title: Role of the MPN subunits in COP9 signalosome assembly and activity, and their regulatory interaction with Arabidopsis Cullin3-based E3 ligases.
abstract: The COP9 signalosome (CSN) is an evolutionarily conserved multisubunit protein complex that regulates a variety of biological processes. Among its eight subunits, CSN5 and CSN6 contain a characteristic MPN (for Mpr1p and Pad1p N-terminal) domain and, in Arabidopsis thaliana, are each encoded by two genes: CSN5A, CSN5B and CSN6A, CSN6B, respectively. We characterized both MPN subunits using a series of single and double mutants within each gene family. Our results indicate that although CSN6A and CSN6B retain mostly redundant functions, CSN5A and CSN5B play unequal roles in the regulation of plant development. Complete depletion of either of the two MPN members results in CSN instability and the decay of various CSN components, along with the complete loss of CUL1, CUL3, and CUL4 derubylation. Furthermore, we demonstrate that CSN interacts with CUL3, in addition to CUL1 and CUL4, and that the lack of CSN activity differentially affects the stability of those three cullins. Interestingly, we also show that optimal CUL3 activity is required to maintain the cellular pool of CSN5, through a posttranscriptional mechanism. Our data suggest the existence of reciprocal regulation between CUL3 and CSN5 accumulation. This study thus completes the genetic analysis of all CSN subunits and confirms the structural interdependence between PCI and MPN subunits in functional CSN complex formation.
authors.affiliation: Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, Conecticut 06520-8104, USA.
authors.forename: Giuliana
authors.initials: G
authors.lastname: Gusmaroli
authors.forename: Pablo
authors.initials: P
authors.lastname: Figueroa
authors.forename: Giovanna
authors.initials: G
authors.lastname: Serino
authors.forename: Xing Wang
authors.initials: XW
authors.lastname: Deng
mesh_terms: D017360:Arabidopsis / Q000033:anatomy & histology / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D000075686:COP9 Signalosome Complex; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D044842:Cullin Proteins; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D007210:Indoleacetic Acids / Q000378:metabolism; D008969:Molecular Sequence Data; D009024:Morphogenesis; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D010447:Peptide Hydrolases / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000033:anatomy & histology / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D020798:Two-Hybrid System Techniques; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism*
chemical_list: C500789:AT1G26830 protein, Arabidopsis; D029681:Arabidopsis Proteins; C497728:COP9 signalosome subunit 5, Arabidopsis; C445070:CSN6B protein, Arabidopsis; D002352:Carrier Proteins; D044842:Cullin Proteins; D007210:Indoleacetic Acids; D046912:Multiprotein Complexes; D021122:Protein Subunits; D044767:Ubiquitin-Protein Ligases; D010447:Peptide Hydrolases; D000075686:COP9 Signalosome Complex; D046988:Proteasome Endopeptidase Complex