Correlation between FOXO1a (FKHR) and FOXO3a (FKHRL1) binding and the inhibition of basal glucose-6-phosphatase catalytic subunit gene transcription by insulin

FoxO3 Regulates the Progress and Development of Aging and Aging-Related Diseases

Aging is an inevitable risk factor for many diseases, including cardiovascular diseases, neurodegenerative diseases, cancer, and diabetes. Investigation into the molecular mechanisms involved in aging and longevity will benefit the treatment of age-dependent diseases and the development of preventative medicine for agingrelated diseases. Current evidence has revealed that FoxO3, encoding the transcription factor (FoxO)3, a key transcription factor that integrates different stimuli in the intrinsic and extrinsic pathways and is involved in cell differentiation, protein homeostasis, stress resistance and stem cell status, plays a regulatory role in longevity and in age-related diseases. However, the precise mechanisms by which the FoxO3 transcription factor modulates aging and promotes longevity have been unclear until now. Here, we provide a brief overview of the mechanisms by which FoxO3 mediates signaling in pathways involved in aging and aging-related diseases, as well as the current knowledge on the role of the FoxO3 transcription factor in the human lifespan and its clinical prospects. Ultimately, we conclude that FoxO3 signaling pathways, including upstream and downstream molecules, may be underlying therapeutic targets in aging and age-related diseases.

Toward a mechanistic understanding of DNA binding by forkhead transcription factors and its perturbation by pathogenic mutations

Forkhead box (FOX) proteins are an evolutionarily conserved family of transcription factors that play numerous regulatory roles in eukaryotes during developmental and adult life. Dysfunction of FOX proteins has been implicated in a variety of human diseases, including cancer, neurodevelopment disorders and genetic diseases. The FOX family members share a highly conserved DNA-binding domain (DBD), which is essential for DNA recognition, binding and function. Since the first FOX structure was resolved in 1993, >30 FOX structures have been reported to date. It is clear now that the structure and DNA recognition mechanisms vary among FOX members; however, a systematic review on this aspect is lacking. In this manuscript, we present an overview of the mechanisms by which FOX transcription factors bind DNA, including protein structures, DNA binding properties and disease-causing mutations. This review should enable a better understanding of FOX family transcription factors for basic researchers and clinicians.

Regulation of autoreactive CD4 T cells by FoxO1 signaling in CNS autoimmunity

Myelin-specific CD4 T effector cells (Teffs), Th1 and Th17 cells, are encephalitogenic in experimental autoimmune encephalomyelitis (EAE), a well-defined murine model of multiple sclerosis (MS) and implicated in MS pathogenesis. Forkhead box O 1 (FoxO1) is a conserved effector molecule in PI3K/Akt signaling and critical in the differentiation of CD4 T cells into T helper subsets. However, it is unclear whether FoxO1 may be a target for redirecting CD4 T cell differentiation and benefit CNS autoimmunity. Using a selective FoxO1 inhibitor AS1842856, we show that inhibition of FoxO1 suppressed the differentiation and expansion of Th1 cells. The transdifferentiation of Th17 cells into encephalitogenic Th1-like cells was suppressed by FoxO1 inhibition upon reactivation of myelin-specific CD4 T cells from EAE mice. The transcriptional balance skewed from the Th1 transcription factor T-bet toward the Treg transcription factor Foxp3. Myelin-specific CD4 T cells treated with the FoxO1 inhibitor were less encephalitogenic in adoptive transfer EAE studies. Inhibition of FoxO1 in T cells from MS patients significantly suppressed the expansion of Th1 cells. Furthermore, FoxO1 inhibition with AS1842856 promoted the development of functional iTreg cells. The immune checkpoint programmed cell death protein-1 (PD-1)-induced Foxp3 expression in CD4 T cells was impaired by FoxO1 inhibition. These data illustrate an important role of FoxO1 signaling in CNS autoimmunity via regulating autoreactive Teff and Treg balance.

Selective inhibition of CBP/p300 HAT by A-485 results in suppression of lipogenesis and hepatic gluconeogenesis

The histone acetyltransferases CREB-binding protein (CBP) and its paralogue p300 are transcriptional coactivators which are essential for a multitude of signaling pathways and energy homeostasis. However, the role of CBP/p300 HAT domain in regulating energy balance is still unclear. Here, C57BL/6 mice fed with either normal chow diet (NCD) or high-fat diet (HFD) were administrated with A-485, a recently reported selective inhibitor of CBP/p300 HAT activity for 1 week and the metabolic change was analyzed. The white adipose tissue (WAT) weight and adipocyte size were reduced in A-485-administrated mice, with decreased expressions of lipogenic genes and transcriptional factors. In the liver of A-485-treated mice, the lipid content and lipogenic gene expressions were lowered while the binding of forkhead box O1 (FOXO1) to glucose-6-phosphatase (G6Pc) promoter was reduced, leading to decreased expression of G6Pc. In primary mouse hepatocytes, A-485 abolished cAMP-elicited mRNA expressions of key gluconeogenic enzymes and promoted FOXO1 protein degradation via increasing its ubiquitination. Thus, A-485 inhibits lipogenesis in WAT and liver as well as decreases hepatic glucose production via preventing FOXO1 acetylation, leading to its protein degradation through a proteasome-dependent pathway. The specific inhibition of CBP/p300 HAT will provide a novel therapeutic approach for metabolic diseases.

No Association Between a Genetic Variant of FOXO3 and Risk of Type 2 Diabetes Mellitus in the Elderly Population of North India

Aging can be considered an evolutionary process that is modulated by various genetic and biochemical processes. Therefore the genetic variants may interplay a role in human longevity as well as age related illness. Forkhead Box O (FOXO) gene is one of the major defensive genes that are known for ameliorating lifespan. FOXO proteins act as nuclear transcription factors that facilitate the action of insulin or insulin-like growth factor (IGF-1) in various physiological processes. The rationale of our study is to find out association between genetic variant rs2253310 of FOXO3 and risk of Type 2 Diabetes Mellitus (T2DM) in elderly population. This case control study involved 172 age sex matched elderly subjects while patients were recruited as per IDF criteria. Clinical, biochemical, ELISA methods were employed for assesement of clinical samples while Taqman method was used for genotyping analysis. Our results revealed that there was no significant difference in genotypic and allelic frequencies for the tested SNP (p > 0.05) between elderly T2DM patients and controls. The SNP rs2253310 was not associated with risk of T2DM in any genetic model. Also no association was found among the studied group between FOXO3 variant and HOMA-IR, HOMA-B index and Fasting plasma glucose. Serum level of inflammatory markers like CRP and TNF-α was significantly higher in patients but its not associated with SNP rs2253310. Our study concluded that, this intronic longevity-associated variant rs2253310 in FOXO3 is not associated with type 2 diabetes in geriatric patients of northern India.

FOXO3a as a sensor of unilateral nerve injury in sensory neurons ipsilateral, contralateral and remote to injury

Emerging evidence supports that the stress response to peripheral nerve injury extends beyond the injured neuron, with alterations in associated transcription factors detected both locally and remote to the lesion. Stress-induced nuclear translocation of the transcription factor forkhead class box O3a (FOXO3a) was initially linked to activation of apoptotic genes in many neuronal subtypes. However, a more complex role of FOXO3a has been suggested in the injury response of sensory neurons, with the injured neuron expressing less FOXO3a. To elucidate this response and test whether non-injured sensory neurons also alter FOXO3a expression, the temporal impact of chronic unilateral L4–6 spinal nerve transection on FOXO3a expression and nuclear localization in adult rat dorsal root ganglion neurons ipsilateral, contralateral or remote to injury relative to naïve controls was examined. In naïve neurons, high cytoplasmic and nuclear levels of FOXO3a colocalized with calcitonin gene related peptide, a marker of the nociceptive subpopulation. One hour post-injury, an acute increase in nuclear FOXO3a in small size injured neurons occurred followed by a significant decrease after 1, 2 and 4 days, with levels increasing toward pre-injury levels by 1 week post-injury. A more robust biphasic response to the injury was observed in uninjured neurons contralateral to and those remote to injury. Nuclear levels of FOXO3a peaked at 1 day, decreased by 4 days, then increased by 1 week post-injury, a response mirrored in C4 dorsal root ganglion neurons remote to injury. This altered expression contralateral and remote to injury supports that spinal nerve damage has broader systemic impacts, a response we recently reported for another stress transcription factor, Luman/CREB3. The early decreased expression and nuclear localization of FOXO3a in the injured neuron implicate these changes in the cell body response to injury that may be protective. Finally, the broader systemic changes support the existence of stress/injury-induced humeral factor(s) influencing transcriptional and potentially behavioral changes in uninjured dorsal root ganglion neurons. Approval to conduct this study was obtained from the University of Saskatchewan Animal Research Ethics Board (protocol #19920164).

