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

The precise function of alphaherpesvirus tegument proteins and their interactions during the viral life cycle

Alphaherpesvirus is a widespread pathogen that causes diverse diseases in humans and animals and can severely damage host health. Alphaherpesvirus particles comprise a DNA core, capsid, tegument and envelope; the tegument is located between the nuclear capsid and envelope. According to biochemical and proteomic analyses of alphaherpesvirus particles, the tegument contains at least 24 viral proteins and plays an important role in the alphaherpesvirus life cycle. This article reviews the important role of tegument proteins and their interactions during the viral life cycle to provide a reference and inspiration for understanding alphaherpesvirus infection pathogenesis and identifying new antiviral strategies.

A cell cycle regulator, E2F2, and glucocorticoid receptor cooperatively transactivate the bovine alphaherpesvirus 1 immediate early transcription unit 1 promoter

Bovine alphaherpesvirus 1 (BoHV-1) infection causes respiratory tract disorders and immune suppression and may induce bacterial pneumonia. BoHV-1 establishes lifelong latency in sensory neurons after acute infection. Reactivation from latency consistently occurs following stress or intravenous injection of the synthetic corticosteroid dexamethasone (DEX), which mimics stress. The immediate early transcription unit 1 (IEtu1) promoter drives expression of infected cell protein 0 (bICP0) and bICP4, two viral transcriptional regulators necessary for productive infection and reactivation from latency. The IEtu1 promoter contains two glucocorticoid receptor (GR) responsive elements (GREs) that are transactivated by activated GR. GC-rich motifs, including consensus binding sites for specificity protein 1 (Sp1), are in the IEtu1 promoter sequences. E2F family members bind a consensus sequence (TTTCCCGC) and certain specificity protein 1 (Sp1) sites. Consequently, we hypothesized that certain E2F family members activate IEtu1 promoter activity. DEX treatment of latently infected calves increased the number of E2F2+ TG neurons. GR and E2F2, but not E2F1, E2F3a, or E2F3b, cooperatively transactivate a 436-bp cis-regulatory module in the IEtu1 promoter that contains both GREs. A luciferase reporter construct containing a 222-bp fragment downstream of the GREs was transactivated by E2F2 unless two adjacent Sp1 binding sites were mutated. Chromatin immunoprecipitation studies revealed that E2F2 occupied IEtu1 promoter sequences when the BoHV-1 genome was transfected into mouse neuroblastoma (Neuro-2A) or monkey kidney (CV-1) cells. In summary, these findings revealed that GR and E2F2 cooperatively transactivate IEtu1 promoter activity, which is predicted to influence the early stages of BoHV-1 reactivation from latency.

IMPORTANCE

Bovine alpha-herpesvirus 1 (BoHV-1) acute infection in cattle leads to establishment of latency in sensory neurons in the trigeminal ganglia (TG). A synthetic corticosteroid dexamethasone consistently initiates BoHV-1 reactivation in latently infected calves. The BoHV-1 immediate early transcription unit 1 (IEtu1) promoter regulates expression of infected cell protein 0 (bICP0) and bICP4, two viral transcriptional regulators. Hence, the IEtu1 promoter must be activated for the reactivation to occur. The number of TG neurons expressing E2F2, a transcription factor and cell cycle regulator, increased during early stages of reactivation from latency. The glucocorticoid receptor (GR) and E2F2, but not E2F1, E2F3a, or E2F3b, cooperatively transactivated a 436-bp cis-regulatory module (CRM) in the IEtu1 promoter that contains two GR responsive elements. Chromatin immunoprecipitation studies revealed that E2F2 occupies IEtu1 promoter sequences in cultured cells. GR and E2F2 mediate cooperative transactivation of IEtu1 promoter activity, which is predicted to stimulate viral replication following stressful stimuli.

Specificity protein 1 (Sp1) and glucocorticoid receptor (GR) stimulate bovine alphaherpesvirus 1 (BoHV-1) replication and cooperatively transactivate the immediate early transcription unit 1 promoter

Bovine alphaherpesvirus 1 (BoHV-1) infections cause respiratory tract disorders and suppress immune responses, which can culminate in bacterial pneumonia. Following acute infection, BoHV-1 establishes lifelong latency in sensory neurons present in trigeminal ganglia (TG) and unknown cells in pharyngeal tonsil. Latently infected calves consistently reactivate from latency after an intravenous injection of the synthetic corticosteroid dexamethasone (DEX), which mimics the effects of stress. The immediate early transcription unit 1 (IEtu1) promoter drives expression of infected cell protein 0 (bICP0) and bICP4, two key viral transcriptional regulators. The IEtu1 promoter contains two functional glucocorticoid receptor (GR) response elements (GREs), and this promoter is transactivated by GR, DEX, and certain Krüppel transcription factors that interact with GC-rich motifs, including consensus specificity protein 1 (Sp1) binding sites. Based on these observations, we hypothesized that Sp1 stimulates productive infection and transactivates key BoHV-1 promoters. DEX treatment of latently infected calves increased the number of Sp1+ TG neurons and cells in pharyngeal tonsil indicating that Sp1 expression is induced by stress. Silencing Sp1 protein expression with siRNA or mithramycin A, a drug that preferentially binds GC-rich DNA, significantly reduced BoHV-1 replication. Moreover, BoHV-1 infection of permissive cells increased Sp1 steady-state protein levels. In transient transfection studies, GR and Sp1 cooperatively transactivate IEtu1 promoter activity unless both GREs are mutated. Co-immunoprecipitation studies revealed that GR and Sp1 interact in mouse neuroblastoma cells (Neuro-2A) suggesting this interaction stimulates IEtu1 promoter activity. Collectively, these studies suggested that the cellular transcription factor Sp1 enhances productive infection and stress-induced BoHV-1 reactivation from latency.IMPORTANCEFollowing acute infection, bovine alphaherpesvirus 1 (BoHV-1) establishes lifelong latency in sensory neurons in trigeminal ganglia (TG) and pharyngeal tonsil. The synthetic corticosteroid dexamethasone consistently induces BoHV-1 reactivation from latency. The number of TG neurons and cells in pharyngeal tonsil expressing the cellular transcription factor specificity protein 1 (Sp1) protein increases during early stages of dexamethasone-induced reactivation from latency. Silencing Sp1 expression impairs BoHV-1 replication in permissive cells. Interestingly, mithramycin A, a neuroprotective antibiotic that preferentially binds GC-rich DNA, impairs Sp1 functions and reduces BoHV-1 replication suggesting that it is a potential antiviral drug. The glucocorticoid receptor (GR) and Sp1 cooperatively transactivate the BoHV-1 immediate early transcript unit 1 (IEtu1) promoter, which drives expression of infected cell protein 0 (bICP0) and bICP4. Mithramycin A also reduced Sp1- and GR-mediated transactivation of the IEtu1 promoter. These studies revealed that GR and Sp1 trigger viral gene expression and replication following stressful stimuli.

Slug, a Stress-Induced Transcription Factor, Stimulates Herpes Simplex Virus 1 Replication and Transactivates a cis-Regulatory Module within the VP16 Promoter

Stress-mediated activation of the glucocorticoid receptor (GR) and specific stress-induced transcription factors stimulate herpes simplex virus 1 (HSV-1) productive infection, explant-induced reactivation, and immediate early (IE) promoters that drive expression of infected cell protein 0 (ICP0), ICP4, and ICP27. Several published studies concluded the virion tegument protein VP16, ICP0, and/or ICP4 drives early steps of reactivation from latency. Notably, VP16 protein expression was induced in trigeminal ganglionic neurons of Swiss Webster or C57BL/6J mice during early stages of stress-induced reactivation. If VP16 mediates reactivation, we hypothesized stress-induced cellular transcription factors would stimulate its expression. To address this hypothesis, we tested whether stress-induced transcription factors transactivate a VP16 cis-regulatory module (CRM) located upstream of the VP16 TATA box (-249 to -30). Initial studies revealed the VP16 CRM cis-activated a minimal promoter more efficiently in mouse neuroblastoma cells (Neuro-2A) than mouse fibroblasts (NIH-3T3). GR and Slug, a stress-induced transcription factor that binds enhancer boxes (E-boxes), were the only stress-induced transcription factors examined that transactivated the VP16 CRM construct. GR- and Slug-mediated transactivation was reduced to basal levels when the E-box, two 1/2 GR response elements (GREs), or NF-κB binding site was mutated. Previous studies revealed GR and Slug cooperatively transactivated the ICP4 CRM, but not ICP0 or ICP27. Silencing of Slug expression in Neuro-2A cells significantly reduced viral replication, indicating Slug-mediated transactivation of ICP4 and VP16 CRM activity correlates with enhanced viral replication and reactivation from latency. IMPORTANCE Herpes simplex virus 1 (HSV-1) establishes lifelong latency in several types of neurons. Periodically cellular stressors trigger reactivation from latency. Viral regulatory proteins are not abundantly expressed during latency, indicating cellular transcription factors mediate early stages of reactivation. Notably, the glucocorticoid receptor (GR) and certain stress-induced transcription factors transactivate cis-regulatory modules (CRMs) essential for expression of infected cell protein 0 (ICP0) and ICP4, key viral transcriptional regulatory proteins linked to triggering reactivation from latency. Virion protein 16 (VP16) specifically transactivates IE promoter and was also reported to mediate early stages of reactivation from latency. GR and Slug, a stress-induced enhancer box (E-box) binding protein, transactivate a minimal promoter downstream of VP16 CRM, and these transcription factors occupy VP16 CRM sequences in transfected cells. Notably, Slug stimulates viral replication in mouse neuroblastoma cells suggesting Slug, by virtue of transactivating VP16 and ICP4 CRM sequences, can trigger reactivation in certain neurons.

The Cell-Mediated Immune Response against Bovine alphaherpesvirus 1 (BoHV-1) Infection and Vaccination

Bovine Alphaherpesvirus 1 (BoHV-1) is one of the major respiratory pathogens in cattle worldwide. Infection often leads to a compromised host immune response that contributes to the development of the polymicrobial disease known as “bovine respiratory disease”. After an initial transient phase of immunosuppression, cattle recover from the disease. This is due to the development of both innate and adaptive immune responses. With respect to adaptive immunity, both humoral and cell-mediated immunity are required to control infection. Thus, several BoHV-1 vaccines are designed to trigger both branches of the adaptive immune system. In this review, we summarize the current knowledge on cell-mediated immune responses directed against BoHV-1 infection and vaccination.

The Bovine Herpesvirus 1 Latency-Reactivation Cycle, a Chronic Problem in the Cattle Industry

Bovine alphaherpesvirus 1 (BoHV-1) is a persistent and recurring disease that affects cattle worldwide. It is a major contributor to bovine respiratory disease and reproductive failure in the US. A major complication of BoHV-1 arises from the lifelong latent infection established in the sensory ganglia of the peripheral nervous system following acute infection. Lifelong latency is marked by periodic reactivation from latency that leads to virus transmission and transient immunosuppression. Physiological and environmental stress, along with hormone fluctuations, can drive virus reactivation from latency, allowing the virus to spread rapidly. This review discusses the mechanisms of the latency/reactivation cycle, with particular emphasis on how different hormones directly regulate BoHV-1 gene expression and productive infection. Glucocorticoids, including the synthetic corticosteroid dexamethasone, are major effectors of the stress response. Stress directly regulates BoHV-1 gene expression through multiple pathways, including β-catenin dependent Wnt signaling, and the glucocorticoid receptor. Related type 1 nuclear hormone receptors, the androgen and progesterone receptors, also drive BoHV-1 gene expression and productive infection. These receptors form feed-forward transcription loops with the stress-induced Krüppel-like transcription factors KLF4 and KLF15. Understanding these molecular pathways is critical for developing novel therapeutics designed to block reactivation and reduce virus spread and disease.

Stress Triggers Expression of Bovine Herpesvirus 1 Infected Cell Protein 4 (bICP4) RNA during Early Stages of Reactivation from Latency in Pharyngeal Tonsil

Bovine herpesvirus 1 (BoHV-1), an important pathogen of cattle, establishes lifelong latency in sensory neurons within trigeminal ganglia (TG) after acute infection. The BoHV-1 latency-reactivation cycle, like other alphaherpesvirinae subfamily members, is essential for viral persistence and transmission. Notably, cells within pharyngeal tonsil (PT) also support a quiescent or latent BoHV-1 infection. The synthetic corticosteroid dexamethasone, which mimics the effects of stress, consistently induces BoHV-1 reactivation from latency allowing early stages of viral reactivation to be examined in the natural host. Based on previous studies, we hypothesized that stress-induced cellular factors trigger expression of key viral transcriptional regulatory genes. To explore this hypothesis, RNA-sequencing studies compared viral gene expression in PT during early stages of dexamethasone-induced reactivation from latency. Strikingly, RNA encoding infected cell protein 4 (bICP4), which is translated into an essential viral transcriptional regulatory protein, was detected 30 min after dexamethasone treatment. Ninety minutes after dexamethasone treatment bICP4 and, to a lesser extent, bICP0 RNA were detected in PT. All lytic cycle viral transcripts were detected within 3 h after dexamethasone treatment. Surprisingly, the latency related (LR) gene, the only viral gene abundantly expressed in latently infected TG neurons, was not detected in PT during latency. In TG neurons, bICP0 and the viral tegument protein VP16 are expressed before bICP4 during reactivation, suggesting distinct viral regulatory genes mediate reactivation from latency in PT versus TG neurons. Finally, these studies confirm PT is a biologically relevant site for BoHV-1 latency, reactivation from latency, and virus transmission. IMPORTANCE BoHV-1, a neurotropic herpesvirus, establishes, maintains, and reactivates from latency in neurons. BoHV-1 DNA is also detected in pharyngeal tonsil (PT) from latently infected calves. RNA-sequencing studies revealed the viral infected cell protein 4 (bICP4) RNA was expressed in PT of latently infected calves within 30 min after dexamethasone was used to initiate reactivation. As expected, bICP4 RNA was not detected during latency. All lytic cycle viral genes were expressed within 3 h after dexamethasone treatment. Conversely, bICP0 and the viral tegument protein VP16 are expressed prior to bICP4 in trigeminal ganglionic neurons during reactivation. The viral latency related gene, which is abundantly expressed in latently infected neurons, was not abundantly expressed in PT during latency. These studies provide new evidence PT is a biologically relevant site for BoHV-1 latency and reactivation. Finally, we predict other alphaherpesvirinae subfamily members utilize PT as a site for latency and reactivation.

