Human AP-endonuclease (Ape1) activity on telomeric G4 structures is modulated by acetylatable lysine residues in the N-terminal sequence
Human AP-endonuclease (Ape1) activity on telomeric G4 structures is modulated by acetylatable lysine residues in the N-terminal sequence
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DOI：
10.1016/j.dnarep.2018.11.010
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发表时间：
2019-01-01
期刊：
影响因子：
3.8
通讯作者：
Tell, Gianluca
中科院分区：
文献类型：
--
作者：
Burra, Silvia;Marasco, Daniela;Tell, Gianluca
端粒稳定性的丧失是癌细胞的一个特征。暴露的端粒容易发生异常的末端连接反应，导致染色体融合和易位。人类端粒含有重复的TTAGGG元件，其中3‘暴露的链可能采用G-四链(G4)结构。端粒富含鸟嘌呤的区域是氧化形成8-氧鸟嘌呤的热点，8-氧鸟嘌呤是一种通过碱基切除修复(BER)途径处理的损伤。这一途径的一个关键角色是APE1，它是处理基本位点的主要人类内切酶。最近的证据表明APE1在端粒生理学中起着重要的作用，但调控APE1在G4-端粒序列上的酶活性的分子细节尚不清楚。通过体外实验，我们证明了APE1可以结合和处理不同的G4结构，并且这种相互作用涉及蛋白质的非结构化N-末端序列中存在的特定的乙酰化赖氨酸残基(即K-27/31/32/35)。APE1对G4结构中碱性位点的切割取决于DNA的构象或损伤的位置，以及蛋白质与核酸之间的静电相互作用。此外，模拟乙酰化蛋白的APE1突变体显示出对基本位点的切割活性增加。我们发现，核磷蛋白(NPM1)与APE1的N端序列结合，在基本的G4结构中起到调节端粒长度和APE1活性的作用。因此，APE1N-末端序列是调节G4-端粒序列上酶活性的重要中继点，而特定的乙酰化赖氨酸残基构成端粒酶活性动态的关键调控位点。
Loss of telomeres stability is a hallmark of cancer cells. Exposed telomeres are prone to aberrant end joining reactions leading to chromosomal fusions and translocations. Human telomeres contain repeated TTAGGG elements, in which the 3' exposed strand may adopt a G-quadruplex (G4) structure. The guanine-rich regions of telomeres are hotspots for oxidation forming 8-oxoguanine, a lesion that is handled by the base excision repair (BER) pathway. One key player of this pathway is Ape1, the main human endonuclease processing abasic sites. Recent evidences showed an important role for Ape1 in telomeric physiology, but the molecular details regulating Ape1 enzymatic activities on G4-telomeric sequences are lacking. Through a combination of in vitro assays, we demonstrate that Ape1 can bind and process different G4 structures and that this interaction involves specific acetylatable lysine residues (i.e. K-27/31/32/35) present in the unstructured N-terminal sequence of the protein. The cleavage of an abasic site located in a G4 structure by Ape1 depends on the DNA conformation or the position of the lesion and on electrostatic interactions between the protein and the nucleic acids. Moreover, Ape1 mutants mimicking the acetylated protein display increased cleavage activity for abasic sites. We found that nucleophosmin (NPM1), which binds the N-terminal sequence of Ape1, plays a role in modulating telomere length and Ape1 activity at abasic G4 structures. Thus, the Ape1 N-terminal sequence is an important relay site for regulating the enzyme's activity on G4-telomeric sequences, and specific acetylatable lysine residues constitute key regulatory sites of Ape1 enzymatic activity dynamics at telomeres.