Differential targeting of T- and N-cadherin in polarized epithelial cells

Chip-Based Sensing of the Intercellular Transfer of Cell Surface Proteins: Regulation by the Metabolic State

Glycosylphosphatidylinositol (GPI)-anchored proteins (GPI-APs) are anchored at the surface of mammalian blood and tissue cells through a carboxy-terminal GPI glycolipid. Eventually, they are released into incubation medium in vitro and blood in vivo and subsequently inserted into neighboring cells, potentially leading to inappropriate surface expression or lysis. To obtain first insight into the potential (patho)physiological relevance of intercellular GPI-AP transfer and its biochemical characterization, a cell-free chip- and microfluidic channel-based sensing system was introduced. For this, rat or human adipocyte or erythrocyte plasma membranes (PM) were covalently captured by the TiO₂ chip surface operating as the acceptor PM. To measure transfer between PM, donor erythrocyte or adipocyte PM were injected into the channels of a flow chamber, incubated, and washed out, and the type and amount of proteins which had been transferred to acceptor PM evaluated with specific antibodies. Antibody binding was detected as phase shift of horizontal surface acoustic waves propagating over the chip surface. Time- and temperature-dependent transfer, which did not rely on fusion of donor and acceptor PM, was detected for GPI-APs, but not typical transmembrane proteins. Transfer of GPI-APs was found to be prevented by α-toxin, which binds to the glycan core of GPI anchors, and serum proteins in concentration-dependent fashion. Blockade of transfer, which was restored by synthetic phosphoinositolglycans mimicking the glycan core of GPI anchors, led to accumulation in the chip channels of full-length GPI-APs in association with phospholipids and cholesterol in non-membrane structures. Strikingly, efficacy of transfer between adipocytes and erythrocytes was determined by the metabolic state (genotype and feeding state) of the rats, which were used as source for the PM and sera, with upregulation in obese and diabetic rats and counterbalance by serum proteins. The novel chip-based sensing system for GPI-AP transfer may be useful for the prediction and stratification of metabolic diseases as well as elucidation of the putative role of intercellular transfer of cell surface proteins, such as GPI-APs, in (patho)physiological mechanisms.

The burden of obesity in asthma and COPD: Role of adiponectin

The influence of obesity on development, severity and prognosis of both asthma and COPD is attracting growing interest. The impact of obesity on the respiratory system ranges from structural modifications (decline of total lung capacity) to humoral alterations. Adipose tissue strongly contributes to the establishment of an inflammatory state being an important source of adipokines. Amongst adipokines, adiponectin is an important component of organ cross talk with adipose tissue exerting protective effects on a variety of pathophysiological processes. Adiponectin is secreted in serum where it abundantly circulates as complexes of different molecular weight. Adiponectin properties are mediated by specific receptors that are widely expressed with AdipoR1, AdipoR2, and T-cadherin being present on epithelial and endothelial pulmonary cells indicating a functional role on lung physiology. In COPD, mild to moderate obesity has been shown to have protective effects on patient's survival, while a higher mortality rate has been observed in patients with low BMI. A specific cluster of obese patients has been identified; in this group, asthma features are particularly severe and difficult to treat. Better understanding of the molecular mechanisms at the base of cross talk among different tissues and organs will lead to identification of new targets for both diagnosis and treatment of asthma and COPD.

Effects of the oestrogen receptor antagonist Fulvestrant on expression of genes that affect organization of the epididymal epithelium

The role of oestrogens in epididymal function is still unclear. Knockout of the oestrogen receptor ESR1 (Esr1(-/-) ) or treatment with the anti-oestrogen Fulvestrant affect epididymal milieu and sperm motility. We investigated the effect of in vivo treatment of rats with Fulvestrant on: (i) expression of genes that may be important for the architecture and function of the epididymal epithelium: prominins 1 and 2, metalloproteinase 7, claudin 7, beta-catenin and cadherin 13, and (ii) levels of oestradiol and testosterone, and expression of oestrogen and androgen receptors, in the initial segment (IS), caput, corpus and cauda epididymis. Fulvestrant (i) reduced gene expression of prominin 1 (variant 1) in the caput, reduced prominin 1 protein content in the caput epididymis and in the efferent ductules, and increased the localization of prominin 1 in microvilli of the caput and corpus; (ii) reduced gene expression of prominin 2 in the corpus and cauda epididymis; (iii) increased the metalloproteinase 7 content in the apical region of principal cells from IS/caput; (iv) reduced in the corpus epididymis, but increased in the efferent ductules, the cadherin 13 mRNA level; (v) reduced testosterone but increased oestradiol levels in the corpus and cauda; (vi) increased the androgen receptor protein content in all regions of the epididymis, and the oestrogen receptor GPER in the corpus and cauda epididymis. In conclusion, treatment with Fulvestrant induced regional-specific changes in hormonal and steroid receptor content, and affected expression of proteins important for epithelial organization and absorption/secretion. The mechanisms of oestrogen action may differ among epididymal regions, which may contribute to determine region-specific sperm functions.

Myosin-1c regulates the dynamic stability of E-cadherin-based cell-cell contacts in polarized Madin-Darby canine kidney cells

Myo1c knockdown causes defects in E-cadherin localization, E-cadherin binding, and cell–cell contact of Madin–Darby canine kidney cells. Expression of wild-type Myo1c, but not motor-dead mutants or those unable to bind membrane, reverses the phenotype, evidence that Myo1c modulates the assembly/maintenance of adherens junctions.

Cooperation between cadherins and the actin cytoskeleton controls the formation and maintenance of cell–cell adhesions in epithelia. We find that the molecular motor protein myosin-1c (Myo1c) regulates the dynamic stability of E-cadherin–based cell–cell contacts. In Myo1c-depleted Madin–Darby canine kidney cells, E-cadherin localization was dis­organized and lateral membranes appeared less vertical with convoluted edges versus control cells. In polarized monolayers, Myo1c-knockdown (KD) cells were more sensitive to reduced calcium concentration. Myo1c separated in the same plasma membrane fractions as E-cadherin, and Myo1c KD caused a significant reduction in the amount of E-cadherin recovered in one peak fraction. Expression of green fluorescent protein (GFP)–Myo1c mutants revealed that the phosphatidylinositol-4,5-bisphosphate–binding site is necessary for its localization to cell–cell adhesions, and fluorescence recovery after photobleaching assays with GFP-Myo1c mutants revealed that motor function was important for Myo1c dynamics at these sites. At 18°C, which inhibits vesicle recycling, Myo1c-KD cells accumulated more E-cadherin–positive vesicles in their cytoplasm, suggesting that Myo1c affects E-cadherin endocytosis. Studies with photoactivatable GFP–E-cadherin showed that Myo1c KD reduced the stability of E-cadherin at cell–cell adhesions. We conclude that Myo1c stabilizes E-cadherin at adherens junctions in polarized epithelial cells and that the motor function and ability of Myo1c to bind membrane are critical.

Role of the adiponectin binding protein, T-cadherin (cdh13), in pulmonary responses to subacute ozone

Adiponectin, an adipose derived hormone with pleiotropic functions, binds to several proteins, including T-cadherin. We have previously reported that adiponectin deficient (Adipo(-/-)) mice have increased IL-17A-dependent neutrophil accumulation in their lungs after subacute exposure to ozone (0.3 ppm for 72 hrs). The purpose of this study was to determine whether this anti-inflammatory effect of adiponectin required adiponectin binding to T-cadherin. Wildtype, Adipo(-/-) , T-cadherin deficient (T-cad(-/-) ), and bideficient (Adipo(-/-)/T-cad(-/-) ) mice were exposed to subacute ozone or air. Compared to wildtype mice, ozone-induced increases in pulmonary IL-17A mRNA expression were augmented in T-cad(-/-) and Adipo(-/-) mice. Compared to T-cad(-/-) mice, there was no further increase in IL-17A in Adipo(-/-)/T-cad(-/-) mice, indicating that adiponectin binding to T-cadherin is required for suppression of ozone-induced IL-17A expression. Similar results were obtained for pulmonary mRNA expression of saa3, an acute phase protein capable of inducing IL-17A expression. Comparison of lung histological sections across genotypes also indicated that adiponectin attenuation of ozone-induced inflammatory lesions at bronchiolar branch points required T-cadherin. BAL neutrophils and G-CSF were augmented in T-cad(-/-) mice and further augmented in Adipo(-/-)/T-cad(-/-) mice. Taken together with previous observations indicating that augmentation of these moieties in ozone exposed Adipo(-/-) mice is partially IL-17A dependent, the results indicate that effects of T-cadherin deficiency on BAL neutrophils and G-CSF are likely secondary to changes in IL-17A, but that adiponectin also acts via T-cadherin independent pathways. Our results indicate that T-cadherin is required for the ability of adiponectin to suppress some but not all aspects of ozone-induced pulmonary inflammation.

Genome-wide association analysis of avian resistance to Campylobacter jejuni colonization identifies risk locus spanning the CDH13 gene

The enteropathogen Campylobacter jejuni is a major worldwide health and economic burden, being one of the leading causes of bacterial gastroenteritis and commonly linked to postinfectious onset of autoimmune disease. Chickens are a major vector for human infection and even though variation in avian colonization level is heritable, no previous studies have identified regions of the genome associated with colonization resistance. We performed a genome-wide association study of resistance to C. jejuni colonization in the avian intestine by controlling for population structure, which revealed a risk locus with genome-wide significance spanning the T-cadherin (CDH13) gene. A second possible risk locus was also identified close to calmodulin (CALM1), a calcium-activated modulator of cadherin function. In addition, gene expression analysis of mRNA sequencing profiles revealed that the relative expression of the two genes is significantly associated with colonization resistance. Functional studies have previously demonstrated involvement of cadherins and calmodulin in C. jejuni intracellular invasion and colonization of human intestinal epithelial cells in vitro. Consistent with this finding, our analysis reveals that variation surrounding these genes is associated with avian colonization resistance in vivo and highlights their potential as possible targets for control of the bacterium in avian and human populations.

Effects of T-cadherin expression on B16F10 melanoma cells

Melanoma is one of the most deadly skin cancers. T-cadherin is an atypical member of the cadherin superfamily as it lacks the transmembrane and cytoplasmic domains and is anchored to cell membranes through glycosylphosphatidylinositol (GPI) anchors. T-cadherin downregulation is associated with a poorer prognosis in various carcinomas, such as lung, ovarian, cervical and prostate cancer, while in the majority of cancer cell lines, T-cadherin re-expression inhibits cell proliferation and invasiveness, increases susceptibility in apoptosis and reduces tumor growth in in vivo models. The functional relevance of T-cadherin gene expression in melanoma progression remains to be clarified. The present study was designed for this purpose. The T-cadherin gene was transfected into B16F10 melanoma cells to express T-cadherin in the cells which were originally deficient in T-cadherin expression. The proliferation, invasiveness, apoptosis and cell cycle of the transfected B16F10 melanoma cells were analyzed. The present study showed that the expression of T-cadherin in B16F10 melanoma cells markedly reduced cell proliferation and permeation through Matrigel-coated membranes, representing invasiveness. The percentage of early apoptotic cells and cells in the G₂/M phase of the cell cycle was markedly increased compared with either parental B16F10 (without transfection) or empty pEGFP-N1 (without T-cadherin gene)-transfected B16F10 cells, suggesting G₂/M arrest, with similarity between the parental and empty pEGFP-N1-transfected B16F10 cells. T-cadherin is important in melanoma progression and may be a possible target for therapy in melanoma and certain other types of cancer.

Mineralocorticoid receptor-dependent proximal tubule injury is mediated by a redox-sensitive mTOR/S6K1 pathway

BACKGROUND/AIMS

The mammalian target of rapamycin (mTOR) is a serine kinase that regulates phosphorylation (p) of its target ribosomal S6 kinase (S6K1), whose activation can lead to glomerular and proximal tubular cell (PTC) injury and associated proteinuria. Increased mTOR/S6K1 signaling regulates signaling pathways that target fibrosis through adherens junctions. Recent data indicate aldosterone signaling through the mineralocorticoid receptor (MR) can activate the mTOR pathway. Further, antagonism of the MR has beneficial effects on proteinuria that occur independent of hemodynamics.

METHODS

Accordingly, hypertensive transgenic TG(mRen2)27 (Ren2) rats, with elevated serum aldosterone and proteinuria, and age-matched Sprague-Dawley rats were treated with either a low dose (1 mg/kg/day) or a conventional dose (30 mg/kg/day) of spironolactone (MR antagonist) or placebo for 3 weeks.

RESULTS

Ren2 rats displayed increases in urine levels of the PTC brush border lysosomal enzyme N-acetyl-β-aminoglycosidase (β-NAG) in conjunction with reductions in PTC megalin, the apical membrane adherens protein T-cadherin and basolateral α-(E)-catenin, and fibrosis. In concert with these abnormalities, Ren2 renal cortical tissue also displayed increased Ser2448 (p)/activation of mTOR and Thr389 (p)-S6K1 and increased 3-nitrotyrosine (3-NT) content, a marker for peroxynitrite. Low-dose spironolactone had no effect on blood pressure but decreased proteinuria and β-NAG comparable to a conventional dose of this MR antagonist. Both doses of spironolactone attenuated ultrastructural maladaptive alterations and led to comparable reductions in (p)-mTOR/(p)-S6K1, 3-NT, fibrosis, and increased expression of α-(E)-catenin, T- and N-cadherin.

CONCLUSIONS

Thereby, MR antagonism improves proximal tubule integrity by targeting mTOR/S6K1 signaling and redox status independent of changes in blood pressure.

T-cadherin structures reveal a novel adhesive binding mechanism

Vertebrate genomes encode 19 classical cadherins and about 100 nonclassical cadherins. Adhesion by classical cadherins depends on binding interactions in their N-terminal EC1 domains, which swap N-terminal beta-strands between partner molecules from apposing cells. However, strand-swapping sequence signatures are absent from nonclassical cadherins, raising the question of how these proteins function in adhesion. Here, we show that T-cadherin, a glycosylphosphatidylinositol (GPI)-anchored cadherin, forms dimers through an alternative nonswapped interface near the EC1-EC2 calcium-binding sites. Mutations within this interface ablate the adhesive capacity of T-cadherin. These nonadhesive T-cadherin mutants also lose the ability to regulate neurite outgrowth from T-cadherin-expressing neurons. Our findings reveal the likely molecular architecture of the T-cadherin homophilic interface and its requirement for axon outgrowth regulation. The adhesive binding mode used by T-cadherin may also be used by other nonclassical cadherins.

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.

Identification of proteins associating with glycosylphosphatidylinositol- anchored T-cadherin on the surface of vascular endothelial cells: role for Grp78/BiP in T-cadherin-dependent cell survival

There is scant knowledge regarding how cell surface lipid-anchored T-cadherin (T-cad) transmits signals through the plasma membrane to its intracellular targets. This study aimed to identify membrane proteins colocalizing with atypical glycosylphosphatidylinositol (GPI)-anchored T-cad on the surface of endothelial cells and to evaluate their role as signaling adaptors for T-cad. Application of coimmunoprecipitation from endothelial cells expressing c-myc-tagged T-cad and high-performance liquid chromatography revealed putative association of T-cad with the following proteins: glucose-related protein GRP78, GABA-A receptor alpha1 subunit, integrin beta3, and two hypothetical proteins, LOC124245 and FLJ32070. Association of Grp78 and integrin beta3 with T-cad on the cell surface was confirmed by surface biotinylation and reciprocal immunoprecipitation and by confocal microscopy. Use of anti-Grp78 blocking antibodies, Grp78 small interfering RNA, and coexpression of constitutively active Akt demonstrated an essential role for surface Grp78 in T-cad-dependent survival signal transduction via Akt in endothelial cells. The findings herein are relevant in the context of both the identification of transmembrane signaling partners for GPI-anchored T-cad as well as the demonstration of a novel mechanism whereby Grp78 can influence endothelial cell survival as a cell surface signaling receptor rather than an intracellular chaperone.

BS-cadherin in the colonial urochordate Botryllus schlosseri: one protein, many functions

Botryllus schlosseri is a colonial urochordate composed of coexisting modules of three asexually derived generations, the zooids and two cohorts of buds, each at disparate developmental stage. Functional zooids are replaced weekly by the older generation of buds through a highly synchronized developmental cycle called blastogenesis (which is, in turn, divided into four major stages, A to D). In this study, we examined the mode of expression of BS-cadherin, a 130-kDa transmembrane protein isolated from this species, during blastogenesis. BS-Cadherin is expressed extensively in internal organs of developing buds, embryos, ampullae and, briefly, in the digestive system of zooids at early blastogenic stage D (in contrast to low mRNA expression at this stage). In vitro trypsin assays on single-cell suspensions prepared from blastogenic stage D zooids, confirmed that BS-cadherin protein is expressed on cell surfaces and is, therefore, functional. BS-Cadherin expression is also upregulated in response to various stress conditions, such as oxidative stress, injury and allorecognition. It plays an important role in colony morphogenesis, because siRNA knockdown during D/A blastogenic transition causes chaotic colonial structures and disrupts oocytes homing onto their bud niches. These results reveal that BS-cadherin protein functions are exerted through a specific spatiotemporal pattern and fluctuating expression levels, in both development/regular homeostasis and in response to various stress conditions.