Krüppel-like factor 2a (KLF2A) suppresses GCRV replication by upregulating serpinc1 expression in Ctenopharyngodon idellus kidney (CIK) cells

Krüppel-like factor 2a (KLF2A), a transcription factor of the krüppel-like family, is involved in regulating the immune molecules and is associated with viral infection. However, the function of KLF2A during viral infections in fish remains unclear. In this study, grass carp (Ctenopharyngodon idellus) was used to predict the target genes regulated by KLF2A. The results showed that the candidate target genes included four members of the serpin gene family (serpinb1l2, serpinc1, serpinh1a, and serpinh1b). Dual-luciferase experiments showed that klf2a positively regulates serpinc1 expression. Dose-dependent klf2a overexpression in C. idellus kidney (CIK) cells significantly upregulated the expression of serpinc1. Overexpressing klf2a or serpinc1 in CIK cells activated interferon responses and suppressed grass carp reovirus (GCRV) replication. Klf2a and serpinc1 co-expression inhibited GCRV replication. These results show that klf2a upregulates serpinc1 mRNA expression, promotes type 1 interferon responses, and suppresses GCRV infection. This study provides insights into the regulatory role and biological functions of KLF2A in host-virus interactions in fish.

1 Cellular protein TTC4 and its cofactor HSP90 are pro-viral for bovine herpesvirus 1

Bovine Herpesvirus Type 1 (BoHV-1) infection causes infectious bovine rhinotracheitis and genital disease in cattle, with significant economic and welfare impacts. However, the role of cellular host factors during viral replication remains poorly characterised. A previously performed genome-wide CRISPR knockout screen identified pro- and antiviral host factors acting during BoHV-1 replication. Herein we validate a pro-viral role for a candidate from this screen: the cellular protein tetracopeptide repeat protein 4 (TTC4). We show that TTC4 transcript production is upregulated during BoHV-1 infection. Depletion of TTC4 protein impairs BoHV-1 protein production but does not reduce production of infectious virions, whereas overexpression of exogenous TTC4 results in a significant increase in production of infectious BoHV-1 virions. TTC4 itself is poorly characterized (especially in the context of virus infection), but is a known co-chaperone of heat shock protein 90 (HSP90). HSP90 has a well-characterized pro-viral role during the replication of diverse herpesviruses, and we therefore hypothesized that HSP90 is also pro-viral for BoHV-1. Drug-mediated inhibition of HSP90 using geldanamycin at sub-cytotoxic concentrations inhibited both BoHV-1 protein production and viral genome replication, indicating a pro-viral role for HSP90 during BoHV-1 infection. Our data demonstrates pro-viral roles for both TTC4 and HSP90 during BoHV-1 replication; possibly, interactions between these two proteins are required for optimal BoHV-1 replication, or the two proteins may have independent pro-viral roles.

Independent Cis-Regulatory Modules within the Herpes Simplex Virus 1 Infected Cell Protein 0 (ICP0) Promoter Are Transactivated by Krüppel-like Factor 15 and Glucocorticoid Receptor

A corticosteroid antagonist impairs Herpes Simplex Virus 1 (HSV-1) productive infection and explant-induced reactivation from latency, suggesting corticosteroids and the glucocorticoid receptor (GR) mediate certain aspects of these complex virus-host interactions. GR-hormone complexes regulate transcription positively and negatively, in part, by binding GR response elements (GREs). Recent studies revealed infected cell protein 0 (ICP0), ICP4, and ICP27 promoter/cis-regulatory modules (CRMs) are cooperatively transactivated by GR and Krüppel-like factor 15 (KLF15), which forms a feed-forward transcription loop. We hypothesized the ICP0 promoter contains independent CRMs that are transactivated by GR, KLF15, and the synthetic corticosteroid dexamethasone (DEX). This hypothesis is based on the finding that the ICP0 promoter contains multiple transcription factor binding sites, and GR and KLF15 cooperatively transactivate the full-length ICP0 promoter. ICP0 promoter sequences spanning -800 to -635 (fragment A) were efficiently transactivated by GR, KLF15, and DEX in monkey kidney cells (Vero), whereas GR and DEX significantly enhanced promoter activity in mouse neuroblastoma cells (Neuro-2A). Furthermore, ICP0 fragment B (-458 to -635) was efficiently transactivated by GR, KLF15, and DEX in Vero cells, but not Neuro-2A cells. Finally, fragment D (-232 to -24) was transactivated significantly in Vero cells by GR, KLF15, and DEX, whereas KLF15 and DEX were sufficient for transactivation in Neuro-2A cells. Collectively, these studies revealed efficient transactivation of three independent CRMs within the ICP0 promoter by GR, KLF15, and/or DEX. Finally, GC-rich sequences containing specificity protein 1 (Sp1) binding sites were essential for transactivation.

Progesterone Sporadically Induces Reactivation from Latency in Female Calves but Proficiently Stimulates Bovine Herpesvirus 1 Productive Infection

Acute infection of the ocular, oral, or nasal cavity by bovine herpesvirus 1 (BoHV-1) culminates in lifelong latency in sensory neurons within trigeminal ganglia. The BoHV-1 latency reactivation cycle, including calves latently infected with commercially available modified live vaccines, can lead to reproductive complications, including abortions. Recent studies demonstrated progesterone stimulated BoHV-1 productive infection and sporadically induced reactivation from latency in male rabbits. The progesterone receptor (PR) and progesterone transactivate the immediate early transcription unit 1 (IEtu1) promoter and the infected cell protein 0 (bICP0) early promoter. These viral promoters drive expression of two viral transcriptional regulatory proteins (bICP0 and bICP4) that are crucial for productive infection. Based on these observations, we hypothesize that progesterone induces reactivation in a subset of calves latently infected with BoHV-1. These studies demonstrated progesterone was less efficient than dexamethasone at initiating reactivation from latency in female calves. Notably, heat stress correlated with enhancing the ability of progesterone to induce reactivation from latency. Previous studies demonstrated that heat stress activates the glucocorticoid receptor (GR), which suggested GR activation augments progesterone-mediated reactivation from latency. Additional studies revealed GR and PR cooperatively stimulated productive infection and synergistically transactivated the IEtu1 promoter when cultures were treated with dexamethasone. Mutating one or both GR binding sites in the IEtu1 promoter blocked transactivation. Collectively, these studies indicated that progesterone intermittently triggered reactivation from latency, and heat stress augmented reactivation from reactivation. Finally, these studies suggest progesterone enhances virus spread in tissues and cells where PR is abundantly expressed. IMPORTANCE Steroid hormone fluctuations are predicted to enhance or initiate bovine herpesvirus 1 (BoHV-1) replication and virus spread in cattle. For example, stress increases the incidence of BoHV-1 reactivation from latency in cattle, and the synthetic corticosteroid dexamethasone consistently induces reactivation from latency. The glucocorticoid receptor (GR) and dexamethasone stimulate key viral regulatory promoters and productive infection, in part because the viral genome contains numerous consensus GR-responsive elements (GREs). The progesterone receptor (PR) and GR belong to the type I nuclear hormone receptor family. PR and progesterone specifically bind to and transactivate viral promoters that contain GREs and stimulate BoHV-1 productive infection. Although progesterone did not induce reactivation from latency in female calves as efficiently as dexamethasone, heat stress enhanced progesterone-mediated reactivation from latency. Consequently, we predict that low levels of stressful stimuli can cooperate with progesterone to induce reactivation from latency or promote virus spread.

Stress Induced Transcription Factors Transactivate the Herpes Simplex Virus 1 Infected Cell Protein 27 (ICP27) Transcriptional Enhancer

Following acute infection, herpes simplex virus 1 (HSV-1) establishes lifelong latency in neurons, including sensory neurons within trigeminal ganglia. During latency, lytic cycle viral gene expression is silenced. However, stressful stimuli can trigger reactivation from latency. The viral tegument protein, VP-16, transactivates all immediate early (IE) promoters during productive infection. Conversely, cellular factors are expected to trigger viral gene expression during early stages of reactivation from latency and in non-neuronal cells that do not support high levels of productive infection. The glucocorticoid receptor (GR), synthetic corticosteroid dexamethasone, and certain stress-induced transcription factors cooperatively transactivate infected cell protein 0 (ICP0) and ICP4 promoters. Since ICP27 protein expression is required for productive infection, we hypothesized that the ICP27 promoter is transactivated by stress-induced transcription factors. New studies have demonstrated that ICP27 enhancer sequences were transactivated by GR and Krüppel-like factor 15 (KLF15). Mutation of a consensus Sp1 binding site within ICP27 enhancer sequences impaired transactivation by GR and KLF15. Chromatin immunoprecipitation studies have demonstrated that GR and KLF15 occupy ICP27 promoter sequences during productive infection. Cells transfected with an ICP27 enhancer fragment revealed the GR and KLF15 occupancy of ICP27 enhancer sequences required the intact Sp1 binding site. Notably, GR and KLF15 form a feed-forward transcription loop in response to stress, suggesting these cellular factors promote viral replication following stressful stimuli.

A Pioneer Transcription Factor and Type I Nuclear Hormone Receptors Synergistically Activate the Bovine Herpesvirus 1 Infected Cell Protein 0 (ICP0) Early Promoter

Following bovine herpesvirus 1 (BoHV-1) acute infection of ocular, oral, or nasal cavities, sensory neurons within trigeminal ganglia are an important site for latency. Stress, as mimicked by the synthetic corticosteroid dexamethasone, consistently induces reactivation from latency. Expression of two key viral transcriptional regulatory proteins, BoHV-1 infected cell protein 0 (bICP0) and bICP4, are regulated by sequences within the immediate early promoter (IEtu1). A separate early promoter also drives bICP0 expression, presumably to ensure sufficient levels of this important transcriptional regulatory protein. Productive infection and bICP0 early promoter activity are cooperatively transactivated by Krüppel-like factor 4 (KLF4) and a type I nuclear hormone receptor (NHR), androgen receptor, glucocorticoid receptor, or progesterone receptor. The bICP0 early promoter contains three separate transcriptional enhancers that mediate cooperative transactivation. In contrast to the IEtu1 promoter, the bICP0 early promoter lacks consensus type I NHR binding sites. Consequently, we hypothesized that KLF4 and Sp1 binding sites are essential for type I NHR and KLF4 to transactivate the bICP0 promoter. Mutating KLF4 and Sp1 binding sites in each enhancer domain significantly reduced transactivation by KLF4 and a type I NHR. Chromatin immunoprecipitation (ChIP) studies demonstrated that occupancy of bICP0 early promoter sequences by KLF4 and type I NHR is significantly reduced when KLF4 and/or Sp1 binding sites are mutated. These studies suggest that cooperative transactivation of the bICP0 E promoter by type I NHRs and a stress-induced pioneer transcription factor (KLF4) promote viral replication and spread in neurons or nonneural cells in reproductive tissue. IMPORTANCE Understanding how stressful stimuli and changes in the cellular milieu mediate viral replication and gene expression in the natural host is important for developing therapeutic strategies that impair virus transmission and disease. For example, bovine herpesvirus 1 (BoHV-1) reactivation from latency is consistently induced by the synthetic corticosteroid dexamethasone, which mimics the effects of stress. Furthermore, BoHV-1 infection increases the incidence of abortion in pregnant cows, suggesting that sex hormones stimulate viral growth in certain tissues. Previous studies revealed that type I nuclear hormone receptors (NHRs) (androgen, glucocorticoid, or progesterone) and a pioneer transcription factor, Krüppel-like factor 4 (KLF4), cooperatively transactivate the BoHV-1 infected cell protein 0 (bICP0) early promoter. Transactivation was mediated by Sp1 and/or KLF4 consensus binding sites within the three transcriptional enhancers. These studies underscore the complexity by which BoHV-1 exploits type I NHR fluctuations to enhance viral gene expression, replication, and transmission in the natural host.

Regulation of Krüppel-Like Factor 15 Expression by Herpes Simplex Virus Type 1 or Bovine Herpesvirus 1 Productive Infection

Expression of Krüppel-like factor 15 (KLF15), a stress-induced transcription factor, is induced during bovine herpesvirus 1 (BoHV-1) reactivation from latency, and KLF15 stimulates BoHV-1 replication. Transient transfection studies revealed that KLF15 and glucocorticoid receptor (GR) cooperatively transactivate the BoHV-1-immediate-early transcription unit 1 (IEtu1), herpes simplex virus type 1 (HSV-1) infected cell protein 0 (ICP0), and ICP4 promoters. The IEtu1 promoter drives expression of bICP0 and bICP4, two key BoHV-1 transcriptional regulatory proteins. Based on these studies, we hypothesized infection is a stressful stimulus that increases KLF15 expression and enhances productive infection. New studies demonstrated that silencing KLF15 impaired HSV-1 productive infection, and KLF15 steady-state protein levels were increased at late stages of productive infection. KLF15 was primarily localized to the nucleus following infection of cultured cells with HSV-1, but not BoHV-1. When cells were transfected with a KLF15 promoter construct and then infected with HSV-1, promoter activity was significantly increased. The ICP0 gene, and to a lesser extent, bICP0 transactivated the KLF15 promoter in the absence of other viral proteins. In contrast, BoHV-1 or HSV-1 encoded VP16 had no effect on KLF15 promoter activity. Collectively, these studies revealed that HSV-1 and BoHV-1 productive infection increased KLF15 steady-state protein levels, which correlated with increased virus production.

