Essential 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. The complex is also involved in phosphorylation of p53/TP53, c-jun/JUN, IkappaBalpha/NFKBIA, ITPK1 and IRF8/ICSBP, 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. Involved in early stage of neuronal differentiation via its interaction with NIF3L1. Component of the CSN complex, composed of COPS1/GPS1, COPS2, COPS3, COPS4, COPS5, COPS6, COPS7 (COPS7A or COPS7B), COPS8 and COPS9. In the complex, it probably interacts directly with COPS1, COPS4, COPS5, COPS6 and COPS7 (COPS7A or COPS7B). Specifically interacts with the ligand binding domain of the thyroid receptor (TR). Does not require the presence of thyroid hormone for its interaction. Interacts with CUL1 and CUL2. Interacts with IRF8/ICSBP1 and with nuclear receptors NR2F1 and NR0B1 (By similarity). Interacts with NIF3L1 (PubMed:12522100). Ubiquitously expressed. Regulated by thyroid hormone and TR. Phosphorylated by CK2 and PKD kinases. Belongs to the CSN2 family.