Evasion of mammalian defense systems by orthopoxviruses

In the course of evolution, viruses have mastered various molecular mechanisms to evade defense reactions of the host organism. The understanding of these mechanisms would promote better comprehension of the crucial reactions directed against infectious agents and further insights into their organization and functioning. A considerable contribution to this field of study can be made by investigating orthopoxviruses pathogenic for humans, such as variola, monkeypox, cowpox, and vaccinia viruses. The experimental data reviewed here suggest that variola virus and other orthopoxviruses, in comparison to other virus families, possess an unsurpassed set of genes whose protein products efficiently modulate the diverse defense reactions of the host.     

Immunomodulatory proteins of orthopoxviruses

The review considers recent data on the structural-functional organization of the genome of orthopoxviruses pathogenic for humans, including the variola, monkeypox, cowpox, and vaccinia viruses. Emphasis was placed on the structure of molecular virulence factors that suppress the inflammatory reactions, immune response, and interferon effects induced by virus infection.     

Immunomodulatory Proteins of Orthopoxviruses

The review considers recent data on the structural–functional organization of the genome of orthopoxviruses pathogenic for humans, including the variola, monkeypox, cowpox, and vaccinia viruses. Emphasis was placed on the structure of molecular virulence factors that suppress the inflammatory reactions, immune response, and interferon effects induced by virus infection.     

植物抗病毒分子机制

在与植物病毒的长期斗争中,植物进化出多种抗病毒机制,其中RNA沉默和R基因介导的病毒抗性是最受人们关注的两种机制.一方面,RNA沉默是植物抵抗病毒侵染的重要手段.植物在病毒侵染过程中可形成病毒来源的双链RNA,经过DCL蛋白的切割、加工形成sRNA,与AGO蛋白结合形成RISC指导病毒RNA的沉默,用于清除病毒.相应地,病毒在与植物的竞争中进化出RNA沉默抑制子,抑制宿主RNA沉默系统以逃避宿主RNA沉默抗病毒反应,增强致病能力.另一方面,植物也进化出R基因介导植物对包括病毒在内的多类病原的抗性.R蛋白直接或间接识别病毒因子,通过一系列的信号转导途径激活植物防御反应,限制病毒的进一步侵染.对植物抗病毒的研究有助于人们对植物抗病分子基础的理解,有重要的科学意义和潜在应用价值.本文综述了植物抗病毒分子机制的重要进展.     

An oligonucleotide microarray for detection and discrimination of orthopoxviruses based on oligonucleotide sequences of two viral genes

An oligonucleotide microarray for detection and identification of orthopoxviruses was developed. Genus specific and orthopoxvirus species-specific regions of the genes encoding chemokine binding and alpha/beta-interferon binding proteins were used as a target. The developed microarray allows the variola, monkeypox, cowpox, vaccinia, camel-pox and ectromelia (mousepox) viruses to be distinguished with a high degree of reliability.     

Variola virus immune evasion proteins

Variola virus, the causative agent of smallpox, encodes approximately 200 proteins. Over 80 of these proteins are located in the terminal regions of the genome, where proteins associated with host immune evasion are encoded. To date, only two variola proteins have been characterized. Both are located in the terminal regions and demonstrate immunoregulatory functions. One protein, the smallpox inhibitor of complement enzymes (SPICE), is homologous to a vaccinia virus virulence factor, the vaccinia virus complement-control protein (VCP), which has been found experimentally to be expressed early in the course of vaccinia infection. Both SPICE and VCP are similar in structure and function to the family of mammalian complement regulatory proteins, which function to prevent inadvertent injury to adjacent cells and tissues during complement activation. The second variola protein is the variola virus high-affinity secreted chemokine-binding protein type II (CKBP-II, CBP-II, vCCI), which binds CC-chemokine receptors. The vaccinia homologue of CKBP-II is secreted both early and late in infection. CKBP-II proteins are highly conserved among orthopoxviruses, sharing approximately 85% homology, but are absent in eukaryotes. This characteristic sets it apart from other known virulence factors in orthopoxviruses, which share sequence homology with known mammalian immune regulatory gene products. Future studies of additional variola proteins may help illuminate factors associated with its virulence, pathogenesis and strict human tropism. In addition, these studies may also assist in the development of targeted therapies for the treatment of both smallpox and human immune-related diseases.     

Roles for host factors in plant viral pathogenicity

The simple, obligate nature of viruses requires them to usurp or divert cellular resources, including host factors, away from their normal functions. The characterization of host proteins, membranes, and nucleic acids that are implicated in viral infection cycles, together with other recent discoveries, is providing fundamental clues about the molecular bases of viral susceptibility. As viruses invade susceptible plants, they create conditions that favor systemic infections by suppressing multiple layers of innate host defenses. When viruses meddle in these defense mechanisms, which are interlinked with basic cellular functions, phenotypic changes can result that contribute to disease symptoms.     

