Nucleotide sequence of a cDNA clone encoding the entire glycoprotein from the New Jersey serotype of vesicular stomatitis virus

Vesicular and uncoated Rab1-dependent cargo carriers facilitate ER to Golgi transport

Secretory cargo is recognized, concentrated and trafficked from endoplasmic reticulum (ER) exit sites (ERES) to the Golgi. Cargo export from the ER begins when a series of highly conserved COPII coat proteins accumulate at the ER and regulate the formation of cargo-loaded COPII vesicles. In animal cells, capturing live de novo cargo trafficking past this point is challenging; it has been difficult to discriminate whether cargo is trafficked to the Golgi in a COPII-coated vesicle. Here, we describe a recently developed live-cell cargo export system that can be synchronously released from ERES to illustrate de novo trafficking in animal cells. We found that components of the COPII coat remain associated with the ERES while cargo is extruded into COPII-uncoated, non-ER associated, Rab1 (herein referring to Rab1a or Rab1b)-dependent carriers. Our data suggest that, in animal cells, COPII coat components remain stably associated with the ER at exit sites to generate a specialized compartment, but once cargo is sorted and organized, Rab1 labels these export carriers and facilitates efficient forward trafficking.This article has an associated First Person interview with the first author of the paper.

Enhancement of the transduction efficiency of a lentiviral vector for neuron-specific retrograde gene delivery through the point mutation of fusion glycoprotein type E

BACKGROUND

Pseudotyping of a lentiviral vector with fusion glycoproteins composed of rabies virus glycoprotein (RVG) and vesicular stomatitis virus glycoprotein (VSVG) segments achieves high gene transfer efficiency through retrograde transport in the nervous system. In our previous study, we determined the junction of RVG/VSVG segments of glycoproteins that enhances the transduction efficiency of the neuron-specific retrograde gene transfer (NeuRet) vector (termed fusion glycoprotein type E or FuG-E).

NEW METHOD

We aimed to optimize the amino acid residue at position 440 in the membrane-proximal region of FuG-E to improve the efficiency of retrograde gene transfer in the brain.

RESULTS

We constructed variants of FuG-E with 18 kinds of single amino acid substitutions at residue 440 to generate lentiviral vectors pseudotyped with these variants, and tested in vivo gene transfer of the vectors in the mouse brain. The FuG-E (P440E) variant, in which proline was substituted by glutamate at residue 440 in FuG-E, showed the greatest retrograde gene transfer efficiency in the brain, bearing the property of the NeuRet vector. The FuG-E (P440E) pseudotype also displayed efficient retrograde gene transfer in the common marmoset brain.

COMPARISON WITH EXISTING METHODS

The NeuRet vector with the FuG-E (P440E) variant demonstrated higher retrograde gene transfer efficiency into different neural pathways compared with the parental FuG-E vector.

CONCLUSIONS

The FuG-E (P440E) pseudotype provides a powerful tool to investigate neural circuit mechanisms underlying various brain functions and for gene therapy trials of neurological and neurodegenerative diseases.

Inhibition of Enveloped RNA Virus Formation by Peptides Corresponding to Glycoprotein Sequences

Peptides, corresponding to amino acid sequences in the cytoplasmic domains of the transmembranal glycoproteins encoded by Sindbis and vesicular stomatitis viruses, inhibited release of virus particles and infectious virus when added to infected cells for a 2h period during a one-cycle growth curve. Each inhibitory peptide was specific for its intended virus. The shortest peptide with antiviral activity for Sindbis virus contained six amino acids, and a related peptide that was acylated at the amino terminus with octanoic acid was ten-fold more potent as an inhibitor. Neither of these peptides affected the synthesis of viral structural proteins, but a third peptide inhibited proteolytic processing of the Sindbis virus E2 glycoprotein. Inhibition of vesicular stomatitis virus particle release was dose-dependent in the range of 50–400 μg ml−1 for a peptide corresponding to the G glycoprotein cytoplasmic domain. We postulate that these peptides competitively inhibit attachment of the glycoprotein to intracellular virus structures during assembly of the virion. Thus, drugs, based on peptides that mimic the protein-protein interactions required for virus assembly, may have therapeutic potential.

Creation of matrix protein gene variants of two serotypes of vesicular stomatitis virus as prime-boost vaccine vectors

To take advantage of live recombinant vesicular stomatitis viruses (rVSVs) as vaccine vectors for their high yield and for their induction of strong and long-lasting immune responses, it is necessary to make live vaccine vectors safe for use without losing their immunogenicity. We have generated safer and highly efficient recombinant VSV vaccine vectors by combining the M51R mutation in the M gene of serotype VSV-Indiana (VSVInd) with a temperature-sensitive mutation (tsO23) of the VSVInd Orsay strain. In addition, we have generated two new serotype VSV-New Jersey (VSVNJ) vaccine vectors by combining M48R and M51R mutations with G22E and L110F mutations in the M gene, rVSVNJ(G22E M48R M51R) [rVSVNJ(GMM)] and VSVNJ(G22E M48R M51R L110F) [rVSVNJ(GMML)]. The combined mutations G21E, M51R, and L111F in the M protein of VSVInd significantly reduced the burst size of the virus by up to 10,000-fold at 37°C without affecting the level of protein expression. BHK21 cells and SH-SY5Y human neuroblastoma cells infected with rVSVInd(GML), rVSVNJ(GMM), and rVSVNJ(GMML) showed significantly reduced cytopathic effects in vitro at 37°C, and mice injected with 1 million infectious virus particles of these mutants into the brain showed no neurological dysfunctions or any other adverse effects. In order to increase the stability of the temperature-sensitive mutant, we have replaced the phenylalanine with alanine. This will change all three nucleotides from UUG (leucine) to GCA (alanine). The resulting L111A mutant showed the temperature-sensitive phenotype of rVSVInd(GML) and increased stability. Twenty consecutive passages of rVSVInd(GML) with an L111A mutation did not convert back to leucine (UUG) at position 111 in the M protein gene.

IMPORTANCE

Recombinant vesicular stomatitis viruses as live vaccine vectors are very effective in expressing foreign genes and inducing adaptive T cell and B cell immune responses. As with any other live viruses in humans or animals, the use of live rVSVs as vaccine vectors demands the utmost safety. Our strategy to attenuate rVSVInd by utilizing a temperature-sensitive assembly-defective mutation of L111A and combining it with an M51R mutation in the M protein of rVSVInd significantly reduced the pathogenicity of the virus while maintaining highly effective virus production. We believe our new temperature-sensitive M gene mutant of rVSVInd(GML) and M gene mutants of rVSVNJ(GMM) and rVSVNJ(GMML) add excellent vaccine vectors to the pool of live viral vectors.

A novel, live-attenuated vesicular stomatitis virus vector displaying conformationally intact, functional HIV-1 envelope trimers that elicits potent cellular and humoral responses in mice

Though vaccination with live-attenuated SIV provides the greatest protection from progressive disease caused by SIV challenge in rhesus macaques, attenuated HIV presents safety concerns as a vaccine; therefore, live viral vectors carrying HIV immunogens must be considered. We have designed a replication-competent vesicular stomatitis virus (VSV) displaying immunogenic HIV-1 Env trimers and attenuating quantities of the native surface glycoprotein (G). The clade B Env immunogen is an Env-VSV G hybrid (EnvG) in which the transmembrane and cytoplasmic tail regions are derived from G. Relocation of the G gene to the 5'terminus of the genome and insertion of EnvG into the natural G position induced a ∼1 log reduction in surface G, significant growth attenuation compared to wild-type, and incorporation of abundant EnvG. Western blot analysis indicated that ∼75% of incorporated EnvG was a mature proteolytically processed form. Flow cytometry showed that surface EnvG bound various conformationally- and trimer-specific antibodies (Abs), and in-vitro growth assays on CD4+CCR5+ cells demonstrated EnvG functionality. Neither intranasal (IN) or intramuscular (IM) administration in mice induced any observable pathology and all regimens tested generated potent Env-specific ELISA titers of 10(4)-10(5), with an IM VSV prime/IN VSV boost regimen eliciting the highest binding and neutralizing Ab titers. Significant quantities of Env-specific CD4+ T cells were also detected, which were augmented as much as 70-fold by priming with IM electroporated plasmids encoding EnvG and IL-12. These data suggest that our novel vector can achieve balanced safety and immunogenicity and should be considered as an HIV vaccine platform.

