Herpes simplex virus enhances chemokine function through modulation of receptor trafficking and oligomerization

Viral modulation of type II interferon increases T cell adhesion and virus spread

During primary varicella zoster virus (VZV) infection, infected lymphocytes drive primary viremia, causing systemic dissemination throughout the host, including the skin. This results in cytokine expression, including interferons (IFNs), which partly limit infection. VZV also spreads from skin keratinocytes to lymphocytes prior to secondary viremia. It is not clear how VZV achieves this while evading the cytokine response. Here, we show that VZV glycoprotein C (gC) binds IFN-γ and modifies its activity, increasing the expression of a subset of IFN-stimulated genes (ISGs), including intercellular adhesion molecule 1 (ICAM1), chemokines and immunomodulatory genes. The higher ICAM1 protein level at the plasma membrane of keratinocytes facilitates lymphocyte function-associated antigen 1-dependent T cell adhesion and expression of gC during infection increases VZV spread to peripheral blood mononuclear cells. This constitutes the discovery of a strategy to modulate IFN-γ activity, upregulating a subset of ISGs, promoting enhanced lymphocyte adhesion and virus spread.

Cell surface nucleocapsid protein expression: A betacoronavirus immunomodulatory strategy

We recently reported that SARS-CoV-2 nucleocapsid (N) protein is abundantly expressed on the surface of both infected and neighboring uninfected cells, where it enables activation of Fc receptor-bearing immune cells with anti-N antibodies (Abs) and inhibits leukocyte chemotaxis by binding chemokines (CHKs). Here, we extend these findings to N from the common cold human coronavirus (HCoV)-OC43, which is also robustly expressed on the surface of infected and noninfected cells by binding heparan sulfate/heparin (HS/H). HCoV-OC43 N binds with high affinity to the same set of 11 human CHKs as SARS-CoV-2 N, but also to a nonoverlapping set of six cytokines. As with SARS-CoV-2 N, HCoV-OC43 N inhibits CXCL12β-mediated leukocyte migration in chemotaxis assays, as do all highly pathogenic and common cold HCoV N proteins. Together, our findings indicate that cell surface HCoV N plays important evolutionarily conserved roles in manipulating host innate immunity and as a target for adaptive immunity.

Phylogenetic and Genomic Characterization of Whole Genome Sequences of Ocular Herpes Simplex Virus Type 1 Isolates Identifies Possible Virulence Determinants in Humans

Purpose

There are limited data on the prevalence and genetic diversity of herpes simplex virus type 1 (HSV-1) virulence genes in ocular isolates. Here, we sequenced 36 HSV-1 ocular isolates, collected by the Bascom Palmer Eye Institute, a university-based eye hospital, from three different ocular anatomical sites (conjunctiva, cornea, and eyelid) and carried out a genomic and phylogenetic analyses.

Methods

The PacBio Sequel II long read platform was used for genome sequencing. Phylogenetic analysis and genomic analysis were performed to help better understand genetic variability among common virulence genes in ocular herpetic disease.

Results

A phylogenetic network generated using the genome sequences of the 36 Bascom Palmer ocular isolates, plus 174 additional strains showed that ocular isolates do not group together phylogenetically. Analysis of the thymidine kinase and DNA polymerase protein sequences from the Bascom Palmer isolates showed multiple novel single nucleotide polymorphisms, but only one, BP-K14 encoded a known thymidine kinase acyclovir resistance mutation. An analysis of the multiple sequence alignment comprising the 51 total ocular isolates versus 159 nonocular strains detected several possible single nucleotide polymorphisms in HSV-1 genes that were found significantly more often in the ocular isolates. These genes included UL6, gM, VP19c, VHS, gC, VP11/12, and gG.

Conclusions

There does not seem to be a specific genetic feature of viruses causing ocular infection. The identification of novel and common recurrent polymorphisms may help to understand the drivers of herpetic pathogenicity and specific factors that may influence the virulence of ocular disease.

Colonization of peripheral ganglia by herpes simplex virus type 1 and 2

Herpes simplex virus type 1 (HSV-1) and 2 (HSV-2) infect and establish latency in neurons of the peripheral nervous system to persist lifelong in the host and to cause recurrent disease. During primary infection, HSV replicates in epithelial cells in the mucosa and skin and then infects neurites, highly dynamic structures that grow or retract in the presence of attracting or repelling cues, respectively. Following retrograde transport in neurites, HSV establishes latency in the neuronal nucleus. Viral and cellular proteins participate in the chromatinization of the HSV genome that regulates gene expression, persistence, and reactivation. HSV-2 modulates neurite outgrowth during primary infection and upon reactivation, probably to facilitate infection and survival of neurons. Whether HSV-1 modulates neurite outgrowth and the underlying mechanism is currently under investigation. This review deals with HSV-1 and HSV-2 colonization of peripheral neurons, with a focus on the modulation of neurite outgrowth by these viruses.

