Dimeric versions of two short N-cadherin binding motifs (HAVDI and INPISG) function as N-cadherin agonists

Endothelial cell spreading on lipid bilayers with combined integrin and cadherin binding ligands

Endothelial cells play a central role in the vascular system, where their function is tightly regulated by both cell-extracellular matrix (e.g., via integrins) and cell-cell interactions (e.g., via cadherins). In this study, we incorporated cholesterol-modified integrin and N-cadherin peptide binding ligands in fluid supported lipid bilayers. Human umbilical vein endothelial cell adhesion, spreading and vinculin localization in these cells were dependent on ligand density. One composition led to observe a higher extent of cell spreading, where cells exhibited extensive lamellipodia formation and a qualitatively more distinct N-cadherin localization at the cell periphery, which is indicative of N-cadherin clustering and a mimic of cell-cell contact formation. The results can be used to reconstitute the endothelial-pericyte interface on biomedical devices and materials.

Potential Therapeutic Applications of N-Cadherin Antagonists and Agonists

This review focuses on the cell adhesion molecule (CAM), known as neural (N)-cadherin (CDH2). The molecular basis of N-cadherin-mediated intercellular adhesion is discussed, as well as the intracellular signaling pathways regulated by this CAM. N-cadherin antagonists and agonists are then described, and several potential therapeutic applications of these intercellular adhesion modulators are considered. The usefulness of N-cadherin antagonists in treating fibrotic diseases and cancer, as well as manipulating vascular function are emphasized. Biomaterials incorporating N-cadherin modulators for tissue regeneration are also presented. N-cadherin antagonists and agonists have potential for broad utility in the treatment of numerous maladies.

N-Cadherin adhesive ligation regulates mechanosensitive neural stem cell lineage commitment in 3D matrices

We demonstrate a novel strategy to independently control cell–ECM and cell–cell interactions of neural stem cells in a 3D matrix.

Designing aromatic N-cadherin mimetic short-peptide-based bioactive scaffolds for controlling cellular behaviour

The development of suitable biomaterials is one of the key factors responsible for the success of the tissue-engineering field. Recently, significant effort has been devoted to the design of biomimetic materials that can elicit specific cellular responses and direct new tissue formation mediated by bioactive peptides. The success of the design principle of such biomimetic scaffolds is mainly related to the cell-extracellular matrix (ECM) interactions, whereas cell-cell interactions also play a vital role in cell survival, neurite outgrowth, attachment, migration, differentiation, and proliferation. Hence, an ideal strategy to improve cell-cell interactions would rely on the judicious incorporation of a bioactive motif in the designer scaffold. In this way, we explored for the first time the primary functional pentapeptide sequence of the N-cadherin protein, HAVDI, which is known to be involved in cell-cell interactions. We have formulated the shortest N-cadherin mimetic peptide sequence utilizing a minimalistic approach. Furthermore, we employed a classical molecular self-assembly strategy through rational modification of the basic pentapeptide motif of N-cadherin, i.e. HAVDI, using Fmoc and Nap aromatic moieties to modify the N-terminal end. The designed N-cadherin mimetic peptides, Fmoc-HAVDI and Nap-HAVDI, self-assembled to form a nanofibrous network resulting in a bioactive peptide hydrogel at physiological pH. The nanofibrous network of the pentapeptide hydrogels resembles the topology of the natural ECM. Furthermore, the mechanical strength of the gels also matches that of the native ECM of neural cells. Interestingly, both the N-cadherin mimetic peptide hydrogels supported cell adhesion and proliferation of the neural and non-neural cell lines, highlighting the diversity of these peptidic scaffolds. Further, the cultured neural and non-neural cells on the bioactive scaffolds showed normal expression of β-III tubulin and actin, respectively. The cellular response was compromised in control peptides, which further establishes the significance of the bioactive motifs towards controlling the cellular behaviour. Our study indicated that our designer N-cadherin-based peptidic hydrogels mimic the structural as well as the physical properties of the native ECM, which has been further reflected in the functional attributes offered by these scaffolds, and thus offer a suitable bioactive domain for further use as a next-generation material in tissue-engineering applications.

Niche-mimicking interactions in peptide-functionalized 3D hydrogels amplify mesenchymal stromal cell paracrine effects

Cells encounter complex environments in vivo where they interact with the extracellular matrix, neighboring cells, and soluble cues, which together influence their fate and function. However, the interplay of these interactions and their collective impact on the regenerative effects of mesenchymal stromal cells (MSCs) remains insufficiently explored. Here, we show that 3D culture in microporous (~125 μm) hydrogels that passively promote cell-cell interactions sensitizes MSCs to growth factors, particularly to IGF-1. IGF-1 enhances MSC paracrine secretion activity, and application of secreted factors to myoblasts potently stimulates their migration and differentiation. In contrast, the paracrine activity of MSCs encapsulated in nanoporous (~10 nm) hydrogels remain unchanged. Blocking N-cadherin on MSCs abrogates the stimulatory effects of IGF-1 in microporous but not nanoporous hydrogels. The role of N-cadherin in regulating MSC function is further clarified by functionalizing alginates with the HAVDI peptide sequence that is derived from the extracellular domain of N-cadherin and that acts to mimic cell-cell interactions. MSCs encapsulated in nanoporous HAVDI-gels, but not in gels functionalized with a scrambled sequence, show heightened paracrine activity in response to IGF-1. These findings reveal how interactions with the matrix, neighboring cells, and soluble factors impact and maximize the regenerative potential of MSCs.

The role of the gap junction perinexus in cardiac conduction: Potential as a novel anti-arrhythmic drug target

Cardiovascular disease remains the single largest cause of natural death in the United States, with a significant cause of mortality associated with cardiac arrhythmias. Presently, options for treating and preventing myocardial electrical dysfunction, including sudden cardiac death, are limited. Recent studies have indicated that conduction of electrical activation in the heart may have an ephaptic component, wherein intercellular coupling occurs via electrochemical signaling across narrow extracellular clefts between cardiomyocytes. The perinexus is a 100-200 nm-wide stretch of closely apposed membrane directly adjacent to connexin 43 gap junctions. Electron and super-resolution microscopy studies, as well as biochemical analyses, have provided evidence that perinexal nanodomains may be candidate structures for facilitating ephaptic coupling. This work has included characterization of the perinexus as a region of close inter-membrane contact between cardiomyocytes (<30 nm) containing dense clusters of voltage-gated sodium channels. Here, we review what is known about perinexal structure and function and the potential that the perinexus may have novel and pivotal roles in disorders of cardiac conduction. Of particular interest is the prospect that cell adhesion mediated by the cardiac sodium channel β subunit (Scn1b) may be a novel anti-arrhythmic target.

The adhesion function of the sodium channel beta subunit (β1) contributes to cardiac action potential propagation

Computational modeling indicates that cardiac conduction may involve ephaptic coupling – intercellular communication involving electrochemical signaling across narrow extracellular clefts between cardiomyocytes. We hypothesized that β1(SCN1B) –mediated adhesion scaffolds trans-activating Na_V1.5 (SCN5A) channels within narrow (<30 nm) perinexal clefts adjacent to gap junctions (GJs), facilitating ephaptic coupling. Super-resolution imaging indicated preferential β1 localization at the perinexus, where it co-locates with Na_V1.5. Smart patch clamp (SPC) indicated greater sodium current density (I_Na) at perinexi, relative to non-junctional sites. A novel, rationally designed peptide, βadp1, potently and selectively inhibited β1-mediated adhesion, in electric cell-substrate impedance sensing studies. βadp1 significantly widened perinexi in guinea pig ventricles, and selectively reduced perinexal I_Na, but not whole cell I_Na, in myocyte monolayers. In optical mapping studies, βadp1 precipitated arrhythmogenic conduction slowing. In summary, β1-mediated adhesion at the perinexus facilitates action potential propagation between cardiomyocytes, and may represent a novel target for anti-arrhythmic therapies.

Dose and Timing of N-Cadherin Mimetic Peptides Regulate MSC Chondrogenesis within Hydrogels

The transmembrane glycoprotein N-cadherin (NCad) mediates cell-cell interactions found during mesenchymal condensation and chondrogenesis. Here, NCad-derived peptides (i.e., HAV) are incorporated into hyaluronic acid (HA) hydrogels with encapsulated mesenchymal stem cells (MSCs). Since the dose and timing of NCad signaling are dynamic, HAV peptide presentation is tuned via alterations in peptide concentration and incorporation of an ADAM10-cleavable domain between the hydrogel and the HAV motif, respectively. HA hydrogels functionalized with HAV result in dose-dependent increases in early chondrogenesis of encapsulated MSCs and resultant cartilage matrix production. For example, type II collagen and glycosaminoglycan production increase ≈9- and 2-fold with the highest dose of HAV (i.e., 2 × 10^-3 m), respectively, when compared to unmodified hydrogels, while incorporation of an efficient ADAM10-cleavable domain between the HAV peptide and hydrogel abolishes increases in chondrogenesis and matrix production. Treatment with a small-molecule ADAM10 inhibitor restores the functional effect of the HAV peptide, indicating that timing and duration of HAV peptide presentation is crucial for robust chondrogenesis. This study demonstrates a nuanced approach to the biofunctionalization of hydrogels to better emulate the complex cell microenvironment during embryogenesis toward stem-cell-based cartilage production.

Loss of E-Cadherin-Dependent Cell-Cell Adhesion and the Development and Progression of Cancer

Classical cadherins are the key molecules that control cell-cell adhesion. Notwithstanding this function, it is also clear that classical cadherins are more than just the "glue" that keeps the cells together. Cadherins are essential regulators of tissue homeostasis that govern multiple facets of cellular function and development, by transducing adhesive signals to a complex network of signaling effectors and transcriptional programs. In cancer, cadherins are often inactivated or functionally inhibited, resulting in disease development and/or progression. This review focuses on E-cadherin and its causal role in the development and progression of breast and gastric cancer. We provide a summary of the biochemical consequences and consider the conceptual impact of early (mutational) E-cadherin loss in cancer. We advocate that carcinomas driven by E-cadherin loss should be considered "actin-diseases," caused by the specific disruption of the E-cadherin-actin connection and a subsequent dependence on sustained actomyosin contraction for tumor progression. Based on the available data from mouse and human studies we discuss opportunities for targeted clinical intervention.

Secret handshakes: cell-cell interactions and cellular mimics

Cell-cell junctions, acting as 'secret handshakes', mediate cell-cell interactions and make multicellularity possible. Work over the previous century illuminated key players comprising these junctions including the cadherin superfamily, nectins, CAMs, connexins, notch/delta, lectins, and eph/Ephrins. Recent work has focused on elucidating how interactions between these complex and often contradictory cues can ultimately give rise to large-scale organization in tissues. This effort, in turn, has enabled bioengineering advances such as cell-mimetic interfaces that allow us to better probe junction biology and to develop new biomaterials. This review details exciting, recent developments in these areas as well as providing both historical context and a discussion of some topical challenges and opportunities for the future.

Self-assembled N-cadherin mimetic peptide hydrogels promote the chondrogenesis of mesenchymal stem cells through inhibition of canonical Wnt/β-catenin signaling

N-cadherin, a transmembrane protein and major component of adherens junction, mediates cell-cell interactions and intracellular signaling that are important to the regulation of cell behaviors and organ development. Previous studies have identified mimetic peptides that possess similar bioactivity as that of N-cadherin, which promotes chondrogenesis of human mesenchymal stem cells (hMSCs); however, the molecular mechanism remains unknown. In this study, we combined the N-cadherin mimetic peptide (HAVDI) with the self-assembling KLD-12 peptide: the resultant peptide is capable of self-assembling into hydrogels functionalized with N-cadherin peptide in phosphate-buffered saline (PBS) at 37 °C. Encapsulation of hMSCs in these hydrogels showed enhanced expression of chondrogenic marker genes and deposition of cartilage specific extracellular matrix rich in proteoglycan and Type II Collagen compared to control hydrogels, with a scrambled-sequence peptide after 14 days of chondrogenic culture. Furthermore, western blot showed a significantly higher expression of active glycogen synthase kinase-3β (GSK-3β), which phosphorylates β-catenin and facilitates ubiquitin-mediated degradation, as well as a lower expression of β-catenin and LEF1 in the N-cadherin peptide hydrogels versus controls. Immunofluorescence staining revealed significantly less nuclear localization of β-catenin in N-cadherin mimetic peptide hydrogels. Our findings suggest that N-cadherin peptide hydrogels suppress canonical Wnt signaling in hMSCs by reducing β-catenin nuclear translocation and the associated transcriptional activity of β-catenin/LEF-1/TCF complex, thereby enhancing the chondrogenesis of hMSCs. Our biomimetic self-assembled peptide hydrogels can serve as a tailorable and versatile three-dimensional culture platform to investigate the effect of biofunctionalization on stem cell behavior.

