Nature Cell Biology
7, 1014 - 1020 (2005)
Published online: 28 August 2005; | doi:10.1038/ncb1301
Neddylation and deneddylation regulate Cul1 and Cul3 protein accumulationJune-Tai Wu1, 2, Hsiu-Chen Lin1, 3, Yen-Chen Hu1
& Cheng-Ting Chien1, 2, 31
Institute of Molecular Biology, Academia Sinica, 115, Taipei, Taiwan. 2
Institute of Molecular Medicine, Medical College, National Taiwan University, 100, Taipei, Taiwan. 3
Graduate Institute of Life Sciences, National Defense Medical Center, 114, Taipei, Taiwan.
Correspondence should be addressed to Cheng-Ting Chien ctchien@gate.sinica.edu.tw Cullin family proteins organize ubiquitin ligase (E3) complexes to target numerous cellular proteins for proteasomal degradation. Neddylation, the process that conjugates the ubiquitin-like polypeptide Nedd8 to the conserved lysines of cullins, is essential for in vivo cullin-organized E3 activities1,
2. Deneddylation, which removes the Nedd8 moiety, requires the isopeptidase activity of the COP9 signalosome (CSN)3,
4. Here we show that in cells deficient for CSN activity, cullin1 (Cul1) and cullin3 (Cul3) proteins are unstable, and that to preserve their normal cellular levels, CSN isopeptidase activity is required. We further show that neddylated Cul1 and Cul3 are unstable — as suggested by the evidence that Nedd8 promotes the instability of both cullins — and that the unneddylatable forms of cullins are stable. The protein stability of Nedd8 is also subject to CSN regulation and this regulation depends on its cullin-conjugating ability, suggesting that Nedd8-conjugated cullins are degraded en bloc. We propose that while Nedd8 promotes cullin activation through neddylation, neddylation also renders cullins unstable. Thus, CSN deneddylation recycles the unstable, neddylated cullins into stable, unneddylated ones, and promotes cullin-organized E3 activity in vivo.
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