Function and localization of urate transporter 1 in mouse kidney

Area of Science:

• Nephrology
• Molecular Biology
• Biochemistry

Background:

• Hereditary renal hypouricemia is linked to mutations in the human urate transporter 1 (hURAT1).
• Mouse renal-specific transporter (RST) shares significant sequence identity with hURAT1, suggesting it may be its mouse homologue.

Purpose of the Study:

• To determine the localization and characteristics of the RST molecule in the mouse kidney.
• To investigate urate transport function mediated by RST using a Xenopus oocyte expression system.

Main Methods:

• Xenopus oocyte expression system to study RST-mediated urate transport kinetics and inhibition.
• Immunohistochemistry and Western blotting to localize and characterize RST protein in mouse kidney.
• Analysis of RST mRNA and protein levels in male versus female kidneys.

Main Results:

• RST transported urate via Michaelis-Menten kinetics with a K(m) of 1213 +/- 222 micro M and V(max) of 268.8 +/- 38.0 pmol/oocyte/hr.
• RST-dependent urate transport was significantly inhibited by probenecid, benzbromarone, and lactate, and enhanced by gluconate substitution for chloride.
• Immunohistochemistry localized RST to the brush border of proximal tubules, and Western blotting detected 70-kD and 62-kD protein bands, with the 70-kD band identified as an N-glycosylated brush border membrane protein.

Conclusions:

• RST functions as a urate transporter in the mouse kidney, exhibiting characteristics similar to hURAT1.
• RST is identified as the mouse homologue of hURAT1 (mURAT1), crucial for urate reabsorption.
• RST expression levels are higher in male mouse kidneys compared to female kidneys.