MBD3/NuRD loss participates with KDM6A program to promote DOCK5/8 expression and Rac GTPase activation in human acute myeloid leukemia

Cancer genome sequencing studies have focused on identifying oncogenic mutations. However, mutational profiling alone may not always help dissect underlying epigenetic dependencies in tumorigenesis. Nucleosome remodeling and deacetylase (NuRD) is an ATP-dependent chromatin remodeling complex that regulates transcriptional architecture and is involved in cell fate commitment. We demonstrate that loss of MBD3, an important NuRD scaffold, in human primary acute myeloid leukemia (AML) cells associates with leukemic NuRD. Interestingly, CHD4, an intact ATPase subunit of leukemic NuRD, coimmunoprecipitates and participates with H3K27Me3/2-demethylase KDM6A to induce expression of atypical guanine nucleotide exchange factors, dedicator of cytokinesis (DOCK) 5 and 8 (DOCK5/8), promoting Rac GTPase signaling. Mechanistically, MBD3 deficiency caused loss of histone deacytelase 1 occupancy with a corresponding increase in KDM6A, CBP, and H3K27Ac on DOCK5/8 loci, leading to derepression of gene expression. Importantly, the Cancer Genome Atlas AML cohort reveals that DOCK5/8 levels are correlated with MBD3 and KDM6A, and DOCK5/8 expression is significantly increased in patients who are MBD3 low and KDM6A high with a poor survival. In addition, pharmacological inhibition of DOCK signaling selectively attenuates AML cell survival. Because MBD3 and KDM6A have been implicated in metastasis, our results may suggest a general phenomenon in tumorigenesis. Collectively, these findings provide evidence for MBD3-deficient NuRD in leukemia pathobiology and inform a novel epistasis between NuRD and KDM6A toward maintenance of oncogenic gene expression in AML.