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Allele-specific expression of GATA2 due to epigenetic dysregulation in double mutated CEBPA AML

ABSTRACT: Transcriptional deregulation is a central event in the development of acute myeloid leukemia (AML). To identify potential disturbances in gene regulation, we conducted an unbiased screen of allele-specific expression (ASE) in 209 AML cases. The gene encoding GATA binding protein 2 (GATA2) displayed ASE more often than any other myeloid or cancer-related gene. GATA2 ASE was strongly associated with CEBPA double mutations (CEBPA DM), with 95% of cases presenting GATA2 ASE. In CEBPA DM AML with GATA2 mutations, the mutated allele was preferentially expressed. We found that GATA2 ASE is a somatic event lost in complete remission, supporting the notion that it plays a role in CEBPA DM AML. Acquisition of GATA2 ASE involved silencing of one allele via promoter methylation, compensated by overactivation of the other allele, thereby preserving expression levels. Notably, promoter methylation was also lost in remission together with GATA2 ASE. In summary, we propose that GATA2 ASE is acquired by epigenetic mechanisms and is a prerequisite for the development of AML with CEBPA DM. This finding constitutes a novel example of an epigenetic hit cooperating with a genetic hit in the pathogenesis of AML.

PROVIDER: EGAS00001004684 | EGA |

REPOSITORIES: EGA

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Project description:The clinical impact of aberrant CEBPA promoter methylation (PM) in AML is controversial discussed. The aim of this study was to clarify the significance of aberrant CEBPA PM with regard to clinical features in a cohort of 572 de novo AML with wildtype CEBPA and normal karyotype. The distal promoter was methylated in 54/572 cases (9.41%) whereas proximal PM was never detected. Methylation of the core promoter was detected in only 8 of 326 cases (2.45%) and thus seems to be a rare event in AML. There was no correlation between CEBPA distal PM, age, sex, white blood cell (WBC) count or Hb levels at diagnosis. We also were not able to detect a significant correlation between the presence of CEBPA distal PM and molecular mutations such as FLT3-ITD, NPM1, AML1, MLL-PTD and IDH1. Solely the frequency of IDH2R140 mutations was significantly reduced in CEBPA distal PM positive compared to CEBPA distal PM negative cases (p=0.01). Furthermore, analysis of CEBPA mRNA expression level revealed no difference between CEBPA distal PM positive and CEBPA distal PM negative cases, suggesting that CEBPA distal PM has no influence on CEBPA expression. CEBPA distal PM did not show impact on overall survival (OS), event free survival (EFS) or incidence of relapse. Also when other mutations were taken into regard no prognostic impact of CEBPA distal PM could be shown. In contrast, a distinct expression profile of CEBPA distal PM positive cases compared to CEBPA mutated and CEBPA distal PM negative cases was observed. In addition, a significantly higher frequency of CEBPA distal PM was detected in RUNX1-RUNX1T1 positive AML compared to the CEBPA witdtype cases. We conclude that the presence of aberrant CEBPA PM has no clinical relevance and is therefore a negligible prognostic marker in de novo AML with normal karyotype. To detect underlying common differences in their gene expression profiles, we investigated 9 CEBPA methylated (unmutated), 8 CEBPA single-mutated, 10 CEBPA double-mutated, and 10 non-methylated/non-mutated cases (Affymetrix HG-U133 Plus 2.0 microarrays; Santa Clara, CA). The microarray sample preparation assay was performed as previously reported. Gene expression raw data were processed according to the manufacturer’s recommendations.

Project description:Genome-wide analysis of single nucleotide polymorphisms in 64 acute myeloid leukemias has revealed that 20% exhibited large regions of homozygosity that could not be accounted for by visible chromosomal abnormalities in the karyotype. Further analysis confirmed that these patterns were due to partial uniparental disomy (UPD). Remission bone marrow was available from five patients showing UPD in their leukemias, and in all cases the homozygosity was found to be restricted to the leukemic clone. Two examples of UPD11p were shown to be of different parental origin as indicated by the methylation pattern of the H19 gene. Furthermore, a previously identified homozygous mutation in the CEBPA gene coincided with a large-scale UPD on chromosome 19. These cryptic chromosomal abnormalities, which seem to be nonrandom, have the characteristics of somatic recombination events and may define an important new subclass of leukemia. Patient No. from Table 1 of Raghavan et al 2005 and Sample name; Patient No: 1 = Sample name: AML sample 35 diagnosis; Patient No: 1 = Sample name: AML sample 107 remission; Patient No: 2 = Sample name: AML sample 37 diagnosis; Patient No: 3 = Sample name: AML sample 10 diagnosis; Patient No: 3 = Sample name: AML sample 44 remission; Patient No: 4 = Sample name: AML sample 20 diagnosis; Patient No: 5 = Sample name: AML sample 65 diagnosis; Patient No: 6 = Sample name: AML sample 69 diagnosis; Patient No: 6 = Sample name: AML sample 94 remission; Patient No: 7 = Sample name: AML sample 40 diagnosis; Patient No: 7 = Sample name: AML sample 41 remission; Patient No: 8 = Sample name: AML sample 64 diagnosis; Patient No: 9 = Sample name: AML sample 7 diagnosis; Patient No: 10 = Sample name: AML sample 49 diagnosis; Patient No: 10 = Sample name: AML sample 106 remission; Patient No: 11 = Sample name: AML sample 76 diagnosis; Patient No: 12 = Sample name: AML sample 79 diagnosis Experiment Overall Design: DNA from 64 diagnostic AML samples were analysed using Affymetrix 10K SNP arrays. Large regions of homozygosity were identified and compared with remission bone marrow where available.

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Allele-specific expression of GATA2 due to epigenetic dysregulation in double mutated CEBPA AML

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