Early expression of herpes simplex virus (HSV) proteins and reactivation of latent infection

Frequent Recurrences of Genital Herpes Are Associated with Enhanced Systemic HSV-Specific T Cell Response

Objectives

Genital herpes simplex virus (HSV) infection is controlled by HSV-specific T cells in the genital tract, and the role of systemic T cell responses is not fully understood. Thus, we analysed T cell responses in patients with recurrent genital herpes (GH).

Methods

T cell responses to HSV-1 and HSV-2 native antigens and the expression of HLA-DR and CD38 molecules on circulating CD8+ T cells were analysed in adults with high frequency of GH recurrences (19 patients) and low frequency of GH recurrences (7 patients) and 12 HSV-2 seronegative healthy controls. The study utilized the interferon-γ Elispot assay for measurement of spot-forming cells (SFC) after ex vivo stimulation with HSV antigens and flow cytometry for analysis of the expression of activation markers in unstimulated T cells.

Results

The patients with high frequency of GH recurrences (mean number of recurrences of 13.3 per year) had significantly enhanced HSV-specific T cell responses than the HSV-2 seronegative healthy controls. Moreover, a trend of higher numbers of SFC was observed in these patients when compared with those with low frequency of GH recurrences (mean number of recurrences of 3.3 per year). Additionally, no differences in CD38 and HLA-DR expression on circulating CD8+ T cells were found among the study groups.

Conclusions

Frequency of GH recurrences positively correlates with high numbers of systemic HSV-specific T cells.

p53 and the Viral Connection: Back into the Future ‡

The discovery of the tumor suppressor p53, through its interactions with proteins of tumor-promoting viruses, paved the way to the understanding of p53 roles in tumor virology. Over the years, accumulating data suggest that WTp53 is involved in the viral life cycle of non-tumor-promoting viruses as well. These include the influenza virus, smallpox and vaccinia viruses, the Zika virus, West Nile virus, Japanese encephalitis virus, Human Immunodeficiency Virus Type 1, Human herpes simplex virus-1, and more. Viruses have learned to manipulate WTp53 through different strategies to improve their replication and spreading in a stage-specific, bidirectional way. While some viruses require active WTp53 for efficient viral replication, others require reduction/inhibition of WTp53 activity. A better understanding of WTp53 functionality in viral life may offer new future clinical approaches, based on WTp53 manipulation, for viral infections.

The potential of currently unavailable herpes virus vaccines

INTRODUCTION

Despite overwhelming experimental work, there are no licensed vaccines against the most frequent Alphaherpesviruses, namely herpes simplex virus 1 and 2 (HSV1 and 2) nor against the Epstein-Barr virus (EBV), a member of the subfamily Gammaherpesvirus.

AREAS COVERED

Since the DNAs of both HSVs reside in the regional sensory ganglia in a latent state (i.e. as circularized episomal molecules), a corresponding vaccine might be useful for immunotherapy rather than for prevention of primary infection. Here we describe the design of a purified subunit vaccine as well as the preparation and efficacy of a recombinant fusion protein consisting of the gD ectodomain from our domestic attenuated HSV1 strain HSZP. The EBV vaccines considered so far, were destined for prevention of infectious mononucleosis (IM) or to prevent formation of EBV related tumors. To design the EBV peptide vaccine, at least 15 carefully selected immunogenic epitopes coming from 12 virus coded proteins were bound to synthetic micro-particle carriers along with a non-specific pathogen recognizing receptor (PRR) stimulating both the T as well as B lymphocytes.

EXPERT COMMENTARY

The efficacy of a novel EBV peptide in the rabbit model was based on criteria such as antibody formation (EA-D detected by ELISA, early and capsid proteins tested by immunoblot), presence of LMP1 antigen and of viral DNA in peripheral white blood cells. Out of 19 peptide combinations used for vaccination, at least 6 showed a satisfactory protective effect.

Opposite Roles of RNase and Kinase Activities of Inositol-Requiring Enzyme 1 (IRE1) on HSV-1 Replication

In response to the endoplasmic reticulum (ER) stress induced by herpes simplex virus type 1 (HSV-1) infection, host cells activate the unfolded protein response (UPR) to reduce the protein-folding burden in the ER. The regulation of UPR upon HSV-1 infection is complex, and the downstream effectors can be detrimental to viral replication. Therefore, HSV-1 copes with the UPR to create a beneficial environment for its replication. UPR has three branches, including protein kinase RNA (PKR)-like ER kinase (PERK), inositol-requiring enzyme 1 (IRE1), and activated transcription factor 6 (ATF6). IRE1α is the most conserved branch of UPR which has both RNase and kinase activities. Previous studies have shown that IRE1α RNase activity was inactivated during HSV-1 infection. However, the effect of the two activities of IRE1α on HSV-1 replication remains unknown. Results in this study showed that IRE1α expression was up-regulated during HSV-1 infection. We found that in HEC-1-A cells, increasing RNase activity, or inhibiting kinase activity of IRE1α led to viral suppression, indicating that the kinase activity of IRE1α was beneficial, while the RNase activity was detrimental to viral replication. Further evidence showed that the kinase activity of IRE1α leads to the activation of the JNK (c-Jun N-terminal kinases) pathway, which enhances viral replication. Taken together, our evidence suggests that IRE1α is involved in HSV-1 replication, and its RNase and kinase activities play differential roles during viral infection.

Herpes Simplex Virus 1 Tegument Protein UL41 Counteracts IFIT3 Antiviral Innate Immunity

The interferon-induced protein with tetratricopeptide repeat 3 (IFIT3 or ISG60) is a host-intrinsic antiviral factor that restricts many instances of DNA and RNA virus replication. Herpes simplex virus 1 (HSV-1), a DNA virus bearing a large genome, can encode many viral proteins to counteract the host immune responses. However, whether IFIT3 plays a role upon HSV-1 infection is little known. In this study, we show for the first time that HSV-1 tegument protein UL41, a viral endoribonuclease, plays an important role in inhibiting the antiviral activity of IFIT3. Here, we demonstrated that ectopically expressed IFIT3 could restrict the replication of vesicular stomatitis virus (VSV) but had little effect on the replication of wild-type (WT) HSV-1. Further study showed that WT HSV-1 infection downregulated the expression of IFIT3, and ectopic expression of UL41, but not the immediate-early protein ICP0, notably reduced the expression of IFIT3. The underlying molecular mechanism was that UL41 diminished the accumulation of IFIT3 mRNA to abrogate its antiviral activity. In addition, our results illustrated that ectopic expression of IFIT3 inhibited the replication of UL41-null mutant virus (R2621), and stable knockdown of IFIT3 facilitated its replication. Taking these findings together, HSV-1 was shown for the first time to evade the antiviral function of IFIT3 via UL41.

IMPORTANCE

The tegument protein UL41 of HSV-1 is an endoribonuclease with the substrate specificity of RNase A, which plays an important role in viral infection. Upon HSV-1 infection, interferons are critical cytokines that regulate immune responses against viral infection. Host antiviral responses are significantly boosted or crippled in the presence or absence of IFIT3; however, whether IFIT3 plays a role during HSV-1 infection is still unknown. Our data show for the first time that IFIT3 has little effect on HSV-1 replication, as UL41 decreases the accumulation of IFIT3 mRNA and subverts its antiviral activity. This study identifies IFIT3 as a novel target of the tegument protein UL41 and provides new insight into HSV-1-mediated immune evasion.

Identification of two novel functional p53 responsive elements in the herpes simplex virus-1 genome

Analysis of the herpes simplex virus-1 (HSV-1) genome reveals two candidate p53 responsive elements (p53RE), located in proximity to the replication origins oriL and oriS, referred to as p53RE-L and p53RE-S, respectively. The sequences of p53RE-L and p53RE-S conform to the p53 consensus site and are present in HSV-1 strains KOS, 17, and F. p53 binds to both elements in vitro and in virus-infected cells. Both p53RE-L and p53RE-S are capable of conferring p53-dependent transcriptional activation onto a heterologous reporter gene. Importantly, expression of the essential immediate early viral transactivator ICP4 and the essential DNA replication protein ICP8, that are adjacent to p53RE-S and p53RE-L, are repressed in a p53-dependent manner. Taken together, this study identifies two novel functional p53RE in the HSV-1 genome and suggests a complex mechanism of viral gene regulation by p53 which may determine progression of the lytic viral replication cycle or the establishment of latency.

