DNA G-quadruplex formation is highly responsive to surrounding conditions, particularly K+ concentration. Malignant cancer cells have a much lower K+ concentration than normal cells because of overexpression of a K+ channel; thus, G-quadruplexes may be unstable in cancer cells. Here, we physicochemically investigated how changes in intracellular chemical environments in vitro and in cells influence G-quadruplex formation and transcription during tumor progression. In vitro, the stable G-quadruplex formation inhibits transcription in a solution containing 150 mM KCl (normal condition). As K+ concentration decreases, which decreases G-quadruplex stability, transcript production from templates with G-quadruplex-forming potential increases. In normal cells, the trend in transcript productions was similar to that in in vitro experiments, with transcription efficiency inversely correlated with G-quadruplex stability. Interestingly, higher transcript levels were produced from templates with G-quadruplex-forming potential in Ras-transformed and highly metastatic breast cancer cells (MDA-MB-231) than in nontransformed and control MCF-7 cells. Moreover, the amount of transcript produced from G-quadruplex-forming templates decreased upon addition of siRNA targeting KCNH1 mRNA, which encodes a potassium voltage-gated channel subfamily H member 1 (KV10.1). Importantly, G-quadruplex dissociation during tumor progression was observed by immunofluorescence using a G-quadruplex-binding antibody in cells. These results suggest that in normal cells, K+ ions attenuate the transcription of certain oncogenes by stabilizing G-quadruplex structures. Our findings provide insight into the novel mechanism of overexpression of certain G-rich genes during tumor progression.

中文翻译：

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肿瘤进展过程中化学环境变化对 DNA G-四链体的不稳定促进转录

DNA G-四链体的形成对周围条件高度敏感，尤其是 K+ 浓度。由于 K+ 通道的过度表达，恶性癌细胞的 K+ 浓度比正常细胞低得多；因此，G-四链体在癌细胞中可能不稳定。在这里，我们物理化学地研究了体外和细胞中细胞内化学环境的变化如何影响肿瘤进展过程中 G-四链体的形成和转录。在体外，稳定的 G-四链体形成抑制了含有 150 mM KCl（正常条件）的溶液中的转录。随着 K+ 浓度的降低，G-四链体稳定性降低，具有 G-四链体形成潜力的模板的转录产物产量增加。在正常细胞中，转录产物的趋势与体外实验相似，转录效率与 G-四链体稳定性呈负相关。有趣的是，在 Ras 转化和高度转移的乳腺癌细胞 (MDA-MB-231) 中，与未转化和对照 MCF-7 细胞相比，具有 G-四链体形成潜力的模板产生了更高的转录水平。此外，在添加靶向 KCNH1 mRNA 的 siRNA 后，由 G-四链体形成模板产生的转录物数量减少，KCNH1 mRNA 编码钾电压门控通道亚家族 H 成员 1 (KV10.1)。重要的是，在细胞中使用 G-四链体结合抗体通过免疫荧光观察到肿瘤进展过程中 G-四链体的解离。这些结果表明，在正常细胞中，K+ 离子通过稳定 G-四链体结构来减弱某些致癌基因的转录。