Viral modulation of type II interferon increases T cell adhesion and virus spread

During primary infection, varicella zoster virus (VZV) infects epithelial cells in the respiratory lymphoid organs and mucosa. Subsequent infection of lymphocytes, T cells in particular, causes primary viremia allowing systemic spread throughout the host, including the skin. This results in the expression of cytokines, including interferons (IFNs) which partly limit primary infection. VZV also spreads from skin keratinocytes to lymphocytes prior to secondary viremia. How VZV infects lymphocytes from epithelial cells while evading the cytokine response has not been fully established. Here, we show that VZV glycoprotein C (gC) binds IFN-γ and modifies its activity. Transcriptomic analysis revealed that gC in combination with IFN-γ increased the expression of a small subset of IFN-stimulated genes (ISGs), including intercellular adhesion molecule 1 (ICAM1), as well as several chemokines and immunomodulatory genes. The higher ICAM1 protein level at the plasma membrane of epithelial cells resulted in lymphocyte function-associated antigen 1 (LFA-1)-dependent T cell adhesion. This gC activity required a stable interaction with IFN-γ and signalling through the IFN-γ receptor. Finally, the presence of gC during infection increased VZV spread from epithelial cells to peripheral blood mononuclear cells. This constitutes the discovery of a novel strategy to modulate the activity of IFN-γ, inducing the expression of a subset of ISGs, leading to enhanced T cell adhesion and virus spread.

Cell Surface Nucleocapsid Protein Expression: A Betacoronavirus Immunomodulatory Strategy

We recently reported that SARS-CoV-2 Nucleocapsid (N) protein is abundantly expressed on the surface of both infected and neighboring uninfected cells, where it enables activation of Fc receptor-bearing immune cells with anti-N antibodies (Abs) and inhibits leukocyte chemotaxis by binding chemokines (CHKs). Here, we extend these findings to N from the seasonal human coronavirus (HCoV)-OC43, which is also robustly expressed on the surface of infected and non-infected cells by binding heparan-sulfate/heparin (HS/H). HCoV-OC43 N binds with high affinity to the same set of 11 human CHKs as SARS-CoV-2 N, but also to a non-overlapping set of 6 cytokines (CKs). As with SARS-CoV-2 N, HCoV-OC43 N inhibits CXCL12β-mediated leukocyte migration in chemotaxis assays, as do all highly pathogenic and endemic HCoV N proteins. Together, our findings indicate that cell surface HCoV N plays important evolutionary conserved roles in manipulating host innate immunity and as a target for adaptive immunity.

Herpes simplex virus interference with immunity: Focus on dendritic cells

Herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) are highly prevalent in the human population. These viruses cause lifelong infections by establishing latency in neurons and undergo sporadic reactivations that promote recurrent disease and new infections. The success of HSVs in persisting in infected individuals is likely due to their multiple molecular determinants involved in escaping the host antiviral and immune responses. Importantly, HSVs infect and negatively modulate the function of dendritic cells (DCs), key immune cells that are involved in establishing effective and balanced immunity against viruses. Here, we review and discuss several molecular and cellular processes modulated by HSVs in DCs, such as autophagy, apoptosis, and the unfolded protein response. Given the central role of DCs in establishing optimal antiviral immunity, particular emphasis should be given to the outcome of the interactions occurring between HSVs and DCs.

Pathogenesis and virulence of herpes simplex virus

Two of the most prevalent human viruses worldwide, herpes simplex virus type 1 and type 2 (HSV-1 and HSV-2, respectively), cause a variety of diseases, including cold sores, genital herpes, herpes stromal keratitis, meningitis and encephalitis. The intrinsic, innate and adaptive immune responses are key to control HSV, and the virus has developed mechanisms to evade them. The immune response can also contribute to pathogenesis, as observed in stromal keratitis and encephalitis. The fact that certain individuals are more prone than others to suffer severe disease upon HSV infection can be partially explained by the existence of genetic polymorphisms in humans. Like all herpesviruses, HSV has two replication cycles: lytic and latent. During lytic replication HSV produces infectious viral particles to infect other cells and organisms, while during latency there is limited gene expression and lack of infectious virus particles. HSV establishes latency in neurons and can cause disease both during primary infection and upon reactivation. The mechanisms leading to latency and reactivation and which are the viral and host factors controlling these processes are not completely understood. Here we review the HSV life cycle, the interaction of HSV with the immune system and three of the best-studied pathologies: Herpes stromal keratitis, herpes simplex encephalitis and genital herpes. We also discuss the potential association between HSV-1 infection and Alzheimer's disease.

