US3 protein kinase of HSV-1 cycles between the cytoplasm and nucleus and interacts with programmed cell death protein 4 (PDCD4) to block apoptosis

Understanding the interplay between oHSV and the host immune system: Implications for therapeutic oncolytic virus development

Oncolytic herpes simplex viruses (oHSV) preferentially replicate in cancer cells while inducing antitumor immunity, and thus, they are often referred to as in situ cancer vaccines. OHSV infection of tumors elicits diverse host immune responses comprising both innate and adaptive components. Although the innate and adaptive immune responses primarily target the tumor, they also contribute to antiviral immunity, limiting viral replication/oncolysis. OHSV-encoded proteins use various mechanisms to evade host antiviral pathways and immune recognition, favoring oHSV replication, oncolysis, and spread. In general, oHSV infection and replication within tumors results in a series of sequential events, such as oncolysis and release of tumor and viral antigens, dendritic cell-mediated antigen presentation, T cell priming and activation, T cell trafficking and infiltration to tumors, and T cell recognition of cancer cells, leading to tumor (and viral) clearance. These sequential events align with all steps of the cancer-immunity cycle. However, a comprehensive understanding of the interplay between oHSV and host immune responses is crucial to optimize oHSV-induced antitumor immunity and efficacy. Therefore, this review aims to elucidate oHSV's communication with innate and adaptive immune systems and use such interactions to improve oHSV's potential as a potent immunovirotherapeutic agent against cancer.

A Guideline Strategy for Identifying a Viral Gene/Protein Evading Antiviral Innate Immunity

Antiviral innate immunity is the first line of defence against viruses. The interferon (IFN) signaling pathway, the DNA damage response (DDR), apoptosis, endoplasmic reticulum (ER) stress, and autophagy are involved in antiviral innate immunity. Viruses abrogate the antiviral immune response of cells to replication in various ways. Viral genes/proteins play a key role in evading antiviral innate immunity. Here, we will discuss the interference of viruses with antiviral innate immunity and the strategy for identifying viral gene/protein immune evasion.

Rapid NETosis Is an Effector Mechanism to Combat Ocular Herpes Infection

Purpose

Neutrophils are known mediators of innate immunity, yet their effector function in herpesvirus infections remains poorly understood. Here, we elucidate the mechanistic action and pivotal role of neutrophil extracellular traps (NETs) during herpes simplex virus type 1 (HSV-1) ocular infection.

Methods

Neutrophils were collected from mice for HSV-1 infection, fluorescence imaging, and immunoblotting assay. Tear samples from healthy subjects and patients with HSV-1 and mice were collected at L. V. Prasad Eye Institute, India, and at the University of Illinois, USA, respectively. For the in vivo study, C57BL/6 mice as well as diversity outbred mice were infected with HSV-1 (McKrae strain) followed by tear fluid collection at various time points (0-10 days). Samples were used for Flow cytometry, ELISA, and immunofluorescence assay. Human transcriptomic profile of keratitis dataset was used evaluate NETosis signaling pathways. We also performed neutrophil depletion studies.

Results

Our data revealed a discernible temporal NET formation (NETosis) predominantly in the infected eye, across normal and diversity outbred murine models and human cases of HSV-1 infection. HSV-1 instigates swift NETosis governed by caspase-1 activation and myeloperoxidase secretion. Distinct accumulations of neutrophils, remaining unengaged in NET release in the contralateral eye post-infection, hinting at a proactive defensive posture in the uninfected eye. Moreover, neutrophil depletion accentuated ocular pathology, augmented viral load, and escalated disease scores, substantiating the protective effects of NETs in curtailing viral replication.

Conclusions

Our report uncovers a previously unexplored mechanism of NETosis through pro-inflammatory cell death in response to ocular HSV-1 infection, and HPSE up-regulation, identifying new avenues for future studies.

PDCD4 restricts PRRSV replication in an eIF4A-dependent manner and is antagonized by the viral nonstructural protein 9

As obligate parasites, viruses have evolved multiple strategies to evade the host immune defense. Manipulation of the host proteasome system to degrade specific detrimental factors is a common viral countermeasure. To identify host proteins targeted for proteasomal degradation by porcine reproductive and respiratory syndrome virus (PRRSV), we conducted a quantitative proteomics screen of PRRSV-infected Marc-145 cells under the treatment with proteasome inhibitor MG132. The data revealed that the expression levels of programmed cell death 4 (PDCD4) were strongly downregulated by PRRSV and significantly rescued by MG132. Further investigation confirmed that PRRSV infection induced the translocation of PDCD4 from the nucleus to the cytoplasm, and the viral nonstructural protein 9 (Nsp9) promoted PDCD4 proteasomal degradation in the cytoplasm by activating the Akt-mTOR-S6K1 pathway. The C-terminal domain of Nsp9 was responsible for PDCD4 degradation. As for the role of PDCD4 during PRRSV infection, we demonstrated that PDCD4 knockdown favored viral replication, while its overexpression significantly attenuated replication, suggesting that PDCD4 acts as a restriction factor for PRRSV. Mechanistically, we discovered eukaryotic translation initiation factor 4A (eIF4A) was required for PRRSV. PDCD4 interacted with eIF4A through four sites (E249, D253, D414, and D418) within its two MA3 domains, disrupting eIF4A-mediated translation initiation in the 5'-untranslated region of PRRSV, thereby inhibiting PRRSV infection. Together, our study reveals the antiviral function of PDCD4 and the viral strategy to antagonize PDCD4. These results will contribute to our understanding of the immune evasion strategies employed by PRRSV and offer valuable insights for developing new antiviral targets.IMPORTANCEPorcine reproductive and respiratory syndrome virus (PRRSV) infection results in major economic losses in the global swine industry and is difficult to control effectively. Here, using a quantitative proteomics screen, we identified programmed cell death 4 (PDCD4) as a host protein targeted for proteasomal degradation by PRRSV. We demonstrated that PDCD4 restricts PRRSV replication by interacting with eukaryotic translation initiation factor 4A, which is required for translation initiation in the viral 5'-untranslated region. Additionally, four sites within two MA3 domains of PDCD4 are identified to be responsible for its antiviral function. Conversely, PRRSV nonstructural protein 9 promotes PDCD4 proteasomal degradation in the cytoplasm by activating the Akt-mTOR-S6K1 pathway, thus weakening the anti-PRRSV function. Our work unveils PDCD4 as a previously unrecognized host restriction factor for PRRSV and reveals that PRRSV develops countermeasures to overcome PDCD4. This will provide new insights into virus-host interactions and the development of new antiviral targets.

Low Prevalence of HSV-1 and Helicobacter pylori in HNSCC and Chronic Tonsillitis Patients Compared to Healthy Individuals

Recent studies identified viral and bacterial factors, including HSV-1 and H. pylori, as possible factors associated with diseases such as chronic tonsillitis and cancers, including head and neck squamous cell carcinoma (HNSCC). We assessed the prevalence of HSV-1/2 and H. pylori in patients with HNSCC, chronic tonsillitis, and healthy individuals using PCR after DNA isolation. Associations were sought between the presence of HSV-1, H. pylori, and clinicopathological and demographic characteristics and stimulant use. HSV-1 and H. pylori were most frequently identified in controls (HSV-1: 12.5% and H. pylori: 6.3%). There were 7 (7.8%) and 8 (8.6%) patients with positive HSV-1 in HNSCC and chronic tonsillitis patients, respectively, while the prevalence of H. pylori was 0/90 (0%) and 3/93 (3.2%), respectively. More cases of HSV-1 were observed in older individuals in the control group. All positive HSV-1 cases in the HNSCC group were associated with advanced tumor stage (T3/T4). The prevalence of HSV-1 and H. pylori was highest in the controls compared to HNSCC and chronic tonsillitis patients, which indicates that the pathogens were not risk factors. However, since all positive HSV-1 cases in the HNSCC group were observed only in patients with advanced tumor stage, we suggested a possible link between HSV-1 and tumor progression. Further follow-up of the study groups is planned.

