Expression of a cellular gene cloned in herpes simplex virus: rabbit beta-globin is regulated as an early viral gene in infected fibroblasts

RNA decay during gammaherpesvirus infection reduces RNA polymerase II occupancy of host promoters but spares viral promoters

In mammalian cells, widespread acceleration of cytoplasmic mRNA degradation is linked to impaired RNA polymerase II (Pol II) transcription. This mRNA decay-induced transcriptional repression occurs during infection with gammaherpesviruses including Kaposi’s sarcoma-associated herpesvirus (KSHV) and murine gammaherpesvirus 68 (MHV68), which encode an mRNA endonuclease that initiates widespread RNA decay. Here, we show that MHV68-induced mRNA decay leads to a genome-wide reduction of Pol II occupancy at mammalian promoters. This reduced Pol II occupancy is accompanied by down-regulation of multiple Pol II subunits and TFIIB in the nucleus of infected cells, as revealed by mass spectrometry-based global measurements of protein abundance. Viral genes, despite the fact that they require Pol II for transcription, escape transcriptional repression. Protection is not governed by viral promoter sequences; instead, location on the viral genome is both necessary and sufficient to escape the transcriptional repression effects of mRNA decay. We propose a model in which the ability to escape from transcriptional repression is linked to the localization of viral DNA within replication compartments, providing a means for these viruses to counteract decay-induced transcript loss.

While transcription and messenger RNA (mRNA) decay are often considered to be the unlinked beginning and end of gene expression, recent data indicate that alterations to either stage can impact the other. Here we study this connection in the context of lytic gammaherpesvirus infection, which accelerates mRNA degradation through the expression of the viral endonuclease muSOX. We show that RNA polymerase II promoter occupancy is broadly reduced across mammalian promoters in response to infection-induced mRNA decay, and that this phenotype correlates with a reduction in the abundance of several proteins involved in transcription. Notably, gammaherpesviral promoters are resistant to the ensuing transcriptional repression. We show that viral transcriptional escape is conferred by localization of the viral DNA within the protective environment of replication compartments, which are sites of viral genome replication and transcription during infection. Collectively, these findings clarify how mRNA degradation by gammaherpesviruses reshapes the cellular environment and selectively dampens host gene transcription.

Infection by Herpes Simplex Virus 1 Causes Near-Complete Loss of RNA Polymerase II Occupancy on the Host Cell Genome

Lytic infection by herpes simplex virus 1 (HSV-1) triggers a change in many host cell programs as the virus strives to express its own genes and replicate. Part of this process is repression of host cell transcription by RNA polymerase II (Pol II), which also transcribes the viral genome. Here, we describe a global characterization of Pol II occupancy on the viral and host genomes in response to HSV-1 infection using chromatin immunoprecipitation followed by deep sequencing (ChIP-seq). The data reveal near-complete loss of Pol II occupancy throughout host cell mRNA genes, in both their bodies and promoter-proximal regions. Increases in Pol II occupancy of host cell genes, which would be consistent with robust transcriptional activation, were not observed. HSV-1 infection induced a more potent and widespread repression of Pol II occupancy than did heat shock, another cellular stress that widely represses transcription. Concomitant with the loss of host genome Pol II occupancy, we observed Pol II covering the HSV-1 genome, reflecting a high level of viral gene transcription. Interestingly, the positions of the peaks of Pol II occupancy at HSV-1 and host cell promoters were different.

IMPORTANCE

We investigated the effect of herpes simplex virus 1 (HSV-1) infection on transcription of host cell and viral genes by RNA polymerase II (Pol II). The approach we used was to determine how levels of genome-bound Pol II changed after HSV-1 infection. We found that HSV-1 caused a profound loss of Pol II occupancy across the host cell genome. Increases in Pol II occupancy were not observed, showing that no host genes were activated after infection. In contrast, Pol II occupied the entire HSV-1 genome. Moreover, the pattern of Pol II at HSV-1 genes differed from that on host cell genes, suggesting a unique mode of viral gene transcription. These studies provide new insight into how HSV-1 causes changes in the cellular program of gene expression and how the virus coopts host Pol II for its own use.

Chromatin dynamics during lytic infection with herpes simplex virus 1

Latent HSV-1 genomes are chromatinized with silencing marks. Since 2004, however, there has been an apparent inconsistency in the studies of the chromatinization of the HSV-1 genomes in lytically infected cells. Nuclease protection and chromatin immunoprecipitation assays suggested that the genomes were not regularly chromatinized, having only low histone occupancy. However, the chromatin modifications associated with transcribed and non-transcribed HSV-1 genes were those associated with active or repressed transcription, respectively. Moreover, the three critical HSV-1 transcriptional activators all had the capability to induce chromatin remodelling, and interacted with critical chromatin modifying enzymes. Depletion or overexpression of some, but not all, chromatin modifying proteins affected HSV-1 transcription, but often in unexpected manners. Since 2010, it has become clear that both cellular and HSV-1 chromatins are highly dynamic in infected cells. These dynamics reconcile the weak interactions between HSV-1 genomes and chromatin proteins, detected by nuclease protection and chromatin immunoprecipitation, with the proposed regulation of HSV-1 gene expression by chromatin, supported by the marks in the chromatin in the viral genomes and the abilities of the HSV-1 transcription activators to modulate chromatin. It also explains the sometimes unexpected results of interventions to modulate chromatin remodelling activities in infected cells.

Heterologous viral promoters incorporated into the human cytomegalovirus genome are silenced during experimental latency

Human cytomegalovirus (HCMV) lytic phase gene expression is repressed upon entry into myeloid lineage cells where the virus establishes latency. Lytic infection is not initiated because the tegument-delivered transactivator protein pp71 fails to enter the nucleus and inactivate the Daxx-mediated cellular intrinsic defense that silences the viral genome. When pp71 is expressed de novo in THP-1 monocytes, it localizes to the nucleus, inactivates the Daxx defense, and initiates lytic infection. We speculated that replacing the native viral promoter that drives pp71 expression with one that is highly and constitutively active in myeloid cells would permit pp71 de novo expression upon infection and that this newly expressed pp71 would accumulate in the nucleus, inactivate the intrinsic defense, and initiate the cascade of lytic gene expression. Surprisingly, we found that this promoter was still subject to normal silencing mechanisms in THP-1 monocytes and primary CD34(+) cells, two independent myeloid lineage cells. A second constitutively active heterologous viral promoter located in a different region of the HCMV genome was also silenced in THP-1 and CD34(+) cells. Furthermore, these two independent heterologous viral promoters inserted into three different regions of the HCMV genome in three different viral strains all required prior expression of the viral immediate early proteins for activation in fibroblasts. From this, we conclude that incorporation within the HCMV genome impacts the proclivity of heterologous viral promoters to initiate transcription. These observations have mechanistic implications for the expression of viral genes and transgenes during both lytic infection and latency.

Linker histones are mobilized during infection with herpes simplex virus type 1

Histones interact with herpes simplex virus type 1 (HSV-1) genomes and localize to replication compartments early during infections. However, HSV-1 genomes do not interact with histones in virions and are deposited in nuclear domains devoid of histones. Moreover, late viral replication compartments are also devoid of histones. The processes whereby histones come to interact with HSV-1 genomes, to be later displaced, remain unknown. However, they would involve the early movement of histones to the domains containing HSV-1 genomes and the later movement away from them. Histones unbind from chromatin, diffuse through the nucleoplasm, and rebind at different sites. Such mobility is upregulated by, for example, phosphorylation or acetylation. We evaluated whether HSV-1 infection modulates histone mobility, using fluorescence recovery after photobleaching. All somatic H1 variants were mobilized to different degrees. H1.2, the most mobilized, was mobilized at 4 h and further so at 7 h after infection, resulting in increases in its "free" pools. H1.2 was mobilized to a "basal" degree under conditions of little to no HSV-1 protein expression. This basal mobilization required nuclear native HSV-1 genomes but was independent of HSV-1 proteins and most likely due to cellular responses. Mobilization above this basal degree, and increases in H1.2 free pools, however, depended on immediate-early or early HSV-1 proteins, but not on HSV-1 genome replication or late proteins. Linker histone mobilization is a novel consequence of cell-virus interactions, which is consistent with the dynamic interactions between histones and HSV-1 genomes during lytic infection; it may also participate in the regulation of viral gene expression.

Transgenic reporter mouse for bioluminescence imaging of herpes simplex virus 1 infection in living mice

Bioluminescence imaging allows spatial and temporal progression of viral infection to be detected and quantified in living mice, thereby providing a new approach for studies of viral-host pathogenesis. It has been necessary to construct and validate recombinant reporter viruses that express firefly luciferase to investigate viral replication and spread with this imaging technology. This strategy greatly limits the ability to analyze multiple strains of virus and/or existing viral mutants, and reporter viruses also may be attenuated relative to the respective parental viruses. To facilitate bioluminescence imaging of herpes simplex virus type 1 (HSV-1), we developed a transgenic reporter mouse that uses the promoter from HSV-1 thymidine kinase to control expression of firefly luciferase. Infection with HSV-1 activated expression of firefly luciferase in corneal and flank models of infection, and amounts of bioluminescence increased in proportion to increasing input titers of virus. Imaging could detect infection with three different strains of HSV-1 with the following relative rank order of bioluminescence produced at the site of infection: McKrae > 17 > KOS. Corneal infection with as few as 1 x 10(3) pfu strain McKrae was detectable above background levels. By comparison, infection with vaccinia virus did not affect bioluminescence in the reporter mouse. Collectively, these data establish a new transgenic reporter mouse for infection with HSV-1, thereby enabling in vivo bioluminescence imaging studies of HSV-1 pathogenesis without constructing new reporter viruses.

Roscovitine inhibits activation of promoters in herpes simplex virus type 1 genomes independently of promoter-specific factors

Flavopiridol, roscovitine, and other inhibitors of Cyclin-Dependent Kinases (CDK) inhibit the replication of a variety of viruses in vitro while proving nontoxic in human clinical trials of their effects against cancer. Consequently, these and other Pharmacological CDK inhibitors (PCIs) have been proposed as potential antivirals. Flavopiridol potently inhibits all tested CDKs and inhibits the transcription of most cellular and viral genes. In contrast, roscovitine and other purine PCIs inhibit with high potency only CDK1, CDK2, CDK5, and CDK7, and they specifically inhibit the expression of viral but not cellular genes. The levels at which purine PCIs inhibit gene expression are unknown, as are the factors which determine their specificity for expression of viral but not cellular genes. We show herein that roscovitine prevents the initiation of transcription of herpes simplex virus type 1 (HSV-1) genes but has no effect on transcription elongation. We further show that roscovitine does not inhibit the initiation or elongation of cellular transcription and that its inhibitory effects are specific for promoters in HSV-1 genomes. Therefore, we have identified a novel biological activity for PCIs, i.e., their ability to prevent the initiation of transcription. We have also identified genome location as one of the factors that determine whether the transcription of a given gene is inhibited by roscovitine. The activities of roscovitine on viral transcription resemble one of the antiherpesvirus activities of alpha interferon and could be used as a model for the development of novel antivirals. The genome-specific effects of roscovitine may also be important for its development against virus-induced cancers.

ICP0, ICP4, or VP16 expressed from adenovirus vectors induces reactivation of latent herpes simplex virus type 1 in primary cultures of latently infected trigeminal ganglion cells

In a previous study, we demonstrated that infected-cell polypeptide 0 (ICP0) is necessary for the efficient reactivation of herpes simplex virus type 1 (HSV-1) in primary cultures of latently infected trigeminal ganglion (TG) cells (W. P. Halford and P. A. Schaffer, J. Virol. 75:3240-3249, 2001). The present study was undertaken to determine whether ICP0 is sufficient to trigger HSV-1 reactivation in latently infected TG cells. To test this hypothesis, replication-defective adenovirus vectors that express wild-type and mutant forms of ICP0 under the control of a tetracycline response element (TRE) promoter were constructed. Similar adenovirus vectors encoding wild-type ICP4, wild-type and mutant forms of the HSV-1 origin-binding protein (OBP), and wild-type and mutant forms of VP16 were also constructed. The TRE promoter was induced by coinfection of Vero cells with the test vector and an adenovirus vector that expresses the reverse tetracycline-regulated transactivator in the presence of doxycycline. Northern blot analysis demonstrated that transcription of the OBP gene in the adenovirus expression vector increased as a function of doxycycline concentration over a range of 0.1 to 10 microM. Likewise, Western blot analysis demonstrated that addition of 3 microM doxycycline to adenovirus vector-infected Vero cells resulted in a 100-fold increase in OBP expression. Wild-type forms of ICP0, ICP4, OBP, and VP16 expressed from adenovirus vectors were functional based on their ability to complement plaque formation in Vero cells by replication-defective HSV-1 strains with mutations in these genes. Adenovirus vectors that express wild-type forms of ICP0, ICP4, or VP16 induced reactivation of HSV-1 in 86% +/- 5%, 86% +/- 5%, and 97% +/- 5% of TG cell cultures, respectively (means +/- standard deviations). In contrast, vectors that express wild-type OBP or mutant forms of ICP0, OBP, or VP16 induced reactivation in 5% +/- 5%, 8% +/- 0%, 0% +/- 0%, and 13% +/- 6% of TG cell cultures, respectively. In control infections, an adenovirus vector expressed green fluorescent protein efficiently in TG neurons but did not induce HSV-1 reactivation. Therefore, expression of ICP0, ICP4, or VP16 is sufficient to induce HSV-1 reactivation in latently infected TG cell cultures. We conclude that this system provides a powerful tool for determining which cellular and viral proteins are sufficient to induce HSV-1 reactivation from neuronal latency.

Efficient gene delivery into epstein-barr virus (EBV)-transformed human B cells mediated by replication-defective herpes simplex virus-1 (HSV-1): A gene therapy model for EBV-related B cell malignancy

Subgroups of the B cell malignancies are known to be associated with Epstein-Barr virus (EBV) infection, especially in immunocompromised patients. These are fatal and refractory to conventional antineoplastic therapy. B cells are usually post-mitotic cells and even mitogen activated or transformed B cells have shown relative resistance against viral mediated gene transfer. To address this issue, we employed a replication-defective herpes simplex virus-1 (HSV-1) to mediate gene transfer into EBV-transformed B cells. The virus expresses the herpes simplex virus thymidine kinase (HSV-TK) and the E. coli lacZ reporter genes and is designated T0Z.1. We used the lymphoblastoid cell line SWEIG as a model for human EBV-related B cell malignancy. This cell line was established by in vitro EBV infection of primary human peripheral blood mononuclear cells. When SWEIG cells were infected with T0Z.1, X-gal staining revealed lacZ expression in more than 20% cells even at multiplicity of infection (MOI) as low as 1 and the expression persisted for at least one week. Ganciclovir (GCV) administration after T0Z.1 infection effectively decreased the number of the infected tumor cells in a dose-responsive manner. Viral toxicity was analyzed by cell proliferation assay (MTS assay) and found to be little even at 10 MOI infection. Three MOI of the virus yielded maximum antineoplastic effect and more than 50% tumor cells were killed by HSV-TK/GCV. These results suggest the potential utility of replication-defective HSV-1 for the treatment of EBV-related B cell malignancies.

High-efficacy thymidine kinase gene transfer to ovarian cancer cell lines mediated by herpes simplex virus type 1 vector

In this report, a replication-defective herpes simplex virus type 1 (HSV-1) vector has been employed to deliver the Escherichia coli LacZ and HSV thymidine kinase (HSVtk) genes to six human ovarian carcinoma cell lines and the efficacy of gene transfer compared to that of adenoviral vectors in vitro. The transduction efficiency of the LacZ-containing virus TOZ.1 was evaluated qualitatively and quantitatively following infection of the different ovarian cancer cell lines. The therapeutic ability of the HSV-T3 vector, which contains the HSVtk gene, was additionally investigated in comparison to the AdCMVHSVTK. Our results show that HSV-1-mediated gene transfer is quantitatively superior to adenoviral vector in five of the six ovarian cancer cell lines at a 100-fold lower dose in vitro. Our preliminary studies suggest that HSV-1 may be a promising alternative vector for ovarian cancer gene therapy.

Herpes simplex virus immediate-early proteins ICP0 and ICP4 activate the endogenous human alpha-globin gene in nonerythroid cells

Globin genes are normally expressed only in erythroid cell lineages. However, we found that the endogenous alpha-globin gene is activated following infection of human fibroblasts and HeLa cells with herpes simplex virus (HSV), leading to accumulation of correctly initiated transcripts driven by the alpha-globin promoter. The alpha1- and alpha2-globin genes were both induced, but expression of beta- or zeta-globin genes could not be detected. Experiments using HSV mutants showed that null mutations in the genes encoding the viral immediate-early proteins ICP4 and ICP22 reduced induction approximately 10-fold, while loss of ICP0 function had a smaller inhibitory effect. Transient transfection experiments showed that ICP0 and ICP4 are each sufficient to trigger detectable expression of the endogenous gene, while ICP22 had no detectable effect in this assay. ICP4 also strongly enhanced expression of transfected copies of the alpha2-globin gene. In contrast, the adenovirus E1a protein did not activate the endogenous gene and inhibited expression of the plasmid-borne alpha2-globin gene. Previous studies have led to the hypothesis that chromosomal alpha-globin genes are subject to chromatin-dependent repression mechanism that prevents expression in nonerythroid cells. Our data suggest that HSV ICP0 and ICP4 either break or bypass this cellular gene silencing mechanism.

Repression of host RNA polymerase II transcription by herpes simplex virus type 1

Lytic infection of mammalian cells with herpes simplex virus type 1 (HSV-1) results in rapid repression of host gene expression and selective activation of the viral genome. This transformation in gene expression is thought to involve repression of host transcription and diversion of the host RNA polymerase (RNAP II) transcription machinery to the viral genome. However, the extent of virus-induced host transcription repression and the mechanisms responsible for these major shifts in transcription specificities have not been examined. To determine how HSV-1 accomplishes repression of host RNAP II transcription, we assayed transcription patterns on several cellular genes in cells infected with mutant and wild-type HSV-1. Our results suggest that HSV-1 represses RNAP II transcription on most cellular genes. However, each cellular gene we examined responds differently to the transcription repressive effects of virus infection, both quantitatively and with respect to the involvement of viral gene products. Virus-induced shutoff of host RNAP II transcription requires expression of multiple immediate-early genes. In contrast, expression of delayed-early and late genes and viral DNA replication appear to contribute little to repression of host cell RNAP II transcription. Modification of RNAP II to the intermediately phosphorylated (II(I)) form appears unlinked to virus-induced repression of host cell transcription. However, full repression of host transcription is correlated with depletion of the hyperphosphorylated (IIO) form of RNAP II.

Herpes simplex type 1:lacZ recombinant viruses. I. Characterization and application to defining the mechanisms of action of known antiherpes agents

Recombinant viruses with the lacZ gene placed under the control of the HSV-1 ICP4, TK and gD regulatory regions were constructed by recombination into the TK locus of HSV-1. Difficulty in isolating ICP4 and gD recombinant viruses with high level, regulated expression of beta-galactosidase was overcome by the use of HSV-1 translational initiation sequences of these genes in place of vector-derived sequences. beta-Galactosidase expression displayed the kinetics particular to each viral class. The maximal expression of beta-galactosidase from the recombinant viruses within a 22-h period (m.o.i. 5) (relative to the ICP4 virus) was gD(3) > gC(2) > ICP4(1) > TK(0.5). The ICP4 virus produces easily quantifiable levels of beta-galactosidase activity for multiplicities of infection from 5 x 10(-4) through 5 over 48 h postinfection. At multiplicities of infection between 2 and 5, ICP4-driven activity was measurable within 2 h postinfection from a monolayer of 3 x 10(4) Vero cells in microtiter wells. Mechanisms of inhibition of several antivirals were probed by using the regulated expression of beta-galactosidase from the ICP4 virus as a marker for viral growth. An experimental antiviral (E3925, IC50 1 microgram/ml) and a neutralizing gD MAb (DUP55306, IC50 0.6 microgram/ml) acted prior to immediate early synthesis, consistent with inhibition of viral entry or uncoating. IFN-gamma inhibited expression of immediate-early synthesis, while having no effect on viral entry. IC50 values for E3925 obtained using either the ICP4 or gD viruses at m.o.i. 0.005, were in good agreement with those obtained by standard plaque assays, but were determined in only 1 day, using a microtiter plate format. Thus, these reporter viruses are useful tools for defining the mechanisms of action of antiherpes agents, while quantitatively reproducing the results for IC50 determinations from standard plaque assays within 24 h in a microtiter plate format.

Herpes simplex virus immediate-early protein ICP22 is required for viral modification of host RNA polymerase II and establishment of the normal viral transcription program

Infection of cells with herpes simplex virus type 1 (HSV-1) results in a rapid alteration of phosphorylation on the large subunit of cellular RNA polymerase II (RNAP II), most likely on its C-terminal domain (S. A. Rice, M. C. Long, V. Lam, C. A. Spencer, J. Virol. 68:988-1001, 1994). This phosphorylation modification generates a novel form of the large subunit which we have designed IIi. In this study, we examine roles that HSV-1 gene products play in this process. An HSV-1 mutant defective in the immediate-early transcriptional activator protein ICP4 is able to efficiently induce IIi. Viruses having mutations in the genes for the ICP0, ICP6, or ICP27 proteins are also competent for IIi formation. In contrast, 22/n199, an HSV-1 mutant which contains a nonsense mutation in the gene encoding the immediate-early protein ICP22, is significantly deficient in IIi induction. This effect is seen in Vero cells, where 22/n199 grows relatively efficiently, and in human embryonic lung (HEL) cells, where 22/n199 growth in more restricted. RNAP II is recruited into viral replication compartments in 22/n199-infected cells, indicating that altered phosphorylation of RNAP II is not a prerequisite for nuclear relocalization of RNAP II. In addition, we show by nuclear run-on transcription analysis that viral gene transcription is deficient in HEL cells infected with 22/n199. Viral late gene transcription does not occur efficiently, and antisense transcription throughout the genome is diminished compared with that of the wild-type HSV-1 infection. These transcriptional effects cannot be explained by differences in viral DNA replication, since 22/n199 replicates its DNA efficiently in HEL cells. Our results demonstrated that ICP22 is necessary for virus-induced aberrant phosphorylation of RNAP II and for normal patterns of viral gene transcription in certain cell lines.

Transduction of foreign regulatory sequences by a replication-defective herpes simplex virus type 1: the rat neuron-specific enolase promoter

Herpes simplex virus type 1 (HSV-1) can transduce genes into non-proliferating cells such as neurons that are refractory to other means of gene transfer. We have been interested to examine the potential usefulness of HSV-1 as a gene transfer vehicle to analyze neuron-specific regulatory sequences. In this study, we have used a replication-defective HSV-1-based vector deleted for the essential immediate early gene 3 (IE3) to transduce a 1.8 kb promoter fragment from the rat neuron-specific enolase gene (nse) linked to the firefly luciferase reporter gene (luc). It has previously been shown that the same promoter fragment is capable of directing neuron-specific expression of a linked reporter gene in transgenic mice. As an internal control for infection and gene expression, we also inserted the chloramphenicol acetyltransferase (cat) gene driven by the SV40 early promoter/enhancer into the thymidine kinase locus of the same vector. We infected (i) non-neuronal BHK-C13 cells which do not express the endogenous nse gene, (ii) differentiated and non-differentiated pheochromocytoma PC12 cells as well as (iii) N1E-115 neuroblastoma cells, all of which do express endogenous nse. All three cell types produced luciferase upon infection, indicating that the same nse promoter fragment that has previously been shown to be regulated in a cell-specific manner in transgenic mice, was not regulated cell type-specifically in the context of the HSV-1 genome.(ABSTRACT TRUNCATED AT 250 WORDS)

The herpes simplex virus type 1 major capsid protein (VP5-UL19) promoter contains two cis-acting elements influencing late expression

The herpes simplex virus type 1 (HSV-1) major capsid protein VP5 gene (UL19) is expressed with beta gamma (gamma 1 [leaky late]) kinetics. We have previously described the construction of recombinant HSV-1 in which the VP5 promoter was engineered to control the expression of the bacterial beta-galactosidase gene as a reporter (C.-J. Huang, S. A. Goodart, M. K. Rice, J. F. Guzowski, and E. K. Wagner, J. Virol. 67:5109-5116, 1993). Here we describe further mutational analysis in recombinant viruses. We have precisely defined the boundaries of the VP5 promoter and identified two regions important for both the level and the kinetics of expression. The 5' boundary was located at -48 relative to the initiation site of transcription by analyzing a series of nested deletions in the upstream sequence, and although a number of cis-acting sites influencing transient expression have been identified upstream of this point, these sites have no role in promoter activity during productive infection. Deletion of an Sp1-binding site located between -48 and the TATA box at -30 greatly reduced VP5 promoter activity late but not early after infection. A cis-acting element whose sequence resembles the human immunodeficiency virus type 1 initiator was located between -2 and +10 in the VP5 sequence by characterizing a series of deletions and site-directed block mutations downstream the TATA box. This element defines the 3' limit of the VP5 promoter, and like the upstream element, disruption of this element also inhibited promoter activity late in the productive cycle.

Expression of the cyclic AMP-dependent protein kinase (PKA) catalytic subunit from a herpes simplex virus vector extends the survival of rat sympathetic neurons in the absence of NGF

Superior cervical ganglion neurons from neonatal rats are dependent on nerve growth factor for their survival both in vivo and in vitro. In culture this requirement can be largely replaced by cAMP or its analogues. Since activation of protein kinase A by cAMP is likely to be the pathway by which it exerts its survival-promoting effect, we have tested the feasibility of using herpes simplex virus (HSV) as a vector for expressing survival-promoting genes in neurons by cloning the catalytic subunit of the cAMP-dependent protein kinase (PKAcat) with a metallothionein gene promoter into the HSV thymidine kinase gene by homologous recombination. About 95% of the neurons became infected using 2.5 p.f.u. per cell. When this construct was used to express PKAcat in superior cervical ganglion neurons, in the presence of nerve growth factor (NGF) increases of 1.9- to 2.4-fold in PKA activity were found 8-10 h after infection; levels remained elevated (1.4- to 2.1-fold) up to 18 h, returning to basal by 24 h. After infection in the absence of NGF, cumulative activity over 24 h was approximately 3.5-fold lower in the first 24 h. Although the level of the inhibitory regulatory subunit type I was raised by 18 h, this is unlikely to completely explain the transient activity of PKAcat. When neurons were induced to express maximum PKAcat levels in the presence of NGF and then deprived of NGF, survival was extended by up to 2 days, demonstrating a direct role for PKA in promoting survival. By this time, some neurite degeneration was beginning which appeared to be partly due to toxic effects of the virus. However, replenishment with NGF supported further survival, showing that at this time the neurons were still viable. Similar rates of survival were obtained using a tsK-based PKAcat vector, but no significant survival was obtained with parental HSV or tsK virus strains. These data demonstrate the feasibility, and highlight some of the problems, of using HSV-based vectors as tools for expressing functional survival proteins in sympathetic neurons.

RNA polymerase II is aberrantly phosphorylated and localized to viral replication compartments following herpes simplex virus infection

During lytic infection, herpes simplex virus subverts the host cell RNA polymerase II transcription machinery to efficiently express its own genome while repressing the expression of most cellular genes. The mechanism by which RNA polymerase II is directed to the viral delayed-early and late genes is still unresolved. We report here that RNA polymerase II is preferentially localized to viral replication compartments early after infection with herpes simplex virus type 1. Concurrent with recruitment of RNA polymerase II into viral compartments is a rapid and aberrant phosphorylation of the large subunit carboxy-terminal domain (CTD). Aberrant phosphorylation of the CTD requires early viral gene expression but is not dependent on viral DNA replication or on the formation of viral replication compartments. Localization of RNA polymerase II and modifications to the CTD may be instrumental in favoring transcription of viral genes and repressing specific transcription of cellular genes.

Binding sites for the herpes simplex virus immediate-early protein ICP4 impose an increased dependence on viral DNA replication on simple model promoters located in the viral genome

We examined the ability of binding sites for the herpes simplex virus immediate-early protein ICP4 to alter the regulation of closely linked promoters by placing strong ICP4 binding sites upstream or downstream of simple TATA promoters in the intact viral genome. We found that binding sites strongly reduced the levels of expression at early times postinfection and that this effect was partially overcome after the onset of viral DNA replication. These data confirm that DNA-bound ICP4 can inhibit the activity of a closely linked promoter and raise the possibility that ICP4 binding sites contribute to temporal regulation during infection.

Activation of RNA polymerase III transcription of human Alu repetitive elements by adenovirus type 5: requirement for the E1b 58-kilodalton protein and the products of E4 open reading frames 3 and 6

We found that transcription of endogenous human Alu elements by RNA polymerase III was strongly stimulated following infection of HeLa cells with adenovirus type 5, leading to the accumulation of high levels of Alu transcripts initiated from Alu polymerase III promoters. In contrast to previously reported cases of adenovirus-induced activation of polymerase III transcription, induction required the E1b 58-kDa protein and the products of E4 open reading frames 3 and 6 in addition to the 289-residue E1a protein. In addition, E1a function was not required at high multiplicities of infection, suggesting that E1a plays an indirect role in Alu activation. These results suggest previously unsuspected regulatory properties of the adenovirus E1b and E4 gene products and provide a novel approach to the study of the biology of the most abundant class of dispersed repetitive DNA in the human genome.

Activation of RNA polymerase III transcription of human Alu repetitive elements by adenovirus type 5: requirement for the E1b 58-kilodalton protein and the products of E4 open reading frames 3 and 6

We found that transcription of endogenous human Alu elements by RNA polymerase III was strongly stimulated following infection of HeLa cells with adenovirus type 5, leading to the accumulation of high levels of Alu transcripts initiated from Alu polymerase III promoters. In contrast to previously reported cases of adenovirus-induced activation of polymerase III transcription, induction required the E1b 58-kDa protein and the products of E4 open reading frames 3 and 6 in addition to the 289-residue E1a protein. In addition, E1a function was not required at high multiplicities of infection, suggesting that E1a plays an indirect role in Alu activation. These results suggest previously unsuspected regulatory properties of the adenovirus E1b and E4 gene products and provide a novel approach to the study of the biology of the most abundant class of dispersed repetitive DNA in the human genome.

Altering central nervous system physiology with a defective herpes simplex virus vector expressing the glucose transporter gene

Because of their postmitotic nature, neurons are difficult subjects for gene transfer. To circumvent this, we have used a defective herpes simplex virus vector to overexpress the rat brain glucose transporter (GT) gene under the control of the human cytomegalovirus ie1 promoter. This vector, designated vIE1GT, was propagated using a herpes simplex virus type 1 temperature-sensitive mutant, ts756. GT expressed from vIE1GT was readily immunoprecipitated from membrane fractions of vIE1GT-infected Vero cells. By using indirect double immunofluorescence techniques, vIE1GT was shown to be capable of enhancing GT expression in cultured hippocampal neurons and glia. Glucose transport in such vIE1GT-infected cultures was increased approximately 2-fold relative to controls. The efficacy of this system in vivo was then tested by microinjection of vIE1GT into adult rat hippocampus. When examined 2 days later, GT expression from vIE1GT was demonstrated in hippocampal neurons by in situ hybridization; a small but significant increase in glucose transport was detected in tissue immediately surrounding the injection site by 2-deoxy[14C]glucose uptake and autoradiography. Such injections did not cause marked cytopathology. Thus, this approach can be used to alter central nervous system physiology in vitro and in vivo.

Repression of the herpes simplex virus 1 alpha 4 gene by its gene product occurs within the context of the viral genome and is associated with all three identified cognate sites

The infected cell protein 4 (ICP-4), the major regulatory protein encoded by the a4 gene of the herpes simplex virus 1, binds two sites (alpha 4-1 proximal, alpha 4-1 distal) at the 5'-untranscribed domain and at the transcription initiation site (alpha 4-2) of the alpha 4 gene. Chimeric genes consisting of the 5'-untranscribed and transcribed noncoding domains of the alpha 4 gene fused to the coding sequences of the thymidine kinase gene were mutagenized to abolish binding of ICP-4 by substitution of bases, including the guanines whose methylation interferes with binding of the protein, and recombined into the viral genome. The cytoplasmic RNAs extracted from infected cells treated with cycloheximide, from untreated infected cells maintained for 4 or 8 hr, and from cells infected first with a virus deleted in the alpha 22 gene and 3 hr later with the test viruses were tested in RNase protection assay for amounts of the chimeric gene RNA relative to amounts of alpha 22 gene RNA. We report the following: (i) Mutation of the alpha 4-2 binding site resulted in a 5-to 6-fold higher accumulation of chimeric gene RNA at 4 hr and as much as 15-fold higher accumulation by 8 hr after infection. (ii) Mutations of alpha 4-1 sites by themselves had no effect on RNA accumulation. However, mutagenesis of all three sites significantly increased mRNA amounts above the levels seen in cells infected with alpha 4-2 site mutants. (iii) The mutations have no effect on accumulation of alpha 4 mRNA in the absence of ICP-4 synthesis and, therefore, the mutations had no effect on RNA stability or transcription rate. (iv) Accumulation of alpha 4 mRNA relative to that of alpha 22 mRNA is highest in the presence of cycloheximide and decreases with time after infection. We conclude that ICP-4 autoregulates the transcription of its own gene in infected cells and that binding of ICP-4 to three sites in its promoter is additive in its effects on this process.

Bone marrow transplant for the haemoglobinopathies: past, present and future

Bone marrow transplantation (BMT) is the only treatment currently available which can cure thalassaemia and sickle cell anaemia. However, it is not without risk and the complications of graft failure, GVHD, veno-occlusive disease, interstitial pneumonitis and infections, together with the toxicity of the conditioning therapy result in a transplant-related mortality in children of 10-20%. For the survivors, long-term sequelae include chronic GVHD, endocrinopathies and an increased incidence of secondary malignancies. The decision to offer BMT to a patient with a haemoglobinopathy must be based on a knowledge of the relative risks of transplant and conventional therapy. However, in sickle cell anaemia, a subset of patients with particularly severe disease can be identified at an early age when the risks associated with BMT are at their lowest. In thalassaemia, chelation therapy can delay the onset of organ damage due to hypertransfusion but is unlikely to prevent it entirely. The results of BMT in children without organ impairment are excellent and BMT must now be considered a real alternative to conventional treatment. Gene therapy is an exciting prospect for the future but recent progress in retroviral gene transfer has been hindered by poor infection efficiencies and expression levels in the target cells. The identification of the positive regulatory elements of both the alpha- and beta-globin genes may resolve some of these problems. Finally, alternative gene delivery systems are being investigated, but the introduction of gene therapy for the haemoglobinopathies into clinical practice may need to await successful gene targeting and replacement.

Inhibition of herpes simplex virus replication and protein synthesis by non-smoked tobacco, tobacco alkaloids and nitrosamines

Inhibitory effects of snuff extract and the tobacco chemicals nicotine, anabasine, diethyl-N-nitrosamine (DEN), and the tobacco-specific nitrosamines (TSNA), N-nitrosonornicotine (NNN) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) on herpes simplex virus type 1 (HSV-1) replication in vitro and on HSV-1 protein synthesis in infected cells were analysed. Snuff extract and nicotine caused a significant reduction of HSV-1 attachment to cell membranes whereas anabasine, DEN, NNN and NNK did not affect adsorption of HSV-1. Virus production assays in the presence of snuff added after virus adsorption resulted in a significantly reduced production of virus at low multiplicities of infection (MOI), but at high MOI the inhibitory effect of snuff extract was less pronounced. DEN, NNN and NNK only affected virus production at toxic concentrations. Nicotine and anabasine reduced virus production in non-toxic doses but not at the concentrations present in snuff extract. In HSV-infected cells exposed to snuff extract, the immediate early (alpha-) infected cell proteins (ICPs) 4 and 27 (as well as the early (beta-) ICPs 6 and 8) were markedly increased, whereas the late (gamma-) ICPs 5, 11 and 29 were reduced. Nicotine had a less pronounced stimulating effect on the production of alpha-proteins but no detectable effect on production of beta- or gamma-proteins. Anabasine, DEN, NNN and NNK did not affect HSV protein synthesis at non-toxic concentrations. Synthesis of thymidine kinase and DNA polymerase was significantly reduced by snuff extract. Also nicotine and anabasine affected thymidine kinase and DNA polymerase but only at toxic concentrations. The production of the cellular protein actin, which almost disappears a few hours after HSV-1 infection, remained at a significant level in HSV-infected cells exposed to snuff. Thus snuff extract blocks the replicative cycle of HSV at an early stage, which results in an increased production of alpha-proteins in the infected cells and in prolonged maintenance of cellular functions. This may be of importance for HSV-induced transformation and the development of HSV-associated tumours.

The herpes simplex virus type 1 immediate-early polypeptide ICP4 is required for expression of globin genes located in the viral genome

We infected Vero cells with ICP4-deficient herpes simplex virus recombinants bearing the rabbit beta-globin and human alpha 2-globin genes under the control of their own promoters and found that globin gene expression occurred only when ICP4 was provided in trans. These results demonstrate that ICP4 is required for the activity of globin promoters located in the viral genome and support the hypothesis that these cellular promoters are functionally equivalent to HSV early regulatory regions.

Identification of dominant-negative mutants of the herpes simplex virus type 1 immediate-early protein ICP0

ICP0 is a 110,000-molecular-weight immediate-early protein of herpes simplex virus type 1 (HSV-1) which is encoded by three exons. It has been shown to function as a promiscuous transactivator of a variety of different HSV-1 and non-HSV-1 promoters in transient expression assays. Analysis of mutations which truncated the carboxy-terminal end of this 775-amino-acid (aa) protein demonstrated that a polypeptide which contained only aa 1 to 553 still possessed significant transactivation potential. Additional carboxy-terminal truncations which sequentially removed aa 245 to 553 and thus the remainder of the third exon resulted in the eventual loss of transactivation capability in these mutants. However, further analysis of these truncated derivatives demonstrated that they behaved as dominant-negative mutants to the wild-type polypeptide. Moreover, one of the mutants was found to act as a promiscuous repressor, in that it could dramatically inhibit a variety of HSV-1 promoters, non-HSV-1 promoters, and heterologous transactivator proteins in transient expression assays, despite having lost almost the entire third exon. These results indicate that a domain encoded by the first two exons probably interacts with, and can effectively titrate, the unknown cellular factor(s) through which ICP0 mediates transactivation.

The ICP4 binding sites in the herpes simplex virus type 1 glycoprotein D (gD) promoter are not essential for efficient gD transcription during virus infection

Activation of the early and late genes of herpes simplex virus type 1 during infection in tissue culture requires functional immediate-early regulatory protein ICP4. ICP4 is a specific DNA-binding protein which recognizes a variety of DNA sequences, many of which contain the consensus ATCGTC. In general, mutations which impair the ability of ICP4 to bind to DNA also eliminate its ability to activate viral early and late promoters both in transfection assays and in the infected cell. However, the role of ICP4 binding sites in the viral genome is unclear; many early and late promoters do not contain consensus binding sites in their vicinity. The glycoprotein D (gD) gene contains two well-characterized ICP4 binding sites upstream of its promoter and a third downstream of the transcription start site. Multimerization of one of these sites has been shown to increase the response of the gD promoter to ICP4 in transfection assays, while their removal reduces stimulation of the gD promoter by ICP4 in vitro. To assess the role of these binding sites during virus infection, we have constructed a recombinant viral genome which has mutations affecting all three. Comparison of the amounts of gD RNA synthesized by the recombinant and wild-type viruses indicated that the mutations had little or no effect on the activity of the gD promoter. Therefore, either the sites have no essential role in gD promoter regulation in the presence of all of the herpes simplex virus type 1 IE polypeptides during a normal infection or they can be functionally substituted by other ICP4 binding sites elsewhere in the genome.

Activity of the simian virus 40 early promoter-enhancer in herpes simplex virus type 1 vectors is dependent on its position, the infected cell type, and the presence of Vmw175

We have studied some of the parameters governing the expression of a foreign promoter-reporter gene construct incorporated into herpes simplex virus (HSV) type 1. These include the genetic background of the parental virus, the site of transgene insertion within the HSV genome, and the infected cell type. The genetic background of the vector constructs denoted delta 3 was an HSV type 1 mutant deleted for nearly the entire coding portion of Vmw175 (ICP4), the product of the essential immediate-early gene IE3. For vectors denoted +, the IE3 deletion had been repaired by marker rescue. We used as a reporter gene the bacterial chloramphenicol acetyltransferase (CAT) gene, driven by the simian virus 40 (SV40) early promoter and enhancer region. The SV40-cat hybrid gene was inserted either into the HSV thymidine kinase (TK) locus to create the vectors TKScat delta 3 and TKScat+ or into an intergenic site within the BamHI z fragment of the short unique portion of the viral genome to create the vectors GScat delta 3 and GScat+. In Vero and BHK cells infected with TKScat delta 3, CAT activity was first detected at 10 h postinfection and continued to accumulate until 36 h postinfection. In cells of primate origin infected with the replication-competent vector TKScat+, or in primate cells which complement the IE3 deficiency and which were infected with TKScat delta 3, CAT activity was significantly lower than in cells of rodent origin. However, levels of CAT were increased in the presence of cycloheximide, suggesting that the low production of CAT in primate cells was due to repression of SV40-cat hybrid gene expression. In contrast with results with TKScat delta 3 and TKScat+, CAT activity was not detectable in any of the tested cell types infected with GScat delta 3 or GScat+ except under conditions of cycloheximide reversal. These results show that while HSV gene products expressed in the presence of Vmw175 inhibited SV40-cat expression in the tk locus in a cell-type-specific manner, HSV gene products expressed in the presence or absence of Vmw175 inhibited SV40-cat expression in the BamHI z locus independently of cell type.

