Glycogen synthase kinase3 beta phosphorylates serine 33 of p53 and activates p53's transcriptional activity

Evolving significance of kinase inhibitors in the management of Alzheimer's disease

Alzheimer's disease is a neurodegenerative problem with progressive loss of memory and other cognitive function disorders resulting in the imbalance of neurotransmitter activity and signaling progression, which poses the need of the potential therapeutic target to improve the intracellular signaling cascade brought by kinases. Protein kinase plays a significant and multifaceted role in the treatment of Alzheimer's disease, by targeting pathological mechanisms like tau hyperphosphorylation, neuroinflammation, amyloid-beta production and synaptic dysfunction. In this review, we thoroughly explore the essential protein kinases involved in Alzheimer's disease, detailing their physiological roles, regulatory impacts, and the newest inhibitors and compounds that are progressing into clinical trials. All the findings of studies exhibited the promising role of kinase inhibitors in the management of Alzheimer's disease. However, it still poses the need of addressing current challenges and opportunities involved with this disorder for the future perspective of kinase inhibitors in the management of Alzheimer's disease. Further study includes the development of biomarkers, combination therapy, and next-generation kinase inhibitors with increased potency and selectivity for its future prospects.

Plasma membrane damage limits replicative lifespan in yeast and induces premature senescence in human fibroblasts

Plasma membrane damage (PMD) occurs in all cell types due to environmental perturbation and cell-autonomous activities. However, cellular outcomes of PMD remain largely unknown except for recovery or death. In this study, using budding yeast and normal human fibroblasts, we found that cellular senescence-stable cell cycle arrest contributing to organismal aging-is the long-term outcome of PMD. Our genetic screening using budding yeast unexpectedly identified a close genetic association between PMD response and replicative lifespan regulations. Furthermore, PMD limits replicative lifespan in budding yeast; upregulation of membrane repair factors ESCRT-III (SNF7) and AAA-ATPase (VPS4) extends it. In normal human fibroblasts, PMD induces premature senescence via the Ca2+-p53 axis but not the major senescence pathway, DNA damage response pathway. Transient upregulation of ESCRT-III (CHMP4B) suppressed PMD-dependent senescence. Together with mRNA sequencing results, our study highlights an underappreciated but ubiquitous senescent cell subtype: PMD-dependent senescent cells.

Tumor suppressor p53 modulates activity-dependent synapse strengthening, autism-like behavior and hippocampus-dependent learning

Synaptic potentiation underlies various forms of behavior and depends on modulation by multiple activity-dependent transcription factors to coordinate the expression of genes necessary for sustaining synaptic transmission. Our current study identified the tumor suppressor p53 as a novel transcription factor involved in this process. We first revealed that p53 could be elevated upon chemically induced long-term potentiation (cLTP) in cultured primary neurons. By knocking down p53 in neurons, we further showed that p53 is required for cLTP-induced elevation of surface GluA1 and GluA2 subunits of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR). Because LTP is one of the principal plasticity mechanisms underlying behaviors, we employed forebrain-specific knockdown of p53 to evaluate the role of p53 in behavior. Our results showed that, while knocking down p53 in mice does not alter locomotion or anxiety-like behavior, it significantly promotes repetitive behavior and reduces sociability in mice of both sexes. In addition, knocking down p53 also impairs hippocampal LTP and hippocampus-dependent learning and memory. Most importantly, these learning-associated defects are more pronounced in male mice than in female mice, suggesting a sex-specific role of p53 in these behaviors. Using RNA sequencing (RNAseq) to identify p53-associated genes in the hippocampus, we showed that knocking down p53 up- or down-regulates multiple genes with known functions in synaptic plasticity and neurodevelopment. Altogether, our study suggests p53 as an activity-dependent transcription factor that mediates the surface expression of AMPAR, permits hippocampal synaptic plasticity, represses autism-like behavior, and promotes hippocampus-dependent learning and memory.

Regulation of eukaryotic protein kinases by Pin1, a peptidyl-prolyl isomerase

The peptidyl-prolyl isomerase Pin1 cooperates with proline-directed kinases and phosphatases to regulate multiple oncogenic pathways. Pin1 specifically recognizes phosphorylated Ser/Thr-Pro motifs in proteins and catalyzes their cis-trans isomerization. The Pin1-catalyzed conformational changes determine the stability, activity, and subcellular localization of numerous protein substrates. We conducted a survey of eukaryotic protein kinases that are regulated by Pin1 and whose Pin1 binding sites have been identified. Our analyses reveal that Pin1 target sites in kinases do not fall exclusively within the intrinsically disordered regions of these enzymes. Rather, they fall into three groups based on their location: (i) within the catalytic kinase domain, (ii) in the C-terminal kinase region, and (iii) in regulatory domains. Some of the kinases downregulated by Pin1 activity are tumor-suppressing, and all kinases upregulated by Pin1 activity are functionally pro-oncogenic. These findings further reinforce the rationale for developing Pin1-specific inhibitors as attractive pharmaceuticals for cancer therapy.

Short Linear Motifs in Colorectal Cancer Interactome and Tumorigenesis

Colorectal tumorigenesis is driven by alterations in genes and proteins responsible for cancer initiation, progression, and invasion. This multistage process is based on a dense network of protein-protein interactions (PPIs) that become dysregulated as a result of changes in various cell signaling effectors. PPIs in signaling and regulatory networks are known to be mediated by short linear motifs (SLiMs), which are conserved contiguous regions of 3-10 amino acids within interacting protein domains. SLiMs are the minimum sequences required for modulating cellular PPI networks. Thus, several in silico approaches have been developed to predict and analyze SLiM-mediated PPIs. In this review, we focus on emerging evidence supporting a crucial role for SLiMs in driver pathways that are disrupted in colorectal cancer (CRC) tumorigenesis and related PPI network alterations. As a result, SLiMs, along with short peptides, are attracting the interest of researchers to devise small molecules amenable to be used as novel anti-CRC targeted therapies. Overall, the characterization of SLiMs mediating crucial PPIs in CRC may foster the development of more specific combined pharmacological approaches.

Glycogen Synthase Kinase 3β: A True Foe in Pancreatic Cancer

Glycogen synthase kinase 3 beta (GSK-3β) is a serine/threonine protein kinase involved in multiple normal and pathological cell functions, including cell signalling and metabolism. GSK-3β is highly expressed in the onset and progression of multiple cancers with strong involvement in the regulation of proliferation, apoptosis, and chemoresistance. Multiple studies showed pro- and anti-cancer roles of GSK-3β creating confusion about the benefit of targeting GSK-3β for treating cancer. In this mini-review, we focus on the role of GSK-3β in pancreatic cancer. We demonstrate that the proposed anti-cancer roles of GSK-3β are not relevant to pancreatic cancer, and we argue why GSK-3β is, indeed, a very promising therapeutic target in pancreatic cancer.

