Effect of IL-1 on the recruitment of Egr-1 and Sp1 at the PPARγ promoter. (a) Schematic diagram of the PPARγ promoter showing the locations of the overlapping binding site for Egr-1 and Sp1. Arrows indicate primers used for ChIP analysis. (b,c) Confluent chondrocytes were treated with 100 pg/mL IL-1 for the indicated time periods, and ChIP assays were performed by using specific anti-Egr-11 (a) and anti-Sp1 (b) antibodies. (a) The results are expressed as fold change of Egr-1 binding to the PPARγ promoter relative to untreated cells and represent the mean ± SD of four independent experiments. (b) Results are expressed as percentage of control (that is, untreated cells) and are the mean ± SD of four independent experiments. *P < 0.05 compared with unstimulated cells. ChIP, chromatin immunoprecipitation; Egr-1, early growth response gene 1; IL, interleukin; PPARγ, peroxisome proliferator-activated receptor gamma; SD, standard deviation; Sp1, specificity protein 1.