Development of cellular signaling pathway inhibitors as new antivirals against influenza

Viral exploitation of the MEK/ERK pathway - A tale of vaccinia virus and other viruses

The VACV replication cycle is remarkable in the sense that it is performed entirely in the cytoplasmic compartment of vertebrate cells, due to its capability to encode enzymes required either for regulating the macromolecular precursor pool or the biosynthetic processes. Although remarkable, this gene repertoire is not sufficient to confer the status of a free-living microorganism to the virus, and, consequently, the virus relies heavily on the host to successfully generate its progeny. During the complex virus-host interaction, viruses must deal not only with the host pathways to accomplish their temporal demands but also with pathways that counteract viral infection, including the inflammatory, innate and acquired immune responses. This review focuses on VACV and other DNA or RNA viruses that stimulate the MEK (MAPK - Mitogen Activated Protein Kinase)/ERK- Extracellular signal-Regulated Kinase) pathway as part of their replication cycle.

Sprouty-Related Ena/Vasodilator-Stimulated Phosphoprotein Homology 1-Domain-Containing Protein-2 Critically Regulates Influenza A Virus-Induced Pneumonia

OBJECTIVES

Influenza A virus causes acute respiratory infections that induce annual epidemics and occasional pandemics. Although a number of studies indicated that the virus-induced intracellular signaling events are important in combating influenza virus infection, the mechanism how specific molecule plays a critical role among various intracellular signaling events remains unknown. Raf/MEK/extracellular signal-regulated kinase cascade is one of the key signaling pathways during influenza virus infection, and the Sprouty-related Ena/vasodilator-stimulated phosphoprotein homology 1-domain-containing protein has recently been identified as a negative regulator of Raf-dependent extracellular signal-regulated kinase activation. Here, we examined the role of Raf/MEK/extracellular signal-regulated kinase cascade through sprouty-related Ena/vasodilator-stimulated phosphoprotein homology 1-domain-containing protein in influenza A viral infection because the expression of sprouty-related Ena/vasodilator-stimulated phosphoprotein homology 1-domain-containing protein was significantly enhanced in human influenza viral-induced pneumonia autopsy samples.

DESIGN

Prospective animal trial.

SETTING

Research laboratory.

SUBJECTS

Wild-type and sprouty-related Ena/vasodilator-stimulated phosphoprotein homology 1-domain-containing protein-2 knockout mice inoculated with influenza A.

INTERVENTIONS

Wild-type or sprouty-related Ena/vasodilator-stimulated phosphoprotein homology 1-domain-containing protein-2 knockout mice were infected by intranasal inoculation of influenza A (A/PR/8). An equal volume of phosphate-buffered saline was inoculated intranasally into mock-infected mice.

MEASUREMENTS AND MAIN RESULTS

Influenza A infection of sprouty-related Ena/vasodilator-stimulated phosphoprotein homology 1-domain-containing protein-2 knockout mice led to higher mortality with greater viral load, excessive inflammation, and enhanced cytokine production than wild-type mice. Administration of MEK inhibitor, U0126, improved mortality and reduced both viral load and cytokine levels. Furthermore, bone marrow chimeras indicated that influenza A-induced lung pathology was most severe when sprouty-related Ena/vasodilator-stimulated phosphoprotein homology 1-domain-containing protein-2 expression was lacking in nonimmune cell populations. Furthermore, microarray analysis revealed knockdown of sprouty-related Ena/vasodilator-stimulated phosphoprotein homology 1-domain-containing protein-2 led to enhanced phosphatidylinositol 3-kinase signaling pathway, resulting that viral clearance was regulated by sprouty-related Ena/vasodilator-stimulated phosphoprotein homology 1-domain-containing protein-2 expression through the phosphatidylinositol 3-kinase signaling pathway in murine lung epithelial cells.

CONCLUSIONS

These data support an important function of sprouty-related Ena/vasodilator-stimulated phosphoprotein homology 1-domain-containing protein-2 in controlling influenza virus-induced pneumonia and viral replication. Sprouty-related Ena/vasodilator-stimulated phosphoprotein homology 1-domain-containing protein-2 may be a novel therapeutic target for controlling the immune response against influenza influenza A virus infection.

The MEK-inhibitor CI-1040 displays a broad anti-influenza virus activity in vitro and provides a prolonged treatment window compared to standard of care in vivo

Influenza viruses (IV) continue to pose an imminent threat to human welfare. Yearly re-occurring seasonal epidemic outbreaks and pandemics with high mortality can occur. Besides vaccination against a limited number of viral strains only a few antiviral drugs are available, which are losing their effectiveness as more and more IV strains become resistant. Thus, new antiviral approaches that omit IV resistance are urgently needed. Here, the dependency on the cellular Raf/MEK/ERK signaling pathway for IV replication opens a new perspective. In consequence, we studied the antiviral potential of the MEK inhibitor Cl-1040 (PD184352). We show that Cl-1040 significantly reduces virus titers in vitro via retention of viral RNP complexes in the cell nucleus. Furthermore, Cl-1040 is effective against a broad range of IV strains, including highly pathogenic avian IV, as well as against a Tamiflu^®-resistant IV strain. Using a mouse model, we demonstrate that Cl-1040 can reduce IV lung titers in vivo. Importantly, the treatment window for Cl-1040 expands up to 48 h post infection when Tamiflu^® treatment has no effect. In conclusion, Cl-1040 offers an interesting perspective for anti-IV approaches.

Progress of small molecular inhibitors in the development of anti-influenza virus agents

The influenza pandemic is a major threat to human health, and highly aggressive strains such as H1N1, H5N1 and H7N9 have emphasized the need for therapeutic strategies to combat these pathogens. Influenza anti-viral agents, especially active small molecular inhibitors play important roles in controlling pandemics while vaccines are developed. Currently, only a few drugs, which function as influenza neuraminidase (NA) inhibitors and M2 ion channel protein inhibitors, are approved in clinical. However, the acquired resistance against current anti-influenza drugs and the emerging mutations of influenza virus itself remain the major challenging unmet medical needs for influenza treatment. It is highly desirable to identify novel anti-influenza agents. This paper reviews the progress of small molecular inhibitors act as antiviral agents, which include hemagglutinin (HA) inhibitors, RNA-dependent RNA polymerase (RdRp) inhibitors, NA inhibitors and M2 ion channel protein inhibitors etc. Moreover, we also summarize new, recently reported potential targets and discuss strategies for the development of new anti-influenza virus drugs.

Fcγ-receptor IIa-mediated Src Signaling Pathway Is Essential for the Antibody-Dependent Enhancement of Ebola Virus Infection

Antibody-dependent enhancement (ADE) of Ebola virus (EBOV) infection has been demonstrated in vitro, raising concerns about the detrimental potential of some anti-EBOV antibodies. ADE has been described for many viruses and mostly depends on the cross-linking of virus-antibody complexes to cell surface Fc receptors, leading to enhanced infection. However, little is known about the molecular mechanisms underlying this phenomenon. Here we show that Fcγ-receptor IIa (FcγRIIa)-mediated intracellular signaling through Src family protein tyrosine kinases (PTKs) is required for ADE of EBOV infection. We found that deletion of the FcγRIIa cytoplasmic tail abolished EBOV ADE due to decreased virus uptake into cellular endosomes. Furthermore, EBOV ADE, but not non-ADE infection, was significantly reduced by inhibition of the Src family protein PTK pathway, which was also found to be important to promote phagocytosis/macropinocytosis for viral uptake into endosomes. We further confirmed a significant increase of the Src phosphorylation mediated by ADE. These data suggest that antibody-EBOV complexes bound to the cell surface FcγRIIa activate the Src signaling pathway that leads to enhanced viral entry into cells, providing a novel perspective for the general understanding of ADE of virus infection.

The inflammatory response triggered by Influenza virus: a two edged sword

Influenza A virus (IAV) is a relevant respiratory tract pathogen leading to a great number of deaths and hospitalizations worldwide. Secondary bacterial infections are a very common cause of IAV associated morbidity and mortality. The robust inflammatory response that follows infection is important for the control of virus proliferation but is also associated with lung damage, morbidity and death. The role of the different components of immune response underlying protection or disease during IAV infection is not completely elucidated. Overall, in the context of IAV infection, inflammation is a 'double edge sword' necessary to control infection but causing disease. Therefore, a growing number of studies suggest that immunomodulatory strategies may improve disease outcome without affecting the ability of the host to deal with infection. This review summarizes recent aspects of the inflammatory responses triggered by IAV that are preferentially involved in causing severe pulmonary disease and the anti-inflammatory strategies that have been suggested to treat influenza induced immunopathology.

