Inhibition of Cellular RNA Polymerase II Transcription by Delta Antigen of Hepatitis Delta Virus

AbstractHepatitis delta virus (HDV) contains a circular, viroid-like RNA and the hepatitis delta antigen (HDAg) protein. The viral RNA is replicated via RNA-dependent RNA synthesis, which is thought to be mediated by host DNA-dependent RNA polymerase II (pol II). The precise mechanism of HDV RNA replication using RNA as a template remains to be elucidated, although it is clear that HDAg is involved. We demonstrate here that both SP1-activated and basal pol II transcription are inhibited by HDAg. This inhibitory effect of HDAg was observedin vivoin transient cotransfection assays as well asin vitroin HeLa nuclear extracts with purified, recombinant HDAg. Thein vitroinhibition of pol II transcription could be reversed with excess HeLa nuclear extracts. Furthermore, HDAg specifically inhibited pol II-mediated transcription but not pol I- or pol III-mediated transcription. These results provide support for the model in which HDAg participates in a complex with host cell pol II transcription factors to mediate pol II-dependent HDV RNA replication, concomitantly inhibiting cellular pol II transcription