The Role of Mitochondrial DNA Alterations in Cancer

描述（由申请人提供）：线粒体在能量代谢、活性氧（ROS）的产生、衰老和细胞凋亡启动中的重要性表明，线粒体是肿瘤发生途径中不可或缺的整合体。线粒体靠近ROS产生位点，有限的DNA修复能力以及缺乏保护性组蛋白使得mtDNA对突变高度敏感。体细胞线粒体DNA （mtDNA）突变已在包括乳腺、肺、膀胱、卵巢和结肠在内的实体肿瘤中报道；并被认为是癌症的普遍现象。然而，这些突变的功能意义从未被研究过。与糖酵解活性升高相关的线粒体细胞含量的显著减少是癌症的一种异常生物能量表型。在肿瘤细胞中观察到线粒体基因表达的下调和升高。肿瘤细胞中有缺陷的线粒体持续处于氧化应激状态，这将产生更高水平的ROS，并导致参与细胞生长和ATP产生调节的基因发生更多突变。直到今天，线粒体在癌症的发展和维持不受控制的细胞生长中所起的作用仍然未知。最近关于线粒体杂交研究的报道表明，导致Leber遗传性视神经病变（LHON）的线粒体突变对细胞凋亡更敏感。我们的假设是，如果在神经退行性疾病中存在对细胞死亡更敏感的突变线粒体，那么癌细胞中就会存在对细胞凋亡更有抵抗力的线粒体DNA突变。为了支持这一假设，我们计划(1)通过分析正常/肿瘤对乳腺癌和细胞系的整个线粒体基因组来鉴定体细胞mtDNA突变，(2)评估反映肿瘤中线粒体生物发生的mtDNA含量，(3)确定mtDNA突变的潜在功能意义，以及(4)通过透射线粒体杂交细胞系统评估突变线粒体对细胞凋亡治疗反应的影响。这项研究项目的结果将帮助我们了解线粒体DNA改变在癌症中的功能作用，并为更有效的治疗开发确定潜在的新靶点。

DESCRIPTION (provided by applicant): The importance of mitochondria in energy metabolism, generation of reactive oxygen species (ROS), aging, and the initiation of apoptosis, have suggested that mitochondria are indispensable integrators in the pathways of tumorigenesis. The close proximity of mitochondria to the ROS producing sites, the limited DNA repair capabilities, and the lack of protective histone proteins render high susceptibility of mtDNA to mutations. Somatic mitochondrial DNA (mtDNA) mutation has been reported in solid tumors including breast, lung, bladder, ovarian, and colon; and has been regarded as a general phenomenon of cancer. However, the functional significance of these mutations has never been investigated. Marked reduction in the cellular content of mitochondria associated with elevated glycolytic activity is an abnormal bio-energetic phenotype of cancer. Both down-regulated and elevated mitochondrial gene expression have been observed in neoplastic cells. Defective mitochondria in tumor cells are constantly under oxidative stress that would generate higher levels of ROS and cause more mutations in genes involved in the regulation of cell growth and ATP production. To this day, the role that mitochondria play in the development of cancer and in maintaining uncontrolled cell growth remains unknown. Recent reports on transmitochondrial cybrid studies demonstrated that mitochondria bearing mutations causing Leber's hereditary optic neuropathy (LHON) are more sensitive to apoptosis. Our hypothesis is that if there are mutant mitochondria that are more sensitive to cell death in neuro-degeneration disease, there will be mitochondrial DNA mutants in cancer cells that are more resistant to apoptosis. To support the hypothesis, we plan to (1) identify somatic mtDNA mutations by the analysis of the entire mitochondrial genome in normal/tumor pairs of breast carcinomas and cell lines, (2) evaluate the mtDNA content that reflects the biogenesis of mitochondria in tumor, (3) determine the potential functional significance of the mtDNA mutations, and (4) assess the effect of mutant mitochondria on cellular response to apoptotic treatment by using the transmitochondrial cybrid cell system. Results from this research project will help us understand the functional role of mitochondrial DNA alterations in cancer and identify potential novel targets for more effective therapeutic development.