ZUP1 and plasma cell myeloma: UCHL5 is a deubiquitylating enzyme (DUB) that is more highly expressed in MM cells than in normal plasma cells.25 Preclinical studies have shown that inhibition of UCHL5 decreases viability and inhibits proliferation of MM cells, and overcomes resistance to bortezomib.25 Many DUBs demonstrate esterase activity, and DUB inhibitors have been studied for anti-myeloma activity.