Overexpression of wild-type p53 alters growth and differentiation of normal human keratinocytes but not human papillomavirus-expressing cell lines.

To examine whether the tumor suppressor gene p53 influences epidermal differentiation, primary cultures of human foreskin keratinocytes and six human papillomavirus (HPV)-positive cell lines were infected with recombinant retroviruses encoding wild-type p53. Overexpression of p53 in organotypic cultures of normal keratinocytes decreased their growth rate and induced premature cell flattening and involucrin expression, a marker of squamous differentiation. However, overexpression of p53 inhibited or delayed production of other epidermal proteins, keratin 10, profilaggrin, and keratinocyte transglutaminase. Furthermore, levels of endogenous cellular p53 dramatically decreased during epidermal differentiation, suggesting that down-regulation of p53 permits complete expression of specific epidermal proteins. Three HPV-immortalized keratinocyte cell lines and three HPV-positive cervical carcinoma-derived cell lines expressed significantly less (< 3-fold) p53 protein than normal keratinocytes. Up-regulation of wild-type p53 (> 5-fold) by retrovirus infection did not significantly inhibit growth or restore normal epithelial differentiation in any line. Thus, overexpression of wild-type p53 can either induce or inhibit expression of specific epidermal proteins in normal keratinocytes but does not reverse immortality or aberrant differentiation of HPV-immortalized or carcinoma-derived cell lines.