Induction of apoptosis and autophagy by sodium selenite in A549 human lung carcinoma cells through generation of reactive oxygen species

Abstract

Selenium in the form of sodium selenite has been reported to exert anti-tumor effects in several cancer cell types by inducing autophagic cell death and apoptosis mediated by reactive oxygen species (ROS). However, the exact molecular pathways underlying these effects have not been fully established. The present study used A549 human lung carcinoma cells for further investigation of the anti-cancer mechanism of sodium selenite. We showed that sodium selenite modulated both the extrinsic and intrinsic apoptotic pathways, which were interconnected by Bid truncation. We used z-VAD-fmk, a pan-caspase inhibitor, to demonstrate that sodium selenite-induced apoptosis was dependent on the activation of caspases. Sodium selenite also increased autophagy, as indicated by an increase in microtubule-associated protein light chain-3 (LC3) puncta, accumulation of LC3II, and elevation of autophagic flux. Pretreatment with bafilomycin A1 enhanced sodium selenite-induced apoptosis, indicating that sodium selenite-induced autophagy functioned as a survival mechanism. Sodium selenite treatment also resulted in generation of ROS, which abrogated mitochondrial membrane potential (MMP) and regulated both apoptosis and autophagy. Phospho-nuclear factor erythroid 2-related factor 2 (p-Nrf2) showed a ROS-dependent translocation to the nucleus, which suggested that Nrf2 might increase cell survival by suppressing ROS accumulation and apoptosis mediated by oxidative stress. Sodium selenite treatment of A549 cells therefore appeared to trigger both apoptosis and cytoprotective autophagy, which were both mediated by ROS. The data suggest that regulation of ROS generation and autophagy can be a potential strategy for treating lung cancer that is resistant to pro-apoptotic therapeutics.