Expression of a dominant negative cadherin mutant inhibits proliferation and stimulates terminal differentiation of human epidermal keratinocytes

JNK inhibition enhances cell-cell adhesion impaired by desmoglein 3 gene disruption in keratinocytes

c-Jun NH2-terminal protein kinase (JNK) and p38 are stress-activated mitogen-activated protein kinases (MAPK) that are phosphorylated by various stimuli. It has been reported that the loss of desmoglein (DSG) 3, a desmosomal transmembrane core molecule, in keratinocytes impairs cell-cell adhesion accompanied by p38 MAPK activation. To understand the biological role of DSG3 in desmosomes and its relationship with stress-activated MAPKs, we established DSG3 knockout keratinocytes (KO cells). Wild-type cells showed a linear localization of DSG1 to cell-cell contacts, whereas KO cells showed a remarkable reduction despite the increased protein levels of DSG1. Cell-cell adhesion in KO cells was impaired over time, as demonstrated by dispase-based dissociation assays. The linear localization of DSG1 to cell-cell contacts and the strength of cell-cell adhesion were promoted by the pharmacological inhibition of JNK. Conversely, pharmacological activation of JNK, but not p38 MAPK, in wild-type cells reduced the linear localization of DSG1 in cell-cell contacts. Our data indicate that DSG1 and DSG2 in KO cells cannot compensate for the attenuation of cell-cell adhesion strength caused by DSG3 deficiency and that JNK inhibition restores the strength of cell-cell adhesion by increasing the linear localization of DSG1 in cell-cell contacts in KO cells. Inhibition of JNK signaling may improve cell-cell adhesion in diseases in which DSG3 expression is impaired.

A reductionist approach to determine the effect of cell-cell contact on human epidermal stem cell differentiation

The balance between stem cell renewal and differentiation is determined by the interplay between intrinsic cellular controls and extrinsic factors presented by the microenvironment, or 'niche'. Previous studies on cultured human epidermis have utilised suspension culture and restricted cell spreading to investigate regulation of differentiation in single keratinocytes. However, keratinocytes are typically adherent to neighbouring cells in vivo. We therefore developed experimental models to investigate the combined effects of cell-ECM adhesion and cell-cell contact. We utilized lipid-modified oligonucleotides to form clusters of keratinocytes which were subsequently placed in suspension to induce terminal differentiation. In this experimental model cell-cell contact had no effect on suspension-induced differentiation of keratinocytes. We next developed a high-throughput platform for robust geometrical confinement of keratinocytes to hexagonal ECM-coated islands permitting direct cell-cell contact between single cells. As in the case of circular islands, differentiation was stimulated on the smallest single hexagonal islands. However, the percentage of involucrin-positive cells on small bowtie islands was significantly lower than on single islands, demonstrating that cell-cell contact reduced differentiation in response to decreased substrate adhesion. None of the small bowtie islands contained two involucrin-positive cells. Rather, if one cell was involucrin-positive the other was involucrin-negative. This suggests that there is intrinsic asymmetry in the effect of cell-cell contact in decreasing differentiation. Thus, our reductionist approaches provide new insights into the effect of the niche on keratinocyte differentiation. STATEMENT OF SIGNIFICANCE: Stem cell behaviour is regulated by a combination of external signals, including the nature of the adhesive substrate and cell-cell interactions. An understanding of how different signals are integrated creates the possibility of developing new biomaterials to promote tissue regeneration and broaden our understanding of skin diseases such as eczema and psoriasis, in which stem cell proliferation and differentiation are perturbed. In this study we have applied two methods to engineer intercellular adhesion of human epidermal stem cells, one involving lipid-modified DNA and the other involving hexagonal micropatterns. We show that the effect of cell-cell adhesion depends on cell-substrate adhesion and uncover evidence that two cells in equivalent environments can nevertheless behave differently.

Cell-Cell Junctions Organize Structural and Signaling Networks

Cell-cell junctions link cells to each other in tissues, and regulate tissue homeostasis in critical cell processes that include tissue barrier function, cell proliferation, and migration. Defects in cell-cell junctions give rise to a wide range of tissue abnormalities that disrupt homeostasis and are common in genetic abnormalities and cancers. Here, we discuss the organization and function of cell-cell junctions primarily involved in adhesion (tight junction, adherens junction, and desmosomes) in two different epithelial tissues: a simple epithelium (intestine) and a stratified epithelium (epidermis). Studies in these tissues reveal similarities and differences in the organization and functions of different cell-cell junctions that meet the requirements for the specialized functions of each tissue. We discuss cell-cell junction responses to genetic and environmental perturbations that provide further insights into their roles in maintaining tissue homeostasis.

Wnt ligand presentation and reception: from the stem cell niche to tissue engineering

Stem cells reside in niches where spatially restricted signals maintain a delicate balance between stem cell self-renewal and differentiation. Wnt family proteins are particularly suited for this role as they are modified by lipids, which constrain and spatially regulate their signalling range. In recent years, Wnt/β-catenin signalling has been shown to be essential for the self-renewal of a variety of mammalian stem cells. In this review, we discuss Wnt-responsive stem cells in their niche, and mechanisms by which Wnt ligands are presented to responsive cells. We also highlight recent progress in molecular visualization that has allowed for the monitoring of Wnt signalling within the stem cell compartment and new approaches to recapitulate this niche signalling in vitro Indeed, new technologies that present Wnt in a localized manner and mimic the three-dimensional microenvironment of stem cells will advance our understanding of Wnt signalling in the stem cell niche. These advances will expand current horizons to exploit Wnt ligands in the rapidly evolving fields of tissue engineering and regenerative medicine.

Isolation and In Vitro Characterization of Epidermal Stem Cells

Colony-forming assays represent prospective methods, where cells isolated from enzymatically dissociated tissues or from tissue cultures are assessed for their proliferative capacity in vitro. Complex tissues such as the epithelial component of the skin (the epidermis) are characterized by a substantial cellular heterogeneity. Analysis of bulk populations of cells by colony-forming assays can consequently be convoluted by a number of factors that are not controlled for in population wide studies. It is therefore advantageous to refine in vitro growth assays by sub-fractionation of cells using flow cytometry. Using markers that define the spatial origin of epidermal cells, it is possible to interrogate the specific characteristics of subpopulations of cells based on their in vivo credentials. Here, we describe how to isolate, culture, and characterize keratinocytes from murine back and tail skin sorted by surface antigens associated with adult stem cell characteristics.

N-Cadherin Induction by ECM Stiffness and FAK Overrides the Spreading Requirement for Proliferation of Vascular Smooth Muscle Cells

In contrast to the accepted pro-proliferative effect of cell-matrix adhesion, the proliferative effect of cadherin-mediated cell-cell adhesion remains unresolved. Here, we studied the effect of N-cadherin on cell proliferation in the vasculature. We show that N-cadherin is induced in smooth muscle cells (SMCs) in response to vascular injury, an in vivo model of tissue stiffening and proliferation. Complementary experiments performed with deformable substrata demonstrated that stiffness-mediated activation of a focal adhesion kinase (FAK)-p130Cas-Rac signaling pathway induces N-cadherin. Additionally, by culturing paired and unpaired SMCs on microfabricated adhesive islands of different areas, we found that N-cadherin relaxes the spreading requirement for SMC proliferation. In vivo SMC deletion of N-cadherin strongly reduced injury-induced cycling. Finally, SMC-specific deletion of FAK inhibited proliferation after vascular injury, and this was accompanied by reduced induction of N-cadherin. Thus, a stiffness- and FAK-dependent induction of N-cadherin connects cell-matrix to cell-cell adhesion and regulates the degree of cell spreading needed for cycling.

Stem cell signaling. An integral program for tissue renewal and regeneration: Wnt signaling and stem cell control

Stem cells fuel tissue development, renewal, and regeneration, and these activities are controlled by the local stem cell microenvironment, the "niche." Wnt signals emanating from the niche can act as self-renewal factors for stem cells in multiple mammalian tissues. Wnt proteins are lipid-modified, which constrains them to act as short-range cellular signals. The locality of Wnt signaling dictates that stem cells exiting the Wnt signaling domain differentiate, spatially delimiting the niche in certain tissues. In some instances, stem cells may act as or generate their own niche, enabling the self-organization of patterned tissues. In this Review, we discuss the various ways by which Wnt operates in stem cell control and, in doing so, identify an integral program for tissue renewal and regeneration.

Cadherin cytoplasmic domains inhibit the cell surface localization of endogenous E-cadherin, blocking desmosome and tight junction formation and inducing cell dissociation

The downregulation of E-cadherin function has fundamental consequences with respect to cancer progression, and occurs as part of the epithelial–mesenchymal transition (EMT). In this study, we show that the expression of the Discosoma sp. red fluorescent protein (DsRed)-tagged cadherin cytoplasmic domain in cells inhibited the cell surface localization of endogenous E-cadherin, leading to morphological changes, the inhibition of junctional assembly and cell dissociation. These changes were associated with increased cell migration, but were not accompanied by the down-regulation of epithelial markers and up-regulation of mesenchymal markers. Thus, these changes cannot be classified as EMT. The cadherin cytoplasmic domain interacted with β-catenin or plakoglobin, reducing the levels of β-catenin or plakoglobin associated with E-cadherin, and raising the possibility that β-catenin and plakoglobin sequestration by these constructs induced E-cadherin intracellular localization. Accordingly, a cytoplasmic domain construct bearing mutations that weakened the interactions with β-catenin or plakoglobin did not impair junction formation and adhesion, indicating that the interaction with β-catenin or plakoglobin was essential to the potential of the constructs. E-cadherin–α-catenin chimeras that did not require β-catenin or plakoglobin for their cell surface transport restored cell–cell adhesion and junction formation.

Expression of wnt and frizzled genes during early sea star development

The Wnt signaling pathway is highly conserved across metazoa and has pleiotropic functions in the development of many animals. Binding of a secreted Wnt ligand to its Frizzled (Fz) receptor activates Dishevelled, which then drives one of three major signaling cascades, canonical (β-catenin), calcium, or planar cell polarity signaling. These pathways have distinct developmental effects and function in different processes in different organisms. Here we report the expression of six wnt and three fz genes during embryogenesis of the sea star, Patiria miniata, as a first step in uncovering the roles of Wnt signaling in the development of this organism. wnt3, wnt4, wnt8, and wnt16 are expressed in nested domains in the endoderm and lateral ectoderm from blastula through late gastrula stages; wnt2 and wnt5 are expressed in the mesoderm and anterior endoderm. Expression of different fz paralogs is detected in the mesoderm; posterior endoderm and ectoderm; and anterior ectoderm. Taken together, this suggests that Wnt signaling can occur throughout most of the embryo and may therefore play multiple roles during sea star development.

Consistent activation of the β-catenin pathway by Salmonella type-three secretion effector protein AvrA in chronically infected intestine

Salmonella infection is a common public health problem that can become chronic and increase the risk of cancer. Live, mutated Salmonella is used to target cancer cells. However, few studies have addressed chronic Salmonella infection in vivo. AvrA is a Salmonella type-three secretion effector that is multifunctional, inhibiting intestinal inflammation and enhancing proliferation. β-catenin is a key player in intestinal renewal, inflammation, and tumorigenesis. We hypothesize that in Salmonella-infected intestine, AvrA chronically activates the β-catenin pathway and increases cell proliferation, thus deregulating the intestinal responses to bacterial infection. We followed mice with Salmonella infection for 27 wk and investigated the physiological effects and role of AvrA on β-catenin in chronically infected intestine. We found that AvrA persistently regulated β-catenin posttranslational modifications, including phosphorylation and acetylation. Moreover, the upstream regulator Akt, transcription factors, T cell factors, nuclear β-catenin, and β-catenin target genes were enhanced in mice infected with Salmonella-expressing AvrA. AvrA has a chronic functional role in promoting intestinal renewal. In summary, we have uncovered an essential role of Salmonella AvrA in chronically activating β-catenin and impacting intestinal renewal in small intestine and colon. Our study emphasizes the importance of AvrA in chronic bacterial infection.

Crossroads of integrins and cadherins in epithelia and stroma remodeling

Adhesion events mediated by cadherin and integrin adhesion receptors have fundamental roles in the maintenance of the physiological balance of epithelial tissues, and it is well established that perturbations in their normal functional activity and/or changes in their expression are associated with tumorigenesis. Over the last decades, increasing evidence of a dynamic collaborative interaction between these complexes through their shared interactions with cytoskeletal proteins and common signaling pathways has emerged not only as an important regulator of several aspects of epithelial cell behavior, but also as a coordinated adhesion module that senses and transmits signals from and to the epithelia surrounding microenvironment. The tight regulation of their crosstalk is particularly important during epithelial remodeling events that normally take place during morphogenesis and tissue repair, and when defective it leads to cell transformation and aggravated responses of the tumor microenvironment that contribute to tumorigenesis. In this review we highlight some of the interactions that regulate their crosstalk and how this could be implicated in regulating signals across epithelial tissues to sustain homeostasis.

Mimicking normal tissue architecture and perturbation in cancer with engineered micro-epidermis

Correct tissue architecture is essential for normal physiology, yet there have been few attempts to recreate tissues using micro-patterning. We have used polymer brush micro-engineering to generate a stratified micro-epidermis with fewer than 10 human keratinocytes. Epidermal stem cells are captured on 100 μm diameter circular collagen-coated disks. Within 24 h they assemble a stratified micro-tissue, in which differentiated cells have a central suprabasal location. For rings with a non-adhesive centre of up to 40 μm diameter, cell–cell and cell–matrix adhesive interactions together result in correct micro-epidermis assembly. Assembly requires actin polymerization, adherens junctions and desmosomes, but not myosin II-mediated contractility nor coordinated cell movement. Squamous cell carcinoma cells on micro-patterned rings exhibit disturbed architecture that correlates with the characteristics of the original tumours. The micro-epidermis we have generated provides a new platform for screening drugs that modulate tissue assembly, quantifying tissue stratification and investigating the properties of tumour cells.

Filaggrin genotype determines functional and molecular alterations in skin of patients with atopic dermatitis and ichthyosis vulgaris

Background

Several common genetic and environmental disease mechanisms are important for the pathophysiology behind atopic dermatitis (AD). Filaggrin (FLG) loss-of-function is of great significance for barrier impairment in AD and ichthyosis vulgaris (IV), which is commonly associated with AD. The molecular background is, however, complex and various clusters of genes are altered, including inflammatory and epidermal-differentiation genes.

Objective

The objective was to study whether the functional and molecular alterations in AD and IV skin depend directly on FLG loss-of-function, and whether FLG genotype determines the type of downstream molecular pathway affected.

Methods and Findings

Patients with AD/IV (n = 43) and controls (n = 15) were recruited from two Swedish outpatient clinics and a Swedish AD family material with known FLG genotype. They were clinically examined and their medical history recorded using a standardized questionnaire. Blood samples and punch biopsies were taken and trans-epidermal water loss (TEWL) and skin pH was assessed with standard techniques. In addition to FLG genotyping, the STS gene was analyzed to exclude X-linked recessive ichthyosis (XLI). Microarrays and quantitative real-time PCR were used to compare differences in gene expression depending on FLG genotype. Several different signalling pathways were altered depending on FLG genotype in patients suffering from AD or AD/IV. Disease severity, TEWL and pH follow FLG deficiency in the skin; and the number of altered genes and pathways are correlated to FLG mRNA expression.

