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

Effects on exocytosis by two HSV-1 mutants unable to block autophagy

IMPORTANCE

Pathogens often hijack extracellular vesicle (EV) biogenesis pathways for assembly, egress, and cell-to-cell spread. Herpes simplex virus 1 (HSV-1) infection stimulated EV biogenesis through a CD63 tetraspanin biogenesis pathway and these EVs activated antiviral responses in recipient cells restricting the infection. HSV-1 inhibits autophagy to evade the host, and increased CD63 exocytosis could be a coping mechanism, as CD63 is involved in both cargo delivery to lysosomes during autophagy and exocytosis. We analyzed exocytosis after infection with two HSV-1 mutants, a ΔICP34.5 and a ΔICP0, that could not inhibit autophagy. Unlike HSV-1(F), neither of these viruses stimulated increased EV biogenesis through the CD63 pathway. ΔICP34.5 stimulated production of microvesicles and apoptotic bodies that were CD63-negative, while ΔICP0 displayed an overall reduced production of EVs. These EVs activated innate immunity gene expression in recipient cells. Given the potential use of these mutants for therapeutic purposes, the immunomodulatory properties of EVs associated with them may be beneficial.

Interactome and Ubiquitinome Analyses Identify Functional Targets of Herpes Simplex Virus 1 Infected Cell Protein 0

Herpes simplex virus 1 (HSV-1) can productively infect multiple cell types and establish latent infection in neurons. Infected cell protein 0 (ICP0) is an HSV-1 E3 ubiquitin ligase crucial for productive infection and reactivation from latency. However, our knowledge about its targets especially in neuronal cells is limited. We confirmed that, like in non-neuronal cells, ICP0-null virus exhibited major replication defects in primary mouse neurons and Neuro-2a cells. We identified many ICP0-interacting proteins in Neuro-2a cells, 293T cells, and human foreskin fibroblasts by mass spectrometry-based interactome analysis. Co-immunoprecipitation assays validated ICP0 interactions with acyl-coenzyme A thioesterase 8 (ACOT8), complement C1q binding protein (C1QBP), ovarian tumour domain-containing protein 4 (OTUD4), sorting nexin 9 (SNX9), and vimentin (VIM) in both Neuro-2a and 293T cells. Overexpression and knockdown experiments showed that SNX9 restricted replication of an ICP0-null but not wild-type virus in Neuro-2a cells. Ubiquitinome analysis by immunoprecipitating the trypsin-digested ubiquitin reminant followed by mass spectrometry identified numerous candidate ubiquitination substrates of ICP0 in infected Neuro-2a cells, among which OTUD4 and VIM were novel substrates confirmed to be ubiquitinated by transfected ICP0 in Neuro-2a cells despite no evidence of their degradation by ICP0. Expression of OTUD4 was induced independently of ICP0 during HSV-1 infection. Overexpressed OTUD4 enhanced type I interferon expression during infection with the ICP0-null but not wild-type virus. In summary, by combining two proteomic approaches followed by confirmatory and functional experiments, we identified and validated multiple novel targets of ICP0 and revealed potential restrictive activities of SNX9 and OTUD4 in neuronal cells.

Diverse Populations of Extracellular Vesicles with Opposite Functions during Herpes Simplex Virus 1 Infection

