BACKGROUND: This study was designed to investigate the effect of lycorine (LY) on the AMPK-mTOR-S6K signaling pathway and to clarify its role in autophagy and apoptosis.

MATERIAL AND METHODS: Various concentrations of LY were used to treat non-small cell lung carcinoma A549 cells. The MTT assay was used to measure cell viability and acridine orange staining was used to detect cell morphology changes. Western blot analysis was used to test the effect of LY on the expression levels of LC3, caspase 3, and other proteins involved in the AMPK-mTOR-S6K signaling pathway.

RESULTS: The half maximal inhibitory concentration (IC50) of LY after 24-h treatment was 8.5 μM, with stronger inhibitory effect of 24-h LY treatment over 12-h LY treatment. Morphological observation showed that lower doses (4 μM and 8 μM) of LY treatment induced A549 cell death mainly caused by autophagy, whereas the higher dose (16 μM) of LY treatment induced A549 cell death, mainly caused by apoptosis. Furthermore, 8 μM LY caused the highest conversion of LC3-II from LC3-I. All LY treatments activated caspase-3. LY treatment also promoted AMPK phosphorylation (Thr172) and inhibited the phosphorylation of mTOR and S6K.

CONCLUSIONS: LY induced apoptosis of A549 cells by regulating the AMPK-mTOR-S6K signaling pathway. Lower levels (4~8 μM) of LY-induced autophagy contributed to LY-induced apoptosis.