The function of herpes simplex virus genes: a primer for genetic engineering of novel vectors

Inhibition of herpes simplex virus type 2 (HSV-2) viral replication by the dominant negative mutant polypeptide of HSV-1 origin binding protein

UL9-C535C, the trans-dominant negative mutant polypeptide of herpes simplex virus type 1 (HSV-1) UL9 origin binding protein, is a potent inhibitor of HSV-1 viral DNA replication. This study focused on testing whether HSV-1 UL9-C535C and a genetically engineered UL9-C535C-encoding HSV-1 recombinant virus CJ83193 could inhibit herpes simplex virus type 2 (HSV-2) infection. First, a stable cell line, R-C535C, expressing a high level of UL9-C535C in the presence of tetracycline and little or no UL9-C535C in the absence of tetracycline was established. The single step growth experiment showed that like HSV-1, the de novo synthesis of HSV-2 could be suppressed approximately 1000-fold by UL9-C535C expressed in R-C535C cells in the presence of tetracycline. Secondly, compared with cells singly infected with HSV-2, co-infection of Vero cells with HSV-2 and CJ83193 reduced the replication efficiency of HSV-2 in co-infected cells by 30-40 fold in a single-step growth assay, which coincided with marked reduction in viral late gene expression, but not the expression of viral immediate-early genes. Taken together, in view of our recent demonstration that CJ83193 can serve as an effective vaccine in preventing HSV-1 infection in mice, one can generate a CJ83193-like HSV-2 recombinant virus that could potentially function as a new therapeutic class of recombinant viral vaccine against HSV-2 infection.

The use of a genetically engineered herpes simplex virus (R7020) with ionizing radiation for experimental hepatoma

The herpes simplex virus (HSV) recombinant virus R7020 is an attenuated virus designed as a candidate for immunization against both HSV-1 and HSV-2 infections. It was extensively tested in an experimental animal system and in a healthy human adult population without significant untoward effects. We report on the use of R7020 with ionizing radiation as an oncolytic agent for hepatomas. Two hepatoma cell lines were studied, Hep3B and Huh7. R7020 replicated to higher titers in Hep3B cells than in Huh7 cells. Tissue culture studies correlated with hepatoma xenograft responses to R7020. R7020 was more effective in mediating Hep3B tumor xenograft regression compared with Huh7. Ionizing radiation combined with R7020 also showed differential results in antitumor efficacy between the two cell lines in tumor xenografts. Ionizing radiation enhanced the replication of R7020 in Hep3B xenografts. Moreover, the combination of ionizing radiation and virus caused a greater regression of xenograft volume than either R7020 or radiation alone. Ionizing radiation had no effect on the replication of R7020 virus in Huh7 xenografts. These results indicate that a regimen involving infection with an appropriate herpesvirus such as R7020 in combination with ionizing radiation can be highly effective in eradicating certain tumor xenografts.

Oncolytic biotherapy: a novel therapeutic plafform

There is a clear need for new, selective, cancer treatments that do not cause the cross-resistance which occurs with currently available chemotherapeutic agents. Gene therapy is a promising approach, but to date, it has shown limited effectiveness in clinical trials because of insufficient gene transduction. Many investigators are now revisiting the 'old' idea of using tumour-specific, replication-selective viruses or bacteria to treat cancer. These agents can be directly oncolytic, but can also be used to simultaneously express therapeutic genes in target cells or induce tumour-specific, cell-mediated immunity. We discuss the promise of this rapidly evolving field and examine the potential barriers to its success.

Nuclear translocation and activation of the transcription factor NFAT is blocked by herpes simplex virus infection

Transcription factors of the NFAT (nuclear factor of activated T cells) family are expressed in most immune system cells and in a range of other cell types. Signaling through NFAT is implicated in the regulation of transcription for the immune response and other processes, including differentiation and apoptosis. NFAT normally resides in the cytoplasm, and a key aspect of the NFAT activation pathway is the regulation of its nuclear import by the Ca(2+)/calmodulin-dependent phosphatase calcineurin. In a cell line stably expressing green fluorescent protein (GFP)-NFAT, this import can be triggered by elevation of intracellular calcium and visualized in live cells. Here we show that the inducible nuclear import of GFP-NFAT is efficiently blocked at early stages of herpes simplex virus (HSV) infection. This is a specific effect, since we observed abundant nuclear accumulation of a test viral protein and no impediment to general nuclear localization signal-dependent nuclear import and retention in infected cells. We show that virus binding at the cell surface is not itself sufficient to inhibit the signaling that induces NFAT nuclear translocation. Since the block occurs following infection in the presence of phosphonoacetic acid but not cycloheximide, we infer that the entry of the virion and early gene transcription are required but the effect is independent of DNA replication or late virus gene expression. A consequence of the block to GFP-NFAT import is a reduction in NFAT-dependent transcriptional activation from the interleukin-2 promoter in infected cells. This HSV-mediated repression of the NFAT pathway may constitute an immune evasion strategy or subversion of other NFAT-dependent cellular processes to promote viral replication.

Effect of immunity on gene delivery into anterior horn motor neurons by live attenuated herpes simplex virus vector

Efficient and prolonged foreign gene expression has been demonstrated in the bilateral anterior horn motor neurons of the spinal cord by intramuscular inoculation with attenuated herpes simplex virus (HSV) expressing latency associated transcript promoter-driven beta-galactosidase (betaH1). To examine the effect of immunity on the gene delivery, betaH1 was applied in rats immunized subcutaneously or intramuscularly with the parent HF strain. Rats were immunized subcutaneously with HF strain and 28 days later when the high antibody titer was maintained, betaH1 was inoculated into the right gastrocnemius muscle. Second, 35 days after inoculation with HF strain into the right gastrocnemius muscle, betaH1 was inoculated at the same site. In both ways of immunization, immunity did not abolish or prevent the transgene expression in the anterior horn motor neurons, but attenuated the range and the number of the beta-galactosidase-positive neurons from about 85% to 50-65% on 28 days after inoculation with betaH1. However, beta-galactosidase activity was observed in a wide range of the bilateral anterior horn motor neurons without significant pathological changes. These findings support the feasibility of the attenuated HSV vector in gene delivery into the central nervous system, even in the presence of immunity.

Identification and characterization of a benzothiophene inhibitor of herpes simplex virus type 1 replication which acts at the immediate early stage of infection

Analysis of a large compound library in a high throughput virus infection assay screen identified the benzothiophene PD146626 as a potent and specific inhibitor of herpes simplex virus type 1 (HSV-1) replication. PD146626 possessed an EC(50) and EC(90) against HSV-1 of 0.1 and 1 microM, respectively, and mediated no detectable cytotoxicity in cells at concentrations up to 1 microM. Western blot analyses and time of addition experiments demonstrated that in the presence of PD146626 HSV-1 underwent a specific block in viral gene expression at the immediate early stage. However, several observations indicated that a cellular function rather than a viral immediate early transactivator protein represented the molecular target for PD146626, including the lack of resistance of VP16 and ICP0 mutant viruses to the compound, the inability to select resistant strains of HSV-1 following exhaustive serial passaging of virus in the presence of the compound, and the sensitivity of human cytomegalovirus, which lacks VP16 and ICP0 homologs, to the compound. Moreover, kinetic studies suggested an unusual pattern of responsiveness of the host cell to PD146626, in that the compound could induce an extended antiviral state in cells after only a brief exposure. Together these results suggest that PD146626 targets a novel cellular function that is critical for the expression of HSV-1 immediate early genes but not host cell genes.

Oncolytic viruses as therapeutic agents

The concept of using viruses as oncolytic agents has a long history. However, relatively new developments are the use of these viruses as gene delivery vehicles and the restriction of viral replication and lysis to tumour cells. The latter is attempted by the use of tumour-specific promoters, which transcriptionally target viral genes involved in replication, or by deletion of viral functions dispensable for replication in tumour cells but essential for productive infection of normal cells. In addition, retargeting of the viral tropism towards tumours by capsid modifications has been examined. Although much progress has been made in developing oncolytic vectors for clinical use, there is still a long way to go to determine which combinations of virus, gene therapy, surgery, radiation, and/or chemotherapy will provide improved therapy for the control and eradication of a variety of human cancers. First controlled clinical trials with an oncolytic adenovirus in combination with chemotherapy have shown encouraging antineoplastic activity. For future vector developments it will be crucial to achieve maximum vector distribution and transgene expression within tumours, to trigger a specific systemic immune effector response against treated and untreated lesions, and to modulate the immune system to avoid immune-mediated inactivation or destruction of the virus. In the context of replication-competent vectors, suicide genes might be used as fail-safe mechanism in the case of a runaway infection.

Participation of type I interferon in the decreased virulence of the UL13 gene-deleted mutant of herpes simplex virus type 1

We isolated a UL13 gene-deleted mutant of the herpes simplex virus type 1 (HSV-1) strain VR3 (VRDelta13) and its revertant virus (VRDelta13R). This deletion mutant still had virus host shutoff (vhs) activity, although a previous report had suggested the possibility of a functional relation between the UL13 product, that is protein kinase (PK), and vhs activity. We compared the in vivo growth of these viruses in BALB/c mice. VRDelta13 was cleared in the early period of intraperitoneal infection. VRDelta13 had a higher sensitivity to the mouse type I interferon (IFN) and showed a higher level of IFN induction in the study period of infection than did VR3 and VRDelta13R. These results suggest that a nonspecific antiviral response (i.e., the IFN system) may contribute to this rapid inhibition of viral replication in vivo.

Expression of interleukin-4 but not of interleukin-10 from a replicative herpes simplex virus type 1 viral vector precludes experimental allergic encephalomyelitis

We have used interleukin (IL)-4 and -10-producing HSV-1 gamma(1)34.5 deletion viruses in gene therapy of a BALB/c model of experimental allergic encephalomyelitis (EAE), a T cell-mediated demyelinating disease of the central nervous system. It is known that in EAE of mice the Th2-type cytokines are down-regulated and the Th1-type cytokines up-regulated during the onset and relapse of the disease. Therefore, we tested two HSV-1 recombinants expressing the Th2-type cytokines IL-4 and IL-10. The recombinant viruses were injected intracranially (i.c.) in BALB/c mice 6 days after induction of EAE. As control groups we used mice without any infection, mice infected with backbone virus R3659 and mock-infected mice. Weights and symptoms of the mice were recorded daily and the tissue specimens were collected at specific time-points. The results indicate that the intracranial infection with IL-4-producing virus (1) precludes EAE symptoms, (2) protects the spinal cord from massive leukocyte infiltrations and (3) prevents demyelination and axonal loss. The IL-10-expressing virus R8308 did not have a similar favorable effect on the recovery of the mice as did the IL-4 virus R8306.

Gene therapy in the neuroendocrine system: its implementation in experimental models using viral vectors

Gene therapy, the transfer of genetic material for therapeutic purposes, has undergone an explosive development in the last few years. Within this context, development of gene therapy approaches for the neuroendocrine system, while incipient, has already generated a core of results which emerge as a promising area of research in neuroendocrinology. The present review presents a brief description of the viral vector-based gene delivery systems being currently used in neuroendocrinology, namely the adenoviral and herpes simplex type-1 (HSV-1)-derived vector systems, as well as an updated account of neuroendocrine pathologies for which gene therapy approaches in animal models are being implemented is provided. Current research efforts include treatment of experimental pituitary tumors by adenoviral vector-mediated transfer of the suicide gene for the HSV-1 thymidine kinase, which converts the prodrug ganciclovir into a toxic metabolite. An adenoviral vector encoding the human retinoblastoma suppressor oncogene has also been successfully used to rescue the phenotype of spontaneous pituitary tumors of the pars intermedia in mice. At the hypothalamic level, an adenovirus harboring the cDNA for arginine vasopressin has been used in Brattleboro rats to correct diabetes insipidus for several weeks. The last part of the review outlines the potential of gene therapy to correct age-associated neurodegenerative processes at the neuroendocrine level. Although effective implementation of gene therapy strategies still faces significant technical obstacles, these are likely to be progressively overcome as gene delivery systems are being improved.

The UL14 protein of herpes simplex virus type 2 translocates the minor capsid protein VP26 and the DNA cleavage and packaging UL33 protein into the nucleus of coexpressing cells

The herpes simplex virus type 2 (HSV-2) gene UL14 encodes a 32 kDa protein which is a minor component of the virion tegument and is expressed late in infection. The UL14 protein shows varied localization patterns in HSV-2-infected and singly expressing cells, suggesting the possibility that it is multifunctional. We have investigated the influence of the UL14 protein on the intracellular localization of capsid proteins and DNA cleavage and packaging proteins in coexpressing cells. VP26 is the minor capsid protein; it binds to hexons of the outer capsid shell and is predominantly cytoplasmic upon sole expression. We have found that VP26 coexpressed with the UL14 protein showed mutual and predominant relocation into the nucleus. At least seven viral genes encode proteins (UL6, UL15, UL17, UL25, UL28, UL32 and UL33) that are required for DNA cleavage and packaging. We have found that the UL33 protein, which was also cytoplasmic by sole expression, was relocated to the nucleus upon expression with the UL14 protein, which again seemed to be a result of mutual influence. Coexpression experiments also suggested the possibility of a mutual influence between the UL14 and UL17 proteins, and the UL17 protein and VP26. Our results suggest that the UL14 protein can influence the intracellular localization patterns of a number of proteins belonging to the capsid or the DNA encapsidation machinery.

Role of cyclin D3 in the biology of herpes simplex virus 1 ICPO

Earlier reports from this laboratory have shown that the promiscuous transactivator infected-cell protein 0 (ICP0) binds and stabilizes cyclin D3, that the binding site maps to aspartic acid 199 (D199), and that replacement of D199 with alanine abolishes binding and reduces the capacity of the mutant virus to replicate in quiescent cells or to cause mortality in mice infected by a peripheral site. The objective of this report was to investigate the role of cyclin D3 in the biology of ICP0. We report the following results. (i) Wild-type ICP0 activates cyclin D-dependent kinase 4 (cdk4) and stabilizes cyclin D1 although ICP0 does not interact with this cyclin. (ii) The D199A mutant virus (R7914) does not activate cdk4 or stabilize cyclin D1, and neither the wild-type nor the mutant virus activates cdk2. (iii) Early in infection of human embryonic lung (HEL) fibroblasts both wild-type and D199A mutant ICP0s colocalize with PML, and in these cells the ND10 nuclear structures are dispersed. Whereas wild-type ICP0 is transported to the cytoplasm between 3 and 9 h. after infection, ICPO containing the D199A substitution remains quantitatively in the nucleus. (iv) To examine the interaction of ICP0 with cyclin D3, we used a previously described mutant carrying a wild-type ICP0 but expressing cyclin D3 (R7801) and in addition constructed a virus (R7916) that was identical except that it carried the D199A-substituted ICP0. Early in infection with R7801, ICP0 colocalized with cyclin D3 in structures similar to those containing PML. At 3 h after infection, ICP0 was translocated to the cytoplasm whereas cyclin D3 remained in the nucleus. The translocation of ICP0 to the cytoplasm was accelerated in cells expressing cyclin D3 compared with that of ICP0 expressed by wild-type virus. In contrast, ICP0 carrying the D199A substitution remained in the nucleus and did not colocalize with cyclin D3. These studies suggest the following conclusions. (i) ICP0 brings to the vicinity of ND10 cyclin D3 and, in consequence, an activated cdk4. The metabolic events occurring at or near that structure and involving cyclin D3 cause the translocation of ICP0 to the cytoplasm. (ii) In the absence of the cyclin D3 binding site in ICP0, cyclin D3 is not brought to ND10, cyclin D is not stabilized, and the function responsible for the translocation of ICP0 is not expressed, and in quiescent HEL fibroblasts the yields of virus are reduced.

Gene therapy in wound repair and regeneration

The potential use of gene therapy to treat human disease increases with the development of various physical, chemical, and biological methods to deliver genes to mammalian cells, and with our rapidly expanding knowledge of the human genome. One area of therapeutic interest for gene therapy is the treatment of wound healing disorders. Most recently, recombinant human growth factor therapy has been examined as a means to treat problem wounds. However, this approach suffers from the difficulty in providing an accurate dose of growth factor and the expense of the recombinant proteins. Delivery of a gene that could be expressed within the wound is an attractive alternative to application of the protein. This review discusses several methods that have been used to deliver genes encoding growth factor proteins into wounds and the advantages/disadvantages of each approach. Novel methods to regulate the expression of the transgene are also presented, highlighting the ability of these unique vector systems to adjust gene dose as the wound heals. We expect that gene therapy will become a significant treatment modality for those wound healing pathologies refractory to other wound management approaches in the years ahead.

Effective treatment of pancreatic tumors with two multimutated herpes simplex oncolytic viruses

Pancreatic cancer is an aggressive, rapidly fatal disease against which current nonsurgical therapy has minimal impact. This study evaluates the efficacy of two novel, replication-competent, multimutated herpes viruses (G207 and NV1020) in an experimental model of pancreatic cancer. Four human pancreatic carcinoma cell lines were exposed to G207 or NV1020, and cell survival and viral progeny production were determined. Flank tumors in athymic mice were subjected to single or multiple injections of 1 x 10(7) G207 or NV1020, and tumor volume was evaluated over time. For all of the cell lines, G207 and NV1020 produced infection, viral replication, and cell lysis (P < 0.05). NV1020 resulted in a higher production of viral progeny compared to G207. The efficacy of viral tumor cell kill was greatest in those cells with the shortest in vitro doubling time. For flank tumors derived from hs766t, single or multiple injections of both viruses were equally effective and significantly reduced flank tumor burden (P < 0.05). Complete hs766t flank tumor eradication was achieved in 25% (5 of 20) of animals treated with G207 and 40% (8 of 20) of animals treated with NV1020. In vivo efficacy correlated with in vivo tumor doubling time. There were no adverse effects related to viral administration observed in any animal. NV1020 and G207 effectively infect and kill human pancreatic cancer cells in vitro and in vivo. Given the lack of effective nonoperative treatments for pancreatic cancer, oncolytic herpes viruses should be considered for clinical evaluation.

Identification of nuclear export signal in UL37 protein of herpes simplex virus type 2

The UL37 gene of herpes simplex virus (HSV) encodes a 120-kDa phosphoprotein associated with the virion. In this study, we have generated a rabbit polyclonal antiserum against HSV-2 UL37 protein, and examined its intracellular localization by immunofluorescence study. In infected cells, specific fluorescence was detectable in the perinuclear region. In transfected cells, UL37 protein was observed mainly in the cytoplasm. Transfection assays of deletion mutants of UL37 protein suggested that the leucine rich region (LRR) containing amino acids 263-273 may be important for cytoplasmic localization. Deletion of the LRR or substitution of the leucine residues resulted in nuclear remaining of UL37 protein. Moreover, the LRR could export green fluorescent protein (GFP) to the cytoplasm as a fusion protein and this export was blocked by leptomycin B treatment, indicating that the LRR acted as a nuclear export signal. These results suggest that UL37 protein fulfills a role as a shuttle between the nucleus and the cytoplasm through the LRR.

The UL34 gene product of herpes simplex virus type 2 is a tail-anchored type II membrane protein that is significant for virus envelopment

The UL34 gene of herpes simplex virus type 2 (HSV-2) is highly conserved in the herpesvirus family. The UL34 gene product was identified In lysates of HSV-2-infected cells as protein species with molecular masses of 31 and 32.5 kDa, the latter being a phosphorylated product. Synthesis of these proteins occurred at late times post-infection and was highly dependent on viral DNA synthesis. Immunofluorescence assays revealed that the UL34 protein was localized in the cytoplasm in a continuous net-like structure, closely resembling the staining pattern of the endoplasmic reticulum (ER), in both HSV-2-infected cells and in cells transiently expressing UL34 protein. Deletion mutant analysis showed that this colocalization required the C terminus of the UL34 protein. The UL34 protein associated with virions but not with A, B or C capsids. We treated virions, HSV-2-infected cells and cells expressing the UL34 protein with a protease in order to examine the topology of the UL34 protein. In addition, we constructed UL34 deletion mutant proteins and examined their intracellular localization. Our data strongly support the hypothesis that the UL34 protein is inserted into the viral envelope as a tail-anchored type II membrane protein and is significant for virus envelopment.

Herpes simplex virus 1 open reading frames O and P are not necessary for establishment of latent infection in mice

Open reading frame (ORF) O and ORF P partially overlap and are located antisense to the gamma(1)34.5 gene within the domain transcribed during latency. In wild-type virus-infected cells, ORF O and ORF P are completely repressed during productive infection by ICP4, the major viral transcriptional activator/repressor. In cells infected with a mutant in which ORF P was derepressed there was a significant delay in the appearance of the viral alpha-regulatory proteins ICP0 and ICP22. The ORF O protein binds to and inhibits ICP4 binding to its cognate DNA site in vitro. These characteristics suggested a role for ORF O and ORF P in the establishment of latency. To test this hypothesis, two recombinant viruses were constructed. In the first, R7538(P-/O-), the ORF P initiator methionine codon, which also serves as the initiator methionine codon for ORF O, was replaced and a diagnostic restriction endonuclease was introduced upstream. In the second, R7543(P-/O-)R, the mutations were repaired to restore the wild-type virus sequences. We report the following. (i) The R7538(P-/O-) mutant failed to express ORF O and ORF P proteins but expressed a wild-type gamma(1)34.5 protein. (ii) R7538(P-/O-) yields were similar to that of the wild type following infection of cell culture or following infection of mice by intracerebral or ocular routes. (iii) R7538(P-/O-) virus reactivated from latency following explanation and cocultivation of murine trigeminal ganglia with Vero cells at a frequency similar to that of the wild type, herpes simplex virus 1(F). (iv) The amount of latent R7538(P-/O-) virus as assayed by quantitative PCR is eightfold less than that of the repair virus. The repaired virus could not be differentiated from the wild-type parent in any of the assays done in this study. We conclude that ORF O and ORF P are not essential for the establishment of latency in mice but may play a role in determining the quantity of latent virus maintained in sensory neurons.

Replication and virulence of early protein 0 and long latency transcript deficient mutants of the Aujeszky's disease (pseudorabies) virus

Early protein 0 (EP0)-deficient recombinant Aujeszky's disease viruses, Ka-ep0lac and Ba-ep0lac derived from strains Kaplan and Bartha, respectively, were constructed to explore the impact of the mutation on replication, virulence and latency of the virus. Inactivation of the EP0 gene resulted in a mutation of long latency transcript (Cheung et al., 1991) that is located on the complementary DNA strand of EP0 and immediate early protein (IE)175 genes. In infection of immortalized porcine kidney cells, the growth rate and yield of both EP0(-) mutant strains were significantly smaller than that of wild-type virus. Ka-ep0lac was found to be highly virulent, while Ba-ep0lac showed an attenuated phenotype in mice. PCR assay and immunohistochemistry showed that the Ba-ep0lac virus was able to establish latency in the mouse trigeminal ganglia. However, latent virus was not able to reactivate in explant reactivation assays. Accordingly, latent Ba-ep0lac has the potential to be exploited as vectors for the delivery of foreign genes to the nervous system.

Long-term gene expression in the anterior horn motor neurons after intramuscular inoculation of a live herpes simplex virus vector

To clarify the feasibility of the herpes simplex virus (HSV) vector in expressing the foreign gene in the motor neuron, we inoculated a live attenuated HSV expressing beta-galactosidase (beta-gal) activity under a latency-associated transcript promoter in the right gastrocnemius muscle of rats. Expression of beta-gal activity was observed 5 days after inoculation in the bilateral anterior horn cells of the spinal cord that innervates the inoculation muscle. However, the spread of beta-gal activity was not observed in the inoculation muscle. Without significant pathological changes, the spread of beta-gal-expressing neurons was observed in the lumbosacral spinal cord until 14 days after inoculation with staining concentrated in the anterior horn cells. Ninety percent of the anterior horn motor neurons expressed beta-gal activity with expression continuing to at least 182 days after inoculation. Thus beta-gal activity was expressed in the bilateral anterior horn cells at the lumbosacral spinal cord that innervates the inoculated muscle for a long time, possibly a life-long period. This indicates that this recombinant HSV vector system to motor neurons may further improve the understanding and treatment of neurological diseases in motor neurons of the spinal cord.

The application of a lentiviral vector for gene transfer in fetal human hepatocytes

BACKGROUND

The applications of traditional retroviral vectors are limited because proviral integrations into the host genome require DNA synthesis. Lentiviruses are considered to be advantageous because of their ability to infect non-dividing cells.

METHODS

To demonstrate the potential of lentiviral vectors, we used a human immunodeficiency virus (HIV)-1 virus encoding the green fluorescence protein (GFP) to infect fetal human hepatocytes. GFP-expressing cells were transplanted into the liver of Balb/C SCID mice via intrasplenic injection.

RESULTS

Primary fetal hepatocytes incorporated the GFP reporter with high (30-40%) efficiency. A cell line derived from human fetal liver (HFL) exhibited similar transduction efficiency to the lentiviral vector. To demonstrate the relationship between lentiviral gene transfer and cell proliferation, cells were subjected to gamma-irradiation, which attenuated the replication of primary fetal hepatocytes. However, lentiviral gene transfer was unaffected by this decrease in cell proliferation. GFP expression in transduced cells was preserved during multiple passages in cell culture. When GFP-expressing cells were transplanted into the liver of Balb/C SCID mice via intrasplenic injection, GFP expression was observed throughout the 3 week duration of the study.

CONCLUSION

These studies establish that human hepatocytes are amenable to lentiviral gene transfer with sustained transgene expression. Incorporation of lentiviral vectors will be helpful in testing strategies for hepatic gene therapy.

A modular set of helper-dependent herpes simplex virus expression vectors

Herpes simplex virus (HSV) has many favorable properties in terms of its potential to serve as a delivery and expression platform for gene-based therapies, including the ability to establish persistent infections, a broad tissue tropism, episomal maintenance of transduced genes, and a large genome that can incorporate many additional cDNAs. Helper-dependent HSV vectors (commonly known as HSV amplicons) are well positioned to exploit the biology of the virus, since they contain only the two cis elements required for HSV replication and packaging and thus do not require the silencing of any viral genes to prevent toxicity to transduced cells over the course of cDNA expression. In this report we describe the development of a set of modular HSV amplicon vectors that can easily be modified to incorporate different genetic elements or alternatively can be used to retrofit existing expression constructs such that they can be packaged into infectious HSV particles.

Mitochondrial distribution and function in herpes simplex virus-infected cells

In this study, mitochondria migrated to a perinuclear region in the cytoplasm in herpes simplex virus (HSV)-infected cells. HSV infection did not promote the expression of cytochrome c oxidase subunit 2 but did promote that of stress-responsive HSP60, both of which are known to be components of mitochondria. The levels of cellular ATP and lactate and mitochondrial membrane potential were maintained for at least 6 h but decreased at the late stage of infection. It was also found that the UL41 and UL46 gene products, both of which are known to be tegument proteins, accumulated in the perinuclear region. The clustering of mitochondria and the accumulation of tegument proteins were completely blocked by the addition of nocodazole and vinblastine. These results suggest that mitochondria respond to the stimulation of HSV infection, migrating with tegument proteins along microtubules to a site around the nucleus, and maintain function until at least the middle stage of infection.

Tolerance induced without immunosuppression in a T-lymphocyte suicide-gene therapy cardiac allograft model in mice

BACKGROUND

Life-long immunosuppression is a major cause of mortality and morbidity in transplant recipients. Gene therapy could provide new ways to obtain tolerance and avoid indefinite immunosuppression. EpTK mice are derived from the FVB/N strain (H2q) and express the thymidine kinase gene of herpesvirus in all mature T cells. Thus any mature dividing T cell can be killed in the presence of ganciclovir. We investigated the survival of alloincompatible C57B1/6 (H2b) hearts heterotopically transplanted into EpTK mice given only ganciclovir from day 0 to day 7 or 14.

METHODS

Abdominal cardiac transplantations were performed in 22 control mice (untreated FVB [n = 15], ganciclovir-treated FVB [n = 5], and untreated EpTK mice [n = 2]) and in 28 EpTK mice given ganciclovir from day 0 to day 7 (n = 15) or day 14 (n = 13). Rejection was defined as complete cessation of cardiac beat. Histologic examination of the grafts was performed at rejection, at day 7, or at day 100. Lymphocyte proliferation assays (concanavalin A stimulation or mixed lymphocyte reaction) were performed at day 7 and at day 100.

