Ksp-cadherin is a functional cell–cell adhesion molecule related to LI-cadherin

Cadherin-16 regulates acoustic sensory gating in zebrafish through endocrine signaling

Sensory thresholds enable animals to regulate their behavioral responses to environmental threats. Despite the importance of sensory thresholds for animal behavior and human health, we do not yet have a full appreciation of the underlying molecular-genetic and circuit mechanisms. The larval zebrafish acoustic startle response provides a powerful system to identify molecular mechanisms underlying establishment of sensory thresholds and plasticity of thresholds through mechanisms like habituation. Using this system, we identify Cadherin-16 as a previously undescribed regulator of sensory gating. We demonstrate that Cadherin-16 regulates sensory thresholds via an endocrine organ, the corpuscle of Stannius (CS), which is essential in zebrafish for regulating Ca2+ homeostasis. We further show that Cadherin-16 regulates whole-body calcium and ultimately behavior through the hormone Stanniocalcin 1l (Stc1l), and the IGF-regulatory metalloprotease, Papp-aa. Finally, we demonstrate the importance of the CS through ablation experiments that reveal its role in promoting normal acoustic sensory gating. Together, our results uncover a previously undescribed brain non-autonomous pathway for the regulation of behavior and underscore Ca2+ homeostasis as a critical process underlying sensory gating in vivo.

Cadherin 16 promotes sensory gating via the endocrine corpuscles of Stannius

Sensory thresholds enable animals to regulate their behavioral responses to environmental threats. Despite the importance of sensory thresholds for animal behavior and human health, we do not yet have a full appreciation of the underlying molecular-genetic and circuit mechanisms. The larval zebrafish acoustic startle response provides a powerful system to identify molecular mechanisms underlying establishment of sensory thresholds and plasticity of thresholds through mechanisms like habituation. Using this system, we identify Cadherin 16 as a previously undescribed regulator of sensory gating. We demonstrate that Cadherin 16 regulates sensory thresholds via an endocrine organ, the corpuscle of Stannius (CS), which is essential in zebrafish for regulating Ca2+ homeostasis. We further show that Cadherin 16 regulates whole-body calcium and ultimately behavior through the hormone Stanniocalcin 1L, and the IGF-regulatory metalloprotease, Papp-aa. Finally, we demonstrate the importance of the CS through ablation experiments that reveal its role in promoting normal acoustic sensory gating. Together, our results uncover a previously undescribed brain non-autonomous pathway for the regulation of behavior and establish Ca2+ homeostasis as a critical process underlying sensory gating in vivo.

Loss of CDH16 expression is a strong independent predictor for lymph node metastasis in Middle Eastern papillary thyroid cancer

Papillary Thyroid Cancer (PTC) is the most common type of thyroid cancer. The membrane-associated glycoprotein cadherin-16 (CDH16) plays a significant role in the embryonal development of thyroid follicles and cell adhesion. Previous studies have indicated a substantial downregulation of CDH16 in PTC. However, its role in Middle Eastern PTC has not been elucidated. We analyzed a tissue microarray comprising 1606 PTC and 240 normal thyroid tissues using immunohistochemistry to assess CDH16 expression and determine its clinico-pathological associations. We also conducted BRAF and TERT mutations analyses through Sanger sequencing. Disease-free survival (DFS) was assessed using Kaplan-Meier curves. CDH16 immunostaining was seen in 100% of normal thyroid tissues but only in 9.4% of PTC tissues (p < 0.0001). The loss of CDH16 expression was associated with aggressive PTC characteristics including bilaterality, multifocality, extrathyroidal extension, tall cell variant, lymph node metastasis (LNM) and distant metastasis. Additionally a correlation between loss of CDH16 expression and BRAF and TERT mutations was identified. Intriguingly, upon conducting multivariate logistic regression analysis, CDH16 was determined to be an independent predictor for LNM (Odds ratio = 2.46; 95% confidence interval = 1.60-3.79; p < 0.0001). Furthermore, CDH16 loss was associated with a shorter DFS (p = 0.0015). However, when we further subdivided CDH16 negative patients based on the co-existence of TERT and/or BRAF mutations, we found that patients with both CDH16 negative expression and TERT mutation exhibited the shortest DFS (p < 0.0001). In conclusion, our results suggest that CDH16 protein expression could serve as a valuable diagnostic tool for PTC. Furthermore, these findings demonstrate that the loss of CDH16 expression is an independent predictor of LNM and may contribute to the aggressiveness of PTC. Therefore, downregulation of CDH16 in PTC might be a potential target for designing novel therapeutic strategies to treat PTC.

The Transcriptome and Epigenome Reveal Novel Changes in Transcription Regulation During Pancreatic Rat Islet Maturation

Islet function is critical for normal glucose homeostasis. Unlike adult β cells, fetal and neonatal islets are more proliferative and have decreased insulin secretion in response to stimuli. However, the underlying mechanisms governing functional maturity of islets have not been completely elucidated. Pancreatic islets comprise different cell types. The microenvironment of islets and interactions between these cell types are critical for β-cell development and maturation. Thus, the study of intact islets is optimal to identify novel molecular mechanisms controlling islet functional development. Transcriptomes and genome-wide histone landscapes of H3K4me3, H3K27me3, and H3K27Ac from intact islets isolated from 2- and 10-week-old Sprague-Dawley rats were integrated to elucidate genes and pathways modulating islet development, as well as the contribution of epigenetic regulation. A total of 4489 differentially expressed genes were identified; 2289 and 2200 of them were up- and down-regulated in 10-week islets, respectively. Ingenuity Pathway Analysis revealed critical pathways regulating functional maturation of islets, including nutrient sensing, neuronal function, immune function, cell replication, and extracellular matrix. Furthermore, we identified significant changes in enrichment of H3K4me3, H3K27me3, and H3K27Ac marks, which correlated with expression changes of genes critical for islet function. These histone marks were enriched at critical transcription factor-binding motifs, such as Hoxa9, C/EBP-β, Gata1, Foxo1, E2f1, E2f3, and Mafb. In addition, our chromatin immunoprecipitation sequencing data revealed multiple potential bivalent genes whose poised states changed with maturation. Collectively, our current study identified critical novel pathways for mature islet function and suggested a role for histone modifications in regulating islet development and maturation.

Mechanism of dimerization and structural features of human LI-cadherin

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

Deletion of Cdh16 Ksp-cadherin leads to a developmental delay in the ability to maximally concentrate urine in mouse

Ksp-cadherin (cadherin-16) is an atypical member of the cadherin superfamily of cell adhesion molecules that is ubiquitously expressed on the basolateral membrane of epithelial cells lining the nephron and the collecting system of the mammalian kidney. The principal aim of the present study was to determine if Ksp-cadherin played a critical role in the development and maintenance of the adult mammalian kidney by generating and evaluating a mouse line deficient in Ksp-cadherin. Ksp-null mutant animals were viable and fertile, and kidneys from both neonates and adults showed no evidence of structural abnormalities. Immunolocalization and Western blot analyses of Na⁺-K⁺-ATPase and E-cadherin indicated that Ksp-cadherin is not essential for either the genesis or maintenance of the polarized tubular epithelial phenotype. Moreover, E-cadherin expression was not altered to compensate for Ksp-cadherin loss. Plasma electrolytes, total CO₂, blood urea nitrogen, and creatinine levels were also unaffected by Ksp-cadherin deficiency. However, a subtle but significant developmental delay in the ability to maximally concentrate urine was detected in Ksp-null mice. Expression analysis of the principal proteins involved in the generation of the corticomedullary osmotic gradient and the resultant movement of water identified misexpression of aquaporin-2 in the inner medullary collecting duct as the possible cause for the inability of young adult Ksp-cadherin-deficient animals to maximally concentrate their urine. In conclusion, Ksp-cadherin is not required for normal kidney development, but its absence leads to a developmental delay in maximal urinary concentrating ability.NEW & NOTEWORTHY Ksp-cadherin (cadherin-16) is an atypical member of the cadherin superfamily of cell adhesion molecules that is ubiquitously expressed on the basolateral membrane of epithelial cells lining the nephron and the collecting system. Using knockout mice, we found that Ksp-cadherin is in fact not required for kidney development despite its high and specific expression along the nephron. However, its absence leads to a developmental delay in maximal urinary concentrating ability.

Crystal structure of the nonclassical cadherin-17 N-terminus and implications for its adhesive binding mechanism

The cadherin superfamily of calcium-dependent cell-adhesion proteins has over 100 members in the human genome. All members of the superfamily feature at least a pair of extracellular cadherin (EC) repeats with calcium-binding sites in the EC linker region. The EC repeats across family members form distinct complexes that mediate cellular adhesion. For instance, classical cadherins (five EC repeats) strand-swap their N-termini and exchange tryptophan residues in EC1, while the clustered protocadherins (six EC repeats) use an extended antiparallel `forearm handshake' involving repeats EC1-EC4. The 7D-cadherins, cadherin-16 (CDH16) and cadherin-17 (CDH17), are the most similar to classical cadherins and have seven EC repeats, two of which are likely to have arisen from gene duplication of EC1-2 from a classical ancestor. However, CDH16 and CDH17 lack the EC1 tryptophan residue used by classical cadherins to mediate adhesion. The structure of human CDH17 EC1-2 presented here reveals features that are not seen in classical cadherins and that are incompatible with the EC1 strand-swap mechanism for adhesion. Analyses of crystal contacts, predicted glycosylation and disease-related mutations are presented along with sequence alignments suggesting that the novel features in the CDH17 EC1-2 structure are well conserved. These results hint at distinct adhesive properties for 7D-cadherins.

Altered Transcription Factor Binding and Gene Bivalency in Islets of Intrauterine Growth Retarded Rats

Intrauterine growth retardation (IUGR), which induces epigenetic modifications and permanent changes in gene expression, has been associated with the development of type 2 diabetes. Using a rat model of IUGR, we performed ChIP-Seq to identify and map genome-wide histone modifications and gene dysregulation in islets from 2- and 10-week rats. IUGR induced significant changes in the enrichment of H3K4me3, H3K27me3, and H3K27Ac marks in both 2-wk and 10-wk islets, which were correlated with expression changes of multiple genes critical for islet function in IUGR islets. ChIP-Seq analysis showed that IUGR-induced histone mark changes were enriched at critical transcription factor binding motifs, such as C/EBPs, Ets1, Bcl6, Thrb, Ebf1, Sox9, and Mitf. These transcription factors were also identified as top upstream regulators in our previously published transcriptome study. In addition, our ChIP-seq data revealed more than 1000 potential bivalent genes as identified by enrichment of both H3K4me3 and H3K27me3. The poised state of many potential bivalent genes was altered by IUGR, particularly Acod1, Fgf21, Serpina11, Cdh16, Lrrc27, and Lrrc66, key islet genes. Collectively, our findings suggest alterations of histone modification in key transcription factors and genes that may contribute to long-term gene dysregulation and an abnormal islet phenotype in IUGR rats.

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

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

Pax8 controls thyroid follicular polarity through cadherin-16

Organization of epithelial cells during follicular lumen formation is crucial for thyroid morphogenesis and function of the thyroid gland; however, the molecular mechanisms underlying this are poorly understood. To investigate this process, we established three-dimensional (3D) epithelial culture model systems using Fischer rat thyroid (FRT) cells or murine primary thyrocytes that developed polarized spherical structures with a central lumen, mimicking thyroid follicles. Using microarray-based differential expression analysis of FRT cells grown under 2D or 3D conditions, followed by RNA-mediated interference (RNAi) and morphogenetic analysis, we identified a key role for the thyroid transcription factor Pax8 and its target cadherin-16 (Cdh16) in the generation of polarized follicle-like structures. Silencing Pax8 expression inhibited the acquisition of apical–basal membrane polarity and impaired lumen formation. Both laminin and β1-integrin (Itgb1) expression was reduced, and cell cytoskeleton polarized distribution was altered. Silencing Cdh16 expression also led to the formation of defective structures characterized by very low laminin expression at the follicle–matrix interface, downregulation of Itgb1, and unpolarized distribution of cell cytoskeleton. Our results demonstrate that Pax8 controls apical–basal follicular polarization and follicle formation through Cdh16.

Summary: Using a 3D culture model of thyroid morphogenesis, it is revealed that thyroid follicular cell polarity depends on the Pax8 transcription factor and is linked to the β1-integrin–laminin pathway through Cdh16.

Regulator of G protein signaling 20 enhances cancer cell aggregation, migration, invasion and adhesion

Several RGS (regulator of G protein signaling) proteins are known to be upregulated in a variety of tumors but their roles in modulating tumorigenesis remain undefined. Since the expression of RGS20 is elevated in metastatic melanoma and breast tumors, we examined the effects of RGS20 overexpression and knockdown on the cell mobility and adhesive properties of different human cancer cell lines, including cervical cancer HeLa, breast adenocarcinoma MDA-MB-231, and non-small cell lung carcinoma H1299 and A549 cells. Expression of RGS20 enhanced cell aggregation, migration, invasion and adhesion as determined by hanging drop aggregation, wound healing, transwell chamber migration and invasion assays. Conversely, shRNA-mediated knockdown of endogenous RGS20 impaired these responses. In addition, RGS20 elevated the expression of vimentin (a mesenchymal cell marker) but down-regulated the expression of E-cadherin, two indicators commonly associated with metastasis. These results suggest that the expression of RGS20 may promote metastasis of tumor cells.

Cadherin 17 is a sensitive and specific marker for metanephric adenoma

Metanephric adenoma (MA) is a rare benign renal neoplasm that shares morphologic and immunophenotypic overlap with epithelial-predominant Wilms tumor (e-WT) and with the solid variant of papillary renal cell carcinoma (s-PRCC). Cadherin 17 (CDH17) is expressed primarily in the normal intestine and digestive tract tumors and has not been detected in tumors from other sites including the kidney. We investigated the diagnostic utility of CDH17 in differentiating between MA, e-WT, and s-PRCC. Immunohistochemical analysis for CDH17, CD57, AMACR, WT-1, and CDX2 was performed on 17 e-WTs, 15 s-PRCCs, and 21 MAs and assessed on the basis of a combined score of extent and intensity. Normal adult kidney parenchyma was negative for CDH17 staining. CDH17 was expressed in the late stages of fetal kidney development at the junction of the glomerular space and proximal nephron. The majority of MAs (81%) demonstrated membranous CDH17 immunoreactivity in all components (acinar, tubular, and papillary), whereas all cases of e-WTs and s-PRCCs were negative (P<0.0001). WT-1 was negative in s-PRCC and was positive in all cases of e-WT and MA. All MAs were strongly positive for CD57; however, this marker was also moderate to strongly positive in 6 (35%) e-WTs and 2 (13%) s-PRCCs. AMACR was strongly positive in all s-PRCCs, but moderate reactivity was seen in 3 (17%) e-WTs and 2 MAs (10%). CDH17 is a sensitive (81%) and highly specific (100%) marker for MA and should be considered in the immunohistochemistry panel for distinguishing MA from its mimics.

Possible roles of LI-Cadherin in the formation and maintenance of the intestinal epithelial barrier

LI-cadherin belongs to the so called 7D-cadherins, exceptional members of the cadherin superfamily which are characterized by seven extracellular cadherin repeats and a small cytosolic domain. Under physiological conditions LI-cadherin is expressed in the intestine and colon in human and mouse and in the rat also in hepatocytes. LI-cadherin was shown to act as a functional Ca²⁺-dependent adhesion molecule, linking neighboring cells and a lot of biophysical and biochemical parameters were determined in the last time. It is also known that dysregulated LI-cadherin expression can be found in a variety of diseases. Although there are several hypothesis and theoretical models concerning the function of LI-cadherin, the physiological role of LI-cadherin is still enigmatic.

Association between the APC gene D1822V variant and the genetic susceptibility of colorectal cancer

Adenomatous polyposis coli (APC) gene polymorphisms are believed to contribute to tumor susceptibility. However, the association between genetic variants (A/T) in the APC gene D1822V polymorphism and colorectal cancer (CRC) susceptibility remains unknown. To determine this association, a case-control study was performed. The genotype of the APC gene D1822V variants was analyzed by DNA sequencing in blood samples collected from 196 patients with CRC and 279 healthy subjects. There were no significant associations between the case and control groups in the distribution of AT [odds ratio (OR), 0.604; 95% confidence interval (CI), 0.355-1.029) and TT genotypes (OR, 0.438; 95% CI, 0.045-4.247) relative to the AA genotype. The ratio of the T allele was significantly lower (P=0.047) in the case group compared with the control group (OR, 0.611; 95% CI, 0.374-0.997), indicating that the T allele conferred a protective effect in CRC. The frequency of the AT genotype among the subjects diagnosed at >45 years of age was lower than those diagnosed at a younger age (P<0.05). The present study demonstrates that the T allele of the D1822V polymorphism may exert a protective effect against CRC, however, these findings require further validation in a larger sample size.

Cadherin-17 interacts with α2β1 integrin to regulate cell proliferation and adhesion in colorectal cancer cells causing liver metastasis

Liver metastasis is the major cause of death associated to colorectal cancer. Cadherin-17 (CDH17) is a non-classical, seven domain, cadherin lacking the conserved cytoplasmic domain of classical cadherins. CDH17 was overexpressed in highly metastatic human KM12SM and present in many other colorectal cancer cells. Using tissue microarrays, we observed a significant association between high expression of CDH17 with liver metastasis and poor survival of the patients. On the basis of these findings, we decided to study cellular functions and signaling mechanisms mediated by CDH17 in cancer cells. In this report, loss-of-function experiments demonstrated that CDH17 caused a significant increase in KM12SM cell adhesion and proliferation. Coimmunoprecipitation experiments demonstrated an interaction between CDH17 and α2β1 integrin with a direct effect on β1 integrin activation and talin recruitment. The formation of this complex, together with other proteins, was confirmed by mass spectrometry analysis. CDH17 modulated integrin activation and signaling to induce specific focal adhesion kinase and Ras activation, which led to the activation of extracellular signal-regulated kinase and Jun N-terminal kinase and the increase in cyclin D1 and proliferation. In vivo experiments showed that CDH17 silencing in KM12 cells suppressed tumor growth and liver metastasis after subcutaneous or intrasplenic inoculation in nude mice. Collectively, our data reveal a new function for CDH17, which is to regulate α2β1 integrin signaling in cell adhesion and proliferation in colon cancer cells for liver metastasis.

LI-cadherin cis-dimerizes in the plasma membrane Ca(2+) independently and forms highly dynamic trans-contacts

LI-cadherin belongs to the family of 7D-cadherins that is characterized by a low sequence similarity to classical cadherins, seven extracellular cadherin repeats (ECs), and a short cytoplasmic domain. Nevertheless, LI-cadherins mediates Ca²⁺-dependent cell–cell adhesion and induces an epitheloid cellular phenotype in non-polarized CHO cells. Whereas several studies suggest that classical cadherins cis-dimerize in a Ca²⁺-dependent manner and interact in trans by strand-swapping tryptophan 2 of EC1, little is known about the molecular interactions of LI-cadherin, which lacks tryptophan 2. We thus expressed fluorescent LI-cadherin fusion proteins in HEK293 and CHO cells, analyzed their cell–cell adhesive properties and studied their cellular distribution, cis-interaction, and lateral diffusion in the presence and absence of Ca²⁺. LI-cadherin highly concentrates in cell contact areas but rapidly leaves those sites upon Ca²⁺ depletion and redistributes evenly on the cell surface, indicating that it is only kept in the contact areas by trans-interactions. Fluorescence resonance energy transfer analysis of LI-cadherin-CFP and -YFP revealed that LI-cadherin forms cis-dimers that resist Ca²⁺ depletion. As determined by fluorescence redistribution after photobleaching, LI-cadherin freely diffuses in the plasma membrane as a cis-dimer (D = 0.42 ± 0.03 μm²/s). When trapped by trans-binding in cell contact areas, its diffusion coefficient decreases only threefold to D = 0.12 ± 0.01 μm²/s, revealing that, in contrast to classical and desmosomal cadherins, trans-contacts formed by LI-cadherin are highly dynamic.

Quantitative and robust assay to measure cell-cell contact assembly and maintenance

Epithelial junction formation and maintenance are multistep processes that rely on the clustering of macromolecular complexes. These events are highly regulated by signalling pathways that involve Rho small GTPases. Usually, when analysing the contribution of different components of Rho-dependent pathways to cell-cell adhesion, the localisation of adhesion receptors at junctions is evaluated by immunofluorescence. However, we find that this method has limitations on the quantification (dynamic range), ability to detect partial phenotypes and to differentiate between the participation of a given regulatory protein in assembly and/or maintenance of cell-cell contacts.In this chapter, we describe a suitable method, the aggregation assay, in which we adapted a quantitative strategy to allow objective and reproducible detection of partial phenotypes. Importantly, this methodology estimates the ability of cells to form junctions and their resistance to mechanical shearing forces (stabilisation).

CDH16/Ksp-cadherin is expressed in the developing thyroid gland and is strongly down-regulated in thyroid carcinomas

Cadherin (CDH)16/kidney-specific-cadherin was first described as a kidney-specific adhesion molecule and thereafter found expressed also in the thyroid gland. We show here that CDH16 fully colocalizes with CDH1/E-cadherin on the basolateral plasma membrane of mouse and human thyrocytes. In thyrocyte cultures, the expression of CDH16 is dependent upon TSH, as other thyroid differentiation markers. In the developing mouse thyroid, CDH16 is expressed at embryonic day 10.5, 1-2 d after the main thyroid-specific transcription factors involved in thyroid cell differentiation. In human thyroid carcinomas, as determined by quantitative RT-PCR, CDH16 expression decreases in papillary, follicular, and anaplastic thyroid carcinomas, and the decrease is more pronounced than that of CDH1. Moreover, by immunofluorescence and confocal microscopy, it appears that although CDH16-negative tumor cells may still be positive for CDH1, CDH1-negative cells are also negative for CDH16, indicating a more extensive loss of the latter and suggesting that CDH16 loss might precede that of CDH1. Loss of CDH16 appears to be a marker of epithelial-mesenchymal transition as indicated by its decrease in cultured thyroid cells after TGF-β treatment. Finally, the decrease in CDH16 is paralleled in part by the decrease in α B-crystallin, which was proposed to mediate the interaction of CDH16 cytosolic tail with the cell cytoskeleton. In conclusion, CDH16 is a thyroid-selective and hormone-dependent adhesion protein that might play a role during thyroid development and that may be a useful marker to monitor thyroid carcinomas.

