Herpes virus induced proteasome-dependent degradation of the nuclear bodies-associated PML and Sp100 proteins.
The PML protein is associated to nuclear bodies (NBs) whose functions are as yet unknown. PML and two other NBs-associated proteins, Sp100 And ISG20 are directly induced by interferons (IFN). PML and Sp100 proteins are covalently linked to SUMO-1, and ubiquitin-like peptide. PML NBs are disorganized in acute promyelocytic leukemia and during several DNA virus infections. In particular, the HSV-1 ICP0 protein is known to delocalize PML from NBs. Thus, NBs could play an important role in oncogenesis, IFN response and viral infections. Here, we show that HSV-1 induced PML protein degradation without altering its mRNA level. This degradation was time- and multiplicity of infection-dependent. Sp100 protein was also degraded, while another SUMO-1 conjugated protein, RanGAP1 and the IFN-induced protein kinase PKR were not. The proteasome inhibitor MG132 abrogated the HSV-1-induced PML and Sp100 degradation and partially restored their NB-localization. HSV-1 induced PML and Sp100 degradation constitutes a new example of viral inactivation of IFN target gene products. (+info
The herpes simplex virus type 1 regulatory protein ICP27 is required for the prevention of apoptosis in infected human cells.
The herpes simplex virus type 1 (HSV-1) ICP27 protein is an immediate-early or alpha protein which is essential for the optimal expression of late genes as well as the synthesis of viral DNA in cultures of Vero cells. Our specific goal was to characterize the replication of a virus incapable of synthesizing ICP27 in cultured human cells. We found that infection with an HSV-1 ICP27 deletion virus of at least three separate strains of human cells did not produce immediate-early or late proteins at the levels observed following wild-type virus infections. Cell morphology, chromatin condensation, and genomic DNA fragmentation measurements demonstrated that the human cells died by apoptosis after infection with the ICP27 deletion virus. These features of the apoptosis were identical to those which occur during wild-type infections of human cells when total protein synthesis has been inhibited. Vero cells infected with the ICP27 deletion virus did not exhibit any of the features of apoptosis. Based on these results, we conclude that while HSV-1 infection likely induced apoptosis in all cells, viral evasion of the response differed among the cells tested in this study. (+info
Herpes simplex virus 1 blocks caspase-3-independent and caspase-dependent pathways to cell death.
Earlier reports have shown that herpes simplex virus 1 (HSV-1) mutants induce programmed cell death and that wild-type HSV blocks the execution of the cell death program triggered by viral gene products, by the effectors of the immune system such as the Fas and tumor necrosis factor pathways, or by nonspecific stress agents such as either osmotic shock induced by sorbitol or thermal shock. A report from this laboratory showed that caspase inhibitors do not block DNA fragmentation induced by infection with the HSV-1 d120 mutant. To identify the events in programmed cell death induced and blocked by HSV-1, we examined cells infected with wild-type virus or the d120 mutant or cells infected and exposed to sorbitol. We report that: (i) the HSV-1 d120 mutant induced apoptosis by a caspase-3-independent pathway inasmuch as caspase 3 was not activated and DNA fragmentation was not blocked by caspase inhibitors even though the virus caused cytochrome c release and depolarization of the inner mitochondrial membrane. (ii) Cells infected with wild-type HSV-1 exhibited none of the manifestations associated with programmed cell death assayed in these studies. (iii) Uninfected cells exposed to osmotic shock succumbed to caspase-dependent apoptosis inasmuch as cytochrome c was released, the inner mitochondrial potential was lost, caspase-3 was activated, and chromosomal DNA was fragmented. (iv) Although caspase-3 was activated in cells infected with wild-type HSV-1 and exposed to sorbitol, cytochrome c outflow, depolarization of the inner mitochondrial membrane, and DNA fragmentation were blocked. We conclude that although d120 induces apoptosis by a caspase-3-independent pathway, the wild-type virus blocks apoptosis induced by this pathway and also blocks the caspase-dependent pathway induced by osmotic shock. The block in the caspase-dependent pathway may occur downstream of caspase-3 activation. (+info
Role for gamma interferon in control of herpes simplex virus type 1 reactivation.
Observation of chronic inflammatory cells and associated high-level gamma interferon (IFN-gamma) production in ganglia during herpes simplex type 1 (HSV-1) latent infection in mice (E. M. Cantin, D. R. Hinton, J. Chen, and H. Openshaw, J. Virol. 69:4898-4905, 1995) prompted studies to determine a role of IFN-gamma in maintaining latency. Mice lacking IFN-gamma (GKO mice) or the IFN-gamma receptor (RGKO mice) were inoculated with HSV-1, and the course of the infection was compared with that in IFN-gamma-competent mice with the same genetic background (129/Sv//Ev mice). A time course study showed no significant difference in trigeminal ganglionic viral titers or the timing of establishment of latency. Spontaneous reactivation resulting in infectious virus in the ganglion did not occur during latency in any of the mice. However, 24 h after the application of hyperthermic stress to mice, HSV-1 antigens were detected in multiple neurons in the null mutant mice but in only a single neuron in the 129/Sv//Ev control mice. Mononuclear inflammatory cells clustered tightly around these reactivating neurons, and by 48 h, immunostaining was present in satellite cells as well. The incidence of hyperthermia-induced reactivation as determined by recovery of infectious virus from ganglia was significantly higher in the null mutant than in control mice: 11% in 129/Sv//Ev controls, 50% in GKO mice (P = 0.0002), and 33% in RGKO mice (P = 0.03). We concluded that IFN-gamma is not involved in the induction of reactivation but rather contributes to rapid suppression of HSV once it is reactivated. (+info
Antiviral therapy for neonatal herpes simplex virus: a cost-effectiveness analysis.
Each year, about 1,600 infants in the United States are infected with neonatal herpes simplex virus. We conducted a cost-effectiveness analysis of antiviral drug therapy (acyclovir) for three forms of herpes simplex virus infection: skin, ear, and mouth (SEM), central nervous system (CNS), and disseminated multiorgan (DIS) disease. Five levels of patient outcomes were examined (normal, mild, moderate, severe, dead). We obtained information on disease occurrence and survival from clinical trials and historical reviews of untreated newborns. We considered approaches for treating all or any of the forms of the disease and compared them with no use of antiviral drugs. The main measure of effectiveness was lives saved, including those of descendants of survivors. Costs were measured from a societal perspective and included direct medical costs, institutional care, and special education. We used a discount rate of 3% and valued dollars at 1995 levels. We also considered the perspective of a managed care organization. From a societal viewpoint relative to no treatment, antiviral therapy for SEM resulted in a gain of 0.8 lives and a cost reduction of $78,601 per case. For the treatment of CNS and DIS disease, antiviral therapy saved more lives but at increased cost, with respective marginal costs per additional life saved of $75,125 and $46,619. From a managed care perspective, antiviral therapy is more cost-effective than from a societal viewpoint because costs of institutional care and special education are not the responsibility of managed care organizations. Development of at-home therapies will further improve the cost-effectiveness of antiviral therapy for neonatal herpes simplex virus infection. (+info
Immunogenicity of herpes simplex virus type 1 mutants containing deletions in one or more alpha-genes: ICP4, ICP27, ICP22, and ICP0.
