A secondary phosphorylation of CREB341 at Ser129 is required for the cAMP-mediated control of gene expression. A role for glycogen synthase kinase-3 in the control of gene expression

Insulin-like growth factor 1 enhances follicle-stimulating hormone-induced phosphorylation of GATA4 in rat granulosa cells

Preovulatory granulosa cell (GC) differentiation is essential for the maturation and release of oocytes from the ovary. We have previously demonstrated that follicle-stimulating hormone (FSH) and insulin-like growth factors (IGFs) closely interact to control GC function. Similarly, we showed that GATA4 mediates FSH actions and it is required for preovulatory follicle formation. This report aimed to determine in vivo the effect of FSH on GATA4 phosphorylation and to investigate whether FSH and IGF1 interact to regulate GATA4 activity. In rat ovaries, treatment with equine chorionic gonadotropin (eCG) increased the phosphorylation of GATA4, which was confined to the nucleus of GCs. Using primary rat GCs, we observed that GATA4 phosphorylation at serine 105 increases the transcriptional activity of this transcription factor. Like FSH, IGF1 stimulated GATA4 phosphorylation at serine 105. Interestingly, GATA4 phosphorylation was significantly higher in cells cotreated with FSH and IGF1 when compared to FSH or IGF1 alone, suggesting that IGF1 augments the effects of FSH on GATA4. It was also found that the enhancing effect of IGF1 requires AKT activity and is mimicked by the inhibition of glycogen synthase kinase-3 β (GSK3β), suggesting that AKT inhibition of GSK3β may play a role in the regulation of GATA4 phosphorylation. The data support an important role of the IGF1/AKT/GSK3β signaling pathway in the regulation of GATA4 transcriptional activity and provide new insights into the mechanisms by which FSH and IGF1 regulate GC differentiation. Our findings suggest that GATA4 transcriptional activation may, at least partially, mediate AKT actions in GCs.

Inhibition of glycogen synthase kinase 3 by lithium, a mechanism in search of specificity

Inhibition of Glycogen synthase kinase 3 (GSK3) is a popular explanation for the effects of lithium ions on mood regulation in bipolar disorder and other mental illnesses, including major depression, cyclothymia, and schizophrenia. Contribution of GSK3 is supported by evidence obtained from animal and patient derived model systems. However, the two GSK3 enzymes, GSK3α and GSK3β, have more than 100 validated substrates. They are thus central hubs for major biological functions, such as dopamine-glutamate neurotransmission, synaptic plasticity (Hebbian and homeostatic), inflammation, circadian regulation, protein synthesis, metabolism, inflammation, and mitochondrial functions. The intricate contributions of GSK3 to several biological processes make it difficult to identify specific mechanisms of mood stabilization for therapeutic development. Identification of GSK3 substrates involved in lithium therapeutic action is thus critical. We provide an overview of GSK3 biological functions and substrates for which there is evidence for a contribution to lithium effects. A particular focus is given to four of these: the transcription factor cAMP response element-binding protein (CREB), the RNA-binding protein FXR1, kinesin subunits, and the cytoskeletal regulator CRMP2. An overview of how co-regulation of these substrates may result in shared outcomes is also presented. Better understanding of how inhibition of GSK3 contributes to the therapeutic effects of lithium should allow for identification of more specific targets for future drug development. It may also provide a framework for the understanding of how lithium effects overlap with those of other drugs such as ketamine and antipsychotics, which also inhibit brain GSK3.

Silencing of hypothalamic FGF11 prevents diet-induced obesity

Fibroblast growth factor 11 (FGF11) is a member of the intracellular fibroblast growth factor family. Here, we report the central role of FGF11 in the regulation of metabolism. Lentiviral injection of Fgf11 shRNA into the arcuate nucleus of the mouse hypothalamus decreased weight gain and fat mass, increased brown adipose tissue thermogenesis, and improved glucose and insulin intolerances under high-fat diet conditions. Fgf11 was expressed in the NPY–expressing neurons, and Fgf11 knockdown considerably decreased Npy expression and projection, leading to increased expression of tyrosine hydroxylase in the paraventricular nucleus. Mechanistically, FGF11 regulated Npy gene expression through the glycogen synthase kinase 3–cAMP response element-binding protein pathway. Our study defines the physiological significance of hypothalamic FGF11 in the regulation of metabolism in response to overnutrition such as high-fat diet.

Potential role of IP3/Ca2+ signaling and phosphodiesterases: Relevance to neurodegeneration in Alzheimer's disease and possible therapeutic strategies

Despite large investments by industry and governments, no disease-modifying medications for the treatment of patients with Alzheimer's disease (AD) have been found. The failures of various clinical trials indicate the need for a more in-depth understanding of the pathophysiology of AD and for innovative therapeutic strategies for its treatment. Here, we review the rational for targeting IP3 signaling, cytosolic calcium dysregulation, phosphodiesterases (PDEs), and secondary messengers like cGMP and cAMP, as well as their correlations with the pathophysiology of AD. Various drugs targeting these signaling cascades are still in pre-clinical and clinical trials which support the ideas presented in this article. Further, we describe different molecular mechanisms and medications currently being used in various pre-clinical and clinical trials involving IP3/Ca⁺² signaling. We also highlight various isoforms, as well as the functions and pharmacology of the PDEs broadly expressed in different parts of the brain and attempt to unravel the potential benefits of PDE inhibitors for use as novel medications to alleviate the pathogenesis of AD.

Elevation of Hyaluronan Synthase by Magnesium Supplementation Mediated through the Activation of GSK3 and CREB in Human Keratinocyte-Derived HaCaT Cells

Skin barrier damage is present in the patients with hereditary disorders of the magnesium channel, but the molecular mechanism has not been fully understood. We found that the expressions of hyaluronan synthase (HAS), HAS2 and HAS3 are influenced by MgCl2 concentration in human keratinocyte-derived HaCaT cells. The exposure of cells to a high concentration (5.8 mM) of MgCl2 induced the elevation of HAS2/3 expression, which was inhibited by mRNA knockdown of nonimprinted in Prader-Willi/Angelman syndrome-like domain containing 4 (NIPAL4). Similarly, the content of hyaluronic acid (HA) was changed according to MgCl2 concentration and the expression of NIPAL4. The MgCl2 supplementation increased the reporter activities of HAS2/3, which were inhibited by NIPAL4 knockdown, indicating that the expressions of HAS2/3 are up-regulated at the transcriptional level. The reporter activities and mRNA levels of HAS2/3, and the production of HA were inhibited by CHIR-99021, a glycogen synthase kinase-3 (GSK3) inhibitor, and naphthol AS-E, a cyclic AMP-response element binding protein (CREB) inhibitor. Furthermore, the mutation in putative CREB-binding sites of promoter region in HAS2/3 genes inhibited the MgCl2 supplementation-induced elevation of promoter activity. Our results indicate that the expressions of HAS2/3 are up-regulated by MgCl2 supplementation in HaCaT cells mediated through the activation of GSK3 and CREB. Magnesium may play a pivotal role in maintaining the skin barrier function and magnesium supplementation may be useful to enhance moisturization and wound repair in the skin.

Lithium orotate: A superior option for lithium therapy?

Bipolar disorder (BD) poses a significant public health concern, with roughly one-quarter of sufferers attempting suicide. BD is characterized by manic and depressive mood cycles, the recurrence of which can be effectively curtailed through lithium therapy. Unfortunately, the most frequently employed lithium salt, lithium carbonate (Li₂ CO₃ ), is associated with a host of adverse health outcomes following chronic use: these unwanted effects range from relatively minor inconveniences (e.g., polydipsia and polyuria) to potentially major complications (e.g., hypothyroidism and/or renal impairment). As these undesirable effects can limit patient compliance, an alternative lithium compound with a lesser toxicity profile would dramatically improve treatment efficacy and outcomes. Lithium orotate (LiC₅ H₃ N₂ O₄ ; henceforth referred to as LiOr), a compound largely abandoned since the late 1970s, may represent such an alternative. LiOr is proposed to cross the blood-brain barrier and enter cells more readily than Li₂ CO₃ , which will theoretically allow for reduced dosage requirements and ameliorated toxicity concerns. This review addresses the controversial history of LiOr, complete with discussions of experimental and clinical efficacy, putative mechanisms of action, adverse effects, and its potential future in therapy.

NOXA-mediated degradation of MCL1 and BCL2L1 causes apoptosis of daunorubicin-treated human acute myeloid leukemia cells

Daunorubicin (DNR) is used clinically to treat acute myeloid leukemia (AML), while the signaling pathways associated with its cytotoxicity are not fully elucidated. Thus, we investigated the DNR-induced death pathway in the human AML cell lines U937 and HL-60. DNR-induced apoptosis in U937 cells accompanied by downregulation of MCL1 and BCL2L1, upregulation of Phorbol-12-myristate-13-acetate-induced protein 1 (NOXA), and mitochondrial depolarization. DNR induced NOX4-mediated reactive reactive oxygen species (ROS) production, which in turn inactivated Akt and simultaneously activated p38 mitogen-activated protein kinase (MAPK). Activated p38 MAPK and inactivated Akt coordinately increased GSK3β-mediated cAMP response element-binding protein (CREB) phosphorylation, which promoted NOXA transcription. NOXA upregulation critically increased the proteasomal degradation of MCL1 and BCL2L1. The same pathway was also responsible for the DNR-induced death of HL-60 cells. Restoration of MCL1 or BCL2L1 expression alleviated DNR-induced mitochondrial depolarization and cell death. Furthermore, ABT-199 (a BCL2 inhibitor) synergistically enhanced the cytotoxicity of DNR in AML cell lines. Notably, DNR-induced DNA damage was not related to NOXA-mediated degradation of MCL1 and BCL2L1. Collectively, these results indicate that the upregulation of NOXA expression through the NOX4-ROS-p38 MAPK-GSK3β-CREB axis results in the degradation of MCL1 and BCL2L1 in DNR-treated U937 and HL-60 cells. This signaling pathway may provide insights into the mechanism underlying DNR-triggered apoptosis in AML cells.

Permissive effect of GSK3β on profibrogenic plasticity of renal tubular cells in progressive chronic kidney disease

Renal tubular epithelial cells (TECs) play a key role in renal fibrogenesis. After persistent injuries that are beyond self-healing capacity, TECs will dedifferentiate, undergo growth arrest, convert to profibrogenic phenotypes, and resort to maladaptive plasticity that ultimately results in renal fibrosis. Evidence suggests that glycogen synthase kinase (GSK) 3β is centrally implicated in kidney injury. However, its role in renal fibrogenesis is obscure. Analysis of publicly available kidney transcriptome database demonstrated that patients with progressive chronic kidney disease (CKD) exhibited GSK3β overexpression in renal tubulointerstitium, in which the predefined hallmark gene sets implicated in fibrogenesis were remarkably enriched. In vitro, TGF-β1 treatment augmented GSK3β expression in TECs, concomitant with dedifferentiation, cell cycle arrest at G2/M phase, excessive accumulation of extracellular matrix, and overproduction of profibrotic cytokines like PAI-1 and CTGF. All these profibrogenic phenotypes were largely abrogated by GSK3β inhibitors or by ectopic expression of a dominant-negative mutant of GSK3β but reinforced in cells expressing the constitutively active mutant of GSK3β. Mechanistically, GSK3β suppressed, whereas inhibiting GSK3β facilitated, the activity of cAMP response element-binding protein (CREB), which competes for CREB-binding protein, a transcriptional coactivator essential for TGF-β1/Smad signaling pathway to drive TECs profibrogenic plasticity. In vivo, in mice with folic acid-induced progressive CKD, targeting of GSK3β in renal tubules via genetic ablation or by microdose lithium mitigated the profibrogenic plasticity of TEC, concomitant with attenuated interstitial fibrosis and tubular atrophy. Collectively, GSK3β is likely a pragmatic therapeutic target for averting profibrogenic plasticity of TECs and improving renal fibrosis.

Mechanisms and Therapeutic Implications of GSK-3 in Treating Neurodegeneration

Neurodegenerative disorders are spreading worldwide and are one of the greatest threats to public health. There is currently no adequate therapy for these disorders, and therefore there is an urgent need to accelerate the discovery and development of effective treatments. Although neurodegenerative disorders are broad ranging and highly complex, they may share overlapping mechanisms, and thus potentially manifest common targets for therapeutic interventions. Glycogen synthase kinase-3 (GSK-3) is now acknowledged to be a central player in regulating mood behavior, cognitive functions, and neuron viability. Indeed, many targets controlled by GSK-3 are critically involved in progressing neuron deterioration and disease pathogenesis. In this review, we focus on three pathways that represent prominent mechanisms linking GSK-3 with neurodegenerative disorders: cytoskeleton organization, the mammalian target of rapamycin (mTOR)/autophagy axis, and mitochondria. We also consider the challenges and opportunities in the development of GSK-3 inhibitors for treating neurodegeneration.

What turns CREB on? And off? And why does it matter?

Altered expression and function of the transcription factor cyclic AMP response-binding protein (CREB) has been identified to play an important role in cancer and is associated with the overall survival and therapy response of tumor patients. This review focuses on the expression and activation of CREB under physiologic conditions and in tumors of distinct origin as well as the underlying mechanisms of CREB regulation by diverse stimuli and inhibitors. In addition, the clinical relevance of CREB is summarized, including its use as a prognostic and/or predictive marker as well as a therapeutic target.

The Scaffold Protein Axin Promotes Signaling Specificity within the Wnt Pathway by Suppressing Competing Kinase Reactions

Scaffold proteins are thought to promote signaling specificity by accelerating reactions between bound kinase and substrate proteins. To test the long-standing hypothesis that the scaffold protein Axin accelerates glycogen synthase kinase 3β (GSK3β)-mediated phosphorylation of β-catenin in the Wnt signaling network, we measured GSK3β reaction rates with multiple substrates in a minimal, biochemically reconstituted system. We observed an unexpectedly small, ∼2-fold Axin-mediated rate increase for the β-catenin reaction when measured in isolation. In contrast, when both β-catenin and non-Wnt pathway substrates are present, Axin accelerates the β-catenin reaction by preventing competition with alternative substrates. At high competitor concentrations, Axin produces >10-fold rate effects. Thus, while Axin alone does not markedly accelerate the β-catenin reaction, in physiological settings where multiple GSK3β substrates are present, Axin may promote signaling specificity by suppressing interactions with competing, non-Wnt pathway targets. This mechanism for scaffold-mediated control of competition enables a shared kinase to perform distinct functions in multiple signaling networks.

Contribution of neuronal calcium sensor 1 (Ncs-1) to anxiolytic-like and social behavior mediated by valproate and Gsk3 inhibition

Peripheral biomarker and post-mortem brains studies have shown alterations of neuronal calcium sensor 1 (Ncs-1) expression in people with bipolar disorder or schizophrenia. However, its engagement by psychiatric medications and potential contribution to behavioral regulation remains elusive. We investigated the effect on Ncs-1 expression of valproic acid (VPA), a mood stabilizer used for the management of bipolar disorder. Treatment with VPA induced Ncs-1 gene expression in cell line while chronic administration of this drug to mice increased both Ncs-1 protein and mRNA levels in the mouse frontal cortex. Inhibition of histone deacetylases (HDACs), a known biochemical effect of VPA, did not alter the expression of Ncs-1. In contrast, pharmacological inhibition or genetic downregulation of glycogen synthase kinase 3β (Gsk3β) increased Ncs-1 expression, whereas overexpression of a constitutively active Gsk3β had the opposite effect. Moreover, adeno-associated virus-mediated Ncs-1 overexpression in mouse frontal cortex caused responses similar to those elicited by VPA or lithium in tests evaluating social and mood-related behaviors. These findings indicate that VPA increases frontal cortex Ncs-1 gene expression as a result of Gsk3 inhibition. Furthermore, behavioral changes induced by Ncs-1 overexpression support a contribution of this mechanism in the regulation of behavior by VPA and potentially other psychoactive medications inhibiting Gsk3 activity.

Edgeworthia gardneri (Wall.) Meisn. Water Extract Ameliorates Palmitate Induced Insulin Resistance by Regulating IRS1/GSK3β/FoxO1 Signaling Pathway in Human HepG2 Hepatocytes

The flower of Edgeworthia gardneri (Wall.) Meisn is commonly used in beverage products in Tibet and has potential health benefits for diabetes. However, the mechanisms underlying anti-insulin resistance (IR) action of the flower of E. gardneri are not fully understood. This study aims to investigate the effects of the water extract of the flower of E. gardneri (WEE) on IR in palmitate (PA)-exposed HepG2 hepatocytes. WEE was characterized by UPLC analysis. PA-treated HepG2 cells were selected as the IR cell model. The cell viability was determined using MTT assay. Moreover, the glucose consumption and production were measured by glucose oxidase method. The glucose uptake and glycogen content were determined by the 2-NBDG (2-deoxy-2-[(7-nitro-2,1,3-benzoxadiazol-4-yl) amino]-D-glucose) glucose uptake assay and anthrone-sulfuric acid assay, respectively. The intracellular triglyceride content was detected by oxidative enzymic method. Protein levels were examined by Western blotting. Nuclear localization of FoxO1 was detected using immunofluorescence analyses and Western blotting. The expression of FoxO1 target genes was detected by quantitative real-time polymerase chain reaction (qRT-PCR). The viability of PA-treated HepG2 cells was concentration-dependently increased by incubation with WEE for 24 h. WEE treatment remarkably increased the consumption and uptake of glucose in PA-exposed HepG2 cells. Moreover, treatment with WEE significantly decreased the PA-induced over-production of glucose in HepG2 cells. After exposure of HepG2 cells with PA and WEE, the glycogen content was significantly elevated. The phosphorylation and total levels of IRβ, IRS1, and Akt were upregulated by WEE treatment in PA-exposed HepG2 cells. The phosphorylation of GSK3β was elevated after WEE treatment in PA-treated cells. WEE treatment also concentration-dependently downregulated the phosphorylated CREB, ERK, c-Jun, p38 and JNK in PA-exposed HepG2 cells. Furthermore, the nuclear protein level and nuclear translocation of FoxO1 were also suppressed by WEE. Additionally, PA-induced changes of FoxO1 targeted genes were also attenuated by WEE treatment. The GLUT2 and GLUT4 translocation were also promoted by WEE treatment in PA-treated HepG2 cells. Taken together, WEE has potential anti-IR effect in PA-exposed HepG2 cells; the underlying mechanism of this action may be associated with the regulation of IRS1/GSK3β/FoxO1 signaling pathway. This study provides a pharmacological basis for the application of WEE in the treatment of metabolic diseases such as type 2 diabetes mellitus.

Therapeutic Modulation of the Immune Response in Arrhythmogenic Cardiomyopathy

BACKGROUND

Inflammation is a prominent feature of arrhythmogenic cardiomyopathy (ACM), but whether it contributes to the disease phenotype is not known.

METHODS

To define the role of inflammation in the pathogenesis of ACM, we characterized nuclear factor-κB signaling in ACM models in vitro and in vivo and in cardiac myocytes from patient induced pluripotent stem cells.

RESULTS

Activation of nuclear factor-κB signaling, indicated by increased expression and nuclear accumulation of phospho-RelA/p65, occurred in both an in vitro model of ACM (expression of JUP^2157del2 in neonatal rat ventricular myocytes) and a robust murine model of ACM (homozygous knock-in of mutant desmoglein-2 [Dsg2^mut/mut]) that recapitulates the cardiac manifestations seen in patients with ACM. Bay 11-7082, a small-molecule inhibitor of nuclear factor-κB signaling, prevented the development of ACM disease features in vitro (abnormal redistribution of intercalated disk proteins, myocyte apoptosis, release of inflammatory cytokines) and in vivo (myocardial necrosis and fibrosis, left ventricular contractile dysfunction, electrocardiographic abnormalities). Hearts of Dsg2^mut/mut mice expressed markedly increased levels of inflammatory cytokines and chemotactic molecules that were attenuated by Bay 11-7082. Salutary effects of Bay 11-7082 correlated with the extent to which production of selected cytokines had been blocked. Nuclear factor-κB signaling was also activated in cardiac myocytes derived from a patient with ACM. These cells produced and secreted abundant inflammatory cytokines under basal conditions, and this was also greatly reduced by Bay 11-7082.

CONCLUSIONS

Inflammatory signaling is activated in ACM and drives key features of the disease. Targeting inflammatory pathways may be an effective new mechanism-based therapy for ACM.

Influence of signaling kinases on functional dynamics of nuclear receptor CAR

Constitutive androstane receptor (CAR) is a xenobiotic nuclear receptor known to regulate genes involved in key physiological processes like drug metabolism, maintenance of energy homeostasis, and cell proliferation. Owing to the diverse regulatory roles played by the receptor, it is critical to understand the precise cellular signals that dictate functional dynamics of CAR. With the objective of exploring the hitherto unknown regulatory pathways modulating CAR, we subjected the CAR protein sequence to a kinase prediction tool and identified several kinases recognizing CAR as a substrate. Using fluorescence live cell imaging and specific inhibitors it was observed that CAR functions under the regulation of mitogen-activated protein kinase (MAPK) and glycogen synthase kinase 3 (GSK3) signaling cascade. Additionally, insulin-like growth factor 1 (IGF1)-mediated inhibition of GSK3 also induced nuclear translocation of CAR linking CAR to the Akt signaling pathway. Identification of T38 residue of CAR as the GSK3 target site further substantiated our observations. Taking cues from these findings, we propose a hypothetical model elucidating the GSK3-mediated regulation of CAR dynamics through the involvement of Akt pathway. Further research into this area is expected to provide novel therapeutic targets in disease conditions like type 2 diabetes and hepatocellular carcinoma.

Molecular control of protein synthesis, glucose metabolism, and apoptosis in the brain of hibernating thirteen-lined ground squirrels

Thirteen-lined ground squirrels (Ictidomys tridecemlineatus) are excellent models for studying acute brain ischemia because they show high resistance to reductions in blood flow and oxygen delivery without evidence of neurological damage. In this study, we analyzed the insulin signaling pathway and regulation of mitochondrial substrate oxidation in three regions of ground squirrel brain (forebrain, cerebellum, and brainstem), comparing summer, late torpor, and interbout arousal conditions. We found select decreases in phospho-Akt in the cerebellum during torpor compared with summer animals, as well as select increases in the forebrain during interbout arousal, suggesting that Akt may influence either metabolism or cytoprotective pathways. The phosphoprotein abundance of glycogen synthase kinase 3 beta (GSK3β) showed the most consistent trend across all three brain regions, with peak increases observed during deep torpor, suggesting a crucial role for this protein during hibernation. Furthermore, all three regions of the brain showed increased phospho-protein abundance of pyruvate dehydrogenase at serine 232 during both deep torpor and interbout arousal, and serine 300 during interbout arousal only, whereas other phosphorylation sites showed a region-specific expression pattern. Information collected from these studies sheds light on the molecular controls governing insulin signaling and fuel utilization in the brain of hibernating ground squirrels.

Role of the p38 MAPK/C/EBPβ Pathway in the Regulation of Phenotype and IL-10 and IL-12 Production by Tolerogenic Bone Marrow-Derived Dendritic Cells

Dendritic cells (DCs) play a major role in innate and adaptive immunity and self-immune tolerance. Immunogenic versus tolerogenic DC functions are dictated by their levels of costimulatory molecules and their cytokine expression profile. The transcription factor C/EBPβ regulates the expression of several inflammatory genes in many cell types including macrophages. However, little is known regarding the role of C/EBPβ in tolerogenic versus immunogenic DCs functions. We have previously reported that bone marrow-derived DCs generated with GM-CSF (GM/DCs) acquire the signature of semi-mature tolerogenic IL-10-producing DCs as opposed to immunogenic DCs generated with GM-CSF and IL-4 (IL-4/DCs). Here, we show that tolerogenic GM/DCs exhibit higher levels of phosphorylation and enhanced DNA binding activity of C/EBPβ and CREB than immunogenic IL-4/DCs. We also show that the p38 MAPK/CREB axis and GSK3 play an important role in regulating C/EBPβ phosphorylation and DNA binding activity. Inhibition of p38 MAPK in GM/DCs resulted in a drastic decrease of C/EBPβ and CREB DNA binding activities, a reduction of their IL-10 production and an increase of their IL-12p70 production, a characteristic of immunogenic IL-4/DCs. We also present evidence that GSK3 inhibition in GM/DCs reduced C/EBPβ DNA binding activity and increased expression of costimulatory molecules in GM/DCs and their production of IL-10. Analysis of GM/DCs of C/EBPβ^-/- mice showed that C/EBPβ was essential to maintain the semimature phenotype and the production of IL-10 as well as low CD4⁺ T cell proliferation. Our results highlight the importance of the p38MAPK-C/EBPβ pathway in regulating phenotype and function of tolerogenic GM/DCs.

