Ultraviolet B irradiation modulates susceptibility to tumour necrosis factor-alpha-induced apoptosis via induction of death receptors in murine fibroblasts.

Ultraviolet B (UVB) irradiation causes cell death by apoptosis in murine fibroblast cells. Tumor necrosis factor-alpha (TNF-alpha) is also a well known inducer of apoptosis, although the physiological significance of this activity is poorly understood. We investigated the effects of pretreatment with UVB (312 nm) on TNF-alpha-induced apoptosis in murine fibroblast cells. UVB enhanced susceptibility to cell death by TNF-alpha in a dose-dependent manner. UVB but not TNF-alpha induced the expression of TNF receptor type-1 (TNFR-1) and type-2 (TNFR-2) in a dose-dependent manner. Expression of Fas (CD95) and Fas-ligand (Fas-L), and significant DNA fragmentation were observed in the cells that died. These results suggest that UVB irradiation modulates susceptibility to TNF-alpha-induced apoptosis through the induction of TNFRs, Fas, and Fas-L in murine fibroblasts.