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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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Enhanced migration of breast and lung cancer cells deficient for cN-II and CD73 via COX-2/PGE2/AKT axis regulation. Cell Oncol (Dordr) 2020; 44:151-165. [PMID: 32970317 DOI: 10.1007/s13402-020-00558-w] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/04/2020] [Indexed: 02/07/2023] Open
Abstract
PURPOSE Purine metabolism involves various intracellular and extracellular enzymes, including cN-II and CD73 that dephosphorylate intracellular and extracellular nucleoside monophosphates into their corresponding nucleosides. We conducted a study to better understand the biological roles of these enzymes in breast and lung cancer cells. METHODS We modified cN-II and/or CD73 expression in human breast cancer cells (MDA-MB-231), human lung cancer cells (NCI-H292) and murine breast cancer cells (4T1) using the CRISPR/Cas9 technique, and evaluated their impact on various cellular parameters such as proliferation, migration, invasion, intracellular nucleotide pools and nucleotide metabolism-related gene expression under extracellular nucleotide stress conditions. RESULTS Intracellular nucleotide contents were found to be altered in the modified cancer cell models both at their basal levels and after exposure to adenosine or AMP. Altered cN-II and CD73 levels were also found to be associated with cell migration and invasion alterations, involving TIMP-2, MMP-2 and MMP-9 expression, as well as alterations in the COX-2/PGE2/AKT pathway. CONCLUSION Our results highlight new cell-specific roles of cN-II and CD73 in cancer cell biology and provide insight into their interactions with different intracellular pathways.
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Davis PR, Miller SG, Verhoeven NA, Morgan JS, Tulis DA, Witczak CA, Brault JJ. Increased AMP deaminase activity decreases ATP content and slows protein degradation in cultured skeletal muscle. Metabolism 2020; 108:154257. [PMID: 32370945 PMCID: PMC7319876 DOI: 10.1016/j.metabol.2020.154257] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/03/2020] [Revised: 04/18/2020] [Accepted: 04/29/2020] [Indexed: 12/15/2022]
Abstract
BACKGROUND Protein degradation is an energy-dependent process, requiring ATP at multiple steps. However, reports conflict as to the relationship between intracellular energetics and the rate of proteasome-mediated protein degradation. METHODS To determine whether the concentration of the adenine nucleotide pool (ATP + ADP + AMP) affects protein degradation in muscle cells, we overexpressed an AMP degrading enzyme, AMP deaminase 3 (AMPD3), via adenovirus in C2C12 myotubes. RESULTS Overexpression of AMPD3 resulted in a dose- and time-dependent reduction of total adenine nucleotides (ATP, ADP and AMP) without increasing the ADP/ATP or AMP/ATP ratios. In agreement, the reduction of total adenine nucleotide concentration did not result in increased Thr172 phosphorylation of AMP-activated protein kinase (AMPK), a common indicator of intracellular energetic state. Furthermore, LC3 protein accumulation and ULK1 (Ser 555) phosphorylation were not induced. However, overall protein degradation and ubiquitin-dependent proteolysis were slowed by overexpression of AMPD3, despite unchanged content of several proteasome subunit proteins and proteasome activity in vitro under standard conditions. CONCLUSIONS Altogether, these findings indicate that a physiologically relevant decrease in ATP content, without a concomitant increase in ADP or AMP, is sufficient to decrease the rate of protein degradation and activity of the ubiquitin-proteasome system in muscle cells. This suggests that adenine nucleotide degrading enzymes, such as AMPD3, may be a viable target to control muscle protein degradation and perhaps muscle mass.
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Affiliation(s)
- Patrick R Davis
- Department of Kinesiology, East Carolina University, United States of America
| | - Spencer G Miller
- Department of Kinesiology, East Carolina University, United States of America
| | - Nicolas A Verhoeven
- Department of Kinesiology, East Carolina University, United States of America
| | - Joshua S Morgan
- Department of Physiology, Brody School of Medicine, East Carolina University, United States of America
| | - David A Tulis
- Department of Physiology, Brody School of Medicine, East Carolina University, United States of America
| | - Carol A Witczak
- Department of Kinesiology, East Carolina University, United States of America; Department of Physiology, Brody School of Medicine, East Carolina University, United States of America; Department of Biochemistry & Molecular Biology, Brody School of Medicine, East Carolina University, Greenville, NC 27834, United States of America
| | - Jeffrey J Brault
- Department of Kinesiology, East Carolina University, United States of America; Department of Physiology, Brody School of Medicine, East Carolina University, United States of America; Department of Biochemistry & Molecular Biology, Brody School of Medicine, East Carolina University, Greenville, NC 27834, United States of America.
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Bricard G, Cros-Perrial E, Machon C, Dumontet C, Jordheim LP. Stably transfected adherent cancer cell models with decreased expression of 5'-nucleotidase cN-II. NUCLEOSIDES NUCLEOTIDES & NUCLEIC ACIDS 2017; 35:604-612. [PMID: 27906612 DOI: 10.1080/15257770.2016.1163375] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
The 5'-nucleotidase cN-II has been shown to be associated with the sensitivity to nucleoside analogues, the survival of cytarabine treated leukemia patients and to cell proliferation. Due to the lack of relevant cell models for solid tumors, we developed four cell lines with low cN-II expression and characterized them concerning their in vitro sensitivity to cancer drugs and their intracellular nucleotide pools. All four cell models had an important decrease of cN-II expression but did not show modified sensitivity, cell proliferation or nucleotide pools. Our cell models will be important for the study of the role of cN-II in human cancer cells.
