Functional analysis of the human concentrative nucleoside transporter-1 variant hCNT1S546P provides insight into the sodium-binding pocket.

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.

Transporters that translocate nucleosides and structural similar drugs: structural requirements for substrate recognition.

Nucleoside transporters (NT) are integral membrane proteins implicated in the salvage of natural nucleobases and nucleosides for nucleic acid synthesis. These proteins also play a crucial role as carriers of nucleoside analogs used in anticancer and antiviral therapies. In fact, differential expression patterns of NT subtypes among tissues and individuals as well as the existence of genetic variants affect nucleoside-derived drug permeation, and consequently, their pharmacokinetic and cytotoxic properties.

Uridine metabolism in HIV-1-infected patients: effect of infection, of antiretroviral therapy and of HIV-1/ART-associated lipodystrophy syndrome.

Background: Uridine has been advocated for the treatment of HIV-1/HAART-associated lipodystrophy (HALS), although its metabolism in HIV-1-infected patients is poorly understood.

Methods: Plasma uridine concentrations were measured in 35 controls and 221 HIV-1-infected patients and fat uridine in 15 controls and 19 patients. The diagnosis of HALS was performed following the criteria of the Lipodystrophy Severity Grading Scale.

Compensatory effects of the human nucleoside transporters on the response to nucleoside-derived drugs in breast cancer MCF7 cells.

Nucleoside transporters (NTs) are involved in the cytotoxicity and transcriptomic response induced by nucleoside analogues. A relationship between the expression of nucleoside transporters and response to therapy has been demonstrated in solid tumours, although the pattern of such expression is highly variable. Thus, a question is whether the transporter expression pattern rather than specific NT proteins might better explain the ability of tumour cells to respond to nucleoside-derived drug therapy.

Functional characterization of a nucleoside-derived drug transporter variant (hCNT3C602R) showing altered sodium-binding capacity.

A novel cloned polymorphism of the human concentrative nucleoside transporter hCNT3 was described and functionally characterized. This variant consists of a T/C transition leading to the substitution of cysteine 602 by an arginine residue in the core of transmembrane domain 13. The resulting hCNT3(C602R) protein has the same selectivity and affinity for natural nucleosides and nucleoside-derived drugs as hCNT3 but much lower concentrative capacity.

Altered expression of nucleoside transporter genes (SLC28 and SLC29) in adipose tissue from HIV-1-infected patients.

Background: Nucleoside transporter proteins (NTs) encoded by members of the SLC28 and SLC29 gene families contribute to nucleoside and nucleobase recycling but also modulate extracellular adenosine levels and thus adenosine-regulated metabolic targets.

Methods: We have examined the expression pattern of NT-encoding genes in human adipose tissue and we have further analysed whether the mRNA related to these genes show changes in their amounts associated with either HIV-1 infection, highly active antiretroviral therapy (HAART) or development of HIV-1-associated lipodystrophy syndrome (HALS).

Results: Human adipocytes express SLC28A1, SLC28A2 and SLC28A3 (encoding hCNT1, hCNT2 and hCNT3, respectively) and SLC29A1 and SLC29A2 (encoding hENT1 and hENT2, respectively).

Human equilibrative nucleoside transporter-1 (hENT1) is required for the transcriptomic response of the nucleoside-derived drug 5'-DFUR in breast cancer MCF7 cells.

Nucleoside analogues are broadly used in cancer treatment. Although nucleoside metabolism is a necessary step in the development of their cytotoxicity, mediated transport across the plasma membrane might be needed for nucleoside-derived drugs to exert their pharmacological action. In this study, we have addressed the question of whether particular plasma membrane transporters contribute to the transcriptomic response associated with nucleoside-derived drug therapy.

Interaction of nucleoside inhibitors of HIV-1 reverse transcriptase with the concentrative nucleoside transporter-1 (SLC28A1).

Human concentrative nucleoside transporter-1 (hCNT1) (SLC28A1) is a widely expressed, high-affinity, pyrimidine-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.

Cell entry and export of nucleoside analogues.

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.