Inhibition of IL-1β-stimulated MMP-12 activity and mRNA expression by PD98059 and SP600125. ASMC were pre-treated for 1 hour with a specific inhibitor for ERK, PD98059 (1 or 10 μM) or for JNK, SP600125 (10 μM), and then were co-treated with 10 ng/ml IL-1β. (A) MMP-12 activity in conditioned media was detected after 48 hours by zymography. The relevant band intensities were quantified by scanning densitometric analysis. (B) MMP-12 mRNA was analysed after 24 hours by real-time RT-PCR. The data are expressed as the percentage of IL-1β alone and are the mean ± SEM from three ASMC donors. *P < 0.05, **P < 0.01 compared with IL-1β alone.