Cadherin Domains Research Articles

New Insight Into Desmosome Structure By Whole Cell Cryo-electron Tomography

Previous electron tomograpic study of conventional plastic sections offered the first 3D insight into desmosome structures and suggested flexibility within the extracellular domains of desmosomal cadherins. And cryo-electron microscopy and tomography of vitreous sections indicated the extracellular inter-desmosmal interface was characterized by highly ordered straight rod-like structures with 5 nm periodicity and a cluster architecture model was generated by sub-volume alignment and average. Meanwhile, some other studies suggest that the desmosome is both a complex and dynamic structure. To better define and understand the precise entire structures of desmosome in both extracellular space and in intracellular spaces, new sample preparation techniques and imaging approaches will be important. Instead of conventional plastic section and cryo-section, we studied the desmosome structures in whole cells which were grown on electron microscopic grids coated with supporting film and which were plunge frozen to liquid nitrogen temperature. In this sample preparation, there was no or minimal manipulation of the structures compared to any other sample preparation techniques. Another major advantage of this study is we were able to image the entire desmosome rather than thin sections. We collected data on a 300 kV accelerating voltage microscope equipped with in-column energy-filter. Three-dimensional reconstructions and post-reconstruction analysis have offered a number of new insights into desmosome structure which may also shed light on the mechanism of desmosome assembling.

Molecular Aspects of Calcium Binding in NCAD12

Cadherins are calcium dependent,transmembrane proteins, which mediate cell-cell adhesion through homophilic interactions. They play a fundamental role in embryogenesis and tissue morphogenesis. The primary structure of cadherins comprises five extracellular domains, a transmembrane segment, and a conserved C-terminal cytoplasmic region, which interacts with the cytoskeleton through catenins. It has been known that cadherins require calcium binding at the interfaces of the extracellular domains for cell adhesion and for protection from proteases. Recent literature has proposed that binding of three calcium ions (Ca1, Ca2 and Ca3) at the domain interfaces causes a conformational change, a “closed” to “open” transition, in the extracellular domain 1, which leads to cell-cell adhesion. However, to date, no solution studies have demonstrated the conformational change upon calcium binding. Despite the important function of calcium binding in cadherin mediated cell adhesion, the characteristics of calcium binding are still unclear .In order to determine the molecular aspects of binding of Ca1, Ca2 and Ca3 in cell adhesion, a comprehensive study of the calcium binding properties is required. Our work focuses on the first two-extracellular domains of neural cadherin (NCAD12). We mutated an essential residue D134 for the binding of Ca3 in NCAD12 wild type. We used Circular dichroism and Fluorescence spectroscopy in order to obtain global and local information of conformational change on calcium binding to NCAD12 wild type and D134A. These studies were repeated with a mutant, D136N, designed to probe the cooperativity between calcium binding sites.Spectroscopic and proteolytic footprinting studies of NCAD12 wild type, D134A and D136N show that these proteins behave differently in presence of calcium. The mutations significantly lowered the stability and increased protease sensitivity in the presence of calcium. These preliminary results imply that binding of Ca3 is a critical step in conformational change.

Characterization of the Kyoto Circling (KCI) Rat Carrying a Spontaneous Nonsense Mutation in the Protocadherin 15 (Pcdh15) Gene

