An interplay of the base excision repair and mismatch repair pathways in active DNA demethylation.
An interplay of the base excision repair and mismatch repair pathways in active DNA demethylation.
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DOI：
10.1093/nar/gkw059
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发表时间：
2016-05-05
影响因子：
14.9
通讯作者：
Ishchenko AA
中科院分区：
文献类型：
--
作者：
Grin I;Ishchenko AA
哺乳动物中的主动DNA去甲基化（ADDM）通过泰特对5-甲基胞嘧啶（5 mC）的羟基化和/或AID/APOBEC家族酶的脱氨基作用而发生。通过碱基切除修复（BER）途径去除所得的5 mC衍生物。目前，尚不清楚细胞如何设法消除紧密间隔的5 mC残基，同时避免产生有毒BER中间体，以及替代DNA修复途径是否参与ADDM。非典型DNA错配修复（ncMMR）可以从DNA中去除烷基化和氧化的核苷酸。在这里，含有氧化性碱基损伤和甲基化位点的噬菌粒DNA被用来检查在小鼠和人的无细胞提取物中ADDM中各种DNA修复途径的参与。我们证明，除了短补丁BER，5-羟甲基尿嘧啶和尿嘧啶错配鸟嘌呤可以处理ncMMR和长补丁BER与伴随的远程5 mC残基的去除。此外，在相同的MMR切口/错配识别区域中存在多个错配以及BER介导的切口形成促进了熟练的ncMMR，导致在鼠细胞中表观遗传学沉默的报告基因的再活化。这些发现表明BER和ncMMR之间的合作，在消除多个错配，可能会发生在哺乳动物细胞在ADDM。
Active DNA demethylation (ADDM) in mammals occurs via hydroxylation of 5-methylcytosine (5mC) by TET and/or deamination by AID/APOBEC family enzymes. The resulting 5mC derivatives are removed through the base excision repair (BER) pathway. At present, it is unclear how the cell manages to eliminate closely spaced 5mC residues whilst avoiding generation of toxic BER intermediates and whether alternative DNA repair pathways participate in ADDM. It has been shown that non-canonical DNA mismatch repair (ncMMR) can remove both alkylated and oxidized nucleotides from DNA. Here, a phagemid DNA containing oxidative base lesions and methylated sites are used to examine the involvement of various DNA repair pathways in ADDM in murine and human cell-free extracts. We demonstrate that, in addition to short-patch BER, 5-hydroxymethyluracil and uracil mispaired with guanine can be processed by ncMMR and long-patch BER with concomitant removal of distant 5mC residues. Furthermore, the presence of multiple mispairs in the same MMR nick/mismatch recognition region together with BER-mediated nick formation promotes proficient ncMMR resulting in the reactivation of an epigenetically silenced reporter gene in murine cells. These findings suggest cooperation between BER and ncMMR in the removal of multiple mismatches that might occur in mammalian cells during ADDM.