Protein kinase C activation upregulates intercellular adhesion of alpha-catenin-negative human colon cancer cell variants via induction of desmosomes.
The alpha-catenin molecule links E-cadherin/ beta-catenin or E-cadherin/plakoglobin complexes to the actin cytoskeleton. We studied several invasive human colon carcinoma cell lines lacking alpha-catenin. They showed a solitary and rounded morphotype that correlated with increased invasiveness. These round cell variants acquired a more normal epithelial phenotype upon transfection with an alpha-catenin expression plasmid, but also upon treatment with the protein kinase C (PKC) activator 12-O-tetradecanoyl-phorbol-13-acetate (TPA). Video registrations showed that the cells started to establish elaborated intercellular junctions within 30 min after addition of TPA. Interestingly, this normalizing TPA effect was not associated with alpha-catenin induction. Classical and confocal immunofluorescence showed only minor TPA-induced changes in E-cadherin staining. In contrast, desmosomal and tight junctional proteins were dramatically rearranged, with a conversion from cytoplasmic clusters to obvious concentration at cell-cell contacts and exposition at the exterior cell surface. Electron microscopical observations revealed the TPA-induced appearance of typical desmosomal plaques. TPA-restored cell-cell adhesion was E-cadherin dependent as demonstrated by a blocking antibody in a cell aggregation assay. Addition of an antibody against the extracellular part of desmoglein-2 blocked the TPA effect, too. Remarkably, the combination of anti-E-cadherin and anti-desmoglein antibodies synergistically inhibited the TPA effect. Our studies show that it is possible to bypass the need for normal alpha-catenin expression to establish tight intercellular adhesion by epithelial cells. Apparently, the underlying mechanism comprises upregulation of desmosomes and tight junctions by activation of the PKC signaling pathway, whereas E-cadherin remains essential for basic cell-cell adhesion, even in the absence of alpha-catenin.
van Hengel
J
J
Department of Molecular Biology, Laboratory of Molecular Cell Biology, University of Ghent and Flanders Interuniversity Institute of Biotechnology (V.I.B.), B-9000 Ghent, Belgium.
Gohon
L
L
Bruyneel
E
E
Vermeulen
S
S
Cornelissen
M
M
Mareel
M
M
von Roy
F
F
D000954:Antigens, Surface / Q000378:metabolism; D015820:Cadherins / Q000378:metabolism; D002448:Cell Adhesion / Q000187:drug effects / Q000502:physiology; D048429:Cell Size / Q000502:physiology; D003110:Colonic Neoplasms; D003598:Cytoskeletal Proteins / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D018076:DNA, Complementary; D003896:Desmosomes / Q000737:chemistry* / Q000201:enzymology*; D003902:Detergents; D006801:Humans; D008854:Microscopy, Electron; D011493:Protein Kinase C / Q000378:metabolism*; D012995:Solubility; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D019108:Tight Junctions / Q000737:chemistry / Q000201:enzymology; D015534:Trans-Activators; D014162:Transfection; D014407:Tumor Cells, Cultured / Q000166:cytology / Q000201:enzymology / Q000648:ultrastructure; D051178:alpha Catenin; D051176:beta Catenin
D000954:Antigens, Surface; C495273:CTNNA1 protein, human; C495270:CTNNB1 protein, human; D015820:Cadherins; D003598:Cytoskeletal Proteins; D018076:DNA, Complementary; D003902:Detergents; D015534:Trans-Activators; D051178:alpha Catenin; D051176:beta Catenin; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate