Identification of immediate-early-type cis-response elements in the promoter for the ribonucleotide reductase large subunit from herpes simplex virus type 2

Herpes Simplex Virus 1 Mutant with Point Mutations in UL39 Is Impaired for Acute Viral Replication in Mice, Establishment of Latency, and Explant-Induced Reactivation

In the process of generating herpes simplex virus 1 (HSV-1) mutations in the viral regulatory gene encoding infected cell protein 0 (ICP0), we isolated a viral mutant, termed KOS-NA, that was severely impaired for acute replication in the eyes and trigeminal ganglia (TG) of mice, defective in establishing a latent infection, and reactivated poorly from explanted TG. To identify the secondary mutation(s) responsible for the impaired phenotypes of this mutant, we sequenced the KOS-NA genome and noted that it contained two nonsynonymous mutations in UL39, which encodes the large subunit of ribonucleotide reductase, ICP6. These mutations resulted in lysine-to-proline (residue 393) and arginine-to-histidine (residue 950) substitutions in ICP6. To determine whether alteration of these amino acids was responsible for the KOS-NA phenotypes in vivo, we recombined the wild-type UL39 gene into the KOS-NA genome and rescued its acute replication phenotypes in mice. To further establish the role of UL39 in KOS-NA's decreased pathogenicity, the UL39 mutations were recombined into HSV-1 (generating UL39^mut), and this mutant virus showed reduced ocular and TG replication in mice comparable to that of KOS-NA. Interestingly, ICP6 protein levels were reduced in KOS-NA-infected cells relative to the wild-type protein. Moreover, we observed that KOS-NA does not counteract caspase 8-induced apoptosis, unlike wild-type strain KOS. Based on alignment studies with other HSV-1 ICP6 homologs, our data suggest that amino acid 950 of ICP6 likely plays an important role in ICP6 accumulation and inhibition of apoptosis, consequently impairing HSV-1 pathogenesis in a mouse model of HSV-1 infection.IMPORTANCE HSV-1 is a major human pathogen that infects ∼80% of the human population and can be life threatening to infected neonates or immunocompromised individuals. Effective therapies for treatment of recurrent HSV-1 infections are limited, which emphasizes a critical need to understand in greater detail the events that modulate HSV-1 replication and pathogenesis. In the current study, we identified a neuroattenuated HSV-1 mutant (i.e., KOS-NA) that contains novel mutations in the UL39 gene, which codes for the large subunit of ribonucleotide reductase (also known as ICP6). This mutant form of ICP6 was responsible for the attenuation of KOS-NA in vivo and resulted in diminished ICP6 protein levels and antiapoptotic effect. Thus, we have determined that subtle alteration of the UL39 gene regulates expression and functions of ICP6 and severely impacts HSV-1 pathogenesis, potentially making KOS-NA a promising vaccine candidate against HSV-1.

Systematic screening of viral entry inhibitors using surface plasmon resonance

Viral binding and entry into host cells for various viruses have been studied extensively, yielding a detailed understanding of the overall viral entry process. As cell entry is an essential and requisite process by which a virus initiates infection, it is an attractive target for therapeutic intervention. The advantages of targeting viral entry are an extracellular target site, relatively easy access for biological interventions, and lower toxicity. Several cell-based strategies and biophysical techniques have been used to screen compounds that block viral entry. These studies led to the discovery of inhibitors against HIV, HCV, influenza, Ebola, and RSV. In recent years, several compounds screened by fragment-based drug discovery have been approved as drugs or are in the final stages of clinical trials. Among fragment screening technologies, surface plasmon resonance has been widely used because it provides accurate information on binding kinetics, allows real-time monitoring of ligand-drug interactions, requires very small sample amounts to perform analyses, and requires no modifications to or labeling of ligands. This review focuses on surface plasmon resonance-based schemes for screening viral entry inhibitors.

A dual reporter cell assay for identifying serotype and drug susceptibility of herpes simplex virus

A dual reporter cell assay (DRCA) that allows real-time detection of herpes simplex virus (HSV) infection was developed. This was achieved by stable transfection of cells with an expression cassette that contains the dual reporter genes, secreted alkaline phosphatase (SEAP) and enhanced green fluorescent protein (EGFP), under the control of an HSV early gene promoter. Baby hamster kidney (BHK) and Chinese hamster ovary (CHO) cell lines were used as parental cell lines because the former is permissive for both HSV serotypes, HSV-1 and HSV-2, whereas the latter is susceptible to infection only by HSV-2. The DRCA permitted differential detection of HSV-1 and HSV-2 by observation of EGFP-positive cells, as substantiated by screening a total of 35 samples. The BHK-based cell line is sensitive to a viral titer as low as a single plaque-forming unit with a robust assay window as measured by a chemiluminescent assay. Evaluations of the DRCA with representative acyclovir-sensitive and acyclovir-resistant HSV strains demonstrated that their drug susceptibilities were accurately determined by a 48-h format. In summary, this novel DRCA is a useful means for serotyping of HSV in real time as well as a rapid screening method for determining anti-HSV susceptibilities.

Strategies for antiviral screening targeting early steps of virus infection

Viral infection begins with the entry of the virus into the host target cell and initiates replication. For this reason, the virus entry machinery is an excellent target for antiviral therapeutics. In general, a virus life cycle includes several major steps: cell-surface attachment, entry, replication, assembly, and egress, while some viruses involve another stage called latency. The early steps of the virus life cycle include virus attachment, receptor binding, and entry. These steps involve the initial interactions between a virus and the host cell and thus are major determinants of the tropism of the virus infection, the nature of the virus replication, and the diseases resulting from the infection. Owing to the pathological importance of these early steps in the progress of viral infectious diseases, the development of inhibitors against these steps has been the focus of the pharmaceutical industry. In this review, Herpes Simplex Virus (HSV), Hepatitis C Virus (HCV), and Human Enterovirus 71 (EV71) were used as representatives of enveloped DNA, enveloped RNA, and non-enveloped viruses, respectively. The current mechanistic understanding of their attachment and entry, and the strategies for antagonist screenings are summarized herein.

The HSV-2 mutant DeltaPK induces melanoma oncolysis through nonredundant death programs and associated with autophagy and pyroptosis proteins

Malignant melanoma is a highly aggressive and drug-resistant cancer. Virotherapy is a novel therapeutic strategy based on cancer cell lysis through selective virus replication. However, its clinical efficacy is modest, apparently related to poor virus replication within the tumors. We report that the growth compromised herpes simplex virus type 2 (HSV-2) mutant, DeltaPK, has strong oncolytic activity for melanoma largely caused by a mechanism other than replication-induced cell lysis. The ratio of dead cells (determined by trypan blue or ethidium homodimer staining) to cells that stain with antibody to the major capsid protein VP5 (indicative of productive infection) was 1.8-4.1 for different melanoma cultures at 24-72 h post-infection. Cell death was due to activation of calpain as well as caspases-7 and -3 and it was abolished by the combination of calpain (PD150606) and pancaspase (benzyloxycarbonyl-Val-Ala-Asp-fluormethyl ketone, z-VAD-fmk) inhibitors. Upregulation of the autopahgy protein Beclin-1 and the pro-apoptotic protein H11/HspB8 accompanied DeltaPK-induced melanoma oncolysis. Intratumoral DeltaPK injection (10(6)-10(7) plaque-forming unit (pfu)) significantly reduced melanoma tumor burden associated with calpain and caspases-7 and -3 activation, Beclin-1 and H11/HspB8 upregulation and activation of caspase-1-related inflammation. Complete remission was seen for 87.5% of the LM melanoma xenografts at 5 months after treatment termination. The data indicate that DeltaPK is a promising virotherapy for melanoma that functions through virus-induced programmed cell death pathways.

