Beta2-microglobulin causes abnormal phosphatidylserine exposure in human red blood cells

The exposure of the aminophospholipid phosphatidylserine on the external leaflet of red blood cell plasma membrane can have several pathophysiological consequences with particular regard to the processes of cell phagocytosis, haemostasis and cell-cell interaction. A significant increase in phosphatidylserine-exposing erythrocytes has been reported in chronic haemodialysis patients and found to be strongly influenced by the uraemic milieu. To identify uraemic compound(s) enhancing phosphatidylserine externalization in erythrocytes, we fractionated by chromatographic methods the ultrafiltrate obtained during dialysis, and examined by flow cytometry the effect of the resulting fractions on phosphatidylserine exposure in human red cells. Chromatographic procedures disclosed a homogeneous fraction able to increase erythrocyte phosphatidylserine exposure. The inducer of such externalization was identified by monodimensional gel electrophoresis and mass spectrometry investigations as beta2-microglobulin. To confirm the beta2-microglobulin effect and to examine the influence of protein glycation (as it occurs in uraemia) on phosphatidylserine erythrocyte exposure, erythrocytes from normal subjects were incubated with recombinant beta2-microglobulin (showing no glycation sites at mass analysis), commercial beta2-microglobulin (8 glycation sites), or with in vitro glycated recombinant beta2-microglobulin (showing multiple glycation sites). Elevated concentrations of beta2-microglobulin (corresponding to plasma levels reached in dialysis patients) increased slightly but significantly the protein's ability to externalize phosphatidylserine on human erythrocytes. Such an effect was markedly enhanced by glycated forms of the protein. Beta2-microglobulin is recognized as a surrogate marker of middle-molecule uraemic toxins and represents a key component of dialysis-associated amyloidosis. Our study adds further evidence to the potential pathophysiologic consequences of beta2-microglobulin accumulation in chronic uraemic patients.     

Plasma Factor in Red Blood Cells Adhesion to Endothelial Cells: Humans and Rats

Erythrocyte adhesion to the vascular endothelium is one of the key determinants of microcirculatory blood flow. Adhesion is a complex process determined by the intricate interaction among red blood cells (RBC), plasma factors, and the vascular endothelium. Rats are commonly used as disease models to investigate the pathophysiology of various hematological disease processes occurring in humans and their response to prospective treatments. The aim of our study was to characterize the adhesion of RBC in adult blood from rat and human subjects, in order to test the validity of rat models for adhesion-related disease processes. We demonstrated that adhesion of RBC from rats (rRBC), to endothelial cells (EC) in plasma-free buffer, is stronger than from human subjects (hRBC). In addition, plasma proteins induced elevation of hRBC (eightfold) but depression of rRBC (threefold) adhesion to EC. It is thus suggested to be aware of the difference in RBC/EC interaction for human and rat subjects, when studying models of blood flow.     

Synthetic peptides that mimic the adhesive recognition signal of fibronectin: differential effects on cell-cell and cell-substratum adhesion in embryonic chick cells

Although fibronectin has been implicated in cell-cell as well as cell-substratum interactions, most experimentation has focused on cell-substratum interactions of fibroblasts. We have examined the effect of the specific peptide GRGDS derived from the cell-binding sequence of fibronectin upon cell-cell and cell-substratum interactions using embryonic cells and tissues. Embryonic chick segmental plate cells undergo compaction (i.e., increased cell-cell adhesion) during the early stages of somitogenesis. Fibronectin has been implicated in this increase in cell-cell interaction. In contrast, precardiac mesoderm undergoes directional migration upon a fibronectin-rich substratum, exhibiting both cell-cell and cell-substratum interactions. The segmental plate cells, which are the precursors of embryonic somites, normally show very little cell-cell or cell-substratum interaction in culture. These cells exhibit a striking increase in intercellular adhesion, but exhibit no cell-substratum adhesion, in the presence of relatively low concentrations of the fibronectin-derived peptide GRGDS. Somite cells, which normally exhibit both cell-cell and cell-substratum adhesion in culture, show complete inhibition of cell-substratum adhesion in the presence of this peptide. Precardiac mesoderm, which normally exhibits both cell-cell and cell-substratum adhesion in culture, shows a marked inhibition of both processes in the presence of GRGDS. Since the finding that a monovalent competitive inhibitor of fibronectin binding can stimulate cell-cell adhesion was unexpected, we propose a "trigger" hypothesis, whereby the peptide recognition signal acts as a specific signal or trigger for the morphogenetic process of compaction. There is a striking specificity to this effect, since synthetic peptides with even conservative changes in the amino acid sequence have no effect. Finally, we find that under certain conditions the effect of the specific peptide is lost in 6-8 hr and the cells resume cell-substratum interactions or, in the case of the segmental plate cells, revert from the compacted state and exhibit a substantial decrease in cell-cell adhesion. Our studies indicate the diversity of cell and tissue responses possible when even a single peptide inhibitor of adhesion, and we have identified the first known activating effect of a fibronectin peptide on cell behavior and differentiation.     

