Aberrant levels or structures of RNA isoforms are a hallmark of many cancers, including acute myeloid leukemia (AML), yet its role in AML chemoresistance remains unclear. We conducted a paired analysis of RNA isoform changes in AML patients before therapy and at relapse post-chemotherapy, identifying and identified intragenic DNA methylation at the proximal promoter of the transcription factor RUNX1, which resulted in elevated expression of the long isoform RUNX1C through its alternative distal promoter. The N-terminal region of RUNX1C orchestrated an isoform-specific transcriptional program that promoted chemoresistance, with its direct target BTG2 playing a role in chemotherapy resistance. BTG2 promoted ribosomal RNA deadenylation, resulting in decreased mRNA expression and stability. Deletion of ribosomal RNA's increased cellular quiescence. Moreover, RNA-based targeting of RUNX1C reactivated quiescent leukemia cells and enhanced chemotherapy efficacy. These findings delineate an isoform-specific transcriptional circuit that governs chemotherapy response, providing a potential therapeutic strategy to mitigate AML recurrence.