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Zakataeva NP. Microbial 5'-nucleotidases: their characteristics, roles in cellular metabolism, and possible practical applications. Appl Microbiol Biotechnol 2021; 105:7661-7681. [PMID: 34568961 PMCID: PMC8475336 DOI: 10.1007/s00253-021-11547-w] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2021] [Revised: 08/21/2021] [Accepted: 08/24/2021] [Indexed: 11/25/2022]
Abstract
5′-Nucleotidases (EC 3.1.3.5) are enzymes that catalyze the hydrolytic dephosphorylation of 5′-ribonucleotides and 5′-deoxyribonucleotides to their respective nucleosides and phosphate. Most 5′-nucleotidases have broad substrate specificity and are multifunctional enzymes capable of cleaving phosphorus from not only mononucleotide phosphate molecules but also a variety of other phosphorylated metabolites. 5′-Nucleotidases are widely distributed throughout all kingdoms of life and found in different cellular locations. The well-studied vertebrate 5′-nucleotidases play an important role in cellular metabolism. These enzymes are involved in purine and pyrimidine salvage pathways, nucleic acid repair, cell-to-cell communication, signal transduction, control of the ribo- and deoxyribonucleotide pools, etc. Although the first evidence of microbial 5′-nucleotidases was obtained almost 60 years ago, active studies of genetic control and the functions of microbial 5′-nucleotidases started relatively recently. The present review summarizes the current knowledge about microbial 5′-nucleotidases with a focus on their diversity, cellular localizations, molecular structures, mechanisms of catalysis, physiological roles, and activity regulation and approaches to identify new 5′-nucleotidases. The possible applications of these enzymes in biotechnology are also discussed. Key points • Microbial 5′-nucleotidases differ in molecular structure, hydrolytic mechanism, and cellular localization. • 5′-Nucleotidases play important and multifaceted roles in microbial cells. • Microbial 5′-nucleotidases have wide range of practical applications.
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Affiliation(s)
- Natalia P Zakataeva
- Ajinomoto-Genetika Research Institute, 1st Dorozhny Proezd, b.1-1, Moscow, 117545, Russia.
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2
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Garcia-Gil M, Camici M, Allegrini S, Pesi R, Tozzi MG. Metabolic Aspects of Adenosine Functions in the Brain. Front Pharmacol 2021; 12:672182. [PMID: 34054547 PMCID: PMC8160517 DOI: 10.3389/fphar.2021.672182] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2021] [Accepted: 04/27/2021] [Indexed: 12/13/2022] Open
Abstract
Adenosine, acting both through G-protein coupled adenosine receptors and intracellularly, plays a complex role in multiple physiological and pathophysiological processes by modulating neuronal plasticity, astrocytic activity, learning and memory, motor function, feeding, control of sleep and aging. Adenosine is involved in stroke, epilepsy and neurodegenerative pathologies. Extracellular concentration of adenosine in the brain is tightly regulated. Adenosine may be generated intracellularly in the central nervous system from degradation of AMP or from the hydrolysis of S-adenosyl homocysteine, and then exit via bi-directional nucleoside transporters, or extracellularly by the metabolism of released nucleotides. Inactivation of extracellular adenosine occurs by transport into neurons or neighboring cells, followed by either phosphorylation to AMP by adenosine kinase or deamination to inosine by adenosine deaminase. Modulation of the nucleoside transporters or of the enzymatic activities involved in the metabolism of adenosine, by affecting the levels of this nucleoside and the activity of adenosine receptors, could have a role in the onset or the development of central nervous system disorders, and can also be target of drugs for their treatment. In this review, we focus on the contribution of 5'-nucleotidases, adenosine kinase, adenosine deaminase, AMP deaminase, AMP-activated protein kinase and nucleoside transporters in epilepsy, cognition, and neurodegenerative diseases with a particular attention on amyotrophic lateral sclerosis and Huntington's disease. We include several examples of the involvement of components of the adenosine metabolism in learning and of the possible use of modulators of enzymes involved in adenosine metabolism or nucleoside transporters in the amelioration of cognition deficits.
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Affiliation(s)
- Mercedes Garcia-Gil
- Department of Biology, Unit of Physiology, University of Pisa, Pisa, Italy.,Interdepartmental Research Center "Nutraceuticals and Food for Health", University of Pisa, Pisa, Italy
| | - Marcella Camici
- Department of Biology, Unit of Biochemistry, University of Pisa, Pisa, Italy
| | - Simone Allegrini
- Department of Biology, Unit of Biochemistry, University of Pisa, Pisa, Italy
| | - Rossana Pesi
- Department of Biology, Unit of Biochemistry, University of Pisa, Pisa, Italy
| | - Maria Grazia Tozzi
- Department of Biology, Unit of Biochemistry, University of Pisa, Pisa, Italy
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3
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Cytosolic 5'-Nucleotidase II Is a Sensor of Energy Charge and Oxidative Stress: A Possible Function as Metabolic Regulator. Cells 2021; 10:cells10010182. [PMID: 33477638 PMCID: PMC7831490 DOI: 10.3390/cells10010182] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2020] [Revised: 01/08/2021] [Accepted: 01/15/2021] [Indexed: 12/20/2022] Open
Abstract
Cytosolic 5'-nucleotidase II (NT5C2) is a highly regulated enzyme involved in the maintenance of intracellular purine and the pyrimidine compound pool. It dephosphorylates mainly IMP and GMP but is also active on AMP. This enzyme is highly expressed in tumors, and its activity correlates with a high rate of proliferation. In this paper, we show that the recombinant purified NT5C2, in the presence of a physiological concentration of the inhibitor inorganic phosphate, is very sensitive to changes in the adenylate energy charge, especially from 0.4 to 0.9. The enzyme appears to be very sensitive to pro-oxidant conditions; in this regard, the possible involvement of a disulphide bridge (C175-C547) was investigated by using a C547A mutant NT5C2. Two cultured cell models were used to further assess the sensitivity of the enzyme to oxidative stress conditions. NT5C2, differently from other enzyme activities, was inactivated and not rescued by dithiothreitol in a astrocytoma cell line (ADF) incubated with hydrogen peroxide. The incubation of a human lung carcinoma cell line (A549) with 2-deoxyglucose lowered the cell energy charge and impaired the interaction of NT5C2 with the ice protease-activating factor (IPAF), a protein involved in innate immunity and inflammation.
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Camici M, Garcia-Gil M, Allegrini S, Pesi R, Tozzi MG. Evidence for a Cross-Talk Between Cytosolic 5'-Nucleotidases and AMP-Activated Protein Kinase. Front Pharmacol 2020; 11:609849. [PMID: 33408634 PMCID: PMC7781041 DOI: 10.3389/fphar.2020.609849] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2020] [Accepted: 11/26/2020] [Indexed: 12/28/2022] Open
Affiliation(s)
- Marcella Camici
- Unità di Biochimica, Dipartimento di Biologia, Università di Pisa, Pisa, Italy
| | - Mercedes Garcia-Gil
- Unità di Fisiologia Generale, Dipartimento di Biologia, Università di Pisa, Pisa, Italy
| | - Simone Allegrini
- Unità di Biochimica, Dipartimento di Biologia, Università di Pisa, Pisa, Italy
| | - Rossana Pesi
- Unità di Biochimica, Dipartimento di Biologia, Università di Pisa, Pisa, Italy
| | - Maria Grazia Tozzi
- Unità di Biochimica, Dipartimento di Biologia, Università di Pisa, Pisa, Italy
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5
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Structure and catalytic regulation of Plasmodium falciparum IMP specific nucleotidase. Nat Commun 2020; 11:3228. [PMID: 32591529 PMCID: PMC7320144 DOI: 10.1038/s41467-020-17013-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2019] [Accepted: 05/28/2020] [Indexed: 11/21/2022] Open
Abstract
Plasmodium falciparum (Pf) relies solely on the salvage pathway for its purine nucleotide requirements, making this pathway indispensable to the parasite. Purine nucleotide levels are regulated by anabolic processes and by nucleotidases that hydrolyse these metabolites into nucleosides. Certain apicomplexan parasites, including Pf, have an IMP-specific-nucleotidase 1 (ISN1). Here we show, by comprehensive substrate screening, that PfISN1 catalyzes the dephosphorylation of inosine monophosphate (IMP) and is allosterically activated by ATP. Crystal structures of tetrameric PfISN1 reveal complex rearrangements of domain organization tightly associated with catalysis. Immunofluorescence microscopy and expression of GFP-fused protein indicate cytosolic localization of PfISN1 and expression in asexual and gametocyte stages of the parasite. With earlier evidence on isn1 upregulation in female gametocytes, the structures reported in this study may contribute to initiate the design for possible transmission-blocking agents. Plasmodium falciparum IMP-specific 5′-nucleotidase 1 (PfISN1) is of interest as a potential malaria drug target. Here, the authors report that IMP is a substrate, and ATP an allosteric activator, of PfISN1 and present PfISN1 crystal structures in the ligand-free state and bound to either IMP or ATP.
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Kapitansky O, Gozes I. ADNP differentially interact with genes/proteins in correlation with aging: a novel marker for muscle aging. GeroScience 2019; 41:321-340. [PMID: 31264075 DOI: 10.1007/s11357-019-00079-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2019] [Accepted: 06/10/2019] [Indexed: 12/25/2022] Open
Abstract
Activity-dependent neuroprotective protein (ADNP) is essential for embryonic development with ADNP mutations leading to syndromic autism, coupled with intellectual disabilities and motor developmental delays. Here, mining human muscle gene-expression databases, we have investigated the association of ADNP transcripts with muscle aging. We discovered increased ADNP and its paralogue ADNP2 expression in the vastus lateralis muscle of aged compared to young subjects, as well as altered expression of the ADNP and the ADNP2 genes in bicep brachii muscle of elderly people, in a sex-dependent manner. Prolonged exercise resulted in decreased ADNP expression, and increased ADNP2 expression in an age-dependent manner in the vastus lateralis muscle. ADNP expression level was further correlated with 49 genes showing age-dependent changes in muscle transcript expression. A high degree of correlation with ADNP was discovered for 24 genes with the leading gene/protein being NMNAT1 (nicotinamide nucleotide adenylyl transferase 1). Looking at correlations differentiating the young and the old muscles and comparing protein interactions revealed an association of ADNP with the cell division cycle 5-like protein (CDC5L), and an aging-muscle-related interactive pathway in the vastus lateralis. In the bicep brachii, very high correlation was detected with genes associated with immune functions as well as mitochondrial structure and function among others. Taken together, the results suggest a direct association of ADNP with muscle strength and implicate ADNP fortification in the protection against age-associated muscle wasting.
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Affiliation(s)
- Oxana Kapitansky
- The Lily and Avraham Gildor Chair for the Investigation of Growth Factors; The Elton Laboratory for Neuroendocrinology; Department of Human Molecular Genetics and Biochemistry, Sackler Faculty of Medicine, Sagol School of Neuroscience and Adams Super Center for Brain Studies, Tel Aviv University, 69978, Tel Aviv, Israel
| | - Illana Gozes
- The Lily and Avraham Gildor Chair for the Investigation of Growth Factors; The Elton Laboratory for Neuroendocrinology; Department of Human Molecular Genetics and Biochemistry, Sackler Faculty of Medicine, Sagol School of Neuroscience and Adams Super Center for Brain Studies, Tel Aviv University, 69978, Tel Aviv, Israel.
