Beta-catenin-independent Wnt pathways: signals, core proteins, and effectors

Combinatorial Wnt signaling landscape during brachiopod anteroposterior patterning

BACKGROUND

Wnt signaling pathways play crucial roles in animal development. They establish embryonic axes, specify cell fates, and regulate tissue morphogenesis from the early embryo to organogenesis. It is becoming increasingly recognized that these distinct developmental outcomes depend upon dynamic interactions between multiple ligands, receptors, antagonists, and other pathway modulators, consolidating the view that a combinatorial "code" controls the output of Wnt signaling. However, due to the lack of comprehensive analyses of Wnt components in several animal groups, it remains unclear if specific combinations always give rise to specific outcomes, and if these combinatorial patterns are conserved throughout evolution.

RESULTS

In this work, we investigate the combinatorial expression of Wnt signaling components during the axial patterning of the brachiopod Terebratalia transversa. We find that T. transversa has a conserved repertoire of ligands, receptors, and antagonists. These genes are expressed throughout embryogenesis but undergo significant upregulation during axial elongation. At this stage, Frizzled domains occupy broad regions across the body while Wnt domains are narrower and distributed in partially overlapping patches; antagonists are mostly restricted to the anterior end. Based on their combinatorial expression, we identify a series of unique transcriptional subregions along the anteroposterior axis that coincide with the different morphological subdivisions of the brachiopod larval body. When comparing these data across the animal phylogeny, we find that the expression of Frizzled genes is relatively conserved, whereas the expression of Wnt genes is more variable.

CONCLUSIONS

Our results suggest that the differential activation of Wnt signaling pathways may play a role in regionalizing the anteroposterior axis of brachiopod larvae. More generally, our analyses suggest that changes in the receptor context of Wnt ligands may act as a mechanism for the evolution and diversification of the metazoan body axis.

Endothelial-to-Mesenchymal Transition in Cardiovascular Pathophysiology

Under different pathophysiological conditions, endothelial cells lose endothelial phenotype and gain mesenchymal cell-like phenotype via a process known as endothelial-to-mesenchymal transition (EndMT). At the molecular level, endothelial cells lose the expression of endothelial cell-specific markers such as CD31/platelet-endothelial cell adhesion molecule, von Willebrand factor, and vascular-endothelial cadherin and gain the expression of mesenchymal cell markers such as α-smooth muscle actin, N-cadherin, vimentin, fibroblast specific protein-1, and collagens. EndMT is induced by numerous different pathways triggered and modulated by multiple different and often redundant mechanisms in a context-dependent manner depending on the pathophysiological status of the cell. EndMT plays an essential role in embryonic development, particularly in atrioventricular valve development; however, EndMT is also implicated in the pathogenesis of several genetically determined and acquired diseases, including malignant, cardiovascular, inflammatory, and fibrotic disorders. Among cardiovascular diseases, aberrant EndMT is reported in atherosclerosis, pulmonary hypertension, valvular disease, fibroelastosis, and cardiac fibrosis. Accordingly, understanding the mechanisms behind the cause and/or effect of EndMT to eventually target EndMT appears to be a promising strategy for treating aberrant EndMT-associated diseases. However, this approach is limited by a lack of precise functional and molecular pathways, causes and/or effects, and a lack of robust animal models and human data about EndMT in different diseases. Here, we review different mechanisms in EndMT and the role of EndMT in various cardiovascular diseases.

Signaling pathways of dental implants' osseointegration: a narrative review on two of the most relevant; NF-κB and Wnt pathways

INTRODUCTION

Cell signaling pathways are the biological reactions that control cell functions and fate. They also directly affect the body reactions to implanted biomaterials. It is well-known that dental implants success depends on a successful integration with the alveolar bone: "osseointegration" which events comprise early and later responses to the implanted biomaterials. The early events are mainly immune-inflammatory responses to the implant considered by its microenvironment as a foreign body. Later reactions are osteogenic aiming to regulate bone formation and remodeling. All these events are controlled by the cell signaling pathways in an incredible harmonious coordination.

AIM

The number of pathways having a role in osseointegration is so big to be reviewed in a single article. So the aim of this review was to study only two of the most relevant ones: the inflammatory Nuclear Factor Kappa B (NF-κB) pathway regulating the early osseointegration events and the osteogenic Wnt pathway regulating later events.

METHODS

We conducted a literature review using key databases to provide an overview about the NF-κB and Wnt cell signaling pathways and their mutual relationship with dental implants. A simplified narrative approach was conducted to explain these cell signaling pathways, their mode of activation and how they are related to the cellular events of osseointegration.

RESULTS AND CONCLUSION

NF-κB and Wnt cell signaling pathways are important cross-talking pathways that are affected by the implant's material and surface characteristics. The presence of the implant itself in the bone alters the intracellular events of both pathways in the adjacent implant's cellular microenvironment. Both pathways have a great role in the success or failure of osseointegration. Such knowledge can offer a new hope to treat failed implants and enhance osseointegration in difficult cases. This is consistent with advances in Omics technologies that can change the paradigm of dental implant therapy.

Tools for investigating O-GlcNAc in signaling and other fundamental biological pathways

Cells continuously fine-tune signaling pathway proteins to match nutrient and stress levels in their local environment by modifying intracellular proteins with O-linked N-acetylglucosamine (O-GlcNAc) sugars, an essential process for cell survival and growth. The small size of these monosaccharide modifications poses a challenge for functional determination, but the chemistry and biology communities have together created a collection of precision tools to study these dynamic sugars. This review presents the major themes by which O-GlcNAc influences signaling pathway proteins, including G-protein coupled receptors, growth factor signaling, mitogen-activated protein kinase (MAPK) pathways, lipid sensing, and cytokine signaling pathways. Along the way, we describe in detail key chemical biology tools that have been developed and applied to determine specific O-GlcNAc roles in these pathways. These tools include metabolic labeling, O-GlcNAc-enhancing RNA aptamers, fluorescent biosensors, proximity labeling tools, nanobody targeting tools, O-GlcNAc cycling inhibitors, light-activated systems, chemoenzymatic labeling, and nutrient reporter assays. An emergent feature of this signaling pathway meta-analysis is the intricate interplay between O-GlcNAc modifications across different signaling systems, underscoring the importance of O-GlcNAc in regulating cellular processes. We highlight the significance of O-GlcNAc in signaling and the role of chemical and biochemical tools in unraveling distinct glycobiological regulatory mechanisms. Collectively, our field has determined effective strategies to probe O-GlcNAc roles in biology. At the same time, this survey of what we do not yet know presents a clear roadmap for the field to use these powerful chemical tools to explore cross-pathway O-GlcNAc interactions in signaling and other major biological pathways.

HOTAIR: A key regulator of the Wnt/β-catenin signaling cascade in cancer progression and treatment

The long non-coding RNA (lncRNA) HOTAIR occupies a central position in the complex domain of cancer biology, particularly concerning its intricate interplay with the Wnt/β-catenin signaling pathway. This comprehensive review explores the multifaceted interactions between HOTAIR and the Wnt/β-catenin cascade, elucidating their profound function in cancer growth, progression, and therapeutic strategies. The study commences by underscoring the pivotal role of the Wnt/β-catenin cascade in governing essential cellular activities, emphasizing its dysregulation as a linchpin in cancer initiation and advancement. It introduces HOTAIR as a crucial regulatory entity, influencing gene expression in both healthy and diseased. The core of this review plunges into the intricacies of HOTAIR's engagement with Wnt/β-catenin signaling. It unravels how HOTAIR, through epigenetic modifications and transcriptional control, exerts its influence over key pathway constituents, including β-catenin, Wnt ligands, and target genes. This influence drives unchecked cancer cell growth, invasion, and metastasis. Furthermore, the review underscores the clinical significance of the HOTAIR-Wnt/β-catenin interplay, elucidating its associations with diverse cancer subtypes, patient prognoses, and prospects as a therapy. It provides insights into ongoing research endeavors to develop HOTAIR-targeted treatments and initiatives to facilitate aberrant Wnt/β-catenin activation. Concluding on a forward-looking note, the article accentuates the broader implications of HOTAIR's involvement in cancer biology, including its contributions to therapy resistance and metastatic dissemination. It underscores the importance of delving deeper into these intricate molecular relationships to pave the way for groundbreaking cancer treatment.

Identification and functional validation of FZD8-specific antibodies

The Wnt pathway is an evolutionarily conserved pathway involved in stem cell homeostasis and tissue regeneration. Aberrant signaling in the Wnt pathway is highly associated with cancer. Developing antibodies to block overactivation of Frizzled receptors (FZDs), the main receptors in the Wnt pathway, is one of the viable options for treating cancer. However, obtaining isoform-specific antibodies is often challenging due to the high degree of homology among the ten FZDs. In this study, by using a synthetic library, we identified an antibody named pF8_AC3 that preferentially binds to FZD8. Guided by the structure of the complex of pF8_AC3 and FZD8, a second-generation targeted library was further constructed, and finally, the FZD8-specific antibody sF8_AG6 was obtained. Cell-based assays showed that these antibodies could selectively block FZD8-mediated signaling activation. Taken together, these antibodies have the potential to be developed into therapeutic drugs in the future.

Want of Wnt in Parkinson's disease: Could sFRP disrupt interplay between Nurr1 and Wnt signaling?

Nuclear receptor related 1 (Nurr1) is a transcription factor known to regulate the development and maintenance of midbrain dopaminergic (mDA) neurons. Reports have confirmed that defect or obliteration of Nurr1 results in neurodegeneration and motor function impairment leading to Parkinson's disease (PD). Studies have also indicated that Nurr1 regulates the expression of alpha-synuclein (α-SYN) and mutations in Nurr1 cause α-SYN overexpression, thereby increasing the risk of PD. Nurr1 is modulated via various pathways including Wnt signaling pathway which is known to play an important role in neurogenesis and deregulation of it contributes to PD pathogenesis. Both Wnt/β-catenin dependent and independent pathways are implicated in the activation of Nurr1 and subsequent downregulation of α-SYN. This review highlights the interaction between Nurr1 and Wnt signaling pathways in mDA neuronal development. We further hypothesize how modulation of Wnt signaling pathway by its antagonist, secreted frizzled related proteins (sFRPs) could be a potential route to treat PD.

Extracellular Vesicles Act as Carriers for Cargo Delivery and Regulate Wnt Signaling in the Hepatocellular Carcinoma Tumor Microenvironment

As the primary type of liver cancer, hepatocellular carcinoma (HCC) causes a large number of deaths every year. Despite extensive research conducted on this disease, the prognosis of HCC remains unclear. Recently, research has largely focused on extracellular vesicles (EVs), and they have been found to participate in various ways in the development of various diseases, including HCC, such as by regulating cell signaling pathways. However, recent studies have reported the mechanisms underlying the regulation of Wnt signaling by EVs in HCC, primarily focusing on the regulation of the canonical pathways. This review summarizes the current literature on the regulation of Wnt signaling by EVs in HCC and their underlying mechanisms. In addition, we also present future research directions in this field. This will deepen the understanding of HCC and provide new ideas for its treatment.

Effect of the Rho-Kinase/ROCK Signaling Pathway on Cytoskeleton Components

The mechanical properties of cells are important in tissue homeostasis and enable cell growth, division, migration and the epithelial-mesenchymal transition. Mechanical properties are determined to a large extent by the cytoskeleton. The cytoskeleton is a complex and dynamic network composed of microfilaments, intermediate filaments and microtubules. These cellular structures confer both cell shape and mechanical properties. The architecture of the networks formed by the cytoskeleton is regulated by several pathways, a key one being the Rho-kinase/ROCK signaling pathway. This review describes the role of ROCK (Rho-associated coiled-coil forming kinase) and how it mediates effects on the key components of the cytoskeleton that are critical for cell behaviour.

Non-canonical WNT signalling in cardiovascular disease: mechanisms and therapeutic implications

WNT signalling comprises a diverse spectrum of receptor-mediated pathways activated by a large family of WNT ligands and influencing fundamental biological processes. WNT signalling includes the β-catenin canonical pathway and the non-canonical pathways, namely the planar cell polarity and the calcium-dependent pathways. Advances over the past decade have linked non-canonical WNT signalling with key mechanisms of atherosclerosis, including oxidative stress, endothelial dysfunction, macrophage activation and vascular smooth muscle cell phenotype regulation. In addition, non-canonical WNT signalling is involved in crucial aspects of myocardial biology, from fibrosis to hypertrophy and oxidative stress. Importantly, non-canonical WNT signalling activation has complex effects in adipose tissue in the context of obesity, thereby potentially linking metabolic and vascular diseases. Tissue-specific targeting of non-canonical WNT signalling might be associated with substantial risks of off-target tumorigenesis, challenging its therapeutic potential. However, novel technologies, such as monoclonal antibodies, recombinant decoy receptors, tissue-specific gene silencing with small interfering RNAs and gene editing with CRISPR-Cas9, might enable more efficient therapeutic targeting of WNT signalling in the cardiovascular system. In this Review, we summarize the components of non-canonical WNT signalling, their links with the main mechanisms of atherosclerosis, heart failure and arrhythmias, and the rationale for targeting individual components of non-canonical WNT signalling for the treatment of cardiovascular disease.

Dose-related shifts in proteome and function of extracellular vesicles secreted by fetal neural stem cells following chronic alcohol exposure

Accumulating evidence indicates that extracellular vesicles (EVs) mediate endocrine functions and also pathogenic effects of neurodevelopmental perturbagens like ethanol. We performed mass-spectrometry on EVs secreted by fetal murine cerebral cortical neural stem cells (NSCs), cultured ex-vivo as sex-specific neurosphere cultures, to identify overrepresented proteins and signaling pathways in EVs relative to parental NSCs in controls, and following exposure of parental NSCs to a dose range of ethanol. EV proteomes differ substantially from parental NSCs, and though EVs sequester proteins across sub-cellular compartments, they are enriched for distinct morphogenetic signals including the planar cell polarity pathway. Ethanol exposure favored selective protein sequestration in EVs and depletion in parental NSCs, and also resulted in dose-independent overrepresentation of cell-cycle and DNA replication pathways in EVs as well as dose-dependent overrepresentation of rRNA processing and mTor stress pathways. Transfer of untreated EVs to naïve cells resulted in decreased oxidative metabolism and S-phase, while EVs derived from ethanol-treated NSCs exhibited diminished effect. Collectively, these data show that NSCs secrete EVs with a distinct proteome that may have a general growth-inhibitory effect on recipient cells. Moreover, while ethanol results in selective transfer of proteins from NSCs to EVs, the efficacy of these exposure-derived EVs is diminished.

Regulatory Effects and Interactions of the Wnt and OPG-RANKL-RANK Signaling at the Bone-Cartilage Interface in Osteoarthritis

Cartilage and the bordering subchondral bone form a functionally active regulatory interface with a prominent role in osteoarthritis pathways. The Wnt and the OPG-RANKL-RANK signaling systems, as key mediators, interact in subchondral bone remodeling. Osteoarthritic osteoblasts polarize into two distinct phenotypes: a low secretory and an activated, pro-inflammatory and anti-resorptive subclass producing high quantities of IL-6, PGE2, and osteoprotegerin, but low levels of RANKL, thus acting as putative effectors of subchondral bone sclerosis. Wnt agonists, Wnt5a, Wisp-1 initiate excessive bone remodeling, while Wnt3a and 5a simultaneously cause loss of proteoglycans and phenotype shift in chondrocytes, with decreased expression of COL2A, aggrecan, and Sox-9. Sclerostin, a Wnt antagonist possesses a protective effect for the cartilage, while DKK-1 inhibits VEGF, suspending neoangiogenesis in the subchondral bone. Experimental conditions mimicking abnormal mechanical load, the pro-inflammatory milieu, but also a decreased OPG/RANKL ratio in the cartilage, trigger chondrocyte apoptosis and loss of the matrix via degradative matrix metalloproteinases, like MMP-13 or MMP-9. Hypoxia, an important cofactor exerts a dual role, promoting matrix synthesis via HIF-1α, a Wnt silencer, but turning on HIF-2α that enhances VEGF and MMP-13, along with aberrant collagen expression and extracellular matrix deterioration in the presence of pro-inflammatory cytokines.

