Quercetin, a natural flavonoid compound, is a potent cancer therapeutic agent widely found in fruit and vegetables. It has been reported to induce growth inhibition and apoptosis in both A549 and H1299 human lung cancer cells. However, the effect of quercetin-induced autophagy on apoptosis and the possible autophagy mechanism in A549 and H1299 cells have not yet been critically examined.

Quercetin-induced autophagy contributes to apoptosis in A549 and H1299 lung cancer cells, which involved the SIRT1/AMPK signaling pathway.

A549 and H1299 cells were treated with different concentrations of quercetin for 24 hours. Cell growth was measured by cell counting kit-8 (CCK-8) assay, whereas apoptosis was assessed by western blotting analysis of apoptotic proteins. The levels of proteins and genes involved in autophagy were determined by western blotting and reverse transcription polymerase chain reaction (RT-PCR), respectively. Autophagosomes were also observed by transmission electron microscopy (TEM) and LC3 immunofluorescence.

Quercetin inhibited cell viability and induced mitochondria-dependent apoptosis in both A549 and H1299 cells in a dose-dependent. Moreover, quercetin also promoted the expression of LC3-II and beclin 1 and suppressed the expression of p62. The mRNA levels of LC3-II, beclin 1, Atg5, Atg7, and Atg12 were upregulated by quercetin treatment. Autophagy inhibition with 3-methyladenine could effectively inhibit quercetin-induced apoptosis. In addition, quercetin dose-dependently elevated the levels of SIRT1 protein and the pAMPK-AMPK ratio. Quercetin-induced autophagy was attenuated by SIRT1 inhibitor EX527 and SirT1 knockdown by small interfering RNA (siRNA). Conclusions: Quercetin-induced autophagy contributes to apoptosis in A549 and H1299 lung cancer cells, which involved the SIRT1/AMPK signaling pathway.