An alternative transcription factor isoform controls AML chemoresistance

Aberrant splicing is a hallmark of many cancers, including Acute Myeloid Leukemia (AML), but its role in post-treatment relapse remains poorly understood. Here, we analyzed the alternative splicing landscape of 19 AML patients during chemotherapy treatment. We found an upregulation of the long isoform of the transcription factor RUNX1 (also known as RUNX1C) in relapsed cohorts, which conferred chemotherapy resistance. Notably, these patients showed elevanted intragenic DNA methylation at the RUNX1 proximal promoter, thereby activating RUNX1C transcript through its alternative distal promoter. Mechanistically the N-terminus region of RUNX1C is required to promote chemoresistance by regulating a distinct RUNX1 transciptional program. Among these target genes, B-cell translocation gene 2 (BTG2) mediates a quiescent-like phenotype by deadenylating ribosomal RNAs to reduce global protein synthesis. Lastly, we harnessed orthogonal RNA-targeting strategies to target RUNX1C isoform, which led to augmented chemotherapy efficacy. Collectively, our finidngs delineate a transcriptional circuity orchestrated by a transcription factor isoform that underpins chemotherapy responsiveness and a potential therapeutic strategy to mitigate disease recurrence. Overall design: To investigate the functions of unique RUNX1 isoforms, MOLM-13 cells were infected with lentiviral constructs expressing each isoform individually. Three days after transduction, cells were collected and RNA isolated and polyA mRNAs were enriched and used to generate cDNA libraries. Barcoded libraries were then sequenced on a NovaSeq. Gene expression analysis was then performed on cells expressing RUNX1 Isoforms, compared to an empty vector control.