Baulch Janet E, Aypar Umut, Waters Katrina M, Yang Austin J, Morgan William F
Department of Radiation Oncology, University of California Irvine, Irvine, California, United States of America.
Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, Minnesota, United States of America.
PLoS One. 2014 Sep 24;9(9):e107722. doi: 10.1371/journal.pone.0107722. eCollection 2014.
Radiation induced genomic instability is a well-studied phenomenon, the underlying mechanisms of which are poorly understood. Persistent oxidative stress, mitochondrial dysfunction, elevated cytokine levels and epigenetic changes are among the mechanisms invoked in the perpetuation of the phenotype. To determine whether epigenetic aberrations affect genomic instability we measured DNA methylation, mRNA and microRNA (miR) levels in well characterized chromosomally stable and unstable clonally expanded single cell survivors of irradiation. While no changes in DNA methylation were observed for the gene promoters evaluated, increased LINE-1 methylation was observed for two unstable clones (LS12 and CS9) and decreased Alu element methylation was observed for the other two unstable clones (115 and Fe5.0-8). These relationships also manifested for mRNA and miR expression. mRNA identified for the LS12 and CS9 clones were most similar to each other (261 mRNA), while the 115 and Fe5.0-8 clones were more similar to each other, and surprisingly also similar to the two stable clones, 114 and 118 (286 mRNA among these four clones). Pathway analysis showed enrichment for pathways involved in mitochondrial function and cellular redox, themes routinely invoked in genomic instability. The commonalities between the two subgroups of clones were also observed for miR. The number of miR for which anti-correlated mRNA were identified suggests that these miR exert functional effects in each clone. The results demonstrate significant genetic and epigenetic changes in unstable cells, but similar changes are almost as equally common in chromosomally stable cells. Possible conclusions might be that the chromosomally stable clones have some other form of instability, or that some of the observed changes represent a sort of radiation signature and that other changes are related to genomic instability. Irrespective, these findings again suggest that a spectrum of changes both drive genomic instability and permit unstable cells to persist and proliferate.
辐射诱导的基因组不稳定性是一个经过充分研究的现象，但其潜在机制仍知之甚少。持续的氧化应激、线粒体功能障碍、细胞因子水平升高和表观遗传变化是导致该表型持续存在的机制之一。为了确定表观遗传异常是否影响基因组不稳定性，我们测量了经过充分表征的染色体稳定和不稳定的克隆扩增单细胞辐射幸存者中的DNA甲基化、mRNA和微小RNA（miR）水平。在所评估的基因启动子中未观察到DNA甲基化变化，但在两个不稳定克隆（LS12和CS9）中观察到LINE-1甲基化增加，而在另外两个不稳定克隆（115和Fe5.0-8）中观察到Alu元件甲基化减少。这些关系在mRNA和miR表达中也有体现。为LS12和CS9克隆鉴定的mRNA彼此最为相似（261种mRNA），而115和Fe5.0-8克隆彼此更相似，令人惊讶的是，它们也与两个稳定克隆114和118相似（这四个克隆中有286种mRNA）。通路分析显示，参与线粒体功能和细胞氧化还原的通路富集，这些主题通常与基因组不稳定性相关。在miR方面也观察到了两个克隆亚组之间的共性。鉴定出反相关mRNA的miR数量表明这些miR在每个克隆中发挥功能作用。结果表明不稳定细胞中存在显著的遗传和表观遗传变化，但类似的变化在染色体稳定细胞中几乎同样常见。可能的结论是，染色体稳定的克隆具有某种其他形式的不稳定性，或者观察到的一些变化代表了一种辐射特征，而其他变化与基因组不稳定性有关。无论如何，这些发现再次表明一系列变化既驱动基因组不稳定性，又允许不稳定细胞持续存在和增殖。
