Matrix metalloproteinases (MMPs) contribute to the matrix-degrading phenotype of mycobacterial diseases. Considering that MMPs could contribute to the mutual exacerbation of both Mycobacterium avium and HIV in coinfections, it is of importance to understand the mechanisms of M. avium-induced MMP induction. Focusing on MMP-9, our work demonstrates that a cyclooxygenase-2 (COX-2)-dependent signalling loop is critical for activation of MMP-9 transcription in RAW264.7 cells and murine bone marrow-derived macrophages. M. avium-stimulated MMP-9 induction involves the p65 and p50 subunits of NF-kappaB and the c-Fos and c-jun subunits of AP-1. The c-Fos gene is upregulated in a MEK1-dependent manner in M. avium-challenged macrophages. M. avium-induced MMP-9 gene induction requires the histone acetyltransferase p300 and chromatin modifications involving phosphorylation of p65 at serine 276 and its acetylation at lysines 221 and 310. At the same time, histone H3 modified by mitogen and stress-activated protein kinase 1 (MSK1)-dependent phosphorylation on serine 10 and by acetylation on lysine 14, typical signatures linked to transcriptional activation, also associates with the MMP-9 promoter following M. avium challenge. Taken together, our results show that co-ordinated post-translational modifications of p65 and histone H3 involving phosphorylation and acetylation drive COX-2-dependent transcriptional activation of the MMP-9 gene in response to challenge of macrophages with M. avium.