WNT signalling events near the cell membrane and their pharmacological targeting for the treatment of cancer

Helicobacter pylori-activated fibroblasts as a silent partner in gastric cancer development

The discovery of Helicobacter pylori (Hp) infection of gastric mucosa leading to active chronic gastritis, gastroduodenal ulcers, and MALT lymphoma laid the groundwork for understanding of the general relationship between chronic infection, inflammation, and cancer. Nevertheless, this sequence of events is still far from full understanding with new players and mediators being constantly identified. Originally, the Hp virulence factors affecting mainly gastric epithelium were proposed to contribute considerably to gastric inflammation, ulceration, and cancer. Furthermore, it has been shown that Hp possesses the ability to penetrate the mucus layer and directly interact with stroma components including fibroblasts and myofibroblasts. These cells, which are the source of biophysical and biochemical signals providing the proper balance between cell proliferation and differentiation within gastric epithelial stem cell compartment, when exposed to Hp, can convert into cancer-associated fibroblast (CAF) phenotype. The crosstalk between fibroblasts and myofibroblasts with gastric epithelial cells including stem/progenitor cell niche involves several pathways mediated by non-coding RNAs, Wnt, BMP, TGF-β, and Notch signaling ligands. The current review concentrates on the consequences of Hp-induced increase in gastric fibroblast and myofibroblast number, and their activation towards CAFs with the emphasis to the altered communication between mesenchymal and epithelial cell compartment, which may lead to inflammation, epithelial stem cell overproliferation, disturbed differentiation, and gradual gastric cancer development. Thus, Hp-activated fibroblasts may constitute the target for anti-cancer treatment and, importantly, for the pharmacotherapies diminishing their activation particularly at the early stages of Hp infection.

Olfactory bulb neurogenesis depending on signaling in the subventricular zone

Olfaction is a crucial sense that is essential for the well-being and survival of individuals. Olfactory bulb (OB) is the first olfactory relay station, and its function depends on newly generated neurons from the subventricular zone (SVZ). These newly born neurons constantly migrate through the rostral migratory stream to integrate into existing neural networks within the OB, thereby contributing to olfactory information processing. However, the mechanisms underlying the contribution of SVZ adult neurogenesis to OB neurogenesis remain largely elusive. Adult neurogenesis is a finely regulated multistep process involving the proliferation of adult neural stem cells (aNSCs) and neural precursor cells, as well as the migration and differentiation of neuroblasts, and integration of newly generated neurons into preexisting neuronal circuitries. Recently, extensive studies have explored the mechanism of SVZ and OB neurogenesis. This review focused on elucidating various molecules and signaling pathways associated with OB neurogenesis dependent on the SVZ function. A better understanding of the mechanisms underlying the OB neurogenesis on the adult brain is an attractive prospect to induce aNSCs in SVZ to generate new neurons to ameliorate olfactory dysfunction that is involved in various diseases. It will also contribute to developing new strategies for the human aNSCs-based therapies.

ANKRD22 knockdown suppresses papillary thyroid cell carcinoma growth and migration and modulates the Wnt/β-catenin signaling pathway

The incidence of thyroid cancer is escalating globally, particularly among women. Studies have demonstrated the abnormal activation of Ankyrin Repeat Domain 22 (ANKRD22) in various cancers, but it remains uncertain whether it is also highly expressed in papillary thyroid carcinoma (PTC). Our objective was to evaluate the role of ANKRD22 in PTC. The expression of ANKRD22 varies among tissues, as validated by the Cancer Genome Atlas, and further predicted using the Tumor Immune Estimation Resource. Predicted results were examined via polymerase chain reaction and western blotting. Subsequently, the expression of ANKRD22 in cells was suppressed by RNA interference, and changes in cell progression were examined in conjunction with the cell counting kit-8 assay, transwell assay, and colony formation assay. Finally, the effects of ANKRD22 knockdown on the Epithelial-to-Mesenchymal transition and the Wnt/β-catenin signaling pathway were investigated through western blotting. An in vivo mice model was established to validate the effect of ANKRD22. This study discovered that ANKRD22 was highly expressed in PTC, which was validated by polymerase chain reaction and western blotting. Knockdown of ANKRD22, significantly reduced thecell viability, colony formation capability, and cell invasion and migration abilities. Furthermore, we found that knockdown of ANKRD22 impaired both tumor Epithelial-to-Mesenchymal transition and the activation of the Wnt/β-catenin signaling pathway. In conclusion, this study revealed that the knockdown of ANKRD22 inhibits the growth and migration of papillary thyroid cell carcinoma by regulating the Wnt/β-catenin signaling pathway.

Rational Construction of a Novel Bioluminescent Substrate for Sensing the Tumor-Associated Hydrolase Notum

Notum, one of the key serine hydrolases in mammals, hydrolyzes the palmitoleoyl moieties of many important proteins and modulates multiple signaling pathways including Wnt/β-catenin signaling. Notum is tightly associated with multiple human diseases, but the reliable and practical tools for sensing Notum activities in complex biological systems are rarely reported. Herein, an efficient strategy was used to rationally construct a specific bioluminescent substrate for Notum. Following computer-aided molecular design and experimental verification, octanoyl luciferin (OL) was selected as the optimum substrate for human Notum, with excellent specificity, high detection sensitivity and high signal-to-noise ratio. Under physiological conditions, OL was readily hydrolyzed by Notum or Notum-containing biological specimens to release d-luciferin that could be easily detected by various fluorescence devices in the presence of luciferase. The applicability of OL for real-time sensing native Notum was examined in living cells, extracellular matrix, and tissue preparations. OL was also used for constructing a high-throughput assay for screening of Notum inhibitors, while a natural compound (bergapten) was newly identified as a potent Notum inhibitor. Collectively, this study devises a reliable and easy-to-use tool for sensing Notum activities in biological systems, which will strongly facilitate hNotum-associated fundamental studies, disease diagnosis, and drug discovery.

