Institute of Clinical Chemistry and Laboratory Diagnostics, Heinrich-Heine-University, Med. Faculty, D-40225 Düsseldorf, Germany, Laboratory of Molecular Pharmacology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA, Center for Physiology and Pathophysiology, Institute of Vegetative Physiology, University of Köln, D-50931 Köln, Germany, Center for Molecular Medicine Cologne, University of Köln, D-50931 Köln, Germany, Cologne Excellence Cluster on Cellular Stress Responses in Aging-associated Diseases, University of Köln, D-50931 Köln, Germany, Department of Pediatrics, Med. Faculty, University of Köln, D-50931 Köln, Germany and Center for Microbiology and Virology, Institute of Virology, Heinrich-Heine-University, Med. Faculty, D-40225 Düsseldorf, Germany.
Nucleic Acids Res. 2013 Nov;41(21):9848-57. doi: 10.1093/nar/gkt768. Epub 2013 Aug 27.
Mitochondrial topoisomerase I is a genetically distinct mitochondria-dedicated enzyme with a crucial but so far unknown role in the homeostasis of mitochondrial DNA metabolism. Here, we present data suggesting a negative regulatory function in mitochondrial transcription or transcript stability. Deficiency or depletion of mitochondrial topoisomerase I increased mitochondrial transcripts, whereas overexpression lowered mitochondrial transcripts, depleted respiratory complexes I, III and IV, decreased cell respiration and raised superoxide levels. Acute depletion of mitochondrial topoisomerase I triggered neither a nuclear mito-biogenic stress response nor compensatory topoisomerase IIβ upregulation, suggesting the concomitant increase in mitochondrial transcripts was due to release of a local inhibitory effect. Mitochondrial topoisomerase I was co-immunoprecipitated with mitochondrial RNA polymerase. It selectively accumulated and rapidly exchanged at a subset of nucleoids distinguished by the presence of newly synthesized RNA and/or mitochondrial RNA polymerase. The inactive Y559F-mutant behaved similarly without affecting mitochondrial transcripts. In conclusion, mitochondrial topoisomerase I dampens mitochondrial transcription and thereby alters respiratory capacity. The mechanism involves selective association of the active enzyme with transcriptionally active nucleoids and a direct interaction with mitochondrial RNA polymerase. The inhibitory role of topoisomerase I in mitochondrial transcription is strikingly different from the stimulatory role of topoisomerase I in nuclear transcription.
线粒体拓扑异构酶 I 是一种具有独特遗传特性的线粒体专用酶，它在维持线粒体 DNA 代谢的动态平衡中起着至关重要但目前尚不清楚的作用。在这里，我们提供的数据表明其在线粒体转录或转录稳定性中具有负调控功能。线粒体拓扑异构酶 I 的缺乏或耗竭会增加线粒体转录物，而过表达则会降低线粒体转录物、耗竭呼吸复合物 I、III 和 IV，降低细胞呼吸并增加超氧化物水平。急性耗尽线粒体拓扑异构酶 I 既不会触发核线粒体生物生成应激反应，也不会代偿性地上调拓扑异构酶 IIβ，这表明线粒体转录物的同时增加是由于局部抑制作用的释放。线粒体拓扑异构酶 I 与线粒体 RNA 聚合酶共同免疫沉淀。它选择性地积累并在一组由新合成的 RNA 和/或线粒体 RNA 聚合酶存在的核区快速交换。无活性的 Y559F 突变体没有影响线粒体转录物，但行为类似。总之，线粒体拓扑异构酶 I 抑制线粒体转录，从而改变呼吸能力。该机制涉及活性酶与转录活性核区的选择性结合，以及与线粒体 RNA 聚合酶的直接相互作用。拓扑异构酶 I 在线粒体转录中的抑制作用与拓扑异构酶 I 在核转录中的刺激作用明显不同。
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