Effect of Sp1 and Egr-1 on PPARγ promoter activity. Chondrocytes were co-transfected with the human PPARγ promoter (1 μg/well) and the internal control pSV40-β-gal (0.5 μg/well) together with increasing concentrations of an expression vector for Egr-1 (a) or Sp1 (b). The total amount of transfected DNA was kept constant by addition of the empty vector. The next day, transfected cells were treated with IL-1 (100 pg/mL) for 18 hours. Luciferase activity values were determined and normalized to β-galactosidase activity. Results are expressed as percentage of control (100 is considered the value of untreated cells) and represent the mean ± SD of four independent experiments. *P < 0.05 compared with cells treated with IL-1 alone (control). Egr-1, early growth response gene 1; IL, interleukin; PPARγ, peroxisome proliferator-activated receptor gamma; SD, standard deviation; Sp1, specificity protein 1.