title: Properties and regulation of glutamine transporter SN1 by protein kinases SGK and PKB.
abstract: The amino acid transporter SN1 with substrate specificity identical to the amino acid transport system N is expressed mainly in astrocytes and hepatocytes where it accomplishes Na(+)-coupled glutamine uptake and efflux. To characterize properties and regulation of SN1, substrate-induced currents and/or radioactive glutamine uptake were determined in Xenopus oocytes injected with cRNA encoding SN1, the ubiquitin ligase Nedd4-2, and/or the constitutively active serum and glucocorticoid inducible kinase S422DSGK1, its isoform SGK3, and the constitutively active protein kinase B T308D,S473DPKB. The substrate-induced currents were enhanced by increasing glutamine and/or Na(+) concentrations, hyperpolarization, and alkalinization (pH 8.0). They were inhibited by acidification (pH 6.0). Coexpression of Nedd4-2 downregulated SN1-mediated transport, an effect reversed by coexpression of S422DSGK1, SGK3, and T308D,S473DPKB. It is concluded that SN1 is a target for the ubiquitin ligase Nedd4-2, which is inactivated by the serum and glucocorticoid inducible kinase SGK1, its isoform SGK3, and protein kinase B.
authors.affiliation: Department of Physiology I, University of Tübingen, Gmelinstr. 5, D-72076, Tübingen, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Boehmer
authors.forename: Ferah
authors.initials: F
authors.lastname: Okur
authors.forename: Iwan
authors.initials: I
authors.lastname: Setiawan
authors.forename: Stefan
authors.initials: S
authors.lastname: Bröer
authors.forename: F
authors.initials: F
authors.lastname: Lang
mesh_terms: D026921:Amino Acid Transport Systems, Neutral; D000818:Animals; D002135:Calcium-Binding Proteins; D056827:Endosomal Sorting Complexes Required for Transport; D005260:Female; D005973:Glutamine / Q000378:metabolism; D006801:Humans; D017874:Immediate-Early Proteins; D066298:In Vitro Techniques; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D008025:Ligases / Q000235:genetics / Q000378:metabolism; D008564:Membrane Potentials; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D000075702:Nedd4 Ubiquitin Protein Ligases; D009687:Nuclear Proteins; D009865:Oocytes / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D018075:RNA, Complementary / Q000235:genetics; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D013379:Substrate Specificity; D044767:Ubiquitin-Protein Ligases; D029867:Xenopus Proteins; D014982:Xenopus laevis; D000099184:Serum-Glucocorticoid Regulated Kinases
chemical_list: D026921:Amino Acid Transport Systems, Neutral; D002135:Calcium-Binding Proteins; D056827:Endosomal Sorting Complexes Required for Transport; D005973:Glutamine; D017874:Immediate-Early Proteins; D007527:Isoenzymes; D008025:Ligases; D026901:Membrane Transport Proteins; D000075702:Nedd4 Ubiquitin Protein Ligases; D009687:Nuclear Proteins; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D018075:RNA, Complementary; D011994:Recombinant Proteins; D044767:Ubiquitin-Protein Ligases; D029867:Xenopus Proteins; D000099184:Serum-Glucocorticoid Regulated Kinases; C403222:system N protein 1; C000618482:Nedd4 protein, Xenopus; C000618483:Nedd4 protein, human; C000618485:Nedd4L protein, human; C000618460:nedd4l protein, Xenopus