Heterotypic and homotypic cell-cell adhesion molecules in endothelial cells

Sickle red blood cells display an abnormal propensity to adhere to cultured bovine aortic endothelial cells when compared to normal red blood cells. The adherence was potentiated three-fold by endothelial cell derived conditioned medium, enriched in multimers of von Willebrand factor. Such adherence was ablated by 80% by either the synthetic peptide (RGDS) or antibody to GPIIb/IIIa, indicating the presence of RGD peptide recognition domain/receptor in either endothelial cells or sickle cells or both. The adherence was also inhibited by 70% by phosphatidylserine, but not by other phospholipids, indicating the presence of putative receptors for this phospholipid in endothelial cells. The labeling of cultured bovine aortic endothelial cells with monoclonal antibodies revealed the localization of MAB D2 to regions of cell-cell contact. The antigen on endothelial cells which cross-reacts with this antibody has a Mr of 130,000. The addition of such an antibody during the plating of endothelial cells disrupted monolayer formation. It appears that a 130-kDa polypeptide antigen in endothelial cells which is recognized by MAB D2, may be a cell-cell adhesion molecule.     

Non-adsorbing macromolecules promote endothelial adhesion of erythrocytes with reduced sialic acids

Background

Abnormal adhesion of red blood cells (RBCs) to vascular endothelium is often associated with reduced levels of sialic acids on RBC membranes and with elevated levels of pro-adhesive plasma proteins. However, the synergistic effects of these two factors on the adhesion are not clear. In this work, we tested the hypothesis that macromolecular depletion interaction originating from non-adsorbing macromolecules can promote the adhesion of RBCs with reduced sialic acid content to the endothelium.

Methods

RBCs are treated with neuraminidase to specifically remove sialic acids from their surface followed by the evaluation of their deformability, zeta potential and membrane proteins. The adhesion of these enzyme-treated RBCs to cultured human umbilical vein endothelial cells (ECs) is studied in the presence of 70 or 500 kDa dextran with a flow chamber assay.

Results

Our results demonstrate that removal of sialic acids from RBC surface can induce erythrocyte adhesion to endothelial cells and that such adhesion is significantly enhanced in the presence of high-molecular weight dextran. The adhesion-promoting effect of dextran exhibits a strong dependence on dextran concentration and molecular mass, and it is concluded to originate from macromolecular depletion interaction.

Conclusion

These results suggest that elevated levels of non-adsorbing macromolecules in plasma might play a significant role in promoting endothelial adhesion of erythrocytes with reduced sialic acids.

General significance

Our findings should therefore be of great value in understanding abnormal RBC–EC interactions in pathophysiological conditions (e.g., sickle cell disease and diabetes) and after blood transfusions.     

Cell-cell interactions mediate the response of vascular smooth muscle cells to substrate stiffness

The vessel wall experiences progressive stiffening with age and the development of cardiovascular disease, which alters the micromechanical environment experienced by resident vascular smooth muscle cells (VSMCs). In vitro studies have shown that VSMCs are sensitive to substrate stiffness, but the exact molecular mechanisms of their response to stiffness remains unknown. Studies have also shown that cell-cell interactions can affect mechanotransduction at the cell-substrate interface. Using flexible substrates, we show that the expression of proteins associated with cell-matrix adhesion and cytoskeletal tension is regulated by substrate stiffness, and that an increase in cell density selectively attenuates some of these effects. We also show that cell-cell interactions exert a strong effect on cell morphology in a substrate-stiffness dependent manner. Collectively, the data suggest that as VSMCs form cell-cell contacts, substrate stiffness becomes a less potent regulator of focal adhesion signaling. This study provides insight into the mechanisms by which VSMCs respond to the mechanical environment of the blood vessel wall, and point to cell-cell interactions as critical mediators of VSMC response to vascular injury.     

Depletion interactions in polymer solutions promote red blood cell adhesion to albumin-coated surfaces

The effects of concentration and molecular weight of neutral dextrans on the adhesion of human red blood cells (RBC) to albumin-coated glass have been investigated using a parallel-plate flow chamber. Results indicate that the adhesion is markedly increased in the presence of 70 kDa and 500 kDa dextran, with this increase reflected by both the number of cells adhering and the strength of the adhesion. This increased adhesiveness is attributed to reduced surface concentrations of the large polymers and hence attractive forces due to depletion interaction. Depletion interaction brings the adjacent surfaces closer, leading to an increased number of binding sites available to the cell and thus more efficient and stronger adhesion of single cells. Our results suggest that depletion might play a role in other specific cell-cell or cell-surface interactions via initiating close contacts to allow specific binding.     

Role of Macromolecular Depletion in Red Blood Cell Adhesion

The adhesion of red blood cells (RBCs) to cells or surfaces is of current basic science and clinical interest yet the details governing this process are still being explored. In this study, the effects of nonadsorbing polymers on the adhesion of RBC to albumin-coated glass have been investigated employing interference reflection microscopy. Our experimental results indicate that adhesion can be induced in the presence of dextran with a molecular mass ≥70 kDa and that the induced forces are strong enough to significantly suppress membrane undulations. The overall dependence of the adhesion energies on the polymer concentration is consistent with the assumption that macromolecular depletion induces this attractive interaction. In conclusion, our results indicate that depletion interaction might play a significant role in RBC adhesion via initiating close contacts, and thus suggest the importance of depletion forces for RBC interactions and its relevance to a wide variety of in vitro and in vivo cell-cell and cell-surface interactions.     

Cloning of an immunoglobulin family adhesion molecule selectively expressed by endothelial cells

To gain fundamental information regarding the molecular basis of endothelial cell adhesive interactions during vascular formation, we have cloned and characterized a unique cell adhesion molecule. This molecule, named endothelial cell-selective adhesion molecule (ESAM), is a new member of the immunoglobulin superfamily. The conceptual protein encoded by cDNA clones consists of V-type and C2-type immunoglobulin domains as well as a hydrophobic signal sequence, a single transmembrane region, and a cytoplasmic domain. Northern blot analysis showed ESAM to be selectively expressed in cultured human and murine vascular endothelial cells and revealed high level expression in lung and heart and low level expression in kidney and skin. In situ hybridization analysis indicated that ESAM is primarily expressed in the developing vasculature of the embryo in an endothelial cell-restricted pattern. Epitope-tagged ESAM was shown to co-localize with cadherins and catenins in cell-cell junctions. In aggregation assays employing ESAM-expressing Chinese hamster ovary cells, this novel molecule was shown to mediate cell-cell adhesion through homophilic interactions. The endothelial cell-selective expression of this immunoglobulin-like adhesion molecule coupled with its in vitro functional profile strongly suggests a role in cell-cell interactions that is critical for vascular development or function.     

Hydroxycarbamide Decreases Sickle Reticulocyte Adhesion to Resting Endothelium by Inhibiting Endothelial Lutheran/Basal Cell Adhesion Molecule (Lu/BCAM) through Phosphodiesterase 4A Activation

Vaso-occlusive crises are the main acute complication in sickle cell disease. They are initiated by abnormal adhesion of circulating blood cells to vascular endothelium of the microcirculation. Several interactions involving an intricate network of adhesion molecules have been described between sickle red blood cells and the endothelial vascular wall. We have shown previously that young sickle reticulocytes adhere to resting endothelial cells through the interaction of α₄β₁ integrin with endothelial Lutheran/basal cell adhesion molecule (Lu/BCAM). In the present work, we investigated the functional impact of endothelial exposure to hydroxycarbamide (HC) on this interaction using transformed human bone marrow endothelial cells and primary human pulmonary microvascular endothelial cells. Adhesion of sickle reticulocytes to HC-treated endothelial cells was decreased despite the HC-derived increase of Lu/BCAM expression. This was associated with decreased phosphorylation of Lu/BCAM and up-regulation of the cAMP-specific phosphodiesterase 4A expression. Our study reveals a novel mechanism for HC in endothelial cells where it could modulate the function of membrane proteins through the regulation of phosphodiesterase expression and cAMP-dependent signaling pathways.     

