title: PDZK1 directly regulates the function of organic cation/carnitine transporter OCTN2.
abstract: Urinary excretion of cationic xenobiotics is believed to be mediated by organic cation transporter (OCT and OCTN) families expressed on both basolateral and brush-border membranes of renal tubules, although the molecular mechanisms for targeting of these transporters to each membrane are poorly understood. Here, to examine the regulatory mechanisms for cell-surface expression and function of these transporters, we evaluated the interaction of these transporters with several PDZ proteins. A pull-down study using recombinant C-terminal proteins of OCTs and OCTNs identified a specific interaction of apical transporters OCTN1 and OCTN2, but not basolateral transporters OCT1 and OCT2, with PDZK1, intestinal and kidney-enriched PDZ protein, and Na+/H+ exchanger regulatory factor 2 (also called E3KARP, SIP-1, or TKA-1). Both yeast two-hybrid and pull-down studies suggested a requirement of the last four amino acids in OCTN1 and OCTN2 for the interaction. The interaction of PDZK1 with the C terminus of OCTN2 was also confirmed in a pull-down study using kidney brush-border membrane vesicles. Immunohistochemical analysis revealed that both PDZK1 and OCTN2 are colocalized in brush-border membranes of the kidney. Finally, double transfection of OCTN2 with PDZK1 stimulated the uptake by OCTN2 of its endogenous substrate carnitine, and this increase could be accounted for by the 6-fold increase in transport capacity. Such an increase was not observed for OCTN2 with deletion of the last four amino acids. Biotinylation study of surface proteins revealed minimal effect of PDZK1 on cell-surface expression of OCTN2. The present findings are the first to identify PDZK1 as a functional regulator of OCTN2 through direct interaction with the C terminus.
authors.affiliation: Division of Pharmaceutical Sciences, Graduate School of Natural Science and Technology, Kanazawa University, Kakuma, Kanazawa, Ishikawa 920-1192, Japan.
authors.forename: Yukio
authors.initials: Y
authors.lastname: Kato
authors.forename: Yoshimichi
authors.initials: Y
authors.lastname: Sai
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Yoshida
authors.forename: Chizuru
authors.initials: C
authors.lastname: Watanabe
authors.forename: Tadayoshi
authors.initials: T
authors.lastname: Hirata
authors.forename: Akira
authors.initials: A
authors.lastname: Tsuji
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D003001:Cloning, Molecular; D005786:Gene Expression Regulation; D006801:Humans; D007668:Kidney; D007700:Kinetics; D008297:Male; D008565:Membrane Proteins / Q000235:genetics / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D027701:Organic Cation Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D000075102:Organic Cation Transporter 2; D010446:Peptide Fragments / Q000737:chemistry; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics; D000074058:Solute Carrier Family 22 Member 5
chemical_list: D008565:Membrane Proteins; D027701:Organic Cation Transport Proteins; D000075102:Organic Cation Transporter 2; D010446:Peptide Fragments; D011993:Recombinant Fusion Proteins; C492020:SLC22A5 protein, human; C491012:Slc22a2 protein, mouse; D000074058:Solute Carrier Family 22 Member 5