Concentration dependent survival and neural differentiation of murine embryonic stem cells cultured on polyethylene glycol dimethacrylate hydrogels possessing a continuous concentration gradient of n-cadherin derived peptide His-Ala-Val-Asp-Lle

N-cadherin cell-cell signaling plays a key role in the structure and function of the nervous system. However, few studies have incorporated bioactive signaling from n-cadherin into tissue engineering matrices. The present study uses a continuous gradient approach in polyethylene glycol dimethacrylate hydrogels to identify concentration dependent effects of n-cadherin peptide, His-Ala-Val-Asp-Lle (HAVDI), on murine embryonic stem cell survival and neural differentiation. The n-cadherin peptide was found to affect the expression of pluripotency marker, alkaline phosphatase, in murine embryonic stem cells cultured on n-cadherin peptide containing hydrogels in a concentration dependent manner. Increasing n-cadherin peptide concentrations in the hydrogels elicited a biphasic response in neurite extension length and mRNA expression of neural differentiation marker, neuron-specific class III β-tubulin, in murine embryonic stem cells cultured on the hydrogels. High concentrations of n-cadherin peptide in the hydrogels were found to increase the expression of apoptotic marker, caspase 3/7, in murine embryonic stem cells compared to that of murine embryonic stem cell cultures on hydrogels containing lower concentrations of n-cadherin peptide. Increasing the n-cadherin peptide concentration in the hydrogels facilitated greater survival of murine embryonic stem cells exposed to increasing oxidative stress caused by hydrogen peroxide exposure. The combinatorial approach presented in this work demonstrates concentration dependent effects of n-cadherin signaling on mouse embryonic stem cell behavior, underscoring the need for the greater use of systematic approaches in tissue engineering matrix design in order to understand and optimize bioactive signaling in the matrix for tissue formation.

STATEMENT OF SIGNIFICANCE

Single cell encapsulation is common in tissue engineering matrices. This eliminates cellular access to cell-cell signaling. N-cadherin, a cell-cell signaling molecule, plays a vital role in the development of neural tissues, but has not been well studied as a bioactive signaling element in neural tissue engineering matrices. The present study uses a systematic continuous gradient approach to identify concentration dependent effects of n-cadherin derived peptide, HAVDI, on the survival and neural differentiation of murine embryonic stem cells. This work underscores the need for greater use to combinatorial strategies to understand the effect complex bioactive signaling, such as n-cadherin, and the need to optimize the concentration of such bioactive signaling within tissue engineering matrices for maximal cellular response.

Water transport through the intestinal epithelial barrier under different osmotic conditions is dependent on LI-cadherin trans-interaction

In the intestine water has to be reabsorbed from the chymus across the intestinal epithelium. The osmolarity within the lumen is subjected to high variations meaning that water transport often has to take place against osmotic gradients. It has been hypothesized that LI-cadherin is important in this process by keeping the intercellular cleft narrow facilitating the buildup of an osmotic gradient allowing water reabsorption. LI-cadherin is exceptional among the cadherin superfamily with respect to its localization along the lateral plasma membrane of epithelial cells being excluded from adherens junction. Furthermore it has 7 but not 5 extracellular cadherin repeats (EC1-EC7) and a small cytosolic domain. In this study we identified the peptide VAALD as an inhibitor of LI-cadherin trans-interaction by modeling the structure of LI-cadherin and comparison with the known adhesive interfaces of E-cadherin. This inhibitory peptide was used to measure LI-cadherin dependency of water transport through a monolayer of epithelial CACO2 cells under various osmotic conditions. If LI-cadherin trans-interaction was inhibited by use of the peptide, water transport from the luminal to the basolateral side was impaired and even reversed in the case of hypertonic conditions whereas no effect could be observed at isotonic conditions. These data are in line with a recently published model predicting LI-cadherin to keep the width of the lateral intercellular cleft small. In this narrow cleft a high osmolarity can be achieved due to ion pumps yielding a standing osmotic gradient allowing water absorption from the gut even if the faeces is highly hypertonic.

Prognostic significance of immunohistochemical epithelial–mesenchymal transition markers in skin melanoma patients

Aim: To investigate secreted protein acidic and rich in cystein (SPARC) and neural cadherin (NCAD), which are associated with epithelial–mesenchymal transition in primary skin melanoma and nodal metastases and their prognostic impact in melanoma patients. Methods: Expression of proteins was assessed by immunochemistry in archival paraffin samples from 103 primary melanoma tumors and 16 nodal metastases. Results: Increased expression of SPARC and NCAD in primary skin melanoma was associated with decreased overall survival, adverse clinicopathological features and particularly with microsatellitosis (SPARC) and ulceration (NCAD). In univariate Cox regression analysis, both biomarkers were significantly associated with the risk of death; the multivariate Cox regression analysis identified no significance. Conclusion: The most important result of our study was that we confirmed the strict correlation between SPARC and NCAD expression and clinicopathological parameters related with melanoma progression, which is a specific clinical equivalent of the molecular mechanisms of epithelial–mesenchymal transition process and confirms its key role in the disease outcome.

Crystal Structure of Human E-Cadherin-EC1EC2 in Complex with a Peptidomimetic Competitive Inhibitor of Cadherin Homophilic Interaction

Cadherins are transmembrane cell adhesion proteins whose aberrant expression often correlates with cancer development and proliferation. We report the crystal structure of an E-cadherin extracellular fragment in complex with a peptidomimetic compound that was previously shown to partially inhibit cadherin homophilic adhesion. The structure reveals an unexpected binding mode and allows the identification of a druggable cadherin interface, thus paving the way to a future structure-guided design of cell adhesion inhibitors against cadherin-expressing solid tumors.

Computational design of novel peptidomimetic inhibitors of cadherin homophilic interactions

We report a first set of peptidomimetic ligands mimicking the adhesive interface identified by recent crystallographic structures of E- and N-cadherin. Compounds 2 and 3 inhibit adhesion of epithelial ovarian cancer (EOC) cells with improved efficacy compared to the ADH-1 peptide, a N-cadherin antagonist that is in early clinical trials in EOC patients.

CDH2 and CDH11 act as regulators of stem cell fate decisions

Accumulating evidence suggests that the mechanical and biochemical signals originating from cell-cell adhesion are critical for stem cell lineage specification. In this review, we focus on the role of cadherin mediated signaling in development and stem cell differentiation, with emphasis on two well-known cadherins, cadherin-2 (CDH2) (N-cadherin) and cadherin-11 (CDH11) (OB-cadherin). We summarize the existing knowledge regarding the role of CDH2 and CDH11 during development and differentiation in vivo and in vitro. We also discuss engineering strategies to control stem cell fate decisions by fine-tuning the extent of cell-cell adhesion through surface chemistry and microtopology. These studies may be greatly facilitated by novel strategies that enable monitoring of stem cell specification in real time. We expect that better understanding of how intercellular adhesion signaling affects lineage specification may impact biomaterial and scaffold design to control stem cell fate decisions in three-dimensional context with potential implications for tissue engineering and regenerative medicine.

Hydrogels that mimic developmentally relevant matrix and N-cadherin interactions enhance MSC chondrogenesis

Methacrylated hyaluronic acid (HA) hydrogels provide a backbone polymer with which mesenchymal stem cells (MSCs) can interact through several cell surface receptors that are expressed by MSCs, including CD44 and CD168. Previous studies showed that this 3D hydrogel environment supports the chondrogenesis of MSCs, and here we demonstrate through functional blockade that these specific cell-material interactions play a role in this process. Beyond matrix interactions, cadherin molecules, a family of transmembrane glycoproteins, play a critical role in tissue development during embryogenesis, and N-cadherin is a key factor in mediating cell-cell interactions during mesenchymal condensation and chondrogenesis. In this study, we functionalized HA hydrogels with N-cadherin mimetic peptides and evaluated their role in regulating chondrogenesis and cartilage matrix deposition by encapsulated MSCs. Our results show that conjugation of cadherin peptides onto HA hydrogels promotes both early chondrogenesis of MSCs and cartilage-specific matrix production with culture, compared with unmodified controls or those with inclusion of a scrambled peptide domain. This enhanced chondrogenesis was abolished via treatment with N-cadherin-specific antibodies, confirming the contribution of these N-cadherin peptides to chondrogenesis. Subcutaneous implantation of MSC-seeded constructs also showed superior neocartilage formation in implants functionalized with N-cadherin mimetic peptides compared with controls. This study demonstrates the inherent biologic activity of HA-based hydrogels, as well as the promise of biofunctionalizing HA hydrogels to emulate the complexity of the natural cell microenvironment during embryogenesis, particularly in stem cell-based cartilage regeneration.

The fibroblast growth factor family: neuromodulation of affective behavior

In this review, we propose a broader view of the role of the fibroblast growth factor (FGF) family in modulating brain function. We suggest that some of the FGF ligands together with the FGF receptors are altered in individuals with affective disorder and modulate emotionality in animal models. Thus, we propose that members of the FGF family may be genetic predisposing factors for anxiety, depression, or substance abuse; that they play a key organizing role during early development but continue to play a central role in neuroplasticity in adulthood; and that they work not only over extended time frames, but also via rapid signaling mechanisms, allowing them to exert an "on-line" influence on behavior. Therefore, the FGF family appears to be a prototype of "switch genes" that are endowed with organizational and modulatory properties across the lifespan, and that may represent molecular candidates as biomarkers and treatment targets for affective and addictive disorders.

Neuronal growth-promoting and inhibitory cues in neuroprotection and neuroregeneration

During development of the nervous system, neurons extend axons over considerable distances in a highly stereospecific fashion in order to innervate their targets in an appropriate manner. This involves the recognition, by the axonal growth cone, of guidance cues that determine the pathway taken by the axons. These guidance cues can act to promote and/or repel growth cone advance. The directed growth of axons is partly governed by cell adhesion molecules (CAMs) on the neuronal growth cone that bind to CAMs on the surface of other axons or nonneuronal cells. In vitro assays have established the importance of the CAMs ((neural cell adhesion molecule NCAM), N-cadherin, and L1) in promoting axonal growth over cells. Compelling evidence implicates the fibroblast growth factor receptor tyrosine kinase as the primary signal transduction molecule in the CAM pathway. CAMs are important constituents of synapses, and they appear to play important and diverse roles in regulating synaptic plasticity associated with learning and memory. Synthetic NCAM peptide mimetics corresponding to the binding site of NCAM for the fibroblast growth factor receptor promote synaptogenesis, enhance presynaptic function, and facilitate memory consolidation. Dimeric versions of functional binding motifs of N-cadherin behave as N-cadherin agonists, promoting both neuritogenesis and neuronal cell survival. Negative extracellular signals that physically direct neurite growth have also been described. The latter include the myelin inhibitory proteins, Nogo, myelin-associated glycoprotein, and oligodendrocyte-myelin glycoprotein. Potentiation of outgrowth-promoting signals, together with antagonism of myelin proteins or their convergent receptor, NgR, and its second messenger pathways, may provide new opportunities in the rational design of treatments for acute brain injury and neurodegenerative disorders.

Spatiotemporal distribution and function of N-cadherin in postnatal Schwann cells: A matter of adhesion?

During embryonic development of the peripheral nervous system (PNS), the adhesion molecule neuronal cadherin (N-cadherin) is expressed by Schwann cell precursors and associated with axonal growth cones. N-cadherin expression levels decrease as precursors differentiate into Schwann cells. In this study, we investigated the distribution of N-cadherin in the developing postnatal and adult rat peripheral nervous system. N-cadherin was found primarily in ensheathing glia throughout development, concentrated at neuron-glial or glial-glial contacts of the sciatic nerve, dorsal root ganglia (DRG), and myenteric plexi. In the sciatic nerve, N-cadherin decreases with age and progress of myelination. In adult animals, N-cadherin was found exclusively in nonmyelinating Schwann cells. The distribution of N-cadherin in developing E17 DRG primary cultures is similar to what was observed in vivo. Functional studies of N-cadherin in these cultures, using the antagonist peptide INPISGQ, show a disruption of the attachment between Schwann cells, but no interference in the initial or long-term contact between Schwann cells and axons. We suggest that N-cadherin acts primarily in the adhesion between glial cells during postnatal development. It may form adherents/junctions between nonmyelinating glia, which contribute to the stable tubular structure encapsulating thin caliber axons and thus stabilize the nerve structure as a whole.

Junctional music that the nucleus hears: cell-cell contact signaling and the modulation of gene activity

Cell-cell junctions continue to capture the interest of cell and developmental biologists, with an emerging area being the molecular means by which junctional signals relate to gene activity in the nucleus. Although complexities often arise in determining the direct versus indirect nature of such signal transduction, it is clear that such pathways are essential for the function of tissues and that alterations may contribute to many pathological outcomes. This review assesses a variety of cell-cell junction-to-nuclear signaling pathways, and outlines interesting areas for further study.

Stimulation of N-cadherin-dependent neurite outgrowth by small molecule peptide mimetic agonists of the N-cadherin HAV motif

N-cadherin is a cell adhesion molecule that promotes axon outgrowth and synapse formation during the development of the central nervous system. In addition, N-cadherin promotes glial cell adhesion and myelination of axons. Therefore, stimulating N-cadherin function with N-cadherin agonists could be used therapeutically to promote regeneration of the nervous system and remyelination after injury or disease. In the extracellular domain of N-cadherin, the amino acid sequence HAV is required for N-cadherin-mediated adhesion and neurite outgrowth. The ADH-1 cyclic peptide, derived from the N-cadherin HAV site, is an effective antagonist of N-cadherin-mediated neurite outgrowth and is currently being tested in clinical trials for cancer chemotherapy. Of interest, a dimeric version of this cyclic peptide, N-Ac-CHAVDINGHAVDIC-NH(2), functions as an N-cadherin agonist. This dimeric peptide agonist and the peptide antagonist ADH-1 both have limitations as drugs due to their metabolic instability and lack of oral delivery. To address this issue Adherex Technologies Inc. generated a small molecule library of peptidomimetics to the HAV region of N-cadherin, which would be more amenable to therapeutic use. We screened the Adherex library for compounds that altered neurite outgrowth and identified eight N-cadherin agonists that stimulated N-cadherin-dependent neurite outgrowth. Five of these agonists also stimulated retinal cell migration. These small molecule agonists may be effective reagents for promoting axon growth and remyelination after injury or disease.

Active matrix metalloproteinase-2 promotes apoptosis of hepatic stellate cells via the cleavage of cellular N-cadherin

BACKGROUND AND AIMS

Hepatic stellate cells (HSC) are known to synthesise excess matrix that characterises liver fibrosis and cirrhosis. Activated HSC express the matrix-degrading matrix metalloproteinase enzymes (MMPs) and their tissue inhibitors (TIMPs). During spontaneous recovery from experimental liver fibrosis, the expression of TIMP-1 declines and hepatic collagenolytic activity increases. This is accompanied by HSC apoptosis. In this study, we examine a potential mechanism whereby MMP activity might induce HSC apoptosis by cleaving N-cadherin at the cell surface.

RESULTS

N-cadherin expression was upregulated in human HSC during activation in culture. Addition of function-blocking antibodies or a peptide targeting the extracellular domain of N-cadherin, to cultured HSC, promoted apoptosis. During apoptosis, there was cleavage of N-cadherin into 20-100 kDa fragments. MMP-2 became activated early during HSC apoptosis and directly cleaved N-cadherin in vitro. Addition of activated MMP-2 to HSCs in culture resulted in enhanced apoptosis and loss of N-cadherin.

CONCLUSIONS

Together, these studies identify a role for both N-cadherin and MMP-2 in mediating HSC apoptosis, where N-cadherin works to provide a cell survival stimulus and MMP-2 promotes HSC apoptosis concomitant with N-cadherin degradation.

Endothelial barrier stabilization by a cyclic tandem peptide targeting VE-cadherin transinteraction in vitro and in vivo

Inflammatory stimuli result in vascular leakage with potentially life threatening consequences. As a key barrier component, loss of vascular endothelial (VE-) cadherin-mediated adhesion often precedes endothelial breakdown. This study aimed to stabilize VE-cadherin transinteraction and endothelial barrier function using peptides targeting the VE-cadherin adhesive interface. After modelling the transinteracting VE-cadherin structure, an inhibiting single peptide (SP) against a VE-cadherin binding pocket was selected, which specifically blocked VE-cadherin transinteraction as analyzed by single molecule atomic force microscopy (AFM). The tandem peptide (TP) consisting of two SP sequences in tandem was designed to strengthen VE-cadherin adhesion by simultaneously binding and cross-bridging two interacting cadherin molecules. Indeed, in AFM experiments TP specifically rendered VE-cadherin transinteraction resistant against an inhibitory monoclonal antibody. Moreover, TP reduced VE-cadherin lateral mobility and enhanced binding of VE-cadherin-coated microbeads to cultured endothelial cells, but acted independently of the actin cytoskeleton. TP also stabilized endothelial barrier properties against the Ca2+ ionophore A23187 and the inhibitory antibody. Finally, TP abolished endothelial permeability increase induced by tumour necrosis factor-α in microperfused venules in vivo. Stabilization of VE-cadherin adhesion by cross-bridging peptides may therefore be a novel therapeutic approach for the treatment of vascular hyperpermeability.

Peptides Targeting the Desmoglein 3 Adhesive Interface Prevent Autoantibody-induced Acantholysis in Pemphigus

Pemphigus vulgaris (PV) autoantibodies directly inhibit desmoglein (Dsg) 3-mediated transinteraction. Because cellular signaling also seems to be required for PV pathogenesis, it is important to characterize the role of direct inhibition in pemphigus acantholysis to allow establishment of new therapeutic approaches. Therefore, we modeled the Dsg1 and Dsg3 sequences into resolved cadherin structures and predicted peptides targeting the adhesive interface of both Dsg3 and Dsg1. In atomic force microscopy single molecule experiments, the self-designed cyclic single peptide specifically blocked homophilic Dsg3 and Dsg1 transinteraction, whereas a tandem peptide (TP) consisting of two combined single peptides did not. TP did not directly block binding of pemphigus IgG to their target Dsg antigens but prevented PV-IgG-induced inhibition of Dsg3 transinteraction in cell-free (atomic force microscopy) and cell-based (laser tweezer) experiments, indicating stabilization of Dsg3 bonds. Similarly, PV-IgG-mediated acantholysis and disruption of Dsg3 localization in HaCaT keratinocytes was partially blocked by TP. This is the first evidence that direct inhibition of Dsg3 binding is important for PV pathogenesis and that peptidomimetics stabilizing Dsg transinteraction may provide a novel approach for PV treatment.

Cadherin switching

The cadherin molecules at adherens junctions have multiple isoforms. Cadherin isoform switching (cadherin switching) occurs during normal developmental processes to allow cell types to segregate from one another. Tumor cells often recapitulate this activity and the result is an aggressive tumor cell that gains the ability to leave the site of the tumor and metastasize. At present, we understand some of the mechanisms that promote cadherin switching and some of the pathways downstream of this process that influence cell behavior. Specific cadherin family members influence growth-factor-receptor signaling and Rho GTPases to promote cell motility and invasion. In addition, p120-catenin probably plays multiple roles in cadherin switching, regulating Rho GTPases and stabilizing cadherins.

