Regulation of interferon-β by MAGI-1 and its interaction with influenza A virus NS1 protein with ESEV PBM

Structural Investigations of Interactions between the Influenza a Virus NS1 and Host Cellular Proteins

The Influenza A virus is a continuous threat to public health that causes yearly epidemics with the ever-present threat of the virus becoming the next pandemic. Due to increasing levels of resistance, several of our previously used antivirals have been rendered useless. There is a strong need for new antivirals that are less likely to be susceptible to mutations. One strategy to achieve this goal is structure-based drug development. By understanding the minute details of protein structure, we can develop antivirals that target the most conserved, crucial regions to yield the highest chances of long-lasting success. One promising IAV target is the virulence protein non-structural protein 1 (NS1). NS1 contributes to pathogenicity through interactions with numerous host proteins, and many of the resulting complexes have been shown to be crucial for virulence. In this review, we cover the NS1-host protein complexes that have been structurally characterized to date. By bringing these structures together in one place, we aim to highlight the strength of this field for drug discovery along with the gaps that remain to be filled.

Avian Influenza NS1 Proteins Inhibit Human, but Not Duck, RIG-I Ubiquitination and Interferon Signaling

The nonstructural protein 1 (NS1) of influenza A viruses is an important virulence factor that controls host cell immune responses. In human cells, NS1 proteins inhibit the induction of type I interferon by several mechanisms, including potentially, by preventing the activation of the retinoic acid-inducible gene I (RIG-I) receptor by the ubiquitin ligase tripartite motif-containing protein 25 (TRIM25). It is unclear whether the inhibition of human TRIM25 is a universal function of all influenza A NS1 proteins or is strain dependent. It is also unclear if NS1 proteins similarly target the TRIM25 of mallard ducks, a natural reservoir host of avian influenza viruses with a long coevolutionary history and unique disease dynamics. To answer these questions, we compared the ability of five different NS1 proteins to interact with human and duck TRIM25 using coimmunoprecipitation and microscopy and assessed the consequence of this on RIG-I ubiquitination and signaling in both species. We show that NS1 proteins from low-pathogenic and highly pathogenic avian influenza viruses potently inhibit RIG-I ubiquitination and reduce interferon promoter activity and interferon-beta protein secretion in transfected human cells, while the NS1 of the mouse-adapted PR8 strain does not. However, all the NS1 proteins, when cloned into recombinant viruses, suppress interferon in infected alveolar cells. In contrast, avian NS1 proteins do not suppress duck RIG-I ubiquitination and interferon promoter activity, despite interacting with duck TRIM25. IMPORTANCE Influenza A viruses are a major cause of human and animal disease. Periodically, avian influenza viruses from wild waterfowl, such as ducks, pass through intermediate agricultural hosts and emerge into the human population as zoonotic diseases with high mortality rates and epidemic potential. Because of their coevolution with influenza A viruses, ducks are uniquely resistant to influenza disease compared to other birds, animals, and humans. Here, we investigate a mechanism of influenza A virus interference in an important antiviral signaling pathway that is orthologous in humans and ducks. We show that NS1 proteins from four avian influenza strains can block the coactivation and signaling of the human RIG-I antiviral receptor, while none block the coactivation and signaling of duck RIG-I. Understanding host-pathogen dynamics in the natural reservoir will contribute to our understanding of viral disease mechanisms, viral evolution, and the pressures that drive it, which benefits global surveillance and outbreak prevention.

