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Journal of Virology, March 2005, p. 2973-2978, Vol. 79, No. 5
0022-538X/05/$08.00+0 doi:10.1128/JVI.79.5.2973-2978.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
DNA Damage Sensors ATM, ATR, DNA-PKcs, and PARP-1 Are Dispensable for Human Immunodeficiency Virus Type 1 Integration
Yasuo Ariumi,1
Priscilla Turelli,1
Mitsuko Masutani,2 and
Didier Trono1*
Department of Microbiology and Molecular Medicine and "Frontiers in Genetics" Research Program, Faculty of Medicine, University of Geneva, Geneva, Switzerland,1
Biochemistry Division, National Cancer Center Research Institute, Tokyo, Japan2
Received 13 August 2004/
Accepted 8 October 2004

ABSTRACT
Integration of a DNA copy of the viral RNA genome is a crucial
step in the life cycle of human immunodeficiency virus type
1 (HIV-1) and other retroviruses. While the virally encoded
integrase is key to this process, cellular factors yet to be
characterized are suspected to participate in its completion.
DNA damage sensors such as ATM (ataxia-telangiectasia mutated),
ATR (ATM- and Rad3-related), DNA-PK (DNA-dependent protein kinase),
and PARP-1 [poly(ADP-ribose) polymerase 1] play central roles
in responses to various forms of DNA injury and as such could
facilitate HIV integration. To test this hypothesis, we examined
the susceptibility to infection with wild-type HIV-1 and to
transduction with a vesicular stomatitis virus G protein (VSV-G)-pseudotyped
HIV-1-derived lentiviral vector of human cells stably expressing
small interfering RNAs against ATM, ATR, and PARP-1. We found
that integration normally occurred in these knockdown cells.
Similarly, the VSV-G-pseudotyped HIV-1-based vector could effectively
transduce ATM and PARP-1 knockout mouse cells as well as human
cells deficient for DNA-PK. Finally, treatment of target cells
with the ATM and ATR inhibitors caffeine and wortmannin was
without effect in these infectivity assays. We conclude that
the DNA repair enzymes ATM, ATR, DNA-PKcs, and PARP-1 are not
essential for HIV-1 integration.

INTRODUCTION
Viral DNA integration is an essential step in the retroviral
life cycle. Following human immunodeficiency virus type 1 (HIV-1)
entry, reverse transcriptase synthesizes a double-stranded DNA
copy of the viral genomic RNA. A so-called preintegration complex
is formed that contains, in addition to the virus genetic material,
the viral proteins integrase (IN), nucleocapsid (NC), virion
protein R (VPR), and matrix (MA), as well as host factors such
as HMGA1, BAF, INI1, Ku, and LEDGF/p75 (
25). The initial DNA
cutting and joining steps of the integration process are mediated
by the viral integrase, but the final repair of residual DNA
gaps must be performed by host factors. In vitro experiments
indicate that cellular DNA polymerase and DNA ligase can mediate
this process (
27). However, which cellular factors are involved
in vivo remains undefined. The catalytic subunit of DNA-dependent
protein kinase (DNA-PKcs) was identified as the product of the
severe combined immunodeficiency (SCID) gene by genetic complementation
(
13). DNA-PK is a multimeric nuclear kinase, comprising a 465-kDa
catalytic subunit (DNA-PKcs) and a DNA-binding heterodimer of
Ku70 and Ku80 (Ku86). DNA-PK is implicated in the regulation
of the nonhomologous DNA end-joining (NHEJ) pathway and in V(D)J
recombination (
13). DNA-PKcs belongs to the phosphatidylinositol
3-kinase-related family, which also includes the ataxia-telangiectasia
mutated (ATM) and ATM- and Rad3-related (ATR) kinases, and are
involved in cell cycle regulation and DNA repair as well (
23).
