Herpes simplex virus type 2 membrane protein UL56 associates with the kinesin motor protein KIF1A

Emerging roles of cytoskeletal transport and scaffold systems in human viral propagation

Viruses have long been recognized as significant pathogens, contributing to multiple global pandemics throughout human history. Recent examples include the 2009 influenza pandemic and the COVID-19 pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in 2019. Despite ongoing experimental and clinical efforts, the development of effective antiviral treatments and vaccines remains challenging due to the high mutation rates of many human pathogenic viruses including influenza virus and SARS-CoV-2. As an alternative approach, antiviral strategies targeting host factors shared by multiple viruses could provide a more universally applicable solution. Emerging evidence suggests that viruses exploit the host cytoskeletal network to facilitate efficient viral replication and propagation. Therefore, a comprehensive understanding of the interactions between viral components and the cytoskeletal machinery may offer valuable insights for the development of broad-spectrum antiviral therapeutics. This review compiles and discusses current knowledge on the interactions between viruses and cytoskeletal elements, including kinesin, dynein, myosin, and vimentin, and explores their potential as therapeutic targets. The potential for these cytoskeletal components to serve as targets for new antiviral interventions is discussed in the context of diverse human viruses, including influenza virus, SARS-CoV-2, herpes simplex virus, human papillomavirus, and human immunodeficiency virus.

A Hitchhiker's Guide Through the Cell: The World According to the Capsids of Alphaherpesviruses

The nucleoplasm, the cytosol, the inside of virions, and again the cytosol comprise the world in which the capsids of alphaherpesviruses encounter viral and host proteins that support or limit them in performing their tasks. Here, we review the fascinating conundrum of how specific protein-protein interactions late in alphaherpesvirus infection orchestrate capsid nuclear assembly, nuclear egress, and cytoplasmic envelopment, but target incoming capsids to the nuclear pores in naive cells to inject the viral genomes into the nucleoplasm for viral transcription and replication. Multiple capsid interactions with viral and host proteins have been characterized using viral mutants and assays that reconstitute key stages of the infection cycle. Keratinocytes, fibroblasts, mucosal epithelial cells, neurons, and immune cells employ cell type-specific intrinsic and cytokine-induced resistance mechanisms to restrict several stages of the viral infection cycle. However, concomitantly, alphaherpesviruses have evolved countermeasures to ensure efficient capsid function during infection.

Getting on the right track: Interactions between viruses and the cytoskeletal motor proteins

The cytoskeleton is an essential component of the cell and it is involved in multiple physiological functions, including intracellular organization and transport. It is composed of three main families of proteinaceous filaments; microtubules, actin filaments and intermediate filaments and their accessory proteins. Motor proteins, which comprise the dynein, kinesin and myosin superfamilies, are a remarkable group of accessory proteins that mainly mediate the intracellular transport of cargoes along with the cytoskeleton. Like other cellular structures and pathways, viruses can exploit the cytoskeleton to promote different steps of their life cycle through associations with motor proteins. The complexity of the cytoskeleton and the differences among viruses, however, has led to a wide diversity of interactions, which in most cases remain poorly understood. Unveiling the details of these interactions is necessary not only for a better comprehension of specific infections, but may also reveal new potential drug targets to fight dreadful diseases such as rabies disease and acquired immunodeficiency syndrome (AIDS). In this review, we describe a few examples of the mechanisms that some human viruses, that is, rabies virus, adenovirus, herpes simplex virus, human immunodeficiency virus, influenza A virus and papillomavirus, have developed to hijack dyneins, kinesins and myosins.

Herpes simplex virus 1 as an oncolytic viral therapy for refractory cancers

The need for efficacious and non-toxic cancer therapies is paramount. Oncolytic viruses (OVs) are showing great promise and are introducing new possibilities in cancer treatment with their ability to selectively infect tumor cells and trigger antitumor immune responses. Herpes Simplex Virus 1 (HSV-1) is a commonly selected OV candidate due to its large genome, relative safety profile, and ability to infect a variety of cell types. Talimogene laherparevec (T-VEC) is an HSV-1-derived OV variant and the first and only OV therapy currently approved for clinical use by the United States Food and Drug Administration (FDA). This review provides a concise description of HSV-1 as an OV candidate and the genomic organization of T-VEC. Furthermore, this review focuses on the advantages and limitations in the use of T-VEC compared to other HSV-1 OV variants currently in clinical trials. In addition, approaches for future directions of HSV-1 OVs as cancer therapy is discussed.

Beyond Immunotherapy: Seizing the Momentum of Oncolytic Viruses in the Ideal Platform of Skin Cancers

Despite the durable remissions induced by ICIs and targeted therapies in advanced melanoma and non-melanoma skin cancers, both subtypes usually relapse. Many systematic therapies have been tested to increase efficacy and delay relapse in ICIs, but their success has been limited. Due the feasibility of this approach, skin cancers have become the ideal platform for intralesional infusions of many novel agents, including oncolytic viruses (OVs). Talimogene laherparepvec (T-VEC) was the first FDA-approved OV for the treatment of unresectable melanoma and this virus opened up further potential for the use of this class of agents, especially in combination with ICIs, in order to achieve deeper and longer immune-mediated responses. However, the recently announced phase III MASTERKEY-265 trial was not able to confirm that the addition of T-VEC to pembrolizumab treatment improves progression-free or overall survival over the use of pembrolizumab alone. Despite these results, numerous studies are currently active, evaluating T-VEC and several other OVs as monotherapies or in regimens with ICIs in different subtypes of skin cancer. This overview provides a comprehensive update on the evolution status of all available OVs in melanoma and non-melanoma skin cancers and summarizes the more interesting preclinical findings, the latest clinical evidence, and the future insights in relation to the expected selective incorporation of some of these OVs into oncological practice.

Genetic Modifications That Expand Oncolytic Virus Potency

Oncolytic viruses (OVs) are a promising type of cancer therapy since they selectively replicate in tumor cells without damaging healthy cells. Many oncolytic viruses have progressed to human clinical trials, however, their performance as monotherapy has not been as successful as expected. Importantly, recent literature suggests that the oncolytic potential of these viruses can be further increased by genetically modifying the viruses. In this review, we describe genetic modifications to OVs that improve their ability to kill tumor cells directly, to dismantle the tumor microenvironment, or to alter tumor cell signaling and enhance anti-tumor immunity. These advances are particularly important to increase virus spread and reduce metastasis, as demonstrated in animal models. Since metastasis is the principal cause of mortality in cancer patients, having OVs designed to target metastases could transform cancer therapy. The genetic alterations reported to date are only the beginning of all possible improvements to OVs. Modifications described here could be combined together, targeting multiple processes, or with other non-viral therapies with potential to provide a strong and lasting anti-tumor response in cancer patients.

