Identification of a Ca2(+)-dependent cell-cell adhesion molecule in endothelial cells

Cell-cell adhesion impacts epithelia response to substrate stiffness: Morphology and gene expression

Monolayer epithelial cells interact constantly with the substrate they reside on and their surrounding neighbors. As such, the properties of epithelial cells are profoundly governed by the mechanical and molecular cues that arise from both the substrate and contiguous cell neighbors. Although both cell-substrate and cell-cell interactions have been studied individually, these results are difficult to apply to native confluent epithelia, in which both jointly regulate the cell phenotype. Specifically, it remains poorly understood about the intertwined contributions from intercellular adhesion and substrate stiffness on cell morphology and gene expression, two essential microenvironment properties. Here, by adjusting the substrate modulus and altering the intercellular adhesion within confluent kidney epithelia, we found that cell-substrate and cell-cell interactions can mask each other's influence. For example, we found that epithelial cells exhibit an elongated morphological phenotype only when the substrate modulus and intercellular adhesions are both reduced, whereas their motility can be upregulated by either reduction. These results illustrate that combinatorial changes of the physical microenvironment are required to alter cell morphology and gene expression.

Micron-scale supramolecular myosin arrays help mediate cytoskeletal assembly at mature adherens junctions

Epithelial cells assemble specialized actomyosin structures at E-Cadherin–based cell–cell junctions, and the force exerted drives cell shape change during morphogenesis. The mechanisms that build this supramolecular actomyosin structure remain unclear. We used ZO-knockdown MDCK cells, which assemble a robust, polarized, and highly organized actomyosin cytoskeleton at the zonula adherens, combining genetic and pharmacologic approaches with superresolution microscopy to define molecular machines required. To our surprise, inhibiting individual actin assembly pathways (Arp2/3, formins, or Ena/VASP) did not prevent or delay assembly of this polarized actomyosin structure. Instead, as junctions matured, micron-scale supramolecular myosin arrays assembled, with aligned stacks of myosin filaments adjacent to the apical membrane, overlying disorganized actin filaments. This suggested that myosin arrays might bundle actin at mature junctions. Consistent with this idea, inhibiting ROCK or myosin ATPase disrupted myosin localization/organization and prevented actin bundling and polarization. We obtained similar results in Caco-2 cells. These results suggest a novel role for myosin self-assembly, helping drive actin organization to facilitate cell shape change.

An Update on Molecular Pathways Regulating Vasculogenic Mimicry in Human Osteosarcoma and Their Role in Canine Oncology

Canine tumors are valuable comparative models for human counterparts, especially to explore novel biomarkers and to understand pathways and processes involved in metastasis. Vasculogenic mimicry (VM) is a unique property of malignant cancer cells which promote metastasis. Thus, it represents an opportunity to investigate both the molecular mechanisms and the therapeutic targets of a crucial phenotypic malignant switch. Although this biological process has been largely investigated in different human cancer types, including osteosarcoma, it is still largely unknown in veterinary pathology, where it has been mainly explored in canine mammary tumors. The presence of VM in human osteosarcoma is associated with poor clinical outcome, reduced patient survival, and increased risk of metastasis and it shares the main pathways involved in other type of human tumors. This review illustrates the main findings concerning the VM process in human osteosarcoma, search for the related current knowledge in canine pathology and oncology, and potential involvement of multiple pathways in VM formation, in order to provide a basis for future investigations on VM in canine tumors.

Central nervous system and peripheral cell labeling by vascular endothelial cadherin-driven lineage tracing in adult mice

Understanding the contribution of endothelial cells to the progenitor pools of adult tissues has the potential to inform therapies for human disease. To address whether endothelial cells transdifferentiate into non-vascular cell types, we performed cell lineage tracing analysis using transgenic mice engineered to express a fluorescent marker following activation by tamoxifen in vascular endothelial cadherin promoter-expressing cells (VEcad-CreER^T2; B6 Cg-Gt(ROSA)26Sort^{m9(CAG-tdTomato)Hze}). Activation of target-cell labeling following 1.5 months of ad libitum feeding with tamoxifen-laden chow in 4–5 month-old mice resulted in the tracing of central nervous system and peripheral cells that include: cerebellar granule neurons, ependymal cells, skeletal myocytes, pancreatic beta cells, pancreatic acinar cells, tubular cells in the renal cortex, duodenal crypt cells, ileal crypt cells, and hair follicle stem cells. As Nestin expression has been reported in a subset of endothelial cells, Nes-CreER^T2 mice were also utilized in these conditions. The tracing of cells in adult Nes-CreER^T2 mice revealed the labeling of canonical progeny cell types such as hippocampal and olfactory granule neurons as well as ependymal cells. Interestingly, Nestin tracing also labeled skeletal myocytes, ileal crypt cells, and sparsely marked cerebellar granule neurons. Our findings provide support for endothelial cells as active contributors to adult tissue progenitor pools. This information could be of particular significance for the intravenous delivery of therapeutics to downstream endothelial-derived cellular targets. The animal experiments were approved by the Boise State University Institute Animal Care and Use Committee (approval No. 006-AC15-018) on October 31, 2018.

Homotypic endothelial nanotubes induced by wheat germ agglutinin and thrombin

Endothelial barrier formation is maintained by intercellular communication through junctional proteins. The mechanisms involved in maintaining endothelial communication subsequent to barrier disruption remain unclear. It is known that low numbers of endothelial cells can be interconnected by homotypic actin-driven tunneling nanotubes (TNTs) which could be important for intercellular transfer of information in vascular physiology. Here we sought insight into the triggers for TNT formation. Wheat germ agglutinin, a C-type lectin and known label for TNTs, unexpectedly caused striking induction of TNTs. A succinylated derivative was by contrast inactive, suggesting mediation by a sialylated protein. Through siRNA-mediated knockdown we identified that this protein was likely to be CD31, an important sialylated membrane protein normally at endothelial cell junctions. We subsequently considered thrombin as a physiological inducer of endothelial TNTs because it reduces junctional contact. Thrombin reduced junctional contact, redistributed CD31 and induced TNTs, but its effect on TNTs was CD31-independent. Thrombin-induced TNTs nevertheless required PKCα, a known mediator of thrombin-dependent junctional remodelling, suggesting a necessity for junctional proteins in TNT formation. Indeed, TNT-inducing effects of wheat germ agglutinin and thrombin were both correlated with cortical actin rearrangement and similarly Ca²⁺-dependent, suggesting common underlying mechanisms. Once formed, Ca²⁺ signalling along TNTs was observed.

Molecular Regulation of Sprouting Angiogenesis

The term angiogenesis arose in the 18th century. Several studies over the next 100 years laid the groundwork for initial studies performed by the Folkman laboratory, which were at first met with some opposition. Once overcome, the angiogenesis field has flourished due to studies on tumor angiogenesis and various developmental models that can be genetically manipulated, including mice and zebrafish. In addition, new discoveries have been aided by the ability to isolate primary endothelial cells, which has allowed dissection of various steps within angiogenesis. This review will summarize the molecular events that control angiogenesis downstream of biochemical factors such as growth factors, cytokines, chemokines, hypoxia-inducible factors (HIFs), and lipids. These and other stimuli have been linked to regulation of junctional molecules and cell surface receptors. In addition, the contribution of cytoskeletal elements and regulatory proteins has revealed an intricate role for mobilization of actin, microtubules, and intermediate filaments in response to cues that activate the endothelium. Activating stimuli also affect various focal adhesion proteins, scaffold proteins, intracellular kinases, and second messengers. Finally, metalloproteinases, which facilitate matrix degradation and the formation of new blood vessels, are discussed, along with our knowledge of crosstalk between the various subclasses of these molecules throughout the text. Compr Physiol 8:153-235, 2018.

Endothelial cell SHP-2 negatively regulates neutrophil adhesion and promotes transmigration by enhancing ICAM-1-VE-cadherin interaction

Intercellular adhesion molecule-1 (ICAM-1) mediates the firm adhesion of leukocytes to endothelial cells and initiates subsequent signaling that promotes their transendothelial migration (TEM). Vascular endothelial (VE)-cadherin plays a critical role in endothelial cell-cell adhesion, thereby controlling endothelial permeability and leukocyte transmigration. This study aimed to determine the molecular signaling events that originate from the ICAM-1-mediated firm adhesion of neutrophils that regulate VE-cadherin's role as a negative regulator of leukocyte transmigration. We observed that ICAM-1 interacts with Src homology domain 2-containing phosphatase-2 (SHP-2), and SHP-2 down-regulation via silencing of small interfering RNA in endothelial cells enhanced neutrophil adhesion to endothelial cells but inhibited neutrophil transmigration. We also found that VE-cadherin associated with the ICAM-1-SHP-2 complex. Moreover, whereas the activation of ICAM-1 leads to VE-cadherin dissociation from ICAM-1 and VE-cadherin association with actin, SHP-2 down-regulation prevented ICAM-1-VE-cadherin association and promoted VE-cadherin-actin association. Furthermore, SHP-2 down-regulation in vivo promoted LPS-induced neutrophil recruitment in mouse lung but delayed neutrophil extravasation. These results suggest that SHP-2-via association with ICAM-1-mediates ICAM-1-induced Src activation and modulates VE-cadherin switching association with ICAM-1 or actin, thereby negatively regulating neutrophil adhesion to endothelial cells and enhancing their TEM.-Yan, M., Zhang, X., Chen, A., Gu, W., Liu, J., Ren, X., Zhang, J., Wu, X., Place, A. T., Minshall, R. D., Liu, G. Endothelial cell SHP-2 negatively regulates neutrophil adhesion and promotes transmigration by enhancing ICAM-1-VE-cadherin interaction.

Vascular endothelial cadherin expression in lung specimens of patients with sepsis-induced acute respiratory distress syndrome and endothelial cell cultures

AIMS

Vascular endothelial (VE) cadherin is a cell adhesion molecule localized at endothelial cell (EC) junctions. As a major component of endothelial adherens junctions, its main function is the maintenance and regulation of EC integrity. In the acute respiratory distress syndrome (ARDS), increased vascular permeability is a major mechanism in pulmonary edema and lung dysfunction. In this study, VE-cadherin expression was investigated in ARDS lungs and control tissue as well as in an ARDS cell culture model.

METHODS

Lung specimens of patients with ARDS due to Gram-negative sepsis (n = 20; control lung tissue: n = 41) and cell cultures of human pulmonary microvascular ECs and human umbilical vein ECs stimulated with LPS, TNF-α and IFN-γ were stained with a VE-cadherin antibody. Staining intensity was semiquantitatively evaluated by conventional light and immunofluorescence microscopy.

RESULTS

VE-cadherin expression was statistically significantly reduced in the endothelium of all vessel types in ARDS lungs compared to control tissue. Cell cultures showing disrupted cellular borders confirmed these results.

CONCLUSION

Reduced expression of VE-cadherin has to be considered as a major mechanism of increased vessel permeability in ARDS. The previously described vessel-type-specific expression pattern of VE-cadherin in the human lung is not influenced by ARDS.

McGregor J. Expression of VE-Cadherin in Peritubular Endothelial Cells during Acute Rejection after Human Renal Transplantation

Genes involved in acute rejection (AR) after organ transplantation remain to be further elucidated. In a previous work we have demonstrated the under-expression of VE-Cadherin by endothelial cells (EC) in AR following murine and human heart transplantation. Serial sections from 15 human kidney Banff-graded transplant biopsies were examined for the presence of VE-Cadherin and CD34 staining by immunohistochemistry (no AR (n = 5), AR grade IA (n = 5), or AR grade IIA (n = 5)). Quantification of peritubular EC staining were evaluated and results were expressed by the percentage of stained cells per surface analysed. There was no difference in CD34 staining between the 3 groups. VE-Cadherin expression was significantly reduced in AR Grade IIA when compared to no AR (P = .01) and to AR grade IA (P = .02). This study demonstrates a reduced VE-Cadherin expression by EC in AR after renal transplantation. The down-regulation of VE-Cadherin may strongly participate in human AR.

Evolution of the cadherin-catenin complex

Adherens junctions are the most common junction type found in animal epithelia. Their core components are classical cadherins and catenins, which form membrane-spanning complexes that mediate intercellular binding on the extracellular side and associate with the actin cytoskeleton on the intracellular side. Junctional cadherin-catenin complexes are key elements involved in driving animal morphogenesis. Despite their ubiquity and importance, comparative studies of classical cadherins, catenins and their related molecules suggest that the cadherin/catenin-based adherens junctions have undergone structural and compositional transitions during the diversification of animal lineages. This chapter describes the molecular diversities related to the cadherin-catenin complex, based on accumulated molecular and genomic information. Understanding when and how the junctional cadherin-catenin complex originated, and its subsequent diversification in animals, promotes a comprehensive understanding of the mechanisms of animal morphological diversification.

Endothelial VE-cadherin expression in human lungs

Cell adhesion molecule vascular endothelial cadherin (VE-cadherin) is the major component of endothelial adherence junctions, maintaining endothelial cell integrity. Studies dealing with constitutive VE-cadherin expression patterns in different pulmonary vessel types (arteries, arterioles, capillaries, venules, veins) or with the influence of physiological factors such as age or sex on VE-cadherin expression have not been published yet. Knowledge of constitutive resp. varying expression patterns not only fundamentally contribute to understanding the role of VE-cadherin in the pathogenesis of pulmonary diseases but also help to develop therapies based on immunotargeting. Hence, endothelial VE-cadherin expression was studied in regular lung tissue. Fifty-eight specimens of regular lung tissue (30 females, 28 males between 1 month and 75 years old) were immunohistochemically stained with an antibody against VE-cadherin. There was strong endothelial expression of VE-cadherin in arteries, arterioles, and capillaries but almost no expression in veins and venules. Neither age nor sex had any influence on the expression pattern or staining intensity. There is a vessel type-specific expression pattern for VE-cadherin in regular human lung tissue, which is not influenced by age or sex. Further studies will have to prove whether this is influenced by pathological conditions, e.g., ARDS.

Systemic inhibition of tumour angiogenesis by endothelial cell-based gene therapy

Angiogenesis and post-natal vasculogenesis are two processes involved in the formation of new vessels, and both are essential for tumour growth and metastases. We isolated endothelial cells from human blood mononuclear cells by selective culture. These blood outgrowth cells expressed endothelial cell markers and responded correctly to functional assays. To evaluate the potential of blood outgrowth endothelial cells (BOECs) to construct functional vessels in vivo, NOD-SCID mice were implanted with Lewis lung carcinoma cells subcutaneously (s.c.). Blood outgrowth endothelial cells were then injected through the tail vein. Initial distribution of these cells occurred throughout the lung, liver, spleen, and tumour vessels, but they were only found in the spleen, liver, and tumour tissue 48 h after injection. By day 24, they were mainly found in the tumour vasculature. Tumour vessel counts were also increased in mice receiving BOEC injections as compared to saline injections. We engineered BOECs to deliver an angiogenic inhibitor directly to tumour endothelium by transducing them with the gene for human endostatin. These cells maintained an endothelial phenotype and decreased tumour vascularisation and tumour volume in mice. We conclude that BOECs have the potential for tumour-specific delivery of cancer gene therapy.

Mechanisms of HER2-induced endothelial cell retraction

BACKGROUND

HER2 overexpression imparts a metastatic advantage in breast cancer. We have shown that HER2 signaling in breast cancer cells induces adjacent endothelial cell (EC) retraction, disrupting endothelial integrity. Because endothelial integrity is dependent on the adherens junctions, we postulated that the mechanism of tumor cell-induced EC retraction involves dissociation of catenin proteins from vascular endothelial (VE) cadherin. In this study, we report a loss of VE-cadherin in tumor-associated EC. We also tested for a change of catenin dissociation from VE-cadherin by manipulating HER2 signaling in tumor cells.

METHODS

We tested confluent monolayers of human EC for downregulation of VE cadherin and dissociation of catenins from VE cadherin after exposure to breast cancer cells or conditioned media. Using immunoprecipitation, we quantitated the remaining complexed catenins to VE-cadherin in tumor-associated EC after different treatments to manipulate HER2 signaling.

RESULTS

Treatment of EC with conditioned media from MCF-7 cells expressing HER2 induced a loss of VE-cadherin expression, and time-dependent dissociation of catenins from VE cadherin. Catenin dissociation from VE-cadherin was enhanced by Heregulin beta1 (P < .05) stimulation and decreased by trastuzumab (P < .05) blockade of HER2 signaling in cancer cells. An increase in EC phosphoSrc (Tyr 416) was seen by 8 hours.

CONCLUSIONS

Our data suggest that HER2 induction of EC retraction involves both down-regulation of VE-cadherin and dissociation of catenins. HER2 signaling appears to regulate this potential metastatic mechanism. Further, Src phosphorylation suggests that this pathway may be involved in this mechanism.

Cell-cell adhesion in lung endothelium

Homotypic cell-cell adhesion is essential for tissue and organ development, remodeling, regeneration, and physiological function. Whereas a significant number of homotypic cell-cell adhesion molecules have been identified, much more is known about those concentrated in epithelia than in endothelia. Among the endothelial cell-cell adhesion molecules, very little is known that is specific to endothelium in the pulmonary and bronchial circulations. This review focuses primarily on homotypic cell-cell adhesion molecules that are or are likely to be important in lung endothelium.

N-cadherin mediates endocytosis of Candida albicans by endothelial cells

Candida albicans is the most common cause of fungal bloodstream infections. To invade the deep tissues, blood-borne organisms must cross the endothelial cell lining of the vasculature. We have found previously that C. albicans hyphae, but not blastospores, invade endothelial cells in vitro by inducing their own endocytosis. Therefore, we set out to identify the endothelial cell receptor that mediates the endocytosis of C. albicans. We determined that endocytosis of C. albicans was not mediated by bridging molecules in the serum and that it was partially dependent on the presence of extracellular calcium. Using an affinity purification procedure, we discovered that endothelial cell N-cadherin bound to C. albicans hyphae but not blastospores. N-cadherin also co-localized with C. albicans hyphae that were being endocytosed by endothelial cells. Chinese hamster ovary (CHO) cells expressing human N-cadherin endocytosed significantly more C. albicans hyphae than did CHO cells expressing either human VE-cadherin or no human cadherins. The expression of N-cadherin by the CHO cells resulted in enhanced endocytosis of hyphae, but not blastospores, indicating the selectivity of the N-cadherin-mediated endocytosis. Down-regulation of endothelial cell N-cadherin expression with small interfering RNA significantly inhibited the endocytosis of C. albicans hyphae. Therefore, a novel function of N-cadherin is that it serves as an endothelial cell receptor, which mediates the endocytosis of C. albicans.

Expression ofVE-cadherin in zebrafish embryos: A new tool to evaluate vascular development

We have identified the zebrafish homologue of VE-cadherin and documented its expression in the developing vascular system. The zebrafish VE-cadherin gene is specifically expressed in the vascular endothelial cell lineage beginning with the differentiation and migration of angioblasts and persists throughout vasculogenesis, angiogenesis, and endocardium development. Staining zebrafish embryos by whole-mount in situ hybridization with the VE-cadherin probe provides a method to screen embryos for vascular defects. To illustrate this utility, we used VE-cadherin expression to demonstrate a conservation of vascular endothelial growth factor-A (VEGF-A) function. The morpholino antisense oligonucleotide knockdown of VEGF-A function in zebrafish embryos results in a loss of angiogenic blood vessels, as indicated by the lack of VE-cadherin expression in the intersegmental vasculature. This loss can be restored in embryos supplemented with either zebrafish or human VEGF-A, the latter indicating that genes crucial to angiogenesis have highly conserved functional activities in vertebrates.

Molecular targets in the inhibition of angiogenesis

Angiogenesis, the process of blood vessel formation, is crucial for malignant tumour growth and metastases; therefore, it has become an attractive target for anticancer therapy. Theoretically applicable to most solid tumours, this therapy may be advantageous over existing cytotoxic therapy, since it is directed at genetically stable endothelium growing within tumours rather than at malignant cells, which acquire resistance to treatment. Many promising angiogenesis inhibitors have been developed, although their activity has yet to be demonstrated in human clinical trials. To improve therapeutic benefit, this may require further insight into tumour angiogenesis, development of appropriate surrogate markers of activity, treatment of early stage neoplastic disease and probably a combination of different classes of antiangiogenesis agents to overcome redundant mechanisms of angiogenesis control.

Effects of cadmium on E-cadherin and VE-cadherin in mouse lung

Exposure to Cd(2+) via inhalation or intratracheal instillation results in pulmonary edema, which is followed by the influx of leukocytes, the proliferation of type II pneumocytes and eventual scarring and fibrotic changes. While the general toxic effects of Cd(2+) in the lung have been well characterized, the specific molecular mechanisms underlying these effects have yet to be elucidated. Previously we have shown that Cd(2+) can disrupt the adhering junctions between various types of epithelial and endothelial cells in culture, most likely by perturbing the function of the Ca(2+) dependent cell adhesion molecules E-cadherin and VE-cadherin respectively. The objectives of this study were to determine whether respiratory exposure to Cd(2+) can alter the localization of E-cadherin and VE-cadherin in the lung, and to determine whether this effect may play a role in the acute pneumotoxic response to Cd(2+). Male CF-1 mice were exposed to CdCl(2) (0, 16.25, 32.5, 65 or 130 nmoles in 50 microl saline) via intratracheal instillation. After 24 hours, the lungs were removed and either subjected to bronchoalveolar lavage or analyzed for histopathologic changes. The results showed that Cd(2+) caused an increase in lung weight and in the protein content of the lavage fluid. These effects were accompanied by a pronounced decrease in the amount of E-cadherin in epithelial cells of the alveoli and small bronchioles and of VE-cadherin in vascular endothelial cells. Assessment of cell membrane integrity with ethidium homodimer-1 showed no evidence of severe injury or death in alveolar epithelial cells. These findings suggest that E-cadherin and VE-cadherin may be important early targets of Cd(2+) toxicity in the lung.

Evidence that E-cadherin may be a target for cadmium toxicity in epithelial cells

E-cadherin is a Ca(2+)-dependent cell adhesion molecule that plays an important role in the development and maintenance of epithelial polarity and barrier function. This commentary describes the results of recent studies showing that the environmental pollutant Cd(2+) can damage the E-cadherin-dependent junctions between many types of epithelial cells and reviews the evidence indicating that this effect results from the direct interaction of Cd(2+) with the E-cadherin molecule. In addition, the implications of these findings with respect to the mechanisms of Cd(2+) toxicity in specific target organs such as lung, kidney, bone, and the vascular endothelium are discussed.

Differential regulation of cadherins by dexamethasone in human osteoblastic cells

Human osteoblasts express a repertoire of cadherins, including N-cadherin (N-cad), cadherin-11 (C11), and cadherin-4 (C4). We have previously shown that direct cell-cell adhesion via cadherins is critical for BMP-2-induced osteoblast differentiation. In this study, we have analyzed the regulation of cadherin expression in normal human trabecular bone osteoblasts (HOB), and osteoprogenitor marrow stromal cells (BMC), during exposure to dexamethasone, another inducer of human bone cell differentiation. Dexamethasone inhibited the expression of both C11 and N-cad mRNA in both BMC and HOB, although the effect was much more pronounced on N-cad than on C11. This action of the steroid was dose dependent, was maximal at 10(-7) M concentration, and occurred as early as after 1 day of incubation. By contrast, expression of C4 mRNA and protein was strongly induced by dexamethasone in BMC and was stimulated in HOB. This stimulatory effect lasted for at least 2 weeks of incubation. A cadherin inhibitor, HAV-containing decapeptide only partially ( approximately 50%) prevented dexamethasone-induced stimulation of alkaline phosphatase activity by BMC, which instead was not altered by incubation with a neutralizing antibody against C4. Therefore, the pattern of cadherin regulation by dexamethasone radically differs form that observed with BMP-2. Dexamethasone effects on certain osteoblast differentiated features, such as induction of alkaline phosphatase activity are not strictly dependent on cadherin function.

Transendothelial migration of monocytes in rat aorta: distribution of F-actin, alpha-catnin, LFA-1, and PECAM-1

To determine changes in the distribution of cell adhesion molecules during diapedesis of monocytes in situ, we labeled aortic whole mounts from hypercholesterolemic rats with Texas red-phalloidin and antibodies to LFA-1, PECAM-1, or alpha-catenin, and analyzed them by laser scanning confocal microscopy. Monocytes transmigrated through circular openings (transmigration passages) formed by pseudopodia that penetrated between adjacent endothelial cells. Transmigrating monocytes remained spherical above the endothelium, while spreading beneath it. The transmigration passage was lined by F-actin and partially by alpha-catenin, suggesting cadherin-mediated heterotypic interactions. LFA-1 was present in clusters at the monocyte cell surface throughout diapedesis, but was concentrated at the margin of the transmigration passage. PECAM-1 was enriched in the endothelial contact regions where the monocytes transmigrated. PECAM-1 was barely detectable in monocytes before and after diapedesis, but appeared during diapedesis at the cell surface in the parts of the monocyte located above the endothelium. PECAM-1 was enriched near the endothelial cell-cell junctions, but was not detected in parts that spread beneath the endothelium. Our results suggest a major role for LFA-1 during diapedesis and reveal dynamic changes in the distribution of PECAM-1, the actin cytoskeleton, and alpha-catenin during monocyte diapedesis in situ.

Protein expression of brain endothelial cell E-cadherin after hypoxia/aglycemia: influence of astrocyte contact

The blood-brain barrier (BBB) plays a crucial role in protecting the central nervous system (CNS) from any changes in homeostasis brought about by pathological conditions. Cerebrovascular permeability is an important factor in the development of cerebral edema following stroke [M. Plateel, E. Teissier, R. Cecchelli, Hypoxia, dramatically increases the nonspecific transport of blood-borne proteins to the brain. J. Neurochem. 68 (1997) 874-877] and any changes in its function can have detrimental neurological consequences. Recently, research has shown that an in vitro model of the BBB is sensitive to short exposures of hypoxia/aglycemia and that changes in endothelial cell calcium flux may be responsible for structural and functional variations in the BBB during ischemic stress [T.J. Abbruscato, T.P. Davis, Combination of hypoxia/aglycemia compromises in vitro BBB. J. Pharmacol. Exp. Ther. 289 (1999) 668-675]. Present experiments investigated bovine brain microvessel endothelial cell (BBMEC) expression of a Ca(2+)-dependent cell-cell adhesion molecule, E-cadherin, which has been shown to be important for blood-brain barrier function [D. Pal, K.L. Audus, T.J. Siahaan, Modulation of cellular adhesion in bovine brain microvessel endothelial cells by a decapeptide. Brain Research 747 (1997) 103-113]. Since it is believed that astrocyte-endothelial cell interaction is crucial for maintenance of in vivo BBB characteristics, we have attempted to optimize our isolation and culturing techniques to produce a reliable, in vitro model of the BBB that is suitable to study pathological conditions. Immunofluoresence experiments showed positive staining for E-cadherin, yet failed to show any change in cellular distribution of E-cadherin upon hypoxic/aglycemic exposure. In addition, culturing BBMECs with C6 conditioned medium (CM) had no effect on the localization of E-cadherin. Western blotting experiments showed that BBMECs express E-cadherin and this protein is decreased in a time dependent manner after various hypoxic/aglycemic exposures when endothelial cells are cultured alone or with C6 astrogliomas grown on a separate culture surface. When C6 astrocytes are grown directly opposed to endothelial cells, with a porous membrane between, we observed a slight attenuation in the decreased BBMEC expression of E-Cadherin after hypoxia/aglycemia exposure. This work has shown that the mammalian brain endothelial/astrocyte co-culture system is a useful model for studies of pathological conditions where BBB characteristics are maintained.

Mast cell granule heparin proteoglycan induces lacunae in confluent endothelial cell monolayers

The addition of rat mast cell granules to confluent bovine pulmonary artery endothelial cell monolayers resulted in the formation of numerous lacunae in the cultures. Several lines of evidence identified heparin proteoglycan as the component of the granule matrix responsible for the effect: presence of the activity in the proteoglycan fraction after chromatography of granule extracts, inhibition of granule activity by digestion with heparinase I, the failure of proteolysis of the proteoglycan fraction with proteinase K to significantly diminish its activity, and the failure of chymase and carboxypeptidase inhibitors to inhibit granule activity. The onset of hole formation was delayed for several hours after granule addition to the culture, and maximal hole formation occurred between 8 and 16 hours and was sustained as long as 24 hours. The lacunae formed by the separation of motile endothelial cells within the monolayer and was not attributable to cell contractile activity or cell loss. Time-lapse video recording showed that the holes were dynamic, individual holes expanding and regressing over a period of hours. Formation of lacunae occurred on gelatin and fibronectin surfaces alike. The presence of active chymase in the granules prevented the action of the proteoglycan. Heparin glycosaminoglycan as distinct from the proteoglycan did not similarly affect the endothelial monolayers but did block the action of granules added subsequently, indicating the likelihood of a heparin-reactive receptor or binding site.

An immunohistochemical study of cadherin 5 (VE-cadherin) in vascular endothelial cells in placentas with gestosis

OBJECTIVE

To evaluate vascular endothelial-cell functioning in placentas with gestosis, using the monoclonal antibody to cadherin 5.

METHODS

The extra-cellular moiety of cadherin 5 was transfected into L-cells to enable us to examine their cell-adhesion activity. The expression of cadherin 5 was evaluated in human umbilical-vein endothelial cells and in placentas with gestosis by immunostaining using the anti-cadherin 5 antibody. A microspectrophotometric study also was conducted of the placentas with gestosis.

RESULTS

We determined the total base sequence for cadherin 5 and found that it is homologous with a known cadherin but is a new, unique clone. Cadherin 5 has cell-adhesion activity and is expressed in endothelial cells at the cell-adhesion surface. The expression of cadherin 5 in endothelial cells took place in the placentas with gestosis, but to a lesser extent than in normal placental endothelial cells.

CONCLUSIONS

The reduced expression of cadherin 5 in placentas with gestosis suggests that endothelial cell functioning is impaired in placentas with gestosis. Cadherin 5 in endothelial cells might influence placental functions and fetal development.