Age-related GSK3β overexpression drives podocyte senescence and glomerular aging

As life expectancy continues to increase, clinicians are challenged by age-related renal impairment that involves podocyte senescence and glomerulosclerosis. There is now compelling evidence that lithium has a potent antiaging activity that ameliorates brain aging and increases longevity in Drosophila and Caenorhabditis elegans. As the major molecular target of lithium action and a multitasking protein kinase recently implicated in a variety of renal diseases, glycogen synthase kinase 3β (GSK3β) is overexpressed and hyperactive with age in glomerular podocytes, correlating with functional and histological signs of kidney aging. Moreover, podocyte-specific ablation of GSK3β substantially attenuated podocyte senescence and glomerular aging in mice. Mechanistically, key mediators of senescence signaling, such as p16^INK4A and p53, contain high numbers of GSK3β consensus motifs, physically interact with GSK3β, and act as its putative substrates. In addition, therapeutic targeting of GSK3β by microdose lithium later in life reduced senescence signaling and delayed kidney aging in mice. Furthermore, in psychiatric patients, lithium carbonate therapy inhibited GSK3β activity and mitigated senescence signaling in urinary exfoliated podocytes and was associated with preservation of kidney function. Thus, GSK3β appears to play a key role in podocyte senescence by modulating senescence signaling and may be an actionable senostatic target to delay kidney aging.

N-terminal phosphorylation regulates the activity of Glycogen Synthase Kinase 3 from Plasmodium falciparum

As the decline of malaria cases stalled over the last five years, novel targets in Plasmodium falciparum are necessary for the development of new drugs. Glycogen Synthase Kinase (PfGSK3) has been identified as a potential target, since its selective inhibitors were shown to disrupt the parasitès life cycle. In the uncanonical N-terminal region of the parasite enzyme, we identified several autophosphorylation sites and probed their role in activity regulation of PfGSK3. By combining molecular modeling with experimental small-angle X-ray scattering data, we show that increased PfGSK3 activity is promoted by conformational changes in the PfGSK3 N-terminus, triggered by N-terminal phosphorylation. Our work provides novel insights into the structure and regulation of the malarial PfGSK3.

Protein of a thousand faces: The tumor-suppressive and oncogenic responses of p53

The p53 protein is a pleiotropic regulator working as a tumor suppressor and as an oncogene. Depending on the cellular insult and the mutational status, p53 may trigger opposing activities such as cell death or survival, senescence and cell cycle arrest or proliferative signals, antioxidant or prooxidant activation, glycolysis, or oxidative phosphorylation, among others. By augmenting or repressing specific target genes or directly interacting with cellular partners, p53 accomplishes a particular set of activities. The mechanism in which p53 is activated depends on increased stability through post-translational modifications (PTMs) and the formation of higher-order structures (HOS). The intricate cell death and metabolic p53 response are reviewed in light of gaining stability via PTM and HOS formation in health and disease.

Transcriptome Analysis of Cells Exposed to Actinomycin D and Nutlin-3a Reveals New Candidate p53-Target Genes and Indicates That CHIR-98014 Is an Important Inhibitor of p53 Activity

Co-treatment with actinomycin D and nutlin-3a (A + N) strongly activates p53. Previously we reported that CHIR-98014 (GSK-3 kinase inhibitor), acting in cells exposed to A + N, prevents activation of TREM2-an innate immunity and p53-regulated gene associated with Alzheimer’s disease. In order to find novel candidate p53-target genes and genes regulated by CHIR-98014, we performed RNA-Seq of control A549 cells and the cells exposed to A + N, A + N with CHIR-98014 or to CHIR-98014. We validated the data for selected genes using RT-PCR and/or Western blotting. Using CRISPR/Cas9 technology we generated p53-deficient cells. These tools enabled us to identify dozens of candidate p53-regulated genes. We confirmed that p53 participates in upregulation of BLNK, APOE and IRF1. BLNK assists in activation of immune cells, APOE codes for apolipoprotein associated with Alzheimer’s disease and IRF1 is activated by interferon gamma and regulates expression of antiviral genes. CHIR-98014 prevented or inhibited the upregulation of a fraction of genes stimulated by A + N. Downregulation of GSK-3 did not mimic the activity of CHIR-98014. Our data generate the hypothesis, that an unidentified kinase inhibited by CHIR-98014, participates in modification of p53 and enables it to activate a subset of its target genes, e.g., the ones associated with innate immunity.

Inhibition of sEH via stabilizing the level of EETs alleviated Alzheimer's disease through GSK3β signaling pathway

Alzheimer's disease (AD) is the most common neurodegenerative disorder characterized by dementia. Inhibition of soluble epoxide hydrolase (sEH) regulates inflammation involving in central nervous system (CNS) diseases. However, the exactly mechanism of sEH in AD is still unclear. In this study, we evaluated the vital role of sEH in amyloid beta (Aβ)-induced AD mice, and revealed a possible molecular mechanism for inhibition of sEH in the treatment of AD. The results showed that the sEH expression and activity were remarkably increased in the hippocampus of Aβ-induced AD mice. Chemical inhibition of sEH by TPPU, a selective sEH inhibitor, alleviated spatial learning and memory deficits, and elevated levels of neurotransmitters in Aβ-induced AD mice. Furthermore, inhibition of sEH could ameliorate neuroinflammation, neuronal death, and oxidative stress via stabilizing the in vivo level of epoxyeicosatrienoic acids (EETs), especially 8,9-EET and 14,15-EET, further resulting in the anti-AD effect through the regulation of GSK3β-mediated NF-κB, p53, and Nrf2 signaling pathways. These findings revealed the underlying mechanism of sEH as a potential therapeutic target in treatment of AD.

Recent advances in drug repurposing using machine learning

Drug repurposing aims to find new uses for already existing and approved drugs. We now provide a brief overview of recent developments in drug repurposing using machine learning alongside other computational approaches for comparison. We also highlight several applications for cancer using kinase inhibitors, Alzheimer's disease as well as COVID-19.

Tau phosphorylation and cochlear apoptosis cause hearing loss in 3×Tg-AD Mouse Model of Alzheimer's Disease

Clinically typical dementia Alzheimer's disease (AD) is associated with abnormal auditory processing. However, possible molecular mechanisms responsible for the auditory pathology of AD patients are not known. According to our past research findings that the thresholds of auditory brainstem response, but not distortion product otoacoustic emissions, were significantly increased in AD mice from 9 months of age and thereafter. Thus, we further explored the possible mechanism of auditory degradation of 3×Tg-AD mice in this study. Our histochemical staining evidence showed the cochlear spiral ganglion neurons (SGN), but not the cochlear hair cells, were lost significantly in the cochlea of 3×Tg-AD mice from 9 months of age and thereafter. Our immunostaining and western blotting evidence showed that phosphorylated tau protein (p-Tau), p-glycogen synthase kinase 3, neurofilament, and apoptosis-related p53, Bcl2-associated X protein, cytochrome c, caspase-9, and caspase-3 were gradually increased, but B-cell lymphoma 2 was gradually decreased with age growth in the cochlea of 3×Tg-AD mice. We suggested that tau hyperphosphorylation and p-Tau 181 aggregation, and mitochondria- and endoplasmic reticulum stress-mediated apoptosis may play a role in the degeneration of SGN in the cochlea. Progressive SGN degeneration in the cochlea may contribute to hearing loss of aging 3×Tg-AD mice.

Neurodegenerative phosphoprotein signaling landscape in models of SCA3

Spinocerebellar ataxia type 3 (SCA3) is a rare neurodegenerative disorder resulting from an aberrant expansion of a polyglutamine stretch in the ataxin-3 protein and subsequent neuronal death. The underlying intracellular signaling pathways are currently unknown. We applied the Reverse-phase Protein MicroArray (RPMA) technology to assess the levels of 50 signaling proteins (in phosphorylated and total forms) using three in vitro and in vivo models expressing expanded ataxin-3: (i) human embryonic kidney (HEK293T) cells stably transfected with human ataxin-3 constructs, (ii) mouse embryonic fibroblasts (MEF) from SCA3 transgenic mice, and (iii) whole brains from SCA3 transgenic mice. All three models demonstrated a high degree of similarity sharing a subset of phosphorylated proteins involved in the PI3K/AKT/GSK3/mTOR pathway. Expanded ataxin-3 strongly interfered (by stimulation or suppression) with normal ataxin-3 signaling consistent with the pathogenic role of the polyglutamine expansion. In comparison with normal ataxin-3, expanded ataxin-3 caused a pro-survival stimulation of the ERK pathway along with reduced pro-apoptotic and transcriptional responses.

The role of glycogen synthase kinase 3 (GSK3) in cancer with emphasis on ovarian cancer development and progression: A comprehensive review

Glycogen synthase kinase 3 (GSK3) is a monomeric serine-threonine kinase discovered in 1980 in a rat skeletal muscle. It has been involved in various cellular processes including embryogenesis, immune response, inflammation, apoptosis, autophagy, wound healing, neurodegeneration, and carcinogenesis. GSK3 exists in two different isoforms, GSK3α and GSK3β, both containing seven antiparallel beta-plates, a short linking part and an alpha helix, but coded by different genes and variously expressed in human tissues. In the current review, we comprehensively appraise the current literature on the role of GSK3 in various cancers with emphasis on ovarian carcinoma. Our findings indicate that the role of GSK3 in ovarian cancer development cannot be decisively determined as the currently available data support both prooncogenic and tumor-suppressive effects. Likewise, the clinical impact of GSK3 expression on ovarian cancer patients and its potential therapeutic implications are also limited. Further studies are needed to fully elucidate the pathophysiological and clinical implications of GSK3 activity in ovarian cancer.

Molecular mechanisms of neurodegeneration in the entorhinal cortex that underlie its selective vulnerability during the pathogenesis of Alzheimer's disease

The entorhinal cortex (EC) is a vital component of the medial temporal lobe, and its contributions to cognitive processes and memory formation are supported through its extensive interconnections with the hippocampal formation. During the pathogenesis of Alzheimer's disease (AD), many of the earliest degenerative changes are seen within the EC. Neurodegeneration in the EC and hippocampus during AD has been clearly linked to impairments in memory and cognitive function, and a growing body of evidence indicates that molecular and functional neurodegeneration within the EC may play a primary role in cognitive decline in the early phases of AD. Defining the mechanisms underlying molecular neurodegeneration in the EC is crucial to determining its contributions to the pathogenesis of AD. Surprisingly few studies have focused on understanding the mechanisms of molecular neurodegeneration and selective vulnerability within the EC. However, there have been advancements indicating that early dysregulation of cellular and molecular signaling pathways in the EC involve neurodegenerative cascades including oxidative stress, neuroinflammation, glia activation, stress kinases activation, and neuronal loss. Dysfunction within the EC can impact the function of the hippocampus, which relies on entorhinal inputs, and further degeneration within the hippocampus can compound this effect, leading to severe cognitive disruption. This review assesses the molecular and cellular mechanisms underlying early degeneration in the EC during AD. These mechanisms may underlie the selective vulnerability of neuronal subpopulations in this brain region to the disease development and contribute both directly and indirectly to cognitive loss.This paper has an associated Future Leader to Watch interview with the first author of the article.

Machine Learning for Discovery of GSK3β Inhibitors

Alzheimer's disease (AD) is the most common cause of dementia, affecting approximately 35 million people worldwide. The current treatment options for people with AD consist of drugs designed to slow the rate of decline in memory and cognition, but these treatments are not curative, and patients eventually suffer complete cognitive injury. With the substantial amounts of published data on targets for this disease, we proposed that machine learning software could be used to find novel small-molecule treatments that can supplement the AD drugs currently on the market. In order to do this, we used publicly available data in ChEMBL to build and validate Bayesian machine learning models for AD target proteins. The first AD target that we have addressed with this method is the serine-threonine kinase glycogen synthase kinase 3 beta (GSK3β), which is a proline-directed serine-threonine kinase that phosphorylates the microtubule-stabilizing protein tau. This phosphorylation prompts tau to dissociate from the microtubule and form insoluble oligomers called paired helical filaments, which are one of the components of the neurofibrillary tangles found in AD brains. Using our Bayesian machine learning model for GSK3β consisting of 2368 molecules, this model produced a five-fold cross validation ROC of 0.905. This model was also used for virtual screening of large libraries of FDA-approved drugs and clinical candidates. Subsequent testing of selected compounds revealed a selective small-molecule inhibitor, ruboxistaurin, with activity against GSK3β (avg IC50 = 97.3 nM) and GSK3α (IC50 = 695.9 nM). Several other structurally diverse inhibitors were also identified. We are now applying this machine learning approach to additional AD targets to identify approved drugs or clinical trial candidates that can be repurposed as AD therapeutics. This represents a viable approach to accelerate drug discovery and do so at a fraction of the cost of traditional high throughput screening.

