小柯机器人

美国麻省理工学院Eliezer Calo和哥伦比亚大学Shan Zha研究团队合作有了新发现。他们揭示了DNA依赖性蛋白激酶催化亚基（DNA-PKcs）在核糖体RNA（rRNA）加工和造血过程中具有KU依赖性功能。该研究于2020年2月26日在线发表在《自然》杂志上。

研究人员使用小鼠模型发现DNA依赖性蛋白激酶（DNA-PK）在rRNA的生物发生和造血过程中具有意想不到的功能。表达无激酶活性的DNA-PKcs丢失了经典的非同源末端连接（cNHEJ）。但是，大多数既表达无激酶活性DNA-PKcs又缺乏肿瘤抑制因子TP53的小鼠会发生髓样疾病，然而先前证明的其他cNHEJ和TP53表达不足的小鼠则死于前B细胞淋巴瘤。DNA-PK自磷酸化DNA-PKcs，这是其最佳表征底物。

在T2609而非S2056位点处阻断DNA-PKcs的磷酸化，导致18S rRNA加工中KU依赖性缺陷、破坏了造血细胞的整体蛋白合成并导致小鼠骨髓衰竭。KU促进DNA-PKcs在多种细胞RNA上的组装，包括U3小核仁RNA，这对于18S rRNA的加工至关重要。U3激活纯化的DNA-PK，并在T2609位点引起DNA-PKcs的磷酸化。DNA-PK，而非其他cNHEJ因子，以rRNA依赖性方式存在于核仁中，并与小亚基加工组共纯化。该研究数据表明，在核糖体生物发生过程中，DNA-PK具有RNA依赖而cNHEJ非依赖的功能，这需要DNA-PKcs的激酶活性及其在T2609位点的磷酸化。

据介绍，DNA依赖性蛋白激酶是经典的非同源末端连接因子，其由KU异二聚体和催化亚基（DNA-PKcs）组成。KU结合到DNA末端，启动cNHEJ、招募并激活DNA-PKcs。KU也与RNA结合，但是尚不清楚这种相互作用在哺乳动物中的相关性。

附：英文原文

Title: DNA-PKcs has KU-dependent function in rRNA processing and haematopoiesis

Author: Zhengping Shao, Ryan A. Flynn, Jennifer L. Crowe, Yimeng Zhu, Jialiang Liang, Wenxia Jiang, Fardin Aryan, Patrick Aoude, Carolyn R. Bertozzi, Verna M. Estes, Brian J. Lee, Govind Bhagat, Shan Zha, Eliezer Calo

Issue&Volume: 2020-02-26

Abstract: The DNA-dependent protein kinase (DNA-PK), which comprises the KU heterodimer and a catalytic subunit (DNA-PKcs), is a classical non-homologous end-joining (cNHEJ) factor1. KU binds to DNA ends, initiates cNHEJ, and recruits and activates DNA-PKcs. KU also binds to RNA, but the relevance of this interaction in mammals is unclear. Here we use mouse models to show that DNA-PK has an unexpected role in the biogenesis of ribosomal RNA (rRNA) and in haematopoiesis. The expression of kinase-dead DNA-PKcs abrogates cNHEJ2. However, most mice that both expressed kinase-dead DNA-PKcs and lacked the tumour suppressor TP53 developed myeloid disease, whereas all other previously characterized mice deficient in both cNHEJ and TP53 expression succumbed to pro-B cell lymphoma3. DNA-PK autophosphorylates DNA-PKcs, which is its best characterized substrate. Blocking the phosphorylation of DNA-PKcs at the T2609 cluster, but not the S2056 cluster, led to KU-dependent defects in 18S rRNA processing, compromised global protein synthesis in haematopoietic cells and caused bone marrow failure in mice. KU drives the assembly of DNA-PKcs on a wide range of cellular RNAs, including the U3 small nucleolar RNA, which is essential for processing of 18S rRNA4. U3 activates purified DNA-PK and triggers phosphorylation of DNA-PKcs at T2609. DNA-PK, but not other cNHEJ factors, resides in nucleoli in an rRNA-dependent manner and is co-purified with the small subunit processome. Together our data show that DNA-PK has RNA-dependent, cNHEJ-independent functions during ribosome biogenesis that require the kinase activity of DNA-PKcs and its phosphorylation at the T2609 cluster.

DOI: 10.1038/s41586-020-2041-2

Source: 

Nature：《自然》，创刊于1869年。隶属于施普林格·自然出版集团，最新IF：69.504
官方网址：http://www.nature.com/
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