MLL-AF4 binds directly to a BCL-2 specific enhancer and impacts H3K27 acetylation

ABSTRACT: Survival rates for children diagnosed with acute lymphoblastic leukemia (ALL) have drastically improved, but those carrying mutations in the Mixed Lineage Leukemia (MLL) gene continue to have a very poor prognosis. The most common MLL mutation in ALL is the t(4;11)(q21;q23) chromosome translocation that fuses MLL in frame with the AF4 gene producing MLL-AF4 and AF4-MLL fusion proteins. Previously, we showed that MLL-AF4 binds to the BCL-2 gene and directly activates it through DOT1L recruitment and increased H3K79me2/3 levels. We went on to show that MLL leukemias are particularly sensitive to treatment with the BCL-2 inhibitor venetoclax which synergizes with both standard chemotherapeutic agents as well as DOT1L inhibitors. Altered expression of other BCL-2 family members is a major cause of resistance to ventoclax, so here we perform a detalied analysis of MLL-AF4 regulation of the entire BCL-2 family. By measuring nascent RNA production, we find that of all the BCL-2 family genes, MLL-AF4 directly controls the transcription of both BCL-2 and MCL-1, but only BCL-2 shows a significant loss of steady state RNA levels. Interestingly however, both MCL-1 and BCL-XL protein levels are dependent on MLL-AF4 activity through an unknown and likely indirect mechanism. Finally, we analyze MLL-AF4 regulation of the BCL-2 gene in greater detail and using Capture C we identify a major BCL-2 specific enhancer consisting of two clusters of H3K27Ac. Loss of MLL-AF4 activity results in a reduction of H2K27Ac levels at the major BCL-2 enhancer, revealing a novel regulatory dependence on MLL-AF4 function at BCL-2.

ORGANISM(S): Homo sapiens

PROVIDER: GSE85988 | GEO | 2016/11/23

SECONDARY ACCESSION(S): PRJNA339938

REPOSITORIES: GEO