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

Manipulation of Host Cell Death Pathways by Herpes Simplex Virus

Herpes simplex virus (HSV)-1 and HSV-2 are ubiquitous human pathogens that infect keratinized epithelial surfaces and establish lifelong latent infection in sensory neurons of the peripheral nervous system. HSV-1 causes oral cold sores, and HSV-2 causes genital lesions characterized by recurrence at the site of the initial infection. In multicellular organisms, cell death plays a pivotal role in host defense by eliminating pathogen-infected cells. Apoptosis and necrosis are readily distinguished types of cell death. Apoptosis, the main form of programmed cell death, depends on the activity of certain caspases, a family of cysteine proteases. Necroptosis, a regulated form of necrosis that is unleashed when caspase activity is compromised, requires the activation of receptor-interacting protein (RIP) kinase 3 (RIPK3) through its interaction with other RIP homotypic interaction motif (RHIM)-containing proteins such as RIPK1. To ensure lifelong infection in the host, HSV carries out sophisticated molecular strategies to evade host cell death responses during viral infection. HSV-1 is a well-characterized pathogen that encodes potent viral inhibitors that modulate both caspase activation in the apoptosis pathway and RIPK3 activation in the necroptosis pathway in a dramatic, species-specific fashion. The viral UL39-encoded viral protein ICP6, the large subunit of the virus-encoded ribonucleotide reductase, functions as a suppressor of both caspase-8 and RHIM-dependent RIPK3 activities in the natural human host. In contrast, ICP6 RHIM-mediated recruitment of RIPK3 in the nonnatural mouse host drives the direct activation of necroptosis. This chapter provides an overview of the current state of the knowledge on molecular interactions between HSV-1 viral proteins and host cell death pathways and highlights how HSV-1 manipulates cell death signals for the benefit of viral propagation.

The Race between Host Antiviral Innate Immunity and the Immune Evasion Strategies of Herpes Simplex Virus 1

Herpes simplex virus 1 (HSV-1) is very successful in establishing acute and latent infections in humans by counteracting host antiviral innate immune responses. HSV-1 has evolved various strategies to evade host antiviral innate immunity and some cellular survival-associated pathways. Since there is still no vaccine available for HSV-1, a continuous update of information regarding the interaction between HSV-1 infection and the host antiviral innate immunity will provide novel insights to develop new therapeutic strategies for HSV-1 infection and its associated diseases. Here, we update recent studies about how HSV-1 evades the host antiviral innate immunity, specifically how HSV-1 proteins directly or indirectly target the adaptors in the antiviral innate immunity signaling pathways to downregulate the signal transduction. Additionally, some classical intracellular stress responses, which also play important roles in defense of viral invasion, will be discussed here. With a comprehensive review of evasion mechanisms of antiviral innate immunity by HSV-1, we will be able to develop potential new targets for therapies and a possible vaccine against HSV-1 infections.

The interplay between human herpes simplex virus infection and the apoptosis and necroptosis cell death pathways

Human herpes simplex virus (HSV) is a ubiquitous human pathogen that establishes a lifelong latent infection and is associated with mucocutaneous lesions. In multicellular organisms, cell death is a crucial host defense mechanism that eliminates pathogen-infected cells. Apoptosis is a well-defined form of programmed cell death executed by a group of cysteine proteases, called caspases. Studies have shown that HSV has evolved strategies to counteract caspase activation and apoptosis by encoding anti-apoptotic viral proteins such as gD, gJ, Us3, LAT, and the ribonucleotide reductase large subunit (R1). Recently, necroptosis has been identified as a regulated form of necrosis that can be invoked in the absence of caspase activity. Receptor-interacting kinase 3 (RIP3 or RIPK3) has emerged as a central signaling molecule in necroptosis; it is activated via interaction with other RIP homotypic interaction motif (RHIM)-containing proteins such as RIP1 (or RIPK1). There is increasing evidence that HSV R1 manipulates necroptosis via the RHIM-dependent inactivation or activation ofRIP3 in a species-specific manner. This review summarizes the current understanding of the interplay between HSV infection and cell death pathways, with an emphasis on apoptosis and necroptosis.

