Hydroxynonenal-activated microsomal prostaglandin E
synthase-1 promoter. Chondrocytes were transfected with (a) microsomal prostaglandin E2 synthase-1 (mPGES-1)-Luc or (b) p3xEgr-1-Luc containing three early growth response factor 1 (Egr-1) binding sites. The total amount of transfected DNA was kept constant using a corresponding empty vector. The next day, they were incubated with single addition of 10 μM 4-hydroxynonenal (HNE) for increasing incubation time periods. Luciferase activity was measured in cell extracts and normalized to β-galactosidase activity. (c) Osteoarthritis chondrocytes were treated with 10 μM HNE at increasing time of incubation and then Egr-1 protein expression was evaluated in the cellular extract by western blot. Data are means ± standard errors of the mean, n = 6, expressed as percentages of untreated cells. Student's unpaired t test: *P < 0.05, **P < 0.01, ***P < 0.001.