Synergistic activation of thermogenic adipocytes by a combination of PPARγ activation, SMAD3 inhibition and adrenergic receptor activation ameliorates metabolic abnormalities in rodents

AIMS/HYPOTHESIS

To treat obesity and related diseases, considerable effort has gone into developing strategies to convert white adipocytes into thermogenic brown-like adipocytes ('browning'). The purpose of this study was to identify the most efficient signal control for browning.

METHODS

To identify the most efficient signal control for browning, we examined rat stromal vascular fraction cells. In addition, physiological changes consequent to signal control were examined in vivo using lean and diet-induced obese (DIO) C57BL/6J mice.

RESULTS

Combined treatment with the peroxisome proliferator-activated receptor γ (PPARγ) agonist rosiglitazone, the SMAD3 inhibitor SIS3 and the adrenergic receptor agonist noradrenaline (norepinephrine) synergistically induced Ucp1, Fgf21 and Cited1 expression, triggering brown adipogenesis. Synergistic induction of Ucp1 by the three agents was negatively regulated by forkhead box O (FOXO)3 via the inhibition of PPARγ-dependent gene transcription. Moreover, the administration of rosiglitazone, SIS3 and the selective β3 adrenergic receptor agonist CL316,243 to DIO mice reduced the amount of body-fat deposits (body weight from day 0 to 14, 12.3% reduction), concomitant with morphological changes in white adipose tissue, an increase in mitochondrial biosynthesis and a marked induction of uncoupling protein 1 (UCP1). Furthermore, administration of the three agents significantly increased serum adiponectin levels (mean 65.56 μg/ml with the three agents vs 20.79 μg/ml in control mice, p < 0.05) and improved glucose and lipid tolerance.

CONCLUSIONS/INTERPRETATION

These results suggest that the combined regulation of PPARγ, SMAD and the adrenergic receptor signalling pathway synergistically induces brown adipogenesis and may serve as an effective strategy to treat obesity and related diseases, including type 2 diabetes.

FOXO3a from the Nucleus to the Mitochondria: A Round Trip in Cellular Stress Response

Cellular stress response is a universal mechanism that ensures the survival or negative selection of cells in challenging conditions. The transcription factor Forkhead box protein O3 (FOXO3a) is a core regulator of cellular homeostasis, stress response, and longevity since it can modulate a variety of stress responses upon nutrient shortage, oxidative stress, hypoxia, heat shock, and DNA damage. FOXO3a activity is regulated by post-translational modifications that drive its shuttling between different cellular compartments, thereby determining its inactivation (cytoplasm) or activation (nucleus and mitochondria). Depending on the stress stimulus and subcellular context, activated FOXO3a can induce specific sets of nuclear genes, including cell cycle inhibitors, pro-apoptotic genes, reactive oxygen species (ROS) scavengers, autophagy effectors, gluconeogenic enzymes, and others. On the other hand, upon glucose restriction, 5′-AMP-activated protein kinase (AMPK) and mitogen activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) -dependent FOXO3a mitochondrial translocation allows the transcription of oxidative phosphorylation (OXPHOS) genes, restoring cellular ATP levels, while in cancer cells, mitochondrial FOXO3a mediates survival upon genotoxic stress induced by chemotherapy. Interestingly, these target genes and their related pathways are diverse and sometimes antagonistic, suggesting that FOXO3a is an adaptable player in the dynamic homeostasis of normal and stressed cells. In this review, we describe the multiple roles of FOXO3a in cellular stress response, with a focus on both its nuclear and mitochondrial functions.

Arsenic trioxide inhibits angiogenesis in vitro and in vivo by upregulating FoxO3a

Arsenic trioxide (As₂O₃) has been used clinically for the treatment of acute promyelocytic leukemia and some solid tumors. However, the mechanisms of its anti-tumor effects are still elusive. Angiogenesis is a key process for tumor initiation, and increasing evidence has supported the role of anti-angiogenesis caused by arsenic in tumor suppression, although the detailed mechanism is not well understood. In the present study, we found that As₂O₃ significantly inhibited the angiogenesis of human umbilical vein endothelial cells (HUVECs) in vitro, and this was mediated by the upregulation of FoxO3a. Knockdown of FoxO3a could restore the angiogenic ability of HUVECs. Moreover, vascular endothelial cell-specific knockout of FoxO3a in mice could disrupt the anti-angiogenesis effect of As₂O₃ and endow the tumors with resistance to As₂O₃ treatments. Our results revealed a new mechanism by which As₂O₃ suppresses angiogenesis and tumor growth.

Longevity-Associated Forkhead Box O3 (FOXO3) Single Nucleotide Polymorphisms are Associated with Type 2 Diabetes Mellitus in Chinese Elderly Women

Background

This study aimed to investigate the association of single nucleotide polymorphisms (SNPs) of Forkhead box O3 (FOXO3) gene with type 2 diabetes mellitus (T2D).

Material/Methods

A total of 843 elderly residents from east China were enrolled in this study, which included 426 patients with type 2 diabetes and 417 controls. Four SNPs were analyzed by qPCR. Genotype frequencies of the 4 SNPs in FOXO3 of the patients and controls were analyzed using logistic regression analysis. The association between each SNP and clinical indicators was analyzed by linear regression analysis.

Results

None of the 4 FOXO3 variants, rs13217795, rs2764264, rs2802292, and rs13220810, were associated with the risk of type 2 diabetes compared to controls. However, rs13217795, rs2764264, and rs2802292 were associated with lower blood glucose levels. Notably, further subgroup analysis indicated that the longevity-associated alleles of FOXO3 SNP (rs13217795, rs2764264, and rs2802292) were associated with lower blood glucose levels in women (TC versus TT, −0.724 mmol/L, P=0.005; CC versus TT, −1.093 mmol/L, P=0.03; TC versus TT, −0.801 mmol/L, P=0.002; CC versus TT, −1.212 mmol/L, P=0.001; TG versus TT, −0.754 mmol/L, P=0.004; and GG versus TT, −1.150 mmol/L, P=0.001) but not in men.

Conclusions

The results indicated that longevity-associated FOXO3 variants were correlated with lower blood glucose levels in elderly women with type 2 diabetes in east China.

FOXO1 functions in the regulation of nicotinamide phosphoribosyltransferase (Nampt) expression

Here, we report that Forkhead Box O1 (FOXO1) protein, a tumor suppressor, regulates expression of nicotinamide phosphoribosyltransferase (Nampt) in human breast cancer MCF-7 cells. Nampt plays an important role in the regulation of cell growth, survival, DNA replication and repair, and angiogenesis in tumorigenesis. We revealed that FOXO1 directly inhibits Nampt expression via binding to FOXO1 binding domains in the 5'-flanking region of the nampt gene. Nampt expression was increased by insulin and downstream phosphatidylinositol 3-kinase (PI3K)/Akt signaling, which was inhibited by FOXO1 overexpression. Accordingly, we showed that FOXO1 is also involved in insulin signaling-induced cell survival and proliferation in MCF-7 cells. These results suggest that FOXO1 plays an important role in human breast cancer cells by regulating nampt gene expression.

Estrogen Improves Insulin Sensitivity and Suppresses Gluconeogenesis via the Transcription Factor Foxo1

Premenopausal women exhibit enhanced insulin sensitivity and reduced incidence of type 2 diabetes (T2D) compared with age-matched men, but this advantage disappears after menopause with disrupted glucose homeostasis, in part owing to a reduction in circulating 17β-estradiol (E₂). Fasting hyperglycemia is a hallmark of T2D derived largely from dysregulation of hepatic glucose production (HGP), in which Foxo1 plays a central role in the regulation of gluconeogenesis. Here, we investigated the action of E₂ on glucose homeostasis in male and ovariectomized (OVX) female control and liver-specific Foxo1 knockout (L-F1KO) mice and sought to understand the mechanism by which E₂ regulates gluconeogenesis via an interaction with hepatic Foxo1. In both male and OVX female control mice, subcutaneous E₂ implant improved insulin sensitivity and suppressed gluconeogenesis; however, these effects of E₂ were abolished in L-F1KO mice of both sexes. In our use of mouse primary hepatocytes, E₂ suppressed HGP and gluconeogenesis in hepatocytes from control mice but failed in hepatocytes from L-F1KO mice, suggesting that Foxo1 is required for E₂ action on the suppression of gluconeogenesis. We further demonstrated that E₂ suppresses hepatic gluconeogenesis through activation of estrogen receptor (ER)α-phosphoinositide 3-kinase-Akt-Foxo1 signaling, which can be independent of insulin receptor substrates 1 and 2 (Irs1 and Irs2), revealing an important mechanism for E₂ in the regulation of glucose homeostasis. These results may help explain why premenopausal women have lower incidence of T2D than age-matched men and suggest that targeting ERα can be a potential approach to modulate glucose metabolism and prevent diabetes.

Novel Mechanism of Foxo1 Phosphorylation in Glucagon Signaling in Control of Glucose Homeostasis

Dysregulation of hepatic glucose production (HGP) serves as a major underlying mechanism for the pathogenesis of type 2 diabetes. The pancreatic hormone glucagon increases and insulin suppresses HGP, controlling blood glucose homeostasis. The forkhead transcription factor Foxo1 promotes HGP through increasing expression of genes encoding the rate-limiting enzymes responsible for gluconeogenesis. We previously established that insulin suppresses Foxo1 by Akt-mediated phosphorylation of Foxo1 at Ser²⁵⁶ in human hepatocytes. In this study, we found a novel Foxo1 regulatory mechanism by glucagon, which promotes Foxo1 nuclear translocation and stability via cAMP- and protein kinase A-dependent phosphorylation of Foxo1 at Ser²⁷⁶ Replacing Foxo1-S276 with alanine (A) or aspartate (D) to block or mimic phosphorylation, respectively, markedly regulates Foxo1 stability and nuclear localization in human hepatocytes. To establish in vivo function of Foxo1-Ser²⁷⁶ phosphorylation in glucose metabolism, we generated Foxo1-S273A and Foxo1-S273D knock-in (KI) mice. The KI mice displayed impaired blood glucose homeostasis, as well as the basal and glucagon-mediated HGP in hepatocytes. Thus, Foxo1-Ser²⁷⁶ is a new target site identified in the control of Foxo1 bioactivity and associated metabolic diseases.

FOXO3a Reverses the Cisplatin Resistance in Ovarian Cancer

OBJECTIVE

Ovarian cancer is one of the most serious disease in female reproductive system. Platinum is the first-line drug for the treatment of ovarian cancer, while the resistance of platinum drug in clinical hindered the relief ovarian cancer. Our previous study found that decreased FOXO3a might be a poor prognosis in human ovarian cancer. In this research, we study whether FOXO3a was involved in the mechanism of platinum drug resistance.

METHODS

The CCK-8 and FACS analysis were used to monitor the survival of ovarian cancer, and the FOXO3a expression was detected by western-blot.

RESULTS

We found that FOXO3a expression upregulated significantly in A2780 compared with A2780/DDP cells with the treatment of platinum. Moreover, overexpression of FOXO3a in ovarian cancer inversed the platinum resistance in ovarian cancer.

CONCLUSION

These observations reminded that the role of FOXO3a might be one of the critical mechanisms in developing platinum drug resistance in ovarian cancer.

Molecular Cloning and Motif Identification of the Sheep Musclin Gene Promoter

Musclin is a bioactive factor that functions in regulating the muscle growth and metabolism. To investigate the transcriptional regulatory mechanism of the gene, the 1.4 kb musclin promoter in sheep was cloned (GenBank accession: JX966391) and the sequence was analyzed to predict the motifs associated with muscle growth. Next the enhanced green fluorescent protein (EGFP) was selected as the reporter gene and various wild-type and motif-mutant vectors were constructed. The transcriptional regulatory activities were compared by observing the fluorescence strength and detecting the EGFP mRNA expression in C2C12 myoblasts transfected with the vectors. The results showed that the different lengths of promoters could drive the transcription of EGFP and the mutation of some motifs up- or downregulated the activity of the promoter. Furthermore, the electrophoresis mobility shift assay showed that these motifs regulated the musclin gene transcription through binding to the corresponding transcriptional factors in sheep muscle tissue.

Activation of CaMKIIγ potentiates T-cell acute lymphoblastic leukemia leukemogenesis via phosphorylating FOXO3a

Ca²⁺/calmodulin–dependent protein kinase II γ (CaMKIIγ) can regulate the proliferation and differentiation of myeloid leukemia cells and accelerate chronic myeloid leukemia blast crisis, but the role of CaMKIIγ in T-cell acute lymphoblastic leukemia (T-ALL) leukemogenesis remains poorly understood. We observed that activated (autophosphorylated) CaMKIIγ was invariably present in T-ALL cell lines and in the majority of primary T-ALL samples. Overexpression of CaMKIIγ enhanced the proliferation, colony formation, in vivo tumorigenesis and increased DNA damage of T-ALL leukemia cells. Furthermore, inhibition of CaMKIIγ activity with a pharmacologic inhibitor, gene knock-out, dominant-negative constructs or enhancement of CaMKIIγ activity by overexpression constructs revealed that the activated CaMKIIγ could phosphorylate FOXO3a. In Jurkat cells, the activated CaMKIIγ phosphorylated FOXO3a via directly or indirectly phosphorylating AKT, excluded FOXO3a from the nucleus and inhibited its transcriptional activity. These results indicate that the activated CaMKIIγ may play a key role in T-ALL leukemogenesis, and targeting CaMKIIγ might be a value approach in the treatment of T-ALL.

Breast cancer suppression by aplysin is associated with inhibition of PI3K/AKT/FOXO3a pathway

Aplysin, a bromosesquiterpene isolated from Aplysia kurodai, was explored as a potential anti-breast cancer agent by us. However, the mechanisms underlying the anticarcinogenic effect of aplysin remain unclear. Here, aplysin was found to remarkably suppress tumor growth in vivo, inhibit cell proliferation and promote apoptosis in vitro. Additionally, we demonstrated that aplysin attained these effects in part by down-regulating PI3K/AKT/FOXO3a signaling pathway. Aplysin treatment inhibited the phosphorylation levels of AKT (Ser-473) and AKT-dependent phosphorylation of FOXO3a (Ser-253) in breast cancer cell lines and breast cancer tissues. The expression levels of FOXO3a-targeted genes were also destabilized by aplysin, cyclin D1 and Bcl-XL were declined; however, p21^CIP1, p27^KIP1, Bim, TRAIL and FasL were increased both in vivo and in vitro. Furthermore, activation of the PI3K/AKT signaling pathway by an activator and silencing of FOXO3a by shRNA protected the cells from aplysin mediated growth suppression and apoptosis. In summary, our findings revealed that aplysin could suppress breast cancer progression by inhibiting PI3K/AKT/FOXO3a pathway, thereby suggesting a potential role of aplysin as a chemoprevention drug for patients with breast cancer.

