Altered processing of integrin receptors during keratinocyte activation

We used monoclonal antibodies against specific integrin subunits to examine the role of integrin receptors in keratinocyte activation. We found that before activation, β1 subunits in keratinocytes showed a diffuse distribution, whereas after activation, keratinocytes organized β1 receptors into marginal adhesion plaques. In immunoprecipitation experiments with antibodies against β1 integrin subunits, we found mostly immature subunits synthesized in keratinocytes freshly harvested from skin. Moreover, integrin receptor complexes immunoprecipitated from these cells by monoclonal antibodies against α2, α3, or α5 subunits contained only immature β1 subunits. With keratinocytes cultured 4-7 days, anti-β1 antibodies immunoprecipitated mostly mature β1 subunits, and integrin complexes immunoprecipitated from cultured cells by anti-α subunit antibodies contained mostly mature β1 subunits. Antibodies directed against β1 subunits also inhibited keratinocyte migration. Based on these results, we suggest that up-regulation of migration by activated keratinocytes depends on changes in processing of pre-β1 subunits to mature β1 subunits. We also studied the distribution of integrin subunits in skin and on keratinocytes migrating out of skin explants. Whereas β1, α2, and α3 subunits were detected in keratinocytes in skin and migrating out of explants, α5 subunits were observed only in migrating Cells.