Coupled cycling programs multicellular self-organization of neural progenitors

Self-organization is central to the morphogenesis of multicellular organisms. However, the molecular platform that coordinates the robust emergence of complex morphological patterns from local interactions between cells remains unresolved. Here we demonstrate that neural self- organization is driven by coupled cycling of progenitor cells. In a coupled cycling mode, intercellular contacts relay extrinsic cues to override the intrinsic cycling rhythm of an individual cell and synchronize the population. The stringency of coupling and hence the synchronicity of the population is programmed by recruitment of a key coupler, β-catenin, into junctional complexes. As such, multicellular self-organization is driven by the same basic mathematical principle that governs synchronized behavior of macro-scale biological systems as diverse as the synchronized chirping of crickets, flashing of fireflies and schooling of fish; that is synchronization by coupling. It is proposed that coupled cycling foreshadows a fundamental adaptive change that facilitated evolution and diversification of multicellular life forms.

Wnt5a is a TLR2/4-ligand that induces tolerance in human myeloid cells

Innate immune responses are rapid, dynamic and highly regulated to avoid overt reactions. This regulation is executed by innate immune tolerance mechanisms that remain obscure. Wnt5a is a signalling protein mainly involved in developmental processes and cancer. The effect of Wnt5a on inflammatory myeloid cells is controversial. Here, we combine primary cell cultures, in vitro binding studies, mass spectrometry and Drosophila protein modelling to show that Wnt5a is a direct ligand of toll-like receptor (TLR) 2 and 4. The binding promotes a MyD88-non-canonical nuclear factor of kappa B (NFκB) and AP-1 signalling cascade, with contradictory profiles in mouse (pro-inflammatory) and human (anti-inflammatory) myeloid immune cells. These data reveal that the true nature of Wnt5a in inflammatory cells, is to regulate TLR signals, and in human myeloid cells it acts as an endogenous, tolerance-associated molecular pattern (TAMP), inducing IL-10 and innate immune tolerance.

Unchain My Heart: Integrins at the Basis of iPSC Cardiomyocyte Differentiation

The cellular response to the extracellular matrix (ECM) microenvironment mediated by integrin adhesion is of fundamental importance, in both developmental and pathological processes. In particular, mechanotransduction is of growing importance in groundbreaking cellular models such as induced pluripotent stem cells (iPSC), since this process may strongly influence cell fate and, thus, augment the precision of differentiation into specific cell types, e.g., cardiomyocytes. The decryption of the cellular machinery starting from ECM sensing to iPSC differentiation calls for new in vitro methods. Conveniently, engineered biomaterials activating controlled integrin-mediated responses through chemical, physical, and geometrical designs are key to resolving this issue and could foster clinical translation of optimized iPSC-based technology. This review introduces the main integrin-dependent mechanisms and signalling pathways involved in mechanotransduction. Special consideration is given to the integrin-iPSC linkage signalling chain in the cardiovascular field, focusing on biomaterial-based in vitro models to evaluate the relevance of this process in iPSC differentiation into cardiomyocytes.

PTEN suppresses the inflammation, viability, and motility of AP-AR42J cells by activating the Wnt/β-catenin pathway

Acute pancreatitis (AP), a kind of common acute abdominal disease and typical chemical inflammation, is commonly caused by pancreatin digestion of the pancreas and surrounding tissues. The gene for phosphate and tension homology deleted on chromosome ten (PTEN) is a tumor suppressor that regulates numerous cellular processes. In the present study, we have elaborately investigated the effect of PTEN on the alleviating of AP and its underlying mechanisms. Firstly, we demonstrated an up-regulation of PTEN in the pancreatic tissues from AP rats by immunochemistry, qRT-PCR and western-blot assays. Subsequently, cellular experiments exhibited that PTEN has a significant inhibition effect on the proliferation, invasion and migration of AP cells. Further underlying mechanism studies showed that the growth of AP cells was mainly restrained by PTEN in the G1 phase through activation of the Wnt/β-catenin pathway, which can be demonstrated by the down-regulation of various pro-inflammatory cytokines such as IL-6, IL-10, TNF and IL-1β. Taking these results together, we can draw the conclusion that PTEN plays a significant role in suppressing the inflammation, viability and motility of acute pancreatitis and could be a potential target for AP therapies.

Acute pancreatitis (AP), a kind of common acute abdominal disease and typical chemical inflammation, is commonly caused by pancreatin digestion of the pancreas and surrounding tissues.

Wnt signalling in the development of axon, dendrites and synapses

Wnts are a highly conserved family of secreted glycoproteins that play essential roles in the morphogenesis and body patterning during the development of metazoan species. In recent years, mounting evidence has revealed important functions of Wnt signalling in diverse aspects of neural development, including neuronal polarization, guidance and branching of the axon and dendrites, as well as synapse formation and its structural remodelling. In contrast to Wnt signalling in cell proliferation and differentiation, which mostly acts through β-catenin-dependent pathways, Wnts engage a diverse array of non-transcriptional cascades in neuronal development, such as the planar cell polarity, cytoskeletal or calcium signalling pathways. In this review, we summarize recent advances in the mechanisms of Wnt signalling in the development of axon, dendrite and synapse formation.

Dishevelled‑2 modulates osteogenic differentiation of human synovial fibroblasts in osteoarthritis

Dishevelled (Dvl)-2 represents one of the cytoplasmic proteins, which serves as a pivotal hub in signaling intermediates through a number of different signaling pathways associated with the Wnt family. The aim of the present study was to investigate the roles and mechanisms of Dvl-2 on synovial fibroblasts (SFBs) in osteoarthritis (OA). A Cell Counting kit-8 (CCK-8) assay was used to determine cell viability. An alkaline phosphatase (ALP) test kit was used to measure the activity of ALP. Western blot and reverse transcription-quantitative polymerase chain reaction analysis were used to evaluate the protein and mRNA expression, respectively. The results suggest that depletion of Dvl-2 significantly decreased the expression of osteoprotegerin (OPG) and ALP (P<0.05) and significantly increased the expression of receptor activator of nuclear factor-κB ligand (RANKL), ALP, osteonectin (ON), osteocalcin (OCN) and osterix (P<0.05). In addition, the depletion of Dvl-2 also significantly inhibited the expression of runt-related transcription factor 2 (Runx-2) and β-catenin in SFBs (P<0.05). The effect of Dvl-2 over-expression was opposite to the effect of Dvl-2 silencing. The inactivation of Wnt3a reversed the effect of Dvl-2 silencing. In conclusion, the results indicate that Dvl-2 regulated osteogenic differentiation of SFBs in OA.

Wnt3a ligand facilitates autophagy in hippocampal neurons by modulating a novel GSK-3β-AMPK axis

Background

In the adult central nervous system (CNS), Wnt signaling regulates dendritic structure and synaptic plasticity. The Wnt signaling pathway can be divided into the canonical (β-catenin-dependent) and non-canonical pathways. In the canonical pathway, the binding of canonical ligands such as Wnt3a to the Frizzled receptor induces inactivation of glycogen synthase kinase-3β (GSK-3β), which stabilizes β-catenin and allows its translocation to the nucleus. However, to date, few studies have focused on β-catenin-independent Wnt signaling or explained the underlying mechanisms connecting Wnt signaling to cellular energy metabolism. A recent study demonstrated negative regulation of 5′ adenosine monophosphate-activated protein kinase (AMPK), a major target of GSK-3β that regulates cellular metabolism under diverse conditions. Mainly based on these observations, we evaluated whether Wnt3a ligand modulates autophagy by regulating the GSK-3β/AMPK axis.

Methods

Cultured primary hippocampal neurons and slices of the CA1 region of rat hippocampus were used. GSK-3β inhibition, AMPK activation, PP2Ac expression, and LC3 processing were examined by western blotting. Autophagic compartments were studied using the CYTO-ID® fluorescent probe, and mature autophagosomes were observed via transmission electron microscopy (TEM).

Results

Wnt3a ligand, acting through the Frizzled receptor, promotes the rapid activation of AMPK by inactivating GSK-3β. Biochemical analysis of downstream targets indicated that Wnt3a ligand modulates autophagy in hippocampal neurons.

Conclusions

Our results revealed new aspects of Wnt signaling in neuronal metabolism. First, AMPK is an additional target downstream of the Wnt cascade, suggesting a molecular mechanism for the metabolic effects previously observed for Wnt signaling. Second, this mechanism is independent of β-catenin, suggesting a relevant role for non-genomic activity of the Wnt pathway in cellular metabolism. Finally, these results have new implications regarding the role of Wnt signaling in the modulation of autophagy in neurons, with a possible role in the removal of accumulated intracellular proteins.

