Inactivation of Dnmt3b in mouse embryonic fibroblasts results in DNA hypomethylation, chromosomal instability, and spontaneous immortalization
Inactivation of Dnmt3b in mouse embryonic fibroblasts results in DNA hypomethylation, chromosomal instability, and spontaneous immortalization
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DOI：
10.1074/jbc.m413246200
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发表时间：
2005-05-06
影响因子：
4.8
通讯作者：
Li, E
中科院分区：
文献类型：
--
作者：
Dodge, JE;Okano, M;Li, E
DNA低甲基化是许多类型实体肿瘤的标志。然而，DNA低甲基化如何在肿瘤发生中起作用仍是个谜。在这项研究中，我们研究了靶向破坏DNA甲基转移酶DNMT3a和DNMT3b如何影响小鼠胚胎成纤维细胞(MEF)的生长。我们的研究得出了以下观察结果。1)Dnmt3b的结构性或条件性缺失，而不是DNMT3A，导致整个基因组中DNA甲基化的部分丧失，这表明除了主要的维持甲基转移酶Dnmt1外，Dnmt3b还是维持MEF细胞DNA甲基化所必需的。2)Dnmt3b缺陷的MEF细胞表现为非整倍体和多倍体，染色体断裂和融合。3)DNMT3b失活可导致MEF细胞提前衰老或自发永生化。4)原发和自发永生化的DNMT3b缺陷型MEF中，由于p53蛋白可被DNA损伤诱导，G(1)到S期检查点是完整的。有趣的是，即使在没有P53诱导的情况下，永生化的Dnmt3b缺陷的MEF中细胞周期蛋白依赖的激酶抑制物p21的蛋白水平也增加了。这些结果表明，DNA低甲基化可能导致基因组不稳定，进而导致Dnmt3b缺陷的MEF通过不依赖于p53的机制自发永生化或提前衰老。
DNA hypomethylation is a hallmark of many types of solid tumors. However, it remains elusive how DNA hypomethylation may contribute to tumorigenesis. In this study, we have investigated how targeted disruption of the DNA methyltransferases Dnmt3a and Dnmt3b affects the growth of mouse embryonic fibroblasts (MEFs). Our studies led to the following observations. 1) Constitutive or conditional deletion of Dnmt3b, but not Dnmt3a, resulted in partial loss of DNA methylation throughout the genome, suggesting that Dnmt3b, in addition to the major maintenance methyltransferase Dnmt1, is required for maintaining DNA methylation in MEF cells. 2) Dnmt3b-deficient MEF cells showed aneuploidy and polyploidy, chromosomal breaks, and fusions. 3) Inactivation of Dnmt3b resulted in either premature senescence or spontaneous immortalization of MEF cells. 4) The G(1) to S-phase checkpoint was intact in primary and spontaneously immortalized Dnmt3b-deficient MEFs because the p53 protein was inducible by DNA damage. Interestingly, protein levels of the cyclin-dependent kinase inhibitor p21 were increased in immortalized Dnmt3b-deficient MEFs even in the absence of p53 induction. These results suggest that DNA hypomethylation may induce genomic instability, which in turn leads to spontaneous immortalization or premature senescence of Dnmt3b-deficient MEFs via a p53-independent mechanism.