title: Proteomics analysis of nucleolar SUMO-1 target proteins upon proteasome inhibition.
abstract: Many cellular processes are regulated by the coordination of several post-translational modifications that allow a very fine modulation of substrates. Recently it has been reported that there is a relationship between sumoylation and ubiquitination. Here we propose that the nucleolus is the key organelle in which SUMO-1 conjugates accumulate in response to proteasome inhibition. We demonstrated that, upon proteasome inhibition, the SUMO-1 nuclear dot localization is redirected to nucleolar structures. To better understand this process we investigated, by quantitative proteomics, the effect of proteasome activity on endogenous nucleolar SUMO-1 targets. 193 potential SUMO-1 substrates were identified, and interestingly in several purified SUMO-1 conjugates ubiquitin chains were found to be present, confirming the coordination of these two modifications. 23 SUMO-1 targets were confirmed by an in vitro sumoylation reaction performed on nuclear substrates. They belong to protein families such as small nuclear ribonucleoproteins, heterogeneous nuclear ribonucleoproteins, ribosomal proteins, histones, RNA-binding proteins, and transcription factor regulators. Among these, histone H1, histone H3, and p160 Myb-binding protein 1A were further characterized as novel SUMO-1 substrates. The analysis of the nature of the SUMO-1 targets identified in this study strongly indicates that sumoylation, acting in coordination with the ubiquitin-proteasome system, regulates the maintenance of nucleolar integrity.
authors: Division of Genomics and Cell Biology, San Raffaele Scientific Institute, Milan, Italy.
authors: Vittoria
authors: V
authors: Matafora
authors: Alfonsina
authors: A
authors: D'Amato
authors: Silvia
authors: S
authors: Mori
authors: Francesco
authors: F
authors: Blasi
authors: Angela
authors: A
authors: Bachi
mesh_terms: D000818:Animals; D002466:Cell Nucleolus / Q000737:chemistry / Q000378:metabolism*; D015853:Cysteine Proteinase Inhibitors / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D007553:Isotope Labeling; D007976:Leupeptins / Q000378:metabolism; D008969:Molecular Sequence Data; D061988:Proteasome Inhibitors; D011499:Protein Processing, Post-Translational; D040901:Proteomics / Q000379:methods*; D025842:SUMO-1 Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: D015853:Cysteine Proteinase Inhibitors; D007976:Leupeptins; D061988:Proteasome Inhibitors; D025842:SUMO-1 Protein; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde