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Because the p300/CBP-mediated hyperacetylation of RelA (p65) is critical for nuclear factor-κB (NF-κB) activation, the attenuation of p65 acetylation is a potential molecular target for the prevention of chronic inflammation. During our ongoing screening study to identify natural compounds with histone acetyltransferase inhibitor (HATi) activity, we identified epigallocatechin-3-gallate (EGCG) as a novel HATi with global specificity for the majority of HAT enzymes but with no activity toward epigenetic enzymes including HDAC, SIRT1, and HMTase. At a dose of 100 μmol/L, EGCG abrogates p300-induced p65 acetylation in vitro and in vivo, increases the level of cytosolic IκBα, and suppresses tumor necrosis factor α (TNFα)–induced NF-κB activation. We also showed that EGCG prevents TNFα-induced p65 translocation to the nucleus, confirming that hyperacetylation is critical for NF-κB translocation as well as activity. Furthermore, EGCG treatment inhibited the acetylation of p65 and the expression of NF-κB target genes in response to diverse stimuli. Finally, EGCG reduced the binding of p300 to the promoter region of interleukin-6 gene with an increased recruitment of HDAC3, which highlights the importance of the balance between HATs and histone deacetylases in the NF-κB–mediated inflammatory signaling pathway. Importantly, EGCG at 50 μmol/L dose completely blocks EBV infection-induced cytokine expression and subsequently the EBV-induced B lymphocyte transformation. These results show the crucial role of acetylation in the development of inflammatory-related diseases. [Cancer Res 2009;69(2):583–92]