RESULTS

All control animals rejected transplants in 7 days (range, 5-9 days), whereas indefinite survival (>100 days) was observed in 89% of the ganciclovir-treated EpTK group, irrespective of the duration of ganciclovir treatment. Graft histology showed extensive cellular infiltrates with myocyte necrosis and arteritis in the control animals but only a mild infiltrate without necrosis or arteritis in the ganciclovir-treated EpTK group. The proliferative responses of the tolerant mice at day 100 were identical to those of naive mice, including a preserved proliferation against the donor's lymphocytes in mixed lymphocyte reaction.

CONCLUSION

Functional transplantation tolerance of a fully incompatible heart can be achieved without immunosuppressive drugs in this model of suicide gene therapy.

Small dense nuclear bodies are the site of localization of herpes simplex virus 1 U(L)3 and U(L)4 proteins and of ICP22 only when the latter protein is present

The herpes simplex virus 1 U(L)3 and U(L)4 open reading frames are expressed late in infection and are not essential for viral replication in cultured cells in vitro. An earlier report showed that the U(L)4 protein colocalizes with the products of the alpha22/U(S)1.5 genes in small nuclear dense bodies. Here we report that the U(L)3 protein also colocalized in these small nuclear dense bodies and the localization of U(L)3 and U(L)4 proteins in these bodies required the presence of alpha22/U(S)1.5 genes. In cells infected with a mutant lacking intact alpha22/U(S)1.5 genes, U(L)3 was diffused throughout the nucleus even though the overall accumulation of the gamma2 U(L)3 protein was decreased. The results suggest that ICP22 acts both as a regulator of U(L)3 accumulation and as the structural component and anchor of these small dense nuclear bodies.

Components of vectors for gene transfer and expression in mammalian cells

Progress in diverse scientific fields has been realized partly by the continued refinement of mammalian gene expression vectors. A growing understanding of biological processes now allows the design of vector components to meet specific objectives. Thus, gene expression in a tissue-selective or ubiquitous manner may be accomplished by selecting appropriate promoter/enhancer elements; stabilization of labile mRNAs may be effected through removal of 3' untranslated regions or fusion to heterologous stabilizing sequences; protein targeting to selected tissues or different organelles is carried out using specific signal sequences; fusion moieties effect the detection, enhanced yield, surface expression, prolongation of half-life, and facile purification of recombinant proteins; and careful tailoring of the codon content of heterologous genes enhances protein production from poorly translated transcripts. The use of viral as well as nonviral genetic elements in vectors allows the stable replication of episomal elements without the need for chromosomal integration. The development of baculovirus vectors for both transient and stable gene expression in mammalian cells has expanded the utility of such vectors for a broad range of cell types. Internal ribosome entry sites are now widely used in many applications that require coexpression of different genes. Progress in gene targeting techniques is likely to transform gene expression and amplification in mammalian cells into a considerably less labor-intensive operation. Future progress in the elucidation of eukaryotic protein degradation pathways holds promise for developing methods to minimize proteolysis of specific recombinant proteins in mammalian cells and tissues.

Identification and characterization of the UL14 gene product of herpes simplex virus type 2

The UL14 gene of herpes simplex virus type 2 (HSV-2) is predicted to encode a 219 amino acid protein with a molecular mass of 23 kDa. In this study, the HSV-2 UL14 gene product has been identified by using a rabbit polyclonal antiserum raised against a recombinant 6 x His-UL14 fusion protein expressed in E. coli. The antiserum reacted specifically with 34, 33 and 28 kDa proteins in HSV-2-infected cell lysates and also with a 34 kDa protein produced by in vitro transcription and translation reactions, suggesting that the 34 kDa protein is the primary translation product of the UL14 gene. The protein was synthesized at late times post-infection (p.i.) and was not detectable in the presence of the viral DNA synthesis inhibitor acycloguanosine. Indirect immunofluorescence studies localized the UL14 protein both to the nucleus and to perinuclear regions of the cytoplasm, and the nuclear UL14 protein was found to co-localize with the scaffolding protein ICP35 at 9 h p.i. However, the protein accumulated in a perinuclear region of the cytoplasm at 12 h p.i., while most of the ICP35 protein localized within assemblons in the nucleus. Although no detectable UL14 protein was associated with intracellular capsids isolated in the presence of 0.5 M NaCl, it was detected in purified virions. Furthermore, the UL14 protein expressed alone was detected both in the nucleus and in the cytoplasm at 24 h after transfection, but was mainly localized to the cytoplasm at later times.

Oncolytic viral therapy for human colorectal cancer and liver metastases using a multi-mutated herpes simplex virus type-1 (G207)

G207 is a multi-mutated, replication-competent type-1 herpes simplex virus designed to target, infect, and lyse neurological tumors. This study examines the feasibility of using G207 in the treatment of human colorectal cancer and defines the biological determinants of its antitumor efficacy. This virus was tested on five human colorectal cancer cell lines in vitro to determine efficacy of infection and tumor cell kill. These results were correlated to measures of tumor cell proliferation. In vivo testing was performed through direct injections of G207 into xenografts of human colorectal cancer tumors grown in flanks of athymic rats. To evaluate an alternate method of administration, hepatic portal vein infusion of G207 was performed in a syngeneic model of liver metastases in Buffalo rats. Among the five cell lines tested, infection rates ranged between 10% and 90%, which correlated directly with S-phase fraction (8.6%-36.6%) and was proportional to response to G207 therapy in vitro (1%-93%). Direct injection of G207 into nude rat flank tumors suppressed tumor growth significantly vs. control (0.58 +/- 0.60 cm(3) vs. 9.16 +/- 3.70 cm(3), P<0. 0001). In vivo tumor suppression correlated with in vitro effect. In the syngeneic liver tumor model, portal infusion resulted in significant reduction in number of liver nodules (13 +/- 10 nodules in G207-treated livers vs. 80 +/- 30 nodules in control livers, P<0.05). G207 infects and kills human colorectal cancer cells efficiently. In vitro cytotoxicity assay and tumor S-phase fraction can be used to predict response to treatment in vivo. This antineoplastic agent can be delivered effectively by both direct tumor injection and regional vascular infusion. G207 should be investigated further as therapy for colorectal cancer and liver metastases.

A novel anti-herpes simplex virus type 1-specific herpes simplex virus type 1 recombinant

A recombinant herpes simplex virus (HSV) capable of inhibiting its own replication as well as the replication of wild-type virus would have greatly increased safety as a general purpose vector for in vivo gene transfer, antitumor therapy, and viral vaccine against HSV infection. By using a tetracycline repressor (tetR)-mediated HSV-1 viral replication switch [Yao and Eriksson (1999). Hum. Gene Ther. 10, 419-427], we have generated a novel anti-HSV-1-specific HSV-1 recombinant (CJ83193) that expresses a trans-dominant negative HSV-1 UL9 origin-binding protein, UL9-C535C. The de novo synthesis of CJ83193 can be suppressed by UL9-C535C by at least 1 x 10(6)-fold in non-tetR-expressing cells, and is subject to tetracycline regulation over a range of four to five orders of magnitude in a tetR-expressing osteosarcoma line. In particular, the UL9-C535C peptides expressed from the CJ83193 genome can inhibit the replication of wild-type HSV-1 by 100- to 200-fold in single-step growth assays. The construction of CJ83193 creates a new general strategy for developing recombinant viral vectors able to function as an intracellular therapy against wild-type viral infections.

