Isolation of paramyxovirus glycoproteins. Association of both hemagglutinating and neuraminidase activities with the larger SV5 glycoprotein

Characterization of Human Parainfluenza Virus Receptor Using Terminal Sialic Acid Linkage-Modified Cells

Human parainfluenza virus type 1 (hPIV1) and type 3 (hPIV3) are respiratory pathogen viruses that bind to terminal sialic acids of glycoconjugates on the cell surface hemagglutinin-neuraminidase glycoprotein. Sialic acid residues are linked to the galactose residue primarily by α2,3 or α2,6 linkages on the terminal of glycoprotein or glycolipids. One of the major determinants of pathogenicity or tissue tropism is virus binding or infection specificity for each sialyl linkage. Sialic linkage-modified human blood cells or mammalian cells that mainly have α2,3- or α2,6-linked sialic acid residues on the surface can be prepared by treatment with linkage-specific sialidases or sialyltransferases. These linkage-modified cells can be used in hemagglutination assays to estimate virus particles' binding specificity, hemadsorption assays to estimate virus glycoproteins' binding specificity, and virus infectivity assays. These methods contribute to identifying the specificity of sialic acid lineage recognition of the hPIV or other sialic acid-binding viruses.

Solid-Phase Binding Assay for Ganglioside Binding of Human Respiroviruses

Human parainfluenza virus types 1 (hPIV-1) and 3 (hPIV-3) belong to the family Paramyxoviridae, subfamily Paramyxoviridae, and genus Respirovirus. The viruses enter by utilizing glycoproteins or glycosphingolipids (gangliosides) containing sialic acid on the cell membrane. We developed a solid-phase binding assay to evaluate hPIV-1, hPIV-3, and Sendai virus' abilities to bind to different types of gangliosides. hPIV1 and hPIV3 show strong binding to neolacto-series gangliosides containing a non-reducing terminal sialic acid residue and different specificity regarding the sialic acid linkages. This solid-phase binding assay is suitable to evaluate other orthomyxoviruses and paramyxoviruses' binding specificities utilizing sialic acids.

Differential Features of Fusion Activation within the Paramyxoviridae

Paramyxovirus (PMV) entry requires the coordinated action of two envelope glycoproteins, the receptor binding protein (RBP) and fusion protein (F). The sequence of events that occurs during the PMV entry process is tightly regulated. This regulation ensures entry will only initiate when the virion is in the vicinity of a target cell membrane. Here, we review recent structural and mechanistic studies to delineate the entry features that are shared and distinct amongst the Paramyxoviridae. In general, we observe overarching distinctions between the protein-using RBPs and the sialic acid- (SA-) using RBPs, including how their stalk domains differentially trigger F. Moreover, through sequence comparisons, we identify greater structural and functional conservation amongst the PMV fusion proteins, as compared to the RBPs. When examining the relative contributions to sequence conservation of the globular head versus stalk domains of the RBP, we observe that, for the protein-using PMVs, the stalk domains exhibit higher conservation and find the opposite trend is true for SA-using PMVs. A better understanding of conserved and distinct features that govern the entry of protein-using versus SA-using PMVs will inform the rational design of broader spectrum therapeutics that impede this process.

Molecular and biological characterization of the immunological potency of Newcastle disease virus oil emulsion-inactivated vaccines prepared from field isolate obtained from vaccinated chickens outbreak

This study was conducted to characterize the immunological parameters of chickens vaccinated with two formulated inactivated vaccines, water in oil (WO) and water in oil in water (WOW), prepared from velogenic Newcastle disease virus (vNDV) genotype VIIj isolated from outbreak among vaccinated chickens. Six groups (G1-G6) of commercial broiler chickens were established (n = 20). The G1-G3 were received homologous (WO and WOW) and heterologous (LaSota) inactivated vaccines, respectively. The G4 was vaccinated with live heterologous (LaSota) vaccine, while G5 and G6 were kept as control positive and control negative non-vaccinated groups. The antibody titers were measured against vNDV and LaSota antigens using hemagglutination inhibition (HI) test, the cytokine gene expressions of IFNγ, IL1β, IL4, IL6, IL8, and IL18 were quantified using real-time RT-PCR, and the virus shedding was titrated on chicken embryo fibroblast cells after challenging by vNDV. The classical clinical signs and 100% mortality were observed only in G5 after vNDV challenging. The highest HI titers were detected in G1, G2, and G3 using NDV/168 antigen with no significant differences among them. These groups showed higher HI titer than G4 (2-4log2). Cytokine gene expression of IFNγ, IL1, IL6, IL8, and IL18 were significantly downregulated in vaccinated chickens with upregulation of IL4 than non-vaccinated challenge group. Viral shedding titers were significantly (0.0001, p ≤ 0.001) reduced in all samples form vaccinated chickens. In conclusion, the prepared vaccines produced highly efficient immunological responses and could be used for controlling the NDV infection.

Assessment of selected media supplements to improve F/HN lentiviral vector production yields

The development of lentiviral-based therapeutics is challenged by the high cost of current Good Manufacturing Practices (cGMP) production. Lentiviruses are enveloped viruses that capture a portion of the host cell membrane during budding, which then constitutes part of the virus particle. This process might lead to lipid and protein depletion in the cell membrane and affect cell viability. Furthermore, growth in suspension also causes stresses that can affect virus production yields. To assess the impact of these issues, selected supplements (Cholesterol Lipid Concentrate, Chemically Defined Lipid Concentrate, Lipid Mixture 1, Gelatin Peptone N3, N-Acetyl-L-Cysteine and Pluronic F-68) were assayed in order to improve production yields in a transient transfection production of a Sendai virus F/HN-pseudotyped HIV-1-based third generation lentiviral vector in FreeStyle 293 (serum-free media) in suspension. None of the supplements tested had a significant positive impact on lentiviral vector yields, but small non-significant improvements could be combined to increase vector production in a cell line where other conditions have been optimised.

Investigation into alternative testing methodologies for characterization of influenza virus vaccine

The objective of this study was to explore various testing methodologies suitable for characterizing sedimented or agglomerated material. To model this, bioCSL's split influenza virus vaccine, Fluvax® was utilized. The investigation was conducted on 5 dispensed lots of commercially manufactured vaccine, formulated for the 2013 Southern Hemisphere season. Vaccine syringes were initially inspected by visual tests; the material was then aseptically pooled for characterization assessment by microscopy and several agglomeration assays. All syringes passed bioCSL's description test where any fine or large sized particles of sediment observed in the vaccine were resuspended upon shaking; inverted light microscopy verified that the sediment morphology was consistent with influenza vaccine. Electron microscopic examination of pooled vaccine material demonstrated the presence of typical influenza structures including split virus, virosomes, whole virus particles and agglomerates. An optical density turbidity assay revealed relatively high protein recoveries in the vaccine supernatant post-centrifugation treatment, thus indicative of a well-dispersed vaccine formulation. This was corroborated by particle sizing analysis using dynamic light scattering which generated reproducible volume particle size distributions of a polydisperse nature. Ultraviolet-visible absorbance profiles further confirmed the presence of some agglomerated material. Data from all methods demonstrated consistent results between all batches of vaccine. Therefore, this investigation revealed the suitability and usefulness of the various methodologies in characterizing the appearance of agglomerated vaccine material. It is suggested that such methods may be applicable and beneficial for the development of a wider spectrum of heterogeneous and agglomerated formulations to provide safe, efficacious and superior quality biopharmaceutical products.

Amino acid substitutions contributing to α2,6-sialic acid linkage binding specificity of human parainfluenza virus type 3 hemagglutinin-neuraminidase

Human parainfluenza virus type 3 (hPIV3) recognizes both α2,3- and α2,6-linked sialic acids, whereas human parainfluenza virus type 1 (hPIV1) recognizes only α2,3-linked sialic acids. To identify amino acid residues that confer α2,6-linked sialic acid recognition of hPIV3, amino acid residues in or neighboring the sialic acid binding pocket of the hPIV3 hemagglutinin-neuraminidase (HN) glycoprotein were substituted for the corresponding residues of hPIV1 HN. Hemadsorption assay with sialyl linkage-modified red blood cells indicated that amino acid residues at positions 275, 277, 372, and 426 contribute to α2,6-linked sialic acid recognition of the HN3 glycoprotein.

Three viruses of the bovine respiratory disease complex apply different strategies to initiate infection

Bovine respiratory disease complex (BRDC) is the major cause of serious respiratory tract infections in calves. The disease is multifactorial, with either stress or reduced immunity allowing several pathogens to emerge. We investigated the susceptibility of bovine airway epithelial cells (BAEC) to infection by the three major viruses associated with the BRDC: bovine respiratory syncytial virus (BRSV), bovine herpesvirus type 1 (BHV-1) and bovine parainfluenza virus type 3 (BPIV3). For this purpose, two culture systems for well-differentiated BAEC were used: the air-liquid interface (ALI) system, where filter-grown BAEC differentiate into a pseudostratified respiratory epithelium and precision-cut lung slices (PCLS) where BAEC are maintained in the original tissue organisation. Comparative infection studies demonstrated that entry and release of BPIV3 occurred specifically via the apical membrane with ciliated cells being the major target cells. By contrast, airway epithelial cells were largely resistant to infection by BHV-1. When the epithelial barrier was abolished by opening tight junctions or by injuring the cell monolayer, BHV-1 infected mainly basal cells. Respiratory epithelial cells were also refractory to infection by BRSV. However, this virus infected neither differentiated epithelial cells nor basal cells when the integrity of the epithelial barrier was destroyed. In contrast to cells of the airway epithelium, subepithelial cells were susceptible to infection by BRSV. Altogether, these results indicate that the three viruses of the same disease complex follow different strategies to interact with the airway epithelium. Possible entry mechanisms are discussed.

Structure of viruses: a short history

This review is a partially personal account of the discovery of virus structure and its implication for virus function. Although I have endeavored to cover all aspects of structural virology and to acknowledge relevant individuals, I know that I have favored taking examples from my own experience in telling this story. I am anxious to apologize to all those who I might have unintentionally offended by omitting their work. The first knowledge of virus structure was a result of Stanley's studies of tobacco mosaic virus (TMV) and the subsequent X-ray fiber diffraction analysis by Bernal and Fankuchen in the 1930s. At about the same time it became apparent that crystals of small RNA plant and animal viruses could diffract X-rays, demonstrating that viruses must have distinct and unique structures. More advances were made in the 1950s with the realization by Watson and Crick that viruses might have icosahedral symmetry. With the improvement of experimental and computational techniques in the 1970s, it became possible to determine the three-dimensional, near-atomic resolution structures of some small icosahedral plant and animal RNA viruses. It was a great surprise that the protecting capsids of the first virus structures to be determined had the same architecture. The capsid proteins of these viruses all had a 'jelly-roll' fold and, furthermore, the organization of the capsid protein in the virus were similar, suggesting a common ancestral virus from which many of today's viruses have evolved. By this time a more detailed structure of TMV had also been established, but both the architecture and capsid protein fold were quite different to that of the icosahedral viruses. The small icosahedral RNA virus structures were also informative of how and where cellular receptors, anti-viral compounds, and neutralizing antibodies bound to these viruses. However, larger lipid membrane enveloped viruses did not form sufficiently ordered crystals to obtain good X-ray diffraction. Starting in the 1990s, these enveloped viruses were studied by combining cryo-electron microscopy of the whole virus with X-ray crystallography of their protein components. These structures gave information on virus assembly, virus neutralization by antibodies, and virus fusion with and entry into the host cell. The same techniques were also employed in the study of complex bacteriophages that were too large to crystallize. Nevertheless, there still remained many pleomorphic, highly pathogenic viruses that lacked the icosahedral symmetry and homogeneity that had made the earlier structural investigations possible. Currently some of these viruses are starting to be studied by combining X-ray crystallography with cryo-electron tomography.

Structure and assembly of a paramyxovirus matrix protein

Many pleomorphic, lipid-enveloped viruses encode matrix proteins that direct their assembly and budding, but the mechanism of this process is unclear. We have combined X-ray crystallography and cryoelectron tomography to show that the matrix protein of Newcastle disease virus, a paramyxovirus and relative of measles virus, forms dimers that assemble into pseudotetrameric arrays that generate the membrane curvature necessary for virus budding. We show that the glycoproteins are anchored in the gaps between the matrix proteins and that the helical nucleocapsids are associated in register with the matrix arrays. About 90% of virions lack matrix arrays, suggesting that, in agreement with previous biological observations, the matrix protein needs to dissociate from the viral membrane during maturation, as is required for fusion and release of the nucleocapsid into the host's cytoplasm. Structure and sequence conservation imply that other paramyxovirus matrix proteins function similarly.

Comparison of differing cytopathic effects in human airway epithelium of parainfluenza virus 5 (W3A), parainfluenza virus type 3, and respiratory syncytial virus

Parainfluenza virus 5 (PIV5) infects a wide range of animals including dogs, pigs, cats, and humans; however, its association with disease in humans remains controversial. In contrast to parainfluenza virus 3 (PIV3) or respiratory syncytial virus (RSV), PIV5 is remarkably non-cytopathic in monolayer cultures of immortalized epithelial cells. To compare the cytopathology produced by these viruses in a relevant human tissue, we infected an in vitro model of human ciliated airway epithelium and measured outcomes of cytopathology. PIV5, PIV3 and, RSV all infected ciliated cells, and PIV5 and PIV3 infection was dependent on sialic acid residues. Only PIV5-infected cells formed syncytia. PIV5 infection resulted in a more rapid loss of infected cells by shedding of infected cells into the lumen. These studies revealed striking differences in cytopathology of PIV5 versus PIV3 or RSV and indicate the extent of cytopathology determined in cell-lines does not predict events in differentiated airway cells.

Phylogenetic and pathogenic analysis of Newcastle disease virus isolated from house sparrow (Passer domesticus) living around poultry farm in southern China

House sparrow (Passer domesticus) is one of the most widely distributed wild birds in China. Five Newcastle disease virus (NDV) strains were isolated from house sparrows living around the poultry farms in southern China. These isolates were characterized by pathogenic assays and phylogenetic analysis. The results showed that all NDV isolates except one were velogenic and virulent for chickens. These four virulent strains for chickens possess the amino acid sequence (112)R/K-R-Q-K/R-R-F(117) in the F(0) cleavage site which is typical of velogenic NDV. Phylogenetic analysis indicated that these isolates belong to genotype VII and were closely related to the strains which were isolated from NDV outbreaks in chickens since 2000. One isolate of NDV from house sparrow belong to genotype II and was proved to be vaccine strain (Chicken/U.S./LaSota/46). The result of this study proved that house sparrow can carry the virulent NDV strains and the same genotype of viruses that are circulating in poultry are existing in house sparrows living around poultry farm in southern China.