Motor Skills: Recruitment of Kinesins, Myosins and Dynein during Assembly and Egress of Alphaherpesviruses

The alphaherpesviruses are pathogens of the mammalian nervous system. Initial infection is commonly at mucosal epithelia, followed by spread to, and establishment of latency in, the peripheral nervous system. During productive infection, viral gene expression, replication of the dsDNA genome, capsid assembly and genome packaging take place in the infected cell nucleus, after which mature nucleocapsids emerge into the cytoplasm. Capsids must then travel to their site of envelopment at cytoplasmic organelles, and enveloped virions need to reach the cell surface for release and spread. Transport at each of these steps requires movement of alphaherpesvirus particles through a crowded and viscous cytoplasm, and for distances ranging from several microns in epithelial cells, to millimeters or even meters during egress from neurons. To solve this challenging problem alphaherpesviruses, and their assembly intermediates, exploit microtubule- and actin-dependent cellular motors. This review focuses upon the mechanisms used by alphaherpesviruses to recruit kinesin, myosin and dynein motors during assembly and egress.

Engagement of Neurotropic Viruses in Fast Axonal Transport: Mechanisms, Potential Role of Host Kinases and Implications for Neuronal Dysfunction

Much remains unknown about mechanisms sustaining the various stages in the life cycle of neurotropic viruses. An understanding of those mechanisms operating before their replication and propagation could advance the development of effective anti-viral strategies. Here, we review our current knowledge of strategies used by neurotropic viruses to undergo bidirectional movement along axons. We discuss how the invasion strategies used by specific viruses might influence their mode of interaction with selected components of the host’s fast axonal transport (FAT) machinery, including specialized membrane-bounded organelles and microtubule-based motor proteins. As part of this discussion, we provide a critical evaluation of various reported interactions among viral and motor proteins and highlight limitations of some in vitro approaches that led to their identification. Based on a large body of evidence documenting activation of host kinases by neurotropic viruses, and on recent work revealing regulation of FAT through phosphorylation-based mechanisms, we posit a potential role of host kinases on the engagement of viruses in retrograde FAT. Finally, we briefly describe recent evidence linking aberrant activation of kinase pathways to deficits in FAT and neuronal degeneration in the context of human neurodegenerative diseases. Based on these findings, we speculate that neurotoxicity elicited by viral infection may involve deregulation of host kinases involved in the regulation of FAT and other cellular processes sustaining neuronal function and survival.

Microtubule-Dependent Trafficking of Alphaherpesviruses in the Nervous System: The Ins and Outs

The Alphaherpesvirinae include the neurotropic pathogens herpes simplex virus and varicella zoster virus of humans and pseudorabies virus of swine. These viruses establish lifelong latency in the nuclei of peripheral ganglia, but utilize the peripheral tissues those neurons innervate for productive replication, spread, and transmission. Delivery of virions from replicative pools to the sites of latency requires microtubule-directed retrograde axonal transport from the nerve terminus to the cell body of the sensory neuron. As a corollary, during reactivation newly assembled virions must travel along axonal microtubules in the anterograde direction to return to the nerve terminus and infect peripheral tissues, completing the cycle. Neurotropic alphaherpesviruses can therefore exploit neuronal microtubules and motors for long distance axonal transport, and alternate between periods of sustained plus end- and minus end-directed motion at different stages of their infectious cycle. This review summarizes our current understanding of the molecular details by which this is achieved.

A GFP-tagged version of the pseudorabies virus protein UL56 localizes to the Golgi and trans-Golgi network through a predicted C-terminal leucine-rich helix in transfected cells

BACKGROUND

Pseudorabies virus (PRV) protein UL56 (pUL56) has been implicated in viral dissemination and virulence in vivo. However, the properties of PRV pUL56 remain largely unknown. In the present study, we aim to investigate the subcellular localization of pUL56 and the underlying molecular basis in transfected cells.

METHODS

Constructs of N-terminal green fluorescent protein (GFP) fused pUL56 and its truncations were employed for investigating subcellular localization and further identifying amino acids crucial for pUL56 localization in transfected Vero cells. Finally, the identified amino acids were replaced with alanine for confirming if these mutations could impair the specific localization of pUL56.

RESULTS

The pUL56 predominantly localized at the Golgi and trans-Golgi network (TGN) through its predicted C-terminal transmembrane helix in transfected Vero cells. A Golgi-associated protein Rab6a, independent of interaction with pUL56, was significantly downregulated by pUL56. Further, we found three truncated pUL56 C-terminal fragments (174-184, 175-185 and 191-195) could restrict GFP in the perinuclear region, respectively. Within these truncations, the ¹⁷⁴proline (P), ¹⁸¹leucine (L), ¹⁸⁵L and ¹⁹¹L were essential for maintaining perinuclear accumulation, thus suggesting an important role of leucine. Alanine (A) mutagenesis assays were employed to generate a series of pUL56 C-terminal mutants on the basis of leucine. Finally, a pUL56 mutant M10 (¹⁷⁴P/A-¹⁷⁷L/A-¹⁸¹L/A-¹⁸⁵L/A-¹⁹¹L/A-¹⁹⁴L/A-¹⁹⁵I/A-^196-197L/A-²⁰⁰L/A) lost Golgi-TGN localization. Thus, our data revealed that the leucine-rich transmembrane helix was responsible for pUL56 Golgi-TGN localization and retention, probably through specific intracellular membrane insertion.

CONCLUSION

Our data indicated that the C-terminal transmembrane helix was responsible for the Golgi-TGN localization of pUL56. In addition, the leucines within C-terminal transmembrane helix were essential for maintaining pUL56 Golgi-TGN retention in cells. Further, the pUL56 can induce downregulation of Golgi-associated protein Rab6a.

Kinetics of Mimivirus Infection Stages Quantified Using Image Flow Cytometry

Due to the heterogeneity of viruses and their hosts, a comprehensive view of viral infection is best achieved by analyzing large populations of infected cells. However, information regarding variation in infected cell populations is lost in bulk measurements. Motivated by an interest in the temporal progression of events in virally infected cells, we used image flow cytometry (IFC) to monitor changes in Acanthamoeba polyphaga cells infected with Mimivirus. This first use of IFC to study viral infection required the development of methods to preserve morphological features of adherent amoeba cells prior to detachment and analysis in suspension. It also required the identification of IFC parameters that best report on key events in the Mimivirus infection cycle. The optimized IFC protocol enabled the simultaneous monitoring of diverse processes including generation of viral factories, transport, and fusion of replication centers within the cell, accumulation of viral progeny, and changes in cell morphology for tens of thousands of cells. After obtaining the time windows for these processes, we used IFC to evaluate the effects of perturbations such as oxidative stress and cytoskeletal disruptors on viral infection. Accurate dose‐response curves could be generated, and we found that mild oxidative stress delayed multiple stages of virus production, but eventually infection processes occurred with approximately the same amplitudes. We also found that functional actin cytoskeleton is required for fusion of viral replication centers and later for the production of viral progeny. Through this report, we demonstrate that IFC offers a quantitative, high‐throughput, and highly robust approach to study viral infection cycles and virus–host interactions. © The Authors. Cytometry Part A published by Wiley Periodicals, Inc. on behalf of International Society for Advancement of Cytometry.

Oncolytic herpes simplex virus and immunotherapy

BACKGROUND

Oncolytic viruses have been proposed to be employed as a potential treatment of cancer. Well targeted, they will serve the purpose of cracking tumor cells without causing damage to normal cells. In this category of oncolytic viral drugs human pathogens herpes simplex virus (HSV) is especially suitable for the cause. Although most viral infection causes antiviral reaction in the host, HSV has multiple mechanisms to evade those responses. Powerful anti-tumor effect can thus be achieved via genetic manipulation of the HSV genes involved in this evading mechanism, namely deletions or mutations that adapt its function towards a tumor microenvironment. Currently, oncolytic HSV (oHSV) is widely use in clinical; moreover, there's hope that its curative effect will be further enhanced through the combination of oHSV with both traditional and emerging therapeutics.

RESULTS

In this review, we provide a summary of the HSV host antiviral response evasion mechanism, HSV expresses immune evasion genes such as ICP34.5, ICP0, Us3, which are involved in inducing and activating host responses, so that the virus can evade the immune system and establish effective long-term latent infection; we outlined details of the oHSV strains generated by removing genes critical to viral replication such as ICP34.5, ICP0, and inserting therapeutic genes such as LacZ, granulocyte macrophage colony-stimulating factor (GM-CSF); security and limitation of some oHSV such G207, 1716, OncoVEX, NV1020, HF10, G47 in clinical application; and the achievements of oHSV combined with immunotherapy and chemotherapy.

CONCLUSION

We reviewed the immunotherapy mechanism of the oHSV and provided a series of cases. We also pointed out that an in-depth study of the application of oHSV in cancer treatment will potentially benefits cancer patients more.

The pUL56 of pseudorabies virus variant induces downregulation of swine leukocyte antigen class I molecules through the lysosome pathway

Pseudorabies virus (PRV) is the causative agent of pseudorabies (PR) which causes large economic losses for Chinese swine industry since breaking out in late 2011. As a member of herpesviruses, PRV is able to escape the host immune elimination and establish latency, resulting in persistent infection. Here, we report that a currently prevalent Chinese PRV variant down-regulated swine leukocyte antigen class I (SLA-I) molecules on the surface of PK-15 cells and targeted them for degradation through lysosome pathway. Viral pUL56 protein, independent of other viral proteins, was associated with this function by inducing degradation of cellular SLA-I heavy chain (HC) in a manner that was dependent on the lysosome machinery. In addition, pUL56 interacted with SLA-I HC and increased its ubiquitination. Further studies demonstrated that the late domains (PPXY motifs) of pUL56 were required for the ubiquitination and degradation of SLA-I HC by pUL56. Together, our findings reveal the mechanisms by which PRV interferes with cytotoxic T lymphocyte (CTL) responses and provide novel insights into the roles of PRV pUL56.

Infection and Transport of Herpes Simplex Virus Type 1 in Neurons: Role of the Cytoskeleton

Herpes simplex virus type 1 (HSV-1) is a neuroinvasive human pathogen that has the ability to infect and replicate within epithelial cells and neurons and establish a life-long latent infection in sensory neurons. HSV-1 depends on the host cellular cytoskeleton for entry, replication, and exit. Therefore, HSV-1 has adapted mechanisms to promote its survival by exploiting the microtubule and actin cytoskeletons to direct its active transport, infection, and spread between neurons and epithelial cells during primary and recurrent infections. This review will focus on the currently known mechanisms utilized by HSV-1 to harness the neuronal cytoskeleton, molecular motors, and the secretory and exocytic pathways for efficient virus entry, axonal transport, replication, assembly, and exit from the distinct functional compartments (cell body and axon) of the highly polarized sensory neurons.

Cytoskeletons in the Closet-Subversion in Alphaherpesvirus Infections

Actin filaments, microtubules and intermediate filaments form the cytoskeleton of vertebrate cells. Involved in maintaining cell integrity and structure, facilitating cargo and vesicle transport, remodelling surface structures and motility, the cytoskeleton is necessary for the successful life of a cell. Because of the broad range of functions these filaments are involved in, they are common targets for viral pathogens, including the alphaherpesviruses. Human-tropic alphaherpesviruses are prevalent pathogens carried by more than half of the world’s population; comprising herpes simplex virus (types 1 and 2) and varicella-zoster virus, these viruses are characterised by their ability to establish latency in sensory neurons. This review will discuss the known mechanisms involved in subversion of and transport via the cytoskeleton during alphaherpesvirus infections, focusing on protein-protein interactions and pathways that have recently been identified. Studies on related alphaherpesviruses whose primary host is not human, along with comparisons to more distantly related beta and gammaherpesviruses, are also presented in this review. The need to decipher as-yet-unknown mechanisms exploited by viruses to hijack cytoskeletal components—to reveal the hidden cytoskeletons in the closet—will also be addressed.

Oncolytic Virotherapy by HSV

Oncolytic virotherapy is a kind of antitumor therapy using viruses with natural or engineered tumor-selective replication to intentionally infect and kill tumor cells. An early clinical trial has been performed in the 1950s using wild-type and non-engineered in vitro-passaged virus strains and vaccine strains (first generation oncolytic viruses). Because of the advances in biotechnology and virology, the field of virotherapy has rapidly evolved over the past two decades and innovative recombinant selectivity-enhanced viruses (second generation oncolytic viruses). Nowadays, therapeutic transgene-delivering "armed" oncolytic viruses (third generation oncolytic viruses) have been engineered using many kinds of viruses. In this chapter, the history, mechanisms, rationality, and advantages of oncolytic virotherapy by herpes simplex virus (HSV) are mentioned. Past and ongoing clinical trials by oncolytic HSVs (G207, HSV1716, NV1020, HF10, Talimogene laherparepvec (T-VEC, OncoVEX^GM-CSF)) are also summarized. Finally, the way of enhancement of oncolytic virotherapy by gene modification or combination therapy with radiation, chemotherapy, or immune checkpoint inhibitors are discussed.

Herpes simplex encephalitis is linked with selective mitochondrial damage; a post-mortem and in vitro study

Herpes simplex virus type-1 (HSV-1) encephalitis (HSE) is the most commonly diagnosed cause of viral encephalitis in western countries. Despite antiviral treatment, HSE remains a devastating disease with high morbidity and mortality. Improved understanding of pathogenesis may lead to more effective therapies. Mitochondrial damage has been reported during HSV infection in vitro. However, whether it occurs in the human brain and whether this contributes to the pathogenesis has not been fully explored. Minocycline, an antibiotic, has been reported to protect mitochondria and limit brain damage. Minocycline has not been studied in HSV infection. In the first genome-wide transcriptomic study of post-mortem human HSE brain tissue, we demonstrated a highly preferential reduction in mitochondrial genome (MtDNA) encoded transcripts in HSE cases (n = 3) compared to controls (n = 5). Brain tissue exhibited a significant inverse correlation for immunostaining between cytochrome c oxidase subunit 1 (CO1), a MtDNA encoded enzyme subunit, and HSV-1; with lower abundance for mitochondrial protein in regions where HSV-1 was abundant. Preferential loss of mitochondrial function, among MtDNA encoded components, was confirmed using an in vitro primary human astrocyte HSV-1 infection model. Dysfunction of cytochrome c oxidase (CO), a mitochondrial enzyme composed predominantly of MtDNA encoded subunits, preceded that of succinate dehydrogenase (composed entirely of nuclear encoded subunits). Minocycline treated astrocytes exhibited higher CO1 transcript abundance, sustained CO activity and cell viability compared to non-treated astrocytes. Based on observations from HSE patient tissue, this study highlights mitochondrial damage as a critical and early event during HSV-1 infection. We demonstrate minocycline preserves mitochondrial function and cell viability during HSV-1 infection. Minocycline, and mitochondrial protection, offers a novel adjunctive therapeutic approach for limiting brain cell damage and potentially improving outcome among HSE patients.

The pseudorabies virus protein, pUL56, enhances virus dissemination and virulence but is dispensable for axonal transport

Neurotropic herpesviruses exit the peripheral nervous system and return to exposed body surfaces following reactivation from latency. The pUS9 protein is a critical viral effector of the anterograde axonal transport that underlies this process. We recently reported that while pUS9 increases the frequency of sorting of newly assembled pseudorabies virus particles to axons from the neural soma during egress, subsequent axonal transport of individual virus particles occurs with wild-type kinetics in the absence of the protein. Here, we examine the role of a related pseudorabies virus protein, pUL56, during neuronal infection. The findings indicate that pUL56 is a virulence factor that supports virus dissemination in vivo, yet along with pUS9, is dispensable for axonal transport.

Oncolytic virotherapy using herpes simplex virus: how far have we come?

Oncolytic virotherapy exploits the properties of human viruses to naturally cytolysis of cancer cells. The human pathogen herpes simplex virus (HSV) has proven particularly amenable for use in oncolytic virotherapy. The relative safety of HSV coupled with extensive knowledge on how HSV interacts with the host has provided a platform for manipulating HSV to enhance the targeting and killing of human cancer cells. This has culminated in the approval of talimogene laherparepvec for the treatment of melanoma. This review focuses on the development of HSV as an oncolytic virus and where the field is likely to head in the future.

Equine herpesvirus type 1 pUL56 modulates innate responses of airway epithelial cells

Recently, the product of equine herpesvirus type 1 (EHV-1) ORF1, a homolog to HSV-1 pUL56, was shown to modulate MHC-I expression and innate immunity. Here, we investigated modulation of respiratory epithelial immunity by EHV-1 pUL56 and compared responses to those of PBMCs, which are important target cells that allow cell-associated EHV-1 viremia. The salient observations are as follows: (i) EHV-1 significantly down-modulated MHC-I and MHC-II expression in equine respiratory epithelial cells (ERECs). MHC-I expression remained unaffected in PBMCs and MHC-II expression was increased. (ii) Infection with an EHV-1 ORF1 deletion mutant partially restored MHC-I and MHC-II expression and altered IFN-alpha and IL-10 mRNA expression. (iii) Deletion of EHV-1 ORF1 also significantly increased chemokine expression and chemotaxis of monocytes and neutrophils in ERECs. Collectively, these results suggest a role for EHV-1 pUL56 in modulation of antigen presentation, cytokine expression and chemotaxis at the respiratory epithelium, but not in PBMC.

Kinesin-3 mediates axonal sorting and directional transport of alphaherpesvirus particles in neurons

During infection of the nervous system, alphaherpesviruses-including pseudorabies virus (PRV)-use retrograde axonal transport to travel toward the neuronal cell body and anterograde transport to traffic back to the cell periphery upon reactivation from latency. The PRV protein Us9 plays an essential but unknown role in anterograde viral spread. To determine Us9 function, we identified viral and host proteins that interact with Us9 and explored the role of KIF1A, a microtubule-dependent kinesin-3 motor involved in axonal sorting and transport. Viral particles are cotransported with KIF1A in axons of primary rat superior cervical ganglion neurons, and overexpression or disruption of KIF1A function, respectively, increases and reduces anterograde capsid transport. Us9 and KIF1A interact early during infection with the aid of additional viral protein(s) but exhibit diminished binding at later stages, when capsids typically stall in axons. Thus, alphaherpesviruses repurpose the axonal transport and sorting pathway to spread within their hosts.

Identification and characterization of equine herpesvirus type 1 pUL56 and its role in virus-induced downregulation of major histocompatibility complex class I

Major histocompatibility complex class I (MHC-I) molecules play an important role in host immunity to infection by presenting antigenic peptides to cytotoxic T lymphocytes (CTLs), which recognize and destroy virus-infected cells. Members of the Herpesviridae have developed multiple mechanisms to avoid CTL recognition by virtue of downregulation of MHC-I on the cell surface. We report here on an immunomodulatory protein involved in this process, pUL56, which is encoded by ORF1 of equine herpesvirus type 1 (EHV-1), an alphaherpesvirus. We show that EHV-1 pUL56 is a phosphorylated early protein which is expressed as different forms and predominantly localizes to Golgi membranes. In addition, the transmembrane (TM) domain of the type II membrane protein was shown to be indispensable for correct subcellular localization and a proper function. pUL56 by itself is not functional with respect to interference with MHC-I and likely needs another unidentified viral protein(s) to perform this action. Surprisingly, pUL49.5, an inhibitor of the transporter associated with antigen processing (TAP) and encoded by EHV-1 and related viruses, appeared not to be required for pUL56-induced early MHC-I downmodulation in infected cells. In conclusion, our data identify a new immunomodulatory protein, pUL56, involved in MHC-I downregulation which is unable to perform its function outside the context of viral infection.

Alphaherpesviruses and the cytoskeleton in neuronal infections

Following infection of exposed peripheral tissues, neurotropic alphaherpesviruses invade nerve endings and deposit their DNA genomes into the nuclei of neurons resident in ganglia of the peripheral nervous system. The end result of these events is the establishment of a life-long latent infection. Neuroinvasion typically requires efficient viral transmission through a polarized epithelium followed by long-distance transport through the viscous axoplasm. These events are mediated by the recruitment of the cellular microtubule motor proteins to the intracellular viral particle and by alterations to the cytoskeletal architecture. The focus of this review is the interplay between neurotropic herpesviruses and the cytoskeleton.

The taking of the cytoskeleton one two three: how viruses utilize the cytoskeleton during egress

The final assembly of nonlytic envelope viruses requires the coordinated transport of either subviral particles or fully formed virions to the plasma membrane for release from the cell. Recent research has delved into the mechanisms viruses employ to hijack the host cell's cytoskeletal system for active transport to the site of final assembly and release. This review will look at recent findings that relate to the transport of virions to the cell periphery and out of the cell.

The varicella-zoster virus ORFS/L (ORF0) gene is required for efficient viral replication and contains an element involved in DNA cleavage

The genome of varicella-zoster virus (VZV), a human alphaherpesvirus, consists of two unique regions, unique long (U(L)) and unique short (U(S)), each of which is flanked by inverted repeats. During replication, four isomers of the viral DNA are generated which are distinguished by the relative orientations of U(L) and U(S). VZV virions predominantly package two isomeric forms of the genome that have a fixed orientation of U(L). An open reading frame (ORF) of unknown function, ORFS/L, also referred to as ORF0, is located at the extreme terminus of U(L), directly adjacent to the a-like sequences, which are known to be involved in cleavage and packaging of viral DNA. We demonstrate here that the ORFS/L protein localizes to the Golgi network in infected and transfected cells. Furthermore, we were able to demonstrate that deletion of the predicted ORFS/L gene is lethal, while retention of the N-terminal 28 amino acid residues resulted in viable yet replication-impaired virus. The growth defect was only partially attributable to the expression of the ORFS/L product, suggesting that the 5' region of ORFS/L contains a sequence element crucial for cleavage/packaging of viral DNA. Consequently, mutations introduced into the extreme 5' terminus of ORFS/L resulted in a defect in DNA cleavage, indicating that the region is indeed involved in the processing of viral DNA. Since the sequence element has no counterpart at the other end of U(L), we concluded that our results can provide an explanation for the almost exclusive orientation of the U(L) seen in packaged VZV DNA.

A common neuronal response to alphaherpesvirus infection

Alphaherpesviruses are a subfamily of the Herpesviridae that can invade the nervous system and establish either lytic or latent infections. The establishment of latent infection can occur only in neurons, indicating a unique virus-host interaction in these cells. Here, we compare results from seven microarray studies that focused on the host response of either neural tissue or isolated neurons to alphaherpesvirus infection. These studies utilized either herpes simplex virus type 1 or pseudorabies virus as the infectious agent. From these data, we have found common host responses spanning a variety of infection models in different species, with different herpesvirus strains, and during all phases of infection including lytic, latent, and reactivation. The repeated observation of transcriptional effects on these genes and gene families indicates their likely importance in host defenses or the viral infectious process. We discuss the possible role of these different genes and genes families in alphaherpesvirus infection.

Herpes simplex virus UL56 interacts with and regulates the Nedd4-family ubiquitin ligase Itch

Background

Herpes simplex virus type 2 (HSV-2) is one of many viruses that exploits and modifies the cellular ubiquitin system. HSV-2 expresses the tegument protein UL56 that has been implicated in cytoplasmic transport and/or release of virions, and is a putative regulatory protein of Nedd4 ubiquitin ligase. In order to elucidate the biological function of UL56, this study examined the interaction of UL56 with the Nedd4-family ubiquitin ligase Itch and its role in the regulation of Itch. Additionally, we assessed the similarity between UL56 and regulatory proteins of Itch and Nedd4, Nedd4-family-interactins proteins (Ndfip).

Results

UL56 interacted with Itch, independent of additional viral proteins, and mediated more striking degradation of Itch, compared to Nedd4. Moreover, it was suggested that the lysosome pathway as well as the proteasome pathway was involved in the degradation of Itch. Other HSV-2 proteins with PY motifs, such as VP5 and VP16, did not mediate the degradation of endogenous Itch. Ndfip1 and Ndfip2 were similar in subcellular distribution patterns to UL56 and colocalized with UL56 in co-transfected cells.

Conclusions

We believe that this is the first report demonstrating the interaction of a HSV-specific protein and Itch. Thus, UL56 could function as a regulatory protein of Itch. The mechanism, function and significance of regulating Itch in HSV-2 infection remain unclear and warrant further investigation.

Herpesvirus systematics

This paper is about the taxonomy and genomics of herpesviruses. Each theme is presented as a digest of current information flanked by commentaries on past activities and future directions. The International Committee on Taxonomy of Viruses recently instituted a major update of herpesvirus classification. The former family Herpesviridae was elevated to a new order, the Herpesvirales, which now accommodates 3 families, 3 subfamilies, 17 genera and 90 species. Future developments will include revisiting the herpesvirus species definition and the criteria used for taxonomic assignment, particularly in regard to the possibilities of classifying the large number of herpesviruses detected only as DNA sequences by polymerase chain reaction. Nucleotide sequence accessions in primary databases, such as GenBank, consist of the sequences plus annotations of the genetic features. The quality of these accessions is important because they provide a knowledge base that is used widely by the research community. However, updating the accessions to take account of improved knowledge is essentially reserved to the original depositors, and this activity is rarely undertaken. Thus, the primary databases are likely to become antiquated. In contrast, secondary databases are open to curation by experts other than the original depositors, thus increasing the likelihood that they will remain up to date. One of the most promising secondary databases is RefSeq, which aims to furnish the best available annotations for complete genome sequences. Progress in regard to improving the RefSeq herpesvirus accessions is discussed, and insights into particular aspects of herpesvirus genomics arising from this work are reported.

Medical application of herpes simplex virus

Herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) are important human pathogens that cause a variety of diseases from mild skin diseases such as herpes labialis and herpes genitalis to life-threatening diseases such as herpes encephalitis and neonatal herpes. A number of studies have elucidated the roles of this virus in viral replication and pathogenicity, the regulation of gene expression, interaction with the host cell and immune evasion from the host system. This research has allowed the development of potential therapeutic agents and vectors for human diseases. This review focuses on the basic functions and roles of HSV gene products and reviews the current knowledge of medical applications of genetically engineered HSV mutants using different strategies. These major HSV-derived vectors include: (i) amplicons for gene delivery vectors; (ii) replication-defective HSV recombinants for vaccine vectors; (iii) replication-attenuated HSV recombinants for oncolytic virotherapy.

