The ubiquitin-proteasome system (UPS) plays an essential role in maintaining cellular homeostasis by degrading ubiquitinated proteins. The immunoproteasome and constitutive proteasome are multisubunit cylindrical complexes each containing three proteolytic subunits; large multifunctional peptidase 2 (LMP2/β1i/PSMB9), MECL-1 (LMP10/β2i/PSMB10), and LMP7 (β5i/PSMB8) in the immunoproteasome, replaced, respectively, by β1 (β1c/PSMB6), β2...