title: Regulation of the glutamate transporter EAAT2 by PIKfyve.
abstract: The Na(+),glutamate cotransporter EAAT2 is expressed in astrocytes and clears glutamate from the synaptic cleft. EAAT2 dependent currrent is stimulated by the serum and glucocorticoid inducible kinase SGK1. Phosphorylation targets of SGK1 include the human phosphatidylinositol-3-phosphate-5-kinase PIKfyve (PIP5K3). Nothing is known, however, on the role of PIKfyve in the regulation of EAAT2. The present experiments thus explored, whether PIKfyve expression modifies EAAT2 dependent currrent and protein abundance in the cell membrane. In Xenopus oocytes expressing EAAT2 but not in water injected oocytes application of glutamate (2 mM) induced an inward current (I(glu)). Coexpression of either, SGK1 or PIKfyve, significantly enhanced I(glu) in EAAT2 expressing oocytes. I(glu) was significantly higher in Xenopus oocytes coexpressing EAAT2, SGK1 and PIKfyve than in Xenopus oocytes expressing EAAT2 and either, SGK1 or PIKfyve, alone. Additional coexpression of the inactive mutant of the serum and glucocorticoid inducible kinase (K127N)SGK1 did not significantly alter I(glu) in EAAT2 expressing oocytes and significantly decreased I(glu) in oocytes coexpressing EAAT2 together with PIKfyve. The stimulating effect of PIKfyve on I(glu) was abrogated by replacement of the serine in the SGK consensus sequence by alanine ((S318A)PIKfyve). Furthermore, additional coexpression of (S318A)PIKfyve virtually abolished I(glu) in Xenopus oocytes coexpressing SGK1 and EAAT2. Confocal microscopy reveals that PIKfyve enhances the EAAT2 protein abundance in the cell membrane. The observations disclose that PIKfyve indeed participates in the regulation of EAAT2.
authors.affiliation: Department of Physiology I, University of Tubingen, Germany.
authors.forename: Eva-Maria
authors.initials: EM
authors.lastname: Gehring
authors.forename: Agathe
authors.initials: A
authors.lastname: Zurn
authors.forename: Fabian
authors.initials: F
authors.lastname: Klaus
authors.forename: Joerg
authors.initials: J
authors.lastname: Laufer
authors.forename: Mentor
authors.initials: M
authors.lastname: Sopjani
authors.forename: Ricco
authors.initials: R
authors.lastname: Lindner
authors.forename: Nathalie
authors.initials: N
authors.lastname: Strutz-Seebohm
authors.forename: Jeremy M
authors.initials: JM
authors.lastname: Tavaré
authors.forename: Christoph
authors.initials: C
authors.lastname: Boehmer
authors.forename: Monica
authors.initials: M
authors.lastname: Palmada
authors.forename: Undine E
authors.initials: UE
authors.lastname: Lang
authors.forename: Guiscard
authors.initials: G
authors.lastname: Seebohm
authors.forename: Florian
authors.initials: F
authors.lastname: Lang
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D001253:Astrocytes / Q000378:metabolism; D055724:Electrophysiological Phenomena; D027342:Excitatory Amino Acid Transporter 2 / Q000378:metabolism*; D018698:Glutamic Acid / Q000494:pharmacology; D006801:Humans; D017874:Immediate-Early Proteins / Q000235:genetics / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D009865:Oocytes / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D014981:Xenopus; D000099184:Serum-Glucocorticoid Regulated Kinases
chemical_list: D027342:Excitatory Amino Acid Transporter 2; D018698:Glutamic Acid; D017874:Immediate-Early Proteins; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D000099184:Serum-Glucocorticoid Regulated Kinases; C492139:PIKFYVE protein, human