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Reactive Oxygen Species (ROS) derived from mitochondrial respiration are frequently cited as a major source of chromosomal DNA mutations that contribute to cancer development and aging. However, experimental evidence showing that ROS released by mitochondria can directly damage nuclear DNA is largely lacking. In this study, we investigated the effects of H2O2 released by mitochondria or produced at the nucleosomes using a titratable chemogenetic approach. This enabled us to precisely investigate to what extent DNA damage occurs downstream of near- and supraphysiological amounts of localized H2O2. Nuclear H2O2 gives rise to DNA damage and mutations and a subsequent p53 dependent cell cycle arrest. Mitochondrial H2O2 release shows none of these effects, even at levels that are orders of magnitude higher than what mitochondria normally produce. We conclude that H2O2 released from mitochondria is unlikely to directly damage nuclear genomic DNA, limiting its contribution to oncogenic transformation and aging. Nuclear DNA damage downstream of mitochondrial ROS is often cited to contribute to cancer initiation and aging. However, here the authors show that although H2O2 induces DNA mutations when produced near DNA, it does not when released by mitochondria. [ABSTRACT FROM AUTHOR]

Forkhead box O (FOXO) transcription factors are negatively regulated by the insulin signaling pathway through phosphoinositide 3-kinase (PI 3-kinase) and protein kinase B (PKB, also called c-Akt). Phosphorylation by PKB [...], β-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 β-catenin with FOXO transcription factors, which are regulated by insulin and oxidative stress signaling. β-Catenin binds directly to FOXO and enhances FOXO transcriptional activity in mammalian cells. In Caenorhabditis elegans, loss of the β-catenin BAR-1 reduces the activity of the FOXO ortholog DAF-16 in dauer formation and life span. Association of β-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 β-catenin in regulating FOXO function that is particularly important under conditions of oxidative stress.

Author(s): Geert J. P. L. Kops [1, 2]; Tobias B. Dansen [3]; Paulien E. Polderman [1]; Ingrid Saarloos [1]; Karel W. A. Wirtz [3]; Paul J. Coffer [4]; Ting-T. Huang [...]

Activity of FOXO (forkhead box O) transcription factors is inhibited by growth factor-PI3K (phosphoinositide 3-kinase)- PKB (protein kinase B)/Akt signalling to control a variety of cellular processes including cell cycle progression. Through comparative analysis of a number of microarray datasets we identified a set of genes commonly regulated by FOXO proteins and PI3K-PKB/Akt, which includes CTDSP2 (Cterminal domain small phosphatase 2). We validated CTDSP2 as a genuine FOXO target gene and show that ectopic CTDSP2 can induce cell cycle arrest. We analysed transcriptional regulation after CTDSP2 expression and identified extensive regulation of genes involved in cell cycle progression, which depends on the phosphatase activity of CTDSP2. The most notably regulated gene is the CDK (cyclin-dependent kinase) inhibitor p21Cip1/Waf1 and in the present study we show that p21Cip1/Waf1 is partially responsible for the cell cycle arrest through decreasing cyclin- CDK activity. Our data suggest that CTDSP2 induces p21Cip1/Waf1 through increasing the activity of Ras. As has been described previously, Ras induces p21Cip1/Waf1 through p53-dependent and p53-independent pathways and indeed both p53 and MEK inhibition can mitigate the CTDSP2-induced p21Cip1/Waf1 mRNA up-regulation. In support of Ras activation by CTDSP2, depletion of endogenous CTDSP2 results in reduced Ras activity and thus CTDSP2 seems to be part of a larger set of genes regulated by FOXO proteins, which increase growth factor signalling upon FOXO activation. [ABSTRACT FROM AUTHOR]

Activity of FOXO (forkhead box O) transcription factors is inhibited by growth factor-PI3K (phosphoinositide 3-kinase)- PKB (protein kinase B)/Akt signalling to control a variety of cellular processes including cell cycle progression. Through comparative analysis of a number of microarray datasets we identified a set of genes commonly regulated by FOXO proteins and PI3K-PKB/Akt, which includes CTDSP2 (Cterminal domain small phosphatase 2). We validated CTDSP2 as a genuine FOXO target gene and show that ectopic CTDSP2 can induce cell cycle arrest. We analysed transcriptional regulation after CTDSP2 expression and identified extensive regulation of genes involved in cell cycle progression, which depends on the phosphatase activity of CTDSP2. The most notably regulated gene is the CDK (cyclin-dependent kinase) inhibitor p21Cip1/Waf1 and in the present study we show that p21Cip1/Waf1 is partially responsible for the cell cycle arrest through decreasing cyclin- CDK activity. Our data suggest that CTDSP2 induces p21Cip1/Waf1 through increasing the activity of Ras. As has been described previously, Ras induces p21Cip1/Waf1 through p53-dependent and p53-independent pathways and indeed both p53 and MEK inhibition can mitigate the CTDSP2-induced p21Cip1/Waf1 mRNA up-regulation. In support of Ras activation by CTDSP2, depletion of endogenous CTDSP2 results in reduced Ras activity and thus CTDSP2 seems to be part of a larger set of genes regulated by FOXO proteins, which increase growth factor signalling upon FOXO activation. [ABSTRACT FROM AUTHOR]