RUNX1 Upregulation by Cytotoxic Drugs Promotes Apoptosis.

Mutations in the gene have been associated with chemotherapy resistance and poor prognosis in patients with acute myeloid leukemia (AML), T-cell acute lymphoblastic leukemia, and myelodysplastic syndromes. However, the underlying mechanisms connecting RUNX1 to the success of therapy remain elusive. Here we explore the hypothesis that RUNX1 is directly involved in the response of hematopoietic cells to cytotoxic agents. RUNX1 was upregulated posttranscriptionally by cytotoxic agents in C57BL/6 mice and hematopoietic cell lines. Upregulation was also seen in primary human AML cells after treatment with cytarabine Upon overexpression, RUNX1 restricted proliferation, promoted apoptosis, and augmented the DNA damage response. This unknown activity of RUNX1 required an intact runt homology domain (RHD), a domain where most leukemia-associated point mutations cluster. Consistent with this, two RHD-defective RUNX1 proteins lacked any antiproliferative or apoptotic activity, and RHD-defective (K83N, N109D) mutant RUNX1 conferred resistance to ionizing radiation when overexpressed in Ba/F3 cells under certain conditions. Our experiments reveal a novel function of RUNX1 and offer an explanation for the link between mutations and chemotherapy and radiation resistance. Moreover, these data suggest that pharmacologic modulation of RUNX1 might be an attractive new approach to treat hematologic malignancies. .