Transcriptomic changes including p53 dysregulation prime DNMT3A mutant cells for transformation

DNMT3A mutations are prevalent in haematologic malignancies. In our mouse model the murine homologue (R878H) of the human 'hotspot' R882H mutation is introduced into the mouse Dnmt3a locus. This results in globally reduced DNA methylation in all tissues. Mice with heterozygous R878H DNMT3A mutations develop γ-radiation induced thymic lymphoma more rapidly than control mice, suggesting a vulnerability to stress stimuli in Dnmt3a^R878H/+ cells. In competitive transplantations, Dnmt3a^R878H/+ Lin^-Sca-1⁺Kit⁺ (LSK) haematopoietic stem/progenitor cells (HSPCs) have a competitive advantage over WT HSPCs, indicating a self-renewal phenotype at the expense of differentiation. RNA sequencing of Dnmt3a^R878H/+ LSKs exposed to low dose γ-radiation shows downregulation of the p53 pathway compared to γ-irradiated WT LSKs. Accordingly, reduced PUMA expression is observed by flow cytometry in the bone marrow of γ-irradiated Dnmt3a^R878H/+ mice due to impaired p53 signalling. These findings provide new insights into how DNMT3A mutations cause subtle changes in the transcriptome of LSK cells which contribute to their increased self-renewal and propensity for malignant transformation.