Impact of post-translational modifications of proteins on the inflammatory process

PTM (post-translational modification) is the chemical modification of a protein after its translation. The well-studied PTM is phosphorylation, but, recently, PTMs have been re-focused by extensive studies on histone modifications and the discovery of the ubiquitin system. Histone acetylation is the well-established epigenetic regulator for gene expression. Recent studies show that different patterns of PTMs and cross-talk of individual modifications (acetylation, methylation, phosphorylation) are keys of gene regulation (known as the ‘histone code’). As well as histone, non-histone proteins are also targets of acetylation. For instance, NF-κB (nuclear factor κB), a transcriptional factor, is regulated dynamically by acetylation/deacetylation. Acetylation of NF-κB [RelA (p65)] at Lys³¹⁰ enhances its transcriptional activity, which is inhibited by SIRT1 deacetylase, type III HDAC (histone deacetylase). We also found that acetylated NF-κB preferentially bound to the IL-8 (interleukin 8) gene promoter, but not to GM-CSF (granulocyte/macrophage colony-stimulating factor), suggesting NF-κB acetylation is involved in selective gene induction as well as an increased level of transcription. A receptor of glucocorticoid, a potent anti-inflammatory agent, is also a target of acetylation. The glucocorticoid receptor is highly acetylated after ligand binding but its deacetylation is necessary for gene repression through binding to NF-κB. As well as acetylation, other PTMs, such as nitration, carbonylation and ubiquitination on transcriptional/nuclear factors, are taking part in the inflammatory process. Cross-talk of individual modifications on proteins deserves further evaluation in the future (as ‘protein code’).