Protocadherin-15 (Pcdh15) plays important roles in the morphogenesis and cohesion of stereocilia bundles and in the maintenance of retinal photoreceptor cells. In humans, mutations in PCDH15 cause Usher syndrome type 1F (USH1F) and non-syndromic deafness DFNB23. In mice, repertories of Pcdh15 mutant alleles have been described as Ames waltzer mutations. For further understanding of Pcdh15 function in vivo and to develop better clinical treatment for the disabling symptoms of USH1F and DFNB23 patients, animal models suitable for clinical as well as pharmacological studies are required. Here we report the characterization of a Pcdh15 mutant allele, Kyoto circling, (Pcdh15(kci)) in the rat. Rats homozygous for Pcdh15(kci) display circling and abnormal swimming behaviors along with the lack of an auditory-evoked brainstem response at the highest intensities of acoustic stimulation. Positional cloning analysis revealed a nonsense mutation (c. 2911C>T, p. Arg971X) in the Pcdh15 gene, which is predicted to result in the truncation of the PCDH15 protein at the 9th domain of cytoplasmic cadherin domains. Histological study revealed severe defects in cochlear hair cell stereocilia, collapse of the organ of Corti, and marked reduction of ganglion cells in adult Pcdh15(kci) mutants. Severe reduction of sensory hair cells was also found in the saccular macula. Since the rat is more advantageous for clinical and pharmacological studies than the mouse, the KCI rat strain may be a better disease model for Pcdh15-deficit USH1F and DFNB23.

Profound, prelingual nonsyndromic deafness maps to chromosome 10q21 and is caused by a novel missense mutation in the Usher syndrome type IF gene PCDH15

We studied a consanguineous family (Family A) from the island of Newfoundland with an autosomal recessive form of prelingual, profound, nonsyndromic sensorineural hearing loss. A genome-wide scan mapped the deafness trait to 10q21-22 (max LOD score of 4.0; D10S196) and fine mapping revealed a 16 Mb ancestral haplotype in deaf relatives. The PCDH15 gene was mapped within the critical region and was an interesting candidate because truncating mutations cause Usher syndrome type IF (USH1F) and two missense mutations have been previously associated with isolated deafness (DFNB23). Sequencing of the PCDH15 gene revealed 33 sequencing variants. Three of these variants were homozygous exclusively in deaf siblings but only one of them was not seen in ethnically matched controls. This novel c.1583 T>A transversion predicts an amino-acid substitution of a valine with an aspartic acid at codon 528 (V528D). Like the two DFNB23 mutations, the V528D mutation in Family A occurs in a highly conserved extracellular cadherin (EC) domain of PCDH15 and is predicted to be more deleterious than the previously identified DFNB23 missense mutations (R134G and G262D). Physical assessment, vestibular and visual function testing in deaf adults ruled out syndromic deafness because of Usher syndrome. This study validates the DFNB23 designation and supports the hypothesis that missense mutations in conserved motifs of PCDH15 cause nonsyndromic hearing loss. This emerging genotype-phenotype correlation in USH1F is similar to that in several other USH1 genes and cautions against a prognosis of a dual sensory loss in deaf children found to be homozygous for hypomorphic mutations at the USH1F locus.

A zinc-dependent adhesion module is responsible for intercellular adhesion in staphylococcal biofilms

Hospital-acquired bacterial infections are an increasingly important cause of morbidity and mortality worldwide. Staphylococcal species are responsible for the majority of hospital-acquired infections, which are often complicated by the ability of staphylococci to grow as biofilms. Biofilm formation by Staphylococcus epidermidis and Staphylococcus aureus requires cell-surface proteins (Aap and SasG) containing sequence repeats known as G5 domains; however, the precise role of these proteins in biofilm formation is unclear. We show here, using analytical ultracentrifugation (AUC) and circular dichroism (CD), that G5 domains from Aap are zinc (Zn(2+))-dependent adhesion modules analogous to mammalian cadherin domains. The G5 domain dimerizes in the presence of Zn(2+), incorporating 2-3 Zn(2+) ions in the dimer interface. Tandem G5 domains associate in a modular fashion, suggesting a "zinc zipper" mechanism for G5 domain-based intercellular adhesion in staphylococcal biofilms. We demonstrate, using a biofilm plate assay, that Zn(2+) chelation specifically prevents biofilm formation by S. epidermidis and methicillin-resistant S. aureus (MRSA). Furthermore, individual soluble G5 domains inhibit biofilm formation in a dose-dependent manner. Thus, the complex three-dimensional architecture of staphylococcal biofilms results from the self-association of a single type of protein domain. Surface proteins with tandem G5 domains are also found in other bacterial species, suggesting that this mechanism for intercellular adhesion in biofilms may be conserved among staphylococci and other Gram-positive bacteria. Zn(2+) chelation represents a potential therapeutic approach for combating biofilm growth in a wide range of bacterial biofilm-related infections.

