TRAP1 regulates autophagy in lung cancer cells

Background: Expression of TRAP1, a member of the HSP90 chaperone family, has been implicated in tumour protective effects, based on its differential mitochondrial localization and function.

Design: This work was designed to provide new insights into the pathways involved in TRAP1-provided cytoprotection on NSCLC. For this, TRAP1-depleted A549 human NSCLC cells and MRC-5 normal lung fibroblasts were produced using a siRNA approach and main cellular quality control mechanisms were investigated.

Results: TRAP1-depleted A549 cells displayed decreased cell viability likely due to impaired mitochondrial function including decreased ATP/AMP ratio, oxygen consumption and membrane potential, as well as increased apoptotic Indicators. Furthermore, the negative impact of TRAP1 depletion on mitochondrial function was not observed in normal MRC-5 lung cells, which might be due to the differential intracellular localization of the chaperone in tumour versus normal cells. Additionally, A549 TRAP1-depleted cells showed increased autophagic flux. Functionally, Autophagy inhibition resulted in decreased cell viability in both TRAP1-expressing and TRAP1-depleted tumour cells with minor effects on MRC-5 cells. Conversely, Autophagy stimulation decreased cell viability of both A549 and MRC-5 TRAP1-expressing cells while in A549 TRAP1-depleted cells, increased Autophagy augmented viability.

Conclusions: Our results show that even though TRAP1 depletion affects both normal MRC-5 and tumour A549 cell proliferation, inhibition of Autophagy per se led to a decrease in tumour cell mass, while having a reduced effect on the normal cell line. The strategy of targeting TRAP1 in NSCLC shows future potential therapeutic applications.

TRAP1; apoptosis; autophagy; cathepsin B; lung cancer; macroautophagy.