Chromatin accessibility, p300, and histone acetylation define PML-RARα and AML1-ETO binding sites in acute myeloid leukemia.

Chromatin accessibility plays a key role in regulating cell type specific gene ex-pression during hematopoiesis but has also been suggested to be aberrantly regulated during leukemogenesis. To un-derstand the leukemogenic chromatin sig-nature, we analyzed acute promyelocytic leukemia, a subtype of leukemia charac-terized by the expression of RARa-fusion proteins, such as PML-RARα. We used nuclease accessibility sequencing in cell lines as well as patient blasts to identify accessible DNA elements and identi-fied > 100 000 accessible regions in each case. Using ChlP-seq, we Identified H2A.Z as a histone modification generally asso-ciated with these accessible regions, whereas unsupervised clustering analy-sis of other chromatin features, including DNA methylation, H2A.Zac, H3ac, H3K9me3, H3K27me3, and the regulatory factor p300, distinguished 6 distinct clus-ters of accessible sites, each with a char-acteristic functional makeup. Of these, PML-RARα binding was found specifi-cally at accessible chromatin regions characterized by p300 binding and hy-poacetylated hlstones. Identifying re-gions with a similar epigenetic make up in t(8;21) acute myeloid leukemia (AML) cells, another subtype of AMLs, revealed that these regions are occupied by the oncofusion protein AML1-ETO. Together, our results suggest that oncofusion pro-teins localize to accessible regions and that chromatin accessibility together with p300 binding and histone acetylation char-acterize AML1-ETO and PML-RARα bind-ing sites. [ABSTRACT FROM AUTHOR]