Department of Pathology and Pathophysiology, Zhejiang University School of Medicine, Hangzhou 310058, China.
J Biol Chem. 2012 Apr 13;287(16):12622-33. doi: 10.1074/jbc.M111.313429. Epub 2012 Feb 24.
DNA polymerase η (Polη) implements translesion DNA synthesis but has low fidelity in replication. We have previously shown that Polη plays an important role in the genesis of nontargeted mutations at undamaged DNA sites in cells exposed to the carcinogen N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Here, we report that MNNG-induced Polη expression in an interferon regulatory factor 1 (IRF1)-dependent manner in human cells. Mutagenesis analysis showed that four critical residues (Arg-82, Cys-83, Asn-86, and Ser-87) located in the IRF family conserved DNA binding domain-helix α3 were involved in DNA binding and POLH transactivation by IRF1. Furthermore, Polη up-regulation induced by IRF1 was responsible for the increase of mutation frequency in a SupF shuttle plasmid replicated in the MNNG-exposed cells. Interestingly, IRF1 was acetylated by the histone acetyltransferase CBP in these cells. Lys → Arg substitution revealed that Lys-78 of helix α3 was the major acetylation site, and the IRF1-K78R mutation partially inhibited DNA binding and its transcriptional activity. Thus, we propose that IRF1 activation is responsible for MNNG-induced Polη up-regulation, which contributes to mutagenesis and ultimately carcinogenesis in cells.
DNA 聚合酶 η（Polη）实施跨损伤 DNA 合成，但在复制过程中的保真度较低。我们之前已经表明，Polη 在细胞暴露于致癌剂 N-甲基-N'-硝基-N-亚硝基胍（MNNG）时，在未受损 DNA 部位的非靶向突变的发生中起着重要作用。在这里，我们报告 MNNG 以干扰素调节因子 1（IRF1）依赖的方式诱导人细胞中的 Polη 表达。诱变分析表明，位于 IRF 家族保守 DNA 结合域-螺旋 α3 中的四个关键残基（Arg-82、Cys-83、Asn-86 和 Ser-87）参与了 DNA 结合和由 IRF1 介导的 POLH 转录激活。此外，IRF1 诱导的 Polη 上调导致 MNNG 暴露细胞中复制的 SupF 穿梭质粒的突变频率增加。有趣的是，IRF1 在这些细胞中被组蛋白乙酰转移酶 CBP 乙酰化。Lys → Arg 取代表明螺旋 α3 中的 Lys-78 是主要的乙酰化位点，并且 IRF1-K78R 突变部分抑制了 DNA 结合及其转录活性。因此，我们提出 IRF1 的激活负责 MNNG 诱导的 Polη 上调，这有助于细胞中的突变和最终致癌作用。
