title: Cloning and functional identification of slc5a12 as a sodium-coupled low-affinity transporter for monocarboxylates (SMCT2).
abstract: We report in the present paper, on the isolation and functional characterization of slc5a12, the twelfth member of the SLC5 gene family, from mouse kidney. The slc5a12 cDNA codes for a protein of 619 amino acids. Heterologous expression of slc5a12 cDNA in mammalian cells induces Na+-dependent transport of lactate and nicotinate. Several other short-chain monocarboxylates compete with nicotinate for the cDNA-induced transport process. Expression of slc5a12 in Xenopus oocytes induces electrogenic and Na+-dependent transport of lactate, nicotinate, propionate and butyrate. The substrate specificity of slc5a12 is similar to that of slc5a8, an Na+-coupled transporter for monocarboxylates. However, the substrate affinities of slc5a12 were much lower than those of slc5a8. slc5a12 mRNA is expressed in kidney, small intestine and skeletal muscle. In situ hybridization with sagittal sections of mouse kidney showed predominant expression of slc5a12 in the outer cortex. This is in contrast with slc5a8, which is expressed in the cortex as well as in the medulla. The physiological function of slc5a12 in the kidney is likely to mediate the reabsorption of lactate. In the intestinal tract, slc5a12 is expressed in the proximal parts, whereas slc5a8 is expressed in the distal parts. The expression of slc5a12 in the proximal parts of the intestinal tract, where there is minimal bacterial colonization, suggests that the physiological function of slc5a12 is not to mediate the absorption of short-chain monocarboxylates derived from bacterial fermentation but rather to mediate the absorption of diet-derived short-chain monocarboxylates. Based on the functional and structural similarities between slc5a8 and slc5a12, we suggest that the two transporters be designated as SMCT1 (sodium-coupled monocarboxylate transporter 1) and SMCT2 respectively.
authors.affiliation: Department of Obstetrics and Gynecology, Medical College of Georgia, Augusta, GA 30912, USA.
authors.forename: Sonne R
authors.initials: SR
authors.lastname: Srinivas
authors.forename: Elangovan
authors.initials: E
authors.lastname: Gopal
authors.forename: Lina
authors.initials: L
authors.lastname: Zhuang
authors.forename: Shirou
authors.initials: S
authors.lastname: Itagaki
authors.forename: Pamela M
authors.initials: PM
authors.lastname: Martin
authors.forename: You-Jun
authors.initials: YJ
authors.lastname: Fei
authors.forename: Vadivel
authors.initials: V
authors.lastname: Ganapathy
authors.forename: Puttur D
authors.initials: PD
authors.lastname: Prasad
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D027682:Cation Transport Proteins / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D003001:Cloning, Molecular; D006801:Humans; D007421:Intestine, Small / Q000378:metabolism; D007668:Kidney / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D027501:Monocarboxylic Acid Transporters / Q000235:genetics* / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism; D009865:Oocytes; D009928:Organ Specificity; D010802:Phylogeny; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D012964:Sodium / Q000378:metabolism*; D051247:Sodium-Glucose Transport Proteins / Q000235:genetics* / Q000378:metabolism*; D014982:Xenopus laevis
chemical_list: D027682:Cation Transport Proteins; D027501:Monocarboxylic Acid Transporters; C508556:Slc5a12 protein, mouse; C507459:Slc5a8 protein, mouse; D051247:Sodium-Glucose Transport Proteins; D012964:Sodium