Judith M. Hönes

GFI1 as a novel prognostic and therapeutic factor for AML/MDS

Genetic and epigenetic aberrations contribute to the initiation and progression of acute myeloid leukemia (AML). GFI1, a zinc-finger transcriptional repressor, exerts its function by recruiting histone deacetylases to target genes. We present data that low expression of GFI1 is associated with an inferior prognosis of AML patients. To elucidate the mechanism behind this, we generated a humanized mouse strain with reduced GFI1 expression (GFI1-KD). Here we show that AML development induced by onco-fusion proteins such as MLL-AF9 or NUP98-HOXD13 is accelerated in mice with low human GFI1 expression. Leukemic cells from animals that express low levels of GFI1 show increased H3K9 acetylation compared to leukemic cells from mice with normal human GFI1 expression, resulting in the upregulation of genes involved in leukemogenesis. We investigated a new epigenetic therapy approach for this subgroup of AML patients. We could show that AML blasts from GFI1-KD mice and from AML patients with low GFI1 levels were more sensitive to treatment with histone acetyltransferase inhibitors than cells with normal GFI1 expression levels. We suggest therefore that GFI1 has a dose-dependent role in AML progression and development. GFI1 levels are involved in epigenetic regulation, which could open new therapeutic approaches for AML patients.

Acute myeloid leukemia cells polarize macrophages towards a leukemia supporting state in a Growth factor independence 1 dependent manner

The growth of malignant cells is not only driven by cell-intrinsic factors, but also by the surrounding stroma. Monocytes/Macrophages play an important role in the onset and progression of solid cancers. However, little is known about their role in the development of acute myeloid leukemia, a malignant disease characterized by an aberrant development of the myeloid compartment of the hematopoietic system. It is also unclear which factors are responsible for changing the status of macrophage polarization, thus supporting the growth of malignant cells instead of inhibiting it. We report herein that acute myeloid leukemia leads to the invasion of acute myeloid leukemia-associated macrophages into the bone marrow and spleen of leukemic patients and mice. In different leukemic mouse models, these macrophages support the in vitro expansion of acute myeloid leukemia cell lines better than macrophages from non-leukemic mice. The grade of macrophage infiltration correlates in vivo with the survival of the mice. We found that the transcriptional repressor Growth factor independence 1 is crucial in the process of macrophage polarization, since its absence impedes macrophage polarization towards a leukemia supporting state and favors an anti-tumor state both in vitro and in vivo. These results not only suggest that acute myeloid leukemia-associated macrophages play an important role in the progression of acute myeloid leukemia, but also implicate Growth factor independence 1 as a pivotal factor in macrophage polarization. These data may provide new insights and opportunities for novel therapies for acute myeloid leukemia.

Enforced GFI1 expression impedes human and murine leukemic cell growth

The differentiation of haematopoietic cells is regulated by a plethora of so-called transcription factors (TFs). Mutations in genes encoding TFs or graded reduction in their expression levels can induce the development of various malignant diseases such as acute myeloid leukaemia (AML). Growth Factor Independence 1 (GFI1) is a transcriptional repressor with key roles in haematopoiesis, including regulating self-renewal of haematopoietic stem cells (HSCs) as well as myeloid and lymphoid differentiation. Analysis of AML patients and different AML mouse models with reduced GFI1 gene expression levels revealed a direct link between low GFI1 protein level and accelerated AML development and inferior prognosis. Here, we report that upregulated expression of GFI1 in several widely used leukemic cell lines inhibits their growth and decreases the ability to generate colonies in vitro. Similarly, elevated expression of GFI1 impedes the in vitro expansion of murine pre-leukemic cells. Using a humanized AML model, we demonstrate that upregulation of GFI1 expression leads to myeloid differentiation morphologically and immunophenotypically, increased level of apoptosis and reduction in number of cKit+ cells. These results suggest that increasing GFI1 level in leukemic cells with low GFI1 expression level could be a therapeutic approach.

Gfi1b: a key player in the genesis and maintenance of acute myeloid leukemia and myelodysplastic syndrome

Differentiation of hematopoietic stem cells is regulated by a concert of different transcription factors. Disturbed transcription factor function can be the basis of (pre)malignancies such as myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML). Growth factor independence 1b (Gfi1b) is a repressing transcription factor regulating quiescence of hematopoietic stem cells and differentiation of erythrocytes and platelets. Here, we show that low expression of Gfi1b in blast cells is associated with an inferior prognosis of MDS and AML patients. Using different models of human MDS or AML, we demonstrate that AML development was accelerated with heterozygous loss of Gfi1b, and latency was further decreased when Gfi1b was conditionally deleted. Loss of Gfi1b significantly increased the number of leukemic stem cells with upregulation of genes involved in leukemia development. On a molecular level, we found that loss of Gfi1b led to epigenetic changes, increased levels of reactive oxygen species, as well as alteration in the p38/Akt/FoXO pathways. These results demonstrate that Gfi1b functions as an oncosuppressor in MDS and AML development.

GFI1 is required for RUNX1/ETO positive acute myeloid leukemia

Author(s): Marneth, Anna E; Botezatu, Lacramioara; Hones, Judith M; Israel, Jimmy CL; Schutte, Judith; Vassen, Lothar; Lams, Robert F; Bergevoet, Saskia M; Groothuis, Laura; Mandoli, Amit; Martens, Joost HA; Huls, Gerwin; Jansen, Joop H; Duhrsen, Ulrich; Berg, Tobias; Moroy, Tarik; Wichmann, Christian; Lo, Mia-Chia; Zhang, Dong-Er; van der Reijden, Bert A; Khandanpour, Cyrus