Influenza virus utilizes N-linked sialoglycans as receptors in A549 cells

Adaptation potential of H3N8 canine influenza virus in human respiratory cells

In 2004, the equine-origin H3N8 canine influenza virus (CIV) first caused an outbreak with lethal cases in racing greyhounds in Florida, USA, and then spread to domestic dogs nationwide. Although transmission of this canine virus to humans has not been reported, it is important to evaluate its zoonotic potential because of the high contact opportunities between companion dogs and humans. To gain insight into the interspecies transmissibility of H3N8 CIV, we tested its adaptability to human respiratory A549 cells through successive passages. We found that CIV acquired high growth properties in these cells mainly through mutations in surface glycoproteins, such as hemagglutinin (HA) and neuraminidase (NA). Our reverse genetics approach revealed that HA2-K82E, HA2-R163K, and NA-S18L mutations were responsible for the increased growth of CIV in human cells. Molecular analyses revealed that both HA2 mutations altered the optimum pH for HA membrane fusion activity and that the NA mutation changed the HA-NA functional balance. These findings suggest that H3N8 CIV could evolve into a human pathogen with pandemic potential through a small number of mutations, thereby posing a threat to public health in the future.

Lipopolysaccharide aggravates canine influenza a (H3N2) virus infection and lung damage via mTOR/autophagy in vivo and in vitro

Influenza A (H3N2) accounts for the majority of influenza worldwide and continues to challenge human health. Disturbance in the gut microbiota caused by many diseases leads to increased production of lipopolysaccharide (LPS), and LPS induces sepsis and conditions associated with local or systemic inflammation. However, to date, little attention has been paid to the potential impact of LPS on influenza A (H3N2) infection and the potential mechanism. Hence, in this study we used canine influenza A (H3N2) virus (CIV) as a model of influenza A virus to investigate the effect of low-dose of LPS on CIV replication and lung damage and explore the underlying mechanism in mice and A549 and HPAEpiC cells. The results showed that LPS (25 μg/kg) increased CIV infection and lung damage in mice, as indicated by pulmonary virus titer, viral NP levels, lung index, and pulmonary histopathology. LPS (1 μg/ml) also increased CIV replication in A549 cells as indicated by the above same parameters. Furthermore, low doses of LPS reduced CIV-induced p-mTOR protein expression and enhanced CIV-induced autophagy-related mRNA/protein expressions in vivo and in vitro. In addition, the use of the mTOR activator, MHY1485, reversed CIV-induced autophagy and CIV replication in A549 and HPAEpiC cells, respectively. siATG5 alleviated CIV replication exacerbated by LPS in the two lines. In conclusion, LPS aggravates CIV infection and lung damage via mTOR/autophagy.

Quantitative proteomics of differentiated primary bronchial epithelial cells from chronic obstructive pulmonary disease and control identifies potential novel host factors post-influenza A virus infection

Background

Chronic obstructive pulmonary disease (COPD) collectively refers to chronic and progressive lung diseases that cause irreversible limitations in airflow. Patients with COPD are at high risk for severe respiratory symptoms upon influenza virus infection. Airway epithelial cells provide the first-line antiviral defense, but whether or not their susceptibility and response to influenza virus infection changes in COPD have not been elucidated. Therefore, this study aimed to compare the susceptibility of COPD- and control-derived airway epithelium to the influenza virus and assess protein changes during influenza virus infection by quantitative proteomics.

Materials and methods

The presence of human- and avian-type influenza A virus receptor was assessed in control and COPD lung sections as well as in fully differentiated primary human bronchial epithelial cells (phBECs) by lectin- or antibody-based histochemical staining. PhBECs were from COPD lungs, including cells from moderate- and severe-stage diseases, and from age-, sex-, smoking, and history-matched control lung specimens. Protein profiles pre- and post-influenza virus infection in vitro were directly compared using quantitative proteomics, and selected findings were validated by qRT-PCR and immunoblotting.

Results

The human-type influenza receptor was more abundant in human airways than the avian-type influenza receptor, a property that was retained in vitro when differentiating phBECs at the air-liquid interface. Proteomics of phBECs pre- and post-influenza A virus infection with A/Puerto Rico/8/34 (PR8) revealed no significant differences between COPD and control phBECs in terms of flu receptor expression, cell type composition, virus replication, or protein profile pre- and post-infection. Independent of health state, a robust antiviral response to influenza virus infection was observed, as well as upregulation of several novel influenza virus-regulated proteins, including PLSCR1, HLA-F, CMTR1, DTX3L, and SHFL.

Conclusion

COPD- and control-derived phBECs did not differ in cell type composition, susceptibility to influenza virus infection, and proteomes pre- and post-infection. Finally, we identified novel influenza A virus-regulated proteins in bronchial epithelial cells that might serve as potential targets to modulate the pathogenicity of infection and acute exacerbations.