A proteomic perspective of inbuilt viral protein regulation: pUL46 tegument protein is targeted for degradation by ICP0 during herpes simplex virus type 1 infection

Much like the host cells they infect, viruses must also regulate their life cycles. Herpes simples virus type 1 (HSV-1), a prominent human pathogen, uses a promoter-rich genome in conjunction with multiple viral trans-activating factors. Following entry into host cells, the virion-associated outer tegument proteins pUL46 and pUL47 act to increase expression of viral immediate-early (α) genes, thereby helping initiate the infection life cycle. Because pUL46 has gone largely unstudied, we employed a hybrid mass spectrometry-based approach to determine how pUL46 exerts its functions during early stages of infection. For a spatio-temporal characterization of pUL46, time-lapse microscopy was performed in live cells to define its dynamic localization from 2 to 24 h postinfection. Next, pUL46-containing protein complexes were immunoaffinity purified during infection of human fibroblasts and analyzed by mass spectrometry to investigate virus-virus and virus-host interactions, as well as post-translational modifications. We demonstrated that pUL46 is heavily phosphorylated in at least 23 sites. One phosphorylation site matched the consensus 14-3-3 phospho-binding motif, consistent with our identification of 14-3-3 proteins and host and viral kinases as specific pUL46 interactions. Moreover, we determined that pUL46 specifically interacts with the viral E3 ubiquitin ligase ICP0. We demonstrated that pUL46 is partially degraded in a proteasome-mediated manner during infection, and that the catalytic activity of ICP0 is responsible for this degradation. This is the first evidence of a viral protein being targeted for degradation by another viral protein during HSV-1 infection. Together, these data indicate that pUL46 levels are tightly controlled and important for the temporal regulation of viral gene expression throughout the virus life cycle. The concept of a structural virion protein, pUL46, performing nonstructural roles is likely to reflect a theme common to many viruses, and a better understanding of these functions will be important for developing therapeutics.

Herpes simplex virus 1 ICP22 inhibits the transcription of viral gene promoters by binding to and blocking the recruitment of P-TEFb

ICP22 is a multifunctional herpes simplex virus 1 (HSV-1) immediate early protein that functions as a general repressor of a subset of cellular and viral promoters in transient expression systems. Although the exact mechanism of repression remains unclear, this protein induces a decrease in RNA polymerase II Serine 2 (RNAPII Ser-2) phosphorylation, which is critical for transcription elongation. To characterize the mechanism of transcriptional repression by ICP22, we established an in vivo transient expression reporter system. We found that ICP22 inhibits transcription of the HSV-1 α, β and γ gene promoters. The viral tegument protein VP16, which plays vital roles in initiation of viral gene expression and viral proliferation, can overcome the inhibitory effect of ICP22 on α-gene transcription. Further immunoprecipitation studies indicated that both ICP22 and VP16 bind to positive transcription elongation factor b (P-TEFb) and form a complex with it in vivo. We extended this to show that P-TEFb regulates transcription of the viral α-gene promoters and affects transcriptional regulation of ICP22 and VP16 on the α-genes. Additionally, ChIP assays demonstrated that ICP22 blocks the recruitment of P-TEFb to the viral promoters, while VP16 reverses this blocking effect by recruiting P-TEFb to the viral α-gene promoters through recognition of the TAATGARAT motif. Taken together, our results suggest that ICP22 interacts with and blocks the recruitment of P-TEFb to viral promoter regions, which inhibits transcription of the viral gene promoters. The transactivator VP16 binds to and induces the recruitment of P-TEFb to viral α-gene promoters, which counteracts the transcriptional repression of ICP22 on α-genes by recruiting p-TEFb to the promoter region.

Prevention of infection transmission during stem cell transplantation

Group of 152 patients (investigated before autologous transplantation) and 35 healthy donors for allogeneic transplantation was examined for the risk of infection transmission that can be associated with the infusion of cryopreserved peripheral blood progenitor cells to the patient and/or cross-contamination of stored grafts. No laboratory signs of active infection were found in 22 donors (63 %) and in 91 patients (60%). The most common was active infection by herpes viruses--50 cases in patients, 21 cases in donors; hepatitis B was found in only two cases. The rate of clinically unsuspected (but dangerous) infections in donors and patients thus remains relatively high in spite of the fact that the system of donor search and the whole transplantation procedure have improved in the last years. The system of safety assurance is extremely important and the whole palette of preventive tests according to EBMT (European Blood and Marrow Transplantation Group) and ISHAGE (International Society for Hemotherapy and Graft Engineering) is fully justified.

