POLRMT regulates the switch between replication primer formation and gene expression of mammalian mtDNA.
POLRMT regulates the switch between replication primer formation and gene expression of mammalian mtDNA.
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DOI：
10.1126/sciadv.1600963
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发表时间：
2016-08
期刊：
影响因子：
13.6
通讯作者：
Larsson NG
中科院分区：
文献类型：
--
作者：
Kühl I;Miranda M;Posse V;Milenkovic D;Mourier A;Siira SJ;Bonekamp NA;Neumann U;Filipovska A;Polosa PL;Gustafsson CM;Larsson NG
在低POLRMT水平下，线粒体转录用于复制引物的形成优先于基因表达。线粒体通过其氧化磷酸化系统提供细胞能量，这需要核和线粒体基因组(MtDNA)编码的基因的协调表达。环状哺乳动物线粒体DNA的转录依赖于单个线粒体RNA聚合酶(POLRMT)。虽然转录启动过程已被熟知，但POLRMT是否也作为线粒体DNA复制的启动子还存在争议。在细胞核中，基因表达所需的RNA聚合酶没有这样的作用。在心脏中有条件地敲除Polrmt会导致严重的线粒体功能障碍，导致幼鼠的扩张性心肌病。我们进一步研究了POLRMT不同表达水平的分子后果，发现POLRMT是启动体内线粒体DNA复制的引物合成所必需的。此外，转录启动的引物形成优先于基因表达。令人惊讶的是，在Polrmt基因敲除小鼠中，线粒体转录因子A(TFAM)存在于一个无线粒体DNA的池中。尽管线粒体DNA严重枯竭，TFAM水平仍然保持不变，因此在没有POLRMT的情况下，TFAM可以防止AAA+Lon蛋白酶的降解。最后，我们报道了线粒体转录延长因子可以补偿Polrmt杂合基因敲除小鼠POLRMT的部分缺失，表明该因子在转录中具有直接调节作用。总之，我们提供了体内证据，证明POLRMT在哺乳动物线粒体DNA的复制中具有关键的调节作用，并且是转录机制的一部分，该机制提供了线粒体DNA复制的引物形成和线粒体基因表达之间的转换。
Mitochondrial transcription for replication primer formation has priority over gene expression at low POLRMT levels. Mitochondria are vital in providing cellular energy via their oxidative phosphorylation system, which requires the coordinated expression of genes encoded by both the nuclear and mitochondrial genomes (mtDNA). Transcription of the circular mammalian mtDNA depends on a single mitochondrial RNA polymerase (POLRMT). Although the transcription initiation process is well understood, it is debated whether POLRMT also serves as the primase for the initiation of mtDNA replication. In the nucleus, the RNA polymerases needed for gene expression have no such role. Conditional knockout of Polrmt in the heart results in severe mitochondrial dysfunction causing dilated cardiomyopathy in young mice. We further studied the molecular consequences of different expression levels of POLRMT and found that POLRMT is essential for primer synthesis to initiate mtDNA replication in vivo. Furthermore, transcription initiation for primer formation has priority over gene expression. Surprisingly, mitochondrial transcription factor A (TFAM) exists in an mtDNA-free pool in the Polrmt knockout mice. TFAM levels remain unchanged despite strong mtDNA depletion, and TFAM is thus protected from degradation of the AAA+ Lon protease in the absence of POLRMT. Last, we report that mitochondrial transcription elongation factor may compensate for a partial depletion of POLRMT in heterozygous Polrmt knockout mice, indicating a direct regulatory role of this factor in transcription. In conclusion, we present in vivo evidence that POLRMT has a key regulatory role in the replication of mammalian mtDNA and is part of a transcriptional mechanism that provides a switch between primer formation for mtDNA replication and mitochondrial gene expression.