A ubiquitously expressed transcription factor, specificity protein 1 (Sp1), interacts with the amyloid precursor protein (APP) promoter and likely mediates APP expression. Promoter-interaction strengths variably regulate the level of APP expression. Here, we examined the interactions of finger 3 of Sp1 (Sp1-f3) with a DNA fragment containing the APP promoter in different ionic solutions using atomic force microscope (AFM) spectroscopy. Sp1-f3 molecules immobilized on an Si substrate were bound to the APP promoter, which was linked to the AFM tips via covalent bonds. The interactions were strongly influenced by Pb2+, considering that substituting Zn2+ with Pb2+ increased the binding affinity of Sp1 for the APP promoter. The results revealed that the enhanced interaction force facilitated APP expression and that APP overexpression could confer a high-risk for disease incidence. An increased interaction force between Sp1-f3 and the APP promoter in Pb2+ solutions was consistent with a lower binding free energy, as determined by computer-assisted analysis. The impact of Pb2+ on cell morphology and related mechanical properties were also detected by AFM. The overexpression of APP caused by the enhanced interaction force triggered actin reorganization and further resulted in an increased Young's modulus and viscosity. The correlation with single-force measurements revealed that altered cellular activities could result from alternation of Sp1-APP promoter interaction. Our AFM findings offer a new approach in understanding Pb2+ associated neurodegeneration.

中文翻译：

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Sp1 和 APP 启动子的相互作用阐明了 Pb2+ 引起神经变性的机制。


普遍表达的转录因子特异性蛋白 1 (Sp1) 与淀粉样前体蛋白 (APP) 启动子相互作用，并可能介导 APP 表达。启动子相互作用强度不同地调节 APP 表达水平。在这里，我们使用原子力显微镜 (AFM) 光谱检查了 Sp1 的指 3 (Sp1-f3) 与包含 APP 启动子的 DNA 片段在不同离子溶液中的相互作用。固定在 Si 基板上的 Sp1-f3 分子与 APP 启动子结合，APP 启动子通过共价键与 AFM 尖端连接。考虑到用 Pb2+ 取代 Zn2+ 增加了 Sp1 对 APP 启动子的结合亲和力，相互作用受到 Pb2+ 的强烈影响。结果表明，相互作用力的增强促进了 APP 的表达，而 APP 的过度表达可能会导致疾病发生的高风险。通过计算机辅助分析确定，Pb2+ 溶液中 Sp1-f3 和 APP 启动子之间相互作用力的增加与较低的结合自由能一致。 AFM 还检测了 Pb2+ 对细胞形态和相关机械性能的影响。相互作用力增强导致 APP 过度表达，引发肌动蛋白重组，进一步导致杨氏模量和粘度增加。与单力测量的相关性表明，Sp1-APP 启动子相互作用的改变可能导致细胞活动的改变。我们的 AFM 研究结果为理解 Pb2+ 相关的神经变性提供了一种新方法。