MECOM promotes leukemia progression and inhibits mast cell differentiation through functional competition with GATA2.

MECOM is a transcription factor critical for the maintenance of hematopoietic stem cells (HSCs) and the pathogenesis of myeloid leukemia. Germline mutations clustered in the C-terminal zinc finger domain (ZFD) of MECOM are known to cause MECOM-associated syndromes, involving bone marrow failure and skeletal anomalies. However, the molecular consequences of these mutations and the precise downstream mechanisms of MECOM remain elusive. Here, we demonstrate that the C-terminal ZFD serves as the dominant DNA-binding module of MECOM, and that disease-associated mutations abrogate its DNA-binding capacity. Mechanistically, we reveal that MECOM functionally antagonizes GATA2 via C-terminal ZFD-mediated DNA binding and recruitment of the corepressor CtBP. This repression promotes myeloid leukemogenesis while suppressing mast cell differentiation. Furthermore, we generated a knockin mouse model harboring a C-terminal ZFD mutation, which successfully recapitulated the clinical phenotypes of MECOM-associated syndromes, including reduction of HSCs and B cells. Collectively, our findings define C-terminal ZFD mutations as loss-of-function mutations with impaired DNA binding, uncover the MECOM-GATA2 axis as a key regulatory pathway, and provide a valuable mouse model for understanding MECOM-associated syndromes.