Through its involvement in gene transcription and heterochromatin formation, DNA methylation regulates how cells interact with their environment. Nevertheless, the extracellular signaling cues that modulate the distribution of this central chromatin modification are largely unclear. DNA methylation is highly abundant at repetitive elements, but its investigation in live cells has been complicated by methodological challenges. Utilizing a CRISPR/dCas9 biosensor that reads DNA methylation of human α-satellite repeats in live cells, we here uncover a signaling pathway linking the chromatin and transcriptional state of repetitive elements to epithelial adherens junction integrity. Specifically, we find that in confluent breast epithelial cell monolayers, α-satellite repeat methylation is reduced by comparison to low density cultures. This is coupled with increased transcriptional activity at repeats. Through comprehensive perturbation experiments, we identify the junctional protein E-cadherin, which links to the actin cytoskeleton, as a central molecular player for signal relay into the nucleus. Furthermore, we find that this pathway is impaired in cancer cells that lack E-cadherin and are not contact-inhibited. This suggests that the molecular connection between cell density and repetitive element methylation could play a role in the maintenance of epithelial tissue homeostasis.

通过参与基因转录和异染色质形成，DNA 甲基化调节细胞与环境的相互作用。然而，调节这种中央染色质修饰分布的细胞外信号线索在很大程度上尚不清楚。DNA 甲基化在重复元件中含量很高，但其在活细胞中的研究因方法学挑战而变得复杂。利用读取活细胞中人类 α 卫星重复序列的 DNA 甲基化的 CRISPR/dCas9 生物传感器，我们在这里揭示了将重复元件的染色质和转录状态与上皮粘附连接完整性联系起来的信号通路。具体来说，我们发现在汇合的乳腺上皮细胞单层中，与低密度培养物相比，α-卫星重复甲基化减少。这与重复序列的转录活性增加相结合。通过全面的扰动实验，我们确定了与肌动蛋白细胞骨架相连的连接蛋白 E-钙粘蛋白是信号传递到细胞核的中心分子参与者。此外，我们发现该通路在缺乏 E-钙粘蛋白且不受接触抑制的癌细胞中受损。这表明细胞密度和重复元件甲基化之间的分子连接可能在维持上皮组织稳态中发挥作用。