 (ICP0), ICP4, and VP16. This study revealed female mice expressing a GR containing a serine to alanine mutation at position 229 (GRS229A) shed significantly lower levels of infectious virus during explant-induced reactivation compared to male GRS229A or wild-type parental C57BL/6 mice. Furthermore, female GRS229A mice contained fewer VP16 + TG neurons compared to male GRS229A mice or wild-type mice during the early stages of explant-induced reactivation from latency. Collectively, these studies revealed that GR transcriptional activity has female-specific effects, whereas male mice can compensate for the loss of GR transcriptional activation.

Stress Hormones Epinephrine and Corticosterone Selectively Reactivate HSV-1 and HSV-2 in Sympathetic and Sensory Neurons

Herpes simplex viruses 1 and 2 (HSV-1 and HSV-2) establish latency in sensory and autonomic neurons, from which they can reactivate to cause recurrent disease throughout the life of the host. Stress is strongly associated with HSV recurrences in humans and animal models. However, the mechanisms through which stress hormones act on the latent virus to cause reactivation are unknown. We show that the stress hormones epinephrine (EPI) and corticosterone (CORT) induce HSV-1 reactivation selectively in sympathetic neurons, but not sensory or parasympathetic neurons. Activation of multiple adrenergic receptors is necessary for EPI-induced HSV-1 reactivation, while CORT requires the glucocorticoid receptor. In contrast, CORT, but not EPI, induces HSV-2 reactivation in both sensory and sympathetic neurons through either glucocorticoid or mineralocorticoid receptors. Reactivation is dependent on different transcription factors for EPI and CORT, and coincides with rapid changes in viral gene expression, although genes differ for HSV-1 and HSV-2, and temporal kinetics differ for EPI and CORT. Thus, stress-induced reactivation mechanisms are neuron-specific, stimulus-specific and virus-specific. These findings have implications for differences in HSV-1 and HSV-2 recurrent disease patterns and frequencies, as well as development of targeted, more effective antivirals that may act on different responses in different types of neurons.

Regulation of herpes simplex virus type 1 latency-reactivation cycle and ocular disease by cellular signaling pathways

Following acute infection, herpes simplex virus type 1 (HSV-1) establishes life-long latency in sensory and other neurons. Recurrent ocular HSV-1 outbreaks are generally due to reactivation from latency. The HSV-1 latency-reactivation cycle is a complex virus-host relationship. The viral encoded latency-associated transcript (LAT) is abundantly expressed in latency and encodes several micro-RNAs and other small non-coding RNAs, which may regulate expression of key viral and cellular genes. Certain cellular signaling pathways, including Wnt/β-catenin and mTOR pathway, mediate certain aspect of the latency-reactivation cycle. Stress, via activation of the glucocorticoid receptor and other stress induced cellular transcription factors, are predicted to trigger reactivation from latency by stimulating viral gene expression and impairing immune responses and inflammation. These observations suggest stress and certain cellular signaling pathways play key roles in regulating the latency-reactivation cycle and recurrent ocular disease.

The Hippocampal Vulnerability to Herpes Simplex Virus Type I Infection: Relevance to Alzheimer's Disease and Memory Impairment

Herpes simplex virus type 1 (HSV-1) as a possible infectious etiology in Alzheimer’s disease (AD) has been proposed since the 1980s. The accumulating research thus far continues to support the association and a possible causal role of HSV-1 in the development of AD. HSV-1 has been shown to induce neuropathological and behavioral changes of AD, such as amyloid-beta accumulation, tau hyperphosphorylation, as well as memory and learning impairments in experimental settings. However, a neuroanatomical standpoint of HSV-1 tropism in the brain has not been emphasized in detail. In this review, we propose that the hippocampal vulnerability to HSV-1 infection plays a part in the development of AD and amnestic mild cognitive impairment (aMCI). Henceforth, this review draws on human studies to bridge HSV-1 to hippocampal-related brain disorders, namely AD and aMCI/MCI. Next, experimental models and clinical observations supporting the neurotropism or predilection of HSV-1 to infect the hippocampus are examined. Following this, factors and mechanisms predisposing the hippocampus to HSV-1 infection are discussed. In brief, the hippocampus has high levels of viral cellular receptors, neural stem or progenitor cells (NSCs/NPCs), glucocorticoid receptors (GRs) and amyloid precursor protein (APP) that support HSV-1 infectivity, as well as inadequate antiviral immunity against HSV-1. Currently, the established diseases HSV-1 causes are mucocutaneous lesions and encephalitis; however, this review revises that HSV-1 may also induce and/or contribute to hippocampal-related brain disorders, especially AD and aMCI/MCI.

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

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

Transactivation of Herpes Simplex Virus 1 (HSV-1) Infected Cell Protein 4 Enhancer by Glucocorticoid Receptor and Stress-Induced Transcription Factors Requires Overlapping Krüppel-Like Transcription Factor 4/Sp1 Binding Sites

Following acute infection, herpes simplex virus 1 (HSV-1) lytic cycle viral gene expression is silenced; consequently, lifelong latency in neurons is established. Certain external stimuli that trigger reactivation from latency also activate the glucocorticoid receptor (GR). The synthetic corticosteroid dexamethasone, but not a GR-specific antagonist, increases the frequency of explant-induced reactivation from latency and stimulates productive infection. Furthermore, dexamethasone increases expression of cellular transcription factors in trigeminal ganglionic neurons: for example, SLUG and three Krüppel-like transcription factor (KLF) family members, KLF4, KLF15, and promyelocytic leukemia zinc finger protein (PLZF). Consequently, we hypothesized that stress-induced transcription factors stimulate expression of ICP4, a viral transcriptional regulator required for productive infection. New studies demonstrated that GR and KLF4, PLZF, or SLUG cooperatively transactivate the ICP4 enhancer upstream of a minimal promoter in monkey kidney cells (Vero) and mouse neuroblastoma cells (Neuro-2A). Strikingly, mutagenesis of two KLF4/Sp1 binding sites reduced GR- plus KLF4-, PLZF-, or SLUG-mediated transactivation to basal levels. A consensus enhancer (E)-Box adjacent to a KLF4/Sp1 binding site was also required for GR- and SLUG-, but not KLF family member-, mediated transactivation of the ICP4 promoter. Chromatin immunoprecipitation studies (ChIP) revealed GR and stress-induced transcription factors occupy ICP4 enhancer sequences. Conversely, specific binding was generally reduced in the KLF4/Sp1 mutant. Furthermore, GR and SLUG occupancy of ICP4 enhancer sequences was reduced in the E-Box mutant. Based on these studies, we suggest stressful stimuli can trigger productive infection because GR and specific stress-induced transcription factors activate ICP4 expression.IMPORTANCE Certain stressful stimuli activate the glucocorticoid receptor (GR) and increase the incidence of herpes simplex virus 1 (HSV-1) reactivation from latency. For example, a corticosteroid antagonist impairs productive infection and virus shedding following explant of trigeminal ganglia from latently infected mice. Infected cell protein 4 (ICP4) is the only immediate early viral transcriptional regulator required for productive infection, suggesting stressful stimuli stimulate ICP4 expression. New studies revealed GR and stress-induced transcription factors identified during reactivation from latency, SLUG and three Krüppel-like transcription factor family members (KLF4, KLF15, and promyelocytic leukemia zinc finger protein), cooperatively transactivate the ICP4 enhancer. Two KLF4 consensus binding sites were crucial for cooperative transactivation of the ICP4 enhancer. A consensus enhancer-box also mediated cooperative transactivation of the ICP4 enhancer by GR and SLUG. The ability of GR and stress-induced transcription factors to transactivate ICP4 enhancer activity is predicted to trigger productive infection following stressful stimuli.

