title: Cloning and functional characterization of human SMCT2 (SLC5A12) and expression pattern of the transporter in kidney.
abstract: Recently, we cloned two Na(+)-coupled lactate transporters from mouse kidney, a high-affinity transporter (SMCT1 or slc5a8) and a low-affinity transporter (SMCT2 or slc5a12). Here we report on the cloning and functional characterization of human SMCT2 (SLC5A12) and compare the immunolocalization patterns of slc5a12 and slc5a8 in mouse kidney. The human SMCT2 cDNA codes for a protein consisting of 618 amino acids. When expressed in mammalian cells or Xenopus oocytes, human SMCT2 mediates Na(+) -coupled transport of lactate, pyruvate and nicotinate. The affinities of the transporter for these substrates are lower than those reported for human SMCT1. Several non-steroidal anti-inflammatory drugs inhibit human SMCT2-mediated nicotinate transport, suggesting that NSAIDs interact with the transporter as they do with human SMCT1. Immunofluorescence microscopy of mouse kidney sections with an antibody specific for SMCT2 shows that the transporter is expressed predominantly in the cortex. Similar studies with an anti-SMCT1 antibody demonstrate that SMCT1 is also expressed mostly in the cortex. Dual-labeling of SMCT1 and SMCT2 with 4F2hc (CD98), a marker for basolateral membrane of proximal tubular cells in the S1 and S2 segments of the nephron, shows that both SMCT1 and SMCT2 are expressed in the apical membrane of the tubular cells. These studies also show that while SMCT2 is broadly expressed along the entire length of the proximal tubule (S1/S2/S3 segments), the expression of SMCT1 is mostly limited to the S3 segment. These studies suggest that the low-affinity transporter SMCT2 initiates lactate absorption in the early parts of the proximal tubule followed by the participation of the high-affinity transporter SMCT1 in the latter parts of the proximal tubule.
authors: Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta, GA 30912-2100, USA.
authors: E
authors: E
authors: Gopal
authors: N S
authors: NS
authors: Umapathy
authors: P M
authors: PM
authors: Martin
authors: S
authors: S
authors: Ananth
authors: J P
authors: JP
authors: Gnana-Prakasam
authors: H
authors: H
authors: Becker
authors: C A
authors: CA
authors: Wagner
authors: V
authors: V
authors: Ganapathy
authors: P D
authors: PD
authors: Prasad
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000737:chemistry; D005455:Fluorescent Antibody Technique; D006801:Humans; D007668:Kidney / Q000737:chemistry*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D027501:Monocarboxylic Acid Transporters / Q000032:analysis* / Q000235:genetics* / Q000502:physiology; D027981:Symporters; D014982:Xenopus laevis
chemical_list: D018076:DNA, Complementary; D027501:Monocarboxylic Acid Transporters; C519836:SLC5A12 protein, human; C508556:Slc5a12 protein, mouse; D027981:Symporters
references: J Biol Chem. 1999 Dec 3;274(49):34948-54
references: 10574970
references: Am J Physiol Renal Physiol. 2001 Jan;280(1):F10-8
references: 11133510
references: J Am Soc Nephrol. 2002 Apr;13(4):866-74
references: 11912245
references: J Biol Chem. 2004 Apr 2;279(14):13293-6
references: 14966140
references: J Physiol. 2004 Jun 15;557(Pt 3):719-31
references: 15090606
references: J Biol Chem. 2004 Oct 22;279(43):44522-32
references: 15322102
references: Kidney Int. 1974 Apr;5(4):261-70
references: 4853933
references: Am J Physiol. 1980 Nov;239(5):F496-506
references: 6159793
references: Biochem J. 1984 Nov 1;223(3):803-7
references: 6508742
references: Biochim Biophys Acta. 1985 Mar 28;814(1):23-34
references: 3978098
references: Annu Rev Physiol. 1985;47:127-41
references: 3888071
references: Biochim Biophys Acta. 1986 Sep 11;860(3):632-40
references: 3741867
references: Biochim Biophys Acta. 1988 Mar 3;938(3):345-52
references: 3349069
references: Am J Physiol. 1989 Jul;257(1 Pt 2):R102-8
references: 2750954
references: Am J Physiol. 1993 Apr;264(4 Pt 1):C761-82
references: 8476015
references: Am J Physiol. 1999 May;276(5 Pt 2):F658-65
references: 10330047
references: Biochem Soc Trans. 2005 Feb;33(Pt 1):237-40
references: 15667316
references: Biochem J. 2005 May 15;388(Pt 1):309-16
references: 15651982
references: Biochem J. 2005 Dec 15;392(Pt 3):655-64
references: 16104846
references: Kidney Int. 2006 Feb;69(3):495-503
references: 16514432
references: Placenta. 2006 Jun-Jul;27(6-7):550-9
references: 16129486
references: Pharm Res. 2006 Jun;23(6):1209-16
references: 16729224
references: J Neurochem. 2006 Jul;98(1):279-88
references: 16805814
references: J Biol Chem. 2006 Sep 15;281(37):26769-73
references: 16873376
references: J Biol Chem. 2007 Apr 20;282(16):11996-2009
references: 17255103