Rhee I, Jair K W, Yen R W, Lengauer C, Herman J G, Kinzler K W, Vogelstein B, Baylin S B, Schuebel K E
The Johns Hopkins Oncology Center, and Johns Hopkins University School of Medicine, Baltimore, Maryland 21231, USA.
Nature. 2000 Apr 27;404(6781):1003-7. doi: 10.1038/35010000.
Hypermethylation is associated with the silencing of tumour susceptibility genes in several forms of cancer; however, the mechanisms responsible for this aberrant methylation are poorly understood. The prototypic DNA methyltransferase, DNMT1, has been widely assumed to be responsible for most of the methylation of the human genome, including the abnormal methylation found in cancers. To test this hypothesis, we disrupted the DNMT1 gene through homologous recombination in human colorectal carcinoma cells. Here we show that cells lacking DNMT1 exhibited markedly decreased cellular DNA methyltransferase activity, but there was only a 20% decrease in overall genomic methylation. Although juxtacentromeric satellites became significantly demethylated, most of the loci that we analysed, including the tumour suppressor gene p16INK4a, remained fully methylated and silenced. These results indicate that DNMT1 has an unsuspected degree of regional specificity in human cells and that methylating activities other than DNMT1 can maintain the methylation of most of the genome.
在多种癌症中，高甲基化与肿瘤易感基因的沉默有关；然而，导致这种异常甲基化的机制却知之甚少。人们普遍认为，典型的DNA甲基转移酶DNMT1负责人类基因组的大部分甲基化，包括癌症中发现的异常甲基化。为了验证这一假设，我们通过同源重组在人结肠癌细胞中破坏了DNMT1基因。我们在此表明，缺乏DNMT1的细胞表现出细胞DNA甲基转移酶活性显著降低，但总体基因组甲基化仅下降了20%。尽管近着丝粒卫星序列显著去甲基化，但我们分析的大多数位点，包括肿瘤抑制基因p16INK4a，仍保持完全甲基化并沉默。这些结果表明，DNMT1在人类细胞中具有出人意料的区域特异性，并且除DNMT1之外的甲基化活性可以维持大部分基因组的甲基化。