FOXO transcription factors at the interface of metabolism and cancer

Diabetes refers to a group of metabolic diseases characterized by impaired insulin signalling and high blood glucose. A growing body of epidemiological evidence links diabetes to several types of cancer but the underlying molecular mechanisms are poorly understood. The signalling cascade connecting insulin and FOXO proteins provides a compelling example for a conserved pathway at the interface between insulin signalling and cancer. FOXOs are transcription factors that orchestrate programs of gene expression known to control a variety of processes in response to cellular stress. Genes regulated by this family of proteins are involved in the regulation of cellular energy production, oxidative stress resistance and cell viability and proliferation. Accordingly, FOXO factors have been shown to play an important role in the suppression of tumour growth and in the regulation of metabolic homeostasis. There is emerging evidence that deregulation of FOXO factors might account for the association between insulin resistance-related metabolic disorders and cancer.

Crystal structures reveal a new and novel FoxO1 binding site within the human glucose-6-phosphatase catalytic subunit 1 gene promoter

Human glucose-6-phosphatase plays a vital role in blood glucose homeostasis and holds promise as a therapeutic target for diabetes. Expression of its catalytic subunit gene 1 (G6PC1) is tightly regulated by metabolic-response transcription factors such as FoxO1 and CREB. Although at least three potential FoxO1 binding sites (insulin response elements, IREs) and one CREB binding site (cAMP response element, CRE) within the proximal region of the G6PC1 promoter have been identified, the interplay between FoxO1 and CREB and between FoxO1 bound at multiple IREs has not been well characterized. Here we present the crystal structures of the FoxO1 DNA binding domain in complex with the G6PC1 promoter. These complexes reveal the presence of a new non-consensus FoxO1 binding site that overlaps the CRE, suggesting a mutual exclusion mechanism for FoxO1 and CREB binding at the G6PC1 promoter. Additional findings include (i) non-canonical FoxO1 recognition sites, (ii) incomplete FoxO1 occupancies at the available IRE sites, and (iii) FoxO1 dimeric interactions that may play a role in stabilizing DNA looping. These findings provide insight into the regulation of G6PC1 gene transcription by FoxO1, and demonstrate a high versatility of target gene recognition by FoxO1 that correlates with its diverse roles in biology.

The hepatic FOXQ1 transcription factor regulates glucose metabolism in mice

AIM/HYPOTHESIS

Hepatic forkhead box q1 (FOXQ1) expression levels are regulated by nutritional and pathophysiological status. In this study we investigated the role of FOXQ1 in the regulation of hepatic gluconeogenesis.

METHODS

We used multiple mouse and cell models to study the role of FOXQ1 in regulating expression of gluconeogenic genes, and cellular and hepatic glucose production.

RESULTS

Expression of hepatic FOXQ1 was regulated by fasting in normal mice and was dysregulated in diabetic mice. Overexpression of FOXQ1 in primary hepatocytes inhibited expression of gluconeogenic genes and decreased cellular glucose output. Hepatic FOXQ1 rescue in db/db and high-fat diet-induced obese mice markedly decreased blood glucose level and improved glucose intolerance. In contrast, wild-type C57 mice with hepatic FOXQ1 deficiency displayed increased blood glucose levels and impaired glucose tolerance. Interestingly, studies into molecular mechanisms indicated that FOXQ1 interacts with FOXO1, thereby blocking FOXO1 activity on hepatic gluconeogenesis, preventing it from directly binding to insulin response elements mapped in the promoter region of gluconeogenic genes.

CONCLUSIONS/INTERPRETATION

FOXQ1 is a novel factor involved in regulating hepatic gluconeogenesis, and the decreased FOXQ1 expression in liver may contribute to the development of type 2 diabetes.

Regulation of Glucose Homeostasis by Glucocorticoids

Glucocorticoids are steroid hormones that regulate multiple aspects of glucose homeostasis. Glucocorticoids promote gluconeogenesis in liver, whereas in skeletal muscle and white adipose tissue they decrease glucose uptake and utilization by antagonizing insulin response. Therefore, excess glucocorticoid exposure causes hyperglycemia and insulin resistance. Glucocorticoids also regulate glycogen metabolism. In liver, glucocorticoids increase glycogen storage, whereas in skeletal muscle they play a permissive role for catecholamine-induced glycogenolysis and/or inhibit insulin-stimulated glycogen synthesis. Moreover, glucocorticoids modulate the function of pancreatic α and β cells to regulate the secretion of glucagon and insulin, two hormones that play a pivotal role in the regulation of blood glucose levels. Overall, the major glucocorticoid effect on glucose homeostasis is to preserve plasma glucose for brain during stress, as transiently raising blood glucose is important to promote maximal brain function. In this chapter we will discuss the current understanding of the mechanisms underlying different aspects of glucocorticoid-regulated mammalian glucose homeostasis.

Forkhead Box P1 (FOXP1) Transcription Factor Regulates Hepatic Glucose Homeostasis

Dysregulation of hepatic gluconeogenesis contributes to the pathogenesis of diabetes, yet the detailed molecular mechanisms remain to be fully elucidated. Here we show that FOXP1, a transcriptional repressor, plays a key role in the regulation of systemic glucose homeostasis. Hepatic expression levels of FOXP1 are decreased in diabetic mice. Modest hepatic overexpression of FOXP1 in mice inhibited the expression of gluconeogenic genes, such as peroxisome proliferators-activated receptor γ coactivator-1α (PGC-1α), phosphoenolpyruvate carboxykinase (PEPCK), and glucose-6-phosphatase (G6PC), leading to a decrease in hepatic glucose production and fasting blood glucose levels in normal mice and different mouse models of diabetes, including db/db diabetic and high-fat diet-induced obese mice. FOXP1 physically interacted with FOXO1 in vivo and competed with FOXO1 for binding to the insulin response element in the promoter region of gluconeogenic genes, thereby interfering expression of these genes. These results identify a previously unrecognized role for FOXP1 in the transcriptional control of hepatic glucose homeostasis.

Age-Based Differences in the Genetic Determinants of Glycemic Control: A Case of FOXO3 Variations

Background

Glucose homeostasis is a trait of healthy ageing and is crucial to the elderly, but less consideration has been given to the age composition in most studies involving genetics and hyperglycemia.

Methods

Seven variants in FOXO3 were genotyped in three cohorts (n = 2037; LLI, MI_S and MI_N; mean age: 92.5±3.6, 45.9±8.2 and 46.8±10.3, respectively) to compare the contribution of FOXO3 to fasting hyperglycemia (FH) between long-lived individuals (LLI, aged over 90 years) and middle-aged subjects (aged from 35–65 years).

Results

A different genetic predisposition of FOXO3 alleles to FH was observed between LLI and both of two middle-aged cohorts. In the LLI cohort, the longevity beneficial alleles of three variants with the haplotype “AGGC” in block 1 were significantly protective to FH, fasting glucose, hemoglobin A_1C and HOMA-IR. Notably, combining multifactor dimensionality reduction and logistic regression, we identified a significant 3-factor interaction model (rs2802288, rs2802292 and moderate physical activity) associated with lower FH risk. However, not all of the findings were replicated in the two middle-aged cohorts.

Conclusion

Our data provides a novel insight into the inconsistent genetic determinants between middle-aged and LLI subjects. FOXO3 might act as a shared genetic predisposition to hyperglycemia and lifespan.

