Viruses and RNA interference in mammalian cells

(WNV) (McCown et al., 2003). An enveloped, segmented, negative-strand RNA virus -
Influenza A virus belongs to the Orthomyxoviridae virus family (Chen et al., 2001) WNV is
an enveloped arbovirus with ss(+)RNA genome, belongs to the Flaviviridae family of
viruses (Chambers et al., 1990). siRNAs were shown to block expression of viral genes in a
specific manner and thus interfering the replication of the mentioned viruses (McCown et
al., 2003).
The acknowledgement of hypothesis, that the mammalian cellular RNAi machinery can
inhibit virus replication with the help of artificial siRNAs, was obtained by investigation of
foot-and-mouth disease virus (FMDV) replication. The VP1-specific siRNAs showed an
inhibitory effect on VP1 of FMDV in BHK-21 cells (baby hamster kidney cells), as well as
in and suckling mice, a commonly used small animal model. VP1 plays a key role in virus
attachment to susceptible cells and is essential during the life cycle of the virus.
Approximately 90% reduction in the expression of FMDV VP1 in BHK-21 cells was
observed with transfection of siRNAs. Suckling mice became significantly less susceptible
to FMDV (Chen et al., 2004).
In 2003 the investigations of SARS-CoV virus with ss(+)RNA genome has led to the
observation, that the infection and replication can be inhibited by siRNAs. They targeted the
replicase 1A region of the virus genome; this appeared to be effective in vitro in different
strains of SARS-CoV. This coronavirus has been identified as a cause of severe acute
respiratory syndrome (SARS). But clinical usefulness of such method of viral replication
inhibition remained to be undemonstrated (He et al., 2003).
Interest in RNAi as an alternative antiviral for human immunodeficiency virus type 1 (HIV-
1) is strong because of the problems of drug resistance, the cost and toxicity of modern
antiviral therapy against this virus (Manjunath et al., 2008). Several reports using siRNA
target sequences have shown potent RNAi activity against HIV-1 replication. Targeting the
region encoding the HIV-1 reverse transcriptase (RT) by siRNAs reduced viral replication
by 90% (Gimenez-Barcons et al., 2007). The siRNAs targeting tat/rev (Novina et al., 2002;
Lee et al., 2002; Coburn et al., 2002 ), pol (Surabhi and Gaynor, 2002),TAR, vif , 3’UTR
region (Jacque et al., 2002), as well as gag and the HIV-1 receptor CD4 (Novina et al.,
2002) and co-receptor CCR5 has led to the suppression of HIV-1.These results suggest that
RNAi represents an important new therapeutic approach for treating HIV-1 infection (Qin et
al., 2002).
It was observed that siRNAs directed against NS4B and core regions of hepatitis C virus
(HCV) specifically decreased quantity of HCV RNA. HCV is a main cause of chronic liver
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