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

BjöRn Hackanson,Christoph Plass,Guido Marcucci,Thomas D Schmittgen,Michael LüBbert,Jinmai Jiang,Romulo M Brena,Kristi L Bennett,Rainer Claus,Clara D Bloomfield,Katie Maharry,Nadya Blagitko-Dorfs,Susan P Whitman,Shih-Shih Chen

doi:10.1158/0008-5472.can-08-0483

Abstract

Functional loss of CCAAT/enhancer binding protein alpha (C/EBP alpha), 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/EBP alpha expression in acute myeloid leukemia (AML). Comprehensive DNA methylation analyses of the CpG island of C/EBP alpha 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/EBP alpha mRNA levels in vitro, C/EBP alpha protein levels decreased. Using a computational microRNA (miRNA) prediction approach and functional studies, we show that C/EBP alpha 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/EBP alpha 3' untranslated region. In this way, C/EBP alpha protein expression is reduced in a posttranscriptional manner. Our results indicate that epigenetic alterations of C/EBP alpha are a frequent event in AML and that epigenetic treatment can result in down-regulation of a key hematopoietic transcription factor.

Highlights

Acute myeloid leukemia (AML) has been extensively studied at the cytogenetic, molecular, and transcriptional level
C/EBPa has gained interest in the AML field, because it has been shown that down-regulation of C/EBPa protein through mutations, posttranslational modifications, and proteinprotein interactions with fusion proteins AML1/ETO or CBFBSMMHC plays a key role in leukemic transformation [6, 8,9,10,11]
To investigate the DNA methylation patterns of C/EBPa comprehensively, we conducted combined bisulfite restriction analysis assay (COBRA) and sodium bisulfite sequencing on bone marrow samples from 15 AML patients and three bone marrow samples from healthy individuals (NBM)

Summary

Introduction

Acute myeloid leukemia (AML) has been extensively studied at the cytogenetic, molecular, and transcriptional level. This knowledge has contributed to the subclassification of AML and translated into significant improvement of therapies [1,2,3]. Leukemic transformation to AML is a multistep process requiring the alterations of genes involved in proliferation/survival and hematopoietic differentiation [4]. Note: Supplementary data for this article are available at Cancer Research Online (http://cancerres.aacrjournals.org/). C/EBPa has gained interest in the AML field, because it has been shown that down-regulation of C/EBPa protein through mutations, posttranslational modifications, and proteinprotein interactions with fusion proteins AML1/ETO or CBFBSMMHC plays a key role in leukemic transformation [6, 8,9,10,11]

Methods

Results

Conclusion