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Affiliation(s)
- Gabriel Bricard
- a Université de Lyon , Lyon , France.,b Université de Lyon , Lyon , France.,c INSERM U1052, Centre de Recherche en Cancérologie de Lyon , Lyon , France.,d CNRS UMR 5286, Centre de Recherche en Cancérologie de Lyon , Lyon , France.,e Centre Léon Bérard , Lyon , France
| | - Emeline Cros-Perrial
- a Université de Lyon , Lyon , France.,b Université de Lyon , Lyon , France.,c INSERM U1052, Centre de Recherche en Cancérologie de Lyon , Lyon , France.,d CNRS UMR 5286, Centre de Recherche en Cancérologie de Lyon , Lyon , France.,e Centre Léon Bérard , Lyon , France
| | - Christelle Machon
- a Université de Lyon , Lyon , France.,b Université de Lyon , Lyon , France.,f Hospices Civils de Lyon , Lyon , France
| | - Charles Dumontet
- a Université de Lyon , Lyon , France.,b Université de Lyon , Lyon , France.,c INSERM U1052, Centre de Recherche en Cancérologie de Lyon , Lyon , France.,d CNRS UMR 5286, Centre de Recherche en Cancérologie de Lyon , Lyon , France.,e Centre Léon Bérard , Lyon , France.,f Hospices Civils de Lyon , Lyon , France
| | - Lars Petter Jordheim
- a Université de Lyon , Lyon , France.,b Université de Lyon , Lyon , France.,c INSERM U1052, Centre de Recherche en Cancérologie de Lyon , Lyon , France.,d CNRS UMR 5286, Centre de Recherche en Cancérologie de Lyon , Lyon , France.,e Centre Léon Bérard , Lyon , France
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Maiuolo J, Oppedisano F, Gratteri S, Muscoli C, Mollace V. Regulation of uric acid metabolism and excretion. Int J Cardiol 2016; 213:8-14. [PMID: 26316329 DOI: 10.1016/j.ijcard.2015.08.109] [Citation(s) in RCA: 665] [Impact Index Per Article: 83.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/10/2015] [Accepted: 08/10/2015] [Indexed: 12/22/2022]
Abstract
Purines perform many important functions in the cell, being the formation of the monomeric precursors of nucleic acids DNA and RNA the most relevant one. Purines which also contribute to modulate energy metabolism and signal transduction, are structural components of some coenzymes and have been shown to play important roles in the physiology of platelets, muscles and neurotransmission. All cells require a balanced quantity of purines for growth, proliferation and survival. Under physiological conditions the enzymes involved in the purine metabolism maintain in the cell a balanced ratio between their synthesis and degradation. In humans the final compound of purines catabolism is uric acid. All other mammals possess the enzyme uricase that converts uric acid to allantoin that is easily eliminated through urine. Overproduction of uric acid, generated from the metabolism of purines, has been proven to play emerging roles in human disease. In fact the increase of serum uric acid is inversely associated with disease severity and especially with cardiovascular disease states. This review describes the enzymatic pathways involved in the degradation of purines, getting into their structure and biochemistry until the uric acid formation.
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Affiliation(s)
- Jessica Maiuolo
- Institute of Research for Food Safety & Health (IRC-FSH), University "Magna Graecia" of Catanzaro, Italy
| | - Francesca Oppedisano
- Institute of Research for Food Safety & Health (IRC-FSH), University "Magna Graecia" of Catanzaro, Italy
| | - Santo Gratteri
- Institute of Research for Food Safety & Health (IRC-FSH), University "Magna Graecia" of Catanzaro, Italy
| | - Carolina Muscoli
- Institute of Research for Food Safety & Health (IRC-FSH), University "Magna Graecia" of Catanzaro, Italy
| | - Vincenzo Mollace
- Institute of Research for Food Safety & Health (IRC-FSH), University "Magna Graecia" of Catanzaro, Italy.
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Rampazzo C, Tozzi MG, Dumontet C, Jordheim LP. The druggability of intracellular nucleotide-degrading enzymes. Cancer Chemother Pharmacol 2015; 77:883-93. [PMID: 26614508 DOI: 10.1007/s00280-015-2921-6] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2015] [Accepted: 11/13/2015] [Indexed: 01/24/2023]
Abstract
Nucleotide metabolism is the target of a large number of anticancer drugs including antimetabolites and specific enzyme inhibitors. We review scientific findings that over the last 10-15 years have allowed the identification of several intracellular nucleotide-degrading enzymes as cancer drug targets, and discuss further potential therapeutic applications for Rcl, SAMHD1, MTH1 and cN-II. We believe that enzymes involved in nucleotide metabolism represent potent alternatives to conventional cancer chemotherapy targets.
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Affiliation(s)
- Chiara Rampazzo
- Department of Biology, University of Padova, 35131, Padua, Italy
| | - Maria Grazia Tozzi
- Department of Biology, Biochemistry Unit, University of Pisa, Pisa, Italy
| | - Charles Dumontet
- Université de Lyon, 69000, Lyon, France.,Université de Lyon 1, 69622, Lyon, France.,Université de Lyon 1, 69000, Lyon, France.,INSERM U1052, Centre de Recherche en Cancérologie de Lyon, 69000, Lyon, France.,CNRS UMR 5286, Centre de Recherche en Cancérologie de Lyon, 69000, Lyon, France.,Centre Léon Bérard, 69008, Lyon, France.,Hospices Civils de Lyon, 69000, Lyon, France
| | - Lars Petter Jordheim
- Université de Lyon, 69000, Lyon, France. .,Université de Lyon 1, 69622, Lyon, France. .,Université de Lyon 1, 69000, Lyon, France. .,INSERM U1052, Centre de Recherche en Cancérologie de Lyon, 69000, Lyon, France. .,CNRS UMR 5286, Centre de Recherche en Cancérologie de Lyon, 69000, Lyon, France. .,Centre Léon Bérard, 69008, Lyon, France. .,Equipe Anticorps-Anticancer, INSERM U1052 - CNRS UMR 5286, Faculté Rockefeller, Centre de Recherche en Cancérologie de Lyon, 8 avenue Rockefeller, 69008, Lyon, France.
