Defining the Regulatory Elements in the Proximal Promoter of ΔNp63 in Keratinocytes: Potential Roles for Sp1/Sp3, NF-Y, and p63

p63, a homolog of the tumor suppressor p53, plays an important role in the formation of stratified epithelium such as those in the epidermis of the skin. The p63 gene gives rise to multiple functionally distinct protein isoforms, including the ΔNp63 class of isoforms, which lacks the N-terminal transactivation domain and is synthesized from an internal promoter. ΔNp63 proteins are the predominant isoforms expressed in keratinocytes and are thought to be important for maintenance of the proliferative capacity of these cells. Here, we have examined the transcriptional control mechanisms that govern the expression ΔNp63 in keratinocytes. We first performed DNase I hypersensitive site mapping and demonstrated that the promoter region of ΔNp63 is in open chromatin state in keratinocytes. To identify the cis-elements that regulate ΔNp63, we have performed transient transfection assays in keratinocytes with several ΔNp63 promoter constructs. This identified a short evolutionarily conserved fragment that harbors most of the transcriptional activity of the ΔNp63 promoter. Biochemical studies of this element have revealed critical roles for CCAAT-box-binding factor (CBF/NF-Y) and Sp1/Sp3 family of proteins. In addition, our data suggest that ΔNp63 is recruited to and can activate its own promoter, possibly through protein–protein interactions, thus providing an auto-regulatory loop of self-regulation. These studies support the notion that unique and distinct pathways control the expression of individual p53 family members and their various isoforms.