Extracellular vesicles (EVs) are released by all types of cells as a means of intercellular communication. Their significance lies in the fact that they can alter recipient cell functions, despite their limited capacity for cargo. We have previously demonstrated that herpes simplex virus 1 (HSV-1) infection influences the cargo and functions of EVs released by infected cells and that these EVs negatively impact a subsequent HSV-1 infection. In the present study, we have implemented cutting-edge technologies to further characterize EVs released during HSV-1 infection. We identified distinct EV populations that were separable through a gradient approach. One population was positive for the tetraspanin CD63 and was distinct from EVs carrying components of the endosomal sorting complexes required for transport (ESCRT). Nanoparticle tracking analysis (NTA) combined with protein analysis indicated that the production of CD63⁺ EVs was selectively induced upon HSV-1 infection. The ExoView platform supported these data and suggested that the amount of CD63 per vesicle is larger upon infection. This platform also identified EV populations positive for other tetraspanins, including CD81 and CD9, whose abundance decreased upon HSV-1 infection. The stimulator of interferon genes (STING) was found in CD63⁺ EVs released during HSV-1 infection, while viral components were found in ESCRT⁺ EVs. Functional characterization of these EVs demonstrated that they have opposite effects on the infection, but the dominant effect was negative. Overall, we have identified the dominant population of EVs, and other EV populations produced during HSV-1 infection, and we have provided information about potential roles.IMPORTANCE Extracellular vesicles mediate cell-to-cell communication and convey messages important for cell homeostasis. Pathways of EV biogenesis are often hijacked by pathogens to facilitate their dissemination and to establish a favorable microenvironment for the infection. We have previously shown that HSV-1 infection alters the cargo and functions of the released EVs, which negatively impact the infection. We have built upon our previous findings by developing procedures to separate EV populations from HSV-1-infected cells. We identified the major population of EVs released during infection, which carries the DNA sensor STING and has an antiviral effect. We also identified an EV population that carries selected viral proteins and has a proviral role. This is the first study to characterize EV populations during infection. These data indicate that the complex interactions between the virus and the host are extended to the extracellular environment and could impact HSV-1 dissemination and persistence in the host.

Marine Algae: A Potential Resource of Anti-HSV Molecules

Herpes simplex viruses (HSVs) are common human pathogens belonging to the subfamily alpha-herpesvirinae that trigger severe infections in neonates and immunocompromised patients. After primary infection, the HSVs establish a lifelong latent infection in the vegetative neural ganglia of their hosts. HSV infections contribute to substantial disease burden in humans as well as in newborns. Despite a fair number of drugs being available for the treatment of HSV infections, new, effective, and safe antiviral agents, exerting different mechanisms of action, are urgently required, mainly due to the increasing number of resistant strains. Accumulating pieces of evidence have suggested that structurally diverse compounds from marine algae possess promising anti-HSV potentials. Several studies have documented a variety of algal polysaccharides possessing anti-HSV activity, including carrageenan and fucan. This review aimed to compile previous anti-HSV studies on marine algae–derived compounds, especially sulfated polysaccharides, along with their mode of action, toward their development as novel natural anti-HSV agents for future investigations.

Biogenesis of Extracellular Vesicles during Herpes Simplex Virus 1 Infection: Role of the CD63 Tetraspanin

Herpes simplex virus 1 (HSV-1) infections afflict more than 80% of the population worldwide. The virus primarily infects mucoepithelial cells and establishes latent reservoirs in neurons in sensory ganglia. Frequent reactivation has been linked to severe diseases, especially in immunocompromised individuals. Earlier, we reported that viral and host factors are packaged in extracellular vesicles (EVs) and delivered to uninfected cells, where they activate antiviral responses and restrict virus infection. Here, we interrogated the effect of HSV-1 infection on EV biogenesis. We found that HSV-1 infection causes a decrease in the amount of intracellular CD63 protein with a concomitant increase in extracellular CD63. This observation correlates with our previous finding that infected cells release more CD63-positive EVs than uninfected cells. The stimulation of CD63 exocytosis requires virus replication. CD63 is a member of the tetraspanin family of proteins that traffics between the plasma membrane and endosomal compartments and has a role in sorting cargo into the EVs. Previously, we reported that in cells depleted of CD63, HSV-1 virus yields increased, and here we provide data showing that in cells overexpressing CD63, HSV-1 virus yields decreased. Taken together, our data indicate that CD63 negatively impacts HSV-1 infection and that the CD63-positive EVs could control the dissemination of the virus in the host. Perhaps EV release by HSV-1-infected cells is a mechanism that controls virus dissemination.IMPORTANCE Intercellular communication, especially in neurons, largely relies on EVs, and modulation of EVs is known to impact physiological processes. Here, we present evidence that HSV-1 infection causes major alterations in the biogenesis of EVs, including an increase in their number and an increase in the CD63-positive population of EVs. These alterations result in an enrichment of the milieu of infection with EVs carrying signatures from infected cells. In addition to changes in the origin and type, EVs released by infected cells have differences in cargo, as they carry viral and host factors determined by the virus. The tetraspanin CD63 negatively impacts the infection, as demonstrated by CD63-knockdown and overexpression assays. A proposed mechanism involves the activation of antiviral responses in cells receiving CD63-positive EVs released by infected cells. Overall, HSV-1 causes major alterations in EVs that could contribute to HSV-1 persistence and pathogenesis.

Molecular characterization of the duck enteritis virus US10 protein

BACKGROUND

There is little information regarding the duck enteritis virus (DEV) US10 gene and its molecular characterization.

METHODS

Duck enteritis virus US10 was amplified and cloned into the recombinant vector pET32a(+). The recombinant US10 protein was expressed in Escherichia coli BL21 cells and used to immunize rabbits for the preparation of polyclonal antibodies. The harvested rabbit antiserum against DEV US10 was detected and analyzed by agar immunodiffusion. Using this antibody, western blotting and indirect immunofluorescence analysis were used to analyze the expression level and subcellular localization of US10 in infected cells at different time points. Quantitative reverse-transcription PCR (qRT-PCR) and pharmacological inhibition tests were used to ascertain the kinetic class of the US10 gene. A mass spectrometry-based strategy was used to identify US10 in purified DEV virions and quantify its abundance.

RESULTS

The recombinant pET32a(+)/US10 protein was expressed as inclusion bodies, purified by gradient urea washing, and used to prepare specific antibodies. The results of qRT-PCR, western blotting, and pharmacological inhibition tests revealed that US10 is mainly transcribed in the late stage of viral replication. However, the presence of the DNA polymerase inhibitor ganciclovir and the protein synthesis inhibitor cycloheximide blocked transcription. Therefore, US10 is a γ2 (true late) gene. Indirect immunofluorescence analysis showed that US10 proteins were initially diffusely distributed throughout the cytoplasm, but with the passage of time, they gradually relocated to a perinuclear region. The US10 protein was detected in purified DEV virions by mass spectrometry, but was not detected by western blotting, indicating that DEV US10 is a minor virion protein.

CONCLUSIONS

The DEV US10 gene is a γ2 gene and the US10 protein is localized in the perinuclear region. DEV US10 is a virion component.

Analysis of the early steps of herpes simplex virus 1 capsid tegumentation

Herpes simplex virus type 1 particles are multilayered structures with a DNA genome surrounded by a capsid, tegument, and envelope. While the protein content of mature virions is known, the sequence of addition of the tegument and the intracellular compartments where this occurs are intensely debated. To probe this process during the initial stages of egress, we used two approaches: an in vitro nuclear egress assay, which reconstitutes the exit of nuclear capsids to the cytoplasm, and a classical nuclear capsid sedimentation assay. As anticipated, in vitro cytoplasmic capsids did not harbor UL34, UL31, or viral glycoproteins but contained US3. In agreement with previous findings, both nuclear and in vitro capsids were positive for ICP0 and ICP4. Unexpectedly, nuclear C capsids and cytoplasmic capsids produced in vitro without any cytosolic viral proteins also scored positive for UL36 and UL37. Immunoelectron microscopy confirmed that these tegument proteins were closely associated with nuclear capsids. When cytosolic viral proteins were present in the in vitro assay, no additional tegument proteins were detected on the capsids. As previously reported, the tegument was sensitive to high-salt extraction but, surprisingly, was stabilized by exogenous proteins. Finally, some tegument proteins seemed partially lost during egress, while others possibly were added at multiple steps or modified along the way. Overall, an emerging picture hints at the early coating of capsids with up to 5 tegument proteins at the nuclear stage, the shedding of some viral proteins during nuclear egress, and the acquisition of others tegument proteins during reenvelopment.