Differential sensitivity of differentiated epithelial cells to respiratory viruses reveals different viral strategies of host infection

To address the initiation of virus infection in the respiratory tract, we established two culture systems for differentiated bovine airway epithelial cells (BAEC). Filter-grown BAEC differentiated under air-liquid interface (ALI) conditions to generate a pseudo-stratified mucociliary epithelium. Alternatively, precision-cut lung slices (PCLS) from the bovine airways were generated that retained the original composition and distribution of differentiated epithelial cells. With both systems, epithelial cells were readily infected by bovine parainfluenza virus 3 (BPIV3). Ciliated cells were the most prominent cell type affected by BPIV3. Surprisingly, differentiated BAEC were resistant to infection by bovine respiratory syncytial virus (BRSV), when the virus was applied at the same multiplicity of infection that was sufficient for infection by BPIV3. In the case of PCLS, infection by BRSV was observed in cells located in lower cell layers but not in epithelial cells facing the lumen of the airways. The identity of the infected cells could not be determined because of a lack of specific antibodies. Increasing the virus titer 30-fold resulted in infection of the ALI cultures of BAEC, whereas in PCLS the ciliated epithelium was still refractory to infection by BRSV. These results indicate that differentiated BAEC are readily infected by BPIV3 but rather resistant to infection by BRSV. Disease caused by BRSV may require that calves encounter environmental stimuli that render BAEC susceptible to infection.

HVJ envelope vector, a versatile delivery system: its development, application, and perspectives

An efficient and minimally invasive vector system is the "bottle neck" of both gene transfer and drug delivery. Numerous viral and non-viral (synthetic) delivery systems have been developed and improved. Hemagglutinating virus of Japan (HVJ, Sendai virus) envelope vector is a novel and unique system which combined the advantages of viral and non-viral vectors with the following features and advantages: (1) safe and easy as a "non-viral" transfection reagent; (2) delivery of various molecules including plasmid DNA, siRNA, protein, antisense oligonucleotide; (3) wide usability from in vitro to in vivo. In this review, the development, application, and perspectives of the HVJ envelope vector will be discussed.

Functions of surface glycoproteins of myxoviruses and paramyxoviruses and their inhibition

Two glycoproteins, HN and F, are present on the surface of paramyxoviruses. HN has receptor-binding amd neuraminidase activities. F is involved in viral penetration, cell fusion and haemolysis and is activated by proteolytic cleavage by a host enzyme into two disulphide-bonded subunits (f1 and F2). The ability of the virus to initiate infection and undergo multiple cycle replication depends on the presence of an activating protease in the host; thus cleavage of F is a major determinant of pathogenesis. The new N-terminus generated on F1 by cleavage is involved in biological activity, and the amino acid sequence of this region of F1 by cleavage is involved in biological activity, and the amino acid sequence of this region of F1 is hydrophobic and highly conserved among para-myxoviruses. In an attempt to design specific inhibitors, oligopeptides and analogous to this region were synthesized and found to be highly active, specific inhibitors of viral penetration, cell fusion and haemolysis. Inhibition is amino-acid-sequence-specific and affected by peptide length, steric configuration and addition of groups to the n-terminal and C-terminal amino acids. Replication of influenza virus was also specifically inhibited by oligopeptides resembling the N-terminus of the HA2 polypeptide. Like that of F1 protein the N-terminus of HA2 is generated by a proteolytic cleavage that activates infectivity. These results have provided information on the action of proteins in viral penetration and membrane fusion and they suggest a possible new approach to chemical inhibition of viral replication. Studies with specific antibodies to each of the paramyxovirus glycoproteins have shown that antibodies to the F protein are essential for effective prevention of the spread of infection. Antibodies to the HN protein, although capable of neutralizing released virus, do not prevent spread to adjacent cells through membrane fusion mediated by the F protein. These findings have implications for the design of effective vaccines against paramyxoviruses and also provided additional insight into the mechanisms involved in the atypical and severe infections observed in individuals who received inactivated paramyxovirus vaccines and were later infected.

Membrane Glycoproteins of Enveloped Viruses

This chapter focuses on the recent information of the glycoprotein components of enveloped viruses and points out specific findings on viral envelopes. Although enveloped viruses of different major groups vary in size and shape, as well as in the molecular weight of their structural polypeptides, there are general similarities in the types of polypeptide components present in virions. The types of structural components found in viral membranes are summarized briefly in the chapter. All the enveloped viruses studied to date possess one or more glycoprotein species and lipid as a major structural component. The presence of carbohydrate covalently linked to proteins is demonstrated by the incorporation of a radioactive precursor, such as glucosamine or fucose, into viral polypeptides, which is resolved by sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis. Enveloped viruses share many common features in the organization of their structural components, as indicated by several approaches, including electron microscopy, surface-labeling, and proteolytic digestion experiments, and the isolation of subviral components. The chapter summarizes the detailed structure of the glycoproteins of four virus groups: (1) influenza virus glycoproteins, (2) rhabdovirus G protein, (3) togavirus glycoprotein, and (4) paramyxovirus glycoproteins The information obtained includes the size and shape of viral glycoproteins, the number of polypeptide chains in the complete glycoprotein structure, and compositional data on the polypeptide and oligosaccharide portions of the molecules.

Electron cryomicroscopy reveals different F1+F2 protein States in intact parainfluenza virions

Electron cryomicrographs of intact parainfluenza virus 5 (PIV5) virions revealed two different surface structures, namely, a continuous layer and distinct individual spikes. The structure of these spikes reconstructed from intact virions was compared with known F ectodomain structures and was found to be different from the prefusion PIV5 F0 structure but, surprisingly, very similar to the human PIV3 F postfusion structure. Hence, we conclude that the individual F1+F2 spikes in intact PIV5 virions also correspond to the postfusion state. Since the observed fusion activity of PIV5 virions has to be associated with prefusion F1+F2 proteins, they have necessarily to be localized in the continuous surface structure. The data therefore strongly suggest that the prefusion state of the F1+F2 protein requires stabilization, most probably by the association with hemagglutinin-neuraminidase. The conversion of F1+F2 proteins from the prefusion toward the postfusion state while embedded in the virus membrane is topologically difficult to comprehend on the basis of established models and demands reconsideration of our current understanding.

Molecular characterization of three new virulent Newcastle disease virus variants isolated in China

Three cases of Newcastle disease virus (NDV) found in nature had the lentogenic motif (112)G-R-Q-G-R-L(117) in their fusion protein cleavage sites. However, both intracerebral pathogenicity and intravenous pathogenicity indexes showed that these NDV isolates were virulent. In comparison with the LaSota live virus vaccine, these viruses had significant genetic variations in the hemagglutinin-neuraminidase gene.

Eosinophil-Mediated Cholinergic Nerve Remodeling

Eosinophils are observed to localize to cholinergic nerves in a variety of inflammatory conditions such as asthma, rhinitis, eosinophilic gastroenteritis, and inflammatory bowel disease, where they are also responsible for the induction of cell signaling. We hypothesized that a consequence of eosinophil localization to cholinergic nerves would involve a neural remodeling process. Eosinophil co-culture with cholinergic IMR32 cells led to increased expression of the M2 muscarinic receptor, with this induction being mediated via an adhesion-dependent release of eosinophil proteins, including major basic protein and nerve growth factor. Studies on the promoter sequence of the M2 receptor indicated that this induction was initiated at a transcription start site 145 kb upstream of the gene-coding region. This promoter site contains binding sites for a variety of transcription factors including SP1, AP1, and AP2. Eosinophils also induced the expression of several cholinergic genes involved in the synthesis, storage, and metabolism of acetylcholine, including the enzymes choline acetyltransferase, vesicular acetylcholine transferase, and acetylcholinesterase. The observed eosinophil-induced changes in enzyme content were associated with a reduction in intracellular neural acetylcholine but an increase in choline content, suggesting increased acetylcholine turnover and a reduction in acetylcholinesterase activity, in turn suggesting reduced catabolism of acetylcholine. Together these data suggest that eosinophil localization to cholinergic nerves induces neural remodeling, promoting a cholinergic phenotype.

