A protein antigenically related to nuclear lamin B mediates the association of intermediate filaments with desmosomes

Abstract

Desmosomes are specialized domains of epithelial cell plasma membranes engaged in the anchoring of intermediate filaments (IF). So far, the desmosomal component(s) responsible for this binding has not been unambiguously identified. In the present work, we have examined bovine muzzle epidermis desmosomes for the presence of protein(s) structurally and functionally related to lamin B, the major receptor for IF in the nuclear envelope (Georgatos, S. D., and G. Blobel. 1987. J. Cell Biol. 105:105-115). By using polyclonal antibodies to lamin B in immunoblotting experiments, we find that a desmosomal protein of 140-kD shares epitope(s) with lamin B. Immunoelectron microscopic and urea extraction experiments show that this protein is a peripheral protein localized at the cytoplasmic side of the desmosomes (desmosomal plaques). Furthermore, this protein binds vimentin in an in vitro assay. Since this binding is inhibited by lamin B antibodies, the epitopes common to the 140-kD protein and to lamin B may be responsible for anchoring of intermediate filaments to desmosomes. These data suggest that lamin B-related proteins (see also Cartaud, A., J. C. Courvalin, M. A. Ludosky, and J. Cartaud. 1989. J. Cell Biol. 109:1745-1752) together with lamin B, provide cells with several nucleation sites, which can account for the multiplicity of IF organization in tissues.