The expression of p53, p21, Bax and induction of apoptosis in normal volunteers in response to different doses of ultraviolet radiation

Background Ultraviolet radiation (UVR) damages keratinocytes. Direct DNA damage may undergo enzymatic repair followed by resumption of the normal cell cycle. Cells may also be eliminated without inflammation by the error-free process of programmed cell death or apoptosis. Necrosis of cells can occur after overwhelming damage. Failure of apoptosis leads to retention of cells with persistent mutations. Objectives This study investigates p53-dependent apoptotic responses in normal skin following solar-simulated radiation (SSR). Methods Sun-protected buttock skin from normal volunteers with no history or clinical evidence of skin cancer was exposed to graded doses of SSR, 0.5, 1, 2 and 3 times the minimal erythema dose (MED). Biopsies taken at a range of time points (4.5, 9, 24, 33, 48 and 72 h) after UVR, quantified the time course and dose-response of apoptosis and the expression of the relevant proteins, p53, p21(waf1/Cip1) and Bax, by single and double labelling techniques. Results Apoptosis was upregulated in a dose-dependent manner as was the expression of p53, p21(waf1/Cip1) and Bax in response to SSR. Following exposure to 3 MEDs it was found that: (i) the maximum number of apoptotic cells occurred at 48 h; (ii) p53 protein expression was upregulated from 4 to 72 h preceding peak p21(waf1/Cip1) protein expression (9-48 h) and peak Bax protein expression (33 h). Conclusions These results suggest that, following SSR, normal human skin induces apoptosis by the p53, p21(waf1/Cip1) , Bax pathway in vivo. In addition, induction of apoptosis and expression of p53, p21(waf1/Cip1) and Bax occurs in a dose-dependent manner.