Inhibition of phosphoinositide 3-kinase enhances TRIF-dependent NF-kappa B activation and IFN-beta synthesis downstream of Toll-like receptor 3 and 4
Department of Medicine, Division of Infectious Diseases and Immunology
Adaptor Proteins, Vesicular Transport; Androstadienes; Chromones; DNA-Binding Proteins; Dendritic Cells; Down-Regulation; Enzyme Inhibitors; Humans; Interferon Regulatory Factor-3; Interferon-beta; Lipopolysaccharides; Membrane Glycoproteins; Morpholines; NF-kappa B; Phosphatidylinositol 3-Kinases; Receptors, Cell Surface; Toll-Like Receptor 3; Toll-Like Receptor 4; Toll-Like Receptors; Transcription Factors; Transcription, Genetic
Phosphoinositide 3-kinases (PI3K) are known to regulate Toll-like receptor (TLR)-mediated inflammatory responses, but their impact on the different pathways of TLR signaling remains to be clarified. Here, we investigated the consequences of pharmacological inhibition of PI3K on Toll-IL-1 receptor domain-containing adapter-inducing IFN-beta (TRIF)-dependent signaling, which induces IFN-beta gene expression downstream of TLR3 and TLR4. First, treatment of monocyte-derived dendritic cells (DC) with wortmannin or LY294002 was found to enhance IFN-beta expression upon TLR3 or TLR4 engagement. In the same models of DC activation, PI3K inhibition increased DNA-binding activity of NF-kappaB, but not interferon response factor (IRF)-3, the key transcription factors required for TLR-mediated IFN-beta synthesis. In parallel, wortmannin-treated DC exhibited enhanced levels of IkappaB kinase (IKK)-alpha/beta phosphorylation and IkappaB-alpha degradation with a concomitant increase in NF-kappaB nuclear translocation. Experiments carried out in HEK 293T cells stably expressing TLR3 or TLR4 confirmed that inhibition of PI3K activity enhances NF-kappaB-dependent promoters as well as IFN-beta promoter activities without interfering with transcription at the positive regulatory domain III-I. Furthermore, wortmannin enhanced NF-kappaB activity induced by TRIF overexpression in HEK 293T cells, while overexpression of catalytically active PI3K selectively attenuated TRIF-mediated NF-kappaB transcriptional activity. Finally, in co-immunoprecipitation experiments, we showed that PI3K physically interacted with TRIF. We conclude that inhibition of PI3K activity enhances TRIF-dependent NF-kappaB activity, and thereby increases IFN-beta synthesis elicited by TLR3 or TLR4 ligands.
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Citation: Eur J Immunol. 2005 Jul;35(7):2200-9. Link to article on publisher's site