Transcription factor AP2 and its role in epidermal-specific gene expression.

The epidermis is a stratified squamous epithelium whose major differentiation-specific products are keratins. To elucidate factors controlling keratinocyte-specific gene expression, we previously identified proximal and distal regulatory elements that act synergistically to drive keratinocyte-specific expression of the gene encoding human epidermal keratin K14. Control by the proximal element is mediated by a transcription factor, KER1, which is more abundant in nuclear extracts of keratinocytes than in extracts of other cell types, including fibroblasts, lymphocytes, and simple epithelial cells. In this report, we identify this factor as transcription factor AP2, shown to be transcribed in cells of epidermal and neural crest lineages. Furthermore, we demonstrate functional AP2 binding sites upstream from three additional epidermal genes, suggesting that AP2 may be generally involved in epidermal gene regulation. Finally, although AP2 is necessary, it is not sufficient for epidermal gene expression: a distal element contributes to tissue-specific expression of the human keratin K14 gene as judged by its ability to enhance expression of a heterologous promoter in keratinocytes but not in hepatoma cells. These results imply that a combination of factors is likely to contribute to epidermal-specific expression of the human keratin K14 gene.