Conclusions

We emphasize further the role of FLG in skin-barrier integrity and the complex compensatory activation of signalling pathways. This involves inflammation, epidermal differentiation, lipid metabolism, cell signalling and adhesion in response to FLG-dependent skin-barrier dysfunction.

A comparison of primary oesophageal squamous epithelial cells with HET-1A in organotypic culture

BACKGROUND INFORMATION

Carcinoma of the oesophagus is the sixth leading cause of cancer death in the western world and is associated with a 5-year survival of less than 15%. Recent evidence suggests that stromal-epithelial interactions are fundamental in carcinogenesis. The advent of co-culture techniques permits the investigation of cross-talk between the stroma and epithelium in a physiological setting. We have characterized a histologically representative oesophageal organotypic model and have used it to compare the most commonly used squamous oesophageal cell line, HET-1A, with primary oesophageal squamous cells for use in studies of the oesophageal epithelium in vitro.

RESULTS

When grown in an organotypic culture with normal fibroblasts, the oesophageal carcinoma cell lines OE21 (squamous) and OE19 (adenocarcinoma) morphologically resembled the tumour of origin with evidence of stromal invasion and mucus production, respectively. However, HET-1A cells, which were derived from normal squamous oesophageal cells, appeared dysplastic and failed to display evidence of squamous differentiation. By comparison with primary oesophageal epithelial cells, the HET-1A cells were highly proliferative and did not express the epithelial markers E-cadherin or CK5/6 (casein kinase 5/6), or the stratified epithelial marker ΔNp63, but did express the mesenchymal markers vimentin and N-cadherin.

CONCLUSION

Studies of epithelial carcinogenesis will benefit from culture systems which allow manipulation of the stromal and epithelial layers independently. We have developed an organotypic culture using primary oesophageal squamous cells and fibroblasts in which a stratified epithelium with a proliferative basal layer that stains strongly for ΔNp63 develops. This model will be suitable for the study of the molecular events in the development of Barrett's oesophagus. The most commonly used normal oesophageal squamous cell line, HET-1A, does not have the characteristics of normal oesophageal squamous cells and should not be used in models of the normal oesophageal epithelium. Until more representative cell lines are available, future studies in oesophageal cancer will be reliant on the availability and manipulation of primary tissue.

RalA function in dermal fibroblasts is required for the progression of squamous cell carcinoma of the skin

A large body of evidence has shown that stromal cells play a significant role in determining the fate of neighboring tumor cells through the secretion of various cytokines. How cytokine secretion by stromal cells is regulated in this context is poorly understood. In this study, we used a bioengineered human tissue model of skin squamous cell carcinoma progression to reveal that RalA function in dermal fibroblasts is required for tumor progression of neighboring neoplastic keratinocytes. This conclusion is based on the observations that suppression of RalA expression in dermal fibroblasts blocked tumorigenic keratinocytes from invading into the dermal compartment of engineered tissues and suppressed more advanced tumor progression after these tissues were transplanted onto the dorsum of mice. RalA executes this tumor-promoting function of dermal fibroblasts, at least in part, by mediating hepatocyte growth factor (HGF) secretion through its effector proteins, the Sec5 and Exo84 subunits of the exocyst complex. These findings reveal a new level of HGF regulation and highlight the RalA signaling cascade in dermal fibroblasts as a potential anticancer target.

Effects of Morphology vs. Cell-Cell Interactions on Endothelial Cell Stiffness

Biological processes such as atherogenesis, wound healing, cancer cell metastasis, and immune cell transmigration rely on a delicate balance between Cell-Cell and cell-substrate adhesion. Cell mechanics have been shown to depend on substrate factors such as stiffness and ligand presentation, while the effects of Cell-Cell interactions on the mechanical properties of cells has received little attention. Here, we use atomic force microscopy to measure the Young's modulus of live human umbilical vein endothelial cells (HUVECs). In varying the degree of Cell-Cell contact in HUVECs (single cells, groups, and monolayers), we observe that increased cell stiffness correlates with an increase in cell area. Further, we observe that HUVECs stiffen as they spread onto a glass substrate. When we weaken Cell-Cell junctions (i.e., through a low dose of cytochalasin B or treatment with a VE-cadherin antibody), we observe that cell-substrate adhesion increases, as measured by focal adhesion size and density, and the stiffness of cells within the monolayer approaches that of single cells. Our results suggest that while morphology can roughly be used to predict cell stiffness, Cell-Cell interactions may play a significant role in determining the mechanical properties of individual cells in tissues by careful maintenance of cell tension homeostasis.

Rho-ROCK-myosin signaling mediates membrane type 1 matrix metalloproteinase-induced cellular aggregation of keratinocytes

Membrane type 1-matrix metalloproteinase (MT1-MMP, MMP14), which is associated with extracellular matrix (ECM) breakdown in squamous cell carcinoma (SCC), promotes tumor formation and epithelial-mesenchymal transition. However, in this report we demonstrate that MT1-MMP, by cleaving the underlying ECM, causes cellular aggregation of keratinocytes and SCC cells. Treatment with an MMP inhibitor abrogated MT1-MMP-induced phenotypic changes, but decreasing E-cadherin expression did not affect MT1-MMP-induced cellular aggregation. As ROCK1/2 can regulate cell-cell and cell-ECM interaction, we examined its role in mediating MT1-MMP-induced phenotypic changes. Blocking ROCK1/2 expression or activity abrogated the cellular aggregation resulting from MT1-MMP expression. Additionally, blocking Rho and non-muscle myosin attenuated MT1-MMP-induced phenotypic changes. Moreover, SCC cells expressing only the catalytically active MT1-MMP protein demonstrated increased cellular aggregation and increased myosin II activity in vivo when injected subcutaneously into nude mice. Together, these results demonstrate that expression of MT1-MMP may be anti-tumorigenic in keratinocytes by promoting cellular aggregation.

p120-catenin is essential for maintenance of barrier function and intestinal homeostasis in mice

Epithelial-cadherin (E-cadherin) is a master organizer of the epithelial phenotype. Its function is regulated in part by p120-catenin (referred to herein as p120), a cytoplasmic binding partner that directly regulates cadherin stability. As it has been suggested that cadherins have a role in inflammatory bowel disease (IBD), we sought to investigate this further by assessing the effect of p120 deficiency in mouse small intestine and colon. p120 conditional KO mice were superficially normal at birth but declined rapidly and died within 21 days. Cell-cell adhesion defects and inflammation led to progressive mucosal erosion and terminal bleeding, similar to what is observed in a dominant-negative cadherin mouse model of IBD. Additionally, selective loss of adherens junctions and accumulation of atypical COX-2-expressing neutrophils in p120-null areas of the colon were observed. To elucidate the mechanism, direct effects of p120 deficiency were assessed in vitro in a polarizing colon cancer cell line. Notably, transepithelial electrical resistance was dramatically reduced, neutrophil binding was increased 30 fold, and levels of COX-2, an enzyme associated with IBD, were markedly increased in neutrophils. Our data suggest that p120 loss disrupts the neonatal intestinal barrier and amplifies neutrophil engagement and that these changes lead to catastrophic inflammation during colonization of the neonatal gut with bacteria and other luminal antigens. Thus, we conclude that p120 has an essential role in barrier function and epithelial homeostasis and survival in the intestine.

RalA suppresses early stages of Ras-induced squamous cell carcinoma progression

Ras proteins activate Raf and PI-3 kinases, as well as exchange factors for RalA and RalB GTPases. Many previous studies have reported that the Ral signaling cascade contributes positively to Ras-mediated oncogenesis. Here, utilizing a bioengineered tissue model of early steps in Ras-induced human squamous cell carcinoma of the skin, we found the opposite. Conversion of Ras-expressing keratinocytes from a premalignant to malignant state induced by decreasing E-cadherin function was associated with and required a knockdown of RalA to a similar degree by shRNA expression in these cells decrease in RalA expression. Moreover, direct ∼2-3 fold knockdown of RalA by shRNA expression in these cells reduced E-cadherin levels and also induced progression to a malignant phenotype. Knockdown of the Ral effector, Exo84, mimicked the effects of decreasing RalA levels in these engineered tissues. These phenomena can be explained by our finding that the stability of E-cadherin in Ras-expressing keratinocytes depends upon this RalA signaling cascade. These results imply that an important component of the early stages in squamous carcinoma progression may be a modest decrease in RalA gene expression that magnifies the effects of decreased E-cadherin expression by promoting its degradation.

Down-regulation of Pkd2 by siRNAs suppresses cell-cell adhesion in the mouse melanoma cells

The Pkd2 gene encodes an integral protein (~130 kDa), named polycystin-2 (PC-2). PC-2 is mainly involved in autosomal dominant polycystic kidney disease. Recently, polycystin-1/polycystin-2 complex has been shown to act as an adhesion complex mediating or regulating cell-cell or cell-matrix adhesion, suggesting that PC-2 may play a role in cell-cell/cell-matrix interactions. Here, we knocked down the expression of Pkd2 gene with small interfering RNAs (siRNAs) in the mouse melanoma cells (B16 cells), indicating that the cells transfected with the targeted siRNAs significantly suppressed cell-cell adhesion, but not cell-matrix adhesion, compared to the cells transfected with non-targeted control (NC) siRNA. This study provides the first directly functional evidence that PC-2 mediates cell-cell adhesion. Furthermore, we demonstrated that PC-2 modulated cell-cell adhesion may be, at least partially, associated with E-cadherin. Collectively, these findings for the first time showed that PC-2 may mediate cell-cell adhesion, at least partially, through E-cadherin.

Focal reduction of alphaE-catenin causes premature differentiation and reduction of beta-catenin signaling during cortical development

Cerebral cortical precursor cells reside in a neuroepithelial cell layer that regulates their proliferation and differentiation. Global disruptions in epithelial architecture induced by loss of the adherens junction component alphaE-catenin lead to hyperproliferation. Here we show that cell autonomous reduction of alphaE-catenin in the background of normal precursors in vivo causes cells to prematurely exit the cell cycle, differentiate into neurons, and migrate to the cortical plate, while normal neighboring precursors are unaffected. Mechanistically, alphaE-catenin likely regulates cortical precursor differentiation by maintaining beta-catenin signaling, as reduction of alphaE-catenin leads to reduction of beta-catenin signaling in vivo. These results demonstrate that, at the cellular level, alphaE-catenin serves to maintain precursors in the proliferative ventricular zone, and suggest an unexpected function for alphaE-catenin in preserving beta-catenin signaling during cortical development.

Rac-dependent cyclin D1 gene expression regulated by cadherin- and integrin-mediated adhesion

Integrin-mediated adhesion to substratum is required for cyclin D1 induction in mesenchymal cells, but we show here that the induction of cyclin D1 persists despite blockade of ECM-integrin signaling in MCF10A mammary epithelial cells. E-cadherin-mediated cell-cell adhesion also supports cyclin D1 induction in these cells, and the combined inhibition of both E-cadherin and integrin adhesion is required to prevent the expression of cyclin D1 mRNA and protein. Our previous studies described a pro-proliferative effect of E-cadherin in MCF10A cells, mediated by Rac, and we now show that Rac is required for cyclin D1 mRNA induction by both E-cadherin and integrin engagement. The levels of p21Cip1 and p27Kip1, Cdk inhibitors that are also targets of integrin signaling, are not affected by E-cadherin-mediated cell-cell adhesion. Finally, we show that the increased expression of cyclin D1 mRNA associated with E-cadherin-dependent cell-cell adhesion is causally linked to an increased entry into S phase. Our results identify Rac signaling to cyclin D1 as a crucial pro-proliferative effect of E-cadherin-mediated cell-cell adhesion.

No place like home: anatomy and function of the stem cell niche

Stem cells are rare cells that are uniquely capable of both reproducing themselves (self-renewing) and generating the differentiated cell types that are needed to carry out specialized functions in the body. Stem cell behaviour, in particular the balance between self-renewal and differentiation, is ultimately controlled by the integration of intrinsic factors with extrinsic cues supplied by the surrounding microenvironment, known as the stem cell niche. The identification and characterization of niches within tissues has revealed an intriguing conservation of many components, although the mechanisms that regulate how niches are established, maintained and modified to support specific tissue stem cell functions are just beginning to be uncovered.

Increased nuclear beta-catenin in suprabasal involved psoriatic epidermis

BACKGROUND

Psoriasis is a common inflammatory skin disease characterized by abnormal keratinocyte proliferation and differentiation, increased angiogenesis and inflammation. There is evidence that some keratinocyte differentiation events are controlled by changes in cell-cell adhesion. beta-catenin is a 94-kDa protein which has a dual function as a component of intercellular adherens junctions and also as a transcription factor as part of the Wnt signalling pathway. beta-catenin is not required for keratinocyte proliferation but has been shown to regulate keratinocyte stem cells and hair follicle morphogenesis.

OBJECTIVES

To investigate the distribution and function of beta-catenin in involved psoriatic epidermis and in epidermal keratinocytes.

METHODS

Biopsies were obtained from patients with psoriasis and from normal controls. The distribution of beta-catenin was investigated using antibodies to both total and unphosphorylated active beta-catenin. Luciferase assays were used to measure transcriptional activation of transglutaminase 1 (TGase 1) and involucrin and to investigate the functional role of beta-catenin in interfollicular keratinocytes.

RESULTS

Increased nuclear beta-catenin was seen in lesional suprabasal psoriatic epidermis compared with uninvolved or normal skin. Increased active unphosphorylated beta-catenin was also detected within the differentiating compartment of involved psoriatic epidermis. Expression of TGase 1 overlapped with beta-catenin in suprabasal lesional psoriasis. The TGase 1 promoter was positively regulated by activated beta-catenin and by the glycogen synthase kinase binding protein, suggesting that beta-catenin and glycogen synthase kinase 3beta may regulate TGase 1 expression.

CONCLUSIONS

This is the first report to convincingly demonstrate increased beta-catenin in involved psoriasis and to implicate beta-catenin in the regulation of TGase 1. This evidence suggests a role for beta-catenin signalling in regulating keratinocyte differentiation in interfollicular skin in addition to previously reported functions in stem cell fate determination, hair follicle regulation and skin tumorigenesis.

Identification of cellular isoform of oviduct-specific glycoprotein: role in oviduct tissue remodeling?

The oviduct is known to secrete mucins (MUC1 and MUC9) under the influence of ovarian steroids. The secreted form of MUC1 binds gametes in the oviduct, whereas the cellular form seen in breast cancers has been implicated in cell adhesion and morphogenesis. The secreted MUC9 or oviduct-specific glycoprotein (OGP), in addition to being a mucin, belongs to family 18 glycosylhydrolases and is known to bind gametes and embryos in the oviduct. Studies in our laboratory have identified non-muscle myosin IIA (involved in cell shape, polarity, and morphogenesis) as the protein partner to OGP in gametes. In view of the crucial role of the cortical cytoskeleton in the selective internalization of tight junctions (TJs) /adherent junctions (AJs) or apical junctional complex (AJC) in simple epithelial cells during tissue remodeling, the present study has been undertaken to evaluate the existence of a cellular form of OGP in oviductal tissue, which itself undergoes cyclic tissue remodeling. In silico analysis of the deduced amino-acid sequence of OGP has revealed the presence of several conserved motifs; these imply that OGP is a component of multi-protein complexes such as TJs. Corroborative immunoelectron-microscopic analysis in peri-ovulatory oviduct epithelia in the bonnet monkey has revealed the presence of OGP at the TJ. Co-localization studies of OGP and cadherin demonstrate that, whereas OGP is localized at the tonofilaments of the TJs, cadherin is localized at the intercellular space of the AJ. The possible role of OGP in oviductal tissue remodeling is discussed in light of the present findings and those reported in the literature.

The morphogenic function of E-cadherin-mediated adherens junctions in epithelial ovarian carcinoma formation and progression

E-cadherin expression is unusually regulated in epithelial ovarian carcinoma. It is not expressed in poorly cohesive ovarian surface epithelial (OSE) target cells, but is expressed in cohesive pre-malignant lesions and in highly cohesive, well-differentiated tumors where it is membrane associated, presumably in adherens junctions. E-cadherin expression is subsequently suppressed, or its function is disrupted, in late-stage invasive tumors. Here, we observed that increased E-cadherin expression in ovarian carcinoma cells was associated with increased E-cadherin promoter activity, increased adherens junction formation, decreased beta-catenin signaling-dependent LEF-1 activity, and the generation of cohesive spheroids in basement membrane gel culture. Forced expression of wild-type E-cadherin in immortalized OSE cells initiated adherens junction formation, decreased LEF-1 activity, decreased the mesenchymal migration that is a characteristic of OSE cells that have been maintained in monolayer culture, and induced the formation of cohesive spheroids in basement membrane gels. Conversely, forced expression of a dominant-negative E-cadherin mutant in ovarian carcinoma cells disrupted adherens junctions, increased mesenchymal cell migration, and prevented spheroidal morphogenesis without altering LEF-1 signaling. Therefore, in addition to suppressing late-stage tumor progression, E-cadherin-mediated adherens junctions may also contribute to the initial emergence of a cohesive morphogenic phenotype that is a hallmark of differentiated epithelial ovarian carcinoma.

E-cadherin cell-cell adhesion in ewing tumor cells mediates suppression of anoikis through activation of the ErbB4 tyrosine kinase

Ability to grow under anchorage-independent conditions is one of the major hallmarks of transformed cells. Key to this is the capacity of cells to suppress anoikis, or programmed cell death induced by detachment from the extracellular matrix. To model this phenomenon in vitro, we plated Ewing tumor cells under anchorage-independent conditions by transferring them to dishes coated with agar to prevent attachment to underlying plastic. This resulted in marked up-regulation of E-cadherin and rapid formation of multicellular spheroids in suspension. Addition of calcium chelators, antibodies to E-cadherin (but not to other cadherins or beta(1)-integrin), or expression of dominant negative E-cadherin led to massive apoptosis of spheroid cultures whereas adherent cultures were unaffected. This correlated with reduced activation of the phosphatidylinositol 3-kinase-Akt pathway but not the Ras-extracellular signal-regulated kinase 1/2 cascade. Furthermore, spheroid cultures showed profound chemoresistance to multiple cytotoxic agents compared with adherent cultures, which could be reversed by alpha-E-cadherin antibodies or dominant negative E-cadherin. In a screen for potential downstream effectors of spheroid cell survival, we detected E-cadherin-dependent activation of the ErbB4 receptor tyrosine kinase but not of other ErbB family members. Reduction of ErbB4 levels by RNA interference blocked Akt activation and spheroid cell survival and restored chemosensitivity to Ewing sarcoma spheroids. Our results indicate that anchorage-independent Ewing sarcoma cells suppress anoikis through a pathway involving E-cadherin cell-cell adhesion, which leads to ErbB4 activation of the phosphatidylinositol 3-kinase-Akt pathway, and that this is associated with increased resistance of cells to cytotoxic agents.

Cadherin inhibition of beta-catenin signaling regulates the proliferation and differentiation of neural precursor cells

The generation and differentiation of neurons during development requires coordination of intercellular interactions with spatio-temporal changes in gene expression. To examine the role of adhesion in cerebral cortical development, we overexpressed full-length cadherin and dominant-negative truncated cadherin in mouse cortical precursors. Full-length cadherin allowed for the maintenance of cell contact between daughter cells following cell division while dominant-negative cadherin decreased cell contact. Paradoxically, both cadherin isoforms inhibited precursor proliferation, induced premature neuronal differentiation, and inhibited beta-catenin dependent signaling. Furthermore, alteration of cadherin or beta-catenin function led to additional changes in precursor identity and division symmetry as demonstrated by altered expression of the radial glial marker, Pax6, and the intermediate precursor marker, Tbr2. Moreover, clonal analysis demonstrated asymmetric distribution of Tbr2 following precursor mitosis. Together, these results show that cadherins affect neural precursor fate determination through a cell-autonomous regulation of catenin signaling distinct from cadherin adhesive function.

Role of p120-catenin in cadherin trafficking

p120-catenin (p120) has emerged over the past several years as an important regulatory component of the cadherin adhesive complex. A core function of p120 in mammalian cells is to stabilize cadherins at the cell membrane by modulating cadherin membrane trafficking and degradation. In this way, p120 levels act as a set point mechanism that tunes cell-cell adhesive interactions. The primary control point for this regulatory activity appears to be at the level of cadherin internalization from the plasma membrane, although p120 may also impact other aspects of cadherin trafficking and turnover. In the following review, the general mechanisms of cadherin trafficking are discussed, and models for how p120 may influence cadherin membrane dynamics are presented. In one model, p120 may function as a "cap" to bind the cadherin cytoplasmic tail and prevent cadherin interactions with endocytic membrane trafficking machinery. Alternatively, p120 may stabilize cell junctions or regulate membrane trafficking machinery through interactions with small GTPases such as Rho A, Rac and Cdc42. Through these mechanisms p120 exerts influence over a wide range of biological processes that are dependent upon tight regulation of cell surface cadherin levels.

Regulation of lung neutrophil recruitment by VE-cadherin

Lung inflammatory disease is characterized by increased polymorphonuclear leukocyte (PMN) infiltration and vascular permeability. PMN infiltration into tissue involves signaling between endothelial cells and migrating PMNs, which leads to alterations in the organization of adherens junctions (AJs). We addressed the possible role of the protein constituents of AJs, endothelium-specific vascular-endothelial (VE)-cadherin, in the migration of PMNs. Studies were made using VE-cadherin mutant constructs lacking the extracellular domain (ΔEXD) or, additionally, lacking the COOH-terminus β-catenin-binding domain (ΔEXDΔβ). Either construct was transduced in pulmonary microvessel endothelia of mice using cationic liposome-encapuslated cDNA constructs injected intravenously. Optimal expression of constructs was seen by Western blot analysis within 24 h. Vessel wall liquid permeability measured as the lung microvessel capillary filtration coefficient increased threefold in ΔEXD-transduced lungs, indicating patency of interendothelial junctions, whereas the control ΔEXDΔβ construct was ineffective. To study lung tissue PMN recruitment, we challenged mice intraperitoneally with LPS (3 mg/kg) for 6 h and measured PMN numbers by bronchoalveolar lavage and their accumulation morphometrically in lung tissue. ΔEXD expression markedly reduced the PMN sequestration and migration seen in nontransfected (control wild type) or ΔEXDΔβ-transfected (negative control) mice challenged with LPS. In addition, ΔEXD transfection suppressed LPS-induced activation of NF-κB and consequent ICAM-1 expression. These results suggest that disassembly of VE-cadherin junctions serves as a negative signal for limiting transendothelial PMN migration secondary to decreased ICAM-1 expression in the mouse model of LPS-induced sepsis.

Dominant-negative E-cadherin inhibits the invasiveness of inflammatory breast cancer cells in vitro

E-cadherin is a transmembrane glycoprotein which mediates epithelial cell-to-cell adhesion function as a tumor suppressor and frequently loss of expression in a wide spectrum of human cancer. However, recent studies demonstrated that E-cadherin was always over-expressed in inflammatory breast cancer (IBC) specimen and cell lines, which is a clinical extreme malignancy of breast cancer. It is hypothesized that the gain and not the loss of the E-cadherin axis contributes to the IBC unique phenotype. To test this assumption, we generated dominant negative mutant E-cadherin high-expression inflammatory breast cancer cells by introduced dominant negative mutant E-cadherin (H-2kd-E-cad) cDNA into human IBC SUM149 cells. Our studies demonstrated that the ability of invasion of SUM149 cells was significantly inhibited by H-2kd-E-cad via down-regulation of MMP-1 and MMP-9 expression. The underlying signal pathway of MAPK phosphorylated Erk 1/2(P44/42) in H-2kd-E-cad-transfected SUM149 cells was significantly down-regulated compared to parental and mock contrast. Our studies provided further functional evidence as the gain of E-cadherin expression dedicated to the IBC malignant phenotype and the blockage of MAPK/Erk activation maybe a promising therapeutic target.

Positive expression of E-cadherin suppresses cell adhesion to fibronectin via reduction of alpha5beta1 integrin in human breast carcinoma cells

E-cadherin mainly mediated the epithelial cell-cell adhesion, and integrin signaling can modulate the signaling pathway of E-cadherin in the different levels. Up to now, however, it is still unclear that whether E-cadherin could interfere with cell-matrix interaction, a typical adhesion through integrins. In this study we investigated the effects of E-cadherin on cell-matrix adhesion and alpha5beta1 integrin expression in human breast carcinoma cells. It was found that either mRNA or protein level of alpha5 and beta1 subunits of integrin decreased in E-cad-231 compared with Mock-231. Furthermore, the promoter activity of alpha5 gene was inhibited in E-cad-231 compared with Mock-231. Consistently, phosphorylated focal adhesion kinase, a closer key downstream protein kinase of integrin signaling, were also down-regulated in E-cad-231. Furthermore, distribution of beta-catenin was observed and data showed beta-catenin was accumulated in the nucleus in Mock-231, while disappeared from the nucleus and mainly accumulated near the cell surface membrane in E-cad-231. LiCl, a molecule that can inhibit the GSK-3beta activity and down-regulate beta-catenin degradation, could inversely stimulate expression of alpha5 and beta1 integrin. Taken together, these results indicated that positive expression of E-cadherin inhibits the cell adhesion to extracellular matrix mediated by alpha5beta1 integrin signaling.

Interleukin-6 promotes human epidermal keratinocyte proliferation and keratin cytoskeleton reorganization in culture

We have studied the effects of interleukin-6 (IL-6) on human epidermal keratinocytes by using serum-free culture conditions that allow the serial transfer, differentiation, and formation of well-organized multilayered epithelia. IL-6 at 2.5 ng/ml or higher concentrations promoted keratinocyte proliferation, with an ED(50) of about 15 ng/ml and a maximum effect at 50 ng/ml. IL-6 was 10-fold less potent than epidermal growth factor (EGF) or transforming growth factor-alpha (TGF-alpha) and supported keratinocyte growth for up to eight cumulative cell generations. IL-6-treated keratinocytes formed highly stratified colonies with a narrower proliferative/migratory rim than those keratinocytes stimulated with EGF or TGF-alpha; confluent epithelial sheets treated with IL-6 also underwent an increase in the number of cell layers. We also examined the effect of IL-6 on the keratin cytoskeleton. Immunostaining with anti-K16 monoclonal antibodies showed that the keratin network was aggregated and reorganized around cell nucleus and that this was not attributable to changes in keratin levels. This is the first report concerning the induction of the reorganization of keratin intermediate filaments by IL-6 in human epidermal keratinocytes.

E-cadherin loss promotes the initiation of squamous cell carcinoma invasion through modulation of integrin-mediated adhesion

Much remains to be learned about how cell-cell and cell-matrix interactions are coordinated to influence the earliest development of neoplasia. We used novel 3D human tissue reconstructs that mimic premalignant disease in normal epidermis, to directly investigate how loss of E-cadherin function directs conversion to malignant disease. We used a genetically tagged variant of Ha-Ras-transformed human keratinocytes (II-4) expressing dominant-interfering E-cadherin fusion protein (H-2kd-Ecad). These cells were admixed with normal human keratinocytes and tumor cell fate was monitored in 3D reconstructed epidermis upon transplantation to immunodeficient mice. Tumor initiation was suppressed in tissues harboring control- and mock-infected II-4 cells that lost contact with the stromal interface. By contrast, H-2kd-Ecad-expressing cells persisted at this interface, thus enabling incipient tumor cell invasion upon in vivo transplantation. Loss of intercellular adhesion was linked to elevated cell surface expression of α2, α3 and β1 integrins and increased adhesion to laminin-1 and Types I and IV collagen that was blocked with β1-integrin antibodies, suggesting that invasion was linked to initial II-4 cell attachment at the stromal interface. Collectively, these results outline a novel aspect to loss of E-cadherin function that is linked to the mutually interdependent regulation of cell-cell and cell-matrix adhesion and has significant consequences for the conversion of premalignancy to cancer.

Regulation of post-embryonic neuroblasts by Drosophila Grainyhead

The Drosophila post-embryonic neuroblasts (pNBs) are neural stem cells that persist in the larval nervous system where they proliferate to produce neurons for the adult CNS. These pNBs provide a good model to investigate mechanisms regulating the maintenance and proliferation of stem cells. The transcription factor Grainyhead (Grh), which is required for morphogenesis of epidermal and tracheal cells, is also expressed in all pNBs. Here, we show that grh is essential for pNBs to adopt the stem cell programme appropriate to their position within the CNS. In grh mutants the abdominal pNBs produced more progeny while the thoracic pNBs, in contrast, divided less and produced fewer progeny than wild type. We investigated three candidates; the Neuroblast identify gene Castor, the signalling molecule Notch and the adhesion protein E-Cadherin, to determine whether they could mediate these effects. Neither Castor nor Notch fulfilled the criteria for intermediaries, and in particular Notch activity was found to be dispensable for the normal proliferation and survival of the pNBs. In contrast E-Cadherin, which has been shown to regulate pNB proliferation, was present at greatly reduced levels in the grh mutant pNBs. Furthermore, ectopic expression of Grh was sufficient to promote ectopic E-Cadherin and two conserved Grh-binding sites were identified in the E-Cadherin/shotgun flanking sequences, arguing that this gene is a downstream target. Thus one way Grh could regulate pNBs is through expression of E-cadherin, a protein that is thought to mediate interactions with the glial niche.