DISTINCT ROLES OF VIRAL US3 AND UL13 PROTEIN KINASES IN HERPES VIRUS SIMPLEX TYPE 1 (HSV-1) NUCLEAR EGRESS

Herpesviruses transport nucleocapsids from the nucleus to the cytoplasm by capsid envelopment into the inner nuclear membrane and de-envelopment from the outer nuclear membrane, a process that is coordinated by nuclear egress complex (NEC) proteins, pUL34, and pUL31. Both pUL31 and pUL34 are phosphorylated by the virus-encoded protein kinase, pUS3, and phosphorylation of pUL31 regulates NEC localization at the nuclear rim. pUS3 also controls apoptosis and many other viral and cellular functions in addition to nuclear egress, and the regulation of these various activities in infected cells is not well understood. It has been previously proposed that pUS3 activity is selectively regulated by another viral protein kinase, pUL13 such that its activity in nuclear egress is pUL13-dependent, but apoptosis regulation is not, suggesting that pUL13 might regulate pUS3 activity on specific substrates. We compared HSV-1 UL13 kinase-dead and US3 kinase-dead mutant infections and found that pUL13 kinase activity does not regulate the substrate choice of pUS3 in any defined classes of pUS3 substrates and that pUL13 kinase activity is not important for promoting de-envelopment during nuclear egress. We also find that mutation of all pUL13 phosphorylation motifs in pUS3, individually or in aggregate, does not affect the localization of the NEC, suggesting that pUL13 regulates NEC localization independent of pUS3. Finally, we show that pUL13 co-localizes with pUL31 inside the nucleus in large aggregates, further suggesting a direct effect of pUL13 on the NEC and suggesting a novel mechanism for both UL31 and UL13 in the DNA damage response pathway. IMPORTANCE Herpes simplex virus infections are regulated by two virus-encoded protein kinases, pUS3 and pUL13, which each regulate multiple processes in the infected cell, including capsid transport from the nucleus to the cytoplasm. Regulation of the activity of these kinases on their various substrates is poorly understood, but importantly, kinases are attractive targets for the generation of inhibitors. It has been previously suggested that pUS3 activity on specific substrates is differentially regulated by pUL13 and, specifically, that pUL13 regulates capsid egress from the nucleus by phosphorylation of pUS3. In this study, we determined that pUL13 and pUS3 have different effects on nuclear egress and that pUL13 may interact directly with the nuclear egress apparatus with implications both for virus assembly and egress and, possibly, the host cell DNA- damage response.

BX795, a kinase inhibitor, inhibit duck plague virus infection via targeting US3 kinase

Duck plague virus (DPV) is a typical DNA virus of waterfowl, it causes huge economic losses to the duck industry due to the higher mortality and lower egg production. The disease is one of the frequent epidemics and outbreaks on duck farms because present vaccines could not provide complete immunity and there are no specific antiviral drugs available. Therefore, the development of antiviral drugs is urgently needed. In this study, we evaluated the antiviral activity of BX795, a specific kinase inhibitor of 3-phosphoinositide-dependent kinase 1 (PDK1), protein kinase B (AKT) and Tank binding kinase 1 (TBK1), against DPV in different duck cells. Our study demonstrated that BX795 reveals prominent antiviral activity in a dose-dependent manner in different types of duck cells. Time-addition and antiviral duration analysis uncovered that BX795 inhibits viral infection therapeutically and its antiviral activity lasts longer than 96 h. Further studies have shown that BX795 prevents cell-to-cell spread of the DPV rather than affects other stage of viral life cycle. Mechanistically, BX795 can inhibit DPV US3 kinase activity, reduce the phosphorylation of US3 substrates, and prevent the interaction between US3 and UL47. Taking together, our study demonstrated BX795, which disrupts the viral kinase activity, is a candidate antiviral agent for DPV.

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.

Regulation of alphaherpesvirus protein via post-translational phosphorylation

An alphaherpesvirus carries dozens of viral proteins in the envelope, tegument and capsid structure, and each protein plays an indispensable role in virus adsorption, invasion, uncoating and release. After infecting the host, a virus eliminates unfavourable factors via multiple mechanisms to escape or suppress the attack of the host immune system. Post-translational modification of proteins, especially phosphorylation, regulates changes in protein conformation and biological activity through a series of complex mechanisms. Many viruses have evolved mechanisms to leverage host phosphorylation systems to regulate viral protein activity and establish a suitable cellular environment for efficient viral replication and virulence. In this paper, viral protein kinases and the regulation of viral protein function mediated via the phosphorylation of alphaherpesvirus proteins are described. In addition, this paper provides new ideas for further research into the role played by the post-translational modification of viral proteins in the virus life cycle, which will be helpful for understanding the mechanisms of viral infection of a host and may lead to new directions of antiviral treatment.

Viral-mediated activation and inhibition of programmed cell death

Viruses are ubiquitous intracellular genetic parasites that heavily rely on the infected cell to complete their replication life cycle. This dependency on the host machinery forces viruses to modulate a variety of cellular processes including cell survival and cell death. Viruses are known to activate and block almost all types of programmed cell death (PCD) known so far. Modulating PCD in infected hosts has a variety of direct and indirect effects on viral pathogenesis and antiviral immunity. The mechanisms leading to apoptosis following virus infection is widely studied, but several modalities of PCD, including necroptosis, pyroptosis, ferroptosis, and paraptosis, are relatively understudied. In this review, we cover the mechanisms by which viruses activate and inhibit PCDs and suggest perspectives on how these affect viral pathogenesis and immunity.

The US3 Kinase of Herpes Simplex Virus Phosphorylates the RNA Sensor RIG-I To Suppress Innate Immunity

Recent studies have demonstrated that the signaling activity of the cytosolic pathogen sensor retinoic acid-inducible gene-I (RIG-I) is modulated by a variety of posttranslational modifications (PTMs) to fine-tune the antiviral type I interferon (IFN) response. Whereas K63-linked ubiquitination of the RIG-I caspase activation and recruitment domains (CARDs) catalyzed by TRIM25 or other E3 ligases activates RIG-I, phosphorylation of RIG-I at S8 and T170 represses RIG-I signal transduction by preventing the TRIM25-RIG-I interaction and subsequent RIG-I ubiquitination. While strategies to suppress RIG-I signaling by interfering with its K63-polyubiquitin-dependent activation have been identified for several viruses, evasion mechanisms that directly promote RIG-I phosphorylation to escape antiviral immunity are unknown. Here, we show that the serine/threonine (Ser/Thr) kinase US3 of herpes simplex virus 1 (HSV-1) binds to RIG-I and phosphorylates RIG-I specifically at S8. US3-mediated phosphorylation suppressed TRIM25-mediated RIG-I ubiquitination, RIG-I-MAVS binding, and type I IFN induction. We constructed a mutant HSV-1 encoding a catalytically-inactive US3 protein (K220A) and found that, in contrast to the parental virus, the US3 mutant HSV-1 was unable to phosphorylate RIG-I at S8 and elicited higher levels of type I IFNs, IFN-stimulated genes (ISGs), and proinflammatory cytokines in a RIG-I-dependent manner. Finally, we show that this RIG-I evasion mechanism is conserved among the alphaherpesvirus US3 kinase family. Collectively, our study reveals a novel immune evasion mechanism of herpesviruses in which their US3 kinases phosphorylate the sensor RIG-I to keep it in the signaling-repressed state. IMPORTANCE Herpes simplex virus 1 (HSV-1) establishes lifelong latency in the majority of the human population worldwide. HSV-1 occasionally reactivates to produce infectious virus and to facilitate dissemination. While often remaining subclinical, both primary infection and reactivation occasionally cause debilitating eye diseases, which can lead to blindness, as well as life-threatening encephalitis and newborn infections. To identify new therapeutic targets for HSV-1-induced diseases, it is important to understand the HSV-1-host interactions that may influence infection outcome and disease. Our work uncovered direct phosphorylation of the pathogen sensor RIG-I by alphaherpesvirus-encoded kinases as a novel viral immune escape strategy and also underscores the importance of RNA sensors in surveilling DNA virus infection.

Low PDCD4 Expression Is Associated With Poor Prognosis of Colorectal Carcinoma

Programmed cell death 4 (PDCD4) is a tumor suppressor gene that inhibits tumor progression, invasion, and metastasis. Decreased PDCD4 expression is associated with poor prognosis in various types of cancers. We evaluated PDCD4 expression and its clinicopathologic correlation, including patient survival, in 289 surgically resected colorectal cancers. Low nuclear PDCD4 expression was identified in 177 (61.2%) cases and was associated with large tumor size, high pT classification, and the presence of lymphovascular and perineural invasion. The 5-year survival rate of patients with low nuclear PDCD4 expression was significantly lower than that of patients with high expression (72.2% vs. 93.3%, P<0.001). American Joint Committee on Cancer stage II and III colorectal cancer patients with low nuclear PDCD4 expression (76.9% and 67.2%, respectively) showed significantly worse overall survival than those with high expression (100% and 92.9%, P=0.002 and 0.032, respectively). Low nuclear PDCD4 expression was an independent poor prognostic factor in colorectal cancer patients (hazard ratio=3.556; 95% confidence interval, 1.739-7.271; P=0.001). Our study suggests that low PDCD4 expression is associated with aggressive behavior and can be used as a prognostic indicator of colorectal cancer patients.

Pseudorabies Virus DNA Polymerase Processivity Factor UL42 Inhibits Type I IFN Response by Preventing ISGF3-ISRE Interaction

Alphaherpesviruses are large dsDNA viruses with an ability to establish persistent infection in hosts, which rely partly on their ability to evade host innate immune responses, notably the type I IFN response. However, the relevant molecular mechanisms are not well understood. In this study, we report the UL42 proteins of alphaherpesvirus pseudorabies virus (PRV) and HSV type 1 (HSV1) as a potent antagonist of the IFN-I-induced JAK-STAT signaling pathway. We found that ectopic expression of UL42 in porcine macrophage CRL and human HeLa cells significantly suppresses IFN-α-mediated activation of the IFN-stimulated response element (ISRE), leading to a decreased transcription and expression of IFN-stimulated genes (ISGs). Mechanistically, UL42 directly interacts with ISRE and interferes with ISG factor 3 (ISGF3) from binding to ISRE for efficient gene transcription, and four conserved DNA-binding sites of UL42 are required for this interaction. The substitution of these DNA-binding sites with alanines results in reduced ISRE-binding ability of UL42 and impairs for PRV to evade the IFN response. Knockdown of UL42 in PRV remarkably attenuates the antagonism of virus to IFN in porcine kidney PK15 cells. Our results indicate that the UL42 protein of alphaherpesviruses possesses the ability to suppress IFN-I signaling by preventing the association of ISGF3 and ISRE, thereby contributing to immune evasion. This finding reveals UL42 as a potential antiviral target.

US3 Serine/Threonine Protein Kinase from MDV-1, MDV-2, and HVT Differentially Regulate Viral Gene Expression and Replication

Gallid alphaherpesvirus 2 (GaHV-2), commonly known as Marek's disease virus type 1 (MDV-1), is an oncogenic avian alphaherpesvirus, and along with its close relatives-Gallid alphaherpesvirus 3 (GaHV-3) or MDV-2 and Meleagrid alphaherpesvirus 1 (MeHV-1) or turkey herpesvirus (HVT)-belongs to the Mardivirus genus. We and others previously showed that MDV-1 U_S3 protein kinase plays an important role in viral replication and pathogenesis, which could be partially compensated by MDV-2 and HVT U_S3. In this study, we further studied the differential roles of MDV-1, MDV-2 and HVT U_S3 in regulating viral gene expression and replication. Our results showed that MDV-2 and HVT U_S3 could differentially compensate MDV-1 U_S3 regulation of viral gene expression in vitro. MDV-2 and HVT U_S3 could also partially rescue the replication deficiency of MDV-1 U_S3 null virus in the spleen and thymus, as determined by immunohistochemistry analysis of MDV-1 pp38 protein. Importantly, using immunohistochemistry and dual immunofluorescence assays, we found that MDV-2 U_S3, but not HVT U_S3, fully compensated MDV-1 U_S3 regulation of MDV-1 replication in bursal B lymphocytes. In conclusion, our study provides the first comparative analysis of U_S3 from MDV-1, MDV-2 and HVT in regulating viral gene expression in cell culture and MDV-1 replication in lymphocytes.

The Proteome and Secretome of Cortical Brain Cells Infected With Herpes Simplex Virus

Infections of the brain with herpes simplex virus type 1 (HSV-1) cause life-threatening Herpes simplex encephalitis (HSE) characterized by viral replication in neurons and neuro-inflammation including an infiltration of peripheral immune cells. HSV-1 reprograms host cells to foster its own replication and for immune evasion, but eventually the immune responses clear the infection in most patients. However, many survivors suffer from long-term neuronal damage and cannot regenerate all brain functions. HSV-1 influences the physiology of neurons, astrocytes, oligodendrocytes and microglia, and significantly changes their protein expression and secretion pattern. To characterize temporal changes upon HSV-1 infection in detail, we inoculated mixed primary cultures of the murine brain cortex, and performed quantitative mass spectrometry analyses of the cell-associated proteome and the secretome. We identified 28 differentially regulated host proteins influencing inflammasome formation and intracellular vesicle trafficking during endocytosis and secretion. The NIMA-related kinase 7 (NEK7), a critical component of the inflammasome, and ArfGap1, a regulator of endocytosis, were significantly up-regulated upon HSV-1 infection. In the secretome, we identified 71 proteins including guidance cues regulating axonal regeneration, such as semaphorin6D, which were enriched in the conditioned media of HSV-1 infected cells. Modulation of inflammasome activity and intracellular membrane traffic are critical for HSV-1 cell entry, virus assembly, and intracellular spread. Our proteome analysis provides first clues on host factors that might dampen the inflammasome response and modulate intracellular vesicle transport to promote HSV infection of the brain. Furthermore, our secretome analysis revealed a set of proteins involved in neuroregeneration that might foster neuronal repair processes to restore brain functions after clearance of an HSV-1 infection.

Role of Marek's Disease Virus (MDV)-Encoded US3 Serine/Threonine Protein Kinase in Regulating MDV Meq and Cellular CREB Phosphorylation

Marek's disease (MD) is a neoplastic disease of chickens caused by Marek's disease virus (MDV), a member of the subfamily Alphaherpesvirinae Like other alphaherpesviruses, MDV encodes a serine/threonine protein kinase, U_S3. The functions of U_S3 have been extensively studied in other alphaherpesviruses; however, the biological functions of MDV U_S3 and its substrates have not been studied in detail. In this study, we investigated potential cellular pathways that are regulated by MDV U_S3 and identified chicken CREB (chCREB) as a substrate of MDV U_S3. We show that wild-type MDV U_S3, but not kinase-dead U_S3 (U_S3-K220A), increases CREB phosphorylation, leading to recruitment of phospho-CREB (pCREB) to the promoter of the CREB-responsive gene and activation of CREB target gene expression. Using U_S3 deletion and U_S3 kinase-dead recombinant MDV, we identified U_S3-responsive MDV genes during infection and found that the majority of U_S3-responsive genes were located in the MDV repeat regions. Chromatin immunoprecipitation sequencing (ChIP-seq) studies determined that some U_S3-regulated genes colocalized with Meq (an MDV-encoded oncoprotein) recruitment sites. Chromatin immunoprecipitation-PCR (ChIP-PCR) further confirmed Meq binding to the ICP4/LAT region, which is also regulated by U_S3. Furthermore, biochemical studies demonstrated that MDV U_S3 interacts with Meq in transfected cells and MDV-infected chicken embryonic fibroblasts in a phosphorylation-dependent manner. Finally, in vitro kinase studies revealed that Meq is a U_S3 substrate. MDV U_S3 thus acts as an upstream kinase of the CREB signaling pathway to regulate the transcription function of the CREB/Meq heterodimer, which targets cellular and viral gene expression.IMPORTANCE MDV is a potent oncogenic herpesvirus that induces T-cell lymphoma in infected chickens. Marek's disease continues to have a significant economic impact on the poultry industry worldwide. U_S3 encoded by alphaherpesviruses is a multifunctional kinase involved in the regulation of various cellular pathways. Using an MDV genome quantitative reverse transcriptase PCR (qRT-PCR) array and chromatin immunoprecipitation, we elucidated the role of MDV U_S3 in viral and cellular gene regulation. Our results provide insights into how viral kinase regulates host cell signaling pathways to activate both viral and host gene expression. This is an important step toward understanding host-pathogen interaction through activation of signaling cascades.

An improved animal model for herpesvirus encephalitis in humans

Herpesviral encephalitis caused by Herpes Simplex Virus 1 (HSV-1) is one of the most devastating diseases in humans. Patients present with fever, mental status changes or seizures and when untreated, sequelae can be fatal. Herpes Simplex Encephalitis (HSE) is characterized by mainly unilateral necrotizing inflammation effacing the frontal and mesiotemporal lobes with rare involvement of the brainstem. HSV-1 is hypothesized to invade the CNS via the trigeminal or olfactory nerve, but viral tropism and the exact route of infection remain unclear. Several mouse models for HSE have been developed, but they mimic natural infection only inadequately. The porcine alphaherpesvirus Pseudorabies virus (PrV) is closely related to HSV-1 and Varicella Zoster Virus (VZV). While pigs can control productive infection, it is lethal in other susceptible animals associated with severe pruritus leading to automutilation. Here, we describe the first mutant PrV establishing productive infection in mice that the animals are able to control. After intranasal inoculation with a PrV mutant lacking tegument protein pUL21 and pUS3 kinase activity (PrV-ΔUL21/US3Δkin), nearly all mice survived despite extensive infection of the central nervous system. Neuroinvasion mainly occurred along the trigeminal pathway. Whereas trigeminal first and second order neurons and autonomic ganglia were positive early after intranasal infection, PrV-specific antigen was mainly detectable in the frontal, mesiotemporal and parietal lobes at later times, accompanied by a long lasting lymphohistiocytic meningoencephalitis. Despite this extensive infection, mice showed only mild to moderate clinical signs, developed alopecic skin lesions, or remained asymptomatic. Interestingly, most mice exhibited abnormalities in behavior and activity levels including slow movements, akinesia and stargazing. In summary, clinical signs, distribution of viral antigen and inflammatory pattern show striking analogies to human encephalitis caused by HSV-1 or VZV not observed in other animal models of disease.

In developed countries, more than 50% of humans are seropositive for the neurotropic Herpes Simplex Virus 1 (HSV-1) and two to four million cases of Herpes simplex encephalitis (HSE) are reported per year worldwide. Primary infection with HSV-1 takes place via the skin or the oral mucosa followed by intraaxonal retrograde spread to sensory ganglia of the peripheral nervous system where HSV-1 usually establishes latency. Further spread to the central nervous system results in HSE, a necrotizing encephalitis effacing predominantly the temporal and frontal lobes of the brain. Mice infected with HSV-1 develop encephalitis, but do not show the typical lesions and exhibit high mortality rates. Here we demonstrate that mice infected with a mutant pseudorabies virus lacking the tegument protein pUL21 and an active viral kinase pUS3 were able to survive the productive infection but developed lymphohistiocytic encephalitis with viral antigen distribution, inflammation and associated behavioral changes comparable to HSE in humans. These striking analogies offer new perspectives to study herpesviral encephalitis in a suitable animal model.

VHS, US3 and UL13 viral tegument proteins are required for Herpes Simplex Virus-Induced modification of protein kinase R

To replicate, spread and persist in the host environment, viruses have evolved several immunological escape mechanisms via the action of specific viral proteins. The model "host shut off" adopted by virion host shut off (VHS) protein of Herpes simplex type 1 (HSV-1) represents an immune evasion mechanism which affects the best-characterized component of the innate immunological response, protein kinase R (PKR). However, up to now, the real mechanism employed by VHS to control PKR is still unknown. In this paper, we implement and extend our previous findings reporting that wild-type HSV-1 is able to control PKR, whereas a VHS mutant virus (R2621) clearly induces an accumulation of phosphorylated PKR in several cell types in a VHS-RNase activity-dependent manner. Furthermore, we demonstrate for the first time a new PKR-regulatory mechanism based on the involvement of Us3 and UL13 tegument viral proteins. The combined approach of transfection and infection assay was useful to discover the new role of both viral proteins in the immunological escape and demonstrate that Us3 and UL13 control the accumulation of the phosphorylated form (ph-PKR). Lastly, since protein kinases are tightly regulated by phosphorylation events and, at the same time, phosphorylate other proteins by inducing post-translational modifications, the interplay between Us3 and VHS during HSV-1 infection has been investigated. Interestingly, we found that VHS protein accumulates at higher molecular weight following Us3 transfection, suggesting an Us3-mediated phosphorylation of VHS. These findings reveal a new intriguing interplay between viral proteins during HSV-1 infection involved in the regulation of the PKR-mediated immune response.

Role of HIF-1α in Cold Ischemia Injury of Rat Donor Heart Via the miR-21/PDCD4 Pathway

BACKGROUND

Hypoxia-inducible factor 1 alpha (HIF-1α) is a transcription factor that plays a major role under hypoxia conditions. Cold storage during heart transplantation causes the donor heart long-term hypoxia. There is some evidence indicating a conceivable HIF-1α/microRNA-21 (miR-21)/phosphatase and tensin homolog (PTEN)/programmed cell death 4 (PDCD4) pathway. We assessed the hypothesis that HIF-1α has a positive effect during donor heart cold storage by making the miR-21 upregulate to reduce the expression of PDCD4.

METHODS

We established the rat heart cold storage model and stratified it into 6-hour groups from 0 to 24 hours. Western blot and quantitative reverse transcription polymerase chain reaction were performed to detect the expression of HIF-1α, miR-21, PDCD4, and PTEN.

RESULTS

After cold storage the expression of HIF-1α increased from 0 to 6 hours and then gradually decreased, but the expression level was relatively higher compared with the control group. The miR-21 was upregulated from 0 to 12 hours then downregulated. The messenger RNA expression of PDCD4 was upregulated gradually, but the protein expression was significantly downregulated at 12th hour then continued to upregulate. Interestingly, the expression level of miR-21 was highest in the 12th hour, which indicated miR-21 could inhibit the PDCD4. We subsequently detected the messenger RNA of PTEN, which can inhibit HIF-1α and be inhibited by miR-21. The expression of PTEN was also significantly downregulated at the 12th hour.

CONCLUSION

In conclusion, there is possible interaction between HIF-1α and miR-21, and the conceivable HIF-1α/miR-21/PTEN/PDCD4 pathway plays a protective role in cold storage of the heart.

lncRNA XIST regulates proliferation and migration of hepatocellular carcinoma cells by acting as miR-497-5p molecular sponge and targeting PDCD4

BACKGROUND

MicroRNAs (miRNAs) play a pivotal role in hepatocellular carcinoma (HCC) progression and have been confirmed to participate in the carcinogenesis and development of HCC. However, the relationship between miR-497-5p and HCC remains unclear.

METHODS

Kaplan-Meier curve analysis and the log-rank test were used to investigate the efficacy of miR-497-5p on overall survival (OS) and disease-free survival (DFS) in patients with HCC. According to in vitro experiments, programmed cell death 4 (PDCD4) was a target of miR-497-5p by the dual-luciferase activity assay. The efficacy of PDCD4 on cell proliferation and metastasis in HCC was examined by transwell assays, CCK-8 assays and reverse transcription quantitative PCR (RT-qPCR). Additionally, we conducted a luciferase activity reporter assay to confirm the interaction between lncRNA XIST and miR-49-5p. Then, to evaluate the relationship between lncRNA XIST and miR-497-5p, several mechanistic experiments, including qRT-PCR, Western blotting, transwell assays and tumor xenograft assays, were performed.

RESULTS

miR-497-5p was upregulated in HCC tissues, and high expression of miR-497-5p resulted in increases in tumor size and tumor number and a higher tumor-node-metastasis (TNM) stage and Edmondson grade in patients with HCC. Silencing miR-497-5p inhibited the proliferation and migration of HCC cells. PDCD4, which was downregulated in HCC tissues, was shown to be a target of miR-497-5p and was negatively correlated with the expression of miR-497-5p. lncRNA XIST was found to act as a miR-497-5p sponge and to regulate the level of PDCD4, which is targeted by miR-497-5p. lncRNA XIST was observed to be downregulated in the HCC tissues and positively correlated with the expression of PDCD4.

CONCLUSIONS

Our findings reveal that the XIST/miR-497-5p/PDCD4 axis participates in HCC development and that XIST could be used as a biomarker of HCC.

Characteristics of herpes simplex virus infection and pathogenesis suggest a strategy for vaccine development

Herpes simplex virus (HSV) can cause oral or genital ulcerative lesions and even encephalitis in various age groups with high infection rates. More seriously, HSV may lead to a wide range of recurrent diseases throughout a lifetime. No vaccines against HSV are currently available. The accumulated clinical research data for HSV vaccines reveal that the effects of HSV interacting with the host, especially the host immune system, may be important for the development of HSV vaccines. HSV vaccine development remains a major challenge. Thus, we focus on the research data regarding the interactions of HSV and host immune cells, including dendritic cells (DCs), innate lymphoid cells (ILCs), macrophages, and natural killer (NK) cells, and the related signal transduction pathways involved in immune evasion and cytokine production. The aim is to explore possible strategies to develop new effective HSV vaccines.

Molecular characterization and antiapoptotic function analysis of the duck plague virus Us5 gene

Thus far, there have been no reports on the molecular characterization and antiapoptotic function of the DPV Us5 gene. To perform molecular characterization of DPV Us5, RT-PCR and pharmacological inhibition tests were used to ascertain the kinetic class of the Us5 gene. Western blotting and an indirect immunofluorescence assay (IFA) were used to analyze the expression level and subcellular localization of Us5 in infected cells at different time points. Us5 in purified DPV virions was identified by mass spectrometry. The results of RT-PCR, Western blotting, and pharmacological inhibition tests revealed that Us5 is transcribed mainly in the late stage of viral replication. The IFA results revealed that Us5 was localized throughout DPV-infected cells but was localized only to the cytoplasm of transfected cells. Mass spectrometry and Western blot analysis showed that Us5 was a virion component. Next, to study the antiapoptotic function of DPV Us5, we found that DPV CHv without gJ could induce more apoptosis cells than DPV-CHv BAC and rescue virus. we constructed a model of apoptosis in duck embryo fibroblasts (DEFs) induced by hydrogen peroxide (H₂O₂). Transfected cells expressing the Us5 gene were protected from apoptosis induced by H₂O₂, as measured by a TUNEL assay, a caspase activation assay and Flow Cytometry assay. The TUNEL assay and Flow Cytometry assay results showed that the recombinant plasmid pCAGGS-Us5 could inhibit apoptosis induced by H₂O₂ in DEF cells. However, caspase-3/7 and caspase-9 protein activity upregulated by H₂O₂ was significantly reduced in cells expressing the recombinant plasmid pCAGGS-Us5. Overall, these results show that the DPV Us5 gene is a late gene and that the Us5 protein is a component of the virion, is localized in the cytoplasm, and can inhibit apoptosis induced by H₂O₂ in DEF cells.

Bclaf1 critically regulates the type I interferon response and is degraded by alphaherpesvirus US3

Type I interferon response plays a prominent role against viral infection, which is frequently disrupted by viruses. Here, we report Bcl-2 associated transcription factor 1 (Bclaf1) is degraded during the alphaherpesvirus Pseudorabies virus (PRV) and Herpes simplex virus type 1 (HSV-1) infections through the viral protein US3. We further reveal that Bclaf1 functions critically in type I interferon signaling. Knockdown or knockout of Bclaf1 in cells significantly impairs interferon-α (IFNα) -mediated gene transcription and viral inhibition against US3 deficient PRV and HSV-1. Mechanistically, Bclaf1 maintains a mechanism allowing STAT1 and STAT2 to be efficiently phosphorylated in response to IFNα, and more importantly, facilitates IFN-stimulated gene factor 3 (ISGF3) binding with IFN-stimulated response elements (ISRE) for efficient gene transcription by directly interacting with ISRE and STAT2. Our studies establish the importance of Bclaf1 in IFNα-induced antiviral immunity and in the control of viral infections.

Us3 Protein Kinase Encoded by HSV: The Precise Function and Mechanism on Viral Life Cycle

All members of the Alphaherpesvirinae subfamily encode a serine/threonine kinase, designated Us3, which is not conserved in the other subfamilies. Us3 is a significant virulence factor for herpes simplex virus type 1 (HSV-1), which is one of the best-characterized members of the Alphaherpesvirinae family. Accumulating evidence indicates that HSV-1 Us3 is a multifunctional protein that plays various roles in the viral life cycle by phosphorylating a number of viral and cellular substrates. Therefore, the identification of Us3 substrates is directly connected to understanding Us3 functions and mechanisms. To date, more than 23 phosphorylation events upregulated by HSV-1 Us3 have been reported. However, few of these have been shown to be both physiological substrates of Us3 in infected cells and directly linked with Us3 functions in infected cells. In this chapter, we summarize the 12 physiological substrates of Us3 and the Us3-mediated functions. Furthermore, based on the identified phosphorylation sites of Us3 or Us3 homolog physiological substrates, we reverified consensus phosphorylation target sequences on the physiological substrates of Us3 and Us3 homologs in vitro and in infected cells. This information might aid the further identification of novel Us3 substrates and as yet unidentified Us3 functions.

The Natural Compound Homoharringtonine Presents Broad Antiviral Activity In Vitro and In Vivo

To complement traditional antivirals, natural compounds that act via host targets and present high barriers to resistance are of increasing interest. In the work reported here, we detected that homoharringtonine (HHT) presents effective antiviral activity. HHT completely inhibited infections of vesicular stomatitis virus (VSV), Newcastle disease virus (NDV), and porcine epidemic diarrhea virus (PEDV) at concentrations of 50, 100, and 500 nM in cell cultures, respectively. Treatment with HHT at doses of 0.05 or 0.2 mg/kg significantly reduced viral load and relieved severe symptoms in PEDV- or NDV-infected animals. HHT treatment, however, moderately inhibited avian influenza virus (AIV) infection, suggesting its potent antiviral action is restricted to a number of classes of RNA viruses. In this study, we also observed that HHT actively inhibited herpes simplex virus type 1 (HSV-1) replication with a 50% inhibitory concentration (IC50) of 139 nM; the treatment with HHT at 1000 nM led to reductions of three orders of magnitude. Moreover, HHT antagonized the phosphorylation level of endogenous and exogenous eukaryotic initiation factor 4E (p-eIF4E), which might regulate the selective translation of specific messenger RNA (mRNA). HHT provides a starting point for further progress toward the clinical development of broad-spectrum antivirals.

The mechanisms and clinical significance of PDCD4 in colorectal cancer

In recent years, the incidence and mortality of colorectal cancer (CRC) have been on a global upward trend. There is an urgent need for effective tools to prevent and treat CRC and reduce morbidity and mortality of CRC patients. Recent evidence suggests that programmed cell death 4 (PDCD4), a novel tumor suppressor gene, inhibits tumor progression at transcriptional and translational levels and regulates multiple signal transduction pathways. However, little is known about the precise mechanisms regulating PDCD4 expression in CRC. In addition, several studies have demonstrated that the expression of in CRC is down-regulated or even absent. PDCD4 is therefore considered to be an independent prognostic factor in CRC and may be a potential support diagnostic tool for distinguishing in normal colon tissue, benign adenoma and CRC. This review will focus on the expression of PDCD4 in CRC and the relevant molecular mechanisms.

Cytoplasmic Translocation of Nucleolar Protein NOP53 Promotes Viral Replication by Suppressing Host Defense

NOP53 is a tumor suppressor protein located in the nucleolus and is translocated to the cytoplasm during infection by vesicular stomatitis virus (VSV) and herpes simplex virus type 1 (HSV-1), as shown in our previous study. Cytoplasmic NOP53 interacts with the retinoic acid-inducible gene I (RIG-I) to remove its K63-linked ubiquitination, leading to attenuation of type I interferon IFN-β. In the present study, we found no obvious translocation of NOP53 in infection by a mutant virus lacking ICP4 (HSV-1/d120, replication inadequate). Blocking cytoplasmic translocation of NOP53 by the deletion of its nuclear export sequence (NES) abrogated its ability to support viral replication. These results demonstrated that NOP53 redistribution is related to viral replication. It is interesting that treatment with poly (I:C) or RIG-I-N (a constitutively-active variant) directly induced NOP53 cytoplasmic translocation. To better assess the function of cytoplasmic NOP53 in viral replication, the NOP53-derived protein N3-T, which contains a human immunodeficiency virus (HIV)-derived cell-penetrating Tat peptide at the C-terminal region of N3 (residues 330–432), was constructed and expressed. The recombinant N3-T protein formed trimers, attenuated the expression of IFN-β and IFN-stimulated genes, as well as decreased the phosphorylation level of interferon regulatory factor 3 (IRF3). Furthermore, N3-T promoted the efficient replication of enveloped and non-enveloped DNA and RNA viruses belonging to 5 families. Our findings expand the understanding of the mechanism by which viruses utilize the nucleolar protein NOP53 for optimal viral replication.

Endoplasmic reticulum-to-Golgi transitions upon herpes virus infection

Background: Herpesvirus capsids are assembled in the nucleus before they are translocated to the perinuclear space by budding, acquiring tegument and envelope, or releasing to the cytoplasm in a "naked" state via impaired nuclear envelope. One model proposes that envelopment, "de-envelopment" and "re-envelopment" are essential steps for production of infectious virus. Glycoproteins gB/gH were reported to be essential for de-envelopment, by fusion of the "primary" envelope with the outer nuclear membrane. Yet, a high proportion of enveloped virions generated from genomes with deleted gB/gH were found in the cytoplasm and extracellular space, suggesting the existence of an alternative exit route. Methods: We investigated the relatedness between the nuclear envelope and membranes of the endoplasmic reticulum and Golgi complex, in cells infected with either herpes simplex virus 1 (HSV-1) or a Us3 deletion mutant thereof, or with bovine herpesvirus 1 (BoHV-1) by transmission and scanning electron microscopy, employing freezing technique protocols that lead to improved spatial and temporal resolution. Results: Scanning electron microscopy showed the Golgi complex as a compact entity in a juxtanuclear position covered by a membrane on the cis face. Transmission electron microscopy revealed that Golgi membranes merge with membranes of the endoplasmic reticulum forming an entity with the perinuclear space. All compartments contained enveloped virions. After treatment with brefeldin A, HSV-1 virions aggregated in the perinuclear space and endoplasmic reticulum, while infectious progeny virus was still produced. Conclusions: The data strongly suggest that virions are intraluminally transported from the perinuclear space via Golgi complex-endoplasmic reticulum transitions into Golgi cisternae for packaging into transport vacuoles. Furthermore, virions derived by budding at nuclear membranes are infective as has been shown for HSV-1 Us3 deletion mutants, which almost entirely accumulate in the perinuclear space. Therefore, de-envelopment followed by re-envelopment is not essential for production of infective progeny virus.

Endoplasmic reticulum-to-Golgi transitions upon herpes virus infection

Background: Herpesvirus capsids are assembled in the nucleus, translocated to the perinuclear space by budding, acquiring tegument and envelope, or released to the cytoplasm via impaired nuclear envelope. One model proposes that envelopment, "de-envelopment" and "re-envelopment" is essential for production of infectious virus. Glycoproteins gB/gH were reported to be essential for de-envelopment, by fusion of the "primary" envelope with the outer nuclear membrane. Yet, a high proportion of enveloped virions generated from genomes with deleted gB/gH were found in the cytoplasm and extracellular space, suggesting the existence of alternative exit routes. Methods: We investigated the relatedness between the nuclear envelope and membranes of the endoplasmic reticulum and Golgi complex, in cells infected with either herpes simplex virus 1 (HSV-1) or a Us3 deletion mutant thereof, or with bovine herpesvirus 1 (BoHV-1) by transmission and scanning electron microscopy, employing freezing technique protocols. Results:  The Golgi complex is a compact entity in a juxtanuclear position covered by a membrane on the cis face. Golgi membranes merge with membranes of the endoplasmic reticulum forming an entity with the perinuclear space. All compartments contained enveloped virions. After treatment with brefeldin A, HSV-1 virions aggregated in the perinuclear space and endoplasmic reticulum, while infectious progeny virus was still produced. Conclusions: The data suggest that virions derived by budding at nuclear membranes are intraluminally transported from the perinuclear space via Golgi -endoplasmic reticulum transitions into Golgi cisternae for packaging. Virions derived by budding at nuclear membranes are infective like Us3 deletion mutants, which  accumulate in the perinuclear space. Therefore, i) de-envelopment followed by re-envelopment is not essential for production of infective progeny virus, ii) the process taking place at the outer nuclear membrane is budding not fusion, and iii) naked capsids gain access to the cytoplasmic matrix via impaired nuclear envelope as reported earlier.

Cellular protein GLTSCR2: A valuable target for the development of broad-spectrum antivirals

Viral infection induces translocation of the nucleolar protein GLTSCR2 from the nucleus to the cytoplasm, resulting in attenuation of the type I interferon IFN-β. Addressing the role of GLTSCR2 in viral replication, we detect that knocking down GLTSCR2 by shRNAs results in significant suppression of viral replication in mammalian and chicken cells. Injection of chicken embryo with the GLTSCR2-specific shRNA-1370 simultaneously or 24 h prior to infection with Newcastle disease virus (NDV) substantially reduces viral replication in chicken embryo fibroblasts. Injection of shRNA-1370 into chicken embryo also reduces the replication of avian influenza virus (AIV). In contrast, GLTSCR2-derived protein G4-T, forming α-helical dimers, increases replication of seven various DNA and RNA viruses in cells. Our studies reveal that alteration of the function of cellular GLTSCR2 plays a role in supporting viral replication. GLTSCR2 should be seriously considered as a therapeutic target for developing broad spectrum antiviral agents to effectively control viral infection.

The suppression of apoptosis by α-herpesvirus

Apoptosis, an important innate immune mechanism that eliminates pathogen-infected cells, is primarily triggered by two signalling pathways: the death receptor pathway and the mitochondria-mediated pathway. However, many viruses have evolved various strategies to suppress apoptosis by encoding anti-apoptotic factors or regulating apoptotic signalling pathways, which promote viral propagation and evasion of the host defence. During its life cycle, α-herpesvirus utilizes an elegant multifarious anti-apoptotic strategy to suppress programmed cell death. This progress article primarily focuses on the current understanding of the apoptosis-inhibition mechanisms of α-herpesvirus anti-apoptotic genes and their expression products and discusses future directions, including how the anti-apoptotic function of herpesvirus could be targeted therapeutically.

Functional prediction of differentially expressed lncRNAs in HSV-1 infected human foreskin fibroblasts

BACKGROUND

One of the most important functions of long noncoding RNAs (lncRNAs) is to control protein coding gene transcription by acting locally in cis, or remotely in trans. Herpes Simplex Virus type I (HSV-1) latently infects over 80 % of the population, its reactivation from latency usually results in productive infections in human epithelial cells, and is responsible for the common cold sores and genital Herpes. HSV-1 productive infection leads to profound changes in the host cells, including the host transcriptome. However, how genome wide lncRNAs expressions are affected by the infection and how lncRNAs expression relates to protein coding gene expression have not been analyzed.

METHODS

We analyzed differentially expressed lncRNAs and their potential targets from RNA-seq data in HSV-1 infected human foreskin fibroblast (HFF) cells. Based on correlations of expression patterns of differentially expressed protein-coding genes and lncRNAs, we predicted that these lncRNAs may regulate, either in cis or in trans, the expression of many cellular protein-coding genes.

RESULTS

Here we analyzed HSV-1 infection induced, differentially expressed lncRNAs and predicted their target genes. We detected 208 annotated and 206 novel differentially expressed lncRNAs. Gene Ontology and Pathway enrichment analyses revealed potential lncRNA targets, including genes in chromatin assembly, genes in neuronal development and neurodegenerative diseases and genes in the immune response, such as Toll-like receptor signaling and RIG-I-like receptor signaling pathways.

CONCLUSIONS

We found that differentially expressed lncRNAs may regulate the expression of many cellular protein-coding genes involved in pathways from native immunity to neuronal development, thus revealing important roles of lncRNAs in the regulation of host transcriptional programs in HSV-1 infected human cells.

Oncolytic herpes simplex virus interactions with the host immune system

Oncolytic viruses (OVs), like oncolytic herpes simplex virus (oHSV), are genetically engineered to selectively replicate in and kill cancer cells, while sparing normal cells. Initial OV infection, cell death, and subsequent OV propagation within the tumor microenvironment leads to a cascade of host responses (innate and adaptive), reflective of natural anti-viral immune responses. These host-virus interactions are critical to the balance between OV activities, anti-viral immune responses limiting OV, and induction of anti-tumor immunity. The host response against oHSV is complex, multifaceted, and modulated by the tumor microenvironment and immunosuppression. As a successful pathogen, HSV has multiple mechanisms to evade such host responses. In this review, we will discuss these mechanisms and HSV evasion, and how they impact oHSV therapy.

Cellular responses to HSV-1 infection are linked to specific types of alterations in the host transcriptome

Pathogen invasion triggers a number of cellular responses and alters the host transcriptome. Here we report that the type of changes to cellular transcriptome is related to the type of cellular functions affected by lytic infection of Herpes Simplex Virus type I in Human primary fibroblasts. Specifically, genes involved in stress responses and nuclear transport exhibited mostly changes in alternative polyadenylation (APA), cell cycle genes showed mostly alternative splicing (AS) changes, while genes in neurogenesis, rarely underwent these changes. Transcriptome wide, the infection resulted in 1,032 cases of AS, 161 incidences of APA, 1,827 events of isoform changes, and up regulation of 596 genes and down regulations of 61 genes compared to uninfected cells. Thus, these findings provided important and specific links between cellular responses to HSV-1 infection and the type of alterations to the host transcriptome, highlighting important roles of RNA processing in virus-host interactions.

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.

Quantitative Trait Locus Based Virulence Determinant Mapping of the HSV-1 Genome in Murine Ocular Infection: Genes Involved in Viral Regulatory and Innate Immune Networks Contribute to Virulence

Herpes simplex virus type 1 causes mucocutaneous lesions, and is the leading cause of infectious blindness in the United States. Animal studies have shown that the severity of HSV-1 ocular disease is influenced by three main factors; innate immunity, host immune response and viral strain. We previously showed that mixed infection with two avirulent HSV-1 strains (OD4 and CJ994) resulted in recombinants that exhibit a range of disease phenotypes from severe to avirulent, suggesting epistatic interactions were involved. The goal of this study was to develop a quantitative trait locus (QTL) analysis of HSV-1 ocular virulence determinants and to identify virulence associated SNPs. Blepharitis and stromal keratitis quantitative scores were characterized for 40 OD4:CJ994 recombinants. Viral titers in the eye were also measured. Virulence quantitative trait locus mapping (vQTLmap) was performed using the Lasso, Random Forest, and Ridge regression methods to identify significant phenotypically meaningful regions for each ocular disease parameter. The most predictive Ridge regression model identified several phenotypically meaningful SNPs for blepharitis and stromal keratitis. Notably, phenotypically meaningful nonsynonymous variations were detected in the UL24, UL29 (ICP8), UL41 (VHS), UL53 (gK), UL54 (ICP27), UL56, ICP4, US1 (ICP22), US3 and gG genes. Network analysis revealed that many of these variations were in HSV-1 regulatory networks and viral genes that affect innate immunity. Several genes previously implicated in virulence were identified, validating this approach, while other genes were novel. Several novel polymorphisms were also identified in these genes. This approach provides a framework that will be useful for identifying virulence genes in other pathogenic viruses, as well as epistatic effects that affect HSV-1 ocular virulence.