Psittacid herpesvirus 1 and infectious laryngotracheitis virus: Comparative genome sequence analysis of two avian alphaherpesviruses

Psittacid herpesvirus 1 (PsHV-1) is the causative agent of Pacheco's disease, an acute, highly contagious, and potentially lethal respiratory herpesvirus infection in psittacine birds, while infectious laryngotracheitis virus (ILTV) is a highly contagious and economically significant avian herpesvirus which is responsible for an acute respiratory disease limited to galliform birds. The complete genome sequence of PsHV-1 has been determined and compared to the ILTV sequence, assembled from published data. The PsHV-1 and ILTV genomes exhibit similar structural characteristics and are 163,025 bp and 148,665 bp in length, respectively. The PsHV-1 genome contains 73 predicted open reading frames (ORFs), while the ILTV genome contains 77 predicted ORFs. Both genomes contain an inversion in the unique long region similar to that observed in pseudorabies virus. PsHV-1 is closely related to ILTV, and it is proposed that it be assigned to the Iltovirus genus. These two avian herpesviruses represent a phylogenetically unique clade of alphaherpesviruses that are distinct from the Marek's disease-like viruses (Mardivirus). The determination of the complete genomic nucleotide sequences of PsHV-1 and ILTV provides a tool for further comparative and functional analysis of this unique class of avian alphaherpesviruses.

Developments in herpes simplex virus vaccines: old problems and new challenges

Vaccination has remained the best method for preventing virus spread. The herpes simplex virus (HSV) candidate vaccines tested till now were mostly purified subunit vaccines and/or recombinant envelope glycoproteins (such as gB and gD). In many experiments performed in mice, guinea pigs and rabbits, clear-cut protection against acute virus challenge was demonstrated along with the reduction of the extent of latency, when established in the immunized host. The immunotherapeutic effect of herpes vaccines seems less convincing. However, introduction of new adjuvants, which shift the cytokine production of helper T-cells toward stimulation of cytotoxic T-cells (TH1 type cytokine response), reveals a promising development. Mathematical analysis proved that overall prophylactic vaccination of seronegative women, even when eliciting 40-60 % antibody response only, would reduce the frequency of genital herpes within the vaccinated population. Even when partially effective, immunotherapeutic vaccination might represent a suitable alternative of chronic chemotherapy in recurrent labial and genital herpes.

Neuronal activity regulates viral replication of herpes simplex virus type 1 in the nervous system

Herpes simplex virus types 1 and 2 (HSV-1, -2) infect and also establish latency in neurons. In the present study, the authors investigated the influence of neuronal activity on the replication of HSV-1. The results showed that the sodium channel blocker tetrodotoxin (TTX) and the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) could significantly increase viral replication in primary neuronal cultures, by two- to fourfold. In contrast, KCl reduced viral production by at least 80% in the same cultures. Inhibitors of GABA(A) receptors completely abolished the effects of GABA. Intravitreously injected TTX in a mouse corneal scarification model enhanced the viral titers > 10-fold in both the trigeminal ganglia and the brain. At 2 h post infection, both TTX and GABA significantly up-regulated the levels of transcription for the viral immediate early (IE) genes ICP0, ICP4, and ICP27, as revealed by real time PCR. These results indicate that the neuronal excitation status may dictate the efficiency of HSV-1 viral replication, probably by regulating the levels of viral IE gene expression. These are the first findings connecting neuronal activity to the molecular mechanisms of HSV replication in the nervous system, which may significantly influence our view of herpesvirus infection and latency.

Murine herpesvirus pathogenesis: a model for the analysis of molecular mechanisms of human gamma herpesvirus infections

Murine herpes virus (MHV), a natural pathogen originally isolated from free-living rodents, constitutes the most amenable animal model for human gamma herpesviruses. Based on DNA sequence homology, this virus was classified as Murid Herpesvirus 4 to subfamily Gammaherpesvirinae. Pilot studies in our laboratory, using mice inoculated by the intranasal route, showed that MHV infects macrophages, B lymphocytes, lung alveolar as well as endothelial cells. From the lungs the virus spreads via the bloodstream to spleen and bone marrow and via the lymphatics to the mediastinal lymph nodes. Similarly to other gamma herpesviruses, MHV established life-long latency maintained in host B lymphocytes and macrophages. An IM-like syndrome (per analogy to EBV) may develop during acute MHV infection, in which the atypical T/CD8+ lymphocytes eliminate viral DNA carrying B cells expressing the M2 latency associated protein. During latency, the MHV LANA (a KSHV LANA homologue) maintains the latent viral genome, assuring its copying and partition to new carrier cells in the course of division of the maternal cell. The nonproductive latency is turned onto virus replication by means of Rta protein. The chronic lymphoproliferative syndrome of unclear pathogenesis, which occurs in a certain part of latent MHV carriers, is related to the expression of gamma herpesvirus common latency-associated genes such as v-cyclin and/or to that of a virus-specific (M11/bcl-2) gene. This review attempts to summarize our knowledge concerning the function of MHV genes (either gamma herpesvirus common or MHV specific) related to immune evasion, latency and lymphoproliferation when highlighting the unsolved problems and/or controversial opinions.

