Inhibition of RNA and interferon synthesis in Krebs-2 cells infected with vesicular stomatitis virus

Near-Complete Genome Sequences of Vesicular Stomatitis Virus Indiana Laboratory Strains HR and T1026R1 and Plaque Isolates 22-20 and 22-25

We report four near-complete genome sequences of vesicular stomatitis virus (VSV) Indiana obtained with Sanger and Illumina next-generation sequencing, namely, laboratory strains HR (heat resistant) and T1026R1 and isolates 22-20 and 22-25. Previously, only the M gene of these viruses had been sequenced, and these sequences were not deposited in GenBank.

We report four near-complete genome sequences of vesicular stomatitis virus (VSV) Indiana obtained with Sanger and Illumina next-generation sequencing, namely, laboratory strains HR (heat resistant) and T1026R1 and isolates 22-20 and 22-25. Previously, only the M gene of these viruses had been sequenced, and these sequences were not deposited in GenBank.

The vesicular stomatitis virus matrix protein inhibits NF-κB activation in mouse L929 cells

A previous study found that NF-κB activation is delayed in L929 cells infected with wild-type (wt) strains of VSV, while activation occurred earlier in cells infected with mutant strain T1026R1 (R1) that encodes a mutation in the cytotoxic matrix (M) protein. The integrity of the other R1 proteins is unknown; therefore our goal was to identify the viral component responsible for preventing NF-κB activation in L929 cells. We found that the M protein inhibits viral-mediated activation of NF-κB in the context of viral infection and when expressed alone via transfection, and that the M51R mutation in M abrogates this function. Addition of an IκB kinase (IKK) inhibitor blocked NF-κB activation and interferon-β mRNA expression in cells infected with viruses encoding the M51R mutation in M. These results indicate that the VSV M protein inhibits activation of NF-κB by targeting an event upstream of IKK in the canonical pathway.

Pathogenicity and immunogenicity for mice of temperature-sensitive mutants of vesicular stomatitis virus

Temperature-sensitive (ts) mutants of vesicular stomatitis (VS) virus were tested for their pathogenicity and immunogenicity in weanling mice. Compared with the wild-type virus (ts(+)), ts mutants representing genetic complementation groups I, II, and IV were considerably less pathogenic for mice infected by the intracerebral route and caused few deaths after intranasal inoculation. Mice were completely resistant to ts(+) and ts mutants by the intraperitoneal route. Resistance to intracerebral challenge with ts(+) VS virus was only minimal in mice vaccinated intraperitoneally with ts(+) or ts mutants and only moderate in mice vaccinated intranasally with three ts mutants. Intranasal vaccination, particularly with group IV mutants, resulted in solid immunity within 3 days to intranasal challenge with ts(+) virus. VS viral neutralizing antibody was present in the bronchial secretions of mice by 12 h after intranasal inoculation of mutant ts IV44; the bronchial antibody titers declined to undetectable levels between 3 and 7 days after vaccination. Neutralizing antibody was detected in the serum of mice by the third day after intranasal vaccination with ts IV44 and persisted at high level for at least 11 days. Certain classes of ts mutants would appear to be promising candidates for use as attenuated, live virus vaccines.

Enhanced interferon production from chick embryo cells aged in in vitro

The plaque-forming efficiency of Sindbis virus decreased as much as 1000-fold, and plaque size was diminished markedly, when tested on chick embryo cell monolayers aged in vitro. The plaquing efficiency and plaque size of Newcastle disease virus was unaffected. The reaction(s) associated with aging in vitro which lead to lowered plaquing efficiency are slowed considerably when cell monolayers are: (1) established in Simpson-Hirst medium rather than standard growth medium; (2) held at 31 degrees ; (3) given a regimen of daily medium changes; or (4) trypsinized and used as young secondary cultures. A loss in the average yield of virus per cell accompanies the loss in plaquing efficiency of Sindbis virus on aged monolayers. Adding actinomycin D to the aged cells at the time of infection eliminated completely the inhibition of Sindbis virus replication. Cells aged for 7 days in vitro were found to produce up to 32 times more interferon than cells 1-2 days old and were more sensitive to the action of interferon. The decrease in efficiency of Sindbis virus plaquing and yield in aged cells is accounted for by their development of an enhanced capacity to synthesize interferon upon appropriate stimulation. The process of contact inhibition and its concomitant regulation of macromolecular synthesis seems implicated in the aging phenomenon in that it may produce a generalized state of "enhanced derepressibility" in the cell.

Cytopathogenesis and inhibition of host gene expression by RNA viruses

Many viruses interfere with host cell function in ways that are harmful or pathological. This often results in changes in cell morphology referred to as cytopathic effects. However, pathogenesis of virus infections also involves inhibition of host cell gene expression. Thus the term "cytopathogenesis," or pathogenesis at the cellular level, is meant to be broader than the term "cytopathic effects" and includes other cellular changes that contribute to viral pathogenesis in addition to those changes that are visible at the microscopic level. The goal of this review is to place recent work on the inhibition of host gene expression by RNA viruses in the context of the pathogenesis of virus infections. Three different RNA virus families, picornaviruses, influenza viruses, and rhabdoviruses, are used to illustrate common principles involved in cytopathogenesis. These examples were chosen because viral gene products responsible for inhibiting host gene expression have been identified, as have some of the molecular targets of the host. The argument is made that the role of the virus-induced inhibition of host gene expression is to inhibit the host antiviral response, such as the response to double-stranded RNA. Viral cytopathogenesis is presented as a balance between the host antiviral response and the ability of viruses to inhibit that response through the overall inhibition of host gene expression. This balance is a major determinant of viral tissue tropism in infections of intact animals.

Selective induction of the monocyte-attracting chemokines MCP-1 and IP-10 in vesicular stomatitis virus-infected human monocytes

It is characteristic of viral infections that monocytes/macrophages and lymphocytes infiltrate infected tissue, and neutrophils are absent. CC and non-ELR CXC chemokines predominantly attract mononuclear leukocytes, whereas the ELR motif-expressing CXC chemokines primarily act on neutrophils. To investigate the general role of chemokines in viral diseases, we determined their release and expression patterns after infection of human monocytes with vesicular stomatitis virus (VSV). Human monocytes were productively infected by VSV. Surprisingly, VSV did not induce the release of the proinflammatory cytokines tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), and IL-6. In contrast, we found a strong induction of the CC chemokine monocyte chemotactic protein-1 (MCP-1) and the non-ELR CXC chemokine interferon-gamma (IFN-gamma) inducible protein-10 (IP-10) by VSV on the gene and protein level. The expression and release of the neutrophil chemoattractants IL-8 and growth-related oncogene-alpha (GRO-alpha) remained unaffected after VSV infection. Our results indicate that the typical monocyte and lymphocyte-dominated leukocyte infiltration of virus-infected tissue is based on a selective induction of mononuclear leukocyte-attracting chemokines.

Inhibition of host RNA polymerase II-dependent transcription by vesicular stomatitis virus results from inactivation of TFIID

During infection with vesicular stomatitis virus (VSV), host-cell mRNA synthesis is inhibited due to shut off of host-cell transcription. The transcriptional activity of nuclear extracts prepared from VSV-infected cells was compared to the activity of nuclear extracts from uninfected cells. An exogenous DNA template was used which contained an adenovirus major late promoter (AdMLP) but lacked upstream activating sequences, so that only basal transcription activity was assayed in these experiments. AdMLP-initiated transcription was decreased by 75% in nuclear extracts from infected cells as early as 3 h p.i. and by >90% by 6 h p.i. Mixing nuclear extracts from uninfected and VSV-infected cells revealed that the inhibition was caused by lack of an active form of a host factor involved in basal transcription rather than by the presence of an excess of inhibitory factor. To determine which transcription factors were lacking from nuclear extracts of infected cells, host transcription initiation factors isolated from uninfected cells by ion-exchange chromatography were added separately to nuclear extracts inactivated by VSV infection. A phosphocellulose column fraction from uninfected cells eluted with 0. 8 M KCl, which contained transcription factor IID (TFIID), overcame the inhibition. The corresponding fraction from infected cells had no detectable activity in a TFIID-dependent in vitro transcription assay. TATA-binding protein (TBP) is the DNA-binding subunit of TFIID and has been shown previously to substitute for TFIID in basal transcription. Purified recombinant TBP also reconstituted the transcription activity of nuclear extracts from infected cells, supporting the idea that TFIID is the target of virus-induced inhibition. Western blot analysis showed that the level of TBP in nuclear extracts or in the 0.8 M KCl column fraction was not changed by VSV infection. These results indicated that VSV infection leads to an inhibition of host transcription by inactivation of TFIID rather than reduction in the level of TFIID.

Activity of vesicular stomatitis virus M protein mutants in cell rounding is correlated with the ability to inhibit host gene expression and is not correlated with virus assembly function

In addition to its role in virus assembly, the matrix (M) protein of vesicular stomatitis virus (VSV) is involved in virus-induced cell rounding and inhibition of host-directed gene expression. Previous experiments have shown that two M protein mutants genetically dissociate the ability of M protein to inhibit host-directed gene expression from its function in virus assembly. M protein from tsO82 virus is fully functional in virus assembly but defective in the inhibition of host-directed gene expression, while the MN1 deletion mutant, which lacks amino acids 4-21, inhibits host-directed gene expression but cannot function in virus assembly. Experiments presented here compared cell rounding induced by these two mutant M proteins to that of wt M protein. BHK cells were transfected with M protein mRNA transcribed in vitro, and the extent of cell rounding was evaluated at 24 hr posttransfection. The MN1 protein was nearly as effective as wt M protein in the induction of cell rounding, while tsO82 M protein expressed from transfected RNA was not able to induce cell rounding above that observed in negative controls without M protein, although it did cause BHK cells to have a less elongated shape. These results indicate that the ability of MN1 and tsO82 M proteins to induce cell rounding is not correlated with their virus assembly function. Instead the cell rounding activity of these mutants is correlated with their ability to inhibit host-directed gene expression. Previous data suggesting that these two cytopathic activities could be dissociated can be readily accounted for by quantitative differences in M protein expression required. Infection of either BHK cells or L cells with tsO82 virus induced cell rounding, although cell rounding was delayed relative to that following infection with wt VSV, suggesting that tsO82 M protein retains some cytopathic activity. The distribution of actin, vimentin, and tubulin in transfected cells was determined by fluorescence microscopy. In cells transfected with tsO82 M mRNA, these cytoskeletal elements were indistinguishable from those of negative control transfected cells. In cells rounded as a result of transfection with wt M or MN1 mRNA, actin-containing filaments were reorganized into a thick perinuclear ring but were not depolymerized. In contrast, tubulin and vimentin appeared to be diffusely distributed throughout the cytoplasm of rounded cells. These results support the idea that cell rounding induced by M protein results from the depolymerization of microtubules and/or intermediate filaments.

The vesicular stomatitis virus matrix protein inhibits transcription from the human beta interferon promoter

