Cadherin switching

Cadherin-11 increases migration and invasion of prostate cancer cells and enhances their interaction with osteoblasts

Cell adhesion molecules have been implicated in the colonization of cancer cells to distant organs. Prostate cancer (PCa) has a propensity to metastasize to bone, and cadherin-11, which is an osteoblast cadherin aberrantly expressed in PCa cells derived from bone metastases, has been shown to play a role in the metastasis of PCa cells to bone. However, the mechanism by which cadherin-11 is involved in this process is not known. Here, we show that expression of cadherin-11 in cadherin-11-negative C4-2B4 cells increases their spreading and intercalation into an osteoblast layer and also stimulates C4-2B4 cell migration and invasiveness. The downregulation of cadherin-11 in cadherin-11-expressing metastatic PC3 cells decreases cell motility and invasiveness. Further, both the juxtamembrane (JMD) and beta-catenin binding domains (CBS) in the cytoplasmic tail of cadherin-11 are required for cell migration and invasion, but not spreading. Gene array analyses showed that several invasion-related genes, including MMP-7 and MMP-15, are upregulated in cadherin-11-expressing, but not in cad11-DeltaJMD-expressing or cad11-DeltaCBS-expressing, C4-2B4 cells. These observations suggest that cadherin-11 not only provides a physical link between PCa cells and osteoblasts but also increases PCa cell motility and invasiveness that may facilitate the metastatic colonization of PCa cells in bone.

P-cadherin expression in gastric carcinoma: its regulation mechanism and prognostic significance

P-cadherin is a member of the cadherin family and is expressed in several solid tumors. This molecule was recently highlighted with the development of a new targeted compound being studied in a clinical trial on solid tumors. In the present study, we examined the protein and messenger RNA (mRNA) expression status of P-cadherin and its promoter methylation in gastric carcinoma cell lines and tissues. Of the 10 cell lines, 4 were found to express P-cadherin protein and mRNA, and the P-cadherin gene was found to be hypomethylated in its promoter region in these cell lines. Nonneoplastic gastric mucosal tissues from gastric carcinoma patients were negative for P-cadherin protein evaluated by immunohistochemistry and Western blotting and had a methylated P-cadherin promoter region. In carcinoma tissues, 70.8% (749/1058) of cases showed P-cadherin protein expression, and P-cadherin positive cases had a well or moderately differentiated histology according to the World Health Organization classification, intestinal-type histology by Lauren classification, and an earlier pT class. Furthermore, patients with P-cadherin expressing tumors had a favorable prognosis by univariate and multivariate survival analyses. In addition, P-cadherin protein expression was found to be significantly correlated with promoter hypomethylation. In summary, P-cadherin is silenced in nonneoplastic gastric mucosa, and P-cadherin expressing tumors constitute a subset of gastric carcinoma with intestinal-type histology and a favorable prognosis. In addition, our findings suggest that P-cadherin promoter methylation underlies the regulation of its expression. These findings may aid patient selection and the interpretation of P-cadherin targeted therapy and clinical trial results.

Zebrafish teeth as a model for repetitive epithelial morphogenesis: dynamics of E-cadherin expression

BACKGROUND

The development of teeth is the result of interactions between competent mesenchyme and epithelium, both of which undergo extensive morphogenesis. The importance of cell adhesion molecules in morphogenesis has long been acknowledged but remarkably few studies have focused on the distribution and function of these molecules in tooth development.

RESULTS

We analyzed the expression pattern of an important epithelial cadherin, E-cadherin, during the formation of first-generation teeth as well as replacement teeth in the zebrafish, using in situ hybridization and whole mount immunostaining to reveal mRNA expression and protein distribution. E-cadherin was detected in every layer of the enamel organ during the different stages of tooth development, but there were slight differences between first-generation and replacement teeth in the strength and distribution of the signal. The dental papilla, which is derived from the mesenchyme, did not show any expression. Remarkably, the crypts surrounding the functional teeth showed an uneven distribution of E-cadherin throughout the pharyngeal region.

CONCLUSIONS

The slight differences between E-cadherin expression in zebrafish teeth and developing mouse and human teeth are discussed in the light of fundamental differences in structural and developmental features of the dentition between zebrafish and mammals. Importantly, the uninterrupted expression of E-cadherin indicates that down-regulation of E-cadherin is not required for formation of an epithelial tooth bud. Further research is needed to understand the role of other cell adhesion systems during the development of teeth and the formation of replacement teeth.

Residual hepatocellular carcinoma after oxaliplatin treatment has increased metastatic potential in a nude mouse model and is attenuated by Songyou Yin

BACKGROUND

The opposite effects of chemotherapy, which enhance the malignancy of treated cancers such as hepatocellular carcinoma (HCC), are not well understood. We investigated this phenomenon and corresponding mechanisms to develop a novel approach for improving chemotherapy efficacy in HCC.

METHODS

Human hepatocellular carcinoma cell lines HepG2 (with low metastatic potential) and MHCC97L (with moderate metastatic potential) were used for the in vitro study. An orthotopic nude mouse model of human HCC was developed using MHCC97L cells. We then assessed the metastatic potential of surviving tumor cells after in vitro and in vivo oxaliplatin treatment. The molecular changes in surviving tumor cells were evaluated by western blot, immunofluorescence, and immunohistochemistry. The Chinese herbal extract Songyou Yin (composed of five herbs) was investigated in vivo to explore its effect on the metastatic potential of oxaliplatin-treated cancer cells.

RESULTS

MHCC97L and HepG2 cells surviving oxaliplatin treatment showed enhanced migration and invasion in vitro. Residual HCC after in vivo oxaliplatin treatment demonstrated significantly increased metastasis to the lung (10/12 vs. 3/12) when re-inoculated into the livers of new recipient nude mice. Molecular changes consistent with epithelial-mesenchymal transition (EMT) were observed in oxaliplatin-treated tumor tissues and verified by in vitro experiments. The Chinese herbal extract Songyou Yin (4.2 and 8.4 g/kg) attenuated EMT and inhibited the enhanced metastatic potential of residual HCC in nude mice (6/15 vs. 13/15 and 3/15 vs. 13/15, respectively).

CONCLUSIONS

The surviving HCC after oxaliplatin treatment underwent EMT and demonstrated increased metastatic potential. Attenuation of EMT by Songyou Yin may improve the efficacy of chemotherapy in HCC.

Expression profile of E-cadherin and N-cadherin in non-muscle-invasive bladder cancer as a novel predictor of intravesical recurrence following transurethral resection

The objective of this study was to investigate the impact of the expression profile of E-cadherin and N-cadherin in newly diagnosed non-muscle-invasive bladder cancer (NMIBC) on the probability of intravesical recurrence in patients undergoing transurethral resection (TUR). This study included 115 consecutive patients diagnosed as having NMIBC following TUR. Expression levels of E-cadherin and N-cadherin in TUR specimens from these patients were measured by immunohistochemical staining. In this series, intravesical recurrence occurred in 35 of 115 patients (30.4%). Immunohistochemical study showed that positive expression of E-cadherin and N-cadherin were noted in 62 (53.9%) and 48 (41.7%) specimens, respectively. Intravesical recurrence was detected in only 7 of 62 patients (11.3%) with positive E-cadherin expression, while 33 of 48 patients (68.8%) with positive N-cadherin expression developed intravesical recurrence. When patients were divided into 4 groups according to the positivities of E-cadherin and N-cadherin expression, intravesical recurrence was detected in 27 of 30 patients (90.0%) with negative E-cadherin as well as positive N-cadherin expression, and the intravesical recurrence-free survival of this group was significantly poorer than those of the remaining 3 groups. Furthermore, negative E-cadherin as well as positive N-cadherin expression was identified as the most powerful independent predictor for intravesical recurrence following TUR on multivariate analysis. These findings suggest that the loss of E-cadherin and gain of N-cadherin expression in on NMIBC appeared to be significantly associated with postoperative recurrence; therefore, the switch from E-cadherin to N-cadherin expression might be involved in the mechanism underlying intravesical recurrence of on NMIBC.

Effect of E-cadherin expression on hormone production in rat anterior pituitary lactotrophs in vitro

Cadherins are a family of transmembrane glycoproteins that mediate cell-to-cell adhesion. A change in cadherin type in cells, i.e., cadherin switching, induces changes in the character of the cell. Recent studies of the developing rat adenohypophysis found that primordial cells co-expressed E- and N-cadherins, but that hormone-producing cells lost E-cadherin and ultimately possessed only N-cadherin. In the present study, we examined the roles of cadherin switching in cytogenesis of anterior pituitary cells by observing prolactin mRNA and protein expression in lactotrophs that were transformed with an E-cadherin expression vector. In hormone-producing cells that were transfected with a pIRES2-ZsGreen1 plasmid with a full-length E-cadherin cDNA (rE-cad-IZ) insert in primary culture, we detected E- and N-cadherins on plasma membrane and E-cadherin in cytoplasm. In these rE-cad-IZ-transfected cells, in situ hybridization revealed prolactin mRNA signals that were at a level identical to that in control cells, while prolactin protein was barely detectable using immunocytochemistry. The mean signal intensity of prolactin protein in rE-cad-IZ-transfected cells was approximately one fourth that in intact cells and in null-IZ-transfected cells (P<0.01). These results suggest that the expression of E-cadherin does not affect prolactin mRNA transcription; rather, it reduces prolactin protein content, presumably by affecting trafficking of secretory granules.

Reduced aquaporin3 expression and survival of keratinocytes in the depigmented epidermis of vitiligo

Activation of the phosphatidylinositol 3-kinase (PI3K)/AKT pathway is critical for the survival of differentiating cells and depends on the E-cadherin-catenin complex. In an earlier study we showed impaired PI3K/AKT activation in vitiliginous keratinocytes (KCs). Recently, aquaporin3 (AQP3) has been reported to co-accumulate with E-cadherin in forming cell-to-cell contacts. Therefore, we examined the expression of AQP3 in vitiliginous KCs and the role of AQP3 in KC survival and differentiation by comparing downstream signaling molecules. AQP3 protein expression was significantly decreased in the depigmented epidermis compared with the normally pigmented epidermis of patients with vitiligo. Transfection of cultured normal human KCs with AQP3 small interfering RNA (siRNA) reduced the expression levels of phosphorylated PI3K, E-cadherin, beta-catenin, and gamma-catenin, regardless of the calcium concentration. These downstream signaling molecules were also decreased in the depigmented epidermis. The results of immunoprecipitation and double staining confirmed colocalization of AQP3 with E-cadherin, as well as an active role of AQP3 in E-cadherin expression of cell-to-cell contacts. Moreover, AQP3 knockdown induced no increase in differentiating markers at high calcium concentrations and reduced survival of KCs, suggesting that reduced AQP3 in vitiliginous KCs might be responsible for their reduced survival.

Matrix-independent stimulation of human tubular epithelial cell migration by Rho kinase inhibitors

Proximal tubular epithelial cells differ from other epithelial cells in the expression of N-cadherin as major adherens junction protein instead of E-cadherin. Migration of proximal epithelial cells (HKC-8) was analyzed by scratch wounding and by a barrier assay, which allowed determination of migration velocity on different extracellular matrices. Migration velocity was about threefold higher on fibronectin compared to collagen IV. The differential migration velocity was reflected by the orientation of F-actin stress fibers. TGF-beta activated secretion of fibronectin and thus increased migration on collagen IV, but did not further promote migration on fibronectin. Pharmacological inhibition of Rho kinases (ROCKs) by Y-27632, hydroxyfasudil and H-1152, or siRNA against ROCKs significantly increased migration velocity independently of the extracellular matrix. Cells at the migration front showed long filopodia, which could not be mimicked by overexpression of consitutively active Cdc42, indicative of a more complex regulation of F-actin structures. N-cadherin was reorganized from tight zipper-like structures into loosened cell-cell contacts upon incubation with Y-27632, but HKC-8 cells still migrated as cohort. Migration through single cell pores in a modified Boyden chamber assay was also stimulated by ROCK inhibitors. ROCK inhibitors enhanced migration of primary cultures of renal tubular cells which consisted of proximal and distal tubular cells expressing N-cadherin and E-cadherin, respectively. There was no indication of a switch in cadherin expression in these cells or a preferential migration of N-cadherin expressing cells. Pharmacologic inhibition of ROCKs may thus favor repair processes in renal tubules by increasing the migratory capacity of tubular epithelial cells.

