Role of the sodium-dependent phosphate co-transporters and of the phosphate complexes of uranyl in the cytotoxicity of uranium in LLC-PK1 cells

Toxicol Appl Pharmacol. 2006 Jul 15;214(2):166-77. doi: 10.1016/j.taap.2005.12.016. Epub 2006 Feb 14.


Although uranium is a well-characterized nephrotoxic agent, very little is known at the cellular and molecular level about the mechanisms underlying the uptake and toxicity of this element in proximal tubule cells. The aim of this study was thus to characterize the species of uranium that are responsible for its cytotoxicity and define the mechanism which is involved in the uptake of the cytotoxic fraction of uranium using two cell lines derived from kidney proximal (LLC-PK(1)) and distal (MDCK) tubule as in vitro models. Treatment of LLC-PK(1) cells with colchicine, cytochalasin D, concanavalin A and PMA increased the sodium-dependent phosphate co-transport and the cytotoxicity of uranium. On the contrary, replacement of the extra-cellular sodium with N-methyl-D-glucamine highly reduced the transport of phosphate and the cytotoxic effect of uranium. Uranium cytotoxicity was also dependent upon the extra-cellular concentration of phosphate and decreased in a concentration-dependent manner by 0.1-10 mM phosphonoformic acid, a competitive inhibitor of phosphate uptake. Consistent with these observations, over-expression of the rat proximal tubule sodium-dependent phosphate co-transporter NaPi-IIa in stably transfected MDCK cells significantly increased the cytotoxicity of uranium, and computer modeling of uranium speciation showed that uranium cytotoxicity was directly dependent on the presence of the phosphate complexes of uranyl UO(2)(PO(4))(-) and UO(2)(HPO(4))(aq). Taken together, these data suggest that the cytotoxic fraction of uranium is a phosphate complex of uranyl whose uptake is mediated by a sodium-dependent phosphate co-transporter system.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cadmium / toxicity
  • Calcium Chloride / pharmacology
  • Carbonates / pharmacology
  • Cell Survival / drug effects
  • Colchicine / pharmacology
  • Computer Simulation
  • Concanavalin A / pharmacology
  • Cytochalasin D / pharmacology
  • Dexamethasone / pharmacology
  • Dose-Response Relationship, Drug
  • Foscarnet / pharmacology
  • Indoles / pharmacology
  • Kidney Tubules, Proximal / cytology
  • Kidney Tubules, Proximal / drug effects
  • Kidney Tubules, Proximal / metabolism
  • LLC-PK1 Cells
  • Maleimides / pharmacology
  • Meglumine / analogs & derivatives
  • Meglumine / pharmacology
  • Phosphates / antagonists & inhibitors
  • Phosphates / pharmacology
  • Phosphates / physiology*
  • Sodium-Phosphate Cotransporter Proteins, Type IIa / metabolism
  • Sodium-Phosphate Cotransporter Proteins, Type IIb / physiology*
  • Swine
  • Tetradecanoylphorbol Acetate / antagonists & inhibitors
  • Tetradecanoylphorbol Acetate / pharmacology
  • Uranium / toxicity*
  • Uranium Compounds


  • Carbonates
  • Indoles
  • Maleimides
  • Phosphates
  • Slc34a1 protein, rat
  • Sodium-Phosphate Cotransporter Proteins, Type IIa
  • Sodium-Phosphate Cotransporter Proteins, Type IIb
  • Uranium Compounds
  • Cadmium
  • Concanavalin A
  • Cytochalasin D
  • hydrogen uranyl phosphate
  • Foscarnet
  • Uranium
  • Meglumine
  • Dexamethasone
  • Calcium Chloride
  • bisindolylmaleimide
  • Tetradecanoylphorbol Acetate
  • Colchicine