MYELOID NEOPLASIA Caspase-3 controls AML 1-ETO – driven leukemogenesis via autophagy modulation in a ULK 1-dependent manner

The t(8;21), which leads to the expression of the AML1-ETO (AE) fusion transcription factor, represents the most frequent chromosomal translocation in acute myeloid leukemia (AML), occurring in;4% to 12% of adult and 12% to 30% of pediatric patients. The leukemogenicity of AE has been evaluated in multiple mouse models. AE-expressing transgenic mice do not develop leukemia in the absence of other secondary events, suggesting that cooperating events are required. Some mouse models of AE-driven AML have been developed, such as expression of AE in Cdkn1a-null hematopoietic stem cells (HSCs) or expression of AML1-ETO9a (AE9a), an alternatively spliced variant of AML1-ETO, in wild-type (WT) HSCs, which leads to fully penetrant AML after a prolonged latency. Our recent studies showed that bothmousemodels could accurately predict cooperating events in human t(8;21) AML. Caspase-3, an executioner caspase, plays multiple roles in cell processes, such as apoptosis, embryonic and hematopoietic development, and homeostasis. Caspase-3 has been found to be essential for normal brain development in some genetic mouse strains; however, Caspase-3–deficient mice are viable and fertile in the C57BL/6 strain with no apparent defects in brain pathology. Caspase-3 has been shown to play important roles at multiple steps in embryonic stem cells and HSCs, affecting self-renewal and differentiation. In the hematopoietic system, loss of Caspase-3 leads to accelerated proliferation and impaired differentiation of bonemarrow cells. Caspase-3 is also involved in the negative regulation of B-cell proliferation following antigen stimulation and activated Caspase-3 participates in T-cell proliferation in response to T-cell stimulation. It has been shown that uncleavedCaspase-3 levels are higher in the peripheral blood cells of AML patients compared with hematologically normal individuals, which suggests that the caspase pathway is dysregulated in AML.We and others have shown that AE is a direct substrate of Caspase-3 and the cleavage sites are TMPD188 and LLLD368.Moreover, a truncatedAE protein (DAE), generated by cleavage of AE at Asp188, worked as a dominant-negative protein by interactingwithAEand interferingwith itsoncogenic functions. Together, these data suggest that AE may accumulate in a Caspase-3 compromised background and thereby accelerate leukemogenesis. In this study, we sought to determine the role of Caspase-3 in leukemogenesis in vivo, by expressing AE9a in Caspase-3 knockout mouse model. We found that loss of Caspase-3 impaired self-renewal and