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

Abstract

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.

Dose-dependent role of Gfi1 in murine hematopoietic stem cell self-renewal and differentiation

“…To this end, we made use of the previously described GFI1 -KD mice which express human GFI1 at around 10-15 % of normal GFI1 levels (10) and Gfi1 -KO mice with a complete loss of Gfi1 expression (8). As a control we used GFI1-36S mice, a mouse strain containing the human GFI1 cDNA sequence at the position of the murine Gfi1 locus, as this is the mouse strain from which GFI1 -KD mice were derived.…”

“…As a control we used GFI1-36S mice, a mouse strain containing the human GFI1 cDNA sequence at the position of the murine Gfi1 locus, as this is the mouse strain from which GFI1 -KD mice were derived. We have shown in the past that GFI1 -36S mice are functionally equivalent to murine Gfi1-WT mice (10, 13, 17, 18). In addition, they do not differ in their number of hematopoietic stem and progenitor cells (Supplementary Figure 1 A and B).…”

“…Our data are in line with other reports highlighting the role of Gfi1 in lineage choice, similar to that of other transcription factors such as IRF8 and PU.1 (21, 22). Our arising hypotheses are that a) knockdown and loss of GFI1 might regulate the choice of symmetric and asymmetric division of HSCs which could explain the leukemia-propagating function of reduced GFI1 levels in CML and AML (10) or b) GFI1 -KD or Gfi1 -KO HSCs exhaust their ability to produce mature cells after a certain time point. As Gfi1 -KO cells have a normal life span in a non-competitive setting in mice if they are kept under SPF conditions (23), further experiments are needed to study the dose-dependent role of Gfi1 in HSC function.…”

“…GFI1 -36S, Gfi1 -KO and GFI1 -KD mice have previously been described (8, 10, 13). Mice were housed in specific pathogen-free conditions at the animal facility of University Hospital Essen, Germany.…”

“…We were now interested whether low levels and loss of Gfi1 indeed negatively affect the stem cell and differentiation capacity of HSCs and how the seemingly contradictory findings between reduced self-renewal capacity and the dose-dependent role of Gfi1 function in myeloid pathogenesis could be reconciled. For the analysis we made use of Gfi1 -knockout (KO) mice, a mouse strain with a complete loss of Gfi1, and GFI1 -knockdown (KD) mice, a mouse strain in which we cloned the human GFI1 sequence into the murine Gfi1 gene locus together with a Neo cassette in the opposite direction of transcription, leading to GFI1 expression of only 10-15% of wild-type levels (10). We show here that GFI1 -KD and Gfi1 -KO mice contain a higher number of hematopoietic progenitors (LSK cells, Lin − Sca1 + c-Kit + ), but HSC (Lin − Sca1 + c-Kit + CD150 + CD48 − ) numbers are strongly reduced.…”