Epithelial cell adhesion molecule (Ep-CAM) modulates cell-cell interactions mediated by classic cadherins.
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.
Litvinov
S V
SV
Department of Pathology, Leiden University, Leiden 2300 RC, The Netherlands. slitvinov@pathology.medfac.leidenuniv.nl
Balzar
M
M
Winter
M J
MJ
Bakker
H A
HA
Briaire-de Bruijn
I H
IH
Prins
F
F
Fleuren
G J
GJ
Warnaar
S O
SO
D000818:Animals; D000951:Antigens, Neoplasm / Q000235:genetics / Q000378:metabolism*; D015820:Cadherins / Q000378:metabolism*; D015815:Cell Adhesion Molecules / Q000235:genetics / Q000378:metabolism*; D002449:Cell Aggregation; D002460:Cell Line; D003599:Cytoskeleton / Q000378:metabolism; D000071858:Epithelial Cell Adhesion Molecule; D004847:Epithelial Cells; D006801:Humans; D007365:Intercellular Junctions; D051379:Mice; D011485:Protein Binding; D011994:Recombinant Proteins / Q000378:metabolism; D013329:Structure-Activity Relationship; D014407:Tumor Cells, Cultured
D000951:Antigens, Neoplasm; D015820:Cadherins; D015815:Cell Adhesion Molecules; D000071858:Epithelial Cell Adhesion Molecule; D011994:Recombinant Proteins