Department of Biochemistry and Molecular Biology, China Medical University, Shenyang, Liaoning 110122, China
Department of Gastrointestinal Surgery, Dalian Municipal Central Hospital, Dalian, Liaoning 116033, China.
Biosci Rep. 2017 Nov 29;37(6). doi: 10.1042/BSR20171128. Print 2017 Dec 22.
It is known that the guanine-rich strands in proto-oncogene promoters can fold into G-quadruplex structures to regulate gene expression. An intramolecular parallel G-quadruplex has been identified in promoter. It acts as a repressor in regulating expression. However, the full guanine-rich region in promoter forms a hybrid parallel/antiparallel G-quadruplex structure under physiological conditions, which means there are some antiparallel and hybrid parallel/antiparallel G-quadruplex structures in this region. In the present study, our data indicate that g3-5 truncation adopts an intramolecular hybrid parallel/antiparallel G-quadruplex under physiological conditions The g3-5 G-quadruplex structure significantly stops polymerization by Klenow fragment in K buffer. Furthermore, the results of circular dichroism (CD) spectra and polymerase stop assay directly demonstrate that the G-quadruplex structure in g3-5 fragment can be stabilized by the G-quadruplex ligand TMPyP4 (5,10,15,20-tetra-(N-methyl-4-pyridyl) porphine). But the dual luciferase assay indicates TMPyP4 has no effect on the formation of g3-5 G-quadruplex in HepG2 cells. The findings in the present study will enrich our understanding of the G-quadruplex formation in proto-oncogene promoters and the mechanisms of gene expression regulation.
已知原癌基因启动子中的鸟嘌呤丰富链可以折叠成 G-四链体结构，从而调节基因表达。在 启动子中已经鉴定出一种分子内平行 G-四链体。它作为一种抑制剂在调节 表达中起作用。然而， 启动子中的完整鸟嘌呤丰富区在生理条件下形成混合平行/反平行 G-四链体结构，这意味着该区域存在一些反平行和混合平行/反平行 G-四链体结构。在本研究中，我们的数据表明，g3-5 截断在生理条件下采用分子内混合平行/反平行 G-四链体结构。g3-5 G-四链体结构显著阻止 Klenow 片段在 K 缓冲液中的聚合。此外，圆二色（CD）光谱和聚合酶停止测定的结果直接表明，G-四链体配体 TMPyP4（5,10,15,20-四-（N-甲基-4-吡啶基）卟啉）可以稳定 g3-5 片段中的 G-四链体结构。但双荧光素酶测定表明 TMPyP4 对 HepG2 细胞中 g3-5 G-四链体的形成没有影响。本研究的结果将丰富我们对原癌基因启动子中 G-四链体形成和基因表达调控机制的理解。