ADH-1 suppresses N-cadherin-dependent pancreatic cancer progression

Pancreatic cancer is one of the most aggressive malignant diseases. We recently reported that N-cadherin plays a key role in tumor progression and metastasis in pancreatic cancer. For this study, we sought to determine if an N-cadherin-blocking peptide (ADH-1) could prevent N-cadherin-mediated tumor progression in a mouse model for pancreatic cancer. The effect of ADH-1 on N-cadherin-mediated cell scattering and migration on collagen I was examined using pancreatic cancer cells. We also examined the influence of ADH-1 on cell apoptosis. Furthermore, in vivo animal studies were performed using orthotopic injection of N-cadherin overexpressing BxPC-3 cells with or without ADH-1 treatment. BxPC-3 and Capan-1 cells exhibited increased expression of N-cadherin in response to collagen I. This increase in N-cadherin promoted cell scattering and migration in response to collagen I. ADH-1 prevented these changes, but did not inhibit upregulation of N-cadherin. TUNEL assays and immunoblots for caspase-3 showed that ADH-1 induced apoptosis in a concentration dependent and N-cadherin dependent manner in pancreatic cancer cells. ADH-1 treatment resulted in significant reductions in tumor growth and lung metastasis in a mouse model for pancreatic cancer. The N-cadherin antagonist, ADH-1 has significant antitumor activity against N-cadherin-expressing cells using in vitro assays and in an orthotopic mouse model for pancreatic cancer, raising the possibility that N-cadherin antagonists have therapeutic potential for the treatment of pancreatic cancer in humans.

Pharmacology of cell adhesion molecules of the nervous system

Cell adhesion molecules (CAMs) play a pivotal role in the development and maintenance of the nervous system under normal conditions. They also are involved in numerous pathological processes such as inflammation, degenerative disorders, and cancer, making them attractive targets for drug development. The majority of CAMs are signal transducing receptors. CAM-induced intracellular signalling is triggered via homophilic (CAM-CAM) and heterophilic (CAM - other counter-receptors) interactions, which both can be targeted pharmacologically. We here describe the progress in the CAM pharmacology focusing on cadherins and CAMs of the immunoglobulin (Ig) superfamily, such as NCAM and L1. Structural basis of CAM-mediated cell adhesion and CAM-induced signalling are outlined. Different pharmacological approaches to study functions of CAMs are presented including the use of specific antibodies, recombinant proteins, and synthetic peptides. We also discuss how unravelling of the 3D structure of CAMs provides novel pharmacological tools for dissection of CAM-induced signalling pathways and offers therapeutic opportunities for a range of neurological disorders.

Soluble cadherins as cancer biomarkers

Molecular activities, regulating a balanced tissue organisation, are frequently disturbed during cancer progression. These include protein ectodomain shedding, a post-translational process that substantially changes the functional properties of the substrate protein. In comparison with normal epithelia, cancer cells almost invariably show diminished cadherin-mediated intercellular adhesion. This review will address cadherin ectodomain shedding and its functional consequence in normal physiology and in the tumor environment. Soluble cadherin fragments may retain specific biological activities during cancer cell invasion, angiogenesis and perineural invasion. When diffusion barriers disappear, soluble cadherins are detected in sera from cancer patients. Soluble N-(neural) cadherin may represent a novel diagnosis/prognostic biomarker showing a correlation with PSA in sera of prostate cancer patients. Furthermore, therapeutic monitoring in pancreas adenomacarcinoma revealed a correlation between circulating soluble N-cadherin and CA 19-9. A better understanding of cadherin regulation in cancer progression will likely increase our awareness of the importance of the combinatorial signals that regulate tissue integrity and eventually result in the identification of new therapeutics targeting cadherins.

N-cadherin is an in vivo substrate for protein tyrosine phosphatase sigma (PTPsigma) and participates in PTPsigma-mediated inhibition of axon growth

Protein tyrosine phosphatase sigma (PTPsigma) belongs to the LAR family of receptor tyrosine phosphatases and was previously shown to negatively regulate axon growth. The substrate for PTPsigma and the effector(s) mediating this inhibitory effect were unknown. Here we report the identification of N-cadherin as an in vivo substrate for PTPsigma. Using brain lysates from PTPsigma knockout mice, in combination with substrate trapping, we identified a hyper-tyrosine-phosphorylated protein of approximately 120 kDa in the knockout animals (relative to sibling controls), which was identified by mass spectrometry and immunoblotting as N-cadherin. beta-Catenin also precipitated in the complex and was also a substrate for PTPsigma. Dorsal root ganglion (DRG) neurons, which highly express endogenous N-cadherin and PTPsigma, exhibited a faster growth rate in the knockout mice than in the sibling controls when grown on laminin or N-cadherin substrata. However, when N-cadherin function was disrupted by an inhibitory peptide or lowering calcium concentrations, the differential growth rate between the knockout and sibling control mice was greatly diminished. These results suggest that the elevated tyrosine phosphorylation of N-cadherin in the PTPsigma(-/-) mice likely disrupted N-cadherin function, resulting in accelerated DRG nerve growth. We conclude that N-cadherin is a physiological substrate for PTPsigma and that N-cadherin (and likely beta-catenin) participates in PTPsigma-mediated inhibition of axon growth.

Soluble N-cadherin fragment promotes angiogenesis

Endothelial cells express two dependent intercellular adhesion molecules: vascular endothelial (VE)-cadherin, specific for endothelial cells, and N-cadherin, also present in neuronal, lens, skeletal and heart muscle cells, osteoblasts, pericytes and fibroblasts. While there exists a vast amount of evidence that VE-cadherin promotes angiogenesis, the role of N-cadherin still remains to be elucidated. We found that a soluble 90-kDa fragment N-cadherin promotes angiogenesis in the rabbit cornea assay and in the chorioallantoic assay when cleaved enzymatically from the extracellular domain of N-cadherin. Soluble N-cadherin stimulates migration of endothelial cells in the wound healing assay and stimulates phosphorylation of extracellular regulated kinase. In vitro experiments with PD173074 and knock-down of N-cadherin and fibroblast growth factor (FGF)-receptor, showed that the pro-angiogenic effect of soluble N-cadherin is N-cadherin- and FGF-receptor-dependent. Our results suggest that soluble N-cadherin stimulates migration of endothelial cells through the FGF-receptor.

N-cadherin-mediated cell motility requires cis dimers

Cadherins are expressed on the cell surface as a dimer in the membrane of one cell (cis dimer) that interacts with a cis dimer on an adjacent cell to form an adhesive trans dimer. It is well established that both cis and trans dimers must form for the cadherin to be an effective adhesion protein. In addition to their adhesive activity cadherins also play an important role in modulating cell behavior by regulating cell motility and signal transduction. Whether or not cis or trans dimers are necessary for the nonadhesive functions of cadherins has not been addressed. Here we show that N-cadherin cis dimers are necessary to induce cell motility in epithelial cells and that N-cadherin's ability to modulate the steady state levels of activated small GTPases requires both cis and trans dimers.

N-cadherin mediated cell contact inhibits germinal vesicle breakdown in mouse oocytes maintained in vitro

The effect of granulosa cell contact on the ability of zona-free oocytes to undergo germinal vesicle breakdown (GVBD) was assessed using a granulosa cell co-culture system. Oocytes contacted granulosa cells in a site-specific manner such that their GV was away from the granulosa cells. Also contact with granulosa cells reduced the percentage of oocytes undergoing GVBD from about 40% to 15%. GVBD was inhibited by contact with granulosa cells but not a granulosa cell-secreted product, since oocytes cultured in the same culture, that were adjacent to the granulosa cell monolayer underwent GVBD at the same rate as controls. Similarly, media collected from granulosa cell cultures did not attenuate the rate of GVBD. The ability of granulosa cell contact to inhibit GVBD was equal to that of db-cAMP. Moreover, the ability of granulosa cells to inhibit GVBD was not mimicked by spontaneously immortalized granulosa cells. This cell specificity appeared to be related to N-cadherin, since granulosa cells and oocytes express N-cadherin and a N-cadherin antibody attenuates the effect of granulosa cell contact. The mechanism through which N-cadherin mediated cell contact maintains meiotic arrest is unknown. It is possible that homophilic N-cadherin binding between the granulosa cells and oocyte acts through a junxtacrine mechanism, which in part may lead in the activation fibroblast growth factor (FGF) receptors that are expressed by the oocyte. The involvement of FGF receptors is supported by the observations that FGF and a N-cadherin peptide known to activate FGF receptors inhibit GVBD.

Plexin B3 promotes neurite outgrowth, interacts homophilically, and interacts with Rin

Background

Plexins, known to date as receptors of semaphorins, are implicated in semaphorin-mediated axon repulsion and growth cone collapse. However, subtype-specific functions of the majority of the nine members of the mammalian plexin family are largely unknown. In order to investigate functional properties of B-plexins, we analyzed the expression of human and murine plexin B3 and expressed full-length human plexins B2 (B2) and B3 (B3) in NIH-3T3 cells.

Results

Unexpectedly, B3 strongly and B2 moderately stimulate neurite outgrowth of primary murine cerebellar neurons. Both plexins mediate Ca²⁺/Mg²⁺-dependent cell aggregation due to homophilic trans-interaction, which is strong in the case of B3 and moderate for B2. Using different deletion constructs we show that the sema domain of B3 is essential for homophilic interaction. Using yeast two-hybrid analysis, we identified the neuron-specific and calmodulin-binding Ras-related GTPase Rin as an interaction partner of the intracellular part of B3, but not of B2. Rin, also known for its neurite outgrowth-inducing characteristics, co-localizes and co-immunoprecipitates with B3 in co-transfected COS-7 cells.

Conclusion

Our data suggest an involvement of homophilic interaction of B3 in semaphorin-independent signaling mechanisms positively influencing neuronal morphogenesis or function. Furthermore the neuron-specific small GTPase Rin is involved in downstream signaling of plexin B3.

The mechanism of cell adhesion by classical cadherins: the role of domain 1

The mechanism by which classical cadherins mediate cell adhesion and, in particular, the roles played by calcium and Trp2, the second amino acid in the N-terminal domain, have long been controversial. We have used antibodies to investigate the respective contributions of Trp2 and calcium to the stability of the N-terminal domain of N-cadherin. Using a peptide antibody to the betaB strand in domain 1, which detects a disordered structure, we show that both Trp2 and calcium play crucial parts in regulating stability of the domain. The epitope for another antibody, mAb GC4, has been mapped to the base of domain 1. Binding of GC4 to this epitope was shown to depend on intramolecular 'docking' of Trp2 into the domain 1 structure. Using this property, we provide evidence that calcium regulates a dynamic equilibrium between docked and undocked Trp2. Finally, a novel technique has been developed to test whether Trp2 cross-intercalation between cadherin molecules from adjacent cells (strand exchange) is central to cadherin-mediated cell adhesion. Guided by crystal structures showing strand exchange, we have introduced single cysteine point mutations into N-cadherin domain 1 in such a way that a disulphide bond will form between opposing N-cadherin molecules during cell adhesion if strand exchange occurs. The bond requires complementary cysteines to be precisely juxtaposed according to the strand exchange model. Our results demonstrate that the disulphide bond forms as predicted. This provides compelling evidence that strand exchange is indeed a primary event in cell adhesion by classical cadherins.

Overcoming the inhibitors of myelin with a novel neurotrophin strategy

Myelin inhibitors activate a p75(NTR)-dependent signaling cascade in neurons that not only inhibits axonal growth but also prevents neurotrophins (NT) from stimulating growth. Most intriguingly, in addition to Trk receptors, neurotrophins also bind to p75(NTR). We have designed a "mini-neurotrophin" called B(AG) to activate TrkB in the absence of p75(NTR) binding. We find that B(AG) is as effective as the natural TrkB ligands (brain-derived neurotrophic factor (BDNF) and NT-4) at promoting neurite outgrowth from cerebellar neurons. Furthermore, the neurite outgrowth responses stimulated by BDNF and B(AG) are inhibited by a common set of reagents, including the Trk receptor inhibitor K252a, as well as protein kinase A and phosphoinositide 3-kinase inhibitors. However, in contrast to BDNF, B(AG) promotes growth in the presence of a myelin inhibitor or when antibodies directly activate the p75(NTR) inhibitory pathway. On the basis of this observation, we postulated that the binding of BDNF to the p75(NTR) might compromise the ability of BDNF to stimulate neurite outgrowth in an inhibitory environment. To test this, we used NGF, and an NGF-derived peptide, to compete for the BDNF/p75(NTR) interaction; remarkably, in the presence of either agent, BDNF acquired the ability to promote neurite outgrowth in the presence of a myelin inhibitor. The data suggest that in an inhibitory environment, the BDNF/p75(NTR) interaction compromises regeneration. Agents that activate Trk receptors in the absence of p75(NTR) binding, or agents that inhibit neurotrophin/p75(NTR) binding, might therefore be better therapeutic candidates than neurotrophins.