Growth-compromised HSV-2 vector Delta RR protects from N-methyl-D-aspartate-induced neuronal degeneration through redundant activation of the MEK/ERK and PI3-K/Akt survival pathways, either one of which overrides apoptotic cascades

We have previously shown that intrastriatal injection of Delta RR, the growth-compromised herpes simplex virus type 2 (HSV-2) vector for the antiapoptotic protein ICP10PK, prevents apoptosis caused by the excitotoxin N-methyl-D-aspartate (NMDA) in a mouse model of glutamatergic neuronal cell death (Golembewski et al. [2007] Exp. Neurol. 203:381-393). Because apoptosis regulation is stimulus and cell type specific, our studies were designed to examine the mechanism of Delta RR-mediated neuroprotection in striatal neurons. Organotypic striatal cultures (OSC) that retain much of the synaptic circuitry of the intact striatum were infected with Delta RR or a growth-compromised HSV-2 vector that lacks ICP10PK (Delta PK) and examined for neuroprotection-associated signaling. The mutated ICP10 proteins (p175 and p95) were expressed in 70-80% of neurons from Delta RR- and Delta PK-infected cultures, respectively, as determined by double-immunofluorescent staining with antibodies to ICP10 and NeuN or GAD65. Delta RR- but not Delta PK-treated OSC were protected from NMDA-induced apoptosis, as verified by ethidium homodimer staining, TUNEL, caspase-3 activation, and poly(AD-ribose) polymerase (PARP) cleavage. Neuroprotection was through ICP10PK-mediated activation of the survival pathways MEK/ERK and PI3-K/Akt, up-regulation of the antiapoptotic proteins Bag-1 and Bcl-2, and phosphorylation (inactivation) of the proapoptotic protein Bad. It was blocked by the MEK inhibitor U0126 or the PI3-K inhibitor LY294002, suggesting that either pathway can prevent NMDA-induced apoptosis. The data indicate that Delta RR-delivered ICP10PK stimulates redundant survival pathways that override proapoptotic cascades. Delta RR is a promising gene therapy platform against glutamatergic cell death.

DeltaRR vaccination protects from KA-induced seizures and neuronal loss through ICP10PK-mediated modulation of the neuronal-microglial axis

Ischemic brain injury and epilepsy are common neurodegenerative diseases caused by excitotoxicity. Their pathogenesis includes microglial production of inflammatory cytokines. Our studies were designed to examine whether a growth compromised HSV-2 mutant (Delta RR) prevents excitotoxic injury through modulation of microglial responses by the anti-apoptotic HSV-2 protein ICP10PK. EOC2 and EOC20 microglial cells, which are differentially activated, were infected with Delta RR or the ICP10PK deleted virus (Delta PK) and examined for virus-induced neuroprotective activity. Both cell lines were non-permissive for virus growth, but expressed ICP10PK (Delta RR) or the PK deleted ICP10 protein p95 (Delta PK). Conditioned medium (CM) from Delta RR-, but not Delta PK-infected cells prevented N-methyl-D-aspartate (NMDA)-induced apoptosis of primary hippocampal cultures, as determined by TUNEL and caspase-3 activation (76.9 +/- 5.3% neuroprotection). Neuroprotection was associated with inhibition of TNF-alpha and RANTES and production of IL-10. The CM from Delta PK-infected EOC2 and EOC20 cells did not contain IL-10, but it contained TNF-alpha and RANTES. IL-10 neutralization significantly (p < 0.01) decreased, but did not abrogate, the neuroprotective activity of the CM from Delta RR-infected microglial cultures indicating that ICP10PK modulates the neuronal-microglial axis, also through induction of various microglial neuroprotective factors. Rats given Delta RR (but not Delta PK) by intranasal inoculation were protected from kainic acid (KA)-induced seizures and neuronal loss in the CA1 hippocampal fields. Protection was associated with a significant (p < 0.001) increase in the numbers of IL-10+ microglia (CD11b+) as compared to Delta PK-treated animals. Delta RR is a promising vaccination/therapy platform for neurodegeneration through its pro-survival functions in neurons as well as microglia modulation.

The growth compromised HSV-2 mutant DeltaRR prevents kainic acid-induced apoptosis and loss of function in organotypic hippocampal cultures

We have previously shown that the HSV-2 anti-apoptotic protein ICP10PK is delivered by the replication incompetent virus mutant DeltaRR and prevents kainic acid (KA)-induced epileptiform seizures and neuronal cell loss in the mouse and rat models of temporal lobe epilepsy. The present studies used DeltaRR and the ICP10PK deleted virus mutant DeltaPK to examine the mechanism of neuroprotection. DeltaRR-infected neuronal cells expressed a chimeric protein in which ICP10PK is fused in frame to LacZ (p175) while retaining ICP10PK kinase activity. DeltaPK-infected neuronal cells expressed a mutant ICP10 protein that is deleted in the PK domain and is kinase negative (p95). p175 and p95 were expressed in CA3 (86+/-3%) and CA1 (69+/-7%) cells from DeltaRR or DeltaPK-infected organotypic hippocampal cultures (OHC) and 80-85% of the ICP10 positive cells co-stained with antibody to beta(III) Tubulin (neuronal marker). DeltaRR, but not DeltaPK, inhibited KA-induced cell death and caspase-3 activation in CA3 neurons, an inhibition seen whether DeltaRR was delivered 2 days before or 2 days after KA administration (95% neuroprotection). Neuroprotection was associated with ERK and Akt activation and was abrogated by simultaneous treatment with the MEK (U0126) and PI3-K (LY294002) inhibitors. DeltaRR-mediated neuroprotection was associated with increased expression of the anti-apoptotic protein Bag-1 and decreased expression of the pro-apoptotic protein Bad. The surviving neurons retained normal synaptic function potentially related to increased expression of the transcription factor CREB. The data indicate that DeltaRR is a promising platform for neuroprotection from excitotoxic injury.

Stress up-regulates neuronal expression of the herpes simplex virus type 2 large subunit of ribonucleotide reductase (R1; ICP10) by activating activator protein 1

Herpes simplex virus type 2 (HSV-2) genes expressed in neuronal cells in response to stress stimuli that trigger latency reactivation are largely unknown. Using a chloramphenicol acetyltransferase (CAT) reporter assay we found that stress caused a significant (P < .001) increase in ICP10 expression in neuronal cells. Up-regulation correlated with activator protein (AP)-1 activation, notably c-Jun and c-Fos that bind cognate elements in the ICP10 promoter. It was blocked by mutation of the AP-1 motifs in the ICP10 promoter. ICP10 expression protected neuronal cells from stress-induced apoptosis. The data suggest that ICP10 may contribute to HSV-2 reactivation by increasing neuronal survival.

Herpes simplex virus type 2 vaccines: new ground for optimism?

The development of effective prophylactic and therapeutic vaccines against genital herpes has proven problematic. Difficulties are associated with the complexity of the virus life cycle (latency) and our relatively poor understanding of the mechanism of immune control of primary and recurrent disease. The types of effector cells and the mechanisms responsible for their activation and regulation are particularly important. Studies from my and other laboratories have shown that recurrent disease is prevented by virus-specific T helper 1 (Th1) cytokines (viz., gamma interferon) and activated innate immunity. Th2 cytokines (viz., interleukin-10 [IL-10]) and regulatory (suppressor) T cells downregulate this immune profile, thereby allowing unimpeded replication of reactivated virus and recurrent disease. Accordingly, an effective therapeutic vaccine must induce Th1 immunity and be defective in Th2 cytokine production, at least IL-10. These concepts are consistent with the findings of the most recent clinical trials, which indicate that (i) a herpes simplex virus type 2 (HSV-2) glycoprotein D (gD-2) vaccine formulated with a Th1-inducing adjuvant has prophylactic activity in HSV-2- and HSV-1-seronegative females, an activity attributed to the adjuvant function, and (ii) a growth-defective HSV-2 mutant (ICP10DeltaPK), which is deleted in the Th2-polarizing gene ICP10PK, induces Th1 immunity and has therapeutic activity in both genders. The ICP10DeltaPK vaccine prevents recurrent disease in 44% of treated subjects and reduces the frequency and severity of recurrences in the subjects that are not fully protected. Additional studies to evaluate these vaccines are warranted.

