Publications

• Facilitated mitochondrial import of antiviral and anticancer nucleoside drugs by human equilibrative nucleoside transporter-3.

  Govindarajan R., Leung G.P., Zhou M., Tse C.M., Wang J., Unadkat J.D.

  Human equilibrative nucleoside transporter-3 (hENT3) was recently reported as a pH-dependent, intracellular (lysosomal) transporter capable of transporting anti-human immunodeficiency virus (HIV) dideoxynucleosides (ddNs). Because most anti-HIV ddNs (e.g., zidovudine, AZT) exhibit clinical mitocho ... >> More

  Human equilibrative nucleoside transporter-3 (hENT3) was recently reported as a pH-dependent, intracellular (lysosomal) transporter capable of transporting anti-human immunodeficiency virus (HIV) dideoxynucleosides (ddNs). Because most anti-HIV ddNs (e.g., zidovudine, AZT) exhibit clinical mitochondrial toxicity, we investigated whether hENT3 facilitates transport of anti-HIV ddNs into the mitochondria. Cellular fractionation and immunofluorescence microscopy studies in several human cell lines identified a substantial presence of hENT3 in the mitochondria, with additional presence at the cell surface of two placental cell lines (JAR, JEG3). Mitochondrial or cell surface hENT3 expression was confirmed in human hepatocytes and placental tissues, respectively. Unlike endogenous hENT3, yellow fluorescent protein (YFP)-tagged hENT3 was partially directed to the lysosomes. Xenopus oocytes expressing NH2-terminal-deleted hENT3 (expressed at the cell surface) showed pH-dependent interaction with several classes of nucleosides (anti-HIV ddNs, gemcitabine, fialuridine, ribavirin) that produce mitochondrial toxicity. Transport studies in hENT3 gene-silenced JAR cells showed significant reduction in mitochondrial transport of nucleosides and nucleoside drugs. Our data suggest that cellular localization of hENT3 is cell type dependent and the native transporter is substantially expressed in mitochondria and/or cell surface. hENT3-mediated mitochondrial transport may play an important role in mediating clinically observed mitochondrial toxicity of nucleoside drugs. In addition, our finding that hENT3 is a mitochondrial transporter is consistent with the recent finding that mutations in the hENT3 gene cause an autosomal recessive disorder in humans called the H syndrome. << Less

  Am. J. Physiol. 296:G910-G922(2009) [PubMed] [EuropePMC]

  This publication is cited by 12 other entries.

• Identification of the endogenous key substrates of the human organic cation transporter OCT2 and their implication in function of dopaminergic neurons.

  Taubert D., Grimberg G., Stenzel W., Schoemig E.

  <h4>Background</h4>The etiology of neurodegenerative disorders, such as the accelerated loss of dopaminergic neurons in Parkinson's disease, is unclear. Current hypotheses suggest an abnormal function of the neuronal sodium-dependent dopamine transporter DAT to contribute to cell death in the dopa ... >> More

  <h4>Background</h4>The etiology of neurodegenerative disorders, such as the accelerated loss of dopaminergic neurons in Parkinson's disease, is unclear. Current hypotheses suggest an abnormal function of the neuronal sodium-dependent dopamine transporter DAT to contribute to cell death in the dopaminergic system, but it has not been investigated whether sodium-independent amine transporters are implicated in the pathogenesis of Parkinson's disease.<h4>Methodology/principal findings</h4>By the use of a novel tandem-mass spectrometry-based substrate search technique, we have shown that the dopaminergic neuromodulators histidyl-proline diketopiperazine (cyclo(his-pro)) and salsolinol were the endogenous key substrates of the sodium-independent organic cation transporter OCT2. Quantitative real-time mRNA expression analysis revealed that OCT2 in contrast to its related transporters was preferentially expressed in the dopaminergic regions of the substantia nigra where it colocalized with DAT and tyrosine hydroxylase. By assessing cell viability with the MTT reduction assay, we found that salsolinol exhibited a selective toxicity toward OCT2-expressing cells that was prevented by cyclo(his-pro). A frequent genetic variant of OCT2 with the amino acid substitution R400C reduced the transport efficiency for the cytoprotective cyclo(his-pro) and thereby increased the susceptibility to salsolinol-induced cell death.<h4>Conclusions/significance</h4>Our findings indicate that the OCT2-regulated interplay between cyclo(his-pro) and salsolinol is crucial for nigral cell integrity and that a shift in transport efficiency may impact the risk of Parkinson's disease. << Less

  PLoS ONE 2:e385-e385(2007) [PubMed] [EuropePMC]

  This publication is cited by 3 other entries.