Arachidonic acid promotes epithelial-to-mesenchymal-like transition in mammary epithelial cells MCF10A

Epidemiological studies and animal models suggest an association between high levels of dietary fat intake and an increased risk of breast cancer. Cancer progression requires the development of metastasis, which is characterized by an increase in cell motility and invasion. Epithelial-to-mesenchymal transition (EMT) is a process, by which epithelial cells are transdifferentiated to a more mesenchymal state. A similar process takes place during tumor progression, when carcinoma cells stably or transiently lose epithelial polarities and acquire a mesenchymal phenotype. Arachidonic acid (AA) is a fatty acid that mediates cellular processes, such as cell survival, angiogenesis, chemotaxis, mitogenesis, migration and apoptosis. However, the role of AA on the EMT process in human mammary epithelial cells remains to be studied. We demonstrate here that AA promotes an increase in vimentin and N-cadherin expression, MMP-9 secretion, a decrease in E-cadherin junctional levels, and the activation of FAK, Src and NF-kappaB in MCF10A cells. Furthermore, AA also promotes cell migration in an Src kinase activity-dependent fashion. In conclusion, our results demonstrate, for the first time, that AA promotes an epithelial-to-mesenchymal-like transition in MCF10A human mammary non-tumorigenic epithelial cells.

GATA3 inhibits breast cancer metastasis through the reversal of epithelial-mesenchymal transition

GATA3, a transcription factor that regulates T lymphocyte differentiation and maturation, is exclusively expressed in early stage well differentiated breast cancers but not in advanced invasive cancers. However, little is understood regarding its activity and the mechanisms underlying this differential expression in cancers. Here, we employed GATA3-positive, non-invasive (MCF-7) and GATA3-negative, invasive (MDA-MB-231) breast cancer cells to define its role in the transformation between these two distinct phenotypes. Ectopic expression of GATA3 in MDA-MB-231 cells led to a cuboidal-like epithelial phenotype and reduced cell invasive activity. These cells also increased E-cadherin expression but decreased levels of vimentin, N-cadherin, and MMP-9. Further, MDA-MB-231 cells expressing GATA3 grew smaller primary tumors without metastasis compared with larger metastatic tumors derived from control MDA-MB-231 cells in xenografted mice. GATA3 was found to induce E-cadherin expression through binding GATA-like motifs located in the E-cadherin promoter. Blockade of GATA3 using small interfering RNA gene knockdown in MCF-7 cells triggered fibroblastic transformation and cell invasion, resulting in distant metastasis. Studies of human breast cancer showed that GATA3 expression correlated with elevated E-cadherin levels, ER expression, and long disease-free survival. These data suggest that GATA3 drives invasive breast cancer cells to undergo the reversal of epithelial-mesenchymal transition, leading to the suppression of cancer metastasis.

CX3CR1/CX3CL1 axis negatively controls glioma cell invasion and is modulated by transforming growth factor-β1

The chemokine CX3CL1 is constitutively expressed in the central nervous system by neurons and astrocytes controlling neuronal survival and neurotransmission. In this work, we analyzed the expression and function of the chemokine CX3CL1 and its receptor, CX3CR1, by human glioma cells. We show that both molecules are expressed on the tumor cell plasma membrane and that soluble CX3CL1 accumulates in the culture supernatants, indicating that the chemokine is constitutively released. We found that CX3CR1 is functional, as all the cell lines adhered to immobilized recombinant CX3CL1 and migrated in response to the soluble form of this chemokine. In addition, the blockade of endogenous CX3CL1 function by means of a neutralizing monoclonal antibody markedly delayed tumor cell aggregation and increased their invasiveness. We also show that CX3CL1 expression is potently modulated by the transforming growth factor-beta1 (TGF-beta1), a key regulator of glioma cell invasiveness. Indeed, both the treatment of glioma cells with recombinant TGF-beta1 and the inhibition of its endogenous expression by siRNA showed that TGF-beta1 decreases CX3CL1 mRNA and protein expression. Overall, our results indicate that endogenously expressed CX3CL1 negatively regulates glioma invasion likely by promoting tumor cell aggregation, and that TGF-beta1 inhibition of CX3CL1 expression might contribute to glioma cell invasive properties.

Cadherin switching and activation of p120 catenin signaling are mediators of gonadotropin-releasing hormone to promote tumor cell migration and invasion in ovarian cancer

Gonadotropin-releasing hormone (GnRH) receptor expression is often elevated in ovarian cancer, but its potential role in ovarian cancer metastasis has just begun to be revealed. Cadherin switching is a crucial step during tumorigenesis, particularly in metastasis. Here, we showed that GnRH is an inducer of E- to P-cadherin switching, which is reminiscent of that seen during ovarian tumor progression. Overexpression of P-cadherin significantly enhanced, whereas knockdown of P-cadherin reduced migration and invasion regardless of E-cadherin expression, suggesting that inappropriate expression of P-cadherin contributes to the invasive phenotype. These effects of P-cadherin were mediated by activation of the Rho GTPases, Rac1, and Cdc42, through accumulation of p120 catenin (p120(ctn)) in the cytoplasm. The use of p120(ctn) small interfering RNA or chimeric cadherin construct to inhibit p120(ctn) expression and cytoplasmic localization, respectively, resulted in significant inhibition of cell migration and invasion, with a concomitant reduction in Rac1 and Cdc42 activation, confirming that the effect was p120(ctn) specific. Similarly, the migratory/invasive phenotype could be reversed by expression of dominant-negative Rac1 and Cdc42. These results identify for the first time cadherin switching and p120(ctn) signaling as important targets of GnRH function and as novel mediators of invasiveness and tumor progression in ovarian cancer.

The RhoA activator GEF-H1/Lfc is a transforming growth factor-beta target gene and effector that regulates alpha-smooth muscle actin expression and cell migration

TGFβ induces various responses, including Rho signaling. How TGFβ stimulates Rho is poorly understood. Our data indicate that GEF-H1 is a target and effector of TGFβ to regulate Rho signaling, gene expression, and cell migration, suggesting that it represents a new marker and possible therapeutic target for degenerative and fibrotic diseases.

