Investigation of the disease mechanism causing Ankyloblepharon-ectodermal defects-cleft lip/palate syndrome and Ectrodactyly-ectodermal dysplasia-clefting syndrome

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The p53 protein family consists of three members: p53, p63 and p73. Knock out mouse studies have revealed that p63 is involved in many cellular processes such as cell fate commitment during development, cell proliferation, differentiation and tissue homeostasis in epithelial tissues. During epithelial and epidermal commitment, pluripotent stem cells depleted of p63 are blocked between the simple epithelial and stratified epidermal fates, and cannot commit to basal epidermal keratinocytes. Analysis of the p63-/- mouse has enabled the identification of mutations in the human p63 gene to be responsible for at least five human syndromes and two non-syndromic human disorders that are characterized by varying degrees of 1) limb deformation, 2) cleft lip/palate and/or 3) ectodermal dysplasia. The two best characterized syndromes, EEC and AEC syndrome, are linked to mutations in the DNA binding domain and the SAM domain, respectively. Recently we have shown that the AEC syndrome is based on a gain of function mechanism. Mutations in the SAM domain cause irreversible aggregation of p63. Surprisingly, the denaturation temperature of the mutants is still significantly higher than the body temperature. The disease mechanism can, therefore, not be explained with a simple thermodynamic destabilization. We now propose to further investigate the disease mechanism. We will identify co-aggregating proteins using mass spectrometry, measure the folding kinetics of the SAM domain mutants and characterize their interaction with chaperones. In addition we will characterize currently known EEC mutants and correlate their degree of residual DNA binding affinity and transcriptional activity in cellular assays with the severity of the patient phenotypes.