Role of glycogen synthase kinase 3 beta as a negative regulator of dorsoventral axis formation in Xenopus embryos

Drebrin Regulates Collateral Axon Branching in Cortical Layer II/III Somatosensory Neurons

Proper cortical lamination is essential for cognition, learning, and memory. Within the somatosensory cortex, pyramidal excitatory neurons elaborate axon collateral branches in a laminar-specific manner that dictates synaptic partners and overall circuit organization. Here, we leverage both male and female mouse models, single-cell labeling and imaging approaches to identify intrinsic regulators of laminar-specific collateral, also termed interstitial, axon branching. We developed new approaches for the robust, sparse, labeling of Layer II/III pyramidal neurons to obtain single-cell quantitative assessment of axon branch morphologies. We combined these approaches with cell-autonomous loss-of-function (LOF) and overexpression (OE) manipulations in an in vivo candidate screen to identify regulators of cortical neuron axon branch lamination. We identify a role for the cytoskeletal binding protein drebrin (Dbn1) in regulating Layer II/III cortical projection neuron (CPN) collateral axon branching in vitro LOF experiments show that Dbn1 is necessary to suppress the elongation of Layer II/III CPN collateral axon branches within Layer IV, where axon branching by Layer II/III CPNs is normally absent. Conversely, Dbn1 OE produces excess short axonal protrusions reminiscent of nascent axon collaterals that fail to elongate. Structure-function analyses implicate Dbn1S142 phosphorylation and Dbn1 protein domains known to mediate F-actin bundling and microtubule (MT) coupling as necessary for collateral branch initiation upon Dbn1 OE. Taken together, these results contribute to our understanding of the molecular mechanisms that regulate collateral axon branching in excitatory CPNs, a key process in the elaboration of neocortical circuit formation.SIGNIFICANCE STATEMENT Laminar-specific axon targeting is essential for cortical circuit formation. Here, we show that the cytoskeletal protein drebrin (Dbn1) regulates excitatory Layer II/III cortical projection neuron (CPN) collateral axon branching, lending insight into the molecular mechanisms that underlie neocortical laminar-specific innervation. To identify branching patterns of single cortical neurons in vivo, we have developed tools that allow us to obtain detailed images of individual CPN morphologies throughout postnatal development and to manipulate gene expression in these same neurons. Our results showing that Dbn1 regulates CPN interstitial axon branching both in vivo and in vitro may aid in our understanding of how aberrant cortical neuron morphology contributes to dysfunctions observed in autism spectrum disorder and epilepsy.

PRC2 mediated KLF2 down regulation: a therapeutic and diagnostic axis during tumor progression

Surgery and chemo-radiotherapy are used as the common first-line treatment options in many cancers. However, tumor relapse is observed in many cancer patients following such first-line treatments. Therefore, targeted therapy according to the molecular cancer biology can be very important in reducing tumor recurrence. In this regard, a wide range of monoclonal antibodies against the growth factors and their receptors can offer more targeted treatment in cancer patients. However, due to the importance of growth factors in the normal biology of body cells, side effects can also be observed following the application of growth factor inhibitors. Therefore, more specific factors should be introduced as therapeutic targets with less side effects. Krüppel-like factors 2 (KLF2) belongs to the KLF family of transcription factors that are involved in the regulation of many cellular processes. KLF2 deregulations have been also reported during the progression of many tumors. In the present review we discussed the molecular mechanisms of KLF2 during tumor growth and invasion. It has been shown that the KLF2 as a tumor suppressor is mainly inhibited by the non-coding RNAs (ncRNAs) through the polycomb repressive complex 2 (PRC2) recruitment. This review is an effective step towards introducing the KLF2 as a suitable diagnostic and therapeutic target in cancer patients.

Lateral thinking in syndromic congenital cardiovascular disease

Syndromic birth defects are rare diseases that can present with seemingly pleiotropic comorbidities. Prime examples are rare congenital heart and cardiovascular anomalies that can be accompanied by forelimb defects, kidney disorders and more. Whether such multi-organ defects share a developmental link remains a key question with relevance to the diagnosis, therapeutic intervention and long-term care of affected patients. The heart, endothelial and blood lineages develop together from the lateral plate mesoderm (LPM), which also harbors the progenitor cells for limb connective tissue, kidneys, mesothelia and smooth muscle. This developmental plasticity of the LPM, which founds on multi-lineage progenitor cells and shared transcription factor expression across different descendant lineages, has the potential to explain the seemingly disparate syndromic defects in rare congenital diseases. Combining patient genome-sequencing data with model organism studies has already provided a wealth of insights into complex LPM-associated birth defects, such as heart-hand syndromes. Here, we summarize developmental and known disease-causing mechanisms in early LPM patterning, address how defects in these processes drive multi-organ comorbidities, and outline how several cardiovascular and hematopoietic birth defects with complex comorbidities may be LPM-associated diseases. We also discuss strategies to integrate patient sequencing, data-aggregating resources and model organism studies to mechanistically decode congenital defects, including potentially LPM-associated orphan diseases. Eventually, linking complex congenital phenotypes to a common LPM origin provides a framework to discover developmental mechanisms and to anticipate comorbidities in congenital diseases affecting the cardiovascular system and beyond.

Prediction of binding affinity of 1,2-diphenyline ketone analogues at adenosine triphosphate binding site of glycogen synthase kinase-3β: a molecular docking and dynamic simulation study

Glycogen synthase kinase (GSK)-3β is one of the downstream signalling molecules involved in phosphorylation of glycogen synthase, a key enzyme involved in the synthesis of glycogen from glucose. GSK-3β regulate some of the critical processes underlying structural and functional synaptic plasticity of neurons. Down regulation or inhibition of GSK-3β enhances long-term potentiation and cognitive functions in animal models of Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. A number of compounds are available to inhibit GSK-3β, however none of them are in clinical practice to treat neurodegenerative diseases. The aim of our study was to predict the molecular interaction and dynamic behaviour of naturally occurring 1,2-diphenyline ketone analogues at the adenosine triphosphate binding site of glycogen synthase kinase (GSK)-3β through simulation studies. Out of all 1,2-diphenyline ketone analogues,1, 3, 5, 6-Tetrahydroxyxanthone (Rank = 1), Secalonic acid F (Rank = 2), and Trihydroxy-2-(2,3-dihydroxy-3-methylbutyl)-7-methoxy-8-(3-methyl-2-butenyl) xanthone (Rank = 3) were found to exhibit lowest docking score of -12.07, -11.49, and -11.24 kcal/mol with dissociation constant of 1.37, 3.84, and 5.99 nM, respectively. The molecular dynamic simulation of rank 1 and rank 3 ligands indicated stable interaction throughout the simulation and interaction analyses has shown that the presence of hydroxyl groups at C1, C3, C5, and C6 around 1,2 diphenyline ketone nucleus to influence their binding affinity at the ATP-binding site of GSK-3β. We predicted that 1,3,5,6-Tetrahydroxyxanthone and 1, 3, 6-Trihydroxy-2-(2,3-dihydroxy-3-methylbutyl)-7-methoxy-8-(3-methyl-2-butenyl) xanthone may act as a potential ligand or lead compound to inhibit GSK-3β and also may play an important role in alleviating neurodegenerative diseases.Communicated by Ramaswamy H. Sarma.

A Genetic Model of Epilepsy with a Partial Alzheimer's Disease-Like Phenotype and Central Insulin Resistance

Studies have suggested an important connection between epilepsy and Alzheimer's disease (AD), mostly due to the high number of patients diagnosed with AD who develop epileptic seizures later on. However, this link is not well understood. Previous studies from our group have identified memory impairment and metabolic abnormalities in the Wistar audiogenic rat (WAR) strain, a genetic model of epilepsy. Our goal was to investigate AD behavioral and molecular alterations, including brain insulin resistance, in naïve (seizure-free) animals of the WAR strain. We used the Morris water maze (MWM) test to evaluate spatial learning and memory performance and hippocampal tissue to verify possible molecular and immunohistochemical alterations. WARs presented worse performance in the MWM test (p < 0.0001), higher levels of hyperphosphorylated tau (S396) (p < 0.0001) and phosphorylated glycogen synthase kinase 3 (S21/9) (p < 0.05), and lower insulin receptor levels (p < 0.05). Conversely, WARs and Wistar controls present progressive increase in amyloid fibrils (p < 0.0001) and low levels of soluble amyloid-β. Interestingly, the detected alterations were age-dependent, reaching larger differences in aged than in young adult animals. In summary, the present study provides evidence of a partial AD-like phenotype, including altered regulation of insulin signaling, in a genetic model of epilepsy. Together, these data contribute to the understanding of the connection between epilepsy and AD as comorbidities. Moreover, since both tau hyperphosphorylation and altered insulin signaling have already been reported in epilepsy and AD, these two events should be considered as important components in the interconnection between epilepsy and AD pathogenesis and, therefore, potential therapeutic targets in this field.

