Plakoglobin is a component of the filamentous subplasmalemmal coat of lens cells.

The plasma membranes of the cells of the superficial layer of the eye lens and the lens fibres are in close intercellular contact, leaving an intermembrane space of approximately 20 nm or less throughout their entire length. This plasma membrane is underlaid by a filamentous, cytoplasmic web containing actin, proteins of the spectrin and band 4.1 families, alpha-actinin and vinculin. Using immunofluorescence microscopy and immunoblotting of gel electrophoretically separated proteins, we show that plakoglobin, the plaque protein common to desmosomal and nondesmosomal adhering junctions, is present in lens cells and is also a component of the subplasmalemmal coat of these cells. Plakoglobin also exists in the extended regions of intercellular contacts between cultured lenticular cells where it often colocalizes with vinculin but does not occur in other vinculin-rich plasma membrane regions such as the focal adhesions at the ventral cell surface. Plakoglobin associated with plasma membrane regions can also be identified in various other adhesive cultured cells, but it is not detected in cells and tissues that do not establish firm intercellular junctions such as erythrocytes, platelets, cultured myeloma cells and smooth muscle tissue. We conclude that plakoglobin occurs, at least in lens cells, throughout the entire subplasmalemmal coat, coexisting in this situation not only with vinculin but also with spectrin and 4.1 protein(s). This colocalization infers the presence of a distinct, complex type of membrane-skeleton assembly involving the actin filament-associated junctional plaque elements plakoglobin and vinculin together with actin-associated proteins of the spectrin and band 4.1 protein families.