Differential expression of cell-cell adhesion proteins and cyclin D in MEK1-transdifferentiated MDCK cells.
Overexpression of a constitutively active mutant of the mitogen-activated protein kinase kinase MEK1 (caMEK1) in epithelial Madin-Darby canine kidney (MDCK)-C7 cells disrupts morphogenesis, induces an invasive phenotype, and is associated with a reduced rate of cell proliferation. The role of cell-cell adhesion molecules and cell cycle proteins in these processes, however, has not been investigated. We now report loss of E-cadherin expression as well as a marked reduction of beta- and alpha-catenin expression in transdifferentiated MDCK-C7 cells stably expressing caMEK1 (C7caMEK1) compared with epithelial mock-transfected MDCK-C7 (C7Mock1) cells. At least part of the remaining alpha-catenin was coimmunoprecipitated with beta-catenin, whereas no E-cadherin was detected in beta-catenin immunoprecipitates. In both cell types, the proteasome-specific protease inhibitors N-acetyl-Leu-Leu-norleucinal (ALLN) and lactacystin led to a time-dependent accumulation of beta-catenin, including the appearance of high-molecular-weight beta-catenin species. Quiescent as well as serum-stimulated C7caMEK1 cells showed a higher cyclin D expression than epithelial C7Mock1 cells. The MEK inhibitor U-0126 inhibited extracellular signal-regulated kinase phosphorylation and cyclin D expression in C7caMEK1 cells and almost abolished their already reduced cell proliferation rate. We conclude that the transdifferentiated and invasive phenotype of C7caMEK1 cells is associated with a diminished expression of proteins involved in cell-cell adhesion. Although beta-catenin expression is reduced, C7caMEK1 cells show a higher expression of U-0126-sensitive cyclin D protein.
Marschitz
I
I
Department of Physiology, University of Innsbruck, A-6010 Innsbruck, Austria.
Lechner
J
J
Mosser
I
I
Dander
M
M
Montesano
R
R
Schramek
H
H
D000818:Animals; D015820:Cadherins / Q000378:metabolism; D015815:Cell Adhesion Molecules / Q000378:metabolism*; D002454:Cell Differentiation / Q000502:physiology; D002455:Cell Division / Q000502:physiology; D002460:Cell Line / Q000166:cytology; D056741:Cyclin D; D016213:Cyclins / Q000378:metabolism*; D003546:Cysteine Endopeptidases / Q000502:physiology; D003598:Cytoskeletal Proteins / Q000378:metabolism; D004285:Dogs; D007668:Kidney / Q000166:cytology / Q000378:metabolism; D048369:MAP Kinase Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases / Q000235:genetics / Q000502:physiology*; D009097:Multienzyme Complexes / Q000502:physiology; D010447:Peptide Hydrolases / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000502:physiology*; D015534:Trans-Activators; D014162:Transfection; D051178:alpha Catenin; D051176:beta Catenin
D015820:Cadherins; D015815:Cell Adhesion Molecules; D056741:Cyclin D; D016213:Cyclins; D003598:Cytoskeletal Proteins; D009097:Multienzyme Complexes; D015534:Trans-Activators; D051178:alpha Catenin; D051176:beta Catenin; D017346:Protein Serine-Threonine Kinases; D048369:MAP Kinase Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases; D010447:Peptide Hydrolases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex