ASH1L links histone H3 lysine 36 dimethylation to MLL Leukemia

Abstract

Numerous studies in multiple systems support that histone H3 lysine 36 dimethylation (H3K36me2) is associated with transcriptional activation; however, the underlying mechanisms are not well defi ned. Here, we show that the H3K36me2 chromatin mark written by the ASH1L histone methyltransferase is preferentially bound in vivo by LEDGF, a mixed-lineage leukemia (MLL)–associated protein that colocalizes with MLL, ASH1L, and H3K36me2 on chromatin genome wide. Furthermore, ASH1L facilitates recruitment of LEDGF and wild-type MLL proteins to chromatin at key leukemia target genes and is a crucial regulator of MLL-dependent transcription and leukemic transformation. Conversely, KDM2A, an H3K36me2 demethylase and Polycomb group silencing protein, antagonizes MLL-associated leukemogenesis. Our studies are the fi rst to provide a basic mechanistic insight into epigenetic interactions wherein placement, interpretation, and removal of H3K36me2 contribute to the regulation of gene expression and MLL leukemia, and suggest ASH1L as a novel target for therapeutic intervention. SIGNIFICANCE: Epigenetic regulators play vital roles in cancer pathogenesis and represent a new frontier in therapeutic targeting. Our studies provide basic mechanistic insight into the role of H3K36me2 in transcription activation and MLL leukemia pathogenesis and implicate ASH1L histone methyltransferase as a promising target for novel molecular therapy.