title: The MHC-II transactivator CIITA inhibits Tat function and HIV-1 replication in human myeloid cells.
abstract: BACKGROUND
  We previously demonstrated that the HLA class II transactivator CIITA inhibits HIV-1 replication in T cells by competing with the viral transactivator Tat for the binding to Cyclin T1 subunit of the P-TEFb complex. Here, we analyzed the anti-viral function of CIITA in myeloid cells, another relevant HIV-1 target cell type. We sinvestigated clones of the U937 promonocytic cell line, either permissive (Plus) or non-permissive (Minus) to HIV-1 replication. This different phenotype has been associated with the expression of TRIM22 in U937 Minus but not in Plus cells.
  
  
  METHODS
  U937 Plus cells stably expressing CIITA were generated and HLA-II positive clones were selected by cell sorting and cloning. HLA and CIITA proteins were analyzed by cytofluorometry and western blotting, respectively. HLA-II DR and CIITA mRNAs were quantified by qRT-PCR. Tat-dependent transactivation was assessed by performing the HIV-1 LTR luciferase gene reporter assay. Cells were infected with HIV-1 and viral replication was evaluated by measuring the RT activity in culture supernatants.
  
  
  RESULTS
  CIITA was expressed only in HLA-II-positive U937 Minus cells, and this was strictly correlated with inhibition of Tat-dependent HIV-1 LTR transactivation in Minus but not in Plus cells. Overexpression of CIITA in Plus cells restored the suppression of Tat transactivation, confirming the inhibitory role of CIITA. Importantly, HIV-1 replication was significantly reduced in Plus-CIITA cells with respect to Plus parental cells. This effect was independent of TRIM22 as CIITA did not induce TRIM22 expression in Plus-CIITA cells.
  
  
  CONCLUSIONS
  U937 Plus and Minus cells represent an interesting model to study the role of CIITA in HIV-1 restriction in the monocytic/macrophage cell lineage. The differential expression of CIITA in CIITA-negative Plus and CIITA-positive Minus cells correlated with their capacity to support or not HIV-1 replication, respectively. In Minus cells CIITA targeted the viral transactivator Tat to inhibit HIV-1 replication. The generation of Plus-CIITA cells was instrumental to demonstrate the specific contribution of CIITA in terms of inhibition of Tat activity and HIV-1 restriction, independently from other cellular factors, including TRIM22. Thus, CIITA acts as a general restriction factor against HIV-1 not only in T cells but also in myeloid cells.
authors.affiliation: Department of Surgical and Morphological Sciences, University of Insubria, Varese, Italy.
authors.forename: Greta
authors.initials: G
authors.lastname: Forlani
authors.affiliation: Viral Pathogens and Biosafety Unit San Raffaele Scientific Institute, Milan, Italy.
authors.forename: Filippo
authors.initials: F
authors.lastname: Turrini
authors.affiliation: Viral Pathogens and Biosafety Unit San Raffaele Scientific Institute, Milan, Italy.
authors.forename: Silvia
authors.initials: S
authors.lastname: Ghezzi
authors.affiliation: Department of Surgical and Morphological Sciences, University of Insubria, Varese, Italy.
authors.forename: Alessandra
authors.initials: A
authors.lastname: Tedeschi
authors.affiliation: AIDS Immunopathogenesis Unit, San Raffaele Scientific Institute, Milan, Italy.
authors.forename: Guido
authors.initials: G
authors.lastname: Poli
authors.affiliation: Department of Surgical and Morphological Sciences, University of Insubria, Varese, Italy. accolla.roberto@gmail.com.
authors.forename: Roberto S
authors.initials: RS
authors.lastname: Accolla
authors.affiliation: Department of Surgical and Morphological Sciences, University of Insubria, Varese, Italy. giovannatosi@yahoo.com.
authors.forename: Giovanna
authors.initials: G
authors.lastname: Tosi
mesh_terms: D002999:Clone Cells; D057809:HEK293 Cells; D015497:HIV-1 / Q000502:physiology*; D006801:Humans; D022423:Myeloid Cells / Q000378:metabolism* / Q000821:virology*; D009687:Nuclear Proteins / Q000378:metabolism*; D010641:Phenotype; D020079:Terminal Repeat Sequences / Q000235:genetics; D015534:Trans-Activators / Q000378:metabolism*; D015533:Transcriptional Activation; D014779:Virus Replication / Q000502:physiology*; D054322:tat Gene Products, Human Immunodeficiency Virus / Q000378:metabolism*
chemical_list: C083728:MHC class II transactivator protein; D009687:Nuclear Proteins; D015534:Trans-Activators; D054322:tat Gene Products, Human Immunodeficiency Virus
keywords: CIITA; HIV-1 replication; Restriction factors; TRIM22; U937 cells