Antagonizing the Glucocorticoid Receptor Impairs Explant-Induced Reactivation in Mice Latently Infected with Herpes Simplex Virus 1

Herpes simplex virus 1 (HSV-1) establishes lifelong latent infections in neurons. Reactivation from latency can lead to serious recurrent disease, including stromal keratitis, corneal scarring, blindness, and encephalitis. Although numerous studies link stress to an increase in the incidence of reactivation from latency and recurrent disease, the mechanism of action is not well understood. We hypothesized that stress, via corticosteroid-mediated activation of the glucocorticoid receptor (GR), stimulates viral gene expression and productive infection during reactivation from latency. Consequently, we tested whether GR activation by the synthetic corticosteroid dexamethasone influenced virus shedding during reactivation from latency using trigeminal ganglion (TG) explants from Swiss Webster mice latently infected with HSV-1, strain McKrae. TG explants from the latently infected mice shed significantly higher levels of virus when treated with dexamethasone. Conversely, virus shedding from TG explants was significantly impaired when they were incubated with medium containing a GR-specific antagonist (CORT-108297) or stripped fetal bovine serum, which lacks nuclear hormones and other growth factors. TG explants from latently infected, but not uninfected, TG contained significantly more GR-positive neurons following explant when treated with dexamethasone. Strikingly, VP16 protein expression was detected in TG neurons at 8 hours after explant whereas infected-cell protein 0 (ICP0) and ICP4 protein expression was not readily detected until 16 hours after explant. Expression of all three viral regulatory proteins was stimulated by dexamethasone. These studies indicated corticosteroid-mediated GR activation increased the number of TG neurons expressing viral regulatory proteins, which enhanced virus shedding during explant-induced reactivation from latency.IMPORTANCE Herpes simplex virus 1 (HSV-1) establishes lifelong latent infections in neurons within trigeminal ganglia (TG); periodically, reactivation from latency occurs, leading to virus transmission and recurrent disease. Chronic or acute stress increases the frequency of reactivation from latency; how this occurs is not well understood. Here, we demonstrate that the synthetic corticosteroid dexamethasone stimulated explant-induced reactivation from latency. Conversely, a glucocorticoid receptor (GR) antagonist significantly impaired reactivation from latency, indicating that GR activation stimulated explant-induced reactivation. The viral regulatory protein VP16 was readily detected in TG neurons prior to infected-cell protein 0 (ICP0) and ICP4 during explant-induced reactivation. Dexamethasone induced expression of all three viral regulatory proteins following TG explant. Whereas the immunosuppressive properties of corticosteroids would facilitate viral spread during reactivation from latency, these studies indicate GR activation increases the number of TG neurons that express viral regulatory proteins during early stages of explant-induced reactivation.

The Glucocorticoid Receptor (GR) Stimulates Herpes Simplex Virus 1 Productive Infection, in Part Because the Infected Cell Protein 0 (ICP0) Promoter Is Cooperatively Transactivated by the GR and Krüppel-Like Transcription Factor 15

Following acute infection, herpes simplex virus 1 (HSV-1) establishes lifelong latency in neurons. Physical, emotional, and chemical stresses are linked to increasing the incidence of reactivation from latency, but the mechanism of action is not well understood. In general, stress increases corticosteroid levels, leading to activation of the glucocorticoid receptor (GR), a pioneer transcription factor. Consequently, we hypothesized that stress-mediated activation of the GR can stimulate productive infection and viral gene expression. New studies demonstrated that the GR-specific antagonist (CORT-108297) significantly reduced HSV-1 productive infection in mouse neuroblastoma cells (Neuro-2A). Additional studies demonstrated that the activated GR and Krüppel-like transcription factor 15 (KLF15) cooperatively transactivated the infected cell protein 0 (ICP0) promoter, a crucial viral regulatory protein. Interestingly, the synthetic corticosteroid dexamethasone and GR or KLF15 alone had little effect on ICP0 promoter activity in transfected Neuro-2A or Vero cells. Chromatin immunoprecipitation (ChIP) studies revealed that the GR and KLF15 occupied ICP0 promoter sequences important for transactivation at 2 and 4 h after infection; however, binding was not readily detected at 6 h after infection. Similar results were obtained for cells transfected with the full-length ICP0 promoter. ICP0 promoter sequences lack a consensus "whole" GR response element (GRE) but contain putative half-GREs that were important for dexamethasone induced promoter activity. The activated GR stimulates expression of, and interacts with, KLF15; consequently, these data suggest KLF15 and the GR form a feed-forward loop that activates viral gene expression and productive infection following stressful stimuli.IMPORTANCE The ability of herpes simplex virus 1 (HSV-1) to periodically reactivate from latency results in virus transmission and recurrent disease. The incidence of reactivation from latency is increased by chronic or acute stress. Stress increases the levels of corticosteroids, which bind and activate the glucocorticoid receptor (GR). Since GR activation is an immediate early response to stress, we tested whether the GR influences productive infection and the promoter that drives infected cell protein 0 (ICP0) expression. Pretreatment of cells with a GR-specific antagonist (CORT-108297) significantly reduced virus replication. Although the GR had little effect on ICP0 promoter activity alone, the Krüppel-like transcription factor 15 (KLF15) cooperated with the GR to stimulate promoter activity in transfected cells. In transfected or infected cells, the GR and KLF15 occupied ICP0 sequences important for transactivation. Collectively, these studies provide insight into how stress can directly stimulate productive infection and viral gene expression.

Stress Hormones Epinephrine and Corticosterone Selectively Modulate Herpes Simplex Virus 1 (HSV-1) and HSV-2 Productive Infections in Adult Sympathetic, but Not Sensory, Neurons

Herpes simplex viruses 1 and 2 (HSV-1 and HSV-2) infect and establish latency in peripheral neurons, from which they can reactivate to cause recurrent disease throughout the life of the host. Stress is associated with the exacerbation of clinical symptoms and the induction of recurrences in humans and animal models. The viruses preferentially replicate and establish latency in different subtypes of sensory neurons, as well as in neurons of the autonomic nervous system that are highly responsive to stress hormones. To determine if stress-related hormones modulate productive HSV-1 and HSV-2 infections within sensory and autonomic neurons, we analyzed viral DNA and the production of viral progeny after treatment of primary adult murine neuronal cultures with the stress hormones epinephrine and corticosterone. Both sensory trigeminal ganglion (TG) and sympathetic superior cervical ganglion (SCG) neurons expressed adrenergic receptors (activated by epinephrine) and the glucocorticoid receptor (activated by corticosterone). Productive HSV infection colocalized with these receptors in SCG but not in TG neurons. In productively infected neuronal cultures, epinephrine treatment significantly increased the levels of HSV-1 DNA replication and production of viral progeny in SCG neurons, but no significant differences were found in TG neurons. In contrast, corticosterone significantly decreased the levels of HSV-2 DNA replication and production of viral progeny in SCG neurons but not in TG neurons. Thus, the stress-related hormones epinephrine and corticosterone selectively modulate acute HSV-1 and HSV-2 infections in autonomic, but not sensory, neurons.IMPORTANCE Stress exacerbates acute disease symptoms resulting from HSV-1 and HSV-2 infections and is associated with the appearance of recurrent skin lesions in millions of people. Although stress hormones are thought to impact HSV-1 and HSV-2 through immune system suppression, sensory and autonomic neurons that become infected by HSV-1 and HSV-2 express stress hormone receptors and are responsive to hormone fluctuations. Our results show that autonomic neurons are more responsive to epinephrine and corticosterone than are sensory neurons, demonstrating that the autonomic nervous system plays a substantial role in HSV pathogenesis. Furthermore, these results suggest that stress responses have the potential to differentially impact HSV-1 and HSV-2 so as to produce divergent outcomes of infection.

