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Transcriptional regulation of APOBEC3 antiviral immunity through the CBF-β/RUNX axis.

Anderson BD, Harris RS - Sci Adv (2015)

Bottom Line: At the core of this complex, Vif heterodimerizes with the transcription cofactor CBF-β, which results in fewer transcription complexes between CBF-β and its normal RUNX partners.Accordingly, the infectivity of Vif-deficient HIV-1 increases in cells lacking CBF-β, demonstrating the importance of CBF-β/RUNX-mediated transcription in establishing the APOBEC3 antiviral state.These findings demonstrate a major layer of APOBEC3 gene regulation in lymphocytes and suggest that primate lentiviruses evolved to hijack CBF-β in order to simultaneously suppress this potent antiviral defense system at both transcriptional and posttranslational levels.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry, Molecular Biology Biophysics, Masonic Cancer Center, Center for Genome Engineering, Institute for Molecular Virology, University of Minnesota, Minneapolis, MN 55455, USA.

ABSTRACT
A diverse set of innate immune mechanisms protects cells from viral infections. The APOBEC3 family of DNA cytosine deaminases is an integral part of these defenses. For instance, APOBEC3D, APOBEC3F, APOBEC3G, and APOBEC3H would have the potential to destroy HIV-1 complementary DNA replication intermediates if not for neutralization by a proteasomal degradation mechanism directed by the viral protein Vif. At the core of this complex, Vif heterodimerizes with the transcription cofactor CBF-β, which results in fewer transcription complexes between CBF-β and its normal RUNX partners. Recent studies have shown that the Vif/CBF-β interaction is specific to the primate lentiviruses HIV-1 and SIV (simian immunodeficiency virus), although related nonprimate lentiviruses still require a Vif-dependent mechanism for protection from host species' APOBEC3 enzymes. We provide a molecular explanation for this evolutionary conundrum by showing that CBF-β is required for expression of the aforementioned HIV-1-restrictive APOBEC3 gene repertoire. Knockdown and knockout studies demonstrate that CBF-β is required for APOBEC3 mRNA expression in the nonpermissive T cell line H9 and in primary CD4(+) T lymphocytes. Complementation experiments using CBF-β separation-of-function alleles show that the interaction with RUNX transcription factors is required for APOBEC3 transcriptional regulation. Accordingly, the infectivity of Vif-deficient HIV-1 increases in cells lacking CBF-β, demonstrating the importance of CBF-β/RUNX-mediated transcription in establishing the APOBEC3 antiviral state. These findings demonstrate a major layer of APOBEC3 gene regulation in lymphocytes and suggest that primate lentiviruses evolved to hijack CBF-β in order to simultaneously suppress this potent antiviral defense system at both transcriptional and posttranslational levels.

No MeSH data available.


Related in: MedlinePlus

New models for APOBEC3-mediated antiviral state and Vif function.(A) CBF-β/RUNX drives transcription of APOBEC3 genes and maintains a robust antiviral state in the absence of HIV-1 infection in CD4+ T cells. (B) In HIV-1– or SIV-infected cells, Vif prevents CBF-β from binding RUNX transcription complexes to down-regulate APOBEC3 gene transcription and simultaneously promote APOBEC3 protein polyubiquitination and proteasomal degradation.
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Figure 4: New models for APOBEC3-mediated antiviral state and Vif function.(A) CBF-β/RUNX drives transcription of APOBEC3 genes and maintains a robust antiviral state in the absence of HIV-1 infection in CD4+ T cells. (B) In HIV-1– or SIV-infected cells, Vif prevents CBF-β from binding RUNX transcription complexes to down-regulate APOBEC3 gene transcription and simultaneously promote APOBEC3 protein polyubiquitination and proteasomal degradation.

Mentions: Here, we show that the transcription cofactor CBF-β is a strong positive regulator of multiple APOBEC3 genes in CD4+ T cells and that this regulation and the overall antiviral state are dependent on a functional interaction between CBF-β and the RUNX proteins (Fig. 4A). CBF-β depletion renders H9 cells permissive to Vif-deficient HIV-1 infection, demonstrating that CBF-β is critical for maintaining the overall APOBEC3 antiviral state in T lymphocytes. Our results suggest a model for virus-infected cells in which Vif hijacks CBF-β to counteract the APOBEC3 antiviral defense through a polyubiquitination mechanism while simultaneously down-regulating transcription of the APOBEC3 genes themselves by precluding CBF-β/RUNX complex formation (Fig. 4B). This model provides a parsimonious and evolutionarily attractive explanation for why the earliest primate lentivirus, likely a simian tropic ancestor to modern HIV-1, adapted Vif to bind CBF-β from among a large pool of other cellular scaffolding possibilities. One can only imagine that the expanded APOBEC3 protein repertoire of higher primates posed too great of a restrictive barrier for an ancient lentiviral zoonosis, until the Vif protein adapted to use CBF-β and down-regulate this restriction mechanism at both the transcriptional and posttranslational levels. Because the APOBEC3 restriction factors are at least as ancient as placental mammals, all modern lentiviruses have a Vif protein to counteract restriction by cellular APOBEC3 enzymes (36). It is likely that the ancestral APOBEC3 counteraction mechanism was CBF-β–independent and that adaption to bind CBF-β was necessary for lentiviral invasion of the primate branches of the mammalian phylogenetic tree. This scenario is concordant with recent data demonstrating that the Vif proteins of nonprimate lentiviruses—FIV, BIV, MVV, and CAEV—function independently of CBF-β (13–16) and with the fact that the mammalian hosts of these viruses have simpler APOBEC3 repertoires (4). It is supported by the existence of many canonical RUNX-binding sites throughout the human APOBEC3 locus (fig. S4) and also by a previous study showing that Vif overexpression in the Jurkat T cell line could affect the transcriptional activity of dozens of RUNX-regulated genes (although APOBEC3 expression was not altered possibly because basal mRNA levels are already too low in Jurkat) (20).


Transcriptional regulation of APOBEC3 antiviral immunity through the CBF-β/RUNX axis.

Anderson BD, Harris RS - Sci Adv (2015)

New models for APOBEC3-mediated antiviral state and Vif function.(A) CBF-β/RUNX drives transcription of APOBEC3 genes and maintains a robust antiviral state in the absence of HIV-1 infection in CD4+ T cells. (B) In HIV-1– or SIV-infected cells, Vif prevents CBF-β from binding RUNX transcription complexes to down-regulate APOBEC3 gene transcription and simultaneously promote APOBEC3 protein polyubiquitination and proteasomal degradation.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4643775&req=5