Biochemical analysis of infected cell polypeptide (ICP)0, ICP4, UL7 and UL23 incorporated into extracellular herpes simplex virus type 1 virions

Herpes simplex virus type 1 (HSV-1) capsids assemble in the nucleus but acquire their teguments from various cellular compartments. Unfortunately, little is known about their exact arrangement and when they coat the newly produced capsids. The complexity of the virions is further highlighted by our recent proteomics analysis that detected the presence of several novel or controversial components in extracellular HSV-1 virions. The present study probes the localization and linkage to the virus particles of some of these incorporated proteins. We confirm the recently reported tight association of infected cell polypeptide (ICP)0 with the capsid and show that this property extends to ICP4. We also confirm our proteomics data and show biochemically that UL7 and UL23 are indeed mature virion tegument components that, unlike ICP0 and ICP4, are salt-extractable. Interestingly, treatment with N-ethylmaleimide, which covalently modifies reduced cysteines, strongly prevented the release of UL7 and UL23 by salts, but did not perturb the interactions of ICP0 and ICP4 with the virus particles. This hitheir at distinct biochemical properties of the virion constituents and the selective implication of reduced cysteines in their organization and dynamics. Finally, the data revealed, by two independent means, the presence of ICP0 and ICP4 on intranuclear capsids, consistent with the possibility that they may at least partially be recruited to the virus particles early on. These findings add significantly to our understanding of HSV-1 virion assembly and to the debate about the incorporation of ICP0 and ICP4 in virus particles.

Interwoven roles of cyclin D3 and cdk4 recruited by ICP0 and ICP4 in the expression of herpes simplex virus genes

Elsewhere this laboratory reported that (i) ICP0 interacts with cyclin D3 but not D1 or D2. The 3 cyclins independently partially rescue DeltaICP0 mutants. (ii) Interaction with cyclin D3 is required for the switch from nuclear to cytoplasmic accumulation of ICP0. (iii) In infected cells cdk4 is activated whereas cdk2 is not. Inhibition of cdk4 results in nuclear retention of ICP0. Overexpression of cyclin D3 reverses the effect of the inhibitor. Here we report the following. (i) cdk4 interacts with ICP0, ICP4, and possibly with ICP8. This interaction is required to recruit cdk4 initially to ND10 and later to the viral replication compartments. (ii) cdk4 inhibitor I reduced or delayed the transcription and ultimately translation of mRNAs of ICP4, ICP27, or ICP8 and to a lesser extent that of the ICP0 gene in wild-type virus-infected cells. (iii) Overexpression of cyclin D3 resulted in a more rapid transcription of these genes. In the presence of inhibitor, the rates of accumulation of the products of these genes resemble those of wild-type virus in the absence of inhibitor. (iv) Overexpression of cyclin D3 also results in mobilization of cdk6 in nuclei of infected cells. We conclude that ICP0 encodes a function that enhances the recruitment of cyclin D3 to ND10 structures to activate cdk4 and that ICP0 along with other viral proteins recruits cdk4 to ND10 structures and ultimately to replication compartments for enhanced expression of viral genes and viral DNA synthesis.

Cellular localization of the herpes simplex virus ICP0 protein dictates its ability to block IRF3-mediated innate immune responses

Interferon regulatory factor 3 (IRF3) is important for innate antiviral responses; accordingly, many viruses target and inactivate IRF3. The ability of the Herpes simplex virus type 1 (HSV-1) immediate early protein ICP0 to inhibit IRF3 is controversial and has not been studied solely in the context of a wild type HSV-1 infection. Discrepancies in the literature surround the mechanism by which ICP0 antagonizes the IRF3 pathway, the cellular localization of ICP0 inhibitory activity and the ability of ICP0 to interfere with interferon and interferon-stimulated gene induction. In this study, we set out to investigate the role of ICP0 localization and the requirement of the proteasome during the inhibition of IRF3 activation within the context of an HSV-1 infection. Collectively, the results presented herein demonstrate that incoming wild type HSV-1 activates IRF3 and that de novo produced ICP0 prevents sustained IRF3 activation following its translocation from the nucleus to the cytoplasm. While previous studies implicate the E3 ubiquitin ligase domain of ICP0 in mediating its biological functions, including the inhibition of IRF3, we show that cytoplasmic ICP0 does not require the proteasome for this activity. Instead, proteasome function is required to localize ICP0 to the cytoplasm where it mediates its inhibitory effect independent of E3 ubiquitin ligase activity. The importance of these findings is discussed within the context of an HSV-1 infection.

Role of herpes simplex virus ICP0 in the transactivation of genes introduced by infection or transfection: a reappraisal

ICP0, a promiscuous transactivator that enhances the expression of genes introduced by infection or transfection, functions in both nucleus and cytoplasm. The nuclear functions include degradation and dispersal of ND10 bodies and suppression of silencing of viral DNA. Subsequently, ICP0 shifts to the cytoplasm. Transfection of DNA prior to infection has no effect on the localization of ICP0 in cells that are efficient expressers of transgenes (e.g., Vero and HEK293) but results in delayed cytoplasmic localization of ICP0 in cells (e.g., HEp-2 and HEL) that are poor transgene expressers. Here, we examined by real-time PCR (qPCR) the accumulation of a transgene and of viral gI mRNAs in Vero or HEp-2 cells that were transfected and then infected with wild-type or DeltaICP0 mutant viruses. The accumulation of transgene mRNA was unaffected by a DeltaICP0 mutant, gradually increased in HEp-2 cells, but increased and then decreased in Vero cells infected with wild-type virus. In both cell lines, accumulation of gI mRNA increased with time and was less affected by the transfected DNA in Vero cells than in HEp-2 cells. The relative kinetics of mRNA accumulation reflected continued synthesis and degradation of the transgene and gI mRNAs. We conclude that the role of ICP0 is to render the DNA templates introduced by transfection or infection accessible by transcriptional factors, that the two cell lines differ with respect to the transcription-ready status of entering foreign DNA in the nucleus, and that ICP0 is not per se the recruiter of transcriptional factors to the accessible DNA templates.

Simian TRIM5alpha proteins reduce replication of herpes simplex virus

Old World monkey TRIM5alpha proteins are known to block the replication of human immunodeficiency virus and other retroviruses in a species-specific fashion. In this report, we show that specific forms of simian TRIM5alpha proteins can restrict herpes simplex virus (HSV) infection. To define the effect of TRIM5alpha on HSV replication, we examined HSV infection in HeLa cell lines that stably express simian and human orthologs of TRIM5alpha proteins. We demonstrated that several simian TRIM5alpha proteins can restrict HSV replication, with the TRIM5alpha protein of rhesus macaques showing the strongest inhibition of HSV infection. We also found that the level of the inhibition of virus replication was viral strain-specific. TRIM5alpha is likely to inhibit HSV at the early stage of infection; however, at later times of infection, the levels of TRIM5alpha are significantly decreased. Thus, some TRIM5alpha proteins exhibit antiviral effects that extend beyond retroviral infections, but HSV may be able to reduce this restriction by reducing TRIM5alpha levels during the later phases of virus replication. Our results also argue that TRIM5alpha is only part of the reduced level of HSV replication in rhesus macaques, which are known to be less susceptible to HSV infection than other primates.

ICP0 enables and monitors the function of D cyclins in herpes simplex virus 1 infected cells

The herpes simplex virus 1 ICP0 is a regulatory protein. Early in infection ICP0 localizes in ND10 bodies and performs two functions: As an E3 ligase in conjunction with E2 UbcH5a conjugating enzyme, it degrades the ND10 components PML and SP100. Concurrently, it suppresses the silencing of viral DNA by dispersing the HDAC1/CoREST/REST/LSD1 repressor complex. Subsequently, ICP0 is exported to the cytoplasm. In cells treated with HDAC inhibitors or transfected with irrelevant DNA, the export is delayed in a DNA dose-dependent fashion. Here, we follow up an observation that ICP0 binds cyclin D3 and that ICP0 mutants unable to bind cyclin D3 are not exported. Moreover, in infected cells cdk4 is activated, but cdk2 is not. We report that (i) cyclin D1, D2, or D3 colocalize with ND10 bodies and ICP0 early in infection and ultimately become incorporated into viral replication compartments, (ii) each of the D cyclins partially rescues DeltaICP0 mutants, and (iii) inhibition of cdk4 by inhibitor I sequesters ICP0 in the nucleus. A key finding is that overexpression of cyclin D3 enables the transport of ICP0 to the cytoplasm. We conclude that (i) ICP0 facilitates the recruitment of cyclin D3 to the sites of viral DNA synthesis, (ii) until its functions are completed, ICP0 is retained in the nucleus, and (iii) a common signal that results in the export of ICP0 to the cytoplasm is the accumulation of a viral DNA-synthesis-dependent late protein.

