Extracellular Domain Of E-cadherin Research Articles

Decreased distribution of lung epithelial junction proteins after intratracheal antigen or lipopolysaccharide challenge: correlation with neutrophil influx and levels of BALF sE-cadherin.

Distribution of airway junctional complex proteins after antigen or lipopolysaccharide challenge in sensitized or naive mice, respectively, was investigated. E-cadherin immunoreactivity was detected continuously along neighboring epithelial cell borders and between adjacent alveolar epithelial cells in naive and saline-challenged mice. Occludin and ZO-1 immunoreactivity were observed in the tight junction areas. Both challenges induced changes in epithelial morphology and phenotype, accompanied initially by focal loss of epithelial E-cadherin that increased in size with time and number of allergen challenges. Allergen challenge also led to focal loss of occludin and ZO-1. Western blot analysis revealed increased levels of sE-cadherin in lavage fluid after either challenge, and this increase correlated with lavage neutrophil numbers (P = 0.002). Immunocytochemistry of lavage cells 6 h after either challenge revealed E-cadherin epitopes within cytoplasmic vacuoles of neutrophils, the major cell type. In contrast, peripheral blood neutrophils or tissue neutrophils before epithelial transmigration were negative, suggesting that in airway inflammation, E-cadherin extracellular domain is cleaved by neutrophils during epithelial penetration, instigating the destabilization of adherens and tight junctions. This junctional deterioration could lead to a progressive decrease in epithelial integrity and induce alterations in epithelial morphology, with consequent enhanced paracellular transit of antigens and pathogens.

Lateral Dimerization of the E-cadherin Extracellular Domain Is Necessary but Not Sufficient for Adhesive Activity

Cadherins are transmembrane glycoproteins involved in Ca(2+)-dependent cell-cell adhesion. Using L cells coexpressing E-cadherin constructs with different epitope tags, we examined the lateral dimerization of E-cadherin and its adhesive activity by co-immunoprecipitation and aggregation assays, respectively. Although the transmembrane domain is required for dimerization, tail-less constructs possessing the transmembrane domain of either N-cadherin or CD45 show dimerization and are active in aggregation assays. Two mutant constructs having either of two amino acid substitutions, W2A or substitutions that disrupt the recognition sequence for endoproteolytic enzymes involved in removal of the precursor segment, cannot form dimers and are inactive in aggregation. These monomeric proteins, like their wild-type dimerizing counterparts, retain their Ca(2+)-dependent resistance to trypsin digestion, suggesting that dimerization per se does not induce a large conformational change. Two other constructs, having either an amino acid substitution, D134A, or a C-terminal deletion of 70 amino acid residues, retain the ability to associate laterally but are inactive in aggregation assays. Staurosporine treatment of cells expressing the latter construct increases aggregation but does not increase the extent of lateral dimerization. Thus, lateral dimerization is necessary, but not sufficient for adhesive activity.

Isoform-Specific Differences in the Size of Desmosomal Cadherin/Catenin Complexes

Isoform-Specific Differences in the Size of Desmosomal Cadherin/Catenin Complexes

Pools of β-Catenin

The tumor suppressive activity of the cell-cell adhesion protein E-cadherin is thought to occur either by increasing cell adhesion and limiting cell migration or by inhibiting β-catenin-mediated signaling to the nucleus to suppress proliferation. Gottardi et al. report that when overexpressed in a colon carcinoma cell line, E-cadherin inhibited anchorage-independent growth by altering β-catenin signaling. By expressing a variety of mutant proteins, the authors determined that the extracellular domain of E-cadherin had no growth inhibitory properties. Thus, the adhesive properties of E-cadherin do not influence growth inhibition. Rather, E-cadherin interacted with a specific subset of cytosolic β-catenin to alter the expression of target genes that regulate tumorigenesis. This small pool of β-catenin is also the same fraction that associated with the target transcription factor LEF/TCF. It remains to be seen if cadherins in general suppress tumor progression in other tumor-derived cells by antagonizing β-catenin signaling activity and what the biochemical nature is of the β-catenin pool that binds to cadherins. C. J. Gottardi, E. Wong, B. M. Gumbiner, E-cadherin suppresses cellular transformation by inhibiting β-catenin signaling in an adhesion-independent manner. J. Cell Biol. 153 , 1049-1059 (2001). [Abstract] [Full Text]

Mutant cadherin affects epithelial morphogenesis and invasion, but not transformation.