Dynamic adhesion of eryptotic erythrocytes to endothelial cells via CXCL16/SR-PSOX

Suicidal death of erythrocytes, or eryptosis, is characterized by cell shrinkage and cell membrane scrambling leading to phosphatidylserine exposure at the cell surface. Eryptosis is triggered by increase of cytosolic Ca2+ activity, which may result from treatment with the Ca2+ ionophore ionomycin or from energy depletion by removal of glucose. The present study tested the hypothesis that phosphatidylserine exposure at the erythrocyte surface fosters adherence to endothelial cells of the vascular wall under flow conditions at arterial shear rates and that binding of eryptotic cells to endothelial cells is mediated by the transmembrane CXC chemokine ligand 16 (CXCL16). To this end, human erythrocytes were exposed to energy depletion (for 48 h) or treated with the Ca2+ ionophore ionomycin (1 μM for 30 min). Phosphatidylserine exposure was quantified utilizing annexin-V binding, cell volume was estimated from forward scatter in FACS analysis, and erythrocyte adhesion to human vascular endothelial cells (HUVEC) was determined in a flow chamber model. As a result, both, ionomycin and glucose depletion, triggered eryptosis and enhanced the percentage of erythrocytes adhering to HUVEC under flow conditions at arterial shear rates. The adhesion was significantly blunted in the presence of erythrocyte phosphatidylserine-coating annexin-V (5 μl/ml), of a neutralizing antibody against endothelial CXCL16 (4 μg/ml), and following silencing of endothelial CXCL16 with small interfering RNA. The present observations demonstrate that eryptotic erythrocytes adhere to endothelial cells of the vascular wall in part by interaction of phosphatidylserine exposed at the erythrocyte surface with endothelial CXCL16.     

Red blood cells initiate leukocyte rolling in postcapillary expansions: a lattice Boltzmann analysis

Leukocyte rolling on the vascular endothelium requires initial contact between leukocytes circulating in the blood and the vessel wall. Although specific adhesion mechanisms are involved in leukocyte-endothelium interactions, adhesion patterns in vivo suggest other rheological mechanisms also play a role. Previous studies have proposed that the abundance of leukocyte rolling in postcapillary venules is due to interactions between red blood cells (RBCs) and leukocytes as they enter postcapillary expansions, but the details of the fluid dynamics have not been elucidated. We have analyzed the interactions of red and white blood cells as they flow from a capillary into a postcapillary venule using a lattice Boltzmann approach. This technique provides the complete solution of the flow field and quantification of the particle-particle forces in a relevant geometry. Our results show that capillary-postcapillary venule diameter ratio, RBC configuration, and RBC shape are critical determinants of the initiation of cell rolling in postcapillary venules. The model predicts that an optimal configuration of the trailing red blood cells is required to drive the white blood cell to the wall.     

Mechanisms of uremic erythrocyte-induced adhesion of human monocytes to cultured endothelial cells

In end-stage renal disease (ESRD) endothelium may represent a key target for the action of circulating elements, such as modified erythrocytes (RBC) and/or plasmatic factors, that may facilitate inflammation and the vasculopathy associated with uremia. We have previously demonstrated that phosphatidylserine (PS) exposure on the surface of RBC from ESRD patients increases RBC-human umbilical vein endothelial cell (HUVEC) interactions and causes decreased nitric oxide (NO) production. We postulated that, besides the pro-inflammatory effects due to decreased NO bio-availability, enhanced ESRD-RBC-HUVEC interactions might directly stimulate pro-inflammatory pathways leading to increased vascular adhesion molecule expression. ESRD-RBC-endothelial cell interactions induced a time-dependent up-regulation of VCAM-1 and ICAM-1 (measured by Western blot (WB) and real-time PCR), associated with mitogen-activated protein kinase (MAPK) activation and impairment of the Akt/endothelial nitric oxide synthase (eNOS) signaling cascade, measured by WB. In reconstitution experiments, normal RBC incubated with uremic plasma showed increased PS exposure and significantly increased VCAM-1 and ICAM-1 mRNA levels when incubated on HUVEC. Interestingly, ESRD-RBC induced increased expression of adhesion molecules was prevented by Annexin-V (AnV, able to mask PS on RBC surface), anti-integrin-alpha(v)beta3, anti-thrombospondin-1 (TSP-1), and PD98059 (a selective inhibitor of MAPK phosphorylation). Moreover, AnV reversed the ESRD-RBC effects on MAPK and Akt/eNOS signaling pathways. Our data demonstrate that, possibly via a direct interaction with the endothelial thrombospondin-(alpha(v)beta3) integrin complex, ESRD-RBC-HUVEC adhesion induces a vascular inflammatory phenotype. Thus, intervention targeting ESRD-RBC increased adhesion to endothelium and/or MAPK and Akt/eNOS pathways may have the potential to prevent vascular lesions under uremic conditions.     

