Kasashima Katsumi, Sumitani Megumi, Satoh Masaaki, Endo Hitoshi
Department of Biochemistry, Jichi Medical University, Shimotsuke, Tochigi, Japan.
Exp Cell Res. 2008 Mar 10;314(5):988-96. doi: 10.1016/j.yexcr.2008.01.005. Epub 2008 Jan 16.
Mitochondrial prohibitin (PHB) proteins have diverse functions, such as the regulation of apoptosis and the maintenance of mitochondrial morphology. In this study, we clarified a novel mitochondrial function of PHB1 that regulates the organization and maintenance of mitochondrial DNA (mtDNA). In PHB1-knockdown cells, we found that mtDNA is not stained by fluorescent dyes, such as ethidium bromide and PicoGreen, although the mitochondrial membrane potential still maintains. We also demonstrated that mtDNA, which is predominantly found in the NP-40-insoluble fraction when isolated from normal mitochondria, is partially released into the soluble fraction when isolated from PHB1-knockdown cells, indicating that the organization of the mitochondrial nucleoids has been altered. Furthermore, we found that PHB1 regulates copy number of mtDNA by stabilizing TFAM protein, a known protein component of the mitochondrial nucleoids. However, TFAM does not affect the organization of mtDNA as observed in PHB1-knockdown cells. Taken together, these results demonstrate that PHB1 maintains the organization and copy number of the mtDNA through both TFAM-independent and -dependent pathways.
线粒体抑制素（PHB）蛋白具有多种功能，如调节细胞凋亡和维持线粒体形态。在本研究中，我们阐明了PHB1一种新的线粒体功能，即调节线粒体DNA（mtDNA）的组织和维持。在PHB1敲低的细胞中，我们发现尽管线粒体膜电位仍保持，但mtDNA不能被诸如溴化乙锭和PicoGreen等荧光染料染色。我们还证明，从正常线粒体分离时主要存在于NP - 40不溶性部分的mtDNA，从PHB1敲低细胞中分离时会部分释放到可溶性部分，这表明线粒体核仁的组织已发生改变。此外，我们发现PHB1通过稳定线粒体核仁的已知蛋白质成分TFAM蛋白来调节mtDNA的拷贝数。然而，如在PHB1敲低细胞中所观察到的，TFAM并不影响mtDNA的组织。综上所述，这些结果表明PHB1通过不依赖TFAM和依赖TFAM的途径维持mtDNA的组织和拷贝数。
