Luteolin sensitizes human liver cancer cells to TRAIL-induced apoptosis via autophagy and JNK-mediated death receptor 5 upregulation

The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a dynamic cytokine that initiates the apoptosis of cancer cells, but exhibits little or no toxicity in normal cells. Luteolin is a flavonoid compound frequently used in the treatment of cancer. In the current study, we demonstrate that treatment with luteolin and TRAIL exerts a synergistic effect and the mechanisms on TRAIL-resistant Huh7 cells. The results demonstrated that luteolin induced an autophagic flux in human liver cancer cells. The attenuation of the autophagic flux by applying the specific inhibitor of autophagy, chloroquine, significantly suppressed DR5 expression. Treatment with genetically modified autophagy-related 5 siRNA abrogated the luteolin-mediated sensitizing effect of TRAIL. Furthermore, pre-treatment with the c-Jun N-terminal kinase (JNK) inhibitor, SP600125, significantly attenuated the luteolin-induced upregulation of DR5 expression, thereby suggesting that JNK activation promotes DR5 expression. Our findings also revealed that Akt phosphorylation was required for TRAIL sensitization. On the whole, the findings of this study indicated that luteolin effectively enhanced TRAIL-initiated apoptosis, and that these effects were likely to be mediated by autophagy and JNK-mediated DR5 expression.