Luteolin Promotes Cell Apoptosis by Inducing Autophagy in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the most common primary liver malignancy and is a leading cause of cancer-related death worldwide. Luteolin, a flavonoid from traditional Chinese medicine, shows anti-cancer activity in many cancer cells, including HCC. However, the mechanism underlying the action of luteolin in HCC, especially its role in regulating cell autophagy, remains unclear. In the present study, we investigated the role of luteolin in regulating cell autophagy and the role of autophagy in luteolin-induced apoptosis.

The 3-(4,5-dimethythiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay (MTT) was used to investigate cell viability. Flow cytometry analysis was used to detect the cell cycle and cell apoptosis. Hoechst 33342 staining was used to detect cell apoptosis. Transmission electron microscopy was used to investigate autophagy. qRT-PCR and western blotting were used to detect apoptosis- and autophagy-related mRNAs and proteins.

Luteolin reduced the viability of SMMC-7721 cells in a time and dose-dependent manner, and induced significant G0/G1-phase arrest. In addition, the results of flow cytometry analysis and Hoechst 33342 staining showed that luteolin treatment increased the number of apoptotic cells obviously, and the results of qRT-PCR and western blotting showed that luteolin treatment increased caspase 8 and decreased bcl-2 at the mRNA and protein levels. Furthermore, luteolin increased the number of intracellular autophagosomes, promoted LC3B-I conversion to LC3B-II, and increased Beclin 1 expression. Finally, co-treatment with the autophagy inhibitor chloroquine weakened the effects of luteolin on cell apoptosis.

Luteolin induced apoptosis in human liver cancer SMMC-7721 cells, partially via autophagy. Thus, luteolin could be used as a regulator of autophagy in HCC treatment.