Molecular hydrogen reduces acute exercise-induced inflammatory and oxidative stress status

Physical exercise induces inflammatory and oxidative markers production in the skeletal muscle and this process is under the control of both endogenous and exogenous modulators. Recently, molecular hydrogen (H2) has been described as a therapeutic gas able to reduced oxidative stress in a number of conditions. However, nothing is known about its putative role in the inflammatory and oxidative status during a session of acute physical exercise in sedentary rats. Therefore, we tested the hypothesis that H2 attenuates both inflammation and oxidative stress induced by acute physical exercise. Rats ran at 80% of their maximum running velocity on a closed treadmill inhaling either the H2 gas (2% H2, 21% O2, balanced with N2) or the control gas (0% H2, 21% O2, balanced with N2) and were euthanized immediately or 3 h after exercise. We assessed plasma levels of inflammatory cytokines [tumor necrosis factor-α (TNF-α), interleukin (IL)-1β and IL-6] and oxidative markers [superoxide dismutase (SOD), thiobarbituric acid reactive species (TBARS) and nitrite/nitrate (NOx)]. In addition, we evaluated the phosphorylation status of intracellular signaling proteins [glycogen synthase kinase type 3 (GSK3α/β) and the cAMP responsive element binding protein (CREB)] that modulate several processes in the skeletal muscle during exercise, including changes in exercise-induced reactive oxygen species (ROS) production. As expected, physical exercise increased virtually all the analyzed parameters. In the running rats, H2 blunted exercise-induced plasma inflammatory cytokines (TNF-α and IL-6) surges. Regarding the oxidative stress markers, H2 caused further increases in exercise-induced SOD activity and attenuated the exercise-induced increases in TBARS 3 h after exercise. Moreover, GSK3α/β phosphorylation was not affected by exercise or H2 inhalation. Otherwise, exercise caused an increased CREB phosphorylation which was attenuated by H2. These data are consistent with the notion that H2 plays a key role in decreasing exercise-induced inflammation, oxidative stress, and cellular stress.

Unique, Intersecting, and Overlapping Roles of C/EBP β and CREB in Cells of the Innate Immune System

CREB and C/EBP β signaling pathways are modulated during inflammation and also targeted by Bacillus anthracis edema toxin (ET), but how these factors individually and jointly contribute to changes in immune cell function is poorly understood. Using CRISPR/Cas9 gene editing, macrophage cell lines lacking CREB and isoforms of C/EBP β were generated and analyzed for changes in responses to LPS, ET, and IL-4. Macrophages lacking C/EBP β suppressed induction of IL-10 and Arg1, while IL-6 was increased in these cells following exposure to LPS. Examination of C/EBP β isoforms indicated the 38 kDa isoform was necessary for the expression of IL-10 and Arg1. ChIP-Seq analysis of CREB and C/EBP β binding to targets on the chromosome of human PBMC identified several regions where both factors overlapped in their binding, suggesting similar gene targeting or cooperative effects. Based on the ChIP-Seq data, a panel of previously unknown targets of CREB and C/EBP β was identified and includes genes such as VNN2, GINS4, CTNNBL1, and SULF2. Isoforms of a transcriptional corepressor, transducin-like enhancer of Split (TLE), were also found to have CREB and C/EBP β binding their promoter and were up regulated by ET. Finally, we explore a possible layer of C/EBP β regulation by a protein complex consisting of adenomatous polyposis coli (APC) and PKA. Collectively, these data provide new insights into the role of CREB and C/EBP β as immunosignaling regulators and targets of an important bacterial virulence factor.

mTOR complex 1 controls the nuclear localization and function of glycogen synthase kinase 3β

Glycogen synthase kinase 3β (GSK3β) phosphorylates and thereby regulates a wide range of protein substrates involved in diverse cellular functions. Some GSK3β substrates, such as c-Myc and Snail, are nuclear transcription factors, suggesting the possibility that GSK3β function is controlled through its nuclear localization. Here, using ARPE-19 and MDA-MB-231 human cell lines, we found that inhibition of mTOR complex 1 (mTORC1) leads to partial redistribution of GSK3β from the cytosol to the nucleus and to a GSK3β-dependent reduction of the levels of both c-Myc and Snail. mTORC1 is known to be controlled by metabolic cues, such as by AMP-activated protein kinase (AMPK) or amino acid abundance, and we observed here that AMPK activation or amino acid deprivation promotes GSK3β nuclear localization in an mTORC1-dependent manner. GSK3β was detected on several distinct endomembrane compartments, including lysosomes. Consistently, disruption of late endosomes/lysosomes through a perturbation of RAS oncogene family member 7 (Rab7) resulted in loss of GSK3β from lysosomes and in enhanced GSK3β nuclear localization as well as GSK3β-dependent reduction of c-Myc levels. These findings indicate that the nuclear localization and function of GSK3β is suppressed by mTORC1 and suggest a link between metabolic conditions sensed by mTORC1 and GSK3β-dependent regulation of transcriptional networks controlling cellular biomass production.

Endoplasmic reticulum stress induces spatial memory deficits by activating GSK-3

Endoplasmic reticulum (ER) stress is involved in Alzheimer's disease (AD), but the mechanism is not fully understood. Here, we injected tunicamycin (TM), a recognized ER stress inducer, into the brain ventricle of Sprague-Dawley (SD) rats to induce the unfolded protein response (UPR), demonstrated by the enhanced phosphorylation of pancreatic ER kinase (PERK), inositol-requiring enzyme-1 (IRE-1) and activating transcription factor-6 (ATF-6). We observed that UPR induced spatial memory deficits and impairments of synaptic plasticity in the rats. After TM treatment, GSK-3β was activated and phosphorylation of cAMP response element binding protein at Ser129 (pS129-CREB) was increased with an increased nuclear co-localization of pY126-GSK-3β and pS129-CREB. Simultaneous inhibition of GSK-3β by hippocampal infusion of SB216763 (SB) attenuated TM-induced UPR and spatial memory impairment with restoration of pS129-CREB and synaptic plasticity. We concluded that UPR induces AD-like spatial memory deficits with mechanisms involving GSK-3β/pS129-CREB pathway.

Neuron-derived transthyretin modulates astrocytic glycolysis in hormone-independent manner

It has been shown that neurons alter the expression of astrocytic metabolic enzymes by secretion of until now unknown molecule(s) into extracellular fluid. Here, we present evidence that neuron-derived transthyretin (TTR) stimulates expression of glycolytic enzymes in astrocytes which is reflected by an increased synthesis of ATP. The action of TTR is restricted to regulatory enzymes of glycolysis: phosphofructokinase P (PFKP) and pyruvate kinase M1/M2 isoforms (PKM1/2). The regulation of PFK and PKM expression by TTR is presumably specific for brain tissue and is independent of the role of TTR as a carrier protein for thyroxine and retinol. TTR induced expression of PKM and PFK is mediated by the cAMP/PKA-dependent pathway and is antagonized by the PI3K/Akt pathway. Our results provide the first experimental evidence for action of TTR as a neuron-derived energy metabolism activator in astrocytes and describe the mechanisms of its action. The data presented here suggest that TTR is involved in a mechanism in which neurons stimulate degradation of glycogen-derived glucosyl units without significant modulation of glucose uptake by glial cells.

