FAK induction in keratinocytes in an in vitro model of reepithelialization

During reepithelialization, keratinocytes must become activated in order to migrate over the provisional extracellular matrix of the wound. Previously we have shown that focal adhesion kinase (FAK) is induced in activated ker atinocytes. The mechanisms responsible for keratinocyte activation are unkn own. Here we use an organ culture system to investigate FAK up-regulation a nd regulation of keratinocyte activation. Normal human skin was cultured on type I collagen. Keratinocytes migrated out of the explant onto the suppor ting collagen. Immunostaining for FAK showed induction in the migrating epi thelium and also in the center of the explant some distance from the cut ed ge. Cells from the center of the explant expressed FAK and showed the activ ated phenotype as defined by their ability to spread on collagen. Since FAK is a tyrosine kinase, the tyrosine kinase inhibitors genistein or herbimyc in A were added to the explant medium for 24 h. Inhibition of tyrosine kina se activity delayed epithelial migration, but keratinocytes were able to be gin migrating after removal of the inhibitors. We conclude that FAK is up-r egulated in keratinocytes in this whole skin explant model. Furthermore FAK . up-regulation and keratinocyte activation are not confined to the migrati ng cells but are found in cells some distance from the skin margin. These d ata suggest that (1) cell migration, contact with wound matrix molecules, l oss of cell-cell contact, or loss of basement membrane contact is not neces sary for FAK up-regulation or keratinocyte activation; and (2) tyrosine kin ase signaling pathways are important for reepithelialization. (C) 2001 Acad emic Press.