RUNX1 Is an Oncogenic Transcription Factor that Regulates MYB and MYC Enhancer Activity in T-ALL

Abstract

RUNX1, a transcription factor required for hematopoiesis and lymphocyte differentiation, is one of the most commonly targeted genes in hematopoietic malignancies. Mutations in the RUNX1 gene are associated with a poor prognosis in a subset of T cell acute lymphoblastic leukemia (T-ALL) and RUNX1 has been proposed as a tumor suppressor in TLX1/3-transformed human T-ALL. Recent ChIP-seq studies in human T-ALL cell lines demonstrated that a large portion of TAL1- and NOTCH1- bound regions contain RUNX binding sites in promoter or enhancer regions, suggesting oncogenic roles for RUNX1 in T-ALL. To interrogate RUNX1 functions in leukemogenesis, we depleted RUNX1 in a T-ALL mouse model and in human T-ALL cell lines. We found that RUNX1 is required for the maintenance of mouse T-ALL growth in vivo and the survival of human T-ALL cell lines in vitro. In addition, inhibition of the RUNX1 activity with a small molecule inhibitor impairs the growth of human T-ALL cell lines and primary patient samples. RUNX1 depletion reduces the expression of a subset of TAL1- and NOTCH1- regulated genes including the MYB and MYC oncogenes, respectively. We demonstrate that RUNX1 regulates transcription factor binding and acetylation of H3K27 at the Myb and Myc enhancer loci. These studies provide genetic and pharmacological evidences that RUNX1 supports T-ALL cell survival and suggest RUNX1 inhibitor as a therapeutic strategy in T-ALL treatment.