Analysis of uridine incorporation in chicken embryo cells infected by vesicular stomatitis virus and its temperature-sensitive mutants: uridine transport

Modification of membrane permeability by animal viruses

Animal viruses modify membrane permeability during lytic infection. There is a co-entry of macromolecules and virion particules during virus penetration and a drastic change in transport and membrane permeability at the late stages of the lytic cycle. Both events are of importance to understand different molecular aspects of viral infection, as virus entry into the cell and the interference of virus infection with cellular metabolism. Other methods of cell permeabilization of potential relevance to understand the mechanism of viral damage of the membrane are also discussed.

Intracellular events following the infection of different cell types with vesicular stomatitis subviral particles

Vesicular stomatitis virus (VSV) subviral particles (nucleocapsids and G-depleted particles) were used to infect various cells (chicken embryo, HeLa, and BHK21 cells). These particles bind to and penetrate into host cells; the association of G-depleted particles to cells was even better than that of normal virions. The parental genomes of subviral particles and virions were degraded at the same rate in the infected cells. Nevertheless, these subviral particles had a very low infectivity, synthesized very little viral macromolecules, and had very little, if any, effect on the various host cells used. Furthermore , subviral particles could be rescued in chicken embryo cells by uv-irradiated VSV virions, demonstrating that subviral particles actually penetrated into cells, and that their arrested cycle could be unblocked up to a certain point. On the other hand, subviral particles were not rescued in HeLa cells, suggesting a dependence on the host cell system.

Virally induced alterations in cellular permeability: a basis of cellular and physiological damage?

Virally induced permeability changes occur when haemolytic paramyxoviruses are added to cells; similar (though not identical) changes take place during infection of cells with viruses from several families (including paramyxoviruses). These changes occur in intact, viable cells, and precede subsequent cytopathic effects, to which they are likely to contribute. There is accumulating evidence to suggest that virally induced permeability changes may also underlie the physiological and clinical consequences of viral infection in certain situations.

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.

Is cytoskeleton involved in vesicular stomatitis virus reproduction?

CER cells infected with vesicular stomatitis virus showed a morphology similar to that observed after cytochalasin B treatment. Temperature-sensitive mutants affected in envelope protein maturation did not induce those morphological changes at a nonpermissive temperature. In addition, the cytoskeleton was not implicated in vesicular stomatitis virus reproduction.

RNA synthesis of vesicular stomatitis virus-infected cells: in vivo regulation of replication

Pulse-labeling of vesicular stomatitis virus-infected HeLa and BHK cells with [3H]uridine throughout the infectious cycle demonstrated two peaks of uridine incorporation into virus-specific RNA molecules. By separating total RNA synthesis into replication and transcription products, we showed that replication occurs over a shorter period of time in one peak synthesis. The biphasic nature of uridine incorporation is in part due to a general membrane phenomenon of reduced metabolite transport during vesicular stomatis virus infection and in part due to the apparent uncoupling of replication and transcription. A change in the ratio of newly synthesized plus and minus strands of the genome length (42S) RNA was found as the infection proceeded. Early in the infection, plus-stranded 42S RNA comprised 40% of the total genome length RNA synthesis, whereas late in infection, only 15 to 20% of the 42S RNA synthesized was complementary to the virion minus strand. Our data suggest that the rate of synthesis of plus-stranded 42S RNA was constant throughout the infection. The rate of virus release was determined by monitoring the uptake of [3H]uridine into released virus particles. Virus maturation and release are closely associated with the assembly of 42S RNA-containing nucleocapsids.

Envelope proteins and replication of vesicular stomatitis virus: in vivo effects of RNA+ temperature-sensitive mutations on viral RNA synthesis

Temperature-sensitive (ts) mutants of vesicular stomatitis virus belonging to complementation groups III and V were investigated for their in vivo RNA synthesis. The sucrose gradient patterns of the RNA species which they produced at nonpermissive temperature (39.2 degrees C) were systematically compared under different experimental conditions: variation of input multiplicity and of time of infection, superinfection with T particles, and temperature shifts. Finally, a more precise analysis of the various RNA species synthesized was carried out. It appeared that the characteristics of RNA synthesis specified at 39.2 degrees C by tsIII or tsV mutants differed from the normal RNA synthesis of vesicular stomatitis virus wild type. Their common depression at 39.2 degrees C in virion-like RNA (38S) production--i.e., so-called genome replication--was tentatively paralleled with the concomitant ts events which have been previously shown to affect the two viral envelope proteins. An overproduction of the RNA transcripts was described for mutants in group III and posed the question of a regulation process to determine the amount of RNA to be transcribed.

The matrix (M) protein of vesicular stomatitis virus regulates transcription

Temperature-sensitive mutants of vesicular stomatitis virus (VSV) belonging to complementation group III contain a lesion in the matrix (M) protein. This results in a 2--5 fold increase in transcription at the nonpermissive temperature. Co-infection of cells with one of these mutants and wild-type virus reverses this mutant phenotype. Separation of the transcriptional and translational products from mutant-infected cells reveals an overall increase in each of the viral mRNA species concomitant with degradation of the M protein at the nonpermissive temperature. The increase in mRNA, however, does not lead to increased synthesis of viral proteins. Quantitation of individual mRNA species indicates that M protein acts as a direct inhibitor of transcription as well as an attenuator of sequential transcription.

Membrane leakiness after viral infection and a new approach to the development of antiviral agents

Viral development induces changes in the permeability properties of the plasma membrane of the host cell. Here it is shown that, because of this leakiness, inhibitors of protein synthesis normally impermeable to uninfected cells are able to enter infected cells and thereby specifically inhibit viral protein synthesis.

Inhibition of RNA synthesis in mouse myeloma cells infected with vesicular stomatitis virus

Infection of mouse myeloma cells (MPC-11) with vesicular stomatitis (VS) virus resulted in rapid and marked reduction in cellular RNA synthesis considerably before cell viability was compromised. Mouse myeloma cells responded maximally to viral infection at a multiplicity of 1 and were considerably more se;sitive to shut-off of RNA synthesis than were mouse L cells or BHK-21 cells. This inhibition of cellular RNA synthesis was shown not to be caused by differential membrane permeability of infected and uninfected MPC-11 cells to [3H]uridine, nor was it due to greater degradation of previously synthesized RNA. VS viral infection appeared not to impede transport of newly synthesized nuclear RNA to the cytoplasm; moreover, infected cells accumulated polyadenylated mRNA at the same rate as did uninfected cells. Polyacrylamide gel electrophoresis of newly synthesized nuclear RNA demonstrated that the polydisperse nature and size distribution were not affected by VS viral infection. Isolated nuclei of infected MPC-11 cells also inhibited greatly impaired capacity to synthesize RNA despite the absence of cytoplasmic factors. Infected-cell cytosol did not inhibit transcription by uninfected-cell nuclei, nor did uninfected-cell cytosol reverse viral inhibition of nuclear transcription. Studies with alpha-amanitin revealed that VS viral infection inhibited the activity of polymerases I, II, and III, but only polymerase II was affected progressively throughout infection and to a much greater extent. These data suggest that, even at low multiplicities of infection, VS virus rapidly shuts off cellular RNA synthesis at the level of nuclear transcription.

Inhibition of pseudorabies virus replication by vesicular stomatitis virus. II Activity of defective interfering particles

Purified defective interfering (DI) particles of vesicular stomatitis virus (VSV) inhibit the replication of a heterologous virus, pseudorabies virus (PSR), in hamster (BHK-21) and rabbit (RC-60) cell lines. In contrast to infectious B particles of VSV, UV irradiation of DI particles does not reduce their ability to inhibit PSR replication. However, UV irradiation progressively reduces the ability of DI particles to cause homologous interference with B particle replication. Pretreatment with interferon does not affect the ability of DI particles to inhibit PSR replication in a rabbit cell line (RC-60) in which RNA, but not DNA, viruses are sensitive to the action of interferon. Under similar conditions of interferon pretreatment, the inhibition of PSR by B particles is blocked. These data suggest that de novo VSV RNA or protein synthesis is not required for the inhibition of PSR replication by DI particles. DI particles that inhibit PSR replication also inhibit host RNA and protein synthesis in BHK-21 and RC-60 cells. Based on the results described and data in the literature, it is proposed that the same component of VSV B and DI particles is responsible for most, if not all, of the inhibitory activities of VSV, except homologous interference.

Differential inhibition of host protein synthesis in L cells infected with RNA - temperature-sensitive mutants of vesicular stomatitis virus

The response of mouse L cells to infection with wild-type (wt) and temperature-sensitive (ts) mutants of vesicular stomatitis virus was monitored by sodium dodecyl sulfate-polyacrylamide gel electrophoresis to delineate the synthesis of host cell and viral proteins. Experiments utilized transcriptase mutants of complementation group I (ts114 and ts13), a group IV mutant (ts44) that is restricted in total RNA synthesis (RNA-1) but not in primary transcription, and a group II mutant (ts52) variably restricted in RNA synthesis (RNA +/-). L cells infected with ts mutants at permissive temperature exhibited the wt response of progressive inhibition of host cell protein synthesis accompanied by accumulation of all five viral proteins. Mutant ts44 (IV) also switched off cell protein synthesis at restrictive temperature and accumulated all five viral proteins, but with disproportionate ratios of N and G proteins. At restrictive temperature, cells infected with group I ts mutants failed to accumulate any viral protein and did not exhibit significant reduction in host cell protein synthesis. These data suggest that vesicular stomatitis virus inhibits cell protein synthesis at a stage of viral infection after transcription and possibly translation but preceding replication of progeny viral RNA.