title: Expression of SLC2A9 isoforms in the kidney and their localization in polarized epithelial cells.
abstract: BACKGROUND
  Many genome-wide association studies pointed out that SLC2A9 gene, which encodes a voltage-driven urate transporter, SLC2A9/GLUT9 (a.k.a. URATv1), as one of the most influential genes for serum urate levels. SLC2A9 is reported to encode two splice variants: SLC2A9-S (512 amino acids) and SLC2A9-L (540 amino acids), only difference being at their N-termini. We investigated isoform-specific localization of SLC2A9 in the human kidney and role of N-terminal amino acids in differential sorting in vitro.
  
  
  RESULTS
  Isoform specific antibodies against SLC2A9 were developed and human kidney sections were stained. SLC2A9-S was expressed in the apical side of the collecting duct while SLC2A9-L was expressed in the basolateral side of the proximal tubule. GFP fused SLC2A9s were expressed in MDCK cells and intracellular localization was observed. SLC2A9-S was expressed at both apical and basolateral membranes, whereas SLC2A9-L was expressed only at the basolateral membrane. Although SLC2A9-L has a putative di-leucine motif at 33th and 34th leucine, deletion of the motif or replacement of leucine did not affect its subcellular localization. When up to 16 amino acids were removed from the N-terminal of SLC2A9-S or when up to 25 amino acids were removed from the N-terminal of SLC2A9-L, there was no change in their sorting. Deletion of 20 amino acids from SLC2A9-S was not expressed in the cell. More than 30 amino acids deletion from SLC2A9-L resulted in expression at both apical and basolateral membranes as well as in the lysosome. When amino acids from 25th and 30th were changed to alanine in SLC2A9-L, expression pattern was the same as wild-type.
  
  
  CONCLUSIONS
  SLC2A9-L was expressed in the basolateral membrane of kidney proximal tubules in humans and this isoform is likely to responsible for urate reabsorption. N-terminal amino acids unique to each isoform played an important role in protein stability and trafficking.
authors.affiliation: Department of Pharmacology and Toxicology, Kyorin University School of Medicine, Mitaka, Tokyo, Japan.
authors.forename: Toru
authors.initials: T
authors.lastname: Kimura
authors.affiliation: Department of Pharmacology and Toxicology, Kyorin University School of Medicine, Mitaka, Tokyo, Japan.
authors.forename: Michi
authors.initials: M
authors.lastname: Takahashi
authors.affiliation: Department of Pediatrics, Kyorin University School of Medicine, Mitaka, Tokyo, Japan.
authors.forename: Kunimasa
authors.initials: K
authors.lastname: Yan
authors.affiliation: Department of Pharmacology and Toxicology, Kyorin University School of Medicine, Mitaka, Tokyo, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Sakurai
mesh_terms: D017398:Alternative Splicing; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D004847:Epithelial Cells / Q000378:metabolism*; D015870:Gene Expression; D051246:Glucose Transport Proteins, Facilitative / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D006801:Humans; D042541:Intracellular Space / Q000378:metabolism; D007668:Kidney / Q000378:metabolism*; D008969:Molecular Sequence Data; D054730:Protein Interaction Domains and Motifs; D020033:Protein Isoforms; D021381:Protein Transport; D017384:Sequence Deletion
chemical_list: D051246:Glucose Transport Proteins, Facilitative; D020033:Protein Isoforms; C411811:SLC2A9 protein, human