title: Role of Rad51 down-regulation and extracellular signal-regulated kinases 1 and 2 inactivation in emodin and mitomycin C-induced synergistic cytotoxicity in human non-small-cell lung cancer cells.
abstract: Emodin (1,3,8-trihydroxy-6-methyl-anthraquinone) is a natural anthraquinone derivative found in the roots and rhizomes of numerous plants. It is a tyrosine kinase inhibitor and has anticancer effects on lung cancer. Rad51 plays a central role in homologous recombination, and high levels of Rad51 expression are observed in chemo- or radioresistant carcinomas. Our previous studies have shown that the mitogen-activated protein kinase kinase (MKK) 1/2-extracellular signal-regulated kinase (ERK) 1/2 signal pathway maintains the expression of Rad51. Therefore, in this study, we hypothesized that emodin could enhance the effects of the antitumor antibiotic mitomycin C (MMC)-mediated cytotoxicity by decreasing the expression of Rad51 and the phosphorylation of ERK1/2. Exposure of the human non-small-cell lung cancer H1703 or A549 cell lines to emodin decreased the MMC-elicited phosphorylated ERK1/2 and Rad51 levels. Moreover, emodin significantly decreased the MMC-elicited Rad51 mRNA and protein levels by increasing the instability of Rad51 mRNA and protein. In emodin- and MMC-cotreated cells, ERK1/2 phosphorylation was enhanced by constitutively active MKK1/2 (MKK1/2-CA), thus increasing Rad51 protein levels and protein stability. The synergistic cytotoxic effects induced by emodin combined with MMC were remarkably decreased by MKK1-CA-mediated enhancement of ERK1/2 activation. Depletion of endogenous Rad51 expression by small interfering Rad51 RNA transfection significantly enhanced MMC-induced cell death and cell growth inhibition. In contrast, overexpression of Rad51 protects lung cancer cells from the synergistic cytotoxic effects induced by emodin and MMC. We conclude that suppression of Rad51 expression or a combination of emodin with chemotherapeutic agents may be considered as potential therapeutic modalities for lung cancer.
authors.affiliation: Molecular Oncology Laboratory, Department of Biochemical Science and Technology, National Chiayi University, Chiayi, Taiwan.
authors.forename: Ying-Jhen
authors.initials: YJ
authors.lastname: Su
authors.forename: Min-Shao
authors.initials: MS
authors.lastname: Tsai
authors.forename: Ya-Hsun
authors.initials: YH
authors.lastname: Kuo
authors.forename: Yu-Fan
authors.initials: YF
authors.lastname: Chiu
authors.forename: Chao-Min
authors.initials: CM
authors.lastname: Cheng
authors.forename: Szu-Ting
authors.initials: ST
authors.lastname: Lin
authors.forename: Yun-Wei
authors.initials: YW
authors.lastname: Lin
mesh_terms: D002289:Carcinoma, Non-Small-Cell Lung / Q000188:drug therapy* / Q000473:pathology; D045744:Cell Line, Tumor; D015536:Down-Regulation; D004357:Drug Synergism; D004642:Emodin / Q000494:pharmacology*; D006801:Humans; D008175:Lung Neoplasms / Q000188:drug therapy* / Q000473:pathology; D020935:MAP Kinase Signaling System; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D016685:Mitomycin / Q000494:pharmacology*; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex / Q000502:physiology; D012333:RNA, Messenger / Q000032:analysis; D051135:Rad51 Recombinase / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000235:genetics / Q000502:physiology
chemical_list: D012333:RNA, Messenger; D016685:Mitomycin; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; C495153:RAD51 protein, human; D051135:Rad51 Recombinase; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease; D004642:Emodin