Multiple cadherin extracellular repeats mediate homophilic binding and adhesion

Cadherins and growth factor receptors - ligand-selective mechano-switches at cadherin junctions

This study investigated possible mechanisms underlying differences between heterophilic and homophilic cadherin adhesions that influence intercellular mechanics and multicellular organization. Results suggest that homophilic cadherin ligation selectively activates force transduction, such that resulting signaling and mechano-transduction amplitudes are independent of cadherin-binding affinities. Epithelial (E-) and neural (N-)cadherin cooperate with distinct growth factors to mechanically activate force transduction cascades. Prior results have demonstrated that E-cadherin and epidermal growth factor receptor form force-sensitive complexes at intercellular junctions. Here, we show that the reconstitution of N-cadherin force transduction requires the co-expression of N-cadherin and fibroblast growth factor receptor. Mechanical measurements further demonstrated that homophilic ligation initiates receptor tyrosine kinase-dependent force transduction cascades, but heterophilic cadherin ligands fail to activate signaling or generate stereotypical mechano-transduction signatures. The all-or-nothing contrast between mechano-transduction by heterophilic versus homophilic cadherin adhesions supersedes differences in cadherin adhesion strength. This mechano-selectivity impacts cell spreading and traction generation on cadherin substrates. Homophilic ligation appears to be a key that selectively unlocks cadherin mechano-transduction. These findings might reconcile the roles of cadherin recognition and cell mechanics in the organization of multicellular assemblies.

Nanoscale Visualization of Drosophila E-cadherin Ectodomain Fragments and Their Interactions Using DNA Origami Nanoblocks

The adhesive function of cell surface proteins can be visually assessed through direct observation; however, the underlying structures that mediate adhesion typically remain invisible at the nanoscale level. This hinders knowledge on the diversity of molecular architectures responsible for cell-cell adhesion. Drosophila E-cadherin (DE-cadherin), a classical cadherin with a unique domain structure, demonstrates adhesive function; however, it lacks a structural model that explains its adhesion mechanism. Here, we present a novel application of DNA origami technology to create a cell-free, flat environment in which full DE-cadherin ectodomains are anchored using SNAP-tags and biotin-streptavidin interactions. DNA origami was assembled into a 120 nm long block, bearing 5 or 14 biotin:streptavidin sites that were evenly spaced on one lateral face. DE-cadherin ectodomain fragments were attached via biotinylated SNAP-tags. These decorated DNA origami nanoblocks were subjected to transmission electron and high-speed atomic force microscopy, which revealed a hinge-like site that separated the membrane-distal and -proximal portions of the DE-cadherin ectodomain, suggesting a role in mechanical flexibility. We also observed interactions between DE-cadherin ectodomains via their membrane-distal portions on single DNA origami nanoblocks. We reconstituted an adhesion-like process via pairing DNA origami nanoblocks using DE-cadherin ectodomain interactions. Homophilic associations of functional DE-cadherin ectodomains between the paired DNA origami nanoblocks were visualized at the nanoscale, displaying strand-like molecular configurations, likely representing the extracellular cadherin repeats without regular arrays of structural elements. This study introduces a DNA origami-based platform for reconstituting and visualizing cadherin ectodomain interactions, with potential applications for a broader range of adhesion molecules.

PDZ Domains from the Junctional Proteins Afadin and ZO-1 Act as Mechanosensors

Intercellular adhesion complexes must withstand mechanical forces to maintain tissue cohesion while also retaining the capacity for dynamic remodeling during tissue morphogenesis and repair. Many cell-cell adhesion complexes contain at least one PSD95/Dlg/ZO-1 (PDZ) domain situated between the adhesion molecule and the actin cytoskeleton. However, PDZ-mediated interactions are characteristically nonspecific, weak, and transient, with multiple binding partners per PDZ domain, micromolar dissociation constants, and bond lifetimes of seconds or less. Here, we demonstrate that the bonds between the PDZ domain of the cytoskeletal adaptor protein afadin and the intracellular domains of the adhesion molecules nectin-1 and JAM-A form molecular catch bonds that reinforce in response to mechanical load. In contrast, the bond between the PDZ3-SH3-GUK (PSG) domain of the cytoskeletal adaptor ZO-1 and the JAM-A intracellular domain becomes dramatically weaker in response to ∼2 pN of load, the amount generated by single molecules of the cytoskeletal motor protein myosin II. Thus, physiologically relevant forces can exert dramatic and opposite effects on the stability of two of the major linkages between cell-cell adhesion proteins and the F-actin cytoskeleton. Our data demonstrate that that PDZ domains can serve as force-responsive mechanical anchors at cell-cell adhesion complexes. More broadly, our findings suggest that mechanical force may serve as a previously unsuspected regulator of the hundreds of PDZ-ligand interactions present in animal cells.

Classical cadherins evolutionary constraints in primates is associated with their expression in the central nervous system

Classical cadherins (CDH) comprise a family of single-pass transmembrane glycoproteins that contribute to tissue morphogenesis by regulating cell-cell adhesion, cytoskeletal dynamics, and cell signaling. CDH are grouped into type I (CDH 1, 2, 3, 4 and 15) and type II (CDH 5, 6, 7, 8, 9, 10, 11, 12, 18, 20, 22 and 24), based on the folding of the cadherin binding domain involved in trans-dimer formation. CDH are exclusively found in metazoans, and the origin and expansion of the gene family coincide with the emergence of multicellularity and vertebrates respectively. This study examined the evolutionary changes of CDH orthologs in primates and the factors that influence selective pressure to investigate the varying constraints exerted among CDH. Pairwise comparisons of the number of amino acid substitutions and of the ratio of non-synonymous substitutions per non-synonymous sites (dN) over synonymous substitutions per synonymous sites (dS), show that CDH2, CDH4, and most type II CDH have been under significantly higher negative selective pressure as compared to CDH1, CDH3, CDH5 and CDH19. Evaluation of gene essentiality as determined by the effect of germline deletion on animal viability, morphogenic phenotype, and reproductive fitness, show no correlation with the with extent of negative selection observed on CDH. Spearman's correlation analysis shows a positive correlation between CDH expression levels (E) in mouse and human tissues and their rate of evolution (R), as observed in most proteins expressed on the cell surface. However, CDH expression in the CNS show a significant E-R negative correlation, indicating that the strong negative selection exerted on CDH2, CDH4, and most type II CDH is associated with their expression in the CNS. CDH participate in a variety of cellular processes in the CNS including neuronal migration and functional assembly of neural circuits, which could profoundly influence animal fitness. Therefore, our findings suggest that the unusually high negative selective pressure exerted on CDH2, CDH4 and most type II CDH is due to their role in CNS formation and function and may have contributed to shape the evolution of the CNS in primates.

Cell Adhesion Molecules as Modulators of the Epidermal Growth Factor Receptor

Cell adhesion molecules (CAMs) are cell surface glycoproteins mediating interactions of cells with other cells and the extracellular matrix. By mediating the adhesion and modulating activity of other plasma membrane proteins, CAMs are involved in regulating a multitude of cellular processes, including growth, proliferation, migration, and survival of cells. In this review, we present evidence showing that various CAMs interact with the epidermal growth factor receptor (EGFR), a receptor tyrosine kinase inducing pro-proliferative and anti-apoptotic intracellular signaling in response to binding to several soluble ligands, including the epidermal growth factor. We discuss that CAMs are involved in regulating EGFR signaling by either potentiating or inhibiting the soluble ligand-dependent activation of EGFR. In addition, CAMs induce soluble ligand-independent forms of EGFR activity and regulate the levels of EGFR and its ligand-induced degradation. The CAM-dependent modulation of EGFR activity plays a key role in regulating the growth, proliferation, and survival of cells. Future research is needed to determine whether these processes can be targeted in both normal and cancerous cells by regulating interactions of EGFR with various CAMs.

Mechanism of the blood-brain barrier modulation by cadherin peptides

Aim

This study was aimed at finding the binding site on the human E-cadherin for Ala-Asp-Thr Cyclic 5 (ADTC5), ADTC7, and ADTC9 peptides as blood-brain barrier modulator (BBBM) for determining their mechanism of action in modulating the blood-brain barrier (BBB).

Methods

ADTC7 and ADTC9 were derivatives of ADTC5 where the Val6 residue in ADTC5 was replaced by Glu6 and Tyr6 residues, respectively. The binding properties of ADTC5, ADTC7, and ADTC9 to the extracellular-1 (EC1) domain of E-cadherin were evaluated using chemical shift perturbation (CSP) method in the two dimensional (2D) 1H-15N-heteronuclear single quantum coherence (HSQC) nuclear magnetic resonance (NMR) spectroscopy. Molecular docking experiments were used to determine the binding sites of these peptides to the EC1 domain of E-cadherin.

Results

This study indicates that ADTC5 has the highest binding affinity to the EC1 domain of E-cadherin compared to ADTC7 and ADTC9, suggesting the importance of the Val6 residue as shown in our previous in vitro study. All three peptides have a similar binding site at the hydrophobic binding pocket where the domain swapping occurs. ADTC5 has a higher overlapping binding site with ADTC7 than that of ADTC9. Binding of ADTC5 on the EC1 domain influences the conformation of the EC1 C-terminal tail.

Conclusions

These peptides bind the domain swapping region of the EC1 domain to inhibit the trans-cadherin interaction that creates intercellular junction modulation to increase the BBB paracellular porosity.

A Simple and Versatile Strategy for Oriented Immobilization of His-Tagged Proteins on Magnetic Nanoparticles

Oriented and covalent immobilization of proteins on magnetic nanoparticles (MNPs) is particularly challenging as it requires both the functionality of the protein and the colloidal stability of the MNPs to be preserved. Here, we describe a simple, straightforward, and efficient strategy for MNP functionalization with proteins using metal affinity binding. Our method involves a single-step process where MNPs are functionalized using a preformed, ready-to-use nitrilotriacetic acid-divalent metal cation (NTA-M2+) complex and polyethylene glycol (PEG) molecules. As a proof-of-concept, we demonstrate the oriented immobilization of a recombinant cadherin fragment engineered with a hexahistidine tag (6His-tag) onto the MNPs. Our developed methodology is simple and direct, enabling the oriented bioconjugation of His-tagged cadherins to MNPs while preserving protein functionality and the colloidal stability of the MNPs, and could be extended to other proteins expressing a polyhistidine tag. When compared to the traditional method where NTA is first conjugated to the MNPs and afterward free metal ions are added to form the complex, this novel strategy results in a higher functionalization efficiency while avoiding MNP aggregation. Additionally, our method allows for covalent bonding of the cadherin fragments to the MNP surface while preserving functionality, making it highly versatile. Finally, our strategy not only ensures the correct orientation of the protein fragments on the MNPs but also allows for the precise control of their density. This feature enables the selective targeting of E-cadherin-expressing cells only when MNPs are decorated with a high density of cadherin fragments.

Engineering the Interactions of Classical Cadherin Cell-Cell Adhesion Proteins

Classical cadherins are calcium-dependent cell-cell adhesion proteins that play key roles in the formation and maintenance of tissues. Deficiencies in cadherin adhesion are hallmarks of numerous cancers. In this article, we review recent biophysical studies on the regulation of cadherin structure and adhesion. We begin by reviewing distinct cadherin binding conformations, their biophysical properties, and their response to mechanical stimuli. We then describe biophysical guidelines for engineering Abs that can regulate adhesion by either stabilizing or destabilizing cadherin interactions. Finally, we review molecular mechanisms by which cytoplasmic proteins regulate the conformation of cadherin extracellular regions from the inside out.

Multiple dimeric structures and strand-swap dimerization of E-cadherin in solution visualized by high-speed atomic force microscopy

Classical cadherins play key roles in cell-cell adhesion. The adhesion process is thought to comprise mainly two steps: X-dimer and strand-swap (SS-) dimer formation of the extracellular domains (ectodomains) of cadherins. The dimerization mechanism of this two-step process has been investigated for type I cadherins, including E-cadherin, of classical cadherins, whereas other binding states also have been proposed, raising the possibility of additional binding processes required for the cadherin dimerization. However, technical limitations in observing single-molecule structures and their dynamics have precluded the investigation of the dynamic binding process of cadherin. Here, we used high-speed atomic force microscopy (HS-AFM) to observe full-length ectodomains of E-cadherin in solution and identified multiple dimeric structures that had not been reported previously. HS-AFM revealed that almost half of the cadherin dimers showed S- (or reverse S-) shaped conformations, which had more dynamic properties than the SS- and X-like dimers. The combined HS-AFM, mutational, and molecular modeling analyses showed that the S-shaped dimer was formed by membrane-distal ectodomains, while the binding interface was different from that of SS- and X-dimers. Furthermore, the formation of the SS-dimer from the S-shaped and X-like dimers was directly visualized, suggesting the processes of SS-dimer formation from S-shaped and X-dimers during cadherin dimerization.

