Component of the COP9 signalosome (CSN) complex that acts as an regulator of the ubiquitin (Ubl) conjugation pathway by mediating the deneddylation of the cullin subunit of SCF-type E3 ubiquitin-protein ligase complexes The CSN complex is involved in the regulation of the mating pheromone response. PCI8 may also be involved in transcriptional and translational control (By similarity). Component of a COP9 signalosome-like (CSN) complex.