Tomosyn is a novel Akt substrate mediating insulin-dependent GLUT4 exocytosis

Int J Biochem Cell Biol. 2015 May;62:62-71. doi: 10.1016/j.biocel.2015.02.013. Epub 2015 Feb 25.

Abstract

Insulin triggers glucose uptake into skeletal muscle and adipose tissues by gaining the available number of glucose transporter 4 (GLUT4) on the cell surface. GLUT4-loaded vesicles are targeted to plasma membrane from the intracellular reservoir through multiple trafficking and fusion processes that are mainly regulated by Akt. However, it is still largely unknown how GLUT4 expression in the cell surface is promoted by insulin. In the present study, we identified tomosyn at Ser-783 as a possible Akt-substrate motif and examined whether the phosphorylation at Ser-783 is involved in the regulation of GLUT4 expression. Both Akt1 and Akt2 phosphorylated the wild-type tomosyn, but not the mutant tomosyn in which Ser-783 was replaced with Ala. Phosphorylation of tomosyn at Ser-783 was also observed in the intact cells by insulin stimulation, which was blocked by PI3K inhibitor, LY294002. In vitro pull-down assay showed that phosphorylation of tomosyn at Ser-783 by Akt inhibited the interaction with syntaxin 4. Insulin stimulation increased GLUT4 in the cell surface of CHO-K1 cells to promote glucose uptake, however exogenous expression of the mutant tomosyn attenuated the increase by insulin. These results suggest that Ser-783 of tomosyn is a target of Akt and is implicated in the interaction with syntaxin 4.

Keywords: Akt; Exocytosis; GLUT4; Phosphorylation; SNARE.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • CHO Cells
  • COS Cells
  • Cells, Cultured
  • Chlorocebus aethiops
  • Cricetinae
  • Cricetulus
  • Exocytosis* / drug effects
  • Exocytosis* / genetics
  • Glucose Transporter Type 4 / metabolism*
  • HEK293 Cells
  • Humans
  • Insulin / pharmacology*
  • Mice
  • Molecular Sequence Data
  • Nerve Tissue Proteins / metabolism
  • Nerve Tissue Proteins / physiology*
  • Oncogene Protein v-akt / metabolism*
  • Phosphorylation
  • R-SNARE Proteins / metabolism
  • R-SNARE Proteins / physiology*

Substances

  • Glucose Transporter Type 4
  • Insulin
  • Nerve Tissue Proteins
  • R-SNARE Proteins
  • STXBP5 protein, human
  • Oncogene Protein v-akt