Dengue virus (DV)-induced changes in the host cell
protein synthesis machinery are not well understood. We investigated the transcriptional changes related to initiation of
protein synthesis. The human
hepatoma cell line, HepG2, was infected with DV serotype 2 for 1 h at a multiplicity of
infection of one.
RNA was extracted after 6, 24 and 48 h. Microarray results showed that 36.5% of the translation factors related to initiation of
protein synthesis had significant differential expression (Z-score >or= +/-2.0). Confirmation was obtained by quantitative real-time reverse transcription-PCR. Of the genes involved in the activation of
mRNA for cap-dependent translation (eIF4 factors), eIF4A, eIF4G1 and
eIF4B were up-regulated while the negative regulator of translation eIF4E-BP3 was down-regulated. This activation was transient since at 24 h post-
infection levels were not significantly different from control cells. However, at 48 h post-
infection, eIF4A,
eIF4E, eIF4G1, eIF4G3,
eIF4B, and eIF4E-BP3 were down-regulated, suggesting that cap-dependent translation could be inhibited during the progression of
infection. To test this hypothesis, phosphorylation of
p70S6K and 4E-BP1, which induce cap-dependent
protein synthesis, was assayed. Both
proteins remained phosphorylated when assayed at 6 h after
infection, while
infection induced dephosphorylation of
p70S6K and 4E-BP1 at 24 and 48 h of
infection, respectively. Taken together, these results provide
biological evidence suggesting that in HepG2 cells DV sustains activation of the cap-dependent machinery at early stages of
infection, but progression of
infection switches
protein synthesis to a cap-independent process.