Recruitment of AtWHY1 and AtWHY3 by a distal element upstream of the kinesin gene AtKP1 to mediate transcriptional repression

A 43-bp distal element, the AtKP1-related element (KPRE), was previously shown to repress the promoter activity of the kinesin gene AtKP1 in Arabidopsis thaliana. In order to identify KPRE-binding factor 1 (KBF1), a combination of ion-exchange chromatography, gel-filtration chromatography and DNA-affinity chromatography was used to purify KBF1 from whole cell extracts of Arabidopsis seedlings. Mass spectrometric identification showed that KBF1 contains two members of the whirly family of transcription factors, AtWHY1 and AtWHY3. KBF1 is a single and double-stranded DNA-binding factor. A ChIP assay showed that AtWHY1 and AtWHY3 bind to the upstream region of AtKP1 gene in vivo. Over-expression of AtWHY1 and AtWHY3 led to an obvious decrease of AtKP1 transcripts, based on quantitative real-time PCR analysis. Interestingly, salicylic acid treatment resulted in an increase of AtWHY1 and AtWHY3 transcripts, and a decrease of AtKP1 transcripts. Thus, AtWHY1 and AtWHY3, as two components of KBF1, can be recruited at the KPRE site to mediate the transcriptional repression of AtKP1. Our results prove that AtKP1 is a new downstream target of the whirly family of transcription factors.

Herpes simplex virus type 2 tegument protein UL56 relocalizes ubiquitin ligase Nedd4 and has a role in transport and/or release of virions

Background

The ubiquitin system functions in a variety of cellular processes including protein turnover, protein sorting and trafficking. Many viruses exploit the cellular ubiquitin system to facilitate viral replication. In fact, herpes simplex virus (HSV) encodes a ubiquitin ligase (E3) and a de-ubiquitinating enzyme to modify the host's ubiquitin system. We have previously reported HSV type 2 (HSV-2) tegument protein UL56 as a putative adaptor protein of neuronal precursor cell-expressed developmentally down-regulated 4 (Nedd4) E3 ligase, which has been shown to be involved in protein sorting and trafficking.

Results

In this study, we visualized and characterized the dynamic intracellular localization of UL56 and Nedd4 using live-cell imaging and immunofluorescence analysis. UL56 was distributed to cytoplasmic vesicles, primarily to the trans-Golgi network (TGN), and trafficked actively throughout the cytoplasm. Moreover, UL56 relocalized Nedd4 to the vesicles in cells transiently expressing UL56 and in cells infected with HSV-2. We also investigated whether UL56 influenced the efficiency of viral replication, and found that extracellular infectious viruses were reduced in the absence of UL56.

Conclusion

These data suggest that UL56 regulates Nedd4 and functions to facilitate the cytoplasmic transport of virions from TGN to the plasma membrane and/or release of virions from the cell surface.

Kaposi's sarcoma-associated herpesvirus ORF45 interacts with kinesin-2 transporting viral capsid-tegument complexes along microtubules

Open reading frame (ORF) 45 of Kaposi's sarcoma-associated herpesvirus (KSHV) is a tegument protein. A genetic analysis with a null mutant suggested a possible role for this protein in the events leading to viral egress. In this study, ORF45 was found to interact with KIF3A, a kinesin-2 motor protein that transports cargoes along microtubules to cell periphery in a yeast two-hybrid screen. The association was confirmed by both co-immunoprecipitation and immunoflorescence approaches in primary effusion lymphoma cells following virus reactivation. ORF45 principally mediated the docking of entire viral capsid-tegument complexes onto the cargo-binding domain of KIF3A. Microtubules served as the major highways for transportation of these complexes as evidenced by drastically reduced viral titers upon treatment of cells with a microtubule depolymerizer, nocodazole. Confocal microscopic images further revealed close association of viral particles with microtubules. Inhibition of KIF3A-ORF45 interaction either by the use of a headless dominant negative (DN) mutant of KIF3A or through shRNA-mediated silencing of endogenous KIF3A expression noticeably decreased KSHV egress reflecting as appreciable reductions in the release of extracellular virions. Both these approaches, however, failed to impact HSV-1 egress, demonstrating the specificity of KIF3A in KSHV transportation. This study thus reports on transportation of KSHV viral complexes on microtubules by KIF3A, a kinesin motor thus far not implicated in virus transportation. All these findings shed light on the understudied but significant events in the KSHV life cycle, delineating a crucial role of a KSHV tegument protein in cellular transport of viral particles.

Translocation of incoming pseudorabies virus capsids to the cell nucleus is delayed in the absence of tegument protein pUL37

After fusion of the envelope of herpesvirus particles with the host cell plasma membrane, incoming nucleocapsids are transported to nuclear pores. Inner tegument proteins pUL36, pUL37, and pUS3 remain attached to the nucleocapsid after entry and therefore might mediate interactions between the nucleocapsid and cellular microtubule-associated motor proteins during transport. To assay for the role of pUL37 in this process, we constructed a pUL37-deleted pseudorabies virus mutant, PrV-DeltaUL37/UL35GFP, which expresses a fusion protein of green fluorescent protein (GFP) and the nonessential small capsid protein pUL35, resulting in the formation of fluorescently labeled capsids. Confocal laser-scanning microscopy of rabbit kidney cells infected with PrV-DeltaUL37/UL35GFP revealed that, whereas penetration was not affected in the absence of pUL37, nuclear translocation of incoming particles was delayed by approximately 1 h compared to PrV-UL35GFP, but not abolished. In contrast, phenotypically complemented pUL37-containing virions of PrV-DeltaUL37/UL35GFP exhibited wild type-like entry kinetics. Thus, the presence of pUL37 is required for rapid nuclear translocation of incoming nucleocapsids.

UL36p is required for efficient transport of membrane-associated herpes simplex virus type 1 along microtubules

Microtubule-mediated anterograde transport is essential for the transport of herpes simplex virus type 1 (HSV-1) along axons, yet little is known regarding the mechanism and the machinery required for this process. Previously, we were able to reconstitute anterograde transport of HSV-1 on microtubules in an in vitro microchamber assay. Here we report that the large tegument protein UL36p is essential for this trafficking. Using a fluorescently labeled UL36 null HSV-1 strain, KDeltaUL36GFP, we found that it is possible to isolate a membrane-associated population of this virus. Although these viral particles contained normal amounts of tegument proteins VP16, vhs, and VP22, they displayed a 3-log decrease in infectivity and showed a different morphology compared to UL36p-containing virions. Membrane-associated KDeltaUL36GFP also displayed a slightly decreased binding to microtubules in our microchamber assay and a two-thirds decrease in the frequency of motility. This decrease in binding and motility was restored when UL36p was supplied in trans by a complementing cell line. These findings suggest that UL36p is necessary for HSV-1 anterograde transport.

