DISTINCT CONFORMATIONS OF P53 ARE OBSERVED AT DIFFERENT STAGES OF KERATINOCYTE DIFFERENTIATION

p53 is a multifunctional protein that has been shown to inhibit the gr owth of transformed cells, arrest the cell cycle of normal cells, regu late gene transcription and influence cellular differentiation, apopto sis and senescence. This study was undertaken to determine if the expr ession of p53 in keratinocytes varied during epidermal differentiation . Fresh frozen-sections of normal human epidermis were subjected to im munofluorescence using a panel of anti-p53 monoclonal antibodies. The monoclonal antibody 122 specifically stained the basal layer of the ep idermis. No staining was observed in other cell layers of the epidermi s using the 122 antibody. When the 240 antibody was used, p53 was only detected in granular layer cells. No other anti-p53 monoclonal antibo dy stained normal epidermis. Immunofluorescent analyses of cultured ke ratinocytes revealed staining patterns that correlated with the staini ng pattern seen in vivo. Immunoprecipitation assays of the cultured ke ratinocytes indicated that each monoclonal antibody, with the exceptio n of DO-1, could only detect a fraction of the total p53 present in th e cultures. This diversity of reactivity was presumed to be due to the masking and exposing of the various epitopes on p53 through the bindi ng of other proteins. Finally, in cultured human keratinocytes, p53 wa s found to be a relatively stable protein with a half-life of 5 h.