Insights into the Low Adhesive Capacity of Human T-cadherin from the NMR Structure of Its N-terminal Extracellular Domain

T-cadherin is unique among the family of type I cadherins, because it lacks transmembrane and cytosolic domains, and attaches to the membrane via a glycophosphoinositol anchor. The N-terminal cadherin repeat of T-cadherin (Tcad1) is approximately 30% identical to E-, N-, and other classical cadherins. However, it lacks many amino acids crucial for their adhesive function of classical cadherins. Among others, Trp-2, which is the key residue forming the canonical strand-exchange dimer, is replaced by an isoleucine. Here, we report the NMR structure of the first cadherin repeat of T-cadherin (Tcad1). Tcad1, as other cadherin domains, adopts a beta-barrel structure with a Greek key folding topology. However, Tcad1 is monomeric in the absence and presence of calcium. Accordingly, lle-2 binds into a hydrophobic pocket on the same protomer and participates in an N-terminal beta-sheet. Specific amino acid replacements compared to classical cadherins reduce the size of the binding pocket for residue 2 and alter the backbone conformation and flexibility around residues 5 and 15 as well as many electrostatic interactions. These modifications apparently stabilize the monomeric form and make it less susceptible to a conformational switch upon calcium binding. The absence of a tendency for homoassociation observed by NMR is consistent with electron microscopy and solid-phase binding data of the full T-cadherin ectodomain (Tcad1-5). The apparent low adhesiveness of T-cadherin suggests that it is likely to be involved in reversible and dynamic cellular adhesion-deadhesion processes, which are consistent with its role in cell growth and migration.

Cadherin 23-like polypeptide in hair bundle mechanoreceptors of sea anemones

We investigated hair bundle mechanoreceptors in sea anemones for a homolog of cadherin 23. A candidate sequence was identified from the database for Nematostella vectensis that has a shared lineage with vertebrate cadherin 23s. This cadherin 23-like protein comprises 6,074 residues. It is an integral protein that features three transmembrane alpha-helices and a large extracellular loop with 44 contiguous, cadherin (CAD) domains. In the second half of the polypeptide, the CAD domains occur in a quadruple repeat pattern. Members of the same repeat group (i.e., CAD 18, 22, 26, and so on) share nearly identical amino acid sequences. An affinity-purified antibody was generated to a peptide from the C-terminus of the cadherin 23-like polypeptide. The peptide is expected to lie on the exoplasmic side of the plasma membrane. In LM, the immunolabel produced punctate fluorescence in hair bundles. In TEM, immunogold particles were observed medially and distally on stereocilia of hair bundles. Dilute solutions of the antibody disrupted vibration sensitivity in anemones. We conclude that the cadherin 23-like polypeptide likely contributes to the mechanotransduction apparatus of hair bundle mechanoreceptors of anemones.

Four-jointed is a Golgi kinase that phosphorylates a subset of cadherin domains.

The atypical cadherin Fat acts as a receptor for a signaling pathway that regulates growth, gene expression, and planar cell polarity. Genetic studies in Drosophila identified the four-jointed gene as a regulator of Fat signaling. We show that four-jointed encodes a protein kinase that phosphorylates serine or threonine residues within extracellular cadherin domains of Fat and its transmembrane ligand, Dachsous. Four-jointed functions in the Golgi and is the first molecularly defined kinase that phosphorylates protein domains destined to be extracellular. An acidic sequence motif (Asp-Asn-Glu) within Four-jointed was essential for its kinase activity in vitro and for its biological activity in vivo. Our results indicate that Four-jointed regulates Fat signaling by phosphorylating cadherin domains of Fat and Dachsous as they transit through the Golgi.

Phosphorylation Inside-Out

A signaling pathway called the Hippo pathway has important roles in the control of tissue organization in development and in the regulation of organ size in the fruit fly. Hippo is a protein kinase that appears to pass signals from atypical cadherin molecules Fat and Dachsous at the cell surface to another intracellular kinase, Warts, which then regulates a transcriptional coactivator. Another protein somewhat distantly related to the protein kinases, Four-jointed, has also been implicated genetically in the pathway. Ishikawa et al . provide evidence that Four-jointed, which is localized to the Golgi complex, is indeed a kinase and that it appears to phosphorylate the cadherin domains of Fat and Dachsous, which will become extracellular domains at the cell surface. H. O. Ishikawa, H. Takeuchi, R. S. Haltiwanger, K. D. Irvine, Four-jointed is a Golgi kinase that phosphorylates a subset of cadherin domains. Science 321 , 401-404 (2008). [Abstract] [Full Text]

Identification of a new RTX-like gene cluster inVibrio cholerae

A gene cluster containing two genes in tandem has been identified in Vibrio cholerae ElTor N16961. Each has more than one cadherin domain and is homologous to the RTX toxin family and was common in various V. cholerae strains. Insertional mutagenesis demonstrated that each gene has a role in Hep-2 cell rounding, hemolytic activity towards human and sheep RBCs and biofilm formation. The mutants showed reduced adherence to intestinal epithelial cells as well as reduction of in vivo colonization in suckling mice. These two genes thus code for RTX-like toxins in V. cholerae and are associated with the pathogenecity of this organism.

A Role for the Cleaved Cytoplasmic Domain of E-cadherin in the Nucleus

Cell-cell contacts play a vital role in intracellular signaling, although the molecular mechanisms of these signaling pathways are not fully understood. E-cadherin, an important mediator of cell-cell adhesions, has been shown to be cleaved by γ-secretase. This cleavage releases a fragment of E-cadherin, E-cadherin C-terminal fragment 2 (E-cad/CTF2), into the cytosol. Here, we study the fate and function of this fragment. First, we show that coexpression of the cadherin-binding protein, p120 catenin (p120), enhances the nuclear translocation of E-cad/CTF2. By knocking down p120 with short interfering RNA, we also demonstrate that p120 is necessary for the nuclear localization of E-cad/CTF2. Furthermore, p120 enhances and is required for the specific binding of E-cad/CTF2 to DNA. Finally, we show that E-cad/CTF2 can regulate the p120-Kaiso-mediated signaling pathway in the nucleus. These data indicate a novel role for cleaved E-cadherin in the nucleus.

Clustered protocadherin family

The brain is a complex system composed of enormous numbers of differentiated neurons, and brain structure and function differs among vertebrates. To examine the molecular mechanisms underlying brain structure and function, it is important to identify the molecules involved in generating neural diversity and organization. The clustered protocadherin (Pcdh) family is the largest subgroup of the diverse cadherin superfamily. The clustered Pcdh proteins are predominantly expressed in the brain and their gene structures in vertebrates are diversified. In mammals, the clustered Pcdh family consists of three gene clusters: Pcdh-alpha, Pcdh-beta, and Pcdh-gamma. During brain development, this family is upregulated by neuronal differentiation, and Pcdh-alpha is then dramatically downregulated by myelination. Clustered Pcdh expression continues in the olfactory bulb, hippocampus, and cerebellum until adulthood. Structural analysis of the first cadherin domain of the Pcdh-alpha protein revealed it lacks the features that classical cadherins require for homophilic adhesiveness, but it contains Pcdh-specific loop structures. In Pcdh-alpha, an RGD motif on a specific loop structure binds beta1-integrin. For gene expression, the gene clusters are regulated by multiple promoters and alternative cis splicing. At the single-cell level, several dozen Pcdh-alpha and -gamma mRNA are regulated monoallelically, resulting in the combinatorial expression of distinct variable exons. The Pcdh-alpha and Pcdh-gamma proteins also form oligomers, further increasing the molecular diversity at the cell surface. Thus, the unique features of the clustered Pcdh family may provide the molecular basis for generating individual cellular diversity and the complex neural circuitry of the brain.

CASY-1, an ortholog of calsyntenins/alcadeins, is essential for learning in Caenorhabditis elegans

Calsyntenins/alcadeins are type I transmembrane proteins with two extracellular cadherin domains highly expressed in mammalian brain. They form a tripartite complex with X11/X11L and APP (amyloid precursor protein) and are proteolytically processed in a similar fashion to APP. Although a genetic association of calsyntenin-2 with human memory performance has recently been reported, physiological roles and molecular functions of the protein in the nervous system are poorly understood. Here, we show that CASY-1, the Caenorhabditis elegans ortholog of calsyntenins/alcadeins, is essential for multiple types of learning. Through a genetic screen, we found that casy-1 mutants show defects in salt chemotaxis learning. casy-1 mutants also show defects in temperature learning, olfactory adaptation, and integration of two sensory signals. casy-1 is widely expressed in the nervous system. Expression of casy-1 in a single sensory neuron and at the postdevelopmental stage is sufficient for its function in salt chemotaxis learning. The fluorescent protein-tagged ectodomain of CASY-1 is released from neurons. Moreover, functional domain analyses revealed that both cytoplasmic and transmembrane domains of this protein are dispensable, whereas the ectodomain, which contains the LG/LNS-like domain, is critically required for learning. These results suggest that learning is modulated by the released ectodomain of CASY-1.

Hyper-adhesion: a new concept in cell–cell adhesion

We have developed a new concept of cell-cell adhesion termed 'hyper-adhesion', the very strong adhesion adopted by desmosomes. This uniquely desmosomal property accounts for their ability to provide the intercellular links in the desmosome-intermediate filament complex. These links are targeted by diseases, resulting in disruption of the complex with severe consequences. Hyper-adhesion is characteristic of desmosomes in tissues and is believed to result from a highly ordered arrangement of the extracellular domains of the desmosomal cadherins that locks their binding interaction so that it is highly resistant to disruption. This ordered arrangement may be reflected by and dependent upon a similarly ordered molecular structure of the desmosomal plaque. Hyper-adhesion can be down-regulated to a more weakly adhesive state by cell signalling involving protein kinase C, which translocates to the desmosomal plaque. Down-regulation takes place in wound edge epithelium and appears to be accompanied by loss of the ordered arrangement causing desmosomes to adopt the type of weaker adhesion characteristic of adherens junctions. We review the evidence for hyper-adhesion and speculate on the molecular basis of its mechanism.

Structural studies on desmosomes

Desmosomes are cadherin-based intercellular junctions that primarily provide mechanical stability to tissues such as epithelia and cardiac muscle. Desmosomal cadherins, which are Ca(2+)-dependent adhesion molecules, are of central importance in mediating direct intercellular interaction. The close association of these proteins, with intracellular components of desmosomes ultimately linked to the cytoskeleton, is believed to play an important role in tissue morphogenesis during development and wound healing. Elucidation of the binding mechanism of adhesive interfaces between the extracellular domains of cadherins has been approached by structural, biophysical and biochemical methods. X-ray crystal structures of isolated extracellular domains of cadherins have provided compelling evidence of the mutual binding of the highly conserved N-terminal residue, Trp(2), from opposing proteins. This binding interface was also implicated by biochemical and cell-adhesion assays and mutagenesis data to be the primary adhesive interface between cells. Recent results based on electron tomography of epidermal desmosomes were consistent with this view, showing cadherin molecules interacting at their N-terminal tips. An integrative structural approach involving X-ray crystallography, cryo-electron tomography and immuno-electron microscopy should give the complete picture of the architecture of this important junction; identifying its various proteins and showing their arrangements and binding interfaces under native conditions. Together with these 'static' approaches, live-cell imaging of cultured keratinocytes should provide important insights into the dynamic property of the assembly and disassembly of desmosomes.

Biochemical and structural analysis of α-catenin in cell–cell contacts

Cadherins are transmembrane adhesion molecules that mediate homotypic cell-cell contact. In adherens junctions, the cytoplasmic domain of cadherins is functionally linked to the actin cytoskeleton through a series of proteins known as catenins. E-cadherin binds to beta-catenin, which in turn binds to alpha-catenin to form a ternary complex. alpha-Catenin also binds to actin, and it was assumed previously that alpha-catenin links the cadherin-catenin complex to actin. However, biochemical, structural and live-cell imaging studies of the cadherin-catenin complex and its interaction with actin show that binding of beta-catenin to alpha-catenin prevents the latter from binding to actin. Biochemical and structural data indicate that alpha-catenin acts as an allosteric protein whose conformation and activity changes depending on whether or not it is bound to beta-catenin. Initial contacts between cells occur on dynamic lamellipodia formed by polymerization of branched actin networks, a process controlled by the Arp2/3 (actin-related protein 2/3) complex. alpha-Catenin can suppress the activity of Arp2/3 by competing for actin filaments. These findings lead to a model for adherens junction formation in which clustering of the cadherin-beta-catenin complex recruits high levels of alpha-catenin that can suppress the Arp2/3 complex, leading to cessation of lamellipodial movement and formation of a stable contact. Thus alpha-catenin appears to play a central role in cell-cell contact formation.

Single nucleotide polymorphisms in the cadherin 23 (CDH23) gene in Polish workers exposed to industrial noise

Single nucleotide polymorphisms (SNPs) are the most frequent type of variation in the human genome and may underlie differential susceptibility to common genetic diseases. A candidate gene for susceptibility to noise-induced hearing loss (NIHL) is Cadherin 23 (CDH23). This study aimed to analyze genetic variation in the CDH23 gene in a group of 10 individuals derived from a cohort of 949 workers exposed to noise, and consisted of five persons from each of the resistant and susceptible extremes. DNA samples were collected and the coding exons of CDH23 were sequenced. We identified a total of 35 SNPs: 11 amino acid substitutions, 8 silent nucleotide changes, and 16 substitutions in intervening sequences. Ten of the 11 amino acid substitutions were previously shown also to segregate in a Cuban population. The nonsynonymous SNPs localized to the part of the gene encoding the extracellular domain of Cadherin 23, in particular ectodomains 5, 13, 14, 15, 16, 17, 19, and 22. One amino acid change occurred at a conserved position in ectodomain 5. Our results provide a framework for future study of polymorphisms in CDH23 as risk factor for NIHL.

β-Catenin is required for the establishment of vegetal embryonic fates in the nemertean, Cerebratulus lacteus

Downstream components of the canonical Wnt signaling pathway that result in the nuclear localization of β-catenin are involved in diverse developmental processes including the formation of the mesendoderm, the regulation of axial properties and asymmetric cell divisions in a wide array of metazoans. The nemertean worm, Cerebratulus lacteus, represents a member of the understudied lophotrochozoan clade that exhibits a highly stereotyped spiral cleavage program in which ectodermal, endodermal, and mesodermal origins are known from intracellular fate mapping studies. Here, the embryonic distribution of β-catenin protein was studied using injection of synthetic mRNA, encoding GFP-tagged β-catenin, into fertilized eggs. During the early cleavage stages β-catenin was destabilized/degraded in animal hemisphere blastomeres and became localized to the nuclei of the four vegetal-most cells at the 64-cell stage, which give rise to definitive larval and adult endoderm. Functional assays indicate that β-catenin plays a key role in the development of the endoderm. Morpholino knockdown of endogenous β-catenin, as confirmed by Western analysis, resulted in the failure to gastrulate, absence of the gut and an animalized phenotype in the resulting larvae, including the formation of ectopic (anterior) apical organ tissue with elongated apical tuft cilia and no indications of dorsoventral polarity. Similarly, over-expression of the cytoplasmic domain of cadherin or a β-catenin-engrailed repressor fusion construct prevented endoderm formation and generated the same animalized phenotype. Injections of mRNA encoding either a stabilized, constitutively activated form of β-catenin or a dominant negative form of GSK3-β converted all or nearly all cells into endodermal fates expressing gut-specific esterase. Thus, β-catenin appears to be both necessary and sufficient to promote endoderm formation in C. lacteus, consistent with its role in endoderm and endomesoderm formation in anthozoan cnidarians, ascidians, and echinoderms. Consistent with the results of other studies, β-catenin may be viewed as playing a role in the development of posterior/vegetal larval fates (i.e., endoderm) in C. lacteus. However, unlike the case found in polychaete annelid and soil nematode embryos, there is no evidence for a role of β-catenin in regulating cell fates and asymmetric cell divisions along the entire anterior–posterior axis.

Sequence and Structural Determinants of Strand Swapping in Cadherin Domains: Do All Cadherins Bind Through the Same Adhesive Interface?

Cadherins are cell surface adhesion proteins important for tissue development and integrity. Type I and type II, or classical, cadherins form adhesive dimers via an interface formed through the exchange, or “swapping”, of the N-terminal β-strands from their membrane-distal EC1 domains. Here, we ask which sequence and structural features in EC1 domains are responsible for β-strand swapping and whether members of other cadherin families form similar strand-swapped binding interfaces. We created a comprehensive database of multiple alignments of each type of cadherin domain. We used the known three-dimensional structures of classical cadherins to identify conserved positions in multiple sequence alignments that appear to be crucial determinants of the cadherin domain structure. We identified features that are unique to EC1 domains. On the basis of our analysis, we conclude that all cadherin domains have very similar overall folds but, with the exception of classical and desmosomal cadherin EC1 domains, most of them do not appear to bind through a strand-swapping mechanism. Thus, non-classical cadherins that function in adhesion are likely to use different protein–protein interaction interfaces. Our results have implications for the evolution of molecular mechanisms of cadherin-mediated adhesion in vertebrates.

P120-catenin is a novel desmoglein 3 interacting partner: Identification of the p120-catenin association site of desmoglein 3

p120-catenin (p120ctn) is an armadillo-repeat protein that directly binds to the intracytoplasmic domains of classical cadherins. p120ctn binding promotes the stabilization of cadherin complexes on the plasma membrane and thus positively regulates the adhesive activity of cadherins. Using co-immunoprecipitation, we show here that p120ctn associates to desmogleins (Dsg) 1 and 3. To determine which region is involved in the association between Dsg3 and p120ctn, we constructed mutant Dsg3 proteins, in which various cytoplasmic subdomains were removed. The tailless Dsg3 constructs ΔIA:AA1-641Dsg3 and Δ641–714Dsg3, which do not contain the intracellular anchor (IA) region, did not coprecipitate with p120cn, nor did they colocalize at the plasma membrane. Immunocytochemical analysis revealed that p120ctn does not localize to desmosomes, but colocalizes with Dsg3 at the cell surface. A biotinylation assay for Dsg3 showed that biotinylated Δ641–714Dsg3 was turned over more rapidly than wild-type Dsg3. These results indicate that the membrane proximal region (corresponding to residues 641–714) in the IA region of Dsg3 is necessary for complex formation with p120ctn, and to maintain free Dsg3 at the cell surface before it is integrated into desmosomes. In summary, we show that p120ctn is a novel interactor of the Dsg proteins, and may play a role in desmosome remodeling.