Plakoglobin and beta-catenin: protein interactions, regulation and biological roles

Mechanism and application of feedback loops formed by mechanotransduction and histone modifications

Mechanical stimulation is the key physical factor in cell environment. Mechanotransduction acts as a fundamental regulator of cell behavior, regulating cell proliferation, differentiation, apoptosis, and exhibiting specific signature alterations during the pathological process. As research continues, the role of epigenetic science in mechanotransduction is attracting attention. However, the molecular mechanism of the synergistic effect between mechanotransduction and epigenetics in physiological and pathological processes has not been clarified. We focus on how histone modifications, as important components of epigenetics, are coordinated with multiple signaling pathways to control cell fate and disease progression. Specifically, we propose that histone modifications can form regulatory feedback loops with signaling pathways, that is, histone modifications can not only serve as downstream regulators of signaling pathways for target gene transcription but also provide feedback to regulate signaling pathways. Mechanotransduction and epigenetic changes could be potential markers and therapeutic targets in clinical practice.

Canonical and noncanonical Wnt signaling: Multilayered mediators, signaling mechanisms and major signaling crosstalk

Wnt signaling plays a major role in regulating cell proliferation and differentiation. The Wnt ligands are a family of 19 secreted glycoproteins that mediate their signaling effects via binding to Frizzled receptors and LRP5/6 coreceptors and transducing the signal either through β-catenin in the canonical pathway or through a series of other proteins in the noncanonical pathway. Many of the individual components of both canonical and noncanonical Wnt signaling have additional functions throughout the body, establishing the complex interplay between Wnt signaling and other signaling pathways. This crosstalk between Wnt signaling and other pathways gives Wnt signaling a vital role in many cellular and organ processes. Dysregulation of this system has been implicated in many diseases affecting a wide array of organ systems, including cancer and embryological defects, and can even cause embryonic lethality. The complexity of this system and its interacting proteins have made Wnt signaling a target for many therapeutic treatments. However, both stimulatory and inhibitory treatments come with potential risks that need to be addressed. This review synthesized much of the current knowledge on the Wnt signaling pathway, beginning with the history of Wnt signaling. It thoroughly described the different variants of Wnt signaling, including canonical, noncanonical Wnt/PCP, and the noncanonical Wnt/Ca2+ pathway. Further description involved each of its components and their involvement in other cellular processes. Finally, this review explained the various other pathways and processes that crosstalk with Wnt signaling.

Downregulation of γ-Catenin by miR-195-5p Inhibits Colon Cancer Progression, Regulating Desmosome Function

Desmosomes are essential structures for ensuring tissue functions, and their deregulation is involved in the development of colorectal cancer (CRC). JUP (γ-catenin) is a desmosome adhesion component that also acts as a signaling hub, suggesting its potential involvement in CRC progression. In this context, we recently demonstrated that miR-195-5p regulated JUP and desmosome cadherins expression. In addition, miR-195-5p gain of function indirectly modulated the expression of key effectors of the Wnt pathway involved in JUP-dependent signaling. Here, our purpose was to demonstrate the aberrant expression of miR-195-5p and JUP in CRC patients and to functionally characterize the role of miR-195-5p in the regulation of desmosome function. First, we showed that miR-195-5p was downregulated in CRC tumors compared to adjacent normal tissue. Then, we demonstrated that JUP expression was significantly increased in CRC tissues compared to adjacent normal tissues. The effects of miR-195-5p on CRC progression were assessed using in vitro transient transfection experiments and in vivo miRNA administration. Increased miR-195-5p in colonic epithelial cells strongly inhibits cell proliferation, viability, and invasion via JUP. In vivo gain of function of miR-195-5p reduced the numbers and sizes of tumors and significantly ameliorated the histopathological changes typical of CRC. In conclusion, our findings indicate a potential pharmacological target based on miR-195-5p replacement as a new therapeutic approach in CRC.

Liver cancer stem cell dissemination and metastasis: uncovering the role of NRCAM in hepatocellular carcinoma

BACKGROUND

Liver cancer stem cells (LCSCs) play an important role in hepatocellular carcinoma (HCC), but the mechanisms that link LCSCs to HCC metastasis remain largely unknown. This study aims to reveal the contributions of NRCAM to LCSC function and HCC metastasis, and further explore its mechanism in detail.

METHODS

117 HCC and 29 non-HCC patients with focal liver lesions were collected and analyzed to assess the association between NRCAM and HCC metastasis. Single-cell RNA sequencing (scRNA-seq) was used to explore the biological characteristics of cells with high NRCAM expression in metastatic HCC. The role and mechanism of NRCAM in LCSC dissemination and metastasis was explored in vitro and in vivo using MYC-driven LCSC organoids from murine liver cells.

RESULTS

Serum NRCAM is associated with HCC metastasis and poor prognosis. A scRNA-seq analysis identified that NRCAM was highly expressed in LCSCs with MYC activation in metastatic HCC. Moreover, NRCAM facilitated LCSC migration and invasion, which was confirmed in MYC-driven LCSC organoids. The in vivo tumor allografts demonstrated that NRCAM mediated intra-hepatic/lung HCC metastasis by enhancing the ability of LCSCs to escape from tumors into the bloodstream. Nrcam expression inhibition in LCSCs blocked HCC metastasis. Mechanistically, NRCAM activated epithelial-mesenchymal transition (EMT) and metastasis-related matrix metalloproteinases (MMPs) through the MACF1 mediated β-catenin signaling pathway in LCSCs.

CONCLUSIONS

LCSCs typified by high NRCAM expression have a strong ability to invade and migrate, which is an important factor leading to HCC metastasis.

LY6/PLAUR domain containing 3 (LYPD3) maintains melanoma cell stemness and mediates an immunosuppressive microenvironment

BACKGROUND

Malignant melanoma is a highly heterogeneous skin cancer with the highest mortality rate among dermatological cancers. Catenins form functional networks in the nucleus to regulate gene expression and determine cell fate. Dysregulation of catenin expression correlates with the malignant characteristics of the tumor. We aimed to investigate the regulatory mechanisms of catenins in melanoma and to further define the function of catenin-related molecular signaling in the tumor microenvironment.

METHODS

In this study, a bioinformatics approach combined with experimental validation was used to explore the potential tumor biology mechanisms of catenin-related signaling.

RESULTS

Melanoma patients can be divided into two catenin clusters. Patients defined by high Junction Plakoglobin (JUP), Plakophilin 1 (PKP1), Plakophilin 3 (PKP3) levels (C2) had shorter survival time than other patients (C1). We demonstrated that JUP regulates Anterior Gradient 2 (AGR2)/LY6/PLAUR Domain Containing 3 (LYPD3) to maintain melanoma stemness and promotes glycolysis. We also found that LYPD3 was co-expressed with S100A9 and associated with immunosuppressive tumor microenvironment (TME).

CONCLUSION

The JUP/AGR2/LYPD3 signaling axis plays an important role in the malignant features of melanoma. Targeting the JUP/AGR2/LYPD3 signaling axis can help develop promising drugs.

Spatiotemporal cell junction assembly in human iPSC-CM models of arrhythmogenic cardiomyopathy

Arrhythmogenic cardiomyopathy (ACM) is an inherited cardiac disorder that causes life-threatening arrhythmias and myocardial dysfunction. Pathogenic variants in Plakophilin-2 (PKP2), a desmosome component within specialized cardiac cell junctions, cause the majority of ACM cases. However, the molecular mechanisms by which PKP2 variants induce disease phenotypes remain unclear. Here we built bioengineered platforms using genetically modified human induced pluripotent stem cell-derived cardiomyocytes to model the early spatiotemporal process of cardiomyocyte junction assembly in vitro. Heterozygosity for truncating variant PKP2R413X reduced Wnt/β-catenin signaling, impaired myofibrillogenesis, delayed mechanical coupling, and reduced calcium wave velocity in engineered tissues. These abnormalities were ameliorated by SB216763, which activated Wnt/β-catenin signaling, improved cytoskeletal organization, restored cell junction integrity in cell pairs, and improved calcium wave velocity in engineered tissues. Together, these findings highlight the therapeutic potential of modulating Wnt/β-catenin signaling in a human model of ACM.

Aquaporin water channels: roles beyond renal water handling

Aquaporin (AQP) water channels are pivotal to renal water handling and therefore in the regulation of body water homeostasis. However, beyond the kidney, AQPs facilitate water reabsorption and secretion in other cells and tissues, including sweat and salivary glands and the gastrointestinal tract. A growing body of evidence has also revealed that AQPs not only facilitate the transport of water but also the transport of several small molecules and gases such as glycerol, H2O2, ions and CO2. Moreover, AQPs are increasingly understood to contribute to various cellular processes, including cellular migration, adhesion and polarity, and to act upstream of several intracellular and intercellular signalling pathways to regulate processes such as cell proliferation, apoptosis and cell invasiveness. Of note, several AQPs are highly expressed in multiple cancers, where their expression can correlate with the spread of cancerous cells to lymph nodes and alter the response of cancers to conventional chemotherapeutics. These data suggest that AQPs have diverse roles in various homeostatic and physiological systems and may be exploited for prognostics and therapeutic interventions.

Desmoglein 2 Functions as a Receptor for Fatty Acid Binding Protein 4 in Breast Cancer Epithelial Cells

Fatty acid binding protein 4 (FABP4) is a secreted adipokine linked to obesity and progression of a variety of cancers. Obesity increases extracellular FABP4 (eFABP4) levels in animal models and in obese breast cancer patients compared with lean healthy controls. Using MCF-7 and T47D breast cancer epithelial cells, we show herein that eFABP4 stimulates cellular proliferation in a time and concentration dependent manner while the non-fatty acid-binding mutant, R126Q, failed to potentiate growth. When E0771 murine breast cancer cells were injected into mice, FABP4 null animals exhibited delayed tumor growth and enhanced survival compared with injections into control C57Bl/6J animals. eFABP4 treatment of MCF-7 cells resulted in a significant increase in phosphorylation of extracellular signal-regulated kinase 1/2 (pERK), transcriptional activation of nuclear factor E2-related factor 2 (NRF2) and corresponding gene targets ALDH1A1, CYP1A1, HMOX1, SOD1 and decreased oxidative stress, while R126Q treatment did not show any effects. Proximity-labeling employing an APEX2-FABP4 fusion protein revealed several proteins functioning in desmosomes as eFABP4 receptor candidates including desmoglein (DSG), desmocollin, junction plankoglobin, desomoplankin, and cytokeratins. AlphaFold modeling predicted an interaction between eFABP4, and the extracellular cadherin repeats of DSG2 and pull-down and immunoprecipitation assays confirmed complex formation that was potentiated by oleic acid. Silencing of DSG2 in MCF-7 cells attenuated eFABP4 effects on cellular proliferation, pERK levels, and ALDH1A1 expression compared with controls.

IMPLICATIONS

These results suggest desmosomal proteins, and in particular desmoglein 2, may function as receptors of eFABP4 and provide new insight into the development and progression of obesity-associated cancers.

Omics Analyses of Stromal Cells from ACM Patients Reveal Alterations in Chromatin Organization and Mitochondrial Homeostasis

Arrhythmogenic cardiomyopathy (ACM) is a genetic disorder characterized by ventricular arrhythmias, contractile dysfunctions and fibro-adipose replacement of myocardium. Cardiac mesenchymal stromal cells (CMSCs) participate in disease pathogenesis by differentiating towards adipocytes and myofibroblasts. Some altered pathways in ACM are known, but many are yet to be discovered. We aimed to enrich the understanding of ACM pathogenesis by comparing epigenetic and gene expression profiles of ACM-CMSCs with healthy control (HC)-CMSCs. Methylome analysis identified 74 differentially methylated nucleotides, most of them located on the mitochondrial genome. Transcriptome analysis revealed 327 genes that were more expressed and 202 genes that were less expressed in ACM- vs. HC-CMSCs. Among these, genes implicated in mitochondrial respiration and in epithelial-to-mesenchymal transition were more expressed, and cell cycle genes were less expressed in ACM- vs. HC-CMSCs. Through enrichment and gene network analyses, we identified differentially regulated pathways, some of which never associated with ACM, including mitochondrial functioning and chromatin organization, both in line with methylome results. Functional validations confirmed that ACM-CMSCs exhibited higher amounts of active mitochondria and ROS production, a lower proliferation rate and a more pronounced epicardial-to-mesenchymal transition compared to the controls. In conclusion, ACM-CMSC-omics revealed some additional altered molecular pathways, relevant in disease pathogenesis, which may constitute novel targets for specific therapies.

Adherens junction proteins on the move—From the membrane to the nucleus in intestinal diseases

The function and structure of the mammalian epithelial cell layer is maintained by distinct intercellular adhesion complexes including adherens junctions (AJs), tight junctions, and desmosomes. The AJ is most integral for stabilizing cell-cell adhesion and conserving the structural integrity of epithelial tissues. AJs are comprised of the transmembrane protein E-cadherin and cytoplasmic catenin cofactors (α, β, γ, and p120-catenin). One organ where malfunction of AJ is a major contributor to disease states is the mammalian intestine. In the intestine, cell-cell adhesion complexes work synergistically to maintain structural integrity and homeostasis of the epithelium and prevent its malfunction. Consequently, when AJ integrity is compromised in the intestinal epithelium, the ensuing homeostatic disruption leads to diseases such as inflammatory bowel disease and colorectal carcinoma. In addition to their function at the plasma membrane, protein components of AJs also have nuclear functions and are thus implicated in regulating gene expression and intracellular signaling. Within the nucleus, AJ proteins have been shown to interact with transcription factors such as TCF/LEF and Kaiso (ZBTB33), which converge on the canonical Wnt signaling pathway. The multifaceted nature of AJ proteins highlights their complexity in modulating homeostasis and emphasizes the importance of their subcellular localization and expression in the mammalian intestine. In this review, we summarize the nuclear roles of AJ proteins in intestinal tissues; their interactions with transcription factors and how this leads to crosstalk with canonical Wnt signaling; and how nuclear AJ proteins are implicated in intestinal homeostasis and disease.

Role of Cell-Cell Junctions in Oesophageal Squamous Cell Carcinoma

Cell-cell junctions comprise various structures, including adherens junctions, tight junctions, desmosomes, and gap junctions. They link cells to each other in tissues and regulate tissue homeostasis in critical cellular processes. Recent advances in cell-cell junction research have led to critical discoveries. Cell-cell adhesion components are important for the invasion and metastasis of tumour cells, which are not only related to cell-cell adhesion changes, but they are also involved in critical molecular signal pathways. They are of great significance, especially given that relevant molecular mechanisms are being discovered, there are an increasing number of emerging biomarkers, targeted therapies are becoming a future therapeutic concern, and there is an increased number of therapeutic agents undergoing clinical trials. Oesophageal squamous cell carcinoma (ESCC), the most common histological subtype of oesophageal cancer, is one of the most common cancers to affect epithelial tissue. ESCC progression is accompanied by the abnormal expression or localisation of components at cell-cell junctions. This review will discuss the recent scientific developments related to the molecules at cell-cell junctions and their role in ESCC to offer valuable insights for readers, provide a global view of the relationships between position, construction, and function, and give a reference for future mechanistic studies, diagnoses, and therapeutic developments.

Plakoglobin and High-Mobility Group Box 1 Mediate Intestinal Epithelial Cell Apoptosis Induced by Clostridioides difficile TcdB

Clostridioides difficile infection (CDI) is the leading cause of antibiotic-associated intestinal disease, resulting in severe diarrhea and fatal pseudomembranous colitis. TcdB, one of the essential virulence factors secreted by this bacterium, induces host cell apoptosis through a poorly understood mechanism. Here, we performed an RNA interference (RNAi) screen customized to Caco-2 cells, a cell line model of the intestinal epithelium, to discover host factors involved in TcdB-induced apoptosis. We identified plakoglobin, also known as junction plakoglobin (JUP) or γ-catenin, a member of the catenin family, as a novel host factor and a previously known cell death-related chromatin factor, high-mobility group box 1 (HMGB1). Disruption of those host factors by RNAi and CRISPR resulted in resistance of cells to TcdB-mediated and mitochondrion-dependent apoptosis. JUP was redistributed from adherens junctions to the mitochondria and colocalized with the antiapoptotic factor Bcl-X_L. JUP proteins could permeabilize the mitochondrial membrane, resulting in the release of cytochrome c. Our results reveal a novel role of JUP in targeting the mitochondria to promote the mitochondrial apoptotic pathway. Treatment with glycyrrhizin, an HMGB1 inhibitor, resulted in significantly increased resistance to TcdB-induced epithelial damage in cultured cells and a mouse ligated colon loop model. These findings demonstrate the critical roles of JUP and HMGB1 in TcdB-induced epithelial cell apoptosis. IMPORTANCE Clostridioides difficile infection (CDI) is the leading cause of hospital-acquired diarrhea. Toxins, especially TcdB, cause epithelial cell apoptosis, but the underlying cell death mechanism is less clear. Through an apoptosis-focused RNAi screen using a bacterium-made small interfering (siRNA) library customized to a human colonic epithelial cell model, we found a novel host factor, plakoglobin (γ-catenin), as a key factor required for cell apoptosis induced by TcdB. Plakoglobin targets and permeabilizes mitochondria after stimulation by TcdB, demonstrating a hitherto underappreciated role of this catenin family member in the apoptosis of intestinal epithelial cells. We also found a previously known cell death-related chromatin factor, HMGB1, and explored the inhibition of HMGB1 for CDI therapy in vivo.

ICAT promotes colorectal cancer metastasis via binding to JUP and activating the NF-κB signaling pathway

Background

The inhibitor of β‐catenin and T‐cell factor (ICAT) is a direct negative regulator of the canonical Wnt signaling pathway, which is an attractive therapeutic target for colorectal cancer (CRC). Accumulating evidence suggests that ICAT interacts with other proteins to exert additional functions, which are not yet fully elucidated.

Methods

The overexpression of ICAT of CRC cells was conducted by lentivirus infection and plasmids transfection and verified by quantitative real‐time reverse transcription‐polymerase chain reaction (real‐time RT‐PCR) and Western blotting. The effect of ICAT on the mobility of CRC cells was assessed by wound healing assay and transwell assay in vitro and lung metastasis in vivo. New candidate ICAT‐interacting proteins were explored and verified using the STRING database, silver staining, co‐immunoprecipitation mass spectrometry analysis (Co‐IP/MS), and immunofluorescence (IF) staining analysis.

Result

Inhibitor of β‐catenin and T‐cell factor overexpression promoted in vitro cell migration and invasion and tumor metastasis in vivo. Co‐IP/MS analysis and STRING database analyses revealed that junction plakoglobin (JUP), a homolog of β‐catenin, was involved in a novel protein interaction with ICAT. Furthermore, JUP downregulation impaired ICAT‐induced migration and invasion of CRC cells. In addition, ICAT overexpression activated the NF‐κB signaling pathway, which led to enhanced CRC cell migration and invasion.

Conclusion

Inhibitor of β‐catenin and T‐cell factor promoted CRC cell migration and invasion by interacting with JUP and the NF‐κB signaling pathway. Thus, ICAT could be considered a protein diagnostic biomarker for predicting the metastatic ability of CRC.

Countering Triple Negative Breast Cancer via Impeding Wnt/β-Catenin Signaling, a Phytotherapeutic Approach

Triple negative breast cancer (TNBC) is characterized as a heterogeneous disease with severe malignancy and high mortality. Aberrant Wnt/β-catenin signaling is responsible for self-renewal and mammosphere generation, metastasis and resistance to apoptosis and chemotherapy in TNBC. Nonetheless, in the absence of a targeted therapy, chemotherapy is regarded as the exclusive treatment strategy for the treatment of TNBC. This review aims to provide an unprecedented overview of the plants and herbal derivatives which repress the progression of TNBC through prohibiting the Wnt/β-catenin pathway. Herbal medicine extracts and bioactive compounds (alkaloids, retinoids. flavonoids, terpenes, carotenoids and lignans) alone, in combination with each other and/or with chemotherapy agents could interrupt the various steps of Wnt/β-catenin signaling, i.e., WNT, FZD, LRP, GSK3β, Dsh, APC, β-catenin and TCF/LEF. These phytotherapy agents diminish proliferation, metastasis, breast cancer stem cell self-renewal and induce apoptosis in cell and animal models of TNBC through the down-expression of the downstream target genes of Wnt signaling. Some of the herbal derivatives simultaneously impede Wnt/β-catenin signaling and other overactive pathways in triple negative breast cancer, including: mTORC1; ER stress and SATB1 signaling. The herbal remedies and their bioactive ingredients perform essential roles in the treatment of the very fatal TNBC via repression of Wnt/β-catenin signaling.

β-cells retain a pool of insulin-containing secretory vesicles regulated by adherens junctions and the cadherin binding protein p120 catenin

The β-cells of the islets of Langerhans are the sole producers of insulin in the human body. In response to rising glucose levels, insulin-containing vesicles inside β-cells fuse with the plasma membrane and release their cargo. However, the mechanisms regulating this process are only partly understood. Previous evidence indicated reductions in α-catenin elevate insulin release, while reductions in β-catenin decrease insulin release. α- and β-catenin contribute to cellular regulation in a range of ways but one is as members of the adherens junction complex and these contribute to the development of cell polarity in b-cells. Therefore, we investigated the effects of adherens junctions on insulin release. We show in INS-1E β-cells knockdown of either E- or N-cadherin had only small effects on insulin secretion, but simultaneous knockout of both cadherins resulted in a significant increase in basal insulin release to the same level as glucose-stimulated release. This double knockdown also significantly attenuated levels of p120 catenin, a cadherin binding partner involved in regulating cadherin turnover. Conversely, reducing p120 catenin levels with siRNA destabilized both E- and N-cadherin, and this was also associated with an increase in levels of insulin secreted from INS-1E cells. Furthermore, there were also changes in these cells consistent with higher insulin release, namely reductions in levels of F-actin and increased intracellular free Ca²⁺ levels in response to KCl-induced membrane depolarization. Taken together, these data provide evidence that adherens junctions play important roles in retaining a pool of insulin secretory vesicles within the cell and establish a role for p120 catenin in regulating this process.

Inflammation in the Pathogenesis of Arrhythmogenic Cardiomyopathy: Secondary Event or Active Driver?

Arrhythmogenic cardiomyopathy (ACM) is a rare inherited cardiac disease characterized by arrhythmia and progressive fibro-fatty replacement of the myocardium, which leads to heart failure and sudden cardiac death. Inflammation contributes to disease progression, and it is characterized by inflammatory cell infiltrates in the damaged myocardium and inflammatory mediators in the blood of ACM patients. However, the molecular basis of inflammatory process in ACM remains under investigated and it is unclear whether inflammation is a primary event leading to arrhythmia and myocardial damage or it is a secondary response triggered by cardiomyocyte death. Here, we provide an overview of the proposed players and triggers involved in inflammation in ACM, focusing on those studied using in vivo and in vitro models. Deepening current knowledge of inflammation-related mechanisms in ACM could help identifying novel therapeutic perspectives, such as anti-inflammatory therapy.

Fibro-fatty remodelling in arrhythmogenic cardiomyopathy

Arrhythmogenic cardiomyopathy (AC) is an inherited disorder characterized by lethal arrhythmias and a risk to sudden cardiac death. A hallmark feature of AC is the progressive replacement of the ventricular myocardium with fibro-fatty tissue, which can act as an arrhythmogenic substrate further exacerbating cardiac dysfunction. Therefore, identifying the processes underlying this pathological remodelling would help understand AC pathogenesis and support the development of novel therapies. In this review, we summarize our knowledge on the different models designed to identify the cellular origin and molecular pathways underlying cardiac fibroblast and adipocyte cell differentiation in AC patients. We further outline future perspectives and how targeting the fibro-fatty remodelling process can contribute to novel AC therapeutics.

