Nucleophosmin (NPM1), an abundant, nucleolar protein with multiple functions affecting cell homeostasis, has also been recently involved in DNA damage repair. The roles of NPM1 in different repair pathways remain however to be elucidated. NPM1 has been described to interact with APE1 (apurinic apyrimidinic endonuclease 1), a key enzyme of the base excision repair (BER) pathway, which could reflect a direct participation of NPM1 in this route. To gain insight into the possible role(s) of NPM1 in BER, we have explored the interplay between the subnuclear localization of both APE1 and NPM1, the in vitro interaction they establish, the effect of binding to abasic DNA on APE1 conformation, and the modulation by NPM1 of APE1 binding and catalysis on DNA. We have found that, upon oxidative damage, NPM1 is released from nucleoli and locates on patches throughout the chromatin, perhaps co-localizing with APE1, and that this traffic could be mediated by phosphorylation of NPM1 on T199. NPM1 and APE1 form a complex in vitro, involving, apart from the core domain, at least part of the linker region of NPM1, whereas the C-terminal domain is dispensable for binding, which explains that an AML leukemia-related NPM1 mutant with an unfolded C-terminal domain can bind APE1. APE1 interaction with abasic DNA stabilizes APE1 structure, as based on thermal unfolding. Moreover, our data suggest that NPM1, maybe by keeping APE1 in an "open" conformation, favours specific recognition of abasic sites on DNA, competing with off-target associations. Therefore, NPM1 might participate in BER favouring APE1 target selection as well as turnover from incised abasic DNA.

中文翻译：

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核糖蛋白与APE1的相互作用：深入了解DNA修复调控。

核糖蛋白（NPM1）是一种丰富的核仁蛋白，具有影响细胞稳态的多种功能，最近也参与了DNA损伤修复。NPM1在不同修复途径中的作用仍有待阐明。NPM1已被描述与APE1（紫杉嘧啶环己内切核酸酶1）相互作用，APE1是碱基切除修复（BER）途径的关键酶，可能反映NPM1直接参与该途径。为了深入了解NPM1在BER中的可能作用，我们探讨了APE1和NPM1的亚核定位，它们建立的体外相互作用，与无碱基DNA结合对APE1构象的影响，以及APE1构象之间的相互作用。 NPM1调节APE1结合并催化DNA。我们发现，在氧化损伤后，NPM1从核仁中释放出来，位于整个染色质上的膜片上，可能与APE1共定位，并且这种运输可能是由T199上NPM1的磷酸化介导的。NPM1和APE1在体外形成复合物，除了核心结构域外，还包含NPM1接头区域的至少一部分，而C末端结构域则可用于结合，这说明与AML白血病相关的NPM1突变体具有未折叠的C端结构域可以结合APE1。基于热展开，APE1与无碱基DNA的相互作用可稳定APE1的结构。此外，我们的数据表明，NPM1可能通过保持APE1处于“开放”构象，有利于DNA上无碱基位点的特异性识别，并与脱靶缔合竞争。因此，