Investigating the Localization of FOXO Transcription Factors in Glioblastoma

The Phosphatidylinositol 3 Kinase (PI3K) pathway is an essential intracellular signaling pathway that regulates cellular growth, survival, and fate. Canonically, the activation of this pathway removes forkhead box subfamily O transcription factors (FOXO -1, -3, and -4) from the nucleus. However, in cancer cells such as glioblastoma multiforme, FOXO factors are at least in part nuclear despite the activation of the PI3K pathway. Previous research indicated that FOXO3 localization was not affected when the pathway was inhibited in breast cancer cells, which challenged the conventional paradigms for FOXO factor regulation. Therefore, we were interested in investigating the nuclear localization of FOXO transcription factors in additional cancer settings such as glioblastoma. By inhibiting PI3K and other pathways linked to FOXO factors, we examined their effects on FOXO transcription factor localization. We found that FOXO factors bypass the regulation by PI3K in order to be localized in the nucleus in glioblastoma cells

Using multiplexed regulation of luciferase activity and GFP translocation to screen for FOXO modulators

<p>Abstract</p> <p>Background</p> <p>Independent luciferase reporter assays and fluorescent translocation assays have been successfully used in drug discovery for several molecular targets. We developed U2transLUC, an assay system in which luciferase and fluorescent read-outs can be multiplexed to provide a powerful cell-based high content screening method.</p> <p>Results</p> <p>The U2transLUC system is based on a stable cell line expressing a GFP-tagged FOXO transcription factor and a luciferase reporter gene under the control of human FOXO-responsive enhancers. The U2transLUC assay measures nuclear-cytoplasmic FOXO shuttling and FOXO-driven transcription, providing a means to analyze these two key features of FOXO regulation in the same experiment. We challenged the U2transLUC system with chemical probes with known biological activities and we were able to identify compounds with translocation and/or transactivation capacity.</p> <p>Conclusion</p> <p>Combining different biological read-outs in a single cell line offers significant advantages over conventional cell-based assays. The U2transLUC assay facilitates the maintenance and monitoring of homogeneous FOXO transcription factor expression and allows the reporter gene activity measured to be normalized with respect to cell viability. U2transLUC is suitable for high throughput screening and can identify small molecules that interfere with FOXO signaling at different levels.</p

DAF-16/FOXO employs the chromatin remodeller SWI/SNF to promote stress resistance and longevity

Organisms are constantly challenged by stresses and privations and require adaptive responses for their survival. The transcription factor DAF-16/FOXO is central nexus in these responses, but despite its importance little is known about how it regulates its target genes. Proteomic identification of DAF-16/FOXO binding partners in Caenorhabditis elegans and their subsequent functional evaluation by RNA interference (RNAi) revealed several candidate DAF-16/FOXO cofactors, most notably the chromatin remodeller SWI/SNF. DAF-16/FOXO and SWI/SNF form a complex and globally colocalize at DAF-16/FOXO target promoters. We show that specifically for gene-activation, DAF-16/FOXO depends on SWI/SNF, facilitating SWI/SNF recruitment to target promoters, in order to activate transcription by presumed remodelling of local chromatin. For the animal, this translates into an essential role of SWI/SNF for DAF-16/FOXO-mediated processes, i.e. dauer formation, stress resistance, and the promotion of longevity. Thus we give insight into the mechanisms of DAF-16/FOXO-mediated transcriptional regulation and establish a critical link between ATP-dependent chromatin remodelling and lifespan regulation

Genome-wide identification of FoxO-dependent gene networks in skeletal muscle during C26 cancer cachexia

BACKGROUND: Evidence from cachectic cancer patients and animal models of cancer cachexia supports the involvement of Forkhead box O (FoxO) transcription factors in driving cancer-induced skeletal muscle wasting. However, the genome-wide gene networks and associated biological processes regulated by FoxO during cancer cachexia are unknown. We hypothesize that FoxO is a central upstream regulator of diverse gene networks in skeletal muscle during cancer that may act coordinately to promote the wasting phenotype. METHODS: To inhibit endogenous FoxO DNA-binding, we transduced limb and diaphragm muscles of mice with AAV9 containing the cDNA for a dominant negative (d.n.) FoxO protein (or GFP control). The d.n.FoxO construct consists of only the FoxO3a DNA-binding domain that is highly homologous to that of FoxO1 and FoxO4, and which outcompetes and blocks endogenous FoxO DNA binding. Mice were subsequently inoculated with Colon-26 (C26) cells and muscles harvested 26 days later. RESULTS: Blocking FoxO prevented C26-induced muscle fiber atrophy of both locomotor muscles and the diaphragm and significantly spared force deficits. This sparing of muscle size and function was associated with the differential regulation of 543 transcripts (out of 2,093) which changed in response to C26. Bioinformatics analysis of upregulated gene transcripts that required FoxO revealed enrichment of the proteasome, AP-1 and IL-6 pathways, and included several atrophy-related transcription factors, including Stat3, Fos, and Cebpb. FoxO was also necessary for the cancer-induced downregulation of several gene transcripts that were enriched for extracellular matrix and sarcomere protein-encoding genes. We validated these findings in limb muscles and the diaphragm through qRT-PCR, and further demonstrate that FoxO1 and/or FoxO3a are sufficient to increase Stat3, Fos, Cebpb, and the C/EBPβ target gene, Ubr2. Analysis of the Cebpb proximal promoter revealed two bona fide FoxO binding elements, which we further establish are necessary for Cebpb promoter activation in response to IL-6, a predominant cytokine in the C26 cancer model. CONCLUSIONS: These findings provide new evidence that FoxO-dependent transcription is a central node controlling diverse gene networks in skeletal muscle during cancer cachexia, and identifies novel candidate genes and networks for further investigation as causative factors in cancer-induced wasting.R01 AR060217 - NIAMS NIH HHS; R01 AR060209 - NIAMS NIH HHS; T32 HD043730 - NICHD NIH HHS; R00 HL098453 - NHLBI NIH HHS; R00HL098453 - NHLBI NIH HHS; R01AR060209 - NIAMS NIH HHS; R01AR060217 - NIAMS NIH HH

Long live FOXO: unraveling the role of FOXO proteins in aging and longevity

Aging constitutes the key risk factor for age-related diseases such as cancer and cardiovascular and neurodegenerative disorders. Human longevity and healthy aging are complex phenotypes influenced by both environmental and genetic factors. The fact that genetic contribution to lifespan strongly increases with greater age provides basis for research on which protective genes are carried by long-lived individuals. Studies have consistently revealed FOXO (Forkhead box O) transcription factors as important determinants in aging and longevity. FOXO proteins represent a subfamily of transcription factors conserved from Caenorhabditis elegans to mammals that act as key regulators of longevity downstream of insulin and insulin-like growth factor signaling. Invertebrate genomes have one FOXO gene, while mammals have four FOXO genes: FOXO1, FOXO3, FOXO4, and FOXO6. In mammals, this subfamily is involved in a wide range of crucial cellular processes regulating stress resistance, metabolism, cell cycle arrest, and apoptosis. Their role in longevity determination is complex and remains to be fully elucidated. Throughout this review, the mechanisms by which FOXO factors contribute to longevity will be discussed in diverse animal models, from Hydra to mammals. Moreover, compelling evidence of FOXOs as contributors for extreme longevity and health span in humans will be addressed

Investigating the Ability of FOXO Factors to Regulate the NOTCH Pathway

Background: Initial studies show that forkhead box (FOXO) transcription factors support maintenance in embryonic, hematogenic, and neural stem cells. Myoblasts, embryonic precursors of myocytes, are essential for forming and maintaining skeletal muscle tissue, which can fuse to form with multinucleated myotubes. In the presence of activated PI3K-AKT pathway, FOXO factors are inactive in muscle and liver cells; however, this regulatory mechanism is bypassed in stem/stem-like cells. FOXO factors directly interact with stem-related genes like OCT4 and SOX2, facilitating their expression. Nevertheless, our understanding of the full range and conservation of FOXO transcription factor function in stem cell environments remains incomplete, leaving gaps in our knowledge. To address this, we adopted a genetic approach to uncover novel roles of FOXO factors in U87MG GBM cells, where previous research has demonstrated their ability to induce the expression of stem genes. By utilizing CRISPR Cas9 genome editing and RNA Seq analysis, we disrupted FOXO4 and identified new target genes, respectively. Our findings indicate that FOXO factors significantly enhance the expression of NOTCH1 and NOTCH3 genes in C2C12 myoblast cells. Based on this, we propose to examine whether FOXO factors redundantly contribute to the activation of the NOTCH pathway in stem or stem-like contexts such as GBM and myoblasts, influencing the fate of the cells. Methods: To test this hypothesis, we propose to examine the ability of FOXO –1, -3, and –4 to promote the NOTCH pathway gene expression and myoblast stem cell fate. We will examine the differential expression levels of NOTCH Pathway genes and the correlation between FOXO factors and myoblast formation. Results: The anticipated results of these procedures will be identifying NOTCH Pathway target genes regulated by FOXO transcription factors to elucidate their roles in myogenesis. Conclusion: We conclude that delineating the roles of FOXO –1, -3, and –4 transcription factors in NOTCH Pathway regulation will help address how they drive stem cell phenotypes in myoblasts and other settings

DAF-16/FoxO in Caenorhabditis elegans and its role in metabolic remodeling

DAF-16, the only forkhead box transcription factors class O (FoxO) homolog in Caenorhabditis elegans, integrates signals from upstream pathways to elicit transcriptional changes in many genes involved in aging, development, stress, metabolism, and immunity. The major regulator of DAF-16 activity is the insulin/insulin-like growth factor 1 (IGF-1) signaling (IIS) pathway, reduction of which leads to lifespan extension in worms, flies, mice, and humans. In C. elegans daf-2 mutants, reduced IIS leads to a heterochronic activation of a dauer survival program during adulthood. This program includes elevated antioxidant defense and a metabolic shift toward accumulation of carbohydrates (i.e., trehalose and glycogen) and triglycerides, and activation of the glyoxylate shunt, which could allow fat-to-carbohydrate conversion. The longevity of daf-2 mutants seems to be partially supported by endogenous trehalose, a nonreducing disaccharide that mammals cannot synthesize, which points toward considerable differences in downstream mechanisms by which IIS regulates aging in distinct groups