Morgan Rhianna K, Molnar Michael M, Batra Harshul, Summerford Bethany, Wadkins Randy M, Brooks Tracy A
School of Pharmacy, Department of BioMolecular Sciences, Division of Pharmacology, University of Mississippi, University, MS 38677, USA.
Department of Chemistry and Biochemistry, University of Mississippi, University, MS 38677, USA.
J Nucleic Acids. 2018 May 16;2018:9281286. doi: 10.1155/2018/9281286. eCollection 2018.
Promoters often contain asymmetric G- and C-rich strands, in which the cytosines are prone to epigenetic modification via methylation (5-mC) and 5-hydroxymethylation (5-hmC). These sequences can also form four-stranded G-quadruplex (G4) or i-motif (iM) secondary structures. Although the requisite sequences for epigenetic modulation and iM/G4 formation are similar and can overlap, they are unlikely to coexist. Despite 5-hmC being an oxidization product of 5-mC, the two modified bases cluster at distinct loci. This study focuses on the intersection of G4/iM formation and 5-hmC modification using the vascular endothelial growth factor (VEGF) gene promoter's CpG sites and examines whether incorporation of 5-hmC into iM/G4 structures had any physicochemical effect on formation, stability, or recognition by nucleolin or the cationic porphyrin, TMPyP4. No marked changes were found in the formation or stability of iM and G4 structures; however, changes in recognition by nucleolin or TMPyP4 occurred with 5-hmC modification wherein protein and compound binding to 5-hmC modified G4s was notably reduced. G4/iM structures in the VEGF promoter are promising therapeutic targets for antiangiogenic therapy, and this work contributes to a comprehensive understanding of their governing principles related to potential transcriptional control and targeting.
启动子通常包含不对称的富含G和C的链，其中胞嘧啶易于通过甲基化（5-甲基胞嘧啶）和5-羟甲基化（5-羟甲基胞嘧啶）进行表观遗传修饰。这些序列还可以形成四链G-四链体（G4）或i-基序（iM）二级结构。尽管表观遗传调控和iM/G4形成所需的序列相似且可能重叠，但它们不太可能共存。尽管5-羟甲基胞嘧啶是5-甲基胞嘧啶的氧化产物，但这两种修饰碱基聚集在不同的位点。本研究利用血管内皮生长因子（VEGF）基因启动子的CpG位点，聚焦于G4/iM形成与5-羟甲基胞嘧啶修饰的交叉点，并研究将5-羟甲基胞嘧啶掺入iM/G4结构是否对其形成、稳定性或被核仁素或阳离子卟啉TMPyP4识别有任何物理化学影响。未发现iM和G4结构的形成或稳定性有明显变化；然而，5-羟甲基胞嘧啶修饰后，核仁素或TMPyP4的识别发生了变化，其中蛋白质和化合物与5-羟甲基胞嘧啶修饰的G4的结合显著减少。VEGF启动子中的G4/iM结构是抗血管生成治疗有前景的治疗靶点，这项工作有助于全面了解其与潜在转录调控和靶向相关的调控原则。
