Mechanism of IFN-β-Mediated Inhibition of IL-8 Gene Expression in Astroglioma Cells

Abstract

IL-8 is a chemokine that recruits migrating neutrophils and leukocytes to areas of inflammation. In noninflamed tissue, IL-8 expression is low but can be rapidly induced by proinflammatory cytokines. Typically, inflammation and transient IL-8 expression are beneficial. However, some diseases are characterized by excessive inflammation and high levels of IL-8. Previous studies have shown that IFN-β can inhibit the expression of IL-8, although the mechanism is unknown. Using chromatin immunoprecipitation assays, we define the IL-8 transcriptional program in the absence or presence of inducing stimuli and/or inhibition by IFN-β. In the absence of stimuli, the IL-8 promoter is acetylated but negatively regulated by corepressor proteins. Upon PMA stimulation, the levels of these corepressors are reduced and the promoter is rapidly bound and activated by transcription factors, including NF-κB p65, C/EBPβ, and c-Fos. In addition, RNA polymerase II is recruited to the IL-8 promoter to initiate transcription. However, in the presence of both PMA and IFN-β, there are diminished levels of histone acetylation, reduced levels of transcription factors such as NF-κB p65 and RNA polymerase II, and an increased presence of corepressor proteins such as histone deacetylases 1 and 3 and silencing mediator of retinoic acid and thyroid hormone receptors. IFN-γ-inducible protein-10 and MCP-1 genes, also regulated by NF-κB, are unaffected by IFN-β, and IFN-β does not prevent the activation, nuclear migration, or binding of NF-κB p65 to the κB element of the IFN-γ-inducible protein-10 promoter. As such, these data show that the inhibitory effects of IFN-β are specific to the IL-8 promoter.

The ING4 Tumor Suppressor Attenuates NF-κB Activity at the Promoters of Target Genes

“…The U251-MG, U118-MG, and U87-MG glioma cell lines were obtained from ATCC and maintained as previously described (5,25,40). U251-MG cells that stably express the Tet repressor (TetR) protein and inducibly express F-ING4 or shRNA specific for p65 (sh-p65), and U118-MG cells that stably express the TetR and that inducibly express shRNA specific for ING4 (shING4) were generated as previously described (26).…”

“…Cells were transfected with 0.3 g of pEGFP-N1/ING4-GFP, using FuGENE 6, and allowed to recover overnight. The next day, cells were stimulated with PMA (50 ng/ml) for 1 h, washed, fixed, permeabilized, and stained as previously described (25).…”

“…Where indicated, U251-TR/F-ING4 cells were grown in complete medium in the absence or presence of Tet (4 g/ml) for 24 h, and U251-TR/sh-p65 cells were grown in the absence or presence of Tet for 48 h. Cells were then incubated in serum-free medium in the absence or presence of Tet overnight and then grown in the absence or presence of PMA (50 ng/ml) for various times. Total RNA was isolated as previously described (25). Two micrograms of total RNA were reverse transcribed and analyzed by PCR.…”

MyD88 Drives the IFN-β Response to Lactobacillus acidophilus in Dendritic Cells through a Mechanism Involving IRF1, IRF3, and IRF7

“…Type I IFNs have been demonstrated to contribute to the induction of a strong Th1 response via upregulation of IL-12 (5), activation of NK cells and various chemokines including the Th1 cell recruiting chemokine CXCL10 (6). IFN-b has also been recognized for its anti-inflammatory activity, as it inhibits the production of IL-1b (7), TNF-a, IFN-g (8), and the neutrophil and leukocyte recruiting chemokine CXCL8 (9,10). However, IFN-b can also be detrimental, as in models of sepsis LPS-induced IFN-b contributes to lethal toxicity (2).…”

Gene Expression in Chronic Fatigue Syndrome

“…During neutrophil pathogen lysis, phagocytic products are released which acts as a positive feedback process to activate IL-8 to recruit more neutrophils (Ito et al, 2004;Sparkman and Boggaram, 2004). Alterations in IL-8 mRNA expression is linked with inflammation (Mukaida, 2003;Nozell et al, 2006;Xie, 2001). An increase in IL-8 expression noted in CFS patients may occur as a result of an increase in oxidative stress during inflammation (Shono et al, 1996;Ito et al, 2004;Sparkman and Boggaram, 2004).…”