Involvement of annexin V in the entry of influenza viruses and role of phospholipids in infection

Identification of an AnnexinB9 involve in white spot syndrome virus infection in red claw crayfish Cherax quadricarinatus

Annexin (Anx) family protein is a highly conserved protein family that plays important roles in immune defense of vertebrates and invertebrates against invading pathogens. In this study, a novel Anx was cloned and characterized from the red claw crayfish, Cherax quadricarinatus. The Open Reading Frame of CqAnxB9 consisted of 930 nucleotide bases pair and encoded 309 amino acids. The CqAnxB9 protein contained three repeat Anx domains and a typical KGLGT sequence. Tissue expression analysis showed that the expression levels of CqAnxB9 were mainly expressed in the intestine, hepatopancreas and hemocytes. After WSSV challenge, CqAnxB9 expression was up-regulated in the hematopoietic tissue (Hpt) cells. Moreover, knockdown of CqAnxB9 inhibited WSSV replication and VP28 expression, suggesting that CqAnxB9 plays a positive role in WSSV infection. Further studies revealed that recombinant CqAnxB9 protein was found to bind to the viral envelop protein VP28. All these findings indicate that new-found CqAnxB9 is likely to promote WSSV infection in crustaceans, which provides a better understanding of the pathogenesis of WSSV.

Proteomic landscape of extracellular vesicles in human retinal cells infected with Staphylococcus aureus and Pseudomonas aeruginosa: Role in endophthalmitis

Extracellular Vesicles (EVs) have evolved as a promising entity for developing diagnostic and therapeutic biomarkers. We profiled global EV proteome of EVs from Human retinal cells (ARPE-19) infected with S. aureus and P. aeruginosa. EVs were isolated by ultracentrifugation and subjected to LC-MS/MS for proteome analysis. In S. aureus infection, sequest identified 864 proteins, of which 81 were differentially expressed in comparison to control. Similarly, in P. aeruginosa infection, of 516 proteins identified, 86 were differentially expressed. Additionally, 38 proteins were exclusive to infected sets. KEGG and Gene Ontology revealed crucial dysregulated pathways involving proteins such as complement cascades, annexins and calpain-2, all playing major role in the pathogenesis of the disease. This study provides insight into the global EV proteome of S. aureus and P. aeruginosa endophthalmitis with their functional correlation and distinctive pattern of expression. Calpain-2 and C8a are attractive biomarkers for bacterial endophthalmitis.

UV-LED irradiation reduces the infectivity of herpes simplex virus type 1 by targeting different viral components depending on the peak wavelength

Herpes simplex virus type 1 (HSV-1) is an enveloped virus that mainly infects humans. Given its high global prevalence, disinfection is critical for reducing the risk of infection. Ultraviolet-light-emitting diodes (UV-LEDs) are eco-friendly irradiating modules with different peak wavelengths, but the molecules degraded by UV-LED irradiation have not been clarified. To identify the target viral molecules of UV-LEDs, we exposed HSV-1 suspensions to UV-LED irradiation at wavelengths of 260-, 280-, 310-, and 365-nm and measured viral DNA, protein, and lipid damage and infectivity in host cells. All UV-LEDs substantially reduced by inhibiting host cell transcription, but 260- and 280-nm UV-LEDs had significantly stronger virucidal efficiency than 310- and 365-nm UV-LEDs. Meanwhile, 260- and 280-nm UV-LEDs induced the formation of viral DNA photoproducts and the degradation of viral proteins and some phosphoglycerolipid species. Unlike 260- and 280-nm UV-LEDs, 310- and 365-nm UV-LEDs decreased the viral protein levels, but they did not drastically change the levels of viral DNA photoproducts and lipophilic metabolites. These results suggest that UV-LEDs reduce the infectivity of HSV-1 by targeting different viral molecules based on the peak wavelength. These findings could facilitate the optimization of UV-LED irradiation for viral inactivation.

Helicobacter pylori binds human Annexins via Lipopolysaccharide to interfere with Toll-like Receptor 4 signaling

Helicobacter pylori colonizes half of the global population and causes gastritis, peptic ulcer disease or gastric cancer. In this study, we were interested in human annexin (ANX), which comprises a protein family with diverse and partly unknown physiological functions, but with a potential role in microbial infections and possible involvement in gastric cancer. We demonstrate here for the first time that H. pylori is able to specifically bind ANXs. Binding studies with purified H. pylori LPS and specific H. pylori LPS mutant strains indicated binding of ANXA5 to lipid A, which was dependent on the lipid A phosphorylation status. Remarkably, ANXA5 binding almost completely inhibited LPS-mediated Toll-like receptor 4- (TLR4) signaling in a TLR4-specific reporter cell line. Furthermore, the interaction is relevant for gastric colonization, as a mouse-adapted H. pylori increased its ANXA5 binding capacity after gastric passage and its ANXA5 incubation in vitro interfered with TLR4 signaling. Moreover, both ANXA2 and ANXA5 levels were upregulated in H. pylori-infected human gastric tissue, and H. pylori can be found in close association with ANXs in the human stomach. Furthermore, an inhibitory effect of ANXA5 binding for CagA translocation could be confirmed. Taken together, our results highlight an adaptive ability of H. pylori to interact with the host cell factor ANX potentially dampening innate immune recognition.

H. pylori is very well adapted to its natural habitat, the human gastric mucosa. For this purpose, the bacterium has evolved a number of highly specific virulence factors, such as the cag-type IV secretion system, vacuolating cytotoxin A (VacA) or secreted gamma-glutamyl transpeptidase. An important function of these bacterial factors is to manipulate the host immune response to enable a chronic H. pylori infection. The present work identifies a new player in this process. Here, we have discovered that H. pylori, as well as several other bacterial species, can bind human annexins (ANX), suggesting a more widespread phenomenon. We show that H. pylori specifically binds ANXA5 via lipid A. The interaction is strictly dependent on calcium and modulated by the phosphorylation status of lipid A. Notably, ANXA5 binding strongly inhibits LPS-mediated Toll-like receptor 4 (TLR4) signal transduction, suggesting that H. pylori exploits ANXs binding to avoid its recognition by this important receptor of the innate immune system. The study thus provides novel molecular and mechanistic insights into a further strategy of H. pylori to successfully evade recognition by the host.

Roles of Glycans and Non-glycans on the Epithelium and in the Immune System in H1-H18 Influenza A Virus Infections

The large variation of influenza A viruses (IAVs) in various susceptible hosts and their rapid evolution, which allows host/tissue switching, host immune escape, vaccine escape, and drug resistance, are difficult challenges for influenza control in all countries worldwide. Access and binding of the IAV to actual receptors at endocytic sites is critical for the establishment of influenza infection. In this chapter, the progress in identification of and roles of glycans and non-glycans on the epithelium and in the immune system in H1-H18 IAV infections are reviewed. The first part of the review is on current knowledge of H1-H16 IAV receptors on the epithelium including sialyl glycans, other negatively charged glycans, and annexins. The second part of the review focuses on H1-H16 IAV receptors in the immune system including acidic surfactant phospholipids, Sia on surfactant proteins, the carbohydrate recognition domain (CRD) of surfactant proteins, Sia on mucins, Sia and C-type lectins on macrophages and dendritic cells, and Sia on NK cells. The third part of the review is about a possible H17-H18 IAV receptor. Binding of these receptors to IAVs may result in inhibition or enhancement of IAV infection depending on their location, host cell type, and IAV strain. Among these receptors, host sialyl glycans are key determinants of viral hemagglutinin (HA) lectins for H1-H16 infections. HA must acquire mutations to bind to sialyl glycans that are dominant on a new target tissue when switching to a new host for efficient transmission and to bind to long sialyl glycans found in the case of seasonal HAs with multiple glycosylation sites as a consequence of immune evasion. Although sialyl receptors/C-type lectins on immune cells are decoy receptors/pathogen recognition receptors for capturing viral HA lectin/glycans protecting HA antigenic sites, some IAV strains do not escape, such as by release with neuraminidase, but hijack these molecules to gain entry and replication in immune cells. An understanding of the virus-host battle tactics at the receptor level might lead to the establishment of novel strategies for effective control of influenza.

CMAS and ST3GAL4 Play an Important Role in the Adsorption of Influenza Virus by Affecting the Synthesis of Sialic Acid Receptors

Influenza A viruses (IAVs) initiate infection by attaching Hemagglutinin (HA) on the viral envelope to sialic acid (SA) receptors on the cell surface. Importantly, HA of human IAVs has a higher affinity for α-2,6-linked SA receptors, and avian strains prefer α-2,3-linked SA receptors, whereas swine strains have a strong affinity for both SA receptors. Host gene CMAS and ST3GAL4 were found to be essential for IAV attachment and entry. Loss of CMAS and ST3GAL4 hindered the synthesis of sialic acid receptors, which in turn prevented the adsorption of IAV. Further, the knockout of CMAS had an effect on the adsorption of swine, avian and human IAVs. However, ST3GAL4 knockout prevented the adsorption of swine and avian IAV and the impact on avian IAV was more distinct, whereas it had no effect on the adsorption of human IAV. Collectively, our findings demonstrate that knocking out CMAS and ST3GAL4 negatively regulated IAV replication by inhibiting the synthesis of SA receptors, which also provides new insights into the production of gene-edited animals in the future.

