Effect of IL-1 on Egr-1 and Sp1 expression in osteoarthritis chondrocytes. Chondrocytes were treated with 100 pg/mL IL-1 for the indicated time periods. Total RNA was isolated and was reverse-transcribed into cDNA, and Egr-1 (a), Sp1 (b), and PPARγ (c) mRNAs were quantified by using real-time polymerase chain reaction. All experiments were performed in triplicate, and negative controls without template RNA were included in each experiment. (a,b) Results are expressed as fold change, and 1 is considered the value of control (that is, untreated cells). (c) Results are expressed as percentage of control (that is, cells treated with IL-1 alone) and are the mean ± SD from four independent experiments. The results represent the mean ± SD of four independent experiments. *P < 0.05 compared with unstimulated cells. Cell lysates were prepared and analyzed for Egr-1 (d), Sp1 (e), and PPARγ (f) protein expression by Western blotting. In the lower panels, the blots were stripped and reprobed with a specific anti-β-actin antibody. The blots are representative of similar results obtained from four independent experiments. Egr-1, early growth response gene 1; IL, interleukin; PPARγ, peroxisome proliferator-activated receptor gamma; SD, standard deviation; Sp1, specificity protein 1.