Schaefer Matthias, Hagemann Sabine, Hanna Katharina, Lyko Frank
Division of Epigenetics, German Cancer Research Center, Heidelberg, Germany.
Cancer Res. 2009 Oct 15;69(20):8127-32. doi: 10.1158/0008-5472.CAN-09-0458. Epub 2009 Oct 6.
The cytosine analogues azacytidine and decitabine are currently being developed as drugs for epigenetic cancer therapy. Although various studies have shown that both drugs are effective in inhibiting DNA methylation, it has also become clear that their mode of action is not limited to DNA demethylation. Because azacytidine is a ribonucleoside, the primary target of this drug may be cellular RNA rather than DNA. We have now analyzed the possibility that azacytidine inhibits the RNA methyltransferase DNMT2. We found that DNMT2 is variably expressed in human cancer cell lines. RNA bisulfite sequencing showed that azacytidine, but not decitabine, inhibits cytosine 38 methylation of tRNA(Asp), a major substrate of DNMT2. Azacytidine caused a substantially stronger effect than decitabine on the metabolic rate of all the cancer cell lines tested, consistent with an effect of this drug on RNA metabolism. Of note, drug-induced loss of RNA methylation seemed specific for DNMT2 target sites because we did not observe any significant demethylation at sites known to be methylated by other RNA methyltransferases. Our results uncover a novel and quantifiable drug activity of azacytidine and raise the possibility that tRNA hypomethylation might contribute to patient responses.
胞嘧啶类似物阿扎胞苷和地西他滨目前正被开发用作表观遗传癌症治疗药物。尽管各种研究表明这两种药物在抑制DNA甲基化方面均有效，但它们的作用方式似乎并不局限于DNA去甲基化。由于阿扎胞苷是一种核糖核苷，该药物的主要靶点可能是细胞RNA而非DNA。我们现在分析了阿扎胞苷抑制RNA甲基转移酶DNMT2的可能性。我们发现DNMT2在人类癌细胞系中表达各异。RNA亚硫酸氢盐测序表明，阿扎胞苷而非地西他滨抑制了DNMT2的主要底物tRNA（Asp）的胞嘧啶38甲基化。阿扎胞苷对所有测试癌细胞系代谢率的影响比地西他滨显著更强，这与该药物对RNA代谢的影响一致。值得注意的是，药物诱导的RNA甲基化缺失似乎对DNMT2靶点具有特异性，因为我们在已知被其他RNA甲基转移酶甲基化的位点未观察到任何显著的去甲基化。我们的结果揭示了阿扎胞苷一种新的可量化的药物活性，并增加了tRNA低甲基化可能影响患者反应的可能性。
