Matrix metalloproteinases (MMPs), in particular MMP-9, have been shown to be induced by cytokines, including TNF-α and contributes to airway inflammation. However, the mechanisms underlying TNF-α-induced MMP-9 expression in human A549 cells remain unclear. Here, we report that TNF-a-induced MMP-9 gene expression was mediated through the TNFR1/TRAF2/PKCα-dependent signaling pathways in A549 cells, determined by zymographic, RT-PCR, and Western blotting analyses. TNF-α-induced MMP-9 expression was reduced by pretreatment with a TNFR Ab. Furthermore, TNF-a-induced TNFR1 and TRAF2 complex formation was revealed by immunoprecipitation using an anti-TNFR1 Ab followed by Western blot analysis against an anti-TRAF2 or anti-TNFR1 Ab. In addition, TNF-α-induced MMP-9 expression was also reduced by pretreatment with the inhibitor of PKCα(Gö6983), c-Src (PP1), EGFR (AG1478), or PI3K (LY294002) or transfection with siRNAs of PKCα, Src, EGFR, Akt, p65, p300, and c-Jun. Onthe other hand, TNF-α stimulated the phosphorylation of c-Src, EGFR, Akt, JNK1/2, and c-Jun, which were inhibited by pretreatment with Gö6983.Wealso showed that TNF-α induced Akt translocation and the formation of an Akt/p65/p300 complex. Pretreatment with the inhibitor of JNK1/2 (SP600125) but not the inhibitor of MEK1/2 (U0126), p38 MAPK (SB202190), or PI3K (LY294002), markedly inhibited TNF-α-induced c-Jun mRNA levels. Taken together, these data suggest that in A549 α, TNF-α induces MMP-9 expression via the TNFR1/TRAF2/PKCα-dependent JNK1/ 2/c-Jun and c-Src/EGFR/PI3K/Akt pathways.
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