Influenza-Host Interplay and Strategies for Universal Vaccine Development

Influenza is an annual epidemic and an occasional pandemic caused by pathogens that are responsible for infectious respiratory disease. Humans are highly susceptible to the infection mediated by influenza A viruses (IAV). The entry of the virus is mediated by the influenza virus hemagglutinin (HA) glycoprotein that binds to the cellular sialic acid receptors and facilitates the fusion of the viral membrane with the endosomal membrane. During IAV infection, virus-derived pathogen-associated molecular patterns (PAMPs) are recognized by host intracellular specific sensors including toll-like receptors (TLRs), C-type lectin receptors, retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs), and nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) either on the cell surface or intracellularly in endosomes. Herein, we comprehensively review the current knowledge available on the entry of the influenza virus into host cells and the molecular details of the influenza virus–host interface. We also highlight certain strategies for the development of universal influenza vaccines.

Role of Post-translational Modifications in Influenza A Virus Life Cycle and Host Innate Immune Response

Throughout various stages of its life cycle, influenza A virus relies heavily on host cellular machinery, including the post-translational modifications (PTMs) system. During infection, influenza virus interacts extensively with the cellular PTMs system to aid in its successful infection and dissemination. The complex interplay between viruses and the PTMs system induces global changes in PTMs of the host proteome as well as modifications of specific host or viral proteins. The most common PTMs include phosphorylation, ubiquitination, SUMOylation, acetylation, methylation, NEDDylation, and glycosylation. Many PTMs directly support influenza virus infection, whereas others contribute to modulating antiviral responses. In this review, we describe current knowledge regarding the role of PTMs in different stages of the influenza virus replication cycle. We also discuss the concerted role of PTMs in antagonizing host antiviral responses, with an emphasis on their impact on viral pathogenicity and host range.

Annexins in Influenza Virus Replication and Pathogenesis

Influenza A viruses (IAVs) are important human respiratory pathogens which cause seasonal or periodic endemic infections. IAV can result in severe or fatal clinical complications including pneumonia and respiratory distress syndrome. Treatment of IAV infections is complicated because the virus can evade host immunity through antigenic drifts and antigenic shifts, to establish infections making new treatment options desirable. Annexins (ANXs) are a family of calcium and phospholipid binding proteins with immunomodulatory roles in viral infections, lung injury, and inflammation. A current understanding of the role of ANXs in modulating IAV infection and host responses will enable the future development of more effective antiviral therapies. This review presents a comprehensive understanding of the advances made in the field of ANXs, in particular, ANXA1 and IAV research and highlights the importance of ANXs as a suitable target for IAV therapy.

The Annexin A1 Receptor FPR2 Regulates the Endosomal Export of Influenza Virus

The Formyl Peptide Receptor 2 (FPR2) is a novel promising target for the treatment of influenza. During viral infection, FPR2 is activated by annexinA1, which is present in the envelope of influenza viruses; this activation promotes virus replication. Here, we investigated whether blockage of FPR2 would affect the genome trafficking of influenza virus. We found that, upon infection and cell treatment with the specific FPR2 antagonist WRW4 or the anti-FPR2 monoclonal antibody, FN-1D6-AI, influenza viruses were blocked into endosomes. This effect was independent on the strain and was observed for H1N1 and H3N2 viruses. In addition, blocking FPR2signaling in alveolar lung A549 epithelial cells with the monoclonal anti-FPR2 antibody significantly inhibited virus replication. Altogether, these results show that FPR2signaling interferes with the endosomal trafficking of influenza viruses and provides, for the first time, the proof of concept that monoclonal antibodies directed against FPR2 inhibit virus replication. Antibodies-based therapeutics have emerged as attractive reagents in infectious diseases. Thus, this study suggests that the use of anti-FPR2 antibodies against influenza hold great promise for the future.

Emerging functions as host cell factors - an encyclopedia of annexin-pathogen interactions

Emerging infectious diseases and drug-resistant infectious agents call for the development of innovative antimicrobial strategies. With pathogenicity now considered to arise from the complex and bi-directional interplay between a microbe and the host, host cell factor targeting has emerged as a promising approach that might overcome the limitations of classical antimicrobial drug development and could open up novel and efficient therapeutic strategies. Interaction with and modulation of host cell membranes is a recurrent theme in the host-microbe relationship. In this review, we provide an overview of what is currently known about the role of the Ca2+ dependent, membrane-binding annexin protein family in pathogen-host interactions, and discuss their emerging functions as host cell derived auxiliary proteins in microbe-host interactions and host cell targets.