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7
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Genetics and mechanisms of NT5C2-driven chemotherapy resistance in relapsed ALL. Blood 2019; 133:2263-2268. [PMID: 30910786 DOI: 10.1182/blood-2019-01-852392] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2019] [Accepted: 03/18/2019] [Indexed: 01/01/2023] Open
Abstract
Mutations in the cytosolic 5' nucleotidase II (NT5C2) gene drive resistance to thiopurine chemotherapy in relapsed acute lymphoblastic leukemia (ALL). Mechanistically, NT5C2 mutant proteins have increased nucleotidase activity as a result of altered activating and autoregulatory switch-off mechanisms. Leukemias with NT5C2 mutations are chemoresistant to 6-mercaptopurine yet show impaired proliferation and self-renewal. Direct targeting of NT5C2 or inhibition of compensatory pathways active in NT5C2 mutant cells may antagonize the emergence of NT5C2 mutant clones driving resistance and relapse in ALL.
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Pesi R, Petrotto E, Colombaioni L, Allegrini S, Garcia-Gil M, Camici M, Jordheim LP, Tozzi MG. Cytosolic 5'-Nucleotidase II Silencing in a Human Lung Carcinoma Cell Line Opposes Cancer Phenotype with a Concomitant Increase in p53 Phosphorylation. Int J Mol Sci 2018; 19:E2115. [PMID: 30037008 PMCID: PMC6073589 DOI: 10.3390/ijms19072115] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2018] [Revised: 07/17/2018] [Accepted: 07/18/2018] [Indexed: 12/28/2022] Open
Abstract
Purine homeostasis is maintained by a purine cycle in which the regulated member is a cytosolic 5'-nucleotidase II (cN-II) hydrolyzing IMP and GMP. Its expression is particularly high in proliferating cells, indeed high cN-II activity or expression in hematological malignancy has been associated to poor prognosis and chemoresistance. Therefore, a strong interest has grown in developing cN-II inhibitors, as potential drugs alone or in combination with other compounds. As a model to study the effect of cN-II inhibition we utilized a lung carcinoma cell line (A549) in which the enzyme was partially silenced and its low activity conformation was stabilized through incubation with 2-deoxyglucose. We measured nucleotide content, reduced glutathione, activities of enzymes involved in glycolysis and Krebs cycle, protein synthesis, mitochondrial function, cellular proliferation, migration and viability. Our results demonstrate that high cN-II expression is associated with a glycolytic, highly proliferating phenotype, while silencing causes a reduction of proliferation, protein synthesis and migration ability, and an increase of oxidative performances. Similar results were obtained in a human astrocytoma cell line. Moreover, we demonstrate that cN-II silencing is concomitant with p53 phosphorylation, suggesting a possible involvement of this pathway in mediating some of cN-II roles in cancer cell biology.
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Affiliation(s)
- Rossana Pesi
- Unità di Biochimica, Dipartimento di Biologia, Università di Pisa, Via San Zeno 51, 56127 Pisa, Italy.
| | - Edoardo Petrotto
- Unità di Biochimica, Dipartimento di Biologia, Università di Pisa, Via San Zeno 51, 56127 Pisa, Italy.
| | - Laura Colombaioni
- Istituto di Neuroscienze, CNR, Via Giuseppe Moruzzi 1, 56124 Pisa, Italy.
| | - Simone Allegrini
- Unità di Biochimica, Dipartimento di Biologia, Università di Pisa, Via San Zeno 51, 56127 Pisa, Italy.
| | - Mercedes Garcia-Gil
- Unità Fisiologia Generale, Dipartimento di Biologia, Università di Pisa, Via San Zeno 31, 56127 Pisa, Italy.
| | - Marcella Camici
- Unità di Biochimica, Dipartimento di Biologia, Università di Pisa, Via San Zeno 51, 56127 Pisa, Italy.
| | - Lars Petter Jordheim
- Université de Lyon, Université Claude Bernard Lyon 1, INSERM 1052, CNRS 5286, Centre Léon Bérard, Centre de Recherche en Cancérologie de Lyon, Lyon 69008, France.
| | - Maria Grazia Tozzi
- Unità di Biochimica, Dipartimento di Biologia, Università di Pisa, Via San Zeno 51, 56127 Pisa, Italy.
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9
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Dieck CL, Tzoneva G, Forouhar F, Carpenter Z, Ambesi-Impiombato A, Sánchez-Martín M, Kirschner-Schwabe R, Lew S, Seetharaman J, Tong L, Ferrando AA. Structure and Mechanisms of NT5C2 Mutations Driving Thiopurine Resistance in Relapsed Lymphoblastic Leukemia. Cancer Cell 2018; 34:136-147.e6. [PMID: 29990496 PMCID: PMC6049837 DOI: 10.1016/j.ccell.2018.06.003] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/18/2017] [Revised: 04/06/2018] [Accepted: 06/06/2018] [Indexed: 11/25/2022]
Abstract
Activating mutations in the cytosolic 5'-nucleotidase II gene NT5C2 drive resistance to 6-mercaptopurine in acute lymphoblastic leukemia. Here we demonstrate that constitutively active NT5C2 mutations K359Q and L375F reconfigure the catalytic center for substrate access and catalysis in the absence of allosteric activator. In contrast, most relapse-associated mutations, which involve the arm segment and residues along the surface of the inter-monomeric cavity, disrupt a built-in switch-off mechanism responsible for turning off NT5C2. In addition, we show that the C-terminal acidic tail lost in the Q523X mutation functions to restrain NT5C2 activation. These results uncover dynamic mechanisms of enzyme regulation targeted by chemotherapy resistance-driving NT5C2 mutations, with important implications for the development of NT5C2 inhibitor therapies.
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Affiliation(s)
- Chelsea L Dieck
- Institute for Cancer Genetics, Columbia University, New York, NY 10032, USA
| | - Gannie Tzoneva
- Institute for Cancer Genetics, Columbia University, New York, NY 10032, USA
| | - Farhad Forouhar
- Hervert Irving Comprehensive Cancer Center, Columbia University, New York, NY 10032, USA; Department of Biological Sciences, Northeast Structural Genomics Consortium, Columbia University, 1212 Amsterdam Avenue, 701 Fairchild Center, New York, NY 10027, USA
| | - Zachary Carpenter
- Department of Systems Biology, Columbia University, New York, NY 10032, USA
| | | | | | - Renate Kirschner-Schwabe
- Department of Pediatric Oncology/Hematology, Charité-Universitätsmedizin Berlin, Berlin 10117, Germany
| | - Scott Lew
- Department of Biological Sciences, Northeast Structural Genomics Consortium, Columbia University, 1212 Amsterdam Avenue, 701 Fairchild Center, New York, NY 10027, USA
| | | | - Liang Tong
- Department of Biological Sciences, Northeast Structural Genomics Consortium, Columbia University, 1212 Amsterdam Avenue, 701 Fairchild Center, New York, NY 10027, USA.
| | - Adolfo A Ferrando
- Institute for Cancer Genetics, Columbia University, New York, NY 10032, USA; Department of Systems Biology, Columbia University, New York, NY 10032, USA; Department of Pediatrics, Columbia University Medical Center, 1130 St. Nicholas Avenue, ICRC 402, New York, NY 10032, USA; Department of Pathology and Cell Biology, Columbia University Medical Center, New York, NY 10032, USA.
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10
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Hnízda A, Škerlová J, Fábry M, Pachl P, Šinalová M, Vrzal L, Man P, Novák P, Řezáčová P, Veverka V. Oligomeric interface modulation causes misregulation of purine 5´-nucleotidase in relapsed leukemia. BMC Biol 2016; 14:91. [PMID: 27756303 PMCID: PMC5070119 DOI: 10.1186/s12915-016-0313-y] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2016] [Accepted: 09/23/2016] [Indexed: 11/10/2022] Open
Abstract
Background Relapsed acute lymphoblastic leukemia (ALL) is one of the main causes of mortality in childhood malignancies. Previous genetic studies demonstrated that chemoresistant ALL is driven by activating mutations in NT5C2, the gene encoding cytosolic 5´-nucleotidase (cN-II). However, molecular mechanisms underlying this hyperactivation are still unknown. Here, we present kinetic and structural properties of cN-II variants that represent 75 % of mutated alleles in patients who experience relapsed ALL (R367Q, R238W and L375F). Results Enzyme kinetics measurements revealed that the mutants are consitutively active without need for allosteric activators. This shows that hyperactivity is not caused by a direct catalytic effect but rather by misregulation of cN-II. X-ray crystallography combined with mass spectrometry-based techniques demonstrated that this misregulation is driven by structural modulation of the oligomeric interface within the cN-II homotetrameric assembly. These specific conformational changes are shared between the studied variants, despite the relatively random spatial distribution of the mutations. Conclusions These findings define a common molecular mechanism for cN-II hyperactivity, which provides a solid basis for targeted therapy of leukemia. Our study highlights the cN-II oligomerization interface as an attractive pharmacological target. Electronic supplementary material The online version of this article (doi:10.1186/s12915-016-0313-y) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Aleš Hnízda
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nam. 2, Prague 6, 166 10, Czech Republic.
| | - Jana Škerlová
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nam. 2, Prague 6, 166 10, Czech Republic
| | - Milan Fábry
- Institute of Molecular Genetics, Academy of Sciences of the Czech Republic, Videnska 1083, Prague 4, 142 20, Czech Republic
| | - Petr Pachl
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nam. 2, Prague 6, 166 10, Czech Republic
| | - Martina Šinalová
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nam. 2, Prague 6, 166 10, Czech Republic
| | - Lukáš Vrzal
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nam. 2, Prague 6, 166 10, Czech Republic
| | - Petr Man
- Institute of Microbiology, Academy of Sciences of the Czech Republic, Videnska 1083, Prague 4, 142 20, Czech Republic
| | - Petr Novák
- Institute of Microbiology, Academy of Sciences of the Czech Republic, Videnska 1083, Prague 4, 142 20, Czech Republic
| | - Pavlína Řezáčová
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nam. 2, Prague 6, 166 10, Czech Republic.,Institute of Molecular Genetics, Academy of Sciences of the Czech Republic, Videnska 1083, Prague 4, 142 20, Czech Republic
| | - Václav Veverka
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nam. 2, Prague 6, 166 10, Czech Republic.
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Cividini F, Cros-Perrial E, Pesi R, Machon C, Allegrini S, Camici M, Dumontet C, Jordheim LP, Tozzi MG. Cell proliferation and drug sensitivity of human glioblastoma cells are altered by the stable modulation of cytosolic 5'-nucleotidase II. Int J Biochem Cell Biol 2015; 65:222-9. [PMID: 26079827 DOI: 10.1016/j.biocel.2015.06.011] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2015] [Revised: 05/31/2015] [Accepted: 06/08/2015] [Indexed: 01/13/2023]
Abstract
Cytosolic 5'-nucleotidase II (cN-II) has been reported to be involved in cell survival, nucleotide metabolism and in the cellular response to anticancer drugs. With the aim to further evaluate the role of this enzyme in cell biology, we stably modulated its expression the human glioblastoma cell ADF in which the transient inhibition of cN-II has been shown to induce cell death. Stable cell lines were obtained both with inhibition, obtained with plasmids coding cN-II-targeting short hairpin RNA, and stimulation, obtained with plasmids coding Green Fluorescence Protein (GFP)-fused wild type cN-II or a GFP-fused hyperactive mutant (GFP-cN-II-R367Q), of cN-II expression. Silenced cells displayed a decreased proliferation rate while the over expressing cell lines displayed an increased proliferation rate as evidenced by impedance measurement using the xCELLigence device. The expression of nucleotide metabolism relevant genes was only slightly different between cell lines, suggesting a compensatory mechanism in transfected cells. Cells with decreased cN-II expression were resistant to the nucleoside analog fludarabine confirming the involvement of cN-II in the metabolism of this drug. Finally, we observed sensitivity to cisplatin in cN-II silenced cells and resistance to this same drug in cN-II over-expressing cells indicating an involvement of cN-II in the mechanism of action of platinum derivatives, and most probably in DNA repair. In summary, our findings confirm some previous data on the role of cN-II in the sensitivity of cancer cells to cancer drugs, and suggest its involvement in other cellular phenomenon such as cell proliferation.
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Affiliation(s)
- F Cividini
- University of Pisa, Department of Biology, Biochemistry Unit, Pisa, Italy.
| | - E Cros-Perrial
- Université de Lyon, F-69000 Lyon, France; Université de Lyon 1, F-69622 Lyon, France; Université de Lyon 1, F-69000 Lyon, France; INSERM U1052, Centre de Recherche en Cancérologie de Lyon, F-69000 Lyon, France; CNRS UMR 5286, Centre de Recherche en Cancérologie de Lyon, F-69000 Lyon, France
| | - R Pesi
- University of Pisa, Department of Biology, Biochemistry Unit, Pisa, Italy
| | - C Machon
- Hospices Civils de Lyon, Centre Hospitalier Lyon-Sud, Laboratoire de Biochimie et Toxicologie, Lyon, France
| | - S Allegrini
- University of Sassari, Department of Chemistry and Pharmacology, Sassari, Italy
| | - M Camici
- University of Pisa, Department of Biology, Biochemistry Unit, Pisa, Italy
| | - C Dumontet
- Université de Lyon, F-69000 Lyon, France; Université de Lyon 1, F-69622 Lyon, France; Université de Lyon 1, F-69000 Lyon, France; INSERM U1052, Centre de Recherche en Cancérologie de Lyon, F-69000 Lyon, France; CNRS UMR 5286, Centre de Recherche en Cancérologie de Lyon, F-69000 Lyon, France
| | - L P Jordheim
- Université de Lyon, F-69000 Lyon, France; Université de Lyon 1, F-69622 Lyon, France; Université de Lyon 1, F-69000 Lyon, France; INSERM U1052, Centre de Recherche en Cancérologie de Lyon, F-69000 Lyon, France; CNRS UMR 5286, Centre de Recherche en Cancérologie de Lyon, F-69000 Lyon, France
| | - M G Tozzi
- University of Pisa, Department of Biology, Biochemistry Unit, Pisa, Italy
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12
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Cytosolic 5'-nucleotidase II interacts with the leucin rich repeat of NLR family member Ipaf. PLoS One 2015; 10:e0121525. [PMID: 25811392 PMCID: PMC4374842 DOI: 10.1371/journal.pone.0121525] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2014] [Accepted: 02/03/2015] [Indexed: 01/17/2023] Open
Abstract
IMP/GMP preferring cytosolic 5'-nucleotidase II (cN-II) is a bifunctional enzyme whose activities and expression play crucial roles in nucleotide pool maintenance, nucleotide-dependent pathways and programmed cell death. Alignment of primary amino acid sequences of cN-II from human and other organisms show a strong conservation throughout the entire vertebrata taxon suggesting a fundamental role in eukaryotic cells. With the aim to investigate the potential role of this homology in protein-protein interactions, a two hybrid system screening of cN-II interactors was performed in S. cerevisiae. Among the X positive hits, the Leucin Rich Repeat (LRR) domain of Ipaf was found to interact with cN-II. Recombinant Ipaf isoform B (lacking the Nucleotide Binding Domain) was used in an in vitro affinity chromatography assay confirming the interaction obtained in the screening. Moreover, co-immunoprecipitation with proteins from wild type Human Embryonic Kidney 293 T cells demonstrated that endogenous cN-II co-immunoprecipitated both with wild type Ipaf and its LRR domain after transfection with corresponding expression vectors, but not with Ipaf lacking the LRR domain. These results suggest that the interaction takes place through the LRR domain of Ipaf. In addition, a proximity ligation assay was performed in A549 lung carcinoma cells and in MDA-MB-231 breast cancer cells and showed a positive cytosolic signal, confirming that this interaction occurs in human cells. This is the first report of a protein-protein interaction involving cN-II, suggesting either novel functions or an additional level of regulation of this complex enzyme.
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13
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al-Rashida M, Iqbal J. Therapeutic potentials of ecto-nucleoside triphosphate diphosphohydrolase, ecto-nucleotide pyrophosphatase/phosphodiesterase, ecto-5'-nucleotidase, and alkaline phosphatase inhibitors. Med Res Rev 2013; 34:703-43. [PMID: 24115166 DOI: 10.1002/med.21302] [Citation(s) in RCA: 78] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The modulatory role of extracellular nucleotides and adenosine in relevance to purinergic cell signaling mechanisms has long been known and is an object of much research worldwide. These extracellular nucleotides are released by a variety of cell types either innately or as a response to patho-physiological stress or injury. A variety of surface-located ecto-nucleotidases (of four major types; nucleoside triphosphate diphosphohydrolases or NTPDases, nucleotide pyrophosphatase/phosphodiesterases or NPPs, alkaline phosphatases APs or ALPs, and ecto-5'-nucleotidase or e5NT) are responsible for meticulously controlling the availability of these important signaling molecules (at their respective receptors) in extracellular environment and are therefore crucial for maintaining the integrity of normal cell functioning. Overexpression of many of these ubiquitous ecto-enzymes has been implicated in a variety of disorders including cell adhesion, activation, proliferation, apoptosis, and degenerative neurological and immunological responses. Selective inhibition of these ecto-enzymes is an area that is currently being explored with great interest and hopes remain high that development of selective ecto-nucleotidase inhibitors will prove to have many beneficial therapeutic implications. The aim of this review is to emphasize and focus on recent developments made in the field of inhibitors of ecto-nucleotidases and to highlight their structure activity relationships wherever possible. Most recent and significant advances in field of NTPDase, NPP, AP, and e5NT inhibitors is being discussed in detail in anticipation of providing prolific leads and relevant background for research groups interested in synthesis of selective ecto-nucleotidase inhibitors.
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Affiliation(s)
- Mariya al-Rashida
- Department of Pharmaceutical Sciences, COMSATS Institute of Information Technology, Abbottabad, 22060, Pakistan
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Filoni DN, Pesi R, Allegrini S, Camici M, Tozzi MG. A native electrophoretic technique to study oligomerization and activity of cytosolic 5′-nucleotidase II. Anal Bioanal Chem 2013; 405:8951-4. [DOI: 10.1007/s00216-013-7313-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2013] [Accepted: 08/15/2013] [Indexed: 11/28/2022]
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Allegrini S, Filoni DN, Galli A, Collavoli A, Pesi R, Camici M, Tozzi MG. Expression of bovine cytosolic 5'-nucleotidase (cN-II) in yeast: nucleotide pools disturbance and its consequences on growth and homologous recombination. PLoS One 2013; 8:e63914. [PMID: 23691116 PMCID: PMC3656857 DOI: 10.1371/journal.pone.0063914] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2012] [Accepted: 04/09/2013] [Indexed: 01/30/2023] Open
Abstract
Cytosolic 5'-nucleotidase II is a widespread IMP hydrolyzing enzyme, essential for cell vitality, whose role in nucleotide metabolism and cell function is still to be exactly determined. Cytosolic 5'-nucleotidase overexpression and silencing have both been demonstrated to be toxic for mammalian cultured cells. In order to ascertain the effect of enzyme expression on a well-known eukaryote simple model, we expressed cytosolic 5'-nucleotidase II in Saccharomyces cerevisiae, which normally hydrolyzes IMP through the action of a nucleotidase with distinct functional and structural features. Heterologous expression was successful. The yeast cells harbouring cytosolic 5'-nucleotidase II displayed a shorter duplication time and a significant modification of purine and pyrimidine derivatives concentration as compared with the control strain. Furthermore the capacity of homologous recombination in the presence of mutagenic compounds of yeast expressing cytosolic 5'-nucleotidase II was markedly impaired.
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Affiliation(s)
- Simone Allegrini
- Dipartimento di Chimica e Farmacia, Università di Sassari, Sassari, Italy.
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Structural basis of substrate specificity and selectivity of murine cytosolic 5'-nucleotidase III. J Mol Biol 2012; 423:540-54. [PMID: 22925580 DOI: 10.1016/j.jmb.2012.08.014] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2012] [Revised: 08/14/2012] [Accepted: 08/19/2012] [Indexed: 11/24/2022]
Abstract
Cytosolic 5'-nucleotidase III (cN-III) is responsible for selective degradation of pyrimidine 5'-monoribonucleotides during maturation of reticulocytes to erythrocytes. The lack of this enzymatic activity due to genetic aberrations or lead poisoning results in a mild to moderate nonspherocytic hemolytic anemia. In affected individuals, pyrimidine nucleotides as well as their precursor polymers and their off-path metabolites accumulate in erythrocytes, interfering with their proper function in ways that are not yet fully understood. This report describes the first X-ray structure of a catalytically inactivated variant of murine cN-III with a natural substrate, uridine 5'-monophosphate, in the active site at 1.74Å resolution. The structure captures in an atomic detail the closed conformation that cN-III adopts upon substrate binding. Structure and sequence analysis coupled with enzymatic characterization of several mutants confirmed that the aromatic ring of a nitrogenous base of substrate nucleotide is stabilized by parallel π-stacking interactions with conserved aromatic rings of Trp113 and His68. The nitrogenous base is further stabilized by T-shaped stacking with the conserved aromatic ring of Tyr114, as well as by polar contacts with side chains of Thr66 and Ser117. Two water molecules help to stabilize the nucleotide binding by bridging it to protein residues Asp72 and His68 via hydrogen bonds. Finally, fully conserved Glu96 is responsible for recognition of ribose ring via two hydrogen bonds. The presented substrate complex structure elucidates how cN-III achieves specificity for pyrimidine 5'-nucleotides and how it selects against purine 5'-nucleotides.
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Filoni DN, Pesi R, Careddu MG, Camici M, Allegrini S, Collavoli A, Scarfone I, Zucchi F, Galli A, Tozzi MG. Initial studies to define the physiologic role of cN-II. NUCLEOSIDES NUCLEOTIDES & NUCLEIC ACIDS 2012; 30:1155-60. [PMID: 22132970 DOI: 10.1080/15257770.2011.628355] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/15/2022]
Abstract
IMP preferring cytosolic 5'-nucleotidase II (cN-II) is a widespread enzyme whose amino acid sequence is highly conserved among vertebrates. Fluctuations of its activity have been reported in some pathological conditions and its mRNA levels have been proposed as a prognostic factor for poor outcome in patients with adult acute myeloid leukemia. As a member of the oxypurine cycle, cN-II is involved in the regulation of intracellular concentration of 5'-inosine monophosphate (IMP), 5'-guanosine monophosphate (GMP), and also 5-phosphoribose 1-pyrophosphate (PRPP) and is therefore involved in the regulation of purine and pyrimidine de novo and salvage synthesis. In addition, several studies demonstrated the involvement of cN-II in pro-drug metabolism. Notwithstanding some publications indicating that cN-II is essential for the survival of several cell types, its role in cell metabolism remains uncertain. To address this issue, we built two eucaryotic cellular models characterized by different cN-II expression levels: a constitutive cN-II knockdown in the astrocytoma cell line (ADF) by short hairpin RNA (shRNA) strategy and a cN-II expression in the diploid strain RS112 of Saccharomyces cerevisiae. Preliminary results suggest that cN-II is essential for cell viability, probably because it is directly involved in the regulation of nucleotide pools. These two experimental approaches could be very useful for the design of a personalized chemotherapy.
