1
|
Stepanova M, Aherne CM. Adenosine in Intestinal Epithelial Barrier Function. Cells 2024; 13:381. [PMID: 38474346 DOI: 10.3390/cells13050381] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2023] [Revised: 02/13/2024] [Accepted: 02/18/2024] [Indexed: 03/14/2024] Open
Abstract
At the intestinal front, several lines of defense are in place to resist infection and injury, the mucus layer, gut microbiome and strong epithelial junctions, to name a few. Their collaboration creates a resilient barrier. In intestinal disorders, such as inflammatory bowel disease (IBD), barrier function is compromised, which results in rampant inflammation and tissue injury. In response to the destruction, the intestinal epithelium releases adenosine, a small but powerful nucleoside that functions as an alarm signal. Amidst the chaos of inflammation, adenosine aims to restore order. Within the scope of its effects is the ability to regulate intestinal epithelial barrier integrity. This review aims to define the contributions of adenosine to mucus production, microbiome-dependent barrier protection, tight junction dynamics, chloride secretion and acid-base balance to reinforce its importance in the intestinal epithelial barrier.
Collapse
Affiliation(s)
- Mariya Stepanova
- Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, Dublin 4, Ireland
- School of Medicine, University College Dublin, Belfield, Dublin 4, Ireland
| | - Carol M Aherne
- Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, Dublin 4, Ireland
- School of Medicine, University College Dublin, Belfield, Dublin 4, Ireland
| |
Collapse
|
2
|
Persaud AK, Bernier MC, Massey MA, Agrawal S, Kaur T, Nayak D, Xie Z, Weadick B, Raj R, Hill K, Abbott N, Joshi A, Anabtawi N, Bryant C, Somogyi A, Cruz-Monserrate Z, Amari F, Coppola V, Sparreboom A, Baker SD, Unadkat JD, Phelps MA, Govindarajan R. Increased renal elimination of endogenous and synthetic pyrimidine nucleosides in concentrative nucleoside transporter 1 deficient mice. Nat Commun 2023; 14:3175. [PMID: 37264059 PMCID: PMC10235067 DOI: 10.1038/s41467-023-38789-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2022] [Accepted: 05/16/2023] [Indexed: 06/03/2023] Open
Abstract
Concentrative nucleoside transporters (CNTs) are active nucleoside influx systems, but their in vivo roles are poorly defined. By generating CNT1 knockout (KO) mice, here we identify a role of CNT1 in the renal reabsorption of nucleosides. Deletion of CNT1 in mice increases the urinary excretion of endogenous pyrimidine nucleosides with compensatory alterations in purine nucleoside metabolism. In addition, CNT1 KO mice exhibits high urinary excretion of the nucleoside analog gemcitabine (dFdC), which results in poor tumor growth control in CNT1 KO mice harboring syngeneic pancreatic tumors. Interestingly, increasing the dFdC dose to attain an area under the concentration-time curve level equivalent to that achieved by wild-type (WT) mice rescues antitumor efficacy. The findings provide new insights into how CNT1 regulates reabsorption of endogenous and synthetic nucleosides in murine kidneys and suggest that the functional status of CNTs may account for the optimal action of pyrimidine nucleoside analog therapeutics in humans.
Collapse
Affiliation(s)
- Avinash K Persaud
- Division of Pharmaceutics & Pharmacology, College of Pharmacy, The Ohio State University, Columbus, OH, 43210, USA
| | - Matthew C Bernier
- Campus Chemical Instrument Center Mass Spectrometry and Proteomics Facility, The Ohio State University, Columbus, OH, 43210, USA
| | - Michael A Massey
- Division of Pharmaceutics & Pharmacology, College of Pharmacy, The Ohio State University, Columbus, OH, 43210, USA
- The Center for Life Sciences Education, College of Arts and Sciences, The Ohio State University, Columbus, OH, 43210, USA
| | - Shipra Agrawal
- Division of Nephrology & Hypertension, Renaissance School of Medicine, Stony Brook University, Stony Brook, NY, 11794, USA
| | - Tejinder Kaur
- Division of Pharmaceutics & Pharmacology, College of Pharmacy, The Ohio State University, Columbus, OH, 43210, USA
| | - Debasis Nayak
- Division of Pharmaceutics & Pharmacology, College of Pharmacy, The Ohio State University, Columbus, OH, 43210, USA
| | - Zhiliang Xie
- Division of Pharmaceutics & Pharmacology, College of Pharmacy, The Ohio State University, Columbus, OH, 43210, USA
| | - Brenna Weadick
- Division of Pharmaceutics & Pharmacology, College of Pharmacy, The Ohio State University, Columbus, OH, 43210, USA
| | - Ruchika Raj
- Division of Pharmaceutics & Pharmacology, College of Pharmacy, The Ohio State University, Columbus, OH, 43210, USA
| | - Kasey Hill
- Pharmacoanalytic Shared Resource (PhASR), The Ohio State University, Columbus, OH, 43205, USA
| | - Nicole Abbott
- Pharmacoanalytic Shared Resource (PhASR), The Ohio State University, Columbus, OH, 43205, USA
| | - Arnav Joshi
- Division of Pharmaceutics & Pharmacology, College of Pharmacy, The Ohio State University, Columbus, OH, 43210, USA
| | - Nadeen Anabtawi
- Division of Pharmaceutics & Pharmacology, College of Pharmacy, The Ohio State University, Columbus, OH, 43210, USA
| | - Claire Bryant
- Center for Clinical & Translational Research, Nationwide Children's Hospital, Columbus, OH, 43210, USA
| | - Arpad Somogyi
- Campus Chemical Instrument Center Mass Spectrometry and Proteomics Facility, The Ohio State University, Columbus, OH, 43210, USA
| | - Zobeida Cruz-Monserrate
- Division of Gastroenterology, Hepatology, and Nutrition, College of Medicine, The Ohio State University, Columbus, OH, 43210, USA
| | - Foued Amari
- Genetically Engineered Mouse Modeling Core, Ohio State University Comprehensive Cancer Center, The Ohio State University, Columbus, OH, 43210, USA
| | - Vincenzo Coppola
- Genetically Engineered Mouse Modeling Core, Ohio State University Comprehensive Cancer Center, The Ohio State University, Columbus, OH, 43210, USA
- Department of Cancer Biology and Genetics, College of Medicine, The Ohio State University, Columbus, OH, 43210, USA
| | - Alex Sparreboom
- Division of Pharmaceutics & Pharmacology, College of Pharmacy, The Ohio State University, Columbus, OH, 43210, USA
| | - Sharyn D Baker
- Division of Pharmaceutics & Pharmacology, College of Pharmacy, The Ohio State University, Columbus, OH, 43210, USA
| | - Jashvant D Unadkat
- Department of Pharmaceutics, College of Pharmacy, University of Washington, Seattle, WA, 98195, USA
- Translational Therapeutics, Ohio State University Comprehensive Cancer Center, Ohio State University, Columbus, OH, 43210, USA
| | - Mitch A Phelps
- Division of Pharmaceutics & Pharmacology, College of Pharmacy, The Ohio State University, Columbus, OH, 43210, USA
- Pharmacoanalytic Shared Resource (PhASR), The Ohio State University, Columbus, OH, 43205, USA
| | - Rajgopal Govindarajan
- Division of Pharmaceutics & Pharmacology, College of Pharmacy, The Ohio State University, Columbus, OH, 43210, USA.
- Translational Therapeutics, Ohio State University Comprehensive Cancer Center, Ohio State University, Columbus, OH, 43210, USA.
| |
Collapse
|
3
|
Altaweraqi RA, Yao SYM, Smith KM, Cass CE, Young JD. HPLC reveals novel features of nucleoside and nucleobase homeostasis, nucleoside metabolism and nucleoside transport. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2020; 1862:183247. [PMID: 32126230 DOI: 10.1016/j.bbamem.2020.183247] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2019] [Revised: 02/16/2020] [Accepted: 02/18/2020] [Indexed: 12/31/2022]
Abstract
Humans possess three members of the cation-coupled concentrative nucleoside transporter CNT (SLC 28) family, hCNT1-3: hCNT1 is selective for pyrimidine nucleosides but also transports adenosine, hCNT2 transports purine nucleosides and uridine, and hCNT3 transports both pyrimidine and purine nucleosides. hCNT1/2 transport nucleosides using the transmembrane Na+ electrochemical gradient, while hCNT3 is both Na+- and H+-coupled. By producing recombinant hCNT3 in Xenopus laevis oocytes, we have used radiochemical high performance liquid chromatography (HPLC) analysis to investigate the metabolic fate of transported [3H] or [14C] pyrimidine and purine nucleosides once inside cells. With the exception of adenosine, transported nucleosides were generally subject to minimal intracellular metabolism. We also used radiochemical HPLC analysis to study the mechanism by which adenosine functions as a low Km, low Vmax permeant of hCNT1. hCNT1-producing oocytes were pre-loaded with [3H] uridine, after which efflux of accumulated radioactivity was measured in transport medium alone, or in the presence of extracellular non-radiolabelled adenosine or uridine. hCNT1-mediated [3H]-efflux was stimulated by extracellular uridine, but inhibited by extracellular adenosine, with >95% of the radioactivity exiting cells being unmetabolized uridine, consistent with a low transmembrane mobility of the hCNT1/adenosine complex. Humans also possess four members of the equilibrative nucleoside transporter ENT (SLC 29) family, hENT1-4. Of these, hENT1 and hENT2 transport both nucleosides and nucleobases into and out of cells, but their relative contributions to nucleoside and nucleobase homeostasis and, in particular, to adenosine signaling via purinoreceptors, are not known. We therefore used HPLC to determine plasma nucleoside and nucleobase concentrations in wild-type, mENT1-, mENT2- and mENT1/mENT2-knockout (KO) mice, and to compare the findings with knockout of mCNT3. Results demonstrated that ENT1 was more important than ENT2 or CNT3 in determining plasma adenosine concentrations, indicated modest roles of ENT1 in the homeostasis of other nucleosides, and suggested that none of the transporters is a major participant in handling of nucleobases.
Collapse
Affiliation(s)
- Reema A Altaweraqi
- Membrane Protein Disease Research Group, Department of Physiology, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
| | - Sylvia Y M Yao
- Membrane Protein Disease Research Group, Department of Physiology, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
| | - Kyla M Smith
- Membrane Protein Disease Research Group, Department of Physiology, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
| | - Carol E Cass
- Membrane Protein Disease Research Group, Department of Oncology, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
| | - James D Young
- Membrane Protein Disease Research Group, Department of Physiology, University of Alberta, Edmonton, Alberta T6G 2H7, Canada.
| |
Collapse
|
4
|
Pastor-Anglada M, Urtasun N, Pérez-Torras S. Intestinal Nucleoside Transporters: Function, Expression, and Regulation. Compr Physiol 2018; 8:1003-1017. [PMID: 29978890 DOI: 10.1002/cphy.c170039] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
The gastrointestinal tract is the absorptive organ for nutrients found in foods after digestion. Nucleosides and, to a lesser extent nucleobases, are the late products of nucleoprotein digestion. These metabolites are absorbed by nucleoside (and nucleobase) transporter (NT) proteins. NTs are differentially distributed along the gastrointestinal tract showing also polarized expression in epithelial cells. Concentrative nucleoside transporters (CNTs) are mainly located at the apical side of enterocytes, whereas equilibrative nucleoside transporters (ENTs) facilitate the basolateral efflux of nucleosides and nucleobases to the bloodstream. Moreover, selected nucleotides and the bioactive nucleoside adenosine act directly on intestinal cells modulating purinergic signaling. NT-polarized insertion is tightly regulated. However, not much is known about the modulation of intestinal NT function in humans, probably due to the lack of appropriate cell models retaining CNT functional expression. Thus, the possibility of nutritional regulation of intestinal NTs has been addressed using animal models. Besides the nutrition-related role of NT proteins, orally administered drugs also need to cross the intestinal barrier, this event being a major determinant of drug bioavailability. In this regard, NT proteins might also play a role in pharmacology, thereby allowing the absorption of nucleoside- and nucleobase-derived drugs. The relative broad selectivity of these membrane transporters also suggests clinically relevant drug-drug interactions when using combined therapies. This review focuses on all these physiological and pharmacological aspects of NT protein biology. © 2017 American Physiological Society. Compr Physiol 8:1003-1017, 2018.
Collapse
Affiliation(s)
- Marçal Pastor-Anglada
- Biochemistry and Molecular Pharmacology Section, Department of Biochemistry and Molecular Biomedicine, Institute of Biomedicine (IBUB), University of Barcelona, Barcelona, Spain.,Oncology Program, National Biomedical Research Institute on Liver and Gastrointestinal Diseases (CIBER EHD), Instituto de Salud Carlos III, Barcelona, Spain.,Genetics, Molecular Biology and Gene Therapy Program, Institut de Recerca Sant Joan de Déu (IR SJD), Esplugues de Llobregat, Barcelona, Spain
| | - Nerea Urtasun
- Biochemistry and Molecular Pharmacology Section, Department of Biochemistry and Molecular Biomedicine, Institute of Biomedicine (IBUB), University of Barcelona, Barcelona, Spain.,Oncology Program, National Biomedical Research Institute on Liver and Gastrointestinal Diseases (CIBER EHD), Instituto de Salud Carlos III, Barcelona, Spain.,Genetics, Molecular Biology and Gene Therapy Program, Institut de Recerca Sant Joan de Déu (IR SJD), Esplugues de Llobregat, Barcelona, Spain
| | - Sandra Pérez-Torras
- Biochemistry and Molecular Pharmacology Section, Department of Biochemistry and Molecular Biomedicine, Institute of Biomedicine (IBUB), University of Barcelona, Barcelona, Spain.,Oncology Program, National Biomedical Research Institute on Liver and Gastrointestinal Diseases (CIBER EHD), Instituto de Salud Carlos III, Barcelona, Spain.,Genetics, Molecular Biology and Gene Therapy Program, Institut de Recerca Sant Joan de Déu (IR SJD), Esplugues de Llobregat, Barcelona, Spain
| |
Collapse
|
5
|
Pastor-Anglada M, Pérez-Torras S. Who Is Who in Adenosine Transport. Front Pharmacol 2018; 9:627. [PMID: 29962948 PMCID: PMC6010718 DOI: 10.3389/fphar.2018.00627] [Citation(s) in RCA: 74] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2018] [Accepted: 05/24/2018] [Indexed: 12/13/2022] Open
Abstract
Extracellular adenosine concentrations are regulated by a panel of membrane transporters which, in most cases, mediate its uptake into cells. Adenosine transporters belong to two gene families encoding Equilibrative and Concentrative Nucleoside Transporter proteins (ENTs and CNTs, respectively). The lack of appropriate pharmacological tools targeting every transporter subtype has introduced some bias on the current knowledge of the role of these transporters in modulating adenosine levels. In this regard, ENT1, for which pharmacology is relatively well-developed, has often been identified as a major player in purinergic signaling. Nevertheless, other transporters such as CNT2 and CNT3 can also contribute to purinergic modulation based on their high affinity for adenosine and concentrative capacity. Moreover, both transporter proteins have also been shown to be under purinergic regulation via P1 receptors in different cell types, which further supports its relevance in purinergic signaling. Thus, several transporter proteins regulate extracellular adenosine levels. Moreover, CNT and ENT proteins are differentially expressed in tissues but also in particular cell types. Accordingly, transporter-mediated fine tuning of adenosine levels is cell and tissue specific. Future developments focusing on CNT pharmacology are needed to unveil transporter subtype-specific events.
Collapse
Affiliation(s)
- Marçal Pastor-Anglada
- Molecular Pharmacology and Experimental Therapeutics, Department of Biochemistry and Molecular Biomedicine, Institute of Biomedicine, University of Barcelona, Barcelona, Spain
- Oncology Program, National Biomedical Research Institute on Liver and Gastrointestinal Diseases – CIBER ehd, Institut de Recerca Sant Joan de Déu, Barcelona, Spain
| | - Sandra Pérez-Torras
- Molecular Pharmacology and Experimental Therapeutics, Department of Biochemistry and Molecular Biomedicine, Institute of Biomedicine, University of Barcelona, Barcelona, Spain
- Oncology Program, National Biomedical Research Institute on Liver and Gastrointestinal Diseases – CIBER ehd, Institut de Recerca Sant Joan de Déu, Barcelona, Spain
| |
Collapse
|
6
|
Claudio-Montero A, Pinilla-Macua I, Fernández-Calotti P, Sancho-Mateo C, Lostao MP, Colomer D, Grandas A, Pastor-Anglada M. Fluorescent nucleoside derivatives as a tool for the detection of concentrative nucleoside transporter activity using confocal microscopy and flow cytometry. Mol Pharm 2015; 12:2158-66. [PMID: 25923048 DOI: 10.1021/acs.molpharmaceut.5b00142] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The abundance and function of transporter proteins at the plasma membrane are likely to be crucial in drug responsiveness. Functional detection of human concentrative nucleoside transporters (hCNTs) is of interest for predicting drug sensitivity because of their ability to transport most nucleoside-derived drugs. In the present study, two fluorescent nucleoside analogues, uridine-furan and etheno-cytidine, were evaluated as tools to study in vivo nucleoside transporter-related functions. These two molecules showed high affinity interactions with hCNT1 and hCNT3 and were shown to be substrates of both transporters. Both fluorescence microscopy and flow cytometry experiments showed that uridine-furan uptake was better suited for distinguishing cells that express hCNT1 or hCNT3. These data highlight the usefulness of fluorescent nucleoside derivatives, as long as they fulfill the requirements of confocal microscopy and flow cytometry, for in vivo analysis of hCNT-related function.
Collapse
Affiliation(s)
- Ana Claudio-Montero
- †Department of Biochemistry and Molecular Biology, University of Barcelona, Institute of Biomedicine (IBUB), Barcelona, Spain.,‡Oncology Programme, National Biomedical Research Institute on Liver and Gastrointestinal Diseases (CIBER ehd), Instituto de Salud Carlos III, Barcelona, Spain.,⊥Department of Organic Chemistry, University of Barcelona, Institute of Biomedicine (IBUB), Barcelona, Spain
| | - Itziar Pinilla-Macua
- †Department of Biochemistry and Molecular Biology, University of Barcelona, Institute of Biomedicine (IBUB), Barcelona, Spain.,‡Oncology Programme, National Biomedical Research Institute on Liver and Gastrointestinal Diseases (CIBER ehd), Instituto de Salud Carlos III, Barcelona, Spain
| | - Paula Fernández-Calotti
- †Department of Biochemistry and Molecular Biology, University of Barcelona, Institute of Biomedicine (IBUB), Barcelona, Spain.,‡Oncology Programme, National Biomedical Research Institute on Liver and Gastrointestinal Diseases (CIBER ehd), Instituto de Salud Carlos III, Barcelona, Spain
| | - Carlos Sancho-Mateo
- #Department of Nutrition, Food Science and Physiology, University of Navarra, Pamplona, Spain
| | - María Pilar Lostao
- #Department of Nutrition, Food Science and Physiology, University of Navarra, Pamplona, Spain
| | - Dolors Colomer
- §Hematopathology Unit, Hospital Clínic and Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Barcelona, Spain
| | - Anna Grandas
- ⊥Department of Organic Chemistry, University of Barcelona, Institute of Biomedicine (IBUB), Barcelona, Spain
| | - Marçal Pastor-Anglada
- †Department of Biochemistry and Molecular Biology, University of Barcelona, Institute of Biomedicine (IBUB), Barcelona, Spain.,‡Oncology Programme, National Biomedical Research Institute on Liver and Gastrointestinal Diseases (CIBER ehd), Instituto de Salud Carlos III, Barcelona, Spain
| |
Collapse
|
7
|
Hypoxia and P1 receptor activation regulate the high-affinity concentrative adenosine transporter CNT2 in differentiated neuronal PC12 cells. Biochem J 2013; 454:437-45. [PMID: 23819782 DOI: 10.1042/bj20130231] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Under several adverse conditions, such as hypoxia or ischaemia, extracellular levels of adenosine are elevated because of increased energy demands and ATP metabolism. Because extracellular adenosine affects metabolism through G-protein-coupled receptors, its regulation is of high adaptive importance. CNT2 (concentrative nucleoside transporter 2) may play physiological roles beyond nucleoside salvage in brain as it does in other tissues. Even though nucleoside transport in brain has mostly been seen as being of equilibrative-type, in the present study, we prove that the rat phaeochromocytoma cell line PC12 shows a concentrative adenosine transport of CNT2-type when cells are differentiated to a neuronal phenotype by treatment with NGF (nerve growth factor). Differentiation of PC12 cells was also associated with the up-regulation of adenosine A1 receptors. Addition of adenosine receptor agonists to cell cultures increased CNT2-related activity by a mechanism consistent with A₁ and A2A receptor activation. The addition of adenosine to the culture medium also induced the phosphorylation of the intracellular regulatory kinase AMPK (AMP-activated protein kinase), with this effect being dependent upon adenosine transport. CNT2-related activity of differentiated PC12 cells was also dramatically down-regulated under hypoxic conditions. Interestingly, the analysis of nucleoside transporter expression after experimental focal ischaemia in rat brain showed that CNT2 expression was down-regulated in the infarcted tissue, with this effect somehow being restricted to other adenosine transporter proteins such as CNT3 and ENT1 (equilibrative nucleoside transporter 1). In summary, CNT2 is likely to modulate extracellular adenosine and cell energy balance in neuronal tissue.
Collapse
|
8
|
The facilitative glucose transporter GLUT12: what do we know and what would we like to know? J Physiol Biochem 2012; 69:325-33. [DOI: 10.1007/s13105-012-0213-8] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2012] [Accepted: 09/12/2012] [Indexed: 12/22/2022]
|
9
|
Cano-Soldado P, Gorraitz E, Errasti-Murugarren E, Casado FJ, Lostao MP, Pastor-Anglada M. Functional analysis of the human concentrative nucleoside transporter-1 variant hCNT1S546P provides insight into the sodium-binding pocket. Am J Physiol Cell Physiol 2012; 302:C257-66. [DOI: 10.1152/ajpcell.00198.2011] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
SLC28 genes, encoding concentrative nucleoside transporter proteins (CNT), show little genetic variability, although a few single nucleotide polymorphisms (SNPs) have been associated with marked functional disturbances. In particular, human CNT1S546P had been reported to result in negligible thymidine uptake. In this study we have characterized the molecular mechanisms responsible for this apparent loss of function. The hCNT1S546P variant showed an appropriate endoplasmic reticulum export and insertion into the plasma membrane, whereas loss of nucleoside translocation ability affected all tested nucleoside and nucleoside-derived drugs. Site-directed mutagenesis analysis revealed that it is the lack of the serine residue itself responsible for the loss of hCNT1 function. This serine residue is highly conserved, and mutation of the analogous serine in hCNT2 (Ser541) and hCNT3 (Ser568) resulted in total and partial loss of function, respectively. Moreover, hCNT3, the only member that shows a 2Na+/1 nucleoside stoichiometry, showed altered Na+ binding properties associated with a shift in the Hill coefficient, consistent with one Na+ binding site being affected by the mutation. Two-electrode voltage-clamp studies using the hCNT1S546P mutant revealed the occurrence of Na+ leak, which was dependent on the concentration of extracellular Na+ indicating that, although the variant is unable to transport nucleosides, there is an uncoupled sodium transport.
Collapse
Affiliation(s)
- Pedro Cano-Soldado
- Departament de Bioquímica i Biologia Molecular, Institut de Biomedicina (IBUB), Universitat de Barcelona and CIBER EHD, Barcelona
| | - Edurne Gorraitz
- Department of Food Science, Physiology and Toxicology, University of Navarra, Pamplona, Spain
| | - Ekaitz Errasti-Murugarren
- Departament de Bioquímica i Biologia Molecular, Institut de Biomedicina (IBUB), Universitat de Barcelona and CIBER EHD, Barcelona
| | - F. Javier Casado
- Departament de Bioquímica i Biologia Molecular, Institut de Biomedicina (IBUB), Universitat de Barcelona and CIBER EHD, Barcelona
| | - M. Pilar Lostao
- Department of Food Science, Physiology and Toxicology, University of Navarra, Pamplona, Spain
| | - Marçal Pastor-Anglada
- Departament de Bioquímica i Biologia Molecular, Institut de Biomedicina (IBUB), Universitat de Barcelona and CIBER EHD, Barcelona
| |
Collapse
|
10
|
Errasti-Murugarren E, Díaz P, Godoy V, Riquelme G, Pastor-Anglada M. Expression and distribution of nucleoside transporter proteins in the human syncytiotrophoblast. Mol Pharmacol 2011; 80:809-17. [PMID: 21825094 DOI: 10.1124/mol.111.071837] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The plasma membrane distribution and related biological activity of nucleoside transporter proteins (NTs) were investigated in human syncytiotrophoblast from term placenta using a variety of approaches, including nucleoside uptake measurements into vesicles from selected plasma membrane domains, NT immunohistochemistry, and subcellular localization (basal, heavy, and light apical membranes as well as raft-enriched membranes from the apical domain). In contrast with other epithelia, in this epithelium, we have identified the high-affinity pyrimidine-preferring human concentrative nucleoside transporter (hCNT) 1 as the only hCNT-type protein expressed at both the basal and apical membranes. hCNT1 localization in lipid rafts is also dependent on its subcellular localization in the apical plasma membrane, suggesting a complex cellular and regional expression. Overall, this result favors the view that the placenta is a pyrimidine-preferring nucleoside sink from both maternal and fetal sides, and hCNT1 plays a major role in promoting pyrimidine salvage and placental growth. This finding may be of pharmacological relevance, because hCNT1 is known to interact with anticancer nucleoside-derived drugs and other molecules, such as nicotine and caffeine, for which a great variety of harmful effects on placental and fetal development, including intrauterine growth retardation, have been reported.
