Aberrant DNA Methylation of the C/EBPalpha Promoter Region in Hematopoietic Malignancies.

The CCAAT/enhancer binding protein alpha (C/EBPalpha) is a transcription factor implicated in myeloid differentiation. Loss of function of C/EBPalpha may impair granulocytic differentiation and thus contribute to leukemogenesis. Inactivation mutations of C/EBPalpha have been reported in hematopoietic malignancies, especially in acute myeloid leukemia (AML). Hypermethylation of CpG islands within gene promoter region is associated with transcriptional inactivation and represents an important mechanism of gene silencing in hematological malignancies. This epigenetic phenomenon acts as an alternative to mutations and deletions to disrupt gene function. In this study, we have analyzed the methylation status of the promoter-associated CpG island of the C/EBPalpha gene in hematopoietic cell lines and primary blood and bone marrow samples from patients with AML, multiple myeloma (MM) and non-Hodgkin’s lymphoma (NHL) by methylation-specific polymerase chain reaction (MSP). C/EBPalpha promoter methylation in L540 cells was associated with transcriptional repression, and treatment with the demethylating 5-aza-2′-deoxycytidine resulted in C/EBPalpha upregulation. MSP analysis of primary patient samples revealed C/EBPalpha hypermethylation in 19.3 % (11/57) of AML, 27.1 % (13/48) of MM and 46.7 % (7/15) of NHL. Aberrant C/EBPalpha methylation was found in AML of all FAB subtypes and throughout all cytogenetic risk groups. In MM, C/EBPalpha hypermethylation occurred in all Salmon and Durie stages as well as in plasma cell leukemia. Our data indicate that hypermethylation of the transcription factor C/EBPalpha is a common finding in various hematopoietic malignancies and may contribute, in addition to genetic aberrations, to the malignant phenotype. Our growing knowledge about epigenetic aberrations not only gives further insight in the pathogenesis of hematopoietic malignancies but also provides a rationale and molecular basis for therapeutic approaches with demethylating agents.