From virus to inflammation: mechanisms of RIG-I-induced IL-1β production

Early detection of viruses by the innate immune system is critical for host defense. Antiviral immunity is initiated by germline encoded pattern recognition receptors (PRRs) that recognize viral pathogen-associated molecular patterns (PAMPs) such as nucleic acids. Intracellular PRRs then drive the production of interferons and cytokines to orchestrate immune responses. One key host factor that is critical for antiviral immunity and for systemic inflammatory reactions including fever is interleukin-1beta (IL-1β). Here we discuss current insights into the molecular mechanisms how the cytosolic RNA helicase RIG-I triggers NF-κB signaling and inflammasome activation specifically for RNA virus-induced IL-1β production.     

Inflammation — a lifelong companion

Inflammation is a key component of the immune system. It has important functions in both defense and pathophysiological events maintaining the dynamic homeostasis of a host organism including its tissues, organs and individual cells. On the cellular level it is controlled by more than 400 currently known genes. Their polymorphisms and environmental conditions give rise to different genotypes in human population. Pro-inflammatory genotype, which dominates in the present population, may be advantageous in childhood but not in elderly people because it is characterized by an increased vulnerability to, and intensity of, inflammatory reactions. These reactions may be the possible reasons of chronic inflammatory diseases, especially in old age. Better understanding of complex molecular and cellular inflammatory mechanisms is indispensable for detailed knowledge of pathogenesis of many diseases, their prevention and directed drug therapy. Here we summarize the basic current knowledge on these mechanisms.     

The time scale in poxvirus evolution

Unlike vertebrates and RNA-containing viruses, the objective estimate of molecular clock for DNA-containing viruses was so far absent. An extended central conservative genomic region of orthopoxviruses (about 102 kbp) and the sequence of DNA polymerase gene (about 3 kbp) of the viruses belonging to various genera from the family Poxviridae were analyzed. During this analysis, the known dating of variola virus (VARV) transfer from West Africa to South America (XVI century) and our own data on close phylogenetic relations between the modem West African and South American VARV isolates were used. As a result of this work, it was calculated for the first time that the rate of mutation accumulation in these DNA-containing viruses amounted to 0.9-1.2 x 10(-6) substitutions per site per year. The poxviruses started separating from the ancestor virus to form the modem genera approximately 500 thousand years ago; the ancestor of the genus Orthopoxvirus separated about 300 thousand years ago; and its division into the modem studied species took place approximately 14 thousand years ago.     

Viral control of mitochondrial apoptosis

Throughout the process of pathogen-host co-evolution, viruses have developed a battery of distinct strategies to overcome biochemical and immunological defenses of the host. Thus, viruses have acquired the capacity to subvert host cell apoptosis, control inflammatory responses, and evade immune reactions. Since the elimination of infected cells via programmed cell death is one of the most ancestral defense mechanisms against infection, disabling host cell apoptosis might represent an almost obligate step in the viral life cycle. Conversely, viruses may take advantage of stimulating apoptosis, either to kill uninfected cells from the immune system, or to induce the breakdown of infected cells, thereby favoring viral dissemination. Several viral polypeptides are homologs of host-derived apoptosis-regulatory proteins, such as members of the Bcl-2 family. Moreover, viral factors with no homology to host proteins specifically target key components of the apoptotic machinery. Here, we summarize the current knowledge on the viral modulation of mitochondrial apoptosis, by focusing in particular on the mechanisms by which viral proteins control the host cell death apparatus.     

Virus-cell interactions: impact on cytokine production, immune evasion and tumor growth

The outcome of a viral infection ranges from benign to fatal with the clinical pictures being very diverse. This is largely due to the virus-cell interactions that occur in the infected organism. Rapidly after infection, cells initiate a first line of defense against the virus. The cells sense viruses through several mechanisms. Among these the ability to respond to accumulation of double-stranded RNA has been particularly well studied and seems to be of importance. On the other hand, the close co-existence of virus and host has allowed viruses to develop mechanisms to down-modulate the initial reaction or to exploit this proinflammatory response in its own advance. This review describes how virus infections affect cellular signal transduction and the mechanisms through which certain viruses modulate this response to dampen the immune response or prevent cell death.     

