Identification of aberrantly methylated DNA genes in hematological malignancies : its application to cancer diagnosis

表观遗传学变化，包括DNA甲基化在肿瘤发生中起着重要作用，除了遗传变化和染色体易位。为阐明恶性血液病中DNA甲基化的变化模式，我们采用甲基化CpG岛扩增/代表性差异分析（MCA/RDA）技术分离了ATL细胞中的异常甲基化DNA区域，并在ATL细胞中鉴定出MEL 1 S基因为低甲基化基因。MEL 1 S基因在ATL细胞中的异常表达使ATL细胞对TGF-β产生耐药性。因此，认为MEL 1 S表达是赋予TGF-β抗性的机制之一。另一方面，在ATL细胞中发现许多基因被高甲基化。其中，KLF 4和EGR 3基因在ATL细胞中进行了研究。EGR 3基因是一个转录因子，对Fas配体基因的转录起关键作用。虽然ATL细胞高度表达Fas抗原，但由于Fas配体表达的丧失，它们逃避凋亡。在ATL细胞中EGR 3基因表达的沉默导致Fas配体表达的缺失，这使得ATL细胞能够逃避Fas-Fas配体诱导的凋亡，我们还用MCA/RDA技术鉴定了与正常CD 19阳性B细胞相比的B细胞慢性淋巴细胞白血病（B-CLL）中的高甲基化和低甲基化DNA区域。我们从B-CLL患者的基因组DNA中分离出5个高甲基化和27个低甲基化的DNA区域。低甲基化DNA区域集中在染色体9 q34、10 q25 -26和19 q13。这些异常甲基化的基因可能与这些血液系统恶性肿瘤的发生有关，检测这些基因的甲基化可用于诊断和估计预后。

Epigenetic changes including DNA methylation play an important role in oncogenesis in addition to genetic changes and chromosomal translocations. To clarify the changed pattern of DNA methylation in hematological malignancies, we isolated aberrantly methylated DNA regions by Methylated CpG island amplification/representative difference assay (MCA/RDA).In ATL cells, MEL1S gene was identified as hypomethylated one in ATL cells. Aberrant expression of MEL1S gene was observed in ATL cells, which enables ATL cells resistant to TGF-β. Therefore, MEL1S expression is considered to be one of mechanisms to confer the resistance to TGF-β. On the other hand, many genes were found to be hypermethylated in ATL cells. Among them, KLF4 and EGR3 genes were studied in ATL cells. EGR3 gene is a transcriptional factor, which is critical for Fas ligand gene transcription. Although ATL cells highly express Fas antigen, they escape from apoptosis due to loss of Fas ligand expression. Silenced EGR3 gene expression in ATL cells is considered to result in loss of Fas ligand expression, which enables ATL cells to escape from Fas-Fas ligand induced apoptosis.With MCA/RDA, we also identified hyper and hypomethylated DNA regions in B-cell chronic lymphocytic leukemia (B-CLL) compared with normal CD19 positive B-cells. We isolated 5 hyper and 27 hypomethylated DNA regions in genomic DNA from B-CLL patient. Hypomethylated DNA regions clustered in chr. 9q34,10q25-26, and 19q13.These aberrantly methylated genes should be implicated in oncogenesis of these hematological malignancies, and detection of these methylation can be used for diagnosis and estimation of the prognosis.