Properties of the six isoforms of p63: p53-like regulation in response to genotoxic stress and cross talk with ΔNp73

Abstract

TP63, a member of the TP53 gene family, encodes two groups of three isoforms (alpha, beta and gamma). The TAp63 isoforms act as transcription factors. The DeltaNp63 isoforms lack the main transcription activation domain and act as dominant-negative inhibitors of transactivation (TA) isoforms. To clarify the role of these isoforms and to better understand their functional overlap with p53, we ectopically expressed each p63 isoform in the p53-null hepatocellular carcinoma cell line Hep3B. All TA isoforms, as well as DeltaNp63alpha, had a half-life of <1 h when transiently expressed and were degraded by the proteasome pathway. The most stable form was DeltaNp63gamma, with a half-life of >8 h. As expected, TA isoforms differed in their transcriptional activities toward genes regulated by p53, TAp63gamma being the most active form. In contrast, DeltaNp63 isoforms were transcriptionally inactive on genes studied and inhibited TA isoforms in a dose-dependent manner. When stably expressed in polyclonal cell populations, TAp63beta and gamma isoforms were undetectable. However, when treated with doxorubicin (DOX), p63 proteins rapidly accumulated in the cells. This stabilization was associated with an increase in phosphorylation. Strikingly, in DOX-treated polyclonal populations, increase in TAp63 levels was accompanied by overexpression of DeltaNp73. This observation suggests complex regulatory cross talks between the different isoforms of the p53 family. In conclusion, p63 exhibits several transcriptional and stress-response properties similar to those of p53, suggesting that p63 activities should be taken into consideration in approaches to improve cancer therapies based on genotoxic agents.

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

“…Plasmids and mutagenesis DNp63a, DN89 b-catenin mutant and DNTCF4-expression vectors have been previously described Cavard et al, 2006;Petitjean et al, 2008). pCMV-p53-expression vector was from Clontech (Mountain View, CA, USA).…”

“…Luciferase assays were performed as previously described (Petitjean et al, 2008), by using 1.8 mg of p53, DNp63a, wildtype or mutant b-catenin-expression vectors, 1 mg of luciferase reporter plasmid, and 0.1 mg of renilla luciferase control plasmid. b-catenin-DNp63 axis in tumour progression C Ruptier et al…”

“…In the case of TP63, TA isoforms are produced from P1 promoter, whereas P2 promoter, located in intron 3, generates DN isoforms (Yang et al, 1998) (Figure 1). By competing with TA isoforms for the binding to their responsive elements (REs), DN isoforms prevent target-gene activation, thus behaving as transdominant-negative isoforms (Yang et al, 1998;Petitjean et al, 2008). Given the similarities in DNA-binding properties between p63, p73 and p53, non-physiological upregulation of DNp63 or DNp73 expression may contribute to the functional inactivation of p53, thereby promoting tumourigenesis in the absence of mutation in p53.…”

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

“…TAp63g is the most active form at transcriptional level and accumulates in a phosphorylated form during DNA damage (by doxorubicin) with a drastically prolonged half-life. 113 This implies a role for TAp63 in DNA damage responses, as for example shown in the ovary, see also the section 'Protecting fertility following chemotherapy'.…”

Regulation of p63 Isoforms by Snail and Slug Transcription Factors in Human Squamous Cell Carcinoma

“…6 Recently, in vitro studies have also shown that ⌬Np63 isoforms inhibit TAp63 isoforms in a dose-dependent manner. 7 In addition to their role in normal development, a potential role for p63 proteins in tumorigenesis is supported by the finding that p63 immunoreactivity is observed in more than 90% of squamous epithelial malignancies. 8 However, because of the lack of reliable antibodies for ⌬N and TAp63, the p63 isoforms expressed in these malignant lesions were not determined in most studies.…”