Inhibition of Bim enhances replication of varicella-zoster virus and delays plaque formation in virus-infected cells

Programmed cell death (apoptosis) is an important host defense mechanism against intracellular pathogens, such as viruses. Accordingly, viruses have evolved multiple mechanisms to modulate apoptosis to enhance replication. Varicella-zoster virus (VZV) induces apoptosis in human fibroblasts and melanoma cells. We found that VZV triggered the phosphorylation of the proapoptotic proteins Bim and BAD but had little or no effect on other Bcl-2 family members. Since phosphorylation of Bim and BAD reduces their proapoptotic activity, this may prevent or delay apoptosis in VZV-infected cells. Phosphorylation of Bim but not BAD in VZV-infected cells was dependent on activation of the MEK/extracellular signal-regulated kinase (ERK) pathway. Cells knocked down for Bim showed delayed VZV plaque formation, resulting in longer survival of VZV-infected cells and increased replication of virus, compared with wild-type cells infected with virus. Conversely, overexpression of Bim resulted in earlier plaque formation, smaller plaques, reduced virus replication, and increased caspase 3 activity. Inhibition of caspase activity in VZV-infected cells overexpressing Bim restored levels of virus production similar to those seen with virus-infected wild-type cells. Previously we showed that VZV ORF12 activates ERK and inhibits apoptosis in virus-infected cells. Here we found that VZV ORF12 contributes to Bim and BAD phosphorylation. In summary, VZV triggers Bim phosphorylation; reduction of Bim levels results in longer survival of VZV-infected cells and increased VZV replication.

Viruses and Langerhans cells

Langerhans cells (LCs) are the resident dendritic cells (DCs) of epidermis in human mucosal stratified squamous epithelium and the skin. A phenotypically similar DC has recently been discovered as a minor population in the murine dermis. In epidermis, LCs function as sentinel antigen-presenting cells that can capture invading viruses such as herpes simplex virus (HSV), varicella-zoster virus (VZV) and human immunodeficiency virus (HIV). This interaction between LCs and viruses results in highly variable responses, depending on the virus as discussed in this review. For example, HSV induces apoptosis in LCs but HIV does not. LCs seem to be the first in a complex chain of antigen presentation to T cells in lymph nodes for HSV and possibly VZV, or they transport virus to T cells, as described for HIV and maybe VZV. Together with epidermal keratinocytes they may also have a role in the initial innate immune response at the site of infection in the epidermis, although this is not fully known. The full spectrum of biological responses of LCs even to these viruses has yet to be understood and will require complementary studies in human LCs in vitro and in murine models in vivo.

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.

Langerhans cells and viral immunity

Langerhans cells (LC) are a unique dendritic cell subset that are located in mucosal stratified squamous epithelium and skin epidermis. Their location is ideally suited for their function as antigen presenting cells that capture invading viruses and induce anti-viral immunity. However, it is becoming evident that the interaction between LC and viruses can result in different responses, depending on the virus and the receptors involved. Here we will discuss the recent data on the similarities and differences in roles of LC in viral immunity to and infection with HIV, herpes simplex and varicella-zoster virus. Although all three viruses interact with LC during initial infection, the effects can be quite different, reflecting differences in biology and pathogenesis.

Involvement of gD/HVEM interaction in NF-kB-dependent inhibition of apoptosis by HSV-1 gD

In the present paper, we aimed to verify whether the interaction of the glycoprotein D (gD) of herpes simplex 1 (HSV-1) with the HSV-1 receptor HVEM is involved in NF-kappaB-dependent protection against apoptosis by gD. To this purpose, first we utilized MAbs that interfere with gD/HVEM interaction and U937 cells that naturally express human HVEM on their surface. Pre-incubation with these MAbs, but not with a control antibody, partially reverted the protection of infectious HSV-1 towards anti-Fas induced apoptosis in U937 cells. Similarly, pre-incubation of UV-inactivated HSV-1 (UV-HSV-1) or recombinant gD with the same MAbs, significantly reduced the inhibition of Fas-mediated apoptosis by UV-HSV-1 or gD, respectively, in U937 cells. Moreover, coculture with stable transfectants expressing at surface level wild type gD protected U937 cells against Fas-induced apoptosis, while coculture with transfectants expressing a mutated form of gD, incapable to bind HVEM, did not protect. Finally, UV-HSV-1 protected against staurosporine-induced apoptosis in U937 cells as well as in the CHO transfectants expressing human HVEM on their surface, but not in the control CHO transfectants, which did not express HVEM. These results suggest that signaling triggered by binding of gD to HVEM could represent an additional mechanism of evasion from premature apoptotic death exerted by HSV-1-gD in HVEM-expressing cells, disclosing new opportunities of cell death manipulation by using gD preparations.

Herpes simplex virus type 1 ICP4 deletion mutant virus d120 infection failed to induce apoptosis in nerve growth factor-differentiated PC12 cells

It has been suggested that terminally differentiated neuronal cells and mitotic cells respond differently in many aspects to herpes simplex virus type 1 (HSV-1) infection. The ICP4-deleted, Us3-defective, HSV-1 mutant strain d120 induces classical apoptosis in a variety of mitotic cell lines. Its behavior in postmitotic cells is not known. Here the authors report that mutant d120 virus failed to induce apoptosis in neuronal-like, nerve growth factor (NGF)-differentiated PC12 cells. More strikingly, rather than inducing apoptosis, d120 infection prolonged the life of nondividing NGF-differentiated PC12 cells in the culture flask. The virus genome had a half-life of 30 days. Unlike in other cells, such as Vero, neither wild-type nor d120 infection of NGF-differentiated PC12 cells induced the nuclear factor (NF)-kappa B p65 pathway, which has been associated with virus-induced apoptosis. Thus, the authors demonstrate, for the first time, that a potent apoptosis inducer mutant d120 failed to induce apoptosis in neuronal-like NGF-differentiated PC12 cells, unlike a number of other cell lines studied. The possible mechanisms involved in the failure of d120 to induce apoptosis in neuronal-like NGF-differentiated PC12 cells are discussed.

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.

Apoptosis and antigen receptor function in T and B cells following exposure to herpes simplex virus

T cells are an essential component of the immune response against herpes simplex virus (HSV) infection. We previously reported that incubation of T cells with HSV-infected fibroblasts inhibits subsequent T cell antigen receptor signal transduction. In the current study, we found that incubation of T cells with HSV-infected fibroblasts also leads to apoptosis in exposed T cells. Apoptosis was observed in Jurkat cells, a T cell leukemia line, and also in CD4(+) cells isolated from human peripheral blood mononuclear cells. Direct infection of these cells with HSV also resulted in apoptosis. Clinical isolates of both HSV type 1 and 2 induced apoptosis in infected T cells at comparable levels to cells infected with laboratory strains of HSV, suggesting an immune evasion mechanism that may be clinically relevant. Further understanding of these viral immune evasion mechanisms could be exploited for better management of HSV infection.

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.

Herpes simplex virus 1 recombinant virions exhibiting the amino terminal fragment of urokinase-type plasminogen activator can enter cells via the cognate receptor

Earlier this laboratory constructed a herpes simplex virus 1 recombinant (R5111) that carries a IL13 ligand inserted into glycoprotein D and can enter cells via the IL13Ralpha2 receptor commonly expressed on the surface of malignant glioma cells. In this report, we describe the properties of two recombinant viruses carrying chiemric gD genes. In R5181 recombinant virus the chimeric gene consisted on the residues 20-155 of urokinase plaminogen activator (uPA) inserted between residues 24 and 25 of gD. In R5182 the insert consisted of a 23-residue sequence encoding the uPA binding domain for the urokinase plaminogen activator receptor (uPAR). These viruses were constructed for three reasons, to increase the number of viruses that specifically target receptors on the surface of malignant glioma cells, to determine whether viruses exhibiting novel ligands could enter cells via receptors anchored to the cell surface via glycosylphosphatidylinositol anchor as has been recently demonstrated for nectin1, and to determine whether receptors other than IL13Ralpha2 could be targeted by genetic engineering of the virus. We report that R5181 but not R5182 recombinant virus was able to enter cells expressing uPAR. The results indicate that HSV-1 recombinant viruses can be engineered to enter cells via a variety of unrelated nonviral receptors, including receptors that are anchored to the cells surface but without transmembrane domains.

