IKKα Causes Chromatin Modification on Pro-Inflammatory Genes by Cigarette Smoke in Mouse Lung

Abstract

Cigarette smoke (CS) induces abnormal and sustained lung inflammation; however, the molecular mechanism underlying sustained inflammation is not known. It is well known that activation of IκB kinase β (IKKβ) leads to transient translocation of active NF-κB (RelA/p65-p50) in the nucleus and transcription of pro-inflammatory genes, whereas the role of IKKα in perpetuation of sustained inflammatory response is not known. We hypothesized that CS activates IKKα and causes histone acetylation on the promoters of pro-inflammatory genes, leading to sustained transcription of pro-inflammatory mediators in mouse lung in vivo and in human monocyte/macrophage cell line (MonoMac6) in vitro. CS exposure to C57BL/6J mice resulted in activation of IKKα, leading to phosphorylation of ser10 and acetylation of lys9 on histone H3 on the promoters of IL-6 and MIP-2 genes in mouse lung. The increased level of IKKα was associated with increased acetylation of lys310 RelA/p65 on pro-inflammatory gene promoters. The role of IKKα in CS-induced chromatin modification was confirmed by gain and loss of IKKα in MonoMac6 cells. Overexpression of IKKα was associated with augmentation of CS-induced pro-inflammatory effects, and phosphorylation of ser10 and acetylation of lys9 on histone H3, whereas transfection of IKKα dominant-negative mutants reduced CS-induced chromatin modification and pro-inflammatory cytokine release. Moreover, phosphorylation of ser276 and acetylation of lys310 of RelA/p65 was augmented in response to CS extract in MonoMac6 cells transfected with IKKα. Taken together, these data suggest that IKKα plays a key role in CS-induced pro-inflammatory gene transcription through phospho-acetylation of both RelA/p65 and histone H3.