Defining interactions and distributions of cadherin and catenin complexes in polarized epithelial cells

MiR-217 is involved in the carcinogenesis of gastric cancer by down-regulating CDH1 expression

GC is one of the most leading malignancies all over the world, and is also the leading cause of cancer-related mortalities. At present, GC remains difficult to diagnose at an early stage. In this study, we first detected the expression of 9 selected miRNAs in the exosomes from 67 GC patients' circular exosomes and found 4 miRNAs level was significantly altered. Meanwhile, one out of 4 candidate miRNAs also had a higher expression in the GC tissue samples, and negative correlated with CDH1 expression. Predicted by bioinformatics tools, confirmed by dual luciferase assay and immunoblotting, we identified that CDH1 is a direct target of miR-217. MiR-217 overexpression enhanced gastric cancer cells proliferation, and reduced exosomal CDH1 level which can be delivered into microenvironment. In conclusion, we constructed the negative correlation between miR-217 and CDH1 level in GC patients and cells; unveiled part of the miR-217 function during the pathogenesis of GC. These findings may give insight into understanding the mechanism of GC pathogenesis and provide new biomarkers for clinical diagnosis.

Changes in E-cadherin rigidity sensing regulate cell adhesion

Mechanical cues are sensed and transduced by cell adhesion complexes to regulate diverse cell behaviors. Extracellular matrix (ECM) rigidity sensing by integrin adhesions has been well studied, but rigidity sensing by cadherins during cell adhesion is largely unexplored. Using mechanically tunable polyacrylamide (PA) gels functionalized with the extracellular domain of E-cadherin (Ecad-Fc), we showed that E-cadherin-dependent epithelial cell adhesion was sensitive to changes in PA gel elastic modulus that produced striking differences in cell morphology, actin organization, and membrane dynamics. Traction force microscopy (TFM) revealed that cells produced the greatest tractions at the cell periphery, where distinct types of actin-based membrane protrusions formed. Cells responded to substrate rigidity by reorganizing the distribution and size of high-traction-stress regions at the cell periphery. Differences in adhesion and protrusion dynamics were mediated by balancing the activities of specific signaling molecules. Cell adhesion to a 30-kPa Ecad-Fc PA gel required Cdc42- and formin-dependent filopodia formation, whereas adhesion to a 60-kPa Ecad-Fc PA gel induced Arp2/3-dependent lamellipodial protrusions. A quantitative 3D cell-cell adhesion assay and live cell imaging of cell-cell contact formation revealed that inhibition of Cdc42, formin, and Arp2/3 activities blocked the initiation, but not the maintenance of established cell-cell adhesions. These results indicate that the same signaling molecules activated by E-cadherin rigidity sensing on PA gels contribute to actin organization and membrane dynamics during cell-cell adhesion. We hypothesize that a transition in the stiffness of E-cadherin homotypic interactions regulates actin and membrane dynamics during initial stages of cell-cell adhesion.

Cell-cell adhesion interface: rise of the lateral membrane

The lateral membrane plays an important role in the mechanical stability of epithelial cell sheet in steady state. In addition, the lateral membrane is continuously remodeled during dynamic processes such as cell extrusion, cytokinesis, and intercellular cell movement. In wound healing, the lateral membrane must be built from flat and spread cells that had crawled into the area of the wound. Thus, forming the lateral membrane is a phenomenon that occurs not only in development but also during homeostatic maintenance and regeneration of differentiated epithelial tissues.

Cell division orientation is coupled to cell-cell adhesion by the E-cadherin/LGN complex

Both cell–cell adhesion and oriented cell division play prominent roles in establishing tissue architecture, but it is unclear how they might be coordinated. Here, we demonstrate that the cell–cell adhesion protein E-cadherin functions as an instructive cue for cell division orientation. This is mediated by the evolutionarily conserved LGN/NuMA complex, which regulates cortical attachments of astral spindle microtubules. We show that LGN, which adopts a three-dimensional structure similar to cadherin-bound catenins, binds directly to the E-cadherin cytosolic tail and thereby localizes at cell–cell adhesions. On mitotic entry, NuMA is released from the nucleus and competes LGN from E-cadherin to locally form the LGN/NuMA complex. This mediates the stabilization of cortical associations of astral microtubules at cell–cell adhesions to orient the mitotic spindle. Our results show how E-cadherin instructs the assembly of the LGN/NuMA complex at cell–cell contacts, and define a mechanism that couples cell division orientation to intercellular adhesion.

Cell–cell adhesion and oriented cell division play key roles in tissue architecture, but how they are coordinated is not known. Here, the authors show that E-cadherin interacts with LGN, and thereby provides a cortical cue that serves to stabilize cortical attachment of astral microtubules at cell–cell adhesions, thus orienting the mitotic spindle.

Epithelial self-healing is recapitulated by a 3D biomimetic E-cadherin junction

Epithelial monolayers undergo self-healing when wounded. During healing, cells collectively migrate into the wound site, and the converging tissue fronts collide and form a stable interface. To heal, migrating tissues must form cell-cell adhesions and reorganize from the front-rear polarity characteristic of cell migration to the apical-basal polarity of an epithelium. However, identifying the "stop signal" that induces colliding tissues to cease migrating and heal remains an open question. Epithelial cells form integrin-based adhesions to the basal extracellular matrix (ECM) and E-cadherin-mediated cell-cell adhesions on the orthogonal, lateral surfaces between cells. Current biological tools have been unable to probe this multicellular 3D interface to determine the stop signal. We addressed this problem by developing a unique biointerface that mimicked the 3D organization of epithelial cell adhesions. This "minimal tissue mimic" (MTM) comprised a basal ECM substrate and a vertical surface coated with purified extracellular domain of E-cadherin, and was designed for collision with the healing edge of an epithelial monolayer. Three-dimensional imaging showed that adhesions formed between cells, and the E-cadherin-coated MTM resembled the morphology and dynamics of native epithelial cell-cell junctions and induced the same polarity transition that occurs during epithelial self-healing. These results indicate that E-cadherin presented in the proper 3D context constitutes a minimum essential stop signal to induce self-healing. That the Ecad:Fc MTM stably integrated into an epithelial tissue and reduced migration at the interface suggests that this biointerface is a complimentary approach to existing tissue-material interfaces.

Synaptopodin couples epithelial contractility to α-actinin-4-dependent junction maturation

A novel tension-sensitive junctional protein, synaptopodin, can relay biophysical input from cellular actomyosin contractility to induce biochemical changes at cell–cell contacts, resulting in structural reorganization of the junctional complex and epithelial barrier maturation.

