title: The intracellular DNA sensor IFI16 gene acts as restriction factor for human cytomegalovirus replication.
abstract: Human interferon (IFN)-inducible IFI16 protein, an innate immune sensor of intracellular DNA, modulates various cell functions, however, its role in regulating virus growth remains unresolved. Here, we adopt two approaches to investigate whether IFI16 exerts pro- and/or anti-viral actions. First, the IFI16 gene was silenced using specific small interfering RNAs (siRNA) in human embryo lung fibroblasts (HELF) and replication of DNA and RNA viruses evaluated. IFI16-knockdown resulted in enhanced replication of Herpesviruses, in particular, Human Cytomegalovirus (HCMV). Consistent with this, HELF transduction with a dominant negative form of IFI16 lacking the PYRIN domain (PYD) enhanced the replication of HCMV. Second, HCMV replication was compared between HELFs overexpressing either the IFI16 gene or the LacZ gene. IFI16 overexpression decreased both virus yield and viral DNA copy number. Early and late, but not immediate-early, mRNAs and proteins were strongly down-regulated, thus IFI16 may exert its antiviral effect by impairing viral DNA synthesis. Constructs with the luciferase reporter gene driven by deleted or site-specific mutated forms of the HCMV DNA polymerase (UL54) promoter demonstrated that the inverted repeat element 1 (IR-1), located between -54 and -43 relative to the transcription start site, is the target of IFI16 suppression. Indeed, electrophoretic mobility shift assays and chromatin immunoprecipitation demonstrated that suppression of the UL54 promoter is mediated by IFI16-induced blocking of Sp1-like factors. Consistent with these results, deletion of the putative Sp1 responsive element from the HCMV UL44 promoter also relieved IFI16 suppression. Together, these data implicate IFI16 as a novel restriction factor against HCMV replication and provide new insight into the physiological functions of the IFN-inducible gene IFI16 as a viral restriction factor.
authors.affiliation: Department of Public Health and Microbiology, University of Turin, Turin, Italy.
authors.forename: Grazia Rosaria
authors.initials: GR
authors.lastname: Gariano
authors.forename: Valentina
authors.initials: V
authors.lastname: Dell'Oste
authors.forename: Matteo
authors.initials: M
authors.lastname: Bronzini
authors.forename: Deborah
authors.initials: D
authors.lastname: Gatti
authors.forename: Anna
authors.initials: A
authors.lastname: Luganini
authors.forename: Marco
authors.initials: M
authors.lastname: De Andrea
authors.forename: Giorgio
authors.initials: G
authors.lastname: Gribaudo
authors.forename: Marisa
authors.initials: M
authors.lastname: Gariglio
authors.forename: Santo
authors.initials: S
authors.lastname: Landolfo
mesh_terms: D000818:Animals; D002522:Chlorocebus aethiops; D003587:Cytomegalovirus / Q000502:physiology*; D003586:Cytomegalovirus Infections / Q000235:genetics / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D004279:DNA, Viral / Q000096:biosynthesis* / Q000235:genetics / Q000276:immunology; D004259:DNA-Directed DNA Polymerase / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D004622:Embryo, Mammalian / Q000276:immunology / Q000378:metabolism / Q000473:pathology / Q000821:virology; D005347:Fibroblasts / Q000276:immunology / Q000378:metabolism / Q000473:pathology / Q000821:virology; D057809:HEK293 Cells; D006801:Humans; D007113:Immunity, Innate / Q000502:physiology*; D051379:Mice; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D020218:Response Elements / Q000502:physiology; D016329:Sp1 Transcription Factor / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D014709:Vero Cells; D014764:Viral Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D014779:Virus Replication / Q000502:physiology*
chemical_list: D004279:DNA, Viral; D009687:Nuclear Proteins; D010750:Phosphoproteins; D016329:Sp1 Transcription Factor; C109367:UL54 protein, Human herpesvirus 5; D014764:Viral Proteins; C076700:IFI16 protein, human; D004259:DNA-Directed DNA Polymerase