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Signaling flux redistribution at toll-like receptor pathway junctions.

ABSTRACT: Various receptors on cell surface recognize specific extracellular molecules and trigger signal transduction altering gene expression in the nucleus. Gain or loss-of-function mutations of one molecule have shown to affect alternative signaling pathways with a poorly understood mechanism. In Toll-like receptor (TLR) 4 signaling, which branches into MyD88- and TRAM-dependent pathways upon lipopolysaccharide (LPS) stimulation, we investigated the gain or loss-of-function mutations of MyD88. We predict, using a computational model built on the perturbation-response approach and the law of mass conservation, that removal and addition of MyD88 in TLR4 activation, enhances and impairs, respectively, the alternative TRAM-dependent pathway through signaling flux redistribution (SFR) at pathway branches. To verify SFR, we treated MyD88-deficient macrophages with LPS and observed enhancement of TRAM-dependent pathway based on increased IRF3 phosphorylation and induction of Cxcl10 and Ifit2. Furthermore, increasing the amount of MyD88 in cultured cells showed decreased TRAM binding to TLR4. Investigating another TLR4 pathway junction, from TRIF to TRAF6, RIP1 and TBK1, the removal of MyD88-dependent TRAF6 increased expression of TRAM-dependent Cxcl10 and Ifit2. Thus, we demonstrate that SFR is a novel mechanism for enhanced activation of alternative pathways when molecules at pathway junctions are removed. Our data suggest that SFR may enlighten hitherto unexplainable intracellular signaling alterations in genetic diseases where gain or loss-of-function mutations are observed.

SUBMITTER: Selvarajoo K

PROVIDER: S-EPMC2561291 | biostudies-literature | 2008

REPOSITORIES: biostudies-literature

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Signaling flux redistribution at toll-like receptor pathway junctions.

Selvarajoo Kumar K Takada Yasunari Y Gohda Jin J Helmy Mohamed M Akira Shizuo S Tomita Masaru M Tsuchiya Masa M Inoue Jun-Ichiro J Matsuo Koichi K

PloS one 20081017 10

Various receptors on cell surface recognize specific extracellular molecules and trigger signal transduction altering gene expression in the nucleus. Gain or loss-of-function mutations of one molecule have shown to affect alternative signaling pathways with a poorly understood mechanism. In Toll-like receptor (TLR) 4 signaling, which branches into MyD88- and TRAM-dependent pathways upon lipopolysaccharide (LPS) stimulation, we investigated the gain or loss-of-function mutations of MyD88. We pred ...[more]

PMID: 18927610

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Project description:BackgroundAccumulating evidence has revealed the pivotal role of epigenetic regulation in the pathogenesis of liver disease. However, the epigenetic mechanism that accounts for hepatic stellate cells (HSCs) activation in liver fibrosis remains largely unknown.MethodsPrimary HSCs were used to screen the differentially expressed histone H3 lysine methyltransferases and demethylases during HSC activation. Loss-of-function experiments were applied to determine the cellular functions of KDM4D in HSCs. Transcriptome analysis was applied to explore the downstream targets of KDM4D. Real-time qPCR, western blotting, immunohistochemical staining, and chromatin immunoprecipitation were performed to uncover the underlying mechanism concerning KDM4D during liver fibrogenesis.FindingsKDM4D was identified as a remarkable up-regulated histone H3 demethylase during HSC activation. The overexpression profile of KDM4D was confirmed in three fibrosis animal models and human fibrotic liver tissues. In vitro Kdm4d knockdown impaired the collagen gel contraction and migration capacity of primary HSCs. In established CCl4-induced mice model, Kdm4d knockdown inhibited fibrosis progression, and promoted fibrosis reversal, with enhanced thinning and splitting of fibrotic septa, as well as a dramatic decrease in collagen area. Whole gene transcriptome analysis showed the regulatory role of KDM4D in Toll-Like Receptor (TLR) signaling pathway. Mechanistically, KDM4D catalyzed histone 3 on lysine 9 (H3K9) di-, and tri-demethylation, which promoted TLR4 expression, and subsequently prompted liver fibrogenesis by activating NF-κB signaling pathways.InterpretationKDM4D facilitates TLR4 transcription through demethylation of H3K9, thus activating TLR4/NF-κB signaling pathways in HSCs, contributing to HSC activation and collagen crosslinking, further, hepatic fibrosis progression. FUND: Shanghai New Hundred Talents Program, Shanghai Municipal Commission of Health and Family Planning, Key Developing Disciplines Program, Shanghai Key disciplines program of Health and Family Planning and Shanghai Sailing Program.

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Signaling flux redistribution at toll-like receptor pathway junctions.

Publications

Signaling flux redistribution at toll-like receptor pathway junctions.

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