ME-609: A Treatment for Recurrent Herpes Simplex Virus Infections

Studies in conventional murine models of HSV infection use immunologically naive animals. These models thus mimic primary infections rather than recurrent infections in humans. We have, therefore, used a newly developed mouse model that more closely mimics recurrent HSV infection in humans. In this model, the mice are infected, and zosteriform HSV-1 infection develops in the presence of a primed immune response using adoptive transfer of immunity (ATI) as we have described previously. Using the ATI mouse model, it has been shown that a more beneficial therapy for recurrent mucocutaneous HSV infection could be achieved by controlling both the viral replication and the inflammatory response to the virus. Topical treatment was initiated in this model at the time of first occurrence of symptoms and was given three times daily for 4 days. Topical treatment with ME-609 (which contains 5% acyclovir and 1% hydrocortisone) in the ATI mouse model was substantially more efficacious than 5% Zovirax® cream, 1% hydrocortisone or no treatment, respectively. The beneficial properties of ME-609 were also found to be superior to those of Zovirax cream when tested in the standard guinea pig model, representing a primary HSV infection. ME-609 represents a novel treatment principle of recurrent HSV infections and the present paper summarizes the preclinical and early clinical experience of ME-609.

The serum and glucocorticoid-regulated protein kinases (SGK) stimulate bovine herpesvirus 1 and herpes simplex virus 1 productive infection

Serum and glucocorticoid-regulated protein kinases (SGK) are serine/threonine protein kinases that contain a catalytic domain resembling other protein kinases: AKT/protein kinase B, protein kinase A, and protein kinase C-Zeta for example. Unlike these constitutively expressed protein kinases, SGK1 RNA and protein levels are increased by growth factors and corticosteroids. Stress can directly stimulate SGK1 levels as well as stimulate bovine herpesvirus 1 (BoHV-1) and herpes simplex virus 1 (HSV-1) productive infection and reactivation from latency suggesting SGK1 can stimulate productive infection. For the first time, we provide evidence that a specific SGK inhibitor (GSK650394) significantly reduced BoHV-1 and HSV-1 replication in cultured cells. Proteins encoded by the three BoHV-1 immediate early genes (bICP0, bICP4, and bICP22) and two late proteins (VP16 and gE) were consistently reduced by GSK650394 during early stages of productive infection. In summary, these studies suggest SGK may stimulate viral replication following stressful stimuli.

Overexpression of thyroid hormone receptor β1 altered thyroid hormone-mediated regulation of herpes simplex virus-1 replication in differentiated cells

Thyroid hormone (T₃) has been suggested to play a role in herpes simplex virus 1 (HSV-1) replication. It was previously reported that HSV-1 replication was suppressed by T₃ in mouse neuroblastoma cells overexpressing thyroid hormone receptor β1 (TRβ1). Using a human neuro-endocrine cells LNCaP differentiated by androgen deprivation, HSV-1 replication was active but decreased by T₃ at very low moi, probably due to low copy of TRβ1. In this study, a recombinant HSV-1 was constructed expressing TRβ1 (HSV-1/TRβ1). Infection of Vero cells (very little TRβ1 expression) with HSV-1/TRβ1 exhibited increased replication in the presence of T₃ compared to the counterpart without TRβ1 overexpression. Interestingly, HSV-1/TRβ1 infection of differentiated LNCaP cells showed strong suppression of viral replication by T₃ and the removal of hormone did not fully reversed the suppression as was observed in parent virus. Quantitative analyses indicated that ICP0 expression was blocked using HSV-1/TRβ1 for infection during T₃ washout, suggesting that overexpression of TRβ1 is likely to delay its inhibitory effect on viral gene expression. Together these results emphasized the importance of TRβ1 in the regulation of HSV-1 replication in differentiated environment with neuronal phenotype.

Bovine Herpes Virus 1 (BHV-1) and Herpes Simplex Virus Type 1 (HSV-1) Promote Survival of Latently Infected Sensory Neurons, in Part by Inhibiting Apoptosis

α-Herpesvirinae subfamily members, including herpes simplex virus type 1 (HSV-1) and bovine herpes virus 1 (BHV-1), initiate infection in mucosal surfaces. BHV-1 and HSV-1 enter sensory neurons by cell-cell spread where a burst of viral gene expression occurs. When compared to non-neuronal cells, viral gene expression is quickly extinguished in sensory neurons resulting in neuronal survival and latency. The HSV-1 latency associated transcript (LAT), which is abundantly expressed in latently infected neurons, inhibits apoptosis, viral transcription, and productive infection, and directly or indirectly enhances reactivation from latency in small animal models. Three anti-apoptosis genes can be substituted for LAT, which will restore wild type levels of reactivation from latency to a LAT null mutant virus. Two small non-coding RNAs encoded by LAT possess anti-apoptosis functions in transfected cells. The BHV-1 latency related RNA (LR-RNA), like LAT, is abundantly expressed during latency. The LR-RNA encodes a protein (ORF2) and two microRNAs that are expressed in certain latently infected neurons. Wild-type expression of LR gene products is required for stress-induced reactivation from latency in cattle. ORF2 has anti-apoptosis functions and interacts with certain cellular transcription factors that stimulate viral transcription and productive infection. ORF2 is predicted to promote survival of infected neurons by inhibiting apoptosis and sequestering cellular transcription factors which stimulate productive infection. In addition, the LR encoded microRNAs inhibit viral transcription and apoptosis. In summary, the ability of BHV-1 and HSV-1 to interfere with apoptosis and productive infection in sensory neurons is crucial for the life-long latency-reactivation cycle in their respective hosts.

A Novel Thyroid Hormone Mediated Regulation of HSV-1 Gene Expression and Replication is Specific to Neuronal Cells and Associated with Disruption of Chromatin Condensation

Previously we showed that thyroid hormone (T3) regulated the Herpes Simplex Virus Type -1 (HSV-1) gene expression and replication through its nuclear receptor TR via histone modification and chromatin remodeling in a neuroblastoma cell line neuro-2a cells (N2a). This observation suggested that T3 regulation may be neuron-specific and have implication in HSV-1 latency and reactivation. In this study, our in vitro latency/reactivation model demonstrated that removal of T3 can de-repress the HSV-1 replication and favor reactivation. Transfection studies and infection assays indicated that HSV-1 thymidine kinase (TK), a key viral gene during reactivation, was repressed by TR/T3 in cells with neuronal origin but not in non-neuronal cells. Additional studies showed that RCC1 (Regulator of Chromosome Condensation 1) was sequestered but efficiently detected upon viral infection in N2a cells. Western blot analyses indicated that addition of T3 repressed the RCC1 expression upon infection. It is likely that diminution of RCC1 upon infection in neuronal cells under the influence of TR/T3 may lead to repression of viral replication/gene expression thus promote latency. Together these results demonstrated that TR/T3 mediated regulation is specific to neuronal cells and differential chromosome condensation may play a critical role in this process.

Sequence and comparative analysis of the genome of HSV-1 strain McKrae

Ocular infection by HSV-1 strain McKrae is neurovirulent in both mice and rabbits and causes fatal encephalitis in approximately 50% of animals. In addition, it spontaneously reactivates with high frequency relative to other HSV-1 strains in rabbits. We sequenced the McKrae strain genome and compared its coding protein sequences with those of six other HSV-1 strains. Most of the 74 predicted protein sequences are conserved; only eleven are less than 98% conserved. Eight proteins were identified to be unique for McKrae based on sequence homology bit score ratio (BSR). These include five proteins showing significant variations (RL1, RS1, UL49A, US7 and US11), two truncated proteins (UL36 and UL56) and one (US10) containing an extended open reading frame. The McKrae strain also has unique features in its 'a' sequence and non-coding sequences, such as LAT and miRNA. These data are indicative of strain variation but need further work to connect observed differences with phenotype effects.

An unhealthy relationship: viral manipulation of the nuclear receptor superfamily

The nuclear receptor (NR) superfamily is a diverse group of over 50 proteins whose function is to regulate the transcription of a vast array of cellular genes. These proteins are able to tune transcription over an extremely dynamic range due to the fact that they may act as either transcriptional activators or repressors depending on promoter context and ligand status. Due to these unique properties, diverse families of viruses have evolved strategies to exploit NRs in order to regulate expression of their own genes and to optimize the cellular milieu to facilitate the viral lifecycle. While the specific NRs targeted by these viruses vary, the strategies used to target them are common. This is accomplished at the cis-level by incorporation of nuclear receptor response elements into the viral genome and at the trans-level by viral proteins that target NRs directly or indirectly to modulate their function. The specific NR(s) targeted by a particular virus are likely to be reflective of the tissue tropism of the virus in question. Thus, the essential role played by NRs in the replication cycles of such diverse viruses underscores the importance of understanding their functions in the context of specific infections. This knowledge will allow appropriate considerations to be made when treating infected individuals with hormone-associated diseases and will potentially assist in the rational design of novel antiviral therapeutics.

Thyroid hormone controls the gene expression of HSV-1 LAT and ICP0 in neuronal cells

Various factors/pathways including hormonal regulation have been suggested to control HSV-1 latency and reactivation. Our computer analysis identified a DNA repeat containing thyroid hormone response elements (TRE) in the regulatory region of HSV-1 LAT. Thyroid hormone (T₃) exerts its function via its receptor (TR), a transcriptional factor. Present study investigated the roles of TR and T₃ on HSV-1 gene expression using cultured neuoroblastoma cell lines. We demonstrated that liganded TR activated LAT transcription but repressed ICP0 transcription in the presence of LAT TRE. The chromatin immunoprecipitation (ChIP) assays showed that TRs were recruited to LAT TREs independently of T₃ and hyperacetylated H4 was associated with promoters that were transcriptionally active. In addition, ChIP results showed that a chromatin insulator protein CTCF was enriched at the LAT TREs in the presence of TR and T₃. In addition, chromatin remodeling factor BRG1 complex is found to participate in the T₃/TR-mediated LAT activation since overexpression of BRG1 enhanced the LAT transcription and the dominant negative mutant K785R abolished the activation. This is the first report revealing that TR exerted epigenetic regulation on HSV-1 ICP0 expression in neuronal cells and could have a role in the complex processes of HSV-1 latency/reactivation.

Numerous conserved and divergent microRNAs expressed by herpes simplex viruses 1 and 2

Certain viruses use microRNAs (miRNAs) to regulate the expression of their own genes, host genes, or both. Previous studies have identified a limited number of miRNAs expressed by herpes simplex viruses 1 and 2 (HSV-1 and -2), some of which are conserved between these two viruses. To more comprehensively analyze the miRNAs expressed by HSV-1 or HSV-2 during productive and latent infection, we applied a massively parallel sequencing approach. We were able to identify 16 and 17 miRNAs expressed by HSV-1 and HSV-2, respectively, including all previously known species, and a number of previously unidentified virus-encoded miRNAs. The genomic positions of most miRNAs encoded by these two viruses are within or proximal to the latency-associated transcript region. Nine miRNAs are conserved in position and/or sequence, particularly in the seed region, between these two viruses. Interestingly, we did not detect an HSV-2 miRNA homolog of HSV-1 miR-H1, which is highly expressed during productive infection, but we did detect abundant expression of miR-H6, whose seed region is conserved with HSV-1 miR-H1 and might represent a functional analog. We also identified a highly conserved miRNA family arising from the viral origins of replication. In addition, we detected several pairs of complementary miRNAs and we found miRNA-offset RNAs (moRs) arising from the precursors of HSV-1 and HSV-2 miR-H6 and HSV-2 miR-H4. Our results reveal elements of miRNA conservation and divergence that should aid in identifying miRNA functions.

Towards an understanding of the herpes simplex virus type 1 latency-reactivation cycle

Infection by herpes simplex virus type 1 (HSV-1) can cause clinical symptoms in the peripheral and central nervous system. Recurrent ocular shedding can lead to corneal scarring and vision loss making HSV-1 a leading cause of corneal blindness due to an infectious agent. The primary site of HSV-1 latency is sensory neurons within trigeminal ganglia. Periodically, reactivation from latency occurs resulting in virus transmission and recurrent disease. During latency, the latency-associated transcript (LAT) is abundantly expressed. LAT expression is important for the latency-reactivation cycle in animal models, in part, because it inhibits apoptosis, viral gene expression, and productive infection. A novel transcript within LAT coding sequences (AL3) and small nonprotein coding RNAs are also expressed in trigeminal ganglia of latently infected mice. In this review, an update of viral factors that are expressed during latency and their potential roles in regulating the latency-reactivation cycle is discussed.

Repeated social stress enhances the innate immune response to a primary HSV-1 infection in the cornea and trigeminal ganglia of Balb/c mice

Three to 5 days after a primary HSV-1 infection, macrophages infiltrate into the trigeminal ganglia (TG) and produce anti-viral cytokines to reduce viral replication. Previous research demonstrated that social disruption stress (SDR) enhances the trafficking of monocytes/macrophages from the bone marrow to the spleen and increases pro-inflammatory cytokine production in vitro and in vivo. The impact of SDR on the trafficking of these cells to loci of herpes simplex virus type 1 (HSV-1) infection and subsequent function has not been examined. The following studies were designed to determine whether SDR would enhance the innate immune response during a primary HSV-1 infection by increasing the number of macrophages in the cornea and TG, thus increasing anti-viral cytokine production and reducing viral replication. BALB/c mice were exposed to six cycles of SDR prior to ocular infection with HSV-1 McKrae virus. Flow cytometric analysis of cells from the TG revealed an increase in the percentage of CD11b+ macrophages in SDR mice compared to controls. Immune cell infiltration into the cornea, however, could not be determined due to low cell numbers. Although gene expression of IFN-beta was decreased, SDR increased gene expression of IFN-alpha, and TNF-alpha, in the cornea and TG. Examination of viral proteins showed decreased expression of infected cell protein 0 (ICP0), glycoprotein B (gB), glycoprotein H (gH) and latency-associated transcript (LAT) in the TG, however, expression of ICP0 and gB were elevated in the cornea of SDR mice. These results indicate that the innate immune response to HSV-1 was altered and enhanced by the experience of repeated social defeat.

Central corticosteroid actions: Search for gene targets

Although many of the physiological effects of corticosteroid stress hormones on neuronal function are well recognised, the underlying genomic mechanisms are only starting to be elucidated. Linking physiology and genomics has proven to be a complicated task, despite the emergence of large-scale gene expression profiling technology in the last decade. This is in part due to the complexity of glucocorticoid-signaling, in part due to the complexity of the brain itself. The presence of a binary receptor system for glucocorticoid hormones in limbic brain structures, the coexistence of membrane and intracellular receptors and the highly contextual action of glucocorticoids contribute to this complexity. In addition, the anatomical complexity, extensive cellular heterogeneity of brain and the modest changes in gene expression (mostly in the range of 10-30%) hamper detection of responsive genes, in particular of low abundant transcripts, such as many neurotransmitter receptors and growth factors. Nonetheless, ongoing research into central targets of glucocorticoids has identified many different functional gene classes that underlie the diverse effects of glucocorticoids on brain function. These functional classes include genes involved in energy metabolism, signal transduction, neuronal structure, vesicle dynamics, neurotransmitter catabolism, cell adhesion, genes encoding neurotrophic factors and their receptors and genes involved in regulating glucocorticoid-signalling. The aim of this review is to give an overview of the current status of the field on identification of central corticosteroid targets, discuss the opportunities and pitfalls and highlight new developments in understanding central corticosteroid action.

Herpes simplex virus type 1 C-terminal variants of the origin binding protein (OBP), OBPC-1 and OBPC-2, cooperatively regulate viral DNA levels in vitro, and OBPC-2 affects mortality in mice

Two in-frame, C-terminal isoforms of the herpes simplex virus type 1 (HSV-1) origin binding protein (OBP), OBPC-1 and OBPC-2, and a unique C-terminal transcript, UL8.5, are specified by HSV-1 DNA. As the first isoform identified, OBPC-1 was initially assumed to be the product of the UL8.5 transcript. Recent evidence has demonstrated, however, that OBPC-1 is a cathepsin B-mediated cleavage product of OBP, suggesting that OBPC-2 is the product of the UL8.5 transcript. Because both OBPC-1 and -2 contain the majority of the OBP DNA binding domain, we hypothesized that both may be involved in regulating origin-dependent, OBP-mediated viral DNA replication. In this paper, we demonstrate that OBPC-2 is, indeed, the product of the UL8.5 transcript. The translational start site of OBPC-2 was mapped, and a virus (M571A) that does not express this protein efficiently was constructed. Using M571A, we have shown that OBPC-2 is able to bind origin DNA, even though it lacks seven N-terminal amino acid residues of the previously mapped OBP DNA binding domain, resulting in a revision of the limits of the OBP DNA binding domain. Consistent with their proposed roles in regulating viral DNA replication, OBPC-1 and -2 act together to down-regulate viral DNA replication in vitro. During functional studies in vivo, OBPC-2 was identified as a factor that increases mortality in the mouse ocular model of HSV-1 infection.

Cathepsin B mediates cleavage of herpes simplex virus type 1 origin binding protein (OBP) to yield OBPC-1, and cleavage is dependent upon viral DNA replication

Although the seven viral proteins required for herpes simplex virus type 1 (HSV-1) DNA replication have been identified, the mechanism by which viral DNA synthesis is regulated is unclear. HSV-1 DNA replication is thought to occur in two stages: origin-dependent DNA replication (stage I) mediated by the origin binding protein (OBP), followed by origin- and OBP-independent DNA replication (stage II). The mechanism that facilitates the switch from stage I to stage II is unknown; however, it must involve the loss of OBP function or OBP itself from the replication initiation complex. Previous studies from this laboratory identified a transcript (UL8.5) and protein (OBPC) that are in frame with and comprise the C terminus of the gene specifying OBP. Because of its DNA binding ability, OBPC has been hypothesized to mediate the switch from stage I to stage II. Here, we identify a second protein (OBPC-2) that is also in frame with the C terminus of OBP but comprises a smaller portion of the protein. We demonstrate that the protein originally identified (OBPC-1) is a cathepsin B-mediated cleavage product of OBP, while OBPC-2 may be the product of the UL8.5 transcript. We further demonstrate that the cleavage of OBP to yield OBPC-1 is dependent upon viral DNA replication. These results suggest that cleavage may be a mechanism by which OBP levels and/or activity are regulated during infection.

Point mutations in herpes simplex virus type 1 oriL, but not in oriS, reduce pathogenesis during acute infection of mice and impair reactivation from latency

In vitro studies of herpes simplex virus type 1 (HSV-1) viruses containing mutations in core sequences of the viral origins of DNA replication, oriL and oriS, that eliminate the ability of these origins to initiate viral-DNA synthesis have demonstrated little or no effect on viral replication in cultured cells, leading to the conclusion that the two types of origins are functionally redundant. It remains unclear, therefore, why origins that appear to be redundant are maintained evolutionarily in HSV-1 and other neurotropic alphaherpesviruses. To test the hypothesis that oriL and oriS have distinct functions in the HSV-1 life cycle in vivo, we determined the in vivo phenotypes of two mutant viruses, DoriL-I(LR) and DoriS-I, containing point mutations in oriL and oriS site I, respectively, that eliminate origin DNA initiation function. Following corneal inoculation of mice, tear film titers of DoriS-I were reduced relative to wild-type virus. In all other tests, however, DoriS-I behaved like wild-type virus. In contrast, titers of DoriL-I(LR) in tear film, trigeminal ganglia (TG), and hindbrain were reduced and mice infected with DoriL-I(LR) exhibited greatly reduced mortality relative to wild-type virus. In the TG explant and TG cell culture models of reactivation, DoriL-I(LR) reactivated with delayed kinetics and, in the latter model, with reduced efficiency relative to wild-type virus. Rescuant viruses DoriL-I(LR)-R and DoriS-I-R behaved like wild-type virus in all tests. These findings demonstrate that functional differences exist between oriL and oriS and reveal a prominent role for oriL in HSV-1 pathogenesis.

Herpes simplex virus type 1 recombinants without the oriL sequence replicate DNA with increased fidelity

Herpes simplex virus type 1 (HSV-1) contains three DNA replication origins (ori) of two types. The oriL is located in the center of the unique long sequences, whereas two copies of oriS, which are structurally different from oriL, are within the reiterated sequences flanking the unique short sequences. Recombinant viruses were constructed from ts+7, which contains a deletion of oriL sequences, to have either the beta-galactosidase gene or the supF amplicon integrated into the thymidine kinase locus. Rescue recombinants also were constructed from the supF-containing recombinant to restore the deleted oriL to the wild type sequences. These recombinants were subjected to mutagenesis assays. Results demonstrated that ts+7 viruses with the deletion in oriL sequences replicated both target genes with higher fidelity compared to those derived from the parental strain KOS. Possible mechanisms leading to the high fidelity of DNA replication mediated by viruses without intact oriL sequences are discussed.

Site-directed mutagenesis of large DNA palindromes: construction and in vitro characterization of herpes simplex virus type 1 mutants containing point mutations that eliminate the oriL or oriS initiation function

Technical challenges associated with mutagenesis of the large oriL palindrome have hindered comparisons of the functional roles of the herpes simplex virus type 1 (HSV-1) origins of DNA replication, oriL and oriS, in viral replication and pathogenesis. To address this problem, we have developed a novel PCR-based strategy to introduce site-specific mutations into oriL and other large palindromes. Using this strategy, we generated three plasmids containing mutant forms of oriL, i.e., pDoriL-I(L), pDoriL-I(R), and pDoriL-I(LR), containing point mutations in the left, right, and both copies, respectively, of the origin binding protein (OBP) binding site (site I) which eliminate OBP binding. In in vitro DNA replication assays, plasmids with mutations in only one arm of the palindrome supported origin-dependent DNA replication, whereas plasmids with symmetrical mutations in both arms of the palindrome were replication incompetent. An analysis of the cloned mutant plasmids used in replication assays revealed that a fraction of each plasmid mutated in only one arm of the palindrome had lost the site I mutation. In contrast, plasmids containing symmetrical mutations in both copies of site I retained both mutations. These observations demonstrate that the single site I mutations in pDoriL-I(L) and pDoriL-I(R) are unstable upon propagation in bacteria and suggest that functional forms of both the left and right copies of site I are required to initiate DNA replication at oriL. To examine the role of oriL and oriS site I in virus replication, we introduced the two site I mutations in pDoriL-I(LR) into HSV-1 DNA to yield the mutant virus DoriL-I(LR) and the same point mutations into the single site I sequence present in both copies of oriS to yield the mutant virus DoriS-I. In Vero cells and primary rat embryonic cortical neurons (PRN) infected with either mutant virus, viral DNA synthesis and viral replication were efficient, confirming that the two origins can substitute functionally for one another in vitro. Measurement of the levels of oriL and oriS flanking gene transcripts revealed a modest alteration in the kinetics of ICP8 transcript accumulation in DoriL-I(LR)-infected PRN, but not in Vero cells, implicating a cell-type-specific role for oriL in regulating ICP8 transcription.

