POLARIZATION-DEPENDENT ASSOCIATION OF PLECTIN WITH DESMOPLAKIN AND THE LATERAL SUBMEMBRANE SKELETON IN MDCK CELLS

The intermediate filament-binding protein plectin and cytokeratin were localised at the cellular periphery of fully polarised Madin-Darby ca nine kidney (MDCK) cells, whereas vimentin was primarily found in a pe rinuclear network. Confocal and immunoelectron microscopy revealed tha t plectin was restricted to areas underlying the lateral plasma membra ne, It colocalised with fodrin, a component of the submembrane skeleto n, and was closely associated with desmosomal plaque structures, Bioch emically, plectin was shown to interact directly with immuno-precipita ted desmoplakin in vitro. Upon loss of cell polarity in low calcium me dium, plectin redistributed to a cytoplasmic vimentin- and cytokeratin -related network, clearly distinct from diffusely distributed fodrin a nd internalised desmoplakin structures, The structural reorganisation of plectin was also reflected by an increased solubility of the protei n in Triton X-100/high salt, and a decrease in its half-life from simi lar to 20 to similar to 5 hours, Furthermore, unlike cytokeratins and vimentin, desmoplakin and fodrin did not associate with plectin attach ed to magnetic beads in cell lysates of unpolarised cells, while all p roteins formed a stable complex in polarised cells, Altogether, these data indicate that plectin is involved in the anchorage of intermediat e filaments to desmosomes and to the submembrane skeleton in polarised MDCK cells.