Attenuation of NF-kappa B signaling response to UVB light during cellular senescence

The ability of cells to adapt to environmental stresses undergoes a progres sive reduction during aging. NF-kappa B-mediated signaling is a major defen sive system against various environmental challenges. The aim of this study was to find out whether replicative senescence affects the response of the NF-kappa B signaling pathway to UVB light in human WI-38 and IMR-90 fibrob lasts. The exposure of early passage fibroblasts to UVB light inhibited the proliferation and induced a hat phenotype similar to that observed in repl icatively senescent fibroblasts not exposed to UVB light. The UVB radiation dose used (153 mJ/cm(2)) did not induce apoptosis in either early or late passage WI-38 fibroblasts. UVB exposure induced a prominent activation of t he NF-kappa B signaling pathway both in early and in late passage WI-38 and IMR-90 fibroblasts. Interestingly, the response to UVB light was significa ntly attenuated in late passage fibroblasts. This attenuation was most prom inent in DNA binding activities of nuclear NF-kappa B complexes. Similar se nescence-related attenuation was also observed in the DNA binding activitie s of nuclear AP-1 and Sp-1 factors after UVB treatment. Immunoblotting and -cytochemistry showed an increase in nuclear localization of p50 and p65 co mponents of NF-kappa B complexes. Supershift experiments showed that the sp ecific NF-kappa B complexes contain p50 and p65 protein components but not p52 and c-Rel proteins. Cytoplasmic I kappa B alpha showed a marked decreas e at protein level but an increase in phosphorylation after UVB treatment. Transient transfection assays with TK5-CAT and TK10-CAT plasmids carrying N F-kappa B-responsive sites of the TNF alpha promoter were used to analyze t he functional activity of the NF-kappa B complexes. Results showed that UVB exposure induced an increase in NF-kappa B-driven CAT expression both in e arly and in late passage fibroblasts though the response was significantly stronger in early passage fibroblasts. Our results show that the induction of NF-kappa B-mediated signaling by UVB light is highly attenuated in senes cent fibroblasts. This attenuation may reduce the stress resistance during cellular senescence. (C) 1999 Academic Press.