Four-dimensional visualization of the simultaneous activity of alternative adeno-associated virus replication origins

The adeno-associated virus (AAV) inverted terminal repeats (ITRs) contain the AAV Rep protein-binding site (RBS) and the terminal resolution site (TRS), which together act as a minimal origin of DNA replication. The AAV p5 promoter also contains an RBS, which is involved in Rep-mediated regulation of promoter activity, as well as a functional TRS, and origin activity of these signals has in fact been demonstrated previously in the presence of adenovirus helper functions. Here, we show that in the presence of herpes simplex virus type 1 (HSV-1) and AAV Rep protein, p5 promoter-bearing plasmids are efficiently amplified to form large head-to-tail concatemers, which are readily packaged in HSV-1 virions if an HSV-1 DNA-packaging/cleavage signal is provided in cis. We also demonstrate simultaneous and independent replication from the two alternative AAV replication origins, p5 and ITR, on the single-cell level using multicolor-fluorescence live imaging, a finding which raises the possibility that both origins may contribute to the AAV life cycle. Furthermore, we assess the differential affinities of Rep for the two different replication origins, p5 and ITR, both in vitro and in live cells and identify this as a potential mechanism to control the replicative and promoter activities of p5.

Stress-induced changes in pathophysiology and interferon gene expression during primary HSV-1 infection

Herpes simplex viruses (HSV) are the cause of the most common clinically recognized herpesvirus infections. The severity and duration of the primary HSV infection have been correlated with the frequency and severity of subsequent recurrences. Reactivation of latent HSV-1 can occur as a result of physical or emotional stress; however, the effects of stress on the modulation of the clinical pathophysiology of primary HSV-1 infections are not well understood. Although it is known that stress can be immunosuppresive, the immunological mechanisms by which stress modulates early immune responses, such as type I interferon gene expression during a primary HSV-1 infection are still not understood. It was hypothesized that due to suppressed early immune responses, stress would increase the severity of a cutaneous primary HSV-1 infection. In this investigation, a cutaneous HSV-1 model in the SKH-1 mouse was characterized and utilized to study the effect of restraint stress on the modulation of the clinical pathophysiology of primary HSV-1. Despite prolonged viral replication at the site of primary infection, restraint stress decreased the clinical severity of primary HSV-1 in the skin of SKH-1 mice. A decrease in type I and type II IFN expression was found in the skin of acutely infected restrained mice when compared to controls at day 3 post-infection using competitive RT-PCR. Using the glucocorticoid-receptor antagonist RU486, IFN-beta and INF-gamma expression were restored in restrained animals to control levels. Treatment with RU486 also increased the clinical severity of the cutaneous infection to control levels in restrained mice. Thus, RST masked the severity of an HSV-1 infection by decreasing its clinical signs while impairing the ability of the host to control viral replication prolonging the infectious period.

Ocular reactivation phenotype of HSV-1 strain F(MP)E, a corticosteroid-sensitive strain

PURPOSE

Elucidate the ocular reactivation of HSV-1 strain F(MP)E.

METHODS

Rabbit corneas were infected with HSV-1 strains McKrae and F(MP)E. Latency was established and rabbits were treated with epinephrine iontophoresis or corticosteroid injection (immunosuppression). Cultured tear films were used to determine the presence of infectious virus. Eyes of immunosuppressed rabbits were also examined by slit lamp biomicroscopy. Trigeminal ganglia were co-cultured on indicator cells at time of sacrifice for detection of virus. Quantitative real-time PCR was used to detect the number of viral genome copies in the trigeminal ganglia.

RESULTS

Acute infections by strains McKrae and F(MP)E were the same. Ocular reactivation of strain F(MP)E by epinephrine iontophoresis was significantly reduced compared to McKrae (P </= 0.0001), but was not significantly different from McKrae after corticosteroid injection (P > 0.29). Slit lamp examination following corticosteroid injection showed a correlation of recurrent herpetic lesions with infectious virus in tear film swabs for both McKrae and F(MP)E. Trigeminal ganglia from rabbits latently infected with each strain and each method of induced reactivation resulted in infectious virus (P >/= 0.69). Genome copies for both strains were present and were highly variable.

CONCLUSIONS

HSV-1 strain F(MP)E has low reactivation following epinephrine iontophoresis compared to McKrae, but has high reactivation like McKrae in response to corticosteroids. The difference in reactivation following epinephrine iontophoresis is not due to a difference in the establishment of latency.

Herpes simplex virus type 1 and bovine herpesvirus 1 latency

Primary infection by herpes simplex virus type 1 (HSV-1) can cause clinical symptoms in the peripheral and central nervous system, upper respiratory tract, and gastrointestinal tract. Recurrent ocular shedding leads to corneal scarring that can progress to vision loss. Consequently, HSV-1 is the leading cause of corneal blindness due to an infectious agent. Bovine herpesvirus 1 (BHV-1) has similar biological properties to HSV-1 and is a significant health concern to the cattle industry. Latency of BHV-1 and HSV-1 is established in sensory neurons of trigeminal ganglia, but latency can be interrupted periodically, leading to reactivation from latency and spread of infectious virus. The ability of HSV-1 and BHV-1 to reactivate from latency leads to virus transmission and can lead to recurrent disease in individuals latently infected with HSV-1. During latency, the only abundant HSV-1 RNA expressed is the latency-associated transcript (LAT). In latently infected cattle, the latency-related (LR) RNA is the only abundant transcript that is expressed. LAT and LR RNA are antisense to ICP0 or bICP0, viral genes that are crucial for productive infection, suggesting that LAT and LR RNA interfere with productive infection by inhibiting ICP0 or bICP0 expression. Numerous studies have concluded that LAT expression is important for the latency-reactivation cycle in animal models. The LR gene has recently been demonstrated to be required for the latency-reactivation cycle in cattle. Several recent studies have demonstrated that LAT and the LR gene inhibit apoptosis (programmed cell death) in trigeminal ganglia of infected animals and transiently transfected cells. The antiapoptotic properties of LAT map to the same sequences that are necessary for promoting reactivation from latency. This review summarizes our current knowledge of factors regulating the latency-reactivation cycle of HSV-1 and BHV-1.

Herpes simplex virus type-1: a model for genome transactions

In many respects, HSV-1 is the prototypic herpes virus. However, HSV-1 also serves as an excellent model system to study genome transactions, including DNA replication, homologous recombination, and the interaction of DNA replication enzymes with DNA damage. Like eukaryotic chromosomes, the HSV-1 genome contains multiple origins of replication. Replication of the HSV-1 genome is mediated by the concerted action of several virus-encoded proteins that are thought to assemble into a multiprotein complex. Several host-encoded factors have also been implicated in viral DNA replication. Furthermore, replication of the HSV-1 genome is known to be closely associated with homologous recombination that, like in many cellular organisms, may function in recombinational repair. Finally, recent data have shed some light on the interaction of essential HSV-1 replication proteins, specifically its DNA polymerase and DNA helicases, with damaged DNA.

Glucocorticoids and central nervous system inflammation

Glucocorticoids (GCs) are well known for their anti-inflammatory and immunosuppressive properties in the periphery and are therefore widely and successfully used in the treatment of autoimmune diseases, chronic inflammation, or transplant rejection. This led to the assumption that GCs are uniformly anti-inflammatory in the periphery and the central nervous system (CNS). As a consequence, GCs are also used in the treatment of CNS inflammation. There is abundant evidence that an inflammatory reaction is mounted within the CNS following trauma, stroke, infection, and seizure, which can augment the brain damage. However an increasing number of studies indicate that the concept of GCs being universally immunosuppressive might be oversimplified. This article provides a review of the current literature, showing that under certain circumstances GCs might fail to have anti-inflammatory effects and sometimes even enhance inflammation.

