3.6.1.12 malfunction down-regulation of the enzyme increases decitabine-induced toxicity in HeLa and MRC-5 cells at a wide range of doses 755999 3.6.1.12 malfunction dUTPase or DCTPP1 downregulation enhances the cytotoxic effect of decitabine producing an accumulation of nucleoside triphosphates containing uracil as well as uracil misincorporation and double-strand breaks in genomic DNA. Downregulation of DCTPP1 or dUTPase increases the toxic effect of decitabine in HeLa cells or in the non-tumoral cell line MRC-5. In contrast, cells transfected with the non-targeting siRNA pool do not exhibit a decrease in viability even in the presence of 0.1 mM decitabine. The protective effect is specific for decitabine since the absence of DCTPP1 or dUTPase do not have a significant impact on cell proliferation after exposure to the canonical nucleoside deoxycytidine or to the cytidine analogue cytarabine. DCTPP1 or dUTPase-deficient cells incubated with decitabine also display a reduced colony-forming capacity compared with control cells 755999 3.6.1.12 malfunction nucleotide pools and the dUTP/dTTP ratio are severely altered in DCTPP1-deficient cells, which exhibit an accumulation of uracil in genomic DNA, the activation of the DNA damage response and both a mitochondrial and nuclear hypermutator phenotype. DNA damage can be reverted by incubation with thymidine, dUTPase overexpression or uracil-DNA glycosylase suppression. Moreover, DCTPP1-deficient cells are highly sensitive to downregulation of nucleoside salvage. DCTPP1-deficient cells accumulate high levels of dCTP and are hypersensitive to exposure to the nucleoside analogues 5-iodo-2'-deoxycytidine and 5-methyl-2'-deoxycytidine. Downregulation of DCTPP1 expression impairs proliferation and perturbs the dNTP pool of MCF-7 cells. DCTPP1-deficient cells are more prone to uracil misincorporation and exhibit an activated DNA damage response (DDR), altered cell cycle progression, and a mutator phenotype that affects both chromosomal and mitochondrial DNA (mtDNA) 756417 3.6.1.12 malfunction potent and selective dCTPase inhibitors enhance the cytotoxic effect of cytidine analogues in leukemia cells 757386 3.6.1.12 metabolism DCTPP1 (dCTP pyrophosphatase 1) and dUTPase are two house-cleaning nucleotidohydrolases involved in the elimination of non-canonical nucleotides. Exposure of HeLa cells to decitabine upregulates the expression of several pyrimidine metabolic enzymes including DCTPP1, dUTPase, dCMP deaminase and thymidylate synthase, thus suggesting their contribution to the cellular response to this anti-cancer nucleoside. In addition to the formation of aza-dCTP (5-aza-2'-deoxycytidine-5'-triphosphate), an alternative cytotoxic mechanism for decitabine may involve the formation of aza-dUMP, a potential thymidylate synthase inhibitor 755999 3.6.1.12 metabolism dCTPP1 plays a role in regulation of Wnt/bcatenin signaling most likely through a direct interaction with USP7. Canonical Wnt/beta-catenin signaling is a fundamental growth control pathway essential for, for example, embryonic development, stem cell maintenance, cell proliferation and tissue homeostasis, pathway regulation, overview. Upon activation the central Wnt pathway component beta-catenin is no longer phosphorylated and degraded by the so-called destruction complex, but rather stabilized and translocated to the nucleus, where it activates the expression of Wnt target genes 755792 3.6.1.12 metabolism the enzyme contributes to the cellular response to the anti-cancer nucleoside decitabine. Exposure of HeLa cells to decitabine upregulates the expression of several pyrimidine metabolic enzymes including DCTPP1, dUTPase, dCMP deaminase and thymidylate synthase. DCTPP1 down-regulation enhances the cytotoxic effect of decitabine producing an accumulation of nucleoside triphosphates containing uracil as well as uracil misincorporation and double-strand breaks in genomic DNA 755999 3.6.1.12 additional information decitabine (5-aza-2x02-deoxycytidine, aza-dCyd) is an anti-cancer drug used clinically for the treatment of myelodysplastic syndromes and acute myeloid leukaemia that can act as a DNA-demethylating or genotoxic agent in a dose-dependent manner. It upregulates the enzyme in HeLa cells. Decitabine is metabolically activated in vivo through consecutive phosphorylations into aza-dCTP (5-aza-2'-deoxycytidine-5'-triphosphate) that is readily incorporated into DNA and extended by the DNA polymerase. Once in DNA, decitabine acts as a suicidal substrate by covalently trapping DNMT (DNA methyltransferase) molecules that attempt to initiate cytosine methylation. The resulting DNA-protein cross-links trigger the proteasomal degradation machinery and lead to the depletion of the DNA methylation activities of the cell. Consequently, the replacement of deoxycytidine by decitabine results in hypomethylation at the promoter DNA regions and the reactivation of epigenetically repressed genes 755999 3.6.1.12 physiological function DCTPP1 hydrolyses the triphosphate form of decitabine with similar kinetic efficiency to its natural substrate dCTP and prevents decitabine-induced global DNA demethylation. The nucleotidohydrolases DCTPP1 and dUTPase are factors involved in the mode of action of decitabine with potential value as enzymatic targets to improve decitabine-based chemotherapy 755999 3.6.1.12 physiological function DCTPP1-deficient cells accumulate high levels of dCTP and are hypersensitive to exposure to the nucleoside analogues 5-iodo-2'-deoxycytidine and 5-methyl-2'-deoxycytidine 733297