Myc-Miz1 signaling promotes self-renewal of leukemia stem cells by repressing Cebp alpha and Cebp delta

摘要

c-Myc (Myc hereafter) is found to be deregulated and/or amplified in most acute myeloid leukemias (AMLs). Almost all AML cells are dependent upon Myc for their proliferation and survival. Thus, Myc has been proposed as a critical anti-AML target. Myc has Max mediated transactivational and Myc-interacting zinc finger protein 1 (Miz1)-mediated transre pressional activities. The role of Myc-Max-mediated transactivation in the pathogenesis of AML has been well studied; however, the role of Myc-Miz1-mediated transrepression in AML is still somewhat obscure. Myc protein harboring a V394D mutation (Myc(V394D)) is a mutant form of Myc that lacks transrepressional activity due to a defect in its ability to interact with Mizt We found that, compared with Myc, the oncogenic function of Myc(V394D) is significantly impaired. The AML/myeloproliferative disorder that develops in mice receiving Myc(V394D)-transduced hematopoietic stem/progenitor cells (HSPCs) is significantly delayed compared with mice receiving Myc-transduced HSPCs. Using a murine MLL-AF9 AML model, we found that AML cells expressing Myc(V394D) (intrinsic Myc deleted) are partially differentiated and show reductions in both colony-forming ability in vitro and leukemogenic capacity in vivo. The reduced frequency of leukemia stem cells (LSCs) among Myc(V394D)-AML cells and their reduced leukemogenic capacity during serial transplantation suggest that Myc-Miz1 interaction is required for the self-renewal of LSCs. In addition, we found that Myc(V394D)-AML cells are more sensitive to chemotherapy than are Myc AML cells. Mechanistically, we found that Myc represses Miz1 mediated expression of CCAAT/enhancer-binding protein alpha (Cebp alpha) and CebpZ delta, thus playing an important role in the pathogenesis of AML by maintaining the undifferentiated state and self renewal capacity of LSCs.