Ionizing radiation and short wavelength UV activate NF-kappaB through two distinct mechanisms.
We examined the mechanisms by which two different types of photonic radiation, short wavelength UV (UV-C) and gamma radiation, activate transcription factor NF-kappaB. Exposure of mammalian cells to either form of radiation resulted in induction with similar kinetics of NF-kappaB DNA binding activity, nuclear translocation of its p65(RelA) subunit, and degradation of the major NF-kappaB inhibitor IkappaBalpha. In both cases, induction of NF-kappaB activity was attenuated by proteasome inhibitors and a mutation in ubiquitin-activating enzyme, suggesting that both UV-C and gamma radiation induce degradation of IkappaBs by means of the ubiquitin/proteasome pathway. However, although the induction of IkappaBalpha degradation by gamma rays was dependent on its phosphorylation at Ser-32 and Ser-36, UV-C-induced IkappaBalpha degradation was not dependent on phosphorylation of these residues. Even the "super repressor" IkappaBalpha mutant, which contains alanines at positions 32 and 36, was still susceptible to UV-C-induced degradation. Correspondingly, we found that gamma radiation led to activation of IKK, the protein kinase that phosphorylates IkappaBalpha at Ser-32 and Ser-36, whereas UV-C radiation did not. Furthermore, expression of a catalytically inactive IKKbeta mutant prevented NF-kappaB activation by gamma radiation, but not by UV-C. These results indicate that gamma radiation and UV-C activate NF-kappaB through two distinct mechanisms.
Li
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N
Laboratory of Gene Regulation and Signal Transduction, Department of Pharmacology, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0636, USA.
Karin
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M
D000906:Antibodies; D002460:Cell Line; D003546:Cysteine Endopeptidases / Q000378:metabolism; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics / Q000528:radiation effects*; D005720:Gamma Rays; D006367:HeLa Cells; D006801:Humans; D020672:I-kappa B Proteins; D007668:Kidney; D007700:Kinetics; D009097:Multienzyme Complexes / Q000378:metabolism; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000528:radiation effects*; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000528:radiation effects; D014162:Transfection; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology / Q000502:physiology; D014466:Ultraviolet Rays
D000906:Antibodies; D015853:Cysteine Proteinase Inhibitors; D004268:DNA-Binding Proteins; D020672:I-kappa B Proteins; D009097:Multienzyme Complexes; D016328:NF-kappa B; C000606204:NFKBIA protein, human; D011994:Recombinant Proteins; D014409:Tumor Necrosis Factor-alpha; D000072000:NF-KappaB Inhibitor alpha; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex