G:C sites distant from 8-oxo-7,8-dihydroguanine (GO, 8-hydroxyguanine) are frequently mutated when the lesion-bearing plasmid DNA is replicated in human cells with reduced Werner syndrome (WRN) protein. To detect the untargeted mutations preferentially, the oxidised guanine base was placed downstream of the reporter supF gene and the plasmid DNA was introduced into WRN-knockdown cells. The total mutant frequency seemed higher in the WRN-knockdown cells as compared to the control cells. Mutation analyses revealed that substitution mutations occurred at the G:C pairs of 5′-GpA-3′/5′-TpC-3′ sites, the preferred sequence for the apolipoprotein B mRNA-editing enzyme, catalytic polypeptide-like 3 (APOBEC3)-family cytosine deaminases, in the supF gene in both control and knockdown cells. These mutations were observed more frequently at G sites than C sites on the DNA strand where the GO base was originally located. This tendency was promoted by the knockdown of the WRN protein. The present results imply the possible involvement of APOBEC3-family cytosine deaminases in the action-at-a-distance (untargeted) mutations at G:C (or G) sites induced by GO and in cancer initiation by oxidative stress.

中文翻译：

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WRN敲低细胞中氧化鸟嘌呤诱导的5'-GpA-3'位点的远距离作用突变

当携带损伤的质粒 DNA 在具有减少的 Werner 综合征 (WRN) 蛋白的人类细胞中复制时，远离 8-oxo-7,8-dihydroguanine (GO, 8-hydroxyguanine) 的 G:C 位点经常发生突变。为了优先检测非靶向突变，将氧化的鸟嘌呤碱基置于报告基因 supF 基因的下游，并将质粒 DNA 引入 WRN 敲低细胞中。与对照细胞相比，WRN 敲低细胞中的总突变频率似乎更高。突变分析显示取代突变发生在 5'-GpA-3'/5'-TpC-3' 位点的 G:C 对，这是载脂蛋白 B mRNA 编辑酶催化多肽样 3 (APOBEC3 )-家族胞嘧啶脱氨酶，在对照和敲低细胞的 supF 基因中。这些突变在 GO 碱基最初所在的 DNA 链上的 G 位点比 C 位点更频繁地观察到。WRN 蛋白的敲低促进了这种趋势。目前的结果表明 APOBEC3 家族胞嘧啶脱氨酶可能参与 GO 诱导的 G:C（或 G）位点的远距离作用（非靶向）突变和氧化应激引发的癌症。