An Active Role of the ΔN Isoform of p63 in Regulating Basal Keratin Genes K5 and K14 and Directing Epidermal Cell Fate

Abstract

BackgroundOne major defining characteristic of the basal keratinocytes of the stratified epithelium is the expression of the keratin genes K5 and K14. The temporal and spatial expression of these two genes is usually tightly and coordinately regulated at the transcriptional level. This ensures the obligate pairing of K5 and K14 proteins to generate an intermediate filament (IF) network that is essential for the structure and function of the proliferative keratinocytes. Our previous studies have shown that the basal-keratinocyte restricted transcription factor p63 is a direct regulator of K14 gene.Methodology/Principal FindingsHere we provide evidence that p63, specifically the ΔN isoform also regulates the expression of the K5 gene by binding to a conserved enhancer within the 5′ upstream region. By using specific antibodies against ΔNp63, we show a concordance in the expression between basal keratins and ΔNp63 proteins but not the TAp63 isoforms during early embryonic skin development. We demonstrate, that contrary to a previous report, transgenic mice expressing ΔNp63 in lung epithelium exhibit squamous metaplasia with de novo induction of K5 and K14 as well as transdifferentiation to the epidermal cell lineage. Interestingly, the in vivo epidermal inductive properties of ΔNp63 do not require the C-terminal SAM domain. Finally, we show that ΔNp63 alone can restore the expression of the basal keratins and reinitiate the failed epidermal differentiation program in the skin of p63 null animals.SignificanceΔNp63 is a critical mediator of keratinocyte stratification program and directly regulates the basal keratin genes.

Notch signaling represses p63 expression in the developing surface ectoderm

“…Our model is consistent with the ability of p63 to directly regulate K14 expression (Romano et al, 2009), the absence of K14 expression in mice and hESCs lacking p63 isoforms (Mills et al, 1999;Romano et al, 2012;ShalomFeuerstein et al, 2011;Yang et al, 1999) and the expression of p63 as early as E9.5 in mouse embryos (Koster and Roop, 2004). Given the predominant expression of ΔNp63 in physiologically normal epidermal tissues and the requirement of ΔNp63 for epidermal development (Romano et al, 2009), ΔNp63 is likely to be the isoform expressed in the surface ectoderm. Future studies analyzing p63 isoform expression in the surface ectoderm and the lineage commitment of p63-expressing ectodermal cells will further reveal the contribution of these cells to keratinocyte formation.…”

“…Alternative splicing of the p63 gene yields transcripts encoding two classes of p63 protein isoforms, TAp63 and ΔNp63. ΔNp63 isoforms lacking the TA domain (Crum and McKeon, 2010;King and Weinberg, 2007) are highly expressed in the early stages of epidermal development and are maintained within the basal layer of the skin (Koster and Roop, 2004;Laurikkala et al, 2006;Romano et al, 2007;Romano et al, 2009). Complete ablation of all p63 isoforms during mouse development leads to limb truncations, craniofacial malformations and the lack of an intact and functional epidermis (Mills et al, 1999;Yang et al, 1999).…”

p63 is a suppressor of tumorigenesis and metastasis interacting with mutant p53

“…Overall the hypothesis of p63 regulating differentiation is supported by solid data, with several transcriptional targets of DNp63 being clearly relevant for epidermal differentiation, 110 such as keratins 14 (KRT14), 22,114 5 and 7 (KRT5, KRT7) 42 or adhesion molecules, 105 indicating a primary role in the formation of the epidermis. However, islets of fully differentiated cells are present in the Trp63 À/À mice, 19 indicating that the absence, or reduced, proliferative potential of the stem cell compartment is responsible for the absence of the epidermis in these knockout mice and the few remaining cells are able to differentiate normally.…”

p53/p63/p73 in the Epidermis in Health and Disease

“…The p63 isoforms play distinct roles in the control of epidermal development; the DNp63 isoforms are much more abundant in the epidermis compared to TAp63, which is strongly expressed in basal epidermal keratinocytes and is markedly down-regulated in the spinous epidermal layer (Laurikkala et al 2006;Romano et al 2009Romano et al , 2012LeBoeuf et al 2010;Shalom-Feuerstein et al 2011). TAp63 is also expressed in response to stresses such as wound healing (Su et al 2009b).…”