Glycogen Synthase Kinase 3β Involvement in Neuroinflammation and Neurodegenerative Diseases

BACKGROUND

GSK-3β activity has been strictly related to neuroinflammation and neurodegeneration. Alzheimer's disease is the most studied neurodegenerative disease, but GSK-3β seems to be involved in almost all neurodegenerative diseases including Parkinson's disease, amyotrophic lateral sclerosis, frontotemporal dementia, Huntington's disease and the autoimmune disease multiple sclerosis.

OBJECTIVE

The aim of this review is to help researchers both working on this research topic or not to have a comprehensive overview on GSK-3β in the context of neuroinflammation and neurodegeneration.

METHOD

Literature has been searched using PubMed and SciFinder databases by inserting specific keywords. A total of more than 500 articles have been discussed.

RESULTS

First of all, the structure and regulation of the kinase were briefly discussed and then, specific GSK-3β implications in neuroinflammation and neurodegenerative diseases were illustrated also with the help of figures, to conclude with a comprehensive overview on the most important GSK-3β and multitarget inhibitors. For all discussed compounds, the structure and IC50 values at the target kinase have been reported.

CONCLUSION

GSK-3β is involved in several signaling pathways both in neurons as well as in glial cells and immune cells. The fine regulation and interconnection of all these pathways are at the base of the rationale use of GSK-3β inhibitors in neuroinflammation and neurodegeneration. In fact, some compounds are now under clinical trials. Despite this, pharmacodynamic and ADME/Tox profiles of the compounds were often not fully characterized and this is deleterious in such a complex system.

The role of Xenopus developmental biology in unraveling Wnt signalling and antero-posterior axis formation

Wnt signalling plays an eminent role in development, stem cell growth, and tissue homeostasis. Much of what we know about Wnt signalling, we owe to research in developmental biology. Here I review some salient discoveries in the older literature, beginning with the Lithium experiments in sea urchin by Curt Herbst in the 1890ies, when unknown to him he observed the gradual effects of Wnt overactivation upon embryonic axis formation. After revisiting key discoveries into Wingless signalling in Drosophila, I examine the role that the Xenopus embryo has played as model system in this regard. Not only were components of the Wnt cascade dissected and secreted Wnt antagonists discovered in Xenopus, but it also played a key role in unveiling the evolutionary conserved role of Wnt signalling in primary body axis formation. I conclude that Xenopus developmental biology has played a major role in elucidating the mechanisms of embryonic Wnt signalling.

Epigenetic Regulation of the Wnt/β-Catenin Signaling Pathway in Cancer

Studies over the past four decades have elucidated the role of Wnt/β-catenin mediated regulation in cell proliferation, differentiation and migration. These processes are fundamental to embryonic development, regeneration potential of tissues, as well as cancer initiation and progression. In this review, we focus on the epigenetic players which influence the Wnt/β-catenin pathway via modulation of its components and coordinated regulation of the Wnt target genes. The role played by crosstalk with other signaling pathways mediating tumorigenesis is also elaborated. The Hippo/YAP pathway is particularly emphasized due to its extensive crosstalk via the Wnt destruction complex. Further, we highlight the recent advances in developing potential therapeutic interventions targeting the epigenetic machinery based on the characterization of these regulatory networks for effective treatment of various cancers and also for regenerative therapies.

Mutagenesis of a Lotus japonicus GSK3β/Shaggy-like kinase reveals functionally conserved regulatory residues

The glycogen synthase kinases 3 family (GSK3s/SKs; serine/threonine protein kinases) is conserved throughout eukaryotic evolution from yeast to plants and mammals. We studied a plant SK kinase from Lotus japonicus (LjSK1), previously implicated in nodule development, by enzyme kinetics and mutagenesis studies to compare it to mammalian homologues. Using a phosphorylated peptide as substrate, LjSK1 displays optimum kinase activity at pH 8.0 and 20 °C following Michaelis-Menten kinetics with K_m and Vmax values of 48.2 μM and 111.6 nmol/min/mg, respectively, for ATP. Mutation of critical residues, as inferred by sequence comparison to the human homologue GSK3β and molecular modeling, showed a conserved role for Lys167, while residues conferring substrate specificity in the human enzyme are not as significant in modulating LjSK1 substrate specificity. Mutagenesis studies also indicate a regulation mechanism for LjSK1 via proteolysis since removal of a 98 residue long N-terminal segment increases its catalytic efficiency by almost two-fold. In addition, we evaluated the alteration of LjSK1 kinase activity in planta, by overexpressing the mutant variants in hairy-roots and a phenotype in nodulation and lateral root development was verified.

Lithium and Therapeutic Targeting of GSK-3

Lithium salts have been in the therapeutic toolbox for better or worse since the 19th century, with purported benefit in gout, hangover, insomnia, and early suggestions that lithium improved psychiatric disorders. However, the remarkable effects of lithium reported by John Cade and subsequently by Mogens Schou revolutionized the treatment of bipolar disorder. The known molecular targets of lithium are surprisingly few and include the signaling kinase glycogen synthase kinase-3 (GSK-3), a group of structurally related phosphomonoesterases that includes inositol monophosphatases, and phosphoglucomutase. Here we present a brief history of the therapeutic uses of lithium and then focus on GSK-3 as a therapeutic target in diverse diseases, including bipolar disorder, cancer, and coronavirus infections.

Characterisation of protein isoforms encoded by the Drosophila Glycogen Synthase Kinase 3 gene shaggy

The Drosophila shaggy gene (sgg, GSK-3) encodes multiple protein isoforms with serine/threonine kinase activity and is a key player in diverse developmental signalling pathways. Currently it is unclear whether different Sgg proteoforms are similarly involved in signalling or if different proteoforms have distinct functions. We used CRISPR/Cas9 genome engineering to tag eight different Sgg proteoform classes and determined their localization during embryonic development. We performed proteomic analysis of the two major proteoform classes and generated mutant lines for both of these for transcriptomic and phenotypic analysis. We uncovered distinct tissue-specific localization patterns for all of the tagged proteoforms we examined, most of which have not previously been characterised directly at the protein level, including one proteoform initiating with a non-standard codon. Collectively, this suggests complex developmentally regulated splicing of the sgg primary transcript. Further, affinity purification followed by mass spectrometric analyses indicate a different repertoire of interacting proteins for the two major proteoforms we examined, one with ubiquitous expression (Sgg-PB) and one with nervous system specific expression (Sgg-PA). Specific mutation of these proteoforms shows that Sgg-PB performs the well characterised maternal and zygotic segmentations functions of the sgg locus, while Sgg-PA mutants show adult lifespan and locomotor defects consistent with its nervous system localisation. Our findings provide new insights into the role of GSK-3 proteoforms and intriguing links with the GSK-3α and GSK-3β proteins encoded by independent vertebrate genes. Our analysis suggests that different proteoforms generated by alternative splicing are likely to perform distinct functions.

Neural defects caused by total and Wnt1-Cre mediated ablation of p120ctn in mice

Background

p120 catenin (p120ctn) is an important component in the cadherin-catenin cell adhesion complex because it stabilizes cadherin-mediated intercellular junctions. Outside these junctions, p120ctn is actively involved in the regulation of small GTPases of the Rho family, in actomyosin dynamics and in transcription regulation. We and others reported that loss of p120ctn in mouse embryos results in an embryonic lethal phenotype, but the exact developmental role of p120ctn during brain formation has not been reported.

Results

We combined floxed p120ctn mice with Del-Cre or Wnt1-Cre mice to deplete p120ctn from either all cells or specific brain and neural crest cells. Complete loss of p120ctn in mid-gestation embryos resulted in an aberrant morphology, including growth retardation, failure to switch from lordotic to fetal posture, and defective neural tube formation and neurogenesis. By expressing a wild-type p120ctn from the ROSA26 locus in p120ctn-null mouse embryonic stem cells, we could partially rescue neurogenesis. To further investigate the developmental role of p120ctn in neural tube formation, we generated conditional p120ctn^fl/fl;Wnt1Cre knockout mice. p120ctn deletion in Wnt1-expressing cells resulted in neural tube closure defects (NTDs) and craniofacial abnormalities. These defects could not be correlated with misregulation of brain marker genes or cell proliferation. In contrast, we found that p120ctn is required for proper expression of the cell adhesion components N-cadherin, E-cadherin and β-catenin, and of actin-binding proteins cortactin and Shroom3 at the apical side of neural folds. This region is of critical importance for closure of neural folds. Surprisingly, the lateral side of mutant neural folds showed loss of p120ctn, but not of N-cadherin, β-catenin or cortactin.

Conclusions

These results indicate that p120ctn is required for neurogenesis and neurulation. Elimination of p120ctn in cells expressing Wnt1 affects neural tube closure by hampering correct formation of specific adhesion and actomyosin complexes at the apical side of neural folds. Collectively, our results demonstrate the crucial role of p120ctn during brain morphogenesis.

IPO11 mediates βcatenin nuclear import in a subset of colorectal cancers

Activation of Wnt signaling entails βcatenin protein stabilization and translocation to the nucleus to regulate context-specific transcriptional programs. The majority of colorectal cancers (CRCs) initiate following APC mutations, resulting in Wnt ligand-independent stabilization and nuclear accumulation of βcatenin. The mechanisms underlying βcatenin nucleocytoplasmic shuttling remain incompletely defined. Using a novel, positive selection, functional genomic strategy, DEADPOOL, we performed a genome-wide CRISPR screen and identified IPO11 as a required factor for βcatenin-mediated transcription in APC mutant CRC cells. IPO11 (Importin-11) is a nuclear import protein that shuttles cargo from the cytoplasm to the nucleus. IPO11-/- cells exhibit reduced nuclear βcatenin protein levels and decreased βcatenin target gene activation, suggesting IPO11 facilitates βcatenin nuclear import. IPO11 knockout decreased colony formation of CRC cell lines and decreased proliferation of patient-derived CRC organoids. Our findings uncover a novel nuclear import mechanism for βcatenin in cells with high Wnt activity.

Rearing system causes changes of behavior, microbiome, and gene expression of chickens

It has been long demonstrated that cage rearing (CR) deprives the animal of the possibility to express natural behaviors and results in stress. However, the effect of the rearing system on gene expression and the molecular levels of the gut microbiome are unknown. 10-wk-old Beijing You chickens were studied in parallel CR and free-range (FR) systems for 30 wk, to investigate the effect of rearing systems on behavior, microbiota composition, and gene expression. From week 40, a match-mismatch design was conducted for 5 wk. The results indicated that CR deprives the animals of natural behaviors, evidenced by sham dust-bathing behavior. A decreased alpha diversity of gut microbiome composition of CR chickens was seen in FR compared to CR-FR chickens (P < 0.001), and the alpha diversity of gut microbiome composition of FR-CR was decreased as compared to FR chickens (P = 0.045). The heat map and beta-diversity analysis showed that the cluster of gut microbial compositions were similar between the mismatch groups (FR-CR and CR-FR), while those of CR showed the lowest diversity from the 4 groups. The relative abundance of gut microbes at genera and species levels was different between comparisons (P < 0.05). Moreover, the CR (both CR and FR-CR) triggered the downregulation of most Kyoto encyclopedia of genes and genomes pathways, while it was upregulated in 2 genetic information processing pathways, compared to FR hens regardless of long or short term. In conclusion, CR deprived chickens of their normal behavior and resulted in changes in the microbiome diversity and pathways and gene expression of chickens.

HUWE1 controls MCL1 stability to unleash AMBRA1-induced mitophagy

Receptor-mediated mitophagy is a crucial process involved in mitochondria quality control. AMBRA1 is a mitophagy receptor for the selective removal of damaged mitochondria in mammalian cells. A critical unresolved issue is how AMBRA1-mediated mitophagy is controlled in response to cellular stress. Here, we investigated the role of BCL2-family proteins on AMBRA1-dependent mitophagy and showed that MCL1 delays AMBRA1-dependent mitophagy. Indeed, MCL1 overexpression is sufficient to inhibit recruitment to mitochondria of the E3 Ubiquitin ligase HUWE1, a crucial dynamic partner of AMBRA1, upon AMBRA1-mediated mitophagy induction. In addition, we found that during mitophagy induced by AMBRA1, MCL1 levels decreased but were sustained by inhibition of the GSK-3β kinase, which delayed AMBRA1-mediated mitophagy. Also, we showed that MCL1 was phosphorylated by GSK-3β at a conserved GSK-3 phosphorylation site (S159) during AMBRA1-mediated mitophagy and that this event was accompanied by HUWE1-dependent MCL1 degradation. Altogether, our results demonstrate that MCL1 stability is regulated by the kinase GSK-3β and the E3 ubiquitin ligase HUWE1 in regulating AMBRA1-mediated mitophagy. Our work thus defines MCL1 as an upstream stress-sensitive protein, functional in AMBRA1-mediated mitophagy.

An expanding GSK3 network: implications for aging research

The last few decades of longevity research have been very exciting. We now know that longevity and healthspan can be manipulated across species, from unicellular eukaryotes to nonhuman primates, and that while aging itself is inevitable, how we age is malleable. Numerous dietary, genetic, and pharmacological studies now point to links between metabolism and growth regulation as a central aspect in determining longevity and, perhaps more importantly, health with advancing age. Here, we focus on a relatively new player in aging studies GSK3, glycogen synthase kinase, a key factor in growth and metabolism whose name fails to convey the extensive breadth of its role in cellular adaptation. First, we provide a brief overview of GSK3, touching on those aspects that are likely relevant to aging. Then, we outline the role of GSK3 in cellular functions including growth signaling, cell fate, and metabolism. Next, we describe evidence demonstrating a direct role for GSK3 in a range of age-related diseases, despite the fact that they differ considerably in their etiology and pathology. Finally, we discuss the role that GSK3 may play in normative aging and how GSK3 might be a suitable target to oppose age-related disease vulnerability.

Bi-directional genetic modulation of GSK-3β exacerbates hippocampal neuropathology in experimental status epilepticus

Glycogen synthase kinase-3 (GSK-3) is ubiquitously expressed throughout the brain and involved in vital molecular pathways such as cell survival and synaptic reorganization and has emerged as a potential drug target for brain diseases. A causal role for GSK-3, in particular the brain-enriched GSK-3β isoform, has been demonstrated in neurodegenerative diseases such as Alzheimer’s and Huntington’s, and in psychiatric diseases. Recent studies have also linked GSK-3 dysregulation to neuropathological outcomes in epilepsy. To date, however, there has been no genetic evidence for the involvement of GSK-3 in seizure-induced pathology. Status epilepticus (prolonged, damaging seizure) was induced via a microinjection of kainic acid into the amygdala of mice. Studies were conducted using two transgenic mouse lines: a neuron-specific GSK-3β overexpression and a neuron-specific dominant-negative GSK-3β (GSK-3β-DN) expression in order to determine the effects of increased or decreased GSK-3β activity, respectively, on seizures and attendant pathological changes in the hippocampus. GSK-3 inhibitors were also employed to support the genetic approach. Status epilepticus resulted in a spatiotemporal regulation of GSK-3 expression and activity in the hippocampus, with decreased GSK-3 activity evident in non-damaged hippocampal areas. Consistent with this, overexpression of GSK-3β exacerbated status epilepticus-induced neurodegeneration in mice. Surprisingly, decreasing GSK-3 activity, either via overexpression of GSK-3β-DN or through the use of specific GSK-3 inhibitors, also exacerbated hippocampal damage and increased seizure severity during status epilepticus. In conclusion, our results demonstrate that the brain has limited tolerance for modulation of GSK-3 activity in the setting of epileptic brain injury. These findings caution against targeting GSK-3 as a treatment strategy for epilepsy or other neurologic disorders where neuronal hyperexcitability is an underlying pathomechanism.

