title: A role for UV-light-induced c-Fos: Stimulation of nucleotide excision repair and protection against sustained JNK activation and apoptosis.
abstract: UV light (UV-C) is a potent inducer of the c-fos gene. Cells lacking c-Fos are hypersensitive to the cytotoxic effect of UV-C indicating a protective role of c-fos induction. Here we show that cells deficient in c-Fos (fos-/-) are unable to remove cyclobutane pyrimidine dimers (CPDs) from DNA and undergo apoptosis at high frequency via the Fas pathway. We also show that in c-Fos-deficient cells the activation of c-Jun N-terminal kinase (JNK) by UV-C differs from the wild-type (wt, fos+/+). In wt cells JNK activation is transient, returning to control level 5-8 h after treatment, whereas in c-Fos-deficient cells JNK activation was long-lasting and did not return to control level. Inhibition of early JNK activation by the JNK inhibitor SP600125 attenuated CPD repair and increased UV-C induced apoptosis whereas inhibition of late JNK activation attenuated the apoptotic response of c-Fos-deficient cells. Late and sustained activation of JNK resulted in upregulation of fas (CD95, apo-1) ligand and induction of caspase 8-dependent apoptosis. The data indicate that the immediate-early induction of the JNK/c-fos pathway stimulates the repair of UV-C induced DNA lesions that protects against apoptosis. If this does not occur, cells do not recover from transcription blockage leading, as shown for c-Fos-deficient cells, to a reduced expression of MKP1, sustained JNK activation and fasL overexpression that finally results in activation of the death receptor pathway. The data support the hypothesis that non-repaired DNA damage is the cause for the late and sustained activation of the MAP kinase pathway in response to genotoxins.
authors.affiliation: Department of Toxicology, University of Mainz, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Christmann
authors.forename: Maja T
authors.initials: MT
authors.lastname: Tomicic
authors.forename: Dorthe
authors.initials: D
authors.lastname: Aasland
authors.forename: Bernd
authors.initials: B
authors.lastname: Kaina
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000528:radiation effects*; D026501:Blotting, Southwestern; D015153:Blotting, Western; D020169:Caspases; D004249:DNA Damage; D004260:DNA Repair; D004789:Enzyme Activation / Q000528:radiation effects; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D016755:Proto-Oncogene Proteins c-jun / Q000235:genetics / Q000502:physiology*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014466:Ultraviolet Rays / Q000009:adverse effects*
chemical_list: D016755:Proto-Oncogene Proteins c-jun; D012333:RNA, Messenger; D020928:Mitogen-Activated Protein Kinases; D020169:Caspases