A cell line that secretes inducibly a reporter protein for monitoring herpes simplex virus infection and drug susceptibility

A cell line modified genetically (Vero-ICP10-SEAP) that responds to infection by herpes simplex virus (HSV) was established. The cell line was constructed by stable transfection of Vero cell with a plasmid encoding the secreted alkaline phosphatase (SEAP) driven by the promoter of the HSV-2 ICP10 gene. Following infection with HSV, the stable line secretes a high level of the SEAP in the supernatants as measured by a chemiluminescence-based assay. The detection system is sensitive to an HSV titer as low as a single plaque-forming unit (PFU), with a linear range up to the equivalent of 2.5 x 10(4) PFU inoculum after infection for 24 h. There was no detectable enhancement in SEAP activities following inoculations with several viruses other than HSV. The Vero-ICP10-SEAP cell line was also utilized to develop an assay for determination of antiviral susceptibility given that the induced SEAP activity appeared to reflect the numbers of plaque. Evaluations of the stable line with representative acyclovir (ACV)-sensitive and-resistant HSV isolates demonstrated that their drug susceptibilities were determined accurately. In summary, this novel SEAP reporter system is a sensitive means for rapid diagnosis, quantitation, and drug susceptibility testing for HSV, with potential to the development of an automated assay.

The herpes simplex virus type 2 R1 protein kinase (ICP10 PK) blocks apoptosis in hippocampal neurons, involving activation of the MEK/MAPK survival pathway

Herpes simplex virus type 1 (HSV-1) and HSV-2 trigger or counteract apoptosis by a cell-specific mechanism. Our studies are based on previous findings that the protein kinase (PK) domain of the large subunit of HSV-2 ribonucleotide reductase (ICP10) activates the Ras/MEK/MAPK pathway (Smith et al., J. Virol. 74:10417, 2000). Because survival pathways can modulate apoptosis, we used cells that are stably or transiently transfected with ICP10 PK, an HSV-2 mutant deleted in ICP10 PK (ICP10DeltaPK) and the MEK-specific inhibitor U0126 to examine the role of ICP10 PK in apoptosis. Apoptosis was induced by staurosporine or D-mannitol in human (HEK293) cells or HEK293 cells stably transfected with the ICP10 PK-negative mutant p139 (JHL15), as determined by morphology, DNA fragmentation, terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling (TUNEL), caspase-3 activation, and poly(ADP-ribose) polymerase (PARP) cleavage. HEK293 cells stably transfected with ICP10 (JHLa1) were protected from apoptosis. ICP10 but not p139 protected neuronally differentiated PC12 cells from death due to nerve growth factor withdrawal, and apoptosis (determined by TUNEL) and caspase-3 activation were seen in primary hippocampal cultures infected with ICP10DeltaPK but not with HSV-2 or a revertant virus [HSV-2(R)]. The data indicate that ICP10 has antiapoptotic activity under both paradigms and that it requires a functional PK activity. The apoptotic cells in primary hippocampal cultures were neurons, as determined by double immunofluorescence with fluorescein-labeled dUTP (TUNEL) and phycoerythrin-labeled antibodies specific for neuronal proteins (TuJ1 and NF-160). Protection from apoptosis was associated with MEK/MAPK activation, as evidenced by (i) increased levels of activated (phosphorylated) MAPK in HSV-2- but not ICP10DeltaPK-infected cultures and (ii) inhibition of MAPK activation by the MEK-specific inhibitor U0126. MEK and MAPK were activated by infection with UV-inactivated but not antibody-neutralized HSV-2, suggesting that activation requires cellular penetration but is independent of de novo viral protein synthesis.

Ras-GAP binding and phosphorylation by herpes simplex virus type 2 RR1 PK (ICP10) and activation of the Ras/MEK/MAPK mitogenic pathway are required for timely onset of virus growth

We used a herpes simplex virus type 2 (HSV-2) mutant with a deletion in the RR1 (ICP10) PK domain (ICP10DeltaPK) and an MEK inhibitor (PD98059) to examine the role of ICP10 PK in virus growth. In HSV-2-infected cells, ICP10 PK binds and phosphorylates the GTPase activating protein Ras-GAP. In vitro binding and peptide competition assays indicated that Ras-GAP N-SH2 and PH domains, respectively, bind ICP10 at phosphothreonines 117 and 141 and a WD40-like motif at positions 160 to 173. Binding and phosphorylation did not occur in cells infected with ICP10DeltaPK. GTPase activity was significantly lower in HSV-2- than in ICP10DeltaPK-infected cells. Conversely, the levels of activated Ras and mitogen-activated protein kinase (MAPK), and the expression and stabilization of the transcription factor c-Fos were significantly increased in cells infected with HSV-2 or a revertant virus [HSV-2(R)] but not with ICP10DeltaPK. PD98059 inhibited MAPK activation and induction-stabilization of c-Fos. Expression from the ICP10 promoter was increased in cells infected with HSV-2 but not with ICP10DeltaPK, and increased expression was ablated by PD98059. ICP10 DNA formed a complex with nuclear extracts from HSV-2-infected cells which was supershifted by c-Fos antibody and was not seen with extracts from ICP10DeltaPK-infected cells. Complex formation was abrogated by PD98059. Onset of HSV-2 replication was significantly delayed by PD98059 (14 h versus 2 h in untreated cells), a delay similar to that seen for ICP10DeltaPK. The data indicate that Ras-GAP phosphorylation by ICP10 PK is involved in the activation of the Ras/MEK/MAPK mitogenic pathway and c-Fos induction and stabilization. This results in increased ICP10 expression and the timely onset of HSV-2 growth.

Rapid diagnosis and quantification of herpes simplex virus with a green fluorescent protein reporter system

A genetically modified cell line (Vero-ICP10-EGFP) was constructed for detection of herpes simplex virus (HSV) by a simple, rapid and direct method. The cell line was developed by stable transfection of Vero cell with a plasmid encoding the green fluorescent protein (GFP) driven by the promoter of the HSV-2 ICP10 gene. As early as 6 h after infection with HSV, fluorescence-emitting cells can be observed under a fluorescence microscope. A single infected cell emitting fluorescence can be observed with soft agar overlay by inverted fluorescence microscopy. No induction of detectable fluorescence was seen following infections with human cytomegalovirus (HCMV), varicella zoster virus (VZV), coxsackievirus A16 and enterovirus 71. Analysis by flow cytometry also demonstrated that intensity of the triggered fluorescence is proportional to the titer of HSV inoculated. Taken together, this novel GFP reporter system could become a useful means for rapid detection and quantification of HSV in clinical specimens.

Herpes simplex virus type 2 growth and latency reactivation by cocultivation are inhibited with antisense oligonucleotides complementary to the translation initiation site of the large subunit of ribonucleotide reductase (RR1)

Antisense oligonucleotides complementary to the translation initiation site of the herpes simplex virus type 2 (HSV-2) large subunit of ribonucleotide reductase (RR1) were studied for their ability to inhibit RR1 expression, HSV-2 growth, and its reactivation from latently infected ganglia. The oligomers caused a significant decrease (90%-97% inhibition) in HSV-2 RR1 expression and inhibited HSV-2 growth, with IC50 and IC90 values of 0.11 and 1.0 microM, respectively. The titers of HSV-2 mutants that are respectively deleted in the PK (ICP10deltaPK) or RR (ICP10deltaRR) domains of RR1 were also significantly (500-20,000-fold) decreased, indicating that the antisense oligomers interfere with the independent contributions of the two RR1 functions (PK and RR) toward virus growth. Inhibition was sequence specific, as evidenced by the failure of a two-base mutant (RR1TImu) to inhibit protein expression and HSV-2 growth. Furthermore, the antisense oligomers inhibited HSV-2 reactivation by cocultivation of latently infected ganglia (0/8). Virus was reactivated from ganglia cultured without oligomers, in the presence of unrelated oligomers (6/8), or in the presence of the two-base mutant RR1TImu (5/8) (p < 0.007 by two-tailed Fisher exact test). HSV-2 growth was not inhibited by antisense oligonucleotides complementary to the splice junction of HSV-2 immediate-early (IE) pre-mRNA 4 and 5 (IE4,5SA) or the translation initiation site of IE mRNA 4 (IE4TI), although the respective HSV-1-specific oligomers inhibit HSV-1 growth.

The PK domain of the large subunit of herpes simplex virus type 2 ribonucleotide reductase (ICP10) is required for immediate-early gene expression and virus growth

The large subunit of herpes simplex virus (HSV) ribonucleotide reductase (RR), RR1, contains a unique amino-terminal domain which has serine/threonine protein kinase (PK) activity. To examine the role of the PK activity in virus replication, we studied an HSV type 2 (HSV-2) mutant with a deletion in the RR1 PK domain (ICP10DeltaPK). ICP10DeltaPK expressed a 95-kDa RR1 protein (p95) which was PK negative but retained the ability to complex with the small RR subunit, RR2. Its RR activity was similar to that of HSV-2. In dividing cells, onset of virus growth was delayed, with replication initiating at 10 to 15 h postinfection, depending on the multiplicity of infection. In addition to the delayed growth onset, virus replication was significantly impaired (1,000-fold lower titers) in nondividing cells, and plaque-forming ability was severely compromised. The RR1 protein expressed by a revertant virus [HSV-2(R)] was structurally and functionally similar to the wild-type protein, and the virus had wild-type growth and plaque-forming properties. The growth of the ICP10DeltaPK virus and its plaque-forming potential were restored to wild-type levels in cells that constitutively express ICP10. Immediate-early (IE) genes for ICP4, ICP27, and ICP22 were not expressed in Vero cells infected with ICP10DeltaPK early in infection or in the presence of cycloheximide, and the levels of ICP0 and p95 were significantly (three- to sevenfold) lower than those in HSV-2- or HSV-2(R)-infected cells. IE gene expression was similar to that of the wild-type virus in cells that constitutively express ICP10. The data indicate that ICP10 PK is required for early expression of the viral regulatory IE genes and, consequently, for timely initiation of the protein cascade and HSV-2 growth in cultured cells.

The large subunit of herpes simplex virus type 2 ribonucleotide reductase (ICP10) is associated with the virion tegument and has PK activity

The large subunit of herpes simplex virus type 2 (HSV-2) ribonucleotide reductase (ICP10) was identified in sucrose gradient-purified HSV-2 virions by immunoprecipitation/immunoblotting with antibody specific for the protein kinase (PK) domain. Immunoblotting of individual gradient fractions indicated that ICP10 cosediments with the major capsid protein and the highest virus titers. ICP10 was not labeled by iodination of purified virions, indicating that it is not located on the virion surface. After envelope glycoproteins were removed by detergent treatment, ICP10 was associated with capsid-tegument particles and became sensitive to trypsin digestion. The capsid-tegument-associated ICP10 was phosphorylated and had PK activity in vitro and on Immobilon membranes. A mutant ICP10 protein deleted in the PK domain (p95) was also associated with purified virions (ICP10deltaPK virus) but it lacked PK activity. The data indicate that ICP10 is contained within the tegument component where it retains intrinsic PK activity.

The herpes simplex virus immediate-early protein ICP0 affects transcription from the viral genome and infected-cell survival in the absence of ICP4 and ICP27

ICP4, ICP0, and ICP27 are the immediate-early (IE) regulatory proteins of herpes simplex virus that have the greatest effect on viral gene expression and growth. Comparative analysis of viral mutants defective in various subsets of these IE genes should help elucidate how these proteins affect cellular and viral processes. This study focuses on the mutant d97, which is defective for the genes encoding ICP4, ICP0, and ICP27 and expresses the bacterial beta-galactosidase (beta-gal) gene from the ICP0 promoter. Together with the d92 virus (ICP4- ICP27-) and the ICP0-complementing cell line L7, d97 provided a unique opportunity to evaluate ICP0 function in the absence of the regulatory activities specified by ICP4 and ICP27. The pattern of protein synthesis in d97-infected cells was unique relative to other IE gene mutants in that it was similar to that seen in the absence of prior viral protein synthesis, possibly approximating the effect of cellular factors and virion components alone. Inactivation of ICP0 in the absence of ICP4 produced a significant decrease in the levels of the early mRNAs ICP6 and thymidine kinase (tk). There was also a marginal reduction in the levels of the IE ICP22 mRNA, and this was most notable at low multiplicity of infection (MOI). In d97-infected L7 cells, the levels of the viral mRNAs were mostly restored to those observed in infections with d92. Nuclear runoff transcription analysis demonstrated that the presence of ICP0 resulted in an increase in the transcription rates of the analyzed genes. The transcription rates of the early genes were dramatically reduced in the absence of ICP0. At low MOI, the transcription rates of ICP6 and tk were comparable to the rate of transcription of a cellular gene. Relevant to the potential use of d97 as a transfer vector, it was also determined that the absence of ICP0 reduced the cellular toxicity of the virus compared to that of d92. The beta-gal transgene expressed from an IE promoter was detected for up to 14 days postinfection; however, the level of beta-gal expression declined dramatically after 1 day postinfection. In the presence of ICP0, the level of expression of beta-gal was increased; however the infected monolayer was destroyed by 3 days postinfection. Therefore, deletion of ICP0 in the absence of ICP4 and ICP27 reduces toxicity and lowers the level of expression of genes from the viral genome.

AP-1 cis-response elements are involved in basal expression and Vmw110 transactivation of the large subunit of herpes simplex virus type 2 ribonucleotide reductase (ICP10)

The promoter of the large subunit of herpes simplex virus type 2 ribonucleotide reductase (ICP10) has two AP-1 cis-response elements, respectively located at positions -62 and -94 relative to the transcription start site (Wymer et al., 1989. J. Virol. 63, 2773-2784). Chloramphenicol acetyl transferase (CAT) analysis with hybrid constructions of the CAT structural gene and the ICP10 promoter or its mutants and gel retardation studies were used to examine the role of the AP-1 cis-response elements in expression from the ICP10 promoter. Basal expression from the wild-type promoter was significantly (75-90%) reduced by mutation of the upstream or downstream AP-1 element. Mutation in the upstream AP-1 element also caused a 60% reduction in c-Jun-mediated activation. Activation was decreased 40% by mutation in the downstream AP-1 element and it was abrogated by mutation of both elements. Similar results were obtained for ACT-deleted mutants and mutants in which CT was mutated to AG. The trans-activation by Vmw110 was also reduced by mutation of the AP-1 elements (10- and 2-fold for the upstream and downstream element, respectively) and it was abrogated by mutation of both AP-1 elements. Mutation of nucleotides adjacent to the AP-1 cis-response elements had no effect on trans-activation. Gel retardation assays with a DNA probe representing the wild-type ICP10 promoter and nuclear extracts from HSV-1-infected cells identified one complex that was not seen with mock-infected cells or with cells infected with a Vmw110-deleted mutant. The complex was not seen when HSV-1-infected cells were reacted with an AP-1-mutant DNA probe, and its formation was competed by an AP-1 but not a mutant AP-1 oligonucleotide. The migration of this complex was retarded by c-Fos antibody, suggesting that both AP-1 and Vmw110 are involved in its formation. A mutant deleted in all sequences upstream of the TATA box was also activated by Vmw110, but this activation was only 2-fold lower than that seen for the wild type and significantly higher (10-fold) than that seen for the double AP-1 mutants. The data suggest that AP-1 elements play a crucial role in ICP10 gene expression/activation.

ATP and SH3 binding sites in the protein kinase of the large subunit of herpes simplex virus type 2 of ribonucleotide reductase (ICP10)

The large subunit of herpes simplex virus type 2 ribonucleotide reductase (ICP10) is a multifunctional protein. It consists of a ribonucleotide reductase and a serine/threonine protein kinase (PK) domain, which has three proline-rich motifs consistent with SH3-binding sites at positions 140, 149, and 396. We used site-directed mutagenesis to identify amino acids required for kinase activity and interaction with signaling proteins. Mutation of Lys176 or Lys259 reduced PK activity (5-8-fold) and binding of the 14C-labeled ATP analog rho-fluorosulfonylbenzoyl 5'-adenosine (FSBA) but did not abrogate them. Enzymatic activity and FSBA binding were abrogated by mutation of both Lys residues, suggesting that either one can bind ATP. Mutation of Glu209 (PK catalytic motif III) virtually abrogated kinase activity in the presence of Mg2+ or Mn2+ ions, suggesting that Glu209 functions in ion-dependent PK activity. ICP10 bound the adaptor protein Grb2 in vitro. Mutation of the ICP10 proline-rich motifs at positions 396 and 149 reduced Grb2 binding 20- and 2-fold, respectively. Binding was abrogated by mutation of both motifs. Grb2 binding to wild type ICP10 was competed by a peptide for the Grb2 C-terminal SH3 motif, indicating that it involves the Grb2 C-terminal SH3.

Transgenic cell lines for detection of animal viruses

Rapid diagnostic assays based on direct detection of viral antigen or nucleic acid are being used with increasing frequency in clinical virology laboratories. Virus culture, however, remains the only way to detect infectious virus and to analyze clinically relevant viral phenotypes, such as drug resistance. Growth of viruses in cell culture is labor intensive and time-consuming and requires the use of many different cell lines. Transgenic technology, together with increasing knowledge of the molecular pathways of virus replication, offers the possibility of using genetically modified cell lines to improve virus growth in cell culture and to facilitate detection of virus-infected cells. Genetically modifying cells so that they express a reporter gene only after infection with a specific virus can allow the detection of infectious virus by rapid and simple enzyme assays such as beta-galactosidase assays without the need for antibodies. Although transgenic cells have recently been successfully used for herpes simplex virus detection, much more work needs to be done to adapt this technology to other human viral pathogens such as cytomegalovirus and respiratory viruses. This review offers some strategies for applying this technology to a wide spectrum of animal viruses.

Herpes simplex ICP27 mutant viruses exhibit reduced expression of specific DNA replication genes

Herpes simplex virus type 1 mutants with certain lesions in the ICP27 gene show a 5- to 10-fold reduction in viral DNA synthesis. To determine how ICP27 promotes amplification of viral DNA, we examined the synthesis, accumulation, and stability of the essential viral replication proteins and steady-state levels of the replication gene transcripts throughout the course of ICP27 mutant virus infections. These studies reveal that in the absence of ICP27, expression of the UL5, UL8, UL52, UL9, UL42, and UL30 genes is significantly reduced at the level of mRNA accumulation. In contrast to that of these beta genes, ICP8 expression is unaltered in mutant virus-infected cells, indicating that ICP27 selectively stimulates only a subset of herpes simplex virus beta genes. Analysis of multiple ICP27 mutant viruses indicates a quantitative correlation between the ability of these mutants to replicate viral DNA and the level of replication proteins produced by each mutant. Therefore, we conclude that the primary defect responsible for restricted viral DNA synthesis in cells infected with ICP27 mutants is insufficient expression of most of the essential replication genes. Of further interest, this analysis also provides new information about the structure of the UL52 gene transcripts.

Cervical cancer: is herpes simplex virus type II a cofactor?

In many ways, cervical cancer behaves as a sexually transmitted disease. The major risk factors are multiple sexual partners and early onset of sexual activity. Although high-risk types of human papillomaviruses (HPV) play an important role in the development of nearly all cases of cervical cancer, other sexually transmitted infectious agents may be cofactors. Herpes simplex virus type 2 (HSV-2) is transmitted primarily by sexual contact and therefore has been implicated as a risk factor. Several independent studies suggest that HSV-2 infections correlate with a higher than normal incidence of cervical cancer. In contrast, other epidemiological studies have concluded that infection with HSV-2 is not a major risk factor. Two separate transforming domains have been identified within the HSV-2 genome, but continued viral gene expression apparently is not necessary for neoplastic transformation. HSV infections lead to unscheduled cellular DNA synthesis, chromosomal amplifications, and mutations. These observations suggest that HSV-2 is not a typical DNA tumor virus. It is hypothesized that persistent or abortive infections induce permanent genetic alterations that interfere with differentiation of cervical epithelium and subsequently induce abnormal proliferation. Thus, HSV-2 may be a cofactor in some but not all cases of cervical cancer.

Characterization of the novel protein kinase activity present in the R1 subunit of herpes simplex virus ribonucleotide reductase

We have compared the protein kinase activities of the R1 subunits from herpes simplex virus types 1 (HSV-1) and 2 (HSV-2) ribonucleotide reductase following expression in Escherichia coli. Autophosphorylation activity was observed when kinase assays were performed with immunoprecipitated R1 or proteins purified to homogeneity, and the activity was stimulated by the basic protein protamine. Transphosphorylation of histones or calmodulin by purified or immunoprecipitated HSV-1 and HSV-2 R1 was not observed, and our results suggest that the activities of these two proteins are similar. We further characterized the protein kinase activity of HSV-1 R1 by producing insertion and deletion mutants constructed with a plasmid expressing R1 amino acids 1 to 449. C-terminal deletion analysis identified the catalytic core of the enzyme as comprising residues 1 to 292, and this polypeptide will be useful for structural determinations by X-ray crystallography. Insertion of a 4-amino-acid sequence at sites within the protein kinase domain identified regions essential for activity; insertions at residues 22 and 112 completely inactivated activity, and an insertion at residue 136 reduced activity sixfold. Similar insertions at residues 257, 262, 292, and 343 had no effect on activity. The ATP analog 5'-fluorosulfonylbenzoyladenosine, which covalently modifies conventional eukaryotic kinases at an essential lysine residue within the active site, did label HSV R1, but this labelling occurred outside the N-terminal domain. These data indicate that the HSV R1 kinase is novel and distinct from other eukaryotic protein kinases.

Multiple Tandemly Repeated Binding Sites for the YY1 Repressor and Transcription Factors AP-1 and SP-1 Are Clustered within Intron-1 of the Gene Encoding the IE110 Transactivator of Herpes simplex Virus Type 1

Expression of the IE110 (ICP0) transactivator protein of HSV appears to be critical for reactivation from the latent state and occurs at immediate-early times during the lytic cycle under the control of an upstream divergent enhancer-promoter region that contains multiple Oct and Sp-1 binding sites overlapping with VP16 response elements. Surprisingly, the large 800-bp first intron of the HSV-1 IE110 gene also proved to have a complex repetitive organization encompassing multiple transcription factor binding sites within four distinct domains. DNaseI footprinting studies revealed that 13 of 17 copies of a 15-bp repeated element represented high-affinity binding sites for the cellular YY1 repressor protein. Between 4 and 7 of these sites are direct tandem repeats and the rest are interpersed with three repeated AT-rich motifs and a dyad symmetry region containing two strong AP-1 binding sites and an adjacent SP-1 binding site on each arm. Several of the YY1 sites also bound weakly to SRF. The intron also contains four clustered purine/pyrimidine tracts of between 16 and 23 bp long. Both the AP-1/AP-2/SP-1 dyad protein binding region and, to a lesser extent, the YY1 tandem-repeat cluster conferred responsiveness to TPA when placed upstream of a heterologous promoter in transient expression assays. The functional significance of the HSV-1 IE110 intron region is unknown as yet, but the novel arrangement of tandemly repeated YY1 sites has the potential to produce structural bending and transcriptional attenuation effects. Interestingly, few of these transcription factor binding motifs are conserved in the equivalent IE110 intron of HSV-2, and the domain appears to represent a unique alternative control region that is specific for HSV-1. Copyright 1995 S. Karger AG, Basel