A partnership with the proteasome; the destructive nature of GSK3

Glycogen Synthase Kinase-3 (GSK3) was originally reported as a key enzyme of glucose homeostasis through regulation of the rate of glycogen synthesis. It has subsequently been found to influence most cellular processes, including growth, differentiation and death, as part of its role in modulating response to hormonal, nutritional and cellular stress stimuli. More than 100 protein targets for GSK3 have been proposed although only a small fraction of these have been convincingly validated in physiological cell systems. The effects of GSK3 phosphorylation on substrates include alteration of enzyme activity, protein localisation, protein:protein interaction and protein stability. This latter form of regulation of GSK3 substrates is the focus of this review. There is an ever-growing list of GSK3 substrates that upon phosphorylation are targeted to the beta-transducin repeat containing protein (β-TrCP), thereby allowing ubiquitination of bound protein by cullin-1 and so initiating destruction at the proteasome. We propose the existence of a GSK3-β-TrCP ‘destruction hit-list’ that allows co-ordinated removal (or stabilisation) of a set of proteins with a common physiological purpose, through control of GSK3. We identify 29 proteins where there is relatively strong evidence for regulation by a GSK3-β-TrCP axis and note common features of regulation and pathophysiology. Furthermore, we assess the potential of pre-phosphorylation (priming) of these targets (normally a prerequisite for GSK3 recognition) to provide a second layer of regulation delineated by the priming kinase that allows GSK3 to mark them for destruction. Finally, we discuss whether this knowledge improves options for therapeutic intervention.

O-GlcNAcylation of protein kinase A catalytic subunits enhances its activity: a mechanism linked to learning and memory deficits in Alzheimer's disease

Alzheimer's disease (AD) is characterized clinically by memory loss and cognitive decline. Protein kinase A (PKA)‐CREB signaling plays a critical role in learning and memory. It is known that glucose uptake and O‐GlcNAcylation are reduced in AD brain. In this study, we found that PKA catalytic subunits (PKAcs) were posttranslationally modified by O‐linked N‐acetylglucosamine (O‐GlcNAc). O‐GlcNAcylation regulated the subcellular location of PKAcα and PKAcβ and enhanced their kinase activity. Upregulation of O‐GlcNAcylation in metabolically active rat brain slices by O‐(2‐acetamido‐2‐deoxy‐d‐glucopyranosylidenamino) N‐phenylcarbamate (PUGNAc), an inhibitor of N‐acetylglucosaminidase, increased the phosphorylation of tau at the PKA site, Ser214, but not at the non‐PKA site, Thr205. In contrast, in rat and mouse brains, downregulation of O‐GlcNAcylation caused decreases in the phosphorylation of CREB at Ser133 and of tau at Ser214, but not at Thr205. Reduction in O‐GlcNAcylation through intracerebroventricular injection of 6‐diazo‐5‐oxo‐l‐norleucine (DON), the inhibitor of glutamine fructose‐6‐phosphate amidotransferase, suppressed PKA‐CREB signaling and impaired learning and memory in mice. These results indicate that in addition to cAMP and phosphorylation, O‐GlcNAcylation is a novel mechanism that regulates PKA‐CREB signaling. Downregulation of O‐GlcNAcylation suppresses PKA‐CREB signaling and consequently causes learning and memory deficits in AD.

A cAMP and CREB-mediated feed-forward mechanism regulates GSK3β in polycystic kidney disease

Glycogen synthase kinase 3β (GSK3β), a serine/threonine protein kinase, is commonly known to be regulated at the level of its activity. However, in some diseases including polycystic kidney disease (PKD), GSK3β expression is increased and plays a pathophysiological role. The current studies aimed to determine the mechanism for the increased GSK3β expression in PKD and its significance to disease progression. In mouse models of PKD, increases in renal GSK3β corresponded with increases in renal cAMP levels and disease progression. In vivo and in vitro studies revealed that GSK3β is a cAMP-responsive gene, and elevated cAMP levels, as seen in PKD, can increase GSK3β expression. In normal mice, vasopressin signaling induced by water deprivation increased GSK3β expression, which decreased following rehydration. Examination of the GSK3β promoter revealed five potential binding sites for the transcription factor, cAMP response element binding protein (CREB). CREB was found to bind to GSK3β promoter and essential for cAMP-mediated regulation of GSK3β. Importantly, this regulation was demonstrated to be part of a feed-forward loop in which cAMP through CREB regulates GSK3β expression, and GSK3β in turn positively regulates cAMP generation. GSK3β or CREB inhibition reduced transepithelial fluid secretion and cyst expansion in vitro Thus, disruption at any point of this destructive cycle may be therapeutically useful to reduce cyst expansion and preserve renal function in PKD.

In Vitro Anticancer Activity of Phlorofucofuroeckol A via Upregulation of Activating Transcription Factor 3 against Human Colorectal Cancer Cells

Phlorofucofuroeckol A (PFF-A), one of the phlorotannins found in brown algae, has been reported to exert anti-cancer property. However, the molecular mechanism for the anti-cancer effect of PFF-A has not been known. Activating transcription factor 3 (ATF3) has been reported to be associated with apoptosis in colorectal cancer. The present study was performed to investigate the molecular mechanism by which PFF-A stimulates ATF3 expression and apoptosis in human colorectal cancer cells. PFF-A decreased cell viability through apoptosis of human colorectal cancer cells. PFF-A increased ATF3 expression through regulating transcriptional activity. The responsible cis-element for ATF3 transcriptional activation by PFF-A was cAMP response element binding protein (CREB), located between positions −147 and −85 of the ATF3 promoter. Inhibition of p38, c-Jun N-terminal kinases (JNK), glycogen synthase kinase (GSK) 3β, and IκB kinase (IKK)-α blocked PFF-A-mediated ATF3 expression. ATF3 knockdown by ATF3 siRNA attenuated the cleavage of poly (ADP-ribose) polymerase (PARP) by PFF-A, while ATF3 overexpression increased PFF-A-mediated cleaved PARP. These results suggest that PFF-A may exert anti-cancer property through inducing apoptosis via the ATF3-mediated pathway in human colorectal cancer cells.

CREB Negatively Regulates IGF2R Gene Expression and Downstream Pathways to Inhibit Hypoxia-Induced H9c2 Cardiomyoblast Cell Death

During hypoxia, gene expression is altered by various transcription factors. Insulin-like growth factor-II (IGF2) is known to be induced by hypoxia, which binds to IGF2 receptor IGF2R that acts like a G protein-coupled receptor, might cause pathological hypertrophy or activation of the mitochondria-mediated apoptosis pathway. Cyclic adenosine monophosphate (cAMP) responsive element-binding protein (CREB) is central to second messenger-regulated transcription and plays a critical role in the cardiomyocyte survival pathway. In this study, we found that IGF2R level was enhanced in H9c2 cardiomyoblasts exposed to hypoxia in a time-dependent manner but was down-regulated by CREB expression. The over-expression of CREB in H9c2 cardiomyoblasts suppressed the induction of hypoxia-induced IGF2R expression levels and reduced cell apoptosis. Gel shift assay results further indicated that CREB binds to the promoter sequence of IGF2R. With a luciferase assay method, we further observed that CREB represses IGF2R promoter activity. These results suggest that CREB plays an important role in the inhibition of IGF2R expression by binding to the IGF2R promoter and further suppresses H9c2 cardiomyoblast cell apoptosis induced by IGF2R signaling under hypoxic conditions.

Herpes Simplex Virus type-1 infection induces synaptic dysfunction in cultured cortical neurons via GSK-3 activation and intraneuronal amyloid-β protein accumulation

Increasing evidence suggests that recurrent Herpes Simplex Virus type 1 (HSV-1) infection spreading to the CNS is a risk factor for Alzheimer’s Disease (AD) but the underlying mechanisms have not been fully elucidated yet. Here we demonstrate that in cultured mouse cortical neurons HSV-1 induced Ca²⁺-dependent activation of glycogen synthase kinase (GSK)-3. This event was critical for the HSV-1-dependent phosphorylation of amyloid precursor protein (APP) at Thr668 and the following intraneuronal accumulation of amyloid-β protein (Aβ). HSV-1-infected neurons also exhibited: i) significantly reduced expression of the presynaptic proteins synapsin-1 and synaptophysin; ii) depressed synaptic transmission. These effects depended on GSK-3 activation and intraneuronal accumulation of Aβ. In fact, either the selective GSK-3 inhibitor, SB216763, or a specific antibody recognizing Aβ (4G8) significantly counteracted the effects induced by HSV-1 at the synaptic level. Moreover, in neurons derived from APP KO mice and infected with HSV-1 Aβ accumulation was not found and synaptic protein expression was only slightly reduced when compared to wild-type infected neurons. These data further support our contention that HSV-1 infections spreading to the CNS may contribute to AD phenotype.

