ΔNp63 transcriptionally regulates ATM to control p53 Serine-15 phosphorylation

BACKGROUND: ΔNp63α is an epithelial progenitor cell marker that maintains epidermal stem cell self-renewal capacity. Previous studies revealed that UV-damage induced p53 phosphorylation is confined to ΔNp63α-positive cells in the basal layer of human epithelium. RESULTS: We now report that phosphorylation of the p53 tumour suppressor is positively regulated by ΔNp63α in immortalised human keratinocytes. ΔNp63α depletion by RNAi reduces steady-state ATM mRNA and protein levels, and attenuates p53 Serine-15 phosphorylation. Conversely, ectopic expression of ΔNp63α in p63-null tumour cells stimulates ATM transcription and p53 Serine-15 phosphorylation. We show that ATM is a direct ΔNp63α transcriptional target and that the ΔNp63α response element localizes to the ATM promoter CCAAT sequence. Structure-function analysis revealed that the ΔNp63-specific TA2 transactivation domain mediates ATM transcription in coordination with the DNA binding and SAM domains. CONCLUSIONS: Germline p63 point mutations are associated with a range of ectodermal developmental disorders, and targeted p63 deletion in the skin causes premature ageing. The ΔNp63α-ATM-p53 damage-response pathway may therefore function in epithelial development, carcinogenesis and the ageing processes.