An essential role for Pax8 in the transcriptional regulation of cadherin-16 in thyroid cells

Cadherin-16 was originally identified as a tissue-specific cadherin present exclusively in kidney. Only recently, Cadherin-16 has been detected also on the plasma membrane of mouse thyrocytes. This last finding prompted us to note that the expression profile of Cadherin-16 resembles that of the transcription factor Pax8, a member of the Pax (paired-box) gene family, predominantly expressed in the developing and adult kidney and thyroid. Pax8 has been extensively characterized in the thyroid and shown to be a master gene for thyroid development and differentiation. In this study, we determined the role of the transcription factor Pax8 in the regulation of Cadherin-16 expression. We demonstrate that the Cadherin-16 minimal promoter is transcriptionally active in thyroid cells as well as in kidney cells, that Pax8 is able to activate transcription from a Cadherin-16 promoter reporter construct, and more importantly, that indeed Pax8 is able to bind in vivo the Cadherin-16 promoter region. In addition, by means of Pax8 RNA interference in thyroid cells and by analyzing Pax8 null mice, we demonstrate that Pax8 regulates also in vivo the expression of Cadherin-16. Finally, we reveal that the expression of Cadherin-16 is TSH dependent in FRTL-5 thyroid cells and significantly reduced in mouse thyroid carcinomas. Therefore, we conclude that Cadherin-16 is a novel downstream target of the transcription factor Pax8, likely since the early steps of thyroid development, and that its expression is associated with the fully differentiated state of the thyroid cell.

The function of 7D-cadherins: a mathematical model predicts physiological importance for water transport through simple epithelia

Background

7D-cadherins like LI-cadherin are cell adhesion molecules and represent exceptional members of the cadherin superfamily. Although LI-cadherin was shown to act as a functional Ca²⁺-dependent adhesion molecule, linking neighboring cells together, and to be dysregulated in a variety of diseases, the physiological role is still enigmatic. Interestingly 7D-cadherins occur only in the lateral plasma membranes of cells from epithelia of water transporting tissues like the gut, the liver or the kidney. Furthermore LI-cadherin was shown to exhibit a highly cooperative Ca²⁺-dependency of the binding activity. Thus it is tempting to assume that LI-cadherin regulates the water transport through the epithelium in a passive fashion by changing its binding activity in dependence on the extracellular Ca²⁺.

Results

We developed a simple mathematical model describing the epithelial lining of a lumen with a content of variable osmolarity covering an interstitium of constant osmolarity. The width of the lateral intercellular cleft was found to influence the water transport significantly. In the case of hypertonic luminal content a narrow cleft is necessary to further increase concentration of the luminal content. If the cleft is too wide, the water flux will change direction and water is transported into the lumen. Electron microscopic images show that in fact areas of the gut can be found where the lateral intercellular cleft is narrow throughout the lateral cell border whereas in other areas the lateral intercellular cleft is widened.

Conclusions

Our simple model clearly predicts that changes of the width of the lateral intercellular cleft can regulate the direction and efficiency of water transport through a simple epithelium. In a narrow cleft the cells can increase the concentration of osmotic active substances easily by active transport whereas if the cleft is wide, friction is reduced but the cells can hardly build up high osmotic gradients. It is now tempting to speculate that 7D-cadherins, owing to their location and their Ca²⁺-dependence, will adapt their binding activity and thereby the width of the lateral intercellular cleft automatically as the Ca²⁺-concentration is coupled to the overall electrolyte concentration in the lateral intercellular cleft. This could provide a way to regulate the water resorption in a passive manner adapting to different osmotic conditions.

