RESUMO
Mammary epithelial regeneration implies the existence of cellular progenitors with retained replicative capacity, prolonged lifespan and developmental potency. Evidence exists that deltaN-p63 isoforms preserve these features by modulating p53 activity in basal epithelia. deltaN-p63 mRNA levels decline at the onset of differentiation suggesting that its transcriptional regulation may contribute to the initiation of differentiation. To study transcriptional regulation of deltaN-p63, a 10.3 kbp fragment containing the deltaN-p63 promoter was isolated. We report here that deltaN-p63 is a positive and negative transcriptional target of p53 and deltaN-p63-alpha, respectively. Disruption of p53 activity or expression abolishes the expression of deltaN-p63-alpha. This regulation is mediated by a p53-binding element sufficient to confer these activities to a heterologous promoter. Chromatin immune-precipitation indicates that, in asynchronously growing cells, p53 occupies this element. In response to DNA damage, deltaN-p63-alpha is recruited to this element as transcription of deltaN-p63 declines. Disruption of deltaN-p63-alpha expression had differential effects on the transcriptional regulation of several p53-target genes. These findings indicate that p53 contributes to the preservation of basal epithelia by driving the expression of deltaN-p63 isoforms. These studies also suggest that in response to genotoxic stress, deltaN-p63-alpha mediates the silencing of its own promoter thereby altering the pattern of p53-target gene expression.