The upstream regulatory region of human papillomavirus type 31 is insensitive to glucocorticoid induction

The upstream regulatory region (URR) of various types of human papillomaviruses (HPVs) has been shown to contain functional glucocorticoid response elements (GREs), including HPV type 11 (HPV11), HPV16, and HPV18. Glucocorticoids have been demonstrated to induce the transcriptional activity of the early promoters of these HPV types. Although it has been assumed that the URR of HPV31 contains at least one GRE, no functionality has been demonstrated. We attempt to show here inducibility of the URR of HPV31 by the synthetic glucocorticoid dexamethasone (dex). By sequence analysis we identified three potential GREs in the URR of HPV31. Gel shift analysis indicated that each of these three sites has the potential to be a functional GRE. However, constructs containing the full-length URR, 5' deletions of the URR, and an internal fragment of the URR containing all three putative GREs were only weakly inducible by dex. Linker scanning mutants, whereby each potential GRE was replaced individually, in double combination, or in triple combination by a unique polylinker, had no effect on dex inducibility. Replacement of each of the three HPV31 GREs with the GRE of HPV18 failed to induce a response to dex. Placement of the HPV18 GRE into the URR of HPV31 in a region similar to its location in the HPV18 URR was also unable to result in a strong dex induction of the HPV31 URR. These data suggest that the lack of dex inducibility is due to the overall context of the HPV31 URR and may be dependent on the requirements of the major early promoter for transcriptional activation. Finally, replacement of the HPV18 GRE with each of the HPV31 GREs in HPV18 only showed weak inducibility, indicating that the three GREs of HPV31 are in fact only weak inducers of dex. Overall, these data suggest that dex responsiveness, along with oncogenic potential, may provide a possible explanation for the classification of HPV31 as an intermediate-risk virus and demonstrate the complexity of transcriptional regulation of the URR of HPV.

A novel permissive role for glucocorticoids in induction of febrile and behavioral signs of experimental herpes simplex virus encephalitis

Herpes simplex virus type 1 (HSV-1) encephalitis may present with fever and behavioral changes, to the extent of a psychotic state and psychomotor agitation. We developed a clinically relevant experimental model of HSV-1 encephalitis and investigated host brain responses associated with its clinical signs and whether these responses depend on the presence of circulating glucocorticoids. Intracerebral inoculation of HSV-1 in rats induced fever, motor hyperactivity and aggressive behavior. In adrenalectomized rats HSV-1 failed to induce these signs, although mortality rate was identical to sham-operated rats. Hypophysectomy or blocking glucocorticoid receptors also prevented HSV-1-induced fever. Dexamethasone replacement therapy to adrenalectomized rats restored the HSV-1-induced fever and behavioral abnormalities. HSV-1 inoculation produced hyperproduction of prostaglandin E(2) by brain slices. This effect was abolished in adrenalectomized rats and was restored by dexamethasone treatment. In intact rats HSV-1 induced brain interleukin-1beta (IL-1beta) gene expression. Adrenalectomy alone caused brain IL-1beta expression, which did not increase after HSV-1 infection. Similarly, HSV-1 induced IL-1beta expression in astrocyte cultures. Removal of cortisol from the culture medium caused basal IL-1beta mRNA expression which was not increased by infection. In conclusion, fever, motor hyperactivity and aggressive behavior during experimental HSV-1 encephalitis are dependent on brain responses, including prostaglandin E(2) and IL-1beta synthesis. Circulating glucocorticoids play an essential permissive role in the induction of these host brain responses.

Origin binding protein-containing protein-DNA complex formation at herpes simplex virus type 1 oriS: role in oriS-dependent DNA replication

Initiation of herpes simplex virus type 1 (HSV-1) DNA replication during productive infection of fibroblasts and epithelial cells requires attachment of the origin binding protein (OBP), one of seven essential virus-encoded DNA replication proteins, to specific sequences within the two viral origins, oriL and oriS. Whether initiation of DNA replication during reactivation of HSV-1 from neuronal latency also requires OBP is not known. A truncated protein, consisting of the C-terminal 487 amino acids of OBP, termed OBPC, is the product of the HSV UL8.5 gene and binds to origin sequences, although OBPC's role in HSV DNA replication is not yet clear. To characterize protein-DNA complex formation at oriS in cells of neural and nonneural lineage, we used nuclear extracts of HSV-infected nerve growth factor-differentiated PC12 and Vero cells, respectively, as the source of protein in gel shift assays. In both cell types, three complexes (complexes A, B, and C) which contain either OBP or OBPC were shown to bind specifically to a probe which contains the highest-affinity OBP binding site in oriS, site 1. Complex A was shown to contain OBPC exclusively, whereas complexes B and C contained OBP and likely other cellular proteins. By fine-mapping the binding sites of these three complexes, we identified single nucleotides which, when mutated, eliminated formation of all three complexes, or complexes B and C, but not A. In transient DNA replication assays, both mutations significantly impaired oriS-dependent DNA replication, demonstrating that formation of OBP-containing complexes B and C is required for efficient initiation of oriS-dependent DNA replication, whereas formation of the OBPC-containing complex A is insufficient for efficient initiation.

Viral infections after renal transplantation

Viral infections are a leading cause of posttransplantation morbidity and mortality. A number of recent developments have altered our understanding and management of these disorders. The pathogenetic roles of several viruses, including human herpesviruses 6 and 8, have been newly established. Molecular-based diagnostic tests now make more rapid diagnosis possible. The licensing of new potent antiviral agents offers a wider choice of drugs for viral prophylaxis and treatment. The use of more potent immunosuppressive agents is responsible in part for the increasing incidence of some viral infections, but this varies among drugs, and individual viruses differ in their sensitivity to immunosuppressive agents. This review summarizes the natural history, diagnosis, prevention, and treatment of many common viral infections after renal transplantation.

Stress-associated immunomodulation and herpes simplex virus infections

Stress has been shown to modulate an individual's immune system through the release of certain signal molecules such as catecholamines, cytokines and glucocorticoids. These signal molecules can significantly alter the host immune system and leave it susceptible to a primary or recurrent viral infection. Focusing on herpes simplex virus types-1 and -2 as examples, the authors explain how stress-associated immunomodulation can influence the recurrence of herpes simplex viral infections. Specific signal molecules such as epinephrine, interleukin-6, cyclic adenosine monophosphate, glucocorticoids and prostaglandins are upregulated during episodes of acute and chronic stress and have been implicated as effectors of herpes simplex viral reactivation and recurrent disease. The authors suggest that the release of immunomodulating signal molecules due to stress can compromise the host's cellular immune response and trigger herpes simplex viral reactivation.

Phosphorylation of the herpes simplex virus type 1 origin binding protein

The herpes simplex virus type 1 (HSV-1) origin binding protein (OBP), the product of the UL9 gene, is one of seven HSV-encoded proteins required for viral DNA replication. OBP performs multiple functions characteristic of a DNA replication initiator protein, including origin-specific DNA binding and ATPase and helicase activities, as well as the ability to interact with viral and cellular proteins involved in DNA replication. Replication initiator proteins in other systems, including those of other DNA viruses, are known to be regulated by phosphorylation; however, the role of phosphorylation in OBP function has been difficult to assess due to the low level of OBP expression in HSV-infected cells. Using a metabolic labeling and immunoprecipitation approach, we obtained evidence that OBP is phosphorylated during HSV-1 infection. Kinetic analysis of metabolically labeled cells indicated that the levels of OBP expression and phosphorylation increased at approximately 4 h postinfection. Notably, when expressed from a transfected plasmid, a recombinant baculovirus, or a recombinant adenovirus (AdOBP), OBP was phosphorylated minimally, if at all. In contrast, superinfection of AdOBP-infected cells with an OBP-null mutant virus increased the level of OBP phosphorylation approximately threefold, suggesting that HSV-encoded viral or HSV-induced cellular factors enhance the level of OBP phosphorylation. Using HSV mutants inhibited at sequential stages of the viral life cycle, we demonstrated that this increase in OBP phosphorylation is dependent on early protein synthesis and is independent of viral DNA replication. Based on gel mobility shift assays, phosphorylation does not appear to affect the ability of OBP to bind to the HSV origins.

