Human organic anion transporter MRP4 (ABCC4) is an efflux pump for the purine end metabolite urate with multiple allosteric substrate binding sites

• Published in: American journal of physiology. Renal physiology 2005-02, Vol.288 (2), p.F327-F333
• Main Authors: Van Aubel, Rémon A M H, Smeets, Pascal H E, van den Heuvel, Jeroen J M W, Russel, Frans G M
• Format: Article
• Language: English
• Subjects: Adenosine Triphosphate - metabolism; Animals; Antimetabolites, Antineoplastic - pharmacokinetics; Cell Culture Techniques; Cyclic AMP - metabolism; Cyclic GMP - metabolism; Humans; Kidney - physiology; Liver - physiology; Membrane Transport Proteins - metabolism; Methotrexate - pharmacokinetics; Mitochondrial Proteins - metabolism; Multidrug Resistance-Associated Proteins - metabolism; Organic Anion Transporters - metabolism; Ribosomal Proteins - metabolism; Spodoptera; Uric Acid - pharmacokinetics
• ISSN: 1931-857X; 1522-1466
• DOI: 10.1152/ajprenal.00133.2004

The end product of human purine metabolism is urate, which is produced primarily in the liver and excreted by the kidney through a well-defined basolateral blood-to-cell uptake step. However, the apical cell-to-urine efflux mechanism is as yet unidentified. Here, we show that the renal apical organic anion efflux transporter human multidrug resistance protein 4 (MRP4), but not apical MRP2, mediates ATP-dependent urate transport via a positive cooperative mechanism (K(m) of 1.5 +/- 0.3 mM, V(max) of 47 +/- 7 pmol x mg(-1) x min(-1), and Hill coefficient of 1.7 +/- 0.2). In HEK293 cells overexpressing MRP4, intracellular urate levels were lower than in control cells. Urate inhibited methotrexate transport (IC50 of 235 +/- 8 microM) by MRP4, did not affect cAMP transport, whereas cGMP transport was stimulated. Urate shifted cGMP transport by MRP4 from positive cooperativity (K(m) and V(max) value of 180 +/- 20 microM and 58 +/- 4 pmol x mg(-1) x min(-1), respectively, Hill coefficient of 1.4 +/- 0.1) to single binding site kinetics (K(m) and V(max) value of 2.2 +/- 0.9 mM and 280 +/- 50 pmol x mg(-1) x min(-1), respectively). Finally, MRP4 could transport urate simultaneously with cAMP or cGMP. We conclude that human MRP4 is a unidirectional efflux pump for urate with multiple allosteric substrate binding sites. We propose MRP4 as a candidate transporter for urinary urate excretion and suggest that MRP4 may also mediate hepatic export of urate into the circulation, because of its basolateral expression in the liver.