Maintenance of the epithelial phenotype is crucial for tissue homeostasis. In the retina, dedifferentiation and loss of integrity of the retinal pigment epithelium (RPE) leads to retinal dysfunction and fibrosis. Transforming growth factor (TGF)-β critically contributes to RPE dedifferentiation and induces various responses, including increased Rho signaling, up-regulation of α-smooth muscle actin (SMA), and cell migration and dedifferentiation. Cellular TGF-β responses are stimulated by different signal transduction pathways: some are Smad dependent and others Smad independent. Alterations in Rho signaling are crucial to both types of TGF-β signaling, but how TGF-β-stimulates Rho signaling is poorly understood. Here, we show that primary RPE cells up-regulated GEF-H1 in response to TGF-β. GEF-H1 was the only detectable Rho exchange factor increased by TGF-β1 in a genome-wide expression analysis. GEF-H1 induction was Smad4-dependant and led to Rho activation. GEF-H1 inhibition counteracted α-SMA up-regulation and cell migration. In patients with retinal detachments and fibrosis, migratory RPE cells exhibited increased GEF-H1 expression, indicating that induction occurs in diseased RPE in vivo. Our data indicate that GEF-H1 is a target and functional effector of TGF-β by orchestrating Rho signaling to regulate gene expression and cell migration, suggesting that it represents a new marker and possible therapeutic target for degenerative and fibrotic diseases.

Expression analysis of epithelial cadherin and related proteins in IBH-6 and IBH-4 human breast cancer cell lines

Epithelial cadherin (E-cadherin) is a 120 kDa cell-cell adhesion molecule involved in the establishment of epithelial adherens junctions. It is connected to the actin cytoskeleton by adaptor proteins such as beta-catenin. Loss of E-cadherin expression/function has been related to tumor progression and metastasis. Several molecules associated with down-regulation of E-cadherin have been described, within them neural cadherin, Twist and dysadherin. Human breast cancer cell lines IBH-6 and IBH-4 were developed from ductal primary tumors and show characteristic features of malignant epithelial cells. In this study expression of E-cadherin and related proteins in IBH-6 and IBH-4 cell lines was evaluated. In IBH-6 and IBH-4 cell extracts, only an 89 kDa E-cadherin form (Ecad89) was detected, which is truncated at the C-terminus and is present at low levels. Moreover, no accumulation of the 86 kDa E-cadherin ectodomain and of the 38 kDa CTF1 fragment was observed. IBH-6 and IBH-4 cells showed an intracellular scattered E-cadherin localization. beta-catenin accompanied E-cadherin localization, and actin stress fibers were identified in both cell types. E-cadherin mRNA levels were remarkably low in IBH-6 and IBH-4 cells. The E-cadherin mRNA and genomic sequence encoding exons 14-16 could not be amplified in either cell line. Neither the mRNA nor the protein of neural cadherin and dysadherin were detected. Up-regulation of Twist mRNA was found in both cell lines. In conclusion, IBH-6 and IBH-4 breast cancer cells show down-regulation of E-cadherin expression with aberrant protein localization, and up-regulation of Twist; these features can be related to their invasive/metastatic characteristics.

Influence of hepatic artery occlusion on tumor growth and metastatic potential in a human orthotopic hepatoma nude mouse model: relevance of epithelial-mesenchymal transition

Hepatic artery ligation (HAL), transarterial embolization (TAE), and transarterial chemoembolization (TACE) have been treatment choices for unresectable hepatocellular carcinoma (HCC). Obstruction of tumor blood supply is one of the most important mechanisms of these therapeutics measures. Here we introduced HAL into a metastatic human HCC orthotopic nude mouse model (using MHCC97L and HepG2 cell lines) to examine the effects of hepatic blood flow obstruction on the metastatic potential of hepatic tumor cells, and to investigate the mechanisms underlying these effects. Our results indicated that HAL inhibited tumor growth but concomitantly elicited tumor adaptation and progression, with increased potential for invasion and distant metastases. The underlying proinvasive mechanism of HAL appeared to be associated with enhanced intratumoral hypoxia and epithelial-mesenchymal transition (EMT) due to hypoxia. This was in accord with the in vitro response of MHCC97L and HepG2 cells to hypoxia. The therapeutic effects of HAL could be enhanced by the phosphatidyl inositol 3-kinase (PI3K) inhibitor LY294002, through arrest of EMT in hepatic tumor cells. It could be useful in the development of mechanism-based combination therapies to enhance the initial antitumor response.

Morphogenesis of the thyroid gland

Congenital hypothyroidism is mainly due to structural defects of the thyroid gland, collectively known as thyroid dysgenesis. The two most prevalent forms of this condition are abnormal localization of differentiated thyroid tissue (thyroid ectopia) and total absence of the gland (athyreosis). The clinical picture of thyroid dysgenesis suggests that impaired specification, proliferation and survival of thyroid precursor cells and loss of concerted movement of these cells in a distinct spatiotemporal pattern are major causes of malformation. In normal development the thyroid primordium is first distinguished as a thickening of the anterior foregut endoderm at the base of the prospective tongue. Subsequently, this group of progenitors detaches from the endoderm, moves caudally and ultimately differentiates into hormone-producing units, the thyroid follicles, at a distant location from the site of specification. In higher vertebrates later stages of thyroid morphogenesis are characterized by shape remodeling into a bilobed organ and the integration of a second type of progenitors derived from the caudal-most pharyngeal pouches that will differentiate into C-cells. The present knowledge of thyroid developmental dynamics has emerged from embryonic studies mainly in chicken, mouse and more recently also in zebrafish. This review will highlight the key morphogenetic steps of thyroid organogenesis and pinpoint which crucial regulatory mechanisms are yet to be uncovered. Considering the co-incidence of thyroid dysgenesis and congenital heart malformations the possible interactions between thyroid and cardiovascular development will also be discussed.

