The C/EBPδ tumor suppressor is silenced by hypermethylation in acute myeloid leukemia

Aberrant DNA methylation is the most frequent molecular alteration in acute myeloid leukemia (AML). To identify methylation-silenced genes in AML, we performed microarray analyses in U937 cells exposed to the demethylating agent 5-azadeoxy-cytidine. Overall, 274 transcripts were significantly induced. Interestingly, C/EBP delta expression was significantly induced (more than 10-fold) by demethylation whereas expression of all other C/EBP family members remained unchanged. The C/EBP delta promoter was strongly methylated in different leukemic cell lines and showed signs of a repressed chromatin state. Analyses of the promoter regions of the entire C/EBP family (alpha, beta, gamma, delta, epsilon, zeta) in bone marrow samples from AML patients (n = 80) and controls (n = 15) by mass spectrometry revealed that C/EBP delta is the most commonly hypermethylated C/EBP gene in AML. Hypermethylation occurred in more than 35% of AML patients at primary diagnosis. A significant correlation (P =.016) was observed between hypermethylation of the C/EBP delta promoter and low expression of C/EBP8 in AML patients. C/EBP delta promoter activity was strongly repressed by methylation in vitro, and transcriptional repression partially depended on MeCP2 activity. C/EBP8 exhibited growth-inhibitory properties in primary progenitor cells as well as in FIt3-ITD-transformed cells. Taken together, C/EBP delta is a novel tumor suppressor gene in AML that is silenced by promoter methylation.