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For virus infection of new host cells, the disassembly of the protective outer protein shell (capsid) is a critical step, but the mechanisms and host-virus interactions underlying the dynamic, active, and regulated uncoating process are largely unknown. Here, we develop an experimentally supported, multiscale kinetics model that elucidates mechanisms of influenza A virus (IAV) uncoating in cells. Biophysical modeling demonstrates that interactions between capsid M1 proteins, host histone deacetylase 6 (HDAC6), and molecular motors can physically break the capsid in a tug-of-war mechanism. Biochemical analysis and biochemical-biophysical modeling identify unanchored ubiquitin chains as essential and allow robust prediction of uncoating efficiency in cells. Remarkably, the different infectivity of two clinical strains can be ascribed to a single amino acid variation in M1 that affects binding to HDAC6. By identifying crucial modules of viral infection kinetics, the mechanisms and models presented here could help formulate novel strategies for broad-range antiviral treatment. [Display omitted] • Mathematical models predict influenza A virus uncoating and infectivity • Models and experiments support a tug-of-war mechanism that physically breaks the capsid • Unanchored cellular ubiquitin chains are essential for uncoating Artcibasova et al. develop multiscale kinetic models to investigate influenza A uncoating. The models and experiments demonstrate a tug-of-war mechanism for uncoating in which unanchored cellular ubiquitin is essential. The models predict the infectivity of clinical influenza strains, which could help formulate novel strategies for antiviral treatment. [ABSTRACT FROM AUTHOR]

Influenza A virus infects 5-20% of the population annually, resulting in ~35,000 deaths and significant morbidity. Current treatments include vaccines and drugs that target viral proteins. However, both of these approaches have limitations, as vaccines require yearly development and the rapid evolution of viral proteins gives rise to drug resistance. In consequence additional intervention strategies, that target host factors required for the viral life cycle, are under investigation. Here we employed arrayed whole-genome siRNA screening strategies to identify cell-autonomous molecular components that are subverted to support H1 N1 influenza A virus infection of human bronchial epithelial cells. Integration across relevant public data sets exposed druggable gene products required for epithelial cell infection or required for viral proteins to deflect host cell suicide checkpoint activation. Pharmacological inhibition of representative targets, RGGT and CHEK1, resulted in significant protection against infection of human epithelial cells by the A/WS/33 virus. In addition, chemical inhibition of RGGT partially protected against H5N1 and the 2009 H1N1 pandemic strain. The observations reported here thus contribute to an expanding body of studies directed at decoding vulnerabilities in the command and control networks specified by influenza virulence factors. [ABSTRACT FROM AUTHOR]

Human APOBEC3G is an antiretroviral protein that was described to act via deamination of retroviral cDNA. However, it was suggested that APOBEC proteins might act with antiviral activity by yet other mechanisms and may also possess RNA deamination activity. As a consequence there is an ongoing debate whether APOBEC proteins might also act with antiviral activity on other RNA viruses. Influenza A viruses are single-stranded RNA viruses, capable of inducing a variety of antiviral gene products. In searching for novel antiviral genes against these pathogens, we detected a strong induction of APOBEC3G but not APOBEC3F gene transcription in infected cells. This upregulation appeared to be induced by the accumulation of viral RNA species within the infected cell and occurred in an NF-κB dependent, but MAP kinase independent manner. It further turned out that APOBEC expression is part of a general IFNβ response to infection. However, although strongly induced, APOBEC3G does not negatively affect influenza A virus propagation. [ABSTRACT FROM AUTHOR]

Influenza A virus infection activates the NLRP3 inflammasome, a multiprotein signaling complex responsible for the proteolytic activation and release of the proinflammatory cytokine IL-1β from monocytes and macrophages. Some influenza A virus (IAV) strains encode a short 90-amino acid peptide (PB1-F2) on an alternative open reading frame of segment 2, with immunomodulatory activity. We recently demonstrated that contemporary IAV PB1-F2 inhibits the activation of NLRP3, potentially by NEK7-dependent activation. PB1-F2 binds to NLRP3 with its C-terminal 50 amino acids, but the exact binding motif was unknown. On the NLRP3 side, the interface is formed through the leucine-rich-repeat (LRR) domain, potentially in conjunction with the pyrin domain. Here, we took advantage of PB1-F2 sequences from IAV strains with either weak or strong NLRP3 interaction. Sequence comparison and structure prediction using Alphafold2 identified a short four amino acid sequence motif (TQGS) in PB1-F2 that defines NLRP3-LRR binding. Conversion of this motif to that of the non-binding PB1-F2 suffices to lose inhibition of NLRP3 dependent IL-1β release. The TQGS motif further alters the subcellular localization of PB1-F2 and its colocalization with NLRP3 LRR and pyrin domain. Structural predictions suggest the establishment of additional hydrogen bonds between the C-terminus of PB1-F2 and the LRR domain of NLRP3, with two hydrogen bonds connecting to threonine and glutamine of the TQGS motif. Phylogenetic data show that the identified NLRP3 interaction motif in PB1-F2 is widely conserved among recent IAV-infecting humans. Our data explain at a molecular level the specificity of NLRP3 inhibition by influenza A virus. [ABSTRACT FROM AUTHOR]

