WRAP53 is essential for Cajal body formation and for targeting the survival of motor neuron complex to Cajal bodies.
WRAP53 is essential for Cajal body formation and for targeting the survival of motor neuron complex to Cajal bodies.
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DOI：
10.1371/journal.pbio.1000521
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发表时间：
2010-11-02
期刊：
影响因子：
9.8
通讯作者：
Farnebo M
中科院分区：
文献类型：
--
作者：
Mahmoudi S;Henriksson S;Weibrecht I;Smith S;Söderberg O;Strömblad S;Wiman KG;Farnebo M
WRAP53 蛋白调节 Cajal 小体（核亚细胞器）的形成和维持，并指导核因子向 Cajal 小体的募集。 WRAP53 基因产生调节 p53 的 p53 反义转录物。该基因还编码一种蛋白质，可将小卡哈尔体特异性 RNA 引导至卡哈尔体。卡哈尔体是参与多种功能的核细胞器，例如处理对剪接很重要的核糖核蛋白。在这里，我们确定 WRAP53 蛋白是卡哈尔体维持和指导运动神经元 (SMN) 复合体在卡哈尔体中存活的重要因素。通过RNA干扰和免疫荧光，我们表明没有WRAP53，卡哈尔小体就会崩溃，并且不能形成新的卡哈尔小体。通过免疫沉淀，我们发现WRAP53与Cajal体标记coilin、剪接调节蛋白SMN和核输入受体importinβ相关，并且WRAP53对于SMN-coilin和SMN-importinβ之间的复合物形成至关重要。此外，WRAP53 的消耗导致 SMN 在细胞质中积累，并阻止 SMN 复合物到达卡哈尔体。因此，WRAP53 介导 SMN 和相关蛋白之间的相互作用，这对于 SMN 的核靶向以及 SMN 复合物随后定位到卡哈尔体非常重要。此外，我们检测到脊髓性肌萎缩症患者的 WRAP53-SMN 结合减少，脊髓性肌萎缩症是全球婴儿死亡的主要原因，由 SMN1 突变引起。这表明 WRAP53 介导的 SMN 运输的丧失会导致脊髓性肌萎缩。卡哈尔小体是 100 多年前由圣地亚哥·拉蒙·卡哈尔 (Santiago Ramón y Cajal) 发现的，是在增殖细胞和神经元的细胞核中发现的亚细胞器。它们涉及多种核功能，包括核糖核蛋白成熟、剪接体形成、组蛋白 mRNA 加工、RNA 聚合酶组装、端粒酶生物发生和组蛋白基因转录。将相关分子集中在卡哈尔体内可能有助于提高特定核功能的效率。在这里，我们确定 WRAP53 蛋白是卡哈尔体维持和指导剪接调节蛋白“运动神经元存活”（SMN）复合物与卡哈尔体的重要因素。我们证明WRAP53是Cajal小体的组成部分，并且WRAP53的敲除会破坏现有的Cajal小体并阻止新Cajal小体的形成。从机制上讲，我们发现WRAP53通过介导SMN、importinβ和coilin之间的相互作用，将SMN复合物从细胞质募集到卡哈尔小体。最后，我们报告了脊髓性肌萎缩症患者中 WRAP53-SMN 结合缺陷，表明其在这种病理学中发挥了作用。这项研究不仅揭示了WRAP53蛋白的新功能，而且增加了我们对卡哈尔小体形成和因子招募到卡哈尔小体背后的分子机制的理解。
The WRAP53 protein regulates the formation and maintenance of Cajal bodies (nuclear sub-organelles), as well as directs the recruitment of nuclear factors to Cajal bodies. The WRAP53 gene gives rise to a p53 antisense transcript that regulates p53. This gene also encodes a protein that directs small Cajal body–specific RNAs to Cajal bodies. Cajal bodies are nuclear organelles involved in diverse functions such as processing ribonucleoproteins important for splicing. Here we identify the WRAP53 protein as an essential factor for Cajal body maintenance and for directing the survival of motor neuron (SMN) complex to Cajal bodies. By RNA interference and immunofluorescence we show that Cajal bodies collapse without WRAP53 and that new Cajal bodies cannot be formed. By immunoprecipitation we find that WRAP53 associates with the Cajal body marker coilin, the splicing regulatory protein SMN, and the nuclear import receptor importinβ, and that WRAP53 is essential for complex formation between SMN–coilin and SMN–importinβ. Furthermore, depletion of WRAP53 leads to accumulation of SMN in the cytoplasm and prevents the SMN complex from reaching Cajal bodies. Thus, WRAP53 mediates the interaction between SMN and associated proteins, which is important for nuclear targeting of SMN and the subsequent localization of the SMN complex to Cajal bodies. Moreover, we detect reduced WRAP53–SMN binding in patients with spinal muscular atrophy, which is the leading genetic cause of infant mortality worldwide, caused by mutations in SMN1. This suggests that loss of WRAP53-mediated SMN trafficking contributes to spinal muscular atrophy. Cajal bodies, discovered more than 100 years ago by Santiago Ramón y Cajal, are sub-organelles found in the nucleus of proliferative cells and neurons. They have been implicated in a variety of nuclear functions including ribonucleoprotein maturation, spliceosome formation, histone mRNA processing, RNA polymerase assembly, telomerase biogenesis, and histone gene transcription. Concentrating relevant molecules within Cajal bodies may serve to increase the efficiency of specific nuclear functions. Here we identify the WRAP53 protein as an essential factor for Cajal body maintenance and for directing the splicing regulatory protein “survival of motor neuron” (SMN) complex to Cajal bodies. We show that WRAP53 is a constitutive component of Cajal bodies, and that knockdown of WRAP53 disrupts existing Cajal bodies and prevents formation of new Cajal bodies. Mechanistically, we find that WRAP53 recruits the SMN complex from the cytoplasm to Cajal bodies by mediating interactions between SMN, importinβ, and coilin. Finally, we report deficient WRAP53–SMN binding in patients with spinal muscular atrophy, suggesting a role in this pathology. This study not only reveals new functions of the WRAP53 protein, but also increases our understanding of the molecular mechanism behind Cajal body formation and recruitment of factors to Cajal bodies.
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