Respiratory virus-induced EGFR activation suppresses IRF1-dependent interferon λ and antiviral defense in airway epithelium

Rhinovirus-Induced SIRT-1 via TLR2 Regulates Subsequent Type I and Type III IFN Responses in Airway Epithelial Cells

IFN responses to viral infection are necessary to establish intrinsic antiviral state, but if unchecked can lead to heightened inflammation. Recently, we showed that TLR2 activation contributes to limitation of rhinovirus (RV)-induced IFN response in the airway epithelial cells. We also demonstrated that compared with normal airway epithelial cells, those from patients with chronic obstructive pulmonary disease (COPD) show higher IFN responses to RV, but the underlying mechanisms are not known. Initially, RV-induced IFN responses depend on dsRNA receptor activation and then are amplified via IFN-stimulated activation of JAK/STAT signaling. In this study, we show that in normal cells, TLR2 limits RV-induced IFN responses by attenuating STAT1 and STAT2 phosphorylation and this was associated with TLR2-dependent SIRT-1 expression. Further, inhibition of SIRT-1 enhanced RV-induced IFN responses, and this was accompanied by increased STAT1/STAT2 phosphorylation, indicating that TLR2 may limit RV-induced IFN responses via SIRT-1. COPD airway epithelial cells showed attenuated IL-8 responses to TLR2 agonist despite expressing TLR2 similar to normal, indicating dysregulation in TLR2 signaling pathway. Unlike normal, COPD cells failed to show RV-induced TLR2-dependent SIRT-1 expression. Pretreatment with quercetin, which increases SIRT-1 expression, normalized RV-induced IFN levels in COPD airway epithelial cells. Inhibition of SIRT-1 in quercetin-pretreated COPD cells abolished the normalizing effects of quercetin on RV-induced IFN expression in these cells, confirming that quercetin exerts its effect via SIRT-1. In summary, we show that TLR2 is required for limiting RV-induced IFNs, and this pathway is dysregulated in COPD airway epithelial cells, leading to exaggerated IFN production.

The Role of EGFR in Influenza Pathogenicity: Multiple Network-Based Approaches to Identify a Key Regulator of Non-lethal Infections

Despite high sequence similarity between pandemic and seasonal influenza viruses, there is extreme variation in host pathogenicity from one viral strain to the next. Identifying the underlying mechanisms of variability in pathogenicity is a critical task for understanding influenza virus infection and effective management of highly pathogenic influenza virus disease. We applied a network-based modeling approach to identify critical functions related to influenza virus pathogenicity using large transcriptomic and proteomic datasets from mice infected with six influenza virus strains or mutants. Our analysis revealed two pathogenicity-related gene expression clusters; these results were corroborated by matching proteomics data. We also identified parallel downstream processes that were altered during influenza pathogenesis. We found that network bottlenecks (nodes that bridge different network regions) were highly enriched in pathogenicity-related genes, while network hubs (highly connected network nodes) were significantly depleted in these genes. We confirmed that this trend persisted in a distinct virus: Severe Acute Respiratory Syndrome Coronavirus (SARS). The role of epidermal growth factor receptor (EGFR) in influenza pathogenesis, one of the bottleneck regulators with corroborating signals across transcript and protein expression data, was tested and validated in additional mouse infection experiments. We demonstrate that EGFR is important during influenza infection, but the role it plays changes for lethal versus non-lethal infections. Our results show that by using association networks, bottleneck genes that lack hub characteristics can be used to predict a gene's involvement in influenza virus pathogenicity. We also demonstrate the utility of employing multiple network approaches for analyzing host response data from viral infections.

Targeting of host cell receptor tyrosine kinases by intracellular pathogens

Intracellular pathogens use complex and tightly regulated processes to enter host cells. Upon initial interactions with signaling proteins at the surface of target cells, intracellular microbes activate and co-opt specific host signaling pathways that mediate cell surface-cytosol communications to facilitate pathogen internalization. Here, we discuss the roles of host receptor tyrosine kinases (RTKs) in the establishment of productive infections by major intracellular pathogens. We evaluate the gaps in the current understanding of this process and propose a comprehensive approach for assessing the role of host cell signaling in the biology of intracellular microorganisms and viruses. We also discuss RTK-targeting strategies for the treatment of various infections.

Alternaria induces airway epithelial cytokine expression independent of protease-activated receptor

BACKGROUND AND OBJECTIVE

A novel fungal allergen, Alternaria (Alt), has been previously shown to associate with the pathogenesis of allergic rhinitis and bronchial asthma, particularly in arid and semi-arid regions. Airway epithelial cells are among the first to encounter Alt, and epithelial cytokine production and subsequent airway inflammation are early events in the response to Alt exposure. However, the underlying mechanism is unclear. As protease-activated receptor 2 (PAR2) has been implicated in most of the Alt-induced biological events, we investigated the regulation of airway inflammation and epithelial cytokine expression by PAR2.

METHODS

Wild-type (WT) and Par2 knockout (Par2-KO) mice were used to evaluate the in vivo role of PAR2. Primary human and mouse airway epithelial cells were used to examine the mechanistic basis of epithelial cytokine regulation in vitro.

RESULTS

Surprisingly, Par2 deficiency had no negative impact on the change of lung function, inflammation and cytokine production in the mouse model of Alt-induced asthma. Alt-induced cytokine production in murine airway epithelial cells from Par2-KO mice was not significantly different from the WT cells. Consistently, PAR2 knockdown in human cells also had no effect on cytokine expression. In contrast, the cytokine expressions induced by synthetic PAR2 agonist or other asthma-related allergens (e.g. cockroach extracts) were indeed mediated via a PAR2-dependent mechanism. Finally, we found that EGFR pathway was responsible for Alt-induced epithelial cytokine expression.

CONCLUSION

The activation of EGFR, but not PAR2, was likely to drive the airway inflammation and epithelial cytokine production induced by Alt.

Interferon gamma inhibits transmissible gastroenteritis virus infection mediated by an IRF1 signaling pathway

Interferon gamma (IFN-γ) is best known for its ability to regulate host immune responses; however, its direct antiviral activity is less well studied. Transmissible gastroenteritis virus (TGEV) is an economically important swine enteric coronavirus and causes acute diarrhea in piglets. At present, little is known about the function of IFN-γ in the control of TGEV infection. In this study, we demonstrated that IFN-γ inhibited TGEV infection directly in ST cells and intestine epithelial IPEC-J2 cells and that the anti-TGEV activity of IFN-γ was independent of IFN-α/β. Moreover, IFN-γ suppressed TGEV infection in ST cells more efficiently than did IFN-α, and the combination of IFN-γ and IFN-α displayed a synergistic effect against TGEV. Mechanistically, using overexpression and functional knockdown experiments, we demonstrated that porcine interferon regulatory factor 1 (poIRF1) elicited by IFN-γ primarily mediated IFN-γ signaling cascades and the inhibition of TGEV infection by IFN-γ. Importantly, we found that TGEV elevated the expression of poIRF1 and IFN-γ in infected small intestines and peripheral blood mononuclear cells. Thus, IFN-γ plays a crucial role in curtailing enteric coronavirus infection and may serve as an effective prophylactic and/or therapeutic agent against TGEV infection.

New therapeutic targets for the prevention of infectious acute exacerbations of COPD: role of epithelial adhesion molecules and inflammatory pathways

Chronic respiratory diseases are among the leading causes of mortality worldwide, with the major contributor, chronic obstructive pulmonary disease (COPD) accounting for approximately 3 million deaths annually. Frequent acute exacerbations (AEs) of COPD (AECOPD) drive clinical and functional decline in COPD and are associated with accelerated loss of lung function, increased mortality, decreased health-related quality of life and significant economic costs. Infections with a small subgroup of pathogens precipitate the majority of AEs and consequently constitute a significant comorbidity in COPD. However, current pharmacological interventions are ineffective in preventing infectious exacerbations and their treatment is compromised by the rapid development of antibiotic resistance. Thus, alternative preventative therapies need to be considered. Pathogen adherence to the pulmonary epithelium through host receptors is the prerequisite step for invasion and subsequent infection of surrounding structures. Thus, disruption of bacterial-host cell interactions with receptor antagonists or modulation of the ensuing inflammatory profile present attractive avenues for therapeutic development. This review explores key mediators of pathogen-host interactions that may offer new therapeutic targets with the potential to prevent viral/bacterial-mediated AECOPD. There are several conceptual and methodological hurdles hampering the development of new therapies that require further research and resolution.

Immunological implications of epidermal growth factor receptor signaling in persistent infections

Infectious diseases account for a large proportion of global health emergencies and are rising more so owing to the paucity of effective vaccination and chemotherapeutic strategies. The severity is compounded by the development of antibiotic resistance among major pathogenic strains, capable of residing in the hostile host microenvironment by hijacking its signaling mechanisms and molecular circuitry. Among such processes, studies on epidermal growth factor receptor (EGFR) have revealed specific contributions of this classical oncogenic signaling axis during distinct infection conditions. Here, we review the current status of EGFR family members in the context of host-pathogen interactions and speculate the possible dimensions of exploration and manipulation of the EGFR pathway for host-directed therapeutic purposes.

IRF1 Maintains Optimal Constitutive Expression of Antiviral Genes and Regulates the Early Antiviral Response

Viral defense at mucosal sites depends on interferons (IFN) and IFN stimulated genes (ISGs), either of which may be constitutively expressed to maintain an “antiviral state” (AVS). However, the mechanisms that govern the AVS are poorly defined. Using a BEAS-2B respiratory epithelial cell line deficient in IRF1, we demonstrate higher susceptibility to infection with vesicular stomatitis virus (VSV) and influenza virus. IRF1-mediated restriction of VSV is IFN-independent, as blockade of types I and III IFNs and JAK-STAT signaling before infection did not affect VSV infection of either parent or IRF1 KO cells. Transcriptome analysis revealed that IRF1 regulates constitutive expression of ~300 genes, including antiviral ISGs: OAS2, BST2, and RNASEL and knockdown of any of these IRF1-dependent genes increased VSV infection. Additionally, IRF1 enhances rapid expression of IFNβ and IFNλ after stimulation with poly I:C and also regulates ISG expression. Mechanistically, IRF1 enhances recruitment of BRD4 to promotor-enhancer regions of ISGs for rapid expression and maintains levels of histone H3K4me1 for optimal constitutive expression. Finally, IRF1 also regulates constitutive expression of TLR2 and TLR3 and promotes signaling through these pattern recognition receptors (PRR). These data reveal multiple roles for IRF1 toward effective anti-viral responses by maintaining IFN-independent constitutive expression of anti-viral ISGs and supporting early IFN-dependent responses to PRR stimulation.

[Effects of respiratory syncytial virus infection on epidermal growth factor receptor, tight junction association proteins and mucin in airway epithelial cells]

OBJECTIVE

To study the effects of respiratory syncytial virus (RSV) infection on epidermal growth factor receptor (EGFR), tight junction association proteins and mucin in the human airway epithelial cells.

METHODS

Human airway epithelial cells NCI-H292 were randomly treated by ultraviolet light-inactivated RSV (control group) or thawed RSV (RSV infection group). After 48 hours of treatment, the protein levels of occludin, E-cadherin, phosphorylated EGFR and EGFR in NCI-H292 cells were measured by Western blot. The distribution and expression levels of occludin and E-cadherin in NCI-H292 cells were examined by immunofluorescence technique. The expression levels of MUC5AC mRNA in NCI-H292 cells were assessed by RT-PCR.

RESULTS

The protein levels of occludin and E-cadherin were significantly reduced in the RSV infection group compared with the control group (P<0.05). The protein levels of phosphorylated EGFR and EGFR increased significantly in the RSV infection group compared with the control group (P<0.05). The MUC5AC mRNA levels also increased significantly in the RSV infection group compared with the control group (P<0.05).

CONCLUSIONS

RSV may down-regulate the tight junction association proteins and up-regulate the expression of MUC5AC in airway epithelial cells, which contributes to epithelial barrier dysfunction. EGFR phosphorylation may play an important role in regulation of airway barrier.

HSP90 inhibitor geldanamycin reverts IL-13- and IL-17-induced airway goblet cell metaplasia

Goblet cell metaplasia, a disabling hallmark of chronic lung disease, lacks curative treatments at present. To identify novel therapeutic targets for goblet cell metaplasia, we studied the transcriptional response profile of IL-13-exposed primary human airway epithelia in vitro and asthmatic airway epithelia in vivo. A perturbation-response profile connectivity approach identified geldanamycin, an inhibitor of heat shock protein 90 (HSP90) as a candidate therapeutic target. Our experiments confirmed that geldanamycin and other HSP90 inhibitors prevented IL-13-induced goblet cell metaplasia in vitro and in vivo. Geldanamycin also reverted established goblet cell metaplasia. Geldanamycin did not induce goblet cell death, nor did it solely block mucin synthesis or IL-13 receptor-proximal signaling. Geldanamycin affected the transcriptome of airway cells when exposed to IL-13, but not when exposed to vehicle. We hypothesized that the mechanism of action probably involves TGF-β, ERBB, or EHF, which would predict that geldanamycin would also revert IL-17-induced goblet cell metaplasia, a prediction confirmed by our experiments. Our findings suggest that persistent airway goblet cell metaplasia requires HSP90 activity and that HSP90 inhibitors will revert goblet cell metaplasia, despite active upstream inflammatory signaling. Moreover, HSP90 inhibitors may be a therapeutic option for airway diseases with goblet cell metaplasia of unknown mechanism.

Diverse Roles of DEAD/DEAH-Box Helicases in Innate Immunity and Diseases

DEAD/DEAH-box helicases are enzymes that belong to the DEAD/H-box family of SF2 helicase superfamily. These enzymes are essential in RNA metabolism, where they are involved in a number of processes that require manipulation of RNA structure. Recent studies have found that some DEAD/DEAH-box helicases play important roles in innate immunity, where they act as sensors of cytosolic DNA/RNA, as adaptor proteins, or as regulators of signaling and gene expression. In spite of their function in immunity, DEAD/DEAH-box helicases can also be hijacked and exploited by viruses to circumvent detection and aid in viral replication. These findings not only imply that DEAD/DEAH-box helicases have a broader function than previously thought, but also give us a much better understanding of immune mechanisms and diseases that arise due to the dysregulation or evasion thereof. In this chapter, we demonstrate the known scope of activities of human DEAD/DEAH-box helicases in innate immunity and interaction with viruses or other pathogens. Additionally, we give an outline of diseases in which they are, or may be, involved in the context of immunity.

The Interferon (IFN) Class of Cytokines and the IFN Regulatory Factor (IRF) Transcription Factor Family

Interferons (IFNs) are a broad class of cytokines elicited on challenge to the host defense and are essential for mobilizing immune responses to pathogens. Divided into three classes, type I, type II, and type III, all IFNs share in common the ability to evoke antiviral activities initiated by the interaction with their cognate receptors. The nine-member IFN regulatory factor (IRF) family, first discovered in the context of transcriptional regulation of type I IFN genes following viral infection, are pivotal for the regulation of the IFN responses. In this review, we briefly describe cardinal features of the three types of IFNs and then focus on the role of the IRF family members in the regulation of each IFN system.

Infant Viral Respiratory Infection Nasal Immune-Response Patterns and Their Association with Subsequent Childhood Recurrent Wheeze

RATIONALE

Recurrent wheeze and asthma are thought to result from alterations in early life immune development following respiratory syncytial virus (RSV) infection. However, prior studies of the nasal immune response to infection have assessed only individual cytokines, which does not capture the whole spectrum of response to infection.

OBJECTIVES

To identify nasal immune phenotypes in response to RSV infection and their association with recurrent wheeze.

METHODS

A birth cohort of term healthy infants born June to December were recruited and followed to capture the first infant RSV infection. Nasal wash samples were collected during acute respiratory infection, viruses were identified by RT-PCR, and immune-response analytes were assayed using a multianalyte bead-based panel. Immune-response clusters were identified using machine learning, and association with recurrent wheeze at age 1 and 2 years was assessed using logistic regression.

MEASUREMENTS AND MAIN RESULTS

We identified two novel and distinct immune-response clusters to RSV and human rhinovirus. In RSV-infected infants, a nasal immune-response cluster characterized by lower non-IFN antiviral immune-response mediators, and higher type-2 and type-17 cytokines was significantly associated with first and second year recurrent wheeze. In comparison, we did not observe this in infants with human rhinovirus acute respiratory infection. Based on network analysis, type-2 and type-17 cytokines were central to the immune response to RSV, whereas growth factors and chemokines were central to the immune response to human rhinovirus.

CONCLUSIONS

Distinct immune-response clusters during infant RSV infection and their association with risk of recurrent wheeze provide insights into the risk factors for and mechanisms of asthma development.

NOTCH3 contributes to rhinovirus-induced goblet cell hyperplasia in COPD airway epithelial cells

RATIONALE

Goblet cell hyperplasia (GCH) is one of the cardinal features of chronic obstructive pulmonary disease (COPD) and contributes to airways obstruction. Rhinovirus (RV), which causes acute exacerbations in patients with COPD, also causes prolonged airways obstruction. Previously, we showed that RV enhances mucin gene expression and increases goblet cell number in a COPD mouse model. This study examines whether RV causes sustained GCH in relevant models of COPD.

METHODS

Mucociliary-differentiated COPD and normal airway epithelial cell cultures and mice with normal or COPD phenotype were infected with RV or sham and examined for GCH by immunofluorescence and/or mucin gene expression. In some experiments, RV-infected COPD cells and mice with COPD phenotype were treated with γ-secretase inhibitor or interleukin-13 neutralising antibody and assessed for GCH. To determine the contribution of NOTCH1/3 in RV-induced GCH, COPD cells transduced with NOTCH1/3 shRNA were used.

RESULTS

RV-infected COPD, but not normal cell cultures, showed sustained GCH and increased mucin genes expression. Microarray analysis indicated increased expression of NOTCH1, NOTCH3 and HEY1 only in RV-infected COPD cells. Blocking NOTCH3, but not NOTCH1, attenuated RV-induced GCH in vitro. Inhibition of NOTCH signalling by γ-secretase inhibitor, but not neutralising antibody to IL-13, abrogated RV-induced GCH and mucin gene expression.

CONCLUSIONS

RV induces sustained GCH via NOTCH3 particularly in COPD cells or mice with COPD phenotype. This may be one of the mechanisms that may contribute to RV-induced prolonged airways obstruction in COPD.

Respiratory syncytial virus activates epidermal growth factor receptor to suppress interferon regulatory factor 1-dependent interferon-lambda and antiviral defense in airway epithelium

Respiratory syncytial virus (RSV) persists as a significant human pathogen that continues to contribute to morbidity and mortality. In children, RSV is the leading cause of lower respiratory tract infections, and in adults RSV causes pneumonia and contributes to exacerbations of chronic lung diseases. RSV induces airway epithelial inflammation by activation of the epidermal growth factor receptor (EGFR), a tyrosine kinase receptor. Recently, EGFR inhibition was shown to decrease RSV infection, but the mechanism(s) for this effect are not known. Interferon (IFN) signaling is critical for innate antiviral responses, and recent experiments have implicated IFN-λ (lambda), a type III IFN, as the most significant IFN for mucosal antiviral immune responses to RSV infection. However, a role for RSV-induced EGFR activation to suppress airway epithelial antiviral immunity has not been explored. Here, we show that RSV-induced EGFR activation suppresses IFN regulatory factor (IRF) 1-induced IFN-λ production and increased viral infection, and we implicate RSV F protein to mediate this effect. EGFR inhibition, during viral infection, augmented IRF1, IFN-λ, and decreased RSV titers. These results suggest a mechanism for EGFR inhibition to suppress RSV by activation of endogenous epithelial antiviral defenses, which may be a potential target for novel therapeutics.

STING-Dependent Interferon-λ1 Induction in HT29 Cells, a Human Colorectal Cancer Cell Line, After Gamma-Radiation

PURPOSE

To investigate the induction of type III interferons (IFNs) in human cancer cells by gamma-rays.

METHODS AND MATERIALS

Type III IFN expression in human cancer cell lines after gamma-ray irradiation in vitro was assessed by reverse transcription-quantitative polymerase chain reaction and enzyme-linked immunosorbent assay. Signaling pathways mediating type III IFN induction were examined by a variety of means, including immunoblotting, flow cytometry, confocal imaging, and reverse transcription-quantitative polymerase chain reaction. Key mediators in these pathways were further explored and validated using gene CRISPR knockout or short hairpin RNA knockdown.

RESULTS

Exposure to gamma-rays directly induced type III IFNs (mainly IFNL1) in human cancer cell lines in dose- and time-dependent fashions. The induction of IFNL1 was primarily mediated by the cytosolic DNA sensors-STING-TBK1-IRF1 signaling axis, with a lesser contribution from the nuclear factor kappa b signaling in HT29 cells. In addition, type III IFN signaling through its receptors serves as a positive feedback loop, further enhancing IFN expression via up-regulation of the kinases in the STING-TBK1 signaling axis.

CONCLUSIONS

Our results suggest that IFNL1 can be up-regulated in human cancer cell lines after gamma-ray treatment. In HT29 cells this induction occurs via the STING pathway, adding another layer of complexity to the understanding of radiation-induced antitumor immunity, and may provide novel insights into IFN-based cancer treatment.

Porcine Epidemic Diarrhea Virus-Induced Epidermal Growth Factor Receptor Activation Impairs the Antiviral Activity of Type I Interferon

Porcine epidemic diarrhea virus (PEDV) causes acute and devastating enteric disease in suckling piglets and results in huge economic losses in the pig industry worldwide. To establish productive infection, viruses must first circumvent the host innate immune response. In this study, we found that PEDV infection stimulated epidermal growth factor receptor (EGFR) activation, which has been linked to not only anticancer therapeutics, but also antiviral signaling. Therefore, we determined whether EGFR activation affected PEDV infection by using an activator or overexpression assay. The data showed that EGFR activation enhanced virus replication in both cases. We also found that specific inhibition of EGFR by either inhibitors or small interfering RNA (siRNA) led to a decrease in virus yields. Further analysis revealed that inhibition of EGFR produced augmentation of type I interferon genes. We next observed that the EGFR downstream cascade STAT3 was also activated upon PEDV infection. Similar to the case of EGFR, specific inhibition of STAT3 by either inhibitor or siRNA increased the antiviral activity of interferon and resulted in decreased PEDV RNA levels, and vice versa. The data on STAT3 depletion in combination with EGFR activation suggest that the attenuation of antiviral activity by EGFR activation requires activation of the STAT3 signaling pathway. Taken together, these data demonstrate that PEDV-induced EGFR activation serves as a negative regulator of the type I interferon response and provides a novel therapeutic target for virus infection.IMPORTANCE EGFR is a transmembrane tyrosine receptor that mediates various cellular events, as well as several types of human cancers. In this study, we investigated for the first time the role of EGFR in PEDV infection. We observed that PEDV infection induced EGFR activation. The role of EGFR activation is to impair the antiviral activity of type I interferon, which requires the involvement of the EGFR downstream signaling cascade STAT3. Our findings reveal a new mechanism evolved by PEDV to circumvent the host antiviral response, which might serve as a therapeutic target against virus infection.

Interferon lambda receptor 1 (IFNL1R) transcript is highly expressed in rhinovirus bronchiolitis and correlates with disease severity

BACKGROUND

As the expression of type III IFN receptor is restricted to the mucosal surfaces, its evaluation could be crucial to characterize the role of IFNλs during bronchiolitis.

OBJECTIVES

This study was designed to investigate airway type III IFN receptor (IFNLR1/IL10RB) expression during respiratory syncytial virus (RSV) or human rhinovirus (HRV) bronchiolitis.

STUDY DESIGN

Seventy-one 1-6 month old infants hospitalized with their first episode of acute RSV or HRV bronchiolitis were selected for this study. Expression of IFNLR1, IL10RB and IFN-stimulated genes (ISGs) MxA and ISG56 in cells of nasopharyngeal washings taken within the first 48 h of admission were determined by a real-time hydrolysis probe RT-PCR assay. The ability of types I and III IFNs to induce the expression of both IFNLR1 and IL10RB in vitro was also evaluated.

RESULTS

Airway IFNLR1 transcript levels were significantly higher in HRV bronchiolitis infants compared to those with RSV bronchiolitis. No differences were recorded for IL10RB-mRNA between RSV or HRV infection. IFNLR1 mRNA levels increased significantly in infants infected with the C species of HRV and in those with a higher clinical score index and with an eosinophil count >3%. There were no correlations in vivo between type III IFN receptors and those of ISGs and neither IFNLR1 nor IL10RB were induced in vitro by IFNs.

CONCLUSIONS

These results suggest that IFNLR1 are increased in HRV-infected infants with more severe bronchiolitis and blood eosinophilia and in those infected with the HRVC species.

Epidermal growth factor receptor inhibitors trigger a type I interferon response in human skin

The Epidermal Growth Factor Receptor (EGFR) is centrally involved in the regulation of key processes of the epithelia, including cell proliferation, survival, differentiation, and also tumorigenesis. Humanized antibodies and small-molecule inhibitors targeting EGFR were developed to disrupt these functions in cancer cells and are currently used in the treatment of diverse metastatic epithelial cancers. By contrast, these drugs possess significant skin-specific toxic effects, comprising the establishment of a persistent inflammatory milieu. So far, the molecular mechanisms underlying these epiphenomena have been investigated rather poorly. Here we showed that keratinocytes respond to anti-EGFR drugs with the development of a type I interferon molecular signature. Upregulation of the transcription factor IRF1 is early implicated in the enhanced expression of interferon-kappa, leading to persistent activation of STAT1 and further amplification of downstream interferon-induced genes, including anti-viral effectors and chemokines. When anti-EGFR drugs are associated to TNF-α, whose expression is enhanced by the drugs themselves, all these molecular events undergo a dramatic enhancement by synergy mechanisms. Finally, high levels of interferon-kappa can be observed in epidermal keratinocytes and also in leukocytes infiltrating the upper dermis of cetuximab-driven skin lesions. Our data suggest that dysregulated activation of type I interferon innate immunity is implicated in the molecular processes triggered by anti-EGFR drugs and leading to persistent skin inflammation.

IFN Regulatory Factors and Antiviral Innate Immunity: How Viruses Can Get Better

The interferon regulatory factor (IRF) family consists of transcriptional regulators that exert multifaceted and versatile functions in multiple biological processes. Their crucial role as central mediators in the establishment and execution of host immunity in response to pathogen-derived signals downstream pattern recognition receptors (PRRs) makes IRFs a hallmark of the host antiviral response. They function as hub molecules at the crossroad of different signaling pathways for the induction of interferon (IFN) and inflammatory cytokines, as well as of antiviral and immunomodulatory genes even in an IFN-independent manner. By regulating the development and activity of immune cells, IRFs also function as a bridge between innate and adaptive responses. As such, IRFs represent attractive and compulsive targets in viral strategies to subvert antiviral signaling. In this study, we discuss current knowledge on the wide array of strategies put in place by pathogenic viruses to evade, subvert, and/or hijack these essential components of host antiviral immunity.

