Abstract
In acute promyelocytic leukemia, granulocytic differentiation is arrested at the promyelocyte stage. The variant t(11;17) translocation produces two fusion proteins, promyelocytic leukemia zinc finger-retinoic acid receptor α (PLZF-RARα) and RARα-PLZF, both of which participate in leukemia development. Here we provide evidence that the activity of CCAAT/enhancer binding protein α (C/EBPα), a master regulator of granulocytic differentiation, is severely impaired in leukemic promyelocytes with the t(11;17) translocation compared with those associated with the t(15;17) translocation. We show that RARα-PLZF inhibits myeloid cell differentiation through interactions with C/EBPα tethered to DNA, using ChIP and DNA capture assays. Furthermore, RARα-PLZF recruits HDAC1 and causes histone H3 deacetylation at C/EBPα target loci, thereby decreasing the expression of C/EBPα target genes. In line with these results, HDAC inhibitors restore in part C/EBPα target gene expression. These findings provide molecular evidence for a mechanism through which RARα-PLZF acts as a modifier oncogene that subverts differentiation in the granulocytic lineage by associating with C/EBPα and inhibiting its activity.