Evaluation of colocalization interactions between the IE110, IE175, and IE63 transactivator proteins of herpes simplex virus within subcellular punctate structures

A number of previous studies have implied that three herpes simplex virus-encoded nuclear transactivator proteins, IE175 (ICP4), IE110 (ICP0), and IE63 (ICP27), may cooperate in transcriptional and posttranscriptional stimulation of viral gene expression. Using double-label immunofluorescence assays (IFA) in transient expression assays, we have examined the intracellular localization of these three proteins in DNA-transfected cells. The IE110 protein on its own forms spherical punctate domains within the nucleus, whereas the IE175 and IE63 proteins alone give uniform and speckled diffuse patterns, respectively. In infected cells, the IE110 punctate granules have been shown to correspond to novel preexisting subnuclear structures referred to as ND10 domains or PODs that contain a variety of cellular proteins, including SP100 and the PML proto-oncogene product. Cotransfection experiments with wild-type nuclear forms of both IE175 and IE110 provided direct evidence for partial redistribution of IE175 into the same punctate granules that contained IE110. Surprisingly, nuclear forms of IE110 were found to move a cytoplasmic form of IE175 into nuclear punctate structures, and a cytoplasmic form of IE110 was able to retain nuclear forms of IE175 in cytoplasmic punctate structures. Therefore, the punctate characteristic of IE110 appeared to both dominate the interactions and override the normal nuclear localization signals. The domains responsible for the interaction mapped to between codons 518 and 768 in 1E110 and to between codons 835 and 1029 in IE175. Importantly, a truncated nuclear form of the 1,298-amino-acid IE175 protein, which lacked the C-terminal domain beyond codon 834, was found to be excluded from the IE110 punctate granules. Cotransfection of nuclear or cytoplasmic IE110 with a truncated nuclear form of IE63 also led to partial redistribution of IE63 into either nuclear or cytoplasmic punctate granules containing IE110. Both the IE63-IE110 and IE175-IE110 colocalization interactions were demonstrated in Vero cells but not in 293 cells. Consequently, they differ from IE110 self-interactions, which correlate with in vitro dimerization and occur efficiently in both cell types. These interactions may help to explain the altered promoter target specificity and synergism observed when IE175 is cotransfected with IE110 in transactivation studies.

The herpes simplex virus type 2 gene which encodes the large subunit of ribonucleotide reductase has unusual regulatory properties

Expression of herpes simplex virus type 2 (HSV-2) encoded ribonucleotide reductase (RR) is required for growth of the virus in non-dividing cells. The functional enzyme is composed of a large (RRA) and small (RRB) subunit and the enzyme is expressed as a delayed early activity. The promoter of RRA contains a cis-acting motif (TAATGARAT) which resembles those found in immediate early (IE) genes suggesting RRA is an IE gene. When primate cells were infected with HSV-2, low levels of RRA transcripts were expressed in the presence of cycloheximide indicating RRA is not a true IE gene. Conditions which allow for efficient RRA RNA expression in the presence of cycloheximide were identified in human cells. A phorbol ester, 12-O-tetradecanoyl phorbol-13- acetate (TPA), and hydroxyurea increased the level of RRA RNA expression in the presence of cycloheximide. Hydroxyurea and TPA also stimulated RRA promoter activity in transient assays suggesting these agents induced factors which transactivated the RRA promoter. Expression of an intact c-myc gene transactivated the RRA promoter more than 30-fold in transient assays. Although expression of an intact retinoblastoma gene (Rb) had a slight stimulatory effect on the RRA promoter, mutant Rb proteins also stimulated the RRA promoter. These studies demonstrated that inducible factors in permissive cells increase the steady state levels of RRA RNA in the presence of cycloheximide.

Sequences of the ribonucleotide reductase-encoding genes of equine herpesvirus 4

The equine herpesvirus 4 (EHV-4) genes encoding the two subunits of the enzyme ribonucleotide reductase (RR) were cloned and their nucleotide (nt) sequences determined. The large subunit (RR1) is predicted to comprise 789 amino acids (aa), which compares with lengths of 790, 775 and 1137 aa for the RR1 proteins encoded by equine herpesvirus 1 (EHV-1) gene 21, varicella zoster virus (VZV) gene 19 and herpes simplex virus type 1 (HSV-1) UL39, respectively. In common with VZV RR1, the EHV-4 RR1 protein lacks the N-terminal domain of HSV-1 RR1 which possesses protein kinase activity. EHV-4 RR1 demonstrates identities of 88, 52 and 29% with the RR1 proteins of EHV-1, VZV and HSV-1, respectively. The small subunit (RR2) is predicted to be 320 aa in length, which compares with lengths of 321, 306 and 340 aa for the RR2 proteins encoded by EHV-1 gene 20, VZV gene 18 and HSV-1 UL40, respectively. The EHV-4 RR2 protein exhibits identities of 90, 60 and 55% with the RR2 proteins of EHV-1, VZV and HSV-1, respectively.

Detection of herpes simplex virus by measurement of luciferase activity in an infected-cell lysate

A stably transformed cell line (BHKICP6LucA6) has been isolated which expresses high levels of luciferase activity following infection with herpes simplex virus (HSV). The genome of this cell line contains an HSV-1 promoter-luciferase chimeric gene. Infected BHKICP6LucA6 cells exhibit a level of luciferase activity 5 x 10(5) higher than mock-infected cells. This signal-to-noise ratio is of a sufficient magnitude that measurement of the luciferase activity of an infected-cell lysate can detect a single infected cell when a practical number of cells is used in the assay. This approach to the detection of infectious virus could be useful in a number of circumstances and may be adaptable to an automated assay which could become a useful means for diagnostic laboratories to detect viruses in clinical specimens.

A novel latency-active promoter is contained within the herpes simplex virus type 1 UL flanking repeats

Herpes simplex virus type 1 (HSV-1) expresses a unique series of RNA molecules, the latency-associated transcripts or LATs, during latent infection of neuronal tissues. Previous studies by others have described a TATA box-containing latency-active promoter, referred to here as LAP1, located approximately 700 bp upstream of the 5' end of the major 2.0-kb LAT. In this report, transient gene expression assays were employed to identify a second, novel latency-active promoter (LAP2) present within a region downstream of LAP1 and 5' proximal to the major 2.0-kb LAT. In contrast to LAP1, this promoter lacks a TATA box but possesses cis-acting regulatory elements and other features frequently observed within eukaryotic housekeeping gene promoters. Unlike most other HSV promoters, LAP2 was down-regulated by the viral transcriptional activators ICP4 and ICP0. The majority of LAP2-positive regulatory elements were located within sequences from -257 to -58 relative to the 5' end of the 2.0-kb LAT, and the basal promoter mapped within sequences from -14 to +28. RNase protection experiments demonstrated that chimeric LAT-chloramphenicol acetyltransferase transcripts produced in the transient assays initiated at or near the 5' end of the major 2-kb LAT. Tn5 insertional mutagenesis of the ICP4 regulatory gene determined that down-regulation of LAP2 required the ICP4 transactivating domain and targeted the minimal promoter region as the site of action by ICP4. Replicating recombinant viruses containing a LAP2-lacZ reporter gene cassette in an ectopic site (glycoprotein C locus) were shown to be active in mouse trigeminal ganglia. Taken together, these experiments suggest that the LAT region of the HSV-1 genome contains at least two latency-active promoters which may play different roles in expressing the various LATs. Alternatively, these promoters may comprise a larger promoter-regulatory complex which may influence transcription during latency.

The RR1 gene of herpes simplex virus type 1 is uniquely trans activated by ICP0 during infection

As has been demonstrated for herpes simplex virus type 2, we show in this report that the herpes simplex virus type 1 ribonucleotide reductase large subunit (RR1) gene is trans activated in transient transfection assays by VP16 and ICP0 but not by ICP4. Deletion analysis demonstrated that responsiveness to induction to VP16 resides in an octamer/TAATGARAT sequence of the RR1 promoter and that the TATA box alone is sufficient to provide induction by ICP0. The induction of the RR1 gene by ICP0 but not by ICP4 suggested that it might be possible to identify the cis-acting element(s) responsive to ICP4 in an ICP4-inducible promoter. To this end, a series of chimeric promoters containing various portions of the regulatory sequences of the RR1 promoter and thymidine kinase (TK) promoter were constructed. The TK promoter is trans activated by both ICP0 and ICP4 in transient transfection assays and by ICP4 in infection. The data show that replacing the RR1 TATA region with the TK TATA region permits ICP4 inducibility even if the rest of the RR1 promoter elements remain intact. To test whether the RR1 gene is induced by ICP0 during infection, four mutant viruses were constructed. (i) TAATGARAT+ has the wild-type RR1 promoter driving chloramphenicol acetyltransferase (CAT) and the RR2 promoter driving the lacZ gene. The RR2 gene codes for the small subunit of the ribonucleotide reductase and is expressed as a beta gene. (ii) TAATGARAT- has a triple-base change in the octamer/TAATGARAT element which renders it unresponsive to VP16 trans activation, eliminating that portion of the activation of the RR1 gene. (iii) TAATGARAT- delta alpha 0 has a deletion of the alpha 0 gene. (iv) TAATGARAT- delta alpha 4 has a deletion of the alpha 4 gene. Infections were carried out in Vero cells at a multiplicity of infection of 10 per cell; cells were assayed for CAT and beta-galactosidase (beta-Gal) activities and for virus yields. The first two infections gave strong CAT and beta-Gal activities and high yields of progeny virus. Infection with the third virus showed no CAT activity but did produce high levels of beta-Gal activity and virus progeny. The fourth infection resulted in strong CAT activity but no beta-Gal activity or progeny virus. The data demonstrated that the RR1 promoter was activated in the absence of ICP4 but not in the absence of ICP0 in these infections.(ABSTRACT TRUNCATED AT 400 WORDS)

Analysis of a herpes simplex virus 2 fragment from the open reading frame of the large subunit of ribonucleotide reductase with transcriptional regulatory activity

Expression of herpes simplex virus 2 (HSV-2)-encoded ribonucleotide reductase (RR) is required for growth in nondividing cells. The functional enzyme is composed of a large and a small subunit. In virus-infected cells, RR is expressed temporally as a delayed early protein. However, the promoter regulatory region of the large subunit can function as an immediate early promoter in transient transfection assays, suggesting that expression may be quite complex. In this study, a 95-bp fragment derived from the open reading frame of the large subunit of RR (RR-A) functioned as a silencer when placed adjacent to a heterologous promoter. If the fragment was placed distal to the promoter, repression was relieved and in human keratinocytes promoter activity was consistently higher than control constructs. Exonuclease III protection assays revealed that nuclear factors from human keratinocytes as well as other primate cells specifically bind to this fragment. A 30-bp motif containing a consensus SP-1 binding site and an alternating Pu/Py element was protected in all cell lines. These results suggest that a 95-bp fragment in the open reading frame of HSV-2 RR-A plays a role in regulating viral gene expression.

An autophosphorylating but not transphosphorylating activity is associated with the unique N terminus of the herpes simplex virus type 1 ribonucleotide reductase large subunit

We report on a protein kinase function encoded by the unique N terminus of the herpes simplex virus type 1 (HSV-1) ribonucleotide reductase large subunit (R1). R1 expressed in Escherichia coli exhibited autophosphorylation activity in a reaction which depended on the presence of the unique N terminus. When the N terminus was separately expressed in E. coli and partially purified, a similar autophosphorylation reaction was observed. Importantly, transphosphorylation of histones and of proteins in HSV-1-infected cell extracts was also observed with purified R1 and with truncated R1 mutants in which most of the N terminus was deleted. Ion-exchange chromatography was used to separate the autophosphorylating activity of the N terminus from the transphosphorylating activity of an E. coli contaminant protein kinase. We propose a putative function for this activity of the HSV-1 R1 N terminus during the immediate-early phase of virus replication.

The herpes simplex virus type 1 ICP6 gene is regulated by a 'leaky' early promoter

Expression from the promoter for the large subunit (ICP6) of the ribonucleotide reductase encoded by herpes simplex virus type 1 (HSV-1) has been examined. Using the lacZ reporter gene fused in-frame with ICP6 regulatory sequences to assay expression quantitatively, we showed that the ICP6 promoter responded very weakly to the alpha-transinducing factor (TIF) in the absence of all other viral gene products, but much more strongly to immediate early proteins. Similar patterns of regulation were observed when the reporter gene construct was located at two different positions within the the viral genome or in a stably transfected Vero cell line. Infection of the stably transfected cells with various HSV-1 mutants identified ICP0 as the major transactivator of the ICP6 promoter.

Isolation of a cell line for rapid and sensitive histochemical assay for the detection of herpes simplex virus

A cell line which can be used in a simple, sensitive, and rapid histochemical assay was isolated for detection of herpes simplex virus (HSV). The cell line was derived by selection of G418 resistant colonies following co-transfection of baby hamster kidney cells with a plasmid which contains a G418 antibiotic resistance marker and a plasmid which contains the Escherichia coli LacZ gene placed behind an inducible HSV promoter. The promoter is from HSV-1UL39 which encodes ICP6, the large subunit of ribonucleotide reductase (RR1). This promoter has a number of features which make it ideal for the detection of HSV. First, there is no constitutive expression from this promoter in uninfected cells. Second, activation of the promoter appears to be specific for HSV. Third, expression from this promoter occurs within hours after infection. Fourth, this promoter is strongly transactivated by the virion associated trans-activator protein VP16. As early as six hours after infection HSV-infected cells can be detected by histochemical staining for beta-galactosidase activity. Infected cells stain intensely blue whereas uninfected cells show no staining, and a single infected cell can easily be recognized in a microscopic field of uninfected cells. Both HSV-1 and HSV-2 are detected with this cell line, but after infection with human cytomegalovirus (HCMV), varicella zoster virus (VZV), adenovirus, and sindbis virus no blue cells were detected. Quantitation of HSV-1 stocks on this cell line by counting blue cell forming units (BFU) reveals that the number of BFU/ml closely approximates the number of plaque forming units (PFU)/ml as determined by plaque assays on the parent cell line. This cell line should provide a useful adjunct in the diagnostic virology laboratory for the rapid detection of HSV in clinical specimens.

Immediate early and functional AP-1 cis-response elements are involved in the transcriptional regulation of the large subunit of herpes simplex virus type 2 ribonucleotide reductase (ICP10)

Expression from the promoter of the herpes simplex virus type 2 (HSV-2) large subunit of ribonucleotide reductase (ICP10) is stimulated by co-transfection with DNA that encodes the virion protein Vmw65 previously shown to activate in trans the transcription of all IE genes (Wymer et al., 1989). Specific cis response elements involved in ICP10 transcriptional regulation were studied by chloramphenicol acetyltransferase analysis with hybrid ICP10 promoter/CAT structural gene constructions containing wild type or site-directed mutations of the promoter sequences. The data indicate that Vmw65 activation requires an intact TAAT-GARAT motif while complex formation requires an intact Oct-1 element, and the AP-1 consensus elements in the ICP10 promoter are functional in vitro. Thus, expression from the wild type and GA-rich mutant constructions was enhanced 10-20-fold by co-transfection with DNA encoding Vmw65. The GARAT and POU homeobox (PHB) binding motifs were required for Vmw65 mediated activation but the mutant in the POU specific box (PSB) binding motif was activated at higher concentrations of Vmw65 DNA (1.0-3.0 micrograms). The PHB and PSB binding motifs were necessary for complex formation as determined by gel retardation analysis with in vitro synthesized OTF-1 and Vmw65 proteins. The GARAT and GA-rich elements were not required. CAT expression from pICP10-cat was enhanced by co-transfection with jun and fos encoding DNA, and the ICP10 promoter complexed with in vitro synthesized jun protein.

Localization of the antigenic sites and intrinsic protein kinase domain within a 300 amino acid segment of the ribonucleotide reductase large subunit from herpes simplex virus type 2

The 140-kDa ribonucleotide reductase (RR1) protein of herpes simplex virus type 2 (HSV-2) functions as the large subunit of virus-specified RR1 and exhibits an intrinsic protein kinase (PK) activity at its unique NH2-terminal region. The N-terminal half of RR1 contains the protein and DNA functions of the morphological transforming region III (mtrIII) of HSV-2. In the present study, we have expressed a number of truncated RR1 derivatives in a mammalian expression vector containing NH2-terminal RR1 gene fragments and amber mutants generated by site-specific mutagenesis. These derivatives, synthesized in transient expression assays, were used as test antigens to localize the epitopes of a panel of HSV-2 RR1-reactive monoclonal antibodies and to fine-map the PK catalytic domain. Our data show that the epitope for HSV-2-specific monoclonal antibody 6A-6 is located in a region of RR1 protein spanning aa 72-350. The epitopes for cross-reactive antibodies to HSV RR1, i.e., 48S and 51S, are formed predominantly by a stretch of amino acid residues specified by aa 350-376 of the RR1 molecule. The 6A-6 antibody utilized in conjunction with the RR1 amber mutants has allowed us to define a 278 aa domain within the NH2-terminal half of the 140-kDa RR1 (aa 72-350) that is sufficient for PK activity.

The UL5 gene of herpes simplex virus type 1: isolation of a lacZ insertion mutant and association of the UL5 gene product with other members of the helicase-primase complex

The UL5 gene product is required continuously during viral DNA synthesis (L. Zhu and S. K. Weller, Virology 166:366-378, 1988) and has been shown to be a component of a three protein helicase-primase complex encoded by herpes simplex virus type 1 (J. J. Crute, T. Tsurumi, L. Zhu, S. K. Weller, P.D. Olivo, M. D. Challberg, E. S. Mocarski, and I. R. Lehman, Proc. Natl. Acad. Sci. USA 86:2186-2189, 1989). The other members of the complex are viral proteins encoded by genes UL8 and UL52. In this study, we isolated a permissive cell line (L2-5) which contains the wild-type UL5 gene under the control of the strong and inducible promoter for the large subunit of herpes simplex virus type 1 ribonucleotide reductase (ICP6). An insertion mutant containing a mutation in the UL5 gene (hr99) was isolated by using the insertional mutagen ICP6::lacZ, in which the Escherichia coli lacZ gene is expressed under control of the viral ICP6 promoter. When grown on Vero cells, hr99 does not form plaques or synthesize viral DNA, although both defects are complemented efficiently on the L2-5 cells. These results confirm that the UL5 gene product is essential for viral growth and DNA replication. Furthermore, since no detectable UL5 protein is synthesized in hr99-infected cells, these cells provide a valuable control not only for the detection of the UL5 protein itself but also for the detection of protein-protein interactions with UL8 and UL52 by coimmunoprecipitation. In addition, the lacZ insertion in hr99 provides a convenient screening system for the introduction of site-specific mutations into the viral genome (L. Zhu and S. K. Weller, J. Virol. 66:469-479, 1992). Thus, hr99 is a valuable tool in the structure-function analysis of the UL5 gene.

Detection of viral DNA within skin of healed recurrent herpes simplex infection and erythema multiforme lesions

The polymerase chain reaction (PCR) was used to detect HSV DNA in genomic DNA extracted from skin biopsies obtained from healed skin of five patients with hyperpigmented macules following recurrent cutaneous HSV infections and from eight patients with HSV-associated erythema multiforme (EM). A 92-bp HSV-1 DNA fragment was found in all the skin biopsies from the site of recurrent HSV infection and in five of eight (62%) biopsies from the EM patients. Virus DNA was not found in tissues distant from the site of HSV recurrence or from a patient without a history of HSV infection. These findings confirm the presence of HSV in healed skin from the site of recurrent HSV disease and are consistent with the concept that HSV is involved in EM pathogenesis.

A gene delivery/recall system for neurons which utilizes ribonucleotide reductase-negative herpes simplex viruses

We present data which show that ribonucleotide (RR)-negative herpes simplex virus type-1 (HSV-1) is a useful vector for gene delivery into neuronal cells. For these studies we used hrR3, a genetically engineered HSV-1 mutant which has an in-frame insertion of the bacterial lacZ gene into the HSV gene that encodes the large subunit (ICP6) of RR. After infection of rat primary sympathetic neuronal cultures with hrR3, the ICP6::lacZ chimeric gene was expressed, as shown by blue staining of the cells upon exposure to X-Gal, a chromogenic beta-galactosidase substrate. When the infection was performed in the presence of acyclovir, hrR3 appeared to become "latent"; neither infectious virus nor beta-galactosidase activity was detectable in these neuronal cultures at 3 weeks after the acyclovir was removed. However, beta-galactosidase activity was inducible in the "latent" cultures by superinfection with ICP6 delta (a RR-negative deletion mutant) without resulting in the "reactivation" of hrR3 and without apparent cytopathic effects. In contrast, superinfection with ICP6 delta + 3.1, a virus derived by marker rescue of ICP6 delta, resulted in the expression of lacZ, the release of hrR3 into the culture medium, and cytopathic effects. The introduction of a foreign gene into neuronal cells by a RR-negative herpes simplex virus, and the subsequent induction of gene expression by another noncomplementing virus, may constitute a prototype gene delivery/recall system for neurons.

Genomic sequences homologous to the protein kinase region of the bifunctional herpes simplex virus type 2 protein ICP10

The large subunit of herpes simplex virus type 2 (HSV-2) ribonucleotide reductase (ICP10) consists of two functional domains. The amino (N)-terminal domain at residues 1-411 has serine/threonine-specific kinase activity (PK domain) and is encoded by a DNA fragment with transforming potential (15,17). The remaining region is required for ribonucleotide reductase activity (RR domain) (14, 15). Computer-assisted comparison of the ICP10 sequence to the EMBL database 21 has revealed sequences within the RR domain that are common to all RR1 proteins. Motifs homologous to the catalytic domains of all PKs were identified in the PK region (15). However, based on this database all other sequences were unique. Secondary structure analysis of the PK and RR junction region of ICP10 identified twist angle variations with helical periodicity characteristic of enhancer elements. Sequences homologous to a segment of the PK domain were amplified and cloned from human DNA using the polymerase chain reaction (PCR), suggesting that the PK domain may have originated from a cellular gene.

Myristylation and polylysine-mediated activation of the protein kinase domain of the large subunit of herpes simplex virus type 2 ribonucleotide reductase (ICP10)

The amino-terminal domain of the large subunit of herpes simplex virus type 2 (HSV-2) ribonucleotide reductase (ICP10) was previously shown to possess protein kinase (PK) activity that localizes to the cytosolic, cytoskeletal, and plasma membrane fractions. Further studies of the PK domain using computer-assisted sequence analysis have identified a single transmembrane segment and fatty acid incorporation findings indicate that ICP10 is myristylated. Myristylation does not depend on a viral enzyme, since myristic acid is incorporated into ICP10 precipitated from cells transfected with an ICP10 expression vector. It is also incorporated into the 57-kDa protein expressed by the amino-terminal PK expression vector. The myristyl moiety is linked through an amide bond. The basic protein polylysine stimulates the kinase activity and alters its divalent cation requirements resulting in 20- to 40-fold stimulation in the presence of 0.1 mM Mn2+. The PK activity is inhibited by antibody to synthetic peptides corresponding to residues 355-369 and 13-26, respectively, located within, and amino-terminal to, the predicted PK catalytic domain.