TGIF1 is a negative regulator of MLL-rearranged acute myeloid leukemia

Members of the TALE (Three-amino acid loop extension) family of atypical homeodomain-containing transcription factors are important downstream effectors of oncogenic fusion proteins involving the mixed lineage leukemia (MLL) gene. A well-characterized member of this protein family is MEIS1, which orchestrates a transcriptional program required for the maintenance of MLL-rearranged acute myeloid leukemia (AML). TGIF1/TGIF2 are relatively uncharacterized TALE transcription factors, which in contrast to the remaining family, have been shown to act as transcriptional repressors. Given the general importance of this family in malignant haematopoiesis we therefore tested the potential function of TGIF1 in the maintenance of MLL-rearranged AML. Gene expression analysis of MLL-rearranged patient blasts demonstrated reduced TGIF1 levels and, in accordance, we find that forced expression of TGIF1 in MLL-AF9 transformed cells promoted differentiation and cell cycle exit in vitro, and delayed leukemic onset in vivo. Mechanistically, we show that TGIF1 interferes with a MEIS1-dependent transcriptional program by associating to MEIS1-bound regions in a competitive manner and that the MEIS1:TGIF1 ratio influence clinical outcome. Collectively, these findings demonstrate that TALE family members can act both positively and negatively on transcriptional programs responsible for leukemic maintenance and provide novel insights into regulatory gene expression circuitries in MLL-rearranged AML.Leukemia accepted article preview online, 28 October 2014. doi:10.1038/leu.2014.307.