IL-10 disrupts the Brd4-docking sites to inhibit LPS-induced CXCL8 and TNF-α expression in monocytes: Implications for chronic obstructive pulmonary disease

Background: IL-10 is well known for its ability to block the expression and production of numerous proinflammatory cytokines, in this manner preventing the development of excessive or chronic immune activation. IL-10-induced transcriptional repression of CXCL8 and TNFA genes consists of 2 distinct phases: an early phase, occurring rapidly and in a protein synthesis-independent manner, followed by a second phase that is more delayed and dependent on protein synthesis. Objective: We sought to identify the mechanisms through which IL-10 rapidly and directly suppresses LPS-induced CXCL8 and TNF-alpha transcription, which might be defective under pathologic conditions. Methods: The molecular events triggered by IL-10 in LPS-activated monocytes at the CXCL8 and TNFA loci were investigated by using the chromatin immunoprecipitation assay. Results: Inhibition of LPS-induced CXCL8 and TNF-alpha expression by IL-10 proceeds through a common mechanism targeting LPS-induced phosphorylation of the nuclear factor kappa B p65 serine 276 residue (pS(276)p65). As a result, all the pS(276)p65-dependent events occurring at the CXCL8 and TNFA loci are consistently reduced, ultimately leading to a reduction in transcript elongation. Additionally, IL-10 selectively controls CXCL8 transcript elongation through histone deacetylase (HDAC) 2-dependent covalent chromatin modifications, disrupting the assembly of the transcriptional machinery. Remarkably, PBMCs from patients with acute-phase chronic obstructive pulmonary disease, which express negligible HDAC2 levels, are scarcely affected by IL-10 in terms of inhibition of CXCL8 expression. Conclusions: This study provides mechanistic evidence that IL-10 creates a chromatin environment that decreases the transcriptional rate of CXCL8 and TNF-alpha to Toll-like receptor 4-activating signals. Data identify novel molecular targets for therapeutic strategies aimed at dampening inflammation in pathologies such as chronic obstructive pulmonary disease, in which reduced intracellular HDAC2 levels have been described.