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:3.1.3.5 (5'-nucleotidase)
3,167 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To determine whether the human equilibrative nucleoside transporter 1 (hENT1), deoxycytidine kinase (dCK), cytoplasmic 5'-nucleotidase (5NT), cytidine deaminase (CDD), topoisomerase I (TOPO I) and topoisomerase II alpha (TOPO II) are involved in clinical resistance to cytarabine (ara-C), we analyzed the level of expression of these parameters by reverse transcriptase polymerase chain reaction (rt-PCR), at diagnosis in the blast cells of 77 acute myeloid leukemia (AML) patients treated with ara-C, including 31 for whom samples were collected at first relapse. By univariate and/or multivariate analyses, patients with expression of 5NT or hENT1 deficiency at diagnosis had significantly shorter disease-free survival (DFS) and overall survival (OS). These results suggest that expression of 5NT and reduced hENT1 in leukemic blasts at diagnosis are correlated with clinical outcome and may play a role in resistance mechanisms to ara-C in patients with AML.
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PMID:Potential mechanisms of resistance to cytarabine in AML patients. 1200 78

Adenosine is an important physiological regulator of the cardiovascular system. The goal of our study was to assess the expression level of nucleoside transporters (NT) in diabetic rat cardiomyocytes and to examine the activities of adenosine metabolizing enzymes. Isolated rat cardiomyocytes displayed the presence of detectable amounts of mRNA for ENT1, ENT2, CNT1, and CNT2. Overall adenosine (10 microM) transport in cardiomyocytes isolated from normal rat was 36 pmol/mg/min. The expression level of equilibrative transporters (ENT1, ENT2) decreased and of concentrative transporters (CNT1, CNT2) increased in myocytes isolated from diabetic rat. Consequently, overall adenosine transport decreased by 30%, whereas Na(+)-dependent adenosine uptake increased 2-fold, and equilibrative transport decreased by 60%. The activity ratio of AMP deaminase/5'-nucleotidase in cytosol of normal cardiomyocytes was 11 and increased to 15 in diabetic cells. The activity of ecto-5'-nucleotidase increased 2-fold in diabetic cells resulting in a rise of the activity ratio of ecto-5'-nucleotidase/adenosine deaminase from 28 to 56.These results indicate that in rat cardiomyocytes diabetes alters activities of adenosine metabolizing enzymes in such a way that conversion of AMP to IMP is favored in the cytosolic compartment, whereas the capability to produce adenosine extracellularly is increased. This is accompanied by an increased unidirectional Na(+)-dependent uptake of adenosine and significantly reduced bidirectional adenosine transport.
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PMID:Prevalence of unidirectional Na+-dependent adenosine transport and altered potential for adenosine generation in diabetic cardiac myocytes. 1636 29

In brain, levels of adenosine increase up to 100-fold during cerebral ischemia. Based on in vitro studies, both astrocytes and neurons contribute to this adenosine release. Neurons release adenosine per se whereas astrocytes release adenine nucleotides that are metabolized to adenosine extracellularly. In contrast, inosine is released from both cell types via a nucleoside transporter. C6 glioma cells, which are derived from astrocytes, release inosine but not adenosine. The present study investigated the relative expression of purine metabolizing enzymes and transporters in neurons, astrocytes and C6 glioma cells by real-time PCR analysis. In agreement with the extracellular formation of adenosine and intracellular formation of inosine by astrocytes, the present study showed high expression of ecto 5'-nucleotidase and AMP deaminase type 3 in astrocytes. The lack of adenosine release from C6 glioma cells was consistent with the absence of expression of the AMP-preferring cytosolic 5'-nucleotidase in these cells. The predominance of nitrobenzylthioinosine (NBMPR) insensitive equilibrative nucleoside transport (ENT2) in all three cell types was consistent with the greater activity of this isoform in comparison to NBMPR-sensitive ENT1 in these rat cells. Thus, cell type differences in adenosine formation and release are primarily a function of differences in expression of purinergic enzymes and transporters.
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PMID:Gene expression for enzymes and transporters involved in regulating adenosine and inosine levels in rat forebrain neurons, astrocytes and C6 glioma cells. 1686 52

