A Functional Enhancer of Keratin14 Is a Direct Transcriptional Target of ΔNp63

Keratin14 (K14) is a prototypic marker of dividing basal keratinocytes where its gene is transcribed at high levels. Transcriptional regulation of K14 is governed by an evolutionarily conserved functional enhancer marked by DNase 1 hypersensitive sites present upstream of the gene. This enhancer is sufficient to confer epidermal-specific gene expression, which is mediated in part by binding of members of activator protein-2 (AP)-2, AP-1, Ets, and Sp1 families of transcription factors. Here we provide evidence that a keratinocyte-specific nuclear protein identified as ΔNp63 binds to a conserved motif within this enhancer. Interestingly, the selective expression profile of ΔNp63 in various cell lines correlates with both the nuclear complex and the expression of K14. Biochemical studies reveal that ΔNp63 can bind to a specific DNA sequence present in the K14 enhancer and this binding leads to transactivation. In addition, chromatin immunoprecipitation experiments with ΔNp63-specific antibodies demonstrate that the enhancer is occupied by ΔNp63 in cultured keratinocytes and in mouse skin epidermal cells in vivo. Finally, we show that ectopic expression of either p63 isoform (ΔN or TA) can induce de novo expression of K14. These studies provide a potential mechanism by which ΔNp63 directly governs the expression of K14 in a keratinocyte-specific manner