Regulation of the glutamate transporter EAAT4 by PIKfyve.
The excitatory amino-acid transporter EAAT4 (SLC1A6), a Na(+),glutamate cotransporter expressed mainly in Purkinje cells, serves to clear glutamate from the synaptic cleft. EAAT4 activity is stimulated by the serum and glucocorticoid inducible kinase SGK1. SGK1-dependent regulation of the Na(+),glucose transporter SGLT1 (SLC5A1) and the creatine transporter CreaT (SLC6A8) has recently been shown to involve the mammalian phosphatidylinositol-3-phosphate-5-kinase PIKfyve (PIP5K3). The present experiments thus explored whether SGK1-dependent EAAT4-regulation similarly involves PIKfyve. In Xenopus oocytes expressing EAAT4, but not in water injected oocytes, glutamate induced a current which was significantly enhanced by coexpression of PIKfyve and SGK1. The glutamate induced current in Xenopus oocytes coexpressing EAAT4 and both, PIKfyve and SGK1, was significantly larger than the current in Xenopus oocytes expressing EAAT4 together with either kinase alone. Coexpression of the inactive SGK1 mutant (K127N)SGK1 did not significantly alter glutamate induced current in EAAT4-expressing Xenopus oocytes and abolished the stimulation of glutamate induced current by coexpression of PIKfyve. The stimulating effect of PIKfyve was abrogated by replacement of the serine with alanine in the SGK consensus sequence ((S318A)PIKfyve). Furthermore, coexpression of (S318A)PIKfyve significantly blunted the stimulating effect of SGK1 on EAAT4 activity. The observations disclose that PIKfyve indeed participates in the regulation of EAAT4.
Alesutan
Ioana S
IS
Department of Physiology I, University of Tübingen, D-72076 Tübingen, Germany.
Ureche
Oana N
ON
Laufer
Joerg
J
Klaus
Fabian
F
Zürn
Agathe
A
Lindner
Ricco
R
Strutz-Seebohm
Nathalie
N
Tavaré
Jeremy M
JM
Boehmer
Christoph
C
Palmada
Monica
M
Lang
Undine E
UE
Seebohm
Guiscard
G
Lang
Florian
F
D000818:Animals; D004594:Electrophysiology; D050581:Excitatory Amino Acid Transporter 4 / Q000378:metabolism*; D018698:Glutamic Acid / Q000494:pharmacology; D006801:Humans; D017874:Immediate-Early Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D009865:Oocytes / Q000378:metabolism; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D051381:Rats; D014982:Xenopus laevis / Q000378:metabolism; D000099184:Serum-Glucocorticoid Regulated Kinases
D050581:Excitatory Amino Acid Transporter 4; D018698:Glutamic Acid; D017874:Immediate-Early Proteins; D017853:Phosphotransferases (Alcohol Group Acceptor); D017346:Protein Serine-Threonine Kinases; D000099184:Serum-Glucocorticoid Regulated Kinases; C493389:Slc1a6 protein, rat; C544731:PIKfyve protein, rat