Musashi-2 regulates normal hematopoiesis and promotes aggressive myeloid leukemia

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Abstract
The authors uncover a new role for the RNA-binding protein Msi2 in the regulation of hematopoietic stem cell homeostasis and leukemogenesis. Msi2 is required for the maintenance of the balance between progenitor renewal and differentiation, and its overexpression cooperates with oncogenic events to induce aggressive leukemia. Msi2 expression is also elevated in human myeloid leukemias and may be a new prognostic marker and therapeutic target in acute myeloid leukemia. RNA-binding proteins of the Musashi (Msi) family are expressed in stem cell compartments and in aggressive tumors, but they have not yet been widely explored in the blood. Here we demonstrate that Msi2 is the predominant form expressed in hematopoietic stem cells (HSCs), and its knockdown leads to reduced engraftment and depletion of HSCs in vivo. Overexpression of human MSI2 in a mouse model increases HSC cell cycle progression and cooperates with the chronic myeloid leukemia–associated BCR-ABL1 oncoprotein to induce an aggressive leukemia. MSI2 is overexpressed in human myeloid leukemia cell lines, and its depletion leads to decreased proliferation and increased apoptosis. Expression levels in human myeloid leukemia directly correlate with decreased survival in patients with the disease, thereby defining MSI2 expression as a new prognostic marker and as a new target for therapy in acute myeloid leukemia (AML).