New viruses for cancer therapy: meeting clinical needs

Early-stage clinical trials of oncolytic virotherapy have reported the safety of several virus platforms, and viruses from three families have progressed to advanced efficacy trials. In addition, preclinical studies have established proof-of-principle for many new genetic engineering strategies. Thus, the virotherapy field now has available a diverse collection of viruses that are equipped to address unmet clinical needs owing to improved systemic administration, greater tumour specificity and enhanced oncolytic efficacy. The current key challenge for the field is to develop viruses that replicate with greater efficiency within tumours while achieving therapeutic synergy with currently available treatments.

Envelope-chimeric entry-targeted measles virus escapes neutralization and achieves oncolysis

Measles virus (MV) is a promising vector for cancer therapy and multivalent vaccination, but high prevalence of pre-existing neutralizing antibodies may reduce therapeutic efficacy, particularly following systemic administration. MV has only one serotype, but here we show that its envelope glycoproteins can be exchanged with those of the closely related canine distemper virus (CDV), generating a chimeric virus capable of escaping neutralization. To target its entry, we displayed on the CDV attachment protein a single-chain antibody specific for a designated receptor. To enhance oncolytic efficacy we armed the virus with a prodrug convertase gene capable of locally activating chemotherapeutic prodrugs. The new virus achieved high titers, was genetically stable, and was resistant to neutralization by sera from both MV-immunized mice and MV-immune humans. The new virus targeted syngeneic murine tumor cells expressing the designated receptor implanted in immunocompetent mice, and synergized with a chemotherapeutic prodrug in a model of oncolysis. Importantly, the chimeric MV remained oncolytic when administered systemically even in the presence of anti-MV antibodies capable of abrogating the therapeutic efficacy of the parental, nonshielded MV. This work shows that targeting, arming, and shielding can be combined to generate a tumor-specific, neutralization-resistant virus that can synergize with chemotherapeutics.

Enzyme-linked immunosorbent assay using glycoprotein and monoclonal antibody for detecting antibodies to vesicular stomatitis virus serotype New Jersey

In this study, an enzyme-linked immunosorbent assay (ELISA) using glycoprotein and a monoclonal antibody (MAb) was developed for the detection of antibodies to vesicular stomatitis virus (VSV) serotype New Jersey (NJ). The glycoprotein to be used as a diagnostic antigen was extracted from partially purified VSV-NJ, and a neutralizing MAb specific to VSV-NJ was incorporated to compete with antibodies in a blocking ELISA using glycoprotein (GP ELISA). The cutoff of the GP ELISA was set at 40% inhibition, which corresponded to a virus neutralization test (VNT) titer of 32. With this threshold, the GP ELISA exhibited 99.6% specificity for naïve sera (n = 3,005) from cattle (n = 1,040), pigs (n = 1,120), and horses (n = 845) from domestic farms. The GP ELISA did not cross-react with sera positive for foot-and-mouth disease virus, swine vesicular disease virus, or VSV serotype Indiana. The GP ELISA was more compatible with the VNT than was the nucleocapsid-based ELISA for VSV-NJ-positive sera (n = 19). Taken together, this GP ELISA could be a useful tool as an alternative to the VNT for detecting antibodies specific to VSV-NJ.

Chapter 9 Fusion of Viral Envelopes with Cellular Membranes

This chapter reviews some characteristic features of membrane fusion activity for each virus and discusses the mechanisms of membrane fusion, especially low pH-induced membrane fusion. It concentrates on the interaction of the hydrophobic segment with the target cell membrane lipid bilayer and suggests the entrance of the segment into the lipid bilayer hydrophobic core as a key step in fusion. The envelope is a lipid bilayer membrane with the virus specific glycoproteins spanning it. The bilayer originates from the host cell membrane and has a lipid composition and transbilayer distribution quite similar to the host's. The viral glycoproteins have the functions of binding to the target cell surface and fusion with the cell membranes. The two functions are carried by a single glycoprotein in influenza virus (HA), vesicular stomatitis virus (VSV) G glycoprotein, and Semliki Forest virus SFV E glycoprotein. In Sendai virus (HVJ), the functions are carried by separate glycoproteins, hemagglutinin-neuraminidase (HN) for binding and fusion glycoprotein (F) for fusion. When viruses encounter target cells, they first bind to the cell surface through an interaction of the viral glycoprotein with receptors.

Matrix protein of VSV New Jersey serotype containing methionine to arginine substitutions at positions 48 and 51 allows near-normal host cell gene expression

The matrix (M) protein of vesicular stomatitis virus (VSV) plays significant roles in the replication of VSV through its involvement in the assembly of virus particles as well as by facilitating the evasion of innate host cell defense mechanisms. The presence of methionine at position 51 (M51) of the matrix (M) protein of the VSV Indiana serotype (VSV(Ind)) has been proven to be crucial for cell rounding and inhibition of host cell gene expression. The M protein of VSV(Ind) with the substitution of M51 with arginine (R:M51R) results in the loss of inhibitory effects on host cell gene expression. The VSV(Ind) expressing the M(M51R) protein became the attractive oncolytic virus which is safer and more tumor-specific because the normal cells can clear the mutant VSV(Ind) easily but tumor cells are susceptible to the virus because a variety of tumor cells lack innate antiviral activities. We have studied the role of the methionines at positions 48 and 51 of the M protein of the New Jersey serotype of VSV (VSV(NJ)) in the induction of cytopathic effects (CPE) and host cell gene expression. We have generated human embryonic kidney 293 cell lines inducibly expressing M proteins with M to R mutations at positions 48 and 51, either separately or together as a double mutant, and examined expression of heat shock protein 70 (HSP70) as an indicator of host cell gene expression. We have also generated recombinant VSV(NJ) encoding the mutant M proteins M(M48R) or M(M48R+M51R) for the first time and tested for the expression of HSP70 in infected cells. Our results demonstrated that the M51 of VSV(NJ) M proteins has a major role in cell rounding and in suppressing the host cell gene expression either when the M protein was expressed alone in inducible cell lines or when expressed together with other VSV proteins by the recombinant VSV(NJ). Amino acid residue M48 may also have some role in cell rounding and in the inhibitory effects of VSV(NJ) M, which was demonstrated by the fact that the cell line expressing the double substitution mutant M(M48R+M51R) exhibited the least cytopathic effects and the least inhibitory effect on host cell gene expression.

Genetic comparison of the rhabdoviruses from animals and plants

There are more than 160 viral species in the Rhabdovidae family, most of which can be grouped into one of the six genera including Vesiculovirus, Lyssavirus, Ephemerovirus, Novirhabdovirus, Cytorhabdovirus, and Nucleorhabdovirus. These viruses are not only morphologically similar but also genetically related. Analysis of viral genes shows that rhabdoviruses are more closely related to each other than to viruses in other families. With the development of reverse genetics, the functions of many cis- and trans-elements important in the process of viral transcription and replication have been clearly defined such as the leader, trailer, and the intergenic sequences. Furthermore, it has been shown that there are two entry sites for the RNA-dependent RNA polymerase: 3' entry for leader synthesis and RNA replication, and direct entry at the N gene start sequence for transcription of the monocistronic mRNAs.

Biological differences between vesicular stomatitis virus Indiana and New Jersey serotype glycoproteins: identification of amino acid residues modulating pH-dependent infectivity

We previously generated recombinant vesicular stomatitis viruses (VSV) based on the Indiana serotype genome which contained either the homologous glycoprotein gene from the Indiana serotype (VSIV-GI) or the heterologous glycoprotein gene from the New Jersey serotype (VSIV-GNJ). The virus expressing the GNJ gene was more pathogenic than the parental VSIV-GI virus in swine, a natural host (26). For the present study, we investigated the biological differences between the GI and GNJ proteins that may be related to the differences in pathogenesis between VSIV-GI and VSIV-GNJ. We show that the capacities of viruses with either the GNJ or GI glycoprotein to infect cultured cells differ depending on the pH. VSIV-GNJ could infect cells at acidic pHs, while the infectivity of VSIV-GI was severely reduced. VSIV-GNJ infection was also more sensitive to inhibition by ammonium chloride, indicating that the GNJ protein had a lower pH threshold for membrane fusion. We applied selective pressure to VSIV-GI by growing it at successively lower pH values and isolated variant viruses in which we identified amino acid changes that conferred low-pH-resistant infectivity. Repeated passage in cell culture at pH 6.8 resulted in the selection of a VSIV-GI variant (VSIV-6.8) that was similar to VSIV-GNJ regarding its pH- and ammonium chloride-dependent infectivity. Sequence analysis of VSIV-6.8 revealed that it had a single amino acid substitution in the amino-terminal region of the glycoprotein (F18L). This alteration was shown to be responsible for the observed phenotype by site-directed mutagenesis of a VSIV-GI full-length cDNA and analysis of the recovered engineered virus. A further adaptation of VSIV-6.8 to pHs 6.6 and 6.4 resulted in additional amino acid substitutions in areas of the glycoprotein that were not previously implicated in attachment or fusion.

Prediction and identification of a permissive epitope insertion site in the vesicular stomatitis virus glycoprotein

We developed a rational approach to identify a site in the vesicular stomatitis virus (VSV) glycoprotein (G) that is exposed on the protein surface and tolerant of foreign epitope insertion. The foreign epitope inserted was the six-amino-acid sequence ELDKWA, a sequence in a neutralizing epitope from human immunodeficiency virus type 1. This sequence was inserted into six sites within the VSV G protein (Indiana serotype). Four sites were selected based on hydrophilicity and high sequence variability identified by sequence comparison with other vesiculovirus G proteins. The site showing the highest variability was fully tolerant of the foreign peptide insertion. G protein containing the insertion at this site folded correctly, was transported normally to the cell surface, had normal membrane fusion activity, and could reconstitute fully infectious VSV. The virus was neutralized by the human 2F5 monoclonal antibody that binds the ELDKWA epitope. Additional studies showed that this site in G protein tolerated insertion of at least 16 amino acids while retaining full infectivity. The three other insertions in somewhat less variable sequences interfered with VSV G folding and transport to the cell surface. Two additional insertions were made in a conserved sequence adjacent to a glycosylation site and near the transmembrane domain. The former blocked G-protein transport, while the latter allowed transport to the cell surface but blocked membrane fusion activity of G protein. Identification of an insertion-tolerant site in VSV G could be important in future vaccine and targeting studies, and the general principle might also be useful in other systems.

The membrane-proximal region of vesicular stomatitis virus glycoprotein G ectodomain is critical for fusion and virus infectivity

The glycoprotein (G) of vesicular stomatitis virus (VSV) is responsible for binding of virus to cells and for mediating virus entry following endocytosis by inducing fusion of the viral envelope with the endosomal membrane. The fusion peptide of G is internal (residues 116 to 137) and exhibits characteristics similar to those of other internal fusion peptides, but recent studies have implicated the region adjacent to the transmembrane domain as also being important for G-mediated membrane fusion. Sequence alignment of the membrane-proximal region of G from several different vesiculoviruses revealed that this domain is highly conserved, suggesting that it is important for G function. Mutational analysis was used to show that this region is not essential for G protein oligomerization, transport to the cell surface, or incorporation into virus particles but that it is essential for acid-induced membrane fusion activity and for virus infectivity. Deletion of the 13 membrane-proximal amino acids (N449 to W461) dramatically reduced cell-cell fusion activity and reduced virus infectivity approximately 100-fold, but mutation of conserved aromatic residues (W457, F458, and W461) either singly or together had only modest effects on cell-cell fusion activity; recombinant virus encoding these mutants replicated as efficiently as wild-type (WT) VSV. Insertion of heterologous sequences in the juxtamembrane region completely abolished membrane fusion activity and virus infectivity, as did deletion of residues F440 to N449. The insertion mutants showed some changes in pH-dependent conformational changes and in virus binding, which could partially explain the defects in membrane fusion activity, but all the other mutants were similar to WT G with respect to conformational changes and virus binding. These data support the hypothesis that the membrane-proximal domain contributes to G-mediated membrane fusion activity, yet the conserved aromatic residues are not essential for membrane fusion or virus infectivity.

Vesicular stomatitis virus glycoprotein is a determinant of pathogenesis in swine, a natural host

There are two major serotypes of vesicular stomatitis virus (VSV), Indiana (VSIV) and New Jersey (VSNJV). We recovered recombinant VSIVs from engineered cDNAs that contained either (i) one copy of the VSIV G gene (VSIV-G(I)); (ii) two copies of the G gene, one from each serotype (VSIV-G(NJ)G(I)); or (iii) a single copy of the G(NJ) gene instead of the G(I) gene (VSIV-G(NJ)). The recombinant viruses expressed the appropriate glycoproteins, incorporated them into virions, and were neutralized by antibodies specific for VSIV (VSIV-G(I)), VSNJV (VSIV-G(NJ)), or both (VSIV-G(NJ)G(I)), according to the glycoprotein(s) they expressed. All recombinant viruses grew to similar titers in cell culture. In mice, VSIV-G(NJ) and VSIV-G(NJ)G(I) were attenuated. However, in swine, a natural host for VSV, the G(NJ) glycoprotein-containing viruses caused more severe lesions and replicated to higher titers than the parental virus, VSIV-G(I). These observations implicate the glycoprotein as a determinant of VSV virulence in a natural host and emphasize the differences in VSV pathogenesis between mice and swine.

The transitional ER defines a boundary for quality control in the secretion of tsO45 VSV glycoprotein

Quality control in the secretory pathway limits forward transport of newly synthesized cargo proteins to those that have acquired their fully folded conformation. To determine which organelles participate in this conformation-dependent sorting process, we analyzed the trafficking of the temperature-sensitive, thermo-reversible folding mutant of vesicular stomatitis virus glycoprotein (tsO45 G protein) in VERO cells. Using temperature blocks, the G protein could be localized to the ER (39.5 degrees C), to the vesiculo-tubular clusters (VTCs, 15 degrees C), and to the trans-Golgi network (TGN, 20 degrees C). To localize the G protein specifically to ER exit sites, we incubated cells at 10 degrees C. The exit sites contained Sec13p, a COPII component, and were devoid of calnexin and other ER chaperones. We found that if the G protein in the exit sites was misfolded by a temperature shift from 10 degrees C to 39.5 degrees C, it failed to enter the VTCs. Instead, it was returned to the reticular ER where it associated with calnexin. However, if the G protein was in the VTCs or beyond, its folding status no longer affected further transport. The observations indicate that quality control took place in the ER and in the ER transitional elements, but not in the VTCs or the Golgi complex. The results provide a way to discriminate biochemically between exit sites and VTCs, two related structures that are difficult to distinguish from each other.

A novel fish rhabdovirus from sweden is closely related to the Finnish rhabdovirus 903/87

A novel rhabdovirus, preliminary designated as the Sea trout rhabdovirus 28/97 (STRV 28/97), was isolated from sea trout (Salmo trutta trutta) in Sweden in 1996. The fish showed central nervous symptoms, and at the autopsy petechial bleedings in the mesenteric fat were visible. STRV 28/97 was shown to be serologically related to the vesiculotype rhabdovirus 903/87 isolated from brown trout (Salmo trutta lacustris) in Finland [1,3]. The sequences for the nucleocapsid protein, phosphoprotein, matrix protein, glycoprotein and beginning of the polymerase protein of STRV 28/97 were determined. At the amino acid level the genes were over 97% similar to virus 903/87. The nucleocapsid proteins, glycoproteins and beginning of the polymerase protein of STRV 28/97 and virus 903/87 were clustered with the vesiculoviruses and the phosphoproteins close to the vesiculoviruses in protein parsimony analysis. The matrix proteins formed a distinct clade in protein parsimony analysis.

Selective control of basolateral membrane protein polarity by cdc42

The rho GTPase cdc42 is implicated in several aspects of cell polarity. A recent study (Kroschewski R, Hall A, Mellman I. Nat Cell Biol 1999;1:8-13) demonstrated that a dominant negative mutant of cdc42 abolishes the polarity of basolateral membrane proteins in MDCK cells, but did not elucidate whether this effect was selective for basolateral proteins or nonselective for all secreted proteins. To answer this question, we analyzed the polarity of newly synthesized membrane and soluble proteins in MDCK cell lines previously induced to overexpress mutant forms of cdc42. GTPase-deficient and dominant negative cdc42 did not affect the apical targeting of a newly synthesized apical membrane protein, but reversed to apical the distribution of two exogenous basolateral membrane proteins. In striking contrast, GTPase-deficient cdc42 did not affect polarized exocytosis of endogenous soluble proteins, either apical or basolateral. The exquisitely selective regulation of polarized protein targeting by cdc42 may allow cells to fine-tune their membrane composition in response to extracellular signals during development, migration and in response to injury.

Glycoprotein exchange vectors based on vesicular stomatitis virus allow effective boosting and generation of neutralizing antibodies to a primary isolate of human immunodeficiency virus type 1

Live recombinant vesicular stomatitis viruses (VSVs) expressing foreign antigens are highly effective vaccine vectors. However, these vectors induce high-titer neutralizing antibody directed at the single VSV glycoprotein (G), and this antibody alone can prevent reinfection and boosting with the same vector. To determine if efficient boosting could be achieved by changing the G protein of the vector, we have developed two new recombinant VSV vectors based on the VSV Indiana serotype but with the G protein gene replaced with G genes from two other VSV serotypes, New Jersey and Chandipura. These G protein exchange vectors grew to titers equivalent to wild-type VSV and induced similar neutralizing titers to themselves but no cross-neutralizing antibodies to the other two serotypes. The effectiveness of these recombinant VSV vectors was illustrated in experiments in which sequential boosting of mice with the three vectors, all encoding the same primary human immunodeficiency virus (HIV) envelope protein, gave a fourfold increase in antibody titer to an oligomeric HIV envelope compared with the response in animals receiving the same vector three times. In addition, only the animals boosted with the exchange vectors produced antibodies neutralizing the autologous HIV primary isolate. These VSV envelope exchange vectors have potential as vaccines in immunizations when boosting of immune responses may be essential.

Genetic analysis of vesicular stomatitis virus-New Jersey from the 1995 outbreak in the western United States

OBJECTIVE

To compare molecular associations between the vesicular stomatitis virus (VSV)-New Jersey isolates of the 1995 outbreak with those from previous outbreaks between 1982 and 1985 in the western United States.

SAMPLE POPULATION

23 virus isolates considered representative of the 1995 outbreak of vesicular stomatitis.

PROCEDURE

Viral gene coding for surface-envelope protein G was evaluated by use of nucleotide sequencing and phylogenetic analysis.

RESULTS

Changes in up to 0.77% of the nucleotide bases and 1.35% of the amino acids were detected among the 1995 viral isolates, whereas changes in up to 3.2 and 2.9% of the nucleotides and amino acids, respectively, were found, compared with the 1982 to 1985 viruses. Insertions or deletions were not found in the entire gene, which spanned 1,554 nucleotide bases.

CONCLUSIONS AND CLINICAL RELEVANCE

Phylogenetic analysis indicated that the 1995 VSV-New Jersey belongs to a lineage distinct from that of the 1982 to 1985 viruses that caused previous outbreaks in the western United States. Furthermore, it also is distinct from strains from Central America and from the Georgian Hazelhurst strain.

Molecular characterization of the glycoproteins from two warm water rhabdoviruses: snakehead rhabdovirus (SHRV) and rhabdovirus of penaeid shrimp (RPS)/spring viremia of carp virus (SVCV)

We have determined the complete coding sequences for the glycoprotein (G) genes from two rhabdoviruses that infect warm water aquatic animals, the snakehead rhabdovirus (SHRV) and rhabdovirus of penaeid shrimp (RPS). Surprisingly, the G nucleotide sequence from RPS, a virus which has been isolated from diseased shrimp in Hawaii on numerous occasions, was over 99% identical to the G nucleotide sequence from spring viremia of carp virus (SVCV), a fish virus from Europe and Asia. This is the first report of SVCV isolation outside of Europe and Asia, and it is also the first report of SVCV infecting a non-vertebrate species. The G gene from SHRV was most closely related to the G genes from the three Novirhabdoviruses, viral hemorrhagic septicemia virus (VHSV), infectious hematopoietic necrosis virus (IHNV), and hirame rhabdovirus (HIRRV), with 47, 37, and 36% amino acid identity, respectively. In addition, a phylogenetic analysis using the amino acid sequence from rhabdovirus G genes indicated that SHRV should be classified within the Novirhabdovirus genus. Finally, the SHRV-G gene was successfully expressed in mammalian cells under the control of the cytomegalovirus (CMV) promoter, establishing that it can potentially be used in the production of pseudotyped retroviruses designed to infect fish.

Qualitative and Quantitative Requirements for CD4+ T Cell-Mediated Antiviral Protection

CD4+ Th cells deliver the cognate and cytokine signals that promote the production of protective virus-neutralizing IgG by specific B cells and are also able to mediate direct antiviral effector functions. To quantitatively and qualitatively analyze the antiviral functions of CD4+ Th cells, we generated transgenic mice (tg7) expressing an MHC class II (I-Ab)-restricted TCR specific for a peptide derived from the glycoprotein (G) of vesicular stomatitis virus (VSV). The elevated precursor frequency of naive VSV-specific Th cells in tg7 mice led to a markedly accelerated and enhanced class switching to virus-neutralizing IgG after immunization with inactivated VSV. Furthermore, in contrast to nontransgenic controls, tg7 mice rapidly cleared a recombinant vaccinia virus expressing the VSV-G (Vacc-IND-G) from peripheral organs. By adoptive transfer of naive tg7 CD4+ T cells into T cell-deficient recipients, we found that 105 transferred CD4+ T cells were sufficient to induce isotype switching after challenge with a suboptimal dose of inactivated VSV. In contrast, naive transgenic CD4+ T cells were unable to adoptively confer protection against peripheral infection with Vacc-IND-G. However, tg7 CD4+ T cells that had been primed in vitro with VSV-G peptide were able to adoptively transfer protection against Vacc-IND-G. These results demonstrate that the antiviral properties of CD4+ T cells are governed by the differentiation status of the CD4+ T cell and by the type of effector response required for virus elimination.

Structure, expression and phylogenetic analysis of the glycoprotein gene of Cocal virus

A cDNA copy of the mRNA of the glycoprotein G of Cocal virus, a rhabdovirus, has been cloned, sequenced and expressed in mammalian cells. The deduced amino acid sequence shows a typical transmembrane glycoprotein, 512 amino acids in length, containing two potential N-linked glycosylation sites. The amino acid sequence showed a high degree of identity with that of the prototype vesicular stomatitis virus serotype Indiana [VSV (IND)] G protein. In addition, phylogenetic analysis of amino acid sequence differences among the G proteins of vesiculoviruses indicated that Cocal virus represents a distinct lineage within the VSV (IND) serotype. Expression of the cloned Cocal G gene in mammalian cells produced a glycoprotein of mol.wt 71000 which was not palmitylated but induced cell fusion at acid pH.

Mutations in a carboxy-terminal region of vesicular stomatitis virus glycoprotein G that affect membrane fusion activity

The envelope glycoprotein G of vesicular stomatitis virus induces membrane fusion at acidic pH. A highly conserved amino terminal region spanning residues 123 to 137 has previously been identified as an internal fusion domain. Here we have substituted specific amino acids within a carboxy terminal region, conserved in five vesiculoviruses encompassing residues 395 to 418, and studied the effect of these mutations on membrane fusion at acid pH and pH-dependent conformational change. Substitution of conserved Gly 395, Gly 404, Gly 406, Asp 409, and Asp 411 with Glu, Ala, Ala, Asn, and Asn, respectively, decreased the cell-cell fusion efficiency, as well as reduced the pH threshold of membrane fusion. Mutation of Gly 404 and Asp 409 to Lys and Ala, respectively, abolished the fusion activity. Mutant Gly 404 Lys also showed markedly altered resistance to trypsin digestion at acidic pH. These results suggest that the region between amino acids 395 to 418 is important for the fusogenic activity of the G protein. The possible role of this domain in conformational changes involved in fusion activity of VSV G is also discussed.

Entry of amphotropic and 10A1 pseudotyped murine retroviruses is restricted in hematopoietic stem cell lines

Although transduction with amphotropic murine leukemia virus (MLV) vectors has been optimized successfully for hematopoietic differentiated progenitors, gene transfer to early hematopoietic cells (stem cells) is still highly restricted. A similar restriction to gene transfer was observed in the mouse stem cell line FDC-Pmix compared with transfer in the more mature myeloid precursor cell line FDC-P1 and the human erythroleukemia cell line K562. Gene transfer was not improved when the vector was pseudotyped with gp70SU of the 10A1 strain of MLV, which uses the receptor of the gibbon ape leukemia virus (Pit1), in addition to the amphotropic receptor (Pit2). Although 10A1 and amphotropic gp70SU bound to FDC-P1, K562, and fibroblasts, no binding to FDC-Pmix cells was detected. This indicates that FDC-Pmix cells lack functional Pit2 and Pit1 receptors. Pseudotyping with the vesicular stomatitis virus G protein improved transduction efficiency in FDC-Pmix stem cells by 2 orders of magnitude, to fibroblast levels, confirming a block to retroviral infection at the receptor level.