Inhibition of canonical WNT signaling pathway by β-catenin/CBP inhibitor ICG-001 ameliorates liver fibrosis in vivo through suppression of stromal CXCL12

Quiescent hepatic stellate cells (HSCs), in response to liver injury, undergo characteristic morphological transformation into proliferative, contractile and ECM-producing myofibroblasts. In this study, we investigated the implication of canonical Wnt signaling pathway in HSCs and liver fibrogenesis. Canonical Wnt signaling pathway activation and inhibition using β-catenin/CBP inhibitor ICG001 was examined in-vitro in TGFβ-activated 3T3, LX2, primary human HSCs, and in-vivo in CCl₄-induced acute liver injury mouse model. Fibroblasts-conditioned medium studies were performed to assess the Wnt-regulated paracrine factors involved in crosstalk between HSCs-macrophages and HSCs-endothelial cells. Canonical Wnt signaling pathway components were significantly up-regulated in-vitro and in-vivo. In-vitro, ICG-001 significantly inhibited fibrotic parameters, 3D-collagen contractility and wound healing. Conditioned medium induced fibroblasts-mediated macrophage and endothelial cells activation was significantly inhibited by ICG-001. In-vivo, ICG-001 significantly attenuated collagen accumulation and HSC activation. Interestingly, ICG-001 drastically inhibited macrophage infiltration, intrahepatic inflammation and angiogenesis. We further analyzed the paracrine factors involved in Wnt-mediated effects and found CXCL12 was significantly suppressed both in-vitro and in-vivo following Wnt inhibition. Wnt-regulated CXCL12 secretion from activated HSCs potentiated macrophage infiltration and activation, and angiogenesis. Pharmacological inhibition of canonical Wnt signaling pathway via suppression of stromal CXCL12 suggests a potential therapeutic approach targeting activated HSCs in liver fibrosis.

Calcium spikes, waves and oscillations in a large, patterned epithelial tissue

While calcium signaling in excitable cells, such as muscle or neurons, is extensively characterized, calcium signaling in epithelial tissues is little understood. Specifically, the range of intercellular calcium signaling patterns elicited by tightly coupled epithelial cells and their function in the regulation of epithelial characteristics are little explored. We found that in Drosophila imaginal discs, a widely studied epithelial model organ, complex spatiotemporal calcium dynamics occur. We describe patterns that include intercellular waves traversing large tissue domains in striking oscillatory patterns as well as spikes confined to local domains of neighboring cells. The spatiotemporal characteristics of intercellular waves and oscillations arise as emergent properties of calcium mobilization within a sheet of gap-junction coupled cells and are influenced by cell size and environmental history. While the in vivo function of spikes, waves and oscillations requires further characterization, our genetic experiments suggest that core calcium signaling components guide actomyosin organization. Our study thus suggests a possible role for calcium signaling in epithelia but importantly, introduces a model epithelium enabling the dissection of cellular mechanisms supporting the initiation, transmission and regeneration of long-range intercellular calcium waves and the emergence of oscillations in a highly coupled multicellular sheet.

Aberrant regulation of Wnt signaling in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most lethal malignancies in the world. Several signaling pathways, including the wingless/int-1 (Wnt) signaling pathway, have been shown to be commonly activated in HCC. The Wnt signaling pathway can be triggered via both catenin β1 (CTNNB1)-dependent (also known as “canonical”) and CTNNB1-independent (often referred to as “non-canonical”) pathways. Specifically, the canonical Wnt pathway is one of those most frequently reported in HCC. Aberrant regulation from three complexes (the cell-surface receptor complex, the cytoplasmic destruction complex and the nuclear CTNNB1/T-cell-specific transcription factor/lymphoid enhancer binding factor transcriptional complex) are all involved in HCC. Although the non-canonical Wnt pathway is rarely reported, two main non-canonical pathways, Wnt/planar cell polarity pathway and Wnt/Ca²⁺ pathway, participate in the regulation of hepatocarcinogenesis. Interestingly, the canonical Wnt pathway is antagonized by non-canonical Wnt signaling in HCC. Moreover, other signaling cascades have also been demonstrated to regulate the Wnt pathway through crosstalk in HCC pathogenesis. This review provides a perspective on the emerging evidence that the aberrant regulation of Wnt signaling is a critical mechanism for the development of HCC. Furthermore, crosstalk between different signaling pathways might be conducive to the development of novel molecular targets of HCC.

Methods to Manipulate and Monitor Wnt Signaling in Human Pluripotent Stem Cells

Human pluripotent stem cells (hPSCs) may revolutionize medical practice by providing: (a) a renewable source of cells for tissue replacement therapies, (b) a powerful system to model human diseases in a dish, and (c) a platform for examining efficacy and safety of novel drugs. Furthermore, these cells offer a unique opportunity to study early human development in vitro, in particular, the process by which a seemingly uniform cell population interacts to give rise to the three main embryonic lineages: ectoderm, endoderm. and mesoderm. This process of lineage allocation is regulated by a number of inductive signals that are mediated by growth factors, including FGF, TGFβ, and Wnt. In this book chapter, we introduce a set of tools, methods, and protocols to specifically manipulate the Wnt signaling pathway with the intention of altering the cell fate outcome of hPSCs.

Structure, phylogeny, and expression of the frizzled-related gene family in the lophotrochozoan annelid Platynereis dumerilii

Background

Wnt signaling pathways are highly conserved signal transduction pathways important for axis formation, cell fate specification, and organogenesis throughout metazoan development. Within the various Wnt pathways, the frizzled transmembrane receptors (Fzs) and secreted frizzled-related proteins (sFRPs) play central roles in receiving and antagonizing Wnt signals, respectively. Despite their importance, very little is known about the frizzled-related gene family (fzs & sfrps) in lophotrochozoans, especially during early stages of spiralian development. Here we ascertain the frizzled-related gene complement in six lophotrochozoan species, and determine their spatial and temporal expression pattern during early embryogenesis and larval stages of the marine annelid Platynereis dumerilii.

Results

Phylogenetic analyses confirm conserved homologs for four frizzled receptors (Fz1/2/7, Fz4, Fz5/8, Fz9/10) and sFRP1/2/5 in five of six lophotrochozoan species. The sfrp3/4 gene is conserved in one, divergent in two, and evidently lost in three lophotrochozoan species. Three novel fz-related genes (fzCRD1-3) are unique to Platynereis. Transcriptional profiling and in situ hybridization identified high maternal expression of fz1/2/7, expression of fz9/10 and fz1/2/7 within animal and dorsal cell lineages after the 32-cell stage, localization of fz5/8, sfrp1/2/5, and fzCRD-1 to animal-pole cell lineages after the 80-cell stage, and no expression for fz4, sfrp3/4, and fzCRD-2, and -3 in early Platynereis embryos. In later larval stages, all frizzled-related genes are expressed in distinct patterns preferentially in the anterior hemisphere and less in the developing trunk.

Conclusions

Lophotrochozoans have retained a generally conserved ancestral bilaterian frizzled-related gene complement (four Fzs and two sFRPs). Maternal expression of fz1/2/7, and animal lineage-specific expression of fz5/8 and sfrp1/2/5 in early embryos of Platynereis suggest evolutionary conserved roles of these genes to perform Wnt pathway functions during early cleavage stages, and the early establishment of a Wnt inhibitory center at the animal pole, respectively. Numerous frizzled receptor-expressing cells and embryonic territories were identified that might indicate competence to receive Wnt signals during annelid development. An anterior bias for frizzled-related gene expression in embryos and larvae might point to a polarity of Wnt patterning systems along the anterior–posterior axis of this annelid.

Electronic supplementary material

The online version of this article (doi:10.1186/s13227-015-0032-4) contains supplementary material, which is available to authorized users.

Caenorhabditis elegans: A Model System for Anti-Cancer Drug Discovery and Therapeutic Target Identification

The nematode Caenorhabditis elegans (C. elegans) offers a unique opportunity for biological and basic medical researches due to its genetic tractability and well-defined developmental lineage. It also provides an exceptional model for genetic, molecular, and cellular analysis of human disease-related genes. Recently, C. elegans has been used as an ideal model for the identification and functional analysis of drugs (or small-molecules) in vivo. In this review, we describe conserved oncogenic signaling pathways (Wnt, Notch, and Ras) and their potential roles in the development of cancer stem cells. During C. elegans germline development, these signaling pathways regulate multiple cellular processes such as germline stem cell niche specification, germline stem cell maintenance, and germ cell fate specification. Therefore, the aberrant regulations of these signaling pathways can cause either loss of germline stem cells or overproliferation of a specific cell type, resulting in sterility. This sterility phenotype allows us to identify drugs that can modulate the oncogenic signaling pathways directly or indirectly through a high-throughput screening. Current in vivo or in vitro screening methods are largely focused on the specific core signaling components. However, this phenotype-based screening will identify drugs that possibly target upstream or downstream of core signaling pathways as well as exclude toxic effects. Although phenotype-based drug screening is ideal, the identification of drug targets is a major challenge. We here introduce a new technique, called Drug Affinity Responsive Target Stability (DARTS). This innovative method is able to identify the target of the identified drug. Importantly, signaling pathways and their regulators in C. elegans are highly conserved in most vertebrates, including humans. Therefore, C. elegans will provide a great opportunity to identify therapeutic drugs and their targets, as well as to understand mechanisms underlying the formation of cancer.

A phenotypic screen in zebrafish identifies a novel small-molecule inducer of ectopic tail formation suggestive of alterations in non-canonical Wnt/PCP signaling

Zebrafish have recently emerged as an attractive model for the in vivo bioassay-guided isolation and characterization of pharmacologically active small molecules of natural origin. We carried out a zebrafish-based phenotypic screen of over 3000 plant-derived secondary metabolite extracts with the goal of identifying novel small-molecule modulators of the BMP and Wnt signaling pathways. One of the bioactive plant extracts identified in this screen - Jasminum gilgianum, an Oleaceae species native to Papua New Guinea - induced ectopic tails during zebrafish embryonic development. As ectopic tail formation occurs when BMP or non-canonical Wnt signaling is inhibited during the tail protrusion process, we suspected a constituent of this extract to act as a modulator of these pathways. A bioassay-guided isolation was carried out on the basis of this zebrafish phenotype, identifying para-coumaric acid methyl ester (pCAME) as the active compound. We then performed an in-depth phenotypic analysis of pCAME-treated zebrafish embryos, including a tissue-specific marker analysis of the secondary tails. We found pCAME to synergize with the BMP-inhibitors dorsomorphin and LDN-193189 in inducing ectopic tails, and causing convergence-extension defects in compound-treated embryos. These results indicate that pCAME may interfere with non-canonical Wnt signaling. Inhibition of Jnk, a downstream target of Wnt/PCP signaling (via morpholino antisense knockdown and pharmacological inhibition with the kinase inhibitor SP600125) phenocopied pCAME-treated embryos. However, immunoblotting experiments revealed pCAME to not directly inhibit Jnk-mediated phosphorylation of c-Jun, suggesting additional targets of SP600125, and/or other pathways, as possibly being involved in the ectopic tail formation activity of pCAME. Further investigation of pCAME's mechanism of action will help determine this compound's pharmacological utility.

Intrinsic ability of adult stem cell in skeletal muscle: an effective and replenishable resource to the establishment of pluripotent stem cells

Adult stem cells play an essential role in mammalian organ maintenance and repair throughout adulthood since they ensure that organs retain their ability to regenerate. The choice of cell fate by adult stem cells for cellular proliferation, self-renewal, and differentiation into multiple lineages is critically important for the homeostasis and biological function of individual organs. Responses of stem cells to stress, injury, or environmental change are precisely regulated by intercellular and intracellular signaling networks, and these molecular events cooperatively define the ability of stem cell throughout life. Skeletal muscle tissue represents an abundant, accessible, and replenishable source of adult stem cells. Skeletal muscle contains myogenic satellite cells and muscle-derived stem cells that retain multipotent differentiation abilities. These stem cell populations have the capacity for long-term proliferation and high self-renewal. The molecular mechanisms associated with deficits in skeletal muscle and stem cell function have been extensively studied. Muscle-derived stem cells are an obvious, readily available cell resource that offers promise for cell-based therapy and various applications in the field of tissue engineering. This review describes the strategies commonly used to identify and functionally characterize adult stem cells, focusing especially on satellite cells, and discusses their potential applications.

Wnt-signalling in the embryonic mammary gland

The first member of the Wnt-family ligands was identified 30 years ago as a factor in mouse mammary tumours whose expression was deregulated due to the promoter activity emanating from the proximal integration of the Mouse Mammary Tumour Virus genome (Nusse and Varmus, Embo J 31:2670-84, 2012). The Wnt-ligands invoke a number of molecular-genetic signalling cascades fundamental to the patterning of developing tissues and organs during embryogenesis as well as during postnatal development. The Wnt-signalling cascade that controls the activities of β-catenin and the T-cell Factor (Tcf)/Lympoid enhancer factor (Lef1) plays a fundamental role in control of all stages of embryonic mammary gland development. We provide here a brief overview of the known aspects of Wnt-signalling activities in the embryonic mammary gland and its interactions with other signalling cascades in this developing tissue.

Functional consequences of Wnt-induced dishevelled 2 phosphorylation in canonical and noncanonical Wnt signaling

Dishevelled (Dvl) proteins are intracellular effectors of Wnt signaling that have essential roles in both canonical and noncanonical Wnt pathways. It has long been known that Wnts stimulate Dvl phosphorylation, but relatively little is known about its functional significance. We have previously reported that both Wnt3a and Wnt5a induce Dvl2 phosphorylation that is associated with an electrophoretic mobility shift and loss of recognition by monoclonal antibody 10B5. In the present study, we mapped the 10B5 epitope to a 16-amino acid segment of human Dvl2 (residues 594-609) that contains four Ser/Thr residues. Alanine substitution of these residues (P4m) eliminated the mobility shift induced by either Wnt3a or Wnt5a. The Dvl2 P4m mutant showed a modest increase in canonical Wnt/β-catenin signaling activity relative to wild type. Consistent with this finding, Dvl2 4Pm preferentially localized to cytoplasmic puncta. In contrast to wild-type Dvl2, however, the P4m mutant was unable to rescue Wnt3a-dependent neurite outgrowth in TC-32 cells following suppression of endogenous Dvl2/3. Earlier work has implicated casein kinase 1δ/ε as responsible for the Dvl mobility shift, and a CK1δ in vitro kinase assay confirmed that Ser(594), Thr(595), and Ser(597) of Dvl2 are CK1 targets. Alanine substitution of these three residues was sufficient to abrogate the Wnt-dependent mobility shift. Thus, we have identified a cluster of Ser/Thr residues in the C-terminal domain of Dvl2 that are Wnt-induced phosphorylation (WIP) sites. Our results indicate that phosphorylation at the WIP sites reduces Dvl accumulation in puncta and attenuates β-catenin signaling, whereas it enables noncanonical signaling that is required for neurite outgrowth.

Activation of Wnt Planar Cell Polarity (PCP) signaling promotes growth plate column formation in vitro

Disrupting the Wnt Planar Cell Polarity (PCP) signaling pathway in vivo results in loss of columnar growth plate architecture, but it is unknown whether activation of this pathway in vitro is sufficient to promote column formation. We hypothesized that activation of the Wnt PCP pathway in growth plate chondrocyte cell pellets would promote columnar organization in these cells that are normally oriented randomly in culture. Rat growth plate chondrocytes were transfected with plasmids encoding the Fzd7 cell-surface Wnt receptor, a Fzd7 deletion mutant lacking the Wnt-binding domain, or Wnt receptor-associated proteins Ror2 or Vangl2, and then cultured as three-dimensional cell pellets in the presence of recombinant Wnt5a or Wnt5b for 21 days. Cellular morphology was evaluated using histomorphometric measurements. Activation of Wnt PCP signaling components promoted the initiation of columnar morphogenesis in the chondrocyte pellet culture model, as measured by histomorphometric analysis of the column index (ANOVA p = 0.01). Activation of noncanonical Wnt signaling through overexpression of both the cell-surface Wnt receptor Fzd7 and receptor-associated protein Ror2 with addition of recombinant Wnt5a promotes the initiation of columnar architecture of growth plate chondrocytes in vitro, representing an important step toward growth plate regeneration.