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.

Efficient replication by herpes simplex virus type 1 involves activation of the IkappaB kinase-IkappaB-p65 pathway

Infection by herpes simplex virus type 1 (HSV-1) induces a persistent nuclear translocation of NFkappaB. To identify upstream effectors of NFkappaB and their effect on virus replication, we employed mouse embryo fibroblast (MEF)-derived cell lines with deletions of either IKK1 or IKK2, the catalytic subunits of the IkappaB kinase (IKK) complex. Infected MEFs were assayed for virus yield, loss of IkappaBalpha, nuclear translocation of p65, and NFkappaB DNA-binding activity. Absence of either IKK1 or IKK2 resulted in an 86 to 94% loss of virus yield compared to that of normal MEFs, little or no loss of IkappaBalpha, and greatly reduced NFkappaB nuclear translocation. Consistent with reduced virus yield, accumulation of the late proteins VP16 and gC was severely depressed. Infection of normal MEFs, Hep2, or A549 cells with an adenovirus vector expressing a dominant-negative (DN) IkappaBalpha, followed by superinfection with HSV, resulted in a 98% drop in virus yield. These results indicate that the IKK-IkappaB-p65 pathway activates NFkappaB after virus infection. Analysis of NFkappaB activation and virus replication in control and double-stranded RNA-activated protein kinase-null MEFs indicated that this kinase plays no role in the NFkappaB activation pathway. Finally, in cells where NFkappaB was blocked because of DNIkappaB expression, HSV failed to suppress two markers of apoptosis, cell surface Annexin V staining and PARP cleavage. These results support a model in which activation of NFkappaB promotes efficient replication by HSV, at least in part by suppressing a host innate response to virus infection.

Cells lacking NF-kappaB or in which NF-kappaB is not activated vary with respect to ability to sustain herpes simplex virus 1 replication and are not susceptible to apoptosis induced by a replication-incompetent mutant virus

Earlier we reported that NF-kappaB is activated by protein kinase R (PKR) in herpes simplex virus 1-infected cells. Here we report that in PKR(-/-) cells the yields of wild-type virus are 10-fold higher than in PKR(+/+) cells. In cells lacking NF-kappaB p50 (nfkb1), p65 (relA), or both p50 and p65, the yields of virus were reduced 10-fold. Neither wild-type nor mutant cells undergo apoptosis following infection with wild-type virus. Whereas PKR(+/+) and NF-kappaB(+/+) control cell lines undergo apoptosis induced by the d120 (Deltaalpha4) mutant of HSV-1, the mutant PKR(-/-) and NF-kappaB(-/-) cell lines were resistant. The evidence suggests that the stress-induced apoptosis resulting from d120 infection requires activation of NF-kappaB and that this proapoptotic pathway is blocked in cells in which NF-kappaB is not activated or absent. Activation of NF-kappaB in the course of viral infection may have dual roles of attempting to curtain viral replication by rendering the cell susceptible to apoptosis induced by the virus and by inducing the synthesis of proteins that enhance viral replication.

Herpes simplex virus type 1 immediate-early gene expression is required for the induction of apoptosis in human epithelial HEp-2 cells

