David Montpoint Jeune

Role of post-translational modifications of CTIP2 in the transcriptional regulation of the HTLV-1 virus

Abstract

The human T-lymphotropic virus-1 is a retrovirus belonging to the genus Deltaretrovirus and the sub-family Oncoviridae. HTLV-1 is an oncogenic virus and the etiologic agent of adult T-cell leukemia/lymphoma (ATLL) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). The main characteristic of HTLV-1 infection is the viral latency inducing a transcriptional repression of viral genes from the 5'and 3' LTRs. Several laboratories, including ours, have characterized the crucial role of the transcriptional cofactors CTIP2 (Chicken Ovalbumine Upstream Promoter Interacting Protein 2, or Bcl11b (B cell leukemia/lymphoma 11b)) in the transcriptional regulation of HIV-1, the etiological agent of AIDS.

This master thesis aims at futher understanding the implication of the transcriptional cofactor CTIP2 in the transcriptional regulation of HTLV-1.

The transcriptional co-factor CTIP2 has a dual role in the transcription regulation of its target genes, as activator or repressor depending on the gene. Our laboratory has previously demonstrated the roles of CTIP2 in the transcriptional regulation of HIV-1 and the p21 gene by recruitment of two different complexes. Several other studies have characterized the transcriptional activation of IL-2 and Cot kinase cellular genes in activated T-cells. To pursue the characterization of the impact of CTIP2 on the transcriptional regulation of HTLV-1, we first studied the effect of the human version of CTIP2 on the repression of transactivation mediated by Tax of the 5' LTR of HTLV-1, compared to the murine version, by transient transfection in T-lymphoid Jurkat cell line. Our results demonstrate that the repression of transactivation mediated by Tax at the 5'LTR obtained with murine CTIP2 and human CTIP2 proteins is "dose-dependent". Secondly, we studied the acetylation of the human version of CTIP2 by western blot, compared to the murine version, by transient transfection in HEK293T cel line. Our results demonstrate that the human version of CTIP protein with a FLAG-tag to the N-terminus is visible by western blot, that the immunoprecipitation with an anti-FLAG antibody also allow us to purify the human version of CTIP2, and that CTIP2 is acetylated in the presence of p300, like the murine version. Finally, we studied the impact of the mutation of the lysine residue K685 of the human version of CTIP2 on the transcriptional regulation of the transactivation mediated by Tax at the 5'LTR of HLTV-1, as well as on the global acetylation of the CTIP2 protein. Our results suggest that, as for the murine version of CTIP2, acetylation of the lysine residue K685 (or K604 of the murine isoform) is primordial as for the repressive activity of CTIP2 on the transactivation mediated by Tax at 5'LTR of HTLV-1.

Taken togetherm our results contribute to a better understanding of the mechanisms involving the transcriptional cofactor CTIP2 that regulate HTLV-1 transcription.