Molecular cloning and characterization of a novel human classic cadherin homologous with mouse muscle cadherin

We used a novel cDNA cloning method based on the cadherin-beta-catenin protein interaction and identified a new human classic-type cadherin, which we named cadherin-15, from adult brain and skeletal muscle cDNA libraries. Sequence analysis revealed that this cadherin was closely related to mouse muscle cadherin and seemed to be its human counterpart. However, its deduced amino acid sequence differed from that of mouse muscle cadherin in that it had an extra 31-amino acid sequence at its C terminus that has been found neither in mouse muscle cadherin nor in any other known classic cadherin. Analysis of cadherin-15 protein expressed in L fibroblasts showed that it was cleaved proteolytically, expressed on the cell surfaces as a mature form of about 124-kDa, and functioned as a cell-cell adhesion molecule in a homophilic and specific manner, but Ca2+ did not protect it against degradation by trypsin. Our findings also suggest that cadherin-15 mediates cell-cell adhesion with a binding strength comparable to that of E-cadherin.

Human osteoblasts express a repertoire of cadherins, which are critical for BMP-2-induced osteogenic differentiation

Direct cell-cell interactions are fundamental for tissue development and differentiation. We have studied the expression and function of cadherins in human osteoblasts during in vitro differentiation. Using reverse transcription-polymerase chain reaction and mRNA hybridization, we found that human trabecular bone osteoblasts (HOBs), osteoprogenitor marrow stromal cells (BMCs), and the osteogenic sarcoma lines, SaOS-2 and MG-63, expressed mRNA for cadherin-11 (C11) and N-cadherin (N-cad). HOBs and BMCs also expressed low levels of cadherin-4 (C4) mRNA. C11 was the most abundant cadherin protein present in human osteoblasts, and its expression was unaffected by bone morphogenetic protein-2 (BMP-2) treatment of either BMCs or HOBs. Likewise, N-cad mRNA did not change during BMP-2 incubation. Conversely, C4 protein, undetectable in transformed cell lines, was down-regulated by BMP-2 treatment of normal cells. Both C11 and C4 were localized to sites of cell-cell contact in both HOBs and BMCs, colocalized with beta-catenin, and bands corresponding to cadherins were coimmunoprecipitated by a beta-catenin antibody, findings indicative of functional cadherins. A decapeptide containing the HAV motif of human N-cad partially inhibited Ca2+-dependent cell-cell adhesion and completely prevented BMP-2-induced stimulation of alkaline phosphatase activity by BMCs. Thus, human osteoblasts and their progenitor cells express a repertoire of multiple cadherins. Cadherin-mediated cell-to-cell adhesion is critical for normal human osteoblast differentiation.

VE-Cadherin mediates endothelial cell capillary tube formation in fibrin and collagen gels

Various cell adhesion molecules mediate the diverse functions of the vascular endothelium, such as cell adhesion, neutrophil migration, and angiogenesis. In order to identify cell adhesion molecules important for angiogenesis, we used an in vitro model (Chalupowicz, Chowdhury, Bach, Barsigian, and Martinez, J. Cell Biol. 130, 207-215, 1995) in which human umbilical vein endothelial cell monolayers are induced to form capillary-like tubes when a second gel, composed of either fibrin or collagen, is formed overlying the apical surface. In the present investigation, we observed that a monoclonal antibody directed against the first extracellular domain of human vascular endothelial cadherin (VE-cadherin, cadherin 5) inhibited the formation of capillary tubes formed between either fibrin or collagen gels. Moreover, when added to preformed capillary tubes, this antibody disrupted the capillary network. In contrast, monoclonal antibodies directed against the extracellular domain of N-cadherin, the alphavbeta3 integrin, and PECAM-1 failed to inhibit capillary tube formation. During capillary tube formation, Western blot and RT-PCR analysis revealed no marked change in VE-cadherin expression. Immunocytochemical studies demonstrated that VE-cadherin was concentrated at intercellular junctions in multicellular capillary tubes. Thus, VE-cadherin plays a specific role in fibrin-induced or collagen-induced capillary tube formation and is localized at areas of intercellular contact where it functions to maintain the tubular architecture. Moreover, its function at tubular intercellular junctions is distinct from that at intercellular junctions present in confluent monolayers, since only the former was inhibited by monoclonal antibodies.

Topography and biological role of integrins in human skin

We report the topography of integrins in the human epidermis and in cultured human keratinocytes. Both in situ and in vitro beta 1 integrins are exposed at the cell-cell adhesion interface while beta 4 is located on the basal membrane in contact with the basal lamina. Such defined sorting identifies discrete cell membrane domains that may be involved in defining, building up, and maintaining epithelial cell polarity. The distribution of integrins is deeply altered in hyperproliferative states like those occurring in several experimental conditions and in epidermal diseases.

Role of cadherins 5 and 13 in the aortic endothelial barrier

We investigated the role of the cadherins 5 and 13 in the solute barrier formed by aortic endothelial cells in vitro. In confluent monolayers of bovine aortic endothelial cells, immunofluorescence with antibodies to the external domain of cadherin 5 (Mab 9H7) or to cadherin 13 (Mab Ec6C10) found staining for both cadherins at endothelial cell borders. Western blotting with an antibody to the characteristic cadherin cytoplasmic tail or with an antibody to the extracellular domain of cadherin 5 revealed a single 125 kD protein band. A second larger band was found at 130 kD with the anti-cadherin 13 Mab which was not recognized by an antibody to the cadherin cytoplasmic tail. A calcium switch strategy was used to investigate the involvement of these cadherins in the endothelial barrier. Changes in the permeability of small solutes in an endothelial cell column produced by a decrease in calcium concentration followed by a return to normal calcium, with or without antibody, were recorded. We found that anti-cadherin 5 IgG (10 micrograms/ml) interfered with the reforming of interendothelial junctions after restoration of calcium at every time point tested for a total of 45 min after restoration of calcium. The anti-cadherin 13 IgG (10 micrograms/ml) did not block reforming of the endothelial barrier in a similar manner. The presence of this antibody delayed only by 15 min the restoration of the normal barrier. Without calcium switch, addition of either monoclonal antibody (10 micrograms/ml) to the endothelial cell column had no effect on solute permeability. These results suggest that cadherin 5 in bovine aortic endothelial cells has a major functional role in forming the calcium-sensitive endothelial junction in vitro and may play an important role in the normal structure and function of the in vivo barrier.

Inhibition of cultured cell growth by vascular endothelial cadherin (cadherin-5/VE-cadherin)

Endothelial cell proliferation is inhibited by the establishment of cell to cell contacts. Adhesive molecules at junctions could therefore play a role in transferring negative growth signals. The transmembrane protein VE-cadherin (vascular endothelial cadherin/cadherin-S) is selectively expressed at intercellular clefts in the endothelium. The intracellular domain interacts with cytoplasmic proteins called catenins that transmit the adhesion signal and contribute to the anchorage of the protein to the actin cytoskeleton. Transfection of VE-cadherin in both Chinese hamster ovary (CHO) and L929 cells confers inhibition of cell growth. Truncation of VE-cadherin cytoplasmic region, responsible for linking catenins, does not affect VE-cadherin adhesive properties but abolishes its effect on cell growth. Seeding human umbilical vein endothelial cells or VE-cadherin transfectants on a recombinant VE-cadherin amino-terminal fragment inhibited their proliferation. These data show that VE-cadherin homotypic engagement at junctions participates in density dependent inhibition of cell growth. This effect requires both the extracellular adhesive domain and the intracellular catenin binding region of the molecule.

