Differential PERP regulation by TP63 mutants provides insight into AEC pathogenesis

Abstract

Ankyloblepharon Ectodermal Dysplasia and Cleft Lip/Palate (AEC) or Hay-Wells Syndrome is an autosomal dominant disorder characterized by a variety of phenotypes in ectodermal derivatives, including severe skin erosions, ankyloblepharon, coarse and wiry hair, scalp dermatitis, and dystrophic nails. AEC is caused by mutations in the gene encoding the TP63 transcription factor, specifically in the Sterile Alpha Motif (SAM) domain. The exact mechanism, however, by which these specific TP63 mutations lead to the observed spectrum of phenotypes is unclear. Analysis of individual TP63 target genes provides a means to understand specific aspects of the phenotypes associated with AEC. PERP is a TP63 target critical for cell-cell adhesion due to its participation in desmosomal adhesion complexes. As PERP null mice display symptoms characteristic of ectodermal dysplasia syndromes, we hypothesized that PERP dysfunction might contribute to AEC. Using luciferase reporter assays, we demonstrate here that PERP induction is in fact compromised with some, but not all, AEC-patient derived TP63 mutants. Through analysis of skin biopsies from AEC patients, we show further that a subset of these display aberrant PERP expression, suggesting the possibility that PERP dysregulation is involved in the pathogenesis of this disease. These findings demonstrate that distinct AEC TP63 mutants can differentially compromise expression of downstream targets, providing a rationale for the variable spectra of symptoms seen in AEC patients. Elucidating how specific TP63 target genes contribute to the pathogenesis of AEC will ultimately help design novel approaches to diagnose and treat AEC.

Special AT-rich Binding Protein-2 (SATB2) Differentially Affects Disease-causing p63 Mutant Proteins

“…5B) (18). The steady-state level of TAp63␣ AEC mutant proteins was lower than that of wild-type TAp63␣ as published previously (18) and is, at least in part, due to decreased stability of the AEC mutant proteins (data not shown). In contrast, loss of the OD, either by truncation or point mutation (I378P), significantly abrogates reporter induction (Fig.…”

“…2E). An essential gene regulated by p63 during ectoderm development is perp (10,18). ChIP analysis showed that overexpressed TA and ⌬Np63␣ (Fig.…”

“…However, the unique mechanisms underlying these disorders are poorly understood. Studies utilizing overexpression of p63 mutant proteins have demonstrated that EEC mutants are unable to activate known p53 family target genes, but AEC mutants retain transcriptional activity for a subset of genes, including the ability to induce perp (18). Because AEC p63␣ mutations are associated with significant craniofacial defects despite intact transcriptional activity, it is likely that mutation-induced changes in p63 transcriptional activity alone cannot account for distinct AEC and EEC phenotypes and that additional factors exist that likely influence AEC mutant proteins (16,18).…”

“…Studies utilizing overexpression of p63 mutant proteins have demonstrated that EEC mutants are unable to activate known p53 family target genes, but AEC mutants retain transcriptional activity for a subset of genes, including the ability to induce perp (18). Because AEC p63␣ mutations are associated with significant craniofacial defects despite intact transcriptional activity, it is likely that mutation-induced changes in p63 transcriptional activity alone cannot account for distinct AEC and EEC phenotypes and that additional factors exist that likely influence AEC mutant proteins (16,18). SATB2 (special AT-rich binding protein-2), a transcription factor that binds DNA in nuclear matrix attachment regions (19) influences gene expression both by orchestrating chromatin structure and by functioning as a transcriptional co-factor (20 -22).…”

Epidermal cell junctions and their regulation by p63 in health and disease

“…Since Perp is strongly reduced in p63 null embryos and in p63-depleted keratinocytes and its absence predisposes to ectodermal dysplasia and skin blistering in mice (ADD (Ihrie et al 2005, its expression was tested in skin biopsies from AEC patients (Beaudry et al 2009); however, only a limited subset of AEC patients showed reduced PERP. This finding, in association to the evidence that the phenotype of Perp null mice is milder compared to the skin phenotype of p63 null mice, suggests that PERP is likely to contribute to the complex pathogenesis of AEC syndrome but is unlikely to be the affected gene mainly responsible for the disease.…”