Department of Neuroscience, Department of Physiology, College of Medicine, Kyung Hee University, Seoul 130-731, Republic of Korea.
Department of Neuroscience, Department of Physiology, College of Medicine, Kyung Hee University, Seoul 130-731, Republic of Korea.
Biochem Biophys Res Commun. 2014 Jul 18;450(1):166-71. doi: 10.1016/j.bbrc.2014.05.082. Epub 2014 May 26.
The nuclear DNA-encoded mitochondrial transcription factor A (TFAM) is synthesized in cytoplasm and transported into mitochondria. TFAM enhances both transcription and replication of mitochondrial DNA. It is unclear, however, whether TFAM plays a role in regulating nuclear gene expression. Here, we demonstrated that TFAM was localized to the nucleus and mitochondria by immunostaining, subcellular fractionation, and TFAM-green fluorescent protein hybrid protein studies. In HT22 hippocampal neuronal cells, human TFAM (hTFAM) overexpression suppressed human Tfam promoter-mediated luciferase activity in a dose-dependent manner. The mitochondria targeting sequence-deficient hTFAM also repressed Tfam promoter activity to the same degree as hTFAM. It indicated that nuclear hTFAM suppressed Tfam expression without modulating mitochondrial activity. The repression required for nuclear respiratory factor-1 (NRF-1), but hTFAM did not bind to the NRF-1 binding site of its promoter. TFAM was co-immunoprecipitated with NRF-1. Taken together, we suggest that nuclear TFAM down-regulate its own gene expression as a NRF-1 repressor, showing that TFAM may play different roles depending on its subcellular localizations.
核 DNA 编码的线粒体转录因子 A（TFAM）在细胞质中合成并运输到线粒体中。TFAM 增强线粒体 DNA 的转录和复制。然而，TFAM 是否在调节核基因表达中发挥作用尚不清楚。在这里，我们通过免疫染色、亚细胞分级和 TFAM-绿色荧光蛋白杂交蛋白研究表明，TFAM 定位于细胞核和线粒体。在 HT22 海马神经元细胞中，人 TFAM（hTFAM）过表达以剂量依赖性方式抑制人 Tfam 启动子介导的荧光素酶活性。缺乏线粒体靶向序列的 hTFAM 也能抑制 Tfam 启动子活性，程度与 hTFAM 相同。这表明核 hTFAM 在不调节线粒体活性的情况下抑制 Tfam 表达。这种抑制需要核呼吸因子-1（NRF-1），但 hTFAM 并不结合其启动子上的 NRF-1 结合位点。TFAM 与 NRF-1 共免疫沉淀。总之，我们认为核 TFAM 作为 NRF-1 抑制剂下调其自身基因表达，表明 TFAM 可能根据其亚细胞定位发挥不同的作用。