Single Step Purification of Glycogen Synthase Kinase Isoforms from Small Scale Transient Expression in HEK293 Cells with a Calcium-Dependent Fragment Complementation System

Purification of proteins for the biophysical analysis of protein interactions occurring in human cells can benefit from methods that facilitate the capture of small amounts of natively processed protein obtained using transient mammalian expression systems. We have used a novel calcium-dependent fragment complementation-based affinity method to effectively purify full length glycogen synthase kinase 3 (GSK3) α and β isoforms to study their interaction with amyloid β peptide (Aβ42). Using these proteins, purified from 1 mg of total cell lysate, we measured an apparent K_D of ≤100 pM between GSK3α/β and immobilized Aβ42 with surface plasmon resonance technology. This approach can be used to retrieve useful quantities of protein for biophysical experiments with small scale mammalian cell culture.

SCF(FBXW7)-mediated degradation of p53 promotes cell recovery after UV-induced DNA damage

Eukaryotic cells have developed sophisticated mechanisms to ensure the integrity of the genome and prevent the transmission of altered genetic information to daughter cells. If this control system fails, accumulation of mutations would increase risk of diseases such as cancer. Ubiquitylation, an essential process for protein degradation and signal transduction, is critical for ensuring genome integrity as well as almost all cellular functions. Here, we investigated the role of the SKP1-Cullin-1-F-box protein (SCF)-[F-box and tryptophan-aspartic acid (WD) repeat domain containing 7 (FBXW7)] ubiquitin ligase in cell proliferation by searching for targets implicated in this process. We identified a hitherto-unknown FBXW7-interacting protein, p53, which is phosphorylated by glycogen synthase kinase 3 at serine 33 and then ubiquitylated by SCF(FBXW7) and degraded. This ubiquitylation is carried out in normally growing cells but primarily after DNA damage. Specifically, we found that SCF(FBXW7)-specific targeting of p53 is crucial for the recovery of cell proliferation after UV-induced DNA damage. Furthermore, we observed that amplification of FBXW7 in wild-type p53 tumors reduced the survival of patients with breast cancer. These results provide a rationale for using SCF(FBXW7) inhibitors in the treatment of this subset of tumors.-Galindo-Moreno, M., Giráldez, S., Limón-Mortés, M. C., Belmonte-Fernández, A., Reed, S. I., Sáez, C., Japón, M. Á., Tortolero, M., Romero, F. SCF(FBXW7)-mediated degradation of p53 promotes cell recovery after UV-induced DNA damage.

Effects of siRNA-Mediated Knockdown of GSK3β on Retinal Ganglion Cell Survival and Neurite/Axon Growth

There are contradictory reports on the role of the serine/threonine kinase isoform glycogen synthase kinase-3β (GSK3β) after injury to the central nervous system (CNS). Some report that GSK3 activity promotes axonal growth or myelin disinhibition, whilst others report that GSK3 activity prevents axon regeneration. In this study, we sought to clarify if suppression of GSK3β alone and in combination with the cellular-stress-induced factor RTP801 (also known as REDD1: regulated in development and DNA damage response protein), using translationally relevant siRNAs, promotes retinal ganglion cell (RGC) survival and neurite outgrowth/axon regeneration. Adult mixed retinal cell cultures, prepared from rats at five days after optic nerve crush (ONC) to activate retinal glia, were treated with siRNA to GSK3β (siGSK3β) alone or in combination with siRTP801 and RGC survival and neurite outgrowth were quantified in the presence and absence of Rapamycin or inhibitory Nogo-A peptides. In in vivo experiments, either siGSK3β alone or in combination with siRTP801 were intravitreally injected every eight days after ONC and RGC survival and axon regeneration was assessed at 24 days. Optimal doses of siGSK3β alone promoted significant RGC survival, increasing the number of RGC with neurites without affecting neurite length, an effect that was sensitive to Rapamycin. In addition, knockdown of GSK3β overcame Nogo-A-mediated neurite growth inhibition. Knockdown of GSK3β after ONC in vivo enhanced RGC survival but not axon number or length, without potentiating glial activation. Knockdown of RTP801 increased both RGC survival and axon regeneration, whilst the combined knockdown of GSK3β and RTP801 significantly increased RGC survival, neurite outgrowth, and axon regeneration over and above that observed for siGSK3β or siRTP801 alone. These results suggest that GSK3β suppression promotes RGC survival and axon initiation whilst, when in combination with RTP801, it also enhanced disinhibited axon elongation.

Late Brain Involvement after Neonatal Immune Activation

The neonatal immune system is still immature, which makes it more susceptible to the infectious agents. Neonatal immune activation is associated with increased permeability of the blood-brain barrier, causing an inflammatory cascade in the CNS and altering behavioral and neurochemical parameters. One of the hypotheses that has been studied is that neuroinflammation may be involved in neurodegenerative processes, such as Alzheimer's disease (AD). We evaluate visuospatial memory, cytokines levels, and the expression of tau and GSK-3β proteins in hippocampus and cortex of animals exposed to neonatal endotoxemia. C57BL/6 mice aging two days received a single injection of subcutaneous lipopolysaccharide (LPS). At 60,120, and 180 days of age, visual-spatial memory was evaluated and the hippocampus and cortex were dissected to evaluate the cytokines levels and expression of tau and GSK-3β proteins. The animals exposed to LPS in the neonatal period present with visuospatial memory impairment at 120 and 180 days of age. Here there was an increase of TNF-α and IL-1β levels in the hippocampus and cortex only at 60 days of age. Here there was an increase in the expression of GSK-3β in hippocampus of the animals at 60, 120, and 180 days of age. In the cortex, this increase occurred in the 120 and 180 days of age. Tau protein expression was high in hippocampus and cortex at 120 days of age and in hippocampus at 180 days of age. The data observed show that neonatal immune activation may be associated with visuospatial memory impairment, neuroinflammation, and increased expression of GSK-3β and Tau proteins in the long term.

Abrogation of FBW7α-dependent p53 degradation enhances p53's function as a tumor suppressor

The gene encoding the tumor suppressor p53 is mutated in most cancers. p53 expression is known to be tightly controlled by several E3 ligases. Here, we show that F-box and WD repeat domain-containing 7α (FBW7α), the substrate-recognition component of the SCF^FBW7 multiprotein E3 ligase complex, targets both WT and tumor-derived mutants of p53 for proteasomal degradation in multiple human cancer cell lines (HCT116 and U2OS). We found that lack of FBW7α stabilizes p53 levels, thereby increasing its half-life. p53 ubiquitylation and subsequent degradation require the F-box and the C-terminal WD40 repeats in FBW7α. The polyubiquitylation of p53 occurred via Lys-48 linkage and involved phosphorylation on p53 at Ser-33 and Ser-37 by glycogen synthase kinase 3β (GSK3β) and DNA-dependent protein kinase (DNA-PK), respectively. These phosphorylation events created a phosphodegron that enhanced p53 binding to FBW7α, allowing for the attachment of polyubiquitin moieties at Lys-132 in p53. FBW7α-dependent p53 polyubiquitylation apparently occurred during and immediately after DNA double-strand breaks induced by either doxorubicin or ionizing radiation. Accordingly, in cells lacking FBW7α, p53 induction was enhanced after DNA damage. Phosphodegron-mediated polyubiquitylation of p53 on Lys-132 had functional consequences, with cells in which FBW7α-mediated p53 degradation was abrogated exhibiting enhancement of their tumorigenic potential. We conclude that p53, which previously has been reported to transactivate FBW7, is also targeted by the same E3 ligase for degradation, suggesting the presence of a regulatory feedback loop that controls p53 levels and functions during DNA damage.