Mechanism and application of genetic recombination in herpesviruses

Herpes simplex virus type 1 (HSV-1) is a ubiquitous human pathogen that latently infects sensory ganglia and encodes over 80 genes in a 152 kbp DNA genome. This well characterised virus provides a model for analysing genetic recombination in herpesviruses, a fundamental biological process by which new combinations of genetic materials are generated. The frequency of homologous recombination was estimated to be 0.0048-0.007 (0.48%-0.7%)/kb of the HSV-1 genome, determined using physical markers. The double-strand break repair model, the current model of homologous recombination, adequately explains L-S inversion of herpesvirus genomes and the recombinogenicity of the a sequence. Several herpesvirus genomes, including HSV-1 consist of a unique sequence bracketed by a pair of inverted repeat sequences. This arrangement is attributed to illegitimate recombination between molecules arranged in an inverse orientation. Junctions of unique and repeated sequences that correspond to the crossover site of illegitimate recombination are recombinogenic. Recombination is important for virus evolution, construction of mutated virus, gene therapy and vaccination in which the potential for recombination between engineered input virus and wild type virus has to be considered.

Transplacental drug delivery: gene and virus delivery to the trophoblast

The development of successful strategies for delivering genes to the placenta may provide new opportunities for modifying trophoblast function in order to learn more about trophoblast physiology and to offer novel therapeutic options for complications of pregnancy that result from placental dysfunction. Replication-deficient recombinant viral vectors are useful vehicles for introducing genes into cells in vitro and in vivo. Recombinant adenovirus and herpes simplex virus vectors are unable to efficiently infect and transduce terminally differentiated trophoblastic cells. However, recombinant adeno-associated virus vectors transduce terminally differentiated trophoblastic cells, and a Sindbis virus construct efficiently transduces and destroys trophoblastic cancer cells. We describe the features that make particular viral vectors attractive for gene transfer to trophoblastic cells.

Colocalization of the herpes simplex virus 1 UL4 protein with infected cell protein 22 in small, dense nuclear structures formed prior to onset of DNA synthesis

Herpes simplex virus 1 infected cell protein 22 (ICP22) localizes in small, dense nuclear bodies of primate cells early in infection and in the more diffuse replicative complexes after the onset of DNA synthesis. UL4, a gamma2 protein, localizes in cytoplasm and in the small nuclear structures containing ICP22 but not in replicative complexes. In rabbit skin cells, both ICP22 and UL4 localize in the dense nuclear bodies late in infection. The results suggest that the small nuclear structures perform a function involving both proteins late in infection.

Functional anatomy of herpes simplex virus 1 overlapping genes encoding infected-cell protein 22 and US1.5 protein

Earlier studies have shown that (i) the coding domain of the alpha22 gene encodes two proteins, the 420-amino-acid infected-cell protein 22 (ICP22) and a protein, US1.5, which is initiated from methionine 147 of ICP22 and which is colinear with the remaining portion of that protein; (ii) posttranslational processing of ICP22 mediated largely by the viral protein kinase UL13 yields several isoforms differing in electrophoretic mobility; and (iii) mutants lacking the carboxyl-terminal half of the ICP22 and therefore DeltaUS1.5 are avirulent and fail to express normal levels of subsets of both alpha (e.g., ICP0) or gamma2 (e.g., US11 and UL38) proteins. We have generated and analyzed two sets of recombinant viruses. The first lacked portions of or all of the sequences expressed solely by ICP22. The second set lacked 10 to 40 3'-terminal codons of ICP22 and US1. 5. The results were as follows. (i) In cells infected with mutants lacking amino-terminal sequences, translation initiation begins at methionine 147. The resulting protein cannot be differentiated in mobility from authentic US1.5, and its posttranslational processing is mediated by the UL13 protein kinase. (ii) Expression of US11 and UL38 genes by mutants carrying only the US1.5 gene is similar to that of wild-type parent virus. (iii) Mutants which express only US1. 5 protein are avirulent in mice. (iv) The coding sequences Met147 to Met171 are essential for posttranslational processing of the US1.5 protein. (v) ICP22 made by mutants lacking 15 or fewer of the 3'-terminal codons are posttranslationally processed whereas those lacking 18 or more codons are not processed. (vi) Wild-type and mutant ICP22 proteins localized in both nucleus and cytoplasm irrespective of posttranslational processing. We conclude that ICP22 encodes two sets of functions, one in the amino terminus unique to ICP22 and one shared by ICP22 and US1.5. These functions are required for viral replication in experimental animals. US1.5 protein must be posttranslationally modified by the UL13 protein kinase to enable expression of a subset of late genes exemplified by UL38 and US11. Posttranslational processing is determined by two sets of sequences, at the amino terminus and at the carboxyl terminus of US1.5, respectively, a finding consistent with the hypothesis that both domains interact with protein partners for specific functions.

Herpes simplex virus 1 regulatory protein ICP22 interacts with a new cell cycle-regulated factor and accumulates in a cell cycle-dependent fashion in infected cells

The herpes simplex virus 1 infected cell protein 22 (ICP22), the product of the alpha22 gene, is a nucleotidylylated and phosphorylated nuclear protein with properties of a transcriptional factor required for the expression of a subset of viral genes. Here, we report the following. (i) ICP22 interacts with a previously unknown cellular factor designated p78 in the yeast two-hybrid system. The p78 cDNA encodes a polypeptide with a distribution of leucines reminiscent of a leucine zipper. (ii) In uninfected and infected cells, antibody to p78 reacts with two major bands with an apparent Mr of 78,000 and two minor bands with apparent Mrs of 62, 000 and 55,000. (ii) p78 also interacts with ICP22 in vitro. (iii) In uninfected cells, p78 was dispersed largely in the nucleoplasm in HeLa cells and in the nucleoplasm and cytoplasm in HEp-2 cells. After infection, p78 formed large dense bodies which did not colocalize with the viral regulatory protein ICP0. (iv) Accumulation of p78 was cell cycle dependent, being highest very early in S phase. (v) The accumulation of ICP22 in synchronized cells was highest in early S phase, in contrast to the accumulation of another protein, ICP27, which was relatively independent of the cell cycle. (vi) In the course of the cell cycle, ICP22 was transiently modified in an aberrant fashion, and this modification coincided with expression of p78. The results suggest that ICP22 interacts with and may be stabilized by cell cycle-dependent proteins.

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 1 induces and blocks apoptosis at multiple steps during infection and protects cells from exogenous inducers in a cell-type-dependent manner

Several publications have attested to the ability of herpes simplex viruses to protect cells against apoptosis. We investigated the ability of the virus to protect cells in continuous cultivation from apoptosis induced by the virus itself, and by other known inducers such as exposure to the tumor necrosis factor alpha (TNFalpha), antibody to Fas, C2-ceramide, osmotic shock (sorbitol), and thermal shock. The salient features of the results were that the virus was able to protect cells against apoptosis by all of the agents tested, and that apoptosis induced by the virus was a very early event that did not require de novo expression of viral genes. However, these events were cell-type specific. Thus: (i) The cell lines tested exhibited fragmented chromosomal DNA following infection with a virus lacking functional alpha4 and US3 genes encoding the major regulatory protein and a viral protein kinase, respectively, but not by wild-type virus. (ii) Wild-type virus protected subconfluent SK-N-SH but not HeLa cells against induction of apoptosis by anti-Fas antibody, TNFalpha, C2-ceramide, and thermal shock. Confluent SK-N-SH cells were not protected from osmotic shock-induced apoptosis by wild-type infection. (iii) Wild-type virus protected SK-N-SH but not HeLa cells against induction of apoptosis by sorbitol, anti-Fas antibody, or TNFalpha and C2-ceramide. (iv) Mutant HSV-1(HFEM)tsB7 at the nonpermissive temperature infects cells but the DNA is not released from capsids, and therefore viral gene expression is restricted to the function of viral proteins introduced into the cell along with the capsid containing the viral DNA. HSV-1(HFEM)tsB7 induced apoptosis in Vero cells but not in SK-N-SH cells infected and maintained at 39.5 degrees C. (v) Tests of two caspase inhibitors showed that they blocked apoptosis induced by C2-ceramide and sorbitol, but were not able to block apoptosis induced by the virus lacking functional alpha4 and US3 genes. We conclude that HSV-1 triggers apoptosis at multiple metabolic checkpoints and in turn has evolved mechanisms to block apoptosis at each point and that some of the pathways of induction are shared with exogenous inducers tested in this study whereas others are not.

Eukaryotic elongation factor 1delta is hyperphosphorylated by the protein kinase encoded by the U(L)13 gene of herpes simplex virus 1

The translation elongation factor 1delta (EF-1delta) consists of two forms, a hypophosphorylated form (apparent Mr, 38,000) and a hyperphosphorylated form (apparent Mr, 40,000). Earlier Y. Kawaguchi, R. Bruni, and B. Roizman (J. Virol. 71:1019-1024, 1997) reported that whereas mock-infected cells accumulate the hypophosphorylated form, the hyperphosphorylated form of EF-1delta accumulates in cells infected with herpes simplex virus 1. We now report that the accumulation of the hyperphosphorylated EF-1delta is due to phosphorylation by U(L)13 protein kinase based on the following observations. (i) The relative amounts of hypo- and hyperphosphorylated EF-1delta in Vero cells infected with mutant virus lacking the U(L)13 gene could not be differentiated from those of mock-infected cells. In contrast, the hyperphosphorylated EF-1delta was the predominant form in Vero cells infected with wild-type viruses, a recombinant virus in which the deleted U(L)13 sequences were restored, or with a virus lacking the U(S)3 gene, which also encodes a protein kinase. (ii) The absence of the hyperphosphorylated EF-1delta in cells infected with the U(L)13 deletion mutant was not due to failure of posttranslational modification of infected-cell protein 22 (ICP22)/U(S)1.5 or of interaction with ICP0, inasmuch as preferential accumulation of hyperphosphorylated EF-1delta was observed in cells infected with viruses from which the genes encoding ICP22/U(S)1.5 or ICP0 had been deleted. (iii) Both forms of EF-1delta were labeled by 32Pi in vivo, but the prevalence of the hyperphosphorylated EF-1delta was dependent on the presence of the U(L)13 protein. (iv) EF-1delta immunoprecipitated from uninfected Vero cells was phosphorylated by U(L)13 precipitated by the anti-U(L)13 antibody from lysates of wild-type virus-infected cells, but not by complexes formed by the interaction of the U(L)13 antibody with lysates of cells infected with a mutant lacking the U(L)13 gene. This is the first evidence that a viral protein kinase targets a cellular protein. Together with evidence that ICP0 also interacts with EF-1delta reported in the paper cited above, these data indicate that herpes simplex virus 1 has evolved a complex strategy for optimization of infected-cell protein synthesis.

The Scope of Viral Vectors for the Transduction of Haemopoietic Cells

Over the last five years significant progress has been made towards the transfer of foreign genetic material to eukaryotic cells. The eventual aim to devise novel therapeutic strategies to treat human diseases, in particular solid tumours and monogenic disorders associated with various enzyme deficiency states. The easy accessibility and the ability of haemopoetic stem cells to self replicate and repopulate makes them desirable targets for gene transfer. In theory the introduction of a small number of gene modifed haemopoetic progenitor cells can allow therapy of an individual for life without any further intervention. This approach has been used for the treatment of single gene defects such as ADA deficiency. Furthermore, gene transfer technology has increasingly been exploited for bone marrow and peripheral blood stem cell marking studies, modification of cell sensitivity to cytotoxic drugs and the genetic modification of leukemic cells with the intention of inducing a leukemia specific cytotoxic T cell response. Vector development is of crucial importance for the successful delivery of genes in haemopoetic stem cells and leukemia cells. The objective of this review is to discuss in detail the properties of current vector technology that are pertinent to haemopoietic cell gene transduction.

Herpes simplex virus 1 alpha regulatory protein ICP0 interacts with and stabilizes the cell cycle regulator cyclin D3

The herpes simplex virus 1 (HSV-1) infected-cell protein 0 (ICP0) has the characteristics of a promiscuous transactivator of genes introduced into cells by infection or transfection. To identify cellular proteins interacting with ICP0, we used a domain of exon II of ICP0 that is known to be crucial for regulatory function of the protein as bait in the yeast two-hybrid screen. Our results were as follows. (i) A cDNA in a positive yeast colony was found to encode cyclin D3, a cell cycle regulator of G1 phase. (ii) A purified chimeric protein consisting of glutathione S-transferase (GST) fused to cyclin D3 specifically formed complexes with ICP0 contained in HSV-1-infected cell lysate. (iii) To enhance the expression of cyclin D3, the gene was inserted into the viral genome and overexpressed in infected cells. The overexpressed cyclin D3 colocalized with ICP0 in nuclear structures characteristic of ND10 and which earlier have been reported to contain ICP0. (iv) The accumulation of cyclin D3 protein in Vero cells infected with an alpha0 deletion mutant was reduced relative to that of cells infected with wild-type virus or a recombinant virus in which the deleted alpha0 sequences were restored. (v) Lysates of Spodoptera frugiperda Sf9 cells doubly infected with baculoviruses genetically engineered to express cyclin D3 and cyclin-dependent kinase 4 (CDK4) phosphorylated GST fused to retinoblastoma protein (GST-pRb) but did not phosphorylate the GST-alpha0(20-241) or GST-alpha0(543-768) fusion protein or immunoprecipitated ICP0 proteins. Moreover, the chimeric GST-ICP0(exon II) protein shown to bind cyclin D3 had no effect on the activity of the kinase on GST-pRb when added to mixtures of lysates of Sf9 cells which coexpressed cyclin D3 and CDK4. These results indicate that ICP0 interacts with, colocalizes with, and stabilizes the cyclin D3 cell cycle regulator and does not affect its interaction with the cyclin-dependent kinase.

