Probing Keratinocyte and Differentiation Specificity of the Human K5 Promoter in Vitro and in Transgenic Mice

The study investigated the regulatory mechanisms of the human K5 gene expression in keratinocytes, both in vitro and in transgenic mice. It was found that 6,000 base pairs of the K5 promoter directed basal cell-specific expression in stratified epithelia, while a truncated 90 bp promoter still targeted expression to stratified epithelia, particularly in the epidermis, hair follicles, and tongue. The truncated promoter showed some deviations in expression patterns, such as from basal to suprabasal in the epidermis and from outer to inner root sheath in hair follicles. Protein-DNA interaction studies revealed that keratinocyte nuclear proteins binding to a segment from -90 to +32 bp are crucial for transcriptional regulation, with some factors shared between K5 and K14 promoters. Mutagenesis indicated that factors near the TATA box and transcription initiation site were key to the cell type specificity of the truncated promoter.