title: Modulation of human UMP/CMP kinase affects activation and cellular sensitivity of deoxycytidine analogs.
abstract: Deoxycytidine analogs are an important class of clinically active antiviral and anticancer agents. The stepwise phosphorylation of these analogs to triphosphate metabolites is crucial for biological action. Human UMP/CMP kinase (UMP/CMPK; cytidylate kinase; EC 2.7.4.14) is thought to be responsible for phosphorylation of UMP, CMP, and dCMP and may also play an important role in the activation of pyrimidine analogs. However, no evidence has verified this notion in intact cells. In this study we explored the functional roles of UMP/CMPK in natural pyrimidine synthesis and metabolism of deoxycytidine analogs, as well as 5-FU in HeLa S3 and HCT8 cells. The amounts of UMP/CMPK protein in different cell lines correlated with UMP, CMP, and dCMP kinase activities and amounts of UMP/CMPK RNA. Modulation of UMP/CMPK by overexpression or down-regulation had no impact on natural pyrimidine nucleotides and cell growth. However, down-regulating UMP/CMPK expression by siRNA led to a decrease in the formation of the triphosphate metabolites, resulting in cellular resistance to these analogs. More diphosphate and triphosphate metabolites of deoxycytidine analogs were detected and cellular sensitivity to these agents was increased in the UMP/CMPK-overexpressing cells. This study indicates that the second step enzyme (UMP/CMPK) is responsible for the phosphorylation of pyrimidine analogs and also has an impact on cellular sensitivity to these analogs in those cell lines.
authors.affiliation: National Institute of Cancer Research, National Health Research Institutes, Zhunan, Miaoli County, Taiwan, ROC. jyliou68@nhri.org.tw
authors.forename: Jieh-Yuan
authors.initials: JY
authors.lastname: Liou
authors.forename: Hui-Ru
authors.initials: HR
authors.lastname: Lai
authors.forename: Chih-Hung
authors.initials: CH
authors.lastname: Hsu
authors.forename: Wei-Ling
authors.initials: WL
authors.lastname: Chang
authors.forename: Mei-Ju
authors.initials: MJ
authors.lastname: Hsieh
authors.forename: Yu-Chun
authors.initials: YC
authors.lastname: Huang
authors.forename: Yung-Chi
authors.initials: YC
authors.lastname: Cheng
mesh_terms: D000970:Antineoplastic Agents / Q000037:antagonists & inhibitors / Q000378:metabolism; D002460:Cell Line; D045744:Cell Line, Tumor; D003841:Deoxycytidine / Q000031:analogs & derivatives* / Q000378:metabolism* / Q000494:pharmacology; D003843:Deoxycytidine Monophosphate / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000502:physiology; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D006367:HeLa Cells; D006801:Humans; D009703:Nucleoside-Phosphate Kinase / Q000037:antagonists & inhibitors* / Q000096:biosynthesis* / Q000502:physiology; D010766:Phosphorylation / Q000187:drug effects; D012333:RNA, Messenger / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D012333:RNA, Messenger; D003841:Deoxycytidine; D003843:Deoxycytidine Monophosphate; C019979:cytidylate kinase; D009703:Nucleoside-Phosphate Kinase