Novel peptide mimetic small molecules of the HAV motif in N-cadherin inhibit N-cadherin-mediated neurite outgrowth and cell adhesion

The cell adhesion molecule, N-cadherin, stabilizes cell-cell junctions and promotes cellular migration during tissue morphogenesis in development. N-cadherin is also implicated in mediating tumor progression and metastasis in cancer. Therefore, developing antagonists of N-cadherin adhesion may be of therapeutic value in cancer treatment. The amino acid sequence HAV in the extracellular domain of N-cadherin is required for N-cadherin-mediated adhesion and migration. A cyclic peptide, ADH-1, derived from the N-cadherin HAV site is an effective antagonist of N-cadherin-mediated processes and is now in clinical trials for cancer chemotherapy. Because it is a peptide, ADH-1 has certain limitations as a drug, namely its metabolic instability and lack of oral delivery. Adherex set out to identify small molecule antagonists of N-cadherin, which would be more amenable to therapeutic use. Using three-dimensional computational screening, Adherex identified a set of small molecules as potential antagonists with sufficient structural similarity to the HAV region of N-cadherin. We tested the ability of these small molecules to interfere with two N-cadherin-dependent processes: neurite outgrowth (axonal migration) and N-cadherin-dependent cell adhesion. We identified 21 N-cadherin antagonists of varying potency. More importantly, our studies demonstrate that these compounds are significantly more potent than ADH-1 at perturbing N-cadherin-mediated processes. The IC(50) of ADH-1 is 2.33 mM while the IC(50) of the small molecules ranges from 4.5 to 30 microM. Given the efficacy of ADH-1 for treating cancer, these small molecule antagonists will be highly effective in treatment of cancer metastasis and conditions of aberrant neurite outgrowth, such as neuropathic pain.

Involvement of members of the cadherin superfamily in cancer

We review the role of cadherins and cadherin-related proteins in human cancer. Cellular and animal models for human cancer are also dealt with whenever appropriate. E-cadherin is the prototype of the large cadherin superfamily and is renowned for its potent malignancy suppressing activity. Different mechanisms for inactivating E-cadherin/CDH1 have been identified in human cancers: inherited and somatic mutations, aberrant protein processing, increased promoter methylation, and induction of transcriptional repressors such as Snail and ZEB family members. The latter induce epithelial mesenchymal transition, which is also associated with induction of "mesenchymal" cadherins, a hallmark of tumor progression. VE-cadherin/CDH5 plays a role in tumor-associated angiogenesis. The atypical T-cadherin/CDH13 is often silenced in cancer cells but up-regulated in tumor vasculature. The review also covers the status of protocadherins and several other cadherin-related molecules in human cancer. Perspectives for emerging cadherin-related anticancer therapies are given.

Rearrangements of the actin cytoskeleton and E-cadherin-based adherens junctions caused by neoplasic transformation change cell-cell interactions

E-cadherin-mediated cell-cell adhesion, which is essential for the maintenance of the architecture and integrity of epithelial tissues, is often lost during carcinoma progression. To better understand the nature of alterations of cell-cell interactions at the early stages of neoplastic evolution of epithelial cells, we examined the line of nontransformed IAR-2 epithelial cells and their descendants, lines of IAR-6-1 epithelial cells transformed with dimethylnitrosamine and IAR1170 cells transformed with N-RasG12D. IAR-6-1 and IAR1170 cells retained E-cadherin, displayed discoid or polygonal morphology, and formed monolayers similar to IAR-2 monolayer. Fluorescence staining, however, showed that in IAR1170 and IAR-6-1 cells the marginal actin bundle, which is typical of nontransformed IAR-2 cells, disappeared, and the continuous adhesion belt (tangential adherens junctions (AJs)) was replaced by radially oriented E-cadherin-based AJs. Time-lapse imaging of IAR-6-1 cells stably transfected with GFP-E-cadherin revealed that AJs in transformed cells are very dynamic and unstable. The regulation of AJ assembly by Rho family small GTPases was different in nontransformed and in transformed IAR epithelial cells. As our experiments with the ROCK inhibitor Y-27632 and the myosin II inhibitor blebbistatin have shown, the formation and maintenance of radial AJs critically depend on myosin II-mediated contractility. Using the RNAi technique for the depletion of mDia1 and loading cells with N17Rac, we established that mDia1 and Rac are involved in the assembly of tangential AJs in nontransformed epithelial cells but not in radial AJs in transformed cells. Neoplastic transformation changed cell-cell interactions, preventing contact paralysis after the establishment of cell-cell contact and promoting dynamic cell-cell adhesion and motile behavior of cells. It is suggested that the disappearance of the marginal actin bundle and rearrangements of AJs may change the adhesive function of E-cadherin and play an active role in migratory activity of carcinoma cells.

Induction of corneal myofibroblasts by lens-derived transforming growth factor beta1 (TGFbeta1): a transgenic mouse model

PURPOSE

Transforming growth factor beta (TGFbeta) is an important cytokine in corneal development and wound healing. Transgenic mice that express an active form of human TGFbeta1 driven by a lens-specific promoter were used in the current study to determine the biological effects of lens-derived TGFbeta1 on postnatal corneal development and homeostasis.

METHODS

The postnatal corneal changes in the TGFbeta1 transgenic mice were examined by fluorescein labeling and histology. Epithelial/endothelial-to-mesenchymal transition (E/EnMT) in the transgenic mouse cornea was demonstrated by immunostaining for alpha-smooth muscle actin (alpha-SMA) and cadherin-11. Expression of E- and N-cadherin in the corneal epithelial and endothelial cells, respectively, was analyzed by in situ hybridization.

RESULTS

Among the established TGFbeta1 transgenic lines, mice from line OVE853 and OVE917 had normal-sized eyeballs but developed a corneal haze after eyelid opening. Histological examination showed that prenatal corneal development appeared to be normal. However, after postnatal day 7 (P7), the corneal endothelial cells in transgenic line OVE853 began to lose normal cell-cell contact and basement membrane structure. The endothelial layer was eventually absent in the inner surface of the transgenic mouse cornea. The morphological changes in the cornea correlated with abnormal expression of alpha-SMA, a molecular marker of EMT, and stress fiber formation in myofibroblast-like cells, which initially appeared in the corneal endothelial layer and subsequently in the corneal epithelial and stromal layers. The E/EnMT in the transgenic mouse cornea was further demonstrated by loss of E- and N-cadherin expression in the corneal epithelial and endothelial cells, respectively, and meanwhile increasing expression of cadherin-11 in both corneal epithelium and stroma.

CONCLUSIONS

Elevated levels of active TGFbeta1 in the anterior chamber can lead to myofibroblast formation in the corneal endothelial layer and subsequently in the corneal epithelial and stromal layers. Our data suggest that the levels of biologically active TGFbeta in the aqueous humor must be under tight control to maintain corneal homeostasis. TGFbeta1 is the major cytokine during wound healing. Therefore, our findings also suggest a potential mechanism to explain the loss of corneal endothelial barrier and corneal opacification after intraocular surgery or trauma.

Cadherins as novel targets for anti-cancer therapy

The cell adhesion molecules N-, VE- and OB-cadherin have been implicated as regulators of tumor growth and metastasis. We discuss evidence that N- and VE-cadherin play a key role in promoting blood vessel formation and stability, processes which are essential for tumor growth. Secondly, we describe the potential involvement of N- and OB-cadherin in the metastatic process. Finally, studies concerning the effects of the N-cadherin antagonist designated ADH-1 on tumor growth are presented. Collectively, these observations suggest that antagonists of N-, VE- and OB-cadherin would be useful as anti-cancer agents.

Potential roles of myosin VI in cell motility

There is now increasing evidence that myosin motor proteins, together with the dynamic actin filament machinery and associated adhesion proteins, play crucial roles in the events leading to motility at the leading edge of migrating cells. Myosins exist as a large superfamily of diverse ATP-dependent motors, and in the present review, we focus on the unique minus-end-directed myosin VI, briefly discussing its potential functions in cell motility.

Discovering the molecular components of intercellular junctions--a historical view

The organization of metazoa is based on the formation of tissues and on tissue-typical functions and these in turn are based on cell-cell connecting structures. In vertebrates, four major forms of cell junctions have been classified and the molecular composition of which has been elucidated in the past three decades: Desmosomes, which connect epithelial and some other cell types, and the almost ubiquitous adherens junctions are based on closely cis-packed glycoproteins, cadherins, which are associated head-to-head with those of the hemi-junction domain of an adjacent cell, whereas their cytoplasmic regions assemble sizable plaques of special proteins anchoring cytoskeletal filaments. In contrast, the tight junctions (TJs) and gap junctions (GJs) are formed by tetraspan proteins (claudins and occludins, or connexins) arranged head-to-head as TJ seal bands or as paracrystalline connexin channels, allowing intercellular exchange of small molecules. The by and large parallel discoveries of the junction protein families are reported.

Suppression of androgen-independent prostate cancer cell aggressiveness by FTY720: validating Runx2 as a potential antimetastatic drug screening platform

PURPOSE

Previously, FTY720 was found to possess potent anticancer effects on various types of cancer. In the present study, we aimed to first verify the role of Runx2 in prostate cancer progression and metastasis, and, subsequently, assessed if FTY720 could modulate Runx2 expression, thus interfering downstream events regulated by this protein.

EXPERIMENTAL DESIGN

First, the association between Runx2 and prostate cancer progression was assessed using localized prostate cancer specimens and mechanistic investigation of Runx2-induced cancer aggressiveness was then carried out. Subsequently, the effect of FTY720 on Runx2 expression and transcriptional activity was investigated using PC-3 cells, which highly expressed Runx2 protein. Last, the involvement of Runx2 in FTY720-induced anticancer effects was evaluated by modulating Runx2 expression in various prostate cancer cell lines.

RESULTS

Runx2 nuclear expression was found to be up-regulated in prostate cancer and its expression could be used as a predictor of metastasis in prostate cancer. Further mechanistic studies indicated that Runx2 accelerated prostate cancer aggressiveness through promotion of cadherin switching, invasion toward collagen I, and Akt activation. Subsequently, we found that FTY720 treatment down-regulated Runx2 expression and its transcriptional activity, as well as inhibited its regulated downstream events. More importantly, silencing Runx2 in PC-3 enhanced FTY720-induced anticancer effects as well as cell viability inhibition, whereas overexpressing Runx2 in 22Rv1 that expressed very low endogenous Runx2 protein conferred resistance in the same events.

CONCLUSION

This study provided a novel mechanism for the anticancer effect of FTY720 on advanced prostate cancer, thus highlighting the therapeutic potential of this drug in treating this disease.

Cordial connections: molecular ensembles and structures of adhering junctions connecting interstitial cells of cardiac valves in situ and in cell culture

Remarkable efforts have recently been made in the tissue engineering of heart valves to improve the results of valve transplantations and replacements, including the design of artificial valves. However, knowledge of the cell and molecular biology of valves and, specifically, of valvular interstitial cells (VICs) remains limited. Therefore, our aim has been to determine and localize the molecules forming the adhering junctions (AJs) that connect VICs in situ and in cell culture. Using biochemical and immunolocalization methods at the light- and electron-microscopic levels, we have identified, in man, cow, sheep and rat, the components of VIC-connecting AJs in situ and in cell culture. These AJs contain, in addition to the transmembrane glycoproteins N-cadherin and cadherin-11, the typical plaque proteins alpha- and beta-catenin as well as plakoglobin and p120, together with minor amounts of protein p0071, i.e. a total of five plaque proteins of the armadillo family. While we can exclude the occurrence of desmogleins, desmocollins and desmoplakin, we have noted with surprise that AJs of VICs in cell cultures, but not those growing in the valve tissue, contain substantial amounts of the desmosomal plaque protein, plakophilin-2. Clusters of AJs occur not only on the main VIC cell bodies but are also found widely dispersed on their long filopodia thus forming, in the tissue, a meshwork that, together with filopodial attachments to paracrystalline collagen fiber bundles, establishes a three-dimensional suprastructure, the role of which is discussed with respect to valve formation, regeneration and function.

