Double plant homeodomain finger 2 (DPF2) is a highly evolutionarily conserved member of the d4 protein family that is ubiquitously expressed in human tissues and was recently shown to inhibit the myeloid differentiation of hematopoietic stem/progenitor and acute myelogenous leukemia cells. Here, we present the crystal structure of the tandem plant homeodomain finger domain of human DPF2 at 1.6-Ă
resolution. We show that DPF2 interacts with the acetylated tails of both histones 3 and 4 via bipartite binding pockets on the DPF2 surface. Blocking these interactions through targeted mutagenesis of DPF2 abolishes its recruitment to target chromatin regions as well as its ability to prevent myeloid differentiation in vivo. Our findings suggest that the histone binding of DPF2 plays an important regulatory role in the transcriptional program that drives myeloid differentiation.T he founding member of the d4 family of proteins, d4, zinc, and double plant homeodomain (PHD) finger 2 (DPF2, also known as requiem/REQ or ubi-d4), was initially discovered as a factor required for apoptosis in myeloid cells (1). d4 proteins, which in humans also include DPF1 and DPF3b, are characterized by an N-terminal requiem domain, a central C2H2-type zinc finger domain, and a C-terminal tandem PHD finger (2). PHD fingers, which contain two zinc finger motifs, are notable for their ability to read a diverse number of posttranslational modifications, including unmodified, methylated, or acetylated lysines, as well as unmodified arginines (3). Besides such putative binding capabilities of the DPF2 tandem PHD finger domain, relatively little is known about the regulation and function of DPF2 or its remaining individual domains. Previous studies have shown that DPF2 bridges SWI/SNF components and RelB/p52 to affect noncanonical NF-ÎșB signaling (4), acts as a globin switching factor (5), and is a target for Staufen-1-mediated mRNA decay (5). Notably, DPF2 is expressed ubiquitously in human tissues compared with DPF1 and DPF3b (6, 7). DPF2, along with DPF1 and DPF3b, has been implicated in a range of human cancers, including cervical cancer and acute myelogenous leukemia (AML) (8-13). Runt-related transcription factor 1 (RUNX1, also known as AML1) functions as an AML tumorsuppressor gene, which is frequently inactivated through somatic mutations and chromosomal translocations, including t(8;21), which produces the AML1-ETO fusion protein (14). Recent work has shown that recruitment of DPF2 into a RUNX1-containing repressor complex inhibits the expression of RUNX1 target genes, including the myeloid-specific microRNA miR-223, and inhibits myeloid differentiation (8). DPF2 recruitment appears to depend on arginine methylation events of RUNX1, as it is blocked by mutation of RUNX1 Arg223 or chemical inhibition of the type I arginine methyltransferase PRMT4. Knockdown of either DPF2 or PRMT4 increases miR-223 gene expression and myeloid differentiation. These findings suggest a model in which DPF2 and RUNX1 form a methylation-dependent repressive co...