Inhibition of GSK3 by Wnt signalling--two contrasting models

A Reporter System Evaluates Tumorigenesis, Metastasis, β-catenin/MMP Regulation, and Druggability

Cancer invasion, metastasis, and therapy resistance are the crucial phenomena in cancer malignancy. The high expression of matrix metalloproteinase 9 (MMP9) is a biomarker as well as a causal factor of cancer invasiveness and metastatic activity. However, a regulatory mechanism underlying MMP9 expression in cancer is not clarified yet. In addition, a new strategy for anticancer drug discovery is becoming an important clue. In the present study, we aimed (i) to develop a novel reporter system evaluating tumorigenesis, invasiveness, metastasis, and druggability with a combination of three-dimensional tumoroid model and Mmp9 promoter and (ii) to examine pharmacological actions of anticancer medications using this reporter system. High expression and genetic amplification of MMP9 were found in colon cancer cases. We found that proximal promoter sequences of MMP9 in murine and human contained conserved binding sites for transcription factors β-catenin/TCF/LEF, glucocorticoid receptor (GR), and nuclear factor kappa-B (NF-κB). The murine Mmp9 promoter (-569 to +19) was markedly activated in metastatic colon cancer cells and additionally activated by tumoroid formation and by β-catenin signaling stimulator lithium chloride. The Mmp9 promoter-driven fluorescent reporter cells enabled the monitoring of activities of MMP9/gelatinase, tumorigenesis, invasion, and metastasis in syngeneic transplantation experiments. We also demonstrated pharmacological actions as follows: dexamethasone and hydrocortisone, steroidal medications binding to GR, inhibited the Mmp9 promoter but did not inhibit tumorigenesis. On the contrary, antimetabolite 5-fluorouracil, a gold standard for colon cancer chemotherapy, inhibited tumoroid formation but did not inhibit Mmp9 promoter activity. Notably, antimalaria medication artesunate inhibited both tumorigenesis and the Mmp9 promoter in vitro, potentially through inhibition of β-catenin/TCF/LEF signaling. Thus, this novel reporter system enabled monitoring tumorigenesis, invasiveness, metastasis, key regulatory signalings such as β-catenin/MMP9 axis, and druggability. Impact Statement Cancer invasion and metastasis have been shown to be driven by matrix metalloproteinase 9 (MMP9), whose expression mechanism is not clarified yet. In addition, a new strategy for anticancer drug discovery is becoming important. We established a novel reporter system evaluating tumorigenesis, invasiveness, metastasis, and druggability with a combination of three-dimensional (3D) tumoroid model and Mmp9 promoter. Using this reporter system, we demonstrated pharmacological actions of anticancer medications such as antimetabolite 5-fluorouracil (5-FU) and antimalaria medication artesunate (ART), which inhibited both tumorigenesis and β-catenin/MMP regulatory signaling. Our study impacts the translational fields of oncology, drug discovery, and organoid model.

TCF/LEF dependent and independent transcriptional regulation of Wnt/β-catenin target genes

During canonical Wnt signalling, the activity of nuclear β-catenin is largely mediated by the TCF/LEF family of transcription factors. To challenge this view, we used the CRISPR/Cas9 genome editing approach to generate HEK 293T cell clones lacking all four TCF/LEF genes. By performing unbiased whole transcriptome sequencing analysis, we found that a subset of β-catenin transcriptional targets did not require TCF/LEF factors for their regulation. Consistent with this finding, we observed in a genome-wide analysis that β-catenin occupied specific genomic regions in the absence of TCF/LEF Finally, we revealed the existence of a transcriptional activity of β-catenin that specifically appears when TCF/LEF factors are absent, and refer to this as β-catenin-GHOST response. Collectively, this study uncovers a previously neglected modus operandi of β-catenin that bypasses the TCF/LEF transcription factors.

Activation of WNT/β-catenin signaling results in resistance to a dual PI3K/mTOR inhibitor in colorectal cancer cells harboring PIK3CA mutations

PIK3CA is a frequently mutated gene in cancer, including about ~15 to 20% of colorectal cancers (CRC). PIK3CA mutations lead to activation of the PI3K/AKT/mTOR signaling pathway, which plays pivotal roles in tumorigenesis. Here, we investigated the mechanism of resistance of PIK3CA-mutant CRC cell lines to gedatolisib, a dual PI3K/mTOR inhibitor. Out of a panel of 29 CRC cell lines, we identified 7 harboring one or more PIK3CA mutations; of these, 5 and 2 were found to be sensitive and resistant to gedatolisib, respectively. Both of the gedatolisib-resistant cell lines expressed high levels of active glycogen synthase kinase 3-beta (GSK3β) and harbored the same frameshift mutation (c.465_466insC; H155fs*) in TCF7, which encodes a positive transcriptional regulator of the WNT/β-catenin signaling pathway. Inhibition of GSK3β activity in gedatolisib-resistant cells by siRNA-mediated knockdown or treatment with a GSK3β-specific inhibitor effectively reduced the activity of molecules downstream of mTOR and also decreased signaling through the WNT/β-catenin pathway. Notably, GSK3β inhibition rendered the resistant cell lines sensitive to gedatolisib cytotoxicity, both in vitro and in a mouse xenograft model. Taken together, these data demonstrate that aberrant regulation of WNT/β-catenin signaling and active GSK3β induced by the TCF7 frameshift mutation cause resistance to the dual PI3K/mTOR inhibitor gedatolisib. Cotreatment with GSK3β inhibitors may be a strategy to overcome the resistance of PIK3CA- and TCF7-mutant CRC to PI3K/mTOR-targeted therapies.

Natural Products to Fight Cancer: A Focus on Juglans regia

Even if cancer represents a burden for human society, an exhaustive cure has not been discovered yet. Low therapeutic index and resistance to pharmacotherapy are two of the major limits of antitumour treatments. Natural products represent an excellent library of bioactive molecules. Thus, tapping into the natural world may prove useful in identifying new therapeutic options with favourable pharmaco-toxicological profiles. Juglans regia, or common walnut, is a very resilient tree that has inhabited our planet for thousands of years. Many studies correlate walnut consumption to beneficial effects towards several chronic diseases, such as cancer, mainly due to the bioactive molecules stored in different parts of the plant. Among others, polyphenols, quinones, proteins, and essential fatty acids contribute to its pharmacologic activity. The present review aims to offer a comprehensive perspective about the antitumour potential of the most promising compounds stored in this plant, such as juglanin, juglone, and the ellagitannin-metabolites urolithins or deriving from walnut dietary intake. All molecules and a chronic intake of the fruit provide tangible anticancer effects. However, the scarcity of studies on humans does not allow results to be conclusive.

High-throughput identification of factors promoting neuronal differentiation of human neural progenitor cells in microscale 3D cell culture

Identification of conditions for guided and specific differentiation of human stem cell and progenitor cells is important for continued development and engineering of in vitro cell culture systems for use in regenerative medicine, drug discovery, and human toxicology. Three-dimensional (3D) and organotypic cell culture models have been used increasingly for in vitro cell culture because they may better model endogenous tissue environments. However, detailed studies of stem cell differentiation within 3D cultures remain limited, particularly with respect to high-throughput screening. Herein, we demonstrate the use of a microarray chip-based platform to screen, in high-throughput, individual and paired effects of 12 soluble factors on the neuronal differentiation of a human neural progenitor cell line (ReNcell VM) encapsulated in microscale 3D Matrigel cultures. Dose-response analysis of selected combinations from the initial combinatorial screen revealed that the combined treatment of all-trans retinoic acid (RA) with the glycogen synthase kinase 3 inhibitor CHIR-99021 (CHIR) enhances neurogenesis while simultaneously decreases astrocyte differentiation, whereas the combined treatment of brain-derived neurotrophic factor and the small azide neuropathiazol enhances the differentiation into neurons and astrocytes. Subtype specification analysis of RA- and CHIR-differentiated cultures revealed that enhanced neurogenesis was not biased toward a specific neuronal subtype. Together, these results demonstrate a high-throughput screening platform for rapid evaluation of differentiation conditions in a 3D environment, which will aid the development and application of 3D stem cell culture models.

Endocytic trafficking factor VPS45 is essential for spatial regulation of lens fiber differentiation in zebrafish

In vertebrate lens, lens epithelial cells cover the anterior half of the lens fiber core. Lens epithelial cells proliferate, move posteriorly and start to differentiate into lens fiber cells at the lens equator. Although FGF signaling promotes this equatorial commencement of lens fiber differentiation, the underlying mechanism is not fully understood. Here, we show that lens epithelial cells abnormally enter lens fiber differentiation without passing through the equator in zebrafish vps45 mutants. VPS45 belongs to the Sec1/Munc18-like protein family and promotes endosome trafficking, which differentially modulates signal transduction. Ectopic lens fiber differentiation in vps45 mutants does not depend on FGF, but is mediated through activation of TGFβ signaling and inhibition of canonical Wnt signaling. Thus, VPS45 normally suppresses lens fiber differentiation in the anterior region of lens epithelium by modulating TGFβ and canonical Wnt signaling pathways. These data indicate a novel role of endosome trafficking to ensure equator-dependent commencement of lens fiber differentiation.

Summary: The endocytic regulator VPS45 suppresses FGF-independent lens fiber differentiation and ensures the spatial pattern of lens development.

Identification of serum β-catenin as a biomarker in patients with HBV-related liver diseases

BACKGROUND

Substantial evidence indicates that β-catenin is a pivotal regulator that contributes to the initiation and development of various types of diseases. Recently, β-catenin can be detected in human serum and also reported to be correlated with several disease progression in a little research. However, very little is known about the relationship between serum β-catenin and HBV-related liver disease.

METHODS

Serum levels of β-catenin, from 77 patients with chronic hepatitis B (CHB), 63 patients with hepatitis B associated liver cirrhosis (HBLC), 61 patients with hepatocellular carcinoma (HCC), 41 healthy HBV carriers (HHCs) and 78 healthy controls (HCs) were measured by ELISA. Correlations of serum β-catenin with viral replication and liver necroinflammation parameters were analyzed. The receiver operating characteristic (ROC) curve was used to assess the discriminating power of serum β-catenin to grade different stages of HBV-related disorders. Human hepatic cell line L02 was transfected with a HBV plasmid, and β-catenin levels and the underlying mechanism were analyzed.

RESULTS

Chronic hepatitis B and HBLC patients but not HHC or HCC showed significantly higher serum β-catenin levels than HCs. β-catenin levels were not correlated with HBV DNA levels but were correlated with necroinflammation parameters. HBV-infected cell model showed elevated levels of phosphorylation at Ser473 in Akt (p-Akt), phosphorylation at Ser9 in GSK3β (p-GSK3β) and β-catenin, all of which was blocked by treatment with Akt inhibitor LY294002. Additionally, ROC analysis of β-catenin for discriminating patients with CHB from HHCs, which yielded an AUC of 0.71 (cutoff value, 42 pg/mL; 95% CI 0.61-0.81) with 64.93% sensitivity, 73.17% specificity and 69.05% accuracy. ROC analysis of β-catenin for discriminating patients with HCC from chronic HBV infection mainly including CHB and HBLC, which yielded an AUC of 0.75 (cutoff value, 42 pg/mL; 95% CI 0.67-0.83) with 66.43% sensitivity, 75.41% specificity and 70.92% accuracy.

CONCLUSIONS

HBV infection enhances β-catenin expression by activating Akt/GSK3β signaling. Serum β-catenin levels are correlated with necroinflammation parameters but not with viral load. Serum β-catenin has potential to discriminate the phase of HBV-related disorders, particularly predicts the patients with CHB from HHCs and also predicting HCC form chronic HBV infection.

Epidermal growth factor receptor: Structure-function informing the design of anticancer therapeutics

Research on the epidermal growth factor (EGF) family and the family of receptors (EGFR) has progressed rapidly in recent times. New crystal structures of the ectodomains with different ligands, the activation of the kinase domain through oligomerisation and the use of fluorescence techniques have revealed profound conformational changes on ligand binding. The control of cell signaling from the EGFR-family is complex, with heterodimerisation, ligand affinity and signaling cross-talk influencing cellular outcomes. Analysis of tissue homeostasis indicates that the control of pro-ligand processing is likely to be as important as receptor activation events. Several members of the EGFR-family are overexpressed and/or mutated in cancer cells. The perturbation of EGFR-family signaling drives the malignant phenotype of many cancers and both inhibitors and antagonists of signaling from these receptors have already produced therapeutic benefits for patients. The design of affibodies, antibodies, small molecule inhibitors and even immunotherapeutic drugs targeting the EGFR-family has yielded promising new approaches to improving outcomes for cancer patients. In this review, we describe recent discoveries which have increased our understanding of the structure and dynamics of signaling from the EGFR-family, the roles of ligand processing and receptor cross-talk. We discuss the relevance of these studies to the development of strategies for designing more effective targeted treatments for cancer patients.

Expression of Gas1 in Mouse Brain: Release and Role in Neuronal Differentiation

Growth arrest-specific 1 (Gas1) is a pleiotropic protein that induces apoptosis of tumor cells and has important roles during development. Recently, the presence of two forms of Gas1 was reported: one attached to the cell membrane by a GPI anchor; and a soluble extracellular form shed by cells. Previously, we showed that Gas1 is expressed in different areas of the adult mouse CNS. Here, we report the levels of Gas1 mRNA protein in different regions and analyzed its expressions in glutamatergic, GABAergic, and dopaminergic neurons. We found that Gas1 is expressed in GABAergic and glutamatergic neurons in the Purkinje-molecular layer of the cerebellum, hippocampus, thalamus, and fastigial nucleus, as well as in dopaminergic neurons of the substantia nigra. In all cases, Gas1 was found in the cell bodies, but not in the neuropil. The Purkinje and the molecular layers show the highest levels of Gas1, whereas the granule cell layer has low levels. Moreover, we detected the expression and release of Gas1 from primary cultures of Purkinje cells and from hippocampal neurons as well as from neuronal cell lines, but not from cerebellar granular cells. In addition, using SH-SY5Y cells differentiated with retinoic acid as a neuronal model, we found that extracellular Gas1 promotes neurite outgrowth, increases the levels of tyrosine hydroxylase, and stimulates the inhibition of GSK3β. These findings demonstrate that Gas1 is expressed and released by neurons and promotes differentiation, suggesting an important role for Gas1 in cellular signaling in the CNS.

Role of glycogen synthase kinase following myocardial infarction and ischemia-reperfusion

Glycogen synthase kinase-3 beta (GSK3β) is principally is a glycogen synthase phosphorylating enzyme that is well known for its role in muscle metabolism. GSK3β is a serine/threonine protein Kinase, which is responsible for several essential roles in mammalian cells. This enzyme is implicated in the pathophysiology of many conditions involved in homeostasis and cellular immigration. GSK3β is involved in several pathways leading to neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease. Increasing evidence has shown the potential importance of GSK3β in ischemic heart disease and ischemia-reperfusion pathologies. Reperfusion injury may occur in tissues after prolonged ischemia following reperfusion. Reperfusion injury can be life threatening. Reperfusion injury occurs due to a change in ionic homeostasis, excess free radical production, mitochondrial damage and cell death. There are however clear, cardiac-protective signals; although the molecular pathophysiology is not clearly understood. In normal physiology, GSK3β has a critical role in the cytoprotective pathway. However, it`s controversial role in ischemia and ischemia-reperfusion is a topic of current interest. In this review, we have opted to focus on GSK3β interactions with mitochondria in ischemic heart disease and expand on the therapeutic interventions.

The regulatory roles of Notch in osteocyte differentiation via the crosstalk with canonical Wnt pathways during the transition of osteoblasts to osteocytes

Osteocytes comprise more than 90% of the cells in bone and are differentiated from osteoblasts via an unknown mechanism. Recently, it was shown that Notch signaling plays an important role in osteocyte functions. To gain insights into the mechanisms underlying the functions of Notch in regulating the transition of osteoblasts to osteocytes, we performed a luciferase assay by cloning the proximal E11 and dentin matrix acidic phosphoprotein 1 (DMP1) promotor regions into pGluc-Basic 2 vectors, which were subsequently transfected into the IDG-SW3 (osteocytes), MC3T3 (osteoblasts) and 293T (non-osteoblastic cells) cell lines. Two approaches were used to activate Notch signaling in vitro. One was a Notch1 extracellular antibody-coated cell culture plate, and the other was transfection of a Hairy/Enhancer of Split 1 (Hes1) overexpression vector. The interaction between the Notch and Wnt signaling pathways was probed by assessing the expression of a series of phosphorylated proteins involved in the cascade of both signaling pathways. Our data suggested that Notch signaling regulates E11 expression through Hes1 activity, while Hes1 solely did not initiate the expression of DMP1. The regulatory function of E11 by Hes1 was not observed in the 293T cell line, indicating a cell context-dependent manner of the Notch signaling pathway. Additionally, we found that Notch inhibited Wnt signaling at the late differentiation stage of osteocytes by both directly repressing phosphorylated Akt and preventing the nuclear aggregation of β-catenin. These findings provide profound understandings of Notch's regulatory function in osteocyte differentiation.

The function of endocytosis in Wnt signaling

Wnt growth factors regulate one of the most important signaling networks during development, tissue homeostasis and disease. Despite the biological importance of Wnt signaling, the mechanism of endocytosis during this process is ill described. Wnt molecules can act as paracrine signals, which are secreted from the producing cells and transported through neighboring tissue to activate signaling in target cells. Endocytosis of the ligand is important at several stages of action: One central function of endocytic trafficking in the Wnt pathway occurs in the source cell. Furthermore, the β-catenin-dependent Wnt ligands require endocytosis for signal activation and to regulate gene transcription in the responding cells. Alternatively, Wnt/β-catenin-independent signaling regulates endocytosis of cell adherence plaques to control cell migration. In this comparative review, we elucidate these three fundamental interconnected functions, which together regulate cellular fate and cellular behavior. Based on established hypotheses and recent findings, we develop a revised picture for the complex function of endocytosis in the Wnt signaling network.

Glycogen synthase kinase 3β inhibition enhances Notch1 recycling

The Notch signaling pathway is essential throughout development and remains active into adulthood, where it performs a critical role in tissue homeostasis. The fact that defects in signaling can lead to malignancy illustrates the need to control Notch activity tightly. GSK3β is an established regulator of the Notch signaling pathway, although its mechanism of action remains unclear. Given the emerging role for GSK3β in receptor trafficking, we tested the idea that GSK3β controls signaling by regulating Notch transport. Consistent with published reports, we find that GSK3β inhibition enhances Notch1 signaling activity. Immunolocalization analysis reveals that Notch1 localization within a tubulovesicular compartment is altered when GSK3β activity is disrupted. We also find that receptor cell surface levels increase following acute GSK3β inhibition. This is followed by elevated Notch intra-cellular domain (NICD) production and a corresponding increase in signaling activity. Moreover, Notch transport assays reveal that receptor recycling rates increase when GSK3β activity is inhibited. Collectively, results presented here support a model where GSK3β regulates signaling by controlling postendocytic transport of Notch1. Given that GSK3β activity is suppressed following stimulation by multiple signal transduction pathways, our findings also suggest that cells can modulate Notch1 activity in response to extracellular signals by mobilizing Notch1 from endosomal stores.

Reciprocal control of lncRNA-BCAT1 and β-catenin pathway reveals lncRNA-BCAT1 long non-coding RNA acts as a tumor suppressor in colorectal cancer

β-catenin plays a major role in tumor development and progression. The present study found that β-catenin was upregulated in 30 samples of colorectal cancer (CRC) tissue as compared to adjacent non-tumor tissues. Analysis of long non-coding RNA (lncRNA) expression profiles using the GSE18560 and GSE44097 datasets, which were generated via the Affymetrix plus 2.0 microarray platform and downloaded from the GEO database, revealed 20 differentially expressed lncRNAs following β-catenin knockdown. We focused on AK091631, a novel lncRNA, which we named lncRNA-β-catenin associated transcript 1 (LncRNA-BCAT1). lncRNA-BCAT1 expression was decreased in CRC tissues, and was negatively associated with β-catenin in both CRC tissues and cell lines. lncRNA-BCAT1 overexpression suppressed CRC cell growth and invasion by downregulating cyclin D1, c-Myc, and MMP-2. These results suggest that lncRNA-BCAT1 overexpression inhibits CRC cell growth and invasion via Wnt/β-catenin pathway blockade, and that lncRNA-BCAT1 is repressed by Wnt/β-catenin signaling. This evidence suggests that lncRNA-BCAT1 is a tumor suppressor and that lncRNA-BCAT1 may be an effective prognostic biomarker in CRC.

Klotho suppresses the renin-angiotensin system in adriamycin nephropathy

Backgrounds

Klotho protein interacts with the transforming growth factor β (TGF-β) receptor and Wnt, which contribute to the progression of renal disease, inhibiting their signals. Renal and circulating klotho levels are diminished in chronic kidney disease.

Methods

Experiments were performed to assess whether supplementation of klotho protein could have protective effects on the kidney. Rats were injected with adriamycin (5 mg/kg) and divided into three groups: those treated with vehicle, those treated with klotho protein and those treated with klotho plus 4-benzyl-2-methyl-1,2,4-thiadiazolidine-3,5-dione (TDZD). Rats without adriamycin treatment were used as a control.

Results

Adriamycin reduced the serum klotho concentration and renal expression of klotho and E-cadherin. Adriamycin also increased the renal expression of Wnt, TGF-β, and angiotensinogen, as well as the renal abundance of β-catenin and angiotensin II. Klotho supplementation suppressed adriamycin-induced elevations of β-catenin and angiotensin II with sustained Wnt expression. Combined treatment with klotho and TDZD reversed the klotho-induced improvements in the renal abundance of β-catenin and angiotensin II as well as the expression of TGF-β and angiotensinogen without affecting E-cadherin.

Conclusions

Our data indicate that Wnt is involved in the pathogenesis of adriamycin nephropathy. Furthermore, klotho supplementation inhibited Wnt signaling, ameliorating renal angiotensin II. Finally, klotho protein appears to suppress epithelial-mesenchymal transition by inhibiting TGF-β and Wnt signaling.

Loss of canonical Wnt signaling is involved in the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia in the older population, however, the precise cause of the disease is unknown. The neuropathology is characterized by the presence of aggregates formed by amyloid-β (Aβ) peptide and phosphorylated tau; which is accompanied by progressive impairment of memory. Diverse signaling pathways are linked to AD, and among these the Wnt signaling pathway is becoming increasingly relevant, since it plays essential roles in the adult brain. Initially, Wnt signaling activation was proposed as a neuroprotective mechanism against Aβ toxicity. Later, it was reported that it participates in tau phosphorylation and processes of learning and memory. Interestingly, in the last years we demonstrated that Wnt signaling is fundamental in amyloid precursor protein (APP) processing and that Wnt dysfunction results in Aβ production and aggregation in vitro. Recent in vivo studies reported that loss of canonical Wnt signaling exacerbates amyloid deposition in a transgenic (Tg) mouse model of AD. Finally, we showed that inhibition of Wnt signaling in a Tg mouse previously at the appearance of AD signs, resulted in memory loss, tau phosphorylation and Aβ formation and aggregation; indicating that Wnt dysfunction accelerated the onset of AD. More importantly, Wnt signaling loss promoted cognitive impairment, tau phosphorylation and Aβ_1-42 production in the hippocampus of wild-type (WT) mice, contributing to the development of an Alzheimer's-like neurophatology. Therefore, in this review we highlight the importance of Wnt/β-catenin signaling dysfunction in the onset of AD and propose that the loss of canonical Wnt signaling is a triggering factor of AD.

Hilbert-Schmidt and Sobol sensitivity indices for static and time series Wnt signaling measurements in colorectal cancer - part A

Background

Ever since the accidental discovery of Wingless [Sharma R.P., Drosophila information service, 1973, 50, p 134], research in the field of Wnt signaling pathway has taken significant strides in wet lab experiments and various cancer clinical trials, augmented by recent developments in advanced computational modeling of the pathway. Information rich gene expression profiles reveal various aspects of the signaling pathway and help in studying different issues simultaneously. Hitherto, not many computational studies exist which incorporate the simultaneous study of these issues.

Results

This manuscript ∙ explores the strength of contributing factors in the signaling pathway, ∙ analyzes the existing causal relations among the inter/extracellular factors effecting the pathway based on prior biological knowledge and ∙ investigates the deviations in fold changes in the recently found prevalence of psychophysical laws working in the pathway. To achieve this goal, local and global sensitivity analysis is conducted on the (non)linear responses between the factors obtained from static and time series expression profiles using the density (Hilbert-Schmidt Information Criterion) and variance (Sobol) based sensitivity indices.

Conclusion

The results show the advantage of using density based indices over variance based indices mainly due to the former’s employment of distance measures & the kernel trick via Reproducing kernel Hilbert space (RKHS) that capture nonlinear relations among various intra/extracellular factors of the pathway in a higher dimensional space. In time series data, using these indices it is now possible to observe where in time, which factors get influenced & contribute to the pathway, as changes in concentration of the other factors are made. This synergy of prior biological knowledge, sensitivity analysis & representations in higher dimensional spaces can facilitate in time based administration of target therapeutic drugs & reveal hidden biological information within colorectal cancer samples.

LRP6 promotes invasion and metastasis of colorectal cancer through cytoskeleton dynamics

Low density lipoprotein (LDL) receptor-related protein-6 (LRP6) is an important co-receptor of Wnt pathway, which plays a predominant role in development and progression of colorectal cancer. Recently, dysregulation of LRP6 has proved to be involved in the progression of cancers, but its biological role and clinical significance in colorectal cancer remain unclear. In present study, we revealed that phosphorylation of LRP6 was aberrantly upregulated in colorectal carcinoma correlating with TNM or Dukes staging and worse prognosis. In addition, phosphorylated LRP6 was positively correlated with nuclear accumulation of β-catenin. Overexpression or activation of LRP6 could activate Wnt signaling and promote tumor cell migration in vitro. The activation of LRP6 could induce microtubule dynamics and actin remodeling, probably through regulation of microtubule-associated protein 1B (MAP1B), microtubule actin cross-linking factor 1 (MACF1) and Rho GTPase--RhoA and Rac1. The investigation suggests that LRP6 may be a potential prognostic marker and therapeutic target in the progression of colorectal cancers.

Wnt signaling in cardiovascular disease: opportunities and challenges

PURPOSE OF REVIEW

Cardiometabolic diseases increasingly afflict our aging, dysmetabolic population. Complex signals regulating low-density lipoprotein receptor-related protein (LRP) and frizzled protein family members - the plasma membrane receptors for the cadre of Wnt polypeptide morphogens - contribute to the control of cardiovascular homeostasis.

RECENT FINDINGS

Both canonical (β-catenin-dependent) and noncanonical (β-catenin-independent) Wnt signaling programs control vascular smooth muscle (VSM) cell phenotypic modulation in cardiometabolic disease. LRP6 limits VSM proliferation, reduces arteriosclerotic transcriptional reprogramming, and preserves insulin sensitivity while LRP5 restrains foam cell formation. Adipose, skeletal muscle, macrophages, and VSM have emerged as important sources of circulating Wnt ligands that are dynamically regulated during the prediabetes-diabetes transition with cardiometabolic consequences. Platelets release Dkk1, a LRP5/LRP6 inhibitor that induces endothelial inflammation and the prosclerotic endothelial-mesenchymal transition. By contrast, inhibitory secreted frizzled-related proteins shape the Wnt signaling milieu to limit myocardial inflammation with ischemia-reperfusion injury. VSM sclerostin, an inhibitor of canonical Wnt signaling in bone, restrains remodeling that predisposes to aneurysm formation, and is downregulated in aneurysmal vessels by epigenetic methylation.

SUMMARY

Components of the Wnt signaling cascade represent novel targets for pharmacological intervention in cardiometabolic disease. Conversely, strategies targeting the Wnt signaling cascade for other therapeutic purposes will have cardiovascular consequences that must be delineated to establish clinically useful pharmacokinetic-pharmacodynamic relationships.

β-Catenin Directs Nuclear Factor-κB p65 Output via CREB-Binding Protein/p300 in Human Airway Smooth Muscle

β-Catenin is a multifunctional protein that apart from its role in proliferative and differentiation events, also acts upon inflammatory processes, mainly via interaction with nuclear factor-κB (NF-κB). However, there is still controversy as to whether β-catenin facilitates or represses NF-κB output. Insights into the molecular mechanisms underlying the interaction between β-catenin and NF-κB have highlighted the cofactors CREB-binding protein (CBP) and p300 as important candidates. Here, we hypothesized that the interaction of β-catenin with CBP/p300 directs NF-κB output. Using human airway smooth muscle (ASM) cells, we found that β-catenin is essential in interleukin -1β (IL-1β)-mediated expression of interleukin-6 (IL-6) by promoting nuclear translocation of the p65 subunit of NF-κB. These effects were independent from WNT pathway activation or other factors that promote β-catenin signaling. In the nucleus, inhibition of either the CBP- or p300-β-catenin interaction could regulate NF-κB output, by enhancing (CBP inhibition) or inhibiting (p300 inhibition) IL-1β-induced expression of IL-6, respectively. Acetylation of p65 by p300 likely underlies these events, as inhibition of the p300-β-catenin interaction diminished levels of acetylated p65 at lysine 310, thereby reducing p65 transcriptional activity. In conclusion, β-catenin is a critical component of NF-κB-mediated inflammation in human ASM, affecting transcriptional output by interacting with the nuclear cofactors CBP and p300. Targeting β-catenin may be an alternative strategy to treat airway inflammation in patients with airway disease, such as asthma.

Wnt/β-catenin signaling links embryonic lung development and asthmatic airway remodeling

Embryonic lung development requires reciprocal endodermal-mesodermal interactions; mediated by various signaling proteins. Wnt/β-catenin is a signaling protein that exhibits the pivotal role in lung development, injury and repair while aberrant expression of Wnt/β-catenin signaling leads to asthmatic airway remodeling: characterized by hyperplasia and hypertrophy of airway smooth muscle cells, alveolar and vascular damage goblet cells metaplasia, and deposition of extracellular matrix; resulting in decreased lung compliance and increased airway resistance. The substantial evidence suggests that Wnt/β-catenin signaling links embryonic lung development and asthmatic airway remodeling. Here, we summarized the recent advances related to the mechanistic role of Wnt/β-catenin signaling in lung development, consequences of aberrant expression or deletion of Wnt/β-catenin signaling in expansion and progression of asthmatic airway remodeling, and linking early-impaired pulmonary development and airway remodeling later in life. Finally, we emphasized all possible recent potential therapeutic significance and future prospectives, that are adaptable for therapeutic intervention to treat asthmatic airway remodeling.

Complexity of the Wnt/β‑catenin pathway: Searching for an activation model

Wnt signaling refers to a conserved signaling pathway, widely studied due to its roles in cellular communication, cell fate decisions, development and cancer. However, the exact mechanism underlying inhibition of the GSK phosphorylation towards β-catenin and activation of the pathway after biding of Wnt ligand to its cognate receptors at the plasma membrane remains unclear. Wnt target genes are widely spread over several animal phyla. They participate in a plethora of functions during the development of an organism, from axial specification, gastrulation and organogenesis all the way to regeneration and repair in adults. Temporal and spatial oncogenetic re-activation of Wnt signaling almost certainly leads to cancer. Wnt signaling components have been extensively studied as possible targets in anti-cancer therapies. In this review we will discuss one of the most intriguing questions in this field, that is how β-catenin, a major component in this pathway, escapes the destruction complex, gets stabilized in the cytosol and it is translocated to the nucleus where it acts as a co-transcription factor. Four major models have evolved during the past 20years. We dissected each of them along with current views and future perspectives on this pathway. This review will focus on the molecular mechanisms by which Wnt proteins modulate β-catenin cytoplasmic levels and the relevance of this pathway for the development and cancer.

Molecular regulation and pharmacological targeting of the β-catenin destruction complex

The β‐catenin destruction complex is a dynamic cytosolic multiprotein assembly that provides a key node in Wnt signalling regulation. The core components of the destruction complex comprise the scaffold proteins axin and adenomatous polyposis coli and the Ser/Thr kinases casein kinase 1 and glycogen synthase kinase 3. In unstimulated cells, the destruction complex efficiently drives degradation of the transcriptional coactivator β‐catenin, thereby preventing the activation of the Wnt/β‐catenin pathway. Mutational inactivation of the destruction complex is a major pathway in the pathogenesis of cancer. Here, we review recent insights in the regulation of the β‐catenin destruction complex, including newly identified interaction interfaces, regulatory elements and post‐translationally controlled mechanisms. In addition, we discuss how mutations in core destruction complex components deregulate Wnt signalling via distinct mechanisms and how these findings open up potential therapeutic approaches to restore destruction complex activity in cancer cells.

Linked Articles

This article is part of a themed section on WNT Signalling: Mechanisms and Therapeutic Opportunities. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.24/issuetoc

Endosomal "sort" of signaling control: The role of ESCRT machinery in regulation of receptor-mediated signaling pathways

The endosomal sorting complexes required for transport (ESCRTs) machinery consists of four protein assemblies (ESCRT-0 to -III subcomplexes) which mediate various processes of membrane remodeling in the cell. In the endocytic pathway, ESCRTs sort cargo destined for degradation into intraluminal vesicles (ILVs) of endosomes. Cargos targeted by ESCRTs include various signaling molecules, mainly internalized cell-surface receptors but also some cytosolic proteins. It is therefore expected that aberrant trafficking caused by ESCRT dysfunction affects different signaling pathways. Here we review how perturbation of ESCRT activity alters intracellular transport of membrane receptors, causing their accumulation on endocytic compartments, decreased degradation and/or altered recycling to the plasma membrane. We further describe how perturbed trafficking of receptors impacts the activity of their downstream signaling pathways, with or without changes in transcriptional responses. Finally, we present evidence that ESCRT components can also control activity and intracellular distribution of cytosolic signaling proteins (kinases, other effectors and soluble receptors). The underlying mechanisms involve sequestration of such proteins in ILVs, their sorting for degradation or towards non-lysosomal destinations, and regulating their availability in various cellular compartments. All these ESCRT-mediated processes can modulate final outputs of multiple signaling pathways.

Identification and characterization of functional single nucleotide polymorphisms (SNPs) in Axin 1 gene: a molecular dynamics approach

Wnt signaling pathway has been reported to play crucial role in intestinal crypt formation and deregulation of this pathway is responsible for colorectal cancer initiation and progression. Axin 1, a scaffold protein, play pivotal role in the regulation of Wnt/β-catenin signaling pathway and has been found to be mutated in several cancers; primarily in colon cancer. Considering its crucial role, a structural and functional analysis of missense mutations in Axin 1 gene was performed in this study. Initially, one hundred non-synonymous single nucleotide polymorphisms in the coding regions of Axin 1 gene were selected for in silico analysis. Six variants (G820S, G856S, E830K, L811V, L847V, and R767C) were predicted to be deleterious by combinatorial prediction. Further investigation of structural attributes confirmed two highly deleterious single nucleotide polymorphisms (G820S and G856S). Molecular dynamics simulation demonstrated variation in different structural attributes between native and two highly deleterious Axin 1 mutant models. Finally, docking analysis showed variation in binding affinity of mutant Axin 1 proteins with two destruction complex members, GSK3β and adenomatous polyposis. The results collectively showed the deleterious effect of the above predicted single nucleotide polymorphisms on the Axin 1 protein structure and could prove to be an adjunct in the disease genotype-phenotype correlation studies.

Entanglement of GSK-3β, β-catenin and TGF-β1 signaling network to regulate myocardial fibrosis

Nearly every form of the heart disease is associated with myocardial fibrosis, which is characterized by the accumulation of activated cardiac fibroblasts (CFs) and excess deposition of extracellular matrix (ECM). Although, CFs are the primary mediators of myocardial fibrosis in a diseased heart, in the traditional view, activated CFs (myofibroblasts) and resulting fibrosis were simply considered the secondary consequence of the disease, not the cause. Recent studies from our lab and others have challenged this concept by demonstrating that fibroblast activation and fibrosis are not simply the secondary consequence of a diseased heart, but are crucial for mediating various myocardial disease processes. In regards to the mechanism, the vast majority of literature is focused on the direct role of canonical SMAD-2/3-mediated TGF-β signaling to govern the fibrogenic process. Herein, we will discuss the emerging role of the GSK-3β, β-catenin and TGF-β1-SMAD-3 signaling network as a critical regulator of myocardial fibrosis in the diseased heart. The underlying molecular interactions and cross-talk among signaling pathways will be discussed. We will primarily focus on recent in vivo reports demonstrating that CF-specific genetic manipulation can lead to aberrant myocardial fibrosis and sturdy cardiac phenotype. This will allow for a better understanding of the driving role of CFs in the myocardial disease process. We will also review the specificity and limitations of the currently available genetic tools used to study myocardial fibrosis and its associated mechanisms. A better understanding of the GSK-3β, β-catenin and SMAD-3 signaling network may provide a novel therapeutic target for the management of myocardial fibrosis in the diseased heart.

Norrin-induced Frizzled4 endocytosis and endo-lysosomal trafficking control retinal angiogenesis and barrier function

Angiogenesis and blood–brain barrier formation are required for normal central nervous system (CNS) function. Both processes are controlled by Wnt or Norrin (NDP) ligands, Frizzled (FZD) receptors, and β-catenin-dependent signalling in vascular endothelial cells. In the retina, FZD4 and the ligand NDP are critical mediators of signalling and are mutated in familial exudative vitreoretinopathy. Here, we report that NDP is a potent trigger of FZD4 ubiquitination and induces internalization of the NDP receptor complex into the endo-lysosomal compartment. Inhibition of ubiquitinated cargo transport through the multivesicular body (MVB) pathway using a dominant negative ESCRT (endosomal sorting complexes required for transport) component VPS4 EQ strongly impairs NDP/FZD4 signalling in vitro and recapitulates CNS angiogenesis and blood-CNS-barrier defects caused by impaired vascular β-catenin signalling in mice. These findings provide evidence for an important role of FZD4 endocytosis in NDP/FZD4 signalling and in CNS vascular biology and disease.

Multiple mechanisms regulate Wnt/ß-catenin signalling. Zhang et al. describe a novel regulatory pathway and show that the activator of canonical Wnt signalling, Norrin, triggers endocytosis of its receptor Frizzled4 by promoting Frizzled4 ubiquitination.

Wnt/β-catenin pathway in the prefrontal cortex is required for cocaine-induced neuroadaptations

Behavioral sensitization is a progressive and enduring enhancement of the motor stimulant effects elicited by repeated administration of drugs of abuse. It can be divided into two distinct temporal and anatomical domains, termed initiation and expression, which are characterized by specific molecular and neurochemical changes. This study examines the role of the Wnt canonical pathway mediating the induction of cocaine sensitization. We found that β-catenin levels in the prefrontal cortex (PFC), amygdala (Amyg) and dorsal striatum (CPu) are decreased in animals that show sensitization. Accordingly, GSK3β activity levels are increased in the same areas. Moreover, β-catenin levels in nuclear fraction, mRNA expression of Axin2 and Wnt7b are decreased in the PFC of sensitized animals. Then, in order to demonstrate that changes in the PFC are crucial for initiation of sensitization, we either rescue β-catenin levels with a systemic treatment of a GSK3β inhibitor (Lithium Chloride) or inhibit Wnt/β-catenin pathway with an intracerebral infusion of Sulindac before each cocaine injection. As expected, rescuing β-catenin levels in the PFC as well as CPu and Amyg blocks cocaine-induced sensitization, while decreasing β-catenin levels exclusively in the PFC exacerbates it. Therefore, our results demonstrate a new role for the Wnt/β-catenin pathway as a required neuroadaptation in inducing behavioral sensitization.

