Specific Reactivation of Latent HIV-1 by dCas9-SunTag-VP64-mediated Guide RNA Targeting the HIV-1 Promoter

Abstract

HIV-1 escapes antiretroviral agents by integrating into the host DNA and forming a latent transcriptionally silent HIV-1 provirus. Transcriptional activation is prerequisite for reactivation and the eradication of latent HIV-1 proviruses. dCas9-SunTag-VP64 transcriptional system has been reported that it can robustly activate the expression of an endogenous gene using a single guide RNA (sgRNA). Here, we systematically investigated the potential of dCas9-SunTag-VP64 with the designed sgRNAs for reactivating latent HIV-1. We found dCas9-SunTag-VP64 with sgRNA 4 or sgRNA 5 targeted from -164 to -146 or -124 to -106 bp upstream of the transcription start sites of HIV-1 could induce high expression of luciferase reporter gene after screening of sgRNAs targeting different regions of the HIV-1 promoter. Further, we confirmed that dCas9-SunTag-VP64 with sgRNA 4 or sgRNA 5 can effectively reactivate latent HIV-1 transcription in several latently infected human T-cell lines. Moreover, we confirmed that the reactivation of latent HIV-1 by dCas9-SunTag-VP64 with the designed sgRNA occurred through specific binding to the HIV-1 LTR promoter without genotoxicity and global T-cell activation. Taken together, our data demonstrated dCas9-SunTag-VP64 system can effectively and specifically reactivate latent HIV-1 transcription, suggesting that this strategy could offer a novel approach to anti-HIV-1 latency.

Figure 1

Design and screen of sgRNAs for dCas9-SunTag-VP64-mediated HIV-1 LTR activation by luciferase assay. (a) Schematic representation of dCas9-VP64 and dCas9-SunTag-VP64 system. dCas9-VP64 system indicated that dCas9 protein was coupled with one copy of VP64, hemagglutinin (HA) epitope tag, and nuclear localization signal (NLS). The dCas9-SunTag-VP64 construct is composed of two expression cassettes. One is dCas9-SunTag, meaning dCas9 is coupled with 24 copies of the v4 version of the GCN4 peptides. The other cassette is scFv-GCN4-sfGFP-VP64, including a specific antibody-fusion VP64 to the GCN4 peptide. HA epitope tag and NLS were included in the two expression plasmids. The sgRNA expression cassette driven by human U6 promoter was used in two gene activation system. (b) Target sequence of sgRNAs in the HIV-1 5′-LTR promoter (from HXB2 reference strain, GenBank accession no. K03455). The sequence of the U3'R and U5 regions in the LTR promoter are underlined. The transcription start site is indicated with (+1). Individual sgRNA target site in the LTR promoter is shown in light gray. The protospacer-adjacent motif (PAM) sequence is indicated in dark gray. (c) Screen of sgRNAs for dCas9-SunTag-VP64 or dCas9-VP64-mediated HIV-1 LTR activation by luciferase assay. HEK293T cells were cotransfected indicated sgRNA with dCas9-SunTag-VP64 or dCas9-VP64, the LTR-luc reporter and internal control pRL-SV40 plasmid at the indicated time. The relative luciferase activity was measured using the dual-luciferase reporter assay system (Promega) at 72 hours post-transfection. The data was analyzed by normalizing individual sgRNA-transfected group to sgRNA negative vector-transfected group in two gene activation systems, respectively. Each data represent the mean ± SD of three independent experiments. *P < 0.05, **P < 0.01, ***P < 0.001; paired t-test. (d) Analysis of transcription elongation of HIV-1 LTR when combining dCas9-VP64 or dCas9-SunTag-VP64 with Tat. HEK293T cells were transfected with the dCas9-VP64 or the dCas9-SunTag-VP64 expression cassette with indicated sgRNA in the presence or absence of Tat at the indicated time. The relative luciferase activity in each group was measured after 72 hours transfection. The data shown was normalized to sgRNA negative vector-transfected group in two gene activation systems, respectively. Each data represent the mean ± SD of three independent experiments. *P < 0.05, **P < 0.01, ***P < 0.001; paired t-test.

Figure 2

dCas9-SunTag-VP64-mediated activation of the HIV-1 5′-LTR in TZM-bl cells. dCas9-VP64 and dCas9-SunTag-VP64 induced transcription of an integrated luciferase reporter in TZM-bl cells. TZM-bl cells were cotransfected with dCas9-VP64 or dCas9-SunTag-VP64 and indicated sgRNA at specified time. Cells were harvested and then subjected to luciferase activity assay after 3-day transfection. The data shown was normalized to sgRNA negative vector-transfected group in two gene activation systems, respectively. Each data represent the mean ± SD of three independent experiments. *P < 0.05, **P < 0.01, ***P < 0.001; paired t-test.

Figure 3

dCas9-SunTag-VP64 reactivates HIV-1 in different latently infected cells. (a) C11 cells or (b) J-Lat clone A10.6 cells were nucleofected with pcDNA3.1(-) vector or dCas9-SunTag-VP64 with indicated sgRNA and were mock treated or treated with 0.5 μmol/l of suberoylanilide hydroxamic acid at the indicated time. The percentage of GFP-expressing cells was measured by flow cytometry at different time points. Fluorescence histograms represented the reactivation efficiency of latent HIV-1 by dCas9-SunTag-VP64. (c) and (d) Time-dependent effects of dCas9-VP64-mediated activation of latent HIV-1 in C11 cells or J-Lat clone A10.6 cells. The data represent the mean ± SD of three independent experiments.

