FOXO4 transcriptional activity is regulated by monoubiquitination and USP7/HAUSP.

FOXO (Forkhead box O) transcription factors are important regulators of cellular metabolism, cell-cycle progression and cell death. FOXO activity is regulated by multiple post-translational modifications, including phosphorylation, acetylation and polyubiquitination. Here, we show that FOXO becomes monoubiquitinated in response to increased cellular oxidative stress, resulting in its re-localization to the nucleus and an increase in its transcriptional activity.

FOXO transcription factor activation by oxidative stress mediated by the small GTPase Ral and JNK.

Forkhead transcription factors of the FOXO class are negatively regulated by PKB/c-Akt in response to insulin/IGF signalling, and are involved in regulating cell cycle progression and cell death. Here we show that, in contrast to insulin signalling, low levels of oxidative stress generated by treatment with H2O2 induce the activation of FOXO4. Upon treatment of cells with H2O2, the small GTPase Ral is activated and this results in a JNK-dependent phosphorylation of FOXO4 on threonine 447 and threonine 451.

Binding of protein kinase B to the plakin family member periplakin.

The serine/threonine kinase protein kinase B (PKB/c-Akt) acts downstream of the lipid kinase phosphoinositide 3-kinase (PI3K) and functions as an essential mediator in many growth-factor-induced cellular responses such as cell cycle regulation, cell survival and transcriptional regulation. PI3K activation generates 3'-phosphorylated phosphatidylinositol lipids (PtdIns3P) and PKB activation requires PtdIns3P-dependent membrane translocation and phosphorylation by upstream kinases. However PKB activation and function is also regulated by interaction with other proteins.

Direct control of the Forkhead transcription factor AFX by protein kinase B.

The phosphatidylinositol-3-OH-kinase (PI(3)K) effector protein kinase B regulates certain insulin-responsive genes, but the transcription factors regulated by protein kinase B have yet to be identified. Genetic analysis in Caenorhabditis elegans has shown that the Forkhead transcription factor daf-16 is regulated by a pathway consisting of insulin-receptor-like daf-2 and PI(3)K-like age-1. Here we show that protein kinase B phosphorylates AFX, a human orthologue of daf-16, both in vitro and in vivo.

Essential role for protein kinase B (PKB) in insulin-induced glycogen synthase kinase 3 inactivation. Characterization of dominant-negative mutant of PKB.

Activation of phosphatidylinositide 3'-OH kinase (PI 3-kinase) is implicated in mediating a variety of growth factor-induced responses, among which are the inactivation of glycogen synthase kinase-3 (GSK-3) and the activation of the serine/threonine protein kinase B (PKB). GSK-3 inactivation occurs through phosphorylation of Ser-9, and several kinases, such as protein kinase C, mitogen-activated protein kinase-activated protein kinase-1 (p90(Rsk)), p70(S6kinase), and also PKB have been shown to phosphorylate this site in vitro. In the light of the many candidates to mediate insulin-induced GSK-3 inactivation we have investigated the role of PKB by constructing a PKB mutant that exhibits dominant-negative function (inhibition of growth factor-induced activation of PKB at expression levels similar to wild-type PKB), as currently no such mutant has been reported.