Bimodal regulation of FoxO3 by AKT and 14-3-3

Biochim Biophys Acta. 2011 Aug;1813(8):1453-64. doi: 10.1016/j.bbamcr.2011.05.001. Epub 2011 May 19.


FoxO3 is a member of FoxO family transcription factors that mediate cellular functions downstream of AKT. FoxO3 phosphorylation by AKT generates binding sites for 14-3-3, which in-turn regulates FoxO3 transcriptional activity and localization. We examine here the functional significance of AKT-FoxO3 interaction and further detail the mechanistic aspects of FoxO3 regulation by AKT and 14-3-3. Our data show that AKT overexpression increases the steady-state levels of FoxO3 protein in a manner dependent on AKT activity and its ability to bind FoxO3. Characterization of the AKT-FoxO3 interaction shows that the three AKT phosphorylation-site-recognition motifs (RxRxxS/T) present on FoxO3, which are required for FoxO3 phosphorylation, are dispensable for AKT binding, suggesting that AKT has a docking point on FoxO3 distinct from the phosphorylation-recognition motifs. Development of a FoxO3 mutant deficient in 14-3-3 binding (P34A), which can be phosphorylated by AKT, established that 14-3-3 binding and not AKT phosphorylation per se controls FoxO3 transcriptional activity. Intriguingly, 14-3-3 binding was found to stabilize FoxO3 by inhibiting its dephosphorylation and degradation rates. Collectively, our data support a model where both AKT and 14-3-3 positively regulate FoxO3 in addition to their established negative roles and that 14-3-3 availability could dictate the fate of phosphorylated FoxO3 toward degradation or recycling.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • 14-3-3 Proteins / chemistry
  • 14-3-3 Proteins / genetics
  • 14-3-3 Proteins / metabolism*
  • Binding Sites
  • Cell Line
  • Forkhead Box Protein O3
  • Forkhead Transcription Factors / chemistry
  • Forkhead Transcription Factors / genetics
  • Forkhead Transcription Factors / metabolism*
  • Hep G2 Cells
  • Humans
  • Models, Biological
  • Mutagenesis, Site-Directed
  • Phosphorylation
  • Protein Interaction Domains and Motifs
  • Proto-Oncogene Proteins c-akt / chemistry
  • Proto-Oncogene Proteins c-akt / genetics
  • Proto-Oncogene Proteins c-akt / metabolism*
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism


  • 14-3-3 Proteins
  • FOXO3 protein, human
  • Forkhead Box Protein O3
  • Forkhead Transcription Factors
  • Recombinant Proteins
  • Proto-Oncogene Proteins c-akt