IRF1 Is a Transcriptional Regulator of ZBP1 Promoting NLRP3 Inflammasome Activation and Cell Death during Influenza Virus Infection

Innate immune sensing of influenza A virus (IAV) induces activation of various immune effector mechanisms, including the nucleotide and oligomerization domain, leucine-rich repeat-containing protein family, pyrin domain containing 3 (NLRP3) inflammasome and programmed cell death pathways. Although type I IFNs are identified as key mediators of inflammatory and cell death responses during IAV infection, the involvement of various IFN-regulated effectors in facilitating these responses are less studied. In this study, we demonstrate the role of IFN regulatory factor (IRF)1 in promoting NLRP3 inflammasome activation and cell death during IAV infection. Both inflammasome-dependent responses and induction of apoptosis and necroptosis are reduced in cells lacking IRF1 infected with IAV. The observed reduction in inflammasome activation and cell death in IRF1-deficient cells during IAV infection correlates with reduced levels of Z-DNA binding protein 1 (ZBP1), a key molecule mediating IAV-induced inflammatory and cell death responses. We further demonstrate IRF1 as a transcriptional regulator of ZBP1. Overall, our study identified IRF1 as an upstream regulator of NLRP3 inflammasome and cell death during IAV infection and further highlights the complex and multilayered regulation of key molecules controlling inflammatory response and cell fate decisions during infections.

Targeted Therapies: Immunologic Effects and Potential Applications Outside of Cancer

Two pharmacologic approaches that are currently at the forefront of treating advanced cancer are those that center on disrupting critical growth/survival signaling pathways within tumor cells (commonly referred to as "targeted therapies") and those that center on enhancing the capacity of a patient's immune system to mount an antitumor response (immunotherapy). Maximizing responses to both of these approaches requires an understanding of the oncogenic events present in a given patient's tumor and the nature of the tumor-immune microenvironment. Although these 2 modalities were developed and initially used independently, combination regimens are now being tested in clinical trials, underscoring the need to understand how targeted therapies influence immunologic events. Translational studies and preclinical models have demonstrated that targeted therapies can influence immune cell trafficking, the production of and response to chemokines and cytokines, antigen presentation, and other processes relevant to antitumor immunity and immune homeostasis. Moreover, because these and other effects of targeted therapies occur in nonmalignant cells, targeted therapies are being evaluated for use in applications outside of oncology.

Repurposing of Kinase Inhibitors as Broad-Spectrum Antiviral Drugs

The high cost of drug development and the narrow spectrum of coverage typically provided by direct-acting antivirals limit the scalability of this antiviral approach. This review summarizes progress and challenges in the repurposing of approved kinase inhibitors as host-targeted broad-spectrum antiviral therapies.

Phenotypic and genetic aspects of epithelial barrier function in asthmatic patients

The bronchial epithelium is continuously exposed to a multitude of noxious challenges in inhaled air. Cellular contact with most damaging agents is reduced by the action of the mucociliary apparatus and by formation of a physical barrier that controls passage of ions and macromolecules. In conjunction with these defensive barrier functions, immunomodulatory cross-talk between the bronchial epithelium and tissue-resident immune cells controls the tissue microenvironment and barrier homeostasis. This is achieved by expression of an array of sensors that detect a wide variety of viral, bacterial, and nonmicrobial (toxins and irritants) agents, resulting in production of many different soluble and cell-surface molecules that signal to cells of the immune system. The ability of the bronchial epithelium to control the balance of inhibitory and activating signals is essential for orchestrating appropriate inflammatory and immune responses and for temporally modulating these responses to limit tissue injury and control the resolution of inflammation during tissue repair. In asthmatic patients abnormalities in many aspects of epithelial barrier function have been identified. We postulate that such abnormalities play a causal role in immune dysregulation in the airways by translating gene-environment interactions that underpin disease pathogenesis and exacerbation.

Aging Impairs Alveolar Macrophage Phagocytosis and Increases Influenza-Induced Mortality in Mice

Influenza viral infections often lead to increased mortality in older people. However, the mechanisms by which aging impacts immunity to influenza lung infection remain unclear. We employed a murine model of influenza infection to identify these mechanisms. With aging, we found reduced numbers of alveolar macrophages, cells essential for lung homeostasis. We also determined that these macrophages are critical for influenza-induced mortality with aging. Furthermore, aging vastly alters the transcriptional profile and specifically downregulates cell cycling pathways in alveolar macrophages. Aging impairs the ability of alveolar macrophages to limit lung damage during influenza infection. Moreover, aging decreases alveolar macrophage phagocytosis of apoptotic neutrophils, downregulates the scavenging receptor CD204, and induces retention of neutrophils during influenza infection. Thus, aging induces defective phagocytosis by alveolar macrophages and increases lung damage. These findings indicate that therapies that enhance the function of alveolar macrophages may improve outcomes in older people infected with respiratory viruses.

Antitumor Effects of Epidrug/IFNα Combination Driven by Modulated Gene Signatures in Both Colorectal Cancer and Dendritic Cells

Colorectal cancer results from the progressive accumulation of genetic and epigenetic alterations. IFN signaling defects play an important role in the carcinogenesis process, in which the inability of IFN transcription regulatory factors (IRF) to access regulatory sequences in IFN-stimulated genes (ISG) in tumors and in immune cells may be pivotal. We reported that low-dose combination of two FDA-approved epidrugs, azacytidine (A) and romidepsin (R), with IFNα2 (ARI) hampers the aggressiveness of both colorectal cancer metastatic and stem cells in vivo and triggers immunogenic cell death signals that stimulate dendritic cell (DC) function. Here, we investigated the molecular signals induced by ARI treatment and found that this drug combination increased the accessibility to regulatory sequences of ISGs and IRFs that were epigenetically silenced in both colorectal cancer cells and DCs. Likewise, specific ARI-induced histone methylation and acetylation changes marked epigenetically affected ISG promoters in both metastatic cancer cells and DCs. Analysis by ChIP-seq confirmed such ARI-induced epigenetically regulated IFN signature. The activation of this signal endowed DCs with a marked migratory capability. Our results establish a direct correlation between reexpression of silenced ISGs by epigenetic control and ARI anticancer activity and provide new knowledge for the development of innovative combined therapeutic strategies for colorectal cancer. Cancer Immunol Res; 5(7); 604-16. ©2017 AACR.

Recognition of Viral RNA by Pattern Recognition Receptors in the Induction of Innate Immunity and Excessive Inflammation During Respiratory Viral Infections

The innate immune system is the first line of defense against virus infection that triggers the expression of type I interferon (IFN) and proinflammatory cytokines. Pattern recognition receptors (PRRs) recognize pathogen-associated molecular patterns, resulting in the induction of innate immune responses. Viral RNA in endosomes is recognized by Toll-like receptors, and cytoplasmic viral RNA is recognized by RIG-I-like receptors. The host innate immune response is critical for protection against virus infection. However, it has been postulated that an excessive inflammatory response in the lung caused by the innate immune response is harmful to the host and is a cause of lethality during influenza A virus infection. Although the deletion of genes encoding PRRs or proinflammatory cytokines does not improve the mortality of mice infected with influenza A virus, a partial block of the innate immune response is successful in decreasing the mortality rate of mice without a loss of protection against virus infection. In addition, morbidity and mortality rates are influenced by other factors. For example, secondary bacterial infection increases the mortality rate in patients with influenza A virus and in animal models of the disease, and environmental factors, such as cigarette smoke and fine particles, also affect the innate immune response. In this review, we summarize recent findings related to the role of PRRs in innate immune response during respiratory viral infection.

The Role of ErbB Receptors in Infection

Members of the epidermal growth factor receptor family (ErbB family) possess a wide distribution and diverse functions ranging from cellular growth to migration and apoptosis. Though highly implicated in a variety of cancers, their involvement in infectious disease is less recognised. A growing body of evidence now highlights the importance of the ErbB family in a variety of infections. Their role as growth factor receptors, along with other characteristics, such as surface expression and continuous intracellular trafficking, make this receptor family ideally placed for exploitation by pathogens. Herein, we review our current understanding of the role of the ErbB family in the context of infectious disease, exploring the mechanisms that govern pathogen exploitation of this system.

A wide and diverse variety of microbes have each evolved distinct mechanisms to exploit ErbB receptors, highlighting this receptor kinase family as a critical factor in initiation and maintenance of pathogen infections.

ErbB family members are utilised by pathogens attempting to gain cellular entry, subvert immune responses, and manipulate the cell cycle of infected host cells. These events support and are necessary for pathogen persistence.

Pathogen-mediated ErbB-exploitation may contribute to cellular transformation and oncogenesis in a variety of cancers.

The use of existing FDA-approved drugs that target ErbB receptors and associated signalling components may offer potential future therapies against infection.

Suppressor of cytokine signaling (SOCS)5 ameliorates influenza infection via inhibition of EGFR signaling

Influenza virus infections have a significant impact on global human health. Individuals with suppressed immunity, or suffering from chronic inflammatory conditions such as COPD, are particularly susceptible to influenza. Here we show that suppressor of cytokine signaling (SOCS) five has a pivotal role in restricting influenza A virus in the airway epithelium, through the regulation of epidermal growth factor receptor (EGFR). Socs5-deficient mice exhibit heightened disease severity, with increased viral titres and weight loss. Socs5 levels were differentially regulated in response to distinct influenza viruses (H1N1, H3N2, H5N1 and H11N9) and were reduced in primary epithelial cells from COPD patients, again correlating with increased susceptibility to influenza. Importantly, restoration of SOCS5 levels restricted influenza virus infection, suggesting that manipulating SOCS5 expression and/or SOCS5 targets might be a novel therapeutic approach to influenza.

The host microRNA miR-301a blocks the IRF1-mediated neuronal innate immune response to Japanese encephalitis virus infection

Effective recognition of viral components and the subsequent stimulation of the production of type I interferons (IFNs) is crucial for the induction of host antiviral immunity. The failure of the host to efficiently produce type I IFNs in response to infection by the Japanese encephalitis virus (JEV) is linked with an increased probability for the disease to become lethal. JEV is a neurotropic virus of the Flaviviridae family that causes encephalitis in humans. JEV infection is regulated by several host factors, including microRNAs, which are conserved noncoding RNAs that participate in various physiological and pathological processes. We showed that the JEV-induced expression of miR-301a led to inhibition of the production of type I IFN by reducing the abundances of the transcription factor IFN regulatory factor 1 (IRF1) and the signaling protein suppressor of cytokine signaling 5 (SOCS5). Mechanistically, induction of miR-301a expression during JEV infection required the transcription factor nuclear factor κB. In mouse neurons, neutralization of miR-301a restored the host innate immune response by enabling IFN-β production, thereby restricting viral propagation. Inhibition of miR-301a in mouse brain rescued the production of IRF1 and SOCS5, increased the generation of IFN-β, and reduced the extent of JEV replication, thus improving mouse survival. Thus, our study suggests that the JEV-induced expression of miR-301a assists viral pathogenesis by suppressing IFN production, which might be targeted by antiviral therapies.

Cell Jamming in the Airway Epithelium

Hallmarks of asthma include chronic airway inflammation, progressive airway remodeling, and airway hyperresponsiveness. The initiation and perpetuation of these processes are attributable at least in part to critical events within the airway epithelium, but the underlying mechanisms remain poorly understood. New evidence now suggests that epithelial cells derived from donors without asthma versus donors with asthma, even in the absence of inflammatory cells or mediators, express modes of collective migration that innately differ not only in the amount of migration but also in the kind of migration. The maturing cell layer tends to undergo a transition from a hypermobile, fluid-like, unjammed phase in which cells readily rearrange, exchange places, and flow, to a quiescent, solid-like, jammed phase in which cells become virtually frozen in place. Moreover, the unjammed phase defines a phenotype that can be perpetuated by the compressive stresses caused by bronchospasm. Importantly, in cells derived from donors with asthma versus donors without asthma, this jamming transition becomes substantially delayed, thus suggesting an immature or dysmature epithelial phenotype in asthma.

An IFIH1 gene polymorphism associated with risk for autoimmunity regulates canonical antiviral defence pathways in Coxsackievirus infected human pancreatic islets

The IFIH1 gene encodes the pattern recognition receptor MDA5. A common polymorphism in IFIH1 (rs1990760, A946T) confers increased risk for autoimmune disease, including type 1-diabetes (T1D). Coxsackievirus infections are linked to T1D and cause beta-cell damage in vitro. Here we demonstrate that the rs1990760 polymorphism regulates the interferon (IFN) signature expressed by human pancreatic islets following Coxsackievirus infection. A strong IFN signature was associated with high expression of IFNλ1 and IFNλ2, linking rs1990760 to the expression of type III IFNs. In the high-responding genotype, IRF-1 expression correlated with that of type III IFN, suggesting a positive-feedback on type III IFN transcription. In summary, our study uncovers an influence of rs1990760 on the canonical effector function of MDA5 in response to an acute infection of primary human parenchymal cells with a clinically relevant virus linked to human T1D. It also highlights a previously unrecognized connection between the rs1990760 polymorphism and the expression level of type III IFNs.

IFN-λ: A New Inducer of Local Immunity against Cancer and Infections

IFN-λ is the newly established type III IFN with unique immunomodulatory functions. In contrast to the IFN-α/β family and to some extent IFN-γ, IFN-λ is apparently acting in specific areas of the body to activate resident immune cells and induces a local immunity, instrumental in preventing particular infections and also keeping transformed cells under control. Mucosal areas of lung and gastrointestinal tracts are now under scrutiny to elucidate the immune mechanisms triggered by IFN-λ and leading to viral protection. New evidence also indicates the crucial role of IFN-λ in promoting innate immunity in solid cancer models. Based on its unique biological activities among the IFN system, new immunotherapeutic approaches are now emerging for the treatment of cancer, infection, and autoimmune diseases. In the present review, we highlight the recent advances of IFN-λ immunomodulatory functions. We also discuss the perspectives of IFN-λ as a therapeutic agent.

Early local immune defences in the respiratory tract

The respiratory immune response consists of multiple tiers of cellular responses that are engaged in a sequential manner in order to control infections. The stepwise engagement of effector functions with progressively increasing host fitness costs limits tissue damage. In addition, specific mechanisms are in place to promote disease tolerance in response to respiratory infections. Environmental factors, obesity and the ageing process can alter the efficiency and regulation of this tiered response, increasing pathology and mortality as a result. In this Review, we describe the cell types that coordinate pathogen clearance and tissue repair through the serial secretion of cytokines, and discuss how the environment and comorbidity influence this response.

