title: Genetic variants of human organic anion transporter 4 demonstrate altered transport of endogenous substrates.
abstract: Apical reabsorption from the urine has been shown to be important for such processes as the maintenance of critical metabolites in the blood and the excretion of nephrotoxic compounds. The solute carrier (SLC) transporter OAT4 (SLC22A11) is expressed on the apical membrane of renal proximal tubule cells and is known to mediate the transport of a variety of xenobiotic and endogenous organic anions. Functional characterization of genetic variants of apical transporters thought to mediate reabsorption, such as OAT4, may provide insight into the genetic factors influencing the complex pathways involved in drug elimination and metabolite reclamation occurring in the kidney. Naturally occurring genetic variants of OAT4 were identified in public databases and by resequencing DNA samples from 272 individuals comprising 4 distinct ethnic groups. Nine total nonsynonymous variants were identified and functionally assessed using uptake of three radiolabeled substrates. A nonsense variant, R48Stop, and three other variants (R121C, V155G, and V155M) were found at frequencies of at least 2% in an ethnic group specific fashion. The L29P, R48Stop, and H469R variants displayed a complete loss of function, and kinetic analysis identified a reduced V(max) in the common nonsynonymous variants. Plasma membrane levels of OAT4 protein were absent or reduced in the nonfunctional variants, providing a mechanistic reason for the observed loss of function. Characterization of the genetic variants of reabsorptive transporters such as OAT4 is an important step in understanding variability in tubular reabsorption with important implications in innate homeostatic processes and drug disposition.
authors.affiliation: Dept. of Bioengineering and Therapeutics Sciences, University of California, San Francisco, California 94143-2911, USA.
authors.forename: James E
authors.initials: JE
authors.lastname: Shima
authors.forename: Takafumi
authors.initials: T
authors.lastname: Komori
authors.forename: Travis R
authors.initials: TR
authors.lastname: Taylor
authors.forename: Doug
authors.initials: D
authors.lastname: Stryke
authors.forename: Michiko
authors.initials: M
authors.lastname: Kawamoto
authors.forename: Susan J
authors.initials: SJ
authors.lastname: Johns
authors.forename: Elaine J
authors.initials: EJ
authors.lastname: Carlson
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Ferrin
authors.forename: Kathleen M
authors.initials: KM
authors.lastname: Giacomini
mesh_terms: D001741:Black or African American / Q000235:genetics; D000595:Amino Acid Sequence; D001213:Asian / Q000235:genetics; D001692:Biological Transport / Q000502:physiology; D002478:Cells, Cultured; D004247:DNA / Q000235:genetics*; D014644:Genetic Variation / Q000502:physiology*; D006801:Humans; D007668:Kidney / Q000502:physiology*; D017058:Mexican Americans / Q000235:genetics; D008969:Molecular Sequence Data; D029362:Organic Anion Transporters, Sodium-Independent / Q000235:genetics* / Q000502:physiology*; D014162:Transfection; D044465:White People / Q000235:genetics
chemical_list: D029362:Organic Anion Transporters, Sodium-Independent; C427207:SLC22A11 protein, human; D004247:DNA