title: Up-regulation of amino acid transporter SLC6A19 activity and surface protein abundance by PKB/Akt and PIKfyve.
abstract: BACKGROUND
  The amino acid transporter B0AT1 (SLC6A19) accomplishes concentrative cellular uptake of neutral amino acids. SLC6A19 is stimulated by serum- &amp; glucocorticoid-inducible kinase (SGK) isoforms. SGKs are related to PKB/Akt isoforms, which also stimulate several amino acid transporters. PKB/Akt modulates glucose transport in part by phosphorylating and thus activating phosphatidylinositol-3-phosphate-5-kinase (PIKfyve), which fosters carrier protein insertion into the cell membrane. The present study explored whether PKB/Akt and/or PIKfyve stimulate SLC6A19.
  
  
  METHODS
  SLC6A19 was expressed in Xenopus oocytes with or without wild-type PKB/Akt or inactive (T308A/S473A)PKB/Akt without or with additional expression of wild-type PIKfyve or PKB/Akt-resistant (S318A)PIKfyve. Electrogenic amino acid transport was determined by dual electrode voltage clamping.
  
  
  RESULTS
  In SLC6A19-expressing oocytes but not in water-injected oocytes, the addition of the neutral amino acid L-leucine (2 mM) to the bath generated a current (I(le)), which was significantly increased following coexpression of PKB/Akt, but not by coexpression of (T308A/S473A)PKB/Akt. The effect of PKB/Akt was augmented by additional coexpression of PIKfyve but not of (S318A)PIKfyve. Coexpression of PKB/Akt enhanced the maximal transport rate without significantly modifying the affinity of the carrier. The decline of I(le) following inhibition of carrier insertion by brefeldin A (5 µM) was similar in the absence and presence of PKB/Akt indicating that PKB/Akt stimulated carrier insertion into rather than inhibiting carrier retrieval from the cell membrane.
  
  
  CONCLUSIONS
  PKB/Akt up-regulates SLC6A19 activity, which may foster amino acid uptake into PKB/Akt-expressing epithelial and tumor cells.
authors.affiliation: Department of Physiology I, University of Tübingen, Tübingen, Germany.
authors.forename: Evgenii
authors.initials: E
authors.lastname: Bogatikov
authors.forename: Carlos
authors.initials: C
authors.lastname: Munoz
authors.forename: Tatsiana
authors.initials: T
authors.lastname: Pakladok
authors.forename: Ioana
authors.initials: I
authors.lastname: Alesutan
authors.forename: Manzar
authors.initials: M
authors.lastname: Shojaiefard
authors.forename: Guiscard
authors.initials: G
authors.lastname: Seebohm
authors.forename: Michael
authors.initials: M
authors.lastname: Föller
authors.forename: Monica
authors.initials: M
authors.lastname: Palmada
authors.forename: Christoph
authors.initials: C
authors.lastname: Böhmer
authors.forename: Stefan
authors.initials: S
authors.lastname: Bröer
authors.forename: Florian
authors.initials: F
authors.lastname: Lang
mesh_terms: D026921:Amino Acid Transport Systems, Neutral / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D015870:Gene Expression; D006801:Humans; D007700:Kinetics; D007930:Leucine / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D021381:Protein Transport; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D015854:Up-Regulation; D014981:Xenopus
chemical_list: D026921:Amino Acid Transport Systems, Neutral; C491436:SLC6A19 protein, human; D019869:Phosphatidylinositol 3-Kinases; C492139:PIKFYVE protein, human; D051057:Proto-Oncogene Proteins c-akt; D007930:Leucine