In addition to causing recurrent labial lesions, herpes simplex virus type 1 (HSV-1) is also the primary source of infectious blindness in the United States. Animal studies have shown that the severity of infection is influenced by several factors, including viral strain. Conventional studies investigating the genetics of viral virulence have focused on characterizing a naturally occurring strain, and engineering mutations into viruses. The purpose of this study was to develop a quantitative trait locus (QTL) computational analysis of HSV-1 genome to identify ocular virulence determinants and associated viral SNPs. Notably, phenotypically meaningful variations were detected in the UL24, UL29 (ICP8), UL41 (VHS), UL53 (gK), UL54 (ICP27), UL56, ICP4, US1 (ICP22), US3 and gG genes. Several genes previously implicated in virulence were identified, validating this approach, while other genes were novel. This is the first time a QTL based approach has been applied to a herpesvirus and it will also be valuable in future virulence, epistasis, and protein-protein interaction studies.

Insights into the function of tegument proteins from the varicella zoster virus

Chickenpox (varicella) is caused by primary infection with varicella zoster virus (VZV), which can establish long-term latency in the host ganglion. Once reactivated, the virus can cause shingles (zoster) in the host. VZV has a typical herpesvirus virion structure consisting of an inner DNA core, a capsid, a tegument, and an outer envelope. The tegument is an amorphous layer enclosed between the nucleocapsid and the envelope, which contains a variety of proteins. However, the types and functions of VZV tegument proteins have not yet been completely determined. In this review, we describe the current knowledge on the multiple roles played by VZV tegument proteins during viral infection. Moreover, we discuss the VZV tegument protein-protein interactions and their impact on viral tissue tropism in SCID-hu mice. This will help us develop a better understanding of how the tegument proteins aid viral DNA replication, evasion of host immune response, and pathogenesis.

The UL13 and US3 Protein Kinases of Herpes Simplex Virus 1 Cooperate to Promote the Assembly and Release of Mature, Infectious Virions

Herpes simplex virus type 1 (HSV-1) encodes two bona fide serine/threonine protein kinases, the US3 and UL13 gene products. HSV-1 ΔUS3 mutants replicate with wild-type efficiency in cultured cells, and HSV-1 ΔUL13 mutants exhibit <10-fold reduction in infectious viral titers. Given these modest phenotypes, it remains unclear how the US3 and UL13 protein kinases contribute to HSV-1 replication. In the current study, we designed a panel of HSV-1 mutants, in which portions of UL13 and US3 genes were replaced by expression cassettes encoding mCherry protein or green fluorescent protein (GFP), respectively, and analyzed DNA replication, protein expression, and spread of these mutants in several cell types. Loss of US3 function alone had largely negligible effect on viral DNA accumulation, gene expression, virion release, and spread. Loss of UL13 function alone also had no appreciable effects on viral DNA levels. However, loss of UL13 function did result in a measurable decrease in the steady-state levels of two viral glycoproteins (gC and gD), release of total and infectious virions, and viral spread. Disruption of both genes did not affect the accumulation of viral DNA, but resulted in further reduction in gC and gD steady-state levels, and attenuation of viral spread and infectious virion release. These data show that the UL13 kinase plays an important role in the late phase of HSV-1 infection, likely by affecting virion assembly and/or release. Moreover, the data suggest that the combined activities of the US3 and UL13 protein kinases are critical to the efficient assembly and release of infectious virions from HSV-1-infected cells.

Phylogenetically Distant Viruses Use the Same BH3-Only Protein Puma to Trigger Bax/Bak-Dependent Apoptosis of Infected Mouse and Human Cells

Viruses can trigger apoptosis of infected host cells if not counteracted by cellular or viral anti-apoptotic proteins. These protective proteins either inhibit the activation of caspases or they act as Bcl-2 homologs to prevent Bax/Bak-mediated outer mitochondrial membrane permeabilization (MOMP). The exact mechanism by which viruses trigger MOMP has however remained enigmatic. Here we use two distinct types of viruses, a double stranded DNA virus, herpes simplex virus-1 (HSV-1) and a positive sense, single stranded RNA virus, Semliki Forest virus (SFV) to show that the BH3-only protein Puma is the major mediator of virus-induced Bax/Bak activation and MOMP induction. Indeed, when Puma was genetically deleted or downregulated by shRNA, mouse embryonic fibroblasts and IL-3-dependent monocytes as well as human colon carcinoma cells were as resistant to virus-induced apoptosis as their Bax/Bak double deficient counterparts (Bax/Bak-/-). Puma protein expression started to augment after 2 h postinfection with both viruses. Puma mRNA levels increased as well, but this occurred after apoptosis initiation (MOMP) because it was blocked in cells lacking Bax/Bak or overexpressing Bcl-xL. Moreover, none of the classical Puma transcription factors such as p53, p73 or p65 NFκB were involved in HSV-1-induced apoptosis. Our data suggest that viruses use a Puma protein-dependent mechanism to trigger MOMP and apoptosis in host cells.

Selective recruitment of host factors by HSV-1 replication centers

Herpes simplex virus type 1 (HSV-1) enters productive infection after infecting epithelial cells, where it controls the host nucleus to make viral proteins, starts viral DNA synthesis and assembles infectious virions. In this process, replicating viral genomes are organized into replication centers to facilitate viral growth. HSV-1 is known to use host factors, including host chromatin and host transcription regulators, to transcribe its genes; however, the invading virus also encounters host defense and stress responses to inhibit viral growth. Recently, we found that HSV-1 replication centers recruit host factor CTCF but exclude γH2A.X. Thus, HSV-1 replication centers may selectively recruit cellular factors needed for viral growth, while excluding host factors that are deleterious for viral transcription or replication. Here we report that the viral replication centers selectively excluded modified histone H3, including heterochromatin mark H3K9me3, H3S10P and active chromatin mark H3K4me3, but not unmodified H3. We found a dynamic association between the viral replication centers and host RNA polymerase II. The centers also recruited components of the DNA damage response pathway, including 53BP1, BRCA1 and host antiviral protein SP100. Importantly, we found that ATM kinase was needed for the recruitment of CTCF to the viral centers. These results suggest that the HSV-1 replication centers took advantage of host signaling pathways to actively recruit or exclude host factors to benefit viral growth.

Dicer1 imparts essential survival cues in Notch-driven T-ALL via miR-21-mediated tumor suppressor Pdcd4 repression

The modulatory function of individual microRNAs (miRNAs) in Notch-driven T-cell acute lymphoblastic leukemias (T-ALLs) has recently been established. Although protumorigenic and tumor-suppressive miRNAs are implicated in disease onset in murine models of Notch-driven T-cell leukemia, whether Dicer1-processed miRNAs are essential for Notch-driven T-ALL is currently unknown. Here we used conditional and inducible genetic loss-of-function approaches to test whether the development and maintenance of Notch-driven T-ALL was dependent on Dicer1 function. Mice with specific inactivation of both Dicer1 alleles in the T-cell lineage did not develop Notch-driven T-ALL. In contrast, loss of 1 functional Dicer1 allele did not significantly perturb T-ALL onset and tumor progression. Inducible inactivation of Dicer1 in early stage polyclonal T-ALL cells was sufficient to abrogate T-ALL progression in leukemic mice, whereas late-stage monoclonal T-ALL cells were counterselected against loss of Dicer1. Lineage-tracing experiments revealed that Dicer1 deficiency led to the induction of apoptosis in T-ALL cells, whereas cell cycle progression remained unaltered. Through microarray-based miRNA profiling, we identified miR-21 as a previously unrecognized miRNA deregulated in both mouse and human T-ALL. Herein, we demonstrate that miR-21 regulates T-ALL cell survival via repression of the tumor suppressor Pdcd4.

Evasion of early antiviral responses by herpes simplex viruses

Besides overcoming physical constraints, such as extreme temperatures, reduced humidity, elevated pressure, and natural predators, human pathogens further need to overcome an arsenal of antimicrobial components evolved by the host to limit infection, replication and optimally, reinfection. Herpes simplex virus-1 (HSV-1) and herpes simplex virus-2 (HSV-2) infect humans at a high frequency and persist within the host for life by establishing latency in neurons. To gain access to these cells, herpes simplex viruses (HSVs) must replicate and block immediate host antiviral responses elicited by epithelial cells and innate immune components early after infection. During these processes, infected and noninfected neighboring cells, as well as tissue-resident and patrolling immune cells, will sense viral components and cell-associated danger signals and secrete soluble mediators. While type-I interferons aim at limiting virus spread, cytokines and chemokines will modulate resident and incoming immune cells. In this paper, we discuss recent findings relative to the early steps taking place during HSV infection and replication. Further, we discuss how HSVs evade detection by host cells and the molecular mechanisms evolved by these viruses to circumvent early antiviral mechanisms, ultimately leading to neuron infection and the establishment of latency.