The epithelial junction experiences mechanical force exerted by endogenous actomyosin activities and from interactions with neighboring cells. We hypothesize that tension generated at cell–cell adhesive contacts contributes to the maturation and assembly of the junctional complex. To test our hypothesis, we used a hydraulic apparatus that can apply mechanical force to intercellular junction in a confluent monolayer of cells. We found that mechanical force induces α-actinin-4 and actin accumulation at the cell junction in a time- and tension-dependent manner during junction development. Intercellular tension also induces α-actinin-4–dependent recruitment of vinculin to the cell junction. In addition, we have identified a tension-sensitive upstream regulator of α-actinin-4 as synaptopodin. Synaptopodin forms a complex containing α-actinin-4 and β-catenin and interacts with myosin II, indicating that it can physically link adhesion molecules to the cellular contractile apparatus. Synaptopodin depletion prevents junctional accumulation of α-actinin-4, vinculin, and actin. Knockdown of synaptopodin and α-actinin-4 decreases the strength of cell–cell adhesion, reduces the monolayer permeability barrier, and compromises cellular contractility. Our findings underscore the complexity of junction development and implicate a control process via tension-induced sequential incorporation of junctional components.

Reevaluating αE-catenin monomer and homodimer functions by characterizing E-cadherin/αE-catenin chimeras

Our results demonstrate that E-cadherin/αE-catenin chimeras homodimerize and do not mimic αE-catenin in the native CCC, and imply that both CCC-bound monomer and cytosolic homodimer αE-catenin are required for strong cell adhesion.

As part of the E-cadherin–β-catenin–αE-catenin complex (CCC), mammalian αE-catenin binds F-actin weakly in the absence of force, whereas cytosolic αE-catenin forms a homodimer that interacts more strongly with F-actin. It has been concluded that cytosolic αE-catenin homodimer is not important for intercellular adhesion because E-cadherin/αE-catenin chimeras thought to mimic the CCC are sufficient to induce cell–cell adhesion. We show that, unlike αE-catenin in the CCC, these chimeras homodimerize, bind F-actin strongly, and inhibit the Arp2/3 complex, all of which are properties of the αE-catenin homodimer. To more accurately mimic the junctional CCC, we designed a constitutively monomeric chimera, and show that E-cadherin–dependent cell adhesion is weaker in cells expressing this chimera compared with cells in which αE-catenin homodimers are present. Our results demonstrate that E-cadherin/αE-catenin chimeras used previously do not mimic αE-catenin in the native CCC, and imply that both CCC-bound monomer and cytosolic homodimer αE-catenin are required for strong cell–cell adhesion.

N-cadherin negatively regulates collective Drosophila glial migration via actin cytoskeleton remodeling

Cell migration is an essential and highly regulated process. During development, glia and neurons migrate over long distances, in most cases collectively, to reach their final destination and build the sophisticated architecture of the nervous system, the most complex tissue of the body. Collective migration is highly stereotyped and efficient, defects in the process leading to severe human diseases that include mental retardation. This dynamic process entails extensive cell communication and coordination, hence the real challenge is to analyze it in the whole organism and at cellular resolution. We here investigate the impact of the N-cadherin adhesion molecule on collective glial migration using the Drosophila developing wing and cell-type specific manipulation of gene expression. We show that N-cadherin timely accumulates in glial cells and that its levels affect migration efficiency. N-cadherin works as a molecular brake in a dosage dependent manner by negatively controlling actin nucleation and cytoskeleton remodeling through α/β catenins. This is the first in vivo evidence for N-cadherin negatively and cell autonomously controlling collective migration.

N-Cadherin-Mediated Signaling Regulates Cell Phenotype for Nucleus Pulposus Cells of the Intervertebral Disc

Juvenile nucleus pulposus (NP) cells of the intervertebral disc (IVD) are large, vacuolated cells that form cell clusters with strong cell-cell interactions. With maturation and aging, NP cells lose their ability to form these cell clusters, with aging-associated changes in NP cell phenotype, morphology, and proteoglycan synthesis that may contribute to IVD degeneration. Therefore, it is important to understand the mechanisms governing juvenile NP cell cluster behavior towards the goal of revealing factors that can promote juvenile, healthy NP cell phenotypes. N-cadherin has been identified as a cell-cell adhesion marker that is present in juvenile NP cells, but disappears with age. The goal of this study was to reveal the importance of N-cadherin in regulating cell-cell interactions in juvenile NP cell cluster formation and test for a regulatory role in maintaining a juvenile NP phenotype in vitro. Juvenile porcine IVD cells, of notochordal origin, were promoted to form cell clusters in vitro, and analyzed for preservation of the juvenile NP phenotype. Additionally, cadherin-blocking experiments were performed to prevent cluster formation in order to study the importance of cluster formation in NP cell signaling. Findings reveal N-cadherin-mediated cell-cell contacts promote cell clustering behavior and regulate NP cell matrix production and preservation of NP-specific markers. Inhibition of N-cadherin-mediated contacts resulted in loss of all features of the juvenile NP cell. These results establish a regulatory role for N-cadherin in juvenile NP cells, and suggest that preservation of the N-cadherin mediated cell-cell contact is important for preserving juvenile NP cell phenotype and morphology.

Nek2 phosphorylates and stabilizes β-catenin at mitotic centrosomes downstream of Plk1

β-Catenin is a multifunctional protein with critical roles in cell-cell adhesion, Wnt signaling, and the centrosome cycle. Whereas the regulation of β-catenin in cell-cell adhesion and Wnt signaling are well understood, how β-catenin is regulated at the centrosome is not. NIMA-related protein kinase 2 (Nek2), which regulates centrosome disjunction/splitting, binds to and phosphorylates β-catenin. Using in vitro and cell-based assays, we show that Nek2 phosphorylates the same regulatory sites in the N-terminus of β-catenin as glycogen synthase kinase 3β (GSK3β), which are recognized by a specific phospho-S33/S37/T41 antibody, as well as additional sites. Nek2 binding to β-catenin appears to inhibit binding of the E3 ligase β-TrCP and prevents β-catenin ubiquitination and degradation. Thus β-catenin phosphorylated by Nek2 is stabilized and accumulates at centrosomes in mitosis. We further show that polo-like kinase 1 (Plk1) regulates Nek2 phosphorylation and stabilization of β-catenin. Taken together, these results identify a novel mechanism for regulating β-catenin stability that is independent of GSK3β and provide new insight into a pathway involving Plk1, Nek2, and β-catenin that regulates the centrosome cycle.

Trim32 reduces PI3K-Akt-FoxO signaling in muscle atrophy by promoting plakoglobin-PI3K dissociation

By promoting dissociation of the desmosomal component plakoglobin from PI3K, the ubiquitin ligase Trim32 reduces PI3K–Akt–FoxO signaling in normal and atrophying muscle, potentially contributing to insulin resistance and catabolic disorders.

Activation of the PI3K–Akt–FoxO pathway induces cell growth, whereas its inhibition reduces cell survival and, in muscle, causes atrophy. Here, we report a novel mechanism that suppresses PI3K–Akt–FoxO signaling. Although skeletal muscle lacks desmosomes, it contains multiple desmosomal components, including plakoglobin. In normal muscle plakoglobin binds the insulin receptor and PI3K subunit p85 and promotes PI3K–Akt–FoxO signaling. During atrophy, however, its interaction with PI3K–p85 is reduced by the ubiquitin ligase Trim32 (tripartite motif containing protein 32). Inhibition of Trim32 enhanced plakoglobin binding to PI3K–p85 and promoted PI3K–Akt–FoxO signaling. Surprisingly, plakoglobin overexpression alone enhanced PI3K–Akt–FoxO signaling. Furthermore, Trim32 inhibition in normal muscle increased PI3K–Akt–FoxO signaling, enhanced glucose uptake, and induced fiber growth, whereas plakoglobin down-regulation reduced PI3K–Akt–FoxO signaling, decreased glucose uptake, and caused atrophy. Thus, by promoting plakoglobin–PI3K dissociation, Trim32 reduces PI3K–Akt–FoxO signaling in normal and atrophying muscle. This mechanism probably contributes to insulin resistance during fasting and catabolic diseases and perhaps to the myopathies and cardiomyopathies seen with Trim32 and plakoglobin mutations.

Dynamics and regulation of epithelial adherens junctions: recent discoveries and controversies

Adherens junctions (AJs) are evolutionarily conserved plasma-membrane structures that mediate cell-cell adhesions in multicellular organisms. They are organized by several types of adhesive integral membrane proteins, most notably cadherins and nectins that are clustered and stabilized by a number of cytoplasmic scaffolds. AJs are key regulators of tissue architecture and dynamics via control of cell proliferation, polarity, shape, motility, and survival. They are absolutely critical for normal tissue morphogenesis and their disruption results in pathological abnormalities in different tissues. Although the field of adherens-junction research dramatically progressed in recent years, a number of important questions remain controversial and poorly understood. This review outlines basic principles that regulate organization of AJs in mammalian epithelia and discusses recent advances and standing controversies in the field. A special attention is paid to the regulation of AJs by vesicle trafficking and the intracellular cytoskeleton as well as roles and mechanisms of adherens-junction disruption during tumor progression and tissue inflammation.

Binding between the junctional proteins afadin and PLEKHA7 and implication in the formation of adherens junction in epithelial cells

Adherens junction (AJ) is a specialized cell-cell junction structure that plays a role in mechanically connecting adjacent cells to resist strong contractile forces and to maintain tissue structure, particularly in the epithelium. AJ is mainly comprised of cell adhesion molecules cadherin and nectin and their associating cytoplasmic proteins including β-catenin, α-catenin, p120(ctn), and afadin. Our series of studies have revealed that nectin first forms cell-cell adhesion and then recruits cadherin to form AJ. The recruitment of cadherin by nectin is mediated by the binding of α-catenin and p120(ctn) to afadin. Recent studies showed that PLEKHA7 binds to p120(ctn), which is associated with E-cadherin, and maintains the integrity of AJ in epithelial cells. In this study, we showed that PLEKHA7 bound to afadin in addition to p120(ctn) and was recruited to the nectin-3α-based cell-cell adhesion site in a manner dependent on afadin, but not on p120(ctn). The binding of PLEKHA7 to afadin was required for the proper formation of AJ, but not for the formation of tight junction, in EpH4 mouse mammary gland epithelial cells. These results indicate that PLEKHA7 plays a cooperative role with nectin and afadin in the proper formation of AJ in epithelial cells.

beta-Catenin protects the epidermis from mechanical stresses

β-Catenin provides stability to epithelia exposed to mechanical stress in part by strengthening adherens junctions in response to tension.

Many tissues in our body experience mechanical stresses caused by both internal and external forces. The skin, for example, must tolerate diverse mechanical insults. In this paper, we report a role for β-catenin in providing stability to epithelia under stress. Loss of β-catenin during epidermal development caused perinatal lethality. Mutant embryos up-regulated stress responses at sites of active morphogenesis, which became more widespread after the stresses associated with birth. In addition, selective loss of tight junctions occurred in focal regions. This was recapitulated in cultured β-catenin–null cells exposed to externally applied forces. In addition, mutant cells were defective in tension-induced engagement of adherens junctions. We found that β-catenin was required to recruit vinculin to the cell cortex and to strengthen the junction’s association with the underlying cytoskeleton in response to tension. These data demonstrate that a complete understanding of the functions of cell adhesion proteins must take into account their roles in response to mechanical stresses.

A functional interaction between the MAGUK protein hDlg and the gap junction protein connexin 43 in cervical tumour cells

Gap junctions, composed of Cxs (connexins), allow direct intercellular communication. Gap junctions are often lost during the development of malignancy, although the processes behind this are not fully understood. Cx43 is a widely expressed Cx with a long cytoplasmic C-terminal tail that contains several potential protein-interaction domains. Previously, in a model of cervical carcinogenesis, we showed that the loss of gap junctional communication correlated with relocalization of Cx43 to the cytoplasm late in tumorigenesis. In the present study, we demonstrate a similar pattern of altered expression for the hDlg (human discs large) MAGUK (membrane-associated guanylate kinase) family tumour suppressor protein in cervical tumour cells, with partial co-localization of Cx43 and hDlg in an endosomal/lysosomal compartment. Relocalization of these proteins is not due to a general disruption of cell membrane integrity or Cx targeting. Cx43 (via its C-terminus) and hDlg interact directly in vitro and can form a complex in cells. This novel interaction requires the N- and C-termini of hDlg. hDlg is not required for Cx43 internalization in W12GPXY cells. Instead, hDlg appears to have a role in maintaining a cytoplasmic pool of Cx43. These results demonstrate that hDlg is a physiologically relevant regulator of Cx43 in transformed epithelial cells.

Structural aspects of adherens junctions and desmosomes

The cadherin-containing intercellular junctions, adherens junctions and desmosomes share an overall logical organization in which the extracellular regions of the cadherins on opposing cells interact, while their cytoplasmic domains are linked to the cytoskeleton through protein assemblies. In adherens junctions, beta-catenin binds to the cytoplasmic domain of cadherins and to alpha-catenin, which links the cadherin/beta-catenin complex to the actin cytoskeleton. In desmosomes, the beta-catenin homolog plakoglobin binds to desmosomal cadherins. The desmosomal cadherin/plakoglobin complex is linked to the intermediate filament system by the protein desmoplakin. In the past decade, components of these systems have been purified to homogeneity and studied biochemically and structurally, providing the beginnings of a mechanistic description of junction architecture and dynamics.

In vivo incorporation of an azide-labeled sugar analog to detect mammalian glycosylphosphatidylinositol molecules isolated from the cell surface

N-Acetylgalactosamine (GalNAc) linked to the first mannose of glycosylphosphatidylinositol (GPI) core has been previously reported to be heterogeneously present on some mammalian GPI-anchored proteins. Here we present a method for profiling GalNAc-containing GPI-anchored proteins in mammalian cells by metabolic labeling with tetraacetylated N-azidoacetylgalactosamine (GalNAz) followed by biotinylation of the incorporated sugar analog. We have labeled both endogenous and recombinant GPI-anchored proteins with GalNAz, and demonstrated that the azide-activated sugar gets incorporated into the GPI glycan, likely as an unsubstituted side branch of the core structure. GalNAz was detected only on GPI molecules attached to proteins, and not on GPI precursors, indicating that GalNAc modification takes place after the GPI anchor is transferred to protein. We have highlighted the utility of this cell labeling approach by demonstrating the ability to examine specific GalNAc-containing GPI-anchored proteins isolated non-destructively from separate membrane domains (apical and basolateral) in polarized epithelial cells. This study represents the first demonstration of site-specific in vivo labeling of a GPI moiety with a synthetic sugar analog.

Quantitative imaging of epithelial cell scattering identifies specific inhibitors of cell motility and cell-cell dissociation

The scattering of cultured epithelial cells in response to hepatocyte growth factor (HGF) is a model system that recapitulates key features of metastatic cell behavior in vitro, including disruption of cell-cell adhesions and induction of cell migration. We have developed image analysis tools that do not require fluorescence tagging and that automatically track and characterize three aspects of scattering in live cells: increase in cell motility, loss of cell-cell adhesion, and spatial dispersion of cells (the redistribution of cells during scattering). We used these tools to screen a library of drugs, and we identified several efficient inhibitors of scattering, which we classified as selective inhibitors of either motility or loss of cell-cell adhesion, or as nonselective inhibitors. We validated the inhibitors and putative targets from this screen in two unrelated model cell lines. Using pharmacological treatments and RNA interference (RNAi), we found that nonsteroidal anti-inflammatory drugs inhibited cell-cell dissociation, that indirubins inhibited cell motility, and that cyclin-dependent kinase 1 and ribosomal S6 kinase were signaling intermediates in HGF-induced cell scattering. This assay is suitable for larger-scale screenings of chemical compounds or RNAi libraries.

Linkage of N-cadherin to multiple cytoskeletal elements revealed by a proteomic approach in hippocampal neurons

The CNS synapse is an adhesive junction differentiated for chemical neurotransmission and is equipped with presynaptic vesicles and postsynaptic neurotransmitter receptors. Cell adhesion molecule cadherins not only maintain connections between pre- and postsynaptic membranes but also modulate the efficacy of synaptic transmission. Although the components of the cadherin-mediated adhesive apparatus have been studied extensively in various cell systems, the complete picture of these components, particularly at the synaptic junction, remains elusive. Here, we describe the proteomic assortment of the N-cadherin-mediated synaptic adhesion apparatus in cultured hippocampal neurons. N-cadherin immunoprecipitated from Triton X-100-solubilized neuronal extract contained equal amounts of β- and α-catenins, as well as F-actin-related membrane anchor proteins such as integrins bridged with α-actinin-4, and Na(+)/K(+)-ATPase bridged with spectrins. A close relative of β-catenin, plakoglobin, and its binding partner, desmoplakin, were also found, suggesting that a subset of the N-cadherin-mediated adhesive apparatus also anchors intermediate filaments. Moreover, dynein heavy chain and LEK1/CENPF/mitosin were found. This suggests that internalized pools of N-cadherin in trafficking vesicles are conveyed by dynein motors on microtubules. In addition, ARVCF and NPRAP/neurojungin/δ2-catenin, but not p120ctn/δ1-catenin or plakophilins-1, -2, -3, -4 (p0071), were found, suggesting other possible bridges to microtubules. Finally, synaptic stimulation by membrane depolarization resulted in an increased 93-kDa band, which corresponded to proteolytically truncated β-catenin. The integration of three different classes of cytoskeletal systems found in the synaptic N-cadherin complex may imply a dynamic switching of adhesive scaffolds in response to synaptic activity.

Loss of E-cadherin expression predicts disease recurrence and shorter survival in colorectal carcinoma

The traditional staging system is currently inadequate for identifying those patients with colorectal carcinoma (CRC) who carry a high risk for poor outcome. In this study, the expression of E-cadherin was evaluated in CRC to determine its correlation with clinico-pathological variables, and association with disease outcome in patients with long-term follow-up. The present series consisted of tissue samples obtained from 230 patients with stage I, II, III, or IV CRC treated during 1981-1990 at Turku University Hospital. Archival paraffin-embedded samples were used to build up tissue microarray blocks, and E-cadherin expression was assessed by immunohistochemistry using an automated staining system. Different grading systems were tested for expression of E-cadherin. Fifty-nine percent of all tumors were positive for E-Cadherin. There was no significant correlation between E-cadherin expression and gender (p < 0.83), localization (p < 0.45), tumor invasion (p < 0.32), or histologic grade (p < 0.41). However, loss of E-cadherin expression was significantly associated with older age (p < 0.03) and lymph node involvement (p < 0.02), and with borderline significance with advanced stage (p < 0.09) and tumor metastasis (p < 0.09). In univariate (Kaplan-Meier) survival analysis, positive E-cadherin significantly (p = 0.009) predicted longer disease-free survival (DFS), and the same was true with disease-specific survival (DSS) as well (p = 0.007). In multivariate (Cox) survival analysis, E-cadherin retained its significance as independent predictor of DFS (HR = 1.56; 95% CI 1.01-2.42, p = 0.043), but not DSS. A sub-group analysis revealed that E-cadherin expression also predicts DFS (p < 0.01) and DSS (p < 0.04) in stage II CRC. Our results implicate the usefulness of E-cadherin expression in predicting disease recurrence and long-term survival in CRC.

Myosin II activity dependent and independent vinculin recruitment to the sites of E-cadherin-mediated cell-cell adhesion

Background

Maintaining proper adhesion between neighboring cells depends on the ability of cells to mechanically respond to tension at cell-cell junctions through the actin cytoskeleton. Thus, identifying the molecules involved in responding to cell tension would provide insight into the maintenance, regulation, and breakdown of cell-cell junctions during various biological processes. Vinculin, an actin-binding protein that associates with the cadherin complex, is recruited to cell-cell contacts under increased tension in a myosin II-dependent manner. However, the precise role of vinculin at force-bearing cell-cell junctions and how myosin II activity alters the recruitment of vinculin at quiescent cell-cell contacts have not been demonstrated.

Results

We generated vinculin knockdown cells using shRNA specific to vinculin and MDCK epithelial cells. These vinculin-deficient MDCK cells form smaller cell clusters in a suspension than wild-type cells. In wound healing assays, GFP-vinculin accumulated at cell-cell junctions along the wound edge while vinculin-deficient cells displayed a slower wound closure rate compared to vinculin-expressing cells. In the presence of blebbistatin (myosin II inhibitor), vinculin localization at quiescent cell-cell contacts was unaffected while in the presence of jasplakinolide (F-actin stabilizer), vinculin recruitment increased in mature MDCK cell monolayers.

Conclusion

These results demonstrate that vinculin plays an active role at adherens junctions under increased tension at cell-cell contacts where vinculin recruitment occurs in a myosin II activity-dependent manner, whereas vinculin recruitment to the quiescent cell-cell junctions depends on F-actin stabilization.

Tissue organization by cadherin adhesion molecules: dynamic molecular and cellular mechanisms of morphogenetic regulation

This review addresses the cellular and molecular mechanisms of cadherin-based tissue morphogenesis. Tissue physiology is profoundly influenced by the distinctive organizations of cells in organs and tissues. In metazoa, adhesion receptors of the classical cadherin family play important roles in establishing and maintaining such tissue organization. Indeed, it is apparent that cadherins participate in a range of morphogenetic events that range from support of tissue integrity to dynamic cellular rearrangements. A comprehensive understanding of cadherin-based morphogenesis must then define the molecular and cellular mechanisms that support these distinct cadherin biologies. Here we focus on four key mechanistic elements: the molecular basis for adhesion through cadherin ectodomains, the regulation of cadherin expression at the cell surface, cooperation between cadherins and the actin cytoskeleton, and regulation by cell signaling. We discuss current progress and outline issues for further research in these fields.

Desmosomes: new perpetrators in tumour suppression

Adherens junctions, which are intercellular adhesive complexes that are crucial for maintaining epithelial homeostasis, are downregulated in many cancers to promote tumour progression. However, the role of desmosomes - adhesion complexes that are related to adherens junctions - in carcinogenesis has remained elusive. Recent studies using mouse genetic approaches have uncovered a role for desmosomes in tumour suppression, demonstrating that desmosome downregulation occurs before that of adherens junctions to drive tumour development and early invasion, suggesting a two-step model of adhesion dysfunction in cancer progression.

MDCK cystogenesis driven by cell stabilization within computational analogues

The study of epithelial morphogenesis is fundamental to increasing our understanding of organ function and disease. Great progress has been made through study of culture systems such as Madin-Darby canine kidney (MDCK) cells, but many aspects of even simple morphogenesis remain unclear. For example, are specific cell actions tightly coupled to the characteristics of the cell's environment or are they more often cell state dependent? How does the single lumen, single cell layer cyst consistently emerge from a variety of cell actions? To improve insight, we instantiated in silico analogues that used hypothesized cell behavior mechanisms to mimic MDCK cystogenesis. We tested them through in vitro experimentation and quantitative validation. We observed novel growth patterns, including a cell behavior shift that began around day five of growth. We created agent-oriented analogues that used the cellular Potts model along with an Iterative Refinement protocol. Following several refinements, we achieved a degree of validation for two separate mechanisms. Both survived falsification and achieved prespecified measures of similarity to cell culture properties. In silico components and mechanisms mapped to in vitro counterparts. In silico, the axis of cell division significantly affects lumen number without changing cell number or cyst size. Reducing the amount of in silico luminal cell death had limited effect on cystogenesis. Simulations provide an observable theory for cystogenesis based on hypothesized, cell-level operating principles.

Epithelial cells perform essential functions throughout the body, acting as both barrier and transporter and allowing an organism to survive and thrive in varied environments. Although the details of many processes that occur within individual cells are well understood, we still lack a thorough understanding of how cells coordinate their behaviors to create complex tissues. In order to achieve deeper insight, we created a list of targeted attributes and plausible rules for the growth of multicellular cysts formed by Madin-Darby canine kidney (MDCK) cells grown in vitro. We then designed in silico analogues of MDCK cystogenesis using object-oriented programming. In silico components (such as the cells and lumens) and their behaviors directly mapped to in vitro components and mechanisms. We conducted in vitro experiments to generate data that would validate or falsify the in silico analogues and then iteratively refined the analogues to mimic that data. Cells in vitro begin to stabilize at around the fifth day even as cysts continue to expand. The in silico system mirrored that behavior and others, achieving new insights. For example, luminal cell death is not strictly required for cystogenesis, and cell division orientation is very important for normal cyst growth.

Formation of extra centrosomal structures is dependent on beta-catenin

beta-Catenin has important roles in cell-cell adhesion and in the regulation of gene transcription. Mutations that stabilize beta-catenin are common in cancer, but it remains unclear how these mutations contribute to cancer progression. beta-Catenin is also a centrosomal component involved in centrosome separation. Centrosomes nucleate interphase microtubules and the bipolar mitotic spindle in normal cells, but their organization and function in human cancers are abnormal. Here, we show that expression of stabilized mutant beta-catenin, which mimics mutations found in cancer, results in extra non-microtubule nucleating structures that contain a subset of centrosome proteins including gamma-tubulin and centrin, but not polo-like kinase 4 (Plk4), SAS-6 or pericentrin. A transcriptionally inactive form of beta-catenin also gives rise to abnormal structures of centrosome proteins. HCT116 human colon cancer cell lines, from which the mutant beta-catenin allele has been deleted, have reduced numbers of cells with abnormal centrosome structures and S-phase-arrested, amplified centrosomes. RNAi-mediated depletion of beta-catenin from centrosomes inhibits S-phase-arrested amplification of centrosomes. These results indicate that beta-catenin is required for centrosome amplification, and mutations in beta-catenin might contribute to the formation of abnormal centrosomes observed in cancers.

Functional role of gangliotetraosylceramide in epithelial-to-mesenchymal transition process induced by hypoxia and by TGF-{beta}

The epithelial-to-mesenchymal transition (EMT) is a basic cellular process that plays a key role in normal embryonic development and in cancer progression/metastasis. Our previous study indicated that EMT processes of mouse and human epithelial cells induced by TGF-β display clear reduction of gangliotetraosylceramide (Gg4) and ganglioside GM2, suggesting a close association of glycosphingolipids (GSLs) with EMT. In the present study, using normal murine mammary gland (NMuMG) cells, we found that levels of Gg4 and of mRNA for the UDP-Gal:β1-3galactosyltransferase-4 (β3GalT4) gene, responsible for reduction of Gg4, were reduced in EMT induced by hypoxia (∼1% O(2)) or CoCl(2) (hypoxia mimic), similarly to that for TGF-β-induced EMT. An increase in the Gg4 level by its exogenous addition or by transfection of the β3GalT4 gene inhibited the hypoxia-induced or TGF-β-induced EMT process, including changes in epithelial cell morphology, enhanced motility, and associated changes in epithelial vs. mesenchymal molecules. We also found that Gg4 is closely associated with E-cadherin and β-catenin. These results suggest that the β3GalT4 gene, responsible for Gg4 expression, is down-regulated in EMT; and Gg4 has a regulatory function in the EMT process in NMuMG cells, possibly through interaction with epithelial molecules important to maintain epithelial cell membrane organization.

The Prognostic Impact of Protein Expression of E-Cadherin-Catenin Complexes Differs between Rectal and Colon Carcinoma

The E-cadherin-catenin complex provides cell-cell adhesion. In order for a carcinoma to metastasize, cancer cells must let go of their hold of neighboring cells in the primary tumor. The presence of components of the E-cadherin-catenin complex in 246 rectal adenocarcinomas was examined by immunohistochemistry and compared to their presence in 219 colon carcinomas. The expression data were correlated to clinical information from the patients' records. There were statistically significant differences in protein expression between the rectal and the colon carcinomas regarding membranous β-catenin, γ-catenin, p120-catenin, and E-cadherin, as well as nuclear β-catenin. In the rectal carcinomas, there was a significant inverse association between the expression of p120-catenin in cell membranes of the primary tumors and the occurrence of local recurrence, while membranous protein expression of β-catenin was inversely related to distant metastases.

p120ctn and P-cadherin but not E-cadherin regulate cell motility and invasion of DU145 prostate cancer cells

Background

Adherens junctions consist of transmembrane cadherins, which interact intracellularly with p120ctn, ß-catenin and α-catenin. p120ctn is known to regulate cell-cell adhesion by increasing cadherin stability, but the effects of other adherens junction components on cell-cell adhesion have not been compared with that of p120ctn.