Herpes simplex virus type 2 UL56 interacts with the ubiquitin ligase Nedd4 and increases its ubiquitination

The herpes simplex virus UL56 gene is conserved among most members of the Alphaherpesvirinae family and plays a critical role in viral pathogenicity in vivo. The HSV-2 UL56 protein (UL56) is a C-terminally anchored type II membrane protein that is predicted to be inserted into the virion envelope, leaving its N-terminal domain in the tegument. UL56 interacts with KIF1A and UL11. Here we report that UL56 also interacts with the ubiquitin ligase Nedd4 and increases its ubiquitination. Nedd4 was identified as a UL56-interacting protein by a yeast two-hybrid screen. UL56 bound to Nedd4 via its PY motifs. Nedd4 was phosphorylated and degraded in wild-type HSV-2-infected cells but not in cells infected with a UL56-deficient mutant. Ubiquitination assays revealed that UL56 increased ubiquitinated Nedd4, which was actively degraded in infected cells. UL56 also caused a decrease in Nedd4 protein levels and the increased ubiquitination in cotransfected cells. However, UL56 itself was not ubiquitinated, despite its interaction with Nedd4. Based on these findings, we propose that UL56 regulates Nedd4 in HSV-2-infected cells, although deletion of UL56 had no apparent effect on viral growth in vitro.

Transport and egress of herpes simplex virus in neurons

The mechanisms of axonal transport of the alphaherpesviruses, HSV and pseudorabies virus (PrV), in neuronal axons are of fundamental interest, particularly in comparison with other viruses, and offer potential sites for antiviral intervention or development of gene therapy vectors. These herpesviruses are transported rapidly along microtubules (MTs) in the retrograde direction from the axon terminus to the dorsal root ganglion and then anterogradely in the opposite direction. Retrograde transport follows fusion and deenvelopment of the viral capsid at the axonal membrane followed by loss of most of the tegument proteins and then binding of the capsid via one or more viral proteins (VPs) to the retrograde molecular motor dynein. The HSV capsid protein pUL35 has been shown to bind to the dynein light chain Tctex1 but is likely to be accompanied by additional dynein binding of an inner tegument protein. The mechanism of anterograde transport is much more controversial with different processes being claimed for PrV and HSV: separate transport of HSV capsid/tegument and glycoproteins versus PrV transport as an enveloped virion. The controversy has not been resolved despite application, in several laboratories, of confocal microscopy (CFM), real-time fluorescence with viruses dual labelled on capsid and glycoprotein, electron microscopy in situ and immuno-electron microscopy. Different processes for each virus seem counterintuitive although they are the most divergent in the alphaherpesvirus subfamily. Current hypotheses suggest that unenveloped HSV capsids complete assembly in the axonal growth cones and varicosities, whereas with PrV unenveloped capsids are only found travelling in a retrograde direction.

Oncolytic virotherapy for malignant melanoma with herpes simplex virus type 1 mutant HF10

BACKGROUND

Many viruses have been engineered and evaluated for their potential as therapeutic agents in the treatment of malignant neoplasm, including malignant melanoma.

OBJECTIVE

In this study, we investigated the efficacy of HF10, an attenuated, replication-competent HSV, in immunocompetent animal models with malignant melanoma.

METHODS

For in vitro study, viral cytotoxicity assays and replication assays were performed both in human and mouse melanoma cells. For the study in vivo, intraperitoneally disseminated or subcutaneous melanoma models were prepared in DBA/2 mice using clone M3 cells, then HF10 was inoculated intraperitoneally or intratumorally. Therapeutic efficacy of HF10 was assessed by survival, tumor growth, and histopathological analysis.

RESULTS

HF10 infection produced cytolytic effects in melanoma cells at various multiplicities of infection (MOI). In the intraperitoneal melanoma model, all mice survived when given intraperitoneal injections of HF10 compared with 100% fatality in the control mice. In the subcutaneous tumor model, intratumoral inoculation of HF10 significantly reduced tumor growth. Histology and immunohistochemistry showed tumor lysis and inflammatory cell infiltration after intratumoral HF10 inoculation. Viral antigen was retained at the inoculation site until 7 days post-infection. HF10-treated intraperitoneal tumor mice were also protected against tumor rechallenge. HF10 also affected the non-inoculated contralateral tumor when injected into the ipsilateral tumor of mice, suggesting that HF10 can induce systemic antitumor immune responses in mice.

CONCLUSION

Oncolytic viral therapy using HF10 was effective in melanoma mouse models, and intratumoral injection of HF10 induced systemic antitumor responses. These results suggest that HF10 is a promising agent for the treatment of advanced melanoma.

Three-dimensional structure of the human cytomegalovirus cytoplasmic virion assembly complex includes a reoriented secretory apparatus

Human cytomegalovirus (HCMV) induces profound changes in infected cell morphology, including a large cytoplasmic inclusion that corresponds to the virion assembly complex (AC). In electron micrographs, the AC is a highly vacuolated part of the cytoplasm. Markers of cellular secretory organelles have been visualized at the outer edge of the AC, and we recently showed that a marker for early endosomes (i.e., early endosome antigen 1) localizes to the center of the AC. Here, we examined the relationship between the AC and components of the secretory apparatus, studied temporal aspects of the dramatic infection-induced cytoplasmic remodeling, examined the three-dimensional structure of the AC, and considered the implications of our observations for models of HCMV virion maturation and egress. We made three major observations. First, in addition to being relocated, the expression levels of some organelle markers change markedly during the period while the AC is developing. Second, based on three-dimensional reconstructions from z-series confocal microscopic images, the observed concentric rings of vesicles derived from the several compartments (Golgi bodies, the trans-Golgi network [TGN], and early endosomes) are arranged as nested cylinders of organelle-specific vesicles. Third, the membrane protein biosynthetic and exocytic pathways from the endoplasmic reticulum to the Golgi bodies, TGN, and early endosomes are in an unusual arrangement that nonetheless allows for a conventional order of biosynthesis and transport. Our model of AC structure suggests a mechanism by which the virus can regulate the order of tegument assembly.

The pseudorabies virus VP1/2 tegument protein is required for intracellular capsid transport

Transport of capsids in cells is critical to alphaherpesvirus infection and pathogenesis; however, viral factors required for transport have yet to be identified. Here we provide a detailed examination of capsid dynamics during the egress phase of infection in Vero cells infected with pseudorabies virus. We demonstrate that the VP1/2 tegument protein is required for processive microtubule-based transport of capsids in the cytoplasm. A second tegument protein that binds to VP1/2, UL37, was necessary for wild-type transport but was not essential for this process. Both proteins were also required for efficient nuclear egress of capsids to the cytoplasm.

