Modulating the strength of cadherin adhesion: evidence for a novel adhesion complex

Identification of differentially expressed genes and signaling pathways in Gaoyou duck ovary at different physiological stages

Introduction

Gaoyou duck is famous in China and abroad for its good production of double-yolk eggs. However, there has been no systematic research on the egg-laying characteristics of the Gaoyou duck, which limits the development and utilization of breed resource.

Methods

To identify the essential genes related to ovarian development, the transcriptome profiles of the ovaries of Gaoyou ducks at different physiological stages were analyzed. The transcriptome profiles of the ovaries of Gaoyou ducks at 150 d (before laying), 240 d (egg laying) and 500 d (nesting) were constructed, and the differentially expressed genes (DEGs) underwent GO (gene ontology) and KEGG (Kyoto Encyclopedia of Genes and Genomes) analyses.

Results

The 6 randomly selected DEGs were verified by real-time fluorescent quantitative PCR that their relative expression was consistent with the transcriptional expression profile. Furthermore, KEGG analysis found that 8 candidate signaling pathways were essential for ovarian development, including the MAPK signaling pathway, Progesterone-mediated oocyte maturation, Cell adhesion molecules (CAMs), NOD-like receptor signaling pathway, ECM-receptor interaction, Focal adhesion, TGF-beta signaling path-way and Phagosome. Finally, 5 key DEGs were identified to participate in ovarian development, including TGIF1, TGFBR2, RAF1, PTK2 and FGF10.

Discussion

Our findings reveal the mechanisms under-lying the molecular regulation of related genes in Gaoyou duck ovarian development.

Mass Spectrometry-Compatible Subcellular Fractionation for Proteomics

We found that nuclear envelopes stabilize against surfactants in the presence of ethylene glycol (EG). We, therefore, developed a novel subcellular fractionation approach for proteomics using RIPA buffer containing EG and phase transfer surfactants. This method involves separating the cells into the cytoplasm, organelles, and nucleus, including intermediate filaments without ultracentrifugation. These fractions are directly applicable to sample preparation for shotgun proteomics as they have no mass spectrometry (MS)-incompatible chemicals, whereas those separated by traditional fractionation protocols require desalting. This protocol is successfully applied to subcellular fractionation with only 3.5 × 10⁵ cells. Here, it was combined with phosphoproteomics and proteomics to identify phosphorylation sites regulating protein subcellular localization. In total, 59 phosphorylation sites on 42 phosphopeptides and 32 proteins showing different enrichment patterns between phosphoproteomics and the corresponding proteomics were identified, which are potential candidate sites to regulate the protein subcellular localization, including serine 706 on CD44 and serine 22 on lamin A/C.

Alternative SiO2 Surface Direct MDCK Epithelial Behavior

The mechanical interactions of cells are mediated through adhesive interactions. In this study, we examined the growth, cellular behavior, and adhesion of MDCK epithelial cells on three different SiO₂ substrates: amorphous glass coverslips and the silicon oxide layers that grow on ⟨111⟩ and ⟨100⟩ wafers. While compositionally all three substrates are almost similar, differences in surface energy result in dramatic differences in epithelial cell morphology, cell-cell adhesion, cell-substrate adhesion, actin organization, and extracellular matrix (ECM) protein expression. We also observe striking differences in ECM protein binding to the various substrates due to the hydrogen bond interactions. Our results demonstrate that MDCK cells have a robust response to differences in substrates that is not obviated by nanotopography or surface composition and that a cell's response may manifest through subtle differences in surface energies of the materials. This work strongly suggests that other properties of a material other than composition and topology should be considered when interpreting and controlling interactions of cells with a substrate, whether it is synthetic or natural.