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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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Determination of the enzymatic activity of cytosolic 5'-nucleotidase cN-II in cancer cells: development of a simple analytical method and related cell line models. Anal Bioanal Chem 2015; 407:5747-58. [PMID: 25998135 DOI: 10.1007/s00216-015-8757-4] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2015] [Accepted: 05/04/2015] [Indexed: 01/03/2023]
Abstract
The cytosolic 5'-nucleotidase (cN-II) has been shown to be involved in the response of cancer cells to cytotoxic agents, and the quantification of its activity in biological samples is of great interest. In this context, we developed and validated an analytical method for determination of cN-II activity in cultured cancer cells. This non-radioactive method, using a Hypercarb column as stationary phase, was validated with a lower limit of quantification of 0.1 μM inosine. We used it to characterize cell line models with modified cN-II expression obtained with stable transfections. We show that the short hairpin RNA (shRNA)-mediated inhibition of cN-II expression in various malignant blood cells is associated with decreased protein expression and enzymatic activity (1.7-6.2-fold) as well as an increased sensitivity to cytotoxic agents (up to 14-fold). On the other hand, expression of green fluorescent protein (GFP)-fused wild type or hyperactive mutant (R367Q) cN-II increased the activity and also decreased the sensitivity to nucleoside analogues. Our results confirm the biological relevance of modulating cN-II in cancer cells, and we present a straightforward validated method for the determination of cN-II activity in cellular samples.
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Cividini F, Filoni DN, Pesi R, Allegrini S, Camici M, Tozzi MG. IMP-GMP specific cytosolic 5'-nucleotidase regulates nucleotide pool and prodrug metabolism. Biochim Biophys Acta Gen Subj 2015; 1850:1354-61. [PMID: 25857773 DOI: 10.1016/j.bbagen.2015.03.017] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2014] [Revised: 03/26/2015] [Accepted: 03/31/2015] [Indexed: 12/20/2022]
Abstract
BACKGROUND Type II cytosolic 5'-nucleotidase (cN-II) catalyzes the hydrolysis of purine and, to some extent, of pyrimidine monophosphates. Recently, a number of papers demonstrated the involvement of cN-II in the mechanisms of resistance to antitumor drugs such as cytarabine, gemcitabine and fludarabine. Furthermore, cN-II is involved in drug resistance in patients affected by hematological malignancies influencing the clinical outcome. Although the implication of cN-II expression and/or activity appears to be correlated with drug resistance and poor prognosis, the molecular mechanism by which cN-II mediates drug resistance is still unknown. METHODS HEK 293 cells carrying an expression vector coding for cN-II linked to green fluorescent protein (GFP) and a control vector without cN-II were utilized. A highly sensitive capillary electrophoresis method was applied for nucleotide pool determination and cytotoxicity exerted by drugs was determined with 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay. RESULTS Over-expression of cN-II causes a drop of nucleoside triphosphate concentration and a general disturbance of nucleotide pool. Over-expressing cells were resistant to fludarabine, gemcitabine and cytarabine independently of cN-II ability to hydrolyze their monophosphates. CONCLUSIONS An increase of cN-II expression is sufficient to cause both a general disturbance of nucleotide pool and an increase of half maximal inhibitory concentration (IC50) of the drugs. Since the monophosphates of cytarabine and gemcitabine are not substrates of cN-II, the protection observed cannot be directly ascribed to drug inactivation. GENERAL SIGNIFICANCE Our results indicate that cN-II exerts a relevant role in nucleotide and drug metabolism through not only enzyme activity but also a mechanism involving a protein-protein interaction, thus playing a general regulatory role in cell survival. SENTENCE Resistance to fludarabine, gemcitabine and cytarabine can be determined by an increase of cN-II both through dephosphorylation of active drugs and perturbation of nucleotide pool.
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Affiliation(s)
- Federico Cividini
- Dipartimento di Biologia, Unità di Biochimica, Università di Pisa, Via San Zeno 51, 56127, Pisa, Italy
| | - Daniela Nicole Filoni
- Dipartimento di Biologia, Unità di Biochimica, Università di Pisa, Via San Zeno 51, 56127, Pisa, Italy; Dipartimento di Chimica e Farmacia, Università di Sassari, Via Muroni 23A, 07100, Sassari, Italy
| | - Rossana Pesi
- Dipartimento di Biologia, Unità di Biochimica, Università di Pisa, Via San Zeno 51, 56127, Pisa, Italy
| | - Simone Allegrini
- Dipartimento di Chimica e Farmacia, Università di Sassari, Via Muroni 23A, 07100, Sassari, Italy.
| | - Marcella Camici
- Dipartimento di Biologia, Unità di Biochimica, Università di Pisa, Via San Zeno 51, 56127, Pisa, Italy
| | - Maria Grazia Tozzi
- Dipartimento di Biologia, Unità di Biochimica, Università di Pisa, Via San Zeno 51, 56127, Pisa, Italy
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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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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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Grazia TM. Inborn errors in purine metabolism: role of 5'-nucleotidases and their involvement in the etiology of neurological impairments. NUCLEOSIDES NUCLEOTIDES & NUCLEIC ACIDS 2012; 30:1276-83. [PMID: 22132987 DOI: 10.1080/15257770.2011.616869] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/15/2022]
Abstract
A number of scientists have been involved for decades in the study of nucleotide metabolism in different species of living beings. We are, therefore, aware of the relevant roles of purine compounds and of the many different ways in which these compounds influence cell life, acting both inside and outside the cells. Nevertheless, the consequences of an alteration (lack of expression, or hypo- or hyperexpression) in the activity of enzymes involved in the metabolism of these compounds are sometimes surprising, and far from being mechanistically explained. Alterations in enzyme activities involved in nucleotide metabolism are frequently associated with syndromes characterized by two different types of problems--one, metabolic, which is expected and can be easily explained, and the second, neurological and behavioral. Neurological and behavioral impairments are more difficult to explain and show a very high degree of individual variability. The molecular bases of the neurological impairment linked to purine metabolism disorders have been extensively studied. These studies have generated a lot of hypotheses but very few certainties. In this short review, neurological and behavioral symptoms linked to the dysfunction of some enzymes involved in purine synthesis, catabolism, and salvage will be briefly described, with particular attention to their metabolic and regulatory consequences. Finally, attention will be focused on the 5'-nucleotidase family members and on their involvement in the regulation of purine and pyrimidine metabolism.
