A Daple-Akt feed-forward loop enhances noncanonical Wnt signals by compartmentalizing β-catenin

Ependyma in Neurodegenerative Diseases, Radiation-Induced Brain Injury and as a Therapeutic Target for Neurotrophic Factors

The neuron loss caused by the progressive damage to the nervous system is proposed to be the main pathogenesis of neurodegenerative diseases. Ependyma is a layer of ciliated ependymal cells that participates in the formation of the brain-cerebrospinal fluid barrier (BCB). It functions to promotes the circulation of cerebrospinal fluid (CSF) and the material exchange between CSF and brain interstitial fluid. Radiation-induced brain injury (RIBI) shows obvious impairments of the blood-brain barrier (BBB). In the neuroinflammatory processes after acute brain injury, a large amount of complement proteins and infiltrated immune cells are circulated in the CSF to resist brain damage and promote substance exchange through the BCB. However, as the protective barrier lining the brain ventricles, the ependyma is extremely vulnerable to cytotoxic and cytolytic immune responses. When the ependyma is damaged, the integrity of BCB is destroyed, and the CSF flow and material exchange is affected, leading to brain microenvironment imbalance, which plays a vital role in the pathogenesis of neurodegenerative diseases. Epidermal growth factor (EGF) and other neurotrophic factors promote the differentiation and maturation of ependymal cells to maintain the integrity of the ependyma and the activity of ependymal cilia, and may have therapeutic potential in restoring the homeostasis of the brain microenvironment after RIBI or during the pathogenesis of neurodegenerative diseases.

Wnt5a protects motor neurons in amyotrophic lateral sclerosis by regulating the Wnt/Ca2+ signaling pathway

OBJECTIVES

We aimed to detect the expression profile of downstream signaling molecules of non-canonical Wnt pathway in SOD1^G93A transgenic mice (ALS mice) and SOD1^G93A mutant motor neuron-like hybrid (NSC-34) cells. Characterizing the molecular mechanism of the Wnt5a-mediated non-canonical Wnt/Ca²⁺ signaling pathway in motor neuron (MN) degeneration may provide a feasible approach to effective treatment of amyotrophic lateral sclerosis (ALS).

METHODS

The expressions of CaMKII-α, CaMKII-β and TAK1 in the spinal cord of SOD1^G93A ALS transgenic mice at different ages were determined using western blotting and immunofluorescence. The level of Ca²⁺ and cell apoptosis were assessed with flow cytometry and cell viability was evaluated using MTS assay. Cell proliferation was analyzed by the EdU cell proliferation assay. Neurite length was measured after treatment with retinoic acid.

RESULTS

CaMKII-α, CaMKII-β, and TAK1 were down-regulated in the spinal cord of ALS mice. Ca²⁺ level and CaMKII-α, CaMKII-β, and TAK1 were down-regulated in SOD1^G93A mutant NSC-34 cells. Expression of Ca²⁺, CaMKII-α, CaMKII-β, and TAK1 were up-regulated in SOD1^G93A mutant NSC-34 cells after Wnt5a overexpression and down-regulated after Wnt5a knockdown. Overexpression of Wnt5a promoted cell viability and proliferation but inhibited cell apoptosis. Contrastingly, Wnt5a knockdown inhibited cell viability and proliferation but promoted cell apoptosis. CaMKII inhibitor KN-93 and CaMKII activator oleic acid reversed changes in cell viability, proliferation, apoptosis, and neurite outgrowth induced by Wnt5a overexpression and knockdown.

CONCLUSIONS

This study demonstrates that Wnt5a protects MNs in ALS by regulating cell viability, proliferation, apoptosis, and neurite growth through the Wnt/Ca²⁺ signaling pathway. Our data indicate that the non-canonical Wnt/Ca²⁺ signaling pathway regulated by Wnt5a is involved in MN degeneration in ALS.

DAPLE orchestrates apical actomyosin assembly from junctional polarity complexes

Establishment of apicobasal polarity and the organization of the cytoskeleton must operate coordinately to ensure proper epithelial cell shape and function. However, the precise molecular mechanisms by which polarity complexes directly instruct the cytoskeletal machinery to determine cell shape are poorly understood. Here, we define a mechanism by which the PAR polarity complex (PAR3–PAR6–aPKC) at apical cell junctions leads to efficient assembly of the apical actomyosin network to maintain epithelial cell morphology. We found that the PAR polarity complex recruits the protein DAPLE to apical cell junctions, which in turn triggers a two-pronged mechanism that converges upon assembly of apical actomyosin. More specifically, DAPLE directly recruits the actin-stabilizing protein CD2AP to apical junctions and, concomitantly, activates heterotrimeric G protein signaling in a GPCR-independent manner to favor RhoA-myosin activation. These observations establish DAPLE as a direct molecular link between junctional polarity complexes and the formation of apical cytoskeletal assemblies that support epithelial cell shape.

The Key Role of the WNT/β-Catenin Pathway in Metabolic Reprogramming in Cancers under Normoxic Conditions

Simple Summary

The canonical WNT/β-catenin pathway is upregulated in cancers and plays a major role in proliferation, invasion, apoptosis and angiogenesis. Recent studies have shown that cancer processes are involved under normoxic conditions. These findings completely change the way of approaching the study of the cancer process. In this review, we focus on the fact that, under normoxic conditions, the overstimulation of the WNT/β-catenin pathway leads to modifications in the tumor micro-environment and the activation of the Warburg effect, i.e., aerobic glycolysis, autophagy and glutaminolysis, which in turn participate in tumor growth.

Abstract

The canonical WNT/β-catenin pathway is upregulated in cancers and plays a major role in proliferation, invasion, apoptosis and angiogenesis. Nuclear β-catenin accumulation is associated with cancer. Hypoxic mechanisms lead to the activation of the hypoxia-inducible factor (HIF)-1α, promoting glycolytic and energetic metabolism and angiogenesis. However, HIF-1α is degraded by the HIF prolyl hydroxylase under normoxia, conditions under which the WNT/β-catenin pathway can activate HIF-1α. This review is therefore focused on the interaction between the upregulated WNT/β-catenin pathway and the metabolic processes underlying cancer mechanisms under normoxic conditions. The WNT pathway stimulates the PI3K/Akt pathway, the STAT3 pathway and the transduction of WNT/β-catenin target genes (such as c-Myc) to activate HIF-1α activity in a hypoxia-independent manner. In cancers, stimulation of the WNT/β-catenin pathway induces many glycolytic enzymes, which in turn induce metabolic reprogramming, known as the Warburg effect or aerobic glycolysis, leading to lactate overproduction. The activation of the Wnt/β-catenin pathway induces gene transactivation via WNT target genes, c-Myc and cyclin D1, or via HIF-1α. This in turn encodes aerobic glycolysis enzymes, including glucose transporter, hexokinase 2, pyruvate kinase M2, pyruvate dehydrogenase kinase 1 and lactate dehydrogenase-A, leading to lactate production. The increase in lactate production is associated with modifications to the tumor microenvironment and tumor growth under normoxic conditions. Moreover, increased lactate production is associated with overexpression of VEGF, a key inducer of angiogenesis. Thus, under normoxic conditions, overstimulation of the WNT/β-catenin pathway leads to modifications of the tumor microenvironment and activation of the Warburg effect, autophagy and glutaminolysis, which in turn participate in tumor growth.

A protein network map of head and neck cancer reveals PIK3CA mutant drug sensitivity

[Figure: see text].

Targeting methionine aminopeptidase 2 in cancer, obesity, and autoimmunity

For over three decades, methionine aminopeptidase 2 (MetAP2) has been a tentative drug target for the treatment of cancer, obesity, and autoimmune diseases. Currently, no MetAP2 inhibitors (MetAP2i) have reached the clinic yet, despite considerable investment by major pharmaceutical companies. Here, we summarize the key series of MetAP2i developed to date and discuss their clinical development, progress, and issues. We coalesce the currently disparate knowledge regarding MetAP2i mechanism of action and discuss discrepancies across varied studies. Finally, we highlight the current knowledge gaps that need to be addressed to enable successful development of MetAP2 inhibitors in clinical settings.

Autophagy and the Wnt signaling pathway: A focus on Wnt/β-catenin signaling

Cellular homeostasis and adaptation to various environmental conditions are importantly regulated by the sophisticated mechanism of autophagy and its crosstalk with Wnt signaling and other developmental pathways. Both autophagy and Wnt signaling are involved in embryogenesis and differentiation. Autophagy is responsible for degradation and recycling of cytosolic materials by directing them to lysosomes through the phagophore compartment. A dual feedback mechanism regulates the interface between autophagy and Wnt signaling pathways. During nutrient deprivation, β-catenin and Dishevelled (essential Wnt signaling proteins) are targeted for autophagic degradation by LC3. When Wnt signaling is activated, β-catenin acts as a corepressor of one of the autophagy proteins, p62. In contrast, another key Wnt signaling protein, GSK3β, negatively regulates the Wnt pathway and has been shown to induce autophagy by phosphorylation of the TSC complex. This article reviews the interplay between autophagy and Wnt signaling, describing how β-catenin functions as a key cellular integration point coordinating proliferation with autophagy, and it discusses the clinical importance of the crosstalk between these mechanisms.

Zika virus NS5 localizes at centrosomes during cell division

Zika virus (ZIKV) nonstructural protein 5 (NS5) plays a critical role in viral RNA replication and mediates key virus-host cell interactions. As with other flavivirus NS5 proteins, ZIKV NS5 is primarily found in the nucleus. We previously reported that the NS5 protein of dengue virus, another flavivirus, localized to centrosomes during cell division. Here we show that ZIKV NS5 also relocalizes from the nucleus to centrosomes during mitosis. In infected cells with supernumerary centrosomes, NS5 was present at all centrosomes. Transient expression of NS5 in uninfected cells confirmed that centrosomal localization was independent of other viral proteins. Live-cell imaging demonstrated that NS5-GFP accumulated at centrosomes shortly after break down of nuclear membrane and remained there through mitosis. Cells expressing NS5-GFP took longer to complete mitosis than control cells. Finally, an analysis of ZIKV NS5 binding partners revealed several centrosomal proteins, providing potential direct links between NS5 and centrosomes.

Tyrosine-Based Signals Regulate the Assembly of Daple⋅PARD3 Complex at Cell-Cell Junctions

Polarized distribution of organelles and molecules inside a cell is vital for a range of cellular processes and its loss is frequently encountered in disease. Polarization during planar cell migration is a special condition in which cellular orientation is triggered by cell-cell contact. We demonstrate that the protein Daple (CCDC88C) is a component of cell junctions in epithelial cells which serves like a cellular “compass” for establishing and maintaining contact-triggered planar polarity. Furthermore, these processes may be mediated through interaction with the polarity regulator PARD3. This interaction, mediated by Daple's PDZ-binding motif (PBM) and the third PDZ domain of PARD3, is fine-tuned by tyrosine phosphorylation on Daple's PBM by receptor and non-receptor tyrosine kinases, such as Src. Hypophosphorylation strengthens the interaction, whereas hyperphosphorylation disrupts it, thereby revealing an unexpected role of Daple as a platform for signal integration and gradient sensing for tyrosine-based signals within the planar cell polarity pathway.

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Daple localizes to cell junction, regulates planar cell migration

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Localization requires Daple's C-terminal PDZ-binding motif (PBM)

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The PBM binds a PDZ module of the polarity determinant PARD3

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The Daple⋅PARD3 interaction is regulated by tyrosine-based signals

Two Isoforms of the Guanine Nucleotide Exchange Factor, Daple/CCDC88C Cooperate as Tumor Suppressors

Previously, Aznar et al., showed that Daple/CCDC88C enables Wnt receptors to transactivate trimeric G-proteins during non-canonical Wnt signaling via a novel G-protein binding and activating (GBA) motif. By doing so, Daple serves two opposing roles; earlier during oncogenesis it suppresses neoplastic transformation and tumor growth, but later it triggers epithelial-to-mesenchymal-transition (EMT). We have identified and characterized two isoforms of the human Daple gene. While both isoforms cooperatively suppress tumor growth via their GBA motif, only the full-length transcript triggers EMT and invasion. Both isoforms are suppressed during colon cancer progression, and their reduced expression carries additive prognostic significance. These findings provide insights into the opposing roles of Daple during cancer progression and define the G-protein regulatory GBA motif as one of the minimal modules essential for Daple’s role as a tumor suppressor.

Prognostic Relevance of CCDC88C (Daple) Transcripts in the Peripheral Blood of Patients with Cutaneous Melanoma

A loss of balance between G protein activation and deactivation has been implicated in the initiation of melanomas, and non-canonical Wnt signaling via the Wnt5A/Frizzled (FZD) pathway has been shown to be critical for the switch to an invasive phenotype. Daple [CCDC88C], a cytosolic guanine nucleotide exchange modulator (GEM) which enhances non-canonical Wnt5A/FZD signaling via activation of trimeric G protein, Gαi, has been shown to serve opposing roles-as an inducer of EMT and invasiveness and a potent tumor suppressor-via two isoforms, V1 (full-length) and V2 (short spliced isoform), respectively. Here we report that the relative abundance of these isoforms in the peripheral circulation, presumably largely from circulating tumor cells (CTCs), is a prognostic marker of cutaneous melanomas. Expression of V1 is increased in both the early and late clinical stages (p < 0.001, p = 0.002, respectively); V2 is decreased exclusively in the late clinical stage (p = 0.003). The two isoforms have opposing prognostic effects: high expression of V2 increases relapse-free survival (RFS; p = 0.014), whereas high expression of V1 tends to decrease RFS (p = 0.051). Furthermore, these effects are additive, in that melanoma patients with a low V2-high V1 signature carry the highest risk of metastatic disease. We conclude that detection of Daple transcripts in the peripheral blood (i.e., liquid biopsies) of patients with melanoma may serve as a prognostic marker and an effective strategy for non-invasive long-term follow-up of patients with melanoma.