Tuberin regulates E-cadherin localization: implications in epithelial-mesenchymal transition

The tuberous sclerosis complex 2 (TSC2) gene encodes the protein tuberin, which functions as a key negative regulator of both mammalian target of rapamycin (mTOR) C1-dependent cell growth and proliferation. Loss-of-function mutations of TSC2 result in mTORC1 hyperactivity and predispose individuals to both tuberous sclerosis and lymphangioleiomyomatosis. These overlapping diseases have in common the abnormal proliferation of smooth muscle-like cells. Although the origin of these cells is unknown, accumulating evidence suggests that a metastatic mechanism may be involved, but the means by which the mTOR pathway contributes to this disease process remain poorly understood. In this study, we show that tuberin regulates the localization of E-cadherin via an Akt/mTORC1/CLIP170-dependent, rapamycin-sensitive pathway. Consequently, Tsc2(-/-) epithelial cells display a loss of plasma membrane E-cadherin that leads to reduced cell-cell adhesion. Under confluent conditions, these cells detach, grow in suspension, and undergo epithelial-mesenchymal transition (EMT) that is marked by reduced expression levels of both E-cadherin and occludin and increased expression levels of both Snail and smooth muscle actin. Functionally, the Tsc2(-/-) cells demonstrate anchorage-independent growth, cell scattering, and anoikis resistance. Human renal angiomyolipomas and lymphangioleiomyomatosis also express markers of EMT and exhibit an invasive phenotype that can be interpreted as consistent with EMT. Together, these results suggest a novel relationship between TSC2/mTORC1 and the E-cadherin pathways and implicate EMT in the pathogenesis of tuberous sclerosis complex-related diseases.

Role of cadherin-17 in oncogenesis and potential therapeutic implications in hepatocellular carcinoma

Cadherin is an important cell adhesion molecule that plays paramount roles in organ development and the maintenance of tissue integrity. Dysregulation of cadherin expression is often associated with disease pathology including tissue dysplasia, tumor formation, and metastasis. Cadherin-17 (CDH17), belonging to a subclass of 7D-cadherin superfamily, is present in fetal liver and gastrointestinal tract during embryogenesis, but the gene becomes silenced in healthy adult liver and stomach tissues. It functions as a peptide transporter and a cell adhesion molecule to maintain tissue integrity in epithelia. However, recent findings from our group and others have reported aberrant expression of CDH17 in major gastrointestinal malignancies including hepatocellular carcinoma (HCC), stomach and colorectal cancers, and its clinical association with tumor metastasis and advanced tumor stages. Furthermore, alternative splice isoforms and genetic polymorphisms of CDH17 gene have been identified in HCC and linked to an increased risk of HCC. CDH17 is an attractive target for HCC therapy. Targeting CDH17 in HCC can inhibit tumor growth and inactivate Wnt signaling pathway in concomitance with activation of tumor suppressor genes. Further investigation on CDH17-mediated oncogenic signaling and cognate molecular mechanisms would shed light on new targeting therapy on HCC and potentially other gastrointestinal malignancies.

Identification of glycoproteins carrying a target glycan-motif by liquid chromatography/multiple-stage mass spectrometry: identification of Lewis x-conjugated glycoproteins in mouse kidney

Certain glycan motifs in glycoproteins are involved in several biological events and diseases. To understand the roles of these motifs, a method is needed to identify the glycoproteins that carry them. We previously demonstrated that liquid chromatography-multiple-stage mass spectrometry (LC-MSn) allowed for differentiation of oligosaccharides attached to Lewis-motifs, such as Lewisx(Lex, Galbeta1-4(Fucalpha1-3)GlcNAc) from other glycans. We successfully discriminated Lex-conjugated oligosaccharides from other N-linked oligosaccharides derived from mouse kidney proteins by using Lewis-motif-distinctive ions, a deoxyhexose (dHex)+hexose (Hex)+N-acetylhexsosamine (HexNAc) fragment (m/z 512), and a Hex+HexNAc fragment (m/z 366). In the present study, we demonstrated that this method could be used to identify the Lex-conjugated glycoproteins. All proteins in the mouse kidney were digested into peptides, and the fucosylated glycopeptides were enriched by lectin-affinity chromatography. The resulting fucosylated glycopeptides were subjected to two different runs of LC-MSn using a Fourier- transform ion cyclotron resonance mass spectrometer (FTICR-MS) and an ion trap-type mass spectrometer. After the first run, we picked out product ion spectra of the expected Lex-conjugated glycopeptides based on the presence of Lewis-motif-distinctive ions and assigned a peptide+HexNAc or peptide+(dHex)HexNAc fragment in each spectrum. Then the fucosylated glycopeptides were subjected to a second run in which the peptide-related fragments were set as precursor ions. We successfully identified gamma-glutamyl transpeptidase 1 (gamma-GTP1), low-density lipoprotein receptor-related protein 2 (LRP2), and a cubilin precursor as Lex-conjugated glycoproteins by sequencing of 2-5 glycopeptides. In addition, it was deduced that cadherin 16, dipeptidase I, H-2 class I histocompatibility antigen, K-K alpha precursor (H2-Kk), and alanyl (membrane) aminopeptidase could be Lex-conjugated glycoproteins from the good agreement between the experimental and theoretical masses and fragment patterns. The results indicated that our method could be applicable for the identification and screening of glycoproteins carrying target glycan-motifs, such as Lewis epitopes.