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.

Inhibition of Stress-Induced Viral Promoters by a Bovine Herpesvirus 1 Non-Coding RNA and the Cellular Transcription Factor, β-Catenin

The ability to establish, maintain, and reactivate from latency in sensory neurons within trigeminal ganglia (TG) is crucial for bovine herpesvirus 1 (BoHV-1) transmission. In contrast to lytic infection, the only viral gene abundantly expressed during latency is the latency-related (LR) gene. The synthetic corticosteroid dexamethasone consistently induces reactivation from latency, in part because the glucocorticoid receptor (GR) transactivates viral promoters that drive expression of key viral transcriptional regulator proteins (bICP0 and bICP4). Within hours after dexamethasone treatment of latently infected calves, LR gene products and β-catenin are not readily detected in TG neurons. Hence, we hypothesized that LR gene products and/or β-catenin restrict GR-mediated transcriptional activation. A plasmid expressing LR RNA sequences that span open reading frame 2 (ORF2-Stop) inhibited GR-mediated transactivation of the BoHV-1 immediate early transcription unit 1 (IEtu1) and mouse mammary tumor virus (MMTV) promoter activity in mouse neuroblastoma cells (Neuro-2A). ORF2-Stop also reduced productive infection and GR steady-state protein levels in transfected Neuro-2A cells. Additional studies revealed that the constitutively active β-catenin mutant reduced the transactivation of the IEtu1 promoter by GR and dexamethasone. Collectively, these studies suggest ORF2 RNA sequences and Wnt/β-catenin signaling pathway actively promote maintenance of latency, in part, by impairing GR-mediated gene expression.

Specific Akt Family Members Impair Stress-Mediated Transactivation of Viral Promoters and Enhance Neuronal Differentiation: Important Functions for Maintaining Latency

Neurotropic Alphaherpesvirinae subfamily members such as bovine herpesvirus 1 (BoHV-1) and herpes simplex virus 1 (HSV-1) establish and maintain lifelong latent infections in neurons. Following infection of ocular, oral, or nasal cavities, sensory neurons within trigeminal ganglia (TG) are an important site for latency. Certain external stressors can trigger reactivation from latency, in part because activation of the glucocorticoid receptor (GR) stimulates productive infection and promoters that drive expression of key viral transcriptional regulators. The Akt serine/threonine protein kinase family is linked to maintaining latency. For example, Akt3 is detected in more TG neurons during BoHV-1 latency than in reactivation and uninfected calves. Furthermore, Akt signaling correlates with maintaining HSV-1 latency in certain neuronal models of latency. Finally, an active Akt protein kinase is crucial for the ability of the HSV-1 latency-associated transcript (LAT) to inhibit apoptosis in neuronal cell lines. Consequently, we hypothesized that viral and/or cellular factors impair stress-induced transcription and reduce the incidence of reactivation triggered by low levels of stress. New studies demonstrate that Akt1 and Akt2, but not Akt3, significantly reduced GR-mediated transactivation of the BoHV-1 immediate early transcription unit 1 (IEtu1) promoter, the HSV-1 infected cell protein 0 (ICP0) promoter, and the mouse mammary tumor virus long terminal repeat (MMTV-LTR). Akt3, but not Akt1 or Akt2, significantly enhanced neurite formation in mouse neuroblastoma cells, which correlates with repairing damaged neurons. These studies suggest that unique biological properties of the three Akt family members promote the maintenance of latency in differentiated neurons.IMPORTANCE External stressful stimuli are known to increase the incidence of reactivation of Alphaherpesvirinae subfamily members. Activation of the glucocorticoid receptor (GR) by the synthetic corticosteroid dexamethasone (DEX) stimulates bovine herpesvirus 1 (BoHV-1) and herpes simplex virus 1 (HSV-1) reactivation. Furthermore, GR and dexamethasone stimulate productive infection and promoters that drive expression of viral transcriptional regulators. These observations lead us to predict that stress-induced transcription is impaired by factors abundantly expressed during latency. Interestingly, activation of the Akt family of serine/threonine protein kinases is linked to maintenance of latency. New studies reveal that Akt1 and Ak2, but not Akt3, impaired GR- and dexamethasone-mediated transactivation of the BoHV-1 immediate early transcription unit 1 and HSV-1 ICP0 promoters. Strikingly, Akt3, but not Akt1 or Akt2, stimulated neurite formation in mouse neuroblastoma cells, a requirement for neurogenesis. These studies provide insight into how Akt family members may promote the maintenance of lifelong latency.

Bovine alphaherpesvirus 1 (BHV1) infection in testes and epididymis from bulls from a slaughterhouse

Bovine alphaherpesvirus 1 (BHV1) is an agent associated with reproductive disease in cattle. Viral pathogenicity is related to disorders such as temporary infertility, embryonic death, and abortions in affected animals. Considering that natural infections in genital organs of males are understudied, this investigation evaluated the presence of BHV1 in both testicular and epididymal tissues obtained from naturally infected bulls by the evaluation of the presence of the BHV1 genome and antigens. Sixty samples of blood and genital organs of 60 bulls that were not vaccinated against BHV1 were assayed. Fragments from testes and head, body, and tail of epididymides were processed and analyzed by nested PCR and immunofluorescence with confocal laser scanning microscopy. Also, the BHV1 gB glycoprotein gene of 14 positive samples was partially sequenced. The percentage of BHV1 presence obtained by the immunolocalization assay corresponded to 95.9% of the testes, 100% of the epidydimal tissue in the head and tail portions, and 98% of the epididymal body. The nested PCR assay detected the viral nucleic acid in 59.2% of the testicular tissue and in 65.3, 75.5, and 83.7% of epididymis head, body, and tail samples, respectively. The partial sequences analyzed presented 100% of identity with other BHV1 strains. Accordingly, BHV1 detection in testes and epididymides of naturally infected bulls suggests that these organs may be sources of viral infection for semen.

Single AAV-Mediated CRISPR-SaCas9 Inhibits HSV-1 Replication by Editing ICP4 in Trigeminal Ganglion Neurons

Herpes simplex keratitis (HSK) is the most common cause of corneal blindness in developed nations, caused by primary or recurrent herpes simplex virus 1 (HSV-1) infection of the cornea. Latent infection of HSV-1, especially in the trigeminal ganglion (TG), causes recurrence of HSV-1 infection. As antiviral treatment is not effective on latent HSV-1, to test the possibility of inhibiting HSV-1 by SpCas9 (Streptococcus pyogenes Cas9) or SaCas9 (Staphylococcus aureus Cas9), ICP0 and ICP4, two important genes required for HSV-1 replication and reactivation, were chosen as targets. In Vero cells, SpCas9 and SaCas9 targeting ICP0 or ICP4 can effectively inhibit the proliferation of HSV-1 without affecting cell viability. No significant guide RNA (gRNA)-dependent off-targets were observed in the human genome by digenome sequencing and deep sequencing verification. Adeno-associated virus 1 (AAV1)-mediated delivery of SaCas9 inhibits HSV-1 replication by targeting ICP4 in mouse primary TG neuronal cells. SpCas9 and SaCas9 are able to inhibit HSV-1 infection in Vero cells and mouse TG neuronal cultures with high efficiency and good biosafety. AAV1-mediated delivery of SaCas9 shows great potential in treating HSK and inhibiting HSV-1 in TG neurons. Further investigations may be needed to test the inhibition of latent infections, which may result in the development of novel methods for treating viral diseases.

