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BMC Biochem. 2006 Jan 9;7:1.

Targeted silencing of Jab1/Csn5 in human cells downregulates SCF activity through reduction of F-box protein levels.

Author information

1
Department of Biology, California Institute of Technology Pasadena, CA 91125, USA. cope@caltech.edu

Abstract

BACKGROUND:

SCF ubiquitin ligases target numerous proteins for ubiquitin dependent proteolysis, including p27 and cyclin E. SCF and other cullin-RING ligases (CRLs) are regulated by the ubiquitin-like protein Nedd8 that covalently modifies the cullin subunit. The removal of Nedd8 is catalyzed by the Jab1/MPN domain metalloenzyme (JAMM) motif within the Csn5 subunit of the Cop9 Signalosome.

RESULTS:

Here, we conditionally knock down Csn5 expression in HEK293 human cells using a doxycycline-inducible shRNA system. Cullin levels were not altered in CSN-deficient human cells, but the levels of multiple F-box proteins were decreased. Molecular analysis indicates that this decrease was due to increased Cul1- and proteasome-dependent turnover. Diminished F-box levels resulted in reduced SCF activity, as evidenced by accumulation of two substrates of the F-box protein Fbw7, cyclin E and c-myc, in Csn5-depleted cells.

CONCLUSION:

We propose that deneddylation of Cul1 is required to sustain optimal activity of SCF ubiquitin ligases by repressing 'autoubiquitination' of F-box proteins within SCF complexes, thereby rescuing them from premature degradation.

PMID:
16401342
PMCID:
PMC1360668
DOI:
10.1186/1471-2091-7-1
[Indexed for MEDLINE]
Free PMC Article

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