Bcl-2 blocks a caspase-dependent pathway of apoptosis activated by herpes simplex virus 1 infection in HEp-2 cells

Silencing of ZFP36L2 increases sensitivity to temozolomide through G2/M cell cycle arrest and BAX mediated apoptosis in GBM cells

Despite the advancements in primary brain tumour diagnoses and treatments, the mortality rate remains high, particularly in glioblastoma (GBM). Chemoresistance, predominantly in recurrent cases, results in decreased mean survival of patients with GBM. We aimed to determine the chemosensitisation and oncogenic characteristics of zinc finger protein 36-like 2 (ZFP36L2) in LN18 GBM cells via RNA interference (RNAi) delivery. We conducted a meta-analysis of microarray datasets and RNAi screening using pooled small interference RNA (siRNA) to identify the druggable genes responsive to GBM chemosensitivity. Temozolomide-resistant LN18 cells were used to evaluate the effects of gene silencing on chemosensitisation to the sub-lethal dose (1/10 of the median inhibitory concentration [IC50]) of temozolomide. ZFP36L2 protein expression was detected by western blotting. Cell viability, proliferation, cell cycle and apoptosis assays were carried out using commercial kits. A human apoptosis array kit was used to determine the apoptosis pathway underlying chemosensitisation by siRNA against ZFP36L2 (siZFP36L2). Statistical analyses were performed using one-way analysis of variance; p > 0.05 was considered significant. The meta-analysis and RNAi screening identified ZFP36L2 as a potential marker of GBM. ZFP36L2 knockdown significantly induced apoptosis (p < 0.05). Moreover, ZFP36L2 inhibition led to increased cell cycle arrest and decreased cell proliferation. Downstream analysis showed that the sub-lethal dose of temozolomide and siZFP26L2 caused major upregulation of BCL2-associated X, apoptosis regulator (BAX). ZFP36L2 has oncogenic and chemosensitive characteristics and may play an important role in gliomagenesis through cell proliferation, cell cycle arrest and apoptosis. This suggests that RNAi combined with chemotherapy treatment such as temozolomide may be a potential GBM therapeutic intervention in the future.

Expression of BAG1 is associated with prognosis in kidney renal clear cell carcinoma based on bioinformatics

Background

BCL2 associated Athano-Gene 1 (BAG1) has been described to be involved in the development and progression of cancer. But the role of BAG1 in kidney renal clear cell carcinoma (KIRC) has remained largely unknown.

Methods

We performed bioinformatic analysis of data from TCGA and GEO dataset. The role of BAG1 in KIRC was explored by Logistic and Cox regression model. The molecular mechanisms of BAG1 was revealed by GSEA.

Results

The current study found that the KIRC tumor samples have a low level of BAG1 mRNA expression compared to the matched normal tissues based on TCGA data and GEO databases. Low expression of BAG1 in KIRC was significantly associated with Sex, clinical pathological stage, tumor-node-metastasis (TNM) stage, hemoglobin levels, cancer status and history of neoadjuvant treatment. Kaplan-Meier survival analysis indicated that KIRC patients with BAG1 high expression have a longer survival time than those with BAG1 low expression (p < 0.000). Cox regression analysis showed that BAG1 remained independently associated with overall survival, with a hazard ratio (HR) of 1.75(CI:1.05–2.90; p = 0.029). GSEA indicated that the signaling pathways including fatty acid metabolism and oxidative phosphorylation were differentially enriched in high BAG1 expression phenotype.

Conclusions

These findings suggested that BAG1 expression may act as a potential favorable prognostic marker and challenging therapeutic target.

Caspase dependent apoptosis is required for anterior regeneration in Aeolosoma viride and its related gene expressions are regulated by the Wnt signaling pathway

Although apoptosis has been widely observed during the regenerative process, the mechanisms by which it is regulated and its roles in regeneration remained unclear. In this study, we introduced Aeolosoma viride, a fresh water annelid with an extraordinary regenerative ability as our model organism to study the functions and regulations of apoptotic caspases. Here we showed that major events of apoptosis were detected near the wounded area and showed spatial correlation with the expression patterns of caspase gene namely Avi-caspase X and two apoptosis regulators namely Avi-Bax and Avi-Bcl-xL. Next, we investigated how Avi-caspase X gene expression and apoptosis influence regeneration following head amputation. RNA interference of Avi-caspase X reduced the amounts of apoptotic cells, as well as the percentage of successful regeneration, suggesting a critical role for apoptosis in anterior regeneration of A. viride. In addition, we also discovered that the expression of apoptotic caspases was regulated by the canonical Wnt signaling pathway. Together, our study showed that caspase dependent apoptosis was critical to the anterior regeneration of A. viride, and could be regulated by the canonical Wnt signaling pathway.

SpBcl2 promotes WSSV infection by suppressing apoptotic activity of hemocytes in mud crab, Scylla paramamosain

White spot syndrome virus (WSSV) is one of the most virulent and widespread pathogens that infect almost all marine crustaceans and therefore cause huge economic losses in aquaculture. The Bcl2 protein plays a key role in the mitochondrial apoptosis pathway, which is a crucial immune response in invertebrates. However, the role of Bcl2 in apoptosis and immunoregulation in mud crab, Scylla paramamosain, is poorly understood. Here, the Bcl2 homolog (SpBcl2) in S. paramamosain was cloned and its role in WSSV infection explored. The expression of SpBcl2 increased at both the transcriptional level and post-transcriptional level after WSSV infection, while the hemocytes apoptosis decreased significantly. Furthermore, there was increase in the level of cytochrome c coupled with an upregulation in the expression of SpBcl2. These results indicated that SpBcl2 suppressed apoptosis by preventing the release of cytochrome c from mitochondria, thereby promoting WSSV replication in mud crab. The findings here therefore provide novel insight into the immune response of mud crabs to WSSV infection.

Transcriptional analysis of host responses to Marek's disease virus infection in chicken thymus

Marek's disease virus (MDV) is a cell-associated alpha-herpesvirus that causes T-cell lymphomas and nervous disorders in chickens. Different from other lymphoid organs, the thymus is the site of T-cell maturation and differentiation. However, the transcriptional response to MDV infection in the chicken thymus is still not known. In this study, we performed genome-wide expression analysis in thymus tissues of RB1B-infected chickens at different time points to investigate the molecular mechanisms of MDV pathogenesis. The number of differentially expressed genes with 2-fold or higher changes (>2) are as follows: 1,250 genes (7 dpi), 834 genes (14 dpi), 1,958 genes (21 dpi), and 2,306 genes (28 dpi). Gene ontology enrichment analysis revealed that the upregulated genes were involved in immune and inflammatory response at 7 dpi; angiogenesis, cytoskeleton organization, cell adhesion, and signal transduction showed different expressions at 21 and 28 dpi. The expression pattern of 18 randomly selected genes was confirmed by real-time RT-PCR. Several differently expressed host genes associated with tumor development are discussed. We identified the global host-gene expression pattern in the thymus of chickens that responded to MDV infection. The present data may provide groundwork for future investigation in the biology and pathogenesis of MDV.

Alzheimer's disease gene signature says: beware of brain viral infections

Background

Recent findings from a genome wide association investigation in a large cohort of patients with Alzheimer's disease (AD) and non demented controls (CTR) showed that a limited set of genes was in a strong association (p > l0^-5) with the disease.

Presentation of the hypothesis

In this report we suggest that the polymorphism association in 8 of these genes is consistent with a non conventional interpretation of AD etiology.

Nectin-2 (NC-2), apolipoprotein E (APOE), glycoprotein carcinoembryonic antigen related cell adhesion molecule- 16 (CEACAM-16), B-cell lymphoma-3 (Bcl-3), translocase of outer mitochondrial membrane 40 homolog (T0MM-40), complement receptor-1 (CR-l), APOJ or clusterin and C-type lectin domain A family-16 member (CLEC-16A) result in a genetic signature that might affect individual brain susceptibility to infection by herpes virus family during aging, leading to neuronal loss, inflammation and amyloid deposition.

Implications of the hypothesis

We hypothesized that such genetic trait may predispose to AD via complex and diverse mechanisms each contributing to an increase of individual susceptibility to brain viral infections

Cellular players in the herpes simplex virus dependent apoptosis balancing act

Apoptosis is triggered as an intrinsic defense against numerous viral infections. Almost every virus encodes apoptotic modulators, and the herpes simplex viruses (HSV) are no exception. During HSV infection, there is an intricate balance between pro- and anti-apoptotic factors that delays apoptotic death until the virus has replicated. Perturbations in the apoptotic balance can cause premature cell death and have the potential to dramatically alter the outcome of infection. Recently, certain cellular genes have been shown to regulate sensitivity to HSV-dependent apoptosis. This review summarizes current knowledge of the cellular genes that impact the apoptotic balance during HSV infection.

HERPES SIMPLEX VIRUS INFECTION AND APOPTOSIS

Consequences of human herpes simplex virus (HSV) infection include the induction of apoptosis and the concomitant synthesis of proteins which act to block this process from killing the infected cell. Recent data has clarified our current understanding of the mechanisms of induction and prevention of apoptosis by HSV. These findings emphasize the fact that modulation of apoptosis by HSV during infection is a multicomponent phenomenon. We review recent evidence showing how this important human pathogen modulates the fundamental cell death process.

Herpes simplex virus type 1 ICP27 induces p38 mitogen-activated protein kinase signaling and apoptosis in HeLa cells

The herpes simplex virus type 1 (HSV-1) protein ICP27 has been implicated in a variety of functions important for viral replication including host shutoff, viral gene expression, activation of mitogen-activated protein kinases p38 and Jun N-terminal protein kinase (JNK), and apoptosis inhibition. In the present study we sought to examine the functions of ICP27 in the absence of viral infection by creating stable HeLa cell lines that inducibly express ICP27. Here, we characterize two such cell lines and show that ICP27 expression is associated with a cellular growth defect. The observed defect is caused at least in part by the induction of apoptosis as indicated by caspase-3 activation, annexin V staining, and characteristic changes in cellular morphology. In an effort to identify the function of ICP27 responsible for inducing apoptosis, we show that ICP27 expression is sufficient to activate p38 signaling to a level that is similar to that observed during wild-type HSV-1 infection. However, ICP27 expression alone is unable to lead to a strong activation of JNK signaling. Using chemical inhibitors, we show that the ICP27-mediated activation of p38 signaling is responsible for the observed induction of apoptosis in the induced cell lines. Our findings suggest that during viral infection, ICP27 activates p38 and JNK signaling pathways via two distinct mechanisms. ICP27 directly activates p38 signaling, leading to stimulation of the host cell apoptotic pathways. In contrast, robust activation of JNK signaling by ICP27 requires one or more delayed early or late viral gene products and may be associated with the inhibition of apoptosis.

Translocation and colocalization of ICP4 and ICP0 in cells infected with herpes simplex virus 1 mutants lacking glycoprotein E, glycoprotein I, or the virion host shutoff product of the UL41 gene

In wild-type herpes simplex virus 1-infected cells, the major regulatory protein ICP4 resides in the nucleus whereas ICP0 becomes dynamically associated with proteasomes and late in infection is translocated and dispersed in the cytoplasm. Inhibition of proteasomal function results in retention or transport of ICP0 to the nucleus. We report that in cells infected with mutants lacking glycoprotein E (gE), glycoprotein I (gI), or the product of the U(L)41 gene, both ICP4 and ICP0 are translocated to the cytoplasm and coaggregate in small dense structures that, in the presence of proteasomal inhibitor MG132, also contain proteasomal components. Gold particle-conjugated antibody to ICP0 reacted in thin sections with dense protein aggregates in the cytoplasm of mutant virus-infected cells. Similar aggregates were present in the nuclei but not in the cytoplasm of wild-type virus-infected cells. Exposure of cells early in infection to MG132 does not result in retention of ICP0 as in wild-type virus-infected cells. The results suggest that the retention of ICP4 and ICP0 in the nucleus is a dynamic process that involves the function of other viral proteins that may include the Fc receptor formed by the gE/gI complex and is not merely the consequence of expression of a nuclear localization signal. It is noteworthy that in DeltaU(L)41-infected cells gE is retained in the trans-Golgi network and is not widely dispersed in cellular membranes.

In transduced cells, the US3 protein kinase of herpes simplex virus 1 precludes activation and induction of apoptosis by transfected procaspase 3

The US3 protein kinase of herpes simplex virus 1 blocks apoptosis induced by replication-incompetent virus mutants, proapoptotic members of the Bcl-2 family of proteins, and by a variety of other agents that act at the premitochondrial level in the proapoptotic cascade. To define the role of US3 in blocking apoptosis at the postmitochondrial level, we investigated the US3 protein kinase in transduced cells that were either transfected with a plasmid encoding procaspase 3 or superinfected with a proapoptotic mutant virus lacking the gene encoding the infected cell protein no. 4. (i) We show that US3 blocks the proteolytic cleavage that generates active caspase 3 from the transfected zymogen procaspase 3, concomitant with inhibition of apoptosis. (ii) Studies based on detection of fluorescence emitted upon cleavage of a synthetic caspase 3 substrate showed that expression of the US3 kinase and appearance of the cleaved substrate were mutually exclusive. (iii) An affinity-purified glutathione S-transferase (GST)-US3 fusion protein, but not the inactive GST-US3(K220N) protein, phosphorylated procaspase 3 in vitro. The studies published earlier on the effect of US3 on the upstream regulatory proteins and current studies suggest that the US3 protein kinase may act on several proteins in the proapoptotic cascade to enable the virus to complete its replication.

Porcine reproductive and respiratory syndrome virus induces apoptosis through a mitochondria-mediated pathway

As with a number of other viruses, Porcine reproductive and respiratory syndrome virus (PRRSV) has been shown to induce apoptosis, although the mechanism(s) involved remain unknown. In this study we have characterized the apoptotic pathways activated by PRRSV infection. PRRSV-infected cells showed evidence of apoptosis including phosphatidylserine exposure, chromatin condensation, DNA fragmentation, caspase activation (including caspase-8, 9, 3), and PARP cleavage. DNA fragmentation was dependent on caspase activation but blocking apoptosis by a caspase inhibitor did not affect PRRSV replication. Upregulation of Bax expression by PRRSV infection was followed by disruption of the mitochondria transmembrane potential, resulting in cytochrome c redistridution to the cytoplasm and subsequent caspase-9 activation. A crosstalk between the extrinsic and intrinsic pathways was demonstrated by dependency of caspase-9 activation on active caspase-8 and by Bid cleavage. Furthermore, in this study we provide evidence of the possible involvement of reactive oxygen species (ROS)-mediated oxidative stress in apoptosis induced by PRRSV. Our data indicated that cell death caused by PRRSV infection involves necrosis as well as apoptosis. In summary, these findings demonstrate mechanisms by which PRRSV induces apoptosis and will contribute to an enhanced understanding of PRRSV pathogenesis.

Herpes simplex virus blocks apoptosis by precluding mitochondrial cytochrome c release independent of caspase activation in infected human epithelial cells

Expression of HSV-1 genes leads to the induction of apoptosis in human epithelial HEp-2 cells but the subsequent synthesis of infected cell protein prevents the process from killing the cells. Thus, viruses unable to produce appropriate prevention factors are apoptotic. We now report that the addition of either a pancaspase inhibitor or caspase-9-specific inhibitor prevented cells infected with an apoptotic HSV-1 virus from undergoing cell death. This result indicated that HSV-1-dependent apoptosis proceeds through the mitochondrial apoptotic pathway. However, the pancaspase inhibitor did not prevent the release of cytochrome c from mitochondria, implying that caspase activation is not required for this induction of cytochrome c release by HSV-1. The release of cytochrome c was first detected at 9 hpi while caspase-9, caspase-3 and PARP processing were detected at 12 hpi. Finally, Bax accumulated at mitochondria during apoptotic, but not wild type HSV-1 infection. Together, these findings indicate that HSV-1 blocks apoptosis by precluding mitochondrial cytochrome c release in a caspase-independent manner and suggest Bax as a target in infected human epithelial cells.

Bcl-2 blocks accretion or depletion of stored calcium but has no effect on the redistribution of IP3 receptor I mediated by glycoprotein E of herpes simplex virus 1

We examined the status of stable, resting intracellular Ca2+ ([Ca2+]i) and the calcium that can be released from intracellular stores in HEp-2 or VAX-3 cells overexpressing Bcl-2 after infection with wild-type or mutant herpes simplex viruses. The mutants included viruses lacking ICP4 or ICP27 and known to induce apoptosis. We report the following. Stable Ca2+ levels decrease after infection with wild-type or mutant viruses in both HEp-2 and VAX-3 cells. The histamine-sensitive calcium stores became depleted in wild-type and mutant virus-infected cells late in infection but increased significantly in DeltaICP4- or DeltaICP27-infected cells prior to depletion. In VAX-3 cells, the depletion in calcium stores did not take place as late as 24 h after infection, concomitant with lack of visually detectable cytopathic effects. Concurrent analyses showed that the amounts of IP3 Ca2+-receptor type I (IP3R-I) remained stable throughout infection, but the intensity of the signal increased and intracellular distribution changed dramatically in both HEp-2 and VAX-3 cells infected with the wild-type and all mutant viruses, except for the mutant lacking glycoprotein E (DeltagE). In transfected HEp-2 cells, gE and gI were more effective at augmenting the signal intensity and redistribution of IP3R-I than gE or gI alone. We conclude the following. (i) Depleted histamine-sensitive calcium stores correlate with appearance of cytopathic effects. (ii) Apoptosis, the calcium stores, and cytopathic effects are regulated by Bcl-2. (iii) The changes in the distribution of IP3R-I are mediated by the viral Fc receptor complex, but the redistribution is not related to changes in stored calcium.

Role of Bcl-2 expression for productive herpes simplex virus 2 replication

Herpes simplex viruses infect a variety of cells in vitro. However, not all infected cells sustain a fully productive replication of these viruses. We have shown that, in U937 monocytoid cells, herpes simplex virus 2 (HSV-2) causes a low-productive infection characterized by apoptosis as cytopathic effect at a late stage of infection. This effect was associated with a down-regulation of the Bcl-2 protein. We therefore asked whether destabilization of Bcl-2 expression could act as a limiting factor for the productive HSV-2 infection. We found that overexpression of Bcl-2 in U937 cells dramatically increased the capability of these cells to sustain a fully productive infection, while protecting against apoptosis induced by HSV-2. Overall, our data indicate that Bcl-2 expression acts as a regulator of HSV-2 replication.

Caspase 3 activation during herpes simplex virus 1 infection

During herpes simplex virus 1 (HSV-1) infection, apoptosis is initiated by immediate early gene transcription and is later modulated by proteins synthesized in infected cells. We have previously shown that procaspase 3 levels are reduced during HSV-1 replication. We now demonstrate that a replication-defective HSV-1 recombinant virus which is incapable of packaging viral DNA into capsids activated caspase 3 but retained the ability to prevent the apoptotic process from killing the infected cells. This implies that HSV-1-dependent apoptosis is not merely a response to abortive infection. Maximum accumulation of the active form of caspase 3 accompanied complete HSV-1-dependent apoptosis. Additionally, caspase 7 was found to be activated during HSV-1-dependent apoptosis. Infected MCF-7 cells which ectopically express caspase 3 underwent more efficient apoptosis than their caspase 3-null parental counterparts, confirming that caspase 3 contributes to HSV-1-dependent apoptosis. However, caspase 3 reconstitution did not make the MCF-7 cells as sensitive as HEp-2 cells to HSV-1-dependent apoptosis, suggesting that other cellular factors may be involved in conferring resistance to this process. These results indicate that caspase 3 activation is a consequence of HSV-1 infection and have important implications in our understanding of the interactions of the virus with host cells.

Estrogen enhances the efficacy of an oncolytic HSV-1 mutant in the treatment of estrogen receptor-positive breast cancer

Oncolytic herpes simplex virus-1 (HSV-1) mutants selectively replicate in and lyse tumor cells. Viral replication is dependent on the cellular proliferative mechanism. Estrogen increases cellular proliferation and decreases apoptosis in estrogen receptor-positive (ER+) human breast cancer cells. We hypothesize that the cellular changes produced by estrogen may enhance oncolytic viral replication and improve the treatment of ER+ breast cancer cells. Estrogen increased proliferation and replication of the HSV-1 mutant, NV1066, in ER+ breast cancer cells. Additionally, cells grown with estrogen had lower rates of apoptosis and higher bcl-2 levels at baseline and after infection. Estrogen enhanced the oncolytic effect of NV1066, with cell kills of 95% and 97% at MOIs of 0.1 and 0.5, compared to 53 and 87% respectively without estrogen (p<0.001). Therapy of ER+ human breast cancer cells with a replication-competent HSV-1 mutant is improved in the presence of estrogen, in contrast to more standard therapies, such as chemotherapy and radiation, which demonstrate decreased efficacy in similar conditions. These data provide the mechanistic basis for the use of oncolytic HSV-1 in patients with hormone receptor-positive breast cancer, particularly if the disease progresses with conventional therapies.

Use of positron emission tomography to target prostate cancer gene therapy by oncolytic herpes simplex virus

Herpes simplex virus (HSV) oncolytic gene therapy is a promising treatment modality against cancer. We have demonstrated that androgen-induced cellular changes enhance oncolytic viral replication and improve efficacy in the treatment of androgen-dependent prostate cancer cell line. Imaging of changes in 2-deoxy-2-[F-18]fluoro-D-glucose (FDG) uptake by positron emission tomography (PET) is a sensitive method of detecting altered cellular metabolism involved in cancer therapy. We therefore hypothesized that FDG-PET can predict tumor response to oncolytic HSV therapy. In this study, androgen increased cell kill (74%) in vitro and enhanced viral yield (2.4-fold) in vivo following HSV therapy. This enhanced efficacy was predicted by high FDG accumulation in intact animals compared to low FDG uptake following orchiectomy (p = 0.002). This proof-of-concept study provides the mechanistic basis for selecting patients for targeted oncolytic viral therapy by means of a noninvasive molecular imaging method in the treatment of prostate cancer.

