by Sangwoon Chung, Isaac K. Sundar, Jae-Woong Hwang, Fiona E. Yull, Timothy S. Blackwell, Vuokko L. Kinnula, Michael Bulger, Hongwei Yao, Irfan Rahman
Nuclear factor (NF)-?B inducing kinase (NIK) is a central player in the non-canonical NF ?B pathway, which phosphorylates I?B kinase a (IKKa) resulting in enhancement of target gene expression. We have recently shown that IKKa responds to a variety of stimuli including oxidants and cigarette smoke (CS) regulating the histone modification in addition to its role in NF-?B activation. However, the primary signaling mechanism linking CS-mediated oxidative stress and TNFa with histone acetylation and pro-inflammatory gene transcription is not well understood. We hypothesized that CS and TNFa increase NIK levels causing phosphorylation of IKKa, which leads to histone acetylation. Methodology
To test this hypothesis, we investigated whether NIK mediates effects of CS and TNFa on histone acetylation in human lung epithelial cells in vitro and in lungs of mouse exposed to CS in vivo. CS increased the phosphorylation levels of IKKa/NIK in lung epithelial cells and mouse lungs. NIK is accumulated in the nuclear compartment, and is recruited to the promoters of pro-inflammatory genes, to induce posttranslational acetylation of histones in response to CS and TNFa. Cells in which NIK is knocked down using siRNA showed partial attenuation of CSE- and TNFa-induced acetylation of histone H3 on pro-inflammatory gene promoters. Additional study to determine the role of IKKß/NF-?B pathway in CS-induced histone acetylation suggests that the canonical pathway does not play a role in histone acetylation particularly in response to CS in mouse lungs. Conclusions
Overall, our findings provide a novel role for NIK in CS- and TNFa-induced histone acetylation, especially on histone H3K9.