mTORC2 Is the Major Second Layer Kinase Negatively Regulating FOXO3 Activity

Abstract

Forkhead box O (FOXO) proteins are transcription factors involved in cancer and aging and their pharmacological manipulation could be beneficial for the treatment of cancer and healthy aging. FOXO proteins are mainly regulated by post-translational modifications including phosphorylation, acetylation and ubiquitination. As these modifications are reversible, activation and inactivation of FOXO factors is attainable through pharmacological treatment. One major regulatory input of FOXO signaling is mediated by protein kinases. Here, we use specific inhibitors against different kinases including PI3K, mTOR, MEK and ALK, and other receptor tyrosine kinases (RTKs) to determine their effect on FOXO3 activity. While we show that inhibition of PI3K efficiently drives FOXO3 into the cell nucleus, the dual PI3K/mTOR inhibitors dactolisib and PI-103 induce nuclear FOXO translocation more potently than the PI3Kδ inhibitor idelalisib. Furthermore, specific inhibition of mTOR kinase activity affecting both mTORC1 and mTORC2 potently induced nuclear translocation of FOXO3, while rapamycin, which specifically inhibits the mTORC1, failed to affect FOXO3. Interestingly, inhibition of the MAPK pathway had no effect on the localization of FOXO3 and upstream RTK inhibition only weakly induced nuclear FOXO3. We also measured the effect of the test compounds on the phosphorylation status of AKT, FOXO3 and ERK, on FOXO-dependent transcriptional activity and on the subcellular localization of other FOXO isoforms. We conclude that mTORC2 is the most important second layer kinase negatively regulating FOXO activity.

FOXO1 stimulates tip cell-enriched gene expression in endothelial cells

“… 15 Several studies have been investigated the subcellular localization of FOXO1 in response to different extra- and intercellular signals, including VEGF. 16 , 17 , 18 Considering the importance of elucidating the mechanism underlying tip vs. stalk definition in the sprouts maturation and FOXO1 activity during VEGF-mediated vessel remodeling, we evaluated the FOXO1-regulated genes using single cell RNA-seq and ChIP-seq analyses in VEGF-treated ECs.…”

Advancements in Psoriasis Research: Skin Microcirculation and Its Prognostic Significance

“…Mammalian target of rapamycin (mTOR) is the main downstream regulator of PI3K/AKT pathway, which can negatively regulate FOXO activity, inhibit FOXO transcription, promote excessive proliferation and inhibit differentiation of keratinocytes [34]. It has been reported that the role of IL-17 and IL-22, which are associated with the psoriasis cascade, depends on the PI3K/AKT/mTOR signaling pathway [35] [36].…”