Role of sialic acid-containing molecules in paramyxovirus entry into the host cell: A minireview

Sialic acid-containing compounds play a key role in the initial steps of the paramyxovirus life cycle. As enveloped viruses, their entry into the host cell consists of two main events: binding to the host cell and membrane fusion. Virus adsorption occurs at the surface of the host cell with the recognition of specific receptor molecules located at the cell membrane by specific viral attachment proteins. The viral attachment protein present in some paramyxoviruses (Respirovirus, Rubulavirus and Avulavirus) is the HN glycoprotein, which binds to cellular sialic acid-containing molecules and exhibits sialidase and fusion promotion activities. Gangliosides of the gangliotetraose series bearing the sialic acid N-acetylneuraminic (Neu5Ac) on the terminal galactose attached in alpha2-3 linkage, such as GD1a, GT1b, and GQ1b, and neolacto-series gangliosides are the major receptors for Sendai virus. Much less is known about the receptors for other paramyxoviruses than for Sendai virus. Human parainfluenza viruses 1 and 3 preferentially recognize oligosaccharides containing N-acetyllactosaminoglycan branches with terminal Neu5Acalpha2-3Gal. In the case of Newcastle disease virus, has been reported the absence of a specific pattern of the gangliosides that interact with the virus. Additionally, several works have described the use of sialylated glycoproteins as paramyxovirus receptors. Accordingly, the design of specific sialic acid analogs to inhibit the sialidase and/or receptor binding activity of viral attachment proteins is an important antiviral strategy. In spite of all these data, the exact nature of paramyxovirus receptors, apart from their sialylated nature, and the mechanism(s) of viral attachment to the cell surface are poorly understood.

Structural studies of the parainfluenza virus 5 hemagglutinin-neuraminidase tetramer in complex with its receptor, sialyllactose

The paramyxovirus hemagglutinin-neuraminidase (HN) functions in virus attachment to cells, cleavage of sialic acid from oligosaccharides, and stimulating membrane fusion during virus entry into cells. The structural basis for these diverse functions remains to be fully understood. We report the crystal structures of the parainfluenza virus 5 (SV5) HN and its complexes with sialic acid, the inhibitor DANA, and the receptor sialyllactose. SV5 HN shares common structural features with HN of Newcastle disease virus (NDV) and human parainfluenza 3 (HPIV3), but unlike the previously determined HN structures, the SV5 HN forms a tetramer in solution, which is thought to be the physiological oligomer. The sialyllactose complex reveals intact receptor within the active site, but no major conformational changes in the protein. The SV5 HN structures do not support previously proposed models for HN action in membrane fusion and suggest alternative mechanisms by which HN may promote virus entry into cells.

Purification of the Porcine rubulavirus attachment protein by liquid isoelectric focusing

Porcine rubulavirus (PoRV) is an emerging virus responsible for meningoencephalitis, respiratory distress, and reproductive alterations in pigs. The hemagglutinin-neuraminidase (HN) glycoprotein is the most exposed and antigenic of the virus proteins. HN plays central roles in PoRV infection; i.e., it recognizes sialic acid-containing cell receptors that mediate virus attachment and penetration; in addition, its neuraminidase (sialic acid hydrolysis) activity has been proposed to be a virulence factor. So, HN is an ideal target for therapeutic treatment and prevention of this viral infection. This work describes a simple, fast, and sensitive method to purify the active form of HN protein based on its isoelectric point. HN was purified at a pH of 4.4, at which a single protein band of 66 kDa was observed on SDS-PAGE. Pure HN showed a maximal enzymatic activity at pH 3.5 and 37 degrees C using bovine fetuin as substrate. However, it retains circa 80% of its activity at a wide temperature range from 30 to 55 degrees C. We also describe improvements of neuraminidase determination method, which permits analysis in a microplate spectrophotometer, thereby increasing the sensitivity and reducing the costs of valuable reagents and biological samples.

The 3D structure of the fusion primed Sendai F-protein determined by electron cryomicroscopy

The three dimensional (3D) structure of the ectodomain of the entire fusion mediating F protein from Sendai virus [MW (trimer) approximately 177 kDa] has been determined by cryoelectron microscopy of single molecules and subsequent 3D reconstruction at a resolution of approximately 16 A. The reconstruction, which has been obtained from the native, proteolytic processed fusion primed F1+F2 form, shows the protein protruding approximately 170 A out of the membrane in a homotrimeric association. It consists of a defined approximately 65 A wide distal head and an adjacent neck, which is connected to an 70 A elongated stalk. Although the overall shape appears to be similar to the recently reported X-ray structure of the Newcastle disease virus F protein, a closer comparison reveals structural differences suggesting that the investigated Sendai F structure represents an advanced state towards the fusion active conformation.

Generation of velogenic Newcastle disease viruses from a nonpathogenic waterfowl isolate by passaging in chickens

A benign Newcastle disease virus (NDV) recently became highly virulent during replication in domestic chickens. It is still unclear whether NDVs circulating among wild waterfowl also have the potential to become highly pathogenic (velogenic) in chickens. To demonstrate experimentally the generation of velogenic NDV from a nonpathogenic waterfowl isolate, we passaged an avirulent goose isolate in chickens. After nine consecutive passages by air-sac inoculation, followed by five passages in chick brain, the virus became highly virulent in chickens, producing a 100% mortality rate, and demonstrating typical velogenic properties in pathogenicity tests. Sequence analysis at the fusion protein cleavage site showed that the original isolate contained the typical avirulent type sequence, E-R-Q-E-R/L, which progressed incrementally to a typical virulent type, K-R-Q-K-R/F, during repeated passage in chickens. These results demonstrate that avirulent viruses, maintained in wild waterfowl in nature and bearing the consensus avirulent type sequence, have the potential to become velogenic after transmission to and circulation in chicken populations. The results also suggest that chickens provide a mechanism for the selection of virulent viruses from an avirulent background.

Rinderpest virus H protein: role in determining host range in rabbits

A major molecular determinant of virus host-range is thought to be the viral protein required for cell attachment. We used a recombinant strain of Rinderpest virus (RPV) to examine the role of this protein in determining the ability of RPV to replicate in rabbits. The recombinant was based on the RBOK vaccine strain, which is avirulent in rabbits, carrying the haemagglutinin (H) protein gene from the lapinized RPV (RPV-L) strain, which is pathogenic in rabbits. The recombinant virus (rRPV-lapH) was rescued from a cDNA of the RBOK strain in which the H gene was replaced with that from the RPV-L strain. The recombinant grew at a rate equivalent to the RPV-RBOK parental virus in B95a cells but at a lower rate than RPV-L. The H gene swap did not affect the ability of the RBOK virus to act as a vaccine to protect cattle against virulent RPV challenge. Rabbits inoculated with RPV-L became feverish, showed a decrease in body weight gain and leukopenia. High virus titres and histopathological lesions in the lymphoid tissues were also observed. Clinical signs of infection were never observed in rabbits inoculated with either RPV-RBOK or with rRPV-lapH; however, unlike RPV-RBOK, both RPV-L and rRPV-lapH induced a marked antibody response in rabbits. Therefore, the H protein plays an important role in allowing infection to occur in rabbits but other viral proteins are clearly required for full RPV pathogenicity to be manifest in this species.

Fusogenic activity of reconstituted newcastle disease virus envelopes: a role for the hemagglutinin-neuraminidase protein in the fusion process

Enveloped viruses, such as newcastle disease virus (NDV), make their entry into the host cell by membrane fusion. In the case of NDV, the fusion step requires both transmembrane hemagglutinin-neuraminidase (HN) and fusion (F) viral envelope glycoproteins. The HN protein should show fusion promotion activity. To date, the nature of HN-F interactions is a controversial issue. In this work, we aim to clarify the role of the HN glycoprotein in the membrane fusion step. Four types of reconstituted detergent-free NDV envelopes were used, on differing in their envelope protein contents. Fusion of the different virosomes and erythrocyte ghosts was monitored using the octadecyl rhodamine B chloride assay. Only the reconstituted envelopes having the F protein, even in the absence of HN protein, displayed residual fusion activity. Treatment of such virosomes with denaturing agents affecting the F protein abolished fusion, indicating that the fusion detected was viral protein-dependent. Interestingly, the rate of fusion in the reconstituted systems was similar to that of intact viruses in the presence of the inhibitor of HN sialidase activity 2,3-dehydro-2-deoxy-N-acetylneuraminic acid. The results show that the residual fusion activity detected in the reconstituted systems was exclusively due to F protein activity, with no contribution from the fusion promotion activity of HN protein.

The hemagglutinin-neuraminidase protein of peste des petits ruminants virus is biologically active when transiently expressed in mammalian cells

The genes coding for the surface glycoproteins hemagglutinin-neuraminidase (HN) of the peste des petits ruminants virus (PPRV) and hemagglutinin (H) of rinderpest virus (RPV) were cloned in a cytomagalovirus promoter driven expression vector and expressed transiently in mammalian cells. The protein expression was apparent 24 h after transfection and the expressed proteins were detected at the cell surface. The transiently expressed PPRV HN protein was found to be biologically active in possessing hemadsorption and neuraminidase activities. On the other hand, RPV H protein exhibited neuraminidase activity but was deficient in hemadsorption activity. The substrate specificity of the neuraminidase activity of these two proteins differed distinctly. The presence of neuraminidase activity in both PPRV HN and RPV H proteins is unusual among members of the morbillivirus genus.

Receptor specificities of human respiroviruses

Through their hemagglutinin-neuraminidase glycoprotein, parainfluenza viruses bind to sialic acid-containing glycoconjugates to initiate infection. Although the virus-receptor interaction is a key factor of infection, the exact nature of the receptors that human parainfluenza viruses recognize has not been determined. We evaluated the abilities of human parainfluenza virus types 1 (hPIV-1) and 3 (hPIV-3) to bind to different types of gangliosides. Both hPIV-1 and hPIV-3 preferentially bound to neolacto-series gangliosides containing a terminal N-acetylneuraminic acid (NeuAc) linked to N-acetyllactosamine (Galbeta1-4GlcNAc) by the alpha2-3 linkage (NeuAcalpha2-3Galbeta1-4GlcNAc). Unlike hPIV-1, hPIV-3 bound to gangliosides with a terminal NeuAc linked to Galbeta1-4GlcNAc through an alpha2-6 linkage (NeuAcalpha2-6Galbeta1-4GlcNAc) or to gangliosides with a different sialic acid, N-glycolylneuraminic acid (NeuGc), linked to Galbeta1-4GlcNAc (NeuGcalpha2-3Galbeta1-4GlcNAc). These results indicate that the molecular species of glycoconjugate that hPIV-1 recognizes are more limited than those recognized by hPIV-3. Further analysis using purified gangliosides revealed that the oligosaccharide core structure is also an important element for binding. Gangliosides that contain branched N-acetyllactosaminoglycans in their core structure showed higher avidity than those without them. Agglutination of human, cow, and guinea pig erythrocytes but not equine erythrocytes by hPIV-1 and hPIV-3 correlated well with the presence or the absence of sialic acid-linked branched N-acetyllactosaminoglycans on the cell surface. Finally, NeuAcalpha2-3I, which bound to both viruses, inhibited virus infection of Lewis lung carcinoma-monkey kidney cells in a dose-dependent manner. We conclude that hPIV-1 and hPIV-3 preferentially recognize oligosaccharides containing branched N-acetyllactosaminoglycans with terminal NeuAcalpha2-3Gal as receptors and that hPIV-3 also recognizes NeuAcalpha2-6Gal- or NeuGcalpha2-3Gal-containing receptors. These findings provide important information that can be used to develop inhibitors that prevent human parainfluenza virus infection.

Electron microscopy of the human respiratory syncytial virus fusion protein and complexes that it forms with monoclonal antibodies

Full-length fusion (F) glycoprotein of human respiratory syncytial virus (HRSV) and a truncated anchorless mutant lacking the C-terminal 50 amino acids were expressed from vaccinia recombinants and purified by immunoaffinity chromatography and sucrose gradient centrifugation. Electron microscopy of full-length F protein in the absence of detergents revealed micelles, (i.e., rosettes) containing two distinct types of protein rods, one cone-shaped and the other lollipop-shaped. Analysis of membrane anchorless F molecules indicated that they were similar to the cone-shaped rods and that rosettes, which they formed on storage, were made up of lollipop-shaped rods. The two forms of F protein may represent different structures that the molecule may adopt before and after activation for its role in membrane fusion. Studies of complexes of these structures with monoclonal antibodies of known specificity provide information on the three-dimensional organization of antigenic sites on the F protein and confirm the oligomeric structure, possibly trimeric, of both full-length F and membrane anchorless F.

Fusion protein of the paramyxovirus SV5: destabilizing and stabilizing mutants of fusion activation

The fusion (F) protein of the paramyxovirus SV5 strain W3A causes syncytium formation without coexpression of the SV5 hemagglutinin-neuraminidase (HN) glycoprotein, whereas the F protein of the SV5 strain WR requires coexpression of HN for fusion activity. SV5 strains W3A and WR differ by three amino acid residues at positions 22, 443, and 516. The W3A F protein residues P22, S443, and V516 were changed to amino acids found in the WR F protein (L22, P443, and A516, respectively). Three single-mutants, three double-mutants, and the triple-mutant were constructed, expressed, and assayed for fusion using three different assays. Mutant P22L did not cause fusion under physiological conditions, but fusion was activated at elevated temperatures. Compared with the W3A F protein, mutant S443P enhanced the fusion kinetics with a faster rate and greater extent, and had a lower activation temperature. Mutant V516A had little effect on F protein-mediated fusion. The double-mutant P22L,S443P was capable of causing fusion, suggesting that the two mutations have opposing effects on fusion activation. The WR F protein requires coexpression of HN to cause fusion at 37 degrees C, and does not cause fusion at 37 degrees C when coexpressed with influenza virus hemagglutinin (HA); however, at elevated temperatures coexpression of WR F protein with HA resulted in fusion activation. In the crystal structure of the core trimer of the SV5 F protein (Baker, K. A., Dutch, R. E., Lamb, R.A., and Jardetzky, T. S. (1999). Mol. Cell 3, 309-319), S443 is the last residue (with interpretable electron density) in an extended chain region and the temperature factor for S443 is high, suggesting conformational flexibility at this point. Thus, the presence of prolines at residues 22 and 443 may destabilize the F protein and thereby decrease the energy required to trigger the presumptive conformational change to the fusion-active state.

A RhoA-derived peptide inhibits syncytium formation induced by respiratory syncytial virus and parainfluenza virus type 3

The fusion glycoproteins of human respiratory syncytial virus (RSV) and human parainfluenza virus type-3 (PIV-3) mediate virus entry and syncytium formation. Interaction between the fusion protein of RSV and RhoA, a small GTPase, facilitates virus-induced syncytium formation. We show here a RhoA-derived peptide inhibits RSV and syncytium formation induced by RSV and PIV-3, both in vitro by inhibition of cell-to-cell fusion and in vivo by reduction of peak titer by 2 log10 in RSV-infected mice. These findings indicate that the interaction between these two paramyxovirus fusion proteins and RhoA is an important target for new antiviral strategies.

Direct evidence that the N-terminal heptad repeat of Sendai virus fusion protein participates in membrane fusion

Recent studies have demonstrated the importance of heptad repeat regions within envelope proteins of viruses in mediating conformational changes at various stages of viral infection. However, it is not clear if heptad repeats have a direct role in the actual fusion event. Here we have synthesized, fluorescently labeled and functionally and structurally characterized a wild-type 70 residue peptide (SV-117) composed of both the fusion peptide and the N-terminal heptad repeat of Sendai virus fusion protein, two of its mutants, as well as the fusion peptide and heptad repeat separately. One mutation was introduced in the fusion peptide (G119K) and another in the heptad repeat region (I154K). Similar mutations have been shown to drastically reduce the fusogenic ability of the homologous fusion protein of Newcastle disease virus. We found that only SV-117 was active in inducing lipid mixing of egg phosphatidylcholine/phosphatidyiglycerol (PC/PG) large unilamellar vesicles (LUV), and not the mutants nor the mixture of the fusion peptide and the heptad repeat. Functional characterization revealed that SV-117, and to a lesser extent its two mutants, were potent inhibitors of Sendai virus-mediated hemolysis of red blood cells, while the fusion peptide and SV-150 were negligibly active alone or in a mixture. Hemagglutinin assays revealed that none of the peptides disturb the binding of virions to red blood cells. Further studies revealed that SV-117 and its mutants oligomerize similarly in solution and in membrane, and have similar potency in inducing vesicle aggregation. Circular dichroism and FTIR spectroscopy revealed a higher helical content for SV-117 compared to its mutants in 40 % tifluorethanol and in PC/PG multibilayer membranes, respectively, ATR-FTIR studies indicated that SV-117 lies more parallel with the surface of the membrane than its mutants. These observations suggest a direct role for the N-terminal heptad repeat in assisting the fusion peptide in mediating membrane fusion.

Structure-function study of a heptad repeat positioned near the transmembrane domain of Sendai virus fusion protein which blocks virus-cell fusion

A synthetic heptad repeat, SV-473, derived from Sendai virus fusion protein is a potent inhibitor of virus-cell fusion. In order to understand the mechanism of the inhibitory effect, we synthesized and fluorescently labeled SV-465, an extended version of SV-473 by one more heptad, its mutant peptide A17,24-SV-465, in which two heptadic leucines were substituted with two alanines, and its enatiomer D-SV-465, composed entirely of Damino acids. Similar mutations in the homologous fusion protein of the Newcastle disease virus drastically reduced its activity. The data revealed that SV-465, but not A17,24-SV-465 or its enantiomer, is highly active in inhibiting Sendai virus-induced hemolysis of red blood cells. None of the peptides interfere with the binding of virions to the target red blood cells as demonstrated by hemagglutinin assay. Fluorescence and circular dichroism (CD) spectroscopy indicated that: (i) only SV-465 could self-assemble in aqueous environment; (ii) only SV-465 could co-assemble with two other biologically active heptad repeats derived from Sendai virus fusion protein; (iii) SV-465 has a higher helical content than A17,24-SV-465 in solution, and (iv) all the peptides bind strongly to zwitterionic and negatively charged phospholipids. Polarized attenuated total reflection infrared spectroscopy revealed that they bound as monomers onto the surface of zwitterionic membranes with predominantly alpha-helical structures. The functional role of the amino acid 465-497 domain in Sendai virus-mediated membrane fusion is discussed in light of these findings.

Membrane fusion promoted by increasing surface densities of the paramyxovirus F and HN proteins: comparison of fusion reactions mediated by simian virus 5 F, human parainfluenza virus type 3 F, and influenza virus HA

The membrane fusion reaction promoted by the paramyxovirus simian virus 5 (SV5) and human parainfluenza virus type 3 (HPIV-3) fusion (F) proteins and hemagglutinin-neuraminidase (HN) proteins was characterized when the surface densities of F and HN were varied. Using a quantitative content mixing assay, it was found that the extent of SV5 F-mediated fusion was dependent on the surface density of the SV5 F protein but independent of the density of SV5 HN protein, indicating that HN serves only a binding function in the reaction. However, the extent of HPIV-3 F protein promoted fusion reaction was found to be dependent on surface density of HPIV-3 HN protein, suggesting that the HPIV-3 HN protein is a direct participant in the fusion reaction. Analysis of the kinetics of lipid mixing demonstrated that both initial rates and final extents of fusion increased with rising SV5 F protein surface densities, suggesting that multiple fusion pores can be active during SV5 F protein-promoted membrane fusion. Initial rates and extent of lipid mixing were also found to increase with increasing influenza virus hemagglutinin protein surface density, suggesting parallels between the mechanism of fusion promoted by these two viral fusion proteins.

Pulmonary neuronal M2 muscarinic receptor function in asthma and animal models of hyperreactivity

In the lungs neuronal M2 muscarinic receptors limit acetylcholine release from postganglionic cholinergic nerves. These inhibitory M2 receptors are dysfunctional in antigen challenged guinea pigs and in humans with asthma which leads to an increase in vagally mediated hyperreactivity. In vitro, eosinophil products act as allosteric antagonists at neuronal M2 muscarinic receptors. In vivo, displacing or neutralising MBP preserves neuronal M2 muscarinic receptor function and prevents hyperreactivity. Thus, there is good evidence from animal studies that after antigen challenge pulmonary M2 muscarinic receptors become dysfunctional because MBP inhibits their function. Loss of function of pulmonary neuronal M2 muscarinic receptors has also been reported in patients with asthma, although the clinical significance of this dysfunction and the mechanisms underlying it are not yet established.

Proper spacing between heptad repeat B and the transmembrane domain boundary of the paramyxovirus SV5 F protein is critical for biological activity

The paramyxovirus, simian virus 5, fusion (F) protein contains seven amino acids between heptad repeat B (a domain required for a biologically active fusion protein) and the presumptive boundary of the transmembrane (TM) domain. The role of the seven membrane proximal residues in stability and fusion promotion was examined by construction of a series of insertion, substitution, and deletion mutants, as manipulation of this region to enable proteolytic cleavage would facilitate production of a soluble F protein. The majority of the mutant F proteins both oligomerized and had kinetics of intracellular transport similar to those of wild-type (wt) F protein. All mutant F proteins were expressed at the cell surface at or near the same level as the wt F protein. However, by using both a qualitative lipid mixing assay and a quantitative content mixing assay for membrane fusion, it was found that mutant F proteins containing insertions in the region between heptad repeat B and the TM domain were unable to induce fusion, whereas the mutant F proteins containing substitutions in this region, together with three of the four mutants with deletions in this region, could induce fusion. Four of the F protein mutants contained a Factor Xa cleavage site, IEGR; however, Factor Xa treatment of cell surfaces released either none or only very small amounts (< 1% of total protein) of the soluble heterodimer F1 + F2. As an alternative method of generating soluble F protein, a glycosyl phosphatidylinositol (GPI) anchor was added to the F protein at three membrane-proximal positions. The highest level of surface expression was observed when the final molecule did not contain a significant insertion of amino acids into the membrane proximal region. Two F-GPI mutants reached the surface at approximately 20% of the levels seen with the wt F protein, and approximately 25% of the cell surface population of these mutants could be cleaved with phosphatidylinositol phospholipase C (PI-PLC) to yield soluble F protein. However, all the F-GPI mutants oligomerized aberrantly and failed to promote fusion. Taken together, these data indicate that the spacing of the region immediately adjacent to the presumptive boundary of the TM domain is extremely important for the fusogenic activity of the SV5 F protein.

Dynamic properties of Newcastle Disease Virus envelope and their relations with viral hemagglutinin-neuraminidase membrane glycoprotein

The lipid composition of Newcastle Disease Virus (NDV) Clone-30 strain shows a low lipid/protein ratio, a high cholesterol/phospholipid molar ratio, and major phospholipids being qualitatively different to other NDV strains. The major fatty acyl constituents are palmitic, stearic, oleic, and linoleic acids; cerebrosides, sulfatides and two kinds of gangliosides are also found in the NDV membrane. It is reported for the first time in NDV that phospholipid classes are asymmetrically distributed over the two leaflets of the membrane: 60 +/- 4.5% of the phosphatidylcholine and 70 +/- 5.0% of the sphingomyelin are in the outer monolayer. Intact viral membranes and reconstituted NDV envelopes showed similar dynamic properties. Hemagglutinin-neuraminidase (HN) and fusion (F) proteins of NDV membrane affect the lipid thermotropic behaviour in reconstituted proteoliposomes made up of a single class of phospholipids. It is shown that the lipid composition is more important than the bulk membrane fluidity/order for both sialidase (neuraminidase) and hemagglutinating HN activities. Sialidase and hemagglutinating activities requires the presence of definite phospholipids (phosphatidylethanolamine) in its environment.

Protection of mice from respiratory Sendai virus infections by recombinant vaccinia viruses

Mechanisms of protection of mice from Sendai virus, which is exclusively pneumotropic and causes a typical respiratory disease, by immunization with recombinant vaccinia viruses (RVVs) were investigated. Although the RVV carrying a hemagglutinin-neuraminidase gene of Sendai virus (Vac-HN) propagated in the noses and lungs of mice by either intranasal (i.n.) or intraperitoneal (i.p.) inoculation, no vaccinia virus antigens were detected in the mucosal layer of upper and lower airways of the i.p.-inoculated mice. The mice immunized i.n. with Vac-HN or Vac-F (the RVV carrying a fusion protein gene of Sendai virus) demonstrated the strong resistance to Sendai virus challenge both in the lung and in the nose, whereas the i.p.-immunized mice showed almost no resistance in the nose but showed a partial resistance in the lung. Titration of Sendai virus-specific antibodies in the nasal wash (NW), bronchoalveolar lavage (BAL), and serum collected from the Vac-F-immunized mice showed that the NW from the i.n.-immunized mice contained immunoglobulin A (IgA) antibodies but no IgG and the BAL from the mice contained both IgA and IgG antibodies. On the other hand, neither IgA nor IgG antibodies were detected in the NW from the i.p.-immunized mice and only IgG antibodies were detected in the BAL, although both i.n.- and i.p.-immunized mice exhibited similar levels of serum IgG, IgA, and neutralizing antibodies. The resistance to Sendai virus in the noses of i.n.-immunized mice could be abrogated by the intranasal instillation of anti-mouse IgA but not of anti-IgG antiserum, while the resistance in the lung was not significantly abrogated by such treatments. These results demonstrate that IgA is a major mediator for the immunity against Sendai virus induced by the RVVs and IgG is a supplementary one, especially in the lung, and that the RVV should be intranasally inoculated to induce an efficient mucosal immunity even if it has a pantropic nature.

Truncation of the COOH-terminal region of the paramyxovirus SV5 fusion protein leads to hemifusion but not complete fusion

The role of the simian virus 5 (SV5) fusion (F) protein 20 residue COOH-terminal region, thought to represent the cytoplasmic tail, in fusion activity was examined by constructing a series of COOH-terminal truncation mutants. When the altered F proteins were expressed in eukaryotic cells, by using the vaccinia virus-T7 transient expression system, all the F proteins exhibited similar intracellular transport properties and all were expressed abundantly on the cell surface. Quantitative and qualitative cell fusion assays indicated that all of the F protein COOH-terminal truncation mutants mediated lipid mixing with similar kinetics and efficiency as that of wild-type F protein. However, the cytoplasmic content mixing activity decreased in parallel with the extent of the deletion in the F protein COOH-terminal truncation mutants. These data indicate that it is possible to separate the presumptive early step in the fusion reaction, hemifusion, and the final stage of fusion, content mixing, and that the presence of the F protein COOH-terminal region is important for the final steps of fusion.

Inhibition of Nef- and phorbol ester-induced CD4 degradation by macrolide antibiotics

Human immunodeficiency virus type 1 (HIV-1) is the causative agent of AIDS. The simian immunodeficiency virus (SIV) causes a similar syndrome in macaques. The product of the nef gene of SIV has been shown to be important for virus replication and disease progression in vivo. In vitro, both SIV and HIV Nef downregulate surface expression of CD4 and accelerate total CD4 turnover. The mechanism by which Nef downregulates CD4 has not been established. A current model suggests that Nef enhances cell surface CD4 endocytosis and degradation in lysosomes. However, this was recently challenged when CD4 was found to accumulate in early endosomes of cells expressing Nef. Because inhibition of Nef function might halt virus replication and disease progression, we tested two macrolide antibiotics for their ability to inhibit Nef function. Concanamycin B (ConB) and bafilomycin A1 (BFLA1) are specific inhibitors of acidification of cell endosomes and lysosomes and, unlike other inhibitors, do not affect transport. Although ConB (25 nM) and BFLA1 (100 nM) blocked phorbol myristate acetate- and Nef-induced CD4 degradation in human monocyte U937 cells, CD4 surface expression was not recovered. Instead, CD4 accumulated in lysosomes. To determine if Nef is directly responsible for CD4 degradation or if they bind to each other in a manner similar to Vpu, transcripts of human CD4 and HIV-1 nef were cotranslated in vitro. Our results indicate that under our experimental conditions, Nef does not affect CD4 stability and does not associate with CD4 in this in vitro system. Our data suggest that (i) CD4 downregulation by Nef results in degradation of CD4 in lysosomes, (ii) inhibition of CD4 degradation by macrolide antibiotics does not restore surface expression, and (iii) the inhibition of CD4 expression by Nef appears to be indirect and is likely to involve cellular factors.

