A Somatic Mutation in Moesin Drives Progression into Acute Myeloid Leukemia

Acute myeloid leukemia (AML) arises when leukemia initiating cells, defined by an primary genetic lesion, acquire subsequent molecular changes whose cumulative effects bypass tumor suppression. The changes that underlie AML pathogenesis not only provide insights into the biology of transformation, but also reveal novel therapeutic opportunities. However, backtracking these events in transformed human AML samples is challenging, if at all possible. Here, we approached this question using a murine in vivo model with an MLL-ENL fusion protein as a primary molecular event. Upon clonal transformation, we identified and extensively verified a recurrent codon-changing mutation (Arg295Cys) in the ERM protein Moesin that dramatically accelerated leukemogenesis. Human cancer-associated Moesin mutations at the conserved Arginine 295 residue similarly enhanced MLL-ENL driven leukemogenesis. Mechanistically, the mutation interrupted the stability of Moesin and conferred a neomorphic activity to the protein, which converged on enhanced ERK activity. Thereby, our studies demonstrate a critical role of ERM proteins in AML, with implications also for human cancer.