Matrix metalloproteinases (MMPs), in particular MMP-9, have been shown to be induced by cytokines including tumor necrosis factor-alpha (TNF-alpha) and contributes to airway inflammation. However, the mechanisms underlying MMP-9 expression induced by TNF-alpha in human A549 cells remain unclear. Here, we showed that TNF-alpha induced production of MMP-9 protein and mRNA is determined by zymographic, Western blotting, RT-PCR and ELISA assay, which were attenuated by inhibitors of MEK1/2 (U0126), JNK (SP600125), and NF-kappaB (helenalin), and transfection with dominant negative mutants of ERK2 (DeltaERK) and JNK (DeltaJNK), and siRNAs for MEK1, p42 and JNK2. TNF-alpha-stimulated phosphorylation of p42/p44 MAPK and JNK were attenuated by pretreatment with the inhibitors U0126 and SP600125 or transfection with dominant negative mutants of DeltaERK and DeltaJNK. Furthermore, the involvement of NF-kappaB in TNF-alpha-induced MMP-9 production was consistent with that TNF-alpha-stimulated degradation of IkappaB-alpha and translocation of NF-kappaB into the nucleus which were blocked by helenalin, but not by U0126 and SP600125, revealed by immunofluorescence staining. The regulation of MMP-9 gene transcription by MAPKs and NF-kappaB was further confirmed by gene luciferase activity assay. MMP-9 promoter activity was enhanced by TNF-alpha in A549 cells transfected with wild-type MMP-9-Luc, which was inhibited by helenalin, U0126, or SP600125. In contrast, TNF-alpha-stimulated MMP-9 luciferase activity was totally lost in cells transfected with mutant-NF-kappaB MMP-9-luc. Moreover, pretreatment with actinomycin D and cycloheximide attenuated TNF-alpha-induced MMP-9 expression. These results suggest that in A549 cells, phosphorylation of p42/p44 MAPK, JNK, and transactivation of NF-kappaB are essential for TNF-alpha-induced MMP-9 gene expression.