CLU1: a regulator of mitochondrial distribution and translation of nuclear-encoded mitochondrial proteins

线粒体是重要的细胞器，与三磷酸腺苷的产生、关键的代谢过程、钙缓冲和细胞死亡有关。线粒体在细胞中的分布对它们的功能至关重要，特别是在像神经元这样的高度极化的细胞中，线粒体会长途旅行，到达轴突和树突中对ATP需求较高的区域。绝大多数线粒体蛋白是在胞浆中合成的，并在细胞器中输入。这提出了一个重要的问题，核编码的线粒体蛋白的合成是否发生在靠近细胞器的地方。我们已经确定哺乳动物CLU1是一个候选分子，既调节核编码的线粒体蛋白的翻译，也调节线粒体的分布。CLU1在从拟南芥到人类的进化过程中高度保守。在植物、酵母和果蝇中，CLU1基因敲除导致靠近细胞核的线粒体聚集。我们有证据表明，哺乳动物CLU1可以类似地影响细胞中线粒体的分布。此外，我们发现CLU1是一种核糖体相关蛋白，直接与RNA结合。此外，CLU1与Astrin-Skap复合体相互作用，Astrin-Skap复合体与有丝分裂过程中的动粒分离有关。一个吸引人的假说是，CLU1可能调节核编码的线粒体蛋白的翻译，或者调节靠近线粒体的核糖核粒的子集的运输，从而影响线粒体的分布。在这里，我们建议：1)通过识别与CLU1结合的靶mRNAs并进行多聚体分析以评估它们在不同条件下的翻译效率，来研究CLU1在核编码线粒体蛋白翻译调控中的可能作用；2)确定CLU1与Astrin-Skap复合体相互作用的作用；3)评估CLU1敲除在体内不同组织中的生理后果。

Mitochondria are essential organelles, implicated in ATP production, crucial metabolic processes, calcium buffering, and cell death. Mitochondria distribution in cells is crucial for their function, especially in highly polarized cells as neurons, where mitochondria travel long distances to reach regions of high ATP demand in axons and dendrites. The vast majority of mitochondrial proteins are synthesized in the cytosol and imported in the organelle. This raises the important question whether synthesis of nuclear-encoded mitochondrial proteins occurs close to the organelle. We have identified mammalian CLU1 as a candidate molecule regulating both translation of nuclear encoded mitochondrial proteins and mitochondrial distribution. CLU1 is highly conserved during evolution, from Arabidopsis thaliana to humans. In plant, yeast, and Drosophila melanogaster, CLU1 knock-out leads to clustering of mitochondria close to the nucleus. We have evidence that mammalian CLU1 can similarly affect mitochondrial distribution in cells. Moreover, we find that CLU1 is a ribosomal-associated protein, which directly binds RNA. In addition, CLU1 interacts with the astrin-SKAP complex, which is implicated in kinetochore separation during mitosis. An attractive hypothesis is that CLU1 might regulate the translation of nuclear-encoded mitochondrial proteins, or the transport of a subset of ribonucleoparticles close to mitochondria, thereby affecting mitochondrial distribution. Here we propose to: 1) investigate a possible the role of CLU1 in regulation of translation of nuclear-encoded mitochondrial proteins, by identifying target mRNAs which are bound by CLU1 and performing polysome profiling to assess the efficiency of their translation under different conditions; 2) identify the role of CLU1 interaction with the astrin-SKAP complex; 3) assess the physiological consequences of CLU1 knock-out in vivo in different tissues of the mouse.