2000 Volume 44 Issue 7 Pages 597-603
The transcriptional mechanism of Borna disease virus (BDV) has been poorly understood. We have analyzed transcription of the virus upon various stimuli in Madin-Darby canine kidney cells which were persistently infected by BDV (MDCK/BDV). Treatment with actinomycin D (ActD) increased the level of BDV RNA, shifting the size of RNA from 1.9kb to 2.3kb beginning 5hr after the treatment. To understand the mechanism of this unique modulation of BDV RNA, we conducted several experiments. The RNA increase occurred at the stage in which synthesis of cellular intrinsic mRNA was intact, suggesting BDV does not compete with cellular transcriptional machinery for intrinsic RNA polymerase II. The BDV transcription was also enhanced by cycloheximide treatment, indicating that newly synthesized viral or cellular proteins are not necessary for viral transcription. However, a shift in the RNA size was not observed for cycloheximide-induced BDV RNA. The increase in viral transcription persisted during the cellular apoptotic process consequent to p53 gene accumulation beginning 1hr after ActD treatment. Caspase inhibitors Z-VAD and DEVD-CHO repressed the apoptotic process but failed to block the increase in BDV transcription. In addition, adenovirus-mediated transduction of wild-type p53 did not alter the BDV transcription, indicating that the increase in BDV transcription was independent of the p53-mediated apoptotic process. Other various stimuli that evoke cellular signal transductions failed to alter BDV transcription. Agents inhibitory to topoisomerase except adriamycin failed to enhance BDV transcription, indicating that the increase in BDV transcription is not mediated by an inhibitory action to the topoisomerase II of ActD. Adriamycin showed an increase and size-shift of BDV RNA similar to ActD. These results suggest that intercalation of the viral genome itself with ActD is related to the stabilization of viral RNA and alteration of RNA size rather than secondary host cell changes.
