Distinct conformations of p53 are observed at different stages of keratinocyte differentiation

p53 is a multifunctional protein that has been shown to inhibit the growth of transformed cells, arrest the cell cycle of normal cells, regulate gene transcription and influence cellular differentiation, apoptosis and senescence. This study was undertaken to determine if the expression of p53 in keratinocytes varied during epidermal differentiation. Fresh frozen-sections of normal human epidermis were subjected to immunofluorescence using a panel of anti-p53 monoclonal antibodies. The monoclonal antibody 122 specifically stained the basal layer of the epidermis. No staining was observed in other cell layers of the epidermis using the 122 antibody. When the 240 antibody was used, p53 was only detected in granular layer cells. No other anti-p53 monoclonal antibody stained normal epidermis. Immunofluorescent analyses of cultured keratinocytes revealed staining patterns that correlated with the staining pattern seen in vivo. Immunoprecipitation assays of the cultured keratinocytes indicated that each monoclonal antibody, with the exception of DO-1, could only detect a fraction of the total p53 present in the cultures. This diversity of reactivity was presumed to be due to the masking and exposing of the various epitopes on p53 through the binding of other proteins. Finally, in cultured human keratinocytes, p53 was found to be a relatively stable protein with a half-life of 5 h.