Curcumin induces apoptosis and protective autophagy in human gastric cancer cells with different degree of differentiation

Abstract

Objective: To investigate the effect of curcumin on the apoptosis and autophagy of human gastric cancer cells with different degree of differentiation. Methods: Gastric cancer cell lines BGC-823 and MKN-28 were treated with curcumin at different concentrations. The effect of curcumin on cell proliferation was measured by MTT assay. Apoptosis was assessed by flow cytometry. Autophagy status was analyzed by acridine orange staining. The expression levels of apoptotic and autophagy-related proteins were detected by Western blot. Results: The cell viability of BGC-823 and MKN-28 was inhibited by curcumin in a time- and dose-dependent manner. At 48 h after treatment, the IC(50) value of BGC-823 (15.18 μmol/L) was close to that of MKN-28 (15.84 μmol/L), and the difference was not statistically significant (P=0.513). Meanwhile, flow cytometry showed that curcumin induced the apoptosis of gastric cancer cells in a dose-dependent manner. Western blot results showed that the expression of pro-apoptotic proteins bax, active-caspase-3 and active-caspase-9 was significantly increased in BGC-823 and MKN-28 cells, whereas that of the anti-apoptotic protein bcl-2 was strikingly reduced. In addition, the formation of acidic vesicular organelles in cytoplasm, conversion of LC3-Ⅰ to LC3-Ⅱ and increased levels of autophagy-related proteins Beclin1, Atg7 and Atg5-Atg12 were observed in curcumin-treated cells. Moreover, activation of PI3K/Akt/mTOR signaling pathway was also significantly suppressed after curcumin treatment. Blocking autophagy by adding the autophagy inhibitor 3-methyladenine (3-MA) significantly promoted the apoptotic cell death induced by curcumin. Conclusions: Curcumin induces apoptosis and protective autophagy in human gastric cancer cells in vitro. Curcumin combined with autophagy inhibitor may provide a more effective strategy for its clinical application.