Butyrate-induced reversal of herpes simplex virus restriction in neuroblastoma cells

Gut microbiota-derived butyrate promotes coronavirus TGEV infection through impairing RIG-I-triggered local type I interferon responses via class I HDAC inhibition

Gut microbiota-derived metabolites are important for the replication and pathogenesis of many viruses. However, the roles of bacterial metabolites in swine enteric coronavirus (SECoV) infection remain poorly understood. Recent studies show that SECoVs infection in vivo significantly alters the composition of short-chain fatty acids (SCFAs)-producing gut microbiota. This prompted us to investigate whether and how SCFAs impact SECoV infection. Employing alphacoronavirus transmissible gastroenteritis virus (TGEV), a major cause of diarrhea in piglets, as a model, we found that SCFAs, particularly butyrate, enhanced TGEV infection both in porcine intestinal epithelial cells and swine testicular (ST) cells at the late stage of viral infection. This effect depended on the inhibited productions of virus-induced type I interferon (IFN) and downstream antiviral IFN-stimulated genes (ISGs) by butyrate. Mechanistically, butyrate suppressed the expression of retinoic acid-inducible gene I (RIG-I), a key viral RNA sensor, and downstream mitochondrial antiviral-signaling (MAVS) aggregation, thereby impairing type I IFN responses and increasing TGEV replication. Using pharmacological and genetic approaches, we showed that butyrate inhibited RIG-I-induced type I IFN signaling by suppressing class I histone deacetylase (HDAC). In summary, we identified a novel mechanism where butyrate enhances TGEV infection by suppressing RIG-I-mediated type I IFN responses. Our findings highlight that gut microbiota-derived metabolites like butyrate can be exploited by SECoV to dampen innate antiviral immunity and establish infection in the intestine.IMPORTANCESwine enteric coronaviruses (SECoVs) infection in vivo alters the composition of short-chain fatty acids (SCFAs)-producing gut microbiota, but whether microbiota-derived SCFAs impact coronavirus gastrointestinal infection is largely unknown. Here, we demonstrated that SCFAs, particularly butyrate, substantially increased alphacoronavirus TGEV infection at the late stage of infection, without affecting viral attachment or internalization. Furthermore, enhancement of TGEV by butyrate depended on impeding virus-induced type I interferon (IFN) responses. Mechanistically, butyrate suppressed the cytoplasmic viral RNA sensor RIG-I expression and downstream type I IFN signaling activation by inhibiting class I HDAC, thereby promoting TGEV infection. Our work reveals novel functions of gut microbiota-derived SCFAs in enhancing enteric coronavirus infection by impairing RIG-I-dependent type I IFN responses. This implies that bacterial metabolites could be therapeutic targets against SECoV infection by modulating antiviral immunity in the intestine.

Sodium Butyrate Induced Neural Stem/Progenitor Cell Death in an Experimental Model of Japanese Encephalitis

The anti-inflammatory and neuroprotective effects of short chain fatty acid (SCFA) butyrate have been explored in a wide array of neurological pathologies. It is a 4-carbon SCFA produced from the fermentation of dietary fibers by the gut-microbiota. As evident from previous literature, butyrate plays a wide array of functions in CNS and interestingly enhances the differentiation potential of Neural stem/Progenitor Cells (NSPCs). Japanese encephalitis virus (JEV) is a well-known member of the Flaviviridae family and has been shown to alter neural stem cell pool of the brain, causing devastating consequences. In this study, we administered sodium butyrate (NaB) post JEV infection in BALB/c mouse model to examine any possible amelioration of the viral infection in NSPCs. In addition, ex vivo neurospheres and in vitro model of NSPCs were also used to study the effect of sodium butyrate in JEV infection. As an unprecedented finding, butyrate treated infected animals presented early onset of symptoms, as compared to their respective JEV infected groups. Alongside, we observed an increased viral load in NSPCs isolated from these animals as well as in cell culture models upon sodium butyrate treatment. Cytometric bead array analysis also revealed an increase in inflammatory cytokines, particularly, MCP-1 and IL-6. Further, increased expression of the key members of the canonical NF-κB pathway, viz-a-viz p-NF-κB, p-Iκ-Bα and p-IKK was observed. Overall, the increased inflammation and cell death caused early symptom progression in NaB-treated JEV infected animal model, which is contradictory to the well documented protective nature of NaB and therefore a better understanding of SCFA-based modulation of the gut-brain axis in viral infections is required.

Regulation of Immune Homeostasis, Inflammation, and HIV Persistence by the Microbiome, Short-Chain Fatty Acids, and Bile Acids

Despite antiretroviral therapy (ART), people living with human immunodeficiency virus (HIV) (PLWH) continue to experience chronic inflammation and immune dysfunction, which drives the persistence of latent HIV and prevalence of clinical comorbidities. Elucidating the mechanisms that lead to suboptimal immunity is necessary for developing therapeutics that improve the quality of life of PLWH. Although previous studies have found associations between gut dysbiosis and immune dysfunction, the cellular/molecular cascades implicated in the manifestation of aberrant immune responses downstream of microbial perturbations in PLWH are incompletely understood. Recent literature has highlighted that two abundant metabolite families, short-chain fatty acids (SCFAs) and bile acids (BAs), play a crucial role in shaping immunity. These metabolites can be produced and/or modified by bacterial species that make up the gut microbiota and may serve as the causal link between changes to the gut microbiome, chronic inflammation, and immune dysfunction in PLWH. In this review, we discuss our current understanding of the role of the microbiome on HIV acquisition and latent HIV persistence despite ART. Further, we describe cellular/molecular cascades downstream of SCFAs and BAs that drive innate or adaptive immune responses responsible for promoting latent HIV persistence in PLWH. This knowledge can be used to advance HIV cure efforts.

Butyrate Reprograms Expression of Specific Interferon-Stimulated Genes

Butyrate is an abundant metabolite produced by gut microbiota. While butyrate is a known histone deacetylase inhibitor that activates expression of many genes involved in immune system pathways, its effects on virus infections and on the antiviral type I interferon (IFN) response have not been adequately investigated. We found that butyrate increases cellular infection with viruses relevant to human and animal health, including influenza virus, reovirus, HIV-1, human metapneumovirus, and vesicular stomatitis virus. Mechanistically, butyrate suppresses levels of specific antiviral IFN-stimulated gene (ISG) products, such as RIG-I and IFITM3, in human and mouse cells without inhibiting IFN-induced phosphorylation or nuclear translocation of the STAT1 and STAT2 transcription factors. Accordingly, we discovered that although butyrate globally increases baseline expression of more than 800 cellular genes, it strongly represses IFN-induced expression of 60% of ISGs and upregulates 3% of ISGs. Our findings reveal that there are differences in the IFN responsiveness of major subsets of ISGs depending on the presence of butyrate in the cell environment, and overall, they identify a new mechanism by which butyrate influences virus infection of cells.IMPORTANCE Butyrate is a lipid produced by intestinal bacteria. Here, we newly show that butyrate reprograms the innate antiviral immune response mediated by type I interferons (IFNs). Many of the antiviral genes induced by type I IFNs are repressed in the presence of butyrate, resulting in increased virus infection and replication. Our research demonstrates that metabolites produced by the gut microbiome, such as butyrate, can have complex effects on cellular physiology, including dampening of an inflammatory innate immune pathway resulting in a proviral cellular environment. Our work further suggests that butyrate could be broadly used as a tool to increase growth of virus stocks for research and for the generation of vaccines.

