title: Novel cystine transporter in renal proximal tubule identified as a missing partner of cystinuria-related plasma membrane protein rBAT/SLC3A1.
abstract: Heterodimeric amino acid transporters play crucial roles in epithelial transport, as well as in cellular nutrition. Among them, the heterodimer of a membrane protein b(0,+)AT/SLC7A9 and its auxiliary subunit rBAT/SLC3A1 is responsible for cystine reabsorption in renal proximal tubules. The mutations in either subunit cause cystinuria, an inherited amino aciduria with impaired renal reabsorption of cystine and dibasic amino acids. However, an unsolved paradox is that rBAT is highly expressed in the S3 segment, the late proximal tubules, whereas b(0,+)AT expression is highest in the S1 segment, the early proximal tubules, so that the presence of an unknown partner of rBAT in the S3 segment has been proposed. In this study, by means of coimmunoprecipitation followed by mass spectrometry, we have found that a membrane protein AGT1/SLC7A13 is the second partner of rBAT. AGT1 is localized in the apical membrane of the S3 segment, where it forms a heterodimer with rBAT. Depletion of rBAT in mice eliminates the expression of AGT1 in the renal apical membrane. We have reconstituted the purified AGT1-rBAT heterodimer into proteoliposomes and showed that AGT1 transports cystine, aspartate, and glutamate. In the apical membrane of the S3 segment, AGT1 is suggested to locate itself in close proximity to sodium-dependent acidic amino acid transporter EAAC1 for efficient functional coupling. EAAC1 is proposed to take up aspartate and glutamate released into luminal fluid by AGT1 due to its countertransport so that preventing the urinary loss of aspartate and glutamate. Taken all together, AGT1 is the long-postulated second cystine transporter in the S3 segment of proximal tubules and a possible candidate to be involved in isolated cystinuria.
authors.affiliation: Department of Bio-System Pharmacology, Graduate School of Medicine, Osaka University, Suita, Osaka 565-0871, Japan;
authors.forename: Shushi
authors.initials: S
authors.lastname: Nagamori
authors.affiliation: Department of Bio-System Pharmacology, Graduate School of Medicine, Osaka University, Suita, Osaka 565-0871, Japan;
authors.forename: Pattama
authors.initials: P
authors.lastname: Wiriyasermkul
authors.affiliation: Institute for Research in Biomedicine Barcelona, The Barcelona Institute of Science and Technology, 08028 Barcelona, Spain; Molecular Genetics Laboratory, Institut d'Investigació Biomèdica de Bellvitge, L'Hospitalet de Llobregat, 08908 Barcelona, Spain; Spanish Biomedical Research Center in Rare Diseases (CIBERER), 08028 Barcelona, Spain;
authors.forename: Meritxell Espino
authors.initials: ME
authors.lastname: Guarch
authors.affiliation: Department of Bio-System Pharmacology, Graduate School of Medicine, Osaka University, Suita, Osaka 565-0871, Japan;
authors.forename: Hirohisa
authors.initials: H
authors.lastname: Okuyama
authors.affiliation: Department of Bio-System Pharmacology, Graduate School of Medicine, Osaka University, Suita, Osaka 565-0871, Japan;
authors.forename: Saya
authors.initials: S
authors.lastname: Nakagomi
authors.affiliation: Department of Bio-System Pharmacology, Graduate School of Medicine, Osaka University, Suita, Osaka 565-0871, Japan;
authors.forename: Kenjiro
authors.initials: K
authors.lastname: Tadagaki
authors.affiliation: Department of Bio-System Pharmacology, Graduate School of Medicine, Osaka University, Suita, Osaka 565-0871, Japan;
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Nishinaka
authors.affiliation: Institute for Research in Biomedicine Barcelona, The Barcelona Institute of Science and Technology, 08028 Barcelona, Spain; Spanish Biomedical Research Center in Rare Diseases (CIBERER), 08028 Barcelona, Spain;
authors.forename: Susanna
authors.initials: S
authors.lastname: Bodoy
authors.affiliation: Department of Bio-System Pharmacology, Graduate School of Medicine, Osaka University, Suita, Osaka 565-0871, Japan;
authors.forename: Kazuaki
authors.initials: K
authors.lastname: Takafuji
authors.affiliation: Department of Bio-System Pharmacology, Graduate School of Medicine, Osaka University, Suita, Osaka 565-0871, Japan;
authors.forename: Suguru
authors.initials: S
authors.lastname: Okuda
authors.affiliation: Department of Bio-Informational Pharmacology, Medical Research Institute, Tokyo Medical and Dental University, Tokyo 113-8510, Japan;
authors.forename: Junko
authors.initials: J
authors.lastname: Kurokawa
authors.affiliation: Department of Bio-System Pharmacology, Graduate School of Medicine, Osaka University, Suita, Osaka 565-0871, Japan;
authors.forename: Ryuichi
authors.initials: R
authors.lastname: Ohgaki
authors.affiliation: Molecular Genetics Laboratory, Institut d'Investigació Biomèdica de Bellvitge, L'Hospitalet de Llobregat, 08908 Barcelona, Spain; Spanish Biomedical Research Center in Rare Diseases (CIBERER), 08028 Barcelona, Spain; Genetic Unit, Department of Physiological Sciences II, Universitat de Barcelona, 08908 Barcelona, Spain;
authors.forename: Virginia
authors.initials: V
authors.lastname: Nunes
authors.affiliation: Institute for Research in Biomedicine Barcelona, The Barcelona Institute of Science and Technology, 08028 Barcelona, Spain; Spanish Biomedical Research Center in Rare Diseases (CIBERER), 08028 Barcelona, Spain; Department of Biochemistry and Molecular Biology, Facultat de Biologia, University of Barcelona, 08028 Barcelona, Spain.
authors.forename: Manuel
authors.initials: M
authors.lastname: Palacín
authors.affiliation: Department of Bio-System Pharmacology, Graduate School of Medicine, Osaka University, Suita, Osaka 565-0871, Japan; ykanai@pharma1.med.osaka-u.ac.jp.
authors.forename: Yoshikatsu
authors.initials: Y
authors.lastname: Kanai
mesh_terms: D000595:Amino Acid Sequence; D026905:Amino Acid Transport Systems / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D026923:Amino Acid Transport Systems, Basic / Q000378:metabolism*; D026921:Amino Acid Transport Systems, Neutral / Q000378:metabolism*; D000818:Animals; D000906:Antibodies / Q000378:metabolism; D015153:Blotting, Western; D002462:Cell Membrane / Q000378:metabolism*; D003555:Cystinuria / Q000378:metabolism*; D050580:Excitatory Amino Acid Transporter 3 / Q000378:metabolism; D005260:Female; D057809:HEK293 Cells; D006801:Humans; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D007668:Kidney / Q000378:metabolism; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D008297:Male; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D011485:Protein Binding; D055503:Protein Multimerization; D011510:Proteolipids / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020218:Response Elements / Q000235:genetics
chemical_list: D026905:Amino Acid Transport Systems; D026923:Amino Acid Transport Systems, Basic; D026921:Amino Acid Transport Systems, Neutral; D000906:Antibodies; D050580:Excitatory Amino Acid Transporter 3; D011510:Proteolipids; D012333:RNA, Messenger; C493399:Slc1a1 protein, mouse; C489858:Slc3a1 protein, mouse; C459184:Slc7a13 protein, mouse; C020485:proteoliposomes
keywords: amino acid transporter; cystine reabsorption; cystinuria; kidney