Varicella-zoster virus ORF63 inhibits apoptosis of primary human neurons

Virus-encoded modulation of apoptosis may serve as a mechanism to enhance cell survival and virus persistence. The impact of productive varicella-zoster virus (VZV) infection on apoptosis appears to be cell type specific, as infected human sensory neurons are resistant to apoptosis, yet human fibroblasts readily become apoptotic. We sought to identify the viral gene product(s) responsible for this antiapoptotic phenotype in primary human sensory neurons. Treatment with phosphonoacetic acid to inhibit viral DNA replication and late-phase gene expression did not alter the antiapoptotic phenotype, implicating immediate-early (IE) or early genes or a virion component. Compared to the parental VZV strain (rOKA), a recombinant virus unable to express one copy of the diploid IE gene ORF63 (rOka deltaORF63) demonstrated a significant induction of apoptosis in infected neurons, as determined by three methods: annexin V staining, deoxynucleotidyltransferase-mediated dUTP-biotin nick end label staining, and transmission electron microscopy. Furthermore, neurons transfected with a plasmid expressing ORF63 resisted apoptosis induced by nerve growth factor withdrawal. These results show that ORF63 can suppress apoptosis of neurons and provide the first identification of a VZV gene encoding an antiapoptotic function. As ORF63 is expressed in neurons during both productive and latent infection, it may play a significant role in viral pathogenesis by promoting neuron survival during primary and reactivated infections.

Apoptosis During Herpes Simplex Virus Infection

Herpes simplex virus (HSV) infection triggers apoptosis in infected cells. However, proteins synthesized later in infected cells prevent apoptotic cell death from ensuing. In vivo data showing that apoptosis accompanies herpes stromal keratitis and encephalitis suggest that apoptotic modulation plays a role in the development of herpetic disease. Tremendous progress has been made toward identifying the viral factors that are responsible for inducing and inhibiting apoptosis during infection. However, the mechanisms whereby they act are still largely unknown. Recent studies have illustrated a wide diversity in the cellular response to HSV-triggered apoptosis, emphasizing the importance of host factors in this process. Together, these findings indicate that apoptosis during HSV infection represents an important virus-host interaction process, which likely influences viral pathogenesis.

T-cell tropism and the role of ORF66 protein in pathogenesis of varicella-zoster virus infection

The pathogenesis of varicella-zoster virus (VZV) involves a cell-associated viremia during which infectious virus is carried from sites of respiratory mucosal inoculation to the skin. We now demonstrate that VZV infection of T cells is associated with robust virion production and modulation of the apoptosis and interferon pathways within these cells. The VZV serine/threonine protein kinase encoded by ORF66 is essential for the efficient replication of VZV in T cells. Preventing ORF66 protein expression by stop codon insertion (pOka66S) impaired the growth of the parent Oka (pOka) strain in T cells in SCID-hu T-cell xenografts in vivo and reduced formation of VZV virions. The lack of ORF66 protein also increased the susceptibility of infected T cells to apoptosis and reduced the capacity of the virus to interfere with induction of the interferon (IFN) signaling pathway following exposure to IFN-gamma. However, preventing ORF66 protein expression only slightly reduced growth in melanoma cells in culture and did not diminish virion formation in these cells. The pOka66S virus showed only a slight defect in growth in SCID-hu skin implants compared with intact pOka. These observations suggest that the ORF66 kinase plays a unique role during infection of T cells and supports VZV T-cell tropism by contributing to immune evasion and enhancing survival of infected T cells.

Selective apoptotic behaviour of bovine herpesvirus 1 in an epithelial-like microenvironment

Apoptosis seems to play an important role in the pathogenic profile of bovine herpesvirus 1 (BHV-1) infection. Nitric oxide (NO) is also important as a signal molecule. In this study, apoptosis was selectively induced in HEp-2 cells in the early stage [1-3 h postinfection (PI)] of BHV-1 multiplication, and this apoptotic process was realised through the caspase-8, and partially through the caspase-3, pathway. BHV-1 infection inhibited staurosporine- (SS-) induced apoptosis only if the SS was added at 6 h PI. The results of this study showed that the 'NO-apoptosis' relation was realised through the caspase-8 pathway ('outer membrane receptor' pathway) at a later stage of infection in apoptosis induced by BHV-1 + SS. Our previous report (Yazici et al., 2004) and this study together showed that BHV-1 might induce and inhibit cell-type-specific pathways of apoptosis.

African green monkey kidney Vero cells require de novo protein synthesis for efficient herpes simplex virus 1-dependent apoptosis

During HSV-1 infection, IE gene expression triggers apoptosis, but subsequent synthesis of infected cell proteins blocks apoptotic death from ensuing. This "HSV-1-dependent" apoptosis was identified in HEp-2/HeLa cells infected with wild-type HSV-1 in the presence of an inhibitor of protein synthesis or a virus lacking ICP27 {HSV-1(vBSDelta27)}. Unlike HEp-2/HeLa cells, vBSDelta27-infected Vero cells fail to exhibit dramatic apoptotic morphologies at times prior to 24 hpi. Here, we examined the basis of these different apoptotic responses to HSV-1. We found that infected Vero cells take substantially longer than HEp-2/HeLa cells to display membrane blebbing, chromatin condensation, DNA laddering, and PARP cleavage. Vero, but not HEp-2/HeLa, cells required de novo protein synthesis to exhibit efficient HSV-1-dependent apoptosis, which included changes in mitochondrial membrane potential, and these factors were produced prior to 3 hpi. Vero cells infected with recombinant viruses devoid of the ICP27 and ICP4 proteins alone or both the ICP27 and ICP22 proteins were apoptotic. These results indicate a requirement for cellular or other viral protein synthesis in Vero cells and provide insight into cell type differences in HSV-1-dependent apoptosis.

Aquatic birnavirus induces apoptosis through activated caspase-8 and -3 in a zebrafish cell line

In this study, the possible influence of temperature on infectious pancreatic necrosis virus (IPNV)-induced apoptosis in a zebrafish liver epithelium (ZLE) cell line was investigated. At a lower temperature (18 degrees C), there was expression of viral proteins VP2 and VP3 at 4 h post-infection (p.i.). At this time no expression was found in the high temperature group at 28 degrees C. The cell survival ratio was 52 and 18% at 24 and 48 h p.i., respectively, during IPNV infection at 18 degrees C. In addition, we assayed for apoptosis in IPNV-infected cells with terminal deoxynucleotidyl transferase (TdT)-mediated end labelling (TUNEL) of DNA at different dosages of virus. We found a ratio of apoptotic cells of 8 and 25% at 12 and 18 h p.i., respectively, in the multiplicity of infection (MOI) 1 group. The MOI 10 group had 20 and 45% apoptotic cells at 12 and 18 h, respectively. Furthermore, at 18 degrees C IPNV activated the caspase-8 and 3 from 1.5 to 2 times at 12 and 18 h p.i., respectively. Taken together, these findings suggest that successful virus replication occurs at the low temperature (18 degrees C) compared with the non-permissive temperature of 28 degrees C. Thus, IPNV replication is capable of activating caspase-8 and -3 and inducing host apoptosis.

Ocular and neuronal cell apoptosis during HSV-1 infection: a review

HSV-1 may activate or suppress the apoptotic pathway in various cells. This review will discuss this apparent dichotomy and place particular emphasis on the different strategies HSV-1 uses to block or suppress the apoptotic pathway in various cell lines and tissues.

Apoptosis induction with 5-fluorocytosine/cytosine deaminase gene therapy for human malignant glioma cells mediated by adenovirus

Previously, we evaluated the therapeutic efficacy of the adenovirus-mediated transduction of the cytosine deaminase (CD) gene and 5-fluorocytosine (5-FC) for malignant gliomas. However, the molecular pathways that mediate the 5-FC/CD gene therapy-induced cell death remains to be elucidated. In this study, we examined the induction of apoptosis and the role of caspases in 5-FC/CD gene therapy using human malignant glioma cells [Gli36delta5 (mutated p53) and U87MG (wild p53)]. The treatment with 5-FC/CD gene-therapy-induced apoptosis both in Gli36delta5 cells and in U87MG cells according to flow cytometric analysis. Immunoblot analysis revealed that caspases 3 and 9 were processed in response to 5-FC/CD in a concentration- and time-dependent manner, but caspase 8 was not. Each caspase 3 and 9 inhibitor significantly reduced apoptosis triggered by 5-FC/CD, but the caspase 8 inhibitor did not affect apoptosis induction. 5-FC/CD significantly promoted the release of cytochorme c from mitochondria in a concentration-dependent manner. These results indicate that 5-FC/CD gene therapy induces apoptosis in human malignant glioma cells and that the apoptotic cell death is mediated by the activation of mitochondrial caspase cascades involving caspases 3 and 9. This is the first report concerning the apoptotic mechanism of 5-FC/CD gene therapy, and these findings could be used to increase the efficacy of suicide gene therapy systems for the treatment of malignant glioma.

The Us3 protein kinase of herpes simplex virus 1 blocks apoptosis and induces phosporylation of the Bcl-2 family member Bad

Viruses have evolved different strategies to interfere with apoptotic pathways in order to halt cellular responses to infection. The herpes simplex virus 1 (HSV-1) Us3 open-reading frame encodes a serine/threonine protein kinase that participates in the inhibition of apoptosis induced by virus infection and other stress agents. Previous studies have shown that Us3 counteracts the virus-induced activation of caspase-3 by acting at a premitochondrial stage. Using stable transfectants that express Us3 under the control of constitutive or inducible promoters we demonstrate that apoptosis induced by treatment with anti-Fas antibody and sorbitol is blocked when Us3 is expressed at levels comparable to those achieved during virus infection. Expression of Us3 correlated with phosphorylation of Bad, a BH3-only proapoptotic Bcl-2 family member that is also a target for growth factor-induced cellular kinases. Bad was phosphorylated by Us3 in in vitro kination assays. These results point to a strategy for viral inhibition of apoptosis based on functional inactivation of a critical component of the cellular death machinery.

Protection by herpes simplex virus glycoprotein D against Fas-mediated apoptosis: role of nuclear factor kappaB

Signals involved in protection against apoptosis by herpes simplex virus 1 (HSV-1) were investigated. Using U937 monocytoid cells as an experimental model, we have demonstrated that HSV-1 rendered these cells resistant to Fas-induced apoptosis promptly after infection. UV-inactivated virus as well as the envelope glycoprotein D (gD) of HSV-1, by itself, exerted a protective effect on Fas-induced apoptosis. NF-kappaB was activated by gD, and protection against Fas-mediated apoptosis by gD was abolished in cells stably transfected with a dominant negative mutant I-kappaBalpha, indicating that NF-kappaB activation plays a role in the antiapoptotic activity of gD in our experimental model. Moreover, NF-kappaB-dependent protection against Fas-mediated apoptosis was associated with decreased levels of caspase-8 activity and with the up-regulation of intracellular antiapoptotic proteins.

The varicella-zoster virus induces apoptosis in vitro in subpopulations of primary human peripheral blood mononuclear cells

Varicella-zoster virus (VZV), a member of Herpesviridae, subfamily alpha-Herpesvirinae, is pathogenic exclusively in the human. Chickenpox is the result of primary infection of VZV. During the viremic stage, VZV infects peripheral blood mononuclear cells (PBMC) and spreads to the periphery. In skin cells it causes typical lesions. Apoptosis has been demonstrated in different cell types by other alpha-herpesviruses. VZV-infected T lymphocytes, B lymphocytes, and monocytes, respectively, were examined in this in vitro study by flow cytometry, immunofluorescence and electron microscopy. All infected cell types showed signs of apoptosis: a lower DNA content, DNA fragmentation, loss of membrane integrity, and an altered nuclear morphology. The results observed led to the suggestion that VZV can induce apoptosis during infection in vivo in the PBMC subpopulations.

The herpes simplex virus 1 US3 protein kinase blocks caspase-dependent double cleavage and activation of the proapoptotic protein BAD

An earlier report showed that the U(S)3 protein kinase blocked the apoptosis induced by the herpes simplex virus 1 (HSV-1) d120 mutant at a premitochondrial stage. Further studies revealed that the kinase also blocks programmed cell death induced by the proapoptotic protein BAD. Here we report the effects of the U(S)3 protein kinase on the function and state of a murine BAD protein. Specifically, (i) in uninfected cells, BAD was processed by at least two proteolytic cleavages that were blocked by a general caspase inhibitor. The untreated transduced cells expressed elevated caspase 3 activity. (ii) In cells cotransduced with the U(S)3 protein kinase, the BAD protein was not cleaved and the caspase 3 activity was not elevated. (iii) Inasmuch as the U(S)3 protein kinase blocked the proapoptotic activity and cleavage of a mutant (BAD3S/A) in which the codons for the regulatory serines at positions 112, 136, and 155 were each replaced with alanine codons, the U(S)3 protein kinase does not act by phosphorylation of these sites nor was the phosphorylation of these sites required for the antiapoptotic function of the U(S)3 protein kinase. (iv) The U(S)3 protein kinase did not enable the binding of the BAD3S/A mutant to the antiapoptotic proteins 14-3-3. Finally, (v) whereas cleavage of BAD at ASP56 and ASP61 has been reported and results in the generation of a more effective proapoptotic protein with an M(r) of 15,000, in this report we also show the existence of a second caspase-dependent cleavage site most likely at the ASP156 that is predicted to inactivate the proapoptotic activity of BAD. We conclude that the primary effect of U(S)3 was to block the caspases that cleave BAD at either residue 56 or 61 predicted to render the protein more proapoptotic or at residue 156, which would inactivate the protein.

Caspase-3-dependent reactivation of latent herpes simplex virus type 1 in sensory neuronal cultures

Life-long latent herpes simplex virus type 1 (HSV-1) is harbored in sensory neurons where sporadic reactivation occurs. Reactivation stimuli may involve activation of apoptotic signaling in the neuron. Previous experiments have demonstrated that reactivation of latent HSV-1 in dorsal root ganglion (DRG) neuronal cultures occurred following nerve growth factor (NGF) deprivation. NGF deprivation stimulates apoptotic signaling by activating the proapoptotic proteolytic enzyme, caspase-3. When DRG neuronal cultures harboring latent HSV-1 were treated with a caspase-3-specific inhibitor, NGF deprivation-induced reactivation was significantly reduced. Interestingly, the caspase-3 inhibitor had no effect on productive HSV-1 infection. Furthermore, activation of caspase-3 with either C2-ceramide or a recombinant adenovirus expressing caspase-3 caused significant HSV-1 reactivation.

A novel apoptotic interaction between HSV-1 and human corneal epithelial cells

PURPOSE

Herpes simplex virus type 1 (HSV-1) infects the cornea possibly causing blindness. The specific mechanisms of herpetic keratitis are unclear. We aimed to investigate whether HSV-1 would up- or down-regulate the apoptotic pathway of human corneal epithelial (HCE) cells.

METHODS

HSV-1 infection of HCE and Vero cells was demonstrated (immunofluorescence) and apoptotic gene expression was quantified (ribonuclease protection assay). Caspase 8 protein activity (colorimetric assay) was quantified and compared to caspase 8 mRNA amounts from RPA experiments. The apoptotic index of HSV-1 infected HCE and Vero cells (apoptotic index = % of apoptotic cells in infected samples/mock treated samples) was obtained and compared to gene expression.