Collapse
Affiliation(s)
- Ekaitz Errasti-Murugarren
- Departament de Bioquímica i Biologia Molecular, Facultat de Biologia, Universitat de Barcelona, Barcelona, Spain
| | | | | | | | | |
Collapse
|
11
|
Cano-Soldado P, Pastor-Anglada M. Transporters that translocate nucleosides and structural similar drugs: structural requirements for substrate recognition. Med Res Rev 2011; 32:428-57. [DOI: 10.1002/med.20221] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Affiliation(s)
- Pedro Cano-Soldado
- Departament de Bioquímica i Biologia Molecular; Institut de Biomedicina de la Universitat de Barcelona (IBUB); Universitat de Barcelona and CIBER EHD; Barcelona Spain
| | - Marçal Pastor-Anglada
- Departament de Bioquímica i Biologia Molecular; Institut de Biomedicina de la Universitat de Barcelona (IBUB); Universitat de Barcelona and CIBER EHD; Barcelona Spain
| |
Collapse
|
12
|
Ham M, Mizumori M, Watanabe C, Wang JH, Inoue T, Nakano T, Guth PH, Engel E, Kaunitz JD, Akiba Y. Endogenous luminal surface adenosine signaling regulates duodenal bicarbonate secretion in rats. J Pharmacol Exp Ther 2010; 335:607-13. [PMID: 20805305 DOI: 10.1124/jpet.110.171520] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Luminal ATP increases duodenal bicarbonate secretion (DBS) via brush border P2Y receptors. Because ATP is sequentially dephosphorylated to adenosine (ADO) and the brush border highly expresses adenosine deaminase (ADA), we hypothesized that luminal [ADO] regulators and sensors, including P1 receptors, ADA, and nucleoside transporters (NTs) regulate DBS. We measured DBS with pH and CO(2) electrodes, perfusing ADO ± adenosine receptor agonists or antagonists or the cystic fibrosis transmembrane conductance regulator (CFTR) inhibitor CFTR(inh)-172 on DBS. Furthermore, we examined the effect of inhibitors of ADA or NT on DBS. Perfusion of AMP or ADO (0.1 mM) uniformly increased DBS, whereas inosine had no effect. The A(1/2) receptor agonist 5'-(N-ethylcarboxamido)-adenosine (0.1 mM) increased DBS, whereas ADO-augmented DBS was inhibited by the potent A(2B) receptor antagonist N-(4-cyanophenyl)-2-[4-(2,3,6,7-tetrahydro-2,6-dioxo-1,3-dipropyl-1H-purin-8-yl)phenoxy]-acetamide (MRS1754) (10 μM). Other selective adenosine receptor agonists or antagonists had no effect. The A(2B) receptor was immunolocalized to the brush border membrane of duodenal villi, whereas the A(2A) receptor was immunolocalized primarily to the vascular endothelium. Furthermore, ADO-induced DBS was enhanced by 2'-deoxycoformycin (1 μM) and formycin B (0.1 mM), but not by S-(4-nitrobenzyl)-6-thioinosine (0.1 mM), and it was abolished by CFTR(inh)-172 pretreatment (1 mg/kg i.p). Moreover, ATP (0.1 mM)-induced DBS was partially reduced by (1R,2S,4S,5S)-4-2-iodo-6-(methylamino)-9H-purin-9-yl]-2-(phosphonooxy)bicyclo[3.1.0]hexane-1-methanol dihydrogen phosphate ester tetraammonium salt (MRS2500) or 8-[4-[4-(4-chlorophenzyl)piperazide-1-sulfonyl)phenyl]]-1-propylxanthine (PSB603) and abolished by both, suggesting that ATP is sequentially degraded to ADO. Luminal ADO stimulates DBS via A(2B) receptors and CFTR. ATP release, ecto-phosphohydrolases, ADA, and concentrative NT may coordinately regulate luminal surface ADO concentration to modulate ADO-P1 receptor signaling in rat duodenum.
Collapse
Affiliation(s)
- Maggie Ham
- Department of Medicine, School of Medicine, University of California, Los Angeles, California, USA
| | | | | | | | | | | | | | | | | | | |
Collapse
|
13
|
Effects of Na+ and H+ on steady-state and presteady-state currents of the human concentrative nucleoside transporter 3 (hCNT3). Pflugers Arch 2010; 460:617-32. [DOI: 10.1007/s00424-010-0846-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2010] [Revised: 04/13/2010] [Accepted: 05/04/2010] [Indexed: 11/26/2022]
|
14
|
Waters NJ, Lombardo F. Use of the Øie-Tozer Model in Understanding Mechanisms and Determinants of Drug Distribution. Drug Metab Dispos 2010; 38:1159-65. [DOI: 10.1124/dmd.110.032458] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
|
15
|
Smith KM, Slugoski MD, Cass CE, Baldwin SA, Karpinski E, Young JD. Cation coupling properties of human concentrative nucleoside transporters hCNT1, hCNT2 and hCNT3. Mol Membr Biol 2009; 24:53-64. [PMID: 17453413 DOI: 10.1080/09687860600942534] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
The SLC28 family of concentrative nucleoside transporter (CNT) proteins in mammalian cells contains members of two distinct phylogenic subfamilies. In humans, hCNT1 and hCNT2 belong to one subfamily, and hCNT3 to the other. All three CNTs mediate inwardly-directed Na(+)/nucleoside cotransport, and are either pyrimidine nucleoside-selective (hCNT1), purine nucleoside-selective (hCNT2), or broadly selective for both pyrimidine and purine nucleosides (hCNT3). While previous studies have characterized cation interactions with both hCNT1 and hCNT3, little is known about the corresponding properties of hCNT2. In the present study, heterologous expression in Xenopus oocytes in combination with radioisotope flux and electrophysiological techniques has allowed us to undertake a side-by-side comparison of hCNT2 with other hCNT family members. Apparent K (50) values for Na(+) activation were voltage-dependent, and similar in magnitude for all three transporters. Only hCNT3 was also able to couple transport of uridine to uptake of H(+). The Na(+)/nucleoside stoichiometry of hCNT2, as determined from both Hill coefficients and direct charge/flux measurements, was 1:1. This result was the same as for hCNT1, but different from that of hCNT3 (2:1). The charge-to-(22)Na(+) uptake stoichiometry was 1:1 for all three hCNTs. In parallel with their division into two separate CNT subfamilies, hCNT2 shares common cation specificity and coupling characteristics with hCNT1, which differ markedly from those of hCNT3.
Collapse
Affiliation(s)
- Kyla M Smith
- The Membrane Protein Research Group, Department of Physiology, University of Alberta, Alberta, Canada
| | | | | | | | | | | |
Collapse
|
16
|
Pastor-Anglada M, Cano-Soldado P, Errasti-Murugarren E, Casado FJ. SLC28 genes and concentrative nucleoside transporter (CNT) proteins. Xenobiotica 2008; 38:972-94. [PMID: 18668436 DOI: 10.1080/00498250802069096] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
The human concentrative nucleoside transporter (hCNT) protein family has three members, hCNT1, 2, and 3, encoded by SLC28A1, A2, and A3 genes, respectively. hCNT1 and hCNT2 translocate pyrimidine- and purine-nucleosides, respectively, by a sodium-dependent mechanism, whereas hCNT3 shows broad substrate selectivity and the unique ability of translocating nucleosides both in a sodium- and a proton-coupled manner. hCNT proteins are also responsible for the uptake of most nucleoside-derived antiviral and anticancer drugs. Thus, hCNTs are key pharmacological targets. This review focuses on several crucial aspects of hCNT biology and pharmacology: protein structure-function, structural determinants for transportability, pharmacogenetics of hCNT-encoding genes, role of hCNT proteins in nucleoside-based therapeutics, and finally hCNT physiology.
Collapse
Affiliation(s)
- M Pastor-Anglada
- Facultat de Biologia, Departament de Bioquimica i Biologia Molecular, Institut de Biomedicina de la Universitat de Barcelona (IBUB), Universitat de Barcelona, Barcelona, Spain.
| | | | | | | |
Collapse
|
17
|
Molina-Arcas M, Trigueros-Motos L, Casado FJ, Pastor-Anglada M. Physiological and pharmacological roles of nucleoside transporter proteins. NUCLEOSIDES NUCLEOTIDES & NUCLEIC ACIDS 2008; 27:769-78. [PMID: 18600539 DOI: 10.1080/15257770802145819] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Nucleoside transporter proteins, CNT and ENT, encoded by gene families SLC28 and SLC29, respectively, mediate the uptake of natural nucleosides (among them adenosine) and are major routes of entry for a variety of nucleoside analogs used in anticancer and antiviral therapies. Expression of NT proteins is apparently redundant in most cell types, and the elucidation of their particular physiological roles still remains elusive. Moreover, transporter-mediated uptake of nucleoside-derived anticancer drugs is crucial for the pharmacogenomic response triggered by these molecules in tumor cells. This review focuses on recent data demonstrating that nucleoside transporters, particularly CNTs, can play physiological roles other than salvage, whereas particular NT isoforms can significantly contribute to the transcriptomic response triggered by nucleoside analogs in cancer cells.