In cells infected by wild-type (wt) vesicular stomatitis virus (VSV) Indiana, host transcription is severely inhibited. DNA cotransfection studies have implicated the VSV matrix (M) protein in this process (B. L. Black and D. S. Lyles, J. Virol. 66:4058-4064, 1992). The M protein inhibited transcription not only from viral promoters in plasmids but also from the chromosomally integrated human immunodeficiency virus type 1 (HIV-1) provirus promoter (S.-Y. Paik, A. C. Banerjea, G. G. Harmison, C.-J. Chen, and M. Schubert, J. Virol. 69:3529-3537, 1995). In this study, we investigated the effect of wt VSV M protein on expression of a reporter gene under control of a cellular promoter (beta-interferon [IFN-beta] promoter), using double transient transfections in BHK and COS-1 cells. The cellular IFN-beta promoter was as susceptible to the inhibitory effect of the M protein as the viral promoters used previously. Viral proteins N, P, and G had no significant effect on reporter gene expression. The M protein gene from VSV mutant T1026R1, which is defective in host transcription inhibition, was cloned and sequenced, and its effect on reporter gene expression was tested. The mutant M protein had a methionine-to-arginine change at position 51 in the protein sequence and did not inhibit transcription from either the IFN-beta promoter or viral promoters. This VSV mutant is a good inducer of IFN, as opposed to the wt virus, which suppresses IFN induction. These results show that the M protein inhibits transcription from cellular as well as viral promoters and that the M protein does not regulate the IFN promoter any differently from viral promoters. While the M protein may play a role in IFN gene regulation, other viral or cellular factors that provide specificity to the induction process must also be involved.

Interferon induction by viruses. XV. Biological characteristics of interferon induction-suppressing particles of vesicular stomatitis virus

A single interferon (IFN) induction-suppressing particle (ISP) of vesicular stomatitis virus (VSV) blocked completely the yield of IFN in a cell otherwise programmed to produce IFN. With mouse L cells as hosts, one lethal hit of UV radiation (D37 = 52.5 ergs/mm2) to the VSV genome sufficed to inactivate ISP activity; however, with "aged" primary chick embryo cells as hosts, it took 198 lethal hits (D37 = 10,395 ergs/mm2). ISP expression in chick cells did not require virus replication or amplified RNA synthesis, but did involve functional virion-associated L protein. ISP in chick cells also were capable of inhibiting, in a multiplicity-dependent manner, the plaquing efficiency of two viruses that require cellular polymerase II (pol II) for replication, e.g., pseudorabies and influenza. The refractory state to IFN inducibility that resulted from infection of chick cells with ISP (VSV tsO5 [UV = 100 hits]) was still extant after 6 days. In contrast, the plaquing efficiency of pseudorabies virus returned to control levels by 5 h after ISP infection. Chick cells infected with UV ISP remained viable, served as hosts for the replication of other viruses, and could be subcultured. Models are presented to account for these contrasting effects. The involvement of viral plus-strand leader RNA as an inhibitor of cellular pol II-dependent RNA synthesis, and the multifunctional activities of the virion-associated L protein, are discussed as possible molecules involved in the action of ISP in chick cells.

Interferon induction by viruses. XIII. Detection and assay of interferon induction-suppressing particles

An assay is described for detecting and measuring the capacity of a single virus particle to suppress completely the yield of interferon from a cell otherwise competent to product interferon. The assay defines virus populations in terms of a newly quantifiable attribute--interferon induction-suppressing particles (ISP). The antagonistic actions of interferon-inducing particles and interferon induction-suppressing particles are thought to determine the interferon-inducing capacity intrinsic to a virus population.