RESULTS

A down-regulation in apoptotic gene expression was observed in HSV-1 infected HCE cells in contrast to Vero cells (infected and mock treated). Caspase 8 protein levels mirrored caspase 8 mRNA levels in HSV-1 infected HCE cells. The apoptotic index also supports this down-regulation. HSV-1 infected human corneal epithelial cells and Vero cells at similar rates.

CONCLUSION

HSV-1 down-regulates the apoptotic pathway of human corneal epithelial cells. This down-regulation of apoptotic gene expression seems to be cell specific. Also infectivity is excluded in playing a role in regulation of the apoptotic pathway because HSV-1 replicated at similar rates in HCE and Vero cells.

Infected cell protein No. 22 is subject to proteolytic cleavage by caspases activated by a mutant that induces apoptosis

Earlier reports have shown that the d120 mutant of herpes simplex virus 1 lacking both copies of the gene encoding the infected cells protein No. 4 (ICP4) induces apoptosis in a variety of cell lines. The programmed cell death induced by this mutant is blocked by overexpression of Bcl-2 or by transduction of infected cells with the gene encoding the viral U(S)3 protein kinase. HEp-2 cells infected with the d120 mutant express predominantly alpha proteins. Studies on these proteins revealed the accumulation of a M(r) 37,500 protein that reacted with antibody directed against the carboxyl-terminal domain of ICP22. We report that the M(r) 37,500 protein is a product of the proteolytic cleavage of ICP22 by a caspase activated by the d120 mutant. Thus the accumulation of the M(r) 37,500 protein was blocked in cells transduced with the U(S)3 protein kinase, in cells overexpressing Bcl-2, or in infected cells treated with the general caspase inhibitor zVAD-fmk. Exposure of ICP22 made in wild-type virus-infected cells to caspase 3 yielded two polypeptides, of which one could not be differentiated from the M(r) 37,500 protein with respect to electrophoretic mobility. We conclude that the cellular apoptotic response targets at least one viral protein for destruction.

Bovine herpesvirus 1 U(S) ORF8 protein induces apoptosis in infected cells and facilitates virus egress

The bovine herpesvirus 1 (BHV-1) U(S) ORF8 protein with homology to the Us9 protein of other alphaherpesviruses induces apoptosis in rabbit kidney (RK13) cells without the presence of other BHV-1-encoded proteins. In this article, we have characterized the cytotoxicity and growth behavior of a BHV-1 recombinant, BHV-1/D8, which fails to express the U(S) ORF8 protein in infected cells. BHV-1/D8 exhibited a reduced cytotoxicity to RK13 cells when compared to the cytotoxicity of control BHV-1 strains. In RK13 cells, the onset of apoptosis was not observed during the infection with BHV-1/D8, and the virus multiplication of BHV-1/D8 was markedly greater than that of control viruses. However, virus release of progeny viruses from the infected RK13 cells into culture supernatant was significantly decreased by the loss of the U(S) ORF8 protein. These data demonstrate that the U(S) ORF8 protein activates the apoptotic process and facilitates virus release from the BHV-1-infected cells.

Reovirus-induced apoptosis requires both death receptor- and mitochondrial-mediated caspase-dependent pathways of cell death

Apoptosis plays an important role in the pathogenesis of many viral infections. Despite this fact, the apoptotic pathways triggered during viral infections are incompletely understood. We now provide the first detailed characterization of the pattern of caspase activation following infection with a cytoplasmically replicating RNA virus. Reovirus infection of HEK293 cells results in the activation of caspase-8 followed by cleavage of the pro-apoptotic protein Bid. This initiates the activation of the mitochondrial apoptotic pathway leading to release of cytochrome c and activation of caspase-9. Combined activation of death receptor and mitochondrial pathways results in downstream activation of effector caspases including caspase-3 and caspase-7 and cleavage of cellular substrates including PARP. Apoptosis is initiated by death receptor pathways but requires mitochondrial amplification producing a biphasic pattern of caspase-8, Bid, and caspase-3 activation.

Friendly fire: redirecting herpes simplex virus-1 for therapeutic applications

Herpes simplex virus-1 (HSV-1) is a relatively large double-stranded DNA virus encoding at least 89 proteins with well characterized disease pathology. An understanding of the functions of viral proteins together with the ability to genetically engineer specific viral mutants has led to the development of attenuated HSV-1 for gene therapy. This review highlights the progress in creating attenuated genetically engineered HSV-1 mutants that are either replication competent (viral non-essential gene deleted) or replication defective (viral essential gene deleted). The choice between a replication-competent or -defective virus is based on the end-goal of the therapeutic intervention. Replication-competent HSV-1 mutants have primarily been employed as antitumor oncolytic viruses, with the lytic nature of the virus harnessed to destroy tumor cells selectively. In replacement gene therapy, replication-defective viruses have been utilized as delivery vectors. The advantages of HSV-1 vectors are that they infect quiescent and dividing cells efficiently and can encode for relatively large transgenes.

Cation-independent mannose 6-phosphate receptor blocks apoptosis induced by herpes simplex virus 1 mutants lacking glycoprotein D and is likely the target of antiapoptotic activity of the glycoprotein

Herpes simplex virus 1 mutants lacking the gene encoding glycoprotein D (gD) and the gD normally present in the envelope of the virus (gD(-/-) stocks) or mutants lacking the gD gene but containing trans-induced gD in their envelopes (gD(-/+)) cause apoptosis in human SK-N-SH cells. The gD(-/-) virions are taken up by endocytosis and are degraded, whereas gD(-/+) viruses replicate but produce gD(-/-) virus. Apoptosis is blocked by delivery of the gD gene in trans. Studies designed to test several hypotheses concerning the role of gD in apoptosis revealed the following. (i) gD(-/-) and gD(-/+) stocks induce fragmentation of cellular DNA in SK-N-SH, HEp-2, HeLa, and Vero cell lines. (ii) Chloroquine blocks apoptosis induced by gD(-/-) stocks but not by gD(-/+) stocks. The drug also rescues gD(-/-) from degradation. (iii) Cells transduced with cation-independent mannose 6-phosphate receptor (CI-MPR) block apoptosis induced by either gD(-/-) or gD(-/+) virus. (iv) Expression of sequences antisense to the cloned CI-MPR gene induced apoptosis by themselves. Wild-type virus but not gD(-/-) or gD(-/+) stocks of mutant virus blocked apoptosis induced by the expression of CI-MPR antisense sequences. These results exclude the possibility that to block apoptosis, gD must interact with its HveA receptor, a member of the tumor necrosis factor alpha receptor family. Instead, the data suggest that gD blocks the influx of lysosomal enzymes into the endosomal compartment by binding to CI-MPR. This conclusion is consistent with published reports that phosphorylated gD interacts with CI-MPR.

Caspase activation in equine influenza virus induced apoptotic cell death

Equine influenza virus (EIV) is the leading cause of acute respiratory infection in horses worldwide. In recent years, the precise mechanism by which influenza infection kills host cells is being re-evaluated. In this report, we examined whether caspases, a group of intracellular proteases, are activated following EIV infection and contribute to EIV-mediated cell death. Western blotting analysis indicated that a nuclear target of caspase-3, poly(ADP-ribose) polymerase (PARP) was proteolytically cleaved in EIV-infected MDCK cells, but not in mock-infected cells. In comparison with caspase-3 specific inhibitor Ac-DEVD-CHO, a general caspase inhibitor Boc-D-FMK provided much stronger inhibition of EIV-induced cytopathic effect and apoptosis. Our results suggest that EIV may activate more than one caspase. Caspase activation and cleavage of its cellular targets may play a critical role in EIV-mediated cytotoxicity.

U(S)3 protein kinase of herpes simplex virus 1 blocks caspase 3 activation induced by the products of U(S)1.5 and U(L)13 genes and modulates expression of transduced U(S)1.5 open reading frame in a cell type-specific manner

The coding domain of the herpes simplex virus type 1 (HSV-1) alpha22 gene encodes two proteins, the 420-amino-acid infected-cell protein 22 (ICP22) and U(S)1.5, a protein colinear with the carboxyl-terminal domain of ICP22. In HSV-1-infected cells, ICP22 and U(S)1.5 are extensively modified by the U(L)13 and U(S)3 viral protein kinases. In this report, we show that in contrast to other viral proteins defined by their properties as alpha proteins, U(S)1.5 becomes detectable and accumulated only at late times after infection. Moreover, significantly more U(S)1.5 protein accumulated in cells infected with a mutant lacking the U(L)13 gene than in cells infected with wild-type virus. To define the role of viral protein kinases on the accumulation of U(S)1.5 protein, rabbit skin cells or Vero cells were exposed to recombinant baculoviruses that expressed U(S)1.5, U(L)13, or U(S)3 proteins under a human cytomegalovirus immediate-early promoter. The results were as follows. (i) Accumulation of the U(S)1.5 protein was reduced by concurrent expression of the U(L)13 protein kinase and augmented by concurrent expression of the U(S)3 protein kinase. The magnitude of the reduction or increase in the accumulation of the U(S)1.5 protein was cell type dependent. The effect of U(L)13 kinase appears to be specific inasmuch as it did not affect the accumulation of glycoprotein D in cells doubly infected by recombinant baculoviruses expressing these genes. (ii) The reduction in accumulation of the U(S)1.5 protein was partially due to proteasome-dependent degradation. (iii) Both U(S)1.5 and U(L)13 proteins activated caspase 3, indicative of programmed cell death. (iv) Concurrent expression of the U(S)3 protein kinase blocked activation of caspase 3. The results are concordant with those published elsewhere (J. Munger and B. Roizman, Proc. Natl. Acad. Sci. USA 98:10410-10415, 2001) that the U(S)3 protein kinase can block apoptosis by degradation or posttranslational modification of BAD.

Interaction of alpha-2-macroglobulin and HSV-1 during infection of neuronal cells

We describe the effect of pretreatment with alpha-2-macroglobulin (A2M) on the susceptibility of the human neuroblastoma SKNMC cell line to infection by herpes virus type 1 (HSV-1). ELISA and co-immunoprecipitation experiments confirmed the A2M-HSV-1 interaction in vitro. Indirect immunofluorescence shows that A2M exacerbated the cytopathic effect induced after HSV-1 infection. However, A2M-pretreated SKNMC cells notably produced fewer HSV-1 particles than did the untreated cells, suggesting that A2M could induce a restrictive infection. Furthermore, high levels of HSV-1 and A2M induced the production of nitric oxide (NO) in SKNMC. Preliminary results suggest that A2M might induce apoptosis in HSV-1-infected cells. These findings affirm the conclusion that A2M may interact directly with HSV-1 and modulate the course of the infection in SKNMC human neuroblastoma cells.

The US3 protein kinase of herpes simplex virus 1 mediates the posttranslational modification of BAD and prevents BAD-induced programmed cell death in the absence of other viral proteins

Earlier studies have shown that the d120 mutant of herpes simplex virus 1, which lacks both copies of the alpha4 gene, induces apoptosis in all cell lines tested. In some cell lines d120-induced apoptosis, manifested by the release of cytochrome c, activation of caspase 3, and fragmentation of cellular DNA, is blocked by the overexpression of Bcl-2. In these cells viral protein kinase U(S)3 delivered in trans blocks apoptosis induced by the mutant virus at a premitochondrial stage. We report that the U(S)3 protein kinase targets the pro-apoptotic BAD member of the Bcl-2 family. Specifically, the U(S)3 protein kinase mediates a posttranslational modification of BAD and blocks its cleavage, which is reported to activate apoptosis. Thus, U(S)3 protein kinase is the sole viral protein required to block activation of caspase 3, prevent cleavage of poly(ADP-ribose) polymerase, and block fragmentation of cellular DNA induced by BAD.

Modulation of apoptosis during herpes simplex virus infection in human cells

Human herpes simplex virus (HSV) is cytolytic and has profound impacts on its host cells. Consequences of HSV infection include the induction of apoptosis and the concomitant synthesis of proteins which act to block this process. We review recent evidence showing how this important human pathogen modulates the fundamental cell death process.

The domains of glycoprotein D required to block apoptosis depend on whether glycoprotein D is present in the virions carrying herpes simplex virus 1 genome lacking the gene encoding the glycoprotein

An earlier report showed that viruses lacking the open reading frames encoding glycoproteins J and D but containing the glycoprotein D in their envelopes (gD-/+ stocks) and viruses lacking both the open reading frames and the glycoproteins in their envelopes (gD-/- stocks) induce apoptosis (G. Zhou, V. Galvan, G. Campadelli-Fiume, and B. Roizman, J. Virol. 74:11782-11791, 2000). Furthermore, apoptosis was blocked by delivery in trans of genes expressing glycoprotein D or J. Whereas gD-/- stocks attach but cannot initiate productive infection, gD-/+ stocks infect cells and produce gD-/- progeny virus. The difference in the infectivity of these two stocks suggested the possibility that the requirements for blocking apoptosis may be different. To test this hypothesis, we cloned into baculoviruses the entire wild-type glycoprotein D (Bac-gD-WT), the ectodomain only (Bac-gD-A), the ectodomain and the transmembrane domain (Bac-gD-B), the ectodomain and the cytoplasmic domain without the transmembrane domain (Bac-gD-C), or the transmembrane domain and the carboxyl-terminal cytoplasmic domain (Bac-gD-D). We report the following. Apoptosis induced by gD-/+ stocks was blocked by delivery in trans of recombinant baculovirus Bac-gD-WT, Bac-gD-A, Bac-gD-B, or Bac-gD-C but not of Bac-gD. Apoptosis induced by gD-/- stocks was blocked by Bac-gD-WT or by a mixture of Bac-gD-B and Bac-gD-D but not by any baculoviruses expressing truncated glycoprotein D alone or by the mixture of Bac-gD-A and Bac-gD-D. We conclude that the requirements to block apoptosis induced by the two virus stocks are different. The gD ectodomain is sufficient to block apoptosis induced by gD, whereas both the ectodomain and the cytoplasmic domain are required to block apoptosis induced by gD-/- stocks. The results indicate that in the case of gD-/- stocks, the transmembrane domain is required either to deliver the ectodomain to the appropriate intracellular compartment or to form multimeric constructs which virtually reconstitute gD through the interaction of transmembrane domains.

