Abstract
Glucose-regulated protein 78 (GRP78) is frequently and highly expressed in various human malignancies and protects cancer cells against apoptosis induced by multifarious stresses, particularly endoplasmic reticulum stress (ER stress). The inhibition of GRP78 expression or activity could enhance apoptosis induced by anti-tumor drugs or compounds. Herein, we will evaluate the efficacy of lysionotin in the treatment of human liver cancer as well as the molecular mechanism. Moreover, we will examine whether inhibition of GRP78 enhanced the sensitivity of hepatocellular carcinoma cells to lysionotin. We found that lysionotin significantly suppressed proliferation and induced apoptosis of liver cancer cells. TEM showed that lysionotin-treated liver cancer cells showed an extensively distended and dilated endoplasmic reticulum lumen. Meanwhile, the levels of the ER stress hallmark GRP78 and UPR hallmarks (e.g., IRE1α and CHOP) were significantly increased in response to lysionotin treatment in liver cancer cells. Moreover, the reactive oxygen species (ROS) scavenger NAC and caspase-3 inhibitor Ac-DEVD-CHO visibly attenuated the induction of GRP78 and attenuated the decrease in cell viability induced by lysionotin. More importantly, the knockdown of GRP78 expression by siRNAs or treatment with EGCG, both induced remarkable increase in lysionotin-induced PARP and pro-caspase-3 cleavage and JNK phosphorylation. In addition, knockdown of GRP78 expression by siRNA or suppression GRP78 activity by EGCG both significantly improved the effectiveness of lysionotin. These data indicated that pro-survival GRP78 induction may contribute to lysionotin resistance. The combination of EGCG and lysionotin is suggested to represent a novel approach in cancer chemo-prevention and therapeutics.