The first reported case of CDH3-related hypotrichosis with juvenile macular dystrophy from Jordan: a case report

BACKGROUND

Pathogenic variants in the Cadherin 3 (CDH3) gene are responsible for the occurrence of Hypotrichosis with Juvenile Macular Dystrophy (HJMD) and Ectodermal Dysplasia, Ectrodactyly and Macular Dystrophy Syndrome (EEMS), both of which are rare autosomal recessive disorders characterized by hypotrichosis and progressive macular dystrophy. The CDH3 gene encodes for P-cadherin, a calcium-binding protein that is essential for cell-cell adhesion, which is expressed in the retinal pigment epithelial cells and hair follicles.

MATERIALS AND METHODS

Fundus examination of both eyes was done in addition to clinical investigation. Genomic DNA was extracted from a whole-blood sample and whole-exome sequencing (WES) was performed to identify the underlying etiology.All identified variants were evaluated for their pathogenicity and causality.

RESULTS

We present the first case of HJMD in a 23-year-old female patient from Jordan. The patient presented to our ophthalmology clinic with poor vision in both eyes. Gross examination revealed sparse scalp hair along with macular dystrophy on fundus exam in both eyes. HJMD was suspected and whole-exome sequencing (WES) confirmed the diagnosis with the identification of a homozygous frameshift deletion (p.Gly277AlafsTer20) localised in exon 7 of the CDH3 gene.

CONCLUSION

Blindness due to progressive macular degeneration is a common manifestation in numerous syndromic recessive disorders such as HJMD. Ophthalmologists should consider the importance of systemic manifestations and genetic testing for the confirmation of diagnosis.

Cell Aggregation Assays for Homophilic Interactions Between Cell Surface Proteins

Many proteins expressed on the cellular surface provide signaling and cell adhesion properties required for vital cellular functions. These binding interactions can occur between different but complementary proteins such as a ligand and receptor, or between the same protein acting as both ligand and receptor. The cell aggregation assay is a straightforward technique to identify homophilic interactions from such proteins. Here we describe the procedure for testing proteins via cell aggregation assays in HEK293T cells.

Extracellular domains of E-cadherin determine key mechanical phenotypes of an epithelium through cell- and non-cell-autonomous outside-in signaling

Cadherins control intercellular adhesion in most metazoans. In vertebrates, intercellular adhesion differs considerably between cadherins of type-I and type-II, predominantly due to their different extracellular regions. Yet, intercellular adhesion critically depends on actomyosin contractility, in which the role of the cadherin extracellular region is unclear. Here, we dissect the roles of the Extracellular Cadherin (EC) Ig-like domains by expressing chimeric E-cadherin with E-cadherin and cadherin-7 Ig-like domains in cells naturally devoid of cadherins. Using cell-cell separation, cortical tension measurement, tissue stretching and migration assays, we show that distinct EC repeats in the extracellular region of cadherins differentially modulate epithelial sheet integrity, cell-cell separation forces, and cell cortical tension with the Cdc42 pathway, which further differentially regulate epithelial tensile strength, ductility, and ultimately collective migration. Interestingly, dissipative processes rather than static adhesion energy mostly dominate cell-cell separation forces. We provide a framework for the emergence of epithelial phenotypes from cell mechanical properties dependent on EC outside-in signaling.

Mechanism of dimerization and structural features of human LI-cadherin

Liver intestine (LI)-cadherin is a member of the cadherin superfamily, which encompasses a group of Ca2+-dependent cell-adhesion proteins. The expression of LI-cadherin is observed on various types of cells in the human body, such as normal small intestine and colon cells, and gastric cancer cells. Because its expression is not observed on normal gastric cells, LI-cadherin is a promising target for gastric cancer imaging. However, because the cell adhesion mechanism of LI-cadherin has remained unknown, rational design of therapeutic molecules targeting this cadherin has been hampered. Here, we have studied the homodimerization mechanism of LI-cadherin. We report the crystal structure of the LI-cadherin homodimer containing its first four extracellular cadherin repeats (EC1-4). The EC1-4 homodimer exhibited a unique architecture different from that of other cadherins reported so far, driven by the interactions between EC2 of one protein chain and EC4 of the second protein chain. The crystal structure also revealed that LI-cadherin possesses a noncanonical calcium ion-free linker between the EC2 and EC3 domains. Various biochemical techniques and molecular dynamics simulations were employed to elucidate the mechanism of homodimerization. We also showed that the formation of the homodimer observed in the crystal structure is necessary for LI-cadherin-dependent cell adhesion by performing cell aggregation assays. Taken together, our data provide structural insights necessary to advance the use of LI-cadherin as a target for imaging gastric cancer.

Pathogenic variants in CDH11 impair cell adhesion and cause Teebi hypertelorism syndrome

Teebi hypertelorism syndrome (THS; OMIM 145420) is a rare craniofacial disorder characterized by hypertelorism, prominent forehead, short nose with broad or depressed nasal root. Some cases of THS have been attributed to SPECC1L variants. Homozygous variants in CDH11 truncating the transmembrane and intracellular domains have been implicated in Elsahy-Waters syndrome (EWS; OMIM 211380) with hypertelorism. We report THS due to CDH11 heterozygous missense variants on 19 subjects from 9 families. All affected residues in the extracellular region of Cadherin-11 (CHD11) are highly conserved across vertebrate species and classical cadherins. Six of the variants that cluster around the EC2-EC3 and EC3-EC4 linker regions are predicted to affect Ca²⁺ binding that is required for cadherin stability. Two of the additional variants [c.164G > C, p.(Trp55Ser) and c.418G > A, p.(Glu140Lys)] are also notable as they are predicted to directly affect trans-homodimer formation. Immunohistochemical study demonstrates that CDH11 is strongly expressed in human facial mesenchyme. Using multiple functional assays, we show that five variants from the EC1, EC2-EC3 linker, and EC3 regions significantly reduced the cell-substrate trans adhesion activity and one variant from EC3-EC4 linker results in changes in cell morphology, focal adhesion, and migration, suggesting dominant negative effect. Characteristic features in this cohort included depressed nasal root, cardiac and umbilical defects. These features distinguished this phenotype from that seen in SPECC1L-related hypertelorism syndrome and CDH11-related EWS. Our results demonstrate heterozygous variants in CDH11, which decrease cell-cell adhesion and increase cell migratory behavior, cause a form of THS, as termed CDH11-related THS.

Non-junctional role of Cadherin3 in cell migration and contact inhibition of locomotion via domain-dependent, opposing regulation of Rac1

Classical cadherins are well-known adhesion molecules responsible for physically connecting neighboring cells and signaling this cell-cell contact. Recent studies have suggested novel signaling roles for "non-junctional" cadherins (NJCads); however, the function of cadherin signaling independent of cell-cell contacts remains unknown. In this study, mesendodermal cells and tissues from gastrula stage Xenopus laevis embryos demonstrate that deletion of extracellular domains of Cadherin3 (Cdh3; formerly C-cadherin in Xenopus) disrupts contact inhibition of locomotion. In both bulk Rac1 activity assays and spatio-temporal FRET image analysis, the extracellular and cytoplasmic Cdh3 domains disrupt NJCad signaling and regulate Rac1 activity in opposing directions. Stabilization of the cytoskeleton counteracted this regulation in single cell migration assays. Our study provides novel insights into adhesion-independent signaling by Cadherin3 and its role in regulating single and collective cell migration.

Engineered peptide modified hydrogel platform for propagation of human pluripotent stem cells

Human pluripotent stem cells (hPSCs) have enormous potential to alleviate cell needs for regenerative medicine, however these cells require expansion in cell colonies to maintain cell-cell contact, thus limiting the scalability needed to meet the demands of cell therapy. While the use of a Rho-associated protein kinase (ROCK) inhibitor will allow for culture of single cell hPSCs, typically only 50% of cells are recovered after dissociation. When hPSCs lose cell-cell contact through E-cadherin, dissociation induced apoptosis occurs. In this study, we hypothesized that the extracellular E-cadherin domain of hPSCs will bind to synthetic E-cadherin peptides presented on a hydrogel substrate, mimicking the required cell-cell contact and thereby retaining single-cell viability and clonogenicity. Hence, the objective of this study was to functionalize alginate hydrogels with synthetic peptides mimicking E-cadherin and evaluate peptide performance in promoting cell attachment, viability, maintaining pluripotency, and differentiation potential. We observed that alginate conjugated with synthetic E-cadherin peptides not only supported initial cell attachment with high viability, but also supported hPSC propagation and high fold expansion. hPSCs propagated on the peptide modified substrates maintained the hPSC characteristic pluripotency and differentiation potential, characterized by both spontaneous and directed differentiation. STATEMENT OF SIGNIFICANCE: Human pluripotent stem cells (hPSCs) have enormous potential to alleviate cell needs for regenerative medicine and cell therapy. However, scalable culture of hPSCs is challenged by its need for maintenance of cell-cell contact, dissociation of which triggers the apoptotic pathway. Hence hPSCs are commonly maintained as colonies over Matrigel coated culture plates. Furthermore, use of xenogenic and undefined Matrigel compromises the translational potential of hPSCs. In this work we have developed a completely defined substrate to enable adherent culture of hPSCs as single cells. This substrate prevents apoptosis of the single cells and allows significant fold expansion of hPSCs while maintaining pluripotency and differentiation potential. The developed substrate is expected to be a cost-effective and translatable alternative to Matrigel.

p120-catenin phosphorylation status alters E-cadherin mediated cell adhesion and ability of tumor cells to metastasize

p120-catenin is considered to be a tumor suppressor because it stabilizes E-cadherin levels at the cell surface. p120-catenin phosphorylation is increased in several types of cancer, but the role of phosphorylation in cancer is unknown. The phosphorylation state of p120-catenin is important in controlling E-cadherin homophilic binding strength which maintains epithelial junctions. Because decreased cell-cell adhesion is associated with increased cancer metastasis we hypothesize that p120-catenin phosphorylation at specific Serine and Threonine residues alters the E-cadherin binding strength between tumor cells and thereby affect the ability of tumor cells to leave the primary tumor and metastasize to distant sites. In this study we show that expression of the p120-catenin phosphorylation dead mutant, by converting six Serine and Threonine sites to Alanine, leads to enhanced E-cadherin adhesive binding strength in tumor cells. We observed a decrease in the ability of tumor cells expressing the p120-catenin phosphorylation mutant to migrate and invade using in-vitro models of cancer progression. Further, tumor cells expressing the phosphorylation mutant form of p120-catenin demonstrated a decrease in ability to metastasize to the lungs using an in-vivo orthotopic mammary fat pad injection model of breast cancer development and metastasis. This suggests that regulation of p120-catenin phosphorylation at the cell surface is important in mediating cell-adhesion, thereby impacting cancer progression and metastasis.

Stepwise polarisation of developing bilayered epidermis is mediated by aPKC and E-cadherin in zebrafish

The epidermis, a multilayered epithelium, surrounds and protects the vertebrate body. It develops from a bilayered epithelium formed of the outer periderm and underlying basal epidermis. How apicobasal polarity is established in the developing epidermis has remained poorly understood. We show that both the periderm and the basal epidermis exhibit polarised distribution of adherens junctions in zebrafish. aPKC, an apical polarity regulator, maintains the robustness of polarisation of E-cadherin- an adherens junction component- in the periderm. E-cadherin in one layer controls the localisation of E-cadherin in the second layer in a layer non-autonomous manner. Importantly, E-cadherin controls the localisation and levels of Lgl, a basolateral polarity regulator, in a layer autonomous as well non-autonomous manner. Since periderm formation from the enveloping layer precedes the formation of the basal epidermis, our analyses suggest that peridermal polarity, initiated by aPKC, is transduced in a stepwise manner by E-cadherin to the basal layer.

S-nitrosylation and its role in breast cancer angiogenesis and metastasis

S-nitrosylation, the modification by nitric oxide of free sulfhydryl groups in cysteines, has become an important regulatory mechanism in carcinogenesis and metastasis. S-nitrosylation of targets in tumor cells contributes to metastasis regulating epithelial to mesenchymal transition, migration and invasion. In the tumor environment, the role of S-nitrosylation in endothelium has not been addressed; however, the evidence points out that S-nitrosylation of endothelial proteins may regulate angiogenesis, adhesion of tumor cells to the endothelium, intra and extravasation of tumor cells and contribute to metastasis.