Ras-induced spreading and wound closure in human epidermal keratinocytes

Although it is known that growth factor signaling cascades are active during epithelial wound healing, signals that regulate reepithelialization after wounding are not very well characterized. The small GTP binding protein Ras is a molecular switch involved in the regulation of signals originating from different growth factor receptors. We have investigated consequences of its activation in primary human keratinocytes. We provide evidence that activation of Ras can lead to shape changes of keratinocytes caused by rearrangements of the actin cytoskeleton that result in membrane protrusion and ruffling. Similar shape changes were found in the migrating tip of newly formed epithelium in mouse wounds. These cytoskeletal changes occur independently of keratinocyte terminal differentiation, and they can determine the speed of wound epithelialization in vitro. Using various mutant constructs and specific pharmacological inhibitors, we found that the effects of activated Ras on the cytoskeleton of keratinocytes are mediated by a phosphatidylinositol 3 kinase-independent activation of Rac. Our results suggest that growth factor-induced, Ras-mediated changes of keratinocyte shape may be an important mechanism that determines the speed of wound epithelialization.

Loss of intercellular adhesion activates a transition from low- to high-grade human squamous cell carcinoma

The relationship between loss of intercellular adhesion and the biologic properties of human squamous cell carcinoma is not well understood. We investigated how abrogation of E-cadherin-mediated adhesion influenced the behavior and phenotype of squamous cell carcinoma in 3D human tissues. Cell-cell adhesion was disrupted in early-stage epithelial tumor cells (HaCaT-II-4) through expression of a dominant-negative form of E-cadherin (H-2Kd-Ecad). Three-dimensional human tissue constructs harboring either H-2Kd-Ecad-expressing or control II-4 cells (pBabe, H-2Kd-EcadDeltaC25) were cultured at an air-liquid interface for 8 days and transplanted to nude mice; tumor phenotype was analyzed 2 days and 2 and 4 weeks later. H-2Kd-Ecad-expressing tumors demonstrated a switch to a high-grade aggressive tumor phenotype characterized by poorly differentiated tumor cells that infiltrated throughout the stroma. This high-grade carcinoma revealed elevated cell proliferation in a random pattern, loss of keratin 1 and diffuse deposition of laminin 5 gamma2 chain. When II-4 cell variants were seeded into type I collagen gels as an in vitro assay for cell migration, we found that only E-cadherin-deficient cells detached, migrated as single cells and expressed N-cadherin. Function-blocking studies demonstrated that this migration was matrix metalloproteinase-dependent, as GM-6001 and TIMP-2, but not TIMP-1, could block migration. Gene expression profiles revealed that E-cadherin-deficient II-4 cells demonstrated increased expression of proteases and cell-cell and cell-matrix proteins. These findings showed that loss of E-cadherin-mediated adhesion plays a causal role in the transition from low- to high-grade squamous cell carcinomas and that the absence of E-cadherin is an important prognostic marker in the progression of this disease.

Influence of the cytoplasmic domain of E-cadherin on endogenous N-cadherin expression in malignant melanoma

E-cadherin is known to be an important molecule in epithelial-mesenchymal transition (EMT). Malignant transformation of melanocytes frequently attends with loss of E-cadherin expression and induction of expression of mesenchymal molecules like N-cadherin. The switch of the cadherin class is an interesting phenomenon of melanoma cells and in EMT in general. Therefore, we analysed the capacity of E-cadherin to regulate expression of N-cadherin in melanocytic cells. Our experiments revealed that melanoma cells downregulate endogenous N-cadherin expression after transient transfection of full-length E-cadherin, but also of the cytoplasmic domain of E-cadherin. Therefore, we concluded that the extracellular domain of E-cadherin and cell-cell contacts are not necessary for negative regulation of N-cadherin. Melanoma cells re-expressing full-length or cytoplasmatic E-cadherin have reduced NFkappaB activity in comparison to mock-transfected cells. Downregulation of NFkappaB activity, either directly or by re-expression of E-cadherin, led to a suppression of N-cadherin promoter activity and N-cadherin expression. Consequently, an NFkappaB-binding site in the N-cadherin promoter was characterized. In summary, our results suggest that N-cadherin is directly regulated by E-cadherin. Loss of E-cadherin induces NFkappaB activity and N-cadherin expression in tumorigenic EMT.

Expression of P-cadherin distinct from that of E-cadherin in re-epithelialization in neonatal rat skin

Our previous study showed that an open wound made in neonatal rat skin was covered by migration of certain undifferentiated populations of keratinocytes as a multilayered cell sheet. In this study, the expression of the components of adherens junctions (AJ), E- and P-cadherins, and beta-catenin, was examined to understand the underlying mechanisms. Both E- and P-cadherins were downregulated in the basal layer at 6 h post-wounding (PW), indicating a reduction in the intercellular adhesiveness. The expression of P-cadherin but not E-cadherin was expanded to the suprabasal layers at the wound margin at 12 h PW. Moreover, the expression pattern of P-cadherin at sites of cell-cell contact was punctate rather than linear. By 24 h PW, cells accumulated beta-catenin in the cytoplasm in a suprabasal layer contacting the basal layer at the wound margin. Both the E- and P-cadherins showed a punctate AJ pattern at the confined suprabasal layer. Such differential expression of the E- and P-cadherins strongly suggests that these two classic cadherins play distinct roles in re-epithelialization. The changing of the E- and/or P-cadherin expression may participate in a delay of terminal differentiation of keratinocytes for cell supply toward a wound.

E-cadherin suppression accelerates squamous cell carcinoma progression in three-dimensional, human tissue constructs

We studied the link between loss of E-cadherin-mediated adhesion and acquisition of malignant properties in three-dimensional, human tissue constructs that mimicked the initial stages of squamous cell cancer progression. Suppression of E-cadherin expression in early-stage, skin-derived tumor cells (HaCaT-II-4) was induced by cytoplasmic sequestration of beta-catenin upon stable expression of a dominant-negative E-cadherin fusion protein (H-2Kd-Ecad). In monolayer cultures, expression of H-2Kd-Ecad resulted in decreased levels of E-cadherin, redistribution of beta-catenin to the cytoplasm, and complete loss of intercellular adhesion when compared with control II-4 cells. This was accompanied by a 7-fold decrease in beta-catenin-mediated transcription and a 12-fold increase in cell migration. In three-dimensional constructs, E-cadherin-deficient tissues showed disruption of architecture, loss of adherens junctional proteins from cell contacts, and focal tumor cell invasion. Invasion was linked to activation of matrix metalloproteinase (MMP)-mediated degradation of basement membrane in H-2Kd-Ecad-expressing tissue constructs that was blocked by MMP inhibition (GM6001). Quantitative reverse transcription-PCR showed a 2.5-fold increase in MMP-2 and an 8-fold increase in MMP-9 in cells expressing the H-2Kd-Ecad fusion protein when compared with controls, and gel zymography showed increased MMP protein levels. Following surface transplantation of three-dimensional tissues, suppression of E-cadherin expression greatly accelerated tumorigenesis in vivo by inducing a switch to high-grade carcinomas that resulted in a 5-fold increase in tumor size after 4 weeks. Suppression of E-cadherin expression and loss of its function fundamentally modified squamous cell carcinoma progression by activating a highly invasive, aggressive tumor phenotype, whereas maintenance of E-cadherin prevented invasion in vitro and limited tumor progression in vivo.

Emerging roles for p120-catenin in cell adhesion and cancer

Although originally identified as a Src substrate, p120-catenin (p120) is now known to regulate cell-cell adhesion through its interaction with the cytoplasmic tail of classical and type II cadherins. New evidence indicates that p120 regulates cadherin turnover at the cell surface, thereby controlling the amount of cadherin available for cell-cell adhesion. This function is necessary but not sufficient to promote strong adhesion, which is further controlled by signals acting on the amino-terminal p120 regulatory domain. p120 also modulates the activities of RhoA, Rac, and Cdc42, suggesting that along with other Src substrates, p120 regulates actin dynamics. Thus, p120 is a master regulator of cadherin abundance and activity, and likely participates in regulating the balance between adhesive and motile cellular phenotypes. This review summarizes recent progress in understanding mechanisms of p120 action, and discusses new implications with respect to roles for p120 in disease and cancer.

Protecting your tail: regulation of cadherin degradation by p120–catenin

Work in various model systems has yielded conflicting views of how p120-catenin participates in adherens junction assembly and regulation. A series of recent studies indicate that a core function of p120-catenin in mammalian cells is to regulate cadherin turnover by modulating the entry of cadherins into degradative endocytic pathways. By this mechanism, cellular levels of p120-catenin perform a 'rheostat' or 'set point' function that controls steady-state cadherin levels. These studies parallel a growing interest in the regulation of cadherin levels at the cell surface by membrane trafficking pathways. Collectively, the findings suggest exciting new roles for p120-catenin at the interface between cadherins and membrane trafficking machinery, and imply novel mechanisms by which p120-catenin may regulate cell adhesion and migration in the context of development and cancer.

VE-cadherin increases the half-life of VEGF receptor 2

VE-cadherin plays a critical role in cell-cell interactions by forming adherens junctions in endothelial cells. VE-cadherin has increasingly been implicated in the cell signaling cascades initiated by the activation of growth factor receptors. Vascular endothelial growth factor receptor 2 (VEGFR-2) is present in regions of cell-cell contact and coimmunoprecipitates with VE-cadherin. In this study, we report that stable overexpression of VE-cadherin in two different endothelial cells induced an increase in VEGFR-2 protein levels. The increase in VEGFR-2 was also induced by overexpression of other classical cadherins such as E-cadherin or N-cadherin. Removing the extracellular domain of VE-cadherin abolished this effect, and a truncated form of VE-cadherin lacking the intracellular domain decreased VEGFR-2 instead of increasing it. VE-cadherin-induced changes in VEGFR-2 levels were paralleled by a corresponding shift in the VEGF-dependent activation of MAPK signaling, which demonstrated the functional relevance of varying the VEGFR-2 levels. Since VE-cadherin upregulated endogenous VEGFR-2 or exogenously expressed VEGFR-2, we hypothesized that the mechanism may be posttranslational. Indeed, the half-life of VEGFR-2 was 70 min in control cells whereas in cells overexpressing VE-cadherin the half-life was extended to 146 min. These results support the existence of a novel layer of functional regulation of VEGFR-2 by VE-cadherin.

Beta-catenin signaling is required for neural differentiation of embryonic stem cells

Culture of embryonic stem (ES) cells at high density inhibits both beta-catenin signaling and neural differentiation. ES cell density does not influence beta-catenin expression, but a greater proportion of beta-catenin is targeted for degradation in high-density cultures. Moreover, in high-density cultures, beta-catenin is preferentially localized to the membrane further reducing beta-catenin signaling. Increasing beta-catenin signaling by treatment with Wnt3a-conditioned medium, by overexpression of beta-catenin, or by overexpression of a dominant-negative form of E-cadherin promotes neurogenesis. Furthermore, beta-catenin signaling is sufficient to induce neurogenesis in high-density cultures even in the absence of retinoic acid (RA), although RA potentiates the effects of beta-catenin. By contrast, RA does not induce neurogenesis in high-density cultures in the absence of beta-catenin signaling. Truncation of the armadillo domain of beta-catenin, but not the C terminus or the N terminus, eliminates its proneural effects. The proneural effects of beta-catenin reflect enhanced lineage commitment rather than proliferation of neural progenitor cells. Neurons induced by beta-catenin overexpression either alone or in association with RA express the caudal neuronal marker Hoxc4. However, RA treatment inhibits the beta-catenin-mediated generation of tyrosine hydroxylase-positive neurons, suggesting that not all of the effects of RA are dependent upon beta-catenin signaling. These observations suggest that beta-catenin signaling promotes neural lineage commitment by ES cells, and that beta-catenin signaling may be a necessary co-factor for RA-mediated neuronal differentiation. Further, enhancement of beta-catenin signaling with RA treatment significantly increases the numbers of neurons generated from ES cells, thus suggesting a method for obtaining large numbers of neural species for possible use in for ES cell transplantation.

Reversal of melanocytic malignancy by keratinocytes is an E-cadherin-mediated process overriding beta-catenin signaling

Loss of E-cadherin in melanoma cells frees them from keratinocytes-mediated proliferation and phenotypic control, which can be restored by forced E-cadherin expression. In this study, E-cadherin and its derivatives were introduced into metastatic melanoma line 1205Lu. E-cadherin and E-cadherin-alpha-catenin fusion protein were functional in mediating cell adhesion, downregulating MCAM(4) in coculture, and inhibiting proliferation regardless of beta-catenin expression levels and activation status. In contrast, cytoplasmic domain-deleted (E-cadDeltaCYT) derivative was not able to reverse malignancy. The results indicate that E-cadherin-mediated cell adhesion is required for keratinocyte-mediated control of melanocytic cells, which can override proliferative activity of beta-catenin.

Transient activation of beta-catenin signalling in adult mouse epidermis is sufficient to induce new hair follicles but continuous activation is required to maintain hair follicle tumours

When beta-catenin signalling is disturbed from mid-gestation onwards lineage commitment is profoundly altered in postnatal mouse epidermis. We have investigated whether adult epidermis has the capacity for beta-catenin-induced lineage conversion without prior embryonic priming. We fused N-terminally truncated, stabilised beta-catenin to the ligand-binding domain of a mutant oestrogen receptor (DeltaNbeta-cateninER). DeltaNbeta-cateninER was expressed in the epidermis of transgenic mice under the control of the keratin 14 promoter and beta-catenin activity was induced in adult epidermis by topical application of 4-hydroxytamoxifen (4OHT). Within 7 days of daily 4OHT treatment resting hair follicles were recruited into the hair growth cycle and epithelial outgrowths formed from existing hair follicles and from interfollicular epidermis. The outgrowths expressed Sonic hedgehog, Patched and markers of hair follicle differentiation, indicative of de novo follicle formation. The interfollicular epidermal differentiation program was largely unaffected but after an initial wave of sebaceous gland duplication sebocyte differentiation was inhibited. A single application of 4OHT was as effective as repeated doses in inducing new follicles and growth of existing follicles. Treatment of epidermis with 4OHT for 21 days resulted in conversion of hair follicles to benign tumours resembling trichofolliculomas. The tumours were dependent on continuous activation of beta-catenin and by 28 days after removal of the drug they had largely regressed. We conclude that interfollicular epidermis and sebaceous glands retain the ability to be reprogrammed in adult life and that continuous beta-catenin signalling is required to maintain hair follicle tumours.

VE-cadherin: adhesion at arm's length

VE-cadherin was first identified in the early 1990s and quickly emerged as an important endothelial cell adhesion molecule. The past decade of research has revealed key roles for VE-cadherin in vascular permeability and in the morphogenic events associated with vascular remodeling. The details of how VE-cadherin functions in adhesion became apparent with structure-function analysis of the cadherin extracellular domain and with the identification of the catenins, a series of cytoplasmic proteins that bind to the cadherin tail and mediate interactions between cadherins and the cytoskeleton. Whereas early work focused on the armadillo family proteins beta-catenin and plakoglobin, more recent investigations have identified p120-catenin (p120(ctn)) and a related group of armadillo family members as key binding partners for the cadherin tail. Furthermore, a series of new studies indicate a key role for p120(ctn) in regulating cadherin membrane trafficking in mammalian cells. These recent studies place p120(ctn) at the hub of a cadherin-catenin regulatory mechanism that controls cadherin plasma membrane levels in cells of both epithelial and endothelial origin.