Intermediate Filaments at the Junction of Mechanotransduction, Migration, and Development

Mechanically induced signal transduction has an essential role in development. Cells actively transduce and respond to mechanical signals and their internal architecture must manage the associated forces while also being dynamically responsive. With unique assembly-disassembly dynamics and physical properties, cytoplasmic intermediate filaments play an important role in regulating cell shape and mechanical integrity. While this function has been recognized and appreciated for more than 30 years, continually emerging data also demonstrate important roles of intermediate filaments in cell signal transduction. In this review, with a particular focus on keratins and vimentin, the relationship between the physical state of intermediate filaments and their role in mechanotransduction signaling is illustrated through a survey of current literature. Association with adhesion receptors such as cadherins and integrins provides a critical interface through which intermediate filaments are exposed to forces from a cell's environment. As a consequence, these cytoskeletal networks are posttranslationally modified, remodeled and reorganized with direct impacts on local signal transduction events and cell migratory behaviors important to development. We propose that intermediate filaments provide an opportune platform for cells to both cope with mechanical forces and modulate signal transduction.

The STAT3-miRNA-92-Wnt Signaling Pathway Regulates Spheroid Formation and Malignant Progression in Ovarian Cancer

Ovarian cancer spheroids constitute a metastatic niche for transcoelomic spread that also engenders drug resistance. Spheroid-forming cells express active STAT3 signaling and display stem cell-like properties that may contribute to ovarian tumor progression. In this study, we show that STAT3 is hyperactivated in ovarian cancer spheroids and that STAT3 disruption in this setting is sufficient to relieve chemoresistance. In an NSG murine model of human ovarian cancer, STAT3 signaling regulated spheroid formation and self-renewal properties, whereas STAT3 attenuation reduced tumorigenicity. Mechanistic investigations revealed that Wnt signaling was required for STAT3-mediated spheroid formation. Notably, the Wnt antagonist DKK1 was the most strikingly upregulated gene in response to STAT3 attenuation in ovarian cancer cells. STAT3 signaling maintained stemness and interconnected Wnt/β-catenin signaling via the miR-92a/DKK1-regulatory pathways. Targeting STAT3 in combination with paclitaxel synergistically reduced peritoneal seeding and prolonged survival in a murine model of intraperitoneal ovarian cancer. Overall, our findings define a STAT3-miR-92a-DKK1 pathway in the generation of cancer stem-like cells in ovarian tumors, with potential therapeutic applications in blocking their progression. Cancer Res; 77(8); 1955-67. ©2017 AACR.

Role of focal adhesion kinase in oocyte-follicle communication

Germ cells require communication with associated somatic cells for normal gametogenesis, as exemplified by an oocyte that interacts with granulosa cells via paracrine factors as well as gap junctions located at sites of contact between these two cell types. The objective of the present study was to define the mechanisms by which cell-cell contact with the oocyte is controlled and to determine the extent that the oocyte actively participates in this association. Proline-rich tyrosine kinase 2 (PTK2), a focal adhesion kinase, was found to be activated at sites of contact between the oocyte and trans-zonal cell processes from the surrounding granulosa cells. In order to determine the functional significance of oocyte-derived PTK2 signaling in oocyte-follicle communication, an oocyte-specific Ptk2 knockout was produced through a breeding strategy pairing a floxed Ptk2-CAT-eGFP mouse with the Zp3-Cre line. Since Ptk2-null mice never develop to birth, this represents the first opportunity to define the role of PTK2 in oocyte-follicle communication. Ablation of Ptk2 within the developing oocyte resulted in lower fertility with reduced numbers of pups, lower rates of blastocyst formation, and reduced cell numbers per blastocyst. Follicles containing Ptk2-null oocytes exhibited reduced oocyte diameter, reduced numbers of connexin 37 and 43 foci at the oocyte surface, and impaired dye coupling between oocyte and granulosa cells. These findings are consistent with a model in which PTK2 plays a critical role in establishing or maintaining oocyte-granulosa cell contacts that are essential for gap junction-mediated communication between granulosa cells and the oocyte.

