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Functional Characterization of Na+/H+ Exchangers of Intracellular Compartments Using Proton-killing Selection to Express Them at the Plasma Membrane
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Cellular localization and functional characterization of the equilibrative nucleoside transporters of antitumor

Yoshio Endo1, Tohru Obata, Daigo Murata

  • 1Department of Experimental Therapeutics, Cancer Research Institute, Kanazawa University, Kanazawa 920-0934, Japan. yendo@kenroku.kanazawa-u.ac.jp

Cancer Science
|August 23, 2007
PubMed

Insights

Equilibrative nucleoside transporters (ENTs) impact antitumor drug effectiveness. Researchers found that hENT1 and hENT2, located on the cell surface, significantly enhanced sensitivity to nucleoside-based chemotherapy, unlike intracellular hENT3 and hENT4.

Area of Science:

  • Pharmacology
  • Molecular Biology
  • Cell Biology

Background:

  • Nucleoside transporters are crucial for the cellular uptake and disposition of nucleosides and their analogs.
  • Antitumor nucleosides are a significant class of chemotherapeutic agents, and their efficacy is often influenced by transporter expression.

Purpose of the Study:

  • To investigate the functional roles of specific equilibrative nucleoside transporters (ENTs) in mediating cellular chemosensitivity to antitumor nucleosides.
  • To determine the subcellular localization and functional impact of human ENT1, ENT2, ENT3, and ENT4 on cancer cell lines.

Main Methods:

  • Stable cell lines (HT-1080 and TMK-1) were engineered to overexpress green fluorescent protein-tagged human ENT1, ENT2, ENT3, and ENT4.
  • Subcellular localization of the overexpressed transporters was assessed.
  • Chemosensitivity assays were performed using established antitumor nucleosides (cytarabine and a related analog) on engineered cell lines compared to mock-transfected controls.

Main Results:

  • hENT1 and hENT2 were confirmed to be localized at the plasma membrane, consistent with their role in nucleoside transport.
  • hENT3 and hENT4 were primarily localized to intracellular organelles.
  • TMK-1 cells overexpressing hENT1 or hENT2 exhibited significantly increased sensitivity to cytarabine and the ethynyl-ribopentofuranosyl cytosine analog.
  • Cell lines expressing hENT3 or hENT4 did not show significant alterations in chemosensitivity to these antitumor nucleosides.

Conclusions:

  • Plasma membrane-localized equilibrative nucleoside transporters, specifically hENT1 and hENT2, play a critical role in enhancing cellular uptake and chemosensitivity to key antitumor nucleoside drugs.
  • Intracellularly localized transporters, hENT3 and hENT4, do not appear to be major contributors to the uptake and efficacy of the tested antitumor nucleosides.
  • Targeting hENT1 and hENT2 may represent a viable strategy to improve the therapeutic outcomes of nucleoside-based chemotherapy.

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