Epigallocatechin Gallate Dose-Dependently Induces Apoptosis or Necrosis in Human MCF-7 Cells

摘要

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 μM (-)-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 μM) do not induce apoptosis, but rather trigger necrotic cell death in MCF-7 cells. Investigations of the possible mechanisms underlying these differ ences revealed that treatment with lower concentrations of EGCG (10-50 μM) directly increased intracellular oxidative stress, while higher con centrations (100-400 μM) did not. Immunoblotting revealed that treat ment of MCF-7 cells with 10-50 μM 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 μM EGCG had no such effect. Moreover, we observed a dose-dependent decrease in in tracellular ATP levels in cells treated with high-dose EGCG. Blockade of reactive oxygen species (ROS) generation and ATP synthesis using an tioxidants 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 treat ment 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, mito chondrial membrane potential changes, and activation of caspase-9 and caspase-3.