The p53 homologue p63 is essential for ectodermal differentiation, such that p63-/- mice lack all squamous epithelia and teeth. The p63 gene expresses at least 6 different transcripts, but information regarding the expression, regulation and function of the different isoforms has remained sparse, due to the lack of adequate reagents directed specifically against the individual proteins. Here we characterize the expression of p63 alpha/delta Np63 alpha in benign and malignant lesions of the oral epithelium, using a specific antibody raised against a peptide derived from the C-terminus of p63 alpha, which does not cross-react with p53 or the other p53 homologue, p73. By immunohistochemical analysis, we show that these p63 isoforms are expressed in the nucleus of many cells. In normal and benign lesions, p63 alpha/delta Np63 alpha-expressing cells are mainly found suprabasally, whereas p53-expressing cells are restricted to the basal-cell layer. By RT-PCR, we show that delta Np63 alpha is the predominant isoform in cell lines from squamous-cell carcinomas of the head and neck, confirming our immunochemical observations. Our data are consistent with studies suggesting a role for p63 in the transit-amplifying population of epidermal cells. Over-expression of p63 alpha, and in particular the delta N form, was frequently seen in carcinomas. Taken together with previous analyses of p63 expression, our data suggest distinct roles for different p63 isoforms in the regulation of growth and/or differentiation of epithelial cells. Moreover, our data are compatible with the notion that p63 can act to promote neoplastic growth in the oral epithelium.
Copyright 2000 Wiley-Liss, Inc.