Ivermectin Inhibits Bovine Herpesvirus 1 DNA Polymerase Nuclear Import and Interferes with Viral Replication

Bovine herpesvirus1 (BoHV-1) is a major bovine pathogen. Despite several vaccines being available to prevent viral infection, outbreaks are frequent and cause important economic consequences worldwide. The development of new antiviral drugs is therefore highly desirable. In this context, viral genome replication represents a potential target for therapeutic intervention. BoHV-1 genome is a dsDNA molecule whose replication takes place in the nuclei of infected cells and is mediated by a viral encoded DNA polymerase holoenzyme. Here, we studied the physical interaction and subcellular localization of BoHV-1 DNA polymerase subunits in cells for the first time. By means of co-immunoprecipitation and confocal laser scanning microscopy (CLSM) experiments, we could show that the processivity factor of the DNA polymerase pUL42 is capable of being autonomously transported into the nucleus, whereas the catalytic subunit pUL30 is not. Accordingly, a putative classic NLS (cNLS) was identified on pUL42 but not on pUL30. Importantly, both proteins could interact in the absence of other viral proteins and their co-expression resulted in accumulation of UL30 to the cell nucleus. Treatment of cells with Ivermectin, an anti-parasitic drug which has been recently identified as an inhibitor of importin α/β-dependent nuclear transport, reduced UL42 nuclear import and specifically reduced BoHV-1 replication in a dose-dependent manner, while virus attachment and entry into cells were not affected. Therefore, this study provides a new option of antiviral therapy for BoHV-1 infection with Ivermectin.

Two Pioneer Transcription Factors, Krüppel-Like Transcription Factor 4 and Glucocorticoid Receptor, Cooperatively Transactivate the Bovine Herpesvirus 1 ICP0 Early Promoter and Stimulate Productive Infection

An important site for bovine herpesvirus 1 (BoHV-1) latency is sensory neurons within trigeminal ganglia (TG). The synthetic corticosteroid dexamethasone consistently induces BoHV-1 reactivation from latency. Expression of four Krüppel-like transcription factors (KLF), i.e., KLF4, KLF6, PLZF (promyelocytic leukemia zinc finger), and KLF15, are induced in TG neurons early during dexamethasone-induced reactivation. The glucocorticoid receptor (GR) and KLF15 form a feed-forward transcription loop that cooperatively transactivates the BoHV-1 immediate early transcription unit 1 (IEtu1) promoter that drives bovine infected cell protein 0 (bICP0) and bICP4 expression. Since the bICP0 gene also contains a separate early (E) promoter, we tested the hypothesis that GR and KLF family members transactivate the bICP0 E promoter. GR and KLF4, both pioneer transcription factors, cooperated to stimulate bICP0 E promoter activity in a ligand-independent manner in mouse neuroblastoma cells (Neuro-2A). Furthermore, GR and KLF4 stimulated productive infection. Mutating both half GR binding sites did not significantly reduce GR- and KLF4-mediated transactivation of the bICP0 E promoter, suggesting that a novel mechanism exists for transactivation. GR and KLF15 cooperatively stimulated bICP0 activity less efficiently than GR and KL4: however, KLF6, PLZF, and GR had little effect on the bICP0 E promoter. GR, KLF4, and KLF15 occupied bICP0 E promoter sequences in transfected Neuro-2A cells. GR and KLF15, but not KLF4, occupied the bICP0 E promoter at late times during productive infection of bovine cells. Collectively, these studies suggest that cooperative transactivation of the bICP0 E promoter by two pioneer transcription factors (GR and KLF4) correlates with stimulating lytic cycle viral gene expression following stressful stimuli.IMPORTANCE Bovine herpesvirus 1 (BoHV-1), an important bovine pathogen, establishes lifelong latency in sensory neurons. Reactivation from latency is consistently induced by the synthetic corticosteroid dexamethasone. We predict that increased corticosteroid levels activate the glucocorticoid receptor (GR). Consequently, viral gene expression is stimulated by the activated GR. The immediate early transcription unit 1 promoter (IEtu1) drives expression of two viral transcriptional regulatory proteins, bovine infected cell protein 0 (bICP0) and bICP4. Interestingly, a separate early promoter also drives bICP0 expression. Two pioneer transcription factors, GR and Krüppel-like transcription factor 4 (KLF4), cooperatively transactivate the bICP0 early (E) promoter. GR and KLF15 cooperate to stimulate bICP0 E promoter activity but significantly less than GR and KLF4. The bICP0 E promoter contains enhancer-like domains necessary for GR- and KLF4-mediated transactivation that are distinct from those for GR and KLF15. Stress-induced pioneer transcription factors are proposed to activate key viral promoters, including the bICP0 E promoter, during early stages of reactivation from latency.

Progesterone increases the incidence of bovine herpesvirus 1 reactivation from latency and stimulates productive infection

Bovine herpesvirus 1 (BoHV-1), including modified live vaccines, can cause abortions in pregnant cows. Progesterone maintains pregnancy and promotes spermiogenesis and testosterone biosynthesis in males: furthermore, progesterone is a neuro-steroid. Recent published studies demonstrated progesterone stimulated the BoHV-1 immediate early transcription unit 1 (IEtu1) promoter, and two glucocorticoid receptor response elements within the promoter were required for progesterone mediated transactivation. In this study, we tested whether progesterone induces reactivation from latency in rabbits. As expected, the synthetic corticosteroid dexamethasone consistently induced reactivation from latency in males and females. While progesterone induced reactivation from latency in approximately one-half of male rabbits, virus shedding was sporadic compared to dexamethasone and less efficient in female rabbits. Progesterone significantly increased productive infection in rabbit skin cells, which correlated with stimulating reactivation. These studies suggest progesterone promotes BoHV-1 spread in cattle, in part, by increasing the frequency of reactivation from latency.

Distinctive features of bovine alphaherpesvirus types 1 and 5 and the virus-host interactions that might influence clinical outcomes

Bovine herpesvirus types 1 (BoHV-1) and 5 (BoHV-5) are two closely related alphaherpesviruses. BoHV-1 causes several syndromes in cattle, including respiratory disease and sporadic cases of encephalitis, whereas BoHV-5 is responsible for meningoencephalitis in calves. Although both viruses are neurotropic, they differ in their neuropathogenic potential. This review summarizes the findings on the specific mechanisms and pathways known to modulate the pathogenesis of BoHV-1 and BoHV-5, particularly in relation to respiratory and neurological syndromes, which characterize BoHV-1 and BoHV-5 infections, respectively.

Bovine herpesvirus 1 can cross the intact zona pellucida of bovine oocytes after artificial infection

Bovine herpesvirus 1 (BHV1) is an important bovine pathogen, responsible for respiratory diseases and reproductive problems. This study investigated the penetration capacity of BHV1 into oocytes after co-incubation for either 1 h or 24 h. Immunofluorescence assays in cumulus-oocyte complexes (COCs) and denuded oocytes (without the presence of cumulus cells) were performed and evaluated using confocal laser scanning microscopy. Blood samples and ovaries from BHV1 seronegative cows were used. The oocytes recovered were divided into two groups. Group I comprised COCs (n = 312) and denuded oocytes (n = 296), which were experimentally infected with BHV1 and incubated for 1 h at 38.5°C and 5% CO₂. Group II comprised COCs (n = 425) and denuded oocytes (n = 405), which were co-incubated with BHV1 under the same conditions for 24 h. The negative control of these two groups was respectively subjected to the same protocol, except for exposure to BHV1. To our knowledge, this study provides the first evidence of BHV1 detection within COCs and denuded oocytes exhibiting intact zona pellucida when co-incubated with the virus for 24 h. Immunolocalization also confirmed the presence of BHV1 in the cytoplasm of the cumulus cells of all COCs exposed to the virus after both incubation periods. In conclusion, detection of BHV1 inside oocytes has a great meaning for the field of animal reproduction. The detection of BHV1 in different layers of cumulus cells also demonstrates that these cells are sources of viral infection.

Bovine Herpesvirus 1 Counteracts Immune Responses and Immune-Surveillance to Enhance Pathogenesis and Virus Transmission

Infection of cattle by bovine herpesvirus 1 (BoHV-1) can culminate in upper respiratory tract disorders, conjunctivitis, or genital disorders. Infection also consistently leads to transient immune-suppression. BoHV-1 is the number one infectious agent in cattle that is associated with abortions in cattle. BoHV-1, as other α-herpesvirinae subfamily members, establishes latency in sensory neurons. Stressful stimuli, mimicked by the synthetic corticosteroid dexamethasone, consistently induce reactivation from latency in latently infected calves and rabbits. Increased corticosteroid levels due to stress have a two-pronged effect on reactivation from latency by: (1) directly stimulating viral gene expression and replication, and (2) impairing antiviral immune responses, thus enhancing virus spread and transmission. BoHV-1 encodes several proteins, bICP0, bICP27, gG, UL49.5, and VP8, which interfere with key antiviral innate immune responses in the absence of other viral genes. Furthermore, the ability of BoHV-1 to infect lymphocytes and induce apoptosis, in particular CD4+ T cells, has negative impacts on immune responses during acute infection. BoHV-1 induced immune-suppression can initiate the poly-microbial disorder known as bovine respiratory disease complex, which costs the US cattle industry more than one billion dollars annually. Furthermore, interfering with antiviral responses may promote viral spread to ovaries and the developing fetus, thus enhancing reproductive issues associated with BoHV-1 infection of cows or pregnant cows. The focus of this review is to describe the known mechanisms, direct and indirect, by which BoHV-1 interferes with antiviral immune responses during the course of infection.

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.

Detection of bovine herpesvirus 1 in genital organs of naturally infected cows

Bovine herpesvirus 1 (BoHV-1) is a causative agent of respiratory diseases in cattle, and infection with BoHV-1 can cause reproductive failure. There are few studies regarding infections in natural conditions in the reproductive organs of bovine animals. In this context, this study investigated the presence of BoHV-1 in the uterus, oviducts, and ovarian tissues of naturally infected cows. The three genital structures were evaluated for the presence or absence of BoHV-1 by immunofluorescence assay using confocal scanning laser microscopy. Blood and genital organ samples of 75 cows unvaccinated against BoHV-1 were used. Fragments of uterus, oviduct, and ovarian tissue were processed and analyzed by confocal scanning laser microscopy. Neutralization by antibodies was observed in 54.7% (41/75) of the serum samples tested. BoHV-1 were detected in the uterus of all the seropositive cows. The oviducts contained BoHV-1 in 73.2% of the samples and the ovaries contained BoHV-1 in 58.5% of the samples from seropositive animals. The presence of the virus was not observed in any of the genital organs of seronegative animals. There was no correlation between the antibody titer and the detection of BoHV-1 in positive tissue in the different genital organs or with the number of infected structures per animal. The detection of BoHV-1 in 100% of the uterus samples from seropositive cows suggests that this organ may be a source of infection for the fetus, resulting in abortion. Further studies on the mechanism by which BoHV-1 infects the fetus via the uterine route should be performed.

Bovine herpesvirus 1 can impact the bovine oocyte development during in vitro maturation

Bovine herpesvirus 1 (BoHV-1) disseminates easily, is difficult to control, and is widely spread in cattle herds worldwide. BoHV-1 causes a broad range of losses to the cattle industry, mainly concerning reproduction. Previous studies involving experimental infection of BoHV-1 in an in vitro embryo production system have reported impairment of embryonic development by BoHV-1. In this study, we evaluated the interference of BoHV-1 in the in vitro maturation system of cumulus-oocyte complexes (COCs) and denuded oocytes (DOs) cultured with a cumulus cell suspension. Blood samples and ovaries were collected from slaughterhouse cows unvaccinated against BoHV-1. Using virus neutralization assays, the seropositive animals were classified according to their antibody titers. The oocytes were recovered by follicular aspiration and divided into two groups, COCs and DOs, which were evaluated for their nuclear maturation capacity using immunofluorescence assays by laser scanning confocal microscopy. Two experiments were carried out: (I) in vitro maturation of COCs and DOs after artificial infection of seronegative animals and (II) in vitro maturation of COCs and DOs of seropositive animals. In experiment I, a difference (P < 0.01) was observed between the maturation rates of the control group COCs (78.2%) and the infected COCs (43.6%). In experiment II, there was a difference (P < 0.01) in the maturation rate between animals with antibody titers ≥16 (56.9%) and the control group (79.4%). Immunofluorescence assays identified BoHV-1 in the COCs and DOs. Therefore, it was concluded that BoHV-1 affects the in vitro maturation process in both in vitro and natural infections.

