Calcium-induced reorganization of desmosomal components in cultured human keratinocytes.

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Abstract
Antibodies raised against individual desmosomal components were used to study Ca-induced desmosome formation in human keratinocytes. When keratinocytes are forced to grow as a monolayer by reducing the level of Ca ions in the culture medium, there is little contact between adjacent cells. Raising the level of Ca ions rapidly induces desmosome formation, and stratification occurs within 24 h. Before addition of Ca, the 115,000- and 100,000 MW core glycoproteins were distributed over the entire cell surface, whereas the plaque proteins (205,000 and 230,000 MW), the 82,000- and 86,000-MW proteins, and the 150,000-MW glycoprotein were located throughout the cytoplasm; 15 min after increasing the Ca ion concentration, all of these molecules appeared at the cell margins. The intensity of peripheral staining increased over the next 2 h and during this time the distribution of keratin filaments changed from predominantly perinuclear to extend throughout the cytoplasm. Keratinocytes could be dissociated with EDTA for up to 2 h after exposure to Ca. After 3 h of exposure to Ca the cells were no longer susceptible to EDTA dissociation and staining for desmosomal plaque antigens persisted in regions of intercellular contact. Desmosomal staining in stratified cultures became greatly reduced within 24 h of lowering the Ca ion concentration again. Stratification apparently occurs by breakdown of desmosomes at lateral surfaces and reformation at surfaces of contact between basal and suprabasal cells, rather than by rearrangement of existing desmosomes. Involucrin-positive cells in the monolayer appeared to contain more 205,000- and 230,000-MW proteins free in the cytoplasm than involucrin-negative cells.