EPIDERMAL GROWTH-FACTOR AND TRANSFORMING GROWTH-FACTOR-ALPHA SPECIFICALLY INDUCE THE ACTIVATION-ASSOCIATED AND HYPERPROLIFERATION-ASSOCIATED KERATIN-6 AND KERATIN-16

Epidermal injury results in activation of keratinocytes which produce and respond to growth factors and cytokines and become migratory. Acti vated keratinocytes express a specific pair of keratin proteins, K6 an d K16, distinct from the keratins in the healthy epidermis. Keratinocy tes can be activated, for example, by binding of the appropriate ligan ds to the epidermal growth factor receptor (EGFR). We have analyzed th e effects of EGFR activation on keratin gene transcription by transfec ting DNAs containing keratin promoters linked to a reporter gene into primary cultures of human epidermal keratinocytes in the presence or a bsence of EGF or transforming growth factor alpha (TGFalpha), two grow th factors that activate EGFR. The activation of EGFR had no effect on the promoters of simple epithelial, basal-layer-specific, or differen tiation-specific keratins. In contrast, the expression of K6 and K16 w as strongly and specifically induced. A 20-bp DNA segment of the K16 g ene promoter conveyed the EGF regulation, functioned in a heterologous construct, and therefore constituted an EGF-responsive element. A nuc lear protein specifically bound to this element and to the analogous s equence of the K6 promoter. Thus, EGF specifically induces K6 and K16, markers of activated keratinocytes, via nuclear proteins that bind to EGF-responsive elements in the promoters of these keratin genes.