The article discusses the results of a study that examined the first human case of avian influenza A H10N8 virus infection reported in China in December 2013. It references a research by HaiYing Chen and colleagues published in "The Lancet," with findings including identification of the virus by sequencing of tracheal aspirate samples obtained a week after illness onset and the virus having avian-like receptor specificity and arose by reassortment events in domestic birds.

Together with inactivated influenza vaccines (IIV), live attenuated influenza vaccines (LAIV) are an important tool to prevent influenza A virus (IAV) illnesses in patients. LAIVs present the advantages to have a needle-free administration and to trigger a mucosal immune response. LAIV is approved for healthy 2- to 49-year old individuals. However, due to its replicative nature and higher rate of adverse events at-risk populations are excluded from the benefits of this vaccine. Using targeted mutagenesis, we modified the nonstructural protein 1 of the currently licensed LAIV in order to impair its ability to bind the host cellular protein CPSF30 and thus its ability to inhibit host mRNA poly-adenylation. We characterized our optimized LAIV (optiLAIV) in three different mouse models mimicking healthy and high-risk patients. Using a neonatal mouse model, we show faster clearance of our optimized vaccine compared to the licensed LAIV. Despite lower replication, optiLAIV equally protected mice against homosubtypic and hetesubtypic influenza strain challenges. We confirmed the safer profile of optiLAIV in Stat1-/- mice (highly susceptible to viral infections) by showing no signs of morbidity compared to a 50% mortality rate observed following LAIV inoculation. Using a human nasal 3D tissue model, we showed an increased induction of ER stress-related genes following immunization with optiLAIV. Induction of ER stress was previously shown to improve antigen-specific immune responses and is proposed as the mechanism of action of the licensed adjuvant AS03. This study characterizes a safer LAIV candidate in two mouse models mimicking infants and severely immunocompromised patients and proposes a simple attenuation strategy that could broaden LAIV application and reduce influenza burden in high-risk populations. IMPORTANCE Live attenuated influenza vaccine (LAIV) is a needle-free, mucosal vaccine approved for healthy 2- to 49-year old individuals. Its replicative nature and higher rate of adverse events excludes at-risk populations. We propose a strategy to improve LAIV safety and explore the possibility to expand its applications in children under 2-year old and immunocompromised patients. Using a neonatal mouse model, we show faster clearance of our optimized vaccine (optiLAIV) compared to the licensed LAIV. Despite lower replication, optiLAIV equally protected mice against influenza virus challenges. We confirmed the safer profile of optiLAIV in Stat1-/-mice (highly susceptible to viral infections) by showing no signs of morbidity compared to a 50% mortality rate from LAIV. OptiLAIV could expand the applications of the current LAIV and help mitigate the burden of IAV in susceptible populations. [ABSTRACT FROM AUTHOR]

The article focuses on research into the impact of compound heterozygous null mutations in the gene IRF7 which encodes the interferon regulatory factor 7 in a child suffering life-threatening influenza. It states the patient's plasmacytoid dendritic cells and leukocytes produced very little Type I and II interferons (IFN) while dermal fibroblasts and pulmonary epithelial cells increased influenza replication and reduced amounts of type I IFN.

CD8+ cytotoxic T cells are critical for viral clearance from the lungs upon influenza virus infection. The contribution of antigen cross-presentation by DCs to the induction of anti-viral cytotoxic T cells remains controversial. Here, we used a recombinant influenza virus expressing a nonstructural 1-GFP (NS1-GFP) reporter gene to visualize the route of antigen presentation by lung DCs upon viral infection in mice. We found that lung CD103+ DCs were the only subset of cells that carried intact GFP protein to the draining LNs. Strikingly, lung migratory CD103+ DCs were not productively infected by influenza virus and thus were able to induce virus-specific CD8+ T cells through the cross-presentation of antigens from virally infected cells. We also observed that CD103+ DC resistance to infection correlates with an increased anti-viral state in these cells that is dependent on the expression of type IIFN receptor. These results show that efficient cross-priming by migratory lung DCs is coupled to the acquisition of an anti-viral status, which is dependent on the type I IFN signaling pathway. [ABSTRACT FROM AUTHOR]