title: Up-regulation of extracellular signal-regulated kinase 1/2-dependent thymidylate synthase and thymidine phosphorylase contributes to cisplatin resistance in human non-small-cell lung cancer cells.
abstract: Chemotherapy for advanced human non-small-cell lung cancer (NSCLC) includes platinum-containing compound such as cisplatin in combination with a second- or third-generation cytotoxic agent. 5-Fluorouracil (5-FU) belongs to antimetabolite chemotherapeutics, and its mechanism of cytotoxicity is involved in the inhibition of thymidylate synthase (TS). TS and thymidine phosphorylase (TP) are key enzymes of the pyrimidine salvage pathway. In this study, we have examined the molecular mechanism of TS and TP in regulating drug sensitivity to cisplatin in NSCLC cell lines. Cisplatin could increase the phosphorylation of mitogen-activated protein kinase kinase 1/2 (MKK1/2)-extracellular signal-regulated kinase 1/2 (ERK1/2) and the protein levels of TS and TP through enhancing the protein stability in A549 and H1975 cells. Blocking ERK1/2 activation by MKK1/2 inhibitor [U0126; 1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenylthio)butadiene)] decreased TS and TP protein levels in both cell lines treated with cisplatin. Depletion of endogenous TS or TP expression by specific small interfering RNA transfection significantly increased cisplatin-induced cell death and growth inhibition. Combined treatment with 5-FU could decrease cisplatin-induced ERK1/2 activation and the induction of TS and TP, which subsequently resulted in synergistic cytotoxic effects. Enforced expression of constitutive active MKK1/2 vectors rescued the protein levels of phospho-ERK1/2, TS, and TP, and the cell viability that were decreased by cisplatin and 5-FU combination. In contrast, U0126 enhanced drug sensitivity to cisplatin and/or 5-FU in lung cancer cells. In conclusion, the up-regulation of ERK1/2-dependent TS and TP can protect human lung cancer cells from cisplatin-induced cytotoxicity.
authors: Department of Internal Medicine, Hsinchu Hospital, Chiayi, Taiwan.
authors: Jen-Chung
authors: JC
authors: Ko
authors: Min-Shao
authors: MS
authors: Tsai
authors: Yu-Fan
authors: YF
authors: Chiu
authors: Shao-Hsing
authors: SH
authors: Weng
authors: Ya-Hsun
authors: YH
authors: Kuo
authors: Yun-Wei
authors: YW
authors: Lin
mesh_terms: D002289:Carcinoma, Non-Small-Cell Lung / Q000188:drug therapy / Q000201:enzymology*; D045744:Cell Line, Tumor; D002945:Cisplatin / Q000494:pharmacology / Q000627:therapeutic use*; D019008:Drug Resistance, Neoplasm / Q000187:drug effects / Q000502:physiology; D055785:Gene Knockdown Techniques / Q000379:methods; D006801:Humans; D008175:Lung Neoplasms / Q000188:drug therapy / Q000201:enzymology*; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology; D019950:Mitogen-Activated Protein Kinase 1 / Q000096:biosynthesis*; D048052:Mitogen-Activated Protein Kinase 3 / Q000096:biosynthesis*; D013939:Thymidine Phosphorylase / Q000096:biosynthesis*; D013940:Thymidylate Synthase / Q000096:biosynthesis*; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology*
chemical_list: D013940:Thymidylate Synthase; D013939:Thymidine Phosphorylase; C535150:MAPK1 protein, human; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D002945:Cisplatin