Quantitative measurement of paramyxovirus fusion: differences in requirements of glycoproteins between simian virus 5 and human parainfluenza virus 3 or Newcastle disease virus

To compare the requirements for paramyxovirus-mediated cell fusion, the fusion (F) and hemagglutinin-neuraminidase (HN) glycoproteins of simian virus 5 (SV5), human parainfluenza virus 3 (HPIV-3), and Newcastle disease virus (NDV) were expressed individually or coexpressed in either homologous or heterologous combinations in CV-1 or HeLa-T4 cells, using the vaccinia virus-T7 polymerase transient expression system. The contribution of individual glycoproteins in virus-induced membrane fusion was examined by using a quantitative assay for lipid mixing based on the relief of self-quenching (dequenching) of fluorescence of the lipid probe octadecyl rhodamine (R18) and a quantitative assay for content mixing based on the cytoplasmic activation of a reporter gene, beta-galactosidase. In these assays, expression of the individual F glycoproteins did not induce significant levels of cell fusion and no cell fusion was observed in experiments when cells individually expressing homologous F or HN proteins were mixed. However, coexpression of homologous F and HN glycoproteins resulted in extensive cell fusion. The kinetics of fusion were found to be very similar for all three paramyxoviruses studied. With NDV and HPIV-3, no cell fusion was detected when F proteins were coexpressed with heterologous HN proteins or influenza virus hemagglutinin (HA). In contrast, SV5 F protein exhibited a considerable degree of fusion activity when coexpressed with either NDV or HPIV-3 HN or with influenza virus HA, although the kinetics of fusion were two- to threefold higher when the homologous SV5 F and HN proteins were coexpressed. Thus, these data indicate that among the paramyxoviruses tested, SV5 has different requirements for cell fusion.

Potentiation by viral respiratory infection of ovalbumin-induced guinea-pig tracheal hyperresponsiveness: role for tachykinins

1. We investigated whether virus-induced airway hyperresponsiveness in guinea-pigs could be modulated by pretreatment with capsaicin and whether viral respiratory infections could potentiate ovalbumin-aerosol-induced tracheal hyperresponsiveness. 2. Animals were inoculated intratracheally with bovine parainfluenza-3 virus or control medium 7 days after treatment with capsaicin (50 mg kg-1, s.c.). Four days after inoculation, tracheal contractions were measured to increasing concentrations of substance P, histamine and the cholinoceptor agonist, arecoline. 3. In tracheae from virus-infected guinea-pigs, contractions in response to substance P, histamine and arecoline were significantly enhanced (P < 0.01) by 144%, 46% and 77%, respectively. Capsaicin pretreatment inhibited the hyperresponsiveness to substance P partly (62%) and to histamine and arecoline completely. 4. In another series of experiments animals were first sensitized with ovalbumin (20 mg kg-1, i.p.). After 14 days animals were exposed to either saline or ovalbumin aerosols for 8 days. After 4 aerosol exposures (4 days) animals were inoculated with either parainfluenza-3 virus or control medium. One day after the last ovalbumin aerosol, tracheal contraction in response to increasing concentrations of substance P, histamine and arecoline was measured. 5. Tracheae from ovalbumin-aerosol-exposed control inoculated animals showed a similar degree of airway hyperresponsiveness to saline-aerosol-exposed virus-treated guinea-pigs. Virus inoculation of ovalbumin-treated animals significantly potentiated the tracheal contractions to substance P compared to either of the treatments alone. The contractions in response to histamine and arecoline were only slightly enhanced. 6. In conclusion, sensory nerves and/or tachykinins are involved in virus-induced airway hyperresponsivenessin guinea-pigs and viral respiratory infections can potentiate the increase in tracheal responsiveness to bronchoconstrictor agonists after ovalbumin exposure.

Pharmacokinetics of antisense oligodeoxyribonucleotides (cyclin B1 and CDC 2 kinase) in the vessel wall in vivo: enhanced therapeutic utility for restenosis by HVJ-liposome delivery

Using a highly efficient viral HVJ (hemagglutinating virus of Japan) liposome-mediated transfer method, we examined the cellular fate of antisense oligodeoxyribonucleotides (oligos) in the vessel wall in vivo. Direct transfer of unmodified FITC (fluorescein isothiocyanate)-labeled oligos into injured rat carotid arteries showed, localized in the medial layer, fluorescence that disappeared within 1 day. In contrast, transfection of unmodified FITC-oligos by the HVJ-liposome method showed, concentrated in the medial layer, high levels of fluorescence that were sustained for at least 1 week. Moreover, we demonstrated nuclear localization and accumulation of fluorescence in the vessel wall using this method. To examine the therapeutic utility of this method, we transferred antisense phosphorothioate oligos against cyclin B1- and CDC2 kinase-encoding genes into balloon-injured rat carotid artery as a potential therapy for experimental restenosis. Two weeks after transfection, antisense oligo treatment directed against either CDC2 kinase or cyclin B1 resulted in a partial, but significant, inhibition in neointima formation. In contrast, transfection of either sense or scrambled control oligos had no effect. Interestingly, co-transfection of antisense oligos against CDC2 kinase and cyclin B resulted in further inhibition of neointima formation, as compared to blockade of either gene target alone. These results demonstrate that: (i) the HVJ-liposome method enhances the half life and nuclear localization of antisense oligos in the vessel wall in vivo; and (ii) HVJ-mediated administration of antisense CDC2 kinase and cyclin B1 oligos produces a sustained inhibition of neointima formation after balloon angioplasty.

Analysis of the primary T-cell response to Sendai virus infection in C57BL/6 mice: CD4+ T-cell recognition is directed predominantly to the hemagglutinin-neuraminidase glycoprotein

Sendai virus infection of C57BL/6 mice elicits a strong CD4+ and CD8+ T-cell response in the respiratory tract. To investigate the specificity of the CD4+ T-cell response, a panel of hybridomas was generated from cells recovered from the respiratory tracts of infected mice. Using vaccinia virus recombinants expressing individual Sendai virus proteins, we found that the majority of these hybridomas (34 of 37) were specific for the hemagglutinin-neuraminidase (HN) glycoprotein. The hybridomas were then analyzed for reactivity to a set of overlapping peptides spanning the entire length of the hemagglutinin-neuraminidase glycoprotein. At least five H-2 I-Ab-restricted epitopes were defined in HN. The strong bias toward recognition of class II epitopes derived from a single viral protein contrasts with T-cell recognition of epitopes of several proteins in influenza A virus as found previously by others.

Relative affinity of the human parainfluenza virus type 3 hemagglutinin-neuraminidase for sialic acid correlates with virus-induced fusion activity

The ability of enveloped viruses to cause disease depends on their ability to enter the host cell via membrane fusion events. An understanding of these early events in infection, crucial for the design of methods of blocking infection, is needed for viruses that mediate membrane fusion at neutral pH, such as paramyxoviruses and human immunodeficiency virus. Sialic acid is the receptor for the human parainfluenza virus type 3 (HPF3) hemagglutinin-neuraminidase (HN) glycoprotein, the molecule responsible for binding of the virus to cell surfaces. In order for the fusion protein (F) of HPF3 to promote membrane fusion, the HN must interact with its receptor. In the present report, two variants of HPF3 with increased fusion-promoting phenotypes were selected and used to study the function of the HN glycoprotein in membrane fusion. Increased fusogenicity correlated with single amino acid changes in the HN protein that resulted in increased binding of the variant viruses to the sialic acid receptor. These results suggest that the avidity of binding of the HN protein to its receptor regulates the level of F protein-mediated fusion and begin to define one role of the receptor-binding protein of a paramyxovirus in the membrane fusion process.

Sequence and structure alignment of paramyxovirus hemagglutinin-neuraminidase with influenza virus neuraminidase

A model is proposed for the three-dimensional structure of the paramyxovirus hemagglutinin-neuraminidase (HN) protein. The model is broadly similar to the structure of the influenza virus neuraminidase and is based on the identification of invariant amino acids among HN sequences which have counterparts in the enzyme-active center of influenza virus neuraminidase. The influenza virus enzyme-active site is constructed from strain-invariant functional and framework residues, but in this model of HN, it is primarily the functional residues, i.e., those that make direct contact with the substrate sialic acid, which have identical counterparts in neuraminidase. The framework residues of the active site are different in HN and in neuraminidase and appear to be less strictly conserved within HN sequences than within neuraminidase sequences.