The product of ORF O located within the domain of herpes simplex virus 1 genome transcribed during latent infection binds to and inhibits in vitro binding of infected cell protein 4 to its cognate DNA site

The partially overlapping ORF P and ORF O are located within the domains of the herpes simplex virus 1 genome transcribed during latency. Earlier studies have shown that ORF P is repressed by infected cell protein 4 (ICP4), the major viral regulatory protein, binding to its cognate site at the transcription initiation site of ORF P. The ORF P protein binds to p32, a component of the ASF/SF2 alternate splicing factors; in cells infected with a recombinant virus in which ORF P was derepressed there was a significant decrease in the expression of products of key regulatory genes containing introns. We report that (i) the expression of ORF O is repressed during productive infection by the same mechanism as that determining the expression of ORF P; (ii) in cells infected at the nonpermissive temperature for ICP4, ORF O protein is made in significantly lower amounts than the ORF P protein; (iii) the results of insertion of a sequence encoding 20 amino acids between the putative initiator methionine codons of ORF O and ORF P suggest that ORF O initiates at the methionine codon of ORF P and that the synthesis of ORF O results from frameshift or editing of its RNA; and (iv) glutathione S-transferase-ORF O fusion protein bound specifically ICP4 and precluded its binding to its cognate site on DNA in vitro. These and earlier results indicate that ORF P and ORF O together have the capacity to reduce the synthesis or block the expression of regulatory proteins essential for viral replication in productive infection.

Capsid assembly and DNA packaging in herpes simplex virus

The genome of HSV-1 contains 80-85 open reading frames. Genetic and biochemical evidence suggests that at least 39 of these genes encode proteins that are components of the HSV-1 virion. The architecture of the HSV-1 virion consists of a trilaminar lipid envelope, an amorphous layer known as the tegument, a capsid shell, and a DNA-containing core. The capsid is an icosahedral shell whose major morphological features are 162 capsomers. It is composed of a major capsid protein called VP5 and three less abundant proteins, VP19C, VP23 and VP26. VP5 is the structural subunit of all 162 capsomers while VP19C and VP23 are located in the space between the capsomers. In addition to the structural proteins, capsid assembly involves participation of the HSV-1-encoded protease and the scaffolding protein, preVP22a. DNA packaging involves participation of DNA, empty capsids, and at least seven additional HSV-1-encoded proteins. Considerable advances have been made in understanding the structure of the capsid shell, largely as the result of applying cryoelectron microscopy techniques. Use of recombinant baculoviruses has allowed for a detailed analysis of the proteins required for capsid assembly. More recently, an in vitro system has been developed which has aided in defining the assembly pathway by identifying intermediates in the assembly of intact capsids. The in vitro system has identified a fragile roundish procapsid which matures into the polyhedral capsid in a transition similar to that undergone by bacteriophage proheads. This review is a summary of our present knowledge with respect to the structure and assembly of the HSV-1 capsid and what is known about the seven genes involved in DNA packaging. Copyright 1997 John Wiley & Sons Ltd.

The range and distribution of murine central nervous system cells infected with the gamma(1)34.5- mutant of herpes simplex virus 1

Wild-type herpes simplex virus 1 (HSV-1) multiplies, spreads, and rapidly destroys cells of the murine central nervous system (CNS). In contrast, mutants lacking both copies of the gamma(1)34.5- gene have been shown to be virtually lacking in virulence even after direct inoculation of high-titered virus into the CNS of susceptible mice (J. Chou, E. R. Kern, R. J. Whitley, and B. Roizman, Science 250:1262-1266, 1990). To investigate the host range and distribution of infected cells in the CNS of mice, 4- to 5-week-old mice were inoculated stereotaxically into the caudate/putamen with 3 x 10(5) PFU of the gamma(1)34.5- virus R3616. Four-micrometer-thick sections of mouse brains removed on day 3, 5, or 7 after infection were reacted with a polyclonal antibody directed primarily to structural proteins of the virus and with antibodies specific for neurons, astrocytes, or oligodendrocytes. This report shows the following: (i) most of the tissue damage caused by R3616 was at the site of injection, (ii) the virus spread by retrograde transport from the site of infection to neuronal cell nuclei at distant sites and to ependymal cells by cerebrospinal fluid, (iii) the virus infected neurons, astrocytes, oligodendrocytes, and ependymal cells and hence did not discriminate among CNS cells, (iv) viral replication in some neurons could be deduced from the observation of infected astrocytes and oligodendrocytes at distant sites, and (v) infected cells were being efficiently cleared from the nervous system by day 7 after infection. We conclude that the gamma(1)34.5- attenuation phenotype is reflected in a gross reduction in the ability of the virus to replicate and spread from cell to cell and is not due to a restricted host range. The block in viral replication appears to be a late event in viral replication.

The pseudorabies virus UL51 gene product is a 30-kilodalton virion component

Positional homologs to the UL51 open reading frame of herpes simplex virus type 1 have been identified throughout the herpesvirus family. However, no respective protein has so far been described for any of the herpesviruses. With rabbit antisera directed against oligopeptides predicted to comprise antigenic regions of the deduced pseudorabies virus (PrV) UL51 protein, a polypeptide with a size of 30 kDa was identified in PrV-infected cell lysates and in purified virions. This molecular mass correlates reasonably well with the predicted mass of 25 kDa of the 236-amino-acid deduced UL51 protein. Antisera raised against peptides derived from different predicted antigenic regions all detected the 30-kDa protein in Western blot (immunoblot) analyses. Specificity was ascertained by peptide competition. Subcellular fractionation showed the presence of the UL51 protein mainly in the nucleus of infected cells. After separation of purified virion preparations into envelope and capsid, the PrV UL51 protein was detected in the capsid fraction. In summary, we identified the first herpesvirus UL51 protein and demonstrate that it represents a structural component of PrV virions.

Interaction of herpes simplex virus 1 alpha regulatory protein ICP0 with elongation factor 1delta: ICP0 affects translational machinery

The herpes simplex virus 1 (HSV-1)-infected cell protein 0 (ICP0) is a promiscuous transactivator, and by necessity, its functions must be mediated through cellular gene products. In an attempt to identify cellular factors interacting with ICP0, we used the carboxyl-terminal domain of ICP0 as "bait" in the yeast (Saccharomyces cerevisiae) two-hybrid system. Our results were as follows: (i) All 43 cDNAs in positive yeast colonies were found to encode the same translation factor, elongation factor delta-1 (EF-1delta). (ii) Purified chimeric protein consisting of glutathione S-transferase (GST) fused to EF-1delta specifically formed complexes with ICP0 contained in HSV-1-infected cell lysate. (iii) Fractionation of infected HEp-2 cells and immunofluorescence studies revealed that ICP0 was localized both in the nucleus and in the cytoplasm. In primary human foreskin fibroblasts, ICP0 was localized predominantly in the cytoplasm throughout HSV-1 infection even early in infection. (iv) Addition of the chimeric protein GST-carboxyl-terminal domain of ICP0 to the rabbit reticulocyte lysate in vitro translation system resulted in a dose-dependent decrease in protein synthesis. In contrast, GST alone or GST fused to the amino-terminal domain of ICP0 had no effect on the in vitro translation system. (v) The predominant forms of EF-1delta on electrophoresis in denaturing gels have apparent Mrs of 38,000 and 40,000. The higher-Mr form is a minor species in mock-infected cells, whereas in human fibroblasts and Vero cells infected with HSV-1, this isoform becomes dominant. These results indicate that ICP0 is present and may have a significant role in the cytoplasm of infected cells, possibly by altering the efficiency of translation of viral mRNAs.