Vascular Endothelial Integrity Affects the Severity of Enterovirus-Mediated Cardiomyopathy

Coxsackievirus and adenovirus receptor (CAR) is present in epithelial and vascular endothelial cell junctions. We have previously shown a hemorrhagic phenotype in germ-line CAR knock-out mouse embryos; we have also found that CAR interacts with ZO-1 and β-catenin. However, the role of CAR in vascular endothelial junction permeability has not been proven. To understand the roles of CAR in the vascular endothelial junctions, we generated endothelium-specific CAR knockout (CAR-eKO) mice. In the absence of CAR, the endothelial cell layer showed an increase in transmembrane electrical resistance (TER, Ω) and coxsackievirus permeability. Evans blue dye and 70 kDa dextran-FITC were delivered by tail vein injection. We observed increased vascular permeability in the hearts of adult CAR-eKO mice compare with wild-type (WT) mice. There was a marked increase in monocyte and macrophage penetration into the peritoneal cavity caused by thioglycolate-induced peritonitis. We found that CAR ablation in endothelial cells was not significantly increased coxsackievirus B3 (CVB3) induced myocarditis in murine model. However, tissue virus titers were significantly higher in CAR-eKO mice compared with WT. Moreover, CVB3 was detected in the brain of CAR-eKO mice. Endothelial CAR deletion affects the expression of major endothelial junction proteins, such as cadherin and platelet endothelial cell adhesion molecule-1 (PECAM-1) in the cultured endothelial cells as well as liver vessel. We suggest that CAR expression is required for normal vascular permeability and endothelial tight junction homeostasis. Furthermore, CVB3 organ penetration and myocarditis severities were dependent on the endothelial CAR level.

Naxos disease - a narrative review

INTRODUCTION

Naxos disease is a rare entity that manifests with woolly hair, keratosis of extremities, and cardiac manifestations that resemble arrhythmogenic right ventricular cardiomyopathy. It is inherited in an autosomal recessive pattern and mutations affecting plakoglobin and desmoplakin have been identified. There is an increased risk of arrhythmias, including sudden cardiac death at a young age. Right ventricular systolic dysfunction often progresses and left ventricular involvement may also occur.

AREAS COVERED

This article reviews historic background, epidemiology, clinical characteristics, genetics, and pathogenesis as well as therapeutic management and future perspectives.

EXPERT OPINION

The principles of evaluation and treatment are based on arrhythmogenic right ventricular cardiomyopathy (ARVC) and general heart failure guidelines, because specific data on Naxos disease are limited. Therefore, larger registries on Naxos disease are welcome in order to gain more knowledge about clinical course and risk stratification. Translational research on pathophysiological mechanisms has evolved, including promising approaches using stem cells for novel targets.

Allosteric inhibitor of β-catenin selectively targets oncogenic Wnt signaling in colon cancer

Abnormal regulation of β-catenin initiates an oncogenic program that serves as a main driver of many cancers. Albeit challenging, β-catenin is an attractive drug target due to its role in maintenance of cancer stem cells and potential to eliminate cancer relapse. We have identified C2, a novel β-catenin inhibitor, which is a small molecule that binds to a novel allosteric site on the surface of β-catenin. C2 selectively inhibits β-catenin, lowers its cellular load and significantly reduces viability of β-catenin-driven cancer cells. Through direct binding to β-catenin, C2 renders the target inactive that eventually activates proteasome system for its removal. Here we report a novel pharmacologic approach for selective inhibition of β-catenin via targeting a cryptic allosteric modulation site. Our findings may provide a new perspective for therapeutic targeting of β-catenin.

Intercalated discs: cellular adhesion and signaling in heart health and diseases

Intercalated discs (ICDs) are highly orchestrated structures that connect neighboring cardiomyocytes in the heart. Three major complexes are distinguished in ICD: desmosome, adherens junction (AJ), and gap junction (GJ). Desmosomes are major cell adhesion junctions that anchor cell membrane to the intermediate filament network; AJs connect the actin cytoskeleton of adjacent cells; and gap junctions metabolically and electrically connect the cytoplasm of adjacent cardiomyocytes. All these complexes work as a single unit, the so-called area composita, interdependently rather than individually. Mutation or altered expression of ICD proteins results in various cardiac diseases, such as ARVC (arrhythmogenic right ventricular cardiomyopathy), dilated cardiomyopathy, and hypotrophy cardiomyopathy, eventually leading to heart failure. In this article, we first review the recent findings on the structural organization of ICD and their functions and then focus on the recent advances in molecular pathogenesis of the ICD-related heart diseases, which include two major areas: i) the ICD gene mutations in cardiac diseases, and ii) the involvement of ICD proteins in signal transduction pathways leading to myocardium remodeling and eventual heart failure. These major ICD-related signaling pathways include Wnt/β-catenin pathway, p38 MAPK cascade, Rho-dependent serum response factor (SRF) signaling, calcineurin/NFAT signaling, Hippo kinase cascade, etc., which are differentially regulated in pathological conditions.

Molecular mechanisms of arrhythmogenic cardiomyopathy

Arrhythmogenic cardiomyopathy is a genetic disorder characterized by the risk of life-threatening arrhythmias, myocardial dysfunction and fibrofatty replacement of myocardial tissue. Mutations in genes that encode components of desmosomes, the adhesive junctions that connect cardiomyocytes, are the predominant cause of arrhythmogenic cardiomyopathy and can be identified in about half of patients with the condition. However, the molecular mechanisms leading to myocardial destruction, remodelling and arrhythmic predisposition remain poorly understood. Through the development of animal, induced pluripotent stem cell and other models of disease, advances in our understanding of the pathogenic mechanisms of arrhythmogenic cardiomyopathy over the past decade have brought several signalling pathways into focus. These pathways include canonical and non-canonical WNT signalling, the Hippo-Yes-associated protein (YAP) pathway and transforming growth factor-β signalling. These studies have begun to identify potential therapeutic targets whose modulation has shown promise in preclinical models. In this Review, we summarize and discuss the reported molecular mechanisms underlying the pathogenesis of arrhythmogenic cardiomyopathy.

Learning impairments and molecular changes in the brain caused by β-catenin loss

Intellectual disability (ID), defined as IQ<70, occurs in 2.5% of individuals. Elucidating the underlying molecular mechanisms is essential for developing therapeutic strategies. Several of the identified genes that link to ID in humans are predicted to cause malfunction of β-catenin pathways, including mutations in CTNNB1 (β-catenin) itself. To identify pathological changes caused by β-catenin loss in the brain, we have generated a new β-catenin conditional knockout mouse (β-cat cKO) with targeted depletion of β-catenin in forebrain neurons during the period of major synaptogenesis, a critical window for brain development and function. Compared with control littermates, β-cat cKO mice display severe cognitive impairments. We tested for changes in two β-catenin pathways essential for normal brain function, cadherin-based synaptic adhesion complexes and canonical Wnt (Wingless-related integration site) signal transduction. Relative to control littermates, β-cat cKOs exhibit reduced levels of key synaptic adhesion and scaffold binding partners of β-catenin, including N-cadherin, α-N-catenin, p120ctn and S-SCAM/Magi2. Unexpectedly, the expression levels of several canonical Wnt target genes were not altered in β-cat cKOs. This lack of change led us to find that β-catenin loss leads to upregulation of γ-catenin (plakoglobin), a partial functional homolog, whose neural-specific role is poorly defined. We show that γ-catenin interacts with several β-catenin binding partners in neurons but is not able to fully substitute for β-catenin loss, likely due to differences in the N-and C-termini between the catenins. Our findings identify severe learning impairments, upregulation of γ-catenin and reductions in synaptic adhesion and scaffold proteins as major consequences of β-catenin loss.