病毒感染与宿主细胞DNA损伤应答

病毒感染宿主细胞后,利用细胞内的营养物质和原料进行复制和增殖,同时能引起宿主细胞启动抗病毒免疫应答的防御机制。此外,近年来的研究还表明病毒感染能够引起宿主细胞的DNA损伤应答,该反应是细胞另一种防止病毒入侵的自我保护机制。同时发现,病毒在长期进化过程中形成了不同的机制来对抗宿主细胞的DNA损伤应答,从而消除细胞对其复制和繁殖产生的不利影响。因此,研究和阐述病毒感染后引起宿主细胞DNA损伤应答途径的机制,可使我们采取相应对策选择新的抗病毒靶点,从而有利于新型抗病毒药物的开发。     

Identification of a pyridopyrimidinone inhibitor of orthopoxviruses from a diversity-oriented synthesis library

Orthopoxviruses include the prototypical vaccinia virus, the emerging infectious agent monkeypox virus, and the potential biothreat variola virus (the causative agent of smallpox). There is currently no FDA-approved drug for humans infected with orthopoxviruses. We screened a diversity-oriented synthesis library for new scaffolds with activity against vaccinia virus. This screen identified a nonnucleoside analog that blocked postreplicative intermediate and late gene expression. Viral genome replication was unaffected, and inhibition could be elicited late in infection and persisted upon drug removal. Sequencing of drug-resistant viruses revealed mutations predicted to be on the periphery of the highly conserved viral RNA polymerase large subunit. Consistent with this, the compound had broad-spectrum activity against orthopoxviruses in vitro. These findings indicate that novel chemical synthesis approaches are a potential source for new infectious disease therapeutics and identify a potentially promising candidate for development to treat orthopoxvirus-infected individuals.     

Toll-like receptors as an escape mechanism from the host defense

Toll-like receptors (TLRs) are probably the most important class of pattern-recognition receptors. Recognition of pathogen-associated molecular patterns (PAMPs) by TLRs, either alone or in heterodimerization with other TLR or non-TLR receptors, induces the production of signals that are responsible for the activation of genes important for an effective host defense, especially those of proinflammatory cytokines. Recent studies also suggest that pathogenic microorganisms can modulate or interfere with TLR-mediated pattern recognition and can use TLRs as an escape mechanism from the host defense. Three major TLR-mediated escape mechanisms have been identified: TLR2-induced immunosuppression, especially through induction of interleukin (IL)-10 release; blockade of TLR recognition; and TLR-mediated induction of viral replication. Thus, TLR signals are not only beneficial to the host, but in certain situations the activation of particular TLR responses by microorganisms might serve as an escape mechanism from the host defense.     

宿主防御肽抗病毒感染机制研究进展

宿主防御肽是一类广泛存在于脊椎动物的小分子多肽,具有广谱的抗菌活性以及抗炎、细胞趋化、促进血管生成和修复损伤等免疫调节功能。以往的研究多集中在宿主防御肽抗细菌和真菌感染的研究上。近年来大量研究发现,宿主防御肽也具有广泛的抗病毒活性,在临床各类病毒病的预防和治疗上具有潜在的应用前景。本文围绕宿主防御肽直接杀伤病毒、调节病毒感染过程和参与宿主抗病毒天然免疫调节这3个方面的作用机制进行综述,为宿主防御肽抗病毒相关研究和相关抗病毒生物药物的研发提供参考和借鉴。     

Interaction of viral proteins with host cell death machinery

In recent years, intense research has been directed towards understanding molecular mechanisms involved in viral pathogenesis. It is now known that many viruses manipulate host defense mechanisms to prevent apoptosis in order to maximize viral replication. Towards the end of their replication cycle, certain viruses direct the synthesis of proteins that induce apoptosis or cell lysis thereby facilitating viral release from the cell. The present review summarizes the current understanding of interactions between viral proteins and the host cell death machinery.     

Smallpox: anything to declare?

Smallpox was eradicated in 1977, but it remains a concern owing to the potential use of the causative agent variola virus in bioterrorism. This article provides an overview of the World Health Organization's spectacular success in achieving the eradication of smallpox. It discusses how variola virus could potentially re-emerge and how prepared we are to counter such a re-emergence. Finally, the potential threat from other orthopoxviruses that exist naturally or that have been genetically engineered is considered. In the words of Rep. Christopher Shay, 'Better to be scared by the improbable possibility than to be unprepared for the catastrophic reality'.     

Orthopoxvirus genes for Kelch-like proteins. I. Analysis of species specific differences by gene structure and organization

Genes and proteins of the kelch superfamily were structurally analyzed in the smallpox (SPV), monkeypox (MPV), cowpox (CPV), and vaccinia (VV) viruses. Genes potentially coding for the kelch-like proteins were found only in the variable terminal regions of the orthopoxvirus genome. The set and sizes of their protein products varied with species. All genes of the superfamily proved to be disrupted by mutations in SPV, which is highly pathogenic for its only host, man. The largest set of kelch-like proteins was observed for CPV, which is low-pathogenic for humans and has the broadest animal host range. The kelch-like proteins of one virus showed low homology to each other, whereas isologs of different viruses were highly homologous. The results testified to the earlier assumption that CPV is the most ancient and an ancestor of the other orthopoxviruses pathogenic for humans.