Biological significance of unmethylated DNA in human testicular cancer.

在这个项目中，我们发现睾丸生殖细胞肿瘤(TGCT)具有独特的表观遗传学特征：与其他体细胞来源的癌症相比，TGCT的DNA相对没有甲基化。此外，我们开发了一种新的睾丸生殖细胞肿瘤(TGCT)的DNA肿瘤标记物，它基于肿瘤的未甲基化DNA图谱。我们已经表明，XIST在TGCT中的表达与X连锁基因的甲基化无关，因此在机制上与女性非活动X染色体中的XIST表达不同。因此，无论XIST如何表达，TGCT中超多的X染色体都是低甲基化和活跃的(J.Urol 2003)。我们已经报道了肿瘤相关基因启动子的异常甲基化在睾丸淋巴瘤中很常见，但在TGCT中却不常见(GCC 2003)。这些数据表明TGCT中的DNA可能以非甲基化的形式普遍调控，因此，似乎很难建立一个基于甲基化的TGCT的DNA标记。或者，我们假设TGCT的非甲基化DNA区域，如果存在的话，可以用作潜在的DNA标记。在众多基因中，我们重点介绍了XIST基因，它只在雄性器官中的生殖细胞中表达。未甲基化的XIST DNA片段仅存在于女性PBL中，而不存在于男性PBL中。我们已经在TGCT组织和匹配的TGCT患者的血浆样本中检测到未甲基化的XIST DNA片段(Lancet)。我们还阐明了几个癌症睾丸抗原基因中TGCT的甲基化特征(GCC，2005)。与原始生殖细胞相比，在TGCT中保持DNA不甲基化的机制正在研究中。

In this project we found testicular germ-cell tumors(TGCTs) carry unique epigenetic profiles : The DNAs of TGCTs are relatively unmethylated in comparison with those of other somatic tissue derived cancer. Furthermore, we developed a novel DNA tumor marker for testicular germ cell tumors(TGCTs) that is based on the unmethylated DNA profile of a neoplasm.We have shown that XIST expression in TGCTs is not associated with the methylation of X-linked genes and is therefore mechanistically distinct from the XIST expression in female inactive X chromosomes. Thus, supernumerical X chromosomes in TGCTs were predominantly hypomethylated and active regardless of XIST expression (J.Urol 2003 ).We have reported that aberrant methylation at the promoter of tumor related genes are common in testicular lymphomas, but not in TGCTs (GCC 2003).These data suggest that DNA of TGCTs may be ubiquitously regulated as unmethylated.Thus, it appears difficult to create a methylation-based DNA marker for TGCTs. Alternatively, we hypothesized that unmethylated DNA regions specific for TGCTs, if they exist, could be used as potential DNA markers. Among various genes, we have focused on the XIST gene, which is solely expressed in germ cells among male organs. Unmethylated XIST DNA fragments only exist in female PBLs, but not in male PBLs. We have detected unmethylated XIST DNA fragments in TGCT tissues and matching plasma samples from the patients with TGCTs (Lancet). We also clarified methylation profiles of TGCTs in several cancer testis antigen(CTA) genes (GCC 2005). Mechanisms for maintaining DNA free from methylation in TGCTs are under investigation in comparison with those in primordeal germ cells.