Akt inhibitor A-443654 induces rapid Akt Ser-473 phosphorylation independent of mTORC1 inhibition.

Abstract

Rapamycin, a natural product inhibitor of the Raptor-mammalian target of rapamycin complex (mTORC1), is known to induce Protein kinase B (Akt/PKB) Ser-473 phosphorylation in a subset of human cancer cell lines through inactivation of S6K1, stabilization of insulin receptor substrate (IRS)-1, and increased signaling through the insulin/insulin-like growth factor-I/phosphatidylinositol 3-kinase (PI3K) axis. We report that A-443654, a potent small-molecule inhibitor of Akt serine/threonine kinases, induces Akt Ser-473 phosphorylation in all human cancer cell lines tested, including PTEN- and TSC2-deficient lines. This phenomenon is dose-dependent, manifests coincident with Akt inhibition and likely represents an alternative, rapid-feedback pathway that can be functionally dissociated from mTORC1 inhibition. Experiments performed in TSC2-/- cells indicate that TSC2 and IRS-1 cooperate with, but are dispensable for, A-443654-mediated Akt phosphorylation. This feedback event does require PI3K activity, however, as it can be inhibited by LY294002 or wortmannin. Small interfering RNA-mediated knockdown of mTOR or Rictor, components of the rapamycin-insensitive mTORC2 complex, but not the mTORC1 component Raptor, also inhibited Akt Ser-473 phosphorylation induced by A-443654. Our data thus indicate that Akt phosphorylation and activity are coupled in a manner not previously appreciated and provide a novel mode of Akt regulation that is distinct from the previously described rapamycin-induced IRS-1 stabilization mechanism.

• Authors: E K-H Han, J D Leverson, T McGonigal, O J Shah, K W Woods, T Hunter, V L Giranda, Y Luo
• Journal: Oncogene (Oncogene) Vol. 26 Issue 38 Pg. 5655-61 (Aug 16 2007) ISSN: 0950-9232 [Print] England
• PMID: 17334390 (Publication Type: Journal Article)

Chemical References

• A 443654
• Chromones
• Enzyme Inhibitors
• Indazoles
• Indoles
• Morpholines
• Multiprotein Complexes
• Phosphoinositide-3 Kinase Inhibitors
• Proteins
• RNA, Small Interfering
• TSC2 protein, human
• Transcription Factors
• Tuberous Sclerosis Complex 2 Protein
• Tumor Suppressor Proteins
• 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one
• Serine
• Mechanistic Target of Rapamycin Complex 1
• Proto-Oncogene Proteins c-akt
• TOR Serine-Threonine Kinases

Topics

• Cell Line, Tumor
• Chromones (pharmacology)
• Dose-Response Relationship, Drug
• Enzyme Inhibitors (pharmacology)
• Humans
• Immunoblotting
• Indazoles (pharmacology)
• Indoles (pharmacology)
• Mechanistic Target of Rapamycin Complex 1
• Morpholines (pharmacology)
• Multiprotein Complexes
• Mutation
• Phosphatidylinositol 3-Kinases (metabolism)
• Phosphoinositide-3 Kinase Inhibitors
• Phosphorylation (drug effects)
• Proteins
• Proto-Oncogene Proteins c-akt (antagonists & inhibitors, metabolism)
• RNA, Small Interfering (genetics)
• Serine (metabolism)
• TOR Serine-Threonine Kinases
• Time Factors
• Transcription Factors (genetics, metabolism)
• Transfection
• Tuberous Sclerosis Complex 2 Protein
• Tumor Suppressor Proteins (genetics, metabolism)