Herpes simplex virus type 1 and bovine herpesvirus 1 latency

The Wnt Signaling Pathway Is Differentially Expressed during the Bovine Herpesvirus 1 Latency-Reactivation Cycle: Evidence That Two Protein Kinases Associated with Neuronal Survival, Akt3 and BMPR2, Are Expressed at Higher Levels during Latency

Sensory neurons in trigeminal ganglia (TG) of calves latently infected with bovine herpesvirus 1 (BoHV-1) abundantly express latency-related (LR) gene products, including a protein (ORF2) and two micro-RNAs. Recent studies in mouse neuroblastoma cells (Neuro-2A) demonstrated ORF2 interacts with β-catenin and a β-catenin coactivator, high-mobility group AT-hook 1 (HMGA1) protein, which correlates with increased β-catenin-dependent transcription and cell survival. β-Catenin and HMGA1 are readily detected in a subset of latently infected TG neurons but not TG neurons from uninfected calves or reactivation from latency. Consequently, we hypothesized that the Wnt/β-catenin signaling pathway is differentially expressed during the latency and reactivation cycle and an active Wnt pathway promotes latency. RNA-sequencing studies revealed that 102 genes associated with the Wnt/β-catenin signaling pathway were differentially expressed in TG during the latency-reactivation cycle in calves. Wnt agonists were generally expressed at higher levels during latency, but these levels decreased during dexamethasone-induced reactivation. The Wnt agonist bone morphogenetic protein receptor 2 (BMPR2) was intriguing because it encodes a serine/threonine receptor kinase that promotes neuronal differentiation and inhibits cell death. Another differentially expressed gene encodes a protein kinase (Akt3), which is significant because Akt activity enhances cell survival and is linked to herpes simplex virus 1 latency and neuronal survival. Additional studies demonstrated ORF2 increased Akt3 steady-state protein levels and interacted with Akt3 in transfected Neuro-2A cells, which correlated with Akt3 activation. Conversely, expression of Wnt antagonists increased during reactivation from latency. Collectively, these studies suggest Wnt signaling cooperates with LR gene products, in particular ORF2, to promote latency.IMPORTANCE Lifelong BoHV-1 latency primarily occurs in sensory neurons. The synthetic corticosteroid dexamethasone consistently induces reactivation from latency in calves. RNA sequencing studies revealed 102 genes associated with the Wnt/β-catenin signaling pathway are differentially regulated during the latency-reactivation cycle. Two protein kinases associated with the Wnt pathway, Akt3 and BMPR2, were expressed at higher levels during latency but were repressed during reactivation. Furthermore, five genes encoding soluble Wnt antagonists and β-catenin-dependent transcription inhibitors were induced during reactivation from latency. These findings are important because Wnt, BMPR2, and Akt3 promote neurogenesis and cell survival, processes crucial for lifelong viral latency. In transfected neuroblastoma cells, a viral protein expressed during latency (ORF2) interacts with and enhances Akt3 protein kinase activity. These findings provide insight into how cellular factors associated with the Wnt signaling pathway cooperate with LR gene products to regulate the BoHV-1 latency-reactivation cycle.

Bovine herpesvirus type 5 replication and induction of apoptosis in vitro and in the trigeminal ganglion of experimentally-infected cattle

Bovine herpesvirus (BoHV) types 1 and 5 are neuroinvasive. Cases of BoHV-1-induced encephalitis are not as frequent as those caused by BoHV-5. In this study, the capability of BoHV-5 to induce apoptosis in cell cultures and in the trigeminal ganglion during acute infection of experimentally-infected cattle was analyzed. Apoptotic changes in cell cultures agree with the ability of the viral strains to replicate in each cell line. Marked differences were observed between the in vitro induction of apoptosis by BoHV-1Cooper and BoHV-5 97/613 strains. Apoptotic neurons were clearly evident in the trigeminal ganglion of BoHV-1-infected calves. For BoHV-5 a fewer number of positive neurons was observed. There is an association between the magnitude of bovine herpesviruses replication and the induction of apoptosis in trigeminal ganglion. These findings suggest that the induction of apoptosis and the innate immune response orchestrate the final outcome of alpha herpesviruses infection of the bovine nervous system.

2,3,7,8-Tetrachlorodibenzo-p-dioxin influences bovine herpesvirus 1 replication through upregulation of SIRT3 and cytoskeletal reorganization

Infection of kidney cells (MDBK) with Bovine Herpesvirus 1 (BoHV-1) is affected by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), which accelerates BoHV-1-induced apoptosis and increases virus replication. Herein, to elucidate the mechanism through TCDD modifies BoHV-1 infection, we analyzed the modulation of a members of Sirtuin proteins family in MDBK cells. We found that mitochondrial SIRT3 was upregulated during infection. This change was accompanied by cytoskeletal rearrangements and cell extensions. All these trends were drastically modified by TCDD. We hypothesize that, taken together, these results might further clarify the processes responsible for the action of TCDD on the BoHV-1 replication, resulting in enhanced virus production.

MG-132 reduces virus release in Bovine herpesvirus-1 infection

Bovine herpesvirus 1 (BoHV-1) can provoke conjunctivitis, abortions and shipping fever. BoHV-1 infection can also cause immunosuppression and increased susceptibility to secondary bacterial infections, leading to pneumonia and occasionally to death. Herein, we investigated the influence of MG-132, a proteasome inhibitor, on BoHV-1 infection in bovine kidney (MDBK) cells. Infection of MDBK cells with BoHV-1 induces apoptotic cell death that enhances virus release. Whereas, MG-132 inhibited virus-induced apoptosis and stimulated autophagy. Protein expression of viral infected cell protein 0 (bICP0), which is constitutively expressed during infection and is able to stimulate Nuclear factor kappa B (NF-κB), was completely inhibited by MG-132. These results were accompanied by a significant delay in the NF-κB activation. Interestingly, the efficient virus release provoked by BoHV-1-induced apoptosis was significantly reduced by MG-132. Overall, this study suggests that MG-132, through the activation of autophagy, may limit BoHV-1 replication during productive infection, by providing an antiviral defense mechanism.

Combinatorial Effects of the Glucocorticoid Receptor and Krüppel-Like Transcription Factor 15 on Bovine Herpesvirus 1 Transcription and Productive Infection

Bovine herpesvirus 1 (BoHV-1), an important bovine pathogen, establishes lifelong latency in sensory neurons. Latently infected calves consistently reactivate from latency following a single intravenous injection of the synthetic corticosteroid dexamethasone. The immediate early transcription unit 1 (IEtu1) promoter, which drives bovine ICP0 (bICP0) and bICP4 expression, is stimulated by dexamethasone because it contains two glucocorticoid receptor (GR) response elements (GREs). Several Krüppel-like transcription factors (KLF), including KLF15, are induced during reactivation from latency, and they stimulate certain viral promoters and productive infection. In this study, we demonstrate that the GR and KLF15 were frequently expressed in the same trigeminal ganglion (TG) neuron during reactivation and cooperatively stimulated productive infection and IEtu1 GREs in mouse neuroblastoma cells (Neuro-2A). We further hypothesized that additional regions in the BoHV-1 genome are transactivated by the GR or stress-induced transcription factors. To test this hypothesis, BoHV-1 DNA fragments (less than 400 bp) containing potential GR and KLF binding sites were identified and examined for transcriptional activation by stress-induced transcription factors. Intergenic regions within the unique long 52 gene (UL52; a component of the DNA primase/helicase complex), bICP4, IEtu2, and the unique short region were stimulated by KLF15 and the GR. Chromatin immunoprecipitation studies revealed that the GR and KLF15 interacted with sequences within IEtu1 GREs and the UL52 fragment. Coimmunoprecipitation studies demonstrated that KLF15 and the GR were associated with each other in transfected cells. Since the GR stimulates KLF15 expression, we suggest that these two transcription factors form a feed-forward loop that stimulates viral gene expression and productive infection following stressful stimuli.IMPORTANCE Bovine herpesvirus 1 (BoHV-1) is an important viral pathogen that causes respiratory disease and suppresses immune responses in cattle; consequently, life-threatening bacterial pneumonia can occur. Following acute infection, BoHV-1 establishes lifelong latency in sensory neurons. Reactivation from latency is initiated by the synthetic corticosteroid dexamethasone. Dexamethasone stimulates lytic cycle viral gene expression in sensory neurons of calves latently infected with BoHV-1, culminating in virus shedding and transmission. Two stress-induced cellular transcription factors, Krüppel-like transcription factor 15 (KLF15) and the glucocorticoid receptor (GR), cooperate to stimulate productive infection and viral transcription. Additional studies demonstrated that KLF15 and the GR form a stable complex and that these stress-induced transcription factors bind to viral DNA sequences, which correlates with transcriptional activation. The ability of the GR and KLF15 to synergistically stimulate viral gene expression and productive infection may be critical for the ability of BoHV-1 to reactivate from latency following stressful stimuli.

The suppression of apoptosis by α-herpesvirus

Apoptosis, an important innate immune mechanism that eliminates pathogen-infected cells, is primarily triggered by two signalling pathways: the death receptor pathway and the mitochondria-mediated pathway. However, many viruses have evolved various strategies to suppress apoptosis by encoding anti-apoptotic factors or regulating apoptotic signalling pathways, which promote viral propagation and evasion of the host defence. During its life cycle, α-herpesvirus utilizes an elegant multifarious anti-apoptotic strategy to suppress programmed cell death. This progress article primarily focuses on the current understanding of the apoptosis-inhibition mechanisms of α-herpesvirus anti-apoptotic genes and their expression products and discusses future directions, including how the anti-apoptotic function of herpesvirus could be targeted therapeutically.

Effects of the synthetic corticosteroid dexamethasone on bovine herpesvirus 1 productive infection

Sensory neurons are a primary site for life-long latency of bovine herpesvirus 1 (BoHV-1). The synthetic corticosteroid dexamethasone induces reactivation from latency and productive infection, in part because the BoHV-1 genome contains more than 100 glucocorticoid receptor (GR) responsive elements (GREs). Two GREs in the immediate early transcription unit 1 promoter are required for dexamethasone induction. Recent studies also demonstrated that the serum and glucocorticoid receptor protein kinase (SGK) family stimulated BoHV-1 replication. Consequently, we hypothesized that dexamethasone influences several aspects of productive infection. In this study, we demonstrated that dexamethasone increased expression of the immediate early protein bICP4, certain late transcripts, and UL23 (thymidine kinase) by four hours after infection. SGK1 expression and Akt phosphorylation were also stimulated during early stages of infection and dexamethasone treatment further increased this effect. These studies suggest that stress, as mimicked by dexamethasone treatment, has the potential to stimulate productive infection by multiple pathways.

2,3,7,8-tetrachlorodibenzo-p-dioxin and the viral infection

Exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a widespread highly toxic environmental contaminant, suppresses immune response and leads to an increased susceptibility to infectious agents. In particular, several studies have provided evidence that TCDD decreases resistance to numerous viruses. Indeed, in vivo and in vitro investigations showed that the presence of TCDD is able to interfere with the replication of both human and animal viruses, such as influenza A viruses, coxsackie virus B3, immunodeficiency virus type-1 (HIV-1), cytomegalovirus (CMV), herpes simplex II, and bovine herpesvirus 1. Moreover, TCDD could induce an exacerbation of latent infection produced by HIV-1, CMV or Epstein-Barr virus. In this review, we first describe the general effects of TCDD exposure on mammalian cells, then we focus on its influence on the viral infections. Overall, the available data support the concept that TCDD exposure may act as an additional risk factor in promoting of viral diseases.

Bovine herpesvirus 1 can efficiently infect the human (SH-SY5Y) but not the mouse neuroblastoma cell line (Neuro-2A)

Bovine herpesvirus 1 (BoHV-1) is a significant bovine pathogen that establishes a life-long latent infection in sensory neurons. Previous attempts to develop immortalized bovine neuronal cells were unsuccessful. Consequently, our understanding of the BoHV-1 latency-reactivation cycle has relied on studying complex virus-host interactions in calves. In this study, we tested whether BoHV-1 can infect human (SH-SY5Y) or mouse (Neuro-2A) neuroblastoma cells. We provide new evidence that BoHV-1 efficiently infects SH-SY5Y cells and yields virus titers approximately 100 fold less than bovine kidney cells. Conversely, virus titers from productively infected Neuro-2A cells were approximately 10,000 fold less than bovine kidney cells. Using a β-Gal expressing virus (gC-Blue), we demonstrate that infection of Neuro-2A cells (actively dividing or differentiated) does not result in efficient virus spread, unlike bovine kidney or SH-SY5Y cells. Additional studies demonstrated that lytic cycle viral gene expression (bICP4 and gE) was readily detected in SH-SY5Y cells: conversely bICP4 was not readily detected in productively infected Neuro-2A cells. Finally, infection of SH-SY5Y and bovine kidney cells, but not Neuro-2A cells, led to rapid activation of the Akt protein kinase. These studies suggest that the Neuro-2A cell line may be a novel cell culture model to identify factors that regulate BoHV-1 productive infection in neuronal cells.

Cellular response markers and cytokine gene expression in the central nervous system of cattle naturally infected with bovine herpesvirus 5

The present study reports an investigation on the phenotype of inflammatory and immune cells, cytokine and viral gene expression in the brains of cattle naturally infected with bovine herpesvirus 5 (BHV5). Brain sections of 38 affected animals were analysed for the nature and extent of perivascular cuffs in the Virchow-Robin space and parenchyma. Histopathological changes were severe in the olfactory bulbs (Obs), hippocampus, piriform, frontal, temporal and parietal cortices/lobes and were characterized by inflammatory infiltrates in Virchow-Robin spaces. The histopathological changes correlated positively with the distribution of BHV5 antigens (r = 0.947; P < 0.005). Cells of CD3+ phenotype were predominant in areas with severe perivascular cuffs. Viral antigens and genomic viral DNA were detected in the Obs and piriform lobe, simultaneously (r = 0.987; P < 0.005). Similarly, pro-inflammatory cytokine genes INFG, IL2, TNF and LTBR were expressed in the same brain areas (P < 0.005). These results provide important information on the inflammatory and immunological events accompanying BHV5 neurological infections. Our findings provide the first evidence for increased immune activation followed by inflammatory cytokine expression, positively correlated with viral replication in the cranial areas of the brain. Taken together, these results suggest that the host immune response and inflammation play a crucial role in the pathogenesis of acute encephalitis by BHV5 in cattle.

Bovine herpesvirus type-1 glycoprotein K (gK) interacts with UL20 and is required for infectious virus production

We have previously shown that the HSV-1 gK and UL20 proteins interact and function in virion envelopment, membrane fusion, and neuronal entry. Alignment of the predicted secondary structures of gKs encoded by BoHV-1, HSV-1, HSV-2, EHV-1 and VZV indicated a high degree of domain conservation. Two BoHV-1 gK-null mutant viruses were created by either gK gene deletion or stop codon insertion. In addition, a V5 epitope-tag was inserted at the carboxyl terminus of gK gene to detect gK. The engineered gK-null mutant viruses failed to replicate and produce viral plaques. Co-immunoprecipitation of gK and UL20 expressed via different methods revealed that gK and UL20 physically interacted in the presence or absence of other viral proteins. Confocal microscopy showed that gK and UL20 colocalized in infected cells. These results indicate that BoHV-1 gK and UL20 may function in a similar manner to other alphaherpesvirus orthologues specified by HSV-1, PRV and EHV-1.

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.

Alphaherpesvirus Latency: A Dynamic State of Transcription and Reactivation

Alphaherpesviruses infect a variety of species from sea turtles to man and can cause significant disease in mammals including humans and livestock. These viruses are characterized by a lytic and latent state in nerve ganglia, with the ability to establish a lifelong latent infection that is interrupted by periodic reactivation. Previously, it was accepted that latency was a dominant state and that only during relatively infrequent reactivation episodes did latent genomes within ganglia become transcriptionally active. Here, we review recent data, focusing mainly on Herpes Simplex Virus type 1 which indicate that the latent state is more dynamic than recently appreciated.

Development of an Indirect ELISA for Serological Diagnosis of Bovine herpesvirus 5

Bovine herpesviruses 1 and 5 (BoHV-1 and BoHV-5) are economically important pathogens, associated with a variety of clinical syndromes, including respiratory and genital disease, reproductive failure and meningoencephalitis. The standard serological assay to diagnose BoHV-1 and BoHV-5 infections is the virus neutralization test (VNT), a time consuming procedure that requires manipulation of infectious virus. In the present study a highly sensitive and specific single dilution indirect ELISA was developed using recombinant glycoprotein D from BoHV-5 as antigen (rgD5ELISA). Bovine serum samples (n = 450) were screened by VNT against BoHV-5a and by rgD5ELISA. Compared with the VNT, the rgD5ELISA demonstrated accuracy of 99.8%, with 100% sensitivity, 96.7% specificity and coefficient of agreement between the tests of 0.954. The rgD5ELISA described here shows excellent agreement with the VNT and is shown to be a simple, convenient, specific and highly sensitive virus-free assay for detection of serum antibodies to BoHV-5.

Regulation of Notch-mediated transcription by a bovine herpesvirus 1 encoded protein (ORF2) that is expressed in latently infected sensory neurons

Bovine herpesvirus 1 (BoHV-1) is an Alphaherpesvirinae subfamily member that establishes life-long latency in sensory neurons. The latency-related RNA (LR-RNA) is abundantly expressed during latency. An LR mutant virus containing stop codons at the amino-terminus of open reading frame (ORF)2 does not reactivate from latency and replicates less efficiently in tonsils and trigeminal ganglia. ORF2 inhibits apoptosis, interacts with Notch family members, and interferes with Notch-dependent transcription suggesting ORF2 expression enhances survival of infected neurons. The Notch signaling pathway is crucial for neuronal differentiation and survival suggesting that interactions between ORF2 and Notch family members regulate certain aspects of latency. Consequently, for this study, we compared whether ORF2 interfered with the four mammalian Notch family members. ORF2 consistently interfered with Notch1-3-mediated transactivation of three cellular promoters. Conversely, Notch4-mediated transcription was not consistently inhibited by ORF2. Electrophoretic shift mobility assays using four copies of a consensus-DNA binding site for Notch/CSL (core binding factor (CBF)-1, Suppressor of Hairless, Lag-2) as a probe revealed ORF2 interfered with Notch1 and 3 interactions with a CSL family member bound to DNA. Additional studies demonstrated ORF2 enhances neurite sprouting in mouse neuroblastoma cells that express Notch1-3, but not Notch4. Collectively, these studies indicate that ORF2 inhibits Notch-mediated transcription and signaling by interfering with Notch interacting with CSL bound to DNA.

β-Catenin, a Transcription Factor Activated by Canonical Wnt Signaling, Is Expressed in Sensory Neurons of Calves Latently Infected with Bovine Herpesvirus 1

Like many Alphaherpesvirinae subfamily members, bovine herpesvirus 1 (BoHV-1) expresses an abundant transcript in latently infected sensory neurons, the latency-related (LR)-RNA. LR-RNA encodes a protein (ORF2) that inhibits apoptosis, interacts with Notch family members, interferes with Notch-mediated transcription, and stimulates neurite formation in cells expressing Notch. An LR mutant virus containing stop codons at the amino terminus of ORF2 does not reactivate from latency or replicate efficiently in certain tissues, indicating that LR gene products are important. In this study, β-catenin, a transcription factor activated by the canonical Wnt signaling pathway, was frequently detected in ORF2-positive trigeminal ganglionic neurons of latently infected, but not mock-infected, calves. Conversely, the lytic cycle regulatory protein (BoHV-1 infected cell protein 0, or bICP0) was not frequently detected in β-catenin-positive neurons in latently infected calves. During dexamethasone-induced reactivation from latency, mRNA expression levels of two Wnt antagonists, Dickkopf-1 (DKK-1) and secreted Frizzled-related protein 2 (SFRP2), were induced in bovine trigeminal ganglia (TG), which correlated with reduced β-catenin protein expression in TG neurons 6 h after dexamethasone treatment. ORF2 and a coactivator of β-catenin, mastermind-like protein 1 (MAML1), stabilized β-catenin protein levels and stimulated β-catenin-dependent transcription in mouse neuroblastoma cells more effectively than MAML1 or ORF2 alone. Neuroblastoma cells expressing ORF2, MAML1, and β-catenin were highly resistant to cell death following serum withdrawal, whereas most cells transfected with only one of these genes died. The Wnt signaling pathway interferes with neurodegeneration but promotes neuronal differentiation, suggesting that stabilization of β-catenin expression by ORF2 promotes neuronal survival and differentiation.

IMPORTANCE

Bovine herpesvirus 1 (BoHV-1) is an important pathogen of cattle, and like many Alphaherpesvirinae subfamily members establishes latency in sensory neurons. Lifelong latency and the ability to reactivate from latency are crucial for virus transmission. Maintaining the survival and normal functions of terminally differentiated neurons is also crucial for lifelong latency. Our studies revealed that BoHV-1 gene products expressed during latency stabilize expression of the transcription factor β-catenin and perhaps its cofactor, mastermind-like protein 1 (MAML1). In contrast to expression during latency, β-catenin expression in sensory neurons is not detectable following treatment of latently infected calves with the synthetic corticosteroid dexamethasone to initiate reactivation from latency. A viral protein (ORF2) expressed in a subset of latently infected neurons stabilized β-catenin and MAML1 in transfected cells. ORF2, β-catenin, and MAML1 also enhanced cell survival when growth factors were withdrawn, suggesting that these genes enhance survival of latently infected neurons.

Infection by Herpes Simplex Virus 1 Causes Near-Complete Loss of RNA Polymerase II Occupancy on the Host Cell Genome

Lytic infection by herpes simplex virus 1 (HSV-1) triggers a change in many host cell programs as the virus strives to express its own genes and replicate. Part of this process is repression of host cell transcription by RNA polymerase II (Pol II), which also transcribes the viral genome. Here, we describe a global characterization of Pol II occupancy on the viral and host genomes in response to HSV-1 infection using chromatin immunoprecipitation followed by deep sequencing (ChIP-seq). The data reveal near-complete loss of Pol II occupancy throughout host cell mRNA genes, in both their bodies and promoter-proximal regions. Increases in Pol II occupancy of host cell genes, which would be consistent with robust transcriptional activation, were not observed. HSV-1 infection induced a more potent and widespread repression of Pol II occupancy than did heat shock, another cellular stress that widely represses transcription. Concomitant with the loss of host genome Pol II occupancy, we observed Pol II covering the HSV-1 genome, reflecting a high level of viral gene transcription. Interestingly, the positions of the peaks of Pol II occupancy at HSV-1 and host cell promoters were different.

IMPORTANCE

We investigated the effect of herpes simplex virus 1 (HSV-1) infection on transcription of host cell and viral genes by RNA polymerase II (Pol II). The approach we used was to determine how levels of genome-bound Pol II changed after HSV-1 infection. We found that HSV-1 caused a profound loss of Pol II occupancy across the host cell genome. Increases in Pol II occupancy were not observed, showing that no host genes were activated after infection. In contrast, Pol II occupied the entire HSV-1 genome. Moreover, the pattern of Pol II at HSV-1 genes differed from that on host cell genes, suggesting a unique mode of viral gene transcription. These studies provide new insight into how HSV-1 causes changes in the cellular program of gene expression and how the virus coopts host Pol II for its own use.

Preparation and characterization of bioadhesive controlled-release gels of cidofovir for vaginal delivery

The aim of this study was to develop mucoadhesive and thermosensitive gels for vaginal delivery that would be able to provide a controlled release of the model drug, cidofovir. The study also monitored the drug's potential antiviral properties. Cidofovir was put into the form of a vaginal gel, using mucoadhesive and thermosensitive polymers such as chitosan, Carbopol 974P, HPMC, and poloxamer 407. The physicopharmaceutical properties and stability of the vaginal gel formulations were evaluated. The gel formulation which was prepared with HPMC K100M exhibited the highest viscosity, as well as maximum adhesiveness, cohesiveness, and mucoadhesion values. The results of antiviral activity studies, which used the bovine herpes virus type 1 virus infection in vitro model using Vero cells, demonstrated the antiherpetic effect of the cidofovir gel containing HPMC K100M, at least under in vitro conditions. The study found that a mucoadhesive vaginal gel containing cidofovir can be a promising and innovative alternative therapeutic system for the treatment of genital herpes simplex virus and human papilloma virus induced infections in women.

Bovine herpesvirus 1 productive infection and immediate early transcription unit 1 promoter are stimulated by the synthetic corticosteroid dexamethasone

The primary site for life-long latency of bovine herpesvirus 1 (BHV-1) is sensory neurons. The synthetic corticosteroid dexamethasone consistently induces reactivation from latency; however the mechanism by which corticosteroids mediate reactivation is unclear. In this study, we demonstrate for the first time that dexamethasone stimulates productive infection, in part, because the BHV-1 genome contains more than 100 potential glucocorticoid receptor (GR) response elements (GREs). Immediate early transcription unit 1 (IEtu1) promoter activity, but not IEtu2 or VP16 promoter activity, was stimulated by dexamethasone. Two near perfect consensus GREs located within the IEtu1 promoter were necessary for dexamethasone-mediated stimulation. Electrophoretic mobility shift assays and chromatin immunoprecipitation studies demonstrated that the GR interacts with IEtu1 promoter sequences containing the GREs. Although we hypothesize that DEX-mediated stimulation of IEtu1 promoter activity is important during productive infection and perhaps reactivation from latency, stress likely has pleiotropic effects on virus-infected cells.

The herpes simplex virus type 1 (HSV-1) latency-associated transcript (LAT) protects cells against cold-shock-induced apoptosis by maintaining phosphorylation of protein kinase B (AKT)

The herpes simplex virus type 1 (HSV-1) latency-associated transcript (LAT) blocks apoptosis and inhibits caspase-3 activation. We previously showed that serum starvation (removal of serum from tissue culture media), which takes several days to induce apoptosis, results in decreased levels of both AKT (protein kinase B) and phosphorylated AKT (pAKT) in cells not expressing LAT. In contrast in mouse neuroblastoma cells expressing LAT, AKT, and pAKT levels remained high. AKT is a serine/threonine protein kinase that promotes cell survival. To examine the effect of LAT on AKT-pAKT using a different and more rapid method of inducing apoptosis, a stable cell line expressing LAT was compared to non-LAT expressing cells as soon as 15 min following recovery from cold-shock-induced apoptosis. Expression of LAT appeared to inhibit dephosphorylation of pAKT. This protection correlated with blocking numerous pro-apoptotic events that are inhibited by pAKT. These results support the hypothesis that inhibiting dephosphorylation of pAKT may be one of the pathways by which LAT protects cells against apoptosis.

Bovine herpesvirus 1 regulatory proteins are detected in trigeminal ganglionic neurons during the early stages of stress-induced escape from latency

Bovine herpesvirus 1 (BHV-1) establishes latency in sensory neurons. The synthetic corticosteroid dexamethasone consistently induces reactivation from latency. Within 90 min after latently infected calves are treated with dexamethasone, two BHV-1 regulatory proteins, BHV-1-infected cell protein 0 (bICP0) and viral protein 16 (VP16), are expressed in the same neuron. In this study, we demonstrate that VP16 and bICP0 can be detected at 22 and 33 min after dexamethasone (DEX) treatment of latently infected calves. However, we were unable to discern whether VP16 or bICP0 was expressed at early times after reactivation. VP16+ neurons consistently express the glucocorticoid receptor suggesting corticosteroid-mediated activation of its receptor rapidly stimulates reactivation from latency.

The number of alphaherpesvirus particles infecting axons and the axonal protein repertoire determines the outcome of neuronal infection

Infection by alphaherpesviruses invariably results in invasion of the peripheral nervous system (PNS) and establishment of either a latent or productive infection. Infection begins with long-distance retrograde transport of viral capsids and tegument proteins in axons toward the neuronal nuclei. Initial steps of axonal entry, retrograde transport, and replication in neuronal nuclei are poorly understood. To better understand how the mode of infection in the PNS is determined, we utilized a compartmented neuron culturing system where distal axons of PNS neurons are physically separated from cell bodies. We infected isolated axons with fluorescent-protein-tagged pseudorabies virus (PRV) particles and monitored viral entry and transport in axons and replication in cell bodies during low and high multiplicities of infection (MOIs of 0.01 to 100). We found a threshold for efficient retrograde transport in axons between MOIs of 1 and 10 and a threshold for productive infection in the neuronal cell bodies between MOIs of 1 and 0.1. Below an MOI of 0.1, the viral genomes that moved to neuronal nuclei were silenced. These genomes can be reactivated after superinfection by a nonreplicating virus, but not by a replicating virus. We further showed that viral particles at high-MOI infections compete for axonal proteins and that this competition determines the number of viral particles reaching the nuclei. Using mass spectrometry, we identified axonal proteins that are differentially regulated by PRV infection. Our results demonstrate the impact of the multiplicity of infection and the axonal milieu on the establishment of neuronal infection initiated from axons.

Alphaherpesvirus genomes may remain silent in peripheral nervous system (PNS) neurons for the lives of their hosts. These genomes occasionally reactivate to produce infectious virus that can reinfect peripheral tissues and spread to other hosts. Here, we use a neuronal culture system to investigate the outcome of axonal infection using different numbers of viral particles and coinfection assays. We found that the dynamics of viral entry, transport, and replication change dramatically depending on the number of virus particles that infect axons. We demonstrate that viral genomes are silenced when the infecting particle number is low and that these genomes can be reactivated by superinfection with UV-inactivated virus, but not with replicating virus. We further show that viral invasion rapidly changes the profiles of axonal proteins and that some of these axonal proteins are rate limiting for efficient infection. Our study provides new insights into the establishment of silent versus productive alphaherpesvirus infections in the PNS.

Antiviral activity of lambda-carrageenan prepared from red seaweed (Gigartina skottsbergii) against BoHV-1 and SuHV-1

The antiviral effect of polysaccharides has been known for many years. Carrageenans are considered a good alternative for the prevention of a wide range of diseases, mainly caused by enveloped viruses. The advantages lie on their high availability, low cost and low induction of resistance. The aim of this study was to evaluate the sensitivity of two viral pathogens of veterinary interest to the presence of lambda-carrageenan. This is the first report of a lambda-carrageenan having antiviral activity against animal viruses belonging to the Alphaherpesvirinae subfamily, BoHV-1 (bovine herpesvirus type 1) strain Cooper and SuHV-1 (suid herpesvirus type 1) strain Bartha. Lambda-carrageenan was able to reduce infectivity of both viruses with a more pronounced effect against BoHV-1. These results proved, as previously shown for human herpes virus type 1, that these compounds could be used as potential antiviral agents in the veterinary field.

Rearing practices identified as risk factors for ostreid herpesvirus 1 (OsHV-1) infection in Pacific oyster Crassostrea gigas spat

Early detection of Pacific oyster spat infected with ostreid herpesvirus 1 (OsHV-1) could prevent introduction of OsHV-1-infected individuals into farming areas or onshore rearing facilities, thus reducing the risk of infection of naïve oysters in such production systems. Experiments were conducted on several hundred oyster spat provided by producers in order to examine whether early rearing practices could be considered as potential risk factors for (1) OsHV-1 infection as detected by molecular methods and (2) spat mortality experimentally induced through thermal challenge. Spat groups collected on oyster beds and hatchery spat reared in growout areas during summer exhibited higher viral DNA contamination and mortalities during the trial than spat kept in onshore rearing facilities. Quantification of viral DNA before and during the trial showed that infection prevalence and intensity changed over time and revealed latent infection initially unsuspected in 3 of 10 groups. Thermal challenge induced a clear increase in the probability of detecting infected individuals, particularly for groups exhibiting significant prevalence of OsHV-1-contaminated spat prior to the challenge. The use of detection methods are discussed in relation to early rearing practices and disease control strategies.

Analysis of a bovine herpesvirus 1 protein encoded by an alternatively spliced latency related (LR) RNA that is abundantly expressed in latently infected neurons

The bovine herpes virus 1 (BoHV-1) encoded latency-related RNA (LR-RNA) is abundantly expressed in latently infected sensory neurons. A LR mutant virus with three stop codons at the amino-terminus of ORF2 does not reactivate from latency or replicate efficiently in certain tissues. ORF2 inhibits apoptosis, interacts with Notch1 or Notch3, and interferes with Notch mediated signaling. Alternative splicing of LR-RNA in trigeminal ganglia yields transcripts that have the potential to encode a protein containing most of ORF2 sequences and parts of other coding sequences located within the LR gene. In this study, we determined that an ORF2 protein fused with reading frame B (15d ORF) was more stable in transfected cells. ORF2 and the 15d ORF stimulated neurite formation in mouse neuroblastoma cells, interfered with Notch3 mediated trans-activation, and had similar DNA binding properties. Increased stability of the 15d ORF is predicted to enhance the establishment of latency.

SOCS1/3 expression levels in HSV-1-infected, cytokine-polarized and -unpolarized macrophages

Macrophage subtypes are characterized as proinflammatory (M1) or immunomodulatory and tissue remodeling (M2). Since macrophages play a pivotal role in controlling Herpes simplex virus type-1 (HSV-1) replication, effects of HSV-1 by 24 h of infection were determined in murine J774A.1 macrophages unpolarized (M0) or polarized to either an M1 or M2 phenotype. Morphology, cell viability, and expression of CD14 (co-receptor for lipopolysaccharide), CD86 (B7.2-immune co-stimulatory molecule), and suppressors of cytokine signaling (SOCS1 and SOCS3) were determined. M1 macrophages were flattened and vacuolated, while M2 cells appeared elongated with a few vacuoles. Compared with unpolarized M0 cells, M1 cells showed a 31% decrease in viability, a 2-fold increase in the number of CD14(+)-CD86(+) cells, no change in SOCS1 expression, and an 11-fold decrease in SOCS3 expression. M2 cells exhibited a 9% decrease in viability, a 26.0% decrease in the number of CD14(+)-CD86(+) cells, and no change in SOCS1/SOCS3 expression levels compared with M0 cells. After HSV-1 infection, all phenotypes appeared rounded, cell viabilities decreased as did numbers of M1 cells expressing CD14 and CD86. At 24 h after infection, M0 control and M2 cells showed greater virus yield than did the M1 cells, presumably reflecting the loss of viable M1 cells. SOCS1 expression was predominant in uninfected M1-polarized cells and in virus-infected control (M0) cells. SOCS1/SOCS3 expression ratio was 7:1 in uninfected M1 macrophages and approached 1:1 in M1 cells at 24 h after infection with HSV-1. In contrast, little differences were seen in SOCS1/SOCS3 expression ratios in uninfected M2-polarized cells or virus-infected M2 cells. These observations suggest that SOCS1/SOCS3 expression ratios can be used to characterize HSV-1-infected and uninfected macrophages.

Identification of B cells as a major site for cyprinid herpesvirus 3 latency

Cyprinid herpesvirus 3 (CyHV-3), commonly known as koi herpesvirus (KHV), is a member of the Alloherpesviridae, and is a recently discovered emerging herpesvirus that is highly pathogenic for koi and common carp. Our previous study demonstrated that CyHV-3 becomes latent in peripheral white blood cells (WBC). In this study, CyHV-3 latency was further investigated in IgM(+) WBC. The presence of the CyHV-3 genome in IgM(+) WBC was about 20-fold greater than in IgM(-) WBC. To determine whether CyHV-3 expressed genes during latency, transcription from all eight open reading frames (ORFs) in the terminal repeat was investigated in IgM(+) WBC from koi with latent CyHV-3 infection. Only a spliced ORF6 transcript was found to be abundantly expressed in IgM(+) WBC from CyHV-3 latently infected koi. The spliced ORF6 transcript was also detected in vitro during productive infection as early as 1 day postinfection. The ORF6 transcript from in vitro infection begins at -127 bp upstream of the ATG codon and ends +188 bp downstream of the stop codon, +20 bp downstream of the polyadenylation signal. The hypothetical protein of ORF6 contains a consensus sequence with homology to a conserved domain of EBNA-3B and ICP4 from Epstein-Barr virus and herpes simplex virus 1, respectively, both members of the Herpesviridae. This is the first report of latent CyHV-3 in B cells and identification of gene transcription during latency for a member of the Alloherpesviridae.

IMPORTANCE

This is the first demonstration that a member of the Alloherpesviridae, cyprinid herpesvirus 3 (CyHV-3), establishes a latent infection in the B cells of its host, Cyprinus carpio. In addition, this is the first report of identification of gene transcription during latency for a member of Herpesvirales outside Herpesviridae. This is also the first report that the hypothetical protein of latent transcript of CyHV-3 contains a consensus sequence with homology to a conserved domain of EBNA-3B from Epstein-Barr virus and ICP4 from herpes simplex virus 1, which are genes important for latency. These strongly suggest that latency is evolutionally conserved across vertebrates.

Immunity to bovine herpesvirus 1: II. Adaptive immunity and vaccinology

Bovine herpesvirus 1 (BHV-1) infection is widespread and causes a variety of diseases. Although similar in many respects to the human immune response to human herpesvirus 1, the differences in the bovine virus proteins, immune system components and strategies, physiology, and lifestyle mean the bovine immune response to BHV-1 is unique. The innate immune system initially responds to infection, and primes a balanced adaptive immune response. Cell-mediated immunity, including cytotoxic T lymphocyte killing of infected cells, is critical to recovery from infection. Humoral immunity, including neutralizing antibody and antibody-dependent cell-mediated cytotoxicity, is important to prevention or control of (re-)infection. BHV-1 immune evasion strategies include suppression of major histocompatibility complex presentation of viral antigen, helper T-cell killing, and latency. Immune suppression caused by the virus potentiates secondary infections and contributes to the costly bovine respiratory disease complex. Vaccination against BHV-1 is widely practiced. The many vaccines reported include replicating and non-replicating, conventional and genetically engineered, as well as marker and non-marker preparations. Current development focuses on delivery of major BHV-1 glycoproteins to elicit a balanced, protective immune response, while excluding serologic markers and virulence or other undesirable factors. In North America, vaccines are used to prevent or reduce clinical signs, whereas in some European Union countries marker vaccines have been employed in the eradication of BHV-1 disease.

Cell-mediated immune responses induced by BHV-1: rational vaccine design

Bovine herpesvirus-1 (BHV-1) is one of the major respiratory pathogens in cattle worldwide. Although antibodies have been correlated with protection and recovery from BHV-1 infection, the cell-mediated immune response is also a critical defense mechanism because cell-to-cell spread occurs before hematogenous spread. Furthermore, induction of robust T-cell memory is critical for the long-term duration of immunity. Among current commercial vaccines, the attenuated conventional vaccines induce a balanced immune response and long-term memory but may result in viral shedding. By contrast, inactivated vaccines primarily elicit a humoral immune response and relative short-term memory. These vaccines do not allow differentiation of vaccinated from infected cattle. Recent efforts are focusing on the development of vaccines that induce a balanced immune response and long-term memory, as well as having differentiation markers. This includes well-defined genetically engineered gene-deleted, subunit and vectored vaccines.

Stress-induced cellular transcription factors expressed in trigeminal ganglionic neurons stimulate the herpes simplex virus 1 ICP0 promoter

Alphaherpesvirinae family members can reactivate from latency following stress. The synthetic corticosteroid dexamethasone induces certain cellular transcription factors in murine and bovine trigeminal ganglionic neurons. Three dexamethasone-induced transcription factors, Krüppel-like factor 15, Slug, and SPDEF, stimulated the herpes simplex virus type 1-infected cell protein 0 (ICP0) promoter more than 150-fold. Conversely, other viral promoters (VP16 and ICP4) were not strongly stimulated, suggesting that the ICP0 promoter is preferentially activated by dexamethasone-simulated stress.

Bovine herpesvirus 1 regulatory proteins bICP0 and VP16 are readily detected in trigeminal ganglionic neurons expressing the glucocorticoid receptor during the early stages of reactivation from latency

Bovine herpesvirus 1 (BHV-1) establishes a lifelong latent infection in sensory neurons following acute infection. Increased corticosteroid levels, due to stress, increases the incidence of reactivation from latency. Within minutes, corticosteroids activate the glucocorticoid receptor and transcription of promoters containing a glucocorticoid receptor element. A single intravenous injection of the synthetic corticosteroid dexamethasone consistently induces reactivation from latency in calves. Lytic cycle viral gene expression is detected within 6 h after dexamethasone treatment of calves latently infected with BHV-1. Cellular transcription factors are induced by dexamethasone in trigeminal ganglionic neurons within 1.5 h after dexamethasone treatment, suggesting they promote viral gene expression during the early phases of reactivation from latency, which we operationally defined as the escape from latency. In this study, immunohistochemistry was utilized to examine viral protein expression during the escape from latency. Within 1.5 h after dexamethasone treatment, bICP0 and a late protein (VP16) were consistently detected in a subset of trigeminal ganglionic neurons. Most neurons expressing bICP0 also expressed VP16. Additional studies revealed that neurons expressing the glucocorticoid receptor also expressed bICP0 or VP16 at 1.5 h after dexamethasone treatment. Two other late proteins, glycoprotein C and D, were not detected until 6 h after dexamethasone treatment and were detected in only a few neurons. These studies provide evidence that VP16 and the promiscuous viral trans-activator (bICP0) are expressed during the escape from latency, suggesting they promote the production of infectious virus in a small subset of latently infected neurons.

Small non-coding RNAs encoded within the herpes simplex virus type 1 latency associated transcript (LAT) cooperate with the retinoic acid inducible gene I (RIG-I) to induce beta-interferon promoter activity and promote cell survival

The herpes simplex virus type 1 (HSV-1) latency-associated transcript (LAT) is abundantly expressed in latently infected trigeminal ganglionic sensory neurons. Expression of the first 1.5 kb of LAT coding sequences restores wild type reactivation to a LAT null HSV-1 mutant. The anti-apoptosis functions of the first 1.5 kb of LAT coding sequences are important for wild type levels of reactivation from latency. Two small non-coding RNAs (sncRNAs) contained within the first 1.5 kb of LAT coding sequences are expressed in trigeminal ganglia of latently infected mice, they cooperate to inhibit apoptosis, and reduce the efficiency of productive infection. In this study, we demonstrated that LAT sncRNA1 cooperates with the RNA sensor, retinoic acid inducible gene I (RIG-I), to stimulate IFN-β promoter activity and NF-κB dependent transcription in human or mouse cells. LAT sncRNA2 stimulated RIG-I induction of NF-κB dependent transcription in mouse neuroblastoma cells (Neuro-2A) but not human 293 cells. Since it is well established that NF-κB interferes with apoptosis, we tested whether the sncRNAs cooperated with RIG-I to inhibit apoptosis. In Neuro-2A cells, both sncRNAs cooperated with RIG-I to inhibit cold-shock induced apoptosis. Double stranded RNA (PolyI:C) stimulates RIG-I dependent signaling; but enhanced cold-shock induced apoptosis. PolyI:C, but not LAT sncRNAs, interfered with protein synthesis when cotransfected with RIG-I, which correlated with increased levels of cold-shock induced apoptosis. LAT sncRNA1 appeared to interact with RIG-I in transiently transfected cells suggesting this interaction stimulates RIG-I.

Suppression of apoptosis by pseudorabies virus Us3 protein kinase through the activation of PI3-K/Akt and NF-κB pathways

The pseudorabies virus (PRV) is a major viral disease that causes huge economic loss in the pig industry globally. Most viruses have been found to generate anti-apoptotic factors that facilitate cell survival in the early stages of infection. This study aimed to investigate the anti-apoptotic effects of PRV and study the underlying mechanisms in the early stage of infection. We investigated and compared whether the two PRV Us3 isoforms, Us3a and Us3b, could block apoptosis induced by virus infection, and further identified molecules involved in the signaling pathways. Our results demonstrated that PRV elicits 3-phosphoinositide dependent protein kinase-1/phosphatidylinositide 3-kinases/Akt (PDK-1/PI3-K/Akt)- and nuclear factor-κB (NF-κB)-dependent signaling in the early stage of infection. Inhibition of the PI3-K/Akt or NF-κB pathway enhanced cell death but no effect was observed on virus replication or PRV gene expression. Transiently-expressed GFP- or His-tagged PRV Us3a and Us3b cDNA protect cells against PRV-, avian reovirus- or bovine ephemeral fever virus-induced apoptosis in the cell lines. Us3a and Us3b transient over-expression upregulated several anti-apopototic signaling events, and the anti-apoptosis activity of Us3a is greater than that of Us3b. Kinase activity-deficient point or double point mutated Us3a lost the kinase activity of Us3a, which showed that kinase activity is required for the anti-apoptosis effect of Us3. Akt and NF-κB activation still occurred in UV-inactivated PRV- and cycloheximide-treated cells. In vivo study showed that PRV-infected trigeminal ganglion increases the expression of anti-apoptosis signaling molecules, including Akt, PDK-1 and IκBα, which is a similar result to that seen in the in vitro experiments. Our study suggests that signaling mechanisms may play important roles in PRV pathogenesis.

HSV-1 as a Model for Emerging Gene Delivery Vehicles

The majority of viral vectors currently used possess modest cargo capability (up to 40 kb) being based on retroviruses, lentiviruses, adenoviruses, and adenoassociated viruses. These vectors have made the most rapid transition from laboratory to clinic because their small genomes have simplified their characterization and modification. However, there is now an increasing need both in research and therapy to complement this repertoire with larger capacity vectors able to deliver multiple transgenes or to encode complex regulatory regions, constructs which can easily span more than 100 kb. Herpes Simplex Virus Type I (HSV-1) is a well-characterized human virus which is able to package about 150 kb of DNA, and several vector systems are currently in development for gene transfer applications, particularly in neurons where other systems have low efficiency. However, to reach the same level of versatility and ease of use as that of smaller genome viral vectors, simple systems for high-titer production must be developed. This paper reviews the major HSV-1 vector systems and analyses the common elements which may be most important to manipulate to achieve this goal.

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.

2,3,7,8-Tetrachlorodibenzo-p-dioxin promotes BHV-1 infection in mammalian cells by interfering with iron homeostasis regulation

Mammalian cells require iron to satisfy metabolic needs or to accomplish specialized functions, and DNA viruses, like bovine herpesvirus 1 (BHV-1), require an iron-replete host to efficiently replicate, so that iron bioavailability is an important component of viral virulence. Cellular iron metabolism is coordinately controlled by the Iron Regulatory Proteins (IRP1 and IRP2), whose activity is affected by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a current and persistent environmental contaminant. Considering that TCDD enhances BHV-1 replication, herein we analyzed the effects of TCDD on iron metabolism during BHV-1 infection in MDBK cells, and presented evidences of a divergent modulation of IRP1 and IRP2 RNA-binding capacity. Moreover, an up-regulation of transferrin receptor 1 (TfR1) and a concomitant down-regulation of ferritin were observed. This scenario led to an expansion of the labile iron pool (LIP) and induces a significant enhance of viral titer, as confirmed by increased levels of BHV-1 infected cell protein 0 (bICP0), the major transcriptional regulatory protein of BHV-1. Taken together, our data suggest that TCDD increases the free intracellular iron availability thereby promoting the onset of BHV-1 infection and rendering bovine cells more vulnerable to the virus.

A protein (ORF2) encoded by the latency-related gene of bovine herpesvirus 1 interacts with DNA

Bovine herpesvirus 1 (BHV-1), like other members of the Alphaherpesvirinae subfamily, establishes latency in sensory neurons. The virally encoded latency-related RNA (LR-RNA) is expressed abundantly in latently infected sensory neurons and encodes several proteins, including ORF2. An LR mutant virus with stop codons at the amino terminus of ORF2 does not reactivate from latency after treatment with the synthetic corticosteroid dexamethasone, in part because it induces higher levels of apoptosis during the establishment of latency. ORF2 inhibits apoptosis, interacts with three cellular transcription factors (Notch1, Notch3, and C/EBP-α), and interferes with Notch-mediated signaling. Consequently, we predict that ORF2 expression is crucial for the latency reactivation cycle in cattle. In this study, we tested whether ORF2 interacts with nucleic acids, because it contains 18% basic amino acids and localizes to the nucleus. A subset of ORF2 proteins was associated with chromatin and preferentially associated with single-stranded DNA in transfected neuroblastoma cells (Neuro-2A). Alanine substitution of serine, threonine, and tyrosine residues in ORF2 increased the steady-state protein levels in Neuro-2A cells, and this protein preferentially interacted with double-stranded DNA. Certain in-frame transposon insertion mutants did not interact with DNA as efficiently as wild-type (wt) ORF2 did. ORF2 purified from bacteria under denaturing conditions preferentially interacted with double-stranded DNA, suggesting that the interaction between ORF2 and DNA was direct. In contrast, ORF2 purified under native conditions preferentially interacted with single-stranded DNA. We suggest that interactions between ORF2 and DNA mediate certain aspects of the latency reactivation cycle.

A bovine herpesvirus 1 protein expressed in latently infected neurons (ORF2) promotes neurite sprouting in the presence of activated Notch1 or Notch3

Bovine herpesvirus 1 (BHV-1) infection induces clinical symptoms in the upper respiratory tract, inhibits immune responses, and can lead to life-threatening secondary bacterial infections. Following acute infection, BHV-1 establishes latency in sensory neurons within trigeminal ganglia, but stress can induce reactivation from latency. The latency-related (LR) RNA is the only viral transcript abundantly expressed in latently infected sensory neurons. An LR mutant virus with stop codons at the amino terminus of the first open reading frame (ORF) in the LR gene (ORF2) is not reactivated from latency, in part because it induces higher levels of apoptosis in infected neurons. ORF2 inhibits apoptosis in transiently transfected cells, suggesting that it plays a crucial role in the latency-reactivation cycle. ORF2 also interacts with Notch1 or Notch3 and inhibits its ability to trans activate certain viral promoters. Notch3 RNA and protein levels are increased during reactivation from latency, suggesting that Notch may promote reactivation. Activated Notch signaling interferes with neuronal differentiation, in part because neurite and axon generation is blocked. In this study, we demonstrated that ORF2 promotes neurite formation in mouse neuroblastoma cells overexpressing Notch1 or Notch3. ORF2 also interfered with Notch-mediated trans activation of the promoter that regulates the expression of Hairy Enhancer of Split 5, an inhibitor of neurite formation. Additional studies provided evidence that ORF2 promotes the degradation of Notch3, but not that of Notch1, in a proteasome-dependent manner. In summary, these studies suggest that ORF2 promotes a mature neuronal phenotype that enhances the survival of infected neurons and consequently increases the pool of latently infected neurons.

Felid herpesvirus type 1 infection in cats: a natural host model for alphaherpesvirus pathogenesis

Feline herpesvirus 1 (FeHV-1) is an alphaherpesvirus that causes feline viral rhinotracheitis, an important viral disease of cats on a worldwide basis. Acute FeHV-1 infection is associated with both upper respiratory and ocular signs. Following the acute phase of the disease lifelong latency is established, primarily in sensory neuronal cells. As is the case with human herpes simplex viruses, latency reactivation can result in recrudescence, which can manifest itself in the form of serious ocular lesions. FeHV-1 infection in cats is a natural host model that is useful for the identification of viral virulence genes that play a role in replication at the mucosal portals of entry or are mediators of the establishment, maintenance, or reactivation of latency. It is also a model system for defining innate and adaptive immunity mechanisms and for immunization strategies that can lead to better protection against this and other alphaherpesvirus infections.

Role of bovine herpesvirus type 5 (BoHV-5) in diseases of cattle. Recent findings on BoHV-5 association with genital disease

Bovine herpesvirus type 5 (BoHV-5) belongs to the family Herpesviridae, subfamily Alphaherpesvirinae, genus Varicellovirus. This virus is a major causative agent of non-suppurative meningoencephalitis in young cattle. It was first isolated in 1962 from a neurological disease outbreak in Australia. BoHV-5 is genetically and antigenically related to bovine herpesvirus type 1 (BoHV-1), a highly prevalent virus responsible for respiratory and genital disease in cattle. Initially, BoHV-5 was considered a subtype of BoHV-1 (BoHV-1.3). However, the exclusive presentation of outbreaks of neurological disease suggested that the virus was a new agent with characteristics of neuropathogenicity. Even though both are neurotropic viruses, only BoHV-5 is capable of replicating extensively in the central nervous system and inducing neurological disease. Occasionally, encephalitis caused by BoHV-1 has been reported. Like other alpha-herpesviruses, BoHV-5 can establish latency in nervous ganglia and, by stress factors or glucocorticoid treatment, latent virus can be reactivated. During episodes of reactivation, the virus is excreted in nasal, ocular and genital secretions and transmitted to other susceptible hosts. Recently, BoHV-5 has been associated with infection of the reproductive tract. The virus has been isolated and the presence of viral DNA has been demonstrated in semen samples from Brazil and Australia and natural transmission of the virus through contaminated semen has also been described. Embryos and oocytes are permissive for BoHV-5 infection and BoHV-5 DNA has been detected in the central nervous system of aborted fetuses. The objective of this review is to compile the limited information on the recent association between BoHV-5 and reproductive disorders in cattle.

The role of microRNAs in viral infection

MicroRNAs (miRNAs) are small non-coding RNA molecules that have emerged in recent years as central regulators of eukaryotic gene expression. In mammalian systems, miRNAs are associated with numerous pathological and physiological pathways. miRNAs are important in many viral infections, with different viral families expressing their own miRNAs, manipulating host miRNA expression, or showing direct or indirect regulation by host or viral miRNAs. In this chapter we will examine the current evidence for interplay between the miRNA pathway and viral infections in mammals.

Histone modifications in herpesvirus infections

In eukaryotic cells, gene expression is not only regulated by transcription factors but also by several epigenetic mechanisms including post-translational modifications of histone proteins. There are numerous histone modifications described to date and methylation, acetylation, ubiquitination and phosphorylation are amongst the best studied. In parallel, certain viruses interact with the very same regulatory mechanisms, hereby manipulating the normal epigenetic landscape of the host cell, to fit their own replication needs. This review concentrates on herpesviruses specifically and how they interfere with the histone-modifying enzymes to regulate their replication cycles. Herpesviruses vary greatly with respect to the cell types they infect and the clinical diseases they cause, yet they share various common features including their capacity to encode viral proteins which affect and interfere with the normal functions of histone-modifying enzymes. Studying the epigenetic manipulation/dysregulation of herpesvirus-host interactions not only generates novel insights into the pathogenesis of these viruses but may also have important therapeutic implications.