The base excision repair enzyme MED1 mediates DNA damage response to antitumor drugs and is associated with mismatch repair system integrity
The base excision repair enzyme MED1 mediates DNA damage response to antitumor drugs and is associated with mismatch repair system integrity
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DOI：
10.1073/pnas.2334585100
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发表时间：
2003-12-09
影响因子：
11.1
通讯作者：
Bellacosa, A
中科院分区：
文献类型：
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作者：
Cortellino, S;Turner, D;Bellacosa, A
甲基化剂的细胞毒性主要是由 DNA 中鸟嘌呤的 O-6 位甲基化形成 O-6-甲基鸟嘌呤 (O-6-meG) 引起的。 O-6-meG 可以在复制过程中引导胸腺嘧啶的错误掺入，产生 O-6-meG:T 错配。错配修复（MMR）系统对这些错配的识别导致细胞周期停滞和细胞凋亡。 MMR 还调节对其他抗肿瘤药物的敏感性。碱基切除修复 (BER) 酶 MED1（也称为 MBD4）与 MMR 蛋白 MLH1 相互作用。发现 MED1 对 O-6-meG:T 错配表现出胸腺嘧啶糖基化酶活性。为了检验这种活性的生物学意义，我们产生了 Med1 基因定向失活的小鼠，并制备了具有不同 Med1 基因型的小鼠胚胎成纤维细胞（MEF）。与野生型和杂合培养物不同，Med1(-/-)MEF 在用甲基化剂 N-甲基-ff-硝基-N-亚硝基鸟苷 (MNNG) 处理后未能经历 G(2)-M 细胞周期停滞和凋亡。铂化合物5-氟尿嘧啶和伊立替康也获得了类似的结果。与 MMR 缺陷细胞的情况一样，Medl(-/-) MEF 对 MNNG 的抗性是由于耐受机制所致，因为 DNA 损伤累积但不引起检查点激活。有趣的是，与 Med1(+/+) 和 Med1(+/-) MER 相比，Med1(-/-) MEF 中几种 MMR 蛋白的稳态量减少。我们得出结论，MED1 在对抗肿瘤药物的 DNA 损伤反应中具有额外的作用，并且与 MMR 系统的完整性相关。 MED1 缺陷（很像 MMR 缺陷）可能会损害 DNA 损伤诱导的细胞周期停滞和细胞凋亡。
Cytotoxicity of methylating agents is caused mostly by methylation of the O-6 position of guanine in DNA to form O-6-methylguanine (O-6-meG). O-6-meG can direct misincorporation of thymine during replication, generating O-6-meG:T mismatches. Recognition of these mispairs by the mismatch repair(MMR) system leads to cell cycle arrest and apoptosis. MMR also modulates sensitivity to other antitumor drugs. The base excision repair (BER) enzyme MED1 (also known as MBD4) interacts with the MMR protein MLH1. MED1 was found to exhibit thymine glycosylase activity on O-6-meG:T mismatches. To examine the biological significance of this activity, we generated mice with targeted inactivation of the Med1 gene and prepared mouse embryonic fibroblasts (MEF) with different Med1 genotype. Unlike wild-type and heterozygous cultures, Med1(-/-)MEF failed to undergo G(2)-M cell cycle arrest and apoptosis upon treatment with the methylating agent N-methyl-ff-nitro-N-nitrosoguanicline (MNNG). Similar results were obtained with platinum compounds' 5-fluorouracil and irinotecan. As is the case with MMR-defective cells, resistance of Medl(-/-) MEF to MNNG was due to a tolerance mechanism because DNA damage accumulated but did not elicit checkpoint activation. Interestingly, steady state amounts of several MMR proteins are reduced in Med1(-/-) MEF, in comparison with Med1(+/+) and Med1(+/-) MER We conclude that MED1 has an additional role in DNA damage response to antitumor agents and is associated with integrity of the MMR system. MED1 defects (much like MMR defects) may impair cell cycle arrest and apoptosis induced by DNA damage.