Overexpression of FoxO1 causes proliferation of cultured pancreatic beta cells exposed to low nutrition

Transcriptome changes of Takifugu obscurus liver after acute exposure to phenanthrene

Phenanthrene (Phe) is a model compound in polycyclic aromatic hydrocarbon (PAH) research. Reportedly, Phe treatment induced oxidative stress and histological disorders to Takifugu obscurus liver. In this study, to further explore the molecular responses of T. obscurus liver to Phe exposure, transcriptome sequencing was applied to compare mRNA transcription profiles between Phe treatment and the control. Compared with the control, 1,581 and 1,428 genes were significantly upregulated and downregulated in Phe treatment, respectively. Further analysis revealed that Phe treatment mainly upregulated genes in Ras-MAPK and PI3K-akt signaling pathways, which represented insulin resistance and further activated the FOXO signaling pathway. The triacylglycerol biosynthesis was promoted but the gluconeogenesis process was inhibited in response to Phe treatment, demonstrating that Phe exposure disturbed the sugar and lipid metabolism. Moreover, Phe treatment upregulated the Apelin-APJ and ErbB signaling pathways, promoting angiogenesis in T. obscurus liver. Insulin resistance, promoted triacylglycerol biosynthesis, and angiogenesis might explain the molecular mechanisms underlying carcinogenic toxicity of Phe. Overall, this study provides new insights to understand the environmental risk of Phe to fishes.

The role of FOXOs and autophagy in cancer and metastasis-Implications in therapeutic development

Autophagy is a highly conserved intracellular degradation process that plays a crucial role in cell survival and stress reactions as well as in cancer development and metastasis. Autophagy process involves several steps including sequestration, fusion of autophagosomes with lysosomes and degradation. Forkhead box O (FOXO) transcription factors regulate the expression of genes involved in cellular metabolic activity and signaling pathways of cancer growth and metastasis. Recent evidence suggests that FOXO proteins are also involved in autophagy regulation. The relationship among FOXOs, autophagy, and cancer has been drawing attention of many who work in the field. This study summarizes the role of FOXO proteins and autophagy in cancer growth and metastasis and analyzes their potential roles in cancer disease management.

Oleic acid increases the transcriptional activity of FoxO1 by promoting its nuclear translocation and β-catenin binding in pancreatic β-cells

In the setting of metabolic overload, chronic elevations of free fatty acids in blood and tissues are associated with pancreatic β-cell lipotoxicity and failure. Ultimately, obesity combined with insulin resistance increases the dysfunctional demand of β-cells and contributes to the development of type 2 diabetes. Forkhead box O1 (FoxO1) is a potent transcriptional regulator of pancreatic β-cell function and tolerance to lipid stress. The present study examined the effects of stearoyl-CoA desaturase 1 (SCD1)-metabolized precursors and products, notably oleic acid, on the compensatory capacity of β-cells and their relationship with regulation of the FoxO1 and Wnt pathways. The trioleate-induced compromise of insulin sensitivity blunted the compensatory response of pancreatic β-cells in primary rat islets. These events were associated with increases in the nuclear accumulation and transcriptional activity of FoxO1. Such effects were also observed in INS-1E cells that were subjected to oleate treatment. The overexpression of human SCD1 that was accompanied by endogenously generated oleic acid also led to an increase in the nuclear abundance of FoxO1. The mechanism of the oleate-mediated subcellular localization of FoxO1 was independent of the fatty acid receptor GPR40. Instead, the mechanism involved diversion of the active β-catenin pool from an interaction with transcription factor 7-like 2 toward FoxO1-mediated transcription in β-cells. Our findings identify a unique role for oleic acid in the compensatory response of pancreatic β-cells and emphasize the importance of FoxO1 in β-cell failure in obesity-induced insulin resistance.

Forced FoxO1:S249V expression suppressed glioma cell proliferation through G2/M cell cycle arrests and increased apoptosis

OBJECTIVE

Forkhead box O1 (FoxO1) plays a crucial role in the development of many tumors. Cyclin D kinase (CDK) 1 could influence the nuclear export and activity of FoxO1 through phosphorylation of serine (S)²⁴⁹. However, the effects of S²⁴⁹ phosphorylation in the development of glioma remain unclear. The aim of the present study is to assess the function of FoxO1:S²⁴⁹V mutant, which was converted S²⁴⁹ phosphorylation site into valine (V) residues in the glioma development.

METHODS

FoxO1-knockdown U251 glioma cells (U251-KD cells) were established by infection of retrovirus particles with FoxO1 siRNA and FoxO1 restored cells (FoxO1:S²⁴⁹V) were obtained by re-introduction of FoxO1:S²⁴⁹V cDNA. We detected mRNA expression by real-time PCR, and cell cycle arrest and apoptosis by flow cytometric assay, and cell proliferation by BrdU assay and CCK-8 assay. The protective effects of FoxO1:S²⁴⁹V were detected by the xenograft tumor formation assay.

RESULTS

The FoxO1 mRNA expression was significantly decreased in the glioma specimens (n = 24). The U251-KD cells showed downregulation of p27 and Bim, while the phosphorylation of CDK1 was upregulated. FoxO1:S²⁴⁹V cells inhibited the phosphorylation of S²⁴⁹, and induced G2/M cell cycle arrest, following reduced cell growth and increased apoptosis. Moreover, FoxO1:S²⁴⁹V expression effectively inhibits the glioma growth.

CONCLUSION

Our findings suggest that the forced FoxO1:S²⁴⁹V suppressed the cell growth through G2/M cell cycle arrests and increased apoptosis in glioma.

Expression and phosphorylation of FOXO1 influences cell proliferation and apoptosis in the gastrointestinal stromal tumor cell line GIST-T1

The mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K) pathways are activated during pathogenesis of gastrointestinal stromal tumors (GISTs). Forkhead box protein O1 (FOXO1) is a transcription factor regulated by the MAPK and PI3K pathways and is associated with multiple metabolic reactions. The present study aims to investigate the association of FOXO1 with cell proliferation and apoptosis in the cell line, GIST-T1. Cell counting kit-8 assay revealed that cell growth was inhibited by the PI3K inhibitor, LY294002, and/or MAPK inhibitor, UO126. Western blotting demonstrated that the expression of p-FOXO1 and B-cell lymphoma 2 (Bcl2) were significantly reduced, whereas the expression of Bcl-2-associated X protein was significantly increased following treatment with LY294002 and/or UO126 (all P<0.05). However, no significant change was revealed in the level of total FOXO1. Flow cytometry revealed that apoptosis was significantly increased by the pathway inhibitors (P<0.05). Specifically, the proportion of cells in the G1 phase was increased whereas the proportion in the S phase was reduced. The changes of protein expression and cell apoptosis were more evident in the LY294002 + UO126 group than in either single-inhibitor group. The results indicated that FOXO1 was able to affect cell proliferation, apoptosis and the cell cycle of GISTs. The regulation of FOXO1 was part of the PI3K and MAPK signaling network, while this regulation was mostly activated by phosphorylation of FOXO1.

Downregulation of Plzf Gene Ameliorates Metabolic and Cardiac Traits in the Spontaneously Hypertensive Rat

The spontaneously hypertensive rat (SHR), one of the most widely used model of essential hypertension, is predisposed to left ventricular hypertrophy, myocardial fibrosis, and metabolic disturbances. Recently, quantitative trait loci influencing blood pressure, left ventricular mass, and heart interstitial fibrosis were genetically isolated within a minimal congenic subline that contains only 7 genes, including mutant Plzf (promyelocytic leukemia zinc finger) candidate gene. To identify Plzf as a quantitative trait gene, we targeted Plzf in the SHR using the transcription activator-like effector nuclease technique and obtained SHR line harboring targeted Plzf gene with a premature stop codon. Because the Plzf targeted allele is semilethal, morphologically normal heterozygous rats were used for metabolic and hemodynamic analyses. SHR- Plzf +/− heterozygotes versus SHR wild-type controls exhibited reduced body weight and relative weight of epididymal fat, lower serum and liver triglycerides and cholesterol, and better glucose tolerance. In addition, SHR- Plzf +/− rats exhibited significantly increased sensitivity of adipose and muscle tissue to insulin action when compared with wild-type controls. Blood pressure was comparable in SHR versus SHR- Plzf +/− ; however, there was significant amelioration of cardiomyocyte hypertrophy and cardiac fibrosis in SHR- Plzf +/− rats. Gene expression profiles in the liver and expression of selected genes in the heart revealed differentially expressed genes that play a role in metabolic pathways, PPAR (peroxisome proliferator-activated receptor) signaling, and cell cycle regulation. These results provide evidence for an important role of Plzf in regulation of metabolic and cardiac traits in the rat and suggest a cross talk between cell cycle regulators, metabolism, cardiac hypertrophy, and fibrosis.

Forkhead box class O family member proteins: The biology and pathophysiological roles in diabetes

Forkhead box class O family member proteins (FoxOs) of transcription factors are essential regulators of cellular homeostasis, including glucose and lipid metabolism, oxidative stress response and redox signaling, cell cycle progression, and apoptosis. Altered FoxO1 expression and activity have been associated with glucose intolerance, dyslipidemia and complications of diabetes. In the liver, they direct carbons to glucose or lipid utilization, thus providing a unifying mechanism for the two abnormalities of the diabetic liver: excessive glucose production, and increased lipid synthesis and secretion. In the pancreas, FoxO1 is necessary to maintain β-cell differentiation, and could be promising targets for β-cell regeneration. In endothelial cells, FoxOs strongly promote atherosclerosis through suppressing nitric oxide production and enhancing inflammatory responses. In the present review, we summarize the basic biology and pathophysiological significance of FoxOs in diabetes.

FoxO1 Plays an Important Role in Regulating β-Cell Compensation for Insulin Resistance in Male Mice

β-Cell compensation is an essential mechanism by which β-cells increase insulin secretion for overcoming insulin resistance to maintain euglycemia in obesity. Failure of β-cells to compensate for insulin resistance contributes to insulin insufficiency and overt diabetes. To understand the mechanism of β-cell compensation, we characterized the role of forkhead box O1 (FoxO1) in β-cell compensation in mice under physiological and pathological conditions. FoxO1 is a key transcription factor that serves as a nutrient sensor for integrating insulin signaling to cell metabolism, growth, and proliferation. We showed that FoxO1 improved β-cell compensation via 3 distinct mechanisms by increasing β-cell mass, enhancing β-cell glucose sensing, and augmenting β-cell antioxidative function. These effects accounted for increased glucose-stimulated insulin secretion and enhanced glucose tolerance in β-cell-specific FoxO1-transgenic mice. When fed a high-fat diet, β-cell-specific FoxO1-transgenic mice were protected from developing fat-induced glucose disorder. This effect was attributable to increased β-cell mass and function. Furthermore, we showed that FoxO1 activity was up-regulated in islets, correlating with the induction of physiological β-cell compensation in high-fat-induced obese C57BL/6J mice. These data characterize FoxO1 as a pivotal factor for orchestrating physiological adaptation of β-cell mass and function to overnutrition and obesity.

The longevity effect of echinacoside in Caenorhabditis elegans mediated through daf-16

Echinacoside (ECH), a natural polyphenolic compound, has been reported to possess important pharmacological activities. However, very little is known about whether or how ECH affects longevity in vivo. We have examined the effects of ECH on the life span and stress tolerance in Caenorhabditis elegans. Our studies demonstrate that the life span of wild-type worms could be extended in the presence of ECH. Furthermore, ECH was found to increase tolerance of worms to heat shock and oxidative stress, while not exerting any influence on pharyngeal pumping rate and progeny production. Our mechanistic studies indicate that supplementation of ECH increases the transcript level of daf-16. ECH treatment also modulates the nuclear localization and transcriptional activities of daf-16, thus fine tunes the expression of daf-16 target genes to promote longevity and increases stress response in C. elegans. Overall, this work reveals the longevity effect of ECH and elucidates the underpinning mechanisms.

Royal Jelly-Mediated Prolongevity and Stress Resistance in Caenorhabditis elegans Is Possibly Modulated by the Interplays of DAF-16, SIR-2.1, HCF-1, and 14-3-3 Proteins

Recent studies suggest that royal jelly (RJ) and its related substances may have antiaging properties. However, the molecular mechanisms underlying the beneficial effects remain elusive. We report that the effects of RJ and enzyme-treated RJ (eRJ) on life span and health span in Caenorhabditis elegans (C elegans) are modulated by the sophisticated interplays of DAF-16, SIR-2.1, HCF-1, and 14-3-3 proteins. Dietary supplementation with RJ or eRJ increased C. elegans life span in a dose-dependent manner. The RJ and eRJ consumption increased the tolerance of C elegans to oxidative stress, ultraviolet irradiation, and heat shock stress. Our genetic analyses showed that RJ/eRJ-mediated life-span extension requires insulin/IGF-1 signaling and the activities of DAF-16, SIR-2.1, HCF-1, and FTT-2, a 14-3-3 protein. Earlier studies reported that DAF-16/FOXO, SIR-2.1/SIRT1, FTT-2, and HCF-1 have extensive interplays in worms and mammals. Our present findings suggest that RJ/eRJ-mediated promotion of longevity and stress resistance in C elegans is dependent on these conserved interplays. From an evolutionary point of view, this study not only provides new insights into the molecular mechanisms of RJ's action on health span promotion in C elegans, but also has imperative implications in using RJ/eRJ as nutraceuticals to delay aging and age-related disorders.

Insight into insulin secretion from transcriptome and genetic analysis of insulin-producing cells of Drosophila

Insulin-producing cells (IPCs) in the Drosophila brain produce and release insulin-like peptides (ILPs) to the hemolymph. ILPs are crucial for growth and regulation of metabolic activity in flies, functions analogous to those of mammalian insulin and insulin-like growth factors (IGFs). To identify components functioning in IPCs to control ILP production, we employed genomic and candidate gene approaches. We used laser microdissection and messenger RNA sequencing to characterize the transcriptome of larval IPCs. IPCs highly express many genes homologous to genes active in insulin-producing β-cells of the mammalian pancreas. The genes in common encode ILPs and proteins that control insulin metabolism, storage, secretion, β-cell proliferation, and some not previously linked to insulin production or β-cell function. Among these novelties is unc-104, a kinesin 3 family gene, which is more highly expressed in IPCs compared to most other neurons. Knockdown of unc-104 in IPCs impaired ILP secretion and reduced peripheral insulin signaling. Unc-104 appears to transport ILPs along axons. As a complementary approach, we tested dominant-negative Rab genes to find Rab proteins required in IPCs for ILP production or secretion. Rab1 was identified as crucial for ILP trafficking in IPCs. Inhibition of Rab1 in IPCs increased circulating sugar levels, delayed development, and lowered weight and body size. Immunofluorescence labeling of Rab1 showed its tight association with ILP2 in the Golgi of IPCs. Unc-104 and Rab1 join other proteins required for ILP transport in IPCs.

Critical physiological and pathological functions of Forkhead Box O tumor suppressors

The Forkhead box, subclass O (FOXO) proteins are critical transcription factors, ubiquitously expressed in the human body. These proteins are characterized by a remarkable functional diversity, being involved in cell cycle arrest, apoptosis, oxidative detoxification, DNA damage repair, stem cell maintenance, cell differentiation, cell metabolism, angiogenesis, cardiac development, aging and others. In addition, FOXO have critical implications in both normal and cancer stem cell biology. New strategies to modulate FOXO expression and activity may now be developed since the discovery of novel FOXO regulators and non-coding RNAs (such as microRNAs) targeting FOXO transcription factors. This review focuses on physiological and pathological functions of FOXO proteins and on their action as fine regulators of cell fate and context-dependent cell decisions. A better understanding of the structure and critical functions of FOXO transcription factors and tumor suppressors may contribute to the development of novel therapies for cancer and other diseases.

The longevity effect of cranberry extract in Caenorhabditis elegans is modulated by daf-16 and osr-1

Nutraceuticals are known to have numerous health and disease preventing properties. Recent studies suggest that extracts containing cranberry may have anti-aging benefits. However, little is known about whether and how cranberry by itself promotes longevity and healthspan in any organism. Here we examined the effect of a cranberry only extract on lifespan and healthspan in Caenorhabditis elegans. Supplementation of the diet with cranberry extract (CBE) increased the lifespan in C. elegans in a concentration-dependent manner. Cranberry also increased tolerance of C. elegans to heat shock, but not to oxidative stress or ultraviolet irradiation. In addition, we tested the effect of cranberry on brood size and motility and found that cranberry did not influence these behaviors. Our mechanistic studies indicated that lifespan extension induced by CBE requires the insulin/IGF signaling pathway and DAF-16. We also found that cranberry promotes longevity through osmotic stress resistant-1 (OSR-1) and one of its downstream effectors, UNC-43, but not through SEK-1, a component of the p38 MAP kinase pathway. However, SIR-2.1 and JNK signaling pathways are not required for cranberry to promote longevity. Our findings suggest that cranberry supplementation confers increased longevity and stress resistance in C. elegans through pathways modulated by daf-16 and osr-1. This study reveals the anti-aging property of widely consumed cranberry and elucidates the underpinning mechanisms.