Overexpression of CREB protein protects from tunicamycin-induced apoptosis in various rat cell types

Endoplasmic reticulum (ER) stress plays an essential role in unfolded protein response induced apoptosis contributing to several pathological conditions. Glycogen synthase kinase-3β (GSK-3β) plays a central role in several apoptotic signaling, including ER stress, as the active form of GSK-3β induces apoptosis. The phosphorylation of cAMP responsive element (CRE) binding protein (CREB) Ser-133 (S133) residue is the end-point of various signaling pathways, like growth factor signaling, while the Ser-129 (S129) residue is phosphorylated by GSK-3β. The significance of the ubiquitously expressed transcription factor CREB is demonstrated in prolonged, tunicamycin (TM)-induced ER stress in this study. In the experiments wild-type (wt) CREB, S129Ala, S133Ala or S129Ala-S133Ala mutant CREB expressing PC12 rat pheochromocytoma cell lines showed increased survival under TM-evoked prolonged ER stress compared to wtPC12 cells. After TM treatment ER stress was activated in all PC12 cell types. Lithium and SB-216763, the selective, well-known inhibitors of GSK-3β, decreased TM-induced apoptosis and promoted cell survival. The proapoptotic BH3-only Bcl-2 family member Bcl-2-interacting mediator of cell death (Bim) level was decreased in the different CREB overexpressing PC12 cells as a result of TM treatment. CREB overexpression also inhibited the sequestration of Bim protein from tubulin molecules, as it was demonstrated in wtPC12 cells. Transient expression of wtCREB diminished TM-induced apoptosis in wtPC12, Rat-1 and primary rat vascular smooth muscle cells. These findings demonstrate a novel role of CREB in different cell types as a potent protector against ER stress.

Activation of lymphotoxin-beta receptor enhances the LPS-induced expression of IL-8 through NF-κB and IRF-1

Lymphotoxin-beta receptor (LTβR), a receptor for LIGHT and LTα1β2, is expressed on the epithelial, stromal, and myeloid cells. LTβR is known to affect the lymphoid organ development and immune homeostasis. However, its role in macrophage function has not been sufficiently elucidated. The effect of LTβR stimulation in the inflammatory activation of macrophages was investigated by treating the human macrophage-like cell line THP-1 with LTβR-specific monoclonal antibody. Interestingly, combined treatment with anti-LTβR antibody and LPS caused the synergistic induction of IL-8 expression at the transcriptional level. Analysis indicated that nuclear factor (NF)-κB activity was enhanced via the mitogen-activated protein kinase (MAPK) and glycogen synthase kinase (GSK)-3β/cAMP response element binding protein (CREB) pathways. In addition, LTβR stimulation induced the expression of interferon regulatory factor (IRF)-1, one of the major transcription factors of IL-8 gene. Down-regulation of IRF-1 expression reduced the enhancing effect caused by LTβR stimulation. This indicates that the LTβR stimulation enhances the LPS-induced expression of IL-8 via the combined action of NF-κB and IRF-1.

Antibody-dependent enhancement infection facilitates dengue virus-regulated signaling of IL-10 production in monocytes

Background

Interleukin (IL)-10 levels are increased in dengue virus (DENV)-infected patients with severe disorders. A hypothetical intrinsic pathway has been proposed for the IL-10 response during antibody-dependent enhancement (ADE) of DENV infection; however, the mechanisms of IL-10 regulation remain unclear.

Principle Finding

We found that DENV infection and/or attachment was sufficient to induce increased expression of IL-10 and its downstream regulator suppressor of cytokine signaling 3 in human monocytic THP-1 cells and human peripheral blood monocytes. IL-10 production was controlled by activation of cyclic adenosine monophosphate response element-binding (CREB), primarily through protein kinase A (PKA)- and phosphoinositide 3-kinase (PI3K)/PKB-regulated pathways, with PKA activation acting upstream of PI3K/PKB. DENV infection also caused glycogen synthase kinase (GSK)-3β inactivation in a PKA/PI3K/PKB-regulated manner, and inhibition of GSK-3β significantly increased DENV-induced IL-10 production following CREB activation. Pharmacological inhibition of spleen tyrosine kinase (Syk) activity significantly decreased DENV-induced IL-10 production, whereas silencing Syk-associated C-type lectin domain family 5 member A caused a partial inhibition. ADE of DENV infection greatly increased IL-10 expression by enhancing Syk-regulated PI3K/PKB/GSK-3β/CREB signaling. We also found that viral load, but not serotype, affected the IL-10 response. Finally, modulation of IL-10 expression could affect DENV replication.

Significance

These results demonstrate that, in monocytes, IL-10 production is regulated by ADE through both an extrinsic and an intrinsic pathway, all involving a Syk-regulated PI3K/PKB/GSK-3β/CREB pathway, and both of which impact viral replication.

IL-10 has multiple cellular functions, including anti-inflammatory and immunomodulatory effects. Clinical studies have demonstrated that the serum levels of IL-10 are significantly increased in DENV-infected patients with severe disorders. However, the molecular mechanism underlying DENV-induced IL-10 production is still unresolved. In this study, we demonstrate a molecular mechanism for DENV-induced IL-10 production, which may be exacerbated by ADE through Fcγ receptor-mediated extrinsic and intrinsic pathways, leading to IL-10/SOCS3-mediated advantages for viral replication. With or without Fcγ receptor- or CLEC5A-mediated DENV infection, a common Syk/PKA-regulated PI3K/PKB activation results in a decrease in GSK-3β activity followed by an increase in CREB-mediated IL-10 expression not only in THP-1 monocytic cells but also in human monocytes. Taken together, we demonstrate a potential regulation and a pathological role for ADE-induced IL-10 overproduction during DENV replication. Therefore, inhibiting immunosuppression by targeting the IL-10 pathways identified in this study may help to prevent the progression of severe dengue diseases.

Nicotinic acetylcholine receptors in glucose homeostasis: the acute hyperglycemic and chronic insulin-sensitive effects of nicotine suggest dual opposing roles of the receptors in male mice

Cigarette smoking causes insulin resistance. However, nicotine induces anti-inflammation and improves glucose tolerance in insulin-resistant animal models. Here, we determined the effects of nicotine on glucose metabolism in insulin-sensitive C57BL/J6 mice. Acute nicotine administration (30 min) caused fasting hyperglycemia and lowered insulin sensitivity acutely, which depended on the activation of nicotinic-acetylcholine receptors (nAChRs) and correlated with increased catecholamine secretion, nitric oxide (NO) production, and glycogenolysis. Chlorisondamine, an inhibitor of nAChRs, reduced acute nicotine-induced hyperglycemia. qRT-PCR analysis revealed that the liver and muscle express predominantly β4 > α10 > α3 > α7 and β4 > α10 > β1 > α1 mRNA for nAChR subunits respectively, whereas the adrenal gland expresses β4 > α3 > α7 > α10 mRNA. Chronic nicotine treatment significantly suppressed expression of α3-nAChR (predominant peripheral α-subunit) in liver. Whereas acute nicotine treatment raised plasma norepinephrine (NE) and epinephrine (Epi) levels, chronic nicotine exposure raised only Epi. Acute nicotine treatment raised both basal and glucose-stimulated insulin secretion (GSIS). After chronic nicotine treatment, basal insulin level was elevated, but GSIS after acute saline or nicotine treatment was blunted. Chronic nicotine exposure caused an increased buildup of NO in plasma and liver, leading to decreased glycogen storage, along with a concomitant suppression of Pepck and G6Pase mRNA, thus preventing hyperglycemia. The insulin-sensitizing effect of chronic nicotine was independent of weight loss. Chronic nicotine treatment enhanced PI-3-kinase activities and increased Akt and glycogen synthase kinase (GSK)-3β phosphorylation in an nAChR-dependent manner coupled with decreased cAMP response element-binding protein (CREB) phosphorylation. The latter effects caused suppression of Pepck and G6Pase gene expression. Thus, nicotine causes both insulin resistance and insulin sensitivity depending on the duration of the treatment.

GSK-3 signaling in developing cortical neurons is essential for radial migration and dendritic orientation

GSK-3 is an essential mediator of several signaling pathways that regulate cortical development. We therefore created conditional mouse mutants lacking both GSK-3α and GSK-3β in newly born cortical excitatory neurons. Gsk3-deleted neurons expressing upper layer markers exhibited striking migration failure in all areas of the cortex. Radial migration in hippocampus was similarly affected. In contrast, tangential migration was not grossly impaired after Gsk3 deletion in interneuron precursors. Gsk3-deleted neurons extended axons and developed dendritic arbors. However, the apical dendrite was frequently branched while basal dendrites exhibited abnormal orientation. GSK-3 regulation of migration in neurons was independent of Wnt/β-catenin signaling. Importantly, phosphorylation of the migration mediator, DCX, at ser327, and phosphorylation of the semaphorin signaling mediator, CRMP-2, at Thr514 were markedly decreased. Our data demonstrate that GSK-3 signaling is essential for radial migration and dendritic orientation and suggest that GSK-3 mediates these effects by phosphorylating key microtubule regulatory proteins.

DOI:http://dx.doi.org/10.7554/eLife.02663.001

In the brain, one of the most striking features of the cerebral cortex is that its neurons are organized into different layers that are specifically connected to one another and to other regions of the brain. How newly generated neurons find their appropriate layer during the development of the brain is an important question; and, in humans, when this process goes awry, it can often result in seizures and mental retardation.

An enzyme called GSK-3 regulates several major signaling pathways important to brain development. The GSK-3 enzyme switches other proteins on or off by adding phosphate groups to them.

Morgan-Smith et al. set out to better understand the role of GSK-3 in brain development by deleting the genes for this enzyme specifically in the cerebral cortex of mice. Mice have two genes that encode slightly different forms of the GSK-3 enzyme. Deleting both of these in different groups of neurons during brain development revealed that a major group of neurons need GSK-3 in order to migrate to the correct layer. Specifically, the movement of neurons from where they arise in the central region of the brain to the outermost layer (a process called radial migration) was disrupted when the GSK-3 genes were deleted.

Morgan-Smith et al. further found that cortical neurons without GSK-3 were unable to develop the shape needed to undertake radial migration because they failed to switch from having many branches to having just two main branches. Additional experiments revealed that these abnormalities did not depend on certain signaling pathways, such as the Wnt-signaling pathway or the PI3K signaling pathway that can control GSK-3 activity.

Instead, Morgan-Smith et al. found that two proteins that are normally targeted by the GSK-3 enzyme have fewer phosphate groups than normal in the cortical neurons that did not contain the enzyme: both of these proteins regulate the shape of neurons by interacting with the molecular ‘scaffolding’ within the cell. The GSK-3 enzyme was already known to modify the activities of many other proteins that affect the migration of cells. Thus, the findings of Morgan-Smith et al. suggest that this enzyme may coordinate many of the mechanisms thought to underlie this process during brain development.

DOI:http://dx.doi.org/10.7554/eLife.02663.002

Inositol hexakisphosphate kinase-1 regulates behavioral responses via GSK3 signaling pathways

Glycogen synthase kinase 3 (GSK3), a prominent enzyme in carbohydrate metabolism, also has a major role in brain function. It is physiologically regulated by the kinase Akt, which phosphorylates GSK3 to inhibit catalytic activity. Inositol hexakisphosphate-1 (IP6K1) generates the inositol pyrophosphate diphosphoinositol pentakisphosphate (IP7), which physiologically inhibits Akt leading to enhanced GSK3 activity. We report that IP6K1 binds and stimulates GSK3 enzymatic activity in a non-catalytic fashion. Physiological relevance is evident in the inhibition of GSK3 activity in the brains of IP6K1-deleted mice. Behavioral alterations of IP6K1 knockout mice resemble those of GSK3 mutants. Accordingly, modulation of IP6K1-GSK3β interaction may exert beneficial effects in psychiatric disorders involving GSK3.

Alteration of cyclic-AMP response element binding protein in the postmortem brain of subjects with bipolar disorder and schizophrenia

BACKGROUND

Abnormalities of cyclic-AMP (cAMP) response element binding protein (CREB) function has been suggested in bipolar (BP) illness and schizophrenia (SZ), based on both indirect and direct evidence. To further elucidate the role of CREB in these disorders, we studied CREB expression and function in two brain areas implicated in these disorders, i.e., dorsolateral prefrontal cortex (DLPFC) and cingulate gyrus (CG).

METHODS

We determined CREB protein expression using Western blot technique, CRE-DNA binding using gel shift assay, and mRNA expression using real-time RT-polymerase chain reaction (qPCR) in DLPFC and CG of the postmortem brain of BP (n=19), SZ (n=20), and normal control (NC, n=20) subjects.

RESULTS

We observed that CREB protein and mRNA expression and CRE-DNA binding activity were significantly decreased in the nuclear fraction of DLPFC and CG obtained from BP subjects compared with NC subjects. However, the protein and mRNA expression and CRE-DNA binding in SZ subjects was significantly decreased in CG, but not in DLPFC, compared with NC.

CONCLUSION

These studies thus indicate region-specific abnormalities of CREB expression and function in both BP and SZ. They suggest that abnormalities of CREB in CG may be associated with both BP and SZ, but its abnormality in DLPFC is specific to BP illness.

Presenilins regulate neurotrypsin gene expression and neurotrypsin-dependent agrin cleavage via cyclic AMP response element-binding protein (CREB) modulation

Presenilins, the catalytic components of the γ-secretase complex, are upstream regulators of multiple cellular pathways via regulation of gene transcription. However, the underlying mechanisms and the genes regulated by these pathways are poorly characterized. In this study, we identify Tequila and its mammalian ortholog Prss12 as genes negatively regulated by presenilins in Drosophila larval brains and mouse embryonic fibroblasts, respectively. Prss12 encodes the serine protease neurotrypsin, which cleaves the heparan sulfate proteoglycan agrin. Altered neurotrypsin activity causes serious synaptic and cognitive defects; despite this, the molecular processes regulating neurotrypsin expression and activity are poorly understood. Using γ-secretase drug inhibitors and presenilin mutants in mouse embryonic fibroblasts, we found that a mature γ-secretase complex was required to repress neurotrypsin expression and agrin cleavage. We also determined that PSEN1 endoproteolysis or processing of well known γ-secretase substrates was not essential for this process. At the transcriptional level, PSEN1/2 removal induced cyclic AMP response element-binding protein (CREB)/CREB-binding protein binding, accumulation of activating histone marks at the neurotrypsin promoter, and neurotrypsin transcriptional and functional up-regulation that was dependent on GSK3 activity. Upon PSEN1/2 reintroduction, this active epigenetic state was replaced by a methyl CpG-binding protein 2 (MeCP2)-containing repressive state and reduced neurotrypsin expression. Genome-wide analysis revealed hundreds of other mouse promoters in which CREB binding is similarly modulated by the presence/absence of presenilins. Our study thus identifies Tequila and neurotrypsin as new genes repressed by presenilins and reveals a novel mechanism used by presenilins to modulate CREB signaling based on controlling CREB recruitment.

An emerging role for the anti-inflammatory cytokine interleukin-10 in dengue virus infection

Infection with dengue virus (DENV) causes both mild dengue fever and severe dengue diseases, such as dengue hemorrhagic fever and dengue shock syndrome. The pathogenic mechanisms for DENV are complicated, involving viral cytotoxicity, immunopathogenesis, autoimmunity, and underlying host diseases. Viral load correlates with disease severity, while the antibody-dependent enhancement of infection largely determines the secondary effects of DENV infection. Epidemiological and experimental studies have revealed an association between the plasma levels of interleukin (IL)-10, which is the master anti-inflammatory cytokine, and disease severity in patients with DENV infection. Based on current knowledge of IL-10-mediated immune regulation during infection, researchers speculate an emerging role for IL-10 in clinical disease prognosis and dengue pathogenesis. However, the regulation of dengue pathogenesis has not been fully elucidated. This review article discusses the regulation and implications of IL-10 in DENV infection. For future strategies against DENV infection, manipulating IL-10 may be an effective antiviral treatment in addition to the development of a safe dengue vaccine.

A novel strategy to increase the proliferative potential of adult human β-cells while maintaining their differentiated phenotype

Our previous studies demonstrated that Wnt/GSK-3/β-catenin and mTOR signaling are necessary to stimulate proliferative processes in adult human β-cells. Direct inhibition of GSK-3, that engages Wnt signaling downstream of the Wnt receptor, increases β-catenin nuclear translocation and β-cell proliferation but results in lower insulin content. Our current goal was to engage canonical and non-canonical Wnt signaling at the receptor level to significantly increase human β-cell proliferation while maintaining a β-cell phenotype in intact islets. We adopted a system that utilized conditioned medium from L cells that expressed Wnt3a, R-spondin-3 and Noggin (L-WRN conditioned medium). In addition we used a ROCK inhibitor (Y-27632) and SB-431542 (that results in RhoA inhibition) in these cultures. Treatment of intact human islets with L-WRN conditioned medium plus inhibitors significantly increased DNA synthesis ∼6 fold in a rapamycin-sensitive manner. Moreover, this treatment strikingly increased human β-cell proliferation ∼20 fold above glucose alone. Only the combination of L-WRN conditioned medium with RhoA/ROCK inhibitors resulted in substantial proliferation. Transcriptome-wide gene expression profiling demonstrated that L-WRN medium provoked robust changes in several signaling families, including enhanced β-catenin-mediated and β-cell-specific gene expression. This treatment also increased expression of Nr4a2 and Irs2 and resulted in phosphorylation of Akt. Importantly, glucose-stimulated insulin secretion and content were not downregulated by L-WRN medium treatment. Our data demonstrate that engaging Wnt signaling at the receptor level by this method leads to necessary crosstalk between multiple signaling pathways including activation of Akt, mTOR, Wnt/β-catenin, PKA/CREB, and inhibition of RhoA/ROCK that substantially increase human β-cell proliferation while maintaining the β-cell phenotype.

Glycogen synthase kinase-3 (GSK-3) regulates TGF-β₁-induced differentiation of pulmonary fibroblasts

BACKGROUND

Chronic lung diseases such as asthma, COPD and pulmonary fibrosis are characterized by abnormal extracellular matrix (ECM) turnover. TGF-β is a key mediator stimulating ECM production by recruiting and activating lung fibroblasts and initiating their differentiation process into more active myofibroblasts. Glycogen synthase kinase-3 (GSK-3) regulates various intracellular signalling pathways; its role in TGF-β₁-induced myofibroblast differentiation is currently largely unknown.

PURPOSE

To determine the contribution of GSK-3 signalling in TGF-β₁-induced myofibroblast differentiation.

EXPERIMENTAL APPROACH

We used MRC5 human lung fibroblasts and primary pulmonary fibroblasts of individuals with and without COPD. Protein and mRNA expression were determined by immunoblotting and RT-PCR analysis respectively.

RESULTS

Stimulation of MRC5 and primary human lung fibroblasts with TGF-β₁ resulted in time- and dose-dependent increases of α-sm-actin and fibronectin expression, indicative of myofibroblast differentiation. Pharmacological inhibition of GSK-3 by SB216763 dose-dependently attenuated TGF-β₁-induced expression of these myofibroblasts markers. Moreover, silencing of GSK-3 by siRNA or pharmacological inhibition by CT/CHIR99021 fully inhibited the TGF-β₁-induced expression of α-sm-actin and fibronectin. The effect of GSK-3 inhibition on α-sm-actin expression was similar in fibroblasts from individuals with and without COPD. Neither smad, NF-κB nor ERK1/2 were involved in the inhibitory actions of GSK-3 inhibition by SB126763 on myofibroblast differentiation. Rather, SB216763 increased the phosphorylation of CREB, which in its phosphorylated form acts as a functional antagonist of TGF-β/smad signalling.

CONCLUSION AND IMPLICATION

We demonstrate that GSK-3 signalling regulates TGF-β₁-induced myofibroblast differentiation by regulating CREB phosphorylation. GSK-3 may constitute a useful target for treatment of chronic lung diseases.

Bak apoptotic function is not directly regulated by phosphorylation

During apoptosis, Bak and Bax permeabilize the mitochondrial outer membrane by undergoing major conformational change and oligomerization. This activation process in Bak is reported to require dephosphorylation of tyrosine-108 close to an activation trigger site. To investigate how dephosphorylation of Bak contributes to its activation and conformational change, one-dimensional isoelectric focusing (1D-IEF) and mutagenesis was used to monitor Bak phosphorylation. On 1D-IEF, Bak extracted from a range of cell types migrated as a single band near the predicted isoelectric point of 5.6 both before and after phosphatase treatment, indicating that Bak is not significantly phosphorylated at any residue. In contrast, three engineered ‘phosphotagged' Bak variants showed a second band at lower pI, indicating phosphorylation. Apoptosis induced by several stimuli failed to alter Bak pI, indicating little change in phosphorylation status. In addition, alanine substitution of tyrosine-108 and other putative phosphorylation sites failed to enhance Bak activation or pro-apoptotic function. In summary, Bak is not significantly phosphorylated at any residue, and Bak activation during apoptosis does not require dephosphorylation.

Myeloid cell IL-10 production in response to leishmania involves inactivation of glycogen synthase kinase-3β downstream of phosphatidylinositol-3 kinase

Leishmania disease expression has been linked to IL-10. In this study, we investigated the regulation of IL-10 production by macrophages infected with Leishmania donovani. Infection of either murine or human macrophages brought about selective phosphorylation of Akt-2 in a PI3K-dependent manner. These events were linked to phosphorylation and inactivation of glycogen synthase kinase-3β (GSK-3β) at serine 9, as the latter was abrogated by inhibition of either PI3K or Akt. One of the transcription factors that is negatively regulated by GSK-3β is CREB, which itself positively regulates IL-10 expression. Infection of macrophages with leishmania induced phosphorylation of CREB at serine 133, and this was associated with enhanced CREB DNA binding activity and induction of IL-10. Similar to phosphorylation of GSK-3β, both phosphorylation of CREB at serine 133 and CREB DNA binding activity were abrogated in cells treated with inhibitors of either PI3K or Akt prior to infection. Furthermore, disruption of this pathway either by inhibition of Akt or by overexpression of GSK-3β markedly attenuated IL-10 production in response to leishmania. Thus, GSK-3β negatively regulates myeloid cell IL-10 production in response to leishmania. Switching off GSK-3β promotes disease pathogenesis.

CREB in long-term potentiation in hippocampus: role of post-translational modifications-studies In silico

The multifunctionality of proteins is dictated by post-translational modifications (PTMs) which involve the attachment of small functional groups such as phosphate and acetate, as well as carbohydrate moieties. These functional groups make the protein perform various functions in different environments. PTMs play a crucial role in memory and learning. Phosphorylation of synaptic proteins and transcription factors regulate the generation and storage of memory. Among these is the cAMP-regulated element binding protein CREB that regulates CRE containing genes like c-fos. Both phosphorylation and acetylation control the function of CREB as a transcription factor. CREB is also susceptible to O-GlcNAc modification, which inhibits its activity. O-GlcNAc modification occurs on the same or neighboring Ser/Thr residues akin to phosphorylation. An interplay between these modifications was shown to operate in nuclear and cytoplasmic proteins. In this study computational methods were utilized to predict different modification sites in CREB. These in silico results suggest that phosphorylation, O-GlcNAc modification and acetylation modulate the transcriptional activity of CREB and thus dictate its contribution to synaptic plasticity.