Inhibition of cellular DNA synthesis by vesicular stomatitis virus

DNA synthesis in mouse myeloma (MPC-11) cells and L cells was rapidly and progressively inhibited by infection with vesicular stomatitis virus (VSV). No significant difference in cellular DNA synthesis inhibition was noted between synchronized and unsynchronized cells, nor did synchronized cells vary in their susceptibility to VSV infection after release from successive thymidine and hydroxyurea blocks. Cellular RNA synthesis was inhibited to about the same extent as DNA synthesis, but cellular protein synthesis was less affected by VSV at the same multiplicity of infection. The effect of VSV on cellular DNA synthesis could not be attributed to degradation of existing DNA or to decreased uptake of deoxynucleoside triphosphates, nor were DNA polymerase and thymidine kinase activities significantly different in VSV-infected and uninfected cell extracts. Analysis by alkaline sucrose gradients of DNA in pulse-labeled uninfected and VSV-infected cells indicated that VSV infection did not appear to influence DNA chain elongation. Cellular DNA synthesis was not significantly inhibited by infection with the VSV polymerase mutant tsG114(I) at the restrictive temperature or by infection with defective-interfering VSV DI-011 (5' end of the genome), but DI-HR-LT (3' end of genome) exhibited initially rapid but not prolonged inhibition of MPC-11 cell DNA synthesis. DNA synthesis inhibitory activity of wild-type VSV was only slowly and partially inactivated by very large doses of UV irradiation. These data suggest that, as in the effect of VSV on cellular RNA synthesis (Weck et al., J. Virol. 30:746-753, 1979), inhibition of cellular DNA synthesis by VSV requires transcription of a small segment of the viral genome.

Comparative production of interferon by explanted lymphoreticular tissue and alveolar macrophages from rabbits and humans

Studies were undertaken to compare interferon production among a variety of lymphoreticular cells, with emphasis on the alveolar macrophage. Explanted cells from rabbit lung, spleen, peritoneum, bone marrow, and blood produced interferon in varying amounts in response to six of the seven viruses studied. The various lymphoreticular tissues responded differently to a single interferon-inducing virus, and each tissue produced varying amounts of interferon when stimulated by different viruses. In addition, glass-adherent rabbit alveolar macrophages produced more interferon than did the nonadherent subpopulation. Human blood and lung cells produced much less interferon than did the equivalent rabbit cells under similar conditions of stimulation. It appeared that interferon production may have been controlled by several variables, including the species, the type of inducer, and the type of tissue and cell.

Polykaryocytosis induced by vesicular stomatitis virus infection in BHK-21 cells

Cytopathological effects by vesicular stomatitis virus (VSV) infection were studied in several cell lines. Marked polykaryocyte formation was observed in monolayers of certain strains of BHK-21 cells infected with VSV. The BHK-21-KB cells were found to be the most susceptible to virus-induced cell fusion. This type of cell fusion was related to intracellular growth of the viruses, and strong cytolytic changes were found to occur following the development of large multinucleated giant cells. The cell-fusing activity was associated with the infectivity of VSV and was neutralized by anti-VSV immune serum. The viruses irradiated for 20 minutes or heated at 60 degrees C for 10 minutes lost completely both infectivity and cell-fusing activity. These experimental results indicate that virus replication was responsible for fusion of BHK cells.

The production of vesicular stomatitis virus by antigen- or mitogen-stimulated lymphocytes and continuous lymphoblastoid lines

A variety of lymphoid cell populations were examined in terms of their ability to replicate vesicular stomatitis virus (VSV), a lytic, RNA-containing virus maturing at the cell surface. The number of cells capable of producing VSV was estimated in terms of infectious centers by the virus plaque assay (VPA), and morphologically by electron microscopy (EM). The lymphoid cells examined in this study included: (a) lymph node cells from delayed hypersensitive guinea pigs stimulated by specific antigen, (b) mouse spleen cells activated by selective bone marrow-derived (B) cell and thymus derived (T) cell mitogens, and (c) cells of human and murine continuous lymphoblastoid or lymphoma lines. In unstimulated cultures of guinea pig lymph node cells there is a background of approximately 1 in 1,000 cells which produces VSV; in purified protein derivative (PPD)-stimulated cultures the number of cells producing virus was 1.6% in the VPA and 1.9% by EM. These cells were large lymphocytes with some morphological features of transformed lymphocytes but were not typical blast cells. A few macrophages were associated with virus in both stimulated and control cultures. These observations indicate that (a) cells responsive to antigens, as detected by a marker virus, were lymphocytes; (b) cells other than lymphocytes (macrophages) were capable of replicating VSV even without antigenic stimulation; and (c) the correlation of results obtained by VPA and morphologic examination was usually quite good. Of the total number of mouse spleen cells stimulated with concanavalin (Con A), a T cell mitogen, 4.5 (EM)-5.7% (VPA) were associated with VSV. These were characteristic transformed lymphocytes, similar to phytohemagglutinin (PHA)-stimulated human lymphocytes. In contrast Escherichia coli lipopolysaccharide (LPS)-treated mouse spleen cultures contained lower numbers of virus plaque-forming cells. The majority of such cells associated with virus displayed extensive rough endoplasmic reticulum. Two cultured murine lymphomas containing lymphocytes with the theta surface marker (L5178Y and EL-4) showed a 15-100-fold higher incidence of virus-producing cells than leukemias (L1210 and C57Bl/6) which did not carry this marker. Similarly, the L2C guinea pig leukemia, a known B cell leukemia, yielded a low percent of virus plaque-forming cells (<2%). However, MOPC-104, a plasma cell tumor presumed to be of B cell origin, was found to be an efficient virus producer. There was a wide variation in the efficiency of VSV replication among human lymphoblastoid lines. One line, Wil-2, produced 80% infectious centers after 24 h of exposure to VSV, and all cells were associated with virus at the EM level. The relationship between the virus-producing cells and different lymphocyte subpopulations as well as the efficiency of the two assays for studying virus-producing lymphocytes is discussed.

