Thymine DNA Glycosylase Can Rapidly Excise 5-Formylcytosine and 5-Carboxylcytosine POTENTIAL IMPLICATIONS FOR ACTIVE DEMETHYLATION OF CpG SITES
Thymine DNA Glycosylase Can Rapidly Excise 5-Formylcytosine and 5-Carboxylcytosine POTENTIAL IMPLICATIONS FOR ACTIVE DEMETHYLATION OF CpG SITES
复制标题
DOI：
10.1074/jbc.c111.284620
复制
发表时间：
2011-10-14
影响因子：
4.8
通讯作者：
Drohat, Alexander C.
中科院分区：
文献类型：
--
作者：
Maiti, Atanu;Drohat, Alexander C.
胸腺嘧啶DNA糖基化酶（TDG）从G. T错配中切除T，并被认为启动脱氨基的5-甲基胞嘧啶（mC）的碱基切除修复（BER）。最近的研究表明，TDG，包括其糖基化酶活性，是必不可少的主动DNA去甲基化和胚胎发育。这些和其他研究结果表明，主动去甲基化可能涉及通过脱氨酶进行的mC脱氨基作用，产生G. T错配，然后是TDG引发的BER。另一种提议是，去甲基化可能涉及mC反复氧化为5-羟甲基胞嘧啶（hmC），然后氧化为5-甲酰基胞嘧啶（fC）和5-羧基胞嘧啶（caC），由泰特（ten eleven translocation）酶介导，通过推定的脱羧酶将caC转化为C。我们以前的研究表明，TDG可以从DNA中切除fC和caC，这可能提供另一种潜在的去甲基化机制。我们在这里表明，TDG快速去除fC，具有比G. T错配更高的活性，并具有显著的caC切除活性，但它不能去除hmC。fC和caC（mC的氧化产物）的TDG切除与其从CpG背景中切除碱基的强特异性一致。我们的研究结果揭示了一个显着的新方面的特异性TDG，告知其催化机制，并建议TDG可以防止FC诱导的突变。结果还表明，一个新的潜在机制，主动DNA去甲基化，涉及TDG切除Tet-produced fC（或caC）和随后的BER。这种机制避免了脱羧酶的需要，并与TDG糖基化酶活性对主动去甲基化和胚胎发育至关重要的发现一致，因为涉及TDG切除脱氨基mC或hmC的机制也是如此。
Thymine DNA glycosylase (TDG) excises T from G.T mispairs and is thought to initiate base excision repair (BER) of deaminated 5-methylcytosine (mC). Recent studies show that TDG, including its glycosylase activity, is essential for active DNA demethylation and embryonic development. These and other findings suggest that active demethylation could involve mC deamination by a deaminase, giving a G.T mispair followed by TDG-initiated BER. An alternative proposal is that demethylation could involve iterative oxidation of mC to 5-hydroxymethylcytosine (hmC) and then to 5-formylcytosine (fC) and 5-carboxylcytosine (caC), mediated by a Tet (ten eleven translocation) enzyme, with conversion of caC to C by a putative decarboxylase. Our previous studies suggest that TDG could excise fC and caC from DNA, which could provide another potential demethylation mechanism. We show here that TDG rapidly removes fC, with higher activity than for G.T mispairs, and has substantial caC excision activity, yet it cannot remove hmC. TDG excision of fC and caC, oxidation products of mC, is consistent with its strong specificity for excising bases from a CpG context. Our findings reveal a remarkable new aspect of specificity for TDG, inform its catalytic mechanism, and suggest that TDG could protect against fC-induced mutagenesis. The results also suggest a new potential mechanism for active DNA demethylation, involving TDG excision of Tet-produced fC (or caC) and subsequent BER. Such a mechanism obviates the need for a decarboxylase and is consistent with findings that TDG glycosylase activity is essential for active demethylation and embryonic development, as are mechanisms involving TDG excision of deaminated mC or hmC.