Histone deacetylase 3 preferentially binds and collaborates with the transcription factor RUNX1 to repress AML1–ETO–dependent transcription in t(8;21) AML

In up to 15% of acute myeloid leukemias (AMLs), a recurring chromosomal translocation, termed t(8;21), generates the AML1?eight?twenty-one (ETO) leukemia fusion protein, which contains the DNA-binding domain of Runt-related transcription factor 1 (RUNX1) and almost all of ETO. RUNX1 and the AML1?ETO fusion protein are coexpressed in t(8;21) AML cells and antagonize each other's gene-regulatory functions. AML1?ETO represses transcription of RUNX1 target genes by competitively displacing RUNX1 and recruiting corepressors such as histone deacetylase 3 (HDAC3). Recent studies have shown that AML1?ETO and RUNX1 co-occupy the binding sites of AML1?ETO?activated genes. How this joined binding allows RUNX1 to antagonize AML1?ETO?mediated transcriptional activation is unclear. Here we show that RUNX1 functions as a bona fide repressor of transcription activated by AML1?ETO. Mechanistically, we show that RUNX1 is a component of the HDAC3 corepressor complex and that HDAC3 preferentially binds to RUNX1 rather than to AML1?ETO in t(8;21) AML cells. Studying the regulation of interleukin-8 (IL8), a newly identified AML1?ETO?activated gene, we demonstrate that RUNX1 and HDAC3 collaboratively repress AML1?ETO?dependent transcription, a finding further supported by results of genome-wide analyses of AML1?ETO?activated genes. These and other results from the genome-wide studies also have important implications for the mechanistic understanding of gene-specific coactivator and corepressor functions across the AML1?ETO/RUNX1 cistrome.