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The cytosolic exonuclease TREX1 inhibits the innate immune response to human immunodeficiency virus type 1.

Yan N, Regalado-Magdos AD, Stiggelbout B, Lee-Kirsch MA, Lieberman J - Nat. Immunol. (2010)

Bottom Line: Here we found that the cytosolic exonuclease TREX1 suppressed interferon triggered by HIV.TREX1 bound to cytosolic HIV DNA and digested excess HIV DNA that would otherwise activate interferon expression via a pathway dependent on the kinase TBK1, the adaptor STING and the transcription factor IRF3.HIV-stimulated interferon production in cells deficient in TREX1 did not involve known nucleic acid sensors.

View Article: PubMed Central - PubMed

Affiliation: Immune Disease Institute and Program in Cellular and Molecular Medicine, Children's Hospital, and Department of Pediatrics, Harvard Medical School, Boston, Massachusetts, USA.

ABSTRACT
Viral infection triggers innate immune sensors to produce type I interferon. However, infection of T cells and macrophages with human immunodeficiency virus (HIV) does not trip those alarms. How HIV avoids activating nucleic acid sensors is unknown. Here we found that the cytosolic exonuclease TREX1 suppressed interferon triggered by HIV. In Trex1(-/-) mouse cells and human CD4(+) T cells and macrophages in which TREX1 was inhibited by RNA-mediated interference, cytosolic HIV DNA accumulated and HIV infection induced type I interferon that inhibited HIV replication and spreading. TREX1 bound to cytosolic HIV DNA and digested excess HIV DNA that would otherwise activate interferon expression via a pathway dependent on the kinase TBK1, the adaptor STING and the transcription factor IRF3. HIV-stimulated interferon production in cells deficient in TREX1 did not involve known nucleic acid sensors.

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HIV-stimulated IFN expression is IRF3-dependentWild type (WT), Trex1−/− (KO) or Trex1−/−Irf3−/− (DKO) primary MEFs were infected as in Fig. 1. (a) HIV-stimulated IFN-β induction, assessed by qRT-PCR 22 hpi, is eliminated in the absence of IRF3. (b) Irf3-deficiency partially rescues HIV infection in Trex1-deficient cells. HIV infection was measured by Luc activity 48 hpi. (c) Increased HIV autointegration in Trex1-deficient cells is not affected by Irf3-deficiency. Error bars indicate S.D. of at least three independent experiments. (d) IRF3 translocates to the nucleus in HIV-infected Trex1−/− cells. WT and Trex1−/− MEFs that were either uninfected or infected with HIV were stained 22 hpi for IRF3 (red) and DAPI (blue). (e) Expression of GFP from an HIV reporter virus (HIV-GFP) is reduced in Trex1−/− MEF compared to WT MEF. Flow cytometry analysis of GFP expression was measured 24 hpi. A representative plot from 3 independent experiments is shown.
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Figure 2: HIV-stimulated IFN expression is IRF3-dependentWild type (WT), Trex1−/− (KO) or Trex1−/−Irf3−/− (DKO) primary MEFs were infected as in Fig. 1. (a) HIV-stimulated IFN-β induction, assessed by qRT-PCR 22 hpi, is eliminated in the absence of IRF3. (b) Irf3-deficiency partially rescues HIV infection in Trex1-deficient cells. HIV infection was measured by Luc activity 48 hpi. (c) Increased HIV autointegration in Trex1-deficient cells is not affected by Irf3-deficiency. Error bars indicate S.D. of at least three independent experiments. (d) IRF3 translocates to the nucleus in HIV-infected Trex1−/− cells. WT and Trex1−/− MEFs that were either uninfected or infected with HIV were stained 22 hpi for IRF3 (red) and DAPI (blue). (e) Expression of GFP from an HIV reporter virus (HIV-GFP) is reduced in Trex1−/− MEF compared to WT MEF. Flow cytometry analysis of GFP expression was measured 24 hpi. A representative plot from 3 independent experiments is shown.

Mentions: IFN-β expression induced by transfected ISD or endogenous retroelements in Trex1−/− cells is mediated by the transcription factor IRF36,7. To investigate whether IRF3 also activates HIV-induced IFN-β expression, we compared IFN-β mRNA and HIV infectivity in WT, Trex1−/− and Trex1−/− Irf3−/− MEFs. Lack of IRF3 completely inhibited IFN-β induction (Fig. 2a). HIV-Luc activity was also partially rescued in Trex1−/− Irf3−/− cells (Fig. 2b). Therefore, IFN-β induction in response to HIV in Trex1−/− cells is mediated by IRF3. Autointegration in the absence of Trex1 was indistinguishable in Trex1−/− and Trex1−/−Irf3−/− cells (Fig. 2c), suggesting that autointegration is not altered by endogenous IFN-β production and that the two effects of TREX1 on HIV infection (blocking autointegration and inhibiting IFN-β induction) operate independently. Similarly in human 293T cells, TREX1 siRNA increased HIV-induced Luc expression from the IFN-β promoter, whereas siRNAs against some other SET complex genes had no effect on IFN-β expression (Supplementary Fig. 1). Therefore protection from IFN-β activation involves TREX1, but not the entire SET complex.


