The Unique NH2-terminally Deleted (ΔN) Residues, the PXXP Motif, and the PPXY Motif Are Required for the Transcriptional Activity of the ΔN Variant of p63

Abstract

p63, a member of the p53 family of transcription factors, is known to be involved in epithelial development. However, its role in tumorigenesis is unclear. Contributing to this uncertainty, the TP63 locus can express multiple gene products from two different promoters. Utilization of the upstream promoter results in expression of the TAp63 variant with an activation domain similar to p53. In contrast, the NH 2 -terminally deleted (⌬N) p63 variant, transcribed from a cryptic promoter in intron 3, lacks such an activation domain. Thus, the TAp63 and ⌬Np63 variants possess a wide ranging ability to up-regulate p53 target genes. Consequentially, the disparity in transactivation potential between p63 variants has given rise to the hypothesis that the ⌬Np63 variant can serve as oncoprotein by opposing the activity of the TAp63 variant and p53. However, recent studies have revealed a transcriptional activity for ⌬Np63. This study was undertaken to address the transcriptional activity of the ⌬Np63 variant. Here, we showed that all NH 2 -terminally deleted p63 isoforms retain a potential in transactivation and growth suppression. Interestingly, ⌬Np63␤ possesses a remarkable ability to suppress cell proliferation and transactivate target genes, which is consistently higher than that seen with ⌬Np63␣. In contrast, ⌬Np63␥ has a weak or undetectable activity dependent upon the cell lines used. We also demonstrate that an intact DNA-binding domain is required for ⌬Np63 function. In addition, we found that the novel activation domain for the ⌬Np63 variant is composed of the 14 unique ⌬N residues along with the adjacent region, including a PXXP motif. Finally, we demonstrated that a PPXY motif shared by ⌬Np63␣ and ⌬Np63␤ is required for optimal transactivation of target gene promoters, suggesting that the PPXY motif is requisite for ⌬Np63 function.p53 functions as a tumor suppressor by transactivating target genes that mediate cell cycle arrest, apoptosis, and other p53-dependent activities. In response to DNA damage, oncogene activation, or other forms of cellular stress, p53 is stabilized by a complex series of post-translational modifications and protein-protein interactions that allow p53 to carry out its tumor suppression activity. Structurally, p53 is organized into several domains, each of which contributes to p53 transcriptional activity. p53 contains two amino-terminal activation domains, AD1 within residues 1-42 and AD2 within residues 43-92, including the proline-rich domain, which enable p53 to form direct associations with transcriptional coactivators. The DNA-binding domain allows for sequence-specific recognition of response elements in p53 target gene promoters. The tetramerization domain directs formation of the p53 tetramer required for DNA binding. Finally, the carboxyl-terminal basic domain has a regulatory function by controlling p53 stability and transcriptional activity (reviewed in Ref. 1).p63, a member of the p53 family of transcription factors, was identified in 1998 (2, 3). Like p53, p63 contains a pr...

p63 in epithelial development

“…The accepted activity was its dominant negative effect exerted towards the TAp63 isoform, as suggested by co-transfection experiments in luciferase reporter assays [3]. However, in addition to the competition between TAp63 and Np63 isoforms, growing evidence indicated that these N-terminal isoforms had different transcriptional specificities a specificity confirmed by functional domain characterization [32][33][34], and microarray analysis showing that both isoforms can induce gene transcription [35,29]. As expected from genes important for developmental and differentiation processes, the more strongly represented classes of target genes are those concerned with cell adhesion, the cytoskeleton, and the cell cycle.…”

PRIMA-1MET/APR-246 targets mutant forms of p53 family members p63 and p73

“…The DN isoforms can block the TA activity of the full-length proteins by forming complexes or by competing for DNA-binding sites (Grob et al, 2001;Stiewe et al, 2002;Chan et al, 2004). Several studies have also shown that DNp63 can activate transcription through an additional N-terminal TA domain (Ghioni et al, 2002;Helton et al, 2006).…”

p53-family proteins and their regulators: hubs and spokes in tumor suppression

“…138 However, this general assumption requires some caution since for instance, DNp63 isoforms are transcriptionally proficient. 139,140 All p53-family transcripts are also subject to alternative splicing at the C-terminus, independent of the promoter used, thus generating a combinatorial variety of isoforms (obtainable adjoining each N-terminal variant with any of the C-terminal variants). The longest C-terminal variant is dubbed a in p63 and p73, and comprises the SAM domain.…”