Sp1 binds to promoter sequences and activates herpes simplex virus 'immediate-early' gene transcription in vitro

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.

Viral cis-regulatory elements as sensors of cellular states and environmental cues

To withstand a hostile cellular environment and replicate, viruses must sense, interpret, and respond to many internal and external cues. Retroviruses and DNA viruses can intercept these cues impinging on host transcription factors via cis-regulatory elements (CREs) in viral genomes, allowing them to sense and coordinate context-specific responses to varied signals. Here, we explore the characteristics of viral CREs, the classes of signals and host transcription factors that regulate them, and how this informs outcomes of viral replication, immune evasion, and latency. We propose that viral CREs constitute central hubs for signal integration from multiple pathways and that sequence variation between viral isolates can rapidly rewire sensing mechanisms, contributing to the variability observed in patient outcomes.

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.

Sp1 facilitates continued HSV-1 gene expression in the absence of key viral transactivators

Productive replication of herpes simplex virus (HSV) relies upon a well-ordered transcriptional cascade flowing from immediate-early (IE) to early (E) to late (L) gene products. While several virus-encoded transcriptional activators are involved in this process, IE and E gene promoters also contain multiple binding sites for the ubiquitously expressed cellular transcription factor Sp1. Sp1 has been previously implicated in activating HSV-1 gene transcription downstream of these sites, but why Sp1-binding sites are maintained in the promoters of genes activated by virus-encoded activators remains unclear. We hypothesized that Sp1 enables continued HSV-1 transcription and replication when viral transactivators are limited. We used a depletion-based approach in human foreskin fibroblasts to investigate the specific contribution of Sp1 to the initiation and progression of the HSV-1 lytic gene cascade. We found that Sp1 increased viral transcript levels, protein expression, and replication following infection with VP16- or ICP0-deficient viruses but had little to no effect on rescued viruses or during wild-type (WT) HSV-1 infection. Moreover, Sp1 promoted WT virus transcription and replication following interferon treatment of fibroblasts and thus may contribute to viral immune evasion. Interestingly, we observed reduced expression of Sp1 and Sp1-family transcription factors in differentiated sensory neurons compared to undifferentiated cells, suggesting that reduced Sp1 levels may also contribute to HSV-1 latent infection. Overall, these findings indicate that Sp1 can promote HSV-1 gene expression in the absence of key viral transactivators; thus, HSV-1 may use Sp1 to maintain its gene expression and replication under adverse conditions.IMPORTANCEHerpes simplex virus (HSV) is a common human pathogen that actively replicates in the epithelia but can persist for the lifetime of the infected host via a stable, latent infection in neurons. A key feature of the HSV replication cycle is a complex transcriptional program in which virus and host-cell factors coordinate to regulate expression of the viral gene products necessary for continued viral replication. Multiple binding sites for the cellular transcription factor Sp1 are located in the promoters of HSV-1 genes, but how Sp1 binding contributes to transcription and replication of wild-type virus is not fully understood. In this study, we identified a specific role for Sp1 in maintaining HSV-1 gene transcription under adverse conditions, as when virus-encoded transcriptional activators were absent or limited. Preservation of Sp1-binding sites in HSV-1 gene promoters may thus benefit the virus as it navigates diverse cell types and host-cell conditions during infection.

A Revision of Herpes Simplex Virus Type 1 Transcription: First, Repress; Then, Express

The herpes virus genome bears more than 80 strong transcriptional promoters. Upon entry into the host cell nucleus, these genes are transcribed in an orderly manner, producing five immediate-early (IE) gene products, including ICP0, ICP4, and ICP22, while non-IE genes are mostly silent. The IE gene products are necessary for the transcription of temporal classes following sequentially as early, leaky late, and true late. A recent analysis using precision nuclear run-on followed by deep sequencing (PRO-seq) has revealed an important step preceding all HSV-1 transcription. Specifically, the immediate-early proteins ICP4 and ICP0 enter the cell with the incoming genome to help preclude the nascent antisense, intergenic, and sense transcription of all viral genes. VP16, which is also delivered into the nucleus upon entry, almost immediately reverses this repression on IE genes. The resulting de novo expression of ICP4 and ICP22 further repress antisense, intergenic, and early and late viral gene transcription through different mechanisms before the sequential de-repression of these gene classes later in infection. This early repression, termed transient immediate-early protein-mediated repression (TIEMR), precludes unproductive, antisense, intergenic, and late gene transcription early in infection to ensure the efficient and orderly progression of the viral cascade.

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.

Mechanism of herpesvirus protein kinase UL13 in immune escape and viral replication

Upon infection, the herpes viruses create a cellular environment suitable for survival, but innate immunity plays a vital role in cellular resistance to viral infection. The UL13 protein of herpesviruses is conserved among all herpesviruses and is a serine/threonine protein kinase, which plays a vital role in escaping innate immunity and promoting viral replication. On the one hand, it can target various immune signaling pathways in vivo, such as the cGAS-STING pathway and the NF-κB pathway. On the other hand, it phosphorylates regulatory many cellular and viral proteins for promoting the lytic cycle. This paper reviews the research progress of the conserved herpesvirus protein kinase UL13 in immune escape and viral replication to provide a basis for elucidating the pathogenic mechanism of herpesviruses, as well as providing insights into the potential means of immune escape and viral replication of other herpesviruses that have not yet resolved the function of it.

The Dietary Flavonol Kaempferol Inhibits Epstein-Barr Virus Reactivation in Nasopharyngeal Carcinoma Cells

Kaempferol (KP, 3,4',5,7-tetrahydroxyflavone), a dietary flavonol, has anti-cancer, antioxidant, anti-inflammatory, antimicrobial, and antimutagenic functions. However, it is unknown whether kaempferol possesses anti-Epstein-Barr virus (EBV) activity. Previously, we demonstrated that inhibition of EBV reactivation represses nasopharyngeal carcinoma (NPC) tumourigenesis, suggesting the importance of identifying EBV inhibitors. In this study, Western blotting, immunofluorescence staining, and virion detection showed that kaempferol repressed EBV lytic gene protein expression and subsequent virion production. Specifically, kaempferol was found to inhibit the promoter activities of Zta and Rta (Zp and Rp) under various conditions. A survey of the mutated Zp constructs revealed that Sp1 binding regions are critical for kaempferol inhibition. Kaempferol treatment repressed Sp1 expression and decreased the activity of the Sp1 promoter, suggesting that Sp1 expression was inhibited. In conclusion, kaempferol efficiently inhibits EBV reactivation and provides a novel choice for anti-EBV therapy and cancer prevention.

