beta-Catenin is a multifunctional protein that mediates Wnt signaling by binding to members of the T cell factor (TCF) family of transcription factors. Here, we report an evolutionarily conserved interaction of beta-catenin with FOXO transcription factors, which are regulated by insulin and oxidative stress signaling. beta-Catenin binds directly to FOXO and enhances FOXO transcriptional activity in mammalian cells. In Caenorhabditis elegans, loss of the beta-catenin BAR-1 reduces the activity of the FOXO ortholog DAF-16 in dauer formation and life span. Association of beta-catenin with FOXO was enhanced in cells exposed to oxidative stress. Furthermore, BAR-1 was required for the oxidative stress-induced expression of the DAF-16 target gene sod-3 and for resistance to oxidative damage. These results demonstrate a role for beta-catenin in regulating FOXO function that is particularly important under conditions of oxidative stress.

FOXO transcription factors have important roles in metabolism, cellular proliferation, stress tolerance, and aging. FOXOs are negatively regulated by protein kinase B/c-Akt-mediated phosphorylation. Here we show that FOXO factors are also subject to regulation by reversible acetylation. We provide evidence that the acetyltransferase CREB-binding protein (CBP) binds FOXO resulting in acetylation of FOXO. This acetylation inhibits FOXO transcriptional activity. Binding of CBP and acetylation are induced after treatment of cells with peroxide stress. Deacetylation of FOXOs involves binding of the NAD-dependent deacetylase hSir2 SIRT1 . Accordingly, hSir2 SIRT1 -mediated deacetylation precludes FOXO inhibition through acetylation and thereby prolongs FOXO-dependent transcription of stress-regulating genes. These data demonstrate that acetylation functions in a second pathway of negative control for FOXO factors and provides a novel mechanism whereby hSir2 SIRT1 can promote cellular survival and increase lifespan.The Forkhead box, class O subfamily of forkhead transcription factors (FOXO) 1 consists of the functionally related proteins FOXO1, FOXO3a, and FOXO4 (also known as FKHR, FKHRL1, and AFX, respectively; Ref. 1). The growth factorstimulated phosphatidylinositol 3-kinase-protein kinase B (PKB)/c-Akt pathway negatively regulates FOXO factors by phosphorylation-mediated nuclear exclusion (2-4). This pathway is evolutionarily conserved between Caenorhabditis elegans and humans. DAF-16, the C. elegans homologue of mammalian FOXO, is also controlled by phosphatidylinositol 3-kinase/PKB signaling. DAF-16 regulates daver formation in larvae, and responses to various environmental stresses and longevity in adult worms (5-8). In parallel, mammalian FOXO transcription factors have been implicated in regulating metabolism, cell cycle progression, and stress tolerance (9, 10; reviewed in Ref. 11).In C. elegans, overexpression of the NAD-dependent deacetylase Sir2 (silent information regulator 2) increases lifespan, which requires DAF-16 (12). The Sir2 family of genes is a highly conserved group of genes with seven human homologues, of which the SIRT1 gene encodes the closest homologue of yeast and C. elegans Sir2, hence named hSir2 SIRT1 (13). Recently, deacetylation of p53 by hSir2 SIRT1 has been demonstrated, and it has been suggested that this functions in increasing cellular resistance against stress. However, subsequent studies (14) showed that in HEK293T cells, which lack functional p53, activation of hSir2 SIRT1 by resveratrol treatment still increases cellular resistance against gamma-radiation, thus suggesting alternative pathways. As DAF-16 is necessary for lifespan extension by Sir2, FOXOs may well function in such an alternative pathway. EXPERIMENTAL PROCEDURESCell Culture, Transfection, and Treatment-HEK293T, DL23 (DLD-1 human colon carcinoma cells expressing a conditionally active version of FOXO3a; Ref. 10), and A14 cells (human insulin receptor overexpressing mouse NIH3T3 cells (15) and C2C12 mouse myoblast...