Functional properties of human vascular endothelial cadherin (7B4/cadherin-5), an endothelium-specific cadherin

Human vascular endothelial cadherin (VE-cadherin, 7B4/cadherin-5) is an endothelial-specific cadherin localized at the intercellular junctions. To directly investigate the functional role of this molecule we cloned the full-length cDNA from human endothelial cells and transfected its coding region into Chinese hamster ovary cells. The product of the transfected cDNA had the same molecular weight as the natural VE-cadherin in human endothelial cells, and reacted with several VE-cadherin mouse monoclonal antibodies. Furthermore, it selectively concentrated at intercellular junctions, where it codistributed with alpha-catenin. VE-cadherin conferred adhesive properties to transfected cells. It mediated homophilic, calcium-dependent aggregation and cell-to-cell adhesion. In addition, it decreased intercellular permeability to high-molecular weight molecules and reduced cell migration rate across a wounded area. Thus, VE-cadherin may exert a relevant role in endothelial cell biology through control of the cohesion and organization of the intercellular junctions.

Differentiation of the microvascular endothelium during early angiogenesis and respiratory onset in the chick chorioallantoic membrane

The present study served to determine the extent of microvascular endothelial differentiation during early stages of morphogenesis (days 4.5-5.5 of the 21-day incubation) in the chick chorioallantoic membrane (CAM). CAM's, which serve as the embryonic lung, were prepared for intravital injections of a graded series of FITC-dextrans and subsequent ultrastructural morphometric analyses of the microvascular units. The precapillary, capillary, and postcapillary microvascular segments presented a continuous endothelium that was substantially thicker than that of adult lung endothelia (DeFouw, 1988). Further, plasmalemmal vesicles were uniformly sparse, while endothelial vacuoles, of variable diameters, were present continuously in the proliferating microvascular units. Average widths and depths of the interendothelial clefts were uniform and suggested complete structural differentiation from the onset of CAM morphogenesis. Based on our recent estimates of CAM microvascular permeability coefficients (Rizzo et al., 1995), the observed endothelial ultrastructure was associated with microvascular selectivity comparable to that of adult pulmonary microvessels (Lanken et al., 1985). Therefore, despite incomplete ultrastructural differentiation of the early CAM microvascular endothelium, these angiogenic microvessels presented adult-like barrier properties. Further they were less permeable than (Wu et al., 1993; Yuan et al., 1993) and ultrastructurally distinct from (Kohn et al., 1992) certain tumorigenic microvessels. Thus, angiogenesis is likely not a routinely homogeneous process, and CAM microvascular permeability characteristics may be teleologically significant.

Postnatal reorganization of actin filaments and differentiation of intercellular boundaries in the rat aortic endothelial cells

Postnatal change in the distribution of actin filaments in endothelial cells was studied in the rat aorta by use of rhodamine-phalloidin staining and confocal laser scanning microscopy. Endothelial cells of the rat aorta possessed two populations of actin filament bundles, namely, peripheral bands at the cell border and stress fibers running longitudinally in the cytoplasm. Aortic endothelial cells of the neonatal rat contained only stress fibers, whereas those of the 10-day-old rat developed both peripheral bands and stress fibers. After 20 days of age, aortic endothelial cells had predominantly peripheral bands with occasional stress fibers around the branch orifices. During postnatal development the length density of stress fibers in aortic endothelial cells decreased, whereas individual stress fibers in endothelial cells were shortened. Electron-microscopic observation revealed that the high intercellular boundaries of aortic endothelial cells at birth decreased in height and developed cytoplasmic interdigitations after 20 days of age. The occurrence of peripheral bands at the cell border is thought to be closely related to formation of cytoplasmic interdigitation which strengthens the mechanical connection between endothelial cells against increasing transmural pressure. Expression of stress fibers in aortic endothelial cells of the neonatal rat is supposed to be affected by longitudinal elongation of the developing aorta, whereas their postnatal decrease is thought to be correlated with the change of fluid shear stress loaded on the aortic endothelium.

Effect of bis (tributyl tin) oxide on permeability of the blood-brain barrier: a transient increase

OBJECTIVES

To study the effect of bis (tributyl tin) oxide (TBTO) on permeability of the blood-brain barrier.

METHODS

Electron microscopy and an x ray microanalyser with lanthanum chloride as a tracer were used, and blood tin concentrations were determined with an atomic absorption spectrophotometer. Adult male wistar rats received 0.05 ml/kg body weight of TBTO orally.

RESULTS

A transient increase in paracellular permeability at the blood-brain barrier was found 2 h after the dose of TBTO. Electron dense lanthanum deposits penetrated tight junctions of the endothelia and permeated the subendothelial space. The x ray microprobe data showed an accumulation of TBTO at the tight junctions at 2 h. Leakage of tracer did not occur at 4 h, but oedematous changes in the surrounding glial cells were prominent between 4 and 8 h and had almost returned to normal by 24 h. By atomic absorption analysis, it was seen that blood tin concentrations rapidly increased at 1 h and rose to a maximum peak at 8 h, then gradually decreased to reach zero at 24 h.

CONCLUSIONS

Accumulated TBTO at tight junctions could have caused the temporary replacement of calcium ion by tin, which induces a transient increase in paracellular permeability throughout the blood-brain barrier.

Complexus adhaerentes, a new group of desmoplakin-containing junctions in endothelial cells: II. Different types of lymphatic vessels

In diverse mammalian species, including (man, cow and rat) the very flat endothelial cells of lymphatic vessels of various organs, including the retothelial meshwork of sinus of lymph nodes, are connected by zonula-like plaque-bearing junctions which differ from the similarly structured junctions of blood vessel endothelia by the presence of desmoplakin or an as yet unknown but closely related plaque protein. These extended junctions, which also contain plakoglobin but none of the presently known desmogleins and desmocollins, are therefore different from the spot-like desmosomes (maculae adhaerentes) present in epithelia, myocardium and dendritic reticulum cells of lymphatic follicles, and are collectively subsumed under the new category of complexus adhaerentes, including the 'syndesmos' connecting the processes of the retothelial cells. The lymphatic endothelial cells possessing these special desmoplakin-containing junctions also contain the calcium-dependent transmembrane glycoproteins, V-cadherin and cadherin 5, of which the latter has also been partly localized to regions with desmoplakin-positive junctions. Possible functional reasons for the formation and maintenance of complexus adhaerentes are discussed as well as the potential value of reagents which allow their identification in relation to physiology and pathology.

Liver-intestine cadherin: molecular cloning and characterization of a novel Ca(2+)-dependent cell adhesion molecule expressed in liver and intestine

A novel member of the cadherin family of cell adhesion molecules has been characterized by cloning from rat liver, sequencing of the corresponding cDNA, and functional analysis after heterologous expression in nonadhesive S2 cells. cDNA clones were isolated using a polyclonal antibody inhibiting Ca(2+)-dependent intercellular adhesion of hepatoma cells. As inferred from the deduced amino acid sequence, the novel molecule has homologies with E-, P-, and N-cadherins, but differs from these classical cadherins in four characteristics. Its extracellular domain is composed of five homologous repeated domains instead of four characteristic for the classical cadherins. Four of the five domains are characterized by the sequence motifs DXNDN and DXD or modifications thereof representing putative Ca(2+)-binding sites of classical cadherins. In its NH2-terminal region, this cadherin lacks both the precursor segment and the endogenous protease cleavage site RXKR found in classical cadherins. In the extracellular EC1 domain, the novel cadherin contains an AAL sequence in place of the HAV sequence motif representing the common cell adhesion recognition sequence of E-, P-, and N-cadherin. In contrast to the conserved cytoplasmic domain of classical cadherins with a length of 150-160 amino acid residues, that of the novel cadherin has only 18 amino acids. Examination of transfected S2 cells showed that despite these structural differences, this cadherin mediates intercellular adhesion in a Ca(2+)-dependent manner. The novel cadherin is solely expressed in liver and intestine and was, hence, assigned the name LI-cadherin. In these tissues, LI-cadherin is localized to the basolateral domain of hepatocytes and enterocytes. These results suggest that LI-cadherin represents a new cadherin subtype and may have a role in the morphological organization of liver and intestine.

Characterization of cadherin-4 and cadherin-5 reveals new aspects of cadherins

Several properties of cadherin-4 and cadherin-5 were characterized by using the cDNA transfection approach. The proteins of both cadherins had a relative molecular mass of about 130 kDa and were present at the cell periphery, especially at cell-cell contact sites. These cadherins were easily digested with trypsin, and Ca2+ protected cadherin-4, but not cadherin-5, from the digestion. In immunoprecipitation, cadherin-4 co-precipitated with two major proteins of 105 kDa and 95 kDa, respectively. The 105 kDa and the 95 kDa proteins are likely to correspond to alpha- and beta-catenins. Cadherin-5 co-precipitated with only one major protein of 95 kDa, but seems to associate with the 105 kDa protein. On the other hand, plakoglobin or gamma-catenin did not co-precipitate well with either cadherin-4 or cadherin-5 in immunoprecipitation, but plakoglobin also appears to associated weakly with these cadherins. Cadherin-4 transfectants aggregated within 30 minutes in a cell aggregation assay, but cadherin-5 transfectants did not aggregate under the same conditions. Furthermore, the transfectants of chimeric cadherin-4 with cadherin-5 cytoplasmic domain showed cell aggregation activity comparable to that of wild-type cadherin-4 transfectants, whereas the transfectants of chimeric cadherin-5 with cadherin-4 cytoplasmic domain did not show appreciable cell aggregation, suggesting that the extracellular domains of cadherins, in conjunction with their cytoplasmic domains, play an important role in cell aggregation activity. These results show that cadherin-4 is very similar to the classical cadherins, whereas cadherin-5 is functionally as well as structurally distinct from classical cadherins.

Immunohistochemical evaluation of alpha-catenin expression in human gastric cancer

E-cadherin (E-cad) plays a major role in the maintenance of cell-cell adhesion in epithelial tissues, and impaired E-cad expression correlates with tumour invasion and metastasis. Alpha-catenin (alpha-cat), an undercoat protein of adherens junctions, binds to the cytoplasmic domain of E-cad and is essential for linking E-cad to actin-based cytoskeleton. We investigated E-cad and alpha-cat expression in 60 human gastric cancers immunohistochemically. The 60 gastric cancers were classified into 18 (30%) in which alpha-cat expression was preserved, and 42 (70%) reduced cases. The reduction of alpha-cat expression was significantly related to dedifferentiation, depth of invasion, infiltrative growth and lymph node metastasis. We also examined the co-expression of alpha-cat and E-cad. Seventeen (28%) tumours preserved both molecules [alpha-cat(+)/E-cad(+)] and 33 (55%) tumours reduced both [alpha-cat(-)/E-cad(-)], whereas 9 (15%) tumours exhibited alpha-cat(-)/E-cad(+). The frequency of lymph node metastasis in alpha-cat(-)/E-cad(+) tumour (67%) was significantly higher than that in alpha-cat(+)/E-cad(+) tumours (24%) and was close to that in alpha-cat(-)/E-cad(-) tumours (82%). The frequency of haematogenous liver metastasis in alpha-cat(-)/E-cad(+) tumours (44%) was significantly higher than that in alpha-cat(+)/E-cad(+) tumours (6%) or alpha-cat(-)/E-cad(-) tumours (9%). Thus, in all E-cad(+) tumours, the frequency of lymph node and liver metastasis was higher in alpha-cat(-) tumours than in alpha-cat(+) tumours. alpha-Cat expression is apparently better at predicting tumour invasion and metastasis than E-cad expression.

Cloning of five human cadherins clarifies characteristic features of cadherin extracellular domain and provides further evidence for two structurally different types of cadherin

The entire coding sequences for five possible human cadherins, named cadherin-4, -8, -11, -12 and -13, were determined. The deduced amino acid sequences of cadherin-4 and cadherin-13 showed high homology with those of chicken R-cadherin or chicken T-cadherin, suggesting that cadherin-4 and cadherin-13 are mammalian homologues of the chicken R-cadherin or T-cadherin. Comparison of the extracellular domain of these proteins with those of other cadherins and cadherin-related proteins clarifies characteristic structural features of this domain. The domain is subdivided into five subdomains, each of which contains a cadherin-specific motif characterized by well-conserved amino acid residues and short amino acid sequences. Moreover, each subdomain has unique features of its own. The comparison also provides additional evidence for two structurally different types of cadherins: the first type includes B-, E-, EP-, M, N-, P- and R-cadherins and cadherin-4; the second type includes cadherin-5 through cadherin-12. Cadherin-13 lacks the sequence corresponding to the cytoplasmic domain of typical cadherins, but the extracellular domain shares most of the features common to the extracellular domain of cadherins, especially those of the first type of cadherins, suggesting that cadherin-13 is a special type of cadherin. These results, and those of other recent cloning studies, indicate that many cadherins with different properties are expressed in various tissues of different organisms.

Cultured microvascular endothelial cells (MVEC) differ in cytoskeleton, expression of cadherins and fibronectin matrix. A study under the influence of interferon-gamma

Endothelial cells are known to undergo transitions in cell shape during long-term culture. Thus, the assumption that the separate phenotypes of microvascular endothelial cells (MVEC) recently isolated from bovine corpus luteum represent constitutively different cell strains cannot automatically be made. For this reason, particular morphological qualities from four of five reported MVEC types were studied. Confluent cultures of MVEC types 1, 3, 4 and 5 were either left untreated or exposed to recombinant bovine interferon-gamma (IFN-gamma; 200 units/0.5 ml culture medium) for 3 days. Paraformaldehyde-fixed monolayers were permeabilized with Triton X-100 prior to the detection of filamentous actin, using phalloidin-FITC. Vimentin filaments, cytokeratin filaments, microtubules, E- and N-cadherins as molecules of cell adhesion plaques, and fibronectin filaments were localized by the application of specific antibodies in combination with epifluorescence microscopy. Cells from untreated single cultures uniformly and reproducibly showed an actin cytoskeleton that distinguished the particular MVEC type. MVEC type 1 presented a circular band of fine actin filaments. MVEC type 3 preferentially had developed a starburst-like actin pattern. MVEC type 4 mainly exhibited a polygonal network. MVEC type 5 showed a prominent circular band of thick microfilament bundles from which short filaments radiated. Cytokeratin filaments were noted in MVEC type 1 only. Vimentin filaments occurred as a dense network constricted to the central area in MVEC type 1, while they were spread out in MVEC types 3 and 4. A wavy path comparable to the course of microtubules was apparent in MVEC type 5. Fibronectin assembled into two differently shaped layers at the basal cell side of each MVEC type. Under IFN-gamma treatment, cytoskeletal diversities were maintained between the MVEC types, yet each MVEC type showed specific modulations to its cytoskeleton and to its fibronectin matrix. Upregulation of anti-E-cadherin labelling was detected in MVEC type 1, showing a fluorescent cell border of linear contour. The upregulation of E-cadherin by IFN-gamma treatment could also be demonstrated by western blotting, which revealed a 135 kDa full-sized molecule and a 95 kDa tryptic fragment characteristic of cadherins. Anti-N-cadherin labelling was evident for MVEC type 5, giving rise to a fluorescent punctate cell margin. Our investigations support the existence of truly separate MVEC types.