Interleukin-1α released from HSV-1-infected keratinocytes acts as a functional alarmin in the skin

Herpes simplex virus-1 (HSV-1) is a human pathogen that utilizes several strategies to circumvent the host immune response. An immune evasion mechanism employed by HSV-1 is retention of interleukin-1β (IL-1β) in the intracellular space, which blocks the pro-inflammatory activity of IL-1β. Here, we report that HSV-1 infected keratinocytes actively release the also pro-inflammatory IL-1α, preserving the ability of infected cells to signal danger to the surrounding tissue. The extracellular release of IL-1α is independent of inflammatory caspases. In vivo recruitment of leukocytes to early HSV-1 micro-infection sites within the epidermis is dependent upon IL-1 signalling. Following cutaneous HSV-1 infection, mice unable to signal via extracellular IL-1α exhibit an increased mortality rate associated with viral dissemination. We conclude that IL-1α acts as an alarmin essential for leukocyte recruitment and protective immunity against HSV-1. This function may have evolved to counteract an immune evasion mechanism deployed by HSV-1.

Phosphorylation of a herpes simplex virus 1 dUTPase by a viral protein kinase, Us3, dictates viral pathogenicity in the central nervous system but not at the periphery

Herpes simplex virus 1 (HSV-1) encodes Us3 protein kinase, which is critical for viral pathogenicity in both mouse peripheral sites (e.g., eyes and vaginas) and in the central nervous systems (CNS) of mice after intracranial and peripheral inoculations, respectively. Whereas some Us3 substrates involved in Us3 pathogenicity in peripheral sites have been reported, those involved in Us3 pathogenicity in the CNS remain to be identified. We recently reported that Us3 phosphorylated HSV-1 dUTPase (vdUTPase) at serine 187 (Ser-187) in infected cells, and this phosphorylation promoted viral replication by regulating optimal enzymatic activity of vdUTPase. In the present study, we show that the replacement of vdUTPase Ser-187 by alanine (S187A) significantly reduced viral replication and virulence in the CNS of mice following intracranial inoculation and that the phosphomimetic substitution at vdUTPase Ser-187 in part restored the wild-type viral replication and virulence. Interestingly, the S187A mutation in vdUTPase had no effect on viral replication and pathogenic effects in the eyes and vaginas of mice after ocular and vaginal inoculation, respectively. Similarly, the enzyme-dead mutation in vdUTPase significantly reduced viral replication and virulence in the CNS of mice after intracranial inoculation, whereas the mutation had no effect on viral replication and pathogenic effects in the eyes and vaginas of mice after ocular and vaginal inoculation, respectively. These observations suggested that vdUTPase was one of the Us3 substrates responsible for Us3 pathogenicity in the CNS and that the CNS-specific virulence of HSV-1 involved strict regulation of vdUTPase activity by Us3 phosphorylation.

IMPORTANCE

Herpes simplex virus 1 (HSV-1) encodes a viral protein kinase Us3 which is critical for pathogenicity both in peripheral sites and in the central nervous systems (CNS) of mice following peripheral and intracranial inoculations, respectively. Whereas some Us3 substrates involved in Us3 pathogenicity in peripheral sites have been reported, those involved in Us3 pathogenicity in the CNS remain to be identified. Here, we report that Us3 phosphorylation of viral dUTPase (vdUTPase) at serine 187 (Ser-187), which has been shown to promote the vdUTPase activity, appears to be critical for viral virulence in the CNS but not for pathogenic effects in peripheral sites. Since HSV proteins critical for viral virulence in the CNS are, in almost all cases, also involved in viral pathogenicity at peripheral sites, this phosphorylation event is a unique report of a specific mechanism involved in HSV-1 virulence in the CNS.

Herpes simplex virus 1 protein kinase Us3 phosphorylates viral dUTPase and regulates its catalytic activity in infected cells

Us3 is a serine-threonine protein kinase encoded by herpes simplex virus 1 (HSV-1). In this study, a large-scale phosphoproteomic analysis of titanium dioxide affinity chromatography-enriched phosphopeptides from HSV-1-infected cells using high-accuracy mass spectrometry (MS) and subsequent analyses showed that Us3 phosphorylated HSV-1-encoded dUTPase (vdUTPase) at serine 187 (Ser-187) in HSV-1-infected cells. Thus, the following observations were made. (i) In in vitro kinase assays, Ser-187 in the vdUTPase domain was specifically phosphorylated by Us3. (ii) Phosphorylation of vdUTPase Ser-187 in HSV-1-infected cells was detected by phosphate-affinity polyacrylamide gel electrophoresis analyses and was dependent on the kinase activity of Us3. (iii) Replacement of Ser-187 with alanine (S187A) in vdUTPase and an amino acid substitution in Us3 that inactivated its kinase activity significantly downregulated the enzymatic activity of vdUTPase in HSV-1-infected cells, whereas a phosphomimetic substitution at vdUTPase Ser-187 restored the wild-type enzymatic activity of vdUTPase. (iv) The vdUTPase S187A mutation as well as the kinase-dead mutation in Us3 significantly reduced HSV-1 replication in human neuroblastoma SK-N-SH cells at a multiplicity of infection (MOI) of 5 but not at an MOI of 0.01, whereas the phosphomimetic substitution at vdUTPase Ser-187 restored the wild-type viral replication at an MOI of 5. In contrast, these mutations had no effect on HSV-1 replication in Vero and HEp-2 cells. Collectively, our results suggested that Us3 phosphorylation of vdUTPase Ser-187 promoted HSV-1 replication in a manner dependent on cell types and MOIs by regulating optimal enzymatic activity of vdUTPase.

The nuclear-cytoplasmic shuttling of virion host shutoff RNase is enabled by pUL47 and an embedded nuclear export signal and defines the sites of degradation of AU-rich and stable cellular mRNAs

The herpes simplex virus host shutoff RNase (VHS-RNase) is the major early block of host responses to infection. VHS-RNase is introduced into cells during infection and selectively degrades stable mRNAs made before infection and the normally short-lived AU-rich stress response mRNAs induced by sensors of innate immunity. Through its interactions with pUL47, another tegument protein, it spares from degradation viral mRNAs. Analyses of embedded motifs revealed that VHS-RNase contains a nuclear export signal (NES) but not a nuclear localization signal. To reconcile the potential nuclear localization with earlier studies showing that VHS-RNase degrades mRNAs in polyribosomes, we constructed a mutant in which NES was ablated. Comparison of the mutant and wild-type VHS-RNases revealed the following. (i) On infection, VHS-RNase is transported to the nucleus, but only the wild-type protein shuttles between the nucleus and cytoplasm. (ii) Both VHS-RNases localized in the cytoplasm following transfection. On cotransfection with pUL47, a fraction of VHS-RNase was translocated to the nucleus, suggesting that pUL47 may enable nuclear localization of VHS-RNase. (iii) In infected cells, VHS-RNase lacking NES degraded the short-lived AU-rich mRNAs but not the stable mRNAs. In transfected cells, both wild-type and NES mutant VHS-RNases effectively degraded cellular mRNAs. Our results suggest that the stable mRNAs are degraded in the cytoplasm, whereas the AU-rich mRNAs may be degraded in both cellular compartments. The selective sparing of viral mRNAs may take place during the nuclear phase in the course of interaction of pUL47, VHS-RNase, and nascent viral mRNAs.

Role of immediate early protein ICP27 in the differential sensitivity of herpes simplex viruses 1 and 2 to leptomycin B

Leptomycin B (LMB) is a highly specific inhibitor of CRM1, a cellular karyopherin-β that transports nuclear export signal-containing proteins from the nucleus to the cytoplasm. Previous work has shown that LMB blocks herpes simplex virus 1 (HSV-1) replication in Vero cells and that certain mutations in viral immediate early protein ICP27 can confer LMB resistance. However, little is known of the molecular mechanisms involved. Here we report that HSV-2, a close relative of HSV-1, is naturally resistant to LMB. To see whether the ICP27 gene determines this phenotypic difference, we generated an HSV-1 mutant that expresses the HSV-2 ICP27 instead of the HSV-1 protein. This recombinant was fully sensitive to LMB, indicating that one or more other viral genes must be important in determining HSV-2's LMB-resistant phenotype. In additional work, we report several findings that shed light on how HSV-1 ICP27 mutations can confer LMB resistance. First, we show that LMB treatment of HSV-1-infected cells leads to suppression of late viral protein synthesis and a block to progeny virion release. Second, we identify a novel type of ICP27 mutation that can confer LMB resistance, that being the addition of a 100-residue amino-terminal affinity purification tag. Third, by studying infections where both LMB-sensitive and LMB-resistant forms of ICP27 are present, we show that HSV-1's sensitivity to LMB is dominant to its resistance. Together, our results suggest a model in which the N-terminal portion of ICP27 mediates a nonessential activity that interferes with HSV-1 replication when CRM1 is inactive. We suggest that LMB resistance mutations weaken or abrogate this activity.