Cell Fusion and Syncytium Formation in Betaherpesvirus Infection

Cell–cell fusion is a fundamental and complex process that occurs during reproduction, organ and tissue growth, cancer metastasis, immune response, and infection. All enveloped viruses express one or more proteins that drive the fusion of the viral envelope with cellular membranes. The same proteins can mediate the fusion of the plasma membranes of adjacent cells, leading to the formation of multinucleated syncytia. While cell–cell fusion triggered by alpha- and gammaherpesviruses is well-studied, much less is known about the fusogenic potential of betaherpesviruses such as human cytomegalovirus (HCMV) and human herpesviruses 6 and 7 (HHV-6 and HHV-7). These are slow-growing viruses that are highly prevalent in the human population and associated with several diseases, particularly in individuals with an immature or impaired immune system such as fetuses and transplant recipients. While HHV-6 and HHV-7 are strictly lymphotropic, HCMV infects a very broad range of cell types including epithelial, endothelial, mesenchymal, and myeloid cells. Syncytia have been observed occasionally for all three betaherpesviruses, both during in vitro and in vivo infection. Since cell–cell fusion may allow efficient spread to neighboring cells without exposure to neutralizing antibodies and other host immune factors, viral-induced syncytia may be important for viral dissemination, long-term persistence, and pathogenicity. In this review, we provide an overview of the viral and cellular factors and mechanisms identified so far in the process of cell–cell fusion induced by betaherpesviruses and discuss the possible consequences for cellular dysfunction and pathogenesis.

Herpes Simplex Virus Type 2 Mucin-Like Glycoprotein mgG Promotes Virus Release from the Surface of Infected Cells

The contribution of virus components to liberation of herpes simplex virus type 2 (HSV-2) progeny virions from the surface of infected cells is poorly understood. We report that the HSV-2 mutant deficient in the expression of a mucin-like membrane-associated glycoprotein G (mgG) exhibited defect in the release of progeny virions from infected cells manifested by ~2 orders of magnitude decreased amount of infectious virus in a culture medium as compared to native HSV-2. Electron microscopy revealed that the mgG deficient virions were produced in infected cells and present at the cell surface. These virions could be forcibly liberated to a nearly native HSV-2 level by the treatment of cells with glycosaminoglycan (GAG)-mimicking oligosaccharides. Comparative assessment of the interaction of mutant and native virions with surface-immobilized chondroitin sulfate GAG chains revealed that while the mutant virions associated with GAGs ~fourfold more extensively, the lateral mobility of bound virions was much poorer than that of native virions. These data indicate that the mgG of HSV-2 balances the virus interaction with GAG chains, a feature critical to prevent trapping of the progeny virions at the surface of infected cells.

"Non-Essential" Proteins of HSV-1 with Essential Roles In Vivo: A Comprehensive Review

Viruses encode for structural proteins that participate in virion formation and include capsid and envelope proteins. In addition, viruses encode for an array of non-structural accessory proteins important for replication, spread, and immune evasion in the host and are often linked to virus pathogenesis. Most virus accessory proteins are non-essential for growth in cell culture because of the simplicity of the infection barriers or because they have roles only during a state of the infection that does not exist in cell cultures (i.e., tissue-specific functions), or finally because host factors in cell culture can complement their absence. For these reasons, the study of most nonessential viral factors is more complex and requires development of suitable cell culture systems and in vivo models. Approximately half of the proteins encoded by the herpes simplex virus 1 (HSV-1) genome have been classified as non-essential. These proteins have essential roles in vivo in counteracting antiviral responses, facilitating the spread of the virus from the sites of initial infection to the peripheral nervous system, where it establishes lifelong reservoirs, virus pathogenesis, and other regulatory roles during infection. Understanding the functions of the non-essential proteins of herpesviruses is important to understand mechanisms of viral pathogenesis but also to harness properties of these viruses for therapeutic purposes. Here, we have provided a comprehensive summary of the functions of HSV-1 non-essential proteins.