Antivirals for Respiratory Viral Infections: Problems and Prospects

In the past two decades, several newly emerging and reemerging viral respiratory pathogens including several influenza viruses (avian influenza and pandemic influenza), severe acute respiratory syndrome coronavirus (SARS-CoV), and Middle East respiratory syndrome coronavirus (MERS-CoV), have continued to challenge medical and public health systems. Thereafter, the development of cost-effective, broad-spectrum antiviral agents is the urgent mission of both virologists and pharmacologists. Current antiviral developments have focused targets on viral entry, replication, release, and intercellular pathways essential for viral life cycle. Here, we review the current literature on challenges and prospects in the development of these antivirals.

Chemical Genomics Identifies the PERK-Mediated Unfolded Protein Stress Response as a Cellular Target for Influenza Virus Inhibition

Influenza A viruses generate annual epidemics and occasional pandemics of respiratory disease with important consequences for human health and the economy. Therefore, a large effort has been devoted to the development of new anti-influenza virus drugs directed to viral targets, as well as to the identification of cellular targets amenable to anti-influenza virus therapy. Here we have addressed the identification of such potential cellular targets by screening collections of drugs approved for human use. We reasoned that screening with a green fluorescent protein-based recombinant replicon system would identify cellular targets involved in virus transcription/replication and/or gene expression and hence address an early stage of virus infection. By using such a strategy, we identified Montelukast (MK) as an inhibitor of virus multiplication. MK inhibited virus gene expression but did not alter viral RNA synthesis in vitro or viral RNA accumulation in vivo. The low selectivity index of MK prevented its use as an antiviral, but it was sufficient to identify a new cellular pathway suitable for anti-influenza virus intervention. By deep sequencing of RNA isolated from mock- and virus-infected human cells, treated with MK or left untreated, we showed that it stimulates the PERK-mediated unfolded protein stress response. The phosphorylation of PERK was partly inhibited in virus-infected cells but stimulated in MK-treated cells. Accordingly, pharmacological inhibition of PERK phosphorylation led to increased viral gene expression, while inhibition of PERK phosphatase reduced viral protein synthesis. These results suggest the PERK-mediated unfolded protein response as a potential cellular target to modulate influenza virus infection.

Influenza A viruses are responsible for annual epidemics and occasional pandemics with important consequences for human health and the economy. The unfolded protein response is a defense mechanism fired by cells when the demand of protein synthesis and folding is excessive, for instance, during an acute virus infection. In this report, we show that influenza virus downregulates the unfolded protein response mediated by the PERK sensor, while Montelukast, a drug used to treat asthma in humans, specifically stimulated this response and downregulated viral protein synthesis and multiplication. Accordingly, we show that PERK phosphorylation was reduced in virus-infected cells and increased in cells treated with Montelukast. Hence, our studies suggest that modulation of the PERK-mediated unfolded protein response is a target for influenza virus inhibition.

[Modulation of transcriptomic signature of the infected host: a new therapeutic strategy for the management of severe viral infections? Example of the flu]

Ces dernières décennies ont été marquées par l’émergence ou la réémergence de virus responsables d’épidémies ou de pandémies plus ou moins sévères. Les stratégies préventives sont prises à défaut, et l’arsenal antiviral curatif est limité d’autant plus que les résistances virales peuvent apparaître rapidement. Par ailleurs, le développement de nouvelles molécules nécessite un délai incompatible avec la réponse rapide nécessaire lors d’une épidémie d’envergure ou d’une pandémie. C’est la raison pour laquelle de nouvelles approches thérapeutiques sont nécessaires. Un concept novateur est le repositionnement de molécules déjà sur le marché en exploitant leur capacité à inverser la réponse transcriptomique cellulaire de l’hôte infecté. En identifiant des molécules qui visent l’hôte et non le virus, cette stratégie permet d’avoir un large spectre d’action et d’être potentiellement actif sur de nouveaux variants. La mise en place de cette stratégie nécessite de caractériser les réponses cellulaires spécifiques de l’infection virale d’intérêt, de cribler in silico des molécules candidates, de les tester sur modèles cellulaires et animaux, avant d’envisager des essais cliniques chez l’homme. Nous présenterons cette démarche en prenant pour exemple l’infection grippale.

Repurposing Kinase Inhibitors as Antiviral Agents to Control Influenza A Virus Replication

Influenza A virus (IAV) infection causes seasonal epidemics of contagious respiratory illness that causes substantial morbidity and some mortality. Regular vaccination is the principal strategy for controlling influenza virus, although vaccine efficacy is variable. IAV antiviral drugs are available; however, substantial drug resistance has developed to two of the four currently FDA-approved antiviral drugs. Thus, new therapeutic approaches are being sought to reduce the burden of influenza-related disease. A high-throughput screen using a human kinase inhibitor library was performed targeting an emerging IAV strain (H7N9) in A549 cells. The inhibitor library contained 273 structurally diverse, active cell permeable kinase inhibitors with known bioactivity and safety profiles, many of which are at advanced stages of clinical development. The current study shows that treatment of human A549 cells with kinase inhibitors dinaciclib, flavopiridol, or PIK-75 exhibits potent antiviral activity against H7N9 IAV as well as other IAV strains. Thus, targeting host kinases can provide a broad-spectrum therapeutic approach against IAV. These findings provide a path forward for repurposing existing kinase inhibitors safely as potential antivirals, particularly those that can be tested in vivo and ultimately for clinical use.

Hepatitis C Virus Nonstructural Protein 5A Inhibits MG132-Induced Apoptosis of Hepatocytes in Line with NF-κB-Nuclear Translocation

Background

Hepatitis C virus (HCV) infection is one of the major causes of cirrhosis and hepatocellular carcinoma. HCV nonstructural protein 5A (NS5A) is an attractive antiviral target and plays an important role in HCV replication as well as hepatocarcinogenesis. The aim of this study was to assess the effect of HCV NS5A protein in the abrogation of apoptotic cell death induced by the proteasome inhibitor MG132.

Methods

Apoptotic responses to MG132 and the expression of molecules involved in NF-κB signaling pathways in human hepatocytes were investigated with or without the expression of HCV NS5A.

Results

HCV NS5A protected HepG2 cells against MG132-induced apoptosis, in line with NF-κB-nuclear translocation. A similar NF-κB-nuclear translocation was observed in Huh7 cells infected with HCV JFH1. In agreement with this, after treatment with MG132, HCV NS5A could elevate the transcription of several NF-κB target genes such as BCL2 and BCLXL to inhibit MG132-induced apoptosis in hepatocytes. HCV HCV NS5A also enhanced phosphorylation of IκBα. Consistent with a conferred prosurvival advantage, HCV NS5A reduced MG132-induced poly(adenosine diphosphate-ribose) polymerase cleavage.

Conclusions

HCV NS5A expression enhances phosphorylation of IκBα, liberates NF-κB for nuclear translocation and downregulates MG132-induced apoptotic pathways in human hepatocytes. It is possible that the disruption of proteasome-associated apoptosis plays a role in the pathogenesis of HCV infection.

Targeting Importin-α7 as a Therapeutic Approach against Pandemic Influenza Viruses

Viral drug resistance is believed to be less likely to occur if compounds are directed against cellular rather than viral proteins. In this study, we analyzed the feasibility of a crucial viral replication factor, namely, importin-α7, as a cellular drug target to combat pandemic influenza viruses. Surprisingly, only five viral lung-to-lung passages were required to achieve 100% lethality in importin-α7⁻/⁻ mice that otherwise are resistant. Viral escape from importin-α7 requirement was mediated by five mutations in the viral ribonucleoprotein complex and the surface glycoproteins. Moreover, the importin-α7⁻/⁻ mouse-adapted strain became even more virulent for wild-type mice than the parental strain. These studies show that targeting host proteins may still result in viral escape by alternative pathways, eventually giving rise to even more virulent virus strains. Thus, therapeutic intervention strategies should consider a multitarget approach to reduce viral drug resistance. IMPORTANCE Here, we investigated the long-standing hypothesis based on in vitro studies that viral drug resistance occurrence is less likely if compounds are directed against cellular rather than viral proteins. Here, we challenged this hypothesis by analyzing, in an in vivo animal model, the feasibility of targeting the cellular factor importin-α7, which is crucial for human influenza virus replication and pathogenesis, as an efficient antiviral strategy against pandemic influenza viruses. In summary, our studies suggest that resistance against cellular factors is possible in vivo, and the emergence of even more virulent viral escape variants calls for particular caution. Thus, therapeutic intervention strategies should consider a multitarget approach using compounds against viral as well as cellular factors to reduce the risk of viral drug resistance and potentially increased virulence.

Peptidomimetic furin inhibitor MI-701 in combination with oseltamivir and ribavirin efficiently blocks propagation of highly pathogenic avian influenza viruses and delays high level oseltamivir resistance in MDCK cells

Antiviral medication is used for the treatment of severe influenza infections, of which the neuraminidase inhibitors (NAIs) are the most effective drugs, approved so far. Here, we investigated the antiviral efficacy of the peptidomimetic furin inhibitor MI-701 in combination with oseltamivir carboxylate and ribavirin against the infection of highly pathogenic avian influenza viruses (HPAIV) that are activated by the host protease furin. Cell cultures infected with the strains A/Thailand/1(KAN-1)/2004 (H5N1) and A/FPV/Rostock/1934 (H7N1) were treated with each agent alone, or in double and triple combinations. MI-701 alone achieved a concentration-dependent reduction of virus propagation. Double treatment of MI-701 with oseltamivir carboxylate and triple combination with ribavirin showed synergistic inhibition and a pronounced delay of virus propagation. MI-701 resistant mutants were not observed. Emergence of NA mutation H275Y conferring high oseltamivir resistance was significantly delayed in the presence of MI-701. Our data indicate that combination with a potent furin inhibitor significantly enhances the therapeutic efficacy of conventional antivirals drugs against HPAIV infection.

Virus-host interactomics: new insights and opportunities for antiviral drug discovery

The current therapeutic arsenal against viral infections remains limited, with often poor efficacy and incomplete coverage, and appears inadequate to face the emergence of drug resistance. Our understanding of viral biology and pathophysiology and our ability to develop a more effective antiviral arsenal would greatly benefit from a more comprehensive picture of the events that lead to viral replication and associated symptoms. Towards this goal, the construction of virus-host interactomes is instrumental, mainly relying on the assumption that a viral infection at the cellular level can be viewed as a number of perturbations introduced into the host protein network when viral proteins make new connections and disrupt existing ones. Here, we review advances in interactomic approaches for viral infections, focusing on high-throughput screening (HTS) technologies and on the generation of high-quality datasets. We show how these are already beginning to offer intriguing perspectives in terms of virus-host cell biology and the control of cellular functions, and we conclude by offering a summary of the current situation regarding the potential development of host-oriented antiviral therapeutics.

Inhibition of influenza virus replication by targeting broad host cell pathways

Antivirals that are currently used to treat influenza virus infections target components of the virus which can mutate rapidly. Consequently, there has been an increase in the number of resistant strains to one or many antivirals in recent years. Here we compared the antiviral effects of lysosomotropic alkalinizing agents (LAAs) and calcium modulators (CMs), which interfere with crucial events in the influenza virus replication cycle, against avian, swine, and human viruses of different subtypes in MDCK cells. We observed that treatment with LAAs, CMs, or a combination of both, significantly inhibited viral replication. Moreover, the drugs were effective even when they were administered 8 h after infection. Finally, analysis of the expression of viral acidic polymerase (PA) revealed that both drugs classes interfered with early events in the viral replication cycle. This study demonstrates that targeting broad host cellular pathways can be an efficient strategy to inhibit influenza replication. Furthermore, it provides an interesting avenue for drug development where resistance by the virus might be reduced since the virus is not targeted directly.

Influenza, a One Health paradigm--novel therapeutic strategies to fight a zoonotic pathogen with pandemic potential

Influenza virus is a paradigm for a pathogen that frequently crosses the species barrier from animals to humans, causing severe disease in the human population. This ranges from frequent epidemics to occasional pandemic outbreaks with millions of death. All previous pandemics in humans were caused by animal viruses or virus reassortants carrying animal virus genes, underlining that the fight against influenza requires a One Health approach integrating human and veterinary medicine. Furthermore, the fundamental question of what enables a flu pathogen to jump from animals to humans can only be tackled in a transdisciplinary approach between virologists, immunologists and cell biologists. To address this need the German FluResearchNet was established as a first nationwide influenza research network that virtually integrates all national expertise in the field of influenza to unravel viral and host determinants of pathogenicity and species transmission and to explore novel avenues of antiviral intervention. Here we focus on the various novel anti-flu approaches that were developed as part of the FluResearchNet activities.