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T-/H-cadherin (CDH13): a new marker for differentiating podocytes

Cadherin molecules are known to be involved in various biological processes other than cell adhesion such as morphogenesis, cell-cell communication, cell recognition or cell signalling. While the classical cadherin molecule is characterized by an extracellular moiety, a transmembrane region and a variable cytoplasmic domain, T-/H-cadherin differs from this pattern due to the absence of a transmembrane region and a cytoplasmic domain, respectively. Its extracellular moiety is bound to the apical cell membrane by a glycosyl-phosphatidyl-inositol anchor and localized to lipid raft domains. As its molecular function and expression pattern is still not fully understood, we used a newly generated anti-T-/H-cadherin antiserum to study immunohistochemically the expression of T-/H-cadherin during the differentiation of foetal human glomeruli. At the early capillary loop stage a strong apical signal comes up for visceral epithelial cells of Bowman's capsule, which begin to differentiate towards podocytes. At the advanced capillary loop stage, when podocytes have become part of the glomerular filtration barrier, the expression pattern, however, becomes more distinct and most likely restricted to the foot processes of the podocytes. We thus postulate a functional role of T-/H-cadherin for the differentiation of the podocytes and the formation of the glomerular capillary network.

LDL induces intracellular signalling and cell migration via atypical LDL-binding protein T-cadherin

Cadherins are a superfamily of adhesion molecules that mediate Ca(2+)-dependent cell-cell adhesion. T-cadherin (T-cad), a unique glycosylphosphatidylinositol-anchored member of the cadherin superfamily, was initially identified by immunoblotting of vascular cell membranes as an atypical low affinity low density lipoprotein (LDL)-binding protein. It is not known whether this heterophilic interaction is physiologically relevant. Expression of T-cadherin is upregulated in vascular cells during atherosclerosis, restenosis and tumour angiogenesis, conditions characterized by enhanced cell migration and growth. Elevated levels of serum low density lipoproteins (LDL), which result in cholesterol accumulation in vascular wall, is a widely accepted risk factor in atherosclerosis development. Additionally to its metabolic effects, LDL can produce hormone-like effects in a number of cell types. This study has utilized HEK293 cells and L929 cells stably transfected with T-cadherin cDNA to investigate T-cad-dependent responses to LDL. Stable expression of T-cad in both HEK293 and L929 cells results in significantly (p < 0.05) elevated specific surface binding of [I125]-LDL. Compared with mock-transfectants, cells expressing T-cad exhibit significantly (p < 0.01) enhanced LDL-induced mobilization of intracellular Ca(2+)-stores and a significantly (p < 0.01) increased migration toward an LDL gradient (0.1% BSA + 60 microg/ml LDL) in Boyden chamber migration assay. Thus LDL-binding to T-cad is capable of activating physiologically relevant intracellular signaling and functional responses.

T-cadherin GPI-anchor is insufficient for apical targeting in MDCK cells

T-cadherin is a 95kDa glycoprotein member of the cadherin family of adhesion molecules attached to the extracellular surface of the cell membrane through a glycosyl-phosphatidylinositol (GPI)-anchor. Whether a T-cadherin ectodomain apical targeting signal or the GPI-anchor itself targets this protein to the apical membrane is not known. Chimeras of the reporter EGFP and T-cadherin have demonstrated that a minimal construct consisting of the C-terminal 25 amino acids including the N690 (omega-site) of T-cadherin was sufficient to GPI-anchor the EGFP protein. However, efficient GPI-anchor with minimal secretion of the protein required an additional 5 residues (omega-1 to omega-5). The GPI-anchored chimeras fractionated to the Triton X-100 detergent insoluble fraction and were released to the cell culture supernatant by phosphoinositide-specific phospho-lipase C digestion. When expressed in MDCK cells, all GPI-anchored chimeras targeted to the basolateral membrane, while the T/N-chimera and the wild-type T-cadherin targeted to the apical membrane. Therefore, T-cadherin is an example of another rare GPI-anchored protein where the anchor itself is not sufficient for apical targeting in MDCK cells.

RhoA and Rac mediate endothelial cell polarization and detachment induced by T-cadherin

T-cadherin (T-cad) is an atypical GPI-anchored member of the cadherin superfamily. Ligation of T-cad receptors on endothelial cells prevents cell spreading, promotes elongation and polarization, decreases adhesion to the matrix, and facilitates migration. This study investigates involvement of Rho GTPases in T-cad signaling. Human umbilical vein endothelial cells were infected with adenoviral vectors expressing dominant-negative and/or constitutively active mutants of RhoA (N19RhoA/RhoA63), ROCK (RB/PH(TT)/CAT), and Rac1 (N17RAC). Mutant-infected and empty vector-infected cells were compared with respect to their ability to detach and polarize when plated on substratum containing recombinant T-cad protein used as a ligand mimicking homophilic T-cad interactions. ROCK involvement was also studied using specific inhibitor Y-27632. Adhesion assays, analysis of cell phenotype, and actin cytoskeleton organization using TRITC-labeled phalloidin demonstrated that T-cad-induced cell polarization includes two complementary components: RhoA/ROCK pathway is necessary for cell contraction, stress fiber assembly, and inhibition of spreading, whereas Rac is required for formation of actin-rich lamellipodia at the leading edges of polarized cells. Individual repression of either pathway only partially prevented cell polarization and detachment, while simultaneous repression of RhoA and Rac pathways fully eliminated responses to homophilic T-cad ligation. In conclusion, these data suggest that T-cad induces cell deadhesion and polarization via RhoA-ROCK- and Rac-dependent mechanisms.