Regulation of herpes simplex virus true late gene expression: sequences downstream from the US11 TATA box inhibit expression from an unreplicated template

The true late genes of herpes simplex virus type 1 (HSV-1) are expressed only after the onset of viral DNA replication. Previous studies demonstrated that late promoters lack elements upstream of the TATA box and suggested that only a subset of TATA elements can function in the context of true late promoters. We determined which structural features of true late promoters are responsible for the stringent requirement for viral DNA replication by inserting a series of simple model constructs into the HSV-1 genome in place of one of the two promoters of the UL24 gene. An oligonucleotide consisting of 19 nucleotides spanning the TATA box of the HSV-1 true late US11 gene drove barely detectable levels of expression; by contrast, the corresponding regions of the Adenovirus type 2 major late promoter and the HSV-1 true late glycoprotein C promoter were much more active. Transcripts driven from all of these minimal TATA box promoters accumulated without viral DNA replication. The activity of the US11 TATA box was stimulated by adding upstream Sp1-binding sites or placing the US11 or rabbit beta-globin cap/leader region (-11 to +39) downstream. The Sp1-TATA and TATA-beta-globin cap/leader constructs remained replication independent, while the TATA-US11 cap/leader promoter displayed true late regulation. These results demonstrate that sequences located within the US11 cap/leader region impose a strict requirement for viral DNA replication on a minimal TATA box promoter.

Adenovirus E1A under the control of heterologous promoters: wide variation in E1A expression levels has little effect on virus replication

Adenovirus early region 1A(E1A) encodes a heterogeneous family of proteins some of which function as transactivators and are required for efficient viral replication in HeLa cells. We have constructed adenovirus type 5 (Ad 5) mutants in which the E1A transcription unit is placed under the control of either the human beta-actin promoter or the human cytomegalovirus immediate early promoter. The level of E1A expression in cells infected with these mutants was several times higher than that in wild-type virus infections. When the same heterologous promoters were inserted upstream of, but in the opposite orientation to, the E1A transcription unit, the level of expression was greatly reduced with respect to wild-type levels of E1A. Despite this variation of at least 40-fold in the concentration of E1A proteins in infected cells, there was no significant difference between wild-type Ad 5 and any of the mutants in their ability to replicate in HeLa cells. These results suggest that very low levels of E1A proteins are sufficient for virus production in cultured cells and that wild-type Ad 5 produces an amount of E1A in excess of that required.

Differential regulation of endogenous and transduced beta-globin genes during infection of erythroid cells with a herpes simplex virus type 1 recombinant

We infected murine erythroleukemia cells with a nondefective herpes simplex virus (HSV) type 1 recombinant bearing the rabbit beta-globin gene under the control of its own promoter, in order to compare the regulation of a cellular gene residing in the viral genome to that of its active endogenous counterpart. We found that the viral globin gene was activated by HSV immediate-early polypeptides, whereas expression of the endogenous beta-globin gene was strongly suppressed: transcription was greatly inhibited, and beta-globin mRNA was rapidly degraded. Degradation of globin mRNA was induced by a component of the infecting virion and required a functional UL41 gene product. These results demonstrate that HSV products can have opposing effects on the expression of homologous genes located in the cellular and viral genomes and suggest that the preferential expression of HSV genes that occurs during infection is not achieved solely through sequence-specific differentiation between viral and cellular promoters or mRNAs.

Temporal regulation of equine herpesvirus type 3 transcription

The transcription of equine herpesvirus type 3 (EHV-3; equine coital exanthema virus) has been examined and found to be temporally regulated into three classes: immediate early (IE), early (E), and late (L). Hybridization of in vivo 32PO4-labeled transcripts revealed that IE transcript(s) are derived exclusively from the inverted repeat segments (IRs) of the viral genome, while E and L transcripts are not restricted to any specific region of the genome. Northern blot analysis of EHV-3 IE RNA revealed a single transcript of approximately 5.7 kb (3.8 MDa). We have previously shown that transcription of equine herpesvirus type 1 (EHV-1) DNA is temporally regulated and produces a single 6 kb IE RNA which is derived from the IRs segments. In this paper, we show that the EHV-1 and EHV-3 IE RNA species are homologous, reflecting the colinearity of the genomes of these two related viruses. While four IE polypeptides are synthesized in EHV-1 infected cells in the presence of actinomycin D following the removal of a cycloheximide block, only one major IE polypeptide (180 kDa) is detectable in EHV-3 infected cells under these conditions. However, immunoprecipitation of EHV-3 infected cell extracts with polyvalent rabbit antisera to IE1 of EHV-1 revealed at least two other viral specific IE polypeptides.

The influence of the herpes simplex virus-1 DNA template environment on the regulation of gene expression

To determine the role of the HSV-1 genome structure and environment on the regulation of gene expression, we constructed recombinant viruses containing a heterologous gene inserted into either the immediate early ICPO or late glycoprotein C (gC) genes of HSV-1. The heterologous gene consisted of the SV40 early promoter (without enhancer sequences) linked to the coding sequences for the bacterial chloramphenicol acetyl transferase (CAT). The expression of CAT was examined in Vero cells infected with either virus (named ICP0-CAT and Sph 6). For both recombinants, expression of CAT was not dependent upon prior viral protein synthesis. The kinetics of expression of CAT-specific mRNA resembled that of the HSV-1 genes into which CAT was inserted. Primer extension analysis revealed that the SV40 promoter is recognized and used when placed in cis in two different HSV-1 genome locations, and Northern hybridization experiments confirmed that the heterologous gene was expressed in the absence of prior viral protein synthesis. Therefore, this gene was not regulated as strictly as an HSV-1 gene, but was influenced by the environment into which it was placed, presumably by factors that are present when the normal viral gene is on.

Control of mRNA stability by the virion host shutoff function of herpes simplex virus

vhs1 is a mutant of herpes simplex virus type 1 that is defective in the virion host shutoff function responsible for the degradation of cellular mRNAs and the concomitant shutoff of host protein synthesis. In this study, the effect of the vhs1 mutation on the metabolism of viral mRNAs was examined by measuring the half-lives and patterns of accumulation of 10 different viral mRNAs representing all kinetic classes. The vhs1 mutation had the effect of dramatically lengthening the cytoplasmic half-lives of all 10 mRNAs. In wild-type virus infections, the 10 mRNAs had similar half-lives, suggesting that little, if any, target mRNA selectivity was exhibited by the vhs function. The vhs1 mutation caused overaccumulation of a number of mRNAs. The effect was most dramatic for the alpha (immediate-early) mRNA for ICP27 and the beta (early) mRNAs encoding thymidine kinase, ICP8, and DNA polymerase. Whereas in wild-type infections these mRNAs increased to peak levels and subsequently declined in abundance, in vhs1 infections they continued to accumulate until late times. A significant but less dramatic overaccumulation was observed for several beta-gamma (delayed-early) and gamma (late) mRNAs. The results suggest that the vhs protein plays an important role in determining the half-lives of viral mRNAs belonging to all kinetic classes and in so doing is important in the normal downregulation at late times of alpha and beta gene expression.

Regulation of cellular genes transduced by herpes simplex virus

Previous studies demonstrated that the rabbit beta-globin gene is transcribed from its own promoter and regulated as a herpes simplex virus (HSV) early gene following insertion into the early HSV thymidine kinase gene in the intact viral genome (J. R. Smiley, C. Smibert, and R. D. Everrett, J. Virol. 61:2368-2377, 1987). We report here that the beta-globin promoter remained under early control after insertion into the late HSV gene encoding glycoprotein C. On the basis of these findings, we concluded that the beta-globin promoter is functionally equivalent to an HSV early-control region. We found that a transduced human alpha-globin gene was also regulated as an early HSV gene, while two linked Alu elements mimicked the behavior of HSV late genes. These results demonstrate that certain aspects of HSV temporal regulation can be duplicated by cellular elements and provide strong support for the hypothesis that the regulation of HSV gene expression can occur through mechanisms that do not rely on recognition of virus-specific temporal control signals.

Promoter sequence and cell type can dramatically affect the efficiency of transcriptional activation induced by herpes simplex virus type 1 and its immediate-early gene products Vmw175 and Vmw110

The activation of transcription of the early and late classes of viral genes during infection by herpes simplex virus type 1 (HSV-1) requires the prior expression of immediate-early (IE) gene products. The IE gene products can also activate certain cellular and heterologous viral promoters. This paper presents a thorough analysis of transactivation of the HSV-1 glycoprotein gD and simian virus 40 early promoters, and two other promoters that are hybrids of both, under a variety of experimental conditions. Two methods of transactivation (superinfection with virus and co-transfection with isolated IE genes) have been used with all four target promoters in a variety of cell types. The conclusions are: (1) promoter sequence affects the efficiency of promoter activation by infectious HSV-1 virus, but this activation is not restricted to HSV promoters; (2) cell type affects the efficiency of promoter activation by HSV-1, and this can lead to a failure to activate a promoter in one cell type but not in others in which activation is generally more efficient; (3) a promoter can be activated to different extents in co-transfection experiments using plasmids carrying isolated IE genes that express Vmw110 or Vmw175 or when both are used together; (4) the pattern of activation of a promoter by the IE gene products in cotransfection experiments varies in different cell types; (5) changes in promoter sequence can alter the pattern of activation by the different IE polypeptides, and this pattern can again differ in different cell types; (6) other apparently minor experimental variables, as might exist between the standard methods used in different laboratories, can also affect the patterns of activation observed. The results are discussed in terms of the mechanism of action of the HSV-1 IE gene products and the limitations of the co-transfection assay.

Analysis of the in vitro translation products of the equine herpesvirus type 1 immediate early mRNA

Equine herpesvirus type 1 (EHV-1) gene expression is coordinately regulated in an alpha, beta, gamma fashion. Viral alpha gene products include a 6.0-kb immediate early (IE) mRNA species (W. L. Gray et al., 1987, Virology 158, 79-87) and at least four closely related IE polypeptides (IEPs) (G.B. Caughman et al., 1985, Virology 145, 49-61). In this report, we describe results obtained from a series of in vitro translation experiments which were performed in an effort to characterize the IEPs and identify the mechanism by which individual IE protein species are generated. Our data indicate that a family of IEPs is generated in vitro from the 6.0-kb mRNA size class and that these IEPs correspond in overall size and antigenicity to those synthesized in infected cells. Using time-course/pulse-chase analyses, we show that production of three of the major IEPs [IE1' (193 kDa), IE3' (166 kDa), and IE4' (130 kDA)] occurs concomitantly, that none of these protein species can be chased completely into another, and that at least two additional minor species appear to be processed following synthesis. Finally, we show that the 6.0-kb mRNA species isolated during early or late stages of the infection cycle can be translated to yield all of the major IE proteins, indicating that production of the family of IEPs is not dependent upon accumulation of the IE mRNA which occurs during a cycloheximide blocked infection cycle. The implications of these findings are discussed as they relate to the origin and production of the IEPs both in vivo and in vitro.

The herpes simplex virus type 1 immediate-early protein ICP4 specifically induces increased transcription of the human ubiquitin B gene without affecting the ubiquitin A and C genes

Lytic infection with herpes simplex virus causes increased ubiquitin gene transcription. This effect is reproduced in cells expressing the viral immediate early protein ICP4 in the absence of other viral proteins but is not seen at the nonpermissive temperature in cells expressing the temperature-sensitive ICP4 protein of HSV-1 tsK. Studies with probes specific to the three human ubiquitin genes indicate that only the Ubi B gene is sensitive to ICP4-mediated induction whereas the Ubi A and C genes are unaffected. The significance of these effects for the mechanism by which ICP4 transcriptionally activates viral and a few cellular genes is discussed.

Abundant expression of herpes simplex virus glycoprotein gB using an adenovirus vector

Herpes simplex virus type 1 (HSV-1) glycoprotein B (gB) is a major component of infected cell membranes and virion envelopes. Glycoprotein B is known to be essential for entry of viruses into cells and may play important roles in virus-induced cell fusion and other alterations in cell morphology. In order to study the biochemical and immunological properties of gB in isolation from other HSV-1 polypeptides we have constructed human adenovirus vectors capable of expressing high levels of gB. The gB gene was coupled to the SV40 early promoter and inserted into the E3 region of two adenovirus vectors, one in which the E1 region was deleted (AdgB-1) and another which contained E1 sequences (AdgB-2). In AdgB-1 the orientation of the chimeric gB-SV40 gene was right to left, i.e., opposite to the direction of late and E3 mRNA transcription, whereas in AdgB-2 the orientation was left to right. Human 293 cells which express E1 functions supported replication of AdgB-1 and gB was expressed in these cells but not in mouse cells and only at very low levels in human cells other than 293. Replication of AdgB-2 was not limited to 293 cells and the virus was able to induce synthesis of gB at levels equal to or higher than those expressed in HSV-1-infected human or mouse cells. Microscopic examination of AdgB-2-infected cells revealed extensive vacuolization in a manner completely uncharacteristic of adenovirus-infected cells, and fluorescent antibody staining indicated that gB was not only present at the cell surface but also concentrated in the cytoplasmic vacuoles.