Host responses to wild-type and attenuated herpes simplex virus infection in the absence of Stat1

Humans and mice lacking the interferon signaling molecule Stat1 are sensitive to a variety of pathogens due to their presumed inability to mount a strong innate immune response. The herpes simplex virus type 1 (HSV-1) virion host shutoff (vhs) protein is a multifunctional immunomodulator that counteracts the innate immune response and viruses lacking vhs are attenuated and effective live vaccines in animal models. To investigate the interplay of viruses with an immunocompromised host, we performed functional genomics analyses on control and Stat1(-/-) mouse corneas infected with wild-type or vhs-null viruses. In control mice, correlative with viral growth, both viruses induced a transient increase in immunomodulators, followed by viral clearance. In contrast, infection of the Stat1(-/-) mice induced a heightened and prolonged induction of inflammatory modulators for both viruses, manifesting as a significant immune cell infiltrate and ocular disease. Moreover, while wild-type virus infection of Stat1(-/-) was always lethal, vhs-null infection was rarely lethal. There was a significant increase in Stat3- and interleukin-6 (IL-6)-dependent transcription in Stat1(-/-) mice, implicating the Stat3 and IL-6 pathways in the observed ocular pathology. Further, infected Stat1(-/-) mice showed phosphorylated Stat3 in the corneal epithelium. Our data show a role for vhs in evading innate host responses and a role for Stat1 in limiting virus infection and for facilitating an appropriate nonpathological inflammatory response.

Nuclear retention of ICP0 in cells exposed to HDAC inhibitor or transfected with DNA before infection with herpes simplex virus 1

The alpha (immediate early) protein ICP0 of herpes simplex virus 1 enhances the expression of genes introduced by infection or transfection. Early in infection it performs two key functions: It blocks the silencing of the viral DNA by cellular proteins and it blocks the IFN stimulated host response to infection. Between 5 and 9 h after infection, ICP0 is translocated to the cytoplasm but remains dynamically associated with proteasomes. In this report we show that in permissive cells that are poor expressors of transfected genes (HEp-2, U2OS, etc.), ICP0 is retained in the nucleus if the cells had been transfected with DNA and then infected. The retention is DNA dose- and size-dependent but not DNA type-dependent. Retention of ICP0 is also a consequence of infection with wild-type virus concomitant with exposure of cells to sodium butyrate. ICP0 is not retained in transfected/infected cells that efficiently express transfected genes (HEK293, rabbit skin cells). The retention of ICP0 in the nucleus is concordant with failure to degrade PML and disperse ND10 structures, and delays in the transition to post alpha genes expression, translocation of components of the CoREST/REST/HDAC1 complex and histone relocation in the infected cell. The data suggest that (i) retention of ICP0 is linked to its function to remodel acetylated DNA but not DNA in heterochromatin. This function is independent of response elements embedded in the DNA and (ii) transfection-resistant cells do take up DNA but process it differently than cells that readily express transfected genes.

Comprehensive characterization of extracellular herpes simplex virus type 1 virions

