Component of the COP9 signalosome complex (CSN), a complex involved in various cellular and developmental processes. The CSN complex is an essential regulator of the ubiquitin (Ubl) conjugation pathway by mediating the deneddylation of the cullin subunits of SCF-type E3 ligase complexes, leading to decrease the Ubl ligase activity of SCF-type complexes such as SCF, CSA or DDB2. Also involved in the deneddylation of non-cullin subunits such as STON2. The complex is also involved in phosphorylation of p53/TP53, c-jun/JUN, IkappaBalpha/NFKBIA, ITPK1, IRF8/ICSBP and SNAPIN, possibly via its association with CK2 and PKD kinases. CSN-dependent phosphorylation of TP53 and JUN promotes and protects degradation by the Ubl system, respectively. Component of the CSN complex, composed of COPS1/GPS1, COPS2, COPS3, COPS4, COPS5, COPS6, COPS7 (COPS7A or COPS7B), COPS8 and COPS9 isoform 1 (PubMed:18850735, PubMed:26456823). In the complex, it probably interacts directly with COPS1, COPS2, COPS3, COPS5, COPS6, COPS7 (COPS7A or COPS7B) and COPS8 (PubMed:18850735). Interacts with TOR1A; the interaction is direct and associates TOR1A and SNAPIN with the CSN complex (PubMed:21102408). Interacts with STON2; controls STON2 neddylation levels (PubMed:21102408). Interacts with ERCC6 (PubMed:26030138). Belongs to the CSN4 family.