Mutant p53 subverts p63 control over KLF4 expression in keratinocytes

Abstract

Genetic experiments established that p63 is crucial for the development and maintenance of pluri-stratified epithelia and KLF4 for the barrier function of the skin. KLF4 is one of the factors that reprogram differentiated cells to iPS. We investigated the relationship between p63 and KLF4 using RNA interference, overexpression, chromatin immunoprecipitation and transient transfections with reporter constructs. We find that p63 directly represses KLF4 in normal keratinocytes (KCs) by binding to upstream promoter sites. Unlike p63, KLF4 levels are high in the upper layers of human skin and increase upon differentiation of KCs in vitro. In HaCaT KCs, which harbor two mutant alleles of p53, inactivation of p63 and of mutant p53 leads to KLF4 repression. p63 and p53 mutants are bound to sites in the KLF4 core promoter. Importantly, expression of the H179Y and R282Q p53 mutants in primary KCs is sufficient to activate endogenous KLF4. Finally, immunohistochemical analysis of tissue arrays confirms increased coexpression of KLF4 and mutant p53 in squamous cell carcinomas. Our data indicate that suppression of KLF4 is part of the growth-promoting strategy of p63 in the lower layers of normal epidermis, and that tumor-predisposing p53 mutations hijack p63 to a different location on the promoter, turning it into an activator of this reprogramming factor.

Glucocorticoid receptor and Klf4 co-regulate anti-inflammatory genes in keratinocytes

“…We previously observed that ΔNp63 expression, the predominant isoform of Trp63 in epidermis (Melino, 2011), was reduced in oral epithelia of K5-GR transgenic mice, suggesting negative regulation by GR (Cascallana et al, 2005). Importantly, ΔNp63 represses Klf4 expression by directly binding its promoter (Cordani et al, 2011), and the expression of both TFs is mutually exclusive in the epidermis, with ΔNp63 having the highest expression basally and Klf4 suprabasally. We first evaluated whether GR could regulate Klf4 indirectly by modulating Trp63 expression, by testing whether Trp63 isoform levels were affected by Dex in control and GR EKO cell lines (Fig.…”

ΔNp63 regulates select routes of reprogramming via multiple mechanisms

“…In skin, DNp63 and Klf4 are expressed in opposite compartments in the basal and superficial layers of the epidermis, respectively, likely because p63 directly binds to the Klf4 promoter and represses it. 53,54 Thus, p63 À / À MEFs might in fact be expected to have increased levels and/ or activity of endogenous Klf4, and as a result enhanced OK reprogramming efficiency because of additive effects of endogenous and exogenous Klf4. Indeed, we found that two out of four MET markers were upregulated in p63 À / À MEFs during OK reprogramming.…”

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

“…Recently, p63 has been shown to directly repress KLF4, a major factor that reprograms differentiated cells into iPS by binding to an upstream promoter site. 116 Indeed, the epidermis shows a mutually exclusive expression of DNp63 and KLF4. Of interest for this discussion, however, is the evidence that mutant p53 counteracts the action of DNp63 on KLF4 expression, suggesting that p63 and KLF4 are not only relevant in the growth-promoting effect of p63 in keratinocytes, but also in the tumor-predisposing p53 mutations which, by hijacking p63, results in KLF4 dysregulation.…”