Histone deacetylase 6 inhibits influenza A virus release by downregulating the trafficking of viral components to the plasma membrane via its substrate, acetylated microtubules

Mammalian cells produce many proteins, such as IFITM3, ISG15, MxA, and viperin, that inhibit influenza A virus (IAV) infection. Here, we show that a new class of host protein, histone deacetylase 6 (HDAC6), inhibits IAV infection. We found that HDAC6-overexpressing cells release about 3-fold less IAV progeny, whereas HDAC6-depleted cells release about 6-fold more IAV progeny. The deacetylase activity of HDAC6 played a role in its anti-IAV function as tubacin, a specific small-molecule inhibitor of HDAC6, increased the release of IAV progeny in a dose-dependent manner. Further, as visualized by electron microscopy, tubacin-treated cells showed an increase in IAV budding at the plasma membrane, the site of IAV assembly. Tubacin is a domain-specific inhibitor and binds to one of the two HDAC6 catalytic domains possessing tubulin deacetylase activity. This indicated the potential involvement of acetylated microtubules in the trafficking of viral components to the plasma membrane. Indeed, as quantified by flow cytometry, there was about a 2.0- to 2.5-fold increase and about a 2.0-fold decrease in the amount of viral envelope protein hemagglutinin present on the plasma membrane of tubacin-treated/HDAC6-depleted and HDAC6-overexpressing cells, respectively. In addition, the viral ribonucleoprotein complex was colocalized with acetylated microtubule filaments, and viral nucleoprotein coimmunoprecipitated with acetylated tubulin. Together, our findings indicate that HDAC6 is an anti-IAV host factor and exerts its anti-IAV function by negatively regulating the trafficking of viral components to the host cell plasma membrane via its substrate, acetylated microtubules.

IMPORTANCE

Host cells produce many proteins that have the natural ability to restrict influenza virus infection. Here, we discovered that another host protein, histone deacetylase 6 (HDAC6), inhibits influenza virus infection. We demonstrate that HDAC6 exerts its anti-influenza virus function by negatively regulating the trafficking of viral components to the site of influenza virus assembly via its substrate, acetylated microtubules. HDAC6 is a multisubstrate enzyme and regulates multiple cellular pathways, including the ones leading to various cancers, neurodegenerative diseases, and inflammatory disorders. Therefore, several drugs targeting HDAC6 are under clinical development for the treatment of a wide range of diseases. Influenza virus continues to be a major global public health problem due to regular emergence of drug-resistant and novel influenza virus strains in humans. As an alternative antiviral strategy, HDAC6 modulators could be employed to stimulate the anti-influenza virus potential of endogenous HDAC6 to inhibit influenza virus infection.

Inhibition of Akt kinase activity suppresses entry and replication of influenza virus

The possibility of the pandemic spread of influenza viruses highlights the need for an effective cure for this life-threatening disease. Influenza A virus, belonging to a family of orthomyxoviruses, is a negative-strand RNA virus which encodes 11 viral proteins. A numbers of intracellular signaling pathways in the host cells interact with influenza the viral proteins, which affect various stages of viral infection and replication. In this study, we investigated how inhibition of Akt kinase activity impacts on influenza virus infection by using "Akt-in", a peptide Akt inhibitor. In PR8 influenza-infected A549 cells, Akt interacted with the NS1 (Non structural protein 1), and hence increased phosphorylation of Akt kinase activity and NS1. Treatment of cells with either "TCL1- or TCL1b-based Akt-in" efficiently suppressed Akt kinase activity while decreasing the levels of phosphorylated NS1; this, in turn, inhibited viral replication in a dose- and time-dependent manner. The inhibitory effect on viral replication appears to not be due to inhibition of the production of inflammatory cytokines, including IL-6 and IL-8, in the host cells. Inhibition of Akt kinase activity in the host cells inhibited the efficiency of viral entry, which is associated with decreased levels of phosphorylated glycogen synthase kinase 3, a substrate of Akt. Thus inhibition of Akt kinase activity in host cells may have therapeutic advantages for influenza virus infection by inhibiting viral entry and replication.

Continuing challenges in influenza

Influenza is an acute respiratory disease in mammals and domestic poultry that emerges from zoonotic reservoirs in aquatic birds and bats. Although influenza viruses are among the most intensively studied pathogens, existing control options require further improvement. Influenza vaccines must be regularly updated because of continuous antigenic drift and sporadic antigenic shifts in the viral surface glycoproteins. Currently, influenza therapeutics are limited to neuraminidase inhibitors; novel drugs and vaccine approaches are therefore urgently needed. Advances in vaccinology and structural analysis have revealed common antigenic epitopes on hemagglutinins across all influenza viruses and suggest that a universal influenza vaccine is possible. In addition, various immunomodulatory agents and signaling pathway inhibitors are undergoing preclinical development. Continuing challenges in influenza include the emergence of pandemic H1N1 influenza in 2009, human infections with avian H7N9 influenza in 2013, and sporadic human cases of highly pathogenic avian H5N1 influenza. Here, we review the challenges facing influenza scientists and veterinary and human public health officials; we also discuss the exciting possibility of achieving the ultimate goal of controlling influenza's ability to change its antigenicity.

Akt inhibitor MK2206 prevents influenza pH1N1 virus infection in vitro

The influenza pH1N1 virus caused a global flu pandemic in 2009 and continues manifestation as a seasonal virus. Better understanding of the virus-host cell interaction could result in development of better prevention and treatment options. Here we show that the Akt inhibitor MK2206 blocks influenza pH1N1 virus infection in vitro. In particular, at noncytotoxic concentrations, MK2206 alters Akt signaling and inhibits endocytic uptake of the virus. Interestingly, MK2206 is unable to inhibit H3N2, H7N9, and H5N1 viruses, indicating that pH1N1 evolved specific requirements for efficient infection. Thus, Akt signaling could be exploited further for development of better therapeutics against pH1N1 virus.

Innate immune response to a H3N2 subtype swine influenza virus in newborn porcine trachea cells, alveolar macrophages, and precision-cut lung slices

Viral respiratory diseases remain of major importance in swine breeding units. Swine influenza virus (SIV) is one of the main known contributors to infectious respiratory diseases. The innate immune response to swine influenza viruses has been assessed in many previous studies. However most of these studies were carried out in a single-cell population or directly in the live animal, in all its complexity. In the current study we report the use of a trachea epithelial cell line (newborn pig trachea cells – NPTr) in comparison with alveolar macrophages and lung slices for the characterization of innate immune response to an infection by a European SIV of the H3N2 subtype. The expression pattern of transcripts involved in the recognition of the virus, interferon type I and III responses, and the host-response regulation were assessed by quantitative PCR in response to infection. Some significant differences were observed between the three systems, notably in the expression of type III interferon mRNA. Then, results show a clear induction of JAK/STAT and MAPK signaling pathways in infected NPTr cells. Conversely, PI3K/Akt signaling pathways was not activated. The inhibition of the JAK/STAT pathway clearly reduced interferon type I and III responses and the induction of SOCS1 at the transcript level in infected NPTr cells. Similarly, the inhibition of MAPK pathway reduced viral replication and interferon response. All together, these results contribute to an increased understanding of the innate immune response to H3N2 SIV and may help identify strategies to effectively control SIV infection.

Novel roles of focal adhesion kinase in cytoplasmic entry and replication of influenza A viruses

Viruses modulate cellular signaling pathways at almost every step of the infection cycle. Cellular signaling pathways activated at later times of influenza infection have previously been investigated; however, early influenza virus-host cell interactions remain understudied. Focal adhesion kinase (FAK) is a cytoplasmic tyrosine kinase that regulates phosphatidylinositol 3-kinase (PI3K) activation and actin reorganization, two critical processes during influenza A virus (IAV) infection in most cell types. Using 6 influenza A virus strains (A/Puerto Rico/8/1934, A/Aichi/2/1968 × A/Puerto Rico/8/1934 reassortant [X-31], A/California/04/2009, mouse-adapted A/California/04/2009, A/WSN/1933, and A/New Caledonia/20/1999), we examined the role of FAK during IAV entry. We found that influenza virus attachment induced PI3K-dependent FAK-Y397 phosphorylation. Pharmacological FAK inhibition or expression of a kinase-dead mutant of FAK led to disruption of the actin meshwork that resulted in sequestration of IAV at the cell periphery and reduced virion localization to early endosomes. Additionally, FAK inhibition impeded viral RNA replication at later times of infection and ultimately resulted in significantly reduced viral titers in both A549 and differentiated normal human bronchial epithelial (NHBE) cells. Although not all tested strains activated FAK, all of them exhibited a reduction in viral replication in response to inhibition of FAK signaling. These findings highlight novel biphasic roles of FAK activation during IAV infection and indicate that FAK serves as a central link between receptor-mediated PI3K activation and actin reorganization during IAV infection.