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Mitra AK, Crews KR, Pounds S, Cao X, Feldberg T, Ghodke Y, Gandhi V, Plunkett W, Dolan ME, Hartford C, Raimondi S, Campana D, Downing J, Rubnitz JE, Ribeiro RC, Lamba JK. Genetic variants in cytosolic 5'-nucleotidase II are associated with its expression and cytarabine sensitivity in HapMap cell lines and in patients with acute myeloid leukemia. J Pharmacol Exp Ther 2011; 339:9-23. [PMID: 21712425 DOI: 10.1124/jpet.111.182873] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Cytosolic 5'-nucleotidase II (NT5C2) is involved in the development of 1-β-d-arabinofuranosylcytosine (ara-C) resistance and has been associated with clinical outcome in patients receiving ara-C-based chemotherapy. NT5C2 inactivates ara-C by dephosphorylating ara-C monophosphate to ara-C. In this study, we sequenced NT5C2 in genomic DNA samples from International HapMap project panels with European [Centre d'Etude du Polymorphisme Humain (CEU); n = 90] or African [Yoruba people in Ibadan, Nigeria (YRI); n = 90] ancestry. We identified 41 genetic variants [one insertion-deletion and 40 single nucleotide polymorphisms (SNPs)], including three nonsynonymous SNPs (Y3A, K47R, and Q136R). Twenty-five SNPs were novel and 16 overlapped with the HapMap data. Subjects with African ancestry had NT5C2 mRNA expression levels that was significantly higher than those with European ancestry (p = 0.005). Furthermore, there was a correlation between NT5C2 mRNA expression and ara-C sensitivity in CEU but not in YRI cell lines. None of the nonsynonymous SNPs demonstrated any effect on NT5C2 activity. The genotypes of several SNPs were significantly associated with NT5C2 mRNA expression and/or ara-C sensitivity in CEU cell lines, but very few were significant in YRI cell lines. Of most interest, SNPs (linkage disequilibrium group CEU.12) in the 5'-untranslated region were associated with NT5C2 expression and ara-C sensitivity in HapMap cell lines and with NT5C2 mRNA expression and ara-C sensitivity in diagnostic leukemic blasts from pediatric patients with acute myeloid leukemia. Functional genomics analysis demonstrated that the promoter SNP rs11191612 was associated with altered luciferase activation in reporter assays and altered DNA-protein binding in gel shift assays. These results suggest that genetic variations in NT5C2 influence its expression and, potentially, cellular responses to nucleoside analogs.
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Affiliation(s)
- Amit K Mitra
- Department of Experimental and Clinical Pharmacology, University of Minnesota, Minneapolis, Minnesota 55455, USA
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Walldén K, Nordlund P. Structural basis for the allosteric regulation and substrate recognition of human cytosolic 5'-nucleotidase II. J Mol Biol 2011; 408:684-96. [PMID: 21396942 DOI: 10.1016/j.jmb.2011.02.059] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2010] [Revised: 02/18/2011] [Accepted: 02/25/2011] [Indexed: 10/18/2022]
Abstract
Cytosolic 5'-nucleotidase II (cN-II) catalyzes the dephosphorylation of 6-hydroxypurine nucleoside 5'-monophosphates and participates in the regulation of purine nucleotide pools within the cell. It interferes with the phosphorylation-dependent activation of nucleoside analogues used in the treatment of cancer and viral diseases. It is allosterically activated by a number of phosphate-containing cellular metabolites such as ATP, diadenosine polyphosphates, and 2,3-bisphosphoglycerate, which couple its activity with the metabolic state of the cell. We present seven high-resolution structures of human cN-II, including a ligand-free form and complexes with various substrates and effectors. These structures reveal the structural basis for the allosteric activation of cN-II, uncovering a mechanism where an effector-induced disorder-to-order transition generates rearrangements within the catalytic site and the subsequent coordination of the catalytically essential magnesium. Central to the activation is the large transition of the catalytically essential Asp356. This study also provides the structural basis for the substrate specificity of cN-II, where Arg202, Asp206, and Phe157 seem to be important residues for purine/pyrimidine selectivity. These structures provide a comprehensive structural basis for the design of cN-II inhibitors. They also contribute to the understanding of how the nucleotide salvage pathway is regulated at a molecular level.
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Affiliation(s)
- Karin Walldén
- Department of Medical Biochemistry and Biophysics, Karolinska Institutet, 17177 Stockholm, Sweden
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Pesi R, Allegrini S, Careddu MG, Filoni DN, Camici M, Tozzi MG. Active and regulatory sites of cytosolic 5'-nucleotidase. FEBS J 2010; 277:4863-72. [PMID: 21029378 DOI: 10.1111/j.1742-4658.2010.07891.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Cytosolic 5'-nucleotidase (cN-II), which acts preferentially on 6-hydroxypurine nucleotides, is essential for the survival of several cell types. cN-II catalyses both the hydrolysis of nucleotides and transfer of their phosphate moiety to a nucleoside acceptor through formation of a covalent phospho-intermediate. Both activities are regulated by a number of phosphorylated compounds, such as diadenosine tetraphosphate (Ap₄A), ADP, ATP, 2,3-bisphosphoglycerate (BPG) and phosphate. On the basis of a partial crystal structure of cN-II, we mutated two residues located in the active site, Y55 and T56. We ascertained that the ability to catalyse the transfer of phosphate depends on the presence of a bulky residue in the active site very close to the aspartate residue that forms the covalent phospho-intermediate. The molecular model indicates two possible sites at which adenylic compounds may interact. We mutated three residues that mediate interaction in the first activation site (R144, N154, I152) and three in the second (F127, M436 and H428), and found that Ap₄A and ADP interact with the same site, but the sites for ATP and BPG remain uncertain. The structural model indicates that cN-II is a homotetrameric protein that results from interaction through a specific interface B of two identical dimers that have arisen from interaction of two identical subunits through interface A. Point mutations in the two interfaces and gel-filtration experiments indicated that the dimer is the smallest active oligomerization state. Finally, gel-filtration and light-scattering experiments demonstrated that the native enzyme exists as a tetramer, and no further oligomerization is required for enzyme activation.
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Affiliation(s)
- Rossana Pesi
- Dipartimento di Biologia, Unità di Biochimica, Università di Pisa, Pisa, Italy
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Redzic ZB, Malatiali SA, Grujicic D, Isakovic AJ. Expression and functional activity of nucleoside transporters in human choroid plexus. Cerebrospinal Fluid Res 2010; 7:2. [PMID: 20150980 PMCID: PMC2820436 DOI: 10.1186/1743-8454-7-2] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2009] [Accepted: 01/11/2010] [Indexed: 01/11/2023] Open
Abstract
Background Human equilibrative nucleoside transporters (hENTs) 1-3 and human concentrative nucleoside transporters (hCNTs) 1-3 in the human choroid plexus (hCP) play a role in the homeostasis of adenosine and other naturally occurring nucleosides in the brain; in addition, hENT1, hENT2 and hCNT3 mediate membrane transport of nucleoside reverse transcriptase inhibitors that could be used to treat HIV infection, 3'-azido-3'-deoxythymidine, 2'3'-dideoxycytidine and 2'3'-dideoxyinosine. This study aimed to explore the expression levels and functional activities of hENTs 1-3 and hCNTs 1-3 in human choroid plexus. Methods Freshly-isolated pieces of lateral ventricle hCP, removed for various clinical reasons during neurosurgery, were obtained under Local Ethics Committee approval. Quantification of mRNAs that encoded hENTs and hCNTs was performed by the hydrolysis probes-based reverse transcription real time-polymerase chain reaction (RT-qPCR); for each gene of interest and for 18 S ribosomal RNA, which was an endogenous control, the efficiency of PCR reaction (E) and the quantification cycle (Cq) were calculated. The uptake of [3H]inosine by the choroid plexus pieces was investigated to explore the functional activity of hENTs and hCNTs in the hCP. Results RT-qPCR revealed that the mRNA encoding the intracellularly located transporter hENT3 was the most abundant, with E-Cq value being only about 40 fold less that the E-Cq value for 18 S ribosomal RNA; mRNAs encoding hENT1, hENT2 and hCNT3 were much less abundant than mRNA for the hENT3, while mRNAs encoding hCNT1 and hCNT2 were of very low abundance and not detectable. Uptake of [3H]inosine by the CP samples was linear and consisted of an Na+-dependent component, which was probably mediated by hCNT3, and Na+-independent component, mediated by hENTs. The latter component was not sensitive to inhibition by S-(4-nitrobenzyl)-6-thioinosine (NBMPR), when used at a concentration of 0.5 μM, a finding that excluded the involvement of hENT1, but it was very substantially inhibited by 10 μM NBMPR, a finding that suggested the involvement of hENT2 in uptake. Conclusion Transcripts for hENT1-3 and hCNT3 were detected in human CP; mRNA for hENT3, an intracellularly located nucleoside transporter, was the most abundant. Human CP took up radiolabelled inosine by both concentrative and equilibrative processes. Concentrative uptake was probably mediated by hCNT3; the equilibrative uptake was mediated only by hENT2. The hENT1 transport activity was absent, which could suggest either that this protein was absent in the CP cells or that it was confined to the basolateral side of the CP epithelium.
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Elucidation of the substrate specificity, kinetic and catalytic mechanism of adenylosuccinate lyase from Plasmodium falciparum. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2008; 1794:642-54. [PMID: 19111634 DOI: 10.1016/j.bbapap.2008.11.021] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/20/2008] [Revised: 11/21/2008] [Accepted: 11/24/2008] [Indexed: 11/20/2022]
Abstract
Adenylosuccinate lyase (ASL) catalyzes two distinct but chemically similar reactions in purine biosynthesis. The first, exclusive to the de novo pathway involves the cleavage of 5-aminoimidazole-4-(N-succinylcarboxamide) ribonucleotide (SAICAR) to 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) and fumarate and the second common to both de novo and the salvage pathways involves the cleavage of succinyl-adenosine monophosphate (SAMP) to AMP and fumarate. A detailed kinetic and catalytic mechanism of the recombinant His-tagged ASL from Plasmodium falciparum (PfASL) is presented here. Initial velocity kinetics, product inhibition studies and transient kinetics indicate a Uni-Bi rapid equilibrium ordered mechanism. Substrate and solvent isotope effect studies implicate the process of C(gamma)-N bond cleavage to be rate limiting. Interestingly, the effect of pH on k(cat) and k(cat)/K(m) highlight ionization of the base only in the enzyme substrate complex and not in the enzyme alone, thereby implicating the pivotal role of the substrate in the activation of the catalytic base. Site-directed mutagenesis implicates a key role for the conserved serine (S298) in catalysis. Despite the absence of a de novo pathway for purine synthesis and most importantly, the absence of other enzymes that can metabolise AICAR in P. falciparum, PfASL catalyzes the SAICAR cleavage reaction with kinetic parameters similar to those of SAMP reaction and binds AICAR with affinity similar to that of AMP. The presence of this catalytic feature allows the use of AICAR or its analogues as inhibitors of PfASL and hence, as novel putative anti-parasitic agents. In support of this, we do see a dose dependent inhibition of parasite growth in the presence of 5-aminoimidazole-4-carboxamide ribonucleoside (AICAriboside) with half-maximal inhibition at 167+/-5 microM.
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Careddu MG, Allegrini S, Pesi R, Camici M, Garcia-Gil M, Tozzi MG. Knockdown of cytosolic 5'-nucleotidase II (cN-II) reveals that its activity is essential for survival in astrocytoma cells. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2008; 1783:1529-35. [PMID: 18445485 DOI: 10.1016/j.bbamcr.2008.03.018] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/13/2007] [Revised: 02/28/2008] [Accepted: 03/31/2008] [Indexed: 11/29/2022]
Abstract
IMP preferring cytosolic 5'-nucleotidase (cN-II) is an ubiquitous nucleotide hydrolysing enzyme. The enzyme is widely distributed and its amino acid sequence is highly conserved among vertebrates. Fluctuations of cN-II activity have been associated with the pathogenesis of neurological disorders. The enzyme appears to be involved in the regulation of the intracellular availability of the purine precursor IMP and also of GMP and AMP, but the contribution of this activity and of its regulation to cell metabolism and to CNS cell functions remains uncertain. To address this issue, we used a vector based short hairpin RNA (shRNA) strategy to knockdown cN-II activity in human astrocytoma cells. Our results demonstrated that 53 h after transduction, cN-II mRNA was reduced to 17.9+/-0.03% of control cells. 19 h later enzyme activity was decreased from 0.7+/-0.026 mU/mg in control ADF cells to 0.45+/-0.046 mU/mg, while cell viability (evaluated by the MTT reduction assay) decreased up to 0.59+/-0.01 (fold vs control) and caspase 3 activity increased from 136+/-5.8 pmol min(-1) mg(-1) in control cells to 639+/-37.5 pmol min(-1) mg(-1) in silenced cells, thus demonstrating that cN-II is essential for cell survival. The decrease of enzyme activity causes apoptosis of the cultured cells without altering intracellular nucleotide and nucleoside concentration or energy charge. Since cN-II is highly expressed in tumour cells, our finding offers a new possible therapeutical approach especially against primary brain tumours such as glioblastoma, and to ameliorate chemotherapy against leukemia.
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Galmarini CM. What does over-expression of cN-II enzyme signify in haematological malignancies? Leuk Res 2007; 31:1325-6. [PMID: 17434583 DOI: 10.1016/j.leukres.2007.02.006] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2007] [Revised: 02/15/2007] [Accepted: 02/15/2007] [Indexed: 11/15/2022]
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Fyrberg A, Albertioni F, Lotfi K. Cell cycle effect on the activity of deoxynucleoside analogue metabolising enzymes. Biochem Biophys Res Commun 2007; 357:847-53. [PMID: 17459340 DOI: 10.1016/j.bbrc.2007.03.176] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2007] [Accepted: 03/28/2007] [Indexed: 11/16/2022]
Abstract
Deoxynucleoside analogues (dNAs) are cytotoxic towards both replicating and indolent malignancies. The impact of fluctuations in the metabolism of dNAs in relation to cell cycle could have strong implications regarding the activity of dNAs. Deoxycytidine kinase (dCK) and deoxyguanosine kinase (dGK) are important enzymes for phosphorylation/activation of dNAs. These drugs can be dephosphorylated/deactivated by 5'-nucleotidases (5'-NTs) and elevated activities of 5'-NTs and decreased dCK and/or dGK activities represent resistance mechanisms towards dNAs. The activities of dCK, dGK, and three 5'-NTs were investigated in four human leukemic cell lines in relationship to cell cycle progression and cytotoxicity of dNAs. Synchronization of cell cultures to arrest in G0/G1 by serum-deprivation was performed followed by serum-supplementation for cell cycle progression. The activities of dCK and dGK increased up to 3-fold in CEM, HL60, and MOLT-4 cells as they started to proliferate, while the activity of cytosolic nucleotidase I was reduced in proliferating cells. CEM, HL60, and MOLT-4 cells were also more sensitive to cladribine, cytarabine, 9-beta-D-arabinofuranosylguanine and clofarabine than K562 cells which demonstrated lower levels and less alteration of these enzymes and were least susceptible to the cytotoxic effects of most dNAs. The results suggest that, in the cell lines studied, the proliferation process is associated with a general shift in the direction of activation of dNAs by inducing activities of dCK/dGK and reducing the activity of cN-I which is favourable for the cytotoxic effects of cladribine, cytarabine and, 9-beta-D-arabinofuranosylguanine. These results emphasize the importance of cellular proliferation and dNA metabolism by both phosphorylation and dephosphorylation for susceptibility to dNAs. It underscores the need to understand the mechanisms of action and resistance to dNAs in order to increase efficacy of dNAs treatment by new rational.
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Affiliation(s)
- Anna Fyrberg
- Division of Clinical Pharmacology, Department of Medicine and Care, Faculty of Health Sciences, Linköping University, SE-581 85 Linköping, Sweden
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Lu Y, Rosenberg PA. NMDA receptor-mediated extracellular adenosine accumulation is blocked by phosphatase 1/2A inhibitors. Brain Res 2007; 1155:116-24. [PMID: 17509540 PMCID: PMC3626428 DOI: 10.1016/j.brainres.2007.04.057] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2006] [Revised: 04/06/2007] [Accepted: 04/10/2007] [Indexed: 10/23/2022]
Abstract
We have previously demonstrated that NMDA receptor-mediated extracellular adenosine accumulation in neuronal cultures is receptor-mediated and requires calcium influx. Because protein kinase C (PKC) is a calcium-dependent enzyme, we hypothesized that activation of PKC might be involved in NMDA-mediated adenosine accumulation. PKC inhibitors, however, did not block NMDA-evoked adenosine accumulation, but rather, stimulated basal adenosine accumulation. These data suggested the possibility that NMDA receptor-mediated adenosine accumulation involves net dephosphorylation rather than phosphorylation of one or more substrates. Thus, inhibition of kinases would be expected to increase adenosine accumulation and inhibition of phosphatases would be expected to block adenosine accumulation. To test this hypothesis, we used the phosphatase 1/2A inhibitors calyculin A and okadaic acid. Both inhibitors significantly reduced NMDA-evoked adenosine accumulation. In contrast phosphatase 2B inhibitors did not block NMDA-evoked adenosine accumulation. These data suggest that NMDA-evoked adenosine accumulation is mediated by activation of phosphatase 1/2A. We have established previously that NMDA-mediated adenosine accumulation is associated with adenosine kinase inhibition. However, adenosine kinase is not a direct substrate for phosphatase 1/2A because inhibition of phosphatase 1/2A did not abolish NMDA-evoked adenosine kinase inhibition. Okadaic acid also had no effect on NO donor-evoked adenosine accumulation, which previously has been shown to be associated with adenosine kinase inhibition. Dephosphorylation of one or more proteins other than adenosine kinase as a consequence of NMDA receptor activation might play an important role in extracellular adenosine regulation, with important consequences for the regulation of excitatory synaptic transmission, plasticity, epileptogenesis, and excitotoxicity.
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Affiliation(s)
- Yin Lu
- Enders Research Building, Department of Neurology, Neurobiology Program, Children's Hospital, Boston, MA 02115, USA
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Walldén K, Stenmark P, Nyman T, Flodin S, Gräslund S, Loppnau P, Bianchi V, Nordlund P. Crystal structure of human cytosolic 5'-nucleotidase II: insights into allosteric regulation and substrate recognition. J Biol Chem 2007; 282:17828-36. [PMID: 17405878 DOI: 10.1074/jbc.m700917200] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cytosolic 5'-nucleotidase II catalyzes the dephosphorylation of 6-hydroxypurine nucleoside 5'-monophosphates and regulates the IMP and GMP pools within the cell. It possesses phosphotransferase activity and thereby also catalyzes the reverse reaction. Both reactions are allosterically activated by adenine-based nucleotides and 2,3-bisphosphoglycerate. We have solved structures of cytosolic 5'-nucleotidase II as native protein (2.2 Angstrom) and in complex with adenosine (1.5 Angstrom) and beryllium trifluoride (2.15 Angstrom) The tetrameric enzyme is structurally similar to enzymes of the haloacid dehalogenase (HAD) superfamily, including mitochondrial 5'(3')-deoxyribonucleotidase and cytosolic 5'-nucleotidase III but possesses additional regulatory regions that contain two allosteric effector sites. At effector site 1 located near a subunit interface we modeled diadenosine tetraphosphate with one adenosine moiety in each subunit. This efficiently glues the tetramer subunits together in pairs. The model shows why diadenosine tetraphosphate but not diadenosine triphosphate activates the enzyme and supports a role for cN-II during apoptosis when the level of diadenosine tetraphosphate increases. We have also modeled 2,3-bisphosphoglycerate in effector site 1 using one phosphate site from each subunit. By comparing the structure of cytosolic 5'-nucleotidase II with that of mitochondrial 5'(3')-deoxyribonucleotidase in complex with dGMP, we identified residues involved in substrate recognition.
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Affiliation(s)
- Karin Walldén
- Department of Biochemistry and Biophysics, Stockholm University, 10691 Stockholm, Sweden
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Recent advances in structure and function of cytosolic IMP-GMP specific 5'-nucleotidase II (cN-II). Purinergic Signal 2006; 2:669-75. [PMID: 18404470 PMCID: PMC2096664 DOI: 10.1007/s11302-006-9009-z] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2005] [Accepted: 03/27/2006] [Indexed: 02/03/2023] Open
Abstract
Cytosolic 5′nucleotidase II (cN-II) catalyses both the hydrolysis of a number of nucleoside monophosphates (e.g., IMP + H2O→inosine + Pi), and the phosphate transfer from a nucleoside monophosphate donor to the 5′position of a nucleoside acceptor (e.g., IMP + guanosine →inosine + GMP). The enzyme protein functions through the formation of a covalent phosphoenzyme intermediate, followed by the phosphate transfer either to water (phosphatase activity) or to a nucleoside (phosphotransferase activity). It has been proposed that cN-II regulates the intracellular concentration of IMP and GMP and the production of uric acid. The enzyme might also have a potential therapeutic importance, since it can phosphorylate some anti-tumoral and antiviral nucleoside analogues that are not substrates of known kinases. In this review we summarise our recent studies on the structure, regulation and function of cN-II. Via a site-directed mutagenesis approach, we have identified the amino acids involved in the catalytic mechanism and proposed a structural model of the active site. A series of in vitro studies suggests that cN-II might contribute to the regulation of 5-phosphoribosyl-1-pyrophosphate (PRPP) level, through the so-called oxypurine cycle, and in the production of intracellular adenosine, formed by ATP degradation.
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Invited Lectures : Overviews Purinergic signalling: past, present and future. Purinergic Signal 2006; 2:1-324. [PMID: 18404494 PMCID: PMC2096525 DOI: 10.1007/s11302-006-9006-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/02/2006] [Indexed: 12/11/2022] Open
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Itoh R, Kimura K. IMP-GMP 5'-nucleotidase in reptiles: occurrence and tissue distribution in a crocodile and three species of lizards. Comp Biochem Physiol B Biochem Mol Biol 2005; 142:107-12. [PMID: 15996884 DOI: 10.1016/j.cbpc.2005.06.005] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2005] [Revised: 06/13/2005] [Accepted: 06/13/2005] [Indexed: 11/23/2022]
Abstract
IMP-hydrolyzing activity (which is reactive with goose anti-pig lung IMP-GMP 5'-nucleotidase (c-N-II: EC.3.1.3.5) serum) was detected in extracts from several tissues (liver, heart, kidney, spleen, stomach, lung and skeletal muscle) from constitutively uricotelic reptiles: a crocodile (Crocodylus siamensis), and three species of lizard (Furcifer oustaleti, Tupinambis rufescens and Varanus gouldi). The activities were markedly high in the livers: 3.0 units/g in the crocodile and 1.4-2.9 units/g in the lizards. These were similar to those previously reported for the livers from chicken and snakes (also constitutively uricotelic), and 4- to 10-fold higher than those in ammoniotelic or ureotelic vertebrates. These findings suggest that the high activity of IMP-GMP 5'-nucleotidase in the liver is a feature of constitutive uricotelism, and that the enzyme may participate in the production of uric acid as an end product of amino acid catabolism.