Immediate Early Proteins of Herpes Simplex Virus Transiently Repress Viral Transcription before Subsequent Activation

HSV-1 transcription during productive replication is believed to comprise a series of activation steps leading to a specific sequence of gene expression. Here, we show that virion components and IE gene products ICP0, ICP4, and ICP22 first repress viral gene transcription to various degrees before subsequently activating specific gene subsets.

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.

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.

Rapamycin enhances lytic replication of Epstein-Barr virus in gastric carcinoma cells by increasing the transcriptional activities of immediate-early lytic promoters

Epstein-Barr virus (EBV), a human herpesvirus, is linked to both epithelial and lymphoid malignancies. Induction of EBV reactivation is a potential therapeutic strategy for EBV-associated tumors. In this study, we assessed the effects of rapamycin on EBV reactivation in gastric carcinoma cells. We found that rapamycin upregulated expression of EBV lytic proteins and increased the viral proliferation triggered by the EBV lytic inducer sodium butyrate. Reverse transcription-qPCR, luciferase activity assays, chromatin immunoprecipitation and western blotting were employed to explore the mechanism by which rapamycin promotes EBV reactivation. Our results showed that rapamycin treatment resulted in increased mRNA levels of EBV immediate-early genes. Rapamycin also enhanced the transcriptional activities of the EBV immediate-early lytic promoters Zp and Rp by strengthening Sp1 binding. Repression of the cellular ataxia telangiectasia-mutated/p53 pathway by siRNA-mediated knockdown of the ataxia telangiectasia-mutated gene significantly abrogated virus reactivation by rapamycin/sodium butyrate treatment, indicating that the ataxia telangiectasia-mutated/p53 pathway is involved in rapamycin-promoted EBV reactivation. Taken together, these findings demonstrate that rapamycin might have the potential to enhance the effectiveness of oncolytic viral therapies developed for EBV-associated malignancies.

Luteolin inhibits Epstein-Barr virus lytic reactivation by repressing the promoter activities of immediate-early genes

The lytic reactivation of Epstein-Barr virus (EBV) has been reported to be strongly associated with several human diseases, including nasopharyngeal carcinoma (NPC). Inhibition of the EBV lytic cycle has been shown to be of great benefit in the treatment of EBV-associated diseases. The administration of dietary compounds is safer and more convenient than other approaches to preventing EBV reactivation. We screened several dietary compounds for their ability to inhibit EBV reactivation in NPC cells. Among them, the flavonoid luteolin showed significant inhibition of EBV reactivation. Luteolin inhibited protein expression from EBV lytic genes in EBV-positive epithelial and B cell lines. It also reduced the numbers of EBV-reactivating cells detected by immunofluorescence analysis and reduced the production of virion. Furthermore, luteolin reduced the activities of the promoters of the immediate-early genes Zta (Zp) and Rta (Rp) and also inhibited Sp1-luc activity, suggesting that disruption of Sp1 binding is involved in the inhibitory mechanism. CHIP analysis revealed that luteolin suppressed the activities of Zp and Rp by deregulating Sp1 binding. Taken together, luteolin inhibits EBV reactivation by repressing the promoter activities of Zp and Rp, suggesting luteolin is a potential dietary compound for prevention of virus infection.

Full trans-activation mediated by the immediate-early protein of equine herpesvirus 1 requires a consensus TATA box, but not its cognate binding sequence

The immediate-early protein (IEP) of equine herpesvirus 1 (EHV-1) has extensive homology to the IEP of alphaherpesviruses and possesses domains essential for trans-activation, including an acidic trans-activation domain (TAD) and binding domains for DNA, TFIIB, and TBP. Our data showed that the IEP directly interacted with transcription factor TFIIA, which is known to stabilize the binding of TBP and TFIID to the TATA box of core promoters. When the TATA box of the EICP0 promoter was mutated to a nonfunctional TATA box, IEP-mediated trans-activation was reduced from 22-fold to 7-fold. The IEP trans-activated the viral promoters in a TATA motif-dependent manner. Our previous data showed that the IEP is able to repress its own promoter when the IEP-binding sequence (IEBS) is located within 26-bp from the TATA box. When the IEBS was located at 100 bp upstream of the TATA box, IEP-mediated trans-activation was very similar to that of the minimal IE(nt -89 to +73) promoter lacking the IEBS. As the distance from the IEBS to the TATA box decreased, IEP-mediated trans-activation progressively decreased, indicating that the IEBS located within 100 bp from the TATA box sequence functions as a distance-dependent repressive element. These results indicated that IEP-mediated full trans-activation requires a consensus TATA box of core promoters, but not its binding to the cognate sequence (IEBS).

Differential effects of Sp cellular transcription factors on viral promoter activation by varicella-zoster virus (VZV) IE62 protein

The immediate early (IE) 62 protein is the major varicella-zoster virus (VZV) regulatory factor. Analysis of the VZV genome revealed 40 predicted GC-rich boxes within 36 promoters. We examined effects of ectopic expression of Sp1-Sp4 on IE62- mediated transactivation of three viral promoters. Ectopic expression of Sp3 and Sp4 enhanced IE62 activation of ORF3 and gI promoters while Sp3 reduced IE62 activation of ORF28/29 promoter and VZV DNA replication. Sp2 reduced IE62 transactivation of gI while Sp1 had no significant influence on IE62 activation with any of these viral promoters. Electrophoretic mobility shift assays (EMSA) confirmed binding of Sp1 and Sp3 but not Sp2 and Sp4 to the gI promoter. Sp1-4 bound to IE62 and amino acids 238-258 of IE62 were important for the interaction with Sp3 and Sp4 as well as Sp1. This work shows that Sp family members have differential effects on IE62-mediated transactivation in a promoter-dependent manner.

Pharmacological manipulation of transcription factor protein-protein interactions: opportunities and obstacles

Much research on transcription factor biology and their genetic pathways has been undertaken over the last 30 years, especially in the field of developmental biology and cancer. Yet, very little is known about the molecular modalities of highly dynamic interactions between transcription factors, genomic DNA, and protein partners. Methodological breakthroughs such as RNA-seq (RNA-sequencing), ChIP-seq (chromatin immunoprecipitation sequencing), RIME (rapid immunoprecipitation mass spectrometry of endogenous proteins), and single-molecule imaging will dramatically accelerate the discovery rate of their molecular mode of action in the next few years. From a pharmacological viewpoint, conventional methods used to target transcription factor activity with molecules mimicking endogenous ligands fail to achieve high specificity and are limited by a lack of identification of new molecular targets. Protein-protein interactions are likely to represent one of the next major classes of therapeutic targets. Transcription factors, known to act mostly via protein-protein interaction, may well be at the forefront of this type of drug development. One hurdle in this field remains the difficulty to collate structural data into meaningful information for rational drug design. Another hurdle is the lack of chemical libraries meeting the structural requirements of protein-protein interaction disruption. As more attempts at modulating transcription factor activity are undertaken, valuable knowledge will be accumulated on the modality of action required to modulate transcription and how these findings can be applied to developing transcription factor drugs. Key discoveries will spawn into new therapeutic approaches not only as anticancer targets but also for other indications, such as those with an inflammatory component including neurodegenerative disorders, diabetes, and chronic liver and kidney diseases.

