Rictor Plays a Pivotal Role in Maintaining Quiescence as well as Stemness of Leukemia Stem Cells in MLL-Driven Leukemia

Little is known about the roles of Rictor/mTORC2 in the leukemogenesis of AML. Here, we demonstrated that Rictor is essential for the maintenance of MLL-driven leukemia by preventing LSCs from exhaustion. Rictor depletion led to a reactive activation of mTORC1 signaling by facilitating the assembly of mTORC1. Hyperactivated mTORC1 signaling in turn drove LSCs into cycling, compromised the quiescence of LSCs and eventually exhausted their capacity to generate leukemia. At the same time, loss of Rictor had led to a reactive activation of FoxO3a in leukemia cells, which acts as negative feedback to restrain greater over-reactivation of mTORC1 activity and paradoxically protects leukemia cells from exhaustion. Simultaneous depletion of Rictor and FoxO3a enabled rapid exhaustion of MLL LSCs and a quick eradication of MLL leukemia. As such, our present findings highlighted a pivotal regulatory axis of Rictor-FoxO3a in maintaining quiescence and the stemness of LSCs. To understand the critical molecular events caused by Rictor loss in MLL-AF9-driven leukemia,the K+G– mice BM cells were sorted from the 1st BMT of RictorΔ/Δ(MA9_R1,MA9_R2,MA9_R3) or control(MA9_C1,MA9_C2,MA9_C3), and subjected to microarray analysis on Affymetrix microarrays.Furthermore, the MLL-NRIP3-driven mice model was chosen for further examination.The K+G– mice BM cells were sorted from the 1st BMT of RictorΔ/Δ(MN3_R1,MN3_R2,MN3_R3) or control(MN3_C1,MN3_C2,MN3_C3), and subjected to microarray analysis on Affymetrix microarrays.