Association of ganglioside-protein conjugates into cell and Sendai virus. Requirement for the HN subunit in viral fusion

Generation of a recombinant Sendai virus that is selectively activated and lyses human tumor cells expressing matrix metalloproteinases

Malignant tumor cells often express matrix metalloproteinases (MMPs) at a high level to enable their dissemination and metastasis. Sendai virus (SeV), a nonsegmented negative strand RNA virus, spreads in the target tissues in vivo via cleavage activation of the viral fusion glycoprotein by a tissue-specific, trypsin-like enzyme. By deleting the viral matrix protein, we previously generated a recombinant SeV that does not bud to mature virions, but is highly fusogenic and spreads extensively from cell to cell in a trypsin-dependent manner. Here, we changed the tryptic cleavage site of the fusion glycoprotein of this virus to a site susceptible to MMPs. The resulting recombinant virus was no longer activated by trypsin but spread efficiently in cultured cells supplemented with MMP2 or MMP9 and in human tumor cell lines expressing these MMPs. Furthermore, the virus spread extensively in tumor cells xenotrasplanted to nude mice without disseminating to the surrounding normal cells, leading to the inhibition of the tumor growth in the mice. These results demonstrate the selective targeting and killing of human tumor cells by recombinant SeV technology and greatly advance the reemerging concept of oncolytic virotherapy, which currently appears to rely largely upon a natural preference of certain viruses for cancer cells.

Coating of liposomes with transferrin: physicochemical study of the transferrin-lipid system

Transferrin was incorporated into the external surface of liposomes that were previously derivatized with ceramides. This new hydrophobic derivative of transferrin was incubated with liposomes at different protein-to-lipid ratios. The surface activity of both native and derivatized transferrin was determined with monomolecular layers as a membrane model. The maximal interaction was found with dipalmitoylphosphatidylcholine in all the experiences.

Selective modification of Sendai virus hemagglutinin neuraminidase by pyridoxal 5'-phosphate: evidence for an allosteric modulation of neuraminidase activity

Incubation of Sendai virus with pyridoxal 5'-phosphate (PLP) causes inhibition of hemolytic activity, a slight reduction of hemagglutinating activity, and an increase in neuraminidase activity. The effects on hemagglutination and neuraminidase are prevented by the presence in the incubation mixture of sialyl lactose, a substrate of hemagglutinin-neuraminidase. Incubation with PLP of the water-soluble enzymatic domain of the neuraminidase has no effect on enzymatic activity, while the allosteric inhibition (Dallocchio et al. (1991) Biochem. Int. 25, 663-668) disappears. Both virus-bound and solubilized neuraminidase are selectively modified by PLP at the lysine-553. Our data suggest that PLP inactivates a previously undetected inhibitory site on the viral neuraminidase, and that a physiological effector is present on the viral envelope.

Crystallization of biologically active hemagglutinin-neuraminidase glycoprotein dimers proteolytically cleaved from human parainfluenza virus type 1

We isolated, purified, and characterized the hemagglutinin-neuraminidase (HN) of human parainfluenza virus type 1, with the ultimate goal of producing crystals suitable for three-dimensional X-ray structure analysis. Pronase was used to cleave the globular head of the HN molecule directly from virus particles, forming HN monomers and dimers. The purified dimers retained neuraminidase and hemadsorption activity and were recognized by 14 anti-HN monoclonal antibodies, demonstrating intact HN antigenic structure and function. N-terminal sequence analysis of the dimers showed that cleavage had occurred at amino acid 136 or 137, freeing the C-terminal 438 or 439 amino acids. On electron micrography, the dimer appeared as two box-shaped structures, each approximately 5 by 5 nm. When the purified HN dimers were crystallized in hanging drops by vapor diffusion against 20% polyethylene glycol 3350, they formed both rectangular plates and needlelike crystals. The rectangular crystals diffracted X-rays, indicating an ordered atomic structure. However, the resolution was approximately 10 A (1 nm), insufficient for three-dimensional structural analysis. Experiments to improve the resolution by increasing the size and quality of the crystals are in progress.

Targeting of poly(rI)-poly(rC) by fusogenic (F protein) immunoliposomes

The aim of this study is to investigate the intracellular delivery of polynucleotides by fusogenic immunoliposomes. We have studied the internalization of poly(rI)-poly(rC) (polyIC) by liposomes into murine L929 cells. The liposomes were prepared by incorporating Sendaï virus fusogenic F protein into the lipid bilayer and targeted by a monoclonal antibody (mAb) bound to the liposomes via protein A (Staphylococcus aureus). The immunoliposomes ensured a sufficient yield of polyIC internalization, which was estimated by its ability to induce antiviral activity. In the absence of RNase treatment free and encapsulated polyIC had the same inducing effect, but in the presence of nuclease only the encapsulated polyIC, and not free polyIC, maintained its antiviral effect. The fusion process making possible the internalization of polyIC was confirmed by the fact that the polyIC effect was mainly inhibited by an anti-F protein mAb which inhibited erythrocyte hemolysis by the virus.

Isolation and characterization of monoclonal antibodies to human parainfluenza virus type 4 and their use in revealing antigenic relation between subtypes 4A and 4B

Eighty monoclonal antibodies (MAbs) against parainfluenza virus type 4(PIV-4) were isolated and characterized. Of 50 MAbs against PIV-4A, 14 reacted with the nucleocapsid (NP) protein, 11 with the hemagglutinin-neuraminidase (HN) glycoprotein, 6 with the fusion (F) glycoprotein, and 19 with the matrix (M) protein. With the aid of the PIV-4A and PIV-2 specific MAbs showing cross-reactivity with PIV-4B, the structural proteins of PIV-4B were identified. gp72, p65, gp65, gp55, p53, and p40 of PIV-4B were assigned to HN, NP, Fo, F1, P, and M proteins, respectively. Based on the results, specificities of the MAbs against PIV-4B were determined. Of 30 hybridoma clones against PIV-4B, 13 clones were found to produce antibodies against the NP protein, 7 against the HN protein, and 10 against the F protein. Epitope mapping of these MAbs was performed with competitive binding assays in ELISA. According to their biological activities, the MAbs against the HN protein of either PIV-4A or 4B could be divided into three groups. The first group showed high hemagglutination inhibition (HI), hemolysis inhibition (HLI), and neutralizing (NT) activities. The second group showed high NT activity, but could not block hemagglutination. The final group showed a lower level of all activities. The MAbs against the F protein of PIV-4A and against PIV-4B were divided into two groups. Some MAbs against the F protein had high titer of NT, suggesting that the F protein had neutralizing-related epitopes. Antigenicity of the NP protein was highly conserved among subtypes of PIV-4. On the other hand, the MAbs against the HN and the F proteins showed high reactivity with the homologous subtype viruses, but low reactivity with the heterologous subtype viruses, indicating that the external glycoproteins exhibited antigenic variations between two subtypes of PIV-4. When the immunological interrelationship among various paramyxoviruses was analyzed. PIV-4 was found to be antigenically related to PIV-2, SV 5, and mumps virus.

Conformation and stability of Sendai virus fusion protein

The conformation and stability of Sendai virus fusion (F) protein were studied by circular dichroism spectroscopy, and the protein predictive models of Chou and Fasman and Robson and Suzuki were used to elucidate the secondary structure of Sendai virus F protein. The F protein conformation is predicted to contain 33% alpha-helix, 53% beta-sheet and 15% beta-turn by the Chou and Fasman model, and 30% alpha-helix, 55% beta-sheet, 9% beta-turn and 7% random coil by the Robson and Suzuki model. C.d. studies of F protein purified in the presence of the non-ionic detergent, n-octylglucoside, indicated the presence of 49% alpha-helix and 31% beta-sheet at pH 7.0, 54% alpha-helix and 28% beta-sheet at pH 9.0 and 50% alpha-helix and 23% beta-sheet at pH 5.4. A small change in conformation of the protein occurred when the pH was titrated from 7.0 to 5.4 and from 7.0 to 9.0 and a more pronounced conformational change occurred when the pH was changed from 9.0 to 5.4. The F protein in 0.2% n-octylglucoside was resistant to denaturation by 4 M guanidine hydrochloride, the reducing agent 20 mM mercaptoethanol, and to increases in temperature from 5 to 80 degrees C. Monoclonal anti-F protein antibody showed an increased binding to whole virus when the pH was changed from 7.0 to 9.0. The antibody binding was decreased when the pH was shifted from 9.0 to 5.4 Maximum haemolytic activity was observed with virus that was preincubated at pH 8.0.(ABSTRACT TRUNCATED AT 250 WORDS)