Hyperglycemia impedes definitive endoderm differentiation of human embryonic stem cells by modulating histone methylation patterns

Exposure to maternal diabetes during fetal growth is a risk factor for the development of type II diabetes (T2D) in later life. Discovery of the mechanisms involved in this association should provide valuable background for therapeutic treatments. Early embryogenesis involves epigenetic changes including histone modifications. The bivalent histone methylation marks H3K4me3 and H3K27me3 are important for regulating key developmental genes during early fetal pancreas specification. We hypothesized that maternal hyperglycemia disrupted early pancreas development through changes in histone bivalency. A human embryonic stem cell line (VAL3) was used as the cell model for studying the effects of hyperglycemia upon differentiation into definitive endoderm (DE), an early stage of the pancreatic lineage. Hyperglycemic conditions significantly down-regulated the expression levels of DE markers SOX17, FOXA2, CXCR4 and EOMES during differentiation. This was associated with retention of the repressive histone methylation mark H3K27me3 on their promoters under hyperglycemic conditions. The disruption of histone methylation patterns was observed as early as the mesendoderm stage, with Wnt/β-catenin signaling being suppressed during hyperglycemia. Treatment with Wnt/β-catenin signaling activator CHIR-99021 restored the expression levels and chromatin methylation status of DE markers, even in a hyperglycemic environment. The disruption of DE development was also found in mouse embryos at day 7.5 post coitum from diabetic mothers. Furthermore, disruption of DE differentiation in VAL3 cells led to subsequent impairment in pancreatic progenitor formation. Thus, early exposure to hyperglycemic conditions hinders DE development with a possible relationship to the later impairment of pancreas specification.

Glucocorticoids activate a synapse weakening pathway culminating in tau phosphorylation in the hippocampus

Evidence suggests that the stress hormones glucocorticoids (GCs) can cause cognitive deficits and neurodegeneration. Previous studies have found GCs facilitate physiological synapse weakening, termed long-term depression (LTD), though the precise mechanisms underlying this are poorly understood. Here we show that GCs activate glycogen synthase kinase-3 (GSK-3), a kinase crucial to synapse weakening signals. Critically, this ultimately leads to phosphorylation of the microtubule associated protein tau, specifically at the serine 396 residue, and this is a causal factor in the GC-mediated impairment of synaptic function. These findings reveal the link between GCs and synapse weakening signals, and the potential for stress-induced priming of neurodegeneration. This could have important implications for our understanding of how stress can lead to neurodegenerative disease.

Retinoic acid exacerbates chlorpyrifos action in ensuing adipogenic differentiation of C3H10T½ cells in a GSK3β dependent pathway

The cell differentiation can be exploited as a paradigm to evaluate the effects of noxious chemicals, on human health, either alone or in combinations. In this regard, the effect of a known cell differentiation agent, retinoic acid (RA) was analyzed in the presence of a noxious chemical chlorpyrifos (CPF), an organophosphate (OP), the receptors of which have recently been localized to mesenchymal stem cells (MSCs). The observed imbalance of adipogenic to skeletal differentiation by CPF together with conundrum about adipogenic potential of RA prompted us to delineate their combinatorial effects on C₃H₁₀T½MSC-like undifferentiated cells. Based on MTT assay, the cellular viability was retained by CPF at concentrations ranging from 0.01–50μM, beyond which it caused cytotoxicity. These non-toxic concentrations also mildly interfered with adipogenesis of C₃H₁₀T½ cells following exposure to adipogenic cocktail. However, upon exposure to RA alone, these MSCs adopted elongated morphology and accumulated lipid vesicles, by day 20, as discerned by phase-contrast and transmission electron microscopy (TEM), in concert with enhanced Oil Red O stained cells. This effect got strongly augmented upon exposure to combination of CPF and RA in a dose-dependent manner. Simultaneous up-regulation in perilipin-1 (PLIN1) and adipsin (ADN) genes, additionally reiterated the adipogenic differentiation. Mechanistically, GSK3β pathway was found to be a major player, whereby inhibiting it with lithium chloride (LiCl) resulted in complete blockage of lipid accumulation, accompanied by complete down regulation of PLIN1 and ADN gene expression. In conclusion, these observations for the first time, lend evidence that exposure of CPF accompanied by RA directs commitment of C₃H₁₀T½ cells to adipogenic differentiation through a process involving a crosstalk at GSK3β signaling.

p120-catenin in canonical Wnt signaling

Canonical Wnt signaling controls β-catenin protein stabilization, its translocation to the nucleus and the activation of β-catenin/Tcf-4-dependent transcription. In this review, we revise and discuss the recent results describing actions of p120-catenin in different phases of this pathway. More specifically, we comment its involvement in four different steps: (i) the very early activation of CK1ɛ, essential for Dvl-2 binding to the Wnt receptor complex; (ii) the internalization of GSK3 and Axin into multivesicular bodies, necessary for a complete stabilization of β-catenin; (iii) the activation of Rac1 small GTPase, required for β-catenin translocation to the nucleus; and (iv) the release of the inhibitory action caused by Kaiso transcriptional repressor. We integrate these new results with the previously known action of other elements in this pathway, giving a particular relevance to the responses of the Wnt pathway not required for β-catenin stabilization but for β-catenin transcriptional activity. Moreover, we discuss the possible future implications, suggesting that the two cellular compartments where β-catenin is localized, thus, the adherens junction complex and the Wnt signalosome, are more physically connected that previously thought.

Recent advances in understanding the cellular roles of GSK-3

Glycogen synthase kinase-3 (GSK-3) is a ubiquitously expressed protein kinase that sits at the nexus of multiple signaling pathways. Its deep integration into cellular control circuits is consummate to its implication in diseases ranging from mood disorders to diabetes to neurodegenerative diseases and cancers. The selectivity and insulation of such a promiscuous kinase from unwanted crosstalk between pathways, while orchestrating a multifaceted response to cellular stimuli, offer key insights into more general mechanisms of cell regulation. Here, we review recent advances that have contributed to the understanding of GSK-3 and its role in driving appreciation of intracellular signal coordination.

Vertebrate Axial Patterning: From Egg to Asymmetry

The emergence of the bilateral embryonic body axis from a symmetrical egg has been a long-standing question in developmental biology. Historical and modern experiments point to an initial symmetry-breaking event leading to localized Wnt and Nodal growth factor signaling and subsequent induction and formation of a self-regulating dorsal "organizer." This organizer forms at the site of notochord cell internalization and expresses primarily Bone Morphogenetic Protein (BMP) growth factor antagonists that establish a spatiotemporal gradient of BMP signaling across the embryo, directing initial cell differentiation and morphogenesis. Although the basics of this model have been known for some time, many of the molecular and cellular details have only recently been elucidated and the extent that these events remain conserved throughout vertebrate evolution remains unclear. This chapter summarizes historical perspectives as well as recent molecular and genetic advances regarding: (1) the mechanisms that regulate symmetry-breaking in the vertebrate egg and early embryo, (2) the pathways that are activated by these events, in particular the Wnt pathway, and the role of these pathways in the formation and function of the organizer, and (3) how these pathways also mediate anteroposterior patterning and axial morphogenesis. Emphasis is placed on comparative aspects of the egg-to-embryo transition across vertebrates and their evolution. The future prospects for work regarding self-organization and gene regulatory networks in the context of early axis formation are also discussed.

Role of Wnt/β-catenin pathway in the nucleus accumbens in long-term cocaine-induced neuroplasticity: a possible novel target for addiction treatment

Cocaine addiction is a chronic relapsing disorder characterized by the loss of control over drug-seeking and taking, and continued drug use regardless of adverse consequences. Despite years of research, effective treatments for psycho-stimulant addiction have not been identified. Persistent vulnerability to relapse arises from a number of long-lasting adaptations in the reward circuitry that mediate the enduring response to the drug. Recently, we reported that the activity of the canonical or Wnt/β-catenin pathway in the prefrontal cortex (PFC) is very important in the early stages of cocaine-induced neuroadaptations. In the present work, our main goal was to elucidate the relevance of this pathway in cocaine-induced long-term neuroadaptations that may underlie relapse. We found that a cocaine challenge, after a period of abstinence, induced an increase in the activity of the pathway which is revealed as an increase in the total and nuclear levels of β-catenin (final effector of the pathway) in the nucleus accumbens (NAcc), together with a decrease in the activity of glycogen synthase kinase 3β (GSK3β). Moreover, we found that the pharmacological modulation of the activity of the pathway has long-term effects on the cocaine-induced neuroplasticity at behavioral and molecular levels. All the results imply that changes in the Wnt/β-catenin pathway effectors are long-term neuroadaptations necessary for the behavioral response to cocaine. Even though more research is needed, the present results introduce the Wnt canonical pathway as a possible target to manage cocaine long-term neuroadaptations.

Selective targeting of CREB-binding protein/β-catenin inhibits growth of and extracellular matrix remodelling by airway smooth muscle

BACKGROUND AND PURPOSE

Asthma is a heterogeneous chronic inflammatory disease, characterized by the development of structural changes (airway remodelling). β-catenin, a transcriptional co-activator, is fundamentally involved in airway smooth muscle growth and may be a potential target in the treatment of airway smooth muscle remodelling.

EXPERIMENTAL APPROACH

We assessed the ability of small-molecule compounds that selectively target β-catenin breakdown or its interactions with transcriptional co-activators to inhibit airway smooth muscle remodelling in vitro and in vivo.

KEY RESULTS

ICG-001, a small-molecule compound that inhibits the β-catenin/CREB-binding protein (CBP) interaction, strongly and dose-dependently inhibited serum-induced smooth muscle growth and TGFβ1-induced production of extracellular matrix components in vitro. Inhibition of β-catenin/p300 interactions using IQ-1 or inhibition of tankyrase 1/2 using XAV-939 had considerably less effect. In a mouse model of allergic asthma, β-catenin expression in the smooth muscle layer was found to be unaltered in control versus ovalbumin-treated animals, a pattern that was found to be similar in smooth muscle within biopsies taken from asthmatic and non-asthmatic donors. However, β-catenin target gene expression was highly increased in response to ovalbumin; this effect was prevented by topical treatment with ICG-001. Interestingly, ICG-001 dose-dependently reduced airway smooth thickness after repeated ovalbumin challenge, but had no effect on the deposition of collagen around the airways, mucus secretion or eosinophil infiltration.

CONCLUSIONS AND IMPLICATIONS

Together, our findings highlight the importance of β-catenin/CBP signalling in the airways and suggest ICG-001 may be a new therapeutic approach to treat airway smooth muscle remodelling in asthma.

Reverse phase protein arrays enable glioblastoma molecular subtyping

In the present study we investigated the phosphorylation status of the 12 most important signaling cascades in glioblastomas. More than 60 tumor and control biopsies from tumor center and periphery (based on neuronavigation) were subjected to selective protein expression analysis using reverse-phase protein arrays (RPPA) incubated with antibodies against posttranslationally modified cancer pathway proteins. The ratio between phosphorylated (or modified) and non-phosphorylated protein was assessed. All samples were histopathologically validated and proteomic profiles correlated with clinical and survival data. By RPPA, we identified three distinct activation patterns within glioblastoma defined by the ratios of pCREB1/CREB1, NOTCH-ICD/NOTCH1, and pGSK3β/GSK3β, respectively. These subclasses demonstrated distinct overall survival patterns in a cohort of patients from a single-institution and in an analysis of publicly available data. In particular, a high pGSK3β/GSK3β-ratio was associated with a poor survival. Wnt-activation/GSK3β-inhibition in U373 and U251 cell lines halted glioma cell proliferation and migration. Gene expression analysis was used as an internal quality control of baseline proteomic data. The protein expression and phosphorylation had a higher resolution, resulting in a better class-subdivision than mRNA based stratification data. Patients with different proteomic profiles from multiple biopsies showed a worse overall survival. The CREB1-, NOTCH1-, GSK3β-phosphorylation status correlated with glioma grades. RPPA represent a fast and reliable tool to supplement morphological diagnosis with pathway-specific information in individual tumors. These data can be exploited for molecular stratification and possible combinatorial treatment planning. Further, our results may optimize current glioma grading algorithms.

Lithium increases synaptic GluA2 in hippocampal neurons by elevating the δ-catenin protein

Lithium (Li⁺) is a drug widely employed for treating bipolar disorder, however the mechanism of action is not known. Here we study the effects of Li⁺ in cultured hippocampal neurons on a synaptic complex consisting of δ-catenin, a protein associated with cadherins whose mutation is linked to autism, and GRIP, an AMPA receptor (AMPAR) scaffolding protein, and the AMPAR subunit, GluA2. We show that Li⁺ elevates the level of δ-catenin in cultured neurons. δ-catenin binds to the ABP and GRIP proteins, which are synaptic scaffolds for GluA2. We show that Li⁺ increases the levels of GRIP and GluA2, consistent with Li⁺-induced elevation of δ-catenin. Using GluA2 mutants, we show that the increase in surface level of GluA2 requires GluA2 interaction with GRIP. The amplitude but not the frequency of mEPSCs was also increased by Li⁺ in cultured hippocampal neurons, confirming a functional effect and consistent with AMPAR stabilization at synapses. Furthermore, animals fed with Li⁺ show elevated synaptic levels of δ-catenin, GRIP, and GluA2 in the hippocampus, also consistent with the findings in cultured neurons. This work supports a model in which Li⁺ stabilizes δ-catenin, thus elevating a complex consisting of δ-catenin, GRIP and AMPARs in synapses of hippocampal neurons. Thus, the work suggests a mechanism by which Li⁺ can alter brain synaptic function that may be relevant to its pharmacologic action in treatment of neurological disease.

Essential role of the Dishevelled DEP domain in a Wnt-dependent human-cell-based complementation assay

Dishevelled (DVL) assembles Wnt signalosomes through dynamic head-to-tail polymerisation by means of its DIX domain. It thus transduces Wnt signals to cytoplasmic effectors including β-catenin, to control cell fates during normal development, tissue homeostasis and also in cancer. To date, most functional studies of Dishevelled relied on its Wnt-independent signalling activity resulting from overexpression, which is sufficient to trigger polymerisation, bypassing the requirement for Wnt signals. Here, we generate a human cell line devoid of endogenous Dishevelled (DVL1- DVL3), which lacks Wnt signal transduction to β-catenin. However, Wnt responses can be restored by DVL2 stably re-expressed at near-endogenous levels. Using this assay to test mutant DVL2, we show that its DEP domain is essential, whereas its PDZ domain is dispensable, for signalling to β-catenin. Our results imply two mutually exclusive functions of the DEP domain in Wnt signal transduction - binding to Frizzled to recruit Dishevelled to the receptor complex, and dimerising to cross-link DIX domain polymers for signalosome assembly. Our assay avoids the caveats associated with overexpressing Dishevelled, and provides a powerful tool for rigorous functional tests of this pivotal human signalling protein.

Bimodal antagonism of PKA signalling by ARHGAP36

Protein kinase A is a key mediator of cAMP signalling downstream of G-protein-coupled receptors, a signalling pathway conserved in all eukaryotes. cAMP binding to the regulatory subunits (PKAR) relieves their inhibition of the catalytic subunits (PKAC). Here we report that ARHGAP36 combines two distinct inhibitory mechanisms to antagonise PKA signalling. First, it blocks PKAC activity via a pseudosubstrate motif, akin to the mechanism employed by the protein kinase inhibitor proteins. Second, it targets PKAC for rapid ubiquitin-mediated lysosomal degradation, a pathway usually reserved for transmembrane receptors. ARHGAP36 thus dampens the sensitivity of cells to cAMP. We show that PKA inhibition by ARHGAP36 promotes derepression of the Hedgehog signalling pathway, thereby providing a simple rationale for the upregulation of ARHGAP36 in medulloblastoma. Our work reveals a new layer of PKA regulation that may play an important role in development and disease.

Protein kinase A (PKA) is a key mediator of cyclic AMP signalling. Here, Eccles et al. show that ARHGAP36 antagonizes PKA by acting as a kinase inhibitor and targeting the catalytic subunit for endolysosomal degradation, thus reducing sensitivity of cells to cAMP and promoting Hedgehog signalling.

Knockdown of GSK3β increases basal autophagy and AMPK signalling in nutrient-laden human aortic endothelial cells

Suppression of the enzyme glycogen synthase kinase 3β (GSK3β) increases both the turnover of damaged cellular material and the activity of the enzyme AMP-activated protein kinase (AMPK) to potentially attenuate the damage inflicted by excess sugar and fat on blood vessels.

High concentrations of glucose and palmitate increase endothelial cell inflammation and apoptosis, events that often precede atherogenesis. They may do so by decreasing basal autophagy and AMP-activated protein kinase (AMPK) activity, although the mechanisms by which this occurs are not clear. Decreased function of the lysosome, an organelle required for autophagy and AMPK, have been associated with hyperactivity of glycogen synthase kinase 3β (GSK3β). To determine whether GSK3β affects nutrient-induced changes in autophagy and AMPK activity, we used a primary human aortic endothelial cell (HAEC) model of type 2 diabetes that we had previously characterized with impaired AMPK activity and autophagy [Weikel et al. (2015) Am. J. Phys. Cell Physiol. 308, C249–C263]. Presently, we found that incubation of HAECs with excess nutrients (25 mM glucose and 0.4 mM palmitate) increased GSK3β activity and impaired lysosome acidification. Suppression of GSK3β in these cells by treatment with a chemical inhibitor or overexpression of kinase-dead GSK3β attenuated these lysosomal changes. Under control and excess nutrient conditions, knockdown of GSK3β increased autophagosome formation, forkhead box protein O1 (FOXO1) activity and AMPK signalling and decreased Akt signalling. Similar changes in autophagy, AMPK and Akt signalling were observed in aortas from mice treated with the GSK3β inhibitor CHIR 99021. Thus, increasing basal autophagy and AMPK activity by inhibiting GSK3β may be an effective strategy in the setting of hyperglycaemia and dyslipidaemia for restoring endothelial cell health and reducing atherogenesis.

Tideglusib induces apoptosis in human neuroblastoma IMR32 cells, provoking sub-G0/G1 accumulation and ROS generation

Neuroblastoma is the most common tumor amongst children amounting to nearly 15% of cancer deaths. This cancer is peculiar in its characteristics, exhibiting differentiation, maturation and metastatic transformation leading to poor prognosis and low survival rates among children. Chemotherapy, though toxic to normal cells, has shown to improve the survival of the patient with emphasis given more towards targeting angiogenesis. Recently, Tideglusib was designed as an 'Orphan Drug' to target the neurodegenerative Alzheimer's disease and gained significant momentum in its function during clinical trials. Duffy et al. recently reported a reduction in cell viability of human IMR32 neuroblastoma cells when treated with Tideglusib at varying concentrations. We investigated the effects of Tideglusib, at various concentrations, compared to Lithium chloride at various concentrations, on IMR32 cells. Lithium, a known GSK-3 inhibitor, was used as a standard to compare the efficiency of Tideglusib in a dose-dependent manner. Cell viability was assessed by MTT assay. The stages of apoptosis were evaluated by AO/EB staining and nuclear damage was determined by Hoechst 33258 staining. Reactive oxygen species (ROS) and mitochondrial membrane potential (ΔΨm) were assessed by DCFDA dye and Rhodamine-123 dye, respectively. Tideglusib reported a significant dose-dependent increase in pro-apoptotic proteins (PARP, Caspase-9, Caspase-7, Caspase-3) and tumor-related genes (FasL, TNF-α, Cox-2, IL-8, Caspase-3). Anti-GSK3 β, pGSK3 β, Bcl-2, Akt-1, p-Akt1 protein levels were observed with cells exposed to Tideglusib and Lithium chloride. No significant dose-dependent changes were observed for the mRNA expression of collagenase MMP-2, the tumor suppressor p53, or the cell cycle protein p21. Our study also reports Tideglusib reducing colony formation and increasing the level of sub-G0/G1 population in IMR32 cells. Our investigations report the significance of Tideglusib as a promising apoptotic inducer in human neuroblastoma IMR32 cells. Our study also reports that LiCl reduced cell viability in IMR32 cells inducing apoptosis mediated by ROS generation.

β-Catenin-Independent Roles of Wnt/LRP6 Signaling

Wnt/LRP6 signaling is best known for the β-catenin-dependent regulation of target genes. However, pathway branches have recently emerged, including Wnt/STOP signaling, which act independently of β-catenin and transcription. We review here the molecular mechanisms underlying β-catenin-independent Wnt/LRP6 signaling cascades and their implications for cell biology, development, and physiology.

Gsk3 Signalling and Redox Status in Bipolar Disorder: Evidence from Lithium Efficacy

Objective. To discuss the link between glycogen synthase kinase-3 (GSK3) and the main biological alterations demonstrated in bipolar disorder (BD), with special attention to the redox status and the evidence supporting the efficacy of lithium (a GSK3 inhibitor) in the treatment of BD. Methods. A literature research on the discussed topics, using Pubmed and Google Scholar, has been conducted. Moreover, a manual selection of interesting references from the identified articles has been performed. Results. The main biological alterations of BD, pertaining to inflammation, oxidative stress, membrane ion channels, and circadian system, seem to be intertwined. The dysfunction of the GSK3 signalling pathway is involved in all the aforementioned "biological causes" of BD. In a complex scenario, it can be seen as the common denominator linking them all. Lithium inhibition of GSK3 could, at least in part, explain its positive effect on these biological dysfunctions and its superiority in terms of clinical efficacy. Conclusions. Deepening the knowledge on the molecular bases of BD is fundamental to identifying the biochemical pathways that must be targeted in order to provide patients with increasingly effective therapeutic tools against an invalidating disorder such as BD.

Phosphorylations of Serines 21/9 in Glycogen Synthase Kinase 3α/β Are Not Required for Cell Lineage Commitment or WNT Signaling in the Normal Mouse Intestine

The WNT signalling pathway controls many developmental processes and plays a key role in maintenance of intestine renewal and homeostasis. Glycogen Synthase Kinase 3 (GSK3) is an important component of the WNT pathway and is involved in regulating β-catenin stability and expression of WNT target genes. The mechanisms underpinning GSK3 regulation in this context are not completely understood, with some evidence suggesting this occurs through inhibitory N-terminal serine phosphorylation in a similar way to GSK3 inactivation in insulin signaling. To investigate this in a physiologically relevant context, we have analysed the intestinal phenotype of GSK3 knockin mice in which N-terminal serines 21/9 of GSK3α/β have been mutated to non-phosphorylatable alanine residues. We show that these knockin mutations have very little effect on overall intestinal integrity, cell lineage commitment, β-catenin localization or WNT target gene expression although a small increase in apoptosis at villi tips is observed. Our results provide in vivo evidence that GSK3 is regulated through mechanisms independent of N-terminal serine phosphorylation in order for β-catenin to be stabilised.

Insulin Signaling in Insulin Resistance States and Cancer: A Modeling Analysis

Insulin resistance is the common denominator of several diseases including type 2 diabetes and cancer, and investigating the mechanisms responsible for insulin signaling impairment is of primary importance. A mathematical model of the insulin signaling network (ISN) is proposed and used to investigate the dose-response curves of components of this network. Experimental data of C2C12 myoblasts with phosphatase and tensin homologue (PTEN) suppressed and data of L6 myotubes with induced insulin resistance have been analyzed by the model. We focused particularly on single and double Akt phosphorylation and pointed out insulin signaling changes related to insulin resistance. Moreover, a new characterization of the upstream signaling of the mammalian target of rapamycin complex 2 (mTORC2) is presented. As it is widely recognized that ISN proteins have a crucial role also in cell proliferation and death, the ISN model was linked to a cell population model and applied to data of a cell line of acute myeloid leukemia treated with a mammalian target of rapamycin inhibitor with antitumor activity. The analysis revealed simple relationships among the concentrations of ISN proteins and the parameters of the cell population model that characterize cell cycle progression and cell death.

Compositional analysis of walnut lipid extracts and properties as an anti-cancer stem cell regulator via suppression of the self-renewal capacity

Colon cancer is a leading cause of cancer-related deaths worldwide. Effects of walnut (Juglans regia L.) lipid extracts (WLEs) on the self-renewal capacity of cancer stem cells (CSCs) in colon cancer were investigated. The dominant component of WLEs was α-linoleic acid (64.6%), followed by α-linolenic acid (14.6%), and oleic acid (12.6%). A higher concentration of γ-tocopherol (37.1%) was also present than of α-tocopherol (0.6%). CD133⁺CD44⁺CSCs treated with WLEs showed inhibition of colony formation and sphere formation, indicating a decrease in the self-renewal capacity. Treatment with WLEs also resulted in down-regulation of protein levels, including Notch1, phospho-GSK3β (p-GSK3β), and β-catenin, which are associated with CSCs and the self-renewing capacity. WLEs rich in essential fatty acids and γ-tocopherol can exert therapeutic actions on colon cancer via targeting of CSCs.