Cell-cell interaction mediated by cadherin-11 directly regulates the differentiation of mesenchymal cells into the cells of the osteo-lineage and the chondro-lineage

We studied cadherin-11 function in the differentiation of mesenchymal cells. Teratomas harboring the cadherin-11 gene generated bone and cartilage preferentially. Cadherin-11 transfectants of C2C12 cells and cadherin-11 and/or N-cadherin transfectants of L cells showed that cadherin-11 together with N-cadherin-induced expression of ALP and FGF receptor 2. These results suggest that cadherin-11 directly regulates the differentiation of mesenchymal cells into the cells of the osteo-lineage and the chondro-lineage in a different manner from N-cadherin.

INTRODUCTION

Cell-cell interaction is an essential event for tissue formation; however, the role of cell-cell adhesion in mesenchymal tissue formation as well as in cell differentiation in this tissue remains unclear. cadherins, which are calcium-dependent cell adhesion receptors, form adherence junctions after adherence and aggregation of cells. Because cadherin-11 as well as N-cadherin has been reported to be a mesenchyme-related cadherin, we examined the cadherin-11 action in teratomas and in the cell lines C2C12 and L cell. Herein, we show that cell-cell interaction mediated by cadherin-11 is responsible for bone and cartilage formation.

MATERIALS AND METHODS

It has been previously reported that N-cadherin-expressing E-cadherin-/- ES transfectants formed neuroepithelium and cartilage in teratomas. Thus, we transfected the E-cadherin-/- ES cell line with the cadherin-11 gene. Moreover, we also transfected C2C12 cells and L cells with the cadherin-11 gene for morphological analysis and study of the induced differentiation at the molecular level.

RESULTS AND CONCLUSION

Teratomas derived from embryonic stem cells in which the cadherin-11 gene had been expressed exogenously contained bone and cartilage preferentially, showing that cadherin-11 is involved in mesenchymal tissue formation, specifically in controlling the differentiation of these cells into osteoblasts and chondrocytes. Therefore, we further examined the functional difference between cadherin-11 and N-cadherin. The expression patterns of cadherin-11 and N-cadherin in cells of the mouse osteoblastic cell line MC3T3-E1 showed that each cadherin was located independently of the cell-cell adhesion site and acted individually. In hanging drop cultures, cadherin-11 L cell transfectants aggregated in a sheet-like structure, whereas N-cadherin transfectants aggregated in a spherical form, indicating that each cadherin confers a different 3D architecture because of its individual adhesive property. To investigate the molecular mechanism of cadherin-11 action in cell differentiation, we analyzed cadherin-11 transfectants of C2C12 cells and cadherin-11 and/or N-cadherin transfectants of L cells and showed that cadherin-11, together with N-cadherin, induced expression of alkaline phosphatase (ALP) and fibroblast growth factor receptor 2. These results suggest that cadherin-11 directly regulates the differentiation of mesenchymal cells into the cells of the osteo-lineage and the chondro-lineage in a different manner from N-cadherin.

A survey of the year 2002 commercial optical biosensor literature

We have compiled 819 articles published in the year 2002 that involved commercial optical biosensor technology. The literature demonstrates that the technology's application continues to increase as biosensors are contributing to diverse scientific fields and are used to examine interactions ranging in size from small molecules to whole cells. Also, the variety of available commercial biosensor platforms is increasing and the expertise of users is improving. In this review, we use the literature to focus on the basic types of biosensor experiments, including kinetics, equilibrium analysis, solution competition, active concentration determination and screening. In addition, using examples of particularly well-performed analyses, we illustrate the high information content available in the primary response data and emphasize the impact of including figures in publications to support the results of biosensor analyses.

A dimeric version of the short N-cadherin binding motif HAVDI promotes neuronal cell survival by activating an N-cadherin/fibroblast growth factor receptor signalling cascade

The HAVDI and INPISGQ sequences have been identified as functional binding motifs in extracellular domain 1 (ECD1) of N-cadherin. Cyclic peptides containing a tandem repeat of the individual motifs function as N-cadherin agonists and stimulate neurite outgrowth. We now show that the cyclic peptide N-Ac-CHAVDINGHAVDIC-NH2 (SW4) containing the HAVDI sequence in tandem is efficacious also in promoting the in vitro survival of several populations of central nervous system neurons in paradigms where fibroblast growth factor-2 (FGF-2) is active. SW4 supported the survival of rat postnatal cerebellar granule neurons plated in serum-free medium and limited the death of differentiated granule neurons induced to die by switch to low K+ medium. In addition, SW4 rescued embryonic hippocampal and cortical neurons from injury caused by glutamic acid excitotoxicity. The neuroprotective effects of SW4 displayed a concentration dependence similar to those inducing neuritogenesis, were inhibited by a monomeric version of the same motif and by a specific FGF receptor antagonist (PD173074), and were not mimicked by the linear peptide. Inhibitors of the phosphatidylinositol 3-kinase (PI 3-kinase), MAP kinase, and p38 kinase signalling pathways did not interfere with SW4 function. These data suggest that SW4 functions by binding to and clustering N-cadherin in neurons and thereby activating and N-cadherin/FGF receptor signalling cascade, and propose that such agonists may represent a starting point for the development of therapeutic agents promoting neuronal cell survival and regeneration.

Cadherin adhesion: mechanisms and molecular interactions

Cadherins constitute a superfamily of cell-cell adhesion molecules expressed in many different cell types that are required for proper cellular function and maintenance of tissue architecture. Classical cadherins are the best understood class of cadherins. They are single membrane spanning proteins with a divergent extracellular domain of five repeats and a conserved cytoplasmic domain. Binding between cadherin extracellular domains is weak, but strong cell-cell adhesion develops during lateral clustering of cadherins by proteins that link the cadherin cytoplasmic domain to the actin cytoskeleton. Understanding how different regions of cadherins regulate cell-cell adhesion has been a major focus of study. Here, we examine evidence of the structure and function of the extracellular domain of classical cadherins in regard to the control of recognition and adhesive contacts between cadherins on opposing cell surfaces. Early experiments that focused on understanding the homotypic, Ca(++)-dependent characteristics of cadherin adhesion are discussed, and data supporting the widely accepted cis- and trans-dimer models of cadherins are analyzed.

Cadherin-mediated cellular signaling

Recent cadherin studies focusing on cellular signaling have shown that several pathways are activated by cadherin-mediated cell-cell contact. Cadherin-mediated contacts activate Rho family GTPases, regulate the availability of beta-catenin to participate in Wnt signaling, and function in receptor tyrosine kinase signaling. Although different classical cadherins bind to the same cytosolic proteins via their cytoplasmic tails, one message that is clear from the recent literature is that downstream signals emanating from cadherin-mediated contacts are both cadherin-specific and cell-context-specific.