Repression of glucocorticoid-stimulated angiopoietin-like 4 gene transcription by insulin

Angiopoietin-like 4 (Angptl4) is a glucocorticoid receptor (GR) primary target gene in hepatocytes and adipocytes. It encodes a secreted protein that inhibits extracellular LPL and promotes adipocyte lipolysis. In Angptl4 null mice, glucocorticoid-induced adipocyte lipolysis and hepatic steatosis are compromised. Markedly, insulin suppressed glucocorticoid-induced Angptl4 transcription. To unravel the mechanism, we utilized small molecules to inhibit insulin signaling components and found that phosphatidylinositol 3-kinase and Akt were vital for the suppression in H4IIE cells. A forkhead box transcription factor response element (FRE) was found near the 15 bp Angptl4 glucocorticoid response element (GRE). Mutating the Angptl4 FRE significantly reduced glucocorticoid-induced reporter gene expression in cells. Moreover, chromatin immunoprecipitation revealed that GR and FoxO1 were recruited to Angptl4 GRE and FRE in a glucocorticoid-dependent manner, and cotreatment with insulin abolished both recruitments. Furthermore, in 24 h fasted mice, significant occupancy of GR and FoxO1 at the Angptl4 GRE and FRE was found in the liver. In contrast, both occupancies were diminished after 24 h refeeding. Finally, overexpression of dominant negative FoxO1 mutant abolished glucocorticoid-induced Angptl4 expression, mimicking the insulin suppression. Overall, we demonstrate that both GR and FoxO1 are required for Angptl4 transcription activation, and that FoxO1 negatively mediates the suppressive effect of insulin.

Deletion of hepatic FoxO1/3/4 genes in mice significantly impacts on glucose metabolism through downregulation of gluconeogenesis and upregulation of glycolysis

Forkhead transcription factors FoxO1/3/4 have pleiotrophic functions including anti-oxidative stress and metabolism. With regard to glucose metabolism, most studies have been focused on FoxO1. To further investigate their hepatic functions, we generated liver-specific FoxO1/3/4 knockout mice (LTKO) and examined their collective impacts on glucose homeostasis under physiological and pathological conditions. As compared to wild-type mice, LTKO mice had lower blood glucose levels under both fasting and non-fasting conditions and they manifested better glucose and pyruvate tolerance on regular chow diet. After challenged by a high-fat diet, wild-type mice developed type 2 diabetes, but LTKO mice remained euglycemic and insulin-sensitive. To understand the underlying mechanisms, we examined the roles of SIRT6 (Sirtuin 6) and Gck (glucokinase) in the FoxO-mediated glucose metabolism. Interestingly, ectopic expression of SIRT6 in the liver only reduced gluconeogenesis in wild-type but not LTKO mice whereas knockdown of Gck caused glucose intolerance in both wild-type and LTKO mice. The data suggest that both decreased gluconeogenesis and increased glycolysis may contribute to the overall glucose phenotype in the LTKO mice. Collectively, FoxO1/3/4 transcription factors play important roles in hepatic glucose homeostasis.

A cytoprotective perspective on longevity regulation

There are many mechanisms of lifespan extension, including the disruption of insulin/insulin-like growth factor 1 (IGF-1) signaling, metabolism, translation, and feeding. Despite the disparate functions of these pathways, inhibition of each induces responses that buffer stress and damage. Here, emphasizing data from genetic analyses in Caenorhabditis elegans, we explore the effectors and upstream regulatory components of numerous cytoprotective mechanisms activated as major elements of longevity programs, including detoxification, innate immunity, proteostasis, and oxidative stress response. We show that their induction underpins longevity extension across functionally diverse triggers and across species. Intertwined with the evolution of longevity, cytoprotective pathways are coupled to the surveillance of core cellular components, with important implications in normal and aberrant responses to drugs, chemicals, and pathogens.

IKBKE phosphorylation and inhibition of FOXO3a: a mechanism of IKBKE oncogenic function

Forkhead box O (FOXO) transcription factors are emerging as key regulators of cell survival and growth. The transcriptional activity and subcellular localization of FOXO are tightly regulated by post-translational modifications. Here we report that IKBKE regulates FOXO3a through phosphorylation of FOXO3a-Ser644. The phosphorylation of FOXO3a resulted in its degradation and nuclear-cytoplasmic translocation. Previous studies have shown that IKBKE directly activates Akt and that Akt inhibits FOXO3a by phosphorylation of Ser32, Ser253 and Ser315. However, the activity of Akt-nonphosphorytable FOXO3a-A3 (i.e., converting 3 serine residues to alanine) was inhibited by IKBKE. Furthermore, overexpression of IKBKE correlates with elevated levels of pFOXO3a-S644 in primary lung and breast tumors. IKBKE inhibits cellular function of FOXO3a and FOXO3a-A3 but, to a much less extent, of FOXO3a-S644A. These findings suggest that IKBKE regulates FOXO3a primarily through phosphorylation of SerS644 and that IKBKE exerts its cellular function, at least to some extent, through regulation of FOXO3a.

Nuclear accumulation of β-catenin and forkhead box O3a in colon cancer: Dangerous liaison

The WNT/β-catenin and phosphoinositide 3-kinase (PI3K/AKT) signaling cascades both have been implicated in the formation and progression of colorectal cancer. Oncogenic PI3K/AKT signaling suppresses the activity of forkhead box O3a (FOXO3a) transcription factor through phosphorylation leading to its nuclear exclusion. Inhibition of the PI3K/AKT signaling by PI3K or AKT inhibitors results in the translocation of FOXO3a to the nucleus, and is considered to be a promising therapeutic strategy for many cancers including colon cancer. Now, however, a new study in Nature Medicine has revealed a nuclear interaction of β-catenin with FOXO3a as a promoter of metastatic progression in colon cancer. The work has important implications for the treatment of colon cancers, suggests a companion biomarker strategy to enable a personalized medicine approach, and offers an alternative therapeutic strategy to overcome resistance to PI3K and AKT inhibitors.

Prolactin signaling mechanisms in ovary

Prolactin is a hormone that is essential for normal reproduction and signals through two types of receptors. Not only is the classical long form of the prolactin receptor identified, but so are many short form receptors in rodents and human tissues. Mouse mutagenesis studies have offered insight into the biology of prolactin family, providing compelling evidence that the different isoforms have independent biological activity. The possibility that short forms mediate cell proliferation is important for a variety of tissues including mammary gland and ovarian follicles. This review summarizes our current knowledge about prolactin signaling and its role in reproduction through either long or short isoform receptors.

Houttuyninum, an active constituent of Chinese herbal medicine, inhibits phosphorylation of HER2/neu receptor tyrosine kinase and the tumor growth of HER2/neu-overexpressing cancer cells

AIMS

The overexpression of HER2/neu receptor plays a key role in tumorigenesis and tumor progression. Small molecules targeting HER2/neu have therapeutic value in cancers that overexpress HER2. In this present study, the effect of houttuyninum, a component in the Chinese herbal medicine Houttuynia cordata Thunb, on HER2/neu tyrosine phosphorylation and its in vivo antitumour activity was investigated.

MAIN METHODS

The phosphorylation and expression of proteins were determined by Western blot analysis. The MTT assay was employed to examine the inhibition of cell proliferation in vitro. Xenografts were established in nude mice for evaluating the antitumour activity of houttuyninum in vivo.

KEY FINDINGS

Houttuyninum inhibited phosphorylation of HER2 in a dose-dependent manner with an IC50 of 5.52 μg/ml without reducing HER2/neu protein expression in MDA-MB-453 cells. Houttuyninum also inhibited the activation of ERK1/2 and AKT, downstream molecules in the HER2/neu-mediated signal transduction pathway. In contrast, tyrosine phosphorylation of EGFR was unaffected when the concentration of houttuyninum was increased to 40 μg/ml in both A431 cells and MDA-MB-468 cells. Additionally, houttuyninum preferentially inhibited the growth of MDA-MB-453 cells that overexpressed HER2/neu; the MDA-MB-468 cells that overexpress EGFR remained unaffected. Administration of houttuyninum in vivo resulted in a significant reduction of phosphorylated HER2 levels and in tumor volumes of the BT474 and N87 xenografts, which both overexpress HER2/neu.

SIGNIFICANCE

Our findings showed that houttuyninum can inhibit the HER2/neu signalling pathway and the tumor growth of cancer cells that overexpress HER2/neu. This drug may provide therapeutic value in the treatment of cancers that involve overexpression of HER2/neu.

The anti-neurodegenerative agent clioquinol regulates the transcription factor FOXO1a

Many diseases of aging including AD (Alzheimer's disease) and T2D (Type 2 diabetes) are strongly associated with common risk factors, suggesting that there may be shared aging mechanisms underlying these diseases, with the scope to identify common cellular targets for therapy. In the present study we have examined the insulin-like signalling properties of an experimental AD 8-hydroxyquinoline drug known as CQ (clioquinol). The IIS [insulin/IGF-1 (insulin-like growth factor-1) signalling] kinase Akt/PKB (protein kinase B) inhibits the transcription factor FOXO1a (forkhead box O1a) by phosphorylating it on residues that trigger its exit from the nucleus. In HEK (human embryonic kidney)-293 cells, we found that CQ treatment induces similar responses. A key transcriptional response to IIS is the inhibition of hepatic gluconeogenic gene expression, and, in rat liver cells, CQ represses expression of the key gluconeogenic regulatory enzymes PEPCK (phosphoenolpyruvate carboxykinase) and G6Pase (glucose-6-phosphatase). The effects on FOXO1a and gluconeogenic gene expression require the presence of Zn2+ ions, reminiscent of much earlier studies examining diabetogenic properties of 8-hydroxyquinolines. Comparative investigation of the signalling properties of a panel of these compounds demonstrates that CQ alone exhibits FOXO1a regulation without diabetogenicity. Our results suggest that Zn2+-dependent regulation of FOXOs and gluconeogenesis may contribute to the therapeutic properties of this drug. Further investigation of this signalling response might illuminate novel pharmacological strategies for the treatment of age-related diseases.

Hepatic suppression of Foxo1 and Foxo3 causes hypoglycemia and hyperlipidemia in mice

Dysregulation of blood glucose and triglycerides are the major characteristics of type 2 diabetes mellitus. We sought to identify the mechanisms regulating blood glucose and lipid homeostasis. Cell-based studies established that the Foxo forkhead transcription factors Forkhead box O (Foxo)-1, Foxo3, and Foxo4 are inactivated by insulin via a phosphatidylinositol 3-kinase/Akt-dependent pathway, but the role of Foxo transcription factors in the liver in regulating nutrient metabolism is incompletely understood. In this study, we used the Cre/LoxP genetic approach to delete the Foxo1, Foxo3, and Foxo4 genes individually or a combination of two or all in the liver of lean or db/db mice and assessed the role of Foxo inactivation in regulating glucose and lipid homeostasis in vivo. In the lean mice or db/db mice, hepatic deletion of Foxo1, rather than Foxo3 or Foxo4, caused a modest reduction in blood glucose concentrations and barely affected lipid homeostasis. Combined deletion of Foxo1 and Foxo3 decreased blood glucose levels, elevated serum triglyceride and cholesterol concentrations, and increased hepatic lipid secretion and caused hepatosteatosis. Analysis of the liver transcripts established a prominent role of Foxo1 in regulating gene expression of gluconeogenic enzymes and Foxo3 in the expression of lipogenic enzymes. Our findings indicate that Foxo1 and Foxo3 inactivation serves as a potential mechanism by which insulin reduces hepatic glucose production and increases hepatic lipid synthesis and secretion in healthy and diabetic states.

Deciphering the role of forkhead transcription factors in cancer therapy

Forkhead O transcription factors (FOXO) are critical for the regulation of cell cycle arrest, cell death, and DNA damage repair. Inactivation of FOXO proteins may be associated with tumorigenesis, including breast cancer, prostate cancer, glioblastoma, rhabdomyosarcoma, and leukemia. Accumulated evidence shows that activation of oncogenic pathways such as phosphoinositide-3-kinase/AKT/IKK or RAS/mitogen-activated protein kinase suppresses FOXO transcriptional activity through the phosphorylation of FOXOs at different sites that ultimately leads to nuclear exclusion and degradation of FOXOs. In addition, posttranslational modifications of FOXOs such as acetylation, methylation and ubiquitination also contribute to modulating FOXO3a functions. Several anti-cancer drugs like paclitaxel, imatinib, and doxorubicin activate FOXO3a by counteracting those oncogenic pathways which restrain FOXOs functions. In this review, we will illustrate the regulation of FOXOs and reveal potential therapeutics that target FOXOs for cancer treatment.

Association analysis of common variants in FOXO3 with type 2 diabetes in a South Indian Dravidian population

Recent studies have identified common variants in forkhead box O3 gene (FOXO3) to be strongly associated with longevity in different populations. But studies have not been carried out to analyse the role of common variants in FOXO3 with type 2 diabetes. Since type 2 diabetes is an age related disorder and FOXO proteins play an important role in the regulation of metabolism, we studied the role of common variants in FOXO3 for association with type 2 diabetes. The study was carried out in 994 type 2 diabetic samples and 984 normoglycemic control samples from a South Indian Dravidian population. In our analysis, we found that there was no association between any of the selected SNPs in FOXO3 with type 2 diabetes. Analysis of these SNPs with diabetes related biochemical and clinical parameters also did not reveal any significant association. Haplotype association of SNPs in FOXO3 with type 2 diabetes was observed, but the frequency of the haplotypes was considerably lower and they do not remain significant after correction for multiple testing. In conclusion, we did not observe any association of SNPs in FOXO3 with type 2 diabetes and related parameters suggesting an entirely different mechanism by which these SNPs influence longevity. However additional studies in other populations are required to completely rule out the association of common variants in FOXO3 with type 2 diabetes.

Whole genome siRNA cell-based screen links mitochondria to Akt signaling network through uncoupling of electron transport chain

Akt activation sequesters FOXO1a away from its target genes and serves as an endpoint of a complex signaling network. A cell-based RNAi screen reveals an extensive network of genes, including UCP5, which directs nuclear localization of FOXO1a. Silencing of UCP5 disrupts the mitochondria and induces JNK1, creating a link to the Akt signaling network.

Forkhead transcription factors (FOXOs) alter a diverse array of cellular processes including the cell cycle, oxidative stress resistance, and aging. Insulin/Akt activation directs phosphorylation and cytoplasmic sequestration of FOXO away from its target genes and serves as an endpoint of a complex signaling network. Using a human genome small interfering RNA (siRNA) library in a cell-based assay, we identified an extensive network of proteins involved in nuclear export, focal adhesion, and mitochondrial respiration not previously implicated in FOXO localization. Furthermore, a detailed examination of mitochondrial factors revealed that loss of uncoupling protein 5 (UCP5) modifies the energy balance and increases free radicals through up-regulation of uncoupling protein 3 (UCP3). The increased superoxide content induces c-Jun N-terminal kinase 1 (JNK1) kinase activity, which in turn affects FOXO localization through a compensatory dephosphorylation of Akt. The resulting nuclear FOXO increases expression of target genes, including mitochondrial superoxide dismutase. By connecting free radical defense and mitochondrial uncoupling to Akt/FOXO signaling, these results have implications in obesity and type 2 diabetes development and the potential for therapeutic intervention.