Houttuynia cordata targets the beginning stage of herpes simplex virus infection

Herpes simplex virus (HSV), a common latent virus in humans, causes certain severe diseases. Extensive use of acyclovir (ACV) results in the development of drug-resistant HSV strains, hence, there is an urgent need to develop new drugs to treat HSV infection. Houttuynia cordata (H. cordata), a natural herbal medicine, has been reported to exhibit anti-HSV effects which is partly NF-κB-dependent. However, the molecular mechanisms by which H. cordata inhibits HSV infection are not elucidated thoroughly. Here, we report that H. cordata water extracts (HCWEs) inhibit the infection of HSV-1, HSV-2, and acyclovir-resistant HSV-1 mainly via blocking viral binding and penetration in the beginning of infection. HCWEs also suppress HSV replication. Furthermore, HCWEs attenuate the first-wave of NF-κB activation, which is essential for viral gene expressions. Further analysis of six compounds in HCWEs revealed that quercetin and isoquercitrin inhibit NF-κB activation and additionally, quercetin also has an inhibitory effect on viral entry. These results indicate that HCWEs can inhibit HSV infection through multiple mechanisms and could be a potential lead for development of new drugs for treating HSV.

IFI16 restricts HSV-1 replication by accumulating on the hsv-1 genome, repressing HSV-1 gene expression, and directly or indirectly modulating histone modifications

Interferon-γ inducible factor 16 (IFI16) is a multifunctional nuclear protein involved in transcriptional regulation, induction of interferon-β (IFN-β), and activation of the inflammasome response. It interacts with the sugar-phosphate backbone of dsDNA and modulates viral and cellular transcription through largely undetermined mechanisms. IFI16 is a restriction factor for human cytomegalovirus (HCMV) and herpes simplex virus (HSV-1), though the mechanisms of HSV-1 restriction are not yet understood. Here, we show that IFI16 has a profound effect on HSV-1 replication in human foreskin fibroblasts, osteosarcoma cells, and breast epithelial cancer cells. IFI16 knockdown increased HSV-1 yield 6-fold and IFI16 overexpression reduced viral yield by over 5-fold. Importantly, HSV-1 gene expression, including the immediate early proteins, ICP0 and ICP4, the early proteins, ICP8 and TK, and the late proteins gB and Us11, was reduced in the presence of IFI16. Depletion of the inflammasome adaptor protein, ASC, or the IFN-inducing transcription factor, IRF-3, did not affect viral yield. ChIP studies demonstrated the presence of IFI16 bound to HSV-1 promoters in osteosarcoma (U2OS) cells and fibroblasts. Using CRISPR gene editing technology, we generated U2OS cells with permanent deletion of IFI16 protein expression. ChIP analysis of these cells and wild-type (wt) U2OS demonstrated increased association of RNA polymerase II, TATA binding protein (TBP) and Oct1 transcription factors with viral promoters in the absence of IFI16 at different times post infection. Although IFI16 did not alter the total histone occupancy at viral or cellular promoters, its absence promoted markers of active chromatin and decreased those of repressive chromatin with viral and cellular gene promoters. Collectively, these studies for the first time demonstrate that IFI16 prevents association of important transcriptional activators with wt HSV-1 promoters and suggest potential mechanisms of IFI16 restriction of wt HSV-1 replication and a direct or indirect role for IFI16 in histone modification.

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

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

Nuclear factor κB2 p52 protein has a role in antiviral immunity through IκB kinase epsilon-dependent induction of Sp1 protein and interleukin 15

In this study we describe a previously unreported function for NFκB2, an NFκB family transcription factor, in antiviral immunity. NFκB2 is induced in response to poly(I:C), a mimic of viral dsRNA. Poly(I:C), acting via TLR3, induces p52-dependent transactivation of a reporter gene in a manner that requires the kinase activity of IκB kinase ε (IKKε) and the transactivating potential of RelA/p65. We identify a novel NFκB2 binding site in the promoter of the transcription factor Sp1 that is required for Sp1 gene transcription activated by poly(I:C). We show that Sp1 is required for IL-15 induction by both poly(I:C) and respiratory syncytial virus, a response that also requires NFκB2 and IKKε. Our study identifies NFκB2 as a target for IKKε in antiviral immunity and describes, for the first time, a role for NFκB2 in the regulation of gene expression in response to viral infection.

The dynamics of HCF-1 modulation of herpes simplex virus chromatin during initiation of infection

Successful infection of herpes simplex virus is dependent upon chromatin modulation by the cellular coactivator host cell factor-1 (HCF-1). This review focuses on the multiple chromatin modulation components associated with HCF-1 and the chromatin-related dynamics mediated by this coactivator that lead to the initiation of herpes simplex virus (HSV) immediate early gene expression.

Reduced expression of PHD2 prolyl hydroxylase gene in primary advanced uterine cervical carcinoma

Decreased PHD2 expression in human carcinomas has been considered a critical factor in supporting tumor angiogenesis and growth. We studied the levels of PHD2 transcript and protein in advanced cervical cancer specimens (n=27) and normal uterine cervical tissue samples (n=27). Real-time quantitative PCR and Western blotting analysis showed significantly lower levels of PHD2 transcript (P=0.0088) and protein (P=0.0095) in cancerous tissues as compared to corresponding normal tissue. Using DNA sequencing analysis, we also found an accumulation of mutations in promoter regions of PHD2 in advanced cervical cancer specimens. Moreover, computer analysis of these mutations showed a loss of binding sites for many transcription factors. Our results suggest PHD2 as a possible target in anti-angiogenic therapies in advanced uterine cervical carcinoma.

Control of alpha-herpesvirus IE gene expression by HCF-1 coupled chromatin modification activities

The immediate early genes of the alpha-herpesviruses HSV and VZV are transcriptionally regulated by viral and cellular factors in a complex combinatorial manner. Despite this complexity and the apparent redundancy of activators, the expression of the viral IE genes is critically dependent upon the cellular transcriptional coactivator HCF-1. Although the role of HCF-1 had remained elusive, recent studies have demonstrated that the protein is a component of multiple chromatin modification complexes including the Set1/MLL1 histone H3K4 methyltransferases. Studies using model viral promoter-reporter systems as well as analyses of components recruited to the viral genome during the initiation of infection have elucidated the significance of HCF-1 chromatin modification complexes in contributing to the final state of modified histones assembled on the viral IE promoters. Strikingly, the absence of HCF-1 results in the accumulation of nucleosomes bearing repressive marks on the viral IE promoters and silencing of viral gene expression.

Kaposi sarcoma-associated herpes virus (KSHV) G protein-coupled receptor (vGPCR) activates the ORF50 lytic switch promoter: a potential positive feedback loop for sustained ORF50 gene expression

KSHV vGPCR, a lytic cycle associated protein, induces several signaling pathways leading to the activation of various transcription factors and consequently the expression of cellular and viral genes. Though the role of vGPCR in KSHV tumorigenicity has been well studied, its function related to the viral life cycle is poorly understood. Reduction in vGPCR by RNA interference also resulted in the reduction in KSHV lytic switch ORF50 gene and protein expression. Induction of vGPCR by doxycycline in BC3.14 cells also resulted in more KSHV production. When this was explored, induction of the ORF50 promoter by vGPCR expression was observed. Further examination of the molecular mechanisms by which vGPCR regulates the ORF50 promoter, using various ORF50 promoter constructs, revealed that induction of ORF50 promoter by vGPCR did not involve AP1 but was dependent on Sp1 and Sp3 transcription factors. vGPCR signaling led to an increase in Sp1 and Sp3 DNA binding activity and a decrease in histone deacetylase (HDAC) activity. These activities were pertussis toxin independent, did not involve Rho and Rac-GTPases and involved the heterotrimeric G protein subunits Galpha12 and Galphaq. Studies using pharmacologic inhibitors and dominant-negative proteins identified phospholipase C, the novel protein kinase C (novel PKC) family and protein kinase D (PKD) as part of the signaling initiated by vGPCR leading to ORF50 promoter activation. Taken together, this study suggests a role for vGPCR in the sustained expression of ORF50 which could lead to a continued activation of lytic cycle genes and ultimately to successful viral progeny formation.

Recruitment of the transcriptional coactivator HCF-1 to viral immediate-early promoters during initiation of reactivation from latency of herpes simplex virus type 1

The transcriptional coactivator host cell factor 1 (HCF-1) is critical for the expression of immediate-early (IE) genes of the alphaherpesviruses herpes simplex virus type 1 (HSV-1) and varicella-zoster virus. HCF-1 may also be involved in the reactivation of these viruses from latency as it is sequestered in the cytoplasm of sensory neurons but is rapidly relocalized to the nucleus upon stimulation that results in reactivation. Here, chromatin immunoprecipitation assays demonstrate that HCF-1 is recruited to IE promoters of viral genomes during the initiation of reactivation, correlating with RNA polymerase II occupancy and IE expression. The data support the model whereby HCF-1 plays a pivotal role in the reactivation of HSV-1 from latency.

Transcriptional control of microRNA expression in C. elegans: promoting better understanding

Transcriptional regulation of microRNA (miRNA) expression is one of the least understood aspects of miRNA biogenesis. In C. elegans the list of miRNAs whose transcriptional control has been described in some detail is currently limited to four: let-7, lin-4, lsy-6, and mir-61. Each of these genes has been shown experimentally to be transcriptionaly regulated by cis- and/or trans-acting factors that either promote or inhibit expression. Additionally, computational methods based on conservation among miRNA genes have yielded predicted regulatory sequences in C. elegans that may function to regulate miRNA expression on a genome-wide scale.

Identification of a liver-specific cAMP response element in the human argininosuccinate synthetase gene

Argininosuccinate synthetase (ASS), a key enzyme in the urea cycle, participates in many metabolic processes including arginine biosynthesis and the citrulline-nitric oxide (NO) cycle. Factors like diets, hormones and pro-inflammatory stimuli are known to regulate ASS gene expression primarily at the transcription level. However, little is known about the cis-elements for transcriptional regulation of the ASS gene. In this study, we employed DNase I hypersensitive sites mapping to identify potential regulatory sites of the gene and revealed a site located at 10 kb upstream of the transcription start site which is responsible for liver-specific cAMP induction. Furthermore, a cAMP response element (CRE) highly conserved among mammals was identified and was experimentally verified. Our results show that liver-specific enhancement of ASS gene expression is mediated in part by the cAMP signaling pathway through a distal CRE site.

High-mobility group protein A1 binds herpes simplex virus gene regulatory sequences and affects their expression

The high-mobility group protein A1 (HMGA1), which regulates mammalian gene expression by altering chromatin architecture, was found to bind at multiple sites within the promoter regions of all of the herpes simplex virus type 1 (HSV-1) immediate early genes, as well as a representative early (tk) gene and one late (gC) gene, both in vitro and in vivo. Infected cell polypeptide (ICP) 4, the major HSV-1 regulatory protein, binds these promoters both in vitro and in vivo, and HMGA1 enhances its in vitro binding. In transient expression experiments, HMGA1 modified the effects of both ICP4 and ICP0, another virus transactivator, on virus gene expression in a promoter-specific manner, but it had no effect on the transactivation of immediate-early promoters by VP16. These data indicate that host-cell architectural chromatin proteins could influence the interactions of host-cell and viral transcription factors with the virus DNA regulatory elements and affect HSV-1 gene expression.

Phosphorylation of Sp1 in response to DNA damage by ataxia telangiectasia-mutated kinase

Sp1, a transcription factor that regulates expression of a wide array of essential genes, contains two SQ/TQ cluster domains, which are characteristic of ATM kinase substrates. ATM substrates are transducers and effectors of the DNA damage response, which involves sensing damage, checkpoint activation, DNA repair, and/or apoptosis. A role for Sp1 in the DNA damage response is supported by our findings: Activation of ATM induces Sp1 phosphorylation with kinetics similar to H2AX; inhibition of ATM activity blocks Sp1 phosphorylation; depletion of Sp1 sensitizes cells to DNA damage and increases the frequency of double strand breaks. We have identified serine 101 as a critical site phosphorylated by ATM; Sp1 with serine 101 mutated to alanine (S101A) is not significantly phosphorylated in response to damage and cannot restore increased sensitivity to DNA damage of cells depleted of Sp1. Together, these data show that Sp1 is a novel ATM substrate that plays a role in the cellular response to DNA damage.

Alleles of the bovine DGAT1 variable number of tandem repeat associated with a milk fat QTL at chromosome 14 can stimulate gene expression

A quantitative trait locus (QTL) affecting milk fat percentage has been mapped to the centromeric end of the bovine chromosome 14 (BTA14). This genomic area includes the DGAT1 gene, which encodes acyl-CoA:diacylglycerol acyltransferase 1, the key enzyme of triglyceride biosynthesis. Genetic and biochemical studies led to the identification of the nonconservative DGAT1-K232A polymorphism as a causal mutation for the QTL. In addition to this, another polymorphism in the 5'-regulatory region of this gene, the DGAT1 variable number of tandem repeat (VNTR), also showed a strong association with milk fat percentage. This promoter VNTR polymorphism affects the number of potential Sp1 binding sites and therefore might have an impact on DGAT1 expression and also milk fat content. Hence, the DGAT1 VNTR polymorphism might be another causal mutation for the BTA14 QTL. However, evidence for Sp1 binding to this polymorphic site and for the capability of DGAT1 VNTR alleles to stimulate gene expression was lacking. In the current work Sp1-VNTR interactions were analyzed by EMSA. In addition, effects of DGAT1 VNTR alleles on gene expression were measured with reporter gene analyses. Conclusions from the results are that 1) the DGAT1 VNTR sequence is indeed a target for Sp1 binding; 2) DGAT1 VNTR alleles can stimulate gene expression in vitro and probably in vivo as well; and 3) although the stimulating effects of the different DGAT1 VNTR alleles did not show significant differences in vitro, their effects on transcription might be different in the chromatin context existing in vivo.

Utp14b: a unique retrogene within a gene that has acquired multiple promoters and a specific function in spermatogenesis

The mouse retrogene Utp14b is essential for male fertility, and a mutation in its sequence results in the sterile juvenile spermatogonial depletion (jsd) phenotype. It is a retrotransposed copy of the Utp14a gene, which is located on the X chromosome, and is inserted within an intron of the autosomal acyl-CoA synthetase long-chain family member 3 (Acsl3) gene. To elucidate the roles of the Utp14 genes in normal spermatogenic cell development as a basis for understanding the defects that result in the jsd phenotype, we analyzed the various mRNAs produced from the Utp14b retrogene and their expression in different cell types. Two classes of transcripts were identified: variant 1, a transcript driven by the host gene promoter, that is predominantly found in germ cells but is ubiquitously expressed at low levels; and variants 2-5, a group of alternatively spliced transcripts containing some unique untranslated exons that are transcribed from a novel promoter that is germ-cell-specific. Utp14b (predominantly variant 1) is expressed at moderately high levels in pachytene spermatocytes, the developmental stage at which the expression of the X-linked Utp14a is suppressed. The levels of both classes of Utp14b transcripts were highest in round spermatids despite the transcription of Utp14a in these cells. We propose that when Utp14b initially inserted into Acsl3, it utilized the Acsl3 promoter to drive expression in pachytene spermatocytes to compensate for inactivation of Utp14a expression. The novel cell-type-specific promoter for Utp14b likely evolved later, as the protein may have acquired a germ cell-specific function in spermatid development.

2-Deoxyglucose: An anticancer and antiviral therapeutic, but not any more a low glucose mimetic

2-Deoxyglucose (2-DG), a non-metabolizable glucose analogue, blocks glycolysis and inhibits protein glycosylation. It has been tested in multiple studies for possible application as an anticancer or antiviral therapeutic. The inhibitory effect of 2-DG on ATP generation made it a good candidate molecule as a calorie restriction mimetic as well. Furthermore, 2-DG has been utilized in numerous studies to simulate a condition of glucose starvation. Because 2-DG disrupts glucose metabolism, protein glycosylation, and ER quality control at the same time, a cellular or pathologic outcome could be easily misinterpreted without clear understanding of 2-DG's effect on each of these aspects. However, the effect of 2-DG on protein glycosylation has rarely been investigated. A recent study suggested that 2-DG causes hyperGlcNAcylation of proteins, while low glucose supply causes hypoGlcNAcylation. In certain aspects of cellular physiology, this difference could be disregarded, but in others, this may possibly cause totally different outcomes.

Combinatorial transcription of herpes simplex virus and varicella zoster virus immediate early genes is strictly determined by the cellular coactivator HCF-1

The mammalian transcriptional coactivator host cell factor-1 (HCF-1) functions in concert with Oct-1 and VP16 to assemble the herpes simplex virus (HSV) immediate early (IE) transcription enhancer core complexes that mediate the high level transcription of these genes upon infection. Although this transcriptional model has been well characterized in vitro, the requirements and significance of the components have not been addressed. Oct-1 was previously determined to be critical but not essential for HSV IE gene expression. In contrast, RNA interference-mediated depletion of HCF-1 resulted in abrogation of HSV IE gene expression. The HSV IE gene enhancer domain is a model of combinatorial transcription and consists of the core enhancer and multiple binding sites for factors such as Sp1 and GA-binding protein. It was striking that HCF-1 was strictly required for VP16-mediated transcriptional induction via the core enhancer as well as for basal level transcription mediated by GA-binding protein and Sp1. HCF-1 was also found to be essential for the induction of varicella zoster virus IE gene expression by ORF10, the VZV ortholog of the HSV IE transactivator VP16, and the autostimulatory IE62 protein. The critical dependence upon HCF-1 demonstrates that this cellular component is a key factor for control of HSV and VZV IE gene expression by functioning as the common element for distinct factors cooperating at the IE gene enhancers. The requirements for this protein supports the model whereby the regulated transport of HCF-1 from the cytoplasm to the nucleus in sensory neurons may control IE gene expression and reactivation of these viruses from the latent state.

Genomic organization of the cadmium-inducible tandem repeat 25-kDa metallothionein of the oligochaete worm Enchytraeus buchholzi

The terrestric oligochaete worm Enchytraeus buchholzi survives in cadmium (Cd)-polluted environments by aid of its Cd-inducible 25 kDa cysteine-rich protein (CRP). Here, we analyze promoter and structure of the crp gene and compare its relationship to MT genes. The crp gene, approximately 12 kbp long, consists of 10 exons with exons 2 to 9 encoding eight almost identical repeats of predominantly 31 amino acids of the CRP. The introns of the crp gene contain various repetitive elements including retrotransposon-like sequences. The 683-bp promoter of the non-constitutive crp gene exhibits a much higher basal activity than the mouse MT-II promoter in HepG2 cells. Essential for crp promoter activity is the distal region (-683/-521) with a GC box and the proximal region (-308/-8) with the four MREa, b, c, d and AP-1, -2, -3 elements, whereas the central portion (-521/-309) with CAAT box, CRE and a XRE causes promoter repression. The TATA box-, MREc- and the AP-2, -3-containing region are required for high crp promoter activity. Our data support the view that the crp gene is a unique MT-gene and has evolved by exon duplications from a MT-like ancestral gene.

During lytic infection herpes simplex virus type 1 is associated with histones bearing modifications that correlate with active transcription

Herpes simplex virus type 1 (HSV-1) is a large (150-kb) double-stranded DNA virus that forms latent infections in neuronal cells of the human peripheral nervous system. Previous work determined that the HSV-1 genome is found in an ordered nucleosomal structure during latent infection. However, during lytic infection, it was unclear whether viral DNA was in a chromatin state. We examined HSV-1 during lytic infection using micrococcal nuclease digestion and chromatin immunoprecipitation. The HSV-1 genome is at least partially nucleosomal, although apparently not in a regular repeating structure. Analysis of histones associated with HSV-1, within both the promoter and the transcribed regions, revealed covalent amino tail modifications similar to those associated with active host mammalian genes. Certain of the modifications were detected in the temporal order expected of the immediate-early, early, and late gene classes. These data suggest that productive infection may be accompanied by acquisition of a permissive chromatin state.

VP16-dependent association of chromatin-modifying coactivators and underrepresentation of histones at immediate-early gene promoters during herpes simplex virus infection

During infection by herpes simplex virus type 1 (HSV-1), the virion protein VP16 activates the transcription of viral immediate-early (IE) genes. Genetic and biochemical assays have shown that the potent transcriptional activation domain of VP16 can associate with general transcription factors and with chromatin-modifying coactivator proteins of several types. The latter interactions are particularly intriguing because previous reports indicate that HSV-1 DNA does not become nucleosomal during lytic infection. In the present work, chemical cross-linking and immunoprecipitation assays were used to probe the presence of activators, general transcription factors, and chromatin-modifying coactivators at IE gene promoters during infection of HeLa cells by wild-type HSV-1 and by RP5, a viral strain lacking the VP16 transcriptional activation domain. The presence of VP16 and Oct-1 at IE promoters did not depend on the activation domain. In contrast, association of RNA polymerase II, TATA-binding protein, histone acetyltransferases (p300 and CBP), and ATP-dependent remodeling proteins (BRG1 and hBRM) with IE gene promoters was observed in wild-type infections but was absent or reduced in cells infected by RP5. In contrast to the previous evidence for nonnucleosomal HSV-1 DNA, histone H3 was found associated with viral DNA at early times of infection. Interestingly, histone H3 was underrepresented on IE promoters in a manner dependent on the VP16 activation domain. Thus, the VP16 activation domain is responsible for recruiting general transcription factors and coactivators to IE promoters and also for dramatically reducing the association of histones with those promoters.

A Protein Sequestering System Reveals Control of Cellular Programs by the Transcriptional Coactivator HCF-1

The mammalian transcriptional coactivator HCF-1 is a critical component of the multiprotein herpes simplex virus immediate early gene enhancer core complex. The protein has also been implicated in basic cellular processes such as cell-cycle progression, transcriptional coactivation, and mRNA processing. Functions have been attributed to HCF-1 primarily from analyses of protein-protein interactions and from the cell-cycle-arrested phenotype of an HCF-1 temperature-sensitive mutant. However, neither the mechanisms involved nor specific cellular transcriptional targets have been identified. As the protein is essential for cell viability and proliferation, a genetic system was developed to specifically sequester the nuclear factor in the cell cytoplasm in a regulated manner. This approach exhibits no significant cell toxicity yet clearly demonstrates the requirement of available nuclear HCF-1 for herpes simplex virus immediate early gene expression during productive infection. Additionally, cellular transcriptional events were identified that contribute to understanding the functions ascribed to the protein and implicate the protein in events that impact the regulation of critical cellular processes.

Down-regulation of Sp1 Activity through Modulation of O-Glycosylation by Treatment with a Low Glucose Mimetic, 2-Deoxyglucose

2-Deoxyglucose (2-DG), a nonmetabolizable glucose analogue, blocks glycolysis at the phosphohexose isomerase step and has been frequently used as a glucose starvation mimetic in studies of a wide variety of physiological dysfuctions. However, the effect of 2-DG on protein glycosylation and related signal pathways has not been investigated in depth. In HeLa, an HPV18-positive cervical carcinoma line, 2-DG treatment down-regulates human papillomavirus early gene transcription. This down-regulation was also achieved by low glucose supply or hypoxia, suggesting that this is a response commonly modulated by cellular glucose or energy level. We investigated how 2-DG and low glucose affect transcriptional activity. Human papillomavirus gene transcription was only marginally affected by the inhibition of ATP synthesis or the supplementation of pyruvate to 2-DG-treated cells, suggesting that poor ATP generation is involved only to a limited extent. 2-DG treatment also inhibited activation of p21 WAF1 promoter, which is controlled by p53 and/or Sp1. In a reporter assay using p21 WAF1 promoter constructs, 2-DG exerted a strong inhibitory effect on Sp1 activity. DNA binding activity of Sp1 in 2-DG-treated HeLa cells was intact, whereas it was severely impaired in cells incubated in a low glucose medium or in hypoxic condition. Unexpectedly, Sp1 was heavily modified with GlcNAc in 2-DG-treated cells, which is at least partially attributed to the inhibitory effect of 2-DG on N-acetyl-beta-D-glucosaminidase activity. Our results suggest that 2-DG, like low glucose or hypoxic condition, down-regulates Sp1 activity, but through hyper-GlcNAcylation instead of hypo-GlcNAcylation.

Analysis of herpes simplex virus ICP0 promoter function in sensory neurons during acute infection, establishment of latency, and reactivation in vivo

We have begun an analysis of the functional architecture of the ICP0 promoter in neurons in vivo with the ultimate goal of determining how this gene is regulated during reactivation in vivo. Promoter/reporter mutants in which the Escherichia coli beta-galactosidase (beta-Gal) gene was driven by various permutations of the ICP0 promoter were employed to permit the analysis of promoter function without the added complications that would arise due to inappropriate regulation of ICP0 protein levels. A whole-ganglion immunohistochemical staining procedure (N. M. Sawtell, J. Virol. 77:4127-4138, 2003) was used for direct comparisons of the expression of the promoter/reporter gene to expression of the native protein in the same cell. In this way, the expression of the putative wild-type promoter could be validated and results for mutant promoters could be compared to expression of the native gene. We found that a DNA fragment from bp -562 through the methionine start codon of the ICP0 gene contained all sequences required for properly regulated ICP0 expression in diverse cell types (including sensory neurons of the trigeminal ganglia [TG]) in vitro and in vivo, as indicated by colocalization of ICP0 and beta-Gal. Truncation of the ICP0 promoter to bp -145 or -129 resulted in the loss of immediate-early (alpha) kinetics. The truncated promoters expressed high levels of the reporter gene with leaky late (gamma1) kinetics in vitro and in some cell types in vivo. Unexpectedly, the truncated promoters did not express in TG neurons. Thus, TAATGARAT or other sequences upstream of bp -145 in the ICP0 promoter are required for basal expression of ICP0 in neurons but are not required for basal expression in other cells in vivo. There was a >95% concordance between reporter and native protein expression detected with the 562-bp promoter in neurons during the acute stage. However, this was not the case during reactivation from latency in vivo, as nearly twice as many neurons contained detectable beta-Gal as contained detectable ICP0. This same 562-bp promoter/reporter cassette, when placed in the context of a latency-associated transcript (LAT) null mutant, resulted in >95% concordance of expression of beta-Gal and ICP0 during reactivation in vivo. These last results strongly suggest that there is a posttranscriptional constraint on the expression of ICP0 protein during reactivation from latency and that this constraint is mediated by LAT.

Single HSV-amplicon vector mediates drug-induced gene expression via dimerizer system

A variety of viral vectors have been used to deliver genes into various tissues. Most have typically relied on either viral or cell-specific mammalian promoters to express transgenes. More recently, regulated promoter systems have been developed to fine-tune gene expression. Due to limited transgene capacity in most viral vectors, regulatory elements are typically subcloned into two separate vectors, which must be delivered simultaneously to a target cell. Here, we have cloned all the components of the rapamycin-based "dimerizer" system into the pantropic HSV-amplicon vector and used it to deliver and regulate red fluorescent protein (RFP) expression in cultured cells in a drug-dose-dependent manner. 293T/17 cells infected at an m.o.i. of 1 transducing unit/cell and induced with 20 nM rapamycin resulted in a 25-fold increase in RFP mRNA levels after 24 h as assessed by quantitative RT-PCR. However, due to a reduced ability to detect RFP optically, only a 5-fold induction in the number of RFP-expressing cells was noted by FACS analysis 48 h after infection. Further, there was at least 100-fold variation in the levels of RFP in individual, infected cells in the induced state. Gene induction in several neuronal models, including primary cell culture and organotypic cultures, as well as in rodent brain, was observed.

Characterization of the human p11 promoter sequence

p11 is expressed in many different cell types, and serves a variety of regulatory functions. In order to better understand the transcriptional control of this protein, the 5' promoter region of the human p11 gene was cloned and sequenced. After confirming the transcription start point (TSP) using 5' rapid amplification of cDNA ends analysis, the 5' promoter was analysed. The sequence lacks a TATA box, but contains a variety of putative regulatory elements. There are two GAS sites, two AP-1 sites, two overlapping Sp-1 sites, and a gamma-IRE site clustered between -1080 and -1450. There is another cluster of putative regulatory sites between the TSP and -550 which contains two Sp-1 sites, two AP-2 sites, one GAS site, one NF-kappaB site, an incomplete CAAT box (8/9) and an overlapping Sp-1/AP-2 site at -17 to -26. Reporter gene constructs containing 4225 and 1498 bases 5' of the TSP demonstrated excellent unidirectional transcriptional activity in both constructs. Reporter genes containing serial 5' deletions were compared to the -1498 construct. The reporter gene which contained base pairs (bp) -36 to +89 had almost no activity. The reporter gene containing -188 to +89 had 50% of the -1498 construct, indicating that this sequence contains at least the minimal promoter. The Sp-1/AP-2 site near the transcription start site was studied by electrophoretic mobility shift and reporter gene assays. Addition of HeLa cell nuclear extract to labeled double-stranded (ds) oligonucleotide containing this sequence resulted in a gel shift which was inhibited by excess unlabeled ds oligonucleotide and by a consensus cold Sp-1 ds oligonucleotide, indicating specific Sp-1 binding. Excess AP-2 or NF-kappaB ds oligonucleotide had no effect on nuclear protein binding to the sequence. Mutation of the p11 wild-type Sp-1/AP-2 sequence eliminated both nuclear protein binding and the sequences ability to compete with native sequence for nuclear binding protein. A -1048 to +89 reporter construct containing a mutated Sp-1/AP-2 site resulted in a 40% decrease in transcriptional activity. Therefore, the 5' flanking sequence of the p11 gene exhibits promoter activity which may be localized to a variety of controlling regions, of which the proximal Sp-1/AP-2 site appears to be important for basal activity via its Sp-1 binding ability.

Inhibition of HSV-1 replication and reactivation by the mutation-insensitive transcription inhibitor tetra-O-glycyl-nordihydroguaiaretic acid

Methylated derivatives of nordihydroguaiaretic acid (NDGA)were previously shown to be potent mutation-resistant inhibitors of herpes simplex virus type 1 (HSV-1) which target Sp1 protein binding to critical viral promoters. The hydrophobic nature of these agents, however, renders them relatively water-insoluble and, therefore, limits their applicability. We report here on the anti-HSV-1 properties of a related but water-soluble glycylated derivative of NDGA, tetra-O-glycyl-NDGA (G(4)N). In yield reduction assays, G(4)N inhibited replication of laboratory and clinical strains of wild type HSV-1 and ACV-resistant (HSV-1(R)) strains of HSV-1 in a dose-dependent manner, with average IC(50) values of 4.7 and 3.2 microM against wild-type and HSV-1(R) strains, respectively. An MTT-based cytotoxicity assay revealed a TC(50) value of 73.2 microM for G(4)N on Vero cells, with no reduction in viability detected at concentrations below 30 microM. Similar to its methylated counterparts, G(4)N was found to inhibit transcription of the HSV-1 ICP4 gene, a major immediate early viral regulator, and gel mobility shift assays showed it can block Sp1 protein binding to cognate sites on the ICP4 promoter. In anticipation of its potential use as a systemic anti-HSV-1 agent, we tested G(4)N in a murine trigeminal ganglia (TG) explant model system, and found G(4)N was able to prevent HSV-1 reactivation from explanted and cultured latently infected TG.

Sp1 is essential for estrogen receptor alpha gene transcription

The exact molecular mechanisms regulating estrogen receptor (ER)alpha expression in breast tumors are unclear, but studies suggest that the regulation is at least partly transcriptional. We therefore undertook a detailed analysis of ERalpha promoter activity in a number of breast cancer cell lines. We find that the majority of ERalpha promoter activity lies within the first 245bp of the 5'-flanking region of the gene. Three elements essential for full ERalpha promoter transcriptional activity were identified within the -245 to -192bp region in transient transactivation assays using linker-scanner mutation analysis. These three elements include two binding sites for the Sp1 family of transcription factors as well as a non-consensus E box. We show that both Sp1 and Sp3 bind to this region using electrophoretic mobility shift assays. Exogenous expression of Sp1 or Sp3 in Sp1/3-negative Drosophila Schneider SL2 cells results in transactivation of the -245 to +212bp fragment of the ERalpha promoter. These data demonstrate that transcription of ERalpha is dependent upon the expression of members of the Sp1 family.

Promoter of FGF8 reveals a unique regulation by unliganded RARalpha

We previously reported that retinoids were inducing a complete switch in the expression of two isoforms from the fgf8 gene. In order to gain insight into the transcriptional mechanisms possibly involved in this regulation, we cloned and sequenced a fragment of genomic DNA encompassing 6 kb of the region 5' upstream of the fgf8 coding sequence and investigated its promoter elements. A comprehensive series of biochemical and cellular experiments determined two distinct functional regions cis-responsive to retinoids and/or their receptors: (i) a canonical RARE (type DR2) which is the cis target of a RARalpha-RXRalpha liganded heterodimer; and (ii) a completely novel type of response element composed of two half-binding sites separated by 87 nucleotides, which we demonstrate to be the target of an unliganded RARalpha homodimer phosphorylated on the Ser77 residue. Combined activities of these cis and trans-acting factors support a model of a complex regulation of fgf8 expression: by alternative binding to two distinct promoter elements, phosphorylated-unliganded-RARalpha homodimer or its liganded form have two distinct and mutually exclusive trans-activating activities, explaining the expression of two different isoforms of fgf8.

A single cell cycle genes homology region (CHR) controls cell cycle-dependent transcription of the cdc25C phosphatase gene and is able to cooperate with E2F or Sp1/3 sites

The cdc25C phosphatase participates in regulating transition from the G2 phase of the cell cycle to mitosis by dephosphorylating cyclin-dependent kinase 1. The tumor suppressor p53 down-regulates expression of cdc25C as part of G2/M checkpoint control. Transcription of cdc25C oscillates during the cell cycle with no expression in resting cells and maximum transcription in G2. We had identified earlier a new mechanism of cell cycle-dependent transcription that is regulated by a cell cycle-dependent element (CDE) in conjunction with a cell cycle genes homology region (CHR). The human cdc25C gene was the first example. CDE/CHR tandem elements have since been found in promoters of many cell cycle genes. Here we show that the mouse cdc25C gene is regulated by a CHR but does not hold a CDE. Therefore, it is the first identified gene with CHR-dependent transcriptional regulation during the cell cycle not relying on a CDE located upstream of it. The CHR leads to repression of cdc25C transcription early in the cell cycle and directs a release of this repression in G2. Furthermore, we find that this CHR can cooperate in cell cycle-dependent transcription with elements placed directly upstream of it binding E2F, Sp1 or Sp3 transcription factors.

Neurons differentially activate the herpes simplex virus type 1 immediate-early gene ICP0 and ICP27 promoters in transgenic mice

Herpes simplex virus type 1 (HSV-1) immediate-early (IE) proteins are required for the expression of viral early and late proteins. It has been hypothesized that host neuronal proteins regulate expression of HSV-1 IE genes that in turn control viral latency and reactivation. We investigated the ability of neuronal proteins in vivo to activate HSV-1 IE gene promoters (ICP0 and ICP27) and a late gene promoter (gC). Transgenic mice containing IE (ICP0 and ICP27) and late (gC) gene promoters of HSV-1 fused to the Escherichia coli beta-galactosidase coding sequence were generated. Expression of the ICP0 and ICP27 reporter transgenes was present in anatomically distinct subsets of neurons in the absence of viral proteins. The anatomic locations of beta-galactosidase-positive neurons in the brains of ICP0 and ICP27 reporter transgenic mice were similar and included cerebral cortex, lateral septal nucleus, cingulum, hippocampus, thalamus, amygdala, and vestibular nucleus. Trigeminal ganglion neurons were positive for beta-galactosidase in adult ICP0 and ICP27 reporter transgenic mice. The ICP0 reporter transgene was differentially regulated in trigeminal ganglion neurons depending upon age. beta-galactosidase-labeled cells in trigeminal ganglia and cerebral cortex of ICP0 and ICP27 reporter transgenic mice were confirmed as neurons by double labeling with antineurofilament antibody. Nearly all nonneuronal cells in ICP0 and ICP27 reporter transgenic mice and all neuronal and nonneuronal cells in gC reporter transgenic mice were negative for beta-galactosidase labeling in the absence of HSV-1. We conclude that factors in neurons are able to differentially regulate the HSV-1 IE gene promoters (ICP0 and ICP27) in transgenic mice in the absence of viral proteins. These findings are important for understanding the regulation of the latent and reactivated stages of HSV-1 infection in neurons.

The transgenic ICP4 promoter is activated in Schwann cells in trigeminal ganglia of mice latently infected with herpes simplex virus type 1

Herpes simplex virus type 1 (HSV-1) establishes a latent infection in neurons of sensory ganglia, including those of the trigeminal ganglia. Latent viral infection has been hypothesized to be regulated by restriction of viral immediate-early gene expression in neurons. Numerous in situ hybridization studies in mice and in humans have shown that transcription from the HSV-1 genome in latently infected neurons is limited to the latency-associated transcripts. In other studies, immediate-early gene (ICP4) transcripts have been detected by reverse transcription-PCR (RT-PCR) in homogenates of latently infected trigeminal ganglia of mice. We used reporter transgenic mice containing the HSV-1(F) ICP4 promoter fused to the coding sequence of the beta-galactosidase gene to determine whether neurons in latently infected trigeminal ganglia activated the ICP4 promoter. Mice were inoculated via the corneal route with HSV-1(F). At 5, 11, 23, and 37 days postinfection (dpi), trigeminal ganglia were examined for beta-galactosidase-positive cells. The numbers of beta-galactosidase-positive neurons and nonneuronal cells were similar at 5 dpi. The number of positive neurons decreased at 11 dpi and returned to the level of mock-inoculated transgenic controls at 23 and 37 dpi. The number of positive nonneuronal cells increased at 11 and 23 dpi and remained elevated at 37 dpi. Viral proteins were detected in neurons and nonneuronal cells in acutely infected ganglia, but were not detected in latently infected ganglia. Colabeling experiments confirmed that the transgenic ICP4 promoter was activated in Schwann cells during latent infection. These findings suggest that the cells that express the HSV-1 ICP4 gene in latently infected ganglia are not neurons.