γ-catenin alleviates cardiac fibrosis through inhibiting phosphorylation of GSK-3β

Cardiac fibrosis is a common pathological change of many cardiovascular diseases. β-catenin has been shown to promote fibrosis. However, the precise role of its homolog γ-catenin in the process of fibrosis remains largely unclear. In this study, we found that the expression of γ-catenin was significantly decreased in angiotensin Ⅱ (Ang Ⅱ)-induced cardiac fibrosis model, contrary to most reports of β-catenin. Overexpression of γ-catenin in cardiac fibroblasts (CFs) significantly inhibited the expression of α-smooth muscle actin (α-SMA), whereas knocking down the expression of γ-catenin with siRNA promoted the occurrence of cardiac fibrosis. Mechanistically, γ-catenin could bind to GSK-3β to inhibit the phosphorylation of GSK-3β, therefore preventing cardiac fibrosis. Our study shows that γ-catenin is an important protective factor in cardiac fibrosis, which provides a new potential target for the treatment of cardiac fibrosis.

Role of smooth muscle cells in coronary artery bypass grafting failure

Atherosclerosis is the underlying pathology of many cardiovascular diseases. The formation and rupture of atherosclerotic plaques in the coronary arteries results in angina and myocardial infarction. Venous coronary artery bypass grafts are designed to reduce the consequences of atherosclerosis in the coronary arteries by diverting blood flow around the atherosclerotic plaques. However, vein grafts suffer a high failure rate due to intimal thickening that occurs as a result of vascular cell injury and activation and can act as 'a soil' for subsequent atherosclerotic plaque formation. A clinically-proven method for the reduction of vein graft intimal thickening and subsequent major adverse clinical events is currently not available. Consequently, a greater understanding of the underlying mechanisms of intimal thickening may be beneficial for the design of future therapies for vein graft failure. Vein grafting induces inflammation and endothelial cell damage and dysfunction, that promotes vascular smooth muscle cell (VSMC) migration, and proliferation. Injury to the wall of the vein as a result of grafting leads to the production of chemoattractants, remodelling of the extracellular matrix and cell-cell contacts; which all contribute to the induction of VSMC migration and proliferation. This review focuses on the role of altered behaviour of VSMCs in the vein graft and some of the factors which critically lead to intimal thickening that pre-disposes the vein graft to further atherosclerosis and re-occurrence of symptoms in the patient.

An explant technique for high-resolution imaging and manipulation of mycobacterial granulomas

A central and critical structure in tuberculosis, the mycobacterial granuloma consists of highly organized immune cells, including macrophages that drive granuloma formation through a characteristic epithelioid transformation. Difficulties in imaging within intact animals as well as the inherent caveats of in vitro assembly models have severely limited the study and experimental manipulation of mature granulomas. Here we describe a new ex vivo granuloma culture technique, wherein mature, fully organized granulomas are microdissected and maintained in three-dimensional culture. This approach, in which granulomas retain key bacterial and host characteristics, enables high-resolution microscopy of granuloma macrophage dynamics, including epithelioid macrophage motility and granuloma consolidation. Through mass spectrometry, we find active production of key phosphotidylinositol species identified previously in human granulomas. We describe a method to transfect isolated granulomas, enabling genetic manipulation. In addition, we provide proof-of-concept for host-directed small molecule screens, identifying PKC signaling as an important regulator of granuloma macrophage organization.

FMRP recruitment of β-catenin to the translation pre-initiation complex represses translation

Canonical Wnt/β-catenin signaling is an essential regulator of various cellular functions throughout development and adulthood. Aberrant Wnt/β-catenin signaling also contributes to various pathologies including cancer, necessitating an understanding of cell context-dependent mechanisms regulating this pathway. Since protein-protein interactions underpin β-catenin function and localization, we sought to identify novel β-catenin interacting partners by affinity purification coupled with tandem mass spectrometry in vascular smooth muscle cells (VSMCs), where β-catenin is involved in both physiological and pathological control of cell proliferation. Here, we report novel components of the VSMC β-catenin interactome. Bioinformatic analysis of the protein networks implies potentially novel functions for β-catenin, particularly in mRNA translation, and we confirm a direct interaction between β-catenin and the fragile X mental retardation protein (FMRP). Biochemical studies reveal a basal recruitment of β-catenin to the messenger ribonucleoprotein and translational pre-initiation complex, fulfilling a translational repressor function. Wnt stimulation antagonizes this function, in part, by sequestering β-catenin away from the pre-initiation complex. In conclusion, we present evidence that β-catenin fulfills a previously unrecognized function in translational repression.

Altered Cell-Cycle Control, Inflammation, and Adhesion in High-Risk Persistent Bronchial Dysplasia

Persistent bronchial dysplasia is associated with increased risk of developing invasive squamous cell carcinoma (SCC) of the lung. In this study, we hypothesized that differences in gene expression profiles between persistent and regressive bronchial dysplasia would identify cellular processes that underlie progression to SCC. RNA expression arrays comparing baseline biopsies from 32 bronchial sites that persisted/progressed to 31 regressive sites showed 395 differentially expressed genes [ANOVA, FDR ≤ 0.05). Thirty-one pathways showed significantly altered activity between the two groups, many of which were associated with cell-cycle control and proliferation, inflammation, or epithelial differentiation/cell-cell adhesion. Cultured persistent bronchial dysplasia cells exhibited increased expression of Polo-like kinase 1 (PLK1), which was associated with multiple cell-cycle pathways. Treatment with PLK1 inhibitor induced apoptosis and G2-M arrest and decreased proliferation compared with untreated cells; these effects were not seen in normal or regressive bronchial dysplasia cultures. Inflammatory pathway activity was decreased in persistent bronchial dysplasia, and the presence of an inflammatory infiltrate was more common in regressive bronchial dysplasia. Regressive bronchial dysplasia was also associated with trends toward overall increases in macrophages and T lymphocytes and altered polarization of these inflammatory cell subsets. Increased desmoglein 3 and plakoglobin expression was associated with higher grade and persistence of bronchial dysplasia. These results identify alterations in the persistent subset of bronchial dysplasia that are associated with high risk for progression to invasive SCC. These alterations may serve as strong markers of risk and as effective targets for lung cancer prevention.Significance: Gene expression profiling of high-risk persistent bronchial dysplasia reveals changes in cell-cycle control, inflammatory activity, and epithelial differentiation/cell-cell adhesion that may underlie progression to invasive SCC. Cancer Res; 78(17); 4971-83. ©2018 AACR.

A Review of Selected Factors of Salivary Gland Tumour Formation and Malignant Transformation

Salivary gland tumours represent about 6% of head and neck neoplasms and about 0.5% of all malignancies in humans. Tumour growth and malignant transformation are complex processes involving various actions of molecules. Furthermore, some malignant salivary gland tumours are deemed to be caused by dedifferentiation or malignant transformation of benign tumours. The mechanisms of this transformation depend on a variety of different elements, such as cell cycle regulators, oncogenes, proteins, angiogenesis factors, and adipocytokines. The authors used PubMed, Medline, and Google websites to find and review the most significant papers related to malignant transformation in benign salivary gland tumours.

Plakoglobin restores tumor suppressor activity of p53R175H mutant by sequestering the oncogenic potential of β-catenin

Tumor suppressor/transcription factor p53 is mutated in over 50% of all cancers. Some mutant p53 proteins have not only lost tumor suppressor activities but they also gain oncogenic functions (GOF). One of the most frequently expressed GOF p53 mutants is Arg175His (p53R175H ) with well-documented roles in cancer development and progression. Plakoglobin is a cell adhesion and signaling protein and a paralog of β-catenin. Unlike β-catenin that has oncogenic function through its role in the Wnt pathway, plakoglobin generally acts as a tumor/metastasis suppressor. We have shown that plakoglobin interacted with wild type and a number of p53 mutants in various carcinoma cell lines. Plakoglobin and mutant p53 interacted with the promoter and regulated the expression of several p53 target genes. Furthermore, plakoglobin interactions with p53 mutants restored their tumor suppressor/metastasis activities in vitro. GOF p53 mutants induce accumulation and oncogenic activation of β-catenin. Previously, we showed that one mechanism by which plakoglobin may suppress tumorigenesis is by sequestering β-catenin's oncogenic activity. Here, we examined the effects of p53R175H expression on β-catenin accumulation and transcriptional activation and their modifications by plakoglobin coexpression. We showed that p53R175H expression in plakoglobin null cells increased total and nuclear levels of β-catenin and its transcriptional activity. Coexpression of plakoglobin in these cells promoted β-catenin's proteasomal degradation, and decreased its nuclear levels and transactivation. Wnt/β-catenin targets, c-MYC and S100A4 were upregulated in p53R175H cells and were downregulated when plakoglobin was coexpressed. Plakoglobin-p53R175H cells also showed significant reduction in their migration and invasion in vitro.

Autoantibody Signaling in Pemphigus Vulgaris: Development of an Integrated Model

Pemphigus vulgaris (PV) is an autoimmune skin blistering disease effecting both cutaneous and mucosal epithelia. Blister formation in PV is known to result from the binding of autoantibodies (autoAbs) to keratinocyte antigens. The primary antigenic targets of pathogenic autoAbs are known to be desmoglein 3, and to a lesser extent, desmoglein 1, cadherin family proteins that partially comprise the desmosome, a protein structure responsible for maintaining cell adhesion, although additional autoAbs, whose role in blister formation is still unclear, are also known to be present in PV patients. Nevertheless, there remain large gaps in knowledge concerning the precise mechanisms through which autoAb binding induces blister formation. Consequently, the primary therapeutic interventions for PV focus on systemic immunosuppression, whose side effects represent a significant health risk to patients. In an effort to identify novel, disease-specific therapeutic targets, a multitude of studies attempting to elucidate the pathogenic mechanisms downstream of autoAb binding, have led to significant advancements in the understanding of autoAb-mediated blister formation. Despite this enhanced characterization of disease processes, a satisfactory explanation of autoAb-induced acantholysis still does not exist. Here, we carefully review the literature investigating the pathogenic disease mechanisms in PV and, taking into account the full scope of results from these studies, provide a novel, comprehensive theory of blister formation in PV.

The role of adherens junction proteins in the regulation of insulin secretion

In healthy individuals, any rise in blood glucose levels is rapidly countered by the release of insulin from the β-cells of the pancreas which in turn promotes the uptake and storage of the glucose in peripheral tissues. The β-cells possess exquisite mechanisms regulating the secretion of insulin to ensure that the correct amount of insulin is released. These mechanisms involve tight control of the movement of insulin containing secretory vesicles within the β-cells, initially preventing most vesicles being able to move to the plasma membrane. Elevated glucose levels trigger an influx of Ca²⁺ that allows fusion of the small number of insulin containing vesicles that are pre-docked at the plasma membrane but glucose also stimulates processes that allow other insulin containing vesicles located further in the cell to move to and fuse with the plasma membrane. The mechanisms controlling these processes are complex and not fully understood but it is clear that the interaction of the β-cells with other β-cells in the islets is very important for their ability to develop the appropriate machinery for proper regulation of insulin secretion. Emerging evidence indicates one factor that is key for this is the formation of homotypic cadherin mediated adherens junctions between β-cells. Here, we review the evidence for this and discuss the mechanisms by which these adherens junctions might regulate insulin vesicle trafficking as well as the implications this has for understanding the dysregulation of insulin secretion seen in pathogenic states.

Beyond cell-cell adhesion: Plakoglobin and the regulation of tumorigenesis and metastasis

Plakoglobin (also known as? -catenin) is a member of the Armadillo family of proteins and a paralog of β -catenin. Plakoglobin is a component of both the adherens junctions and desmosomes, and therefore plays a vital role in the regulation of cell-cell adhesion. Similar to β -catenin, plakoglobin is capable of participating in cell signaling in addition to its role in cell-cell adhesion. In this context, β -catenin has a well-documented oncogenic potential as a component of the Wnt signaling pathway. In contrast, while some studies have suggested a tumor promoting activity of plakoglobin in a cell/malignancy specific context, it generally acts as a tumor/metastasis suppressor. How plakoglobin acts as a growth/metastasis inhibitory protein has remained, until recently, unclear. Recent evidence suggests that plakoglobin may suppress tumorigenesis and metastasis by multiple mechanisms, including the suppression of oncogenic signaling, interactions with various proteins involved in tumorigenesis and metastasis, and the regulation of the expression of genes involved in these processes. This review is primarily focused on various mechanisms by which plakoglobin may inhibit tumorigenesis and metastasis.

Arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) in clinical practice

Arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) is an inherited myocardial disease characterized by fibro-fatty replacement of the right ventricular myocardium, and associated with paroxysmal ventricular arrhythmias and sudden cardiac death (SCD). It is currently the second most common cause of SCD after hypertrophic cardiomyopathy in young people <35 years of age, causing up to 20% of deaths in this patient population. This condition has a male preponderance and is more commonly found in individuals of Italian and Greek descent. To date, there is no single diagnostic test for ARVC/D and the diagnosis is made based on clinical, electrocardiographic, and radiological findings according to the Revised 2010 Task Force Criteria. In this review, we will discuss the mainstay treatment which includes pharmacotherapy, implantable cardioverter-defibrillator insertion for abortion of sudden cardiac death, and in the advanced stages of the disease cardiac transplantation.

Significant Down-Regulation of "Biological Adhesion" Genes in Porcine Oocytes after IVM

Proper maturation of the mammalian oocyte is a compound processes determining successful monospermic fertilization, however the number of fully mature porcine oocytes is still unsatisfactory. Since oocytes’ maturation and fertilization involve cellular adhesion and membranous contact, the aim was to investigate cell adhesion ontology group in porcine oocytes. The oocytes were collected from ovaries of 45 pubertal crossbred Landrace gilts and subjected to two BCB tests. After the first test, only granulosa cell-free BCB⁺ oocytes were directly exposed to microarray assays and RT-qPCR (“before IVM” group), or first in vitro matured and then if classified as BCB⁺ passed to molecular analyses (“after IVM” group). As a result, we have discovered substantial down-regulation of genes involved in adhesion processes, such as: organization of actin cytoskeleton, migration, proliferation, differentiation, apoptosis, survival or angiogenesis in porcine oocytes after IVM, compared to oocytes analyzed before IVM. In conclusion, we found that biological adhesion may be recognized as the process involved in porcine oocytes’ successful IVM. Down-regulation of genes included in this ontology group in immature oocytes after IVM points to their unique function in oocyte’s achievement of fully mature stages. Thus, results indicated new molecular markers involved in porcine oocyte IVM, displaying essential roles in biological adhesion processes.

The canonical way to make a heart: β-catenin and plakoglobin in heart development and remodeling

The main mediator of the canonical Wnt pathway, β-catenin, is a major effector of embryonic development, postnatal tissue homeostasis, and adult tissue regeneration. The requirement for β-catenin in cardiogenesis and embryogenesis has been well established. However, many questions regarding the molecular mechanisms by which β-catenin and canonical Wnt signaling regulate these developmental processes remain unanswered. An interesting question that emerged from our studies concerns how β-catenin signaling is modulated through interaction with other factors. Recent experimental data implicate new players in canonical Wnt signaling, particularly those which modulate β-catenin function in many its biological processes, including cardiogenesis. One of the interesting candidates is plakoglobin, a little-studied member of the catenin family which shares several mechanistic and functional features with its close relative, β-catenin. Here we have focused on the function of β-catenin in cardiogenesis. We also summarize findings on plakoglobin signaling function and discuss possible interplays between β-catenin and plakoglobin in the regulation of embryonic heart development. Impact statement Heart development, function, and remodeling are complex processes orchestrated by multiple signaling networks. This review examines our current knowledge of the role of canonical Wnt signaling in cardiogenesis and heart remodeling, focusing primarily on the mechanistic action of its effector β-catenin. We summarize the generally accepted understanding of the field based on experimental in vitro and in vivo data, and address unresolved questions in the field, specifically relating to the role of canonical Wnt signaling in heart maturation and regeneration. What are the modulators of canonical Wnt, and particularly what are the potential roles of plakoglobin, a close relative of β-catenin, in regulating Wnt signaling?Answers to these questions will enhance our understanding of the mechanism by which the canonical Wnt signaling regulates development of the heart and its regeneration after damage.

Probing the canonicity of the Wnt/Wingless signaling pathway

The hallmark of canonical Wnt signaling is the transcriptional induction of Wnt target genes by the beta-catenin/TCF complex. Several studies have proposed alternative interaction partners for beta-catenin or TCF, but the relevance of potential bifurcations in the distal Wnt pathway remains unclear. Here we study on a genome-wide scale the requirement for Armadillo (Arm, Drosophila beta-catenin) and Pangolin (Pan, Drosophila TCF) in the Wnt/Wingless(Wg)-induced transcriptional response of Drosophila Kc cells. Using somatic genetics, we demonstrate that both Arm and Pan are absolutely required for mediating activation and repression of target genes. Furthermore, by means of STARR-sequencing we identified Wnt/Wg-responsive enhancer elements and found that all responsive enhancers depend on Pan. Together, our results confirm the dogma of canonical Wnt/Wg signaling and argue against the existence of distal pathway branches in this system.

Our manuscript addresses the question of whether either of the canonical transduction components, beta-catenin or TCF, can be bypassed when the Wnt pathway is activated. By using somatic cell genetics in Drosophila cells (via CRISPR/Cas9 editing) in combination with RNA-seq and STARR-seq (Self-transcribing-active-regulatory-region-sequencing) as functional read-outs, we provide firm evidence against the existence of distal branches in the Wnt pathway.

Loss of desmoglein 2 promotes tumorigenic behavior in pancreatic cancer cells

The ability to maintain cell-cell adhesion is crucial for tissue integrity and organization. Accordingly, loss of cohesiveness plays a critical role in cancer invasion and metastasis. Desmosomes are cell junctions providing strong intercellular adhesive strength and dysregulation of desmosomal constituents contributes to cancer progression through altered cell signaling pathways. Here, we focused on the desmosomal adhesion molecules Desmoglein 2 (Dsg2) and Desmocollin 2 (Dsc2), and their contribution to migration and invasion in pancreatic cancer cells. Silencing of Dsg2 but not Dsc2 resulted in loss of cell cohesion and enhanced migration, and invasion of pancreatic adenocarcinoma cells. To identify potential pathways regulated by Dsg2, we performed kinase arrays and detected the activity of ERK and growth factor receptors to be significantly enhanced in Dsg2-deficient cells. Consequently, inhibition of ERK phosphorylation in Dsg2 knockdown cells normalized migration. Loss of Dsg2 resulted in reduced levels of the desmosomal adapter protein and transcriptional regulator Plakoglobin (PG) in an ERK-dependent manner, whereas other desmosomal molecules were not altered. Overexpression of PG rescued enhanced migration induced by silencing of Dsg2. These results identify a novel pro-migratory pathway of pancreatic cancer cells in which loss of Dsg2 reduces the levels of PG via deregulated MAPK signaling.

Lonidamine-ethyl ester-mediated remodelling of the Sertoli cell cytoskeleton induces phosphorylation of plakoglobin and promotes its interaction with α-catenin at the blood–testis barrier

Several compounds affect male fertility by disrupting the adhesion of germ cells to Sertoli cells, which results in the release of undeveloped germ cells into the seminiferous tubule lumen that are incapable of fertilising the ovum. Indazole carboxylic acids are one class of compounds exhibiting such effects and they have been investigated as non-hormonal contraceptives for potential human use. The aims of this study were to investigate the effects of lonidamine-ethyl ester, an indazole carboxylic acid, on spermatogenesis and cell junctions, in particular, desmosomes. We found two doses of lonidamine-ethyl ester at 50 mg kg–1 to disrupt Sertoli–germ cell adhesion. By light and fluorescent microscopy, pronounced changes were observed in the distribution of actin microfilaments and intermediate filaments, as well as in the localisation of plakoglobin, a protein with structural and signalling roles at the desmosome and adherens junction at the blood–testis barrier. Furthermore, immunoblotting and immunoprecipitation experiments using testis lysates revealed a significant upregulation (P < 0.01) of plakoglobin and Tyr-phosphorylated plakoglobin. Co-immunoprecipitation experiments showed an increase in the interaction between plakoglobin and fyn proto-oncogene, an Src family non-receptor tyrosine kinase, after treatment, as well as an increase in the interaction between plakoglobin and α-catenin. Taken collectively, these data indicate that a disruption of Sertoli cell and spermatocyte–spermatid adhesion in the seminiferous epithelium by lonidamine-ethyl ester results in the phosphorylation of plakoglobin, thereby promoting its interaction with α-catenin at the blood–testis barrier.

The WNT-less wonder: WNT-independent β-catenin signaling

β-catenin is known as an Armadillo protein that regulates gene expression following WNT pathway activation. However, WNT-independent pathways also activate β-catenin. During the establishment of the melanocyte lineage, β-catenin plays an important role. In the context of physiopathology, β-catenin is activated genetically or transiently in various cancers, including melanoma, where it can be found in the nucleus of tumors. In this review, we discuss alternative pathways that activate β-catenin independent of WNTs and highlight what is known regarding these pathways in melanoma. We also discuss the role of β-catenin as a transcriptional regulator in various cell types, with emphasis on the different transcription factors it associates with independent of WNT induction. Finally, the role of WNT-independent β-catenin in melanocyte development and melanomagenesis is also discussed.

Beta-Catenin and Plakoglobin Expression during Zebrafish Tooth Development and Replacement

We analyzed the protein distribution of two cadherin-associated molecules, plakoglobin and β-catenin, during the different stages of tooth development and tooth replacement in zebrafish. Plakoglobin was detected at the plasma membrane already at the onset of tooth development in the epithelial cells of the tooth. This pattern remained unaltered during further tooth development. The mesenchymal cells only showed plakoglobin from cytodifferentiation onwards. Plakoglobin 1a morpholino-injected embryos showed normal tooth development with proper initiation and differentiation. Although plakoglobin is clearly present during normal odontogenesis, the loss of plakoglobin 1a does not influence tooth development. β-catenin was found at the cell borders of all cells of the successional lamina but also in the nuclei of surrounding mesenchymal cells. Only membranous, not nuclear, β-catenin, was found during morphogenesis stage. However, during cytodifferentiation stage, both nuclear and membrane-bound β-catenin was detected in the layers of the enamel organ as well as in the differentiating odontoblasts. Nuclear β-catenin is an indication of an activated Wnt pathway, therefore suggesting a possible role for Wnt signalling during zebrafish tooth development and replacement.

Genetic analysis of intestinal polyp development in Collaborative Cross mice carrying the Apc (Min/+) mutation

Background

Colorectal cancer is an abnormal tissue development in the colon or rectum. Most of CRCs develop due to somatic mutations, while only a small proportion is caused by inherited mutations. Familial adenomatous polyposis is an inherited genetic disease, which is characterized by colorectal polyps. It is caused by inactivating mutations in the Adenomatous polyposis coli gene. Mice carrying and non-sense mutation in Adenomatous polyposis coli gene at site R850, which designated Apc^R850X/+ (Min), develop intestinal adenomas, while the bulk of the disease is in the small intestine. A number of genetic modifier loci of Min have been mapped, but so far most of the underlying genes have not been identified. In our previous studies, we have shown that Collaborative Cross mice are a powerful tool for mapping loci responsible for phenotypic variation. As a first step towards identification of novel modifiers of Min, we assessed the phenotypic variation between 27 F1 crosses between different Collaborative cross mice and C57BL/6-Min lines.

Results

Here, C57BL/6-Min male mice were mated with females from 27 Collaborative cross lines. F1 offspring were terminated at 23 weeks old and multiple phenotypes were collected: polyp counts, intestine length, intestine weight, packed cell volume and spleen weight. Additionally, in eight selected F1 Collaborative cross-C57BL/6-Min lines, body weight was monitored and compared to control mice carry wildtype Adenomatous polyposis coli gene. We found significant (p < 0.05) phenotypic variation between the 27 F1 Collaborative cross-C57BL/6-Min lines for all the tested phenotypes, and sex differences with traits; Colon, body weight and intestine length phenotypes, only. Heritability calculation showed that these phenotypes are mainly controlled by genetic factors.

Conclusions

Variation in polyp development is controlled, an appreciable extent, by genetic factors segregating in the Collaborative cross population and suggests that it is suited for identifying modifier genes associated with Apc^Min/+ mutation, after assessing sufficient number of lines for quantitative trait loci analysis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12863-016-0349-6) contains supplementary material, which is available to authorized users.