Agonistic and antagonistic roles for TNIK and MINK in non-canonical and canonical Wnt signalling

Wnt signalling is a key regulatory factor in animal development and homeostasis and plays an important role in the establishment and progression of cancer. Wnt signals are predominantly transduced via the Frizzled family of serpentine receptors to two distinct pathways, the canonical ß-catenin pathway and a non-canonical pathway controlling planar cell polarity and convergent extension. Interference between these pathways is an important determinant of cellular and phenotypic responses, but is poorly understood. Here we show that TNIK (Traf2 and Nck-interacting kinase) and MINK (Misshapen/NIKs-related kinase) MAP4K signalling kinases are integral components of both canonical and non-canonical pathways in Xenopus. xTNIK and xMINK interact and are proteolytically cleaved in vivo to generate Kinase domain fragments that are active in signal transduction, and Citron-NIK-Homology (CNH) Domain fragments that are suppressive. The catalytic activity of the Kinase domain fragments of both xTNIK and xMINK mediate non-canonical signalling. However, while the Kinase domain fragments of xTNIK also mediate canonical signalling, the analogous fragments derived from xMINK strongly antagonize this signalling. Our data suggest that the proteolytic cleavage of xTNIK and xMINK determines their respective activities and is an important factor in controlling the balance between canonical and non-canonical Wnt signalling in vivo.

Wnt signaling in myogenesis

The formation of skeletal muscle is a tightly regulated process that is critically modulated by Wnt signaling. Myogenesis is dependent on the precise and dynamic integration of multiple Wnt signals allowing self-renewal and progression of muscle precursors in the myogenic lineage. Dysregulation of Wnt signaling can lead to severe developmental defects and perturbation of muscle homeostasis. Recent work has revealed novel roles for the non-canonical planar cell polarity (PCP) and AKT/mTOR pathways in mediating the effects of Wnt on skeletal muscle. In this review, we discuss the role of Wnt signaling in myogenesis and in regulating the homeostasis of adult muscle.

Wnt5a and Wnt11 are essential for second heart field progenitor development

Wnt/β-catenin has a biphasic effect on cardiogenesis, promoting the induction of cardiac progenitors but later inhibiting their differentiation. Second heart field progenitors and expression of the second heart field transcription factor Islet1 are inhibited by the loss of β-catenin, indicating that Wnt/β-catenin signaling is necessary for second heart field development. However, expressing a constitutively active β-catenin with Islet1-Cre also inhibits endogenous Islet1 expression, reflecting the inhibitory effect of prolonged Wnt/β-catenin signaling on second heart field development. We show that two non-canonical Wnt ligands, Wnt5a and Wnt11, are co-required to regulate second heart field development in mice. Loss of Wnt5a and Wnt11 leads to a dramatic loss of second heart field progenitors in the developing heart. Importantly, this loss of Wnt5a and Wnt11 is accompanied by an increase in Wnt/β-catenin signaling, and ectopic Wnt5a/Wnt11 inhibits β-catenin signaling and promotes cardiac progenitor development in differentiating embryonic stem cells. These data show that Wnt5a and Wnt11 are essential regulators of the response of second heart field progenitors to Wnt/β-catenin signaling and that they act by restraining Wnt/β-catenin signaling during cardiac development.

Wnt5a can both activate and repress Wnt/β-catenin signaling during mouse embryonic development

Embryonic development is controlled by a small set of signal transduction pathways, with vastly different phenotypic outcomes depending on the time and place of their recruitment. How the same molecular machinery can elicit such specific and distinct responses, remains one of the outstanding questions in developmental biology. Part of the answer may lie in the high inherent genetic complexity of these signaling cascades, as observed for the Wnt-pathway. The mammalian genome encodes multiple Wnt proteins and receptors, each of which show dynamic and tightly controlled expression patterns in the embryo. Yet how these components interact in the context of the whole organism remains unknown. Here we report the generation of a novel, inducible transgenic mouse model that allows spatiotemporal control over the expression of Wnt5a, a protein implicated in many developmental processes and multiple Wnt-signaling responses. We show that ectopic Wnt5a expression from E10.5 onwards results in a variety of developmental defects, including loss of hair follicles and reduced bone formation in the skull. Moreover, we find that Wnt5a can have dual signaling activities during mouse embryonic development. Specifically, Wnt5a is capable of both inducing and repressing β-catenin/TCF signaling in vivo, depending on the time and site of expression and the receptors expressed by receiving cells. These experiments show for the first time that a single mammalian Wnt protein can have multiple signaling activities in vivo, thereby furthering our understanding of how signaling specificity is achieved in a complex developmental context.

Wnt pathway inhibition via the targeting of Frizzled receptors results in decreased growth and tumorigenicity of human tumors

The Wnt/β-catenin pathway, which signals through the Frizzled (Fzd) receptor family and several coreceptors, has long been implicated in cancer. Here we demonstrate a therapeutic approach to targeting the Wnt pathway with a monoclonal antibody, OMP-18R5. This antibody, initially identified by binding to Frizzled 7, interacts with five Fzd receptors through a conserved epitope within the extracellular domain and blocks canonical Wnt signaling induced by multiple Wnt family members. In xenograft studies with minimally passaged human tumors, this antibody inhibits the growth of a range of tumor types, reduces tumor-initiating cell frequency, and exhibits synergistic activity with standard-of-care chemotherapeutic agents.

Activation of canonical Wnt signalling is required for TGF-β-mediated fibrosis

The transforming growth factor-β (TGF-β) signalling pathway is a key mediator of fibroblast activation that drives the aberrant synthesis of extracellular matrix in fibrotic diseases. Here we demonstrate a novel link between transforming growth factor-β and the canonical Wnt pathway. TGF-β stimulates canonical Wnt signalling in a p38-dependent manner by decreasing the expression of the Wnt antagonist Dickkopf-1. Tissue samples from human fibrotic diseases show enhanced expression of Wnt proteins and decreased expression of Dickkopf-1. Activation of the canonical Wnt pathway stimulates fibroblasts in vitro and induces fibrosis in vivo. Transgenic overexpression of Dickkopf-1 ameliorates skin fibrosis induced by constitutively active TGF-β receptor type I signalling and also prevents fibrosis in other TGF-β-dependent animal models. These findings demonstrate that canonical Wnt signalling is necessary for TGF-β-mediated fibrosis and highlight a key role for the interaction of both pathways in the pathogenesis of fibrotic diseases.

Aberrant activation of the TGF-β pathway leads to fibrotic disease. Distler and colleagues show that TGF-β-mediated fibrosis requires the decrease of Dickkopf-1, an antagonist of canonical Wnt signalling, suggesting that the two pathways interact for the manifestation of this disease.

Redundant functions of Rac GTPases in inner ear morphogenesis

Development of the mammalian inner ear requires coordination of cell proliferation, cell fate determination and morphogenetic movements. While significant progress has been made in identifying developmental signals required for inner ear formation, less is known about how distinct signals are coordinated by their downstream mediators. Members of the Rac family of small GTPases are known regulators of cytoskeletal remodeling and numerous other cellular processes. However, the function of Rac GTPases in otic development is largely unexplored. Here, we show that Rac1 and Rac3 redundantly regulate many aspects of inner ear morphogenesis. While no morphological defects were observed in Rac3(-/-) mice, Rac1(CKO); Rac3(-/-) double mutants displayed enhanced vestibular and cochlear malformations compared to Rac1(CKO) single mutants. Moreover, in Rac1(CKO); Rac3(-/-) mutants, we observed compromised E-cadherin-mediated cell adhesion, reduced cell proliferation and increased cell death in the early developing otocyst, leading to a decreased size and malformation of the membranous labyrinth. Finally, cochlear extension was severely disrupted in Rac1(CKO); Rac3(-/-) mutants, accompanied by a loss of epithelial cohesion and formation of ectopic sensory patches underneath the cochlear duct. The compartmentalized expression of otic patterning genes within the Rac1(CKO); Rac3(-/-) mutant otocyst was largely normal, however, indicating that Rac proteins regulate inner ear morphogenesis without affecting cell fate specification. Taken together, our results reveal an essential role for Rac GTPases in coordinating cell adhesion, cell proliferation, cell death and cell movements during otic development.

Waif1/5T4 inhibits Wnt/β-catenin signaling and activates noncanonical Wnt pathways by modifying LRP6 subcellular localization

Wnt proteins can activate distinct signaling pathways, but little is known about the mechanisms regulating pathway selection. Here we show that the metastasis-associated transmembrane protein Wnt-activated inhibitory factor 1 (Waif1/5T4) interferes with Wnt/β-catenin signaling and concomitantly activates noncanonical Wnt pathways. Waif1 inhibits β-catenin signaling in zebrafish and Xenopus embryos as well as in mammalian cells, and zebrafish waif1a acts as a direct feedback inhibitor of wnt8-mediated mesoderm and neuroectoderm patterning during zebrafish gastrulation. Waif1a binds to the Wnt coreceptor LRP6 and inhibits Wnt-induced LRP6 internalization into endocytic vesicles, a process that is required for pathway activation. Thus, Waif1a modifies Wnt/β-catenin signaling by regulating LRP6 subcellular localization. In addition, Waif1a enhances β-catenin-independent Wnt signaling in zebrafish embryos and Xenopus explants by promoting a noncanonical function of Dickkopf1. These results suggest that Waif1 modulates pathway selection in Wnt-receiving cells.

GABARAPL1 negatively regulates Wnt/β-catenin signaling by mediating Dvl2 degradation through the autophagy pathway

Wnt signaling is critical for many biological processes and is tightly regulated. In this study, we found that GABARAPL1 (GABA(A) receptor-associated protein like 1, GABARAPL1) interacts with Dvl2 by both yeast two-hybrid screening and immunoprecipitation experiments. Furthermore, we observed that p62 is required for the interaction of Dvl2 and GABARAPL1. Luciferase assays indicated that GABARAPL1 represses Wnt/β-catenin signaling stimulated by Wnt1, Dvl2 and β-catenin. We further demonstrated that GABARAPL1 mediates degradation of Dvl2 and the effect is blocked by addition of 3-MA, a specific inhibitor of autophagy. Finally, we provided evidence that over-expression of GABARAPL1 inhibits proliferation and tumor growth of MCF7 cells in vitro and in nude mice. Taken together, our results suggested that GABARAPL1 as a tumor repressor inhibits Wnt signaling via mediating Dvl2 degradation through the autophagy pathway.

International Union of Basic and Clinical Pharmacology. LXXX. The class Frizzled receptors

The receptor class Frizzled, which has recently been categorized as a separate group of G protein-coupled receptors by the International Union of Basic and Clinical Pharmacology, consists of 10 Frizzleds (FZD(1-10)) and Smoothened (SMO). The FZDs are activated by secreted lipoglycoproteins of the Wingless/Int-1 (WNT) family, whereas SMO is indirectly activated by the Hedgehog (HH) family of proteins acting on the transmembrane protein Patched (PTCH). Recent years have seen major advances in our knowledge about these seven-transmembrane-spanning proteins, including: receptor function, molecular mechanisms of signal transduction, and the receptor's role in embryonic patterning, physiology, cancer, and other diseases. Despite intense efforts, many question marks and challenges remain in mapping receptor-ligand interaction, signaling routes, mechanisms of specificity and how these molecular details underlie disease and also the receptor's important role in physiology. This review therefore focuses on the molecular aspects of WNT/FZD and HH/SMO signaling discussing receptor structure, mechanisms of signal transduction, accessory proteins, receptor dynamics, and the possibility of targeting these signaling pathways pharmacologically.

The β-catenin/Tcf4/survivin signaling maintains a less differentiated phenotype and high proliferative capacity of human corneal epithelial progenitor cells

It is clear that the microenvironment or niche plays an important role in determining the fate of stem cells: being stem cells or differentiated. However, the intrinsic pathways controlling the fate of adult stem cells in different niches are largely unknown. This study was to explore the role of β-catenin/Tcf4/survivin signaling in determining the fate of human corneal epithelial stem cells in different media. We observed that the low calcium serum-free media, especially CnT-20, promoted proliferative capacity, colony forming efficiency and stem cell-like phenotype of human corneal epithelial cells (HCECs) when compared with the cells cultured in a high calcium serum-containing medium SHEM. Three key factors in Wnt signaling, β-catenin, Tcf4 and survivin, were found to be expressed higher by HCECs grown in CnT-20 than those cultured in SHEM, as evaluated by real-time PCR, Western blotting and immunostaining. Transfection of siRNA-Tcf4 at 10-50nM knocked down Tcf4, and also significantly suppressed its down stream molecule survivin at both mRNA and protein levels in HCECs. Furthermore, Tcf4 silencing significantly suppressed the proliferative capacity of HCECs, measured by WST-1 assay, compared with the control groups, untreated or transfected with non-coding sequence siRNA-fluorescein. These findings demonstrate that low calcium serum free media promote ex vivo expansion of corneal epithelial progenitor cells that retain a less differentiated phenotype and high proliferative capacity via β-catenin/Tcf4/survivin signaling, a novel intrinsic pathway. This study may have high impact and clinic implication on the expansion of corneal epithelial stem cells in regenerative medicine, especially for ocular surface reconstruction.

Association of β-catenin, Wnt1, Smad4, Hoxa9, and Bmi-1 with the prognosis of esophageal squamous cell carcinoma

In our previous study, Human Signal Transduction in Cancer Gene Array was used in 12 fresh tumor samples to detect the gene expression profiles in the esophageal squamous cell carcinoma (ESCC) tissues matched adjacent non-cancerous samples. Among genes up-regulated at least twofold, β-catenin, Wnt1, Smad4, Hoxa9, and Bmi-1 were found. So subsequently, the aim of this study was to investigate the prognosis and clinicopathologic roles of β-catenin, Wnt1, Smad4, Hoxa9, and Bmi-1 in ESCC tissue. The mRNA and protein expression levels of β-catenin, Wnt1, Smad4, Hoxa9, and Bmi-1 genes in 70 ESCC and adjacent non-cancerous paraffin-embedded samples were determined by Real-Time Quantitative PCR (RT-PCR) and immunohistochemical staining. The mRNA expression level of β-catenin, Wnt1, Smad4, Hoxa9, and Bmi-1 in ESCC was significantly higher than that in the adjacent non-cancerous tissues (0.0821 ± 0.0416 vs. 0.0185 ± 0.0201, P = 0.0000; 1.9934 ± 1.9888 vs. 0.8863 ± 0.665, P = 0.0184; 0.0298 ± 0.0215 vs. 0.0189 ± 0.0187, P = 0.0017; 2.098 ± 0.091 vs. 1.016 ± 0.078, P = 0.0000; 2.181 ± 2.158 vs. 0.931 ± 0.894, P = 0.0152; respectively), and the protein expression level of determined genes was also significantly higher than that in the adjacent non-cancerous tissues (0.2835 ± 0.0844 vs. 0.2352 ± 0.0670, P = 0.0003; 0.3830 ± 0.0947 vs. 0.2721 ± 0.1474, P = 0.0000; 0.2637 ± 0.0348 vs. 0.2042 ± 0.0180, P = 0.0000; 0.2058 ± 0.0316 vs. 0.1218 ± 0.0518, P = 0.0000; 0.2736 ± 0.0834 vs. 0.2251 ± 0.0571, P = 0.0001; respectively). Then, the overexpression of mRNA and protein levels of β-catenin, Wnt1 and Bmi-1 was aggressively associated with lymph node metastasis, advanced pathological stage, and prognosis of the patients with ESCC (P < 0.05). The up-expression of Hoxa9 mRNA and protein was also aggressively associated with lymph node metastasis and advanced pathological stage (P < 0.05); however, the overexpression of Hoxa9 protein was not associated with the prognosis (P > 0.05). Meanwhile, the hypo-expression of Smad4 mRNA was aggressively associated with advanced pathological stage and prognosis of the patients with ESCC (P < 0.05); however, the hypo-expression of Smad4 protein was neutral to the prognosis and lymph node metastasis (P > 0.05). β-catenin, Wnt1, Smad4, Hoxa9, and Bmi-1 protein expression analysis showed that the positive outcomes of the combined detection of Wnt1 and β-catenin expression or Wnt1, β-catenin and Bmi-1 expression were significantly worse than those of a single target protein expression (P < 0.05). Meantime, the prognosis of the combined positive expression of Wnt1, β-catenin, and Bmi-1 was poorer than that in the combined positive expression of Wnt1 and β-catenin (P < 0.05). The prognosis of ESCC patients with the overexpression of Wnt1/β-catenin and Bmi-1 was relatively poor, and the level of Wnt1/β-catenin and Bmi-1 was conversely correlated with advanced pathological stage and lymph node metastasis. The expression level of Smad4 and Hoxa9 mRNA was also associated with the prognosis of the patients with ESCC, pathological stage, and lymph node metastasis; however, they might not be the independent prognostic factor.

Association of Wnt1/beta-catenin with clinical pathological characteristics and prognosis of esophageal squamous cell carcinoma

The aim of this study was to investigate the correlation between Wnt1/beta-catenin expression and the clinicopathologic features and prognosis of patients with esophageal squamous cell carcinoma (ESCC). The mRNA and protein expression levels of Wnt1/beta-catenin genes in 70 ESCC and 15 adjacent noncancerous paraffin-embedded samples were determined by real-time quantitative polymerase chain reaction and immunohistochemical staining. The mRNA expression level of Wnt1/beta-catenin in ESCC was significantly higher than that in the adjacent noncancerous tissues (1.9934 +/- 1.9888 vs. 0.8863 +/- 0.665, p = 0.0184; 0.2854 +/- 0.1298 vs. 0.0128 +/- 0.0158, p = 0.0000, respectively), and the overexpression of Wnt1/beta-catenin mRNA was aggressively associated with lymph node metastasis and advanced pathological stage (p < 0.0001). The protein expression level of Wnt1/beta-catenin was also significantly higher than that in the adjacent noncancerous tissues (0.3830 +/- 0.0947 vs. 0.2721 +/- 0.1474, p = 0.0002; 0.2835 +/- 0.0844 vs. 0.2352 +/- 0.0670, p = 0.0210, respectively); however, the overexpression was not associated with clinicopathologic characteristics. Meanwhile, the protein expression level of Wnt1 had no relevance with that of beta-catenin. The overexpression of Wnt1/beta-catenin might be an important molecular marker to predict the clinicopathologic stage and prognosis of ESCC, and the level of Wnt1/beta-catenin mRNA was conversely correlated with lymph node metastasis and advanced pathological stage. The overexpression of Wnt1/beta-catenin mRNA should also predict poor prognosis of ESCC; however, it might not be an independent prognostic factor.

Relationship of β-catenin, Wnt1, Smad4, Hoxa9 and Bmi-1 expression with the prognosis of esophageal squamous cell carcinoma

AIM: To investigate the association of β-catenin, Wnt1, Smad4, Hoxa9 and Bmi-1 expression with the prognosis and clinicopathologic characteristics of patients with esophageal squamous cell carcinoma (ESCC).

METHODS: Seventy paraffin-embedded ESCC specimens collected at Nanjing First Hospital from July 2002 to December 2003 were studied. The mRNA and protein expression of β-catenin, Wnt1, Smad4, Hoxa9 and Bmi-1 in these specimens was detected by real-time quantitative RT-PCR and immunohistochemistry. The correlation between the expression of these markers with the prognosis and clinicopathologic characteristics of ESCC patients was then analyzed.

RESULTS: The mRNA expression levels of β-catenin, Wnt1, Smad4, Hoxa9 and Bmi-1 in ESCC were significantly higher than those in tumor-adjacent non-cancerous tissue (0.0821 ± 0.0416 vs 0.0185 ± 0.0201, P = 0.0000; 1.9934 ± 1.9888 vs 0.8863 ± 0.665, P = 0.0184; 0.0298 ± 0.0215 vs 0.0189 ± 0.0187, P = 0.0017; 2.098 ± 0.091 vs 1.016 ± 0.078, P = 0.0000; 2.181 ± 2.158 vs 0.931 ± 0.894, P = 0.0152). The protein expression levels of β-catenin, Wnt1, Smad4, Hoxa9 and Bmi-1 in ESCC were also significantly higher than those in tumor-adjacent non-cancerous tissue (0.2835 ± 0.0844 vs 0.2352 ± 0.0670, P = 0.0003; 0.3830 ± 0.0947 vs 0.2721 ± 0.1474, P = 0.0000; 0.2637 ± 0.0348 vs 0.2042 ± 0.0180, P = 0.0000; 0.2058 ± 0.0316 vs 0.1218 ± 0.0518, P = 0.0000; 0.2736 ± 0.0834 vs 0.2251 ± 0.0571, P = 0.0001). Except for Smad4, the mRNA and protein levels of all the other markers were closely associated with pathological stage and lymph node metastasis in ESCC patients (all P < 0.05). The protein level of Hoxa9 was not associated with the prognosis of ESCC (P > 0.05). The hypo-expression of Smad4 mRNA was closely associated with advanced pathological stage, lymph node metastasis and prognosis in patients with ESCC (all P < 0.05). The Smad4 protein expression level was associated with pathological stage (P < 0.05), but not with prognosis and lymph node metastasis (P > 0.05). Multivariate logistic regression analysis showed that the prognostic factors for ESCC patients included positive protein expression of β-catenin, Wnt1 or Bmi-1 (χ² = 17.65, P = 0.0072).

CONCLUSION: The prognosis of ESCC patients with Wnt1/β-catenin and Bmi-1 overexpression is relatively poor. The levels of Wnt1/β-catenin and Bmi-1 are conversely correlated with advanced pathological stage and lymph node metastasis in ESCC. Although the mRNA expression levels of Smad4 and Hoxa9 are also associated with prognosis, pathological stage and lymph node metastasis in ESCC patients, they might not be independent prognostic factors for ESCC.

Dishevelled-DEP domain interacting protein (DDIP) inhibits Wnt signaling by promoting TCF4 degradation and disrupting the TCF4/beta-catenin complex

The TCF4/beta-catenin complex, the executor of canonical Wnt/beta-catenin signaling, is regulated by a variety of factors. Among these, Dishevelled (Dvl) is a critical regulator that releases beta-catenin from degradation and stabilizes TCF4/beta-catenin complex. Here, we report that DDIP (Dishevelled-DEP domain Interacting Protein, also named as Spats1, spermatogenesis associated, serine-rich 1), a novel protein that interacts with Dvl, regulates Wnt signaling. We provide evidence that DDIP suppresses Lef-1 luciferase reporter activity stimulated by Wnt1, Dvl2 or beta-catenin, interacts with the TCF4/beta-catenin complex, and disrupts the interaction of TCF4 and beta-catenin by promoting TCF4 degradation through the proteasome pathway. Our results indicate that DDIP is a negative regulator of the canonical Wnt signaling.

Emerging links between CDK cell cycle regulators and Wnt signaling

Wnt/beta-catenin signaling controls many aspects of cell behavior throughout development and in adults. One of its best-known and cancer-relevant functions is to stimulate cell proliferation. Recent work has implicated Wnt components in regulating mitotic events, suggesting that the cell cycle and Wnt signaling are directly linked. This concept has now been substantially strengthened with the finding that the mitotic CDK14/cyclin Y complex promotes Wnt signaling through phosphorylation of the LRP6 co-receptor, a key regulatory nexus in the Wnt/beta-catenin pathway. Thus, an unexpectedly tight collaboration between the mitotic cell cycle machinery and Wnt signaling is emerging, suggesting that this pathway might orchestrate mitotic processes.

The importance of Wnt signaling in cardiovascular development

Cardiac development is comprised of a series of morphological events tightly controlled both spatially and temporally. The molecular pathways controlling early cardiac differentiation are poorly understood, but Wnt signaling is emerging as a critical pathway for multiple aspects of early cardiovascular development. The Wnt pathway plays multiple roles in regulating cellular behavior including proliferation, differentiation, cell migration, and cell polarity. Recent data have demonstrated that Wnt activity is important for early precardiac mesoderm differentiation but must be inhibited in subsequent steps for cardiomyocyte differentiation to proceed. Given the important role that Wnt signaling plays in both the differentiation of cardiomyocytes from pluripotential stem cells and tissue regeneration in general, an increased understanding of this pathway is likely to enhance our knowledge about both cardiovascular development and reparative mechanisms.

Towards an integrated view of Wnt signaling in development

Wnt signaling is crucial for embryonic development in all animal species studied to date. The interaction between Wnt proteins and cell surface receptors can result in a variety of intracellular responses. A key remaining question is how these specific responses take shape in the context of a complex, multicellular organism. Recent studies suggest that we have to revise some of our most basic ideas about Wnt signal transduction. Rather than thinking about Wnt signaling in terms of distinct, linear, cellular signaling pathways, we propose a novel view that considers the integration of multiple, often simultaneous, inputs at the level of both Wnt-receptor binding and the downstream, intracellular response.

A new look at TCF and beta-catenin through the lens of a divergent C. elegans Wnt pathway

The canonical Wnt/beta-catenin pathway is extensively characterized, broadly conserved, and clinically important. In this review, we describe the C. elegans Wnt/beta-catenin asymmetry pathway and suggest that some of its unusual features may have important implications for the canonical Wnt/beta-catenin pathway.