The U(S)3 protein kinase blocks apoptosis induced by the d120 mutant of herpes simplex virus 1 at a premitochondrial stage

Earlier studies have shown that the d120 mutant of herpes simplex virus 1, which lacks both copies of the alpha4 gene, induces caspase-3-dependent apoptosis in HEp-2 cells. Apoptosis was also induced by the alpha4 rescuant but was blocked by the complementation of rescuant with a DNA fragment encoding the U(S)3 protein kinase (R. Leopardi and B. Roizman, Proc. Natl. Acad. Sci. USA 93:9583-9587, 1996, and R. Leopardi, C. Van Sant, and B. Roizman, Proc. Natl. Acad. Sci. USA 94:7891-7896, 1997). To investigate its role in the apoptotic cascade, the U(S)3 open reading frame was cloned into a baculovirus (Bac-U(S)3) under the control of the human cytomegalovirus immediate-early promoter. We report the following. (i) Bac-U(S)3 blocks processing of procaspase-3 to active caspase. Procaspase-3 levels remained unaltered if superinfected with Bac-U(S)3 at 3 h after d120 mutant infection, but significant amounts of procaspase-3 remained in cells superinfected with Bac-Us3 at 9 h postinfection with d120 mutant. (ii) The U(S)3 protein kinase blocks the proapoptotic cascade upstream of mitochondrial involvement inasmuch as Bac-U(S)3 blocks release of cytochrome c in cells infected with the d120 mutant. (iii) Concurrent infection of HEp-2 cells with Bac-U(S)3 and the d120 mutant did not alter the pattern of accumulation or processing of ICP0, -22, or -27, and therefore U(S)3 does not appear to block apoptosis by targeting these proteins.

Requirements for the nuclear-cytoplasmic translocation of infected-cell protein 0 of herpes simplex virus 1

Earlier studies have shown that wild-type infected-cell protein 0 (ICP0), a key herpes simplex virus regulatory protein, translocates from the nucleus to the cytoplasm of human embryonic lung (HEL) fibroblasts within several hours after infection (Y. Kawaguchi, R. Bruni, and B. Roizman, J. Virol. 71:1019-1024, 1997). Translocation of ICP0 was also observed in cells infected with the d120 mutant, in which both copies of the gene encoding ICP4, the major regulatory protein, had been deleted (V. Galvan, R. Brandimarti, J. Munger, and B. Roizman, J. Virol. 74:1931-1938, 2000). Furthermore, a mutant (R7914) carrying the D199A substitution in ICP0 does not bind or stabilize cyclin D3 and is retained in the nucleus (C. Van Sant, P. Lopez, S. J. Advani, and B. Roizman, J. Virol. 75:1888-1898, 2001). Studies designed to elucidate the requirements for the translocation of ICP0 between cellular compartments revealed the following. (i) Translocation of ICP0 to the cytoplasm in productive infection maps to the D199 amino acid, inasmuch as wild-type ICP0 delivered in trans to cells infected with an ICP0 null mutant was translocated to the cytoplasm whereas the D199A-substituted mutant ICP0 was not. (ii) Translocation of wild-type ICP0 requires a function expressed late in infection, inasmuch as phosphonoacetate blocked the translocation of ICP0 in wild-type virus-infected cells but not in d120 mutant-infected cells. Moreover, whereas in d120 mutant-infected cells ICP0 was translocated rapidly from the cytoplasm to the nucleus at approximately 5 h after infection, the translocation of ICP0 in wild-type virus-infected cells extended from 5 to at least 9 h after infection. (iii) In wild-type virus-infected cells, the MG132 proteasomal inhibitor blocked the translocation of ICP0 to the cytoplasm early in infection, but when added late in infection, it caused ICP0 to be relocated back to the nucleus from the cytoplasm. (iv) MG132 blocked the translocation of ICP0 in d120 mutant-infected cells early in infection but had no effect on the ICP0 aggregated in vesicle-like structures late in infection. However, in d120 mutant-infected cells treated with MG132 at late times, proteasomes formed a shell-like structure around the aggregated ICP0. These structures were not seen in wild-type virus or R7914 mutant-infected cells. The results indicate the following. (i) In the absence of beta or gamma protein synthesis, ICP0 dynamically associates with proteasomes and is translocated to the cytoplasm. (ii) In cells productively infected beyond alpha gene expression, ICP0 is retained in the nucleus until after the onset of viral DNA synthesis and the synthesis of gamma2 proteins. (iii) Late in infection, ICP0 is actively sequestered in the cytoplasm by a process mediated by proteasomes, inasmuch as interference with proteasomal function causes rapid relocation of ICP0 to the nucleus.

Herpes simplex virus type 1 blocks the apoptotic host cell defense mechanisms that target Bcl-2 and manipulates activation of p38 mitogen-activated protein kinase to improve viral replication

Wild-type (wt) herpes simplex virus type 1 (HSV-1) suppresses cell death. We investigated the apoptotic pathways triggered during infection with mutant viruses tsk and 27lacZ (which lack functional ICP4 and ICP27 viral proteins, respectively) and examined the mechanisms used by wt HSV-1 to protect against programmed cell death induced by the DNA-damaging compound cisplatin. In our studies, we used BHK and HeLa cells, with similar results. We suggest that a decrease in the levels of Bcl-2 protein is a key event during apoptosis induced by the mutant viruses and that Bcl-2 levels are targeted by (i) a decrease of bcl-2 RNA, (ii) caspase-related proteolysis, and (iii) p38 mitogen-activated protein kinase (p38MAPK)-dependent destabilization of Bcl-2 protein. We show that wt HSV-1, but not the mutant viruses, maintains bcl-2 RNA and protein levels during infection and protects from the cisplatin-induced decrease in bcl-2 RNA; our data suggest that both ICP27 and ICP4 are required for this function. Additionally, wt HSV-1 evades but does not actively block activation of caspases. Although wt HSV-1 induces p38MAPK activation during infection, it prevents p38MAPK-dependent destabilization of Bcl-2 and exploits p38MAPK stimulation to enhance transcription of specific viral gene promoters to increase viral yields.

Accumulation of herpes simplex virus type 1 early and leaky-late proteins correlates with apoptosis prevention in infected human HEp-2 cells

We previously reported that a recombinant ICP27-null virus stimulated, but did not prevent, apoptosis in human HEp-2 cells during infection (M. Aubert and J. A. Blaho, J. Virol. 73:2803-2813, 1999). In the present study, we used a panel of 15 recombinant ICP27 mutant viruses to determine which features of herpes simplex virus type 1 (HSV-1) replication are required for the apoptosis-inhibitory activity. Each virus was defined experimentally as either apoptotic, partially apoptotic, or nonapoptotic based on infected HEp-2 cell morphologies, percentages of infected cells with condensed chromatin, and patterns of specific cellular death factor processing. Viruses d27-1, d1-5, d1-2, M11, M15, M16, n504R, n406R, n263R, and n59R are apoptotic or partially apoptotic in HEp-2 cells and severely defective for growth in Vero cells. Viruses d2-3, d3-4, d4-5, d5-6, and d6-7 are nonapoptotic, demonstrating that ICP27 contains a large amino-terminal region, including its RGG box RNA binding domain, which is not essential for apoptosis prevention. Accumulations of viral TK, VP16, and gD but not gC, ICP22, or ICP4 proteins correlated with prevention of apoptosis during the replication of these viruses. Of the nonapoptotic viruses, d4-5 did not produce gC, indicating that accumulation of true late gene products is not necessary for the prevention process. Analyses of viral DNA synthesis in HEp-2 cells indicated that apoptosis prevention by HSV-1 requires that the infection proceeds to the stage in which viral DNA replication takes place. Infections performed in the presence of the drug phosphonoacetic acid confirmed that the process of viral DNA synthesis and the accumulation of true late (gamma(2)) proteins are not required for apoptosis prevention. Based on our results, we conclude that the accumulation of HSV-1 early (beta) and leaky-late (gamma(1)) proteins correlates with the prevention of apoptosis in infected HEp-2 cells.