Higher resistance of porcine trigeminal ganglion neurons towards pseudorabies virus-induced cell death compared with other porcine cell types in vitro

Trigeminal ganglion (TG) neurons are important target cells for many alphaherpesviruses, constituting major sites for latency/reactivation events. Here, the in vitro kinetics of productive infection of the swine alphaherpesvirus pseudorabies virus (PRV) and resulting cell death in primary porcine TG neurons were determined, and these were compared with similar kinetics in many other porcine cell types. Confocal microscopy showed that all TG neurons expressed late genes such as viral glycoproteins, and that these glycoproteins were processed through the Golgi and reached the cell surface as in other cell types, albeit with a delay of +/-2-6 h. However, TG neurons were much more resistant towards PRV-induced cell death compared with all other porcine cell types tested (non-neuronal TG cells, superior cervical ganglion neurons, epithelial kidney cells, arterial endothelial cells, dermal fibroblasts and cells derived from a porcine swine kidney cell line). About half of the TG neurons survived up to 96 h post-inoculation (end of experiment), whereas all other cell types almost completely succumbed within 2 days post-inoculation. In addition, infection with a strongly pro-apoptotic PRV strain that misses the anti-apoptotic US3 protein did not lead to substantial apoptosis in TG neurons, even at 72 h post-inoculation. Thus, primary porcine TG neurons can be infected with PRV in vitro, and are remarkably more resistant to PRV-induced cell death compared with other porcine cell types, suggesting a cell type-specific resistance to alphaherpesvirus-induced cell death that may have important implications for different aspects of the virus life cycle, including latency/reactivation events.

Molecular mechanisms of virus spread and virion components as tools of virulence. A review

Despite of differences in replication strategy among virus families, some basic principles have remained similar. Analogous mechanisms govern virus entry into cells and the use of enzymes which direct the replication of the virus genome. The function of many cell surface receptors (such as glycosoaminoglycans, glycoproteins, proteins) which interact with viral capsid proteins or envelope glycoproteins has recently been elucidated. The list of cellular receptors (Table I) is still far from being final. The capsid components, similarly as the envelope glycoproteins, may form specific pocket like sites, which interact with the cell surface receptors. Neutralizing antibodies usually react with antigenic domains adjacent to the receptor binding site(s) and hamper the close contact inevitable for virion attachment. In the case of more complex viruses, such as herpes simplex virus, different viral glycoproteins interact with several cellular receptors. At progressed phase of adsorption the virions are engulfed into endocytic vesicles and the virion fusion domain(s) become(s) activated. The outer capsid components of reoviruses which participate in adsorption and fusion may get activated already in the lumen of digestive tract, i.e. before their engulfment by resorptive epithelium cells. Activation of the hydrophobic fusion domain(s) is a further important step allowing to pass through the lipid bilayer when penetrating the cell membrane in order to reach the cytosol. Activation of the virion fusion domain is accomplished by a conformation change, which occurs at acid pH (influenza virus hemagglutinin, sigma 1 protein of the reovirus particle) and/or after protease treatment. The herpes simplex virus fusion factors (gD and gH) undergo conformation changes by a pH-independent mechanism triggered due to interaction with the cell surface receptor(s) and mediated by mutual interactions with the viral envelope glycoproteins. The virion capsid or envelope components participating in the entry and membrane fusion are not the only tools of virulence. The correct function of virus coded proteins, which participate in replication of the viral genome, and/or in the supply of necessary nucleotides, may be very essential. In the case of enteroviruses, which RNA interacts with ribosomes directly, the correct configuration of the non-coding viral RNA sequence is crucial for initiation of translation occurring in the absence of the classical "cap" structure.

Potential risk of infection transmission during storage and transplantation of hematological progenitor cells. Safety assurance

In a group of 71 patients and 22 donors the danger of infection transmission by infusion of cryopreserved peripheral blood progenitor cells to the patient and/or cross contamination of stored grafts was evaluated. No laboratory signs of active infection were found in 15 donors (13 related, 2 unrelated; 68%) and in 55 patients (77%). Active infection by herpesviruses was the most common (in 13 patients and 7 donors), hepatitis B being found in only one case. The cytomegalovirus IgG test was the most common marker of previous infection; it was found in 14 donors and 55 patients. The rate of clinically unsuspected infections in donors and patients including cases requiring immediate treatment among the patients group is relatively high and fully justifies the practice of prophylactic serological testing in the whole range of tests according to the European Blood and Marrow Transplantation Group and International Society for Hematotherapy and Graft Engineering in both autologous and allogeneic transplantations of hematopoietic stem cells.