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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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Burke AC, Giles FJ. Elacytarabine – lipid vector technology overcoming drug resistance in acute myeloid leukemia. Expert Opin Investig Drugs 2011; 20:1707-15. [DOI: 10.1517/13543784.2011.625009] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Affiliation(s)
- Aine Carol Burke
- Adelaide and Meath Hospital, Incorporating the National Children's Hospital, Tallaght, Dublin 24, Ireland
| | - Frank James Giles
- National University of Ireland Galway & Trinity College Dublin, HRB Clinical Research Facility, Dublin, Ireland
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15
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Kulkarni SS, Karlsson HKR, Szekeres F, Chibalin AV, Krook A, Zierath JR. Suppression of 5'-nucleotidase enzymes promotes AMP-activated protein kinase (AMPK) phosphorylation and metabolism in human and mouse skeletal muscle. J Biol Chem 2011; 286:34567-74. [PMID: 21873433 PMCID: PMC3186409 DOI: 10.1074/jbc.m111.268292] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2011] [Revised: 08/18/2011] [Indexed: 11/06/2022] Open
Abstract
The 5'-nucleotidase (NT5) family of enzyme dephosphorylates non-cyclic nucleoside monophosphates to produce nucleosides and inorganic phosphates. We hypothesized that gene silencing of NT5 enzymes to increase the intracellular availability of AMP would increase AMP-activated protein kinase (AMPK) activity and metabolism. We determined the role of cytosolic NT5 in metabolic responses linked to the development of insulin resistance in obesity and type 2 diabetes. Using siRNA to silence NT5C2 expression in cultured human myotubes, we observed a 2-fold increase in the AMP/ATP ratio, a 2.4-fold increase in AMPK phosphorylation (Thr(172)), and a 2.8-fold increase in acetyl-CoA carboxylase phosphorylation (Ser(79)) (p < 0.05). siRNA silencing of NT5C2 expression increased palmitate oxidation by 2-fold in the absence and by 8-fold in the presence of 5-aminoimidazole-4-carboxamide 1-β-d-ribofuranoside. This was paralleled by an increase in glucose transport and a decrease in glucose oxidation, incorporation into glycogen, and lactate release from NT5C2-depleted myotubes. Gene silencing of NT5C1A by shRNA injection and electroporation in mouse tibialis anterior muscle reduced protein content (60%; p < 0.05) and increased phosphorylation of AMPK (60%; p < 0.05) and acetyl-CoA carboxylase (50%; p < 0.05) and glucose uptake (20%; p < 0.05). Endogenous expression of NT5C enzymes inhibited basal lipid oxidation and glucose transport in skeletal muscle. Reduction of 5'-nucleotidase expression or activity may promote metabolic flexibility in type 2 diabetes.
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Affiliation(s)
- Sameer S. Kulkarni
- From the Departments of Molecular Medicine and Surgery and Physiology and Pharmacology, Karolinska Institutet, S-171 77 Stockholm, Sweden
| | - Håkan K. R. Karlsson
- From the Departments of Molecular Medicine and Surgery and Physiology and Pharmacology, Karolinska Institutet, S-171 77 Stockholm, Sweden
| | - Ferenc Szekeres
- From the Departments of Molecular Medicine and Surgery and Physiology and Pharmacology, Karolinska Institutet, S-171 77 Stockholm, Sweden
| | - Alexander V. Chibalin
- From the Departments of Molecular Medicine and Surgery and Physiology and Pharmacology, Karolinska Institutet, S-171 77 Stockholm, Sweden
| | - Anna Krook
- From the Departments of Molecular Medicine and Surgery and Physiology and Pharmacology, Karolinska Institutet, S-171 77 Stockholm, Sweden
| | - Juleen R. Zierath
- From the Departments of Molecular Medicine and Surgery and Physiology and Pharmacology, Karolinska Institutet, S-171 77 Stockholm, Sweden
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16
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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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17
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Mirzaee S, Eriksson S, Albertioni F. Differences in cytosolic and mitochondrial 5'-nucleotidase and deoxynucleoside kinase activities in Sprague-Dawley rat and CD-1 mouse tissues: implication for the toxicity of nucleoside analogs in animal models. Toxicology 2009; 267:159-64. [PMID: 19913594 DOI: 10.1016/j.tox.2009.11.009] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2009] [Revised: 11/04/2009] [Accepted: 11/05/2009] [Indexed: 11/17/2022]
Abstract
Cytosolic and mitochondrial deoxynucleoside kinases (dNKs), as well as 5'deoxynucleotidases (5'-dNTs), control intracellular and intramitochondrial phosphorylation of natural nucleotides and nucleoside analogs used in antiviral and cancer chemotherapy. The balance in the activities of these two groups of enzymes to a large extent determines both the efficacy and side effects of these drugs. Because of the broad and overlapping substrate specificities of the nucleoside kinases and 5'-NTs, their tissue distribution and roles in the metabolism of both natural nucleosides and their analogs are still not fully elucidated. Here, the activity of dNKs: dCK and TK (TK1 and TK2) as well as 5'-dNTs: CN1, CN2 and dNT (dNT1 and dNT2) were determined in 14 different adult mouse and rat tissues. In most cases tissue activities of TK1, TK2 and dCK were 2-3-fold higher in the mouse, a similar pattern was found with CN1 and dNTs although with several exceptions, e.g., TK2 activities in muscle extracts from rats were 2-10-fold higher than in the mouse. Furthermore CN1 activities in hepatic, renal and adipose extracts were 2-3-fold higher in the rat. CN2 had higher levels in the testis, spleen, pancreas and diaphragm and lower level in the lung of mouse compared to rat tissues. The result suggests that a major difference in these activity profiles between mouse and rat may account for discrepancies in pharmacological response of the two animals to certain nucleoside compounds, and may help to improve the usefulness of animal models in future efforts of drug discovery.
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Affiliation(s)
- Saeedeh Mirzaee
- Cancer Center Karolinska Department of Oncology and Pathology, Karolinska University Hospital, SE-17176 Stockholm, Sweden
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18
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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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19
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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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20
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Suzuki K, Sugawara T, Oyake T, Uchiyama T, Aoki Y, Tsukushi Y, Onodera S, Ito S, Murai K, Ishida Y. Clinical significance of high-Km 5'-nucleotidase (cN-II) mRNA expression in high-risk myelodysplastic syndrome. Leuk Res 2007; 31:1343-9. [PMID: 17350683 DOI: 10.1016/j.leukres.2007.01.018] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2006] [Revised: 01/18/2007] [Accepted: 01/30/2007] [Indexed: 11/22/2022]
Abstract
We analyzed cytosolic high-Km 5'-nucleotidase (cN-II) and deoxycytidine kinase (dCK) mRNA expression in bone marrow mononuclear cells (BMMNC) of patients with high-risk myelodysplastic syndrome (MDS) using quantitative real-time polymerase chain reaction (rt-PCR). At diagnosis, the cN-II mRNA expression of patients was higher than that of healthy volunteers, but the dCK mRNA expression showed no significant difference. Patients with ara-C-containing chemotherapies whose BMMNC showed a high level of cN-II expression (greater than the median value) had shorter median overall survival (15 months versus 22 months, p<0.01) and shorter median post-chemotherapy survival (10 months versus 16 months, p=0.012). These data suggest that the expression level of cN-II mRNA might be a prognostic factor of high-risk MDS.
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Affiliation(s)
- Keijiro Suzuki
- Department of Hematology/Oncology, Iwate Medical University, Japan.
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21
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Löfgren C, Albertioni F, Paul C. High activity and incomplete cross resistance of nucleoside analogues cladribine and fludarabine versus Ara-C on leukemic cells from patients with AML. Ther Drug Monit 2006; 27:641-6. [PMID: 16175139 DOI: 10.1097/01.ftd.0000175157.94192.dc] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The in vitro activity and cross-resistance pattern of the purine analogues cladribine and fludarabine and the pyrimidine analogue cytarabine on leukemic cells from 170 patients with AML was evaluated using a bioluminescence assay. In in vivo mimicking concentrations, cladribine (50 nmol/L) and fludarabine (2 micromol/L) were more cytotoxic than cytarabine (0.5 micromol/L). The cytotoxic effect of fludarabine correlated weakly to cytarabine (r = 0.37, P < 0.001). The cytotoxic effect of cladribine correlated better to cytarabine (r = 0.49, P = 0.0002) but best to fludarabine (r = 0.82, P < 0.001). There was an absence of correlation between either cladribine or fludarabine and daunorubicin (0.2 micromol/L). Of 45 highly Ara-C-resistant samples, cladribine exerted high or intermediate effect in 54% and fludarabine in 52%. These in vitro data indicate that cladribine and fludarabine are active drugs in the treatment of AML. The cross resistance to cytarabine was not complete, and the drugs can be valuable either as alternatives to Ara-C or in combination therapy for treatment of leukemia resistant to standard therapy.
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Affiliation(s)
- C Löfgren
- Department of Clinical Hematology, Karolinska University Hospital, Stockholm, Sweden.
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22
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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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23
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Al-Madhoun AS, Johnsamuel J, Barth RF, Tjarks W, Eriksson S. Evaluation of Human Thymidine Kinase 1 Substrates as New Candidates for Boron Neutron Capture Therapy. Cancer Res 2004; 64:6280-6. [PMID: 15342416 DOI: 10.1158/0008-5472.can-04-0197] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Thymidine analogs containing o-carboranylalkyl groups at the 3-position were screened as potential substrates for human thymidine kinase 1 (TK1), an enzyme that is selectively expressed in a variety of rapidly proliferating cells, including tumor cells. On the basis of previous studies, 12 of these were identified as potential delivery agents for boron neutron capture therapy, a therapeutic method used for the treatment of high-grade brain tumors. Compound 4 with a pentylene spacer between the o-carborane cage and the thymidine scaffold and compound 10, which has an additional dihydroxypropyl substituent at the o-carborane cage, were the best substrates for TK1 with kcat/Km values of 27% and 36% relative to that of thymidine, respectively. These compounds showed partial competitive inhibition for thymidine phosphorylation by TK1. Neither compound was a substrate of recombinant human thymidine phosphorylase nor were their respective 5'-monophosphates substrates of 5'-deoxynucleotidase 1, thereby indicating potential in vivo stability. The octanol/water partition coefficient for compound 10 was 2.09, suggesting that it has excellent physiochemical properties for crossing the blood brain barrier and penetrating brain tissue. The in vitro cytotoxic effect of the 12 analogs was moderate to low in mammalian cell cultures with IC50 values between 10 and 160 micromol/L. Compounds 4 and 10 were taken up selectively and retained by the murine fibroblast L929 cell line, in contrast to its TK1-deficient variant. These findings suggest that compound 10 is a promising candidate for selective delivery of boron-10 to malignant cells, and additional in vivo studies are planned to evaluate it for boron neutron capture therapy of brain tumors.
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Affiliation(s)
- Ashraf S Al-Madhoun
- Department of Molecular Biosciences, Division of Veterinary Medical Biochemistry, Swedish University of Agricultural Sciences, Biomedical Center, Uppsala, Sweden.
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24
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Löfgren C, Hjortsberg L, Blennow M, Lotfi K, Paul C, Eriksson S, Albertioni F. Mechanisms of cross-resistance between nucleoside analogues and vincristine or daunorubicin in leukemic cells. Biochem Biophys Res Commun 2004; 320:825-32. [PMID: 15240122 DOI: 10.1016/j.bbrc.2004.06.016] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2004] [Indexed: 11/25/2022]
Abstract
The aim of this study was to clarify the biochemical and molecular mechanisms behind the cross-resistance to nucleoside analogues (NAs) in four erythroleukemic cell lines with acquired resistance to the anthracycline daunorubicin and to the vinca alkaloid vincristine, expressing high levels of p-glycoprotein (P-gp, MDR1). All resistant strains exhibited cross-resistance to NA (cladribine and cytosine arabinoside)-induced apoptosis, assessed by caspase-3-like activation and were less sensitive to NA cytotoxicity in MTT assay. Real-time PCR and enzyme activity analysis showed reduced amounts of deoxycytidine kinase (35-80%) and elevated levels of 5'-nucleotidases (50-100%). The ratio 5'-nucleotidase to deoxycytidine kinase increased between 2.5- and 7.5-folds in resistant cells. This is in agreement with the observation that 5'-nucleotidase/deoxycytidine kinase ratio might be an important factor in predicting resistance to NAs. Implications of this finding for combining anthracyclines or vinca alkaloids with NAs toward leukemic cells are discussed.
