Attenuation of NF-kappaB signaling response to UVB light during cellular senescence.
The ability of cells to adapt to environmental stresses undergoes a progressive reduction during aging. NF-kappaB-mediated signaling is a major defensive system against various environmental challenges. The aim of this study was to find out whether replicative senescence affects the response of the NF-kappaB signaling pathway to UVB light in human WI-38 and IMR-90 fibroblasts. The exposure of early passage fibroblasts to UVB light inhibited the proliferation and induced a flat phenotype similar to that observed in replicatively senescent fibroblasts not exposed to UVB light. The UVB radiation dose used (153 mJ/cm2) did not induce apoptosis in either early or late passage WI-38 fibroblasts. UVB exposure induced a prominent activation of the NF-kappaB signaling pathway both in early and in late passage WI-38 and IMR-90 fibroblasts. Interestingly, the response to UVB light was significantly attenuated in late passage fibroblasts. This attenuation was most prominent in DNA binding activities of nuclear NF-kappaB complexes. Similar senescence-related attenuation was also observed in the DNA binding activities of nuclear AP-1 and Sp-1 factors after UVB treatment. Immunoblotting and -cytochemistry showed an increase in nuclear localization of p50 and p65 components of NF-kappaB complexes. Supershift experiments showed that the specific NF-kappaB complexes contain p50 and p65 protein components but not p52 and c-Rel proteins. Cytoplasmic IkappaBalpha showed a marked decrease at protein level but an increase in phosphorylation after UVB treatment. Transient transfection assays with TK5-CAT and TK10-CAT plasmids carrying NF-kappaB-responsive sites of the TNFalpha promoter were used to analyze the functional activity of the NF-kappaB complexes. Results showed that UVB exposure induced an increase in NF-kappaB-driven CAT expression both in early and in late passage fibroblasts though the response was significantly stronger in early passage fibroblasts. Our results show that the induction of NF-kappaB-mediated signaling by UVB light is highly attenuated in senescent fibroblasts. This attenuation may reduce the stress resistance during cellular senescence.
Helenius
M
M
Department of Cell Biology, University of Jyväskylä, Jyväskylä, Finland.
Mäkeläinen
L
L
Salminen
A
A
D016227:Benzoquinones; D002460:Cell Line; D002461:Cell Line, Transformed; D016922:Cellular Senescence / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism / Q000502:physiology / Q000528:radiation effects; D006801:Humans; D047029:Lactams, Macrocyclic; D016328:NF-kappa B / Q000378:metabolism*; D047428:Protein Kinase Inhibitors; D011809:Quinones / Q000494:pharmacology; D017828:Rifabutin / Q000031:analogs & derivatives; D015398:Signal Transduction; D020032:Tyrphostins / Q000494:pharmacology; D014466:Ultraviolet Rays
D016227:Benzoquinones; D004791:Enzyme Inhibitors; D047029:Lactams, Macrocyclic; D016328:NF-kappa B; D047428:Protein Kinase Inhibitors; D011809:Quinones; D020032:Tyrphostins; D017828:Rifabutin; C020754:herbimycin