FoxO1, the transcriptional chief of staff of energy metabolism

FoxO1, one of the four FoxO isoforms of Forkhead transcription factors, is highly expressed in insulin-responsive tissues, including pancreas, liver, skeletal muscle and adipose tissue, as well as in the skeleton. In all these tissues FoxO1 orchestrates the transcriptional cascades regulating glucose metabolism. Indeed, FoxO1 is a major target of insulin which inhibits its transcriptional activity via nuclear exclusion. In the pancreas, FoxO1 regulates β-cell formation and function by a balanced dual mode of action that suppresses β-cell proliferation but promotes survival. Hepatic glucose production is promoted and lipid metabolism is regulated by FoxO1 such that under insulin resistance they lead to hyperglycemia and dyslipidemia, two features of type 2 diabetes. In skeletal muscle FoxO1 maintains energy homeostasis during fasting and provides energy supply through breakdown of carbohydrates, a process that leads to atrophy and underlies glycemic control in insulin resistance. In a dual function, FoxO1 regulates energy and nutrient homeostasis through energy storage in white adipose tissue, but promotes energy expenditure in brown adipose tissue. In its most recently discovered novel role, FoxO1 acts as a transcriptional link between the skeleton and pancreas as well as other insulin target tissues to regulate energy homeostasis. Through its expression in osteoblasts it controls glucose metabolism, insulin sensitivity and energy expenditure. In a feedback mode of regulation, FoxO1 is also a target of insulin signaling in osteoblasts. Insulin suppresses activity of osteoblastic FoxO1 thus promoting beneficial effects of osteoblasts on glucose metabolism. The multiple actions of FoxO1 in all glucose-regulating organs, along with clinical studies suggesting that its glycemic properties are conserved in humans, establish this transcription factor as a master regulator of energy metabolism across species.

A simple matter of life and death-the trials of postnatal Beta-cell mass regulation

Pancreatic beta-cells, which secrete the hormone insulin, are the key arbiters of glucose homeostasis. Defective beta-cell numbers and/or function underlie essentially all major forms of diabetes and must be restored if diabetes is to be cured. Thus, the identification of the molecular regulators of beta-cell mass and a better understanding of the processes of beta-cell differentiation and proliferation may provide further insight for the development of new therapeutic targets for diabetes. This review will focus on the principal hormones and nutrients, as well as downstream signalling pathways regulating beta-cell mass in the adult. Furthermore, we will also address more recently appreciated regulators of beta-cell mass, such as microRNAs.

Cdc2: a monopotent or pluripotent CDK?

Cell cycle progression is controlled by both extracellular and intracellular signalling molecules. It has been generally believed that cdc2/CDK1 only control G(2)-M transition in mammalian and many other higher eukaryotic cells. Accumulating evidence shows that cdc2 not only promotes G(2)-M transition but is also capable of regulating G(1) progress and G(1)-S transition via association with multiple interphase cyclins; cdc2 activity can be inhibited by p21 and p27, two traditional G(1) CDK inhibitors. In addition, cdc2-cyclin B controls pronuclear union in interphase fertilized eggs. These data suggest that cdc2 may be a pluripotent CDK. Although mechanisms responsible for the multiple functions of cdc2 remain to be further investigated, interactions of cdc2 with pRb and with several important transcription factors may provide a clue to the pluripotent role of cdc2.

Targeting Forkhead box O1 from the concept to metabolic diseases: lessons from mouse models

Forkhead box O (FOXO) transcription factors have been implicated in regulating the metabolism, cellular proliferation, stress resistance, apoptosis, and longevity. Through the insulin receptor substrate → phosphoinositide 3-kinase → Akt signal cascade, FOXO integrates insulin action with the systemic nutrient and energy homeostasis. Activation of FOXO1 in liver induces gluconeogenesis via phosphoenolpyruvate carboxykinase (PEPCK)/glucose 6-phosphate pathway, and disrupts mitochondrial metabolism and lipid metabolism via heme oxygenase 1/sirtuin 1/Ppargc1α pathway. In skeletal muscle, FOXO1 activation underpins the carbohydrate/lipid switch during fasting state. Inhibition of FOXO1 under physiological conditions accounts for maintenance of skeletal muscle mass/function and adipose differentiation. In pancreatic β-cells, nuclear translocation of FOXO1 antagonizes pancreatic and duodenal homeobox 1 and attenuates β-cells proliferation and insulin secretion. Regardless, FOXO1 promotes the proliferation of β-cells through induction of Cyclin D1 in low nutrition, and elicits antioxidant mechanism to protect against β-cell failure during oxidative insults. In the brain, FOXO1 controls food intake through transcriptional regulation of the orexigenic neuropeptide Y, agouti-related protein, and carboxypeptidase E. In this article, we review the role of FOXO1 in the regulation of metabolism and energy expenditure based on recent findings from mouse models, and discuss the therapeutic value of targeting FOXO1 in metabolic diseases.