Phosphorylation of the exocyst protein Exo84 by TBK1 promotes insulin-stimulated GLUT4 trafficking

Maeran Uhm, Merlijn Bazuine, Peng Zhao, Shian Huey Chiang, Tingting Xiong, Sheelarani Karunanithi, Louise Chang, Alan R. Saltiel

Research output: Contribution to journalArticlepeer-review

26 Scopus citations

Abstract

Insulin stimulates glucose uptake through the translocation of the glucose transporter GLUT4 to the plasma membrane. The exocyst complex tethers GLUT4-containing vesicles to the plasma membrane, a process that requires the binding of the G protein (heterotrimeric guanine nucleotide-binding protein) RalA to the exocyst complex. We report that upon activation of RalA, the protein kinase TBK1 phosphorylated the exocyst subunit Exo84. Knockdown of TBK1 blocked insulin-stimulated glucose uptake and GLUT4 translocation; knockout of TBK1 in adipocytes blocked insulin-stimulated glucose uptake; and ectopic overexpression of a kinase-inactive mutant of TBK1 reduced insulin-stimulated glucose uptake in 3T3-L1 adipocytes. The phosphorylation of Exo84 by TBK1 reduced its affinity for RalA and enabled its release from the exocyst. Overexpression of a kinase-inactive mutant of TBK1 blocked the dissociation of the TBK1/RalA/exocyst complex, and treatment of 3T3-L1 adipocytes with specific inhibitors of TBK1 reduced the rate of complex dissociation. Introduction of phosphorylation-mimicking or nonphosphorylatable mutant forms of Exo84 blocked insulin-stimulated GLUT4 translocation. Thus, these data indicate that TBK1 controls GLUT4 vesicle engagement and disengagement from the exocyst, suggesting that exocyst components not only constitute a tethering complex for the GLUT4 vesicle but also act as "gatekeepers" controlling vesicle fusion at the plasma membrane.

Original languageEnglish (US)
Article numbereaah5085
JournalScience signaling
Volume10
Issue number471
DOIs
StatePublished - Mar 21 2017
Externally publishedYes

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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