Identification of the Cleavage Domain within Glycoprotein G of Herpes Simplex Virus Type 2

Glycoprotein G (gG) from herpes simplex virus type 1 and 2 (HSV-1 and HSV-2, respectively) functions as a viral chemokine binding protein (vCKBP). Soluble recombinant forms of gG of HSV-1 and HSV-2 (SgG1 and SgG2, respectively) enhance chemokine-mediated leukocyte migration, in contrast to most known vCKBPs, including those from animal alpha-herpesviruses. Furthermore, both proteins bind to nerve growth factor (NGF), but only SgG2 enhances NGF-dependent neurite outgrowth. The basis and implications of this functional difference between the two proteins are still unknown. While gG1 and gG2 are positional homologues in the genome, they share very limited sequence homology. In fact, US4, the open reading frame encoding gG is the most divergent genetic locus between these viruses. Full-length gG1 and gG2 are type I transmembrane proteins located on the plasma membrane of infected cells and at the viral envelope. However, gG2 is larger than gG1 and is cleaved during protein maturation, secreting the N-terminal domain to the supernatant of infected cells, whereas gG1 is not. The enzyme involved in gG2 cleavage and the functional relevance of gG2 cleavage and secretion are unknown. We aim to identify the gG2 sequence required for cleavage to determine its functional role in future experiments. Our results prove the existence of at least two cleavage motifs in gG2 within the amino acid region 314-343. Transfer of this sequence to a fusion protein results in cleavage. Finally, we show that propeptide convertases like furin are responsible for gG2 cleavage.

Herpes Simplex Virus 2 Counteracts Neurite Outgrowth Repulsion during Infection in a Nerve Growth Factor-Dependent Manner

Herpes simplex virus 2 (HSV-2) is a prevalent human pathogen that establishes lifelong latency in neurons of the peripheral nervous system. Colonization of neurons is required for HSV-2 persistence and pathogenesis. The viral and cellular factors required for efficient infection of neurons are not fully understood. We show here that nonneuronal cells repel neurite outgrowth of sensory neurons, while HSV-2 infection overcomes this inhibition and, rather, stimulates neurite outgrowth. HSV-2 glycoprotein G and nerve growth factor contribute to this phenotype, which may attract neurites to sites of infection and facilitate virus spread to neurons. Understanding the mechanisms that modulate neurite outgrowth and facilitate HSV-2 infection of neurons might foster the development of therapeutics to reduce HSV-2 colonization of the nervous system and provide insights on neurite outgrowth and regeneration.

During primary infection, herpes simplex virus 2 (HSV-2) replicates in epithelial cells and enters neurites to infect neurons of the peripheral nervous system. Growth factors and attractive and repulsive directional cues influence neurite outgrowth and neuronal survival. We hypothesized that HSV-2 modulates the activity of such cues to increase neurite outgrowth. To test this hypothesis, we exposed sensory neurons to nerve growth factor (NGF) and mock- or HSV-2-infected HEK-293T cells, since they express repellents of neurite outgrowth. We show that HEK-293T cells secrete factors that inhibit neurite outgrowth, while infection with HSV-2 strains MS and 333 reduces this repelling phenotype, increasing neurite numbers. The HSV-2-mediated restoration of neurite outgrowth required the activity of NGF. In the absence of infection, however, NGF did not overcome the repulsion mediated by HEK-293T cells. We previously showed that recombinant, soluble glycoprotein G of HSV-2 (rSgG2) binds and enhances NGF activity, increasing neurite outgrowth. However, the effect of gG2 during infection has not been investigated. Therefore, we addressed whether gG2 contributes to overcoming neurite outgrowth repulsion. To do so, we generated viruses lacking gG2 expression and complemented them by exogenous expression of gG2. Overall, our results suggest that HSV-2 infection of nonneuronal cells reduces their repelling effect on neurite outgrowth in an NGF-dependent manner. gG2 contributed to this phenotype, but it was not the only factor. The enhanced neurite outgrowth may facilitate HSV-2 spread from epithelial cells into neurons expressing NGF receptors and increase HSV-2-mediated pathogenesis.

IMPORTANCE Herpes simplex virus 2 (HSV-2) is a prevalent human pathogen that establishes lifelong latency in neurons of the peripheral nervous system. Colonization of neurons is required for HSV-2 persistence and pathogenesis. The viral and cellular factors required for efficient infection of neurons are not fully understood. We show here that nonneuronal cells repel neurite outgrowth of sensory neurons, while HSV-2 infection overcomes this inhibition and, rather, stimulates neurite outgrowth. HSV-2 glycoprotein G and nerve growth factor contribute to this phenotype, which may attract neurites to sites of infection and facilitate virus spread to neurons. Understanding the mechanisms that modulate neurite outgrowth and facilitate HSV-2 infection of neurons might foster the development of therapeutics to reduce HSV-2 colonization of the nervous system and provide insights on neurite outgrowth and regeneration.

Vaccines against Genital Herpes: Where Are We?

