Inhibition of autophagy enhances heat-induced apoptosis in human non-small cell lung cancer cells through ER stress pathways

The occurrence and mechanisms of autophagy induced by heat stress are not well known in lung cancer cells. Here, we have demonstrated that heat stress induces autophagy in A549 and NCI-H460 cells through morphological and biochemical analyses. The inhibition of autophagy by chloroquine, 3-methyladenine and Beclin 1 siRNA enhanced heat-induced apoptosis. Moreover, the combination of chloroquine and heat stress inhibited tumor growth and enhanced apoptosis in vivo experiments. In addition, heat-induced autophagy involved the ER stress pathway (PERK- or IRE1-dependent). Further, heat treatment led to the increased phosphorylation of AMPK and the decreased phosphorylation of mTOR in vitro and in vivo. Knockdown of GRP78 inhibited the AMPK-mTOR pathway, and the AMPK inhibitor compound C decreased heat-induced autophagy, suggesting that activation of ER stress was involved in autophagy induction and promotion of the AMPK-mTOR pathway. In conclusion, our data suggested that the heat treatment of lung cancer cells triggered protective autophagy, as mediated by ER stress. Thus, inhibition of autophagy can be a promising strategy to enhance hyperthermia in the treatment of lung cancer patients.