Roles of Tax and HBZ proteins in post-transcriptional control of cellular gene expression

HTLV-1 is a retrovirus capable of inducing severe pathologies such as the adult T-cell leukemia/lymphoma (ATLL) and the HTLV-1 associated myelopathy/ tropical spastic paraperesis (HAM/TSP). HTLV- 1 is a positive stranded RNA virus encoding typical retroviral genes as well as essential regulatory and accessory genes. Two of them, Tax and HBZ, have been more and more in the spotlights for playing crucial roles in the virus persistence and oncogenicity. The majority of HTLV-1 Tax and HBZ studies have focused on the impact of the oncoproteins on transcriptional events. Con- sequently, little is known in the case of post-transcription, including splicing. Aberrant splicing is common in cancer cells and people living with HTLV-1 display altered splicing patterns. Here, we uncovered potential roles of HTLV-1 Tax and HBZ proteins in the regulation of alternative splicing events (ASEs) upon HTLV-1 infection. By using Jurkat cells inducibly expressing Tax or HBZ, we identi ed Tax and/or HBZ dependent alternative splicing events. Tax and HBZ had globally opposite e ects on splicing (Tax fosters inclusion and HBZ exclusion). However, the shared ASEs triggered by Tax and HBZ are regulated similarly. We also noticed that the viral Tax and HBZ proteins impact di erent set of genes at the transcriptional and splicing level and alternatively spliced genes were enriched for known cancer genes. Next, we investigated AS events in HTLV-1 infected individuals. Interestingly, several ASEs shared between T cells expressing Tax or HBZ and people living with HTLV-1 highlighted genes already known for their role in HTLV-1 leukemogenesis. New targets of HTLV-1 were also discov- ered. Of particular interest, we show that the protein tyrosine phosphatase receptor type c gene (PTPRC) encoding CD45, a critical regulator of immune response, is controlled by alternative splicing in Tax and HBZ expressing cells as well as in ATLL patients. We built a comprehensive interactome map of Tax and HBZ with cellular host proteins and identi ed 44 and 111 new protein-protein interactions for Tax and HBZ, respectively. Interestingly, Tax and HBZ interact with RNA binding Proteins having diverse functions on mRNA fate. This may indicate a global regulation of gene expression throughout mRNA life. Finally, we further investigated one partner of Tax in particular, U2AF65, a crucial protein in- volved in alternative splicing. While a precise mechanism on how Tax modulates U2AF65-dependent splicing still needs to be fully determined, our study highlights U2AF65 as a potential major player in HTLV-1 biology.Laboratory of Viral Interactome