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.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Amino Acid Transport Systems, Neutral*
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Animals
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Calcium-Binding Proteins*
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Endosomal Sorting Complexes Required for Transport
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Female
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Glutamine / metabolism
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Humans
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Immediate-Early Proteins
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In Vitro Techniques
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Isoenzymes / genetics
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Isoenzymes / metabolism
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Kinetics
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Ligases / genetics
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Ligases / metabolism
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Membrane Potentials
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Membrane Transport Proteins / genetics
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Membrane Transport Proteins / metabolism*
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Nedd4 Ubiquitin Protein Ligases
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Nuclear Proteins*
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Oocytes / metabolism
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Protein Serine-Threonine Kinases / genetics
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Protein Serine-Threonine Kinases / metabolism*
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Proto-Oncogene Proteins / genetics
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Proto-Oncogene Proteins / metabolism*
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Proto-Oncogene Proteins c-akt
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RNA, Complementary / genetics
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Recombinant Proteins / genetics
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Recombinant Proteins / metabolism
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Substrate Specificity
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Ubiquitin-Protein Ligases*
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Xenopus Proteins
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Xenopus laevis
Substances
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Amino Acid Transport Systems, Neutral
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Calcium-Binding Proteins
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Endosomal Sorting Complexes Required for Transport
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Immediate-Early Proteins
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Isoenzymes
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Membrane Transport Proteins
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Nuclear Proteins
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Proto-Oncogene Proteins
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RNA, Complementary
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Recombinant Proteins
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Xenopus Proteins
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system N protein 1
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Glutamine
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Nedd4 Ubiquitin Protein Ligases
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Nedd4 protein, Xenopus
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Nedd4 protein, human
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Nedd4L protein, human
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nedd4l protein, Xenopus
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Ubiquitin-Protein Ligases
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Protein Serine-Threonine Kinases
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Proto-Oncogene Proteins c-akt
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serum-glucocorticoid regulated kinase
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Ligases