A regulatory feedback loop involving p63 and IRF6 links the pathogenesis of 2 genetically different human ectodermal dysplasias

Abstract

The human congenital syndromes ectrodactyly ectodermal dysplasia-cleft lip/palate syndrome, ankyloblepharon ectodermal dysplasia clefting, and split-hand/foot malformation are all characterized by ectodermal dysplasia, limb malformations, and cleft lip/palate. These phenotypic features are a result of an imbalance between the proliferation and differentiation of precursor cells during development of ectoderm-derived structures. Mutations in the p63 and interferon regulatory factor 6 (IRF6) genes have been found in human patients with these syndromes, consistent with phenotypes. Here, we used human and mouse primary keratinocytes and mouse models to investigate the role of p63 and IRF6 in proliferation and differentiation. We report that the ΔNp63 isoform of p63 activated transcription of IRF6, and this, in turn, induced proteasomemediated ΔNp63 degradation. This feedback regulatory loop allowed keratinocytes to exit the cell cycle, thereby limiting their ability to proliferate. Importantly, mutations in either p63 or IRF6 resulted in disruption of this regulatory loop: p63 mutations causing ectodermal dysplasias were unable to activate IRF6 transcription, and mice with mutated or null p63 showed reduced Irf6 expression in their palate and ectoderm. These results identify what we believe to be a novel mechanism that regulates the proliferation-differentiation balance of keratinocytes essential for palate fusion and skin differentiation and links the pathogenesis of 2 genetically different groups of ectodermal dysplasia syndromes into a common molecular pathway.

A novel RIPK4–IRF6 connection is required to prevent epithelial fusions characteristic for popliteal pterygium syndromes

“…38 This increase in IRF6 may then lead to p63 degradation in keratinocytes, thereby restricting the proliferative potential and promoting keratinocyte differentiation. 39 Our data do not exclude that under certain conditions an interplay between IRF6 and p63 directly enhances RIPK4 promoter activity.…”

Notch1 controls development of the extravillous trophoblast lineage in the human placenta

“…N1ICD binds to the IRF6 gene in keratinocytes and activates its expression (33). In turn, IRF6 promotes proteasomal degradation of p63 (30). An analogous mechanism could regulate p63 in vCTBs, because IRF6 rapidly increased after N1ICD expression.…”

“…S8). In addition, N1ICD increased expression of IFN regulatory factor 6 (IRF6), a negative regulator of p63 (30) (Fig. 5 D and F and SI Appendix, Fig.…”

Smad4-Irf6 genetic interaction and TGFβ-mediated IRF6 signaling cascade are crucial for palatal fusion in mice

“…We found that p21 expression was restored in E14. Previous studies have demonstrated that IRF6 induces degradation of the p63 isoform ∆Np63 and that this is linked with the pathogenesis of VWS and PPS (Moretti et al, 2010;Thomason et al, 2010). In addition, ∆Np63 represses transcription of p21 in vitro and in vivo (Laurikkala et al, 2006;Welsh and O'Brien, 2009;Westfall et al, 2003).…”

“…Among the genes that have been associated with NSCL/P, IRF6 has been implicated in the largest percentage of cases (Koillinen et al, 2005;Srichomthong et al, 2005). Mutation of IRF6 can lead to the autosomal-dominant conditions VWS and PPS, which are characterized by oral clefting and lower lip pits (Kondo et al, 2002;Moretti et al, 2010). VWS and PPS are allelic variants of the same condition caused by different mutations of the same gene.…”