Rhinovirus Delays Cell Repolarization in a Model of Injured/Regenerating Human Airway Epithelium

Rhinovirus (RV), which causes exacerbation in patients with chronic airway diseases, readily infects injured airway epithelium and has been reported to delay wound closure. In this study, we examined the effects of RV on cell repolarization and differentiation in a model of injured/regenerating airway epithelium (polarized, undifferentiated cells). RV causes only a transient barrier disruption in a model of normal (mucociliary-differentiated) airway epithelium. However, in the injury/regeneration model, RV prolongs barrier dysfunction and alters the differentiation of cells. The prolonged barrier dysfunction caused by RV was not a result of excessive cell death but was instead associated with epithelial-to-mesenchymal transition (EMT)-like features, such as reduced expression of the apicolateral junction and polarity complex proteins, E-cadherin, occludin, ZO-1, claudins 1 and 4, and Crumbs3 and increased expression of vimentin, a mesenchymal cell marker. The expression of Snail, a transcriptional repressor of tight and adherence junctions, was also up-regulated in RV-infected injured/regenerating airway epithelium, and inhibition of Snail reversed RV-induced EMT-like features. In addition, compared with sham-infected cells, the RV-infected injured/regenerating airway epithelium showed more goblet cells and fewer ciliated cells. Inhibition of epithelial growth factor receptor promoted repolarization of cells by inhibiting Snail and enhancing expression of E-cadherin, occludin, and Crumbs3 proteins, reduced the number of goblet cells, and increased the number of ciliated cells. Together, these results suggest that RV not only disrupts barrier function, but also interferes with normal renewal of injured/regenerating airway epithelium by inducing EMT-like features and subsequent goblet cell hyperplasia.

IRF1 Downregulation by Ras/MEK Is Independent of Translational Control of IRF1 mRNA

Oncogenic activation of Ras/MEK downregulates the expression of interferon regulatory factor 1 (IRF1), which is a prerequisite for oncolytic viruses to replicate in cancer cells [1]. Moreover, restoration of IRF1 expression is essential to induce apoptosis of cancer cells treated with a MEK inhibitor [2]. However, the molecular mechanisms that underlie IRF1 downregulation by Ras/MEK remain unclear. In this study, we determined whether Ras/MEK activation modulates IRF1 expression at its translational level. MEK inhibition increased the activity of IRF1 promoter construct in Ras transformed NIH3T3 cells and wild type MEF, but not in IRF1 deficient MEF, indicating that IRF1 protein is required for the transcriptional activation of IRF1. By conducting reporter analysis using IRF1 5’- and 3’- UTR constructs, we determined that cis elements on 5’- and 3’-UTR of IRF1 mRNA are not involved in the IRF1 regulation by Ras/MEK. We further compared the recruitment of ribosomes to IRF1 mRNA in RasV12 cells treated with or without the MEK inhibitor by conducting polysome analysis. No difference was observed in the polysomal distribution of IRF1 mRNA between RasV12 cells treated with and without the MEK inhibitor. These results suggest that regulation of IRF1 translation is independent of IRF1 downregulation by Ras/MEK.

Distinct Patterns of Expression of Transcription Factors in Response to Interferonβ and Interferonλ1

After viral infection, type I and III interferons (IFNs) are coexpressed by respiratory epithelial cells (RECs) and activate the ISGF3 transcription factor (TF) complex to induce expression of a cell-specific set of interferon-stimulated genes (ISGs). Type I and III IFNs share a canonical signaling pathway, suggesting that they are redundant. Animal and in vitro models, however, have shown that they are not redundant. Because TFs dictate cellular phenotype and function, we hypothesized that focusing on TF-ISG will reveal critical combinatorial and nonredundant functions of type I or III IFN. We treated BEAS-2B human RECs with increasing doses of IFNβ or IFNλ1 and measured expression of TF-ISG. ISGs were expressed in a dose-dependent manner with a nonlinear jump at intermediate doses. At subsaturating combinations of IFNβ and IFNλ1, many ISGs were expressed in a pattern that we modeled with a cubic equation that mathematically defines this threshold effect. Uniquely, IFNβ alone induced early and transient IRF1 transcript and protein expression, while IFNλ1 alone induced IRF1 protein expression at low levels that were sustained through 24 h. In combination, saturating doses of these 2 IFNs together enhanced and sustained IRF1 expression. We conclude that the cubic model quantitates combinatorial effects of IFNβ and IFNλ1 and that IRF1 may mediate nonredundancy of type I or III IFN in RECs.

Links between recognition and degradation of cytoplasmic viral RNA in innate immune response

Recognition and degradation of viral RNA are essential for antiviral innate immune responses. Cytoplasmic viral RNA is recognized by retinoic acid-inducible gene I (RIG-I)-like receptors, which trigger type I interferon (IFN) production. Secreted type I IFN activates ubiquitously expressed type I IFN receptor and induces IFN-stimulated genes (ISGs). To suppress viral replication, several nucleases degrade viral RNA. RNase L is an ISG with endonuclease activity that degrades viral RNA, producing small RNA that activates RIG-I, resulting in the amplification of type I IFN production. Moreover, recent studies have elucidated novel links between viral RNA recognition and degradation. The RNA exosome is a protein complex that includes nucleases and is essential for host and viral RNA decay. Although the small RNAs produced by the RNA exosome do not activate RIG-I, several accessory factors of the RNA exosome promote RIG-I activation. Zinc-finger antiviral protein (ZAP) is an accessory factor that recognizes viral RNA and promotes viral RNA degradation via the RNA exosome. ZAPS is an alternative splicing form of ZAP and promotes RIG-I oligomerization and ATPase activity, resulting in RIG-I activation. DDX60 is another cofactor involved in the viral RNA degradation via the RNA exosome. The DDX60 protein promotes RIG-I signaling in a cell-type specific manner. These observations imply that viral RNA degradation and recognition are linked to each other. In this review, I discuss the links between recognition and degradation of viral RNA.

Oncolytic Viruses: Exploiting Cancer's Deal with the Devil

Tumor cells harbor tens to thousands of genetic and epigenetic alterations that disrupt cellular pathways, providing them with growth and survival advantages. However, these benefits come at a cost, with uncontrolled cell growth, defective apoptosis, sustained pathological angiogenesis, immune evasion, and a metastatic phenotype occurring at the expense of the antiviral response of the individual tumor cell. Oncolytic virotherapy is an emerging therapeutic strategy that uses replication-competent viruses to selectivity kill cancer cells by exploiting their impaired antiviral response. In this review, we outline our understanding of the alterations in signaling pathways that simultaneously contribute to the malignant phenotype and virus-mediated killing of cancer cells.

A systems approach to understanding human rhinovirus and influenza virus infection

Human rhinovirus and influenza virus infections of the upper airway lead to colds and the flu and can trigger exacerbations of lower airway diseases including asthma and chronic obstructive pulmonary disease. Novel diagnostic and therapeutic targets are still needed to differentiate between the cold and the flu, since the clinical course of influenza can be severe while that of rhinovirus is usually more mild. In our investigation of influenza and rhinovirus infection of human respiratory epithelial cells, we used a systems approach to identify the temporally changing patterns of host gene expression from these viruses. After infection of human bronchial epithelial cells (BEAS-2B) with rhinovirus, influenza virus or co-infection with both viruses, we studied the time-course of host gene expression changes over three days. We modeled host responses to these viral infections with time and documented the qualitative and quantitative differences in innate immune activation and regulation.

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Human bronchial epithelial cells (BEAS-2B) were infected with rhinovirus (RV16), influenza A virus (H1N1) or both viruses.

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Steady-state RNA was profiled from five biological replicate samples by microarray hybridization at multiple times over three days.

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The changing patterns of key biological processes for each virus or both viruses together were analyzed.

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The data reveal similarities and differences in innate immune responses, cytokine activation, regulation of apoptosis as well as other processes that have implications for host recovery from viral infection.

Decoding protein networks during virus entry by quantitative proteomics

Virus entry into host cells relies on interactions between viral and host structures including lipids, carbohydrates and proteins. Particularly, protein–protein interactions between viral surface proteins and host proteins as well as secondary host protein–protein interactions play a pivotal role in coordinating virus binding and uptake. These interactions are dynamic and frequently involve multiprotein complexes. In the past decade mass spectrometry based proteomics methods have reached sensitivities and high throughput compatibilities of genomics methods and now allow the reliable quantitation of proteins in complex samples from limited material. As proteomics provides essential information on the biologically active entity namely the protein, including its posttranslational modifications and its interactions with other proteins, it is an indispensable method in the virologist's toolbox. Here we review protein interactions during virus entry and compare classical biochemical methods to study entry with novel technically advanced quantitative proteomics techniques. We highlight the value of quantitative proteomics in mapping functional virus entry networks, discuss the benefits and limitations and illustrate how the methodology will help resolve unsettled questions in virus entry research in the future.

Putting the Squeeze on Airway Epithelia

Asthma is characterized by chronic inflammation, airway hyperresponsiveness, and progressive airway remodeling. The airway epithelium is known to play a critical role in the initiation and perpetuation of these processes. Here, we review how excessive epithelial stress generated by bronchoconstriction is sufficient to induce airway remodeling, even in the absence of inflammatory cells.

The unique regulation and functions of type III interferons in antiviral immunity

Type I interferons (IFNs) were long considered to be the sole IFN species produced by virus-infected cells until the discovery of type III IFNs (IFNλs), decades later. Like type I IFNs, type III IFNs are induced by and protect against viral infections, leading to the initial conclusion that the two IFN species are identical in regulation and biological functions. However, the two systems differ in the tissue expression of their receptor, resulting in different roles in vivo. The unique nature of IFNλs has been further demonstrated by recent studies revealing differences in the regulation of type I and III IFN expression, and how these proteins elicit specific cellular responses. This review focuses on the distinctive features of type III IFNs in antiviral innate immunity.

DDX60 Is Involved in RIG-I-Dependent and Independent Antiviral Responses, and Its Function Is Attenuated by Virus-Induced EGFR Activation

RIG-I-mediated type I interferon (IFN) production and nuclease-mediated viral RNA degradation are essential for antiviral innate immune responses. DDX60 is an IFN-inducible cytoplasmic helicase. Here, we report that DDX60 is a sentinel for both RIG-I activation and viral RNA degradation. We show that DDX60 is an upstream factor of RIG-I that activates RIG-I signaling in a ligand-specific manner. DDX60 knockout attenuates RIG-I signaling and significantly reduces virus-induced type I IFN production in vivo. In addition, we show that DDX60 is involved in RIG-I-independent viral RNA degradation. DDX60 and RIG-I adaptor MAVS double-knockout mice reveal a role for DDX60-dependent RNA degradation in antiviral responses. Several viruses induced DDX60 phosphorylation via epidermal growth factor receptor (EGFR), leading to attenuation of the DDX60 antiviral activities. Our results define DDX60 as a sentinel for cytoplasmic antiviral response, which is counteracted by virus-mediated EGF receptor activation.

Influenza induces IL-8 and GM-CSF secretion by human alveolar epithelial cells through HGF/c-Met and TGF-α/EGFR signaling

The most severe complication of influenza is viral pneumonia, which can lead to the acute respiratory distress syndrome. Alveolar epithelial cells (AECs) are the first cells that influenza virus encounters upon entering the alveolus. Infected epithelial cells produce cytokines that attract and activate neutrophils and macrophages, which in turn induce damage to the epithelial-endothelial barrier. Hepatocyte growth factor (HGF)/c-Met and transforming growth factor-α (TGF-α)/epidermal growth factor receptor (EGFR) are well known to regulate repair of damaged alveolar epithelium by stimulating cell migration and proliferation. Recently, TGF-α/EGFR signaling has also been shown to regulate innate immune responses in bronchial epithelial cells. However, little is known about whether HGF/c-Met signaling alters the innate immune responses and whether the innate immune responses in AECs are regulated by HGF/c-Met and TGF-α/EGFR. We hypothesized that HGF/c-Met and TGF-α/EGFR would regulate innate immune responses to influenza A virus infection in human AECs. We found that recombinant human HGF (rhHGF) and rhTGF-α stimulated primary human AECs to secrete IL-8 and granulocyte macrophage colony-stimulating factor (GM-CSF) strongly and IL-6 and monocyte chemotactic protein 1 moderately. Influenza infection stimulated the secretion of IL-8 and GM-CSF by AECs plated on rat-tail collagen through EGFR activation likely by TGF-α released from AECs and through c-Met activated by HGF secreted from lung fibroblasts. HGF secretion by fibroblasts was stimulated by AEC production of prostaglandin E₂ during influenza infection. We conclude that HGF/c-Met and TGF-α/EGFR signaling enhances the innate immune responses by human AECs during influenza infections.

MiR-23a facilitates the replication of HSV-1 through the suppression of interferon regulatory factor 1

MicroRNAs (miRNAs) are small, non-coding RNAs that negatively regulate gene expression. It has been reported that miRNAs are involved in host-virus interaction, but evidence that cellular miRNAs promote virus replication has been limited. Here, we found that miR-23a promoted the replication of human herpes simplex virus type 1 (HSV-1) in HeLa cells, as demonstrated by a plaque-formation assay and quantitative real-time PCR. Furthermore, interferon regulatory factor 1 (IRF1), an innate antiviral molecule, is targeted by miR-23a to facilitate viral replication. MiR-23a binds to the 3′UTR of IRF1 and down-regulates its expression. Suppression of IRF1 expression reduced RSAD2 gene expression, augmenting HSV-1 replication. Ectopic expression of IRF1 abrogated the promotion of HSV-1 replication induced by miR-23a. Notably, IRF1 contributes to innate antiviral immunity by binding to IRF-response elements to regulate the expression of interferon-stimulated genes (ISGs) and apoptosis, revealing a complex interaction between miR-23a and HSV-1. MiR-23a thus contributes to HSV-1 replication through the regulation of the IRF1-mediated antiviral signal pathway, which suggests that miR-23a may represent a promising target for antiviral treatments.