Impact of mithramycin on interleukin (IL)-1β-induced phosphorylation of mitogen-activated protein kinases. Primary human chondrocytes were pretreated with the indicated doses of mithramycin for 30 min and then stimulated with IL-1β for 20 min. Protein extracts (20 μg per lane) were analyzed by Western blotting with phosphorylation-specific and total antibodies. The resulting bands are shown. ERK, extracellular signal-regulated kinase; JNK, c-Jun N-terminal kinase.