Phytochemicals as Chemo-Preventive Agents and Signaling Molecule Modulators: Current Role in Cancer Therapeutics and Inflammation

Cancer is one of the deadliest non communicable diseases. Numerous anticancer medications have been developed to target the molecular pathways driving cancer. However, there has been no discernible increase in the overall survival rate in cancer patients. Therefore, innovative chemo-preventive techniques and agents are required to supplement standard cancer treatments and boost their efficacy. Fruits and vegetables should be tapped into as a source of compounds that can serve as cancer therapy. Phytochemicals play an important role as sources of new medication in cancer treatment. Some synthetic and natural chemicals are effective for cancer chemoprevention, i.e., the use of exogenous medicine to inhibit or impede tumor development. They help regulate molecular pathways linked to the development and spread of cancer. They can enhance antioxidant status, inactivating carcinogens, suppressing proliferation, inducing cell cycle arrest and death, and regulating the immune system. While focusing on four main categories of plant-based anticancer agents, i.e., epipodophyllotoxin, camptothecin derivatives, taxane diterpenoids, and vinca alkaloids and their mode of action, we review the anticancer effects of phytochemicals, like quercetin, curcumin, piperine, epigallocatechin gallate (EGCG), and gingerol. We examine the different signaling pathways associated with cancer and how inflammation as a key mechanism is linked to cancer growth.

Rho-associated kinase1 promotes laryngeal squamous cell carcinoma tumorigenesis and progression via the FAK signaling pathway

Laryngeal squamous cell carcinoma (LSCC) is one of the most common head and neck squamous cell carcinomas (HNSCC). Rho-associated kinase1 (ROCK1) is considered to promote progression of numerous cancers, however, its role in LSCC is still unknown. Here, the expression level of ROCK1 is higher in LSCC tissues than non-tumor tissues, and the expression level of ROCK1 is positively correlated with advanced stage and poor survival prognosis. ROCK1 knockdown in TU686 and TU212 cells dramatically inhibits cellular proliferation, migration and invasion. Whereas the overexpression of ROCK1 reversed these changes. FAK signaling pathway plays an essential role in promoting LSCC progression. Inhibiting FAK activity with TAE226 observably impairs the tumor-promoting effects. In conclusion, ROCK1 promotes LSCC tumorigenesis and progression via the FAK signaling pathway, targeting the ROCK1 molecule may represent potential targets for clinical LSCC treatment.

Overexpression of GDP dissociation inhibitor 1 gene associates with the invasiveness and poor outcomes of colorectal cancer

GDP dissociation inhibitor (GDI) regulates the GDP/GTP exchange reaction of most Rab proteins by inhibiting GDP dissociation. This study evaluated the potential prognostic and predictive value of GDI1 in colorectal cancer (CRC). To address the prognostic power of GDI1, we performed individual and pooled survival analyses on six independent CRC microarray gene expression datasets. GDI1-enriched signatures were also analyzed. Kaplan-Meier and Cox proportional analyses were employed for survival analysis. An immunohistochemistry (IHC) analysis was performed to validate the clinical relevance and prognostic significance of the GDI1 protein level in CRC tissue samples. The results revealed that GDI1 mRNA level was significantly linked with the aggressiveness of CRC, which is compatible with gene set enrichment analysis. A meta-analysis and pooled analysis demonstrated that a higher mRNA GDI1 expression was dramatically correlated with a worse survival in a dose-dependent manner in CRC patients. Further IHC analysis validated that the protein expression of GDI1 in both cytoplasm and membrane also significantly impacted the outcome of CRC patients. In CRC patients with stage III, chemotherapy significantly reduced the relative risk of death in low-GDI1 subgroup (hazard ratio (HR) = 0.22; 95% confidence interval (95% CI) 0.09-0.56, p = 0.0003), but not in high-GDI1 subgroup (HR = 0.63; 95% CI 0.35-1.14, p = 0.1137). Therefore, both high mRNA and protein levels of GDI1 were significantly related to poor outcomes in CRC patients. GD11 may serve as a prognostic biomarker for CRC.

Misregulation of Wnt Signaling Pathways at the Plasma Membrane in Brain and Metabolic Diseases

Wnt signaling pathways constitute a group of signal transduction pathways that direct many physiological processes, such as development, growth, and differentiation. Dysregulation of these pathways is thus associated with many pathological processes, including neurodegenerative diseases, metabolic disorders, and cancer. At the same time, alterations are observed in plasma membrane compositions, lipid organizations, and ordered membrane domains in brain and metabolic diseases that are associated with Wnt signaling pathway activation. Here, we discuss the relationships between plasma membrane components-specifically ligands, (co) receptors, and extracellular or membrane-associated modulators-to activate Wnt pathways in several brain and metabolic diseases. Thus, the Wnt-receptor complex can be targeted based on the composition and organization of the plasma membrane, in order to develop effective targeted therapy drugs.

Role of Phytochemicals in Cancer Chemoprevention: Insights

Cancer is a condition where the body cells multiply in an uncontrollable manner. Chemoprevention of cancer is a broad term that describes the involvement of external agents to slow down or suppress cancer growth. Synthetic and natural compounds are found useful in cancer chemoprevention. The occurrence of global cancer type varies, depending on many factors such as environmental, lifestyle, genetic etc. Cancer is often preventable in developed countries with advanced treatment modalities, whereas it is a painful death sentence in developing and low-income countries due to the lack of modern therapies and awareness. One best practice to identify cancer control measures is to study the origin and risk factors associated with common types. Based on these factors and the health status of patients, stage, and severity of cancer, type of treatment is decided. Even though there are well-established therapies, cancer still stands as one of the major causes of death and a public health burden globally. Research shows that most cancers can be prevented, treated, or the incidence can be delayed. Phytochemicals from various medicinal plants were reported to reduce various risk factors associated with different types of cancer through their chemopreventive role. This review highlights the role of bioactive compounds or natural products from plants in the chemoprevention of cancer. There are many plant based dietary factors involved in the chemoprevention process. The review discusses the process of carcinogenesis and chemoprevention using plants and phytocompounds, with special reference to five major chemopreventive phytocompounds. The article also summarizes the important chemopreventive mechanisms and signaling molecules involved in the process. Since the role of antioxidants in chemoprevention is inevitable, an insight into plant-based antioxidant compounds that fight against this dreadful disease at various stages of carcinogenesis and disease progression is discussed. This will fill the research gap in search of chemopreventive natural compounds and encourage scientists in clinical trials of anticancer agents from plants.

