A Role for the Fifth G-Track in G-Quadruplex Forming Oncogene Promoter Sequences during Oxidative Stress: Do These "Spare Tires" Have an Evolved Function?
A Role for the Fifth G-Track in G-Quadruplex Forming Oncogene Promoter Sequences during Oxidative Stress: Do These "Spare Tires" Have an Evolved Function?
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DOI：
10.1021/acscentsci.5b00202
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发表时间：
2015-08-26
影响因子：
18.2
通讯作者：
Burrows, Cynthia J.
中科院分区：
文献类型：
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作者：
Fleming, Aaron M.;Zhou, Jia;Burrows, Cynthia J.
不受控制的炎症或氧化应激产生缺电子物质，使基因组氧化，增加其在癌症中的不稳定性。调节c-MYC、KRAS、VEGF、BCL-2、HIF-1 α和RET癌基因的G-四链体（G4）序列例如是环和5 '-核心鸟嘌呤（G）处氧化的靶标，如本研究中通过VEGF G4的CO 3中心点氧化所示。观察到的产物包括8-氧代-7，8-二氢鸟嘌呤（OG）、螺亚氨基二乙内酰脲（Sp）和5-胍基乙内酰脲（Gh）。我们先前的研究发现，OG和Gh，当存在于VEGF和c-MYC的解析结构的四个G轨道中时，不是生物相关KCl溶液中碱基切除修复（BER）DNA糖基化酶的底物。我们现在假设，在距离参与折叠的G4轨道几个核苷酸远的地方发现的第五个G轨道可以作为“备用轮胎”，促进受损的G轨道挤出成一个大环，然后成为BER的底物。热力学、光谱学和DMS足迹研究证实了在VEGF G4的环或核心位置用OG或Gh替换受损的G轨道的第五域。现在发现这些新的“备用轮胎”含有Gh的链在环中是用NEIL 1、NEIL 2和NEIL 3 DNA糖基化酶引发BER的底物。结果支持一个假设，其中监管G4携带“备胎”的第五G-轨道，以帮助在修复过程中，当这些序列被破坏的自由基氧物种，在大量的这些序列中观察到的功能。此外，在启动子区域中氧化碱基的形成和修复可以构成表观遗传修饰的另一个实例，在这种情况下是鸟嘌呤碱基，以调节基因表达，其中G4序列充当氧化应激的传感器。
Uncontrolled inflammation or oxidative stress generates electron-deficient species that oxidize the genome increasing its instability in cancer. The G-quadruplex (G4) sequences regulating the c-MYC, KRAS, VEGF, BCL-2, HIF-1 alpha, and RET oncogenes, as examples, are targets for oxidation at loop and 5'-core guanines (G) as showcased in this study by CO3 center dot- oxidation of the VEGF G4. Products observed include 8-oxo-7,8-dihydroguanine (OG), spiroiminodihydantoin (Sp), and 5-guanidinohydantoin (Gh). Our previous studies found that OG and Gh, when present in the four G-tracks of the solved structure for VEGF and c-MYC, were not substrates for the base excision repair (BER) DNA glycosylases in biologically relevant KCl solutions. We now hypothesize that a fifth G-track found a few nucleotides distant from the G4 tracks involved in folding can act as a "spare tire," facilitating extrusion of a damaged G-run into a large loop that then becomes a substrate for BER. Thermodynamic, spectroscopic, and DMS footprinting studies verified the fifth domain replacing a damaged G-track with OG or Gh at a loop or core position in the VEGF G4. These new "spare tire"-containing strands with Gh in loops are now found to be substrates for initiation of BER with the NEIL1, NEIL2, and NEIL3 DNA glycosylases. The results support a hypothesis in which regulatory G4s carry a "spare-tire" fifth G-track for aiding in the repair process when these sequences are damaged by radical oxygen species, a feature observed in a large number of these sequences. Furthermore, formation and repair of oxidized bases in promoter regions may constitute an additional example of epigenetic modification, in this case of guanine bases, to regulate gene expression in which the G4 sequences act as sensors of oxidative stress.