Cell line dependent involvement of ceramide in ultraviolet light-induced apoptosis

Ultraviolet light (UV) activates an acid sphingomyelinase (ASMase) pathway, which hydrolyzes sphingomyeline to ceramide. Ceramide has been found to be a second messenger, which activates the c-jun N-terminal kinase (JNK) that is required for apoptotic cell death. However, the role of ceramide in UV- induced JNK activation and apoptosis remains controversial. In this study, we examined the correlation among ceramide production, JNK activation and c ell apoptosis after UV-irradiation in three cell lines: 293 (kidney), Jurka t (lymphocytes) and MCF-7 (breast) were used in this study. The ceramide pr oduction was analyzed using the diacylglycerol kinase assay method. The JNK activation was measured by Western blot analysis using an antibody specifi cally recognizing phosphorylated JNK. Cell apoptosis was determined by morp hological change or flow cytometry. Our data show that UV-irradiation induc es ceramide production in both 293 and Jurkat cells. Inhibition of ceramide production by desipramine (25-50 muM) reduced UV-induced JNK activation in both 293 and Jurkat cells; and protects 293 cells from UV-induced apoptosi s. However, inhibition of ceramide production does not prevent Jurkat cells from UV-induced apoptosis. In addition, our data demonstrates that UV-irra diation induces JNK activation and apoptosis of MCF-7 cells without product ion of detectable amounts of ceramide after UV-irradiation. These results s uggest that UV-induced JNK activation and apoptosis can be mediated through a ceramide dependent or an independent pathway.