5-fluorouracil is efficiently removed from DNA by the base excision and mismatch repair systems
5-fluorouracil is efficiently removed from DNA by the base excision and mismatch repair systems
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DOI：
10.1053/j.gastro.2007.09.003
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发表时间：
2007-12-01
期刊：
影响因子：
29.4
通讯作者：
Jiricny, Josef
中科院分区：
文献类型：
--
作者：
Fischer, Franziska;Baerenfaller, Katja;Jiricny, Josef
背景与目的：5-氟尿嘧啶（FU）是结肠癌化疗的支柱之一。虽然它是作为胸苷酸合酶抑制剂开发的，但其细胞毒性也与其掺入 RNA 相关。令人惊讶的是，虽然 FU 也掺入 DNA 中，但人们对其在核酸中的代谢知之甚少。方法：使用人类细胞提取物和含有与腺嘌呤配对或与鸟嘌呤错配的单个 FU 残基的环状 DNA 底物，我们研究了 FU 加工的酶学。结果：在带切口的圆形基质中，FU/G 错配可通过错配修复 (MMR) 有效修复。在共价闭合环状 DNA 中，对 MMR 具有抵抗力，FU/G 修复由胸腺嘧啶 DNA 糖基化酶或尿嘧啶 DNA 糖基化酶启动，而 FU/A 对则由 UNG 处理。甲基化 CpG 结合域 4 蛋白和单链选择性单功能尿嘧啶 DNA 糖基化酶 1 并未检测到对 FU 去除有贡献；然而，由于这些重组酶分别处理寡核苷酸底物中的 FU/G 和 FU/A，因此它们也可能参与 VIVO 中的 FU 代谢。结论：FU 加工过程中 MMR 和 DNA 糖基化酶的功能冗余应确保药物在干扰重要的 DNA 代谢过程（例如转录）之前从 DNA 中有效去除。然而，在 FU 处理的细胞中，核苷酸池中的胸腺嘧啶被耗尽。因此，修复合成可能会受到抑制，并在 DNA 中留下细胞毒性缺口或断裂。而且，从DNA上去除的FU和/或5-氟尿嘧啶-2'-脱氧尿苷-5'-三磷酸会增加药物的细胞内浓度，从而加剧其细胞毒性。
Background & Aims: 5-Fluorouracil (FU) is one of the mainstays of colon cancer chemotherapy. Although developed as an inhibitor of thymidylate synthase, its cytotoxicity has been linked also to its incorporation into RNA. Surprisingly, although FU is incorporated also into DNA, little is known about its metabolism in this nucleic acid. Methods: Using extracts of human cells and circular DNA substrates containing a single FU residue either paired with adenine or mispaired with guanine, we studied the enzymology of FU processing. Results: In nicked circular substrates, FU/G mispairs were efficiently repaired by mismatch repair (MMR). In covalently closed circular DNA, which is refractory to MMR, FU/G repair was initiated by either thymine-DNA glycosylase or uracil-DNA glycosylase, whereas FU/A pairs were processed by UNG. Methylated CpG binding domain 4 protein and single-strand selective monofunctional uracil-DNA glycosylase 1 did not detectably contribute to FU removal; however, because these recombinant enzymes process FU/G and FU/A in oligonucleotide substrates, respectively, they too may be involved in FU metabolism in VIVO. Conclusions: The functional redundancy of MMR and DNA glycosylases in FU processing should ensure that the drug is efficiently removed from DNA before it can interfere with essential DNA metabolic processes, such as transcription. However, in FU-treated cells, the nucleotide pools are depleted of thymine. The repair synthesis might thus be inhibited and leave cytotoxic gaps or breaks in DNA. Moreover, FU and/or 5-fluorouracil-2'-deoxyuridine-5'-triphosphate removed from DNA will increase the intracellular concentration of the drug and thus exacerbate its cytotoxicity.