Influenza A Virus Agnostic Receptor Tropism Revealed Using a Novel Biological System with Terminal Sialic Acid Knockout Cells

Avian or human influenza A viruses bind preferentially to avian- or human-type sialic acid receptors, respectively, indicating that receptor tropism is an important factor for determining the viral host range. However, there are currently no reliable methods for analyzing receptor tropism biologically under physiological conditions. In this study, we established a novel system using MDCK cells with avian- or human-type sialic acid receptors and with both sialic acid receptors knocked out (KO). When we examined the replication of human and avian influenza viruses in these KO cells, we observed unique viral receptor tropism that could not be detected using a conventional solid-phase sialylglycan binding assay, which directly assesses physical binding between the virus and sialic acids. Furthermore, we serially passaged an engineered avian-derived H4N5 influenza virus, whose PB2 gene was deleted, in avian-type receptor KO cells stably expressing PB2 to select a mutant with enhanced replication in KO cells; however, its binding to human-type sialylglycan was undetectable using the solid-phase binding assay. These data indicate that a panel of sialic acid receptor KO cells could be a useful tool for determining the biological receptor tropism of influenza A viruses. Moreover, the PB2KO virus experimental system could help to safely and efficiently identify the mutations required for avian influenza viruses to adapt to human cells that could trigger a new influenza pandemic. IMPORTANCE The acquisition of mutations that allow avian influenza A virus hemagglutinins to recognize human-type receptors is mandatory for the transmission of avian viruses to humans, which could lead to a pandemic. In this study, we established a novel system using a set of genetically engineered MDCK cells with knocked out sialic acid receptors to biologically evaluate the receptor tropism for influenza A viruses. Using this system, we observed unique receptor tropism in several virus strains that was undetectable using conventional solid-phase binding assays that measure physical binding between the virus and artificially synthesized sialylglycans. This study contributes to elucidation of the relationship between the physical binding of virus and receptor and viral infectivity. Furthermore, the system using sialic acid knockout cells could provide a useful tool to explore the sialic acid-independent entry mechanism. In addition, our system could be safely used to identify mutations that could acquire human-type receptor tropism.

[The issues in detection of avian-type receptors for influenza viruses]

Influenza viruses utilize sialic acid-containing glycoconjugates as receptors. The distribution of receptors in host tissues has been investigated in many species to understand the ecology of influenza viruses in nature and the mechanisms of interspecies transmission of the viruses. On the other hand, lectins, which have been widely used to detect these receptor molecules, have many different characteristics from antibodies and thus, require special attention in interpreting the results of lectin staining. In particular, lectins derived from Maackia amurensis, which has been used to detect Siaα2-3Gal, the avian-type receptor for influenza viruses, have been used without fully understanding its characteristics. This led to some confusion in interpreting the distribution of influenza virus receptors in host tissues. How accurately do we know the distribution of avian-type receptors in host animals? In this article, we would like to suggest reviewing the influenza virus receptors by providing issues related to Maackia lectins.

Self-assembled sialyllactosyl probes with aggregation-enhanced properties for ratiometric detection and blocking of influenza viruses

Infection and dissemination of influenza viruses (IVs) causes serious health concerns worldwide. However, effective tools for the accurate detection and blocking of IVs remain elusive. Here, we develop a new sialyllactosyl probe with self-assembled core-shell structure for the ratiometric detection and blocking of IVs. N,N'-diaryl-dihydrodibenzo[a,c]phenazines were used to form the core structure by hydrophobic assembly in an aqueous solution with an aggregation-enhanced blue fluorescence mission. Subsequently, dicyanomethylene-4H-pyran-based sialyllactosides were used for self-assembly with the core structure, producing the sialyllactosyl probe that emits a red fluorescence due to Förster resonance energy transfer. The probe developed has been proven to be available for (1) the fluorescence ratiometric detection of IVs through selective interaction with the sialyllactosyl-binding proteins on the virus surface, and (2) effectively blocking the invasion of human-infecting IVs towards host cells as accentuated by the sialyllactosides on the surface of the probes.

Glycosphingolipids and Infection. Potential New Therapeutic Avenues

Glycosphingolipids (GSLs), the main topic of this review, are a subclass of sphingolipids. With their glycans exposed to the extracellular space, glycosphingolipids are ubiquitous components of the plasma membrane of cells. GSLs are implicated in a variety of biological processes including specific infections. Several pathogens use GSLs at the surface of host cells as binding receptors. In addition, lipid-rafts in the plasma membrane of host cells may act as platform for signaling the presence of pathogens. Relatively common in man are inherited deficiencies in lysosomal glycosidases involved in the turnover of GSLs. The associated storage disorders (glycosphingolipidoses) show lysosomal accumulation of substrate(s) of the deficient enzyme. In recent years compounds have been identified that allow modulation of GSLs levels in cells. Some of these agents are well tolerated and already used to treat lysosomal glycosphingolipidoses. This review summarizes present knowledge on the role of GSLs in infection and subsequent immune response. It concludes with the thought to apply glycosphingolipid-lowering agents to prevent and/or combat infections.

