3.4. DDX21 suppresses DENV replication
We set up knockdown and over-expression conditions for
DDX21 respectively followed by DENV infection, and then analyzed
the viral RNA level by RT-qPCR. The results showed that DDX21
knockdown resulted in an increase in DENV RNA level (Fig. 4A)
whereas DENV levels were reduced in DDX21 overexpressing cells
(Fig. 4B). These results demonstrate that DDX21 negatively regulates
DENV replication in cells.
Next we evaluated the role of DDX21 in the innate immune
response. We used the dual-luciferase assay to monitor the IFN-bpromoter
activity and interferon stimulated response element
(ISRE) activity in DDX21-overexpressing 293T cells during DENV
infection. The reporter assays showed that the transcription level of
IFN-b and ISRE was increased by approximately 1.6- and 1.3- fold
respectively in DDX21 overexpressed cells compared to vector
control group (Fig. 4C). After DENV infection, the transcription level
of IFN-b and ISRE was increased greatly by approximately 10.9- and
15.2- fold respectively in DDX21 overexpressed cells compared to
control group (Fig. 4D). These results suggested that DDX21 may
contribute to IFN-b production and ISRE activation during the early
stage of DENV infection, thereby inhibiting DENV replication.