The catalytic domain of SETD1B regulates H3K4me3 breadth and Myc expression in MLL-r leukemia (RNA-seq)

Histone H3 lysine 4 tri-methylation (H3K4me3) is abundant in MLL-rearranged (MLL-r) acute myeloid leukemia (AML) cells, but the enzymes responsible and their roles remain unclear. In this study, we perform a CRISPR-tiling screen against known H3K4 methylation modifiers in MLL-r AML model. We found the non-redundant roles of H3K4 methyltransferase SETD1B for growth regulation in NrasG12D or FLT3-ITD-expressing AML cells that exhibit cytokine-independent growth. The disruption of SETD1B catalytic SET domain causes cell cycle arrest, apoptosis, cell differentiation and a downregulation of gene expression, especially in the MYC pathway. H3K4me3 and SETD1B are distributed to the gene body of Myc, and the loss of SETD1B SET domain result in a significant decrease in H3K4me3 breadth. Overexpression of MYC significantly restores the growth defect and transcriptional perturbation in SETD1B SET domain mutant cells. In the meantime, the expression of MYC does not rescue the reduced H3K4me3 breadth and RNA polymerase II elongation in SETD1B mutant cells. A disruption of H3K4 demethylase KDM5C enhances global H3K4me3 level and promotes the proliferation of AML cell, and partially rescues the defective cell growth of SETD1B SET domain mutant cells. These data indicate that SETD1B is required for both H3K4me3 breadth and Myc expression to support advanced AML cell proliferation. Thus, a thorough understanding of the SETD1B-mediated H3K4me3 breadth will be critical for the development of markers and therapies for leukemia subtypes that are MYC-dependent.