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

Human alpha-herpesvirus 1 (HSV-1) viral replication and reactivation from latency are expedited by the glucocorticoid receptor

Acute human alpha-herpesvirus 1 (HSV-1) infection leads to infection of neurons within trigeminal ganglia (TG), brainstem, and other regions of the central nervous system. Lytic cycle viral gene expression is subsequently silenced, a subset of neurons survive infection, and life-long latency is established. In contrast to lytic infection, the latency-associated transcript (LAT) is the only viral gene product abundantly expressed in latently infected neurons. Stress (acute or chronic), UV light, or heat stress increases the incidence of reactivation from latency in humans and mouse models of infection. Ironically, these divergent reactivation stimuli activate the glucocorticoid receptor (GR). Recent studies revealed GR and Krüppel-like factors (KLF), KLF4 or KLF15 for example, cooperatively transactivate the infected cell protein 0 (ICP0) promoter and cis-regulatory motifs that activate ICP4 and ICP27 promoter activity. GR and KLF4 are "pioneer transcription factors" that specifically bind DNA even when it exists as heterochromatin; consequently, chromatin is remodeled, and transcription is activated. Conversely, a VP16 cis-regulatory motif is transactivated by GR and Slug but not KLF family members. Female mice that express a GR containing a serine → alanine mutation at position 229 (GRS229A) shed significantly lower HSV-1 levels compared with age-matched male GRS229A mice or wild-type parental C57BL/6 mice during reactivation from latency. These observations imply GR and stress-induced cellular transcription factors play an important role during reactivation from latency by activating key viral promoters. GR activation may also enhance virus spread by impairing immune and inflammatory responses.

Murine nasal-associated lymphoid tissue (NALT) harbors human alphaherpesvirus 1 (HSV-1) DNA during latency, and dexamethasone triggers viral replication

Human alphaherpesvirus 1 (HSV-1) acute infection causes conjunctivitis, encephalitis, genital lesions, and herpes esophagitis. Following acute infection, HSV-1 and other alpha-herpesvirinae subfamily members establish life-long latency in neurons within the trigeminal ganglia and central nervous system. Notably, certain animal alpha-herpesvirinae subfamily members, including bovine alphaherpesvirus 1 (BoHV-1), canine herpesvirus 1, equine herpesvirus 4, and pseudorabies virus, establish a quiescent/latent infection in tonsils. BoHV-1 viral gene expression and virus shedding from tonsils also occur during reactivation from latency in calves. Consequently, we tested whether nasopharyngeal lymphoid tissue (NALT) harbors HSV-1 DNA in latently infected mice because it is structurally and functionally comparable with tonsils. NALT prepared from latently infected mice consistently contained viral DNA, but infectious virus was not detected. In contrast to latently infected TG neurons, the HSV-1 latency-associated transcript was not detected in NALT of latently infected mice. HSV-1 DNA levels, immediate early RNA expression, and virus shedding were readily detected when NALT explants were cultured with a medium containing the synthetic corticosteroid dexamethasone for 48 h. Increased viral DNA and virus production were not detected in NALT explants when incubated with a medium lacking dexamethasone. Sorting cells from NALT of HSV-1 latently infected mice revealed that dendritic cells, microfold cells, and natural killer cells, but not B or T cells, harbor HSV-1 DNA, and infectious virus was readily detected when cultured in medium containing dexamethasone. In summary, certain NALT cells consistently contain viral DNA in latently infected mice, and dexamethasone triggers viral gene expression and virus production.

IMPORTANCE

Human alphaherpesvirus 1 (HSV-1) acute infection causes various diseases, including herpes esophagitis. HSV-1 subsequently establishes lifelong latency in neurons within the trigeminal ganglia and central nervous system. Viral DNA, but not infectious virus, was consistently detected in nasopharyngeal lymphoid tissue (NALT) of latently infected mice. NALT is structurally and functionally comparable with the tonsils of other mammals, including humans. RNA and protein expression of infected cell protein 0 (ICP0) and ICP4 plus virus production were consistently detected when NALT explants were cultured with a medium containing dexamethasone, a synthetic corticosteroid. Sorting NALT cells from HSV-1 latently infected mice revealed dendritic cells, microfold cells, and natural killer cells that harbor HSV-1 DNA. Virus shedding was readily detected when viral DNA-positive NALT cells were cultured in a medium containing dexamethasone. These studies revealed that specific NALT cells harbor viral DNA, and dexamethasone triggered viral replication and virus production, suggesting that reactivation from a latent or quiescent infection had occurred.

Distinct effects of glucocorticoid on pseudorabies virus infection in neuron-like and epithelial cells

Pseudorabies virus (PRV) is a porcine neurotropic alphaherpesvirus that infects peripheral tissues of its host, spreads into the nervous system, and establishes a life-long latency in neuronal cells. During productive infection, PRV replicates rapidly and causes pseudorabies or Aujeszky's disease. Reactivation from latent infection in the nervous system may lead to anterograde axonal transport of progeny virions, leading to recurrent infection of the epithelial layer and virus spread. Dexamethasone (DEX), a member of the glucocorticoid family that is widely used in clinical treatment as a high-efficiency glucocorticoid receptor (GR) agonist, is known to trigger reactivation of alphaherpesviruses like PRV and the closely related bovine alphaherpesvirus 1. In the current study, two cell type-dependent distinct regulatory mechanisms of glucocorticoid during PRV infection are described. In neuron-like cells, DEX upregulates expression of PRV IE180 and promotes viral productive infection. In addition, we found that GR activates the IE180 promoter by binding multiple GR response elements. The amino acids A465, P631, and I634 in GR were found to be critical for IE180 promoter activation. The impact of DEX on PRV productive infection in epithelial cells was also investigated. Interestingly, DEX was found to downregulate IE180 expression and suppress PRV infection in epithelial cells. Mechanistically, in epithelial cells, activation of the IE180 promoter by the VP16/Oct-1 (octamer-binding transcription factor 1) complex was suppressed by DEX-mediated degradation of Oct-1 in epithelial cells. In summary, our work reveals two distinct, cell type-dependent biological functions of glucocorticoid during PRV infection in neuron-like and epithelial cells, respectively.IMPORTANCEPseudorabies virus (PRV) can infect mucosal epithelium and the peripheral nervous system of its host, resulting in acute infection in epithelial cells and neuronal cells. In this study, we describe that glucocorticoid promotes PRV replication in neuron-like cells while it suppresses productive infection in epithelial cells through distinct regulations of the viral transactivator IE180, thereby revealing a cell type-dependent regulatory mechanism of glucocorticoid on PRV infection. Therefore, our findings provide a new perspective on the role of glucocorticoids during PRV infection.

Mechanisms of HSV gene regulation during latency and reactivation

Herpes simplex virus 1 and 2 (HSV-1 and HSV-2) are prevalent human pathogens associated with many diseases. After productive (lytic) infection in peripheral tissues, HSV establishes lifelong latent infection in neurons of the peripheral nervous system. Periodic reactivation from latency, triggered by certain stimuli, can resume the lytic cycle. Lytic infection, latent infection and reactivation follow distinct viral gene expression patterns. The switch between the different infection programs is controlled by complicated regulatory mechanisms involving numerous viral and host molecules. Recent studies integrating cutting-edge technologies including neuronal culture techniques have greatly improved our understanding of the molecular details of latency and reactivation but many questions remain. This review summarizes the current knowledge about how HSV gene expression is regulated during latency and reactivation and discusses the important questions remaining to be addressed in future.

Glucocorticoid receptor and specificity protein 1 (Sp1) or Sp3 transactivate HSV-1 ICP0 promoter sequences but a GC-rich binding antibiotic, Mithramycin A, impairs reactivation from latency

Glucocorticoid receptor (GR) activation enhances Human alpha-herpes virus 1 (HSV-1) replication and explant-induced reactivation from latency. Furthermore, GR and Krüppel-like factor 15 (KLF15) cooperatively transactivate cis-regulatory modules (CRMs) that drive expression of infected cell protein 0 (ICP0), ICP4, and ICP27. KLF and specificity protein (Sp) family members bind GC-rich or C-rich sequences and belong to the same super-family of transcription factors. Based on these observations, we hypothesized CRMs spanning the ICP0 promoter are transactivated by GR and Sp1 or Sp3. CRM-A (-800 to -635), CRM-B (-485 to -635), and CRM-D (-232 to -24), but not CRM-C, were significantly transactivated by GR, DEX, and Sp1 or Sp3 in mouse neuroblastoma cells (Neuro-2A). Mutagenesis of Sp1/Sp3 binding sites were important for transactivation of CRM-A and CRM-B. Chromatin immunoprecipitation studies revealed significantly higher levels of GR occupied ICP0 promoter sequences when Sp1 or Sp3 was over-expressed suggesting these transcriptions factors recruit GR to ICP0 CRM sequences. Mithramycin A, an antibiotic that preferentially binds GC-rich DNA and impairs Sp1/Sp3 dependent transactivation and reduced virus shedding during reactivation from latency in mice latently infected with HSV-1. These studies indicate GR and certain stress-induced cellular transcription factors preferentially bind GC rich DNA, which stimulates HSV-1 gene expression and reactivation from latency in trigeminal ganglia of latently infected mice.

Stress Can Induce Bovine Alpha-Herpesvirus 1 (BoHV-1) Reactivation from Latency

Bovine alpha-herpesvirus 1 (BoHV-1) is a significant problem for the cattle industry, in part because the virus establishes latency, and stressful stimuli increase the incidence of reactivation from latency. Sensory neurons in trigeminal ganglia and unknown cells in pharyngeal tonsils are importantsites for latency. Reactivation from latency can lead to reproductive problems in pregnant cows, virus transmission to young calves, suppression of immune responses, and bacterial pneumonia. BoHV-1 is also a significant cofactor in bovine respiratory disease (BRD). Stress, as mimicked by the synthetic corticosteroid dexamethasone, reproducibly initiates reactivation from latency. Stress-mediated activation of the glucocorticoid receptor (GR) stimulates viral replication and transactivation of viral promoters that drive the expression of infected cell protein 0 (bICP0) and bICP4. Notably, GR and Krüppel-like factor 15 (KLF15) form a feed-forward transcription loop that cooperatively transactivates immediate early transcription unit 1 (IEtu1 promoter). Two pioneer transcription factors, GR and KLF4, cooperatively transactivate the bICP0 early promoter. Pioneer transcription factors bind silent viral heterochromatin, remodel chromatin, and activate gene expression. Thus, wepredict that these novel transcription factors mediate early stages of BoHV-1 reactivation from latency.

Examination of neuro-inflammation and senescence in brainstem of aged mice latently infected with human alphaherpesvirus 1 (HSV-1)

Human alphaherpesvirus 1 (HSV-1) establishes life-long latency in sensory neurons in trigeminal ganglia (TG), brainstem neurons, and other CNS neurons. Two important segments of the brainstem were examined in this study: principal sensory nucleus of the spinal trigeminal tract (Pr5) because it receives direct afferent inputs from TG, and locus coeruleus (LC) because it is indirectly connected to Pr5 and LC sends axonal projections to cortical structures, which may facilitate viral spread from brainstem to the brain. The only viral gene abundantly expressed during latency is the latency associated transcript (LAT). Previous studies revealed 8-week old female C57Bl/6 mice infected with a LAT null mutant (dLAT2903) versus wild-type (wt) HSV-1 exhibit higher levels of senescence markers and inflammation in LC of females. New studies revealed 1-year old mice latently infected with wt HSV-1 or dLAT2903 contained differences in neuroinflammation and senescence in Pr5 and LC versus young mice. In summary, these studies confirm HSV-1 promotes neuro-inflammation in the brainstem, which may accelerate neurodegenerative disease.

A review of HSV pathogenesis, vaccine development, and advanced applications

Herpes simplex virus (HSV), an epidemic human pathogen threatening global public health, gains notoriety for its complex pathogenesis that encompasses lytic infection of mucosal cells, latent infection within neurons, and periodic reactivation. This intricate interplay, coupled with HSV's sophisticated immune evasion strategies, gives rise to various diseases, including genital lesions, neonatal encephalitis, and cancer. Despite more than 70 years of relentless research, an effective preventive or therapeutic vaccine against HSV has yet to emerge, primarily due to the limited understanding of virus-host interactions, which in turn impedes the identification of effective vaccine targets. However, HSV's unique pathological features, including its substantial genetic load capacity, high replicability, transmissibility, and neurotropism, render it a promising candidate for various applications, spanning oncolytic virotherapy, gene and immune therapies, and even as an imaging tracer in neuroscience. In this review, we comprehensively update recent breakthroughs in HSV pathogenesis and immune evasion, critically summarize the progress made in vaccine candidate development, and discuss the multifaceted applications of HSV as a biological tool. Importantly, we highlight both success and challenges, emphasizing the critical need for intensified research into HSV, with the aim of providing deeper insights that can not only advance HSV treatment strategies but also broaden its application horizons.

Glucocorticoid receptor and specificity protein 1 (Sp1) or Sp3, but not the antibiotic Mithramycin A, stimulates human alphaherpesvirus 1 (HSV-1) replication

Following acute human alphaherpesvirus 1 (HSV-1) infection of oral-facial mucosal surfaces, sensory neurons in trigeminal ganglia (TG) are important sites for life-long latency. Neurons in the central nervous system, including brainstem, also harbor viral genomes during latency. Periodically, certain cellular stressors trigger reactivation from latency, which can lead to recurrent HSV-1 disease: herpes labialis, herpes stromal keratitis, and encephalitis for example. Activation of the glucocorticoid receptor (GR) by stressful stimuli enhances HSV-1 gene expression, replication, and explant-induced reactivation. GR and certain stress-induced Krüppel like factors (KLF) cooperatively transactivate cis-regulatory modules (CRM) that drive expression of viral transcriptional regulatory proteins (ICP0, ICP4, and ICP27). These CRMs lack GR response elements (GRE); however, specificity protein 1 (Sp1) binding sites are crucial for GR and KLF15 or KLF4 mediated transactivation. Hence, we tested whether Sp1 or Sp3 regulate viral replication and transactivation of the ICP0 promoter. During early stages of explant-induced reactivation from latency, the number of Sp3+ TG neurons were significantly higher relative to TG from latently infected mice. Conversely, Sp1+ TG neurons were only increased in females, but not male mice, during explant-induced reactivation. Sp1 siRNA significantly reduced HSV-1 replication in cultured mouse (Neuro-2A) and monkey (CV-1) cells. Mithramycin A, an antibiotic that has anti-tumor activity preferentially interacts with GC-rich DNA, including Sp1 binding sites, significantly reduced HSV-1 replication indicating it has antiviral activity. GR and Sp1 or Sp3 transactivated the HSV-1 ICP0 promoter in Neuro-2A and CV-1 cells confirming these transcription factors enhance viral replication and gene expression.