Genital herpes is a venereal disease caused by herpes simplex virus (HSV). Although HSV symptoms can be reduced with antiviral drugs, there is no cure. Moreover, because HSV infected individuals are often unaware of their infection, it is highly likely that they will transmit HSV to their sexual partner. Once infected, an individual has to live with HSV for their entire life, and HSV infection can lead to meningitis, encephalitis, and neonatal herpes as a result of vertical transmission. In addition, HSV infection increases the rates of human immunodeficiency virus (HIV) infection and transmission. Because of the high burden of genital herpes, HSV vaccines have been developed, but none have been very successful. In this review, we discuss the current status of genital herpes vaccine development.

The multilayered complexity of the chemokine receptor system

The chemokines receptor family are membrane-expressed class A-specific seven-transmembrane receptors linked to G proteins. Through interaction with the corresponding ligands, the chemokines, they induce a wide variety of cellular responses including cell polarization, movement, immune and inflammatory responses, as well as the prevention of HIV-1 infection. Like a Russian matryoshka doll, the chemokine receptor system is more complex than initially envisaged. This review focuses on the mechanisms that contribute to this dazzling complexity and how they modulate the signaling events triggered by chemokines. The chemokines and their receptors exist as monomers, dimers and oligomers, their expression pattern is highly regulated, and the ligands can bind distinct receptors with similar affinities. The use of novel imaging-based technologies, particularly real-time imaging modalities, has shed new light on the very dynamic conformations that chemokine receptors adopt depending on the cellular context, and that affect chemokine-mediated responses. This complex scenario presents both challenging and exciting opportunities for drug discovery.

Mechanism of action of the viral chemokine-binding protein E163 from ectromelia virus

Chemokines interact with glycosaminoglycans (GAGs) at the cellular surface and to specific cell-surface receptors to activate signaling pathways. The GAG interaction allows the formation of a chemotactic gradient of chemokine required for cell haptotaxis and chemokine oligomerization. Poxviruses encode secreted chemokine-binding proteins with no sequence similarity to their cellular counterparts to modulate the host immune system. The E163 protein from ectromelia virus, the causative agent of mousepox, binds chemokines through their GAG-binding domain. In addition, E163 interacts with GAGs to be anchored at the cell surface, but its ability to interfere with chemokine-GAG interactions has not been demonstrated. We report the identification of the GAG-binding regions in E163 and the generation of mutant forms deficient of GAG binding. Chemokine binding assays show that some of the E163 GAG-binding sites are also involved in the interaction with chemokines. By using recombinant GAG-binding mutant forms we demonstrate that E163 prevents the interaction of chemokines with cell-surface GAGs, providing mechanisms for the immunomodulatory activity of the viral chemokine-binding protein E163.

HSV-2 glycoprotein J promotes viral protein expression and virus spread

HSV-2 spread is predominantly dependent on cell-to-cell contact. However, the underlying mechanisms remain to be determined. Here we demonstrate that HSV-2 gJ, which was previously assigned no specific function, promotes HSV-2 cell-to-cell spread and syncytia formation. In the context of viral infection, knockout or knockdown of gJ impairs HSV-2 cell-to-cell spread among epithelial cells or from epithelial cells to neuronal cells, which leads to decreased virus production, whereas ectopic expression of gJ enhances virus production. Mechanistically, gJ increases the expression levels of HSV-2 proteins, and also enhances viral protein expression and replication of heterologous viruses like HIV-1 and JEV, suggesting that HSV-2 gJ likely functions as a regulator of viral protein expression and virus production. Findings in this study provide a basis for further understanding the role of gJ in HSV-2 replication.

Chemokine Subversion by Human Herpesviruses

Viruses use diverse molecular mechanisms to exploit and evade the immune response. Herpesviruses, in particular, encode functional chemokine and chemokine receptor homologs pirated from the host, as well as secreted chemokine-binding proteins with unique structures. Multiple functions have been described for herpesvirus chemokine components, including attraction of target cells, blockade of leukocyte migration, and modulation of gene expression and cell entry by the virus. Here we review current concepts about how human herpesvirus chemokines, chemokine receptors, and chemokine-binding proteins may be used to shape a proviral state in the host.

Remodeling our concept of chemokine receptor function: From monomers to oligomers

The chemokines direct leukocyte recruitment in both homeostatic and inflammatory conditions, and are therefore critical for immune reactions. By binding to members of the class A G protein-coupled receptors, the chemokines play an essential role in numerous physiological and pathological processes. In the last quarter century, the field has accumulated much information regarding the implications of these molecules in different immune processes, as well as mechanistic insight into the signaling events activated through their binding to their receptors. Here, we will focus on chemokine receptors and how new methodological approaches have underscored the role of their conformations in chemokine functions. Advances in biophysical-based techniques show that chemokines and their receptors act in very complex networks and therefore should not be considered isolated entities. In this regard, the chemokine receptors can form homo- and heterodimers as well as oligomers at the cell surface. These findings are changing our view as to how chemokines influence cell biology, identify partners that regulate chemokine function, and open new avenues for therapeutic intervention.

Infectious Laryngotracheitis Virus Viral Chemokine-Binding Protein Glycoprotein G Alters Transcription of Key Inflammatory Mediators In Vitro and In Vivo

Infectious laryngotracheitis virus (ILTV) is an alphaherpesvirus that infects chickens, causing upper respiratory tract disease and significant losses to poultry industries worldwide. Glycoprotein G (gG) is a broad-range viral chemokine-binding protein conserved among most alphaherpesviruses, including ILTV. A number of studies comparing the immunological parameters between infection with gG-expressing and gG-deficient ILTV strains have demonstrated that expression of gG is associated with increased virulence, modification of the amount and the composition of the inflammatory response, and modulation of the immune responses toward antibody production and away from cell-mediated immune responses. The aims of the current study were to examine the establishment of infection and inflammation by ILTV and determine how gG influences that response to infection. In vitro infection studies using tracheal organ tissue specimen cultures and blood-derived monocytes and in vivo infection studies in specific-pathogen-free chickens showed that leukocyte recruitment to the site of infection is an important component of the induced pathology and that this is influenced by the expression of ILTV gG and changes in the transcription of the chicken orthologues of mammalian CXC chemokine ligand 8 (CXCL8), chicken CXCLi1 and chicken CXCLi2, among other cytokines and chemokines. The results from this study demonstrate that ILTV gG interferes with chemokine and cytokine transcription at different steps of the inflammatory cascade, thus altering inflammation, virulence, and the balance of the immune response to infection.IMPORTANCE Infectious laryngotracheitis virus is an alphaherpesvirus that expresses gG, a conserved broad-range viral chemokine-binding protein known to interfere with host immune responses. However, little is known about how gG modifies virulence and influences the inflammatory signaling cascade associated with infection. Here, data from in vitro and in vivo infection studies are presented. These data show that gG has a direct impact on the transcription of cytokines and chemokine ligands in vitro (such as chicken CXCL8 orthologues, among others), which explains the altered balance of the inflammatory response that is associated with gG during ILTV infection of the upper respiratory tract of chickens. This is the first report to associate gG with the dysregulation of cytokine transcription at different stages of the inflammatory cascade triggered by ILTV infection of the natural host.

Regulation of CCR7-dependent cell migration through CCR7 homodimer formation

The chemokine receptor CCR7 contributes to various physiological and pathological processes including T cell maturation, T cell migration from the blood into secondary lymphoid tissues, and tumor cell metastasis to lymph nodes. Although a previous study suggested that the efficacy of CCR7 ligand-dependent T cell migration correlates with CCR7 homo- and heterodimer formation, the exact extent of contribution of the CCR7 dimerization remains unclear. Here, by inducing or disrupting CCR7 dimers, we demonstrated a direct contribution of CCR7 homodimerization to CCR7-dependent cell migration and signaling. Induction of stable CCR7 homodimerization resulted in enhanced CCR7-dependent cell migration and CCL19 binding, whereas induction of CXCR4/CCR7 heterodimerization did not. In contrast, dissociation of CCR7 homodimerization by a novel CCR7-derived synthetic peptide attenuated CCR7-dependent cell migration, ligand-dependent CCR7 internalization, ligand-induced actin rearrangement, and Akt and Erk signaling in CCR7-expressing cells. Our study indicates that CCR7 homodimerization critically regulates CCR7 ligand-dependent cell migration and intracellular signaling in multiple cell types.

Varicella zoster virus glycoprotein C increases chemokine-mediated leukocyte migration

Varicella zoster virus (VZV) is a highly prevalent human pathogen that establishes latency in neurons of the peripheral nervous system. Primary infection causes varicella whereas reactivation results in zoster, which is often followed by chronic pain in adults. Following infection of epithelial cells in the respiratory tract, VZV spreads within the host by hijacking leukocytes, including T cells, in the tonsils and other regional lymph nodes, and modifying their activity. In spite of its importance in pathogenesis, the mechanism of dissemination remains poorly understood. Here we addressed the influence of VZV on leukocyte migration and found that the purified recombinant soluble ectodomain of VZV glycoprotein C (rSgC) binds chemokines with high affinity. Functional experiments show that VZV rSgC potentiates chemokine activity, enhancing the migration of monocyte and T cell lines and, most importantly, human tonsillar leukocytes at low chemokine concentrations. Binding and potentiation of chemokine activity occurs through the C-terminal part of gC ectodomain, containing predicted immunoglobulin-like domains. The mechanism of action of VZV rSgC requires interaction with the chemokine and signalling through the chemokine receptor. Finally, we show that VZV viral particles enhance chemokine-dependent T cell migration and that gC is partially required for this activity. We propose that VZV gC activity facilitates the recruitment and subsequent infection of leukocytes and thereby enhances VZV systemic dissemination in humans.