The extending network of FOXO transcriptional target genes

The evolutionarily conserved Forkhead box O (FOXO) family of transcription factors regulates multiple transcriptional targets involved in various cellular processes, including proliferation, stress resistance, apoptosis, and metabolism. Target gene regulation appears to be controlled in a cell-type-specific manner due to association of FOXO isoforms with specific cofactors. Many of the cellular processes modulated by FOXO are themselves deregulated in tumorigenesis, and deletion of Foxo genes has demonstrated that these transcription factors function as tumor suppressors. Our understanding of the regulation of FOXO activity, and defining specific transcriptional targets, may provide clues to the molecular mechanisms controlling cell fate decisions. In this review we describe the functional consequences of FOXO activation based on our current knowledge of transcriptional targets.

Feedback regulation of hepatic gluconeogenesis through modulation of SHP/Nr0b2 gene expression by Sirt1 and FoxO1

Protein deacetylase Sirt1 has been implicated in the regulation of hepatic gluconeogenesis; however, the mechanisms are not fully understood. To further elucidate how Sirt1 regulates gluconeogenesis, we took a loss-of-function approach by deleting the coding DNA sequence for the catalytic domain of the Sirt1 gene in the liver of a wild-type mouse (LKO(Sirt)¹) or a genetic diabetic mouse in which hepatic insulin receptor substrates 1 and 2 are deleted (DKO(Irs½)). Whereas LKO(Sirt)¹ mice exhibited normal levels of fasting and fed blood glucose, inactivation of Sirt1 in DKO(Irs½) mice (TKO(Irs½:Sirt)¹) reduced blood glucose levels and moderately improved systemic glucose tolerance. Pyruvate tolerance was also significantly improved in TKO(Irs½:Sirt)¹ mice, suggesting that Sirt1 promotes hepatic gluconeogenesis in this diabetic mouse model. To understand why inactivation of hepatic Sirt1 does not alter blood glucose levels in the wild-type background, we searched for a potential cause and found that expression of small heterodimer partner (SHP, encoded by the Nr0b2 gene), an orphan nuclear receptor, which has been shown to suppress the activity of forkhead transcription factor FoxO1, was decreased in the liver of LKO(Sirt)¹ mice. Furthermore, our luciferase reporter assays and chromatin immunoprecipitation analysis revealed that the Nr0b2 gene is a target of FoxO1, which is also regulated by Sirt1. After the gene is upregulated, Nr0b2 can feed back and repress FoxO1- and Sirt1-activated G6pc and Pdk4 gene expression. Thus, our results suggest that Sirt1 can both positively and negatively regulate hepatic gluconeogenesis through FoxO1 and Nr0b2 and keep this physiological process in control.

Aromatase is a direct target of FOXL2: C134W in granulosa cell tumors via a single highly conserved binding site in the ovarian specific promoter

Background

Granulosa cell tumors (GCT) of the ovary often express aromatase and synthesize estrogen, which in turn may influence their progression. Recently a specific point mutation (C134W) in the FOXL2 protein was identified in >94% of adult-type GCT and it is likely to contribute to their development. A number of genes are known to be regulated by FOXL2, including aromatase/CYP19A1, but it is unclear which are direct targets and whether the C134W mutation alters their regulation. Recently, it has been reported that FOXL2 forms a complex with steroidogenic factor 1 (SF-1) which is a known regulator of aromatase in granulosa cells.

Methodology/Principal Findings

In this work, the human GCT-derived cell lines KGN and COV434 were heterozygous and wildtype for the FOXL2:C134W mutation, respectively. KGN had abundant FOXL2 mRNA expression but it was not expressed in COV434. Expression of exogenous FOXL2:C134W in COV434 cells induced higher expression of a luciferase reporter for the ovarian specific aromatase promoter, promoter II (PII) (−516bp) than expression of wildtype FOXL2, but did not alter induction of a similar reporter for the steroidogenic acute regulatory protein (StAR) promoter (−1300bp). Co-immunoprecipitation confirmed that FOXL2 bound SF-1 and that it also bound its homologue, liver receptor homologue 1 (LRH-1), however, the C134W mutation did not alter these interactions or induce a selective binding of the proteins. A highly conserved putative binding site for FOXL2 was identified in PII. FOXL2 was demonstrated to bind the site by electrophoretic mobility shift assays (EMSA) and site-directed mutagenesis of this element blocked its differential induction by wildtype FOXL2 and FOXL2:C134W.

Conclusions/Significance

These findings suggest that aromatase is a direct target of FOXL2:C134W in adult-type GCT via a single distinctive and highly conserved binding site in PII and therefore provide insight into the pathogenic mechanism of this mutation.

Effects of catechin-rich green tea on gene expression of gluconeogenic enzymes in rat hepatoma H4IIE cells

Rat hepatoma H4IIE cells were stimulated with dexamethasone and dibutyryl cAMP to increase gene expressions of gluconeogenic enzymes, glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK). Inclusion of catechin-rich green tea beverage (GTB) in the culture medium reduced the up-regulation of these genes as well as that of hepatocyte nuclear factor 4 alpha (HNF4alpha) gene. GTB was fractionated into chloroform-soluble (Fraction I), ethyl acetatesoluble (Fraction II), methanol-soluble (Fraction III) and residual (Fraction IV) fractions. Fractions II and III containing catechins caused an attenuation of the up-regulated expression of these genes as well as the down-regulation of HNF4alpha gene expression. Fraction IV had a synergistic effect on the up-regulation by dexamethasone/dibutyryl cAMP of the PEPCK gene expression and upregulated HNF4alpha gene expression. These results suggest that GTB down-regulated the expression of the HNF4alpha gene to cause the down-regulated gene expression of gluconeogenic enzymes. One reason why GTB did not down-regulate hepatic PEPCK gene expression in previous animal experiments may be that the component(s) acting to up-regulate PEPCK gene expression was more effective in vivo than in cultured cells.

Genetic and functional assessment of the role of the rs13431652-A and rs573225-A alleles in the G6PC2 promoter that are strongly associated with elevated fasting glucose levels

OBJECTIVE

Genome-wide association studies have identified a single nucleotide polymorphism (SNP), rs560887, located in a G6PC2 intron that is highly correlated with variations in fasting plasma glucose (FPG). G6PC2 encodes an islet-specific glucose-6-phosphatase catalytic subunit. This study examines the contribution of two G6PC2 promoter SNPs, rs13431652 and rs573225, to the association signal.

RESEARCH DESIGN AND METHODS

We genotyped 9,532 normal FPG participants (FPG <6.1 mmol/l) for three G6PC2 SNPs, rs13431652 (distal promoter), rs573225 (proximal promoter), rs560887 (3rd intron). We used regression analyses adjusted for age, sex, and BMI to assess the association with FPG and haplotype analyses to assess comparative SNP contributions. Fusion gene and gel retardation analyses characterized the effect of rs13431652 and rs573225 on G6PC2 promoter activity and transcription factor binding.

RESULTS

Genetic analyses provide evidence for a strong contribution of the promoter SNPs to FPG variability at the G6PC2 locus (rs13431652: β = 0.075, P = 3.6 × 10(-35); rs573225 β = 0.073 P = 3.6 × 10(-34)), in addition to rs560887 (β = 0.071, P = 1.2 × 10(-31)). The rs13431652-A and rs573225-A alleles promote increased NF-Y and Foxa2 binding, respectively. The rs13431652-A allele is associated with increased FPG and elevated promoter activity, consistent with the function of G6PC2 in pancreatic islets. In contrast, the rs573225-A allele is associated with elevated FPG but reduced promoter activity.

CONCLUSIONS

Genetic and in situ functional data support a potential role for rs13431652, but not rs573225, as a causative SNP linking G6PC2 to variations in FPG, though a causative role for rs573225 in vivo cannot be ruled out.

