Effects of IL-1β and biomechanical injury on 78-kDa glucose-regulated protein (GRP78) and C/EBP binding protein (CHOP) expression in chondrocytes. (A) SDS-PAGE/western blot analysis was performed to examine expression of GRP78 and CHOP in passage-1 human knee chondrocytes that we treated with IL-1β (10 ng/ml) and the positive control UPR inducer tunicamycin (TM, 2.5 μg/ml), for 18 hours. In all, 13 different donors (3 grade I, 5 between grade I and II, and 5 grade II) were studied; results of 4 donors are shown. See Table 1 for donor-grading information. CHOP induction by IL-1β was detected in only one grade I and one grade II knee cartilage donor of 13. (B) Primary bovine-knee chondrocytes embedded in alginate were subjected to mechanical injury, and cell protein extracted as described (Methods). Data representative of three individual experiments.