Varicella zoster virus (VZV) causes two main pathologies in humans, chickenpox during primary infection, and shingles following reactivation. The latter is a painful condition that is often followed by chronic pain in a large numbers of shingles patients. Despite the existence of a vaccine, shingles-related complications cause expenses of more than $1 billion per year in the USA alone. Following primary infection, the virus infects leukocytes including T cells, spreading to the skin causing chickenpox. Direct infection of neurons from leukocytes has also been postulated. Given the relevance of leukocytes in VZV biology and the importance of chemokines in directing their migration, we investigated whether VZV modulates the function of chemokines. Our results show that VZV glycoprotein C potentiates the activity of chemokines, inducing higher migration of human leukocytes at low chemokine concentration. This may attract additional susceptible leukocytes to the site of infection enhancing virus spread and pathogenesis.

Ameloblastin Peptides Modulates the Osteogenic Capacity of Human Mesenchymal Stem Cells

During amelogenesis the extracellular enamel matrix protein AMBN is quickly processed into 17 kDa (N-terminus) and 23 kDa (C-terminus) fragments. In particular, alternatively spliced regions derived by exon 5/6 within the N-terminus region are known to be critical in biomineralization. Human mesenchymal stem cells (hMSC) also express and secrete AMBN, but it is unclear if this expression has effects on the hMSC themselves. If, as suggested from previous findings, AMBN act as a signaling molecule, such effects could influence hMSC growth and differentiation, as well as promoting the secretion of other signaling proteins like cytokines and chemokines. If AMBN is found to modulate stem cell behavior and fate, it will impact our understanding on how extracellular matrix molecules can have multiple roles during development ontogenesis, mineralization and healing of mesenchymal tissues. Here we show that synthetic peptides representing exon 5 promote hMSC proliferation. Interestingly, this effect is inhibited by the application of a 15 aa peptide representing the alternatively spliced start of exon 6. Both peptides also influence gene expression of RUNX2 and osteocalcin, and promote calcium deposition in cultures, indicating a positive influence on the osteogenic capacity of hMSC. We also show that the full-length AMBN-WT and N-terminus region enhance the secretion of RANTES, IP-10, and IL-8. In contrast, the AMBN C-terminus fragment and the exon 5 deleted AMBN (DelEx5) have no detectable effects on any of the parameters investigated. These findings suggest the signaling effect of AMBN is conveyed by processed products, whereas the effect on proliferation is differentially modulated through alternative splicing during gene expression.

Secreted herpes simplex virus-2 glycoprotein G alters thermal pain sensitivity by modifying NGF effects on TRPV1

Genital herpes is a painful disease frequently caused by the neurotropic pathogen herpes simplex virus type 2 (HSV-2). We have recently shown that HSV-2-secreted glycoprotein G (SgG2) interacts with and modulates the activity of the neurotrophin nerve growth factor (NGF). This interaction modifies the response of the NGF receptor TrkA, increasing NGF-dependent axonal growth. NGF is not only an axonal growth modulator but also an important mediator of pain and inflammation regulating the amount, localization, and activation of the thermal pain receptor transient receptor potential vanilloid 1 (TRPV1). In this work, we addressed whether SgG2 could contribute to HSV-2-induced pain. Injection of SgG2 in the mouse hindpaw produced a rapid and transient increase in thermal pain sensitivity. At the molecular level, this acute increase in thermal pain induced by SgG2 injection was dependent on differential NGF-induced phosphorylation and in changes in the amount of TrkA and TRPV1 in the dermis. These results suggest that SgG2 alters thermal pain sensitivity by modulating TRPV1 receptor.

Vaccination with the Secreted Glycoprotein G of Herpes Simplex Virus 2 Induces Protective Immunity after Genital Infection