Quality by Design-Driven Process Development of Severe Fever With Thrombocytopenia Syndrome Vaccine

Owing to the biological activity of the vaccine, the complicated production process, sterility, and uniformity of the product, the producing process of the vaccine is complicated and the product quality hard to control. In recent years, with the development of basic science such as cell biology, molecular biology, and metabolic engineering, bioprocess engineering research has developed rapidly. Therefore, U.S. Food and Drug Administration and European Medicines Agency conduct stringent control over the development of biomedical process engineering and product quality. This case study describes an example of Quality by Design-driven process development for manufacturing a human vaccine produced with Vero cells. Cell density in harvest fermentation broth and antigenic titer were chosen as 2 critical quality attributes. The study through 3 rounds design of experiment revealed that H₂O₂ and cell boost 4 had a significant effect on antigenic titer. Ethanolamine had significant improvement in the final concentration of cells. Through the Monte Carlo simulation, the design spaces and control space of process parameters were determined. A successful validation in a bioreactor was executed to verify the results of a spinner flask. Our investigation presents a successful case of Quality by Design principle, which encourages other researchers to combine the methodology into other biopharmaceutical manufacturing process.

Effects of innate immunity on herpes simplex virus and its ability to kill tumor cells

Several clinical trials have or are being performed testing the safety and efficacy of different strains of oncolytic viruses (OV) for malignant cancers. OVs represent either naturally occurring or genetically engineered strains of viruses that exhibit relatively selective replication in tumor cells. Several types of OV have been derived from herpes simplex virus 1 (HSV1). Tumor oncolysis depends on the processes of initial OV infection of tumor, followed by subsequent propagation of OV within the tumor itself. The role of the immune responses in these processes has not been extensively studied. On the contrary, effects of the immune response on the processes of wild-type HSV1 infection and propagation in the central nervous system have been studied and described in detail. The first line of defense against a wild-type HSV1 infection in both naive and immunized individuals is provided by innate humoral (complement, cytokines, chemokines) and cellular (macrophages, neutrophils, NK cells, gammadelta T cells, and interferon-producing cells) responses. These orchestrate the lysis of virions and virus-infected cells as well as provide a link to effective adaptive immunity. The role of innate defenses in curtailing the oncolytic effect of genetically engineered HSV has only recently been studied, but several of the same host responses appear to be operative in limiting anticancer effects by the replicating virus. The importance of this knowledge lies in finding avenues to modulate such initial innate responses, in order to allow for increased oncolysis of tumors while minimizing host toxicity.

Human neuron-committed teratocarcinoma NT2 cell line has abnormal ND10 structures and is poorly infected by herpes simplex virus type 1

Herpes simplex virus type 1 (HSV-1) immediate-early regulatory protein ICP0 stimulates the initiation of lytic infection and reactivation from quiescence in human fibroblast cells. These functions correlate with its ability to localize to and disrupt centromeres and specific subnuclear structures known as ND10, PML nuclear bodies, or promyelocytic oncogenic domains. Since the natural site of herpesvirus latency is in neurons, we investigated the status of ND10 and centromeres in uninfected and infected human cells with neuronal characteristics. We found that NT2 cells, a neuronally committed human teratocarcinoma cell line, have abnormal ND10 characterized by low expression of the major ND10 component PML and no detectable expression of another major ND10 antigen, Sp100. In addition, PML is less extensively modified by the ubiquitin-like protein SUMO-1 in NT2 cells compared to fibroblasts. After treatment with retinoic acid, NT2 cells differentiate into neuron-like hNT cells which express very high levels of both PML and Sp100. Infection of both NT2 and hNT cells by HSV-1 was poor compared to human fibroblasts, and after low-multiplicity infection yields of virus were reduced by 2 to 3 orders of magnitude. ICP0-deficient mutants were also disabled in the neuron-related cell lines, and cells quiescently infected with an ICP0-null virus could be established. These results correlated with less-efficient disruption of ND10 and centromeres induced by ICP0 in NT2 and hNT cells. Furthermore, the ability of ICP0 to activate gene expression in transfection assays in NT2 cells was poor compared to Vero cells. These results suggest that a contributory factor in the reduced HSV-1 replication in the neuron-related cells is inefficient ICP0 function; it is possible that this is pertinent to the establishment of latent infection in neurons in vivo.

Complement depletion facilitates the infection of multiple brain tumors by an intravascular, replication-conditional herpes simplex virus mutant

Intravascular routes of administration can provide a means to target gene- and virus-based therapies to multiple tumor foci located within an organ, such as the brain. However, we demonstrate here that rodent plasma inhibits cell transduction by replication-conditional (oncolytic) herpes simplex viruses (HSV), replication-defective HSV, and adenovirus vectors. In vitro depletion of complement with mild heat treatment or in vivo depletion by treatment of athymic rats with cobra venom factor (CVF) partially reverses this effect. Without CVF, inhibition of cell infection by HSV is observed at plasma dilution as high as 1:32, while plasma from CVF-treated animals displays anti-HSV activity at lower dilutions (1:8). When applied to the therapy of intracerebral brain tumors, in vivo complement depletion facilitates the initial infection (assayed at the 2-day time point) by an intra-arterial replication-conditional HSV of tumor cells, located within three separate and distinct human glioma masses. However, at the 4-day time point, no propagation of HSV from initially infected tumor cells could be observed. Previously, we have shown that the immunosuppressive agent, cyclophosphamide (CPA), facilitates the in vivo propagation of an oncolytic HSV, delivered intravascularly, within infected multiple intracerebral masses, by inhibition of both innate and elicited anti-HSV neutralizing antibody response (K. Ikeda et al., Nat. Med. 5:881-889, 1999). In this study, we thus show that the addition of CPA to the CVF treatment results in a significant increase in viral propagation within infected tumors, measured at the 4-day time period. The concerted action of CVF and CPA significantly increases the life span of athymic rodents harboring three separate and large glioma xenografts after treatment with intravascular, oncolytic HSV. Southern analysis of viral genomes analyzed by PCR reveals the presence of the oncolytic virus in the brains, livers, spleens, kidneys, and intestine of treated animals, although none of these tissues displays evidence of HSV-mediated gene expression. In light of clinical trials of oncolytic HSV for malignant brain tumors, these findings suggest that antitumor efficacy may be limited by the host innate and elicited humoral responses.

Gene therapy of brain tumors: problems presented by physiological barriers

The explosion of molecular techniques for gene discovery and their application to a variety of diseases has uncovered numerous gene abnormalities that can result in disease. These discoveries have provided the needed understanding and genetic materials to apply gene therapy approaches in the treatment of several diseases, including those of the central nervous system. A variety of different anticancer complementary DNAs (cDNA) have been shown to possess biological efficacy when used in the appropriate experimental setting. However, efficient and effective delivery of these cDNAs remains a major obstacle for future clinical applications. The focus of this review will be to describe the obstacles that impede the process of gene therapy and oncolytic viral therapy of brain tumors and to describe how important new discoveries derived from other disciplines are being used to address problems encountered in the gene/ viral therapy of this disease.

A high-titer lentiviral production system mediates efficient transduction of differentiated cells including beating cardiac myocytes

Human immunodeficiency virus (HIV, lentivirus) type-1 based vectors have a number of attractive features for gene therapy, including the ability to transduce non-dividing cells and long term transgene expression. We used a three-plasmid expression system to generate pseudotyped lentivirus-based vectors by transient transfection of human embryonic kidney 293T cells in the presence of sodium butyrate, which is known to activate the long terminal repeat-directed expression of HIV. Using this system we successfully generated versatile high titer lentivirus at titers of up to 2 x 10(8) transducing units/ml (TU/ml), and improved transduction efficiency in various cell types from seven to over twenty fold. We demonstrate its applicability of these vectors for the efficient transduction of non-dividing cells, including post mitotic beating rat cardiac myocytes and well-differentiated rat L6 myofibers. While both lentivirus-based and murine retrovirus-based vectors effectively transduced dividing cardiac fibroblasts and L6 muscle myoblasts in culture, lentivirus-based vectors also efficiently transduced cardiac myocytes and yielded titers of (6.3 +/- 1.2) x 10(5) TU/ml; however murine retrovirus-based vectors showed low transduction efficiency with titers reaching only (8.9 +/- 2.1) x 10(2) TU/ml. Furthermore, even 12 days after induction of differentiation of L6 myofibers, lentivirus-mediated transduction of beta-galactosidase (beta-Gal) at approximately 30-40% of the maximum expression levels achieved in replicating myoblasts. In contrast, the expression of beta-Gal following transduction of the myofibers by murine retrovirus-based vectors fell to less than 1% of an already reduced level of transduction in undifferentiated confluent myoblasts. These results demonstrate that lentivirus-based vectors can efficiently transduce both well-differentiated cardiac myocytes and differentiated myofibers. This appears to be an efficient method and provides a new tool for research and therapy for cardiovascular diseases.

The herpes simplex virus type 1 latency-associated transcript promoter is activated through Ras and Raf by nerve growth factor and sodium butyrate in PC12 cells

Herpes simplex virus establishes latent infections in the nuclei of sensory neurons. These infections are characterized by the abundant expression of a series of 5' coterminal transcripts termed the latency-associated transcripts (LATs). Available evidence indicates that LAT expression is specifically regulated in latently infected neurons. Although previous studies have examined the regulation of LAT expression in neuronal and nonneuronal cells, the mechanism of regulation of LAT expression in neuronal cells in response to external factors has not been investigated. To address this question, we characterized the activity of LAT promoter fusion constructs in PC12 cells following treatment with nerve growth factor (NGF) and/or sodium butyrate (NaB), agents that affect expression of cell cycle-associated genes. Expression from the LAT promoter was induced 8- to 12-fold by either NGF or NaB alone and 40- to 60-fold when the two agents were added simultaneously. Fibroblast growth factor also induced expression from the LAT promoter but to a lesser extent than NGF. Treatment with factors such as epidermal growth factor, phorbol myristate acetate, cyclic AMP, or KCI had no significant effect on LAT promoter activity. Notably, promoter-reporter constructs containing immediate-early (ICP0 and ICP4), early (ICP8 and UL9), and late (UL10 and UL30) viral promoters were induced only two- to fourfold by NGF, suggesting that the LAT promoter may be unusual among herpes simplex virus genes in the magnitude of its response to this factor. To identify pathways leading to LAT activation in vitro, we characterized the response of the LAT promoter to NGF and/or NaB in PC12-derived cell lines containing mutations in specific signal transduction pathways. We found that activation of the LAT promoter requires Ras activation and that activation of the serine/threonine kinase, Raf, is sufficient to induce LAT expression. Together, these results indicate that the LAT promoter is regulated via the Ras/Raf signal transduction pathway in response to external factors such as NGF and NaB and that LAT expression may be regulated by NGF in latently infected neurons.

Human herpes viruses latent infection in the nervous system

The neurotropic herpes viruses, HSV-1, HSV-2 and VZV, colonize and establish latent infection in human peripheral sensory ganglia. Recurrent diseases due to reactivation of these viral pathogens can take place despite an effective immune response. Molecular, cellular, physiological and immune mechanisms work in concert to enable the establishment of latency, the maintenance of the latent state for the entire life of the host, and the reactivation infection. Although all three viruses belong to the same family and establish latent infection in the same tissue, the clinical pattern of their reactivation is quite different. This review covers current knowledge of the basis of these infections, and offers a theory explaining the basis of HSV-1 latent infection and the differences of the disorders caused by HSV-1 and VZV reactivation in humans.

Real-time analysis of the transcriptional regulation of HIV and hCMV promoters in single mammalian cells

The regulation of human cytomegalovirus (hCMV) and human immunodeficiency virus (HIV) gene expression has been studied in single intact mammalian cells. Viral promoters were placed upstream of the firefly luciferase reporter gene and the resulting hybrid reporter constructs were stably integrated into the HeLa cell genome. A highly sensitive photon-counting camera system was used to study the level of gene expression in single intact cells. Luciferase expression was studied in the absence of activators of viral gene expression, in the presence of the HIV-1 TAT transactivator protein, or in the presence of sodium butyrate, a non-viral activator of gene expression. In the absence of any activator of gene expression, while expression was undetectable in most cells, significant levels of basal luciferase activity were observed in a few cells, indicating heterogeneity in gene expression in the cell population. In the presence of the general activator of viral gene expression, sodium butyrate, transcriptional activation from the viral promoters gave rise to significant and relatively homogeneous levels of luciferase expression in a majority of cells. The luciferase imaging technology was used for the real-time analysis of changes of gene expression within a single cell. This non-invasive reporter assay should become important for studies of the temporal regulation of gene expression in single cells.

Induction of herpes simplex virus type 1 immediate-early gene expression by a cellular activity expressed in Vero and NB41A3 cells after growth arrest-release

Infected cell protein 0 (ICP0), a major immediate-early regulatory protein of herpes simplex virus type 1 (HSV-1), activates expression of all classes of HSV genes as well as a variety of heterologous viral and cellular genes. Previous studies have shown that a cellular activity expressed maximally in Vero cells 8 h after release from growth arrest in the G0/G1 phase of the cell cycle can enhance plaque formation and gene expression of a mutant virus (7134) lacking both copies of the gene encoding ICP0 (W. Cai and P. Schaffer, J. Virol. 65:4078-4090, 1991). This observation suggests that the cellular activity can substitute for ICP0 to activate viral gene expression. To further characterize this cellular activity, Vero and NB41A3 (mouse neuroblastoma) cells were transfected at various times after release from growth arrest with promoter-chloramphenicol acetyltransferase (CAT) constructs containing promoters representing the major kinetic classes of HSV genes, and CAT activity was measured from 2 to 24 h postrelease. The results of these tests demonstrate that CAT expression from immediate-early promoter-CAT plasmids was enhanced 10- and 3-fold when Vero and NB41A3 cells were transfected at 6 and 2 h postrelease, respectively. In contrast, only low levels of immediate-early promoter-driven CAT activity were apparent when cells were transfected at later times postrelease. No significant stimulation of CAT activity was observed from promoter-CAT plasmids containing representative early or late HSV promoters or a heterologous viral (simian virus 40 early) promoter. Differences in the efficiency of uptake of plasmid DNA by cells at various times postrelease did not account for the observed differences in CAT expression. Unlike Vero cells, in which cell division resumed after release from growth arrest, division of NB41A3 cells did not resume. Rather, these cells displayed morphological features suggestive of a differentiated phenotype. Collectively, these findings demonstrate that a cellular activity expressed in Vero and NB41A3 cells after release from growth arrest can activate HSV gene expression by enhancing immediate-early gene expression.

The effect of short-chain fatty acids on the susceptibility of human umbilical vein endothelial cells to human cytomegalovirus infection

We have compared the replication of three strains of human cytomegalovirus (HCMV), HCMV AD-169, HCMV Towne, or HCMV RC-256, an insertional mutant of Towne containing the LacZ gene of E. coli, in human umbilical vein endothelial cells (HUVEC) and human forskin fibroblasts (HFF). We also examine the effects of salts of short-chain fatty acids on the susceptibility of HUVEC to infection by HCMV. All three virus strains replicated in both cell types, but 10-to 100-fold less virus was produced in HUVEC cells than HFF. For all virus strains, expression of HCMV IE-1 antigen in HFF was > 70% 24 h after inoculation. In contrast, the number of HUVEC exhibiting IE-1 antigen at 24 h was < 15%. Treatment of HUVEC with sodium butyrate, sodium hexanoate, or sodium propionate prior to virus inoculation increased the IE-1 and late HCMV antigen expression in a dose- and time-dependent manner. Virus yield was also increased. This increased susceptibility was inhibited by cycloheximide and tunicamycin, indicating a requirement for new cellular protein synthesis. Treatment with both sodium hexanoate and propionate after virus inoculation increased HUVEC susceptibility to HCMV infection. Treatment of HUVEC with sodium butyrate after virus inoculation also increased HCMV IE-1 antigen expression, but only after removal of the drug. These studies demonstrate that the susceptibility of HUVEC to HCMV infection can be increased by the treatment of the host cell with salts of short-chain fatty acids, such as sodium butyrate, before or after virus inoculation.

Molecular biology of herpes simplex virus type 1 latency in the nervous system

Herpes simplex virus (HSV) is one of the best studied examples of viral ability to remain latent in the human nervous system and to cause recurrent disease by reactivation. Intensive effort was directed in recent years to unveil the molecular viral mechanisms and the virus-host interactions associated with latent HSV infection. The discovery of the state of the latent viral DNA in nervous tissues and of the presence of latency-associated gene expression during latent infection, both differing from the situation during viral replication, provided important clues relevant to the pathogenesis of latent HSV infection. This review summarizes the current state of knowledge on the site of latent infection, the molecular phenomena of latency, and the mechanisms of the various stages of latency: acute infection, establishment and maintenance of latency, and reactivation. This information paved the way to recent trials aiming to use herpes viruses as vectors to deliver genes into the nervous system, an issue that is also addressed in this review.

Sodium butyrate-inducible replication of human cytomegalovirus in a human epithelial cell line

Replication of human cytomegalovirus (HCMV) in a human epithelial thyroid papillary carcinoma cell line (TPC-1) was restricted. However, pretreatment of these cells with 5 mM sodium butyrate (NaB) for 24 hr before infection enhanced both HCMV yield and infectious center titer to a similar level of that seen in human embryonic lung fibroblast cells. Immunofluorescence staining, gel electrophoresis, and Northern blot analysis revealed that TPC-1 cells are nonpermissive for expression of HCMV major immediate early (IE1) functions, but many of the cells become permissive after being treated with NaB. The presence of cycloheximide during NaB pretreatment of the cells efficiently diminished the stimulatory effect of NaB on expression of the IE1 gene. Therefore, it appeared that NaB induces the synthesis of a cellular protein(s) which apparently plays an important role in the conversion of nonpermissive cells to a permissive state for expression of this critical viral gene. Transient chloramphenicol acetyltransferase (CAT) assay experiments indicated that in TPC-1 cells the HCMV-CAT construct which contains the complete IE1 promoter regulatory region was expressed poorly, whereas a high level of CAT activity was detectable in the NaB-treated cells. Therefore, these results suggest that the enhancing effect of NaB on HCMV replication is expressed through some host cellular factor(s), and the HCMV IE1 promoter regulatory region is most likely to be the primary target of NaB action.

The octamer-binding protein Oct-2 represses HSV immediate-early genes in cell lines derived from latently infectable sensory neurons

Transcription of herpes simplex virus (HSV) immediate-early (IE) genes does not occur in sensory neurons latently infected with the virus or following infection of neuronal cell lines. In neuronal cell lines this inability results from the weak activity of the viral IE promoters, which is caused by a neuron-specific repressor factor that binds specifically to the TAATGARAT motif in these promoters and to related octamer elements. Cells expressing this repressor contain an additional octamer-binding protein that is absent from permissive cells. We identify this factor as the lymphocyte- and neuron-specific octamer-binding protein Oct-2 and show that Oct-2 mRNA is also present in dorsal root ganglion neurons, the natural site of HSV latency in vivo. Moreover, artificially elevated expression of Oct-2 can repress the IE promoter. The potential role of Oct-2 in the initiation and maintenance of in vivo latent infection with HSV is discussed.

Differentiation of the U937 macrophage cell line removes an early block of HSV-1 infection

In the human macrophage-like cell line U937, which is resistant to infection with herpes simplex virus type 1 (HSV-1), it was previously shown that resistance can be overcome by inducing differentiation of the cells by treatment with phorbol 12-myristate 13-acetate (PMA). The present data show that differentiation, and not PMA treatment alone, enabled HSV-1 replication, because vitamin D3 and mezerein were also able to cause U937 cells to differentiate to a state permissive for HSV-1 infection. Additionally, a portion of the undifferentiated cells underwent a productive infection when treated with PMA 2 days after infection, suggesting persistence of HSV-1 in these cells. The nonpermissiveness of the undifferentiated cells was further defined. Resistance did not involve differences in virus uptake, because the amounts of viral DNA in the infected cells and nuclei of differentiated and undifferentiated U937 cells were not significantly different early after infection. However, only very low levels of RNA for HSV-1 immediate-early, early, and late genes could be detected in the undifferentiated U937 cells by Northern blot analysis compared with the differentiated U937 cells. These data suggest that the primary block in HSV-1 replication in undifferentiated U937 cells occurred after transport of the viral DNA to the cell nucleus but prior to steady-state accumulation of viral RNA for immediate-early genes.

