STRUCTURAL AND FUNCTIONAL CONSEQUENCES OF P63 MUTATIONS CAUSATIVE OF AEC SYNDROME

p63, a p53 family member, is a tetrameric transcription factor required for the development and differentiation of stratified epithelia. Heterozygous mutations in p63 are causative of a group of autosomal dominant human disorders characterized by ectodermal dysplasia, orofacial clefting and limb malformations. More specifically, mutations clustering in the C-terminal domain of p63 cause Ankyloblepharon-Ectodermal defects-Cleft lip/palate (AEC) syndrome, a life-threatening disorder characterized by severe extended skin erosions. Here we show that multiple AEC-associated p63 mutations lead to protein misfolding and aggregation, as observed also in human keratinocytes isolated from an AEC patient and in mouse keratinocytes obtained from a conditional knock-in mouse model for AEC syndrome, recently generated in our laboratory, that phenocopies the skin clinical features found in human patients. In AEC mice the aggregated p63 mutant protein causes an impaired expression of endogenous p63 target genes, among which are keratins and desmosomal proteins involved in cell adhesion and in mechanical resistance, leading to severe skin fragility and erosions. Importantly, we found that abolishing the aggregation of p63, by introducing mutations that drastically reduce the aggregation propensity of AEC mutants, allowed to rescue p63 transcriptional functions, thus suggesting that impaired p63 transactivation activity is uniquely associated in AEC syndrome with exposure of aggregation-prone sequences. In addition, our studies focused on the therapeutic potential of these findings and suggested possible approaches to treat the AEC syndrome based on targeting and strengthening the endogenous protein disaggregation machinery or using drugs designed to chemically assist the correct folding of the mutant protein.