GFI1b As a Novel Oncosuppressor in AML

The proper differentiation of hematopoietic stem cells (HSCs) is regulated by a concert of different so called transcription factors (TFs). A disturbed function of these TFs can be the basis of malignant diseases such as acute myeloid leukemia (AML) or myelodysplastic syndrome (MDS). Growth Factor Independence 1b (Gfi1b) is a repressing transcription factor, with a key role in maintaining the quiescence of HSCs and the proper emergence and maturation of erythrocytes and platelets. Here we show that low expression of GFI1B in blast cells is associated with an inferior prognosis of AML and MDS patients. Using three different mice models of human AML (Nup98-HoxD13, MLL-AF9 and expression of a mutated K-Ras), we could show that reduced expression of Gfi1b accelerates AML development in mice and the latency is even more shortened when Gfi1b is conditionally deleted. Using a limiting dilution assay of transplantation of different number of Gfi1b-wildtype and Gfi1b-deficient cells, we could show that loss of Gfi1b significantly enhanced stemness of leukemic cells. Since Gfii1b is involved in epigenetic regulation of gene expression, we analyzed effect of loss of Gfi1b on an epigenetic level by analyzing the whole genome using Chip-Seq. We found that loss of Gfi1b leads to genome wide increased level of H3K9 acetylation of genes and hence expression of these genes involved in leukemia development. On a molecular level, we found that loss of Gfi1b not only increases the levels of reactive oxygen species (ROS), but also induces gene expression changes of key AML-pathways such as the p38/ AKT pathways. These results demonstrate that Gfi1b functions as an oncosuppressor in MDS/AML development.