C-terminal Mutations in RUNX1 Induce Differentiation Block and Alter Transcription through Changes in Enhancer-Promoter Interactions [RNA-Seq]

The hematopoietic master regulator RUNX1 is frequently mutated in myeloid and lymphoid malignancies. Analyses of RUNX1 mutations across hematopoietic tissues revealed frequent mutations outside of the N-terminal DNA binding domain. The vast majority of these C-terminal mutations were found to be nonsense and frameshifts resulting in truncated protein products predicted to escape nonsense mediated decay pathways. We modeled this class of truncation mutation using the pathogenic RUNX1 R320* mutation found in both germline and sporadic hematological disease. Homozygous knock-in of RUNX1 R320* in K562 leukemia cells resulted in a megakaryocytic differentiation block and DNA damage sensitivity phenotypes. Gene expression analysis demonstrated that RUNX1 R320* dysregulated unique gene sets when compared to RUNX1 knockdown in addition to shared genes related to megakaryocyte and platelet function. DNA binding across the genome was examined between RUNX1 wild-type and RUNX1 R320* through ChIP-seq, revealing that RUNX1 R320* differential binding was most enriched at enhancer regions. To detect RUNX1 R320* dysregulated enhancer-promoter (E-P) connections we performed GRID-seq and uncovered extensive remodeling of E-P interactions genome-wide in RUNX1 R320* cells. Furthermore, we uncovered a novel role for FOXK2 at RUNX1 regulated enhancers. Analysis of the well-studied MYC enhancer region demonstrated cooperation between RUNX1 R320* and FOXK2 at hematopoietic MYC enhancers NDME and BENC resulting in the significant upregulation of the MYC oncogene. In conclusion, the truncation of RUNX1 results in impaired megakaryocytic differentiation, unique transcriptional alterations, and remodeling of enhancer-promoter connections in cooperation with FOXK2, together contributing to leukemogenesis.