Hemidesmosomes in the epithelial cell line 804G: their fate during wound closure, mitosis and drug induced reorganization of the cytoskeleton.

Recently, we identified a novel epithelial cell line, 804G, derived from rat bladder, which readily forms hemidesmosomes in vitro. One of the major structural components of the plaques of 804G cell hemidesmosomes is a 230 kDa antigen recognized by autoantibodies in the sera of patients with bullous pemphigoid (BP). An additional polypeptide of 180 kDa also localizes to the hemidesmosome plaque of 804G cells as determined by immunoelectron microscopy. Using confocal fluorescence/phase microscopy, we have employed both 230 kDa and 180 kDa antibody probes to monitor the fate of hemidesmosomes following closure of in vitro wounds, during mitosis, and following drug induced disruption of the cytoskeleton. The punctate cell-substratum associated staining generated by the hemidesmosomal antibodies in stationary unwounded 804G cell cultures is greatly diminished or even lost in cells which enter wound sites, presumably in response to enhanced cell motility. Few, if any hemidesmosomes are observed at the ultrastructural level in cells which have migrated into the wound area. However, as closure of the wound becomes complete, staining along the substratum attached surface of cells returns. During mitosis, there is no obvious loss of hemidesmosomal antigens along the basal surface of 804G cells, and formed hemidesmosomes can be observed in mitotic cells at the ultrastructural level. In 804G cells treated with colchicine, the typical subnuclear pattern of distribution of hemidesmosomal antigens is unaffected. In contrast, following treatment of 804G cells with cytochalasin D, hemidesmosomal antigens become concentrated at the cell periphery and no longer appear in the subnuclear region. Furthermore, formed hemidesmosomes are observed at the cell periphery of cytochalasin D-treated cells by electron microscopy. We suggest that hemidesmosomal plaques are mobile within the plasma membrane. We speculate that hemidesmosomal interactions with extracellular ligands are dynamic and we discuss a possible mechanism by which cytochalasin D induces reorganization of hemidesmosomes along the basal surface of 804G cells.