Krüppel-like Factor 4 Supports the Expansion of Leukemia Stem Cells in MLL-AF9-driven Acute Myeloid Leukemia

Abstract

Acute myeloid leukemia (AML) is an aggressive malignancy of the bone marrow with five-year overall survival of less than 10% in patients over the age of 65. Limited progress has been made in the patient outcome because of the inability to selectively eradicate the leukemic stem cells (LSC) driving the refractory and relapsed disease. Herein, we investigated the role of the reprogramming factor KLF4 in AML because of its critical role in the self-renewal and stemness of embryonic and cancer stem cells. Using a conditional Cre-lox Klf4 deletion system and the MLL-AF9 retroviral mouse model, we demonstrated that loss-of-KLF4 does not significantly affect the induction of leukemia but markedly decreased the frequency of LSCs evaluated in limiting-dose transplantation studies. Loss of KLF4 in leukemic granulocyte-macrophage progenitors (L-GMP), a population enriched for AML LSCs, showed lessened clonogenicity and percentage in the G2/M phase of the cell cycle. RNAseq analysis of purified L-GMPs revealed decreased expression of stemness genes and MLL-target genes and upregulation of the RNA sensing helicase DDX58. However, silencing of DDX58 in KLF4 knockout leukemia indicated that DDX58 is not mediating this phenotype. CRISPR/Cas9 deletion of KLF4 in MOLM13 cell line and AML patient-derived xenograft cells showed impaired expansion in vitro and in vivo associated with a defective G2/M checkpoint. Collectively, our data suggest a mechanism in which KLF4 promotes leukemia progression by establishing a gene expression profile in AML LSCs supporting cell division and stemness.

Role of the bone marrow vascular niche in chemotherapy for MLL-AF9-induced acute myeloid leukemia

“…In line with our earlier observations, we found that the expression levels of numerous mRNAs associated with the development of leukemia, including Dusp6 , 27 Klf4 , 28 and Plxnb2 , 29 were significantly elevated in ECs and resting leukemia cells after chemotherapy (Fig. 4D).…”

KLF4-mediated upregulation of the NKG2D ligand MICA in acute myeloid leukemia: a novel therapeutic target identified by enChIP

“…These experiments were, however, performed in immunodeficient mouse models, and a putative innate immune response to NKG2D-L positive AML was not addressed. KLF4 is one of the Yamanaka factors able to induce pluripotent stem cells and was recently shown to promote leukemia stem cell division and stemness [ 35 ]. This finding may seem paradoxical but makes sense considering that the NKG2D-L expression is an early cellular response to malignant transformation in order to alert the innate immune system to dangerous cells – which is characterized by high KLF4 expression.…”