Effect of TAK1 knockdown on matrix metalloproteinase (MMP) gene expression and IL-6 production. (a) To determine if TAK1 deficiency affects MMP3 gene expression, real-time quantitative PCR was performed. TAK1 or scrambled control (sc) small interfering RNA-treated fibroblast-like synoviocytes (FLSs) were stimulated with IL-1β (2 ng/ml) for 24 h and MMP3 gene expression was assayed and normalized to GAPDH. Data are shown as relative expression units (REU). IL-1β-induced MMP3 gene expression in the absence of TAK1 was significantly decreased compared with sc control (56 ± 14% inhibition, n = 5, *p = 0.01). Med, medium. (b) The effect of TAK1 knockdown on IL-6 production was assayed by ELISA. Cell supernatants were collected from FLSs stimulated with IL-1β (2 ng/ml) for 24 h. TAK1-deficient FLSs produced significantly less IL-6 compared with sc control (53 ± 3% inhibition, n = 4, *p = 0.02).