Bovine Leukemia Virus (BLV)

Bovine leukemia virus (BLV) is a retrovirus naturally infecting cattle and causing enzootic bovine leukemia (EBL). The main feature of BLV infection is viral latency due to genetic and epigenetic repressions of viral gene expression from the main viral promoter, the 5’LTR, thereby allowing the virus to escape the host immune system and induce tumor development. Recent data have demonstrated that the regulation of BLV transcription is not solely dependent on the 5’LTR. Indeed, two new active promoters have been identified despite the transcriptional repression of the 5’LTR: a cluster of 5 independent RNAPIII promoters is responsible for the expression of 10 viral miRNAs and a RNAPII promoter located in the 3’LTR is responsible for the expression of antisense transcripts. In our previous work, we demonstrated the in vivo recruitment of the cellular factor CTCF to three conserved CTCF binding motifs along the provirus and suggested their importance in both the regulation of BLV transcriptional activities and in the deregulation of the three-dimensional (3D) chromatin architecture surrounding the BLV integration site, potentially affecting cellular gene expression . Currently, we aim at further studying the functional role of CTCF in the context of two BLV latently-infected cell lines. More precisely, we will first study the impact of depleting CTCF on both viral/cellular transcriptome and 3D chromatin architecture by performing RNA-seq, ChIP-seq and 4C-seq experiments. In addition, we will assess the individual role of each of the three viral CTCF binding sites by disrupting CTCF binding by a recent CRISPRi approach, and perform additional RNA-seq, ChIP-seq and 4C-seq experiments. Altogether, this study will highlight CTCF as a new effector of BLV transcriptional regulation and BLV-induced physiopathology, which could serve as a valuable model for human retroviruses such as HTLV-1 and HIV-1.