title: Casticin potentiates TRAIL-induced apoptosis of gastric cancer cells through endoplasmic reticulum stress.
abstract: BACKGROUND
  Casticin is one of the main active components obtained from Fructus Viticis and has been reported to exert anti-carcinogenic activity on a variety of cancer cells but the precise mechanism underlying this activity remains unclear.
  
  
  METHODS
  Apoptotic activities of casticin (1.0 µmol/l) and TRAIL (25, 50 ng/ml) alone or in combination in the gastric cancer cell lines BGC-823, SGC-7901 and MGC-803 were detected by the use of a cell apoptosis ELISA detection kit, flow cytometry (FCM) with propidium iodide (PI) staining and activities of caspase-3, -8 and -9 by ELISA and cleavage of polyADP-ribose polymerase (PARP) protein using western blot analysis. Death receptors (DR) expression levels were evaluated using FCM analysis and western blotting. 2', 7'-dichlorofluorescein diacetate (DCFH-DA) was used as a probe to measure the increase in reactive oxygen species (ROS) levels in cells. Multiple interventions, such as siRNA transfection and pharmacological inhibitors were used to explore the mechanisms of these actions.
  
  
  RESULTS
  Subtoxic concentrations of casticin significantly potentiated TRAIL-induced cytotoxicity and apoptosis in BGC-823, SGC-7901 and MGC-803 cells. Casticin dramatically upregulated DR5 receptor expression but had no effects on DR4 or decoy receptors. Deletion of DR5 by siRNA significantly reduced the apoptosis induced by the co-application of TRAIL and casticin. Gene silencing of the CCAAT/enhancer binding protein homologous protein (CHOP) and pretreatment with salubrinal, an endoplasmic reticulum (ER) stress inhibitor, attenuated casticin-induced DR5 receptor expression, and apoptosis and ROS production. Casticin downregulated the expression levels of the cell survival proteins cFLIP, Bcl-2, XIAP, and survivin. In addition, casticin also induced the expressions of DR5 protein in other gastric cancer cells (SGC-7901 and MGC-803).
  
  
  CONCLUSIONS
  Casticin enhances TRAIL-induced apoptosis through the downregulation of cell survival proteins and the upregulation of DR5 receptors through actions on the ROS-ER stress-CHOP pathway.
authors.affiliation: Medical College, Hunan Normal University, Changsha, China. caojianguo2005@yahoo.com.cn
authors.forename: Yuan
authors.initials: Y
authors.lastname: Zhou
authors.forename: Li
authors.initials: L
authors.lastname: Tian
authors.forename: Lingzhi
authors.initials: L
authors.lastname: Long
authors.forename: Meifang
authors.initials: M
authors.lastname: Quan
authors.forename: Fei
authors.initials: F
authors.lastname: Liu
authors.forename: Jianguo
authors.initials: J
authors.lastname: Cao
mesh_terms: D017209:Apoptosis / Q000187:drug effects* / Q000235:genetics; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects*; D005419:Flavonoids / Q000494:pharmacology* / Q000633:toxicity; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D055786:Gene Knockout Techniques; D006801:Humans; D034622:RNA Interference; D017382:Reactive Oxygen Species / Q000378:metabolism; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand / Q000235:genetics / Q000378:metabolism; D013274:Stomach Neoplasms / Q000235:genetics / Q000378:metabolism*; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000494:pharmacology* / Q000633:toxicity
chemical_list: D051017:Apoptosis Regulatory Proteins; D005419:Flavonoids; D017382:Reactive Oxygen Species; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; D053221:TNF-Related Apoptosis-Inducing Ligand; C054133:casticin
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