title: Differential expression of microRNAs in Francisella tularensis-infected human macrophages: miR-155-dependent downregulation of MyD88 inhibits the inflammatory response.
abstract: Francisella tularensis is a Gram-negative, facultative intracellular pathogen that replicates in the cytosol of macrophages and is the causative agent of the potentially fatal disease tularemia. A characteristic feature of F. tularensis is its limited proinflammatory capacity, but the mechanisms that underlie the diminished host response to this organism are only partially defined. Recently, microRNAs have emerged as important regulators of immunity and inflammation. In the present study we investigated the microRNA response of primary human monocyte-derived macrophages (MDMs) to F. tularensis and identified 10 microRNAs that were significantly differentially expressed after infection with the live vaccine strain (LVS), as judged by Taqman Low Density Array profiling. Among the microRNAs identified, miR-155 is of particular interest as its established direct targets include components of the Toll-like receptor (TLR) pathway, which is essential for innate defense and proinflammatory cytokine production. Additional studies demonstrated that miR-155 acted by translational repression to downregulate the TLR adapter protein MyD88 and the inositol 5'-phosphatase SHIP-1 in MDMs infected with F. tularensis LVS or the fully virulent strain Schu S4. Kinetic analyses indicated that miR-155 increased progressively 3-18 hours after infection with LVS or Schu S4, and target proteins disappeared after 12-18 hours. Dynamic modulation of MyD88 and SHIP-1 was confirmed using specific pre-miRs and anti-miRs to increase and decrease miR-155 levels, respectively. Of note, miR-155 did not contribute to the attenuated cytokine response triggered by F. tularensis phagocytosis. Instead, this microRNA was required for the ability of LVS-infected cells to inhibit endotoxin-stimulated TNFα secretion 18-24 hours after infection. Thus, our data are consistent with the ability of miR-155 to act as a global negative regulator of the inflammatory response in F. tularensis-infected human macrophages.
authors.affiliation: Inflammation Program, University of Iowa, Coralville, Iowa, United States of America; Department of Internal Medicine, University of Iowa, Iowa City, Iowa, United States of America; Veteran's Administration Medical Center, Iowa City, Iowa, United States of America.
authors.forename: Sarmistha
authors.initials: S
authors.lastname: Bandyopadhyay
authors.affiliation: Inflammation Program, University of Iowa, Coralville, Iowa, United States of America; Graduate Training Program in Molecular and Cellular Biology, University of Iowa, Iowa City, Iowa, United States of America.
authors.forename: Matthew E
authors.initials: ME
authors.lastname: Long
authors.affiliation: Inflammation Program, University of Iowa, Coralville, Iowa, United States of America; Department of Internal Medicine, University of Iowa, Iowa City, Iowa, United States of America; Graduate Training Program in Molecular and Cellular Biology, University of Iowa, Iowa City, Iowa, United States of America; Veteran's Administration Medical Center, Iowa City, Iowa, United States of America.
authors.forename: Lee-Ann H
authors.initials: LA
authors.lastname: Allen
mesh_terms: D000328:Adult; D001428:Bacterial Vaccines; D015536:Down-Regulation / Q000187:drug effects; D005604:Francisella tularensis / Q000276:immunology / Q000502:physiology*; D006801:Humans; D007249:Inflammation / Q000235:genetics / Q000276:immunology / Q000378:metabolism / Q000382:microbiology; D000072181:Inositol Polyphosphate 5-Phosphatases; D008024:Ligands; D008070:Lipopolysaccharides / Q000494:pharmacology; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism* / Q000382:microbiology*; D035683:MicroRNAs / Q000235:genetics*; D053594:Myeloid Differentiation Factor 88 / Q000096:biosynthesis / Q000235:genetics*; D000072183:Phosphatidylinositol-3,4,5-Trisphosphate 5-Phosphatases; D010744:Phosphoric Monoester Hydrolases / Q000096:biosynthesis / Q000235:genetics; D014176:Protein Biosynthesis / Q000187:drug effects; D051193:Toll-Like Receptors / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
chemical_list: D001428:Bacterial Vaccines; D008024:Ligands; D008070:Lipopolysaccharides; C542542:MIRN146 microRNA, human; C524942:MIRN155 microRNA, human; D035683:MicroRNAs; D053594:Myeloid Differentiation Factor 88; D051193:Toll-Like Receptors; D014409:Tumor Necrosis Factor-alpha; D010744:Phosphoric Monoester Hydrolases; D000072181:Inositol Polyphosphate 5-Phosphatases; C000606430:INPP5D protein, human; D000072183:Phosphatidylinositol-3,4,5-Trisphosphate 5-Phosphatases