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Induction of type-C RNA virus by cycloheximide: increased expression of virus-specific RNA
Abstract:
Mouse cells contain the genetic information for multiple endogenous type-C RNA viruses. The mechanisms by which the cell controls expression of these naturally integrated viruses are not yet known. Recently, chemicals that inhibit protein synthesis have been shown to induce a specific type-C virus at high frequency from BALB/c mouse embryo cells. In the present studies, virus activation in response to a representative translational inhibitor, cycloheximide, is demonstrated to be transient, with virus release primarily occurring within the first 12-24 hr following drug exposure. Analysis of virus-specific RNA in cells by molecular hybridization revealed an absolute increase in viral RNA concentration in cycloheximide-treated cells. This was blocked by simultaneous exposure of the cells to actinomycin D. Further, inhibition of RNA synthesis during but not subsequent to cycloheximide exposure prevented virus activation. These findings show that virus induction by cycloheximide requires de novo RNA synthesis during but not after drug exposure and suggest that the required RNA species may be that of the virus itself. The present results are consistent with the hypothesis that translational inhibitors prevent synthesis of a labile protein whose normal action is to inhibit viral RNA transcription or to cause degradation of viral RNA.
Insights
Cycloheximide, a protein synthesis inhibitor, transiently activates endogenous type-C viruses in mouse cells. This induction requires new RNA synthesis during drug exposure, suggesting a regulatory protein normally suppresses viral RNA.
Area of Science:
- Molecular Biology
- Virology
- Cell Biology
Background:
- Mouse cells harbor genetic information for multiple endogenous type-C RNA viruses.
- Mechanisms controlling the expression of these integrated viruses are not fully understood.
- Chemicals inhibiting protein synthesis can induce type-C virus expression in mouse cells.
Purpose of the Study:
- To investigate the mechanism of virus induction by cycloheximide, a translational inhibitor.
- To determine the role of de novo RNA and protein synthesis in cycloheximide-induced viral activation.
Main Methods:
- BALB/c mouse embryo cells were treated with cycloheximide.
- Virus release was quantified over time.
- Virus-specific RNA levels were analyzed using molecular hybridization.
- The effects of actinomycin D (RNA synthesis inhibitor) were assessed.
Main Results:
- Cycloheximide-induced virus activation was transient, with peak release within 12-24 hours.
- Viral RNA concentration increased significantly in treated cells.
- This increase was blocked by actinomycin D.
- Inhibiting RNA synthesis during cycloheximide exposure prevented virus activation, but not if RNA synthesis was inhibited later.
Conclusions:
- Cycloheximide-induced type-C virus activation necessitates de novo RNA synthesis during drug treatment.
- These findings support a model where cycloheximide disrupts the synthesis of a labile protein that normally represses viral RNA transcription or promotes viral RNA degradation.