title: Evidence for purine nucleoside phosphorylase (PNP) release from rat C6 glioma cells.
abstract: Intracellular purine turnover is mainly oriented to preserving the level of triphosphate nucleotides, fundamental molecules in vital cell functions that, when released outside cells, act as receptor signals. Conversely, high levels of purine bases and uric acid are found in the extracellular milieu, even in resting conditions. These compounds could derive from nucleosides/bases that, having escaped to cell reuptake, are metabolized by extracellular enzymes similar to the cytosolic ones. Focusing on purine nucleoside phosphorylase (PNP) that catalyzes the reversible phosphorolysis of purine (deoxy)-nucleosides/bases, we found that it is constitutively released from cultured rat C6 glioma cells into the medium, and has a molecular weight and enzyme activity similar to the cytosolic enzyme. Cell exposure to 10 μM ATP or guanosine triphosphate (GTP) increased the extracellular amount of all corresponding purines without modifying the levels/activity of released PNP, whereas selective activation of ATP P2Y1or adenosine A2Ametabotropic receptors increased PNP release and purine base formation. The reduction to 1% in oxygen supply (2 h) to cells decreased the levels of released PNP, leading to an increased presence of extracellular nucleosides and to a reduced formation of xanthine and uric acid. Conversely, 2 h cell re-oxygenation enhanced the extracellular amounts of both PNP and purine bases. Thus, hypoxia and re-oxygenation modulated in opposite manner the PNP release/activity and, thereby, the extracellular formation of purine metabolism end-products. In conclusion, extracellular PNP and likely other enzymes deputed to purine base metabolism are released from cells, contributing to the purinergic system homeostasis and exhibiting an important pathophysiological role.
authors.affiliation: Department of Medical, Oral and Biotechnological Sciences, University of Chieti-Pescara, Chieti, Italy.|Aging Research Center and Translational Medicine (CeSI-MeT), University of Chieti-Pescara, Chieti, Italy.
authors.forename: Patricia
authors.initials: P
authors.lastname: Giuliani
authors.affiliation: Department of Medical, Oral and Biotechnological Sciences, University of Chieti-Pescara, Chieti, Italy.|Aging Research Center and Translational Medicine (CeSI-MeT), University of Chieti-Pescara, Chieti, Italy.
authors.forename: Mariachiara
authors.initials: M
authors.lastname: Zuccarini
authors.affiliation: Department of Medical, Oral and Biotechnological Sciences, University of Chieti-Pescara, Chieti, Italy.|Aging Research Center and Translational Medicine (CeSI-MeT), University of Chieti-Pescara, Chieti, Italy.
authors.forename: Silvana
authors.initials: S
authors.lastname: Buccella
authors.affiliation: Department of Pharmacy and Biotechnology, University of Bologna, Bologna, Italy.
authors.forename: Luis Emiliano
authors.initials: LE
authors.lastname: Peña-Altamira
authors.affiliation: Department of Pharmacy and Biotechnology, University of Bologna, Bologna, Italy.
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Polazzi
authors.affiliation: Department of Pharmacy and Biotechnology, University of Bologna, Bologna, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Virgili
authors.affiliation: Department of Pharmacy and Biotechnology, University of Bologna, Bologna, Italy.
authors.forename: Barbara
authors.initials: B
authors.lastname: Monti
authors.affiliation: Department of Pharmacy and Biotechnology, University of Bologna, Bologna, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Poli
authors.affiliation: Department of Medicine, Division of Neurology, McMaster University - Juravinski Hospital, Hamilton, Ontario, Canada.
authors.forename: Michel P
authors.initials: MP
authors.lastname: Rathbone
authors.affiliation: Department of Medical, Oral and Biotechnological Sciences, University of Chieti-Pescara, Chieti, Italy.|Aging Research Center and Translational Medicine (CeSI-MeT), University of Chieti-Pescara, Chieti, Italy.
authors.forename: Patrizia
authors.initials: P
authors.lastname: Di Iorio
authors.affiliation: Department of Medical, Oral and Biotechnological Sciences, University of Chieti-Pescara, Chieti, Italy.|Aging Research Center and Translational Medicine (CeSI-MeT), University of Chieti-Pescara, Chieti, Italy.
authors.forename: Renata
authors.identifier: 0000-0003-1412-738X
authors.initials: R
authors.lastname: Ciccarelli
authors.affiliation: Department of Medical, Oral and Biotechnological Sciences, University of Chieti-Pescara, Chieti, Italy.|Aging Research Center and Translational Medicine (CeSI-MeT), University of Chieti-Pescara, Chieti, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Caciagli
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D005910:Glioma / Q000201:enzymology*; D011683:Purine-Nucleoside Phosphorylase / Q000378:metabolism*; D051381:Rats
chemical_list: D011683:Purine-Nucleoside Phosphorylase
keywords: extracellular PNP; modulation of enzyme activity; purine metabotropic receptors; purine release; rat C6 glioma cells