Determination and analysis of the DNA sequence of highly attenuated herpes simplex virus type 1 mutant HF10, a potential oncolytic virus

A spontaneously occurring herpes simplex virus type 1 (HSV-1) mutant, designated HF10, replicates very efficiently and induces extensive cell fusion in most transformed cells as well as Vero cells, but is highly attenuated in mice when inoculated by peripheral routes of infection. Recent studies have shown that HF10 is a promising agent for use in oncolytic virotherapy. In this study, we sequenced the genome of HF10 and compared it with that of HSV-1 strain 17, a reference strain with the syn+ phenotype. The sequencing covered whole regions corresponding to all open reading frames of strain 17, and the overall putative amino acid identity between HF10 and strain 17 was 99.1% except for proteins encoded by three genes with frame-shift mutations. HF10 had a number of deletions and insertions in the genome, resulting in the lack of the functional expression of UL43, UL49.5, UL55, UL56 and latency-associated transcripts. Additionally, HF10 had amino acid changes in genes involved in the regulation of syncytium formation, including UL1, UL20, UL22, UL24, UL27 and UL53. The proteins encoded by UL1, UL2, UL11, UL44, US1, US7, US8.5, US10 and US12 exhibited a relatively high divergence. These data provide the genetic background of HF10 and insight into the molecular mechanism of HSV-1 replication and pathogenicity.

Association of two membrane proteins encoded by herpes simplex virus type 2, UL11 and UL56

Herpes simplex virus (HSV) acquires envelope by budding into trans-Golgi network (TGN)-derived vesicles. Previous studies showed that the UL11 gene product enables efficient virion envelopment and export from infected cells and is incorporated into virions as tegument protein. At its N-terminus, UL11 is dually acylated by myristoic and palmitoic acids. Fatty acylation of UL11 provides both membrane binding strength and Golgi-targeting specificity. We show here that UL11 interacts with UL56 protein, a tail-anchored type II membrane protein encoded by HSV, which associated with the Golgi apparatus and cytoplasmic vesicles. We previously showed that UL56 is involved in vesicular transport in infected cells. The UL11-UL56 complex localized to the perinuclear region of the cytoplasm in infected cells. Fatty acylation of UL11 was important for the formation of the UL11-UL56 protein complex. Taken together, our results identify a novel interaction between two HSV proteins facilitated by mutual interactions with Golgi-derived vesicles.

Viral interactions with the cytoskeleton: a hitchhiker's guide to the cell

The actin and microtubule cytoskeleton play important roles in the life cycle of every virus. During attachment, internalization, endocytosis, nuclear targeting, transcription, replication, transport of progeny subviral particles, assembly, exocytosis, or cell-to-cell spread, viruses make use of different cellular cues and signals to enlist the cytoskeleton for their mission. Viruses induce rearrangements of cytoskeletal filaments so that they can utilize them as tracks or shove them aside when they represent barriers. Viral particles recruit molecular motors in order to hitchhike rides to different subcellular sites which provide the proper molecular environment for uncoating, replicating and packaging viral genomes. Interactions between subviral components and cytoskeletal tracks also help to orchestrate virus assembly, release and efficient cell-to-cell spread. There is probably not a single virus that does not use cytoskeletal and motor functions in its life cycle. Being well informed intracellular passengers, viruses provide us with unique tools to decipher how a particular cargo recruits one or several motors, how these are activated or tuned down depending on transport needs, and how cargoes switch from actin tracks to microtubules to nuclear pores and back.

Molecular motors hijacking by intracellular pathogens

Cargoes are transported intracellularly along cytoskeletal tracks composed of actin or tubulin. Their movement involves the action of molecular motor proteins that generate directed movement along microtubules or actin filaments. The three classes of molecular motors--kinesins, dyneins and myosins--are involved in a multiplicity of biological movements such as mitosis, positioning of organelles, intracellular transports and also vesicular sorting through membrane tubulation and fission and delivery to their target compartment. Intracellular pathogens use this molecular machinery to reach their site of replication, to leave their host or to control the dynamics of membrane exchanges with their replication compartment.

Viral stop-and-go along microtubules: taking a ride with dynein and kinesins

Incoming viral particles move from the cell surface to sites of viral transcription and replication. By contrast, during assembly and egress, subviral nucleoprotein complexes and virions travel back to the plasma membrane. Because diffusion of large molecules is severely restricted in the cytoplasm, viruses use ATP-hydrolyzing molecular motors of the host for propelling along the microtubules, which are the intracellular highways. Recent studies have revealed that, besides travelling inside endocytic or exocytic vesicles, viral proteins interact directly with dynein or kinesin motors. Understanding the molecular mechanisms of cytoplasmic viral transport will aid in the construction of viral vectors for human gene therapy and the search for new antiviral targets.

HF10, an attenuated herpes simplex virus (HSV) type 1 clone, lacks neuroinvasiveness and protects mice against lethal challenge with HSV types 1 and 2

Herpes simplex virus (HSV), a neurotropic virus, establishes life-long and, although rare, life-threatening infection in humans, and it may precipitate substantial medical and psychosocial morbidity. Here we show that HSV-1 strain HF clone 10 (HF10) exhibits impaired neuroinvasiveness in peripheral olfactory, vomeronasal and trigeminal conduits following intranasal as well as corneal inoculation. HF10 attenuation likely arises from multiple defects of HSV genes, so that HF10 will not revert to a virulent phenotype. Intranasal vaccination of mice with HF10 conferred significant protection against lethal challenge with HSV-1 and HSV-2 via the intranasal and intravaginal routes. Thus, we propose that HF10 explicitly meets the prerequisites for a candidate live attenuated HSV vaccine.

Herpes simplex virus and varicella-zoster virus: why do these human alphaherpesviruses behave so differently from one another?

Members of the Herpesviridae family of viruses are classified into the alpha, beta and gamma subfamilies. The alpha subfamily is estimated to have diverged from the beta and gamma subfamilies 200-220 million years ago. The ancestors of the herpes simplex virus (HSV) and the varicella-zoster virus (VZV), two ubiquitous and clinically important human pathogens, appeared 70-80 million years ago. As these viruses coevolved with their specific primate hosts, genetic rearrangements led to the development of the contemporary alphaherpesviruses and their distinct complement of genes. Here the distinct features of HSV and VZV are discussed in terms of their transmissibility, clinical picture, tissue tropism, establishment of latency/reactivation and immune evasion, which can, at least in part, be explained by differences in their genomes.