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Affiliation(s)
- Roichi Itoh
- Department of Home Economics, Tokyo Kasei Gakuin University, 2600 Aiharamachi, Machida-city, Tokyo 194-0292, Japan.
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31
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Hunsucker SA, Mitchell BS, Spychala J. The 5'-nucleotidases as regulators of nucleotide and drug metabolism. Pharmacol Ther 2005; 107:1-30. [PMID: 15963349 DOI: 10.1016/j.pharmthera.2005.01.003] [Citation(s) in RCA: 201] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/07/2005] [Indexed: 11/19/2022]
Abstract
The 5'-nucleotidases are a family of enzymes that catalyze the dephosphorylation of nucleoside monophosphates and regulate cellular nucleotide and nucleoside levels. While the nucleoside kinases responsible for the initial phosphorylation of salvaged nucleosides have been well studied, many of the catabolic nucleotidases have only recently been cloned and characterized. Aside from maintaining balanced ribo- and deoxyribonucleotide pools, substrate cycles that are formed with kinase and nucleotidase activities are also likely to regulate the activation of nucleoside analogues, a class of anticancer and antiviral agents that rely on the nucleoside kinases for phosphorylation to their active forms. Both clinical and in vitro studies suggest that an increase in nucleotidase activity can inhibit nucleoside analogue activation and result in drug resistance. The physiological role of the 5'-nucleotidases will be covered in this review, as will the evidence that these enzymes can mediate resistance to nucleoside analogues.
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Affiliation(s)
- Sally Anne Hunsucker
- Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
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Wu JZ, Larson G, Walker H, Shim JH, Hong Z. Phosphorylation of ribavirin and viramidine by adenosine kinase and cytosolic 5'-nucleotidase II: Implications for ribavirin metabolism in erythrocytes. Antimicrob Agents Chemother 2005; 49:2164-71. [PMID: 15917509 PMCID: PMC1140532 DOI: 10.1128/aac.49.6.2164-2171.2005] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Many nucleoside analog drugs, such as ribavirin and viramidine, are activated or metabolized in vivo through 5'-phosphorylation. In this report, we determined the steady-state kinetic parameters for 5'-monophosphorylation of ribavirin and viramidine by adenosine kinase. The apparent Km for ribavirin is 540 microM, and k(cat) is 1.8 min-1. Its catalytic efficiency of 3.3 x 10(-3) min-1 . microM-1 is 1,200-fold lower than that of adenosine. In contrast to the common belief that ribavirin is exclusively phosphorylated by adenosine kinase, cytosolic 5'-nucleotidase II was found to catalyze ribavirin phosphorylation in vitro. The reaction is optimally stimulated by the physiological concentration of ATP or 2,3-bisphosphoglycerate. In phosphate-buffered saline plus ATP and 2,3-bisphosphoglycerate, the apparent Km for ribavirin is 88 microM, and k(cat) is 4.0 min-1. These findings suggest that cytosolic 5'-nucleotidase II may be involved in ribavirin phosphorylation in vivo. Like ribavirin, viramidine was found to be phosphorylated by either adenosine kinase or cytosolic 5'-nucleotidase II, albeit with a much lower activity. The catalytic efficiency for viramidine phosphorylation is 10- to 330-fold lower than that of ribavirin, suggesting that other nucleoside kinase(s) may be involved in viramidine phosphorylation in vivo. Both ribavirin and viramidine are not phosphorylated by deoxycytidine kinase and uridine-cytidine kinase. The coincidence of presence of high concentrated 2,3-bisphosphoglycerate in erythrocytes suggests that cytosolic 5'-nucleotidase II could play an important role in phosphorylating ribavirin and contribute to anabolism of ribavirin triphosphate in erythrocytes. Elucidation of ribavirin and viramidine phosphorylation mechanism should shed light on their in vivo metabolism, especially the ribavirin-induced hemolytic anemia in erythrocytes.
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Affiliation(s)
- Jim Zhen Wu
- Drug Discovery, Valeant Pharmaceuticals International, 3300 Hyland Avenue, Costa Mesa, CA 92626, USA.
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33
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Allegrini S, Scaloni A, Careddu MG, Cuccu G, D'Ambrosio C, Pesi R, Camici M, Ferrara L, Tozzi MG. Mechanistic studies on bovine cytosolic 5'-nucleotidase II, an enzyme belonging to the HAD superfamily. ACTA ACUST UNITED AC 2005; 271:4881-91. [PMID: 15606776 DOI: 10.1111/j.1432-1033.2004.04457.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Cytosolic 5'-nucleotidase/phosphotransferase specific for 6-hydroxypurine monophosphate derivatives (cN-II), belongs to a class of phosphohydrolases that act through the formation of an enzyme-phosphate intermediate. Sequence alignment with members of the P-type ATPases/L-2-haloacid dehalogenase superfamily identified three highly conserved motifs in cN-II and other cytosolic nucleotidases. Mutagenesis studies at specific amino acids occurring in cN-II conserved motifs were performed. The modification of the measured kinetic parameters, caused by conservative and nonconservative substitutions, suggested that motif I is involved in the formation and stabilization of the covalent enzyme-phosphate intermediate. Similarly, T249 in motif II as well as K292 in motif III also contribute to stabilize the phospho-enzyme adduct. Finally, D351 and D356 in motif III coordinate magnesium ion, which is required for catalysis. These findings were consistent with data already determined for P-type ATPases, haloacid dehalogenases and phosphotransferases, thus suggesting that cN-II and other mammalian 5'-nucleotidases are characterized by a 3D arrangement related to the 2-haloacid dehalogenase superfold. Structural determinants involved in differential regulation by nonprotein ligands and redox reagents of the two naturally occurring cN-II forms generated by proteolysis were ascertained by combined biochemical and mass spectrometric investigations. These experiments indicated that the C-terminal region of cN-II contains a cysteine prone to form a disulfide bond, thereby inactivating the enzyme. Proteolysis events that generate the observed cN-II forms, eliminating this C-terminal portion, may prevent loss of enzymic activity and can be regarded as regulatory phenomena.
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Affiliation(s)
- Simone Allegrini
- Dipartimento di Scienze del Farmaco, Università di Sassari, Italy.
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Fernandez-Calotti P, Jordheim LP, Giordano M, Dumontet C, Galmarini CM. Substrate cycles and drug resistance to 1-beta-D-arabinofuranosylcytosine (araC). Leuk Lymphoma 2005; 46:335-46. [PMID: 15621823 DOI: 10.1080/10428190400015683] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Acute myelogenous leukemia (AML) is the most common form of acute leukemia in adults. After diagnosis, patients with AML are mainly treated with standard induction chemotherapy combining cytarabine (araC) and anthracyclines. The majority of them achieve complete remission (CR) (65-80%). However, prospects for long-term survival are poor for the majority of patients. Resistance to chemotherapy therefore remains a major obstacle in the effective treatment of patients with AML. In this review, we highlight the current knowledge of substrate cycles involved in normal deoxynucleoside triphosphate (dNTPs) metabolism and their possible role in drug resistance to araC.
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Affiliation(s)
- Paula Fernandez-Calotti
- Laboratorio de Immunología Oncológica-IIHEMA, Academia Nacional de Medicina, Buenos Aires, Argentina.
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35
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Bretonnet AS, Jordheim LP, Dumontet C, Lancelin JM. Regulation and activity of cytosolic 5′-nucleotidase II. FEBS Lett 2005; 579:3363-8. [PMID: 15946667 DOI: 10.1016/j.febslet.2005.05.014] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2005] [Revised: 05/17/2005] [Accepted: 05/18/2005] [Indexed: 11/20/2022]
Abstract
In many vertebrate tissues, cytosolic 5'-nucleotidase II (cN-II) either hydrolyses or phosphorylates a number of purine (monophosphorylated) nucleosides through a scheme common to the Haloacid Dehalogenase superfamily members. It possesses a pivotal role in purine cellular metabolism and it acts on anti-tumoural and antiviral nucleoside analogues, thus being of potential therapeutic importance. cN-II is Mg2+-dependent, regulated and stabilised by several factors such as allosteric effectors ATP and 2,3-DPG, although these are not directly involved in the reaction stoichiometry. We review herein the experimental knowledge currently available about this remarkable enzymatic activity.
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Affiliation(s)
- A S Bretonnet
- Laboratoire de RMN Biomoléculaire, Université Claude Bernard--Lyon I, UMR CNRS 5180 Sciences Analytiques, ESCPE Lyon, 69622 Villeurbanne, France
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36
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Barsotti C, Pesi R, Giannecchini M, Ipata PL. Evidence for the involvement of cytosolic 5'-nucleotidase (cN-II) in the synthesis of guanine nucleotides from xanthosine. J Biol Chem 2005; 280:13465-9. [PMID: 15699053 DOI: 10.1074/jbc.m413347200] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In this paper, we show that in vitro xanthosine does not enter any of the pathways known to salvage the other three main natural purine nucleosides: guanosine; inosine; and adenosine. In rat brain extracts and in intact LoVo cells, xanthosine is salvaged to XMP via the phosphotransferase activity of cytosolic 5'-nucleotidase. IMP is the preferred phosphate donor (IMP + xanthosine --> XMP + inosine). XMP is not further phosphorylated. However, in the presence of glutamine, it is readily converted to guanyl compounds. Thus, phosphorylation of xanthosine by cytosolic 5'-nucleotidase circumvents the activity of IMP dehydrogenase, a rate-limiting enzyme, catalyzing the NAD(+)-dependent conversion of IMP to XMP at the branch point of de novo nucleotide synthesis, thus leading to the generation of guanine nucleotides. Mycophenolic acid, an inhibitor of IMP dehydrogenase, inhibits the guanyl compound synthesis via the IMP dehydrogenase pathway but has no effect on the cytosolic 5'-nucleotidase pathway of guanine nucleotides synthesis. We propose that the latter pathway might contribute to the reversal of the in vitro antiproliferative effect exerted by IMP dehydrogenase inhibitors routinely seen with repletion of the guanine nucleotide pools.
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Affiliation(s)
- Catia Barsotti
- Department of Physiology and Biochemistry, University of Pisa, Via San Zeno 51, 56127 Pisa, Italy
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37
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Barsotti C, Ipata PL. Metabolic regulation of ATP breakdown and of adenosine production in rat brain extracts. Int J Biochem Cell Biol 2005; 36:2214-25. [PMID: 15313467 DOI: 10.1016/j.biocel.2004.04.015] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2004] [Revised: 04/28/2004] [Accepted: 04/28/2004] [Indexed: 02/07/2023]
Abstract
ATP concentration is dramatically affected in ischemic injury. From previous studies on ATP mediated purine and pyrimidine salvage in CNS, we observed that when "post-mitochondrial" extracts of rat brain were incubated with ATP at 3.6 mM, a normoxic concentration, formation of IMP always preceded that of adenosine, a well known neuroactive nucleoside and a homeostatic cellular modulator. This observation prompted us to undertake a study aimed at assessing the precise pathways and kinetics of ATP breakdown, a process considered to be the major source of adenosine in rat brain. The results obtained using post-mitochondrial extracts strongly suggest that the breakdown of intracellular ATP at normoxic concentration follows almost exclusively the pathway ATP<=>ADP<=>AMP --> IMP --> inosine<=>hypoxanthine, with little, if any, intracellular adenosine production. At low ischemic concentration, intracellular ATP breakdown follows the pathway ATP<=>ADP<=>AMP --> adenosine --> inosine<=>hypoxanthine with little IMP formation. At the same time, extracellular ATP, whose concentration is known to be enhanced during ischemia, is actively broken down to adenosine through the pathway ATP --> ADP --> AMP --> adenosine, catalysed by the well characterized ecto-enzyme cascade system. Moreover, we show that during intracellular GTP catabolism, xanthosine, in addition to guanosine, is generated through the so called "ribose 1-phosphate recycling for nucleoside interconversion". These results considerably extend our knowledge on the long debated question of the extra or intracellular origin of adenosine in CNS, suggesting that at least in normoxic conditions, intracellular adenosine is of extracellular origin.