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Affiliation(s)
- Christina Löfgren
- Department of Hematology, Huddinge University Hospital, Stockholm, Sweden.
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25
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Affiliation(s)
- Vera Bianchi
- Department of Biology, University of Padua, I-35131 Padua, Italy.
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26
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Mazzon C, Rampazzo C, Scaini MC, Gallinaro L, Karlsson A, Meier C, Balzarini J, Reichard P, Bianchi V. Cytosolic and mitochondrial deoxyribonucleotidases: activity with substrate analogs, inhibitors and implications for therapy. Biochem Pharmacol 2003; 66:471-9. [PMID: 12907246 DOI: 10.1016/s0006-2952(03)00290-9] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Nucleoside analogs act as prodrugs that must be converted to 5'-phosphates by intracellular kinases to become active in the treatment of viral and oncological diseases. Activation may be reversed by dephosphorylation if the 5'-phosphates are substrates for 5'-nucleotidases. Dephosphorylation by cytosolic enzymes decreases the efficacy of the analogs, whereas dephosphorylation by mitochondrial enzymes may decrease mitochondrial toxicity. Both effects may influence the outcome of therapy. We investigated the dephosphorylation of the 5'-phosphates of commonly used nucleoside analogs by two cytosolic (cN-II and dNT-1) and one mitochondrial (dNT-2) nucleotidase. Most uracil/thymine nucleotide analogs were dephosphorylated by all three human enzymes but cytosine-containing nucleotide analogs were inactive. Only cN-II showed some activity with the monophosphates of the two purine analogs 2-chloro-2'-deoxyadenosine and 9-beta-D-arabinosylguanine. We conclude that overproduction of any of the three 5'-nucleotidases cannot explain development of resistance against cytosine analogs but that overproduction of cN-II could lead to resistance against purine analogs. Of the tested analogs, only (E)-5-(2-bromovinyl)-2'-deoxyuridine was preferentially dephosphorylated by mitochondrial dNT-2. We propose that in future developments of analogs this aspect be considered in order to reduce mitochondrial toxicity. We tested inhibition of dNT-1 and dNT-2 by a large variety of synthetic metabolically stable nucleoside phosphonate analogs and found one (PMcP-U) that inhibited dNT-1 and dNT-2 competitively and a second (DPB-T) that inhibited dNT-2 by mixed inhibition. Both inhibitors are useful for specific 5'-nucleotidase assays and structural studies and may open up possibilities for therapy.
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Affiliation(s)
- Cristina Mazzon
- Department of Biology, University of Padova, 35131 Padova, Italy
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27
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Galmarini CM, Thomas X, Graham K, El Jafaari A, Cros E, Jordheim L, Mackey JR, Dumontet C. Deoxycytidine kinase and cN-II nucleotidase expression in blast cells predict survival in acute myeloid leukaemia patients treated with cytarabine. Br J Haematol 2003; 122:53-60. [PMID: 12823345 DOI: 10.1046/j.1365-2141.2003.04386.x] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The cytotoxic activity of cytarabine (ara-C) in leukaemic blasts depends on activating enzymes such as deoxycytidine kinase (dCK) and inactivating enzymes such as the 5'-nucleotidases. We have analysed dCK and 'high-Km' 5'-nucleotidase (cN-II) mRNA expression by the quantitative real-time polymerase chain reaction at diagnosis in leukaemic blasts from 115 acute myeloid leukaemia (AML) patients treated with ara-C. The prognostic value of these parameters as well as that of the cN-II/dCK ratio was determined. In univariate analyses: (1) low levels of dCK, high levels of cN-II and a high cN-II/dCK ratio predicted shorter disease-free survival (DFS); (2) low levels of dCK and cN-II/dCK ratio also predicted shorter overall survival (OS). In a multivariate analysis taking into account other clinical and laboratory variables: (1) high cN-II expression, a high cN-II/dCK ratio, age >/= 60 years and an unfavourable karyotype were independent prognostic factors for DFS; and (2) a high cN-II/dCK ratio, age >/= 60 years and an unfavourable karyotype predicted shorter OS. Age, karyotype and cN-II/dCK ratio were used to define a prognostic score that permitted the identification of high- and low-risk groups. Our results suggest that dCK and cN-II mRNA expression in leukaemic blasts at diagnosis is correlated with clinical outcome and may play a functional role in the resistance to ara-C in patients with AML.
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28
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Galmarini CM, Thomas X, Calvo F, Rousselot P, Rabilloud M, El Jaffari A, Cros E, Dumontet C. In vivo mechanisms of resistance to cytarabine in acute myeloid leukaemia. Br J Haematol 2002; 117:860-8. [PMID: 12060121 DOI: 10.1046/j.1365-2141.2002.03538.x] [Citation(s) in RCA: 134] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Factors that reduce the intracellular concentration of triphosphorylated cytarabine (ara-CTP), the active form of cytarabine (ara-C), may induce chemoresistance in acute myeloid leukaemia (AML) patients. These factors include reduced influx of ara-C by the hENT1 transporter, reduced phosphorylation by deoxycytidine kinase (dCK), and increased degradation by high Km cytoplasmic 5'-nucleotidase (5NT) and/or cytidine deaminase (CDD). Increased levels of DNA polymerase alpha (DNA POL) and reduced levels of topoisomerase I (TOPO I) and topoisomerase II (TOPO II) have also been detected in ara-C-resistant cell lines. To determine whether these factors are implicated in clinical ara-C resistance, we analysed the expression of these parameters at diagnosis, using reverse transcription polymerase chain reaction, in the blast cells of 123 AML patients treated with ara-C. At diagnosis, hENT1, dCK, CDD, 5NT, TOPO I, TOPO II, DNA POL and MDR1 were expressed in 83%, 22%, 7%, 37%, 59%, 37%, 39% and 16% of patients respectively. In univariate analysis, patients with expression of 5NT or DNA POL at diagnosis had significantly shorter disease-free survival (DFS). In multivariate analysis, DNA POL positivity and hENT1 deficiency were related to a shorter DFS. In univariate analysis, patients with 5NT-positive blasts had significantly shorter overall survival (OS). In multivariate analysis, shorter OS was related to DNA POL positivity. These results suggest that expression of DNA POL, 5NT and hENT1 at diagnosis may be resistance mechanisms to ara-C in AML patients.
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Affiliation(s)
- Carlos M Galmarini
- Unité INSERM 453, Laboratoire de Cytologie Analytique, Faculté de Médecine Rockefeller, 8 avenue Rockefeller, 69373 Lyon, France.
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29
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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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30
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Månsson E, Liliemark E, Söderhäll S, Gustafsson G, Eriksson S, Albertioni F. Real-time quantitative PCR assays for deoxycytidine kinase, deoxyguanosine kinase and 5'-nucleotidase mRNA measurement in cell lines and in patients with leukemia. Leukemia 2002; 16:386-92. [PMID: 11896543 DOI: 10.1038/sj.leu.2402388] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2001] [Accepted: 11/14/2001] [Indexed: 11/09/2022]
Abstract
The relative levels of the deoxycytidine kinase (dCK), deoxyguanosine kinase (dGK), and the 5'-nucleotidase (5'-NT) are of importance for the effect of many nucleoside analogues used in the treatment of hematological malignancies. To elucidate dCK, dGK and 5'-NT gene expressions in cell lines and in samples from patients with leukemia, we have established a real-time quantitative PCR (RQ-PCR) method. From the available dCK, dGK and 5'-NT cDNA sequences we designed specific primers and fluorogenic probes for the respective genes. The mRNA of dCK, dGK and 5'-NT was also measured by semi-quantitative RT-PCR, the enzyme activities by a radioactive substrate-based technique and Western blot was used to measure the amount of dCK and dGK protein. A MOLT-4 wild-type and its 9-beta-D-arabinofuranosylguanine (Ara-G)-resistant subline was used for the methods comparisons and the RQ-PCR assay was used in 35 samples from pediatric patients with ALL and AML. The results from RQ-PCR for the cell lines were in agreement with the semi-quantitative RT-PCR. The mRNA expression for dCK, dGK and 5'-NT (expressed as the ratio of the respective gene and the reference gene) in pediatric ALL and AML patients showed a large interindividual variability from 0.06 to 2.34, non-detectable to 0.06 and 0.04 to 0.30, respectively. These results show that the quantitative evaluation by RQ-PCR is a valuable tool in the determination of dCK, dGK and 5'-NT mRNA levels in cell lines and in clinical samples which were expressed at various levels. This rapid, convenient and specific method is suitable for further studies of these genes in clinical samples.
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Affiliation(s)
- E Månsson
- Department of Medicine, Division of Clinical Pharmacology, Karolinska Hospital, Stockholm, Sweden
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31
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Galmarini CM, Graham K, Thomas X, Calvo F, Rousselot P, El Jafaari A, Cros E, Mackey JR, Dumontet C. Expression of high Km 5'-nucleotidase in leukemic blasts is an independent prognostic factor in adults with acute myeloid leukemia. Blood 2001; 98:1922-6. [PMID: 11535530 DOI: 10.1182/blood.v98.6.1922] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Cytarabine (ara-C) requires activation into its triphosphorylated form, ara-CTP, to exert cytotoxic activity. Cytoplasmic 5'-nucleotidase (5NT) dephosphorylates ara-CMP, a key intermediate, preventing accumulation of ara-CTP and may reduce cellular sensitivity to the cytotoxic activity of ara-C. To determine whether the level of expression of 5NT is correlated with clinical outcome in patients with acute myeloid leukemia (AML) treated with ara-C, this study analyzed the levels of messenger RNA expression of high Km 5NT by real-time polymerase chain reaction at diagnosis in blast cells of 108 patients with AML. High Km 5NT was expressed at diagnosis in the blast cells of 54% of patients. In univariate analysis, (1) patients whose blast cells contained high levels (values greater than the median value for total population) of high Km 5NT at diagnosis had significantly shorter disease-free survival (DFS) than patients with low levels of high Km 5NT (11 months versus 17.5 months, P =.02) and (2) high levels of high Km 5NT also predicted significantly shorter overall survival (15.7 months versus 39 months, P = .01) in young patients (< or = 57 years; median value for the entire population). In a multivariate analysis taking into account age, karyotype risk, and other factors found to have prognostic significance in univariate analysis, (1) high Km 5NT expression was an independent prognostic factor for DFS and (2) high levels of high Km 5NT also predicted significantly shorter overall survival in young patients. These results demonstrate that the expression of high levels of high Km 5NT in blast cells is correlated with outcome in patients with AML.
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Affiliation(s)
- C M Galmarini
- Unité INSERM 453-Laboratoire de Cytologie Analytique, Faculté de Médécine Rockefeller, Lyon, France.
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32
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Galmarini CM, Mackey JR, Dumontet C. Nucleoside analogues: mechanisms of drug resistance and reversal strategies. Leukemia 2001; 15:875-90. [PMID: 11417472 DOI: 10.1038/sj.leu.2402114] [Citation(s) in RCA: 371] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Nucleoside analogues (NA) are essential components of AML induction therapy (cytosine arabinoside), effective treatments of lymphoproliferative disorders (fludarabine, cladribine) and are also used in the treatment of some solid tumors (gemcitabine). These important compounds share some general common characteristics, namely in terms of requiring transport by specific membrane transporters, metabolism and interaction with intracellular targets. However, these compounds differ in regard to the types of transporters that most efficiently transport a given compound, and their preferential interaction with certain targets which may explain why some compounds are more effective against rapidly proliferating tumors and others on neoplasia with a more protracted evolution. In this review, we analyze the available data concerning mechanisms of action of and resistance to NA, with particular emphasis on recent advances in the characterization of nucleoside transporters and on the potential role of activating or inactivating enzymes in the induction of clinical resistance to these compounds. We performed an extensive search of published in vitro and clinical data in which the levels of expression of nucleoside-activating or inactivating enzymes have been correlated with tumor response or patient outcome. Strategies aiming to increase the intracellular concentrations of active compounds are presented.