MAGI1 inhibits interferon signaling to promote influenza A infection

We have shown that membrane-associated guanylate kinase with inverted domain structure-1 (MAGI1), a scaffold protein with six PSD95/DiscLarge/ZO-1 (PDZ) domains, is involved in the regulation of endothelial cell (EC) activation and atherogenesis in mice. In addition to causing acute respiratory disease, influenza A virus (IAV) infection plays an important role in atherogenesis and triggers acute coronary syndromes and fatal myocardial infarction. Therefore, the aim of this study is to investigate the function and regulation of MAGI1 in IAV-induced EC activation. Whereas, EC infection by IAV increases MAGI1 expression, MAGI1 depletion suppresses IAV infection, suggesting that the induction of MAGI1 may promote IAV infection. Treatment of ECs with oxidized low-density lipoprotein (OxLDL) increases MAGI1 expression and IAV infection, suggesting that MAGI1 is part of the mechanistic link between serum lipid levels and patient prognosis following IAV infection. Our microarray studies suggest that MAGI1-depleted ECs increase protein expression and signaling networks involve in interferon (IFN) production. Specifically, infection of MAGI1-null ECs with IAV upregulates expression of signal transducer and activator of transcription 1 (STAT1), interferon b1 (IFNb1), myxovirus resistance protein 1 (MX1) and 2'-5'-oligoadenylate synthetase 2 (OAS2), and activate STAT5. By contrast, MAGI1 overexpression inhibits Ifnb1 mRNA and MX1 expression, again supporting the pro-viral response mediated by MAGI1. MAGI1 depletion induces the expression of MX1 and virus suppression. The data suggests that IAV suppression by MAGI1 depletion may, in part, be due to MX1 induction. Lastly, interferon regulatory factor 3 (IRF3) translocates to the nucleus in the absence of IRF3 phosphorylation, and IRF3 SUMOylation is abolished in MAGI1-depleted ECs. The data suggests that MAGI1 inhibits IRF3 activation by maintaining IRF3 SUMOylation. In summary, IAV infection occurs in ECs in a MAGI1 expression-dependent manner by inhibiting anti-viral responses including STATs and IRF3 activation and subsequent MX1 induction, and MAGI1 plays a role in EC activation, and in upregulating a pro-viral response. Therefore, the inhibition of MAGI1 is a potential therapeutic target for IAV-induced cardiovascular disease.

A New Story of the Three Magi: Scaffolding Proteins and lncRNA Suppressors of Cancer

Scaffolding molecules exert a critical role in orchestrating cellular response through the spatiotemporal assembly of effector proteins as signalosomes. By increasing the efficiency and selectivity of intracellular signaling, these molecules can exert (anti/pro)oncogenic activities. As an archetype of scaffolding proteins with tumor suppressor property, the present review focuses on MAGI1, 2, and 3 (membrane-associated guanylate kinase inverted), a subgroup of the MAGUK protein family, that mediate networks involving receptors, junctional complexes, signaling molecules, and the cytoskeleton. MAGI1, 2, and 3 are comprised of 6 PDZ domains, 2 WW domains, and 1 GUK domain. These 9 protein binding modules allow selective interactions with a wide range of effectors, including the PTEN tumor suppressor, the β-catenin and YAP1 proto-oncogenes, and the regulation of the PI3K/AKT, the Wnt, and the Hippo signaling pathways. The frequent downmodulation of MAGIs in various human malignancies makes these scaffolding molecules and their ligands putative therapeutic targets. Interestingly, MAGI1 and MAGI2 genetic loci generate a series of long non-coding RNAs that act as a tumor promoter or suppressor in a tissue-dependent manner, by selectively sponging some miRNAs or by regulating epigenetic processes. Here, we discuss the different paths followed by the three MAGIs to control carcinogenesis.

Genome-Wide Association Study of Ocular Sarcoidosis Confirms HLA Associations and Implicates Barrier Function and Autoimmunity in African Americans

Purpose: Identify genes associated with ocular sarcoidosis (OS).Methods: We genotyped 1.1 million genetic variants to identify significant OS associations, defined as those that achieved p < 5 × 10-8 in a genome-wide comparison of OS cases to healthy controls in our European- or African-American cohorts (EA, AA). Potential functional roles of all associated variants were assessed.Results: Eight significant non-HLA variants were found in AA OS cases compared to healthy controls and confirmed as at least suggestive when comparing OS to non-OS cases. Seven of these were within MAGI1 and include transcription factor binding sites and expression quantitative trait loci. Our EA cohort, while showing similar effect sizes at variants within MAGI1, had no significant variants. Association analysis of HLA-DRB1 alleles confirmed association to OS in EA to *04:01.Conclusion: Our results support organ-specific genetic risk in OS in a compelling candidate, MAGI1, known to be associated with barrier function and autoimmunity.

Roles of the Non-Structural Proteins of Influenza A Virus

Influenza A virus (IAV) is a segmented, negative single-stranded RNA virus that causes seasonal epidemics and has a potential for pandemics. Several viral proteins are not packed in the IAV viral particle and only expressed in the infected host cells. These proteins are named non-structural proteins (NSPs), including NS1, PB1-F2 and PA-X. They play a versatile role in the viral life cycle by modulating viral replication and transcription. More importantly, they also play a critical role in the evasion of the surveillance of host defense and viral pathogenicity by inducing apoptosis, perturbing innate immunity, and exacerbating inflammation. Here, we review the recent advances of these NSPs and how the new findings deepen our understanding of IAV–host interactions and viral pathogenesis.

Surveillance of influenza A virus subtype H5N1 in a live bird market in Yangon, Myanmar: 2017-2018

A survey of influenza A viruses (IAVs) in the Mingalar Taung Nyunt live bird market (MTN-LBM), Yangon, Myanmar, was conducted from December 2017 to December 2018. During the survey, 455 swab samples were collected from broilers, layers, backyard chickens and ducks from the MTN-LBM. Ninety-one pooled samples were screened for IAVs by real-time RT-PCR specific to the M gene. Positive pooled samples were individually retested for IAVs. In total, 2.63% of individual samples (12/455) were positive for IAVs. Out of 12 samples, seven samples from layer chickens and the environment were identified as IAV subtype H5N1. In this study, four IAVs were successfully isolated and further characterized by whole genome sequencing. Whole genome sequence analysis revealed that the viruses were characterized as highly pathogenic avian influenza virus subtype H5N1 (HPAIV-H5N1) of clade 2.3.2.1c. Phylogenetic and genetic analyses showed that Myanmar HPAIV-H5N1 was closely related to HPAIV-H5N1 clade 2.3.2.1c isolated from China and Vietnam in 2014. Our results suggested that the live bird market in Myanmar represents a significant risk of HPAIV-H5N1 transmission in poultry and humans. Moreover, HPAIV-H5N1 clade 2.3.2.1c is widely distributed in South-East Asia including Myanmar.

The Central Role of Non-Structural Protein 1 (NS1) in Influenza Biology and Infection

Influenza (flu) is a contagious viral disease, which targets the human respiratory tract and spreads throughout the world each year. Every year, influenza infects around 10% of the world population and between 290,000 and 650,000 people die from it according to the World Health Organization (WHO). Influenza viruses belong to the Orthomyxoviridae family and have a negative sense eight-segment single-stranded RNA genome that encodes 11 different proteins. The only control over influenza seasonal epidemic outbreaks around the world are vaccines, annually updated according to viral strains in circulation, but, because of high rates of mutation and recurrent genetic assortment, new viral strains of influenza are constantly emerging, increasing the likelihood of pandemics. Vaccination effectiveness is limited, calling for new preventive and therapeutic approaches and a better understanding of the virus-host interactions. In particular, grasping the role of influenza non-structural protein 1 (NS1) and related known interactions in the host cell is pivotal to better understand the mechanisms of virus infection and replication, and thus propose more effective antiviral approaches. In this review, we assess the structure of NS1, its dynamics, and multiple functions and interactions, to highlight the central role of this protein in viral biology and its potential use as an effective therapeutic target to tackle seasonal and pandemic influenza.

A Novel Role for PDZ-Binding Motif of Influenza A Virus Nonstructural Protein 1 in Regulation of Host Susceptibility to Postinfluenza Bacterial Superinfections

Influenza A viruses (IAVs) have multiple mechanisms for altering the host immune response to aid in virus survival and propagation. While both type I and II interferons (IFNs) have been associated with increased bacterial superinfection (BSI) susceptibility, we found that in some cases type I IFNs can be beneficial for BSI outcome. Specifically, we have shown that antagonism of the type I IFN response during infection by some IAVs can lead to the development of deadly BSI. The nonstructural protein 1 (NS1) from IAV is well known for manipulating host type I IFN responses, but the viral proteins mediating BSI severity remain unknown. In this study, we demonstrate that the PDZ-binding motif (PDZ-bm) of the NS1 C-terminal region from mouse-adapted A/Puerto Rico/8/34-H1N1 (PR8) IAV dictates BSI susceptibility through regulation of IFN-α/β production. Deletion of the NS1 PDZ-bm from PR8 IAV (PR8-TRUNC) resulted in 100% survival and decreased bacterial burden in superinfected mice compared with 0% survival in mice superinfected after PR8 infection. This reduction in BSI susceptibility after infection with PR8-TRUNC was due to the presence of IFN-β, as protection from BSI was lost in Ifn-β^-/- mice, resembling BSI during PR8 infection. PDZ-bm in PR8-infected mice inhibited the production of IFN-β posttranscriptionally, and both delayed and reduced expression of the tunable interferon-stimulated genes. Finally, a similar lack of BSI susceptibility, due to the presence of IFN-β on day 7 post-IAV infection, was also observed after infection of mice with A/TX98-H3N2 virus that naturally lacks a PDZ-bm in NS1, indicating that this mechanism of BSI regulation by NS1 PDZ-bm may not be restricted to PR8 IAV. These results demonstrate that the NS1 C-terminal PDZ-bm, like the one present in PR8 IAV, is involved in controlling susceptibility to BSI through the regulation of IFN-β, providing new mechanisms for NS1-mediated manipulation of host immunity and BSI severity.

Upsetting the Balance: When Viruses Manipulate Cell Polarity Control

The central importance of cell polarity control is emphasized by the frequency with which it is targeted by many diverse viruses. It is clear that in targeting key polarity control proteins, viruses affect not only host cell polarity, but also influence many cellular processes, including transcription, replication, and innate and acquired immunity. Examination of the interactions of different virus proteins with the cell and its polarity controls during the virus life cycles, and in virally-induced cell transformation shows ever more clearly how intimately all cellular processes are linked to the control of cell polarity.

Zoonotic Potential of Influenza A Viruses: A Comprehensive Overview

Influenza A viruses (IAVs) possess a great zoonotic potential as they are able to infect different avian and mammalian animal hosts, from which they can be transmitted to humans. This is based on the ability of IAV to gradually change their genome by mutation or even reassemble their genome segments during co-infection of the host cell with different IAV strains, resulting in a high genetic diversity. Variants of circulating or newly emerging IAVs continue to trigger global health threats annually for both humans and animals. Here, we provide an introduction on IAVs, highlighting the mechanisms of viral evolution, the host spectrum, and the animal/human interface. Pathogenicity determinants of IAVs in mammals, with special emphasis on newly emerging IAVs with pandemic potential, are discussed. Finally, an overview is provided on various approaches for the prevention of human IAV infections.

EVOLUTIONARY DYNAMICS OF STRUCTURAL AND FUNCTIONAL DOMAINS OF INFLUENZA A VIRUS NS1 PROTEIN

Influenza A virus (IAV) NS1 protein is one of the key viral factors responsible for virus-host interactions. NS1 counteracts host antiviral defense, participates in the processing and export of cellular mRNAs, regulates the activity of viral RNA polymerase and the expression of viral genes, and influences the cellular signaling systems. Multiple NS1 functions are carried out due to the interactions with cellular factors, the number of which exceeds one hundred. It is noteworthy that only two segments of IAV genome - NS and NP - did not undergo reassortment and evolved in the course of genetic drift, beginning with the pandemic of 1918 to the present. This fact may indicate the importance of NS1 and its numerous interactions with cellular factors in the interspecific adaptation of the virus. The review presents data on the evolution of the human IAV NS1 protein and analysis of the amino acid substitutions in the main structural and functional domains of NS1 protein during evolution.

