mTORC2 Is the Major Second Layer Kinase Negatively Regulating FOXO3 Activity

Area of Science:

• Molecular Biology
• Cell Signaling
• Pharmacology

Background:

• Forkhead box O (FOXO) proteins are crucial transcription factors implicated in cancer and aging.
• FOXO activity is regulated by post-translational modifications, offering potential for pharmacological intervention.
• Protein kinases play a significant role in modulating FOXO signaling pathways.

Purpose of the Study:

• To investigate the effects of specific kinase inhibitors on FOXO3 activity and localization.
• To identify key kinases regulating FOXO3 nuclear translocation and transcriptional activity.
• To elucidate the role of mTORC1 and mTORC2 in FOXO regulation.

Main Methods:

• Utilized specific inhibitors against PI3K, mTOR, MEK, ALK, and other receptor tyrosine kinases (RTKs).
• Assessed FOXO3 nuclear translocation, phosphorylation status of AKT, FOXO3, and ERK.
• Measured FOXO-dependent transcriptional activity and subcellular localization of other FOXO isoforms.

Main Results:

• Inhibition of PI3K promoted FOXO3 nuclear entry; dual PI3K/mTOR inhibitors were more potent than PI3Kδ inhibitors.
• Specific inhibition of mTOR (affecting both mTORC1 and mTORC2) potently induced FOXO3 nuclear translocation.
• Rapamycin (mTORC1 specific) did not affect FOXO3 localization, while MAPK pathway inhibition had no effect.
• Upstream RTK inhibition showed only weak induction of nuclear FOXO3.

Conclusions:

• mTORC2 is identified as the primary kinase negatively regulating FOXO activity.
• Targeting mTORC2 presents a promising therapeutic strategy for modulating FOXO signaling in cancer and aging.
• Understanding kinase regulation of FOXO proteins is critical for developing novel treatments.