Activation of c-Jun N-terminal kinase is required for ultraviolet B-induced apoptosis of murine peritoneal macrophages in vitro

The mechanisms of ultraviolet B (UVB)-induced apoptosis and the role of c-Jun N-terminal kinase (JNK) mitogen activated protein kinase (MAPK) in murine peritoneal macrophages, the terminally differentiated non-dividing cells were investigated. Exposure of macrophages to UVB 100 mJ/cm2 induced rapid apoptosis concurrent with activation of JNK and mitochondrial cytochrome c release leading to procaspase-3 activation. Late into the UVB-induced apoptosis, a caspase-mediated cleavage of Bid was observed. Caspase inhibitors N-Benzylocarbonyl-Val–Asp–fluoromethyl ketone and N-Acetyl-Asp–Glu–Val–Asp-aldehyde inhibited the UVB-induced apoptosis without preventing the release of cytochrome c and JNK activation. The inhibition of JNK MAPK prevented UVB-induced apoptosis, concomitant with inhibition in cytochrome c release and procaspase-3 activation. However, it had no effect on procaspase-8 activation. These results indicate that activation of JNK MAPK upstream of caspases might play an important role in the apoptotic process of macrophages exposed to UVB irradiation.