Construction and characteristics of an E-cadherin-related three-dimensional suspension growth model of ovarian cancer

Ovarian cancer is the deadliest of all gynecologic malignancies. Metastatic ovarian cancer cells exist mainly in the form of multi-cellular spheroids (MCSs) in the ascites of patients with advanced ovarian cancer. We hypothesized that E-cadherin, as an important cell-adhesion molecule, might play an important role in the formation and survival of MCSs. Therefore, we established a three-dimensional suspension culture model of ovarian cancer cells that express high levels of E-cadherin to investigate their growth, proliferation, and resistance to chemotherapeutic drugs by CCK-8 assays. Compared to the cell suspension masses formed by cells with low or absent E-cadherin expression, the MCSs of high E-cadherin SKOV-3 cells had larger volumes, tighter cellular connections, and longer survival times. Although the suspension cell masses of all three cell lines were proliferatively stagnant, possibly due to cell cycle arrest at G1/S, cell mortality at 72 h after cisplatin treatment was significantly decreased in the high E-cadherin SKOV-3 cells compared to SKOV-3 cells without E-cadherin expression and to OVCAR-3 cells with low E-cadherin expression. We conclude, therefore, E-cadherin plays a vital role in MCS formation, maintenance, and drug resistance in ovarian cancer and could be a potential target for late-stage ovarian cancer treatment.

BMP signalling controls the malignant potential of ascites-derived human epithelial ovarian cancer spheroids via AKT kinase activation

Epithelial ovarian cancer (EOC) cells have the ability to form multi-cellular aggregates in malignant ascites which dramatically alters cell signalling, survival, and metastatic potential. Herein, we demonstrate that patient ascites-derived EOC cells down-regulate endogenous bone morphogenetic protein (BMP) signalling by decreasing BMP ligand expression when grown in suspension culture to form spheroids. Enforced BMP signalling in these cells via constitutively-active BMP type I ALK3(QD) receptor expression causes the formation of smaller, more loosely-aggregated spheroids. Additionally, ALK3(QD)-expressing spheroids have an increased rate of adhesion and dispersion upon reattachment to substratum. Inhibition of endogenous BMP signalling using recombinant Noggin or small molecule inhibitor LDN-193189, on the other hand, opposed these phenotypic changes. To identify potential targets that impact the phenotype of EOC spheroids due to activated BMP signalling, we performed genome-wide expression analyses using Affymetrix arrays. Using the online Connectivity Map resource, the BMP signalling gene expression signature revealed that the AKT pathway is induced by activated BMP signalling in EOC cells; this finding was further validated by phospho-AKT immuno-blotting. In fact, treatment of EOC spheroids with an AKT inhibitor, Akti-1/2, reduced BMP-stimulated cell dispersion during reattachment as compared to controls. Thus, we have identified AKT as being one important downstream component of activated BMP signalling on EOC spheroid pathobiology, which may have important implications on the metastatic potential of this malignancy.

Multicellular spheroids in ovarian cancer metastases: Biology and pathology

Epithelial ovarian cancer (EOC) has a relatively high mortality rate ( approximately 55%). One of the presiding causes is that the current chemotherapeutic regimes are unable to achieve sustained remission, despite frequently producing a positive response at first treatment. One of the reasons that EOC is difficult to treat is that the mechanism of dissemination is unusual. EOC dissemination characteristically involves local invasion of pelvic and abdominal organs. Unlike many epithelial cancers, initial dissemination rarely requires the vasculature, although the vasculature is often implicated in the advanced stages of disease. Recently, it has become apparent that aggregates of malignant cells (spheroids) contained within malignant ascites represent a significant impediment to efficacious treatment of late stage EOC. In vivo, spheroids are present in the malignant ascites of EOC patients, while in vitro cultured spheroids are capable of tumorgenesis in vivo and display a reduced response to chemotherapeutic drugs when compared to monolayers. A major problem associated with the current generation of chemotherapy agents is that they do not address the anchorage- and vascular-independent growth conditions associated with a 3-dimensional structure that has formed and/or grown in suspension. Thus, spheroid formation may represent a key component of platinum/taxane-sensitive recurrence. If this is correct, a better understanding of spheroid biology may contribute to the identification of new treatment opportunities for the sustained treatment of metastatic EOC. This review article outlines the key biological features of spheroids, specifically discussing their role in EOC dissemination and chemo-response as well as providing insights into spheroid functionality.

PCDH24-induced contact inhibition involves downregulation of beta-catenin signaling

Elevated expression of the protocadherin LKC (PCDH24) in HCT116 colon carcinoma cells has been shown to induce contact inhibition, thereby completely abolishing tumor formation in vivo (Carcinogenesis, 2002; 23(7):1139-1148). To clarify the molecular mechanism behind this effect, we performed 2-DE/MS and DNA microarray analyses in order to compare protein and gene expression patterns of parental HCT116 and PCDH24-expressing HTC116 derivative cells. The data revealed drastic changes in phenotypic markers between parental and PCDH24-expressing cells. We found that in PCDH24-expressing cells beta-catenin, a major player in TCF/lef signaling, is retained in a submembranous location. beta-catenin retention coincided with a subsequent decrease in downstream targets of beta-catenin such as CD44, PLAUR, Myc, cyclin D1 and Met. From these findings we propose a novel model for the suppression of beta-catenin signaling by PCDH24 that leads to contact inhibition.

A dominant vimentin mutant upregulates Hsp70 and the activity of the ubiquitin-proteasome system, and causes posterior cataracts in transgenic mice

Vimentin is the main intermediate filament (IF) protein of mesenchymal cells and tissues. Unlike other IF-/- mice, vimentin-/- mice provided no evidence of an involvement of vimentin in the development of a specific disease. Therefore, we generated two transgenic mouse lines, one with a (R113C) point mutation in the IF-consensus motif in coil1A and one with the complete deletion of coil 2B of the rod domain. In epidermal keratins and desmin, point mutations in these parts of the alpha-helical rod domain cause keratinopathies and desminopathies, respectively. Here, we demonstrate that substoichiometric amounts of vimentin carrying the R113C point mutation disrupted the endogenous vimentin network in all tissues examined but caused a disease phenotype only in the eye lens, leading to a posterior cataract that was paralleled by the formation of extensive protein aggregates in lens fibre cells. Unexpectedly, central, postmitotic fibres became depleted of aggregates, indicating that they were actively removed. In line with an increase in misfolded proteins, the amounts of Hsp70 and ubiquitylated vimentin were increased, and proteasome activity was raised. We demonstrate here for the first time that the expression of mutated vimentin induces a protein-stress response that contributes to disease pathology in mice, and hypothesise that vimentin mutations cause cataracts in humans.

Identification of a novel intermediate filament-linked N-cadherin/gamma-catenin complex involved in the establishment of the cytoarchitecture of differentiated lens fiber cells

Tissue morphogenesis and maintenance of complex tissue architecture requires a variety of cell-cell junctions. Typically, cells adhere to one another through cadherin junctions, both adherens and desmosomal junctions, strengthened by association with cytoskeletal networks during development. Both beta- and gamma-catenins are reported to link classical cadherins to the actin cytoskeleton, but only gamma-catenin binds to the desmosomal cadherins, which links them to intermediate filaments through its association with desmoplakin. Here we provide the first biochemical evidence that, in vivo, gamma-catenin also mediates interactions between classical cadherins and the intermediate filament cytoskeleton, linked through desmoplakin. In the developing lens, which has no desmosomes, we discovered that vimentin became linked to N-cadherin complexes in a differentiation-state specific manner. This newly identified junctional complex was tissue specific but not unique to the lens. To determine whether in this junction N-cadherin was linked to vimentin through gamma-catenin or beta-catenin we developed an innovative "double" immunoprecipitation technique. This approach made possible, for the first time, the separation of N-cadherin/gamma-catenin from N-cadherin/beta-catenin complexes and the identification of multiple members of each of these isolated protein complexes. The study revealed that vimentin was associated exclusively with N-cadherin/gamma-catenin junctions. Assembly of this novel class of cadherin junctions was coincident with establishment of the unique cytoarchitecture of lens fiber cells. In addition, gamma-catenin had a distinctive localization to the vertices of these hexagonally shaped differentiating lens fiber cells, a region devoid of actin; while beta-catenin co-localized with actin at lateral cell interfaces. We believe this novel vimentin-linked N-cadherin/gamma-catenin junction provides the tensile strength necessary to establish and maintain structural integrity in tissues that lack desmosomes.

