POTENTIAL ROLE FOR FOCAL ADHESION KINASE IN MIGRATING AND PROLIFERATING KERATINOCYTES NEAR EPIDERMAL WOUNDS AND IN CULTURE

In normal, differentiating skin, hemidesmosomes make the stable attach ment of basal epidermal keratinocytes to the dermis by linking the cyt oplasmic keratin intermediate filaments to components of the basal lam ina. In contrast, laterally migrating and proliferating basal keratino cytes in culture and presumably in repairing wounds use focal adhesion s to form dynamic attachments to the dermis by linking actin microfila ments to the extracellular matrix. Focal adhesion kinase (FAK), a non- receptor protein tyrosine kinase concentrated along with phosphotyrosi ne-containing proteins in the focal adhesions of some cultured cells, is activated in vitro when cells attach, form focal adhesions, and spr ead. This report finds that FAK is activated, as determined from its i ncreased phosphotyrosine content and from its increased labeling with [gamma-P-32]ATP, in immunoprecipitates from human cultured keratinocyt es attached and spreading on fibronectin compared to those attached bu t not spreading on polylysine. Furthermore, immunofluorescence shows t hat both FAK and phosphotyrosine are concentrated in the focal adhesio ns of cultured keratinocytes attached and spreading on extracellular m atrix components known to facilitate cellular migration (fibronectin, collagens I or IV, and epiligrin). Finally, immunohistochemistry local izes FAK to the epidermal-dermal junction in repairing partial thickne ss burn wounds. FAK is found at the epidermal-dermal junction at sites and times which coincide with actively migrating or rapidly prolifera ting basal keratinocytes, suggesting that this distribution represents FAK concentrated and activated in adhesions analogous to the focal ad hesions seen in cultured cells. Hence, FAK appears to have an importan t in vivo role in the reepithelialization of human wounds.