MDCK cells were engineered to reversibly express mutant E-cadherin protein with a large extracellular deletion. Mutant cadherin overexpression reduced the expression of endogenous E- and K-cadherins in MDCK cells to negligible levels, resulting in decreased cell adhesion. Despite severe impairment of the cadherin adhesion system, cells overexpressing mutant E-cadherin formed fluid-filled cysts in collagen gel cultures and responded to hepatocyte growth factor/scatter factor (HGF/SF) that induced cellular extension formation with a frequency similar to that of control cysts. However, cells were shed from cyst walls into the lumen and into the collagen matrix prior to and during HGF/SF induced tubule extension. Despite the propensity for cell dissociation, MDCK cells lacking cadherin adhesion molecules were not capable of anchorage-independent growth in soft agar and cell proliferation rate was not affected. Thus, cadherin loss does not induce transformation, despite inducing an invasive phenotype, a later stage of tumor progression. These experiments are especially relevant to tumor progression in cells with altered E-cadherin expression, particularly tumor samples with identified E-cadherin extracellular domain genomic mutations.

Cleavage and Shedding of E-cadherin after Induction of Apoptosis

Apoptotic cell death induces dramatic molecular changes in cells, becoming apparent on the structural level as membrane blebbing, condensation of the cytoplasm and nucleus, and loss of cell-cell contacts. The activation of caspases is one of the fundamental steps during programmed cell death. Here we report a detailed analysis of the fate of the Ca(2+)-dependent cell adhesion molecule E-cadherin in apoptotic epithelial cells and show that during apoptosis fragments of E-cadherin with apparent molecular masses of 24, 29, and 84 kDa are generated by two distinct proteolytic activities. In addition to a caspase-3-mediated cleavage releasing the cytoplasmic domain of E-cadherin, a metalloproteinase sheds the extracellular domain from the cell surface during apoptosis. Immunofluorescence analysis confirmed that concomitant with the disappearance of E-cadherin staining at the cell surface, the E-cadherin cytoplasmic domain accumulates in the cytosol. In the presence of inhibitors of caspase-3 and/or metalloproteinases, cleavage of E-cadherin was almost completely blocked. The simultaneous cleavage of the intracellular and extracellular domains of E-cadherin may provide a highly efficient mechanism to disrupt cadherin-mediated cell-cell contacts in apoptotic cells, a prerequisite for cell rounding and exit from the epithelium.

Expression of E-cadherin in bone and soft tissue sarcomas: A possible role in epithelial differentiation

The cadherin-mediated cell-cell adhesion system is now known to play a critical role in both the morphogenesis of cancer cells and suppression of their invasion. However, the pattern of expression of E-cadherin, the major cadherin of epithelial cells in bone and soft tissue sarcomas, remains unclear. This prompted us to study E-cadherin expression in a variety of bone and soft tissue sarcomas. Using the monoclonal antibody HECD-1, raised against the extracellular domain of E-cadherin, we observed immunoreactivity in 1 pleomorphic rhabdomyosarcoma, 2 of 5 diffuse mesotheliomas, 4 of 5 clear cell sarcomas, 1 of 5 epithelioid sarcomas, and 10 synovial sarcomas. Other types of bone and soft tissue sarcoma (4 osteosarcomas, 4 chondrosarcomas, 3 primitive neuroectodermal tumors, 1 fibrosarcoma, 4 malignant fibrous histiocytomas, 5 liposarcomas, 4 leiomyosarcomas, 6 alveolar and 5 embryonal rhabdomyosarcomas, 4 angiosarcomas, 4 malignant peripheral nerve sheath tumors, 2 extraskeletal myxoid chondrosarcomas, 2 extraskeletal osteosarcomas, and 3 alveolar soft part sarcomas) were completely negative for E-cadherin. Our findings indicate that E-cadherin is expressed in certain kinds of soft tissue sarcomas, especially those with epithelioid features, suggesting that E-cadherin plays a role in the constitution of their architecture.

Inhibition of adhesion and induction of epithelial cell invasion by HAV-containing E-cadherin-specific peptides.