Collapse
Affiliation(s)
- Míriam Molina-Arcas
- Regulació dels Sistemes de Transport (RST), Departament de Bioquímica i Biologia Molecular, Institut de Biomedicina, Universitat de Barcelona (IBUB) and CIBER (EHD), Barcelona, Spain
| | | | | | | |
Collapse
|
18
|
Loo DDF, Hirayama BA, Sala-Rabanal M, Wright EM. How drugs interact with transporters: SGLT1 as a model. J Membr Biol 2008; 223:87-106. [PMID: 18592293 DOI: 10.1007/s00232-008-9116-6] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2008] [Accepted: 05/20/2008] [Indexed: 11/29/2022]
Abstract
Drugs are transported by cotransporters with widely different turnover rates. We have examined the underlying mechanism using, as a model system, glucose and indican (indoxyl-beta-D-glucopyranoside) transport by human Na+/glucose cotransporter (hSGLT1). Indican is transported by hSGLT1 at 10% of the rate for glucose but with a fivefold higher apparent affinity. We expressed wild-type hSGLT1 and mutant G507C in Xenopus oocytes and used electrical and optical methods to measure the kinetics of glucose (using nonmetabolized glucose analogue alpha-methyl-D-glucopyranoside, alphaMDG) and indican transport, alone and together. Indican behaved as a competitive inhibitor of alphaMDG transport. To examine protein conformations, we recorded SGLT1 capacitive currents (charge movements) and fluorescence changes in response to step jumps in membrane voltage, in the presence and absence of indican and/or alphaMDG. In the absence of sugar, voltage jumps elicited capacitive SGLT currents that decayed to steady state with time constants (tau) of 3-20 ms. These transient currents were abolished in saturating alphaMDG but only slightly reduced (10%) in saturating indican. SGLT1 G507C rhodamine fluorescence intensity increased with depolarizing and decreased with hyperpolarizing voltages. Maximal fluorescence increased approximately 150% in saturating indican but decreased approximately 50% in saturating alphaMDG. Modeling indicated that the rate-limiting step for indican transport is sugar translocation, whereas for alphaMDG it is dissociation of Na+ from the internal binding sites. The inhibitory effects of indican on alphaMDG transport are due to its higher affinity and a 100-fold lower translocation rate. Our results indicate that competition between substrates and drugs should be taken into consideration when targeting transporters as drug delivery systems.
Collapse
Affiliation(s)
- Donald D F Loo
- Department of Physiology, David Geffen School of Medicine at UCLA, 10833 LeConte Avenue, Los Angeles, CA 90095-1751, USA.
| | | | | | | |
Collapse
|
19
|
Grden M, Podgorska M, Kocbuch K, Rzepko R, Szutowicz A, Pawelczyk T. High glucose suppresses expression of equilibrative nucleoside transporter 1 (ENT1) in rat cardiac fibroblasts through a mechanism dependent on PKC-zeta and MAP kinases. J Cell Physiol 2008; 215:151-60. [PMID: 17941087 DOI: 10.1002/jcp.21296] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Recently it was demonstrated that the elevated concentration of glucose but not lack of insulin is responsible for suppression of equilibrative nucleoside transporter (ENT1) in diabetic rat cardiac fibroblasts (CFs). The present study was undertaken to determine the signaling pathway utilized by glucose to regulate the expression of ENT1 in the primary culture of rat CFs. Pretreatment of CFs with Go 6983, an isozyme non-selective PKC inhibitor, prevented the high glucose (25 mM) effect on ENT1 mRNA level and nitrobenzylthioinosine (NBTI)-sensitive adenosine uptake. Similar effect was observed with a cell-permeable PKC-zeta pseudosubstrate, whereas Go 6976 a selective inhibitor of Ca(2+)-dependent PKC-alpha and PKC-beta isozymes had little effect on high glucose-induced suppression of ENT1 mRNA level. Incubation of CFs with nitric oxide (NO) donors (SNAPE, SNP) or NO synthase inhibitors (L-NAME, L-NMMA) prior to exposition of CFs to high glucose did not change the glucose effect on ENT1 mRNA level. The high glucose-induced suppression of ENT1 expression was blocked by PD9859 (an inhibitor of MEK), whereas neither wortmannin (an inhibitor of PI3K) nor rapamycin (an inhibitor of mTOR) affected the glucose action on ENT1 transcript level. Highly effective in preventing the high glucose effect on ENT1 mRNA level were GW 5074 (an inhibitor of Raf kinase) and SB 203580 (selective p38 MAPK inhibitor). These findings indicate that high glucose suppresses the expression of ENT1 in CFs by NO independent manner involving the signaling through PKC-zeta, Raf-1, MEK, and p38 MAPK pathways.
Collapse
Affiliation(s)
- Marzena Grden
- Department of Molecular Medicine, Medical University of Gdansk, Gdansk, Poland
| | | | | | | | | | | |
Collapse
|
20
|
Compensatory effects of the human nucleoside transporters on the response to nucleoside-derived drugs in breast cancer MCF7 cells. Biochem Pharmacol 2008; 75:639-48. [DOI: 10.1016/j.bcp.2007.10.005] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2007] [Revised: 10/02/2007] [Accepted: 10/05/2007] [Indexed: 11/24/2022]
|
21
|
Markovic I, Segal M, Djuricic B, Redzic Z. Kinetics of nucleoside uptake by the basolateral side of the sheep choroid plexus epithelium perfusedin situ. Exp Physiol 2008; 93:325-33. [DOI: 10.1113/expphysiol.2007.040980] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
|
22
|
Pastor-Anglada M, Errasti-Murugarren E, Aymerich I, Casado FJ. Concentrative nucleoside transporters (CNTs) in epithelia: from absorption to cell signaling. J Physiol Biochem 2007; 63:97-110. [PMID: 17722647 DOI: 10.1007/bf03174089] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Concentrative and Equilibrative Nucleoside Transporter proteins (CNT and ENT, respectively) are encoded by gene families SLC28 and SLC29. They mediate the uptake of natural nucleosides and a variety of nucleoside-derived drugs, mostly used in anticancer therapy. CNT and ENT proteins are mostly localized in the apical and basolateral sides, respectively, in (re)absorptive epithelia. This anatomic distribution determines nucleoside and nucleoside-derived vectorial flux. CNT expression (particularly CNT2) is associated with differentiation and is also nutritionally regulated in intestinal epithelia, whereas ENT protein amounts (mostly ENT1) are increased when cells are exposed to proliferative stimuli such as EGF, TGF-alpha or wounding. Although all these features suggest a role for NT proteins in nucleoside salvage and (re)absorption, recent data demonstrate that CNT2 might be under purinergic control, in a manner that is dependent on energy metabolism. A physiological link between CNT2 function and intracellular metabolism is also supported by the evidence that extracellular adenosine can activate the AMP-dependent kinase (AMPK), by a mechanism which relies upon adenosine transport and phosphorylation. Thus the complex pattern of NT isoform expression in mammalian cells can fulfill physiological roles other than salvage.
Collapse
Affiliation(s)
- M Pastor-Anglada
- Departament de Bioquímica i Biologia Molecular, Institut de Biomedicina de la Universitat de Barcelona, Spain.
| | | | | | | |
Collapse
|
23
|
Loo DDF, Hirayama BA, Karakossian MH, Meinild AK, Wright EM. Conformational dynamics of hSGLT1 during Na+/glucose cotransport. ACTA ACUST UNITED AC 2007; 128:701-20. [PMID: 17130520 PMCID: PMC2151600 DOI: 10.1085/jgp.200609643] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
This study examines the conformations of the Na+/glucose cotransporter (SGLT1) during sugar transport using charge and fluorescence measurements on the human SGLT1 mutant G507C expressed in Xenopus oocytes. The mutant exhibited similar steady-state and presteady-state kinetics as wild-type SGLT1, and labeling of Cys507 by tetramethylrhodamine-6-maleimide had no effect on kinetics. Our strategy was to record changes in charge and fluorescence in response to rapid jumps in membrane potential in the presence and absence of sugar or the competitive inhibitor phlorizin. In Na+ buffer, step jumps in membrane voltage elicited presteady-state currents (charge movements) that decay to the steady state with time constants τmed (3–20 ms, medium) and τslow (15–70 ms, slow). Concurrently, SGLT1 rhodamine fluorescence intensity increased with depolarizing and decreased with hyperpolarizing voltages (ΔF). The charge vs. voltage (Q-V) and fluorescence vs. voltage (ΔF-V) relations (for medium and slow components) obeyed Boltzmann relations with similar parameters: zδ (apparent valence of voltage sensor) ≈ 1; and V0.5 (midpoint voltage) between −15 and −40 mV. Sugar induced an inward current (Na+/glucose cotransport), and reduced maximal charge (Qmax) and fluorescence (ΔFmax) with half-maximal concentrations (K0.5) of 1 mM. Increasing [αMDG]o also shifted the V0.5 for Q and ΔF to more positive values, with K0.5's ≈ 1 mM. The major difference between Q and ΔF was that at saturating [αMDG]o, the presteady-state current (and Qmax) was totally abolished, whereas ΔFmax was only reduced 50%. Phlorizin reduced both Qmax and ΔFmax (Ki ≈ 0.4 μM), with no changes in V0.5's or relaxation time constants. Simulations using an eight-state kinetic model indicate that external sugar increases the occupancy probability of inward-facing conformations at the expense of outward-facing conformations. The simulations predict, and we have observed experimentally, that presteady-state currents are blocked by saturating sugar, but not the changes in fluorescence. Thus we have isolated an electroneutral conformational change that has not been previously described. This rate-limiting step at maximal inward Na+/sugar cotransport (saturating voltage and external Na+ and sugar concentrations) is the slow release of Na+ from the internal surface of SGLT1. The high affinity blocker phlorizin locks the cotransporter in an inactive conformation.
Collapse
Affiliation(s)
- Donald D F Loo
- Department of Physiology, David Geffen School of Medicine at UCLA, University of California, Los Angeles, CA 90095, USA.
| | | | | | | | | |
Collapse
|
24
|
Larráyoz IM, Fernández-Nistal A, Garcés A, Gorraitz E, Lostao MP. Characterization of the rat Na+/nucleoside cotransporter 2 and transport of nucleoside-derived drugs using electrophysiological methods. Am J Physiol Cell Physiol 2006; 291:C1395-404. [PMID: 16837649 DOI: 10.1152/ajpcell.00110.2006] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The Na+-dependent nucleoside transporter 2 (CNT2) mediates active transport of purine nucleosides and uridine as well as therapeutic nucleoside analogs. We used the two-electrode voltage-clamp technique to investigate rat CNT2 (rCNT2) transport mechanism and study the interaction of nucleoside-derived drugs with the transporter expressed in Xenopus laevis oocytes. The kinetic parameters for sodium, natural nucleosides, and nucleoside derivatives were obtained as a function of membrane potential. For natural substrates, apparent affinity ( K0.5) was in the low micromolar range (12–34) and was voltage independent for hyperpolarizing membrane potentials, whereas maximal current ( Imax) was voltage dependent. Uridine and 2′-deoxyuridine analogs modified at the 5-position were substrates of rCNT2. Lack of the 2′-hydroxyl group decreased affinity but increased Imax. Increase in the size and decrease in the electronegativity of the residue at the 5-position affected the interaction with the transporter by decreasing both affinity and Imax. Fludarabine and formycin B were also transported with higher Imaxthan uridine and moderate affinity (102 ± 10 and 66 ± 6 μM, respectively). Analysis of the pre-steady-state currents revealed a half-maximal activation voltage of about −39 mV and a valence of about −0.8. K0.5for Na+was 2.3 mM at −50 mV and decreased at hyperpolarizing membrane potentials. The Hill coefficient was 1 at all voltages. Direct measurements of radiolabeled nucleoside fluxes with the charge associated showed a ratio of two positive inward charges per nucleoside, suggesting a stoichiometry of two Na+per nucleoside. This discrepancy in the number of Na+molecules that bind rCNT2 may indicate a low degree of cooperativity between the Na+binding sites.
Collapse
Affiliation(s)
- Ignacio M Larráyoz
- Department of Physiology and Nutrition, University of Navarra, Pamplona, Spain
| | | | | | | | | |
Collapse
|
25
|
Podgorska M, Kocbuch K, Grden M, Szutowicz A, Pawelczyk T. Reduced ability to release adenosine by diabetic rat cardiac fibroblasts due to altered expression of nucleoside transporters. J Physiol 2006; 576:179-89. [PMID: 16873415 PMCID: PMC1995644 DOI: 10.1113/jphysiol.2006.111278] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Adenosine produced by cardiac cells is known to attenuate the proliferation of cardiac fibroblasts (CFs), inhibit collagen synthesis, and protect the myocardium against ischaemic and reperfusion injury. Diabetic patients' hearts exhibit ventricular hypertrophy and demonstrate reduced tolerance to hypoxia or ischaemia. In this study, we characterize the effects of glucose and insulin on processes that determine the release of adenosine from CFs. We showed that during ATP depletion, rat CFs cultured in the absence of insulin release significantly less adenosine compared to cells grown in the presence of insulin. Moreover, under both conditions the quantity of released adenosine depends on glucose concentration. We demonstrate that this is due to altered expression of nucleoside transporters. High glucose (25 mm) induced 85% decrease in nucleoside transporter ENT1 mRNA levels. Decrease of the insulin level below 10(-11) m resulted in over 3-fold increase in the nucleoside transporter CNT2 mRNA content. Measurements of adenosine transport in CFs cultured in the presence of 5 mm glucose and 10 nm insulin showed that the bidirectional equilibrative adenosine transport accounted for 70% of the overall adenosine uptake. However, cells grown in the presence of high glucose (25 mm) demonstrated 65% decrease of the bidirectional equilibrative adenosine transport. Experiments on CFs cultured in the absence of insulin showed that the unidirectional Na(+)-dependent adenosine uptake rose in these cells more than 4-fold. These results indicate that the development of diabetes may result in an increased uptake of interstitial adenosine by CFs, and reduction of the ability of these cells to release adenosine during ATP deprivation.
Collapse
Affiliation(s)
- Marzena Podgorska
- Department of Molecular Medicine, Medical University of Gdansk, ul. Debinki 7, paw. 29, 80-211 Gdansk, Poland
| | | | | | | | | |
Collapse
|
26
|
Fernández-Veledo S, Huber-Ruano I, Aymerich I, Duflot S, Casado F, Pastor-Anglada M. Bile acids alter the subcellular localization of CNT2 (concentrative nucleoside cotransporter) and increase CNT2-related transport activity in liver parenchymal cells. Biochem J 2006; 395:337-44. [PMID: 16390326 PMCID: PMC1422760 DOI: 10.1042/bj20051232] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
CNT2 (concentrative nucleoside cotransporter) is a plasma membrane high-affinity Na+-coupled adenosine transporter, also localized in intracellular structures. This transporter protein may play additional roles other than nucleoside salvage, since it has recently been shown to be under purinergic control via K(ATP) channels, by a mechanism that does not seem to involve changes in its subcellular localization. In an attempt to identify the agents that promote CNT2 trafficking, bile acids were found to increase CNT2-related transport activity in a K(ATP) channel-independent manner in both Fao hepatoma and rat liver parenchymal cells. A maximum effect was recorded after treatment with hydrophilic anions such as TCA (taurocholate). However, this effect did not involve changes in the amount of CNT2 protein, it was instead associated with a subcellular redistribution of CNT2, resulting in an accumulation of the transporter at the plasma membrane. This was deduced from subcellular fractionation studies, biotinylation of plasma membrane proteins and subsequent CNT2 detection in streptavidin precipitates and in vivo confocal microscopic analysis of the distribution of a YFP (yellow fluorescent protein)-CNT2 construct. The induction of CNT2 translocation, triggered by TCA, was inhibited by wortmannin, dibutyryl-AMPc, PD98059 and colchicine, thus suggesting the involvement of the PI3K/ERK (phosphoinositide 3-kinase/extracellular-signal related kinase) pathway in microtubule-dependent activation of recombinant CNT2. These are novel effects of bile-acid physiology and provide the first evidence for short-term regulation of CNT2 translocation into and from the plasma membrane.
Collapse
Affiliation(s)
- Sonia Fernández-Veledo
- Departament de Bioquímica i Biologia Molecular, Universitat de Barcelona, Diagonal 645, E-08028 Barcelona, Spain
| | - Isabel Huber-Ruano
- Departament de Bioquímica i Biologia Molecular, Universitat de Barcelona, Diagonal 645, E-08028 Barcelona, Spain
| | - Ivette Aymerich
- Departament de Bioquímica i Biologia Molecular, Universitat de Barcelona, Diagonal 645, E-08028 Barcelona, Spain
| | - Sylvie Duflot
- Departament de Bioquímica i Biologia Molecular, Universitat de Barcelona, Diagonal 645, E-08028 Barcelona, Spain
| | - F. Javier Casado
- Departament de Bioquímica i Biologia Molecular, Universitat de Barcelona, Diagonal 645, E-08028 Barcelona, Spain
| | - Marçal Pastor-Anglada
- Departament de Bioquímica i Biologia Molecular, Universitat de Barcelona, Diagonal 645, E-08028 Barcelona, Spain
- To whom correspondence should be addressed (email )
| |
Collapse
|
27
|
Aymerich I, Foufelle F, Ferré P, Casado FJ, Pastor-Anglada M. Extracellular adenosine activates AMP-dependent protein kinase (AMPK). J Cell Sci 2006; 119:1612-21. [PMID: 16569664 DOI: 10.1242/jcs.02865] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Adenosine monophosphate (AMP)-activated protein kinase (AMPK) is a heterotrimeric complex that senses intracellular energy status and exerts rapid regulation on energy-demanding and -consuming metabolic pathways. Although alterations in the intracellular adenosine nucleotide pool are traditionally assumed to be the consequence of changes in energy metabolism, in this study we have addressed the question of whether extracellular adenosine contributes to AMPK regulation. In the intestinal rat epithelial cell line IEC-6, addition of adenosine rapidly increases AMP intracellular concentrations and upregulates alpha1AMPK, thus promoting phosphorylation of its downstream target acetyl-CoA carboxylase (ACC). The effect of adenosine on AMPK signaling is completely blocked by transducing IEC-6 cells with an adenoviral vector expressing a mutated alpha1 subunit, resulting in a dominant-negative effect on endogenous AMPK activity. These effects are blocked by 5'-iodotubercidine (5'-ITU), an inhibitor of adenosine kinase. Moreover, inhibition of adenosine transport through the concentrative adenosine plasma membrane transporter CNT2 with formycin B results in the blockade of adenosine-mediated AMPK signaling. Extracellular adenosine is equally able to activate AMPK and promote ACC phosphorylation in liver parenchymal cell models in a manner that is also inhibited by 5'-ITU. In summary, this study shows that adenosine, when added at physiological concentrations, activates AMPK and promotes ACC phosphorylation. Adenosine must be transported and phosphorylated to exert its action. Thus, nucleoside transporters might be novel players in the complex regulation of AMPK and energy metabolism.