Influenza A virus enhances its propagation through the modulation of Annexin-A1 dependent endosomal trafficking and apoptosis

The influenza virus infects millions of people each year and can result in severe complications. Understanding virus recognition and host responses to influenza infection will enable future development of more effective anti-viral therapies. Previous research has revealed diverse yet important roles for the annexin family of proteins in modulating the course of influenza A virus (IAV) infection. However, the role of Annexin-A1 (ANXA1) in IAV infection has not been addressed. Here, we show that ANXA1 deficient mice exhibit a survival advantage, and lower viral titers after infection. This was accompanied with enhanced inflammatory cell infiltration during IAV infection. ANXA1 expression is increased during influenza infection clinically, in vivo and in vitro. The presence of ANXA1 enhances viral replication, influences virus binding, and enhances endosomal trafficking of the virus to the nucleus. ANXA1 colocalizes with early and late endosomes near the nucleus, and enhances nuclear accumulation of viral nucleoprotein. In addition, ANXA1 enhances IAV-mediated apoptosis. Overall, our study demonstrates that ANXA1 plays an important role in influenza virus replication and propagation through various mechanisms and that we predict that the regulation of ANXA1 expression during IAV infection may be a viral strategy to enhance its infectivity.

DAMPs and influenza virus infection in ageing

Influenza A virus (IAV) is a serious global health problem worldwide due to frequent and severe outbreaks. IAV causes significant morbidity and mortality in the elderly population, due to the ineffectiveness of the vaccine and the alteration of T cell immunity with ageing. The cellular and molecular link between ageing and virus infection is unclear and it is possible that damage associated molecular patterns (DAMPs) may play a role in the raised severity and susceptibility of virus infections in the elderly. DAMPs which are released from damaged cells following activation, injury or cell death can activate the immune response through the stimulation of the inflammasome through several types of receptors found on the plasma membrane, inside endosomes after endocytosis as well as in the cytosol. In this review, the detriment in the immune system during ageing and the links between influenza virus infection and ageing will be discussed. In addition, the role of DAMPs such as HMGB1 and S100/Annexin in ageing, and the enhanced morbidity and mortality to severe influenza infection in ageing will be highlighted.

Lipid composition of viral envelope of three strains of influenza virus - not all viruses are created equal

While differences in the rate of virus fusion and budding from the host cell membrane have been correlated with pathogenicity, no systematic study of the contribution of differences in viral envelope composition has previously been attempted. Using rigorous virus purification, marked differences between virions and host were observed. Over 125 phospholipid species have been quantitated for three strains of influenza (HKx31- H3N2, PR8- H1N1, and VN1203- H5N1) grown in eggs. The glycerophospholipid composition of purified virions differs from that of the host or that of typical mammalian cells. Phosphatidylcholine is the major component in most mammalian cell membranes, while in purified virions phosphatidylethanolamine dominates. Due to its effects on membrane curvature, it is likely that the variations in its content are important to viral processing during infection. This integrated method of virion isolation with systematic analysis of glycerophospholipids provides a tool for the assessment of species specific biomarkers of viral pathogenicity.

Annexin V incorporated into influenza virus particles inhibits gamma interferon signaling and promotes viral replication

During the budding process, influenza A viruses (IAVs) incorporate multiple host cell membrane proteins. However, for most of them, their significance in viral morphogenesis and infectivity remains unknown. We demonstrate here that the expression of annexin V (A5) is upregulated at the cell surface upon IAV infection and that a substantial proportion of the protein is present in lipid rafts, the site of virus budding. Western blotting and immunogold analysis of highly purified IAV particles showed the presence of A5 in the virion. Significantly, gamma interferon (IFN-γ)-induced Stat phosphorylation and IFN-γ-induced 10-kDa protein (IP-10) production in macrophage-derived THP-1 cells was inhibited by purified IAV particles. Disruption of the IFN-γ signaling pathway was A5 dependent since downregulation of its expression or its blockage reversed the inhibition and resulted in decreased viral replication in vitro. The functional significance of these results was also observed in vivo. Thus, IAVs can subvert the IFN-γ antiviral immune response by incorporating A5 into their envelope during the budding process.