PARP-1 is another nuclear enzyme participating in this type
of event, as it catalyzes the transfer of an ADP-ribosyl moiety
from its substrate NAD
+ to various nuclear proteins, including
PARP-1 itself, histone H1, DNA topoisomerase, and DNA-dependent
protein kinase, in response to DNA double-stranded breaks (
1,
6). These DNA damage sensors play central roles in responses
to various forms of DNA injury and, as such, could facilitate
HIV integration. As well, these molecules could prevent apoptotic
events that might be triggered by the exposure of free DNA ends
created during reverse transcription and integration, be it
at the extremities of the linear viral DNA or within the target
cell chromosome. To probe a possible involvement of these cellular
proteins in these crucial aspects of HIV-1 replication, we used
single-round assays to measure the infectivity of HIV-1 and
HIV-1-derived lentiviral vectors in cells rendered defective
for DNA damage sensors by RNA interference or gene knockout
or by pharmacological inhibition.

MATERIALS AND METHODS
Cell culture.
Mouse embryonic fibroblasts (MEFs) derived from PARP-1 wild-type
(PARP-1
+/+), PARP-1
/ (
19), ATM wild-type (ATM
+/+),
and ATM
/ mice (
26). M059J (DNA-PKcs
/),
M059K (DNA-PKcs
+/+) (
12), 293T, and P4.2 (
5) cells were maintained
under similar conditions in Dulbecco's modified Eagle's medium
(DMEM) supplemented with 10% fetal calf serum at 37°C. The
wild-type J1 and PARP-1-deficient embryonic stem (ES) cells
were cultured as described previously (
17).
RNA interference.
Oligonucleotides with the following sense and antisense sequences were used for the cloning of small hairpin RNA (shRNA)-encoding sequences in lentiviral vectors: ATM, 5'-GATCCCCGGATTTGCGTATTACTCAGTTCAAGAGACTGAGTAATACGCAAATCCTTTTTGGAAA-3' (sense),5'-AGCTTTTCCAAAAAGGATTTGCGTATTACTCAGTCTCTTGAACTGAGTAATACGCAAATCCGGG-3' (antisense); ATR, 5'-GATCCCCGGCGTCGTCTCAGCTCGTCTTCAAGAGAGACGAGCTGAGACGACGCCTTTTTGGAAA-3' (sense), 5'-AGCTTTTCCAAAAAGGCGTCGTCTCAGCTCGTCTCTCTTGAAGACGAGCTGAGACGACGCCGGG-3' (antisense); PARP-1 #1, 5'-GATCCCCGCTCTATCGAGTCGAGTACTTCAAGAGAGTACTCGACTCGATAGAGCTTTTTGGAAA-3' (sense), 5'-AGCTTTTCCAAAAAGCTCTATCGAGTCGAGTACTCTCTTGAAGTACTCGACTCGATAGAGCGGG-3' (antisense); PARP-1 #2, 5'-GATCCCCGAGCGGGCGCGCCTCTTGCTTCAAGAGAGCAAGAGGCGCGCCCGCTCTTTTTGGAAA-3' (sense), 5'-AGCTTTTCCAAAAAGAGCGGGCGCGCCTCTTGCTCTCTTGAAGCAAGAGGCGCGCCCGCTCGGG-3' (antisense); PARP-1 #3, 5'-GATCCCCGGACTCGCTCCGGATGGCCTTCAAGAGAGGCCATCCGGAGCGAGTCCTTTTTGGAAA-3' (sense), 5'-AGCTTTTCCAAAAAGGACTCGCTCCGGATGGCCTCTCTTGAAGGCCATCCGGAGCGAGTCCGGG-3' (antisense); PARP-1 #4, 5'-GATCCCCGCGCTTCTGCACCAACTCATTCAAGAGATGAGTTGGTGCAGAAGCGCTTTTTGGAAA-3' (sense), 5'-AGCTTTTCCAAAAAGCGCTTCTGCACCAACTCATCTCTTGAATGAGTTGGTGCAGAAGCGCGGG-3' (antisense); PARP-1 #5, 5'-GATCCCCGTTGCTGATGGGTAGTACCTTCAAGAGAGGTACTACCCATCAGCAACTTTTTGGAAA-3' (sense), 5'-AGCTTTTCCAAAAAGTTGCTGATGGGTAGTACCTCTCTTGAAGGTACTACCCATCAGCAACGGG-3' (antisense). The oligonucleotides above were annealed and subcloned into the BglII-HindIII site of pSUPER (4). To construct pLVsiRNA against ATM, ATR, and PARP-1 #1 to 5, the BamHI-SalI fragments of the corresponding pSUPER plasmid were subcloned into the BamHI-SalI site of pRDI292 (3).
