Mitochondrial Genetics Group, Hudson Institute of Medical Research, 27-31 Wright Street, Clayton, VIC, 3168, Australia.
Department of Molecular and Translational Sciences, Faculty of Medicine, Nursing and Health Sciences, Monash University, 27-31 Wright Street, Clayton, VIC, 3168, Australia.
Clin Epigenetics. 2018 Dec 17;10(1):157. doi: 10.1186/s13148-018-0590-0.
Different cell types possess different copies of mtDNA to support their specific requirements for cellular metabolism. Cell-specific mtDNA copy numbers are established through cell-specific mtDNA replication during cell differentiation. However, cancer cells are trapped in a "pseudo-differentiated" state as they fail to expand mtDNA copy number. Global DNA methylation can regulate this process, as induced DNA demethylation promotes differentiation of cancer cells and expansion of mtDNA copy number.
To determine the role that mtDNA methylation plays in regulating mtDNA replication during tumorigenesis, we have characterized the patterns of mtDNA methylation using glioblastoma and osteosarcoma tumor models that have different combinations of mtDNA genotypes and copy number against common nuclear genome backgrounds at different stages of tumor progression. To ensure the reliability of the findings, we have applied a robust experimental pipeline including three approaches, namely whole-mtDNA bisulfite-sequencing with mtDNA-genotype-specific analysis, pyrosequencing, and methylated immunoprecipitation against 5mC and 5hmC. We have determined genotype-specific methylation profiles, which were modulated through tumor progression. Moreover, a strong influence from the nuclear genome was also observed on mtDNA methylation patterns using the same mtDNA genotype under different nuclear genomes. Furthermore, the numbers of mtDNA copy in tumor-initiating cells affected mtDNA methylation levels in late-stage tumors.
Our findings highlight the influences that the nuclear and mitochondrial genomes have in setting mtDNA methylation patterns to regulate mtDNA copy number in tumorigenesis. They have important implications for assessing global DNA methylation patterns in tumorigenesis and the availability of mtDNA template for mtDNA replication.
不同的细胞类型拥有不同的 mtDNA 拷贝数，以支持其细胞代谢的特定需求。细胞特异性 mtDNA 拷贝数是通过细胞分化过程中的细胞特异性 mtDNA 复制建立的。然而，癌细胞被困在“假性分化”状态，因为它们无法扩大 mtDNA 拷贝数。全局 DNA 甲基化可以调节这个过程，因为诱导的 DNA 去甲基化促进癌细胞的分化和 mtDNA 拷贝数的扩增。
为了确定 mtDNA 甲基化在肿瘤发生过程中调节 mtDNA 复制的作用，我们使用具有不同 mtDNA 基因型和拷贝数组合的神经胶质瘤和骨肉瘤肿瘤模型，在肿瘤进展的不同阶段，对 mtDNA 甲基化模式进行了特征描述，这些模型具有共同的核基因组背景。为了确保研究结果的可靠性，我们应用了一个强大的实验方案，包括三种方法，即用 mtDNA 基因型特异性分析、焦磷酸测序和针对 5mC 和 5hmC 的甲基化免疫沉淀进行全 mtDNA 亚硫酸氢盐测序。我们确定了基因型特异性的甲基化图谱，这些图谱在肿瘤进展过程中发生了调节。此外，我们还观察到，在不同的核基因组下，使用相同的 mtDNA 基因型，核基因组对 mtDNA 甲基化模式也有很强的影响。此外，肿瘤起始细胞中的 mtDNA 拷贝数也会影响晚期肿瘤中的 mtDNA 甲基化水平。
我们的研究结果强调了核基因组和线粒体基因组在建立 mtDNA 甲基化模式以调节肿瘤发生中 mtDNA 拷贝数的影响。它们对于评估肿瘤发生中的全局 DNA 甲基化模式以及 mtDNA 复制的 mtDNA 模板可用性具有重要意义。