IMPORTANCE

Many enveloped viruses, including influenza A viruses, bud from the plasma membrane of their host cells and incorporate cellular surface proteins into viral particles. However, for the vast majority of these proteins, only the observation of their incorporation has been reported. We demonstrate here that the host protein annexin V is specifically incorporated into influenza virus particles during the budding process. Importantly, we showed that packaged annexin V counteracted the antiviral activity of gamma interferon in vitro and in vivo. Thus, these results showed that annexin V incorporated in the viral envelope of influenza viruses allow viral escape from immune surveillance. Understanding the role of host incorporated protein into virions may reveal how enveloped RNA viruses hijack the host cell machinery for their own purposes.

Entry of influenza A virus: host factors and antiviral targets

Influenza virus is a major human pathogen that causes annual epidemics and occasional pandemics. Moreover, the virus causes outbreaks in poultry and other animals, such as pigs, requiring costly and laborious countermeasures. Therefore, influenza virus has a substantial impact on health and the global economy. Here, we review entry of this important pathogen into target cells, an essential process by which viral genomes are delivered from extracellular virions to sites of transcription/replication in the cell nucleus. We summarize current knowledge on the interaction of influenza viruses with their receptor, sialic acid, and highlight the ongoing search for additional receptors. We describe receptor-mediated endocytosis and the recently discovered macropinocytosis as alternative virus uptake pathways, and illustrate the subsequent endosomal trafficking of the virus with advanced live microscopy techniques. Release of virus from the endosome and import of the viral ribonucleoproteins into the host cell nucleus are also outlined. Although a focus has been on viral protein function during entry, recent studies have revealed exciting information on cellular factors required for influenza virus entry. We highlight these, and discuss established entry inhibitors targeting viral and host factors, as well as the latest prospects for designing novel 'anti-entry' compounds. New entry inhibitors are of particular importance for current efforts to develop the next generation of anti-influenza drugs - entry is the first essential step of virus replication and is an ideal target to block infection efficiently.

Antigen-specific B-cell receptor sensitizes B cells to infection by influenza virus

Influenza A virus-specific B lymphocytes and the antibodies they produce protect against infection. However, the outcome of interactions between an influenza haemagglutinin-specific B cell via its receptor (BCR) and virus is unclear. Through somatic cell nuclear transfer we generated mice that harbour B cells with a BCR specific for the haemagglutinin of influenza A/WSN/33 virus (FluBI mice). Their B cells secrete an immunoglobulin gamma 2b that neutralizes infectious virus. Whereas B cells from FluBI and control mice bind equivalent amounts of virus through interaction of haemagglutinin with surface-disposed sialic acids, the A/WSN/33 virus infects only the haemagglutinin-specific B cells. Mere binding of virus is not sufficient for infection of B cells: this requires interactions of the BCR with haemagglutinin, causing both disruption of antibody secretion and FluBI B-cell death within 18 h. In mice infected with A/WSN/33, lung-resident FluBI B cells are infected by the virus, thus delaying the onset of protective antibody release into the lungs, whereas FluBI cells in the draining lymph node are not infected and proliferate. We propose that influenza targets and kills influenza-specific B cells in the lung, thus allowing the virus to gain purchase before the initiation of an effective adaptive response.

Chimeric adenoviral vector Ad5F35L containing the Ad5 natural long-shaft exhibits efficient gene transfer into human T lymphocytes

Adoptive therapy using T cells modified with tumour antigen-specific T cell receptor (TCR) genes has become a popular area of research in tumour biotherapy research. However, the efficiency of this treatment is low. To increase the efficiency of this therapy, the antigen specific TCR expression in the T cells needs to be improved. Adenoviral vector-mediated gene expression is an attractive approach to bypass the issue of TCR gene modification. The efficiency of adenovirus vector serotype 5 (Ad5) infection is low due to the absence of coxsackievirus B-adenovirus receptor (CAR) expression in T cells. In the present study, a chimeric adenoviral vector (Ad5F35L) was generated; this construct contained both the natural long-shaft of Ad5 and the Ad35 knob. A transduction study showed that the Ad5F35L vector exhibited a higher transduction efficiency in human primary T lymphocytes than the Ad5 vector and the Ad5F35S vector, which contained the Ad35 natural short-shaft and the Ad35 knob. Similar transduction efficiencies were observed for both CD4(+) T lymphocytes and CD8(+) T lymphocytes and the transfection was independent of the expression of cell surface receptors. The activation of T lymphocytes resulted in an improvement of the Ad5F35L transduction efficiency in CD4(+) T cells and a decrease in Ad5F35L transduction efficiency in CD8(+) T cells. The results demonstrate that Ad5F35L is a promising viral vector and will facilitate the clinical application of tumour antigen-specific TCR gene therapy.

Annexin-phospholipid interactions. Functional implications

Annexins constitute an evolutionary conserved multigene protein superfamily characterized by their ability to interact with biological membranes in a calcium dependent manner. They are expressed by all living organisms with the exception of certain unicellular organisms. The vertebrate annexin core is composed of four (eight in annexin A6) homologous domains of around 70 amino acids, with the overall shape of a slightly bent ring surrounding a central hydrophilic pore. Calcium- and phospholipid-binding sites are located on the convex side while the N-terminus links domains I and IV on the concave side. The N-terminus region shows great variability in length and amino acid sequence and it greatly influences protein stability and specific functions of annexins. These proteins interact mainly with acidic phospholipids, such as phosphatidylserine, but differences are found regarding their affinity for lipids and calcium requirements for the interaction. Annexins are involved in a wide range of intra- and extracellular biological processes in vitro, most of them directly related with the conserved ability to bind to phospholipid bilayers: membrane trafficking, membrane-cytoskeleton anchorage, ion channel activity and regulation, as well as antiinflammatory and anticoagulant activities. However, the in vivo physiological functions of annexins are just beginning to be established.

An overview of influenza A virus receptors

Influenza A viruses are spherical particles that attach to cells through bonds between hemagglutinin and specific cellular receptors. Numerous studies performed have recently revealed that Sialic acid (SA) is a crucial component of influenza A virus receptors. This brief review summarizes recent advances in our understanding of influenza A virus receptors. The introduction describes the classification of influenza A virus receptors and the review continues with a survey of the distribution of SA in different tissue and host. This is followed by research applications of influenza A virus receptors, and explanation of why receptor studies are so important on a world-wide scale.

Proteomic analysis of chicken embryonic trachea and kidney tissues after infection in ovo by avian infectious bronchitis coronavirus

Background

Avian infectious bronchitis (IB) is one of the most serious diseases of economic importance in chickens; it is caused by the avian infectious coronavirus (IBV). Information remains limited about the comparative protein expression profiles of chicken embryonic tissues in response to IBV infection in ovo. In this study, we analyzed the changes of protein expression in trachea and kidney tissues from chicken embryos, following IBV infection in ovo, using two-dimensional gel electrophoresis (2-DE) coupled with matrix-assisted laser desorption/ionization time-of-flight tandem mass spectrometry (MALDI-TOF-TOF MS).

Results

17 differentially expressed proteins from tracheal tissues and 19 differentially expressed proteins from kidney tissues were identified. These proteins mostly related to the cytoskeleton, binding of calcium ions, the stress response, anti-oxidative, and macromolecular metabolism. Some of these altered proteins were confirmed further at the mRNA level using real-time RT-PCR. Moreover, western blotting analysis further confirmed the changes of annexin A5 and HSPB1 during IBV infection.

Conclusions

To the best of our knowledge, we have performed the first analysis of the proteomic changes in chicken embryonic trachea and kidney tissues during IBV infection in ovo. The data obtained should facilitate a better understanding of the pathogenesis of IBV infection.

Implications for lipids during replication of enveloped viruses

Enveloped viruses, which include many medically important viruses such as human immunodeficiency virus, influenza virus and hepatitis C virus, are intracellular parasites that acquire lipid envelopes from their host cells. Success of replication is intimately linked to their ability to hijack host cell mechanisms, particularly those related to membrane dynamics and lipid metabolism. Despite recent progress, our knowledge of lipid mediated virus-host interactions remains highly incomplete. In addition, diverse experimental systems are used to study different stages of virus replication thus complicating comparisons. This review aims to present a unifying view of the widely diverse strategies used by enveloped viruses at distinct stages of their replication cycles.

Targeting inside-out phosphatidylserine as a therapeutic strategy for viral diseases

Targeting exposed anionic phospholipids on a spectrum of virus-infected cells can protect against lethal virus infections in vivo.

Bisecting GlcNAc mediates the binding of annexin V to Hsp47

The bisecting N-acetylglucosamine (GlcNAc) structure, formed through catalysis by UDP-N-acetylglucosamine : beta-D-mannoside beta-1,4-N-acetylglucosaminyltansferase III (GnT-III), is responsible for a variety of biological functions. We have previously shown that annexin V, a member of the calcium/phospholipid-binding annexin family of proteins, has binding activity toward the bisecting GlcNAc structure. In this study, we reported on a search for potential target glycoproteins for annexin V in a rat hepatoma cell line, M31. Using a glutathione S-transferase (GST)-annexin V immobilized sepharose 4B affinity column to trap interacting proteins produced by the GnT-III-transfected M31 cells, we isolated a 47 kDa protein. It was identified as Hsp47 by an N-terminal sequence analysis. Immunoprecipitation experiments showed that annexin V interacted with Hsp47. The association of annexin V and Hsp47 was abolished by treatment with N-glycosidase F or preincubation with sugar chains containing bisecting GlcNAc, suggesting that the bisecting GlcNAc plays an important role in the interaction. An oligosaccharide analysis of Hsp47 purified from GnT-III-transfected M31 cells was shown to have the bisecting GlcNAc structure, as detected by erythroagglutinating phytohemagglutinin (E4-PHA) and matrix assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry (MS) analysis. Surface plasmon resonance analysis showed that annexin V was bound to Hsp47, bearing a bisecting GlcNAc with a Kd of 5.5 microM, whereas no significant binding was observed in the case of Hsp47 without a bisecting GlcNAc. In addition, immunofluorescence microscopy revealed the colocalization of annexin V, Hsp47, and a bisecting GlcNAc sugar chain around the Golgi apparatus. Collectively, these results suggest that the binding of annexin V to Hsp47 is mediated by a bisecting GlcNAc oligosaccharide structure and that Hsp47 is an intracellular ligand glycoprotein for annexin V.

Phosphatidylserine on HIV envelope is a cofactor for infection of monocytic cells

HIV-1 is an enveloped retrovirus that acquires its outer membrane as the virion exits the cell. Because of the association of apoptosis with the progression of AIDS, HIV-1-infected T cells or macrophages might be expected to express elevated levels of surface phosphatidylserine (PS), a hallmark of programmed cell death. Virions produced by these cells would also be predicted to have PS on the surface of their envelopes. In this study, data are presented that support this hypothesis and suggest that PS is required for macrophage infection. The PS-specific protein annexin V was used to enrich for virus particles and to inhibit HIV-1 replication in primary macrophages, but not T cells. HIV-1 replication was also significantly inhibited with vesicles consisting of PS, but not phosphatidylcholine. PS is specifically required for HIV-1 infection because viruses pseudotyped with vesicular stomatitis virus G and amphotropic murine leukemia virus envelopes were not inhibited by PS vesicles or annexin V. These data indicate that PS is an important cofactor for HIV-1 infection of macrophages.

Heparin-protein interactions

Heparin, a sulfated polysaccharide belonging to the family of glycosaminoglycans, has numerous important biological activities, associated with its interaction with diverse proteins. Heparin is widely used as an anticoagulant drug based on its ability to accelerate the rate at which antithrombin inhibits serine proteases in the blood coagulation cascade. Heparin and the structurally related heparan sulfate are complex linear polymers comprised of a mixture of chains of different length, having variable sequences. Heparan sulfate is ubiquitously distributed on the surfaces of animal cells and in the extracellular matrix. It also mediates various physiologic and pathophysiologic processes. Difficulties in evaluating the role of heparin and heparan sulfate in vivo may be partly ascribed to ignorance of the detailed structure and sequence of these polysaccharides. In addition, the understanding of carbohydrate-protein interactions has lagged behind that of the more thoroughly studied protein-protein and protein-nucleic acid interactions. The recent extensive studies on the structural, kinetic, and thermodynamic aspects of the protein binding of heparin and heparan sulfate have led to an improved understanding of heparin-protein interactions. A high degree of specificity could be identified in many of these interactions. An understanding of these interactions at the molecular level is of fundamental importance in the design of new highly specific therapeutic agents. This review focuses on aspects of heparin structure and conformation, which are important for its interactions with proteins. It also describes the interaction of heparin and heparan sulfate with selected families of heparin-binding proteins.