Regulation of herpes simplex virus immediate-early gene promoters in mouse neuroblastoma cells

The non-permissivity of C1300 mouse neuroblastoma cells for herpes simplex virus (HSV) infection is due to a failure of such cells to transcribe the immediate-early (IE) genes following viral infection. We have transfected both C1300 cells and permissive cells with constructs in which each of the 5 IE promoters drives expression of the readily assayable chloramphenicol acetyl transferase (CAT) gene. These experiments show that the lack of IE gene transcription in C1300 cells is due to the weak activity of the five IE promoters in these cells compared to that observed in a range of permissive cell types. This effect is mediated both by up-stream elements and by sequences present in the minimal promoter. The different effects of DNA concentration on the activities of the minimal and complete promoters suggests that the up-stream sequences act by binding a repressor factor present in C1300 cells whilst the weak activity of the minimal promoter results from the absence of a positive factor in such cells.

Cell lines derived from dorsal root ganglion neurons are nonpermissive for HSV and express only the latency-associated transcript following infection

The effect of herpes simplex virus type 1 infection in a series of immortalized dorsal root ganglion cell lines has been investigated. Following infection of one of these lines, the viral immediate-early genes are not transcribed and the lytic cycle is aborted at an early stage. In contrast these cells do support transcription of the gene encoding the latency-associated transcripts which are the only viral RNAs present in latently infected ganglia in vivo. These cell lines are therefore a suitable model system for studies of the processes regulating the interaction of HSV with neuronal cell types and the establishment of latent infections in vivo.

The herpes simplex virus protein Vmw65 can trans-activate both viral and cellular promoters in neuronal cells

Transcription of the herpes simplex virus (HSV) immediate-early (IE) genes in lytic infection is dependent upon the formation of a complex between the cellular transcription factor Oct-1 and the HSV virion protein Vmw65. This complex then binds to the TAATGARAT sequence in the IE promoters and trans-activates the IE genes. Following infection of neuronal cells such as the C1300 neuroblastoma cell line, however, the viral (IE) genes are not transcribed and the lytic cycle is aborted at an early stage. We show here that the cellular factors necessary to form a trans-activating complex with Vmw65 are present in C1300 cells and that trans-activation of both viral and cellular promoters by Vmw65 can be observed in these cells. In contrast with permissive cells, however, trans-activation is only observed in C1300 cells at a high concentration of the target viral promoter and not at a low concentration of the target promoter, regardless of the amount of Vmw65 transfected. The significance of these effects for the regulation of latent infection and cellular gene expression in neuronal cells is discussed.

Octamer motif mediates transcriptional repression of HSV immediate-early genes and octamer-containing cellular promoters in neuronal cells

C1300 mouse neuroblastoma cells are nonpermissive for infection with herpes simplex virus owing to a failure of viral immediate-early gene transcription following infection. The weak activity of the immediate-early gene promoters in these cells is mediated by the binding of a repressor factor to the octamer-related TAATGARAT motifs in these promoters. This repressor activity is specific to cells of neuronal origin (being absent in a range of permissive nonneuronal cells) and is also able to repress the activity of cellular octamer-containing promoters introduced into C1300 cells. The role of this repressor in the regulation of octamer-containing cellular genes in neuronal cells and in the control of latent infections with herpes simplex virus is discussed.

Regulated transcription of herpes simplex virus immediate-early genes in neuroblastoma cells

C1300 neuroblastoma cells are nonpermissive for infection with herpes simplex virus but can be rendered permissive by pretreatment with sodium butyrate. This increased permissivity which is specific for HSV is caused by increased transcription of the viral immediate-early genes following infection of butyrate-treated cells and can be observed for at least 24 hr following withdrawal of butyrate. The use of C1300 cells as a model system for studying the regulation of immediate-early gene expression in neuronal cells in vitro and its possible relevance to the study of the processes regulating latent infection in vivo is discussed.