Figure 4: New models for APOBEC3-mediated antiviral state and Vif function.(A) CBF-β/RUNX drives transcription of APOBEC3 genes and maintains a robust antiviral state in the absence of HIV-1 infection in CD4+ T cells. (B) In HIV-1– or SIV-infected cells, Vif prevents CBF-β from binding RUNX transcription complexes to down-regulate APOBEC3 gene transcription and simultaneously promote APOBEC3 protein polyubiquitination and proteasomal degradation.
Mentions: Here, we show that the transcription cofactor CBF-β is a strong positive regulator of multiple APOBEC3 genes in CD4+ T cells and that this regulation and the overall antiviral state are dependent on a functional interaction between CBF-β and the RUNX proteins (Fig. 4A). CBF-β depletion renders H9 cells permissive to Vif-deficient HIV-1 infection, demonstrating that CBF-β is critical for maintaining the overall APOBEC3 antiviral state in T lymphocytes. Our results suggest a model for virus-infected cells in which Vif hijacks CBF-β to counteract the APOBEC3 antiviral defense through a polyubiquitination mechanism while simultaneously down-regulating transcription of the APOBEC3 genes themselves by precluding CBF-β/RUNX complex formation (Fig. 4B). This model provides a parsimonious and evolutionarily attractive explanation for why the earliest primate lentivirus, likely a simian tropic ancestor to modern HIV-1, adapted Vif to bind CBF-β from among a large pool of other cellular scaffolding possibilities. One can only imagine that the expanded APOBEC3 protein repertoire of higher primates posed too great of a restrictive barrier for an ancient lentiviral zoonosis, until the Vif protein adapted to use CBF-β and down-regulate this restriction mechanism at both the transcriptional and posttranslational levels. Because the APOBEC3 restriction factors are at least as ancient as placental mammals, all modern lentiviruses have a Vif protein to counteract restriction by cellular APOBEC3 enzymes (36). It is likely that the ancestral APOBEC3 counteraction mechanism was CBF-β–independent and that adaption to bind CBF-β was necessary for lentiviral invasion of the primate branches of the mammalian phylogenetic tree. This scenario is concordant with recent data demonstrating that the Vif proteins of nonprimate lentiviruses—FIV, BIV, MVV, and CAEV—function independently of CBF-β (13–16) and with the fact that the mammalian hosts of these viruses have simpler APOBEC3 repertoires (4). It is supported by the existence of many canonical RUNX-binding sites throughout the human APOBEC3 locus (fig. S4) and also by a previous study showing that Vif overexpression in the Jurkat T cell line could affect the transcriptional activity of dozens of RUNX-regulated genes (although APOBEC3 expression was not altered possibly because basal mRNA levels are already too low in Jurkat) (20).

Bottom Line: At the core of this complex, Vif heterodimerizes with the transcription cofactor CBF-β, which results in fewer transcription complexes between CBF-β and its normal RUNX partners.Accordingly, the infectivity of Vif-deficient HIV-1 increases in cells lacking CBF-β, demonstrating the importance of CBF-β/RUNX-mediated transcription in establishing the APOBEC3 antiviral state.These findings demonstrate a major layer of APOBEC3 gene regulation in lymphocytes and suggest that primate lentiviruses evolved to hijack CBF-β in order to simultaneously suppress this potent antiviral defense system at both transcriptional and posttranslational levels.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry, Molecular Biology Biophysics, Masonic Cancer Center, Center for Genome Engineering, Institute for Molecular Virology, University of Minnesota, Minneapolis, MN 55455, USA.

ABSTRACT
A diverse set of innate immune mechanisms protects cells from viral infections. The APOBEC3 family of DNA cytosine deaminases is an integral part of these defenses. For instance, APOBEC3D, APOBEC3F, APOBEC3G, and APOBEC3H would have the potential to destroy HIV-1 complementary DNA replication intermediates if not for neutralization by a proteasomal degradation mechanism directed by the viral protein Vif. At the core of this complex, Vif heterodimerizes with the transcription cofactor CBF-β, which results in fewer transcription complexes between CBF-β and its normal RUNX partners. Recent studies have shown that the Vif/CBF-β interaction is specific to the primate lentiviruses HIV-1 and SIV (simian immunodeficiency virus), although related nonprimate lentiviruses still require a Vif-dependent mechanism for protection from host species' APOBEC3 enzymes. We provide a molecular explanation for this evolutionary conundrum by showing that CBF-β is required for expression of the aforementioned HIV-1-restrictive APOBEC3 gene repertoire. Knockdown and knockout studies demonstrate that CBF-β is required for APOBEC3 mRNA expression in the nonpermissive T cell line H9 and in primary CD4(+) T lymphocytes. Complementation experiments using CBF-β separation-of-function alleles show that the interaction with RUNX transcription factors is required for APOBEC3 transcriptional regulation. Accordingly, the infectivity of Vif-deficient HIV-1 increases in cells lacking CBF-β, demonstrating the importance of CBF-β/RUNX-mediated transcription in establishing the APOBEC3 antiviral state. These findings demonstrate a major layer of APOBEC3 gene regulation in lymphocytes and suggest that primate lentiviruses evolved to hijack CBF-β in order to simultaneously suppress this potent antiviral defense system at both transcriptional and posttranslational levels.

No MeSH data available.


Related in: MedlinePlus