Calcium-induced intercellular adhesion of keratinocytes does not involve accumulation of beta 1 integrins at cell-cell contacts and does not involve changes in the levels or phosphorylation of catenins.
On initiation of terminal differentiation human epidermal keratinocytes detach from the underlying basement membrane as a result of inactivation and subsequent loss of integrins from the cell surface. Assembly of keratinocytes into multilayered sheets requires functional E- and P-cadherin and when stratification is inhibited in low calcium medium differentiating keratinocytes continue to express functional integrins. Using immunofluorescence microscopy, we found that on addition of calcium ions to keratinocyte monolayers there was colocalisation of the beta 1 integrins and E-cadherin along the lateral membranes except for a zone close to the substratum which exclusively contained integrins. Quantitative immunoelectron microscopy showed that on induction of stable cell-cell contacts the density of beta 1 integrins was the same on the apical and lateral membranes, suggesting that the accumulation of integrins on the lateral membranes observed by immunofluorescence microscopy is due to the increased area of contact between adjacent cells and not to an increase in receptor density. There were no changes in the levels of catenins and their degree of phosphorylation after induction of cell-cell contacts. These observations provide new sights into the mechanism of calcium-dependent intercellular adhesion of keratinocytes.