Olivera Harris Maite, Kallenberger Lia, Artola Borán Mariela, Enoiu Milica, Costanzo Vincenzo, Jiricny Josef
Institute of Molecular Cancer Research, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland; Department of Biology, Swiss Federal Institute of Technology (ETH), Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.
Institute of Molecular Cancer Research, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.
DNA Repair (Amst). 2015 Apr;28:1-7. doi: 10.1016/j.dnarep.2015.01.014. Epub 2015 Feb 4.
The cytotoxicity of SN1-type alkylating agents such as N-methyl-N'-nitrosourea (MNU), N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), or the cancer chemotherapeutics temozolomide, dacarbazine and streptozotocin has been ascribed to the persistence of O(6)-methylguanine ((me)G) in genomic DNA. One hypothesis posits that (me)G toxicity is caused by futile attempts of the mismatch repair (MMR) system to process (me)G/C or (me)G/T mispairs arising during replication, while an alternative proposal suggests that the latter lesions activate DNA damage signaling, cell cycle arrest and apoptosis directly. Attempts to elucidate the molecular mechanism of (me)G-induced cell killing in vivo have been hampered by the fact that the above reagents induce several types of modifications in genomic DNA, which are processed by different repair pathways. In contrast, defined substrates studied in vitro did not undergo replication. We set out to re-examine this phenomenon in replication-competent Xenopus laevis egg extracts, using either phagemid substrates containing a single (me)G residue, or methylated sperm chromatin. Our findings provide further support for the futile cycling hypothesis.
诸如N-甲基-N'-亚硝基脲（MNU）、N-甲基-N'-硝基-N-亚硝基胍（MNNG）等SN1型烷基化剂，或癌症化疗药物替莫唑胺、达卡巴嗪和链脲佐菌素的细胞毒性，已归因于基因组DNA中O(6)-甲基鸟嘌呤（(me)G）的持续存在。一种假说是，(me)G毒性是由错配修复（MMR）系统徒劳地尝试处理复制过程中出现的(me)G/C或(me)G/T错配所致，而另一种观点则认为，后一种损伤直接激活DNA损伤信号传导、细胞周期停滞和细胞凋亡。由于上述试剂会在基因组DNA中诱导多种类型的修饰，且这些修饰由不同的修复途径处理，因此在体内阐明(me)G诱导细胞杀伤的分子机制的尝试受到了阻碍。相比之下，体外研究的特定底物不会进行复制。我们着手使用含有单个(me)G残基的噬菌粒底物或甲基化精子染色质，在具有复制能力的非洲爪蟾卵提取物中重新研究这一现象。我们的发现为徒劳循环假说提供了进一步的支持。