Wild-type herpes simplex virus type 1 (HSV-1) induces apoptosis in human epithelial HEp-2 cells, but infected cell proteins produced later in infection block the process from killing the cells. Thus, HSV-1 infection in the presence of the translational inhibitor cycloheximide (CHX) results in apoptosis. Our specific goal was to gain insight as to the viral feature(s) responsible for triggering apoptosis during HSV-1 infection. We now report the following. (i) No viral protein synthesis or death factor processing was detected after infection with HSV-1(HFEMtsB7) at 39.5 degrees C; this mutant virus does not inject its virion DNA into the nucleus at this nonpermissive temperature. (ii) No death factor processing or apoptotic morphological changes were detected following infection with UV-irradiated, replication-defective viruses possessing transcriptionally active incoming VP16. (iii) Addition of the transcriptional inhibitor actinomycin D prevented death factor processing upon infection with the apoptotic, ICP27-deletion virus HSV-1(vBSDelta27). (iv) Apoptotic morphologies and death factor processing were not observed following infection with HSV-1(d109), a green fluorescent protein-expressing recombinant virus possessing deletions of all five immediate-early (IE) (or alpha) genes. (v) Finally, complete death factor processing was observed upon infection with the VP16 transactivation domain-mutant HSV-1(V422) in the presence of CHX. Based on these findings, we conclude that (vi) the expression of HSV-1 alpha/IE genes is required for the viral induction of apoptosis and (vii) the transactivation activity of VP16 is not necessary for this induction.

Varicella-zoster virus-infected human sensory neurons are resistant to apoptosis, yet human foreskin fibroblasts are susceptible: evidence for a cell-type-specific apoptotic response

The induction of apoptosis or programmed cell death in virus-infected cells is an important antiviral defense mechanism of the host, and some herpesviruses have evolved strategies to modulate apoptosis in order to enhance their survival and spread. In this study, we examined the ability of varicella-zoster virus (VZV) to induce apoptosis in primary human dorsal root ganglion neurons and primary human foreskin fibroblasts (HFFs). Three independent methods (annexin V, TUNEL [terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling] staining, and electron microscopy) were used to assess apoptosis in these cells on days 1, 2, and 4 postinoculation. By all three methods, apoptosis was readily detected in VZV-infected HFFs. In stark contrast, apoptosis was not detected during productive VZV infection of neurons. The low-passage clinical isolate Schenke and the tissue culture-adapted ROka strain both induced apoptosis in HFFs but not in neurons, suggesting that this cell-type-specific apoptotic phenotype was not VZV strain specific. These data show that the regulation of apoptosis differs markedly between HFFs and neurons during productive VZV infection. Inhibition of apoptosis during infection of neurons may play a significant role in the establishment, maintenance, and reactivation of latent infection by promoting survival of these postmitotic cells.

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 domains of glycoprotein D required to block apoptosis induced by herpes simplex virus 1 are largely distinct from those involved in cell-cell fusion and binding to nectin1

Glycoprotein D (gD) interacts with two alternative protein receptors, nectin1 and HveA, to mediate herpes simplex virus (HSV) entry into cells. Fusion of the envelope with the plasma membrane requires, in addition to gD, glycoproteins gB, gH, and gL. Coexpression of the four glycoproteins (gD, gB, gH, and gL) promotes cell-cell fusion. gD delivered in trans is also capable of blocking the apoptosis induced by gD deletion viruses grown either in noncomplementing cells (gD(-/-)) or in complementing cells (gD(-/+)). While ectopic expression of cation-independent mannose-6 phosphate receptor blocks apoptosis induced by both stocks, other requirements differ. Thus, apoptosis induced by gD(-/-) virus is blocked by full-length gD (or two gD fragments reconstituting a full-length molecule), whereas ectopic expression of the gD ectodomain is sufficient to block apoptosis induced by gD(-/+) virus. In this report we took advantage of a set of gD insertion-deletion mutants to map the domains of gD required to block apoptosis by gD(-/-) and gD(-/+) viruses and those involved in cell-cell fusion. The mutations that resulted in failure to block apoptosis were the same for gD(-/-) and gD(-/+) viruses and were located in three sites, one within the immunoglobulin-type core region (residues 125, 126, and 151), one in the upstream connector region (residues 34 and 43), and one in the C-terminal portion of the ectodomain (residue 277). A mutant that carried amino acid substitutions at the three glycosylation sites failed to block apoptosis but behaved like wild-type gD in all other assays. The mutations that inhibited polykaryocyte formation were located in the upstream connector region (residues 34 and 43), at the alpha1 helix (residue 77), in the immunoglobulin core and downstream regions (residue 151 and 187), and at the alpha3 helix (residues 243 and 246). Binding of soluble nectin1-Fc to cells expressing the mutant gDs was generally affected by the same mutations that affected fusion, with one notable exception (Delta277-310), which affected fusion without hampering nectin1 binding. This deletion likely identifies a region of gD involved in fusion activity at a post-nectin1-binding step. We conclude that whereas mutations that affected all functions (e.g., upstream connector region and residue 151) may be detrimental to overall gD structure, the mutations that affect specific activities identify domains of gD involved in the interactions with entry receptors and fusogenic glycoproteins and with cellular proteins required to block apoptosis. The evidence that glycosylation of gD is required for blocking apoptosis supports the conclusion that the interacting protein is the mannose-6 phosphate receptor.