An Arg-Gly-Asp-directed receptor on the surface of human melanoma cells exists in an divalent cation-dependent functional complex with the disialoganglioside GD2

The disialogangliosides GD2 and GD3 play a major role in the ability of human melanoma cells to attach to Arg-Gly-Asp-containing substrates such as fibronectin and vitronectin, since pretreatment of these cells with monoclonal antibodies to the oligosaccharide of GD2 and GD3 can inhibit their attachment and spreading on such adhesive proteins. This report demonstrates that human melanoma cells (M21) synthesize and express a glycoprotein receptor that shares antigenic epitopes with the vitronectin receptor on human fibroblasts and is capable of specifically recognizing the Gly-Arg-Gly-Asp-Ser-Pro sequence. In the presence of calcium, GD2, the major ganglioside of M21 cells, colocalized with this receptor on the surface of human melanoma cells and their focal adhesion plaques as demonstrated by double-label transmission immunoelectron microscopy and indirect immunofluorescence. Biochemical evidence is presented indicating that the vitronectin receptor on M21 human melanoma cells contains associated calcium and GD2. This ganglioside copurified with the glycoprotein receptor for vitronectin on affinity columns containing either an Arg-Gly-Asp-containing peptide, concanavalin A, or lentil lectin. This major Arg-Gly-Asp-directed receptor on M21 cells could be metabolically labeled with 45Ca2+. Chelation of this ion with EDTA caused the dissociation of GD2 from the receptor and rendered the remaining glycoprotein incapable of binding to an Arg-Gly-Asp-containing peptide. Reconstitution experiments demonstrated a requirement for calcium, and not magnesium, for receptor binding to Arg-Gly-Asp and indicated that addition of ganglioside can enhance this interaction.

Localization of functional sites on the hemagglutinin-neuraminidase glycoprotein of Sendai virus by sequence analysis of antigenic and temperature-sensitive mutants

To locate the various functions associated with the hemagglutinin-neuraminidase (HN) glycoprotein of Sendai virus in the primary structure of the protein, a temperature-sensitive (ts) mutant and seven antigenic mutants were sequenced. The ts mutant was defective in its ability to agglutinate erythrocytes and infect host cells, while its neuraminidase activity was normal. Its sequence revealed two closely spaced amino acid substitutions (residues 262 and 264) and one distant substitution (residue 461). Revertants could not be isolated, suggesting that more than one of the substitutions is responsible for the defective hemagglutinating activity. The antigenic mutants were selected with monoclonal antibodies that delineate four nonoverlapping antigenic sites (I-IV) and separately inhibit hemagglutinating, neuraminidase, and hemolysis activities. Mutants selected with antibodies to antigenic sites I-III were used to map these functions on the primary sequence of HN. Each antigenic mutant had a single point mutation in the HN gene that resulted in an amino acid substitution in the protein. A site II mutant selected with an antibody which inhibits hemolysin activity had a substitution at amino acid 420, while a mutant selected with antibody that inhibits only erythrocyte binding (site III) had a substitution at amino acid 541. Two antigenic mutants selected with an antibody that inhibits hemagglutination and neuraminidase activities (site I) had amino acid substitutions in close proximity (residues 277 and 279) to the two closely spaced substitutions of the ts mutant. These findings suggest that the region defined by the ts mutant and these two antigenic mutants is involved in host cell binding. Antigenic mutants selected with another site I antibody had amino acid changes at residue 184, indicating that antigenic site I is discontinuous in the primary sequence. This antibody blocks only hemagglutination, but mutants selected with it had a decreased neuraminidase activity. This finding supports the idea that the neuraminidase site is close to, but distinct from, the hemagglutination site.