Synergistic Activation of Bovine Herpesvirus 1 Productive Infection and Viral Regulatory Promoters by the Progesterone Receptor and Krüppel-Like Transcription Factor 15

Bovine herpesvirus 1 (BoHV-1), including modified live vaccines, readily infects the fetus and ovaries, which can lead to reproductive failure. The BoHV-1 latency reactivation cycle in sensory neurons may further complicate reproductive failure in pregnant cows. The immediate early transcription unit 1 (IEtu1) promoter drives expression of important viral transcriptional regulators (bICP0 and bICP4). This promoter contains two functional glucocorticoid receptor (GR) response elements (GREs) that have the potential to stimulate productive infection following stressful stimuli. Since progesterone and the progesterone receptor (PR) can activate many GREs, we hypothesized that the PR and/or progesterone regulates productive infection and viral transcription. New studies demonstrated that progesterone stimulated productive infection. Additional studies revealed the PR and Krüppel-like transcription factor 15 (KLF15) cooperated to stimulate productive infection and IEtu1 promoter activity. IEtu1 promoter activation required both GREs, which correlated with the ability of the PR to interact with wild-type (wt) GREs but not mutant GREs. KLF15 also cooperated with the PR to transactivate the bICP0 early promoter, a promoter that maintains bICP0 protein expression during productive infection. Intergenic viral DNA fragments (less than 400 bp) containing two GREs and putative KLF binding sites present within genes encoding unique long 52 (UL-52; component of DNA primase/helicase complex), Circ, bICP4, and IEtu2 were stimulated by KLF15 and the PR more than 10-fold, suggesting that additional viral promoters are activated by these transcription factors. Collectively, these studies suggest progesterone and the PR promote BoHV-1 spread to reproductive tissues, thus increasing the incidence of reproductive failure.IMPORTANCE Bovine herpesvirus 1 (BoHV-1) is the most frequently diagnosed cause of abortions in pregnant cows and can cause "abortion storms" in susceptible herds. Virulent field strains and even commercially available modified live vaccines can induce abortion, in part because BoHV-1 replicates efficiently in the ovary and corpus luteum. We now demonstrate that progesterone and the progesterone receptor (PR) stimulate productive infection. The BoHV-1 genome contains approximately 100 glucocorticoid receptor (GR) response elements (GREs). Interestingly, the PR can bind and activate many promoters that contain GREs. The PR and Krüppel-like transcription factor 15 (KLF15), which regulate key steps during embryo implantation, cooperate to stimulate productive infection and two viral promoters that drive expression of key viral transcriptional regulators. These studies suggest that the ability of progesterone and the PR to stimulate productive infection has the potential to promote virus spread in reproductive tissue and induce reproductive failure.

The bovine herpesvirus 1 regulatory proteins, bICP4 and bICP22, are expressed during the escape from latency

Following acute infection of mucosal surfaces by bovine herpesvirus 1 (BoHV-1), sensory neurons are a primary site for lifelong latency. Stress, as mimicked by the synthetic corticosteroid dexamethasone, consistently induces reactivation from latency. Two viral regulatory proteins (VP16 and bICP0) are expressed within 1 h after calves latently infected with BoHV-1 are treated with dexamethasone. Since the immediate early transcription unit 1 (IEtu1) promoter regulates both BoHV-1 infected cell protein 0 (bICP0) and bICP4 expressions, we hypothesized that the bICP4 protein is also expressed during early stages of reactivation from latency. In this study, we tested whether bICP4 and bICP22, the only other BoHV-1 protein known to be encoded by an immediate early gene, were expressed during reactivation from latency by generating peptide-specific antiserum to each protein. bICP4 and bICP22 protein expression were detected in trigeminal ganglionic (TG) neurons during early phases of dexamethasone-induced reactivation from latency, operationally defined as the escape from latency. Conversely, bICP4 and bICP22 were not readily detected in TG neurons of latently infected calves. In summary, it seems clear that all proteins encoded by known BoHV-1 IE genes (bICP4, bICP22, and bICP0) were expressed during early stages of dexamethasone-induced reactivation from latency.

The Cellular Coactivator HCF-1 Is Required for Glucocorticoid Receptor-Mediated Transcription of Bovine Herpesvirus 1 Immediate Early Genes

Following productive infection, bovine herpesvirus 1 (BoHV-1) establishes latency in sensory neurons. As in other alphaherpesviruses, expression of BoHV-1 immediate early (IE) genes is regulated by an enhancer complex containing the viral IE activator VP16, the cellular transcription factor Oct-1, and transcriptional coactivator HCF-1, which is assembled on an IE enhancer core element (TAATGARAT). Expression of the IE transcription unit that encodes the viral IE activators bICP0 and bICP4 may also be induced by the activated glucocorticoid receptor (GR) via two glucocorticoid response elements (GREs) located upstream of the enhancer core. Strikingly, lytic infection and reactivation from latency are consistently enhanced by glucocorticoid treatment in vivo As the coactivator HCF-1 is essential for IE gene expression of alphaherpesviruses and recruited by multiple transcription factors, we tested whether HCF-1 is required for glucocorticoid-induced IE gene expression. Depletion of HCF-1 reduced GR-mediated activation of the IE promoter in mouse neuroblastoma cells (Neuro-2A). More importantly, HCF-1-mediated GR activation of the promoter was dependent on the presence of GRE sites but independent of the TAATGARAT enhancer core element. HCF-1 was also recruited to the GRE region of a promoter lacking the enhancer core, consistent with a direct role of the coactivator in mediating GR-induced transcription. Similarly, during productive lytic infection, HCF-1 and GR occupied the IE region containing the GREs. These studies indicate HCF-1 is critical for GR activation of the viral IE genes and suggests that glucocorticoid induction of viral reactivation proceeds via an HCF-1-GR mechanism in the absence of the viral IE activator VP16.IMPORTANCE BoHV-1 transcription is rapidly activated during stress-induced reactivation from latency. The immediate early transcription unit 1 (IEtu1) promoter is regulated by the GR via two GREs. The IEtu1 promoter regulates expression of two viral transcriptional regulatory proteins, infected cell proteins 0 and 4 (bICP0 and bICP4), and thus must be stimulated during reactivation. This study demonstrates that activation of the IEtu1 promoter by the synthetic corticosteroid dexamethasone requires HCF-1. Interestingly, the GRE sites, but not the IE enhancer core element (TAATGARAT), were required for HCF-1-mediated GR promoter activation. The GR and HCF-1 were recruited to the IEtu1 promoter in transfected and infected cells. Collectively, these studies indicate that HCF-1 is critical for GR activation of the viral IE genes and suggest that an HCF-1-GR complex can stimulate the IEtu1 promoter in the absence of the viral IE activator VP16.

Detection of bovine herpesvirus 1 in cumulus-oocyte complexes of cows

Bovine herpesvirus 1 (BoHV-1) is the causative agent of infectious bovine rhinotracheitis (IBR) and is also associated with reproductive failure. This study investigated the presence of BoHV-1 in cumulus-oocyte complexes (COCs) of naturally-infected cows without clinical signs of IBR. The presence of BoHV-1 in COCs was evaluated by immunofluorescence using confocal laser scanning microscopy. Blood samples and ovaries from 82 cows that had not been vaccinated against BoHV-1 were collected for serological analysis. COCs were divided into two pools: COCs derivate from seropositive cows and from seronegative cows. Then, the samples were processed for confocal microscopy analysis. The results indicated that 61% (50/82) of cows were seropositive for BoHV-1. A total of 719 COCs were obtained from the cows and processed. None of 276 COCs from the 32 seronegative cows presented BoHV-1. However, BoHV-1 was present in the cytoplasm of cumulus cells from 158 out of 443 COCs aspirated from the seropositive cows. The detection of BoHV-1 in the COCs of seropositive cows suggests that the COCs of naturally-infected, asymptomatic cows may be infected with BoHV-1.

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.