Schmidt Wolfgang M, Sedivy Roland, Forstner Birgit, Steger Günther G, Zöchbauer-Müller Sabine, Mader Robert M
Department of Clinical Pharmacology, Section of Cardiovascular Medicine, Medical University of Vienna, Währinger Gürtel, Vienna, Austria.
Mol Carcinog. 2007 Sep;46(9):766-72. doi: 10.1002/mc.20307.
Epigenetic silencing is a prominent feature of cancer. Here, we investigated the expression of DNA demethylase and three DNA methyltransferases during colorectal tumorigenesis comparing the genes encoding DNA methyltransferases 1 (DNMT1), 3A, and 3B (DNMT3A and DNMT3B) with methyl-CpG binding domain protein 2 (MBD2), recently described as the only active DNA demethylase. Total RNA isolated from normal colonic mucosa (n = 24), benign adenomas (n = 18), and malignant colorectal carcinomas (n = 32) was analyzed by reverse transcriptase-PCR with subsequent quantification by capillary gel electrophoresis. In contrast to MBD2, expression of DNMT1 and DNMT3A increased in parallel to the degree of dysplasia, with significant overexpression in the malignant lesion when compared with mucosa or with benign lesions (DNMT1). Pairwise comparisons between tumors and matched, adjacent healthy mucosa tissue (n = 13) revealed that expression of all three genes encoding DNA methyltransferases increased by two- to three-fold. Our data suggest a relevant role of the DNA methyltransferases during colorectal tumorigenesis. This increase is not counterbalanced by enhanced expression of the demethylating component MBD2. As a consequence, epigenetic regulation in the adenoma-carcinoma sequence may be driven by increased methylating activity rather than suppressed demethylation.
表观遗传沉默是癌症的一个显著特征。在此，我们研究了结直肠癌发生过程中DNA去甲基化酶和三种DNA甲基转移酶的表达情况，将编码DNA甲基转移酶1（DNMT1）、3A和3B（DNMT3A和DNMT3B）的基因与最近被描述为唯一活性DNA去甲基化酶的甲基-CpG结合域蛋白2（MBD2）进行比较。从正常结肠黏膜（n = 24）、良性腺瘤（n = 18）和恶性结直肠癌（n = 32）中分离的总RNA通过逆转录聚合酶链反应进行分析，随后通过毛细管凝胶电泳进行定量。与MBD2相反，DNMT1和DNMT3A的表达与发育异常程度平行增加，与黏膜或良性病变相比，在恶性病变中显著过表达（DNMT1）。肿瘤与匹配的相邻健康黏膜组织（n = 13）之间的成对比较显示，编码DNA甲基转移酶的所有三个基因的表达增加了两到三倍。我们的数据表明DNA甲基转移酶在结直肠癌发生过程中发挥了相关作用。这种增加并没有被去甲基化成分MBD2的表达增强所抵消。因此，腺瘤-癌序列中的表观遗传调控可能是由甲基化活性增加而非去甲基化受抑制驱动的。