Methodology/Principal Findings

We show that depletion of p120ctn by small interfering RNA (siRNA) in DU145 prostate cancer and MCF10A breast epithelial cells reduces the expression levels of the adherens junction proteins, E-cadherin, P-cadherin, ß-catenin and α-catenin, and induces loss of cell-cell adhesion. p120ctn-depleted cells also have increased migration speed and invasion, which correlates with increased Rap1 but not Rac1 or RhoA activity. Downregulation of P-cadherin, β-catenin and α-catenin but not E-cadherin induces a loss of cell-cell adhesion, increased migration and enhanced invasion similar to p120ctn depletion. However, only p120ctn depletion leads to a decrease in the levels of other adherens junction proteins.

Conclusions/Significance

Our data indicate that P-cadherin but not E-cadherin is important for maintaining adherens junctions in DU145 and MCF10A cells, and that depletion of any of the cadherin-associated proteins, p120ctn, ß-catenin or α-catenin, is sufficient to disrupt adherens junctions in DU145 cells and increase migration and cancer cell invasion.

AlphaE-catenin regulates actin dynamics independently of cadherin-mediated cell-cell adhesion

αE-catenin has cell–cell contact–dependent and –independent functions in regulating actin and membrane dynamics.

αE-catenin binds the cell–cell adhesion complex of E-cadherin and β-catenin (β-cat) and regulates filamentous actin (F-actin) dynamics. In vitro, binding of αE-catenin to the E-cadherin–β-cat complex lowers αE-catenin affinity for F-actin, and αE-catenin alone can bind F-actin and inhibit Arp2/3 complex–mediated actin polymerization. In cells, to test whether αE-catenin regulates actin dynamics independently of the cadherin complex, the cytosolic αE-catenin pool was sequestered to mitochondria without affecting overall levels of αE-catenin or the cadherin–catenin complex. Sequestering cytosolic αE-catenin to mitochondria alters lamellipodia architecture and increases membrane dynamics and cell migration without affecting cell–cell adhesion. In contrast, sequestration of cytosolic αE-catenin to the plasma membrane reduces membrane dynamics. These results demonstrate that the cytosolic pool of αE-catenin regulates actin dynamics independently of cell–cell adhesion.

Conductin/axin2 and Wnt signalling regulates centrosome cohesion

Activated Wnt/beta-catenin signalling is a characteristic of many cancers and drives cell-cycle progression. Here, we report a mechanism linking Wnt/beta-catenin signalling to centrosome separation. We show that conductin/axin2, a negative regulator of beta-catenin, localizes at the centrosomes by binding to the centriole-associated component C-Nap1. Knockout or knockdown of conductin leads to premature centrosome separation--that is, splitting--which is abolished by knockdown of beta-catenin. Conductin promotes phosphorylation of the amino-terminal serine (Ser 33/37) and threonine (Thr 41) residues of centrosome-associated beta-catenin. Beta-catenin mutated at these residues causes centrosomal splitting, whereas a phospho-mimicking mutant of beta-catenin does not. Importantly, beta-catenin-induced splitting is not inhibited by blocking beta-catenin-dependent transcription. Treatment with Wnts and inhibition of glycogen synthase kinase 3 block beta-catenin phosphorylation and induce centrosomal splitting. These data indicate that Wnt/beta-catenin signalling and conductin regulate centrosomal cohesion by altering the phosphorylation status of beta-catenin at the centrosomes.

DeltaA mRNA and protein distribution in the zebrafish nervous system

Physical interaction between the transmembrane proteins Delta and Notch allows only a subset of neural precursors to become neurons, as well as regulating other aspects of neural development. To examine the localization of Delta protein during neural development, we generated an antibody specific to zebrafish Delta A (Dla). Here, we describe for the first time the subcellular localization of Dla protein in distinct puncta at cell cortex and/or membrane, supporting the function of Dla in direct cell-cell communication. In situ RNA hybridization and immunohistochemistry revealed dynamic, coordinated expression patterns of dla mRNA and Dla protein in the developing and adult zebrafish nervous system. Dla expression is mostly excluded from differentiated neurons and is maintained in putative precursor cells at least until larval stages. In the adult brain, dla mRNA and Dla protein are expressed in proliferative zones normally associated with stem cells.

β-Catenin expression in benign and malignant salivary gland tumors

OBJECTIVE

To assess the expression of β-catenin in benign and malignant salivary gland tumors and to investigate the possible role of β-catenin in the behavior of salivary gland tumors.

STUDY DESIGN

Paraffin embedded tissues from 45 salivary gland tumors were studied immunohistochemically for expression of β-catenin.

RESULT

Reduced/aberrant β-catenin expression was seen in benign and malignant salivary gland tumors. Cytoplasmic localization and reduced membranous expression were comparatively observed more in malignant salivary gland tumors. Additionally, in pleomorphic adenomas (PAs), β-catenin exhibited intense staining in cells arranged in the form of ducts/tubules, whereas cells in clusters and sheets showed weaker immunoreactivity.

CONCLUSION

Reduced and cytoplasmic localization of β-catenin could indicate lack of differentiation, invasive potential, and aggressive behavior in malignant salivary gland tumors. Furthermore, change in expression based on the arrangement of tumor cells may suggest that β-catenin may have a role in morphological variations seen in PAs.

Characterization of newly established bovine intestinal epithelial cell line

Membranous epithelial cells (M cells) of the follicle-associated epithelium in Peyer's patches have a high capacity for transcytosis of several viruses and microorganisms. Here, we report that we have successfully established a bovine intestinal epithelial cell line (BIE cells) and developed an in vitro M cell model. BIE cells have a cobblestone morphology and microvilli-like structures, and strongly express cell-to-cell junctional proteins and cytokeratin, which is a specific intermediate filament protein of epithelial cells. After co-culture with murine intestinal lymphocytes or treatment with supernatant from bovine PBMC cultured with IL-2, BIE cells acquired the ability of transcytosis. Therefore, BIE cells have typical characteristics of bovine intestinal epithelial cells and also have the ability to differentiate into an M cell like linage. In addition, our results indicate that contact between immune cells and epithelial cells may not be absolutely required for the differentiation of M cells. We think that BIE cells will be useful for studying the transport mechanisms of various pathogens and also the evaluation of drug delivery via M cells.

Wheat proteins enhance stability and function of adhesion molecules in cryopreserved hepatocytes

Cryopreserved hepatocytes with good hepatospecific functions upon thawing are important for clinical transplantation and for in vitro drug toxicity testing. However, cryopreservation reduces viability and certain hepatospecific functions, but the most pronounced change is diminished attachment efficiency of hepatocytes. Adhesion of cells to the extracellular matrix and cell-cell contacts are crucial for many aspects of cellular function. These processes are partly mediated and controlled by cellular adhesion molecules. The mechanisms responsible for reduced attachment efficiency of cryopreserved hepatocytes are not well understood. To address this question, we investigated the effect of a new cryopreservation procedure, using wheat proteins (WPs) or mixtures of recombinant forms of wheat freezing tolerance-associated proteins, on the stability of three important adhesion molecules (beta1-integrin, E-cadherin, and beta-catenin). Immunoblot analyses revealed that the levels of beta1-integrin, E-cadherin, and beta-catenin were much lower in cryopreserved rat hepatocytes, when compared to fresh cells. Protein expression of the adhesion molecules was generally lower in cells cryopreserved with DMSO, compared to WPs. Moreover, the stability of the adhesion molecules was not affected by cryopreservation to the same degree, with more pronounced decreases occurring for beta1-integrin (62-74%) > beta-catenin (51-58%) > E-cadherin (21-37%). However, when hepatocytes were cryopreserved with partially purified WPs (SulWPE, AcWPE) or with mixtures of recombinant wheat proteins, there was a clear protective effect against the loss of protein expression of beta1-integrin, E-cadherin, and beta-catenin. Protein expression was only 10-20% lower than that observed in fresh hepatocytes. These findings clearly demonstrate that WPs, and more particularly, partially purified WPs and recombinant wheat proteins, were more efficient for cryopreservation of rat hepatocytes by maintaining good expression of these adhesion molecules. These promising results could lead to a new and improved cryopreservation technology for applications such as clinical transplantation of hepatocytes.

Discovering the molecular components of intercellular junctions--a historical view

The organization of metazoa is based on the formation of tissues and on tissue-typical functions and these in turn are based on cell-cell connecting structures. In vertebrates, four major forms of cell junctions have been classified and the molecular composition of which has been elucidated in the past three decades: Desmosomes, which connect epithelial and some other cell types, and the almost ubiquitous adherens junctions are based on closely cis-packed glycoproteins, cadherins, which are associated head-to-head with those of the hemi-junction domain of an adjacent cell, whereas their cytoplasmic regions assemble sizable plaques of special proteins anchoring cytoskeletal filaments. In contrast, the tight junctions (TJs) and gap junctions (GJs) are formed by tetraspan proteins (claudins and occludins, or connexins) arranged head-to-head as TJ seal bands or as paracrystalline connexin channels, allowing intercellular exchange of small molecules. The by and large parallel discoveries of the junction protein families are reported.

Molecular mechanisms of metastasis in prostate cancer

Prostate cancer (PCa) preferentially metastasizes to the bone marrow stroma of the axial skeleton. This activity is the principal cause of PCa morbidity and mortality. The exact mechanism of PCa metastasis is currently unknown, although considerable progress has been made in determining the key players in this process. In this review, we present the current understanding of the molecular processes driving PCa metastasis to the bone.

An acidic extracellular pH induces Src kinase-dependent loss of beta-catenin from the adherens junction

Little attention has been paid to the role of adherens junctions (AJs) in acidic extracellular pH (pHe)-induced cell invasion. Incubation of HepG2 cells in acidic medium (pH 6.6) induced cell dispersion from tight cell clusters, and this change was accompanied by downregulation of beta-catenin at cell junctions and a rapid activation of c-Src. Pretreatment with PP2 prevented the acidic pH-induced downregulation of beta-catenin at AJ and in the membrane fractions. The acidic pHe-induced c-Src activation increased tyrosine phosphorylation of beta-catenin and decreased the amount of beta-catenin-associated E-cadherin. The depletion of membrane-bound beta-catenin coincided with enhanced cell migration and invasion, and this acidic pHe-increased cell migration and invasion was prevented by PP2. In conclusion, this study characterizes a novel signaling pathway responsible for acidic microenvironment-promoted migration and invasive behaviors of cancer cells.

Beta-catenin mediates alteration in cell proliferation, motility and invasion of prostate cancer cells by differential expression of E-cadherin and protein kinase D1

We have previously demonstrated that Protein Kinase D1 (PKD1) interacts with E-cadherin and is associated with altered cell aggregation and motility in prostate cancer (PC). Because both PKD1 and E-cadherin are known to be dysregulated in PC, in this study we investigated the functional consequences of combined dysregulation of PKD1 and E-cadherin using a panel of human PC cell lines. Gain and loss of function studies were carried out by either transfecting PC cells with full-length E-cadherin and/or PKD1 cDNA or by protein silencing by siRNAs, respectively. We studied major malignant phenotypic characteristics including cell proliferation, motility, and invasion at the cellular level, which were corroborated with appropriate changes in representative molecular markers. Down regulation or ectopic expression of either E-cadherin or PKD1 significantly increased or decreased cell proliferation, motility, and invasion, respectively, and combined down regulation cumulatively influenced the effects. Loss of PKD1 or E-cadherin expression was associated with increased expression of the pro-survival molecular markers survivin, beta-catenin, cyclin-D, and c-myc, whereas overexpression of PKD1 and/or E-cadherin resulted in an increase of caspases. The inhibitory effect of PKD1 and E-cadherin on cell proliferation was rescued by coexpression with beta-catenin, suggesting that beta-catenin mediates the effect of proliferation by PKD1 and E-cadherin. This study establishes the functional significance of combined dysregulation of PKD1 and E-cadherin in PC and that their effect on cell growth is mediated by beta-catenin.

Molecular components of the adherens junction

Adherens junctions serve to couple individual cells into various arrangements required for tissue structure and function. The central structural components of adherens junctions are transmembrane adhesion receptors, and their associated actin-binding/regulatory proteins. The molecular machineries that organize these adhesion receptor complexes into higher order junction structures, and the functional consequences of this junctional organization will be discussed.

The many faces of actin: matching assembly factors with cellular structures

Actin filaments are major components of at least 15 distinct structures in metazoan cells. These filaments assemble from a common pool of actin monomers, but do so at different times and places, and in response to different stimuli. All of these structures require actin-filament assembly factors. To date, many assembly factors have been identified, including Arp2/3 complex, multiple formin isoforms and spire. Now, a major task is to figure out which factors assemble which actin-based structures. Here, we focus on structures at the plasma membrane, including both sheet-like protrusive structures (such as lamellipodia and ruffles) and finger-like protrusions (such as filopodia and microvilli). Insights gained from studies of adherens junctions and the immunological synapse are also considered.

beta-Catenin is a Nek2 substrate involved in centrosome separation

beta-Catenin plays important roles in cell adhesion and gene transcription, and has been shown recently to be essential for the establishment of a bipolar mitotic spindle. Here we show that beta-catenin is a component of interphase centrosomes and that stabilization of beta-catenin, mimicking mutations found in cancers, induces centrosome splitting. Centrosomes are held together by a dynamic linker regulated by Nek2 kinase and its substrates C-Nap1 (centrosomal Nek2-associated protein 1) and Rootletin. We show that beta-catenin binds to and is phosphorylated by Nek2, and is in a complex with Rootletin. In interphase, beta-catenin colocalizes with Rootletin between C-Nap1 puncta at the proximal end of centrioles, and this localization is dependent on C-Nap1 and Rootletin. In mitosis, when Nek2 activity increases, beta-catenin localizes to centrosomes at spindle poles independent of Rootletin. Increased Nek2 activity disrupts the interaction of Rootletin with centrosomes and results in binding of beta-catenin to Rootletin-independent sites on centrosomes, an event that is required for centrosome separation. These results identify beta-catenin as a component of the intercentrosomal linker and define a new function for beta-catenin as a key regulator of mitotic centrosome separation.

Expression of the E-cadherin-catenins complex in sentinel node is related to tumor morphology but not to spread to nonsentinel nodes

The sentinel node (SN) technique has gained a key role in breast cancer surgery, allowing for an accurate staging of the axillary status with a minimally invasive resection. In this study, we explored the implication of three proteins (E-cadherin, a- and b-catenins) that form the cadherin-catenin complex, a receptorial structure strictly involved in tumoral vascular invasion and embolization in this biologic event. We studied the immunohistochemical expression of the complex in patients with metastatic SN, matching the group with involved nonsentinel lymph nodes (NSNs) with that having free axillary NSNs. The simultaneous staining of the SN metastases for the three proteins has been considered an indicator of preserved function. Our data confirmed the lack of cadherin-catenin complex in tumors with lobular morphology even in SN metastasis, but statistical evaluation could not prove a significant relation between complex integrity and NSN involvement. Moreover, considering traditional histopathologic parameters, only vascular peritumoral embolization was related to an increased risk of metastatic spread to axillary NSNs.

Bacteroides fragilis toxin stimulates intestinal epithelial cell shedding and gamma-secretase-dependent E-cadherin cleavage

Enterotoxigenic Bacteroides fragilis - organisms that live in the colon - secrete a metalloprotease toxin, B. fragilis toxin. This toxin binds to a specific intestinal epithelial cell receptor and stimulates cell proliferation, which is dependent, in part, on E-cadherin degradation and beta-catenin-T-cell-factor nuclear signaling. Gamma-secretase (or presenilin-1) is an intramembrane cleaving protease and is a positive regulator of E-cadherin cleavage and a negative regulator of beta-catenin signaling. Here we examine the mechanistic details of toxin-initiated E-cadherin cleavage. B. fragilis toxin stimulated shedding of cell membrane proteins, including the 80 kDa E-cadherin ectodomain. Shedding of this domain required biologically active toxin and was not mediated by MMP-7, ADAM10 or ADAM17. Inhibition of gamma-secretase blocked toxin-induced proteolysis of the 33 kDa intracellular E-cadherin domain causing cell membrane retention of a distinct beta-catenin pool without diminishing toxin-induced cell proliferation. Unexpectedly, gamma-secretase positively regulated basal cell proliferation dependent on the beta-catenin-T-cell-factor complex. We conclude that toxin induces step-wise cleavage of E-cadherin, which is dependent on toxin metalloprotease and gamma-secretase. Our results suggest that differentially regulated beta-catenin pools associate with the E-cadherin-gamma-secretase adherens junction complex; one pool regulated by gamma-secretase is important to intestinal epithelial cell homeostasis.

Cinderella no longer: alpha-catenin steps out of cadherin's shadow

To date, alpha-catenin has been best understood as an important cytoplasmic component of the classical cadherin complex responsible for cell-cell adhesion. By virtue of its capacity to bind F-actin, alpha-catenin was commonly envisaged to support cadherin function by coupling the adhesion receptor to the actin cytoskeleton. But is alpha-catenin solely the cadherin's handmaiden? A range of recent developments suggest, instead, that its biological activity is much more complex than previously appreciated. Evidence from cellular systems and model organisms demonstrates a clear, often dramatic, role for alpha-catenin in tissue organization and morphogenesis. The morphogenetic impact of alpha-catenin reflects its capacity to mediate functional cooperation between cadherins and the actin cytoskeleton, but is not confined to this. alpha-catenin has a role in regulating cell proliferation and cadherin-independent pools of alpha-catenin may contribute to its functional impact.

Axon behavior in the olfactory nerve reflects the involvement of catenin-cadherin mediated adhesion

The projection of olfactory sensory neuron (OSN) axons to the olfactory bulb (OB) is a complex but well-regulated process. Although odorant receptor proteins, and other molecules, are implicated in this process, our understanding remains incomplete. We demonstrate that axons remain restricted to the outer olfactory nerve layer (ONLo) until they are proximal to their target glomeruli, where they enter the inner ONL (ONLi), dividing the ONL into extension and sorting zones. Sorting is likely contingent on cell:cell interactions mediated in part by cell adhesion molecules. The cadherins are a large family of adhesion molecules whose function is contingent on their intracellular binding partners, the catenins, which in turn link to the cytoskeleton. We previously demonstrated that the organization of the cytoskeleton changed as olfactory sensory neuron axons moved from the ONLo to the ONLi. To further assess the role of cadherin mediated adhesion in the developing mouse ONL, we localized alpha-, beta-, gamma-, delta-, and p120-catenins as well as neural cadherin (N-cadherin; CDH2) in the OB. alpha- and beta-catenins are found throughout the OB and are uniform throughout the ONL. In contrast, gamma-catenin and CDH2 are expressed predominantly in the ONLo during perinatal development, but are uniform across the ONL beginning at P7 and into adulthood. Finally, p120- and delta-catenins are expressed in nonoverlapping patterns by olfactory axons and OB neuronal dendrites, respectively. We conclude that gamma-catenin-mediated CDH2 adhesion may influence OSN targeting by restricting axons to the ONLo until they reach the appropriate domain of the OB.

The role of matrix metalloproteinases-2, -7 and -9 and ?-catenin in high grade endometrial carcinoma

AIMS

To determine the expression of matrix metalloproteinases (MMPs)-2, -7 and -9 and beta-catenin in uterine serous carcinoma (USC) and endometrioid endometrial carcinoma (EEC) and to investigate any difference in expression between EEC and USC which might explain the mechanism of invasion and aggressive behaviour of USC.

METHODS AND RESULTS

Tissue microarrays were created from the viable central part and from the invasive edge of 20 cases of grade 3 EEC and 73 cases of USC. Immunohistochemistry was performed using antibodies to MMPs-2, -7 and -9 and beta-catenin. MMPs-2, -7 and -9 and beta-catenin were present in both tumour types; there was significantly higher expression of MMPs-2 and -9 in EEC compared with USC and significantly increased expression of MMPs-2 and -9 by carcinoma cells at the invasive edge of USC.

CONCLUSIONS

MMPs-2, -7 and -9 and beta-catenin are present in EEC and USC. The increased expression of MMPs-2 and -9 by carcinoma cells at the invasive edge of USC is possibly due to increased binding of MMPs secreted by the stromal cells to carcinoma cells, thus equipping the USC carcinoma cells with proteases for invasion.