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

Proc Natl Acad Sci U S A. 2021 Feb 9;118(6):e1922864118. doi: 10.1073/pnas.1922864118.

Abstract

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 E2A-PBX1-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.

Keywords: E2A-PBX1 leukemia; EBF1; MED1; Mediator; RUNX1.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • B-Lymphocytes / pathology
  • Carcinogenesis / genetics*
  • Carcinogenesis / pathology
  • Cell Cycle Checkpoints
  • Cell Proliferation / genetics
  • Cell Survival
  • Core Binding Factor Alpha 2 Subunit / metabolism
  • DNA, Neoplasm / metabolism
  • Down-Regulation / genetics
  • Gene Expression Regulation, Leukemic
  • Genes, Neoplasm
  • Homeodomain Proteins / metabolism*
  • Humans
  • Leukemia / genetics*
  • Leukemia / pathology*
  • Mediator Complex Subunit 1 / metabolism*
  • Oncogene Proteins, Fusion / metabolism*
  • Protein Binding
  • Protein Stability
  • Transcription, Genetic*

Substances

  • Core Binding Factor Alpha 2 Subunit
  • DNA, Neoplasm
  • Homeodomain Proteins
  • Mediator Complex Subunit 1
  • Oncogene Proteins, Fusion
  • RUNX1 protein, human
  • E2A-Pbx1 fusion protein