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Journal of Virology, August 2004, p. 8931-8934, Vol. 78, No. 16
0022-538X/04/$08.00+0 DOI: 10.1128/JVI.78.16.8931-8934.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.
Department of Biochemistry, Nara Medical University, Kashihara, Nara 634-8521,1 Department of Microbiology, Kobe Institute of Health, Kobe, Hyogo 650-0046,2 Department of Virology, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka 565-0871, Japan3
Received 4 February 2004/ Accepted 12 April 2004
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B-dependent target genes, including the human immunodeficiency virus type 1 (HIV-1) long terminal repeat (LTR) in reporter constructs (12, 21, 22). In addition, HIV-1 integration is abolished in PARP-1/ cells (11), suggesting that PARP-1 plays a role in HIV-1 integration. Based on these reports, PARP-1 is probably an important cellular factor involved in HIV-1 replication. Although these studies propose that PARP-1 is involved in HIV-1 replication in murine cells, the function of PARP-1 in HIV-1 replication in human cells remains unclear. To assess the significance of PARP-1 in HIV-1 replication in natural host cells, we developed small interfering RNA (siRNA) directed against PARP-1 and examined the effect of established siRNA on HIV-1 gene expression as well as viral replication in human cells. Establishment of siRNA directed against PARP-1. Silencing of gene expression by RNA interference (RNAi) is a new methodology used to assess the role of cellular and viral factors in HIV-1 replication. siRNA, typically comprising a duplex of two 21-mer RNAs with 19 complementary nucleotides and 3'-terminal noncomplementary dimers of uridine, can induce the RNAi-mediated specific suppression of target genes in mammalian cells (9). Five siRNA candidates directed against PARP-1 were designed according to the information found at the siRNA Target Finder website (http://www.ambion.com/techlib/misc/siRNA_finder.html) and were prepared with a Silencer siRNA construction kit (Ambion, Austin, Tex.), according to the manufacturer's instructions. The nucleotide sequences of the siRNA target sites in the PARP-1 gene (Fig. 1A) were as follows: PARP siRNA1, 5'-AAAAGTCCCACACTGGTACCA-3' (nucleotides [nt] 297 to 317); PARP siRNA2, 5'-AACCCCAAAGGAATTCCGAGA-3' (nt 1161 to 1181); PARP siRNA3, 5'-AACAAACTGGAACAGATGCCG-3' (nt 1954 to 1974); PARP siRNA4, 5'-AAGCCTCCGCTCCTGAACAAT-3' (nt 2401 to 2421); and PARP siRNA5, 5'-AAGATAGAGCGTGAAGGCGAA-3' (nt 2671 to 2691). All of the position numbers of the PARP-1 nucleotide sequences described here correspond to those of the human PARP-1 cDNA sequence (GenBank accession no. M32721). As controls, siRNAs directed against ß-actin and Apaf-1 were purchased from QIAGEN (Tokyo, Japan). RNAiFect transfection reagent (QIAGEN) showed the highest transfection efficiency of the siRNA as well as the lowest cytotoxicity among several kinds of transfection reagents tested and thus was used throughout the experiments. In order to examine the effect of siRNAs for the expression of PARP-1 as well as for HIV-1 replication in various human cell lines, HeLa and J111 (a human acute monocytic leukemia cell line) cells were used in this study. HeLa (Fig. 1B) and J111 (Fig. 1C) cells were transfected with siRNAs against PARP-1 (143 nM), as well as control siRNAs. Forty-eight hours after transfection, cells were lysed in a sample buffer containing sodium dodecyl sulfate (SDS). Samples were separated by SDS-polyacrylamide gel electrophoresis and transferred onto a polyvinylidene fluoride membrane. Then immunoblot analysis for PARP-1 and ß-actin was performed. As shown in Fig. 1B and C, the expression of PARP-1 in cells transfected with PARP siRNA2 (lane 2), PARP siRNA 3 (lane 3), PARP siRNA4 (lane 4), or PARP siRNA5 (lane 5) was significantly reduced compared with that in mock-transfected cells (lane 8). On the other hand, PARP siRNA1 (lane 1) as well as control siRNAs (lanes 6 and 7) had almost no effect on the level of PARP-1 (Fig. 1B and C). In addition, the level of ß-actin was moderately reduced in cells transfected with siRNA against ß-actin (Fig. 1B and C, lane 6). Four siRNAs against PARP-1 (lanes 2 to 5) reduced the level of PARP-1 more effectively in HeLa cells (Fig. 1B) than in J111 cells (Fig. 1C). This might be due to the higher endogenous level of PARP-1 in J111 cells than in HeLa cells (M. Kameoka, unpublished results) and/or may be due to less efficient transfection of siRNAs into J111 cells. In fact, a lower concentration (72 nM) of PARP siRNA5 still effectively suppressed the expression of PARP-1 in HeLa cells, but not in J111 cells (data not shown). PARP siRNA5 most successfully suppressed the expression of PARP-1 in both cell lines (Fig. 1B and C, lane 5), and PARP siRNA4 also effectively suppressed the expression of PARP-1 in HeLa cells (Fig. 1B, lane 4). Thus, we used PARP siRNA4 and PARP siRNA5 for further studies.
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FIG. 1. (A) Schematic illustration of functional domains of the human PARP-1. F1 and F2, Zn fingers; NLS, nuclear localization signal; BRCT, BRCA1 C-terminal domain. Arrows below the diagram represent the target sites of siRNA designed in this study. (B and C) Immunoblot analysis of cells transfected with siRNA. HeLa (B) and J111 (C) cells were transfected with the indicated siRNAs (143 nM) (lanes 1 to 7) or mock transfected (lane 8). Forty-eight hours after transfection, the cells were harvested. Then samples were immunostained with anti-PARP polyclonal antibody (R&D Systems, Minneapolis, Minn.) (upper panel) or anti-ß-actin monoclonal antibody (Sigma-Aldrich) (lower panel). After incubation of the samples with peroxidase-labeled secondary antibodies, the immunocomplex was visualized with ECL Plus enhanced chemiluminescence Western blotting detection reagents (Amersham-Pharmacia Biotech).
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FIG. 2. siRNA directed against PARP-1 suppresses HIV-1 replication. HeLa (A) and J111 (B) cells were transfected with the indicated siRNAs (143 nM) (lanes 1 to 4) or mock transfected (lanes 5 and 6). Twenty-four hours after siRNA transfection, the cells were mock infected (lane 6) or infected with pNL-Luc (50 ng of p24) (lanes 1 to 5). Forty-eight hours after infection, the cells were lysed in 100 µl of lysis buffer (LCß-PCG-51; Toyo Ink Mfg., Tokyo, Japan) and the luciferase activity in 20-µl aliquots of lysate was determined with a luciferase assay system (Promega) and TR717 microplate luminometer (Applied Biosystems). Then the relative luciferase activity was calculated by comparing it with the luciferase activity of mock-transfected, pNL-Luc-infected samples (lane 5), which was defined as 100 relative light units (RLU). The data represent the means and standard deviations (error bars) of six independent experiments. The expression levels of PARP-1and ß-actin were confirmed by immunoblot analysis (bottom).
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TABLE 1. Quantification of HIV-1 DNA in siRNA-transfected, pNL-Luc-infected cells
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) (Pepro Tech EC, Ltd., London, United Kingdom) or phorbol 12-myristate 13-acetate (PMA) (Sigma-Aldrich), the level of ß-galactosidase activity was elevated in MAGIC-5A cells mock transfected (Fig. 3, lane 5) or transfected with control siRNAs (lanes 3 and 4). In contrast, TNF-
and PMA only slightly enhanced ß-galactosidase activity in MAGIC-5A cells transfected with siRNAs against PARP-1 (Fig. 3, lanes 1 and 2). These results suggest that the activation of integrated HIV-1 LTR promoter was suppressed in cells transfected with siRNA directed against PARP-1.
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FIG. 3. siRNA directed against PARP-1 suppresses the activation of the integrated HIV-1 LTR promoter in MAGIC-5A. MAGIC-5A cells were transfected with the indicated siRNAs (36 nM) (lanes 1 to 4) or mock transfected (lane 5). Forty-two hours after transfection, the cells were mock treated or treated with TNF- (10 ng/ml) or PMA (100 nM) for 6 h. Then the cells were lysed in 100 µl of lysis buffer (LCß-PCG-51), and the ß-galactosidase activity in 10-µl aliquots of lysate was determined by using a Galacto-Light Plus system (Applied Biosystems) and TR717 microplate luminometer (Applied Biosystems). The ß-galactosidase activities are indicated as the relative values of TNF- -induced (white bar) and PMA-induced (black bar) enhancement (fold activation) over mock-treated samples. The data represent the means and standard deviations (error bars) of four independent experiments. The expression levels of PARP-1 and ß-actin were confirmed by immunoblot analysis (bottom).
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B-dependent gene expression in murine cells (12, 21). In addition, although a discrepancy exists between two reports on the efficiency of integration of HIV-1-based lentivirus vectors in PARP-1/ cells (11, 25), their results indicate that HIV-1 LTR promoter-dependent expression of green fluorescent protein is reduced in PARP-1/ cells compared with PARP-1+/+ cells. Taken together with the observations made in this report, PARP-1 could be an important cofactor for efficient HIV-1 gene expression in human and murine cells. We propose here that siRNAs directed against PARP-1 are useful to examine the mechanism by which PARP-1 regulates the HIV-1 replication in human cells. In addition, PARP-1 may be a therapeutic target for the development of anti-HIV-1 drugs. Three independent lines of PARP-1/ mice were developed (16, 17, 29). These animals are viable and fertile and do not show an overtly abnormal phenotype, except for the spontaneous development of skin hyperplasia observed only in one line (29), indicating that PARP-1 is probably dispensable for normal life. Recent reports show that siRNAs directed against viral and cellular genes, which play important roles in the HIV-1 life cycle, can inhibit HIV-1 replication (2-4, 6, 13, 15, 20, 23, 24, 27) and therefore potentially be applied to the development of therapeutic agents against HIV-1 (26, 28). To prevent the appearance of siRNA-resistant mutants (3), it is necessary to develop a strategy that simultaneously targets multiple host factors, which are required for efficient viral replication (26, 28). We believe that PARP-1 may serve as a cellular target for RNAi-mediated gene silencing to inhibit HIV-1 replication.
This work was supported in part by a Grant-in-Aid for Scientific Research (KAKENHI) from the Ministry of Education, Culture, Sports, Science and Technology of Japan.
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B transcriptional activation. Biol. Chem. 380:953-959.[CrossRef][Medline]
B activation in poly(ADP-ribose) polymerase-1 deficient mice. EMBO J. 18:4446-4454.[CrossRef][Medline]
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