Pioneer transcription factors, progesterone receptor and Krüppel like transcription factor 4, cooperatively stimulate the bovine herpesvirus 1 ICP0 early promoter and productive late protein expression

Alphaherpesvirus in Pets and Livestock

Herpesviruses are a group of DNA viruses capable of infecting multiple mammalian species, including humans. This review primarily summarizes four common alphaherpesviruses found in pets and livestock (feline, swine, canine, and bovine) in aspects such as epidemiology, immune evasion, and latency and reactivation. Despite the fact that they primarily infect specific hosts, these viruses have the potential for cross-species transmission due to genetic mutations and/or recombination events. During infection, herpesviruses not only stimulate innate immune responses in host cells but also interfere with signaling pathways through specific proteins to achieve immune evasion. These viruses can remain latent within the host for extended periods and reactivate under certain conditions to trigger disease recurrence. They not only affect the health of animals and cause economic losses but may also pose a potential threat to humans under certain circumstances. This review deepens our understanding of the biological characteristics of these animal alphaherpesviruses and provides an important scientific basis for the prevention and control of related diseases.

Transcriptomic analysis reveals bovine herpesvirus 1 infection regulates innate immune response resulted in restricted viral replication in neuronal cells

BACKGROUND

Bovine herpesvirus 1 (BoHV-1) is a major pathogen that affects the global bovine population, primarily inducing respiratory and reproductive disorders. Its ability to establish latent infections in neuronal cells and to reactivate under certain conditions poses a continual threat to uninfected hosts. In this study, we aimed to analyze the replication characteristics of BoHV-1 in neuronal cells, as well as the effects of viral replication on host cell immunity and physiology.

METHODS

Using the Neuro-2a neuronal-origin cell line as a model, we explored the dynamics of BoHV-1 replication and analyzed differential gene expression profiles post-BoHV-1 infection using high-throughput RNA sequencing.

RESULTS

BoHV-1 demonstrated restricted replication in Neuro-2a cells. BoHV-1 induced apoptotic pathways and enhanced the transcription of interferon-stimulated genes and interferon regulatory factors while suppressing the complement cascade in Neuro-2a cells.

CONCLUSIONS

Different from BoHV-1 infection in other non-highly differentiated somatic cells result in viral dominance, BoHV-1 regulated the innate immune response in neuronal cells formed a "virus-nerve cell" relative equilibrium state, which may account for the restricted replication of BoHV-1 in neuronal cells, leading to a latent infection. These findings provide a foundation for further research into the mechanism underlying BoHV-1-induced latent infection in nerve cells.

Biogenesis and function of exosome lncRNAs and their role in female pathological pregnancy

Preeclampsia, gestational diabetes mellitus, and recurrent spontaneous abortion are common maternal pregnancy complications that seriously endanger women's lives and health, and their occurrence is increasing year after year with a rejuvenation trend. In contrast to biomarkers found freely in tissues or body fluids, exosomes exist in a relatively independent environment and provide a higher level of stability. As backbone molecules, guidance molecules, and signaling molecules in the nucleus, lncRNAs can regulate gene expression. In the cytoplasm, lncRNAs can influence gene expression levels by modifying mRNA stability, acting as competitive endogenous RNAs to bind miRNAs, and so on. Exosomal lncRNAs can exist indefinitely and are important in intercellular communication and signal transduction. Changes in maternal serum exosome lncRNA expression can accurately and timely reflect the progression and regression of pregnancy-related diseases. The purpose of this paper is to provide a reference for clinical research on the pathogenesis, diagnosis, and treatment methods of pregnancy-related diseases by reviewing the role of exosome lncRNAs in female pathological pregnancy and related molecular mechanisms.

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.

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.

Structures and consequences of pioneer factor binding to nucleosomes

Pioneer transcription factors are able to bind a partially exposed motif on the surface of a nucleosome, enabling the proteins to target sites in silent regions of chromatin that have been compacted by linker histone. The targeting of nucleosomal DNA by pioneer factors has been observed in vitro and in vivo, where binding can promote local nucleosome exposure that allows other transcription factors, nucleosome remodelers, and histone modifiers to engage the chromatin and elicit gene activation or further repression. Pioneer factors thereby establish new gene expression programs during cell fate changes that occur during embryonic development, regeneration, and cancer. Here, we review recent biophysical studies that reveal the structural features and strategies used by pioneer factors to accomplish nucleosome binding and the consequential changes to nucleosomes that can lead to DNA accessibility.

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.