Herpes simplex virus 2 (HSV-2) infects the genital mucosa and establishes a life-long infection in sensory ganglia. After primary infection HSV-2 may reactivate causing recurrent genital ulcerations. HSV-2 infection is prevalent, and globally more than 400 million individuals are infected. As clinical trials have failed to show protection against HSV-2 infection, new vaccine candidates are warranted. The secreted glycoprotein G (sgG-2) of HSV-2 was evaluated as a prophylactic vaccine in mice using two different immunization and adjuvant protocols. The protocol with three intramuscular immunizations combining sgG-2 with cytosine-phosphate-guanine dinucleotide (CpG) motifs and alum induced almost complete protection from genital and systemic disease after intra-vaginal challenge with HSV-2. Robust immunoglobulin G (IgG) antibody titers were detected with no neutralization activity. Purified splenic CD4+ T cells proliferated and produced interferon-γ (IFN-γ) when re-stimulated with the antigen in vitro. sgG-2 + adjuvant intra-muscularly immunized mice showed a significant reduction of infectious HSV-2 and increased IFN-γ levels in vaginal washes. The HSV-2 DNA copy numbers were significantly reduced in dorsal root ganglia, spinal cord, and in serum at day six or day 21 post challenge. We show that a sgG-2 based vaccine is highly effective and can be considered as a novel candidate in the development of a prophylactic vaccine against HSV-2 infection.

Monitoring Scavenging Activity of Chemokine Receptors

Migration and positioning of cells is fundamental for complex functioning of multicellular organisms. During an immune response, cells are recruited from remote distances to a distinct location. Cells that are passively transported leave the circulation stimulated by locally produced signals and follow chemotactic cues to reach specific destinations. Such gradients are short (<150 μm) and require a source of production where the concentration is the highest and a sink in apposition where the attractant dissipates and the concentration is the lowest. Several straight forward methods exist to identify in vitro and in vivo cells producing chemoattractants. This can be achieved at the transcriptional level and by measuring secreted proteins. However, to demonstrate the activity of sinks in vitro and in vivo is more challenging. Cell-mediated dissipation of an attractant must be revealed by measuring its uptake and subsequent destruction. Elimination of chemoattractants such as chemokines can be monitored in vitro using radiolabeled ligands or more elegantly with fluorescent-labeled chemoattractants. The latter method can also be used in vivo and enables to monitor the process in real time using time-lapse video microscopy. In this chapter, we describe methods to produce fluorescently labeled chemokines either as fusion proteins secreted from insect cells or as recombinant bacterial proteins that can enzymatically be labeled. We discuss methods that were successfully used to demonstrate sink activities of scavenger receptors. Moreover, fluorescent chemokines can be used to noninvasively analyze receptor expression and activity in living cells.

Piracy on the molecular level: human herpesviruses manipulate cellular chemotaxis

Cellular chemotaxis is important to tissue homeostasis and proper development. Human herpesvirus species influence cellular chemotaxis by regulating cellular chemokines and chemokine receptors. Herpesviruses also express various viral chemokines and chemokine receptors during infection. These changes to chemokine concentrations and receptor availability assist in the pathogenesis of herpesviruses and contribute to a variety of diseases and malignancies. By interfering with the positioning of host cells during herpesvirus infection, viral spread is assisted, latency can be established and the immune system is prevented from eradicating viral infection.

Genome-Wide Gene Expression Analysis Identifies the Proto-oncogene Tyrosine-Protein Kinase Src as a Crucial Virulence Determinant of Infectious Laryngotracheitis Virus in Chicken Cells

Given the side effects of vaccination against infectious laryngotracheitis (ILT), novel strategies for ILT control and therapy are urgently needed. The modulation of host-virus interactions is a promising strategy to combat the virus; however, the interactions between the host and avian ILT herpesvirus (ILTV) are unclear. Using genome-wide transcriptome studies in combination with a bioinformatic analysis, we identified proto-oncogene tyrosine-protein kinase Src (Src) to be an important modulator of ILTV infection. Src controls the virulence of ILTV and is phosphorylated upon ILTV infection. Functional studies revealed that Src prolongs the survival of host cells by increasing the threshold of virus-induced cell death. Therefore, Src is essential for viral replication in vitro and in ovo but is not required for ILTV-induced cell death. Furthermore, our results identify a positive-feedback loop between Src and the tyrosine kinase focal adhesion kinase (FAK), which is necessary for the phosphorylation of either Src or FAK and is required for Src to modulate ILTV infection. To the best of our knowledge, we are the first to identify a key host regulator controlling host-ILTV interactions. We believe that our findings have revealed a new potential therapeutic target for ILT control and therapy.

IMPORTANCE

Despite the extensive administration of live attenuated vaccines starting from the mid-20th century and the administration of recombinant vaccines in recent years, infectious laryngotracheitis (ILT) outbreaks due to avian ILT herpesvirus (ILTV) occur worldwide annually. Presently, there are no drugs or control strategies that effectively treat ILT. Targeting of host-virus interactions is considered to be a promising strategy for controlling ILTV infections. However, little is known about the mechanisms governing host-ILTV interactions. The results from our study advance our understanding of host-ILTV interactions on a molecular level and provide experimental evidence that it is possible to control ILT via the manipulation of host-virus interactions.