Hsuuw Yan-Der, Chan Wen-Hsiung
Department of Bioscience Technology, Chung Yuan Christian University, Chung Li, Taiwan.
Ann N Y Acad Sci. 2007 Jan;1095:428-40. doi: 10.1196/annals.1397.046.
The catechins, a family of polyphenols found in tea, can evoke various responses, including cell death. However, the precise molecular mechanisms of these effects are unknown. Here, we demonstrate that treatment of human MCF-7 cells with 50 microM (-)-Epigallocatechin-3-gallate (EGCG), a catechin that is highly abundant in green tea, can induce apoptotic changes, including mitochondrial membrane potential changes and activation of c-Jun N-terminal kinase (JNK), caspase-9, and caspase-3. In contrast, higher concentrations of EGCG (100-400 microM) do not induce apoptosis, but rather trigger necrotic cell death in MCF-7 cells. Investigations of the possible mechanisms underlying these differences revealed that treatment with lower concentrations of EGCG (10-50 microM) directly increased intracellular oxidative stress, while higher concentrations (100-400 microM) did not. Immunoblotting revealed that treatment of MCF-7 cells with 10-50 microM EGCG caused increases in Bax protein levels and decreases in Bcl-2 protein levels, shifting the Bax-Bcl-2 ratio to favor apoptosis, while treatment with 100-400 microM EGCG had no such effect. Moreover, we observed a dose-dependent decrease in intracellular ATP levels in cells treated with high-dose EGCG. Blockade of reactive oxygen species (ROS) generation and ATP synthesis using antioxidants and ATP synthesis inhibitors revealed that ROS and ATP play important roles to switch cell death types with apoptosis or necrosis. Collectively, these results indicate for the first time that EGCG treatment has a dose-dependent effect on ROS generation and intracellular ATP levels in MCF-7 cells, leading to either apoptosis or necrosis, and that the apoptotic cascade involves JNK activation, Bax expression, mitochondrial membrane potential changes, and activation of caspase-9 and caspase-3.
儿茶素是茶叶中发现的一类多酚，可引发多种反应，包括细胞死亡。然而，这些效应的确切分子机制尚不清楚。在此，我们证明用50微摩尔（-）-表没食子儿茶素-3-没食子酸酯（EGCG）处理人MCF-7细胞，EGCG是绿茶中含量极高的一种儿茶素，可诱导凋亡变化，包括线粒体膜电位变化以及c-Jun氨基末端激酶（JNK）、半胱天冬酶-9和半胱天冬酶-3的激活。相比之下，较高浓度的EGCG（100 - 400微摩尔）不会诱导凋亡，而是在MCF-7细胞中引发坏死性细胞死亡。对这些差异潜在机制的研究表明，用较低浓度的EGCG（10 - 50微摩尔）处理可直接增加细胞内氧化应激，而较高浓度（100 - 400微摩尔）则不会。免疫印迹显示，用10 - 50微摩尔EGCG处理MCF-7细胞会导致Bax蛋白水平升高和Bcl-2蛋白水平降低，使Bax - Bcl-2比值向有利于凋亡的方向转变，而用100 - 400微摩尔EGCG处理则没有这种效果。此外，我们观察到用高剂量EGCG处理的细胞中细胞内ATP水平呈剂量依赖性下降。使用抗氧化剂和ATP合成抑制剂阻断活性氧（ROS）生成和ATP合成表明，ROS和ATP在将细胞死亡类型转换为凋亡或坏死方面发挥重要作用。总体而言，这些结果首次表明EGCG处理对MCF-7细胞中的ROS生成和细胞内ATP水平具有剂量依赖性影响，导致凋亡或坏死，并且凋亡级联反应涉及JNK激活、Bax表达、线粒体膜电位变化以及半胱天冬酶-9和半胱天冬酶-3的激活。
