Functional impact of COP9 signalosome and DEN1 interaction

Nedd8 conjugation (neddylation) and deconjugation (deneddylation) of cullin-RING ubiquitin ligases (CRLs) represent important posttranslational modifications (Schmaler & Dubiel, 2010). Deneddylation is performed by the COP9 signalosome (CSN) a highly conserved protein complex. CSN subunit 5 (CSN5) features a metalloprotease Jamm/MPN+ motif responsible for deneddylation. CSN5 per se does not have such an activity. The CSN is associated with a variety of proteins including deubiquitinating enzymes (e.g. USP15) as well as kinases and important regulatory proteins. Here we demonstrate the association of CSN with an other deneddylase called deneddylase 1 (DEN1): a cysteine protease highly specific for Nedd8.

We have characterized both deneddylases in detail. The data reveal a direct interaction of CSN and DEN1. Binding of DEN1 to the CSN in mammals is accomplished via the N-terminal part of COP9 signalosome subunit CSN1. Downregulation of CSN1 protects ectopically expressed His-DEN1 from proteasomal degradation, whereas overexpression of CSN1 destabilizes His-Den1. Furthermore, we identified Nedd8 as a novel key regulator of DEN1 stability.