The Good and Bad of β-Catenin in Kidney Development and Renal Dysplasia

Congenital renal malformations are a major cause of childhood and adult onset chronic kidney disease. Identifying the etiology of these renal defects is often challenging since disruptions in the processes that drive kidney development can result from disruptions in environmental, genetic, or epigenetic cues. β-catenin is an intracellular molecule involved in cell adhesion, cell signaling, and regulation of gene transcription. It plays essential roles in kidney development and in the pathogenesis of renal dysplasia. Here, we review the function of β-catenin during kidney development and in the genesis of renal dysplasia.

Mice with Hepatic Loss of the Desmosomal Protein γ-Catenin Are Prone to Cholestatic Injury and Chemical Carcinogenesis

γ-Catenin, an important component of desmosomes, may also participate in Wnt signaling. Herein, we dissect the role of γ-catenin in liver by generating conditional γ-catenin knockout (KO) mice and assessing their phenotype after bile duct ligation (BDL) and diethylnitrosamine-induced chemical carcinogenesis. At baseline, KO and wild-type littermates showed comparable serum biochemistry, liver histology, and global gene expression. β-Catenin protein was modestly increased without any change in Wnt signaling. Desmosomes were maintained in KO, and despite no noticeable changes in gene expression, differential detergent fractionation revealed quantitative and qualitative changes in desmosomal cadherins, plaque proteins, and β-catenin. Enhanced association of β-catenin to desmoglein-2 and plakophilin-3 was observed in KO. When subjected to BDL, wild-type littermates showed specific changes in desmosomal protein expression. In KO, BDL deteriorated baseline compensatory changes, which manifested as enhanced injury and fibrosis. KO also showed enhanced tumorigenesis to diethylnitrosamine treatment because of Wnt activation, as also verified in vitro. γ-Catenin overexpression in hepatoma cells increased its binding to T-cell factor 4 at the expense of β-catenin-T-cell factor 4 association, induced unique target genes, affected Wnt targets, and reduced cell proliferation and viability. Thus, γ-catenin loss in liver is basally well tolerated. However, after insults like BDL, these compensations at desmosomes fail, and KO show enhanced injury. Also, γ-catenin negatively regulates tumor growth by affecting Wnt signaling.

High-mobility group box 1 enhances the inflammatory process in diabetic lung

Diabetes mellitus generates metabolic changes associated with inflammatory events that may eventually affect all body tissues. Both high-mobility group box 1 (HMGB1) and β-catenin are active players in inflammation. The study aimed to determine whether HMGB1 modulates the β-catenin activity in supporting inflammation, using an experimental type 1 diabetes mouse model. The protein and gene expression of HMGB1 were significantly increased (2-fold) in the diabetic lung compared to control and were positively correlated with the HMGB1 levels detected in serum. Co-immunoprecipitation of HMGB1 with RAGE co-exists with activation of PI3K/AKT1 and NF-kB signaling pathways. At the same time β-catenin was increased in nuclear fraction (3.5 fold) while it was down-regulated in diabetic plasma membrane (2-fold). There was no difference of β-catenin gene expression between the control and diabetic mice. β-Catenin phosphorylation at Ser552 was higher in diabetic nuclear fraction, suggesting that AKT1 activation promotes β-catenin nuclear translocation. In addition, c-Jun directly binds β-catenin indicating the transcriptional activity of β-catenin in diabetes, sustained by significantly COX2 increase by 6-fold in the cytosolic extract of diabetic lung compared to control. Taken together, the data support the new concept that HMGB1 maintains the inflammation through RAGE/AKT1/β-catenin pathway in the diabetic lung.

Circulating tumor cell clusters-associated gene plakoglobin and breast cancer survival

Breast cancer recurrence is a major cause of the disease-specific death. Circulating tumor cells (CTCs) are negatively associated with breast cancer survival. Plakoglobin, a cell adhesion protein, was recently reported as a determinant of CTCs types, single or clustered ones. Here, we aim to summarize the studies on the roles of plakoglobin and evaluate the association of plakoglobin and breast cancer survival. Plakoglobin as a key component in both cell adhesion and the signaling pathways was briefly reviewed first. Then the double-edge functions of plakoglobin in tumors and its association with CTCs and breast cancer metastasis were introduced. Finally, based on an open-access database, the association between plakoglobin and breast cancer survival was investigated using univariate and multivariate survival analyses. Plakoglobin may be a molecule functioning as a double-edge sword. Loss of plakoglobin expression leads to increased motility of epithelial cells, thereby promoting epithelial-mesenchymal transition and further metastasis of cancer. However, studies also show that plakoglobin can function as an oncogene. High expression of plakoglobin results in clustered tumor cells in circulation with high metastatic potential in breast cancer and shortened patient survival. Plakoglobin may be a potential prognostic biomarker that can be exploited to develop as a therapeutic target for breast cancer.

Novel Role for γ-Catenin in the Regulation of Cancer Cell Migration via the Induction of Hepatocyte Growth Factor Activator Inhibitor Type 1 (HAI-1)

γ-catenin (Plakoglobin), a well-described structural protein functioning at the adherens junctions and desmosomes, was shown to be either lost or weakly expressed in non-small cell lung cancer (NSCLC) cells and tumor tissues. However, the tumor suppressive affects of γ-catenin were not fully understood. In this study, we have identified a novel role for the affects of γ-catenin on non-small cell lung cancer (NSCLC) cell migration. Expression of γ-catenin in NSCLC cells resulted in reduced cell migration as determined by both scratch assays and trans-well cell migration assays. Moreover, the affects of γ-catenin on cell migration were observed to be p53-dependent. Mechanistically, the anti-migratory effects seen via γ-catenin were driven by the expression of hepatocyte growth factor activator inhibitor Type I (HAI-1 or SPINT-1), an upstream inhibitor of the c-MET signaling pathway. Furthermore, the re-expression of γ-catenin sensitized NSCLC cells to c-MET inhibitor-mediated growth inhibition. Taken together, we identify γ-catenin as a novel regulator of HAI-1, which is a critical regulator of HGF/c-MET signaling. Therefore, targeting γ-catenin-mediated HAI-1 expression might be a useful strategy to sensitize NSCLC to c-MET inhibitors.

Pathogenesis of Arrhythmogenic Cardiomyopathy

Arrhythmogenic cardiomyopathy (ACM) is a primary myocardial disease. It is characterized by frequent ventricular arrhythmias and increased risk of sudden cardiac death typically arising as an early manifestation before the onset of significant myocardial remodelling. Myocardial degeneration, often confined to the right ventricular free wall, with replacement by fibrofatty scar tissue, develops in many patients. ACM is a familial disease but genetic penetrance can be low and disease expression is highly variable. Inflammation might promote disease progression. It also appears that exercise increases disease penetrance and accelerates its development. More than 60% of probands harbour mutations in genes that encode desmosomal proteins, which has raised the possibility that defective cell-cell adhesion might play a role in disease pathogenesis. Recent advances have implicated changes in the canonical wingless-type mouse mammary tumour virus integration site (Wnt)/β-catenin and Hippo signalling pathways and defects in forwarding trafficking of ion channels and other proteins to the intercalated disk in cardiac myocytes. In this review we summarize the current understanding of the pathogenesis of ACM and highlight future research directions.

δ-Catenin interacts with LEF-1 and negatively regulates its transcriptional activity

δ-Catenin and β-catenin belong to different subfamilies of armadillo proteins but share some common binding partners, such as E-cadherin. This is the first study that demonstrated a novel common binding partner for δ-catenin and β-catenin, lymphoid enhancer factor-1 (LEF-1). We found that the N-terminus of δ-catenin (amino acids 85-325) bound to the middle region of LEF-1 unlike β-catenin. Overexpressed δ-catenin entered the nucleus and inhibited LEF-1-mediated transcriptional activity in Bosc23 and DLD-1 cell lines. The current study provided novel insights that will provide a better understanding of the effects of δ-catenin on Wnt/LEF-1-mediated transcriptional activity.