Collapse
Affiliation(s)
- Ivette Aymerich
- Departament de Bioquímica i Biologia Molecular, Universitat de Barcelona, 08071 Barcelona, Spain
| | | | | | | | | |
Collapse
|
28
|
Hu H, Endres CJ, Chang C, Umapathy NS, Lee EW, Fei YJ, Itagaki S, Swaan PW, Ganapathy V, Unadkat JD. Electrophysiological Characterization and Modeling of the Structure Activity Relationship of the Human Concentrative Nucleoside Transporter 3 (hCNT3). Mol Pharmacol 2006; 69:1542-53. [PMID: 16446384 DOI: 10.1124/mol.105.018945] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We characterized the electrophysiology, kinetics, and quantitative structure-activity relationship (QSAR) of the human concentrative nucleoside transporter 3 (hCNT3) expressed in Xenopus laevis oocytes by measuring substrate-induced inward currents using a two-microelectrode voltage-clamp system. At membrane potentials between -30 and -150 mV, sodium activation of gemcitabine transport was sigmoidal, with a K0.5 of 8.5+/-0.3 mM for Na+ and a Hill coefficient of 2.2+/-0.25 independent of membrane potential. We measured the Imax and K0.5 for substrate at -50 mV for the nucleoside analog drugs gemcitabine (638+/-58 nA, 59.7+/-17.5 microM), ribavirin (546+/-37 nA, 61.0+/-13.2 microM), AZT (420+/-4 nA, 310+/-9 microM), and 3-deazauridine (506+/-30 nA, 50.8+/-9.90 microM). K0.5 and Imax for substrate were dependent on membrane potential (both increasing as the membrane became more hyperpolarized) for all four drugs. hCNT3 also exhibited pre-steady-state currents. The quantitative structure-activity relationship (QSAR) was examined using comparative molecular field analysis and comparative molecular similarity indices analysis of the inward currents induced by 27 nucleoside analogs with substitutions at both the ribose and the nucleobase. Two statistically significant QSAR models identified electrostatic interaction as the major force in hCNT3 transport and attributed a critical role to the 3'-hydroxyl position of hCNT3 substrates. Steric hindrance at the 3-position and positive charge at the 5-position of the pyrimidine ring were favorable for transport. Two hCNT3 pharmacophore models revealed the minimal features required for hCNT3 transport as two hydrogen bond acceptors at 3'-OH and 5'-O and the hydrophobic center occupied by the base ring.
Collapse
Affiliation(s)
- Huankai Hu
- Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta, USA
| | | | | | | | | | | | | | | | | | | |
Collapse
|
29
|
Pascual I, Berjón A, Lostao MP, Barber A. Transport of d-galactose by the gastrointestinal tract of the locust, Locusta migratoria. Comp Biochem Physiol B Biochem Mol Biol 2006; 143:20-6. [PMID: 16314134 DOI: 10.1016/j.cbpb.2005.09.008] [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: 02/21/2005] [Revised: 09/02/2005] [Accepted: 09/05/2005] [Indexed: 11/24/2022]
Abstract
Due to exoskeleton, the absorption of nutrients in adult insects takes place across the gastrointestinal tract epithelium. In most physiological studies, sugar intestinal absorption has been described as a diffusional process and to date no sugar transporter has been cloned from the digestive tract of insects. In the present work, the existence of a saturable transport system for galactose in the gastric caeca of Locusta migratoria is clearly demonstrated. This transport shows a relatively high affinity for galactose (apparent K0.5=2-3 mM) and is inhibited by glucose, 2-deoxyglucose and with less potency by fructose and alpha-methyl-d-glucoside. The absence of sodium or the presence of phloridzin hardly affects galactose absorption, indicating that it is not mediated by a SGLT1-like transporter. The absence of K+, Cl-, Mg2+ and Ca2+ or changes in the pH do not modify galactose absorption either. Nevertheless, phloretin, cytochalasin B and theophylline (inhibitors of facilitative transporters) decrease sugar uptake around 50%. Xenopus laevis oocytes microinjected with poly A+ RNA isolated from gastric caeca show sodium-independent galactose uptake that is three times higher than in non-injected oocytes, further supporting the existence of a mRNA coding for at least one equilibrative sugar transporter in L. migratoria gastric caeca.
Collapse
Affiliation(s)
- I Pascual
- Departamento de Fisiología y Nutrición, University of Navarra, C/ Irunlarrea s.n., 31008 Pamplona, Spain
| | | | | | | |
Collapse
|
30
|
Rodríguez-Mulero S, Errasti-Murugarren E, Ballarín J, Felipe A, Doucet A, Casado FJ, Pastor-Anglada M. Expression of concentrative nucleoside transporters SLC28 (CNT1, CNT2, and CNT3) along the rat nephron: Effect of diabetes. Kidney Int 2005; 68:665-72. [PMID: 16014043 DOI: 10.1111/j.1523-1755.2005.00444.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
BACKGROUND The renal reabsorption of natural nucleosides and a variety of nucleoside-derived drugs relies on the function of the apically located, Na(+)-dependent, concentrative nucleoside transporters CNT1, CNT2, and CNT3 (SLC28A1, SLC28A2, and SLC28A3). The aims of this study were to determine the segmental localization of the three SLC28 family members and to establish whether streptozotocin-induced diabetes alters their expression. METHODS SLC28 expression was measured by real-time polymerase chain reaction (PCR) on microdissected sections of rat nephrons. Diabetes was induced by streptozotocin treatment and the biochemical profiles of control, diabetic, and insulin-treated rats were established. The effect of diabetes on SLC28 expression was assessed in those segments that significantly express SLC28 genes. RESULTS CNT1-3 mRNAs were expressed in the proximal tubule and glomerulus. In addition, CNT2 and CNT3 mRNAs were expressed in the outer medullary and cortical collecting duct, respectively. Diabetes reduced expression of the three CNTs in almost all nephron segments, and this effect was not prevented by an insulin treatment that normalized all blood and urine parameters. Diabetes increased CNT1 and CNT3 expression in the glomerulus and insulin treatment decreased it. CONCLUSION The relative distribution of SLC28 gene expression suggests a role for the proximal tubule in renal nucleoside clearance and an accessory role for CNT2 and CNT3, in adenosine-mediated regulation of collecting duct functions. Diabetes probably may impair nucleoside clearance independently of insulin.
Collapse
|
31
|
Smith KM, Slugoski MD, Loewen SK, Ng AML, Yao SYM, Chen XZ, Karpinski E, Cass CE, Baldwin SA, Young JD. The Broadly Selective Human Na+/Nucleoside Cotransporter(hCNT3) Exhibits Novel Cation-coupled Nucleoside TransportCharacteristics. J Biol Chem 2005; 280:25436-49. [PMID: 15870078 DOI: 10.1074/jbc.m409454200] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The concentrative nucleoside transporter (CNT) protein family in humans is represented by three members, hCNT1, hCNT2, and hCNT3. hCNT3, a Na+/nucleoside symporter, transports a broad range of physiological purine and pyrimidine nucleosides as well as anticancer and antiviral nucleoside drugs, and belongs to a different CNT subfamily than hCNT1/2. H+-dependent Escherichia coli NupC and Candida albicans CaCNT are also CNT family members. The present study utilized heterologous expression in Xenopus oocytes to investigate the specificity, mechanism, energetics, and structural basis of hCNT3 cation coupling. hCNT3 exhibited uniquely broad cation interactions with Na+, H+, and Li+ not shared by Na+-coupled hCNT1/2 or H+-coupled NupC/CaCNT. Na+ and H+ activated hCNT3 through mechanisms to increase nucleoside apparent binding affinity. Direct and indirect methods demonstrated cation/nucleoside coupling stoichiometries of 2:1 in the presence of Na+ and both Na+ plus H+, but only 1:1 in the presence of H+ alone, suggesting that hCNT3 possesses two Na+-binding sites, only one of which is shared by H+. The H+-coupled hCNT3 did not transport guanosine or 3'-azido-3'-deoxythymidine and 2',3'-dideoxycytidine, demonstrating that Na+- and H+-bound versions of hCNT3 have significantly different conformations of the nucleoside binding pocket and/or translocation channel. Chimeric studies between hCNT1 and hCNT3 located hCNT3-specific cation interactions to the C-terminal half of hCNT3, setting the stage for site-directed mutagenesis experiments to identify the residues involved.
Collapse
Affiliation(s)
- Kyla M Smith
- Membrane Protein Research Group, Departments of Physiology and Oncology, University of Alberta Cross Cancer Institute, Edmonton, Alberta T6G 2H7, Canada
| | | | | | | | | | | | | | | | | | | |
Collapse
|
32
|
Pastor-Anglada M, Cano-Soldado P, Molina-Arcas M, Lostao MP, Larráyoz I, Martínez-Picado J, Casado FJ. Cell entry and export of nucleoside analogues. Virus Res 2005; 107:151-64. [PMID: 15649561 DOI: 10.1016/j.virusres.2004.11.005] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Some nucleoside analogues currently used as antiretroviral agents might promote mutagenesis besides their putative ability to interfere with endogenous nucleotide metabolism and/or inhibit viral transcription. The intracellular concentration of nucleosides and nucleobases is to some extent the result of the metabolic background of the specific cell line used for infection studies, its particular suit of enzymes and transporters. This review focuses on the transporter-mediated pathways implicated in either the uptake or the efflux of nucleoside- and nucleobase-derivatives. From a biochemical point of view, four different types of transport processes for nucleoside-related antiviral drugs have been described: (1) equilibrative uniport, (2) substrate exchange, (3) concentrative Na+- or H+-dependent uptake and finally, (4) substrate export through primary ATP-dependent active efflux pumps. These mechanisms are mainly related to the following set of transporter families: Concentrative Nucleoside Transporter (CNT), Equilibrative Nucleoside Transporter (ENT), Organic Anion Transporter (OAT) and Organic Cation Transporter (OCT), Peptide Transporter (PEPT) and Multidrug Resistance Protein (MRP). The basic properties of these carrier proteins and their respective role in the transport across the plasma membrane of nucleoside-derived antiviral drugs are reviewed.
Collapse
Affiliation(s)
- Marçal Pastor-Anglada
- Departament de Bioquímica i Biologia Molecular, Universitat de Barcelona, Diagonal 645, 08028 Barcelona, Spain.
| | | | | | | | | | | | | |
Collapse
|
33
|
Aymerich I, Duflot S, Fernández-Veledo S, Guillén-Gómez E, Huber-Ruano I, Casado FJ, Pastor-Anglada M. The concentrative nucleoside transporter family (SLC28): new roles beyond salvage? Biochem Soc Trans 2005; 33:216-9. [PMID: 15667311 DOI: 10.1042/bst0330216] [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: 12/28/2022]
Abstract
The concentrative nucleoside transporter (CNT) family (SLC28) has three members: SLC28A1 (CNT1), SLC28A2 (CNT2) and SLC28A3 (CNT3). The CNT1 and CNT2 transporters are co-expressed in liver parenchymal cells and macrophages, two suitable models in which to study cell cycle progression. Despite initial observations suggesting that these transporter proteins might contribute to nucleoside salvage during proliferation, their subcellular localization and regulatory properties suggest alternative roles in cell physiology. In particular, CNT2 is a suitable candidate for modulation of purinergic responses, since it is under the control of the adenosine 1 receptor. Increasing evidence also suggests a role for CNT2 in energy metabolism, since its activation relies on the opening of ATP-sensitive K+ channels. Animal and cell models genetically modified to alter nucleoside transporter expression levels may help to elucidate the particular roles of CNT proteins in cell physiology.
Collapse
Affiliation(s)
- I Aymerich
- Departament de Bioquímica i Biologia Molecular, Facultat de Biologia, Universitat de Barcelona, Diagonal 645, 08071 Barcelona, Spain
| | | | | | | | | | | | | |
Collapse
|
34
|
Cano-Soldado P, Larráyoz IM, Molina-Arcas M, Casado FJ, Martinez-Picado J, Lostao MP, Pastor-Anglada M. Interaction of Nucleoside Inhibitors of HIV-1 Reverse Transcriptase with the Concentrative Nucleoside Transporter-1 (Slc28A1). Antivir Ther 2004. [DOI: 10.1177/135965350400900617] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Human concentrative nucleoside transporter-1 (hCNT1) (SLC28A1) is a widely expressed, high-affinity, pyrimi-dine-preferring, nucleoside transporter implicated in the uptake of naturally occurring pyrimidine nucleosides as well as a variety of derivatives used in anticancer treatment. Its putative role in the uptake of other pyrimidine nucleoside analogues with antiviral properties has not been studied in detail to date. Here, using a hCNT1 stably transfected cell line and the two-electrode voltage-clamp technique, we have assessed the interaction of selected pyrimidine-based antiviral drugs, inhibitors of HIV-1 reverse transcriptase such as zidovudine (AZT), stavudine (d4T), lamivudine (3TC) and zalcitabine (ddC), with hCNT1. hCNT1 transports AZT and d4T with low affinity, whereas 3TC and ddC are not translocated, the latter being able to bind the transporter protein. Selectivity appears to rely mostly upon the presence of a hydroxyl group in the 3′-position of the ribose ring. Thus, hCNT1 cannot be considered a broad-selectivity pyrimidine nucleoside carrier; in fact, very slight changes in substrate structure provoke a dramatic shift in selectivity.
Collapse
Affiliation(s)
- Pedro Cano-Soldado
- Departament de Bioquímica i Biologia Molecular, Universitat de Barcelona, Barcelona, Spain
| | - Ignacio M Larráyoz
- Departamento de Fisiología y Nutrición, Universidad de Navarra, Pamplona, Spain
| | - Míriam Molina-Arcas
- Departament de Bioquímica i Biologia Molecular, Universitat de Barcelona, Barcelona, Spain
| | - F Javier Casado
- Departament de Bioquímica i Biologia Molecular, Universitat de Barcelona, Barcelona, Spain
| | - Javier Martinez-Picado
- IrsiCaixa Foundation, Hospital Germans Trias i Pujol, Universitat Autònoma de Barcelona, Badalona, Spain
| | - M Pilar Lostao
- Departamento de Fisiología y Nutrición, Universidad de Navarra, Pamplona, Spain
| | - Marçal Pastor-Anglada
- Departament de Bioquímica i Biologia Molecular, Universitat de Barcelona, Barcelona, Spain
| |
Collapse
|
35
|
Smith KM, Ng AML, Yao SYM, Labedz KA, Knaus EE, Wiebe LI, Cass CE, Baldwin SA, Chen XZ, Karpinski E, Young JD. Electrophysiological characterization of a recombinant human Na+-coupled nucleoside transporter (hCNT1) produced in Xenopus oocytes. J Physiol 2004; 558:807-23. [PMID: 15194733 PMCID: PMC1665023 DOI: 10.1113/jphysiol.2004.068189] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Human concentrative nucleoside transporter 1 (hCNT1) mediates active transport of nucleosides and anticancer and antiviral nucleoside drugs across cell membranes by coupling influx to the movement of Na(+) down its electrochemical gradient. The two-microelectrode voltage-clamp technique was used to measure steady-state and presteady-state currents of recombinant hCNT1 produced in Xenopus oocytes. Transport was electrogenic, phloridzin sensitive and specific for pyrimidine nucleosides and adenosine. Nucleoside analogues that induced inwardly directed Na(+) currents included the anticancer drugs 5-fluorouridine, 5-fluoro-2'-deoxyuridine, cladribine and cytarabine, the antiviral drugs zidovudine and zalcitabine, and the novel thymidine mimics 1-(2-deoxy-beta-d-ribofuranosyl)-2,4-difluoro-5-methylbenzene and 1-(2-deoxy-beta-d-ribofuranosyl)-2,4-difluoro-5-iodobenzene. Apparent K(m) values for 5-fluorouridine, 5-fluoro-2'-deoxyuridine and zidovudine were 18, 15 and 450 microm, respectively. hCNT1 was Na(+) specific, and the kinetics of steady-state uridine-evoked Na(+) currents were consistent with an ordered simultaneous transport model in which Na(+) binds first followed by uridine. Membrane potential influenced both ion binding and carrier translocation. The Na(+)-nucleoside coupling stoichiometry, determined directly by comparing the uridine-induced inward charge movement to [(14)C]uridine uptake was 1: 1. hCNT1 presteady-state currents were used to determine the fraction of the membrane field sensed by Na(+) (61%), the valency of the movable charge (-0.81) and the average number of transporters present in the oocyte plasma membrane (6.8 x 10(10) per cell). The hCNT1 turnover rate at -50 mV was 9.6 molecules of uridine transported per second.
Collapse
Affiliation(s)
- Kyla M Smith
- Membrane Protein Research Group, Department of Physiology, Faculty of Pharmacy, 7-55 Medical Sciences Building, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|