Virus entry into a polarized epithelial cell line (MDCK): similarities and dissimilarities between influenza C virus and bovine coronavirus

9-O Acetylated Gangliosides in Health and Disease

Glycosphingolipids comprise a lipid class characterized by the presence of sugar moieties attached to a ceramide backbone. The role of glycosphingolipids in pathophysiology has gained relevance in recent years in parallel with the development of analytical technologies. Within this vast family of molecules, gangliosides modified by acetylation represent a minority. Described for the first time in the 1980s, their relation to pathologies has resulted in increased interest in their function in normal and diseased cells. This review presents the state of the art on 9-O acetylated gangliosides and their link to cellular disorders.

Dengue virus enters and exits epithelial cells through both apical and basolateral surfaces and perturbs the apical junctional complex

Dengue is the most relevant mosquito-borne viral disease in the world. It has been estimated that 390 million infections of dengue occur each year. Dengue virus (DENV) infection can be asymptomatic or can produce a self-limited febrile illness called dengue fever (DF) or a severe form of the infection called severe dengue. In some viruses, the entry and egress from cells, occur in a specific domain of polarized endothelial and epithelial cells. In this study, we investigated whether the entry and release of DENV was polarized in epithelial cells, and evaluated the effect of DENV infection on cellular junctions of epithelial cells. We used MDCK epithelial cells, which serve as an excellent model to study a functional barrier due to the presence of an apical junctional complex (AJC), and showed that entry and release of DENV from the cells, is bipolar. Additionally, we performed paracellular flux, diffusion of membrane lipid, immunofluorescence and immunoblotting assays to evaluate the integrity of the AJC during DENV infection. We observed that at later stages of infection, DENV altered the barrier function causing a decrease in the transepithelial electrical resistance and the degradation and delocalization of TJ and AJ proteins. The present study contributes to understand how DENV traverse epithelia in order to cause a productive infection, and provides insights into the mechanism of DENV pathogenesis.

Upsetting the Balance: When Viruses Manipulate Cell Polarity Control

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

Coronavirus entry and release in polarized epithelial cells: a review

Most coronaviruses cause respiratory or intestinal infections in their animal or human host. Hence, their interaction with polarized epithelial cells plays a critical role in the onset and outcome of infection. In this paper, we review the knowledge regarding the entry and release of coronaviruses, with particular emphasis on the severe acute respiratory syndrome and Middle East respiratory syndrome coronaviruses. As these viruses approach the epithelial surfaces from the apical side, it is not surprising that coronavirus cell receptors are exposed primarily on the apical domain of polarized epithelial cells. With respect to release, all possibilities appear to occur. Thus, most coronaviruses exit through the apical surface, several through the basolateral one, although the Middle East respiratory syndrome coronavirus appears to use both sides. These observations help us understand the local or systematic spread of the infection within its host as well as the spread of the virus within the host population. Copyright © 2014 John Wiley & Sons, Ltd.

Differential sensitivity of bat cells to infection by enveloped RNA viruses: coronaviruses, paramyxoviruses, filoviruses, and influenza viruses

Bats (Chiroptera) host major human pathogenic viruses including corona-, paramyxo, rhabdo- and filoviruses. We analyzed six different cell lines from either Yinpterochiroptera (including African flying foxes and a rhinolophid bat) or Yangochiroptera (genera Carollia and Tadarida) for susceptibility to infection by different enveloped RNA viruses. None of the cells were sensitive to infection by transmissible gastroenteritis virus (TGEV), a porcine coronavirus, or to infection mediated by the Spike (S) protein of SARS-coronavirus (SARS-CoV) incorporated into pseudotypes based on vesicular stomatitis virus (VSV). The resistance to infection was overcome if cells were transfected to express the respective cellular receptor, porcine aminopeptidase N for TGEV or angiotensin-converting enzyme 2 for SARS-CoV. VSV pseudotypes containing the S proteins of two bat SARS-related CoV (Bg08 and Rp3) were unable to infect any of the six tested bat cell lines. By contrast, viral pseudotypes containing the surface protein GP of Marburg virus from the family Filoviridae infected all six cell lines though at different efficiency. Notably, all cells were sensitive to infection by two paramyxoviruses (Sendai virus and bovine respiratory syncytial virus) and three influenza viruses from different subtypes. These results indicate that bat cells are more resistant to infection by coronaviruses than to infection by paramyxoviruses, filoviruses and influenza viruses. Furthermore, these results show a receptor-dependent restriction of the infection of bat cells by CoV. The implications for the isolation of coronaviruses from bats are discussed.

Sialic Acid Receptors of Viruses

Sialic acid linked to glycoproteins and gangliosides is used by many viruses as a receptor for cell entry. These viruses include important human and animal pathogens, such as influenza, parainfluenza, mumps, corona, noro, rota, and DNA tumor viruses. Attachment to sialic acid is mediated by receptor binding proteins that are constituents of viral envelopes or exposed at the surface of non-enveloped viruses. Some of these viruses are also equipped with a neuraminidase or a sialyl-O-acetyl-esterase. These receptor-destroying enzymes promote virus release from infected cells and neutralize sialic acid-containing soluble proteins interfering with cell surface binding of the virus. Variations in the receptor specificity are important determinants for host range, tissue tropism, pathogenicity, and transmissibility of these viruses.

Sialic acids as receptor determinants for coronaviruses

Among coronaviruses, several members are able to interact with sialic acids. For bovine coronavirus (BCoV) and related viruses, binding to cell surface components containing N-acetyl-9- O-acetylneuraminic acid is essential for initiation of an infection. These viruses resemble influenza C viruses because they share not only the receptor determinant, but also the presence of an acetylesterase that releases the 9- O-acetyl group from sialic acid and thus abolishes the ability of the respective sialoglycoconjugate to function as a receptor for BCoV. As in the case of influenza viruses, the receptor-destroying enzyme of BCoV is believed to facilitate the spread of virus infection by removing receptor determinants from the surface of infected cells and by preventing the formation of virus aggregates. Another coronavirus, porcine transmissible gastroenteritis virus (TGEV) preferentially recognizes N-glycolylneuraminic acid. TGEV does not contain a receptor-destroying enzyme and does not depend on the sialic acid binding activity for infection of cultured cells. However, binding to sialic acids is required for the enteropathogenicity of TGEV. Interaction with sialoglycoconjugates may help the virus to pass through the sialic acid-rich mucus layer that covers the viral target cells in the epithelium of the small intestine. We discuss that the BCoV group of viruses may have evolved from a TGEV-like ancestor by acquiring an acetylesterase gene through heterologous recombination.

Structure, function and evolution of the hemagglutinin-esterase proteins of corona- and toroviruses

Virus attachment to host cells is mediated by dedicated virion proteins, which specifically recognize one or, at most, a limited number of cell surface molecules. Receptor binding often involves protein-protein interactions, but carbohydrates may serve as receptor determinants as well. In fact, many different viruses use members of the sialic acid family either as their main receptor or as an initial attachment factor. Sialic acids (Sias) are 9-carbon negatively-charged monosaccharides commonly occurring as terminal residues of glycoconjugates. They come in a large variety and are differentially expressed in cells and tissues. By targeting specific Sia subtypes, viruses achieve host cell selectivity, but only to a certain extent. The Sia of choice might still be abundantly present on non-cell associated molecules, on non-target cells (including cells already infected) and even on virus particles themselves. This poses a hazard, as high-affinity virion binding to any of such "false'' receptors would result in loss of infectivity. Some enveloped RNA viruses deal with this problem by encoding virion-associated receptor-destroying enzymes (RDEs). These enzymes make the attachment to Sia reversible, thus providing the virus with an escape ticket. RDEs occur in two types: neuraminidases and sialate-O-acetylesterases. The latter, originally discovered in influenza C virus, are also found in certain nidoviruses, namely in group 2 coronaviruses and in toroviruses, as well as in infectious salmon anemia virus, an orthomyxovirus of teleosts. Here, the structure, function and evolution of viral sialate-O-acetylesterases is reviewed with main focus on the hemagglutinin-esterases of nidoviruses.

Basolateral localization of fiber receptors limits adenovirus infection from the apical surface of airway epithelia

Recent identification of two receptors for the adenovirus fiber protein, coxsackie B and adenovirus type 2 and 5 receptor (CAR), and the major histocompatibility complex (MHC) Class I alpha-2 domain allows the molecular basis of adenoviral infection to be investigated. Earlier work has shown that human airway epithelia are resistant to infection by adenovirus. Therefore, we examined the expression and localization of CAR and MHC Class I in an in vitro model of well differentiated, ciliated human airway epithelia. We found that airway epithelia express CAR and MHC Class I. However, neither receptor was present in the apical membrane; instead, both were polarized to the basolateral membrane. These findings explain the relative resistance to adenovirus infection from the apical surface. In contrast, when the virus was applied to the basolateral surface, gene transfer was much more efficient because of an interaction of adenovirus fiber with its receptors. In addition, when the integrity of the tight junctions was transiently disrupted, apically applied adenovirus gained access to the basolateral surface and enhanced gene transfer. These data suggest that the receptors required for efficient infection are not available on the apical surface, and interventions that allow access to the basolateral space where fiber receptors are located increase gene transfer efficiency.

Isolation of hemagglutination-defective mutants for the analysis of the sialic acid binding activity of transmissible gastroenteritis virus

The surface protein S of transmissible gastroenteritis virus (TGEV) has a sialic acid binding activity that enables the virus to agglutinate erythrocytes. A protocol is described that has been successfully applied to the isolation of hemgglutination-defective mutants. The potential of these mutants for the characterization of the sialic acid-binding site and the function of the binding activity is discussed.

The development of the kidney

This chapter describes the earlier stages of development of the vertebrate metanephric kidney. It focuses on the mouse and descriptive morphology is used for considering both molecular mechanisms, underpinning kidney morphogenesis and differentiation, and the ways in which these processes can go awry and lead to congenital kidney disorders—particularly in humans. The mature kidney is a fairly complex organ attached to an arterial input vessel and two output vessels, the vein and the ureter. Inside, the artery and vein are connected by a complex network of capillaries that invade a large number of glomeruli, the proximal entrance to nephrons, which are filtration units that link to an arborized collecting-duct system that drains into the ureter. The ability of the kidney and isolated metanephrogenic mesenchyme, to develop in culture means that the developing tissues can be subjected to a wide variety of experimental procedures designed to investigate their molecular and cellular properties and to test hypotheses about developmental mechanisms.

Molecular characterization of gp40, a mucin-type glycoprotein from the apical plasma membrane of Madin-Darby canine kidney cells (type I)

gp40 has been recently identified as a major apical cell-surface sialoglycoprotein of type-I Madin-Darby canine kidney cells, a cell line widely used for the study of polarized transport. The determination of two internal amino acid sequences of the purified glycoprotein by Edman degradation enabled us to isolated the cDNA encoding the 18.6 kDa protein backbone of gp40. Sequence analysis revealed that gp40 is a type-I membrane protein which has several characteristics in common with glycophorin A and other mucin-type glycoproteins. At least 14 serine/threonine residues were found to be used for O-glycosylation. No potential sites for N-glycosylation were detected. gp40 turned out to represent the canine homologue of a cell-surface antigen expressed by various epithelial and non-epithelial cells in rat and mouse. Potential O-glycosylation sites, transmembrane and cytoplasmic domains were found to be highly conserved in the three species. gp40 was detected in canine lung, intestine, kidney, brain and heart but not in liver and spleen. The subline II of Madin-Darby canine kidney cells was found not to express gp40. Stable expression of gp40 in transfected type-II cells revealed that gp40 is predominantly delivered to the apical plasma membrane. N-Glycans and a glycosylphosphatidylinositol anchor, both proposed apical targeting signals, are absent from gp40, indicating that other determinants are responsible for its polarized transport.