IMPORTANCE

We found that FAK links early activation of PI3K and actin reorganization, thereby regulating influenza virus entry. Surprisingly, we also found that FAK can regulate viral RNA replication independently of its role in entry. Our study addresses a knowledge gap in the understanding of signaling events triggered by influenza virus that mediate its internalization and initiation of the infection cycle. Understanding of these fundamental molecular events will be necessary to identify novel host targets, such as FAK, and development of future anti-influenza virus therapeutics.

Will omics help to cure the flu?

Influenza virus infections are still a major burden to mankind and our antiviral arsenal against these pathogens is limited. The cellular responses to infection might provide novel targets for intervention strategies. Josset et al. combined comparative transcriptome analysis with literature-based prediction tools for in silico identification of novel host-directed drugs.

Raf/MEK/ERK pathway activation is required for Junín virus replication

In the present work we investigated the importance of the Raf/MEK/ERK signalling pathway in the multiplication of the arenavirus Junín (JUNV) in monkey and human cell cultures. We established that JUNV induces a biphasic activation of ERK and we proved that a specific inhibitor of the ERK pathway, U0126, impairs viral replication. Furthermore, U0126 exerted inhibitory action against the arenaviruses Tacaribe and Pichinde. Moreover, treatment with known ERK activators such as phorbol 12-myristate 13-acetate and serum increased viral yields whereas ERK silencing by small interfering RNAs caused the inhibition of viral multiplication. Therefore, activation of the Raf/MEK/ERK signalling pathway is required to ensure efficient JUNV replication and may constitute a host target for the development of novel effective therapeutic strategies to deal with arenavirus infections.

Multiscale modeling of influenza A virus infection supports the development of direct-acting antivirals

Influenza A viruses are respiratory pathogens that cause seasonal epidemics with up to 500,000 deaths each year. Yet there are currently only two classes of antivirals licensed for treatment and drug-resistant strains are on the rise. A major challenge for the discovery of new anti-influenza agents is the identification of drug targets that efficiently interfere with viral replication. To support this step, we developed a multiscale model of influenza A virus infection which comprises both the intracellular level where the virus synthesizes its proteins, replicates its genome, and assembles new virions and the extracellular level where it spreads to new host cells. This integrated modeling approach recapitulates a wide range of experimental data across both scales including the time course of all three viral RNA species inside an infected cell and the infection dynamics in a cell population. It also allowed us to systematically study how interfering with specific steps of the viral life cycle affects virus production. We find that inhibitors of viral transcription, replication, protein synthesis, nuclear export, and assembly/release are most effective in decreasing virus titers whereas targeting virus entry primarily delays infection. In addition, our results suggest that for some antivirals therapy success strongly depends on the lifespan of infected cells and, thus, on the dynamics of virus-induced apoptosis or the host's immune response. Hence, the proposed model provides a systems-level understanding of influenza A virus infection and therapy as well as an ideal platform to include further levels of complexity toward a comprehensive description of infectious diseases.

Influenza A viruses are contagious pathogens that cause an infection of the respiratory tract in humans, commonly referred to as flu. Each year seasonal epidemics occur with three to five million cases of severe illness and occasionally new strains can create pandemics like the 1918 Spanish Flu with a high mortality among infected individuals. Currently, there are only two classes of antivirals licensed for influenza treatment. Moreover, these compounds start to lose their effectiveness as drug-resistant strains emerge frequently. Here, we use a computational model of infection to reveal the steps of virus replication that are most susceptible to interference by drugs. Our analysis suggests that the enzyme which replicates the viral genetic code, and the processes involved in virus assembly and release are promising targets for new antivirals. We also highlight that some drugs can change the dynamics of virus replication toward a later but more sustained production. Thus, we demonstrate that modeling studies can be a tremendous asset to the development of antiviral drugs and treatment strategies.