The E-cadherin/catenin complex, an organizer of epithelial structure and function, is disturbed in invasive cancer. The HAV (histidine alanine valine) sequence in the first extracellular domain of E-cadherin is crucial for homophilic interactions between cadherins. We report that specific peptides containing an HAV sequence interfere with the functions of the E-cadherin/catenin complex. Cells either expressing specific cadherins or not were challenged with both cadherin and noncadherin peptides comprising a central HAV sequence. Specific E-cadherin peptides inhibited cell aggregation, disturbed the epithelial morphotype and were able to stimulate invasion of cells expressing E-cadherins. Conditioned medium, containing E-cadherin fragments, also stimulated invasion in contrast to conditioned medium from which the E-cadherin fragments were removed. Our studies show that E-cadherin functions are inhibited by homologous proteolytic HAV-containing fragments that are released in an autocrine manner and subsequently inhibit the E-cadherin/catenin complex. In this way such cadherin fragments may induce and support cancer invasion.

Simultaneous loss of E-cadherin and catenins in invasive lobular breast cancer and lobular carcinoma in situ.

Loss of expression of the intercellular adhesion molecule E-cadherin frequently occurs in invasive lobular breast carcinomas as a result of mutational inactivation. Expression patterns of E-cadherin and the molecules comprising the cytoplasmic complex of adherens junctions, alpha-, beta- and gamma-catenin, were studied in a series of 38 lobular breast carcinomas with known E-cadherin mutation status. The effect of loss of E-cadherin by mutational inactivation (or other mechanisms) on the expression of catenins was investigated. Complete loss of plasma membrane-associated E-cadherin expression was observed in 32 out of 38 invasive lobular carcinomas, for which in 21 cases a mutation was found in the extracellular domain of E-cadherin. In total, 15 frameshift mutations of small deletions or insertions, ranging from 1 to 41 bp, three non-sense mutations, and three splice mutations were identified. Mutations were scattered over the whole coding region and no hot spots could be detected. In all cases, simultaneous loss of E-cadherin and alpha- and beta-catenin expression was found; in 50 per cent of these cases, additional loss of gamma-catenin was observed. In six invasive lobular carcinomas, expression of both E-cadherin and catenins was retained. In none of these carcinomas was an E-cadherin mutation detected. Lobular carcinoma in situ adjacent to invasive lobular carcinoma showed simultaneous loss of E-cadherin and catenins in all the cases studied--remarkably, also, in four cases positive for E-cadherin and catenin expression in the invasive component. These results indicate that simultaneous loss of E-cadherin and alpha-, beta- and gamma-catenin may be an important step in the formation of lobular carcinoma in situ, as a precursor of invasive lobular breast cancer. Events additional to E-cadherin inactivation must be involved in the transition of lobular carcinoma in situ to invasive lobular carcinoma.

The amino-terminal domain of desmoplakin binds to plakoglobin and clusters desmosomal cadherin-plakoglobin complexes.

The desmosome is a highly organized plasma membrane domain that couples intermediate filaments to the plasma membrane at regions of cell-cell adhesion. Desmosomes contain two classes of cadherins, desmogleins, and desmocollins, that bind to the cytoplasmic protein plakoglobin. Desmoplakin is a desmosomal component that plays a critical role in linking intermediate filament networks to the desmosomal plaque, and the amino-terminal domain of desmoplakin targets desmoplakin to the desmosome. However, the desmosomal protein(s) that bind the amino-terminal domain of desmoplakin have not been identified. To determine if the desmosomal cadherins and plakoglobin interact with the amino-terminal domain of desmoplakin, these proteins were co-expressed in L-cell fibroblasts, cells that do not normally express desmosomal components. When expressed in L-cells, the desmosomal cadherins and plakoglobin exhibited a diffuse distribution. However, in the presence of an amino-terminal desmoplakin polypeptide (DP-NTP), the desmosomal cadherins and plakoglobin were observed in punctate clusters that also contained DP-NTP. In addition, plakoglobin and DP-NTP were recruited to cell-cell interfaces in L-cells co-expressing a chimeric cadherin with the E-cadherin extracellular domain and the desmoglein-1 cytoplasmic domain, and these cells formed structures that were ultrastructurally similar to the outer plaque of the desmosome. In transient expression experiments in COS cells, the recruitment of DP-NTP to cell borders by the chimera required co-expression of plakoglobin. Plakoglobin and DP-NTP co-immunoprecipitated when extracted from L-cells, and yeast two hybrid analysis indicated that DP-NTP binds directly to plakoglobin but not Dsg1. These results identify a role for desmoplakin in organizing the desmosomal cadherin-plakoglobin complex and provide new insights into the hierarchy of protein interactions that occur in the desmosomal plaque.

Homophilic adhesion of E-cadherin occurs by a co-operative two-step interaction of N-terminal domains.

Cluster formation of E-cadherin on the cell surface is believed to be of major importance for cell-cell adhesion. To mimic this process the extracellular part of mouse E-cadherin (ECAD) was recombinantly fused to the assembly domain of rat cartilage oligomeric matrix protein (COMP), resulting in the chimeric protein ECAD-COMP. The COMP domain formed a five-stranded alpha-helical coiled-coil. This enabled the formation of a pentameric ECAD with bundled C-termini and free N-termini. The pentameric protein construct ECAD-COMP and the monomeric ECAD were expressed in human embryonal kidney 293 cells. Electron microscopy, analytical ultracentrifugation, solid phase binding and cell attachment assays revealed that pentamers showed strong self-association and cell attachment, whereas monomers exhibited no activity. At the high internal concentration in the pentamer the N-terminal EC1 domains of two E-cadherin arms interact to form a ring-like structure. Then the paired domains interact with a corresponding pair from another pentamer. None of the four other extracellular domains of E-cadherin is involved in this interaction. Based on these results, an in vivo mechanism is proposed whereby two N-terminal domains of neighbouring E-cadherins at the cell surface first form a pair, which binds with high affinity to a similar complex on another cell. The strong dependence of homophilic interactions on C-terminal clustering points towards a regulation of E-cadherin mediated cell-cell adhesion via lateral association.

Novel E-cadherin-mediated adhesion in peripheral nerve: Schwann cell architecture is stabilized by autotypic adherens junctions.

Previous studies (Blank, W. F., M. B. Bunge, and R. P. Bunge. 1974. Brain Res. 67:503-518) showed that Schwann cell paranodal membranes were disrupted in calcium free medium suggesting that cadherin mediated mechanisms may operate to maintain the integrity of the paranodal membrane complex. Using antibodies against the fifth extracellular domain of E-cadherin, we now show by confocal laser and electron immunomicroscopy that E-cadherin is a major adhesive glycoprotein in peripheral nervous system Schwann cells. E-Cadherin is not found, however, in compact myelin bilayers. Rather, it is concentrated at the paranodes, in Schmidt-Lanterman incisures, and at the inner and outer loops. At these loci, E-cadherin is associated with subplasmalemmal electron densities that coordinate in register across several cytoplasmic turns of a single Schwann cell. F-Actin and beta-catenin, two proteins implicated in cellular signaling, also co-localize to E-cadherin positive sites. These complexes are autotypic adherens-type junctions that are confined to the plasma membrane synthesized by a single Schwann cell; E-cadherin was never observed between two Schwann cells, nor between Schwann cells and the axon. Our findings demonstrate that E-cadherin and its associated proteins are essential components in the architecture of the Schwann cell cytoplasmic channel network, and suggest that this network has specialized functions in addition to those required for myelinogenesis.

Intracellular domain of desmoglein 3 (pemphigus vulgaris antigen) confers adhesive function on the extracellular domain of E-cadherin without binding catenins.

For the extracellular (EC) domain of E-cadherin to function in homophilic adhesion it is thought that its intracytoplasmic (IC) domain must bind alpha- and beta-catenins, which link it to the actin cytoskeleton. However, the IC domain of pemphigus vulgaris antigen (PVA or Dsg3), which is in the desmoglein subfamily of the cadherin gene superfamily, does not bind alpha- or beta-catenins. Because desmogleins have also been predicted to function in the cell adhesion of desmosomes, we speculated that the PVA IC domain might be able to act in a novel way in conferring adhesive function on the EC domain of cadherins. To test this hypothesis we studied aggregation of mouse fibroblast L cell clones that expressed chimeric cDNAs encoding the EC domain of E-cadherin with various IC domains. We show here that the full IC domain of PVA as well as an IC subdomain containing only 40 amino acids of the PVA intracellular anchor (IA) region confer adhesive function on the E-cadherin EC domain without catenin-like associations with cytoplasmic molecules or fractionation with the cell cytoskeleton. This IA region subdomain is evolutionarily conserved in desmogleins, but not classical cadherins. These findings suggest an important cell biologic function for the IA region of desmogleins and demonstrate that strong cytoplasmic interactions are not absolutely necessary for E-cadherin-mediated adhesion.

Extracellular Domain of Pemphigus Vulgaris Antigen (Desmoglein 3) Mediates Weak Homophilic Adhesion

Pemphigus vulgaris antigen is in the cadherin supergene family. We hypothesized that the extracellular domain of pemphigus vulgaris antigen might mediate homophilic cell adhesion because 1) the originally described cadherins (e.g., E-cadherin) mediate this type of adhesion, 2) pemphigus vulgaris antigen is localized in desmosomes that are cell adhesion junctions, and 3) autoantibodies in pemphigus vulgaris patients cause loss of cell adhesion. To test this hypothesis we used a system developed for E-cadherin that, when transfected into L cells (mouse fibroblasts), has been shown to cause aggregation. Because this aggregation requires the cytoplasmic domain of E-cadherin to bind to catenins, we made a chimeric cDNA construct that encodes the extracellular domain of pemphigus vulgaris antigen and the cytoplasmic domain of E-cadherin. Analysis by immunofluorescence and flow cytometry with pemphigus vulgaris sera indicated that the pemphigus vulgaris antigen extracellular domain of this chimeric molecule (PVEC) was expressed on the cell surface of transiently transfected cells and permanently transfected L-cell clones. Immunoprecipitation of the chimeric molecule from extracts of these clones showed that the E-cadherin cytoplasmic domain bound catenins. Surprisingly, these L-cell clones displayed only slight aggregation compared to an L-cell clone transfected with E-cadherin. This weak aggregation was, however, specific and homophilic, as determined by cell sorting of only PVEC transfectants into aggregates from mixtures of PVEC and neomycin resistance gene transfectants, one of which was labeled with a fluorescent dye. We conclude that the extracellular domain of pemphigus vulgaris antigen mediates weak homophilic adhesion and is not interchangeable in function with the extracellular domain of E-cadherin.

Extracellular Domain of Pemphigus Vulgaris Antigen (Desmoglein 3) Mediates Weak Homophilic Adhesion

Pemphigus vulgaris antigen is in the cadherin supergene family. We hypothesized that the extracellular domain of pemphigus vulgaris antigen might mediate homophilic cell adhesion because 1) the originally described cadherins (e.g., E-cadherin) mediate this type of adhesion, 2) pemphigus vulgaris antigen is localized in desmosomes that are cell adhesion junctions, and 3) autoantibodies in pemphigus vulgaris patients cause loss of cell adhesion. To test this hypothesis we used a system developed for E-cadherin that, when transfected into L cells (mouse fibroblasts), has been shown to cause aggregation. Because this aggregation requires the cytoplasmic domain of E-cadherin to bind to catenins, we made a chimeric cDNA construct that encodes the extracellular domain of pemphigus vulgaris antigen and the cytoplasmic domain of E-cadherin. Analysis by immunofluorescence and flow cytometry with pemphigus vulgaris sera indicated that the pemphigus vulgaris antigen extracellular domain of this chimeric molecule (PVEC) was expressed on the cell surface of transiently transfected cells and permanently transfected L-cell clones. Immunoprecipitation of the chimeric molecule from extracts of these clones showed that the E-cadherin cytoplasmic domain bound catenins. Surprisingly, these L-cell clones displayed only slight aggregation compared to an L-cell clone transfected with E-cadherin. This weak aggregation was, however, specific and homophilic, as determined by cell sorting of only PVEC transfectants into aggregates from mixtures of PVEC and neomycin resistance gene transfectants, one of which was labeled with a fluorescent dye. We conclude that the extracellular domain of pemphigus vulgaris antigen mediates weak homophilic adhesion and is not interchangeable in function with the extracellular domain of E-cadherin.