Synip phosphorylation does not regulate insulin-stimulated GLUT4 translocation

Biochem Biophys Res Commun. 2005 Jul 8;332(3):880-4. doi: 10.1016/j.bbrc.2005.05.027.


Insulin causes the rapid translocation of the glucose transporter GLUT4 from intracellular sites to the plasma membrane in fat and muscle cells. There is considerable evidence that the signaling to this trafficking process is downstream of the insulin-activated protein kinase Akt. One Akt substrate that connects signaling to trafficking is a 160 kDa GTPase activating protein for Rabs. Another potential connecting substrate is the protein Synip, which associates with the SNARE syntaxin4. A recent study presents evidence that Akt phosphorylates Synip on serine 99, at least in vitro, and proposes that this phosphorylation enables GLUT4 translocation by causing the dissociation of Synip from syntaxin4. In the present study we show that marked overexpression of Synip mutant S99A, which lacks this phosphorylation site, has no effect on insulin-stimulated GLUT4 translocation in 3T3-L1 adipocytes. This finding is strong evidence that phosphorylation of Synip on serine 99 is not required for GLUT4 translocation.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 3T3-L1 Cells
  • Adipocytes / drug effects
  • Adipocytes / metabolism
  • Amino Acid Substitution
  • Animals
  • Binding Sites
  • Biological Transport, Active / drug effects
  • Cell Membrane / metabolism
  • Gene Expression
  • Glucose Transporter Type 4
  • Insulin / pharmacology*
  • Membrane Proteins / metabolism
  • Mice
  • Monosaccharide Transport Proteins / genetics
  • Monosaccharide Transport Proteins / metabolism*
  • Muscle Proteins / genetics
  • Muscle Proteins / metabolism*
  • Mutagenesis, Site-Directed
  • Phosphorylation
  • Protein-Serine-Threonine Kinases / metabolism
  • Proto-Oncogene Proteins / metabolism
  • Proto-Oncogene Proteins c-akt
  • Qa-SNARE Proteins
  • Recombinant Fusion Proteins / chemistry
  • Recombinant Fusion Proteins / genetics
  • Recombinant Fusion Proteins / metabolism
  • Serine / chemistry
  • Signal Transduction
  • Transfection
  • Vesicular Transport Proteins / chemistry*
  • Vesicular Transport Proteins / genetics
  • Vesicular Transport Proteins / metabolism*


  • Glucose Transporter Type 4
  • Insulin
  • Membrane Proteins
  • Monosaccharide Transport Proteins
  • Muscle Proteins
  • Proto-Oncogene Proteins
  • Qa-SNARE Proteins
  • Recombinant Fusion Proteins
  • Slc2a4 protein, mouse
  • Stxbp4 protein, mouse
  • Vesicular Transport Proteins
  • Serine
  • Protein-Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-akt