FOXO3 Inhibits Human Gastric Adenocarcinoma (AGS) Cell Growth by Promoting Autophagy in an Acidic Microenvironment

Background/Aims: Previous studies have shown that FOXO3, a member of the forkhead box O (FOXO) family, regulates autophagy in various cells. To date, whether the induction of autophagy in gastric cancer (GC) cells is triggered by an acidic microenvironment is unclear. Little is known about the relationship between FOXO3 and acidic microenvironments in GC. The aims of our study were to investigate the roles of FOXO3 and the acidic microenvironment in autophagy and to determine how FOXO3 and the acidic microenvironment regulate GC cell growth through autophagy. Methods: We cultured human gastric adenocarcinoma (AGS) cells in media with different pH values in vitro, transfected the cells with FOXO3a plasmids and then detected autophagy in the cells under different conditions. In addition, we also performed cell counting kit 8 (CCK8), wound and cell invasion assays to test cell viability and invasion, respectively. We employed real-time PCR, western blotting and mRFP-GFP-LC3 vectors to detect the expression of various autophagy indicators. Results: We found that cells treated with FOXO3 and exposed to an acidic microenvironment displayed suppressed growth compared with control cells. We also found that the protein expression levels of several autophagy makers, such as LC3I, LC3II and Beclin-1, were higher in FOXO3 plasmid-transfected AGS cells cultured in an acidic microenvironment than in control cells, while P62 protein expression levels were clearly decreased in FOXO3 plasmid-transfected cells compared with control cells. Moreover, we observed autophagic flux in AGS cells overexpressing FOXO3 and exposed to low pH conditions. Conclusion: These findings suggest that FOXO3 inhibits AGS cell growth by promoting autophagy in an acidic microenvironment. Furthermore, the results showed that anticancer therapies targeting FOXO3 and low pH conditions may be useful in the treatment of GC. (C) 2018 The Author(s) Published by S. Karger AG, Basel.