Kinetic evidence for peptide-induced oligomerization of the molecular chaperone DnaK at heat shock temperatures

The pre-steady-state kinetics of the binding of a fluorescent peptide (dansyl-KLIGVLSSLFRPK, fVSV13) to the Escherichia coli molecular chaperone DnaK were investigated over a range of temperatures (25-42 degrees C). At 42 degrees C, over a wide range of peptide concentrations, the fVSV13 peptide bound to DnaK with biphasic kinetics: a rapid burst in the DnaK-fVSV13 signal in the first 5 s was followed by a gradual reduction in the signal over the next 100 s. The descending portion of each biphasic trace followed the equation F(t) = DeltaF exp(-kdt) + Finfinity, where DeltaF, kd, and Finfinity are the amplitude, the apparent first-order rate constant, and the fluorescence end point, respectively. Both DeltaF and kd increased with increasing concentrations of DnaK, which suggests that the loss of the DnaK-fVSV13 signal is caused by a bimolecular reaction. We propose that (i) the fVSV13 peptide binds to and induces a conformational change in the DnaK monomer [E + P right harpoon over left harpoon (EP)*]; and (ii) the conformational change promotes the formation of oligomeric DnaK-peptide complexes [En + (EP)* right harpoon over left harpoon En-EP]. The term (EP)* denotes a monomeric DnaK-peptide complex in which the bound peptide is fluorescent; En-EP denotes an oligomeric DnaK-peptide complex in which the fluorescence of the bound peptide is quenched. Numerical fitting of the stopped-flow data to reactions (i) and (ii) yielded values for the four rate constants. When the proposed kinetic model was tested by conducting experiments in the presence of excess peptide or excess ATP&sbd;conditions which inhibit oligomerization&sbd;DnaK-fVSV13 complex formation proceeded to stable asymptotes, with no reduction in the DnaK-fVSV13 signal at long times.

Identification of amino acids controlling the low-pH-induced conformational change of rabies virus glycoprotein

The glycoprotein (G) of rabies virus assumes at least three different conformations: the native state detected at the viral surface above pH 7, the activated state involved in the first step of the fusion process, and the fusion-inactive conformation (I). A new category of monoclonal antibodies (MAbs) which recognized specifically the I conformation at the viral surface has recently been described. These MAbs (17A4 and 29EC2) became neutralizing when the virus was preincubated at acidic pH to induce the conformational change toward the I state of G. Mutants escaping neutralization were then selected. In this study, we have investigated the fusion and the low-pH-induced fusion inactivation properties of these mutants. All of these mutants have fusion properties similar to those of the CVS parental strain, but five mutants (E282K, M44I, M44V, V392G, and M396T) were considerably slowed in their conformational change leading to the I state. These mutants allow us to define regions that control this conformational change. These results also reinforce the idea that structural transition toward the I state is irrelevant to the fusion process. Other mutations in amino acids 10, 13, and 15 are probably located in the epitopes of selecting MAbs. Furthermore, in electron microscopy, we observed a hexagonal lattice of glycoproteins at the viral surface of mutants M44I and V392G as well as strong cooperativity in the conformational change toward the I state. This finding demonstrates the existence of lateral interactions between the spikes of a rhabdovirus.

The glycoprotein genes and gene junctions of the fish rhabdoviruses spring viremia of carp virus and hirame rhabdovirus: analysis of relationships with other rhabdoviruses

The nucleotide sequences of the glycoprotein genes and all of the internal gene junctions of the fish pathogenic rhabdoviruses spring viremia of carp virus (SVCV) and hirame rhabdovirus (HIRRV) have been determined from cDNA clones generated from viral genomic RNA. The SVCV glycoprotein gene sequence is 1588 nucleotides (nt) long and encodes a 509 amino acid (aa) protein. The HIRRV glycoprotein gene sequence comprises 1612 nt, coding for a 508 aa protein. In sequence comparisons of 15 rhabdovirus glycoproteins, the SVCV glycoprotein gene showed the highest amino acid sequence identity (31.2-33.2%) with vesicular stomatitis New Jersey virus (VSNJV), Chandipura virus (CHPV) and vesicular stomatitis Indiana virus (VSIV). The HIRRV glycoprotein gene showed a very high amino acid sequence identity (74.3%) with the glycoprotein gene of another fish pathogenic rhabdovirus, infectious hematopoietic necrosis virus (IHNV), but no significant similarity with glycoproteins of VSIV or rabies virus (RABV). In phylogenetic analyses SVCV was grouped consistently with VSIV, VSNJV and CHPV in the Vesiculovirus genus of Rhabdoviridae. The fish rhabdoviruses HIRRV, IHNV and viral hemorrhagic septicemia virus (VHSV) showed close relationships with each other, but only very distant relationships with mammalian rhabdoviruses. The gene junctions are highly conserved between SVCV and VSIV, well conserved between IHNV and HIRRV, but not conserved between HIRRV/IHNV and RABV. Based on the combined results we suggest that the fish lyssa-type rhabdoviruses HIRRV, IHNV and VHSV may be grouped in their own genus within the family Rhabdoviridae. Aquarhabdovirus has been proposed for the name of this new genus.

Folding, unfolding, and refolding of the vesicular stomatitis virus glycoprotein

Folding and refolding of the vesicular stomatitis virus (VSV) glycoprotein (G protein), New Jersey serotype, were studied both in infected cells and after urea denaturation and reduction of isolated protein in vitro. To assess the contribution of disulfide bonds to the conformation of this type I membrane glycoprotein, reduced and alkylated forms were compared with unreduced G proteins by their mobility on SDS-polyacrylamide gels and by their reactivity with conformation-dependent monoclonal antibodies (MAbs). Pulse-chase experiments showed that G protein folding in the endoplasmic reticulum (ER) of infected cells occurred rapidly (estimated half-time of 1-2 min) and involved transient association with the ER chaperone calnexin. Inhibition of glycosylation by tunicamycin slowed the folding process and emergence from the ER but did not prevent the appearance of a conformationally mature transport-competent G protein. For in vitro refolding studies, native G protein isolated from virus particles was denatured and reduced with urea and beta-mercaptoethanol. When rapidly diluted into a denaturant-free buffer containing oxidized glutathione and the nonionic detergent octyl glucoside, the G protein regained considerable native structure, as determined by reactivity with five monoclonal antibodies specific for different conformation-dependent epitopes. Whereas the refolding process was slow and inefficient in vitro relative to folding in the cell, this observation nonetheless demonstrated that an integral fully glycosylated membrane protein can be refolded to form a structure similar to that of the original protein processed during in vivo synthesis. If, however, unfolded nonglycosylated G protein was the starting material, refolding in vitro failed. In summary, we have shown that VSV G protein folding can be analyzed both in vivo and in vitro and that folding in the cell involves at least one chaperone and can occur in vivo even if not glycosylated.

Palmitylation of the influenza virus hemagglutinin (H3) is not essential for virus assembly or infectivity

The C terminus of the influenza virus hemagglutinin (HA) contains three cysteine residues that are highly conserved among HA subtypes, two in the cytoplasmic tail and one in the transmembrane domain. All of these C-terminal cysteine residues are modified by the covalent addition of palmitic acid through a thio-ether linkage. To investigate the role of HA palmitylation in virus assembly, we used reverse genetics technique to introduce substitutions and deletions that affected the three conserved cysteine residues into the H3 subtype HA. The rescued viruses contained the HA of subtype H3 (A/Udorn/72) in a subtype H1 helper virus (A/WSN/33) background. Rescued viruses which do not contain a site for palmitylation (by residue substitution or substitution combined with deletion of the cytoplasmic tail) were obtained. Rescued virions had a normal polypeptide composition. Analysis of the kinetics of HA low-pH-induced fusion of the mutants showed no major change from that of virus with wild-type (wt) HA. The PFU/HA ratio of the rescued viruses grown in eggs ranged from that of virus with wt HA to 16-fold lower levels, whereas the PFU/HA ratio of the rescued viruses grown in MDCK cells varied only 2-fold from that of virus with wt HA. However, except for one rescued mutant virus (CAC), the mutant viruses were attenuated in mice, as indicated by a > or = 400-fold increase in the 50% lethal dose. Interestingly, except for one mutant virus (CAC), all of the rescued mutant viruses were restricted for replication in the upper respiratory tract but much less restricted in the lungs. Thus, the HA cytoplasmic tail may play a very important role in the generation of virus that can replicate in multiple cell types.

