Fig. (4) Down-regulation of TGF-β1-induced TIMP-4 RNA expression by (A) ERK (U0126) and (B) Sp1 (mithramycin) inhibitors as analyzed by RT-PCR. Human knee chondrocytes were kept in serum-deficient medium for 24 h, subjected to the indicated treatments for 24 h and mRNA levels analyzed by TIMP-4 and GAPDH RT-PCR. The right panels are cumulative graphic depictions of mean TIMP- 4/GAPDH ratios of three (A) or two (B) separate experiments.