Expression of cell-cell and cell-matrix adhesion proteins by sinusoidal endothelial cells in the normal and cirrhotic human liver

We compared the expression of cell-cell and cell-matrix adhesion proteins by sinusoidal endothelial cells in normal human liver, in which the endothelial lining of hepatic sinusoids is discontinuous and devoid of basement membrane, and in cirrhosis, during which sinusoids might undergo a process of capillarization and acquire a continuous lining and a typical basement membrane. In normal liver, sinusoidal endothelial cells displayed a very restricted repertory of cell-adhesion molecules: the intercellular adhesion molecules PECAM-1 and CD34 were undetectable and only two integrins, alpha 1 beta 1 and alpha 5 beta 1, were present, whereas the laminin receptors alpha 6 beta 1 and alpha 2 beta 1 were undetectable and the beta 3 integrins were faintly expressed. In capillarized sinusoids, sinusoidal endothelial cells displayed striking changes in their repertory of cell-adhesion molecules, including the expression of PECAM-1 protein and messenger RNAs and the induction of the laminin receptors alpha 6 beta 1 and alpha 2 beta 1. Such changes co-localized with subendothelial laminin deposits. In conclusion, normal sinusoidal endothelial cells express a distinctive set of cell-adhesion molecules, adapted to their structural and microenvironmental characteristics, and this repertory is dramatically modified during sinusoidal capillarization, possibly as a consequence of the concomitant matrix changes.

An N-cadherin-like protein contributes to solute barrier maintenance in cultured endothelium

We investigated the role of cadherins in the solute barrier maintained by endothelial cells in vitro. Cell-column chromatographic measurement of endothelial barrier showed that reducing normal extracellular calcium from 1.2 to 0.12 mM increased endothelial permeability to 250% of baseline after 20 min. Restoring normal calcium restored the barrier within 15 min which remained stable for at least 60 min. We used sulfo-NHS-biotin and anti-cadherin antibodies to characterize endothelial proteins with possible roles in the maintenance of endothelial barrier. The non-specific probe sulfo-NHS-biotin identified at least ten endothelial cell surface proteins, with greatest labelling occurring at molecular weights of 125 and 145 kD. Six proteins, including the 125 and 145 kD proteins, associated with the cytoskeleton. Western blotting for the presence of classical cadherins containing the conserved cytoplasmic sequence CDPTAPPYDSLLVFDYEG detected two bands at 145 and 125 kD which associated with the cytoskeleton. Western blotting with an antibody, which recognizes FHLRAHAVDINGNQV, an extracellular homotypic binding region of N-cadherin, detects three bands. Of these three, one protein had a molecular weight of 125 kD and was associated with the cytoskeleton. Immunofluorescence with both N-cadherin and anti-peptide 1 antibodies found staining at endothelial cell borders. The utility of a newly developed cell-column calcium switch assay was tested by verifying the functional role of the previously described epithelial cadherin, uvomorulin, in epithelial barrier. We then applied this method to endothelial cell columns and found the N-cadherin antibody interfered with the reforming of interendothelial junctions. These results suggest that, as in epithelial cells, cadherins in bovine endothelial cells have a functional role in forming the calcium sensitive endothelial junction and may play an important role in the formation of normal barrier.

Molecular biology of cadherins in the nervous system

Cadherins are cell-cell adhesion molecules belonging to the Ca(2+)-dependent cadherin superfamily. In the last few years the number of cadherins identified in the nervous system has increased considerably. Cadherins are integral membrane glycoproteins. They are structurally closely related and interspecies homologies are high. The function is mediated through a homophilic binding mechanism, and intracellular proteins, directly or indirectly connected to the cadherins and the cytoskeleton, are necessary for cadherin activity. Cadherins have been implicated in segregation and aggregation of tissues at early developmental stages and in growth and guidance of axons during nervous system development. These functions are modified by changes in type(s) and amount of cadherins expressed at different developmental stages. The regulatory elements guiding cadherin expression are currently being elucidated.

Roles of calcium ions in hyphal tip growth

A role for Ca2+ in the tip growth process of fungal hyphae and other eukaryotic walled cells has been widely explored, following the earlier indications of their importance by Jaffe, Steer, and their colleagues. Analysis of the literature on fungi, with selected comparison with other tip-growing plant cells, shows that the growth rate and morphology of hyphae are sensitive to factors which influence intracellular Ca2+. These factors include variations in extracellular Ca2+ concentrations, Ca2+ ionophores, inhibitors of Ca2+ transport, and calmodulin- and Ca(2+)-binding dyes and buffers introduced into the cytoplasm. The effects of these agents appear to be mediated by a tip-high gradient of cytoplasmic free Ca2+ which is obligatorily present in all critically examined growing tips. Most recent observations agree that the gradient is very steep, declining rapidly within 10 to 20 microns of the tip. This gradient seems to be generated by the combined effects of an influx of Ca2+, via plasma membrane, possibly stretch-activated, channels localized in the hyphal tip, and subapical expulsion or sequestration of these ions. Expulsion probably involves a plasma membrane Ca(2+)-ATPase, but it is not yet possible to differentiate among mitochondria, endoplasmic reticulum, or vacuoles as the dominant sites of sequestration. It is suggested that regulation of the Ca2+ gradient in turn modulates the properties of the actin-based component of the cytoskeleton, which then controls the extensibility, and, possibly, the synthesis of the hyphal apex. Regulatory feedback mechanisms intrinsic to this model of tip growth regulation are briefly discussed, together with suggestions for future experiments which are crucial to its further elucidation and establishment.

Inducible expression of MS-1 high-molecular-weight protein by endothelial cells of continuous origin and by dendritic cells/macrophages in vivo and in vitro

Recently, we have described a monoclonal antibody, named MS-1, which identifies a novel high-molecular-weight protein expressed by noncontinuous, sinusoidal endothelia and by interstitial dendritic cells in certain normal human organs (S Goerdt, LJ Walsh, GF Murphy, JS Pober, J Cell Biol 1991, 113:1425-1437; and LJ Walsh, S Goerdt, JS Pober, H Sueki, GF Murphy, Lab Invest 1991, 65: 732-741). In this report, we demonstrate in studying a variety of skin lesions that MS-1 antigen can also be expressed by endothelia of continuous origin under certain pathological conditions. Among the skin lesions tested, MS-1 antigen expression by endothelial cells of continuous origin is frequently observed in wound healing tissue, in cutaneous T-cell lymphoma, in psoriasis, and in melanoma metastasis, ie, in 100%, 80%, 71%, and 71% of cases, respectively. In contrast, endothelial MS-1 antigen expression rarely occurred in other skin lesions, including vascular tumors, six of which were Kaposi's sarcomas (13% and 0% of cases with vascular MS-1 expression, respectively). The percentage of cases with MS-1+ vessels is only marginally different in malignant versus benign lesions (55% versus 31%); when melanocytic nevi, primary melanomas, and melanoma metastases are compared, however, an increase in the percentage of cases with MS-1+ vessels is seen (31%, 50%, and 71%, respectively). Apart from wound healing, the relative number of MS-1+ vessels in a given lesion amounts to less than 5% compared with the number of continuous type vessels stained by monoclonal antibody 1F10 (S Goerdt, F Steckel, K Schulze-Osthoff, H-H Hagemeier, E Macher, C Sorg, Exp Cell Biol 1989, 57: 185-192). In addition, the occurrence of MS-1+ vessels is not related to the overall vascularity of a given lesion. Thus, the conditions for MS-1 antigen expression by endothelia of continuous origin cannot as yet be exactly defined. Furthermore, we have noticed that the number of MS-1+ dendritic cells varies considerably in skin lesions; in the early patch lesions of Kaposi's sarcoma and in juvenile xanthogranuloma MS-1+ cells even constitute the major cell type. This prompted us to investigate MS-1 antigen expression and its regulation in cultured human monocytes/macrophages. Expression of MS-1 antigen by these cells regularly starts at day 3 of culture and reaches its maximal value at day 9, after which it declines.(ABSTRACT TRUNCATED AT 400 WORDS)