Akt2 phosphorylates Synip to regulate docking and fusion of GLUT4-containing vesicles.
We have identified an unusual potential dual Akt/protein kinase B consensus phosphorylation motif in the protein Synip (RxKxRS(97)xS(99)). Surprisingly, serine 97 is not appreciably phosphorylated, whereas serine 99 is only a specific substrate for Akt2 but not Akt1 or Akt3. Although wild-type Synip (WT-Synip) undergoes an insulin-stimulated dissociation from Syntaxin4, the Synip serine 99 to phenylalanine mutant (S99F-Synip) is resistant to Akt2 phosphorylation and fails to display insulin-stimulated Syntaxin4 dissociation. Furthermore, overexpression of WT-Synip in 3T3L1 adipocytes had no effect on insulin-stimulated recruitment of glucose transporter 4 (GLUT4) to the plasma membrane, whereas overexpression of S99F-Synip functioned in a dominant-interfering manner by preventing insulin-stimulated GLUT4 recruitment and plasma membrane fusion. These data demonstrate that insulin activation of Akt2 specifically regulates the docking/fusion step of GLUT4-containing vesicles at the plasma membrane through the regulation of Synip phosphorylation and Synip-Syntaxin4 interaction.
Yamada
Eijiro
E
Department of Medicine and Molecular Science, Gunma University Graduate School of Medicine, Maebashi, Gunma, 371-8511, Japan.
Okada
Shuichi
S
Saito
Tsugumichi
T
Ohshima
Kihachi
K
Sato
Minoru
M
Tsuchiya
Takafumi
T
Uehara
Yutaka
Y
Shimizu
Hiroyuki
H
Mori
Masatomo
M
D016475:3T3 Cells; D017667:Adipocytes / Q000187:drug effects / Q000378:metabolism; D000818:Animals; D000911:Antibodies, Monoclonal / Q000378:metabolism; D015153:Blotting, Western; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D003847:Deoxyglucose / Q000378:metabolism; D051275:Glucose Transporter Type 4; D049452:Green Fluorescent Proteins / Q000378:metabolism; D007328:Insulin / Q000378:metabolism; D007700:Kinetics; D008561:Membrane Fusion; D051379:Mice; D018613:Microscopy, Confocal; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D009124:Muscle Proteins / Q000378:metabolism*; D010766:Phosphorylation; D011233:Precipitin Tests; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D013997:Time Factors; D022161:Transport Vesicles / Q000378:metabolism*; D033921:Vesicular Transport Proteins / Q000378:metabolism*
D000911:Antibodies, Monoclonal; D051275:Glucose Transporter Type 4; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D011518:Proto-Oncogene Proteins; C495693:Slc2a4 protein, mouse; C120000:Stxbp4 protein, mouse; D033921:Vesicular Transport Proteins; D049452:Green Fluorescent Proteins; D003847:Deoxyglucose; C494922:Akt2 protein, mouse; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt