title: Emodin enhances gefitinib-induced cytotoxicity via Rad51 downregulation and ERK1/2 inactivation.
abstract: Emodin, a tyrosine kinase inhibitor, is a natural anthraquinone derivative found in the roots and rhizomes of numerous plants. It reportedly exhibits an anticancer effect on lung cancer. Gefitinib (Iressa) is a selective epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor for human non-small cell lung cancer (NSCLC). However, the molecular mechanism of how emodin combined with gefitinib decreases NSCLC cell viability is unclear. The recombinase protein Rad51 is essential for homologous recombination repair, and Rad51 overexpression is resistant to DNA double-strand break-inducing cancer therapies. In this study, we found that emodin enhanced the cytotoxicity induced by gefitinib in two NSCLC cells lines, A549 and H1650. Emodin at low doses of 2-10 microM did not affect ERK1/2 activation, mRNA, and Rad51 protein levels; however, it enhanced a gefitinib-induced decrease in phospho-ERK1/2 and Rad51 protein levels by enhancing Rad51 protein instability. Expression of constitutively active MKK1/2 vectors (MKK1/2-CA) significantly rescued the reduced phospho-ERK1/2 and Rad51 protein levels as well as cell viability on gefitinib and emodin cotreatment. Blocking of ERK1/2 activation by U0126 (an MKK1/2 inhibitor) lowered Rad51 protein levels and cell viability in emodin-treated H1650 and A549 cells. Knockdown of Rad51 expression by transfection with si-Rad51 RNA enhanced emodin cytotoxicity. In contrast, Rad51 overexpression protected the cells from the cytotoxic effects induced by emodin and gefitinib. Consequently, emodin-gefitinib cotreatment may serve as the basis for a novel and better therapeutic modality in the management of advanced lung cancer.
authors.affiliation: Molecular Genetics of Microorganisms Laboratory, Department of Biochemical Science and Technology, National Chiayi University, Chiayi, Taiwan.
authors.forename: Ruey-Shyang
authors.initials: RS
authors.lastname: Chen
authors.forename: Jhih-Yuan
authors.initials: JY
authors.lastname: Jhan
authors.forename: Ying-Jhen
authors.initials: YJ
authors.lastname: Su
authors.forename: Wei-Ting
authors.initials: WT
authors.lastname: Lee
authors.forename: Chao-Min
authors.initials: CM
authors.lastname: Cheng
authors.forename: Shih-Ci
authors.initials: SC
authors.lastname: Ciou
authors.forename: Szu-Ting
authors.initials: ST
authors.lastname: Lin
authors.forename: Show-Mei
authors.initials: SM
authors.lastname: Chuang
authors.forename: Jen-Chung
authors.initials: JC
authors.lastname: Ko
authors.forename: Yun-Wei
authors.initials: YW
authors.lastname: Lin
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000378:metabolism / Q000633:toxicity; D017209:Apoptosis / Q000502:physiology; D002070:Butadienes / Q000378:metabolism; D045744:Cell Line, Tumor; D004642:Emodin / Q000378:metabolism*; D000077156:Gefitinib; D006801:Humans; D048369:MAP Kinase Kinase 1 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D009570:Nitriles / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000378:metabolism / Q000633:toxicity; D011799:Quinazolines / Q000633:toxicity*; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D051135:Rad51 Recombinase / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology
chemical_list: D000970:Antineoplastic Agents; D002070:Butadienes; D009570:Nitriles; D047428:Protein Kinase Inhibitors; D011799:Quinazolines; D034741:RNA, Small Interfering; C113580:U 0126; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D048369:MAP Kinase Kinase 1; D051135:Rad51 Recombinase; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease; D004642:Emodin; D000077156:Gefitinib