Control of the distribution of hemidesmosome components in cultured keratinocytes: Ca2+ and phorbol esters.

DJM-1 cells (a human squamous cell carcinoma cell line) grown in low Ca2+ medium did not form cell-cell junctions of desmosome-keratin intermediate filament (KIF). When they were shifted to normal (high) Ca2+ medium, rapid translocation of desmoplakins from the cytosol to the plasma membrane to form desmosomes and reorganization of 180 kd-hemidesmosome proteins were induced almost simultaneously. In correlation with these morphological responses, the Ca2+ shift caused a breakdown of inositol phospholipids, a formation of diacylglycerol (DAG) and inositol trisphosphate (IP3), protein kinase C (PKC) activation, and Ca2+ influx. 12-0-tetradecanoylphorbol-13-acetate (TPA)-treatment of low Ca(2+)-grown DJM-1 cells also caused desmosome formation in association with PKC activation. These TPA effects were cancelled with PKC inhibitors, 1-(5-isoquinolinylsulfomyl)-2-methylpiperazine (H7) and staurosporine. Treatment with other PKC-activating agents, phorbol-12,13-butyrate (PDBu) and diaoctanoylglycerol (DOG), also induced desmosome formation. TPA-treatment of normal Ca(2+)-grown cells collapsed the organized distribution of the 180 kd-hemidesmosome protein and appeared to detach this protein from the cell-matrix adhering sites. This effect was also inhibited by H7. These results suggest that PKC activation plays important roles in upregulation of cell-cell junctions and downregulation of cell-matrix junctions in association with differentiation of keratinocytes.