PERP regulation by TP63 mutants provides insight into AEC pathogenesis

Division of Radiation and Cancer Biology, Department of Radiation Oncology, Stanford University School of Medicine, 269 Campus Drive, Stanford,CA 94305-5152, USA.
American Journal of Medical Genetics Part A (Impact Factor: 2.16). 09/2009; 149A(9):1952-7. DOI: 10.1002/ajmg.a.32760
Source: PubMed


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.

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    • "Thus, differences in temporal expression, isoform combination, biochemical properties and transcription activity of p63 protein(s) can have a profound impact on the set of genes transcribed, at a given time in a given cell. A combination of isoform-specific siRNA-mediated downregulation in primary keratinocytes and in vivo, coupled to analysis of knock-out and disease specific knock-in mice, has allowed to determine the key target genes required for epidermal morphogenesis that are involved in pathogenesis of p63-linked ectodemal dysplasias [62] [65] [72] [73]. These studies showed that the protein kinase IKKa is a transcriptional target of DNp63 and, indeed, DNp63 mutants found in ED are unable to activate the IKKa expression. "
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    ABSTRACT: TP53 belongs to a small gene family that includes, in mammals, two additional paralogs, TP63 and TP73. The p63 and p73 proteins are structurally and functionally similar to p53 and their activity as transcription factors is regulated by a wide repertoire of shared and unique post-translational modifications and interactions with regulatory cofactors. p63 and p73 have important functions in embryonic development and differentiation but are also involved in tumor suppression. The biology of p63 and p73 is complex since both TP63 and TP73 genes are transcribed into a variety of different isoforms that give rise to proteins with antagonistic properties, the TA-isoforms that act as tumor-suppressors and DN-isoforms that behave as proto-oncogenes. The p53 family as a whole behaves as a signaling "network" that integrates developmental, metabolic and stress signals to control cell metabolism, differentiation, longevity, proliferation and death. Despite the progress of our knowledge, the unresolved puzzle of complexity, redundancy and hierarchy in the p53 family continues to represent a formidable challenge.
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    • "In general, these observations and functionrelevant conclusions have emphasized that the loss of PERP protein results in decreased cell-cell adhesion combined with skin blistering, documented by many gaps between the epidermal cells, in particular in the basal cell layer. PERP is also thought to contribute to the " cleaning " of PERP-containing stratified epithelia by the induction and promotion of apoptotic programs and to suppress tumor formation and spreading (see the aforementioned reviews) and PERP dysregulation might result in the pathogenesis of certain genetic diseases of the skin, scalp, hair and nails (Beaudry et al. 2009). In addition, Attardi and colleagues have reported that PERP influences papilloma development in mice (Marques et al. 2005). "
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    ABSTRACT: Protein PERP (p53 apoptosis effector related to PMP-22) is a small (21.4 kDa) transmembrane polypeptide with an amino acid sequence indicative of a tetraspanin character. It is enriched in the plasma membrane and apparently contributes to cell-cell contacts. Hitherto, it has been reported to be exclusively a component of desmosomes of some stratified epithelia. However, by using a series of newly generated mono- and polyclonal antibodies, we show that protein PERP is not only present in all kinds of stratified epithelia but also occurs in simple, columnar, complex and transitional epithelia, in various types of squamous metaplasia and epithelium-derived tumors, in diverse epithelium-derived cell cultures and in myocardial tissue. Immunofluorescence and immunoelectron microscopy allow us to localize PERP predominantly in small intradesmosomal locations and in variously sized, junction-like peri- and interdesmosomal regions ("tessellate junctions"), mostly in mosaic or amalgamated combinations with other molecules believed, to date, to be exclusive components of tight and adherens junctions. In the heart, PERP is a major component of the composite junctions of the intercalated disks connecting cardiomyocytes. Finally, protein PERP is a cobblestone-like general component of special plasma membrane regions such as the bile canaliculi of liver and subapical-to-lateral zones of diverse columnar epithelia and upper urothelial cell layers. We discuss possible organizational and architectonic functions of protein PERP and its potential value as an immunohistochemical diagnostic marker.
    Full-text · Article · May 2013 · Cell and Tissue Research
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    • "Perp null mice exhibited frequent basal-suprabasal blistering in the skin and oral cavity (47), and developed ectodermal dysplasia and palmoplantar keratoderma (67). A normal pattern of PERP membrane staining was observed in most AEC patients, although in two unrelated patients PERP expression was reduced in the basal and suprabasal layers of the skin (68), consistent with either reduced PERP expression or with protein delocalization due to alterations of other desmosomal components. Similarly, in mouse mutant epidermis Perp was not affected, even though AEC mouse keratinocytes had significantly reduced Perp protein levels. "
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    ABSTRACT: Ankyloblepharon, ectodermal defects, cleft lip/palate (AEC) syndrome is a rare autosomal dominant disorder caused by mutations in the p63 gene, essential for embryonic development of stratified epithelia. The most severe cutaneous manifestation of this disorder is the long-lasting skin fragility associated with severe skin erosions after birth. Using a knock-in mouse model for AEC syndrome we found that skin fragility was associated with microscopic blistering between the basal and suprabasal compartments of the epidermis and reduced desmosomal contacts. Expression of desmosomal cadherins and desmoplakin was strongly reduced in AEC mutant keratinocytes and in newborn epidermis. A similar impairment in desmosome gene expression was observed in human keratinocytes isolated from AEC patients, in p63-depleted keratinocytes and in p63 null embryonic skin, indicating that p63 mutations causative of AEC syndrome have a dominant-negative effect on the wild-type p63 protein. Among the desmosomal components, desmocollin 3, desmoplakin and desmoglein 1 were the most significantly reduced by mutant p63 both at the RNA and protein levels. Chromatin immunoprecipitation experiments and transactivation assays revealed that p63 controls these genes at the transcriptional level. Consistent with reduced desmosome function, AEC mutant and p63-deficient keratinocytes had an impaired ability to withstand mechanical stress, which was alleviated by EGFR inhibitors known to stabilize desmosomes. Our study reveals that p63 is a crucial regulator of a subset of desmosomal genes and that this function is impaired in AEC syndrome. Reduced mechanical strength resulting from p63 mutations can be alleviated pharmacologically by increasing desmosome adhesion with possible therapeutic implications.
    Full-text · Article · Oct 2012 · Human Molecular Genetics
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