Capillarisenol C, a novel bisphenol from Artemisia capillaris, induces ER stress-mediated cytotoxic autophagy in liver cancer cells.

In our previous work, we isolated a novel bisphenol named capillarisenol C (Cap C) from Artemisia capillaris. The preliminary activity screening study showed that Cap C can cause cytotoxicity to hepatocellular carcinoma cells, but its mechanism is still largely unclear. In this study, we confirmed that Cap C sharply reduced the viabilities of HepG2 and Huh7 cells in a concentration- and time-dependent manner by using CCK8 assay. We aimed to investigate the molecular mechanism underlying the cytotoxicity of Cap C in liver cancer cells. The mechanism study results showed that the apoptosis inhibitor z-vad-fmk had no significantly effects on Cap C-induced HepG2 cell death. Further mechanistic studies showed that MAP1LC3-II (LC3-II) expression, LC3 puncta and GFP-p62 puncta were increased under Cap C treatment. In addition, Cap C-induced cell death was attenuated by treatment with chloroquine (CQ) or knockdown of autophagy-related gene 7 (ATG7). Western blot analysis showed that Cap C treatment led to activation ER stress protein sensors EIF2AK3/PERK and ERN1/IRE1 as well as EIF2A/eIF2α phosphorylation which have been reported to promote cytotoxic autophagy in cancer cells. Moreover, Cap C-induced cell death was abrogated with the ER stress inhibitor 4-phenylbutyrate (4-PBA) treatment. Our results demonstrated that Cap C led to autophagic cell death in liver cancers potentially by activating ER stress-related PERK- eIF2α axis and IRE1 upregulation.