Influenza virus and redox mediated cell signaling: a complex network of virus/host interaction

Several viruses, including influenza, induce an imbalance of intracellular redox state toward pro-oxidant conditions. Through different mechanisms these alterations contribute both to influenza virus replication and to the pathogenesis of virus-induced disease. At the same time, influenza virus activates several intracellular signaling pathways involved in important physiological functions of the cell. Interestingly, many of these pathways are finely regulated by small changes in intracellular redox state, and the virus-induced redox imbalance might also control viral replication through this mechanism. Here we review the main intracellular redox-sensitive pathways activated upon influenza infection and involved in regulating viral replication.     

Viral mimicry of cytokines,chemokines and their receptors

Viruses have evolved elegant mechanisms to evade detection and destruction by the host immune system. One of the evasion strategies that have been adopted by large DNA viruses is to encode homologues of cytokines, chemokines and their receptors--molecules that have a crucial role in control of the immune response. Viruses have captured host genes or evolved genes to target specific immune pathways, and so viral genomes can be regarded as repositories of important information about immune processes, offering us a viral view of the host immune system. The study of viral immunomodulatory proteins might help us to uncover new human genes that control immunity, and their characterization will increase our understanding of not only viral pathogenesis, but also normal immune mechanisms. Moreover, viral proteins indicate strategies of immune modulation that might have therapeutic potential.     

Autophagy during Early Virus–Host Cell Interactions

Autophagy refers to the conserved, multi-step mechanism that delivers cytosolic cargoes to vesicles of the endo-lysosomal system for degradation. It maintains cellular homeostasis by ensuring the continuous degradation of misformed/senescent intracellular components and the associated recycling of nutrients. Autophagy also represents an important cell-intrinsic defense mechanism against invasion by intracellular pathogens, including viruses. Autophagy might oppose viral invasion by targeting viral particles or viral components for degradation. It can also promote the interaction of viral constituents with receptors specialized in the activation of innate immunity pathways or facilitate the activation of anti-viral adaptive immunity. In response to such pressures, viruses have evolved various sophisticated strategies to avoid anti-viral autophagic responses or to manipulate the autophagic machinery to promote their own replication. This review focuses on our current knowledge of autophagy-related events that take place at early stages during interaction of viruses with host cells as well as on their associated consequences in terms of virus replication and cell fate.     

Downregulation of autophagy by herpesvirus Bcl-2 homologs

The critical role of the cellular autophagy pathway in viral infection and pathogenesis has become increasingly apparent. Mounting evidences suggest that viruses have developed different strategies to meticulously modulate intracellular autophagy for their own benefits, thereby either promoting efficient viral replication or facilitating viral persistence. While our understanding of these strategies is still in its incipient stage, recent advances demonstrate that gamma herpesvirus Bcl-2 homolog (vBcl-2), which protects virus-infected cells from apoptosis, also suppresses cellular autophagy pathway through its direct interaction with the autophagy protein Beclin1. Interestingly, vBcl-2 has evolved to harbor the enhanced anti-autophagic activity compared to its host counterpart, suggesting an important role of cellular autophagy in response to viral infection and virus-associated pathogenesis. Thus, a detailed study of vBcl-2-mediated regulation of autophagy signal transduction pathway may lead to a better understanding of not only how virus escapes from host innate immunity but also how autophagy regulates viral infection and environmental stresses.     

Systems biology of virus-host signaling network interactions

Viruses have evolved to manipulate the host cell machinery for virus propagation, in part by interfering with the host cellular signaling network. Molecular studies of individual pathways have uncovered many viral host-protein targets; however, it is difficult to predict how viral perturbations will affect the signaling network as a whole. Systems biology approaches rely on multivariate, context-dependent measurements and computational analysis to elucidate how viral infection alters host cell signaling at a network level. Here we describe recent advances in systems analyses of signaling networks in both viral and non-viral biological contexts. These approaches have the potential to uncover virus- mediated changes to host signaling networks, suggest new therapeutic strategies, and assess how cell-to-cell variability affects host responses to infection. We argue that systems approaches will both improve understanding of how individual virus-host protein interactions fit into the progression of viral pathogenesis and help to identify novel therapeutic targets.     

Disruption of virus-host cell interactions and cell signaling pathways as an anti-viral approach against influenza virus infections

Influenza is still one of the major plagues worldwide with the threatening potential to cause pandemics. In recent years, increasing levels of resistance to the four FDA approved anti-influenza virus drugs have been described. This situation underlines the urgent need for novel anti-virals in preparation for future influenza epidemics or pandemics. Although the anti-virals currently in use target viral factors such as the neuraminidase or the M2 ion channel, there is an increase in pre-clinical approaches that focus on cellular factors or pathways that directly or indirectly interact with virus replication. This does not only include inhibitors of virus-supportive signaling cascades but also interaction blockers of viral proteins with host cell proteins. This review aims to highlight some of these novel approaches that represent a paradigm change in anti-viral strategies against the influenza virus. Although most of these approaches are still in an early phase of preclinical development they might be very promising particularly with respect to the prevention of viral resistance to potential drugs.     

