Mechanism of juglone-induced apoptosis of MCF-7 cells by the mitochondrial pathway

Abstract

This study investigated the nature and mechanism of juglone-induced apoptosis in the human breast cancer cell line MCF-7. The inhibitory effect of juglone on MCF-7 cell growth was evaluated by the dimethylthiazol tetrazolium assay. Morphological apoptotic changes were characterized using an inverted microscope, Hoechst 33258 fluorescence staining, and Giemsa staining. The rate of cell apoptosis, intracellular levels of reactive oxygen species (ROS), and mitochondrial membrane potential were detected using flow cytometry. Intracellular Ca2+ concentrations were detected using laser scanning confocal fluorescence microscopy. Expression of the proteins Bcl-2, Bax, and cytochrome C was assessed by western blotting. Caspase-3 activity was quantified using a caspase-3 activity kit. Juglone inhibited the growth of MCF-7 cell line with an IC50 of 11.99 μM. The rates of MCF-7 cell apoptosis at 24 h after exposure to 5, 10, and 20 μM juglone were 9.29, 20.67, and 28.39%, respectively; compared to unexposed cells, juglone-exposed cells exhibited significant elevation in intracellular ROS level, decrease in mitochondrial membrane potential, and increase in intracellular Ca2+ concentration. Juglone upregulated the expression of Bax, and downregulated the expression of Bcl-2, promoting the release of cytochrome C, thereby upregulating the activity of caspase-3. The results suggest that the mechanism of juglone-induced apoptosis in MCF-7 cells is characterized by elevated ROS levels, reduced Bcl-2 expression, increased Bax expression, decreased mitochondrial membrane potential, increased intracellular Ca2+ concentration, outer mitochondrial-membrane rupture, cytochrome C release, and caspase-3 activation.