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Affiliation(s)
- C M Galmarini
- Unité INSERM 453, Laboratoire de Cytologie Analytique, Faculté de Médécine Rockefeller, Lyon, France
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Van Rompay AR, Johansson M, Karlsson A. Phosphorylation of nucleosides and nucleoside analogs by mammalian nucleoside monophosphate kinases. Pharmacol Ther 2000; 87:189-98. [PMID: 11008000 DOI: 10.1016/s0163-7258(00)00048-6] [Citation(s) in RCA: 173] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Nucleoside monophosphate kinases catalyze the reversible phosphotransferase reaction between nucleoside triphosphates and monophosphates, i.e., monophosphates are converted to their corresponding diphosphate form. These enzymes play an important role in the synthesis of nucleotides that are required for a variety of cellular metabolic processes, as well as for RNA and DNA synthesis. Human tissues contain a thymidylate kinase, a uridylate-cytidylate kinase, five isozymes of adenylate kinase, and several guanylate kinases. Nucleoside monophosphate kinases are also required for the pharmacological activation of therapeutic nucleoside and nucleotide analogs. This overview is focused on the substrate specificity, tissue distribution, and subcellular location of the mammalian monophosphate kinases and their role in the activation of nucleoside and nucleotide analogs.
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Affiliation(s)
- A R Van Rompay
- Division of Clinical Virology, Karolinska Institute, Huddinge University Hospital, S-141 86, Stockholm, Sweden
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34
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Sala-Newby GB, Freeman NV, Skladanowski AC, Newby AC. Distinct roles for recombinant cytosolic 5'-nucleotidase-I and -II in AMP and IMP catabolism in COS-7 and H9c2 rat myoblast cell lines. J Biol Chem 2000; 275:11666-71. [PMID: 10766785 DOI: 10.1074/jbc.275.16.11666] [Citation(s) in RCA: 30] [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
Catabolism of AMP during ATP breakdown produces adenosine, which restores energy balance. Catabolism of IMP may be a key step regulating purine nucleotide pools. Two, cloned cytosolic 5'-nucleotidases (cN-I and cN-II) have been implicated in AMP and IMP breakdown. To evaluate their roles directly, we expressed recombinant pigeon cN-I or human cN-II at similar activities in COS-7 or H9c2 cells. During rapid (more than 90% in 10 min) or slower (30-40% in 10 min) ATP catabolism, cN-I-transfected COS-7 and H9c2 cells produced significantly more adenosine than cN-II-transfected cells, which were similar to control-transfected cells. Inosine and hypoxanthine concentrations increased only during slower ATP catabolism. In COS-7 cells, 5'-nucleotidase activity was not rate-limiting for inosine and hypoxanthine production, which was therefore unaffected by cN-II- and actually reduced by cN-I- overexpression. In H9c2 cells, in which 5'-nucleotidase activity was rate-limiting, only cN-II overexpression accelerated inosine and hypoxanthine formation. Guanosine formation from GMP was also increased by cN-II. Our results imply distinct roles for cN-I and cN-II. Under the conditions tested in these cells, only cN-I plays a significant role in AMP breakdown to adenosine, whereas only cN-II breaks down IMP to inosine and GMP to guanosine.
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Affiliation(s)
- G B Sala-Newby
- University of Bristol, Bristol Heart Institute, Bristol BS2 8HW, United Kingdom.
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Rampazzo C, Johansson M, Gallinaro L, Ferraro P, Hellman U, Karlsson A, Reichard P, Bianchi V. Mammalian 5'(3')-deoxyribonucleotidase, cDNA cloning, and overexpression of the enzyme in Escherichia coli and mammalian cells. J Biol Chem 2000; 275:5409-15. [PMID: 10681516 DOI: 10.1074/jbc.275.8.5409] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
5'(3')-Deoxyribonucleotidase is a ubiquitous enzyme in mammalian cells whose physiological function is not known. It was earlier purified to homogeneity from human placenta. We determined the amino acid sequences of several internal peptides and with their aid found an expressed sequence tag clone with the complete cDNA for a murine enzyme of 23.9 kDa. The DNA was cloned into appropriate plasmids and introduced into Escherichia coli and ecdyson-inducible 293 and V79 cells. The recombinant enzyme was purified to homogeneity from transformed E. coli and was found to be identical with the native enzyme. After induction with ponasterone, the transfected mammalian cells showed a gradual increase of enzyme activity. A human expressed sequence tag clone contained a large part of the cDNA of the human enzyme but lacked the 5'-end corresponding to 51 amino acids of the murine enzyme. Several polymerase chain reaction-based approaches to find this sequence met with no success. A mouse/human hybrid cDNA that had substituted the missing human 5'-end with the corresponding mouse sequence coded for a fully active enzyme.
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Affiliation(s)
- C Rampazzo
- Department of Biology, University of Padova, I-35131 Padova, Italy
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36
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Gazziola C, Moras M, Ferraro P, Gallinaro L, Verin R, Rampazzo C, Reichard P, Bianchi V. Induction of human high K(M) 5'-nucleotidase in cultured 293 cells. Exp Cell Res 1999; 253:474-82. [PMID: 10585270 DOI: 10.1006/excr.1999.4681] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Human 293 cells were stably transfected with a plasmid introducing a receptor for the ecdysone analog muristerone. The cells were further stably transfected with muristerone-inducible expression vectors carrying either the cDNA for the human high K(M) 5'-nucleotidase or the coding sequence of the nucleotidase linked to the 5'-end of the sequence for the green fluorescent protein. Upon induction, both types of transfectants overproduced nucleotidase activity in a time- and dose-dependent manner. Western blots gave values close to the expected subunit molecular masses of 65 and 92 kDa, respectively, excluding processing of the induced proteins. Cells induced to overexpress the nucleotidase showed a decreased growth rate and contained smaller pools of each of the four common ribonucleoside triphosphates. They showed no increased resistance to the toxicity of 2-chlorodeoxyadenosine.
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Affiliation(s)
- C Gazziola
- Department of Biology, University of Padova, Padova, 35131, Italy
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