title: Implication of intracellular ROS formation, caspase-3 activation and Egr-1 induction in platycodon D-induced apoptosis of U937 human leukemia cells.
abstract: Platycodon D is a major constituent of triterpene saponins found in the root of Platycodon grandiflorum, Platycodi Radix, which is widely used in traditional Oriental medicine for the treatment of many chronic inflammatory diseases. The results of previous studies have shown that this compound has in vitro growth-inhibitory activity in human cancer cells, however, the mechanism by which this action occurs is poorly understood. In this study, we examined the effects of platycodon D on the production of reactive oxygen species (ROS) and evaluated the association of these effects with apoptotic tumor cell death using a human leukemic U937 cell line. The results of this study demonstrate that platycodon D mediates ROS production, and that this mediation is followed by a decrease in mitochondrial membrane potential (MMP, DJm), activation of caspase-3, and cleavage of poly (ADP-ribose) polymerase (PARP). Both the cytotoxic effects and apoptotic characteristics induced by platycodon D treatment were significantly inhibited by z-DEVD-fmk, a caspase-3 inhibitor, which demonstrates the important role that caspase-3 plays in the observed cytotoxic effect. Additionally, the transcription factor early growth response-1 (Egr-1) gene was transcriptionally activated and the levels of non-steroidal anti-inflammatory drug (NSAID)-activated gene-1 (NAG-1) protein were elevated in platycodon D-treatedU937 cells. However, the quenching of ROS generation in response to treatment with a ROS scavenger, N-acetyl-L-cysteine, reversed the platycodon D-induced apoptosis effects via inhibition of Egr-1 activation, ROS production, MMP collapse, and the subsequent activation of caspase-3. Although further studies are needed to demonstrate that increased expression of Egr-1 by platycodon D leads directly to NAG-1 induction and subsequent apoptosis, our observations clearly indicate that ROS induced through Egr-1 activation are involved in the early molecular events involved in the platycodon D-induced apoptotic pathway.
authors.affiliation: Department of Biochemistry, Dongeui University College of Oriental Medicine, Busan 614-052, South Korea.
authors.forename: Dong Yeok
authors.initials: DY
authors.lastname: Shin
authors.forename: Gi Young
authors.initials: GY
authors.lastname: Kim
authors.forename: Wei
authors.initials: W
authors.lastname: Li
authors.forename: Byung Tae
authors.initials: BT
authors.lastname: Choi
authors.forename: Nam Deuk
authors.initials: ND
authors.lastname: Kim
authors.forename: Ho Sung
authors.initials: HS
authors.lastname: Kang
authors.forename: Yung Hyun
authors.initials: YH
authors.lastname: Choi
mesh_terms: D000972:Antineoplastic Agents, Phytogenic / Q000302:isolation & purification / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D053148:Caspase 3 / Q000187:drug effects / Q000378:metabolism; D051766:Early Growth Response Protein 1 / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D016403:Lymphoma, Large B-Cell, Diffuse / Q000188:drug therapy* / Q000473:pathology; D008518:Medicine, East Asian Traditional; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D018517:Plant Roots; D031238:Platycodon / Q000737:chemistry*; D011065:Poly(ADP-ribose) Polymerases / Q000187:drug effects / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D012503:Saponins / Q000302:isolation & purification / Q000494:pharmacology*; D014315:Triterpenes / Q000302:isolation & purification / Q000494:pharmacology*; D020298:U937 Cells
chemical_list: D000972:Antineoplastic Agents, Phytogenic; C497325:EGR1 protein, human; D051766:Early Growth Response Protein 1; D017382:Reactive Oxygen Species; D012503:Saponins; D014315:Triterpenes; C108953:platycodin D; D011065:Poly(ADP-ribose) Polymerases; D053148:Caspase 3