RESUMO
In acute myeloid leukemia (AML), specific genomic aberrations induce aberrant methylation, thus directly influencing the transcriptional programing of leukemic cells. Therefore, therapies targeting epigenetic processes are advocated as a promising therapeutic tool for AML treatment. However, to develop new therapies, a comprehensive understanding of the mechanism(s) driving the epigenetic changes as a result of acquired genetic abnormalities is necessary. This understanding is still lacking. In this study, we performed genome-wide CpG-island methylation profiling on pediatric AML samples. Six differentially methylated genomic regions within two genes, discriminating inv(16)(p13;q22) from non-inv(16) pediatric AML samples, were identified. All six regions had a hypomethylated phenotype in inv(16) AML samples, and this was most prominent at the regions encompassing the meningioma (disrupted in balanced translocation) 1 (MN1) oncogene. MN1 expression primarily correlated with the methylation level of the 3' end of the MN1 exon-1 locus. Decitabine treatment of different cell lines showed that induced loss of methylation at the MN1 locus can result in an increase of MN1 expression, indicating that MN1 expression is coregulated by DNA methylation. To investigate this methylation-associated mechanism, we determined the expression of DNA methyltransferases in inv(16) AML. We found that DNMT3B expression was significantly lower in inv(16) samples. Furthermore, DNMT3B expression correlated negatively with MN1 expression in pediatric AML samples. Importantly, depletion of DNMT3B impaired remethylation efficiency of the MN1 exon-1 locus in AML cells after decitabine exposure. These findings identify DNMT3B as an important coregulator of MN1 methylation. Taken together, this study shows that the methylation level of the MN1 exon-1 locus regulates MN1 expression levels in inv(16) pediatric AML. This methylation level is dependent on DNMT3B, thus suggesting a role for DNMT3B in leukemogenesis in inv(16) AML, through MN1 methylation regulation.
Assuntos
DNA (Citosina-5-)-Metiltransferases/metabolismo , Metilação de DNA/genética , Regulação Leucêmica da Expressão Gênica , Leucemia Mieloide Aguda/genética , Proteínas Supressoras de Tumor/genética , Adolescente , Azacitidina/análogos & derivados , Azacitidina/farmacologia , Carcinogênese/genética , Linhagem Celular Tumoral , Criança , Pré-Escolar , Ilhas de CpG/genética , Metilação de DNA/efeitos dos fármacos , Decitabina , Epigênese Genética/genética , Éxons/genética , Feminino , Humanos , Lactente , Recém-Nascido , Leucemia Mieloide Aguda/sangue , Leucemia Mieloide Aguda/patologia , Masculino , Hibridização de Ácido Nucleico/métodos , Análise de Sequência com Séries de Oligonucleotídeos/métodos , Proteínas de Fusão Oncogênica/genética , Regiões Promotoras Genéticas/genética , Transativadores , DNA Metiltransferase 3BRESUMO
Overexpression of the BRE (brain and reproductive organ-expressed) gene defines a distinct pediatric and adult acute myeloid leukemia (AML) subgroup. Here we identify a promoter enriched for active chromatin marks in BRE intron 4 causing strong biallelic expression of a previously unknown C-terminal BRE transcript. This transcript starts with BRE intron 4 sequences spliced to exon 5 and downstream sequences, and if translated might code for an N terminally truncated BRE protein. Remarkably, the new BRE transcript was highly expressed in over 50% of 11q23/KMT2A (lysine methyl transferase 2A)-rearranged and t(8;16)/KAT6A-CREBBP cases, while it was virtually absent from other AML subsets and normal tissues. In gene reporter assays, the leukemia-specific fusion protein KMT2A-MLLT3 transactivated the intragenic BRE promoter. Further epigenome analyses revealed 97 additional intragenic promoter marks frequently bound by KMT2A in AML with C-terminal BRE expression. The corresponding genes may be part of a context-dependent KMT2A-MLLT3-driven oncogenic program, because they were higher expressed in this AML subtype compared with other groups. C-terminal BRE might be an important contributor to this program because in a case with relapsed AML, we observed an ins(11;2) fusing CHORDC1 to BRE at the region where intragenic transcription starts in KMT2A-rearranged and KAT6A-CREBBP AML.
Assuntos
Rearranjo Gênico , Leucemia Mieloide Aguda/genética , Proteínas do Tecido Nervoso/genética , Domínios e Motivos de Interação entre Proteínas/genética , Ativação Transcricional , Translocação Genética , Linhagem Celular , Cromossomos Humanos Par 11 , Cromossomos Humanos Par 16 , Epigênese Genética , Éxons , Regulação Leucêmica da Expressão Gênica , Histona-Lisina N-Metiltransferase/genética , Histonas/metabolismo , Humanos , Íntrons , Proteína de Leucina Linfoide-Mieloide/genética , Proteínas Nucleares/genética , Regiões Promotoras GenéticasRESUMO
Nucleophosmin (NPM1) mutations occur frequently in adult cytogenetically normal acute myeloid leukemia (CN-AML) and confer favorable outcome. We investigated the frequency and prognostic significance of NPM1 mutations in childhood AML (n=298), specifically focusing on the CN-AML subgroup (n=100). Mutations were found in 8.4%, and clustered significantly in the CN-AML subgroup (22%). No mutations were found in patients below the age of 3 years; in CN-AML, there was an increasing incidence above this age. In the overall group, NPM1 mutations conferred an independent favorable prognostic impact on event-free survival (5-year pEFS 66 vs 39%; P=0.02), which did not translate into a significantly better overall survival (5-year pOS 68 vs 56%; P=0.30). However, when the favorable cytogenetic subgroups [inv(16) and t(8;21)] were excluded from the NPM1 wild-type group, the difference in pOS was borderline statistically significant (68 vs 45%; P=0.07). In the CN-AML cohort, NPM1 mutations were an independent prognostic factor on pEFS (80 vs 39%; P=0.01), and pOS (85 vs 60%; P=0.06), which was not influenced by FLT3/ITD. However, in NPM1 wild-type CN-AML, FLT3/ITD-positive patients had a significantly worse outcome (pEFS 48 vs 18%; P<0.001). We conclude that NPM1 mutations confer a favorable prognosis in childhood AML and in CN-AML in particular.