Host–virus interaction and viral evasion

With each infectious pandemic or outbreak, the medical community feels the need to revisit basic concepts of immunology to understand and overcome the difficult times brought about by these infections. Regarding viruses, they have historically been responsible for many deaths, and such a peculiarity occurs because they are known to be obligate intracellular parasites that depend upon the host's cell machinery for their replication. Successful infection with the production of essential viral components requires constant viral evolution as a strategy to manipulate the cellular environment, including host internal factors, the host's nonspecific and adaptive immune responses to viruses, the metabolic and energetic state of the infected cell, and changes in the intracellular redox environment during the viral infection cycle. Based on this knowledge, it is fundamental to develop new therapeutic strategies for controlling viral dissemination, by means of antiviral therapies, vaccines, or antioxidants, or by targeting the inhibition or activation of cell signaling pathways or metabolic pathways that are altered during infection. The rapid recovery of altered cellular homeostasis during viral infection is still a major challenge. Here, we review the strategies by which viruses evade the host's immune response and potential tools used to develop more specific antiviral therapies to cure, control, or prevent viral diseases.     

病毒利用UPP逃避抗病毒反应的研究进展

泛素-蛋白酶体途径是溶酶体外蛋白降解的主要系统,在许多细胞功能中发挥重要作用。越来越多的证据表明病毒参与泛素-蛋白酶体途径,干扰IFN信号通路和免疫受体表达、凋亡抑制及介导病毒潜伏。深入理解病毒利用泛素-蛋白酶体途径逃避宿主抗病毒反应的策略,有助于揭示病毒的致病机理和鉴定抗病毒药物新靶标。     

Lipid droplets fuel SARS-CoV-2 replication and production of inflammatory mediators

Viruses are obligate intracellular parasites that make use of the host metabolic machineries to meet their biosynthetic needs. Thus, identifying the host pathways essential for the virus replication may lead to potential targets for therapeutic intervention. The mechanisms and pathways explored by SARS-CoV-2 to support its replication within host cells are not fully known. Lipid droplets (LD) are organelles with major functions in lipid metabolism, energy homeostasis and intracellular transport, and have multiple roles in infections and inflammation. Here we described that monocytes from COVID-19 patients have an increased LD accumulation compared to SARS-CoV-2 negative donors. In vitro, SARS-CoV-2 infection were seen to modulate pathways of lipid synthesis and uptake as monitored by testing for CD36, SREBP-1, PPARγ, and DGAT-1 expression in monocytes and triggered LD formation in different human cell lines. LDs were found in close apposition with SARS-CoV-2 proteins and double-stranded (ds)-RNA in infected Vero cells. Electron microscopy (EM) analysis of SARS-CoV-2 infected Vero cells show viral particles colocalizing with LDs, suggestive that LDs might serve as an assembly platform. Pharmacological modulation of LD formation by inhibition of DGAT-1 with A922500 significantly inhibited SARS-CoV-2 replication as well as reduced production of mediators pro-inflammatory response. Taken together, we demonstrate the essential role of lipid metabolic reprograming and LD formation in SARS-CoV-2 replication and pathogenesis, opening new opportunities for therapeutic strategies to COVID-19.     

Influenza virus replication in lung epithelial cells depends on redox‐sensitive pathways activated by NOX4‐derived ROS

An overproduction of reactive oxygen species (ROS) mediated by NADPH oxidase 2 (NOX2) has been related to airway inflammation typical of influenza infection. Virus‐induced oxidative stress may also control viral replication, but the mechanisms underlying ROS production, as well as their role in activating intracellular pathways and specific steps of viral life cycle under redox control have to be fully elucidated. In this study, we demonstrate that influenza A virus infection of lung epithelial cells causes a significant ROS increase that depends mainly on NOX4, which is upregulated at both mRNA and protein levels, while the expression of NOX2, the primary source of ROS in inflammatory cells, is downregulated. Inhibition of NOX4 activity through chemical inhibitors or RNA silencing blocks the ROS increase, prevents MAPK phosphorylation, and inhibits viral ribonucleoprotein (vRNP) nuclear export and viral release. Overall these data, obtained in cell lines and primary culture, describe a so far unrecognized role for NOX4‐derived ROS in activating redox‐regulated intracellular pathways during influenza virus infection and highlight their relevance in controlling specific steps of viral replication in epithelial cells. Pharmacological modulation of NOX4‐mediated ROS production may open the way for new therapeutic approaches to fighting influenza by targeting cell and not the virus.     

Towards high-throughput characterization of small molecule mechanisms of action

Drug discovery is hampered by the lack of general strategies to characterize the mechanisms of action and intracellular targets of bioactive small molecules. Genomics and proteomics promise to aid in this process. Genome-wide approaches in yeast have proven useful to infer the targets and target pathways of small molecules. These approaches are being systematically transferred into mammalian cell culture systems in order to interrogate more complex pathways in a more relevant setting. Advances in proteomics and in vivo genetic screening in multicellular model organism systems are also becoming increasingly powerful and amenable to high-throughput. Current methodologies and technologies are discussed, including how these global approaches complement affinity-based target identification strategies.     

HIV Nef increasing viral particle infectivity may be through affecting the protein transport of HIV factors or host cellular factors which promote viral assembly or budding

Human immunodeficiency virus type 1 (HIV 1) has evolved to encode multifunctional accessory proteins to promote the viral life cycle. Nef, a HIV 1 encoded accessory protein that originally thought to be a negative factor that inhibited viral replications, has been reported increasing HIV1 viral particle infectivity through a still unknown mechanism. Recently, lots of experimental evidences showed that Nef could extensively interact with multiple key factors of protein intracellular trafficking pathways, such as adaptor protein families (APs), to promote the HIV pathogenesis through down-regulation of the membrane localization of MHC1 and CD4 molecules.Taking together with the current progresses of the biological nature of Nef in recent years, here, we proposed that the Nef also could increase the infectivity of viral particle possibly through affecting the protein transport pathways of HIV1 factors or other host cellular factors that promote viral assembly or budding. If true, this will let us better understand how Nef manipulate the host cell environment to promote the HIV pathogenicity and will also provide more choices for developing novel therapeutic strategies.     

泛素-蛋白酶体途径在病毒感染中的作用

泛素-蛋白酶体途径——降解溶酶体外蛋白的主要细胞内系统,在许多细胞功能中发挥重要作用。为自身利益如病毒出芽、凋亡抑制和免疫逃避,许多病毒已经进化出了利用泛素-蛋白酶体途径的不同策略。深入理解泛素-蛋白酶体途径在病毒感染中的作用有助于揭示一些病毒病的致病机理和发现新的分子靶标以开发抗病毒药物。因此,将泛素-蛋白酶体途径在病毒感染中的作用方面的最新进展作一综述。     

Extensive viral mimicry of 22 AIDS-related autoantigens by HIV-1 proteins and pathway analysis of 561 viral/human homologues suggest an initial treatable autoimmune component of AIDS

HIV-1 viral proteins, particularly the env protein, are homologous to 22 AIDS autoantigens, suggesting their creation by antiviral antibodies subsequently targeting human homologues. They include antibodies to T-cell receptors, CD4 and CD95, complement components, IgG, TNF and other immune-related proteins. Autoantibodies may compromise the immune system via knockdown of these key proteins, and autoimmune attack on the immune system itself, as supported by immune activation in early stages of infection and during the transition to AIDS. Over 500 human proteins contain pentapeptides or longer consensi, identical to viral peptides. Such homology explains the extensive viral/human interactome, likely related to the ability of viral homologues to compete with human counterparts as binding partners. Pathway analysis of these homologous proteins revealed their involvement in immune-related networks (e.g. natural killer cell toxicity/toll, T-cell/B-cell receptor signalling/antigen processing) and viral and bacterial entry and defence pathways (phagosome/lysosome pathways, DNA sensing/NOD/RIG-1 pathways) relevant to AIDS pathogenesis. At its inception, AIDS may have an autoimmune component selectively targeting the immune system. Immunosuppressive therapy or antibody removal, which has already achieved some success, might be therapeutically beneficial, particularly if targeted at removal of the culpable antibodies, via affinity dialysis.     

Effects of polyphenol compounds on influenza A virus replication and definition of their mechanism of action

A set of polyphenol compounds was synthesized and assayed for their ability in inhibiting influenza A virus replication. A sub-set of them showed low toxicity. The best compounds within this sub-set were 4 and 6g, which inhibited the viral replication in a dose-dependent manner. The antiviral activity of these molecules was demonstrated to be caused by their interference with intracellular pathways exploited for viral replication: (1) MAP kinases controlling nuclear-cytoplasmic traffic of viral ribonucleoprotein complex; (2) redox-sensitive pathways, involved in maturation of viral hemagglutinin protein.     

Human immunodeficiency virus type 1 Nef: adapting to intracellular trafficking pathways.

The Nef protein of primate lentiviruses is a unique protein that has evolved in several ways to manipulate the biology of an infected cell to support viral replication, immune evasion, pathogenesis, and viral spread. Nef is a small (25- to 34-kDa), myristoylated protein that binds to a collection of cellular factors and acts as an adaptor to generate novel protein interactions to accomplish specific functions. Of the many biological activities attributed to Nef, the reduction of surface levels of the viral receptor (CD4) and antigen-presenting molecules (major histocompatibility complex class I) has been intensely examined; recent evidence demonstrates that Nef utilizes multiple, distinct pathways to affect these proteins. To accomplish this, Nef promotes the formation of multiprotein complexes, recruiting host adaptor proteins to commandeer intracellular vesicular trafficking routes. The altered trafficking of several other host molecules has also been reported, and an emerging theory suggests that Nef generates pleiotrophic effects in the secretory and endocytic pathways that reprogram intracellular protein trafficking and may ultimately provide an efficient platform for viral assembly. This review critically discusses some of the major findings regarding the impact of human immunodeficiency virus type 1 Nef on host protein transport and addresses some emerging directions in this area of human immunodeficiency virus biology.