The complete genome structure and phylogenetic relationship of infectious hematopoietic necrosis virus

Infectious hematopoietic necrosis virus (IHNV), a member of the family Rhabdoviridae, causes a severe disease with high mortality in salmonid fish. The nucleotide sequence (11,131 bases) of the entire genome was determined for the pathogenic WRAC strain of IHNV from southern Idaho. This allowed detailed analysis of all 6 genes, the deduced amino acid sequences of their encoded proteins, and important control motifs including leader, trailer and gene junction regions. Sequence analysis revealed that the 6 virus genes are located along the genome in the 3' to 5' order: nucleocapsid (N), polymerase-associated phosphoprotein (P or M1), matrix protein (M or M2), surface glycoprotein (G), a unique non-virion protein (NV) and virus polymerase (L). The IHNV genome RNA was found to have highly complementary termini (15 of 16 nucleotides). The gene junction regions display the highly conserved sequence UCURUC(U)7RCCGUG(N)4CACR (in the vRNA sense), which includes the typical rhabdovirus transcription termination/polyadenylation signal and a novel putative transcription initiation signal. Phylogenetic analysis of M, G and L protein sequences allowed insights into the evolutionary and taxonomic relationship of rhabdoviruses of fish relative to those of insects or mammals, and a broader sense of the relationship of non-segmented negative-strand RNA viruses. Based on these data, a new genus, piscivirus, is proposed which will initially contain IHNV, viral hemorrhagic septicemia virus and Hirame rhabdovirus.

Photolabeling identifies a putative fusion domain in the envelope glycoprotein of rabies and vesicular stomatitis viruses

Vesicular stomatitis and rabies viruses enter cells through receptor-mediated endocytosis, followed by fusion of the viral with the endosomal membrane. The latter step is catalyzed by the viral envelope glycoprotein, which, in the low pH environment of the endosome, undergoes a conformational transition to a fusion-competent state. To investigate whether fusion competence involves the low pH exposure of a hydrophobic fusion region(s), we have applied hydrophobic photolabeling using the recently developed phospholipid analogue 1-O-hexadecanoyl-2-O-[9-[[[2-[125I]iodo-4-(trifluoromethyl-3H- diazirin-3-yl)benzyl]oxy]carbonyl] nonanoyl]-sn-glycero-3-phosphocholine ([125I]TID-PC/16) (Weber, T., and Brunner, J. (1995) J. Am. Chem. Soc. 117, 3084-3095). Rosettes of rabies virus glycoprotein, whole rabies virus, or vesicular stomatitis virus were incubated with large unilamellar vesicles containing [125I]TID-PC/16. Following reagent activation, the labeled glycoprotein was isolated and analyzed. In all cases, labeling of the glycoprotein strongly increased as the pH was lowered from 7.0 to 6.0, suggesting the exposure at acidic pH of a domain capable of interacting with membranes. To identify the labeled region(s), CNBr fragments were generated and analyzed by SDS-polyacrylamide followed by autoradiography. In rabies glycoprotein, the labeled segment was found to be contained within fragment RCr5 (residues 103-179). Glycoprotein from vesicular stomatitis virus was labeled within fragment VCr1 (residues 59-221). These results demonstrate that rhabdovirus glycoprotein contains a domain that at low pH is capable of interacting with a target membrane in a hydrophobic manner. This domain may play a role similar to that of the fusion peptide found in many other viral fusion proteins.

Recombinant vesicular stomatitis viruses from DNA

We assembled a DNA clone containing the 11,161-nt sequence of the prototype rhabdovirus, vesicular stomatitis virus (VSV), such that it could be transcribed by the bacteriophage T7 RNA polymerase to yield a full-length positive-strand RNA complementary to the VSV genome. Expression of this RNA in cells also expressing the VSV nucleocapsid protein and the two VSV polymerase subunits resulted in production of VSV with the growth characteristics of wild-type VSV. Recovery of virus from DNA was verified by (i) the presence of two genetic tags generating restriction sites in DNA derived from the genome, (ii) direct sequencing of the genomic RNA of the recovered virus, and (iii) production of a VSV recombinant in which the glycoprotein was derived from a second serotype. The ability to generate VSV from DNA opens numerous possibilities for the genetic analysis of VSV replication. In addition, because VSV can be grown to very high titers and in large quantities with relative ease, it may be possible to genetically engineer recombinant VSVs displaying foreign antigens. Such modified viruses could be useful as vaccines conferring protection against other viruses.

The glycoprotein G of rhabdoviruses

Rhabdoviruses show an RNA-containing helically-wound nucleocapsid either enclosed by or enclosing a membrane M protein, surrounded by a lipid bilayer through which dynamic protein trimers made up of non-covalently associated monomers of glycoprotein G (G) project outside. Mature monomeric rhabdoviral G has more than 500 amino acids, 2-6 potential glycosylation sites, 12-16 highly conserved cysteine residues, 2-3 stretches of a-d hydrophobic heptad-repeats, a removed amino terminal hydrophobic signal peptide, a close to the carboxy terminal hydrophobic transmembrane sequence and a carboxy terminal short hydrophylic cytoplasmic domain. Association-dissociation between monomers-trimers and displacement of the trimers along the plane of the lipid membrane, are induced by changes in the external conditions (pH, temperature, detergents, etc.). Throughout conformational changes the G trimers are responsible for the virus attachment to cell receptors, for low-pH membrane fusion and for reacting with host neutralizing monoclonal antibodies (MAbs). Antigenic differences could exist between monomers and trimers, which may have implications for future vaccine developments. The family Rhabdoviridae is made up of the Lyssavirus (rabies), the Vesiculovirus (vesicular stomatitis virus, VSV) and many rhabdoviruses infecting fish, plants, and arthropod insects. All these reasons make the G of rhabdoviruses an ideal subject to study comparative virology and to investigate new vaccine technologies.

Characterization of the putative fusogenic domain in vesicular stomatitis virus glycoprotein G

The envelope glycoprotein G of vesicular stomatitis virus induces membrane fusion at low pH. Site-directed mutagenesis of specific amino acids within a segment spanning amino acids 123 to 137 of G protein, which is highly conserved in vesiculoviruses and was previously shown by us to be involved in fusogenic activity (Y. Li, C. Drone, E. Sat, and H. P. Ghosh, J. Virol. 67:4070-4077, 1993), was used to determine the role of this region in low-pH-induced membrane fusion. The mutant glycoproteins expressed in COS cells were assayed for acid-pH-induced cell-cell fusion. Substitution of the variant Pro-123 with Leu had no effect on the fusogenic activity, while substitution of conserved Phe-125 and Asp-137 with Tyr and Asn, respectively, shifted the pH optimum of membrane fusion to a more acidic pH value and decreased the fusion efficiency. The deletion of amino acid residues 124 to 127, 131 to 137, or 124 to 137 produced mutants defective in transport. Mutation of the conserved residues Gly-124 and Pro-127 to Ala and to Gly or Leu, respectively, inhibited cell-cell fusion activity by about 90% without affecting transport of the mutant proteins to the cell surface, suggesting that these two residues may be present within the fusion peptide and thus may be directly involved in fusion. This highly conserved domain containing neutral amino acids of G protein may therefore represent the putative fusion domain of vesicular stomatitis virus G protein.

Localization of T helper cell epitopes in the vesicular stomatitis virus: the nucleoprotein is responsible for serotype cross-reactive T help

The glycoprotein (G) of vesicular stomatitis virus (VSV) is known to contain the biologically relevant sites for virus-neutralizing antibodies as well as T helper (Th) cell epitopes. The capacity of other VSV proteins to elicit potent Th cell responses has not yet been investigated. Additionally, a short-lived cross-reactivity between the two serologically distinct VSV serotypes Indiana (IND) and New Jersey (NJ) on the T helper cell level has been reported. Here we address the question of whether the VSV nucleoprotein (N) or matrix protein (M) can elicit T help to VSV-G-specific B cells and which of the VSV proteins contains the elements responsible for the IND/NJ cross-reactivity. The N, G, and M of the VSV Indiana serotype produced in a recombinant baculovirus system were assayed for the ability to activate VSV-specific Th cells to induce immunoglobulin class switch of neutralizing antibody responses in vivo in C57BL/6 (H-2b) mice. All three VSV-IND proteins helped in the production of neutralizing IgG antibodies to the homologous VSV-Indiana serotype but only VSV-IND N was able to trigger an IgG response to the heterologous VSV-New Jersey serotype. This data suggest that Th epitope(s) in the VSV-IND N are responsible for the observed cross-reactivity of T helper cells.