Discovery of novel forkhead box O1 inhibitors for treating type 2 diabetes: improvement of fasting glycemia in diabetic db/db mice

Excessive hepatic glucose production through the gluconeogenesis pathway is partially responsible for the elevated glucose levels observed in patients with type 2 diabetes mellitus (T2DM). The forkhead transcription factor forkhead box O1 (Foxo1) plays a crucial role in mediating the effect of insulin on hepatic gluconeogenesis. Here, using a db/db mouse model, we demonstrate the effectiveness of Foxo1 inhibitor, an orally active small-molecule compound, as a therapeutic drug for treating T2DM. Using mass spectrometric affinity screening, we discovered a series of compounds that bind to Foxo1, identifying among them the compound, 5-amino-7-(cyclohexylamino)-1-ethyl-6-fluoro-4-oxo-1,4-dihydroquinoline-3-carboxylic acid (AS1842856), which potently inhibits human Foxo1 transactivation and reduces glucose production through the inhibition of glucose-6 phosphatase and phosphoenolpyruvate carboxykinase mRNA levels in a rat hepatic cell line. Oral administration of AS1842856 to diabetic db/db mice led to a drastic decrease in fasting plasma glucose level via the inhibition of hepatic gluconeogenic genes, whereas administration to normal mice had no effect on the fasting plasma glucose level. Treatment with AS1842856 also suppressed an increase in plasma glucose level caused by pyruvate injection in both normal and db/db mice. Taken together, these findings indicate that the Foxo1 inhibitor represents a new class of drugs for use in treating T2DM.

Effects of the novel Foxo1 inhibitor AS1708727 on plasma glucose and triglyceride levels in diabetic db/db mice

Recent evidence suggests that the forkhead transcription factor Foxo1 plays an important role in the regulation of glucose and triglyceride metabolism at the gene transcription level for glucose-6 phosphatase (G6Pase), phosphoenolpyruvate carboxykinase (PEPCK), and apolipoprotein C-III (apoC-III). Here, we report on the pharmacological effects of the novel Foxo1 inhibitor AS1708727, which we identified by compound screening. Chronic treatment of diabetic db/db mice with AS1708727 for four days significantly reduced blood glucose and triglyceride levels with decrease of gene expression levels of hepatic G6Pase, PEPCK, and apoC-III. No reports have yet examined the influence of Foxo1 inhibitors on these pharmacological effects. In this study, we newly identified a Foxo1 inhibitor compound capable of exerting both an anti-hypertriglyceridemic and anti-hyperglycemic effect. These effects were dependent on maintaining a stable blood concentration of AS1708727 and achieving a high rate of compound transition to the liver. We also investigated the action mechanism of AS1708727 on gluconeogenesis in vitro and in vivo. The compound inhibited gene expression of key gluconeogenic molecules and suppressed gluconeogenesis in Fao hepatocyte cells in vitro. Further, in the pyruvate challenge study using db/db mice in vivo, AS1708727 suppressed increases in blood glucose level by inhibiting gluconeogenic gene expression. These results indicate that the novel Foxo1 inhibitor AS1708727 may exert anti-diabetic and anti-hypertriglyceridemic effects by improving blood glucose and triglyceride metabolism at the gene expression level, and may represent a new class of drugs useful for treating type 2 diabetes mellitus and hypertriglyceridemia.

Impact of prolactin receptor isoforms on reproduction

Prolactin is a hormone involved in growth, development, reproduction, metabolism, water and electrolyte balance, brain and behavior, and immunoregulation. Its actions on reproductive processes represent the largest group of functions identified for this hormone. Besides the classic long form of the prolactin receptor, many short form receptors have been identified in rodents and human tissues. Mouse mutagenesis studies have offered insight into the biology of the prolactin family, providing compelling evidence that different isoforms have independent biological activity. The possibility that short forms mediate cell proliferation is important for a variety of tissues including mammary glands and ovarian follicles. This review summarizes the current knowledge about prolactin signaling and its role in reproduction through either long or short isoform receptors.

Zinc-dependent effects of small molecules on the insulin-sensitive transcription factor FOXO1a and gluconeogenic genes

Metal-binding compounds have recently been reported to have anti-hyperglycaemic properties in vivo. In the current study, we have investigated the ability of these compounds and related structures to induce insulin-like signal transduction to downstream effectors such as the transcription factor FOXO1a and the key gluconeogenic regulatory enzymes phosphoenolpyruvate carboxykinase (PEPCK) and glucose 6-phosphatase (G6Pase). Our results indicate that β-thujaplicin, diethyldithiocarbamate (DEDTC) and its clinically-used dimer disulfiram, induce insulin-like dose-dependent effects on signalling to FOXO1a in a manner that is strictly dependent on the presence of zinc ions, as other ions including aluminium, cobalt, copper, lithium and manganese cannot substitute. The most potent compound tested on gluconeogenesis is disulfiram, which in the presence of 10 μM zinc, inhibited both PEPCK and G6Pase with an IC50 of 4 μM. Our results demonstrate that metal-binding compounds with diverse structures can induce zinc-dependent insulin-like effects on signal transduction and gene expression.

Glucose-6-phosphatase catalytic subunit gene family

Glucose-6-phosphatase catalyzes the hydrolysis of glucose 6-phosphate (G6P) to glucose and inorganic phosphate. It is a multicomponent system located in the endoplasmic reticulum that comprises several integral membrane proteins, namely a catalytic subunit (G6PC) and transporters for G6P, inorganic phosphate, and glucose. The G6PC gene family contains three members, designated G6PC, G6PC2, and G6PC3. The tissue-specific expression patterns of these genes differ, and mutations in all three genes have been linked to distinct diseases in humans. This minireview discusses the disease association and transcriptional regulation of the G6PC genes as well as the biological functions of the encoded proteins.

A new fork for clinical application: targeting forkhead transcription factors in cancer

Forkhead O transcription factors (FOXO) play a pivotal role in the regulation of a myriad of cellular functions including cell cycle arrest, cell death, and protection from stress stimuli. Activation of cell survival pathways such as phosphoinositide-3-kinase/AKT/IKK or RAS/mitogen-activated protein kinase are known to phosphorylate FOXOs at different sites which cause FOXOs nuclear exclusion and degradation, resulting in the suppression of FOXO's transcriptional activity. Perturbation of FOXO's function leads to deregulated cell proliferation and accumulation of DNA damage, resulting in diseases such as cancer. Emerging evidence shows that active FOXO proteins are crucial for keeping cells in check; and inactivation of FOXO proteins is associated with tumorigenesis, including breast cancer, prostate cancer, glioblastoma, rhabdomyosarcoma, and leukemia. Moreover, clinically used drugs like paclitaxel, imatinib, and doxorubicin have been shown to achieve their therapeutic effects through activation of FOXO3a and FOXO3a targets. In this review, we will focus the novel functions of FOXOs revealed in recent studies and further highlight FOXOs as new therapeutic targets in a broad spectrum of cancers.

Ablation of ARNT/HIF1beta in liver alters gluconeogenesis, lipogenic gene expression, and serum ketones

We have previously shown that expression of the transcription factor ARNT/HIF1beta is reduced in islets of humans with type 2 diabetes. We have now found that ARNT is also reduced in livers of diabetics. To study the functional effect of its reduction, we created mice with liver-specific ablation (L-ARNT KO) using ARNT loxP mice and adenoviral-mediated delivery of Cre. L-ARNT KO mice had normal blood glucose but increased fed insulin levels. These mice also exhibited features of type 2 diabetes with increased hepatic gluconeogenesis, increased lipogenic gene expression, and low serum beta-hydroxybutyrate. These effects appear to be secondary to increased expression of CCAAT/enhancer-binding protein alpha (C/EBPalpha), farnesoid X receptor (FXR), and sterol response element-binding protein 1c (SREBP-1c) and a reduction in phosphorylation of AMPK without changes in the expression of enzymes in ketogenesis, fatty acid oxidation, or FGF21. These results demonstrate that a deficiency of ARNT action in the liver, coupled with that in beta cells, could contribute to the metabolic phenotype of human type 2 diabetes.