Tumor protein p63, typically referred to as p63, also known as transformation-related protein 63 is a protein that in humans is encoded by the TP63 (also known as the p63) gene.
The TP63 gene was discovered 20 years after the discovery of the p53 tumor suppressor gene and along with p73 constitutes the p53 gene family based on their structural similarity. Despite being discovered significantly later than p53, phylogenetic analysis of p53, p63 and p73, suggest that p63 was the original member of the family from which p53 and p73 evolved.
Tumor protein p63 is a member of the p53 family of transcription factors. p63 -/- mice have several developmental defects which include the lack of limbs and other tissues, such as teeth and mammary glands, which develop as a result of interactions between mesenchyme and epithelium. TP63 encodes for two main isoforms by alternative promoters (TAp63 and ΔNp63). ΔNp63 is involved in multiple functions during skin development and in adult stem/progenitor cell regulation. In contrast, TAp63 has been mostly restricted to its apoptotic function and more recently as the guardian of oocyte integrity. Recently, two new functions have been attributed to TAp63 in heart development and premature aging.
p63 staining on prostate cancer tissue using antibody clone IHC063
Both cleft lip with or without a cleft palate and cleft palate only features have been seen to segregate within the same family with a TP63 mutation. Recently, induced pluripotent stem cells have been produced from patients affected by EEC syndromes by cell reprogramming. The defective epithelial commitment could be partially rescued by a small therapeutic compound.
TP63 has been observed overexpressed in Vulvar Squamous Cell Carcinoma samples, in association with hypermethylation-Induced inactivation of the IRF6 tumor suppressor gene.  Indeed, mRNA levels of TP63 tested higher in Vulvar cancer samples when compared with those of normal skin and preneoplastic vulvar lesions, thus underscoring an epigenetic cross-link between IRF6 gene and the oncogene TP63. 
p63 immunostaining has utility for head and neck squamous cell carcinomas, differentiating prostatic adenocarcinoma (the most common type of prostate cancer) and benign prostatic tissue; normal prostatic glands stain with p63 (as they have basal cells), while the malignant glands in prostatic adenocarcinoma (which lacks these cells) do not.
P63 is also helpful in distinguishing poorly differentiated squamous cell carcinoma from small cell carcinoma or adenocarcinoma. P63 should be strongly stained in poorly differentiated squamous cell, but negative in small cell or adenocarcinoma.
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