Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.1.21 (thymidine kinase)
7,561 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Loss of the transcription factor p53 implies mRNA losses of target genes such as the p53R2 subunit of human ribonucleotide reductase (RNR). We hypothesized that other genes in the dNTP supply system would compensate for such p53R2 losses and looked for this in our own data and in data of the Gene Expression Omnibus (GEO). We found that the de novo dNTP supply system compensates for p53R2 losses with increases in RNR subunit R1, R2, or both. We also found compensatory increases in cytosolic deoxycytidine kinase (dCK) and thymidine kinase 1 (TK1) and in mitochondrial deoxyguanosine kinase (dGK), all of the salvage dNTP supply system; in contrast, the remaining mitochondrial salvage enzyme thymidine kinase 2 (TK2) decreased with p53 loss. Thus, TK2 may be more dedicated to meeting mitochondrial dNTP demands than dGK which may be more obligated to assist cytosolic dNTP supply in meeting nuclear DNA dNTP demands.
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PMID:dNTP Supply Gene Expression Patterns after P53 Loss. 2320 1

Nucleoside analogs serve as important chemotherapeutic agents in a number of severe diseases such as cancer and viral infections. These agents are pro-drugs that have to be taken up and phosphorylated in several steps to be trapped in the cells and transformed to active metabolites that inhibit essential steps in the replication of viruses or malignant cells. The anabolic deoxynucleoside kinases (dNKs) and catabolic 5'-nucleotidases(5'-NTs) are involved in maintaining substrate cycles, and act as regulators for the intracellular pools of active nucleotide metabolites. In this chapter the expression patterns of the four dNKs i.e.cytosolic deoxycytidine kinase (dCK) and thymidine kinase 1 (TK1) and the mitochondrial thymidine kinase 2 (TK2) and deoxyguanosine kinase (dGK) as well as the six intracellular 5'-NTs: cN-IA, cN-IB, cN-II, cN-III, cdN, mdN, present in animal cells and tissues will be described. Their role as primary controllers of the accumulation and activation of important anti viral and anti cancer nucleoside analogs in different tissues involved in the pathophysiology of these diseases will be evaluated. The predictability of using the ratios between the activities of the dNKs and 5'-NTs for estimating efficacy and side effects of nucleoside drug candidates will be discussed as well as recommendations on how to use this information to improve future therapies with nucleoside drugs.
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PMID:Is the expression of deoxynucleoside kinases and 5'-nucleotidases in animal tissues related to the biological effects of nucleoside analogs? 2399 17

Mitochondrial thymidine kinase 2 (TK2) and deoxyguanosine kinase (dGK) catalyze the initial rate limiting phosphorylation of deoxynucleosides and are essential enzymes for mitochondrial function. Chemotherapy using nucleoside analogs is often associated with mitochondrial toxicities. Here we showed that incubation of U2OS cells with didanosine (ddI, 2',3'-dideoxyinosine), a purine nucleoside analog used in the highly active antiretroviral therapy (HAART), led to selective degradation of both mitochondrial TK2 and dGK while the cytosolic deoxycytidine kinase (dCK) and thymidine kinase 1 (TK1) were not affected. Addition of guanosine to the ddI-treated cells prevented the degradation of mitochondrial TK2 and dGK. The levels of intracellular reactive oxygen species and protein oxidation in ddI-treated and control cells were also measured. The results suggest that down-regulation of mitochondrial TK2 and dGK may be a mechanism of mitochondrial toxicity caused by antiviral and anticancer nucleoside analogs.
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PMID:Down-regulation of mitochondrial thymidine kinase 2 and deoxyguanosine kinase by didanosine: implication for mitochondrial toxicities of anti-HIV nucleoside analogs. 2497 98

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.
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PMID:Zidovudine induces downregulation of mitochondrial deoxynucleoside kinases: implications for mitochondrial toxicity of antiviral nucleoside analogs. 2518 42


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