Autophagy regulates chemoresistance of gastric cancer stem cells via the Notch signaling pathway.

OBJECTIVE: Gastric cancer is the most common gastrointestinal malignancy and the leading cause of cancer-related deaths in East Asia. Increasing evidence has revealed that autophagy is closely associated with tumor initiation and progression. The present work aimed to investigate the role of autophagy in adjuvant chemotherapy for gastric cancer. MATERIALS AND METHODS: Gastric cancer stem cells (CSCs) were isolated from gastric cancer cell lines using the cell surface markers CD44 and CD54 and cultured in a three-dimensional cell culture system. Western blotting was used to detect their protein expression levels in gastric CSCs. In addition, the cells were treated with inhibitors to investigate the underlying mechanisms of autophagy. RESULTS: After isolation of gastric CSCs expressing CD44 and CD54, Western blot analysis showed that the levels of the autophagic marker LC3II were markedly enhanced in CD44+CD54+ gastric CSCs. Moreover, the ratio of LC3II/LC3I protein levels was higher in CD44+CD54+ gastric CSCs than in non-CSCs. By contrast, both a chemotherapeutic agent (5-fluorouracil) and autophagy inhibitor (chloroquine) exhibited an inhibitory effect on the cell viability of gastric CSCs, and their combination further enhanced such inhibitory effects. Mechanistically, the addition of Notch inhibitor decreased the cell viability of gastric CSCs treated with 5-fluorouracil and chloroquine. In addition, 5-fluorouracil and chloroquine both increased the expression of Notch1 in gastric CSCs. CONCLUSIONS: These findings show that autophagy regulated drug sensitivity of gastric cancer cells through the Notch signaling pathway.