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Differential roles of p63 isoforms in epidermal development: Selective genetic complementation in p63 null mice

Biochemistry Laboratory, IDI-IRCCS, c/o University of Rome Tor Vergata, 00133 Rome, Italy.
Cell Death and Differentiation (Impact Factor: 8.39). 07/2006; 13(6):1037-47. DOI: 10.1038/sj.cdd.4401926
Source: PubMed

ABSTRACT Epidermal development requires the transcription factor p63, as p63-/- mice are born dead, without skin. The gene expresses two proteins, one with an amino-terminal transactivation domain (TAp63) and one without (deltaNp63), although their relative contribution to epidermal development is unknown. To address this issue, we reintroduced TAp63alpha and/or deltaNp63alpha under the K5 promoter into p63-/- mice by in vivo genetic complementation. Whereas p63-/- and p63-/-;TA mice showed extremely rare patches of poorly differentiated keratinocytes, p63-/-;deltaN mice showed significant epidermal basal layer formation. Double TAp63alpha/deltaNp63alpha complementation showed greater patches of differentiated skin; at the ultrastructural level, there was clear reformation of a distinct basal membrane and hemidesmosomes. At the molecular level, deltaNp63 regulated expression of genes characteristic of the basal layer (K14), interacting (by Chip, luc assay) with the third p53 consensus site. Conversely, TAp63 transcribed the upper layer's genes (Ets-1, K1, transglutaminases, involucrin). Therefore, the two p63 isoforms appear to play distinct cooperative roles in epidermal formation.

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    • "These results suggest that TAp63 opposes ΔNp63 function, thereby preventing a premature reduction in proliferative potential. Thus, it is likely that p63 function reflects a cooperative effect between TAp63 and ΔNp63 isoforms (Candi et al., 2006; Truong et al., 2006; Zhang et al., 2014). Whereas the amino (N)-terminal functions of p63 are relatively well studied, carboxy (C)-terminal functions in vivo are poorly understood. "
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    ABSTRACT: The transcription factor p63 (Trp63) plays a key role in homeostasis and regeneration of the skin. The p63 gene is transcribed from dual promoters, generating TAp63 isoforms with growth suppressive functions and dominant-negative ΔNp63 isoforms with opposing properties. p63 also encodes multiple carboxy (C)-terminal variants. Although mutations of C-terminal variants have been linked to the pathogenesis of p63-associated ectodermal disorders, the physiological role of the p63 C-terminus is poorly understood. We report here that deletion of the p63 C-terminus in mice leads to ectodermal malformation and hypoplasia, accompanied by a reduced proliferative capacity of epidermal progenitor cells. Notably, unlike the p63-null condition, we find that p63 C-terminus deficiency promotes expression of the cyclin-dependent kinase inhibitor p21(Waf1/Cip1) (Cdkn1a), a factor associated with reduced proliferative capacity of both hematopoietic and neuronal stem cells. These data suggest that the p63 C-terminus plays a key role in the cell cycle progression required to maintain the proliferative potential of stem cells of many different lineages. Mechanistically, we show that loss of Cα, the predominant C-terminal p63 variant in epithelia, promotes the transcriptional activity of TAp63 and also impairs the dominant-negative activity of ΔNp63, thereby controlling p21(Waf1/Cip1) expression. We propose that the p63 C-terminus links cell cycle control and the proliferative potential of epidermal progenitor cells via mechanisms that equilibrate TAp63 and ΔNp63 isoform function. © 2015. Published by The Company of Biologists Ltd.
    Development 12/2014; 142(2). DOI:10.1242/dev.118307 · 6.27 Impact Factor
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    • "In these studies , ΔNp63í µí»¼ was able to partially restore the epidermal basal layer, but not differentiation marker expression, whereas TAp63í µí»¼ reconstitution resulted in a phenotype similar to p63(−/−) mice [36]. Reconstitution of a combination of ΔNp63í µí»¼ and TAp63í µí»¼ resulted in a more complete epidermis formation containing patches with a more organized structure that expressed markers of differentiation [36]. It is possible that differences with respect to the differentiation status of the epidermis generated by reconstitution of ΔNp63í µí»¼ in the later two studies could be due to the mouse model used, but in contrast to the first model discussed, partial epidermal restoration by ΔNp63í µí»¼ is a common feature of both. "
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    ABSTRACT: Mouse models have informed us that p63 is critical for normal epidermal development and homeostasis. The p53/p63/p73 family is expressed as multiple protein isoforms due to a combination of alternative promoter usage and C-terminal alternative splicing. These isoforms can mimic or interfere with one another, and their balance ultimately determines biological outcome in a context-dependent manner. While not frequently mutated, p63, and in particular the ΔNp63 subclass, is commonly overexpressed in human squamous cell cancers. In vitro keratinocytes and murine transgenic and transplantation models have been invaluable in elucidating the contribution of altered p63 levels to cancer development, and studies have identified the roles for ΔNp63 isoforms in keratinocyte survival and malignant progression, likely due in part to their transcriptional regulatory function. These findings can be extended to human cancers; for example, the novel recognition of NF κ B/c-Rel as a downstream effector of p63 has identified a role for NF κ B/c-Rel in human squamous cell cancers. These models will be critical in enhancing the understanding of the specific molecular mechanisms of cancer development and progression.
    04/2013; 2013:632028. DOI:10.1155/2013/632028
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    • "Intriguingly, these regions robustly express the p63 N-terminal truncated isoform D Np63. It is noteworthy that a detailed analysis revealed the presence of " patches " of fully differentiated cells on the back of p63 null embryos (Mills et al. 1999 ; Candi et al. 2006 ) . This compelling evidence proved that p63-depleted epithelial cells are still fully committed to strati fi cation, but lack replenishing capability; i.e., they are defective in stemness. "
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    ABSTRACT: Stem cells are characterized by the ability to renew themselves (self-renewal) and the capability to generate all the cells within the human body. These features are achieved by a fine-tuned control of proliferation and maintenance of the undifferentiated condition. Transcription factors such as Nanog, Sox, and Oct-4 and extrinsic factors (LIF, BMP, and FGF) have been demonstrated to play a critical role in the regulation of stemness. Because stem cells are under consideration in clinics for cell-based therapy, it is important to understand the molecular mechanisms underlying stemness. In this chapter, we revisit stem cell biology and add a new layer of complexity. In particular, we will discuss the role of the p53 family (p53, p63, and p73) in the regulation of self-renewal, proliferation, and differentiation of stem cells.
    p53 in the Clinics, 01/2013: chapter p53 family and stem cell biology; , ISBN: ISBN 978-1-4614-3675-1
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