RUNX1 Is a Key Target in t(4;11) Leukemias that Contributes to Gene Activation through an AF4-MLL Complex Interaction

Summary The Mixed Lineage Leukemia (MLL) protein is an important epigenetic regulator required for the maintenance of gene activation during development. MLL chromosomal translocations produce novel fusion proteins that cause aggressive leukemias in humans. Individual MLL fusion proteins have distinct leukemic phenotypes even when expressed in the same cell type, but how this distinction is delineated on a molecular level is poorly understood. Here, we highlight a unique molecular mechanism whereby the RUNX1 gene is directly activated by MLL-AF4 and the RUNX1 protein interacts with the product of the reciprocal AF4-MLL translocation. These results support a mechanism of transformation whereby two oncogenic fusion proteins cooperate by activating a target gene and then modulating the function of its downstream product.
Graphical Abstract Highlights ► A common set of target genes directly regulated by MLL-AF4 is identified ► RUNX1 is a target gene that is specifically upregulated in t(4;11) patients ► MLL-AF4 controls RUNX1 gene expression by stabilizing ENL and AF9 binding ► RUNX1 cooperates with an AF4-MLL complex to activate gene targets
Children and adults with acute leukemias caused by the mixed lineage leukemia (MLL) gene have very poor survival rates, most likely due to the fact that MLL is a regulator of epigenetic information. Milne and colleagues now show that a protein named RUNX1 cooperates with two different MLL mutations to alter the epigenetic information content of the cell, directly contributing to the poor prognosis of MLL-associated leukemias.