Role of the sodium-dependent phosphate co-transporters and of the phosphate complexes of uranyl in the cytotoxicity of uranium in LLC-PK1 cells
Résumé
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-PK1) and distal (MDCK) tubule as in vitro models. Treatment of LLC-PK1 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 UO2(PO4)- and UO2(HPO4)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. © 2006 Elsevier Inc. All rights reserved.
Mots clés
colchicine
concanavalin A
cytochalasin D
foscarnet
meglumine
phorbol 13 acetate 12 myristate
phosphate
sodium
sodium phosphate cotransporter
uranium
uranyl acetate
animal cell
article
cell strain
computer model
controlled study
cytotoxicity
in vitro study
kidney cell
kidney distal tubule
kidney proximal tubule
nephrotoxicity
nonhuman
phosphate transport
protein function
rat
Animals
Cadmium
Calcium Chloride
Carbonates
Cell Survival
Colchicine
Computer Simulation
Concanavalin A
Cytochalasin D
Dexamethasone
Dose-Response Relationship
Drug
Foscarnet
Indoles
Kidney Tubules
Proximal
LLC-PK1 Cells
Maleimides
Meglumine
Phosphates
Sodium-Phosphate Cotransporter Proteins
Type IIa
Type IIb
Swine
Tetradecanoylphorbol Acetate
Uranium
Uranium Compounds