This study assessed the antiproliferative activity of sapacitabine (CYC682, CS-682) in a panel of 10 human cancer cell lines with varying degrees of resistance or sensitivity to the commonly used nucleoside analogues ara-C and gemcitabine. Growth inhibition studies using sapacitabine and CNDAC were performed in the panel of cell lines and compared with both nucleoside analogues and other anticancer compounds including oxaliplatin, doxorubicin, docetaxel and seliciclib. Sapacitabine displayed antiproliferative activity across a range of concentrations in a variety of cell lines, including those shown to be resistant to several anticancer drugs. Sapacitabine is biotransformed by plasma, gut and liver amidases into CNDAC and causes cell cycle arrest predominantly in the G(2)/M phase. No clear correlation was observed between sensitivity to sapacitabine and the expression of critical factors involved in resistance to nucleoside analogues such as deoxycytidine kinase (dCK), human equilibrative nucleoside transporter 1, cytosolic 5'-nucleotidase and DNA polymerase-alpha. However, sapacitabine showed cytotoxic activity against dCK-deficient L1210 cells indicating that in some cells, a dCK-independent mechanism of action may be involved. In addition, sapacitabine showed a synergistic effect when combined with gemcitabine and sequence-specific synergy with doxorubicin and oxaliplatin. Sapacitabine is therefore a good candidate for further evaluation in combination with currently used anticancer agents in tumour types with unmet needs.
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PMID:Antiproliferative effects of sapacitabine (CYC682), a novel 2'-deoxycytidine-derivative, in human cancer cells. 1763 78

Cytarabine (ara-C) is the key agent for treating acute myeloid leukemia (AML). After being transported into leukemic cells by human equilibrative nucleoside transporter 1 (hENT1), ara-C is phosphorylated to ara-C triphosphate (ara-CTP), an active metabolite, and then incorporated into DNA, thereby inhibiting DNA synthesis. Deoxycytidine kinase (dCK) and cytosolic 5'-nucleotidase II (cN-II) are associated with the production of ara-CTP. Because ara-C's cytotoxicity depends on ara-CTP production, parameters that are most related to ara-CTP formation would predict ara-C sensitivity and the clinical outcome of ara-C therapy. The present study focused on finding any correlation between the capacity to produce ara-CTP and ara-C-metabolizing factors. In vitro ara-CTP production, mRNA levels of hENT1, dCK, and cN-II, and ara-C sensitivity were evaluated in 34 blast samples from 33 leukemic patients including 26 with AML. A large degree of heterogeneity was seen in the capacity to produce ara-CTP and in mRNA levels of hENT1, dCK, and cN-II. Despite the lack of any association between each of the transcript levels and ara-CTP production, the ratio of dCK/cN-II transcript levels correlated significantly with the amount of ara-CTP among AML samples. The HL-60 cultured leukemia cell line and its three ara-C-resistant variants (HL-60/R1, HL-60/R2, HL-60/R3), which were 8-, 10-, and 500-fold more resistant than HL-60, respectively, were evaluated similarly. The dCK/cN-II ratio was again proportional to ara-CTP production and to ara-C sensitivity. The dCK/cN-II ratio may thus predict the capacity for ara-CTP production and ultimately, ara-C sensitivity in AML.
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PMID:Intracellular cytarabine triphosphate production correlates to deoxycytidine kinase/cytosolic 5'-nucleotidase II expression ratio in primary acute myeloid leukemia cells. 1942 33

Adenosine has been shown to exert direct antihypertrophic effects on the heart, and plasma adenosine levels have been shown to be elevated in patients with heart failure. It has therefore been proposed that endogenously synthesized adenosine may function as a cardiac antihypertrophic factor. The present study was aimed to determine whether the adenosine system is altered in a potential adaptive manner following phenylephrine-induced hypertrophy in cultured neonatal rat ventricular myocytes. Phenylephrine produced significant hypertrophy as determined by cell size and atrial natriuretic peptide gene expression, which was accompanied by significantly increased gene and protein expression of adenosine A(1), A(2a), and A(3) receptors. These effects and the hypertrophic response were prevented by the alpha(1)-adrenoceptor antagonist prazosin as well as pharmacological agonists for all adenosine receptor subtypes. The upregulation of adenosine receptors by phenylephrine was also abrogated by adenosine 5'-(alpha,beta-methylene)diphosphate, an inhibitor of ectosolic 5'-nucleotidase. Moreover, phenylephrine significantly increased production of adenosine from myocytes in the presence of a nucleoside transport and adenosine deaminase inhibitor, the combination of which abrogated the hypertrophic effect of phenylephrine. The latter effect was reversed by adenosine receptor antagonists. Phenylephrine also produced a significant upregulation in expression levels of equilibrative nucleoside transporter 1 although expression levels of equilibrative nucleoside transporter 2 were unaffected. Taken together, our results suggest an adaptive upregulation of the adenosine system to phenylephrine-induced cardiomyocyte hypertrophy that serves to limit the hypertrophic effect of alpha(1-)adrenoceptor activation.
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PMID:Compensatory upregulation of the adenosine system following phenylephrine-induced hypertrophy in cultured rat ventricular myocytes. 1996 59

Although the nucleoside pyrimidine analogue gemcitabine is the most effective single agent in the palliation of advanced pancreatic cancer, cellular resistance to gemcitabine treatment is a major problem in the clinical scene. To clarify the molecular mechanisms responsible for chemoresistance to gemcitabine, mRNA expression of the key enzymes including cytidine deaminase (CDA), deoxycytidine kinase (dCK), 5'-nucleotidase (NT5), equilibrative nucleoside transporter 1 and 2 (ENT1 and ENT2), dCMP deaminase (dCMPK), ribonucleotide reductase M1 and M2 (RRM1 and RRM2), thymidylate synthase (TS) and CTP synthase (CTPS) was examined. The interacellular uptake of gemcitabine was greatly impaired in the chemoresistant cell lines due to dysfunction of ENT1 and ENT2. Protein expression of ENT1 and ENT2 and their protein coding sequences were not altered. Immunohistochemical and western blot analyses revealed that localization of ENT2 on the plasma membrane was disrupted. These data suggest that the disrupted localization of ENT2 is one of causes of the impaired uptake of gemcitabine, resulting in a gain of chemoresistance to gemcitabine.
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PMID:Disrupted plasma membrane localization of equilibrative nucleoside transporter 2 in the chemoresistance of human pancreatic cells to gemcitabine (dFdCyd). 2120 85

Microglial cells invade the brain as amoeboid precursors and acquire a highly ramified morphology in the postnatal brain. Microglia express all essential purinergic elements such as receptors, nucleoside transporters and ecto-enzymes, including CD39 (NTPDase1) and CD73 (5'-nucleotidase), which sequentially degrade extracellular ATP to adenosine. Here, we show that constitutive deletion of CD39 and CD73 or both caused an inhibition of the microglia ramified phenotype in the brain with a reduction in the length of processes, branching frequency and number of intersections with Sholl spheres. In vitro, unlike wild-type microglia, cd39-/- and cd73-/- microglial cells were less complex and did not respond to ATP with the transformation into a more ramified phenotype. In acute brain slices, wild-type microglia retracted approximately 50% of their processes within 15 min after slicing of the brain, and this phenomenon was augmented in cd39-/- mice; moreover, the elongation of microglial processes towards the source of ATP or towards a laser lesion was observed only in wild-type but not in cd39-/- microglia. An elevation of extracellular adenosine 1) by the inhibition of adenosine transport with dipyridamole, 2) by application of exogenous adenosine or 3) by degradation of endogenous ATP/ADP with apyrase enhanced spontaneous and ATP-induced ramification of cd39-/- microglia in acute brain slices and facilitated the transformation of cd39-/- and cd73-/- microglia into a ramified process-bearing phenotype in vitro. These data indicate that under normal physiological conditions, CD39 and CD73 nucleotidases together with equilibrative nucleoside transporter 1 (ENT1) control the fate of extracellular adenosine and thereby the ramification of microglial processes.
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PMID:The adenosine generating enzymes CD39/CD73 control microglial processes ramification in the mouse brain. 2837 99

Glioblastoma multiforme is one of the most malignant types of cancer. This is mainly due to a cell subpopulation with an extremely aggressive potential, called glioblastoma stem-like cells (GSCs). These cells produce high levels of extracellular adenosine which has been associated with increased chemoresistance, migration, and invasion in glioblastoma. In this study, we attempted to elucidate the mechanisms that control extracellular adenosine levels in GSC subtypes. By using primary and U87MG-derived GSCs, we associated increased extracellular adenosine with the mesenchymal phenotype. [³H]-adenosine uptake occurred mainly through the equilibrative nucleoside transporters (ENTs) in GSCs, but mesenchymal GSCs have lower expression and ENT1-mediated uptake activity than proneural GSCs. By analyzing expression and enzymatic activity, we determined that ecto-5'-nucleotidase (CD73) is predominantly expressed in proneural GSCs, driving AMPase activity. While in mesenchymal GSCs, both CD73 and Prostatic Acid Phosphatase (PAP) contribute to the AMP (adenosine monophosphate) hydrolysis. We did not observe significant differences between the expression of proteins involved in the metabolization of adenosine among the GCSs subtypes. In conclusion, the lower expression and activity of the ENT1 transporter in mesenchymal GSCs contributes to the high level of extracellular adenosine that these GSCs present.
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PMID:Decreased Equilibrative Nucleoside Transporter 1 (ENT1) Activity Contributes to the High Extracellular Adenosine Levels in Mesenchymal Glioblastoma Stem-Like Cells. 3282 70

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