Biophysical and molecular properties of annexin-formed channels

The annexins are water soluble proteins possessing a hydrophilic surface, which belong to a family of proteins which (a) bind ('annex') both calcium and phospholipids, and (b) form voltage-dependent calcium channels within planar lipid bilayers. Annexins types are diverse (94 annexins in 45 species) and they belong to an enormous multigene family that ranges throughout all eukaryotic kingdoms. Although the structure of these proteins is now well known their functional and physiological roles remain largely unknown and circumstantial. Various experimental approaches provided evidence that annexins function as Ca(2+) channels that could act as regulators of membrane fusion. The identity of annexins is derived from the conserved 34 kDa C-terminal domain which comprises four repeats - except for annexin VI, with eight repeats - of a sequence of approximately seventy amino acids, which holds the area known as the 'endonexin fold', with its identifying GXGTDE. Annexins have been placed into three subgroups of (1) tetrad core and short amino terminal, (2) tetrad core and long amino terminal, and (3) octad core and short amino terminal. The repeats are highly conserved, each forming a compact alpha-helical domain comprising five alpha-helices wound in a right-handed superhelix. Four domains are formed, arranged in a nearly flat and cyclical array, with domains I and IV, and II and III respectively forming two tightly organised modules with almost twofold symmetry. A hydrophilic pore lies at the centre of the molecule, forming a prominent ion channel coated with charged and highly conserved residues. The annexin molecule is slightly curved, with both a convex and a concave face. The cation/anion permeability ratios and the selectivity sequence of the ion channels formed by several annexins confirm the selectivity of the annexins for Ca(2+) over other divalent cations, and reveals the importance of structural sites, e.g. amino acid positions 17, 78, 95 and 112 for the identification of the ion channel's position, function and regulation. Some are sensitive to low doses of the phenothiazine drugs, trifluoperazine (an anti-schizophrenia drug) and promethazine (anti nausea drug) La(3+) and Cd(2+), (blockers of voltage-gated Ca(2+) channels) nifedipine (an inhibitor of non-activating Ca(2+) channels). There are two main competing models used to explain in vitro ion channel activity of annexins: one involves changes in the conductance of ion via electrostatic disturbance of the membrane surface; the other involves a much more extensive alteration in protein structure and a correspondingly deeper penetration into the membrane.

Interaction of heparin with annexin V

The energetics and kinetics of the interaction of heparin with the Ca2+ and phospholipid binding protein annexin V, was examined and the minimum oligosaccharide sequence within heparin that binds annexin V was identified. Affinity chromatography studies confirmed the Ca2+ dependence of this binding interaction. Analysis of the data obtained from surface plasmon resonance afforded a Kd of approximately 21 nM for the interaction of annexin V with end-chain immobilized heparin and a Kd of approximately 49 nM for the interaction with end-chain immobilized heparan sulfate. Isothermal titration calorimetry showed the minimum annexin V binding oligosaccharide sequence within heparin corresponds to an octasaccharide sequence. The Kd of a heparin octasaccharide binding to annexin V was approximately 1 microM with a binding stoichiometry of 1:1.

Transfection of a rat hepatoma cell line with a construct expressing human liver annexin V confers susceptibility to hepatitis B virus infection

Previously, we have found that human liver annexin V (hA-V; in earlier reports referred as Endonexin II) is a specific hepatitis B surface antigen (HBsAg) binding protein. In this study, we demonstrate that transfection of rat hepatoma FTO 2B cells, a cell line that is not infectable by hepatitis B virus (HBV) and does not express hA-V, with a construct containing the hA-V gene, resulted in hA-V expressing cells susceptible to HBV infection. After in vitro infection, transfected FTO cells (assigned as FTO 9.1 cells) expressing hA-V in cultures were shown to contain HBV-precore/core, X mRNAs, and covalently closed circular (ccc) DNA as detected by polymerase chain reaction (PCR). The presence of HBV ccc and replicative intermediate DNA was also demonstrated by Southern blot hybridization assay. HBV DNA secreted in the culture medium was also evident as determined by quantitative branched DNA (bDNA) assay. HBsAg and hepatitis B core antigen (HBcAg) could also be detected by an immunocytochemical method in 10% to 15% of the cells at day 3 and day 5 after infection. Infectivity of in vitro-propagated HBV was demonstrated by infection of the naive FTO 9.1 cells with the culture supernatant from HBV-carrier cultures. In contrast to primary cultures of human hepatocytes and FTO 9.1 cells, primary rat and mouse hepatocytes, as well as rat hepatoma cell lines that do not express hA-V, are not susceptible to HBV infection. These findings suggest that hA-V plays a key role in the initial step of HBV infection and that the species-specific susceptibility to HBV infection and replication in hepatocytes is associated with the expression of hA-V.

Animal virus receptors

The term 'receptor' is generally accepted as the cell-surface component that participates in virus binding and facilitates subsequent viral infection. Recent advances in technology have permitted the identification of several virus receptors, increasing our understanding of the significance of this initial virus-cell and virus-host interaction. Virus binding was previously considered to involve simple recognition and attachment to a single cell surface molecule by virus attachment proteins. The classical concept of these as single entities that participate in a lock-and-key-type process has been superseded by new data indicating that binding can be a multistep process, often involving different virus-attachment proteins and more than one host-cell receptor.