Mutational analysis of the vesicular stomatitis virus glycoprotein G for membrane fusion domains

The spike glycoprotein G of vesicular stomatitis virus (VSV) induces membrane fusion at low pH. We used linker insertion mutagenesis to characterize the domain(s) of G glycoprotein involved in low-pH-induced membrane fusion. Two or three amino acids were inserted in frame into various positions in the extracellular domain of G, and 14 mutants were isolated. All of the mutants expressed fully glycosylated proteins in COS cells. However, only seven mutant G glycoproteins were transported to the cell surface. Two of these mutants, D1 and A6, showed wild-type fusogenic properties. The mutant A2 had a temperature-sensitive defect in the transport of the mutant G glycoprotein to the cell surface. The other four mutants, H2, H5, H10, and A4, although present in cell surface, failed to induce cell fusion when cells expressing these mutant glycoproteins were exposed to acidic pH. These four mutant G proteins could form trimers, indicating that the defect in fusion was not due to defective oligomerization. One of these mutations, H2, is within a region of conserved, uncharged amino acids that has been proposed as a possible fusogenic sequence. The mutation in H5 was about 70 amino acids downstream of the mutation in H2, while mutations in H10 and A4 were about 300 amino acids downstream of the mutation in H2. Conserved sequences were also noted in the H10 and A4 segment. The results suggest that in the case of VSV G glycoprotein, the fusogenic activity may involve several spatially separated regions in the extracellular domain of the protein.

The genome of bovine ephemeral fever rhabdovirus contains two related glycoprotein genes

A 3789 nucleotide region of the bovine ephemeral fever virus (BEFV) genome, located 1.65 kb downstream of the N gene, has been cloned and sequenced. The region contains two long open reading frames (ORFs) which are bounded by putative consensus (AACAGG) and polyadenylation (CATG[A]7) sequences and are separated by an intergenic region of 53 nucleotides. Discrete mRNAs corresponding to each ORF have been identified. The first ORF encodes a polypeptide comprising 623 residues which was identified by peptide sequencing as the virion G protein. The deduced amino acid sequence of the G protein includes putative signal and transmembrane domains and five potential glycosylation sites. The second ORF encodes a polypeptide of 586 amino acids which also has characteristics of a rhabdovirus glycoprotein, including putative signal and transmembrane domains and eight potential glycosylation sites, and appears to correspond to a 90-kDa nonstructural glycoprotein (GNS) identified in BEFV-infected cells (Walker et al. [1991] J. Gen. Virol. 72, 67-74). A database search indicated that both the G and GNS proteins share significant amino acid sequence homology with other rhabdovirus G proteins and with each other. Highest homology scores for each protein were with sigma virus and vesicular stomatitis virus serotypes.

Disulfide-bonded discontinuous epitopes on the glycoprotein of vesicular stomatitis virus (New Jersey serotype)

Intrachain disulfide bonds between paired cysteines in the glycoprotein (G) of vesicular stomatitis virus (VSV) are required for the recognition of discontinuous epitopes by specific monoclonal antibodies (MAbs) (W. Keil and R. R. Wagner, Virology 170:392-407, 1989). Cleavage by Staphylococcus aureus V8 protease of the 517-amino-acid VSV-New Jersey G protein, limited to the glutamic acid at residue 110, resulted in a protein (designated GV8) with greatly retarded migration by polyacrylamide gel electrophoresis (PAGE) under nonreducing conditions. By Western blot (immunoblot) analysis, protein GV8 was found to lose discontinuous epitope IV, which maps within the first 193 NH2-terminal amino acids. These data, coupled with those obtained by PAGE migration of a vector-expressed, truncated protein (G1-193) under reducing and nonreducing conditions, lead us to postulate the existence of a major loop structure within the first 193 NH2-terminal amino acids of the G protein, possibly anchored by a disulfide bond between cysteine 108 and cysteine 169, encompassing epitope IV. Site-directed mutants in which 10 of the 12 cysteines were individually converted to serines in vaccinia virus-based vectors expressing these single-site mutant G proteins were also constructed, each of which was then tested by immunoprecipitation for its capacity to recognize epitope-specific MAbs. These results showed that mutations in NH2-terminal cysteines 130, 174, and, to a lesser extent, 193 all resulted in the loss of neutralization epitope VIII. A mutation at NH2-terminal cysteine 130 also resulted in the loss of neutralization epitope VII, as did a mutation at cysteine 108 to a lesser extent. Both epitopes VII and VIII disappeared when mutations were made in COOH-distal cysteine 235, 240, or 273, the general map locations of epitopes VII and VIII. These studies also reveal that distal, as well as proximal, cysteine residues markedly influence the disulfide-bond secondary structure, which ostensibly determines the conformational structure of the VSV-New Jersey G protein required for presentation of the major discontinuous epitopes recognized by neutralizing MAbs.

Subunit interactions of vesicular stomatitis virus envelope glycoprotein stabilized by binding to viral matrix protein

The mechanism by which viral glycoproteins are incorporated into virus envelopes during budding from host membranes is a major question of virus assembly. Evidence is presented here that the envelope glycoprotein (G protein) of vesicular stomatitis virus binds to the viral matrix protein (M protein) in vitro with the specificity, reversibility, and affinity necessary to account for virus assembly in vivo. The assay for the interaction is based on the ability of M protein to stabilize the interaction of G protein subunits, which exist as trimers of identical subunits in the virus envelope. The interaction with M protein was shown by using G proteins labeled with fluorescent probes capable of detecting subunit dissociation and reassociation in vitro. The results show that the M protein isolated from virions either as purified soluble protein or as nucleocapsid-M protein complexes interacts with the G protein in vitro and that the reaction is reversible. The interaction between the G and M proteins was not serotype specific, but no interaction between the vesicular stomatitis virus M protein and the influenza virus hemagglutinin could be detected. These results support the conclusion that the interactions described here are the ones that govern assembly of G protein into virus envelopes in vivo.

Fatty acid acylation is not required for membrane fusion activity or glycoprotein assembly into VSV virions

We have investigated the role of fatty acid acylation on two properties of the glycoprotein (G protein) from the Indiana serotype of vesicular stomatitis virus (VSV). Using a mutated G protein described previously (CS-2) that is not palmitylated, we found that fatty acid acylation was not required for the low pH-induced membrane fusion activity of VSV G protein. Transient expression of CS in HeLa cells resulted in syncytia formation that was indistinguishable from that induced by wild-type G protein. In addition, we found that expression of CS complemented a temperature-sensitive mutant of VSV (tsO45) as well as the wild-type protein. These results indicate that the presence of palmitate on the cytoplasmic domain of VSV G protein is not required for any step in the life cycle of the virus.

Murine infection by vesicular stomatitis virus: initial characterization of the H-2d system

BALB/c mice and congenic H-2Ld-deficient BALB/c-H-2dm2 (dm2) mice were experimentally infected intranasally with isolates of vesicular stomatitis virus (VSV). The survival of infected hosts, viral replication in lungs and brains, and histopathologic in the two mouse strains were compared. In both strains of mice, mortality occurred during the period 7 to 10 days postinfection. However, dm2 mice were relatively resistant to lethal infections. Viral replication occurred at low levels in the lungs of both strains and did not evoke significant pathologic changes. In contrast, viral replication in the brains was much greater; in the BALB/c strain, this was accompanied by more frequent and more severe pathologic changes. In general, mice surviving at day 10 had effectively cleared virus from central nervous system but not respiratory sites. Evidence is presented that viral replication occurs first in the nasal cavity and is transmitted both to the lungs and to the olfactory bulb where focal cytopathology occurs. Virus enters the ventricles, causing encephalitis; necrosis occurs around the ventricles and in the lumbosacral region of the spinal cord. Necrotic lesions were accompanied by mononuclear infiltration. Mice immunized with virus of the same serotype or with a vaccinia virus hybrid encoding the VSV glycoprotein were protected from lethal infection; in contrast, mice immunized with heterotypic virus were susceptible to challenge.

Fatty acylation of rabies virus proteins

The fatty acylation of rabies virus (CVS strain) proteins was investigated. [3H]palmitic acid was found to be incorporated into the glycoprotein G and to a lesser extent into the membrane-associated protein M2. The fatty acid linkage on G was sensitive to sodium borohydride, mercaptoethanol, and hydroxylamine, indicating that the linkage was of the thiolester type. Bromelain digestion indicated that the palmitoylation site on G was located in the intracytoplasmic domain or in the transmembrane domain in which there is only one cysteine in position 461. Therefore, palmitoylation is likely to occur at this position. In the case of M2, the linkage was also sensitive to hydroxylamine and sodium borohydride and to a lesser extent to mercaptoethanol, suggesting that the linkage also occurred on a cysteine.

A toxin-resistant mouse L-cell mutant defective in protein transport along the secretory pathway

Using methods designed for isolation of mutants defective in receptor-mediated endocytosis, a novel L-cell mutant was obtained that exhibits resistance to three different protein toxins as well as alterations in secretion. This mutant, LEFIC, is resistant to modeccin, Pseudomonas exotoxin, and ricin. These toxins, which enter the cytoplasm via receptor-mediated endocytosis, are thought to penetrate into cells at the level of late endosomes or the trans Golgi network. Early endosomal acidification appears to be normal in the mutant based on its accumulation of iron from transferrin and its sensitivity to diphtheria toxin A chain-transferrin conjugate. Within the secretory pathway two delays in transport of vesicular stomatitis virus (VSV) G protein were observed in LEFIC: a 20-30 min delay in acquisition of Endo H resistance and a 1-2 hr delay in appearance of newly synthesized G protein on the cell surface. Movement of endogenous proteins along the secretory pathway was also affected in LEFIC. Fibronectin secretion was delayed by 15 min, and membrane proteins were delayed in arrival at the cell surface. The phenotype of LEFIC is consistent with a defect in a component or compartment shared by both the late endocytic and constitutive secretory pathways.

Intracellular formation of two soluble glycoproteins in BHK cells infected with vesicular stomatitis virus serotype New Jersey

Infection of BHK 21 cells with VSV serotype New Jersey gave rise to three intracellular viral glycoproteins: the membrane-integrated G protein and the two soluble glycoproteins Gs and Gss which lacked the cytoplasmic and transmembrane domains as was deduced from limited chemical cleavage of the glycoproteins by hydroxylamine. Both soluble glycoproteins were completely protected by the microsomal membrane against proteolytic digestion. The soluble glycoproteins were formed in the endoplasmic reticulum because both were fully endo H sensitive after a 5-min pulse with [35S]methionine. Protease inhibitors and lysosomorphic agents had no effect on the yield of Gs and Gss. Tunicamycin treatment of VSV-infected cells reduced extensively viral particle maturation without affecting significantly the release of Gs and Gss. Two other glycosylation inhibitors, swainsonine and deoxynojirimycin did not decrease virus particle formation and secretion of both soluble glycoproteins. Since the glycosylation inhibitors showed a differential effect on the processing and transport of the glycoproteins a precursor-product relationship between G protein and soluble glycoproteins is highly unlikely. Both soluble glycoproteins were also synthesized in vitro in a reticulocyte lysate without microsomal membranes when primed with RNA extracted from VSV-infected cells or with newly transcribed mRNA from nucleocapsids in a coupled transcription system. Thus, proteases localized in the lumen of the ER seemed to be not essential for the generation of both soluble glycoproteins.

Analysis of the kinetics of antiviral memory T help in vivo: characterization of short-lived cross-reactive T help

To evaluate the kinetics of functional effector and memory T help in vivo the effect of priming with one serotype of vesicular stomatitis virus-Indiana (VSV-IND) on the antibody response to a serologically distinct heterologous second serotype (VSV-New Jersey: VSV-NJ) was studied. Mice primed with VSV-IND 4 or 8 days before being given a second infection of VSV-NJ developed an earlier and enhanced IgG response to neutralizing determinants of the second VSV serotype. However, this enhanced response was not detected in mice primed 15 or more days prior to a second infection. After 15 days, mice challenged with the heterologous VSV-NJ mounted a strictly normal primary response without evidence of suppression. It was shown by in vivo time-kinetics experiments that efficient VSV cross-reactive T help, capable of enhancing the IgG response is short lived and cyclosporin A resistant. Adoptive transfer experiments demonstrated in the absence of experimental evidence for suppression that this short-lived capacity to enhance neutralizing IgG antibody responses is mediated by T cells. These findings have implications for understanding antiviral protection and immunological memory against related but serologically distinct viruses.

Palmitoylation of the influenza A virus M2 protein

The M2 proteins of a variety of influenza A viruses of different subtypes were shown to possess associated palmitate. Susceptibility to removal by reduction or treatment with hydroxylamine is consistent with attachment via a thioester linkage to cysteine. The absence of the acyl group from the M2 proteins of several equine viruses of the H3N8 subtype correlates with the replacement of cysteine 50 with phenylalanine and points to this as the site of palmitate attachment.

Polymerase errors accumulating during natural evolution of the glycoprotein gene of vesicular stomatitis virus Indiana serotype isolates

We report the entire glycoprotein (G) gene nucleotide sequences of 26 vesicular stomatitis virus Indiana serotype (VSV IND) type 1 isolates from North and Central America. These sequences are also compared with partial G gene sequences of VSV IND type 2 (Cocal) and type 3 (Alagoas) viruses and the complete G gene sequences of the more distantly related VSV New Jersey (NJ) and Chandipura viruses. Phylogenetic analysis of the G gene sequences by maximum parsimony revealed four major lineages or subtypes within the classical VSV IND (type 1) viruses, each with a distinct geographic distribution. A high degree of VSV genetic diversity was found in Central America, with several virus subtypes of both VSV IND and NJ serotypes existing in this mainly enzootic disease region. Nineteen percent sequence variation but no deletions or insertions were evident within the 5' noncoding and the coding regions of the VSV IND type 1 G genes. In addition to numerous base substitutions, the 3' noncoding regions of these viruses also contained numerous base insertions and deletions. This resulted in striking variation in G gene sizes, with gene lengths ranging from 1,652 to 1,868 nucleotides. As the VSV IND type 1 subtypes have diverged from the common ancestor with the NJ subtypes, their G mRNAs have accumulated more 3' noncoding sequence inserts, ranging up to 303 nucleotides in length. These primarily consist of an imprecise reiteration of the sequence UUUUUAA, apparently generated by a unique polymerase stuttering error. Analysis of the deduced amino acid sequence differences among VSV IND type 1 viruses revealed numerous substitutions within defined antigenic epitopes, suggesting that immune selection may play a role in the evolution of these viruses.

Vesicular stomatitis virion-associated transcriptase activity was suppressed in vitro by a synthetic 21 amino acid oligopeptide prepared to mimic the carboxy-terminus of NS protein

To study the biological function of the NS protein of vesicular stomatitis virus (VSV), we prepared 21 species of synthetic oligopeptides with 11-21 amino acid residues, corresponding to every portion of the amino acid sequence of NS protein (Indiana serotype), and tested their effects on the VS virion (VSV) transcriptase activity in vitro. Only one peptide affected the virion-associated transcriptase activity of VSV Indiana, by reducing the incorporation of [3H]GMP into acid-insoluble fraction (IC50 = 26 microM). This peptide, the amino acid sequence of which corresponded to the carboxy (C)-terminal region of NS protein, also inhibited the New Jersey serotype virus transcriptase activity, as expected from a high degree of homology found between the amino acid sequences of the C-terminal regions of NS protein of both serotype viruses. Electrophoretic analysis on acrylamide gels of RNA transcripts revealed that the inhibitory synthetic peptide decreased the frequency of the initiation of transcription with no apparent effect on the chain-elongation process of viral transcription. As expected from its highly conserved amino acid sequence, these results suggest that the C-terminal domain of VSV NS protein is involved in initiating viral RNA synthesis.

Vesicular stomatitis New Jersey virus glycoprotein gene sequence and neutralizing epitope stability in an enzootic focus

Vesicular stomatitis New Jersey (VS NJ) virus is capable of undergoing rapid evolution in nature and therefore has the potential for antigenic variation. We selected an area of Costa Rica where VS NJ virus is enzootic to study whether this virus used the mechanism of antigenic variation to persist in nature. Three sentinel herds and three nonsentinel herds were observed from 1986 to 1988. Eleven VS NJ virus isolates were collected from naturally infected cattle. Remarkably, nine animals that were bled prior to reinfection with VS NJ virus had neutralizing antibody titers up to 1: 102,400 yet virus was isolated from, and disease was observed in, these animals. Sequence analysis of the portion of the glycoprotein gene coding for the neutralizing epitopes demonstrated that all virus isolates were 98-100% similar with no indication of specific genetic variation. The 3' end of the glycoprotein gene also remained stable in that all isolates were again 98-100% similar in nucleotide sequence. Each isolate was neutralized to equivalent titers with monoclonal antibodies directed against four neutralizing epitopes on the glycoprotein. Additionally, preisolation sera from each animal were able to neutralize the virus that caused the subsequent disease. These results provide evidence that antigenic variation is not a mechanism used by VS NJ virus to persist in an enzootic focus of Costa Rica.