Expression of vhs and VP16 during HSV-1 helper virus-free amplicon packaging enhances titers

Recently developed helper virus-free methods of herpes simplex virus (HSV) amplicon vector packaging provide stocks that are virtually devoid of the cytotoxic component normally associated with traditional helper virus-based packaging methods. These approaches involve cotransfection of amplicon plasmid DNA with either a five-cosmid set or a bacterial artificial chromosome (BAC) that contains the HSV genome without its cognate pac signals. Helper virus-free amplicon packaging produces low-titer stocks (<10(5) expressing particles/ml) that exhibit a high frequency of pseudotransduction. In an effort to enhance amplicon titers, we introduced in trans a genomic copy of the virion host shutoff (vhs) protein-encoding gene UL41 into both cosmid- and BAC-based packaging strategies. Cotransfection of this plasmid with the amplicon and packaging reagents results in a 10-fold higher amplicon titer, and stocks that do not exhibit the pseudotransduction phenomenon. To further enhance packaging efficiency, the HSV transcriptional activator VP16 was introduced into packaging cells 1 day before the packaging components. Pre-loading of packaging cells with VP16 led to an additional enhancement of amplicon titers, an effect that did not occur in the absence of vhs. Increased helper virus-free amplicon titers resulting from these modifications will make in vivo transduction experiments more feasible.

Neural precursor cells for delivery of replication-conditional HSV-1 vectors to intracerebral gliomas

Cellular delivery of a replication-conditional herpes simplex virus type 1 (HSV-1) vector provides a means for gene therapy of invasive tumor cells. LacZ-bearing neural precursor cells, which can migrate and differentiate in the brain, were infected with a ribonucleotide reductase-deficient HSV-1 mutant virus (rRp450) that replicates only in dividing cells. Replication of rRp450 in neural precursor cells was blocked prior to implantation into the tumor by growth arrest in late G1 phase through treatment with mimosine. Viral titers in the medium of mimosine-treated, rRp450-infected neural precursor cells were below detection levels 3 days after infection. In culture, after removal of mimosine and passaging, cells resumed growth and replication of rRp450 so that, 7 days later, virus was present in the medium and cell death was evident. Mimosine-treated neural precursor cells injected into established intracerebral CNS-1 gliomas in nude mice migrated extensively throughout the tumor and into the surrounding parenchyma beyond the tumor over 3 days. Mimosine-treated neural precursor cells, infected with rRp450 and injected into intracerebral CNS-1 tumors, also migrated within the tumor with the appearance of foci of HSV-thymidine kinase-positive (TK+) cells, presumably including tumor cells, distributed throughout the tumor and in the surrounding parenchyma over a similar period. This migratory cell delivery method has the potential to expand the range of delivery of HSV-1 vectors to tumor cells in the brain.

Hydrocortisone activation of human herpesvirus 8 viral DNA replication and gene expression in vitro

BACKGROUND

Patients undergoing chronic steroid therapy for organ transplantation are at increased risk for development of human herpes virus 8(HHV-8)-associated Kaposi's sarcoma (KS). It has also been reported that following steroid withdrawal, KS lesions often undergo partial or complete regression.

METHODS

We have examined the effect of corticosteroid treatment on HHV-8 replication, gene expression, and lytic protein expression in BCBL-1 cells in vitro. BCBL-1 cells were collected after culture for 24-72 hr with hydrocortisone (HC) 1-5 microM, phorbol ester 20 ng/ml (positive control), and culture medium only (negative control). HHV-8 genomic conformation was examined by Gardella gel analysis. mRNA expression of viral cyclin (v-Cyc), viral Bcl-2 (v-Bcl-2), viral macrophage inflammatory protein-I (v-MIP-I), viral interferon regulatory factor-1(v-IRF-1), and viral tegument protein (TP) was examined by RT-PCR Southern blot. Viral protein expression within the cells was examined by indirect immunofluorescence using 5 different HHV-8 positive antisera from 4 renal transplant recipients and 1 patient with classic KS.

RESULTS

Gardella gel analysis revealed that HC induced an accumulation of the linear replicative genomic form of the virus in a time-dependent fashion. Southern blot analysis of the RT-PCR products revealed that HC induced increased expression of v-IRF-1, v-Bcl-2, and TP mRNA, with little discernible effect on v-Cyc, and v-MIP-I. Immunofluorescence revealed that HC induced increased numbers of cells expressing lytic antigens.

CONCLUSIONS

These data indicate that hydrocortisone acts directly on BCBL-1 cells to activate the lytic cycle of HHV-8 and provide further support for the hypothesis that HHV-8 is activated in corticosteroid-treated immunocompromised patients.

Molecular aspects of herpes simplex virus I latency, reactivation, and recurrence

The application of molecular biology in the study of the pathogenesis of herpes simplex virus type 1 (HSV-1) has led to significant advances in our understanding of mechanisms that regulate virus behavior in sensory neurons and epithelial tissue. Such study has provided insight into the relationship of host and viral factors that regulate latency, reactivation, and recurrent disease. This review attempts to distill decades of information involving human, animal, and cell culture studies of HSV-1 with the goal of correlating molecular events with the clinical and laboratory behavior of the virus during latency, reactivation, and recurrent disease. The purpose of such an attempt is to acquaint the clinician/scientist with the current thinking in the field, and to provide key references upon which current opinions rest.

Cellular transcription factors enhance herpes simplex virus type 1 oriS-dependent DNA replication

The herpes simplex virus type 1 (HSV-1) origin of DNA replication, oriS, contains three binding sites for the viral origin binding protein (OBP) flanked by transcriptional regulatory elements of the immediate-early genes encoding ICP4 and ICP22/47. To assess the role of flanking sequences in oriS function, plasmids containing oriS and either wild-type or mutant flanking sequences were tested in transient DNA replication assays. Although the ICP4 and ICP22/47 regulatory regions were shown to enhance oriS function, most individual elements in these regions, including the VP16-responsive TAATGARAT elements, were found to be dispensable for oriS function. In contrast, two oriS core-adjacent regulatory (Oscar) elements, OscarL and OscarR, at the base of the oriS palindrome were shown to enhance oriS function significantly and additively. Specifically, mutational disruption of either element reduced oriS-dependent DNA replication by 60 to 70%, and disruption of both elements reduced replication by 90%. The properties of protein-DNA complexes formed in gel mobility shift assays using uninfected and HSV-1-infected Vero cell nuclear extracts demonstrated that both OscarL and OscarR are binding sites for cellular proteins. Whereas OscarR does not correspond to the consensus binding site of any known transcription factor, OscarL contains a consensus binding site for the transcription factor Sp1. Gel mobility shift and supershift experiments using antibodies directed against members of the Sp1 family of transcription factors demonstrated the presence of Sp1 and Sp3, but not Sp2 or Sp4, in the protein-DNA complexes formed at OscarL. The abilities of OscarL and OscarR to bind their respective cellular proteins correlated directly with the efficiency of oriS-dependent DNA replication. Cooperative interactions between the Oscar-binding factors and proteins binding to adjacent OBP binding sites were not observed. Notably, Oscar element mutations that impaired oriS-dependent DNA replication had no detectable effect on either basal or induced levels of transcription from the ICP4 and ICP22/47 promoters, as determined by RNase protection assays. The Oscar elements thus appear to provide binding sites for cellular proteins that facilitate oriS-dependent DNA replication but have no effect on transcription of oriS-flanking genes.