Frizzled7 Activates β-Catenin-Dependent and β-Catenin-Independent Wnt Signalling Pathways During Developmental Morphogenesis: Implications for Therapeutic Targeting in Colorectal Cancer

Frizzled₇ activates β-catenin-dependent and β-catenin-independent Wnt signalling pathways, is highly conserved through evolution from the ancient phylum hydra to man, plays essential roles in stem cells, tissue homeostasis and regeneration in the adult, and is upregulated in diverse cancers. Much of what is known about the core components of the Wnt signalling pathways was derived from studying the function of Frizzled₇ orthologues in the development of lower organism. As we interrogate Frizzled₇ signalling and function for therapeutic targeting in cancer, it is timely to revisit lower organisms to gain insight into the context dependent and dynamic nature of Wnt signalling for effective drug design.

Ubiquitin-Specific Proteases: Players in Cancer Cellular Processes

Ubiquitination represents a post-translational modification (PTM) essential for the maintenance of cellular homeostasis. Ubiquitination is involved in the regulation of protein function, localization and turnover through the attachment of a ubiquitin molecule(s) to a target protein. Ubiquitination can be reversed through the action of deubiquitinating enzymes (DUBs). The DUB enzymes have the ability to remove the mono- or poly-ubiquitination signals and are involved in the maturation, recycling, editing and rearrangement of ubiquitin(s). Ubiquitin-specific proteases (USPs) are the biggest family of DUBs, responsible for numerous cellular functions through interactions with different cellular targets. Over the past few years, several studies have focused on the role of USPs in carcinogenesis, which has led to an increasing development of therapies based on USP inhibitors. In this review, we intend to describe different cellular functions, such as the cell cycle, DNA damage repair, chromatin remodeling and several signaling pathways, in which USPs are involved in the development or progression of cancer. In addition, we describe existing therapies that target the inhibition of USPs.

Wnt signaling related transcripts and their relationship to energy metabolism in C2C12 myoblasts under temperature stress

Temperature stress is one of the main environmental stressors affecting the welfare, health and productivity of livestock. Temperature changes can modify cell membrane components, disrupting the crosstalk between the cell and its surroundings by affecting signaling pathways including Wnt signaling pathway, which subsequently disrupts cell energy metabolism. The present study aims to understand the effect of temperature stress on the expression of genes involved in Wnt signaling pathways, and their interaction with energy metabolism in C2C12 myoblasts cells. The C2C12 cells were exposed to cold stress (35 °C), mild heat stress (39 °C) and severe heat stress (41 °C), whereas 37 °C was used as control temperature. Transcript levels of important genes involved in Wnt signaling including Axin2, Tnks2, Sfrp1, Dkk1, Dact1, Cby1, Wnt5a, Wnt7a, Wnt11, Porcn, Ror2, Daam1, and Ppp3ca were significantly altered under severe heat stress (41 °C), whereas eight Wnt signaling-related transcripts (Daam1, Ppp3ca, Fzd7, Wnt5a, Porcn, Tnks2, Lrp6, and Aes) were significantly altered under cold stress (35 °C) compared to control. Under heat stress transcripts of the Wnt/β-catenin inhibitors (Sfrp1, Dkk1, and Cby1) and negative regulators (Dact1 and Axin2) are activated. A positive correlation between oxidative phosphorylation and Wnt-related transcripts was found under high temperatures. Transcripts of the cell membrane receptors, including Lrp6 and Fzd7, and the members of Wnt/Ca⁺² signaling pathway, including Ppp3ca and Porcn were downregulated under cold stress. Many Wnt signaling-related transcripts were positively correlated with glycolysis under cold stress. These findings indicate a cross-talk between Wnt signaling and energy metabolism under thermal stress.

Single-Cell Profiling and SCOPE-Seq Reveal Lineage Dynamics of Adult Ventricular-Subventricular Zone Neurogenesis and NOTUM as a Key Regulator

In the adult ventricular-subventricular zone (V-SVZ), neural stem cells (NSCs) generate new olfactory bulb (OB) neurons and glia throughout life. To map adult neuronal lineage progression, we profiled >56,000 V-SVZ and OB cells by single-cell RNA sequencing (scRNA-seq). Our analyses reveal the molecular diversity of OB neurons, including fate-mapped neurons, lineage progression dynamics, and an NSC intermediate enriched for Notum, which encodes a secreted WNT antagonist. SCOPE-seq technology, which links live-cell imaging with scRNA-seq, uncovers cell-size transitions during NSC differentiation and preferential NOTUM binding to proliferating neuronal precursors. Consistently, application of NOTUM protein in slice cultures and pharmacological inhibition of NOTUM in slice cultures and in vivo demonstrated that NOTUM negatively regulates V-SVZ proliferation. Timely, context-dependent neurogenesis demands adaptive signaling among neighboring progenitors. Our findings highlight a critical regulatory state during NSC activation marked by NOTUM, which attenuates WNT-stimulated proliferation in NSC progeny.

CrossTORC and WNTegration in Disease: Focus on Lymphangioleiomyomatosis

The mechanistic target of rapamycin (mTOR) and wingless-related integration site (Wnt) signal transduction networks are evolutionarily conserved mammalian growth and cellular development networks. Most cells express many of the proteins in both pathways, and this review will briefly describe only the key proteins and their intra- and extracellular crosstalk. These complex interactions will be discussed in relation to cancer development, drug resistance, and stem cell exhaustion. This review will also highlight the tumor-suppressive tuberous sclerosis complex (TSC) mutated, mTOR-hyperactive lung disease of women, lymphangioleiomyomatosis (LAM). We will summarize recent advances in the targeting of these pathways by monotherapy or combination therapy, as well as future potential treatments.

Wnt/β-Catenin Signaling and Immunotherapy Resistance: Lessons for the Treatment of Urothelial Carcinoma

Urothelial cell carcinoma (UCC) is a significant public health burden. It accounts for approximately 90 percent of all bladder cancers with an estimated 200,000 annual deaths globally. Platinum based cytotoxic chemotherapy combinations are the current standard of care in the frontline setting for metastatic UCC. Even with these treatments the median overall survival is estimated to be about 15 months. Recently, immune checkpoint inhibitors (ICIs) have demonstrated superior clinical benefits compared to second line chemotherapy in UCC treatment. However only a minority of patients (~20%) respond to ICIs, which highlights the need to better understand the mechanisms behind resistance. In this review, we (i) examine the pathophysiology of Wnt/β-catenin signaling, (ii) discuss pre-clinical evidence that supports the combination of Wnt/β-catenin inhibitors and ICI, and (iii) propose future combination treatments that could be investigated through clinical trials.

Stem Cell Signaling Pathways in the Small Intestine

The ability of stem cells to divide and differentiate is necessary for tissue repair and homeostasis. Appropriate spatial and temporal mechanisms are needed. Local intercellular signaling increases expression of specific genes that mediate and maintain differentiation. Diffusible signaling molecules provide concentration-dependent induction of specific patterns of cell types or regions. Differentiation of adjacent cells, on the other hand, requires cell–cell contact and subsequent signaling. These two types of signals work together to allow stem cells to provide what organisms require. The ability to grow organoids has increased our understanding of the cellular and molecular features of small “niches” that modulate stem cell function in various organs, including the small intestine.

Parkinson's disease, aging and adult neurogenesis: Wnt/β-catenin signalling as the key to unlock the mystery of endogenous brain repair

A common hallmark of age-dependent neurodegenerative diseases is an impairment of adult neurogenesis. Wingless-type mouse mammary tumor virus integration site (Wnt)/β-catenin (WβC) signalling is a vital pathway for dopaminergic (DAergic) neurogenesis and an essential signalling system during embryonic development and aging, the most critical risk factor for Parkinson's disease (PD). To date, there is no known cause or cure for PD. Here we focus on the potential to reawaken the impaired neurogenic niches to rejuvenate and repair the aged PD brain. Specifically, we highlight WβC-signalling in the plasticity of the subventricular zone (SVZ), the largest germinal region in the mature brain innervated by nigrostriatal DAergic terminals, and the mesencephalic aqueduct-periventricular region (Aq-PVR) Wnt-sensitive niche, which is in proximity to the SNpc and harbors neural stem progenitor cells (NSCs) with DAergic potential. The hallmark of the WβC pathway is the cytosolic accumulation of β-catenin, which enters the nucleus and associates with T cell factor/lymphoid enhancer binding factor (TCF/LEF) transcription factors, leading to the transcription of Wnt target genes. Here, we underscore the dynamic interplay between DAergic innervation and astroglial-derived factors regulating WβC-dependent transcription of key genes orchestrating NSC proliferation, survival, migration and differentiation. Aging, inflammation and oxidative stress synergize with neurotoxin exposure in "turning off" the WβC neurogenic switch via down-regulation of the nuclear factor erythroid-2-related factor 2/Wnt-regulated signalosome, a key player in the maintenance of antioxidant self-defense mechanisms and NSC homeostasis. Harnessing WβC-signalling in the aged PD brain can thus restore neurogenesis, rejuvenate the microenvironment, and promote neurorescue and regeneration.

Roles of nAChR and Wnt signaling in intestinal stem cell function and inflammation

Nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels that signal using endogenous acetylcholine (ACh) and the agonist, nicotine. The nAChR signaling pathway is a central regulator of physiological homeostasis in the central and peripheral nervous systems. The receptors are expressed not only in the nervous system, but also play a pivotal role in regulation of epithelial cell growth, migration, differentiation, and inflammation processes in various mammalian non-neuronal cells. In the intestine, the Wnt signaling pathway plays a central role in the epithelium and is a principal regulator of intestinal stem cell (ISC) identity and proliferation. Since Wnt signaling was first described more than 40 years ago in ISCs, large amounts of scientific evidence have demonstrated remarkable long-term self-renewal capacity of ISCs. Intestinal organoids are commonly used for studying ISC biology and intestinal pathophysiology. The contribution of non-neuronal nAChR signaling to Wnt signaling in the intestine has received less attention. Experiments using cultured intestinal organoids that lack nerve and immune cells were performed. Endogenous ACh is synthesized in the intestinal epithelium and drives organoid growth and differentiation through activation of nAChR signaling. Furthermore, nAChR signaling is coordinated with Wnt signaling for regulation of ISC function. Elucidating the mechanism of the coordinated activities of nAChR and Wnt signaling in the intestine provides new insight into epithelial homeostasis, and may be of particular relevance in inflammatory bowel diseases such as ulcerative colitis and Crohn's disease.

Molecular Pharmacology of Class F Receptor Activation

The class Frizzled (FZD) or class F of G protein-coupled receptors consists of 10 FZD paralogues and Smoothened (SMO). FZDs coordinate wingless/Int-1 signaling and SMO mediates Hedgehog signaling. Class F receptor signaling is intrinsically important for embryonic development and its dysregulation leads to diseases, including diverse forms of tumors. With regard to the importance of class F signaling in human disease, these receptors provide an attractive target for therapeutics, exemplified by the use of SMO antagonists for the treatment of basal cell carcinoma. Here, we review recent structural insights in combination with a more detailed functional understanding of class F receptor activation, G protein coupling, conformation-based functional selectivity, and mechanistic details of activating cancer mutations, which will lay the basis for further development of class F-targeting small molecules for human therapy. SIGNIFICANCE STATEMENT: Stimulated by recent insights into the activation mechanisms of class F receptors from structural and functional analysis of Frizzled and Smoothened, we aim to summarize what we know about the molecular details of ligand binding, agonist-driven conformational changes, and class F receptor activation. A better understanding of receptor activation mechanisms will allow us to engage in structure- and mechanism-driven drug discovery with the potential to develop more isoform-selective and potentially pathway-selective drugs for human therapy.

Macrophages as an Emerging Source of Wnt Ligands: Relevance in Mucosal Integrity

The Wnt signaling pathway is a conserved pathway involved in important cellular processes such as the control of embryonic development, cellular polarity, cellular migration, and cell proliferation. In addition to playing a central role during embryogenesis, this pathway is also an essential part of adult homeostasis. Indeed, it controls the proliferation of epithelial cells in different organs such as intestine, lung, and kidney, and guarantees the maintenance of the mucosa in physiological conditions. The origin of this molecular pathway is the binding between Wnt ligands (belonging to a family of 19 different homologous secreted glycoproteins) and their specific membrane receptors, from the Frizzled receptor family. This specific interaction triggers the activation of the signaling cascade, which in turn activates or suppresses the expression of different genes in order to change the behavior of the cell. On the other hand, alterations of this pathway have been described in pathological conditions such as inflammation, fibrosis, and cancer. In recent years, macrophages-among other cell types-have emerged as a potential source of Wnt ligands. Due to their high plasticity, macrophages, which are central to the innate immune response, are capable of adopting different phenotypes depending on their microenvironment. In the past, two different phenotypes were described: a proinflammatory phenotype-M1 macrophages-and an anti-inflammatory phenotype-M2 macrophages-and a selective expression of Wnt ligands has been associated with said phenotypes. However, nowadays it is assumed that macrophages in vivo move through a continual spectrum of functional phenotypes. In both physiological and pathological (inflammation, fibrosis and cancer) conditions, the accumulation and polarization of macrophages conditions the future of the tissue, facilitating various scenarios, such as resolution of inflammation, activation of fibrosis, and cancer development due to the modulation of the Wnt signaling pathway, in autocrine and paracrine manner. In this work, we provide an overview of studies that have explored the role of macrophages and how they act as a source of Wnt ligands and as mediators of mucosal integrity.

AdipoRon Attenuates Wnt Signaling by Reducing Cholesterol-Dependent Plasma Membrane Rigidity

The increasing prevalence of adult and adolescent obesity and its associated risk of colorectal cancer reinforces the urgent need to elucidate the underlying mechanisms contributing to the promotion of colon cancer in obese individuals. Adiponectin is an adipose tissue-derived adipokine, whose levels are reduced during obesity. Both epidemiological and preclinical data indicate that adiponectin suppresses colon tumorigenesis. We have previously demonstrated that both adiponectin and AdipoRon, a small-molecule adiponectin receptor agonist, suppress colon cancer risk in part by reducing the number of Lgr5⁺ stem cells in mouse colonic organoids. However, the mechanism by which the adiponectin signaling pathway attenuates colon cancer risk remains to be addressed. Here, we have hypothesized that adiponectin signaling supports colonic stem cell maintenance through modulation of the biophysical properties of the plasma membrane (PM). Specifically, we investigated the effects of adiponectin receptor activation by AdipoRon on the biophysical perturbations linked to the attenuation of Wnt-driven signaling and cell proliferation as determined by LEF luciferase reporter assay and colonic organoid proliferation, respectively. Using physicochemical sensitive dyes, Di-4-ANEPPDHQ and C-laurdan, we demonstrated that AdipoRon decreased the rigidity of the colonic cell PM. The decrease in membrane rigidity was associated with a reduction in PM free cholesterol levels and the intracellular accumulation of free cholesterol in lysosomes. These results suggest that adiponectin signaling plays a role in modulating cellular cholesterol homeostasis, PM biophysical properties, and Wnt-driven signaling. These findings are noteworthy because they may in part explain how obesity drives colon cancer progression.

WNT-3A-induced β-catenin signaling does not require signaling through heterotrimeric G proteins

The network of Wingless/Int-1 (WNT)-induced signaling pathways includes β-catenin-dependent and -independent pathways. β-Catenin regulates T cell factor/lymphoid enhancer-binding factor (TCF/LEF)-mediated gene transcription, and in response to WNTs, β-catenin signaling is initiated through engagement of a Frizzled (FZD)/LDL receptor-related protein 5/6 (LRP5/6) receptor complex. FZDs are G protein-coupled receptors, but the question of whether heterotrimeric G proteins are involved in WNT/β-catenin signaling remains unanswered. Here, we investigate whether acute activation of WNT/β-catenin signaling by purified WNT-3A requires functional signaling through heterotrimeric G proteins. Using genome editing, we ablated expression of G_s/G_olf/G_q/G₁₁/G₁₂/G₁₃/G_z in HEK293 (ΔG7) cells, leaving the expression of pertussis toxin (PTX)-sensitive G_i/o proteins unchanged, to assess whether WNT-3A activates WNT/β-catenin signaling in WT and ΔG7 cells devoid of functional G protein signaling. We monitored WNT-3A-induced activation by detection of phosphorylation of LDL receptor-related protein 6 (LRP6), electrophoretic mobility shift of the phosphoprotein Dishevelled (DVL), β-catenin stabilization and dephosphorylation, and TCF-dependent transcription. We found that purified, recombinant WNT-3A efficiently induces WNT/β-catenin signaling in ΔG7 cells in both the absence and presence of G_i/o-blocking PTX. Furthermore, cells completely devoid of G protein expression, so called Gα-depleted HEK293 cells, maintain responsiveness to WNT-3A with regard to the hallmarks of WNT/β-catenin signaling. These findings corroborate the concept that heterotrimeric G proteins are not required for this FZD- and DVL-mediated signaling branch. Our observations agree with previous results arguing for FZD conformation-dependent functional selectivity between DVL and heterotrimeric G proteins. In conclusion, WNT/β-catenin signaling through FZDs does not require the involvement of heterotrimeric G proteins.

Dickkopf1: An immunomodulatory ligand and Wnt antagonist in pathological inflammation

The Wnt signaling pathway plays essential roles in tissue or organ homeostasis by regulating cell proliferation and differentiation. Upon tissue or organ injury, inflammation is coupled with tissue repair and regeneration process. The canonical Wnt signaling transduction pathway is crucial for cell proliferation, cell differentiation, and tissue regeneration. Dickkopf1 (DKK1) is a quintessential Wnt antagonist that inhibits the Wnt-mediated tissue repair process. Recent studies reported increased levels of DKK1 in many diseases such as cancer, infection, and musculoskeletal diseases. In many cases, the role of DKK1 has been identified as a pro-inflammatory ligand and the expression levels are associated with poor disease outcomes. A variety of cell types including platelets, endothelial cells, and cancer cells secrete DKK1 upon stimuli. This puts DKK1 in a unique place to view immune responses from multicellular interactions in tissue injury and repair process. In this review, we discuss recent efforts to address the underlying mechanism regarding the pro-inflammatory role of DKK1 in cancer, bone diseases, and other inflammatory diseases.

Divergent Axin and GSK-3 paralogs in the beta-catenin destruction complexes of tapeworms

The Wnt/beta-catenin pathway has many key roles in the development of animals, including a conserved and central role in the specification of the primary (antero-posterior) body axis. The posterior expression of Wnt ligands and the anterior expression of secreted Wnt inhibitors are known to be conserved during the larval metamorphosis of tapeworms. However, their downstream signaling components for Wnt/beta-catenin signaling have not been characterized. In this work, we have studied the core components of the beta-catenin destruction complex of the human pathogen Echinococcus multilocularis, the causative agent of alveolar echinococcosis. We focused on two Axin paralogs that are conserved in tapeworms and other flatworm parasites. Despite their divergent sequences, both Axins could robustly interact with one E. multilocularis beta-catenin paralog and limited its accumulation in a heterologous mammalian expression system. Similarly to what has been described in planarians (free-living flatworms), other beta-catenin paralogs showed limited or no interaction with either Axin and are unlikely to function as effectors in Wnt signaling. Additionally, both Axins interacted with three divergent GSK-3 paralogs that are conserved in free-living and parasitic flatworms. Axin paralogs have highly segregated expression patterns along the antero-posterior axis in the tapeworms E. multilocularis and Hymenolepis microstoma, indicating that different beta-catenin destruction complexes may operate in different regions during their larval metamorphosis.

Wnt/β-Catenin Signaling Pathway Governs a Full Program for Dopaminergic Neuron Survival, Neurorescue and Regeneration in the MPTP Mouse Model of Parkinson's Disease

Wingless-type mouse mammary tumor virus (MMTV) integration site (Wnt) signaling is one of the most critical pathways in developing and adult tissues. In the brain, Wnt signaling contributes to different neurodevelopmental aspects ranging from differentiation to axonal extension, synapse formation, neurogenesis, and neuroprotection. Canonical Wnt signaling is mediated mainly by the multifunctional β-catenin protein which is a potent co-activator of transcription factors such as lymphoid enhancer factor (LEF) and T-cell factor (TCF). Accumulating evidence points to dysregulation of Wnt/β-catenin signaling in major neurodegenerative disorders. This review highlights a Wnt/β-catenin/glial connection in Parkinson's disease (PD), the most common movement disorder characterized by the selective death of midbrain dopaminergic (mDAergic) neuronal cell bodies in the subtantia nigra pars compacta (SNpc) and gliosis. Major findings of the last decade document that Wnt/β-catenin signaling in partnership with glial cells is critically involved in each step and at every level in the regulation of nigrostriatal DAergic neuronal health, protection, and regeneration in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD, focusing on Wnt/β-catenin signaling to boost a full neurorestorative program in PD.

Canonical and Non-Canonical Wnt Signaling in Immune Cells

Cell differentiation, proliferation, and death are vital for immune homeostasis. Wnt signaling plays essential roles in processes across species. The roles of Wnt signaling proteins and Wnt ligands have been studied in the past, but the context-dependent mechanisms and functions of these pathways in immune responses remain unclear. Recent findings regarding the role of Wnt ligands and Wnt signaling in immune cells and their immunomodulatory mechanisms suggest that Wnt ligands and signaling are significant in regulating immune responses. We introduce recent key findings and future perspectives on Wnt ligands and their signaling pathways in immune cells as well as the immunological roles and functions of Wnt antagonists.

A molecular mechanism for Wnt ligand-specific signaling

Wnt signaling is key to many developmental, physiological, and disease processes in which cells seem able to discriminate between multiple Wnt ligands. This selective Wnt recognition or "decoding" capacity has remained enigmatic because Wnt/Frizzled interactions are largely incompatible with monospecific recognition. Gpr124 and Reck enable brain endothelial cells to selectively respond to Wnt7. We show that Reck binds with low micromolar affinity to the intrinsically disordered linker region of Wnt7. Availability of Reck-bound Wnt7 for Frizzled signaling relies on the interaction between Gpr124 and Dishevelled. Through polymerization, Dishevelled recruits Gpr124 and the associated Reck-bound Wnt7 into dynamic Wnt/Frizzled/Lrp5/6 signalosomes, resulting in increased local concentrations of Wnt7 available for Frizzled signaling. This work provides mechanistic insights into the Wnt decoding capacities of vertebrate cells and unravels structural determinants of the functional diversification of Wnt family members.

WNT signalling: mechanisms and therapeutic opportunities

This themed section of the British Journal of Pharmacology stems from the EMBO Conference: Wnt Meeting 2016 held from the 14^th to 16^th September 2016 in Brno, Czech Republic.

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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.

