For PSMD5 over expression experiment, RPN1-tagged cells were transfected in either 6-well plates (Cat. No. 3506; Costar) or 10 cm dishes using 1 µg or 5 µg of HA-PSMD5, respectively. All the transfections were performed with Lipofectamine 3000 (Cat. No. L3000015; Thermo Fisher Scientific) in Opti-MEM reduced serum medium (Cat. No. 31985070; Life Technologies), following the manufacturer’s protocol. Cells were incubated at 37 °C in a humidified atmosphere containing 5 % CO₂ for 48 h before harvesting.