title: MicroRNA-146a and RBM4 form a negative feed-forward loop that disrupts cytokine mRNA translation following TLR4 responses in human THP-1 monocytes.
abstract: Within hours after its initiation, the severe systemic inflammatory response of sepsis shifts to an adaptive anti-inflammatory state with coincident immunosuppression. This anti-inflammatory phenotype is characterized by diminished proinflammatory cytokine gene expression in response to toll-like receptor (TLR) stimulation with bacterial endotoxin/lipopolysaccharide (LPS), also known as endotoxin tolerance/adaptation. Our and other studies have established that gene-specific reprogramming following TLR4 responses independently represses transcription and translation of proinflammatory genes such as tumor necrosis factor alpha (TNFα). We also previously demonstrated that TNFα and interleukin (IL)-6 mRNA translation is repressed in endotoxin-adapted THP-1 human monocytes by an miRNA-based mechanism involving the argonaute family protein argonaute 2 (Ago2). Here, we further define the molecular nature of reprogramming translation by showing that TLR4-induced microRNA-146 promotes a feed-forward loop that modifies the subcellular localization of the RNA-binding protein RBM4 (RNA-binding motif protein 4) and promotes its interaction with Ago2. This interaction results in the assembly of a translation-repressor complex that disrupts TNFα and IL-6 cytokine synthesis in endotoxin-adapted THP-1 monocytes. This novel molecular path prevents the phosphorylation of RBM4 on serine-309 by p38 MAPK (mitogen-activated protein kinase), which leads to RBM4 accumulation in the cytosol and interaction with Ago2. We further find that microRNA-146a knockdown by antagomirs or protein phosphatase inhibition by okadaic acid increases p38 MAPK phosphorylation and results in RBM4 serine-309 phosphorylation and nuclear relocalization, which disrupts RBM4 and Ago2 interactions and restores TLR4-dependent synthesis of TNFα and IL-6. We conclude that miR-146a has a diverse and critical role in limiting an excessive acute inflammatory reaction.
authors.affiliation: Department of Internal Medicine, East Tennessee State University College of Medicine, Johnson City, TN, USA.
authors.forename: Laura
authors.initials: L
authors.lastname: Brudecki
authors.forename: Donald A
authors.initials: DA
authors.lastname: Ferguson
authors.forename: Charles E
authors.initials: CE
authors.lastname: McCall
authors.forename: Mohamed
authors.initials: M
authors.lastname: El Gazzar
mesh_terms: D056704:Adaptive Immunity; D060565:Argonaute Proteins / Q000378:metabolism; D002454:Cell Differentiation / Q000235:genetics; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism*; D004731:Endotoxins / Q000276:immunology; D025461:Feedback, Physiological; D005786:Gene Expression Regulation / Q000235:genetics; D006706:Homeostasis; D006801:Humans; D007108:Immune Tolerance; D018836:Inflammation Mediators / Q000378:metabolism*; D015850:Interleukin-6 / Q000235:genetics / Q000378:metabolism*; D035683:MicroRNAs / Q000235:genetics; D009000:Monocytes / Q000276:immunology*; D011485:Protein Binding / Q000235:genetics; D014176:Protein Biosynthesis / Q000235:genetics; D021381:Protein Transport / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000378:metabolism*; D018805:Sepsis / Q000276:immunology*; D051197:Toll-Like Receptor 4 / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000378:metabolism*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: C466422:AGO2 protein, human; D060565:Argonaute Proteins; D004731:Endotoxins; D018836:Inflammation Mediators; D015850:Interleukin-6; C542542:MIRN146 microRNA, human; D035683:MicroRNAs; C473692:RBM4 protein, human; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; C495345:TLR4 protein, human; D051197:Toll-Like Receptor 4; D014409:Tumor Necrosis Factor-alpha; D048051:p38 Mitogen-Activated Protein Kinases
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