Licochalcone A induces apoptosis through endoplasmic reticulum stress via a phospholipase Cγ1-, Ca(2+)-, and reactive oxygen species-dependent pathway in HepG2 human hepatocellular carcinoma cells

A-Young Choi, Ji Hyun Choi, Keun-Young Hwang, Yeon Ju Jeong, Wonchae Choe, Kyung-Sik Yoon, Joohun Ha, Sung Soo Kim, Jang Hyun Youn, Eui-Ju Yeo, Insug Kang
Apoptosis: An International Journal on Programmed Cell Death 2014, 19 (4): 682-97
Licochalcone A (LicA), an estrogenic flavonoid, induces apoptosis in multiple types of cancer cells. In this study, the molecular mechanisms underlying the anti-cancer effects of LicA were investigated in HepG2 human hepatocellular carcinoma cells. LicA induced apoptotic cell death, activation of caspase-4, -9, and -3, and expression of endoplasmic reticulum (ER) stress-associated proteins, including C/EBP homologous protein (CHOP). Inhibition of ER stress by CHOP knockdown or treatment with the ER stress inhibitors, salubrinal and 4-phenylbutyric acid, reduced LicA-induced cell death. LicA also induced reactive oxygen species (ROS) accumulation and the anti-oxidant N-acetylcysteine reduced LicA-induced cell death and CHOP expression. In addition, LicA increased the levels of cytosolic Ca(2+), which was blocked by 2-aminoethoxydiphenyl borate (an antagonist of inositol 1,4,5-trisphosphate receptor) and BAPTA-AM (an intracellular Ca(2+) chelator). 2-Aminoethoxydiphenyl borate and BAPTA-AM inhibited LicA-induced cell death. Interestingly, LicA induced phosphorylation of phospholipase Cγ1 (PLCγ1) and inhibition of PLCγ1 reduced cell death and ER stress. Moreover, the multi-targeted receptor tyrosine kinase inhibitors, sorafenib and sunitinib, reduced LicA-induced cell death, ER stress, and cytosolic Ca(2+) and ROS accumulation. Finally, LicA induced phosphorylation of vascular endothelial growth factor receptor 2 (VEGFR2) and c-Met receptor and inhibition of both receptors by co-transfection with VEGFR2 and c-Met siRNAs reversed LicA-induced cell death, Ca(2+) increase, and CHOP expression. Taken together, these findings suggest that induction of ER stress via a PLCγ1-, Ca(2+)-, and ROS-dependent pathway may be an important mechanism by which LicA induces apoptosis in HepG2 hepatocellular carcinoma cells.

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