Constructs, virus production, infection, transduction, and titrations.
The wild-type X4 HIV-1 proviral DNA clone (R9) and the vesicular stomatitis virus G protein (VSV-G)-pseudotyped HIV-1-based vector system have been described previously (18). We used the second-generation packaging construct pCMV-
R8.91 (28), the envelope plasmid pMDG, and the green fluorescent protein (GFP)-expressing vector pWPTS-GFP. HIV-1 and retroviral vector particles were produced by transient transfection of 293T cells with FuGENE6 (Roche). Titrations were performed using the multinucleate activation of galactosidase indicator assay in CD4+ long terminal repeat (LTR)-ß-Gal HeLa-derived P4.2 cells (5) or by GFP fluorescence-activated cell sorter (FACS) analysis with a FACStrak apparatus (Becton Dickinson).
Western blotting.
Cells were lysed in buffer containing 50 mM Tris-HCl (pH 8.0), 150 mM NaCl, 4 mM EDTA, 1% Nonidet P-40, 0.1% sodium dodecyl sulfate (SDS), 1 mM dithiothreitol, and 1 mM phenylmethylsulfonyl fluoride. Supernatants from these lysates were subjected to SDS-polyacrylamide gel electrophoresis (SDS-PAGE), followed by immunoblotting analysis using anti-ATM (NB100-104; GeneTex), anti-ATR (RB-ATR10-UP50; GeneTex), anti-Chk2 (NT; ProSci), anti-
-tubulin (B-5-1-2; Sigma), or anti-PARP-1 (C2-10; Alexis) antibodies as previously described (1).

RESULTS
Neither ATM nor ATR is essential for HIV-1 integration.
To analyze the effect of ATM and ATR on HIV-1 integration efficiency,
we first used lentiviral vector-mediated RNA interference to
knock down these proteins stably in CD4
+ LTR-ß-Gal
HeLa-derived P4.2 cells (
5). shRNA-encoding sequences were cloned
downstream from a polymerase III promoter within the context
of an HIV-1-derived self-inactivating lentiviral vector, a puromycin
marker allowing for the selection of transduced cells (
3). Western
blotting of lysates demonstrated very effective downregulation
of both kinases, either alone or in combination, in cells transduced
with lentivectors expressing the corresponding shRNAs (Fig.
1a). Importantly, ATM/ATR knockdown cells exhibited normal growth
rates (not illustrated). We thus exposed these and control P4.2
cells to a VSV-G-pseudotyped GFP-expressing HIV-1-derived lentiviral
vector and analyzed transduction efficiency by FACS (Fig.
1b).
The various P4.2 derivatives were equally susceptible to lentivector-mediated
transduction. Moreover, wild-type HIV-1 exhibited similar levels
of infectivity in control and knockdown cells (Fig.
1c). As
well, the transduction efficiency of the HIV-derived lentiviral
vector was comparable in ATM knockout and ATM wild-type MEFs
(Fig.
1d) (
26). Finally, P4.2 cells were treated with 4 mM caffeine
or 4 µM wortmannin, conditions previously shown to inhibit
the ATM and ATR kinases (
20,
21), before exposure to wild-type
HIV-1 or a GFP-expressing lentiviral vector. Neither drug affected
HIV-1 infection (Fig.
2a) or transduction (Fig.
2b) efficiency.
Of note, under none of the above conditions did we observe significant
retrovirus-induced cell death (not illustrated). We conclude
that ATM and ATR are not required for efficient HIV-1 integration.
DNA-PK is dispensable for HIV-1 integration.
