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Epithelial cell adhesion molecule (Ep-CAM) modulates cell-cell interactions mediated by classic cadherins.

Litvinov SV, Balzar M, Winter MJ, Bakker HA, Briaire-de Bruijn IH, Prins F, Fleuren GJ, Warnaar SO - J. Cell Biol. (1997)

Bottom Line: Similarly, the detergent-insoluble fractions of alpha- and beta-catenins decreased in cells overexpressing Ep-CAM.While the total beta-catenin content remains unchanged, a reduction in total cellular alpha-catenin is observed as Ep-CAM expression increases.The ability of Ep-CAM to modulate the cadherin-mediated cell-cell interactions, as demonstrated in the present study, suggests a role for this molecule in development of the proliferative, and probably malignant, phenotype of epithelial cells, since an increase of Ep-CAM expression was observed in vivo in association with hyperplastic and malignant proliferation of epithelial cells.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathology, Leiden University, Leiden 2300 RC, The Netherlands. slitvinov@pathology.medfac.leidenuniv.nl

ABSTRACT
The contribution of noncadherin-type, Ca2+-independent cell-cell adhesion molecules to the organization of epithelial tissues is, as yet, unclear. A homophilic, epithelial Ca2+-independent adhesion molecule (Ep-CAM) is expressed in most epithelia, benign or malignant proliferative lesions, or during embryogenesis. Here we demonstrate that ectopic Ep-CAM, when expressed in cells interconnected by classic cadherins (E- or N-cadherin), induces segregation of the transfectants from the parental cell type in coaggregation assays and in cultured mixed aggregates, respectively. In the latter assay, Ep-CAM-positive transfectants behave like cells with a decreased strength of cell-cell adhesion as compared to the parental cells. Using transfectants with an inducible Ep-CAM-cDNA construct, we demonstrate that increasing expression of Ep-CAM in cadherin-positive cells leads to the gradual abrogation of adherens junctions. Overexpression of Ep-CAM has no influence on the total amount of cellular cadherin, but affects the interaction of cadherins with the cytoskeleton since a substantial decrease in the detergent-insoluble fraction of cadherin molecules was observed. Similarly, the detergent-insoluble fractions of alpha- and beta-catenins decreased in cells overexpressing Ep-CAM. While the total beta-catenin content remains unchanged, a reduction in total cellular alpha-catenin is observed as Ep-CAM expression increases. As the cadherin-mediated cell-cell adhesions diminish, Ep-CAM-mediated intercellular connections become predominant. An adhesion-defective mutant of Ep-CAM lacking the cytoplasmic domain has no effect on the cadherin-mediated cell-cell adhesions. The ability of Ep-CAM to modulate the cadherin-mediated cell-cell interactions, as demonstrated in the present study, suggests a role for this molecule in development of the proliferative, and probably malignant, phenotype of epithelial cells, since an increase of Ep-CAM expression was observed in vivo in association with hyperplastic and malignant proliferation of epithelial cells.

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Ultrastructure of the aggregates formed by HCA/C  and HCA/CEp cells. Reflection contrast micrographs of cross  sections through the aggregates formed in 90 min by each cell  type reveals a tight organization of the HCA/C aggregates and  loosely interconnected cells forming the HCA/CEp aggregates.  (A) Electron microscopy on the preparations shows the abundant  presence of the adherens junctions between HCA/C cells (arrows). In contrast, microvilli (B, arrow) were found at the intercellular space between the cells of internal layers of HCA/CEp  cells. In HCA/C cells, microvilli were present almost exclusively  at the apical membrane of the outer layer of cells in the aggregate  and not on the surface of the cells from internal layers. Bars: (left)  10 μm; (right) 0.25 μm.
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Figure 10: Ultrastructure of the aggregates formed by HCA/C and HCA/CEp cells. Reflection contrast micrographs of cross sections through the aggregates formed in 90 min by each cell type reveals a tight organization of the HCA/C aggregates and loosely interconnected cells forming the HCA/CEp aggregates. (A) Electron microscopy on the preparations shows the abundant presence of the adherens junctions between HCA/C cells (arrows). In contrast, microvilli (B, arrow) were found at the intercellular space between the cells of internal layers of HCA/CEp cells. In HCA/C cells, microvilli were present almost exclusively at the apical membrane of the outer layer of cells in the aggregate and not on the surface of the cells from internal layers. Bars: (left) 10 μm; (right) 0.25 μm.

Mentions: Despite the fact that after 90 min no substantial differences in aggregation extent were observed between the control and the Ep-CAM transfectants, the structure of the aggregates formed by these two cell lines differed substantially. As can be seen on cross sections, the HCA/C aggregates were composed of tightly interconnected cells, in contrast to HCA/CEp aggregates, which were formed by loosely interconnected cells (Fig. 10). In the internal layers of the HCA/C aggregates, the membranes of the cells were interconnected by multiple adherence junctions (Fig. 10), whereas in HCA/CEp cell aggregates the cell–cell contacts were rare and often did not contain morphologically distinguishable adherens junctions. The membranes of neighboring cells in these aggregates were mainly not in close proximity. In these intercellular spaces, microvilli were often observed (Fig. 10), which were present in HCA/C aggregates at the outer surface of the external layer of cells only.