Influenza A Virus-Host Protein Interactions Control Viral Pathogenesis

The influenza A virus (IAV), a member of the Orthomyxoviridae family, is a highly transmissible respiratory pathogen and represents a continued threat to global health with considerable economic and social impact. IAV is a zoonotic virus that comprises a plethora of strains with different pathogenic profiles. The different outcomes of viral pathogenesis are dependent on the engagement between the virus and the host cellular protein interaction network. The interactions may facilitate virus hijacking of host molecular machinery to fulfill the viral life cycle or trigger host immune defense to eliminate the virus. In recent years, much effort has been made to discover the virus–host protein interactions and understand the underlying mechanisms. In this paper, we review the recent advances in our understanding of IAV–host interactions and how these interactions contribute to host defense and viral pathogenesis.

Signalling at tight junctions during epithelial differentiation and microbial pathogenesis

Tight junctions are a component of the epithelial junctional complex, and they form the paracellular diffusion barrier that enables epithelial cells to create cellular sheets that separate compartments with different compositions. The assembly and function of tight junctions are intimately linked to the actomyosin cytoskeleton and, hence, are under the control of signalling mechanisms that regulate cytoskeletal dynamics. Tight junctions not only receive signals that guide their assembly and function, but transmit information to the cell interior to regulate cell proliferation, migration and survival. As a crucial component of the epithelial barrier, they are often targeted by pathogenic viruses and bacteria, aiding infection and the development of disease. In this Commentary, we review recent progress in the understanding of the molecular signalling mechanisms that drive junction assembly and function, and the signalling processes by which tight junctions regulate cell behaviour and survival. We also discuss the way in which junctional components are exploited by pathogenic viruses and bacteria, and how this might affect junctional signalling mechanisms.

The PDZ3 domain of the cellular scaffolding protein MAGI-1 interacts with the Coxsackievirus and adenovirus receptor (CAR)

The Coxsackievirus and adenovirus receptor (CAR) is an essential cellular protein that is involved in cell-cell adhesion, protein trafficking, and viral infection. The major isoform of CAR is selectively sorted to the basolateral membrane of polarized epithelial cells where it co-localizes with the cellular scaffolding protein membrane-associated guanylate kinase with inverted domain structure-1 (MAGI-1). Previously, we demonstrated CAR interacts with MAGI-1 through a PDZ-domain dependent interaction. Here, we show that the PDZ3 domain of MAGI-1 is exclusively responsible for the high affinity interaction between the seven exon isoform of CAR and MAGI-1 using yeast-two-hybrid analysis and confirming this interaction biochemically and in cellular lysates by in vitro pull down assay and co-immunoprecipitation. The high affinity interaction between the PDZ3 domain and CAR C-terminus was measured by fluorescence resonance energy transfer. Further, we investigated the biological relevance of this high affinity interaction between CAR and the PDZ3 domain of MAGI-1 and found that it does not alter CAR-mediated adenovirus infection. By contrast, interruption of this high affinity interaction altered the localization of MAGI-1 indicating that CAR is able to traffic MAGI-1 to cell junctions. These data deepen the molecular understanding of the interaction between CAR and MAGI-1 and indicate that although CAR plays a role in trafficking PDZ-based scaffolding proteins to cellular junctions, association with a high affinity intracellular binding partner does not significantly alter adenovirus binding and entry via CAR.

Tight junctions and the regulation of gene expression

Tight junctions (TJ) regulate the paracellular passage of ions and molecules through the paracellular pathway and maintain plasma membrane polarity in epithelial and endothelial cells. Apart from these canonical functions, several proteins of the TJ have been found in recent years to regulate gene expression. This function is found in proteins that shuttle between the nucleus and TJs, and in integral TJ proteins. In this review, we will describe these proteins and their known mechanisms of gene regulation.

Identification of host cell factors involved in influenza A virus infection

As obligatory intracellular parasites, viruses need to take control of the metabolic pathways of the infected cells in order to complete their replication. Such an extraordinary ability must rely on specific, essential protein–protein interactions with key components of the cellular machinery. Besides providing valuable information about host–virus relationships, these studies can lead to the identification of novel pharmacological targets for an antiviral chemotherapeutic approach, based on the inhibition of host factors essential for viral replication. Here, we will review the most recent studies identifying host cell proteins involved in the influenza virus lifecycle.