Role of individual subunits of the Neurospora crassa CSN complex in regulation of deneddylation and stability of cullin proteins.

• Main Authors: Jiyong Wang, Qiwen Hu, Huijie Chen, Zhipeng Zhou, Weihua Li, Ying Wang, Shaojie Li, Qun He
• Format: Article
• Language: English
• Published: Public Library of Science (PLoS) 2010-12-01
• Series: PLoS Genetics
• Online Access: http://europepmc.org/articles/PMC2996332?pdf=render
• ISSN: 1553-7390; 1553-7404

The Cop9 signalosome (CSN) is an evolutionarily conserved multifunctional complex that controls ubiquitin-dependent protein degradation in eukaryotes. We found seven CSN subunits in Neurospora crassa in a previous study, but only one subunit, CSN-2, was functionally characterized. In this study, we created knockout mutants for the remaining individual CSN subunits in N. crassa. By phenotypic observation, we found that loss of CSN-1, CSN-2, CSN-4, CSN-5, CSN-6, or CSN-7 resulted in severe defects in growth, conidiation, and circadian rhythm; the defect severity was gene-dependent. Unexpectedly, CSN-3 knockout mutants displayed the same phenotype as wild-type N. crassa. Consistent with these phenotypic observations, deneddylation of cullin proteins in csn-1, csn-2, csn-4, csn-5, csn-6, or csn-7 mutants was dramatically impaired, while deletion of csn-3 did not cause any alteration in the neddylation/deneddylation state of cullins. We further demonstrated that CSN-1, CSN-2, CSN-4, CSN-5, CSN-6, and CSN-7, but not CSN-3, were essential for maintaining the stability of Cul1 in SCF complexes and Cul3 and BTB proteins in Cul3-BTB E3s, while five of the CSN subunits, but not CSN-3 and CSN-5, were also required for maintaining the stability of SKP-1 in SCF complexes. All seven CSN subunits were necessary for maintaining the stability of Cul4-DDB1 complexes. In addition, CSN-3 was also required for maintaining the stability of the CSN-2 subunit and FWD-1 in the SCF(FWD-1) complex. Together, these results not only provide functional insights into the different roles of individual subunits in the CSN complex, but also establish a functional framework for understanding the multiple functions of the CSN complex in biological processes.