Upstream stimulatory factor family binds to the herpes simplex virus type 1 latency-associated transcript promoter

Manipulation of Oxidative Stress Responses by Non-Thermal Plasma to Treat Herpes Simplex Virus Type 1 Infection and Disease

Herpes simplex virus type 1 (HSV-1) is a contagious pathogen with a large global footprint, due to its ability to cause lifelong infection in patients. Current antiviral therapies are effective in limiting viral replication in the epithelial cells to alleviate clinical symptoms, but ineffective in eliminating latent viral reservoirs in neurons. Much of HSV-1 pathogenesis is dependent on its ability to manipulate oxidative stress responses to craft a cellular environment that favors HSV-1 replication. However, to maintain redox homeostasis and to promote antiviral immune responses, the infected cell can upregulate reactive oxygen and nitrogen species (RONS) while having a tight control on antioxidant concentrations to prevent cellular damage. Non-thermal plasma (NTP), which we propose as a potential therapy alternative directed against HSV-1 infection, is a means to deliver RONS that affect redox homeostasis in the infected cell. This review emphasizes how NTP can be an effective therapy for HSV-1 infections through the direct antiviral activity of RONS and via immunomodulatory changes in the infected cells that will stimulate anti-HSV-1 adaptive immune responses. Overall, NTP application can control HSV-1 replication and address the challenges of latency by decreasing the size of the viral reservoir in the nervous system.

Liver X Receptors Suppress Activity of Cholesterol and Fatty Acid Synthesis Pathways To Oppose Gammaherpesvirus Replication

Gammaherpesviruses are oncogenic pathogens that persist in ~95% of the adult population. Cellular metabolic pathways have emerged as important regulators of many viral infections, including infections by gammaherpesviruses that require several lipid synthetic pathways for optimal replication. Liver X receptors (LXRs) are transcription factors that are critical regulators of cellular fatty acid and cholesterol synthesis pathways. Not surprisingly, LXRs are attractive therapeutic targets in cardiovascular disease. Here we describe an antiviral role for LXRs in the context of gammaherpesvirus infection of primary macrophages. We show that type I interferon increased LXR expression following infection. Surprisingly, there was not a corresponding induction of LXR target genes. Rather, LXRs suppressed the expression of target genes, leading to decreased fatty acid and cholesterol synthesis, two metabolic pathways that support gammaherpesvirus replication. This report defines LXR-mediated restriction of cholesterol and lipid synthesis as an intrinsic metabolic mechanism to restrict viral replication in innate immune cells.IMPORTANCE Fatty acid and cholesterol synthesis pathways of the host play important roles in diverse biological systems. Importantly, these two metabolic pathways are also usurped by a number of viruses to facilitate viral replication. In this report, we show that suppression of these pathways by liver X receptors in primary macrophages creates an intrinsic antiviral state that attenuates gammaherpesvirus replication by limiting viral access to the two metabolic pathways.

HSV1 latent transcription and non-coding RNA: A critical retrospective

Virologists have invested great effort into understanding how the herpes simplex viruses and their relatives are maintained dormant over the lifespan of their host while maintaining the poise to remobilize on sporadic occasions. Piece by piece, our field has defined the tissues in play (the sensory ganglia), the transcriptional units (the latency-associated transcripts), and the responsive genomic region (the long repeats of the viral genomes). With time, the observed complexity of these features has compounded, and the totality of viral factors regulating latency are less obvious. In this review, we compose a comprehensive picture of the viral genetic elements suspected to be relevant to herpes simplex virus 1 (HSV1) latent transcription by conducting a critical analysis of about three decades of research. We describe these studies, which largely involved mutational analysis of the notable latency-associated transcripts (LATs), and more recently a series of viral miRNAs. We also intend to draw attention to the many other less characterized non-coding RNAs, and perhaps coding RNAs, that may be important for consideration when trying to disentangle the multitude of phenotypes of the many genetic modifications introduced into recombinant HSV1 strains.

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.

Interactions between the products of the Herpes simplex genome and Alzheimer's disease susceptibility genes: relevance to pathological-signalling cascades

The products of the Herpes simplex (HSV-1) genome interact with many Alzheimer's disease susceptibility genes or proteins. These in turn affect those of the virus. For example, HSV-1 binds to heparan sulphate proteoglycans (HSPG2), or alpha-2-macroglobulin (A2M), and enters cells via nectin receptors, which are cleaved by gamma-secretase (APH1B, PSEN1, PSEN2, PEN2, NCSTN). The virus also binds to blood-borne lipoproteins and apolipoprotein E (APOE) is able to modify its infectivity. Viral uptake is cholesterol- and lipid raft-dependent (DHCR24, HMGCR, FDPS, RAFTLIN, SREBF1). The virus is transported to the nucleus via the dynein and kinesin (KNS2) motors associated with the microtubule network (MAPT). Amyloid precursor protein (APP) plays a role in this transport. Nuclear export is mediated via disruption of the nuclear lamina and binding to LMNA. Herpes simplex activates kinases (CDC2 and casein kinase 2) whose substrates include APOE, APP, MAPT, PSEN2, and SREBF1. A viral protein is also able to delete mitochondrial DNA, a situation prevalent in Alzheimer's disease. The virus binds to the host transcription factors transcription factor CP2 (TFCP2) and POU2F1 that control many other genes associated with Alzheimer's disease. Viral latency is controlled by IL6 and IL1B and at different stages of its life cycle the virus can either promote or attenuate apoptosis via Fas and tumor necrosis factor pathways (FAS, TNF, DAPK1, PARP1). Viral evasion strategies include inhibition of the antigen processor TAP2, the production of an Fc immunoglobulin receptor mimic (FCER1G) and inhibition of the viral-activated kinase EIF2AK2. These and other host/viral interactions, targeted to certain Alzheimer's disease susceptibility genes, support the idea that some form of synergy between the pathogen and genetic factors may play a role in the pathology of late-onset Alzheimer's disease.

The Usf-1 transcription factor is a novel target for the stress-responsive p38 kinase and mediates UV-induced Tyrosinase expression

The stress-activated signalling cascade leading to phosphorylation of the p38 family of kinases plays a crucial role during development and in the cellular response to a wide variety of stress-inducing agents. Although alterations in gene expression characteristic of the stress response require the regulation of key transcription factors by the p38 family, few downstream targets for this signalling pathway have been identified. By examining the ability of pigment cells to respond to UV irradiation as part of the UV-induced tanning response, we show that while the microphthalmia-associated transcription factor Mitf regulates basal Tyrosinase expression, it is the ubiquitous basic helix-loop-helix-leucine zipper transcription factor Usf-1 that is required for the UV activation of the Tyrosinase promoter. Consistent with this we demonstrate that Usf-1 is phosphorylated and activated by the stress-responsive p38 kinase. The results suggest that activation of Usf-1 by p38 at a wide variety of viral and cellular promoters will provide a link between stimuli as diverse as UV irradiation, glucose, viral infection and pro-inflammatory cytokines, and the changes in gene expression associated with the stress response.

Inducible cyclic AMP early repressor produces reactivation of latent herpes simplex virus type 1 in neurons in vitro

Herpes simplex virus type 1 (HSV-1) establishes a latent infection in neurons of the peripheral nervous system. During latent HSV-1 infection, viral gene expression is limited to latency-associated transcripts (LAT). HSV-1 remains latent until an unknown mechanism induces reactivation. The ability of the latent virus to periodically reactivate and be shed is essential to the transmission of disease. In vivo, the stimuli that induce reactivation of latent HSV-1 include stress, fever, and UV damage to the skin at the site of initial infection. In vitro, in primary neurons harboring latent HSV-1, nerve growth factor (NGF) deprivation or forskolin treatment induces reactivation. However, the mechanism involved in the induction of reactivation remains poorly understood. An in vitro neuronal model of HSV-1 latency was used to investigate potential mechanisms involved in the induction of reactivation of latent HSV-1. In situ hybridization analysis of neuronal cultures harboring latent HSV-1 showed a marked, rapid decrease in the percentage of LAT-positive neurons following induction of reactivation by NGF deprivation or forskolin treatment. Western blot analysis showed a corresponding increase in expression of the cellular transcription factor inducible cyclic AMP early repressor (ICER) during reactivation. In transient-transfection assays, ICER downregulated LAT promoter activity. Expression of ICER from a recombinant adenoviral vector induced reactivation and decreased the percentage of LAT-positive neurons in neuronal cultures harboring latent HSV-1. These results indicate that ICER represses LAT expression and induces reactivation of latent HSV-1.

Regulation of cdc2 gene expression by the upstream stimulatory factors (USFs)

cdc2 gene expression is under the control of multiple factors. Although E2F/DP proteins have been reported to play a central role, they cannot account for all aspects of the fine modulation of cdc2 gene expression during cell cycle and embryonic development. To characterize the transcription factors that control cdc2 gene expression during nerve cell differentiation in avians, we have previously cloned the quail cdc2 gene promoter region. We had identified an octamer (CAGGTGGC) containing an E-box, which has important activity in regulating cdc2 transcription. Using in vivo genomic footprinting experiments, we show here that this motif, currently named IG, is the target of binding proteins at different stages of neuroretina development, confirming its importance as a regulatory response element for cdc2 gene expression. A subset of Helix-Loop-Helix family of transcription factors, known as Upstream Stimulatory Factors (USFs) specifically bind to this sequence as dimers. Moreover, our results indicate that USFs transactivate the promoter of cdc2 via the IG motif. These data may help to better understand the mechanisms that control cell division in differentiating nerve cells.

ATF/CREB elements in the herpes simplex virus type 1 latency-associated transcript promoter interact with members of the ATF/CREB and AP-1 transcription factor families

The herpes simplex virus type 1 (HSV-1) latency-associated transcript (LAT) promoter 1 (LP1) is an inducible and cell type-specific promoter involved in regulating the production of an 8.3-kb primary LAT transcript during acute and latent infection of peripheral sensory neurons and during subsequent virus reactivation. A number of cis-acting regulatory elements have been identified in LP1, including two cyclic-AMP (cAMP) response element (CRE)-like sequences, designated CRE-1 and CRE-2. CRE-1 has previously been shown to confer cAMP responsiveness to LP1 and to regulate reactivation of HSV-1 from latency in vivo. A role for CRE-2 in modulating inducible activity is not yet as clear; however, it has been shown to support basal expression in neuronal cells in vitro. Electrophoretic mobility shift (EMS) analyses demonstrate that the LP1 CRE-like elements interact with distinct subsets of neuronal ATF/CREB and Jun/Fos proteins including CREB-1, CREB-2, ATF-1, and JunD. The factor-binding properties of each LP1 CRE element distinguish them from each other and from a highly related canonical CRE binding site and the TPA response element (TRE). LP1 CRE-1 shares binding characteristics of both a canonical CRE and a TRE. LP1 CRE-2 is more unusual in that it shares more features of a canonical CRE site than a TRE with two notable exceptions: it does not bind CREB-1 very well and it binds CREB-2 better than the canonical CRE. Interestingly, a substantial proportion of the C1300 neuroblastoma factors that bind to CRE-1 and CRE-2 have been shown to be immunologically related to JunD, suggesting that the AP-1 family of transcription factors may be important in regulating CRE-dependent LP1 transcriptional activity. In addition, we have demonstrated the two HSV-1 LP1 CRE sites to be unique with respect to their ability to bind neuronal AP1-related factors that are regulated by cAMP. These studies suggest that both factor binding and activation of bound factors may be involved in cAMP regulation of HSV-1 LP1 through the CRE elements, and indicate the necessity of investigating the expression and posttranslational modification of a variety of ATF/CREB and AP-1 factors during latency and reactivation.