title: Modulation of Rad51, ERCC1, and thymidine phosphorylase by emodin result in synergistic cytotoxic effect in combination with capecitabine.
abstract: Thymidine phosphorylase (TP) is the rate-limiting enzyme for the activation of capecitabine (pro-drug of fluorouracil), and as a useful predictor of tumor response to capecitabine-based chemotherapy. Overexpression of Rad51 and ERCC1 induce resistance to chemotherapeutic agents. Emodin, one of the main bioactive anthraquinone derivatives in the roots and rhizomes of numerous plants, possesses potent antitumor effects. Accordingly, we aimed to explore the molecular mechanism of emodin enhances the capecitabine-induced cytotoxicity through controlling Rad51, ERCC1, and TP expression in human non-small cell lung cancer (NSCLC). The results show that capecitabine increases the phosphorylation of MKK1/2-ERK1/2 and protein levels of Rad51 and ERCC1 through enhancing the protein stability. Depletion of endogenous Rad51 or ERCC1 expression by specific small interfering RNA transfection significantly increases capecitabine-induced cell death and growth inhibition. Emodin enhances the capecitabine-induced cytotoxic effects through ERK1/2 inactivation and decreasing the Rad51 and ERCC1 protein levels induced by capecitabine. Enhancement of ERK1/2 signaling by constitutively active MKK1/2 (MKK1/2-CA) results in increasing Rad51 and ERCC1 protein levels and cell viability in NSCLC cell lines treated with emodin and capecitabine. Interestingly, emodin enhances TP mRNA and protein expression in capecitabine treated NSCLC cell lines, and depletion of the TP expression decreases the cytotoxic effects induced by capecitabine and emodin. We conclude that enhancing the cytotoxicity to capecitabine by emodin is mediated by down-regulation the expression of Rad51 and ERCC1 and up-regulation TP expression.
authors.affiliation: Department of Internal Medicine, Hsinchu Hospital, Department of Health, The Executive Yuan, Taiwan.
authors.forename: Jen-Chung
authors.initials: JC
authors.lastname: Ko
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: Shao-Hsing
authors.initials: SH
authors.lastname: Weng
authors.forename: Ying-Chen
authors.initials: YC
authors.lastname: Su
authors.forename: Yun-Wei
authors.initials: YW
authors.lastname: Lin
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D000069287:Capecitabine; D016923:Cell Death / Q000187:drug effects; D045744:Cell Line, Tumor; D004268:DNA-Binding Proteins / Q000096:biosynthesis* / Q000235:genetics; D003841:Deoxycytidine / Q000031:analogs & derivatives* / Q000494:pharmacology; D004357:Drug Synergism; D004642:Emodin / Q000494:pharmacology*; D004720:Endonucleases / Q000096:biosynthesis* / Q000235:genetics; D005472:Fluorouracil / Q000031:analogs & derivatives* / Q000494:pharmacology; D055785:Gene Knockdown Techniques; D006801:Humans; D048369:MAP Kinase Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D048370:MAP Kinase Kinase 2 / Q000037:antagonists & inhibitors / Q000378:metabolism; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D055550:Protein Stability; D012333:RNA, Messenger / Q000096:biosynthesis; D051135:Rad51 Recombinase / Q000096:biosynthesis* / Q000235:genetics; D013939:Thymidine Phosphorylase / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D000970:Antineoplastic Agents; D004268:DNA-Binding Proteins; D012333:RNA, Messenger; D003841:Deoxycytidine; D000069287:Capecitabine; C543750:TYMP protein, human; D013939:Thymidine Phosphorylase; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; C495153:RAD51 protein, human; D051135:Rad51 Recombinase; C071447:ERCC1 protein, human; D004720:Endonucleases; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease; D004642:Emodin; D005472:Fluorouracil