EpCAM homo-oligomerization is not the basis for its role in cell-cell adhesion

Cell-surface tumor marker EpCAM plays a key role in proliferation, differentiation and adhesion processes in stem and epithelial cells. It is established as a cell-cell adhesion molecule, forming intercellular interactions through homophilic association. However, the mechanism by which such interactions arise has not yet been fully elucidated. Here, we first show that EpCAM monomers do not associate into oligomers that would resemble an inter-cellular homo-oligomer, capable of mediating cell-cell adhesion, by using SAXS, XL-MS and bead aggregation assays. Second, we also show that EpCAM forms stable dimers on the surface of a cell with pre-formed cell-cell contacts using FLIM-FRET; however, no inter-cellular homo-oligomers were detectable. Thus, our study provides clear evidence that EpCAM indeed does not function as a homophilic cell adhesion molecule and therefore calls for a significant revision of its role in both normal and cancerous tissues. In the light of this, we strongly support the previously suggested name Epithelial Cell Activating Molecule instead of the Epithelial Cell Adhesion Molecule.

δ-Protocadherins: Organizers of neural circuit assembly

The δ-protocadherins comprise a small family of homophilic cell adhesion molecules within the larger cadherin superfamily. They are essential for neural development as mutations in these molecules give rise to human neurodevelopmental disorders, such as schizophrenia and epilepsy, and result in behavioral defects in animal models. Despite their importance to neural development, a detailed understanding of their mechanisms and the ways in which their loss leads to changes in neural function is lacking. However, recent results have begun to reveal roles for the δ-protocadherins in both regulation of neurogenesis and lineage-dependent circuit assembly, as well as in contact-dependent motility and selective axon fasciculation. These evolutionarily conserved mechanisms could have a profound impact on the robust assembly of the vertebrate nervous system. Future work should be focused on unraveling the molecular mechanisms of the δ-protocadherins and understanding how this family functions broadly to regulate neural development.

Linking E-cadherin mechanotransduction to cell metabolism through force-mediated activation of AMPK

The response of cells to mechanical force is a major determinant of cell behaviour and is an energetically costly event. How cells derive energy to resist mechanical force is unknown. Here, we show that application of force to E-cadherin stimulates liver kinase B1 (LKB1) to activate AMP-activated protein kinase (AMPK), a master regulator of energy homeostasis. LKB1 recruits AMPK to the E-cadherin mechanotransduction complex, thereby stimulating actomyosin contractility, glucose uptake and ATP production. The increase in ATP provides energy to reinforce the adhesion complex and actin cytoskeleton so that the cell can resist physiological forces. Together, these findings reveal a paradigm for how mechanotransduction and metabolism are linked and provide a framework for understanding how diseases involving contractile and metabolic disturbances arise.

Overexpression of Cathepsin E Interferes with Neuronal Differentiation of P19 Embryonal Teratocarcinoma Cells by Degradation of N-cadherin

Cathepsin E (CatE), an aspartic protease, has a limited distribution in certain cell types such as gastric cells. CatE is not detectable in the normal brain, whereas it is increasingly expressed in damaged neurons and activated microglia of the pathological brain. Neurons expressing high levels of CatE showed apparent morphological changes, including a marked shrinkage of the cytoplasmic region and beading of neurites, suggesting neuronal damage. The intracellular level of CatE in neurons is strictly regulated at both transcriptional and translational levels. Although the up-regulation of CatE may cause pathological changes in neurons, little information is available about the precise outcome of the increased expression of CatE in neurons. In this study, we have attempted to clarify the outcome of up-regulated CatE gene expression in neurons using the P19 cell neuronal differentiation after the overexpression of CatE. We unexpectedly found that the overexpression of CatE interfered with neuronal differentiation of P19 cells through an impairment of cell aggregate formation. Pepstatin A, an aspartic protease inhibitor, restored the impaired cell aggregation of P19/CatE cells. The small number of P19 cells differentiated into neurons had abnormal morphology characterized by their fusiform cell bodies with short processes. Furthermore, CatE proteolytically cleaved the extracellular domain of N-cadherin. These observations suggest that the overexpression of CatE interferes with neuronal differentiation of P19 cells through an impairment of cell aggregate formation, possibly through proteolytic degradation of N-cadherin.

Biophysical basis of cadherin mediated cell-cell adhesion

Classical cadherin transmembrane cell-cell adhesion proteins play essential roles in tissue morphogenesis and in mediating tissue integrity. Cadherin ectodomains from opposing cells interact to form load-bearing trans dimers that mechanically couple cells. Cell-cell adhesion is believed to be strengthened by cis clustering of cadherins on the same cell surface. This review summarizes biophysical studies of the structure, interaction kinetics and biomechanics of classical cadherin ectodomains. We first discuss the structure and equilibrium binding kinetics of classical cadherin trans and cis dimers. We then discuss how mechanical stimuli alters the kinetics of cadherin interaction and tunes adhesion. Finally, we highlight open questions on the role of mechanical forces in influencing cadherin structure, function and organization on the cell surface.

Self-assembly of keratin peptides: Its implication on the performance of electrospun PVA nanofibers

Drawing inspiration from the field of designer self-assembling materials, this work is aimed to focus on the self-assembling nature of extracted peptides. Hair keratin, a proteinacious reject in tanning industry has been chosen since they have been extracted and used for wide range of applications. Keratin source was subjected to five hydrolysis treatments (viz., sulphitolysis, β-mercaptoethanol, ionic liquid, thioglycolic acid and alkali) and assayed for functional groups. This was followed by the prediction of secondary structure using circular dichroism, determining the microstructural level to which the extracted peptide has self-assembled. Sulphitolysis and thioglycolic acid based hydrolysates exist in monomeric conformation, whereas β-mercaptoethanol based hydrolysate exhibited dimeric conformation. The subsequent part of the study is to incorporate these peptides into the nanofibers to study the structural implication of keratin peptides on its characteristics. Accordingly, the peptides were electrospun with PVA and subjected to morphological, mechanical, thermal and biological characterizations. Monomeric nanofiber mat has high tensile strength of around 5.5 MPa and offered lower mass transport resistance, whereas dimeric mat has high Tm of around 290 °C and was more biocompatible. These results help in understanding the extraction-structure-function aspect of the hydrolysates stressing the role of extraction methods on the choice of application.

E-cadherin roles in animal biology: A perspective on thyroid hormone-influence

The establishment, remodeling and maintenance of tissular architecture during animal development, and even across juvenile to adult life, are deeply regulated by a delicate interplay of extracellular signals, cell membrane receptors and intracellular signal messengers. It is well known that cell adhesion molecules (cell-cell and cell-extracellular matrix) play a critical role in these processes. Particularly, adherens junctions (AJs) mediated by E-cadherin and catenins determine cell-cell contact survival and epithelia function. Consequently, this review seeks to encompass the complex and prolific knowledge about E-cadherin roles during physiological and pathological states, particularly focusing on the influence exerted by the thyroid hormone (TH).

Three Dimensional Conjugation of Recombinant N-Cadherin to a Hydrogel for In Vitro Anisotropic Neural Growth

Living cells are extensively being studied to build functional tissues that are useful for both fundamental and applied bioscience studies. Increasing evidence suggests that cell-cell adhesion controlled by intercellular cadherin junction plays important roles in the quality of the resulting engineered tissue. These findings prompted efforts to interrogate biological effects of cadherin at a molecular scale; however, few efforts were made to harness the effects of cadherin on cells cultured in an in vivo-like three dimensional matrix. To this end, this study reports a hydrogel matrix three dimensionally functionalized with a controlled number of Fc-tagged recombinant N-cadherins (N-Cad-Fc). To retain the desired conformation of N-Cad, these cadherins were immobilized and oriented to the gel by anti-Fc-antibodies chemically coupled to gels. The gels were processed to present N-Cad-Fc in uniaxially aligned microchannels or randomly oriented micropores. Culturing cortical cells in the functionalized gels generated a large fraction of neurons that are functional as indicated by increased intracellular calcium ion concentrations with the microchanneled gel. In contrast, direct N-Cad-Fc immobilization to microchannel or micropore walls of the gel limited the growth of neurons and increased the glial to neuron ratio. The results of this study will be highly useful to organize a wide array of cadherin molecules in a series of biomaterials used for three-dimensional cell culture and to regulate phenotypic activities of tissue-forming cells in an elaborate manner.

Roles for E-cadherin cell surface regulation in cancer

Loss of E-cadherin expression often occurs in tumors, but many metastases retain E-cadherin. Regulation of the adhesive activity of E-cadherin at the cell surface is important for metastasis of mammary tumor cells, and cancer-associated missense mutations in E-cadherin selectively affect the mechanism of cell surface regulation.

The loss of E-cadherin expression in association with the epithelial–mesenchymal transition (EMT) occurs frequently during tumor metastasis. However, metastases often retain E-cadherin expression, an EMT is not required for metastasis, and metastases can arise from clusters of tumor cells. We demonstrate that the regulation of the adhesive activity of E-cadherin present at the cell surface by an inside-out signaling mechanism is important in cancer. First, we find that the metastasis of an E-cadherin–expressing mammary cell line from the mammary gland to the lung depends on reduced E-cadherin adhesive function. An activating monoclonal antibody to E-cadherin that induces a high adhesive state significantly reduced the number of cells metastasized to the lung without affecting the growth in size of the primary tumor in the mammary gland. Second, we find that many cancer-associated germline missense mutations in the E-cadherin gene in patients with hereditary diffuse gastric cancer selectively affect the mechanism of inside-out cell surface regulation without inhibiting basic E-cadherin adhesion function. This suggests that genetic deficits in E-cadherin cell surface regulation contribute to cancer progression. Analysis of these mutations also provides insights into the molecular mechanisms underlying cadherin regulation at the cell surface.

S-nitrosylation regulates VE-cadherin phosphorylation and internalization in microvascular permeability

The adherens junction complex, composed mainly of vascular endothelial (VE)-cadherin, β-catenin, p120, and γ-catenin, is the main element of the endothelial barrier in postcapillary venules.S-nitrosylation of β-catenin and p120 is an important step in proinflammatory agents-induced hyperpermeability. We investigated in vitro and in vivo whether or not VE-cadherin isS-nitrosylated using platelet-activating factor (PAF) as agonist. We report that PAF-stimulates S-nitrosylation of VE-cadherin, which disrupts its association with β-catenin. In addition, based on inhibition of nitric oxide production, our results strongly suggest that S-nitrosylation is required for VE-cadherin phosphorylation on tyrosine and for its internalization. Our results unveil an important mechanism to regulate phosphorylation of junctional proteins in association with S-nitrosylation.

Identification of E-cadherin signature motifs functioning as cleavage sites for Helicobacter pylori HtrA

The cell adhesion protein and tumour suppressor E-cadherin exhibits important functions in the prevention of gastric cancer. As a class-I carcinogen, Helicobacter pylori (H. pylori) has developed a unique strategy to interfere with E-cadherin functions. In previous studies, we have demonstrated that H. pylori secretes the protease high temperature requirement A (HtrA) which cleaves off the E-cadherin ectodomain (NTF) on epithelial cells. This opens cell-to-cell junctions, allowing bacterial transmigration across the polarised epithelium. Here, we investigated the molecular mechanism of the HtrA-E-cadherin interaction and identified E-cadherin cleavage sites for HtrA. Mass-spectrometry-based proteomics and Edman degradation revealed three signature motifs containing the [VITA]-[VITA]-x-x-D-[DN] sequence pattern, which were preferentially cleaved by HtrA. Based on these sites, we developed a substrate-derived peptide inhibitor that selectively bound and inhibited HtrA, thereby blocking transmigration of H. pylori. The discovery of HtrA-targeted signature sites might further explain why we detected a stable 90 kDa NTF fragment during H. pylori infection, but also additional E-cadherin fragments ranging from 105 kDa to 48 kDa in in vitro cleavage experiments. In conclusion, HtrA targets E-cadherin signature sites that are accessible in in vitro reactions, but might be partially masked on epithelial cells through functional homophilic E-cadherin interactions.

N-cadherin-based adherens junction regulates the maintenance, proliferation, and differentiation of neural progenitor cells during development

This review addresses our current understanding of the regulatory mechanism by which N-cadherin, a classical cadherin, affects neural progenitor cells (NPCs) during development. N-cadherin is responsible for the integrity of adherens junctions (AJs), which develop in the sub-apical region of NPCs in the neural tube and brain cortex. The apical domain, which contains the sub-apical region, is involved in the switching from symmetric proliferative division to asymmetric neurogenic division of NPCs. In addition, N-cadherin-based AJ is deeply involved in the apico-basal polarity of NPCs and the regulation of Wnt-β-catenin, hedgehog (Hh), and Notch signaling. In this review, we discuss the roles of N-cadherin in the maintenance, proliferation, and differentiation of NPCs through components of AJ, β-catenin and αE-catenin.

Amyloid precursor protein dimerization and synaptogenic function depend on copper binding to the growth factor-like domain

Accumulating evidence suggests that the copper-binding amyloid precursor protein (APP) has an essential synaptic function. APP synaptogenic function depends on trans-directed dimerization of the extracellular E1 domain encompassing a growth factor-like domain (GFLD) and a copper-binding domain (CuBD). Here we report the 1.75 Å crystal structure of the GFLD in complex with a copper ion bound with high affinity to an extended hairpin loop at the dimerization interface. In coimmunoprecipitation assays copper binding promotes APP interaction, whereas mutations in the copper-binding sites of either the GFLD or CuBD result in a drastic reduction in APP cis-orientated dimerization. We show that copper is essential and sufficient to induce trans-directed dimerization of purified APP. Furthermore, a mixed culture assay of primary neurons with HEK293 cells expressing different APP mutants revealed that APP potently promotes synaptogenesis depending on copper binding to the GFLD. Together, these findings demonstrate that copper binding to the GFLD of APP is required for APP cis-/trans-directed dimerization and APP synaptogenic function. Thus, neuronal activity or disease-associated changes in copper homeostasis likely go along with altered APP synaptic function.

Giant cadherins Fat and Dachsous self-bend to organize properly spaced intercellular junctions

The cadherins Fat and Dachsous regulate cell polarity and proliferation via their heterophilic interactions at intercellular junctions. Their ectodomains are unusually large because of repetitive extracellular cadherin (EC) domains, which raises the question of how they fit in regular intercellular spaces. Cadherins typically exhibit a linear topology through the binding of Ca(2+) to the linker between the EC domains. Our electron-microscopic observations of mammalian Fat4 and Dachsous1 ectodomains, however, revealed that, although their N-terminal regions exhibit a linear configuration, the C-terminal regions are kinked with multiple hairpin-like bends. Notably, certain EC-EC linkers in Fat4 and Dachsous1 lost Ca(2+)-binding amino acids. When such non-Ca(2+)-binding linkers were substituted for a normal linker in E-cadherin, the mutant E-cadherins deformed more extensively than the wild-type molecule. To simulate cadherin structures with non-Ca(2+)-binding linkers, we used an elastic network model and confirmed that bent configurations can be generated by deformation of non-Ca(2+)-binding linkers. These findings suggest that Fat and Dachsous self-bend due to the loss of Ca(2+)-binding amino acids from specific EC-EC linkers, and can therefore adapt to confined spaces.

Bead aggregation assays for the characterization of putative cell adhesion molecules

Cell-cell adhesion is fundamental to multicellular life and is mediated by a diverse array of cell surface proteins. However, the adhesive interactions for many of these proteins are poorly understood. Here we present a simple, rapid method for characterizing the adhesive properties of putative homophilic cell adhesion molecules. Cultured HEK293 cells are transfected with DNA plasmid encoding a secreted, epitope-tagged ectodomain of a cell surface protein. Using functionalized beads specific for the epitope tag, the soluble, secreted fusion protein is captured from the culture medium. The coated beads can then be used directly in bead aggregation assays or in fluorescent bead sorting assays to test for homophilic adhesion. If desired, mutagenesis can then be used to elucidate the specific amino acids or domains required for adhesion. This assay requires only small amounts of expressed protein, does not require the production of stable cell lines, and can be accomplished in 4 days.

Identification of four novel PCDH19 Mutations and prediction of their functional impact

The PCDH19 gene encodes protocadherin-19, a transmembrane protein with six cadherin (EC) domains, containing adhesive interfaces likely to be involved in neuronal connection. Over a hundred mostly private mutations have been identified in girls with epilepsy, with or without intellectual disability (ID). Furthermore, transmitting hemizygous males are devoid of seizures or ID, making it difficult to establish the pathogenic nature of newly identified variants. Here, we describe an integrated approach to evaluate the pathogenicity of four novel PCDH19 mutations. Segregation analysis has been complemented with an in silico analysis of mutation effects at the protein level. Using sequence information, we compared different computational prediction methods. We used homology modeling to build structural models of two PCDH19 EC-domains, and compared wild-type and mutant models to identify differences in residue interactions or biochemical properties of the model surfaces. Our analysis suggests different molecular effects of the novel mutations in exerting their pathogenic role. Two of them interfere with or alter functional residues predicted to mediate ligand or protein binding, one alters the EC-domain folding stability; the frame-shift mutation produces a truncated protein lacking the intracellular domain. Interestingly, the girl carrying the putative loss of function mutation presents the most severe phenotype.

CLASP2 interacts with p120-catenin and governs microtubule dynamics at adherens junctions

The microtubule plus end–binding protein CLASP2 localizes to adherens junctions via direct interaction with p120-catenin and is required for adherens junction stability.

Classical cadherins and their connections with microtubules (MTs) are emerging as important determinants of cell adhesion. However, the functional relevance of such interactions and the molecular players that contribute to tissue architecture are still emerging. In this paper, we report that the MT plus end–binding protein CLASP2 localizes to adherens junctions (AJs) via direct interaction with p120-catenin (p120) in primary basal mouse keratinocytes. Reductions in the levels of p120 or CLASP2 decreased the localization of the other protein to cell–cell contacts and altered AJ dynamics and stability. These features were accompanied by decreased MT density and altered MT dynamics at intercellular junction sites. Interestingly, CLASP2 was enriched at the cortex of basal progenitor keratinocytes, in close localization to p120. Our findings suggest the existence of a new mechanism of MT targeting to AJs with potential functional implications in the maintenance of proper cell–cell adhesion in epidermal stem cells.

Covalent and density-controlled surface immobilization of E-cadherin for adhesion force spectroscopy

E-cadherin is a key cell-cell adhesion molecule but the impact of receptor density and the precise contribution of individual cadherin ectodomains in promoting cell adhesion are only incompletely understood. Investigating these mechanisms would benefit from artificial adhesion substrates carrying different cadherin ectodomains at defined surface density. We therefore developed a quantitative E-cadherin surface immobilization protocol based on the SNAP-tag technique. Extracellular (EC) fragments of E-cadherin fused to the SNAP-tag were covalently bound to self-assembled monolayers (SAM) of thiols carrying benzylguanine (BG) head groups. The adhesive functionality of the different E-cadherin surfaces was then assessed using cell spreading assays and single-cell (SCSF) and single-molecule (SMSF) force spectroscopy. We demonstrate that an E-cadherin construct containing only the first and second outmost EC domain (E1-2) is not sufficient for mediating cell adhesion and yields only low single cadherin-cadherin adhesion forces. In contrast, a construct containing all five EC domains (E1-5) efficiently promotes cell spreading and generates strong single cadherin and cell adhesion forces. By varying the concentration of BG head groups within the SAM we determined a lateral distance of 5–11 nm for optimal E-cadherin functionality. Integrating the results from SCMS and SMSF experiments furthermore demonstrated that the dissolution of E-cadherin adhesion contacts involves a sequential unbinding of individual cadherin receptors rather than the sudden rupture of larger cadherin receptor clusters. Our method of covalent, oriented and density-controlled E-cadherin immobilization thus provides a novel and versatile platform to study molecular mechanisms underlying cadherin-mediated cell adhesion under defined experimental conditions.

