Altered expression of the p53-regulated proteins, p21Waf1/Cip1, MDM2, and Bax in ultraviolet-irradiated human skin.

The distribution of p21WAf1/CiP1, MDM2, and Bax/Bcl-2 proteins in ultraviolet (UV)-irradiated and nonirradiated human skin was examined immunohistochemically and compared with p53 protein levels. Sun-protected buttock skin from three volunteers was exposed to solar simulated irradiation, and biopsies were performed 0.5, 1, 2, 4, and 24 hours after irradiation as well as control unirradiated skin from the opposite buttock. A similar staining pattern was observed in each of the three volunteers. P53 protein was detectable in all skin samples examined. P21Waf1/CiP1 protein was visible in the nuclei of cells at 4 hours, and staining intensity increased at 24 hours. MDM2 protein expression was noted in isolated nuclei in the epidermis at 24 hours. Bax cytoplasmic staining was evident in the basal layer of the epidermis of all samples, and this staining appeared to increase in intensity in the 4- and 24-hour specimens. There was no Bcl-2 immunohistochemical staining in any sample. These results suggest that p53 and genes/proteins under the control of p53 are altered/ activated in normal human skin in response to UV exposure.