title: HIV-1 transcriptional silencing caused by TRIM22 inhibition of Sp1 binding to the viral promoter.
abstract: BACKGROUND
  Intracellular defense proteins, also referred to as restriction factors, are capable of interfering with different steps of the viral life cycle. Among these, we have shown that Tripartite motif 22 (TRIM22) suppresses basal as well as phorbol ester-induced HIV-1 long terminal repeat (LTR)-mediated transcription, independently of its E3 ubiquitin ligase activity, nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kB) binding to the U3 region and Tat interaction with the TAR region of the HIV-1 LTR. As basal HIV-1 transcription is driven by the transcription factor specificity protein 1 (Sp1), we have investigated whether TRIM22 could interfere with Sp1-driven transcriptional activation of the HIV-1 LTR.
  
  
  RESULTS
  293T cells, devoid of endogenous TRIM22 expression, were transfected with a TRIM22-expressing plasmid together with reporter plasmids driven by the HIV-1 LTR promoter either containing or lacking Sp1 binding sites or with reporter plasmids driven by non-viral promoter sequences either containing or lacking the three Sp1 binding sites from the HIV-1 LTR. These reporter assays showed that TRIM22 efficiently inhibited Sp1-driven transcription. Knocking down TRIM22 expression in the CD4(+) SupT1 T cell line increased the replication of Sp1-dependent HIV-1 variants. TRIM22 did not interact with Sp1, but prevented binding of Sp1 to the HIV-1 promoter, as demonstrated in protein-DNA pull down and chromatin immunoprecipitation assays.
  
  
  CONCLUSIONS
  TRIM22 acts as a suppressor of basal HIV-1 LTR-driven transcription by preventing Sp1 binding to the HIV-1 promoter.
authors.affiliation: Viral Pathogens and Biosafety Unit, Division of Immunology, Transplantation and Infectious Diseases, San Raffaele Scientific Institute, P2-P3 Laboratories, DIBIT, Via Olgettina n.58, 20132, Milan, Italy. turrini.filippo@hsr.it.
authors.forename: Filippo
authors.initials: F
authors.lastname: Turrini
authors.affiliation: Viral Pathogens and Biosafety Unit, Division of Immunology, Transplantation and Infectious Diseases, San Raffaele Scientific Institute, P2-P3 Laboratories, DIBIT, Via Olgettina n.58, 20132, Milan, Italy. sara.marelli.11@ucl.ac.uk.|Viral Oncology Unit, UCL Cancer Institute, London, UK. sara.marelli.11@ucl.ac.uk.
authors.forename: Sara
authors.initials: S
authors.lastname: Marelli
authors.affiliation: Viral Pathogens and Biosafety Unit, Division of Immunology, Transplantation and Infectious Diseases, San Raffaele Scientific Institute, P2-P3 Laboratories, DIBIT, Via Olgettina n.58, 20132, Milan, Italy. kajaste.anna@hsr.it.|San Raffaele Telethon Institute for Gene Therapy (TIGET), San Raffaele Scientific Institute, 20132, Milan, Italy. kajaste.anna@hsr.it.
authors.forename: Anna
authors.initials: A
authors.lastname: Kajaste-Rudnitski
authors.affiliation: Department of Infectious Diseases, Integrative Virology, University Hospital Heidelberg and German Center for Infection Research, Heidelberg, Germany. marina.lusic@med.uni-heidelberg.de.
authors.forename: Marina
authors.initials: M
authors.lastname: Lusic
authors.affiliation: Service of Molecular Virology, Department of Molecular Biology, Université Libre de Bruxelles (ULB), Gosselies, Belgium. cvlint@ulb.ac.be.
authors.forename: Carine
authors.initials: C
authors.lastname: Van Lint
authors.affiliation: Laboratory of Experimental Virology, Department of Medical Microbiology, Center for Infection and Immunity Amsterdam (CINIMA), Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands. a.t.das@amc.uva.nl.
authors.forename: Atze T
authors.initials: AT
authors.lastname: Das
authors.affiliation: Laboratory of Experimental Virology, Department of Medical Microbiology, Center for Infection and Immunity Amsterdam (CINIMA), Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands. a.harwig@amc.uva.nl.
authors.forename: Alex
authors.initials: A
authors.lastname: Harwig
authors.affiliation: Laboratory of Experimental Virology, Department of Medical Microbiology, Center for Infection and Immunity Amsterdam (CINIMA), Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands. b.berkhout@amc.uva.nl.
authors.forename: Ben
authors.initials: B
authors.lastname: Berkhout
authors.affiliation: Viral Pathogens and Biosafety Unit, Division of Immunology, Transplantation and Infectious Diseases, San Raffaele Scientific Institute, P2-P3 Laboratories, DIBIT, Via Olgettina n.58, 20132, Milan, Italy. vicenzi.elisa@hsr.it.
authors.forename: Elisa
authors.initials: E
authors.lastname: Vicenzi
mesh_terms: D001665:Binding Sites; D015496:CD4-Positive T-Lymphocytes / Q000821:virology; D004268:DNA-Binding Proteins / Q000378:metabolism; D015967:Gene Expression Regulation, Viral; D017930:Genes, Reporter; D057809:HEK293 Cells; D016325:HIV Long Terminal Repeat; D015497:HIV-1 / Q000235:genetics* / Q000502:physiology; D006801:Humans; D015778:Minor Histocompatibility Antigens; D011401:Promoter Regions, Genetic; D012097:Repressor Proteins / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism*; D017384:Sequence Deletion; D016329:Sp1 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D000070584:Tripartite Motif Proteins; D017735:Virus Latency; D014779:Virus Replication / Q000235:genetics
chemical_list: D004268:DNA-Binding Proteins; D015778:Minor Histocompatibility Antigens; D012097:Repressor Proteins; D016329:Sp1 Transcription Factor; C094314:TRIM22 protein, human; D000070584:Tripartite Motif Proteins