CSN6 is one subunit of the constitutive photomorphogenesis 9 (COP9) signalosome 
(CSN), which is an evolutionarily conserved multiprotein complex found in plants 
and animals and originally described as a repressor of light-dependent growth 
and transcription in Arabidopsis. CSN is homologous to the 19S lid subcomplex of 
the 26S proteasome, thus it has been postulated to be a regulator of the 
ubiquitin-proteasome pathway. In mammalian cells, it consists of eight subunits 
(CSN1-CSN8). Among the CSN subunits, CSN5 and CSN6 are the only two that each 
contains an MPN (Mpr1p and Pad1p N-terminal) domain. The deneddylating activity 
of an MPN domain toward cullin-RING ubiquitin ligases (CRL) may coordinate 
CRL-mediated ubiquitination activity. More and more studies about CSN6 are 
emerging, and its overexpression is found in many types of cancers. Evidence has 
shown that CSN6 is a molecule platform between protein degradation and signal 
transduction. Here, we provide a summary of human CSN6, especially its roles in 
cancer, hoping that it can lay the groundwork for cancer prevention or therapy.