CDK8 regulates the angiogenesis of pancreatic cancer cells in part via the CDK8-β-catenin-KLF2 signal axis

BACKGROUND

CDK8 is associated with the transcriptional Mediator complex and has been shown to regulate several transcription factors implicated in cancer. As a pancreatic cancer oncogene, the role of CDK8 in cancer angiogenesis remains unclear. Here, we investigated the contribution of CDK8 in pancreatic cancer angiogenesis and examined the underlying molecular mechanisms.

METHODS

CDK8 expression was evaluated via immunohistochemistry, western blotting, and qRT-PCR in relation to the clinicopathological characteristics of pancreatic cancer patients. The effects of silencing or overexpressing CDK8 on cancer angiogenesis were assessed in vitro by western blotting assays in pancreatic cancer cell lines and in vivo with nude mice xenograft models.

RESULTS

Compared with adjacent normal tissues, pancreatic cancer tissues showed upregulation of CDK8 expression, which was inversely correlated with T grade, liver metastasis, size, lymph node metastasis and poor survival. CDK8 overexpression promoted angiogenesis in pancreatic cancer via activation of the CDK8-β-catenin-KLF2 signaling axis, as demonstrated by the upregulation and downregulation of signals representing the rate-limiting steps in angiogenesis. Silencing CDK8 inhibited angiogenesis in pancreatic cancer in vitro. Additionally, these results were confirmed in nude mice xenograft models in vivo.

CONCLUSIONS

CDK8 promotes angiogenesis in pancreatic cancer via activation of the CDK8-β-catenin-KLF2 signaling axis, thus providing valid targets for the treatment of pancreatic cancer.

Reversal of hyperactive Wnt signaling-dependent adipocyte defects by peptide boronic acids

Deregulated Wnt signaling and altered lipid metabolism have been linked to obesity, diabetes, and various cancers, highlighting the importance of identifying inhibitors that can modulate Wnt signaling and aberrant lipid metabolism. We have established a Drosophila model with hyperactivated Wnt signaling caused by partial loss of axin, a key component of the Wnt cascade. The Axin mutant larvae are transparent and have severe adipocyte defects caused by up-regulation of β-catenin transcriptional activities. We demonstrate pharmacologic mitigation of these phenotypes in Axin mutants by identifying bortezomib and additional peptide boronic acids. We show that the suppressive effect of peptide boronic acids on hyperactive Wnt signaling is dependent on α-catenin; the rescue effect is completely abolished with the depletion of α-catenin in adipocytes. These results indicate that rather than targeting the canonical Wnt signaling pathway directly, pharmacologic modulation of β-catenin activity through α-catenin is a potentially attractive approach to attenuating Wnt signaling in vivo.

GSK3 and its interactions with the PI3K/AKT/mTOR signalling network

Glycogen Synthase Kinase-3 (GSK3 or GSK-3) is a promiscuous protein kinase and its phosphorylation of its diverse substrates has major influences on many areas of physiology and pathology, including cellular metabolism, lineage commitment and neuroscience. GSK3 was one of the first identified substrates of the heavily studied oncogenic kinase AKT, phosphorylation by which inhibits GSK3 activity via the formation of an autoinhibitory pseudosubstrate sequence. This has led to investigation of the role of GSK3 inhibition as a key component of the cellular responses to growth factors and insulin, which stimulate the class I PI 3-Kinases and in turn AKT activity and GSK3 phosphorylation. GSK3 has been shown to phosphorylate several upstream and downstream components of the PI3K/AKT/mTOR signalling network, including AKT itself, RICTOR, TSC1 and 2, PTEN and IRS1 and 2, with the potential to apply feedback control within the network. However, it has been clear for some time that functionally distinct, insulated pools of GSK3 exist which are regulated independently, so that for some GSK3 substrates such as β-catenin, phosphorylation by GSK3 is not controlled by input from PI3K and AKT. Instead, as almost all GSK3 substrates require a priming phosphorylated residue to be 4 amino acids C-terminal to the Ser/Thr phosphorylated by GSK3, the predominant form of regulation of the activity of GSK3 often appears to be through control over these priming events, specific to individual substrates. Therefore, a major role of GSK3 can be viewed as an amplifier of the electrostatic effects on protein function which are caused by these priming phosphorylation events. Here we discuss these different aspects to GSK3 regulation and function, and the functions of GSK3 as it integrates with signalling through the PI3K-AKT-mTOR signalling axis.

The many postures of noncanonical Wnt signaling in development and diseases

Wnt signaling regulates many aspects of vertebrate development. Its dysregulation causes developmental defects and diseases including cancer. The signaling can be categorized in two pathways: canonical and noncanonical. Canonical pathway plays a key role in regulating proliferation and differentiation of cells whilst noncanonical Wnt signaling mainly controls cellular polarity and motility. During development, noncanonical Wnt signaling is required for tissue formation. Recent studies have shown that noncanonical Wnt signaling is involved in adult tissue development and cancer progression. In this review, we try to describe and discuss the mechanisms behind the biological effects of noncanonical Wnt signaling, diseases caused by its dysregulation, and implications in adult tissue development biology.

The emergence of mesencephalic trigeminal neurons

Background

The cells of the mesencephalic trigeminal nucleus (MTN) are the proprioceptive sensory neurons that innervate the jaw closing muscles. These cells differentiate close to the two key signalling centres that influence the dorsal midbrain, the isthmus, which mediates its effects via FGF and WNT signalling and the roof plate, which is a major source of BMP signalling as well as WNT signalling.

Methods

In this study, we have set out to analyse the importance of FGF, WNT and BMP signalling for the development of the MTN. We have employed pharmacological inhibitors of these pathways in explant cultures as well as utilising the electroporation of inhibitory constructs in vivo in the chick embryo.

Results

We find that interfering with either FGF or WNT signalling has pronounced effects on MTN development whilst abrogation of BMP signalling has no effect. We show that treatment of explants with either FGF or WNT antagonists results in the generation of fewer MTN neurons and affects MTN axon extension and that inhibition of both these pathways has an additive effect. To complement these studies, we have used in vivo electroporation to inhibit BMP, FGF and WNT signalling within dorsal midbrain cells prior to, and during, their differentiation as MTN neurons. Again, we find that inhibition of BMP signalling has no effect on the development of MTN neurons. We additionally find that cells electroporated with inhibitory constructs for either FGF or WNT signalling can differentiate as MTN neurons suggesting that these pathways are not required cell intrinsically for the emergence of these neurons. Indeed, we also show that explants of dorsal mesencephalon lacking both the isthmus and roof plate can generate MTN neurons. However, we did find that inhibiting FGF or WNT signalling had consequences for MTN differentiation.

Conclusions

Our results suggest that the emergence of MTN neurons is an intrinsic property of the dorsal mesencephalon of gnathostomes, and that this population undergoes expansion, and maturation, along with the rest of the dorsal midbrain under the influence of FGF and WNT signalling.

Role of microtubule-associated protein tau phosphorylation in Alzheimer's disease

As a major microtubule-associated protein, tau plays an important role in promoting microtubule assembly and stabilizing microtubules. In Alzheimer's disease (AD) and other tauopathies, the abnormally hyperphosphorylated tau proteins are aggregated into paired helical filaments and accumulated in the neurons with the form of neurofibrillary tangles. An imbalanced regulation in protein kinases and protein phosphatases is the direct cause of tau hyperphosphorylation. Among various kinases and phosphatases, glycogen synthase kinase-3β (GSK-3β) and protein phosphatase 2A (PP2A) are the most implicated. Accumulation of the hyperphosphorylated tau induces synaptic toxicity and cognitive impairments. Here, we review the upstream factors or pathways that can regulate GSK-3β or PP2A activity mainly based on our recent findings. We will also discuss the mechanisms that may underlie tau-induced synaptic toxicity.

Glycogen Synthase Kinase 3: A Kinase for All Pathways?

