Cilli Piera, Ventura Ilenia, Minoprio Anna, Meccia Ettore, Martire Alberto, Wilson Samuel H, Bignami Margherita, Mazzei Filomena
Department of Environment and Primary Prevention, Istituto Superiore di Sanità, 00161 Roma, Italy Department of Science, University Roma Tre, 00154 Roma, Italy.
Department of Environment and Primary Prevention, Istituto Superiore di Sanità, 00161 Roma, Italy.
Nucleic Acids Res. 2016 Jun 20;44(11):5190-203. doi: 10.1093/nar/gkw170. Epub 2016 Mar 14.
DNA trinucleotide repeat (TNR) expansion underlies several neurodegenerative disorders including Huntington's disease (HD). Accumulation of oxidized DNA bases and their inefficient processing by base excision repair (BER) are among the factors suggested to contribute to TNR expansion. In this study, we have examined whether oxidation of the purine dNTPs in the dNTP pool provides a source of DNA damage that promotes TNR expansion. We demonstrate that during BER of 8-oxoguanine (8-oxodG) in TNR sequences, DNA polymerase β (POL β) can incorporate 8-oxodGMP with the formation of 8-oxodG:C and 8-oxodG:A mispairs. Their processing by the OGG1 and MUTYH DNA glycosylases generates closely spaced incisions on opposite DNA strands that are permissive for TNR expansion. Evidence in HD model R6/2 mice indicates that these DNA glycosylases are present in brain areas affected by neurodegeneration. Consistent with prevailing oxidative stress, the same brain areas contained increased DNA 8-oxodG levels and expression of the p53-inducible ribonucleotide reductase. Our in vitro and in vivo data support a model where an oxidized dNTPs pool together with aberrant BER processing contribute to TNR expansion in non-replicating cells.
DNA三核苷酸重复序列（TNR）扩增是包括亨廷顿舞蹈症（HD）在内的多种神经退行性疾病的病因。氧化DNA碱基的积累及其碱基切除修复（BER）处理效率低下是导致TNR扩增的因素之一。在本研究中，我们研究了dNTP池中嘌呤dNTP的氧化是否提供了促进TNR扩增的DNA损伤来源。我们证明，在TNR序列中8-氧鸟嘌呤（8-氧代脱氧鸟苷，8-oxodG）的BER过程中，DNA聚合酶β（POLβ）可以掺入8-氧代鸟苷一磷酸（8-oxodGMP），形成8-oxodG:C和8-oxodG:A错配。OGG1和MUTYH DNA糖基化酶对它们的处理会在相反的DNA链上产生间距很近的切口，这有利于TNR扩增。HD模型R6/2小鼠的证据表明，这些DNA糖基化酶存在于受神经退行性变影响的脑区。与普遍存在的氧化应激一致，相同的脑区DNA 8-氧代鸟苷水平升高，p53诱导的核糖核苷酸还原酶表达增加。我们的体外和体内数据支持一个模型，即氧化的dNTP池与异常的BER处理共同导致非复制细胞中的TNR扩增。
