Haematopoietic malignancies caused by dysregulation of a chromatin-binding PHD finger

Histone H3 Lys4 methylation (H3K4me) was proposed as a critical component in regulating the gene expression, epigenetic states, and cellular identities1. The biological meaning of H3K4me is interpreted via conserved modules including plant homeodomain (PHD) fingers that recognize varied H3K4me states1,2. The dysregulation of PHD finger has been implicated in a variety of human diseases including cancers and immune or neurological disorders3. Here we report that fusing an H3K4-trimethylation (H3K4me3)-binding PHD finger, such as the C-terminal PHD finger of JARID1A or PHF23 (JARID1A(PHD3), PHF23(PHD)), to a common fusion partner nucleoporin-98 (NUP98) as identified in human leukemias4,5, generated potent oncoproteins that arrested hematopoietic differentiation and induced acute myeloid leukemia (AML). In these processes, a PHD finger that specifically recognizes H3K4me3/2 marks was essential for leukemogenesis. Mutations in PHD fingers that abrogated H3K4me3-binding also abolished leukemic transformation. NUP98-PHD fusion prevented the differentiation-associated removal of H3K4me3 at many loci encoding lineage-specific transcription factors (Hox(s), Gata3, Meis1, Eya1, Pbx1), and enforced their active gene transcription. Mechanistically, NUP98-PHD fusions act as ‘chromatin boundary factors’, dominating over polycomb-mediated gene silencing to ‘lock’ developmentally crucial loci into an active chromatin state (H3K4me3 with induced histone acetylation), a state that defined leukemia stem cells. Collectively, our studies represent the first report wherein the deregulation of PHD finger, ‘effector’ of specific histone modification, perturbs the epigenetic dynamics on developmentally critical loci, catastrophizes cellular fate decision-making, and even causes oncogenesis during development.