Replication defective mutants of HSV have been proposed both as vaccine candidates and as vehicles for gene therapy because of their inability to produce infectious progeny. The immunogenicity of these HSV replication mutants, at both qualitative and quantitative levels, will directly determine their effectiveness for either of these applications. We have previously reported (Brehm et al., J. Virol., 71, 3534, 1997) that a replication defective mutant of HSV-1, which expresses a substantial level of viral genes without producing virus particles, is as efficient as wild-type HSV-1 in eliciting an HSV-specific cytotoxic T-lymphocyte (CTL) response. In this report, we have further evaluated the immunogenic potential of HSV-1-derived replication defective mutants by examining the generation of HSV-specific CTL following immunization with viruses that are severely restricted in viral gene expression due to mutations in one or more HSV alpha genes (ICP4, ICP27, ICP22, and ICP0). To measure the CTL responses induced by the HSV alpha-mutants, we have targeted two H-2Kb-restricted CTL epitopes: an epitope in a virion protein, gB (498-505), and an epitope in a nonvirion protein, ribonucleotide reductase (RR1 822-829). The HSV mutants used in this study are impaired in their ability to express gB while a majority of them still express RR1. Our findings demonstrate that a single immunization with these mutants is able to generate a strong CTL response not only to RR1 822-829, but also to gB498-505 despite their inability to express wild-type levels of gB. Furthermore, a single immunization with any individual mutant can also provide immune protection against HSV challenge. These results suggest that mutants which are restricted in gene expression may be used as effective immunogens in vivo. (+info
Ectopic expression of DNA encoding IFN-alpha 1 in the cornea protects mice from herpes simplex virus type 1-induced encephalitis.
A novel approach to combat acute herpes simplex virus type 1 (HSV-1) infection has recently been developed by administration with a plasmid DNA construct encoding cytokine genes. Cytokines, especially type I IFNs (IFN-alpha and IFN-beta) play an important role in controlling acute HSV-1 infection. The purpose of the present study was to investigate the potential efficacy of ectopically expressed IFN-alpha 1 against ocular HSV-1 infection following in situ transfection of mouse cornea with a naked IFN-alpha 1-containing plasmid DNA. Topical administration of the IFN-alpha 1 plasmid DNA exerted protection against ocular HSV-1 challenge in a time- and dose-dependent manner and antagonized HSV-1 reactivation. In addition, IFN-alpha 1-transfected eyes expressed a fivefold increase in MHC class I mRNA over vector-treated controls. The protective efficacy of the IFN-alpha 1 transgene antagonized viral replication, as evidenced by the reduction of the viral gene transcripts (infected cell polypeptide 27, thymidine kinase, and viral protein 16) and viral load in eyes and trigeminal ganglia during acute infection. The administration of neutralizing Ab to IFN-alpha beta antagonized the protective effect of the IFN-alpha 1 transgene in mice. Collectively, these findings demonstrate the potential of using naked plasmid DNA transfection in the eye to achieve ectopic gene expression of therapeutically active agents. (+info
Intranuclear delivery of an antiviral peptide mediated by the B subunit of Escherichia coli heat-labile enterotoxin.
We report an intracellular peptide delivery system capable of targeting specific cellular compartments. In the model system we constructed a chimeric protein consisting of the nontoxic B subunit of Escherichia coli heat-labile enterotoxin (EtxB) fused to a 27-mer peptide derived from the DNA polymerase of herpes simplex virus 1. Viral DNA synthesis takes places in the nucleus and requires the interaction with an accessory factor, UL42, encoded by the virus. The peptide, designated Pol, is able to dissociate this interaction. The chimeric protein, EtxB-Pol, retained the functional properties of both EtxB and peptide components and was shown to inhibit viral DNA polymerase activity in vitro via disruption of the polymerase-UL42 complex. When added to virally infected cells, EtxB-Pol had no effect on adenovirus replication but specifically interfered with herpes simplex virus 1 replication. Further studies showed that the antiviral peptide localized in the nucleus, whereas the EtxB component remained associated with vesicular compartments. The results indicate that the chimeric protein entered through endosomal acidic compartments and that the Pol peptide was cleaved from the chimeric protein before being translocated into the nucleus. The system we describe is suitable for delivery of peptides that specifically disrupt protein-protein interactions and may be developed to target specific cellular compartments. (+info