title: Monoubiquitination of nuclear RelA negatively regulates NF-κB activity independent of proteasomal degradation.
abstract: Termination and resolution of inflammation are tightly linked to the inactivation of one of its strongest inducers, NF-κB. While canonical post-stimulus inactivation is achieved by upregulation of inhibitory molecules that relocate NF-κB complexes to the cytoplasm, termination of the NF-κB response can also be accomplished directly in the nucleus by posttranslational modifications, e.g., ubiquitination of the RelA subunit. Here we reveal a functional role for RelA monoubiquitination in regulating NF-κB activity. By employing serine-to-alanine mutants, we found that hypo-phosphorylated nuclear RelA is monoubiquitinated on multiple lysine residues. Ubiquitination was reversed by IκBα expression and was reduced when nuclear translocation was inhibited. RelA monoubiquitination decreased NF-κB transcriptional activity despite prolonged nuclear presence and independently of RelA degradation, possibly through decreased CREB-binding protein (CBP) co-activator binding. Polyubiquitin-triggered proteasomal degradation has been proposed as a model for RelA inactivation. However, here we show that proteasomal inhibition, similar to RelA hypo-phosphorylation, resulted in nuclear translocation and monoubiquitination of RelA. These findings indicate a degradation-independent mechanism for regulating the activity of nuclear RelA by ubiquitination.
authors.affiliation: Division of Neurobiology, Department of Neurology and Neuroscience, Weill Cornell Medical College, New York, NY 10065, USA.
authors.forename: Karin
authors.initials: K
authors.lastname: Hochrainer
authors.forename: Gianfranco
authors.initials: G
authors.lastname: Racchumi
authors.forename: Sheng
authors.initials: S
authors.lastname: Zhang
authors.forename: Costantino
authors.initials: C
authors.lastname: Iadecola
authors.forename: Josef
authors.initials: J
authors.lastname: Anrather
mesh_terms: D021581:Active Transport, Cell Nucleus; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D006801:Humans; D020672:I-kappa B Proteins / Q000096:biosynthesis; D009154:Mutation; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D051996:Transcription Factor RelA / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D054875:Ubiquitination
chemical_list: D020672:I-kappa B Proteins; D016328:NF-kappa B; C000606204:NFKBIA protein, human; C498143:RELA protein, human; D051996:Transcription Factor RelA; D000072000:NF-KappaB Inhibitor alpha; D046988:Proteasome Endopeptidase Complex