Identification and cloning of a novel monocarboxylate transporter gene

Purpose: To identify and clone the cDNAs encoding renal formate and (or) oxalate transporters in order to investigate the mechanism of Cl^- reabsorption in the proximal tubule. Methods: According to the sequence of a bacterial formate - oxalate exchanger (Oxlt), we tested whether the mammalian EST database contained a kidney cDNA with similarity to Oxlt. The gene was analyzed to locate the distribution with a mouse multiple-tissues Northern blot. Results: An EST with significant similarity to Oxlt was identified in a mouse renal cDNA library. The sequence of this EST clone had an open reading frame encoding a predicted protein of 429 amino acids. Database searching with the coding sequence revealed significant homology to the MCT family of monocarboxylate transporter (MCT). There were 33% identity with mouse MCT2,30% with mouse MCT1 and 29% with rat MCT3 in amino acid sequence. Amino acid 14-158 were 25% identical to the corresponding sequence of Oxlt. Northern blot analysis of mouse multiple-tissue indicated that transcript encoding novel protein highly expressed in kidney. There were barely detectable expression in liver and heart. Conclusions: A novel MCT family member with selection expression in the kidney was identified. It may be a candidate to mediate renal tubular formate transport.