title: Molecular cloning and characterization of NKT, a gene product related to the organic cation transporter family that is almost exclusively expressed in the kidney.
abstract: We have identified a gene product (NKT) encoding an apparently novel transcript that appears to be related to the organic ion transporter family and is expressed almost exclusively in the kidney. Analysis of the deduced 546-amino acid protein sequence indicates that NKT is a unique gene product which shares a similar transmembrane domain hydropathy profile as well as transporter-specific amino acid motifs with a variety of bacterial and mammalian nutrient transporters. Nevertheless, the overall homology of NKT to two recently cloned organic ion transport proteins (NLT and OCT-1) is significantly greater; together these three gene products may represent a new subgroup of transporters. The NKT was characterized further with respect to its tissue distribution and its expression during kidney development. A 2.5-kilobase transcript was found in kidney and at much lower levels in brain, but not in a number of other tissues. Studies on the embryonic kidney indicate that the NKT transcript is developmentally regulated with significant expression beginning at mouse gestational day 18 and rising just before birth, consistent with a role in differentiated kidney function. Moreover, in situ hybridization detected specific signals in mouse renal proximal tubules. NKT was mapped by linkage disequilibrium to mouse chromosome 19, the same site to which several mouse mutations localize, including that for osteochondrodystrophy (ocd). Although initial experiments in a Xenopus oocyte expression system failed to demonstrate transport of known substrates for OCT-1, the homology to OCT-1 and other transporters, along with the proximal tubule localization, raise the possibility that this gene may play a role in organic solute transport or drug elimination by the kidney.
authors.affiliation: Renal and Genetics Divisions, Department of Medicine, Harvard Medical School and Brigham and Women's Hospital, Boston, Massachusetts 02115, USA.
authors.forename: C E
authors.initials: CE
authors.lastname: Lopez-Nieto
authors.forename: G
authors.initials: G
authors.lastname: You
authors.forename: K T
authors.initials: KT
authors.lastname: Bush
authors.forename: E J
authors.initials: EJ
authors.lastname: Barros
authors.forename: D R
authors.initials: DR
authors.lastname: Beier
authors.forename: S K
authors.initials: SK
authors.lastname: Nigam
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics*; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D017403:In Situ Hybridization; D007668:Kidney / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics*; D051379:Mice; D008969:Molecular Sequence Data; D027362:Organic Anion Transport Protein 1; D027361:Organic Anion Transporters; D027702:Organic Cation Transporter 1; D018807:Polymorphism, Single-Stranded Conformational; D012995:Solubility
chemical_list: D002352:Carrier Proteins; D008565:Membrane Proteins; D027362:Organic Anion Transport Protein 1; D027361:Organic Anion Transporters; D027702:Organic Cation Transporter 1; C105033:Slc22a6 protein, mouse