The study of ultraviolet B-induced apoptosis in cultured mouse keratinocytes and in mouse skin.

The responsibility of ultraviolet B (UVB) radiation for the induction of apoptosis in epidermal cells in vitro and in vivo was examined. Using cultured mouse keratinocytes, PAM212 cells, the morphological development of apoptotic cells (AC) after UVB irradiation was observed, and their DNA status was also examined. In addition, histochemical analysis was performed to establish whether the UVB-mediated sunburn cells (SBC) were AC or not. The cultured cells exposed to UVB showed the morphological characteristics of AC, and the electrophoresis of DNA isolated from these cells showed characteristic fragmentation, i.e. 'DNA ladder'. DNA fragmentation was detectable with UVB doses of more than 50 mJ/cm2, and it appeared 12 h after irradiation, indicating endonuclease-mediated DNA damage. In vivo experimentation using the TdT-mediated dUTP-biotin nick end labeling method (TUNEL) for detection of AC showed scattered positive cells in the basal layer of the UVB-irradiated mouse ear skin. The distributed pattern of the TUNEL-positive cells was similar to that of SBCs. These findings suggest that UVB is a causative factor of apoptosis in the epidermal cells, and that SBC is formed as a result of the apoptosis.