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Journal of Virology, July 2004, p. 7270-7273, Vol. 78, No. 13
0022-538X/04/$08.00+0 DOI: 10.1128/JVI.78.13.7270-7273.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.
Inhibition of Virus Production in JC Virus-Infected Cells by Postinfection RNA Interference
Yasuko Orba,1,2 Hirofumi Sawa,1,2,3* Hiroshi Iwata,1,2 Shinya Tanaka,1,2 and Kazuo Nagashima1,2
Laboratory of Molecular and Cellular Pathology,1
21st Century COE Program for Zoonosis Control, Hokkaido University Graduate School of Medicine, Kita-ku, Sapporo 060-8638 ,3
CREST, JST, Sapporo, Japan2
Received 25 February 2004/
Accepted 30 March 2004

ABSTRACT
RNA interference has been applied for the prevention of virus
infections in mammalian cells but has not succeeded in eliminating
infections from already infected cells. We now show that the
transfection of JC virus-infected SVG-A human glial cells with
small interfering RNAs that target late viral proteins, including
agnoprotein and VP1, results in a marked inhibition both of
viral protein expression and of virus production. RNA interference
directed against JC virus genes may thus provide a basis for
the development of new strategies to control infections with
this polyomavirus.

TEXT
JC virus (JCV) belongs to the polyomavirus family of double-stranded
DNA viruses and causes progressive multifocal leukoencephalopathy
(PML) in humans (
23). PML is often observed in immunosuppressed
individuals, such as those with AIDS or advanced malignancies.
Although highly active antiretroviral therapy, which includes
treatment with protease inhibitors, improves the survival rate
of patients with AIDS-related PML (
2,
7), current therapeutic
approaches to PML are not satisfactory. Treatment with cytosine
arabinoside (
8) or cidofovir (
15) has failed to prove efficacious
in individuals with PML. Trials of topotecan, which inhibits
DNA topoisomerase and blocks JCV replication in vitro (
11),
are currently under way in such individuals. RNA interference
(RNAi) with small interfering RNAs (siRNAs) has recently become
a widely used approach for repressing cellular or viral gene
expression (
5,
6,
10,
16). Although several studies have shown
that virus infections can be prevented by a prior or concomitant
administration of siRNAs, the elimination of established infections
from cells or tissues by RNAi has not been demonstrated (
1).
To attempt to inhibit JCV production in infected cells, we designed the following siRNAs (Dharmacon) to target three different JCV proteins (Fig. 1a): VP274 and VP691 for VP1, Ag122 and Ag147 for agnoprotein, and LT78 and LT134 for the large T antigen (T-Ag). The JCV early and late RNAs are generated by alternative splicing. The early RNAs encode T-Ag and the small t antigen (14), whereas the major late RNA encodes both agnoprotein and VP1 (21). We introduced the JCV-specific siRNAs into cells of the SVG-A (simian virus 40 [SV40]-transformed human fetal glial cells) line (13) that had been inoculated with JCV (Mad-1/SVE
strain; 1,024 hemagglutination activity units per 3 x 105 cells) 4 days previously. JCV late proteins, including VP1 and agnoprotein, were detected by an immunoblot analysis at 2 days postinfection (dpi) and were abundant at 4 dpi (Fig. 1b). At 4 and 6 dpi, each siRNA (120 pmol per 6 x 104 cells) was introduced individually into SVG-A cells by the use of Lipofectamine 2000 (Invitrogen) (Fig. 1c). About 80% of the SVG-A cells were successfully transfected with a fluorescein-conjugated Ag122 siRNA (data not shown). The abundance of JCV proteins in siRNA-transfected cells was examined 48 h after the second transfection by an immunoblot analysis with antibodies specific for agnoprotein (3, 18, 19), VP1 (12, 22), or SV40 T-Ag (Ab-2; Oncogene Research Products) (20). Cells transfected with Ag122, Ag147, or VP274 manifested a marked depletion of viral proteins compared with cells transfected with a control siRNA with a scrambled sequence which is not present in mammalian cells (Dharmacon) (Fig. 1d). Ag122 inhibited the expression of VP1 as well as that of agnoprotein in a dose-dependent manner, but it did not affect the abundance of T-Ag, lamin A/C, or actin (Fig. 1d and e). The antibodies to SV40 T-Ag did not allow for differentiation between JCV T-Ag and SV40 T-Ag in SV40-transformed cells, as these two proteins share >70% amino acid sequence identity (4). We therefore assessed the effects of LT78 and LT134 on JCV T-Ag expression by reverse transcription (RT) and PCR; the abundance of JCV T-Ag mRNA was not affected by the transfection of cells with either siRNA (data not shown).
We also examined the effects of Ag122 and VP274 siRNAs by an
indirect immunofluorescence analysis in JCV-infected cells.
At 48 h posttransfection, methanol-fixed cells were stained
with antibodies to VP1 or agnoprotein and then with Alexa Fluor
488-conjugated goat antibodies to rabbit immunoglobulin G (Molecular
Probes). Cells positive for VP1 or agnoprotein were visualized
with a laser-scanning confocal microscope (Olympus) and counted
in six fields of view. The proportion of agnoprotein-positive
cells was significantly reduced for cells transfected with Ag122,
VP274, or both siRNAs compared with the value for cells transfected
with the scrambled siRNA (Fig.
2a). Similarly, the percentage
of VP1-positive cells was also reduced by transfection with
Ag122, VP274, or both Ag122 and VP274. We confirmed the inhibition
of the expression of agnoprotein and VP1 in cells transfected
with Ag122, VP274, or both siRNAs by an immunoblot analysis
(Fig.
2b). The extent of inhibition of viral protein expression
achieved with the combination of Ag122 and VP274 did not differ
significantly from that achieved with either siRNA alone. The
observed inhibition of both agnoprotein and VP1 expression by
either Ag122 or VP274 was likely due to the degradation of the
polycistronic late RNA for both of these proteins induced by
each siRNA.
It is thought that siRNAs target mRNAs containing the same sequences
and induce their cleavage. We therefore examined the effects
of Ag122 and VP274 on the abundance of JCV mRNAs. Total RNAs
were isolated from cells 12 or 24 h after transfection with
a siRNA, treated with DNase I, and subjected to RT with a Superscript
first-strand synthesis system (Invitrogen) followed by real-time
quantitative PCR with a GeneAmp5700 instrument (Applied Biosystems).
The amount of each viral mRNA was normalized to that of ß-actin
mRNA in the same sample. The abundance of agnoprotein and VP1
mRNAs was significantly reduced in JCV-infected cells transfected
with Ag122, VP274, or both siRNAs (Fig.
3). The reduction in
the amounts of viral mRNAs, however, was not as large as that
in the amounts of the encoded proteins. We eliminated the possibility
of contamination of the viral DNA in the RT-PCR samples by (i)
performing a DNase I treatment prior to RT-PCR, without the
reverse transcriptase, and (ii) performing an RNase A treatment
prior to the reverse transcriptase reaction. For both treatments,
the RT-PCR signal was lost, suggesting that there was no contamination
of the viral DNA in the RT-PCR samples. Whereas siRNAs are known
to be incorporated into an RNA-induced silencing complex and
to direct RNA-induced silencing complex-mediated sequence-specific
mRNA degradation (
9), the detailed mechanism of this process
remains unclear. One possible explanation for the difference
in the magnitude of the effects of the JCV-specific siRNAs on
the amounts of viral RNAs and proteins is that the target mRNA
bound with a siRNA might be detected by RT-PCR before its degradation.
To examine the effect of RNAi on JCV production, we measured
the hemagglutination activity (
17,
22) of JCV-infected SVG-A
cells 36 h after siRNA transfection. The hemagglutination activities
of cells transfected with Ag122, VP274, or both of these siRNAs
were 6.7, 9.3, and 4.1%, respectively, of that for cells transfected
with the scrambled siRNA (Fig.
4). Thus, siRNAs that target
agnoprotein or VP1 greatly inhibited JCV production in infected
cells.
In summary, we have achieved a marked inhibition of JCV production
by RNAi in cells already infected with the virus. Our results
may have important implications for the development of a new
approach to the treatment of PML. The application of an RNAi-based
antiviral strategy for PML will require an efficient and specific
delivery of siRNAs to the central nervous system.

ACKNOWLEDGMENTS
We thank Mayumi Sasada for technical assistance.
This study was supported in part by grants from the Ministry of Education, Science, Sports, and Culture and by grants from the Ministry of Health, Labour and Welfare, Japan.

FOOTNOTES
* Corresponding author. Mailing address: Laboratory of Molecular and Cellular Pathology, Hokkaido University School of Medicine, N15, W7, Kita-ku, Sapporo 060-8638, Japan. Phone: 81-11-706-5053. Fax: 81-11-706-7806. E-mail:
h-sawa{at}patho2.med.hokudai.ac.jp.


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Journal of Virology, July 2004, p. 7270-7273, Vol. 78, No. 13
0022-538X/04/$08.00+0 DOI: 10.1128/JVI.78.13.7270-7273.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.
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