Identification of the miRNA-mRNA regulatory network of small cell osteosarcoma based on RNA-seq

Small cell osteosarcoma (SCO) is a rare subtype of osteosarcoma characterized by highly aggressive progression and a poor prognosis. The miRNA and mRNA expression profiles of peripheral blood mononuclear cells (PBMCs) were obtained in 3 patients with SCO and 10 healthy individuals using high-throughput RNA-sequencing. We identified 37 dysregulated miRNAs and 1636 dysregulated mRNAs in patients with SCO compared to the healthy controls. Specifically, the 37 dysregulated miRNAs consisted of 27 up-regulated miRNAs and 10 down-regulated miRNAs; the 1636 dysregulated mRNAs consisted of 555 up-regulated mRNAs and 1081 down-regulated mRNAs. The target-genes of miRNAs were predicted, and 1334 negative correlations between miRNAs and mRNAs were used to construct an miRNA-mRNA regulatory network. Dysregulated genes were significantly enriched in pathways related to cancer, mTOR signaling and cell cycle signaling. Specifically, hsa-miR-26b-5p, hsa-miR-221-3p and hsa-miR-125b-2-3p were significantly dysregulated miRNAs and exhibited a high degree of connectivity with target genes. Overall, the expression of dysregulated genes in tumor tissues and peripheral blood samples of patients with SCO measured by quantitative real-time polymerase chain reaction corroborated with our bioinformatics analyses based on the expression profiles of PBMCs from patients with SCO. Thus, hsa-miR-26b-5p, hsa-miR-221-3p and hsa-miR-125b-2-3p may be involved in SCO tumorigenesis.

Potential Mechanisms of Action of Dietary Phytochemicals for Cancer Prevention by Targeting Cellular Signaling Transduction Pathways

Cancer is a severe health problem that significantly undermines life span and quality. Dietary approach helps provide preventive, nontoxic, and economical strategies against cancer. Increased intake of fruits, vegetables, and whole grains are linked to reduced risk of cancer and other chronic diseases. The anticancer activities of plant-based foods are related to the actions of phytochemicals. One potential mechanism of action of anticancer phytochemicals is that they regulate cellular signal transduction pathways and hence affects cancer cell behaviors such as proliferation, apoptosis, and invasion. Recent publications have reported phytochemicals to have anticancer activities through targeting a wide variety of cell signaling pathways at different levels, such as transcriptional or post-transcriptional regulation, protein activation and intercellular messaging. In this review, we discuss major groups of phytochemicals and their regulation on cell signaling transduction against carcinogenesis via key participators, such as Nrf2, CYP450, MAPK, Akt, JAK/STAT, Wnt/β-catenin, p53, NF-κB, and cancer-related miRNAs.

The biochemistry, signalling and disease relevance of RYK and other WNT-binding receptor tyrosine kinases

The receptor tyrosine kinases (RTKs) are a well-characterized family of growth factor receptors that have central roles in human disease and are frequently therapeutically targeted. The RYK, ROR, PTK7 and MuSK subfamilies make up an understudied subset of WNT-binding RTKs. Numerous developmental, stem cell and pathological roles of WNTs, in particular WNT5A, involve signalling via these WNT receptors. The WNT-binding RTKs have highly context-dependent signalling outputs and stimulate the β-catenin-dependent, planar cell polarity and/or WNT/Ca²⁺ pathways. RYK, ROR and PTK7 members have a pseudokinase domain in their intracellular regions. Alternative signalling mechanisms, including proteolytic cleavage and protein scaffolding functions, have been identified for these receptors. This review explores the structure, signalling, physiological and pathological roles of RYK, with particular attention paid to cancer and the possibility of therapeutically targeting RYK. The other WNT-binding RTKs are compared with RYK throughout to highlight the similarities and differences within this subset of WNT receptors.

Wingless/Wnt Signaling in Intestinal Development, Homeostasis, Regeneration and Tumorigenesis: A Drosophila Perspective

In mammals, the Wnt/β-catenin signal transduction pathway regulates intestinal stem cell maintenance and proliferation, whereas Wnt pathway hyperactivation, resulting primarily from the inactivation of the tumor suppressor Adenomatous polyposis coli (APC), triggers the development of the vast majority of colorectal cancers. The Drosophila adult gut has recently emerged as a powerful model to elucidate the mechanisms by which Wingless/Wnt signaling regulates intestinal development, homeostasis, regeneration, and tumorigenesis. Herein, we review recent insights on the roles of Wnt signaling in Drosophila intestinal physiology and pathology.

Podoplanin regulates mammary stem cell function and tumorigenesis by potentiating Wnt/β-catenin signaling

Stem cells (SCs) drive mammary development, giving rise postnatally to an epithelial bilayer composed of luminal and basal myoepithelial cells. Dysregulation of SCs is thought to be at the origin of certain breast cancers; however, the molecular identity of SCs and the factors regulating their function remain poorly defined. We identified the transmembrane protein podoplanin (Pdpn) as a specific marker of the basal compartment, including multipotent SCs, and found Pdpn localized at the basal-luminal interface. Embryonic deletion of Pdpn targeted to basal cells diminished basal and luminal SC activity and affected the expression of several Wnt/β-catenin signaling components in basal cells. Moreover, Pdpn loss attenuated mammary tumor formation in a mouse model of β-catenin-induced breast cancer, limiting tumor-initiating cell expansion and promoting molecular features associated with mesenchymal-to-epithelial cell transition. In line with the loss-of-function data, we demonstrated that mechanistically Pdpn enhances Wnt/β-catenin signaling in mammary basal cells. Overall, this study uncovers a role for Pdpn in mammary SC function and, importantly, identifies Pdpn as a new regulator of Wnt/β-catenin signaling, a key pathway in mammary development and tumorigenesis.

