The diverse mutation profiles, expression patterns, and co-expression patterns shown in the different cancer types may be due to a number of factors, including proteasome structural diversity in different tissues and the need for an assortment of various proteasome subunits (i.e. immunoproteasome, PSMB8-10), as well as, differences in proteasome regulation (i.e. proteasome activators, PSME1-2) [68–74]. Here, PSME1 is linked to cancer.