Cross-Talks in the p53 Family: ΔNp63 is an Anti-Apoptotic Target for ΔNp73α and p53 Gain of Function Mutants

Abstract

The p53 family of transcription factors plays a pivotal role in the control of the cellular response to DNA damaging agents. In addition to pro-apoptotic molecules such as p53, TAp73 and TAp63, this gene family also encodes for the anti-apoptotic molecules deltaNp73, deltaNp63, deltaNp53, and p53 mutants are often found in tumor cells, that have the role to limit and to modulate the pro-apoptotic side of the family. The ratio between the different members of the family is critical to make the life or death decision following DNA damage and is tightly regulated by post-translational and transcriptional mechanisms. In this study we have uncovered a novel positive feedback that involves the transcriptional activation of the anti-apoptotic molecule deltaNp63 by the anti-apoptotic molecules deltaNp73 and mutant p53, and that is put into motion upon treatment with a subset of DNA damaging agents such as Doxorubicin and 5-FU. DeltaNp73 and mutant p53 associate with the deltaNp63 promoter inducing its transcription and this is enhanced by doxorubicin treatment. Furthermore we have observed that deltaNp73- and mutp53-mediated activation of the deltaNp63 promoter requires the functionality of the proximal CCAAT boxes of this promoter, being hampered by mutation of CCAAT boxes or by dominant negative NFYA expression. This mechanism may serve as an additional control of the response of a normal cell to DNA damage or as an anti-apoptotic barrier of cancer cells subjected to DNA damage.

TP63 P2 promoter functional analysis identifies β-catenin as a key regulator of ΔNp63 expression

“…b-catenin-DNp63 axis in tumour progression C Ruptier et al binding sites by testing full-length P2 promoter or deletion mutants by luciferase assay. Although p53 was able to repress the activity of P2 promoter, as already described (Lanza et al, 2006), an enhanced P2 activity was observed in the presence of DNp63a (Figure 2d). However, these effects did not require the presence of the putative p53RE, as p53RE-deleted (À740/ þ 139 Dp 53RE) and -truncated (À404/ þ 139) P2 fragments were still activated by DNp63a.…”

“…Figure 1 shows the structure of the promoter and the position of putative RE (detailed in Supplementary Figure 1). Several regulatory elements located within the TP63 P2 promoter, including a p53RE (Lanza et al, 2006), a TATA box, three CAAT boxes and a SP1/SP3 site (Romano et al, 2006), were confirmed in our in silico analysis. However, we failed to identify the STAT3 RE previously reported (Chu et al, 2008).…”

“…In silico analysis revealed the presence of a potential p53RE, previously identified by others (Waltermann et al, 2003;Lanza et al, 2006), and two TCF/LEF-binding elements (TBEs). TCF/LEF transcription factors are activated through a signalling cascade involving b-catenin, a key protein of the Wnt/b-catenin pathway frequently deregulated in many epithelial cancers, including SCC (Ninomiya et al, 2000;Kudo et al, 2007).…”

“…In fact, repression of the P2 promoter by p53 has further been confirmed in keratinocytes (Lanza et al, 2006). As DNp63 and p53 share similar DNA-binding specificities (Yang et al, 1998), we investigated the possibility that DNp63a regulates its own promoter.…”

Are interactions with p63 and p73 involved in mutant p53 gain of oncogenic function?

“…In addition, many SCC cells express both mutant p53 and DNp63 (Hibi et al, 2000). Moreover, one recent study revealed that the hot-spot R175H mutant p53 can induce the expression of DNp63 after a subset of DNA damage treatment including doxorubicin (Lanza et al, 2006). This phenomenon seems to be mediated by CCAAT box and NF-Y protein, and is consistent with another study showing that mutant p53 can interact with NF-Y transcription factors to stimulate the expression of proliferative cell cycle genes after DNA damage (Di Agostino et al, 2006).…”