Interferon production and inhibition of host synthesis in cells infected with vesicular stomatitis virus

Infection of L cells with wild-type (L(1)) vesicular stomatitis virus at high or low multiplicities does not result in the production of interferon; however, infection of L cells with low multiplicities of a small-plaque mutant (S(2)) results in the synthesis of large amounts of interferon. In chick embryo (CE) cells, both viruses induce synthesis of interferon; there is no significant multiplicity effect in CE cells. The rate and efficiency of shutoff of macromolecular synthesis in the different host cells is a critical factor in determining the ability of the viruses to induce interferon synthesis. If host ribonucleic acid or protein synthesis is shut off by the virus before the required new ribonucleic acid is transcribed or translated, interferon production does not occur. The relative yield of the two viruses in CE and L cells is not related to the effects of interferon produced during the course of infection.

Cells persistently infected with Newcastle disease virus. II. Ribonucleic acid and protein synthesis in cells infected with mutants isolated from persistently infected L cells

A comparison of the replication patterns in L cells and in chick embryo (CE) cell cultures was carried out with the Herts strain of Newcastle disease virus (NDV(o)) and with a mutant (NDV(pi)) isolated from persistently infected L cells. A significant amount of virus progeny, 11 plaque-forming units (PFU)/cell, was synthesized in L cells infected with NDV(o), but the infectivity remained cell-associated and disappeared without being detectable in the medium. In contrast, in L cells infected with NDV(pi), progeny virus (30 PFU/cell) was released efficiently upon maturation. It is suggested that the term "covert" rather than "abortive" be used to describe the infection of L cells with NDV(o). In both L and CE cells, the latent period of NDV(pi) was 2 to 4 hr longer than for NDV(o). The delay in synthesis of viral ribonucleic acid (RNA) in the case of NDV(pi) coincided with the delay in the inhibition of host RNA and protein synthesis. Although both NDV(o) and NDV(pi) produced more progeny and more severe cell damage in CE cells than in L cells, the shut-off of host functions was significantly less efficient in CE cells than in L cells. Paradoxically, no detectable interferon was produced in CE cells by either of the viruses, whereas in L cells most of the interferon appeared in the medium after more than 90% of host protein synthesis was inhibited. These results suggest that the absence of induction of interferon synthesis in CE cells infected with NDV is not related to the general shut-off of host cell synthetic mechanisms but rather to the failure of some more specific event to occur. In spite of the fact that NDV(pi) RNA synthesis commenced 2 to 4 hr later than that of NDV(o), interferon was first detected in the medium 8 hr after infection with both viruses. This finding suggests that there is no relation between viral RNA synthesis and the induction of interferon synthesis.