Figure 4

dCas9-SunTag-VP64 system mediated the induction of latent HIV-1 in ACH2 cells. ACH2 cells were nucleofected with pcDNA3.1(-) plasmid or dCas9-SunTag-VP64 with indicated sgRNA at specified time. At 72 hours post-transfection, the supernatants were collected and analyzed for p24 antigen by enzyme-linked immunosorbent assay. ACH2 cells mock treated were used as the basal expression level of p24, and cells treated with 0.5 μmol/l suberoylanilide hydroxamic acid were shown as positive control. The data represent the mean ± SD of three independent experiments in triplicate. *P < 0.05, **P < 0.01, ***P < 0.001; paired t-test.

Figure 5

Absence of dCas9-SunTag-VP64 system-related cytotoxicity and T cell activation. (a) Jurkat T cells were transfected with pcDNA3.1(-) or dCas9-SunTag-VP64 and sgRNA 4 or sgRNA 5 or with a sgRNA negative vector at the indicated time. At 72 hours post-transfection, cell proliferation was measured using CCK-8 kit. The data shown are the cell viability of pcDNA3.1(-)-treated group divided by that of the dCas9-SunTag-VP64 with sgRNA-transfected groups. The data represent the mean ± SD of three independent experiments. (b) Jurkat T cells were nucleofected with pcDNA3.1(-) or with dCas9-SunTag-VP64 and sgRNA 4 or sgRNA 5 or with a sgRNA negative vector at the indicated time. Cell cycle progression was analyzed by flow cytometry after 72 hours transfection. Each experiment was replicated three times. (c) Jurkat T cells were nucleofected with pcDNA3.1(-) vector or dCas9-SunTag-VP64 along with indicated sgRNA. At 72 hours post-transfection, cells were harvested and then stained by propidium iodide and subjected to cell death assay. The results are presented as fluorescence histograms. (d) Cell proliferation assay, (e) cell cycle progression, (f) cell death detection were performed in primary CD4⁺ T cells as the methods described in Jurkat T cells. The data represent the mean ± SD of three independent experiments in triplicate. (g) Primary CD4⁺ T cells were nucleofected with pcDNA3.1(-) plasmid or dCas9-SunTag-VP64 with indicated sgRNA at specified time. Cells treated with prostratin (1 μmol/l) were used as positive control. Cells untreated were represented as mock. The expression of CD25 and CD69 was detected by flow cytometry using antibodies against CD25 and CD69. The results are representative of three independent experiments.

Figure 6

Analysis of effects of dCas9-SunTag-VP64 system in HIV-1 latently infected cell models. (a) The cell viability of C11, A10.6, and ACH2 cells nucleofected with dCas9-SunTag-VP64 with indicated sgRNA was measured by CellTiter-Glo luminescent assay kit at different time post-transfection. The data from dCas9-SunTag-VP64 with sgRNA 4-treated group was relative to sgRNA negative control in such three latently infected cell lines at indicated time, respectively. The data represent the mean ± SD of three independent experiments. (b) Cell death assay were performed as the methods described in Jurkat T cells. The data represent the mean ± SD of three independent experiments in triplicate.

Figure 7

dCas9-SunTag-VP64 specifically binds to the LTR to reactivate latent HIV-1. (a) Schematic representation of the deletion of the sgRNA 4 target site in the LTR-luc reporter vector aligned with wild type of LTR-luc vector. (b) Cotransfection of dCas9-SunTag-VP64 with sgRNA 4 or with sgRNA negative vector and the LTR-luc or LTR(ΔsgRNA4)-luc reporter plasmids into HEK293T cells at the indicated time. The luciferase activity induced by dCas9-SunTag-VP64 with sgRNA 4 was normalized to that of sgRNA-negative vector in each group at 72 hours post-transfection. The data represent the mean ± SD of three experiments. *P < 0.05, **P < 0.01, ***P < 0.001; paired t-test. (c) Analysis of dCas9-SunTag-VP64 with sgRNA 4-specific binding to the HIV-1 5′-LTR promoter by a chromatin immunoprecipitation assay. C11 cells were nucleofected with dCas9-SunTag-VP64 and indicated sgRNA at the indicated time. Chromatin fragments were immunoprecipitated with anti-HA antibody or normal mouse IgG and then amplified by primers specific for HIV-1 5′-LTR promoter. (d) Analysis of the fold change of immunoprecipitated chromatin fragments from cells treated with dCas9-SunTag-VP64 with sgRNA 4 or with sgRNA negative vector group by quantitative polymerase chain reaction. The signal was normalized to that of input in each group. The data represent the mean ± SD of three experiments. *P < 0.05, **P < 0.01, ***P < 0.001; paired t-test.

Figure 8

Off-target analysis for Cas9/sgRNA4 in latently infected cell clone C11. (a) Schematic representation of Cas9/sgRNA4-mediated genome deletions. The gray box in the 5′- and 3′-LTR of HIV-1 genome (10.4 kb) indicate CRISPR/Cas9 target sites. F-HG and R-HG (arrows) located at outsides of the integrated HIV-1 genome were used for amplifying genome deletion events. (b) Polymerase chain reaction products validated Cas9/sgRNA4-induced HIV-1 proviral genome deletions. C11 cells were untransfected (mock) or nucleofected with Cas9 and indicated sgRNA at a mass ration of 3:1. Genomic DNA was extracted 3 days post-transfection and then subjected to polymerase chain reaction using the F-HG and R-HG primers. (c) Off-target analysis for Cas9/sgRNA4. Eight potential off-target sites were amplified from Cas9/sgRNA4-treated cells and the mock cells. The closest gene name is used to indicate the amplicon presented on top of the lines. These amplicons were subjected to T7E1 assay to reveal any off target sites between the targeted cells and the mock cells by gel electrophoresis.