Department of Pediatric Oncology/Hematology, Erasmus MC-Sophia Children's Hospital, Rotterdam, The Netherlands.
Dutch Childhood Oncology Group (DCOG), The Hague, The Netherlands.
Oncogene. 2018 Jan 4;37(1):107-115. doi: 10.1038/onc.2017.293. Epub 2017 Sep 11.
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.
在急性髓系白血病（AML）中，特定的基因组异常会导致异常甲基化，从而直接影响白血病细胞的转录程序。因此，靶向表观遗传过程的治疗方法被认为是治疗 AML 的一种有前途的治疗工具。然而，为了开发新的治疗方法，需要全面了解获得性遗传异常导致的表观遗传变化的机制。目前，这方面的认识仍然不足。在本研究中，我们对儿科 AML 样本进行了全基因组 CpG 岛甲基化谱分析。鉴定出了两个基因中六个区分 inv(16)(p13;q22)与非 inv(16)儿科 AML 样本的差异甲基化基因组区域。所有六个区域在 inv(16)AML 样本中均表现出低甲基化表型，其中以包含脑膜瘤（平衡易位）1（MN1）癌基因的区域最为明显。MN1 表达主要与 MN1 外显子 1 位点 3'端的甲基化水平相关。不同细胞系的地西他滨处理表明，MN1 基因座诱导性去甲基化可导致 MN1 表达增加，表明 MN1 表达受 DNA 甲基化的共同调控。为了研究这种与甲基化相关的机制，我们检测了 inv(16)AML 中的 DNA 甲基转移酶表达。我们发现，inv(16)样本中 DNMT3B 的表达显著降低。此外，在儿科 AML 样本中，DNMT3B 表达与 MN1 表达呈负相关。重要的是，DNMT3B 耗竭会损害地西他滨暴露后 AML 细胞中 MN1 外显子 1 位点的重新甲基化效率。这些发现确定了 DNMT3B 是 MN1 甲基化的重要共调节因子。综上所述，本研究表明，MN1 外显子 1 位点的甲基化水平调节 inv(16)儿科 AML 中的 MN1 表达水平。这种甲基化水平依赖于 DNMT3B，因此提示 DNMT3B 在 inv(16)AML 的白血病发生中通过 MN1 甲基化调节发挥作用。
