Mediator subunit MED1 is required for E2A-PBX1-mediated oncogenic transcription and leukemic cell growth

Yu Ling Lee, Keiichi Ito, Wen Chieh Pi, I. Hsuan Lin, Chi Shuen Chu, Sohail Malik, I. Hsin Cheng, Wei Yi Chen*, Robert G. Roeder

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

15 Scopus citations


The chimeric transcription factor E2A-PBX1, containing the N-terminal activation domains of E2A fused to the C-terminal DNA-binding domain of PBX1, results in 5% of pediatric acute lymphoblastic leukemias (ALL). We recently have reported a mechanism for RUNX1-dependent recruitment of E2A-PBX1 to chromatin in pre-B leukemic cells; but the subsequent E2A-PBX1 functions through various coactivators and the general transcriptional machinery remain unclear. The Mediator complex plays a critical role in cell-specific gene activation by serving as a key coactivator for gene-specific transcription factors that facilitates their function through the RNA polymerase II transcriptional machinery, but whether Mediator contributes to aberrant expression of E2A-PBX1 target genes remains largely unexplored. Here we show that Mediator interacts directly with E2A-PBX1 through an interaction of the MED1 subunit with an E2A activation domain. Results of MED1 depletion by CRISPR/Cas9 further indicate that MED1 is specifically required for E2APBX1-dependent gene activation and leukemic cell growth. Integrated transcriptome and cistrome analyses identify pre-B cell receptor and cell cycle regulatory genes as direct cotargets of MED1 and E2A-PBX1. Notably, complementary biochemical analyses also demonstrate that recruitment of E2A-PBX1 to a target DNA template involves a direct interaction with DNA-bound RUNX1 that can be further stabilized by EBF1. These findings suggest that E2A-PBX1 interactions with RUNX1 and MED1/Mediator are of functional importance for both gene-specific transcriptional activation and maintenance of E2A-PBX1-driven leukemia. The MED1 dependency for E2A-PBX1-mediated gene activation and leukemogenesis may provide a potential therapeutic opportunity by targeting MED1 in E2A-PBX1+ pre-B leukemia.

Original languageEnglish
Article numbere1922864118
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number6
StatePublished - 9 Feb 2021


  • E2A-PBX1 leukemia
  • EBF1
  • MED1
  • Mediator
  • RUNX1


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