Mechanism of activation of PKB/Akt by the protein phosphatase inhibitor calyculin A

Mercedes Pozuelo-Rubio, Nick R Leslie, Jane Murphy, Carol MacKintosh

Research output: Contribution to journalArticlepeer-review

5 Citations (Scopus)


The protein phosphatase inhibitor calyculin A activates PKB/Akt to ~50% of the activity induced by insulin-like growth factor 1 (IGF1) in HeLa cells promoting an evident increased phosphorylation of Ser473 despite the apparent lack of Thr308 phosphorylation of PKB. Nevertheless, calyculin A-induced activation of PKB seems to be dependent on basal levels of Thr308 phosphorylation, since a PDK1-dependent mechanism is required for calyculin A-dependent PKB activation by using embryonic stem cells derived from PDK1 wild-type and knockout mice. Data shown suggest that calyculin A-induced phosphorylation of Ser473 was largely blocked by LY294002 and SB-203580 inhibitors, indicating that both PI3-kinase/TORC2-dependent and SAPK2/p38-dependent protein kinases contributed to phosphorylation of Ser473 in calyculin A-treated cells. Additionally, our results suggest that calyculin A blocks the IGF1-dependent Thr308 phosphorylation and activation of PKB, likely due to an enhanced Ser612 phosphorylation of insulin receptor substrate 1 (IRS1), which can be inhibitory to its activation of PI3-kinase, a requirement for PDK1-induced Thr308 phosphorylation and IGF1-dependent activation of PKB. Our data suggest that PKB activity is most dependent on the level of Ser473 phosphorylation rather than Thr308, but basal levels of Thr308 phosphorylation are a requirement. Additionally, we suggest here that calyculin A regulates the IGF1-dependent PKB activation by controlling the PI3-kinase-associated IRS1 Ser/Thr phosphorylation levels.
Original languageEnglish
Pages (from-to)147-156
Number of pages10
JournalCell Biochemistry and Biophysics
Issue number3
Publication statusPublished - 1 Dec 2010


  • Animals
  • Chromones
  • Embryonic Stem Cells
  • Enzyme Inhibitors
  • Imidazoles
  • Insulin Receptor Substrate Proteins
  • Insulin-Like Growth Factor I
  • Mice
  • Mitogen-Activated Protein Kinase 11
  • Morpholines
  • Oxazoles
  • Phosphatidylinositol 3-Kinases
  • Phosphoprotein Phosphatases
  • Phosphorylation
  • Protein-Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-akt
  • Pyridines


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