A humanized MDCK cell line for the efficient isolation and propagation of human influenza viruses

Here, we developed hCK, a Madin-Darby canine kidney (MDCK) cell line that expresses high levels of human influenza virus receptors and low levels of avian virus receptors. hCK cells supported human A/H3N2 influenza virus isolation and growth much more effectively than conventional MDCK or human virus receptor-overexpressing (AX4) cells. A/H3N2 viruses propagated in hCK cells also maintained higher genetic stability than those propagated in MDCK and AX4 cells.

Recent approaches for directly profiling cell surface sialoform

Sialic acids (SAs) are nine-carbon monosaccharides existing at the terminal location of glycan structures on the cell surface and secreted glycoconjugates. The expression levels and linkages of SAs on cells and tissues, collectively known as sialoform, present the hallmark of the cells and tissues of different systems and conditions. Accordingly, detecting or profiling cell surface sialoforms is very critical for understanding the function of cell surface glycans and glycoconjugates and even the molecular mechanisms of their underlying biological processes. Further, it may provide therapeutic and diagnostic applications for different diseases. In the past decades, several kinds of SA-specific binding molecules have been developed for detecting and profiling specific sialoforms of cells and tissues; the experimental materials have expanded from frozen tissue to living cells; and the analytical technologies have advanced from histochemistry to fluorescent imaging, flow cytometry and microarrays. This review summarizes the recent bioaffinity approaches for directly detecting and profiling specific SAs or sialylglycans, and their modifications of different cells and tissues.

Sialylglycan-Assembled Supra-Dots for Ratiometric Probing and Blocking of Human-Infecting Influenza Viruses

The seasonal outbreak of influenza causes significant morbidity and mortality worldwide because a number of influenza virus (IV) strains have been shown to infect and circulate in humans. Development of effective means to timely monitor as well as block IVs is still a challenging task. Whereas conventional fluorescence probes rely on a fluorimetric change upon recognizing IVs, here we developed simple "Supra-dots" that are formed through the aqueous supramolecular assembly between a blue-emitting polymer dot and red-emitting sialylglycan probes for the ratiometric detection of IVs. Tuning the Förster resonance energy transfer from polymer dots to glycan probes by selective sialylglycan-virus recognition enables the fluorescence ratiometric determination of IVs, whereas the presence of unselective, control viruses quenched the fluorescence of the Supra-dots. Meanwhile, we show that the Supra-dots can effectively inhibit the invasion of a human-infecting IV toward a human cell line, thereby making possible a unique bifunctional, supramolecular probe for influenza theranostics.

Alteration of N-glycan expression profile and glycan pattern of glycoproteins in human hepatoma cells after HCV infection

BACKGROUND

Hepatitis C virus (HCV) infection causes chronic liver diseases, liver fibrosis and even hepatocellular carcinoma (HCC). However little is known about any information of N-glycan pattern in human liver cell after HCV infection.

METHODS

The altered profiles of N-glycans in HCV-infected Huh7.5.1 cell were analyzed by using mass spectrometry. Then, lectin microarray, lectin pull-down assay, reverse transcription-quantitative real time PCR (RT-qPCR) and western-blotting were used to identify the altered N-glycosylated proteins and glycosyltransferases.

RESULTS

Compared to uninfected cells, significantly elevated levels of fucosylated, sialylated and complex N-glycans were found in HCV infected cells. Furthermore, Lens culinaris agglutinin (LCA)-binding glycoconjugates were increased most. Then, the LCA-agarose was used to precipitate the specific glycosylated proteins and identify that fucosylated modified annexin A2 (ANXA2) and heat shock protein 90 beta family member 1 (HSP90B1) was greatly increased in HCV-infected cells. However, the total ANXA2 and HSP90B1 protein levels remained unchanged. Additionally, we screened the mRNA expressions of 47 types of different glycosyltransferases and found that α1,6-fucosyltransferase 8 (FUT8) was the most up-regulated and contributed to strengthen the LCA binding capability to fucosylated modified ANXA2 and HSP90B1 after HCV infection.

CONCLUSIONS

HCV infection caused the altered N-glycans profiles, increased expressions of FUT8, fucosylated ANXA2 and HSP90B1 as well as enhanced LCA binding to Huh7.5.1.

GENERAL SIGNIFICANCE

Our results may lay the foundation for clarifying the role of N-glycans and facilitate the development of novel diagnostic biomarkers and therapeutic targets based on the increased FUT8, fucosylated ANXA2 and HSP90B1 after HCV infection.

Methadone enhances human influenza A virus replication

Growing evidence has indicated that opioids enhance replication of human immunodeficiency virus and hepatitis C virus in target cells. However, it is unknown whether opioids can enhance replication of other clinically important viral pathogens. In this study, the interaction of opioid agonists and human influenza A/WSN/33 (H1N1) virus was examined in human lung epithelial A549 cells. Cells were exposed to morphine, methadone or buprenorphine followed by human H1N1 viral infection. Exposure to methadone differentially enhanced viral propagation, consistent with an increase in virus adsorption, susceptibility to virus infection and viral protein synthesis. In contrast, morphine or buprenorphine did not alter H1N1 replication. Because A549 cells do not express opioid receptors, methadone-enhanced H1N1 replication in human lung cells may not be mediated through these receptors. The interaction of methadone and H1N1 virus was also examined in adult mice. Treatment with methadone significantly increased H1N1 viral replication in lungs. Our data suggest that use of methadone facilitates influenza A viral infection in lungs and might raise concerns regarding the possible consequence of an increased risk of serious influenza A virus infection in people who receive treatment in methadone maintenance programs.

Inhibition of endoplasmic reticulum-resident glucosidases impairs severe acute respiratory syndrome coronavirus and human coronavirus NL63 spike protein-mediated entry by altering the glycan processing of angiotensin I-converting enzyme 2

Endoplasmic reticulum (ER)-resident glucosidases I and II sequentially trim the three terminal glucose moieties on the N-linked glycans attached to nascent glycoproteins. These reactions are the first steps of N-linked glycan processing and are essential for proper folding and function of many glycoproteins. Because most of the viral envelope glycoproteins contain N-linked glycans, inhibition of ER glucosidases with derivatives of 1-deoxynojirimycin, i.e., iminosugars, efficiently disrupts the morphogenesis of a broad spectrum of enveloped viruses. However, like viral envelope proteins, the cellular receptors of many viruses are also glycoproteins. It is therefore possible that inhibition of ER glucosidases not only compromises virion production but also disrupts expression and function of viral receptors and thus inhibits virus entry into host cells. Indeed, we demonstrate here that iminosugar treatment altered the N-linked glycan structure of angiotensin I-converting enzyme 2 (ACE2), which did not affect its expression on the cell surface or its binding of the severe acute respiratory syndrome coronavirus (SARS-CoV) spike glycoprotein. However, alteration of N-linked glycans of ACE2 impaired its ability to support the transduction of SARS-CoV and human coronavirus NL63 (HCoV-NL63) spike glycoprotein-pseudotyped lentiviral particles by disruption of the viral envelope protein-triggered membrane fusion. Hence, in addition to reducing the production of infectious virions, inhibition of ER glucosidases also impairs the entry of selected viruses via a post-receptor-binding mechanism.

Measurement of aberrant glycosylation of prostate specific antigen can improve specificity in early detection of prostate cancer

INTRODUCTION

We previously identified prostate cancer (PCa)-associated aberrant glycosylation of PSA, where α2,3-linked sialylation is an additional terminal N-glycan on free PSA (S2,3PSA). We then developed a new assay system measuring S2,3PSA using a magnetic microbead-based immunoassay. We compared the diagnostic accuracy of conventional PSA and percent-free PSA (%fPSA) tests.

METHODS

We used MagPlex beads to measure serum S2,3PSA levels using anti-human fPSA monoclonal antibody (8A6) for capture and anti-α2,3-linked sialic acid monoclonal antibody (HYB4) for detection. We determined the cutoff values in a training test and measured serum S2,3PSA levels in 314 patients who underwent biopsy, including 138 PCa and 176 non-PCa patients with PSA of <10.0 ng/ml. Serum S2,3PSA levels were presented as mean fluorescence intensity (MFI). Receiver operating characteristic curves were used to evaluate the diagnostic accuracy of total PSA, %fPSA, and S2,3PSA.

RESULTS

We determined an MFI cutoff value of 1130 with a sensitivity of 95.0% and specificity of 72.0% for the diagnosis of PCa in the training test. In the validation study, the area under the curve for the detection of PCa with S2,3PSA was 0.84, which was significantly higher than that with PSA or %fPSA.

CONCLUSIONS

Although the present study is small and preliminary, these results suggest that the measurement of serum S2,3PSA using a magnetic microbead-based immunoassay may improve the accuracy of early detection of PCa and reduce unnecessary prostate biopsy.