title: Zidovudine induces downregulation of mitochondrial deoxynucleoside kinases: implications for mitochondrial toxicity of antiviral nucleoside analogs.
abstract: Mitochondrial thymidine kinase 2 (TK2) and deoxyguanosine kinase (dGK) catalyze the initial phosphorylation of deoxynucleosides in the synthesis of the DNA precursors required for mitochondrial DNA (mtDNA) replication and are essential for mitochondrial function. Antiviral nucleosides are known to cause toxic mitochondrial side effects. Here, we examined the effects of 3'-azido-2',3'-dideoxythymidine (AZT) (zidovudine) on mitochondrial TK2 and dGK levels and found that AZT treatment led to downregulation of mitochondrial TK2 and dGK in U2OS cells, whereas cytosolic deoxycytidine kinase (dCK) and thymidine kinase 1 (TK1) levels were not affected. The AZT effects on mitochondrial TK2 and dGK were similar to those of oxidants (e.g., hydrogen peroxide); therefore, we examined the oxidative effects of AZT. We found a modest increase in cellular reactive oxygen species (ROS) levels in the AZT-treated cells. The addition of uridine to AZT-treated cells reduced ROS levels and protein oxidation and prevented the degradation of mitochondrial TK2 and dGK. In organello studies indicated that the degradation of mitochondrial TK2 and dGK is a mitochondrial event. These results suggest that downregulation of mitochondrial TK2 and dGK may lead to decreased mitochondrial DNA precursor pools and eventually mtDNA depletion, which has significant implications for the regulation of mitochondrial nucleotide biosynthesis and for antiviral therapy using nucleoside analogs.
authors.affiliation: Department of Anatomy, Physiology, and Biochemistry, Swedish University of Agricultural Sciences, Uppsala, Sweden.
authors.forename: Ren
authors.initials: R
authors.lastname: Sun
authors.affiliation: Department of Anatomy, Physiology, and Biochemistry, Swedish University of Agricultural Sciences, Uppsala, Sweden.
authors.forename: Staffan
authors.initials: S
authors.lastname: Eriksson
authors.affiliation: Department of Anatomy, Physiology, and Biochemistry, Swedish University of Agricultural Sciences, Uppsala, Sweden liya.wang@slu.se.
authors.forename: Liya
authors.initials: L
authors.lastname: Wang
mesh_terms: D000963:Antimetabolites / Q000494:pharmacology / Q000633:toxicity; D000998:Antiviral Agents / Q000633:toxicity; D045744:Cell Line, Tumor; D004261:DNA Replication / Q000235:genetics; D004272:DNA, Mitochondrial / Q000096:biosynthesis; D015536:Down-Regulation; D006801:Humans; D008928:Mitochondria / Q000187:drug effects / Q000201:enzymology*; D009705:Nucleosides / Q000737:chemistry; D016877:Oxidants / Q000494:pharmacology; D018384:Oxidative Stress / Q000187:drug effects; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000096:biosynthesis*; D017382:Reactive Oxygen Species / Q000378:metabolism; D013937:Thymidine Kinase / Q000096:biosynthesis*; D014529:Uridine / Q000494:pharmacology; D015215:Zidovudine / Q000494:pharmacology* / Q000633:toxicity
chemical_list: D000963:Antimetabolites; D000998:Antiviral Agents; D004272:DNA, Mitochondrial; D009705:Nucleosides; D016877:Oxidants; D017382:Reactive Oxygen Species; D015215:Zidovudine; D017853:Phosphotransferases (Alcohol Group Acceptor); C020018:deoxyribonucleoside kinases; C105339:thymidine kinase 2; C019165:deoxyguanosine kinase; D013937:Thymidine Kinase; D014529:Uridine