Flotillins directly interact with γ-catenin and regulate epithelial cell-cell adhesion

Flotillin-1 and flotillin-2 are two homologous, membrane raft associated proteins. Although it has been reported that flotillins are involved in cell adhesion processes and play a role during breast cancer progression, thus making them interesting future therapeutic targets, their precise function has not been well elucidated. The present study investigates the function of these proteins in cell-cell adhesion in non-malignant cells. We have used the non-malignant epithelial MCF10A cells to study the interaction network of flotillins within cell-cell adhesion complexes. RNA interference was used to examine the effect of flotillins on the structure of adherens junctions and on the association of core proteins, such as E-cadherin, with membrane rafts. We here show that the cadherin proteins of the adherens junction associate with flotillin-2 in MCF10A cells and in various human cell lines. In vitro, flotillin-1 and flotillin-2 directly interact with γ-catenin which is so far the only protein known to be present both in the adherens junction and the desmosome. Mapping of the interaction domain within the γ-catenin sequence identified the Armadillo domains 6-8, especially ARM domain 7, to be important for the association with flotillins. Furthermore, depletion of flotillins significantly influenced the morphology of the adherens junction in human epithelial MCF10A cells and altered the association of E-cadherin and γ-catenin with membrane rafts. Taken together, these observations suggest a functional role for flotillins, especially flotillin-2, in cell-cell adhesion in non-malignant epithelial cells.

Inhibition of cell adhesion by a cadherin-11 antibody thwarts bone metastasis

Cadherin-11 (CDH11) is a member of the cadherin superfamily mainly expressed in osteoblasts but not in epithelial cells. However, prostate cancer cells with a propensity for bone metastasis express high levels of cadherin-11 and reduced levels of E-cadherin. Downregulation of cadherin-11 inhibits interaction of prostate cancer cells with osteoblasts in vitro and homing of prostate cancer cells to bone in an animal model of metastasis. These findings indicate that targeting cadherin-11 may prevent prostate cancer bone metastasis. To explore this possibility, a panel of 21 monoclonal antibodies (mAb) was generated against the extracellular (EC) domain of cadherin-11. Two antibodies, mAbs 2C7 and 1A5, inhibited cadherin-11-mediated cell-cell aggregation in vitro using L-cells transfected with cadherin-11. Both antibodies demonstrated specificity to cadherin-11, and neither antibody recognized E-cadherin or N-cadherin on C4-2B or PC3 cells, respectively. Furthermore, mAb 2C7 inhibited cadherin-11-mediated aggregation between the highly metastatic PC3-mm2 cells and MC3T3-E1 osteoblasts. Mechanistically, a series of deletion mutants revealed a unique motif, aa 343-348, in the cadherin-11 EC3 domain that is recognized by mAb 2C7 and that this motif coordinated cell-cell adhesion. Importantly, administration of mAb 2C7 in a prophylactic setting effectively prevented metastasis of PC3-mm2 cells to bone in an in vivo mouse model. These results show that targeting the extracellular domain of cadherin-11 can limit cellular adhesion and metastatic dissemination of prostate cancer cells.

IMPLICATIONS

Monotherapy using a cadherin-11 antibody is a suitable option for the prevention of bone metastases.

Tuning the kinetics of cadherin adhesion

Cadherins are Ca(2+)-dependent cell-cell adhesion proteins that maintain the structural integrity of the epidermis; their principle function is to resist mechanical force. This review summarizes the biophysical mechanisms by which classical cadherins tune adhesion and withstand mechanical stress. We first relate the structure of classical cadherins to their equilibrium binding properties. We then review the role of mechanical perturbations in tuning the kinetics of cadherin adhesion. In particular, we highlight recent studies that show that cadherins form three types of adhesive bonds: catch bonds, which become longer lived and lock in the presence of tensile force; slip bonds, which become shorter lived when pulled; and ideal bonds, which are insensitive to tugging.

Cadherin point mutations alter cell sorting and modulate GTPase signaling

This study investigated the impact of cadherin binding differences on both cell sorting and GTPase activation. The use of N-terminal domain point mutants of Xenopus C-cadherin enabled us to quantify binding differences and determine their effects on cadherin-dependent functions without any potential complications arising as a result of differences in cytodomain interactions. Dynamic cell-cell binding measurements carried out with the micropipette manipulation technique quantified the impact of these mutations on the two-dimensional binding affinities and dissociation rates of cadherins in the native context of the cell membrane. Pairwise binding affinities were compared with in vitro cell-sorting specificity and ligation-dependent GTPase signaling. Two-dimensional affinity differences greater than five-fold correlated with cadherin-dependent in vitro cell segregation, but smaller differences failed to induce cell sorting. Comparison of the binding affinities with GTPase signaling amplitudes further demonstrated that differential binding also proportionally modulates intracellular signaling. These results show that differential cadherin affinities have broader functional consequences than merely controlling cell-cell cohesion.

Cadherins in brain morphogenesis and wiring

Cadherins are Ca(2+)-dependent cell-cell adhesion molecules that play critical roles in animal morphogenesis. Various cadherin-related molecules have also been identified, which show diverse functions, not only for the regulation of cell adhesion but also for that of cell proliferation and planar cell polarity. During the past decade, understanding of the roles of these molecules in the nervous system has significantly progressed. They are important not only for the development of the nervous system but also for its functions and, in turn, for neural disorders. In this review, we discuss the roles of cadherins and related molecules in neural development and function in the vertebrate brain.

Cadherin recognition and adhesion

Classical cadherins are the principle adhesive proteins at cohesive intercellular junctions, and are essential proteins for morphogenesis and tissue homeostasis. Because subtype-dependent differences in cadherin adhesion are at the heart of cadherin functions, several structural and biophysical approaches have been used to elucidate relationships between cadherin structures, biophysical properties of cadherin bonds, and cadherin-dependent cell functions. Some experimental approaches appeared to provide conflicting views of the cadherin binding mechanism. However, recent structural and biophysical data, as well as computer simulations generated new insights into classical cadherin binding that increasingly reconcile diverse experimental findings. This review summarizes these recent findings, and highlights both the consistencies and remaining challenges needed to generate a comprehensive model of cadherin interactions that is consistent with all available experimental data.