Abstract
TP63 (p63), a member of the tumor suppressor TP53 (p53) gene family, is essential for ectodermal tissue development and suppresses malignant progression of carcinomas. The most abundant isoform, ΔNp63α (referred to as p63), lacks the N-terminal transactivation (TA) domain, and was originally characterized as a dominant-negative type suppressor against p53 family proteins. It also binds to TCF/LEF to inhibit β-catenin. Nevertheless, transcriptional activation by p63 has also been observed in varied systems. To understand the puzzling results, we analyzed the structure-function relationship of p63 in the control of β-catenin-dependent transcription. p63 acted as a suppressor of moderately induced β-catenin. However, when nuclear targeted S33Y β-catenin was applied to cause the maximum enhancer activation, p63 displayed a β-catenin-coactivating function. The DNA-binding domain of p63 and the target sequence facilitated it. Importantly, we newly found that, despite the absence of TA domain, p63 was associated with p300, a general adaptor protein and chromatin modifier causing transcriptional activation. C-terminal α domain of p63 was essential for p300-binding and for the coactivator function. These results were related to endogenous p63-p300 complex formation and Wnt/β-catenin-responsive gene regulation by p63 in squamous cell carcinoma lines. The novel p63-p300 interaction may be involved in positive regulation of gene expression in tissue development and carcinogenesis.