Escitalopram Ameliorates Cognitive Impairment in D-Galactose-Injected Ovariectomized Rats: Modulation of JNK, GSK-3β, and ERK Signalling Pathways

Though selective serotonin reuptake inhibitors (SSRIs) have been found to increase cognitive performance in some studies on patients and animal models of Alzheimer's disease (AD), other studies have reported contradictory results, and the mechanism of action has not been fully described. This study aimed to examine the effect of escitalopram, an SSRI, in an experimental model of AD and to determine the involved intracellular signalling pathways. Ovariectomized rats were administered D-galactose (150 mg/kg/day, i.p) over ten weeks to induce AD. Treatment with escitalopram (10 mg/kg/day, p.o) for four weeks, starting from the 7^th week of D-galactose injection, enhanced memory performance and attenuated associated histopathological changes. Escitalopram reduced hippocampal amyloid β 42, β-secretase, and p-tau, while increasing α-secretase levels. Furthermore, it decreased tumor necrosis factor-α, nuclear factor-kappa B p65, and NADPH oxidase, while enhancing brain-derived neurotrophic factor, phospho-cAMP response element binding protein, and synaptophysin levels. Moreover, escitalopram diminished the protein expression of the phosphorylated forms of c-Jun N-terminal kinase (JNK)/c-Jun, while increasing those of phosphoinositide 3-kinase (PI3K), protein kinase B (Akt), glycogen synthase kinase-3β (GSK-3β), extracellular signal-regulated kinase (ERK) and its upstream kinases MEK and Raf-1. In conclusion, escitalopram ameliorated D-galactose/ovariectomy-induced AD-like features through modulation of PI3K/Akt/GSK-3β, Raf-1/MEK/ERK, and JNK/c-Jun pathways.

Resveratrol exerts a protective effect in chronic unpredictable mild stress-induced depressive-like behavior: involvement of the AKT/GSK3β signaling pathway in hippocampus

BACKGROUND

Chronic unpredictable mild stress (CUMS) is an important contributing factor for depression with inflammatory response alteration, neuron apoptosis, and decreased neurogenesis. Previous study reported that the administration of resveratrol alleviated depression by normalizing the increased proinflammatory cytokine levels and inhibiting apoptosis in the hippocampus. However, the upstream signaling pathway that regulates cytokines and apoptosis in the antidepressant effect of resveratrol remains unclear.

OBJECTIVE

The objective of this study is to investigate the possible mechanism of the effect of resveratrol on depression.

METHODS

Male Sprague Dawley rats were exposed to CUMS for four consecutive weeks to elicit depressive-like behavior. The rats in the drug treatment groups were injected with resveratrol (40 or 80 mg/kg/day) and fluoxetine (10 mg/kg/day) intraperitoneally for 4 weeks. Rats in two additional groups were administered LY294002 by bilateral stereotaxic microinjection into the lateral ventricle before resveratrol administration. Behavioral tests, including sucrose preference test, forced swim test, and open field test, were used after 4 weeks of a CUMS procedure to appraise depressive-like behavior. Then, the proinflammatory cytokines (TNF-α, IL-6, and IL-1β) in the hippocampus and prefrontal cortex (PFC) tissues of rats were measured. Apoptosis-related molecules such as Bax and Bcl-2 mRNA levels in the hippocampus were analyzed. Furthermore, p-Akt/Akt and p-GSK3β/GSK3β protein expression in the hippocampus were also measured.

RESULTS

The results show that rats were subjected to CUMS procedure exhibited depressive-like behavior, increased TNF-α, IL-6, and IL-1β levels in hippocampus and PFC, alteration of Bax and Bcl-2 mRNA levels in hippocampus, decreased p-Akt/Akt and p-GSK3β/GSK3β protein expression in hippocampus, and an increased apoptotic cell percentage in the hippocampal CA1 region. However, resveratrol (40 or 80 mg/kg) treatment reversed these behavioral and molecular changes in CUMS rats. The positive control drug fluoxetine showed a similar effect as the resveratrol treatment. When rats were injected with LY294002 before resveratrol treatment, the antidepressant effect of resveratrol was significantly attenuated, TNF-α, IL-6 and IL-1β levels in hippocampus and PFC increased again, Bax mRNA levels increased and Bcl-2 mRNA levels decreased in hippocampus, and Akt/GSK3β protein expression in hippocampus decreased.

CONCLUSIONS

The findings in the present study suggest that the antidepressant effect of resveratrol treatment may act through activation of the Akt/GSK3β signaling pathway and then regulation of proinflammatory cytokine expression and alteration of apoptosis.

The Alzheimer's disease-associated TREM2 gene is regulated by p53 tumor suppressor protein

TREM2 mutations evoke neurodegenerative disorders, and recently genetic variants of this gene were correlated to increased risk of Alzheimer's disease. The signaling cascade originating from the TREM2 membrane receptor includes its binding partner TYROBP, BLNK adapter protein, and SYK kinase, which can be activated by p53. Moreover, in silico identification of a putative p53 response element (RE) at the TREM2 promoter led us to hypothesize that TREM2 and other pathway elements may be regulated in p53-dependent manner. To stimulate p53 in synergistic fashion, we exposed A549 lung cancer cells to actinomycin D and nutlin-3a (A + N). In these cells, exposure to A + N triggered expression of TREM2, TYROBP, SYK and BLNK in p53-dependent manner. TREM2 was also activated by A + N in U-2 OS osteosarcoma and A375 melanoma cell lines. Interestingly, nutlin-3a, a specific activator of p53, acting alone stimulated TREM2 in U-2 OS cells. Using in vitro mutagenesis, chromatin immunoprecipitation, and luciferase reporter assays, we confirmed the presence of the p53 RE in TREM2 promoter. Furthermore, activation of TREM2 and TYROBP by p53 was strongly inhibited by CHIR-98014, a potent and specific inhibitor of glycogen synthase kinase-3 (GSK-3). We conclude that TREM2 is a direct p53-target gene, and that activation of TREM2 by A + N or nutlin-3a may be critically dependent on GSK-3 function.

