Human urate transporter 1 (hURAT1) mediates the transport of orotate

Orotate is a precursor of pyrimidine synthesis. The kidney uses exogenous orotate for the synthesis of uridine diphosphosugars, which are used in the glycosylation of collagen in glomerular and tubular basement membranes. Orotate uptake occurs in the liver and kidney, but its molecular mechanism is largely unknown. Since orotate has been shown to be a substrate of the renal urate/anion exchanger in brush border membrane vesicle studies, we investigated whether human URAT1 (hURAT1) mediates the transport of orotate using HEK293 cells expressing hURAT1 (HEK-hURAT1). hURAT1 mediated a time- and dose-dependent uptake of orotate (K(m) 5.2 mu M). hURAT1-mediated [(3)H] orotate transport was inhibited strongly by non-labeled (cold) orotate and the uricouric agent benzbromarone, and moderately inhibited by urate, nicotinate, and another uricouric agent, probenecid. This is the first report demonstrating that hURAT1 mediates the transport of orotate. hURAT1 may function as one of the entrance pathways in renal proximal tubular cells.