Overexpressed ACBD3 has prognostic value in human breast cancer and promotes the self-renewal potential of breast cancer cells by activating the Wnt/beta-catenin signaling pathway

Acyl-CoA binding domain containing 3 (ACBD3) is involved in the maintenance of Golgi structure and function through its interaction with the integral membrane protein. However, the clinical significance and biological role of ACBD3 in breast cancer remain unclear. Herein, we found that the mRNA and protein levels of ACBD3 were markedly up-regulated in breast cancer cells and tissues. Immunohistochemical analysis of breast cancer tissues demonstrated that ACBD3 overexpression was significantly associated with advanced clinicopathological features. Univariate and multivariate analysis indicated that ACBD3 overexpression correlates with poor prognosis in breast cancer. Furthermore, overexpressing ACBD3 promoted, while silencing ACBD3 inhibited, self-renewal and tumorigenesis in breast cancer cells in vitro and in vivo respectively. Importantly, upregulating ACBD3 promoted the self-renewal and tumorigenesis of breast cancer cells via activating the Wnt/beta-catenin signaling, and the pro-self-renewal effect of ACBD3 in breast cancer was antagonized by the Wnt signaling inhibitor TCF4-siRNA and Lef1-siRNA.These findings indicate that ACBD3 may represent candidate therapeutic targets to enable the elimination of breast cancer stem cells, providing the preclinical proof-of-concept for the prevention and treatment of breast cancer.

The Central Role of Wnt Signaling and Organoid Technology in Personalizing Anticancer Therapy

The Wnt pathway is at the heart of organoid technology, which is set to revolutionize the cancer field. We can now predetermine a patient's response to any given anticancer therapy by exposing tumor organoids established from the patient's own tumor. This cutting-edge biomedical platform translates to patients being treated with the correct drug at the correct dose from the outset, a truly personalized and precise medical approach. A high throughput drug screen on organoids also allows drugs to be tested in limitless combinations. More recently, the tumor cells that are resistant to the therapy given to a patient were selected in culture using the patient's organoids. The resistant tumor organoids were then screened empirically to identify drugs that will kill the resistant cells. This information allows diagnosis in real-time to either prevent tumor recurrence or effectively treat the recurring tumor. Furthermore, the ability to culture stem cell-derived epithelium as organoids has enabled us to begin to understand how a stem cell becomes a cancer cell or to pin-point the genetic alteration that underlies a given genetic syndrome. Here we summarize these advances and the central role of Wnt signaling, and identify the next challenges for organoid technology.

Inhibition of nuclear Wnt signalling: challenges of an elusive target for cancer therapy

The highly conserved Wnt signalling pathway plays an important role in embryonic development and disease pathogenesis, most notably cancer. The 'canonical' or β-catenin-dependent Wnt signal initiates at the cell plasma membrane with the binding of Wnt proteins to Frizzled:LRP5/LRP6 receptor complexes and is mediated by the translocation of the transcription co-activator protein, β-catenin, into the nucleus. β-Catenin then forms a complex with T-cell factor (TCF)/lymphoid enhancer binding factor (LEF) transcription factors to regulate multiple gene programmes. These programmes play roles in cell proliferation, migration, vasculogenesis, survival and metabolism. Mutations in Wnt signalling pathway components lead to constitutively active Wnt signalling that drives aberrant expression of these programmes and development of cancer. It has been a longstanding and challenging goal to develop therapies that can interfere with the TCF/LEF-β-catenin transcriptional complex. This review will focus on the (i) structural considerations for targeting the TCF/LEF-β-catenin and co-regulatory complexes in the nucleus, (ii) current molecules that directly target TCF/LEF-β-catenin activity and (iii) ideas for targeting newly discovered components of the TCF/LEF-β-catenin complex and/or downstream gene programmes regulated by these complexes.

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.

WNT signalling events near the cell membrane and their pharmacological targeting for the treatment of cancer

WNT signalling is an essential signalling pathway for all multicellular animals. Although first described more than 30 years ago, new components and regulators of the pathway are still being discovered. Considering its importance in both embryonic development and adult homeostasis, it is not surprising that this pathway is often deregulated in human diseases such as cancer. Recently, it became clear that in addition to cytoplasmic components such as β-catenin, other, membrane-bound or extracellular, components of the WNT pathway are also altered in cancer. This review gives an overview of the recent discoveries on WNT signalling events near the cell membrane. Furthermore, membrane-associated components of the WNT pathway, which are more accessible for therapeutic intervention, as well therapeutic approaches that already target those components will be discussed. In this way, we hope to stimulate the development of effective anti-cancer therapies that target this fascinating pathway.

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.

The crystal structure of full-length Sizzled from Xenopus laevis yields insights into Wnt-antagonistic function of secreted Frizzled-related proteins

The Wnt-signaling pathway is crucial to cell proliferation, differentiation, and migration. The secreted Frizzled-related proteins (sFRPs) represent the largest family of secreted Wnt inhibitors. However, their function in antagonizing Wnt signaling has remained somewhat controversial. Here, we report the crystal structure of Sizzled from Xenopus laevis, the first full-length structure of an sFRP. Tethered by an inter-domain disulfide bond and a linker, the N-terminal cysteine-rich domain (CRD) and the C-terminal netrin-like domain (NTR) of Sizzled are arranged in a tandem fashion, with the NTR domain occluding the groove of CRD for Wnt accessibility. A Dual-Luciferase assay demonstrated that removing the NTR domain and replacing the CRD groove residues His-116 and His-118 with aromatic residues may significantly enhance antagonistic function of Sizzled in inhibiting Wnt3A signaling. Sizzled is a monomer in solution, and Sizzled CRD exhibited different packing in the crystal, suggesting that sFRPs do not have a conserved CRD dimerization mode. Distinct from the canonical NTR domain, the Sizzled NTR adopts a novel α/β folding with two perpendicular helices facing the central mixed β-sheet. The subgroup of human sFRP1/2/5 and Sizzled should have a similar NTR domain that features a highly positively charged region, opposite the NTR-CRD interface, suggesting that the NTR domain in human sFRPs, at least sFRP1/2/5, is unlikely to bind to Wnt but is likely involved in biphasic Wnt signaling modulation. In summary, the Sizzled structure provides the first insights into how the CRD and the NTR domains relate to each other for modulating Wnt-antagonistic function of sFRPs.