title: Emodin induces a reactive oxygen species-dependent and ATM-p53-Bax mediated cytotoxicity in lung cancer cells.
abstract: Emodin (1,3,8-trihydroxy-6-methyl-anthraquinone), a natural anthraquinone compound isolated from the rhizome of rhubarb, has been reported to suppress tumor growth in many clinical situations. Here, we demonstrate that emodin induces apoptosis in human lung adenocarcinoma A549 cells by activating a reactive oxygen species-elicited ATM-p53-Bax signaling pathway. In response to emodin treatment, p53 protein increases in A549 cells, which in turn up-regulates Bax expression. Co-treating cells with either a p53 inhibitor or respectively knocking down the expression of p53 and Bax by shRNA extensively diminished emodin-induced cell viability, caspase 3 activation and the release of cytochrome c from the mitochondria, indicating the crucial role for p53/Bax in emodin-mediated cytotoxicity. Pre-treating cells with the antioxidant ascorbic acid not only prohibited the induction of reactive oxygen species by emodin, but also inhibited the up-regulation of p53. Upon emodin treatment, p53 is phosphorylated at Ser(15), which is accompanied by the ATM phosphorylation at Ser(1981). Both of these events could also be blocked by the presence of ascorbic acid. Moreover, knockdown of ATM by siRNA significantly reduced p53 phosphorylation and stabilization, indicating the upstream role of emodin-induced reactive oxygen species generation in ATM activation and following p53 phosphorylation and stabilization. Taken together, our results demonstrate that emodin-induced reactive oxygen species generation activates an ATM-p53-Bax-dependent signaling pathway, which consequently leads to mitochondria-dependent apoptotic cell death in human lung adenocarcinoma A549 cells.
authors.affiliation: Department of Life Science, Fu Jen Catholic University, Taipei County, Taiwan.
authors.forename: Jin-Mei
authors.initials: JM
authors.lastname: Lai
authors.forename: Jinghua Tsai
authors.initials: JT
authors.lastname: Chang
authors.forename: Chi-Luan
authors.initials: CL
authors.lastname: Wen
authors.forename: Shih-Lan
authors.initials: SL
authors.lastname: Hsu
mesh_terms: D002282:Adenocarcinoma, Bronchiolo-Alveolar / Q000201:enzymology / Q000378:metabolism; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D064007:Ataxia Telangiectasia Mutated Proteins; D053148:Caspase 3 / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000378:metabolism*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004642:Emodin / Q000494:pharmacology*; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D051034:Inhibitor of Apoptosis Proteins; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism; D008928:Mitochondria / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D034622:RNA Interference; D017382:Reactive Oxygen Species / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D000077022:Survivin; D016159:Tumor Suppressor Protein p53 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D025521:Tumor Suppressor Proteins / Q000378:metabolism*; D051028:bcl-2-Associated X Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: D000970:Antineoplastic Agents; C107489:BIRC5 protein, human; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D051034:Inhibitor of Apoptosis Proteins; D008869:Microtubule-Associated Proteins; D017382:Reactive Oxygen Species; D000077022:Survivin; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; D051028:bcl-2-Associated X Protein; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases; D053148:Caspase 3; D004642:Emodin