Super-Enhancer-Driven IGF2BP2 and IGF2BP3 Promote DDX21 Expression in Acute Myeloid Leukemia

Background : Acute myeloid leukemia (AML) is a hematological malignancy with a median overall survival (OS) of 8.5 months and a 5-year OS rate of 24.0%. Considering that relapse and drug resistance are major obstacles affecting the survival of AML patients, it is urgent to investigate the deeper pathogenesis of AML. Epigenetic modifications are extensively involved in the leukemogenesis of AML, especially N6-methyladenosine (m ⁶A) RNA methylation and super-enhancers (SEs). However, the relationship between m ⁶A and SEs in AML has not been elucidated.

Methods : Chromatin immunoprecipitation (ChIP) sequencing data from Gene Expression Omnibus (GEO) cohort were analyzed to search SE-related genes. The mechanisms of m ⁶A-binding proteins IGF2BP2 and IGF2BP3 on DDX21 were explored via methylated RNA immunoprecipitation (MeRIP), RNA immunoprecipitation (RIP) and luciferase reporter assays. The potential roles of DDX21 in AML were verified through functional assays in vitro and in vivo.

Results: Two SE-associated genes, IGF2BP2 and IGF2BP3, were identified in AML. There were high enrichment of H3K27ac, H3K4me1 and BRD4 in IGF2BP2 and IGF2BP3. BRD4 inhibitor JQ1 or BRD4 knockdown could lead to the suppression of IGF2BP2/3 expression, indicating the activation by SE machinery on the transcription of IGF2BP2/3. As m ⁶A-binding proteins, IGF2BP2 and IGF2BP3 enhanced the stability of DDX21 mRNA in an m ⁶A-dependent manner. DDX21 was highly expressed in AML patients, and elevated DDX21 expression suggested a poor survival. Functionally, DDX21 deficiency inhibited proliferation, facilitated apoptosis and arrested cell cycle of AML cells in vitro . I n vivo, knockdown of DDX21 substantially reduced tumor load and prolonged survival of recipient mice.

Conclusions: Dysregulation of SE-IGF2BP2/IGF2BP3-DDX21 axis promotes the progression of AML, which paves the way to develop more effective therapeutic strategies.