Consequences of COP9 signalosome and 26S proteasome interaction.
The COP9 signalosome (CSN) occurs in all eukaryotic cells. It is a regulatory particle of the ubiquitin (Ub)/26S proteasome system. The eight subunits of the CSN possess sequence homologies with the polypeptides of the 26S proteasome lid complex and just like the lid, the CSN consists of six subunits with PCI (proteasome, COP9 signalosome, initiation factor 3) domains and two components with MPN (Mpr-Pad1-N-terminal) domains. Here we show that the CSN directly interacts with the 26S proteasome and competes with the lid, which has consequences for the peptidase activity of the 26S proteasome in vitro. Flag-CSN2 was permanently expressed in mouse B8 fibroblasts and Flag pull-down experiments revealed the formation of an intact Flag-CSN complex, which is associated with the 26S proteasome. In addition, the Flag pull-downs also precipitated cullins indicating the existence of super-complexes consisting of the CSN, the 26S proteasome and cullin-based Ub ligases. Permanent expression of a chimerical subunit (Flag-CSN2-Rpn6) consisting of the N-terminal 343 amino acids of CSN2 and of the PCI domain of S9/Rpn6, the paralog of CSN2 in the lid complex, did not lead to the assembly of an intact complex showing that the PCI domain of CSN2 is important for complex formation. The consequence of permanent Flag-CSN2 overexpression was de-novo assembly of the CSN complex connected with an accelerated degradation of p53 and stabilization of c-Jun in B8 cells. The possible role of super-complexes composed of the CSN, the 26S proteasome and of Ub ligases in the regulation of protein stability is discussed.
Huang
Xiaohua
X
Division of Molecular Biology, Department of Surgery, Charité, Universitätsmedizin Berlin, Germany.
Hetfeld
Bettina K J
BK
Seifert
Ulrike
U
Kähne
Thilo
T
Kloetzel
Peter-Michael
PM
Naumann
Michael
M
Bech-Otschir
Dawadschargal
D
Dubiel
Wolfgang
W
D000818:Animals; D017360:Arabidopsis / Q000201:enzymology / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D000075686:COP9 Signalosome Complex; D002478:Cells, Cultured; D010450:Endopeptidases / Q000235:genetics / Q000378:metabolism; D005347:Fibroblasts / Q000201:enzymology / Q000378:metabolism; D006801:Humans; D051379:Mice; D046912:Multiprotein Complexes / Q000378:metabolism*; D009842:Oligopeptides; D010447:Peptide Hydrolases / Q000378:metabolism*; D010455:Peptides / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology
D029681:Arabidopsis Proteins; C474638:CSN2 protein, Arabidopsis; D046912:Multiprotein Complexes; D009842:Oligopeptides; D010455:Peptides; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; C085706:FLAG peptide; D010450:Endopeptidases; D010447:Peptide Hydrolases; C472775:Rpn6 protein, S cerevisiae; D000075686:COP9 Signalosome Complex; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease