Fig. 3. Effects of OSM, ERK inhibitor (U0126), and ERK siRNA on the protein expression of MMP-2 and MMP-9. Cells were pretreated with the ERK inhibitor U0126 (10 and 25 µM) for 1 h before treatment with or without OSM (20 ng/mL) for 48 h. Protein expression of MMP-2 and MMP-9 was analyzed via Western blotting (A). The expression was quantified and expressed as mean±SEM (B). U0126 significantly suppressed OSM-induced MMP-2 expression (p<0.05) yet did not affect OSM-induced MMP-9 expression. Western blot analysis of MMP-2 and MMP-9 expression 24 h after transfection with ERK siRNA with or without OSM treatment for 48 h (C). OSM-induced expression of MMP-2 and MMP-9 was significantly decreased by ERK siRNA compared to OSM alone, with no effect on GAPDH protein expression. Non-targeting negative control siRNA did not affect OSM-induced MMP-2 and -9 protein expression. The results are representative of three independent experiments. The expression was quantified and expressed as mean±SEM (D). Data indicate mean±SEM; ^*p<0.05. OSM, oncostatin M; ERK, extracellular signal-regulated kinase; MMP, matrix metalloproteinase.