Inhibition of N-cadherin and beta-catenin function reduces axon-induced Schwann cell proliferation

N-cadherin and beta-catenin are involved in cell adhesion and cell cycle in tumor cells and neural crest. Both are expressed at key stages of Schwann cell (SC) development, but little is known about their function in the SC lineage. We studied the role of these molecules in adult rat derived SC-embryonic dorsal root ganglion cocultures by using low-Ca(2+) conditions and specific blocking antibodies to interfere with N-cadherin function and by using small interfering RNA (siRNA) to decrease beta-catenin expression in both SC-neuron cocultures and adult rat-derived SC monocultures. N-cadherin blocking conditions decreased SC-axon association and reduced axon-induced SC proliferation. In SC monocultures, beta-catenin reduction diminished the proliferative response of SCs to the mitogen beta1-heregulin, and, in SC-DRG cocultures, beta-catenin reduction inhibited axon-contact-dependent SC proliferation. Stimulation of SC cultures with beta1-heregulin increased total beta-catenin protein amount, phosphorylation of GSK-3beta and beta-catenin presence in nuclear extracts. In conclusion, our findings suggest a previously unrecognized contribution of beta-catenin and N-cadherin to axon-induced SC proliferation.

Structure and function of desmosomes

Desmosomes are prominent adhesion sites that are tightly associated with the cytoplasmic intermediate filament cytoskeleton providing mechanical stability in epithelia and also in several nonepithelial tissues such as cardiac muscle and meninges. They are unique in terms of ultrastructural appearance and molecular composition with cell type-specific variations. The dynamic assembly properties of desmosomes are important prerequisites for the acquisition and maintenance of tissue homeostasis. Disturbance of this equilibrium therefore not only compromises mechanical resilience but also affects many other tissue functions as becomes evident in various experimental scenarios and multiple diseases.

Intermediate filament scaffolds fulfill mechanical, organizational, and signaling functions in the cytoplasm

Intermediate filaments (IFs) are cytoskeletal polymers whose protein constituents are encoded by a large family of differentially expressed genes. Owing in part to their properties and intracellular organization, IFs provide crucial structural support in the cytoplasm and nucleus, the perturbation of which causes cell and tissue fragility and accounts for a large number of genetic diseases in humans. A number of additional roles, nonmechanical in nature, have been recently uncovered for IF proteins. These include the regulation of key signaling pathways that control cell survival, cell growth, and vectorial processes including protein targeting in polarized cellular settings. As this discovery process continues to unfold, a rationale for the large size of this family and the context-dependent regulation of its members is finally emerging.

Cadherin-11 is expressed in detrusor smooth muscle cells and myofibroblasts of normal human bladder

OBJECTIVES

It has recently been found that detrusor smooth muscle cells and myofibroblasts are coupled via gap junctions. However, gap junctions cannot account for strong physical interaction between cells, which has prompted the search for intercellular adhesion molecules. Cadherin-11 is a candidate for such a molecule, since it mediates the interaction of dermal myofibroblasts in contractile wound granulation tissue. We therefore hypothesised that the physical adhesion between detrusor smooth muscle cells and myofibroblasts is mediated by cadherin-11. The aim of this study was to test this hypothesis.

METHODS

Bladder biopsies from eight radical cystectomy specimens were snap-frozen, sectioned, and stained for E-cadherin; cadherin-11; alpha-catenin; beta-catenin; gamma-catenin; and smooth muscle cell/myofibroblast markers connexin-43, vimentin, desmin, smooth muscle actin, and smoothelin. Specimens were analysed by using binocular epifluorescent and confocal laser-scanning microscopy.

RESULTS

Specific positive membranous expression of all adhesion complex molecules except E-cadherin was detected in detrusor suburothelial tissue. All biopsies showed a similar punctate pattern of expression for cadherin-11 within bundles of smooth muscle cells and a suburothelial layer of cells. Cadherin-11 was specifically located at the cell membrane, in distinct linear domains.

CONCLUSIONS

To our knowledge this is the first time evidence has been provided for cadherin-mediated smooth muscle and suburothelial myofibroblast cell-cell interaction in the human bladder. Cadherin-11 most probably plays an important role in the intercellular physical coupling of detrusor smooth muscle cells and also of myofibroblasts.