Research ArticleIMMUNOLOGY

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

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Science Advances  18 Sep 2015:
Vol. 1, no. 8, e1500296
DOI: 10.1126/sciadv.1500296
  • Fig. 1 CBF-β knockdown and deletion decreases expression of APOBEC3 mRNAs and proteins.

    (A) CBF-β mRNA levels relative to TBP in H9 and knockdown derivatives by real-time quantitative polymerase chain reaction (RT-qPCR) (n = 3 with mean ± SD shown). (B) Representative immunoblots of CBF-β and APOBEC3G protein levels in the parental H9 T cell line and shRNA-transduced pools. Tubulin (TUB) is a loading control. (C) RT-qPCR of APOBEC3 mRNA levels relative to TBP in cells transduced with a control shRNA or a CBF-β–specific shRNA (n = 3 with mean ± SD shown; N.D., not detected). (D) Schematic of CRISPR/Cas9 disruption of CBF-β exon 2. (E) Representative immunoblots of CBF-β and APOBEC3G protein levels in H9 cells and a CBF-β knockout derivative. (F) RT-qPCR of APOBEC3 mRNA levels relative to TBP in H9 cells and a CBF-β knockout derivative (n = 3 with mean ± SD shown).

  • Fig. 2 RUNX interaction is necessary to restore APOBEC3G expression in CBF-β–depleted cells.

    (A) Schematic depicting established phenotypes of CBF-β separation-of-function mutants. Residue N104 is required for CBF-β transcription function with RUNX proteins, whereas F68 is required for Vif-E3 ligase-mediated degradation of APOBEC3 enzymes. (B) Histogram reporting FOXP3 promoter activity as measured by firefly luciferase levels relative to a Renilla luciferase cotransfection control. The indicated CBF-β expression construct, RUNX1 expression construct, and appropriate empty vector controls were cotransfected with luciferase vectors into CBF-β knockdown 293T cells 48 hours before luciferase activity measurement (n = 3; mean ± SD shown). Representative immunoblots from a single experimental replicate are shown below. (C) Representative immunoblots showing Vif functionality [APOBEC3G-HA (hemagglutinin) degradation activity] in the presence of the indicated FLAG–CBF-β constructs 48 hours after transfection into CBF-β knockdown 293T cells. (D) Immunoblots showing the results of a representative complementation experiment using CBF-β knockdown H9 cells and the indicated HA–CBF-β expression constructs or controls. APOBEC3G levels are low in the absence of CBF-β or in the presence of CBF-β N104K (even with higher expression levels relative to the other constructs). In contrast, APOBEC3G levels are restored by expressing wild-type CBF-β or the F68D mutant.

  • Fig. 3 CBF-β knockout protects HIV-1 from APOBEC3-mediated restriction.

    (A) Schematic of HIV-1 single-cycle infectivity assay. (B) Relative infectivity of Vif-proficient and Vif-deficient viruses produced in H9 cells or CBF-β knockout clones (n = 2; mean ± SD shown). Vif-proficient viral infectivity for each cell line is set to 100% to facilitate comparisons. (C) Representative immunoblots of relevant cellular and viral proteins from the experiment depicted in (B), as well as additional data from mock-treated cells.

  • Fig. 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.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/1/8/e1500296/DC1

    Fig. S1. CBF-β knockdown or knockout causes decreased A3F protein levels.

    Fig. S2. CBF-β knockdown in primary human CD4+ T cells results in a concomitant reduction in the mRNA levels of APOBEC3D, APOBEC3F, and APOBEC3G.

    Fig. S3. CBF-β knockdown renders H9 cells more permissive to Vif-deficient HIV-1 replication.

    Fig. S4. Schematic of predicted and ChIP-validated RUNX-binding sites within the human APOBEC3 locus.

    Table S1. qPCR primer and probe information.

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. CBF-β knockdown or knockout causes decreased A3F protein levels.
    • Fig. S2. CBF-β knockdown in primary human CD4+ T cells results in a concomitant reduction in the mRNA levels of APOBEC3D, APOBEC3F, and APOBEC3G.
    • Fig. S3. CBF-β knockdown renders H9 cells more permissive to Vif-deficient HIV-1 replication.
    • Fig. S4. Schematic of predicted and ChIP-validated RUNX-binding sites within the human APOBEC3 locus.
    • Table S1. qPCR primer and probe information.

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