Distinct functions of antigenic sites of the HN glycoprotein of Sendai virus

Monoclonal antibodies specific for the hemagglutinin-neuraminidase (HN) glycoprotein of Sendai virus were used to examine the antigenic structure of HN and its role in the initiation of infection and immunity. Using 10 anti-HN antibodies, four distinct antigenic sites designated I-IV were topographically mapped on the HN molecule by competitive-binding assays. To relate the biological functions of HN to its antigenic structure, anti-HN antibodies were analyzed for their inhibitory activity in neuraminidase, hemagglutination, and hemolysis inhibition tests. Antibodies to antigenic site I inhibited hemagglutination and one of these antibodies also inhibited neuraminidase activity. Antibodies to site II inhibited neither activity. However, hemolysis an F protein activity was inhibited, suggesting that these antibodies which bind to HN interfere with F-mediated fusion. Antigenic sites III and IV had different effects on the hemagglutinating and neuraminidase functions of HN: Site III antibodies inhibited hemagglutination while antibodies to site IV only inhibited neuraminidase activity. Antibodies to each antigenic site inhibited virus production. Since antibodies to sites I and III inhibited hemagglutination, it is likely that they block virus adsorption. Antibodies to HN site II only inhibited hemolysis, and therefore, may prevent virus penetration. Antibodies reacting with site IV inhibited virus production after virus penetration. Since neuraminidase activity was the only function inhibited, the viral enzyme may be involved in virus release. The fact that site IV antibodies inhibited neuraminidase but not hemagglutination suggests that these sites are distinct.

The interaction of Sendai virus glycoprotein-bearing recombinant vesicles with cell surfaces

Sendai virus glycoproteins HN and F were purified by immunoaffinity chromatography from virions disrupted by beta-D-octylglucoside. The purified glycoproteins were reconstituted in recombinant vesicles with phosphatidylcholine or phosphatidylethanolamine and phosphatidylserine. P815 or EL-4 cells treated with glycoprotein HN/F-phosphatidylcholine recombinant vesicles acquired the glycoproteins and retained them in the plasma membrane for 4 h as demonstrated by surface immunofluorescence specific for each protein. Cells treated with glycoprotein HN-phosphatidylcholine recombinant vesicles initially bore glycoprotein HN on the surface but the protein eluted within 2 h. Surfaces of cells treated with glycoprotein F-phosphatidylcholine recombinant vesicles did not acquire the glycoprotein. Cells treated with glycoprotein HN-phosphatidylethanolamine: phosphatidylserine recombinant vesicles or glycoprotein F-phosphatidylethanolamine: phosphatidylserine recombinant vesicles in the presence of 5 mM Ca2+ acquired each protein for at least 2 h. Experiments showed that the acquired glycoproteins capped with antibody and that when glycoproteins HN and F were together on the surface they co-capped. Acquired viral glycoproteins did not co-cap with intrinsic H-2 glycoproteins.

Targeting of loaded Sendai virus envelopes by covalently attached insulin molecules to virus receptor-depleted cells: fusion-mediated microinjection of ricin A and simian virus 40 DNA

Insulin molecules were covalently attached to detergent-solubilized Sendai virus envelope glycoproteins (HN and F polypeptides) by the use of the crosslinking reagent succinimidyl 4-(p-maleimidophenyl)butyrate (SMPB). Reconstitution of modified viral glycoproteins (carrying covalently attached insulin) together with unmodified viral glycoproteins resulted in the formation of "fusogenic" viral envelopes bearing insulin molecules. Reconstitution of such fusogenic viral envelopes in the presence of ricin A or simian virus 40 (SV40) DNA resulted in the formation of viral envelopes bearing insulin molecules and loaded with ricin A or SV40 DNA. Such viral envelopes were able to bind to hepatoma tissue culture cells (HTCC) from which Sendai virus receptors were removed by treatment with neuraminidase. Incubation of viral envelopes loaded with ricin A with virus receptor-depleted HTCC resulted in fusion-mediated injection of the toxin, as inferred from inhibition of protein synthesis and decrease in cell viability of the microinjected cells. Fusion-mediated injection of SV40 DNA was inferred from the appearance of SV40 tumor antigen in microinjected cells. Binding and fusion of the loaded viral envelopes to neuraminidase-treated HTCC was mediated solely by the virus-associated insulin molecules. Addition of free insulin molecules inhibited binding of the viral envelopes and, consequently, the microinjection of ricin A and SV40 DNA.

Use of virus-attached antibodies or insulin molecules to mediate fusion between Sendai virus envelopes and neuraminidase-treated cells

Anti-human erythrocyte antibodies or insulin molecules were covalently coupled to the glycoproteins (the hemagglutinin/neuraminidase and the fusion polypeptides) of Sendai virus envelopes with N-succinimidyl 3-(2-pyridyldithio)propionate and succinimidyl 4-(p-maleimidophenyl)butyrate as cross-linking reagents. Reconstituted Sendai virus envelopes, bearing covalently attached anti-human erythrocyte antibodies or insulin molecules, were able to bind to but not fuse with virus receptor depleted human erythrocytes (neuraminidase-treated human erythrocytes). Only coreconstitution of Sendai virus glycoproteins, bearing attached anti-human erythrocyte antibodies or insulin molecules with intact, untreated viral glycoproteins, led to the formation of fusogenic, targeted reconstituted Sendai virus envelopes. Binding and fusion of reconstituted Sendai virus envelopes, bearing anti-human erythrocyte antibodies or insulin molecules, with neuraminidase-treated human erythrocytes were blocked by the monovalent fraction, obtained after papain digestion of immunoglobulins, made of anti-human erythrocyte antibodies or free insulin molecules, respectively. The results of this work demonstrate an active role of the viral binding protein (hemagglutinin/neuraminidase polypeptide) in the virus membrane fusion process and show a novel and efficient method for the construction of targeted, fusogenic Sendai virus envelopes.

An alternative route of infection for viruses: entry by means of the asialoglycoprotein receptor of a Sendai virus mutant lacking its attachment protein

During the first stage of infection, the paramyxovirus Sendai virus attaches to host cells by recognizing specific receptors on the cell surface. Productive virus-cell interactions result in membrane fusion between the viral envelope and the cell surface membrane. It has recently been shown that the ganglioside GD1a and its more complex homologs GT1b and GQ1b are cell surface receptors for Sendai virus. We report in this paper that the temperature-sensitive mutant ts271 of the Enders strain of Sendai virus lacks the viral attachment protein HN and the biological activities of hemagglutination and sialidase activity associated with it when the virus is grown at 38 degrees C. This HN- virus was unable to infect or agglutinate conventional host cells that contained receptor gangliosides and were readily infected by the parental wild-type virus. The HN- virus did, however, attach to and infect Hep G2 cells, a line of hepatoma cells that retains the asialoglycoprotein receptor (ASGP-R) upon continuous culture. This receptor is a mammalian lectin that recognizes galactose- or N-acetylgalactosamine-terminated proteins. In accordance with the known properties of this receptor, infection by the HN- virus was abolished by treatment of Hep G2 cells with sialidase, by the presence of Ca2+ chelators, and by competition with N-acetylgalactosamine, asialoorosomucoid, and antibody to the receptor. F, the only glycoprotein on the HN- virus, was shown to compete with the galactose-terminated protein asialoorosomucoid for the ASGP-R. The ability of the HN- virus to cause cell-cell fusion of Hep G2 cells indicated that attachment of this virus to the ASGP-R still permitted viral entry by its usual mode--i.e., membrane fusion at the cell surface. These results open up the possibility that enveloped viruses, which contain glycosylated proteins or lipids, may make use of naturally occurring lectins in addition to their normal receptors as a means of attachment to host cells.