Nedd8對cullin-RING泛素接合脢及其受質的影響
The effects of Nedd8 on cullin-RING ubiquitin ligases and their substrates
Date Issued
2006
Date
2006
Author(s)
Wu, June-Tai
DOI
en-US
Abstract
Ubiquitin-proteasome mediated proteolysis is an essential pathway involved in many cellular processes. Ubiquitin is a small polypeptide. Polymerized ubiquitin chains are first attached to the proteins designated to be degraded by a substrate specific ubiquitin E3 ligase, a process called ubiquitylation. The ubiquitylated protein is then recognized by the 19S proteasome and subsequently degraded by the 20S proteasome. Cullins are scaffold proteins that assemble substrate binding receptors/adaptors, and Roc1 into cullin-RING E3 ligase (CRL) complexes transferring ubiquitin moieties onto many cellular proteins. Nedd8 is an ubiquitin-like polypeptide that can be transferred onto the conserved lysines of cullins, a process called neddylation. Deneddylation, the reverse reaction that removes the Nedd8 moieties from cullins, is carried out by COP9 signalosome (CSN). Neddylation is essential for CRL activities in vivo. How deneddylation affects the activities CRLs hasn’t been fully explored. In this thesis, I first showed that cullin1 (Cul1) and cullin3 (Cul3) proteins are unstable in CSN mutant cells. Moreover, deneddylating activity in CSN is required to preserve Cul1 and Cul3 protein levels. In addition to cullins, Nedd8 and Slimb, one of the substrate receptors in Cul1 organized E3 (SCF), are also unstable in CSN mutant cells. These data indicate that the several CRL components could be protected by CSN from neddylation-induced degradations. The significance of CSN-mediated protection on CRLs is suggested by synergistic interaction between CSN5 mutant and several cullin mutants, Nedd8 mutant, as well as a dominant-negative Slimb mutant. Because neddylation-induced degradation of Slimb depends on SCF activity, rescuing Cul1 and Nedd8 protein levels in CSN mutant cells was found to paradoxically compromise SCFSlimb activity. This result is possibly due to the enhanced neddylation-induced degradation of Slimb. The significance of neddylation-induced degradation of cullins and Nedd8 is to preserve substrate degradation in this context, implying another layer of complexity in regulating CRL activity through neddylation and deneddylation. Finally, I found the protein levels of two SCFSlimb substrates changed differently in CSN mutant cells, implying that substrates may play a role on modulating the effects of neddylation and deneddylation on SCFSlimb
Subjects
泛素
cullin-RING接合脢
cullin
Nedd8
CSN複合體
neddylation
deneddylation
Ubiquitin
cullin-RING ligase (CRL)
CSN complex
Type
other
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