title: BRD4 Couples NF-κB/RelA with Airway Inflammation and the IRF-RIG-I Amplification Loop in Respiratory Syncytial Virus Infection.
abstract: The airway mucosa expresses protective interferon (IFN) and inflammatory cytokines in response to respiratory syncytial virus (RSV) infection. In this study, we examine the role of bromodomain containing 4 (BRD4) in mediating this innate immune response in human small airway epithelial cells. We observe that RSV induces BRD4 to complex with NF-κB/RelA. BRD4 is functionally required for expression of the NF-κB-dependent inflammatory gene regulatory network (GRN), including the IFN response factor 1 (IRF1) and IRF7, which mediate a cross talk pathway for RIG-I upregulation. Mechanistically, BRD4 is required for cyclin-dependent kinase 9 (CDK9) recruitment and phospho-Ser 2 carboxy-terminal domain (CTD) RNA polymerase (Pol) II formation on the promoters ofIRF1,IRF7, andRIG-I, producing their enhanced expression by transcriptional elongation. We also find that BRD4 independently regulates CDK9/phospho-Ser 2 CTD RNA Pol II recruitment to the IRF3-dependent IFN-stimulated genes (ISGs).In vivo, poly(I·C)-induced neutrophilia and mucosal chemokine production are blocked by a small-molecule BRD4 bromodomain inhibitor. Similarly, BRD4 inhibition reduces RSV-induced neutrophilia, mucosal CXC chemokine expression, activation of the IRF7-RIG-I autoamplification loop, mucosal IFN expression, and airway obstruction. RSV infection activates BRD4 acetyltransferase activity on histone H3 Lys (K) 122, demonstrating that RSV infection activates BRD4in vivoThese data validate BRD4 as a major effector of RSV-induced inflammation and disease. BRD4 is required for coupling NF-κB to expression of inflammatory genes and the IRF-RIG-I autoamplification pathway and independently facilitates antiviral ISG expression. BRD4 inhibition may be a strategy to reduce exuberant virus-induced mucosal airway inflammation.IMPORTANCEIn the United States, 2.1 million children annually require medical attention for RSV infections. A first line of defense is the expression of the innate gene network by infected epithelial cells. Expression of the innate response requires the recruitment of transcriptional elongation factors to rapidly induce innate response genes through an unknown mechanism. We discovered that RSV infection induces a complex of bromodomain containing 4 (BRD4) with NF-κB and cyclin-dependent kinase 9 (CDK9). BRD4 is required for stable CDK9 binding, phospho-Ser 2 RNA Pol II formation, and histone acetyltransferase activity. Inhibition of BRD4 blocks Toll-like receptor 3 (TLR3)-dependent neutrophilia and RSV-induced inflammation, demonstrating its importance in the mucosal innate responsein vivoOur study shows that BRD4 plays a central role in inflammation and activation of the IRF7-RIG-I amplification loop vital for mucosal interferon expression. BRD4 inhibition may be a strategy for modulating exuberant mucosal airway inflammation.
authors.affiliation: Department of Internal Medicine, University of Texas Medical Branch, Galveston, Texas, USA.|Sealy Center for Molecular Medicine, University of Texas Medical Branch, Galveston, Texas, USA.
authors.forename: Bing
authors.initials: B
authors.lastname: Tian
authors.affiliation: Department of Internal Medicine, University of Texas Medical Branch, Galveston, Texas, USA.|Sealy Center for Molecular Medicine, University of Texas Medical Branch, Galveston, Texas, USA.
authors.forename: Jun
authors.initials: J
authors.lastname: Yang
authors.affiliation: Department of Internal Medicine, University of Texas Medical Branch, Galveston, Texas, USA.|Sealy Center for Molecular Medicine, University of Texas Medical Branch, Galveston, Texas, USA.|Institute for Translational Sciences, University of Texas Medical Branch, Galveston, Texas, USA.
authors.forename: Yingxin
authors.initials: Y
authors.lastname: Zhao
authors.affiliation: Department of Pediatrics, University of Texas Medical Branch, Galveston, Texas, USA.
authors.forename: Teodora
authors.initials: T
authors.lastname: Ivanciuc
authors.affiliation: Department of Internal Medicine, University of Texas Medical Branch, Galveston, Texas, USA.
authors.forename: Hong
authors.initials: H
authors.lastname: Sun
authors.affiliation: Sealy Center for Molecular Medicine, University of Texas Medical Branch, Galveston, Texas, USA.|Department of Pediatrics, University of Texas Medical Branch, Galveston, Texas, USA.
authors.forename: Roberto P
authors.initials: RP
authors.lastname: Garofalo
authors.affiliation: Department of Internal Medicine, University of Texas Medical Branch, Galveston, Texas, USA arbrasie@utmb.edu.|Sealy Center for Molecular Medicine, University of Texas Medical Branch, Galveston, Texas, USA.|Institute for Translational Sciences, University of Texas Medical Branch, Galveston, Texas, USA.
authors.forename: Allan R
authors.initials: AR
authors.lastname: Brasier
mesh_terms: D000818:Animals; D018797:Cell Cycle Proteins; D002460:Cell Line; D000071457:DEAD Box Protein 58 / Q000378:metabolism*; D004195:Disease Models, Animal; D004847:Epithelial Cells / Q000276:immunology / Q000821:virology; D054884:Host-Pathogen Interactions; D006801:Humans; D007113:Immunity, Innate; D050835:Interferon Regulatory Factors / Q000378:metabolism*; D008810:Mice, Inbred C57BL; D009687:Nuclear Proteins / Q000378:metabolism*; D011971:Receptors, Immunologic; D018357:Respiratory Syncytial Virus Infections / Q000473:pathology; D018113:Respiratory Syncytial Virus, Human / Q000472:pathogenicity*; D051996:Transcription Factor RelA / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*; D000092468:Bromodomain Containing Proteins
chemical_list: D018797:Cell Cycle Proteins; D000071457:DEAD Box Protein 58; D050835:Interferon Regulatory Factors; D009687:Nuclear Proteins; D011971:Receptors, Immunologic; D051996:Transcription Factor RelA; D014157:Transcription Factors; C441289:BRD4 protein, human; D000092468:Bromodomain Containing Proteins; C498143:RELA protein, human; C452820:RIGI protein, human
keywords: BRD4; CDK9; Pol II CTD; RSV; acetylation; phosphorylation; transcriptional elongation