The Signaling of UV-induced Apoptosis in Melanocytes

Ultraviolet B (UVB) radiation may activate or deteriorate cultured human epidermal melanocytes, depending on the doses and culture conditions. In this study, we examined whether apoptosis of melanocytes can be induced by physiologic doses of UVB irradiation. PI staining for DNA condensation and flow cytometric analyses demonstrated the apoptotic cell death of melanocytes after UVB irradiation. The level of p53 and Bax revealed a dose-dependent increase with increasing dose of UVB, but the level of Bcl-2 remained unchanged. Confocal microscopic examination showed that Bax moved trom a diffuse to a punctate distribution after UVB irradiation. However, there were no changes in the pattern of Bcl-2. We next examined the downstream targets of apoptosis. Our results showed that a precursor form of caspase-3 disappeared with increasing doses of UVB. We also observed cleavage of poly(ADP-ribose) polymerase (PARP) after UVB irradiation. In addition, UVB irradiation resulted in a remarkable activation of c-Jun N-terminal kinase (JNK). These results indicate that UVB may induce apoptosis via JNK activation in human melanocytes.