Regulation of TAL1 in T-cell leukemia

About This Grant

TAL1 is a hematopoietic-specific member of the basic helix-loop-helix family of transcription factors (TFs) required for hematopoietic stem cell (HSC) function and the development of all hematopoietic lineages1-4. Aberrant activation of TAL1 oncogene associates with up to 60% of T-cell acute lymphoblastic leukemia (T-ALL) patients5-7. Its ectopic expression also led to development of leukemia or lymphoma in mice8,9. Deletion of TAL1 in T-ALL cells lost leukemic phenotype and induced apoptosis10. Furthermore, the TAL1 expressing (TAL1+) TALL subtype associates with poor prognosis and high rate of relapse indicating that dysregulation of TAL1 oncogene plays an important role in T cell leukemogenesis. In order to comprehensively understand the role of TAL1 domain structure in T-ALL pathogenesis, we employed unbiased sgRNA tiling library scanning of TAL1 exons for structural and functional domains in resolution of 3.9 base pairs (bp)/sgRNA. We identified that two lysine residues, K221 and K222, are critical for T-ALL cell function and survival. K221 and K222 sites of TAL1 are key targets for HAT mediated acetylation in vivo. The level of acetyl-TAL1 is lower in TAL1+ T-ALL cell lines than that of differentiated erythroid cells. Furthermore, we generated unacetyl-mimicking TAL1K221,222R (TAL1K2R) and acetyl-mimickingTAL1K221,222Q (TAL1K2Q) knock-in (KI) Jurkat cells and TAL1K2R and TAL1K2Q conditional KI (cKI) mice. While TAL1K2R Jurkat cells behaves similar to TAL1+ T-ALL cells that promote leukemic transcription profile for leukemia survival, TAL1K2Q cells facilitated T-cell differentiation and blocked leukemogenesis in xenograft mouse models, suggesting that acetylation status of TAL1 dynamically regulates TAL1 function in normal hematopoiesis vs leukemogenesis. In addition, IP-LC/LC MS revealed that TAL1K2Q mainly associates with HAT complexes while TAL1K2R interacts with HDACs and leukemic TFs. Based on these preliminary data, we hypothesize that acetylation status of K221 and K222 of TAL1 act as a molecular switch to control its ability to interact with TFs and epigenetic factors, as well as TAL1 mediated transcription circuit for normal hematopoiesis and T-ALL leukemogenesis. In this proposal, we will investigate: 1) key novel factors that are differentially associated with TAL1K2R and TAL1K2Q in controlling TAL1 transcription function in T-ALL; 2) the underlying mechanisms of TAL1 acetylation on TAL1-driven transcriptional regulation; 3) the biological function of TAL1 mutants in BM HSC regulation and T-cell leukemogenesis. To achieve this goal, we generated several mouse models of human T-ALL disease that are not only critical and essential to study how TAL1 acetylation alters HSC/LSC function during T-ALL development, but also potentially lead to the development of new therapeutic strategies targeting TAL1 modifications for T-ALL treatment. Success of the proposed studies, especially using our unique mouse models of human T-ALL disease, will lead to a better understanding of mechanism by which aberrant expression of TAL1 oncogene leads to T-ALL and how TAL1 acetylation status switches its ability to alter hematopoietic transcription regulatory networks in T-ALL.