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Affiliation(s)
- Catia Barsotti
- Department of Physiology and Biochemistry, University of Pisa, Via San Zeno 51, 56127 Pisa, Italy.
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38
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Feng JY, Parker WB, Krajewski ML, Deville-Bonne D, Veron M, Krishnan P, Cheng YC, Borroto-Esoda K. Anabolism of amdoxovir: phosphorylation of dioxolane guanosine and its 5'-phosphates by mammalian phosphotransferases. Biochem Pharmacol 2004; 68:1879-88. [PMID: 15450953 DOI: 10.1016/j.bcp.2004.06.019] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2004] [Accepted: 06/14/2004] [Indexed: 11/24/2022]
Abstract
Amdoxovir [(-)-beta-D-2,6-diaminopurine dioxolane, DAPD], the prodrug of dioxolane guanosine (DXG), is currently in Phase I/II clinical development for the treatment of HIV-1 infection. In this study, we examined the phosphorylation pathway of DXG using 15 purified enzymes from human (8), animal (6), and yeast (1) sources, including deoxyguanosine kinase (dGK), deoxycytidine kinase (dCK), high Km 5'-nucleotidase (5'-NT), guanylate (GMP) kinase, nucleoside monophosphate (NMP) kinase, adenylate (AMP) kinase, nucleoside diphosphate (NDP) kinase, 3-phosphoglycerate (3-PG) kinase, creatine kinase, and pyruvate kinase. In addition, the metabolism of 14C-labeled DXG was studied in CEM cells. DXG was not phosphorylated by human dCK, and was a poor substrate for human dGK with a high Km (7 mM). Human 5'-NT phosphorylated DXG with relatively high efficiency (4.2% of deoxyguanosine). DXG-MP was a substrate for porcine brain GMP kinase with a substrate specificity that was 1% of dGMP. DXG-DP was phosphorylated by all of the enzymes tested, including NDP kinase, 3-PG kinase, creatine kinase, and pyruvate kinase. The BB-isoform of human creatine kinase showed the highest relative substrate specificity (47% of dGDP) for DXG-DP. In CEM cells incubated with 5 microM DXG for 24 h, 0.015 pmole/10(6) cells (approximately 7.5 nM) of DXG-TP was detected as the primary metabolite. Our study demonstrated that 5'-nucleotidase, GMP kinase, creatine kinase, and NDP kinase could be responsible for the activation of DXG in vivo.
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Affiliation(s)
- Joy Y Feng
- Gilead Sciences, 4 University Place, 4611 University Drive, Durham, NC 27707, USA.
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Proudfoot M, Kuznetsova E, Brown G, Rao NN, Kitagawa M, Mori H, Savchenko A, Yakunin AF. General enzymatic screens identify three new nucleotidases in Escherichia coli. Biochemical characterization of SurE, YfbR, and YjjG. J Biol Chem 2004; 279:54687-94. [PMID: 15489502 DOI: 10.1074/jbc.m411023200] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
To find proteins with nucleotidase activity in Escherichia coli, purified unknown proteins were screened for the presence of phosphatase activity using the general phosphatase substrate p-nitrophenyl phosphate. Proteins exhibiting catalytic activity were then assayed for nucleotidase activity against various nucleotides. These screens identified the presence of nucleotidase activity in three uncharacterized E. coli proteins, SurE, YfbR, and YjjG, that belong to different enzyme superfamilies: SurE-like family, HD domain family (YfbR), and haloacid dehalogenase (HAD)-like superfamily (YjjG). The phosphatase activity of these proteins had a neutral pH optimum (pH 7.0-8.0) and was strictly dependent on the presence of divalent metal cations (SurE: Mn(2+) > Co(2+) > Ni(2+) > Mg(2+); YfbR: Co(2+) > Mn(2+) > Cu(2+); YjjG: Mg(2+) > Mn(2+) > Co(2+)). Further biochemical characterization of SurE revealed that it has a broad substrate specificity and can dephosphorylate various ribo- and deoxyribonucleoside 5'-monophosphates and ribonucleoside 3'-monophosphates with highest affinity to 3'-AMP. SurE also hydrolyzed polyphosphate (exopolyphosphatase activity) with the preference for short-chain-length substrates (P(20-25)). YfbR was strictly specific to deoxyribonucleoside 5'-monophosphates, whereas YjjG showed narrow specificity to 5'-dTMP, 5'-dUMP, and 5'-UMP. The three enzymes also exhibited different sensitivities to inhibition by various nucleoside di- and triphosphates: YfbR was equally sensitive to both di- and triphosphates, SurE was inhibited only by triphosphates, and YjjG was insensitive to these effectors. The differences in their sensitivities to nucleotides and their varied substrate specificities suggest that these enzymes play unique functions in the intracellular nucleotide metabolism in E. coli.
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Affiliation(s)
- Michael Proudfoot
- Banting and Best Department of Medical Research, University of Toronto, Ontario M5G 1L6, Canada
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40
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Affiliation(s)
- Vera Bianchi
- Department of Biology, University of Padua, I-35131 Padua, Italy.
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41
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Itoh R, Kimura K. IMP-GMP 5'-nucleotidase in reptiles: occurrence in a turtle, a tortoise and three species of snakes. Comp Biochem Physiol B Biochem Mol Biol 2003; 135:657-62. [PMID: 12892757 DOI: 10.1016/s1096-4959(03)00147-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
IMP-hydrolyzing activity, which is reactive with goose anti-pig lung IMP-GMP 5'-nucleotidase (c-N-II: EC.3.1.3.5) serum, was detected in extracts from liver, heart, kidney, spleen, stomach, skeletal muscle and lung from several species of reptiles: The values found in liver (U/mg protein) of one animal were: 4.5 for an ammono-ureotelic turtle (Trionyx sinensis japonicus); 3.7 for an ureo-uricotelic tortoise (Testudo elegans); 13-23 for three species of uricotelic snakes: Elaphe quadrivirgata, Elaphe conspicillata and Elaphe climacophora. These findings suggest that in the liver of snakes, c-N-II may participate in the production of uric acid as an end product of amino acid metabolism.
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Affiliation(s)
- Roichi Itoh
- Department of Home Economics, Tokyo Kasei Gakuin University, 2600 Aiharamachi, Machida-city, Tokyo 194-0292, Japan.
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Itoh R, Kimura K. Occurrence of IMP-GMP 5'-nucleotidase in three fish species: a comparative study on Trachurus japonicus, Oncorhynchus masou masou and Triakis scyllium. Comp Biochem Physiol B Biochem Mol Biol 2002; 132:401-8. [PMID: 12031466 DOI: 10.1016/s1096-4959(02)00049-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
IMP-hydrolyzing activity, which is reactive with goose anti-pig lung IMP-GMP 5'-nucleotidase (EC.3.1.3.5) serum, was detected in extracts from various tissues of Trachurus japonicus (a marine teleost), Oncorhynchus masou masou (a freshwater teleost) and Triakis scyllium (an elasmobranch). Kinetic characteristics of the reactive enzymatic activity were similar to those of IMP-GMP 5'-nucleotidase from mammals and birds. In all species studied, the activity was highest in the liver (4-6 micromol of Pi released from IMP/min/mg of protein). The second highest activity was observed in the head portion of Oncorhynchus kidney (4 micromol of Pi released from IMP/min/mg of protein), which was twofold higher than that of its body portion. In all three species, the activity was lowest in white skeletal muscle among the tissues studied (0.1-0.3 micromol of Pi released from IMP/min/mg of protein), while the activity in red skeletal muscle was sixfold to 10-fold higher than that in white muscle.
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Affiliation(s)
- Roichi Itoh
- Department of Home Economics, Tokyo Kasei Gakuin University, 2600 Aiharamachi, Machida-city, Tokyo 194-0292, Japan.
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Barsotti C, Tozzi MG, Ipata PL. Purine and pyrimidine salvage in whole rat brain. Utilization of ATP-derived ribose-1-phosphate and 5-phosphoribosyl-1-pyrophosphate generated in experiments with dialyzed cell-free extracts. J Biol Chem 2002; 277:9865-9. [PMID: 11782482 DOI: 10.1074/jbc.m111418200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The object of this work stems from our previous studies on the mechanisms responsible of ribose-1-phosphate- and 5-phosphoribosyl-1-pyrophosphate-mediated nucleobase salvage and 5-fluorouracil activation in rat brain (Mascia, L., Cappiello M., Cherri, S., and Ipata, P. L. (2000) Biochim. Biophys. Acta 1474, 70-74; Mascia, L., Cotrufo, T., Cappiello, M., and Ipata, P. L. (1999) Biochim. Biophys. Acta 1472, 93-98). Here we show that when ATP at "physiological concentration" is added to dialyzed extracts of rat brain in the presence of natural nucleobases or 5-fluorouracil, adenine-, hypoxanthine-, guanine-, uracil-, and 5-fluorouracil-ribonucleotides are synthesized. The molecular mechanism of this peculiar nucleotide synthesis relies on the capacity of rat brain to salvage purine and pyrimidine bases by deriving ribose-1-phosphate and 5-phosphoribosyl-1-pyrophosphate from ATP even in the absence of added pentose or pentose phosphates. The levels of the two sugar phosphates formed are compatible with those of synthesized nucleotides. We propose that the ATP-mediated 5-phosphoribosyl-1-pyrophosphate synthesis occurs through the action of purine nucleoside phosphorylase, phosphopentomutase, and 5-phosphoribosyl-1-pyrophosphate synthetase. Furthering our previous observations on the effect of ATP in the 5-phosphoribosyl-1-pyrophosphate-mediated 5-fluorouracil activation in rat liver (Mascia, L., and Ipata, P. L. (2001) Biochem. Pharmacol. 62, 213-218), we now show that the ratio [5-phosphoribosyl-1-pyrophosphate]/[ATP] plays a major role in modulating adenine salvage in rat brain. On the basis of our in vitro results, we suggest that massive ATP degradation, as it occurs in brain during ischemia, might lead to an increase of the intracellular 5-phosphoribosyl-1-pyrophosphate and ribose-1-phosphate pools, to be utilized for nucleotide resynthesis during reperfusion.
