The temporal and spatial distribution of p21(WAF) expression in skin appendages

p21(WAF) is a cyclin-dependent kinase inhibitor which is widely expressed i n epidermal structures. Using a combination of double immunocytochemical st aining and combined ill situ hybridization. we show that there is a strikin g exclusivity between the expression of Ki67 and p21(WAF) in the hair matri x. Some cells that are Ki67-positive also express p53, but as they exit the cell cycle they assume p21(WAF)-positive/p53-negative status. By contrast, cells in the interfollicular epidermis of psoriatic lesions, in the sebace ous gland, and in the outer root sheath are p21(WAF)-positive/p53-positive but Ki67-negative. These results suggest that in some anatomical parts of t he epidermis, p21(WAF) expression can accompany p53 expression, whereas in other parts, the expression of these markers is reciprocal, suggesting that other pathways may he controlling p21WAF expression. In order to define, f unctionally, the presence of p53-independent p21(WAF) expression in skin, w e examined lesions of Bowen's disease in which both alleles of p53 were ina ctivated. p21(WAF) expression was still observed, confirming a role for p53 -independent expression of p21(WAF) in human skin in vivo.