Abstract
Bovine leukemia virus latency is a viral strategy used to escape from the host immune system and contribute to tumor development. However, a highly expressed BLV micro-RNA cluster has been reported, suggesting that the BLV silencing is not complete. Here, we demonstrate the in vivo recruitment of RNA polymerase III to the BLV miRNA cluster both in BLV-latently infected cell lines and in ovine BLV-infected primary cells, through a canonical type 2 RNAPIII promoter. Moreover, by RPC6-knockdown, we showed a direct functional link between RNAPIII transcription and BLV miRNAs expression. Furthermore, both the tumor- and the quiescent-related isoforms of RPC7 subunits were recruited to the miRNA cluster. We showed that the BLV miRNA cluster was enriched in positive epigenetic marks. Interestingly, we demonstrated the in vivo recruitment of RNAPII at the 3′LTR/host genomic junction, associated with positive epigenetic marks. Functionally, we showed that the BLV LTR exhibited a strong antisense promoter activity and identified cis-acting elements of an RNAPII-dependent promoter. Finally, we provided evidence for an in vivo collision between RNAPIII and RNAPII convergent transcriptions. Our results provide new insights into alternative ways used by BLV to counteract silencing of the viral 5′LTR promoter.
Highlights
Transcription of BLV genes initiates at the U3/R junction in the 5′-long terminal repeat (LTR) and is regulated by cellular transcription factors for which several binding sites have been identified in the LTR9–19, by the viral transactivator TAXBLV20 and by the chromatin status of the BLV provirus[21,22,23,24,25]
We decided to investigate the in vivo recruitment to the BLV provirus of RNAPIII by performing chromatin immunoprecipitation (ChIP) assays
Some evidence support the notion that the miRNA cluster is transcribed by the RNA polymerase III, a direct functional link between RNAPIII transcriptional activity and BLV miRNAs expression has not been reported to date
Summary
Transcription of BLV genes initiates at the U3/R junction in the 5′-long terminal repeat (LTR) and is regulated by cellular transcription factors for which several binding sites have been identified in the LTR9–19, by the viral transactivator TAXBLV20 and by the chromatin status of the BLV provirus[21,22,23,24,25]. We have previously demonstrated that the 5′LTR RNA polymerase II-driven transcriptional repression is due to the epigenetic state of the 5′LTR characterized by weak histone acetylation and DNA CpG hypermethylation associated to closed chromatin in a lymphoma-derived BLV-infected L267 ovine cell line harboring a fully competent provirus[19,21,25]. In addition to the RNAPIII recruitment, we demonstrated an RNAPII recruitment at the junction between the 3′LTR and the host genome which was associated with positive epigenetic marks typical of transcriptionally active promoters. ChIP-seq experiments performed in a BLV-infected cell line confirmed the high RNAPIII recruitment to the BLV miRNA cluster and the RNAPII occupancy just downstream of this region, suggesting a collision phenomenon between these two polymerase machineries and stalling of RNAPII
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call