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Affiliation(s)
- Catia Barsotti
- Department of Physiology and Biochemistry, University of Pisa, Via Santa Maria 55, 56126 Pisa, Italy
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Barsotti C, Ipata PL. Pathways for alpha-D-ribose utilization for nucleobase salvage and 5-fluorouracil activation in rat brain. Biochem Pharmacol 2002; 63:117-22. [PMID: 11841784 DOI: 10.1016/s0006-2952(01)00845-0] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Recently, interest has increased in the use of alpha-D-ribose (Rib) as a naturally occurring nutriceutical for enhancement of cardiac and muscular performance. Most likely the elevation of available PRPP, following Rib administration, plays a key role in the salvage of purine nucleobases, thus, accelerating the restitution of ATP pool. In addition, administration of Rib improves some of the neurological symptoms in patients with adenylosuccinase deficiency. In this paper, we show that rat brain extract can catalyze the Rib-mediated salvage of both adenine and uracil, as well as the activation of the pyrimidine pro-drug, 5-fluorouracil (5-FU). The results strongly support that the pentose may be converted to both PRPP and Rib1-P for the salvage of the adenine and uracil, respectively. Most likely two-reaction pathway, composed of ribokinase and PRPP synthetase, is responsible of the PRPP formation, needed to salvage adenine to adenine nucleotides. A two-reaction pathway, composed of ribokinase and phosphopentomutase, appears to be responsible of the Rib1-P formation, needed to salvage uracil to uracil-nucleotides and to activate 5-FU to cytotoxic 5-FU-ribonucleotides. alpha-D-2'-Deoxyribose (deoxyRib) has a negligible effect on both the salvage of natural nucleobases to deoxyribonucleotides and on the activation of 5-FU to cytotoxic 5-FU-deoxynucleotides.
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Affiliation(s)
- Catia Barsotti
- Laboratory of Biochemistry, Department of Physiology and Biochemistry, University of Pisa, Via S. Maria 55, 56126, Pisa, Italy
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Abstract
Erythrocyte maturation is accompanied by RNA degradation and release of mononucleotides. Pyrimidine 5'-nucleotidase, PN-I, has been purified and characterized. The molecular and enzymatic properties determined for the enzyme shows a 36-kDa and 5.1 pI monomeric protein with no disulfide bridges and no phosphate content. The activity is dependent on Mg(2+), while it is inactivated by heavy metals and by thiol-reactive reagents. PN-I is specific for pyrimidine nucleoside monophosphates, including the antineoplastic agents 5'-AZTMP and 5'-Ara-CMP. PN-I possess phosphotransferase activity able to exchange phosphate between pyrimidine nucleoside monophosphates and pyrimidine nucleosides, including AZT and Ara-Cyd. Amino acid sequence has been obtained from tryptic and CNBr peptides. PN-I cDNA sequence, coding for a 286-residue protein, has been retrieved from tag database, amplified by PCR, and expressed in Escherichia coli. The recombinant protein was fully active and showed identical properties with respect to PN-I. Substantial identity has been revealed with the partial sequences reported for p36, an alpha-interferon-induced protein. The significance of this identity is discussed.
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Affiliation(s)
- Adolfo Amici
- Istituto di Biochimica, Facoltà di Medicina e Chirurgia, Università di Ancona, Via Ranieri 65, Ancona, 60131, Italy.
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Allegrini S, Scaloni A, Ferrara L, Pesi R, Pinna P, Sgarrella F, Camici M, Eriksson S, Tozzi MG. Bovine cytosolic 5'-nucleotidase acts through the formation of an aspartate 52-phosphoenzyme intermediate. J Biol Chem 2001; 276:33526-32. [PMID: 11432867 DOI: 10.1074/jbc.m104088200] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cytosolic 5'-nucleotidase/phosphotransferase (cN-II), specific for purine monophosphates and their deoxyderivatives, acts through the formation of a phosphoenzyme intermediate. Phosphate may either be released leading to 5'-mononucleotide hydrolysis or be transferred to an appropriate nucleoside acceptor, giving rise to a mononucleotide interconversion. Chemical reagents specifically modifying aspartate and glutamate residues inhibit the enzyme, and this inhibition is partially prevented by cN-II substrates and physiological inhibitors. Peptide mapping experiments with the phosphoenzyme previously treated with tritiated borohydride allowed isolation of a radiolabeled peptide. Sequence analysis demonstrated that radioactivity was associated with a hydroxymethyl derivative that resulted from reduction of the Asp-52-phosphate intermediate. Site-directed mutagenesis experiments confirmed the essential role of Asp-52 in the catalytic machinery of the enzyme and suggested also that Asp-54 assists in the formation of the acyl phosphate species. From sequence alignments we conclude that cytosolic 5'-nucleotidase, along with other nucleotidases, belong to a large superfamily of hydrolases with different substrate specificities and functional roles.
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Affiliation(s)
- S Allegrini
- Dipartimento di Scienze del Farmaco, Università di Sassari, via Muroni 23/A, 07100 Sassari Italy
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Mascia L, Cappiello M, Cherri S, Ipata PL. In vitro recycling of alpha-D-ribose 1-phosphate for the salvage of purine bases. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1474:70-4. [PMID: 10699492 DOI: 10.1016/s0304-4165(99)00217-2] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
In this paper, we extend our previous observation on the mobilization of the ribose moiety from a purine nucleoside to a pyrimidine base, with subsequent pyrimidine nucleotides formation (Cappiello et al., Biochim. Biophys. Acta 1425 (1998) 273-281). The data show that, at least in vitro, also the reverse process is possible. In rat brain extracts, the activated ribose, stemming from uridine as ribose 1-phosphate, can be used to salvage adenine and hypoxanthine to their respective nucleotides. Since the salvage of purine bases is a 5-phosphoribosyl 1-pyrophosphate-dependent process, catalyzed by adenine phosphoribosyltransferase and hypoxanthine guanine phosphoribosyltransferase, our results imply that Rib-1P must be transformed into 5-phosphoribosyl 1-pyrophosphate, via the successive action of phosphopentomutase and 5-phosphoribosyl 1-pyrophosphate synthetase; and,in fact, no adenosine could be found as an intermediate when rat brain extracts were incubated with adenine, Rib-1P and ATP, showing that adenine salvage does not imply adenine ribosylation, followed by adenosine phosphorylation. Taken together with our previous results on the Rib-1P-dependent salvage of pyrimidine nucleotides, our results give a clear picture of the in vitro Rib-1P recycling, for both purine and pyrimidine salvage.
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Affiliation(s)
- L Mascia
- Department of Physiology and Biochemistry, University of Pisa, Via S. Maria 55, 56126, Pisa, Italy
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Rampazzo C, Gazziola C, Ferraro P, Gallinaro L, Johansson M, Reichard P, Bianchi V. Human high-Km 5'-nucleotidase effects of overexpression of the cloned cDNA in cultured human cells. EUROPEAN JOURNAL OF BIOCHEMISTRY 1999; 261:689-97. [PMID: 10215885 DOI: 10.1046/j.1432-1327.1999.00320.x] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
5'-Nucleotidases participate, together with nucleoside kinases, in substrate cycles involved in the regulation of deoxyribonucleotide metabolism. Three major classes of nucleotidases are known, one on the plasma membrane and two in the cytosol. The two cytosolic classes have been named high-Km nucleotidases and 5'(3')-nucleotidases. Starting from two plasmids with partial sequences (Oka, J., Matsumoto, A., Hosokawa, Y. & Inoue, S. (1994) Biochem. Biophys. Res. Commun. 205, 917-922) we cloned the complete cDNA of the human high-Km nucleotidase into vectors suitable for transfection of Escherichia coli or mammalian cells. After transfection, E. coli overproduced large amounts of the enzyme. Most of the enzyme was present in inclusion bodies that also contained many partially degraded products of the protein. Part of the enzyme, corresponding to approximately 2% of the soluble proteins, was in a soluble active form. Stably transfected human 293 cells were obtained with a vector where the 3'-end of the nucleotidase coding sequence is linked to the 5'-end of the green fluorescent protein coding sequence. Several green clones overproduced both mRNA and fusion protein. Two clones with 10-fold higher enzyme activity were analyzed further. The nucleotidase activity of cell extracts showed the same substrate specificity and allosteric regulation as the high-Km enzyme. The growth rate of the two clones did not differ from the controls. The cells were not resistant to deoxyguanosine or deoxyadenosine, and did not show an increased ability to phosphorylate dideoxyinosine. Both ribonucleoside and deoxyribonucleoside triphosphate pools were decreased slightly, suggesting participation of the enzyme in their regulation.
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Affiliation(s)
- C Rampazzo
- Department of Biology, University of Padova, Italy
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Abstract
Chemotherapy for chronic hepatitis B virus (HBV) infection is inherently difficult for a variety of reasons that are related to unusual features of both HBV replication strategy and host cell metabolism. Previous attempts to treat chronic HBV infection using nucleoside analogues have been almost universally disappointing, but several recently developed nucleoside analogues have been identified as potent, non-toxic inhibitors of HBV replication. These fall into two broad categories: nucleosides having the 'unnatural' L-configuration, and deoxyguanosine analogues with modified-sugar configurations, represented by lamivudine and penciclovir respectively. Both lamivudine and penciclovir (in its orally available form, famciclovir) have progressed to phase III clinical trials against chronic HBV infection, with promising preliminary results. However, chemotherapy for chronic HBV is necessarily long term, which increases the risks for development of viral resistance and cumulative toxicity. Such risks might be minimized by the use of appropriate drug combinations, rational selection of which requires knowledge of the pharmacokinetics and mechanisms of action of the individual agents. An appreciation of cellular deoxynucleoside metabolism and its regulation, the complexities of which are still emerging, is an indispensable aid to understanding the biological activities of deoxynucleoside analogues. The modes of action of lamividine and penciclovir, and how these two deoxynucleoside analogues may interact in vitro and in vivo as inhibitors of HBV replication, are examined here in the context of cellular deoxynucleoside metabolism.
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Affiliation(s)
- T Shaw
- Victorian Infectious Diseases Reference Laboratory, North Melbourne, Victoria, Australia
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Spychala J, Chen V, Oka J, Mitchell BS. ATP and phosphate reciprocally affect subunit association of human recombinant High Km 5'-nucleotidase. Role for the C-terminal polyglutamic acid tract in subunit association and catalytic activity. EUROPEAN JOURNAL OF BIOCHEMISTRY 1999; 259:851-8. [PMID: 10092873 DOI: 10.1046/j.1432-1327.1999.00099.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
IMP-specific, High Km 5'-nucleotidase (EC 3.1.3.5) is an ubiquitous enzyme, the activity of which is highly regulated by substrate, ATP, and inorganic phosphate. The cDNA encoding this enzyme has recently been cloned and found to contain a unique stretch of nine glutamic and four aspartic acid residues at the C-terminus. To study the effects of this acidic tail, and of ATP and inorganic phosphate on enzyme function, we generated several structural modifications of the 5'-nucleotidase cDNA, expressed the corresponding proteins in Escherichia coli and compared their molecular and kinetic properties. As with the enzyme purified from human placenta, all recombinant proteins were activated by ATP and inhibited by inorganic phosphate. Although the S0.5-values were higher, the specific activities of the purified protein variants (except that truncated at the C-terminus) were similar. The molecular mass of the full-length enzyme subunit has been estimated at 57.3 kDa and the molecular mass of the native protein, as determined by gel-filtration chromatography, was estimated to be 195 kDa. Increasing the concentration of NaCl to 0.3 M promoted oligomerization of the protein and the formation of aggregates of 332 kDa. ATP induced further oligomerization to 715 kDa, while inorganic phosphate reduced the estimated molecular mass to 226 kDa. In contrast to the truncation of 30 amino acids at the N-terminus, which did not alter enzyme properties, the removal of the polyglutamic/aspartic acid tail of 13 residues at the C-terminus caused profound kinetic and structural changes, including a 29-fold decrease in specific activity and a significant increase in the sensitivity to inhibition by inorganic phosphate in the presence of AMP. Structurally, there was a dramatic loss of the ability to form oligomers at physiological salt concentration which was only partially restored by the addition of NaCl or ATP. These data suggest an important function of the polyglutamic acid tract in the process of association and dissociation of 5'-nucleotidase subunits.
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Affiliation(s)
- J Spychala
- Department of Pharmacology, University of North Carolina at Chapel Hill 27599-7365, USA.
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