To test the effect of DNA-PKcs on HIV-1 integration efficiency,
we compared the lentiviral vector susceptibility of a pair of
human malignant glioma cell lines, the DNA-PKcs-deficient M059J
and its DNA-PKcs-proficient counterpart, M059K (
12). At two
different multiplicities of infection (MOI), transduction efficiency
of a GFP-expressing HIV-derived vector was twice as high in
DNA-PKcs-deficient cells compared to control cells, without
significant cell death upon infection (Fig.
3 and data not shown).
Therefore, the catalytic subunit of DNA-PK is not essential
for HIV-1 integration or for protecting cells from retrovirus-induced
apoptosis.
PARP-1 is not crucial for HIV-1 integration.
To test a possible effect of PARP-1 on HIV-1 integration, we
measured the infectivity of the VSV-G-pseudotyped GFP-expressing
HIV-1-derived lentiviral vector in PARP-1 knockout and control
MEFs (
19). At low MOI (0.7), transduction efficiency was strongly
decreased in the PARP-1 knockout cells (Fig.
4a). However, at
the MOI of 70, the GFP vector transduced up to 50% of these
targets (Fig.
4a). Therefore, we used as targets the PARP-1
knockout ES cells that were used to generate the mice from which
the MEFs were subsequently derived (226-47 and 210-58), with
PARP-1 wild-type ES cells (J1) as a control (
17). The HIV-derived
vector transduced both types of ES cells equally well, even
at low MOI (0.6) (Fig.
4b). To confirm this finding, we established
HeLa-derived cells stably knocked downed for PARP-1 by lentivector-mediated
RNA interference (Fig.
5a). We then used these cells as targets
for HIV-1 infection or transduction with the GFP-expressing
HIV-based vector. Consistent with our results in the mouse PARP-1
knockout ES cells, normal levels of HIV-1 susceptibility were
recorded in the PARP-1 knockdown human cells (Fig.
5b and c).
Taken together, these data indicate that PARP-1 is not a key
player in the early steps of HIV-1 infection.

DISCUSSION
It is strongly suspected that host cellular factors participate
in HIV-1 integration (
25), and it has been proposed that DNA
damage sensors might influence this process. Following the initial
cutting and joining reaction mediated by the viral integrase,
the host cell DNA harbors a partially repaired double-stranded
break, the ends of which are held together by single-strand
links to the viral DNA. It has been postulated that this integration
intermediate elicits a DNA damage response that repairs the
gaps and prevents double-stranded break-triggered apoptosis.
Consistent with this model, Daniel et al. reported that HIV-1
and avian sarcoma virus integration was impaired in cells transiently
expressing a dominant-negative form of ATR, as well as in the
presence of the ATM and ATR inhibitors wortmannin and caffeine
(
8,
9). Since they did not observe a difference in the retrovirus
sensitivity of ATM-deficient versus ATM-proficient cells, they
concluded that ATR was the enzyme playing an essential role
in the early steps of retroviral infection. However, we found
here that neither the knockdown of ATM and ATR by RNA interference
nor the treatment of target cells with caffeine or wortmannin
at concentrations similar to the ones previously used by Daniel
et al. had any effect on HIV-1 transduction efficiency or retrovirus-induced
cell death. While it could be that RNA interference left low
amounts of functional kinases, our drug-based results are difficult
to reconcile with Daniel et al.'s observations. Differences
in the experimental approaches may account for this discrepancy,
but our data strongly suggest that neither ATM nor ATR is crucial
for HIV-1 integration or for preventing retrovirus-induced cell
death.
