title: COP9 signalosome- and 26S proteasome-dependent regulation of SCFTIR1 accumulation in Arabidopsis.
abstract: Ubiquitination and proteasome-mediated degradation of proteins are crucial for eukaryotic physiology and development. The largest class of E3 ubiquitin ligases is made up of the cullin-RING ligases (CRLs), which themselves are positively regulated through conjugation of the ubiquitin-like peptide RUB/NEDD8 to cullins. RUB modification is antagonized by the COP9 signalosome (CSN), an evolutionarily conserved eight-subunit complex that is essential in most eukaryotes and cleaves RUB from cullins. The CSN behaves genetically as an activator of CRLs, although it abolishes CRL activity in vitro. This apparent paradox was recently reconciled in different organisms, as the CSN was shown to prevent autocatalytic degradation of several CRL substrate adaptors. We tested for such a mechanism in the model plant Arabidopsis by measuring the impact of a newly identified viable csn2 mutant on the activity and stability of SCF(TIR1), a receptor to the phytohormone auxin and probably the best characterized plant CRL. Our analysis reveals that not only the F-box protein TIR1 but also relevant cullins are destabilized in csn2 and other Arabidopsis csn mutants. These results provide an explanation for the auxin resistance of csn mutants. We further observed in vivo a post-translational modification of TIR1 dependent on the proteasome inhibitor MG-132 and provide evidence for proteasome-mediated degradation of TIR1, CUL1, and ASK1 (Arabidopsis SKP1 homolog). These results are consistent with CSN-dependent protection of Arabidopsis CRLs from autocatalytic degradation, as observed in other eukaryotes, and provide evidence for antagonist roles of the CSN and 26S proteasome in modulating accumulation of the plant CRL SCF(TIR1).
authors.affiliation: Institut de Biologie Environnementale et Biotechnologie, UMR 6191, CNRS-Commissariat à l'Energie Atomique, UniversitédelaMéditerranée Aix-Marseille II, Centre d'Etudes Nucléaires Cadarache, F-13108 Saint Paul lez Durance Cedex, France.
authors.forename: Johannes
authors.initials: J
authors.lastname: Stuttmann
authors.forename: Esther
authors.initials: E
authors.lastname: Lechner
authors.forename: Raphael
authors.initials: R
authors.lastname: Guérois
authors.forename: Jane E
authors.initials: JE
authors.lastname: Parker
authors.forename: Laurent
authors.initials: L
authors.lastname: Nussaume
authors.forename: Pascal
authors.initials: P
authors.lastname: Genschik
authors.forename: Laurent D
authors.initials: LD
authors.lastname: Noël
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D000075686:COP9 Signalosome Complex; D044842:Cullin Proteins / Q000235:genetics / Q000378:metabolism; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D044783:F-Box Proteins / Q000235:genetics / Q000378:metabolism*; D007210:Indoleacetic Acids / Q000378:metabolism; D007976:Leupeptins / Q000494:pharmacology; D009154:Mutation; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000235:genetics / Q000378:metabolism*; D011499:Protein Processing, Post-Translational / Q000502:physiology*; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination / Q000187:drug effects / Q000502:physiology*; D014452:Ubiquitins / Q000235:genetics / Q000378:metabolism
chemical_list: C120363:ASK1 protein, Arabidopsis; D029681:Arabidopsis Proteins; C507061:CONSTITUTIVE PHOTOMORPHOGENIC 9 protein, Arabidopsis; C474638:CSN2 protein, Arabidopsis; C100318:Cullin 1; D044842:Cullin Proteins; D015853:Cysteine Proteinase Inhibitors; D044783:F-Box Proteins; D007210:Indoleacetic Acids; D007976:Leupeptins; D010940:Plant Proteins; C513170:RUB1 protein, Arabidopsis; D011956:Receptors, Cell Surface; C501405:TIR1 protein, Arabidopsis; D014452:Ubiquitins; C046131:auxin receptor, plant; D000075686:COP9 Signalosome Complex; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde