H3K9 acetylation–NF-κB–AP-1 nexus targeted by ITE limits TNF-α–induced MMP-9 expression in monocytic cells

Matrix metalloproteinase 9 (MMP-9) plays a key role in the pathogenesis of inflammatory diseases and is upregulated by TNF-α. ITE (2-[1'H-indole-3'-carbonyl]-thiazole-4-carboxylic acid methyl ester) functions as an endogenous ligand for the aryl hydrocarbon receptor and is involved in inflammation. It is still uncertain whether ITE could affect TNF-α-induced MMP-9 expression in monocytic cells. In this study, we explored the effect of ITE on TNF-α-induced MMP-9 expression and the underlying mechanisms involved. Our results show that pretreatment of THP-1 monocytic cells with ITE significantly blocked TNF-α-induced MMP-9 expression at both the mRNA and protein secretion levels. Similar results were seen in primary human monocytes. The inhibition of MMP-9 by ITE occurs independently of TNFR1/2 modulation and apoptotic processes. RNA transcription data revealed that ITE suppresses the genes associated with inflammatory pathways. Mechanistically, histone modification profiling identified H3K9 acetylation as an epigenetic regulatory mark of TNF-α-induced MMP-9 expression. ChIP-qPCR data revealed that ITE pretreatment decreased TNF-α-triggered transcriptionally permissive acetylation marks at H3K9 in the MMP-9 promoter. Pharmacological inhibition of histone acetylation mimics the action of ITE in suppressing TNF-α-induced MMP-9 gene expression. Conversely, the acetylation induced by trichostatin A effectively reverses the inhibitory action of ITE. Moreover, increased TNF-α-induced binding of NF-κB or AP-1 at the MMP-9 promoter region was inhibited by ITE, resulting in suppression of MMP-9 gene expression. In conclusion, our study demonstrates that ITE reduces the TNF-α-induced MMP-9 expression via the H3K9 acetylation/NF-κB/AP-1 axis, highlighting a potential mechanism for mitigating MMP-9-related inflammatory disorders.