Cao Ji, Xu Danqing, Wang Duoduo, Wu Rui, Zhang Lei, Zhu Hong, He Qiaojun, Yang Bo
Department of Pharmacology, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou 310058, China.
Free Radic Biol Med. 2009 Sep 1;47(5):536-47. doi: 10.1016/j.freeradbiomed.2009.05.024. Epub 2009 May 28.
N-(4-hydroxyphenyl) retinamide (4-HPR), as a synthetic retinoid, has been shown to inhibit carcinogenesis in a variety of cancers. Extensive studies have indicated that ROS are involved in 4-HPR-mediated apoptosis. Herein, we provide further evidence that the Akt signaling pathway is involved in 4-HPR-mediated apoptosis. Of note is the fact that the expression of PI3K (p110) does not change obviously, and neither LY294002 nor insulin could influence the apoptosis induced by 4-HPR. These observations implicate the direct interaction between Akt and ROS. Our data also reveal that 4-HPR-mediated ROS evoke Akt conformational change by forming an intramolecular disulfide bond; N-acetylcysteine and glutathione, as thiol antioxidants, significantly abate the ROS generation in 4-HPR-exposed cells. Further experiments indicate that the conformational change in Akt not only disrupts Akt-Hsp90 binding, but also enhances Akt-PP2A interaction. All these results collectively suggest that 4-HPR-induced apoptosis is associated with a ROS-mediated conformational change in Akt, and this change, as a consequence, mediates dephosphorylation of Akt via regulating Akt-Hsp90 or Akt-PP2A complex formation.
N-(4-羟基苯基)视黄酸（4-HPR）作为一种合成类视黄醇，已被证明能抑制多种癌症的致癌作用。广泛的研究表明，活性氧（ROS）参与了4-HPR介导的细胞凋亡。在此，我们提供进一步的证据表明，Akt信号通路参与了4-HPR介导的细胞凋亡。值得注意的是，磷脂酰肌醇-3激酶（PI3K，p110）的表达没有明显变化，LY294002和胰岛素均不能影响4-HPR诱导的细胞凋亡。这些观察结果表明Akt与ROS之间存在直接相互作用。我们的数据还显示，4-HPR介导的ROS通过形成分子内二硫键引起Akt构象变化；N-乙酰半胱氨酸和谷胱甘肽作为硫醇抗氧化剂，可显著减少4-HPR处理细胞中ROS的产生。进一步的实验表明，Akt的构象变化不仅破坏了Akt与热休克蛋白90（Hsp90）的结合，还增强了Akt与蛋白磷酸酶2A（PP2A）的相互作用。所有这些结果共同表明，4-HPR诱导的细胞凋亡与ROS介导的Akt构象变化有关，并且这种变化通过调节Akt-Hsp90或Akt-PP2A复合物的形成介导Akt的去磷酸化。