Glycogen synthase kinase-3 (GSK-3) is an unusual protein-serine kinase in that it is primarily regulated by inhibition and lies downstream of multiple cell signaling pathways. This raises a variety of questions in terms of its physiological role(s), how signaling specificity is maintained and why so many eggs have been placed into one basket. There are actually two baskets, as there are two isoforms, GSK-3α and β, that are highly related and largely redundant. Their many substrates range from regulators of cellular metabolism to molecules that control growth and differentiation. In this chapter, we review the characteristics of GSK-3, update progress in understanding the kinase, and try to answer some of the questions raised by its unusual properties. Indeed, the kinase may trigger transformation in our thinking of how cellular signals are organized and controlled.

Pre-bilaterian origin of the blastoporal axial organizer

The startling capacity of the amphibian Spemann organizer to induce naïve cells to form a Siamese twin embryo with a second set of body axes is one of the hallmarks of developmental biology. However, the axis-inducing potential of the blastopore-associated tissue is commonly regarded as a chordate feature. Here we show that the blastopore lip of a non-bilaterian metazoan, the anthozoan cnidarian Nematostella vectensis, possesses the same capacity and uses the same molecular mechanism for inducing extra axes as chordates: Wnt/β-catenin signaling. We also demonstrate that the establishment of the secondary, directive axis in Nematostella by BMP signaling is sensitive to an initial Wnt signal, but once established the directive axis becomes Wnt-independent. By combining molecular analysis with experimental embryology, we provide evidence that the emergence of the Wnt/β-catenin driven blastopore-associated axial organizer predated the cnidarian-bilaterian split over 600 million years ago.

GSK3β regulates AKT-induced central nervous system axon regeneration via an eIF2Bε-dependent, mTORC1-independent pathway

Axons fail to regenerate after central nervous system (CNS) injury. Modulation of the PTEN/mTORC1 pathway in retinal ganglion cells (RGCs) promotes axon regeneration after optic nerve injury. Here, we report that AKT activation, downstream of Pten deletion, promotes axon regeneration and RGC survival. We further demonstrate that GSK3β plays an indispensable role in mediating AKT-induced axon regeneration. Deletion or inactivation of GSK3β promotes axon regeneration independently of the mTORC1 pathway, whereas constitutive activation of GSK3β reduces AKT-induced axon regeneration. Importantly, we have identified eIF2Bε as a novel downstream effector of GSK3β in regulating axon regeneration. Inactivation of eIF2Bε reduces both GSK3β and AKT-mediated effects on axon regeneration. Constitutive activation of eIF2Bε is sufficient to promote axon regeneration. Our results reveal a key role of the AKT-GSK3β-eIF2Bε signaling module in regulating axon regeneration in the adult mammalian CNS.

DOI:http://dx.doi.org/10.7554/eLife.11903.001

The central nervous system consists of the neurons that make up the brain, retina, and spinal cord. Neurons transmit electrical signals along a cable-like structure called an axon. However, an axon cannot regenerate itself, and so injuries that crush or sever the axons can lead to permanent damage. This happens for two reasons: neurons don’t have the same regenerative ability as other cells, and the environment in the central nervous system restricts cell growth.

The optic nerve transmits visual information from the eye to the brain. Studies in mice with a damaged optic nerve show that it is possible to regenerate the axons of neurons that lack a protein known as PTEN. These studies revealed one molecular pathway by which eliminating PTEN helps to boost the regrowth of axons.

Now, Guo et al. identify another independent pathway by which eliminating PTEN helps promote axon regeneration in damaged mouse optic nerves. This pathway starts with a growth-promoting enzyme called AKT, which is turned on in neurons that lack PTEN. Indeed, injecting mice with an active form of this enzyme caused the optic nerve fiber to regrow in mice whose optic nerve had been crushed.

Further experiments revealed that AKT activates a pathway in which another enzyme called GSK3β acts on a protein called eIF2Bε. A future challenge is to simultaneously manipulate the different signaling pathways that have been linked to axon regrowth to investigate whether this combined approach could help repair damage to the central nervous system.

DOI:http://dx.doi.org/10.7554/eLife.11903.002

Molecular specification of germ layers in vertebrate embryos

In order to generate the tissues and organs of a multicellular organism, different cell types have to be generated during embryonic development. The first step in this process of cellular diversification is the formation of the three germ layers: ectoderm, endoderm and mesoderm. The ectoderm gives rise to the nervous system, epidermis and various neural crest-derived tissues, the endoderm goes on to form the gastrointestinal, respiratory and urinary systems as well as many endocrine glands, and the mesoderm will form the notochord, axial skeleton, cartilage, connective tissue, trunk muscles, kidneys and blood. Classic experiments in amphibian embryos revealed the tissue interactions involved in germ layer formation and provided the groundwork for the identification of secreted and intracellular factors involved in this process. We will begin this review by summarising the key findings of those studies. We will then evaluate them in the light of more recent genetic studies that helped clarify which of the previously identified factors are required for germ layer formation in vivo, and to what extent the mechanisms identified in amphibians are conserved across other vertebrate species. Collectively, these studies have started to reveal the gene regulatory network (GRN) underlying vertebrate germ layer specification and we will conclude our review by providing examples how our understanding of this GRN can be employed to differentiate stem cells in a targeted fashion for therapeutic purposes.

Two homolog wheat Glycogen Synthase Kinase 3/SHAGGY--like kinases are involved in brassinosteroid signaling

BACKGROUND

Glycogen Synthase Kinase 3/SHAGGY-like kinases (GSKs) are multifunctional non-receptor ser/thr kinases. Plant GSKs are involved in hormonal signaling networks and are required for growth, development, light as well as stress responses. So far, most studies have been carried out on Arabidopsis or on other eudicotyledon GSKs. Here, we evaluated the role of TaSK1 and TaSK2, two homolog wheat (Triticum aestivum) GSKs, in brassinosteroid signaling. We explored in addition the physiological effects of brassinosteroids on wheat growth and development.

RESULTS

A bin2-1 like gain-of-function mutation has been inserted respectively in one of the homoeologous gene copies of TaSK1 (TaSK1-A.2-1) and in one of the homoeologous gene copies of TaSK2 (TaSK2-A.2-1). Arabidopsis plants were transformed with these mutated gene copies. Severe dwarf phenotypes were obtained closely resembling those of Arabidopsis bin2-1 lines and Arabidopsis BR-deficient or BR-signaling mutants. Expression of BR downstream genes, SAUR-AC1, CPD and BAS1 was deregulated in TaSK1.2-1 and TaSK2.2-1 transgenic lines. Severe dwarf lines were partially rescued by Bikinin beforehand shown to inhibit TaSK kinase activity. This rescue was accompanied with changes in BR downstream gene expression levels. Wheat embryos and seedlings were treated with compounds interfering with BR signaling or modifying BR levels to gain insight into the role of brassinosteroids in wheat development. Embryonic axis and scutellum differentiation were impaired, and seedling growth responses were affected when embryos were treated with Epibrassinolides, Propiconazole, and Bikinin.

CONCLUSIONS

In view of our findings, TaSKs are proposed to be involved in BR signaling and to be orthologous of Arabidopsis Clade II GSK3/SHAGGY-like kinases. Observed effects of Epibrassinolide, Propiconazole and Bikinin treatments on wheat embryos and seedlings indicate a role for BR signaling in embryonic patterning and seedling growth.

Novel β-carbolines against colorectal cancer cell growth via inhibition of Wnt/β-catenin signaling

Wnt signaling pathway is aberrantly activated in a variety of cancers, especially in colorectal cancer (CRC), because of mutations in the genes encoding adenomatous polyposis coli (APC), β-catenin and Axin. Small-molecule antagonists of Wnt/β-catenin signaling are attractive candidates for developing effective therapeutics for CRC. In this study, we have identified a novel Wnt signaling inhibitor, isopropyl 9-ethyl-1- (naphthalen-1-yl)-9H-pyrido[3,4-b]indole-3- carboxylate (Z86). Z86 inhibited Wnt reporter activities and the expression of endogenous Wnt signaling target genes in mammalian cells and antagonized the second axis formation of Xenopus embryos induced by Wnt8. We showed that Z86 treatment inhibits GSK3β (Ser9) phosphorylation, leading to its overactivation and promoting the phosphorylation and degradation of β-catenin. In vitro, Z86 selectively inhibited the growth of CRC cells with constitutive Wnt signaling and caused obvious G1-phase arrest of the cell cycle. Notably, in a nude mouse model, Z86 inhibited dramatically the xenografted tumor growth of CRC. Daily intraperitoneal injection of Z86 at 5 mg/kg resulted in >70% reduction in the tumor weight of HCT116 cell origin that was associated with decreased GSK3β (Ser9) phosphorylation and increased β-catenin phosphorylation. Taken together, our findings provide a novel promising chemotype for CRC therapeutics development targeting the canonical Wnt signaling.

BH3 domain-independent apolipoprotein L1 toxicity rescued by BCL2 prosurvival proteins

The potent trypanolytic properties of human apolipoprotein L1 (APOL1) can be neutralized by the trypanosome variant surface antigen gene product known as serum resistance-associated protein. However, two common APOL1 haplotypes present uniquely in individuals of West African ancestry each encode APOL1 variants resistant to serum resistance-associated protein, and each confers substantial resistance to human African sleeping sickness. In contrast to the dominantly inherited anti-trypanosomal activity of APOL1, recessive inheritance of these two trypanoprotective APOL1 alleles predisposes to kidney disease. Proposed mechanisms of APOL1 toxicity have included BH3 domain-dependent autophagy and/or ion channel activity. We probed these potential mechanisms by expressing APOL1 in Xenopus laevis oocytes. APOL1 expression in oocytes increased ion permeability and caused profound morphological deterioration (toxicity). Coexpression of BCL2 family members rescued APOL1-associated oocyte toxicity in the order MCL1 ∼ BCLW > BCLXL ∼ BCL2A1 ≫ BCL2. Deletion of nine nominal core BH3 domain residues abolished APOL1-associated toxicity, but missense substitution of the same residues abolished neither oocyte toxicity nor its rescue by coexpressed MCL1. The APOL1 BH3 domain was similarly dispensable for the ability of APOL1 to rescue intact mice from lethal trypanosome challenge. Replacement of most extracellular Na(+) by K(+) also reduced APOL1-associated oocyte toxicity, allowing demonstration of APOL1-associated increases in Ca(2+) and Cl(-) fluxes and oocyte ion currents, which were similarly reduced by MCL1 coexpression. Thus APOL1 toxicity in Xenopus oocytes is BH3-independent, but can nonetheless be rescued by some BCL2 family proteins.

Wnt affects symmetry and morphogenesis during post-embryonic development in colonial chordates

Background

Wnt signaling is one of the earliest and most highly conserved regulatory pathways for the establishment of the body axes during regeneration and early development. In regeneration, body axes determination occurs independently of tissue rearrangement and early developmental cues. Modulation of the Wnt signaling in either process has shown to result in unusual body axis phenotypes. Botryllus schlosseri is a colonial ascidian that can regenerate its entire body through asexual budding. This processes leads to an adult body via a stereotypical developmental pathway (called blastogenesis), without proceeding through any embryonic developmental stages.

Results

In this study, we describe the role of the canonical Wnt pathway during the early stages of asexual development. We characterized expression of three Wnt ligands (Wnt2B, Wnt5A, and Wnt9A) by in situ hybridization and qRT-PCR. Chemical manipulation of the pathway resulted in atypical budding due to the duplication of the A/P axes, supernumerary budding, and loss of the overall cell apical-basal polarity.

Conclusions

Our results suggest that Wnt signaling is used for equivalent developmental processes both during embryogenesis and asexual development in an adult organism, suggesting that patterning mechanisms driving morphogenesis are conserved, independent of embryonic, or regenerative development.

Electronic supplementary material

The online version of this article (doi:10.1186/s13227-015-0009-3) contains supplementary material, which is available to authorized users.

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.

Overexpression of Laccaria bicolor aquaporin JQ585595 alters root water transport properties in ectomycorrhizal white spruce (Picea glauca) seedlings

The contribution of hyphae to water transport in ectomycorrhizal (ECM) white spruce (Picea glauca) seedlings was examined by altering expression of a major water-transporting aquaporin in Laccaria bicolor. Picea glauca was inoculated with wild-type (WT), mock transgenic or L. bicolor aquaporin JQ585595-overexpressing (OE) strains and exposed to root temperatures ranging from 5 to 20°C to examine the root water transport properties, physiological responses and plasma membrane intrinsic protein (PIP) expression in colonized plants. Mycorrhization increased shoot water potential, transpiration, net photosynthetic rates, root hydraulic conductivity and root cortical cell hydraulic conductivity in seedlings. At 20°C, OE plants had higher root hydraulic conductivity compared with WT plants and the increases were accompanied by higher expression of P. glauca PIP GQ03401_M18.1 in roots. In contrast to WT L. bicolor, the effects of OE fungi on root and root cortical cell hydraulic conductivities were abolished at 10 and 5°C in the absence of major changes in the examined transcript levels of P. glauca root PIPs. The results provide evidence for the importance of fungal aquaporins in root water transport of mycorrhizal plants. They also demonstrate links between hyphal water transport, root aquaporin expression and root water transport in ECM plants.

Canonical Wnt signalling regulates epithelial patterning by modulating levels of laminins in zebrafish appendages

The patterning and morphogenesis of body appendages – such as limbs and fins – is orchestrated by the activities of several developmental pathways. Wnt signalling is essential for the induction of limbs. However, it is unclear whether a canonical Wnt signalling gradient exists and regulates the patterning of epithelium in vertebrate appendages. Using an evolutionarily old appendage – the median fin in zebrafish – as a model, we show that the fin epithelium exhibits graded changes in cellular morphology along the proximo-distal axis. This epithelial pattern is strictly correlated with the gradient of canonical Wnt signalling activity. By combining genetic analyses with cellular imaging, we show that canonical Wnt signalling regulates epithelial cell morphology by modulating the levels of laminins, which are extracellular matrix components. We have unravelled a hitherto unknown mechanism involved in epithelial patterning, which is also conserved in the pectoral fins – evolutionarily recent appendages that are homologous to tetrapod limbs.

Highlighted article: In the zebrafish fin, a Wnt gradient dictates the expression of laminin α5, which signals via integrin α3 to control epithelial cell morphology.

GSK3 and Polo-like kinase regulate ADAM13 function during cranial neural crest cell migration

ADAMs are cell surface metalloproteases that control multiple biological processes by cleaving signaling and adhesion molecules. ADAM13 controls cranial neural crest (CNC) cell migration both by cleaving cadherin-11 to release a promigratory extracellular fragment and by controlling expression of multiple genes via its cytoplasmic domain. The latter activity is regulated by γ-secretase cleavage and the translocation of the cytoplasmic domain into the nucleus. One of the genes regulated by ADAM13, the protease calpain8, is essential for CNC migration. Although the nuclear function of ADAM13 is evolutionarily conserved, it is unclear whether the transcriptional regulation is also performed by other ADAMs and how this process may be regulated. We show that ADAM13 function to promote CNC migration is regulated by two phosphorylation events involving GSK3 and Polo-like kinase (Plk). We further show that inhibition of either kinase blocks CNC migration and that the respective phosphomimetic forms of ADAM13 can rescue these inhibitions. However, these phosphorylations are not required for ADAM13 proteolysis of its substrates, γ-secretase cleavage, or nuclear translocation of its cytoplasmic domain. Of significance, migration of the CNC can be restored in the absence of Plk phosphorylation by expression of calpain-8a, pointing to impaired nuclear activity of ADAM13.

The ubiquitin ligase RNF220 enhances canonical Wnt signaling through USP7-mediated deubiquitination of β-catenin

Wnt/β-catenin signaling plays critical roles in embryonic development and disease. Here, we identify RNF220, a RING domain E3 ubiquitin ligase, as a new regulator of β-catenin. RNF220 physically interacts with β-catenin, but instead of promoting its ubiquitination and proteasomal degradation, it stabilizes β-catenin and promotes canonical Wnt signaling. Our analysis showed that RNF220 interacts with USP7, a ubiquitin-specific peptidase, which is required for RNF220 to stabilize β-catenin. The RNF220/USP7 complex deubiquitinates β-catenin and enhances canonical Wnt signaling. Interestingly, the stability of RNF220 itself is negatively regulated by Gsk3β, which is a key component of the β-catenin destruction complex and is inhibited upon Wnt stimulation. Accordingly, the RNF220/USP7 complex works as a positive feedback regulator of β-catenin signaling. In colon cancer cells with stimulated Wnt signaling, knockdown of RNF220 or USP7 impairs Wnt signaling and expression of Wnt target genes, suggesting a potentially novel role of RNF220 in Wnt-related tumorigenesis.

Reduced striatal dopamine DA D2 receptor function in dominant-negative GSK-3 transgenic mice

Glycogen synthase kinase-3 (GSK-3) is a serine/threonine kinase with constitutive activity involved in cellular architecture, gene expression, cell proliferation, fate decision and apoptosis, among others. GSK-3 expression is particularly high in brain where it may be involved in neurological and psychiatric disorders such as Alzheimer׳s disease, bipolar disorder and major depression. A link with schizophrenia is suggested by the antipsychotic drug-induced GSK-3 regulation and by the involvement of the Akt/GSK-3 pathway in dopaminergic neurotransmission. Taking advantage of the previous development of dominant negative GSK-3 transgenic mice (Tg) showing a selective reduction of GSK-3 activity in forebrain neurons but not in dopaminergic neurons, we explored the relationship between GSK-3 and dopaminergic neurotransmission in vivo. In microdialysis experiments, local quinpirole (DA D2-R agonist) in dorsal striatum reduced dopamine (DA) release significantly less in Tg mice than in wild-type (WT) mice. However, local SKF-81297 (selective DA D1-R agonist) in dorsal striatum reduced DA release equally in both control and Tg mice indicating a comparable function of DA D1-R in the direct striato-nigral pathway. Likewise, systemic quinpirole administration - acting preferentially on presynaptic DA D2- autoreceptors to modulate DA release-reduced striatal DA release similarly in both control and Tg mice. Quinpirole reduced locomotor activity and induced c-fos expression in globus pallidus (both striatal DA D2-R-mediated effects) significantly more in WT than in Tg mice. Taking together, the present results show that dominant negative GSK-3 transgenic mice show reduced DA D2-R-mediated function in striatum and further support a link between dopaminergic neurotransmission and GSK-3 activity.

GSK-3 – at the crossroads of cell death and survival

Glycogen synthase kinase 3 (GSK-3) is involved in various signaling pathways controlling metabolism, differentiation and immunity, as well as cell death and survival. GSK-3 targets transcription factors, regulates the activity of metabolic and signaling enzymes, and controls the half-life of proteins by earmarking them for degradation. GSK-3 is unique in its mode of substrate recognition and the regulation of its kinase activity, which is repressed by pro-survival phosphoinositide 3-kinase (PI3K)–AKT signaling. In turn, GSK-3 exhibits pro-apoptotic functions when the PI3K–AKT pathway is inactive. Nevertheless, as GSK-3 is crucially involved in many signaling pathways, its role in cell death regulation is not uniform, and in some situations it promotes cell survival. In this Commentary, we focus on the various aspects of GSK-3 in the regulation of cell death and survival. We discuss the effects of GSK-3 on the regulation of proteins of the BCL-2 family, through which GSK-3 exhibits pro-apoptotic activity. We also highlight the pro-survival activities of GSK-3, which are observed in the context of nuclear factor κB (NFκB) signaling, and we discuss how GSK-3, by impacting on cell death and survival, might play a role in diseases such as cancer.

Wnt activation of immortalized brain endothelial cells as a tool for generating a standardized model of the blood brain barrier in vitro

Reproducing the characteristics and the functional responses of the blood–brain barrier (BBB) in vitro represents an important task for the research community, and would be a critical biotechnological breakthrough. Pharmaceutical and biotechnology industries provide strong demand for inexpensive and easy-to-handle in vitro BBB models to screen novel drug candidates. Recently, it was shown that canonical Wnt signaling is responsible for the induction of the BBB properties in the neonatal brain microvasculature in vivo. In the present study, following on from earlier observations, we have developed a novel model of the BBB in vitro that may be suitable for large scale screening assays. This model is based on immortalized endothelial cell lines derived from murine and human brain, with no need for co-culture with astrocytes. To maintain the BBB endothelial cell properties, the cell lines are cultured in the presence of Wnt3a or drugs that stabilize β-catenin, or they are infected with a transcriptionally active form of β-catenin. Upon these treatments, the cell lines maintain expression of BBB-specific markers, which results in elevated transendothelial electrical resistance and reduced cell permeability. Importantly, these properties are retained for several passages in culture, and they can be reproduced and maintained in different laboratories over time. We conclude that the brain-derived endothelial cell lines that we have investigated gain their specialized characteristics upon activation of the canonical Wnt pathway. This model may be thus suitable to test the BBB permeability to chemicals or large molecular weight proteins, transmigration of inflammatory cells, treatments with cytokines, and genetic manipulation.

Development of hypothalamic serotoninergic neurons requires Fgf signalling via the ETS-domain transcription factor Etv5b

Serotonin is a monoamine neurotransmitter that is involved in numerous physiological functions and its dysregulation is implicated in various psychiatric diseases. In all non-placental vertebrates, serotoninergic (5-HT) neurons are present in several regions of the brain, including the hypothalamus. In placental mammals, however, 5-HT neurons are located in the raphe nuclei only. In all species, though, 5-HT neurons constitute a functionally and molecularly heterogeneous population. How the non-raphe 5-HT populations are developmentally encoded is unknown. Using the zebrafish model we show that, in contrast to the raphe populations, hypothalamic 5-HT neurons are generated independently of the ETS-domain transcription factor Pet1 (Fev). By applying a combination of pharmacological tools and gene knockdown and/or overexpression experiments, we demonstrate that Fgf signalling acts via another ETS-domain transcription factor, Etv5b (Erm), to induce hypothalamic 5-HT neurons. We provide evidence that Etv5b exerts its effects by regulating cell cycle parameters in 5-HT progenitors. Our results highlight a novel role for Etv5b in neuronal development and provide support for the existence of a developmental heterogeneity among 5-HT neurons in their requirement for ETS-domain transcription factors.

Fine-tuning of voltage sensitivity of the Kv1.2 potassium channel by interhelix loop dynamics

Many proteins function by changing conformation in response to ligand binding or changes in other factors in their environment. Any change in the sequence of a protein, for example during evolution, which alters the relative free energies of the different functional conformations changes the conditions under which the protein will function. Voltage-gated ion channels are membrane proteins that open and close an ion-selective pore in response to changes in transmembrane voltage. The charged S4 transmembrane helix transduces changes in transmembrane voltage into a change in protein internal energy by interacting with the rest of the channel protein through a combination of non-covalent interactions between adjacent helices and covalent interactions along the peptide backbone. However, the structural basis for the wide variation in the V50 value between different voltage-gated potassium channels is not well defined. To test the role of the loop linking the S3 helix and the S4 helix in voltage sensitivity, we have constructed a set of mutants of the rat Kv1.2 channel that vary solely in the length and composition of the extracellular loop that connects S4 to S3. We evaluated the effect of these different loop substitutions on the voltage sensitivity of the channel and compared these experimental results with molecular dynamics simulations of the loop structures. Here, we show that this loop has a significant role in setting the precise V50 of activation in Kv1 family channels.

Unfolded protein response activates glycogen synthase kinase-3 via selective lysosomal degradation

The unfolded protein response (UPR) is a stress response that is activated upon disturbed homeostasis in the endoplasmic reticulum. In Alzheimer's disease, as well as in other tauopathies, the UPR is activated in neurons that contain early tau pathology. A recent genome-wide association study identified genetic variation in a UPR transducer as a risk factor for tauopathy, supporting a functional connection between UPR activation and tau pathology. Here we show that UPR activation increases the activity of the major tau kinase glycogen synthase kinase (GSK)-3 in vitro via a selective removal of inactive GSK-3 phosphorylated at Ser(21/9). We demonstrate that this is mediated by the autophagy/lysosomal pathway. In brain tissue from patients with different tauopathies, lysosomal accumulations of pSer(21/9) GSK-3 are found in neurons with markers for UPR activation. Our data indicate that UPR activation increases the activity of GSK-3 by a novel mechanism, the lysosomal degradation of the inactive pSer(21/9) GSK-3. This may provide a functional explanation for the close association between UPR activation and early tau pathology in neurodegenerative diseases.

The way Wnt works: components and mechanism

The canonical Wnt/β-catenin pathway is an ancient and evolutionarily conserved signaling pathway that is required for the proper development of all metazoans, from the basal demosponge Amphimedon queenslandica to humans. Misregulation of Wnt signaling is implicated in many human diseases, making this pathway an intense area of research in industry as well as academia. In this review, we explore our current understanding of the molecular steps involved in the transduction of a Wnt signal. We will focus on how the critical Wnt pathway component, β-catenin, is in a "futile cycle" of constant synthesis and degradation and how this cycle is disrupted upon pathway activation. We describe the role of the Wnt pathway in major human cancers and in the control of stem cell self-renewal in the developing organism and in adults. Finally, we describe well-accepted criteria that have been proposed as evidence for the involvement of a molecule in regulating the canonical Wnt pathway.

TiO2-based phosphoproteomic analysis of schistosomes: characterization of phosphorylated proteins in the different stages and sex of Schistosoma japonicum

Protein phosphorylation is an important posttranslational modification in many organisms that regulates numerous cellular processes. However, it remains poorly characterized in schistosomes, the causative agent of schistosomiasis in humans and related animals. In the present study, we characterized phosphorylated proteins in different stages and sex of Schistosoma japonicum (S. japonicum) including schistosomula (14 days), adult females (35 days), and adult males (35 days) by a titanium dioxide (TiO(2)) based phosphoproteomic method. A total of 180 phosphopeptides were identified in 148 proteins. Our further studies revealed that heat shock protein 90 (Hsp90), one of the phosphoproteins codetected in the different stage and sex of schistosomes, may play an important role in the regulation of schistosome development by directly or indirectly interacting with other codetected signal molecules. Additionally, some phosphoproteins were shown to be detected in a gender-specific manner, and the expressions of these proteins were further validated either by immunohistochemistry or by real-time reverse transcription polymerase chain reaction (RT-PCR) at transcript levels between male and female schistosomes. In summary, these findings as well as the providing of an inventory of phosphoproteins are expected to provide new insights into schistosome development and sexual maturation and then may result in the development of novel interventions against schistosomiasis.

The β-catenin destruction complex

The Wnt/β-catenin pathway is highly regulated to insure the correct temporal and spatial activation of its target genes. In the absence of a Wnt stimulus, the transcriptional coactivator β-catenin is degraded by a multiprotein "destruction complex" that includes the tumor suppressors Axin and adenomatous polyposis coli (APC), the Ser/Thr kinases GSK-3 and CK1, protein phosphatase 2A (PP2A), and the E3-ubiquitin ligase β-TrCP. The complex generates a β-TrCP recognition site by phosphorylation of a conserved Ser/Thr-rich sequence near the β-catenin amino terminus, a process that requires scaffolding of the kinases and β-catenin by Axin. Ubiquitinated β-catenin is degraded by the proteasome. The molecular mechanisms that underlie several aspects of destruction complex function are poorly understood, particularly the role of APC. Here we review the molecular mechanisms of destruction complex function and discuss several potential roles of APC in β-catenin destruction.

Wnt/beta-catenin signaling and small molecule inhibitors

Wnt/β-catenin signaling is a branch of a functional network that dates back to the first metazoans and it is involved in a broad range of biological systems including stem cells, embryonic development and adult organs. Deregulation of components involved in Wnt/β-catenin signaling has been implicated in a wide spectrum of diseases including a number of cancers and degenerative diseases. The key mediator of Wnt signaling, β-catenin, serves several cellular functions. It functions in a dynamic mode at multiple cellular locations, including the plasma membrane, where β-catenin contributes to the stabilization of intercellular adhesive complexes, the cytoplasm where β-catenin levels are regulated and the nucleus where β-catenin is involved in transcriptional regulation and chromatin interactions. Central effectors of β-catenin levels are a family of cysteine-rich secreted glycoproteins, known as Wnt morphogens. Through the LRP5/6-Frizzled receptor complex, Wnts regulate the location and activity of the destruction complex and consequently intracellular β- catenin levels. However, β-catenin levels and their effects on transcriptional programs are also influenced by multiple other factors including hypoxia, inflammation, hepatocyte growth factor-mediated signaling, and the cell adhesion molecule E-cadherin. The broad implications of Wnt/β-catenin signaling in development, in the adult body and in disease render the pathway a prime target for pharmacological research and development. The intricate regulation of β-catenin at its various locations provides alternative points for therapeutic interventions.

Chronic inhibition of glycogen synthase kinase-3 protects against rotenone-induced cell death in human neuron-like cells by increasing BDNF secretion

Mitochondrial dysfunction is a common feature of many neurodegenerative disorders. Likewise, activation of glycogen synthase kinase-3 (GSK-3) has been proposed to play an important role in neurodegeneration. This multifunctional protein kinase is involved in a number of cellular functions and we previously showed that chronic inhibition of GSK-3 protects neuronal cells against mitochondrial dysfunction-elicited cell death, through a mechanism involving increased glucose metabolism and the translocation of hexokinase II (HKII) to mitochondria. Here, we sought to gain deeper insight into the molecular basis of this neuroprotection. We found that chronic inhibition of GSK-3, either genetically or pharmacologically, elicited a marked increase in brain-derived neurotrophic factor (BDNF) secretion, which in turn conferred resistance to mitochondrial dysfunction through subcellular re-distribution of HKII. These results define a molecular pathway through which chronic inhibition of GSK-3 may protect neuronal cells from death. Moreover, they highlight the potential benefits of enhanced neurotrophic factor secretion as a therapeutic approach to treat neurodegenerative diseases.

Inhibition of gecko GSK-3β promotes elongation of neurites and oligodendrocyte processes but decreases the proliferation of blastemal cells

GSK-3β signaling is involved in regulation of both neuronal and glial cell functions, and interference of the signaling affects central nervous system (CNS) development and regeneration. Thus, GSK-3β was proposed to be an important therapeutic target for promoting functional recovery of adult CNS injuries. To further clarify the regulatory function of the kinase on the CNS regeneration, we characterized gecko GSK-3β and determined the effects of GSK-3β inactivation on the neuronal and glial cell lines, as well as on the gecko tail (including spinal cord) regeneration. Gecko GSK-3β shares 91.7-96.7% identity with those of other vertebrates, and presented higher expression abundance in brain and spinal cord. The kinase strongly colocalized with the oligodendrocytes while less colocalized with neurons in the spinal cord. Phosphorylated GSK-3β (pGSK-3β) levels decreased gradually during the normally regenerating spinal cord ranging from L13 to the 6th caudal vertebra. Lithium injection increased the pGSK-3β levels of the corresponding spinal cord segments, and in vitro experiments on neurons and oligodendrocyte cell line revealed that the elevation of pGSK-3β promoted elongation of neurites and oligodendrocyte processes. In the normally regenerate tails, pGSK-3β kept stable in 2 weeks, whereas decreased at 4 weeks. Injection of lithium led to the elevation of pGSK-3β levels time-dependently, however destructed the regeneration of the tail including spinal cord. Bromodeoxyuridine (BrdU) staining demonstrated that inactivation of GSK-3β decreased the proliferation of blastemal cells. Our results suggested that species-specific regulation of GSK-3β was indispensable for the complete regeneration of CNS.

Nemo-like kinase, a multifaceted cell signaling regulator

Nemo-like kinase (NLK) is an evolutionarily conserved MAP kinase-related kinase. Although NLK was originally identified as a Drosophila gene affecting cell movement during eye development, recent studies show that NLK also contributes to cell proliferation, differentiation, and morphological changes during early embryogenesis and nervous system development in vertebrates. In addition, NLK has been reported to be involved in the development of several human cancers. NLK is able to play a role in multiple processes due to its capacity to regulate a diverse array of signaling pathways, including the Wnt/β-catenin, Activin, IL-6, and Notch signaling pathways. Although the molecular mechanisms that regulate NLK activity remain unclear, our recent research has presented a new model for NLK activation. Here, we summarize the current understanding of the function and regulation of NLK and discuss the aspects of NLK regulation that remain to be resolved.