The cytosolic exonuclease TREX1 inhibits the innate immune response to human immunodeficiency virus type 1.

Yan N, Regalado-Magdos AD, Stiggelbout B, Lee-Kirsch MA, Lieberman J - Nat. Immunol. (2010)

HIV-stimulated IFN expression is IRF3-dependentWild type (WT), Trex1−/− (KO) or Trex1−/−Irf3−/− (DKO) primary MEFs were infected as in Fig. 1. (a) HIV-stimulated IFN-β induction, assessed by qRT-PCR 22 hpi, is eliminated in the absence of IRF3. (b) Irf3-deficiency partially rescues HIV infection in Trex1-deficient cells. HIV infection was measured by Luc activity 48 hpi. (c) Increased HIV autointegration in Trex1-deficient cells is not affected by Irf3-deficiency. Error bars indicate S.D. of at least three independent experiments. (d) IRF3 translocates to the nucleus in HIV-infected Trex1−/− cells. WT and Trex1−/− MEFs that were either uninfected or infected with HIV were stained 22 hpi for IRF3 (red) and DAPI (blue). (e) Expression of GFP from an HIV reporter virus (HIV-GFP) is reduced in Trex1−/− MEF compared to WT MEF. Flow cytometry analysis of GFP expression was measured 24 hpi. A representative plot from 3 independent experiments is shown.
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Figure 2: HIV-stimulated IFN expression is IRF3-dependentWild type (WT), Trex1−/− (KO) or Trex1−/−Irf3−/− (DKO) primary MEFs were infected as in Fig. 1. (a) HIV-stimulated IFN-β induction, assessed by qRT-PCR 22 hpi, is eliminated in the absence of IRF3. (b) Irf3-deficiency partially rescues HIV infection in Trex1-deficient cells. HIV infection was measured by Luc activity 48 hpi. (c) Increased HIV autointegration in Trex1-deficient cells is not affected by Irf3-deficiency. Error bars indicate S.D. of at least three independent experiments. (d) IRF3 translocates to the nucleus in HIV-infected Trex1−/− cells. WT and Trex1−/− MEFs that were either uninfected or infected with HIV were stained 22 hpi for IRF3 (red) and DAPI (blue). (e) Expression of GFP from an HIV reporter virus (HIV-GFP) is reduced in Trex1−/− MEF compared to WT MEF. Flow cytometry analysis of GFP expression was measured 24 hpi. A representative plot from 3 independent experiments is shown.
Mentions: IFN-β expression induced by transfected ISD or endogenous retroelements in Trex1−/− cells is mediated by the transcription factor IRF36,7. To investigate whether IRF3 also activates HIV-induced IFN-β expression, we compared IFN-β mRNA and HIV infectivity in WT, Trex1−/− and Trex1−/− Irf3−/− MEFs. Lack of IRF3 completely inhibited IFN-β induction (Fig. 2a). HIV-Luc activity was also partially rescued in Trex1−/− Irf3−/− cells (Fig. 2b). Therefore, IFN-β induction in response to HIV in Trex1−/− cells is mediated by IRF3. Autointegration in the absence of Trex1 was indistinguishable in Trex1−/− and Trex1−/−Irf3−/− cells (Fig. 2c), suggesting that autointegration is not altered by endogenous IFN-β production and that the two effects of TREX1 on HIV infection (blocking autointegration and inhibiting IFN-β induction) operate independently. Similarly in human 293T cells, TREX1 siRNA increased HIV-induced Luc expression from the IFN-β promoter, whereas siRNAs against some other SET complex genes had no effect on IFN-β expression (Supplementary Fig. 1). Therefore protection from IFN-β activation involves TREX1, but not the entire SET complex.

Bottom Line: Here we found that the cytosolic exonuclease TREX1 suppressed interferon triggered by HIV.TREX1 bound to cytosolic HIV DNA and digested excess HIV DNA that would otherwise activate interferon expression via a pathway dependent on the kinase TBK1, the adaptor STING and the transcription factor IRF3.HIV-stimulated interferon production in cells deficient in TREX1 did not involve known nucleic acid sensors.

View Article: PubMed Central - PubMed

Affiliation: Immune Disease Institute and Program in Cellular and Molecular Medicine, Children's Hospital, and Department of Pediatrics, Harvard Medical School, Boston, Massachusetts, USA.

ABSTRACT
Viral infection triggers innate immune sensors to produce type I interferon. However, infection of T cells and macrophages with human immunodeficiency virus (HIV) does not trip those alarms. How HIV avoids activating nucleic acid sensors is unknown. Here we found that the cytosolic exonuclease TREX1 suppressed interferon triggered by HIV. In Trex1(-/-) mouse cells and human CD4(+) T cells and macrophages in which TREX1 was inhibited by RNA-mediated interference, cytosolic HIV DNA accumulated and HIV infection induced type I interferon that inhibited HIV replication and spreading. TREX1 bound to cytosolic HIV DNA and digested excess HIV DNA that would otherwise activate interferon expression via a pathway dependent on the kinase TBK1, the adaptor STING and the transcription factor IRF3. HIV-stimulated interferon production in cells deficient in TREX1 did not involve known nucleic acid sensors.

Show MeSH
Related in: MedlinePlus