The herpes simplex virus type 1 (HSV-1) genome is contained in a capsid wrapped by a complex tegument layer and an external envelope. The poorly defined tegument plays a critical role throughout the viral life cycle, including delivery of capsids to the nucleus, viral gene expression, capsid egress, and acquisition of the viral envelope. Current data suggest tegumentation is a dynamic and sequential process that starts in the nucleus and continues in the cytoplasm. Over two dozen proteins are assumed to be or are known to ultimately be added to virions as tegument, but its precise composition is currently unknown. Moreover, a comprehensive analysis of all proteins found in HSV-1 virions is still lacking. To better understand the implication of the tegument and host proteins incorporated into the virions, highly purified mature extracellular viruses were analyzed by mass spectrometry. The method proved accurate (95%) and sensitive and hinted at 8 different viral capsid proteins, 13 viral glycoproteins, and 23 potential viral teguments. Interestingly, four novel virion components were identified (U(L)7, U(L)23, U(L)50, and U(L)55), and two teguments were confirmed (ICP0 and ICP4). In contrast, U(L)4, U(L)24, the U(L)31/U(L)34 complex, and the viral U(L)15/U(L)28/U(L)33 terminase were undetected, as was most of the viral replication machinery, with the notable exception of U(L)23. Surprisingly, the viral glycoproteins gJ, gK, gN, and U(L)43 were absent. Analyses of virions produced by two unrelated cell lines suggest their protein compositions are largely cell type independent. Finally, but not least, up to 49 distinct host proteins were identified in the virions.

Expression of gamma interferon-dependent genes is blocked independently by virion host shutoff RNase and by US3 protein kinase

Gamma interferon receptor alpha (IFN-gammaR alpha) is stable but posttranslationally modified in herpes simplex virus 1(F) [HSV-1(F)]-infected cells. Studies with antibody directed to the phosphorylation site indicate that IFN-gammaR alpha is phosphorylated by the U(S)3 kinase. The modification is abolished in cells infected with DeltaU(S)3, DeltaU(L)13, or Delta(U(S)3/U(L)13) mutant virus. Transcripts of the IFN-gamma-dependent genes do not accumulate in cells transduced with the U(S)3 protein kinase and treated with IFN-gamma. In contrast, the accumulation of IFN-gamma-dependent gene transcripts is suppressed in cells infected with the wild-type virus, in cells infected with the DeltaU(S)3 mutant virus, and to a lesser extent in the DeltaU(L)41 virus-infected cells. The accumulation of IFN-gamma-dependent gene transcripts in DeltaU(L)41-infected cells could be due at least in part to a significant delay and reduction in the accumulation of the U(S)3 protein. The results suggest that the expression of IFN-gamma-dependent genes is blocked independently by the degradation of IFN-gamma-dependent gene transcripts--a function of the virion host shutoff RNase--and by posttranslational modification of the IFN-gammaR alpha protein.

Enhanced pathogenesis of an attenuated herpes simplex virus for mice lacking Stat1

Mice lacking the Stat1 interferon signaling gene were infected with herpes simplex virus type 1 (HSV-1) or an attenuated recombinant lacking virion host shutoff (Delta vhs). Delta vhs virus-infected Stat1(-/-) mice showed levels of replication equivalent to that of the wild-type virus-infected control mice but reduced relative to wild-type virus-infected Stat1(-/-) mice. Stat1 deficiency relieves the immunomodulatory deficiency of Delta vhs virus, but not its inherent growth defect. Also Vhs is dispensable for reactivation.

Herpes simplex virus virion host shutoff attenuates establishment of the antiviral state

Herpes simplex virus mutants lacking the vhs protein are severely attenuated in animal models of pathogenesis and exhibit reduced growth in primary cell culture. As a result of these properties, viruses with vhs deleted have been proposed as live-attenuated vaccines. Despite these findings and their implications for vaccines, the mechanisms by which vhs promotes infection in cell culture and in vivo are not understood. In this study we demonstrate that vhs-deficient viruses replicate to reduced levels in interferon (IFN)-primed cells and that this deficit has both IFN-dependent and IFN-independent components. Furthermore, vhs-defective viruses induce increased and physiologically active levels of IFN, increased amounts of IFN-stimulated transcripts, and more phosphorylated eIF2alpha. In addition, we demonstrate greater accumulation of viral RNAs following infection with a vhs-deficient virus. This leads to the hypothesis that attenuation of viruses lacking vhs may be attributed to increased levels of double-stranded RNA, a potent pathogen-associated molecular pattern. Together these data show that vhs likely functions to reduce innate immune responses and thereby acts as a critical determinant of viral pathogenesis.