Abstract 3334: KLF4 promotes self-renewal by repressing DYRK2-mediated degradation of c-Myc in leukemic stem cells: development of targeted therapy
Authors: Park Chun Shik , Shen Ye , Suppipat Koramit , Tomolonis Julie , Puppi Monica , Mistretta Toni-Ann , Ma Leyuan , Green Michael , Lacorazza Daniel 
Published: July 2016

Abstract
Chronic myeloid leukemia (CML) is the first blood cancer known to originate from a single hematopoietic stem cell (HSC) by expression of BCR-ABL, a product of the chromosomal translocation t(9;22), that slowly progress to a lethal fast-growing leukemia caused by malignant reprogramming of progenitor cells (blast crisis). Although CML can be successfully managed with targeted therapy by suppressing BCR-ABL kinase activity with tyrosine kinase inhibitors (TKI), patients remain in remission as long as they adhere to a lifelong treatment. The leukemic stem cell (LSC) population emerges as a key ‘CML reservoir’ that escapes TKI therapy by developing BCR-ABL-independent mechanisms of self-renewal and survival. LSC still remains an elusive target because of our poor understanding of specific self-renewal mechanisms and inability to selectively eliminate LSC without damaging normal hematopoiesis. Thus, there is a need for alternative drugs for relapse patients to prevent reactivation of BCR-ABL-positive LSC after stopping chemotherapy or emergence of chemoresistance and as frontline therapy to achieve treatment-free remission. We found that somatic deletion of the transcriptional factor Krüppel-like factor 4 (KLF4) in BCR-ABL(p210)-induced CML severely impaired disease maintenance. This inability to sustain CML in the absence of KLF4 was caused by attrition of LSCs in bone marrow and the spleen and impaired ability of LSCs to recapitulate leukemia in secondary recipients. This data suggest that KLF4 promotes self-renewal of LSCs whereas serial transplantation indicates that KLF4 restricts stress self-renewal of normal HSCs and thus inhibition of KLF4 function would impair LSC self-renewal without altering blood production. Analyses of global gene expression in purified LSCs and genome-wide binding of KLF4 in a murine CML cell line revealed that KLF4 represses the gene encoding for the dual-specificity tyrosine-(Y)-phosphorylation regulated kinase 2 (DYRK2). Immunoblots revealed elevated levels of DYRK2 protein in KLF4-deficient LSCs purified from the bone marrow of CML mice. Because phosphorylation of c-Myc and p53 by DYRK2 induces proteosomal degradation and cell death, respectively, we found that DYRK2 upregulation in KLF4-deficient LSCs was associated with a reduction of c-Myc protein and increased cleavage of PARP. As a proof-of-principle of the therapeutic potential of this finding, we explored the efficacy of vitamin K3 to eradicate LSCs by inhibiting the ubiquitin E3 ligase SIAH2 in charge of DYRK2 degradation. Vitamin K3 efficiently reduced cell viability in a panel of human-derived CML cell lines by inducing Dyrk2 expression and apoptosis. The identification of Dyrk2 as a critical mediator of LSC downfall is an innovative paradigm poised to support the development of LSC-specific therapy to induce treatment-free remission in CML patients.
Citation Format: Chun Shik Park, Ye Shen, Koramit Suppipat, Julie Tomolonis, Monica Puppi, Toni-Ann Mistretta, Leyuan Ma, Michael Green, Daniel Lacorazza. KLF4 promotes self-renewal by repressing DYRK2-mediated degradation of c-Myc in leukemic stem cells: development of targeted therapy. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3334.