Protective role of autophagy in matrine-induced gastric cancer cell death

Abstract

Matrine has potent antitumor activity against a broad variety of cancer cells and our previous study showed that both autophagy and apoptosis were activated during matrine-induced gastric cancer cell death. The aim of the present study was to determine the significance of autophagy in antineoplastic effects of matrine and the molecular mechanism by which matrine induces autophagy in gastric cancer cells. Western blot analysis showed that exposure of gastric cancer cells to matrine resulted in the extent of autophagy increasing in a dose- and time-dependent manner by detecting micro-tubule-associated protein 1 light chain 3 (LC3). This induction was due to activation of autophagic flux, as supported using the lysosome inhibitor, bafilomycin A1, which produced an accumulation of LC3-II. Propidium iodide staining demonstrated that matrine induced cell death in a dose-dependent manner and the autophagy inhibitor 3-methyladenine (3-MA) or bafilomycin A1 enhanced lethality of matrine against gastric cancer cells. Moreover, after pretreatment with 3-MA, some of the gastric cancer cells treated with matrine exhibited prototypical characteristics of apoptosis by transmission electron microscopy. The ability of 3-MA to increase matrine-induced apoptosis was further confirmed by Annexin V-FITC/PI staining. Also, the combination of matrine and 3-MA was more potent than matrine alone in inhibiting the proliferation of SGC-7901 cells assessed by sulphorhodamine B assay. Furthermore, administration of the pan-caspase inhibitor zVAD-fmk or autophagy inducer rapamycin decreased the matrine-induced cell death. In addition, matrine treatment did not inhibit the phosphorylation of Akt and its downstream effectors mammalian target of rapamycin (mTOR) as well as p70 ribosomal protein S6 kinase (p70S6K), although the levels of the total Akt and mTOR were decreased. These results suggest that autophagy was activated as a protective mechanism against matrine-induced apoptosis and inhibition of autophagy may be an attractive strategy for enhancing the antitumor potential of matrine in gastric cancer.