Epithelial cell adhesion molecule (Ep-CAM) modulates cell-cell interactions mediated by classic cadherins.

Litvinov SV, Balzar M, Winter MJ, Bakker HA, Briaire-de Bruijn IH, Prins F, Fleuren GJ, Warnaar SO - J. Cell Biol. (1997)

Ultrastructure of the aggregates formed by HCA/C  and HCA/CEp cells. Reflection contrast micrographs of cross  sections through the aggregates formed in 90 min by each cell  type reveals a tight organization of the HCA/C aggregates and  loosely interconnected cells forming the HCA/CEp aggregates.  (A) Electron microscopy on the preparations shows the abundant  presence of the adherens junctions between HCA/C cells (arrows). In contrast, microvilli (B, arrow) were found at the intercellular space between the cells of internal layers of HCA/CEp  cells. In HCA/C cells, microvilli were present almost exclusively  at the apical membrane of the outer layer of cells in the aggregate  and not on the surface of the cells from internal layers. Bars: (left)  10 μm; (right) 0.25 μm.
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Related In: Results  -  Collection

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Figure 10: Ultrastructure of the aggregates formed by HCA/C and HCA/CEp cells. Reflection contrast micrographs of cross sections through the aggregates formed in 90 min by each cell type reveals a tight organization of the HCA/C aggregates and loosely interconnected cells forming the HCA/CEp aggregates. (A) Electron microscopy on the preparations shows the abundant presence of the adherens junctions between HCA/C cells (arrows). In contrast, microvilli (B, arrow) were found at the intercellular space between the cells of internal layers of HCA/CEp cells. In HCA/C cells, microvilli were present almost exclusively at the apical membrane of the outer layer of cells in the aggregate and not on the surface of the cells from internal layers. Bars: (left) 10 μm; (right) 0.25 μm.
Mentions: Despite the fact that after 90 min no substantial differences in aggregation extent were observed between the control and the Ep-CAM transfectants, the structure of the aggregates formed by these two cell lines differed substantially. As can be seen on cross sections, the HCA/C aggregates were composed of tightly interconnected cells, in contrast to HCA/CEp aggregates, which were formed by loosely interconnected cells (Fig. 10). In the internal layers of the HCA/C aggregates, the membranes of the cells were interconnected by multiple adherence junctions (Fig. 10), whereas in HCA/CEp cell aggregates the cell–cell contacts were rare and often did not contain morphologically distinguishable adherens junctions. The membranes of neighboring cells in these aggregates were mainly not in close proximity. In these intercellular spaces, microvilli were often observed (Fig. 10), which were present in HCA/C aggregates at the outer surface of the external layer of cells only.

Bottom Line: Similarly, the detergent-insoluble fractions of alpha- and beta-catenins decreased in cells overexpressing Ep-CAM.While the total beta-catenin content remains unchanged, a reduction in total cellular alpha-catenin is observed as Ep-CAM expression increases.The ability of Ep-CAM to modulate the cadherin-mediated cell-cell interactions, as demonstrated in the present study, suggests a role for this molecule in development of the proliferative, and probably malignant, phenotype of epithelial cells, since an increase of Ep-CAM expression was observed in vivo in association with hyperplastic and malignant proliferation of epithelial cells.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathology, Leiden University, Leiden 2300 RC, The Netherlands. slitvinov@pathology.medfac.leidenuniv.nl

ABSTRACT
The contribution of noncadherin-type, Ca2+-independent cell-cell adhesion molecules to the organization of epithelial tissues is, as yet, unclear. A homophilic, epithelial Ca2+-independent adhesion molecule (Ep-CAM) is expressed in most epithelia, benign or malignant proliferative lesions, or during embryogenesis. Here we demonstrate that ectopic Ep-CAM, when expressed in cells interconnected by classic cadherins (E- or N-cadherin), induces segregation of the transfectants from the parental cell type in coaggregation assays and in cultured mixed aggregates, respectively. In the latter assay, Ep-CAM-positive transfectants behave like cells with a decreased strength of cell-cell adhesion as compared to the parental cells. Using transfectants with an inducible Ep-CAM-cDNA construct, we demonstrate that increasing expression of Ep-CAM in cadherin-positive cells leads to the gradual abrogation of adherens junctions. Overexpression of Ep-CAM has no influence on the total amount of cellular cadherin, but affects the interaction of cadherins with the cytoskeleton since a substantial decrease in the detergent-insoluble fraction of cadherin molecules was observed. Similarly, the detergent-insoluble fractions of alpha- and beta-catenins decreased in cells overexpressing Ep-CAM. While the total beta-catenin content remains unchanged, a reduction in total cellular alpha-catenin is observed as Ep-CAM expression increases. As the cadherin-mediated cell-cell adhesions diminish, Ep-CAM-mediated intercellular connections become predominant. An adhesion-defective mutant of Ep-CAM lacking the cytoplasmic domain has no effect on the cadherin-mediated cell-cell adhesions. The ability of Ep-CAM to modulate the cadherin-mediated cell-cell interactions, as demonstrated in the present study, suggests a role for this molecule in development of the proliferative, and probably malignant, phenotype of epithelial cells, since an increase of Ep-CAM expression was observed in vivo in association with hyperplastic and malignant proliferation of epithelial cells.

Show MeSH
Related in: MedlinePlus