A novel RUNX1 mutation which precludes its methylation has been found in a familial AML pedigree.
Loss of RUNX1 methylation in HSCs confers resistance to apoptosis induced by ER stress and radiation, a hallmark of a pre-leukemic clone.
RUNX1 is among the most frequently mutated genes in human leukemia, and the loss or dominant-negative suppression of RUNX1 function is found in myelodysplastic syndrome and acute myeloid leukemia (AML). However, how post-translational modifications (PTMs) of RUNX1 affect its in vivo function and whether PTM dysregulation of RUNX1 can cause leukemia are largely unknown. We performed targeted deep sequencing on a family with 3 occurrences of AML and identified a novel RUNX1 mutation R237K. The mutated R237 residue is a methylation site by PRMT1 and loss of methylation has been reported to impair transcriptional activity of RUNX1 in vitro. To explore biological significance of RUNX1 methylation in vivo, we utilized RUNX1 R233K/R237K double mutant mice, in which 2 arginine-to-lysine mutations precluded RUNX1 methylation. Genetic ablation of RUNX1 methylation led to loss of quiescence and expansion of hematopoietic stem cells (HSCs), and changed the genomic and epigenomic signature of phenotypic HSCs to a poised progenitor state. Further, loss of RUNX1 R233/R237 methylation suppressed endoplasmic reticulum stress-induced unfolded protein response genes including Atf4, Ddit3, and Gadd34, radiation-induced p53 downstream genes, Bbc3, Pmaip1, and Cdkn1a, and subsequent apoptosis in HSCs. Mechanistically, ATF4 was identified as a direct transcriptional target of RUNX1. Collectively, defects in RUNX1 methylation in HSCs confer resistance to apoptosis and survival advantage under stress conditions, a hallmark of a pre-leukemic clone which may predispose affected individuals to leukemia. Our study will lead to a better understanding of how dysregulation of PTMs can contribute to leukemogenesis.