Department of Biotechnology and Life Science, Tokyo University of Agriculture and Technology, 2-24-16 Naka-cho, Koganei, Tokyo 184-8588, Japan.
School of Bioscience and Biotechnology, Tokyo University of Technology, 1404-1 Katakuramachi, Hachioji, Tokyo 192-0982, Japan.
Molecules. 2018 Apr 18;23(4):944. doi: 10.3390/molecules23040944.
G-quadruplex (G4) is a DNA/RNA conformation that consists of two or more G-tetrads resulting from four-guanine bases connected by Hoogsteen-type hydrogen bonds, which is often found in the telomeres of chromatin, as well as in the promoter regions of genes. The function of G4 in the genomic DNA is being elucidated and some G4-protein interactions have been reported; these are believed to play a role in vital cellular functions. In this study, we focused on CpG methylation, a well-known epigenetic modification of the genomic DNA, especially found in the promoter regions. Although many G4-forming sequences within the genomic DNA harbor CpG sites, the relationship between CpG methylation and the binding properties of associated proteins remains unclear. We demonstrated that the binding ability of vascular endothelial growth factor () G4 DNA to VEGF165 protein was significantly decreased by CpG methylation. We identified the binding activity of G4 DNA oligonucleotides derived from gene promoter regions to SP1, a transcription factor that interacts with a G4-forming DNA and is also altered by CpG methylation. The effect of methylation on binding affinity was accompanied by changes in G4 structure and/or topology. Therefore, this study suggested that CpG methylation might be involved in protein binding to G4-forming DNA segments for purposes of transcriptional regulation.
四链体（G4）是一种 DNA/RNA 构象，由通过 Hoogsteen 型氢键连接的四个鸟嘌呤碱基组成的两个或更多 G-四联体组成，常存在于染色质的端粒以及基因的启动子区域。G4 在基因组 DNA 中的功能正在阐明，并且已经报道了一些 G4-蛋白相互作用；这些相互作用被认为在重要的细胞功能中发挥作用。在这项研究中，我们专注于 CpG 甲基化，这是基因组 DNA 中一种众所周知的表观遗传修饰，特别是在启动子区域。尽管基因组 DNA 中的许多形成 G4 的序列都含有 CpG 位点，但 CpG 甲基化与相关蛋白结合特性之间的关系尚不清楚。我们表明，CpG 甲基化显著降低了血管内皮生长因子（VEGF）G4 DNA 与 VEGF165 蛋白的结合能力。我们鉴定了来自基因启动子区域的 G4 DNA 寡核苷酸与 SP1 的结合活性，SP1 是一种与形成 G4 的 DNA 相互作用的转录因子，也受 CpG 甲基化的影响。甲基化对结合亲和力的影响伴随着 G4 结构和/或拓扑结构的变化。因此，本研究表明 CpG 甲基化可能参与蛋白与形成 G4 的 DNA 片段的结合，以实现转录调控。
