TAFII250 Is Critical in AML1-ETO Mediated Leukemogenesis

Background: Rearrangement between chromosome 8 and 21 is the most frequently observed chromosomal translocation. In AML patients, it leads to the formation of a novel fusion protein AML1-ETO. AML1-ETO functions as a transcriptional regulator to suppress myeloid differentiation and to promote self-renewal of hematopoiesis stem cells, which are of importance in leukemia development. However, AML1-ETO has no enzymatic function, thus targeting AML1-ETO directly is technically difficult. TAFII250, a largest subunit of the transcription factor IID complex (TFIID) serves to bring other components of basal transcription machinery to the preinitiation complex during the transcription initiation. And TAFII250 also plays a crucial role in the expression of genes involved in cell cycle and apoptosis. Yet despite the importance of these processes, there is no direct evidence implicating TAFII250 in cancer development. We have reported that acetylation of AML1-ETO on lysine 43 is critical for AML1-ETO mediated leukemogenesis and used a peptide pulldown strategy to identify proteins that preferring interact with acetylated AML1-ETO and identified TAFII250. Here, we are going to report the functions of TAFII250 in AML1-ETO induced leukemogenesis.

Methods: We used Kasumi-1 and SKNO-1 cell lines derived from t(8; 21)AML patients, and a mouse AML1-ETO exon 9a (AE9a) expressing cell line developed from bone marrow cells of mice injected with bone marrow cells infected with AE9a to perform in vitro and in vivo studies.

Results: We demonstrate that TAFII250 associates with AML1-ETO in AML cells through its bromodomain recognizing acetylated lysine 43 on AML1-ETO. The knockdown of TAFII250 completely abolished the proliferation of AML1-ETO expressing cells and has little influence on cell growth of non AML1-ETO expressing cells K562 and CD34+ cells. In addition, when we examined cleaved caspase 3 and PARP by western and measured annexin-V through flow cytometry, we found that the deficiency of TAFII250 induces apoptosis in AML1-ETO expressing cells. Further, the co-immunoprecipitation assay revealed that the deficiency of TAFII250 blocks the binding of AML1-ETO to CBFb (core binding factor beta subunit) and the recruitment of AML1-ETO at the promoter regions of a subset of its target genes. Consequently, loss of TAFII250 interferes with the expression of these genes. The depletion of TAFII250 also has negative effect on the self-renewal of leukemic cells, promoting their differentiation. Most importantly, the loss of TAFII250 severely impairs leukemia development in AE9a expressing cells.

Conclusions: Together, these results reveal an essential role of TAFII250 in AML1-ETO mediated leukemogenesis and imply that TAFII250 might be a therapeutic target for AML1-ETO expressing AMLs.