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.

Engineered herpes simplex virus 1 is dependent on IL13Ralpha 2 receptor for cell entry and independent of glycoprotein D receptor interaction

In the first stage of engineering a herpes simplex virus (HSV)-1 that specifically targets human malignant glioma cells, we constructed a recombinant virus designated R5111 in which we have ablated the binding sites for sulfated proteoglycans in glycoproteins B and C, replaced the amino-terminal 148 aa in glycoprotein C by IL-13 flanked at its amino terminus with a signal peptide, and inserted a second copy of IL-13 after the amino acid 24 of glycoprotein D. In the process, the binding site for HveA, a viral entry receptor, was disrupted. We have also transformed a cell line (J1.1) lacking HSV-1 receptors to express IL13Ralpha2 receptor (J13R cells). We report the following: the R5111 recombinant virus replicates as well as wild-type virus in a variety of cell lines including cell lines derived from brain tumors. R5111 failed to replicate in the parent J1.1 cell line but multiplied to titers similar to those obtained in other cell lines in the J13R cell line. On the basis of the evidence that R5111 can use the IL13Ralpha2 receptor for entry, we conclude that HSV-1 can use receptors other than HveA or nectins, provided it can bind to them. The domains of gD that interact with HveA and nectin receptors are independent of each other. Lastly, the fusogenic activities of the glycoproteins in the viral envelope are not dependent on a set of unique interactions between glycoprotein D and its receptor. The construction of R5111 opens the way for construction of viruses totally dependent on selected receptors for entry or imaging of targeted cells.

Truncated forms of glycoprotein D of herpes simplex virus 1 capable of blocking apoptosis and of low-efficiency entry into cells form a heterodimer dependent on the presence of a cysteine located in the shared transmembrane domains

Earlier studies have shown that herpes simplex virus 1 (HSV-1) virions of mutant lacking glycoprotein D (gD) and made in either complementing (gD(-/+) stocks) or noncomplementing cells (gD(-/-) stocks) induce apoptosis. Subsequent studies have shown that apoptosis induced by gD(-/-) mutant virus stocks can be blocked by in trans delivery of viral genes that encode either intact gD or a mixture of two genes encoding the glycoprotein ectodomain plus transmembrane domain (gD-B) and transmembrane domain plus the cytoplasmic carboxyl terminus of the protein (gD-D), respectively. Since the presence of the transmembrane domains was critical for precluding apoptosis in the bipartite system, the question arose whether the two components, gD-B and gD-D, form a heterodimer mediated by an unpaired cysteine located in the transmembrane domain. We report the following. (i) The substitution of the unpaired cysteine with serine in either gD-B or gD-D truncated forms of gD disabled the ability of gD-D and gD-B to block apoptosis. (ii) Immunoprecipitation of gD-D coprecipitated gD-B only from lysates of cells transduced with gD-D and gD-B containing the cysteine in the transmembrane domains. Replacement of cysteine with serine ablated coprecipitation of the components. (ii) The mixture of gD-D and gD-B complemented at a low level gD(-/+) virions. We conclude that the gD-B and gD-D can form a heterodimer dependent on the presence of cysteines in the transmembrane domain and the heterodimer can substitute for intact gD but at a much reduced efficiency.

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.