A novel type of adhering junction in an epithelioid tumorigenic rat cell culture line

• Published in: Cell and tissue research 1998-10, Vol.294 (1), p.11-25
• Main Authors: Schmelz, M, Way, D L, Borgs, P, Peitsch, W K, Schmidt, H, Witte, M H, Witte, C L, Franke, W W, Moll, R
• Format: Article
• Language: English
• Subjects: alpha Catenin; Animals; beta Catenin; Cadherins - metabolism; Cell Adhesion Molecules - metabolism; Cytoskeletal Proteins - metabolism; Desmocollins; Desmogleins; Desmoplakins; Desmosomes - metabolism; Desmosomes - ultrastructure; gamma Catenin; Intercellular Junctions - metabolism; Intercellular Junctions - ultrastructure; Membrane Proteins - metabolism; Mice; Mice, Nude; Microscopy, Electron; Microscopy, Fluorescence; Neoplasms, Experimental - metabolism; Neoplasms, Experimental - pathology; Phosphoproteins - metabolism; Rats; Trans-Activators; Tumor Cells, Cultured; Vinculin - metabolism; Zonula Occludens-1 Protein
• ISSN: 0302-766X; 1432-0878
• DOI: 10.1007/s004410051152

Two major types of plaque-bearing adhering junctions are commonly distinguished: the actin microfilament-anchoring adhaerens junctions (AJs) and the desmosomes anchoring intermediate-sized filaments (IFs). Both types of junction usually possess the common plaque protein, plakoglobin, whereas the other plaque proteins and the transmembrane cadherins are mutually exclusive. For example, AJs contain E-, N-, or P-cadherin in combination with alpha- and beta-catenin, vinculin and alpha-actinin, whereas in desmosomes, desmogleins and desmocollins are associated with desmoplakin and one or several of the plakophilins (PP1-3). Here we describe a novel type of adhering junction comprising proteins of both AJs and desmosomes and the tight junction (TJ) plaque protein, ZO-1, in a newly established, liver-derived tumorigenic rat cell line (RMEC-1). By immunofluorescence microscopy, cell-cell contacts are characterized by mostly continuous-appearing lines which are usually resolved by electron microscopy as extended arrays of closely spaced small plaque subunits. These plaque-covered regions are positive for plakoglobin, alpha- and beta-catenin, the arm-repeat protein p120, vinculin, desmoplakin and protein ZO-1. They are positive for E-cadherin in cultures early on in passaging, but tend to turn negative for all known cadherins in densely grown cultures. On immunoblotting SDS-PAGE-separated proteins from dense-grown cell monolayers, "pan-cadherin" antibodies have reacted with a band at approximately 140 kDa, identified as N-cadherin by peptide fingerprinting of the immunoprecipitated protein, which for reasons not yet clear is modified or masked in immunolocalization experiments. The exact histological derivation of RMEC-1 cells is not known. However, the observations of several endothelial markers and the fact that all cells are rich in IFs containing vimentin and/or desmin, while only subpopulations also reveal IFs containing CKs 8 and 18, is suggestive of a mesenchymal, probably endothelial origin. We discuss the molecular relationship of this novel type of extended junction with other types of adhering junctions.