Enhanced release of soluble urokinase receptor by endothelial cells in contact with peripheral blood cells

The urokinase receptor (uPAR) on the cell surface plays an important role in extracellular proteolysis, cell migration and adhesion. Soluble uPAR (suPAR) has been recently discovered in plasma, but its origin is unclear. Our results now demonstrate that both unstimulated blood mononuclear and endothelial cells can release suPAR and that the release is enhanced when either mononuclear cells or thrombocytes are cultured together with endothelial cells. Co-culture without cell-cell contacts fails to enhance suPAR release. We also found suPAR fragments, known to be potent inducers of chemotaxis, in co-culture growth medium samples. Taken together, our results suggest that normal plasma suPAR can be produced by endothelial and mononuclear cells and that suPAR release in cell-cell contacts may have a regulatory role in cell adhesion.     

Coculture with endothelial cells enhances vascular smooth muscle cell adhesion and spreading via activation of beta1-integrin and phosphatidylinositol 3-kinase/Akt

The interactions between endothelial cells (ECs) and vascular smooth muscle cells (VSMCs) play significant roles in the homeostasis of the blood vessel during vascular remodeling. Cell adhesion and spreading are an essential process for VSMC migration, survival and proliferation in the events of vascular physiology and pathophysiology. However, effects of ECs on adhesion and spreading of VSMCs have not been characterized yet. Here, the interaction of ECs and VSMCs on adhesion and spreading of VSMCs were investigated by using a coculture system. The results showed that VSMCs cocultured with ECs exhibited a significant increase in the number of adherent and spreading cells, and much more mRNA (twofold, P<0.01) and protein (threefold, P<0.05) expression of beta(1)-integrin comparing to the control, i.e., VSMCs cultured alone. Furthermore, the enhanced functional activity of beta(1)-integrin expression was confirmed by FACS. A beta(1)-integrin blocking antibody (P5D2) could inhibit the EC-induced VSMC adhesion and spreading. It was demonstrated that in correspondence with enhanced cell adhesion, ECs also prompted focal adhesion complex assembly and stress fiber formation of VSMCs. The phosphatidylinositol 3-kinase (PI3K)/Akt pathway was more pronouncedly activated in response to VSMC attachment. Our results for the first time show that coculture with ECs enhances VSMC adhesion and spreading by up-regulating beta(1)-integrin expression and activating the PI3K/Akt pathway, suggesting that the interaction between ECs and VSMCs serves an important role in vascular homeostasis and remodeling.     

EndoCAM: a novel endothelial cell-cell adhesion molecule

Cell-cell adhesion is controlled by many molecules found on the cell surface. In addition to the constituents of well-defined junctional structures, there are the molecules that are thought to play a role in the initial interactions of cells and that appear at precise times during development. These include the cadherins and cell adhesion molecules (CAMs). Representatives of these families of adhesion molecules have been isolated from most of the major tissues. The notable exception is the vascular endothelium. Here we report the identification of a cell surface molecule designated "endoCAM" (endothelial Cell Adhesion Molecule), which may function as an endothelial cell-cell adhesion molecule. EndoCAM is a 130-kD glycoprotein expressed on the surface of endothelial cells both in culture and in situ. It is localized to the borders of contiguous endothelial cells. It is also present on platelets and white blood cells. Antibodies against endoCAM prevent the initial formation of endothelial cell-cell contacts. Despite similarities in size and intercellular location, endoCAM does not appear to be a member of the cadherin family of adhesion receptors. The serologic and protease susceptibility characteristics of endoCAM are different from those of the known cadherins, including an endogenous endothelial cadherin. Although the precise biologic function of endoCAM has not been determined, it appears to be one of the molecules responsible for regulating endothelial cell-cell adhesion processes and may be involved in platelet and white blood cell interactions with the endothelium.     

Cytoadhesion and falciparum malaria: going with the flow

Sequestration of parasitized red blood cells in the cerebral vasculature is the predisposing event to the development of cerebral malaria during infection with Plasmodium falciparum. The adhesive interaction between these cells and receptors on the endothelial cell (cytoadhesion) occurs in the dynamic environment of the microcirculation, but most studies have neglected this factor and have concentrated on measuring adhesion in static (no flow) assays. Such studies ignore the markedly different rheological properties of parasitized red blood cells that become apparent when adhesion is examined under dynamic, flow conditions that resemble those of the circulation in vivo. Here, Brian Cooke and Ross Coppel review a number of novel aspects of cytoadhesion that have been identified using flow-based assays, and discuss their relevance to the pathophysiology, investigation and clinical management of falciparum malaria.     

Flow-conditioned HUVECs support clustered leukocyte adhesion by coexpressing ICAM-1 and E-selectin

Endothelial sequestration of circulating monocytes is a key event in early atherosclerosis. Hemodynamics is proposed to regulate monocyte-endothelial cell interactions by direct cell activation and establishment of flow environments that are conducive or prohibitive to cell-cell interaction. We investigated fluid shear regulation of monocyte-endothelial cell adhesion in vitro using a disturbed laminar shear system that models in vivo hemodynamics characteristic of lesion-prone vascular regions. Human endothelial cell monolayers were flow conditioned for 6 h before evaluation of monocyte adhesion under static and dynamic flow conditions. Results revealed a distinctive clustered cell pattern of monocyte adhesion that strongly resembles in vivo leukocyte adhesion in early- and late-stage atherosclerosis. Clustered monocyte cell adhesion correlated with endothelial cells coexpressing intercellular adhesion molecule-1 (ICAM-1) and E-selectin as result of a flow-induced, selective upregulation of E-selectin expression in a subset of ICAM-1-expressing cells. Clustered monocyte cell adhesion assayed under static conditions exhibited a spatial variation in size and frequency of occurrence, which demonstrates differential regulation of endothelial cell adhesiveness by the local flow environment. Dynamic adhesion studies conducted with circulating monocytes resulted in clustered cell adhesion only within the disturbed flow region, where the monocyte rate of motion is sufficiently low for cell-cell interaction. These studies provide evidence and reveal mechanisms of local hemodynamic regulation of endothelial adhesiveness and endothelial monocyte interaction that lead to localized monocyte adhesion and potentially contribute to the focal origin of arterial diseases such as atherosclerosis.     

ADAM15 overexpression in NIH3T3 cells enhances cell-cell interactions.

ADAM15 is a member of the family of metalloprotease-disintegrins that have been shown to interact with integrins in an RGD- and non-RGD-dependent manner. In the present study, we examined the effects of ADAM15 overexpression on cell-matrix and cell-cell interactions in NIH3T3 cells. Tetracycline-regulated ADAM15 overexpression in NIH3T3 cells leads to an inhibition of migration on a fibronectin-coated filter in a Boyden chamber assay and in a scratch wound model. The effects of ADAM15 overexpression on cell migration are not due to changes in matrix attachment or to the lack of extracellular signal-regulated kinase signaling response to PDGF or fibronectin. However, a decrease in monolayer permeability with ADAM15 overexpression and altered cell morphology suggest a possible increase in cell-cell interaction. Analysis of adhesion of NIH3T3 cells to a polyclonal population of cells retrovirally transduced to overexpress ADAM15 demonstrates a 45% increase in cell adhesion, compared with enhanced green fluorescent protein-expressing control cells. In addition, we demonstrate localization of HA-epitope-tagged ADAM15 to cell-cell contacts in an epithelial cell line that forms extensive cell-cell contact structures. Thus, overexpression of ADAM15 in NIH3T3 cells appears to enhance cell-cell interactions, as suggested by decreased cell migration, altered cell morphology at the wound edge, decreased monolayer permeability, and increased cell adhesion to monolayers of cells expressing ADAM15 by retroviral transduction.     

Wnt-1 modulates cell-cell adhesion in mammalian cells by stabilizing beta-catenin binding to the cell adhesion protein cadherin

Wnt-1 homologs have been identified in invertebrates and vertebrates and play important roles in cellular differentiation and organization. In Drosophila, the products of the segment polarity genes wingless (the Wnt-1 homolog) and armadillo participate in a signal transduction pathway important for cellular boundary formation in embryonic development, but functional interactions between the proteins are unknown. We have examined Wnt-1 function in mammalian cells in which armadillo (beta-catenin and plakoglobin) is known to bind to and regulate cadherin cell adhesion proteins. We show that Wnt-1 expression results in the accumulation of beta-catenin and plakoglobin. In addition, binding of beta-catenin to the cell adhesion protein, cadherin, is stabilized, resulting in a concomitant increase in the strength of calcium-dependent cell-cell adhesion. Thus, a consequence of the functional interaction between Wnt-1 and armadillo family members is the strengthening of cell-cell adhesion, which may lead to the specification of cellular boundaries.