Chen Taiping, Hevi Sarah, Gay Frédérique, Tsujimoto Naomi, He Timothy, Zhang Bailin, Ueda Yoshihide, Li En
Epigenetics Program, Novartis Institutes for Biomedical Research, 250 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
Nat Genet. 2007 Mar;39(3):391-6. doi: 10.1038/ng1982. Epub 2007 Feb 18.
Studies have shown that DNA (cytosine-5-)-methyltransferase 1 (DNMT1) is the principal enzyme responsible for maintaining CpG methylation and is required for embryonic development and survival of somatic cells in mice. The role of DNMT1 in human cancer cells, however, remains highly controversial. Using homologous recombination, here we have generated a DNMT1 conditional allele in the human colorectal carcinoma cell line HCT116 in which several exons encoding the catalytic domain are flanked by loxP sites. Cre recombinase-mediated disruption of this allele results in hemimethylation of approximately 20% of CpG-CpG dyads in the genome, coupled with activation of the G2/M checkpoint, leading to arrest in the G2 phase of the cell cycle. Although cells gradually escape from this arrest, they show severe mitotic defects and undergo cell death either during mitosis or after arresting in a tetraploid G1 state. Our results thus show that DNMT1 is required for faithfully maintaining DNA methylation patterns in human cancer cells and is essential for their proliferation and survival.
研究表明，DNA（胞嘧啶-5-）-甲基转移酶1（DNMT1）是负责维持CpG甲基化的主要酶，是小鼠胚胎发育和体细胞存活所必需的。然而，DNMT1在人类癌细胞中的作用仍极具争议。在此，我们利用同源重组在人结肠癌细胞系HCT116中产生了一个DNMT1条件等位基因，其中几个编码催化结构域的外显子两侧为loxP位点。Cre重组酶介导的该等位基因的破坏导致基因组中约20%的CpG-CpG二联体发生半甲基化，同时激活G2/M检查点，导致细胞周期在G2期停滞。尽管细胞逐渐从这种停滞中逃脱，但它们表现出严重的有丝分裂缺陷，并在有丝分裂期间或在四倍体G1状态停滞之后发生细胞死亡。因此，我们的结果表明，DNMT1是人类癌细胞中忠实地维持DNA甲基化模式所必需的，对其增殖和存活至关重要。
