Mechanism of activation of PKB/Akt by the protein phosphatase inhibitor Calyculin A.
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.
Pozuelo-Rubio
Mercedes
M
Centro Andaluz de Biología Molecular y Medicina Regenerativa, CABIMER (SC4), Americo Vespucio s/n, Seville, Spain. merce_pozo@yahoo.es
Leslie
Nick R
NR
Murphy
Jane
J
Mackintosh
Carol
C
D064413:3-Phosphoinositide-Dependent Protein Kinases; D000818:Animals; D002867:Chromones / Q000494:pharmacology; D053595:Embryonic Stem Cells / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D007093:Imidazoles / Q000494:pharmacology; D055504:Insulin Receptor Substrate Proteins / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D008387:Marine Toxins; D051379:Mice; D048290:Mitogen-Activated Protein Kinase 11 / Q000378:metabolism; D009025:Morpholines / Q000494:pharmacology; D010080:Oxazoles / Q000494:pharmacology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D011725:Pyridines / Q000494:pharmacology
D064413:3-Phosphoinositide-Dependent Protein Kinases; D002867:Chromones; D004791:Enzyme Inhibitors; D007093:Imidazoles; D055504:Insulin Receptor Substrate Proteins; D007334:Insulin-Like Growth Factor I; D008387:Marine Toxins; D048290:Mitogen-Activated Protein Kinase 11; D009025:Morpholines; D010080:Oxazoles; D019869:Phosphatidylinositol 3-Kinases; D010749:Phosphoprotein Phosphatases; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D011725:Pyridines; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C059041:calyculin A; C578564:Pdpk1 protein, mouse; C093642:SB 203580