Effects of knockdown of C/EBP binding protein CHOP, X-box binding protein (XBP1), and 78-kDa glucose-regulated protein (GRP78) on release of nitric oxide (NO) and matrix metalloproteinase-3 (MMP-3) in response to IL-1β in chondrocytes. (A) Cultured human knee chondrocytes (passage 1) were transfected with siRNAs of CHOP, GRP78 and XBP1 and respective control (ctrl) siRNAs. Knockdown of expression of CHOP, GRP78 and XBP1 was confirmed by western blot. (B) Chondrocytes with validated knockdown of CHOP, GRP78 and XBP1 were treated with IL-1β (10 ng/ml) for 18 hours, and release of NO and MMP-3 determined. Data representative of experiments on three different human knee chondrocyte donors.