Molecular mechanisms controlling E-cadherin expression in breast cancer

Disruption of cell-cell adhesion, which is essential for the maintenance of epithelial plasticity and is mediated by a class of proteins called cadherins, is an initial event in the progression of cancer. Cadherins are Ca(2+)-dependent transmembrane proteins that are associated with actin via other cytoplasmic proteins. Disruption of cell-cell adhesion during cancer progression is an important event during cancer initiation and metastasis. E-cadherin, one of the most widely studied tumor suppressors in breast cancer, belongs to a family of calcium-dependent cell adhesion molecules. Various signaling molecules and transcription factors regulate the expression of E-cadherin. Loss of E-cadherin has been reported to induce epithelial-mesenchymal transition in several cancers. This review highlights recent advances in defining the mechanisms that regulate E-cadherin expression in breast cancer.

Out, in and back again: PtdIns(4,5)P(2) regulates cadherin trafficking in epithelial morphogenesis

The morphogenesis of epithelial cells in the tissue microenvironment depends on the regulation of the forces and structures that keep cells in contact with their neighbours. The formation of cell-cell contacts is integral to the establishment and maintenance of epithelial morphogenesis. In epithelial tissues, the misregulation of the signalling pathways that control epithelial polarization induces migratory and invasive cellular phenotypes. Many cellular processes influence cadherin targeting and function, including exocytosis, endocytosis and recycling. However, the localized generation of the lipid messenger PtdIns(4,5)P(2) is emerging as a fundamental signal controlling all of these processes. The PtdIns(4,5)P(2)-generating enzymes, PIPKs (phosphatidylinositol phosphate kinases) are therefore integral to these pathways. By the spatial and temporal targeting of PIPKs via the actions of its functional protein associates, PtdIns(4,5)P(2) is generated at discrete cellular locales to provide the cadherin-trafficking machinery with its required lipid messenger. In the present review, we discuss the involvement of PtdIns(4,5)P(2) and the PIPKs in the regulation of the E-cadherin (epithelial cadherin) exocytic and endocytic machinery, the modulation of actin structures at sites of adhesion, and the direction of cellular pathways which determine the fate of E-cadherin and cell-cell junctions. Recent work is also described that has defined phosphoinositide-mediated E-cadherin regulatory pathways by the use of organismal models.

Regulatory roles of the cadherin superfamily

Charged with the task of providing a molecular link between adjacent cells, the cadherin superfamily consists of over 100 members and populates the genomes of organisms ranging from vertebrates to cniderians. This breadth hints at what decades of research has confirmed: that cadherin-based adhesion and signaling events regulate diverse cellular processes including cell-sorting, differentiation, cell survival, proliferation, cell polarity, and cytoskeletal organization.

Cadherins and cancer: how does cadherin dysfunction promote tumor progression?

It has long been recognized that the cell-cell adhesion receptor, E-cadherin, is an important determinant of tumor progression, serving as a suppressor of invasion and metastasis in many contexts. Yet how the loss of E-cadherin function promotes tumor progression is poorly understood. In this review, we focus on three potential underlying mechanisms: the capacity of E-cadherin to regulate beta-catenin signaling in the canonical Wnt pathway; its potential to inhibit mitogenic signaling through growth factor receptors and the possible links between cadherins and the molecular determinants of epithelial polarity. Each of these potential mechanisms provides insights into the complexity that is likely responsible for the tumor-suppressive action of E-cadherin.

Cadherins and cancer: how does cadherin dysfunction promote tumor progression?

It has long been recognized that the cell-cell adhesion receptor, E-cadherin, is an important determinant of tumor progression, serving as a suppressor of invasion and metastasis in many contexts. Yet how the loss of E-cadherin function promotes tumor progression is poorly understood. In this review, we focus on three potential underlying mechanisms: the capacity of E-cadherin to regulate beta-catenin signaling in the canonical Wnt pathway; its potential to inhibit mitogenic signaling through growth factor receptors and the possible links between cadherins and the molecular determinants of epithelial polarity. Each of these potential mechanisms provides insights into the complexity that is likely responsible for the tumor-suppressive action of E-cadherin.

E-cadherin/catenin complexes are formed cotranslationally in the endoplasmic reticulum/Golgi compartments

Cadherins are synthesized with a proregion that lies between a short amino-terminal signal sequence and the first extracellular domain. Following synthesis, the proregion is cleaved, an event that is mandatory for the mature cadherin to function in adhesion. The authors have previously reported that catenins coimmunoprecipate with pro-N-cadherin, and that the N-cadherin/catenin complex forms in the Golgi/endoplasmic reticulum. It is clear that N- and E-cadherin confer significantly different characteristics on cells, and it is possible that N- and E-cadherin/catenin complex formation is equally different. To investigate this, the authors generated an antibody against the proregion of E-cadherin and have used it to examine the assembly of the E-cadherin/catenin complex.

Regulation of cadherin trafficking

Cadherins are a large family of cell-cell adhesion molecules that tether cytoskeletal networks of actin and intermediate filaments to the plasma membrane. This function of cadherins promotes tissue organization and integrity, as demonstrated by numerous disease states that are characterized by the loss of cadherin-based adhesion. However, plasticity in cell adhesion is often required in cellular processes such as tissue patterning during development and epithelial migration during wound healing. Recent work has revealed a pivotal role for various membrane trafficking pathways in regulating cellular transitions between quiescent adhesive states and more dynamic phenotypes. The regulation of cadherins by membrane trafficking is emerging as a key player in this balancing act, and studies are beginning to reveal how this process goes awry in the context of disease. This review summarizes the current understanding of how cadherins are routed and how the interface between cadherins and membrane trafficking pathways regulates cell surface adhesive potential. Particular emphasis is placed on the regulation of cadherin trafficking by catenins and the interplay between growth factor signaling pathways and cadherin endocytosis.

Co-operative roles for E-cadherin and N-cadherin during lens vesicle separation and lens epithelial cell survival

The classical cadherins are known to have both adhesive and signaling functions. It has also been proposed that localized regulation of cadherin activity may be important in cell assortment during development. In the context of eye development, it has been suggested that cadherins are important for separation of the invaginated lens vesicle from the surface ectoderm. To test this hypothesis, we conditionally deleted N-cadherin or E-cadherin from the presumptive lens ectoderm of the mouse. Conditional deletion of either cadherin alone did not produce a lens vesicle separation defect. However, these conditional mutants did exhibit common structural deficits, including microphthalmia, severe iris hyperplasia, persistent vacuolization within the fibre cell region, and eventual lens epithelial cell deterioration. To assess the co-operative roles of E-cadherin and N-cadherin within the developing lens, double conditional knockout embryos were generated. These mice displayed distinct defects in lens vesicle separation and persistent expression of another classical cadherin, P-cadherin, within the cells of the persistent lens stalk. Double mutant lenses also exhibited severe defects in lens epithelial cell adhesion and survival. Finally, the severity of the lens phenotype was shown to be sensitive to the number of wild-type E- and N-cadherin alleles. These data suggest that the co-operative expression of both E- and N-cadherin during lens development is essential for normal cell sorting and subsequent lens vesicle separation.

Immunohistochemical observation of co-expression of E- and N-cadherins in rat organogenesis

Cadherins are a family of transmembrane glycoproteins that mediate cell-to-cell adhesion. Isoforms, including E- and N-cadherin, have been identified and shown to regulate morphogenesis through homophilic binding. In the ontogeny, the expressions of E- and N-cadherin change spatiotemporally, and the changes in cadherin isoforms, called cadherin switching, impact the mechanical adhesion of cells. Furthermore, cadherin functions as a receptor that transfers information from outside to inside cells, and in terms of switching, it affects cell phenotypes. To observe the expression patterns of E- and N-cadherins during embryogenesis and to identify cells that transiently coexpress both cadherins, we employed a recently developed immunohistochemical double staining technique in rat fetuses. At embryonic day 9, embryonic ectodermal cells more dominantly expressed E-cadherin, while mesodermal cells more dominantly expressed N-cadherin. At embryonic day 10, the expression pattern of E-cadherin in the surface ectoderm and endoderm and that of N-cadherin in the neuroectoderm were established. After embryonic day 10, unique co-expression of E- and N-cadherin was observed in primordia, such as the bulbus cordis, otic pit, notochord, and Rathke’s pouch. In the present study, it was possible to visualize the expression patterns of E- and N-cadherin during early fetal development, which enabled us to morphologically clarify cadherin switching.

Organization and signaling of endothelial cell-to-cell junctions in various regions of the blood and lymphatic vascular trees

Adhesive intercellular junctions between endothelial cells are formed by tight junctions and adherens junctions. In addition to promoting cell-to-cell adhesion, these structures regulate paracellular permeability, contact inhibition of endothelial cell growth, cell survival, and maintenance of cell polarity. Furthermore, adherens junctions are required for the correct organization of new vessels during embryo development or during tissue proliferation in the adult. Extensive research on cultured epithelial and endothelial cells has resulted in the identification of many molecular components of tight junctions and adherens junctions. Such studies have revealed the complexity of these structures, which are formed by membrane-associated adhesion proteins and a network of several intracellular signaling partners. This review focuses on the structural organization of junctional structures and their functional interactions in the endothelium of blood vessels and lymphatics. We emphasize the way that these structures regulate endothelial cell homeostasis by transferring specific intracellular signals and by modulating activation and signaling of growth factor receptors.

Molecular and pathological signatures of epithelial-mesenchymal transitions at the cancer invasion front

Reduction of epithelial cell-cell adhesion via the transcriptional repression of cadherins in combination with the acquisition of mesenchymal properties are key determinants of epithelial-mesenchymal transition (EMT). EMT is associated with early stages of carcinogenesis, cancer invasion and recurrence. Furthermore, the tumor stroma dictates EMT through intensive bidirectional communication. The pathological analysis of EMT signatures is critically, especially to determine the presence of cancer cells at the resection margins of a tumor. When diffusion barriers disappear, EMT markers may be detected in sera from cancer patients. The detection of EMT signatures is not only important for diagnosis but can also be exploited to enhance classical chemotherapy treatments. In conclusion, further detailed understanding of the contextual cues and molecular mediators that control EMT will be required in order to develop diagnostic tools and small molecule inhibitors with potential clinical implications.

Differential growth factor regulation of N-cadherin expression and motility in normal and malignant oral epithelium

Aberrant expression of N-cadherin is associated with tumor progression in squamous cell carcinomas (SCCs). Consequently, we examined the regulation of N-cadherin by TGFbeta1, an important mediator of keratinocyte and SCC function. N-cadherin expression was increased in oral SCC (OSCC) cell lines, regulating motility and correlating with TGFbeta1 production. Moreover, in normal keratinocytes TGFbeta1 increased expression of N-cadherin to regulate motility. TGFbeta1-mediated N-cadherin expression in the oral keratinocytes was blocked using siRNA targeting Smads. Unexpectedly, we found that EGF blocked TGFbeta1-mediated N-cadherin expression in oral keratinocytes and not in OSCC cells. Mechanistically, EGF enhanced Smad phosphorylation in the linker region, and attenuated TGFbeta1-mediated phosphorylation of Smad at the C-terminus, localization of Smad to the nucleus as well as Smad-driven promoter activity exclusively in oral keratinocytes but not in OSCC cells. The effect of EGF on TGFbeta1-mediated Smad-driven promoter activity and N-cadherin expression was reversed when activation of ERK1/2 was blocked. Although EGF and TGFbeta1 independently promoted migration of both oral keratinocytes and OSCC cells, EGF decreased TGFbeta1-mediated migration of oral keratinocytes but enhanced migration of OSCC cells. Together, these data support a model wherein EGF signaling has an important negative regulatory role on TGFbeta1-mediated N-cadherin expression and motility in normal oral keratinocytes, and in which loss of this regulatory mechanism accompanies malignant transformation of the oral epithelium.

Rho GTPases in cancer cell biology

Rho GTPases contribute to multiple cellular processes that could affect cancer progression, including cytoskeletal dynamics, cell cycle progression, transcriptional regulation, cell survival and vesicle trafficking. In vitro several Rho GTPases have oncogenic activity and/or can promote cancer cell invasion, and this correlates with increased expression and activity in a variety of cancers. Conversely, other family members appear to act as tumour suppressors and are deleted, mutated or downregulated in some cancers. Genetic models are starting to provide new information on how Rho GTPases affect cancer development and progression. Here, we discuss how Rho GTPases could contribute to different steps of cancer progression, including proliferation, survival, invasion and metastasis.