Promoter Hypermethylation in Benign Breast Epithelium in Relation to Predicted Breast Cancer Risk

Introduction: The tumor suppressor genes RASSF1A, APC, H-cadherin, RARβ2, and cyclin D2 are methylated more frequently in breast cancer than in adjacent benign tissue. However, it is unclear whether promoter methylation of tumor suppressor genes in benign breast tissue is associated with an increased risk for breast cancer.

Methods: Promoter hypermethylation was measured in benign and malignant breast samples obtained by fine needle aspiration biopsy from 27 breast cancer patients and 55 unaffected women whose risk of breast cancer had been defined using the Gail, Claus, and BRCAPRO models.

Results: Cyclin D2 methylation occurred in 57% of tumor samples but not in corresponding benign breast samples and in only one sample from an unaffected patient (P &lt; 0.0001). RARβ2 methylation occurred in 32% of benign breast samples from cancer patients but only 9% of similar samples from unaffected women (P = 0.002). Promoter methylation of RASSF1A and APC occurred more frequently (70% and 56%, respectively) in unaffected women at high-risk for breast cancer as defined by the Gail model than in low/intermediate risk women (29% and 20%, P = 0.04 and P = 0.03). Of the Gail model risk factors, only number of prior breast biopsies was highly correlated with APC and RASSF1A methylation (P = 0.0001 and 0.02, respectively).

Conclusions: Since cyclin D2 promoter methylation occurs almost exclusively in tumors, it may be possible to exploit it for the early detection of breast cancer. Promoter methylation of APC, RARβ2, and RASSF1A in benign breast epithelium is associated with epidemiologic markers of increased breast cancer risk.

Cell adhesion molecule T-cadherin regulates vascular cell adhesion, phenotype and motility

T-cadherin (T-cad), an unusual glycosylphosphatidylinositol (GPI)-anchored member of the cadherin family of cell adhesion molecules, is widely expressed in the cardiovascular system. The expression profile of T-cad within diseased (atherosclerotic and restenotic) vessels indicates some relationship between expression of T-cad and the phenotypic status of resident cells. Using cultures of human aortic smooth muscle cells (SMC) and human umbilical vein endothelial cells (HUVEC) we investigate the hypothesis that T-cad may function in modulating adhesive properties of vascular cells. Coating of culture plates with recombinant T-cad protein or with antibody against the first amino-terminal domain of T-cad (anti-EC1) significantly decreased adhesion and spreading of SMC and HUVEC. HUVECs adherent on T-cad or anti-EC1 substratum exhibited an elongated morphology and associated redistribution of the cytoskeleton and focal adhesions to a distinctly peripheral location. These changes are characteristic of the less-adhesive, motile or pro-migratory, pro-angiogenic phenotype. Boyden chamber migration assay demonstrated that the deadhesion induced by T-cad facilitates cell migration towards a serum gradient. Overexpression of T-cad in vascular cells using adenoviral vectors does not influence cell adhesion or motility per se, but increases the detachment and migratory responses induced by T-cad substratum. The data suggest that T-cad acts as an anti-adhesive signal for vascular cells, thus modulating vascular cell phenotype and migration properties.

Comparative expression patterns of T-, N-, E-cadherins, beta-catenin, and polysialic acid neural cell adhesion molecule in rat cochlea during development: implications for the nature of Kölliker's organ

We investigated the expression patterns of several cell adhesion molecules (CAMs) during rat cochlea ontogeny, from embryo day 16 to adulthood, with the use of immunohistochemistry: neural cadherin (N-cad) and polysialic acid neural CAM (PSA-NCAM) as two different neural CAM paradigms; epithelial cadherin (E-cad), which was restricted to the epitheloid phenotype; and the cytoplasmic domain-free truncated-cadherin (T-cad). We made the following observations. (1) T-cad was present in all types of fibrocyte and in subdomains within the pillar cells. (2) E- and N-cad were expressed with mutually exclusive patterns and did not overlap with T-cad. All cochlear epithelial cells, including the sensory outer hair cells (OHCs), were E-cad-positive, except for the negative inner hair cells (IHCs) and the nonsensory Kölliker's organ domain close to the IHCs. N-cad expression appeared first in the developing IHCs and then in the neighboring Kölliker's organ in an increasingly mediolateral gradient in opposition to the E-cad gradient. The OHCs, which are never N-cad positive, intensively expressed E-cad, as did the Hensen cells at the beginning of their differentiation. (3) The cadherin-linked molecule beta-catenin, absent in fibrocytes, was detected in all epithelial cell membranes and was prominent in the E-cad-rich modiolar extremity of Kölliker's organ. (4) Gradual PSA-NCAM expression was observed in the lateral portion of Kölliker's organ, and the intense PSA-NCAM expression was seen surrounding the IHCs. As development proceeded, PSA-NCAM immunoreactivity progressively became restricted to the basal poles of the IHCs, where it remained in the adult rat cochlea, suggesting a synaptic plasticity. Synaptic plasticity in rat cochlea and hypotheses about T-cad functions and neosensory features of the Kölliker's organ are discussed.

Cadherin-13, a mediator of calcium-dependent cell-cell adhesion, is silenced by methylation in chronic myeloid leukemia and correlates with pretreatment risk profile and cytogenetic response to interferon alfa

PURPOSE

Cadherin-13 (CDH13) is a newly characterized cadherin molecule responsible for selective cell recognition and adhesion, the expression of which is decreased by methylation in a variety of human cancers, indicating that the CDH13 gene functions as a tumor suppressor gene. Although defective progenitor-stromal adhesion is a well-recognized feature of chronic myeloid leukemia (CML), the role of CDH13 abnormalities has not been evaluated in this disease.

PATIENTS AND METHODS

We examined the methylation status of the CDH13 promoter in 179 chronic phase (CP)-CML patients and in 52 advanced-phase samples and correlated it with mRNA expression using methylation-specific polymerase chain reaction (PCR) and reverse transcriptase PCR.

RESULTS

Aberrant de novo methylation of the CDH13 promoter region was observed in 99 (55%) of 179 of CP-CML patients, and 90 of the patients failed to express CDH13 mRNA (P <.0001). Advanced-stage samples (n = 52) showed concordant methylation results with their corresponding CP tumors, indicating that CDH13 methylation was not acquired during the course of the disease. Nevertheless, absence of CDH13 expression was more frequently observed among Sokal high-risk patients (P =.01) and was also independently associated with a shorter median progression-free survival time (P =.03) and poor cytogenetic response to interferon alfa treatment (P =.0001).

CONCLUSION

Our data indicate that the silencing of CDH13 expression by aberrant promoter methylation occurs at an early stage in CML pathogenesis and probably influences the clinical behavior of the disease.

T-cadherin-mediated cell growth regulation involves G2 phase arrest and requires p21(CIP1/WAF1) expression

Members of the cadherin family have been implicated as growth regulators in multiple tumor types. Based on recent studies from our laboratory implicating T-cadherin expression in mouse brain tumorigenesis, we examined the role of T-cadherin in astrocytoma growth regulation. In this report, we show that T-cadherin expression increased during primary astrocyte physiologic growth arrest in response to contact inhibition and serum starvation in vitro, suggesting a function for T-cadherin in astrocyte growth regulation. We further demonstrate that transient and stable reexpression of T-cadherin in deficient C6 glioma cell lines results in growth suppression. In addition, T-cadherin-expressing C6 cell lines demonstrated increased homophilic cell aggregation, increased cell attachment to fibronectin, and decreased cell motility. Cell cycle flow cytometry demonstrated that T-cadherin reexpression resulted in G2 phase arrest, which was confirmed by mitotic index analysis. This growth arrest was p53 independent, as T-cadherin could still mediate growth suppression in p53(-/-) mouse embryonic fibroblasts. T-cadherin-expressing C6 cell lines exhibited increased p21(CIP1/WAF1), but not p27(Kip1), expression. Lastly, T-cadherin-mediated growth arrest was dependent on p21(CIP1/WAF1) expression and was eliminated in p21(CIP1/WAF1)-deficient fibroblasts. Collectively, these observations suggest a novel mechanism of growth regulation for T-cadherin involving p21(CIP1/WAF1) expression and G2 arrest.

Identification and expression analysis of the human mu-protocadherin gene in fetal and adult kidneys

We recently cloned mu-protocadherin, a developmentally regulated cell adhesion molecule that contains an extracellular region with four cadherin-like ectodomains and a triply repeating mucin domain in its longer isoform. Expression of mu-protocadherin in L929 cells resulted in cellular aggregation, confirming its role in intercellular adhesion. We now identify the human mu-protocadherin ortholog and study its distribution in vivo and its targeting in polarized epithelia. Basic Local Alignment Search Tool searches and fluorescent in situ hybridization analysis on the basis of human-mouse synteny reveal that mu-protocadherin maps to 11p15.5, matching a previously identified gene called MUCDHL. At least three different splicing isoforms exist for MUCDHL that vary in expression in the fetal kidney. Mu-protocadherin is apically expressed along the brush border of the proximal convoluted tubule of the adult kidney. Transfection of truncated forms of mu-protocadherin into polarized Madin-Darby canine kidney cells reveals that the NH(2) terminus is essential for targeting to the apical surface. These results suggest that although human mu-protocadherin may mediate a homotypic adhesive interaction, it may have additional functions in terminally differentiated epithelia.

Expression of T-cadherin in Basal keratinocytes of skin

T-cadherin is a unique member of the cadherin superfamily that shares the ectodomain organization with classical cadherins, but lacks both transmembrane and cytoplasmic regions and is instead anchored to the plasma membrane through a glycosyl-phosphatidylinositol (GPI) moiety. The function of T-cadherin has not been revealed yet. The special structure of T-cadherin might endow this molecule with specific intracellular targeting properties and functions that are distinct from classical cadherins. T-cadherin was originally cloned from chicken embryo brain and then was also found in mouse and human nervous and cardiovascular systems; however, T-cadherin in the keratinocytes and skin tissue is still an unknown area that remains to be explored. To test whether the unusual truncated T-cadherin is expressed in keratinocytes, we performed the reverse transcriptase-polymerase chain reaction of T-cadherin, as well as several classical cadherins (E-, P-, and N-cadherin), on the mouse keratinocyte cell line Pam212, fibroblast NIH3T3, and melanoma cell B16. The result indicated that mouse keratinocytes expressed the mRNA of truncated T-cadherin apart from classical cadherins, E-, and P-cadherin. To confirm the expression of T-cadherin in mouse keratinocytes, immunocytochemistry staining was carried out on Pam212 cells by using rabbit anti-T-cadherin antibody and rat antimouse E- and P-cadherin antibody. The result of immunofluorescence staining proved that T-cadherin was expressed in mouse keratinocytes. In order to analyze the distribution patterns of T-cadherin and classical cadherins on the keratinocytes, 3D scanning was performed by using a confocal microscope. From the Z-sections and XZ-sections, it was clearly demonstrated that T-cadherin was distributed diffusely on the whole cell surface, while E- and P-cadherin were concentrated on the cell-cell contacts. To examine the expression and the localization of T-cadherin on skin tissue, the frozen sections of the mouse back skin were immunohistochemically labeled by using anti-T-cadherin antibody. It was found that T-cadherin was intensively expressed only on the basal cell layer of the mouse skin. Apart from mouse keratinocytes and mouse skin, we further examined the expression of T-cadherin in human keratinocytes and human skin by western blot, immunocytochemistry, and immunohistochemistry staining. The same results were achieved with human samples. In this study, we found and verified that T-cadherin was expressed on the mouse and human keratinocytes and specifically localized on the basal cell layer of skin. The nature of T-cadherin function and its mechanism of localization at the basal cell layer of skin are important issues to be addressed concerning this unique member of the cadherin family and its physiologic and pathologic roles in the skin.

The glycosyl phosphatidylinositol anchor of human T-cadherin binds lipoproteins

T-cadherin (T-cad) is a Ca(2+)-dependent cell adhesion glycoprotein bound to the plasma membrane via a glycosylphosphatidylinositol (GPI) anchor. T-cad expressed on vascular smooth muscle cells (SMC) binds lipoproteins on blot. To analyze the molecular basis for the interaction of T-cad with lipoproteins we expressed recombinant human T-cad in HEK293 cells. Whereas membrane-bound T-cad from SMC and T-cad transfected HEK293 cells bind lipoproteins, T-cadherin proteins cleaved from the cell surface by phosphatidylinositol-specific phospholipase C (PI-PLC) do not. The lipoprotein-binding function is also lacking both for a recombinant human T-cad expressed in HEK293 cells without the GPI signal sequence, and for a human T-cad form expressed in Escherichia coli that contains the signal sequence for GPI attachment but is not modified with a GPI. We conclude that the GPI moiety of T-cadherin is necessary and sufficient to mediate lipoprotein binding.

LDL binds to surface-expressed human T-cadherin in transfected HEK293 cells and influences homophilic adhesive interactions

T-cadherin (T-cad) is an unusual glycosylphosphatidylinositol-anchored member of the cadherin family of cell adhesion molecules. Binding of low density lipoproteins (LDLs) to T-cad can be demonstrated on Western blots of smooth muscle cell lysates, membranes and purified proteins. Using HEK293 cells transfected with human T-cad cDNA (T-cad+), we have investigated the adhesion properties of expressed mature and precursor proteins and examined the postulate that LDL represents a physiologically relevant ligand for T-cad. T-cad+ exhibits an increased Ca(2+)-dependent aggregation (vs. control) that was reduced by selective proteolytic cleavage of precursor T-cad and abolished after either proteolytic or phosphatidylinositol-specific phospholipase C (PI-PLC) cleavage of both mature and precursor proteins, indicating that both proteins function in intercellular adhesion. T-cad+ exhibited a significantly increased specific cell surface-binding of [(125)I]-LDL that was sensitive to PI-PLC pre-treatment of cells. Ca(2+)-dependent intercellular adhesion of T-cad+ was significantly inhibited by LDL. Our results support the suggestion that LDL is a physiologically relevant ligand for T-cad.

Tissue-inherent fate of GPI revealed by GPI-anchored GFP transgenesis

To clarify the fate of glycosylphosphatidylinositol (GPI) in mammals, we developed GPI-anchored enhanced green fluorescent protein (EGFP-GPI) and transgenic mice carrying this fusion construct. When it was introduced to culture cells, the EGFP-GPI protein was correctly sorted to plasma membranes and microsomes depending on GPI biosynthesis. Transgenic mice carrying EGFP-GPI were found to show a broad transgene expression. Histologically, a prominent polarized localization of EGFP-GPI protein was observed in various epithelia, the nervous system and liver and secreted from some exocrine glands, as well as non-polarized presence in non-epithelial tissues, demonstrating a tissue-inherent manner of GPI sorting.

T-cadherin and signal-transducing molecules co-localize in caveolin-rich membrane domains of vascular smooth muscle cells

Cadherins are a family of cellular adhesion proteins mediating homotypic cell-cell binding. In contrast to classical cadherins, T-cadherin does not possess the transmembrane and cytosolic domains known to be essential for tight mechanical coupling of cells, and is instead attached to the cell membrane by a glycosylphosphatidylinositol (GPI) anchor. This study explores the hypothesis that T-cadherin might function as a signal-transducing protein. Membranes from human and rat vascular smooth muscle cells were fractionated using Triton X-100 solubilization and density gradient centrifugation techniques. We demonstrate that T-cadherin is enriched in a minor detergent-insoluble low-density membrane domain and co-distributes with caveolin, a marker of caveolae. This domain was enriched in other GPI-anchored proteins (CD-59, uPA receptor) and signal-transducing molecules (G alpha s protein and Src-family kinases), but completely excluded cell-cell and cell-matrix adhesion molecules (N-cadherin and beta1-integrin). Coupling of T-cadherin with signalling molecules within caveolae might enable cellular signal transduction.