Daniel et al. also observed that retrovirus infection induced apoptosis in DNA-PK-deficient scid cells as well as in Ku86- or XRCC4-defective cells. They further reported that an integrase-inactive viral mutant virus failed to trigger this process in scid cells (7, 8, 10). Based on this result, they proposed that the chromosomal breaks induced by retroviral integration could be lethal unless repaired by components of the NHEJ pathway. In the present study, we found that transduction by an HIV-1-derived lentiviral vector was twice as effective in DNA-PKcs-deficient M059J cells as in control M059K cells. This indicates that DNA-PKcs, if anything, may negatively interfere with HIV-1 integration, reminiscent of its recently proposed inhibition of adeno-associated virus integration (24). Baekelandt et al., using DNA-PKcs-deficient scid MEFs as well as Ku-deficient xrs-5 and xrs-6 cells as targets, also demonstrated that DNA-PK is not required for efficient lentivirus integration (2). As well, Bushman and collaborators observed that cells with marked defects in NHEJ, such as Nalm-6 LIG4/ cells, exhibited high levels of retrovirus-induced cytotoxicity but that the latter phenomenon was independent from integration. Instead, they found that the formation of 2-LTR viral circles was defective in these cells, suggesting that the proapoptotic signal originated from the accumulation of free viral DNA ends, not from residual gaps in the chromosomal DNA (14, 16). Noteworthy, the 2-LTR circles defect was not apparent in DNA-PKcs-deficient cells, perhaps because this protein is only required for NHEJ of DNA ends with hairpins or long single-stranded overhangs and is not a feature of the final product of viral reverse transcription (16).
Controversy also exists about a possible effect of PARP-1 on HIV-1 integration. Ha et al. (11) found that transduction by an HIV-1 pseudovirus was almost abolished in PARP-1 knockout MEFs. Based on this result, they suggested that PARP-1 is required for efficient HIV-1 integration. Using the same type of target cells, we confirmed their initial observation. However, we investigated further the issue because we knew that our PARP-1 knockout MEFs show extensive hyperploidy compared with PARP-1 wild-type MEF cells (19). We therefore suspected that PARP-1-independent genetic changes might account for their HIV susceptibility phenotype. Confirming this hypothesis, we did not observe any difference in the HIV transduction sensitivity of the parental PARP-1 knockout ES cells. Moreover, HIV-1 infectivity was not affected by the knockdown of PARP-1 in human cells. Consistent with our results, Siva and Bushman showed that PARP-1 is not strictly required for infection of murine cells by retroviruses (22). Moreover, Kameoka et al. demonstrated that HeLa or human lymphoid T cells expressing PARP-1-specific small interfering RNAs fully supported HIV-1 integration, although viral replication was impaired in these targets, owing to a defect in LTR-mediated transcription (15).
While we did not assess a possible role of DNA damage sensors in HIV integration in cells such as primary human T lymphocytes or macrophages, we note that previous claims about the involvement of these proteins in this crucial step of the retroviral life cycle were based on experimental systems comparable to ours. Furthermore, the extensive experience accumulated with HIV-derived vectors in a broad range of targets has so far not disclosed cell-specific requirements for HIV integration cofactors (25).
In sum, our data indicate that the DNA damage sensors ATM, ATR, DNA-PK, and PARP-1 neither are required for efficient HIV-1 integration nor play crucial roles in protecting the cell against retrovirus-induced cell death. Whether these molecules modulate retroviral integration site selection and what other cellular proteins serve as bona fide integrase cofactors remain open questions.

ACKNOWLEDGMENTS
We thank B. Mangeat, S. Vianin, and E. Buhlmann for help with
the experiments and H. Suzuki, T. Ochiya, O. Niwa, R. Iggo,
A. Telenti, and J. Turner for the gift of reagents.
This work was supported by the Swiss National Science Foundation.

FOOTNOTES
* Corresponding author. Mailing address: Department of Microbiology and Molecular Medicine, Faculty of Medicine, University of Geneva, 1211, Geneva 4, Switzerland. Phone: 41-22-379 5720. Fax: 41-22-379 5721. E-mail:
Didier.trono{at}medecine.unige.ch.


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Journal of Virology, March 2005, p. 2973-2978, Vol. 79, No. 5
0022-538X/05/$08.00+0 doi:10.1128/JVI.79.5.2973-2978.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
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Ariumi, Y., Trono, D.
(2006). Ataxia-Telangiectasia-Mutated (ATM) Protein Can Enhance Human Immunodeficiency Virus Type 1 Replication by Stimulating Rev Function. J. Virol.
80: 2445-2452
[Abstract]
[Full Text]