Co-occurring protein phosphorylation are functionally associated

Post-translational modifications (PTMs) add a further layer of complexity to the proteome and regulate a wide range of cellular protein functions. With the increasing number of known PTM sites, it becomes imperative to understand their functional interplays. In this study, we proposed a novel analytical strategy to explore functional relationships between PTM sites by testing their tendency to be modified together (co-occurrence) under the same condition, and applied it to proteome-wide human phosphorylation data collected under 88 different laboratory or physiological conditions. Co-occurring phosphorylation occurs significantly more frequently than randomly expected and include many known examples of cross-talk or functional connections. Such pairs, either within the same phosphoprotein or between interacting partners, are more likely to be in sequence or structural proximity, be phosphorylated by the same kinases, participate in similar biological processes, and show residue co-evolution across vertebrates. In addition, we also found that their co-occurrence states tend to be conserved in orthologous phosphosites in the mouse proteome. Together, our results support that the co-occurring phosphorylation are functionally associated. Comparison with existing methods further suggests that co-occurrence analysis can be a useful complement to uncover novel functional associations between PTM sites.

In addition to gene expression and translation control, post-translational modifications (PTMs) represent another level to regulate proteins functions. Different PTM sites within a protein usually co-operate to fulfill their functional roles. Recent advances in high-throughput mass spectrometry (MS) technologies have facilitated the proteome-wide identification of PTM sites, giving rise to both challenge and opportunity to understand their functional relationships. Previously, several data mining approaches have been developed to explore the global PTM interplays. In this study, we proposed to infer functional associations between PTM sites from the correlation of their modification status across many biological conditions, which was not exploited before. In practice, we tested if a pair of sites are modified together under the same condition significantly more often than expected (co-occurrence). As a proof of principle, we applied this analytical strategy to human phosphorylation because we could collect data sets of proteome-wide coverage under 88 different conditions. We demonstrated that sites with co-occurring phosphorylation status are functionally associated from several lines of evidence. The co-occurrence analysis can also uncover functionally connected phosphosites with clear biological evidence which are missed by other approaches. With increasing proteome-wide data for other types of PTMs under different conditions, the co-occurrence analysis can be integrated with other methods to identify novel PTM associations.

Latcripin-13 domain induces apoptosis and cell cycle arrest at the G1 phase in human lung carcinoma A549 cells

Latcripin-13 domain, isolated from the transcriptome of Lentinula edodes C91-3, contains a regulator of chromosome condensation (RCC1) domain/β-lactamase-inhibitor protein II (BLIP-II) and a plant homeodomain (PHD). Latcripin-13 domain has been shown to have antitumor effects. However, the underlying molecular pharmacology is largely unknown. We report here that Latcripin-13 domain induced cell cycle arrest in the G1 phase and caused the apoptosis of human lung carcinoma A549 cells via the GSK3β-cyclin D1 and caspase-8/NF-κB signaling pathways. Western blot analysis showed that Latcripin-13 domain decreased cyclin D1 and cyclin-dependent kinase 4 (CDK4), while it increased the ratio of GSK3β/phosphorylated GSK3β. Importantly, Latcripin-13 domain induced nuclear fragmentation and chromatin condensation in the A549 cells. In addition, treatment of the A549 cells with Latcripin-13 domain resulted in the loss of mitochondrial membrane potential, accompanied by an increase in the Bax/Bcl-2 ratio and activation of caspase-3, -8, and -9. Intriguingly, western blot analysis revealed that NF-κB was significantly downregulated by Latcripin-13 domain. These results demonstrated that Latcripin-13 domain induced apoptosis and cell cycle arrest at G1 phase in the A549 cells, providing a mechanism for the antitumor effects of Latcripin-13 domain.

Agmatine Protects Against 6-OHDA-Induced Apoptosis, and ERK and Akt/GSK Disruption in SH-SY5Y Cells

6-Hydroxydopamine (6-OHDA), a metabolite of dopamine is known to induce dopaminergic cell toxicity which makes that a suitable agent inducing an experimental model of Parkinson's disease (PD). Agmatine has been shown to protect against some cellular and animal PD models. This study was aimed to assess whether agmatine prevents 6-OHDA-induced SH-SY5Y cell death and if yes, then how it affects Akt/glycogen synthesis kinase-3β (GSK-3β) and extracellular signal-regulated kinases (ERK) signals. The cells were treated with different drugs, and their viability was examined via MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide) assay and morphological observation. Western blot studies were done to assess cleaved caspase-3, Akt/GSK-3β, and ERK proteins. 6-OHDA-induced cell death and caspase-3 cleavage, while agmatine prevented those changes. 6-OHDA also decreased the amount of phosphorylated Akt (pAkt)/Akt while increased GSK-3β activity which was prevented by agmatine. Additionally, this toxin increased pERK/ERK ratio which was averted again by agmatine. The PI3/Akt inhibitor, LY294002, impeded the changes induced by agmatine, while ERK inhibitor (PD98059) did not disturb the effects of agmatine, and by itself, it preserved the cells against 6-OHDA toxicity. This study revealed that agmatine is protective in 6-OHDA model of PD and affects Akt/GSK-3β and ERK pathways.

Andrographolide activates the canonical Wnt signalling pathway by a mechanism that implicates the non-ATP competitive inhibition of GSK-3β: autoregulation of GSK-3β in vivo

Andrographolide activates the canonical Wnt pathway and induces the transcription of Wnt target genes through a mechanism independent of Wnt ligand binding to its receptor, by direct substrate-competitive inhibition of GSK-3.

Activation of glycogen synthase kinase 3β ameliorates diabetes-induced kidney injury

Increase in protein synthesis contributes to kidney hypertrophy and matrix protein accumulation in diabetes. We have previously shown that high glucose-induced matrix protein synthesis is associated with inactivation of glycogen synthase kinase 3β (GSK3β) in renal cells and in the kidneys of diabetic mice. We tested whether activation of GSK3β by sodium nitroprusside (SNP) mitigates kidney injury in diabetes. Studies in kidney-proximal tubular epithelial cells showed that SNP abrogated high glucose-induced laminin increment by stimulating GSK3β and inhibiting Akt, mTORC1, and events in mRNA translation regulated by mTORC1 and ERK. NONOate, an NO donor, also activated GSK3β, indicating that NO may mediate SNP stimulation of GSK3β. SNP administered for 3 weeks to mice with streptozotocin-induced type 1 diabetes ameliorated kidney hypertrophy, accumulation of matrix proteins, and albuminuria without changing blood glucose levels. Signaling studies showed that diabetes caused inactivation of GSK3β by activation of Src, Pyk2, Akt, and ERK; GSK3β inhibition activated mTORC1 and downstream events in mRNA translation in the kidney cortex. These reactions were abrogated by SNP. We conclude that activation of GSK3β by SNP ameliorates kidney injury induced by diabetes.

