title: An anthraquinone derivative, emodin sensitizes hepatocellular carcinoma cells to TRAIL induced apoptosis through the induction of death receptors and downregulation of cell survival proteins.
abstract: Recombinant tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is currently under clinical trials for cancer, however many tumor cells, including hepatocellular carcinoma (HCC) develop resistance to TRAIL-induced apoptosis. Hence, novel agents that can alleviate TRAIL-induced resistance are urgently needed. In the present report, we investigated the potential of emodin to enhance apoptosis induced by TRAIL in HCC cells. As observed by MTT cytotoxicity assay and the externalization of the membrane phospholipid phosphatidylserine, we found that emodin can significantly potentiate TRAIL-induced apoptosis in HCC cells. When investigated for the mechanism(s), we observed that emodin can downregulate the expression of various cell survival proteins, and induce the cell surface expression of both TRAIL receptors, death receptors (DR) 4 as well as 5. In addition, emodin increased the expression of C/EBP homologous protein (CHOP) in a time-dependent manner. Knockdown of CHOP by siRNA decreased the induction of emodin-induced DR5 expression and apoptosis. Emodin-induced induction of DR5 was mediated through the generation of reactive oxygen species (ROS), as N-acetylcysteine blocked the induction of DR5 and the induction of apoptosis. Also, the knockdown of X-linked inhibitor of apoptosis protein by siRNA significantly reduced the sensitization effect of emodin on TRAIL-induced apoptosis. Overall, our experimental results clearly indicate that emodin can indeed potentiate TRAIL-induced apoptosis through the downregulation of antiapoptotic proteins, increased expression of apoptotic proteins, and ROS mediated upregulation of DR in HCC cells.
authors.affiliation: Department of Pharmacology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, 117597, Singapore.
authors.forename: Aruljothi
authors.initials: A
authors.lastname: Subramaniam
authors.forename: Ser Yue
authors.initials: SY
authors.lastname: Loo
authors.forename: Peramaiyan
authors.initials: P
authors.lastname: Rajendran
authors.forename: Kanjoormana A
authors.initials: KA
authors.lastname: Manu
authors.forename: Ekambaram
authors.initials: E
authors.lastname: Perumal
authors.forename: Feng
authors.initials: F
authors.lastname: Li
authors.forename: Muthu K
authors.initials: MK
authors.lastname: Shanmugam
authors.forename: Kodappully Sivaraman
authors.initials: KS
authors.lastname: Siveen
authors.forename: Joo-In
authors.initials: JI
authors.lastname: Park
authors.forename: Kwang Seok
authors.initials: KS
authors.lastname: Ahn
authors.forename: Kam M
authors.initials: KM
authors.lastname: Hui
authors.forename: Alan P
authors.initials: AP
authors.lastname: Kumar
authors.forename: Gautam
authors.initials: G
authors.lastname: Sethi
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D006528:Carcinoma, Hepatocellular / Q000188:drug therapy*; D045744:Cell Line, Tumor / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects*; D019008:Drug Resistance, Neoplasm; D004642:Emodin / Q000494:pharmacology*; D006801:Humans; D008113:Liver Neoplasms / Q000188:drug therapy*; D017382:Reactive Oxygen Species / Q000378:metabolism; D053218:Receptors, Death Domain / Q000378:metabolism*; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000494:pharmacology*; D051742:Transcription Factor CHOP / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D051017:Apoptosis Regulatory Proteins; C497249:DDIT3 protein, human; D017382:Reactive Oxygen Species; D053218:Receptors, Death Domain; D053221:TNF-Related Apoptosis-Inducing Ligand; C505653:TNFSF10 protein, human; D051742:Transcription Factor CHOP; D004642:Emodin