Mechanisms of Nucleobase Transport in Rabbit Choroid Plexus

Washington, Carla; Giacomini, Kathleen M.

doi:10.1074/jbc.270.39.22816

Cited by 30 publications

(6 citation statements)

References 13 publications

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“…Of particular note is that the affinity of both purine and pyrimidine bases for this co-transporter is high (apparent K m values in the range 1-10 µM) and that adenine is not a permeant. Recently, a Na + -dependent nucleobase transporter in rabbit choroid plexus has been described with properties distinct from those nucleobase co-transporters in kidney and heart [22].…”

Section: Introductionmentioning

confidence: 99%

Hypoxanthine enters human vascular endothelial cells (ECV 304) via the nitrobenzylthioinosine-insensitive equilibrative nucleoside transporter

Osses

Pearson

Yudilevich

et al. 1996

Biochemical Journal

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The transport properties of the nucleobase hypoxanthine were examined in the human umbilical vein endothelial cell line ECV 304. Initial rates of hypoxanthine influx were independent of extracellular cations: replacement of Na+ with Li+, Rb+, N-methyl-D-glucamine or choline had no significant effect on hypoxanthine uptake by ECV 304 cells. Kinetic analysis demonstrated the presence of a single saturable system for the transport of hypoxanthine in ECV 304 cells with an apparent K(m) of 320 +/- 10 microM and a Vmax of 5.6 +/- 0.9 pmol/10(6) cells per s. Hypoxanthine uptake was inhibited by the nucleosides adenosine, uridine and thymidine (apparent Ki 41 +/- 6, 240 +/- 27 and 59 +/- 8 microM respectively) and the nucleoside transport inhibitors nitrobenzylthioinosine (NBMPR), dilazep and dipyridamole (apparent Ki 2.5 +/- 0.3, 11 +/- 3 and 0.16 +/- 0.006 microM respectively), whereas the nucleobases adenine, guanine and thymine had little effect (50% inhibition at > 1 mM). ECV 304 cells were also shown to transport adenosine via both the NBMPR-sensitive and -insensitive nucleoside carriers. Hypoxanthine specifically inhibited adenosine transport via the NBMPR-insensitive system in a competitive manner (apparent Ki 290 +/- 14 microM). These results indicate that hypoxanthine entry into ECV 304 endothelial cells is mediated by the NBMPR-insensitive nucleoside carrier present in these cells.

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Section: Introductionmentioning

confidence: 99%

Hypoxanthine enters human vascular endothelial cells (ECV 304) via the nitrobenzylthioinosine-insensitive equilibrative nucleoside transporter

Osses

Pearson

Yudilevich

et al. 1996

Biochemical Journal

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“…In particular, CNT1, which transports pyrimidine nucleosides more preferentially than purine nucleosides, is highly expressed in the epithelial tissues such as small intestine, kidney, and liver (8 -11). It is also known that CNT1 is localized at the apical membrane of intestinal epithelial cells, suggesting its physiological and pharmacological roles in the absorption of nucleosides and their analogs in the small intestine.However, transporters specific for nucleobases have not been identified in mammals, although their presence has long been postulated (3,4,(12)(13)(14)(15)(16)(17). Our earlier study using the everted sacs of the rat small intestine demonstrated that the uptake transport of 5-fluorouracil (5-FU), 2 a uracil analog used for cancer chemotherapy, occurs in a saturable and sodium-dependent * This work was supported in part by a grant-in-aid for young scientists (B) from the Ministry of Education, Culture, Sports, Science and Technology, Japan, and a grant-in-aid for research in Nagoya City University.…”

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confidence: 99%

“…However, transporters specific for nucleobases have not been identified in mammals, although their presence has long been postulated (3,4,(12)(13)(14)(15)(16)(17). Our earlier study using the everted sacs of the rat small intestine demonstrated that the uptake transport of 5-fluorouracil (5-FU), 2 a uracil analog used for cancer chemotherapy, occurs in a saturable and sodium-dependent * This work was supported in part by a grant-in-aid for young scientists (B) from the Ministry of Education, Culture, Sports, Science and Technology, Japan, and a grant-in-aid for research in Nagoya City University.…”

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confidence: 99%

Identification and Functional Characterization of the First Nucleobase Transporter in Mammals

Yamamoto

Inoue

Murata

et al. 2010

Journal of Biological Chemistry

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Nucleobases are important compounds that constitute nucleosides and nucleic acids. Although it has long been suggested that specific transporters are involved in their intestinal absorption and uptake in other tissues, none of their molecular entities have been identified in mammals to date. Here we describe identification of rat Slc23a4 as the first sodiumdependent nucleobase transporter (rSNBT1). The mRNA of rSNBT1 was expressed highly and only in the small intestine. When transiently expressed in HEK293 cells, rSNBT1 could transport uracil most efficiently. The transport of uracil mediated by rSNBT1 was sodium-dependent and saturable with a Michaelis constant of 21.2 M. Thymine, guanine, hypoxanthine, and xanthine were also transported, but adenine was not. It was also suggested by studies of the inhibitory effect on rSNBT1-mediated uracil transport that several nucleobase analogs such as 5-fluorouracil are recognized by rSNBT1, but cytosine and nucleosides are not or only poorly recognized. Furthermore, rSNBT1 fused with green fluorescent protein was mainly localized at the apical membrane, when stably expressed in polarized Madin-Darby canine kidney II cells. These characteristics of rSNBT1 were almost fully in agreement with those of the carrier-mediated transport system involved in intestinal uracil uptake. Therefore, it is likely that rSNBT1 is its molecular entity or at least in part responsible for that. It was also found that the gene orthologous to the rSNBT1 gene is genetically defective in humans. This may have a biological and evolutional meaning in the transport and metabolism of nucleobases. The present study provides novel insights into the specific transport and metabolism of nucleobases and their analogs for therapeutic use.Nucleosides are essential components of DNA and RNA, the genomic memory devices, and also play pivotal roles as energy sources and in signal transductions (1, 2). In mammals, nucleosides can be synthesized via the de novo pathway from small precursor molecules, such as aspartate, glutamine, glycine, and 10-formyltetrahydrofolate, and via the salvage pathway from nucleobases. In the salvage pathway, the supply of nucleobases mainly occurs from extracellular sources, typically those produced by digestion of dietary nucleic acids in the intestinal lumen. There also occurs redistribution of nucleosides/nucleobases via bloodstream from the tissues that are highly active in de novo synthesizing and/or degrading nucleosides. Therefore, carrier-mediated transport systems are needed for the efficient trafficking across cellular membranes of nucleosides and nucleobases, which are hydrophilic and hence can little permeate otherwise (3, 4).The transporters involved in the cellular uptake of nucleosides have been well characterized in mammals, including humans (5-7). There are two families of transporters, which are sodium-coupled concentrative nucleoside transporters (CNT1/SLC28A1, CNT2/SLC28A2, and CNT3/SLC28A3) and equilibrative nucleoside transporters (ENT1/SLC29A1 and ENT2/SLC29A2...

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“…16,17) Equilibrative nucleobase transport has been observed in human erythrocytes, human T-lymphoblastoid cells, LLC-PK1 cells, rabbit cornea cells and S49 mouse-derived lymphoma cells, [18][19][20][21] whereas concentrative nucleobase transport occurs in kidney, intestine, placenta, and choroid plexus. 19,[22][23][24][25][26] However, little is yet known about the molecular basis of nucleobase transport in mammalian cells.…”

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confidence: 99%

Characterization of Nucleobase Transport by Mouse Sertoli Cell Line TM4

Kato

Maeda

Akaike

et al. 2009

Biological & Pharmaceutical Bulletin

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In the spermatogenesis, many nucleosides and nucleobases are needed for the salvage nucleotide biosynthesis. One of the roles of Sertoli cells is to provide such nutrients to spermatogenic cells located within the bloodtestis barrier (BTB). We have already shown that nucleoside transporters are expressed and are functional in primary-cultured rat Sertoli cells and TM4 cells derived from mouse testis. Here, we examined the uptakes of purine ([ 3 H]guanine) and pyrimidine ([ 3 H]uracil) nucleobases using TM4 cells. Uptakes of both nucleobases were time-and concentration-dependent, and kinetic analysis indicated the involvement of high-affinity transport systems. Uptake of uracil was significantly reduced in the absence of Na ؉ , although guanine uptake was mainly mediated by a sodium-independent transport system in TM4 cells. Guanine uptake was inhibited by other purine nucleobases, but not by pyrimidine nucleobases. Only pyrimidine nucleobases reduced uracil uptake. In addition, mycophenolic acid, an inosine monophosphate dehydrogenase inhibitor, up-regulated guanine uptake. These results suggested that there are distinct transport systems for purine and pyrimidine nucleobases in cells of mouse Sertoli cell line TM4.

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Mechanisms of Nucleobase Transport in Rabbit Choroid Plexus

Cited by 30 publications

References 13 publications

Hypoxanthine enters human vascular endothelial cells (ECV 304) via the nitrobenzylthioinosine-insensitive equilibrative nucleoside transporter

Hypoxanthine enters human vascular endothelial cells (ECV 304) via the nitrobenzylthioinosine-insensitive equilibrative nucleoside transporter

Identification and Functional Characterization of the First Nucleobase Transporter in Mammals

Characterization of Nucleobase Transport by Mouse Sertoli Cell Line TM4

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