Epigenetic Modification of CCAAT/Enhancer Binding Protein α Expression in Acute Myeloid Leukemia

Functional loss of CCAAT/enhancer binding protein α ( C/EBPα ), a master regulatory transcription factor in the hematopoietic system, can result in a differentiation block in granulopoiesis and thus contribute to leukemic transformation. Here, we show the effect of epigenetic aberrations in regulating C/EBPα expression in acute myeloid leukemia (AML). Comprehensive DNA methylation analyses of the CpG island of C/EBPα identified a densely methylated upstream promoter region in 51% of AML patients. Aberrant DNA methylation was strongly associated with two generally prognostically favorable cytogenetic subgroups: inv(16) and t(15;17). Surprisingly, while epigenetic treatment increased C/EBPα mRNA levels in vitro , C/EBPα protein levels decreased. Using a computational microRNA (miRNA) prediction approach and functional studies, we show that C/EBPα mRNA is a target for miRNA-124a. This miRNA is frequently silenced by epigenetic mechanisms in leukemia cell lines, becomes up-regulated after epigenetic treatment, and targets the C/EBPα 3′ untranslated region. In this way, C/EBPα protein expression is reduced in a posttranscriptional manner. Our results indicate that epigenetic alterations of C/EBPα are a frequent event in AML and that epigenetic treatment can result in down-regulation of a key hematopoietic transcription factor. [Cancer Res 2008;68(9):3142–51]