Differential localization of VE- and N-cadherins in human endothelial cells: VE-cadherin competes with N-cadherin for junctional localization

The two major cadherins of endothelial cells are neural (N)-cadherin and vascular endothelial (VE)- cadherin. Despite similar level of protein expression only VE-cadherin is located at cell-cell contacts, whereas N-cadherin is distributed over the whole cell membrane. Cotransfection of VE-cadherin and N-cadherin in CHO cells resulted in the same distribution as that observed in endothelial cells indicating that the behavior of the two cadherins was not cell specific but related to their structural characteristics. Similar amounts of alpha- and beta-catenins and plakoglobin were associated to VE- and N-cadherins, whereas p120 was higher in the VE-cadherin complex. The presence of VE-cadherin did not affect N-cadherin homotypic adhesive properties or its capacity to localize at junctions when cotransfectants were cocultured with cells transfected with N-cadherin only. To define the molecular domain responsible for the VE-cadherin-dominant activity we prepared a chimeric construct formed by VE-cadherin extracellular region linked to N-cadherin intracellular domain. The chimera lost the capacity to exclude N-cadherin from junctions indicating that the extracellular domain of VE-cadherin alone is not sufficient for the preferential localization of the molecule at the junctions. A truncated mutant of VE-cadherin retaining the full extracellular domain and a short cytoplasmic tail (Arg621-Pro702) lacking the catenin-binding region was able to exclude N-cadherin from junctions. This indicates that the Arg621-Pro702 sequence in the VE-cadherin cytoplasmic tail is required for N-cadherin exclusion from junctions. Competition between cadherins for their clustering at intercellular junctions in the same cell has never been described before. We speculate that, in the endothelium, VE- and N-cadherin play different roles; whereas VE-cadherin mostly promotes the homotypic interaction between endothelial cells, N-cadherin may be responsible for the anchorage of the endothelium to other surrounding cell types expressing N-cadherin such as vascular smooth muscle cells or pericytes.

T-cadherin is a major glycophosphoinositol-anchored protein associated with noncaveolar detergent-insoluble domains of the cardiac sarcolemma

Sucrose-density flotation analysis of Triton-insoluble membrane domains isolated from highly purified sheep ventricular sarcolemma revealed the presence of two major 120- and 100-kDa proteins. Both species migrated in two-dimensional isoelectric focussing/SDS gels with an apparent pI of approximately 4.3, suggesting that they might be related. Microsequence analysis of peptides derived from the 100-kDa protein yielded amino acid sequences with high homology to T-cadherin, a truncated cadherin lacking a cytoplasmic domain. The similarity was confirmed using antibodies to chicken T-cadherin that reacted with both proteins on immunoblots. T-cadherin was released from the detergent-insoluble sarcolemmal fraction by phospholipase C treatment indicating that it is linked to the membrane by a glycophosphoinositol anchor. T-cadherin could be ADP-ribosylated by a transferase that was also present in the caveolin-enriched Triton-insoluble fraction. T-cadherin-containing membrane fragments cofractionated on sucrose gradients with caveolin-3, a marker protein for myocyte caveolae. However, immunopurified caveolin-3-containing membranes contained no associated T-cadherin. Immunocytochemical analysis of cultured rat atrial myocytes revealed that T-cadherin and caveolin have related but nonoverlapping staining patterns. These results suggest that T-cadherin is a major glycophosphoinositol-linked protein in cardiac myocytes and that it may be located in plasma membrane "rafts" distinct from but possibly adjacent to caveolae.

Trabecular myocytes of the embryonic heart require N-cadherin for migratory unit identity

The myocardial wall of the vertebrate heart changes from a simple epithelium to a trabeculated structure during embryogenesis. This process occurs when epithelioid cardiomyocytes migrate toward the endocardium, which we show is coincident with up-regulation of the cell adhesion molecule, N-cadherin. To study the role of N-cadherin expressed at the trabeculation stage, a replication-defective retrovirus expressing a dominant negative mutant of N-cadherin (delta N-cadherin) was engineered. Control viruses were designed to express beta-galactosidase or a full-length N-cadherin. Viruses were introduced into epithelioid presumptive myocytes at the time they initiate the epithelial-mesenchymal transformation. Individual cells infected with control viruses generated daughter myocytes which migrated toward endocardium as a tight cluster, thereby generating a clone that forms a single or at most two trabeculae. In contrast, myocytes expressing delta N-cadherin were sparsely distributed within the myocardium and failed to form the ridge-shaped clone. Thus, in addition to its known roles in myocyte epithelialization and intercalated disc formation, N-cadherin appears to play a role in homotypic interactions between nonepithelial migratory myocytes during trabecular formation of the embryonic heart.

The brain chondroitin sulfate proteoglycan brevican associates with astrocytes ensheathing cerebellar glomeruli and inhibits neurite outgrowth from granule neurons

Brevican is a nervous system-specific chondroitin sulfate proteoglycan that belongs to the aggrecan family and is one of the most abundant chondroitin sulfate proteoglycans in adult brain. To gain insights into the role of brevican in brain development, we investigated its spatiotemporal expression, cell surface binding, and effects on neurite outgrowth, using rat cerebellar cortex as a model system. Immunoreactivity of brevican occurs predominantly in the protoplasmic islet in the internal granular layer after the third postnatal week. Immunoelectron microscopy revealed that brevican is localized in close association with the surface of astrocytes that form neuroglial sheaths of cerebellar glomeruli where incoming mossy fibers interact with dendrites and axons from resident neurons. In situ hybridization showed that brevican is synthesized by these astrocytes themselves. In primary cultures of cerebellar astrocytes, brevican is detected on the surface of these cells. Binding assays with exogenously added brevican revealed that primary astrocytes and several immortalized neural cell lines have cell surface binding sites for brevican core protein. These cell surface brevican binding sites recognize the C-terminal portion of the core protein and are independent of cell surface hyaluronan. These results indicate that brevican is synthesized by astrocytes and retained on their surface by an interaction involving its core protein. Purified brevican inhibits neurite outgrowth from cerebellar granule neurons in vitro, an activity that requires chondroitin sulfate chains. We suggest that brevican presented on the surface of neuroglial sheaths may be controlling the infiltration of axons and dendrites into maturing glomeruli.