Rheumatoid arthritis synovial fibroblasts exhibit increased proteolysis of long-lived proteins when autophagy isblocked in the presence of TNF-α. (a) The source of the counts in the long-lived protein degradation assay was determined by comparing the protein flux of long-lived proteins for two rheumatoid arthritis (RA) lines and two control (Ctl) lines cultured for 24 hours with 10 ng/ml TNFα with that of cells cultured with 12.5 μM chloroquine (CQ) or 0.5 μM proteasome inhibitor (PI) in addition to 10 ng/ml TNFα. (b) The effect of the protein degradation pathways on each other in RA synovial fibroblasts and control fibroblasts was determined by comparing the proteolysis remaining after the addition of 12.5 μM CQ or 0.5 μM PI to separate wells or the same well of the same cell line for 24 hours. (c) The proteolysis remaining after cells were cultured without TNFα or with12.5 μM CQ or 0.5 μM PI in addition to 10 ng/ml TNFα was compared with that when cells were cultured with 10 ng/ml TNFα for 24 hours. This was determined for four RA lines and three control lines. Significant differences in control lines compared with RA synovial fibroblast lines: *P < 0.05, **P < 0.01.