Loss of Krüppel-Like Factor 4 (KLF4) Impairs the Self-Renewal of Leukemic Stem Cells

Abstract 911

The identification of pathways that differentially regulate the self-renewal in normal hematopoietic stem cells (HSC) and leukemic stem cells (LSC) is critical for effective treatment of relapsed leukemia without affecting normal hematopoiesis. Krüppel-like factor 4 (KLF4) is a bi-functional transcription factor that can either activate or repress transcription and thus function as an oncogene or a tumor suppressor depending on the cellular context. We have previously shown that loss of KLF4 leads to increased self-renewal of HSC in serial bone marrow transplantation. In this work, we investigated whether KLF4 also regulates self-renewal in LSCs using a mouse model of somatic deletion of KLF4 in hematopoietic cells (Klf4^fl/fl Vav-iCre⁺) and the BCR-ABL-induced chronic myeloid leukemia (CML) model. Mice transplanted with wild type bone marrow (BM) cells transduced with retrovirus carrying BCR-ABL (p210) (n=18) showed an expansion of myeloid cells (GFP⁺ Gr1⁺) with a median survival of 19 days. In contrast, mice transplanted with KLF4-deficient BM cells transduced with BCR-ABL retrovirus (n=12) exhibited prolonged survival with a median survival of 27 days (p<0.0011). Progression of leukemia was monitored in peripheral blood, BM and the spleen by flow cytometry. Mice transplanted with KLF4-deficient cells showed expansion of myeloid leukemic cells (GFP⁺ Gr1⁺) in the first two weeks after BM transplant, which was followed by a progressive loss of myeloid cells and an expansion of B cells (GFP⁺ B220⁺). In control group, 90% of leukemic mice succumbed from CML whereas more than 50% of KLF4-deficient leukemic mice developed mixed CML and B-ALL leukemia. These results suggest that loss of KLF4 impairs the maintenance of BCR-ABL-induced CML, while allowing expansion of BCR-ABL positive B cells (GFP⁺ B220⁺). Since KLF4 deletion prevented continuous expansion of myeloid leukemic cells (GFP⁺ Gr1⁺), we postulated that KLF4 may be critical to LSC maintenance. Thus, we analyzed the frequency of LSCs (GFP⁺ Lin^–c-Kit⁺ Sca-1⁺and GFP⁺ Lin^– c-Kit⁺ Sca-1⁺Flt3^–) in BM and the spleen. We found that LSCs were significantly reduced in recipients of BCR-ABL-transduced KLF4-deficient BM cells 18 days after transplantation (n=6, p <0.001). These studies demonstrate that KLF4 has different roles in the maintainenance of LSCs and normal HSCs and that inactivation of KLF4 provides a therapeutic strategy for eradicating LSCs without damaging normal HSC.