Sustained GSK3 activity markedly facilitates nerve regeneration

Promotion of axonal growth of injured DRG neurons improves the functional recovery associated with peripheral nerve regeneration. Both isoforms of glycogen synthase kinase 3 (GSK3; α and β) are phosphorylated and inactivated via phosphatidylinositide 3-kinase (PI3K)/AKT signalling upon sciatic nerve crush (SNC). However, the role of GSK3 phosphorylation in this context is highly controversial. Here we use knock-in mice expressing GSK3 isoforms resistant to inhibitory PI3K/AKT phosphorylation, and unexpectedly find markedly accelerated axon growth of DRG neurons in culture and in vivo after SNC compared with controls. Moreover, this enhanced regeneration strikingly accelerates functional recovery after SNC. These effects are GSK3 activity dependent and associated with elevated MAP1B phosphorylation. Altogether, our data suggest that PI3K/AKT-mediated inhibitory phosphorylation of GSK3 limits the regenerative outcome after peripheral nerve injury. Therefore, suppression of this internal 'regenerative break' may potentially provide a new perspective for the clinical treatment of nerve injuries.

The role of cell signalling in the crosstalk between autophagy and apoptosis

Not surprisingly, the death of a cell is a complex and well controlled process. For several decades, apoptosis, the first genetically programmed death process to be identified has taken centre stage as the principal mechanism of programmed cell death (type I cell death) in mammalian tissues. Apoptosis has been extensively studied and its contribution to the pathogenesis of disease well documented. However, apoptosis does not function alone in determining the fate of a cell. More recently, autophagy, a process in which de novo formed membrane enclosed vesicles engulf and consume cellular components, has been shown to engage in complex interplay with apoptosis. As a result, cell death has been subdivided into the categories apoptosis (Type I), autophagic cell death (Type II), and necrosis (Type III). The boundary between Type I and II cell death is not completely clear and as we will discuss in this review and perhaps a discrete difference does not exist, due to intrinsic factors among different cell types and crosstalk among organelles within each cell type. Apoptosis may begin with autophagy and autophagy can often end with apoptosis, inhibition or a blockade of caspase activity may lead a cell to default into Type II cell death from Type I.

Glycogen synthase kinase-3 inhibitors as potent therapeutic agents for the treatment of Parkinson disease

Parkinson's disease (PD) is a devastating neurodegenerative disorder characterized by degeneration of the nigrostriatal dopaminergic pathway. Because the current therapies only lead to temporary, limited improvement and have severe side effects, new approaches to treat PD need to be developed. To discover new targets for potential therapeutic intervention, a chemical genetic approach involving the use of small molecules as pharmacological tools has been implemented. First, a screening of an in-house chemical library on a well-established cellular model of PD was done followed by a detailed pharmacological analysis of the hits. Here, we report the results found for the small heterocyclic derivative called SC001, which after different enzymatic assays was revealed to be a new glycogen synthase kinase-3 (GSK-3) inhibitor with IC(50) = 3.38 ± 0.08 μM. To confirm that GSK-3 could be a good target for PD, the evaluation of a set of structurally diverse GSK-3 inhibitors as neuroprotective agents for PD was performed. Results show that inhibitors of GSK-3 have neuroprotective effects in vitro representing a new pharmacological option for the disease-modifying treatment of PD. Furthermore, we show that SC001 is able to cross the blood-brain barrier, protects dopaminergic neurons, and reduces microglia activation in in vivo models of Parkinson disease, being a good candidate for further drug development.

Use of insulin to increase epiblast cell number: towards a new approach for improving ESC isolation from human embryos

Human embryos donated for embryonic stem cell (ESC) derivation have often been cryopreserved for 5-10 years. As a consequence, many of these embryos have been cultured in media now known to affect embryo viability and the number of ESC progenitor epiblast cells. Historically, these conditions supported only low levels of blastocyst development necessitating their transfer or cryopreservation at the 4-8-cell stage. As such, these embryos are donated at the cleavage stage and require further culture to the blastocyst stage before hESC derivation can be attempted. These are generally of poor quality, and, consequently, the efficiency of hESC derivation is low. Recent work using a mouse model has shown that the culture of embryos from the cleavage stage with insulin to day 6 increases the blastocyst epiblast cell number, which in turn increases the number of pluripotent cells in outgrowths following plating, and results in an increased capacity to give rise to ESCs. These findings suggest that culture with insulin may provide a strategy to improve the efficiency with which hESCs are derived from embryos donated at the cleavage stage.

The peripheral messenger RNA expression of glycogen synthase kinase-3β genes in Alzheimer's disease patients: a preliminary study

OBJECTIVE

To explore the peripheral leucocytic messenger RNA (mRNA) expression of glycogen synthase kinase-3β (GSK-3β) gene in Alzheimer's disease (AD) patients.

METHODS

Using TaqMan relative quantitative real-time polymerase chain reaction, we analyzed leucocytic gene expression of GSK-3β in 48 AD patients and 49 healthy controls. Clinical data of AD patients were also collected.

RESULTS

The mRNA expression level of the GSK-3β gene was significantly higher in the AD group (3.13±0.62) than in the normal group (2.77±0.77). Correlational analyses showed that the mRNA expression level of GSK-3β gene in AD patients was associated with the age of onset (P=0.047), age (P=0.055), and Behavioral Pathology in Alzheimer's Disease Rating Scale total score (P=0.062) and subscores: aggressiveness score (P=0.073) and anxieties and phobias score (P=0.067). Through multivariate regression model, older age, higher anxieties and phobias score and aggressiveness score were associated with higher mRNA expression level of GSK-3β gene.

CONCLUSION

In AD patients, the mRNA expression level of the GSK-3β gene is increased and may be related to age and behavioural pathology in AD.

Glycogen synthase kinase 3 inhibition promotes adult hippocampal neurogenesis in vitro and in vivo

Glycogen synthase kinase-3 (GSK-3) is a serine/threonine kinase originally identified as a regulator of glycogen metabolism but it also plays a pivotal role in numerous cellular functions, including differentiation, cell cycle regulation, and proliferation. The dentate gyrus of the hippocampus, together with the subventricular zone of the lateral ventricles, is one of the regions in which neurogenesis takes place in the adult brain. Here, using a chemical genetic approach that involves the use of several diverse inhibitors of GSK-3 as pharmacological tools, we show that inhibition of GSK-3 induces proliferation, migration, and differentiation of neural stem cells toward a neuronal phenotype in in vitro studies. Also, we demonstrate that inhibition of GSK-3 with the small molecule NP03112, called tideglusib, induces neurogenesis in the dentate gyrus of the hippocampus of adult rats. Taken together, our results suggest that GSK-3 should be considered as a new target molecule for modulating the production and integration of new neurons in the hippocampus as a treatment for neurodegenerative diseases or brain injury and, consequently, its inhibitors may represent new potential therapeutic drugs in neuroregenerative medicine.

Pharmacological inhibition of GSK3 attenuates DNA damage-induced apoptosis via reduction of p53 mitochondrial translocation and Bax oligomerization in neuroblastoma SH-SY5Y cells

Glycogen synthase kinase-3 (GSK3) and p53 play crucial roles in the mitochondrial apoptotic pathway and are known to interact in the nucleus. However, it is not known if GSK3 has a regulatory role in the mitochondrial translocation of p53 that participates in apoptotic signaling following DNA damage. In this study, we demonstrated that lithium and SB216763, which are pharmacological inhibitors of GSK3, attenuated p53 accumulation and caspase-3 activation, as shown by PARP cleavage induced by the DNA-damaging agents doxorubicin, etoposide and camptothecin. Furthermore, each of these agents induced translocation of p53 to the mitochondria and activated the mitochondrial pathway of apoptosis, as evidenced by the release of cytochrome C from the mitochondria. Both mitochondrial translocation of p53 and mitochondrial release of cytochrome C were attenuated by inhibition of GSK3, indicating that GSK3 promotes the DNA damage-induced mitochondrial translocation of p53 and the mitochondrial apoptosis pathway. Interestingly, the regulation of p53 mitochondrial translocation by GSK3 was only evident with wild-type p53, not with mutated p53. GSK3 inhibition also reduced the phosphorylation of wild-type p53 at serine 33, which is induced by doxorubicin, etoposide and camptothecin in the mitochondria. Moreover, inhibition of GSK3 reduced etoposide-induced association of p53 with Bcl2 and Bax oligomerization. These findings show that GSK3 promotes the mitochondrial translocation of p53, enabling its interaction with Bcl2 to allow Bax oligomerization and the subsequent release of cytochrome C. This leads to caspase activation in the mitochondrial pathway of intrinsic apoptotic signaling.

Tau as a therapeutic target for Alzheimer's disease

Neurofibrillary tangles (NFTs) are one of the pathological hallmarks of Alzheimer's disease (AD) and are primarily composed of aggregates of hyperphosphorylated forms of the microtubule associated protein tau. It is likely that an imbalance of kinase and phosphatase activities leads to the abnormal phosphorylation of tau and subsequent aggregation. The wide ranging therapeutic approaches that are being developed include to inhibit tau kinases, to enhance phosphatase activity, to promote microtubule stability, and to reduce tau aggregate formation and/or enhance their clearance with small molecule drugs or by immunotherapeutic means. Most of these promising approaches are still in preclinical development whilst some have progressed to Phase II clinical trials. By pursuing these lines of study, a viable therapy for AD and related tauopathies may be obtained.

GSK-3 promotes cell survival, growth, and PAX3 levels in human melanoma cells

GSK-3 is a serine/threonine kinase involved in a diverse range of cellular processes. GSK-3 exists in two isoforms, GSK-3α and GSK-3β, which possess some functional redundancy but also play distinct roles depending on developmental and cellular context. In this article, we found that GSK-3 actively promoted cell growth and survival in melanoma cells, and blocking this activity with small-molecule inhibitor SB216763 or gene-specific siRNA decreased proliferation, increased apoptosis, and altered cellular morphology. These alterations coincided with loss of PAX3, a transcription factor implicated in proliferation, survival, and migration of developing melanoblasts. We further found that PAX3 directly interacted with and was phosphorylated in vitro on a number of residues by GSK-3β. In melanoma cells, direct inhibition of PAX3 lead to cellular changes that paralleled the response to GSK-3 inhibition. Maintenance of PAX3 expression protected melanoma cells from the anti-tumor effects of SB216763. These data support a model wherein GSK-3 regulates proliferation and morphology of melanoma through phosphorylation and increased levels of PAX3.

GSK-3β: A Bifunctional Role in Cell Death Pathways

Although glycogen synthase kinase-3 beta (GSK-3β) was originally named for its ability to phosphorylate glycogen synthase and regulate glucose metabolism, this multifunctional kinase is presently known to be a key regulator of a wide range of cellular functions. GSK-3β is involved in modulating a variety of functions including cell signaling, growth metabolism, and various transcription factors that determine the survival or death of the organism. Secondary to the role of GSK-3β in various diseases including Alzheimer's disease, inflammation, diabetes, and cancer, small molecule inhibitors of GSK-3β are gaining significant attention. This paper is primarily focused on addressing the bifunctional or conflicting roles of GSK-3β in both the promotion of cell survival and of apoptosis. GSK-3β has emerged as an important molecular target for drug development.

Insulin increases epiblast cell number of in vitro cultured mouse embryos via the PI3K/GSK3/p53 pathway

High-quality embryos give rise to embryonic stem cells (ESCs) at greater efficiencies than poor-quality embryos. However, most embryos available for human ESC derivation are of a reduced quality as a result of culture in relatively simple media up to 10 years earlier, before cryopreservation, or before compaction. In the present study, we used a mouse model to determine whether a culture with insulin from the 8-cell stage could increase the number of ESC progenitor epiblast cells in blastocysts, as well as endeavor to determine the molecular mechanism of the insulin's effect. Culture in media containing 1.7 ρM insulin increased epiblast cell number (determined by Oct4 and Nanog co-expression), and proportion in day 6 blastocysts. The inhibition of phosphoinositide 3 kinase (PI3K) (via LY294002), an early second messenger of the insulin receptor, blocked this effect. The inhibition of glycogen synthase kinase 3 (GSK3) or p53, 2 s messengers inactivated by insulin signaling (via CT99021 or pifithrin-α, respectively), increased epiblast cell numbers. When active, GSK3 and p53 block the transcription of Nanog, which is important for maintaining pluripotency. A simultaneous inhibition of GSK3 and p53 had no synergistic effects on epiblast cell number. The induced activation of GSK3 and p53, via the inhibition of proteins responsible for their inactivation (PKA via H-89 and SIRT-1 via nicotinamide, respectively), blocked the insulin's effect on the epiblast.From our findings, we conclude that insulin increases epiblast cell number via the activation of PI3K, which ultimately inactivates GSK3 and p53. Furthermore, we suggest that the inclusion of insulin in culture media could be used as a strategy for increasing the efficiency with which the ESC lines can be derived from cultured embryos.