The Combined Inhibition of Autophagy and Diacylglycerol Acyltransferase-Mediated Lipid Droplet Biogenesis Induces Cancer Cell Death during Acute Amino Acid Starvation

Abstract

Lipid droplets (LDs) are dynamic organelles involved in the management of fatty acid trafficking and metabolism. Recent studies suggest that autophagy and LDs serve complementary roles in the protection against nutrient stress, but the autophagy–LD interplay in cancer cells is not well understood. Here, we examined the relationship between autophagy and LDs in starving HeLa cervical cancer- and MDA-MB-231 breast cancer cells. We found that acute amino acid depletion induces autophagy and promotes diacylglycerol acyltransferase 1 (DGAT1)-mediated LD accumulation in HeLa cells. Inhibition of autophagy via late-stage autophagy inhibitors, or by knocking down autophagy-related 5 (ATG5), reduced LD accumulation in amino acid-starved cancer cells, suggesting that autophagy contributes to LD biogenesis. On the contrary, knockdown of adipose triglyceride lipase (ATGL) increased LD accumulation, suggesting that LD breakdown is mediated by lipolysis under these conditions. Concurrent inhibition of autophagy by silencing ATG5 and of LD biogenesis using DGAT inhibitors was effective in killing starving HeLa cells, whereas cell survival was not compromised by suppression of ATGL-mediated lipolysis. Autophagy-dependent LD biogenesis was also observed in the aggressive triple-negative MDA-MB-231 breast cancer cells deprived of amino acids, but these cells were not sensitized to starvation by the combined inhibition of LD biogenesis and autophagy. These findings reveal that while targeting autophagy-driven and DGAT-mediated LD biogenesis reduces the resilience of HeLa cervical cancer cells to amino acid deprivation, this strategy may not be successful in other cancer cell types.