Heterotypic trans-interaction of LI- and E-cadherin and their localization in plasmalemmal microdomains

Cadherins are calcium-dependent adhesion molecules important for tissue morphogenesis and integrity. LI-cadherin and E-cadherin are the two prominent cadherins in intestinal epithelial cells. Whereas LI-cadherin belongs to the subfamily of 7D (seven-domain)-cadherins defined by their seven extracellular cadherin repeats and short intracellular domain, E-cadherin is the prototype of classical cadherins with five extracellular domains and a highly conserved cytoplasmic part that interacts with catenins and thereby modulates the organization of the cytoskeleton. Here, we report a specific heterotypic trans-interaction of LI- with E-cadherin, two cadherins of distinct subfamilies. Using atomic force microscopy and laser tweezer experiments, the trans-interaction of LI- and E-cadherin was characterized on the single-molecule level and on the cellular level, respectively. This heterotypic interaction showed similar binding strength (20-52 pN at 200-4000 nm/s) and lifetime (0.8 s) as the respective homotypic interactions of LI- and E-cadherin. VE-cadherin, another classical cadherin, did not bind to LI-cadherin. In enterocytes, LI-cadherin and E-cadherin are located in different membrane regions. LI-cadherin is distributed along the basolateral membrane, whereas the majority of E-cadherin is concentrated in adherens junctions. This difference in membrane distribution was also reflected in Chinese hamster ovary cells stably expressing either LI- or E-cadherin. We found that LI-cadherin is localized almost exclusively in cholesterol-rich fractions, whereas E-cadherin is excluded from these membrane fractions. Given their different membrane localization in enterocytes, the heterotypic trans-interaction of LI- and E-cadherin might play a role during development of the intestinal epithelium when the cells do not yet have elaborate membrane specializations.

Conditional inactivation of the E-cadherin gene in thyroid follicular cells affects gland development but does not impair junction formation

We have conditionally inactivated the E-cadherin gene in the thyroid follicular cells of mouse embryo to unravel its role in thyroid development. We used the Cre-loxP system in which the Cre-recombinase was expressed under the control of the tissue-specific thyroglobulin promoter that becomes active at embryonic d 15. At postnatal d 7, thyroid follicle lumens in the knockout mice were about 30% smaller with respect to control mice and had an irregular shape. E-cadherin was almost completely absent in thyrocytes, beta-catenin was significantly reduced, whereas no change in gamma-catenin was detected. alpha-Catenin was also reduced on the cell plasma membrane. Despite the dramatic loss of E-cadherin and beta-catenin, cell-cell junctions were not affected, the distribution of tight junction proteins was unaltered, and no increase of thyroglobulin circulating in the blood was observed. In addition, we found that other members of the cadherin family, the R-cadherin and the Ksp-cadherin, were expressed in thyrocytes and that their membrane distribution was not altered in the E-cadherin conditional knockout mouse. Our results indicate that E-cadherin has a role in the development of the thyroid gland and in the expression of beta-catenin, but it is not essential for the maintenance of follicular cell adhesion.

Intestinal LI-cadherin acts as a Ca2+-dependent adhesion switch

Cadherins are Ca(2+)-dependent transmembrane glycoproteins that mediate cell-cell adhesion and are important for the structural integrity of epithelia. LI-cadherin and the classical E-cadherin are the predominant two cadherins in the intestinal epithelium. LI-cadherin consists of seven extracellular cadherin repeats and a short cytoplasmic part that does not interact with catenins. In contrast, E-cadherin is composed of five cadherin repeats and a large cytoplasmic domain that is linked via catenins to the actin cytoskeleton. Whereas E-cadherin is concentrated in adherens junctions, LI-cadherin is evenly distributed along the lateral contact area of intestinal epithelial cells. To investigate if the particular structural properties of LI-cadherin result in a divergent homotypic adhesion mechanism, we analyzed the binding parameters of LI-cadherin on the single molecule and the cellular level using atomic force microscopy, affinity chromatography and laser tweezer experiments. Homotypic trans-interaction of LI-cadherin exhibits low affinity binding with a short lifetime of only 1.4 s. Interestingly, LI-cadherin binding responds to small changes in extracellular Ca(2+) below the physiological plasma concentration with a high degree of cooperativity. Thus, LI-cadherin might serve as a Ca(2+)-regulated switch for the adhesive system on basolateral membranes of the intestinal epithelium.